Facile Exchange of Terminal, Doubly Bridging, and Quadruply Bridging Carbonyl Ligands in Solution: Crystal Structure and Solution Dynamics of LWM₃(CO)₁₂H, L=C₅H₅, C₅Me₅ and M=Os, Ru

Abstract

In the series of the tetranuclear mixed-metal clusters LWM₃(CO)₁₂H, L = C₅H₅, C₅Me₅ and M = Os, Ru, the cluster cores adapt different geometries from tetrahedron (isomer a), distorted tetrahedron (isomer b) to butterfly arrangement (isomers c and d) in the solid state (see scheme 1). For the last two butterfly isomers, a CO ligand adapted a π-bonded μ ₄-η ² bridging mode (as a four electron donor) to stabilize the cluster. In solution state, these isomers undergo rapid interconversion on the time scale of ¹H NMR spectroscopy, suggesting that the π-bonded CO ligands is in equilibrium with the regular, terminal or doubly bridging CO ligands. Hydrogenation of LWM₃(CO)₁₂H in refluxing toluene solution produces LWM₃(CO)₁₁H₃ which adapted a tetrahedral cluster core structure. The fluxionaity of these hydride complexes in solution will be discussed.