Synthesis of dendrimers terminated by DABCO ligands and applications of its palladium nanoparticles for catalyzing Suzuki–Miyaura and Mizoroki–Heck couplings

Abstract

A new kind of silica-supported third-generation dendrimers capped by 1,4-diaza-bicyclo[2.2.2]octane (DABCO) group-stabilized palladium(0) nanoparticles, and their enhanced catalytic activity in Suzuki-Miyaura and Mizoroki-Heck reactions in excellent yield under mild conditions, was reported. The resulting silica-supported dendrimer-stabilized palladium(0) nanoparticles with a particle size of 10-20 nm were prepared in situ by treatment with PdCl 2 and hydrazine in ethanol at 60 C for 24 h. The catalyst as prepared was characterized by FT-IR, X-ray diffraction, thermal analysis, elementary analysis (EA), scanning electron microscopy and transmission electron microscopy. Recycling experiments showed that the catalyst could be easily recovered by simple filtration and reused for up to five cycles without losing its activity.

Dendrimer-Stabilized Ru Nanoparticles Immobilized in Organo-Silica Materials for Hydrogenation of Phenols

“…According to TEM data (Figure 1), dendr-G2-meso-SiO 2 support had a structure with straight hexagonal channels of SBA-15 type [53,66]. Herein the pore diameter was 5.5-7.5 nm.…”

“…Therefore they were not removed from the carrier structure, which is typical in a number of works, using dendrimers only as templates for regular pore formation and uniform particle size distribution [41,[71][72][73]. Herein the sol-gel method allows diffusion limitations to be avoided, inevitable, when bulky dendrimer or dendron is anchored to the surface of ready carrier [64][65][66][67][68][69]. The materials obtained were characterized by infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS) and solid-state nuclear magnetic resonance (NMR) spectroscopy, that confirmed the presence in their structures of fragments, inherent in the SiO 2 bulk support [74,75] [76][77][78][79][80].…”

“…Traditional hybrid catalysts, based on amorphous or mesoporous silica and PPI or PAMAM dendrimers, are synthesized via dendron immobilization onto the surface of ready carrier [41,[63][64][65][66][67][68][69][70]. These materials are characterized by low dendrimer content and irregular dendrimer coating of the surface: anchoring of subsequent bulky dendrons is hindered due to diffusion limitations (bulky dendrons interfere with each other).…”

Engineered mesoporous ionic‐modified γ‐Fe2O3@hydroxyapatite decorated with palladium nanoparticles and its catalytic properties in water

“…Functionalization of a support by organic ligands, containing nitrogen, sulfur, silicon, phosphorus or carbon as coordinating atoms to the metal surface, has been used to stabilize nanoparticles against aggregation and increase their anchorage and also improve their catalytic activity . 1,4‐Diazabicyclo[2.2.2]octane (DABCO) has been used as a catalyst for some organic transformations such as aza‐Michael addition, Knoevenagel condensation, allylic trifluoromethylthiolation of Morita–Baylis–Hillman carbonates, N ‐methylation of indoles and nucleophilic substitution reactions of benzyl halides.…”

Terephthalic acid derived ligand‐stabilized palladium nanocomposite catalyst for Heck coupling reaction: without surface‐modified heterogeneous catalyst

“…Aminopropyl‐functionalized clay has been used as a support to prepare a palladium nanocatalyst for Heck and Suzuki cross‐coupling reactions . Whereas a colloidal catalyst was not recycled quantitatively, with some exceptions on heterogeneous supports (such as silica, zeolites, carbon nanotubes, graphite oxide and graphene, polymers, metal–organic frameworks), on the other hand, surface‐modified palladium nanocomposites were used as heterogeneous catalysts wherein effective recovery of the catalyst was reported …”