Isomerization Involving a Quadruply Bridging Carbonyl Ligand

An X-ray analysis of(C5Me5)MoRu3(CO)12H at 110 K showed a butterfly metal framework, on which the oxygen atom of the disordered μ4-η2-CO ligand is linked to either the Ru or the Mo atom at two opposite wingtip positions, providing a unique example of isomerism involving the quadruply bridging CO ligand. These two butterfly isomers exist in solution together with a third tetrahedral isomer and undergo slow exchange with this last isomer on the NMR time scale, as demonstrated by 1H and 13C NMR studies.