Synthesis and characterization of new pacman-type transition metal complexes and their application as nitrogenase mimics in the catalytic dinitrogen activation

今天，二氮的活化是工业相关合成的最重要的反应之一，从社会的角度来看，为不断增长的世界人口提供食物。在工业上，铁催化的哈伯-博世工艺每年用于从二氮和二氢中生产约1.5亿吨氨。然而，这个过程需要大量的能量。因此，开发在环境条件下转化氮的均相催化剂是当今研究的一个重要目标。然而，它也是小分子活化中最具挑战性的问题之一，这一问题已经吸引了许多科学家50多年。然而，这一研究领域的探索仍然相当少，迄今为止只知道两种均相体系，它们能够在催化条件下将二氮还原为氨。本研究计划的主要目的是合成具有大环pacman型配体的新型双金属配合物。然后，对这些配合物作为还原二氮催化剂的应用进行了研究。首先合成杯吡咯配体，然后在thf中加入多种过渡金属前体[MoCl3(thf)3]进行转化。钼和铁应该是优先考虑的金属，因为它们对氮酶有很强的吸引力。杯吡咯是一类很有前途的大环配体，它结合了配位性质、独特的设计特征和希夫碱缩合过程的合成通用性，有助于配体的合成和产生结构控制。根据空间和电子的要求，有许多可能改变两个亚胺之间芳烃的大小和吡咯之间R基团的性质。此外，不同的金属可以被引入到杯吡咯配体的口袋中。由此产生的双金属分子裂缝有利于广泛的化学计量学和催化小分子化学。在充分表征后，配合物在二氮气氛下用钠汞合金转化。通过缓慢加入钴二酚将二氮还原为氨，研究了二氮活化的催化电位。三氟化镥作为氧化还原等价物。研究结果将与以往的文献报道进行比较，并对催化剂的电子和空间性能进行修饰，以提高催化效率。

Today, the activation of dinitrogen is one of the most important reactions both for industry relevant syntheses and, in a societal point of view, to warrant food for a growing world population. In industry, the iron-catalyzed Haber-Bosch process is used to produce about 150 million tons of ammonia per year from dinitrogen and dihydrogen. However, this process requires a high amount of energy. The development of homogenous catalysts for converting dinitrogen at ambient conditions is therefore an important target of research today. However, it is also one of the most challenging problems in small molecule activation, which has fascinated many scientists for more than 50 years. Nevertheless, this research field is still rather poorly explored and only two homogeneous systems are known up to date, which are able to reduce dinitrogen to ammonia under catalytic conditions. The primary object of the research plan is the synthesis of novel bimetallic complexes with macrocyclic pacman-type ligands. Afterwards, these complexes are examined towards their application as catalysts for the reduction of dinitrogen. First of all, the calixpyrrole ligands are going to be synthesized and subsequently converted with a variety of transition metal precursors, [MoCl3(thf)3] in thf. Molybdenum and iron should be the priority metals, because of the strong focus to nitrogenase enzymes. Calixpyrroles are a promising class of macrocyclic ligand which combines the coordinative properties with the exceptional design characteristics and synthetic versatility of Schiff-base condensation procedures that can assist in ligand synthesis and engender structural control in the resultant bimetallic complexes. Depending on the steric and electronic demands, there are many possibilities to vary both the size of the arene between the two imins and the nature of the R groups between the pyrrols. Additionally, different metals can be introduced into the pockets of the calixpyrrole ligand. The resultant bimetallic molecular cleft facilitates extensive stoichiometric and catalytic small-molecule chemistry. After a full characterization, the complexes are converted with sodium-amalgam under an atmosphere of dinitrogen. The catalytic potential in the activation of dinitrogen is investigated by slow addition of cobaltocene to reduce the dinitrogen to ammonia. Luthidinium triflate acts as a redox equivalent. The results will be compared to previous literature reports and the catalysts will be modified in terms of electronic and steric properties to improve the catalytic efficiency.