Regioselectivity in the rhodium catalysed 1,4-hydrosilylation of isoprene. Aspects on reaction conditions and ligands

The regioselectivity in the Rh catalysed 1,4-hydrosilylation of isoprene was investigated. Variation of solvents and temperature did not significantly affect the isomer distribution between tail-product (I) and head-product (II). The choice of ligands had the greater influence, where RhI-based catalysts with the strong electron withdrawing ligand CO favoured production of isomer II, while RhI catalysts with strong electron donating ligands (for example triarylphosphines) gave isomer I as the main product. In contrast to the square planar carbonyl complex RhCl(CO)(PPh3)2, the square planar thiocarbonyl complex RhCl(CS)(PPh3)2, gave I as the major isomer.