Synthesis and characterization of a new enantiopure hydroxylated phosphine, its rhodium(I) and (III) complexes and their performance in catalytic carbonylation

The enantiomerically pure hydroxylated phosphine (1S,2S.5R)-1-diphenylphosphinomethyl-2-isopropyl-5-methyl-cyclohexanol 3 was prepared in a two-step stereoselective process from the commercially available and low cost (-)-menthone. Reaction of this new ligand with the appropriate rhodium precursor gave the respective Rh(I) and Rh(III) complexes. For rhodium(I) the binuclear complex tran-P,P-bis-{mu-chlorocarbonyl[(1S,2S,5R)-1-diphenylphosphinomethyl-2-isopropyl-5-methyl-cyclohexanol-P]-rhodium(I)} 6 was obtained by reaction with [Rh(mu-Cl)(CO)(2)](2). For Rh(III), two isomeric edge-sharing bioctahedral (ESBO) complexes. tirans-O,O-trans-P.P-bis{(OC-6-32)-[mu-chlorodichloro[(1S,2S,5R)-1-diphenylphosphinomethyl-2-isopropyl-5-methylcyclohexanol-O,P]rhodium(III) 7a and trans-O,O-cis-P,P-bis{(OC-6-32)-mu-chlorodichloro[(1S,2S,5R)-1-diphenyphosphinomethyl-2-isopropyl-5-methyl-cyclohexanol-O,P]rhodium(III): 7b, and the partially hydrolyzed product, trans-O,O-cis-P,P-(OC-32)- mu-chloro-mu-hydroxo-tetrachlorobis[(1S,2S,5R)-1-diphenylphosphinomethyl-2-isopropyl-5-methyl-cyclohexanol-O,P]dirhodium(III)} 8 were characterized in solid state by single-crystal X ray diffraction analysis. The O-axial-P-equatorial trans-O,O arrangements observed in compounds 7a,b and 8 are preferred over the more common O-equatorial-P-equatorial Structure, presumably due to the stereo-electronic coordination preferences of the chiral hydroxylated phosphine. To the best Of Our knowledge, the ligand arrangement observed in 7b and 8 is unique among ESBO complexes. The rhodium(I) complex 6 is active as a catalyst precursor in the hydroformylation of styrene. yielding initial turnover frequencies up to 440 h(-1) and selectivities up to 74% in the branched aldehyde. Unfortunately, no enantiomeric excesses have been observed within experimental error. (C) 2003 Elsevier Ltd. All rights reserved.