TRINUCLEAR AND TETRA-NUCLEAR MU-ALKYNE CLUSTERS FROM [RU2(MU-CO)-(MU-C2R2)(ETA-C5H5)2] (R = PH OR CF3)

The unsaturated Ru=Ru double-bonded complexes [Ru2(mu-CO)(mu-C2R2)(eta-C5H5)2](R = Ph 1a or CF3 1b) react at room temperature with [Fe2(CO)9] to produced the new mixed-metal trinuclear complexes [Ru2Fe(CO)3(mu-CO)(mu3-CO)(mu3--C2R2)(eta-C5H5)2](R = Ph 2 or CF3 3) 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(mu-CO)(mu3-CO)(mu3-C2R2)(eta-C5H5)2] (R = Ph 4 or CF3 5). 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 pi 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(CH5) edge, pi 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 pi 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 mu-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 pi-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 la with [Co2(CO)8] at room temperature gives the tetranuclear cluster [Ru2Co2(CO)4(mu3-CO)2(mu4-C2Ph2)(eta-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 mu3-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.