Note

New tetrahedrane complexes from molybdenum alkynyls andCo2(CO)8

Julio Perez a,*, Lucıa Riera a, Vıctor Riera a, Santiago Garcıa-Granda b,Esther Garcıa-Rodrıguez b, David George Churchill c, Melvyn Rowen Churchill c,

Thomas S. Janik d

a Departamento de Quımica Organica e Inorganica /I.U.Q.O.E.M., 33071 Oviedo, Spainb Departamento de Quımica Fısica y Analıtica, Facultad de Quımica, Universidad de Oviedo-C.S.I.C., 33071 Oviedo, Spain

c Department of Chemistry, State University of New York, Buffalo, NY 14260-3000, USAd State University of New York College at Fredonia, Fredonia, NY, 14063, USA

Received 21 March 2002; accepted 14 May 2002

This paper is dedicated to Professor Rafael Uson, a pioneer of organometallic chemistry in Spain

Abstract

The molybdenum alkynyl complexes [Mo(C�/CPh)(h3-allyl)(CO)2(bipy)] (1) and [Mo(C�/CH)(h3-allyl)(CO)2(N�/N)] (N�/N�/

2,2?-bipyridine, 2a; 1,10-phenanthroline, 2b) react with dicobalt octacarbonyl to give the new tetrahedrane trimetallic complexes

[Co2(CO)6(m-h2:h2-M�/C�/CPh)], M�/{Mo(h3-C3H5)(CO)2(bipy)} (3) and [Co2(CO)6(m-h2:h2-M�/C�/CH)], M�/{Mo(h3-

C3H5)(CO)2(N�/N)} (N�/N�/bipy, 4a; phen, 4b), respectively. These new compounds were characterized by analytical (C, H, N),

spectroscopic (IR, 1H NMR) and crystallographic (single crystal X-ray diffraction) means.

# 2003 Elsevier Science B.V. All rights reserved.

Keywords: Tetrahedrane complexes; Molybdenum alkynyls; Crystal structures

1. Introduction

The reactions of acetylenes with [Co2(CO)8] to afford

[(m-h2:h2-R1�/C�/C�/R2)Co2(CO)6] complexes are classi-

cal processes in organometallic chemistry. In some

instances, the stability of the products allowed the

derivatization of the R substituents, and a subsequent

demetallation step afforded the new acetylenes [1]. On

the other hand, [(m-h2:h2-R1�/C�/C�/R2)Co2(CO)6] com-

plexes react with CO, olefins and acetylenes to afford

C�/C coupled products with high regioselectivity [2].

Similar [(m-h2:h2-R�/C�/C�/MLn)Co2(CO)6] compounds

can be obtained by reaction of metal alkynyl complexes

[3], LnM�/C�/C�/R, with [Co2(CO)8], although this

chemistry has been much less studied. The first com-

pounds of this kind, namely, the complexes [(m-h2:h2-

CpFe(CO)(L)�/C�/C�/R)(Co2(CO)6)] (R�/Me, Ph; L�/

CO, PMe2Ph) were reported by Yamazaki in 1972 [4],

and the structure of the derivative with R�/Ph, L�/CO

was determined by X-ray diffraction by Bruce in 1986

[5]. Riera found that complexation to the {Co2(CO)6}

unit stabilized the otherwise difficult to obtain trans

geometry of the alkynyl [Mn(C�/CPh)(CO)4(PCy3)],

which could be liberated by treatment with [I(py)2]BF4

[6].

We have recently reported the preparation of newalkynyl complexes [Mo(C�/CR)(h3-allyl)(CO)2(N�/N)]

(R�/H, Ph; N�/N�/2,2?-bipyridine, 1,10-phenanthro-

line) [7]. Their reactions with [Co2(CO)8], as well as the

crystallographical characterization of two products, are

the subject of this paper.

2. Experimental

2.1. General procedures

All manipulations were carried out under dinitrogen

using standard Schlenk techniques. Solvents were dis-* Corresponding author. Tel.: �/34-98-5102-985; fax: �/34-98-5103-

446

Inorganica Chimica Acta 347 (2003) 189�/193

www.elsevier.com/locate/ica

0020-1693/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.

PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 4 4 2 - 1

tilled from freshly wired Na (hexanes), Na/benzophe-

none (THF) and CaH2 (CH2Cl2) prior to use. CD2Cl2was degassed by three freeze-pump-thaw cycles, dried

over 4 A molecular sieves and stored in the dark in aYoung tube. Elemental analyses were obtained using a

Perkin�/Elmer 240-B microanalyzer. The IR and NMR

spectra were recorded on Perkin�/Elmer FT 1720-X and

Bruker AC-200 or AC-300 spectrometers, respectively.

[Mo(C�/CPh)(h3-allyl)(CO)2(bipy)] (1) and [Mo(C�/

CH)(h3-allyl)(CO)2(N�/N)] (N�/N�/bipy, 2a; phen, 2b)

were prepared according to literature procedures [7]. All

other chemicals were used as received from commercialsources.

2.2. X-ray crystallographic analyses for 3 and 4b

The most relevant crystal and refinement data are

collected in Table 3.

2.3. Preparation of compounds [Co2(CO)6(m-h2:h2-M�/

C�/CR)]

2.3.1. [Co2(CO)6(m-h2:h2-M�/C�/CPh)], M�/

{Mo(h3-C3H5)(CO)2(bipy)} (3)

[Co2(CO)8] (0.12 g, 0.33 mmol) was added to a

solution of [Mo(C�/CPh)(h3-allyl)(CO)2(bipy)] (1) (0.15

g, 0.33 mmol) in THF (20 ml). The solution was stirred

for 45 min and then the solvent was evaporated under

reduced pressure. The residue was extracted withCH2Cl2/hexane (1:2) and filtered through alumina

(activation grade IV). The volatiles were removed in

vacuo, and the residue was washed with hexane (3�/10

ml). Slow diffusion of hexane into a solution of 3 in

CH2Cl2 at �/20 8C produced dark red crystals. A single

crystal obtained in this way was used for the X-ray

analysis. Yield: 73% (0.17 g). Anal. Calc. for C29H18Co2-

MoN2O8: C, 47.31; H, 2.46; N, 3.80. Found: C, 47.2; H,2.5; N, 3.7%. IR (THF): 2062, 2024, 1993, 1939, 1886,

1862 (nCO). 1H NMR(CD2Cl2): 8.76, 8.13, 8.09 and 7.94

[m, 2H each, bipy], 7.39 [m, 3H, Ph], 7.23 [m, 2H, Ph],

3.11 [d (JHs,c�/6.6 Hz), 2H, Hsyn ], 3.02 [m, 1H, Hc ], 1.70

[d (JHa,c�/9.4 Hz), 2H, Hanti ].

2.3.2. [Co2(CO)6(m-h2:h2-M�/C�/CH)], M�/{Mo(h3-

C3H5)(CO)2(bipy)} (4a)

[Co2(CO)8] (0.11 g, 0.32 mmol) was added to a

solution of [Mo(C�/CH)(h3-C3H5)(CO)2(bipy)] (2a)

(0.12 g, 0.32 mmol) in THF (20 ml). The solution was

stirred for 45 min and the solvent was evaporated under

vacuum. The solid was extracted with CH2Cl2/hexane

(1:2) and filtered through alumina (activation grade IV).

Slow diffusion of hexane into a CH2Cl2 solution of 4a at

�/20 8C afforded dark red crystals, one of which wassuitable for an X-ray experiment. Yield: 61% (0.13 g).

Anal. Calc. for C23H14Co2MoN2O8: C, 41.84; H, 2.14;

N, 4.24. Found: C, 42.1; H, 2.1; N, 4.3%. IR (THF):

2063, 2024, 1992, 1940, 1886, 1865 (nCO). 1H

NMR(CD2Cl2): 8.75, 8.15, 7.99 and 7.47 [m, 2H each,

bipy], 6.52 [s, 1H, Mo�/C�/CH ], 3.05 [sbr, 2H, Hsyn ], 2.93

[m, 1H, Hc ], 1.69 [d (JHa,c�/9.1 Hz), 2H, Hanti ].

