Abstract
Oxidovanadium(V) and dioxidovanadium(V) compounds, [VO(OEt)L] (1) and [Et3NH][VO2L] (2), were synthesized using an aroylhydrazone Schiff base (5-bromo-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H2L). They were characterized by elemental analysis, Fourier-transform infrared spectroscopy (FT-IR), (1H and 51V) nuclear magnetic resonance (NMR), electrospray ionization mass spectrometry (ESI-MS) and single crystal X-ray diffraction analyses. Both complexes were immobilized on functionalized carbon nanotubes and activated carbon. The catalytic performances of 1 and 2, homogenous and anchored on the supports, were evaluated for the first time towards the MW-assisted peroxidative oxidation (with tert-butylhydroperoxide, TBHP) of cyclohexane under heterogeneous conditions. The immobilization of 1 and 2 on functionalized carbon materials improved the efficiency of catalytic oxidation and allowed the catalyst recyclability with a well-preserved catalytic activity.
Highlights
IntroductionThe homogenous catalytic systems present some limitations concerning catalyst separation from the reaction products, recycling and potential application to continuous flow processes
We reported the immobilization of six oxidovanadium(V) complexes on various carbon supports and studied their catalytic activities towards oxidation of alkanes and alcohols [13], and recognized advantages of the use of adequately treated carbon nanotubes as supports
In pursuit of our interest in designing metal complexes derived from aroylhydrazones as catalysts for oxidation reactions [4,13,35,36,37,38,39,40,41,42,43,44], we report the synthesis and characterization of an oxidovanadium(V) and a dioxidovanadium(V) complex derived from the aroylhydrazone Schiff base (5-bromo-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H2 L) [36]
Summary
The homogenous catalytic systems present some limitations concerning catalyst separation from the reaction products, recycling and potential application to continuous flow processes These shortcomings can be overcome by anchoring the complexes onto solid supports, and that combination can provide both the useful properties of the homogeneous catalysts and the advantages of the heterogeneous systems [13,14,15,16,17]. The use of carbon materials as supports has additional advantages, given their tunable texture and surface chemistry, able to fit the envisaged applications [17,18,19,20,21,22,23] Several carbon supports, such as activated carbon, carbon nanotubes, mesoporous carbon xerogels, graphenes, nanodiamonds, etc., have been used for this purpose [13,14,15,16,17,18,19,20,21,22,23].
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