Mechanisms in manganese oxidation catalysis with 1,4,7-triazacyclononane based ligands

The first report of catalytic activity of manganese complexes based on the ligand N,N′,N″-trimethyl-1,4,7-triazacyclononane (Me₃tacn) in oxidations with H₂O₂ was in the mid-1990s. Although initially limited by extensive disproportionation of H₂O₂, within a short time solvents and additives were identified that could suppress this wasteful side reaction. These initial successes spurred more general interest in these complexes and over the following quarter century efforts toward broadening substrate scope and controlling (enantio)selectivity have revealed their versatility. In parallel considerable effort has been directed to elucidate the species that can form under a wide range of conditions both for their relevance to bioinorganic chemistry (enzymes and the oxygen evolving complexes) and to identifying species formed during oxidation reactions. In this chapter, the focus is on the spectroscopy and electrochemistry of these complexes and mechanistic insight gained over the last 25 years.