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 trans-P,P-bis-{μ -chlorocarbonyl[(1S,2S,5R) -1-diphenylphosphinomethyl-2-isopropyl-5-methyl-cyclohexanol-P]rhodium(I)} 6 was obtained by reaction with [Rh(μ-Cl)(CO)2]2. For Rh(III), two isomeric edge-sharing bioctahedral (ESBO) complexes, trans-O,O-trans-P,P-bis{(OC-6-32)-μ-chlorodichloro[(1S,2S,5R) -1-diphenylphosphinomethyl-2-isopropyl-5-methyl-cyclohexanol-O,P]rhodium(III)} 7a and trans-O,O-cis-P,P-bis{(OC-6-32)-μ -chlorodichloro[(1S,2S,5R) -1-diphenylphosphinomethyl-2-isopropyl-5-methyl-cyclohexanol-O,P]rhodium(III)} 7b, and the partially hydrolyzed product, trans-O,O-cis-P,P-(OC-6-32)-{μ -chloro-μ-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. © 2003 Elsevier Ltd. All rights reserved.