Sensitized Photocatalytic CO2 Reduction With Earth Abundant 3d Metal Complexes Possessing Dipicolyl-Triazacyclononane Derivatives.

Martin Obermeier,Oliver S Wenger,Matthias Schwalbe,Fabian Beckmann,Raoul S Schaer

doi:10.3389/fchem.2021.751716

Martin Obermeier, Oliver S Wenger + Show 3 more

Open Access

https://doi.org/10.3389/fchem.2021.751716

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Abstract

Complexes based on nitrogen and sulfur containing ligands involving 3d metal centers are known for the electrocatalytic reduction of CO2. However, photocatalytical activation has rarely been investigated. We herein present results on the light-driven CO2 reduction using either Ir(dFppy)3 [Ir, dFppy = 2-(4,6-difluorophenyl)pyridine] or [Cu(xant)(bcp)]+, (Cu, xant = xantphos, bcp = bathocuproine) as photosensitizer in combination with TEA (triethylamine) as sacrificial electron donor. The 3d metal catalysts have either dptacn (dipicolyl-triazacyclononane, L N3 ) or dpdatcn (dipicolyl-diazathiocyclononane, L N2S ) as ligand framework and Fe3+, Co3+ or Ni2+ as central metal ion. It turned out that the choice of ligand, metal center and solvent composition influences the selectivity for product formation, which means that the gaseous reduction products can be solely CO or H2 or a mixture of both. The ratio between these two products can be controlled by the right choice of reaction conditions. With using Cu as photosensitizer, we could introduce an intermolecular system that is based solely on 3d metal compounds being able to reduce CO2.

Highlights

Due to the fact that the global energy demand is projected to increase, there will still be a high necessity of usage of fossil fuels over the couple of decades, as the development of renewable energy sources cannot adjust with the same speed (Sönnchen, 2020)
The complexes were prepared by first synthesizing the corresponding ligands 1,4-di(picolyl)-1,4,7-triazacyclononane LN3 and 1-thia-4,7-di(picolyl)-diazacyclononane LN2S
LN2S was prepared in a similar fashion: First N,N’-bistosyl-bis(2-aminoethyl)sulfide was synthesized via sodium ethoxide driven SN2 reaction of cysteamine hydrochloride and 2-chloroethylamine hydrochloride (Wilson, 2007), followed by tosylation as described earlier for LN3 (Friscourt et al, 2012)

Summary

INTRODUCTION

Due to the fact that the global energy demand is projected to increase, there will still be a high necessity of usage of fossil fuels over the couple of decades, as the development of renewable energy sources cannot adjust with the same speed (Sönnchen, 2020). Significant progress has been made for the CO2 to CO reduction with catalytic systems based on heavier transition metals such as rhenium or ruthenium (Tamaki et al, 2013; Tamaki et al, 2015; Gotico et al, 2018) These metals are expensive and rare, which leads to the need of finding complexes based on earthabundant metals to perform the activation and conversion of CO2 (Takeda et al, 2017; Dalle et al, 2019). We started out to synthesize a series of complexes with earth abundant transition metals (Fe, Co and Ni) and either a macrocyclic sulfur free or sulfur containing ligand (Scheme 1) We present their photocatalytic activity in the presence of different photosensitizers, Ir ([Ir(dFppy)3], dFppy 2-(4,6difluorophenyl)pyridine) and Cu ([Cu(xant)(bcp)]PF6, xant xantphos, bcp bathocuproine)

DISCUSSION AND RESULTS

CONCLUSION

DATA AVAILABILITY STATEMENT