Synthesis and properties of push-pull imidazole derivatives with application as photoredox catalysts

Two new push-pull molecules with imidazole-4,5-dicarbonitrile acceptor, thiophene and 2-methoxythiophene donors with potential use in photoredox catalysis were designed and prepared. The synthesis started from commercially available imidazole-4,5-dicarbonitrile and its bromination and N-methylation. Subsequent Suzuki-Miyaura cross-coupling with (5-methoxy)thiophene-derived boronic acids afforded target push-pull derivatives. Beside common analytical methods, the molecular structure of 5-methoxythiophen-2-yl derivative has also been verified by X-ray analysis. DSC analyses showed remarkable thermal stabilities of both target derivatives with T-m and T-D values above 150 and 270 degrees C, respectively. Fundamental properties and extent of the intramolecular charge-transfer were further studied by UV-VIS absorption spectra and DFT calculations. Fundamental photoredox properties of target imidazole derivatives were elucidated. Both push-pull molecules were preliminary tested as photoredox catalysts in cross-dehydrogenative coupling reaction between tetrahydroisoquinoline and nitromethane and the results were compared with those obtained by pyrazine2,3-dicarbonitrile-derived catalyst. [GRAPHICS]