Tedros A. Balema Senior Project: Investigation of Cyclometalated Palladium(II) Complexes using NNC Pincer Imine Ligands

8/12/2019 Tedros A. Balema Senior Project: Investigation of Cyclometalated Palladium(II) Complexes using NNC Pincer Imine Ligands

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Acknowledgements

I would like to thank my advisor Dr. Craig Anderson for his assistance and guidance in this

project. I would like to thank Emily McLaughlin for being a constant source of answers and

her patience during the school year. I would also like to thank Team Chem a.k.a “Craig’s

Crew” for being there with me to the end. Good luck with all your future endeavours. I would

also like to thank the rest of my friends for their encouragement and support in my years at

Bard. I dedicate this project to my family, they have shaped the person I am today and

without them I would never have gotten this far.



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Abstract

Palladium is one of the many transition metals that are used to activate C-H and C-X bonds.

Imine NNC pincer ligands and imine NC ligands were reacted with palladium sources to

form palladium(II) complexes. These complexes were subject to various characterisation

methods including NMR, LC-MS, and X-Ray crystallography. The successful formation of

the palladium(II) products suggested two probable mechanisms: concerted oxidative addition

and sigma bond metathesis. It was also noticeable that the palladium(II) complexes all

demonstrated a certain degree of regioselectivity in their syntheses. C-X bonds that formed

6-membered rings were selectively activated over C-H bonds to form the more frequently

observed 5-membered rings; in addition sp2 C-H bonds were selectively activated over sp3 C-

H bonds. The synthesis of palladium(IV) were also attempted, unfortunately no such complex

was isolated and characterised; however in one case a ligand substitution reaction was

reported.



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Table of Contents

Abstract ............................................................................................................................... 3

I. Introduction ..................................................................................................................... 5

II. Results & Discussion .................................................................................................... 13

III. Conclusion & Future Work ........................................................................................ 26

IV. References ................................................................................................................... 29

V. Experimental ................................................................................................................ 31

Synthesis of Starting Materials ........................................................................................ 31

Synthesis of Ligands ........................................................................................................ 32

Synthesis of Palladium(II) Complexes .............................................................................. 35

Attempted Synthesis of Palladium(IV) Complexes ............................................................ 39

Recrystallisations ............................................................................................................ 40

Appendix A:1H NMR &

13C NMR Spectra of Starting Materials.................................. 43

Appendix B:1H NMR &

13C NMR Spectra of Ligands ................................................... 48

Appendix C: IR Spectra of Ligands ................................................................................. 63

Appendix D:1H NMR,

13C NMR &

31P NMR Spectra of Palladium(II) Complexes ..... 71

Appendix E: LC-MS Spectra of Palladium(II) Complexes ............................................. 90

Appendix F: Crystal Structures ....................................................................................... 94



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I. Introduction

In nature we see a wide array of hydrocarbons that contain C-H bonds such as alkanes; this

very common yet immensely significant bond is a consequence of its lack of selectivity once

activated. This presence of strong and localized C–C and C–H bonds due to the molecules

having no empty orbitals of low energy, or having filled orbitals of high energy, that could

readily participate in a chemical reaction.1 The main reaction that C-H bonds can participate

in, however, is combustion reactions that tend to produce either carbon dioxide or carbon

monoxide (depending on the level of oxygen present) and water among other side products

(i.e. radicals). These common compounds do not necessarily have much significance when it

comes to synthesising valuable specialty compounds using C-H bonds. As a result, chemists

have tried a myriad of methods to not just simply activate the bonds but to do selectively and

also to functionalise these hydrocarbons into more useful compounds and reagents.2

Transition metals have been used in promoting C-H activation for many years.

Although the use of transition metals in reactions, Fenton’s reagent (hydroxylation) and

mercury salts (direct mercuration), involving hydrocarbons and other C-H compounds goes

back to the late nineteenth century;3 The first known instance of selective C-H activation goes

back to 1962. Chatt used a Ru(0)-diphosphine complex in the preparation of hydrido-

complexes of ruthenium(II).4 From there the list of transition metals capable of C-H

activation have been increased including Ru, Ir, W, Pt, Rh and Pd.3

It was during the 1960s that reactions involving the cyclometalation (i.e., the cleavage

of a C-H bond in a metal-coordinated phosphine or amine ligand) in the formation of cyclic

rings with aromatic compounds were performed. It was shown that palladium (II) derivatives

induce the oxidative coupling of arenes and the arylation of alkenes (the Fujiwara reaction).5,6

Meanwhile Shilov witnessed the first case of C-H activation through an oxidative addition

pathway using Pt(IV) as the oxidant and Pt(II) as the catalyst during the 70s.3 Since then



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Periana has made Shilov reactions more efficient by using a series of methane conversions

through Hg(II), Pt(II) and Pd(II) salt catalysts.7

As mentioned before, palladium is one of the transition metals that are able to

participate in C-H bond activation reactions. Although palladium exists in multiple oxidation

states, the palladium(0) and the palladium(II) states dominate in terms of usefulness in

organic methods meanwhile palladium(IV) has been becoming increasingly useful.8 As the

even-numbered oxidation states of palladium increases we find increased stability which can

be rationalised by palladium’s unlikeness to undergo one-electron or radical processes hence

two-electron oxidation or reduction are highly favoured.9 Due to palladium’s ability to

undergo reversible 2 electron processes has made it a highly effective catalyst since with each

different oxidation state (i.e. 0, +2, and +4) we observe different sets of chemical properties

and application. As a result transformations such as alcohol oxidation and cycloisomerization

are performed by Pd(II) while cross-couplings and olefin hydrogenation are usually

performed by Pd(0). 9

In the case of palladium(IV) complexes, although various complexes had been

proposed and a few pentafluorophenylpalladium(IV) complexes have been isolated, it wasn’t

until 1986 that an organopalladium(IV) complex had been fully characterised by Byers et

al.10 In the synthesis of the organopalladium(IV) complexes, oxidative addition reactions with

organohalides with palladium(II) complexes were used. In their study they found that,

mechanistically, the oxidative addition of MeI and PhCH2Br to PdMe2(bpy) and

PdMe2(phen) are consistent with the occurrence of the classical S N2 mechanism, involving

Pd(II) as the nucleophile.11

The kinetic studies verified this assertion by using 'H NMR

spectra at low temperatures allow detection of cationic intermediates to observe

PdMe2(NMe2CH2CH2 NMe2) reacts with methyl triflate in CD3CN to form

[PdMe3(NMe2CH2CH2 NMe2(NCCD3)]+

OSO2CF3-

.10,12

However it is important to note that in



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comparison to platinum chemistry, the cations are fluxional and this is a demonstration of

palladium(IV)’s greater lability, which would also make such complexes favourable towards

reductive elimination.10 It is also important to note that this S N2 approach in palladium(IV)

synthesis is not the established standard and such syntheses are open to other mechanistic

approaches.

Another mechanistic approach in synthesising palladium(IV) complexes is σ-bond

metathesis; which also has been applied to palladium(II) chemistry. This mechanism, σ-bond

metathesis, is considered as the predominant pathway when C–H bond activation is

accomplished with electron-poor metal centres such as high-valent early transition metals.13

This mechanism (in a modified form) has also been proposed for late transition metals. In

Perutz’s model it is proposed that due to the significant electron density at late transition

metal centres, it is the metal that assists in stabilizing the organometallic complex alongside

the ligands.14 Thus in palladium’s case this becomes highly plausible, because first of all, as

palladium increases in oxidation state its electron density would increases due to the presence

of the donor electron ligand. This then creates a stabilising effect in which σ-bonds are

activated and formed between the ligands and the metal centre.

