Synthesis, structure, and bonding nature of ethynediyl-bridged bis(silylene) dinuclear complexes of tungsten and molybdenum

Article abstract of DOI:10.1021/om200096z

Reactions of Ph₂HSiC≡CSiHPh₂ with 2 equiv of the labile complexes Cp*(CO)₂M(NCMe)Me (1a, M = W; 2, M = Mo; Cp* = η⁵-C₅Me₅) gave the novel CC-bridged dinuclear complexes Cp*(CO)₂M(SiPh ₂)(μ-CC)(SiPh₂)M(CO)₂Cp* (5, M = W; 6, M = Mo), whose molecular structures were determined by X-ray crystallography. The CC bridge interacts with both the metal and silylene centers of two Cp*(CO)₂M(SiPh₂) fragments to form two M-Si-C three-membered-ring skeletons which are linked nearly perpendicularly to each other. The W-Si bond distances of 5 are comparable to those of typical base-stabilized tungsten silylene complexes. The C-C bond distance is much longer than a typical C≡C triple-bond distance and is similar to a typical C=C double-bond distance. The bonding nature and electronic structure of 5 were disclosed by a DFT study of the model complex Cp(CO)₂W(SiH ₂)(μ-CC)(SiH₂)W(CO)₂Cp (5M; Cp = η⁵-C₅H₅). This study demonstrates that 5M is an ethynediyl-bridged bis(silylene) dinuclear tungsten complex which contains various charge transfer (CT) interactions between the tungsten (W), silylene (SiH₂), and ethynediyl (CC), as follows. (1) CTs occur from the lone pairs (φ^CC_lp) and π orbital (φ ^CC_π) of the ethynediyl to the unoccupied d orbital (d^W_unoc) of the W and from the occupied d orbital (d ^W_occ) of the W to the π* orbital (φ^CC_π*) of the ethynediyl. (2) CTs occur from the lone pair orbital (φ^Si_lp) of the silylene to d^W_unoc and from d^W_occ to the empty p orbital (φ^Si_p) of the silylene. (3) CT occurs from φ^CC_π to φ^Si_p, which leads to considerably strong Si-C bonding interactions and a considerably large elongation of the C-C distance. The mixing of φ^CC_π into φ^CC_π* induces π orbital polarization of the CC moiety in one plane and a reverse π orbital polarization in the perpendicular plane. These polarizations in addition to the CT from d ^W_occ to φ^CC_π* also participate in the C-C bond weakening of the ethynediyl. Reaction of 1a with 1 equiv of Ph₂HSiC≡CSiHPh₂ afforded a mixture of the mononuclear acetylide-silylene complex Cp*(CO)₂W(CCSiHPh ₂)(SiPh₂) (7) and dinuclear complex 5. Addition of 1a to the mixture resulted in the conversion of 7 to 5, indicating the intermediacy of 7 in the formation of 5 in the 1:2 reaction of the bis(silyl)acetylene and 1a. A similar 1:1 reaction using molybdenum complex 2 strongly suggests the formation of an equilibrium mixture of the acetylide-silylene complex Cp*(CO)₂Mo(CCSiHPh₂)(SiPh₂) (8) and silapropargyl/alkynylsilyl complex Cp*(CO)₂Mo(η ³-Ph₂SiCCSiHPh₂) (9) in addition to dinuclear complex 6. Mononuclear complexes 8 and 9 were converted to 6 upon reaction with 2. The fluxional behavior of dinuclear complexes 5 and 6 in solution is also described.

Full text of DOI:10.1021/om200096z

ARTICLE
pubs.acs.org/Organometallics
Synthesis, Structure, and Bonding Nature of Ethynediyl-Bridged
Bis(silylene) Dinuclear Complexes of Tungsten and Molybdenum
Hiroyuki Sakaba,*,† Hiroyuki Oike,† Masaaki Kawai,† Masato Takami,† Chizuko Kabuto,† Mausumi Ray,‡,#
Yoshihide Nakao,‡ Hirofumi Sato,‡ and Shigeyoshi Sakaki*,§
†Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
‡Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku,
Kyoto 615-8510, Japan
§Fukui Institute for Fundamental Chemistry, Kyoto University, Nishihiraki-cho, Takano, Sakyo-ku, Kyoto 606-8103, Japan
S Supporting Information
b
ABSTRACT: Reactions of Ph2HSiCtCSiHPh2 with 2 equiv of the labile complexes
Cp*(CO)2M(NCMe)Me (1a, M d W; 2, M d Mo; Cp* d η5-C5Me5) gave the novel
CC-bridged dinuclear complexes Cp*(CO)2M(SiPh2)(μ-CC)(SiPh2)M(CO)2Cp* (5,
M d W; 6, M d Mo), whose molecular structures were determined by X-ray
crystallography. The CC bridge interacts with both the metal and silylene centers of
two Cp*(CO)2M(SiPh2) fragments to form two MꢀSiꢀC three-membered-ring
skeletons which are linked nearly perpendicularly to each other. The WꢀSi bond
distances of 5 are comparable to those of typical base-stabilized tungsten silylene
complexes. The CꢀC bond distance is much longer than a typical CtC triple-bond
distance and is similar to a typical CdC double-bond distance. The bonding nature and
electronic structure of 5 were disclosed by a DFT study of the model complex
Cp(CO)2W(SiH2)(μ-CC)(SiH2)W(CO)2Cp (5M; Cp d η5-C5H5). This study
demonstrates that 5M is an ethynediyl-bridged bis(silylene) dinuclear tungsten
complex which contains various charge transfer (CT) interactions between the tungsten (W), silylene (SiH2), and ethynediyl
(CC), as follows. (1) CTs occur from the lone pairs (jCClp) and π orbital (jCCπ) of the ethynediyl to the unoccupied d orbital
(dWunoc) of the W and from the occupied d orbital (dWocc) of the W to the π* orbital (jCCπ*) of the ethynediyl. (2) CTs occur from
the lone pair orbital (jSilp) of the silylene to dWunoc and from dWocc to the empty p orbital (jSip) of the silylene. (3) CT occurs from
jCC to jSip, which leads to considerably strong SiꢀC bonding interactions and a considerably large elongation of the CꢀC
π
distance. The mixing of jCCπ into jCCπ* induces π orbital polarization of the CC moiety in one plane and a reverse π orbital
polarization in the perpendicular plane. These polarizations in addition to the CT from dWocc to jCCπ* also participate in the CꢀC
bond weakening of the ethynediyl. Reaction of 1a with 1 equiv of Ph2HSiCtCSiHPh2 afforded a mixture of the mononuclear
acetylideꢀsilylene complex Cp*(CO)2W(CCSiHPh2)(SiPh2) (7) and dinuclear complex 5. Addition of 1a to the mixture resulted
in the conversion of 7 to 5, indicating the intermediacy of 7 in the formation of 5 in the 1:2 reaction of the bis(silyl)acetylene and
1a. A similar 1:1 reaction using molybdenum complex 2 strongly suggests the formation of an equilibrium mixture of the
acetylideꢀsilylene complex Cp*(CO)2Mo(CCSiHPh2)(SiPh2) (8) and silapropargyl/alkynylsilyl complex Cp*(CO)2Mo-
(η3-Ph2SiCCSiHPh2) (9) in addition to dinuclear complex 6. Mononuclear complexes 8 and 9 were converted to 6 upon reaction
with 2. The fluxional behavior of dinuclear complexes 5 and 6 in solution is also described.
’ INTRODUCTION
structural features, bonding natures, electronic structures, and re-
action behavior.
The SiꢀH bond activation of hydrosilanes by transition-metal
complexes is a versatile method for producing complexes with
transition-metalꢀsilicon bonds.1 Recently, this method has been
widely applied for synthesizing a variety of base-stabilized2ꢀ6 and
base-free7ꢀ13 transition-metal silylene complexes. Silylene com-
plexes14 are interesting research targets in coordination chem-
istry, organometallic chemistry, synthetic chemistry, and theoretical
chemistry because of their interesting bonding natures, electronic
structures, and important roles as intermediates in various metal-
catalyzed transformation reactions of organosilicon compounds.
In this regard, silylene complexes have been investigated in many
experimental2ꢀ16 and theoretical works17,18 to understand their
In the course of our synthetic studies of tungsten and molyb-
denum complexes with novel silicon-containing ligands using the
labile complexes (η5-C5Me4R)(CO)2M(NCMe)Me (1a, M d
W, R d Me; 1b, M d W, R d Et; 2, M d Mo, R d Me) and
hydrosilanes,19 the unique tungsten silylene complexes (η5-C5-
Me4R)(CO)2W(CCtBu)(SiPh2) (3a, R d Me; 3b, R d Et) were
recently obtained via SiꢀH bond activation of Ph2HSiCtCtBu
by 1a,b(Scheme1).19b The novel bonding nature of these complexes
Received: February 2, 2011
Published: August 10, 2011
r
2011 American Chemical Society
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Organometallics
ARTICLE
Scheme 1
was revealed by a theoretical study of the model complex Cp-
(CO)2W(CCH)(SiH2) (3M, Cp d η5-C5H5), as follows. It is
an acetylideꢀsilylene complex which involves two kinds of
charge transfer (CT) interactions between the silylene and
acetylide moieties; one is the CT from the lone pair orbital of
the silylene to the π* orbital of the acetylide, and the other is the
CT from the π orbital of the acetylide to the empty p orbital of
the silylene (Scheme 1).18a These interactions demonstrate an
intriguing relationship to the reaction of silylene with acetylene
to form silacyclopropene, and the (SiH2)(CCH) moiety of 3M
can be viewed as an intermediate species trapped by the W center
in the silacyclopropene formation reaction.20
A subsequent theoretical study on the relative stability of the
acetylideꢀsilylene complex Cp(CO)2M(CCH)(SiH2) (M d W,
Mo) and its structural isomer, the silapropargyl/alkynylsilyl
complex Cp(CO)2M(η3-H2SiCCH), showed that the tungsten
center favors the acetylideꢀsilylene complex, whereas the mo-
lybdenum center favors the silapropargyl/alkynylsilyl complex.18c
This theoretical prediction about the molybdenum system was
recently realized by the successful synthesis of Cp*(CO)2Mo-
(η3-Ph2SiCCtBu) (4) by reacting 2 with Ph2HSiCtCtBu
(Scheme 1).19c In the acetylideꢀsilylene and silapropargyl/
alkynylsilyl complexes, one of the two π systems in the acetylide
and alkynyl moieties is involved in bonding interactions. In
considering the availability of two π systems in the acetylide,
we were interested in a μ-ethynediyl ligand. This electronically
flexible C2 ligand can bridge two metal fragments using two π
systems in several ways, as shown below, and may be used to form
a novel dinuclear framework composed of metal, silicon, and
carbon atoms in combination with two metal and two silicon
centers.
