Silanes heterolytic cleavage

B. Heterolytic Cleavage of Silanes on Electrophilic Cationic Centers... 

The side-on (r)2) bonding in M r 2-H2 and other a-complexes has been termed non-classical, on analogy to the 3-center, 2-electron bonding in non-classical carbocations and boranes (Fig. 2). One of the first questions raised when H2 complexes were discovered is whether they would be important in catalytic reactions. As will be shown below the answer is an emphatic yes, as exemplified by the elegant asymmetric catalytic hydrogenation systems of Nobel-laureate Ryoji Noyori. Also, the mechanism of catalytic silane alcoholysis directly involves two different a complexes M(r 2-Si-H) and M(r 2-H2). In both of these systems, the crucial step is heterolytic cleavage of the H H and/or Si-H bond, the primary subject of this review. 

There are much fewer examples in the literature of the heterolytic cleavage of Si H bonds compared to H-H and even fewer other examples in which a cr-silane complex was observed as an intermediate in the activation. We have synthesized alkyl-substituted diimine ligands with sidearms containing labile functional groups that reserve a vacant site for binding and activation of sigma bonds as shown in Eq. (32) (108,109). 

At -40°C or lower (unstable towards heterolytic cleavage). The silane in the silane complex is EtjSiH. 

Se-Heterocyclics 15, 606 Si-Heterocyclics (s. a. Alkoxy-silanes, cyclic) 13, 649 Heterogeneous s. under Reaction, Reduction Heterolytic C-cleavage... 

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