Redox transformations of triphenylantimony(V) catecholate complexes based on alkyl gallates

The electrochemical transformations of triphenylantimony(V) catecholate complexes containing fragments of alkyl gallates (RO(O)C–(OH)Cat)SbPh3 (R = CH3 (1), C8H17 (2), and C12H25 (3)); (RO(O)C–(OH ∙ NEt3)Cat)SbPh3 (4); and ROC(O)GallH3 (R = CH3 (5), C8H17 (6), and C12H25 (7)) in acetonitrile were studied. The electrochemical oxidation of alkyl gallates 5–7 proceeds in two irreversible stages and leads to formation of o-quinoid products. At the first stage, the oxidation of antimony(V) compounds is electrochemically quasi-reversible and leads to the formation of unstable cationic complexes. The second irreversible redox transfer results in ligand decoordination and destruction of the compounds. Three redox stages were observed for complex 4. The triethylamine-deprotonated hydroxy group is oxidized at the first electrochemical step that leads to a further intramolecular transfer, forming a stable intermediate, whose oxidation occures in quasireversible manner.