Homogeneous Supported Synthesis Using Ionic Liquid Supports: Tunable Separation Properties

Recyclable Hypervalent Iodine Reagents in Modern Organic Synthesis

Hypervalent iodine (HVI) reagents have gained much attention as versatile oxidants because of their low toxicity, mild reactivity, easy handling, and availability. Despite their unique reactivity and other advantageous properties, stoichiometric HVI reagents are associated with the disadvantage of generating non-recyclable iodoarenes as waste/co-products. To overcome these drawbacks, the syntheses and utilization of various recyclable hypervalent iodine reagents have been established in recent years. This review summarizes the development of various recyclable non-polymeric, polymer-supported, ionic-liquid-supported, and metal–organic framework (MOF)-hybridized HVI reagents.

1 Introduction

2 Polymer-Supported Hypervalent Iodine Reagents

2.1 Polymer-Supported Hypervalent Iodine(III) Reagents

2.2 Polymer-Supported Hypervalent Iodine(V) Reagents

3 Non-Polymeric Recyclable Hypervalent Iodine Reagents

3.1 Non-Polymeric Recyclable Hypervalent Iodine(III) Reagents

3.2 Recyclable Non-Polymeric Hypervalent Iodine(V) Reagents

3.3 Fluorous Hypervalent Iodine Reagents

4 Ionic-Liquid/Ion-Supported Hypervalent Iodine Reagents

5 Metal–Organic Framework (MOF)-Hybridized Hypervalent Iodine Reagents

6 Conclusion

Effect of noncovalent interactions in ion pairs on hypervalent iodines: inversion of regioselectivity in sulfonyloxylactonization

The noncovalent interactions between the sulfonyloxy group and the cationic nitrogen-containing heterocyclic moiety substituted in hypervalent iodines caused specific regioselectivity in the sulfonyloxylactonization of 2-vinyl benzoic acids.

Comparing the Thermal and Electrochemical Stabilities of Two Structurally Similar Ionic Liquids

Here we focus on the thermal and variable temperature electrochemical stabilities of two ionic liquids (ILs) having a common tributyloctyl phosphonium cation [P_4,4,4,8]⁺ and two different orthoborate anions: bis(mandelato)borate [BMB]⁻ and bis(salicylato)borate [BScB]⁻. The thermo-gravimetric analysis data suggest that [P_4,4,4,8][BScB] is thermally more stable than [P_4,4,4,8][BMB] in both nitrogen atmosphere and air, while the impedance spectroscopy reveals that [P_4,4,4,8][BScB] has higher ionic conductivity than [P_4,4,4,8][BMB] over the whole studied temperature range. In contrast, the electrochemical studies confirm that [P_4,4,4,8][BMB] is more stable and exhibits a wider electrochemical stability window (ESW) on a glassy carbon electrode surface as compared to [P_4,4,4,8][BScB]. A continuous decrease in the ESWs of both ILs is observed as a function of operation temperature.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C-C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of using hypervalent iodine compounds as an environmentally sustainable alternative to heavy metals.

Thermal stability of imidazolium-based ionic liquids

This work highlights the factors tuning the thermal stability of imidazolium-based ionic liquids (IL) associated to bis(trifluoromethanesulfonyl)imide anion [NTf2]. The decomposition temperatures (Td) were evaluated by thermogravimetric analyses (TGA) with optimized parameters to obtain reproducible Td. The impact of the alkyl chain length and of the presence of functional groups and unsaturations on Td were evaluated. The thermal behaviour was governed by Van der Waals interactions between alkyl chains, and by inter and intra coulombic interactions such as hydrogen bonds.

Synthesis of Cyanamides from Isoselenocyanates Promoted by Recyclable Ionic Liquid-Supported (Diacetoxyiodo)Benzene

One-pot synthesis of cyanamides from isoselenocyanates through deselenisation promoted by ionic liquid-supported hypervalent iodine(III) reagent 1-(4-diacetoxyiodobenzyl)-3-methylimidazolium tetrafluoroborate ([dibmim]+[BF4]−) was developed. This approach provided a simple, mild and environmentally benign way to construct cyanamides in good yields. Moreover, powder Se and [dibmim]+[BF4]− could be easily recycled. It was the first example of [dibmim]+[BF4]− to be used as a deselenising agent.

