Buddhadeb Dutta

Immobilization of palladium in mesoporous silica matrix: preparation, characterization, and its catalytic efficacy in carbon-carbon coupling reactions.

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.

Catalytic olefin epoxidation over cobalt(II)-containing mesoporous silica by molecular oxygen in dimethylformamide medium

A cobalt(II) Schiff base complex has been immobilized onto the surface of Si–MCM-41 to prepare a new catalyst. The amine group-containing organic moiety 3-aminopropyl-triethoxysilane had first been anchored on the surface of Si–MCM-41 via a silicon alkoxide route. Upon condensation with salicylaldehyde, the amine group affords a bidentate Schiff-base moiety in the mesoporous matrix, which is subsequently used for anchoring of cobalt(II) centers. The prepared catalyst has been characterized by UV-vis, infrared (IR), EPR spectroscopic and small angle X-ray diffraction (XRD) analyses, and N2 sorption studies. The catalytic activity was tested in epoxidation reactions of olefinic compounds, including styrene and allyl alcohol, with molecular oxygen at atmospheric pressure in dimethylformamide medium in the absence of additional sacrificial reductant. The reactions seemed to proceed through a radical formation mechanism. The immobilized catalyst showed good activity and epoxide selectivity in the alkene epoxidation. Notably, the catalyst can be recovered and reused without any loss of activity.

Synthesis of symmetrically functionalized oligo(p-phenylenevinylene) by Pd-catalyzed Heck coupling reaction

A facile method for synthesis of end-substituted oligo(p-phenylenevinylene) (OPV) with hydrophilic poly(ethylene glycol) (PEG) segment has been established using Pd(0)-catalyzed Heck coupling reaction. The OPVs are symmetrically end-substituted with a hydrophilic poly(ethylene glycol) segment. The prepared oligo(phenylenevinylene)s exhibit the expected photoluminescence properties.

Facile synthesis of palladium nanoparticles in Y-zeolite matrix: an efficient catalyst for Heck coupling reaction

A new facile and reliable route for synthesis of nano-sized Pd(0) particles onto zeolitic matrix has been developed. [Pd(NH3)4] 2+ ions have been first immobilised in NaY matrix by ion exchange, then upon reaction with hydrazine hydrate [Pd(NH3)4] 2+ ions were directly reduced to nano-sized Pd(0) particles almost instantaneously. Transmission electron microscopic (TEM) analysis reveals that well separated nano-sized (10-20 nm) palladium(0) particles have been formed onto the surface of the zeolite crystals. X-ray powder diffraction analysis supports that the particles are highly dispersed in the zeolite matrix. The prepared nano-composite is found to be highly catalytically active in a variety of Heck cross-coupling reactions.