Catalysis^cubed Reloaded─Cyclopropanations inside Porphyrin-Based Supramolecular M₈L₆ Aggregates

Cube-shaped metallosupramolecular M₈L₆ cages were used to encapsulate cobalt catalysts, which bear porphyrins in the first and the second coordination spheres. When evaluating the catalysts in radical cyclopropanations of styrene derivatives with terminal alkene groups, it turned out that the transformation generally strongly benefits from this in terms of catalyst performance (TON), which also strongly depends on the counterion and the solvent. Furthermore, a shift of the diastereoselectivity toward the cis-configured isomer was observed when the caged catalysts were used compared to their free analogues. However, internal 1,2-disubstituted alkene functions could essentially not be transformed into cyclopropanes in this confined arrangement. All of these features─the selective transformation of terminal alkenes as well as the enhanced activity of the catalyst in transformations of these substrates and the change in the stereochemical outcome of the reaction─nicely demonstrate the benefit of compartmentalization of transition metal catalysts in the unique microenvironment of a metallosupramolecular cage.