Si-H-M complexes

Since the first recognized Si-H o complexes were reported by Jetz and Graham [77] for the product from the reaction of Re2(CO)io with R2SiH2 (R = Me, Ph), many examples have been found. Schubert [78] and Crabtree [79] reviewed earlier work on r/ -coordinated H-Si bonds and recently Corey and Braddock-Wilking [80] have reviewed transition metal chemistry of hydrosilation. By comparison with other a complexes, the structures of silane complexes more closely resemble those of oxidative addition products rather than those of simple a complexes with an unstretched X-H bond. This is maybe because the Si-H bond has a much greater basicity than other a donor ligands like H-H and C-H and thus acts as a 

Activation of Substrates with Non-Polar Single Bonds 

Careful analysis of the crystal structures of type of Cp(CO)2Mn(H-SiR3) complexes indicates that the Mn-Si distance becomes considerably longer as the oxidative addition proceeds while the Mn-H distance becomes a little longer and r(Si-H) remains about same [81]. Based on the structural analysis a reaction trajectory for oxidative addition of silane to a metal was proposed. The H atom of the Si-H unit approaches Mn, and the Si-H unit then pivots, increasing the Mn-Si interaction. This is similar to the trajectory for the interaction of an agostic C-H bond with a metal atom, as mentioned earlier in this chapter, and is consistent with theoretical work [83]. 

While the majority of J7 -silane complexes characterized to date are mononuclear species, there are several dinuclear or polynuclear metal complexes with bridging M-H-Si interaction. A Si-H-M interaction was unambiguously identi-hed in compound 25 by X-ray structure determination, showing the Si-H bond distance of 1.58 A. This is 7% longer than in free silane and represents a rare case of unstretched silane a complex [84]. The unique unstretched silane o bond is further documented in the tetrahedral geometry around the silicon atom, which is largely retained, as opposed to the more distorted geometry at the Si atom in the extensively studied mononuclear Mn complexes. 

Recently, several complexes with an agostic Si-H-M have appeared in the literature [85]. The majority of them has at least one SiMe2 bridging ligand. Yttrium complex 26 exhibits unusual multiple Si-H-M agostic interactions, which were characterized by X-ray structural determination and other spectroscopic methods 

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