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

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The reaction of pentacarbonyl(pyrazolin-3-ylidene)chromium complexes, ▪ ( 2a– c) (R = Ph ( a), C 6H 4NMe 2-4 ( b); (C 5H 4)FeCp ( c)), with [AuCl(SMe 2)], H[AuCl 4], [PdCl 2(NCPh) 2] and [PtCl 2(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 ▪ (Fc = (C 5H 4)FeCp) is readily displaced by trifluoroacetate. The analogous substitution of iodide for the chloride ligands in ▪ (M = Pd, Pt) give the corresponding diiodo complexes although in a much slower reaction. In contrast, the reaction of silver trifluoroacetate with ▪ 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 ▪ (R = C 6H 4NMe 2-4) with [AuCl(SMe 2)] and [PdCl 2(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 ▪ with the palladium complex [PdCl 2(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.