Ivan J. B. Lin

Coinage Metal−N-Heterocyclic Carbene Complexes

2.3.5. Multi-NHCs Linked by Spacers 3568 2.4. The Ag2O Route 3570 2.4.1. Feasibility 3570 2.4.2. Complications 3571 2.4.3. Theoretical Consideration 3572 2.5. Applications 3572 2.5.1. Ag(I)-NHCs in NHC Transfer 3572 2.5.2. Ag(I)-NHCs in Catalysis 3572 2.5.3. Ag(I)-NHCs in Medicine 3572 2.5.4. Ag(I)-NHCs in Nanomaterials 3573 3. Au(I)and Au(III)-NHCs 3573 3.1. Historical Background 3573 3.2. General Synthetic Methods 3573 3.3. Formation of Au(I)and Au(III)-NHCs 3574 3.3.1. Neutral [Au(NHC)L] 3574 3.3.2. Ionic [Au(NHC)L][Anion] 3576 3.3.3. Multinuclear Au(I)-NHCs 3578 3.3.4. Other Classes of Au(I)-NHCs 3578 3.3.5. Au(III)-NHC Complexes 3579 3.4. Applications 3579 3.4.1. Au(I)and Au(III)-NHCs in Catalysis 3579 3.4.2. Au(I)-NHCs in Medicine 3580 4. Cu(I)and Cu(II)-NHCs 3581 4.1. Historical Background 3581 4.2. General Synthetic Methods 3582 4.3. Formation of Cu(I)and Cu(II)-NHCs 3583 4.3.1. Complexes Containing the Cu(NHC)2 Core 3583 4.3.2. [Cu(NHC)(Halide)] 3583 4.3.3. [Cu(NHC)(Ligand)] 3584 4.3.4. Multinuclear Cu(I)and Cu(II)-NHCs 3589 4.4. Catalysis 3591 4.4.1. Past Events 3591 4.4.2. Recent Advancements 3591 5. Photoluminescence 3592 6. Conclusions 3594 7. Abbreviations 3594 8. Acknowledgments 3595 9. References 3595

SILVER(I) N-HETEROCYCLIC CARBENES

This review presents a detailed overview on the synthesis of AgI–NHCs and their role as carbene transferring agents as an easy access to various important transition metal-NHC complexes. The nature of NHC ligands, counter anions and solvents are recognized as key factors in the determination of AgI–NHCs and their derivatives. The lack of Ag–Ccarbene bond coupling in various AgI–NHCs suggests the lability of Ag–Ccarbene bond, which appears to be an appropriate reason in the transfer of carbene. It has been suggested by various authors that carbene transfer from AgI–NHCs is particularly useful when the carbene N-functionality contains base sensitive functional groups or acidic hydrogen. Importantly AgI–NHCs are less air sensitive than the free carbenes and are easy to synthesize. These properties allow them to be handled easily in further operations. Apart from the carbene transferring property, the nature of Ag–Ccarbene bond, the influence of NHC on the Ag…Ag contacts and the molecular aggregation to generate novel structural motifs and supramolecular assemblies have also been emphasized.

Supramolecular liquid crystals of amide functionalized imidazolium salts

Liquid crystalline 1-acetamido-3-alkylimidazolium bromide, hexafluorophosphate and tetrafluoroborate salts with 3-alkyl chains of carbon number n = 10, 12, 14, 16 and 18 were prepared. The single crystal structure of the PF6− salt of n = 12 self-organizes to form a framework of a hydrogen bonded ribbon polymer. The mesomorphic behaviors of these compounds were studied by polarized optical microscopy, differential scanning calorimetry and powder X-ray diffraction. The presence of extended hydrogen bonding interactions in these acetamidoimidazolium salts allows them to have a wide temperature range of the mesophase. Anions have a profound effect on the phase transition temperature, suggesting that both ionic and hydrogen bonding interactions play dominant roles in the mesomorphic behavior of these liquid crystalline compounds.

