Synthesis and Characterisation of Sigma- and Pi-Bonded Metallaphosphacarboranes

Two new metallaphosphacarboranes have been synthesised from [7, 8-nido-CPB9H11]- by deprotonation followed by treatment with a metal fragment. Starting with [HNMe3][7, 8-nido-CPB9H11] deprotonation and reaction with a source of {(indenyl)Co}2+ affords the -bonded cobaltaphosphacarborane 3-(-C9H7)-3,1,2-closo-CoCPB9H10 (1) the first half-sandwich 3,1,2-metallaphosphacarborane. The indenyl ligand conformation in 1 (cisoid between the indenyl bridgehead carbon atoms and cage heteroatoms, with the cage carbon atom lying below the indenyl C-C bond) reveals that the structural trans effect in a phosphacarborane ligand is weakest for carbon and therefore varies in the order B > P > C. Starting with [HNC5H11][7, 8-nido-CPB9H11] deprotonation and reaction with half an equivalent of [Ru(p-cymene)Cl2]2 affords the sigma-bonded ruthenaphosphacarborane 8-{Ru(p-cymene)Cl(C5H11N)}-7, 8-nido-CPB9H11 (2), the first example of a molecule with a phosphacarborane sigma-bonded to a metal to be crystallographically characterised.