Organometallic Approaches to Nitrogen Fixation

化学中的重大挑战之一是发现了一种温和的过程，将分子氮(N2)转化为更高价值的有机氮物种，如胺。氨(NH3)在世界范围内是由哈伯-博世工艺生产的，该工艺已有100多年的历史，仍然是唯一一种工业规模使用氮气作为原料的工艺。相比之下，等电子分子一氧化碳(CO)被用于各种不同的工业过程，如氢甲酰化、醋酸合成和羰基化。即使在100年后，我们仍然没有成功地开发出分子氮的新工业工艺，这一事实令人尴尬，但同时也提醒人们，在工业环境中使用这种非活性小分子的困难程度。在生物方面，自然界使用固氮酶从大气中的氮气中产生氨，这一过程被称为固氮；关于这种酶的活性部位Fe-Moco因子的信息是已知的，但关于这一过程如何在活性部位发生的细节尚不清楚。然而，在固氮化学方面有一些令人兴奋的最新发展，使这个梦想继续存在。已经开发了许多均相模型系统，它们使用化学计量的质子和还原剂从氮气中生产氨；这些与工业无关，但确实说明了解决这个问题的巧妙方法，并说明了配体设计在充当催化剂的金属络合物组成中的重要性。从生物方面来说，最近对Fe-MoCo酶活性部位的桥联碳化物的测定尤其优雅。最近，有人提出，固氮酶伴随氨形成的氢气产生与氮气结合步骤有关，并与铁氢化物有关。这项建议将探索新的研究途径，利用在有机金属化学领域取得的巨大进展，并将其应用于氮素活化领域。预计新的基础知识将增加，这将扩大我们目前对无处不在的氮气分子如何为子孙后代利用的理解。预计这项研究将为新科学家提供与绿色化学和可持续发展相关的培训。

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.