Imidazolium salts immobilization

An ionic liquid was fully immobilized, rather than merely supported, on the surface of silica through a multiple-step synthesis as shown in Fig. 15 (97). A ligand tri(m-sulfonyl)triphenyl phosphine tris(l-butyl-3-methyl-imidazolium) salt (tppti) was prepared so that the catalyst, formed from dicarbonylacetylacetonate rhodium and the ligand (P/Rh = 10), could be soluble in both [BMIMJBFq and [BMIM]PF6. The supported ionic liquid-catalyst systems showed nearly three times higher rate of reaction (rate constant = 65 min ) that a biphasic system for the hydroformylation of 1-hexene at 100°C and 1500 psi in a batch reactor, but the n/i selectivity was nearly constant the same for the two ( 2.4). Unfortunately, both the supported and the biphasic ionic liquid systems exhibited similar metal leaching behavior. 

A benzene imidazolium-tagged ruthenium complex immobilized in [G4GiGiIm]PF6 is a highly enantioselective IL biphasic transfer hydrogenation catalyst (isopropanol/KOH) of acetophenone as compared with conventional (untagged) complexes (Figure Along the same lines, a diimide-imidazolium salt moiety associated with... 

The hydroformylation of 1-hexene was also performed using a combination of [Rh(acac)(GO)2] with specially designed diphenyl-2-iV-methylpyridinium bis(trifluoromethanesulfonyl)amide ligand immobilized in triquaternary imidazolium or monoquaternary imidazolium salts (Figure 11). ... 

In the last few years, biphasic reactions using ionic liquids in catalytic hydrosilylation by polysiloxanes have been also reported. Such catalytic systems are based on platinum (364) and rhodium (365) complexes, immobilized mainly in imidazolium salts as ionic liquids. 

In 2011, the same group reported the immobilization of an enantiomerically pure imidazolium salt derived from chiral binaphthyl on the surface of magnetite Fe304 and the formation of two catalysts derived thereof - a molecular Pd complex 84 and Pd NPs 85 (Scheme 3.47) [73]. These two catalysts were successfully... 

Other immobilized NHC-based rhodium catalysts targeted for screening in hydroformylation were synthesized by groups of Luis and Trzeciak (Scheme 2.166) [58, 59]. In the first step, Merrifield resin was functionalized to the corresponding bis(hydroxyethyl)amine derivatives. This material was converted into the corresponding dichlorides by chlorination with thionylchloride. Addition of an excess of 1-methylimidazol produced the immobilized bis-imidazolium salt. A... 

ILs can also be covalently immobilized on inorganic materials of silica, mesoporous silicates, aluminosilicate, and alumina. For that three ways are known (Scheme 10). The first method is the co-condensation of a trialkoxysdylalkyl onium salt and triethoxysilane (Scheme 10-A) [37-39]. The second one is the immobilization by the reaction between surface hydroxyl groups of the solid and the alkoxysilyl group (Scheme 10-B) [40,41]. For the last one (Scheme 10-C), the inorganic materials modified with alkyl halide (usually propylchloride) are used [42-46] on them, corresponding amine, phosphine, or pyridine can be immobilized and quaternized. For the preparation of imidazolium-based immobilized IL, imidazole is fixed on the modified support in the presence of alkali compounds, followed by quaternization with alkyl halides. 

It is interesting to explore the structure when an organometallic complex is involved in the supported IL thin film. Catalyst models were prepared by immobilization of [Pd(DPPF)-(CF3C02)2] (DPPF, l,l -bis(diphenylphosphino)ferrocene) and CF3SO3H in imidazolium salts [(MeRR lmljfCFjSOj] supported on silica (R=H, Me R = Et, Bu, and hexyl) [62]. For comparison, a series of reference... 

Another substituted derivative of BINAP was used by Lemaire et al. [109]. The ammonium salt catalysts (7 and 8, Fig. 41.10) were prepared in situ from the bro-mohydrates and [Ru( /3-2-methylallyl)2(/72-COD)], and immobilized in several ionic liquids. By comparative studies of the hydrogenation of ethyl acetoacetate, the best results were obtained with imidazolium- and pyridinium-containing ionic liquids. No significant ee was observed with the phosphonium salt. This observation was attributed to problems of solubility and to the ability of complexation for the phosphonium ion. From the anionic side, use of the [BF4] anion appeared superior compared to [PF6] and [(CF3S02)2N]A... 

ILs have also been designed to be Brmsted acids by covalently tethering an aUcanesulfonic acid group to the imidazolium or phosphonium cation of the IL The synthetic approach consists in the synthesis of a zwitterion in a first step then in a second step the zwitterion is acidified (Scheme 1) [20]. These salts are very viscous liquids. They can be used as both solvents and catalysts, or as functionalized Br0nsted acids that can be immobilized in more classical ILs. 

It is known that tetraalkylammonium salts can undergo dealkylation processes that are either thermally or chemieally indueed. The dealkylation of the imidazolium nucleus ( Hoffman elimination ) was also observed in the catalytic hydrodimerization of butadiene by Pd(ii) compounds immobilized in ILs (Scheme 13). ... 

The hydrogenation of polymers such as NBR (acrylonitrile-butadiene rubber), SBR (styrene-butadiene rubber), and PBD (polybutadiene) has been also performed by Ru(ll) compounds associated with phosphine ligands immobilized in classical imidazolium ILs or polyether-modified ammonium salts. ... 

The application of ionic Hquids in catalysis has been reviewed by Hardacre and Parvulescu [127] hence, only selected examples are discussed herein. Molten salts have been used as an immobilization medium for homogeneous selox catalysis [128], for example, RuClj [129], Cu(C104)2 [130], or CuCl [131] (the latter in conjunction with molecular sieve 3A as a heterogeneous solid acid promoter). Van Doorslaer et al. [132] also reported the use of imidazolium ionic liquids for Pd(II)-acetate-catalyzed oxidation of alcohols to ketones, wherein, for... 

---