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

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 20.6 h−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.

Consideration was given to poly(hexafluoropropylene oxide) [pHFPO] and the extension of its applications to include utilization in a fluorous triarylphosphine suitable for Fluorous Biphase Catalysis (FBC). Little is known about how the change in the structure of fluorinated tail from rigid perfluoropolyalkyls to flexible perfluoropolyalkylethers (PFPAEs) could affect partition coefficients and catalytic hydrogenation in FBC. This paper communicates the results and compares them to related perfluorpolyoalkyl systems.Figure optionsDownload as PowerPoint slideHighlights
► A triarylphosphine ligand that incorporates the perfluoropolyalkylether.
► Polyhexafluoropropylene oxide with a –C(O)OCH2– spacer is synthesized.
► A Wilkinson's catalyst derivative is synthesized with this ligand.
► The catalyst is employed as a Fluorous Biphase Catalyst for the hydrogenation of 2-cyclohexen-1-one.
► Turnover frequencies as well as partition coefficients and Rh leaching studies are reported.