Structural and spectroscopic characteristics of [Ni{(Ph2P)2N-S-CHMePh-P,P′}X2], X = Cl, Br: Catalytic activity and selectivity in Kumada and Suzuki–Miyaura coupling reactions

The [Ni{(Ph2P)2N-S-CHMePh-P,P′}Br2] complex was prepared by a ligand-exchange reaction between [Ni(dme)Br2] (dme is 1,2-dimethoxyethane) and the P–N–P ligand (Ph2P)2N(S-CHMePh). X-ray crystallography revealed a square planar NiP2Br2 coordination sphere, i.e., the presence of a four-membered Ni–P–N–P ring. The same structural features with nearly equal values of the X–Ni–X, P–Ni–P and P–N–P angles have been earlier revealed for the isomorphous [M{(Ph2P)2N-S-CHMePh-P,P′}Cl2], M = Ni, Pd, complexes. The structure of the above complexes significantly differs from that of [Ni(dppp)Cl2] (dppp is 1,3-bis{diphenylphosphine}propane). This NiP2Cl2-type complex comprises a six-membered Ni–P–C–C–C–P ring, with significantly larger P–Ni–P and much smaller Cl–Ni–Cl angles. The 1H and 31P NMR properties of [Ni{(Ph2P)2N-S-CHMePh-P,P′}Br2] are consistent with its crystal structure. The [Ni{(Ph2P)2N-S-CHMePh-P,P′}X2] complexes were tested as catalysts in Kumada and Suzuki–Miyaura coupling reactions, and their reactivity was compared with that of [Ni(dppp)Cl2]. The differences observed in their catalytic efficiency are discussed with regards to their structural characteristics.