Tetraethylammonium dicarbonyl(dicyanomethylene)[tris(3,5-dimethyl-1-pyrazolyl)hydroborato]molybdenum(0)

Crystals of [(C2H5)(4)N][(Tp(Me2))(CO)(2)Mo=C(CN)(2)] [Tp(Me2) is (3,5- dimethyl-1-pyrazolyl) hydroborato], (1), the first example of an air-stable carbene complex bearing a metal-centred negative charge, contain discrete anions and cations separated by typical van der Waals distances. The coordination of the anion in ( 1) is octahedral about Mo, with the Tp(Me2) ligand occupying three adjacent coordination sites and the two carbonyl ligands and the dicyanocarbene ligand occupying the remaining three sites. The anion contains an approximate mirror plane, which passes through the plane of the dicyanocarbene ligand, the Mo atom and one of the Tp(Me2) rings.