The cis‐[Ru^II(bpy)₂(H₂O)₂]²⁺ Water‐Oxidation Catalyst Revisited

Abstract

The only operating mechanism in the oxidation of water to dioxygen catalyzed by the mononuclear cis-[RuII(bpy)2(H2O)2]2+ complex when treated with excess CeIV was unambiguously established. Theoretical calculations together with 18O-labeling experiments (see plot) revealed that it is the nucleophilic attack of water on a Ru=O group

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).…”

“…[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). Alternatively,a ttack of water on one oxo moietyv ia af ive-membered-ring transition state facilitated by the second oxo group, which abstracts ap roton, has ab arrier of 29.9 kcal mol À1 .T he barrier was further decreased to 24.5 kcal mol À1 when as econd water molecule was used to assist proton transfer via as even-membered-ring transition state.…”

Intramolecular Proton Transfer Boosts Water Oxidation Catalyzed by a Ru Complex

“…18,19,20,21,22 When combined with the theoretical analysis, via density functional theory (DFT) calculations, spectroscopic and electrochemical measurements provide detailed information on the nature of reaction intermediates and activation free energies along the catalytic cycle of water oxidation. 23,24,25,26,27,28,29,30 Strong sigma donation groups like carboxylate ligands in 2,2'-bipyridine-6,6'-dicarboxylic acid (H 2 bda; see Chart 1 for a drawing), together with seven coordination have allowed easy access to reactive species in high oxidation states such as [Ru V (O)(bda)(pic) 2 ] + (pic is 4-picoline) where the metal center is at formal oxidation state of V. 31 Additional tuning of the activation energy barriers can result from supramolecular interactions, based on π-π stacking of ligands with π -extended conjugation such as isoquinoline and its derivatives favoring formation of dinuclear peroxo intermediates. 32,33 Furthermore, hydrogen bonding interactions can play a significant role in the kinetics as demonstrated with strategically substituted fluro-2,2'-bpy ligands.…”

Mechanistic Analysis of Water Oxidation Catalyst cis-[Ru(bpy)2(H2O)2]2+: Effect of Dimerization

“…It was found that the cis configuration is more stable in the absence of light, but under illumination the complex undergoes cis-trans isomerization. Later, it was shown that upon addition of Ce IV , cis-[Ru(bpy) 2 (H 2 O) 2 ] 2+ acts as a water oxidation catalyst, yet its performance is limited by having few turnovers [18]. Interestingly, in the same work, trans-[Ru(bpy) 2 2 ] 2+ is believed to involve a water nucleophilic attack on the Ru V =O species produced in a series of proton-coupled electron transfer reactions, which occur upon oxidation [18].…”