Synthesis, DelocPlization and Reactivity in Stable ... · Synthesis of 13-Hl SCN Synthesis of [1-H] Cl Proton Transfer Reactions (NMR Scale) [1-H] Cl with D20 [LH] Cl with 2 [2-H]

Synthesis, DelocPlization and Reactivity in Stable Diaminocarbenes

Shilpi Gupta

A thesis subrnitted in conformity with the requirements for the degree of Master's of Science Graduate Department of Chemistry

University of Toronto

@ Copyright by Shilpi Gupta (1 999)

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Synthesis, Delocalbtion and Reactivity of Stable Dmrninocarbenes Master's of Science, 1999 Shilpi Gupta Department of Chemistry, University of Toronto

Abstract

The synthesis and reactivity of stable diaminocarbenes has been investigated. The

synthetic routes utilized were reductive dehydrosulhuization of tetra-substituted thioureas and 1,l-

elimination of HCI frorn carbenium salt, [N2CH]+ CI-. Synthesis of sterically crowded thioureas

suffers from low yields. The dehydrosulfurization of aminals has been discovered as a new one-

step synthesis for thioureas and carbenium salts.

Dehydrosulfurization was also investigated for urotropin and 1,3,5-trialkyl-hexahydro-

sym-triazines (investigated as precursors for polycarbenes). The dehydrosulfurization of sym-

triazines gave ring degradation products and [C2H2(NR)2CH]+ SCN-. Reaction of carbenes and

analogs with alcohols and alkoxides was investigated. The aromatic 61r-delocalization in carbenes

and related heterocycles was studied at the RHF 1 6-3lG* and B3LYP / 6-3 IG* level. The

obtained Lowdin bond orders correlate with the aromatic ring cument (IH-NMR) making them an

excellent computational tool to study the extent of ammatic delocalization.

- Table of Contents - A bstrac t

List of Tables

List of Figures

Ab breviations

Acknowledgments

Chapter 1

1.1

1.1.0

1.2

1.3

1.4

Chapter 2

2.1

2.1.1

2.1.2

2.1.3

2.2

2.3

2.4

2.4.1

2.5

2.5.1

2.5.2

2.5.3

Introduction

Carbenes and Carbenium Ions

S ynthesis

Oxidative Addition of Alkoxides and Alcohols

Metal-Carbene Complexes

Thioureas and Thiourea Derivatives

Results and Discussion

Dehydrosulfurization of Arninals (RzN)2CH2 with Sa

Applications of Thioureas

Objectives

Mechanism and Product Distribution

l=S via [l-R] CI

Synthesis of 3=!3

Synthesis of Imidazolium Salts

Deprotonation of [l-H] CI to give 1

Properties of Imidazolium Salts

Basicity of Carbenes and Acidity of Imidazolium Salts

Ion pairing

Hy bridization

ii

vii

viii

xi

xii

Solubilities of Carbenium Salts

Deprotonation Strategy to give 2 from [2-H] SCN

Deprotonation Strategy to give 3 from [3-LI] SCN

Other Deprotonation Bases

Aromatic, Anti-Aromatic and Linear Conjugated

Pol ycarbenes

1,3,S-tn-te~-butyl-hexahydro-sync-triazine with S8

Multistep approaches for the synthesis of Il-'Bu

1,3,5-tri-terr-butyl-hexahydro-sym-trimine and conformations

in other 1,3,5-triazines

Dehydrosulfurization of Urotropin

Reaction of Carbenes and Carbene Analogs with Alkoxides

and Alcohols

Reactions of Carbenes with Alkoxides and Alcohols

Reactions of L'Si: with Alkoxides and Alcohols

Reactions of LGe: with Alkoxides and Alcohols

Synthesis of 1-Hz

Reaction of 1 with Fe(C0)s

Reaction of 2 with Fe(C0)s

Aromatic Delocalization in Stable Carbenes: Correlation of

Experimental and Computational Data

Introduction

Vibrational Data as Criterion for Aromaticity

Delocalization of Carbene Derivatives

HOMO-LUMO Gaps

Structural Investigation of Carbenes and Protonated Carbenes

The Basicity of Diaminocarbenes

Chapter 3

3 .O

3.1

3.2

3.3

3.4

Carbenium Cations as Ionic Liquids

Conclusions and Future Goals

Experimentd 86

General Experimental 87

Synthesis of 2=!3 88

Synthesis of l=S via [1-H] CI 9 1

Attempted Synthesis of 3=S 92

Dehydrosulfurization of 1,3,5-tn-terf-buty l-hexahydro-sym- 95

triazine

Synthesis of 13-Hl SCN

Synthesis of [1-H] Cl

Proton Transfer Reactions (NMR Scale)

[1-H] Cl with D20

[LH] Cl with 2

[2-H] SCN with 1

[3-Hj SCN with 1

[l-Kj Cl with [3-HJ SCN

Synthesis of 1

Synthesis of 2 from 12-81 SCN

Attempted Synthesis of 3

S ynthesis of 1,3,5-tn- te^-butyl-hexahydro-sym-triazine

Synthesis of 1-Hz

Preparation of tert-butoxy lithium

Attempted Synthesis of L'Si-(0tBu)Li

Appendix 1

Appendix 2

Appendix 3

Attempted Synthesis of LGe-(0tBu)Li

Attempted Synthesis of 1-(OtBu)Li

Attempted Synthesis of 2-(OtBu)Li

Attempted Synthesis of L'Si-(0tBu)CI

Attempted Synthesis of L1Si(0tBu)2 with BuOLi

Attempted Synthesis of L'S~(O~BU)~ with 'BUOH

Attempted Synthesis of L'Si(0Me)z

Attempted Synthesis of L'Si-(0tBu)H

Attempted Synthesis of LGe-(0tBu)H

Attempted Synthesis of 1-(0'Bu)H

Attempted Synthesis of 2-(0tBu)H

Synthesis of 2-(0Me)H

Preparation of tert-butoxy copper

Attempted Synthesis of L'Si-(OtBu)Cu

Attempted Synthesis of 1=Fe(C0)2

Attempted S ynthesis of 2=Fe(C0)2

X-ray Crystal Structure Data

References

A bbreviations of Compounds

List of Tables

Table 1 Table 2 Table 3 Table 4 Table 5 Table 6

Table 7 Table 8

Table 9


Table 16

Table 17 Table 18

Table 19

Table 20


Thioureas in medicine Influence of different reaction conditions on 2=S, 12-HJ SCN fomation Influence of different reactions on 3-C, 3=S, [3-Hl SCN formation Influence of counter ion and aromaticity on chernical shifts

% s character in C-H carbon of carbenium salts

Solubilities of carbenium salts Sublimation fractions for deprotonation of [2-H] SCN with LDA

Sublimation fractions for dehydrosulfurization of 1,3,5-tri-tert-butyl-

hexahydro-sym-triazine ( 140 OC, 26 h)

Sublimation fractions for large scale dehydrosulfurization of 1,3,5-tri-te+

butyl-hexahydro-sym-triazine(150 OC,58h) Conformations of hexahydro-sym-triazines Summary of reactions of 1,2, L'Si:, LGe: with alkoxides and alcohols

Increasing delocalization as obtained from computational IR frequencies Correlation between bond order and NMR data

Correlation between Eg and aromatic stability Correlation between computational IR frequencies and Eg for carbenes

and it's derivatives Normal modes, Eg, bond orders, and experimental NMR data of selected

diazoles Normal modes of selected 1,l-dihydro- 1,3-diazoles Comparison of experimental and calculated structures of L'CH+ cations

using B3LYPl6-3 IG*, W/6-3 lG*, MW6-3 le*, and AM 1 methods

Comparison of experimental and calculated structures of LCH+ cations

using B3LYP16-3 L G*, HF/6-3 le*, MP2/6-3 1 G*, and AM 1 methods Comparison of experimental and calculated structures of 1 cations using

B3LYP/6-3 lG*y HFl6-3 lG*, MP2f6-3 lG*, and AM1 methods Calculated tme energies &cal) for carbenes and derivatives Sublimation fractions for Method A Sublimation fractions for Method B Sublimation fractions for Method C Sublimation fractions for 1-C formation

Sublimation fractions for 3-H2:S8 (1 : 1/4)

vii

List of Figures

Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Fipre 18 Figure 19 Figure 20 Figure 21a Figure 21b Fipre 22 Figure 23 Figure 24a Figure 24b Figure 25 Figure 26a Figure 26b Figure 27 Figure 28 Figure 29 Figure 30 Figure 31

Hydrolysis of chlorofom

Representation of electronic structure of carbenes

Arduengo's carbene

Aromatic divalent carbenes la and lb and non-aromatic carbene 2 Synthetic strategies to obtain diaminocarbenes via a carbenoid

Reaction scheme for silylenoid species formation Synthetic strategy for a-haloorganolithium species

Reaction scheme for carbenoid synthesis

First transition metalcarbene complex

Geometrical positions of the carbene ligand Attempted synthesis of l=Fe(C0)2 General equation for the synthesis of carbene from thiourea Literature methods to obtain thiourea General reaction scheme for the synthesis of thioureas from arninals

Synthesis of the first thiourea Tautomerism in thioureas

Synthesis of cyclic thioureas Thiourea derivatives as vulcanization accelerators

Synthesis of 2=S from CS2/pylI2 method ORTEP view of [2-Hl SCN Possible mechanisms for the oxidation of arninals

Possible reaction schemes I,II,III for the sulfurization of aminals

Synthesis of 2=S from dehydrosulfurization of 2-Hz with Se

Synthesis of l=S from 1 in a one-pot reaction

Possible sulfur containing heterocyclic compunds Possible structure of the 100-125 O C fraction: "Zwitterion" formation

Synthesis of 3=S 1H NMR of sublimate at 150 O C (3=S) 1 3 ~ NMR of sublimate at 150 OC (3=S)

ORTEP view of 3-C ORTEP view of [3-II] SCN Synthesis of [l-8] CI from glyoxal

Attempted synthesis of [l-tI] CI fiom diazadiene ORTEP view of [l-HJ CI

Fipre 32 Figure 33 Figure 34 Figure 35 Figure 36 Figure 37 Fipre 38 Figure 39 Figure 40 Figure 41 Figure 42 Figure 43 Figure 44 Fipre 45 Fipre 46 Fipre 47 Figure 48 Figure 49 Figure 50a

Fipre 5Ob Figure SOC Figure 51 Figure 52 Figure 53 Figure 54 Figure 55 Figure 56 Figure 57 Figure 58 Figure 59 Figure 60 Figure 61 Figure 62 Figure 63 Figure 64

Synthesis of 1 by deprotonation of [1-Hl CI ORTEP view of 1 Deuterium exchange reaction of [1-A] CI Proton exchange between [1-Hl CI and 2 Proton exchange between (2-Hl SCN and 1 Proton exchange behueen [3-Hl SCN and 1 Proton exchange between [l-Hl CI and [3-H] SCN Deprotonation of [2-H] SCN to give 2 Deprotonation of [3-A] SCN to give 3 1H NMR of 80-90 O C fraction (3) Structure of 3-CHO Reaction of SCN- with nBuLi Reaction schemes for [3-H] CI formation Delocal ized pol y -car benes

Synthetic strategies for tris-carbene Synthesis of Il-Me Decomposition products of the reaction of 9 with S8

ORTEP view of [l-Hl SCN Reaction scheme for the dehydrosulfurization of 1,3,5-tri-tert-butyl-

hexahydro-sym-triazine Possible sulfur-exchanp reaction between 9 and 15 13C NMR simulation of mono-, bis-, tri- substituted thiourea Attempted synthesis of 16 Synthesis of 1,3,5-tn-tert-buty l-hexahydro-syrn-triazine

Graphical representation of melting point of 9

Synthesis of methylurotropinium thiocyanate

ORTEP view of [5-CH31 SCN Decomposition of halogen-substituted carbene species to carbenoid Reductive elirnination of aicohols

Synthesis of 2 - ( 0 t ~ u ) ~ i Reaction of 1 with tBuOLi

Reactions of 1,2, LGe: with tBuOH Synthesis of 2-(0Me)H using 1: 1 ratio of 2 to MeOH ORTEP view of 24330 Attempted synthesis of L'Si-(0tBu)Cu Attempted synthesis of L'Si-(0tBu)Li

Figure 65 Figure 66 Figure 67 Figure 68 Figure 69 Figure 70 Figure 71 Figure 72 Figure 73a Figure 73b Figure 73c Figure 74 Figure 75

Attempted synthesis of L'Si-(O*Bu)CI Attempted synthesis of L'Si-(0'Bu)H Attempted synthesis of LGe-(O%)Li Synthesis of 1-H2 Synthesis of a bis-carbene complex q 1 complex formation: l=Fe(CO)4 Attempted synthesis of 2=Fe(CO)4 The stable carbene 1 and it's derivatives Reaction between L'CH+ and LC: Reaction between L'CH2 and LC: Reaction between L'CH2 and L CH+ General representation of ionic liquids Ionic liquids and Carbenium Salts

THF Et20 HMPA TMS Me nPr fBu Et iPr PY GCMS IR NMR h d A equiv mm01 Ph Et3N PES CDC13 C6D6 D2O PP=' r. t. t~ mins. Ca.

SYm asym

tetrafiy drofuran diethyl ether hexarnethylphosphoric triamide teuamethy lsilane methy l n-propy i tert- buty 1 ethy 1 iso-prop y l pyridine gas chromatography 1 mass spectrometry in fra-red nuclear magnetic resonance hour(s) day (s) heat equivalent miili mole(s) pheny 1 triethy lamine photo electron spectroscopy deuterated chlorofonn deuterated benzene deuterated water parts per million room temperature retention tirne minutes approximatel y symmetnc asymmetric

Acknowledgments

1 would like to begin by thanking my supervisor, Prof. Michael K. Denk, for his

continuous support, guidance and encouragement over the past twenty months and for giving me

the opportunity to work on some really stimulating projects. 1 like to thank rny CO-workers, past

and present (Ken, Sébastien and Jose), for making the lab a pleasant place to work in. Thanks aiso

goes to al1 the volunteers in the lab, especially, John and Neeti, for keeping up with me when 1 got

so very frustrated.

1 am grateful to Dr. Alan Lough for his keen interest and patience in obtaining those

beautiful X-ray structures. My sincere gratitude gws to the lab technicians, Sarnia and Pam, for

al1 those srniles and for being there for me. Thanks also goes to Dr. Tim Burrow for his advise on

some NMR experiments, and to Dan Mathers and Dr. Alex Young for mass-spectral work.

Lastly, but definiteiy, not the least, 1 like to thank my parents who have k e n my backbone

every single moment. Words fail to express how deeply grateful I am for the unconditional love

and moral support they have given me every single day.

xii

Chapter 1: Introduction

1.1 Carbenes and Carbeniwn Ions

Carbenes are highly reactive species (lifetimes under 1 sec); the parent species being

CH2 (methylene). The concept that carbenes might play a significant role as reactive

intermediates dates back to the early kinetic investigations of Hine who postulated the

intermediacy of C12C: in the hydrolysis of chloroform (Fig. 1) [ 11.

- OH . fast

CCI2 - CO + HCO; H20

Fig. 1. Hydrolysis of chlorofon

Methylene has been the subject of the now classical spectroscopic studies by Herzberg's

group [2]. Unlike most other carbenes, methylene has a triplet ground state, but the singlet state

is only slightly higher in energy.

The diaminocarbenes la and 2 al1 have a singlet ground state (Fig. 2). The singlet state

of carbenes with it's empty p-orbital is isoelectronic with carbocations and is stabilized more by

conjugation than the triplet state which has a singly occupied p-orbital [3].

Triplet state Singlet state

Fig. 2. Representation of electronic structure of carbcnes

A number of carbenes have been isolated in frozen matrices and investigated

spectroscopically [4]. Carbenes have been the subject of many computational studies. Most of

the older results are now obsolete as a result of better and better experimental data and new

computational data [4]. The extreme reactivity of carbenes made the goal of obtaining stable

15

carbenes seem futile, although early studies by Wanzlick claimed that diaminocarbenes can

persist in solution and at rwm temperature for prolonged periods of time.

In 1964, Wanzlick proposed that enetetramines can dissociate into diaminocarbenes but

was unable to present unambiguous proof for the presence of free carbenes 151. The goal of

obtaining stable carbenes was finally realized in 1991 when Arduengo et al. described the

synthesis and structure of 1,3-Di-adarnantyl-irnidazole-2-ylidene, the first unambiguously stable

carbene [6a-il.

Arduengo's carbene

1 ad

Fig. 3. Arduengo's carbene

Many other studies have since appeared on the subject of diaminocarbenes from

Arduengo's group [6]. The question if diaminocarbenes require steric and electronic stabilization

or just electronic stabilization was answered by Our study of the corresponding saturated

systems. [7].

This study addresses a number of controversial or unexplored aspects of the chemistry of

stable diaminocarbenes. This thesis c m be grouped around the subjects:

Synthesis

Aromatic defocalization

Reactivity

New Topologies

16

1.1.0 Synthesis

Arduengo's published procedure for the synthesis of stable carbenes requires the

deprotonation of irnidazolium salts with NaH in DMSO 161. This rnethod is inconvenient for the

large scale reaction and is aiso unsuitable for the synthesis of volatile carbenes because of the

separation from DMSO. The use of DMSO is thus problematic for a general and a specific

reason:

DMSO is not easy to purify and very hygroscopic.

For volatile carbenes, such as 1 and 2 (Fig. 4), the removal of a high boiling solvent like

DMSO (bp = 189 OC) will inevitably lead to the loss of much of the formed carbene.

As demonstrated in this thesis, the deprotonation of the imidazolium salt [l-Hl Cl with

"BuLi in THF is a simple alternative. Separation of the carbene 1 from LiCl formed in the

reaction was no problem and the carbene is easily isolated by sublimation in Ca. 72 % isolated

y ield.

R R R I I I (2.: R = adamantyl cN): - @,E: mesityl

N N I

met hyl I R R

I R

iso-propyl t e s bu ty 1

1 a l b 2

Fig. 4. Aromatic divalent carbenes l a and l b and non-aromatic carbene 2

The synthesis of the imidazolium sdts was achieved in a patented three-component

condensation from glyoxal, a primary amine and formaldehyde. The synthetic details are

sketchy and the reactions as described are laborious. No proper purification and work up

procedures are given. This thesis descnbes a simplified procedure for the synthesis of the

imidazolium salts and two new methods for obtaining the thiocyanate salts.

17

The fact that diaminocarbenes can be obtained by deprotonation of imidazolium salts

raises the question of how basic diaminocarbenes reaily are. This question was investigated by

computational methods and by the study of proton exchange equilibria. The deprotonation of

imidazolium salts with "BuLi and other organometallic bases can take place by two different

pathways.

Fig. 5. Synthetic strategies to obtain diaminocarbenes via a carbenoid

These are, general deprotonation that would lead directly to the carbene (route a) or

metallation that would imply the intermediacy of a carbenoid (route b) (Fig. 5).

Carbenoids were postulated as intermediates by Witîig et. al. in 1941. According to G. L.

Closs and R. A. Moss, a carbenoid is a species that is responsible for electrophilic reactions

instead of a carbene (81. The terni is used pnmarily to characterize a type of mechanistic

behavior and compounds in general that have a metal atom and an electronegative leaving group

on the sarne carbon atom.

1.2 Oxidative Adclition of Alkoxides and AlcohoIs

Analogous to carbenoids, (alkoxysilyl)lithium compounds having alkoxy groups have

been described by the group of K. Tamao (Fig. 6) [9].

@ \ ,Nu Nu - Si, ' Li

Fig. 6. Reaction scheme for silylenoid species

The possible stability of carbenoids N2CLi-OR and N2CCu-OR was investigated by

reacting carbenes N2C: with Li-Alkoxides and Cu-Alkoxides as well as alcohols. Silylenes and

germylenes were likewise investigated. Reactions of carbenes 1 and 2. and germylene, LGe:

with tBu0Li (Fig. 7) and 'BuOCu failed to give the corresponding alkoxy species excepting

silylene, L'Si:. In the case of the addition of alcohols, addition was observed for L'Si:, and

carbene 2.

'Bu 1

'BU I

N I

E = C, Si, Ge

Fig. 7. Synthetic strategy for a-haloorganolitùium species

a-haloorganolithium compounds 1.2A are themally unstable (Fig. 8) [ 1 O]. They are

reactive since the heteroatom works as a leaving group.

1.2A

Fig. 8. Reaction scheme for carbenoid synthesis

1.3 Metnl-Carbene Complexes

The first synthesis of a transition metalsarbene complex 1.3A (Fig. 9) by E. O. Fischer

and A. Maasbol in 1964 opened the gates of organometallic research, such as, in organic

syntheses and catalytic reactions [ 1 I l .

Fig. 9. First transition metal carbene complex

In ail (C0)4Fe(carbene) complexes whose structures are known from diffraction studies

or spectroscopy, the carbene ligands are good donors but poor s-acceptors because of one or

two a-substituents having lone pairs. The carbene ligand always occupies the apical position

(1.3B and 13C), with it's orientation determined by stenc factors (Fig. 10). This is in accord . with a theoretical andysis on site preferences for transition metal penta-coordination [ I l ] .

1.3B 1.3C

Fig. 10 Geometrical positions of the carbene ligand

In this thesis, the reaction of the diaminocarbenes 1 and 2 with Fe(C0)s was

investigated. The X-ray structure could not be obtained as the product (yellow, powdery) did not

20

crystallize even after layering or by heating the sublimed product under reduced pressure. The

presence of a carbene complex was concluded from NMR (lH, 1 3 ~ ) and Fî-IR spectroscopy.

Solubility problems and synthetic aspects are discussed.

ncat

?

1 1 =Fe(CO)2

Fig. 1 1. Attempted synthesis of 1 =Fe(CO).L

1.4 Thioureas and Thiourea Derivatives

Thioureas are used in the pharmaceutical sector, in plant protection, in various technical

applications, and in the synthesis of heterocycles [12]. In the context of this study, we were

interested in thioureas as starting materials for the synthesis of stable carbenes.

Fig. 12. General equation for the synthesis of carbene h m thioureû

The synthesis of the parent compound, thiourea NHz-C(S)-NH~ from calcium

cyanamide is straightforward and is the bais of the current technical process (SKW, Germany).

A number of different methods are available for the synthesis of thioureas bearing substituents

on nitrogen (361. Thiourea is not a good starting material for the synthesis of its N-substituted

derivatives because electrophiles react with the sulfur in most cases. A closer examination of the

synthetic repertoire reveals serious deficiencies:

21

The methods described in the literature are generally incompatible with bulky substituents

on the nitrogen atoms. For example, compound 4 (Fig. 13) could not be prepared by known

methods in yields higher than 1

yield - 70 60 50 18 a

a) yield without 12 = O %

Fig. 13. Literature methods to obtain ihiourea

Existing methods typically use the highly toxic and extremely flammable carbon disulfide or

the toxic and expensive isothiocyanates R-N=C=S as starting materials.

The standard synthesis of thioureas from isothiocyanates and amines is restricted to the

synthesis of RI-NH-C(S)-NR*R~.

This thesis presents a new synthesis for diaminocarbenes, thioureas and stable carbenium

cations. The carbenes are obtained by the reductive dehydrosulfurization of tetra-substituted

thioureas and I,l-elimination of HCl from carbenium salt, [N2CH]+ CI-. The thioureas and

carbenium salis are obtained by the subsequent reaction of amines with formaldehyde and

elemental sulfur. The reaction of the aminals R ~ R ~ N - C H ~ - N R ~ R ~ with typically 114 molar

equivaleni of Se takes place readily between 150 - 180 OC and leads to the formation of

thioureas in modest yields with the major products being the carbenium saits, [N2CH]+ SCN-.

Fig. 14. General reaction scheme for the synthesis of thioureas via aminais

22

The carbenium cation thiocyanates were converted into the carbenes. However,

sublimation work up leads to a broad spectnim of decomposition products (1H NMR).

Chapter 2: Results and Discussion

24

2.1 Dehydrosulfurization of Aïninais (Rm2CH2 with Sa

Thiourea was first prepared by Reynolds by thermal rearrangement of ammonium

rhodanide at Ca. 150 OC (Fig. 15) [Ml.

