Immobilization in ionic liquids

Catalysts immobilized in ionic liquids are sometimes leached into the product phase. It may therefore be necessary to design new catalysts for use in ionic liquids. 

Processes in which catalysts immobilized in ionic liquids have been combined with product extraction using SCCO2 show considerable promise [20], The ionic liquids are poorly soluble in the SCCO2 which allows products to be extracted without contamination from the ionic liquid or the catalyst. 

Oberson de Souza, M. and de Souza, R. F. Ethylene oligomerization with Ni(MeCN)6(BF4)2 in homogeneous phase, immobilized in ionic liquids or heterogenized in zeolite. Current Top. Catal., 3, 2002, 267-273. 

Catalytic asymmetric Diels-Alder reactions in ionic liquids, using an air- and moisture-stable chiral BlNOL-indium complex prepared from ( S)-BINOL and InClj, have also reported [46]. The reactions of various dienes with 2-methacrolein or 2-bromoacrolein proceeded in an ionic hquid with good yields and excellent enantioselectivities (up to 98% ee). The chiral In(lll) catalyst immobilized in ionic liquid [hmim][PF 5] could be reused seven times without any significant loss in catalytic activity (Scheme 7.13). 

Yadav JS, Subba Reddy BV, Reddy JSS (2002) DylOTflj-immobilized in ionic liquids a novel and recyclable reaction media for the synthesis of 2,3-unsaturated glycopyranosides. J Chem Soc Perkin Trans 1 2390-2394... 

Yadav, J.S., Reddy, B.V.S., Gayathri, K.U. and Prasad, A.R. (2002) Scandium triflate immobilized in ionic liquids A novel and recyclable catalytic system for hetero-Diels-Alder reactions. Synthesis-Stuttgart, 17, 2537-2541. 

Friedel-Crafts alkylation. Secondary alkyl mesylates are adequate alkyl donors in this reaction." Both Sc(OTf)3 and TfOH can be used as the catalyst. It has also been reported that Sc(OTf js immobilized in ionic liquid forms a recyclable system for arene alkylation with alkenes. ... 

Many catalyst complexes that are suitable for operation and immobilization in ionic liquids are ionic themselves with the charge either located at the metal center or in the ligand sphere. Thus, these complexes are accessible to electrospray ionization mass spectroscopy (ESI-MS). However, it is not a trivial task to investigate an ionic catalyst complex next to the vast excess of ionic liquid ions. Dyson s group reported a combination of ESI-MS with quadropole ion trap methods that enabled the detection of, e.g. several cationic Rh-complexes in the ionic liquid [BMIM][PF6] [62]. They could demonstrate that the detection limit of their methodology (catalyst concentrations down to 1 x 10 mol 1 were analyzed) is so low that even complexes in the typically very low concentration of a catalytic experiment could be easily characterized, even in the presence of a large excess of ionic liquid ions. 

As a further oxygen source tert-butyl hydroperoxide (TBHP) was applied in combination with dioxomolybdenum(VI) complexes immobilized in ionic liquid for the epoxidation of ds-cyclooctene [155]. Again, a strong dependence of reactivity, selectivity and the ability for recycling conditions on the chosen ionic liquid and solvent was described. 

A particularly successful concept for catalyst immobilization in ionic liquids is the use of ionic ligands. Some examples of Pd-complexes carrying ionic ligands that have been applied in Heck reactions are listed in Table 5.3-9. Entries 1 and... 

Let us first make a very general but nevertheless very true and important statement One should never try to immobilize and reqrcle a bad catalyst. That in particular is true for catalyst immobilization in ionic liquids. 

Kantam ML, Neeraja V, Kavita B, Neelima B, Chaudhuri MK, Hussain S (2005) Cu(aeac)2 immobilized in ionic liquids a recoverable and reusable catalytic system for aza-miehael reactions. Adv Synth Catal 347 763-766... 

Recently, various Hoveyda-type carbenes were attached to different resins or insoluble inorganic supports preferentially via the 2-alkoxybenzylidene fragment. An alternative method involves the use of tagged catalysts, which can be easily separated from untagged products by a phase-transfer event (precipitation or hquid-hquid partition). One particularly innovative method involves a catalyst immobilization in ionic liquids (IL). Because of their interesting properties such as ease of reuse, nonvolatility, and good ability to dissolve... 

Immobilized in ionic liquids, Dy(OTf)3 can become an easily recyclable green catalyst. It has been reported that Dy(OTf)3 in an ionic liquid can be recycled up to six times with no loss of reactivity when catalyzing the reaction of indoles with ketones, aldehydes, or imines. The reaction does not proceed without the catalyst. 

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