Synthesis and Characterisation of Sigma‐ and Pi‐Bonded Metallaphosphacarboranes

Two new metallaphosphacarboranes have been synthesised from [7, 8‐ nido ‐CPB 9 H 11 ] – by deprotonation followed by treatment with a metal fragment. Starting with [HNMe 3 ][7, 8‐ nido ‐CPB 9 H 11 ] deprotonation and reaction with a source of {(indenyl)Co} 2+ affords the η‐bonded cobaltaphosphacarborane 3‐(η‐C 9 H 7 )‐3,1,2‐ closo ‐CoCPB 9 H 10 ( 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 [HNC 5 H 11 ][7, 8‐ nido ‐CPB 9 H 11 ] deprotonation and reaction with half an equivalent of [Ru( p ‐cymene)Cl 2 ] 2 affords the σ‐bonded ruthenaphosphacarborane 8‐{Ru( p ‐cymene)Cl(C 5 H 11 N)}‐7, 8‐ nido ‐CPB 9 H 11 ( 2 ), the first example of a molecule with a phosphacarborane σ‐bonded to a metal to be crystallographically characterised.