Controlling radical-type reactivity with transition metals and supramolecular cages

To sustain our demand for the various products obtained through catalysis, it is desirable to move from precious metals (such as palladium, platinum, iridium, etc.) to base metals (cobalt, iron, manganese, etc.). The efficient use of base-metals is, however, associated with new challenges due to their preferred one-electron reactivity. Metallo-enzymes are well known for performing effective radical reactions, which has inspired several scientists to also develop efficient and selective synthetic catalysts that operate via radical-type mechanisms. Cobalt porphyrin catalysts, for example, have been used to achieve a wide variety of selective radical transformations including challenging C–H and C=C bond activations.
In addition to the ligands directly connected to the metal center, the second coordination sphere plays a significant role in tuning the reactivity of metallo-enzymes. In order to functionally mimic this second coordination sphere supramolecular cages have been developed. Examples have been shown in which bimolecular decomposition pathways, frequently encountered in metallo-radical catalysis, are already suppressed by partial encapsulation. In this Thesis full encapsulation of catalysts in a cubic supramolecular cage is investigated to completely avoid bimetallic decomposition pathway. Furthermore, supramolecular cages enable pre-organization of the substrate and induce selectivity for specific substrates and products in competitive reactions. In addition, the development of a protocol for cobalt catalyzed formation of N-heterocycles from aliphatic azides, and a detailed mechanistic study regarding this reaction, are also described in this Thesis.