Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 97. Synthesis and crystal structures of the molybdenumditungsten compounds [MoW2{µ-σ,σ′ : η4-C(Ph)C(Ph)C(C6H4Me-4)C(C6H4Me-4)}(CO)6(η-C5H5)2]·2CH2Cl2and [MoW2(µ-C2Ph2){µ-C2(C6H4Me-4)2}(CO)4(η-C5H5)2]·0.5CH2Cl2

Abstract

Treatment of [MoW2(µ-CC6H4Me-4)2(µ-CO)2(CO)4(η-C5H5)2] with PhCCPh in n-hexane at reflux temperatures affords a chromatographically separable mixture of the two trimetal compounds [MoW2{µ-σ,σ′ : η4-C(Ph)C(Ph)C(C6H4Me-4)C(C6H4Me-4)}(CO)6(η-C5H5)2](2) and [MoW2(µ-C2Ph2){µ-C2(C6H4Me-4)2}(CO)4(η-C5H5)2](3), the structures of which have been established by X-ray diffraction. In the molecule of (2) there is a bent W–Mo–W [143.2(1)°] spine with one short [2.562(1)A] and one long [2.987(1)A] metal–metal bond. The longer of the two Mo–W linkages is bridged by a C(Ph)C(Ph)C(C6H4Me-4)C(C6H4Me-4) fragment, with all four carbon atoms of the C4 chain ligating the molybdenum atom, and with the two terminal carbon atoms σ bonded to the tungsten. Each tungsten atom carries two CO groups and a C5H5 ring, and the molybdenum is also co-ordinated by two CO ligands. All six CO groups deviate slightly from linearity [M(Mo or W)–C–O 171.4–173.9°] due to their weakly semi-bridging the metal–metal bonds. The structure of compound (3) is based on an essentially equilateral triangle of metal atoms with the W–W bond [2.752(1)A] weakly semi-bridged by two CO groups (mean W–C–O 170°) and with the Mo–W bonds (mean 2.706 A) bridged, respectively, by the alkynes C2Ph2 and C2(C6H4Me-4)2. Each tungsten atom is co-ordinated by a C5H5 ring, and the molybdenum atom is ligated by two CO groups. The molecule is an interesting example of an unsaturated trimetal cluster with 44 valence electrons. The n.m.r. data (1H and 13C-{1H}) for complexes (2) and (3) are in agreement with the structures established by X-ray diffraction.