Syntheses and properties of ditelluroxanes and oligochalcogenoxanes: Hypervalent oligomers with Te-O apical linkages in the main chain

The reaction of ditelluroxanes [Ar2Te-O-TeAr2](2+)[X](2)(-) (2) (Ar= p-toly l) with a telluroxide 1, a selenoxide T or a carboxylate 10 to produce olig ochalcogenoxanes with hypervalent Te-O apical linkages in their main chain is described. The Te-125 NMR chemical shifts of 2 (2a: X = CF3SO3- 2b: X- = CF3CO2-,2c: X- = CH3CO2-, 2d: X = Cl-) are shifted downfield with decreasi ng nucleophilicity of the counteranions. This result reflects both the cati onic character and the reactivity of the Te atoms of 2. The reaction of 2 a with one. two. three. or four equivalents of telluroxide la (Ar p-tolyl) s electively gave a tritelluroxane 3a, tetratelluroxane 4a, pentatelluroxane 5a. and hexatelluroxane 6a, respectively. In contrast, the reaction of 2b w ith an excess of la produced only tritelluroxane 3b. An equilibrium between the oligotelluroxanes was confirmed by crossover experiments of the reacti ons of 2 a with 4 a and of 2 a with 1 b (Ar = Ph). The selective equilibriu m formation of a selenoxaditelluroxane 8 or a bis(selenoxa)ditelluroxane 9 was achieved by the reaction of 2a with one or two equivalents of selenoxid e 7, respectively. The association constant of 2 a with 7 to form 8 was est imated to be K-a (2.18 +/- 0.12)x 10(4) M-1 in CD3CN at -40 degreesC. The r eaction of 2a with two equivalents of carboxylates 10a-d gave a mixture of bis(carboxy late) ditelluroxanes 11a-c and diaryldicarboxytelluranes 12b-d, respectively, in which the product ratio of these depended upon the electr on-withdrawing ability of 10. The reaction of 3a with two equivalents of 10 a-d afforded 11a - d in all cases. The present results suggest that the sig ma*-n orbital interaction plays an essential role in the reactivity of dite lluroxanes 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.