Highly Efficient and Recyclable Au Nanoparticle-Supported Palladium(II) Interphase Catalysts and Microwave-Assisted Alkyne Cyclotrimerization Reactions in Ionic Liquids

Abstract

The gold nanoparticles with core diameter of 3.9-4.7 nm were stabilized with octanethiolate and dipyridylphosphinicamido undecanethiolate. Without varying the size of central Au cores, palladium complexes were immobilized onto these Au nanoparticles through chelation to the surface-bound dipyridyls. Hybrid catalysts of this type were dissolvable and precipitable, and their structures and reactions were investigated by solution nuclear magnetic resonance (NMR) spectroscopy with a resolution typically attained for soluble systems. These surface-bound Pd(II) complexes were highly effective catalysts for [2+2+2] alkyne cyclotrimerization reactions to give highly congested benzene rings with fairly good selectivity. The catalytic reactivity of these interphase catalysts was even higher than that of their unbound counterparts. In addition, they can be easily separated and quantitatively recovered by simple filtration. The recovered catalysts can be effectively recycled many times and their electron microscopy images and NMR spectra showed negligible difference from those of freshly prepared. The complete transformation by Au-bound Pd(II) catalyst with a loading of 4 mol % can be achieved within 1 h for most alkynes. The same catalysis can be further accelerated in ionic liquid under microwave conditions to give nearly 100% of cyclotrimerized products in minutes.

Selective Fluorescence Sensing of Zinc and Mercury Ions with Hydrophilic 1,2,3-Triazolyl Fluorene Probes

“…1-Azidobutane was synthesized in a 80% yield by reaction of 1-bromobutane with NaN 3 in DMSO at 95 °C for 24 h. Likewise, 1-azido-11-undecanethiol was synthesized in 80% overall yield from 1-bromo-11-undecanol (Scheme 2). The NMR data of 1-azidobutane and 1-azido-11-undecanethiol agreed with values reported in the literature 52,53…”

Nanoparticles as Semi‐Heterogeneous Catalyst Supports

“…The subsequent drop in activity was due to reduction of the cobalt species rather than catalyst leaching, thus, reactivity was restored upon oxidation. A recent study carried out by Yu et al [30] reported a similar activity enhancement for a heterogenized palladium-bipyridyl complex in alkyne cyclotrimerization reactions, which was attributed to interphase effects.…”

The Beneficial Sinergy of MW Irradiation and Ionic Liquids in Catalysis of Organic Reactions

“…Cyclotrimerization of alkynes to benzenes was brilliantly achieved using Pd catalyst supported on Au nanoparticles stabilized with thiolates [117]. With a loading of 4 mol % Au-bound Pd(II) catalyst, most of tested alkynes reacted completely in 1 h. The method became appealing when MW Intramolecular Stetter reaction was performed under MW irradiation, either solventless or in ILs, with thiazolium-based ionic liquids that, in turn, were prepared by a one-pot, solvent-free, MW-assisted reaction (Scheme 44) [116].…”

“…Cyclotrimerization of alkynes to benzenes was brilliantly achieved using Pd catalyst supported on Au nanoparticles stabilized with thiolates [117]. With a loading of 4 mol % Au-bound Pd(II) catalyst, most of tested alkynes reacted completely in 1 h. The method became appealing when MW Scheme 44.…”