Synthesis and characterisation of fifteen-electron dihalo(carbonyl)tungsten(iii) complexes, Tp*WX₂(CO) (X = Br, I)

The oxidation of Tp*W^III(NCMe)(CO) [Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate] by iodine in refluxing acetonitrile produces paramagnetic Tp*W^IIII₂(CO), with μ_eff = 1.70 μ_B and ν(CO) = 1881 cm^-1. The analogous bromo complex, Tp*W^IIIBr₂(CO) (μ_eff = 1.72 μ_B, ν(CO) = 1905 cm^-1), is produced by the oxidative decarbonylation of Tp*WI(CO)₃ with bromoacetonitrile in refluxing tetrahydrofuran. The crystal structures of both complexes reveal mononuclear, six-coordinate, distorted octahedral metal complexes bearing facial Tp* and mutually cis halide and carbonyl ligands. The structures, magnetic moments and spectroscopic data (including isotropically shifted NMR spectra) are consistent with a low-spin, doublet ground state in these, the first reported, 15-electron, d³ dihalo(carbonyl)-W(iii) complexes.