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

The [Ni{(Ph 2P) 2N-S-CHMePh-P,P′}Br 2] complex was prepared by a ligand-exchange reaction between [Ni(dme)Br 2] (dme is 1,2-dimethoxyethane) and the P-N-P ligand (Ph 2P) 2N(S-CHMePh). X-ray crystallography revealed a square planar NiP 2Br 2 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{(Ph 2P) 2N-S-CHMePh-P,P′}Cl 2], M = Ni, Pd, complexes. The structure of the above complexes significantly differs from that of [Ni(dppp)Cl 2] (dppp is 1,3-bis{diphenylphosphine}propane). This NiP 2Cl 2-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{(Ph 2P) 2N-S-CHMePh-P,P′}Br 2] are consistent with its crystal structure. The [Ni{(Ph 2P) 2N-S-CHMePh-P,P′}X 2] complexes were tested as catalysts in Kumada and Suzuki-Miyaura coupling reactions, and their reactivity was compared with that of [Ni(dppp)Cl 2]. The differences observed in their catalytic efficiency are discussed with regards to their structural characteristics. © 2012 Elsevier B.V. All rights reserved