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

• Published in: Inorganica Chimica Acta Vol. 357; no. 14; pp. 4313 - 4321
• Main Authors: Lee, Hon Man, Chiu, Pei Ling, Zeng, Jing Yao
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-11-2004
• Subjects: Palladium complex; Phosphine-functionalized N-heterocyclic carbene; Suzuki coupling reaction; X-ray determination; X-ray determination; Suzuki coupling reaction; Palladium complex; Phosphine-functionalized N-heterocyclic carbene
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2004.06.025

Ligand precursors, L
·
HCl (L
=
(1-R)-(3-diphenylphosphanylethyl)-imidazol-2-ylidene; R
=
mesity, aryl, naphthylmethyl), for the phosphine-functionalized
N-heterocyclic carbene (NHC) were synthesized by a convenient procedure. PdLCl
2 (
4) were prepared by a one pot reaction of PdCl
2, sodium acetate, and L
·
HCl in DMSO. Catalytic studies have shown that complex
4 is efficient in Suzuki coupling reactions of aryl bromides with phenylboronic acid.
A series of imidazolium chlorides as ligand precursors, L
·
HCl (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 (β-chloroethyl)imidazolium chlorides, which were subsequently reacted with HPPh
2 producing L
·
HCl in good yield. Palladium complexes of L, PdLCl
2 (
4), were prepared by a one pot reaction of PdCl
2, sodium acetate, and L
·
HCl 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.