Optimal functionalization of a molecular electrocatalyst for hydride transfer

Area of Science:

• Catalysis
• Sustainable Chemistry
• Electrochemistry

Background:

• Hydride transfer (HT) catalysts are key for efficient (photo)electroreduction reactions.
• Instability of the 2-pyridinide (2-PyH^-*) intermediate, due to protonation forming inactive dihydropyridine (DHP*), limits CO2 photoelectroreduction selectivity.
• Ring functionalization of pyridine (Py) is explored to tune the stability and activity of the 2-PyH^-* intermediate.

Purpose of the Study:

• To analyze how functionalizing the pyridine ring impacts the catalytic activity of the 2-PyH^-* intermediate.
• To investigate the relationship between electron density modulation and the stability/reactivity of the intermediate.
• To identify promising substituents for enhancing CO2 photoelectroreduction on p-GaP.

Main Methods:

• Computational analysis of pyridine ring functionalization effects on the 2-PyH^-* intermediate.
• Evaluation of how electron-withdrawing groups influence intermediate stability and hydride transfer (HT) barriers.
• Prediction of substituent performance based on electronic properties and HT barriers.

Main Results:

• Electron-withdrawing groups enhance 2-PyH^-* stability by reducing ring electron density, mitigating protonation side reactions.
• The change in electron count on the substituent group effectively describes both stability against protonation and HT barrier magnitude.
• -CH2-CH2F is predicted as the best substituent, significantly improving 2-PyH^-* stability with a minimal increase in the HT barrier.

Conclusions:

• Pyridine ring functionalization is a viable strategy to optimize hydride transfer catalysts for CO2 reduction.
• Careful selection of electron-withdrawing substituents can enhance intermediate stability without overly compromising catalytic activity.
• -CH2-CH2F, -CH=CH2, and -CH2F show promise, with -CH2-CH2F being the most favorable candidate for further investigation.