Systematic Influence of Electronic Modification of Ligands on the Catalytic Rate of Water Oxidation by a Single-Site Ru-Based Catalyst

Catalytic water oxidation is an important process for the development of clean energy solutions and energy storage. Despite the significant number of reports on active catalysts, systematic control of the catalytic activity remains elusive. In this study, descriptors are explored that can be correlated with catalytic activity. [Ru(tpy)(pic)₂ (H₂ O)](NO₃ )₂ and [Ru(EtO-tpy)(pic)₂ (H₂ O)](NO₃ )₂ (where tpy=2,2' : 6',2"-terpyridine, EtO-tpy=4'-(ethoxy)-2,2':6',2"-terpyridine, pic=4-picoline) are synthesized and characterized by NMR, UV/Vis, EPR, resonance Raman, and X-ray absorption spectroscopy, and electrochemical analysis. Addition of the ethoxy group increases the catalytic activity in chemically driven and photocatalytic water oxidation. Thus, the effect of the electron-donating group known for the [Ru(tpy)(bpy)(H₂ O)]²⁺ family is transferable to architectures with a tpy ligand trans to the Ru-oxo unit. Under catalytic conditions, [Ru(EtO-tpy)(pic)₂ (H₂ O)](NO₃ )₂ displays new spectroscopic signals tentatively assigned to a peroxo intermediate. Reaction pathways were analyzed by using DFT calculations. [Ru(EtO-tpy)(pic)₂ (H₂ O)](NO₃ )₂ is found to be one of the most active catalysts functioning by a water nucleophilic attack mechanism.

Synthesis, UV-visible spectroelectrochemistry and theoretical characterization of new polypyridyl Ru(II) complexes containing 2,4,6-tris(2-pyridyl)-1,3,5-triazine as precursors for water oxidation catalysts

In this work, we report the syntheses and physicochemical characterization of new chloro and aqua complexes of Ru(ii) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) and 2,2'-bipyridines substituted with donor and acceptor groups in the 4,4'-positions. The aqua complexes behave as precursors for water oxidation catalysts at pH = 1 using Ce(iv) as a sacrificial oxidant. Besides, the oxidized forms Ru(iv) and Ru(v) have been characterized at different pH values by electrochemistry, UV-Visible spectroscopy and spectroelectrochemistry. The reaction mechanisms were studied by combining mixing and stopped-flow experiments with spectrophotometric monitoring in the UV-visible region and all the rate constants were determined together with the corresponding TON and TOF values at pH = 1. Calculations based on Density Functional Theory (DFT and TD-DFT) were performed to support the experimental data.

A ruthenium water oxidation catalyst containing a bipyridine glycoluril ligand

A mononuclear ruthenium complex [Ru(tpy)(bpg)H₂O]²⁺ bearing a bipyridine glycoluril ligand (bpg) = 4b,5,7,7a-tetrahydro-4b,7a-nepiminomethan-oimino-6H-imidazo[4,5-f][1,10]phenanthroline-6,13-dione acts as a robust water oxidation catalyst (WOC) at pH = 1 using Ce(iv) as a sacrificial oxidant.