Synthesis And Properties Of Chiral N-Heterocyclic Carbene Ligands,pPd Complexes And Pd,Au Nanoparticles

Anewair-stable,convenienttohandle1-(2,3,4,6-tetra-O-acetyl-?-D-glucopyranosyl)-3-alkyl(aryl)-imidazol-2-ylidene]Pd(pyridine)Br₂ was conveniently synthesized from the imidazolium halide salts 1-(2,3,4,6-tetra-O-acetyl-?-D-glucopyranosyl)-3-alkyl(aryl)-midazolium bromideby the reaction with Pd(OAc)₂ in pyridine in presence of KBr.Glucopyranosyl-based NHCs-Pd(pyridine)Br₂ contain multiple chiral centers on the sugar ring.The molecular structures of complex have been determined by liquid chromatography-high resolution mass spectrometry(LC-HRMS),elemental analysis(EA)and liquid nuclear magnetic resonance.¹H NMR and ¹³C NMR chemical shifts of glucopyranosyl-based NHCs-Pd(pyridine)Br₂ were fully assigned.We found that the influence of the carbon and proton chemical environment on sugar ring is more obvious than that on the butyl chain after the formation of NHCs-Pd(II)-Py metal bond in the presence of multiple weakly coordinated oxygen.Ultra-small Pd nanoparticles(Pd UNPs)represent a distinctive type of nanomaterials making them very attractive for broad applications.Herein,chiral sugar-substituted N-heterocyclic carbenes with different lengths of alkyl chain(sugar-NHCs-C_nH_2n+1)were first used to prepare ultra-small,water-soluble Pd nanoparticles(Pd@NHCs-sugar UNPs)via an efficient ligand exchange strategy,which can be handled under air and are stable over 10 months.The Pd@NHCs-sugar UNPs were highly monodisperse,with tunable core diameters from 1.7 to 2.1nm,an effect of the particle size revealed on the N-substituents aliphatic chains was observed.To check the accessibility of the surface,this Pd@NHCs-sugar UNPs were tested as catalysts for recycle Suzuki reaction in eco-friendly aqueous solution without any precipitation of metallic Pd.The presence of longer aliphatic group in sugar-NHCs-C_nH_2n+1 makes them obtained higher catalyst activity and stability.Chiral gold nanoparticles modified by sugar-substituted N-heterocyclic carbenes(Au@NHCs-sugar NPs)were synthesized via two different chemical reduced methods.The Au@NHCs-sugar NPs were highly monodisperse,with tunable core diameters from 2.5 to 3.8 nm,which depending on the specific N-substituents,the molar ratio of sugar-based benzimidazolium haloaurate salt and bromide salt.The Au@NHCs-sugar NPs can be handled under air and are stable over18 months.