The first fluorous biphase hydrogenation catalyst incorporating a perfluoropolyalkylether: [RhCl(PPh2(C6H4C(O)OCH2CF(CF3)(OCF2CF(CF3))nF))3] with n = 4–9

Abstract

The phosphine oxide (4-diphenylphosphinyl) poly(hexafluoropropylene oxide) methylene benzoate [(C6H5)2P(O)(C6H4C(O)OCH2CF(CF3)(OCF2CF(CF3))nF] (with n=4–9) 1, was prepared by the reaction of [4-diphenylphosphinyl] benzoyl chloride with poly(hexafluoropropylene oxide) (pHFPO) methylene alcohol and triethylamine. Subsequent reduction of 1 with HSiCl3 produced the phosphine 2, (4-diphenylphosphino) pHFPO methylene benzoate, [(C6H5)2P(C6H4C(O)OCH2CF(CF3)(OCF2CF(CF3))nF]. The phosphine ligand 2 was incorporated into tris(4-diphenylphosphino) pHFPO methylene benzoate rhodium chloride 4. Partition coefficients in perfluoromethylcyclohexane (PFMCH):toluene were determined using 19F NMR spectroscopy for both 2 and 4 as 98:2 and 81:19, respectively. Compound 4 was also shown to function as a fluorous biphase catalyst, catalyzing the hydrogenation of 2-cyclohexen-1-one in biphasic (1:1 toluene:PFMCH; 1:3:3 toluene:hexanes:Krytox® K6 [F(CF(CF3)CF2O)5CF2CF3]) and monophasic (1:3:3 toluene:hexanes:PFMCH) solvent systems with average turnover frequencies of 30.7, 17.1 and 20.6h−1, respectively. Rh leaching studies were undertaken to confirm the recycling ability of the catalyst 4 and the average percentage loss of Rh per cycle in the three solvent systems (1:1 toluene:PFMCH; 1:3:3 toluene:hexanes:Krytox® K6 [F(CF(CF3)CF2O)5CF2CF3]; 1:3:3 toluene:hexanes:PFMCH) was determined to be 0.35%, 0.17% and 0.30%, respectively.