The potential of electromerism for the tuning of redox reactivity on a large scale is demonstrated in a systematic study on copper complexes with redox-active diguanidine ligands.

Abstract

In this work, we demonstrate that electromerism could be used to regulate the redox reactivity. Electron self-exchange rates k _ex were measured for a series of diamagnetic, monocationic Cu^I complexes with two redox-active diguanidine ligands and the corresponding paramagnetic, dicationic complexes. The electronic structures of the paramagnetic, dicationic complexes differ. Some complexes are exclusively present as Cu^II complexes with reduced, neutral diguanidine ligands. In other complexes, an equilibrium is established between the Cu^II electromer and the Cu^I electromer with the unpaired electron delocalized on the two partially-oxidized ligands. For these complexes, the k _ex values increase with increasing contribution of the Cu^I electromer. One of the dicationic molecules is exclusively present as Cu^I complex with radical ligands in dichloromethane at room temperature, and as Cu^II electromer with neutral ligands at 200 K. Consequently, the electron self-exchange rate k _ex is maximal at room temperature, and strongly decreases with decreasing temperature. The temperature effect is much stronger than for similar complexes that remain in the Cu^II form at all temperatures, demonstrating the use of electromerism to control the redox reactivity on a large scale.