Addition of Group IVB hydrides to olefins

As one descends Group IVB of the Periodic Table from Si to Ge to Sn to Pb, the ease of addition of the hydrides (e.g. R3MH) to olefins increases markedly with the decrease in strength of the M—H bonds. Thus trialkyl-silanes require either heating to about 300X under olefin pressures of at least 300 atm, or UV irradiation, or catalysis by, for example, peroxides, certain metal salts or tertiary amines. Trialkylgermanes and trialkyl-stannanes add to activated terminal carbon-carbon double bonds at 120°C and 90 C respectively, and a catalyst is not necessary, e.g. 

Tri-n-butyl-lead hydride is so reactive that it adds rapidly to olefins and acetylenes in ether solution without a catalyst even at 0 C, e.g. 

The addition of Si—H bonds to olefins and acetylenes is of some importance industrially in the production of intermediates for silicone manufacture. 

Addition may occur by thermal reaction under pressure, but proceeds better imder UV irradiation or when catalyzed. The thermal, photolytic or peroxide catalyzed reactions involve free-radical chain mechanisms. Radicals are first produced from the silicon hydride, 

The chain propagation step is often not very important, as the silyl radicals are very efficient chain transfer agents. 

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