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

Abstract New Cu II complexes [Cu(H 2 O)(μ-L 1 )Na(H 2 O)] n ·2 n H 2 O ( 4 ), [Cu(H 2 O)(μ-HL 2 )Na(H 2 O)] n ·2 n H 2 O ( 5 ) and [Cu(H 2 O)(μ-L 3 )Na(H 2 O)] n ·2 n H 2 O ( 6 ), bearing the SO 3 − or COO − -functionalized arylhydrazones of β-diketones (AHBDs) 3-(2-hydroxy-3-sulfo-5-nitrophenylhydrazone)pentane-2,4-dione (H 3 L 1 , 1 ), 3-(2-hydroxy-3,5-disulfophenylhydrazone)pentane-2,4-dione (H 4 L 2 , 2 ) or 1-ethoxy-2-(2-hydroxy-4-carboxyphenylhydrazone)butane-1,3-dione (H 3 L 3 , 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) [Zn 0.74 Al 0.26 (OH) 2 ]ǀ(NO 3 ) 0.26 ·0.23H 2 O and characterized by X-ray powder diffraction patterns (XRPD), UV–vis, IR spectroscopies, thermogravimetric (TG) and differential thermal (DTA) analyses. The heterogenized Cu II AHBD-LDH systems catalyze the peroxidative oxidation (with TBHP or H 2 O 2 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.