Photochemical C––H Bond Activation by Gold, Platinum, Tungsten, and Osmium Complexes

To meet the increasing demand for environmentally benign and sustainable chemical processes, the use of light in organic synthesis is blossoming. Over the past decades, luminescent transition metal complexes have been extensively studied as photosensitizers due to their excellent photophysical properties and flexibility in structure modification. The visible-light photo-catalysis has been developed rapidly, from “proof of concept” to “a useful strategy,” in a broad range of organic transformation reactions that can be used in practical organic synthesis. Compared with the extensive literatures on ruthenium and iridium complexes used in visible-light catalysis, the summaries on gold, platinum tungsten (except polyoxotungstates), and osmium complexes catalyzed photochemical reactions are scarce. In this article, the recent developments in photochemical reactions catalyzed by gold (Au), platinum (Pt), tungsten (W), and osmium (Os) complexes, as well as the mechanistic studies and their applications in organic synthesis are summarized. The photochemical reactions discussed herein mainly refer to the ones with transition metal complexes that absorb light in the UV–visible spectral region and which serve as a photo-redox catalyst or a photosensitizer.