Catalysis by a Metastable Photoswitchable Cage.

The introduction of ortho-methyl substituents on aryl-substituted ortho-tetrafluoroazobenzene photoswitches breaks the π-conjugation and improves photoswitching selectivity and increases the thermal half-life of the metastable isomer. Using this approach, a visible-light-responsive ligand was assembled with a non-switchable ligand and palladium(II) ions into a mixture of molecular cages. When irradiated with 530 nm light, the system converges to form a single product, a metastable, mixed-ligand molecular cage. This cage can be reversibly disassembled using 424 nm light, an example of integrative self-sorting controlled by light. The metastable assembly can catalyze both Michael addition and nitroaldol reactions. Importantly, visible light accesses a metastable catalytic state inaccessible under thermodynamic control. We demonstrate that the active assembled species can be switched on and off at will using visible irradiation and the metastable species is the most catalytically active assembly.