Reusable Mesoporous Solid-Based Pd Catalysts for C-C bonds formation OF Water
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Abstract
Environmentally benign, operationally simple, and robust reactions,particularly those employing reusable solid catalysts andwater as a solvent, are of significant interest to the chemical industry.Here, heterogeneous palladium catalysts supported onordered mesoporous carbonaceous nanocomposites includingcarbon-silica, CoO-C and quaternary ammonium phase transferagent modified mesoporous carbonaceous resins, were appliedto the water-mediated C-C bonds formation.The mesoporous Pd/CoO-C catalyst showed a high yield of biphenyl(49 %) in the water-mediated Suzuki coupling reactionof chlorobenzene and phenylboronic acid. Product yields inthe reaction of aryl chlorides containing electron-withdrawinggroups attached to their benzene ring can reach approximately90 %. Very small Pd clusters consisting of approximately 3atoms and Pd-O bonds formed on the interface between CoOand Pd nanoparticles. The unsaturated coordinative Pd may beresponsible for the activation of chlorobenzene in the absenceof any additives or ligands. A nitrogen-containing functionalgroup modified and ordered mesoporous resin material wasalso used to support a reusable solid Pd catalyst. The graftedquaternary N coordination with highly dispersed Pd NPscreates an electronically rich environment for surface atomsand causes a distinct enhancement in the stabilization and accessibilityof these particles to organic substances in aqueoussolution. The mesoporous Pd catalysts are active in the C-2arylation of N-methylindole when water is used as the solventwithout any other additive or the exclusion of air. The catalysislikely occurs on the Pd surface rather than in solution.Thiol-functionalized mesoporous silica, which can trap solublePd species, was used to confirm the negligible leaching insolution and therefore heterogeneous reaction. These heterogeneouscatalyst are stable, showing unobvious activity loss afterten catalytic runs.Additionally, uniform mesopores and the hydrophobic natureof the carbon support may also facilitate the mass transfer ofthe reactant molecules and enrichment inside pores.