Ethynediyl-bridged dinuclear complexes exhibit characteristic
geometries, bonding natures, electronic structures, and physico-
chemical properties.21ꢀ42 Also, they are building blocks for the
synthesis of bare carbon chains stabilized by transition-metal
complexes.21a,b,41 In this regard, various ethynediyl-bridged di-
nuclear complexes have been synthesized and investigated in
many experimental21ꢀ40 and theoretical works.22b,38,41,42 Three
possible bonding modes have been proposed so far: namely,
the acetylenic form LnMꢀCtCꢀMLn, the cumulenic form
LnMdCdCdMLn, and the dimetalla-1,3-butadiyne form
LnMtCꢀCtMLn.21b,38,41 Among these three valence bond
descriptions, most of the synthesized complexes contain the
acetylenic structure.22ꢀ32 The cumulenic structure has been found
in a few titanium,31,33 tantalum,34 ruthenium,32 and manganese35
complexes, and the dimetalla-1,3-butadiyne structure is limited
to tungsten,36ꢀ39 molybdenum,40 and manganese35 complexes.
Here, we examined the reaction of Ph2HSiCtCSiHPh2 with 2
equiv of 1a or 2 and found the formation of the ethynediyl-
bridged dinuclear bis(silylene) complexes Cp*(CO)2M(SiPh2)-
(μ-CC)(SiPh2)M(CO)2Cp* (5, M d W; 6, M d Mo). Our
present study provides a unique opportunity to investigate the
interactions of two π systems of the ethynediyl with two metal
and two silylene centers. We report their synthesis, solid-state
structure, dynamic behavior in solution, and formation mecha-
nism. A detailed theoretical study on the bonding nature and
electronic structure of Cp(CO)2W(SiH2)(μ-CC)(SiH2)W(CO)2-
Cp (5M), a model complex of 5, is also described.
’ RESULTS AND DISCUSSION
1. Synthesis and Structure of Cp*(CO)2M(SiPh2)(μ-CC)-
(SiPh2)M(CO)2Cp* (5, M d W; 6, M d Mo). The reaction of
Ph2HSiCtCSiHPh2 with 2 equiv of the acetonitrile complex
Cp*(CO)2W(NCMe)Me (1a) in toluene occurred at room
temperature to give the dinuclear complex Cp*(CO)2W(SiPh2)-
(μ-CC)(SiPh2)W(CO)2Cp* (5) as an air-sensitive orange solid
in 55% isolated yield (Scheme 2).43 The liberation of methane
1
and acetonitrile was confirmed by H NMR comparison with
their authentic samples in an NMR tube reaction. A similar
reaction using the molybdenum complex Cp*(CO)2Mo(NCMe)-
Me (2) afforded the corresponding dimolybdenum complex 6 in
51% yield.
Single crystals of 5 and 6 were grown from toluene/hexane
and toluene/pentane solutions, respectively, and subjected to
X-ray crystal analysis. In the tungsten complex 5 (Figure 1), two
Cp*(CO)2W(SiPh2) fragments are linked by the ethynediyl
bridge, which interacts with both of the tungsten and silicon
centers, and two WꢀSiꢀC three-membered-ring skeletons are
arranged almost perpendicularly to each other, as shown by
the dihedral angle Si1ꢀC1ꢀC2ꢀSi2 = 88.0(3)°. Each tungsten
center adopts a highly distorted four-legged piano-stool geome-
try with acute SiꢀWꢀC angles of Si1ꢀW1ꢀC1 (47.55(12)°),
Si1ꢀW1ꢀC3 (63.77(15)°), Si2ꢀW2ꢀC2 (48.35(13)°), and
Si2ꢀW2ꢀC6 (61.94(14)°). The WꢀSi bond distances
(W1ꢀSi1 d 2.4801(14) Å, W2ꢀSi2 d 2.4773(13) Å) in 5
are considerably shorter than that (2.567(2) Å) in the mono-
nuclear acetylideꢀsilylene complex 3b19b and are in the range of
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ARTICLE
Scheme 2
WꢀSi bond distances (2.45ꢀ2.51 Å) in base-stabilized silylene
tungsten complexes,2c,3a,15a suggesting the increased partial
double-bond character of the WꢀSi bond in 5 compared with
that in 3b. The increased silylene character is also demonstrated
by the sum of the three XꢀSiꢀY angles (X, Y d W and C(ipso)
of the two phenyl groups on Si): 356.1° about Si1 and 356.7°
about Si2. These values are larger than the corresponding angle
(348.3°) in 3b and close to the expected value (360°) for sp2
hybridization. The WꢀC(ethynediyl) bond distances (W1ꢀC1
d 2.089(5) Å, W2ꢀC2 d 2.068(4) Å) are in the range of WꢀC
(alkynyl) bond distances (2.05ꢀ2.09 Å) in di- and polynuclear
complexes containing a Cp*(CO)2W(μ-η1:η2-CCR) fragment44,45
and are somewhat longer than the WꢀCCtBu bond distance
(2.050(7) Å) in 3b. Notably, the C1ꢀC2 bond distance of
1.343(6) Å is significantly elongated from the CꢀC triple-bond
silylene complexes Cp*(CO)2M(SiMes2)(SiMe3) (M d W,
Mo), it is interesting to note the somewhat large differences
between the WꢀSi and MoꢀSi bond distances and the opposite
tendency in the variation of the MꢀSi and MꢀC(ethynediyl)
bond distances described above. These observations suggest that
the MꢀC(ethynediyl) interaction seems to be balanced with the
strength of the metalꢀsilylene interaction. For dinuclear com-
plexes 5 and 6, the possible contribution of several resonance
structures is conceivable: bis(silylene)-type structure A, bis-
(carbene)-type structure B, 1,4-disilabutadienyl-bridged struc-
ture C,47 and 1,4-disilabutatriene-bridged structure D48,49
(Scheme 2). Considering the relatively high silylene character
of 5 and 6, A is suggested to be a major contributor. However, the
double-bond-like distance of the C1ꢀC2 bond in 5 and 6 may
imply some interesting contributions of BꢀD. A detailed discus-
sion on the bonding nature and electronic structure of a model
complex of 5 based on the DFT calculations is described below.
2. Mechanistic Investigation of the Formation of Dinuc-
lear Complexes 5 and 6. To obtain mechanistic information on
the formation of dinuclear complex 5, the 1:1 reaction of 1a with
Ph2HSiCtCSiHPh2 was investigated. Toluene-d8 was vacuum-
transferred into an NMR tube containing an equimolar mixture
of 1a and the bis(silyl)acetylene at ꢀ196 °C, and the mixture was
warmed to room temperature. When the 1H NMR spectrum was
measured after 5 min, a new set of Cp* and SiH signals ascribed to
the mononuclear complex Cp*(CO)2W(CCSiHPh2)(SiPh2)
(7) were observed at 1.69 and 5.41 ppm, respectively, in addition
to the signals of 5 (7:5 = 76:24) (Scheme 3). On a preparative
scale, a relatively pure, orange solid of 7 was isolated, and the
structure was characterized on the basis of variable-temperature
NMR spectra in THF-d8. The 29Si{1H} NMR spectrum at room
temperature showed a single signal at ꢀ39.2 ppm due to the
SiHPh2 group, while the spectrum at ꢀ70 °C exhibited two
signals at ꢀ39.0 and ꢀ46.7 (1JWSi d 41 Hz) ppm. Assignment of
46
distance of 1.208(5) Å in Ph2HSiCtCSiHPh2 to a typical
CꢀC double-bond distance.
The overall structural features of the molybdenum analogue 6
(Figure 2) resembles well those of 5, as shown by its character-
istic angles: the dihedral angle Si1ꢀC1ꢀC2ꢀSi2 = 87.6(5)°, the
sum of the three XꢀSiꢀY angles (X, Y d Mo and C(ipso) of the
two phenyl groups on Si) of 356.2° about Si1 and 356.9° about Si2,
and acute SiꢀMoꢀC angles of Si1ꢀMo1ꢀC1 (47.86(17)°),
Si1ꢀMo1ꢀC3 (63.2(3)°), Si2ꢀMo2ꢀC2 (48.29(16)°), and
Si2ꢀMo2ꢀC6 (61.8(2)°). A comparison of the bond distances
of the MꢀSiꢀC three-membered-ring skeletons between 5 and
6 revealed a contrasting difference in the MꢀSi and MꢀC bond
distances. The MoꢀSi bond distances (Mo1ꢀSi1 d 2.4646(19)
Å, Mo2ꢀSi2 d 2.4562(19) Å) in 6, which are comparable to the
MoꢀSi bond distances (2.4439(14)ꢀ2.5008(9) Å) of base-
stabilized silylene molybdenum complexes with a Cp(/)
-
(CO)2Mo fragment,2a,8e are 0.015ꢀ0.02 Å shorter than the
WꢀSi bond distances (W1ꢀSi1 d 2.4801(14) Å, W2ꢀSi2 d
2.4773(13) Å) in 5, whereas the MoꢀC(ethynediyl) bond
distances (Mo1ꢀC1 d 2.120(6) Å, Mo2ꢀC2 d 2.089(6) Å)
in 6 are 0.03ꢀ0.02 Å longer than the WꢀC(ethynediyl) bond
distances (W1ꢀC1 d 2.089(5) Å, W2ꢀC2 d 2.068(4) Å) in 5.
Though no such clear differences are found in the bond distances
of Si1ꢀC1 (1.876(5) Å for 5 vs 1.886(7) Å for 6) and Si2ꢀC2
(1.898(5) Å for 5 vs 1.889(6) Å for 6) considering the standard
deviations, these SiꢀC bond distances are elongated consider-
ably compared with the SiꢀC(sp) bond distance (1.833(3) Å) in
Ph2HSiCtCSiHPh246 and are longer than or comparable to the
SiꢀC(phenyl) bond distances (1.863(7)ꢀ1.877(5) Å) in 5 and 6.
Given the small difference between the bond distances of WdSi
(2.3850(12) Å)8a and ModSi (2.3872(7) Å)8e in the base-free
1
29
the former signal to SiHPh2 is supported by its Hꢀ Si cor-
29
relation with a SiH signal at 4.97 ppm in the 1Hꢀ Si HMQC
spectrum, and the latter signal was assigned to WSiPh2. This tem-
perature-dependent observation is probably due to the inter-
conversion between 7 and a trace amount of its silapropargyl/
alkynylsilyl isomer; see below for the corresponding molybde-
13
num system. In the 1Hꢀ C HMBC spectrum at ꢀ70 °C, two
signals showing correlations with the SiH signal were observed at
186.5 and 137.7 ppm and assigned to acetylide carbon atoms.