Imine ligands are known to be effective electron donors due to nitrogen having a

“hard” nature. This “hard” nature allows for the nitrogen to coordinate with the metal (in this

case palladium) via a σ bond. Since palladium is more electrophilic than platinum and

demonstrates reactive properties while in its even numbered oxidation states, the coordination

of nitrogen or donation of an electron pair to palladium should be quite favourable. The imine

functionality also uses the nitrogen’s π orbitals, making it a poor π-acceptor; hence very little

back-bonding interaction is able to occur further justifying the effectiveness of an imine

ligand coordinating to a palladium centre. When palladium(II) complexes are formed, the

palladium centre is electron rich. This allows the palladium to be reactive and also act as a



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nucleophile in S N2 reactions to could potentially cause palladium(IV) complexes to be

formed; should the palladium(II) be reacted in an oxidative addition process with reagents

such as MeI or PhCH2Br.10 On a side note, the presence of aromatic rings increases the

presence of π bonds in the system adding an increasingly electron rich environment.

Chelating ligands have been known for quite some time to greatly influence the

stability and reactivity in transition metal complexes. Among the various types of chelations

that chemists have been experimenting with in the past decades, terdentate pincer ligands

stand out for their ability to ensure high stability and enhanced reactivities to many transition

metal complexes.15 Ever since their initial synthesis by Shaw and van Koten in the 1970s,

pincer ligand complexes have been shown to display rare or unusual structural/bonding

features.16,17

In the case of NNC ligands, we can easily expect highly stable complexes. This

assertion comes from the observation that NNC ligands display “hard” N-based donor

moieties, which would imply that such ligands could not only stabilise the lower oxidation

states of palladium (0, +2) but also stabilise the higher ones (+4). With the imine

functionality combined with such chelation and aromaticity of the attached phenyl/naphtyl

groups, NNC ligands could potentially produce highly stable and functional palladium(II) and

palladium(IV) complexes.

In the formation of the palladium(II) complexes, which are the precursors to the

synthesis of palladium(IV) complexes, the first set of reactions will consist of

cyclometalations. Looking at the electronic design behind aromatic ligands with imine

functionality, it should be reasonable for such reactions to occur. Cyclometalation is a

transition metal-mediated activation of a C-X bond (X being Br, Cl, I, or H) to form a metal-

ligand cycle with a new metal-carbon σ bond.18 There are various factors that dictate how a

cyclometalation reaction may or may not proceed. These factors include: the substituents,

ring size, electronics of the C-R bond and the electronics of the newly formed ring.



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Substituents used in cyclometalation are important because if the substituent has

molecules located at the ortho- position, it could either promote or block cyclometalation

from occurring at that position resulting in orthometalation.13 Ring size is also another factor

to consider since there is somewhat of an observance that there is a greater preference to form

5-membered rings, versus other numbered rings, as it provides greater electronic stability in

the complex.13

Electronics of the C-R bond, aromatic C sp2-H bonds tends to be favoured over

aryl Csp3-H bond activation due to the greater kinetic lability of aromatic protons versus

protons in other hydrocarbons (i.e. olefins, alkanes).13 Finally the electronics of the ring itself

or endo/exo preference, generally there tends to be a greater preference of the endo-ring over

the exo-ring.13 The endo-ring structure in this project consists of the metal centre, an imine

and an aromatic ring; which would be more energetically favoured since the ring is stabilised

by the resonance of the aromaticity of the naphthyl group.

In the cyclometalation mechanism, a weak coordinating ligand in the metal precursor

is usually replaced by the donor site, labelled E, of the potentially cyclometalated ligand. The

effectiveness of E is determined by its basicity and steric effects; however most E donor

groups tend to follow the hard-soft acid-base principles described by Pearson.19

With this

principle in mind, soft transition metals (i.e. the platinum group metals) should favour

bonding to phosphines and sulfides as “soft” Lewis bases. However there are exceptions

where “hard” bases can bond effectively with “soft” platinum group metals, such as amine

donors bonding with palladium(II).20 Even though such hard-soft mismatches can produce

successful cyclometalations it has also been observed that there tends to be difficulties in

regioselectivity.13

Hence with these ideas in mind, the first thing that happens is that the initial ligand

coordinates to the metal source making complex A (figure 1, shown below). In many cases

donor group E can substitute weakly and moderately bonded ligands, increasing stability



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affording complex B. Next an intermediate before C-H activation, complex C, is formed

through by decoordinating of a ligand from complex A or a donor site from complex B. At

this stage the most important factor is note is the M-E bond strength. The strength of the M-E

bond depends on both electronic and steric factors or on the nature of the donor group E

either way one of those factors should dictate the stability of the M-E bond. Should the bond

be too strong or stable, ligand dissociation from complex B becomes much more difficult

making the production of complex C unlikely. Meanwhile should the M-E bond be too weak,

the reaction equilibrium could shift back to the starting materials hence no complex C is

formed.

Figure 1, transmetalation scheme using E-donor groups13 With this background knowledge and proposed effects of imine and NNC ligands the

characterisation and determination of successful syntheses of the palladium(II) and

palladium(IV) complexes may go forward. In our studies the main variables identified

included reaction conditions, structural identity of the complexes made and their ability to be

converted from a palladium(II) into a palladium(IV) complex.

Reaction conditions are significant considering that changing factors such as the

solvent, reaction time, or reaction temperature can determine whether or not one can isolated



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the desired product. For example, heating a reaction for too long could lead to undesirable

consequences and could lead to the production of extra and/or unwanted products or the

complete decomposition of produced complex. Solvents can be of some significance since

solvents do have interactions with complexes and different solvents could have different

effects usually depending on its particle size and polarity.

The structural identity of the complex is important since it enables us to determine

whether or not the cyclometalations have been performed successfully. This means

characterising the ligands to be used and looking at the structure of the given ligand. Whether

the ligands will undergo C-X or C-H activation and if it does undergo C-H activation which

C-H bond is preferred.

There are several methods of characterisation that shall be used to determine the

identities of products;1H NMR,

13C NMR, LC-MS, X-ray diffraction (whenever suitable

crystals are successfully obtained) and elemental analyses.

NMR spectroscopy can easily help us determine whether or not a ligand and metal

(palladium) has successfully cyclometalated by observing shifts in the basic ligand

“backbone” which are highlighted by phase shifts in the imine position. LC-MS can verify

the presence of the cyclometalated ring since the main ion would possess both the m/z values

of the palladium centre and the chelated ligand backbone as one value while other smaller

ligands tend to detach themselves from the metal centre. However X-ray crystal diffraction,

would prove to be a much more effective way in determining structural information since it

can display not just the 3D structure of the product but also bond lengths and angles. With

proper structures present it could give better insight in the mechanistic manner of such

syntheses. Ligands used are shown below in figure 2.



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Figure 2, Ligands to be used

In the proposed sample reaction schemes, shown below in scheme 1, the chelation of

the ligand in question is very important. With NNC chelated ligands, a palladium(II) source

shall be used (i.e. palladium(II) acetate) in the cyclometalation reaction; which should be

appropriate due to the given electronics and stability behind such a chelation. Meanwhile the

NC chelated ligands will have to be reacted with a palladium(0) source

Tetrakis(triphenylphosphine)palladium(0)) due in part to the lack of donor electrons. Since

the mechanism in the production of palladium(IV) products is not well known, methyl iodide

will be used a basis to test whether or not an oxidative addition like mechanism occurs.

