A Copper(I) Complex with Two Unpaired Electrons, Synthesised by Oxidation of a Copper(II) Complex with Two Redox‐Active Ligands

Two homoleptic copper(II) complexes [Cu(L1)(2)] and [Cu(L2)(2)] with anionic redox‐active ligands were synthesised, one with urea azine (L1) and the other with thio‐urea azine (L2) ligands. One‐electron oxidation of the complexes initiates an unprecedented redox‐induced electron transfer process, leading to monocationic copper(I) complexes [Cu(L1)(2)](+) and [Cu(L2)(2)](+) with two oxidised ligands. While [Cu(L1)(2)](+) is best described as a Cu(I) complex with two neutral radical ligands that couple antiferromagnetically, [Cu(L2)(2)](+) is a Cu(I) complex with two clearly different ligand units in the solid state and with a magnetic susceptibility close to a diamagnetic compound. Further one‐electron oxidation of the complex with L1 ligands results in a dication [Cu(L1)(2)](2+), best described as a Cu(I) complex with a twofold oxidised, monocationic ligand and a neutral radical ligand. The stability in at least three redox states, the accumulation of spin density at the ligands and the facile ligand‐metal electron transfer make these complexes highly attractive for a variety of applications; here the catalytic aerobic oxidation of alcohols to aldehydes is tested.