Unlocking Photocatalytic Activity of Acridinium Salts by Anion-Binding Co-Catalysis

The in situ generation of active photoredox organic catalysts upon anion-binding co-catalysis by making use of the ionic nature of common photosensitizers is reported. Hence, the merge of anion-binding and photocatalysis permitted the modulation of the photocatalytic activity of simple acridinium halide salts, building an effective anion-binding - photoredox ion pair complex able to promote a variety of visible light driven transformations, such as anti-Markovnikov addition to olefins, Diels-Alder and the desilylative C-C bond forming reactions. Anion-binding studies, together with steady-state and time-resolved spectroscopy analysis, supported the postulated ion pair formation between the thiourea hydrogen-bond donor organocatalyst and the acridinium salt, which proved essential for unlocking the photocatalytic activity of the photosensitizer. The merge of anion-binding and photoredox catalysis for the modular, in situ photocatalytic activation of acridinium salts is reported. This approach leads to an enhancement of the stability and selectivity of the photoactive ion pair species, which proved effective to promote several visible light-mediated photoredox reactions. image