NH4SCN (NHù2CS

Fig. 15. Synthesis o f the first Thiourea

The reaction between carbon disulfide and amrnonia or ammonium carbonate under

pressure at Ca. 140 O C has not achieved industrial application [14]. Thiourea has three functional

groups: arnino, imino, and thiol. This results from tautomerism between thiourea and isothiourea

(Fig. 16).

Thiourea Isothiourea

Fig. 16. Tautomerism in thioureas

Because of this polyfunctionality and also because of its complex-forming properties,

thiourea has been widely used for more than 30 yean mainly as starting material for nitrogen-

and sulfur-containing heterocycles and formamidinesulfinic acid, as a reaction partner for

aldehydes, and as a component of addition cornpounds and complexes [ 15-19].

Cyclic thioureas have been obtained by the methods known for open-chah thioureas,

and by the reaction of diamines with thiourea [20].

Fig. 17. Synthesis of cyclic thioureas

25

2.1.1 Applications of Thioureas

Thioureas have a wide range of uses, e.g. for producing and modifying textile and

dyeing auxiliaries [2 1, 221, in the production and modification of synthetic resins [23], in repro

technology [24], in the production of pharmaceuticals (sulfathiazoles, tetramisole [25], and

cephalosporins [26], in the production of industriai cleaning agents (e.g., for photographic tanks

[27], and metal surfaces in general [28. 29]), for engraving metal surfaces [30], as an

isomerization catalyst in the conversion of maleic to furnaric acid [3 11, in copper refining

electrolysis [32], in electroplating (e.g., of copper) [35]. and as an antioxidant (e.g., in

biochemistry) [36]. Other uses are as an additive for slurry explosives [35], as a viscosity

stabilizer for polymer solutions (e.g., in drilling muds [36]) and as a mobility buffer in

petroleum extraction [37]. The removal of mercury from waste water of the chlorine-alkali

electrolysis process is possible with thioureas [38]. Thioureas can also be used to extract gold

and silver from minerals [38,39].

Vulcanization accclcmtor,

H

Fig. 18. Thiourea derivatives as vulcanization accelerators

The N-substituted thioureas, that we are investigating, may find use as accelerators for

the vulcanization of polychloroprene and ethylene-propylene-diene terpolymers (EPDM) 1401

(Fig. 18, Table 1).

I Compound Use

thyrotherapeutic agent (th yreostatic)

thyrotherapeutic agent (thyreostatic)

thyrotherapeutic agent (thyreostatic)

ultrashort general narcotic, anesthetic

propy lthiouraci 1 :

rnethylthiouracil

thiamy ta1 a

Table 1 Thioureas in medicine

2.1.2 Objectives

Thiourea 2=S was initially obtained in our group from carbon disulfide / 12 / pyridine:

Fig. 19. Synthesis of 2 5 h m CS2 1 py 1 12 method

27

However, this method suffen from the use of toxic and expensive pyridine and from low

yields (15-20 %). The objective is to directly convert aminals into thioureas using the one-step

dehydrosulfurization approach . This approach has the advantage that aminals form readily and

in high yields even with sterically bulky secondary amines, especially if the reaction leads to

cyclic products. The reaction was investigated first for the Bu-arninal 2-H2 with elemental

sulfur because the desired product 2=S had already been obtained and hlly characterized from

2-C and CSz. Reaction of 2-Hz with S8 (no solvent) starts at 170 OC as evidenced by the color

change and gas evolution. The reaction gives only a small yield of 2=S. Investigation of the

sublimation residue showed that the main product (21%) of the sulfurization of 2-H2 is the

carbenium salt, (2-rn SCN. [&Hl SCN was characterized by single crystal X-ray diffraction

[data set, appendix I l (Fig. 20).

Fig. 20. ORTEP view with hydrogen atoms omitted for clarity. Thermal ellipsoids are at the 50%

probability IeveI. Seiected bond distances [pm] and bond angles [O] as follows: C(1)-N(1) 131.3(2),

C(1)-N(2) 131.4(2), N ( l W ( 2 ) 147.3(2), C(S)-C(3) 15I.7(3), N(2>-C(4) 149.2(2),

N(3)-C(12) 157.8, N(3)-H( IA) 4 14.6, C(2)-C(3) 15 1.7(3), N(3-(12)-H(IA) 14 1.43(O.S),

N( I)-C(I>-N(2) 1 13.80(16), C(1)-N(lW(2) 108.83(15), N(I)-C(2-(3) 102.47(16), H...(N)

24 l(2).

28

2.1.3 Mechanisrn and Product Distribution

The breaking of a C-H bond at the comparatively low temperature of 170 O C is

surprising and requires the proposal of an adequate mechanism. The strength of a typical C-H

bond mles out a direct homolytic fission. It is likely that the initial step of the reaction is the

oxidation of the aminal by a S radical (e. g. 'S-(S)6-S) to the mesomerically stabilized radical

L'CH;?]+' (Fig. Sla).

R-S IL 'BU

I

[;&H

I 'Bu

Fig. 2la. Possible mechanisms for the oxidation of aminals

The radical cation can now loose a proton or a H radical. Both processes are facilitated

by the fact that the cation and radical character of the nitrogen atom is partially delocalized into

the C-H bond via hyperconjugation (interaction of the nitrogen p-orbital with the C-H B*

orbital). The relative importance of the two steps cannot be evaluated with the data at hand. A

computational study is in progress. For al1 the investigated reaction conditions, both the thiourea

and the carbenium cation were fonned. Under the reaction conditions, the carbenium salts and

the thiourea were stable. This rules out the consecutive formation of one from the other (Fig.

21 b). A branching like the one invoked by the mechanistic hypothesis above offers a convenient

explanaiion of this expenmental obsetvation .

III

Fig. 21 b. Possible reaction schemes 1, II and II1 for the sulhization of minais.

Apart from a mechanistic insight, the variation of the reaction conditions had a synthetic

goal, narnely to maxirnize the yield of 2=S or [2-H] SCN. To this end, three different protocols

(A, B, C) were investigated: the amount of sulfur used is an obvious parameter to be studied.

2-H2 2-S 2-C (2-H) SCN

Fig. 22. Synthesis of 2=S h m dehydrosulfiirization of 2-Hz with S8

Method A restricts the arnount of sulfur to the stoichiometrically necessary lower limit

(1/4 equivalent). Method B uses one equivalent which corresponds to a four fold excess of

sulfur under otherwise identical reaction conditions.

Method A gave the highest yield of 2=!3 (15% ) apart from 12-H] SCN (2 1 %) and 2-C

(37 96). A mass loss of 1.85 g was unaccountable after adding up the weights of dl fractions of

the sublimed material.

In order to compare how the different reaction conditions influence the formation of

2=S, and [2-H] SCN, the weights and % yields of each of the corresponding fractions were

tabulated (Table 2).

.-

Table 2. Influence of different reaction conditions on 2=S and [2-Hl SCN formation

The dehydrosulfurization leads to the formation of H2S which in tum could react with

the arninal by protonation. It was therefore attempted to increase the overall yield by adding acid

scavengers. However, addition of K2C03 lowered the yields and gave a more complex product

spectmm as indicated by the 1H NMR of the crude reaction mixtures. The use of additives was

not pursued any further.

Increasing the amount of sulfur (Method B) leads to a decreased yield of both the

thiourea and the carbenium salt (10 %). It is noteworthy, that the thiourea isolated by

sublimation is now contaminated (contrast to Method A) by the unsaturated thiourea l=S and a

number of other compounds that were characterized only by their GC-MS traces. The total

combined weight of the thiourea fractions (7.00 g) exceeds the theoretically possible amount of

5.76 g. It must be concluded, that a substantial part of the volatile Fraction consists of elemental

3 1

sulfur and in fact the total amount of re-isolated sulfur could be as high as 75 1 (6.16 g) of the

total arnount at the beginning of the reaction.

The yield of [2-H] SCN cm be detemined and allows the conclusion that an excess of

sulfur is unfavorable for its formation. Method C is identical to Method A, but the reaction time

has now been increased from 1 h (A) to 30 h (C). This increases the yield of [2-H] SCN from 21

% (A) to 43 1 (C). This clearly demonstrates. that the formation of 12-H] SCN is a slow

process that must involve an unknown intermediate. The thiourea has been ruled out as

intennediate because it is stable under the reaction conditions.

2.2 l=S via [l-H] Cl

The formation of l=S under the given reaction conditions is the result of a

dehydrogenation reaction. Pure 2=S can be transformed into l=S by heating with elemental

sulfur at 170 O C for 18 h. This does not, however, give pure 1=S but always ieads to mixhires of

l=S and the starting material 2=S. Reaction of the stable carbene 1 with S8 in THF at r. t.

proved to be the only way to obtain pure 1=S (Fig. 23).

1 l=S

Fig. 23 Synthesis of I=S fiom 1 in a one-pot reaction

Reaction of 1 with Sg gave two volatile prducts ( 1 0 - 125 O C ) , l=S and a black micro

crystalline product. This black micro-crystalline compound was poorly soluble in benzene (5

g/L ) and gave colorless solutions in chlorofomi. This could be due to decomposition with

CDC13 or poor solubility. The IH NMR in CDClj showed signais at 6(lH, ppm): 1.56 (int. 14 ),

7.06 (d, kt. 1.5 ), 7.36 (int. 2.3), and 7.62 (int. 1).

32

These second set of signals can be tentatively ascribed to compounds of type 2.2A or 23B (Fig.

24a). In view of the volatility of the second component, structure 2.2A seems more likely.

2.2 A 2.2 B

Fig. 24a. Possible sultùr-containing heterocyclic compounds

The sublimation of the black cornpound between 100 -125 OC requires that the

compound has a low molecular weight. It is therefore surprising, that the compound is insoluble

in benzene. The color and solubility of the compound could point towards a zwitterion Z.

I I 'Bu 'BU

Fig. 24b. Possible structure of the 100-125 OC fraction: "Zwitterion" formation

2.3 Synthesis of 3=S

The attempts to obtain the thiourea 3-S analogous to 2=S from the corresponding

diamine 3-C and CS2 (boih with and without the addition of iodine) led to product mixtures and

insoluble and presumably polymeric materials.

The dehydrosulfurization strategy was tried instead. This approach was successfbl as

evidenced by the presence of the thiocarbonyl signal (185.3 ppm) in the I3c NMR spectrum, but

large amounts of the 1,3-diamine and other unidentified / side products were fomed and the

thiourea could not be obtained in pure form.

3-Hz 3 5 3-C 13-Hl SCN

Fig. 25. Synthesis of 3=S

The dehydrosulfurization of 3-Hz differs from the analogous reaction of 2-Hz in three

important ways:

1. The required minimal reaction temperature is substantially lower for the six-membered

ring (1 10 OC) than for the five-membered ring (160 OC).

2. The amount of diamine formed in the reaction is rnuch higher in the case of the six-

membered ring than in the case of the five-membered ring.

3. The volatile fraction contains two additional compounds in substantial quantities for the

six-membered ring, while only traces of impurities were observed in the case of the five

membered ring.

The reasons for these differences are speculative and further variation of the ring size

and the steric bulk of the substituents (here: Bu) is clearly desirable. The formation of the

carbenium cation salt is favored by prolonged reaction times in both cases.

The number of 'Bu signals (4) in the NMR of the sublimate at 150 O C (Fig. 26a)

suggests the presence of 3=S (1.25 ppm, int. 6.5), J-C (1.12 ppm, int. 1) and two unidentified

side products (1.43 ppm, int. 1.4 and 1.60 ppm, int. 1).

Atso, the 13C NMR of the sublimate shows the C=S resonance at 185.32 ppm which is a

direct evidence for the presence of thiourea (Fig. 26b).

Fig. 26a. I H NMR in CDC13 of the sublimate ai 150 O C

Fig. 26b. I3c NMR in CDCl3 otthe sublimate at 150 O C

The yield of 3=S varies between 0% - 40% depending on the reaction temperature and reaction

time (Table 3).

3-H2 : S8 3432 : Sa T [OC] crude 3-c 33s [3-H] S a [mols] [ml t[hl extract 9byields %yields % yields

[ m s l 1:l 1.89 : 2.44 150 3.8gi 2% 40% 122%~

13

Table 3. Influence of different reaction conditions on the formation of products: X, 3=S, (SHI SCN

this reaction was done in a sublimation f l u k and the crude mixture was the sum of the weighi of the yellow crystalline solid on the finger and a black solid at the bottom of the flask. The residue was a mixture of 3=S, [SHI SCN, 3-C and one other unidentified product. The weights of the fractions are measured from the relative intensities of the 'BU signals. ii this fraction is a yellow oil and the NMR shows a mixture of three different products with 3=S being the major product.

High reaction temperatures and long reaction times favor the formation of [3-Hl SCN;

low reaction temperatures favor the formation of 3-C; intermediate reaction temperatures ( 150

OC) favor the formation of 3=S. Attempts to confirm the formation of 3=S by an X-ray structure

led to the isolation and structural characterization of the 1,3-diamine 3-C instead (Fig. 27).

Fig. 27. ORTEP view with hydrogen atoms omitted for cliuîty. Thermal ellipsoids are at the 50%

probability leveI Selected bond distances [pm] a d bond angles [O] as follows: N(l)-C(l) 146.40(13),

C(1 W ( 2 ) 152.34(14), C(2)-C(3) 152.23(15), N(l)-C(4) 147.88(13), N(1 +C(1 )-C(2) 1 1 1.76(9),

36

Attempts to grow crystals of 3=S by sublimation (150- 160 OC) or crystallization (1 :2

mixture of CHC13 and hexanes) were unsuccessful. The sublimation residues consist of pure

carbenium sait 13-H] SCN. The sait is obtained in an overall yield of 34 % (reaction conditions:

190 OC / 40 h) and has been unambiguously characterized by single crystal X-ray

crystailography (appendix 1, Fig. 28).

Fig. 28. ORTEP view with hydrogen atoms ornitted for clarity. Thennd ellipsoids are at the 50%

probability level. Selected bond distances [pm] and bond angles [O] as follows: N(l)-C(I) 130.2(6),

C(2)-C(3) 139.7(7), S( l ) -C(7) 160.0(12), N ( l M ( 4 ) 146.6(7), C(1)-N( 1 ) -C(2) 1 16.0(5), N(1)-

C( 1 )-N( 1)#2 129.5( 10). C(3)-C(2)-N(l) 108.9(5), C ( 2 ) # 1 4 ( 3 j C ( 2 ) 24.7(4), H--(N) 394(5).

37

2.4 Synthesis of Imidazoüum Sdts from Glyoxai

The imidazolium salts are now of considerable interest as starting materials for the

synthesis of Arduengo carbenes [6h].They form easily from a primary amine, glyoxal,

formaldehyde and hydrochloric acid (Fig. 29). The reaction has so far (1998) only been

descri bed 'BU 'BU

'BUNH~ (2 eq.) ' c P I

O 6NHCll24hA THF N I

'BU I

'BU

Fig. 29. Synthesis of [l-H] CI fiom glyoxal

in three patents [41a,b] that give no details on the synthesis, work up and purification. The

mechanism of this one-pot condensation reaction is also unclear.

The intermediate formation of the corresponding 1,4-diazadienes from the primary

amine and glyoxal was considered as a mechanistic possibility. It was therefore desirable to find

out if the imidazolium salts can be obtained directly from the diazadiene. Mixtures of 1,3-Di-

ter?-butyl-l,4-diazadiene, formaldehyde (35 % in water) and hydrochlonc acid in different

solvents did not produce any imidazolium salt and only shifts of diazadiene were present (IH

NMR).

Fig. 30. Attempted synthesis of (1-Hl CI Born diazadiene

It was therefore decided to establish the experimentai details missing in the patent. The

patent requires first the addition of paraformaldehyde to 6N HCl followed by addition of tert-

butylamine and finaily glyoxal.

38

M e r 24 h stimng at r.t.. the lH-NMR (CDC13) of the aqueous phase shows the signas

of [1-HICI (1.79, 7.45 and 10.0 ppm) and a second unidentified component (1.45 s, 4.99 m,

8.30 br., 9.75 br.) The signals of the unknown second component are in agreement with the

formation of [1-HJOH. An attempt to conven this "hydroxide" into the chloride with MqSiC1

failed, but the formation of 11-HJCI can be completed by heating the crude reaction mixture to

reflux for 24 h. The resulting dark brown viscous liquid was sublimed at 90-180 OC oil bath

temperature. The sublimate is a creamy off-white solid and poorly soluble in CDC13). it is free

of [1-aC1. The brown. solid sublimation residue is pure [1-HICI. Total yield is 64 96.

[l-HJCI. was charactetized by single crystal X-ray crystallography (appendix 1, Fig. 3 1).


probabilîty level. Selected bond distances [pm] and bond angles [O] as follows: C(l)-Cl(I) 328.4(6),

H(lA)-CI(l) 267(5), C(1j-N(1) 1335(7), N ( l j C ( 2 ) 137.7(7), N(2)-C(8) 15 1.7(6), C(3)-C(2)

135.9(7), C(1)-N(IW(2) 108.3(4), C(3)-C(2)-N(l) 107.1(5), N(l)-C(l)-N(2) 108.8(5).

39

2.4.1 Deprotonation of [l-Hl CI to give 1

The irnidazolium salt was deprotonated with "BuLi in THE sublimation gave 72% of

carbene 1 (white powdery, sublimation temp. 60-80 OC).

'BU 'BU I "BuLi THF 1 2S°C I 8 h

b - QU-H (g)

Fig. 32. Synthesis of 1 by deprotonation of (1-Hl CI

Notes:

1. The 1H NMR shifts of the imidazolium salt (in CDCl3) are critically dependent on the

water content of the compound.

2. The 'Bu-cornpound has not been described in the literature, but the 1H NMR data of the

ipr-cornPound has been reported and closely matches that of the Bu compound.

3. Formation of the imidazolium salt is incomplete after 1 h of reflux.

4. 1H NMR of the crude reaction mixture showed two different BU-signals.

5. 1H NMR showed the sublimation residue to be pure imidazolium salt, the sublimate

shows signals at &lH, CDC13, ppm): 1.45 + 1.49 (int. ratio 3: l ) , 1.72, 2.59 ( t ) , 2.77 (d),

4.19 (s, weak), 5.80 (s, weak) and was not further analyzed.

6. The signals of the sublimate are identical to the impurity in the crude material.

7. Attempted deprotonation of 11-Ii] CI with THF I NaH at room temperature did not lead

to the formation of carbene and showed only signals for Il-IQ Cl.

The carbene 1 was further characterized by single crystal X-ray crystallography

(appendix 1, Fig. 33).

Fig, 33. ORTEP view with hydrogen atoms omitted for clarity. Thermal ellipsoids are at the 50%

probability level. Selected bond distances [pm] and bond angles [O] as follows: N(l)-C(I) 136.6(2),

N(l)-C(2) 138.0(2), C(2)-C(3) i34.1(2), N(l)-C(4) 148.9(2), C(1)-N(lbC(2) 112.57(12),

C(3)- C(2)-N(1) 106.23(14), N(2)-C(1)-N(t) 102.19(12).

2.5 Properties of Imidazolium Salts

2.5.1 Basicity of Carbenes and Acidity of Imidazolium Salts

The imidazoliurn sait [l-ZT] Cl is the C-protonated derivative of the stable carbene 1. It

seemed interesting to compare the structures of the carbene with the structure of the carbenium

cation and to establish the relative basicity of different carbenes through proton exchange

reactions. In a preliminary snidy, it was investigated if the imidazolium salt possesses any

significant CH acidity . To this end, mixture of [l-8] Cl and D20 was investigated, but did not

show any H / D exchange products.

Fig. 34. Deuterium exchange reaction of Il-Hl CI

It can therefore be concluded, that the acidity of the imidazolium salt is quite low,

presumably c 20. The [1-Hl Cl salt was first pumped Ln vacuo at oil bath temperature of 180-

190 O C for 18 h to dry the salt. The exchange experiment was perforxned in a flame sealed NMR

tube. No exchange was observed over a period of 7 d at 25 OC and at 1 10 O C for 22 h.

The relative basicity of the carbenes 1 and 2 was studied through a competition experiment.

Fig. 35. Proton exchange reaction behveen Il-Hl Ci and 2

A sealed NMR sample of an equimolar mixture of [bH] Cl and 2 (Fig. 35) in C a 6

showed signals for the conjugate base, narnely the carbene 1. The two carbenes are present in a

ratio of 1 1 2 = 1 1 18. The signals of the carbenium salts were not observed because they are

insoluble in C&j.

For the mixture [2-8] SCN I l (Fig.36), equilibration led to a ratio of 1 1 2 = 7 1 1.

'BU 'BU 'BU 'BU 1 SCN- 1 1 SCN - 1

CbDb [Y. + cN): - N 25 O C ["H N + [)

I 'BU

I 'BU I

'BU I

'BU

12-Hl SCN 1 [l-HI SCN 2

Fig. 36. Proton exchange behveen I2-HI SCN and 1

After 21 d, this ratio changed to 1 I 2 = 2.7 1 1 (Fig. 36). This indicates that the

protonation equilibrium is slow.

Apart from the tBu signals of the newly formed carbeme 2 (1.36 ppm). new signals at

1.67. 1.83, 2.73, and 6.29 ppm which contribute to the formation of [l-H] SCN (1.83, 6.29). It

is noteworthy, that the saturated carbenium salt [2-Hl SCN is insoluble in benzene (absence of

signals in C6&) while the unsaturated salt [l-H] SCN is soluble in benzene (20 gL) . Although the data indicate that the two carbenes are of similar basicity, the obtained data

could also reflect the relative solubilities of the two imidazolium salts. It was therefore

necessary to repeat the investigation in a solvent that dissolves d l 4 compounds without reacting

with them. THF was investigated but found unsuitable because of signal overlap with the b u -

signals and the N-CH2 signals. The 13c NMR of the mixture of 2 and [1-Hl CI (Fig. 35) showed

resonance at 16 1.46 ppm which indicates the formation of [ 2 - 9 CI. The signals for Ç(CH3)3

and CH3 were hidden under THE So, a different solvent was desired that would dissolve both

the reactants and the product.

HMPA dissolves [3-R] SCN but does not dissolve [1-A] CI. Although HMPA is very

inert towards reducing agents - many reductions with elemental Li, Na and K can be

conducted in HMPA - oxygen transfer reaction between HMPA and the carbenes 1 and 2 can

not be ruled out. The sarne reaction was tried in HMPA, but 11-HJ CI was completely insoluble

in HMPA even though 2 is soluble and stable in HMPA. The reaction mixture only showed

chernical shifts for 2.

43

It was found, that the unsaturated carbene 1 is inert towards HMPA. A mixture of 1 and

HMPA (1: 1) in C& showed only carbene signals at 1.44 and 7.09 ppm. In neat HMPA the

shifts are 1.54 and 7.34 ppm. These values are slightly shifted vs. the values determined in

C@6. The signal of the ring protons is slightly broadened. The reason for this line broadening is

unclear.

A mixture of 1 and [3-H] SCN in HMPA was also measured with a D20 insert and TMS

as intemal reference (Fig. 37). Although the signals for the supposedly formed carbene 3 could

not be unambiguously assigned because they are partially hidden by the strong and broad

HMPA signal at 2.6 ppm. proton exchange must have taken place because the carbene 1 has

been consumed (no signals) and the salt [l-Hl SCN has been fonned (1.76,7.2 and 10.7 pprn).

'BU 'Bu 'Bu 'Bu I ' s o l - 1 1 SCN -

HMPA/DtO CF. + cN): N - 25 OC

I I 'BU 'BU

I 'Bu

l 'BU

13-H] SCN 1 3 [i-Hl SCN

Fig. 37. Proton exchange between 13-HI SCN and 1

Due to it's poor solubility in benzene (10 g L ) , the signals of [3-H] SCN were completely

invisible. The signal at 1.38 pprn is assigned to the new carbene 3, the signal at 4.5 pprn to

HDO. A signal at 1.02 pprn remains unaccounted for.

