Cobalt-assisted silicon-silicon bond activation

Article abstract of DOI:10.1021/om0604831

A number of oligosilylalkynes were converted to the respective dicobalt hexacarbonyl complexes. These compounds were found to be surprisingly reactive, indicating Si-Si bond activation in the coordination sphere of the cobalt atoms. The presence of more t

Full text of DOI:10.1021/om0604831

Organometallics 2006, 25, 4897-4908
4897
Cobalt-Assisted Silicon-Silicon Bond Activation
Michaela Zirngast, Christoph Marschner, and Judith Baumgartner*
Institut fu¨r Anorganische Chemie, Technische UniVersita¨t Graz, Stremayrgasse 16, A-8010 Graz, Austria
ReceiVed June 1, 2006
A number of oligosilylalkynes were converted to the respective dicobalt hexacarbonyl complexes.
These compounds were found to be surprisingly reactive, indicating Si-Si bond activation in the coordi-
nation sphere of the cobalt atoms. The presence of more than one silicon-silicon bond restricted clean
conversions, and therefore the pentamethyldisilanylphenylacetylene complex was prepared, which engaged
in defined reactions. The rearrangement of an oligosilylalkyne dicobalt hexacarbonyl complex to a dicobalt
hexacarbonyl bis(dialkylsilylene) complex was observed. The reaction of tris(trimethylsilyl)silane with
dicobalt octacarbonyl yielded the product of formal replacement of two carbonyl ligands with dimethyl-
silylene groups.
silylalkynes coordinated to the dicobalt hexacarbonyl fragment
there are only three containing an oligosilyl unit.9 Also the
number of compounds with a cobalt-oligosilyl substructure is
still very small.10,11 As we have recently started to investigate
the chemistry of oligosilylalkynes,12 we also became interested
in the possibility of studying cobalt complexes of these
compounds.
Introduction
Over the last decades organocobalt chemistry has developed
into a very vital field of organic and inorganic synthesis.1 The
fact that two carbonyl ligands in dicobalt octacarbonyl can be
replaced by an alkyne was recognized in the early 1950s.2 Since
then, numerous complexes of this and related types have been
prepared.3
One reason for the huge interest in this class of compounds
is the stabilization of a positive charge in the R-position of an
alkyne upon complexation. The Nicholas reaction, which is the
reaction of a cobalt-coordinated propargyl alcohol with a nucleo-
phile, depends on this effect.4
Also silyl-substituted alkynes have been subjected success-
fully to complexation conditions with dicobalt octacarbonyl.5
To assess the enhanced chemical reactivity of silyl groups in
the R-position of a complexed alkyne, Corriu et al. have investi-
gated the reactivity of methoxy- and halosilyl alkynes.6 Reac-
tions such as alkylation, reduction, hydrolysis, and halogenation
could be carried out at the coordinated compounds.6 In a
subsequent study the enhanced reactivity of the Si-H bond of
a coordinated hydrosilylalkyne was found and investigated.7 In
another report Brook and co-workers have studied the prospects
of generating transition metal-stabilized silylium cations.8 It is
interesting to notice that among all the reported examples of
Results and Discussion
Our first attempts to obtain a cobalt carbonyl oligosilylalkyne
complex concentrated on bis[tris(trimethylsilyl)silyl]acetylene
(1), which is easily available from tris(trimethylsilyl)silyl
chloride and dilithium acetylide. However, while the reaction
of bis(trimethylsilyl)acetylene with dicobalt octacarbonyl
has been reported,5 we were not able to obtain the bis[tris-
(trimethylsilyl)silyl]acetylene complex. As it is likely that steric
reasons are responsible for this failure, we replaced one of the
bulky tris(trimethylsilyl)silyl groups with trimethylsilyl. None-
theless, also [tris(trimethylsilyl)silyl]trimethylsilylacetylene (2)
did not react with dicobalt octacarbonyl.
* Corresponding author. Tel: ++43-316-873-8219. Fax: ++43-316-
873-8701. E-mail: baumgartner@tugraz.at.
(1) (a) Schore, N. E. Chem. ReV. 1988, 88, 1081-1119. (b) Welker, M.
E. Curr. Org. Chem. 2001, 5, 785-807.
(2) Sternberg, H. W.; Greenfield, H.; Friedel, R. A.; Wotjz, J.; Markby,
R. Wender, I. J. Am. Chem. Soc. 1954, 76, 1457-1458.
(3) (a) Dickson. R. S.; Fraser, P. J. AdV. Organomet. Chem. 1974, 12,
323-377. (b) Went, M. J. AdV. Organomet. Chem. 1997, 41, 69-125.
(4) (a) Nicholas, K. M. Acc. Chem. Res. 1987, 20, 207-214. (b) Mu¨ller,
T. J. J. Eur. J. Org. Chem. 2001, 2021-2033. (c) Green, J. R. Curr. Org.
Chem. 2001, 5, 809-826. (d) Teobald, B. J. Tetrahedron 2002, 58, 4133-
4170.
(5) (a) Kru¨erke, U.; Hu¨bel, W. Chem. Ber. 1961, 94, 2829-2856. (b)
Seyferth, D.; White, D. L. J. Organomet. Chem. 1971, 32, 317-322. (c)
Pannell, K. H.; Crawford, G. M. J. Coord. Chem. 1973, 2, 251-255.
(6) Corriu, R. J. P.; Moreau, J. J. E.; Praet, H. Organometallics 1989, 8,
2779-2786.
(7) Corriu, R. J. P.; Moreau, J. J. E.; Praet, H. Organometallics 1990, 9,
2086-2091.
Complete removal of the silyl substituent on one side of the
alkyne (3) eventually led to success, and we were able to obtain
the first oligosilylacetylene dicobalt hexacarbonyl complex (3a).
(9) (a) Werz, D. B.; Schulte, J. H.; Rausch, B. J.; Gleiter, R.; Rominger,
F. Eur. J. Inorg. Chem. 2004, 2585-2593. (b) Semenov, V. V.; Cherepen-
nikova, N. F.; Kornev, A. N.; Naumova, E. V.; Makarenko, N. P.; Khorshev,
S. Ya.; Domrachev, G. A.; Bochkova, O. A. IzV. Akad. Nauk, Ser. Khim.
1996, 2561-2567. (c) Ando, W.; Hojo, F.; Sekigawa, S.; Nakayama, N.;
Shimizu, T. Organometallics 1992, 11, 1009-1011.
(10) (a) Hengge, E.; Siegl, H.; Stadelmann, B. J. Organomet. Chem. 1994,
479, 187-192. (b) Hengge, E.; Eibl, M.; Stadelmann, B. Monatsh. Chem.
1993, 124, 523-528. (c) Hengge, E.; Eibl, M. Organometallics 1991, 10,
3185-3189.
(11) (a) Pakkanen, T.; Kerber, R. C. Inorg. Chim. Acta 1981, 49, 47-
52. (b) Kerber, R. C.; Pakkanen, T. Inorg. Chim. Acta 1979, 37, 61-65.
(8) (a) Ruffolo, R.; Decken, A.; Girard, L.; Gupta, H. K.; Brook, M. A.;
McClinchey, M. J. Organometallics 1994, 13, 4328-4335. (b) Ruffolo,
R.; Kainz, S.; Gupta, H. K.; Brook, M. A.; McGlinchey, M. J. J. Organomet.
Chem. 1997, 547, 217-226.
10.1021/om0604831 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/25/2006

