Development and Synthesis of MOC-CPOnes : Metal-Organic Cages Based on Photo-Responsive Cyclopropenone Ligands

The development of light-responsive metal-organic cages is of interest in order to mimic natural processes in model systems and for host-guest related applications, e.g. recognition, separation, stabilisation of reactive species, catalysis and drug delivery. The majority of examples for a structural transformation of a light-responsive cage are reported based on the reversible photochromism of “photo-switches”. In contrast, light-responsive cages and their structural transformation based on irreversible photo-reactions are underdeveloped. In order to change this, cyclopropenone-containing ligands have been developed for the first time. The photoreaction of cyclopropenones to yield alkynes is well studied. The previously “angled” cyclopropenone moiety changes to a linear alkyne after light-induced decarbonylation. Based on this photolysis, the concept of MOC-CPOnes, metal‑organic cages based on photo‑responsive cyclopropenone ligands, resulting in the structural transformation of a pre‑assembled cage into a new structure after photodecarbonylation is presented.

In the investigation of a 1st generation of cyclopropenone-containing ligands, a synthetic strategy was developed and in a proof-of-concept, the photoreaction-induced structural transformation of a CoII helicate with cyclopropenone-containing ligands into a tetrahedron with alkyne-containing ligands was successfully demonstrated. Additional insight into the impact of the N‑heterocyclic substrates on the previously investigated synthetic strategy was given by systematic studies on N‑heterocyclic cyclopropenone‑containing model systems and the report of their respective mononuclear complexes. Based on these findings, changes to the ligand structure were investigated in a 2nd generation of MOC-CPOnes.


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