Organosilicon chemistry. Part 24. Homogeneous rhodium-catalysed hydrosilation of alkenes and alkynes: the role of oxygen or hydroperoxides

Abstract

The hydrosilation of propene, hex-1-ene, and hex-1-yne, catalysed by [RhCl(PPh₃)₃] has been reinvestigated. When all reagents are carefully purified, the hydrosilation reaction is completely inhibited but can be initiated by the addition of oxygen or t-butyl hydroperoxide. The rate and extent of reaction in the latter case is unaffected by the presence of phenolic radical traps. For optimum reaction, stoicheiometric quantities of hydroperoxide are required. In the hex-1-yne system, variation of the PPh₃: Rh ratio gives maximum activity at 1 : 1 and, with this stoicheiometry, the reaction rate is relatively insensitive to purification of the reagents. It is suggested that the role of oxygen or hydroperoxide is to remove triphenylphosphine from the system, by oxidation, generating a highly active catalyst with a low PPh₃: Rh ratio. In the ‘clean’ conditions isomerisation of hex-1-ene proceeds rapidly, being catalysed by the silyl complex [RhH(Cl)(SiR₃)(PPh₃)₂].