Palladium and rhodium complexes with planar-chiral carborane ligands

Base degradation of the prochiral 1-diphenylphosphanyl-2phenyl-1,2-dicarba- closo-dodecaborane (1) affords the planar-chiral 7-diphenylphosphanyl-8-phe nyl-7,8-dicarbanido-undecaborate anion (2). Resolution of the racemic anion carried out using a well-established procedure, gave the internally diaste reomeric palladium complexes 3R-R and 3R-S, These complexes were separated by fractional crystallization. A single-crystal X-ray analysis of 3R-R esta blished the exo-nido bonding of the carborane ligand via the phosphorus ato m and the adjacent BH group, and the (R) configuration of the carborane Lig and. The enantiomerically pure anions of 2 were liberated from the diastere omerically pure palladium complexes 3R-R and 3R-S, respectively, by subsequ ent addition of HCl and NaCN. The exo-nido-rhodium-carborane complexes 4-8 were prepared by heating 2eR or 2eS with [Rh(COD)Cl](2) and/or a chiral che lating phosphane, such as DIOP and BINAP, under reflux. The chiral complexe s were tested under enantioselective catalysis conditions such as hydrogena tion of acetamidocinnamic acid, hydrogenation of ketopantolactone, and hydr osilylation of acetophenone.