Chemistry of vinylidene complexes

A novel metal-chain extension reaction: synthesis of (X)[Os(CO)3(CN-t-Bu)]nMn(CO)5 (X = Cl, Br, I; n = 1, 2, 3)

Complexes of formula (X)[Os(CO)3(CN-t-Bu)]nMn(CO)5 (X = Cl, Br, I; n = 1, 2, 3) have been prepared by the reaction of Os(CO)4(CN-t-Bu) with Mn(CO)5(X) in hexane at room temperature. The characterization of the complexes included the crystal structures of compounds with X = I, n = 1, 3 and X = Cl, Br, n = 2 (2ClA and 2BrB). The trinuclear products were isolated as two isomers. The major isomer (2XA) has an isocyanide ligand attached to each osmium atom, whereas the minor isomer (2XB) has both of these ligands bound to the terminal Os atom. The structures contain OsnMn chains with unbridged Os—Mn bonds (range of lengths are 2.870(1)–2.9245(8) Å) and for compounds with n = 2 or 3 Os—Os bonds (range of lengths are 2.8812(4)–2.8928(5) Å). The mechanism of formation is believed to involve replacement of a CO ligand with the 18e- ligand Os(CO)4(CN-t-Bu) at the metal with the coordinated halide, followed by a rearrangement in which the halide ligand migrates to the donor Os atom with concomitant migration in the reverse direction of a carbonyl ligand. The preparation of (OC)4(t-BuNC)OsMn(CO)4(Cl) with an Os–Mn dative bond is also reported along with the (OC)4(t-BuNC)OsRe(CO)4(X) analogues.Key words: manganese–osmium, rhenium–osmium, dinuclear, metal chain, dative metal–metal bond.