Supported IL catalyst

Ni B, Headley AD (2010) lonic-Uquid-supported (ILS) catalysts for asymmetric organic synthesis. Chem-Eur J 16 4426-4436... 

For example, the homogeneous base case with 1-hexene as a substrate showed a fej, of 0.4 min at a reaction temperature of 50 °C, while the supported IL catalyst achieved a fejj of 11.2 min for the same reaction at 30 °C. The enhanced activity of the rhodium complex in an IL phase had been observed previously and may be explained by the absence of any coordinating solvent [17]. In an acetone solution under hydrogen pressure the complex exhibited coordination of two solvent molecules to the metal center. In theory, if the catalysis is carried out in an IL... 

The concept of supported IL catalysis depicted in Figure 1 has recently been introduced [22]. Preparation of the supported IL catalyst involved dissolving [Rh(nbd)(PPh3)2][PFg] in a mixture of [BMlM][PFg] and acetone, followed by addition of silica gel. The acetone was removed under vacuum, leaving the catalyst in which the IL and rhodium catalyst were immobilized on the silica support. The catalyst was used in a Robinson-Mahoney reactor to hydrogenate 1-hexene, cyclohexene and 2,3-dimethyl-2-butene. Moderate to excellent yields could be obtained and 18 batch runs without significant loss of activity were achieved. Compared with liquid-liquid biphasic catalysis the amount of IL required was drastically reduced. 

Design, Preparation, and Properties of Covalently Supported IL Catalysts... 

The supported IL catalysts discussed above can be denoted as nano-lL catalysts. The major characteristics of these catalysts are the formation of two-dimensional nano-IL layers or zero-dimensional confined nano-lL particles. A new molecularly defined or molecularly supported IL catalyst can be obtained if the IL molecule is covalently linked to solid support surface. Scheme 2.14 [68]. Compared to the supported IL catalysts discussed above, here the IL molecules work solely in catalytic reactions, and possibly offer the largest number of catalytically available IL molecules. However, it will result in a disadvantage, that is, the high dispersion of IL molecules on the solid surface might cause the loss of the specific ionic environment As is well known, sometimes the ionic environment is crucial to gain good activity when compared to molecular solvents. So its application in such reactions would be Hmited. 

Scheme 2.14 Schematic illustration of the preparation of covalently supported IL catalyst.

Hydroformylation Reactions of Unsaturated Alcohol and Ester Inspired by the excellent performance of the supported IL-phase catalyst in the hydroformylation reactions of olefins, its catalytic activity in the hydroformylation reaction of unsaturated alcohol and ester was also explored. Scheme 2.22 [95]. The supported IL catalysts were prepared via impregnation of silica gel in a dichloromethane solution of HRhCOfPPhjjj, PPhj, and IL[BMIm][PFJ(Rh/PPh3/SILPC).Allyl alcohols with different structures could be smoothly transformed into the corresponding aldehydes with about 90% yields. The ratio of linear aldehyde to branched aldehyde was about 22. In succession, Rh/PPhj/SILPC was removed and Ru/PPhj/SILPC was added directly, and the aldehyde could be completely converted to diol after the hydrogenation reaction. 

Catalytic Activation of COj Carbon dioxide activation in or by IL is one of the most successful discoveries of IL catalysis [100]. The potential for carbon dioxide activation in or by IL might be derived from the high solubility of carbon dioxide in IL and its special properties. As a typical reaction, the cyclic carbonate synthesis from dioxide and epoxide has been studied extensively from homogeneous to supported IL catalyst, Scheme 2.25. 

A sulfuric acid-functionalized IL covalently supported on a polymer was successfully prepared for the esterification reactions [115], The catalyst was prepared by copolymerization of vinyl benzene, divinylbenzene, and vinyl chloromethyl benzene, followed by covalent attachment of imidazole group, reacted with 1,3-propane sultone, and then treated by sulfuric acid. Compared to the results when using free l-(3-sulfopropyl)-3-H-imidazolium hydrosulfate ([SOjH-PHImJpSOJ) as catalyst directly, those of the polymer-supported IL catalyst showed similar activity. For the esterification reaction of acetic acid and butanol, the yields to butyl acetate were... 

Asymmetric catalysis is an important technique for the synthesis of chiral compounds. The introduction of supported IL catalyst into the field of asymmetric catalysis might offer new approaches to improve the catalytic performance and also the reusabiUty of chiral catalysts. The first example of a supported IL asymmetric catalyst is the proUne-catalyzed aldol reaction [116]. In this work, the IL molecule covalently attached to modified silica gel was used as the support for IL-phase containing L-proUne. The modification of the silica gel surface by the IL molecule is crucial to gain high enantioselectivity. In the model reaction of acetone and benzaldehyde, the yield to 4-hydroxy-4-phenylbutan-2-one was 51% with 64% ee. Otherwise, the yield was only 38% with 12% ee without the silica gel modification. 

The recent progress on supported IL catalyst system was discussed. It might combine the advantages of homogeneous and heterogeneous catalysis, including... 

---