Scheme 1, proposed reactions with NNC and NC chelated ligands



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II. Results & Discussion

One of premises of the mechanism behind the product formation of palladium(II) complexes

was through transmetalation where a weak coordinating ligand in the metal precursor is

replaced by the donor site, labelled E, of the potentially cyclometalated ligand. Another

premise was a sigma bond metathesis mechanism. It is important to note that although we

have final products, final products do not necessarily prove mechanistic approaches. The only

sure way of verifying any mechanistic approach would be through the application of kinetic

studies or isolation. Do to the practical limitations, we shall assume both mechanistic

approaches in the formation of palladium(II) are applicable and in the presence of the data try

to ascertain as to which mechanism would be more likely according to the appropriate

products and reagents. Figure 3, below, shows the palladium(II) cyclometalated products:

Figure 3, the cyclometalated palladium(II) products



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Compounds TB-01, [Pd(I)(C15H17 N2)], and TB-02, [Pd(Br)(C15H17 N2)], are made

from halogenated ligands with NNC chelation and palladium(II) acetate as the source of the

transition metal centre. Since these compounds possess halide groups on the naphtyl ring, the

most clear mechanistic path would be the activation of the C-X, X being the halide, bond.

When looking at the reaction from a sigma bond metathesis perspective we see that in the

very first step we have a direct addition of electrons from N^N chelation, which does fall

within the characteristics typical of “hard” N-based donor. This is then followed by the

activation of the C-X bond, this activation is further aided by the fact the acetates are good

leaving groups and negative ligands thus the bonding is not as strong.21

As a result, the metal centre is able to accept another source of electrons to replace

and remove the presence of the weak ligands for greater stability. The metathesis mechanism

is also encouraged by the presence of the naphtyl ring on the ligand; this provides greater

stability and also makes the C-X bond stand out further from the highly stable naphtyl ring.

Once the C-X bond is activated, there still is the issue of the weak acetate ligand still bonded

to the metal centre while there is a presence of halide ions in the vicinity the complex would

benefit electronically by replacing the acetate with a halide, hence a direct substitution

occurs. As it is with all concerted oxidative addition processes, the nucleophile forms a

transition state with the substrate. Since intermediate states are stable enough to be isolated

and the palladium centre in this case is far too electron-rich the weakest bonded-ligands are

released until a stable complex is formed; resulting in the removal of the acetate ligands. The

possibility of sigma bond metathesis mechanism also becomes less likely as we consider that

C-X bond are much more active versus C-H bonds and sigma bond metathesis requires C-H

activation not C-X.22

The concerted oxidative mechanism is shown below in scheme 2.



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Scheme 2, concerted oxidative addition cyclometalation in the formation of the Pd(II) complex withhalogenated ligands resulting in products TB-01 and TB-02. “X” denotes a halide

Looking at the LC-M/S data for TB-01 and TB-02, both of which have a mass-to-

charge ratio value of 331m/z, this matches the value of the parent ion minus the halide ligand

(bromide or iodide). This mass-to-charge ratio verifies the successful formation of a 6-

membered metallocyclic ring, which is the desired outcome of a cyclometalation reaction. In

the LC-MS spectra it is also noticeable that the parent ion did not break apart from the metal

centre unlike the smaller halide ligands.

With the aid of X-ray crystallography, this structure was verified in the case of TB-01

(shown in figure4). It is important to notice that the 6-membered metallocyclic ring is on the

same plane as the naphtyl ring, and also the methyl groups off the terminal nitrogen of the

NNC chelation are at an axial position to the plan of the rings. This may suggest some

physical/steric contribution which may contribute to the outcome of its synthesis.



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Figure 4, ORTEP of TB-01 When given the non-halogenated NNC complex, TB-06 [Pd(OAc)(C16H19 N2)], it

would appear that a sigma bond metathesis mechanism is the most probable. This comes

from the observation that C-H and not C-X activation does occur, which is a required for

sigma bond metathesis. Thus in scheme 3, this would be the most likely mechanism.

Scheme 3, sigma bond metathesis mechanism in the formation of the Pd(II) complex TB-06

The LC-MS verifies the successful formation of a palladium 6-membered

metallocyclic ring with a mass-to-charge ratio value of 345 m/z minus the acetate ligand. The

structure was even further analysed using X-ray crystallography yielding an ORTEP image



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(figure 5), confirming the structure of TB-06 and a verification of a successful C-H

activation reaction mechanism.

Figure 5, ORTEP image of TB-06 Another aromatic ligand to consider as well are thiophenes, however the focus was

narrowed down to observe C-H activation (hence no halo-thiophenes). In the formation of

TB-07 [Pd(OAc)(C9H14 N2S)], sigma bond metathesis would be most likely mechanism.

Concerted oxidative addition mechanism is highly unlikely since there no presence of C-X

bonds. At the same time due to the size of the thiophene ring and its bonding in relation to the

palladium centre, there would be too much steric hindrance to favour any concerted oxidative

addition transition state formation. The mechanism for the formation of TB-07 is shown

below in scheme 4.



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Scheme 4, sigma bond metathesis mechanism in the formation of the Pd(II) complex TB-07 The sigma bond metathesis and concerted oxidative addition mechanism question

doesn’t only apply for NNC chelated ligands but also other chelation, the CN ligands. When

we look at the halogenated complexes TB-03 [Pd(I)(PPh3)(C20H19 N)] and TB-04

[Pd(Br)(PPh3)(C20H19 N)], the possibility of a oxidative addition is favourable. The

introduction of the large donor ligand in the presence of neutral triphenylphosphine ligands

would cause the overall complex to possess a greater positive charge thus attracting the

electron density of the adjacent C-X bond (X being a halide). At the same time,

triphenylphosphine is a very stable leaving group making it easier to remove and later on

dissociate from the X- ion resulting in a direct substitution.

At the same time, the positions of the two triphenylphosphine ligands on the metal

centre do not really have any preference or hindrance with respect to each other there will be

a lack of selectivity resulting in the formation of diastereomers. The possibility of a sigma

bond metathesis is very low since a halide and a phosphine would have to eliminate together

and sigma bond metathesis does not change the oxidation number of the palladium centre.

The transition states assumes that there should be some kind of steric crowding which

would force the triphenylphosphine ligands to be pushed out until structural stability is



19

achieved. Just like in the sigma bond metathesis there does not appear to be a significant

preferential position either triphenylphosphine ligands hence resulting in cis/trans

diastereomers, shown below in scheme 5.

Scheme 5, concerted oxidative addition cyclometalation in the formation of the Pd(II) complex withhalogenated ligands resulting in products TB-03 and TB-04. “X” denotes a halide

This observation was confirmed by the NMR spectra, where in the1H NMR, There

were clear pairs of peaks of similar nature at each significant phase shift of complex TB-03:

the imine (peaks c, 8.84 and 9.73 ppm), the tertiary carbon (peaks b, 3.15 and 4.20 ppm) and

the methyl group (peaks a, 1.40 and 1.74 ppm). This observation is also further confirmed by

the 31P NMR where there were two distinct phosphorus peaks at 29.43 ppm and 75.01 ppm.

The possibility of the peaks being misinterpreted or as either free-floating triphenylphosphate

(-6.00 ppm) or its oxide (23.00 ppm) was eliminated since the given peaks do not coincide

within acceptable range of the literature values;23 Both spectra are shown in the figure 6

below.



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Figure 6,1H NMR of TB-03 (top) and

31P NMR of TB-03 (bottom). The two sets of peaks represent the two

diastereomers Similar observations were also made in the spectra of TB-04. In which the 1H NMR

showed the presence of diastereomers. However unlike the TB-03 are not close to equal, one

diasteromer clear is in greater abundance compared to the other since we don’t see the other



21

diasteromer in both the31

P NMR (the spectrum show only one peak at 74.97 ppm) and the

13C NMR. The data would suggest that there may be a little more favouritism in the bromide

reaction where although both are formed, one is favoured over the other perhaps due to

position/steric reasons. The 1H NMR of TB-04 is shown below in figure 7.

