C–S Bond cleavage in reactions of thiolate nucleophiles with bridging thioethers in anionic ditungsten(III) complexes

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Abstract
The complexes [PPh4][Cl3W(µ-Cl)(µ-SR2)2WCl3](R = Me, Et, or SR2= tetrahydrothiophene) react with thiolate anions, SR′–(R′= C6H4Me-4), via a nucleophilic displacement of the R group to yield the appropriate mixed thioether, RSR′, and the dianion [Cl3W(µ-SR2)(µ-SR)(µCl)WCl3]2–. The structure of the complex [PPh4]2[Cl3W(µ-SEt2)(µ-SEt)(µ-Cl)WCl3]·2CH2Cl2 was determined by single-crystal X-ray diffraction, which shows that the anion possesses a confacial bioctahedral framework. A very short W–W interatomic distance [2.4418(6)Å] is indicative of a metal–metal triple bond. The unique combination of bridging ligands in this complex, all of which are trans to terminal chlorides, allows a comparison to be made between the W–Sthioether W–Sthiolate and W–Cl bond lengths. The configuration of the ethyl group on the µ-SEt group is axial with reference to the µ-SEt2 ligand. This geometry is retained upon dissolution in dichloromethane or acetonitrile for sufficient time to record the 1H NMR spectra, but equilibration with the equatorial isomer occurs over a period of ca. 2 or 6 h respectively. A kinetic study of this process revealed that it is first order, with a forward rate constant of 1.32 × 10–4 s–1. An absolute assignment of all the proton resonances for both isomers was achieved.

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