Activation and Functionalization of Dinitrogen in the Presence of Molecular Hydrogen Promoted by Transition Metal Complexes

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The quest for functionalization of dinitrogen has been a challenging task for decades, owing to its high redox potential. The transition metal dinitrogen complex made by Allen and Senoff provoked the researchers to functionalize dinitrogen and produce ammonia either stoichiometrically or catalytically using mild reaction conditions. Predominantly there are two methodologies available for the functionalization of dinitrogen. In the first methodology, proton and electron sources are used for the functionalization of dinitrogen, which is similar to biological nitrogen fixation. In the second methodology, molecular hydrogen is used for the functionalization of dinitrogen, which is similar to the Haber–Bosch process. Nonetheless, the Haber–Bosch process is the only successful industrial methodology for the production of ammonia. However, this methodology is highly energy consuming. Hence, there is a necessity for a practically viable homogeneous catalyst that could replace the heterogeneous Haber–Bosch process and thus conserve energy. However, there are very few reports on the utilization of molecular hydrogen for the functionalization of dinitrogen owing to the difficulty in handling dinitrogen and molecular hydrogen in a single, reactor because the relatively more acidic molecular hydrogen could replace the dinitrogen. Nonetheless, only the proton part of H2 has been used and yet it is hoped to utilize the hydride part of H2 in the near future. This review article describes the various endeavors made by the researchers to utilize molecular hydrogen for the functionalization of dinitrogen.