Highly efficient enantioselective catalysis in supercritical carbon dioxide using the perfluoroalkyl-substituted ligand (R,S)-3-(HF6)-F-2-BINAPHOS

Perfluoroalkyl-substitution of the aryl groups in the BINAPHOS skeleton was achieved using a synthetic strategy based on the Cu(I)-catalyzed cross cou pling of arylmagnesium bromide and F(CF2)(6)(CH2)(2)I. The rhodium complexe s of the new ligand (R.S)-3-(HF6)-F-2-BINAPHOS (10) exhibited spectroscopic properties and reactivities similar to those of the unsubstituted parent c ompounds. The substitution provided a high affinity of the ligand and its c omplexes for scCO(2) allowing the development of ecologically benign protoc ols for catalytic asymmetric synthesis and even the spectroscopic detection of catalytically active intermediates. Using this new system. a large vari ety of substrates were hydroformylated in scCO(2) with rates and enantiosel ectivities comparable to those of the parent system in benzene solution. At the same time, the CO2-philic substitution pattern resulted in a significa ntly higher regioselectivity towards the desired chiral aldehydes. Prelimin ary results indicated for the first time also a remarkable potential of BIN APHOS-derived ligands for asymmetric hydrogenation reactions. The possibili ty to develop new work-up schemes for product purification and/or catalyst immobilisation based on scCO(2) as the only medium for catalysis and extrac tion (CESS process) was experimentally verified using a rhodium catalyst co ntaining 10. (C) 2001 Elsevier Science B.V, All rights reserved.