Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 29. Synthesis of rhenium–tungsten compounds; X-ray crystal structures of [ReW2(µ-Br)(µ-L)(µ-CC6H4Me-4)(µ3-CC6H4Me-4)(CO)3(η-C5H5)2](L = CO or O)

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Abstract
The compound [W(CR)(CO)2(η-C5H5)](R = C6H4Me-4) reacts with the rhenium compounds [Re2(CO)10], [Re2(µ-Br)2(thf)2(CO)6](thf = tetrahydrofuran), and [ReBr(NCMe)2(CO)3] to afford, respectively, the cluster complexes [Re2W(µ3-CR)(CO)10(η-C5H5)], [Re2W(µ-Br)2(µ3-CR)-(CO)7(η-C5H5)], and [ReW2(µ-Br)(µ-CR)(µ3-CR)(µ-CO)(CO)3(η-C5H5)2]. The latter compound has been structurally characterised by an X-ray diffraction study. A ReW2 triangle of metal atoms [W–W 2.620(1), Re–W 2.867(1) and 2.912(1)Å] is asymmetrically capped by a CC6H4Me-4 ligand [µ3-C–Re 2.248(12), µ3-C–W 2.035(14) and 2.050(11)Å], and is edge-bridged by CC6H4Me-4, Br, and CO groups, with the latter being asymmetrically bound [W–C–O 155(1)°].The two tungsten atoms carry cyclopentadienyl ligands, and the rhenium atom three terminally bound CO groups. The compound [ReW2(µ-Br)(µ-CR)(µ3-CR)(µ-CO)(CO)3(η-C5H5)2] readily oxidises in air to afford the oxo-bridged species [ReW2(µ-Br)(µ-O)(µ-CR)(µ3-CR)(CO)3(η-C5H5)2] which was also characterised by X-ray diffraction. This complex is structurally similar to its precursor but with the significant differences of the µ-CO ligand being replaced by µO and the capping CC6H4Me-4 being very asymmetrically bound to the metal triangle [µ3-C–Re 2.515(20), µ3-C–W 2.017(19) and 2.114(18)Å]. In addition to reacting with oxygen, the compound [ReW2(µ-Br)(µ-CR)(µ3-CR)(µ-CO)(CO)3(η-C5H5)2] reacts with sulphur. The nature of the product is described, and the n.m.r. spectra (1H and 13C-{1H}) of all the new compounds are reported and discussed in relation to their established or proposed structures.

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