A convenient synthesis of phosphine-functionalized N-heterocyclic carbene ligand precursors, structural characterization of their palladium complexes and catalytic application in Suzuki coupling reaction

摘要

A series of imidazolium chlorides as ligand precursors, (LHCl)-H-. (L=(1-R)-(3-diphenylphosphanylethyl)-imidazol-2-ylidene; R = aryl, benzyl, naphthylmethyl), for the phosphine-functionalized N-heterocyclic carbene (NHC), L, were prepared by a convenient synthetic procedure of reacting 1,2-dichloroethane with appropriate N-substituted imidazoles to give (beta-chloroethyl)imidazolium chlorides, which were subsequently reacted with HPPh2 producing (LHCl)-H-. in good yield. Palladium complexes of L, PdLCl2 (4), were prepared by a one pot reaction of PdCl2, sodium acetate, and (LHCl)-H-. in DMSO. Complexes 4b (R = naphthylmethyl) and 4e (R = m-methoxybenzyl) were characterized by X-ray crystallography. Catalytic studies have shown that the palladium complexes are efficient in Suzuki coupling reactions of aryl bromides with phenylboronic acid. (C) 2004 Elsevier B.V. All rights reserved.