Copper(II) complexes of arylhydrazones of β-diketones immobilized on Zn–Al layered double hydroxides as effective recyclable catalysts for peroxidative oxidation of alkanes

New CuII complexes [Cu(H2O)(μ-L1)Na(H2O)]n·2nH2O (4), [Cu(H2O)(μ-HL2)Na(H2O)]n·2nH2O (5) and [Cu(H2O)(μ-L3)Na(H2O)]n·2nH2O (6), bearing the SO3− or COO−-functionalized arylhydrazones of β-diketones (AHBDs) 3-(2-hydroxy-3-sulfo-5-nitrophenylhydrazone)pentane-2,4-dione (H3L1, 1), 3-(2-hydroxy-3,5-disulfophenylhydrazone)pentane-2,4-dione (H4L2, 2) or 1-ethoxy-2-(2-hydroxy-4-carboxyphenylhydrazone)butane-1,3-dione (H3L3, 3), were synthesized and characterized by elemental analysis, IR spectroscopy, ESI-MS and X-ray analysis (for 4). 4–6 were immobilized on the layered double hydroxides (LDH) [Zn0.74Al0.26(OH)2]ǀ(NO3)0.26·0.23H2O and characterized by X-ray powder diffraction patterns (XRPD), UV–vis, IR spectroscopies, thermogravimetric (TG) and differential thermal (DTA) analyses. The heterogenized CuIIAHBD-LDH systems catalyze the peroxidative oxidation (with TBHP or H2O2 as oxidant) of alkanes (cyclohexane, n-pentane, n-hexane, n-heptane, n-octane) mainly to alcohols, under mild conditions, and can be recycled at least five times without significant loss of activity, with overall yields of 10–15% per cycle depending on the catalyst used. Regioselectivity at position 2 of the alkane is favoured by the heterogenized catalysts.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (130 K)Download as PowerPoint slideHighlights► CuII-arylhydrazones of β-diketones (CuIIAHBD) complexes have been prepared. ► CuIIAHBD immobilized on ZnAl-layered double hydroxides (LDH). ► CuIIAHBD-LDH systems catalyze the peroxidative oxidation of alkanes. ► CuIIAHBD-LDH can be recycled at least five times without activity loss.