Pyrimidopteridine N-Oxide Organic Photoredox Catalysts: Characterization, Application and Non-Covalent Interaction in Solid State.

Herein we report the photo- and electrochemical characterization of pyrimidopteridine N-oxide-based heterocycles. The potential of their application as organic photoredox catalysts is showcased in the photomediated contra-thermodynamic E→Z isomerization of cinnamic acid derivatives and oxidative cyclization of 2-phenyl benzoic acid to benzocoumarin using molecular oxygen as a mild oxidant. Furthermore, unprecedented intermolecular non-covalent n-π-hole interactions in solid state are discussed based on crystallographic and theoretical data.

Effects of Imidazole-Type Ligands in Cu/TEMPO-Mediated Aerobic Alcohol Oxidation.

Selective aerobic oxidation of benzyl alcohol to benzaldehyde by a (bpy)Cu(IM)/TEMPO catalyst (IM represents differently substituted imidazoles) has been studied by simultaneous operando electron paramagnetic resonance/UV-vis/attentuated total reflectance infrared spectroscopy in combination with cyclic voltammetry to explore the particular role of imidazole in terms of ligand and/or base as well as of its substitution pattern on the catalytic performance. For molar ratios of IM/Cu ≥ 2, a (bpy)Cu(IM)(IM) complex is formed, in which the Cu-N distances and/or angles for the two IM ligands a and b are different. The coordination of a second IM molecule boosts the oxidation of Cu to Cu and, thus, helps to activate O by electron transfer from Cu to O.

Straightforward synthesis of tetraalkynylpyrazines and their photophysical properties.

Tetrafold Sonogashira reactions of tetrachloropyrazine were investigated to provide a one-step synthesis of various tetraalkynylpyrazines. The reaction conditions were thoroughly optimized using modern catalysts and ligands, and products were generally isolated in good to excellent yields. Furthermore, photophysical and electrochemical properties of selected compounds were studied and compared with those of previously reported tetraalkynylpyridines and benzenes.

Electron- and Energy-Transfer Processes in a Photocatalytic System Based on an Ir(III)-Photosensitizer and an Iron Catalyst.

The reaction pathways of bis-(2-phenylpyridinato-)(2,2'-bipyridine)iridium(III)hexafluorophosphate [Ir(ppy)2(bpy)]PF6 within a photocatalytic water reduction system for hydrogen generation based on an iron-catalyst were investigated by employing time-resolved photoluminescence spectroscopy and time-dependent density functional theory. Electron transfer (ET) from the sacrificial reagent to the photoexcited Ir complex has a surprisingly low probability of 0.4% per collision.

Direct electrochemistry of horseradish peroxidase immobilized in a chitosan-[C4mim][BF4] film: determination of electrode kinetic parameters.

The direct electrochemistry of a HRP-chi-[C(4)mim][BF(4)] film (where HRP = horseradish peroxidase, chi = chitosan, and [C(4)mim][BF(4)] = the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluoroborate) has been studied by cyclic voltammetry on a glassy carbon electrode. The mechanism for the electrochemical reaction of HRP is suggested to be EC for the reduction, and CE for the following re-oxidation, as the oxidative peak potential remained approximately unchanged across the scan rate range. The half wave potential of HRP reduction was found to be pH dependent, suggesting that a concomitant proton and electron transfer is occurring.