Catalysts supported ionic liquids

Keywords Carbonylation Homogeneous catalysis Hydroformylation Immobilisation Ionic liquids Supported catalysts... 

Figure 13.9 Schematic showing continuous flow biocatalytic process using ionic liquid-supported catalyst in supercritical C02. (Reproduced with permission from [90]. Copyright (2007) Wiley-VCH Verlag).

Hydroformylation Reactions with an Ionic Liquid-Supported Catalyst. .. 58... 

In order to merge the advantages of homogeneous and heterogeneous catalysts, rhodium catalysts have also been immobilized. Several polymer-supported or ionic liquid-supported catalysts have been developed as weU [40-42]. 

Fig. 8. a) 3D representation of the aluminum plates fixing the ionic liquid-supported catalyst, b) 2D scheme of the structured catalytic wall microreactor. Adapted from Kiwi-Minsker et al. (2010). Reproduced by permission of Elsevier. 

Recently, iodobenzoates anchored onto an ionic liquid support (6.4) were coupled to various aryl boronic acids (6.5) in aqueous media using Pd(OAc)2 as the catalyst at 80°C to give the coupled product 6.6 (Scheme 6.3). Compounds 6.6 were purified simply by washing the reaction mixture with ether, which removed the unreacted starting materials and the side product 6.7 without the need of chromatography. Compounds 6.6 were then cleaved from the ionic liquid support... 

Supported aqueous phase (Chapter 3, Section 3.6, Chapter 5, Section 5.2.5) and supported ionic liquid phase catalysts, Chapter 7, Section 7.3) are probably not suitable for use with higher alkenes because the liquid feed slowly dissolves some of the water or ionic liquid changing the nature of the catalyst and leading to catalyst leaching. 

Organochloroaluminate ionic liquids as catalysts, 42 495-496 Organochromium catalysis attachment to support, 33 92-93 kinetics of polymerization, 33 93 support effects, 33 94-95 termination mechanism, 33 93-94 Organochromium catalysts, 33 58, 92-95... 

SILP hydroformylation catalysts were prepared by dissolving appropriate amounts of Rh(CO)2 (acac) and ligand in dried methanol followed by stirring for 30 min. Afterwards, the ionic liquid was added to the solution. After stirring for another 30 min, the support was added and the solution stirred for 60 min. Finally, the methanol was removed in vacuo and a pale red powder was obtained. The supported ionic liquid-phase catalyst was stored imder argon for further use. 

The first fixed-bed application of a supported ionic liquid-phase catalyst was hydroformylation of propylene, with the reactants concentrated in the gas phase (265). The catalyst was a rhodium-sulfoxantphos complex in two ionic liquids on a silica support. The supported ionic liquid phase catalysts were conveniently prepared by impregnation of a silica gel with Rh(acac)(CO) and ligands in a mixture of methanol and ionic liquids, [BMIMJPFg and [BMIM][h-C8Hi70S03], under an argon atmosphere. 

An area in which functionalised ionic liquids are already playing an important role in catalysis is heterogenisation on solid supports. The general concept involves the immobilisation of imidazolium and other cationic fragments onto solid supports using appropriate functional groups attached to the cation. An ionic catalyst then resides within the ionic matrix and several examples of such supported ionic liquid phase catalysts are provided in the subsequent chapters of this book. The concept is illustrated in Figure... 

As in many other areas of catalysis in ionic liquids, the research of the past years in ionic liquid supported olefin metathesis has been dominated by demonstrating the general feasibility in this reaction medium. With the development of the task-specific complexes new prospects have been opened and the improved recyclability of these compounds relative to the common metathesis catalysts is impressive. Apart from more active and stable catalysts, the development of enantioselective catalysts and of continuous processes are likely to be the next goals. 

In the previous sections the use of catalysts dissolved in ionic liquids has been documented with a variety of examples from the most recent literature. They were classified are catalytic systems based on the adoption of Strategies A, B and C, when solvent-less conditions were not adopted. In an ideal liquid-liquid biphasic system, the IL must dissolve the catalytic intermediates and, in part, the substrate to avoid that mass transfer limits reaction rates. Moreover, products should have a limited solubility in the IL to allow a facile product removal or extraction, and, possibly, the recycle of the ionic liquid-trapped catalyst. The separation of the catalyst from the products is made easier if solid support-immobilised ILs are used. The preference for a solid catalyst is dictated not only by the easier separation but also, as outlined by Mehnert in an excellent review article, " by (i) the possible use of fixed bed reactors, and (ii) the use of a limited amount of IL, a generally expensive chemical which can limit the economic viability of the process. In this section attention will be focused only on the most recent examples of solid-phase assisted catalysis using ionic liquids, following Strategy D. Examples prior to 2006 are covered in recent reviews and will not be discussed here. " ... 

A series of supported chiral VO(salen) complexes anchored on silica, single-wall carbon nanotube, achvated carbon or ionic liquids have been prepared through the simple methods based on the addition of mercapto groups to terminal C=C double bonds (Scheme 7.17) [58]. The four recoverable catalysts and the standard VO(salen) complex 37 were tested for the enantioselechve cyanosilylation of benzaldehyde using trimethylsilyl cyanide (Table 7.9). It should be noted that the ionic liquid-supported IL-VO(salen) showed the highest catalyhc achvity, though the ee-value was considerably reduced compared to the soluble 37 in [bmim][PF6] (entries 4 and 5). 

Table 7.14 Asymmetric Michael addition of cyclohexanone to P-nitrostyrene using ionic liquid-supported chiral pyrrolidines as a catalyst.

Mori M, Gomez Garcia R, Belleville MP et al (2005) A new way to conduct enzymatic synthesis in an active membrane using ionic liquids as catalyst support. Catal Today 104 313-317... 

Bordoloi A, Sahoo S, Lefebvre F, Halligudi SB (2008) Heteropoly acid-based supported ionic liquid-phase catalyst for the selective oxidation of alcohols. J Catal 259 232-239... 

Audic N, Clavier H, Mauduit M, Giiillemin JC (2003) An ionic liquid-supported ruthenium carbene complex a robust and recyclable catalyst for ring-closing olefin metathesis in ionic liquids. J Am Chem Soc 125 9248-49... 

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