Synthesis of a carborane-substituted bis(phosphanido) cobaltate(i), ligand substitution, and unusual P(4) fragmentation

Oxidative addition of the P–P single bond of an ortho-carborane-derived 1,2-diphosphetane (1,2-C(2)(PMes)(2)B(10)H(10)) (Mes = 2,4,6-Me(3)C(6)H(2)) 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)(2)C(2)B(10)H(10)}(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 P(4), the electron-rich bis(phosphanido) moiety abstracts a single phosphorus atom with formation of a new P(3) chain, while the remaining three P atoms derived from P(4) form an η(3)-coordinating cyclo-P(3) 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(4) chain in its molecular structure.