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, (RR)-Et-Duphos, (RR)-i-Pr-Duphos, (RR)-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)(1) were prepared independently by treatment of PdL2(Ph)(I) (L-2 = TMEDA, (PPh3)(2)) with diphos*. Oxidative addition of PhI to the complexes M((RR)-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.