Hydrosilylation of conjugated dienes

Not intensively studied, but usually occurs by 1,4-addition, and only at high temperature. Pd catalysts are active with conjugated olefins but not with non conjugated ones. 

The yield of the 1 1 adduct rises up to 85% at 100 °C with r-allyl PdCl as catalyst. Moreover, the reaction is highly stereoselective as the pure Z isomer is obtained by treatment of butadiene with RjSiH in the presence of Cr(CO)g under UV irradiation [35]. 

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Dienes. Hydrosilylation of conjugated dienes often leads to a complex mixture of products composed of regio- and stereoisomers of 1 1 addition, 1 2 addition products, and oligomers. Dihydrosilanes may form silacycloalkanes as well. In contrast... 

Stereoselective hydrosilylation of conjugated dienes gives chiral monoaddition products, sometimes as a mixture of regioisomers. The yield and enantiomeric excess of the products depend on the nature of the chiral organometallic catalyst used. 

The hydrosilylation of conjugated dienes such as butadiene and isoprene using HjPtClg as the catalyst proceeds only at elevated temperatures giving a mixture of products. The hydrosilylation of butadiene with HSiMeCl2 affords a 1 1 mixture of monoadduct and diadduct (combined yield 50%), the former including but-2-enylsilane as major (85-90%) and but-3-enylsilane as minor products (15-10%) ... 

Nickel complexes also exhibit a high catalytic activity toward the hydrosilylation of conjugated dienes under mild conditions. The reaction usually occurs in the manner of a 1,4-addition, but the regio- and stereoselectivity is rather low compared with that achieved by palladium catalysts. 

Scheme 10.7 Hydrosilylation of conjugated dienes catalyzed by chromium carbonyl (partially reproduced from Ref [49]).

Hydrosilylation of conjugated dienes proceeds predominantly across positions 1 and 4, although 1,2-addition can also occur, for example, hydrosilylation of 1,3-butadiene by trichlorosilane leads to 1,4-addition. 

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