Guangsheng Pang

Synthesis and characterization of novel chiral NHC-palladium complexes and their application in copper-free Sonogashira reactions.

A new series of chiral N-heterocyclic carbene (NHC) palladium complexes were synthesized from a relatively inexpensive amino acid, l-phenylalanine. All these compounds were fully characterized by (1)H-NMR, (13)C-NMR and elemental analysis. The X-ray molecular structures of two of the complexes were reported. The catalytic activity of the four palladium complexes was successfully tested in the Sonogashira reaction under copper free conditions in air. The palladium complex 3a provided good activity in the Sonogashira coupling reaction.

Cheap Cu(I)/Hexamethylenetetramine (HMTA) Catalytic System for C-N Coupling Reactions

Abstract An efficient C-N coupling reaction of aryl chlorides or bromides with imidazole was successfully performed with cheap and commercially available catalytic system Cu(I)/HMTA. Both aryl bromides and aryl chlorides have been effectively catalyzed by Cu/HMTA, giving products in moderate to good yields. Moreover, aryl halides bearing either electron-withdrawing groups or electron-donating groups could be used in the reaction. GRAPHICAL ABSTRACT

Palladium complexes with picolyl functionalized N-heterocyclic carbene ligands and their application in the Mizoroki–Heck reaction

A series of Pd complexes of picoline-functionalized N-heterocyclic carbenes with different substituents were synthesized. The molecular structures of selected complexes were determined by X-ray diffraction studies, showing a pseudo-square-planar structure with a Pd center surrounded by carbene, pyridine, and two chloride ligands. The influence of the different substituents on the structure and reactivity of the complexes has been studied. The catalytic properties of the complexes were investigated in the Mizoroki–Heck reaction for cross-coupling of bromobenzene with a variety of aryl halides. Their performances varied in these reactions but showed good product regioselectivities.

Synthesis and catalytic properties of a heterocyclic–carbene complex of palladium

The palladium N-heterocyclic carbene complex trans-[PdCl2{1,3-bis(2,6-diisopropylphenyl)-imidazol-2-ylidene}(NC5H5)] has been prepared and its X-ray molecular structure is reported. The complex is highly catalytically active in the cross-coupling reaction of phenylhalides with phenylthiol to afford diphenyl sulfide and is efficient for the coupling of chlorobenzene.

Synthesis of novel chiral unsymmetrical imidazolinium bromides

N-heterocyclic carbenes have been successfully used as ligands in organometallic catalysis, and also as organocatalysts in different reactions. A series of novel chiral unsymmetrical imidazolinium salts which are precursors of N-heterocylic carbenes were synthesised effectively from the relatively inexpensive amino acid L-phenylalanine in six steps. These chiral unsymmetrical imidazolinium bromides were fully characterised by NMR and elemental analysis, and their specific rotations were obtained.

Green Synthesis of Alkane Bridged Bisimidazolium Salts Under Solvent-Free Conditions

Abstract A series of N-aryl or N-methyl substituted bisimidazolium dichloride or dibromide salts with different alkyl bridge lengths (n = 1–4) have been synthesized starting from N-arylimidazoles or N-methylimidazoles with dialkyl bromides or the less expensive but less reactive dialkyl chlorides under solvent-free conditions. This green protocol provided most bisimidazolium chloride and bromide salts in good yields, and the reaction time was shortened to a few hours. In two examples, we showed either bisimidazolium dichloride (1a) or dibromide salt (3c) can be easily converted to the corresponding dihexafluorophosphate salt (1a′ or 3c′) in near quantitative yield. GRAPHICAL ABSTRACT

Efficient synthesis of alkane-bridged N,N ′-diaryl bisimidazolium chlorides under solvent-free conditions

A series of N, N’-diaryl bisimidazolium dichlorides with different alkyl bridged length (n = 2–6, 10) was synthesised from N-arylimidazoles with the less expensive, but less reactive dialkyl chlorides effectively in solvent-free conditions at ambient pressure. Compared with conventional methods, this protocol features a short reaction time, good yields and an eco-friendly process.

Synthesis of xylylene-bridged dipalladium complexes with imidazole and triazole-based di-N-heterocyclic carbene (NHC) ligands

The di-N-heterocyclic carbene (NHC) dipalladium complexes, [(PdPyBr2)2(di-NHCimi)] and [(PdPyBr2)2(di-NHCtri)], di-NHCimi and di-NHCtri represent an imidazolylidene and a triazolylidene, respectively, featuring a 1,4-xylylene spacer between the carbene units, have been prepared. The influences of the imidazolylidene and triazolidene backbone and different substituents on the catalytic activity have been investigated in the Mizoroki–Heck reaction of styrene with bromobenzene.

Solvent–free synthesis of some triazole-based bis(N-heterocyclic carbene) ligands

Two series of bistriazolium dibromides with different alkyl bridged length (n = 2–4) were synthesised through a simple solvent-free method. Six of these compounds were prepared from the reaction of 1-R-1H-1,2,4-triazole with dibromoalkane in moderate to excellent yield (45–98%). However, the other six compounds were prepared from the reaction of alkyl bridged bistriazole with bromoalkane in 55–99% yield. All compounds are new and were fully characterised by IR, NMR and elemental analyses.

Synthesis of novel NHC-pyrrole-NHC C-N-C Pincer proligands

Abstract Two novel pyrrole-functionalized bis(benzoimidazolium) salts, which are novel NHC-pyrrole-NHC C-N-C Pincer proligands were synthesized in high yield. Both of these compounds are fully characterized by 1H and 13C NMR, IR and elemental analysis.