Catalytic system having an organotellurium ligand on graphene oxide: immobilization of Pd(0) nanoparticles and application in heterogeneous catalysis of cross-coupling reactions

First heterogeneous catalytic system, having a covalently linked hybrid bidentate organotellurium ligand [i.e., PhTe-CH2-CH2-NH2] on the surface of graphene oxide, has been synthesized with immobilized and stabilized Pd(0) nanoparticles. To the best of our knowledge, it is the first such catalytic system in which a heterogenized organotellurium ligand has been used. It has been well-characterized using different physicochemical characterization techniques viz. P-XRD, XPS, HR-TEM, EELS, FE-SEM, EDX, TGA, BET surface area analysis, FT-IR spectroscopy, and Raman spectroscopy. The Pd content of the final system has been quantified using ICP-OES. Its applications have been explored in Suzuki-Miyaura C-C cross coupling and C-O cross coupling reactions. Hot filtration experiments corroborate the heterogeneous nature of the catalysis. It is recyclable for up to five reaction cycles in Suzuki-Miyaura and C-O cross coupling with marginal loss in performance. It also catalyzes the reactions of chloroarenes such as chlorobenzene, 4-chloroaniline, 1-chloro-4-nitrobenzene, 4-chloroacetophenone, 4-chlorobenzophenone for Suzuki coupling, and 1-chloro-4-nitrobenzene, 4-chlorobenzonitrile, chlorobenzene, and 4-chlorotoluene for C-O coupling. P-XRD, FE-SEM, and EDX study reveals that the catalytic system retains its structural originality and functionality after recycling.

Reusable Catalyst for Transfer Hydrogenation of Aldehydes and Ketones Designed by Anchoring Palladium as Nanoparticles on Graphene Oxide Functionalized with Selenated Amine

The treatment of graphene oxide with ClCH₂COOH, thionyl chloride, and 2-(phenylselenyl)ethylamine successively has resulted in functionalization of its surface with selenated ethylamine molecules which may act as chelating (Se, N) ligands. The graphene oxide grafted with (Se, N) donor sites (GO-Se) on treatment with Na₂PdCl₄ and NaOH gave GO-Se anchored with Pd(0) nanoparticles (NPs) (GO-Se-Pd). The X-ray diffraction (powder), FT-IR, XPS, Raman spectroscopy, thermogravimetric analysis (TGA), and electron microscopic techniques (SEM and HR-TEM) authenticated the formation of GO-Se-Pd. The distribution of Pd(0) NPs of size ∼1-3 nm on GO-Se was found nearly uniform. The transfer hydrogenation of carbonyl compounds (aldehydes/ketones) with 2-propanol was catalyzed with GO-Se-Pd. The catalyst equivalent to 0.25 mol % of Pd was sufficient to convert aldehydes and ketones to alcohols in good yield (nearly quantitative for some substrates) and found somewhat more efficient for aldehydes than ketones. The reusability of GO-Se-Pd studied for transfer hydrogenation of 4-anisaldehyde to the corresponding alcohol can be understood by ∼96% conversion even in the sixth catalytic run. Flame AAS analysis of GO-Se-Pd revealed negligible leaching of Pd even after the sixth catalytic reaction cycle. Hot filtration experiments suggested the heterogeneous nature of the catalyst.