The binuclear trimethyl/triethylantimony(V) bis-catecholate derivatives of four-electron reduced 4,4′-di-(3-methyl-6-tert-butyl-o-benzoquinone)

The reaction of 4,4′-di-(3-methyl-6-tert-butyl-o-benzoquinone) (Q-Q) with trimethyl- or triethylstibine proceeds as a two-electron oxidative addition of each quinone moiety and allows to prepare binuclear bis-catecholates R3Sb(Cat-Cat)SbR3 with a nearly quantitative yield (R = Me, 1; R = Et, 2). The products 1 and 2 were characterized by IR-, 1H and 13C NMR spectroscopy. Molecular structure of triethylantimony(V) bis-catecholate 2 was confirmed by single-crystal X-ray analysis. Each Sb(V) atom adopts square pyramidal geometry with Cat moiety in basal positions, dihedral angle between Cat fragments is 74.27(5)°. The oxidation of bis-catecholates by ferrocenium tetrafluoroborate or tetrabromo-p-benzoquinone leads to loss of one trialkylantimony(V) moiety forming paramagnetic salts containing one-side decoordinated mononuclear semiquinone-catecholato [R3Sb(Cat-SQ)]− anion detected by EPR. The oxidation of 1 by air oxygen allows to prepare mononuclear quinone-catecholate Me3Sb(Cat-Q) (3).