The Effect of N-Donor Ligands on Activation of [Ru(tpy)(L-py)(AcCN)]²⁺ Precatalysts in CO₂ Reduction Reaction...

The electrocatalytic reduction of CO₂ to CO in anhydrous media requires the formation of the M-CO₂ bond. Using [Ru(tpy)(bpy)S]²⁺ as a model, and substituting a pyridine of bipyridine(bpy) for L = 123-triazole(123-trz), oxazole(oz), pyrrole(pyrr), pyrazole(prz), or NHC was computationally studied using TPPSh/def2-svp for geometries, SP correction with def2-tzvp, and implicit acetonitrile solvation. Complexes with pyrr, prz, and NHC undergo both reductions on the tpy ligand, shifting the second reduction to more negative potentials compared to bpy, 123-trz, and oz (which are at least 0.15 V more positive). For the latter, the second reduction occurs on the bidentate ligand generating [Ru(tpy^·)(py-L^·)AcCN]⁰. The general reaction path features two reductions, solvent dissociation to a pentacoordinated complex, and CO₂ association, except for NHC, where theoretical and experimental data suggest dissociation after the first reduction. Dissociation barriers varied from 19.0 (oz) to 12.9 kcal/mol (prz), while association barriers ranged from 9.0 (NHC) to 3.8 kcal/mol (oz). Finally, the cis/trans product ratio from CO₂ association is directly influenced by the τ₅ distortion parameter, serving as a qualitative indicator of selectivity.