Complexation-Induced Reduction of Cu^II to Cu^I Promoted by a Distorted Tetrahedral N₄-Type Schiff-Base Ligand

Although spontaneous or complexation-induced reductions of CuII to CuI have occasionally been observed, controlling these processes remains a challenge. Herein, we report the synthesis of CuI complexes via the complexation-induced reduction of CuII complexes with pyridine-containing N4 Schiff-base ligand L incorporating a biphenyl unit (L = N,N'-([1,1'-biphenyl]-2,2'-diyl)bis(1-(6-methylpyridin-2-yl)methanimine)). Such a reduction has not yet been observed in previously reported CuII complexes with pyridine-containing N4 Schiff-base ligands, strongly suggesting that the torsional distortion of the ligand framework induced by the biphenyl moiety effectively promotes the complexation-induced reduction of CuII to CuI. The CuI complexes were thoroughly characterized by 1H NMR spectroscopy, UV–vis–NIR spectroscopy, and single-crystal X-ray diffraction analyses. The [CuI(L)]+ complex undergoes a reversible redox process with its oxidized species, which was identified as a CuII complex based on spectroelectrochemical measurements and theoretical calculations.