These characteristic 29Si and 13C signals of 7 (29Si, ꢀ46.7 (1JWSi d
41 Hz) ppm; 13C, 186.5 and 137.7 ppm) are close to those of the
SiCC framework (29Si, ꢀ40.9 (1JWSi d 41 Hz) ppm; 13C, 178.9
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ARTICLE
Figure 2. ORTEP drawings of (A) the whole structure and (B) the two
Cp*(CO)2Mo(SiPh2)C fragments of 6. Thermal ellipsoids are drawn at
the 50% probability level, and all hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (deg): Mo1ꢀSi1 = 2.4646(19),
Mo1ꢀC1 = 2.120(6), Mo2ꢀSi2 = 2.4562(19), Mo2ꢀC2 = 2.089(6),
Si1ꢀC1 = 1.886(7), Si1ꢀC7 = 1.864(7), Si1ꢀC13 = 1.863(7), Si2ꢀC2
= 1.889(6), Si2ꢀC19 = 1.872(7), Si2ꢀC25 = 1.872(7), C1ꢀC2 =
1.322(9); Si1ꢀMo1ꢀC1 = 47.86(17), Si2ꢀMo2ꢀC2 = 48.29(16),
Mo1ꢀSi1ꢀC1 = 56.46(19), Mo1ꢀSi1ꢀC7 = 122.1(2), Mo1ꢀSi1ꢀ
C13 = 124.7(3), C7ꢀSi1ꢀC13 = 109.4(3), Mo2ꢀSi2ꢀC2 = 55.63(19),
Mo2ꢀSi2ꢀC19 = 126.1(3), Mo2ꢀSi2ꢀC25 = 121.5(2), C19ꢀSi2ꢀ
C25 = 109.3(3), Mo1ꢀC1ꢀSi1 = 75.7(3), Mo1ꢀC1ꢀC2 = 151.2(5),
Mo2ꢀC2ꢀSi2 = 76.1(3), Mo2ꢀC2ꢀC1 = 164.6(5).
Figure 1. ORTEP drawings of (A) the whole structure and (B) the two
Cp*(CO)2W(SiPh2)C fragments of 5. Thermal ellipsoids are drawn at
the 50% probability level, and all hydrogen atoms are omitted for clarity.
Selected bond lengths (Å) and angles (deg): W1ꢀSi1 = 2.4801(14),
W1ꢀC1 = 2.089(5), W2ꢀSi2 = 2.4773(13), W2ꢀC2 = 2.068(4), Si1ꢀ
C1 = 1.876(5), Si1ꢀC7 = 1.864(5), Si1ꢀC13 = 1.877(5), Si2ꢀC2 =
1.898(5), Si2ꢀC19 = 1.865(5), Si2ꢀC25 = 1.867(5), C1ꢀC2 =
1.343(6); Si1ꢀW1ꢀC1 = 47.55(12), Si2ꢀW2ꢀC2 = 48.35(13),
W1ꢀSi1ꢀC1 = 55.23(15), W1ꢀSi1ꢀC7 = 122.36(16), W1ꢀSi1ꢀ
C13 = 124.17(18), C7ꢀSi1ꢀC13 = 109.6(2), W2ꢀSi2ꢀC2 =
54.49(13), W2ꢀSi2ꢀC19 = 125.84(16), W2ꢀSi2ꢀC25 = 121.44(14),
C19ꢀSi2ꢀC25 = 109.4(2), W1ꢀC1ꢀSi1 = 77.22(18), W1ꢀC1ꢀC2 =
151.1(3), W2ꢀC2ꢀSi2 = 77.16(17), W2ꢀC2ꢀC1 = 165.1(4).
cooling to ꢀ80 °C: 1.76 and 4.90 ppm for the major component
and 1.62 and 5.80 ppm for the minor component in a ratio of
55:45. The SiH region of the variable-temperature spectra is
shown in Figure 3. In the 29Si{1H} NMR spectrum, only a single
signal appeared at ꢀ38.0 ppm at room temperature, whereas two
sets of signals were observed at ꢀ90 °C: ꢀ39.0 (SiHPh2) and
ꢀ14.4 (MoSiPh2) ppm for the major component and ꢀ24.0
(SiHPh2) and 55.2 (MoSiPh2) ppm for the minor component.
and 147.3 ppm) in the acetylideꢀsilylene tungsten complex
Cp*(CO)2W(CCSiMe3)(SiPh2).19d When the 76:24 mixture of
7 and 5 was treated with an amount of 1a equimolar with the
amount of 7 in toluene-d8, 7 was consumed to give 5 in 79% yield
based on 7, thereby demonstrating the intermediacy of 7 in the
formation of 5 from the bis(silyl)acetylene and 2 equiv of 1a.
The 1:1 reaction using the molybdenum analogue 2 led to
intriguing observations (Scheme 3). Similar to the case for the
reaction with 1a described above, the room-temperature 1H NMR
spectrum of the reaction mixture in toluene-d8 contained a set of
Cp* and SiH signals at 1.64 and 5.44 ppm in addition to signals
attributed to dinuclear complex 6 in a composition ratio of 82:18.
From a preparative reaction, a yellow solid was isolated, and its
room-temperature 1H NMR spectrum showed the same Cp* and SiH
signals as above. When variable-temperature 1H NMR spectra were
recorded in THF-d8, the Cp* and SiH signals (1.73 and 5.20 ppm at
room temperature) decoalesced into two sets of signals upon
1
29
The assignment of the SiHPh2 signals was based on Hꢀ Si
correlations in the 1Hꢀ Si HMQC spectrum. Additional struc-
29
13
tural information was obtained by the 1Hꢀ C HMBC spectrum
at ꢀ90 °C, which showed signals at 190.5 and 143.7 ppm
that correlated with the major SiH signal and those at 90.9 and
103.0 ppm that correlated with the minor SiH signal. The char-
acteristic 1H, 29Si, and 13C signals of the major component (1H,
4.90 ppm; 29Si, ꢀ14.4 ppm; 13C, 190.5 and 143.7 ppm) were
similar to those of 7 (1H, 4.97 ppm; 29Si, ꢀ46.7 ppm; 13C, 186.5
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Scheme 3
Figure 3. SiH region of the variable-temperature 1H NMR spectra of 8
and 9 in THF-d8.
Figure 4. Variable-temperature 1H NMR spectra of 6 in CD2Cl2.
and 137.7 ppm), taking into account the difference in metal
centers. The 29Si and 13C signals of the minor component (29Si,
55.2 ppm; 13C, 90.9 and 103.0 ppm) were relatively close to
those of the silapropargyl/alkynylsilyl complex Cp*(CO)2Mo-
(η3-Ph2SiCCiPr) (29Si, 46.2 ppm; 13C, 51.4 and 129.0 ppm).19c
Relatively large differences in the 13C chemical shifts were
ascribed to the different substituents (SiHPh2 and iPr) at the alkynyl
carbon atom. These observations strongly suggest the intercon-
version between the acetylideꢀsilylene complex Cp*(CO)2Mo-
(CCSiHPh2)(SiPh2) (8, major) and silapropargyl/alkynylsilyl
complex Cp*(CO)2Mo(η3-Ph2SiCCSiHPh2) (9, minor) for the
dynamic behavior, and it is consistent with the aforementioned
theoretical finding that the molybdenum center favors the silapro-
pargyl/alkynylsilyl complex more than does the tungsten center.18c
The observation of a single 29Si resonance at room temperature is
explained by the chemical shift differences between the SiHPh2
and SiPh2 signals. In fast interconversion on the NMR time scale,
a small chemical shift difference between the SiHPh2 signals
(ꢀ39.0 ppm for 8 and ꢀ24.0 ppm for 9) leads to a sharp,
coalesced signal. In contrast, a large difference between the SiPh2
signals (ꢀ14.4 ppm for 8 and 55.2 ppm for 9) causes significant
signal broadening and results in no detectable signals. The
reaction of the mixture of 8 and 9 with 2 afforded the dinuclear
complex 6 in quantitative yield (Scheme 3). Although the
differences in reactivity between 8 and 9 toward 2 are not clear,
the formation of 6 is suggested to occur via SiꢀH bond activation
of 8, which would require less steric hindrance around the SiHPh2
group and a smaller structural change in the conversion to 6 than
would be expected in 9.
3. Dynamic Behavior of Dinuclear Complexes 5 and 6.
Despite the asymmetric solid-state structures of 5 and 6, when
their H NMR spectra were measured at room temperature, a
1
single Cp* signal was observed in each spectrum, suggesting the
1
existence of dynamic processes. The variable-temperature H
NMR spectra of 6 in CD2Cl2 showed interesting spectral changes
(Figure 4). When the temperature was lowered to ꢀ90 °C, the
sharp Cp* signal broadened and decoalesced into two signals at
1.69 and 1.58 ppm, and broad aromatic signals became sharp and
well-resolved. Similar behavior was observed in the 13C{1H}
NMR spectra (Figure 5A,B); a single C5Me5 signal was split into
two signals at 10.3 and 9.9 ppm at ꢀ90 °C. In accord with the
decoalescence of the Cp* signals in the 1H and 13C NMR spectra,
two 29Si signals were observed at 5.3 and ꢀ5.0 ppm at ꢀ90 °C,
whereas no signals were detected at room temperature, probably
due to their significant broadening. For the aromatic carbon
signals, only one set of broad signals was observed at 136.7, 135.4
(v br), 130.4, and 127.8 ppm in the room-temperature 13C{1H}
NMR spectrum (Figure 5A), whereas approximately 13 signals
appeared at ꢀ90 °C (Figure 5B). In addition, the room-tempera-
ture spectrum showed two broad signals at 240.1 and 230.2 ppm,
which were assigned to the ethynediyl and CO ligands, respectively
(Figure 5A). At ꢀ90 °C, the former decoalesced into two signals
at 241.2 and 239.8 ppm and the latter split into four signals at
231.5, 230.6, 228.8, and 226.6 ppm (Figure 5B). Assignment of
the four signals to the CO ligands was confirmed by the observa-
tion of their increased intensities compared to those of the signals
at 241.2 and 239.8 ppm in the 13C{1H} NMR spectrum of
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Scheme 4
two CO signals at 223.5 and 222.0 ppm and two sets of phenyl
carbon signals at 137.9, 137.2, 136.3, 134.3, 130.7, 129.8, 128.2,
and 127.4 ppm (Figure 6A), in contrast to the single CO signal
and one set of phenyl carbon signals in the corresponding spec-
trum of 6 (Figure 5A). This observation indicates the possibility
of another dynamic process that operates faster in 6 at room
temperature. Cisꢀcis interconversion by pseudorotation52 around
the metal centers is a likely dynamic process in 5 and 6, which are
composed of two four-legged piano-stool type fragments. This
process may cause stereochemical inversion (site exchange of the
silylene and ethynediyl ligands) at the metal centers to lead to
their similar dynamic behavior, and another process would be
required to explain the difference observed in their room-tem-
perature 13C{1H} NMR spectra. Although some changes in their
coordination mode might be related to this difference, as sug-
gested from the contrasting variable-temperature observations
for mononuclear tungsten complex 7 and molybdenum com-
plexes 8 and 9, more detailed studies are necessary to elucidate
the entire mechanism, including investigation of intramolecular
dynamic processes of closely related mononuclear acetylideꢀ
silylene and silapropargyl/alkynylsilyl complexes.
