Tri- and tetra-nuclear µ-alkyne clusters from [Ru2(µ-CO)(µ-C2R2)(η-C5H5)2](R = Ph or CF3)

Abstract

The unsaturated RuRu double-bonded complexes [Ru₂(µ-CO)(µ-C₂R₂)(η-C₅H₅)₂](R = Ph 1a or CF₃1b) react at room temperature with [Fe₂(CO)₉] to produce the new mixed-metal trinuclear complexes [Ru₂Fe(CO)₃(µ-CO)(µ₃-CO)(µ₃-C₂R₂)(η-C₅H₅)₂](R = Ph 2 or CF₃3) in good yield. Similarly, complexes 1a and 1b react with [Ru(CO)₄(C₂H₄)] at room temperature to afford the analogous triruthenium complexes [Ru₃(CO)₃(µ-CO)(µ₃-CO)(µ₃-C₂R₂)(η-C₅H₅)₂](R = Ph 4 or CF₃5). The new complexes exist in two geometric forms which can be regarded as ‘rotamers’, differing only in the metal atom to which the alkyne ligand is π bound. The structure of complex 2 has been determined by X-ray diffraction and shows a triangular metal core with a triply bridging alkyne ligand bonding parallel to the (C₅H₅)Ru–Ru(C₅H₅) edge, π bound to the Fe(CO)₃ unit, giving the molecule a plane of symmetry. The major isomers of 3 and 4 and the minor isomer of 5 also have this structure. An X-ray diffraction study on the major isomer of the latter, 5b, revealed that this adopts the other geometric form which has the alkyne π bound to a Ru(C₅H₅) unit, with no plane of symmetry. The rotation of the alkyne relative to the {M(C₅H₅)}₂M(CO)₃ triangle is accompanied by a shift of the µ-CO ligand to bridge a {M(C₅H₅)}M(CO)₃ edge of the M₃ triangle, i.e. as in the other isomer, the edge opposite the π-bound metal is bridged. A similar structure is observed for the minor isomers of 3 and 4. Fluxional interconversion was observed for the isomers of 4 at elevated temperatures. Reaction of 1a with [Co₂(CO)₈] at room temperature gives the tetranuclear cluster [Ru₂Co₂(CO)₄(µ₃-CO)₂(µ₄-C₂Ph₂)(η-C₅H₅)₂]6 as one of the products. An X-ray diffraction study showed that this 60-electron complex has a closo-Co₂Ru₂C₂ octahedral core with each CoRu₂ face capped by a µ₃-CO ligand. Complex 6 can also be regarded as a ‘butterfly’ type structure with the Co atoms at the wing-tips and the diphenylethyne ligand bridging all four metal atoms.