Synthesis and Structure of <i>m</i>-Terphenyl Thio-, Seleno-, and Telluroethers

Several routes for the synthesis of <i>m</i>-terphenyl thio-, seleno-, and telluroethers were investigated. <i>m</i>-Terphenyl iodides react with diphenyl diselenides or ditellurides (CsOH·H<sub>2</sub>O, DMSO, 110 °C) to give the desired compounds in 19−84% yield which significantly extends the previously reported such reactions because <i>o</i>-benzyne cannot be an intermediate as previously suggested. However, the most general synthetic route was that involving reaction of 2,6-diaryl Grignard reagents with sulfur, selenium, or tellurium electrophiles. The <i>m</i>-terphenyl thio-, seleno-, and telluroethers were characterized spectroscopically and, in one case, by single-crystal X-ray analysis. Certain of these compounds showed atropisomerism and barriers for interconversion of isomers were determined by variable-temperature NMR spectroscopy. The barriers for interconverting the <i>syn</i> and <i>anti</i> atropisomers increase on going from the analogous S to Se to Te compounds. Calculations on this isomerization revealed that the barriers are due to rotation about the aryl−aryl bond and that the barriers for rotation about the aryl−chalcogen bond are much lower.