Influence of Functionalized Substituents on the Electron‐Transfer Abilities of Copper Guanidinoquinoline Complexes

Abstract

The influence of functionalized ligands on the electron‐transfer abilities of copper guanidinoquinoline complexes as entatic state models has been examined. An electron donating group (OCH3) or electron withdrawing group (Br) was introduced in 6‐position of the quinoline unit of the ligands TMGqu and DMEGqu. The electron self‐exchange rates k11 of the copper complexes with these ligands were determined using the Marcus cross relation. The k11 values of the functionalized complexes are smaller or equal to the values of their unsubstituted forms. These results were complemented by the examination of the reorganization energies of the electron‐transfer via Eyring theory and DFT calculations. The higher reorganization energies of the [Cu(DMEG6Xqu)2]+/2+ (X = H, Br, OCH3) systems correspond with their decelerated electron‐transfer velocities. Additionally, the calculated molecular electrostatic potentials show the influence of the functional groups on the electron‐transfer. With the addition of the substituent a further charge distribution over the CH3O‐/Br‐group leads to a larger reorganization required during the oxidation reaction. The impact of the functionalization of the ligand on the electron‐transfer of the [Cu(GUA6Xqu)2]+/2+ cations reveals a closer insight in the electronic structure of the complexes and its influence on their electron‐transfer abilities.