Electron-Accepting Molecules Containing Telluropyranyl Groups. The Effect of Tellurium Oxidation State on Reduction Potentials

Article abstract of DOI:10.1021/jo00387a002

Telluropyran-4-ones and benzotelluropyran-4-ones could not be oxidized to the corresponding tellurones or telluroxides with hydrogen peroxide, m-chlorobenzoic acid, sodium metaperiodate, N-chlorosuccinimide, tert-butyl hypochloride, or 40percent peracetic acid.Oxidative addition products were obtained from peracetic acid to give telluropyranone 10-Te-4 tellurane diacetates.Chlorine, bromine, and iodine gave oxidative adittion products as well.The electrochemical reduction of the 10-Te-4 telluranes as followed by cyclic voltammetry and coulometry was initial two-electron reduction to give the telluropyranone and 2 equiv of the halide or acetate.The reductions were irreversible, perhaps because of the good leaving-group character of the halide or acetate ligands attached to Te. 2,6-Disubstituted telluropyrylium salts in pyridine with triphenylphosphine under aerobic conditions gave oxidative dimerizations to produce 1,1-dioxo(telluropyranylidene)telluropyrans, which, in the case of 2,2'6,6'-tetraphenyl derivative, displayed reversible reductions by cyclic voltammetry.Under an argon atmosphere in degassed solvents, the telluropyrylium salts did not give oxidative dimerization.The reaction of the 2,6-disubstituted telluropyrylium salts and triphenylphosphine oxide in pyridine under argon gave the dioxo(telluropyranylidene)telluropyrans and triphenylphosphine. 2-Phenyl-7-methoxybenzotelluropyrylium perchlorate reacted with triphenylphosphine, pyridine, and air or with triphenylphosphine oxide (as a melt) to give the 1,1'-dioxo(benzotelluropyranylidene)benzotelluropyran.The ditelluroxide gave a reversible reduction by cyclic voltammetry, with E^o being 0.2 V more negative than for the tetraphenyl(telluropyranylidene)telluropyran tellurone.The condensation of malononitrile with telluropyranone diacetates gave dicyanomethylidene adduct that display reversible reduction waves by cyclic voltammetry.As was observed with the telluropyranone 10-Te-4 telluranes, the oxidative addition of peracetic acid or halogens gave 10-Te-4 telluranes whose first reduction waves are much less negative but irreversible.The condensation of Meldrum's acid with 4-ethoxytelluropyrylium and 4-ethoxybenzotelluropyrylium salts gave adducts with reversible or partially reversible reduction waves.