Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 70. Tetranuclear metal compounds with rhenium–molybdenum or –tungsten bonds. Crystal structures of [Mo2Re2(µ3-CC6H4Me-4)2(µ-CO)2(CO)7(η-C5H5)2]·1.5CH2Cl2 and [W2Re2(µ-H)(µ3-σ:σ′:η2-CCH2)(µ3-CMe)(µ-CO)(CO)8(η-C5H5)2]

Abstract

Reactions between the compounds [M(CC₆H₄Me-4)(CO)₂(η-C₅H₅)](M = Mo or W) and [Re₂(µ-H)(µ-σ:η-CHCHBuⁿ)(CO)₈] afford the tetranuclear metal complexes [M₂Re₂(µ₃-CC₆H₄Me-4)₂(µ-CO)₂(CO)₇(η-C₅H₅)₂]. The corresponding reaction between [W(CMe)(CO)₂(η-C₅H₅)] and the dirhenium compound yields a mixture of the cluster compounds [W₂Re₂(µ₃-CMe)₂(µ-CO)₂(CO)₇(η-C₅H₅)₂], [W₂Re₂(µ-H)(µ₃-σ:σ′:η²-CCH₂)(µ₃-CMe)(µ-CO)(CO)₈(η-C₅H₅)₂], and [WRe₂(µ₃CMe)(CO)₁₀(η-C₅H₅)]. The molecular structures of [Mo₂Re₂(µ₃-CC₆H₄Me-4)₂(µ-CO)₂(CO)₇(η-C₅H₅)₂]·1.5CH₂Cl₂ and [W₂Re₂(µ-H)(µ₃-σ:σ′:η²-CCH₂)(µ₃-CMe)(µ-CO)(CO)₈(η-C₅H₅)₂] have been established by X-ray diffraction studies. Crystals of the former contain two very similar crystallographically independent molecules in the asymmetric unit and there are three molecules of CH₂Cl₂ of crystallisation. The structure has a tetrahedral core of metal atoms (mean metal–metal separations 2.914 Å) with two of the faces of the tetrahedron capped by p-tolylmethylidyne ligands and two of the Mo–Re edges of the tetrahedron asymmetrically bridged by CO groups [Mo–C–O 155(3) and 157(3)°]. Each rhenium atom carries three orthogonal terminal CO ligands, with the remaining CO group being terminally attached to a molybdenum atom. As expected, the C₅H₅ moieties ligate the Mo atoms. In [W₂Re₂(µ-H)(µ₃-σ:σ′:η²-CCH₂)(µ₃-CMe)(µ-CO)(CO)₈(η-C₅H₅)₂] the four metal atoms adopt a near-planar ‘butterfly’ arrangement, having a W–Re spine [2.923(1)Å] and with a W and a Re atom at the wing-tip positions. The W₂Re triangle is capped by a CMe group which lies perceptibly closer to the tungsten atoms than the rhenium. On the other side of the W₂Re₂ plane, the WRe₂ triangle is triply bridged by the CCH₂ group. The latter is σ bonded to the W and Re atoms which form the spine of the butterfly, and is η²-co-ordinated to the Re atom at the wing-tip position. A CO ligand asymmetrically bridges [W–C–O 159(2)°] the W–Re edge of the WRe₂ triangle and, although not located by X-ray diffraction, the hydrido ligand must bridge the Re–Re edge [3.023(1)Å], since the latter is perceptibly longer than the other metal–metal separations (mean 2.951 Å). Each rhenium atom is ligated by three terminal CO groups, and the tungsten atom is co-ordinated by two such groups. There is a C₅H₅ ligand bonded to each tungsten centre. The ¹H and ¹³C-{¹H} n.m.r. spectra of the new compounds are reported and discussed.