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This study investigates the thermal expansion properties of argentophilic and aurophilic contacts in coordination complexes of the form [(iPrNHC)2Ag]ClO4 and [(iPrNHC)2Au]ClO4. Using X-ray crystallography distinct structural changes and phase transitions at varying temperatures are revealed. Both complexes exhibit a similar strong temperature dependence of the metallophilic distances. Analysis shows that the shallower, more anharmonic aurophilic interaction is counterbalanced by the smaller vibrational amplitude of the heavier gold atoms, resulting in comparable thermal elongation despite differing atomic dynamics. [ABSTRACT FROM AUTHOR]

The metalation of 1,3-diaryl-4-(arylsulfanyl)imidazolium and 1,3-diaryl-4-(arylsulfonyl)imidazolium chlorides with copper(I) oxide has been studied. The resulting Cu/NHC complexes have been studied as catalysts for the carboxylation of phenylacetylene, benzoxazole, and benzothiazole. The main patterns of this reaction behavior and the dependence of the catalysis efficiency on the NHC structure were revealed. [ABSTRACT FROM AUTHOR]

N-heterocyclic carbene (NHC)–gold and –silver complexes have attracted the interest of the scientific community because of their multiple applications and their versatility in being chemically modified in order to improve their biological properties. However, most of these complexes contain one or more chiral centers, and have been obtained and studied as racemic mixture. In particular, concerning the interesting biological and medicinal properties, many questions about how the chirality may influence these properties still remain unanswered. Aiming at a better understanding, herein a series of enantiopure NHC–gold and –silver complexes was synthesized, characterized and biologically evaluated in different in vitro systems. The individuated complexes exerted different properties based on the complexed metal and the specific configuration, with the (R)-gold–NHC complexes being the most active, particularly as anti-inflammatory molecules. Docking simulations indicated a different binding mode for each enantiomer. Moreover, anticancer and antibacterial activities were also evaluated for the considered enantiomers. Overall, the reported data may contribute to a better understanding of the different biological properties exerted by the enantiopure gold and silver complexes.

The recent advances in the N‐heterocyclic carbene (NHC)‐organocatalyzed generation of azolium enolate intermediates and their subsequent interception with electrophiles are highlighted. The NHC‐bound azolium intermediates are generated by the addition of NHCs to suitably substituted aldehydes, acid derivatives or ketenes. A broad range of coupling partners can intercept the azolium enolates to form [2+n] cycloadducts (n=2,3,4) and various α‐functionalized compounds. The enantioselective synthesis of the target compounds are achieved with the use of chiral NHCs. Herein, we summarized the development that occurred in this subclass of NHC catalysis. [ABSTRACT FROM AUTHOR]

A novel Pd−NHC functionalized metal–organic framework (MOF) based on MIL‐101(Cr) was synthesized and used as an efficient heterogeneous catalyst in the C‐C bond formation reactions. Using this heterogeneous Pd catalyst system, the Suzuki−Miyaura coupling reaction was accomplished well in water, and coupling products were obtained in good to excellent yields in short reaction time. The Pd−NHC−MIL‐101(Cr) was characterized using some different techniques, including Fourier transform‐infrared, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy, inductively coupled plasma and elemental analysis. The microscopic techniques showed the discrete octahedron structure of MIL‐101(Cr), which is also stable after chemical modification process to prepare the catalyst system. The TEM images of the catalyst showed the existence of palladium nanoparticles immobilized in the structure of the catalyst, while no reducing agent was used. It seems that the NHC groups and imidazolium moieties in the structure of the MOF can reduce Pd (II) to Pd (0) species. This modified MOF substrate can also prevent aggregation of Pd nanoparticles, resulting in high stability of them in organic transformation. The Pd−NHC−MIL‐101(Cr) catalyst system could be simply extracted from the reaction mixture, providing an efficient synthetic method for the synthesis of biaryls derivatives using the aforementioned coupling reaction. The Pd−NHC−MIL‐101(Cr) catalyst could be recycled in this organic reaction with almost consistent catalytic efficiency. [ABSTRACT FROM AUTHOR]

In this study, using the wB97XD functional, quantum chemical calculations were used to analyze the solvent effect on the structural, electronic and spectroscopic (IR and UV) features of the Ni(CO)2(NHC)2 complex (NHC = 1H-imidazol-2-ylidene). Using the self-consistent reaction field theory (SCRF) based on the Polarizable Continuum Model (PCM), the solvent effects were examined. The solvation model utilized the radii and non-electrostatic terms of the solvent model density (SMD). The linear correlations between these parameters and solvent polarity functions including both the dielectric constant (ε) and refractive index (nD) of the liquid medium, were explored. Correlations of the calculated spectral parameters ( (CO) and λmax) with the Kirkwood–Bauer–Magat equation (KBM) and improved form of this equation were explored. The natural transition orbitals (NTOs) was utilized for illustration of the nature of the most intense electronic transition in the studied complex. [ABSTRACT FROM AUTHOR]

An atom-economic synthetic route to benzimidazolium salts is presented. The annulated polycyclic systems: 1,3-bis(2,4,6-trimethylphenyl)-1H-benzo[d]imidazol-3-ium chloride (1-Cl), 1,3-bis(2,6-diisopropylphenyl)-1H-benzo[d]imidazol-3-ium chloride (2-Cl), 1,3-diphenyl-1H-benzo[d]imidazol-3-ium chloride (3-Cl), and 1,3-di(pyridin-2-yl)-1H-benzo[d]imidazol-3-ium chloride (4-Cl) were prepared in a two-step synthesis avoiding chromatographic work-up. In the key step triethyl orthoformate is reacted with the corresponding N1,N2-diarylbenzene-1,2-diamines and then further transformed in situ, by alkoxy abstraction using trimethylsilyl chloride (TMSCl), and concomitant imidazole ring closure.