The 13~(1H) spectrurn of the sample shows the signals for [1-H] SCN (29.49

[C(çH3)3], 60.12 [Ç(CH3h], 121.45 [ÇH=ÇH], 134.66 [ç+-Hl, 160.91 [SÇN-1) and for 3

(29.04,39.42,60.78). The signal for the carbene carbon of 3 was not observed, presumably due

to low intensity.

Although the carbenium salts show variation in solubility, they are al1 non-volatile. Their

ionic composition was verified by X-ray structures (appendix 1). The structures do noi show any

covalent bonding between the carbenium ions and the counter ions CI- and SCN-. In solution,

the NMR shifts of the carbenium salts depends on the nature of the counter ion (Table 4). This is

strong indication for the formation of ion pairs in solution.

11-a CI Il-H] SCN [2=Ef] Cl [SEI] SCN W(CH3)3) 1.8 1 1.84 1.55 1.52

NCcH) 7.7 1 7.4 1 4.05 4.1 1 & C D 0 119.71 1 19.47 57.20 56.86

Table 4. Influence of counter ion and aromaticity on the chemical shifts

A mixture of [LH] Cl and [3-H] SCN was investigated to find out if the contact ion

pairs exchange rapidly on the NMR time scale. At room temperature, there was only one set of

signals for each of the salts. This implies a rapid exchange of the counter ions; in the case of

slow exchange, signal broadening or even four different sets of signals would be expected.

[i- H] Cl [3- H] SCN 11- H] SCN 13- Hl CI

Fig. 38. Proton exchange between 11-m CI and [SHI SCN

The acidity of C- H bonds cm be estimated from the ' J (C,H) coupling constant. The

empirical relation denved from compounds with known hybridizations like ethylene (sp2) is:

IJ (c,H) = 5 * (% S) [in Hz1

Although the equation [69] is strictly valid only for hydrocarbons, it can nevertheless be used to

estimate the relative acidity of other sets of closely related compounds. For the carbenium

cations the following sequence of relative C-H acidities was established (Table 5) .

carbenium 1 J (c,H) 96s p

sa1 t [Hz] [l-Hl CI 2 19.7 44 [2-H] cli 201.4 40 [l-Hl SCN 201.3 40 12-H] SCN 199.9 40 13-H] SCN 189.1 3 8

Table 5. % s character in the C-H carbon of the carbenium salts

i obtained by I. Rodezno (unpublished results)

The data are interesting in two respects. First, the effect of ion pairing is clearly visible

from the difference of the coupling constants for the pair [1-H] SCN and [l-H] CI (Av = 8.4

Hz). Second, for [2-H] CI and [2-H] SCN, the coupling constants are very similar (Av = 1.50

Hz). It is also interesting to note that different types of carbenium ion salts can show similar

CH-acidity, e.g., 12-Hl CI / [1-Hl SCN (Av = O. 10 Hz).

2.5.4 Solubilities of Carbenium Salts

The solubility of the carbenium salts in waier and organic solvents was investigated to

properly plan the synthetic work-up and reactions. Table 6 reveals the important influence of the

counter ion.

22 50 20 [SHI SCN 100 1 50 10

Table é. Solubilities of carbenium salts in g/L

46

While the chloride [1-Hl CI is very soluble in chloroform and water, the thiocyanate [l-Hl SCN

is only moderately soluble. A possible explanation is a higher degree of covalency in the

thiocyanate. Solubility data of [2-Hl salts will eventually complete the picture and allow a

consistent interpretation.

2.6 Deprotonation Stntegy to give 2 from [2-H] SCN

The fact that the thiocyanate salts [1-Hl SCN. 12-Hl SCN and [3-Hl SCN can be

obtained from very inexpensive starting materials through hydrodesulfurization makes them

attractive starting materials for the synthesis of stable carbenes.

'BU 'BU

LDA (2.1 cq.) LiSCN 25 OC, THF

I - LDA-H I 'BU 'BU

(2-HI SCN 2

Fig. 39. Deprotonation of 12-HI SCN to give 2

A number of different deprotonation bases were investigated. Diaminocarbenes were

fonned, but, upon attempted sublimation, only decomposition products were isolated. This

cannot be explained with low thermal stability of the carbenes, as al1 carbenes under

investigation were previously obtained by alternative methods (deprotonation of the carbenium

chloride salt, reduction of thioureas) and found to be thermally stable. The characteristic odor of

sulfur compounds noticed in the decomposition products suggests most likely the reaction of

carbene 2 with the counter ion SCN-• This hypothesis suggests a possible modification of work

up to prevent the decomposition reaction. Work up in this thesis consisted of simple transfer of

the crude reaction mixture to the sublimation flask. If decomposition is indeed caused by the

reaction of carbene with the side product LiSCN, the high solubility of the carbene in

hydrocarbons should allow separation of the carbene from the thiocyanate prior to sublimation.

47

The deprotonation base and the nature of the carbenium cation were found to be important.

While [3-Hl SCN gave the conesponding carbene &er sublimation when LDA in THF was

used as deprotonation base, no carbene could be isolated when "BuLi was used as base.

In the case of 12-H] SCN, the carbene could be generated with LDA but decomposes upon

sublimation work up.

Ring opening hydrolysis of the carbenes 2 and 3 was found to be a side reaction during

the isolation of 2 and 3. The 1H NMR of the sublimate at 50 O C showed resonances at 6 ( 1 ~ ,

C&, ppm): 1.32 (int. l), 1.36 (2, int. 1) and 1.55 (int. 3.5) along with resonances for 2-CHO

6(lH, CaDa, ppm): 0.85(s), 1 .Ol(s), 2.7 1(t), 3.34(t), and 8.40(s). Signals of 12-H] SCN were

absent. The signais at 1.32 and 1.55 ppm remain to be identified.

2.7 Deprotonation Strategy to give 3 from [3-H] SCN

The synthesis of 3 from the easily accessible thiocyanate 13-Hl SCN by deprotonation is

particularly important in view of the inaccessibility of the thiourea 3=S (Fig. 40).

'Bu 'BU 'BU I

il C - H -

THF NH I

'Bu

[SHI SCN 3 3-CHO

i ) 2. t equiv. of "BuLi or LDA or Cdimethylamino-pyridine

Fig. 40. Deprotonation of [%Hl SCN to give 3

The sublimation gave the following fractions (Table 7).

Sublimation Weigbt Appearanee

90 - 100 0.04 black grandar residue 0.5 1 black solid

Table 7. Sublimation hctîons for the deprotonation of P-m SCN wiîh LDA

48

The coiorless liquid (80-90 OC, Table 7) was identified by 1H NMR to be 3 (6(1H): 1.38,

1.67,2.67 ppm) (Fig. 41).

n t -

Fig. 41. I H NMR in CgDg of the 80-90 OC fiaction (colorless oil)

The sublimation residue contained a rninor product with signais at 0.85 and 1.03

ppm. This product is tentatively identified as the ring opened hydrolysis product 3-CHO. This

interpretation is also supported by the isolation and structurai characterization of the analogous

2-CHO.

Fig. 42. Stnicture of 3-CHO

2.8 Other Deprotonation Bases

4-Dimethylamino pyridine as possible deprotonation base was tested for both [2-H]

SCN and 13-H] SCN but did not react (r. t., 4 h, 1H NMR). The use of "BuLi was also

unsuccessful in the deprotonation of [2-tn SCN and [3-EI] SCN. This is in line with the known

nactivity of the thiocyanate ion (Fig. 43).

Fig. 43 Reaction of SCN' with "BuLi

DMF Chloride

'BP Mtthod 1 rNH DMF Chloride

Fig. 44. Reaction schemes for 13-HI CI formation

'9 ,& Mtthod 2 *O C h

PbCI2 or HCI N te:

A solution to this problem would be the use of chloride salts instead of thiocyanate salts.

Two methods for the synthesis of chloride salts are curiently being investigated (Fig. 44).

50

f 9 Aromatic, Anü-Ammatic d Linear Coqjugated Poly-carbenes

The strong aromatic delocalization in the diaminocarbene 1 suggests that polycarbenes

of the general type (R-N-C:), should also be delocalized.

Fig. 45. Delocalized poly-carbenes

Calculations (M. Denk, unpublished results) indicated, that the aromatic carbene 7 (Fig.

45) is perfectly planar (MP2 / 6-3lG*) (LNCN = 108.20, LCNC = 13 1.80) while the anti-

aromatic carbene 6 adopts an envelope geometry (LNCN = 87.g0, LCNC = 85.30). The C-N

bond distances in 7 were found to be equal and short (137.6 pm). The anti-aromatic carbene 6

shows elongated C-N bond distance ( 14 1.3 pm).

None of the representatives in Fig. 45 excluding 1 has been obtained. Especially, the

aromatically stabilized tris-carbene 7 was considered to be a candidate of potential high

stability. Possible strategies for the synthesis of 7 are oudined in Fig. 46. Investigations in this

thesis are restricted to the synthesis from the possible desulfurization of tris thiourea 11. The

desulfurization method had been previously developed in Our group and is well suited for the

synthesis of both stable and transient diaminocarbenes [7]. The trimerkation of isonitriles is

endothermic (MP2 / 6-3 1 G* level).

5 1

The synthesis of the tris thiouna 1lfBu proved to be a formidable task. While the îris-

methyl derivative Il-Me cm be obtained via a traditionai multistep synthesis. al1 other membea

have k e n obtained from ultra high pressure trimerizations [42].

w

dchydrogcnation

\ k//" F/ F

RA *\R fi' S

11 only known for R = Me, Et, "Pr, "Bu, Ph

Fig. 46. Synthetic strategies for tris-carbene

The group of Yoichi Taguchi in Japan succeeded in trimerizhg Me isothiocyanate (12-Me) to

1,3,5-trimethyl- l,3,5-triazine-2,4,6 (lH,3H,SH)-tnthione (Il-Me) (Fig. 47) under high pressure

(800 MPa) [42]. The reaction also requires catalysis by Et3N: or pyridine. Sterically hindered

pyridines do not catalyze the reaction.

Fig. 47. Synthesis of 1bMe

52

The rate of trimerization of 12-Me was found to be proportional to the amount of

triethylarnine catalyst used. Ethyl isothiocyanate also trimerized in high yield under the same

reaction conditions. Bulkier groups like R = "Pr, "Bu, allyl, Ph, and cyclohexyl gave very low

yields. A second protocol using DBU as catalyst under 800 MPa at 130 O C for 20 h resulted in

the trimerization of "Pr and "Bu isothiocyanates in good yields but failed for larger alkyl groups

( i ~ r , tBu). Allyl isothiocyanate polymerized in the presence of DBU but the trimer was obtained

in the presence of triethylamine at even higher pressures ( 1200 MPa) in good yield (421.

This serves to illustrate that general methodologies for the synthesis of tris-thione-

triazines 11 remain yet to be developed.

Attempts by Martin Ma in Our group to develop catalysts for the low pressure

trimerization of 12 to give 11 were unsuccesful. It was therefore decided to investigate the

transformation of 9 -> 11 by dehydrosulfurization. The transformations 9 -> 7 and 10 -> 7 are

cumntly under investigation in our laboratory. The transformation of aminals into carbenium

cations is demonstrated in this work for 1-Hz, 2-Hz and 3-H2.

2.10 Reactivity of lJJ- tri-tefi-butyl-hexahydro-sym-triazine with Sg

The reaction of 1,3,5-tri-tert-butyl-hexahydro-sym-Win with eIemental sulfur ai 140 -

160 OC gave mixtures that were separateci by sublimation (Fig. 48). The degradation products 13

and 14 that form the volatile part are readily explained. No mechanistic explanation can be

offered for the formation of [1-HJ SCN (17% yield, sublimation residue). Although surprising

and unexplained, the formation of [l-H] SCN (17 %) constitutes an inexpensive and fast

synthesis for this compound.

Sublimation weight Appearance Assignment Temp. [% yield]

--80 35 crystalline, yellow 14 80 - 120 36 crystalline, yellow 13 120 - 140 - oily, orange 13114= 1.5/1 residue 17 flaky, oranp;e [l-a] SCN

Table 8. Dehydrosul~t ion of 1,3,S-tri-tert-butyl-hexahydr0csym-triaPne (140 OC, 26 h),

53

The absence of Il-'Bu was confirmed by NMR (IH, ' 3 ~ ) and GCIMS. Upon dissolving

the sublimation residue in CHC13 and layering with twice the volume of hexanes, a brown

precipitate was obtained.

'BU SCN - I [EH +

I 'Bu

Il-HI SCN

314 S*

'BU

yN4 , N ~ N \

'BU S 'Bu

Fig. 48 Decomposition products of the reaction of 9 with Sg

This presumably polymeric material is insoluble in water and displays a characteristic

NH band (3643 cm-'), and a strong and broad band at 2061 cm-1 (-N=C=S), and an N-C=C

band (1651 cm-').

While the formation of 13-Di-teri-butyl thiourea 13 is supported by NMR (IH, 1 3 ~ ) and

GC/MS, evidence for the formation of tert-butyl thiourea 14 is less convincing (lH, 1 3 ~ NMR).

Table 8 illustrates the fractions obtained by a typical work-up.

The CHCl3-soluble part of the sublimation residue is pure [l-Hl SCN and was

characterized by single crystal X-ray crystallography (Fig. 49).


probability b e l . Selected bond distances [pm] and bond angles [O] as follows: S( 1 )-C( 12) 164.94( 18).

Repeating the reaction led to the product distribution outlined in Table 9.

sublimation temp. weight ~ppearance - ~orn~chents-. r Oc1 Egramsl

6 0 - 100 1.55 oily, yellow 2 + 14 100 - 140 140 - 180 180 - 195 195 - 200 200 - 220 residue

1 .O0 flaky, yellow 2 O. 12 creamy, yellow 2 0.47 creamy, yellow 2 0.26 oily, yellow [BUNCS + 15 0.63 crearny, pale yellow 2 + 14 0.5 flaky, pale yellow 1 + ~BUNCS +

15

Table 9. Sublimation fiactions obtained fiom large scale dehydrosulfuritation o f 1,3,5-tri-tert- butyl-hexahydro-sym-criaine at 150 OC, 58 h

None of these fractions contained Il-tBu and the residue was not [1-H] SCN (lH, 1 3 ~ ,

GC/MS). A possible reaction scherne for the formation of the tris-thiourea would be as follows

(Fig. SOa,b) .

'BU, 4 'Bu HN N'

Fig. SOa. Reaction scheme for the dehydrosulfurization of 1,3,5-tri-tert-butyi-hexahy&o-sym-triazine

Fig. SOb. Possible sulk-exchange reaction between 9 and 15

56

A 13C NMR simulation software was used to simulate t h e I 3 ~ NMR shifts for mono-,

bis- or tri-substituted thioureas (Fig. SOC).

Fig. SOC. I3c NMR simulation of mono-, bis-, tri- substinited thiourea

2.10.1 Multistep Approaches for the Synthesis of Il-'Bu

Compound 16 is a necessary intermediate in the synthesis of Il-<Bu from 13. It is

therefore reasonable to use it as starting rnaterial for future dehydrosulfurization reactions.

Preliminary results indicate the formation of 16 from 13, parafonaldehyde and ten-butyl amine

(Fig. 5 1).

1 'BU-NH, s 1 THF

BU. K :BU N N 'BU-N NJBU -

H H 25 C 2d /J r

Fig. 51. Attempted synthesis of 16

The crude reaction mixture showed lH NMR signals at 1.37 and 1.47 ppm but the

observed relative intensity (1 8 : 1 1.3) deviates from the required intensity ratio of 18 : 9.

57

This may be due to the superposition of the signals of 16 and another unidentified product. The

formation of the triazine 9 c m be ruled out on the basis of its 1H NMR data (1.05, 3.45 ppm).

The 13-Di-tert-butyl thiourea used in the reaction was contarninated with 28% mono-tert-butyl

thiourea (IH NMR). This presumably led to a mixture of products upon reacting it with

paraformaldehyde and tert-butyl amine.

The 13C(lH} spctmm of the crude in CDCl3 showed strong signals at 29.41 and 29.87

ppm, with weak signals at 30.97, 122.63, 128.5, 134.25 and 224 ppm. No signal around 180

pprn was observed and also no signals for quarternary carbon around 50 ppm were observed.

From the FT-IR data (NaCl, nujol), bands at 3301 and 3266 cm-' appear as a doublet indicating

an NH2 stretch.

Al1 these results support the absence of the mono-substituted thiourea and the presence

of a mixture of 13 and 14 (1H NMR).

2.11 1,3,5-tri-tert-butyl-hexahydro-sym-triazine and conformations in other 1,3,5-triazines

As discussed in chapter 2.9, 1,3,5-tri-tert-butyl-hexahydro-sym-triazine 9 is a potential

starting material for the synthesis of the tris-carbene 7. Like most hexahydro-sym-triazines, 9 is

in equilibrium with the imine CHZ=N(~BU) 4. This chapter will discuss the synthesis and

properties of 9 and its derivatives.

1,3,5-triazacyclohexane, the most simple of hexahydro-triazines was obtained in 1895

from a mixture of aqueous formaldehyde-ammonium chloride upon addition of potassium

carbonate but has never been obtained as such [42]. Obviously, this compound transforms into

the very stable urotropin with it's tetra-aza-adamantane structure. In solution, the compound is in

equilibrium with irnine CH2=NH. Hexahydro-synt-triazines with substituents on nitrogen can

not form urotropin and are typically more stable, but can also dissociate into imines.

Hexahydro-sym-triazines can exist in different conformations as Table IO shows

structurally c harac terized exarnples (Cambridge Database up to May 1 998).

58

As the data show, the equatonal, axial, axial (eaa) conformation is the most common,

eea and even aaa conformations are known.

Ri = R2 = R3 Conformation Ref. aaa 57 eaa eaa eea eee eee eea eea eea eaa eaa eaa

PhOCH7- eaa 66

Table 10. Conformations of hexahydro- l,3,5-triazines (hexahydro-sym-uiazines)

Reaction of 'Bu-NH2 with parafomaldehyde gives 1,3,5-tri-tert-butyl-hexahydro-sym-

triazine after one day of reaction at r. t. The use of paraformaldehyde is convenient because its

dissolution allows to monitor the reaction [S. Rodezno, unpublished results]. The triazines

separate from aqueous solution as oily layers that c m be separated and drkd with Ba0 or KOH.

For MeNH2, no phase separation was observed and the product was isolated by repeated

extraction with Et20.

Reaction time is only 20 mins. in this case. 33% solutions of fonnaidehyde react even

faster but lead io products of lower punty.

ta..

Fig. 52. Synthesis of 1,3,5-tri-tert-butyl-hexahydro-sym-tnazine

As generally found for hexahydro-sym-triazines, compound 9 is in equilibrium with 4.

The formation of 9 is favored in concentrated solutions.

59

This equilibrium leads to the pualing observation, that in C&, the ratio of 9 1 4 is

concentration dependent. As expected, dilution leads to a decrease of 9 1 4. In the more polar

CDC13, sipals for 9 are weak or even absent, while the polar imine 4 is obviously stabilized by

polar solvents.

Attempts to obtain crystds for the triazine 9 failed and gave only sticky oils. This could

be due to the fact that 9 is a mixture of different anomers. However, a melting curve recorded

for 9 gave only one small inflection point at 5 OC (Fig. 53).

Melting point of 1,3,5-tri-tee-butyl hexa hydro-s- triazine

Fig. 53. Graphical representation of the meiting point of 9

60

2.12 Dehydrosulfurization of Urotropin

Urotropin is nlated to the hexahydro-s-triazines studied in this thesis. Attempts to obtain

dehydrosulfunzation products with cage structure led to the formation of methylurotropiniurn

thiocyanate [S-CH31 SCN as the only identifiable product (Fig. 54). The compound was

characterized by single crystal X-ray crystallography (Fig. 55).

5 [S-CH3] SCN

Fig. 54. Synthesis of methylurotropiniurn thiocyanate

+ unidentified cornpounds

Fig. 55. ORTEP view with hydrogen atoms omined for clruity. Thermal ellipsoids are at the 50%

probability level. Selected bond distances [pm] and bond angles [O] as follows: N(4)-C(6) 116.2(3),

S(I>-C(6) 165.2(2), N(2)-C(2)#1 153.12(17), N(2+C(5) 148.0(3), C(3)#1-N(3) 147.59(17),

C(SbN(2>-C(2) 1 1 l.l4( IO), C(2+N(2+C(l) lO8.l7(lO), C(2*1-N(2)-C(l) 108.17(10), N(1+

C(2+N(2) 1 10.18( 121, N(l)-C(3&N(3) 1 1 1.78(12), N(lH(4)-N(1)#1 1 1 1.80(16), N(4)-C(6)-

S(1) 179.7(2).

61

The fluoride analog of the salt has been introduced recently as a source of naked fluoride

ions by Clarke et al. Methylurotropinium fluoride dihydrate can be obtained from urotropin and

methyl iodide via 1-meihylhexamethylenetetraarnine iodide, which is then converted to the

corresponding fluoride by metathesis with AgF. The compound has high thermal stability and

the large size of the cation makes it a g w d source of F- ions. More recently, Robert Gnann and

coworkers have reported a single-step one pot synthesis of this compound and it's application in

the isolation of the anhydrous fluoride as well as in a coupling reaction [43].

2.13 Reaction of Carbones and Carbene Analogs with Alkoxides

The oxidative addition of metal salts MX with X = RO, Hal, NR2 etc. leads to

carbenoids. Carbenoids are typically obtained by lithium-halogen exchange from 1, l-dihalo-

alkane. They only possess marginal stability and decompose above -100 O C to give the typicai

decomposition products of free carbenes [44].

Fig. 56. Decomposition of halogen substituted carbene species to carbenoid

The reductive elimination of alcohols from ester-arninals N2CH-OR to give carbenes

N2C: has been applied for the synthesis of tetraamino-olefins from amines and ortho-esters (Fig.

57).

Fig. 57. Reductive elirnination of alcohols

62

There is, however, no evidence for the operation of this mechanism other than the formation of

the enetetraamine. Even the thermodynamic equilibrium between N2CH-OR / N2C: + ROH is

unclear at present. Silylenoids, the sila-analogs of carbenoids have received little attention but

are now investigated by the group of K. Tamao at Kyoto [44]. The possible oxidative addition

of alcohols to carbenes 1 and 2, L'Si: and LGe: was investigated to this end.

The oxidative addition of tBuOCu, 'BuOLi, tBuOH and MeOH to the carbenes 1 and 2

as well as their sila- and germa-analogs was investigated. The [BuOLi in this study was obtained

from BuOH (as received) and nBuLi.

The [BuOCu has the unique property of strong affinity towards n-accepting ligands [93,

941 and was obtained from tBuOLi and CUI and purified by sublimation ( 130 - 150 OC, 0.1

Torr).

The reaction of tBuOH with carbenes 1 and 2, L'Si: and LGe: was investigated. To

study the effect of steric hindrance, BuOH was replaced with MeOH.

2.13.1 Reactions of Carbenes with Alkoxides and Alcohols

Carbenes 1 and 2 did not react with tBuOCu both at r. t. and after prolonged heating at

110 OC for 7-10 d. The reaction of carbene 2 with tBuOLi showed absence of starting materiai

and the presence of new signals at 1.32 (2H), 1.35 (1 H) and 3.05 ppm (0.5H) that suggested the

formation of 2-(0t~u)~i

dilute sample.

1 'BUOL~ - THF

(Fig. 58). A 1 3 ~ NMR of this sample could not be obtained due to a

' ~ p

[NU"" +

I 'Bu

Fig. 58. Synthesis of 2-(0fBu)~i

63

Attempts to repeat the reaction only led to the formation of the hydrolysis product 2-

CHO that was charactenzed by single crystal X-ray crystallography. No reaction occurred

between tBuOLi and 1 (25 OC 1 7 d followed by 100 O C 1 14 d) (Fig. 59).

'BU 'BU I I

1 'BUOL~ N O 'BU

N Li I

'BU I

'Bu

Fig. 59. Reaction of I with 'BuOLi

Reactions of tBuOH with 1 and 2 only gave hydrolysis reaction and were not pursued

any further (Fig. 60).

