Syntheses and Properties of Ditelluroxanes and Oligochalcogenoxanes: Hypervalent Oligomers with Te−O Apical Linkages in the Main Chain

Abstract

The reaction of ditelluroxanes [Ar2Te-O-TeAr]2+[X]2- (2) (Ar = p-tolyl) with a telluroxide 1, a selenoxide 7, or a carboxylate 10 to produce oligochalcogenoxanes with hypervalent Te-O apical linkages in their main chain is described. The 125Te NMR chemical shifts of 2 (2a: X- = CF3SO3-, 2b: X- = CF3CO2-, 2c: X- = CH3CO2-, 2d: X- = Cl-) are shifted downfield with decreasing nucleophilicity of the counteranions. This result reflects both the cationic character and the reactivity of the Te atoms of 2. The reaction of 2a with one, two, three, or four equivalents of telluroxide 1a (Ar = p-tolyl) selectively gave a tritelluroxane 3a, tetratelluroxane 4a, pentatelluroxane 5a, and hexatelluroxane 6a, respectively. In contrast, the reaction of 2b with an excess of 1a produced only tritelluroxane 3b. An equilibrium between the oligotelluroxanes was confirmed by crossover experiments of the reactions of 2a with 4a and of 2a with 1b (Ar = Ph). The selective equilibrium formation of a selenoxaditelluroxane 8 or a bis(selenoxa)ditelluroxane 9 was achieved by the reaction of 2a with one or two equivalents of selenoxide 7, respectively. The association constant of 2a with 7 to form 8 was estimated to be Ka = (2.18+/-0.12) x 10(4) M(-1) in CD3CN at -40 degrees C. The reaction of 2a with two equivalents of carboxylates 10a-d gave a mixture of bis(carboxylate)ditelluroxanes and diaryldicarboxytelluranes 12b-d, respectively, in which the product ratio of these depended upon the electron-withdrawing ability of 10. The reaction of 3a with two equivalents of 10a-d afforded 11a-d in all cases. The present results suggest that the sigma*-n orbital interaction plays an essential role in the reactivity of ditelluroxanes and in the formation of self-assembled oligochalcogenoxanes, and that a hypervalent bond via a sigma*-n orbital interaction is viable as a new supramolecular synthon for molecular assembly.