Synthesis, characterization and applications of complexes involving redox-active ligands

We developed a new type of redox-active ligand, involving two N-heterocyclic carbenes and two phenolate units. The strong electron donating properties of the NHC moieties were utilized to stabilize complexes in high oxidation states while the phenolate groups were used as redox-active units. Group 10 metal complexes were developed. Their oxidation chemistry showed the formation of phenoxyl radicals, reaching up to two-electron oxidized, bis(phenoxyl) complexes. We also report the first Ni(III) complex with NHC donors. The ligand was also used to develop metal complexes with nitride ligands. The nitridomanganese complex proved to be unstable and degraded in successive intramolecular nitride-NHC reductive couplings. The degradation afforded a peculiar organic salt with three fused rings forming a central triazone pattern. Conversely, the chromium nitride complex could be isolated and thoroughly characterized. The one-electron oxidized product was generated reversibly at low temperature but readily evolved at room temperature. In a parallel work, we also developed new types of sterically hindered salen ligands to form distorted copper salen complexes as molecular models of galactose oxidase. The copper salen catalysts showed to be effective for the aerobic oxidation of non-activated alcohol substrates.