Figure 5. 13C{1H} NMR spectra of 6 in CD2Cl2 (A) at 27 °C and (B)
ꢀ90 °C and (C) the low-field region of 6* at ꢀ90 °C. The asterisks mark
the signals of toluene contained as a crystal solvent.
Figure 6. 13C{1H} NMR spectra of 5 in CD2Cl2 (A) at 27 °C and (B) at
ꢀ90 °C. The asterisks mark the signals of toluene contained as a crystal
solvent.
4. Bonding Nature and Electronic Structure of the Ethy-
nediyl-Bridged Bis(silylene) Dinuclear Tungsten Complex
Cp(CO)2W(SiH2)(μ-CC)(SiH2)W(CO)2Cp (5M). 4.1. Optimized
Geometries of 5M, Its Isomer Cp(CO)2(SiH2)WꢀCtCꢀW(SiH2)-
(CO)2Cp (10) without the Si---C Interaction, the Dicarbido-Bridged
Dinuclear Tungsten Complex (MeO)3WtCꢀCtW(OMe)3 (11),
and the Tungsten Carbyne Complex Cp(CO)2WtCH (12). The
geometries of the CC and SiPh2 moieties of 5 are considerably
different from those of 3b, as described above. Thus, it is worth
investigating the bonding nature of 5. (i) Which bonding mode
of the acetylenic form WꢀCtCꢀW, the cumulenic form
WdCdCdW, and the dimetalla-1,3-butadiyne form WtCꢀ
CtW is involved in 5? (ii) Can the SiꢀCꢀCꢀSi moiety of 5 be
characterized as the deprotonated 1,4-disilabutadiene [Ph2SidCꢀ
CdSiPh2]2ꢀ or the 1,4-disilabutatriene Ph2SidCdCdSiPh2 (C
or D in Scheme 2)? (iii) Is a bonding interaction formed between
the Si and C atoms? In this section, we theoretically investigated
Cp(CO)2W(SiH2)(μ-CC)(SiH2)W(CO)2Cp (5M, Cp d η5-C5-
H5) with the DFT method, where 5M was employed as a model of 5.
For a clear understanding of the bonding nature of 5M, we
also theoretically investigated the model ethynediyl-bridged bis-
(silylene) dinuclear tungsten complex Cp(CO)2(SiH2)Wꢀ
CtCꢀW(SiH2)(CO)2Cp (10), in which the CC and SiH2 groups
take positions opposite to each other; in other words, no interaction
exists between them (Scheme 4). The typical dicarbido-bridged
13CO-enriched 6* (Figure 5C). Complex 6* was prepared by the
reaction of 13CO-enriched 2* with Ph2HSiCtCSiHPh2. Thus,
the NMR spectra corresponding to the solid-state structure of 6
were obtained by low-temperature measurements.
1
In the variable-temperature H NMR spectra of 5, consider-
able broadening of the Cp* signal occurred upon cooling to
ꢀ90 °C, although decoalescence was not observed (see the
Supporting Information, Figures S1 and S2). On the other hand,
the variable-temperature 13C{1H} NMR spectra showed decoa-
lescence of the C5Me5 and ethynediyl signals (Figure 6); two
decoalesced signals were observed at 10.2 and 10.0 ppm for the
former and 235.2 and 231.6 ppm for the latter at ꢀ90 °C
(Figure 6B), similar to the spectrum of 6 (Figure 5B). Three
CO signals were observed at 223.6, 221.5, and 220.7 ppm with a
relative intensity of 2:1:1, and the first signal was attributable to
the coincidental overlap of two signals. The number of aromatic
carbon signals was increased, and they were considerably broad
compared to those at room temperature. The low-temperature
13C{1H} NMR spectrum of 5 resembled that of 6, although
differences in the signal widths were observed; the sharper, de-
coalesced signals for 6 suggest a slower dynamic process at
ꢀ90 °C. However, the room-temperature spectrum of 5 showed
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Figure 7. Optimized geometries (determined by the DFT(B3PW91)/BS-I method) of (A) Cp(CO)2W(SiH2)(μ-CC)(SiH2)W(CO)2Cp (5M), (B)
Cp(CO)2(SiH2)WꢀCtCꢀW(SiH2)(CO)2Cp (10), (C) (MeO)3WtCꢀCtW(OMe)3 (11), (D) Cp(CO)2WtCH (12), and (E) Cp(CO)2W-
(CCH)(SiH2) (3M). Bond lengths are given in Å, along with the Wiberg bond indices in parentheses (from DFT(B3PW91)/BS-II NBO calculations).
3M was reported in ref 18a.
Table 1. SelectedOptimizedParametersa of Cp(CO)2W(SiH2)-
dinuclear tungsten complex (MeO)3WtCꢀCtW(OMe)3 (11)
(μ-CC)(SiH2)W(CO)2Cp (5M), Cp(CO)2(SiH2)WꢀCtCꢀ
and the mononuclear tungsten carbyne complex Cp(CO)2W-
W(SiH2)(CO)2Cp (10), (MeO)3WtCꢀCtW(OMe)3 (11),
tCH (12) were also investigated here for comparison of 5M
Cp(CO)2WtCH (12), and Cp(CO)2W(CCH)(SiH2) (3M)
and Experimental Parameters of Cp*(CO)2W(SiPh2)
(μ-CC)(SiPh2)W(CO)2Cp* (5)
with 11 and 12 (Scheme 4). Complex 10 is not unusual, because
the similar ethynediyl-bridged dinuclear tungsten complex Cp-
(CO)3WꢀCtCꢀW(CO)3Cp was experimentally isolated;26
note that the silylene may be viewed as being similar to a CO
ligand, since the silylene has a lone pair and an empty p orbital as
5M
5
10
11
12
3Mb
W1ꢀSi1
W2ꢀSi2
W1ꢀC1
W2ꢀC2
Si1ꢀC1
Si2ꢀC2
Si1ꢀC2
Si2ꢀC1
C1ꢀC2
2.485 2.4801(14) 2.387
2.492 2.4773(13) 2.387
2.616
does the CO. Complexes 11 and 12 are models of experimentally
isolated (tBuO)3WtCꢀCtW(OtBu)3
and CpL2WtCR
36ꢀ38
(L d CO, P(OMe)3 and R d Ph, Me),53respectively.
2.043 2.089(5)
2.034 2.068(4)
1.881 1.876(5)
1.890 1.898(5)
2.908
2.104 1.781 1.804 2.014
2.105 1.781
The optimized geometry of 5M (Figure 7) agrees well with the
experimental geometry of 5, as shown in Table 1. The WꢀSi
distance in 5M is somewhat shorter than that of the mononuclear
tungsten acetylideꢀsilylene complex Cp(CO)2W(CCH)(SiH2)
(3M)18a (Figure 7 and Table 1). The angle R between the lone
pair of the SiH2 group and the WꢀSi bond is 11° in 5M, which is
much smaller than that (35°) of 3M (see Scheme 5 for the
definition of the angle R). This small angle indicates the lone pair
of the SiH2 does not deviate very much from the WꢀSi axis. Also,
the WꢀSi bond index is moderately larger in 5M than in 3M; see
Figure 7 for the Wiberg bond indices. In 10, the interaction
between the SiH2 and CC moieties is absent because the SiH2
moiety takes a position trans to the CC moiety (Figure 7). The
WꢀSi distance of 10 is somewhat shorter than that of 5M by 0.10 Å,
and the WꢀSi bond index is about 2 times larger than that of 5M.
All these results indicate that the WꢀSi bonding interaction is
moderately stronger in 5M than in 3M but considerably weaker
than in 10 and that the SiH2 moiety interacts with both of the W
and the CC moieties in 5M. The weaker WꢀSi bond in 5M in
comparison to that in 10 is an indication of the presence of a
bonding interaction between the SiH2 and CC moieties in 5M, as
will be discussed below in more detail.
1.968
1.957
2.827
1.337 1.343(6)
1.242 1.378
1.299
49.7
W1ꢀSi1ꢀC1 54.0
W2ꢀSi2ꢀC2 53.0
55.23(15)
54.49(13)
W1ꢀC1ꢀC2 152.0 151.1(3)
W2ꢀC2ꢀC1 159.0 165.1(4)
179.0 180.0
179.2 179.8
152.1
a The DFT (B3PW91)/BS-I method was employed. Bond lengths are
given in angstroms and bond angles in degrees. b Reference 18a.
The WꢀC distance in 5M is moderately shorter than in 10 and
somewhat longer than in 3M. However, it is considerably longer
than the WꢀC double-bond distance (about 1.9 Å)54 and much
longer than the WꢀC triple-bond distances of 11 and 12. Also,
the WꢀC bond index is somewhat larger in 5M than in 10, is
similar to that of 3M, and is much smaller than in 11 and 12. All
these results rule out the possibility that 5M involves a WꢀC
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Scheme 5
weaker than those of the pure ethynediyl complex 10 and 1,4-
disilabutatriene 13.
