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

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 Ph₂HSiCtCSiHPh₂with 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 (j^CC_lp) and π orbital (j^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 (j^CC_π*) of the ethynediyl. (2) CTs occur from

the lone pair orbital (j^Si_lp) of the silylene to d^W_unocand from d^W_occto the empty p orbital (j^Si_p) of the silylene. (3) CT occurs from

j^CCto j^Si_p, which leads to considerably strong SiꢀC bonding interactions and a considerably large elongation of the CꢀC

π

distance. The mixing of j^CC_πinto j^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_occto j^CC_π*also participate in the CꢀC

bond weakening of the ethynediyl. Reaction of 1a with 1 equiv of Ph₂HSiCtCSiHPh₂aﬀorded 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.¹Recently, this method has been

widely applied for synthesizing a variety of base-stabilized^2ꢀ6and

base-free^7ꢀ13transition-metal silylene complexes. Silylene com-

plexes¹⁴are 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

experimental^2ꢀ16and theoretical works^17,18to 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,¹⁹the unique tungsten silylene complexes (η⁵-C₅-

Me₄R)(CO)₂W(CC^tBu)(SiPh₂) (3a, R d Me; 3b, R d Et) were

recently obtained via SiꢀH bond activation of Ph₂HSiCtC^tBu

by 1a,b(Scheme1).^19bThe novel bonding nature of these complexes

Received: February 2, 2011

Published: August 10, 2011

r

2011 American Chemical Society

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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).^18aThese 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-Ph₂SiCC^tBu) (4) by reacting 2 with Ph₂HSiCtC^tBu

(Scheme 1).^19cIn 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 C₂ligand 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.^21ꢀ42Also, they are building blocks for the

synthesis of bare carbon chains stabilized by transition-metal

complexes.^21a,b,41In this regard, various ethynediyl-bridged di-

nuclear complexes have been synthesized and investigated in

many experimental^21ꢀ40and theoretical works.^22b,38,41,42Three

possible bonding modes have been proposed so far: namely,

the acetylenic form L_nMꢀCtCꢀML_n, the cumulenic form

L_nMdCdCdML_n, and the dimetalla-1,3-butadiyne form

L_nMtCꢀCtML_n.^21b,38,41Among these three valence bond

descriptions, most of the synthesized complexes contain the

acetylenic structure.^22ꢀ32The cumulenic structure has been found

in a few titanium,^31,33tantalum,³⁴ruthenium,³²and manganese³⁵

complexes, and the dimetalla-1,3-butadiyne structure is limited

to tungsten,^36ꢀ39molybdenum,⁴⁰and manganese³⁵complexes.

Here, we examined the reaction of Ph₂HSiCtCSiHPh₂with 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

Ph₂HSiCtCSiHPh₂with 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).⁴³The 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 3b^19band are in the range of

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Scheme 2

WꢀSi bond distances (2.45ꢀ2.51 Å) in base-stabilized silylene

tungsten complexes,^2c,3a,15asuggesting 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) fragment^44,45

and are somewhat longer than the WꢀCC^tBu 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,⁴⁷and 1,4-disilabutatriene-bridged structure D^48,49

(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

Ph₂HSiCtCSiHPh₂was investigated. Toluene-d₈was 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

SiHPh₂group, while the spectrum at ꢀ70 °C exhibited two

signals at ꢀ39.0 and ꢀ46.7 (¹J_WSid 41 Hz) ppm. Assignment of

46

distance of 1.208(5) Å in Ph₂HSiCtCSiHPh₂to 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,8eare 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

Ph₂HSiCtCSiHPh₂⁴⁶and 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)^8aand ModSi (2.3872(7) Å)^8ein the base-free

1

29

the former signal to SiHPh₂is 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 (¹J_WSid

41 Hz) ppm; ¹³C, 186.5 and 137.7 ppm) are close to those of the

SiCC framework (²⁹Si, ꢀ40.9 (¹J_WSid 41 Hz) ppm; ¹³C, 178.9

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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).^19dWhen 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-d₈contained 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 SiHPh₂signals 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 (SiHPh₂and 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 SiPh₂signals. In fast interconversion on the NMR time scale,

a small chemical shift diﬀerence between the SiHPh₂signals

(ꢀ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 CD₂Cl₂showed 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 C₅Me₅signal 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 pseudorotation⁵²around

