In silico high throughput screening of Manganese-based complexes for binding of pyridine in catalytic homogeneous hydrogenation

Abstract

Addressing the resources needed to produce sustainable and environmentally friendly products is key within the field of catalysis. One of the key applications of catalysis is the storage of renewable hydrogen. This could be achieved through liquid organic hydrogen carriers (LOHCs), which participate in homogeneous catalysis. This field emphasizes high selectivity through the use of transition-metal complexes. A suitable LOHC candidate could be pyridine, a type of N-heterocycle, which serves as a benchmark for successful binding to the metal complex. The binding of pyridine can be enhanced by substituting noble metals with transition metals, such as manganese, which has shown promising catalytic activity. We perform high-throughput screening with DFT calculation for the following systems: PNP, PONOP, NNN, and NONON, which vary in their backbones. Every metal complex consists of three various configurations: the alignment of the auxiliary carbonyl ligand with the hydride atom (config 1), pyridine (config 2) and the lutidine part of the nitrogen pincer atom (config 3). The catalytic performance is studied by determining the stable and reactive complexes, as well as their specific configurations. Only positive binding energies, in terms of the ΔGreaction, are observed. This indicates that no complexes show strong binding of the metal to pyridine. However, the phenyl-substituted system exhibits the lowest binding energies, of which the third configuration is the most favored for all ligand types. This holds for the trans-positioning of the auxiliary carbonyl ligand with the lutidine part of the nitrogen pincer atom,mainly for the NNN-based complex. Still, the preferred configurations do not correlate with the strengthened metal-pyridine binding and weakening of the metal-auxiliary carbonyl ligand bond length. In terms of reactivity, the nitrogen-based complexes show the highest hydride charges, which could be assumed to provide high reactivity. However, the hydridic behavior of the complexes does not correspond with the stability of the phenyl substituents and all remaining complexes. After the reactivity of the complexes is considered, we can enable fine-tuning of specific backbones to forecast trends observed in reactivity. The phenyl-substituent can be used as a starting point due to its delocalized system and electron-donating property for fine-tuning. Nitrogen-based complexes enable fine-tuning of the reactivity because they depend on the ligand scaffold rather than the substituents. In addition, variation in binding energies for every substituent is most commonly observed for nitrogen-based complexes. The nitrogen-based complex can therefore be used to performimproved ligand design with the fine-tuning ability of the phenyl substituent.