Utilising excited state organic anions for photoredox catalysis: activation of (hetero)aryl chlorides by visible light-absorbing 9-anthrolate anions.

The tricyclic aromatic ketone 9-anthrone and its derivatives are under basic conditions in equilibrium with their corresponding anionic forms. Unlike the neutral species, the 9-anthrolate anions can be excited by blue LED light and thus, are able to initiate a photoinduced electron transfer (PET) reaction. To demonstrate the synthetic applicability of the catalytic system, various (hetero)aryl chlorides were converted in C-C and C-Het bond-forming reactions affording the corresponding arylation products in moderate to excellent yields. The reactions proceed under very mild conditions without the need for a sacrificial electron donor. Besides 9-anthrone, other closely related derivatives were synthesised and investigated concerning their ability to catalyse demanding reductive transformations. Based on spectroscopic findings and radical trapping experiments a conceivable mechanism is proposed.