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

Abstract

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.

Characterization of Reaction Intermediates Involved in the Water Oxidation Reaction of a Molecular Cobalt Complex

“…The above-described reaction mechanism suggests that the formation of Co IV (O) complex is not required at higher pH, and ligand oxidation reactions can drive the formation of O–O bond. However, in the TAML system, the formation of Co IV (O) species has been demonstrated and very recently identified by electrochemical mass spectrometry . Likewise, Co­(O) isoelectronic to Co V (O) mediated WO has been described in the case of [Co III -bTAML] − complex .…”

“…However, in the TAML system, the formation of Co IV (O) species has been demonstrated 32 and very recently identified by electrochemical mass spectrometry. 101 Likewise, Co(O) isoelectronic to Co V (O) mediated WO has been described in the case of [Co III -bTAML] − complex. 30 Therefore, the fine-tuning of ligand systems plays a crucial role in modulating the reaction mechanism.…”

The New Era of High-Throughput Nanoelectrochemistry

“…137 Yu et al 138 used a similar approach to extract femtoliter volumes of cytoplasm from single cells for downstream time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis, expanding the applications of nanopipettes to in situ mass spectrometry. 139 Similar techniques have been developed to deliver molecules inside single cells with high spatial resolution. 140−144 Despite these studies being linked to high-throughput downstream biological analysis, the number of collectable samples is still limited by the lack of automation.…”

“…Bury et al used an adaptation of the technique to perform subcellular biopsies from human tissue with micrometer precision . Yu et al used a similar approach to extract femtoliter volumes of cytoplasm from single cells for downstream time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis, expanding the applications of nanopipettes to in situ mass spectrometry . Similar techniques have been developed to deliver molecules inside single cells with high spatial resolution. − …”

Homogeneous electrochemical water oxidation catalyzed by cobalt complexes with an amine–pyridine ligand

“…[16][17][18][19][20] The intermediates for water oxidation catalyzed by cobalt complexes are commonly Co(IV) species, which are nucleophilically attacked by water molecules and participate in O-O bond formation. [21][22][23] To improve the water oxidation catalytic activity of cobalt complexes, various efforts have been made to design and synthesize ligands capable of stabilizing Co(IV) intermediate species with higher reactivity. [24][25][26][27] Recent literature has revealed that some noninnocent organic ligands of cobalt complexes can participate in the water oxidation catalytic cycle via ligand oxidation.…”