Formic Acid Dehydrogenation by Ruthenium Catalyst – Computational and Kinetic Analysis with the Energy Span Model

The ruthenium (cis-RuCl₂(DPPM)₂) based catalytic dehydrogenation reaction of formic acid in the presence of an amine base in a biphasic system experimentally tested by Treigerman and Sasson (ChemistrySelect 2017, 2, 5816) was studied computationally to ascertain its mechanism. The energy span model was applied on the double-hybrid DFT computed energy profile to comprehend its kinetics. The catalytic network includes three possible interconnected cycles depending on the ancillary ligands, going through decarboxylation, protonation and H₂ release. The dihydride cycle proves to be the most efficient after pre-activation steps coming from the other cycles. The turnover frequency (TOF) determining intermediate (TDI) is the formatohydride species, while the TOF determining transition state (TDTS) corresponds to a formate decarboxylation. Herein we include the effect of reactants concentrations to the energy span model, which proved to be essential to comprehend the experimental ESI-MS results and to propose a more accurate mechanism.