Rhodium-catalysed hydrosilylation: the direct production of alkenyl(triethyl)silanes from alk-1-enes and triethylsilane

Abstract

Hex-1-ene undergoes reaction with triethylsilane in 1,2-dichloroethane solution in the presence of [(C 5Me 5Rh) 2Cl 4] catalyst (1) to give the normal hydrosilylation product n-hexyl(triethyl)silane (2), as well as the unexpected E-hex-1-en-1-yl(triethyl)silane (3) and E-hex-2-en-1-yl(triethyl)silane (4). These reactions proceeded smoothly and were not significantly influenced by air, moisture, radical initiators, or radical traps. The relative proportions of (2) and (3) [(4) was a minor product] were determined by the temperature and the ratio of olefin to silane, the vinylsilane (3) being favoured by lower temperatures and a high olefin-to-silane ratio. Under optimum conditions selectivity as high as 69% towards (3) could be achieved. Ethylene, styrene, hept-1-ene, and non-1-ene gave similar results. Other rhodium catalysts were tested; of these, the best was [Rh(PPh 3) 3Cl] which could give results similar to (1). However, the reproducible initiation of these reactions was very difficult, as traces of oxygen were needed and (1) is the catalyst of choice for forming (3). The mechanisms of the reactions leading to (2), (3), and (4) are discussed in the light of kinetic and other data.