Quantitative Electromerism of a Well-defined Mononuclear Copper Complex Through Reversible Intramolecular...

Copper amine oxidases are enzymes that exhibit in their active site a mononuclear copper complex and a 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor; in the oxidative half of the catalytic cycle, the enzymes regulate their activity by a temperature-dependent electron transfer equilibrium between the Cu^II complex with the reduced, aminoquinol form of the cofactor and the reactive Cu^I complex with the corresponding oxidized, semiquinone form of the cofactor. Here, we report the first mononuclear copper complex with redox-active ligands showing quantitative, reversible electromerism between a Cu^II eletromer with reduced, neutral ligand and a Cu^I electromer with an oxidized, radical monocationic ligand. The Cu^II form, being exclusively present at low temperature, exhibits a lower enthalpy (like the enzymes), but the Cu^I complex exhibits a higher entropy and is exclusively present at room temperature in CH₂ Cl₂ solution. Further analysis, based on six different copper complexes, discloses a large solvent effect on electromerism.