Fig. 60. Reactions of I,2 and LGe: with 'BUOH (1:2)

No reaction was observed between 1 and MeOH even after heating over a penod of 7 d

ai 100 O C . Reaction of 2 with MeOH showed signals for 2-(0Me)H at &'H, C&, ppm): 1.13,

2.73, 2.94, 3.24, 5.23 and a minor product: 6(lH, C6D6, ppm): 0.86, 1.01, 2.57, 8.40 identified

as 2-CHO upon sublimation work up (Fig. 61).

'BU 1 McOH 'BU I

'Bu I

25 OC

Mat

I NH

'BU I

'BU I

'Bu

2 240Me)H 2-CHO

Fig. 61. Synthesis of 24OMe)H using I : 1 ratio of 2 to MeOH

Compound 2-CHO was characterized by single crystal X-ray crystallography (Fig. 62).

Fig. 62. ORTEP view with hydrogen atoms ornitted for clarity. Thermai ellipsoiâs are at the 50%

probability level. Selected bond distances [pm] and bond angles [O] as iollows: N( l ) -C( l ) 134.14(18),

N(l s ( 2 ) l49.38( 18). C( 1 ) -C(6) 152.5(2), C(6)-N(2) 145.86(18), O(I)-C(11 j N ( 1 ) l23.98(14),

C(t)-N(lH(2) 1 l8.7O(ll), N( l ) -C( l jC(6) II4.15(12).

2.13.2 Reactions of L'Si: with Alkoxides and Alcohob

The reaction of L'Si: with tBuOCu gave new product signals at &lH, C6D6): 1.28

(18H), 1.32 (9.8H), and a broad doublet at 5.80 (PH) after heating (LOO OC, 10 d) dong with a

color change of the solution from orange to dark brown and a black film on the upper parts of

the NMR tube. This indicates the formation of copper requiring the oxidation of L'Si: (1H and

13C NMR) (Fig. 63).

L'SI: L~S~-(O~BU)CU

Fig. 63. Attempted synthesis o f L's~-(O<BU)CU

[BuOLi reacts slowly at r. t. with L'Si:. A new product forms after 24 h with 'Bu signals

at 61~: 1.28 ( 18H) and 1.32 ( 13H) ppm. On the basis of the signal intensities, the product is

very likely not L'Si-(0tBu)LI. An unexplained signal (broad doublet) is observed at 5.79 ppm.

The same results were obtained upon repeating the reaction on a larger scale (1 g). Again,

signals of the starting materials (1.27 and 1.41 ppm) were present after 24 h at 25 OC and even

after prolonged heating (7 d 1 100 OC).

'Bu 'BU I t

L'Si:

Fig. 64. Attempted synthesis o f L'S~-@BU)L~

66

Attempts to obtain compounds of type L'Si(0R)Cl or L'Si(0R)z from the silane L'Sic12

did not succeed. Reaction of L'Sic12 with tBuOLi (1:l) at 25 O C or at refluxing temperature

produced a color change but no new products (Fig. 65). Use of BuOH + pyridine instead of

BuOLi also did not give substitution products.

8 THF

N CI I

- LiCl

'BU I

'BU

L'Sic12 L'S~-(O~BU)CI

Fig. 65. Attempted synthesis of L' s ~ - ( O ~ ) C I

tBuOH readily adds to the silylene L'Si:. The product was isolated by sublimation of the

crude mixture 45 O C - 80 O C (oil bath, 0.1 Torr) as off-white crystals (56% yield) and

characterized as L'Si-(0tBu)H (IH, 13C NMR) (Fig. 66).

'BU 'BU l I

2 'BUOH

N THF H I

'BU I

'BU

L'Si: L's~- (0%)~

Fig. 66. Attempted synthesis of L~s~-(oBu)H

Surprisingly, no reaction of L'Si: was observed with MeOH.

2.13.3 Reactions of LGe: with Alkoxides and Alcohols

No reaction was observed between LGe: and tBuOCu or tBuOLi (Fig. 67).

LGe: LG~-(O'BU)L~

Fig. 67. Attempted synthesis of LG~-(O~BU)L~

Reaction of LGe: with 'BUOH (Fig. 60) or MeOH only led to the formation of 2-C and

the starting material LGe: ('H NMR). Table 11 summarizes the outcome of the reactions of

carbenes 1 and 2, L'Si: and LGe: with alkoxides and alcohols.

t ~ u ~ ~ u t ~ u ~ ~ i t ~ u ~ ~ MeOH

1 - - - - 2 - + + +

L'Si: + + + - LGe: - - + +

Table 11. Surnmary of reactions of 1,2, L'Si:, LGe: with alkoxides and alcohols

+ indicates reaction, - indicates no reaction

2.14 Synthesis of 1-Hz

The carbenes prepared in this thesis were investigated by core electron spectroscopy in

the group of A. Hitchcock at McMaster University.

Photo electron spectroscopy is a method that allows to determine the binding energies of

electrons in individual occupied orbitals. Core electron spectroscopy [45], on the other hand,

allows to map unoccupied orbitals. This method involves the excitation of core electrons into

the unoccupied bonding or anti-bonding orbitals.

68

The energy and the intensity of the transition, for instance, allow to determine whether a

x* orbital is localized or delocalized.

For the purpose of cornparison of spectml data, the synthesis of 1-H2.was atternpted.

Reaction of [1-H] CI with BH3-THF, LiAIH4 or catalytic hydrogenation of 1 (H2 / Pd) was

studied. The reaction of [l-HI Cl with BH3 gave a broad product spectrum and was not

investigated further. With LiAIH4, 1-H2 was obtained but decomposed whenever attempts were

made to isolate the compound (Fig. 68).

118 LiAlH, THF 'BU I

abH 25 OC 5 min

N - LiCI - [*yH

I N H

'BU I

'BU

(1-HI CI

Fig. 68. Synthesis of 1-Hq

In solution, 1-H2 is stable indefinitely (fiame-seded NMR tube) but decomposes rapidly

upon exposure to minimal traces of air or moisture. Thus, al1 attempts to isolate the compound

in pure form only led to greyish solids that are presumed to be polymeric bH2. The instability

of l w H 2 is surprising in view of the fact that a number of derivatives e. g. [1-a+, 1=0 and l=S

are thermaily robust and can be isolated by sublimation without difficulties. It is likely that the

N-CH=CH-N fragment is stable only in conjugation with -M substituents such as C=O, C=S

etc. The sila analog L'SiH2 is also very air-sensitive but can be isolated by distillation (M.

Denk, personal communication).

69

2.15 Reaction of 1 with Fe(C0)s

The stable silylene, L'Si:, readily reacts with metal carbonyls to give silylene complexes

(L'Si)2Ni(C0)2 [46], L'Si=Fe(CO)q (unpublished results) and other L'Si-metal complexes.

To establish the relative reactivity of stable silylenes and stable carbenes, the reaction of

1 with Fe(C0)S was investigated.

With electron-rich carbene ligands, thermal disproportionation has been found to yield

biscarbene complexes (Fig. 69) [47,48] .

M = Cr, Mo, W

Fig. 69. Synthesis of a bis-carbene complex

The reaction of 1 with Fe(CO)5 (1:2) resulted in the formation of a yellow, powdery

solid that was isolated by sublimation at 70 O C in vacuo in low yields and starting material 1

that sublimed at 60 OC in vacuo. The CO stretching frequencies (V = 2024, 19 12, 1898 cm- l ) of

the yellow sublimate at 70 OC indicate the presence of terminal carbonyl groups. The

sublimation residue (brown solid) did not show CO bands.

1 1 ~ F e ( c 0 ) ~

Fig. 11. Attempted synthesis of l=Fe(COh

70

Based on the unusually high volatility (80 OC I 0.1 Torr), the q S carbene complex

1=Fe(C0)2 is more likely than the ql complex (Fig. 70). This is supported by the IR specinim

mat shows two strong bands (v(C0): 1898 (asym.), 1912 (sym.) cm-').

'BU ?

1 1 =Fe(CO)4

Fig. 70. q l complex formation: l=Fe(CO)4

Attempts to crystallize the yellow sublimate failed both by layering a 1 :2 solution of

THF and hexanes and by heating it in a flame-sealed NMR tube to 1 10 OC (oven) over a period

of 7 to 14 d. The sublimate transformed into a brown tarry material upon heating. Due to it's

poor solubility in C&, NMR was measured in THF with a drop of TMS and a D20 insert as a

lock solvent. The shifts for rert-butyl carbon and the quaternary carbon were overlapped by

strong THF signais (26.38 ppm, 68.22 ppm). Signals at 129.01 ppm (N<+-N) and 21 8.77

ppm (CO) indicated the presence of a metal carbonyl complex. HMPA was also found to have

poor solubility for l=Fe(CO)z. Work towards fïnding a better solvent is in progress.

The fact that the carbene carbon seems to be absent could be explained by the formation

of the known complex $-(Dinadiene) Fe(C0)3 or the complex q4-(Diazadiene) Fe(C0)z.

2.16 Reaction of 2 with Fe(C0)s

To establish possible differences in reactivity between the arornatic carbene 1 and the

saturated carbene 2, the reaction of 2 with Fe(C0)s was investigated. At 25 OC, *H NMR

showed signals for 2-CHO and 2.

71

After heating at 110 OC for 16 h. dong with signals for 2 and 2-CHO, new signals at

1.17+ 1.5 1 (int. ratio 9 : l), 5.25+6.80+7.74 (int. ratio 2 : 1 : 1) developed. No change was seen

in the spectmm after continuing to heat for 7 d. The appearance of new signals indicated a

reac tion .

Fig. 71. Aaempted synthesis of 2=Fe(CO)4

When repeated on a larger scale (0.14 g 2 + 0.30 g Fe(C0)5), different results were

different. The FT-IR data of the crude mixture suggested the presence of an Fe(C0)2 fragment

with two strong CO bands at v = 1848 cm-' and 1908 cm-'. Sublimation gave two fractions: 45-

50 OC, colorless crystalline, 40 mg and 60-70 OC, purple, crystalline, 9 mg. Both the volatile

fractions were characterized as 2-CHO by IR specuoscopy. The sublimation residue (33 mg,

brown powder) showed CO frequencies at 1842 cm-1 and 19 15 cm-'.

2.17 Aromatie Delocalization in Stable Carbenes: Correlation of Experimental and

Cornputationd data

2.17.1 Introduction

The relative extent of aromatic delocalization in stable diaminocarbenes (1,3-

imidazolylidenes, 1) and the related species 1=0, l=S and 11-Hl+ was studied at the B3LYP /

6-3 lG* level. The criteria used to evaluate the relative extent of aromatic delocalization were:

HOMO-LUMO gaps (Eg), bond order (Mulliken and Lowdin), C=C stretching frequencies and

experimental NMFt data (1H and 1 3 ~ NMR).

72

For the derivatives of the carbenes, the C=C stretching frequencies, the HOMO-LUMO

gap energies and the bond orden lead to different sequences of increasing delocalization.

corn pou nd l-HZ 110 [I-HI+ 1 6 1 L' B' LW+

V [ C ~ [cm- J 1 706 1 649 164 1 1638 1630 1626 1591

Table 12. Increasing delocalization as obtained fiom complrtational IR fiequencies

compound 1-Hz 1 4 1 L'B' 1 1 - ~ + LIN+

Bond Order 1.86 1.77 1.72 1 .71 1.68 1 .58

Table 13. Correlation between bond order and NMR data

- - -

corn pou nd L'Ba 1 4 [~-HI+ f L'N+ ~ -HZ

Eg! [eV] 82.00 235.86 248.12 248.2 1 248.87 1591.4

Table 14. Conelation between Eg and aromatic stability

The only criterion that directly correlates with experimental data is the Lowdin bond

The recent synthesis of stable, diaminocarbenes 1 [6] and the isostructural stable

silylenes [49], germylenes [SOI and phosphenium cations [5 1, 521 has triggered an ongoing

debate about the extent of aromatic delocalization in these species. While there is liale doubt

that heterocycles 1 are aromatically stabilized to some extent or the other, the extent of

delocalization, that is the relative importance of the mesomeric structure l b us. la , is unclear

(Fig. 4).

R R R I I 1

[*.: R = adamantyl c): - @: mesityl

I metbyl

I R R

I R ~ - P ~ O P Y ~

ter& buty l

Fig. 4. Aromatic divalent carbenes la and 1 b and non-ammatic carbene 2

73

The controversy is essentially caused by the need to reconcile computational data

with experimental data that are obtained from such different approaches as single crystal X-

ray crystallography, NMR, neutron diffraction and the measurement of optical and magnetic

properties.

Surprisingly, little attention has k e n paid to the investigation of delocalization

through computationally derived bond orders in species 1. Bond orders can only be obtained

by calculations but they can correlate with vibrational data. E. g. the stretching frequency of

the C=C double bond in heterocycles 1 should correspond to the bond order and should

decrease with increasing delocalization (Fig. 4).

Examination of experimental IR data for the compounds L'E: (E = C, Si, Ge) in our

group has shown that the CC-stretching frequencies are weak and easily obscured by other

strong bands (VCN, VW). The CC-stretching bands are however easily measured by Raman

spectroscopy and are in fact the strongest bands in the region 2500 - 800 cm-'.

Some disadvantages of the experimental approach remain. Only a srnall number of

possible compounds of type 1 have been characterized and the precise location of vcc band

can become obscured by Davidov splitting or symmetry enforced splitting resulting from the

syrnmetry of the solid (space group).

An obvious alternative would be the accurate calculation of vcc. The calculation of

accurate vibratory spectral data from fint principles is still a formidable task. Without going

into the details of the problem, the difficulties are arnply illustrated by an inspection of the

contemporary arsenal of computational methods. Among the overwhelming number of

different semi-empirical methods: ab initio methods, density hinctional methods and hybrid

density functional methods, only one approach, the B3LYP hybrid method, has consistently

delivered accurate vibrational frequencies [8,56].

The accuracy of B3LYP 1 6-31G* calculations is typically better than 2 W. Even

better agreement between experiment and theory can be achieved by the introduction of

scaling factors. These factors depend on the type of bond investigated and can be optimized

by a least squares fit of experimental and computational values [8].

74

In the context of this study, the goal is not to maximize agreement between

experimental and computational values (vibratory data), but, rather to study trends in the

delocalization for the family of heterocycles 1 and 2 with divalent fragments, E.

'Bu I ci-

& N

I 'BU

'Bu I

N

I (1-HI Cl 1-Hz 1- l=S

Fig. 72. The stable carbene 1 and its derivatives

B3LYP / 6-31G* calculations are more time consuming than HF / 6-31G*

calculations. Even for R = H, the calculation of the heterocycles 1 and 2 requires 30 - 40 h of

CPU time on a Silicon Graphics Workstation with a R4400 processor and 128 MB of RAM.

The calculations are useful beyond the goal of obtaining vcc data. Like other DFi'

methods, the B3LYP method automatically includes electron correlation. While the effect of

electron correlation on the structural accuracy is not always clear [ I l ] , electron correlation

can be essential to obtain accurate thermochemical data like heats of formation etc. The

B3LYP 1 6-31G* data of this work will thus allow to calculate the relative themodynamic

stabilities of the delocalized heterocycles 1 and 2 from thermochemical cycles like isodesmic

hydrogenation reactions.

The remainder of this chapter will investigate the relative stability of carbene

derivatives 1, silylenes, gennylenes, nitrenium cations, phosphenium cations, arsenium

cations and the yet unknown borylene anions and their aluminum and gallium counterparts.

2.17.2 Vibrational data as criterion for aromaticity

The use of v c c will inevitably draw the criticism that the frequencies vc=c reflect the

sum of the o-sigma and 2-bond order so that the change in vcsc may not reveal much about

the R-delocalization.

For the delocalized heterocycles LE:, the C=C bond orden and stretching frequencies

show a high degree of localization for the anionic diazoles of gallium and aluminum. For the

cationic arsenium and phosphenium heterocycles. the bond orders approach the hypothetical

value of 1.5 that would correspond to complete delocalization. The 1.1 -dihydro species

L'EH2 have bond orders lower than 2. This presumably reflects the fact that the C2N2 system

is capable of some r-delocalization even in the absence of cyclic aromatic delocalization.

2.17.3 Delocalization of ~arbène Derivatives

Table 15 compares the data of the stable carbene 1 with those of other heterocycles of first

row elements.

Table 15. Correlation between computational R frequencies and Eg for carbenes and it's derivatives.

While the non-delocalized systems show only small variation of vcc, the

corresponding aromatic systems cover a large frequency range from 1574 cm-' (L'As+) to

1656 cm-' (L'AI-).

It must be emphasized that, contras, to common beliefs, delocalization cannot be

equated with stability in the thennodynamic or kinetic sense. A good criterion for the relative

reactivity of compounds within a given series is the difference between the energy of the

highest occupied orbital (HOMO) and the lowest unaccupied orbital (LUMO).

These energies can be correlated with the degree of delocalization for some

representatives and can be entirely uncorrelated for others, as Table 15 demonstrates.

The vibrational data should correspond to experimental data for aromatic

delocalization. The deshielding of ring protons in the lH-NMR spectra is probably the most

widely used and accepted critenon for aromatic delocalization. As Table 16 demonstrates, the

correlation between IH-NMR data and the vc* data is moderate. The NMR data, however,

correlates very well with the C=C bond orders.

v(c=Q mcc B ~ C N BONE 6 Mulliken Mulliken Mulliken n 13r

L'AS+

L'N+

L'P+

L'Ce:

[ 1-HI+

L'Ga'

L ' A r

L'Si:

L' B-

1

l=S

1 4

Table 16. Normal modes (in cm-l), HOMO-LUMO gap energies (in Hartrees x loo3), bond orders and experimental NMR data (in ppm) of selected diazoles. Computational values at the B3LYP / 6-3 1 G* level, al1 NMR data in C&j unless stated otherwise. The individual entries are Iisted in the order of hcreasing C=C LBwdin bond order. i) in CDCl3. ii) G. Boche, P. Andrews, K. Hanns, M. Marsch, K. S. Rimgappa, M. Schimeczek, C. Willeke, J. Am. Chem. Soc. 1996, U& 49254930. The reported N-metbyl-N,-benylsystem has nvo inequivalent ring protons. 6' H in DMSO: 9.00 and 8.83 ppm, îhe value given in the table is the average of these two shifts.

The series of decreasing bond orders is not without surprises. First, the most

delocalized system is the one with a heavy heteroelement E (As+). This is contrary to

common chemical perception that heavy elements are less likely to participate in

delocalization due to poor p-p n-overlap. The special position of arsenic in the nitrogen,

phosphorus, arsenic triad may reflect the high effective nuclear charge of arsenic resulting

from ci-contraction.

For the group 14 elements, the senes is equally disturbing. The germylene is the most

delocalized system, the carbene the least, the silylene occupies a middle position. The high

degree of localization in the carbene is surprising in view of the highly deshielded ring

protons (6(lH. C&): 6.99 ppm).

A second general trend emerges: the 1 3 ~ chemical shifts of the ring protons correlate

with the C=C bond order.

For the non-aromatic species L'EH2, there is still substantial variation of the C=C

bond order. The Gallium derivative L'Ga- is in fact nearly as delocalized as the urea 1=0. A

participation of low lying d-orbitals is a likely explanation.

V(C,-C) Eg BOCC B ~ C N BONE 6IEi Mulliken Mulliken Mulliken 6 13c Ldwdin Lowdin LUwdin

L'GaH2 1689.8 96.784 1.76738 1.00281 0.8024 - 1.77612 1.2402 1 1 .O2563

Table 17. Normal modes of selected I , 1 -dihydro- 1 J-diazoles

2.17.4 HOMO-LUMO Gaps

HOMO-LUMO gaps have often been used as a tool to compare the relative reactivity

of aromatic species by using e.g. UV 1 VIS absorption bands corresponding to the HOMO-

LUMO transition. As demonstrated by Terlouw et al., the PES data of stable carbenes are in

excellent agreement with BJLYP 1 6-3 lG* data. The B3LYP 1 6-3 lG* method is thus a valid

method for the evaluation of HOMO-LUMO energy gaps.

The HOMO-LUMO gaps of the investigated carbenoid compounds reveal an

interesting pattern. The neutral group 14 species (E = C, Si, Ge) and the cationic group 15

species (E = N+. P+, As+) possess large Eg values. By contrast, the anionic group 13 species

(E = B-, Al- and Ga-) have low Eg values and will presumably be much more reactive than

the carbenes, nitrenium ions and their heavy congeners. It is certainly not accidental that al1

species with high HOMO-LUMO gaps have since been isolated and structurally

characterized while no experimental evidence has been presented for the existence of the

anionic diazoles featuring group 13 elements. Their isolation will presumably be difficult if

not impossible.

The low Eg values of the group 13 diazoles are even more surprising if one considers

the fairly strong delocalization operating in these systems (C=C bond orders, v(cc)).

2.17.5 Structural Investigation of Carbenes and Protonated Carbenes

As mentioned before, the carbenes 1 and 2 are obtained from the corresponding

proton salts [l-H] CI and [2-H] Cl. It seemed interesting to see what structural differences, if

any, exist between the carbeniurn cations and the respective carbenes. Table 18 compares the

experimental structures of delocalized carbenium cations with those calculated at different

levels of theory.

The experimentally obtained structures of the two carbenium cation salts, [1-Ei] CI

and [1-Hl SCN are identical within the limits of the X-ray method (30 criterion).

[L'CH]+ IL'C~+ [L'CH]+ [L'CHI+ [L'CHI+ [L'CHI+ B3LYPI HF160 m l & AM1 CI'

31G+ SCN-

6-31G* 31G* X-ray X-ray

N-E 133.6 131.3 134.0 137.3 133.2(7) 133.26(19)

N- WV)

C-c

C-H

N-E-N

N - C X

R-N-C

E-N-C

E-N-R

mi

Table 18. Cornparison of experirnentai and calculated structures of L'CH' cations using B3LYP 16-3 IG*, HF 16-3 IG*, MP2 16-3 IG* and AM1 methods i) sum of bond angles amund nitmgen (Z(RNC+ENC+ENR)) .

The C-H bond distances are not listed because hydrogen atoms can not be refined with

sufficient accuracy. The closest contacts between the ring atoms and the counter ion are:

C(1) ... CI(1) = 328.4(6) pm (11-H'l CI)

C(1) ... N(3) = 32 1.7(2) pm ([1-H] SCN)

A similar cornparison is made for the salts, [2-EI] Cl and [2-EI] SCN (Table 19). The closest

contacts between the ring atoms and the counter ion are:

C(1) ... Cl(1) = 326.9(1) pm ([2-II] Cl)

C( 1 ). ..N(3) = 242(2) pm ([ZEi] SCN)

ILCHI+ ILCHI+ [ L C H ~ [mm+ ILCHI+ [KHI+ B3LYP HF/& MP21 AM1 CI' SCNw 16-31C* 31C* 6-31G* X-ray X-ra y

N-E 131.5 129.8 131.6 135.2 131.15(17) 13 1.3(2)

N- C(W

C-c

C-H

N-E-N

N-C-C

R-N-C

E-N-C

E-N-R

Symme

Table 19. Cornparison of experimental and calculated structures of LCH+ cations using B3LYP / 6-3 IG* HF / 6-3 l e* , MP2 1 6-3 1 G* and AM 1 methods i) Jose Rodezno, M. Denk, A. J. Lough, unpublished results. ii) sum of bond angles around nitrogen mRNC+ENC+ENR)) .

Ali computationally derived structures of the carbenium cations are in good to excellent

agreement with the experimental values. The AM1 bond distances between the ring atorns are

consistently too long. The agreement between the B3LYP 1 6-31G* structures and the true

structures is particularly striking. The BJLYP structures are thus a very adequate start geometry

for the calculation of the vibrational data (Tables 18, 19). The counterion has no influence on

the ring geometry. This finding and the fact that the structures of the salts are virtually identical

to the structures that were calculated for the isolated cations confirrns that the cornpounds are

completely ionic.

For carbene 1, the agreement between computational and experimental structural

parameters is equally impressive (Table 20).

