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)2I2(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)2I4] (5a), [Ni(trz)2I2(TfO)2] (6a) and [Ni(trz)2(CO)2] (9) were determined by single-crystal X-ray diffraction studies.