Immobilization of Palladium in Mesoporous Silica Matrix: Preparation, Characterization, and Its Catalytic Efficacy in Carbon−Carbon Coupling Reactions

Abstract

Palladium(0) has been immobilized into the silica-based mesoporous material to develop catalyst Pd(0)-MCM-41, which is found to be highly active in carbon-carbon coupling reactions. [Pd(NH3)4]2+ ions have been incorporated into the mesoporous material during synthesis of MCM-41 and subsequently upon treatments with hydrazine hydrate Pd2+ ions present in mesoporous silica matrix were reduced to Pd(0) almost instantaneously. The catalyst has been characterized by small-angle X-ray diffraction, N2 sorption, and transmission electron microscopy (TEM). TEM and surface area measurements clearly demonstrate that the immobilization of Pd(0) into the mesoporous silica has a significant effect on pore structure of the catalyst. Nevertheless, after immobilization of palladium the meso-porosity of the material is retained, as evidenced in the nitrogen sorption measurement. The TEM micrograph shows that both MCM-41 and Pd(0)-MCM-41 have similar types of external surface morphology; however, Pd(0)-MCM-41 was less ordered. Pd(0)-MCM-41 showed high catalytic activity toward carbon-carbon bond formation reactions like Heck and Sonogashira coupling, as evidenced in high turn-over numbers. In contrast to many other Pd-based catalysts reported so far, Pd(0)-MCM-41 acts as a truly heterogeneous catalyst in C-C coupling reactions. Notably, the new heterogeneous catalyst is found to be efficient in the activation of arylchloride to give impressive conversion in cross coupling (15-45% for Heck and 30% for Sonogashira) reactions under mild conditions.

Bifunctional Mesoporous Silica Catalyst for C–C Bond Forming Tandem Reactions

“…All previous studies of Sonogashira reactions employed excess amounts of base or K 2 CO 3 , often much more than the stoichiometric ratios. [15,23,25] Thus, a series of Sonogashira reactions using different mol ratios of K 2 CO 3 with respect to 0.5 mmol phenylacetylene and 0.5 mmol iodobenzene were performed. Various mol ratios of K 2 CO 3 with respect to one of the reactants, that is, phenylacetylene or p-iodobenzaldehyde, as both of them are limiting reactants, were used.…”

“…In addition, the bifunctional catalyst was proven to catalyze the Sonogashira reaction without the presence of any toxic or expensive phosphane ligands or copper co-catalysts that are commonly used in Sonogashira reactions. [15,23,25] …”

Silica-supported palladium: Sustainable catalysts for cross-coupling reactions

“…Pd(0)-MCM-41 showed high catalytic activity toward C C bond formation reactions like Heck and Sonogashira coupling, with high TONs. This catalyst was also efficient in the activation of aryl chloride to give impressive conversion in cross-coupling reactions under mild conditions [22].…”

Pd/MOx Materials Synthesized by Sol‐Gel Coprecipitation as Catalysts for Carbon–Carbon Coupling Reactions of Aryl Bromides and Chlorides

“…There are only a few heterogeneous catalysts known up to now that exhibit such high TON (8600-9300) and TOF (1450-1550 h -1 ) in the reaction of an aryl chloride. [11,12,[22][23][24][25] In the reaction of nonactivated aryl chlorides like chlorobenzene only conversions lower than 10 % were observed. A further optimization of the variety of reactions parameters like base or solvent is necessary for improvements in this complex reaction system.…”