Antimony(V) catecholato complexes based on 4,5-dialkylsubstituted o-benzoquinone. The spectroscopic and electrochemical studies. Crystal structure of [Ph4Sb]+[Ph2Sb(4,5-Cat)2]−

Triphenylantimony(III) and triethylantimony(III) readily react with 4,5-(1,1,4,4-tetramethyl-butane-1,4-diyl)-o-benzoquinone to form catecholato complexes R3Sb(4,5-Cat) (R = Ph (1), Et (2); 4,5-Cat is dianionic 4,5-(1,1,4,4-tetramethyl-butane-1,4-diyl)-catecholate). In polar solvents (CHCl3, acetone) complex 1 transforms easily to ionic complex compound [Ph4Sb]+[Ph2Sb(4,5-Cat)2]− (3) with diphenyl-bis-[4,5-(1,1,4,4-tetramethyl-butane-1,4-diyl)-catecholato]antimony(V) complex anion. Complexes were characterized by IR, 1H, 13C NMR spectroscopy, cyclic voltammometry. Molecular structure of 3·CHCl3 was confirmed by X-ray analysis. Cyclic voltammometry of 1 and 3 shows that both complexes undergo reversible one-electron oxidation to quite stable paramagnetic o-semiquinonato species [Ph3Sb(4,5-SQ)]+ and [Ph2Sb(4,5-SQ)(4,5-Cat)] (0.75 and 0.49 V in CH2Cl2 vs. Ag/AgCl/KCl, respectively).