Antimony(V) and Tin(IV) Complexes with Redox-Active O,N,O-Donor Ligand in the Electrosynthesis of Symmetrical Disulfides

Reactions of electrochemically generated antimony(V) and tin(IV) complex species containing a tridentate O,N,O-donor ligand with various thiols were studied. Among main group metal complexes with N,N-bis(2-hydroxy-di-3,5-tert-butylphenyl)amine (CatH2–NH–CatH2), compounds [Me2Sn(Cat-N-SQ)] (I), [Et2Sn(Cat-N-SQ)] (II), [Ph2Sn(Cat-N-SQ)] (III), [(c-C6H11)2Sb(Cat-N-Cat)] (IV), and [Ph3Sb(Cat-NH-Cat)] (V) are the most active, able to mediate the oxidation of thiols (1-hexanethiol, cyclohexanethiol, and 4-methoxythiophenol), to symmetrical disulfides were identified. The anodic activation of Sb(V) and Sn(IV) complexes involves organic ligands and gives rise to intermediates that react with thiols. During the mediated electrosynthesis, the initial complex species is regenerated in solution. The use of metal complex mediators decreases the anodic overvoltage of the thiol oxidation in comparison with direct electrochemical synthesis. The yields of products depend on complex and thiol structures or ratio. The highest efficiency in the electrocatalytic reactions was found for the [Ph3Sb(Cat-NH-Cat)] complex, which should be used for the synthesis of disulfides.