Synthesis of a carborane-substituted bis(phosphanido) cobaltate(I), ligand substitution, and unusual P₄ fragmentation

Oxidative addition of the P–P single bond of an ortho-carborane-derived 1,2-diphosphetane (1,2-C₂(PMes)₂B₁₀H₁₀) (Mes = 2,4,6-Me₃C₆H₂) to cobalt(−I) and nickel(0) sources affords the first heteroleptic complexes of a carborane-bridged bis(phosphanido) ligand. The complexes also incorporate labile ligands suitable for further functionalisation. Thus, the cobalt(I) complex [K([18]crown-6)][Co{1,2-(PMes)₂C₂B₁₀H₁₀}(cod)] (cod = 1,5-cyclooctadiene) bearing a labile cyclooctadiene ligand undergoes facile ligand exchange reactions with isonitriles and tert-butyl phosphaalkyne with retention of the bis(phosphanido) ligand. However, in the reaction with one equivalent of P₄, the electron-rich bis(phosphanido) moiety abstracts a single phosphorus atom with formation of a new P₃ chain, while the remaining three P atoms derived from P₄ form an η³-coordinating cyclo-P₃ ligand. In contrast, when the same reaction is performed with two equivalents of the cobalt(I) complex, a dinuclear product is formed which features an unusual P₄ chain in its molecular structure.