4898 Organometallics, Vol. 25, No. 20, 2006
Zirngast et al.
Figure 2. Molecular structure and numbering of 4a. Selected bond
lengths [Å] and bond angles [deg] with SDs: Co(1)-C(2) 1.981-
(3), Co(1)-C(1) 2.020(3), Co(1)-Co(2) 2.4574(7), Co(2)-C(13)
1.813(4), Si(1)-C(1) 1.876(3), Si(1)-Si(4) 2.3601(14), Si(1)-
Si(3) 2.3683(14), Si(1)-Si(2) 2.3820(15), O(1)-C(12) 1.138(4),
C(1)-C(2) 1.346(5), C(2)-Co(1)-C(1) 39.31(13), C(2)-Co(1)-
Co(2) 51.11(9), C(2)-Co(2)-C(1) 39.38(13), C(1)-Si(1)-Si(4)
110.41(11), C(1)-Si(1)-Si(3) 111.55(11), Si(4)-Si(1)-Si(3)
108.06(5), Si(4)-Si(1)-Si(2) 106.80(5), Si(3)-Si(1)-Si(2) 109.66(5),
Si(1)-C(1)-Co(2) 133.46(18), C(1)-C(2)-C(3) 142.2(3).
Figure 1. Molecular structure and numbering of 3a. Selected bond
lengths [Å] and bond angles [deg] with SDs: Co(1)-C(11) 1.957-
(10), Co(1)-C(10) 2.013(9), Co(1)-Co(2) 2.469(2), O(2)-C(13)
1.127(13), Si(1)-C(10) 1.878(10), Si(1)-Si(2) 2.348(4), Si(1)-
Si(4) 2.362(4), Si(1)-Si(3) 2.367(4), C(10)-C(11) 1.310(15),
C(11)-Co(1)-C(10) 38.5(4), C(11)-Co(1)-Co(2) 50.3(3), C(10)-
Co(1)-Co(2) 52.4(3), C(10)-Si(1)-Si(2) 115.8(3), C(10)-Si(1)-
Si(4) 108.0(3), Si(2)-Si(1)-Si(4) 111.06(15), C(10)-Si(1)-Si(3)
106.4(3), Si(2)-Si(1)-Si(3) 108.39(15), Si(4)-Si(1)-Si(3) 106.67-
(14), C(11)-C(10)-Si(1) 142.7(8), C(11)-C(10)-Co(1) 68.4(6),
Si(1)-C(10)-Co(1) 137.6(5), C(11)-C(10)-Co(2) 67.3(6), Si(1)-
C(10)-Co(2) 134.6(5), Co(1)-C(10)-Co(2) 75.5(3), C(10)-
C(11)-Co(2) 74.2(6), C(10)-C(11)-Co(1) 73.1(6).
Attempts to carry out chromatographic purification resulted in
a vigorous decomposition reaction on silica gel. These properties
clearly suggested that in the cobalt-complexed oligosilylalkynes
the Si-Si bonds are highly activated, similar to the Si-H bonds
in Corriu’s compounds.7
Also phenyl[tris(trimethylsilyl)silyl]acetylene (4) reacted smoothly
to complex 4a.
Experiments to react compound 4a with oxygen, hydrogen,
water, alcohols, phenylacetyene, and acetone gave complicated
reaction mixtures in all cases, even at low temperatures. We
assumed that the reason for this situation was the fact that there
are three activated Si-Si bonds present in 4a. Therefore, we
decided to simplify the system and used pentamethydisilanyl-
phenylacetylene (8) to prepare the dicobalt complex 8a. This
compound contains only one Si-Si bond, and it offers the
additional advantage that, if related chemistry occurs as in
Corriu’s case,7 the same products would be obtained. This was
indeed the case, as we could see from the reaction of 8a with
methanol, which gave the known methoxy compound 9.6
Reaction of 8a with water gave silanol 10, which condensed
further to the respective disiloxane (10a) under the reaction
conditions.
Both compounds were subjected to crystal structural analysis
(Figures 1 and 2). In a similar way, also other compounds con-
taining the silylated phenyl acetylene unit, including the known
compound 7a,5 could be obtained.
Chromatographic purification of dicobalt carbonyl alkyne
complexes is a common practice.3 It is also known that these
complexes are fairly air stable. However, this was not the case
with our compounds containing the oligosilyl unit (3a-6a),
which rapidly decomposed when exposed to ambient conditions.
Corriu7 and others13 have shown that it is possible to add 2
equiv of dicobalt octacarbonyl to a dialkynylsilane.7 We wanted
(12) (a) Fischer, R.; Frank, D.; Gaderbauer, W.; Kayser, C.; Mechtler,
C.; Baumgartner, J.; Marschner, C. Organometallics 2003, 22, 3723-3731.
(b) Mechtler, C.; Zirngast, M.; Baumgartner, J.; Marschner, C. Eur. J. Inorg.
Chem. 2004, 3254-3261. (c) Mechtler, C.; Zirngast, M.; Gaderbauer, W.;
Wallner, A.; Baumgartner, J.; Marschner, C. J. Organomet. Chem. 2006,
691, 150-158.
(13) (a) Lang, H.; Weinmann, M.; Zsolnai, L. J. Organomet. Chem. 1996,
522, 277-289. (b) Gleiter, R.; Stahr, H. Tetrahedron Lett. 1996, 37, 1179-
1182.

Cobalt-Assisted Silicon-Silicon Bond ActiVation
Organometallics, Vol. 25, No. 20, 2006 4899
Scheme 1. Schematic Formation of Silyl-Silylene
Transition Metal Complexes via 1,2 and 1,3 Shifts
to find out if this is also possible for a dialkynyloligosilane.
The double metalation of the 1,4-bis(oligosilyl)ethynylbenzene
11 to 11a proceeded without any problem.
of a cobalt silyl-silylene complex as a reactive intermediate in
a similar manner, as described in more detail below.
From Chalk and Harrod’s seminal studies on hydrosilation
chemistry the reaction of hydrosilanes with dicobalt octacarbonyl
is known to yield cobalt tetracarbonyl silyl complexes.16 As we
were not aware of an example where this reaction was carried
out successfully with an oligohydrosilane, we reacted tris-
(trimethylsilyl)silane with dicobalt octacarbonyl in the expecta-
tion of obtaining the tris(trimethylsilyl)silyl cobalt tetracarbonyl
complex. Much to our surprise we did not obtain this compound
but complex 14, where two of the carbonyl ligands of the
starting material have been replaced by bridging dimethyl-
silylene groups. While 14 is already known from the reaction
of dicobalt octacarbonyl with 1,1,2,2-tetramethyldisilane,11 we
have now determined its crystal structure and 29Si NMR shifts.
We also treated 2,2-bis(phenylethynyl)hexamethyltrisilane38
(12) with dicobalt octacarbonyl. NMR spectroscopy of the
reaction with 1 equiv indicated clean and complete formation
of the expected monocomplexed product 12a. Upon reaction
with another equivalent of dicobalt octacarbonyl, 12b was
obtained. While we were able to obtain a crystal structure of
12a, attempts to crystallize 12b and to determine its crystal
structure indicated that 12b had suffered the formal loss of
trimethysilylphenylacetylene and rearranged to the disilylene
complex 13.
The formation of 14 seems to be related to the formation of
13. Similar Si-Si bond activation chemistry of oligosilanes17
has been reported before for several other metals such as iron,18
rhodium, and iridium,19 but almost exclusively under irradiation
conditions. Especially the groups of Pannell, Ogino, and Tilley
have studied this field thoroughly. For many rearrangements
and redistribution reactions of oligosilyl transition metal com-
plexes silyl-silylene complexes are essential intermediates.20
A 1,2 silyl shift allows oligosilyl transition metal complexes to
avoid coordinative unsaturation, which may occur in the event
of ligand dissociation. A further 1,3 shift usually of an alkyl
group can establish an equilibrium between the silyl-silylene
complex and a related silylene-silyl complex (Scheme 1).
As for the reaction mechanism leading to the formation of
14, we also assume the involvement of silyl-silylene intermedi-
ates. We still believe that the initial step of the reaction sequence
is the expected bimolecular oxidative addition, which leads to
The structural motif of silylenes as bridging ligands for
dicobalt complexes is not new. Similar complexes have been
obtained by reaction of dicobalt octacarbonyl with hydro- and
disilanes.11,14 The reaction mechanism for the transformation
of 12b to 13 is not quite clear yet, but it should be noted that
the cleavage of silyl acetylene bonds in the coordination sphere
of cobalt is not without precedence.15 The fact that the
transformation involves methyl migration from a trimethylsilyl
group to the central silicon atom seems to imply the involvement
(16) (a) Chalk, A. J.; Harrod, J. F. J. Am. Chem. Soc. 1965, 87, 1133-
1135. (b) Chalk, A. J.; Harrod, J. F. J. Am. Chem. Soc. 1967, 89, 1640-
1647.
(17) For a review on the topic of Si-Si bond activation by transition
metals see: Sharma, H. K.; Pannell, K. H. Chem. ReV. 1995, 95, 1351-
1374.
(18) (a) Jones, K. L.; Pannell, K. H. J. Am. Chem. Soc. 1993, 115,
11336-11340. (b) Pannell, K. H.; Rozell, J. M., Jr.; Hernandez, C. J. Am.
Chem. Soc. 1989, 111, 4482-4485.
(14) (a) Borgdorff, J.; Duffy, N. W.; Robinson, B. H.; Simpson, J. Inorg.
Chim. Acta 1994, 224, 73-79. (b) Bourg, S.; Boury, B.; Carre´, F.; Corriu,
R. J. P. Organometallics 1997, 16, 3097-3099. (c) Bourg, S.; Boury, B.;
Carre´, F. H.; Corriu, R. J. P. Organometallics 1998, 17, 167-172.
(15) Fritch, J. R.; Vollhardt, K. P. C.; Thompson, M. R.; Day, V. W. J.
Am. Chem. Soc. 1979, 101, 2768-2770.
(19) (a) Mitchell, G. P.; Tilley, T. D.; Yap, G. P. A.; Rheingold, A. L.
Organometallics 1995, 14, 5472-5474. (b) Mitchell, G. P.; Tilley, T. D.
Organometallics 1996, 15, 3477-3479.
(20) For reviews covering silyl-silylene transition metal complexes
see: ref 17 and: (a) Okazaki, M.; Tobita, H.; Ogino, H. Dalton Trans.
2003, 493-506. (b) Ogino, H. Chem Rec. 2002, 2, 291-306.

