THE REACTION OF SOME SUBSTITUTED ORTHO-BENZOQUINONES WITH ELEMENTAL TELLURIUM AND WITH TELLURIUM(II) COMPOUNDS

The oxidation of elemental tellurium by three ortho-benzoquinones (RO,: R = Cl4C6, Br4C6 or 3,5-But2H2C6) is a direct route to the corresponding tellurium(IV) catecholates Te(O2R)2. The analogous reaction with organotellurium(II) TeR'2 [R' = Me2, Et2, Ph(Et) or Ph(Br)] gives the products Te(O2R)R'2. The reactions proceed in each case by one-electron transfer, since the presence of the semiquinone radical RO2. in the reaction mixture has been demonstrated by ESR spectroscopy. The Te(O2R)2 species resist further oxidation, and also show weak donor and acceptor properties. The structure of the compound Te(O2C6H2But2-3,5)2(bipy) 1 (bipy = 2,2'-bipyridine) has been determined by X-ray crystallography. Crystal parameters: triclinic, space group P1BAR, a = 10.388(2), b = 14.468(3), c = 15.820(3) angstrom, alpha = 106.00(1), beta = 115.98(2), gamma = 94.98(2)-degrees, Z = 2 and R = 0.0424 for 3424 reflections. For Te(O2C6Cl4).18-crown-6 2 (18-crown-6-1,4,7,10,13,16-hexaoxacyclooctadecane), the crystal parameters are: monoclinic, space group P2(1)/n, a = 10.809(4), b = 18.571(7), c = 19.287(9) angstrom, beta = 91.53(4)-degrees, Z = 4 and R = 0.057 for 3768 reflections. In 1 the bipy is co-ordinated by weak Te-N interactions, with clear evidence for a stereochemically active lone pair, while in 2 the cryptand ring is situated around the axis of the presumed lone pair.