Transition metal catalysis in fluorous media: application of a new immobilization principle to rhodium-catalyzed hydrogenation of alkenes

Abstract

Biphase systems were generated by combining toluene solutions of alkenes (2-cyclohexen-1-one, 1-dodecene, cyclododecene, 4-bromostyrene) and CF 3C 6F 11 solutions of the pre-catalyst ClRh[P(CH 2CH 2(CF 2) 5CF 3) 3] 3 (( 1); 1.1–0.8 mol%) and placed under 1 atm of H 2. The perfluoroalkyl segments in ( 1) confer high affinities for fluorocarbons. After 8–26 h at 45°C, the CF 3C 6F 11 phases were separated, and extracted with an equal volume of toluene. GLC analyses of the toluene solutions showed 98–87% yields of the hydrogenation products cyclohexanone, dodecane, cyclododecane, and 4-bromoethylbenzene (turnover numbers 120–87). The CF 3C 6F 11 phases were charged with new toluene solutions of 2-cyclohexen-1-one or 1-dodecene, and similarly treated with H 2. There was no significant loss of catalyst activity over three cycles. A preparative reaction gave cyclohexanone in 89% yield. Some CC isomerization could be detected during the course of 1-dodecene hydrogenation, and ( 1) gave a dihydride complex in the absence of alkene.