Ionic liquid crystals of imidazolium salts with a pendant hydroxyl group

A 2-hydroxyl pendant group was anchored on the N-alkyl chain of imidazolium ionic liquid crystals. This hydroxyl group enhanced the hydrogen bonding interactions between neighboring compounds and, therefore, widened the temperature range of the mesophase, as compared to those without the hydroxyl group. Many room temperature ionic liquid crystals were formed. Polarized optical microscopy, differential scanning calorimetry, X-ray diffraction and infrared spectroscopy were used to study the properties of these materials. The molecular structure of one of the compounds was determined by single crystal X-ray diffraction, in order to have a better understanding of the structure relation between the solid and liquid crystal.

Helical mono and dinuclear mercury(II) N-heterocyclic carbene complexes

Abstract A series of mono and dicationic carbene precursors have been synthesized. Reactions of these precursors with Hg(OAc)2 produce helical mononuclear and dinuclear mercury(II) carbene complexes. Five structures, including two ligand precursors and three mercury(II) carbene complexes have been analyzed by single crystal X-ray diffraction. Several intermediates have been identified during the course of reaction. Based on these observed intermediates, three different reaction pathways have been proposed.

Ionic liquids and ionic liquid crystals of vinyl functionalized imidazolium salts

1-Vinyl-3-alkylimidazolium salts ([CnVIm]X, (where, CnVIm = vinylimidazolium cation with alkyl chains of CnH2n+1; n = 4, 6, 8, 10, 12, 14, 16 and 18 for X = Br and I, and n = 12, 14, 16 and 18 for X = BF4 and PF6), were prepared and characterized. Ethyl substituted congeners [C16EIm]Br and [C16EIm]I were also prepared to understand the unique property of the vinyl substitution. Salts with shorter alkyl chain lengths (n ≤ 12) are either room temperature or close to room temperature ionic liquids, whereas those with longer alkyl chain lengths are ionic liquid crystals with SmA mesophase. Diffractograms from powder X-ray diffraction studies suggest that in the solid state the [CnVIm]Br series salts adopt a double bilayer structure, whereas the ethyl substituted analogues and salts in the I−, BF4− and PF6− series have a simple bilayer structure. The thermal behavior of [C16VIm]Br and [C16VIm]I was compared with their saturated congeners. The vinyl functionalized salts, have slightly higher melting points and much higher clearing points than those of the saturated congeners, and therefore wider mesophases are found for the formers. Nuclear magnetic resonance spectroscopic studies suggest that vinyl functionalization provides additional hydrogen bonding interactions between the cations and anions.

Self-Assembly of Silver(I) and Gold(I) N-Heterocyclic Carbene Complexes in Solid State, Mesophase, and Solution

The assembly of silver(I) and gold(I) complexes of functionalized N-heterocyclic carbenes (NHCs) of the type [M(C(n),amide-imy)(2)][anion] were studied, in which C(n),amide-imy stands for an NHC of imidazol-2-ylidene having one N-alkyl substituent (C(n)H(2n+1)) and one N-acetamido substituent, while the anions are Br(-), NO(3)(-), BF(4)(-) or PF(6)(-). A single crystal X-ray diffraction study reveals that self-assembly of [Ag(C(10),amide-imy)(2)][PF(6)] through Coulombic, hydrogen bonding, and hydrophobic interactions gives a lamellar structure with tubular architecture around the metal ion head core. Self-assembly of these functionalized NHC complexes also leads to the formation of the first example of thermotropic liquid crystals of silver(I)-NHCs and gels of gold(I)-NHC. Results from an infrared spectroscopy study show that the degree of chain motion in the gel state is smaller than that in the mesophase, yet comparable to that in the solid state. In addition, the technique of nuclear magnetic resonance diffusion ordered spectroscopy was found for the first time to be a good tool to study the phase transition of gels. Xerogels of gold(I)-NHCs display fibers, oriental lantern-shaped bundles of belts and helical fibers when observed under scanning electron and transmission electron microscopes.