81

In most cases, the computational values are well within the 3 0 range of the

experimental values. Protonation of 1 produces only minor structural changes: the CN bond

distance decreases by Ca. 3 pm and the N-C-N angle opens from 102 to 109 degrees. The

calculated bond distances of the C2N2C: ring deviate frorn the experirnental values in a

systematic fashion. In short, the HF approach over-estimates localization, while the B3LYP

and MP2 methods over-estimate delocalization. As was noted above, in the case of the

protonated carbene [l-Hl+, the semi empirical AM1 method substantially over-estimates the

bond distances within the ring and can not be considered adequate for the calculation of

diaminocarbenes and presumably, carbenes in general.

6 3 lG* 3 lG* 6-3 1 G" N-E 137.2 135.2 137.3 138.2 136.6(2)

N- c m C-C

N-E-N

N-C-C

R-N-C

E-N-C

E-N-R

mi Point-

Table 20 Cornparison of experirnental and calculated stnicnires of 1 using B3LYP / 6-3 lG*, HF / 6- 3 1G8, MP2 / 63 lG* and AM1 methods i) sum of bond angles around nitrogen (Z(RNC+ENC+ENR)) .

82

2.17.6 The Basicity of Diaminocarbenes

BJLYP data are now widely recognized as giving highly accurate (emr < 2 kcal / mol)

thennochernical data. With the B3LYP / 6-31G* data at hand, the relative gas phase acidity of

protonated diaminocarbenes can now be calculated from proton transfer reactions. The me

energies of formation were calculated at O Kelvin and were corrected for zero point vibrational

energy. The calculations show. that the aromatic carbene is less basic than the non-arornatic

carbene by 2.07 kcd / mol.

-2.07 kcal

Fig. 73a. Reaction between L'CH+ and LC:

The relative stability of the aromatic and the non aromatic carbene can be obtained from

the isodesmic reaction b (Fig. 73b). The result shows, that the aromatic carbene is substantially

more stable than the non aromatic carbene.

H H H H

Fig. 73b. Reaction between L'CH2 and LC:

The relative stability of the aromatic and non-arornatic carbenium cation, however, can

be evaluated with the transfer hydrogenation reaction c (Fig. 73c). The result shows, that the

unsaturated carbenium cation possesses nearly the same aromatic stabilization energy as the

arornatic carbene (-12.52 kcal vs. -14.59 kcal).

Fig. 73c. Reaction between L'Ch and LW

Table 2 1 shows the true energy calculations for the carbenes and carbene derivatives.

Energy ZPE True Energy (B3LYP 16 - (B3LYP 1 3 1G') 6-3 1 G*)

LC: -227.37 17 1 12 0.094104 -227.2776072

Table 21. CalcuIated true energies (Kcal) for carbenes and derivatives

2.18 Carbenium Cations as Ionic Liquids

Salts that are liquid at ambient temperature ("Ionic Liquids") can act as solvents for a

broad range of chernical processes [53]. They have no vapor pressure but are often irnrniscible

with water and organic solvents. Nearly al1 currently used ionic liquids are irnidazolium salts of

general type A [54, 551. The carbenium cations obtained in this thesis are either of type A with

R = R'= 'Bu or of type B (R = RI= tBu).

Fig. 74. General representation of ionic liquids

The equivalence of R and R' makes the carbenium cations highly symmetric and presumably

raises the melting point.

84

Ionic liquids of type B have not been previously investigated and further work on these

compounds seems promising. In any case, the synthesis of [l-Al SCN and [2-H] SCN is a new

and potentially usef'ul approach for the synthesis of ionic liquids.

1-Butylpyridinium nitrate

1 12-Hl SCN 12-HI CI

Fig. 75. Ionic Liquids and Carbenium Salts

2.19 Conclusions and Future Goals

The attempt to find new methods for the synthesis of stable carbenes led to a new

synthesis for thioureas and a new synthesis for diaminocarbenium cation salts. Proton transfer

studies between diaminocarbenes and carbenium cation salts allowed the comparison of the

relative basicity of carbenes 1 and 2.

Hexahydro-sym-triazines were investigated as potential starting materials for aromatic

tris-carbenes (R-N-C:)3, but, failed to give the required tris-thiourea or the tris-carbenium

cation. The dehydrosulfurization of hexahydro-sym-triazines led to ring degradation products

85

ÿ BU-MI-CS-NH-Bu (36%), tBu-NH-CS-NH2 (35%)] that were completely identified for R =

'Bu. The unexpected product (17%) of the reaction was the cyclic carbenium cation

[C2H2(NR)2Cm+ SCN- whose mechanism is unclear.

The aromatic 6~-delocalization in Arduengo carbenes and related heterocycles was

studied at the RHF / 6-3 lG* and B3LW / 6-3 1 G* level. The obtained Lowdin bond orders are a

quantitative indicator for delocalization. They correspond directly to the deshielding of the ring

protons (1H and 1 3 ~ resonances) of the N-CH=CH-N ring fragment.

The basicity of diaminocarbenes was investigated using B3LYP 1 6-3 1 G* method and

experimentally. The caiculations showed that the aromatic carbene is less basic than the non-

aromatic carbene by 2.07 Kcal 1 mol. The calculations also revealed that the unsaturated

carbenium cation possesses almost similar aromatic stabilization energy as the aromatic carbene.

The oxidative addition of alkoxides and alcohols to carbenes 1 and 2, silylene L'Si: and

gemylene LGe: was investigated. Results indicated that the saturated carbene 2 readily adds to

alcohols and alkoxides as opposed to the non-aromatic analog. Silylene reacted readily with tert-

butanol, tert-butoxy lithium and tert-butoxy copper but failed to show any reaciion with

methanol.

In summary, through this thesis, the synthesis, aromatic delocalization and reactivity of

stable diaminocarbenes has been investigated. The stable carbenes 1 and 3 were obtained using

the deprotonation of carbenium cations as a new synthetic approach. The problems encumbered

in obtaining tris-thiourea and ultimately tris-carbene (R-N-C:)3 were addressed and different

strategies such as deprotonation of a tris-carbenium cation, dehydrosulfurization of a tris-

thiourea, or dehydrogenation of 1,3,5-ui-tert-butyl-hexahydro-sym-triazine or the trimerization

of R-N=C: (Fig. 46) have k e n suggested. The tris-carbenes have not been obtained before and

should possess aromatic stabilization. Computational studies on tris-carbenes are in progress.

The carbenium salts [l-Hl SCN, [2-Hl SCN, [3-H] SCN, and [l-H] CI have been

obtained for the first time. Their poiential as ionic liquids ("low-melting" salts) is a study in

progress,

Chapter 3: Experimental

3.0 General Experimentai Unless noted otherwise, ail starting materials were obtained from commercial suppliers

and were used without further purification. Chloroform, methanol, ethanol, teri-butylamine,

hexamethyl formamide, and diethyl ether were dried by sonicating 30 mins. over CaH2. Tetrahydrofuran, hexanes, and benzene were distilled from blue or purple potassium /

benzophenone solutions under nitrogen prior to use. Deuterated solvents (CDCI3, C6D6) were dried by 30 mins. sonication with Ca& followed by deoxygenation with three freeze-pump thaw cycles. The aminals were dned and stond over KOH as solutions in ether under argon. Al1

reactions involving organometallic reagents or amines were carried out under Argon (99.996)

with the usuai Schlenk equipment or in a nitrogen filled glove box (Braun, 0 2 < 2 ppm, H20 < 2 ppm). 1H NMR spectra were recorded on a Gemini 200 MHz spectrometer in CDC13 unless otherwise indicated. Chernical shifts are expressed in parts per million (ppm, 6) downfield frorn tetramethylsilane. Multiplet signais are reported as s, singlet; d, doublet; t, triplet; q, quartet; qt,

quintet; m, multiplet and br, broad. Coupling constants are given in Hertz. 1 3 ~ NMR spectra were recorded on a Varian Unity 500 MHz or 400 MHz instruments as solutions in CDC13 unless otherwise indicated. The l3C NMR shifts were simulated on a 1 3 ~ NMR ACD software.

IR spectra were recorded in nujol with sodium chloride plates using a Nicolet SDXB FT-IR spectrometer or a Perkin Elmer AVATAR 360 FI'-IR spectrometer and are reported in wave numbers (cm-1). Electron impact mass spectra were obtained on a Fisons 301000 GC-MS

instrument. The reactions with elemental sulfur typically required heating to 170 O C oil bath

temperature and were conducted in round bottom flask with directly attached reflux condenser ("boiler flask"). These flasks have the advantage that no greased joints are exposed to the high

temperatures of the aggressive sulfurization mixtures. This prevented the contamination of the reaction mixtures with grease and also eliminated the problem of frozen joints encountered

previously with these reactions. Due to the high temperatures, the reflux reactions were

conducted with standing water in the condenser jacket or with no cooling water at ail. Poly(ethy1ene glycol) (Aldrich cat. # 37,299-4) was used as heating fluid up to 220 OC.

The glycol baths emit toxic fumes and were operated in fume hoods at al1 times. They have the advantage that the heating fluid is soluble in water. This greatly facilitates cleaning of the glassware especially prior to transfer into the glove box. The solubilities of carbenium cation

salts were determined as follows: 1. A srnall arnount of salt was taken in a schlenk tube and dned by heating under vacuum for

1 h. 2. Using a Hamilton micro-syringe (0.5 r d ) , the corresponding solvent was added to the salt

until saturated. the soluble part was syrînged out and the insoluble materiai was weighed out. The difference was used to detemine the amount that dissolved.

2=s 2-C 12-HI SCN

2 14glmol 172g/mol 24 1 glmol

Method A In a 250 mL boiler flask, Se (3 g, 11.65 mmol, 1 equiv. ) was added to 2-Hz (8.59 g,

46.6 mmol, 4 equiv.) at r. t.. The mixture was slowly heated to 170 OC in a polyglycol bath.

Standing water in the condenser. Gas evolution began at 60 OC oil bath temperature, at about 70 OC, the color of the mixture tumed from yellow to orange. At 85 OC, the mixture turned black

and a yellow oil appears on the lower parts of the condenser. After 1 h heating at 170 O C oil bath

temperature, the gas evolution had ceased and the mixture was allowed to cool to room

temperature. The crude mixture (black tany solid at the bottom + yellowish orange solid on the condenser, total of 8.69 g) was extracted with 70 mL of chloroform under constant stimng (1 h). The solution was decanted from the insoluble material with a synnge and sublimed in vacuo

after evaporation of the solvent. The sublimate consisted of two different fractions namely

unreacted starting material 2-C (40 - 120 O C , 3.00 g, 37 %) [88] and the thiourea, 2=S (120 - 150 OC, 1.52 g, 15 %). The residue was identified as the carbenium cation salt (2.32 g, 21 %).

Combined yield: 73 %. The detailed results of Method A are presented in Table 22.

Sublimation weigbt Appearance Assigament temp. [gramsl [Tl

45 - LOO 1 -42 white, crystalline+yellow oil 2-C 100 - 120 1.58 yetlow solid 2-C 120 - 140 0.05 dark yellow, crystalline 2=!3 140 - 150 0.20 yellowish-brown, crystalline 2=S

150 1.2 1 yellowish - orange, crystalline 2=S residue 2.32 black, shiny solid [2-Hl S C N

Table 22. Sublimation fractions (temperature, weight, appearance and assignment) for Method A

Method B In a 250 mL boiler flask equipped with a magnetic stimng bar and an argon inlet Sg

(8.2 1 g, 32.0 1 mmol, 1 equiv.) was added to 1-HZ (5.90 g, 32.0 1 mmol, 1 equiv.).The neat mixture was heated slowly to 110 O C and kept at this temperature for about 30 mins. (continuous gas evolution). The temperature was raised to 170 O C when gas evolution was

observed and remained there for 22 h. The crude mixture was extracted with 50 rnL of chloroform under constant stirring (1 h). The solution was decanted from the insoluble material with a syringe and sublimed in vacuo after evaporation of the solvent. The amount of sulfur can not be determined from the NMR spectra of the individual fractions and the total yield of 2=S could therefore not be obtained. The ratio of 2=S to l=S is however easily available from the IH NMR spectra (Table 23).

Sublimation Weight Appearance 2=S/l=S Other components îemp. [ P w (by GC-MS) pc]

60- 100 2.04 white, crystalline solid 1.7 6 100- 130 1 .O2 orange, crystalline solid 1.9 4 130 - 140 2.4 1 orange, crystalline solid 1.3 5 140 - 150 0.14 orange, powdery 0.7 6 150 - 155 0.73 orange, oily film 0.8 4 155 - 160 0.66 yellow oily film - 1 160 0.02 orange powdery solid - 5 160 - 165 0.1 1 orange-black solid - 2 residue 1.5 1 black, shiny solid - [2-H] SCN (0.78 g)+l

Table 23. Sublimation fractions (temperature, weight, appearance and assignment) for Method B

Method C In a 500 mL boiler fiask equipped with a magnetic stimng bar and an argon inlet, Sg

(5.70 g, 22.24 mmol, 1 equiv.) was added to 1 4 2 (16.40 g, 88.97 mmol, 4 equiv.) without

solvent and running water in the condenser. Gas evolution began at 90 OC. At LOO OC, an orange solid deposited on the walls of the round-bottom and a yellow deposit on the walls of the

condenser. The mixture was slowly heated to 160 O C for 30 h giving a black solid at the bonom and an orangish-yellow solid on the walls of the condenser (total weight = 18.37 g). The crude

mixture (16.41 g) was extracted with 100 m . of CHCl3. The solution was decanted from the

insoluble material using a syringe into a sublimation flask and sublimed in vacuo after evaporating the solvent. Table 24 demonstrates the individual fractions obtained from Method C (160 OC, 30 h).

Subümation weight A P P W ~ ~ LCS/LtC=S Other components tempe IgramsI (by GC-MS) [OC]

90- 150 0.94 paie yellow, flaky solid 5.9 3 150 - 165 0.36 yellow,oily film 2.7 4 165 - 170 1.4 1 orange-yellow,flaky 2.1 5 170- 175 0.57 orange- yellow ,flaky 4.2 2 residue 9.22 black,shiny solid - [%Hl SCN

+ 1 unidentified

Table 24. Sublimation fhctions (temperature, weight, appearance and assignment) for Method C

1,3-DiJcrt- butyle thylenediamhe (2-C) 1H NMR (200 MHz, CDC13, 25 OC): 6= 1 .O9 ppm [s, (C(C&)3], 2.65 [S. NC&].

EI-MS (40 eV, pos. ions): d z (rel. Int. %) = 57(37), 71(75), 77(1 l), 84(29),

100(20), 1 13(92), 127(40), 157(2), 169(20), 183(100), 199(4).

1,3-Di-te~-butyl-irnidazolidene-2-thione (2=S) 1H NMR (200 MHz, CDC13, 25 OC): S = 1.60 ppm [s, C(CH3)3], 3.44 [s, NCfUJ.

13C{iH} NMR (400 MHz, CDCI3, 25 OC): 6 = 28.1 1 ppm [C(ÇH3)3], 44.50 [NÇHz], 56.68 [ç(CH3)3], 183.66 [ç=S].

13C NMR (400 MHz, CDCl3, 25 OC): 6 = 28.1 1 ppm [q, I J (C,H) = 126.70 Hz,

C(ÇH3)3], 44.50 [t, lJ (CH) = 148.6 Hz, NÇHz], 56.68 [s, Ç(CH3)3], 183.66 [Ç=S].

GC/MS (40 eV, pos. ions): m/z (rei. Int. %) = 41(30), 57(50), 74(15), 84(7), 102(100), 1 15(10), 143(40), 157(35), 214(60).

FT-IR (NaCl; nujol): 651s m, 722s w, 745s w, 841br vw, 885br vw, 940s w,

1033s m, 1119br w, 1199br s, 1264s m, 1315br s, 1365sh m, 1630s m,

1655sh w, 2054br m, 2472br W.

1,3-Di~ert-butyi-imid~olinium tbiocyanate ([Z-tfl SCN) 1H NMR (200 MHz, CDC13, 25 OC): 6 = 1.52 ppm [C(C&)3], 4.11 WC&], 8.09

[CU+] 13C(lH} NMR (500 MHz, CDCl3, 25 OC): 6 = 27.92 ppm [(C(ÇH3)31, 45.37 [NCHÎI,

56.86 [ç(CH3)3], 130.8 1 [Smœ], 152.33 EH+]. l3C NMR (400 MHz, CDQ, 25 OC): 6 = 27.92 ppm [q, ' J (C,H) = 128.1 Hz,

(C(çH3)3], 45.37 [t, lJ (C,H)= 150.8 Hz, NÇHZ], 56.86 [s, Ç(CH3)3], 130.81 [s, Sm-], 152.33 [d, lJ(C,H) = 199.9 Hz, CH+].

FT-IR (NaCl; nujol): 736s s, 761sh m, 888sh w, 907s s, 1060s w, 1 167br w, 1215s w, 1301br rn, 1632br rn, 2066br m, 2203br w, 272Sbr w,3644s W.

3.2 Synthesis of 1,3-Di~e~-butyCimidz1~)lylidene-2~thione (13s) via 1,3-Di-ferf-butyC imidazoiiwn chloride ( [ L a CI)

In a sublimation flask with a teflon joint cap and a stir bar, 2.5 M nBuLi in hexanes (1.86

g, 29 mmol, 2.1 equiv.) was added to [1-H] Cl (3.01 g, 14 mmol, 1 equiv.) in 20 mL of THF leading to an exothemic reaction and stirred until gas evolution ceased after 2 h. THF was

evaporated from the mixture (total weight of the crude = 4.1 1 g). Sg (0.90 g, 3.5 mmol, 1/4

equiv.) was added to the mixture followed by 20 rnL THF to mix the 2 solids for 17 h followed by evaporating the solvent (total weight of the crude = 5.5 1 g). The mixture sublimed at 84- 150

OC oil bath temperature (0.42 g, 38% yield). Table 25 shows the sublimation fractions obtained.

Sublimation Weight Appearance Assignment

temp. [ OC] [~mmsl

84- 100 O. 17 yellow-white crystalline l=S

100 - 125 1 .O0 white crystals+black solid l=S (white)

125 - 130 0.03 yellow crystailine i=S

130 0.02 yellow-white crystalline l=S

130 - 140 0.05 yellow, crystaltine I=S

140- 150 O. 12 yellow. crystalline l=S

Table 25. Sublimation fractions (temperature, weight, appearance, assignment) for l=S formation

1,3-Di-te~-butyCimid~oIyüdene-2-thione (14) 1H NMR (200 MHz, Cd&, 25 OC): 6 = 1.66 ppm [s, C(C&)3], 6.28 [s, NCEI]. lJC{lH] NMR (400 MHz, C&j, 25 O C ) : 6 = 28.09 ppm [C(ÇH3)3], 58.90 [C(ÇH3)3],

1 13.03 EH== 162.35 [L'*SI. l3C NMR (400 MHz, C6&* 25 OC): 6 = 28.09 ppm [q, C(çH3)3. IJ (C,H) = 127.4

HZ, 3 1 (CTH) = 4.4 HZ 1, 58-90 [s, C(cH3h, *J (CTH) = 3.6 HZ], 113.03

[d, ÇH=CH, l J (C,W = 194.05 Hz, 2J (C,H) = 10.2 Hz], 162.35 [s, C S ] .

3.3 Attempted Synthesis of 1,s-Di-terf-butyl-hexahydropy~imidin*2-ton (3=S)

Method A: Reaction of 1,3-Di-tert-butyl- l,3-diaminopropane with CS2 (NO IODINE)

'BU 'BU I CS, PY I

+ 20 h, nflw

1,3-Di-tert-butyl- l,3-diaminopropane (4.6 g, 35.3 mmol, 1 equiv.) was heated to reflux

with CS2 (35.3 mmol, 2.12 ml, 1 equiv.) and 10 rnL pyridine in a boiler flask. Little gas

evolution was observed. After 12 h reflux, pyridine was removed under vacuum and 50 mL of dichloromethane was added to the dark red remaining oil. The solution was stirred for 30 min

and filtered giving an insoluble part (1.27 g pink powder) and a filtrate (2.44 g red paste).

1H NMR (200 MHz, CDC13, 25 OC): 6 = 1 .O4 ppm [s, 18H, (CK3)3], 1.26 [s,

13.2H1, 1.38 [s, 3.3H], 1.63 [qt, 2.2H], 2.89 [t, 3.1 Hl, 3.30 [s, br, 1.68Hl.

Method B: Reaction of 1,3- Di-tert-butyl- l,3-diaminopropane with CS2 ( W m IODINE)

'Bu I

PY 12

20 h, nflw

'BU I

'Bu

3-C (14.49 g, 1 1 I mrnol, 1 equiv.) is reacted with CS2 (1 1 1 mmol, 6.7 mL, 1 equiv.) in 20 mL of pyridine in a boiler flask. Upon addition of CS2, the mixture turned yellow but no gas

evolution is visible. Addition of iodine (14.31 g, 11 1 mmol, 1 equiv.) was followed by boiling for 24 h. A small sarnple (0.2 mL) was washed with two 10 mL portions of water to remove py and salts. The dark brown rapidly solidifying remaining oil was analyzed by proton NMR. The

oil was then extracted with benzene, the benzene evaporated and the yellow solid residue

analyzed by proton NMR: 2 singlets in the region: 1.615 and 1.491 ppm, none of which could be assigned to 3=S were observed.

1H NMR

93

(200 MHz, CDC13,25 OC): 6 = 1.69 ppm [s, 18H. (Cu93 1, 1.55 [s, 18H, (CH3)3], 1.53 [SI, 1.32, 1.40 [t, 3.IHI.

Method C: Dehydrosulfurization of 3-HZ with Sg

'Bu

In a 250 rnL boiler flask equipped with a magnetic stir bar, Sg (1.99 g, 7.8 mmol, 1

equiv.) was added to 3-H2 (6.17 g, 31.1 mmol, 4 equiv.). The mixture was stirred for

approximately 5 mins. and then heated to reflux. Running water used in the condenser. At 135

O C oil bath temperature, gas evolution (monitored via an oil bubbler) and color change (yellow

to dark orange and finally brown) was observed. The temperature was slowly increased to 194

O C and kept there for 18 h. A black solid at the bottom of the round boitom flask and an orange

solid on the walls of the condenser observed (total weight = 4.77 g). The crude mixture was

transferred to a sublimation flask using 50 mL THF. The sublimate consisted of two different

fractions namely 3-C (50 - 140 O C , 2.61 g, 45 %) and the thiourea, 3=S (140 - 150 OC, 0.40 g, 6 5%). The residue was identified as the carbenium cation salt (0.07 g, 0.9 %). Combined yield: 52

%. The fraction at 140-150 O C was a mixture of four compounds, three of which were

unidentified and the third was the thiourea, 3=S. Table 26 demonstrates the different fractions

obtained upon sublimation.

Temperature Weight Appearance Assigoment

50 -150 2.61 white, crystalline 3-C

150 0.40 orange,crystalline 3=S+unidentified

residue 0.07 orangish-brown 3=S+unidentified

Tabk 26. Sublimation fractions (weight, temperature and assignment) for 3-E12:Sg (1: 1/4)

12-Didert-butyirexahydro-pyrimidine-2-thione (3PS) 1H NMR (200 MHz, CDCI3, 25 OC): 6 = 1.25 ppm [s, C(Cfùh], 1.97 [qt,

NCH2C&CH2N], 2.90 [t, NCb]. 13C{lH) NMR (400 MHz, CDC13, 25 OC): 6 = 28.10 ppm [C(cH 3)3 J , 29.25

[NCH&H2CH2N], 42.39 [NçHz], 52.09 [ç(CH3)3], 185.32 KÇ=S]. 13C NMR (500 MHz, CDCln 25 OC): 6 = 28.10 ppm [q, C(ÇH3)3, I J (C,H)= 124.22 .

HZ], 29.25 ft, NCH&H2CH2N], 42.39 FIçH21, 52.09 E(CH3)3J. 185.32 T_C=S].

