Highly efficient enantioselective catalysis in supercritical carbon dioxide using the perfluoroalkyl-substituted ligand (R,S)-3-H2F6-BINAPHOS

Article abstract of DOI:10.1016/S0022-328X(00)00778-6

Perfluoroalkyl-substitution of the aryl groups in the BINAPHOS skeleton was achieved using a synthetic strategy based on the Cu(I)-catalyzed cross coupling of arylmagnesium bromide and F(CF₂)₆(CH₂)₂I. The rhodium complexes of the new ligand (R,S)-3-H²F⁶-BINAPHOS (10) exhibited spectroscopic properties and reactivities similar to those of the unsubstituted parent compounds. The substitution provided a high affinity of the ligand and its complexes for scCO₂ allowing the development of ecologically benign protocols for catalytic asymmetric synthesis and even the spectroscopic detection of catalytically active intermediates. Using this new system, a large variety of substrates were hydroformylated in scCO₂ with rates and enantioselectivities comparable to those of the parent system in benzene solution. At the same time, the CO₂-philic substitution pattern resulted in a significantly higher regioselectivity towards the desired chiral aldehydes. Preliminary results indicated for the first time also a remarkable potential of BINAPHOS-derived ligands for asymmetric hydrogenation reactions. The possibility to develop new work-up schemes for product purification and/or catalyst immobilisation based on scCO₂ as the only medium for catalysis and extraction (CESS process) was experimentally verified using a rhodium catalyst containing 10.