Polyfunctional Sterically Hindered Catechols with Additional Phenolic Group and Their Triphenylantimony(V) Catecholates: Synthesis, Structure, and Redox Properties

New polyfunctional sterically hindered 3,5-di-tert-butylcatechols with an additional phenolic group in the sixth position connected by a bridging sulfur atom—(6-(CH(2)-S-tBu(2)Phenol)-3,5-DBCat)H(2) (L(1)), (6-(S-tBu(2)Phenol)-3,5-DBCat)H(2) (L(2)), and (6-(S-Phenol)-3,5-DBCat)H(2) (L(3)) (3,5-DBCat is dianion 3,5-di-tert-butylcatecolate)—were synthesized and characterized in detail. The exchange reaction between catechols L(1) and L(3) with triphenylantimony(V) dibromide in the presence of triethylamine leads to the corresponding triphenylantimony(V) catecholates (6-(CH(2)-S-tBu(2)Phenol)-3,5-DBCat)SbPh(3) (1) and (6-(S-Phenol)-3,5-DBCat)SbPh(3) (2). The electrochemical properties of catechols L(1)–L(3) and catecholates 1 and 2 were investigated using cyclic voltammetry. The electrochemical oxidation of L(1)–L(3) at the first stage proceeds with the formation of the corresponding o-benzoquinones. The second process is the oxidation of the phenolic moiety. Complexes 1 and 2 significantly expand their redox capabilities, owing to the fact that they can act as the electron donors due to the catecholate metallocycle capable of sequential oxidations, and as donors of the hydrogen atoms, thus forming a stable phenoxyl radical. The molecular structures of the free ligand L(1) and complex 1 in the crystal state were determined by single-crystal X-ray analysis.