Proton-Coupled Oxidation of Aldimines and Stabilization of H-Bonded Phenoxyl Radical-Phenol Skeletons

Coligands Controlled Reactivities of Ruthenium(II) Precursors: Antiferromagnetically Coupled Ruthenium(III)-Phenoxyl versus Ruthenium(II)-Phenoxyl Forms

The study disclosed that the reactivities of [RuII (PPh3)3Cl2] and [RuII(PPh3)3(CO)(H)Cl] precursors toward a trimethoxyarylimino-phenol derivative are sensibly different. The former promotes methoxy demethylation reaction affording a [Phenolato-RuIII-Phenolato] unit, while the latter containing π-acidic CO and hydride as coligands leads to C-H activation reaction, generating a [Phenolato-RuII-Aryl] unit. Notably, the oxidized analogues of these two forms produce antiferromagnetically coupled [RuIII-phenoxyl] and paramagnetic [RuII-phenoxyl] forms, which exhibit diverse reactivities. Surprisingly, the magnetically coupled [RuIII-phenoxyl] form obtained from [Phenolato-RuIII-Phenolato] motif leads to coligand, PPh3 oxidation and undergoes dimerization, making a Ru-Ru bond (2.599(2) Å), while the [RuII-phenoxyl] form obtained from [Phenolato-RuII-Aryl] motif leads to C-C coupling and H abstraction reactions. The coupling reaction affords a 4,4'-dibenzosemiquinonate anion radical complex, but the H-abstraction of the phenoxyl form gives a [RuII-Phenol] complex. For comparison, [RuII(IQR 0)] and [RuII(ISQR·-)] complexes were also isolated, where IQR 0 and ISQR·- are p-R-o-iminobenzoquinone and p-R-o-iminobenzosemiquinonate anion radicals. However, they fail to promote any bond-formation reaction. The molecular and electronic structures of the ruthenium (II/III) complexes were confirmed by single-crystal X-ray crystallography, EPR spectroscopy, and DFT calculations.

A Methoxylation-Promoted CPET Reaction

The manuscript discloses a methoxylation reaction to an aromatic carbonyl function that carries out a CPET reaction oxidizing a transition metal ion. Spontaneous methoxylation of a redox non-innocent fragment coordinated to a high spin cobalt(II) ion, promoted concerted proton electron transfer (CPET) reaction oxidizing cobalt(II) to cobalt(III) in air and subsequent demethoxylation induced reduction of cobalt(III) to cobalt(II) producing H2 O2 are authenticated. The cobalt(III)/cobalt(II) electron transfer (ET) potential of the designed complex in CH2 Cl2 is -0.27 V vs Fc+ /Fc redox couple. However, in presence of MeOH the reduction potential decreases to -1.02 V due to CPET involving MeOH proton. In CH2 Cl2 /CHCl3 spontaneous demethoxylation occurs giving back the original complex and reactive methoxyl radical that reacts with O2 producing H2 O2 . Overall one molecule of MeOH produces one molecule of H2 O2 . To analyze the involvement of the proton, the rate constants of the CPET reactions in CH2 Cl2 -MeOH (2 : 1) and CH2 Cl2 -CD3 OD (2 : 1) and the demethoxylation reaction in CHCl3 at 330 K were determined by time drive UV-Vis spectroscopy.

On the non-innocence and reactive versus non-reactive nature of α-diketones in a set of diruthenium frameworks

Slightly modified ligand designs in diruthenium setups have major impacts on the reactivity/stability of coordination complexes. The 1,2-bis(2-hydroxyphenyl)ethane-1,2-dione bridge is also potentially redox non-innocent.

Antioxidant product analysis of Hulu Tea (Tadehagi triquetrum)

Phytophenols from Hulu Tea can produce not only homodimers but also a heterodimer through the antioxidant activity.