Controlling Radical-Type Reactivity with Transition Metals and Supramolecular Cages

In modern society transition metal catalysis plays an important role in a wide variety of chemical transformations. In the context of sustainable chemistry it is desirable to move from precious metals (such as palladium, platinum, iridium, etc.) to base metal catalysts (cobalt, iron, manganese, etc.), which are found in natural metallo-enzymes. These complexes mainly react through one-electron pathways involving (coordinated) radicals. Although it is difficult to tune the reactivity of free radicals, highly selective reactions can be performed in close proximity of a transition metal. Especially cobalt porphyrin complexes have been studied in detail to develop a broad range of radicaltype transformations with exceptional selectivity and activity. Controlled formation of ‘substrate radicals’ in low concentrations is a key feature of these metallo-radical catalysts.