In situ Reaction Monitoring in Photocatalytic Organic Synthesis

Abstract

Visible‐light photocatalysis provides numerous useful methodologies for synthetic organic chemistry. However, the mechanisms of these reactions are often not fully understood. Common mechanistic experiments mainly aim to characterize excited state properties of photocatalysts and their interaction with other species. Recently, in situ reaction monitoring using dedicated techniques was shown to be well‐suited for the identification of intermediates and to obtain kinetic insights, thereby providing more holistic pictures of the reactions of interest. This minireview surveys these technologies and discusses selected examples where reaction monitoring was used to elucidate the mechanism of photocatalytic reactions.

A Photoreactor-Interfaced Mass Spectrometer: An Online Platform to Monitor Photochemical Reactions

“…In previous studies, online reactors coupled with ESI have successfully detected short-lived transient intermediates formed in organometallic photochemical reactions, but they typically utilize high-powered broad-spectrum irradiation regimes without detailed kinetics analysis. − In contrast, this relatively simple and widely applicable apparatus rapidly acquires both kinetic and mechanistic information without altering the experimental conditions, as demonstrated by two examples: (i) the photoinitiated polymerization of methyl methacrylate and (ii) the photocatalyzed alkyne insertion into a 1,2,3-benzotriazinone.…”

Metallaphotocatalytic Platforms Based on Covalent Organic Frameworks for Cross‐Coupling Reactions

“…Therefore, it is important to follow the metal site evolution during catalysis, including the change in oxidation state and coordination environments to understand the activity. It is imperative to develop operando spectroscopic characterizations such as in situ X‐ray absorption near‐edge structure (XANES) and electronic paramagnetic resonance (EPR) spectroscopy to probe the evolution of active sites and reactive intermediates [45] . More coordination configurations and the resulted reactivity should be explored in addition to the reported ones (to imine and pyridyl nitrogen of COFs skeletons or introduced ligand moiety), e. g., using monomer bearing other coordination sites (O, S, P, and B etc.)…”