12-Te-5 Pertelluranes from 1,2-Oxatellurolyl-1-ium Halides. Synthesis, Structure, and Reactivity. The Quest for Delocalization in 10-Te-3 Telluranes and 12-Te-5 Pertelluranes of Thiathiophthene Structure

Article abstract of DOI:10.1021/jo00360a012

The oxidative addition of chlorine or bromine to 1,2-oxatellurolyl-1-ium chlorides or bromides, respectively, at 0 deg C occurs rapidly to give 12-Te-5 pertelluranes.The structure of 3,5-diphenyl-1,2-oxatellurolylium tribromide (9) was determined unambiguously by single-crystal X-ray crystallographic analysis.Pertelluranes were neutral in solution (CH2Cl2), as determined by conductance studies.The pertelluranes were easily reduced electrochemically to halide ions and the oxatellurolylium halide and were susceptible to nucleophilic attack by Michael addition on the enone segment.Spectroscopic and crystallographic comparison of the pertelluranes with the corresponding oxatellurolylium halides and of dioxatellurapentalenes with the corresponding pertellurane analogues suggested ionic bonding between Te and the halides or O for all four of these systems.Theoretical treatment with CNDO/2 calculations by the program GEOMORV suggested ionic bonding of O and halides to the Te with little ?-delocalization involving Te-O and Te-C bonds in both the tellurane and pertellurane systems.A low-lying ?^* LUMO in the pertelluranes was predicted, consistent with the susceptibility to nucleophilic attack, as observed experimentally.