Evidence of a rhodium catalytic species containing a bridging 1,2-diphosphine in styrene hydroformylation

Abstract

A systematic analysis of the effect of pressure, temperature and ligand∶metal molar ratio on the selectivity of styrene hydroformylation catalysed by rhodium and (3R,4R)-1-benzyl-3,4-bis(diphenylphosphino)pyrrolidine ligand I was carried out. The enantioselective discrimination was insignificant in all cases and the regioselectivity nearly identical to that obtained with the Rh–PEtPh₂ catalyst under the same reaction conditions. An NMR study was performed in order to elucidate the species formed in both systems under catalytic reaction conditions. Molecular mechanics calculations were also carried out in an attempt to rationalize the catalytic and NMR experiments. Thus, evidence is provided for bridging co-ordination of the diphosphine I in different rhodium complexes. The presence of these species in the hydroformylation reaction accounts for the selectivity observed. The results for this catalytic system were compared with those for related diphosphines already reported.