The Si1ꢀC1 and Si2ꢀC2 distances of 5M are considerably
shorter than the SiꢀC1 distance of 3M, but the Si1ꢀC2 and
Si2ꢀC1 distances of 5M are much longer than the SiꢀC2
distance of 3M (Figure 7 and Table 1). The Si1ꢀC1 and Si2ꢀC2
bond indices of 5M are somewhat larger than the SiꢀC1 and
SiꢀC2 bond indices of 3M. On the other hand, the Si1ꢀC2 and
Si2ꢀC1 bond indices (0.065 and 0.075, respectively) are very
small in 5M, as expected from the geometry of 5M. These
Si1ꢀC1 and Si2ꢀC2 distances of 5M are similar to a SiꢀC single
bond, and their bond indices are somewhat smaller than that of
the SiꢀC single bond.56
It is worth comparing the bond distances and bond indices
among the H2SiCCSiH2 moieties of 5M, 1,4-disilabutatriene
H2SidCdCdSiH2 (13), and its dianion [H2SiCCSiH2]2ꢀ (13-
an) (Figure 8), where the geometries of 13 and 13-an were
optimized at the triplet and singlet states, respectively.57 The
SiꢀC1 and SiꢀC2 distances of 13 and 13-an are moderately
shorter than the Si1ꢀC1 and Si2ꢀC2 distances of 5M, while the
C1ꢀC2 distances of 13 and 13-an are considerably shorter than
that of 5M. Consistently, the SiꢀC1 and SiꢀC2 bond indices of
13 and 13-an are somewhat larger and the C1ꢀC2 bond index is
considerably larger than those of 5M. Hence, the Si1ꢀC1 and
Si2ꢀC2 bonds of 5M are somewhat weaker and the C1ꢀC2
bond of 5M is considerably weaker than those of 13 and 13-an.
All these results indicate that the Si1ꢀC1 and Si2ꢀC2 bonding
interactions of 5M can be understood to be a SiꢀC single bond.
It is noted that the SiCCSi dihedral angle is 89° in 5M but 180°
in 13 and 13-an, indicating that the SiCCSi moiety of 5M is
considered not to be a disilabutatriene. For a clearer under-
standing, we calculated H2SiCCSiH2 (13d) and [H2SiCCSiH2]2ꢀ
(13d-an), whose SiCC angle and SiCCSi dihedral angle were taken
to be the same as those of 5M, but the other moieties were opti-
mized at the triplet and singlet states, respectively (see Figure 8).
Apparently, the SiꢀC bond indices are somewhat larger and the
C1ꢀC2 bond index is considerably larger in both 13d and 13d-
an than in 5M, as shown in Figure 8. These results indicate that
the H2SiꢀCꢀCꢀSiH2 moiety of 5M is much different from that
of 13d and 13d-an, suggesting that various CT interactions are
formed between the SiH2, CC, and W moieties in 5M to
significantly change the electronic structure of the H2SiCCSiH2
moiety in 5M, as will be discussed below in detail. We also
calculated the 1,4-disila-1,3-butadiene H2SidCHꢀCHdSiH2
(14), which is a silicon analogue of 1,3-butadiene, H2CdCHꢀ
CHdCH2, and the deprotonated 1,4-disilabutadiene [H2SiC-
CSiH2]2ꢀ (14-an) (see the Supporting Information, Figure S9).
The SiꢀC and CꢀC bond indices of 14 and 14-an are much
different from those of 5M, suggesting that the H2Siꢀ
CꢀCꢀSiH2 moiety of 5M is different from that of the depro-
tonated disilabutadiene (see the Supporting Information for the
details).
Figure 8. Geometries of H2SiCCSiH2 (13) and[H2SiCCSiH2]2- (13-an).
Bond lengths are given in angstroms and bond angles in degrees. Wiberg
bond indexes (from DFT(B3PW91)/BS-II NBO calculations) are given
in parentheses. For 13d and 13d-an, the geometry was optimized except
for the SiCC angle and SiCCSi dihedral angle, which were taken to be
the same as those of 5M. The geometries of 13 and 13-an were
optimized by the DFT(B3PW91)/BS-I method at triplet and singlet
states, respectively.
multiple bond. The WCC angle is 156° in 5M, while it is about
180° in 10, including a typical Wꢀethynediyl bond. Also, the
WCCW dihedral angle is 89° in 5M, while it is 24° in 10. These
results suggest that the WꢀC bond of 5M is much different from
that of a pure ethynediyl complex.
The C1ꢀC2 distance of 5M is considerably longer than that of
10, somewhat longer than that of 3M, and somewhat shorter
than that of 11. Consistent with the bond distance, the C1ꢀC2
bond index is considerably smaller in 5M than in 3M and much
smaller than in 10, but moderately larger than in 11. This
C1ꢀC2 distance of 5M is similar to that of a CꢀC double bond
and considerably longer than that of the 1,4-disilabutatriene
H2SidCdCdSiH2 (13), which is a silicon analogue of the
butatriene H2CdCdCdCH2 (Figure 8).55 The CC bond index
of 5M is between those of CꢀC single and CdC double bonds
and is much smaller than that of 13 (Figure 8).55 From all these
results, it is concluded that the C1ꢀC2 bond of 5M is much
The W atomic and its d orbital populations of 5M are similar to
those of 3M but somewhat smaller than those of 10 (Table 2).
The electron population of the SiH2 moiety is moderately smal-
ler in 5M than in 3M but much smaller than in 10, indicating that
the SiH2 moiety of 5M is much different from that of the pure
silylene complex 10. The electron population of the CC moiety
is considerably larger in 5M than in 10, 3M, and acetylene
(HCtCH).58 These results indicate that the CC moiety of 5M is
different from those of the pure ethynediyl complex 10 and the
acetylideꢀsilylene complex 3M. It is also noted that the
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Table 2. NBOa Populations of Several Important Atoms and
Groups in Cp(CO)2W(SiH2)(μ-CC)(SiH2)W(CO)2Cp (5M),
Cp(CO)2(SiH2)WꢀCtCꢀW(SiH2)(CO)2Cp (10), and
Cp(CO)2W(CCH)(SiH2) (3M)
d orbitals of the W center. They are named jLUMO+2(W) etc.
hereafter; see Figure 10A for these MOs. In SiH2, the HOMO
and LUMO play important roles to form CT interactions in 5M.
The LUMO mainly consists of an empty p orbital, and the
HOMO is a lone pair orbital (Figure 10B). The LUMO and
HOMO are named jSip and jSilp, respectively. In [CC]2ꢀ, π*, π,
and lone pair orbitals play important roles in forming CT
interactions. The degenerate LUMOs are two π* orbitals, which
5M
10
3M
W
74.214
5.879
74.373
5.958
74.240
5.874
d
are perpendicular to each other. They are named jCC and
π1*
jCCπ2*, respectively (Figure 10C). HOMO and HOMO-2 are
Si
13.022
15.322
6.493
13.207
15.564
6.265
13.070
15.350
6.186
SiH2
C1
C2
CC
two lone pair orbitals, which are named jCC and jCC
,
lp1
lp2
respectively. The degenerate HOMO-1's are two π orbitals,
6.464
6.296
6.563
which are named jCCπ1 and jCCπ2, respectively.
12.957
12.560
12.749
HOMO, HOMO-1, HOMO-2, and HOMO-3 of 5M are
doubly degenerate; see Figure 9 and Figure S11 in the Support-
ing Information for these MOs. As shown by the weights of
fragment MOs of Scheme 7A, the HOMO of 5M mainly consists
of the occupied d orbital of W2 (dWocc) which overlaps with
jCCπ* in a bonding way. This corresponds to π-back-donation
from W2 (dWocc) to the CC moiety (jCCπ*); see CT(dWocc f
jCCπ*) in Scheme 8. Another back-donation from W1 dWocc to
jSi1p of SiH2 is involved in this HOMO; see CT(dWocc f jSip).
HOMO-1 mainly consists of dWocc. As shown in Scheme 7B,
HOMO-2 involves several kinds of CT interactions which
a DFT(B3PW91)/BS-II NBO calculations.
population of the CC moiety of 5M is somewhat larger than
those of 13 and 13d-an,59 while it is somewhat smaller than in
13d and 13-an.59 The population of the SiH2 moiety of 5M is
considerably smaller than those of 13, 13d, 13-an, and 13d-an.59
These populations of the CC and SiH2 moieties of 5M are
considerably different from those of the deprotonated disilabu-
tadiene [H2SiCCSiH2]2ꢀ (14-an) (see the Supporting Informa-
tion for details). From these results, it is concluded that the
H2SiꢀCꢀCꢀSiH2 moiety of 5M is neither a disilabutatriene nor
a disilabutadiene dianion and the CꢀC moiety has a significant
population on the π* orbital.
4.2. MO Analyses and Population in Fragment MOs. To get
a clear picture of the bonding interactions, we inspected the
MOs of 5M (Figure 9) and we analyzed the MOs by representing
them with a linear combination of the MOs of fragments, using
eq 1,60,61 where 5M is considered to consist of five moieties, as
shown in Scheme 6.
are formed between the W, CC, and SiH2, as follows: dW
occ
of W1 largely participates in HOMO-2, into which the unoccupi-
ed jCC and jSi1 mix in a bonding way. These interactions
π*
p
correspond to CT(dWocc f jCCπ*) and CT(dWocc f jSip) (see
Scheme 8). Also, dW
of W2 largely participates in this
unoc
HOMO-2 into which the occupied jSi2lp, jCClp, and jCC
π
moderately mix in a bonding way with the dWunoc orbital. These
correspond to CT(jSilp f dWunoc), CT(jCClp f dWunoc), and
CT(jCCπ f dWunoc) (see Scheme 8). However, the presence of
jCC and jCC is not clearly observed in this HOMO-2
π
π*
ψ ðABCDEÞ ¼ aijj ðAÞ þ bikj ðBÞ þ cilj ðCÞ
∑
∑
∑
i
j
k
l
(Figure 9). This is interpreted in terms of the π orbital polariza-
tion of the CC moiety, as follows: as shown in Scheme 9A, the
mixing of jCCπ* into jCCπ considerably increases the contribu-
tion of the C1 p orbital but considerably decreases that of the C2
p orbital. This polarized π1 bonding orbital is observed in
HOMO-2. In the π2 space perpendicular to the π1, the reverse
polarization occurs to increase the p orbital of C2 and decrease
the p orbital of C1. These polarizations lead to nearly equivalent
atomic populations of the C1 and C2 atoms (Table 2) and
simultaneously lead to the weakening of the π bonding nature
in 5M. Also, the jSilp and jSip orbitals are not clearly observed in
HOMO-2, though their weights are somewhat large, as shown in
Scheme 7B. This is because the bonding mixing of jSip and the
antibonding mixing of jSi with dW of the W lead to a
j
k
l
þ
dimj ðDÞ þ einj ðEÞ
ð1Þ
∑
∑
m
n
m
n
ψi(ABCDE) represents the ith MO of the total system ABCDE,
jj(A) is the jth MO of fragment [Cp(CO)2W]+ , jk(B) is the
A
kth MO of the fragment (SiH2)B, jl(C) is the lth MO of frag-
ment [CC]2ꢀC, jm(D) is the mth MO of the fragment (SiH2)D,
and jn(E) is the nth MO of the fragment [Cp(CO)2W]+ , where
E
the suffixes AꢀE correspond to the moieties AꢀE shown in
Scheme 6. aij, bik, cil, dim, and ein are expansion coefficients of
jj(A), jk(B), jl(C), jm(D), and jn(E), respectively. We
evaluated the electron population of the fragment MO by eq 2
lp
occ
distorted bonding orbital, as shown in Scheme 9B. As shown
in Scheme 7C, HOMO-3 mainly consists of jCCπ, which over-
laps with jSip and dWunoc in a bonding way. These correspond to
CT(jCCπ f jSip) and CT(jCCπ f dWunoc) (see Scheme 8).
