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 Cu-II complexes [Cu(H2O)(mu-L-1)Na(H2O)](n)center dot 2nH(2)O (4), [Cu(H2O)(mu-HL2)Na(H2O)](n)center dot 2nH(2)O (5) and [Cu(H2O)(mu-L-3)Na(H2O)](n)center dot 2nH(2)O (6), bearing the SO3- or COO--functionalized arylhydrazones of beta-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)]vertical bar(NO3)(0.26)center dot 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 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. (C) 2012 Elsevier B.V. All rights reserved.