Catalytic activation of nitrous oxide: boryl versus hydride nickel complexes

Abstract

The selective reduction of nitrous oxide (N₂O), a potent greenhouse gas with harmful effects on the ozone layer, remains a significant challenge in small-molecule activation. Herein, we report the efficient deoxygenation of N₂O using bis(phosphino)boryl-nickel hydride (3) and bis-boryl nickel complexes (4 and 5) under mild conditions (1–2 bar N₂O, 2–5 mol% catalyst loading, and 25 °C). Both catalytic systems exhibit high activity in the presence of boranes and diboranes, achieving complete N₂O conversion within 30 minutes using catecholborane as the reductant. Mechanistic investigations, including stoichiometric experiments, kinetic studies, and density functional theory (DFT) calculations support the formation of nickel boroxide intermediates, (^RPBP)Ni–OBR₂, as key species within the catalytic cycle, while pathways involving nickel hydroxide species, (^RPBP)Ni–OH, are disfavored. These results provide valuable mechanistic insights into key aspects of N₂O reduction chemistry thereby enabling the rational design of transition-metal catalysts for the activation of small-molecules.