Structural and spectroscopic characteristics of [Ni{(Ph2P)(2)N-S-CHMePh-P,P ''}X-2], X = Cl, Br: Catalytic activity and selectivity in Kumada and Suzuki-Miyaura coupling reactions
Abstract
The [Ni{(Ph2P)(2)N-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 (Ph2P)(2)N(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)(2)N-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 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 H-1 and P-31 NMR properties of [Ni{(Ph2P)(2)N-S-CHMePh-P,P'}Br-2] are consistent with its crystal structure.
The [Ni{(Ph2P)(2)N-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. (C) 2012 Elsevier B.
V. All rights reserved.