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Issue 44, 2019
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Polymer immobilized tantalum(v)–amino acid complexes as selective and recyclable heterogeneous catalysts for oxidation of olefins and sulfides with aqueous H2O2

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Abstract

Polymer supported heterogeneous peroxotantalum(V) catalysts were prepared by anchoring Ta(V)-diperoxo species to chloromethylated poly(styrene–divinylbenzene) resin functionalized with amino acids asparagine (L-Asn) and arginine (L-Arg). The structurally well-defined catalysts, [Ta(O2)2(L)2]-MR, [L = asparagine (catalyst 1) or arginine (catalyst 2) and MR = Merrifield resin], were comprehensively characterized by elemental analysis (CHN, ICP-OES, energy dispersive X-ray spectroscopy), spectral studies (FT-IR, Raman, 13C NMR, diffuse reflectance UV-vis and XPS), SEM, XRD, Brunauer–Emmett–Teller (BET) and thermogravimetric analysis (TGA). The supported peroxotantalum (pTa) compounds displayed excellent catalytic performance in epoxidation of alkenes with 30% H2O2, under solvent free reaction conditions. Styrene was epoxidized with >99% selectivity with the highest TOF of 1040 h−1 obtained within 30 min reaction time, whereas the TOF for norbornene epoxidation was 2000 h−1 within 1 h with >95% epoxide selectivity. Furthermore, the immobilized catalysts facilitated chemoselective oxidation of a broad range of organic sulfides to the desired sulfoxides with H2O2 in methanol, under mild reaction conditions. The oxidations proceeded with a high H2O2 efficiency percentage and are amenable to ready scalability. The heterogeneous catalysts could be easily recovered and reused for several consecutive catalytic cycles with undiminished activity/selectivity profiles in all cases. The developed catalytic strategies are operationally simple and, being free from halogenated solvent or any other toxic auxiliaries, environmentally clean.

Graphical abstract: Polymer immobilized tantalum(v)–amino acid complexes as selective and recyclable heterogeneous catalysts for oxidation of olefins and sulfides with aqueous H2O2

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Publication details

The article was received on 12 Aug 2019, accepted on 13 Oct 2019 and first published on 14 Oct 2019


Article type: Paper
DOI: 10.1039/C9NJ04180J
New J. Chem., 2019,43, 17251-17266

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    Polymer immobilized tantalum(V)–amino acid complexes as selective and recyclable heterogeneous catalysts for oxidation of olefins and sulfides with aqueous H2O2

    G. Saikia, K. Ahmed, C. Rajkhowa, M. Sharma, H. Talukdar and N. S. Islam, New J. Chem., 2019, 43, 17251
    DOI: 10.1039/C9NJ04180J

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