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The di-N-heterocyclic carbene (NHC) dipalladium complexes, [(PdPyBr2)2(di-NHCimi)] and [(PdPyBr2)2(di-NHCtri)], di-NHCimi and di-NHCtrirepresent 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

A novel tridentate chiral imidazolium hexafluorophosphate, a precursor for N-heterocyclic carbene (NHC) ligand, was synthesized from (S)-proline in five steps in 24% overall yield. The compound was characterized by NMR and elemental analysis. Its molecular structure was determined by X-ray diffraction analysis. This chiral compound has two stereogenic centers which are within two chelating side chains and its specific rotation is -19.6°. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: It was found that an air-stable NHC–palladium complex of Pd[(s)-3-C3H5-4-(C5H5CH2)-1-(2,6- i Pr2C6H3)-C3H3N2](C5H5N)Br2 derived from l-phenylalanine is an effective pre-catalyst for copper-free and phosphine-free Sonogashira reaction of alkynes under aerobic conditions in short reaction time. Moreover, the palladium compound would be reused to catalyze the hydroarylation of alkyne prepared from Sonogashira reaction, which makes firstly Sonogashira/Hydroarylation sequential reactions successful. The arylation of alkynes underwent with a high regio- and stereoselectivity and only trans-arylation of alkyne was observed. No Z/E isomerization of the olefin was observed in the system. [Copyright &y& Elsevier]

Abstract: A series of di-NHC ligands with alkyl bridges of different chain lengths (n =2–4) and their bi-palladium complexes (4, 5 and 6) have been prepared. The molecular structure of 4 and 6 were determined by X-ray diffraction studies. The structures of complex 4 consist of two pseudo-square-planar subunits in a trans configuration, however 6 consist of two subunits in a cis configuration with π–π stacking between two pyridines. The influence of the different bridges on the structure and reactivity of the complexes has been studied. The catalytic activity of the new binuclear palladium complexes was successfully tested in the Mizoroki–Heck reaction of styrene with bromobenzene. The complex with 2 and 4 carbon linker gave higher yield, while the one with 3 carbon linker gave better regioselectivity. [ABSTRACT FROM AUTHOR]

A chemical diagram is presented that depicts the controlled mono- and double-Heck Reaction catalyzed by a dicarbene dipalladium complex.