15N NMR (500 MHz, CDCls, 25 OC): 6 = -325.13 ppm. GC/MS (40 eV, pos. ions): d z (rel. Int. %) = 41(45), 57(40), 72(12), 98(10),

1 16(85), l2S(lS), l57(lS), 17 1 (IO), 197(7), 227(40), 228(30).

'BU I 'BU SCN - 'Bu

I 'BU

I I (Ni 314 S, [EH + HN

HN CH~N(~BU)

N N - 140 OC 26 h

+ >s 'BU / - Gu 1 H2N

'BU 'BU

4 9 (1-H] SCN 13 14

In a 100 rnL ~wagelock@ stainless steel cylinder with valve, Sg (0.61 g, 2.38 mmol, 0.75

equiv.) was added to the triazine (0.8 1 g, 3.18 mmol, 1 equiv.), closed under vacuum and heated

to 140 OC for 26 h. No over pressure developed after heating. The orange brown reaction

mixture was extracted with 60 rnL of CHC13 and decanted with a syringe into a sublimation flask. Evaporation gave 0.63 g of an orange solid. Sublimation gave 2 volatile fractions, tert-

butyl thiourea (50 - 80 OC, 0.2 1 g, 35949, 1,3-Di-tert-butyl thiourea (80 - 120 O C , 0.15 g, 36%) and a third fraction (120 - 140 OC, 0.02 g, 10% 14, 16% 13). The sublimation residue consisted

of essentially pure [l-H] SCN (0.13 g, 171). No evidence was found for the formation of 11- t Bu.

1,3-Di-te~-butyl-thiou~e8 (13) 1H NMR (200 MHz, CDC13.25 OC): 6 = 1.47 ppm [s, C(C&)3], 5.75 [s, m. 13C{lH) NMR ( 5 0 MHz, CDC13, 25 OC): 6 = 29.41 ppm [C(ÇH3)3], 53.23 [ç(CH3)3],

180.03 E=S].

EI-MS (70 eV): m/z (rel. int. 96): 41(26), 57(100), 77(35), 83(10), 115(8), 13 1(21), I87(32).

Tert-butyl thiourea (14) 1H NMR (200 MHz, CDC13, 25 OC): 6 = 1.38 ppm [s, C(CH3)3], 9.28 [s, N&l,

9.36 [s, NyI.

W { l H } NMR (400 MHz, CDC13, 25 OC): 6 = 29.65 ppm [C(ÇH3)3], 56.1 9 [C(CHs)3 1, 186.99 c=S] .

FT-IR (NaCl; nujol): 724br w, 941br m, 975br m, 1040br w, 1238br m, 1543br

m, 1686br w, l873br w, 2099br w, 236 1 br w, 2724br m, 3 175br m.

1,s-Di-tert-butyl-imidwolinium thiocyanate ([1-H] SCN) 1H NMR (200 MHz, CDC13, 25 OC): 6 = 1.84 ppm [s, C(C&)s], 7.41 [s,

N C & a , 9.1 5 [s, @-II]. 13C{IH) NMR (500 MHz, CDC13, 25 OC): 6 = 30.02 ppm [C(ÇH3)3], 6 1 .O4 [Ç(CH3)3],

119.47 [NCH=ÇH], 133.49 PH]. FT-IR (NaCl; nujol): 65 1s w, 707s w, 723br m, 801br w, 883s w, 974br m,

1019br m, 1173br s, 1205br rn, 1261br w, 1305br w, 1652br w, 2053br

rn, 2342sh w, 2360s rn, 2672br w, 2724br m, 3 158br w, 3566br w, 3641s

S.

97

3.5 Synthesis of 1 f -DiJeH=butyl-hexahydro-pyrimidinim- thiocyanate (13-H1 SCN)

In a 250 mL boiler flask, Sg (1.46 g, 5.70 mmol, 1 equiv.) and 3-H2 (4.52 g, 22.79

mmol, 4 equiv.) were slowly heated to 190 O C oil bath temp for 40 h (reflux). Gas evolution

started at 1 10 O C , ceased at 160 O C and started again at 190 OC. The crude mixture (total weight = 4.67 g) consisted of a black solid at the bottom of the flask and a yellowish-orange solid on the rims of the flask. The crude mixture was extracted with 30 mL of CHC13. The solution was

decanted with a syringe to a sublimation flask. The solvent was evaporated in vacuo.

Sublimation gave a yellow oil (0.03 g) at 160 O C . The sublimation residue was essentially pure

13-H1 SCN (black, shiny, granula solid, 1.96 g, 34% yield).

1,3-Di-tert -buty l-hexah ydro-pyrimidinium thiocyanate ([3-H] SCN) 1H NMR (200 MHz, CDC13, 25 OC): 6 = 1.53 ppm [s, C(C&h], 2.16 [qt,

NCH2C&CH2NIr 3.59 [t, NCk], 7.96 [s, C-H+3.

lJC{lH} NMR (500 MHz, CDC13, 25 OC): 6 = 19.78 ppm [NCHSH2CH2N], 27.49

[C(ÇH3)3], 39.70 [NGHs], 6 1.16 E(CH3)3], 130.96 [SÇN-1, 146.34

EH+]* 13C NMR (500 MHz, CDC13, 25 OC): 6 = 19.78 ppm [t, 132.44 Hz,

NCHSH2CH2N],27.49 [q, *J (C,H) = 127.64 Hz, C(çH,)fJ, 39.70 [t, 1J (CH) = 143.96, NGHz], 61.16 [s, Ç(CH3)3], 130.96 [s, SÇN-1, 146.34 [d,

1J (C,H) = 189.06 Hz, CH+]. (NaCl; nujol): 942s w, 980s m, 1009br m, 1092s m. 1192s s, 1236s s, 1331s s, 1369s s, 139Sbr m, 141 1br rn, 1461br s, 1672br s, 2057br s,

3.6 Synthesis of 1,3-Di~e~-butyl-imidszoIium chloride ([l-rn CI)

'BUNH, (2 cq.) . I .

ter?-butyl amine (4.40 g, 60 mmol, 2 equiv.) was added to paraformaldehyde (0.90 g, 30

mmol, 1 equiv.) in 6N HCI (5 mL, 30 mmol, 1 equiv.) at 25 O C in a round-bottom flask. To this

mixture, 40% wlw glyoxal (3.44 mL, 30 mmol, 1 equiv.) was added slowly after which the solution tumed reddish and the colorless deposit re-dissolved. An exothermic reaction was

observed after the addition of glyoxal. After 24 h stimng at r. t., the mixture was refiuxed at 110

OC for 18 h. The resulting mixture (dark brown, viscous liquid) was evaporated using a

Brinkmann Rotavapor-R until the residue was solid crystalline. This residue was nearly pure [l- H) CI, but further purification is possible by subliming off the remaining (unidentified)

impurities. The sali is not volatile up to 200 OC. The sublimation residue was essentially pure [l- H] CI (brown, hygroscopic, smoked in air and hard in texture, 4.16 g, 64% yield).

1,s-Di-tert- buty 1-irnidazolium chloride (Il-H] CI)

1H NMR (200 MHz, CDC13, 25 OC): 6 = 1.8 1 ppm [s, C(913)3], 7.7 1 [d, Cuza , 'J (C,H) = 1.8 HZ], 10.48 [s, C-B+].

UC(1HJ NMR (500 MHz, CDC13, 25 OC): 6 = 30.29 ppm [C(ÇH3)3], 60.76 [Ç(CHsh], 119.71 [çH=ÇH], 134.51 L W ] .

13C NMR (500 MHz, CDCls, 25 OC): 6 = 30.29 ppm [q, C(ÇHsà, 1J (C,H) = 128.2

Hz, 3J (C,H) = 128.9 Hz], 60.76 [s, Ç(CHsh], 1 19.7 1 [d, ÇH=CH, l J (C,H) = 199.9 Hz], 134.51 [d, CH+, lJ(C,H) = 219.7 Hz].

FT-IR (NaCl; nujol): 61 lsh w, 639s m, 723sh m, 745s m, 808br m, 829sh m, 864br m, 885sh m, 913s vw, 934s w, 955s w, 977br w, 1019s m, 1096br m,

1124s m, 1 138s m, 1173s w, 1209s m, 1265s m, 1293s w, 1307s w, 1377s

s, 1469s s, 1546s w, 1631s w, 1961br w, 2081br w, 2313br w, 2418br w,

2460br w, 2509sh w, 2608sh m, 2678sh m, 2720s m, 29 17br s, 3 156br m, 3360br m.

3.7 Proton Traasfer Reactions (NMR Scale)

To see if the C+-H proton exchanges with deuterium, [l-H] Cl was first pumped in

vacuo at oil bath temperature of 180- 190 OC for 18 h to dry the salt and then measured in &O. The NMR tube was now flame sealed and re-measured after 6 d at 25 O C and after 66 d at 25 OC followed by heating in the oven for 18 h at 1 10 OC.

1H NMR (200 MHz, D20(TMS int. ref.), 25 OC): 6 = 0.27 ppm [s, 18H, C(C&)3],

1 -25 [s, 0.2H], 3.39 [s, HDO], 6.1 1 [s, 0.2H], 6.3 1 [s, 1 AH, Nm=CH], 7.35 [s, 0.9H, C+-fJ], 7.41 [SI.

1H NMR (200 MHz, D2O(TMS int. ref.), 25 OC. 66 d): 6 = 0.29 ppm [s, 18H,

C(C&)3], 1.28 [s, 0.2H], 3.44 [s, HDO], 6.13 [s, 0.2H], 6.33 [s, 1.6H, NC&a] , 7.38 [s, 0.9H, C+-II], 7.44 [SI.

1H NMR (200 MHz, DzO(TMS int. ref.), 1 10 OC, 18 h): 6 = 0.29 ppm [s, 18H,

C(C&)3], 1.28 [s, 0.2H], 3.44 [s, HDO], 6.13 [s, 0.2H], 6.33 [s, 1.6H,

NC&a] . 7.38 [s, 0.9H, C+-fI], 7.44 [s].

In an NMR tube, 2 (55 mg, 0.3 mmol, 1 equiv.) was added to [1-H] CI (65 mg, 0.3

mmol, 1 equiv.) in the gIove box and dissolved in C@6 and then flarne sealed and measured at 25 O C .

1H NMR (200 MHz, C 9 6 , 25 OC): 6 = 0.92 ppm [s, 9H, NHC(C&)3], 1 .O3 [s, 9H, N(CHO)C(CH3)31, 1.34 b, 18H, C(C&)3,21, 1.5 1 b, 18H. ~ ( ~ ~ ) 3 , 11, 2.56 [t, 2H, WC&], 3.07 [s, 4H, NC&, 21, 6.8 1 [s, 2H, NCH=Cfl 11.

3.7.3 12-H] SCN with 1

'BU 'BU 'BU 'BU I SCN- I I SCN- I

CbD6 [y. + cN): - N 25 OC [kH N + (1:

l 'BU

I 'Bu

I 'BU

I 'BU

(2-Hl SCN 1 (1-Hl SCN 2

1 (0.03 g, 0.17 rnrnol, 1 equiv.) was added to 12-H] SCN (0.04 g, 0.17 mmol, 1 equiv.)

in C a 6 in a sealed NMR tube and measured at 25 OC.

1H NMR (200 MHz, C6D6,25 OC): 6 = 1 -36 ppm [s, 18H, C(C&)3,2], 1 .52 [s, 18H, C(C&)3,l], 3.05 [s, 4H, N C b , 2],6.79 [s, 2H, NCH=CH, 11.

lJC{'H) NMR (500 MHz, C&. 25 O C ) : 6 = 29.95 ppm [C(ÇH3h, 2],3 1.48 [C(ÇHî)j, 11, 44.52 [NH2,2], 55.80 c(CH3)3,1], 1 15.05 [NCH, 11.

3.7.4 [3-H] SCN with 1

'Bu 'BU 'BU t ~ u

I sCN- I I I SCN -

25 OC

I I N

'Bu 'BU I

'BU I

'Bu

In an NMR tube, a solution of 1 (0.03 g, 0.17 mmol, 1 equiv.) in 0.5 mL of HMPA was

flame-sealed immediately. After letting it sit for 2 d at 25 OC, the seal was opened under inert

atmosphere and a D20 insert with a drop of TMS were added and the sample was measured. To the sample, a solution of [3-H] SCN (0.04 g, 0.17 mmol, 1 equiv.) in 0.3 rnL of HMPA was

now added and measured.

1H NMR (200 MHz, HMPND20, 25 OC): 6 = 1 .O2 ppm [s], 1.38 [s, 18H, C(C&)3, 31, 1-76 [s, br, 18H, C(C&)3, (1-Hl SCN], 4.5 [s, fIDO], 7.2 [br, NCfL [l- H] SCN], 10.7 [s, C+-H, [1-H] SCN].

i 3 ~ { 1 ~ ) NMR (400 MHz, HMPAID20, 25 O C ) : 8 = 29.04 ppm [C(ÇH3)3, 31, 29.49

[C(GH3)3, [I-H] SCNI, 29.75 [CGH3)3, 11, 39.42 [NcH2,3], 60.12

[Ç(CH3)3. 11-H] SCNI, 60.78 [ç(CH3)3,3], 12 1.45 [%H=cH, [1-H] SCN], 134.66 [ç+-H, [l-H] SCN].

3.7.5 11-H] CI with [3-H] SCN

'BU CI - 'BU

SCN - SCN - 'BU I I I CI -

(1- Hl CI (3- H) SCN (1- SCN (3- Hi CI

In an NMR tube, [3-H] SCN (35 mg, O. 14 mmol, 1 equiv.) was added to [1-Hl CI (30 mg, O. 14 mmol, 1 equiv.) in CDC13 and the NMR tube was flarne sealed under vacuum.

1H NMR (200 MHz, CDCl3,25 OC): 6 = 1.54 ppm [s, C(C&)3, [3-Hl SCN], 1.74 [s,

C(CH3)3. [ 3 - 9 CI], 1.80 [s, C(C&h, [1-Hl Cl], 2.15 [qt, NCH2C&, [3-

H] SCN], 2.55 Pr, NCH2C&, [3-Hl CI], 3.59 [t, NCH2, [3-H] SCN], 7.45 [S. br], 7.80 [s, NCH, [Lm Cl]. 8.02 [s, C+-H, [3-H] SCN], 9.0 1 [s,

br], 9.97 [s, C+-H, [1-H] CI].

'BU $u ' a- I "BuLi THF 1

Q;c- * 25°C 18h b

- "Bu-H (g) g c :

N f - LiCl N

'BU I

'BU

1,3-Di-ter?-butyl-imidazolium chloride (2.01 g, 9.3 mrnol, I equiv.) was dissolved in 15

rnL of dry THF in a 100 mL schlenk flask to give a dark brown solution. On complete

dissolution, of n-butyl lithium (0.59 g, 9.3 mmol, 1 equiv.) was added slowly which led to

warming up of the reaction flask. Gas evolution was monitored via an oil bubbler. Once the gas

evolution ceased, the mixture was stirred overnight for 18 h followed by sublimation between

60-80 O C oil bath temperature.

1,3-Di-tert-butyl-imida.~oIe-2-yIidene (1) 1H NMR (200 MHz, CgD6.25 OC): 6 = 1.5 1 ppm [s, C(C&)3], 6.79 [s, C B = a . 13C(lH) NMR (400 MHz, CaD6, 25 O C ) : 6 = 3 1.46 ppm [C(ÇH3)3], 55.76 [Ç(CHsh],

115.00 [çH=ÇH], 212.87 [L'Ç:].

i3C NMR (400 MHz, Cg&, 25 OC): 6 = 3 1 -46 ppm [q, C(ÇH3)3, l J (C,H) = 126.6 Hz, 3J (C,H) = 4.4 Hz], 55.76 [s, Ç(CH3)3,25 (C,H) = 1 2.1 Hz, 3~ (C,H) = 3.6

Hz], 115.00 [d, ÇH=CH, 1J (C,H) = 185.3 Hz, 25 (C,H) = 13.2 Hz], 212.87 [s, L'G:].

1sN NMR (500 MHz, Co&, 25 OC): 6 =-167.62 ppm. EI-MS (70 eV): m/z (rel. int. %): 41 (20), 57 (32), 69 (100), 82 (3), 95 (IO), 11 1

(IO), 125 (13), 181 (48) FI+].

104

3.9 Synthesis of 1,3-Di-tert-butyl-imidazolin-2-ylidene (2) from 1,3-Di-tert-butyl- imidazolium-2-thiocyanate ([2-H] SCN)

N/ 25 OC, THF N'

'Bu

LDA (2.1 cq.)

- LDA-H

12-HI SCN 2 2-CHO

In a sublimation flask equipped with a stir bar, a 2 M solution of LDA in heptane / T W / ethyl benzene (O. 19 g, 1.74 mmol, 2.1 equiv.) in 20 mL of THF was added to 12-H] SCN (0.2 g, 0.83 mmol, 1 equiv.) and stirred at room temperature for 30 mins.. The crude mixture (0.35 g) showed strong 1H NMR signals of 2. However, sublimation did not yield the pure carbene, but instead, gave a multitude of at least four decomposition products (50 OC, white solid, 0.014 g),

one of which was identified as 2-CHO. It must be concluded, that the carbene can be formed from the thiocyanate, but reacts either with the thiocyanate itself or with reaction products

formed from the thiocyanate and the base (LDA).

Crude mixture: 1,3-Di-tert-butyl-imidazolin-2-ylidene (2) 'H NMR (200 MHz, C&,, 25 O C ) : 6 = 1.36 ppm [s, C(CH3)3], 3.03 [s, NCfà21.

Sublimate at 50 O C : N-FormyCN,N1-DiJert-butyl-ethylenediamine (2-CHO) 1H NMR (200 MHz, C&j, 25 O C ) : 6 = 0.85 ppm [s, NHC(C&),], 1.01 [s,

N(CHO)C(C&)3], 1.32, 1.36, 1.55, 2.71 [t, NHCm], 3.34 [t,

N(CHO)C&], 8.40 [s, W.

3.10 Attempted Synthesis of 1~3-Di-te~-butyl-hexPbydro-pyrimidine-2-y1idene (3)

THF

13-Hl SCN 3

i) 2.1 equiv of "BuLi or LDA or 4-dimethylamino-pyridhe

A sublimation flask attached to an oil bubbler was used as the vesse1 for this reaction.

2.0 M solution of LDA in heptane I THF / ethyl benzene (0.49 g, 4.60 mmol, 2.1 equiv.) was

added slowly to a solution of [3-Hl SCN (0.56 g, 2.19 mmol, 1 equiv.) in 20 mL of THF. The cmde mixture (black solution, total weight = 0.99 g) was stirred for 20 mins. and then analyzed

by 1H NMR and GC/MS and later sublimed in vacuo. At 80 - 90 O C oil bath, a coiorless oil

collected (weight = 0.2 g, yield of 3 = 471). At 90 - 100 OC oil bath, black granular solid

collecied on the cold finger (weight = 0.04 g)

Fraction 1 (80 - 90 OC): 193-Di-tert-butyl-hexahydro-pyrimidine-2dene (3) lH NMR (200 MHz, C6D6, 25 OC): 6 = 1.38 ppm [s, C(C&jh], 1.67 [qt, NCH*C&],

2.67 [t, NC&].

Fraction 2 (90 - 100 OC) lH NMR (200 MHz, C a 6 , 25 OC): 6 = 0.86 ppm [s, 9H, C(C&)3NH], 1 .O3 [s, 9H,

C(C&)3N-CHO], 2.47 [qt, 2H, NCH2C&], 3.34 [t, 4H, NC&], 8.41 [s,

Na-

In a 100 mL Schlenk flask, CH2=0 (1 .O7 g, 35.68 mrnol, 1 equiv.) was added dropwise

to a solution of Bu-NH2 (3.13 g, 42.82 rnmol, 1.2 equiv.) in 4 rnL of diethyl ether leading to an

exothermic reaction. The mixture was stirred for 20 mins. and extracted the ether layer. Upon

evaporation of ether, an oily liquid (1.8 1 g, 20% yield, m.p. = 5 OC) was obtained. The yields

were 27% when repeated on a larger scale (5 g of 'Bu-NH2).

1,3,5-tri-fert-butyl-hexahydro-sym-triazine (9) in C&5 1H NMR (200 MHz, C & j i 25 OC): 6 = 1.12 ppm [s, C(C&)3], 3.72 [s, NC&]. 13C(lH} NMR (500 MHz, CaD6, 25 OC): 6 = 27.25 pprn [C(ÇH3)3], 52.85 [Ç(CH3h],

63.77 mcH2].

1,3,5-tri-tert-butyl-hexahydro-sym-ttiazine (9) in CDCI3 'H NMR (200 MHz, CDCl3,25 OC): 6 = 1.05 ppm [s, C(C&)3], 3.45 [s, NC&]. 13C{lH} NMR (500 MHz, CDC13,25 OC): 6 = 26.8 pprn [C(ÇH3)3], 53.1 [ç(CH3)3 1, 63.94

[ N a 2 1 - Tert-butyl imine (4) in C6& 1H NMR (200 MHz, CDC13* 25 OC): 6 = 1.08 ppm [s, C(CH3)3], 4.54 [s, NCk].

Tert-butyl imine (4) in CDCl3 1H NMR (200 MHz, CDC13.25 OC): 6 = 1.12 ppm [s, C(C&)3], 7.28 [m, NC&]. l3C(IH} NMR (500 MHz, CDC13,25 O C ) : 6= 28.9 pprn [C(ÇH3)3], 58.1 [ç(CH3)3], 147.1

lY=a321..

3.12 Synthesis of lJ-Di~ert-bu~l-2J~ydro-imidsu,1e (&Hz)

'BU 1/8 LiAIH, THF 'BU 1 Cl - I

&H 25 OC 5 min

N - LlCI cNyH I

N H

t ~ u I

'BU

[l-H] CI (2.38 g, 10.98 mmol, 1 equiv.) was dissolved in 12 mL of THF (15 min

stimng, r. 1.). A freshly prepared solution of LiAlH4 (0.2 1 g, 5.49 mmol, 0.5 equiv.) in 12 mL of THF was stirred until dissolved (15 rnins. stimng). 3 mL of the LiAIH4 solution was added under constant stirring to [l-81 CI in THF (gas evolution). After stirring the mixture 5 mins., the mixture was exttacted with IO mL THE The solution was decanted from the insoluble

material using a syringe into a sublimation flask. The crude mixture (dark brown solid, 0.27 g) was analyzed by NMR followed by

sublimation in vacuo at -80 OC oil bath temperature (grey powder, 0.04 g, 2.2% yield) and a

black residue (0.21 g). The spectroscopie data chiiractenze the primary reaction product as the

desired bH2. However, al1 attempts to isolate the compound in pure form only led to greyish

solids that are presumed to be polymeric bH2. The instability of 1-Hz is most surprising in

view of the fact that a number of derivatives such as [ L a + , 1=0 and 1=S are thermally robust

and can be isolated by sublimation without difficulties. It is likely that the N-CH=CH-N fragment is stable only in conjugation with -M substituents such as C=O, C=S etc.

1,3-Di-ter?-butyl-2,3dihydr01imidazole (1-HZ) 1H NMR (200 MHz, C@6,2S O C ) : 6 = 1 .O0 ppm [s, C(C33)3], 4.26 [s, L'Ch], 5.49

[s, cu=a1. 13C{lH} NMR ( 4 0 MHz, CaDs, 25 OC): 6 = 27.01 ppm [C(ÇH3)3], 52.76 [Ç(CHsh],

66.52 [ÇHa], 1 16.28 mÇH=çH].

13C NMR (400 MHz, C&, 25 OC): 6= 27.01 ppm [q, C(ÇH3h, 1J (C,H) = 125.2 Hz, 35 (C,H) = 4.3 Hz], 52.76 [s, Ç(CH3)jJ. 66.52 [t? NzÇH2, 1J (C,H) = 145

Hz], 116.28 [d, NCH=çH, lJ(C,H) =181.65 Hz, ~J(C,H) = 11 Hz].