4900 Organometallics, Vol. 25, No. 20, 2006
Zirngast et al.
Scheme 2. Tentative Mechanism for the Formation of 14
Scheme 3. Formation of 14 via the Rearrangement of a
Dicobalt Complex
other signals indicate the presence of (CO)4CoSiMe3 and a
number of methylated oligosilanes including resonances for
double- and triple-silylated silicon atoms.
To find out if similar chemistry occurs also with germanium,
the reaction of dicobalt octacarbonyl was repeated with tris-
(trimethylsilyl)germane. Given the chemical similarity between
silicon and germanium, we expected to observe similar chem-
istry that probably would feature a dimethylgermylene ligand.
However, we could isolate neither the tris(trimethylsilyl)germyl
cobalt tetracarbonyl complex (16) nor a silylene or germylene
complex related to 14 but rather the tetracobalt germanium
complex 15,24 which was already known from the reaction of
germanium tetrabromide with sodium tetracarbonylcobaltate or
alternatively from the reaction of dicobalt octacarbonyl with
germane (GeH4).24
the formation of tris(trimethylsilyl)silyl cobalt tetracarbonyl.
Loss of a carbonyl ligand then initiates the formation of a bis-
(trimethylsilyl)silylene(trimethylsilyl) cobalt tricarbonyl complex
(type A) via an intramolecular 1,2 silyl migration (Scheme 2).
The formed compound is in equilibrium with a [methylbis-
(trimethylsilyl)silyl](dimethylsilylene) cobalt tricarbonyl isomer
(type B) (Scheme 2). Bimolecular reductive elimination of two
silyl(dimethylsilylene)cobalt tricarbonyl (type B) complexes can
give rise to the formation of 14 and a disilane.21 Alternatively,
the silyl-silylene complexes can also extrude a silylene frag-
ment such as dimethylsilylene, which can be trapped by either
tris(trimethylsilyl)silane22 or dicobalt octacarbonyl. The resulting
coordinatively unsaturated fragment would stabilize itself by
another 1,2 shift and the formation of another silyl-silylene
complex (Scheme 2). The trapping product with the dicobalt
complex could also undergo silyl-silylene rearrangement
processes, which lead to the formation of 14 (Scheme 3), as
has been shown for a related diiron complex.23
Changing the stoichiometry of the reaction to 2 equiv of tris-
(trimethylsilyl)germane eventually allowed us to isolate the tris-
(trimethylsilyl)germyl cobalt tetracarbonyl complex 16 besides
a substantial amount of 15. Again the 29Si NMR spectrum of
the reaction mixture indicated the presence of (CO)4CoSiMe3.
The possibility for different silyl-silylene complexes to
undergo bimolecular reductive elimination allows for the
formation of several different disilanes. The additional involve-
ment of silylene trapping chemistry, which can also lead to
follow-up chemistry with cobalt carbonyls, further complicates
the course of the reaction. This situation is reflected by the 29Si
NMR spectra of the reaction. Besides the resonance for 14,
On the basis of these observations we can postulate a possible
mechanism for the formation of 15 (Scheme 4). Starting from
the initial formation of 16, a 1,2 shift related to the chemistry
described above seems reasonable. However, at this point the
(21) Brookes, A.; Knox, S. A. R.; Stone, F. G. A. J. Chem. Soc. A 1971,
3469-3471.
(22) Pannell, K. H.; Brun, M.-C.; Sharma, H.; Jones K.; Sharma, S.
Organometallics 1994, 13, 1075-1077.
(24) (a) Schmid, G.; Etzrodt, G. J. Organomet. Chem. 1977, 107, 367-
371. (b) Boese, R.; Schmid, G. J. Chem. Soc., Chem. Commun. 1979, 349-
350. (c) Gerlach, R. F.; Mackay, K. M.; Nicholson, B. K. J. Organomet.
Chem. 1979, 178, C30-C32.
(23) Ueno, K.; Hamashima, N.; Shimoi, M.; Ogino, H. Organometallics
1991, 10, 959-962.

Cobalt-Assisted Silicon-Silicon Bond ActiVation
Organometallics, Vol. 25, No. 20, 2006 4901
Scheme 4. Possible Mechanism for the Formation of 14
Figure 3. Molecular structure and numbering of 5. Selected bond
lengths [Å] and bond angles [deg] with SDs: Si(1)-C(1) 1.858(3),
Si(1)-Si(2) 2.3569(13), Si(1)-Si(3) 2.3581(13), C(1)-C(2) 1.214(4),
C(2)-C(3) 1.440(4), C(1)-Si(1)-Si(2) 105.49(10), C(1)-Si(1)-
Si(3) 104.37(10), Si(2)-Si(1)-Si(3) 120.92(5), C(2)-C(1)-Si(1)
174.4(3), C(1)-C(2)-C(3) 179.4(4).
dissociation of the more stable germylene, instead of the silylene,
is more likely.25,26 Insertion of the germylene into the cobalt-
cobalt bond of dicobalt octacarbonyl, which is a known pro-
cess,26 concludes the sequence, which replaces one trimethylsilyl
group by a cobalt tetracarbonyl unit. Repetition of the sequences
dissociation of CO, 1,2 shift, dissociation of germylene, insertion
into the Co-Co bondsoccurs until all silyl groups are replaced
by cobalt tetracarbonyl moieties. Loss of three carbonyl ligands,
which is probably favored for steric reasons, finally leads to
the formation of 15 (Scheme 4).
Attempts to react other silicon-silicon containing compounds
such as tetrakis(trimethylsilyl)silane or dodecamethylcyclo-
hexasilane with dicobalt octacarbonyl were not successful. We
therefore assume that the reaction of the cobalt complex with
Si-Si bonds does not take place in an intermolecular fashion
but requires either previous coordination via the alkynyl unit
or the oxidative addition into the Si-H bond to occur within
the coordination sphere of the complex.
X-ray Crystallography. Compounds 3a, 4a, 5, 7a, 8a, 9,
10a, 12a, 13, 14, 15, and 16 were subjected to single-crystal
X-ray diffraction analysis. Except for 5 all of these are cobalt
complexes. Interestingly the structural features of 5 (Figure 3)
are somewhat different compared to the recently obtained
structure of 4.38 The acetylenic bond distance is relatively long
(1.21 Å) compared to 1.19 Å in 4. Also the Si-Si bond lengths
are somewhat longer. The fact that the hydride substituent does
Figure 4. Molecular structure and numbering of 7a. Of two
crystallographically independent molecules in the asymmetric unit,
only one is shown. Selected bond lengths [Å] and bond angles [deg]
with SDs: Co(1)-C(2) 1.965(7), Co(1)-C(1) 1.998(7), Co(1)-
Co(2) 2.4717(14), Si(1)-C(1) 1.856(7), Si(1)-C(9) 1.861(7),
O(1)-C(12) 1.114(9), C(1)-C(2) 1.333(10), C(2)-Co(1)-C(1)
39.3(3), C(2)-Co(1)-Co(2) 51.8(2), C(2)-Co(2)-Co(1) 50.9(2),
C(1)-Co(2)-Co(1) 51.8(2), C(1)-Si(1)-C(9) 110.5(3), C(1)-
Si(1)-C(11) 107.8(4), Si(1)-C(1)-Co(2) 132.4(4), Si(1)-C(1)-
Co(1) 130.9(4), C(1)-C(2)-C(3) 142.3(7).
not require much space causes an expansion of the Si-Si-Si
angle to almost 121°. While the connection between the phenyl
and the alkyne moiety is almost perfectly linear, a slight bending
was observed for the C-C-Si angle (174°). The hydrogen atom
on silicon was found and not calculated.
The structural features of the silylated alkynyl dicobalt hexa-
carbonyl complexes (Figures 1, 2, 4-9) are listed in Table 2.
Compared to the already substantial number of structurally
characterized alkynyl dicobalt hexacarbonyl complexes,3b the
silylated complexes do not exhibit extraordinary structural
(25) (a) Pannell, K. H.; Sharma, S. Organometallics 1991, 10, 1655-
1656. (b) Sharma, S.; Pannell, K. H. Organometallics 2000, 19, 1225-
1231.
(26) McIndoe, J. S.; Nicholson, B. K. J. Organomet. Chem. 1999, 577,
181-188.