HOMO-4 and HOMO-6 involve the bonding interaction be-
occ
F ðAÞ ¼ ½a2 þ aijbikSjk
þ
∑
l
aijcilSjl
∑
∑
j
ij
i
k
þ
aijdimSjm
þ
aijeinSjnꢁ
∑
n
ð2Þ
∑
tween jCC and dWunoc, as shown in Figure 9, which corre-
m
lp
sponds to CT(jCClp f dWunoc). Though CT(jCCπ f jSip) is
found in HOMO-3, CT(jSilp f jCCπ*) is not clearly observed
where Fj(A) represents how much electron population jj(A)
possesses in the total system ABCDE and Sjk is the overlap
integral between jj(A) and jk(B). The sum of the populations
of all MOs of the fragment A is the same as the sum of the
Mulliken atomic populations in the fragment A.
in the MOs of 5M, unlike the case for 3M. This is because jSi
lp
expands toward the W center in 5M but toward the CC moiety
in 3M.
As shown in Table 3, the population of jHOMO-1(W) is close
to 2.0e in 5M and the population of the jHOMO (W) is similar to
that of Cp(CO)2(SiH2)WꢀCtCꢀW(SiH2)(CO)2Cp (10) but
Important MOs of [Cp(CO)2W]+ are LUMO+2, LUMO+1,
LUMO, HOMO, and HOMO-1, which mainly consist of the
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Figure 9. Several important KohnꢀSham MOs in Cp(CO)2W(SiH2)(μ-CC)(SiH2)W(CO)2Cp (5M). Orbital energies (in eV) are given in
parentheses. HOMO, HOMO-1, HOMO-2, and HOMO-3 are doubly degenerate; see Figure S11 in the Supporting Information for the other set.
is considerably smaller than that of Cp(CO)2W(CCH)(SiH2)
(3M). Because 10 has an acetylenic structure (WꢀCtCꢀW), it
is a d4 complex (+II oxidation state of W). Thus, the similar
population of jHOMO(W) indicates that 5M is understood to be
a d4 complex as well. It is likely that the considerably smaller pop-
ulation of jHOMO(W) in 10 than in 3M arises from the larger
CT(jHOMO(W) f jSip),62 which will be discussed below in
more detail. The population of jSip is moderately larger in 5M
than in 10 but somewhat smaller than in 3M. The population of
jCCπ in 5M is similar to that of 3M but considerably smaller than
that of 10. These results indicate that CT(jCCπ f jSip) occurs
to an extent similar to that in 3M. This conclusion is supported
by the geometry of 5M and the feature of HOMO-3; the geo-
metry suggests the presence of SiꢀC bonding interactions, and
HOMO-3 displays the presence of a bonding overlap between
jSip and jCCπ (see HOMO-3 of Figure 9). The population of
jSi is considerably larger in 5M than in 3M but considerably
π*
lp
smaller than in 10 (Table 3). The population of jCC is
somewhat larger in 5M than in 3M but considerably larger than
in 10. Though the poor overlap between jSilp and jCCπ* in 5M
suggests that CT(jSilp f jCCπ*) is considerably weaker in 5M
than in 3M, the population of jCCπ* is large in 5M. These results
indicate that CT(dWocc f jCCπ*) is stronger in 5M than in 3M.
The considerable weight of jCCπ* in the HOMO (Scheme 7A)
and the considerably smaller population in jHOMO(W) of 5M
also support this conclusion. The population of jCClp1 in 5M is
similar to that of 10 but moderately larger than that of 3M. The
population of jCC is somewhat smaller in 5M than in 10.
lp2
These results indicate that CT(jCClp f dWunoc) is moderately
weaker in 5M than in 3M but somewhat stronger than in 10.
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Scheme 6
(see Figure 7 for the orientation of SiH2). Also, CT(jSi
f
lp
dWunoc) and CT(dWocc f jSip) are formed in 5M. Because the
lone pair of SiH2 expands toward the W, the above CTs are
stronger in 5M than in 3M and, hence, the WꢀSi bond of 5M is
somewhat stronger than that of 3M.
The above results lead to the following conclusions. (1) The
H2SiCCSiH2 moiety is not understood to be a disilabutatriene or
a metal-substituted disilabutadiene. (2) The CC moiety can be
understood as an ethynediyl dianion and the SiH2 moiety as a
silylene. (3) The bonding nature should be understood in terms
of various CT interactions between the W, SiH2, and CC
moieties (see Scheme 8). Though it is difficult to understand
the H2SiCCSiH2 moiety as disilabutatriene or metal-substituted
disilabutadiene, the conclusions (2) and (3) are not inconsistent
with the experimental and computational results.
’ CONCLUDING REMARKS
The ethynediyl-bridged bis(silylene) dinuclear complexes
Cp*(CO)2M(SiPh2)(μ-CC)(SiPh2)M(CO)2Cp* (5, M d W;
6, M d Mo) were synthesized by the reaction of Ph2HSiCtC-
SiHPh2 with 2 equiv of acetonitrile complexes 1a and 2, res-
pectively, via activation of two SiꢀH bonds of the bis(silyl)-
acetylene. X-ray crystal analysis of 5 and 6 revealed a novel
linkage between the ethynediyl bridge and two Cp*(CO)2M-
(SiPh2) moieties. Two MꢀSiꢀC three-membered-ring skeletons
are linked nearly perpendicularly to each other. The WꢀSi bond
distance of 5 is considerably shorter than that of the mononuclear
acetylideꢀsilylene complex 3b, and the ethynediyl bond distance is
significantly elongated from the triple-bond distance of Ph2HSiCtC-
SiHPh2 to a typical CꢀC double-bond distance. These structural
features are rationalized by the theoretical calculations described below.
Reaction of the tungsten acetonitrile complex 1a with 1 equiv
of Ph2HSiCtCSiHPh2 afforded a mixture of mononuclear
acetylideꢀsilylene complex 7 and dinuclear complex 5. Addition
of 1a to the mixture led to the conversion of 7 to 5, indicating the
intermediacy of 7 in the production of 5 in the 1:2 reaction of the
bis(silyl)acetylene with 1a. A similar 1:1 reaction using the
molybdenum acetonitrile complex 2 also afforded a mixture of
mononuclear and dinuclear complexes. In contrast to the tung-
sten system, however, the equilibrium of two mononuclear com-
plexes, acetylideꢀsilylene complex 8 and silapropargyl/alkynyl-
silyl complex 9, was strongly suggested by variable-temperature
NMR studies of the mixture. Treatment of the equilibrium mix-
ture with 2resulted in their clean conversion to dinuclear complex 6.
The bonding nature and electronic structure of 5 were dis-
closed by a DFT study of the model complex Cp(CO)2W-
(SiH2)(μ-CC)(SiH2)W(CO)2Cp (5M, Cp d η5-C5H5). The
computational results demonstrate that 5M is neither a 1,4-
disilabutatriene-bridged dinuclear tungsten complex nor a cu-
mulenic (WdCdCdW) complex but an ethynediyl-bridged
bis(silylene) dinuclear tungsten complex which contains various
charge transfer (CT) interactions (see Scheme 8) between the
tungsten (W), silylene (SiH2), and ethynediyl (CC), as follows.
Figure 10. Several important KohnꢀSham MOs in [Cp(CO)2W]+, SiH2,
and [CC]2ꢀ. In part C, the LUMO and HOMO-1 are doubly degenerate.
The other orbital perpendicular to this picture exists beside this orbital.
4.4. Summary of the Bonding Nature of 5M. The CT
interactions discussed above are shown in Scheme 8. As dis-
cussed above, the CꢀC bond in 5M is weaker than a typical CꢀC
triple bond but is comparable to a CꢀC double bond. This result
is interpreted as follows: CT(dWocc f jCCπ*) and CT(jCCπ f
jSip) considerably weaken the CꢀC bond of 5M. The mixing of
jCCπ into jCCπ* induces π orbital polarization of the CC moiety
in one plane and reverse π orbital polarization in the perpendi-
cular plane. These polarizations are also responsible for con-
siderable weakening of the CC bond. Because CT(jSi
f
(1) CTs occur from the lone pairs (jCClp) and π orbital (jCC
)
π
lp
jCCπ*) is considerably weak in 5M due to a poor overlap
between them, only CT(jCCπ f jSip) contributes to the SiꢀC
bonding interaction in 5M. The Si1ꢀC1 bond index of 5M is
somewhat larger than the SiꢀC1 bond index of 3M, but the
Si1ꢀC2 bond index of 5M is much smaller than the SiꢀC2 bond
of the ethynediyl to the unoccupied d orbital (dWunoc) of the W
and from the occupied d orbital (dWocc) of the W to the π* orbital
(jCCπ*) of the ethynediyl. (2) CTs occur from the lone pair
orbital (jSilp) of the silylene to dW
and from dW to the
occ
unoc
empty p orbital (jSip) of the silylene. (3) CT occurs from jCC
π
index of 3M. This is because the C1 pπ orbital overlaps with jSi1
to jSip, which leads to considerably strong SiꢀC bonding
p
in 5M but the C2 pπ orbital cannot overlap with jSi1 in 5M
interactions and considerably large elongation of the CꢀC
p
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Scheme 7. Weights (in Percent) of Fragment MOs
Scheme 8. Bonding Nature of 5M
Scheme 9
distance. (4) The mixing of jCCπ into jCCπ* induces π orbital
polarization of the CC moiety in one plane and a reverse π orbital
polarization in the perpendicular plane. These polarizations in
addition to the CT(dWocc f jCCπ*) also participate in the CꢀC
bond weakening of the ethynediyl. Thus, 5M is understood to be
a new category of an ethynediyl-bridged bis(silylene) dinuclear
transition-metal complex including interesting CT interactions
and polarizations.
