Metal Complexes with Bridging M—H—Si Interactions

DINUCLEAR METAL COMPLEXES WITH BRIDGING M—H—SI INTERACTIONS 

At the time this article was written, the only mononuclear complexes for which a metal-hydrogen-silicon three-center bond was unambiguously proved belong to the (ir-arene) (OC)2M(H)SiR3 family. Some less certain 

The distinction between between mono- and dinuclear metal complexes is only a formal one in terms of bonding (consider one substituent at silicon the second metal atom instead of an organic group, halide, or hydride substituent). The structural and spectroscopic features related to the three-center bond should therefore be more or less the same as previously discussed. 

The crystal structures of 13 (Fig. 5) and 12 provide unambiguous proof for the presence of Ti—H—Si three-center bonds (57). To emphasize the similarities with mononuclear complexes, we consider one Si—H bond of the silane (Cp2Ti)PhSiH2 to be added to the titanium center of another Cp2Ti—SiH2Ph in 12 and to a Cp2TiH molecule in 13 (type I). In both complexes oxidative addition is arrested at a point corresponding to H in Eq. (5). 

In the H-NMR spectra of 12 and 13, separate signals in the Si—H region and in the metal hydride region are observed (57). The molecules are therefore not fluxional on the NMR time scale with respect to hydrogen 

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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. 

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