The reaction of some substituted ortho-benzoquinones with elemental tellurium and with tellurium(II) compounds

Abstract

The oxidation of elemental tellurium by three ortho-benzoquinones (RO2: 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 P, a= 10.388(2), b= 14.468(3), c= 15.820(3)Å, α= 106.00(1), β= 115.98(2), γ= 94.98(2)°, 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 P21/n, a= 10.809(4), b= 18.571(7), c= 19.287(9)Å, β= 91.53(4)°, 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.