Layered Double Hydroxide Supported Nanopalladium Catalyst for Heck-, Suzuki-, Sonogashira-, and Stille-Type Coupling Reactions of Chloroarenes

Abstract

Layered double hydroxide and Merrifield resin supported nanopalladium(0) catalysts are prepared by an exchange of PdCl(4)(2-) followed by reduction and well characterized for the first time. The ligand-free heterogeneous layered double hydroxide supported nanopalladium (LDH-Pd(0)) catalyst using the basic LDH in place of basic ligands indeed exhibits higher activity and selectivity in the Heck olefination of electron-poor and electron-rich chloroarenes in nonaqueous ionic liquids (NAIL) over the homogeneous PdCl(2) system. Using microwave irradiation, the rate of the Heck olefination reaction is accelerated, manifold with the highest turnover frequency ever recorded in the case of both electron-poor and electron-rich chloroarenes. The basic LDH-Pd(0) shows a superior activity over a range of supported catalysts, from acidic to weakly basic Pd/C, Pd/SiO(2,) Pd/Al(2)O(3), and resin-PdCl(4)(2-) in the Heck olefination of deactivated electron-rich 4-chloroanisole. The use of LDH-Pd(0) is extended to the Suzuki-, Sonogashira-, and Stille-type coupling reactions of chloroarenes in an effort to understand the scope and utility of the reaction. The catalyst is quantitatively recovered from the reaction by a simple filtration and reused for a number of cycles with almost consistent activity in all the coupling reactions. The heterogeneity studies provide an insight into mechanistic aspects of the Heck olefination reaction and evidence that the reaction proceeds on the surface of the nanopalladium particles of the heterogeneous catalyst. TEM images of the fresh and used catalyst indeed show that the nanostructured palladium supported on LDH remains unchanged at the end of the reaction, while the XPS and evolved gas detection by TGA-MS of the used catalyst identify ArPdX species on the heterogeneous surface. Thus, the ligand-free nanopalladium supported on LDH, synthesized by the simple protocol, displays superior activity over the other heterogeneous catalysts inclusive of nanopalladium in the C-C coupling reactions of chloroarenes.

Synthesis and property of polymer nanospheres with Pd/P4VP shells via surface RAFT polymerization

“…The oxidation form of Pd is possibly palladium oxide, which may result from the surface oxidation of palladium nanoparticles when they are exposed to air. A similar phenomenon was also reported by others [42,43].…”

“…The two peak components at the BEs [36,42]. The other set of peaks at 337.7 eV (Pd 3d 5/2 ) and 342.9 eV (Pd 3d 3/2 ) is ascribed to the Pd 2+ [38,43]. Calculating the integration areas of these two doublets using XPS-PEAK software, it can be estimated that the atomic ratio of Pd 0 /Pd 2+ was about 59:41.…”

“…The increased oxidation form of Pd possibly results from the surface oxidation of palladium nanoparticles during the Heck reaction [42,43].…”

A hydrotalcite-based catalyst system for the single-stage liquid-phase synthesis of MIBK

“…The deposition of highly dispersed Pd supported on hydrotalcites has been executed using various synthesis methods, such as co-precipitation [18], deposition-precipitation [26], impregnation [27][28][29] or by use of Pd clusters in a polymer [30]. However, the main focus of these studies was on the hydrogenation reaction and no attention has been given on the basic function.…”

Functional Materials - Syntheses, Characterisation and Catalytic Applications

“…73,74 For example, palladium supported on calcined MgAl-LDH has been used for the one-pot synthesis of 4-methyl-2-pentanone (methyl isobutylketone) from acetone and hydrogen at an atmospheric pressure. 75 Choudary et al 76 studied Pd(0) catalysts supported on MgAl-LDHs prepared by ion-exchange with PdCl 4 2− , followed by reduction. They observed that the catalysts, used in ionic liquids, not only exhibited higher activity and selectivity than the homogeneous PdCl 2 system in the Heck olefination of electron-poor and electron-rich chloroarenes, but also showed superior activity in the C-C coupling reactions of chloroarens compared with other heterogeneous catalysts involving Pd(0) on supports such as silica, alumina or Merrifield's resin.…”