Structural Effects on Dioxygen Evolution from Ru(V)−Oxo Complexes

Abstract

AbstractA series of ruthenium(V)−oxo compounds, LRu(V)O(n) [L=bipyridinedicarboxylate (BDA), alpha‐hydroxycarboxylate (AHA), porphyrin (POR), dimethylglyoximate (DMG), and nitrilotriacetate (NTA); n=+1,0, −1] are evaluated by Density Functional Theory for their ability to produce dioxygen through coupling of Ru(V)−oxo species, bimetallic peroxides (LRu(IV)‐O−O−Ru(IV)L), and dioxygen (LRu(IV)‐O2) complexes. Anionic Ru−oxo complexes (AHA)2RuO− (2) and (NTA)Ru(O)Cl− (5 e) have prohibitively large free energies of coupling, while neutral and monocationic species (1 b, 3–5 a–d) show small to moderate free energies of coupling. Transition states for O−O coupling were found for (NTA)RuO (5 a), (NTA)RuO(NH3) (5 c), (NTA)RuO(Pyr) (5 d), (DMG)2ClRu(O) (8) and (POR)RuO(Cl) (9), yielding moderate activation energies in the range of 18–22 kcal/mol. The overall oxygen evolution reaction (OER) free energies decrease in favourability as the coordination number of LRuO decreases, i. e. 7>6>5. The modest activation energies and free energies along the reaction coordinate for (NTA)(L)RuO and (POR)ClRu(O) suggest that these species would undergo kinetically and thermodynamically favorable oxygen evolution.