Transfer of heterocyclic carbene ligands from chromium to gold, palladium and platinum

The reaction of pentacarbonyl(pyrazolin-3-ylidene)chromium complexes, [GRAPHICS] (2a-c) (R = Ph (a), C6H4NMe2-4 (b); (C5H4)FeCp (c)), with [AuCl(SMe2)], H[AuCl4], [PdCl2(NCPh)(2)] and [PtCl2(NCPh)(2)] gives, by transfer of the heterocyclic carbene ligand, new chloro pyrazolin-3-ylidene complexes of gold(I) and gold(III), dichloro bis(pyrazolin-3-ylidene) palladium and dichloro bis(pyrazolin-3-ylidene) platinum in high yield. The chloride ligand in [GRAPHICS] (Fc = (C5H4)FeCp) is readily displaced by trifluoroacetate. The analogous substitution of iodide for the chloride ligands in [GRAPHICS] (M = Pd, Pt) give the corresponding diiodo complexes although in a much slower reaction. In contrast, the reaction of silver trifluoroacetate with [GRAPHICS] affords a binuclear Pd-Ag complex containing two pyrazolin-3-ylidene and three trifluoroacetate ligands two of whom occupy bridging positions between Pd and Ag. The reactions of the pyrazolidin-3-ylidene complex [GRAPHICS] (R = C6H4NMe2-4) with [AuCl(SMe2)] and [PdCl2(NCPh)(2)] yield chloro pyrazolidin-3-ylidene gold and dichloro bis(pyrazolidin-3-ylidene) palladium complexes. The related dichloro bis(tetrahydropyrimidin-4-ylidene) palladium complex is formed in the reaction of [GRAPHICS] with the palladium complex [PdCl2(NCPh)(2)]. The solid-state structures of several of these heterocyclic carbene complexes including the structure of the binuclear Pd-Ag complex are established by X-ray structure analyses. (C) 2007 Elsevier B.V. All rights reserved.