Catalytic and stoichiometric stepwise conversion of side-on bound dinitrogen to ammonia mediated by a uranium complex

Abstract The well-defined catalytic conversion of dinitrogen (N 2 ) to ammonia (NH 3 ) by molecular complexes is of fundamental interest and important for providing an atomic-level understanding of reactivity that can be related to industrial and biological nitrogen-fixation processes. Molecular catalytic N 2 to NH 3 conversion currently involves the reduction and protonation of terminal or bridging end-on bound metal–N 2 complexes. However, catalytic N 2 to NH 3 conversion by side-on bound metal–N 2 molecular complexes is relevant to both the industrial and biological nitrogen-fixation processes. Here, using a uranium triamidoamine complex, we report catalytic N 2 to NH 3 conversion involving side-on bound N 2 binding. Stoichiometric reactions reveal stepwise reduction of N 2 from free N 2 to bridging side-on bound forms and subsequently to bridging nitrides, uniquely accessing four different states of side-on bound N 2 for the same molecular system. This reveals the roles of N 2 , N 2 2− , N 2 3− , N 2 4− and N 3− in the catalytic conversion of N 2 to NH 3 when involving side-on bridging N 2 .