Probing Ligand Effects on O–O Bond Formation of Ru-Catalyzed Water Oxidation: A Computational Survey

Abstract

Ligand effects of some representative monomeric Ru-based water oxidation catalysts on the key O-O formation step are revealed in this work. Three effects, namely, cis-effect, net charge effect, and steric hindrance effect, are identified, which can exert sizable modulation on the O-O formation barriers for the two widely accepted O-O formation mechanisms of WNA (water nucleophilic attack) and I2M (direct coupling of two high-valent metal oxo units). The study demonstrates that, through the way of ligand design, there remains a large space for improving O-O bond formation reactivity.

Molecular Catalysts for Water Oxidation

“…195,196 In one case, a turnover number of >100 000 was achieved with a Ce(IV) oxidant. 197 Computational work has provided insight into the competition between the WNA and the OCP mechanisms, 198 and improved performance has been achieved by incorporating the catalysts into a nanofibrous coordination polymer. 199 A three-component light-driven water-oxidation system composed of a conventional photosensitizer, persulfate as a sacrificial electron acceptor, and the same type of wateroxidation catalyst (WOC) as catalyst produced oxygen with an excellent quantum yield of 17%.…”

Quantum Chemical Modeling of Homogeneous Water Oxidation Catalysis

“…If there is an anionic group coordinated to the Ru center, this group can function as ag eneral base to abstract the protond uring the attack. [130,133,137,138,140] Sala et al reportedac ombined experimental and computational study on water oxidation mediated by cis-[(bpy) 2 2 + species. [130] The direct coupling of the two oxo groups had av ery high barrier( 57.5 kcal mol À1 ;F igure 29).…”

“…Kang et al calculated both the direct couplinga nd the water attack pathways for as eries of Ru V =Oc omplexes with differentl igands. [137] Three factors affected the relative barriers:t he cis effect, the net charge effect, and the steric effect. Recently,F an et al showedt hat, if the total charge of the high-valent Ru V complex increased from + 1t o+ 2, the water attack pathway became more favored.…”

Role of ligands in catalytic water oxidation by mononuclear ruthenium complexes

“…This dinuclear intermediate is also [ 84 ]. First, the tetradentate ligand containing a phenyl or carbene group can lead the Ru complex to favor the WNA route towards the O-O bond formation since a cis-structure is usually preferred by the phenyl A c c e p t e d M a n u s c r i p t 19 or carbene group with regard to a proton-accepting fragment.…”