4902 Organometallics, Vol. 25, No. 20, 2006
Zirngast et al.
Figure 5. Molecular structure and numbering of 8a. Selected bond
lengths [Å] and bond angles [deg] with SDs: Co(1)-C(13) 1.984-
(3), Co(1)-C(14) 1.996(3), Co(1)-Co(2) 2.4798(9), Co(2)-C(13)
1.970(3), Co(2)-C(14) 1.992(3), Si(1)-C(14) 1.856(3), Si(1)-Si-
(2) 2.3503(13), C(13)-Co(1)-C(14) 39.50(12), C(13)-Co(1)-Co-
(2) 50.90(9), C(14)-Co(1)-Co(2) 51.49(8), C(14)-Si(1)-Si(2)
110.72(10).
Figure 6. Molecular structure and numbering of 9. Of two
crystallographically independent molecules in the asymmetric unit,
only one is shown. Selected bond lengths [Å] and bond angles [deg]
with SDs: Co(1)-C(1) 1.801(4), Co(1)-C(2) 1.812(4), Co(1)-
Co(2) 2.4705(9), O(1)-C(1) 1.132(4), O(7)-C(17) 1.385(5), C(1)-
Co(1)-C(2) 99.37(17), C(1)-Co(1)-Co(2) 149.08(11), C(2)-
Co(1)-Co(2) 100.45(11), O(7)-Si(1)-C(15) 105.91(16).
characteristics. Co-Co distances are close to the average of
2.47 Å. Also the elongation of the acetylenic bond to values
between 1.31 and 1.35 Å groups nicely around the average of
1.34 Å. The Si-C bond lengths of 1.87 Å (3a, 4a) and 1.85 Å
(7a-13) still reflect the slightly shortened Si-Csp connection
compared to typical Si-Csp3 bonds. The angles around the
alkyne carbon atoms are perfectly within the range of what
would be expected for the phenyl-substituted carbon (140-143°)
but are somewhat less expanded for the silicon-substituted
carbon (145-148°). Again the hydrogen atom on silicon was
found and not calculated. Only compound 13 (Figure 9), with
the rearranged cobalt cluster sidearm, exhibits a coordinated
unit with a higher sp-character (angles of 146° and 153°).
Compound 13 (Figure 9) contains two dicobalt cluster units.
One unit is a conventional dicobalt hexacarbonyl acetylene
complex, but the other one can be interpreted as a dicobalt octa-
carbonyl in which the two bridging carbonyl groups have been
replaced by dialkylsilylene groups. Structures of similar com-
pounds have been studied previously by Corriu.14b,c The Co-
Co bond length in this unit is elongated to 2.67 Å. The Si-Co
distances are in the range between 2.27 and 2.30 Å. The Co-
Si-Co angles are, at 72°, rather small, as expected for a three-
membered ring. However, also the C-Si-C angles are, at 103°
and 105°, rather small, indicating a high p-orbital character. The
situation for the structure of the more prototypic compound 14
(Figure 10) is very similar to what was found for 13. Two
virtually identical, but crystallographically independent mol-
ecules are present in the asymmetric unit. The Co-Co bond
length is 2.66 Å, and the Si-Co distances are close to 2.28 Å.
The Co-Si-Co angles are at 71°, and the C-Si-C angles are,
Figure 7. Molecular structure and numbering of 10a. Selected bond lengths [Å] and bond angles [deg] with SDs: Co(1)-C(9) 1.817(7),
Co(1)-C(1) 1.992(5), Co(1)-Co(2) 2.4810(12), Co(2)-C(2) 1.966(5), Co(2)-C(1) 1.986(5), Si(1)-O(7) 1.6398(19), Si(1)-C(15) 1.852-
(6), O(1)-C(9) 1.132(8), C(2)-Co(1)-C(1) 40.0(2), C(2)-Co(1)-Co(2) 50.86(15), C(1)-Co(1)-Co(2) 51.32(15), C(2)-Co(2)-C(1)
40.1(2), O(7)-Si(1)-C(1) 107.2(2), Si(1)-O(7)-Si(1)#1 158.4(4).

Cobalt-Assisted Silicon-Silicon Bond ActiVation
Organometallics, Vol. 25, No. 20, 2006 4903
Figure 8. Molecular structure and numbering of 12a. Of two crystallographically independent molecules in the asymmetric unit, only one
is shown. Selected bond lengths [Å] and bond angles [deg] with SDs: Co(1)-C(1) 1.789(6), Co(1)-C(3) 1.814(6), Co(1)-C(14) 1.976(5),
Co(1)-C(13) 1.996(5), Co(1)-Co(2) 2.4776(10), Si(1)-Si(2) 2.358(2), Si(2)-C(21) 1.838(5), Si(2)-C(13) 1.856(5), O(1)-C(1) 1.146-
(6), C(13)-C(14) 1.340(7), C(1)-Co(1)-C(3) 97.3(2), C(1)-Co(1)-C(2) 102.9(3), C(1)-Co(1)-C(14) 98.4(2), C(3)-Co(1)-C(14) 104.6-
(2), C(2)-Co(1)-C(14) 137.6(2), C(1)-Co(1)-C(13) 101.7(2), C(3)-Co(1)-C(13) 141.2(2), C(2)-Co(1)-C(13) 99.9(2), C(14)-Co(1)-
C(13) 39.42(19).
Figure 9. Molecular structure and numbering of 13. Selected bond lengths [Å] and bond angles [deg] with SDs: Co(1)-C(2) 1.763(3),
Co(1)-Si(2) 2.2775(12), Co(1)-Co(2) 2.6734(11), Co(2)-C(5) 1.760(3), Co(2)-Si(1) 2.2731(10), Co(3)-C(7) 1.805(4), Co(3)-C(15)
2.000(3), Co(3)-Co(4) 2.4602(11), Co(4)-C(10) 1.803(4), C(2)-Co(1)-C(3) 105.60(15), C(2)-Co(1)-C(1) 109.73(14), C(3)-Co(1)-
C(1) 94.45(14), C(2)-Co(1)-Si(2) 98.96(11), C(1)-Co(1)-Si(2) 150.86(10), C(2)-Co(1)-Si(1) 83.63(10), C(3)-Co(1)-Si(1) 166.30-
(11), C(1)-Co(1)-Si(1) 91.79(10), Si(2)-Co(1)-Si(1) 86.31(4).
with values close to 102°, even smaller than in 13. In Corriu’s
molecules14 the silylene units are always connected by an alkyl
chain tether. Therefore, the distances between the coordinating
silicon (2.69-2.87 Å) atoms are within the range of the longest
reported Si-Si bonds. For the cases of compounds 13 (Si‚‚‚Si
) 3.12 Å) and 14 (Si‚‚‚Si ) 3.05 Å) these distances are longer
but still considerably shorter than the sum of their van der Waals
radii.
The crystal structure of compound 15 was determined previ-
ously at ambient temperature.24b As our structure (Figure 11)
was obtained at 100 K, it is slightly different but in essence
confirms the data from the previous analysis. As a difference
we observed a formal doubling of a cell constant and as a conse-
quence two independent molecules in the asymmetric unit. The
structure consists of a tetrahedron assembled from three cobalt
and one germanium atom. The three cobalt atoms bear three
carbonyl ligands and acquire a distorted octahedral geometry.
The fourth valence of the germanium atom is saturated by a
bond to a cobalt tetracarbonyl unit. The three cobalt atoms of
the tetrahedron form an approximate equilateral triangle with
bond angles close to 60°. The respective angles around ger-
manium are extended to approximately 69°. The Ge-Co bond
lengths within the tetrahedron are between 2.27 and 2.30 Å,
while the exocyclic bond is, at 2.34 Å, somewhat longer. The

