Oxidative P-P Bond Addition to Cobalt(-I): Formation of a Low-Spin Cobalt(III) Phosphanido Complex.

The first homoleptic cobalt phosphanido complex [K(thf)4 ][Co{1,2-(PtBu2 )2 C2 B10 H12 }2 ] (1) was prepared by an unprecedented oxidative P-P bond addition of an ortho-carborane-substituted 1,2-diphosphetane to cobalt(-I) in [K(thf)0.2 ][Co(η4 -cod)2 )] (cod=1,5-cycloctadiene). Compound 1 is a rare distorted tetrahedral 3d6 complex with a low-spin ground state configuration. Magnetic measurements revealed that the complex is diamagnetic between 2 to 270 K in the solid state and at 298 K in [D8 ]THF solution. Based on DFT calculations, the unusual singlet ground state is caused by the strong σ-donor and moderate π-donor properties of the bis(phosphanido) ligand.