FT-IR (nujol; NaCl): 639s m, 723br w, 808br w, 871br vw, 1026sh w, 1096sh w,

1 124s m, 1 152s w, 1173s w, 1202s s, 1258s m, 1286s w, 1370sh m, 1377s

s, 1462s s, 1504s vw, 1539s w, 1553s w, 1616s m, 1652s w, 2425br w, 2727s m, 2903br s, 3 156sh rn, 3416br m.

3.13 Preparation of tert-butoxy lithium

To a solution of tert-butanol (2.25 g, 30.4 mrnol, 2.90 mL, 1 equiv.) in 20 rnL of dry

THF, 12.16 rnL of 2.5 M "BuLi (1.94g, 30.4 mmol, 1 equiv.) in hexanes was added dropwise under argon atrnosphere while stimng. The resulting pale yellow mixture was refluxed at 100 OC oil bath for 2-3 h. Gas evolution was monitored via a bubbler. The tert-butoxide lithium thus

prepared was diluted with THF to make a solution of 24.3 a.

1H NMR (200 MHz, C a 6 , 25 O C ) : 6= 1.28 ppïïi [s, (C&)3C].

13C{lH) NMR (400 MHz, C6D6, 25 OC): 6 = 25.79 ppm [(ÇH3)$OH], 35.56 [(çH3)sCOLi], 66.84 [(CH3)3c-OLi], 67.80 [(CH3)3Ç-OH].

3.14 Attempted Synthesis of l ~ - D i - t e H - b u t y E 2 - I i t h i 0 1 2 ~ e H - b u t o x y ~ l e (L'Si-

(0tBu)Li)

'BU 'BU I I

t '6u0li -i

N THF

I 'BU

I 'BU

L'Si: L's~-(o'Bu)L~

L'Si: (0.04 g, 2 1.9 mmol, 1 equiv.) was added to 'BuOLi ( 0.02 g, 2 1.9 mmol, 1 equiv.) in 5 rnL of TKF. The reaction mixture was stirred for 1 h, the solvent was evaporated and a

sample was analyzed in C6D6 after 1 h and after 24 h. In both cases, new signals were observed other than the starting material. The NMR sample was also subjected to heating at 1 0 O C for 7 d giving the same results. Upon repeating the reaction on a 1 g scale, same results were

obtained.

lEi NMR (200MHz, C6D6, 25 OC): O= 1.27 ppm [s, 9H, (CfuhC-OLi)], 1.28 [s, int. 11, 1.32 [s, int. 1.41, 1.41 [s, 18H, C(C&)3], 5.80 [dl, 6.75 [s, 2H, CH=CH.

l3C{1H} NMR (400 MHz, C&j, 25 OC): 6 = 30.84 ppm [L'Si:, C(ÇH3)3J, 32.03 [L'Si- (o@u)L~, NCGH3)3], 33.05 [OCGH3)3], 33.60 [(ÇH3)3C-OLi] , 5 1.18, 5 1.68, 54.05 [L'Si:, Ç(CH3)3 1, 66.83 [(CH3)3~-OLi], 67.83 [OÇ(CH3)3 1, t 1 1.90 si-(o~Bu)L~, CH-, 120 [L'Si:, ÇH=ÇH].

3.15 Attempted Synthesis of 1,3-Di-tert-butyl-2-lithi0-2-?ert-butoxy~ (LGe- (0tBu)Li)

'BU I

'BU 1 'BUOL~

I O'BU - ("<

THF N Li I

'BU I

'BU

LGe: L G ~ - ( o ~ B ~ ) L ~

A 1 : 1 mixture of tBuOLi (0.02 g, 0.08 mmol, 1 equiv.) and LGe: (0.02 g, 0.08 mmol, 1 equiv.) in was flame-sealed and measured at 25 O C immediately and then after 2-7 d at

100 oc.

1H NMR (200MHz, C6D6, 25 OC): 6 = 1 .O4 ppm [s, NHC(C&)3 1, 1.27 [s, 9H, (CY3)3C-OLil, 1.30 [s, 18H, C(C&)3, LGe:], 2.57 [s, N C k , 2-Cl, 3.28 [s, 4H, NC&, LGe:].

3.16 Attempted Synthesis of 1 , 3 - D i - t e r ? - b u t y l - 2 , 3 - d i h y d r o - 1 - I i t h i o i (1-(0tBu)Li)

'BU 'BU I I

1 'BUOL~

THF N Li I

'BU I

'BU

1H NMR of a 1 : 1 mixture of 1 (0.02 g, O. 11 mmol, 1 equiv.) and tBuOLi (0.02 g, 0.1 1

mmol, 1 equiv.) was rneasured in C6D6 bath at 25 for 7 d and after heating in the oven at 100 O C over a period of 14 d.

lEI NMR (200MHz, C6&, 25 OC): Ô = 1.27 ppm [ 9H, (ChhC-OLi)], 1.43 [s], 1.50 [s, 18H, C(C&)3NC: ],6.78 [s, 2H, N a = a .

110

3.17 Attempted Synthesis of 1 , 3 - D i - t e r t - b u t g l - 2 - l i t h i 0 - 2 J e r f - b u t o ~ (2-

(0tBu)Li)

'BU 'Bu 'BU I I

+ THF Li

I I NH

'BU 'BU I

'BU

'H NMR of a 1 : 1 mixture of 2 (0.02 g, O. 1 1 mmol, 1 equiv.) and tBuOLi (0.02 g, O. 1 I mmol, 1 equiv.) was measured in C6D6 both at 25 O C and after 22 h at 1ûû O C .

1H NMR (200MHz, C&, 25 OC): 6 = 0.92 ppm [s, 9H, NHC(C&h], 1 .O4 [s, 9H, N(CHO)C(CLI3)3], 1.32 [s, int. 11, 1.35 [s, int. 21, 3.05 [S. NCHz], 8.49 [s,

NHI .

3.18 Attempted Synthesis of 1,3-Di-te~-butyl-2-chloro-2-terf-butox y-l (L'Si-(0tBu)CI)

'Bu 'BU I 1 'BUOL~ I

THF O'BU

/ \ N Cl I

- LiCt 'BU

I 'BU

A solution of 'BuOLi (0.24 g, 2.96 mmol, f equiv.) in 1 1 rnL THF was added to L'SKI2 (0.79 g, 2.96 rnmol, 1 equiv.) at 25 OC and stirred.

rH NMR ( 2 0 0 M H ~ C6D6, 25 OC): 6 = 1.24 ppm [s, 18H, C(W3)3 1, 5.75 [s, 2H, NCH-.

3.19 Attempted Synthesis of 1,3-Di~tert-butyl-2-di-terf-butoxy-1,3~aza-2-si10le with ~ B U O L ~ (L'Si(0tBu)z)

A solution of BuOLi ( 0.18 g, 2.25 mmol, 2 equiv.) in 8.4 mL THF was added (constant stimng, under argon) at 25 O C to L'SiCI2(0.30 g, 1.13 mrnol, 1 equiv.) and stirnd until dissolved.

1 H NMR (2ûûMHz, C a , 25 OC): 6 = 1.25 ppm [s, 18H, C(qIg)3 j, 1.27 [s, 9H,

(CH93 C-OLi)] ,5. 75 [s, 2H, NCH=Ca.

3.20 Attempted Synthesis of 1,3-Di-tert-butyl-2-di-tert-butoxy-l,3-diaza-2-silole with

'BUOH (L1Si(OtBu)2)

'BU 'Bu

In a schlenk flask, a solution of BuOH (0.55 g, 7.48 mmol, 2 equiv.) in 40 mL of

pyridine was added to L'SiCI2 (0.8 g, 3.74 mmol, 1 equiv.) and s h e d for 30 mins..

1H NMR (200MHz. Cd%, 25 OC): 6 = 1.25 ppm [s, 18H, C ( ~ I S ) ~ 1, 5.75 [s, 2H, NCH=m,6.67 [t,2H,Ha.],6.99 D, 2H,Hk], 8.53 [d, lH, HG 1.

'BU 'BU I I

N OMe

/ N CI PY N OMe I I

'BU 'BU HG

A solution of MeOH (0.07 g. 2.24 mmol, 2 equiv.) in 10 mL pyridine was slowly added

to L'Sic12 (0.3 g, 1.12 mmol, 1 equiv.) under constant stimng at 25 OC. The color changed from

pale yellow to reddish brown after 1 h of stimng and finally went dark green after 3 h of

stimng. 1H NMR in C a 6 of the dark green solid was taken after 9 h of stimng (color remained

dark green) after evaporating pyridine.

1H NMR (2mMHz9 C d k , 25 O C ) : 6 = 1.00 ppm [s, 3H, CbOH], 1.25 [s, 18H. C(C&)3I9 1-27 [br, SI, 1.38 [br, s], 1.42 Es], 3.42 [ml, 5.76 [s, 2H, NcH=CHl, 6.34 Pr], 6.56 Dr], 6.76 [br, 2H, Ha], 7.03 [t, 2H, H ~ I , 7.37 Pr, 2H, HG 1, 1 1.95 [br, s].

3.22 Synthesis of 1 , 3 - D i - t e r t - b u t y 1 - 2 - h y d r i d o - 2 - t e r t - b u t o ~ e (L'Si- (0tBu)H)

'BU I

'BU I

2 'BUOH

THF

LW: L~S~-(O~BU)H

A solution of tBuOH (0.74 g, 9.98 mrnol, 2 equiv.) in 10 mL of THF at 25 OC was added slowly to L'Si: (0.98 g, 4.99 mmol, 1 equiv.) under constant stimng for 1 h at 25 OC. No change in color observed after stimng. This mixture was then sublimed in vacuo at 50-80 OC oil bath.

1H NMR (200MHz, C a , 25 OC): 6 = 1.29 ppm [s, MH, NC(C&)3], 1.33 [s, 9H,

O(C&h 1,577 [s, 1 H, Si -a , 5.80 [s, 2H, NC&Ca. i3C{1H) NMR (400 MHz, CdD6, 25 O C ) : 6 = 30.83 ppm mC(ÇH3)3], 32.01 [OC(ÇHsh],

5 1.17 [NÇ(CHsh], 72.96 [Oc(CH3h], 1 1 1.87 [NCH=çH]. EI-MS (70 eV): m/z (rel. int. %): t~ = 5.23 mins. : 41(20), 57(100), 70(5), 84(5),

97(lS), 1 12(10), 141 (5). t~ = 13-92 mins. : 41 (43), 57(72), 69(22), 83(20), 97(100), 109(10), 123(15), 137(10), 151(5), 179(5). t~ = 16.73 mins. :

41(52), 57( lm), 69(20), 83(32), 97(100), 109(10), 123(10), 137(8), 15 1(5), 177(7). t~ = 17. 14 rnins. : 4 l(62), 57(73), 69(25), 83(25), 97(100), 109(12), 123( 14), 137( IO), 15 l(7), 179(5).

3.23 Attempted Synthesis of 1,3-DI-te~-butyl-2-bydrid0-2~ert-butoxy-l,3~i~- germolidine (LGe-(0tBu)H)

'Bu 'BU 1 I

2 'BUOH

THF I

'Bu I

'BU

A solution of BuOH (0.27 g, 3.71 rnrnol, 2 equiv.) in 10 mL of THF was added slowly to LGe: (0.45 g, 1.85 mmol, 1 equiv.) at 25 OC and stirred for 2 h. The reaction was monitored

by 1H NMR after 2 h and after 48 h of stimng at 25 OC.

iH NbIR (200MH2, C6D6, 25 OC, 2 h ): 6 = 0.76 ppm [s, L&], 1.04 [s, C(C&)3], 1 2 2 [s], 1.34 [s], 1.40 [s], 1.47 [s, 9H, (Ch)$-OH], 2.58 [d, NC&],

2.75 [SI. 1H NMR (200MH2, C&, 25 O C , 48 h ) : 6 = 1 -04 [s, C(C&)3], 1 -22 [s], 1.36 [s],

1.49 [s, 9H, (C&)3C-OH], 2.58 [br, NC&].

3.24 Attemp ted S ynthesis of 1,3-Di-tert-buw-2-hydrido-2 ~er t -bu tox y (1-

(OtBu)H)

'Bu 'BU I

2 'BUOH I N, ,O'BU

THF N I

'BU I

'BU

A solution of BuOH (0.42 g, 5.66 mmol, 2 equiv.) in 10 rnL of THF was slowly added

to 1 (0.5 1 g, 2.83 mmol, 1 equiv.) at 25 O C and stined for 2 h. Solvent was evaporated and the

resuiting mixture was sublimed in vacuo at 25 - 40 OC oil bath temperature to give white

crystalline solid on the cold finger.

1H NMR (2OOMHz, C D 6 , 25 O C , crude): 6 = 1.14 ppm [s, 9H, (O(C&)3)(H)], 1.52

[s, 1 8H, C(CtIj)3 J, 6.80 [s, 2H, NC&CU. 1H NMR (200MH2, C a a , 25 OC, sublimed 25-40 OC): 6 = 0.85 ppm [s, 9H.

NHC(C&j)3], 1 .O8 [s, 98, N(CHO)C(C&)3 1, 1.1 9 [s], 1.5 1 [S. 1 8H, C(CIi3)3 J,6.78 [s, 2H, NCH=CM.

3.25 Attempted Synthesis of 1 ,3 -D i - te r t -buty l -2 -hydr ido-2Jer t~b~ i toxym (2-

(0tBu)H)

'Bu 'BU I I

1.6 'BUOH

'MF I

'BU I

'BU

A solution of BuOH (0.09 g, 1.2 mmol, 1.6 equiv.) in 5 mL of THF was slowly added to

2 (0.14 g, 0.75 mrnol, 1 equiv.) at 25 O C under constant stimng for 2 h and a sample was

measured in C&j.

lH NMR (200MHz9 Cdh , 25 OC, 2h ): 6 = 0.95 ppm [s, NHC(C&)3], 1 .O3 [s,

N(CHO)C(C&)d, 1-15 [SI, 1-29 [s, (C&)3], 2.92 [m, NHC&], 3.01 lm, N(CHO)C&], 5.4 Pr, 'BUOH, 8.2 [s, m.

'BU 1 McOH 'BU I I

2s "c N OMe

I I 'BU 'Bu

I 'BU

In a sublimation fiask equipped with a stir bar, MeOH ( 0.09 g, 2.82 mmol, 1 equiv.) was

slowly added to 2 (0.52 g, 2.82 mmol, 1 equiv.) under constant stimng at 25 O C leading to an exothemic reaction. After stining the mixture for 15 mins., any excess MeOH was evaporated

followed by sublimation in vacuo, giving a clear oil in the pan at 47-50 O C oil bath temperature.

lH NMR (200 MHz, C a s , 25 OC): 6 = 1.13 ppm [s, C(C&)3], 2.73 [t, C&N(t%u)CH, 2-(OMe)H], 2.94 [t, C&N(tBu)COMe, 2-(OMe)H], 3.24 [s, OC&], 5.23 fs, Ca.

~ J C { ~ H ) NMR (400 MHz, C&, 25 O C ) : 6 = 27.79 ppm [C(ÇH3)3], 44.49 [NçH2], 49.82

[0CH31, 52-01 Iç(CH3)3], 98.30 [Lç(OCH3)(H)]. l s ~ { 1 ~ } NMR (500 MHz, C&, 25 O C ) : 6 = -243.8 pprn [x (CHO)], -3 14.44

mC(CH3h], -323.83 EH].

3827 Preparation of tert-butoxy copper

THF Cul + 'BUOL~ 'BUOCU

1.2 1 O "c - Li1

To 10 rnL T W , Cu1 (3.47 g, 18.21 mmol) was added and the mixture stirred until dissolved. To this mixture, a solution of tBuOLi (1.22 g, 15.2 mmol, 1 equiv.) in 10 mL of THF was added dropwise at O OC (ice bath). The color changed from orange to yellow and finally

dark orange-brown. The crude mixture was extracted with THE The solution was decanted

€rom the insoluble material using a syringe into a sublimation fiask and sublimed in vacuo after evaporating the solvent. At 130-150 O C , a pale yellow powder collected on the finger which was

pure tBuOCu (219 mg, 1 1% yield). Continued sublimation did not yield further material.

lH NMR (200 MHz, C&, 25 OC): 6 = 1.26 ppm [s, C(C&)3].

3.28 Attempted Synthesis of 1,3-Di-te~-butyl-2-~upm-2~e~-butoxy-lJ-di~-2-siloIe

(L'Si-(0tBu)Cu)

L'Si: L'S~-@BU)CU

In an NMR tube, L'Si: (28.7 mg, 0.1 5 mmol, 1 equiv.) was added to tBuOCu (20 mg, 0.15 mmol, 1 equiv.) in C& giving an orange solution. The NMR tube was fiame-sealed and

analyzed by IH NMR. The NMR tube was then heated in the oven at 100 OC for 10 d giving a black precipitate on the upper parts of the NMR tube and a brown solution. This mixture was

also analyzed by lH NMR.

1H NMR

1H NMR

'JC{lH}

(200 MHz, C & j , 25 OC): 6 = 1.26 pprn [s, 9H, C(C&)3, 'BuOCu]., 1.4 1 [s, 18H, C(CY3)3, L'Si:], 6.74 [s, 2H, N a L'Si:].

(200 MHz, C & j , 100 OC): 6 = 1 2 6 ppm [s, 9H, C(C&)3, tBuOCu]., 1.28

[s, 18H 1, 1.32 [s, int. 9.8H], 1.41 [s, 18H, C(Cfi3)3, L'Si:], 5.80 [br, d, 2H], 6.74 [s, SH, N C L L'Si:].

MR (400 MHz, CaDs, 100 OC): 6 = 3 1.14 ppm [C(ÇH3)3, L'Si:], 32.20, [C(ÇHg)3, L'Si-(OtBu)Cu], 33.2 1 [OC(ÇH3)3, L'Si-(OfBu)Cu], 35.55, 35.77, 35.92, 5 1.34, 5 1.84 [NÇ(CH3h, L'Si-(OtBu)Cu],

54-01 (NÇ(CH3h , L'Si:], 66.2 1, 73.0 [OÇ(CHsh , L'Si-(OtBu)Cu], 1 l2.O6[NÇH, L'Si-(OtBu)Cu], 120.16 E H , L'Si:].

3.29 Attempted Synthesis of qS-(1,3-Di~e~-butyl-l,3-imidazolylidene) iron (0) dicarbonyl (l=Fe(CO)z)

neat

In a schlenk flask, Fe(C0)s (2.34 g, 1 1.8 mmol, 2 equiv.) was added neat to 1 (1 .O7 g, 5.91 mmol, 1 equiv.) slowly through a syringe under constant stirring. Gas evolution was

observed briefly for 2 mins.. A dark brown film formed around the walls of the flask after

stirring 5 mins.. After stirring for 19 h, the mixture (dark brown solid film, 1.67 g) was

sublimed. At 60 OC oil bath, clear crystalline solid collected on the lower parts of the finger.

Then, at 70 OC, yellow crystalline solid deposited on top of the clear crystals (weight of

sublimed product = 0.185 g, 1 1% yield), (weight of brown residue = 1 .O6 g).

1H NMR (200 MHz, CaD6, 25 O C ) : 6 = 1.49 ppm [s, br, C(a3)3], 6.75 [s, br,

CH=CM. 13C{lH} NMR (500 MHz, THFD20 insert, 25 OC): 6= 107.37 [s], 129.01 [NÇH], 218.77

PPm ml* FT-IR (nujol; NaCI, sublimate at 60-80 O C ) : 597br w, 625br m, 653s vw, 688s

vw, 702s m, 730br m, 766sh w, 780br m, 794s rn, 8 15sh w, 829s m, 864br

vw, 913br vw, 934br vw, 948br vw, 970s w, 99 1 br w, 1033br w, 1096br

m, 1138s m, 1181sh w, 1202s s, 1237s s, 1265sh m, 1279sh w, 1321br s,

1349sh m, 1377s s, 1413sh w, 1462br s, 1525s vw, 1560s m, 1574s m, 163 1sh m, 1673br s, 1736sh vw, 1898s s, 1912s s, 2003sh w, 2024s s,

23 13br w, 2348s vw, 2418br w, 2678br w, 2734br w, 2910br s, 3 107s m, 3142s m, 3184sh m. (nujol; NaCl, sublimation residue): 569br m, 618br s, 653s s, 702br w,

745s s, 80lbr m, 822s m, 843s s, 871sh w, 941br w, 984sh w, 1026s m, 1047s m, 1 1 10s s, 1 124s s, 1173sh m, 1209br s, 1237s s, 1265s m, 1300s

m, 1321br w, 1377br s, 1406sh m, 1469br s, 1504s m, 1539s s, 1567s s,

159Sbr m, 1877br s, 2017s m, 2207s w, 2277sh w, 23 13s w, 2376s w, 2397s w, 2460s w, 2474s w, 2608s w, 2643sh w, 2664br w, 2734s w,

2917brs, 3lOOsm, 3177ss.

FT-IR

3 3 Attempted Synhesis of ~$(1,3-Di-terf-buty1-imidazolîdene-2-ylidene) iron (O)

te tracarbony l(2=l?e(CO)4)

In an NMR tube, Fe(C0)s (0.09 g, 0.44 mmol, 2 equiv.) was added to 2 (0.04 g, 0.22

mmol, 1 equiv.) and flame sealed. The NMR sample was measured in C6D6 ai 25 O C followed

by heating at 1 10 O C for 16 h and upto 7 d.

The same reaction was repeated on a larger scale. In a schlenk flask, Fe(CO)5 (0.30 g,

1.54 rnmol, 2 equiv.) was added slowly to 2 (0.14 g, 0.77 mmol, 1 equiv.) leading to gas

evolution for 15 seconds. A brown film formed after 5 mins.. 1H NMR was recorded after 16 h.

After 4 d of stirring at 25 O C , a dark brown film covered the walls of the flask. 0.10 g of the

crude was transferred to a sublimation flask using 60 mL of hexanes. The mixture was sublimed

in vacuo giving two volatile fractions: 45-50 OC (colorless, crystalline solid, 40 mg), 60-70 O C

(purple, crystalline solid, 9 mg) and the sublimation residue (brown solid, 33 mg).

FT-IR

FT-IR

1H NMR (200 MHz, Co&. 25 OC): 6 = 0.86 ppm [s, C(C&hNH], 1.01 [s,

C(C&)3NCHO], 1.3 1 [ml, 2.55 [s, br], 2.70 [t, NHC&], 3.32 [t, N(CHO)C&], 8.40 [s, m. (nujol; NaCI, crude mixture): 720br w, 806br vw, 899s w, 959br w, 1018s w, 1058s m, 1098br vw, 11Slbr w, 1204s m, 1238s w, 1264s w, 1304s m, 1377s s, 1463s s, 1629s s, 1848br s, 1908s s, 2665sh w, 2725br m, 2904br

S.

(nujol; NaCl, sublimate at 45-50 OC): 1018s m. 1032s m, 1052s m, 1098s

m, 1138s m, 1198s s, 1211s m, 1231s m, 1264s w, 1284s w, 1297sh w, 131 1s m, 1364sh s, 1377s s, 1463s s, 1516br w, 1563s w, 1643s s, 1663sh

119

s, 1716s w, 2400br w, 2659br w, 272Sbr w, 2851br s, 2924s s, 2957sh s,

3303s m. (nujol; NaCl, sublimation residue): 726br w, 746br w, 766br W. 806br m, 832br m, 899s m, 919br w, 939br w, 959br w, 972br w, 101 8s m, 1032s

rn, 1058s m, 1098br m, 1138s m, 1204br s, 123 1s m, 1264s m, 1297s s,

1377br s, 1463br s, 1490sh m, 1516s w, 1555s w, 1629br s, l663sh m, 842br s, 1915br s, 1975s m, 2001s m, 220br w, 2453br w, 2665br w,

2725br w, 2858br s, 3 1 17br m, 3303s m.

