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

• Published in: Nature chemistry 2019-02, Vol.11 (2), p.154-160
• Main Authors: Falcone, Marta, Barluzzi, Luciano, Andrez, Julie, Fadaei Tirani, Farzaneh, Zivkovic, Ivica, Fabrizio, Alberto, Corminboeuf, Clemence, Severin, Kay, Mazzanti, Marinella
• Format: Article
• Language: English
• Subjects: 639/638/263/910; Analytical Chemistry; Biochemistry; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Computer applications; Coordination compounds; Inorganic Chemistry; Nitrides; Nitrogenase; Organic Chemistry; Physical Chemistry; Reducing agents; Reduction; Uranium
• ISSN: 1755-4330; 1755-4349
• DOI: 10.1038/s41557-018-0167-8

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 N 2 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–(N 2 ) complex differs significantly from that of the nitride–(N 2 ). Computational studies show a different bonding scheme for the dinitrogen where the bridging nitride does participate in the binding and consequent activation of N 2 , while the oxide does not. Nitrogen fixation—the direct conversion of dinitrogen into ammonia or other nitrogen-containing products—is notoriously difficult to promote under mild conditions. Now, the reactivity of a multimetallic diuranium( iii ) complex recently found capable of reducing and functionalizing N 2 has been explored, replacing its nitride bridge with an oxo bridge, which resulted in a markedly different reactivity.