Oxygenation studies. Part V. Further rhodium(I) catalysts for the co-oxygenation of terminal alkenes

Abstract

The complexes Rh(CN)(Ph 3P) 3, (III), Rh(OCN)(Ph 3P) 3, (IV), Rh(SCND) (Ph 3P) 3, (V), are catalysts for the co-oxygenation of l-octene and Ph 3P. Eight other Rh(I) complexes show little or no catalytic activity. Comparisons with RhCl(Ph 3P) 3, (I), in benzene at 22.5 °C show that initial rates of co-oxygenation, rates of decay, and ratios of heteroco-oxygenation to homo-co-oxygenation increase in the order (I), (III), (IV), (V). The behaviour of (I) in the presence of Ph 2PO 2H and on increasing [Ph 3P] is distinctly different from that of the other three complexes. At 60 °C [O 2] becomes a rate limiting factor for all four complexes. Only (V) shows evidence of thermal instability at the higher temperature. The catalytic oxygenation is less efficient with styrene as the olefinic substrate. An outline scheme involving two interconnected catalytic cycles is proposed for these reactions.