Appendix 1: X-ray Crystal Structure Data

X-Ray data for [2-8] SCN

Table 1. Crystal data and structure refinement for k98 1 15 Identification code k98 1 15 Empirical formula Cl2 H23 N3 S Formula weight 24 1.39 Temperature 150.0(1) K Wavelength 0.71073 A Crystal system Monoclinic Space group P2( l )ln Unit ce11 dimensions a = 6.9049(2) A

b = 14.7905(5) A c = l3.6393(5) A

Volume 1382.64(8) A3 z 4 Density (calculated) Absorption coefficient l=(Om Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 26.38" Absorption correction Refinernent method Data / restraints 1 parameters Goodness-of-fit on F~ Find R indices [I>2sigma(I)'J R indices (dl data) Extinction coefficient Largest diff. peak and hole

528 0.32 x 0.30 x 0.25 mm3 4.08 to 26.38O. 0<=h<=8, k=k<= 18, - 17<=1<= 16 10253 28 16 [R(int) = 0.0351 99.3 % Denzo-SMN (multi-scan, Scalepack) Full-mauix least-squares on F~ 2816101 156 1 .O60 R1 =0.0483, wR2 =0.1233 R1 =0.0599, wR2 =O.l315 0.007(3) 0.487 and -0.355 e.A-3

Table 2. Atomic coordinates ( x 104) and equivalent isotropic displacement parameten (A2x 103)for kg8 1 15. U(eq) is defined as one third of the tnce of the orthogonalized edij tensor.

continued

Table 3. Bond lengths [A J and mgles [O] for kg8 1 15.

N( 1 )-C(8) 1.49 l(2) N(2)-C(3) 1.463(3) N(2)-C(4) 1.492(2) c(2)-c(3) 1.5 17(3) C(4)-CG) 1.496(3) C(4)-c(7) 1.497(3) C(4)-C(6) 1.506(3) c(8)-c(9) 1.522(3) C(8)-C( 10) 1.525(3) C(8)-C(l1) 1.526(2) S( 1 )-C( 12) 1.640(2) C( 12)-N(3) 1.158(3) N( 1 )-C( 1 )-N(2) 1 13.80(16) C( 1 )-N( 1)-C(2) 108.83(15) C( 1 )-N( 1 )-C(8) 127.88(15) C(2)-N( 1 )-C(8) 122.37(14) C( 1 )-N(2)-C(3) tW.lO(l5) C(1 )-N(2)-C(4) 126.49( 15) C(3)-N(2)-C(4) 124.21(15) N( 1 )-C(2)-C(3) 102.47( 16) N(2)-C(3)-C(2) 1 03 .OS( 16) N(2)-C(4)-C(5) 107.82(17) N(2)-C(4)-C(7) 109.45(16) C(5)-C(4)-C(7) 1 1 1.6(3) N(2)-C(4)-C(6) 1 08.94( 1 5) C(5)-C(4)-C(6) 1 08.9(3) C(7)-C(4)-C(6) 1 10.0(2) N( 1 )-C(8)-C(9) 1 09.52( 14) N( 1 )-C(8)-C( 1 O) 1 08.34( 14) C(9)-C(8)-C( 10) 1 10.50( 16) N(1)-C(8)-C(l1) 107.82(15) C(9)-C(8)-C(l1) 1 10.66( 16) C(l0)-C(8)-C( 1 1) 109.93(15) N(3)-C(l2)-S(1) 179.2(2)

Symmetry transformations used to generate equivalcnt atoms:

continued

Table 4. Anisotropic displacement parameters (A2x lo3) for 188 1 15. The anisotropic displacement faetor exponent takes the form: -zp2[ h2 a * 2 ~ 1 l + ... + 2 h k a* b* ~ 1 2 1

Table 5. Hydrogen coordinates ( x lo4) and isotropie displacement parameten (A2x 10 3) for k98 1 15.

continued

Table 6. Torsion angles [O] for k98 1 15.

Symmetry transformations used to generate equivalent atoms:

X-Ray data for [l-LFJ SCN

Table 1. Crystai data and structure refinement for k98216: Identification code kg8216 Empirical formula Cl2 H21 N3 S Formula weight 239.38 Temperature 100.0(1) K Wavelength 0.7 1073 A Crystal system Monoclinic Space g~oup P2( 1 )/c Unit cell dimensions a = 8.6054(3) A

b = 12.9849(6) A c = 12.5793(5) A

volume 1365.07( 10) A3 z 4 Density (calculated) 1.165 ~ ~ / m ~ Absorption coefficient FOJO) Ciystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 26.36" Absorption correction Refhement method Data / restraints 1 parameters Goodness-of-fit on F~ Final R indices [1>2sigma(I)] R indices (al1 data) Largcst diff. peak and hole

Full-matrix least-squares on F~ 2768/0/ 151 1 .O96 Rl = 0.0387, wR2 = 0.0996 R 1 = 0.0579, wR2 = 0.1052 0.256 and -0.258 e.A-3

Table 2. Atomic coordinates ( x lo4) and equivalent isouopic displacement parameters (A2x U(eq) is defined as one third of the trace of the orthogonaiized uij tensor.

103) for

contimued

Table 3. Bond lengths [A] and angles [O] for k98216.

Symmetry transformations used to generate quivalent atoms:

continued

Tabk 4. Anisotropic displacernent parameters (A2x 103) for k98216. The anisotropic displacement factor exponent takes the fonn: -2p2[ h2 a*2u1 l + ... + 2 h k a* b* ~ 1 2 ]

Table 5. Hydrogcn coordinates ( x lo4) and isotropie displacement parameters (A2x 10 3, for kg82 f 6.

X-Ray data for [l-H] Cl

Table 1. Crystal data and structure refinement for k9855: Identification code kg855 Empirical formula Cl1 HH20CIN2 Formula weight 2 16.75 Temperature 150.0(1) K Wavelength 0.71073 A CrystaI system Monoclinic Space group P2(l)/n Unit ce11 dimensions a = 9.0360(18) A

b = 12.022(2) A c = ll.Ml(2) A

Volume 12~ .7 (4 ) A3 z 4 Density (calculated) 1.175 h4g/m3 Absorption coefficient 0.280 mm' F((K@) 472 Crystal size 0.08 x 0.08 x 0.05 mm3 Theta range for data collection 4.37 to 23.02O. Index ranges 0<=hc=9,0<=k<= 13, - 12<=1<= 12 Reflections collected 63 15 Independent reflections 1695 [R(int) = 0.1 141 Completeness to theta = 23-02" 99.2 % Absorption correction Denzo-SMN Refinement method Full-matrix least-squares on F~ Data / restraints / parameters 1695 1 O 1 138 Goodness-of-fit on F~ 1 .O53 Final R indices [1>2sigma(I)] RI = 0.0697, wR2 = 0.1766 R indices (al1 data) R1 = 0.1 108, wR2 = 0.1948 Extinction coefficient 0.0 14(5) Largest di ff. peak and hole 0.362 and -0.264 =.A-3

Table 2. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (A2x 103) for 18855. U(eq) is defined as one third of the trace of the orthogonalized uij tensor.

continued

Table 3. Bond lengths [A] and angles [O] for k9855.

CI(1 )-H(1 A) 2.70(5) CI(1)-C(1) 3.284(6) N(2)-C( 1 ) 1.332(7) N(2)-C(3) 1.372(7) NW-C(8) 1.5 17(6) N( 1 )-a 1) 1.3337) N( 1 )-Cm 1.378(7) N( 1 )-C(4) 1.5 14(6) c(3)-c(2) 1.360(7) C( 1 )-H( 1 A) 0.89(5) C(4)-C(7) 1.5 1 O(7) c(4)-c(5) 1.5 15(8) c(4)-c(6) 1.5 19(8) C(8)-C( 10) 1 S O I (8) C(8)-C( I 1) 1.5 1 9(7) C(g)-c(9) 1.524(8) H( 1A)-Cl( 1 )-C( 1) 12.9( 1 O) C( 1 )-N(2)-C(3) 1 08.6(4) C( 1)-N(2)-C(8) 124.6(4) C(3)-N(2)-C(8) 126.7(4) C( 1 )-N(1)-C(2) 108.3(4) C( 1 )-N( 1 )-C(4) 125.8(4) C(2)-N(1 )-C(4) 125.9(4) C(2)-C(3)-N(2) 107.2(5) H( 1 A)-C( 1)-N(2) W 3 ) H( 1 A)-C( 1 )-N( 1 ) 125(3) N(2)-C( 1 )-N(1) 108.8(5) H( 1 A)-C( 1 )-Cl( 1 ) 43(3) N(2)-C(1 )-Cl( 1 ) 1 13 3 3 ) N( 1)-C(1 )-Cl( 1) 113.0(3) C(1 )-H( 1A)-Cl(1) 1 24(4) C(7)-C(4)-N( 1 ) 108.8(4) C(7)-C(4)-C(5) 110.3(5) N( 1)-C(4)-C(5) 107.4(4) C(7)-C(4)-C(6) 1 1 1.7(5) N( 1 )-C(4)-C(6) 106.9(4) C(5)-C(4)-C(6) 1 1 1.6(4) C(3)-C(2)-N(1) 107.1 (5) C(1 O)-C(8)-N(2) 107.9(4) C( 10)-C(8)-C( 1 1) 1 1 1.9(5) N(2)-C(8)-C( 1 1) 107.1(4) C( 10)-C(8)-C(9) 1 10.7(5) N(2)-C(8)-C(9) 107.7(4) C(l1 )-C(8)-C(9) 1 1 1.4(5)


continued

Table 4. Anisotropiç displacement parameters (A2x 103) for k9855. The anisotropic displacement factor exponent takes the fom: -zp2[ h2 aa2u1 + ... + 2 h k a* b* ~ 1 2 ]

Table 5. Hydrogen coordinates ( x 104) and isotropie displacement parameters (A2x 10 3, for k9855.

X-Ray data for 1

Table 1. Crystal data and structure refinement for k9868: Identification code kg868 Empirical formula Cl1 H20N2 Formula weight 180.29 Temperature 173.0(1) K Wavelength 0.71073 A Crystai system Orthorhombic Space group Pbca Unit cell dimensions a = 1 1.3495(5) A oc= 90°.

b = 11.6211(6) A p= 90.. c = 17.31 13(5) A y = 90".

VoIume ~83.3(2) A3 Z 8 Density (calculated) 1.049 ~ ~ / m ~ Absorption coefficient R ~ ) Crystal size Theta range for data collection Index ranges Reflections collected Independent refiections Absorption correction Refinement method Data / restraints / parameters Goodness-of-fit on F2 Final R indices [I>2sigma(l)] R indices (dl data) Extinction coefficient Largest diff. peak and hole

Full-rnatrix least-squares on F* 2318 / O / 125 1.073 R1 = O.O4Sl, wR2 = 0.1224 R 1 = 0.0722, wR2 = 0.1427 0.007 l(29) O. 19 1 and -0.157 e.A-3

Table 2. Atomic coordinates ( x lo4) and equivalent isotropie displacement parameten (A2x 103) for k9868. U(eq) is defined as one third of the trace of the orthogonalized uij tensor.

Table 3. Bond lengths [Al and angles [O] for 18868.

N( 1) 1.366(2) N( 1 )-w) 1.3 80(2) N( 1 )-C(4) 1.489(2) C( l)-N(2) 1.366(2) N(2)-C(3) 1.380(2) N(2)-c(8) 1.493(2) c(2)-c(3) 1.34 l(2) c(4)-c(5) 1.508(3) c(4)-c(6) 1.5 17(2) c(4)-c(7) 1.523(2) C(8)-C( 1 1 ) 1.5 18(2) C(8)-C( 1 O) 1.52 l(2) c(8)-c(9) 1.522(2) C( 1 )-N(1 )-C(2) 1 12.57( 12) C( 1 )-N(1 )-C(4) 123.74( 12) C(2)-N(1)-C(4) 123.53(13) w k c ( 1 )-N( 1) 102.19(12) C( 1 )-N(2)-C(3) 1 12.20(12) C( 1 )-N(2)-C(8) 122.04( 13) C(3)-N(2)-C(8) 125.74(12) C(3)-C(2)-N( 1 ) 106.23(14) C(2)-C(3)-N(2) 106.81(14) N( 1)-C(4)-C(5) 109,04(13) N( 1)-C(4)-C(6) 108.60(12) C(5)-C(4)-C(6) 109.8(2) N( 1)-C(4)-C(7) 1 08.78( 1 3) C(5)-C(4)-C(7) 1 10.5(2) C(6)-C(4)-C(7) 1 10.04(14) N(2)-C(8)-C( 1 1 ) 1 08.47( 12) N(2)-C(8)-C( 10) 110.13(13) C(l1)-C(8)-C(l0) 109.50(14) N(2)-C(8)-C(9) 107.92( 1 3) C( 1 1 )-C(8)-C(9) 1 10.54( 1 5) C( 10)-C(8)-C(9) 1 10.25(14)

Symmetry transformations used to genente equivalent atoms:

continued

Table 4. Anisotropic displacement parameten (A2x lo3) for k9868. The anisotropic displacement factor exponent takes the form: -zp2[ h2 a12u1 l + ... + 2 h k a* b* ~ 1 2 ]

ul 1 $2 u33 u23 u13 u'2

Table 5. Hydrogen coordinates ( x 104) and isotropie displacement parameters (A2x 10 3, for k9868.

X-Ray data for 2-CHO

Table 1. Crystal data and structure refinement for k98215a. Identification code kg82 15a Empirical formula Cl 1 H24 N2 O Formula weight 200.32 Temperature 100.q1) K Wavelength 0.71073 A Crystd systern Monoclinic Space group P2(l)/c Unit ce11 dimensions a = 11.5511(13)A a= 90°.

b = 10.4564(15) A @ 1 12.562(8)O. c = 11.2846(13) A y = 90".

Volume 1258.7(3) A3 z 4 ûensity (calculated) 1.057 ~ g m i ~ Absorption coefficient F ( o w Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 26.45" Absorption correction Refinement method Data / restraints / parameters Goodness-of-fit on F~ Final R indices [1>2sigma(I) J R indices (ail data) Extinction coefficient Largest diff. peak and hole

0.068 mm' l 448

Full-matrix least-squares on F~ 2565 1 O / 138 0.995 RI = 0.0450, wR2 = O. 1077 R 1 = 0.0807, wR2 = 0.1 197 0.022(5) O. 165 and -0.153 e.A-3

Table 2. Atomic coordinates ( x lo4) and equivalent isotropic displacement parameten (A2x 103) for kg82 1%. U(eq) is defined as one third of the trace of the onhogonalized uij tensor.

continued

Table 3. Bond lengths [Al and angles [O] for k9821Sa.

Symrnetry txïmsformations used to genente equivalent atoms:

continued

Table 4. Anisotropic displacernent parameters (A2x 1 03) for 1882 1 Sa. The anisotropic displacement factor exponent takes the form: -2p2[ h2 a * 2 ~ 1 + ... + 2 h k a* b* u12 ]

u l l u22 u33 u23 u13 u12

Table 5. Hydrogen coordinates ( x lo4) and isotropic displacement parameters (A2x 10 3, for kg82 1%.

MW 7044(14) 3284(15) 6461(16) 33(5) H( 1 A) 592 1 3143 8405 37 W B ) 5 197 3345 6895 37 H(3A) 2798 3641 7353 53 H(3B) 1939 3489 5862 53 M3C) 3353 3983 6292 53 H(4A) 367 1 81 1 53 12 56 H(4B) 3964 2279 5134 56 H(4C) 2548 1772 4569 56 W5A) 2 180 1351 7527 51 #(SB) 2570 245 6772 51 W C ) 1475 1226 6004 5 1 CI(6A) 7016 1383 8066 39 ii(6B) 6 198 1420 6549 39 9(8A) 9540 2573 9109 63 3(8B) 1028 1 1689 8480 63 J(8C) 9066 1147 8666 63 3(9A) 9409 4216 7472 64 3(9B) 8703 3904 5977 64 3(9C) 10052 3295 6768 64 J(1OA) 8056 603 637 1 52 3( 1 OB) 9254 1110 6129 52 3( 1 OC) 7892 1664 5297 52 J(11A) 4089 626 8679 37

X-Ray chta for 3-C

Table 1. Crystal data and structure refinement for k98 1 16. Identification code kg8 116 EmpiricaI fonnula Cl 1 H2 H24 N2 Formula weight 186.34 Temperature 150.0( 1) K Wavelength 0.71073 A Crystal system Monoclinic Space group P2(1)/n Unit ce11 dimensions a = 9.479 l(3) A

b = 8.6096(4) A c = 16.0961(3) A

Volume 1279.68(8) A3 z 4 Density (calculated) 0.967 ~ g / m ~ Absorption coefficient F(OQ0) Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 26.38" Absorption correction Max. and min. transmission Refinement method Data / restraints / parameters Goodness-of-fit on F~ Final R indices [1>2sigma(I)] R indices (al1 data) Extinction coefficient Largest diff. peak and hole

0.057 mm-l 424 0.32 x 0.25 x 0.18 mm3 4.41 to 26.38O. O<=h<= 1 1, k = k < = 10. -20<=1<= f 9 9557 2604 [R(int) = 0.0361 99.4 96 Denzo-SUN 0.9898 and 0.9820 Full-rnatrix least-squares on F~ 2604 / O / 142 1 .O40 R1 = 0.0372, wR2 = 0.0902 R1 = 0.05 15, wR2 = 0.0970 0.008(6) 0.173 and -0.132 e.A-3

Table 2. Atomic coordinates ( n 104) and equivalent isotropie displacement parameten (A2x 103) for kg8 1 16. U(eq) is defined as one third of the hece of the orthogonalized uij tensor.

continued

Tabk 3. Bond lengths [Aj and angles [O] for k98116.


continued

Table 4. Anisotropic displacement parameters (A2x 103) for kg81 16. The anisotropic displacement factor exponent takes the fom: -2n2[ h2 ar2u l l + ... + 2 h k a* b* U 1

Table 5. Hydrogen coordinates ( x lo4) and isotropie displamnent parameters (A2x 10 3)for k98 1 16.

X-Ray àata for [5-CH31 SCN

Table 1. Crystal data and structure refinement for k98 198. Identification code kg8 198 Empirical formula C8H15N5S Formula weight 213.31 Temperature lOO.O(l) K Wavelength 0.71073 A Crystal system Monoclinic Space group P21 Unit ce11 dimensions a = 6.71 12(3) A a= 90".

b = 6.8423(4) A p= 97.800(4)". c = 10.8167(6) A y = 90".

Volume 492. i 1 (5) A3 z 2 Densi ty (calculated) 1.440 ~ g / m 3 Absorption coefficient 0.297 mm' l F(oOQ 228 Crystal size 0.35 x 0.35 x 0.10 mm3 Theta range for data collection 4.55 to 26.34". Index ranges k=hc=8,0<=kc=8, - 13<=1<= 13 Re flections collec ted 3073 Independent reflections 1 076 [R(in t) = 0.0631 Completeness to theta = 26.34" 98.8 % Absorption correction Denzo-SMN Max. and min. transmission 0.9709 and 0.903 1 Re finement method Full-matrix least-squares on F~ Data / restraints 1 parameters 1076 / O / 76 Goodness-of-fit on F~ 1.080 Final R indices [1>2sigma(I)] R 1 = 0.0340, wR2 = 0.0839 R indices (al1 data) R 1 = 0.0380, wR2 = 0.0864 Largest diff. peak and hole 0.3 14 and -0.258 =.A-3

Table 2. Atomic coordinates ( x lo4) and equivalent isotropie displacement parameters (A2x 103) for k98 198. U(eq) is defined as one third of the trace of the orthogonalired tJij tensor.

continued

Table 3. Bond lengths [Al and angles [O] for 188198.

. - - - - -

Symmetry transfomations used to generate equivalent atoms: #1 x,-y+lR,z

continued

Table 4. Anisotropiç displacement parameters (A2x 103) for k98198. The anisotropic displacement factor exponent takes the fom: -2n2[ h2 a * * ~ l + ... + 2 h k a* b* U ]

Table 5. Hydrogen coordinates ( n 104) and imtropic displacement parameten (A2x 10 3, for kg8 198.

X-Ray data for [3-rn SCN

Table 1. Crystal data and swcture refinement for kg8 l67a. Identification code k98 167a Empiricd formula Cl3 H25 N3 S Formula weight 255 .42 Temperature 100.0(1) K Wavelength 0.7 1073 A Crystal system Orthorhombic Space group Im2m Unit ce11 dimensions a = 6.9330( 1 2) A a==90°.

b = 10.1506(10) A p= 90'. c = 1 0.5640(17) A y = 90".

Volume 743.43( 19) A3 z 2 Density (calculated) 1.141 ~ ~ / 1 n 3 Absorption coefficient 0.203 mm' l F(o(Jw 280 Crystal size Theta range for data collection Index ranges Reflections collected Independent reflections Completeness to theta = 24.98" Absorption correction Max. and min. transmission Refinement method Data 1 restraints / parameters Goodness-of-fit on F~ Final R indices [I>2sigma(I)] R indices (al1 data) Absolute structure parameter Largest di ff. peak and hole

0.25 x 0.18 x 0.12 mm3 5.25 to 24.98'. -8<=h<=O, -1 l<=k<=ll, - 12<=1<=12 2376 7 16 [R(int) = 0.0821 98.3 % Denzo-SMN 0.9760 and 0.9509 Full-matrix least-squares on F~ 7l6/ 13/63 0.949 RI = 0.0705, wR2 = 0.1767 Rl = 0.0833, wR2 = 0.185 1 0.6(3) 0.659 and -0.259 e.A-3

Table 2. Atornic coordinates ( x 104) and equivalent isotropie displacement parameters (A2x103) for k98 l67a U(eq) is defined as one third of the rrace of the orthogonalizeâ uij tensor.

continued

Table 3. Bond lengths [Al and angles [O] for k98167a.

Symrnetry transformations used to generate equivalent atoms: #l -x+ 1 ,y,z #2 -x+l,y,-z #3 x,y,-z

Table 4. Anisotmpic displacernent parameters (A2x 1o3)for kg8 l67a. The anisotmpic displacement factor exponent cakes the fom: -2ir2[ h2a*2~1 l + ... + 2 h k a* b* ~ 1 2 ]

ul l $2 u33 u23 u13 u12

Tabk S. Hydrogen coordinates ( x 104) anisotropic displacement parameters (A2x 103) for k98167a.

Appendix 2: References

147

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1126.

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Chem. Rev. 1 9 7 8 , a 383-405. c) W. Sander, G. Bucher, S. Wierlacher, Chem. Rev.

1993, a 1583-162 1.

[5] a) H.-W. Wanzlick, E. Schikora, Angew. Chem. 1 9 6 0 , z 494. b) &W. Wanzlick, E.

Schikora, Chem. Ber. 1961, & 2389-2393. c) H.-W. Wanzlick, H.-J. Kleiner, Angew.

Chem. 1961, 493. d) H.-W. Wanzlick, Angew. Chem. 1 9 6 2 , a 129-134. e) H.-W.

Wanzlick, Angew. Chem. Int. Ed. Engl. 1962, L 75-80. f) H.-W. Wanzlick and H.

Ahrens, Chem. Ber. 1964, 2447-2445. g ) H.-W. Wanzlick, B. Lachmann, E.

Schikora, ibid. 1965 ,s 3 170-3 177. h) H.-W. Wanzlick, H. J. Schonherr, Angew. Chem.

1968, j& 153- 154; Angew. Chem. Int. Ed. Engl. 1968, 14 1 - 142.

[6] a) D. A. Dixon, A. J. Arduengo, I. Phys. Chem 1991, ei, 4180-41 82. b) A. J. Arduengo,

H.V. R. Dias, J. C. Calabrese, F. Davidson, Inorg. Chem. 1993, z, 1541- 1542. c) A. J.

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Appendix: 3 Abbreviations of Compounds

te: 'BA te; te:

1=s 2=S 3=s 1 4

(3-HI SCN (5-CH31 SCN

- .

'BA 'B: 'Bi te; [i-H] Cl (2-Hl CI Il-Hl SCN 12-H] SCN

1 =Fe(CO)2 2=Fe(CO)4 L'Si: LGe:

Documents

Synthesis, DelocPlization and Reactivity in Stable ... · Synthesis of 13-Hl SCN Synthesis of [1-H] Cl Proton Transfer Reactions (NMR Scale) [1-H] Cl with D20 [LH] Cl with 2 [2-H]