A new method for the synthesis of complexes PtIV(NHC)X4L (NHC is N-heterocyclic carbene of imidazole or benzimidazole series; X = Cl, Br; L is N-coordinated pyridine or NHC) based on mechanochemical oxidation of complexes PtII(NHC)X2L with dichloroiodobenzene (PhICl2) or pyridinium hydrobromide perbromide (PyHBr3) was proposed. Mechanochemical activation led to reduction in the synthesis time and increase in the selectivity of halogenation and yields of the target PtIV complexes (74-98%) as compared to the reaction in solutions. [ABSTRACT FROM AUTHOR]

Iron is of interest as a catalyst because of its established use in the Haber-Bosch process and because of its high abundance and low toxicity. Nitrogen-heterocyclic carbenes (NHC) are important ligands in homogeneous catalysis and iron-NHC complexes have attracted increasing attention in recent years but still face problems in terms of stability under oxidative conditions. The structure of the iron(II) complex [1,1′-bis(pyridin-2-yl)-2,2-bi(1 H-imidazole)-κ N3][3,3′-bis(pyridin-2-yl-κ N)-1,1′-methanediylbi(1 H-imidazol-2-yl-κ C2)](trimethylphosphane-κ P)iron(II) bis(hexafluoridophosphate), [Fe(C17H14N6)(C16H12N6)(C3H9P)](PF6)2, features coordination by an organic decomposition product of a tetradentate NHC ligand in an axial position. The decomposition product, a C-C-coupled biimidazole, is trapped by coordination to still-intact iron(II) complexes. Insights into the structural features of the organic decomposition products might help to improve the stability of oxidation catalysts under harsh conditions. [ABSTRACT FROM AUTHOR]

Cross-coupling reactions, such as Buchwald-Hartwig arylamination and direct intramolecular biaryl coupling by C-H activation, were carried out using various Palladium-N-heterocyclic carbenes (Pd-NHC) as catalysts. The yields were good to excellent. The latter strategy was adopted to transform two dibenzylbutane lignans, isolated from the leaves of Ocotea macrophylla (Lauraceae), into the corresponding dibenzocyclooctane lignans in good overall yields. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. [ABSTRACT FROM AUTHOR]

Abstract: The selective alkylation of functionalized 2-(1H-imidazol-1-yl)pyridines 1 furnishes 3-methyl-1-pyridinyl-1H-imidazolium salts 2, which can be deprotonated to deliver strongly electron-donating bidentate N-heterocyclic carbene ligands (NHC). The synthesis of these ligands and their application in the iridium-catalyzed C–H activated borylation of arenes with its current scope and limitations are reported. [Copyright &y& Elsevier]

Abstract: In this work we show that the intramolecular C–H insertion of diazo-acetamides catalysed by di-rhodium(II) complexes can be highly influenced by the axial ligand on the di-rhodium(II) complex. Axially monocoordinated NHC–Rh2(OAc)4 complexes have a distinct reactivity from the parent Rh2(OAc)4 complex affording the cyclisation products in different rates and selectivities. Surprisingly, a new reaction mode emerged when using these complexes which led to a decarbonylation pathway. [Copyright &y& Elsevier]

Abstract: A new route was used to synthesize half-sandwich rhodium complexes containing both N-heterocyclic carbenes (NHC) and carborane ligands. The rhodium carbene complexes Cp∗Rh(L)[S2C2(B10H10)] (Cp∗ =pentamethylcyclopentadienyl, L=1,3-dimethylimidazolin-2-ylidene; 4) can be obtained from the reaction of Cp∗Rh(L)Cl2 (2) with Li2S2C2(B10H10) or from the reaction of Cp∗Rh[S2C2(B10H10)] (3) with silver–NHC complex prepared by direct reaction of an imidazolium precursor and Ag2O. Complexes 2 and 4 were characterized by IR, NMR spectroscopy, element analysis and X-ray structure analyses. [Copyright &y& Elsevier]

The effect of the structural properties of graphene materials on the local structure of –OH anchored Ir(I)–NHC complexes is herein investigated. For that, two partially reduced graphene oxides exhibiting different sheet properties due to an adequate selection of the crystalline characteristics of their parent graphite were used. The main differences among them were the size of Csp2 domains within their graphenic layers and the distribution of functional groups at the basal planes and edges. Anchoring of N-methylimidazolium moieties through the graphene –OH functional groups and subsequent formation of the Ir(I)–NHC complexes resulted in graphene-based hybrid materials. The structural differences of the support have an influence in the interaction of the supported iridium compounds with the graphene sheet. The oxygenated functional groups in the material with a smaller graphene sheet are closer leaving larger Csp2 domains in the graphene layer, favoring their interaction with the supported iridium atoms therefore displacing the chlorido ligand from the first coordination shell. In contrast, the hybrid material in which the distribution of the oxygenated functional groups within the basal planes of the graphenic layer is more homogeneous shows partial chlorido displacement. This fact has an influence on the electrocatalytic performance of the iridium-based hybrid materials as water oxidation catalysts (WOCs), exhibiting improved catalytic activity the catalyst having coordinated chlorido ligands. Image 1 • Hybrid materials comprised of graphene modified with Ir-NHC complexes are suitable electrocatalysts for water oxidation. • EXAFS analysis evidences that the parent graphite influences the iridium local structure in the hybrid materials. • The iridium local structure determines the electrocatalytic behavior in water oxidation. [ABSTRACT FROM AUTHOR]