Exopolyhedral Ligand Orientation Controls Diastereoisomer in Mixed-Metal Bis(Carboranes) †

Heterobimetallic derivatives of a bis(carborane), [μ(7,8)-(1′,3′−3′-Cl-3′-PPh(3)-closo-3′,1′,2′-RhC(2)B(9)H(10))-2-(p-cymene)-closo-2,1,8-RuC(2)B(9)H(10)] (1) and [μ(7,8)-(1′,3′−3′-Cl-3′-PPh(3)-closo-3′,1′,2′-RhC(2)B(9)H(10))-2-Cp-closo-2,1,8-CoC(2)B(9)H(10)] (2) have been synthesised and characterised, including crystallographic studies. A minor co-product during the synthesis of compound 2 is the new species [8-{8′-2′-H-2′,2′-(PPh(3))(2)-closo-2′,1′,8′-RhC(2)B(9)H(10)}-2-Cp-closo-2,1,8-CoC(2)B(9)H(10)] (3), isolated as a mixture of diastereoisomers. Although, in principle, compounds 1 and 2 could also exist as two diastereoisomers, only one (the same in both cases) is formed. It is suggested that the preferred exopolyhedral ligand orientation in the rhodacarboranes in the non-observed diastereoisomers would lead to unacceptable steric crowding between the PPh(3) ligand and either the p-cymene (compound 1) or Cp (compound 2) ligand of the ruthenacarborane or cobaltacarborane, respectively.