Unraveling the Effect of Aromatic Groups in Mn(I)NNN Pincer Complexes on Carbon Dioxide Activation Using Density Functional Study.

Vidya Avasare,Saurabh Vinod Parmar,Sourav Pal

doi:10.3389/fchem.2021.778718

Abstract

Carbon dioxide utilization is necessary to reduce carbon footprint and also to synthesize value-added chemicals. The transition metal pincer complexes are attractive catalysts for the hydrogenation of carbon dioxide to formic acid. There is a need to understand the factors affecting the catalytic performance of these pincer complexes through a structure–activity relationship study using computational methods. It is a well-established fact that aromatic functionalities offer stability and selectivity to transition metal catalysts. However, their impact on the performance of the catalysts is lesser known in the case of metal pincer complexes. Hence, it is necessary to investigate the catalytic performance of Mn(I)NNN pincer complexes with variably activated aromatic functionalities. In this context, 15 catalysts are designed by placing different types of aromatic rings at the pincer carbons and two terminal nitrogen of Mn(I)NNN pincer complexes. A benzene moiety, placed at C2–C3 carbons of Mn(I)NNN pincer complex with identical aromatic groups at the terminal nitrogen, is found to be most efficient toward CO2 hydrogenation than the rest of the catalysts. On the other hand, when N,N-dimethyl aniline is placed at C2–C3 carbons of Mn(I)NNN pincer complexes, then the catalytic performance is significantly decreased. Thus, the present study unravels the impact of aromatic groups in Mn(I)NNN pincer complexes toward the catalytic hydrogenation of carbon dioxide.

Highlights

The burning of fossil fuels continuously increases CO2 concentration in the atmosphere, leading to a substantial and negative impact on the world climate
About 33,890.8 million tons of CO2 was released into the atmosphere in 2018, and the global CO2 concentration in the atmosphere reached 407.65 (BP Statistical Review of World Energy, 2019; Global Monitoring Division, 2019) Nearly ∼35 GT of CO2 is being added to the atmosphere per year, and there is a considerable gap between the amount of CO2 produced and utilized
The two strong electrons withdrawing the pyrimidine groups are attached to the Mn(I)NNN pincer ring nitrogen in catalysts 1e, 2e, and 3e (Figure 2). All these 15 Mn(I)NNN pincer complexes are further used to explore their catalytic performance toward carbon dioxide hydrogenation (Figure 3)

Summary

INTRODUCTION

The burning of fossil fuels continuously increases CO2 concentration in the atmosphere, leading to a substantial and negative impact on the world climate. The flexibility in the modification could be useful to fine-tune structural and electronic properties of the metal pincer complexes to make them more reactive as well as more selective (Peris and Crabtree, 2018) In this context, Mn pincer complexes in catalytic carbon dioxide hydrogenation have seen much progress over a much shorter time (Bertini et al, 2017; Garbe et al, 2017; Kar et al, 2017). 15 Mn(I)NNN pincer complexes are designed to understand steric and electronic factor ligands on the catalytic efficacy toward carbon dioxide hydrogenation (Figure 2). The two strong electrons withdrawing the pyrimidine groups are attached to the Mn(I)NNN pincer ring nitrogen in catalysts 1e, 2e, and 3e (Figure 2) All these 15 Mn(I)NNN pincer complexes are further used to explore their catalytic performance toward carbon dioxide hydrogenation (Figure 3)

AND DISCUSSION

CONCLUSION

Findings

DATA AVAILABILITY STATEMENT