Copper (Cu) is one of the most abundant and less toxic transition metals compared to metals lower on the periodic table. Rich in redox chemistry, Cu is able to undergo oxidation/reduction with O2 or H2O2 as oxidant to perform organic transformations. Inspired by the reactivity of previously describe bidentate Cu complexes, our lab has synthesized new tridentate Cu-complexes equipped with tunable hydrogen bonding. In this project, tridentate Cu-complexes are made with different ligand scaffolds and anions. Single Crystal X-ray crystallography shows that the mononuclear Cu cores are stabilized via two intramolecular H-bonds between ureanyl H-donor of the ligand and the coordinated anions. Shorter H-bonds are observed in complexes bonded with more basic anions and more electronwithdrawing ureanyl substituents. Three oxidation states of the system are observed by CV and characterized by UV-vis absorption, electron paramagnetic resonance (EPR) and X-ray absorption spectroscopies (XAS), which indicate that redox couples are ligand-localized. The reactivity of the complexes in their highest oxidation states towards substrates with weak O-H bond (e.g. 4-substituted-2,6-di-tert-butylphenols) indicates that these complexes act as 2H+/2e- oxidants, differing from the 1H+/1e- reactivity of well-studied [CuOH]2+ system.

Redox-active tridentate copper complexes with symmetric tunable hydrogen bonds

ACS Spring Meeting 2021

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