Ferrocene-Containing Tin(IV) Complexes Based on <i>o</i>-Benzoquinone and <i>o</i>-Iminobenzoquinone Ligands. Synthesis, Molecular Structure, and Electrochemical Properties

The addition of different substituted <i>o</i>-benzoquinones and <i>o</i>-iminobenzoquinones to tin(II) bis(<i>o</i>-iminophenolates) of the types (Fc-IP)₂Sn^II and (Fc-4,6-IP)₂Sn^II (where Fc-IP is anion 2-(ferrocenylmethyleneamino)phenolate [Fc-C(H)═N(C₆H₄)O^-] and Fc-4,6-IP is anion 2-(ferrocenylmethyleneamino)-4,6-di-<i>tert</i>-butylphenolate [Fc-C(H)═N(4,6-tBu-C₆H₂)O^-]) in tetrahydrofuran leads to the oxidation of Sn(II) to Sn(IV) with formation of the corresponding tin(IV) catecholates (Fc-4,6-IP)₂Sn^IV(3,6-Cat) (<b>1</b>), (Fc-IP)₂Sn^IV(3,6-Cat) (<b>2</b>), (Fc-4,6-IP)₂Sn^IV(4-Cl-3,6-Cat) (<b>3</b>), (Fc-IP)₂Sn^IV(4-Cl-3,6-Cat) (<b>4</b>), (Fc-4,6-IP)₂Sn^IV(4,5-Cl₂-3,6-Cat) (<b>5</b>), and (Fc-IP)₂Sn^IV(4,5-Cl₂-3,6-Cat) (<b>6</b>) or the <i>o</i>-amidophenolates (Fc-4,6-IP)₂Sn^IV(AP-Me) (<b>7</b>), (Fc-IP)₂Sn^IV(AP-iPr) (<b>8</b>), and (Fc-4,6-IP)₂Sn^IV(AP-iPr) (<b>9</b>). Here ligands 3,6-Cat, 4-Cl-3,6-Cat, and 4,5-Cl₂-3,6-Cat are dianions 3,6-di-<i>tert</i>-butyl-, 4-chloro-3,6-di-<i>tert</i>-butyl-, and 4,5-dichloro-3,6-di-<i>tert</i>-butylcatecholates, respectively, and AP-Me and AP-iPr are dianions 4,6-di-<i>tert</i>-butyl-<i>N</i>-(2,6-dimethylphenyl)-<i>o</i>-amidophenolate and 4,6-di-<i>tert</i>-butyl-<i>N</i>-(2,6-diisopropylphenyl)-<i>o</i>-amidophenolate, respectively. Complexes <b>1</b>-<b>9</b> have been characterized in detail by IR spectroscopy, cyclic voltammetry, and ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy. The molecular structures of tin(IV) complexes <b>5</b>, <b>7</b>, and <b>9</b> in the crystalline state were determined by single-crystal X-ray diffraction analysis. Complexes demonstrate a series of successive oxidations involving alternately catecholato/<i>o</i>-amidophenolato centers and ferrocenyl moieties. The relative oxidation potentials of these redox centers depend on the acceptor properties of the redox-active chelating O,O' or O,N ligand. An increase in the acceptor properties of redox-active <i>o</i>-quinonato-type ligands leads to an increase in the oxidation potentials of redox ligands as well as the following oxidation of ferrocenyl group(s). In two series of complexes, (Fc-4,6-L)₂SnL' and (Fc-L)₂SnL', where L' is AP-iPr, AP-Me, 3,6-Cat, 4-Cl-3,6-Cat, and 4,5-Cl₂-3,6-Cat, a more pronounced convergence of the oxidation potentials of the redox-active <i>o</i>-quinonato ligand and ferrocenyl group occurs in the series (Fc-L)₂SnL'.