2.3.3. [Co2(CO)6(m-h2:h2-M�/C�/CH)], M�/{Mo(h3-

C3H5)(CO)2(phen)} (4b)

The procedure was similar to that described for 4a,

using [Mo(C�/CH)(h3-C3H5)(CO)2(bipy)] (2b) (0.08 g,

0.20 mmol) and [Co2(CO)8] (0.068 g, 0.20 mmol) in THF

(20 mL). The complex 4b was obtained as a dark red

microcrystalline solid. Yield: 65% (0.09 g). Anal. Calc.

for C25H14Co2MoN2O8: C, 43.89; H, 2.06; N, 4.09.Found: C, 44.1; H, 2.0; N, 4.1%. IR (THF): 2063, 2024,

1992, 1940, 1886, 1865 (nCO). 1H NMR(CD2Cl2): 9.10

[dd(JH2,3�/JH9,8�/5.1 Hz, JH2,4�/JH7,9�/1.4 Hz), 2H,

H2,9], 8.49 [dd(JH4,3�/JH7,8�/8.0 Hz), 2H, H4,7], 7.98 [s,

2H, H5,6], 7.80 [dd, 2H, H3,8], 6.54 [s, 1H, Mo�/C�/CH ],

3.15 [d (JHs,c�/5.8 Hz), 2H, Hsyn ], 2.87 [m, 1H, Hc ], 1.77

[d (JHa,c�/9.9 Hz), 2H, Hanti ].

3. Results and discussion

The complexes [Mo(C�/CPh)(h3-allyl)(CO)2(bipy)] (1)

[7] and [Mo(C�/CH)(h3-allyl)(CO)2(N�/N)] (N�/N�/

bipy, 2a; phen, 2b) [7] reacted smoothly with

[Co2(CO)8] (see Section 2) in either CH2Cl2 or tetra-

hydrofuran (THF). Hexane, usually employed as solventfor the reaction of acetylenes with [Co2(CO)8], could not

be used due to the insolubility of the molybdenum

alkynyls used as reagents. The reactions were accom-

panied by gas (CO) evolution and by a darkening in the

color of the solutions. Furthermore, the reactions could

be conveniently monitored by IR spectroscopy in the

2200�/1600 cm�1 region. The reaction products could be

purified by column chromatography followed by crys-tallization in CH2Cl2/hexane mixtures at low tempera-

ture, and were isolated in good yields (see Section 2).

Examination of the 1H NMR spectra of the isolated

products, discussed below, showed them to consist of

single compounds. The comparison between the IR

spectra of the isolated products, obtained as crystalline

solids, and those of the reaction crudes, indicated that

the isolated species were the only reaction products. Thepresence of six bands in the nCO region of their IR

spectra in THF clearly pointed to their polynuclear

nature. IR and 1H NMR spectroscopic data, C, H, N

analysis and single-crystal X-ray determinations (see

below) established a composition [(m-h2:h2-R�/C�/C�/

Mo(h3-C3H5)(CO)2(N�/N)(Co2(CO)6)](R�/Ph, N�/

N�/bipy, 3; R�/H, N�/N�/bipy, 4a; N�/N�/phen,

4b) for the new complexes, as presented in Scheme 1.The IR spectra of complexes 3 and 4a�/b present two