Figure 7,1H NMR of TB-04 the two sets of peaks represent the two diastereomers

In the case of TB-05 [Pd(PPh3)2(C20H19 N)]+, the results become more ambiguous.

Although the 1H NMR and the 13C NMR verify the imine ligand back bone, it would appear

that the complex possesses two symmetrical phosphine ligands; verified by a large intense

peak at 29.03 ppm. When the structure for this complex was proposed, it would appear that it

has a palladium(I) centre. Although an oxidation state of 1 is not common for a palladium

complex, it might be possible that it could exist but not as a neutral complex: it would have to

exist as an ion, however the counter ion is not known.22

Another question would be what mechanism could have formed this compound; if it

exists as an ion it could mean that it most likely an isolated intermediate (shown in figure 8



22

below). This is probable because given the reaction conditions in its synthesis: the solvent

was toluene (non-polar); the reagents were ligand LR (which is a non-halogenated NC

chelated ligand) and tetrakis(triphenylphosphine)palladium(0). From this assemblage of

conditions it is unlikely to form a neutral palladium complex since there is no negative ligand

present.

Figure 8, TB-05 most likely structure as an intermediate ion

In all these reactions so far, it is noticeable that we a sense of regioselectivity judging

from the products given. Looking at the given ligands it is noticeable that we have two

possibilities for C-H activation in the forming of TB-05, TB-06, and TB-07. The possibilities

include sp2 position that would result in a 5-membered cyclometalated ring or a sp3 position

that would result in a 6-membered ring. Regardless of the ligand, all showed the latter option

especially when the possibility of activating the adjacent hydrogen is eliminated (in the case

of non-halogenated ligands) with the presence of a methyl group. At the same time,

halogenated ligands also show that sp3 C-X bonds that form 6-membered rings were

selectively active versus sp3 C-H bonds. This would suggest that the preference of activation

in these reactions depend heavily on the nature of the naphtyl ring and not as much on the

imine chelation part (labelled R). Figure 9 better illustrates this observation.



23

Figure 9, Regioselectivity of the cyclometalation reactions for the halogenated rings (left) and non-halogenatedrings (right), note that sites of activation forms the 6-membered metallocyclic rings

It was observed that in both sets of chelated compounds we can see that there is a

hierarchy in the reactions depending on the structure. It was observed that ligands with an

iodide tended to produce larger yields and purer complexes when compared to their bromide

counterparts. Since the possibility of a concerted oxidative addition type reaction mechanism

is there, it would make sense that the iodide is more effective since iodide is a much better

nucleophile and leaving group compared to bromide. The brominated products tended to

show very low yields and difficulty in purification despite the use of multiple techniques such

as washing with cold (0˚C) diethyl ether, and recrystallisation. The most effective complexes

in terms of yield and purity tended to be the complexes that were able to go through C-H

activation. Since these syntheses involved C-H activation, it would appear that the sigma

bond metathesis mechanism route would be the most likely (since there is no presence of a

nucleophile).

Using the complexes that had the largest yields and purity, converting them from a

palladium(II) complex to palladium(IV) was attempted. Using the approach of an oxidative

reaction, complexes TB-01, TB-03, TB-05 and TB-06 were reacted with methyl iodide to

observe at least a direct addition process, shown in scheme 6:



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Scheme 6, Attempted palladium(IV) syntheses, each complex was attempted with both a stirr and a refluxmethod

What was observed was that in the synthesis of TB-08 was that the complex TB-01

completed decomposed in both long term stirring and considerable reflux time suggesting

that either a conversion to a palladium(IV) complex is possible as a transition state before

decomposition; or that the reagent (methyl iodide) may not be the most appropriate in this

case since TB-01 has an iodide present as a ligand maintain the charge balance of the

complex. As a result the presence of two iodides in the complex would not necessarily be

favourable due the palladium centre being overly electron rich and also the issue of steric

crowding causing the complex to be more unstable.

In the synthesis of TB-10 and TB-11, it was quite clear that these two complexes

couldn’t possibly be isolated. Besides the observation that phosphines are neutral ligands and

causes a sizable steric hindrance, similar to TB-08, the complex wouldn’t favourably

accomodate the physical insertion of both or either an extra iodide or a methyl group.



25

In TB-09 case, it would appear that a completely different product was observed. It

would appear that the there was a subsitution reaction occur where the acetate ligand was

replaced with an iodide ligand, as shown in scheme 7 below:

Scheme 7, the substitution reaction of TB-06 in TB-09.5

This substitution may go through a S N2 mechanism. This mechanism becomes more likely

when we consider that acetate is a good leaving group, iodide is a good nucleophile and the

side product methyl acetate is produced. In the proton NMR this structure is confirmed by the

presence of a methyl acetate peak at 10.94 ppm and slight changes in phase shifts in the

significant peaks in the complex thus affirming the NNC imine “back bone”. Thus when

looking at the formation of the palladium(IV) forms of palladium(II) complexes perhaps a

wider range of ligands/ligand-sources should be considered that would not only satisfy steric

conditions but also electronic balances perhaps hypervalent iodides could be applicable.



26

III. Conclusion & Future Work

After observing and analysing the data for the products of the syntheses of palladium(II)

complexes this can give an insight to the potential mechanisms that such reactions go

through. In looking at halogenated NNC chelated complexes, TB-01 and TB-02, the

mechanistic approach proposed is the concerted oxidative addition approach. This coming

from the presence of a nucleophile (the halide) and also the bond activated is not C-H but

rather C-X, which is a bond that is much easier to activate. At the same time the quantity of

the yield and the purity of the products seem to depend on the halogen in question which is

also directly related to the halide’s nature as a nucleophile, i.e. iodide is a better nucleophile

than bromide.

In the case of the C-H activated NNC chelated complexes, TB-06 and TB-07, the

sigma bond metathesis mechanism is the most likely. The absence of a nucleophile increases

this possibility. At the same confirmation of their structures through NMR and X-ray

crystallography further affirms this notion. The yields of these reactions may not be

necessarily as large as the yields on the iodide variation but the purity of the complexes were

higher. However in the case of TB-07, the presence of side products is significant which also

suggests that there may also be other reaction mechanism on a smaller scale perhaps due to

the thiophene based ligand.

Moving on to the halogenated imine complexes, TB-03 and TB-04, the most likely

mechanism for their syntheses would be a concerted oxidative addition considering that a

sigma bond metathesis does not change a palladium centre’s oxidation states while a

oxidative addition increases it from 0 to 2. The isolation of the diastereomers would be

considered difficult whether it is through crystallisation for X-ray diffraction analysis or even

analysis through LC-MS since distinguishing between the two diastereomers becomes more



27

troublesome since the would-be result would contain the same parent ions and also physically

it would be difficult to form a proper crystal for X-ray diffraction.

Meanwhile for TB-05, it is still not clear what the full structure is however I propose

that this complex (which goes through C-H activation in its synthesis) could be an

intermediate until the presence of a stronger ligand is present. The proposed structure with

two phosphine ligands and the imine ligand would make this complex have a palladium(I)

centre, which in itself highly unlikely. Thus making this complex an ideal intermediate since

phosphines could easily be replaced by other ligands such as acetates or even halides.

In all cases, regioselectivity was observed by the sp2 activation of C-X and C-H bonds

on the naphtyl rings. This was observed by formation the 6-membered cyclometalated ring.

The regioselectivity can be controlled by either having a halide present on the ligand or by

eliminating competitive C-H bonds by substituting their positions with methyl groups.

For the palladium(IV) syntheses, the mechanisms are not clear. One reason is that a

palladium(IV) product was unable to be isolated for characterisation hence in all but one case

the mechanistic approach eludes this project. The exception was in the synthesis of TB-09

from TB-06. Instead of a palladium(IV) product we have a different palladium(II) product

from what we started with, TB-09.5. This product suggests very strongly for a substitution

type reaction since the acetate ligand was replaced with the iodide from the methyl iodide

reagent.

