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Facile hydrogenation of N-heteroarenes by magnetic nanoparticles supported sub-nanometric Rh catalysts in aqueous medium

Abstract

The hydrogenation of nitrogen-containing heterocyclic precursors in aqueous medium at low temperature without imposing molecular hydrogen pressure, is quite challenging. Herein, we report the synthesis and performance of a novel catalyst capable of facile hydrogenation (employing tetrahydroxydiboron (THDB) as the reductant) of N-heteroarenes in water at 80 C with good recyclability. Rhodium particles in the sub-nano region (< 1 nm) were produced by in-situ reduction of a Rh precursor on freshly prepared superparamagnetic iron oxide nanoparticles (SPIONs, Fe3O4), using aqueous ammonia as the reducing agent at 50 C. HRTEM images and elemental mapping reveal homogenous distribution of < 1 nm Rh particles within the matrix of Fe3O4 nanoparticles having average size was within a narrow range of 7-9 nm. The superparamagnetic nature of the composite was confirmed by VSM analysis. The Rh@Fe3O4 catalyst was found to be highly efficient in the heterogeneous hydrogenation of nitrogen-containing heterocyclic compounds with quantitative conversion. It showed selectivity towards the hydrogenation of 1,2,3,4-tetrahydroquinoline (py-THQ) in water using THDB with very high TOF of 2500 h-1. These results are compared with the conversion and selectivity data obtained from the reduction by molecular hydrogen gas pressure. The catalytic activity is extended to the successful hydrogenation of simple aromatics like benzene, toluene etc. Isotopic labelling studies were performed to know the source of hydrogen in quinoline hydrogenation in presence of THDB. It was found that it could be used for 16 consecutive cycles with gaseous hydrogen, without any undesired byproducts; it also retained its original crystallinity.

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Publication details

The article was received on 09 May 2018, accepted on 27 Jul 2018 and first published on 09 Aug 2018


Article type: Paper
DOI: 10.1039/C8CY00936H
Citation: Catal. Sci. Technol., 2018, Accepted Manuscript
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    Facile hydrogenation of N-heteroarenes by magnetic nanoparticles supported sub-nanometric Rh catalysts in aqueous medium

    M. N. N. Shaikh, A. N. Kalanthoden, A. Helal, Md. A. Aziz, M. Bououdina and A. Syed, Catal. Sci. Technol., 2018, Accepted Manuscript , DOI: 10.1039/C8CY00936H

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