Thermal and Photoreductive Elimination from the Tellurium Center of π‑Conjugated Tellurophenes

This
study introduces small molecule tellurophenes that can undergo photoreductive
elimination. A tellurophene compound with strong light absorption
properties and extended π-conjugation, 2,5-bis­[5-(N,N′-dihexylisoindigo)]­tellurophene
(1), has been synthesized. Halogen oxidative addition
to the tellurium center from various halogen sources gives the dibromo-
(1Br2) and dichloro- (1Cl2) adducts, leading to a red-shift in the
optical absorption properties. In the presence of excess opposing
halogen, 1Br2 and 1Cl2 can interconvert, with equilibrium favoring
the dichlorotellurophene adduct. Reductive elimination reactions were
studied using optical absorption spectroscopy, NMR spectroscopy, thermogravimetric
analysis, and matrix-assisted laser desorption/ionization (MALDI)
analysis. Thermal reductive elimination from 1Br2 and 1Cl2 occurs in the solid-state to restore 1. Photoreductive
elimination occurs under irradiation with green (505 nm) light in
solution in the presence of a halogen trap with some decomposition.
This is the first example of photoreductive elimination from a mononuclear
tellurophene complex.