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

今天，双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，也是为不断增长的世界人口提供食物的最重要的反应之一。在工业上，铁催化的哈伯-博施工艺每年用于从二氮和二氢生产约1.5亿吨氨。然而，这个过程需要大量的能量。因此，开发用于在环境条件下转化二氮的均相催化剂是当今研究的重要目标。然而，它也是小分子活化中最具挑战性的问题之一，50多年来吸引了许多科学家。然而，这一研究领域仍然是相当差的探索和只有两个均相系统是已知的，到目前为止，这是能够还原二氮氨在催化条件下。本研究计划的主要目标是合成新型大环pacman型配体的双金属配合物。然后，这些配合物被检查对它们的应用作为催化剂用于还原二氮。首先，将合成杯吡咯配体，随后在THF中与各种过渡金属前体[MoCl 3（THF）3]转化。钼和铁应是优先金属，因为对固氮酶的强烈关注。杯吡咯是一类很有前途的大环配体，它结合了席夫碱缩合过程的特殊设计特征和合成通用性，可以帮助配体合成并在所得的双金属配合物中产生结构控制。根据空间和电子需求，有许多可能性来改变两个亚胺之间的芳烃的大小和吡咯之间的R基团的性质。此外，不同的金属可以被引入杯吡咯配体的口袋中。由此产生的双分子裂缝促进了广泛的化学计量和催化小分子化学。在充分表征之后，在二氮气氛下用钠汞齐转化络合物。通过缓慢加入二茂钴将二氮还原为氨，研究了二氮活化中的催化潜力。三氟甲磺酸钌作为氧化还原等价物。将结果与以前的文献报道进行比较，并在电子和空间性质方面对催化剂进行改性以提高催化效率。

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.