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

氮气是大气中含量最丰富的气体。它在工业上被大规模转化，用于各种含氮材料，特别是确保有足够的全球粮食产量来支持不断增长的人口的化肥。目前的工业方法是Haber Bosch工艺，在高压气体压力(150至350大气压)、高温(350至550摄氏度)下运行，需要氢气(目前从碳氢化合物来源生产)才能将氮气转化为有用的前体化合物氨。这使得这一过程的能源(因此成本)非常密集，消耗了世界能源供应的约2%和世界天然气供应的约3-5%。与自然形成鲜明对比的是，合成化学家出类拔萃地在极端温和的条件下(大气压和温和的温度)进行同样的转化。模仿大自然的成就将是一次戏剧性的突破，不仅是作为一项独立的科学成就，而且还可能彻底改变从大气氮中提取氨的工业生产。因此，人们花了相当大的努力来阐明含金属固氮酶(氮转化)酶是如何实现这一转化的。最近的发现已经开始澄清复杂固氮酶催化剂的某些方面，特别是这种酶的休眠状态(当它不活跃地将氮转化为氨时的结构)的一致性。这些最近的实验发现结合计算研究为合成化学家提供了洞察力和灵感，揭示了固氮酶包含一些非常不寻常的特征。它们还突显了人类目前的系统距离自然进化的解决方案有多远，或许解释了我们目前对催化剂的依赖，这些催化剂需要非常苛刻的条件。这项建议中的研究涉及合成新的功能模型系统，这些系统具有最近在固氮酶中发现的重要(和不寻常的)特征。准确的模型络合物的生成是阐明酶机制的关键一步；我们简化的模型系统将使系统研究在非常复杂的酶结构中很难直接研究的关键参数。必须了解这些参数，因为它们是氮的快速转化的关键。这类性质的研究对固氮酶尤其重要，因为它的工作机制在实验上定义得很差，只有不活跃的休息状态才有物理特征。因此，这项工作将使人们从根本上理解在温和条件下实现大气氮的固定和功能化所需的关键因素。如果我们了解氮是如何通过金属酶转化为氨的，那么我们就朝着能够实现跟随自然脚步的目标迈进了一大步；最终能够从空气中提取氮，并在温和的条件下将其转化为日常生活所必需的产品。

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.