Catalytic and structural studies on complexes of a binaphthyl-phosphino-oxazoline auxiliary: The meta dialkyl effect on enantioselectivity

The chiral phosphino-oxazoline ligand (S,R)-2-[4-(isopropyl)oxazol-2-yl]-2' -bis(3,5-dimethylphenylphosphino)-1,1'-binaphthyl, 6b, its Pd-dichloro comp lex, 9, the p-cyanoaryl complex [PdBr(p-NC-C6H4](6b)], 10, a model for the Heck reaction, the cationic 1,3-diphenylallyl derivative [Pd(eta(3)-PhCHCHC HPh)(6b)]OTf, 11, a model for the allylic allylation, and the Rh- and Ir-1, 5-COD compounds [M(1,5-COD)(6b)]BF4, 12 and 13, respectively, have been pre pared. In enantioselective catalytic experiments, the presence of the 3,5-d imethylphenyl groups generally increases the observed ee. The solid-state s tructure of PdCl2(6b), 9, has been determined. 2-D and variable-temperature NMR experiments suggest that one of the two 3,5-dimethyl P-aryl rings inte racts selectively with the remaining ligands. Consequently, the entire chir al pocket becomes slightly more rigid and the correlation with substrate im proves.