Oxidation of Organic Substrates with RuIV=O Complexes Formed by Proton-Coupled Electron Transfer

Abstract

We describe our recent progress in mechanistic investigations on substrate oxidation reactions with Ru IV =O complexes having pyridylamine ligands. The Ru IV =O complexes are synthesized from the corresponding Ru II -OH 2 complexes either through a proton-coupled electron-transfer procedure using a cerium(IV) complex as an oxidant or by bulk electrolysis. We have verified the presence of an adduct-formation equilibrium between the Ru IV =O complex and a substrate in water, which strongly affects the reaction mechanism of the substrate oxidation. We have also shown that the reaction rates of the substrate oxidation in water are independent of the spin states of the Ru IV centers and of the bond-dissociation enthalpy of the C-H bond of the substrate. Additionally, we have applied the Ru II -OH 2 complexes as catalysts for photocatalytic substrate oxidations and have observed very efficient catalytic activity.

A Diprotonated Porphyrin as an Electron Mediator in Photoinduced Electron Transfer in Hydrogen-Bonded Supramolecular Assemblies

“…As an electron donor, a Ru II –polypyridyl complex bearing a carboxyl group at the periphery ( Ru II COOH ) has been selected to form a hydrogen-bonded supramolecular assembly with H 4 DPP 2+ . In addition to the electron-donating ability of Ru II COOH , the complex would also be the precursor of an oxidation catalyst in supramolecular hetero-triads enabling photocatalytic oxidation reactions. , On the other hand, benzyl viologen ( BV 2+ ) derivatives have been employed as an electron acceptor because of the high reduction potentials . Note that the one-electron-reduced species ( BV •+ ) is relatively stable, enabling to form a long-lived ET state in supramolecules.…”

Water oxidation utilizing a ruthenium complex featuring a phenolic moiety inspired by the oxygen-evolving centre (OEC) of photosystem II

“…Although the inherent paramagnetism of the hexacoordinated Ru IV ]O species (S = 1), X-band EPR of Ru IV ]O generally exhibit no EPR signal because of a large spin coupling exhibited in a zero magnetic eld. [65][66][67][68][69][70][71][72][73][74][75][76] Mukai reported that a powder sample of 2,6di-tert-butyl-4-phenyl phenoxyl radical displayed a sharp EPR signal at g = 2.0047. 77 In solution, both the 2,6-di-tert-butyl-4phenyl phenoxyl radical and the 2,4,6-di-tert-butyl phenoxyl radical demonstrated EPR signals at g = 2.0044 and 2.0046, Scheme 1 Redox behavior of [1] 2+ at pH < 9.8 (upper) and pH > 9.8 (lower).…”

Ru(iv)–Ru(iv) complexes having the doubly oxido-bridged core with a bridging carbonato or hydrogencarbonato ligand

“…A number of studies on the electronic structures, catalytic oxidation reactions and model reactions with sMMO analogues with diiron centers, 2 or some with dinickel centers 3 have been reported in homogeneous systems, which are not limited to the rich chemistry of mononuclear metal–oxido species by, e.g. the 8 th group iron, 4 ruthenium, 5 and osmium 6 centers. However, reports on those with diruthenium centers are limited although, only recently, a light-driven methane monooxygenation with the dinuclear Ru( iv )–Ru( iv ) complex was reported.…”