The Role of Electronic Structure in the Hydrogen Evolution Reaction Dynamics as Catalyzed by Ru-based Complexes

Abstract

The catalytic activity for the hydrogen evolution reaction of three structurally related ruthenium catalysts is compared: a di-nuclear [Ru 2 (OTf)(m-H)(Me 2 dad)(dbcot) 2 ] (C1) and two mononuclear analogues (C2, C3). The reaction mechanism is analyzed at a molecular level by using ab-initio DFT calculation to determine singular-points on the potential energy surface (PES). Then, time dependent behavior is investigated by calculationing molecular dynamic (MD) trajectories, within the Dynamic Reaction Coordinate (DRC) paradigm. Displacement of molecular hydrogen results the ratedetermining step. C2 shows a promising low activation barrier: 8.6 kcal/mol, although H 2 release is kinetically slower. C3 yields molecular hydrogen but fails its release, even when provided with kinetic energy larger than the activation barrier (24.4 kcal/mol), revealing unforeseen mechanistic traps, beyond purely energetic considerations. This work underscores how ligand coordination flexibility critically affects the efficiency of hydrogen catalysis, paving the way for the rational design of novel catalysts.