title: Nickel(II) complexes of bidentate N-heterocyclic carbene/phosphine ligands: efficient catalysts for Suzuki coupling of aryl chlorides.
abstract: Nickel(II) complexes of bidentate N-heterocyclic carbene (NHC)/phosphane ligand L were prepared and structurally characterized. Unlike palladium, which forms [PdCl(2)(L)], the stable nickel product isolated is the ionic [Ni(L)(2)]Cl(2). These Ni(II) complexes are highly robust in air. Among different N-substituents on the ligand framework, the nickel complex of ligand L bearing N-1-naphthylmethyl groups (2 a) is a highly effective catalyst for Suzuki cross-coupling between phenylboronic acid and a range of aryl halides, including unreactive aryl chlorides. The activities of 2 a are largely superior to those of other reported nickel NHC complexes and their palladium counterparts. Unlike the previously reported [NiCl(2)(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane), 2 a can effectively catalyze the cross-coupling reaction without the need for a catalytic amount of PPh(3), and this suggests that the PPh(2) functionality of hybrid NHC ligand L can partially take on the role of free PPh(3). However, for unreactive aryl chlorides at low catalyst loading, the presence of PPh(3) accelerates the reaction.
authors.affiliation: Department of Chemistry, National Changhua University of Education, Changhua, Taiwan.
authors.forename: Chun-Chin
authors.initials: CC
authors.lastname: Lee
authors.forename: Wei-Chi
authors.initials: WC
authors.lastname: Ke
authors.forename: Kai-Ting
authors.initials: KT
authors.lastname: Chan
authors.forename: Chun-Liang
authors.initials: CL
authors.lastname: Lai
authors.forename: Ching-Han
authors.initials: CH
authors.lastname: Hu
authors.forename: Hon Man
authors.initials: HM
authors.lastname: Lee