Synthesis and characterization of {[(COD)Rh(bis-(2R,3R)-2,5-diethylphospholanobenzene)](+)BARF(-)} for use in homogeneous catalysis in supercritical carbon dioxide

Reaction of [(COD)(2)Cl2Rh] (COD: cyclo-octadiene) with sodium tetrakis((3, 5-trifluoromethyl)phenyl)borate (NaBARF) in the presence of an excess of CO D yields [(COD)(2)Rh](+)BARF(-). The COD ligands are readily displaced by t he bidentate ligand 1,2-bis((2R,5R)-2,5-diethylphosphalono)benzene (Et-DuPH OS) to form [(COD)Rh(Et-DuPHOS)]BARF, the structure of which has been deter mined by X-ray crystallography. BARF was selected as the counterion in orde r to achieve solubility in supercritical carbon dioxide for use in asymmetr ic hydrogenation and hydroformylation reactions. Density-functional theory calculations were used to study the intermediates in asymmetric hydroformyl ation of styrene. The energies of the two-enantiomer models differ by 11.3 kcal mol(-1). (C) 2001 Elsevier Science B.V. All rights reserved.