Facile Immobilization of a Lewis Acid Polyoxometalate onto Layered Double Hydroxides for Highly Efficient N‐Oxidation of Pyridine‐Based Derivatives and Denitrogenation

Abstract

N-Oxides are a class of highly important compounds which are widely used as synthetic intermediates. In this paper, we demonstrate for the first time the use of a polyoxometalate (POM) based composite material, as highly efficient heterogeneous catalyst for the N-oxidation of pyridines and its derivatives in the presence of H2O2 at room temperature. The composite was prepared by intercalation of the [La(PW11O39)2] 11-anion into a tris(hydroxymethyl)aminomethane (Tris) modified layered double hydroxides (LDHs). Additionally, the Tris-LDH-La(PW11)2-based catalyst has been employed for the denitrogenation of a model oil mixture in the presence of [bmim]BF4 and H2O2. Deep denitrogenation can be achieved in 40 minutes at 75 °C. Finally, the heterogeneous catalyst can be easily recovered and reused at least ten times without measurable decrease of the catalytic activity and disintegration of the Tris-LDH-La(PW11)2 structure.

Modular Polyoxometalate–Layered Double Hydroxides as Efficient Heterogeneous Sulfoxidation and Epoxidation Catalysts

“…The FTIR spectrum of La(PW 11 ) 2 exhibits characteristic peaks centred at =1093, 950, 882 and 769 cm −1 (Figure a), which can be attributed to the asymmetric and symmetric vibrations of W−O t , the asymmetric vibration of W−O c −W and the asymmetric vibration of W−O e −W (t, terminal; c, corner sharing; e, edge sharing), respectively. These W−O stretching bands can be observed clearly in the FTIR spectra of Mg 3 Al‐ILs‐La(PW 11 ) 2 and Mg 3 Al‐La(PW 11 ) 2 .…”

“…The FTIR spectrum of La(PW 11 ) 2 exhibits characteristicp eaks centred at n = 1093, 950, 882 and 769 cm À1 (Figure 1a), which can be attributedt ot he asymmetric and symmetric vibrations of WÀO t ,t he asymmetric vibration of WÀO c ÀWa nd the asymmetric vibration of WÀO e ÀW( t, terminal;c ,c orner sharing;e , edge sharing), [22] respectively.T hese WÀOs tretching bands can be observed clearly in the FTIR spectra of Mg 3 Al-ILs-La(PW 11 ) 2 and Mg 3 Al-La(PW 11 ) 2 .Ifw et ake Mg 3 Al-ILs-La(PW 11 ) 2 as an exam-ple, the WÀOs tretching vibrationsl ed to peaks located at n = 1089, 954, 889 and 775 cm À1 ,w hich are slightly shiftedd ue to the strong electrostatic interactions and hydrogen bondingb etween the host layers and intercalated POMs. [23] Moreover, the peak at n = 1051 cm À1 can be assigned to the stretching vibration of the PÀOb ond, which appearsa tn = 1046 cm À1 in the spectrum of La(PW 11 ) 2 .T he FT-IR spectrum of Mg 3 Al-ILs-La(PW 11 ) 2 also exhibits new CÀHs tretching vibrations at n = 2930 and 2856 cm À1 caused by the alkyl chain ÀCH 2 and ÀCH 3 groups,a nd the C=Ns tretching band appears at n = 1658 cm À1 ,w hicho riginates from the imidazole ring of the IL.…”

Polyoxometalate (POM)-Layered Double Hydroxides (LDH) Composite Materials: Design and Catalytic Applications

“…Our group successfully prepared a Lewis acid POM-LDH catalyst by intercalating [La(PW11O39)2] 11− anions into LDH modified with tris(hydroxymethyl)aminomethane (Tris) [56]. As shown in Figure 9, the resulting Tris-LDH-La(PW11)2 composite shows excellent selectivity, high yield, and high efficiency for the N-oxidation of pyridines and its derivatives at room temperature in the presence of H2O2.…”

“…Taking into consideration the fact that POMs possess excellent redox properties while the LDHs have a number of active basic sites that can efficiently Another family of organic compounds that received much attention in recent decades is the heterocyclic N-oxides because of their wide use as versatile synthetic intermediates, their biological significance, their use as protecting groups, as oxidants, as auxiliary agents, as ligands in metal complexes, as surrogates for heterocyclic boronic acids, and catalysts [54,55]. Our group successfully prepared a Lewis acid POM-LDH catalyst by intercalating [La(PW 11 O 39 ) 2 ] 11− anions into LDH modified with tris(hydroxymethyl)aminomethane (Tris) [56]. As shown in Figure 9, the resulting Tris-LDH-La(PW 11 ) 2 composite shows excellent selectivity, high yield, and high efficiency for the N-oxidation of pyridines and its derivatives at room temperature in the presence of H 2 O 2 .…”

Self-Assembly in Polyoxometalate and Metal Coordination-Based Systems: Synthetic Approaches and Developments

“…The formation of LDH-based materials is driven by weak interlayer interactions, and as a consequence, they offer an excellent opportunity for the development of composite compounds by exchanging the anionic and solvent content of the interlayer cavities with the desirable components. For example, exploitation of supramolecular interactions between the LDH layers and POM clusters, have given a wide range of materials with interesting catalytic properties tailored for applications in epoxidations, N-oxidations and desulfurisations [88][89][90][91][92]. …”