Copper(I)-Dioxygen Reactivity in the Isolated Cavity of a Nanoscale Molecular Architecture

Copper(I) and copper(II) complexes supported by a bulky tetradentate N-4 ligand, [Cu-I(TIPT(3)tren)(CH3CN)]ClO4 (1) and [Cu-II(TIPT(3)tren)Cl]BF4 (2), were synthesized and characterized, where TIPT is 2,2,6,6-tetraisopropyl-1,3:5,1-terphenyl and tren is tris(2-aminoethyl)amine. The copper(II) chloride complex 2 exhibits a trigonal-bipyramidal structure, as usually observed for the tren ligand system, in which the chloride ligand occupies an axial position and is encapsulated in an isolated cavity consisting of three TIPT substituents. Such a trigonal-bipyramidal structure is stabilized in acetone, in which hydrogen-bonding interactions between the anilino N-H groups and the oxygen atom of the acetone molecules, entrapped in the hydrophobic clefts between the TIPT substituents, play an important role. The reaction of copper(I) complex 1 and O-2 in an acetone-containing solvent at -110 degrees C gave end-on copper(II) superoxide complex 3 together with putative side-on copper(III) peroxide complex 4, as was evident from detailed studies by variable-temperature UV/Vis, resonance Raman, and H-1 and H-2 NMR spectroscopy. The formation of 3 and 4 was also validated by DFT calculations.