Imidazolium grafting

In another approach, heterogeneous olefin epoxidation catalysts were prepared by electrostatic attachment of binuclear peroxotungstate complexes onto an imidazolium-grafted silica support by ion-exchange [78]. The catalyst was made by initial grafting of the imidazolium-cations onto a pre-dried silica support by treatment with l-octyl-3-(3-triethoxysilypropyl)-imidazolium hexafluorophosphate. 

Fig. 5.6-5 Olefin epoxidation with H2O2 using a supported ionic liquid catalyst containing an imidazolium-grafted silica support with electrostatic attached ( W(=0)(02)2(H20) 2(H-0)r complex anions [79],...

The first use of room temperature ionic liquids as potential novel soluble phases for combinatorial synthesis has recently been described. As model reaction the Knoevenagel condensation of salicyl aldehyde grafted on to an imidazolium-derived ionic liquid was studied under the action of microwave irradiation (Scheme 12.19) [66]. Reactions were performed without additional solvent in the presence of a basic catalyst, utilizing microwave irradiation in a designated monomode microwave reac-... 

Odourless and non-volatile organosulfur compounds grafted to an imidazolium ionic liquid scaffold has been synthesized. The sulfoxides have been used for an efficient oxidation of primary allylic and benzylic alcohols into aldehydes and secondary alcohols to ketones under Swern oxidation conditions and the corresponding sulfides can be recovered and recycled.110... 

Different methods for the immobilisation of ionic liquids have been tested. These can be divided into two different categories a) via the inorganic anion (method of incipient wetness and b) via the organic cation, here a methyl-alkyl-imidazolium cation. The method of incipient wetness was presented by Hoelderich [5], we concentrate on the immobilisation of ionic liquids by the methods of grafting or by synthesising organically modified MCM 41 materials (Sol gel method) (seeFigure 1). 

An alternative sol-gel strategy has been reported for the preparation of a closely related material. Using the approach of the initial grafting of the imidazolium cation onto pre-dried silica, followed by treatment with PdCl2, non-acidic supported palladium-based ILs were also prepared and used in Suzuki-Miyaura coupling reactions. ... 

In addition, immobilized ionic liquids have been employed for the 0-acylation and A-acylation. Kara et al. have investigated the reactions that supported ionic liquids in Upase-catalyzed asymmetric acylation of 7-phenylethanol with vinyl acetate in the reaction temperature range of 25-60°C and found that the immobilized [EMlM][NTfJ can stabilize the lipase against inactivation and maintain good enantioselectivity [152]. Furthermore, Paun s group via grafting 7,5-dimethyl-5-(5-triethoxysilylpropyl)-imidazolium tetrafluoroborate or bis (trifluoromethyl)... 

The other immobilization methods include carbon nanotubes and nanoparticles. PolyCglycidyl methacrylate)-grafted multiwalled carbon nanotubes (MWNT) were covalently attached to A-butyl imidazolium bromide. An indium tin oxide (ETO) electrode coated with such MWNT-IL successfully immobilized tyrosinase and showed sensing response toward phenol at the range of 0.01-0.08 mM at ambient pH and temperature [60]. Similarly, glassy carbon (GC) electrode was coated with... 

MW heating of supported thioureas w-substituted by an ester function used as a grafting element to the imidazolium moiety in the presence of diethylamine... 

Scheme 1 Immobilization of chloroaluminate-based IL by grafting of imidazolium chloride followed by the addition of AIQ, [11].

Figure 4.3 Immobilization of chloroaluminate-based ionic liquid by grafting of imidazolium chloride (a] and the scheme of the concept of supported ILs (b]. From Ref. [4], Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission.

Silica grafted imidazolium-based ionic liquids efficient heterogeneous catalysts for chemical fixation of COj to a cyclic carbonate. Energy Environ. Sci.,... 

In situ generation of Pd-NHC complexes in an imidazolium-type ionic liquid matrix and grafting of the catalyst on the surface of silica was reported by Karimi and Enders [41]. Pal-ladium(II) anchored on an ionic Uquid matrix, derived from A-3-(3-trimethoxysilylpropyl)-3-methyl imidazolium chloride, displays high thermal stabihty up to 280 °C. Catalyst 8... 

Figure 8.16 Plausible mechanism over carboxyl-functionalized imidazolium-based IL grafted onto cross-linked divinylbenzene polymer (adapted from Ref [61]).

The case of chemically grafted cations is by far the most studied form of ionosilicas [76]. This is due to the chemical versatility of the cationic precursors that are most often derived from imidazolium, ammonium, pyridinium, or phospho-nium compounds. Due to their ease of derivatization, in most cases the cationic substructure is functionalized with hydrolyzable trialkoxysilyl groups. As ionosilicas are often inspired with ionic liquids, imidazolium-containing ionosilicas have an outstanding position in this field. 

The other three cases are less common. In the case of chemically anchored anionic species, mostly carboxylate [78,79] or sulfonate groups have been investigated. Examples for chemically fixed cation/anion pairs are scarce here, ammonium carboxylate [80,81] or, more related to water-immiscible ionic liquids, guanidinium sulfonimide ion pairs [82] have been reported. The chemical grafting of zwitterionic species is nearly always related to immobilized ammonium or imidazolium sulfonate zwitterions that are easily formed upon reaction of nucleophiles (amines or imidazoles) with sultones [83-85]. 

Surface-functionalized ionosilicas are generally synthesized either via postsynthesis grafting or hydrolysis-cocondensation reactions involving trialkoxysily-lated ionic precursors. Scheme 16.5 illustrates the two different synthetic methods involving a monosilylated imidazolium precursor 3-methyl-l-(3-(trie-thoxysilyl)propyl)-imidazolium chloride. 

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