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

TheN,N-bis(2-amino-3,5-di-tert-butylphenyl)amine pincer ligand was coordinated to copper. Depending on the copper source, a mononuclear complex1(+)or a trimer2could be isolated and were structurally characterized. Complex1(+)consists of two deprotonated iminobenzoquinone ligands coordinated to a Cu(I) center. Complex2is 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. In2, the metal ions are bridged by an anilido nitrogen. The coordination sphere of each copper is completed to four by a neighboring iminosemiquinone moiety. Complex1(+)belongs to an electron-transfer series. The paramagnetic complexes1and1(2+)were generated and characterized by EPR and Vis-NIR spectroscopy. Complex1exhibits an isotropic resonance at g = 2.00, which is reminiscent of Cu(I) iminosemiquinone species. The dication1(2+)exhibits a metal-based ground spin state and hence is described as a Cu(II) iminobenzoquinone complex. Both1and1(+)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 of1produces2via ligand release and disproportionation. Conversely, oxidation of2affords1(+). Finally, carbon-nanotube-supported complex2is active towards electrocatalytic reduction of H2O2.

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