Isomerization Involving a Quadruply Bridging Carbonyl Ligand: Dynamics and Crystal Structure of (C₅Me₅)MoRu₃(CO)₁₂H

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.