4904 Organometallics, Vol. 25, No. 20, 2006
Zirngast et al.
Table 1. Comparison of 29Si and 13C NMR Shifts of Alkynylsilanes and the Respective Dicobalt Hexacarbonyl Complexesa
13
13
alkynyl silane
29Sicentral [ppm]
C
[ppm]
cobalt complex
29Sicentral [ppm]
C
[ppm]
alkynyl
alkynyl
3
4
5
6
7
8
-100.7
-100.5
-90.2
-57.7
-18.2
-36.9
96.8/83.4
3a
4a
5a
6a
7a
8a
9
11a
12a
12b
-67.7
-67.1
-55.3.
-33.8
0.7
90.5/82.9
108.6/88.4
110.2/86.2
109.9/90.2
105.8/94.1
108.1/93.1
105.3/91.1
109.1/90.3
110.2/86.9
111.4/75.8
107.9/71.5
109.1/77.9
106.0/79.8
107.0/80.1
105.9/79.8
109.7/76.1
107.9/72.5
107.9/72.5
-18.0
MeOSiMe2CCPh35
6.9
11
12
-100.5
-80.8
-66.9
-53.3
-53.7
a 29Si: the resonance for the Si atom attached to the alkynyl unit is shown. 13C: the alkynyl carbon shifts: C(R)/C(Si).
Table 2. Selected Bond Lengths and Angles of Cobalt Complexes of Silyl Alkynes
compound
Co-Co [Å]
CtC [Å]
Calkyne-Si [Å]
Calkyne-Co [Å]
R-C-C/C-C-Si [deg]
3a
4a
7a
8a
9
10a
12a
13
2.469(2)
1.310(15)
1.349(5)
1.330(10)
1.345(4)
1.344(5)
1.356(8)
1.340(7)
1.332(4)
1.878(10)
1.873(4)
1.858(7)
1.856(3)
1.843(4)
1.852(6)
1.856(5)
1.857(3)
1.939-2.021
1.966-2.033
1.966-1.998
1.970-1.996
1.951-1.994
1.966-1.992
1.966-2.010
1.989-2.000
-/142.7
142.6/145.1
142.4/148.5
143.3/148.1
140.5/148.1
139.8/147.2
140.6/145.9
146.4/153.2
2.4573(7)
2.4717(13)
2.4798(9)
2.4705(9)
2.4810(12)
2.4776(10)
2.4602(11)
Table 3. Crystallographic Data for Compounds 3a, 4a, 5, 7a, 8a, and 9
3a
4a
5
7a
8a
9
empirical formula
Mw
Co2O6Si4C17H28
558.61
100(2)
Co2O6Si4C23H32
634.7
100(2)
Si3C14H24
276.60
100(2)
Co2O6SiC17H14
460.23
100(2)
Co2O6Si2C19H20
518.39
100(2)
Co4O14Si2C34H28
952.46
100(2)
temperature [K]
size [mm]
cryst syst
space group
a [Å]
0.20 × 0.20 × 0.20 0.40 × 0.20 × 0.20 0.35 × 0.35 × 0.20 0.30 × 0.28 × 0.19 0.36 × 0.30 × 0.26 0.40 × 0.28 × 0.18
orthorhombic
Pbca
12.731(3)
14.117(3)
29.964(6)
90
90
90
5385(2)
8
1.378
monoclinic
P2(1)
9.601(2)
9.874(2)
15.963(3)
90
91.95(3)
90
1512(5)
2
monoclinic
P2(1)/n
14.197(3)
6.021(2)
20.974(4)
90
95.61(3)
90
1784(2)
4
monoclinic
Cc
8.396(2)
14.220(3)
32.546(7)
90
94.61(3)
90
3873(2)
8
monoclinic
P2(1)/n
8.673(2)
11.268(2)
24.248(5)
90
91.57(3)
90
2369(2)
4
triclinic
P1h
7.983(2)
15.895(3)
16.094(3)
101.32(3)
98.75(3)
97.44(3)
1952(2)
2
b [Å]
c [Å]
R [deg]
â [deg]
γ [deg]
V [Å3]
Z
F
calc [g cm-3
]
1.394
1.288
656
1.030
0.248
600
1.578
1.803
1856
1.453
1.531
1056
1.620
1.795
960
absorp coeff [mm-1
F(000)
]
1.436
2304
θ range
2.10 < θ < 22.00
2.12 < θ < 24.00
9722/4668
99.5
4668/1/325
1.08
1.66 < θ < 25.00
12 008/3138
99.9
3138/0/164
1.15
2.51 < θ < 26.37
15 066/7654
99.6
7654/2/476
1.08
1.68 < θ < 26.36
18 272/4822
99.7
4822/0/267
0.92
1.31 < θ < 26.37
15 609/7837
98.5
7837/0/493
0.93
no. of reflns collected/unique 27 703/3298
completeness to θ [%]
no. of data/restraints/params
goodness of fit on F2
99.9
3298/12/275
1.40
final R indices [I > 2σ(I)]
R1)0.098,
wR2)0.187
R1)0.102,
wR2)0.188
R1)0.033,
wR2)0.067
R1)0.035,
wR2)0.068
0.50/-0.25
R1)0.070,
wR2)0.175
R1)0.078,
wR2)0.182
0.81/-0.43
R1)0.061,
wR2)0.123
R1)0.073,
wR2)0.129
1.26/-0.56
R1)0.043,
wR2)0.096
R1)0.067,
wR2)0.104
0.59/-0.36
R1)0.043,
wR2)0.089
R1)0.072,
wR2)0.096
0.74/-0.37
R indices (all data)
largest diff peak/hole [e-/ Å3] 0.63/-0.58
Co-Co bond lengths between 2.59 and 2.62 Å are within the
range of what was observed for other tricobalt group 14
tetrahedral clusters.
the compared structures contained triorganogermyl moieties.
While there are a substantial number of crystal structures con-
taining the tris(trimethylsilyl)germyl unit in the Cambridge
Crystallographic Database, most of these compounds are varia-
tions of the tris(trimethylsilyl)germyl anion with different
counterions. However, comparison of 16 with the few remaining
structures reveals that Si-Ge bond distances of 2.40 Å are
exactly within the range of what to expect.
NMR Spectroscopy. The cobalt complexes have been
investigated for their 29Si and 13C NMR spectroscopic properties
(Table 1). 29Si NMR shifts are usually very sensitive to the
electronic situation. A comparison of the chemical shifts of the
central silicon atoms of tris(trimethylsilyl)silyl compounds
substituted with sp-, sp2-, and sp3-hybridized carbon atoms
shows resonances at ca. -100 ppm for (Me3Si)3Si-CtCR,38
ca. -82 ppm for (Me3Si)3Si-CHdCHR,27 -76.8 ppm for (Me3-
Si)3Si-Ph,28 and ca. -79 ppm for (Me3Si)3Si-CH2CH3.29 For
The crystal structure of 16 (Figure 12) again revealed two
crystallographically independent molecules. Cobalt has a trigonal
bipyramidal coordination sphere with the tris(trimethylsilyl)-
germyl group occupying an apical position. The bond to the
carbonyl group in trans position to the germanium atom is
slightly elongated (1.86 and 1.83 Å) compared to the carbonyls
in equatorial position (1.79-1.80 Å). The equatorial carbonyl
ligands on cobalt are oriented in a staggered conformation with
respect to the trimethylsilyl groups on germanium. A search in
the Cambridge Crystallographic Database (CCDC) for tetra-
valent germanium compounds with germanium connected to
cobalt gave bond distances ranging from 2.29 to 2.48 Å. With
measured values above 2.52 Å compound 16 falls out of this
range. The reason for this is likely due to the fact that most of

Cobalt-Assisted Silicon-Silicon Bond ActiVation
Organometallics, Vol. 25, No. 20, 2006 4905
Table 4. Crystallographic Data for Compounds 10a, 12a, 13, 14, 15, and 16
10a
12a
13
14
15
16
empirical formula
Mw
Co4O13Si2C32H22
906.40
Co2O6Si3C28H28
662.63
Co4O12Si2C23H14
774.24
Co4O12Si4C20H24
804.47
Co4O13GeC13
672.44
Co2O8Ge2Si6C26H54
926.27
temperature [K]
size [mm]
cryst syst
space group
a [Å]
100(2)
100(2)
100(2)
100(2)
100(2)
100(2)
0.36 × 0.30 × 0.26 0.45 × 0.35 × 0.22 0.43 × 0.35 × 0.20 0.40 × 0.28 × 0.18 0.40 × 0.28 × 0.18 0.48 × 0.36 × 0.28
monoclinic
C2/c
28.608(6)
9.055(2)
15.553(3)
90
113.67(3)
90
3690(2)
4
orthorhombic
Pna2(1)
18.228(4)
9.707(2)
35.846(7)
90
90
90
6343(2)
8
1.388
triclinic
P1h
monoclinic
P2(1)/c
14.389(3)
14.801(3)
15.668(3)
90
110.96(3)
90
3116(2)
4
triclinic
P1h
monoclinic
P2(1)
15.840(3)
9.423(2)
15.874(3)
90
111.46(3)
90
2205(8)
2
9.054(2)
10.563(2)
15.355(3)
79.76(3)
78.22(3)
83.52(3)
1410(5)
2
7.978(2)
16.020(3)
16.653(3)
72.76(3)
77.30(3)
78.54(3)
1953(6)
4
b [Å]
c [Å]
R [deg]
â [deg]
γ [deg]
V [Å 3]
Z
F
calc [g cm-3
]
1.632
1.893
1816
1.823
2.457
768
1.715
2.300
1616
2.276
4.890
1288
1.395
2.289
952
absorp coeff [mm-1
F(000)
]
1.196
2720
θ range
1.55 < θ < 25.00
2.17 < θ < 25.00
41 693/11 131
99.9
11131/1/716
1.01
1.97 < θ < 25.00
9951/4867
98.0
4867/0/373
1.09
1.52 < θ < 26.37
24434/6362
99.8
6362/0/369
0.94
1.34 < θ < 26.33
15 627/7836
98.4
7836/0/559
1.09
1.38 < θ < 26.37
17 048/8685
98.7
8685/1/416
1.09
no. of reflns collected/unique 12 832/3255
completeness to θ [%]
no. of data/restraints/params
goodness of fit on F2
99.8
3255/0/233
1.31
final R indices [I > 2σ(I)]
R1)0.071,
R1)0.055,
wR2)0.142
R1)0.059,
wR2)0.145
3.81/-1.93
R1)0.032,
wR2)0.077
R1)0.037,
wR2)0.080
0.55/-0.36
R1)0.040,
wR2)0.083
R1)0.075,
wR2)0.094
0.75/-0.46
R1)0.043,
wR2)0.089
R1)0.072,
wR2)0.096
0.74/-0.37
R1)0.075,
wR2)0.177
R1)0.077,
wR2)0.179
1.51/-1.49
wR2)0.141
R indices (all data)
R1)0.079,
wR2)0.145
largest diff peak/hole [e-/Å3] 0.84/-0.68
compounds 3 and 4 a downfield shift to -67 ppm is observed
upon complexation. This value is in accordance with other
π-organosilyl transition metal complexes.30 It shows that the
silicon interacts with the metal complex and hints at the
electrophilicity observed. Similar downfield shifts are also
observed for the other compounds in this series (Table 1).
Resonances at +0.7 ppm for 7a and at -18.0 ppm for 8a are
close to those for the methyl-substituted compounds tetramethyl-
silane (0.0 ppm) and hexamethyldisilane31 (-19.4 ppm).
Conclusion
The synthesis of the first examples of tris(trimethylsilyl)-
silylacetylene dicobalt hexacarbonyl complexes has revealed
unusual reactivity of these compounds, which is likely due to
silicon-silicon bond activation in the coordination sphere of
cobalt. With a more simple system containing only one Si-Si
bond, chemistry that is related to Corriu’s Si-H bond activation
examples7 could be observed. Reaction of tris(trimethylsilyl)-
The 29Si NMR resonances for the silylene units in compounds
13 and 14 are, as expected, observed at very low field. Shifts
for 13 were found at +214.8 and +191.1 ppm and at +213.4
ppm for the bis(dimethylsilylene) compound 14. These values
are in accordance with data found by Corriu et al., whose shifts
were in the range between +178 and +210 ppm.14b,c For
dimethylsilylene units bridging to different dimetallic systems
very similar resonances have been observed.32,33
13C NMR spectroscopic investigations of alkynes coordinated
to the dicobalt hexacarbonyl fragment have shown that silyl-
substituted alkynes show a different behavior compared to alkyl-
and aryl-substituted compounds.34 While the latter usually
experience a downfield shift upon complexation, the situation
for the phenylsilylalkynes shows an upfield shift for the carbon
attached to silicon while the carbon connected to phenyl is not
affected much.
(27) Markov, J.; Baumgartner, J.; Oehme, H.; Gross, T.; Marschner, C.
In Organosilicon Chemistry VI; Auner, N.; Weis, J., Eds.; Wiley-VCH:
Weinheim, 2005; pp 309-313.
(28) Herzog U.; Roewer G. J. Organomet. Chem. 1997, 544, 217-223.
(29) Marschner, C. Eur. J. Inorg. Chem. 1998, 221-226.
(30) Pannell, K. H.; Bassindale, A. R.; Fitch J. W. J. Organomet. Chem.
1981, 209, C65-C68.
(31) Dubowchik, G. M.; Gottschall, D. W.; Grossman, M. J.; Norton,
R. L.; Yoder, C. H. J. Am. Chem. Soc. 1982, 104, 4211-4214.
(32) Cunningham, J. L.; Duckett, S. B. Dalton Trans. 2005, 744-759.
(33) (a) Takao, T.; Amako, M.-A.; Suzuki, H. Organometallics 2003,
22, 3855-3876. (b) Zhang, Y.; Cervantes-Lee, F.; Pannell, K. H. Orga-
nometallics 2003, 22, 2517-2524.
(34) Happ, B.; Bartik, T.; Zucchi, C.; Rossi, M. C.; Ghelfi, F.; Palyi,
G.; Varadi, G.; Szalontai, G.; Horvath, I. T.; Chiesi-Villa, A.; Guastino C.
Organometallics 1995, 14, 809-819.
Figure 10. Molecular structure and numbering of 14. Of two
crystallographically independent molecules in the asymmetric unit,
only one is shown. Selected bond lengths [Å] and bond angles [deg]
with SDs: Co(1)-C(1) 1.795(4), Co(1)-Si(1) 2.2852(13), Co(1)-
Si(2) 2.2875(12), Co(1)-Co(2) 2.6587(9), Co(2)-Si(2) 2.2839-
(13), Co(2)-Si(1) 2.2841(12), Si(1)-C(7) 1.874(4), O(1)-C(1)
1.132(4), C(3)-Co(1)-C(1) 107.38(17), C(3)-Co(1)-C(2) 109.49-
(16), C(1)-Co(1)-C(2) 96.63(17), C(3)-Co(1)-Si(1) 88.90(12),
C(1)-Co(1)-Si(1) 160.80(12), C(2)-Co(1)-Si(1) 87.09(13), C(3)-
Co(1)-Si(2) 95.27(12), C(1)-Co(1)-Si(2) 84.08(12), C(2)-Co-
(1)-Si(2) 153.62(12),Si(1)-Co(1)-Si(2) 84.34(5).