With all these experimental observations in mind this project would be a positive

candidate for further expansion. For thiophene imine ligands further study should be done on

the halogenated forms of the thiophene ring and also the different position of the sulphur on

the thiophene ring which may pose some electronic significance in product formation. For the

naphtyl imine ligands different chelations could be explored such as benzyl amines, since the



28

chelation off the imine group of the ligands would pose both a steric and an electronic issue

in the synthesis of such complexes. At the same time adding and substituting different

functionalities could be another approach to increase the range of palladium(II) products.

With characterisation, applications for these complexes would have to be considered; perhaps

applying the complexes to catalysis experiments so see if these complexes have some use in

facilitating transmetalation reactions or in organic synthesis.

Palladium(IV) complexes remain to be a challenge and hence further studies would

have to performed to ascertain what conditions should any palladium(II) complex be set at.

Perhaps the reagents used to increase the oxidation state of the palladium should be

considerably stronger perhaps the application of hypervalent iodides could be used. The

substitution reaction observed in TB-9.5 is also an interesting spring board, to figure out what

ligands could be replaced in a already prepared palladium(II) complex could perhaps provide

a more favourable condition for the synthesis or conversion to palladium(IV).

Overall the experiments have provided positive results and further study should be

encouraged, especially long-term kinetic studies that could pin-point the mechanistic

approach in the palladium(II) syntheses.



29

IV. References

1. Bergman, R. G. Nature 2007, 446, 391-393.

2. Labinger, J. A.; Bercaw, J. E. Nature 2002, 417, 507-514.

3. Chatt, J.; Davidson, J. M. J. Chem. Soc. 1965, 843.

4. Shilov, A. E.; Shul'pin, G. B. Chem. Rev. 1997, 97, 2879-2932.

5. van Helden, R.; Verberg, G. Recl. Trav. Chim. Pays-Bas 1965, 84, 1263.

6. Fujiwara, Y.; Moritani, I.; Danno, S.; et al. J. Am. Chem. Soc. 1969, 91, 7166.

7. Crabtree R. H. Chem. 2004 , 689, 4083.

8. Crabtree, R. H. The Organometallic Chemistry of the Transition Metals; Wiley: Hoboken,

2005.

9. Negishi, E. Handbook of Organopalladium Chemistry for Organic Synthesis; Wiley-

Interscience: New York, 2002.

10. Byers, P. K.; Canty, A. J.; Skelton, B. W.;White, A. H. J. Chem. SOC.Chem. Commun.,

1986, 1722.

11. Byers, P. K.; Canty, A .J.; Crespo, M.; Puddephatt, R J.; Scott, J. D. Organometallics,

1988, 7, 1363.

12. de Graaf, W. ; Boersrna, J.; Srneets, W. J. J.; Spek, A. L.; van Koten, G. Organometallics ,

1989, 8, 2907.

13. Albrecht, M. Chem. Rev., 2010, 110, 576.

14. Perutz, R. N.; Sabo-Etienne, S. Angew. Chem. Int. Ed. 2007, 46 , 2578.

15. Zargarian, D; Castonguay, A; Spasyuk, D. M. Topics in Organometallic Chemistry, 2012,

40, 131-173.

16. Moulton, C. J.; Shaw, B. L. Dalton Trans. 1976. 1020-1024.

17. van Koten. G.; Jastrzebski J. T.; Noltes, B. H; ; Spek J. G.; Schoone, A. L. J Organomet

Chem, 1978, 148, 233-245.



30

18. Bruce, M. I. Angew. Chem. Int. Ed., 2003, 16, 2, 73-86.

19. Pearson, R. G. Chemical Hardness; Wiley-VCH: Weinheim, Germany, 1997.

20. Cope, A. C.; Friedrich, E. C. J. Am. Chem. Soc. 1968, 90, 909.

21. Cheung H.; Tanke, R. S.; Torrence, G.P. Ullmann's Encyclopaedia of Industrial

Chemistry; Wiley-VCH: Weinheim, 2005.

22. Granell, J; Martínez, M.; Dalton Trans., 2012, 41, 11243

23. NMR Notes. A Guide to NMR Reference Compounds: NMR Reference Compounds for

31P Spectra. http://www.nmrnotes.org/NMRPages/refcomps.html

(accessed April 7, 2014).

24. Kurono, N.; Honda, E; Komatsu, F, Orito, K; Tokuda, M. Tetrahedron, 2004, 60, 1761.



31

V. Experimental

The solvents and reactants used in the following reported synthesis were purchased from

Sigma Aldrich

and Biogene Organics unless otherwise noted. The compounds were

characterised using NMR spectroscopy and LC-MS. The LC-MS spectra were performed at

Bard College using Varian 212 LC chromatography pump and Varian 500-MS. NMR spectra

were performed at Bard College using Varian MR-400 MHz spectrometer (1H, 400 MHz;

13C, 100 MHz) and referenced to CDCl3 (1H, 13C, and 31P) and (CD3)2CO (13C). The σ values

are given in ppm and J values are given in Hz. Abbreviations used: s = singlet; d = doublet; t

= triplet; m = multiplet; q = quarter; NMR labelling as shown below:

Synthesis of Starting Materials24

8-bromo-1-naphthaldehyde was obtained by stirring 8-bromonaphthalen-1-yl methanol (500

mg, 3.20 mmol) in a solution of methylene chloride (15 mL), PCC (682 mg, 3.20 mmol), and

silica gel (1.400 g) for four hours at room temperature, producing an orange solid. The

residue was then extracted with diethyl ether, washed twice with water and brine, dried over

magnesium sulphate, resulting in a white solid.1H NMR (400 MHz, CDCl

3): δ = {7.39 [t,

3 J (H-H)= 7.8, 1H, H

c]; 7.57 [t,

3 J (H-H)=7.9, 1H, H

f ]; 7.88-7.93 [m, 3H, H

g,d,e]; 8.01 [dd,

3 J (H-H)=8.2, 4J(H-H)=1.3, 1H, H b], aromatics}; 11.44 [s, 3H, H

a].

13C NMR (100 MHz,

CDCl3): δ = 26.57 [C

a]; {125.56; 126.97; 128.31; 128.70; 130.03; 130.42; 133.17, 133.48;

134.18; 135.91 aromatics}; 192.50 [Ch].

8-iodo-1-naphthaldehyde was obtained by stirring 8-iodonaphthalen-1-yl methanol (500 mg,

1.80 mmol) in a solution of methylene chloride (15 mL), PCC (570 mg, 2.60 mmol), and

silica gel (1.170 g) for four hours at room temperature, producing a dark orange solid. The

solid was extracted with diethyl ether, washed twice with water and brine, dried over

magnesium sulphate, resulting in a pale yellow solid. 1H NMR (400 MHz, CDCl3): δ = {7.23



32

[t,3 J (H-H)= 7.8, 1H, H

c]; 7.54 [t,

3 J (H-H)=7.8, 1H, H

f ]; 7.88 [dd,

3J(H-H) =1.4, 1H, H

g];

7.93 [dd,3 J (H-H)=8.2,

4J(H-H)=1.0, 1H, H

d ]; 7.97 [dd,

3 J (H-H)=8.2,

4J(H-H)=1.4, 1H, H

e];

8.27 [dd, 3 J (H-H)=7.4, 4J(H-H)=1.2, 1H, H b], aromatics}; 11.70 [s, 3H, Ha]. 13C NMR (100

MHz, CDCl3): δ = 89.67 [Ca]; {125.88; 127.29; 129.33; 130.03; 133.17; 133.87, 135.20;

135.60; 136.22; 141.08 aromatics}; 191.48 [Ch].