Carboxylic acid functionalized imidazolium salts: sequential formation of ionic, zwitterionic, acid-zwitterionic and lithium salt-zwitterionic liquid crystals

Carboxylic acid functionalized imidazolium salts, their deprotonated carboxylate zwitterions and acid-zwitterion adducts have been studied, and are denoted as [N-Cn,N′-CO2H-Im][X] (Cn = CnH2n+1; X = Cl−, Br−, BF4− and PF6−), [N-Cn,N′-CO2-Im] and [(N-Cn,N′-CO2-Im)2H][anion] (anion = NO3− and Br−), respectively. Crystal structures of [N-C10,N′-CO2-Im]Br and [N-Cn,N′-CO2-Im]·2H2O studied by single-crystal X-ray diffraction indicate that carboxylic acid and carboxylate groups provide rich C–H⋯Br and/or C–H⋯O hydrogen bonding interactions in the construction of helical architecture. Except the PF6− salts, all the other types of compounds with long alkyl chains exhibit wide range SmA mesophase. Zwitterions and adducts represent two new classes of imidazolium based liquid crystals. The adducts [(N-Cn,N′-CO2-Im)2H]Br display wider mesophase range than the other series of compounds. Mixtures of lithium salts with zwitterion of [N-C10,N′-CO2-Im] form lithium containing liquid crystals at or near room temperature. A preliminary study of the mixtures of [N-C10,N′-CO2-Im]/[LiClO4] (3 : 1) and [N-C10,N′-CO2-Im]/[LiBF4] (3 : 1) placed between two ITO glasses shows that lithium ion conductivities increase upon increasing the temperature in the mesophase, yet decrease beyond the clearing temperature.

Structural, photophysical, and catalytic properties of Au(I) complexes with 4-substituted pyridines.

Ionic gold(I) complexes with general formula of [Au(Py)2][AuCl2] and [Au(Py)2][PF6] (Py = 4-substituted pyridines) have been synthesized. Structures of five Au(I) complexes and a Ag(I) complex were determined by single crystal X-ray diffraction. Evidence for cationic aggregation of [Au(py)2][PF6] complexes in solution was obtained by conductivity measurements and by the isosbestic point observed from variable temperature UV-visible absorption spectra. All compounds were luminous in the solid state. Calculations employing density functional theory were performed to shed light on the nature of the electronic transitions. While the [Au(4-dmapy)2][AuCl2] (4-dmapy = 4-dimethylaminopyridine) and [Au(4-pic)2][AuCl2] (4-pic = 4-picoline) emissions were found to be mainly ligand in nature, their [PF6](-) counterparts involved a Au...Au-interaction imbedded in the highest occupied molecular orbital. [Au(4-dmapy)2][AuCl2] was found to be an efficient catalyst for Suzuki cross-coupling of aryl bromide and phenylboronic acid.

Au(I)-benzimidazole/imidazole complexes. Liquid crystals and nanomaterials

Three series of Au(I)-imidazole complexes with stoichiometries of [Au(Cn-bim)Cl], [Au(Cn-im)Cl], and [Au(Cn-im)2][NO3] x 2H2O (Cn-bim = N-CnH2n+1 -substituted benzimidazole and Cn-im = N-CnH2n+1-substituted imidazole) together with the compound of [Au(C18-bim)2][NO3] are synthesiszed. Typical structures of each series are determined by single crystal X-ray diffraction. The last series of compounds, are liquid crystals, and exhibit a wider mesophase range than their Ag(I) analogues. These Au(I) complexes form Au nanostructures both through chemical reduction or thermolysis. For the first time, N-long chain imidazole is utilized to stabilize colloidal Au in solution. Also for the first time, unique examples of simple thermolysis to produce large Au plates of nanothickness are demonstrated. Formation of a plate-like morphology through fusion of sphere-like nanoparticles at an early stage is evidenced by TEM images.