Hydrosilation radical promotion

Reactions of silanes are often best catalyzed by hydrosilation catalysts such as Pt or Pd. Similarly, C — H bonds are formed in the addition of phosphines or amines to C = C or C = C bonds. Reactions are catalyzed (acid, base, or metal) or free radical promoted, e.g. ... 

Free radical promoted hydrosilation of olefins typically gives poorer conversions than are produed by hydrosilation mediated by metal catalysts. However, they are not subject to isomerization of the olefin, a side reaction that can be a nuisance in metal-catalyzed hydrosilations. This is due to the extremely efficient hydrogen atom transfer reaction from Si-H to carbon radicals and the resulting very short lifetimes of the latter. The generally accepted mechanism for these processes is illustrated in Scheme 1. 

The term hydrosilation (or hydrosilylation) refers to the addition of a molecule containing a Si-H bond across the multiple bond of a substrate, usually an alkene, alkyne, or carbonyl compound (equation 1). The reaction can be promoted by UV-light, radiation (y- and X rays), radical initiators, Lewis acids, nucleophiles, or, most importantly, transition metal catalysts. Hydrosilation is related to the important processes of hydrogenation (see Hydrogenation) and hydroboration (see Hydroboration), all of which belong to the general reaction class of hydroelementation. 

Hydrosilation can be promoted by peroxides that initiate the reaction by hydrogen abstraction from the silane and propagate in a fashion similar to that of classical organic free radical additions ... 

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