Mild oxidative functionalization of alkanes and alcohols catalyzed by new mono- and dicopper(II) aminopolyalcoholates

The new mono- and dicopper(II) complexes [Cu(H3L1)(NCS)] (1) and [Cu2(μ-HL2)2(NCS)2] (2) were easily self-assembled from Cu(CH3COO)2·H2O, NaNCS, NaOH and N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine (H4L1) or N-ethyldiethanolamine (H2L2), respectively. They were fully characterized by IR spectroscopy, ESI-MS(±), elemental and single-crystal X-ray diffraction analyses, and applied as homogeneous catalysts for (i) the oxidation of alkanes by t-BuOOH in air to alkyl peroxides, alcohols and ketones, and in turn the oxidation of alcohols to ketones, and (ii) the single-pot aqueous medium hydrocarboxylation, by CO, H2O and K2S2O8, of various linear and cyclic Cn (n = 5–8) alkanes into the corresponding Cn+1 carboxylic acids. Compound 1 was significantly more active in the oxygenation of alkanes and oxidation of alcohols, allowing to achieve 18% yield (TON = 800) of oxygenates in the oxidation of cyclohexane, and 78% yield (TON = 780) of cyclohexanone in the oxidation of cyclohexanol. In alkane hydrocarboxylations, 1 and 2 exhibited comparable activities with the total yields (based on alkane) of carboxylic acids attaining 39%. The selectivity parameters for oxidative transformations were measured and discussed, supporting free-radical mechanisms.

Graphical abstractNew mono- and dicopper(II) complexes bearing aminopolyalcoholate N,O-ligands have been easily self-assembled and shown to act as versatile homogeneous catalysts for the oxygenation of alkanes and alcohols as well as the hydrocarboxylation of different alkanes, under mild conditions.Figure optionsDownload full-size imageDownload high-quality image (205 K)Download as PowerPoint slideHighlights► Synthesis and X-ray crystal structures of mono- and dicopper(II) complexes. ► Homogeneous oxidation catalysts. ► Oxidation of alkanes and alcohols by t-BuOOH. ► Cu-catalyzed transformation of cyclic and linear Cn alkanes to Cn+1 carboxylic acids.