Dehydrocoupling general reaction

Because of these limitations, considerable effort has been focused on the development of new synthetic routes to polysilanes. The early transition metal-catalysed dehydrocoupling process discovered in 1985 [eqn (10.8)] is potentially very attractive however, the molecular weights of the polysilanes formed to date are generally fairly low (Mn<8000)." The catalysts used for these coupling reactions are usually titanocene or zirconocene derivatives." " " ... 

Dehydrocoupling (also referred to as dehydrocondensation) provides a versatile route to the synthesis of E-E bonds. The generalized dehydrocoupling reaction is shown in Eq. (1). 

Relatively little work has been reported on the dehydrocoupling of Si-H/ H-C bonds. The thermodynamics of this type of reaction are similar to those of Si-H/Si-H reactions, the stronger Si-C bond in the product (compared to an Si-Si bond) compensating for the stronger C-H bond of the reactant. The kinetic difficulty in realizing this type of reaction is typical of the general difficulty of catalytically activating nonpolar C-H bonds. 

There is some ambiguity as to whether the alkenyl- and alkynylsilane-forming reactions are true dehydrocoupling reactions. According to the definition as embodied in Eq. (1), this would require the direct activation of a C-H bond, such as the = C—H bond of an olefin. The general consensus is that the alkenyl- and alkynylsilane-forming reactions are more likely to take place via an insertion of the olefin into an M-Si bond, followed by /3-hydride elimination [Eqs. (18) and (19)] in the case of electron-rich metal complexes,1616 or by bond metathesis of M-Si and H -C= in the case... 

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