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 SiPh₂moieties 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]^2ꢀor 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 SiH₂groups

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 C₅Me₅and 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. SelectedOptimizedParameters^aof 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

3M^b

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(O^tBu)₃

and CpL₂WtCR

36ꢀ38

(L d CO, P(OMe)₃and 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 SiH₂group 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 SiH₂does 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 SiH₂and 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 SiH₂moiety 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 SiH₂and 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

^aThe DFT (B3PW91)/BS-I method was employed. Bond lengths are

given in angstroms and bond angles in degrees. ^bReference 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)⁵⁴and 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 H₂SiCCSiH₂moieties 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.⁵⁷The

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 H₂SiꢀCꢀCꢀSiH₂moiety 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

CꢀCꢀSiH₂moiety 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).⁵⁵The 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).⁵⁵From 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 SiH₂moiety is moderately smal-

ler in 5M than in 3M but much smaller than in 10, indicating that

the SiH₂moiety 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).⁵⁸These 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. NBO^aPopulations 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 j_LUMO+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 j^Si_pand j^Si_lp, 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 j^CCand

π1*

j^CC_π2*, 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 j^CCand j^CC

,

lp1

lp2

respectively. The degenerate HOMO-1's are two π orbitals,

6.464

6.296

6.563

which are named j^CC_π1and j^CC_π2, 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 (d^W_occ) which overlaps with

j^CC_π*in a bonding way. This corresponds to π-back-donation

from W2 (d^W_occ) to the CC moiety (j^CC_π*); see CT(d^W_occf

j^CC_π*) in Scheme 8. Another back-donation from W1 d^W_occto

j^Si1_pof SiH₂is involved in this HOMO; see CT(d^W_occf j^Si_p).

HOMO-1 mainly consists of d^W_occ. As shown in Scheme 7B,

HOMO-2 involves several kinds of CT interactions which

^aDFT(B3PW91)/BS-II NBO calculations.

population of the CC moiety of 5M is somewhat larger than

those of 13 and 13d-an,⁵⁹while it is somewhat smaller than in

13d and 13-an.⁵⁹The population of the SiH₂moiety of 5M is

considerably smaller than those of 13, 13d, 13-an, and 13d-an.⁵⁹

These populations of the CC and SiH₂moieties 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

H₂SiꢀCꢀCꢀSiH₂moiety 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,^60,61where 5M is considered to consist of five moieties, as

shown in Scheme 6.

are formed between the W, CC, and SiH₂, as follows: d^W

occ

of W1 largely participates in HOMO-2, into which the unoccupi-

ed j^CCand j^Si1mix in a bonding way. These interactions

π*

p

correspond to CT(d^W_occf j^CC_π*) and CT(d^W_occf j^Si_p) (see

Scheme 8). Also, d^W

of W2 largely participates in this

unoc

HOMO-2 into which the occupied j^Si2_lp, j^CC_lp, and j^CC

π

moderately mix in a bonding way with the d^W_unocorbital. These

correspond to CT(j^Si_lpf d^W_unoc), CT(j^CC_lpf d^W_unoc), and

CT(j^CC_πf d^W_unoc) (see Scheme 8). However, the presence of

j^CCand j^CCis not clearly observed in this HOMO-2

π

π*

ψ ðABCDEÞ ¼ a_ijj ðAÞ þ b_ikj ðBÞ þ c_ilj 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 j^CC_π*into j^CC_πconsiderably increases the contribu-

tion of the C1 p orbital but considerably decreases that of the C2

p orbital. This polarized π₁bonding orbital is observed in

HOMO-2. In the π₂space 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 j^Si_lpand j^Si_porbitals 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 j^Si_pand the

