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

By means of DFT and multiconfigurational <i>ab initio</i> 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.