RESUMO
A heteroleptic [Pd2L2L'2]4+ coordination cage containing a photoswitchable azobenzene-derived ligand catalyzes the Michael addition reaction between methyl vinyl ketone and benzoyl nitromethane within its cavity. The corresponding homoleptic cages are catalytically inactive. The heteroleptic cage can be reversibly disassembled and reassembled using 530 and 405 nm light, respectively, allowing catalysis within the cage to be switched OFF and ON at will.
RESUMO
A photoswitchable ligand and palladium(II) ions form a dynamic mixture of self-assembled metallosupramolecular structures. The photoswitching ligand is an ortho-fluoroazobenzene with appended pyridyl groups. Combining the E-isomer with palladium(II) salts affords a double-walled triangle with composition [Pd3 L6 ]6+ and a distorted tetrahedron [Pd4 L8 ]8+ (1 : 2 ratio at 298â K). Irradiation with 410â nm light generates a photostationary state with approximately 80 % of the E-isomer of the ligand and results in the selective disassembly of the tetrahedron, the more thermodynamically stable structure, and the formation of the triangle, the more kinetically inert product. The triangle is then slowly transformed back into the tetrahedron over 2â days at 333â K. The Z-isomer of the ligand does not form any well-defined structures and has a thermal half-life of 25â days at 298â K. This approach shows how a thermodynamically preferred self-assembled structure can be reversibly pumped to a kinetic trap by small perturbations of the isomer distribution using non-destructive visible light.
RESUMO
A photoswitchable ligand based on azobenzene is self-assembled with palladium(II) ions to form a [Pd2 (E-L)4 ]4+ cage. Irradiation with 470â nm light results in the near-quantitative switching to a monomeric species [Pd(Z-L)2 ]2+ , which can be reversed by irradiation with 405â nm light, or heat. The photoswitching selectivity towards the metastable isomer is significantly improved upon self-assembly, and the thermal half-life is extended from 40â days to 850â days, a promising approach for tuning photoswitching properties.