Linear Scaling Relationships to Predict pKa's and Reduction Potentials for Bioinspired Hydrogenase Catalysis

Biomimetic catalysts inspired by the active site of the [FeFe] hydrogenase enzyme can convert protons into molecular hydrogen. Minimizing the overpotential of the electrocatalytic process remains a major challenge for practical application of the catalyst. The catalytic cycle of the hydrogen production follows an ECEC mechanism (E represents an electron transfer step, and C refers to a chemical step), in which the electron and proton transfer steps can be either sequential or coupled (PCET). In this study, we have calculated the pK(a)'s and the reduction potentials for a series of commonly used ligands (80 different complexes) using density functional theory. We establish that the required acid strength for protonation at the Fe-Fe site correlates with the standard reduction potential of the di-iron complexes with a linear energy relationship. These linear relationships allow for fast screening of ligands and tuning of the properties of the catalyst. Our study also suggests that bridgehead ligand properties, such as bulkiness and aromaticity, can be exploited to alter or even break the linear scaling relationships.

Automated summary

Inspired by the active site of [FeFe] hydrogenase enzyme, biomimetic catalysts have been developed to convert protons into molecular hydrogen. The study utilized density functional theory to calculate pK(a)s and reduction potentials of various ligands, revealing a linear relationship between acid strength required for protonation at the Fe-Fe site and the standard reduction potential of di-iron complexes. This linear relationship allows for efficient screening of ligands and adjustment of catalyst properties.