1,3-DIPHENYLALLYL COMPLEXES OF PALLADIUM(II) - NMR, X-RAY, AND CATALYTIC STUDIES

A series of 1,3-diphenylallyl complexes of Pd(II) containing achiral as well as new and commercially available chiral auxiliaries has been prepared, and their allyl C-13-NMR characteristics have been recorded. Some results for the catalytic allylic alkylation reaction are given with the best new result, for (R)-BIPHEMP (BIPHEMP = 2,2'-bis(diphenylphosphino)-6,6'-dimethylbiphenyl), showing an enantiomeric excess of 90%. The solid-state structure for the complex [Pd(eta(3)-PhCHCHCHPh)(TMEDA)]BF4, 2a, has been determined by X-ray diffraction. Molecular mechanics methods have been used to understand some differences between the chiral pockets of selected chelating phosphine ligands. The selective allyl isomerization dynamics for the methoxy-BIPHEMP complex [Pd(eta(3)-PhCHCHCHPh)-(2,2'-bis-diphenylphosphino)-6,6'-dimethoxybiphenyl)]PF6, 2n, and the ferrocene-based JOSIPHOS complex (JOSIPHOS = (R)-{1-[(S)-(diphenylphosphino)ferrocenyl]ethyl}dicylohexylphosphine), [Pd(eta(3)-PhCHCHCHPh){CpFe(C5H3(1-CH(CH3)PCy(2))-2-PPh(2))}]CF3SO3, 9, have been followed by 2-D exchange spectroscopy. The observed ee for 9 does not correlate with expectations based on C-13 data, together with a ground state population analysis; i.e., the reaction kinetics for different diastereomers may be important. The 1,3-diphenylallyl substrate is special in that its phenyl groups can stack with the phenyl groups of the chiral auxiliary.