Département de chimie moléculaire

The N,N-bis(2-amino-3,5-di-tert-butylphenyl)amine pincer ligand was coordinated to copper. Depending on the copper source, a mononuclear complex 1+ or a trimer 2 could be isolated and were structurally characterized. Complex 1+ consists of two deprotonated iminobenzoquinone ligands coordinated to a Cu(I) center. Complex 2 is trinuclear with a (3:3) (M:L) stoichiometry, featuring a three-fold repetition of a unit made of a Cu(II) center coordinated to a tridentate ligand radical-dianion. In 2, the metal ions are bridged by an anilido nitrogen. The coordination sphere of each copper is completed to four by a neighboring iminosemiquinone moiety. Complex 1+ belongs to an electron-transfer series. The paramagnetic complexes 1 and 12+ were generated and characterized by EPR and Vis-NIR spectroscopy. Complex 1 exhibits an isotropic resonance at g = 2.00, which is reminiscent of Cu(I) iminosemiquinone species. The dication 12+ exhibits a metal-based ground spin state and hence is described as a Cu(II) iminobenzoquinone complex. Both 1 and 1+ show a NIR band (954, 980 nm) of high intensity (> 20 mm–1 cm–1) assigned to ligand-based charge transfer transitions. Two-electron reduction of 1 produces 2 via ligand release and disproportionation. Conversely, oxidation of 2 affords 1+. Finally, carbon-nanotube-supported complex 2 is active towards electrocatalytic reduction of H2O2.