Complexes of the Bis(di‐ tert ‐butyl‐aniline)amine Pincer Ligand: The Case of Copper

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 1 2+ 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 1 2+ 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 m m –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 H 2 O 2 .