A Ruthenium(III)–Oxyl Complex Bearing Strong Radical Character

Abstract

Proton-coupled electron-transfer oxidation of a Ru -OH complex, having an N-heterocyclic carbene ligand, gives a Ru -O species, which has an electronically equivalent structure of the Ru =O species, in an acidic aqueous solution. The Ru -O complex was characterized by spectroscopic methods and DFT calculations. The oxidation state of the Ru center was shown to be close to +3; the Ru-O bond showed a lower-energy Raman scattering at 732 cm and the Ru-O bond length was estimated to be 1.77(1) Å. The Ru -O complex exhibits high reactivity in substrate oxidation under catalytic conditions; particularly, benzaldehyde and the derivatives are oxidized to the corresponding benzoic acid through C-H abstraction from the formyl group by the Ru -O complex bearing a strong radical character as the active species.

An Active‐Site Sulfonate Group Creates a Fast Water Oxidation Electrocatalyst That Exhibits High Activity in Acid

“…These data, though preliminary, are in some agreement with those reported by Shimoyama et al. for their [Ru III ]‐oxyl (Figure S38) [20a] . We cannot rule out the presence of an EPR‐silent Ru IV species [20e] …”

“…Analysis of Figures S32–S34 concludes (Table S6) that when 18 OH 2 is used instead of H 2 O or D 2 O, three peaks at 871.2, 832.4 (equally intense), and 808.7 (less intense) shift as expected for a Ru‐O harmonic oscillator. The peaks seen in H 2 O compare with 732 cm −1 for a [Ru III ]‐oxyl with strong σ‐donor trans to the oxyl, [20a] and 780–833 cm −1 for Ru IV oxo species [20b–d] . Shimoyama et al.…”

“…Shimoyama et al. ascribe their lower value to the [Ru III ]‐oxyl formulation, [20a] but one cannot rule out the effect of the strongly donating N ‐heterocyclic carbene.…”

N‐Heterocyclic Carbene Iron(III) Porphyrin‐Catalyzed Intramolecular C(sp3)–H Amination of Alkyl Azides

“…We are particularly interested in developing Fe porphyrin catalysts bearing an N‐heterocyclic carbene (NHC) axial ligand, in view of the increase in the catalytic efficiency of Ru II porphyrins in carbene and aryl‐nitrene C−H insertion reactions upon introduction of an NHC axial ligand . Also, the oxo ligand of heme Fe–oxo species displays oxyl radical character, and for a Ru=O complex the oxo ligand trans to NHC ligand was reported to have strong oxyl radical character . Previously we demonstrated microwave‐accelerated iron porphyrin catalyzed intermolecular phosphoryl‐, sulfonyl‐, and aryl‐nitrene transfer reactions .…”

Synthesis and structures of 4,5-dimethyl-1,3-bis(pyridin-2-ylmethyl)-1H-imidazolium chloride and 1,1′-bis(pyridin-2-ylmethyl)-2,2′-bis(4,5-dimethylimidazole)

“…Numerous complexes of different transition metals with tridentate N-hetero cyclic ligands of this type were described in the literature. [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] Here we report an attempt to synthesize a new N-hetero cyclic carbene pincer ligand containing picolyl sub stituents.…”