TRANSITION-METAL CATALYSIS IN FLUOROUS MEDIA - APPLICATION OF A NEW IMMOBILIZATION PRINCIPLE TO RHODIUM-CATALYZED HYDROGENATION OF ALKENES

Biphase systems were generated by combining toluene solutions of alken es (2-cyclohexen-1-one, 1-dodecene, cyclododecene, 4-bromostyrene) and CF3C6F11 solutions of the pre-catalyst ClRh[P(CH2CH2(CF2)(5)CF3)(3)]( 3) ((1); 1.1-0.8 mol%) and placed under 1 atm of H-2. The perfluoroalk yl segments in (1) confer high affinities for fluorocarbons. After 8-2 6 h at 45 degrees C, the CF3C6F11 phases were separated, and extracted with an equal volume of toluene. GLC analyses of the toluene solution s showed 98-87% yields of the hydrogenation products cyclohexanone, do decane, cyclododecane, and 4-bromoethylbenzene (turnover numbers 120-8 7). The CF3C6F11 phases were charged with new toluene solutions of 2-c yclohexen-1-one or 1-dodecene, and similarly treated with H-2. There w as no significant loss of catalyst activity over three cycles. A prepa rative reaction gave cyclohexanone in 89% yield. Some C=C isomerizatio n could be detected during the course of 1-dodecene hydrogenation, and (1) gave a dihydride complex in the absence of alkene. (C) 1998 Elsev ier Science B.V. All rights reserved.