Organic Photocatalysis: Carbon Nitride Semiconductors vs. Molecular Catalysts

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.