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Table 3. Populationsa of Fragment MOs in Cp(CO)2W(SiH2)-
(μ-CC)(SiH2)W(CO)2Cp (5M), Cp(CO)2(SiH2)WꢀCtCꢀ
W(SiH2)(CO)2Cp (10), and Cp(CO)2W(CCH)(SiH2) (3M)
Synthesis of Cp*(CO)2Mo(SiPh2)(μ-CC)(SiPh2)Mo(CO)2Cp*
(6). On a vacuum line, toluene (2.5 mL) was vacuum-transferred into a
reaction flask containing 2 (60 mg, 0.17 mmol) and Ph2HSiCtC-
SiHPh2 (32 mg, 0.082 mmol) at ꢀ196 °C. The mixture was thawed at
ꢀ70 °C and warmed to room temperature with stirring. After 30 min at
room temperature, the volatiles were removed in vacuo. The residual
solid was washed with hexane (2 ꢂ 2 mL) to give 6 as an air-sensitive
orange solid (41 mg, 51%). Data for 6 are as follows. 1H NMR (400 MHz,
CD2Cl2, 27 °C): δ 1.81 (s, 30H, Cp*), 6.6ꢀ7.8 (vbr m, 20H, Ph). 1H
NMR (400 MHz, CD2Cl2, ꢀ90 °C): δ 1.58 (s, 15H, Cp*), 1.69 (s, 15H,
Cp*), 6.85 (br s, 4H, Ph), 7.05ꢀ7.25 (br m, 6H, Ph), 7.35ꢀ7.6 (br m,
6H, Ph), 7.84 (br m, 4H, Ph). 13C{1H} NMR (150 MHz, CD2Cl2,
27 °C): δ 11.1 (C5Me5), 105.5 (C5Me5), 127.8 (br, Ph), 130.4 (br, Ph),
135.4 (vbr, Ph), 136.7 (br, Ph), 230.2 (br, CO), 240.1 (br, μ-CC).
13C{1H} NMR (150 MHz, CD2Cl2, ꢀ90 °C): δ 9.9 (C5Me5), 10.3
(C5Me5), 104.3 (C5Me5), 104.5 (C5Me5), 126.2 (Ph), 127.4 (Ph), 128.4
(Ph), 130.1 (Ph), 130.5 (Ph), 130.9 (Ph), 133.6 (Ph), 133.9 (Ph), 134.3
(Ph), 135.1 (Ph), 135.7 (Ph), 136.9 (Ph), 137.0 (Ph), 226.6 (CO),
228.8 (CO), 230.6 (CO), 231.5 (CO), 239.8 (μ-CC), 241.2 (μ-CC).
29Si{1H} NMR (119 MHz, CD2Cl2, ꢀ90 °C): δ ꢀ5.0, 5.3. Anal. Calcd
Synthesis of 13CO-Enriched Cp*(CO)2Mo(SiPh2)(μ-CC)-
(SiPh2)Mo(CO)2Cp* (6*). In a 50 mL Schlenk flask containing
Cp*(CO)3MoMe (279 mg, 0.84 mmol) and benzene (10.5 mL) was
introduced 13CO (2.0 mmol). The solution was irradiated with a 100 W
medium-pressure Hg lamp with vigorous stirring for 15 min at 10 °C.
After removal of the volatiles, hexane (9.5 mL) was added, and the
solution was filtered to remove an insoluble orange solid. The solvent
was removed in vacuo, and the residual solid was sublimed at 70 °C to
give 13CO-enriched Cp*(CO)3MoMe (239 mg, 86%), which was con-
verted to 13CO-enriched 2* by photolysis in MeCN in 30% yield in a
manner similar to the synthesis of 2.19c The reaction of Ph2HSiCtCSiHPh2
(33 mg, 0.084 mmol) with 2* (60 mg, 0.17 mmol) gave 6* (14 mg, 17%)
after recrystallization from toluene/pentane.
1:1 Reaction of 1a with Ph2HSiCtCSiHPh2. On a vacuum line,
toluene-d8 (0.5 mL) was vacuum-transferred into an NMR tube contain-
ing 1a (7 mg, 16 μmol) and Ph2HSiCtCSiHPh2 (6 mg, 15 μmol) at
ꢀ196 °C, and the tube was flame-sealed. The mixture was thawed at
ꢀ70 °C and warmed to room temperature. After 5 min at room
temperature, the 1H NMR spectrum showed the formation of 7 and 5
in a ratio of 76 to 24. From a preparative-scale reaction of 1a (100 mg,
0.23 mmol) with Ph2HSiCtCSiHPh2 (90 mg, 0.23 mmol) in toluene
(5.3 mL), an air-sensitive orange solid (24 mg) was isolated in ca. 95%
purity by removing the solvent and washing the residual solid with
hexane and pentane. Attempts to purify 7 by recrystallization were un-
successful, and it was characterized by low-temperature 1H, 13C, and 29Si
NMR spectra. Data for 7 are as follows. 1H NMR (400 MHz, toluene-d8,
27 °C): δ 1.69 (s, 15H, Cp*), 5.41 (s, 1H, SiH), 7.00ꢀ7.05 (m, 6H, Ph),
7.05ꢀ7.10 (m, 6H, Ph), 7.47ꢀ7.60 (m, 4H, Ph), 7.67ꢀ7.75 (m, 4H,
Ph). 1H NMR (600 MHz, THF-d8, ꢀ70 °C): δ 1.86 (s, 15H, Cp*), 4.97
(s, 1H, SiH), 7.01ꢀ7.75 (m, 20H, Ph). 13C{1H} NMR (150 MHz, THF-
d8, ꢀ70 °C): δ 11.0 (C5Me5), 103.6 (C5Me5), 128.4 (Ph), 128.5 (Ph),
128.7 (Ph), 128.8 (Ph), 129.1 (Ph), 130.3 (Ph), 130.5 (Ph), 130.7 (Ph),
131.2 (Ph), 132.3 (Ph), 132.6 (Ph), 134.0 (Ph), 135.5 (Ph), 135.9 (Ph),
136.5 (Ph), 137.7 (WCC), 186.5 (WCC), 226.2 (CO), 230.7 (CO).
29Si{1H} NMR (79 MHz, toluene-d8, 27 °C): δ ꢀ39.2 (SiHPh2). The
WSiPh2 signal was not observed. 29Si{1H} NMR (119 MHz, THF-d8,
ꢀ70 °C): δ ꢀ46.7 (1JWSi d 41 Hz, WSiPh2), ꢀ39.0 (SiHPh2).
1:1 Reaction of 2 with Ph2HSiCtCSiHPh2. On a vacuum line,
toluene-d8 (0.5 mL) was vacuum-transferred into an NMR tube contain-
ing 2 (8 mg, 23 μmol) and Ph2HSiCtCSiHPh2 (9 mg, 23 μmol) at
ꢀ196 °C, and the tube was flame-sealed. The mixture was thawed at
ꢀ70 °C and warmed to room temperature. After 20 min at room tem-
perature, the 1H NMR spectrum showed the formation of mononuclear
5M
10
3M
[Cp(CO)2W]+
j
j
j
j
j
LUMO+2(W)
LUMO+1(W)
LUMO(W)
0.013
0.015
0.638
0.794
1.454
1.910
0.011
0.411
0.835
1.778
1.844
0.376
1.157
1.489
1.863
HOMO(W)
HOMO-1(W)
SiH2
jSi
jSi
0.575
0.941
0.540
1.256
0.665
0.793
P
lp
[C2]2ꢀ or [CCH]ꢀ
0.453 b
jCC
jCC
jCC
jCC
0.097 b
1.276
1.812 c
0.397
1.264
1.469
π*
lp1
π
1.277
1.492 c
for C50H50O4Si2Mo2 C7H8: C, 64.89; H, 5.54. Found: C, 64.87; H, 5.79.
3
1.472
1.635
lp2
a DFT(B3PW91)/BS-II calculations. See Table S1 in the Supporting
Information for BS-III calculations. b Average of the populations in
jCCπ*1 and jCCπ*2. c Average of the populations in jCCπ1 and jCC
’ EXPERIMENTAL SECTION
.
π2
General Procedures. All materials were manipulated under an
atmosphere of nitrogen in a glovebox or by standard vacuum and Schlenk
techniques. NMR spectra were recorded on a JEOL JNM-GSX400 or a
Bruker AV-600 spectrometer, and IR spectra were obtained on a
Shimadzu FTIR-8100 M spectrometer. Benzene, hexane, pentane,
toluene, toluene-d8, and THF-d8 were distilled from sodium benzophe-
none ketyl, and dichloromethane-d2 was distilled from calcium hydride.
Ph2HSiCtCSiHPh2,63 Cp*(CO)2W(NCMe)Me (1a),19a and Cp*-
(CO)2Mo(NCMe)Me (2)19c were synthesized according to the litera-
ture methods. 13C-enriched CO (99.3%) was purchased from Isotec and
used without further purification.
Synthesis of Cp*(CO)2W(SiPh2)(μ-CC)(SiPh2)W(CO)2Cp*
(5). On a vacuum line, toluene (6 mL) was vacuum-transferred into a
reaction flask containing 1a (100 mg, 0.23 mmol) and Ph2HSiCtC-
SiHPh2 (43 mg, 0.11 mmol) at ꢀ196 °C. The mixture was thawed at
ꢀ70 °C and warmed to room temperature with stirring. After 90 min at
room temperature, the volatiles were removed in vacuo. The residual
solid was washed with hexane (1 mL) and then with hexane/toluene
(1.1/0.9 mL) to give 5 as an air-sensitive orange solid (69 mg, 55%).
Data for 5 are as follows. 1H NMR (400 MHz, CD2Cl2, 27 °C): δ 1.91 (s,
30H, Cp*), 7.0ꢀ7.1 (br m, 4H, Ph), 7.1ꢀ7.2 (br m, 6H, Ph), 7.45ꢀ7.55
(br s, 6H, Ph), 7.7ꢀ7.8 (br s, 4H, Ph). 1H NMR (600 MHz, CD2Cl2,
ꢀ90 °C): δ 1.75 (br s, 30H, Cp*), 6.7ꢀ7.0 (br s, 4H, Ph), 7.0ꢀ7.35 (br
m, 6H, Ph), 7.35ꢀ7.7 (br s, 6H, Ph), 7.7ꢀ8.0 (br s, 4H, Ph). 13C{1H}
NMR (100 MHz, CD2Cl2, 27 °C): δ 11.0 (C5Me5), 104.4 (C5Me5),
127.4 (Ph), 128.2 (Ph), 129.8 (Ph), 130.7 (Ph), 134.3 (Ph), 136.3(Ph),
137.2 (Ph), 137.9 (Ph), 222.0 (CO), 223.5 (CO), 235.8 (μ-CC).
