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]·1.5CH2Cl2and [W2Re2(µ-H)(µ3-σ:σ′:η2-CCH2)(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 A) 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)A] 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)A], since the latter is perceptibly longer than the other metal–metal separations (mean 2.951 A). 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.