Low Coordinate Fe(I) Species as Functional Mimics of Nitrogenase Enzymes.

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Nitrogen is the most abundant gas in the atmosphere. It is industrially converted on an immense scale for use in a variety of nitrogen containing materials, particularly in fertilizers that ensure there is sufficient global food production to support the ever growing population. The current industrial method, the Haber Bosch process, operates under intense gas pressure (150 to 350 atmospheres), at raised temperatures (350 to 550 C), and requires hydrogen (currently produced from hydrocarbon sources) to transform nitrogen into the useful precursor compound ammonia. This renders the process incredibly energy (and therefore cost) intensive, consuming ~2 % of the world's energy supply and ~3-5 % of the world's natural gas supply. In stark contrast nature, the synthetic chemist par excellence, performs the same conversion under drastically milder conditions (1 atmosphere pressure and mild temperatures). Mimicking nature's achievement would be a dramatic breakthrough, not only as a stand alone scientific achievement but also in potentially revolutionising the industrial production of ammonia from atmospheric nitrogen. As such a considerable effort has been expended into elucidating how the metal containing nitrogenase (nitrogen transforming) enzymes achieve this conversion. Recent findings have begun to clarify some aspects of the complex nitrogenase catalyst, particularly the identity of the resting state of this enzyme (the structure when it is not actively converting nitrogen to ammonia). These recent experimental findings combined with computational studies provide insight and inspiration for the synthetic chemist revealing the nitrogenase contains a number of highly unusual features. They also highlight how far from nature's evolved solution humankind's current systems are, perhaps explaining our current dependence on catalysts requiring very severe conditions. The research in this proposal involves the synthesis of new functional model systems that possess the vital (and unusual) features recently identified in the nitrogenase enzymes. The generation of accurate model complexes is a crucial step in elucidating enzyme mechanisms; our simplified model systems will enable the systematic study of crucial parameters that are very difficult to study directly in the very complex enzyme structure. It is imperative to understand these parameters as they are key to the facile transformation of nitrogen. Studies of this nature are particularly important for the nitrogenase enzyme as its operating mechanism is experimentally poorly defined, with only the inactive resting state physically characterised. This body of work therefore will afford a fundamental comprehension of the crucial factors required to achieve the fixation and functionalisation of atmospheric nitrogen under mild conditions. If we understand how nitrogen is converted to ammonia by metallo-enzymes then we have taken a giant leap towards being able to achieve our goal of following in nature's footsteps; and ultimately being able to take nitrogen out of the air and readily transform it, under mild conditions, into products essential to every day life.