Design of Reversible Low Redox Potential Systems Using Five-Membered Trichalcogenaheterocycles Containing Heavy Chalcogens; Sulfur, Selenium, and Tellurium

Abstract

Abstract 4-Isopropyl-7-methoxy-1,3,2-benzodichalcogenastannoles and 2,2-bis(η5-pentamethylcyclopentadienyl)-1,3,2-benzodichalcogenatitanoles, a synthetic equivalent of unstable ortho-benzenedichalcogenol, were prepared from 2-isopropyl-5-methoxybenzenechalcogenols in moderate yields by ortho-lithiation, chalcogenation, and protection with dichlorodimethylstannane and bis(η5-pentamethylcyclopentadienyl)titanocene dichloride, respectively. Some of the solid-state structures of the new-type stannoles and titannoles were confirmed by X-ray crystallographic analyses. Transformation into 4-isopropyl-7-methoxy-1,2,3-benzotrichalcogenoles was successfully carried out, namely by reacting the stannoles or titannoles with electrophiles containing one sulfur or selenium unit. The molecular structures of the new trichalcogenoles were determined by NMR, IR, mass spectra, X-ray crystallographic analyses, and theoretical calculations. In particular, it was elucidated that heavier multi-chalcogen linkages, selenium-selenium and selenium–tellurium bonds in the benzotrichalcogenoles were present in the five-membered ring by multi-nuclear NMR spectra in solution and confirmed by X-ray crystallographic analyses in the solid-state. The redox properties of the trichalcogenoles were studied by cyclic voltammetry. The voltammograms exhibited well-defined reversible one-electron redox couples. New type radical cations were isolated in quantitative yields in the one-electron oxidation of the trichalcogenoles with equimolar amounts of NOPF6. The structures of the radical cation salts were analyzed by 31P-NMR, ESR spectra, elemental analyses, and theoretical calculations. One-electron reduction of the radical cations on treatment with one equivalent of samarium(II) iodide gave the neutral trichalcogenoles quantitatively.