Abstract
1,2,3-Triazole is an interesting N-heterocyclic framework which can act as both a hydrogen bond donor and metal chelator. In the present study, C–H hydrogen bonding of the 1,2,3-triazole ring was surveyed theoretically and the results showed a good agreement with the experimental observations. The click-modified magnetic nanocatalyst Pd@click-Fe3O4/chitosan was successfully prepared, in which the triazole moiety plays a dual role as both a strong linker and an excellent ligand and immobilizes the palladium species in the catalyst matrix. This nanostructure was well characterized and found to be an efficient catalyst for the CO gas-free formylation of aryl halides using formic acid (HCOOH) as the most convenient, inexpensive and environmentally friendly CO source. Here, the aryl halides are selectively converted to the corresponding aromatic aldehydes under mild reaction conditions and low Pd loading. The activity of this catalyst was also excellent in the Suzuki cross-coupling reaction of various aryl halides with phenylboronic acids in EtOH/H2O (1 : 1) at room temperature. In addition, this catalyst was stable in the reaction media and could be magnetically separated and recovered several times.
Highlights
New advances in the chemical synthesis and catalysis areas are strongly tied to green chemistry
Due to ambivalent character of triazoles, they can act as both an N-donor ligand and hydrogen donor, showing the complexations with both metal cations and anions. 1,2,3-Triazols as the nitrogen-rich heterocycles have developed as interesting candidates for use in transition-metal catalysis
The novel magnetic catalyst Pd@click-MNPs/CS containing 1,2,3triazole unit was synthesized through a ‘‘click’’ reaction, in which 1,2,3-triazole moiety acts as a strong linker and a Pdchelator. 1,2,3-Triazole having several N-donor positions can be strongly coordinated to palladium(II) ions and stabilize the catalytic sites in the solid catalyst matrix
Summary
New advances in the chemical synthesis and catalysis areas are strongly tied to green chemistry. Carbonylation has become a powerful strategy for the preparation of carbonylcontaining organic combinations.[32,33,34] To date, many researchers have focused their studies on the new CO gas-free carbonylation systems[35,36,37] and reported the various carbonyl sources such as formic acid,[38,39] Mo(CO)[6,40] oxalic acid[36] and Nformylsaccharin.[41] Formic acid is an eco-friendly, cheap and available carbonyl source and can generate a carbon monoxide (CO) molecule in situ during the reaction process.[42] The formic acid-assisted carbonylation catalyzed by palladium catalysts[38,39] is an efficient approach for constructing carbonyl compounds In another part of this work, the Pd@click-MNPs/CS was employed as a recyclable catalyst in the Suzuki–Miyaura crosscoupling of diverse aryl halides with phenylboronic acids in green solvent at room temperature. The effects of the solvent and its polarity on the most stable structure of this compound and 1HNMR signal of triazole proton in the gas phase, DMSO and in CDCl3 solvent were theoretically investigated
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