Immobilization cationic catalyst

Table 12-9. The main types of immobilized cationic catalysts.

A variation of the SHB technology to immobilize cationic molecular catalysts on silica is shown in Figure 16.5 b. This involves SHB immobilization of the counter-... 

Some attempts have been made to use a cationic metal complex intercalate as a catalyst these efforts are briefly reviewed in an account of the catalyst type (b) in Fig. 1. The results advocate the possibility of the immobilization of catalyst solution in the interlayer spaces. The catalytic activity of Cu -TSM or Cu Pd -TSM swelled with water or an organic solvent for the reaction involving molecular oxygen is introduced in the following section. 

Similarly to Bianchini s approach, De Rege [26] also immobilized cationic [((R,R)-Me-duphos (26))Rh-(COD)]OTf complex noncovalently by the hydrogenbonding interaction of triflate counterion with surface silanols ofMCM-41 support. In contrast to the results obtained by Bianchini et al. [25c], the catalytic activity and selectivities of the immobilized 26-Rh complex on MCM-41 were equal to or greater than the homogeneous counterparts (Scheme 2.7). Moreover, the catalysts were recyclable (up to four times, with no loss of activity) and did not leach. Here again, the counteranion was very important for the successful immobilization of the catalyst onto MCM-41. Whereas, the DuPhos-Rh complex with triflate anion was effectively immobilized (6.7 wt% based on Rh), tlie analogous complex with the lipophilic BArp anion [BArp = R(3,l-((. i )2-C J I i was not loaded onto the support. 

Table 2. Hydrogenation of methyl-acetamidecinnamate [MAC] with free and immobilized cationic rhodium catalysts...

Diphosphine-rhodium catalysts bound to inorganic supports via isocyana-to-alkyl-trialkoxysilane linkers meet all requirements to be of practical use i. the preparation method is probably the most simple, general and efficient known so far, ii. immobilized cationic rhodium complexes with "molecular weights" as low as 5 kD exhibit a comparable performance in enantioselective catalytic... 

Ionic polymerizations catalyzed by immobilized complexes, in particular Lewis acids on polymer supports, so-called solid superacids, are now extensively developed. A variety of cationic catalyst (protonic and Lewis acids), their combinations (complexes) and complexes with different supports are summarized in a review [111] (Table 12-9). 

An ion exchange resin has been used to immobilize a cationic catalyst. Although in this case the cationic center was formed by... 

Besides, it is worth mentioning that despite ionic liquids having the appropriate composition might be an alternative to the less environment friendly H2SO4 and HF acids, it would be much more interesting from the practical viewpoint to immobilize these ionic liquids on solid supports so as the resulting catalyst contains ionic complexes in which either anion or cation is covalently bonded to the porous carrier (70,71). In this respect, it has been shown that the imidazolium-type ionic liquid immobilized on a high surface area (946 m /g) ordered mesoporous silica (Si-MCM-41) performed relatively well for the alkylation reaction at temperatures around 80° C, with a selectivity to isooctanes of about 60 wt% (72). Nevertheless, as usually occurs in solid acid alkylation, the activity of immobilized IL catalyst starts to fall at a certain time on stream after which butenes dimerization instead of alkylation becomes the predominant reaction (72). 

It should be noted that degradation did not occur on the bare platinum immersed in liquid electrolyte, indicating that this was a specific phenomenon on the catalyst surface-polymer electrolyte interface (Okada et al. 2000). Unlike liquid electrolytes, the polymer electrolyte has immobile cation-exchange sites (sulfonic acid groups on side chains), so when they bind impurity metal cations, the constrained electric double layer lowers the electric field in the electrochemical double layer (Okada et al. 2001). 

M. Egi, K. Azechi, S. Akai, Reusable and durable immobilized-cationic gold(I) catalysts for environmentally benign bond-forming reactions, Adv. Synth. Catal. 353 (2011) 287-290. 

The cationic nature of the copper(I) catalyst means that it is immobilized in the ionic liquid. This permits the PMMA product to be obtained, with negligible copper contamination, by a simple extraction procedure with toluene (in which the ionic liquid is not miscible) as the solvent. The ionic liquid/catalyst solution was subsequently reused. 

PMo 12-polymer composite film catalyst [9]. This demonstrates that PM012 catalyst was not in a crystal state but in an amorphous-like state, indicating that PM012 catalyst was molecularly dispersed on the PS support via chemical interaction. As attempted in this work, it is believed that heteropolyanions (PMoi204o ) were strongly immobilized on the cationic sites of the PS bead as charge-compensating components. 

Cationic palladium(II) complexes are homogeneous catalysts for both intramolecular and inter-molecular hydroamination reactions.267 Palladium species immobilized on silica can be prepared by the simple addition of alkyl- or hydroxopalladium(II) complexes to partially dehydroxylated silica. The silica-bound species are more stable than their molecular precursors and are efficient catalysts for the cyclization of aminoalkynes.268... 

The preparation of this type of catalyst is quite simple. HPAs such as phos-photungstic acid were adsorbed onto inorganic supports such as clays, alumina, and active carbon. Subsequently, the metal complex was added to form the immobilized catalyst. If necessary, the catalyst can be pre-reduced. These types of catalysts were developed mainly for enantioselective hydrogenations. For instance, a supported chiral catalyst that was based on a cationic Rh(DIPAMP) complex, phosphotungstic acid and alumina showed an ee-value of 93% with a TOF of about 100 IT1 in the hydrogenation of 2-acetamidoacrylic acid methyl ester (Fig. 42.4 Table 42.2). 

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