Rhodium-diphosphine catalysts for the hydroformylation of styrene:: the influence of the excess of ligand and the chelate ring size on the reaction selectivity

This study discusses the hydroformylation of styrene using rhodium systems containing four structurally related diphosphines: 1,2-bis(diphenylphosphine)ethane 1 (dppe), 1,3-bis(diphenylphosphine)propane 2 (dppp), (R,R)-2,3-bis(diphenylphosphine)butane 3 (chiraphos) and (S,S)-2,4-bis(diphenylphosphine)pentane 4 (bdpp). A systematic analysis of the effect of the pressure, temperature and the ligand to metal molar ratio for these catalytic systems shows that the five- and six-membered ring chelating diphosphines behave different. The regio- and enantioselectivity observed provide evidence of the catalytic species involved in the process. By analyzing the selectivity of the catalytic systems formed by mixing PEtPh2 and the chiral diphosphine ligands, we propose a model describing the equilibria among the catalytic species. (C) 1999 Elsevier Science B.V. All rights reserved.