1,3-Diphenylallyl Complexes of Pd(II). NMR, X-ray and Catalytic Studies

A series of 1,3-diphenylallyl complexes of Pd(I1) containing achiral as well as new and commercially available chiral auxiliaries has been prepared, and their allyl 13C-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(dipheny1phosphino)- 6,6'-dimethylbiphenyl), showing an enantiomeric excess of 90%. The solid-state structure for the complex [Pd(v3-PhCHCHCHPh)(TMEDA)lBF2da,, 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(v3-PhCHCHCHPh)- (2,2'-bis-diphenylphosphino)-6,6'-dimethoxybiphenyl)IPF2~n,, a nd the ferrocene-based JOSIPHOS complex (JOSIPHOS = (R)-{l-[(S)-(diphenylphosphino)ferrocenyllethyl}dicyclohexylphosphine), [Pd(q3-PhCHCHCHPh){C pFe(C5H3(1-CH(CH3)PCy2)-2-PPh2)IC} F3S03,9, have been followed by 2-D exchange spectroscopy. The observed ee for 9 does not correlate with expectations based on 13C 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.