Reactivity and Properties of Cationic Ditelluroxane : Application to Polytelluroxane and Molecular Assembly

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The reactions of ditellturoxanes Ar_2Te^+-O-Te^+Ar_2 2X^-2 (Ar=p-tolyl) with a telluroxide 1, a selenoxide 7, and a carboxylate 10 that produce oligochalcogenoxanes bearing a hypervalent Te-O apical linkage in the main chain were sttudied.The ^<125>Te NMR chemical shifts of 2a-d were shifted downfield with decreasing the nucleophilicity of counteranions (X^-). This result reflects both the cationic character and the reactivity on the Te atoms of 2. The reaction of 2a (X^-=CF_3SO_3^-) with 1, 2, 3, or 4 eqtuiv of a tellturoxide 1a (Ar=p-tolyl) selectively gave oligotelluroxanes trimer 3a, tetramer 4a, pentamer 5a, or hexamer 6a, respectively. By contrast, the reaction of 2b (X^-=CF_3CO_2^-) with an excess of 1a afforded only trimer 3b. Equilibrium between oligotelluroxanes was confirmed by the crossover experiments for the reactions of 2a with 4a and of 2a with 1b (Ar=Ph). The reactivity and equilibritum properties of oligotelluroxanes were also supported by DFT calculations.The reactio … More n of 2a with 1 or 2 equiv of a selenoxide 7 exclusively produced a selenoxa-ditelluroxane trimer 8 or a bis (selenoxa)-ditelluroxane tetramer 9, respectively. Eqtuilibrium between these oligochalcogenoxanes was confirmed by the crossover experiments, The association constant of 2a with 7 forming 8 was found to be K_a=(2.18±0.12)x10^4 M^<-1> in CD_3CN at -40℃.The reaction of 2a with 2 equiv of carboxylates 10a-d gave a mixture of ditelluroxanebis (carboxylate) adducts 11a-c and diaryldicarboxytelluranes 12b-d, respectively, the prodtuct ratio of which depends on the electron-withdrawing ability of 10. The reaction of a tritelluroxane 3a with 2 equiv of 10a-d afforded 11a-d in all cases.The reaction of 2a with 1 equiv of phthalate 14 gave a [2+2]-assembled macrocyclic multitellurane 15, which was confirmed by X-ray crystallographic analysis.The present restults suggest that σ^*-n orbital interaction plays an essential role in the reactivity of ditellturoxanes and formations of self-assembled oligochalcogenoxanes. Thus, hypervalent bonds via σ^*-n orbital interactiont in heteroatoms could serve as a new supramolecular synthon for molecular assembly. Less