Visible Light‐Gated Organocatalysis Using a RuII‐Photocage

The light‐gated organocatalysis via the release of 4‐N,N‐dimethylaminopyridine (DMAP) by irradiation of the [Ru(bpy)2(DMAP)2]2+ complex with visible light was investigated. As model reaction the acetylation of benzyl alcohols with acetic anhydride was chosen. The pre‐catalyst releases one DMAP molecule on irradiation at wavelengths longer than 455 nm. The photochemical process was characterized by steady‐state irradiation and ultrafast transient absorption spectroscopy. The latter enabled the observation of the 3MLCT state and the spectral features of the penta‐coordinated intermediate [Ru(bpy)2(DMAP)]2+. The released DMAP catalyzes the acetylation of a wide range of benzyl alcohols with chemical yields of up to 99 %. Control experiments revealed unequivocally that it is the released DMAP which takes the role of the catalyst. 4‐Dimethylaminopyridine was successfully released from a RuII‐photocage by visible‐light irradiation and shown to catalyze the acetylation reactions of various benzylalcohols in a one‐pot process. The described example constitutes a rare example of visible light‐gated catalysis via the photorelease of an organocatalyst.