Abstract
AbstractVisible light photocatalysis relies mainly on expensive noble metal complexes and organic dyes that are not recyclable. Heterogeneous semiconductors, which are mainly applied for artificial photosynthesis and wastewater treatment, are a promising sustainable alternative and gain increasing attention. Inorganic and organic semiconductors with suitable bandgaps are among the most widely studied heterogeneous photocatalysts due to their high stability and recyclability. More recently, microporous materials, such as conjugated organic polymers, covalent organic frameworks, and metal organic frameworks that can be tuned and designed on a molecular level showed promising results. This review provides an overview of the most common heterogeneous photocatalysts with a focus on their applicability in organic synthesis.
Highlights
Metal OxidesIrradiation with UV-light is, often associated with severe drawbacks as high-energy photons can cause selectivity issues by, for example, activating substrates or reagents directly
When a semiconductor absorbs photons with sufficiently high energy, electrons are excited from the valence band (VB) to the conduction band (CB), generating simultaneously an oxidizing and a reducing species on a single particle
This review provides an overview of the most common, purely heterogeneous photocatalysts, that were successfully applied in organic synthesis focusing on catalysts and strategies that enable the use of visible light (> 400 nm)
Summary
Irradiation with UV-light is, often associated with severe drawbacks as high-energy photons can cause selectivity issues by, for example, activating substrates or reagents directly To overcome such issues, strategies that enable the utilization of visible light are intensively investigated. The same group reported on a TiO2 P25 catalyzed multicomponent Ugi-type reaction of N,N-dimethylanilines (9) with isocyanides (10) and water that results in the formation of αamino amides (11, Scheme 3).[11] The formation of a surface complex between the aniline derivative (9) and TiO2 was proposed to be responsible for visible light absorption. Kappe in the field of multiphasic continuous flow chemistry He subsequently moved to the Max-Planck Institute of Colloids and Interfaces for postdoctoral work, and was promoted to Group Leader in 2018. The authors hypothesized that surface poisoning from organic compounds, most likely derived from indole, is responsible for catalyst deactivation
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