The role of bridging ligands in dinitrogen reduction and functionalization by uranium multimetallic complexes

Cooperativity between metal centres is identified as a crucial step in dinitrogen reduction both for the industrial Haber–Bosch process and for the natural fixation of nitrogen by nitrogenase enzymes, but the mechanism of N2 reduction remains poorly understood. This is in large part because multimetallic complexes that reduce and functionalize dinitrogen in the absence of strong alkali reducing agents are crucial to establish a structure–activity relationship, but remain extremely rare. Recently, we reported a multimetallic nitride-bridged diuranium(iii) complex capable of reducing and functionalizing dinitrogen. Here we show that an analogous complex assembled with an oxo instead of a nitride linker also effects the four-electron reduction of dinitrogen, but the reactivity of the resulting oxo–(N2) complex differs significantly from that of the nitride–(N2). Computational studies show a different bonding scheme for the dinitrogen where the bridging nitride does participate in the binding and consequent activation of N2, while the oxide does not