Non‐Innocent Ligands as Mediators for Visible‐Light‐Initiated Element–Carbon Bond Homolysis in Main Group Chemistry

Photoinitiated homolysis of element–carbon bonds is an important method for the generation of carbon-centered radicals in catalysis and organometallic or polymer chemistry. In this respect, the use of earth-abundant main group elements such as aluminum or silicon is attractive. Generally, subvalent species derived from these typically redox-inactive elements are unstable and within their high-valent configuration +III (Al) or +IV (Si) comparatively strong E─C bonds are formed. Therefore, E─C homolysis usually requires shortwave UV irradiation, which hampers their use as radical sources. Some reports in the literature show that visible-light-induced E─C homolysis is possible when a redox non-innocent ligand (NIL) is coordinated to the organometallic fragment. In a simplified view, the NILs provide chromophoric moieties, which can absorb energy in form of light and subsequently convert it to break the element–carbon bonds. The resulting main group element radicals are in turn stabilized by delocalization of the unpaired electron, effectively lowering the dissociation energy of the E─C bond. In this article, the effects of NILs as mediators for visible-light-induced E─C bond homolysis in main group chemistry are discussed on the basis of selected literature reports, and future opportunities and challenges are highlighted.