Figure 10, labelled protons and carbons of 8-iodo-1-naphthaldehyde and 8-bromo-1-naphthaldehyde

Synthesis of Ligands

Ligand [C15H17 N2Br], LE, was obtained by stirring N, N –dimethylethylenediamine (21.0

mg, 0.238 mmol) and 8-bromo-1-naphthyladehyde (50.0 mg, 0.213 mmol) together in

methylene chloride (15 mL) at room temperature for one hour. The solvent was removed

resulting in a light brown oil. Yield: 37.0 mg (57.0%). [C15H17 N2Br], LE. 1H NMR (400

MHz, CDCl3): δ = 2.35 [s, 6H, Ha]; 2.74 [t, 2H, H b]; 3.81 [t, 2H, Hc]; {7.28-8.00, 6H,

aromatics}; 9.59 [s, 1H, Hd ].

13C NMR (100 MHz, CDCl3): δ = 45.73 [C

a]; 49.51 [C

c];

59.55[C b]; {126.17; 126.24; 128.95; 129.71; 130.98; 132.99, aromatics}; 163.88 [Cd ]. FTIR

(neat) 2895, 1676 (cm-1

).

Ligand [C19H16BrN], LF, was obtained by combining 8-bromo-1-naphthaldehyde (32.9 mg,

0.140 mmol), S-(-)-α-methylbenzylamine (21.6 mg, 0.178 mmol) and stirring the mixture in

methylene chloride (10 mL) at room temperature for 90 minutes. The solvent was removed

resulting in a pale brown oil. Yield: 42.5 mg (70.5 %). [C19H16BrN], LF. 1H NMR (400



33

MHz, CDCl3): δ = 1.69 [d, 3H, Ha]; 4.68 [q, 1H, H b]; {7.27-9.03, 11H, aromatics}; 9.64 [s,

1H, Hc]. 13C NMR (100 MHz, CDCl3): δ = 24.12 [Ca]; 70.20 [C b]; {126.50; 126.70; 127.32;

127.45; 128.91; 129.40; 130.48; 131.42; 133.40; 134.33; 134.17; 135.56; 136.29; 145.18,

aromatics}; 162.09 [Cc]. FTIR (neat) 2966, 1633 (cm

-1).

Ligand [C15H17 N2I], LG, was obtained by combining N, N –dimethylethylenediamine (25.0

mg, 0. 283 mmol) and 8-iodo-1-naphthyladehyde (78.0 mg, 0.277 mmol) and stirring the

mixture in methylene chloride (15 mL) at room temperature for one hour. The solvent was

removed resulting in a light brown oil. Yield: 78.0 mg (80.1%). [C15H17 N2I], LG. 1H NMR

(400 MHz, CDCl3): δ = 2.37 [s, 3H, Ha]; 2.80 [m, 2H, H b]; 3.84 [t, 2H, Hc]; {7.10-8.28, 6H,


13C NMR(100 MHz, CDCl

3): δ = 45.78 [C

a]; 59.30 [C

b];

59.59[Cc]; {126.02; 126.87; 129.68; 129.78; 131.39; 132.69; 135.45; 141.20, aromatics};

163.24 [Cd ]. FTIR (neat) 2816, 1634 (cm

-1).

Ligand [C19H16IN], LH, was obtained by combining 8-iodo-1-naphthaldehyde (100.0 mg,

0.355 mmol), S-(-)-α-methylbenzylamine (47.9 mg, 0.394 mmol) and stirring the mixture in

methylene chloride (15 mL) at room temperature for ninety minutes. The solvent was

removed resulting in a pale brown oil. Yield: 126.2 mg (92.4%). [C19H16IN], LH. 1H NMR

(400 MHz, CDCl3): δ = 1.77 [d, 3H, Ha]; 4.72 [q, 1H, H b]; {7.07-8.21, 11H, aromatics}; 9.85

[s, 1H, Hc].

1H NMR (400 MHz, CDCl3): δ = 1.70 [d, H

a]; 4.68 [q, H

b]; {7.27-9.03, 11H,

aromatics}; 9.64 [s, 1H, Hc].

13C NMR (100 MHz, (CD3)2CO): δ = 23.58 [C

a]; 69.64 [C

b];

{126.23; 126.64; 126.74; 128.24; 129.20; 129.84; 130.98; 133.13; 135.10; 136.05; 145.30,

aromatics}; 160.50 [C b]. FTIR (neat) 2966, 1630 (cm-1).

Ligand [C16H20 N2], LQ, was obtained by combining N,N-dimethylethylenediamine (332.6

mg, 3.77 mmol) and 642.2 mg 2-methyl-1-napthaldehyde (516.0, 3.78 mmol) in methylene

chloride (15 mL) stirred for 40 minutes then refluxed for 15 minutes. The solvent was



34

removed, and the mixture returned to solution in hexanes (6 mL) and stirred for 2 hours. The

solvent was removed resulting in pale orange oil. Yield: 693.4 mg (76.5 %). [C16H20 N2], LQ.

1H NMR (400 MHz, CDCl

3): δ = 2.37 [s, 6H, H

a]; 2.57 [s, 3H, H

e]; 2.76 [t, 2H, H

c]; 3.91 [t,

2H, H b]; {7.32-8.49, 6H, aromatics}, 8.94 [s, 1H, H

d ].

13C NMR (100 MHz, CDCl3): δ =

20.66 [Ce]; 46.24 [Ca]; 60.52[C b]; 61.33 [Cc]; {125.33; 125.52; 127.18; 128.54; 129.46;

129.81; 130.80; 132.72; 135.91; 162.00, aromatics}; 161.97 [Cd ]. FTIR (neat) 2815, 1678

(cm-1).

Ligand [C20H19 N], LR, was obtained by combining 2-methyl-1-naphthaldehyde (140.4 mg,

0.825 mmol) and S-(-)-α-methylbenzylamine (140.5 mg, 1.16 mmol) in methylene chloride

(15 mL) and refluxing for 2 hours. The solvent was removed resulting in colourless oil.

Yield: 226.3 mg (71.4 %). [C20H19 N], LR. 1H NMR (400 MHz, CDCl3): δ = 1.72 [d, 3H,

Ha]; 2.56 [s, 3H, Hd ]; 4.70 [q, 1H, H b]; {7.31-8.50, 11H, aromatics}; 9.06 [s, 1H, Hc]. 13C

NMR (100 MHz, CDCl3): δ = 20.80 [Cd ]; 25.97 [C

a]; 72.06 [C

b]; {125.22; 125.56; 127.17;

127.21; 127.39; 128.62; 129.00; 129.56; 129.89; 130.78; 132.05; 132.80; 136.06; 145.53,

aromatics}; 159.64 [Cc]. FTIR (neat) 2976, 1638 (cm-1).

Ligand [C9H14 N2S], LW, was obtained by stirring N, N –dimethylethylenediamine (39.0 mg,

0.450 mmol) and 3-thiophene carboxaldehyde (50.0 mg, 0.450 mmol) together in methylene

chloride (15 mL) at room temperature for three hours. The solvent was removed resulting in

brown oil. Yield: 75.2 mg (91.0 %). [C9H14 N2S], LW. 1H NMR (400 MHz, CDCl3): δ = 2.25

[s, 6H, Ha]; 2.56 [m, 2H, H b]; 3.63 [q, 2H, Hc]; 7.46 [d, J= 8 , 1H, Hf ]; 7.53[s , 1H, He];

7.54[d , J = 4; 1H, Hg]; 8.25 [s, 1H, Hd ]. 13C NMR(100 MHz, CDCl3): δ = 45.74 [Ca]; 59.87

[C b]; 59.89 [Cc]; 125.55 [Ce]; 126.91 [Cg]; 128.52 [Cf ]; 140.52 [Ch]; 155.92 [Cd ]. FTIR

(neat) 2848, 1639 (cm-1).



