Using boryl-substitution and improved Suzuki–Miyaura cross-coupling to access new phosphorescent tellurophenes

Abstract

A new di(isopropoxy)boryl –B(OⁱPr)₂ tellurophene precursor is described, from which several previously inaccessible phosphorescent borylated tellurophenes are formed via exchange of the –OⁱPr groups. One such tellurophene Mes(ⁱPrO)B-Te-6-B(OⁱPr)Mes, bearing a sterically encumbered mesityl (Mes) substituent at each boron center, exhibits bright yellow-orange phosphorescence in the solid state at room temperature and in the presence of the known quencher O₂. Furthermore, Suzuki–Miyaura cross-coupling between the newly prepared borylated tellurophenes and the test substrate 2-bromothiophene was examined with the pre-catalyst Cl(XPhos)Pd(aminobiphenyl). While more electron deficient boryl groups such as catecholatoboryl (–Bcat) yield significant protodeboronation in place of productive C–C bond formation, efficient formation of the desired thiophene-capped tellurophene thienyl-Te-6-thienyl was noted from tellurophenes bearing the readily accessible pinacolatoboryl (–Bpin) and 1,8-naphthalenediaminatoboryl (–Bdan) functional groups. These findings open the door for the efficient synthesis of aryl tellurophenes and polytellurophenes via the ubiquitous Suzuki–Miyaura coupling of borylated tellurophenes, which was previously hampered by protodeboronation.