Mono-and dinuclear palladium(II) N,S-heterocyclic carbene complexes with N spacers and their Suzuki coupling activities

Abstract

Mixed-ligand N,S-heterocyclic carbene (NSHC) complexes, trans-[PdBr 2(NSHC)(Py)] (NSHC=3-benzyl-or 3-propyl-benzothiazolin-2-ylidene), have been obtained from bridge-cleavage reactions of the dinuclear complex, [Pd(m-Br)Br(NSHC)]2, in pyridine at room temperature. Use of neutral N-bidentate donors (L=pyrazine, 1,2-bis(4-pyridyl)ethane, 4,4′-bipyridine and trans-1,2-bis(4-pyridyl)-ethylene) yields the dinuclear spacer-bridged [Pd2Br4(NSHC)2(μ-L)] complexes. The X-ray single-crystal structures of the pyridyl, bridging pyrazine and 1,2-bis(4-pyridyl)ethane complexes are reported. These air-stable complexes are active in the Suzuki-Miyaura coupling reactions of selected aryl bromides. The dinuclear complexes are generally more active than their mononuclear pyridyl analogues. The benzyl derivatives consistently outperform the n-propyl counterparts. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.