Ionic liquid catalysis

The range of ligands developed for ionic liquid catalysis is much smaller than that for other immobilization solvents such as water and fluorous phases as off the shelf ligands and catalysts can often be used in ionic liquids. For example, a number of catalysts that were developed to operate in organic solvents under homogeneous conditions are salts themselves and do not need to be modified for use in ionic liquids [25],... 

Yonker, C. R. and Linehan, J. C., A high-pressure NMR investigation of reaction chemistries in a simple salt hydrate,. Supercrit. Fluids, 29, 257 2004. Mehnert, C. R, Supported ionic liquid catalysis, Chem. Eur. ]., 11,50,2005. Giernoth, R. and Bankmann, D., Transition-metal free synthesis of perdeuter-ated imidazolium ionic liquidsby alkylation and H/D exchange, Eur. J. Org. Chem., 2008 (in print). DOT 10.1002/ejoc.200700784. 

The major problem associated with aqueous catalysis is the limited and often very low solubility of certain organic reactants in water. Much work is needed to find practical solutions for these hydrophobic reactants. Possibilities deserving further attention include the application of fluorous biphasic catalysis or nonaqueous ionic liquid catalysis. The potential of organic reactions compatible with or even promoted by water is not yet fully exploited. 

Lansalot-Matras, C. and Moreau, C., Dehydration of fructose into 5-hydroxymethylfurfural in the presence of ionic liquids. Catalysis Commun 2003, 4(10), 517-520. 

The hydroformylation of 1-hexene by supported ionic liquid catalysis (SILC) was recently reported by researchers at ExxonMobil. In this system, the active catalyst HRh(CO)(tppti)3 (tppti = tri(m-sulfonyl)triphenyl phosphine tris(l-butyl-3-methyl-imidazolium)) is contained within the ionic liquid phase while excess tppti ligand is immobilized in the support material. TOP values of 65 min" were obtained with silc while an unsupported biphasic ionic liquid medium gave TOP values of 23 min. ... 

Supported ionic liquid catalysis is one of the main examples of SLPC adopted [120] to take advantage of ionic liquid properties without the drawbacks evidenced in Section 2.3.6. The viability of this concept has been confirmed by several studies that have successfully confined various ionic phases to the surface of support materials and explored their potential catalytic applications. Although most of the evaluated supports were silica based, several studies have focused on polymeric materials, including membranes. These materials were prepared by using two different immobilization approaches. The first involves the covalent attachment of ionic liquids to the support surface whereas the second simply deposits the ionic liquid phases containing catalytically active species on the surface of the support. 

Gruttadauria et al. [71a] utilized the previously described supported ionic liquid catalysis (SILC) concept for the L-proline-catalyzed aldol reaction (Scheme 2.33). 

Chen L, Huang XJ, Li YQ, Zhou MY, Zheng WJ (2009) A one-pot multicomponent reaction for the synthesis of 2-amino-2-chromenes promoted by N, N-dimethylamino-functionalized basic ionic liquid catalysis under solvent-free condition. Monatsh fUr Chem 140 45 7... 

Mehnert CP (2005) Supported ionic liquid catalysis. Chem Eur J 11 50-56... 

Catalyst leaching was not observed and the same catalyst was used for 18 batch runs without significant loss of activity. Both hydroformylations and hydrogenations clearly showed that supported ionic liquid catalysis is a very useful and efficient principle. 

In the context of this chapter we aim to illustrate the state-of-the-art in this rapidly progressing field of ionic liquid catalysis, exemplified for selective hydrogenation and Heck reactions. Other applications of nanoparticulate catalyst systems have been reported in hydrosilylation reactions [268], Suzuki [269] and Stille coupling [270]. 

To evaluate a priori whether mass transfer or solubility issues will seriously affect the probability for success in multiphasic ionic liquid catalysis the following considerations may be valuable. 

In summary, the few initial studies conducted so r on the inter cial structure between ionic liquids and solid sur ces clearly suggest - in a more general context - that confinement of ionic liquids on solid sur ces definitely induces some distinctive, structural control of the molecular kyering of the ionic liquid and of the ionic hquid distribution (i.e. wetting ability). However, further investigations are surely needed to elucidate these effects in the context of supported ionic liquid catalysis in more detail. 

Afeworki, Supported ionic liquid catalysis for hydroformylation and hydrt enation reactions, 2003, 226th ACS National Meeting, New York. USA. 

Ionic Liquids in Context Separations and Engineering Green Synthesis Nuclear and Electrochemistry Ionic Liquid Systems Properties of Ionic Liquids Catalysis I Catalysis II... 

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