antibonding mixing of j^Siwith d^Wof the W lead to a

j

k

l

þ

d_imj ðDÞ þ e_inj ðEÞ

ð1Þ

∑

m

n

m

n

ψ_i(ABCDE) represents the ith MO of the total system ABCDE,

j_j(A) is the jth MO of fragment [Cp(CO)₂W]⁺, j_k(B) is the

A

kth MO of the fragment (SiH₂)_B, j_l(C) is the lth MO of frag-

ment [CC]^2ꢀ_C, j_m(D) is the mth MO of the fragment (SiH₂)_D,

and j_n(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. a_ij, b_ik, c_il, d_im, and e_inare expansion coefficients of

j_j(A), j_k(B), j_l(C), j_m(D), and j_n(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 j^CC_π, which over-

laps with j^Si_pand d^W_unocin a bonding way. These correspond to

CT(j^CC_πf j^Si_p) and CT(j^CC_πf d^W_unoc) (see Scheme 8).

HOMO-4 and HOMO-6 involve the bonding interaction be-

occ

F ðAÞ ¼ ½a²þ a_ijb_ikS_jk

þ

∑

l

a_ijc_ilS_jl

∑

j

ij

i

k

þ

a_ijd_imS_jm

þ

a_ije_inS_jnꢁ

∑

n

ð2Þ

∑

tween j^CCand d^W_unoc, as shown in Figure 9, which corre-

m

lp

sponds to CT(j^CC_lpf d^W_unoc). Though CT(j^CC_πf j^Si_p) is

found in HOMO-3, CT(j^Si_lpf j^CC_π*) is not clearly observed

where F_j(A) represents how much electron population j_j(A)

possesses in the total system ABCDE and S_jkis the overlap

integral between j_j(A) and j_k(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 j^Si

lp

expands toward the W center in 5M but toward the CC moiety

in 3M.

As shown in Table 3, the population of j_HOMO-1(W) is close

to 2.0e in 5M and the population of the j_HOMO(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 d⁴complex (+II oxidation state of W). Thus, the similar

population of j_HOMO(W) indicates that 5M is understood to be

a d⁴complex as well. It is likely that the considerably smaller pop-

ulation of j_HOMO(W) in 10 than in 3M arises from the larger

CT(j_HOMO(W) f j^Si_p),⁶²which will be discussed below in

more detail. The population of j^Si_pis moderately larger in 5M

than in 10 but somewhat smaller than in 3M. The population of

j^CC_πin 5M is similar to that of 3M but considerably smaller than

that of 10. These results indicate that CT(j^CC_πf j^Si_p) 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

j^Si_pand j^CC_π(see HOMO-3 of Figure 9). The population of

j^Siis considerably larger in 5M than in 3M but considerably

π*

lp

smaller than in 10 (Table 3). The population of j^CCis

somewhat larger in 5M than in 3M but considerably larger than

in 10. Though the poor overlap between j^Si_lpand j^CC_π*in 5M

suggests that CT(j^Si_lpf j^CC_π*) is considerably weaker in 5M

than in 3M, the population of j^CC_π*is large in 5M. These results

indicate that CT(d^W_occf j^CC_π*) is stronger in 5M than in 3M.

The considerable weight of j^CC_π*in the HOMO (Scheme 7A)

and the considerably smaller population in j_HOMO(W) of 5M

also support this conclusion. The population of j^CC_lp1in 5M is

similar to that of 10 but moderately larger than that of 3M. The

population of j^CCis somewhat smaller in 5M than in 10.

lp2

These results indicate that CT(j^CC_lpf d^W_unoc) 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(j^Si

f

lp

d^W_unoc) and CT(d^W_occf j^Si_p) are formed in 5M. Because the

lone pair of SiH₂expands 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

H₂SiCCSiH₂moiety 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 SiH₂moiety 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 H₂SiCCSiH₂moiety 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-

SiHPh₂with 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-

SiHPh₂to 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 Ph₂HSiCtCSiHPh₂aﬀorded 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(d^W_occf j^CC_π*) and CT(j^CC_πf

j^Si_p) considerably weaken the CꢀC bond of 5M. The mixing of

j^CC_πinto j^CC_π*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(j^Si

f

(1) CTs occur from the lone pairs (j^CC_lp) and π orbital (j^CC

)

