Reactions and Dynamics of cr-Silane Complexes

The reactions of hydrosilanes have been well reviewed16 and only major points concerning c-silane complexes will be addressed here. Dynamics and reactivity have not been as extensively studied as those for H2 complexes, but are remarkably similar, e.g., hydrosilylation is well known and directly analogous to homogeneous hydrogenation. It is generally assumed that the mechanisms are the same.1 Alkene insertion into a -Si bond is quite common also, and dienes can be photocatalyti-cally hydrosilylated in the presence of Cr(CO)6 [Eq. (11.19)].67 The mechanism is 

Although not as many examples of heterolysis of silane Si-H bonds are known as compared to splitting of H-H bonds, the Si is highly activated toward nucleophilic attack when coordinated to electrophilic cationic centers because of depletion of the electron density from the Si-H bond.55 The Si-H bond in free silanes is 

At room temperature heterolytic cleavage of the Si-H bonds in 13 occurs in CH2C12  

If this reaction is carried out in the presence of alcohols, however, homogeneous catalysis of silane alcoholysis occurs with high efficiency and selectivity  

It is important to note that kinetic and mechanistic studies are consistent with direct nucleophilic attack by ROH on a /2-Si-H bond rather than initial OA.69 Cationic [CpFe(CO)(PR3)(HSiEt3)]+ is observed by NMR at room temperature but only in the presence of excess silane (sacrificial removal of trace H20 as Et3SiOH) and cannot be isolated as a solid. 40 [CpFe(CO)(PR3)]+ as well as [Mn(CO)3(P)2]+ (P = P(OCH2)3CMe) also catalyze silane alcoholysis [Eq. (1121)] in the pres- 

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