Title:

Steric influence at the 6,6’-positions in Mn-Bipy complexes and the resulting impact on electrochemical CO2 reduction

Abstract: Manganese bipyridine complexes have demonstrated CO2 reduction at comparable efficiencies and lower overpotentials than their rhenium counterparts. Modification of the ligand backbone impacts the redox behavior and selectivity of the catalysts. Previous investigations have shown that steric bulk near the metal center (at the 6,6’-positions) hinders off-cycle dimer formation, leading to higher turnover but also higher overpotentials. However, these complexes often use aromatic substituents, which electronically inhibit dimer formation and shift the selectivity of products formed. In order to decouple these factors, we synthesized complexes with aliphatic substituents at the 6- or 6,6’-positions. It was found that even slight steric hindrance at the 6,6’-positions leads to similar product selectivity to that observed with bulkier substituents, while dimer formation can be selectively observed under different electrochemical conditions. Experimental trends unique to these complexes can be correlated to their calculated characteristics, allowing for better ligand design principles.

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