Identifying Metal-Oxo/Peroxo Intermediates in Catalytic Water Oxidation by In Situ Electrochemical Mass Spectrometry.

Molecular catalysis of water oxidation has been intensively investigated, but its mechanism is still not yet fully understood. This study aims at capturing and identifying key short-lived intermediates directly during the water oxidation catalyzed by a cobalt-tetraamido macrocyclic ligand complex using a newly developed an in situ electrochemical mass spectrometry (EC-MS) method. Two key ligand-centered-oxidation intermediates, [(L2-)CoIIIOH] and [(L2-)CoIIIOOH], were directly observed for the first time, and further confirmed by 18O-labeling and collision-induced dissociation studies. These experimental results further confirmed the rationality of the water nucleophilic attack mechanism for the single-site water oxidation catalysis. This work also demonstrated that such an in situ EC-MS method is a promising analytical tool for redox catalytic processes, not only limited to water oxidation.

External Oxidant-Free Dehydrogenative Lactonization of 2-Arylbenzoic Acids via Visible-Light Photocatalysis.

An external oxidant-free C-H functionalization/C-O bond formation reaction for constructing benzo-3,4-coumarins accompanied by quantitative H2 evolution has been developed. High functional group tolerance and excellent reaction efficiency are shown in this transformation. Meanwhile, the substrates containing heterocyclic substituents such as thienyl-, pyridinyl-, and pyrrolylbenzoic acids displayed good performance. Importantly, this reaction can be performed with good efficiency on a gram scale. A cyclic voltammetry study and density functional theory calculations could provide insight into the mechanism of this reaction.