Hydride complexes Agostic

In conclusion, one can look at the silyl hydride complexes in a number of ways, either as coordinated silane with a very elongated Si- -H bond or as complexes of hypervalent silicon moieties with an agostic Si-H bond [109]. It should be pointed out that the ability of Si to become hypervalent in the vicinity of a transition metal fragment has some important consequence on the reactivity of silane derivative in metathesis reaction with lanthanide complexes [115]. 

Generally, synthetic procedures for a-silane complexes are similar to those that produce silyl hydride complexes and involve addition of silane to an unsaturated complex, often generated by photolytic or thermolytic dissociation of CO as for CpMn(CO)2(silane). Agostic, H2, or solvento complexes are also excellent precursors because silanes tend to bind as well or more strongly than H2 or weak donors such as THF. Addition of a primary or secondary silane to solutions of Mo(CO)(R2PC2H4PR2)2 forms yellow silane complexes [Eq. (11.4)]. The less... 

Analogous situations exist with allyl hydrides and propene complexes, agostic propene, propene hydrides, and isopropyl complexes. Exchange of hydride with methylene carbene is relevant to the Fischer-Tropsch reaction,... 

Agostic versus hypervalent Si-H interactions in half-sandwich complexes of Nb and Ta have been studied by Merkulov et al Among others, a strong increase of Vhsi has been observed by them in a series of chlorosilyl hydride complexes of tantalum, Cp(ArN)Ta(PMe3)(H)(SiCl R 3) when passing from n = 0 (14 Hz) to n = 3 (50 Hz). 

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