Triaryl-Heptazine Photocatalysts for the Oxidation of C–H and C–C Bonds in Nitrogen-Containing Molecules

Open-shell intermediates have become central to modern organic synthesis, placing photoredox catalysis -and therefore the development of photocatalysts-as a crucial area of research. We report the development of a photocatalytic platform based on triaryl-heptazines, which possess high level of tunability and high potency for oxidation reactions. A representative set of four photocatalysts from this family were synthesized and fully characterized (UV-Vis absorption and emission spectroscopy, cyclic voltammetry and time-correlated single photon counting) showing high excited-state reduction potentials and long excited-state lifetimes. DFT and time-dependent DFT studies were performed and account for the observed photochemical properties. One of these photocatalysts was then deployed for oxidative transformations of nitrogen-containing molecules, namely N-methyl oxidation to N-formyl compounds and C-C bond cleavage of cyclic N-protected amines. In both cases, this triaryl heptazine catalysts displays synthetically significant features, notably in terms of selectivity and substrate scope. Moreover, mechanistic investigations provided valuable insights into the behavior of this photocatalyst in the reaction.