Synthesis, Structure, and Bonding Nature of Ethynediyl-Bridged Bis(silylene) Dinuclear Complexes of Tungsten and Molybdenum

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• 作者：Hiroyuki Sakaba ; Hiroyuki Oike ; Masaaki Kawai ; Masato Takami ; Chizuko Kabuto ; Mausumi Ray ; Yoshihide Nakao ; Hirofumi Sato ; Shigeyoshi Sakaki
• 刊名：Organometallics
• 出版年：2011
• 出版时间：September 12, 2011
• 年：2011
• 卷：30
• 期：17
• 页码：4515-4531
• 全文大小：1629K
• 年卷期：v.30,no.17(September 12, 2011)
• ISSN：1520-6041

文摘

Reactions of Ph₂HSiC鈮SiHPh₂ with 2 equiv of the labile complexes Cp*(CO)₂M(NCMe)Me (1a, M 鈺?W; 2, M 鈺?Mo; Cp* 鈺?畏⁵-C₅Me₅) gave the novel CC-bridged dinuclear complexes Cp*(CO)₂M(SiPh₂)(渭-CC)(SiPh₂)M(CO)₂Cp* (5, M 鈺?W; 6, M 鈺?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鈥揝i鈥揅 three-membered-ring skeletons which are linked nearly perpendicularly to each other. The W鈥揝i bond distances of 5 are comparable to those of typical base-stabilized tungsten silylene complexes. The C鈥揅 bond distance is much longer than a typical C鈮 triple-bond distance and is similar to a typical C鈺怌 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)(渭-CC)(SiH₂)W(CO)₂Cp (5M; Cp 鈺?畏⁵-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 (蠁^CC_lp) and 蟺 orbital (蠁^CC_蟺) 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 蟺* orbital (蠁^CC_蟺*) of the ethynediyl. (2) CTs occur from the lone pair orbital (蠁^Si_lp) of the silylene to d^W_unoc and from d^W_occ to the empty p orbital (蠁^Si_p) of the silylene. (3) CT occurs from 蠁^CC_蟺 to 蠁^Si_p, which leads to considerably strong Si鈥揅 bonding interactions and a considerably large elongation of the C鈥揅 distance. The mixing of 蠁^CC_蟺 into 蠁^CC_蟺* induces 蟺 orbital polarization of the CC moiety in one plane and a reverse 蟺 orbital polarization in the perpendicular plane. These polarizations in addition to the CT from d^W_occ to 蠁^CC_蟺* also participate in the C鈥揅 bond weakening of the ethynediyl. Reaction of 1a with 1 equiv of Ph₂HSiC鈮SiHPh₂ afforded a mixture of the mononuclear acetylide鈥搒ilylene 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 acetylide鈥搒ilylene complex Cp*(CO)₂Mo(CCSiHPh₂)(SiPh₂) (8) and silapropargyl/alkynylsilyl complex Cp*(CO)₂Mo(畏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.