Organometallic Approaches to Nitrogen Fixation

化学领域的一个重大挑战是发现一种温和的过程，将分子氮（N2）转化为含有更高价值的有机氮物质，如胺。氨（NH3）在世界范围内由Haber-Bosch工艺生产，该工艺已有100多年的历史，并且仍然是唯一在工业规模上使用N2作为原料的工艺。相比之下，等电子分子一氧化碳（CO）用于各种不同的工业过程，如氢甲酰化，乙酸合成和羰基化。事实上，即使在100年后，我们还没有成功地开发出一种新的分子氮工业工艺，这是令人尴尬的，但与此同时，这也提醒了我们在工业环境中使用这种不活跃的小分子的困难程度。在生物方面，自然界利用固氮酶从大气中的N2产生氨，这一过程被称为固氮；这种酶的活性位点Fe-Moco因子的信息是已知的，但这个过程如何在活性位点发生的细节是未知的。然而，最近在固氮化学方面取得了一些令人兴奋的进展，使这个梦想得以实现。已经开发了许多均相模型系统，使用化学计量量的质子和还原剂从N2产生氨；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构成作为催化剂的金属络合物中的重要性。从生物学的角度来看，最近对Fe-Moco酶活性位点的桥接碳化物的测定特别优雅。最近，有人提出，伴随着氮酶形成氨的产氢与N2结合步骤有关，并涉及铁氢化物。本提案将探索新的研究途径，利用有机金属化学领域取得的巨大进展，并将其应用于二氮活化领域。预计新的基础知识将积累，这将扩大我们目前对如何利用无处不在的N2分子的理解，为子孙后代服务。预计这项研究还将为与绿色化学和可持续性有关的新科学家提供培训。

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.