Triphenylantimony(V) catecholato complexes with 4-(2,6-dimethylphenyliminomethyl)pyridine. Structure, redox properties: The influence of pyridine ligand

Abstract

The complexation of triphenylantimony(V) catecholates (3,6-DBCat)SbPh3 (1), (4,5-pip-3,6-DBCat)SbPh3 (2) and (4,5-Cl2-3,6-DBCat)SbPh3 (3) with neutral 4-(2,6-dimethylphenyliminomethyl)pyridine (Py-CHN–Ar) leads to the formation of hexacoordinated complexes (3,6-DBCat)SbPh3·(Py-CHN–Ar) (4), (4,5-pip-3,6-DBCat)SbPh3·(Py-CHN–Ar) (5) and (4,5-Cl2-3,6-DBCat)SbPh3·(Py-CHN–Ar) (6) (where 3,6-DBCat is 3,6-di-tert-butyl-catecholate, 4,5-pip-3,6-DBCat is 4,5-(N,N′-piperazine-1,4-diyl)-3,6-di-tert-butyl-catecholate, 4,5-Cl2-3,6-DBCat is 4,5-dichloro-3,6-di-tert-butyl-catecholate) containing NPyridine-coordinated neutral donor ligand Py-CHN–Ar. In the absence of donor ligands chlorine-containing catecholate 3 undergoes rearrangement in acetonitrile to form ionic complex [Ph4Sb]+[(4,5-Cl2-3,6-DBCat)2SbPh2]- (7). Complexes have been isolated and characterized by spectroscopic methods and cyclic voltammetry. The pyridine-containing catecholate (3,6-DBCat)SbPh3·Py (8) was also synthesized in order to compare it's the electrochemical behaviour with those of iminopyridine complexes 4–6. The presence of NPyridine-coordinated iminopyridine ligand changes the mechanism of catecholate oxidation in 4 and 6: the first oxidation wave (at Eox1p = 0.94 V for 4 and 0.99 V for 6) is two-electron and corresponds to the oxidation of dianionic catecholate ligand to a coordinated o-benzoquinone. In contrast to catecholates 4 and 6, the electrochemical behaviour of piperazine-containing catecholate 5 does not practically differ from that one for initial catecholate 2. The molecular structures of complexes 3–7 in crystals have been determined by single-crystal X-ray analysis.