Computational studies on mercury halides as ligands in organometallic transition complexes

Mercury is present in the structure of several heterometallic clusters, usually bridging three or four transition metal centres.1 Heterobimetallic compounds with a single M-Hg bond were prepared in the past, and the simpliest situation is represented by the {HgX} fragment (X = halide or pseudohalide) bonded to a transition metal fragment. Compounds of this type can be obtained following different synthetic approaches, such as the reaction of HgX2 with suitable precursors or the insertion of Hg in a M-X bond. The most common transition metals belong to the Groups 6 - 9, with CO, cyclopentadienide (Cp) and related species as ancillary ligands. Selected examples are the complexes [M(HgX)(Cp)(CO)3] (M = Cr, Mo, W), [M(HgX)(CO)5], (M = Mn, Re), [Fe(HgX)(Cp)(CO)2] and [Co(HgX)(CO)4].2 To the best of our knowledge, the nature of the M-Hg bond was never computationally investigated. In this communication we report the outcomes of DFT calculations on model compounds having general formulae [M(HgX)(Cp)(CO)n] (M = Cr, Mo, W, n = 3; M = Fe, Ru, Os, n = 2; X = Cl, Br, I) and [M(HgX)(CO)n] (M = Mn, Tc, Re, n = 5; M = Co, Rh, Ir, n = 4; X = Cl, Br, I). The nature of the M-Hg bond, the factors affecting the bond strength and the behaviour of {HgX} as Lewis acid or base were studied in detail. 1 E. Rosenberg, K. I. Hardcastle, Comprehensive Organometallic Chemistry II, vol. 10 (1995) 323. 2 S. V. Maslennikov et al., Russ. J. Gen. Chem. 72 (2002) 1495; J. Granifo and M. E. Vargas, J. Organomet. Chem. 408 (1991) 357; M. Cano and J. A. Campo, Polyhedron 10 (1991) 133; R. Kumar et al., J. Organomet. Chem. 323 (1987) 53; J. R. Chipperfield et al., J. Chem. Soc. Dalton Trans. (1977) 485 and references therein.