Pursuing the Complete OFF State in Photoswitchable Catalysis

Practically, all photoswitchable catalysts exhibit residual activity in the OFF state. Herein, we present a ruthenium initiator with a built-in photoswitch whose metathetical performance is completely shut off by light. The system is made of Hoveyda−Grubbs second-generation complexes appended, along with background ligands, to a gold nanoparticle surface via azobenzene linkers. Under dark or visible light - the precatalysts, in the presence of an olefin, undergo initiation, diffuse from the surface into bulk solution, and commence metathesis reaction. When the conditions are changed to ultraviolet, the isomerization of the azo switches takes place, burying the precatalysts within the bulky organic monolayer, thus preventing their initiation and thereby halting the reaction. Despite the irreversibility of the process, this work opens up opportunities for the remote deactivation of catalysts without their chemical decomposition and control of more complex tasks such as chemical selectivity.