19 Heterogeneous Photocatalysis in Organic Synthesis

Abstract In recent years, heterogeneous photocatalysis has emerged as a very appealing approach, not only for the degradation of pollutants, but also for the synthesis of chemicals. Although the main use of heterogeneous photocatalysis so far has been the mineralization and complete degradation of organic compounds, interest in the application of heterogeneous (photo)catalysts in organic synthesis is growing due to their potential application in the fabrication of renewable fuels as well as in the preparation of compounds and intermediates especially valuable to the chemical industry, such as pharmaceuticals or polymers. The synthesis of organic molecules assisted by heterogeneous photocatalysts has been dominated by the use of inorganic metal oxide semiconductors, especially titanium(IV) oxide; the use of other semiconductor materials, such as inorganic chalcogenides, carbon-based semiconductors, or metal–organic frameworks has been less explored. In this chapter we show that, in spite of the potential and the large number of heterogeneous photocatalysts already studied, the state of the art of heterogeneous photocatalysis in organic synthesis is still unsatisfactory and much below expectation, particularly in reactions other than oxidation and reduction, such as cross couplings, oxidative decarboxylations, and cycloadditions.