Photocatalytic Ketyl Radical Initiated C-ketyl-C-sp2/C-sp3 Coupling on ZnIn2S4

Visible-light-driven C-C bond formation utilizing ketyl radical (C-ketyl) species has attracted increasing attention recently, as it provides a direct route for the synthesis of complex molecules. However, the most-developed homogeneous photocatalytic systems for the generation and utilization of ketyl radicals usually entail noble metal-based (e. g., Ru and Ir) photosensitizers, which suffer from not only high cost but also potential degradation and hence pose challenges in product separation and purification. In contrast, readily accessible, inexpensive, and recyclable semiconductors represent a class of attractive and alternative photocatalysts but remain much less explored for photocatalytic ketyl radical initiated C-C bond formation. This work demonstrates that a wide range of industrially important chemicals, including substituted chromanes and tertiary alcohols, can be produced on ZnIn2S4 under visible light irradiation through intramolecular cyclization (C-ketyl-C-sp2) and intermolecular cross-coupling (C-ketyl-C-sp3) reactions, respectively, using ketyl radicals. A suite of experimental studies aided by computational investigation were carried out to shed light on the mechanistic insights of these two types of ketyl radical initiated C-C coupling reactions on ZnIn2S4.