A Light-Activated Olefin Metathesis Catalyst Equipped with a Chromatic Orthogonal Self-Destruct Function

A sulfur‐chelated photolatent ruthenium olefin metathesis catalyst has been equipped with supersilyl protecting groups on the N‐heterocyclic carbene ligand. The silyl groups function as an irreversible chromatic kill switch, thus decomposing the catalyst when it is irradiated with 254 nm UV light. Therefore, different types of olefin metathesis reactions may be started by irradiation with 350 nm UV light and prevented by irradiation with shorter wavelengths. The possibility to induce and impede catalysis just by using light of different frequencies opens the pathway for stereolithographic applications and novel light‐guided chemical sequences. Light giveth and light taketh: A new catalyst promotes olefin metathesis when irradiated with UV‐A and is decomposed by UV‐C. Complex light‐guided chemical processes based on olefin metathesis, including polymerization, can be carried out by this protocol.