Organometallic Approaches to Nitrogen Fixation

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One of the grand challenges in chemistry is the discovery of a mild process for conversion of molecular nitrogen (N2) into higher value organo-nitrogen containing species, such as amines. Ammonia (NH3) is produced worldwide by the Haber-Bosch process, which is over 100 years old, and is still the only process that uses N2 as a feedstock on an industrial scale. In contrast, the isoelectronic molecule carbon monoxide (CO) is used in a variety of different industrial processes, such as hydroformylation, the acetic acid synthesis, and carbonylation. The fact that even after 100 years we have not been successful at developing a new industrial process for molecular nitrogen is embarrassing, but at the same time, a reminder of the level of difficulty of the problem of using this unreactive small molecule in an industrial setting. On the biological side, nature produces ammonia from atmospheric N2 using the enzyme Nitrogenase in a process referred to as nitrogen fixation; information about the active site of this enzyme, the Fe-Moco factor, is known but the details on how this process occurs at the active site are unknown. However, there have been some exciting recent developments in nitrogen fixation chemistry that keep this dream alive. A number of homogeneous model systems have been developed that produce ammonia from N2 using stoichiometric amounts of protons and reductants; these are not industrially relevant but do illustrate ingenious ways to approach this problem and speak to the importance of ligand design in the makeup of the metal complex that acts as the catalyst. From the biological side, the recent determination of the bridging carbide at the active site of the Fe-Moco enzyme is particularly elegant. More recently, it has been proposed that the hydrogen production that accompanies ammonia formation by nitrogenase is relevant to the N2 binding step and implicates Fe hydrides. This proposal will explore new avenues of research that take advantage of great advances made in the realm of organometallic chemistry and apply them to the area of dinitrogen activation. It is anticipated that new fundamental knowledge will accrue that will expand our present understanding of how the ubiquitous N2 molecule can be harnessed for future generations. It is also expected that this research will provide training to new scientists that will be relevant to green chemistry and sustainability.