Mono-, di- and polynuclear copper(II) compounds derived from N-butyldiethanolamine: structural features, magnetism and catalytic activity for the mild peroxidative oxidation of cyclohexane

Abstract

The new mononuclear [Cu(Hbdea)₂]·2Hdnba (1), dinuclear [Cu₂(μ-Hbdea)₂(N₃)₂] (2) and [Cu₂(μ-Hbdea)₂(pta)₂]·2H₂O (3), and 1D polymeric [Cu₂(μ-Hbdea)₂(μ-tpa)]_n·2nH₂O (4) copper(II) compounds have been prepared by self-assembly, in aqueous alkali medium and at ambient conditions, from Cu(II) acetate, N-butyldiethanolamine (H₂bdea) and the corresponding auxiliary reagents, 3,5-dinitrobenzoic acid (Hdnba), sodium azide, p-toluic acid (Hpta) and terephthalic acid (H₂tpa), respectively. They have been fully characterized by IR spectroscopy, FAB-MS⁺, elemental and single-crystal X-ray diffraction analyses, the latter also revealing intensive intermolecular hydrogen bonding in 2–4, resulting in the extension of the structural motifs and generation of tetrameric aggregates (in 2) and 1D (in 3) or 2D (in 4) supramolecular networks. All compounds constitute the first examples of Cu complexes derived from N-butyldiethanolamine, while 4 represents also the first coordination polymer bearing this ligand. Magnetic susceptibility measurements reveal that compound 1 follows the Curie-Weiss law, whereas 2–4 follow the Bleaney-Bowers dinuclear model displaying antiferromagnetic coupling. Compounds 1–4 act as valuable catalyst precursors for the mild peroxidative oxidation of cyclohexane, by aqueous H₂O₂ in acidic MeCN medium, to cyclohexanol and cyclohexanone with overall yields up to 38%. The effects of various acid additives (promoters) have been studied, showing the preferable use of trifluoroacetic (TFA), nitric and hydrochloric acids.