Self-assembly generation, structural features, and oxidation catalytic properties of new aqua-soluble copper(ii)-aminoalcohol derivatives

Abstract

Self-assembly reactions of copper(II) nitrate with aminoalcohols {bis(2-hydroxyethyl)amino-tris(hydroxymethyl)methane (H₅bis-tris) or 1,3-bis(tris(hydroxymethyl)methylamino)propane (H₆bis-tris-propane)} as main N,O-building blocks, and isonicotinic acid (Hinic) or sodium azide (NaN₃) as ancillary ligand sources resulted in two new copper(II) compounds [{Cu(H_4.5bis-tris)(inic)}₂](NO₃)·2H₂O (1) and [Cu(H₅bis-tris-propane)(N₃)]·2H₂O (2). The obtained products were isolated as stable microcrystalline solids and fully characterized including by single-crystal X-ray diffraction, which disclosed the six-coordinate copper(II) centers with distorted octahedral {CuN₂O₄} or {CuN₃O₃} environments. The structures of 1 and 2 feature the formation of complex 3D H-bonded networks that were topologically classified as cbs-3,4-Cmmm-2 and sxd underlying nets, respectively. Both compounds 1 and 2 are soluble in water (S_{25 °C} ≈ 6–12 mg mL⁻¹) and act as efficient homogeneous catalysts for the mild and acid-promoter-free oxidation, by aqueous hydrogen peroxide, of C₅–C₈ cycloalkanes (cyclopentane, cyclohexane, cycloheptane, and cyclooctane) to give the corresponding cyclic alcohols and ketones. The influence of various reaction parameters (time, solvent composition, loading of substrate, oxidant, and catalyst, presence of a radical trap), bond- and regioselectivity features, and substrate scope were investigated and discussed in detail. A notable feature of the present catalysts concerns their high activity without the requirement for any promoter or co-catalyst, resulting in up to 46% total product yields based on cycloalkane.