Counterion exchange

On addition of R4N+C104, counterion exchange occurs with the establishment of the corresponding CIO equilibria... 

One of the first significant advances in the chemistry of TT-allylpalladium complexes was the discovery that alkenes could be directly converted into the corresponding allyl complex by substitution into the allylic C—H bond. A variety of recipes have now been reported that can accomplish this transformation. Initially, palladium chloride17-23 or its more soluble forms, sodium or lithium tetrachloropalladate24-27 and bisacetonitrile palladium dichloride,28-30 in alcohol or aqueous acetic acid solvent were employed. The use of palladium trifluoroacetate, followed by counterion exchange with chloride, represents the mildest and most effective means available to accomplish this reaction.31... 

Anions counterion binding, counterion exchange, aggregation, precipitation... 

Incorporation of an ionic component into a donor/acceptor molecule is a very effective way of suppressing electron back-transfer. One interesting example consists of the photo-oxidation of leuko crystal violet (LCV) to crystal violet (CV, the dye) by benzophe-none bearing a quaternary ammonium ion (Tazuke Kitamura 1984). In this case, the cation radical of LCV formed is repulsed by the ammonium positive charge. At the same time, the benzophenone anion radical remains stabilized by the attached cationic atmosphere (Scheme 5-16). As shown in the scheme, two favorable results are achieved the stabilization of an ion radical pair by counterion exchange and the charge separation by coulombic repulsion between the two positive charges. This leads to 100% efficiency of the photo-oxidation. With unsubstituted benzophenone itself, the efficiency does not exceed 20%. 

Over the last decade, noncovalent bonding interactions between appropriate Jt-elec-tron-deficient and Jt-electron-rich recognition sites have been exploited in our laboratories for the synthesis of catenanes and rotaxanes. 271 In the example illustrated in Figure 10, the bis(hexafluorophosphate) salt 11-2PF6 was treated 28 with trons-bis(pyridine)ethylene (12) in the presence of the previously formed macrocyclic polyether bis-p-phenylene-34-crown-10 (13). The resulting [2]catenane 14-4PF6 was isolated in 43 % yield after counterion exchange. 

Porphyrin-containing [2]catenanes have been synthesized by Gunter et al.,1311 following the template-directed synthetic strategy outlined in Figure 15. The bis(hexa-fluorophosphate) salt 15-2PF6 was treated with the dibromide 16 in the presence of the previously formed macrocyclic polyether 22 or 23. After counterion exchange,... 

A typical counterion-exchange sequence of a cation-exchange membrane containing S03 group as fixed charge is ... 

A similar counterion-exchange sequence is obtained for anions in an anion-exchange membrane containing quaternary ammonium groups as fixed charges ... 

The equilibrium reaction between neutral hexacoordinate chelates and pentacoordinate siliconium halide salts is discussed in Section III.A.4 (Eq. 17). This reaction can be driven completely to the ionic side by replacement of the chloro ligand by better leaving groups triflate and bromide (Eq. (18), listed again with compound labels see Section III.A.4.iv). The products of this counterion-exchange reaction are stable siliconium salts 90(OTf)-92(OTf), 90(Br)-92(Br), which no... 

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