35

Figure 11, labelled protons and carbons of the ligands Synthesis of Palladium(II) Complexes

Compound [Pd(I)(C15H17 N2)], TB-01, was obtained from refluxing excess palladium (II)

acetate (31.0 mg, 0.138 mmol) and ligand LG (48.8 mg, 0.138 mmol) in toluene for 12 hours.

The solvent was removed producing a yellow oil. The product was washed and triturated in

ice-cold diethyl ether yielding a yellow solid. Yield: 21.0 mg (68%). [Pd(I)(C15H17 N2)], TB-

01. 1H NMR (400 MHz, CDCl3): δ = 2.83 [s, 6H, Ha]; 3.97 [m, 2H, H b]; 4.03 [q, 2H, Hc];

{7.16-8.17, 6H, aromatics}; 9.12 [s, 1H, Hd ]. 13C NMR(100 MHz, (CD3)2CO): δ = 49.68

[Ca]; 60.63 [C b]; 61.13 [Cc]; {123.10; 125.08; 125.45; 128.81; 133.52; 135.37; 136.94;

138.85; 141.51; 149.88, aromatics}; 160.60 [Cd ]. E.S.I., (Parent Ion)-I m/z = 331.

Compound [Pd(Br)(C15H17 N2)], TB-02, was obtained from refluxing palladium (II) acetate

(57.0 mg, 0.254 mmols) and LE (77.7mg, 255 mmols) in toluene for 12 hours. The solvent



36

was removed producing a red oil. The product was washed and triturated in ice-cold diethyl

ether yielding a red solid. Yield: 15 mg (14%). [Pd(Br)(C15H17 N2)], TB-02.1H NMR (400

MHz, CDCl3): δ = 2.82 [s, 6H, H

a]; 4.02 [m, 2H, H

b]; 4.09 [q, 2H, H

c]; {7.18-8.29, 6H,


13C NMR(100 MHz, (CD3)2CO): δ = 49.32 [C

a]; 60.97 [C

b];

60.98 [Cc]; {123.39; 125.26; 125.67; 128.39; 133.52; 135.37; 137.17; 138.85; 139.60;

144.82, aromatics}; 160.75 [Cd ]. E.S.I., (Parent Ion)-Br m/z = 331.

Compound [Pd(I)(PPh3)(C20H19 N)], TB-03, was obtained from refluxing

tetrakis(triphenylphosphine)palladium(0) (90.3 mg, 0.0779 mmols) and LH (30.0 mg, 0.0779

mmols) in toluene for 36 hours. The solvent was removed producing a dark brown film. The

product was washed and triturated in ice-cold diethyl ether yielding a light-brown solid.

Yield: 28.4 mg, 49%. [Pd(I)(PPh3)(C20H19 N)], TB-03. 1H NMR (400 MHz, CDCl3): δ = 1.40

[s, 3H, Ha]; 3.15 [s, 1H, H b]; 4.09 [q, 2H, Hc]; {7.18-8.29, 6H, aromatics}; 8.84 [s, 1H, Hd ].

13C NMR(100 MHz, (CD3)2CO): δ = 24.85 [C

a]; 69.99 [C

b]; {124.54; 125.25; 125.84;

126.58; 127.60; 127.95; 128.30; 128.33; 129.00; 129.23; 129.99; 131.00; 131.70; 132.72;

135.60; 141.42, aromatics}; 160.44 [Cc]. 31P NMR (162 MHz, CDCl3): δ = 29.43.

Compound [C15H17BrN2Pd], TB-04, was obtained from refluxing

tetrakis(triphenylphosphine)palladium(0) (96.0 mg, 0.0831 mmols) and LF (30.0 mg, 0.0888

mmols) in toluene for 24 hours. The solvent was removed producing a brown oil. The

product was washed and triturated in ice-cold diethyl ether yielding a dark brown solid.

Yield: 9.06 mg, 16%. [C15H17BrN2Pd], TB-04. 1H NMR (400 MHz, CDCl3): δ = 2.37 [s, 6H,

Ha]; 4.05 [m, 2H, H b]; 4.64 [q, 2H, Hc]; {7.16-7.92, 6H, aromatics}; 9.01 [s, 1H, Hd ]. 13C

NMR(100 MHz, (CD3)2CO): δ = 51.03 [Ca]; 55.49 [C b]; 60.04 [Cc]; {124.15; 125.88; 126.97;

127.99; 128.75; 131.05; 131.75; 133.17; 134.89; 141.89, aromatics}; 59.54 [Cd ].

31P NMR

(162 MHz, CDCl3): δ = 74.97.



37

Compound [Pd(PPh3)2(C20H19 N)], TB-05, was obtained from refluxing

tetrakis(triphenylphosphine)palladium(0) (127 mg, 0.110 mmols) and LR (30.1 mg, 0.110

mmols) in toluene for 12 hours producing. The solvent was removed a dark-brown solid. The

product was washed and triturated in ice-cold diethyl ether yielding a light-brown solid.

Yield: 63.1 mg, 58%. [Pd(PPh)2(C20H19 N)], TB-05. 1H NMR (400 MHz, CDCl3): δ = 1.69 [s,

3H, Hd ]; 2.51 [s, 1H, Ha]; 4.67 [q, 1H, H b]; {7.18-8.29, 6H, aromatics}; 9.04 [s, 1H, Hc]. 13C

NMR (100 MHz, CD3Cl3): δ = 19.68 [Cd ]; 25.48 [Ca]; 71.40 [Cc]; {124.54; 125.25; 125.88;

126.58; 127.60; 127.99; 128.31; 128.39; 129.01; 129.33; 130.03; 131.05; 131.75; 132.77;

135.60; 145.42, aromatics}; 159.03 [Cc]. 31P NMR (162 MHz, CDCl3): δ = 29.03.

Compound [Pd(OAc)(C16H19 N2)], TB-06, was obtained from refluxing palladium (II) acetate

(70.0 mg, 0.332 mmols) and LQ (74.3 mg, 0.331 mmols) in toluene for 12 hours. The solvent

was removed producing brown oil. The product was washed and triturated in ice-cold diethyl

ether yielding a yellow solid. Yield: 20.0 mg (15%). [Pd(OAc)(C16H19 N2)], TB-06. 1H NMR

(400 MHz, CDCl3): δ = 2.67 [s, 3H, He]; 2.75 [s, 6H, Ha]; 4.02 [m, 2H, H b]; 4.09 [q, 2H, Hc];

{7.18-7.90, 5H, aromatics}; 8.61 [s, 1H, Hd ].

13C NMR (100 MHz, CDCl

3): δ = 21.03 [C

e];

49.32 [Ca]; 60.52 [C

b]; 61.82 [C

c]; {124.98; 126.68; 127.57; 129.11; 129.40; 131.47; 136.43;

136.96; 138.26; 141.39, aromatics}; 156.91 [Cd ]. E.S.I., (Parent Ion) -OAc m/z = 345.

Compound [Pd(OAc)(C9H14 N2S)], TB-07, was obtained from refluxing palladium (II) acetate

(36.9 mg, 0.165 mmols) and LW (30.0 mg, 0.165 mmols) in toluene for 12 hours. The

solvent was removed producing dark-red oil. The product was washed and triturated in ice-

cold diethyl ether yielding a red solid. Yield: 18.1 mg, 39%. [Pd(OAc)(C9H14 N2S)], TB-07.

