Electronic Effects Drive Selectivity in CO₂ Reduction Catalysis by Heptacoordinated Cobalt Complexes.

Area of Science:

• Catalysis
• Electrochemistry
• Computational Chemistry

Background:

• Controlling selectivity in CO2 reduction catalysis is crucial for efficient conversion.
• Cobalt and iron complexes with a specific ligand (L, DBPy-PyA) were previously shown to catalyze H2 and CO production.

Purpose of the Study:

• To demonstrate that ligand electronic properties, in addition to metal center, can control selectivity in CO2 reduction.
• To investigate the mechanistic pathways governing selectivity using computational and experimental methods.

Main Methods:

• Electrochemical and photochemical catalysis using cobalt complexes with varying ligand electronic properties (unsubstituted, electron-rich, electron-deficient).
• Density Functional Theory (DFT) calculations to study reaction energetics.
• Microkinetic modeling to analyze reaction pathways.

Main Results:

• Electron-deficient cobalt complexes (CoL^CF3) selectively produced CO (up to 87% selectivity).
• Unsubstituted (CoL) and electron-rich (CoL^OMe) cobalt complexes predominantly produced H2 (82% and 55% selectivity, respectively).
• DFT and microkinetic modeling revealed that ligand electronics influence metal-hydride formation and facilitate ligand-assisted proton transfer.

Conclusions:

• Ligand tuning is a powerful strategy for controlling selectivity in molecular CO2 reduction.
• Adjusting ligand electronic properties allows for tunable syngas (CO/H2) ratios under both electrochemical and photochemical conditions.