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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]

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]

A series of [PdPyCl2]2(di-NHC) complexes were prepared (di-NHC are two 1-(2,6-dimethylphenyl)imidazolidene molecules bridged by an aliphatic -(CH2) n- linker ( n = 3, 4, 5, 6, and 10)). All complexes were fully characterized by NMR spectroscopy and elemental analyses. The crystal structures of four complexes ( n = 3, 4, 5 and 6) were determined by X-ray diffraction. The influence of the distant methyl group on the structural features and catalytic activity with increasing of length of linker was investigated by comparing the results of these 2,6-dimethylphenyl palladium complexes with those of their known mesityl analogues. X-ray studies show the distant methyl substitution has big impact on the structure feature of the complexes with the shorter linker between two NHC (ethylene and propylene), but has a little or no effect on that of the complexes with longer linker (butylene and hexylene). Catalytic results of the arylation of styrene show that the remote substitute has big effect on the regioselectivity of the product in all complexes with shorter and longer linkers, but has a limited effect on the yield. [ABSTRACT FROM AUTHOR]

Abstract: The phosphine-free mono- and double-Heck reaction of terminal olefins with electron-deficient and electron-rich aryl halides (iodides and bromides) is described. These reactions are catalyzed by the dicarbene dipalladium complex 1 by controlling the stoichiometry of the aryl halide and the olefine, the loading of the palladium catalyst, as well as using different base, and with or without additive. The procedure of double-Heck reaction allows β,β-diarylation and β,β′-diarylation of terminal olefins and affords trisubstituted olefins in good to excellent yields. [Copyright &y& Elsevier]

palladium complexes of ferrocenyl-functionalized N-heterocyclic carbenes with different substituents were synthesized. The molecular structures of selected complexes were determined by X-ray diffraction and show a pseudo-square-planar structure with a central palladium atom surrounded by carbene, pyridine, and two chloride ligands. The influence of the different substituents on the structure and reactivity of the complexes was studied. The catalytic properties of the complexes were investigated in the Larock indolization reactions of 2-bromoanilines with diphenylacetylene. Their performances slightly varied in this reaction, but the complex with mesityl substituent showed the best activity. [ABSTRACT FROM AUTHOR]

Abstract: Reactions of different alkane-bridged (n =1–3) di-NHC precursors, bisimidazolium chlorides with the NiCl2 in presents of K2CO3 in acetonitrile give the corresponding 16-electron binuclear complexes of the type Ni(di-NHC)(μ-O)2CO in moderate yield. The molecular structures of 1–3 have been determined by X-ray crystallography, which revealed a cis-chelating di-NHC on a slightly distorted square-planar nickel center with κ2-cabonato ligand. The influence of the different di-NHC ligands on the structure and reactivity of the complexes has been studied. The catalytic properties of the complexes were investigated in the Kumada reaction for cross-coupling of phenylmagnesium bromide with a variety of aryl halides. The complex 3 which has the longest linker between two NHCs shows the best catalytic activity in these reactions. [Copyright &y& Elsevier]

A series of imidazole-based and benzimidazole-based di-NHC dipalladium complexes with alkyl bridges of different chain lengths were prepared. All complexes were fully characterized by NMR spectroscopy and elemental analyses. The crystal structures of three complexes were determined by X-ray diffraction. X-ray studies show the length of linker effects the solid structure of these complexes and π-π stacking plays an important role for the configuration of NHC-Pd-Py subunits. The activity of NHC-palladium complexes was investigated in the mono- and double-Heck reactions, and the imidazole-based palladium complex bearing the shortest ethylene bridge shows the best activity and selectivity in both reactions. [ABSTRACT FROM AUTHOR]

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]