π

lp

j^CC_π*) is considerably weak in 5M due to a poor overlap

between them, only CT(j^CC_πf j^Si_p) 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 (d^W_unoc) of the W

and from the occupied d orbital (d^W_occ) of the W to the π* orbital

(j^CC_π*) of the ethynediyl. (2) CTs occur from the lone pair

orbital (j^Si_lp) of the silylene to d^W

and from d^Wto the

occ

unoc

empty p orbital (j^Si_p) of the silylene. (3) CT occurs from j^CC

π

index of 3M. This is because the C1 p_πorbital overlaps with j^Si1

to j^Si_p, which leads to considerably strong SiꢀC bonding

p

in 5M but the C2 p_πorbital cannot overlap with j^Si1in 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 j^CC_πinto j^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(d^W_occf j^CC_π*) 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. Populations^aof 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.^19cThe 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

WSiPh₂signal was not observed. ²⁹Si{¹H} NMR (119 MHz, THF-d₈,

ꢀ70 °C): δ ꢀ46.7 (¹J_WSid 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

_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

j^Si

0.575

0.941

0.540

1.256

0.665

0.793

P

lp

[C₂]^2ꢀor [CCH]^ꢀ

0.453 ^b

j^CC

0.097 ^b

1.276

1.812 ^c

0.397

1.264

1.469

π*

lp1

π

1.277

1.492 ^c

for C₅₀H₅₀O₄Si₂Mo₂C₇H₈: C, 64.89; H, 5.54. Found: C, 64.87; H, 5.79.

3

1.472

1.635

lp2

^aDFT(B3PW91)/BS-II calculations. See Table S1 in the Supporting

Information for BS-III calculations. ^bAverage of the populations in

j^CC_π*1and j^CC_π*2. ^cAverage of the populations in j^CC_π1and j^CC

’ 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-d₈were distilled from sodium benzophe-

none ketyl, and dichloromethane-d₂was distilled from calcium hydride.

Ph₂HSiCtCSiHPh₂,⁶³Cp*(CO)₂W(NCMe)Me (1a),^19aand Cp*-

(CO)₂Mo(NCMe)Me (2)^19cwere 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 C₅₀H₅₀O₄Si₂W₂C₇H₈: C, 55.62; H, 4.75.

3

Found: C, 55.48; H, 4.85.

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Table 4. Crystallographic Data of 5 C₇H₈and 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 F²with SHELXL-97.⁶⁸All 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 functional^70,71was 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 3b^19bthan does the B3LYP func-

tional.^70,72We 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)⁷³and their valence electrons were represented

by the (341/321/21) basis sets.⁷³The usual cc-pVDZ⁷⁴basis sets were

employed for Si, C, and O, and the usual 6-31G⁷⁵basis 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.^76,77For the other atoms, the cc-pVTZ basis

sets⁷⁴were employed, where the f polarization function was excluded to

save computational time. This BS-II system was used to evaluate the

Wiberg bond index⁷⁸and 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,^72,79,80where 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)⁸¹was used for all

these computations. NBO population analysis was carried out with the

method proposed by Weinhold et al.⁸²Molecular orbitals were drawn

with the MOLEKEL program package (version 4.3).⁸³

3

5 C₇H₈

6 C₇H₈

3

formula

fw

C₅₀H₅₀O₄Si₂W₂C₇H₈C₅₀H₅₀O₄Si₂Mo₂C₇H₈

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) (cm^ꢀ1

)

4.590

5.817

no. of rﬂns collected 71 469

79 189

no. of unique reﬂns

R_int

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-d₈solution 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 MoSiPh₂signal 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 C₃₈H₃₆O₂Si_2-

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 C₇H₈and 6 C₇H₈are given in Table 4. Single crystals

Present Address

^#Department of Chemistry, Northwestern University, 2145

Sheridan Road, Evanston, Illinois 60208, USA

3

of 5 C₇H₈and 6 C₇H₈were obtained by recrystallization from toluene/

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

CrystalClear⁶⁴and corrected for Lorentz and polarization effects. The

structure was solved by direct methods (SIR97 or SHELXS-97),^65,66and

expanded using Fourier techniques (DIRDIF99).⁶⁷All 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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dx.doi.org/10.1021/om200096z |Organometallics 2011, 30, 4515–4531

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

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