4906 Organometallics, Vol. 25, No. 20, 2006
Zirngast et al.
Figure 11. Molecular structure and numbering of 15 (only one of two independent molecules shown). Selected bond lengths [Å] and bond
angles [deg] with SDs: Co(1)-C(1) 1.830(6), Co(1)-Ge(1) 2.2746(13), Co(1)-Co(3) 2.5945(13), Co(1)-Co(2) 2.6215(15), Co(2)-Ge-
(1) 2.2899(12), Co(2)-Co(3) 2.6014(12), Co(3)-Ge(1) 2.2999(11), Co(4)-Ge(1) 2.3438(13), O(1)-C(1) 1.126(8), Ge(1)-Co(1)-Co(3)
55.91(4), Ge(1)-Co(1)-Co(2) 55.22(4), Co(3)-Co(1)-Co(2) 59.83(4), Ge(1)-Co(2)-Co(3) 55.66(3), Ge(1)-Co(2)-Co(1) 54.67(4), Co-
(3)-Co(2)-Co(1) 59.57(4), Ge(1)-Co(3)-Co(1) 54.99(3), Ge(1)-Co(3)-Co(2) 55.29(4), Co(1)-Co(3)-Co(2) 60.60(4).
ples of oligosilyl cobalt compounds. Further investigations in
this direction are currently under way.
The reaction of tris(trimethylsilyl)germane with dicobalt octa-
carbonyl led to the cleavage of all germanium-silicon bonds
and the formation of a naked germanium atom connected to
four cobalt carbonyl units. A likely explanation for this reaction
involves several silyl-germylene cobalt complex intermediates.
Experimental Section
General Remarks. All reactions involving air-sensitive com-
pounds were carried out under an atmosphere of dry nitrogen or
argon using either Schlenk techniques or a glovebox. All solvents
besides CDCl3 were dried over sodium/potassium alloy under nitro-
gen and were freshly distilled prior to use. Potassium tert-butoxide
was purchased exclusively from Merck. Dicobalt octacarbonyl was
freshly sublimed prior to use. All other chemicals were obtained
from different suppliers and used without further purification.
1H (300 MHz), 13C (75.4 MHz), and 29Si (59.3 MHz) NMR
spectra were recorded on a Varian INOVA 300 spectrometer.
Samples for 29Si spectra were either dissolved in a deuterated solvent
or measured with a D2O capillary in order to provide an external
lock frequency signal. To compensate for the low isotopic
abundance of 29Si, the INEPT pulse sequence was used for the
amplification of the signal.36 Elemental analysis was carried out
using a Heraeus Vario Elementar. GC analyses were carried out
using a HP 5890 series II (capillary column DB-1HT; 15 m × 0.251
mm; 0.1 µm) with a flame ionization detector or a HP 5971A mass
spectrometer.
Figure 12. Molecular structure and numbering of 16 (only one of
two independent molecules shown). Selected bond lengths [Å] and
bond angles [deg] with SDs: Co(1)-C(1) 1.802(13), Co(1)-Ge-
(1) 2.5292(19), Ge(1)-Si(3) 2.401(3), Si(1)-C(6) 1.836(12), C(1)-
O(1) 1.136(16), Si(1)-Ge(1)-Si(2) 109.04(11), Si(3)-Ge(1)-
Co(1) 110.36(9), Si(1)-Ge(1)-Co(1) 108.44(9), Si(2)-Ge(1)-
Co(1) 110.79(9).
silane with dicobalt octacarbonyl yielded a dicobalt hexa-
carbonyl complex with two bridging dimethylsilylene ligands.
The formation of this compound can be rationalized by the
occurrence of silyl-silylene metal complexes. Such complexes
are well established in the chemistry of numerous metals and
have been discussed also for cobalt.25 The rather facile structural
rearrangement and degradation of the coordinated oligosilyl
residue seem to be responsible for the noticeable lack of exam-
The following starting materials were synthesized according to
literature procedure: tris(trimethylsilyl)silylethyne (3),37 tris(tri-
(35) Denmark, S. E.; Kallemeyn, J. M. J. Org. Chem. 2005, 70, 2839-
2842.
(36) (a) Morris, G. A.; Freeman, R. J. Am. Chem. Soc. 1979, 101, 760-
762. (b) Helmer, B. J.; West, R. Organometallics 1982, 1, 877-879.
(37) Fischer, R.; Frank, D.; Gaderbauer, W.; Kayser, C.; Mechtler, C.;
Baumgartner, J.; Marschner, C. Organometallics 2003, 22, 3723-3731.

