Synthesis and reactivity of first-row transition metal pyridylpyrrolide and bis(pyrrolide)pyridyl complexes: Towards the development of two new redox non-innocent ligand systems for small molecule activation

Transition metal complexes containing redox non-innocent ligands have the capability to store and release electrons while maintaining the metal oxidation state. For chemical processes which require electrons for bond-making or breaking, such metal complexes can provide multiple electrons depending on the character of both the metal and ligand system. A new redox non-innocent ligand platform is the pyridylpyrrolide, with an electron-rich pyrrolide moiety capable of undergoing oxidation, and a pyridyl moiety with an empty π* orbital able to receive an electron upon reduction. In addition, the modular structure of the ligand allows for facile substitution for both electronic and steric tunability. Several metal-pyridylpyrrolide complexes have previously been synthesized, but this work is the first to look at the redox capabilities of the ligand. Reactivity of divalent nickel and copper complexes, as well as monovalent copper complexes, was investigated. Ligand-based oxidations result in alteration of the ligand portion of the complex, and reductions produce unexpected products upon metal-based reactivity. A second ligand platform which contains one pyridyl and two pyrrolide moieties is also developed, and preliminary studies show the ligand is capable of being oxidized by two electrons. An Fe(IV) complex has been synthesized and oxidized by one electron to produce an Fe(IV) complex containing a monoanionic, singly oxidized ligand. This result demonstrates that transition metal complexes containing dianionic bis(pyrrolide)pyridyl ligand can act as potent electron reservoirs for reactions with small molecule substrates.