Synthesis of a carborane-substituted bis(phosphanido) cobaltate(i), ligand substitution, and unusual P fragmentation.

Oxidative addition of the P-P single bond of an -carborane-derived 1,2-diphosphetane (1,2-C(PMes)BH) (Mes = 2,4,6-MeCH) 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)CBH}(cod)] (cod = 1,5-cyclooctadiene) bearing a labile cyclooctadiene ligand undergoes facile ligand exchange reactions with isonitriles and -butyl phosphaalkyne with retention of the bis(phosphanido) ligand. However, in the reaction with one equivalent of P, the electron-rich bis(phosphanido) moiety abstracts a single phosphorus atom with formation of a new P chain, while the remaining three P atoms derived from P form an η-coordinating -P 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 P chain in its molecular structure.