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]·2CH2Cl2 and [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)Å] and one long [2.987(1)Å] 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)Å] weakly semi-bridged by two CO groups (mean W–C–O 170°) and with the Mo–W bonds (mean 2.706 Å) 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.