Excited-state antiaromaticity relief in photoactive amine–boranes promotes transfer hydrogenation to electron-poor olefins†

By means of DFT and multiconfigurational ab initio simulations, this work showcases the potential ability of photoactive amine–boranes to undergo transfer hydrogenation for the reduction of unsaturated compounds. Following absorption of UV-A light, the model amine–borane populates a low-lying triplet state. Then, the reduction of carbon–carbon double bonds proceeds through low activation barriers, one order of magnitude lower than those in the electronic ground state. The crucial role of excited-state antiaromaticity relief in facilitating this process is demonstrated by the noticeably higher barriers shown by non-triplet-antiaromatic amine–boranes for the same transformation. Overall, this work provides new design rules for developing more efficient amine–boranes for light-mediated reduction reactions.