LA-Enhanced Activation of Small Molecules by Mn-Complexes

Small, gaseous molecules represent the most important building blocks in many biological systems. Employing these building blocks, complex compounds such as amino acids, sugars DNA and proteins can be gained. However, these molecules represent (very) inert gases such as nitrogen but also carbon dioxide. In order to convert these molecules into a valuable form, the presence of a catalyst is required. In biological systems, such as bacteria and plants, this transformation is achieved via a fine-tuned interaction of (transition)metals and acids in an aqueous media under very mild conditions. Over the past decades, attempts have been made to study and mimic the reactivity of diverse biological systems. In the field of activating of carbon dioxide many of these investigations were based on the use of noble metals. Although good results have been achieved, questions about sustainability arise when using precious metals, as these metals are rather rare and their production consumes a lot of energy. In the field of nitrogen activation, researchers have focused on the element molybdenum for decades and, more recently, on iron. Even if a lot of progress has been made in the field of nitrogen activation in recent years, the potential in this area seems not to be fully reached. This project deals with the activation of gaseous dinitrogen and carbon dioxide in order to convert them into valuable platform chemicals such as ammonia, formic acid or methanol. This is to be achieved with the aid of the base element manganese in combination with boron-based acids. The efficient use of manganese-based catalysts for the production of formic acid and methanol has already been described over the last few years. In the course of this project, the reactivities for the production of methanol from carbon dioxide shall to be increased and a potential conversion carbon dioxide into methane will be investigated. In the field of dinitrogen activation by manganese-based catalysts, fundamental work is initially required, since there is barely preliminary work present. Subsequently, the conversion of dinitrogen to ammonia or other relevant nitrogen-based compounds shall be realized.

Small gaseous molecules represent the fundamental building blocks of every biological system. With the help of these building blocks, complex compounds such as amino acids, sugars, and subsequently DNA and proteins can be constructed. However, these are (very) unreactive gases such as nitrogen and carbon dioxide. To convert these molecules into a usable form, the presence of a catalyst is required. In biological systems, such as bacteria and plants, this occurs through a sophisticated interplay of (transition) metals and acids in an aqueous environment under very mild conditions. Over the past decades, efforts have been made to investigate and mimic the reactivity of various biological systems. Many of these studies, particularly in the activation of carbon dioxide, relied on the use of noble metals. Although high reactivities were achieved, the use of noble metals raises concerns regarding sustainability, as these metals are very rare and their extraction requires significant energy. In the field of nitrogen activation, researchers focused for decades on the element molybdenum and, more recently, also on iron. Even though significant progress has been made in nitrogen activation in recent years, the potential in this area is still far from being fully exploited. The aim of this project was the activation of gaseous nitrogen and carbon dioxide in order to convert them into valuable bulk chemicals such as ammonia, formic acid, or methanol. This was intended to be achieved using the base metal manganese in combination with boron-based acids. For this purpose, a specific ligand was to be synthesized. Due to synthetic complications, the direction of the project shifted toward a macrocyclic ligand, which was successfully prepared. Furthermore, the properties of this ligand were investigated using iron as the central atom, as iron is often more suitable for many analytical methods than manganese. A variety of novel and interesting iron compounds were thus synthesized, and their properties for the activation of (small) molecules were investigated. The results obtained enable novel perspectives for further studies on (iron) complexes supported by this type of macrocyclic ligands.