An ionic liquid immobilized copper complex for catalytic epoxidation

A catalytic system consisting of copper complex and hydrogen peroxide in Emim ionic liquid medium was effective in the epoxidation of olefins and terpenes. The catalyst and the ionic liquid mixture was recycled and reused consistently.

The Synthesis of 4-Tosyloxy-2-Substituted Phenols using New Solid Pyridinium Salt Supported [Hydroxyl(Tosyloxy)Iodo]Benzene Reagents

Two new solid pyridinium salt supported HTIB reagents ( N-{4-[hydroxyl(tosyloxy)iodo]benzyl}pyridinium tetrafluoroborate and N-{4-[hydroxyl(tosyloxy)iodo]phenylcarbamoylmethyl}pyridinium tetrafluoroborate) were synthesised using a pyridinium salt as a cationic support. Although the former was hygroscopic the latter was stable in air and in a highly humid atmosphere over a few weeks. The latter has an extra amide linkage. The structures of both compounds were established by IR, 1H NMR, 13C NMR, MS and elemental analysis. Then, two 4-tosyloxy-2-substituted phenols were successfully prepared using the new reagents. Both reagents were easily regenerated in high yields.

A Facile Synthesis of Ionic Liquid-Supported Iodosylbenzenes

A synthesis of two ionic liquid-supported iodosylbenzenes,1-(4-iodosylbenzyl)pyridinium tetrafluoroborate and 1-(4-iodosylbenzyl)-3-methylimidazolium tetrafluoroborate, which are potentially useful oxidising agents in organic synthesis is reported. Both compounds are stable, active, and easy to handle. The chemical structures of both compounds were characterised by 1H NMR, 13C NMR, IR, MS and elemental analysis.

Trigonal tricationic ionic liquids: a generation of gas chromatographic stationary phases

Trigonal tricationic ionic liquids (ILs) are a new class of ILs that appear to be unique when used as gas chromatographic stationary phases. They consist of four core structures; (1) A = mesitylene core, (2) B = benzene core, (3) C = triethylamine core, and (4) D = tri(2-hexanamido)ethylamine core; to which three identical imidazolium or phosphonium cationic moieties were attached. These were coated on fused silica capillaries, and their gas chromatographic properties were evaluated. They were characterized using a linear solvation parameter model and a number of test mixtures. On the basis of the literature, it is known that both monocationic and dicationic ILs possess almost identical polarities, solvation characteristics, and chromatographic selectivities. However, some of the trigonal tricationic ILs were quite different. The different solvation parameters and higher apparent polarities appear to generate from the more rigid trigonal geometry of these ILs, as well as their ability to retain the positive charges in relatively close proximity to one another in some cases. Their unique selectivities, retention behaviors, and separation efficiencies were demonstrated using the Grob mixture, a flavor and fragrance test mixture, alcohols/alkanes test, and FAME isomer separations. Two ILs C1 (methylimidazolium substitution) and C4 (2-hydroxyethylimidazolium substitution) had higher apparent polarities than any know IL (mono, di, and tricationic ILs) or commercial stationary phases. The tri(2-hexanamido)ethylamine core IL series proved to be very interesting in that it not only showed the highest separation efficiency for all test mixtures, but it also is the first IL stationary phase (containing NTf(2)(-) anions) that eliminates peak tailing for alcohols and other H-bonding analytes. The thermal stabilities were investigated using three methods: thermogravimetric analysis (TGA) method, temperature programmed gas chromatographic method (TPGC), and isothermal gas chromatographic method. The D core series had a high working temperature range, exceptional selectivities, and higher separation efficiencies than comparable polarity commercial columns. It appears that this specific type of multifunctional ILs may have the most promising future as a new generation of gas chromatographic stationary phases.

"Nonsolvent" applications of ionic liquids in biotransformations and organocatalysis

The application of room-temperature ionic liquids (RTILs) as (co)solvents and/or reagents is well documented. However, RTILS also have "nonsolvent" applications in biotransformations and organocatalysis. Examples are the anchoring of substrates to RTILs; ionic-liquid-coated enzymes (ILCE) and enzyme-IL colyophilization; the construction of biocatalytic ternary reaction systems; the combination of enzymes, RTILs, membranes, and (bio)electrochemistry; and ionic-liquid-supported organocatalysts. These strategies provide more robust, more efficient, and more enantioselective bio- and organocatalysts with many practical applications. As shown herein, RTILs offer a wide range of promising alternatives to conventional chemistry.

