1,3-Dimethylimidazolium formate

Klein et al. revealed a new catalytic mechanism of FA decomposition in the presence of IL 1,3-dimethylimidazolium ([mmim]) performing a Bom-Oppenheimer molecular dynamics (BO-MD)[200, 201] simulation at an elevated temperature of 3,000 K. It was shown that formate (HC02 ) dissociates into hydride (H ) and carbon dioxide (CO2), which was proposed to be the ratedetermining step. This decomposition pathway can be explained by the stabilization of the hydride in the strong electrostatic field (cation and anion shells) of the IL. Calculated radial distribution functions (RDF) shed light on the solvation of the formate in the ionic liquid 1,3-dimethylimidazolium formate [mmim] [HCOO] [202]. 

Another means of in situ metal-carbene complex formation in an ionic liquid is the direct oxidative addition of the imidazolium cation to a metal center in a low oxidation state (see Scheme 5.2-2, route b)). Cavell and co-workers have observed oxidative addition on heating 1,3-dimethylimidazolium tetrafluoroborate with Pt(PPli3)4 in refluxing THF [32]. The Pt-carbene complex formed can decompose by reductive elimination. Winterton et al. have also described the formation of a Pt-car-bene complex by oxidative addition of the [EMIM] cation to PtCl2 in a basic [EMIM]C1/A1C13 system (free CP ions present) under ethylene pressure [33]. The formation of a Pt-carbene complex by oxidative addition of the imidazolium cation is displayed in Scheme 5.2-4. 

Normally acylation reactions would be considered standard chemistry but replacing an aryl bromide with a ketone under relatively mild conditions warrants attention. Here 23 is treated with 1,3-dimethylimidazolium iodide (1,3-dii) in refluxing THE leading to the formation of the ketone 24 (Equation 8) <1997H(45)2159>. 

Scheme 5. Formation of a Pt-carbene complex by oxidative addition of 1,3-dimethylimidazolium ion.

Reactions proceed faster and more smoothly when the reactants are dissolved, because of diffusion. Although reactions in the solid state are known [1] they are often condensations in which a molecule of water is formed and reaction takes place in a thin film of water at the boundary of the two solid surfaces. Other examples include the formation of a liquid product from two solids, e.g. dimethylimidazolium chloride reacts with aluminum chloride to produce the ionic liquid, dimethylimidazolium tetrachloroaluminate [2]. It is worth noting, however, that not all of the reactant(s) have to be dissolved and reactions can often be readily performed with suspensions. Indeed, so-called sol-id-to-solid conversions, whereby a reactant is suspended in a solvent and the product precipitates, replacing the reactant, have become popular in enzymatic transformations [3]. In some cases, the solvent may be an excess of one of the reactants. In this case the reaction is often referred to as a solvolysis, or, when the reactant is water, hydrolysis. 

In order to eliminate the possibility for in situ carbene formation Raubenheimer et al. synthesized l-alkyl-2,3-dimethylimidazolium triflate ionic liquids and applied these as solvents in the rhodium catalyzed hydroformylation of l-hejEne and 1-dodecene [178]. Both, the classical Wilkinson type complex [RhCl(TPP)3] and the chiral, stereochemically pure complex (—)-(j7 -cycloocta-l,5-diene)-(2-menthyl-4,7-dimethylindenyl)rhodium(i) were applied. The Wilkinson catalyst showed low selectivity towards n-aldehydes whereas the chiral catalyst formed branched aldehydes predominantly. Hydrogenation was significant with up to 44% alkanes being formed and also a significant activity for olefin isomerization was observed. Additionally, hydroformylation was found to be slower in the ionic liquid than in toluene. Some of the findings were attributed by the authors to the lower gas solubility in the ionic liquid and the slower diffusion of the reactive gases H2 and CO into the ionic medium. 

The hyperbranched PILs represent effective stabilizers in heterogeneous polymerization reactions. When employing water-soluble PEHO-ClImOTs as the emulsifier in the 2,2 -azobis(2-methylpropionitrile) (AIBN) initiated mini-emulsion polymerization of styrene, stable polystyrene (PS) latexes were obtained. Characterization by means of transmission electron microscopy (TEM) indicated the presence of spherical PS nanoparticles (see Figure 7.5). Further studies revealed that, by modifying parameters such as the PIL/monomer ratio and the duration of the ultra-sonication treatment prior to the polymerization, the mean diameter of the obtained PS particles can be varied from 40 nm to 110 nm. In contrast to PEHOClImOTs, the use of the low-molecular-weight ILs 1,3-dimethylimidazolium tosylate or 1-butyl-3-methylimidazolium tosylate did not result in the formation of stable latexes. 

R. Yang, H. Zhang, D. Kirichenko, K Rogers, R. D., Ionic liquids via reaction of the zwitterionic l,3-dimethylimidazolium-2-carboxylate with protic adds. Overcoming synthetic limitations and establishing new halide free protocols for the formation of ILs. Green Chem, 2007, 9 (1), 90-98. 

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