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

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.