Synthesis and structure of 1,2,4-triazol-2-ium-5-ylidene complexes of Hg(II), Pd(II), Ni(II), Ni(0), Rh(I) and Ir(I)

The reaction of M(OAc)(2) [M = Hg(II), Pd(II), Ni(II)] or M(acac)(CO)(2) [M = Rh(I), Ir(I)] with dicationic 1,2,4-triazolium salts 2 affords a series of water-soluble 1,2,4-triazol-2-ium-5-ylidene complexes 4-8, arising from deprotonation-complexation of the N-heterocyclic ligand. Reduction of [Ni(trz)(2)I-2(TfO)(2)] (trz = 1,2,4-triazol-2-ium-5-ylidene) (6a) with zinc powder in the presence of carbon monoxide results in the formation of the corresponding Ni(0)-carbene complexe 9. The latter has also been prepared by the reaction of Ni(CO)4 with the corresponding in situ generated triazoliumylidene. The solid state structure of [Hg(trz)(2)(dmso)(TfO)(4)] (4), [Pd(trz)(2)I-4] (5a), [Ni(trz)(2)I-2(TfO)(2)] (6a) and [Ni(trz)(2)(CO)(2)] (9) were determined by single-crystal X-ray diffraction studies. (C) 2002 Elsevier Science B.V. All rights reserved.