Redox-Inactive Metal Ions That Enhance the Nucleophilic Reactivity of an Alkylperoxocopper(II) Complex

Abstract

The importance of redox-inactive metal ions in modulating the reactivity of redox-active biological systems is a subject of great current interest. In this work, the effect of redox-inactive metal ions (M3+ = Sc3+, Y3+, Yb3+, La3+) on the nucleophilic reactivity of a mononuclear ligand-based alkylperoxocopper(II) complex, [Cu(Pr-i(2)-tren-C(CH3)(2)O-2)](+) (1), was examined. 1 was prepared by the addition of hydrogen peroxide and triethylamine to the solution of [Cu(Pr-i(3)-tren)(CH3CN)](+) (Pr-i(3)-tren = tris[2-(isopropylamino)ethyl]amine) via the formation of [Cu(Pr-i(3)-tren)(O2H)](+) (2) in methanol (CH3OH) at 30 degrees C. 1 was characterized using density functional theory (DFT) calculations and spectroscopic methods such as UV-vis, resonance Raman (rR), and electron paramagnetic resonance (EPR). DFT calculations support the electronic structure of 1 with an intermediate geometry between the trigonal-bipyramidal and square-pyramidal geometries, which is consistent with the observed EPR signal exhibiting a signal with g(perpendicular to) = 2.03 (A(perpendicular to) = 16 G) and g(parallel to) = 2.19 (A(parallel to) = 158 G). The Cu-O bond stretching frequency of 1 was observed at 507 cm(-1) for O-16(2) species (486 cm(-1) for O-18(2) species), and its O-O vibrational energy was determined to be 799 cm(-1) for O-16(2) species (759 cm(-1) for O-18(2) species) by rR spectroscopy. The reactivity of 1 was investigated in oxidative nucleophilic reactions. The positive slope of the Hammett plot (rho = 2.3(1)) with para-substituted benzaldehydes and the reactivity order with 1 degrees-, 2 degrees-, and 3 degrees-CHO demonstrate well the nucleophilic character of this copper(II) ligand-based alkylperoxo complex. The Lewis acidity of M3+ improves the oxidizing ability of 1. The modulated reactivity of 1 with M3+ was revealed to be an opposite trend of the Lewis acidity of M3+ in aldehyde deformylation.