Chiral Palladium(0)trans-Stilbene Complexes:  Synthesis, Structure, and Oxidative Addition of Phenyl Iodide

The chiral Pd(0) trans -stilbene complexes Pd(diphos*)( trans -stilbene) (diphos* = ( R, R )-Me-Duphos, ( R, R )-Et-Duphos, ( R, R )-i-Pr-Duphos, ( R, R )-Me-BPE, ( S, S )-Me-FerroLANE, ( S, S )-Me-DuXantphos, ( S, S )-Et-FerroTANE, ( R, S )-CyPF-t-Bu, ( R, S )-PPF-t-Bu, ( R, S )-BoPhoz) and Ni(( R, R )-Me-Duphos)( trans -stilbene) were prepared by NaBH(OMe) 3 reduction of the corresponding M(diphos*)Cl 2 compounds in the presence of trans -stilbene. The rate of oxidative addition of phenyl iodide to the stilbene complexes, which gave Pd(diphos*)(Ph)(I), depended on the ligand (larger for increased ligand bite angles and reduced steric bulk) and was markedly faster than oxidative addition to mixtures of Pd(dba) 2 and diphos*. The complexes Pd(diphos*)(Ph)(I) were prepared independently by treatment of PdL 2 (Ph)(I) (L 2 = TMEDA, (PPh 3 ) 2 ) with diphos*. Oxidative addition of PhI to the complexes M(( R, R )-Me-Duphos)( trans -stilbene) occurred in the rate order Pd > Ni ≫ Pt. The complexes Pd(diphos*)Cl 2, Pd(diphos*)( trans -stilbene), and Pd(diphos*)(Ph)(I), as well as some analogous Ni compounds, were structurally characterized by X-ray crystallography.