Taramatee Ramnial

Polymorphism of Zn[Au(CN)2]2 and Its Luminescent Sensory Response to NH3 Vapor

Four polymorphic forms of the complex Zn[Au(CN)2]2 have been synthesized and both structurally and spectroscopically characterized. In each of the four polymorphs, a zinc center in a tetrahedral geometry with a Au(CN)2(-) unit at each tetrahedral vertex is observed. All four structures contain three-dimensional networks based on corner-sharing tetrahedra. Because of the long Au(CN)2(-) bridging unit, the extra space not occupied by one network is filled by two to five additional interpenetrated networks. Short gold-gold bonds with lengths ranging from 3.11 to 3.33 A hold the interpenetrated networks together. Three of the four polymorphs are luminescent, having solid-state emissions with wavelengths ranging from 390 to 480 nm. A linear correlation between the emission energy and the gold-gold distance was observed. Upon exposure to ammonia vapor, the polymers altered their structures and emission energies, with the emission wavelength shifting to 500 nm for {Zn(NH3)2[Au(CN)2]2}, which adopts a two-dimensional layer structure with octahedral, trans-oriented NH3 groups. The adsorption route is dependent on the polymorph used, with NH3 detection limits as low as 1 ppb. Desorption of the ammonia occurred over 30 min at room temperature.

Carbon-Centered Strong Bases in Phosphonium Ionic Liquids

Phosphonium ionic liquids (PhosILs), most notably tetradecyl(trihexyl)phosphonium decanoate (PhosIL-C(9)H(1)9COO), are solvents for bases such as Grignard reagents, isocyanides, Wittig reagents (phosphoranes), and N-heterocyclic carbenes (NHCs). The stability of the organometallic species in PhosIL solution is anion dependent. Small bases, such as hydroxide, react with the phosphonium ions and promote C-H exchange as suggested by deuterium-labeling studies. A method to dry and purify the ionic liquids is described and this step is important for the successful use of basic reagents in PhosIL. NHCs have been generated in PhosIL, and these persistent solutions catalyze organic transformations such as the benzoin condensation and the Kumada-Corriu cross-coupling reaction. Phosphoranes were generated in PhosIL, and their reactivity with various organic reagents was also tested. Inter-ion contacts involving tetraalkylphosphonium ions have been assessed, and the crystal structure of [(n-C(4)H(90)(4)P][CH(3)CO(2).CH(3)CO(2)H] has been determined to aid the discussion. Decomposition of organometallic compounds may also proceed through electron-transfer processes that, inter alia, may lead to decomposition of the IL, and hence the electrochemistry of some representative phosphonium and imidazolium ions has been studied. A radical derived from the electrochemical reduction of an imidazolium ion has been characterized by electron paramagnetic resonance spectroscopy.

An imidazol-2-ylidene borane complex exhibiting inter-molecular [C–Hδ+⋯Hδ−–B] dihydrogen bonds

The structure of 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene·BH3, (1·BH3) has been determined by X-ray crystallography; the high melting solid exhibits head-to-tail alignment of the molecular dipoles in the solid state, with the closest intermolecular contact being a simple well-defined example of an unconventional [C–Hδ+⋯Hδ−–B] dihydrogen bond.

Reactions of N-heterocyclic carbenes (NHCs) with one-electron oxidants: possible formation of a carbene cation radicalElectronic supplementary information (ESI) available: spectroscopic data, calculated atomic coordinates and cyclic voltammograms. See http://www.rsc.org/suppdata/cc/b3/b314110a/

One-electron oxidation of N-heterocyclic carbenes (NHCs) has been carried out using oxidising agents such as tetracyanoethylene (TCNE) and ferrocenium [Cp(2)Fe](+); the formation of carbene radical cations is postulated.

Electrochemical reduction of an imidazolium cation: a convenient preparation of imidazol-2-ylidenes and their observation in an ionic liquid

1,3-Bis(2,4,6-trimethylphenyl)imidazolium chloride is reduced electrochemically and chemically to produce a nucleophilic carbene, namely 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene. The carbene was also shown to be compatible with and persistent in the ionic liquid tetradecyl(trihexyl)phosphonium chloride.

Grignard reagents in ionic solvents: electron transfer reactions and evidence for facile Br-Mg exchange.

Grignard reagents form persistent solutions in phosphonium ionic liquids possessing O-donor anions and these solutions are excellent reaction media for electron transfer processes and transmetallation reactions.

From the reactivity of N-heterocyclic carbenes to new chemistry in ionic liquids

N-Heterocyclic carbenes have numerous applications in synthetic chemistry. We detail the reactivity and chemistry of these molecules including investigations into their reactions with small reagents, their use for the preparation of polarised azines and their potential application as NLO materials. The chemistry of imidazolium salts, which are related to NHCs by the addition of a proton, is also discussed. New chemistry for ionic liquids is also revealed.

Phosphonium-Based Ionic Liquids as Efficient Borane Carriers

Phosphonium-based ionic liquids form new ionic liquids when treated with borane (BH3), and these ionic liquids are useful for reduction reactions involving carbonyl compounds. Alane (AlH3) reacts with the phosphonium cation, nevertheless the resulting solutions are capable of reducing esters to aldehydes. Phosphonium-based ionic liquids may serve as useful materials for reactive gas transport, and hence may serve as a fluid alternative to porous materials and may provide a convenient method of safely transporting boron hydrides for a variety of applications.

N-HETEROCYCLIC CARBENES: EXOTIC MOLECULES AS PRECURSORS TO UNUSUAL HYDROGEN BONDS

Hydrogen bonds are weak directional forces that are evident in a large number of chemical systems. Although they have been studied for over a century, the range of donor-acceptor pairs continues to be extended. Recently, isolable N-heterocyclic carbenes have been prepared and these molecules provide a novel route into a number of unusual hydrogen bonds. Here we briefly review structural studies on these interactions.

Non-classical NHC transfers from the reaction of (IMes)AgCl with osmium carbonyl clusters

N-Heterocyclic carbene transfer reactions were attempted using IMesAgCl and two osmium clusters. The products isolated from these reactions suggest that NHC transfers can be unpredictable.