Heterogeneous hydrogenation of bicyclo[2.2.2]octenes on Rh/TPPTS/LDH catalysts

The Rh-TPPTS complex was heterogenized onto layered double hydroxides (LDH) Zn3AlCl and Co2FeCO3 using ion-exchange procedure. Before ion exchange, the Rh precursor [Rh(cod)Cl]2 was dissolved together with the TPPTS ligand in deionised water and stirred for 12 h. After stirring, the LDH was added to the solution and stirred for another 24 h, then filtered, washed with deionised water, and dried under vacuum at room temperature for 16 h. The characterization of the catalysts was carried out using several techniques: ICP-AES, N2 adsorption–desorption isotherms at −196 °C, thermal analysis, powder X-ray diffraction, XPS and DRIFTs. Substrates were prepared via Diels–Alder reaction of various 2H-pyran-2-ones with N-substituted maleimides in an aqueous medium with microwave irradiation. The catalytic tests were performed in a stirred stainless-steel autoclave using H2 pressures in the range 20–40 atm, 30 mg catalyst and 30 mg substrate, at different temperatures. Hydrogenation of bicyclo[2.2.2]octenes showed that these strained and functionalized cycloadducts were inert to classic catalysts but could be hydrogenated by using ionic-immobilized Rh-ligand complexes on the LDH. The Rh-TPPTS/Zn3AlCl was found to exhibit a pretty high activity and selectivity for such reactions leading to heteropolycyclic derivatives. The heterogeneous catalyst was easily recycled with no leaching.

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