intense nCO absorptions at 1939 and 1862 cm�1 for 3

and at 1940 and 1865 cm�1 for 4a�/b that can be

J. Perez et al. / Inorganica Chimica Acta 347 (2003) 189�/193190

assigned to the cis -Mo(CO)2 moieties. The nCO cis -

Mo(CO)2 bands of complexes 3 and 4a�/b are little

shifted with respect to those of the mononuclear

alkynyls, indicating that the coordination to the

{Co2(CO)6} fragment of the acetylenic unit does not

alter significantly the electron density at the molybde-

num center. The additional four bands in the IR of 3

and 4a�/b correspond to the C�/O stretches of the

{Co2(CO)6} unit. The fact that only four bands for the

{Co2(CO)6} part of the IR can be seen for 3 and 4a�/b,

whereas six bands are present in the IR of typical

[(acetylene) Co2(CO)6] complexes results from band

overlap in the spectra in THF solution (even broader

spectra are obtained in CH2Cl2, whereas 3 and 4a�/b are

insoluble in hexane). The 1H NMR spectra of complexes

3 and 4a�/b show typical sets of three signals indicative

of symmetric, static h3-allyl ligands, and four-signal sets

for the N�/N chelates (see Section 2), revealing the

presence of a mirror plane in the molecules, as it

happens in the precursor alkynyls. In complexes 4a�/b

the C2-bound hydrogens, which occurred at 2.12 ppm in

the alkynyl (2a) and at 2.11 ppm in (2b, Fig. 1), appear

at 6.52 ppm in 4a and at 6.54 ppm in 4b. Similar upfield

shifts were observed in other [m-LnM�/C�/CH)-

(Co2(CO)8)] compounds [8].13C NMR, which is very informative for acetylenic

derivatives [9], could not be used for complexes 3 and

4a�/b given that their limited solubility precluded the

observation of the (inherently weak) acetylenic signals

employing adquisition times over which these com-

pounds are stable (extensive decomposition was ob-

served upon standing eight hours at room temperature

in either CDCl3 or CD2Cl2 solution). Hence, the

structures of 3 and 4b were determined by X-ray

diffraction, and the results are given in Fig. 2(a) and

Tables 1 and 3 (3) and in Fig. 2(b) and Tables 2 and 3

(4b).

The two molecules contain Co2C2 cores of approxi-

mately tetrahedral geometry, and {Mo(h3-C3H5)-

(CO)2(N�/N)} units as substituents at one of the

‘acetylenic’ carbons. In accordance with the spectro-

scopic data (see above), the molybdenum fragments

present a pseudooctahedral geometry, with the acetyle-

nic carbon and the h3-allyl group in trans positions, and

the two cis carbonyls and the two nitrogens defining an

equatorial plane. The allyl group is symmetrically

placed, with its open face pointing towards the CO’s,

as is usual in [MoX(h3-allyl)(CO)2(N�/N)] compounds

[10].As is normally encountered in the structure of

dicobalt hexacarbonyl adducts of LnM�/C�/C�/R com-

plexes,1 the main discrepancies between the structures of

3 and 4b, and those of the starting alkynyls 1 and 2b is

the lengthening of the C�/C distances from the typical

acetylenic values of 1.20(3) A for 1 and 1.166(6) A for

2b,2 to 1.320(7) A for 3 and 1.324(7) A for 4b; and the

loss of the linearity of the Mo�/C�/C�/R unit: the angle

C(ipso )�/C�/C shifts from 174(2) in 1 to 143.9(5)8 in 3,

and the Mo�/C�/C angles change from 169.6(19)8 in 1

and 177.9(4)8 in 2b to 144.6(4)8 in 3 and 141.7(4)8 in 4b.

Among the limited number of structures of [(m-LnM�/

C�/C�/R)(Co2(CO)6)] complexes crystallographically de-

termined, the only molybdenum example is, as far as we

Scheme 1.

Fig. 1. Assignation of the hydrogens in the 1H NMR spectra for the

ligand 1,10-phenanthroline.

1 Co2(CO)6 adducts of acetylenes are usually oily materials, see

Refs. [1,8b].2 These values are even slightly shorter than those found in organic

acetylenes, see Ref. [3], a fact that was interpreted as indicative of little

p-acceptor character in the alkynyl ligand of these compounds, see

Ref. [13].

J. Perez et al. / Inorganica Chimica Acta 347 (2003) 189�/193 191

Fig. 2. (a) Molecular structure and numbering scheme of 3. (b) Molecular structure and numbering scheme of 4b.

