Gold nanoparticles stabilized by PEG-tagged imidazolium salts as recyclable catalysts for the synthesis of propargylamines and the cycloisomerization of γ-alkynoic acids

Abstract

Water-soluble gold nanoparticles prepared in the presence of PEG-tagged tris-imidazolium bromide, containing Au(0) and Au(i) species, are reusable catalysts.

N-Heterocyclic carbenes as “smart” gold nanoparticle stabilizers: State-of-the art and perspectives for biomedical applications

“…[71] Recently, the use of PEGylated imidazolium (bromide and tetrafluoroborate) and tris-imidazolium (bromide) salts contain-ing triazole linkers, as stabilizers for the preparation of water- soluble gold nanoparticles by reduction of tetrachloroauric acid (HAuCl4) with NaBH4 was reported (Table 1). [72] TEM analysis confirmed the formation of spherical and well-dispersed nanopar-ticles of mean diameters from 4.5 to 5.6 nm. Unfortunately, whilst a number of spectroscopic data indicate that the heterocycle lig-and is close to the surface of the metal, no conclusive experi-mental evidence with respect to its nature, either imidazolium or carbene, could be obtained.…”

“…Unfortunately, whilst a number of spectroscopic data indicate that the heterocycle lig-and is close to the surface of the metal, no conclusive experi-mental evidence with respect to its nature, either imidazolium or carbene, could be obtained. [72] It should be noted that, in gen-eral, although NHCs have been demonstrated as suitable ligands for the stabilization of gold nanoparticles through a variety of meth-ods, the mechanism by which such NHC@AuNPs form is yet to be fully elucidated. For example, XPS studies of chiral (L/D)-histidin-2-ylidene stabilized gold nanoparticles, formed using well defined organometallic Au(I) complexes, showed the concomitant presence of Au(I) and Au(0) in the nanoparticles.…”

Catalytically Active Gold Nanomaterials Stabilized byN‐heterocyclic Carbenes

“…The most active AuNPCat was investigated in detail to understand the binding mechanism of the ligand. XPS and NMR data suggests the formation of carbene‐AuNP bonds [79] …”

An organometallic approach for the preparation of Au–TiO2 and Au-g-C3N4 nanohybrids: improving the depletion of paracetamol under visible light

“…The most intense doublet at 83.6 eV and 87.3 eV can be assigned to metallic gold; the less intense doublet can be attributed to the presence of Au(I) oxidation state. These partially oxidized Au NPs have been recently described for Au NPs stabilised with PEG tagged imidazolium salts [29] or stabilized with the same g-C 3 N 4 substrate [30]. The presence of gold atoms in positive oxidation states is attributed to a higher fraction of surface atoms with low coordination numbers when small size nanoparticles are grafted on the carbon nitride surface [31].…”