Merrifield resin supported peroxomolybdenum(vi) compounds: recoverable heterogeneous catalysts for the efficient, selective and mild oxidation of organic sulfides with H2O2

Abstract

We have generated new heterogeneous catalysts by immobilizing dioxomonoperoxomolybdenum(VI) on amino acid functionalized Merrifield resin, which exhibit excellent activity, stability and selectivity for the oxidation of thioethers and dibenzothiophene (DBT) to the corresponding sulfoxides or sulfones by H 2 O 2 at ambient temperature. The synthetic protocols are high-yielding, halogen-free, environmentally clean and safe, and operationally simple. The catalysts, [MoO 2 (O 2 )(L) 2 ] 2− -MR [L = valine (MRVMo) or alanine (MRAMo) and MR = Merrifield resin] were prepared by reacting H 2 MoO 4 with 30% H 2 O 2 and the respective amino acid functionalized resin, at near neutral pH. The compounds were characterized by elemental analysis, spectral studies (FTIR, Raman, 13 C NMR and 95 Mo NMR, diffuse reflectance UV-Vis and XPS), SEM, EDX, XRD, Brunauer-Emmett-Teller (BET) and TGA-DTG analysis. The easy recyclability of the catalysts for several catalytic cycles without change in activity and selectivity, their complete chemoselectivity towards the sulfur group of substrates bearing other oxidation prone functional groups, are important "green" attributes of these catalysts. † Electronic supplementary information (ESI) available: 13 C NMR chemical shifts and thermogravimetric data, N 2 adsorption/desorption isotherms, FTIR spectra, bar diagram for the recyclability of the catalyst, calculation for the efficiency of H 2 O 2 , characterization of sulfoxides and sulfones. See

Macromolecular peroxo complexes of Vanadium(V) and Molybdenum(VI): Catalytic activities and biochemical relevance

“…Our interest in attaching pMo species to insoluble polymer resin to obtain macrocomplexes has been stimulated mainly by the prospect of generating newer potential heterogeneous catalysts for organic oxidations. We have selected two types of polymer matrices for immobilization of pMo species, viz., amino acid functionalized Merrifield resin (MR) 66 and poly(acrylonitrile) (PAN). 65 PAN was chosen due to its being an insoluble, non-toxic, cost-effective and commercially available reagent.…”

“…[ 66 The synthesis of the poly(acrylonitrile) anchored compound, PANMo was achieved by allowing the polymer to swell in a reaction mixture consisting of peroxomolybdenum species, generated in situ by reacting H 2 MoO 4 with 30% H 2 O 2 . 65 The compounds were characterized by elemental analysis, spectral studies (FTIR, 13 C NMR and 95 Mo NMR and diffuse reflectance UV-Vis), SEM, EDX, Brunauer-Emmett-Teller (BET) and TGA-DTG analysis.…”

“…We have generated a series of polymer-bound complexes by anchoring peroxo species of V(V), Mo(VI) or W(VI) to pendant functional groups of WSPs, 61-63 as well as insoluble polymer resins. [64][65][66] Interestingly, the soluble macrocomplexes exhibited unique oxidant activity as well as biochemical properties including anti-bacterial 61 and enzyme inhibitory activities. 62,63 Significantly, immobilization of the pV and pMo species enhanced their stability as well as their ability to resist degradation under the effect of the enzyme catalase.…”

“…65 The catalysts exhibit excellent activity, stability and selectivity for oxidation of thioethers and dibenzothiophene (DBT) to the corresponding sulfoxides by 30% H 2 O 2 , one of the most sustainable oxidant, at ambient temperature. 66 In addition, a pair of pMo and pW compounds supported on poly(acrylonitrile) matrix heterogeneously catalyzed oxidative bromination of range of activated aromatic substrates with H 2 O 2 65 under ecologically acceptable reaction conditions. These interesting features highlight the synthetic value of the catalytic protocols.…”

“…61 In view of these interesting findings, anchoring of peroxometallates to WSPs has recently been recognized as a promising new field. 10 Furthermore, a set of new heterogeneous catalysts have been developed by immobilization of pMo species on insoluble polymer supports viz., amino acid functionalized Merrifield resins 66 and poly(acrylonitrile). 65 The catalysts exhibit excellent activity, stability and selectivity for oxidation of thioethers and dibenzothiophene (DBT) to the corresponding sulfoxides by 30% H 2 O 2 , one of the most sustainable oxidant, at ambient temperature.…”