Counteranion effects

One important point to stress from these results is the possibihty of using copper chloride instead of copper triflate to prepare the complexes. It is well known that in organic solvents there is a dramatic counteranion effect on the activity and enantioselectivity of these catalysts. On the other hand, the rapid anion exchange produced in the ionic hquid resulted in better performance of the complexes, as the bis(triflyl)imide behaves in a similar way to the triflate counteranion. 

In iminium catalysis, both we and the group of MacMillan had observed a strong counteranion effect on the yield and enantioselectivity of the reactions. Inspired by recent use of chiral phosphoric acid derivatives... 

In their recent papers, Guiochon and co-workers are essentially advocating for the domination of the first process [158-160]. They are explaining the counteranion effect on the basis of the formation of a neutral ionic complex, followed by its adsorption on the hydrophobic stationary phase. Similarity in adsorption behavior of anionic and cationic species is interpreted as a confirmation of their adsorption in the form of neutral complexes. 

The unique counteranion effect was also crucial in analogous catalytic reactions of allenylsulfonamides using an achiral gold(I) precatalyst in the presence of the... 

Scheme 11.24 Chiral counteranion effect on the gold catalyzed hydroamination/cyclization of aminoallenes [118],...

Columnar and cubic mesophases were also observed for imidazolium salts of bromide and Tf N" (only Col in the latter case) substituted with a L-glutamic acid 12 although ionic conductivities were larger for the Col phase of the bistriflimide salt [44], Counteranion effects (BF, PFg, CF SOj", Tf N") on the ionic conductivities in columnar ionic mesophases were measured for trialkoxybenzyl-A/-methylim-idazolium and analogous 2-methyl-A/-methylimidazolium salts 13, the optical textures of 13 is shown in Fig. 4.6 [46]. 

Other workers have shown that the use of copolymers of pyrrole with substituted pyrroles (/V-methylpyrrole, in this case) can be used to alter the switching potential.37 In our laboratories, studies involving a functionalized PPy38 have shown that the switching characteristics are markedly affected by the counteranion incorporated during the synthesis. Obviously, this counteranion effect can be amplified by the presence of certain substituents. 

Counteranion effects on the [Os(bipy)2(PVP)ioCl] redox polymer were stud-ied 052,153) para-toluene sulphonate (pTS ), NOJ, SO4, and Cl electrolytes, significant solvent transfer was observed that was thought to be related to the increased solvent content of the polymer layers in the initial state when converted into these salt forms. The large movement of solvent in pTS electrolytes was confirmed from isotopic substitution of H2O with In perchlorate no... 

Hara K, Akiyama R, Sawamura M (2005) Suong counteranion effects on the catalytic activity of cationic silicon Lewis Acids in Mukaiyama Aldol and Diels-Alder reactions. Org Lett 7 5621... 

Meanwhile, it was found by Asai and colleagues [48] that tetraphenylphosphonium salts having such anions as Cl, Br , and Bp4 work as photoinitiators for radical polymerization. Based on the initiation effects of changing counteranions, they proposed that a one-electron transfer mechanism is reasonable in these initiation reactions. However, in the case of tetraphenylphosphonium tetrafluoroborate, it cannot be ruled out that direct homolysis of the p-phenyl bond gives the phenyl radical as the initiating species since BF4 is not an easily pho-tooxidizable anion [49]. Therefore, it was assumed that a similar photoexcitable moiety exists in both tetraphenyl phosphonium salts and triphenylphosphonium ylide, which can be written as the following resonance hybrid [17] (Scheme 21) ... 

A relation between A jjv and molecular weight controlling mechanisms was discovered and the effect of initiator system, solvent and temperature on a mv was explained. The present work has led to an understanding of the effect of counteranion on PIB molecular weight. These studies provide better insight into the detailed mechanism of isobutylene polymerization, in particular into the initiation and the molecular weight controlling events. 

VI. Effect of Counteranion, Solvent and Temperature on Molecular Weight... 

Effect of Counteranion on Molecular Weights In Isobutylene Polymerization... 

Alkyl sulfonates are very effective cationic initiators of e-caprolactone, although only the more reactive methyl triflate and methyl fluorosulfate result in a high conversion. The mechanism of polymerization in the presence of these initiators is believed to involve methylation of the exocyclic carbonyl oxygen, followed by partial ring opening of the activated lactone by the counteranion (Fig. 

Anionic effects were observed by FT-IR-ATR spectrometry with a membrane containing not ionophore 2 but a different kind of ionophore, ETH 129 [13]. When the lipophilic counteranion, SCN, was used for the primary ion solutions, the spectra from both the complexed cation and corresponding counteranion were seen, of which the stoichiometric ratio was nearly equal to that of ETH 129 complex-SCN salt at relatively high concentrations of the primary ion solutions. With KTpCIPB in the membrane. 

Spontaneous hydrolyses of carboxylic anhydrides, diaryl carbonates and aryl chloroformates are faster in cationic than in anionic micelles, regardless of the nature of the counteranion in the cetyltrimethylammonium micelle (Al-Lohedan et al., 1982b Bunton et al., 1984). This charge effect does not seem to be related to substrate hydrophobicity, although the extent of micellar inhibition (relative to reaction in water) is clearly dependent upon substrate hydrophobicity for anhydride hydrolyses. 

In general, the choice of counteranion has a minor effect on catalyst performance, with typical examples being selected from BF4, OTD, PFg, or BARF-. In one example, however, it was noted that [(R.R)-Et-DuPhos Rh CODJOTf gave superior selectivity for the reduction of / -/ disubstituted a-dehydroamino acid derivatives than the corresponding BARF complex when performed in a range of solvents, including supercritical carbon dioxide [39]. 

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