Cobalt-Assisted Silicon-Silicon Bond ActiVation
Organometallics, Vol. 25, No. 20, 2006 4907
methylsilyl)silylphenylacetylene (4),38 MgBr2‚Et2O,39 trimethyl-
silylphenylacetylene (7),40 pentamethyldisilylphenylacetylene (8),29,41
1,4-bis[tris(trimethylsilyl)silylethynyl]benzene (11),38 2,2-bis-
(phenylalkynyl)octamethyltrisilane (12),38 tris(trimethylsilyl)silane,42
and tris(trimethylsilyl)germane.43
added dropwise to the deep red solution. The solution turned color-
less, and cooled 2 M H2SO4 (10 mL) was added. The mixture was
extracted several times with diethyl ether and dried over Na2SO4.
The solvent was removed in a vacuum and the remaining oil
subjected to distillation (130 °C, 1 mbar). 6 was obtained as a light
yellow oil (0.131 g, 75%). 29Si NMR (C6D6, δ ppm): -15.6, -57.7.
13C NMR (C6D6, δ ppm): 132.1, 128.4, 128.1, 124.4, 109.9, 90.2,
X-ray Structure Determination. For X-ray structure analyses
the crystals were mounted onto the tip of glass fibers, and data
collection was performed with a Bruker-AXS SMART APEX CCD
diffractometer using graphite-monochromated Mo KR radiation
1
10.7, 3.3, -0.8. H NMR (C6D6, δ ppm): 7.42 (m, 2H), 6.92 (m,
3H), 1.21 (t, 3H, J ) 8 Hz), 0.92 (q, 2H, J ) 8 Hz), 0.28 (s, 18H).
MS: m/z (%) 304(55) M+, 275(20), 261(15), 231(20), 203(70),
187(23), 159(48), 130(69), 102(81), 73(100). Anal. Calcd for
C16H28Si3 (304.65): C 63.08, H 9.26. Found: C 62.87, H 9.21.
2
(0.71073 Å). The data were reduced to Fo and corrected for
absorption effects with SAINT44 and SADABS,45 respectively. The
structures were solved by direct methods and refined by full-matrix
least-squares method (SHELXL97).46 If not noted otherwise, all
non-hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were located in calculated positions
to correspond to standard bond lengths and angles. All diagrams
were drawn with 30% probability thermal ellipsoids, and all
hydrogen atoms were omitted for clarity.
Pentamethyldisilanylphenylacetylene (8). The compound was
prepared as described in ref 41 as a colorless liquid. 29Si NMR
(C6D6, δ ppm): -19.0, -36.9. 13C NMR (C6D6, δ ppm): 138.4,
132.1, 128.4, 123.9, 108.1, 93.1, -2.5, -2.9. 1H NMR (C6D6,
δ ppm): 7.42 (m, 2H), 6.93 (m, 3H), 0.29 (s, 6H), 0.18 (s, 9H).
MS: m/z (%) 232(23) M+, 217(70), 181(5), 159(100), 129 (21),
105(12), 73(65).
Crystallographic data (excluding structure factors) for the
structures of compounds 3a, 4a, 5, 7a, 8a, 9, 10a, 12a, 13, 14, 15,
and 16 reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publica-
tion nos. CCDC-606613 (3a), CCDC-606606 (4a), CCDC-606610
(5), CCDC-606608 (7a), CCDC-606612 (8a), CCDC-606614 (9),
CCDC-606616 (10a), CCDC-606609 (12a), CCDC-606607 (13),
CCDC-606611 (14), CCDC-606615 (15), and CCDC-614323 (16).
Copies of the data can be obtained free of charge on application
via the Internet at: http://www.ccdc.cam.ac.uk/products/csd/
request/.
General Procedure A. A pentane solution of the alkynyl silane
was added dropwise at room temperature to Co2(CO)8 (1 or 1.02
equiv) dissolved in pentane. After stirring for 12 h the solvent was
reduced in a vacuum and the residue recrystallized at -70 °C.
Bis(trimethylsilyl)silylphenylacetylene (5). To a solution of tris-
(trimethylsilyl)silylphenylacetylene (2.86 g, 8.20 mmol) in THF
was added potassium tert-butoxide (0.966 g, 8.61 mmol). After an
immediate color change to deep red the solution was stirred for
3 h and MgBr2‚Et2O (2.12 g, 8.20 mmol) was added. After 2 h the
mixture was poured onto 2 M H2SO4/Et2O, extracted several times
with diethyl ether, and dried over Na2SO4. The solvent was removed
in a vacuum and the remaining oil distilled (140 °C, 1 mbar).
Colorless crystals of 5 were obtained (2.17 g, 96%). 29Si NMR
(C6D6, δ ppm): -14.3, -90.2. 13C NMR (C6D6, δ ppm): 138.4,
132.0, 128.4, 124.4, 110.2, 86.2, 0.5. 1H NMR (C6D6, δ ppm): 7.42
(m, 2H), 6.91 (m, 3H), 4.00 (s, 1H), 0.29 (s, 18H). MS: m/z (%)
276(8) M+, 261(37), 233(8), 217(100), 202(37), 187(81), 159(25),
129(18), 116(36), 102(4), 73(61). Anal. Calcd for C14H24Si3
(276.60): C 60.79, H 8.75. Found: C 60.02, H 8.92.
Preparation of the Dicobalt Hexacarbonyl Complex of Tris-
(trimethylsilyl)silylacetylene (3a). Tris(trimethylsilyl)silylacetylene
(3) (0.200 g, 0.733 mmol) and Co2(CO)8 (0.256 g, 0.748 mmol)
were reacted according to procedure A. Deep red crystals were
obtained after recrystallization (0.371 g, 90%). 29Si NMR (C6D6,
δ ppm): -12.3, -67.7. 13C NMR (C6D6, δ ppm): 201.0, 90.5, 82.9,
1
1.4. H NMR (C6D6, δ ppm): 6.25 (s, 1H), 0.27 (s, 27H). Anal.
Calcd for C17H28Co2O6Si4 (558.61): C 36.55, H 5.05. Found: C
36.71, H 5.12.
Preparation of the Dicobalt Hexacarbonyl Complex of Tris-
(trimethylsilyl)silylphenylacetylene (4a). Tris(trimethylsilyl)silyl-
phenylacetylene (4) (0.100 g, 0.287 mmol) and Co2(CO)8 (0.098
g, 0.287 mmol) were reacted according to procedure A. Deep red
crystals were obtained after recrystallization (0.171 g, 94%). 29Si
NMR (C6D6, δ ppm): -11.9, -67.1. 13C NMR (C6D6, δ ppm):
200.6, 139.2, 129.9, 128.7, 127.9, 111.4, 75.8, 2.4. 1H NMR (C6D6,
δ ppm): 7.52 (m, 2H), 7.05 (m, 2H), 6.96 (m, 1H), 0.28 (s, 27H).
Anal. Calcd for C23H32Co2O6Si4 (634.70): C 43.52, H 5.08.
Found: C 43.28, H 4.99.
Preparation of the Dicobalt Hexacarbonyl Complex of Bis-
(trimethylsilyl)silylphenylacetylene (5a). Bis(trimethylsilyl)silyl-
phenylacetylene (5) (0.100 g, 0.362 mmol) and Co2(CO)8 (0.124 g,
0.362 mmol) were reacted according to procedure A. The reaction
mixture was stirred for 5 h. A red oil was obtained (0.135 g, 95%).
29Si NMR (C6D6, δ ppm): -13.9, -55.3. 13C NMR (C6D6,
1
δ ppm): 200.5, 138.4, 131.9, 129.9, 128.0, 107.9, 71.5, 0.3. H
NMR (C6D6, δ ppm): 7.64 (m, 2H), 7.04 (m, 3H), 4.29 (s, 1H),
0.24 (s, 18H). Anal. Calcd for C20H24Co2O6Si3 (562.52): C 42.70,
H 4.30. Found: C 42.71, H 4.42.
Ethylbis(trimethylsilyl)silylphenylacetylene (6). Tris(trimethyl-
silyl)silylphenylacetylene (0.200 g, 0.573 mmol) was dissolved in
THF, and potassium tert-butoxide (0.065 g, 0.583 mmol) was added.
After 2 h a mixture of THF and ethyl bromide (1 mL each) was
Preparation of the Dicobalt Hexacarbonyl Complex of Ethyl-
bis(trimethylsilyl)silylphenylacetylene (6a). Ethylbis(trimethyl-
silyl)silylphenylacetylene (6) (0.122 g, 0.400 mmol) and Co2(CO)8
(0.136 g, 0.400 mmol) were reacted according to procedure A.
Black crystals were obtained after recrystallization (0.224 g, 95%).
29Si NMR (C6D6, δ ppm): -14.9, -33.8. 13C NMR (C6D6,
δ ppm): 200.6, 138.4, 130.1, 128.8, 128.2, 109.1, 77.9, 10.5, 7.8,
(38) Mechtler, C.; Zirngast, M.; Baumgartner, J.; Marschner, C. Eur. J.
Inorg. Chem. 2004, 3254-3261.
(39) Nu¨tzel, K. Houben-Weyl, Methoden d. Org. Chem.; Mu¨ller, E., Ed.;
Georg Thieme Verlag: Stuttgart, 1973; Vol. 13/2a, p 76.
(40) Benkeser, R. A.; Hickner, R. A. J. Am. Chem. Soc. 1958, 80, 5298-
5300.
1
0.7. H NMR (C6D6, δ ppm): 7.59 (m, 2H), 7.01 (m, 2H), 6.97
(m, 1H), 1.17 (m, 5H), 0.23 (s, 18H). Anal. Calcd for C22H28Co2O6-
Si3 (590.58): C 44.74, H 4.78. Found: C 44.17, H 4.88.
(41) Ishikawa, M.; Sugisawa, H.; Fuchikami, T.; Kumada, M.; Yambe,
T.; Kawakami, H.; Fukui, K.; Ueki, Y.; Shizuka, H. J. Am. Chem. Soc.
1982, 104, 2872-2878.
Preparation of the Dicobalt Hexacarbonyl Complex of Tri-
methylsilylacetylene (7a). Trimethylsilylphenylacetylene (7) (0.200
g, 1.147 mmol) and Co2(CO)8 (0.400 g, 1.170 mmol) were reacted
according to procedure A. Deep red crystals were obtained after
recrystallization (0.525 g, 98%). 29Si NMR (C6D6, δ ppm): 0.7.
13C NMR (C6D6, δ ppm): 200.2, 138.4, 129.9, 129.2, 128.3, 106.0,
(42) Gilman, H.; Smith, C. L. J. Organomet. Chem. 1968, 14, 91-101.
(43) Fischer, J.; Baumgartner, J.; Marschner, C. Organometallics 2005,
24, 1263-1268.
(44) SAINTPLUS: Software Reference Manual, Version 6.45; Bruker-
AXS: Madison, WI, 1997-2003.
(45) Blessing, R. H. Acta Crystallogr. A 1995, 51, 33-38: SADABS,
Version 2.1; Bruker AXS, 1998.
1
79.8, 0.6. H NMR (C6D6, δ ppm): 7.40 (m, 2H), 6.95 (m, 3H),
0.19 (s, 9H). Anal. Calcd for C17H14Co2O6Si (460.24): C 44.36, H
3.07. Found: C 44.24, H 3.01.
(46) Sheldrick, G. M. SHELX97, Programs for Crystal Structure Analysis
(Release 97-2); Universita¨t Go¨ttingen: Go¨ttingen (Germany), 1998.