PEG-linked geminal dicationic ionic liquids as selective, high-stability gas chromatographic stationary phases

It is known that room-temperature ionic liquids (RTILs) have wide applicability in many scientific and technological fields. In this work, a series of three new dicationic room-temperature ionic liquids functionalized with poly(ethylene glycol) (PEG) linkages were synthesized and characterized via a linear solvation model. The application of these ILs as new GC stationary phases was studied. The efficient separation of several mixtures containing compounds of different polarities and 24 components of a flavor and fragrance mixture indicated comparable or higher resolving power for the new IL stationary phases compared to the commercial polysiloxane and poly(ethylene glycol)-based stationary phases. In addition, the selectivities of the IL stationary phases could be quite unique. The separation of a homologous alkane and alcohol mixture displayed the "dual nature" of these ionic liquids as GC stationary phases. The thermal stability study showed the column robustness up to 350 degrees C. The high separation power, unique selectivity, high efficiency and high thermal stability of the new dicationic ionic liquids indicate that they may be applicable as a new type of robust GC stationary phase.

Reaction Rates as a Function of Scale within Ionic Liquids: Microscale in Droplet Microreactors versus Macroscale Reactions in the Case of the Grieco Three-Component Condensation Reaction

Task-specific ionic liquids (TSILs) and more specifically binary task-specific ionic liquids (BTSILs), a unique subclass, have been shown to be excellent supports for solution-phase chemistry. The negligible volatility of ionic liquids enables their use as stable droplet microreactors in atmospheric environments without oil protection or confinement. These droplets can be moved, merged and mixed by electrowetting on a chip. Solution-phase synthesis can be performed on these open digital microfluidic labs-on-a-chip as illustrated by a study of the Grieco three-component reaction in [tmba][NTf(2)]-droplet (tmba=N-trimethyl-N-butylammonium NTf(2)=bis(trifluoromethylsulfonyl)imide) microreactors. A detailed study of matrices and scale effects on conversion and kinetic rates of this three-component condensation is presented in this paper. Reactions have been shown to be slower in droplets than in batches in the absence of additional mixing. Also, a significant influence of the ionic-liquid matrix has been observed. Finally, an increase of droplet's temperature resulted in a kinetics enhancement so as to reach macroscale reaction rates, probably because of a much better mixing of reaction's components involving a Marangoni's effect.

Physicochemical properties of nitrile-functionalized ionic liquids

A series of ionic liquids (ILs) based on nitrile-functionalized imidazolium, pyridinium, and quaternary ammonium as cations and chlorides and tetrafluoroborate, hexafluorophosphate, dicyanamide, and bis(trifluoromethanesulfonyl)imide as anions have been prepared and characterized. The physicochemical properties such as spectroscopic, thermal, solubility, surface, electrochemical, tribological, and toxic properties were comparatively studied. The results showed that the incorporation of a CN group to cations could result in remarkable changes in these properties. The reason resulting in such remarkable differences in the properties may be attributed to the conformational changes in the imidazolium groups caused by the interaction between the CN group with other neighboring cations or anions and the enhancement in hydrogen-bonding interactions due to the incorporation of a CN group.

Ionic Liquid Supports Stable Under Conditions of Peptide Couplings, Deprotections and Traceless Suzuki Reactions

Ionic liquid supports (ILS) functionalized with carboxylic, alcoholic or amino groups were synthesized, based on 1-methylimidazolium and pyridinium cations, and bromide, chloride, iodide and tetrafluoroborate anions. These reactive ionic liquids were fully characterized by NMR and HRMS. Ionic liquids based on 1-(6-aminohexyl)-3-methylimidazolium iodide have been used in the conditions of peptide chemistry such as coupling and deprotection reactions. A method for attaching (bromophenyl)silanes to the ionic liquid supports was also developed to introduce traceless linkers. An ionic liquid with attached bromobenzene was reacted with ArB(OH)2 under the Suzuki cross-coupling conditions and the resulting compound was cleaved by bromodesilylation with Br2/pyridine to give the substituted products in good yields. The substrate loading of the ILS is high and can be tuned to between 2.5 and 5.0 mmol/g.