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

Abstract

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 Tm and TD values above 150 and 270 °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 pyrazine-2,3-dicarbonitrile-derived catalyst.

Structure‐Catalytic Activity in a Series of Push‐Pull Dicyanopyrazine/Dicyanoimidazole Photoredox Catalysts

“…The synthetic approach towards DPZ derivatives 1–7 is outlined in Scheme , the synthesis of DCI molecules 8–9 has been published previously . The synthesis of DPZ derivatives utilizes Suzuki‐Miyaura or Sonogashira cross‐coupling reactions of 5,6‐dichloropyrazine‐2,3‐dicarbonitrile 10 with appropriately substituted boronic acid derivatives 11–15 or terminal acetylenes 16–17 .…”

“…As can be seen, the excited state oxidation potentials E ox * remained almost unaltered, whereas the E red * were found within the range of 1.39 to 2.07 V. Hence, all DPZ catalysts are capable to oxidize aromatic amines, e. g. N ‐phenyltetrahydroisoquinoline (THIQ) with the oxidation potential of 0.79 V (see below). The DCI catalysts 8 and 9 possess the calculated E ox/red * values of −1.78/1.35 and −1.48/1.75 V (no electrochemical data measurable) …”

DFT and TD-DFT study on quadratic NLO response and optoelectronic activity in novel Y-shaped imidazole-based push-pull chromophores

“…In particular, the relationship between structure and property indicates that the molecular hyperpolarizability depends on the π-system building blocks, such as (hetero)aromatic rings and double-bonded fragments [9]. For the construction of suitable p-bridge in charge transfer chromophores, imidazoles have proved to be highly efficient five-membered heteroaromatics [17][18][19].…”