Organic Photocatalysis: Carbon Nitride Semiconductors vs. Molecular Catalysts

Abstract

The development of novel chemical transformations calls for environmentally friendly synthetic methods. Visible light photoredox catalysis has gained attention as a versatile tool to address these challenges. Due to the well‐defined structure of homogeneous transition metal‐based catalysts and organic dyes, they have been widely used to drive a wide variety of organic transformations. On the other hand, due to low cost, simple preparation procedure, and chemical stability of carbon nitride semiconductors, they have been known almost exclusively in environmental applications and water splitting. Until recently the applicability of carbon nitride semiconductors in organic synthesis has remained hidden from the broad community of organic chemists. In this review, we summarize reactions mediated by heterogeneous carbon nitride photocatalysts and common homogeneous photocatalysts in the same organic reactions, such as carbon‐carbon or carbon‐heteroatom bond formation reactions. We compare performance of both groups of catalysts in the discussed organic reactions.

Emerging Concepts in Carbon Nitride Organic Photocatalysis

“…[67] At the same time, application of carbon nitrides in organic photoredox catalysis has been summarized in the dedicated reviews. [68,69,70,71] Recapitulating available literature we conclude that, in general, CN-based photocatalysts of sophisticated structure, such as those featuring heterojunction and exquisite morphology, are employed in water splitting and environmental applications (model reactions), while CNs photocatalysts with large surface area and stoichiometry close to C 3 N 4 are commonly employed in organic synthesis.…”

“…Overall, a comprehensive summary on CNs synthesis, characterization, properties, and environmental applications are available in reviews [67] . At the same time, application of carbon nitrides in organic photoredox catalysis has been summarized in the dedicated reviews [68,69,70,71] …”

Photoredox Organic Synthesis Employing Heterogeneous Photocatalysts with Emphasis on Halide Perovskite

“…The heterogeneous photocatalysts employed in the aforementioned complex photoredox organic synthesis under visible light has not yet been thoroughly reviewed, to the best of our knowledge.W en oticed that metal oxides, C 3 N 4 , [15] plasmatic nanostructures fororganic pollutants degradation, [16] simple organic compound transformation/decomposition via oxidations or reductionsh ave been previously illustrated. [12b,d] We also noted that perovskites for photocatalysis towards water splitting, CO 2 reduction etc.h ave also been recently reviewed.…”

Dichloromethylation of enones by carbon nitride photocatalysis

“…The organic semiconductors have also been efficiently employed in a continuous flow system for chemical synthesis eliminating the last obstacle (poor light penetration in heterogeneous solidliquid mixture) on the way to widespread applications in organic synthesis 2 . Because of their low cost, ease of synthesis and stability against reactive intermediates and photobleaching, CNs already play an important role as heterogeneous photocatalysts for organic transformations [3][4][5] . CNs are also very versatile, and can be tailored depending on the application by bandgap engineering at the atomic and molecular level 6,7 .…”