Geometrical Constraints Weaken a Nickel–Hydrogen Bond and Enable the Homolytic H2 Evolution Mechanism
4 affiliations
- 1Department of Chemistry
- 2University of North Carolina at Chapel Hill
- 3Yale University
- 4Brookhaven National Laboratory
Abstract
Mechanistic studies of the hydrogen evolution reaction (HER) are helping advance catalysis towards energy storage technologies based on water splitting. Homolytic H–H bondforming pathways are one of the fundamental mechanisms of HER, yet well-defined examples of bimetallic coupling in molecular HER catalysts remain extremely rare. A planar tetradentate bipyridine diphosphinite ligand (PONNOP) is reported that constrains the geometry of nickel complexes, weakening the Ni–H bond dissociation free energy and enabling H2 evolution via the homolytic pathway. Crystallography, magnetism, absorption spectroscopy, and computational studies provide insight into the electronic structure enforced by the rigid tetradentate PONNOP ligand, which results in a very weak Ni–H bond in a transiently formed metal hydride. Cyclic voltammetry and chronoamperometry studies are consistent with electrocatalytic HER via the homolytic mechanism. The ability of a tetradentate ligand to induce M–H bond-weakening is discussed as a possible design element in HER by Earth-abundant catalysts.
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BibTeX
@misc{richter2026geometrical,
title = {{Geometrical Constraints Weaken a Nickel–Hydrogen Bond and Enable the Homolytic H2 Evolution Mechanism}},
author = {Grant A. Richter and Quinton J. Bruch and Bethany M. Stratakes and Abhishek Das and Jeremy E. Weber and Carrie L. Donley and Patrick L. Holland and Mehmed Z. Ertem and Alexander J. M. Miller},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010612/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010612/v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - Geometrical Constraints Weaken a Nickel–Hydrogen Bond and Enable the Homolytic H2 Evolution Mechanism
AU - Grant A. Richter
AU - Quinton J. Bruch
AU - Bethany M. Stratakes
AU - Abhishek Das
AU - Jeremy E. Weber
AU - Carrie L. Donley
AU - Patrick L. Holland
AU - Mehmed Z. Ertem
AU - Alexander J. M. Miller
PY - 2026
DA - 2026/10/16
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010612/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010612/v1
AB - Mechanistic studies of the hydrogen evolution reaction (HER) are helping advance catalysis towards energy storage technologies based on water splitting. Homolytic H–H bondforming pathways are one of the fundamental mechanisms of HER, yet well-defined examples of bimetallic coupling in molecular HER catalysts remain extremely rare. A planar tetradentate bipyridine diphosphinite ligand (PONNOP) is reported that constrains the geometry of nickel complexes, weakening the Ni–H bond dissociation free energy and enabling H2 evolution via the homolytic pathway. Crystallography, magnetism, absorption spectroscopy, and computational studies provide insight into the electronic structure enforced by the rigid tetradentate PONNOP ligand, which results in a very weak Ni–H bond in a transiently formed metal hydride. Cyclic voltammetry and chronoamperometry studies are consistent with electrocatalytic HER via the homolytic mechanism. The ability of a tetradentate ligand to induce M–H bond-weakening is discussed as a possible design element in HER by Earth-abundant catalysts.
ER -