Synthesis, separation, and stereochemical studies of chiral-at-metal rhodium(III) complexes. Crystal structure of (S-Rh,R(C))-[(eta(5)-C(5)Me(5))RhCl{Ph(2)PCH(Me)CH(2)PPh(2)}]BF4

The synthesis of chiral-at-metal [(eta(5)-C(5)Me(5))RhX(prophos)]X (prophos = (R)-1,2-propanediylbis(diphenylphosphine); X = Cl (2a, 2a'), I (4a)) complexes from [{(eta(5)-C(5)Me(5))RhX)(2)-(mu-X)(2)] in methanol is reported (de = 54 and greater than or equal to 98, respectively). The rhodium center is configurationally stable in the iodo complex, but the chloro analogue epimerizes in polar solvents. Complexes 2 and 4 are formed through the dinuclear intermediates [{(eta(5)-C(5)Me(5))RhX(2)}(2)(mu-prophos)] and the monodentate diphosphine complexes [(eta(5)-C(5)Me(5))RhX(2)(prophos)] with high stereoselectivity. The determination of the absolute configuration of 2a and 2a' complexes comes from the X-ray diffraction study of [(eta(5)-C(5)Me(5))RhCl(prophos)]BF4 (2b) obtained from mixtures of 2a and 2a' by anion exchange. In 2b the chiral metal exhibits an S absolute configuration.