Table 1

Selected bond lengths (A) and bond angles (8) for complex 3

Bond lengths

Mo(1)�/C(1) 1.957(6) Co(1)�/C(4) 1.474(7)

Mo(1)�/C(2) 1.962(6) Co(2)�/C(4) 1.937(5)

Mo(1)�/N(1) 2.237(4) Co(1)�/Co(2) 2.4687(16)

Mo(1)�/N(2) 2.238(4) Co(1)�/C(9) 1.795(8)

Mo(1)�/C(5) 2.331(6) Co(1)�/C(10) 1.800(7)

Mo(1)�/C(6) 2.244(6) Co(1)�/C(19) 1.770(8)

Mo(1)�/C(7) 2.346(6) Co(2)�/C(8) 1.796(7)

Mo(1)�/C(3) 2.234(5) Co(2)�/C(18) 1.772(7)

C(1)�/O(1) 1.161(6) Co(2)�/C(20) 1.794(8)

C(2)�/O(2) 1.156(6) C(9)�/O(9) 1.140(7)

C(5)�/C(6) 1.399(9) C(10)�/O(10) 1.137(8)

C(6)�/C(7) 1.393(9) C(19)�/O(19) 1.137(8)

C(3)�/C(4) 1.320(7) C(8)�/O(8) 1.138(7)

C(4)�/C(41) 1.474(7) C(18)�/O(18) 1.131(7)

Co(1)�/C(3) 2.066(4) C(20)�/O(20) 1.129(8)

Co(2)�/C(3) 2.049(5)

Bond angles

C(11)�/Mo(1)�/C(2) 83.2(2) Mo(1)�/C(3)�/C(4) 144.6(4)

N(1)�/Mo(1)�/N(2) 72.34(16) Mo(1)�/C(3)�/Co(1) 134.6(2)

C(1)�/Mo(1)�/N(1) 169.53(19) Mo(1)�/C(3)�/Co(2) 137.0(3)

C(2)�/Mo(1)�/N(2) 170.50(19) Co(1)�/C(3)�/Co(2) 73.74(17)

C(1)�/Mo(1)�/C(3) 81.6(2) Co(1)�/C(4)�/Co(2) 77.2(2)

C(2)�/Mo(1)�/C(3) 86.3(2) C(3)�/C(49)�/C(41) 143.9(5)

N(1)�/Mo(1)�/C(3) 88.98(17) C(4)�/C(3)�/Co(2) 68.4(3)

N(2)�/Mo(1)�/C(3) 102.4(2) C(4)�/C(3)�/Co(1) 67.0(3)

Table 2

Selected bond lengths (A) and bond angles (8) for complex 4b

Bond lengths

Mo�/C(1) 2.355(6) C(5)�/H(5) 0.984(48)

Mo�/C(2) 2.245(5) Co(2)�/C(21) 1.801(6)

Mo�/C(3) 2.321(6) Co(2)�/C(22) 1.770(6)

Mo�/N(40) 2.257(4) Co(2)�/C(23) 1.800(6)

Mo�/N(51) 2.241(4) C(21)�/O(21) 1.136(7)

Mo�/C(11) 1.958(6) C(22)�/O(22) 1.135(8)

Mo�/C(12) 1.947(6) C(23)�/O(23) 1.132(8)

Mo�/C(4) 2.208(4) Co(3)�/C(4) 2.057(5)

C(1)�/C(2) 1.397(8) Co(3)�/C(5) 1.955(6)

C(2)�/C(3) 1.402(10) Co(3)�/C(31) 1.785(6)

C(4)�/C(5) 1.324(7) Co(3)�/C(32) 1.808(6)

C(11)�/O(11) 1.145(7) Co(3)�/C(33) 1.771(6)

C(12)�/O(12) 1.157(6) C(31)�/O(31) 1.138(7)

Co(2)�/Co(3) 2.488(2) C(32)�/O(32) 1.140(7)

Co(2)�/C(4) 2.064(4) C(33)�/O(33) 1.138(7)

Co(2)�/C(5) 1.968(5)

Bond angles

C(11)�/Mo�/C(12) 74.8(2) Mo�/C(4)�/C(5) 141.7(4)

C(11)�/Mo�/N(51) 167.0(2) Co(3)�/Co(2)�/C(4) 52.7(1)

C(12)�/Mo�/N(40) 170.2(2) Co(3)�/Co(2)�/C(5) 50.4(2)

N(40)�/Mo�/N(51) 73.2(1) C(21)�/Co(2)�/C(22) 99.1(2)

