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.