1H NMR (400 MHz, CDCl3): δ = 2.70 [s, 6H, Ha]; 3.70 [m, 2H, H b]; 3.79 [q, 2H, Hc]; 7.04

[dd, J = 8, 2H, He/f ]; 8.31 [s, 1H, Hd ]. 13C NMR (100 MHz, CDCl3): δ = 45.66 [Ca1]; 48.26

[Ca]; 59.98 [C b]; 64.05 [Cc]; 124.90 [Cg]; 125.88 [Ce]; 126.09 [Cf ]; 128.26 [Ch]; 156.20 [Cd ].



38

Figure 12, labelled protons and carbons of the palladium(II) complexes



39

Attempted Synthesis of Palladium(IV) Complexes

Compound [Pd(I)2(Me)(C9H14 N2S)], TB-08, the synthesis was attempted by refluxing TB-01

(10.1 mg, 0.0221 mmols) and excess methyl iodide (6.00 mg, 0.0441 mmols) in toluene for

12 hours. The solvent was removed producing a dark brown solid. The product was washed

and triturated in ice-cold diethyl ether yielding a yellow solid. 1H NMR Spectra showed

decomposition of the complex TB-01. The synthesis was also attempted by stirring TB-01

(10.0 mg, 0.0220 mmols) and methyl iodide (3.10 mg, 0.0220 mmols) in toluene at room

temperature for 48 hours. 1H NMR Spectra showed slight decomposition of the complex TB-

01 but overall no reaction.

Compound [Pd(OAc)(I)(Me)(C16H19 N2)], TB-09, the synthesis was attempted by refluxing

TB-06 (30.1 mg, 0.0742 mmols) and excess methyl iodide (10.0 mg, 0.0742 mmols) in

toluene for 12 hours. The solvent was removed producing a red-brown solid. The product was

washed and triturated in ice-cold diethyl ether yielding an orange solid. Yield: 15.2 mg

(43%), however it proved to be a different compound, TB-09.5 [Pd(I)(C16H19 N2)], 1H NMR

(400 MHz, CDCl3): δ = 2.81 [s, 6H, Ha]; 3.91 [m, 2H, H

b]; 4.04 [q, 2H, H

c]; {7.10-7.93, 6H,

aromatics}; 8.96 [s, 1H, Hd ]. The synthesis was also attempted by stirring TB-06 (15.0 mg,

0.0371 mmols) and methyl iodide (5.01 mg, 0.0371 mmols) in toluene at room temperature

for 72 hours. The 1H NMR spectra showed no overall reaction.

Compound [Pd(OAc)(I)(Me)(C16H19 N2)], TB-09, the synthesis was attempted by refluxing

TB-06 (30.1 mg, 0.0742 mmols) and excess methyl iodide (10.0 mg, 0.0742 mmols) in

toluene for 12 hours, producing a red-brown solid. The product was washed and triturated in

ice-cold diethyl ether yielding an orange solid. Yield: 15.2 mg (43%), however it proved to

be a different compound, TB-09.5 [Pd(I)(C16H19 N2)],1H NMR (400 MHz, CDCl

3): δ = 2.73

[s, 3H, H

e

]; 2.81 [s, 6H, H

a

], 3.91 [m, 2H, H

b

]; 4.04 [q, 2H, H

c

]; {7.10-7.93, 6H, aromatics};



40

8.96 [s, 1H, Hd ]. The synthesis was also attempted by stirring TB-06 (15.0 mg, 0.0371

mmols) and methyl iodide (5.01 mg, 0.0371 mmols) in toluene at room temperature for 72

hours. The 1H NMR spectra showed no reaction.

[Pd(I)(OAc)(Me)(PPh3)(C20H19 N)], TB-10, the synthesis was attempted by refluxing TB-03

(15.1 mg, 0.0200 mmols) and methyl iodide (2.80 mg, 0.0200 mmols) in toluene for 12

hours. The solvent was removed producing a yellow solid. The product was washed and

triturated in ice-cold diethyl ether yielding a dark yellow solid. The 1H NMR spectra showed

complete decomposition of TB-03. The synthesis was also attempted by stirring TB-03 (30.0

mg, 0.0401 mmols) and methyl iodide (5.60 mg, 0.0400 mmols) in toluene for 120 hours.

The1H NMR spectra showed significant decomposition of TB-03, but no desired product.

[Pd(I)(Me)(PPh3)2(C20H19 N)], TB-11, the synthesis was attempted by refluxing TB-05 (20.0

mg, 0.0225 mmols) and methyl iodide (3.00 mg, 0.0225 mmols) in toluene for 12 hours. The

solvent was removed producing a dark brown solid. The product was washed and triturated in

ice-cold diethyl ether yielding a brown solid. The 1H NMR spectra showed complete

decomposition of TB-05. The synthesis was also attempted by stirring TB-05 (30.0 mg,

0.0331 mmols) and excess methyl iodide (5.00 mg, 0.0400 mmols) in toluene for 72 hours.

The1H NMR spectra showed slight decomposition of TB-05, but no desired product.

Recrystallisations

TB-01: Trial 1: approximately 3 mg of TB-01 were dissolved in a minimal amount of

acetone and layered on top with cold diethyl ether. The system was left at room temperature

and after 5 days, crystals were formed. Crystals were sent for X-Ray diffraction studies,

however no crystal structure was refined.


chloroform and placed in a 1-dram vial. The vial was placed in a scintillation vial which was



41

filled with 5 mL of pentane. The system was left at room temperature and after 3 days,

crystals were formed. Crystals were sent for X-Ray diffraction studies and the structure was

determined and refined.


chloroform and layered on top with pentane. The system was left at room temperature and

after 4 days, crystals were formed. Suitable crystals for X-Ray diffraction studies were not

available.



filled with 5 mL of diethyl ether. The system was left at room temperature and after 4 days,

crystals were formed. Crystals have yet to be sent for X-Ray diffraction studies.

TB-03: approximately 3 mg of TB-03 were dissolved in a minimal amount of chloroform

and placed in a 1-dram vial. The vial was placed in a scintillation vial which was filled with 5

mL of diethyl ether. The system was left at room temperature and after 4 days, powder was

formed instead of crystals. The fine powder was dissolved for NMR spectral analysis.

TB-05: approximately 3 mg of TB-03 were dissolved in a minimal amount of chloroform

and placed in a 1-dram vial. The vial was placed in a scintillation vial which was filled with 5

mL of diethyl ether. The system was left at room temperature and after 3 days, powder was

formed instead of crystals. The fine powder was dissolved for NMR spectral analysis.

TB-06: approximately 3 mg of TB-06 were dissolved in a minimal amount of acetone and

layered on top with diethyl ether. The system was left at room temperature and after 3 days,

crystals were formed. Crystals were sent for X-Ray diffraction studies, crystal structure was

determined and refined.



42


chloroform and layered on top with diethyl ether. The system was left at room temperature

and after 2 days, crystals were formed. Suitable crystals for X-Ray diffraction studies were

not available.



filled with 5 mL of diethyl ether. The system was left at room temperature and after 3 days,

crystals were formed. Crystals have yet to be sent for X-Ray diffraction studies.



43

Appendix A:

1H NMR &

13C NMR Spectra

of

Starting Materials



44



45



46



47



48

Appendix B:

1H NMR &

13C NMR Spectra

of

Ligands



49



50



51



52



53



54



55



56



57



58



59



60



61



62



63

Appendix C:

IR Spectra

of

Ligands



64



65



66



67



68



69



70



71

Appendix D:

1H NMR,

13C NMR &

31P NMR Spectra

of

Palladium(II) Complexes



72



73



74



75



76



77



78



79



80



81



82





84





86



87



88



89



90

Appendix E:

LC-MS Spectra

of

Palladium(II) Complexes



91



92



93



94

Appendix F:

Crystal Structures



95



96

Documents

Tedros A. Balema Senior Project: Investigation of Cyclometalated Palladium(II) Complexes using NNC Pincer Imine Ligands