Ionic supported catalysis

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. 

In comparison to traditional biphasic catalysis using water, fluorous phases or polar organic solvents, catalysis in ionic liquids represents a new and advanced way to combine the specific advantages of homogeneous and heterogeneous catalysis. In many applications the use of a defined transition metal complex immobilised on a liquid ionic support has already shown its unique potential. 

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). 

Mehnert CP, Cook RA, Dispenziete NC, Afework M (2002) Supported ionic hquid catalysis - a new concept for homogeneous hydroformylation cattilysis. J Am Chem Soc 124 12932-12933... 

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

Supported liquid-phase catalysis,in which the catalyst is dissolved in a small volume of solvent, adsorbed on, usually, a hydrophilic solid, seeks to resolve issues associated with substrate solubility in multi-phase catalysis and performance/catalyst leaching in supported catalysis reports on the hydroformylation of long-chain alkenes under both supported aqueous phase and supported ionic liquid-phase regimes have been reported. 

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 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. 

This section summarizes the recent progress in supported ionic hquid catalysis, demonstrating synthetic apphcations where the ionic liquid can play its role as either iimocent solvent (SILP) or the catalyst itsdf (SILC), depending on the specific cation/anion combination and the reaction under investigation. 

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

Mehnert, C.P., Mozeleski, E.J., and Cook, R.A. (2002) Supported ionic liquid catalysis investigated for hydrogenation reactions. Chem. Common., 8 (24), 3010-3011. 

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