4908 Organometallics, Vol. 25, No. 20, 2006
Zirngast et al.
Preparation of the Dicobalt Hexacarbonyl Complex of Penta-
methyldisilanylphenylacetylene (8a). 1,1,1,2,2-Pentamethyldi-
silanylphenylacetylene (8) (0.100 g, 0.430 mmol) and Co2(CO)8
(0.147 g, 0.430 mmol) were reacted according to procedure A. The
reaction mixture was stirred for only 4 h. Red crystals were obtained
after recrystallization (0.211 g, 95%). 29Si NMR (C6D6, δ ppm):
-15.8, -18.0. 13C NMR (C6D6, δ ppm): 200.5, 138.3, 130.1, 129.9,
129.1, 107.0, 80.1, -0.6, -1.8. 1H NMR (C6D6, δ ppm): 7.61 (m,
3H), 6.96 (m, 2H), 0.43 (s, 6H), 0.09 (s, 9H). Anal. Calcd for
C19H20Co2O6Si2 (518.40): C 44.02, H 3.89. Found: C 43.70, H
3.84.
Methanolysis of 8a (9). The same amount and procedure as for
8a was used, but after stirring for 4 h methanol (0.017 mL, 0.430
mmol) was added. The conversation was complete after 3 days
(NMR control). The solvent was removed and the remaining solid
recrystallized from pentane at -30 °C. Red crystals (0.156 g, 76%)
were obtained. 29Si NMR (C6D6, δ ppm): 6.9. 13C NMR (C6D6,
δ ppm): 200.2, 138.3, 130.1, 129.9, 128.4, 105.9, 79.8, 50.7, -0.7.
1H NMR (C6D6, δ ppm): 7.68 (m, 2H), 7.02 (m, 3H), 3.32 (s,
3H), 0.37 (s, 6H). Anal. Calcd for C17H14Co2O7Si (476.24): C
42.87, H 2.96. Found: C 42.26, H 3.07.
Preparation of the Tetracobalt Dodecacarbonyl Complex
of 2,2-Bis(phenylethynyl)octamethyltrisilane (12b) and Its Re-
arrangement Product (13). 2,2-Bis(phenylethynyl)octamethyl-
trisilane (12) (0.100 g, 0.265 mmol) and Co2(CO)8 (0.182 g, 0.531
mmol) were reacted according to procedure A for 16 h. NMR
spectroscopic characterization indicated quantitative formation of
12b. 29Si NMR (C6D6, δ ppm): -13.0, -53.7. 13C NMR (C6D6, δ
1
ppm): 200.4, 138.3, 131.8, 130.3, 128.9, 107.9, 72.5, -0.4. H
NMR (C6D6, δ ppm): 7.70 (m, 2H), 7.33 (m, 4H), 7.07 (m, 4H),
0.27 (s, 18H).
After recrystallization from pentane black crystals (0.229 g) were
obtained. Single-crystal structure analysis showed the formation
of 13. Subsequent spectroscopic characterization showed the
complete conversion of 12b to 13. 29Si NMR (C6D6, δ ppm): 214.8,
191.1 (HMBC). 13C NMR (C6D6, δ ppm): 219.1, 200.3, 137.8,
1
130.7, 130.2, 128.4, 107.8, 88.6, 14.5, 12.5, 9.9. H NMR (C6D6,
δ ppm): 7.55 (m, 2H), 6.99 (m, 3H), 1.18 (s, 3H), 0.73 (s, 3H),
0.60 (s, 3H). Anal. Calcd for C23H14Co4O12Si2 (774.25): C 35.68,
H 1.82. Found: C 35.61, H 1.89.
Preparation of µ2-(Me2Si)2Co2(CO)6 (14). To a solution of tris-
(trimethylsilyl)silane (0.586 g, 2.357 mmol) in heptane (3 mL) was
added dropwise Co2(CO)8 (0.806 g, 2.357 mmol) in heptane (5 mL).
After stirring at 50 °C for 8 days complete conversion was observed.
Cooling the solution to -70 °C caused the precipitation of black
crystals (0.210 g, 22%) of 14. 29Si NMR (C6D6, δ ppm): 213.4
(HMBC). 13C NMR (C6D6, δ ppm): 221.1, 11.9. 1H NMR (C6D6,
δ ppm): 0.71 (s, 12H). Anal. Calcd for C10H12Co2O6Si2 (402.24):
C 29.86, H 3.01. Found: C 29.74, H 2.76.
Preparation of µ3-(germylidyncobaltotetracarbonyl)cyclotris-
(cobalt tricarbonyl) (15). To a solution of tris(trimethylsilyl)-
germane (0.230 g, 0.784 mmol) in pentane (2 mL) was added
dropwise Co2(CO)8 (0.268 g, 0.784 mmol) in pentane (4 mL). After
stirring at room temperature for 16 h complete conversion was
observed. Cooling the solution to -70 °C caused the precipitation
of black crystals (0.152 g, 58%) of 15. 13C NMR (C6D6, δ ppm):
201.5, 201.0, 193.5. Anal. Calcd for C13Co4GeO13 (672.47): C
23.22. Found: 23.57.
Preparation of Tris(trimethylsilyl)germyl Cobalt Tetracar-
bonyl (16). A solution of tris(trimethylsilyl)germane (0.200 g, 0.682
mmol) in pentane (3 mL) was added dropwise to Co2(CO)8 (0.117
g, 0.341 mmol) in pentane (3 mL). After stirring at room
temperature for 3 days complete conversion of the germane was
observed. Cooling the solution to -70 °C caused the precipitation
of black (15) and yellow (16) crystals. 29Si NMR (C6D6, δ ppm):
0.0. 13C NMR (C6D6, δ ppm): 200.9, 2.5. 1H NMR (C6D6, δ
ppm): 0.34 (s, 27H). Anal. Calcd for C13H27CoGeO4Si3 (463.15):
C 33.71, H 5.88. Found: C 33.37, H 5.98.
Hydrolysis of 8a and Subsequent Condensation (10 and 10a).
1,1,1,2,2-Pentamethyldisilylphenylacetylene (8) (0.200 g, 0.860
mmol) and Co2(CO)8 (0.294 g, 0.860 mmol) were reacted according
to procedure A. After complete conversion (2.5 h) water (0.031
mL, 1.72 mmol) was added. NMR spectra after 4 h indicated a
mixture of 10 and 10a. After cooling to -30 °C dark red crystals
(0.110 g, 28%) precipitated. A crystal structure analysis showed
the crystals to be compound 10a. NMR analysis of the mother liquor
indicated the presence of 10, which slowly reacted to 10a.
NMR Data. Silanol (10): 29Si NMR (C6D6, δ ppm): 5.1. 13C
NMR (C6D6, δ ppm): 200.1, 138.1, 130.1, 129.2, 128.3, 104.7,
1
76.9, 1.4. H NMR (C6D6, δ ppm): 7.65 (m, 5H), 1.70 (s, 1H),
0.32 (s, 6H).
Siloxane (10a): 29Si NMR (C6D6, δ ppm): -1.5. 13C NMR
(C6D6, δ ppm): 200.1, 138.2, 130.2, 129.1, 128.5, 105.3, 77.6, 2.5.
1H NMR (C6D6, δ ppm): 7.01 (m, 5H), 0.48 (s, 12H). Anal. Calcd
for C32H22Co4O13Si2 (906.41): C 42.40, H 2.45. Found: C 42.07,
H 2.65.
Preparation of the Tetracobalt Dodecacarbonyl Complex of
1,4-Bis[tris(trimethylsilyl)silylethynyl]benzene (11a). 1,4-Bis[tris-
(trimethylsilyl)silylethynyl]benzene (11) (0.073 g, 0.118 mmol) and
Co2(CO)8 (0.081 g, 0.236 mmol) were reacted according to
procedure A. Black crystals were obtained after recrystallization
(0.131 g, 94%). 29Si NMR (C6D6, δ ppm): -11.9, -66.9. 13C NMR
(C6D6 δ ppm): 200.4, 139.3, 130.2, 109.7, 76.1, 2.3. 1H NMR (C6D6
δ ppm): 7.65 (s 4H), 0.30 (s 54H). Anal. Calcd for C40H58Co4O12-
Si8 (1191.30): C 40.33, H 4.91. Found: C 40.07, H 4.97.
Preparation of the Dicobalt Hexacarbonyl Complex of 2,2-
Bis(phenylethynyl)octamethyltrisilane (12a). 2,2-Bis(phenyl-
ethynyl)octamethyltrisilane (12) (0.200 g, 0.531 mmol) and Co2(CO)8
(0.182 g, 0.531 mmol) were reacted according to procedure A for
2 h. Black crystals were obtained after recrystallization (0.324 g,
92%). 29Si NMR (C6D6, δ ppm): -12.3, -53.3. 13C NMR (C6D6,
δ ppm): 200.3, 138.3, 135.7, 131.8, 130.3, 128.9, 128.6, 128.5,
Acknowledgment. This study was supported by the Austrian
Science Foundation (FWF) via the projects P18382-N11 and
Y120. The continued generous supply of chlorosilanes by
Wacker AG Burghausen is gratefully acknowledged. The
authors would also like to thank the reviewers of this paper for
several helpful comments.
1
123.8, 111.7, 107.9, 90.0, 72.5, -0.3. H NMR (C6D6, δ ppm):
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
7.84 (m, 2H), 7.46 (m, 2H), 7.05 (m, 3H), 6.98 (m, 3H), 0.36 (s,
18H). Anal. Calcd for C28H28Co2O6Si3 (662.64): C 50.75, H 4.26.
Found: C 49.98, H 4.37.
OM0604831