13C{1H} NMR (150 MHz, CD2Cl2, ꢀ90 °C): δ 10.0 (br, C5Me5),
10.2 (br, C5Me5), 103.2 (br, C5Me5), 126.0 (br, Ph), 127.4 (Ph), 130.2
(br, Ph), 131.2 (br, Ph), 133.4 (br, Ph), 134.4 (br, Ph), 136.4 (br, Ph),
137.5 (br, Ph), 220.7 (br, CO), 221.5 (br, CO), 223.6 (br, CO), 231.6
(br, μ-CC), 235.2 (br, μ-CC). 29Si{1H} NMR (119 MHz, C7D8, 27 °C):
δ ꢀ21.2 (br). 29Si{1H} NMR (119 MHz, CD2Cl2, ꢀ90 °C): δ ꢀ17.2,
ꢀ29.8. Anal. Calcd for C50H50O4Si2W2 C7H8: C, 55.62; H, 4.75.
3
Found: C, 55.48; H, 4.85.
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Table 4. Crystallographic Data of 5 C7H8 and 6 C7H8
atoms for the dinuclear complexes were refined using the riding model.
The refinement was carried out using full-matrix least-squares methods
on F2 with SHELXL-97.68 All calculations were performed using the
CrystalStructure crystallographic software package.69
Computational Details. The geometry of Cp(CO)2W(SiH2)(μ-
CC)(SiH2)W(CO)2Cp (5M) was optimized with density functional
theory (DFT), where the B3PW91 functional70,71 was employed for the
exchange-correlation term, because this functional presented better agree-
ment of the optimized geometry of Cp(CO)2W(CCH)(SiH2) (3M)18a
with the experimental geometry of 3b19b than does the B3LYP func-
tional.70,72 We ascertained that none of the equilibrium geometries
exhibited any imaginary frequency.
Two kinds of basis set systems, BS-I and BS-II, were mainly used in
this work. In BS-I, core electrons of W were replaced with the effective
core potentials (ECPs)73 and their valence electrons were represented
by the (341/321/21) basis sets.73 The usual cc-pVDZ74 basis sets were
employed for Si, C, and O, and the usual 6-31G75 basis set was used for
H. This BS-I system was used for geometry optimization. In BS-II, the
core electrons of W were replaced with the StuttgartꢀDresdenꢀBonn
(SDB) ECPs and their valence electrons were represented by the (311111/
22111/411/11) basis sets.76,77 For the other atoms, the cc-pVTZ basis
sets74 were employed, where the f polarization function was excluded to
save computational time. This BS-II system was used to evaluate the
Wiberg bond index78 and population changes. Another basis set system,
BS-III, was employed to check the reliability of the Mulliken population
analysis with the BS-II system, because a very diffuse function tends to
present an unreasonable Mulliken population in several cases. In BS-III, the
valence electrons of W were represented by the (541/541/111/1) basis
set,72,79,80 where its core electrons were replaced with the same ECPs as
those of BS-I. For the other atoms, the same basis sets as those of BS-I were
employed. The BS-III-calculated Mulliken populations are similar to the BS-
II-calculated values (see Table S1 in the Supporting Information). Hence,
we present only the BS-II-calculated populations in the discussion.
The Gaussian 03 program package (revision C.02)81 was used for all
these computations. NBO population analysis was carried out with the
method proposed by Weinhold et al.82 Molecular orbitals were drawn
with the MOLEKEL program package (version 4.3).83
3
3
5 C7H8
6 C7H8
3
3
formula
fw
C50H50O4Si2W2 C7H8 C50H50O4Si2Mo2 C7H8
3
3
1230.95
1055.13
cryst size (mm)
cryst syst
space group
a (Å)
0.10 ꢂ 0.10 ꢂ 0.10
monoclinic
P21/n
0.20 ꢂ 0.20 ꢂ 0.10
monoclinic
P21/n
15.754(4)
17.657(5)
18.402(4)
91.8710(10)
5116(2)
4
15.703(4)
17.614(4)
18.481(4)
92.0150(10)
5109(2)
4
b (Å)
c (Å)
β (deg)
V (Å3)
Z
F(000)
2432
2176
μ(Mo KR) (cmꢀ1
)
4.590
5.817
no. of rflns collected 71 469
79 189
no. of unique reflns
Rint
11 510
0.054
556
11 501
0.113
no. of variables
R1 (I > 2σ(I))
wR2 (all data)
GOF
556
0.0292
0.0672
0.822
0.0601
0.1397
0.875
and dinuclear complexes in a composition ratio of 82 to 18. From a
preparative-scale reaction of 2 (90 mg, 0.26 mmol) with Ph2HSiCtC-
SiHPh2 (104 mg, 0.266 mmol) in toluene (5.5 mL), an air-sensitive
yellow solid (74 mg, 42%) was isolated. Variable-temperature 1H NMR
analysis of a THF-d8 solution of the solid revealed an equilibrium mix-
ture of two complexes, which were characterized as 8 and 9 on the basis
of low-temperature 1H, 13C, and 29Si NMR spectra. Data for 8 and 9 are
1
as follows. H NMR (400 MHz, toluene-d8, 27 °C): δ 1.64 (s, 15H,
Cp*), 5.44 (s, 1H, SiH), 7.03ꢀ7.09 (m, 12H, Ph), 7.46ꢀ7.58 (m, 4H,
Ph), 7.59ꢀ7.69 (m, 4H, Ph). 1H NMR (600 MHz, THF-d8, ꢀ80 °C):
δ 1.62 (s, 15H, Cp*, 9), 1.76 (s, 15H, Cp*, 8), 4.90 (s, 1H, SiH, 8), 5.80
(s, 1H, SiH, 9), 6.80ꢀ8.10 (m, 40H, Ph). 13C{1H} NMR (150 MHz,
THF-d8, 27 °C): δ 10.9 (C5Me5), 104.8 (C5Me5), 128.6 (Ph), 128.8
(Ph), 130.5 (Ph), 130.9 (Ph), 133.0 (Ph), 133.1 (Ph), 135.9 (Ph), 136.4
(Ph), 236.6 (CO). The signals of MoCC were not observed. 13C{1H}
NMR (150 MHz, THF-d8, ꢀ90 °C): δ 10.8 (C5Me5, 9), 11.1 (C5Me5,
8), 90.9 (Ph2SiCC, 9), 103.0 (Ph2SiCC, 9), 104.4 (C5Me5, 9), 104.7
(C5Me5, 8), 128.9 (Ph), 129.3 (Ph), 130.9 (Ph), 131.2 (Ph), 131.3 (Ph),
131.5 (Ph), 131.7 (Ph), 132.0 (Ph), 132.9 (Ph), 134.3 (Ph), 134.5 (Ph),
135.6 (Ph), 135.9 (Ph), 136.0 (Ph), 136.2 (Ph), 136.4 (Ph), 137.0 (Ph),
143.7 (MoCC, 8), 190.5 (MoCC, 8), 233.6 (CO), 236.5 (CO), 237.9
(CO), 238.6 (CO). 29Si{1H} NMR (79 MHz, THF-d8, 27 °C): δ ꢀ
38.0 (SiHPh2). The MoSiPh2 signal was not observed. 29Si{1H} NMR
(119 MHz, THF-d8, ꢀ90 °C): δ ꢀ39.0 (SiHPh2, 8), ꢀ24.0 (SiHPh2, 9),
ꢀ14.4 (MoSiPh2, 8), 55.2 (MoSiPh2, 9). Anal. Calcd for C38H36O2Si2-
Mo: C, 67.44; H, 5.36. Found: C, 66.77; H, 5.34.
’ ASSOCIATED CONTENT
S
Supporting Information. CIF files containing X-ray crys-
b
tallographic data for complexes 5 and 6, figures giving the NMR
spectra of 5ꢀ9, text giving the complete reference of Gaussian 03, a
table giving DFT/BS-III-calculated Mulliken populations in fragment
MOs of 5M, text giving a comparison between 5M and 14, and tables
of Cartesian coordinates and total energies of 5M. This material is
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: sakaba@m.tohoku.ac.jp (H.S.); sakaki@moleng.kyoto-u.
ac.jp (S.S.).
X-ray Crystal Structure Determinations. Selected crystallo-
graphic data for 5 C7H8 and 6 C7H8 are given in Table 4. Single crystals
Present Address
#Department of Chemistry, Northwestern University, 2145
Sheridan Road, Evanston, Illinois 60208, USA
3
3
of 5 C7H8 and 6 C7H8 were obtained by recrystallization from toluene/
3
3
hexane and toluene/pentane, respectively. The diffraction data were
collected on a Rigaku AFC10/Saturn instrument with graphite-mono-
chromated Mo KR radiation at ꢀ100 °C. The data were processed using
CrystalClear64 and corrected for Lorentz and polarization effects. The
structure was solved by direct methods (SIR97 or SHELXS-97),65,66 and
expanded using Fourier techniques (DIRDIF99).67 All non-hydrogen
atoms were refined anisotropically except for disordered toluene, with
site occupation factors of 0.65/0.35 for 5 and 0.70/0.30 for 6. Hydrogen
’ ACKNOWLEDGMENT
This work was financially supported by Grants-in-Aid on basic
research for Scientific Research (Nos. 1835005 and 22550051),
Priority Areas for “Molecular Theory” (No. 461), Specially
Promoted Research (No. 22000009), the NAREGI project from
4528
dx.doi.org/10.1021/om200096z |Organometallics 2011, 30, 4515–4531

Organometallics
ARTICLE
the Ministry of Education, Science, Sports, and Culture, and a
Research Grant of the Japan Society for the Promotion of Science
for Young Scientists. Some of the theoretical calculations were
performed with the SGI workstation at the Institute for Molec-
ular Science, Okazaki, Japan.
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to a mononuclear metal center has been discussed for 1-zircona-2,5-
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(49) In relation to 1,4-disilabutatriene coordination, μ-trans-buta-
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(H2CCCCH2)MCp2 (M d Ti,50 Zr51), which have almost planar
MCCCCM skeletons and have been best described as a 2,5-dime-
tallabicyclo[2.2.0]hex-1(4)-ene structure.50 The contribution of the
corresponding 2,5-dimetalla-3,6-disilabicyclo[2.2.0]hex-1(4)-ene type
structure to complexes 5 and 6 is, however, ruled out because of the
nearly perpendicular geometry of the MSiCCSiM (M d W, Mo)
moieties and very small Si1ꢀC2 and Si2ꢀC1 bond indices (0.065 and
0.075, respectively) compared to the Si1ꢀC1 and Si2ꢀC2 bond indices
(0.705 and 0.675, respectively) for 5M, a model complex of 5. See
Figure 7A and the theoretical study in the text.
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4530
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Organometallics
ARTICLE
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