C(11)�/Mo�/C(4) 80.0(2) C(22)�/Co(2)�/C(23) 100.9(3)

C(12)�/Mo�/C(4) 86.2(2) C(31)�/Co(3)�/C(33) 97.6(3)

N(40)�/Mo�/C(4) 86.2(1) C(33)�/Co(3)�/C(32) 100.9(2)

N(51)�/Mo�/C(4) 87.1(2) C(4)�/C(5)�/H(5) 142.0(26)

J. Perez et al. / Inorganica Chimica Acta 347 (2003) 189�/193192

know, Lang’s compound [Mo2(h5-C5H5)(CO)4{m4-

h2:2:2:2-Me3SiC�/C�/C�/C�/SiMe3)Co2(CO)6}] [11], in

which one acetylenic moiety completes a tetrahedral

core with the Co2(CO)6 fragment, whereas a secondM2C2 tetrahedrane includes a Mo2Cp2(CO)4 fragment.

However, it should be noted that dicobalt hexacarbonyl

adducts of tungsten (II) alkynyls have been used in

organic synthesis [12].

The reaction of molybdenum alkynyls 1 and 2a�/b

with [Co2(CO)8] to give the 3 and 4a�/b polymetallic

compounds contrasts with the cleavage of the Mo�/

alkynyl bond that takes place when 1 reacts with othertransition-metal compounds [13].

On the other hand, the thermal stability of 3 and 4a�/b

is limited. Thus, in contrast with the metal�/metal bond

formation reported upon thermally induced decarbony-

lation by Akita and Moro-oka with iron alkynyl-

Co2(CO)6 adducts [8], heating of the THF solutions of

3 and 4a�/b led to decomposition through Mo�/C bond

scission, as evidenced by the identification of[Mo(CO)4(N�/N)] (N�/N�/bipy, phen) as the major

product in the resulting solutions by IR spectroscopy.

This ease of demetallation of the C2 unit may be useful

with regard to the application of complexes 3 and 4a�/b

in organic synthesis.

4. Supplementary material

Crystallographic data (excluding structure factors) for

the structural analysis have been deposited with the

Cambridge Crystallographic Data Centre, CCDC Nos.

181564 and 181565 for compounds 3 and 4b, respec-

tively. Copies of this information may be obtained freeof charge from The Director, CCDC, 12 Union Road,

Cambridge, CB2 1EZ, UK (fax: �/44-1223-336-033;

e-mail: deposit@ccdc.cam.ac.uk or www: http://

www.ccdc.cam.ac.uk).

Acknowledgements

We thank Ministerio de Ciencia y Tecnologıa and

Ministerio de Educacion for support of this work

(projects BQU-0220, PR-01-GE-7 and BQU-2000-

0219) and for a predoctoral fellowship (to L.R.)

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Table 3

Crystal data and refinement details for complexes 3 and 4b

3 4b

Formula C29H18Co2MoN2O8 C25H14Co2MoN2O8

fw 736.25 684.2

Crystal system monoclinic monoclinic

Space group P21/c P21/c

a (A) 12.320(2) 9.188(5)

b (A) 16.504(13) 15.890(8)

c (A) 14.255(6) 17.638(8)

a (8) 90 90

b (8) 94.58(3) 101.82(3)

g (8) 90 90

V (A3) 2889(3) 2521(2)

Z 4 8

T (K) 293(2) 297(2)

Dcalc (g cm�3) 1.693 1.803

F (000) 1464 1352

l (Mo Ka) (A) 0.71073 0.71073

Crystal size (mm) 0.11�0.18�0.21 0.18�0.20�0.22

m (mm�1) 1.615 1.828

Scan range (8) 1.435u525.97 2.55u522.5

No. of reflections

measured

5663 7098

No. of independent

reflections

2998 3306

Data/restraints/parameters 2998/0/451 3306/0/361

Goodness-of-fit on F2 1.008 1.04

R1/wR2 [I �2s (I )] 0.039/0.081 0.0295/0.0289

R1/wR2 (all data) 0.131/0.105 0.0507/0.0336

J. Perez et al. / Inorganica Chimica Acta 347 (2003) 189�/193 193