Cations phosphonium

Some straightforward, efficient cyclopentanellation procedures were developed recently. Addition of a malonic ester anion to a cyclopropane-1,1-dicarboxylic ester followed by a Dieckmann condensation (S. Danishefsky, 1974) or addition of iJ-ketoester anions to a (l-phenylthiocyclopropyl)phosphonium cation followed by intramolecular Wittig reaction (J.P, Marino. 1975) produced cyclopentanones. Another procedure starts with a (2 + 21-cycloaddition of dichloroketene to alkenes followed by regioselective ring expansion with diazomethane. The resulting 2,2-dichlorocyclopentanones can be converted to a large variety of cyclopentane derivatives (A.E. Greene. 1979 J.-P. Deprds, 1980). 

Another approach to a donor adduct of the methylene phosphenium cation is the addition of a phosphonium cation to the phosphaalkyne. The reaction of the protic cation [HPPhal + lCFaSOa] with CjoHuCP produced a white powder which was identified as the P-phosphonio-substituted phosphaalkene [74]. Alternatively to the elimination reaction the phosphaalkynes were protonated. C-protonation of adamantylphosphaacetylene and ferf-butylphosphaacetylene occurred in superacid media under formation of phosphavinyl cations. From these spirocyclic betaines by reaction of l-Ad-C=P (Ad = adamantyl) withB(OTf)3 a phosphavinyl cation could be detected [75]. 

RTILs consist of large, unsymmetrical ions, such as 1,3-dialkyl-imidazolium, 1-alkylpyridinium, 1-alkylpyrazolium, tetralkylammonium or tetralkyl-phosphonium cations and tetrachloroaluminate, tetrafluoroborate, hexafluorophosphate, trifluoromethanesulfonate or bis((trifluoromethyl) sulfonyl)imide anions. 

Except for the PBS/SAP-qC16 (n-hexadecyl tri-n-butyl phosphonium cation modified saponite) system, the degree of degradation is the same for other samples. This indicates that MMT or alkylammonium cations, and at the same time other properties, have no effect on the biodegradability of PBS. The accelerated degradation of PBS matrix in the presence of SAP-qC16 may be due to the presence of alkylpho-sphonium surfactant. This kind of behavior is also observed in the case of PLA/MMT-based nanocomposite systems. 

The parameters of organophosphorus betaines 5, 6,15,17, 20, 21, 24, 25, and 31 and the corresponding phosphonium cations R3P+ CHR1] 2, as well as cations of silylated phosphonium salts R CHR -SiR2,82 84 are quite similar. The 31P NMR signals of the betaines lie in the region typical of tetracoordinated phosphorus.85,86... 

All studied model compounds can distinctly be divided into three groups (Table VII). The first group is composed of substances in which the sulfur, selenium or cyclopentadienyl anion acts as an anionic center. They exist only in open betaine forms, and their PES do not contain local minima corresponding to cyclic isomers. The second group contains compounds with arsonium cationic and oxide anionic centers and silicon and germanium betaines with arsonium and amide centers. They exist as cyclic isomers and their PES have no local minima corresponding to the open forms. Finally, the third group consists of six studied compounds with phosphonium cationic and oxide or amide anionic centers and arsonium-imide betaine. Their PES have minima for both cyclic and open forms separated by low barriers. 

Evidence for a major mode of catalyst deactivation in this system came from the observation of phosphonium cations (HPR3) in the reaction mixture, which could form through the pro to nation of free PR3 by the acidic dihydride complex. It is not known which species decomposes to release free PR3, but the decomposition pathway is exacerbated by the subsequent reactivity in which protonation of phosphine removes a proton from the metal dihydride, effectively removing a second metal species from the cycle. 

The phosphonium cationic center is well known for its ability to stabilize adjacent anionic centers (i.e. Wittig reagents), however we have shown it to be capable of activating (or destabilizing) cationic electrophilic sites.15 As noted... 

If no acid (or electrophile) is present, the initial molecule may serve this purpose, thus triggering a father-son reaction. Myriads of such reactions have been described. A simple example is given in Scheme 2.22, where the reduction of a phosphonium cation generates the corresponding ylid in a 50% yield. It should be emphasized that the overall electron stoichiometry is unity despite the fact that the reduction consumes two electrons. This type of reaction should thus be envisaged before concluding that one-electron stoichiometries are necessarily indicative of radical coupling reactions. 

Anion-based organic dye nanoparticles can be also synthesized on the basis of the ion-association method. In this case, hydrophobic phosphazenium cations such as tetrakis[tris(dimethylamino) phosphoranylideneamino]phosphonium cation are effective for ion-pair formation with anionic dyes. A neutral polymer stabilizer polyvinylpyrrolidone (PVP) that is soluble in water is sometimes added for preventing agglomeration... 

The first catalysts utilized in phase transfer processes were quaternary onium salts. In particular, benzyltriethylammonium chloride was favored by Makosza (7 ) whereas Starks utilized the more thermally stable phosphonium salts (6,8). In either case, the catalytic process worked in the same way the ammonium or phosphonium cation exchanged for the cation associated with the nucleophilic reagent salt. The new reagent, Q+Nu , dissolved in the organic phase and effected substitution. 

By the presence of long alkyl chains in the molecule (tetraalkyl-ammonium or phosphonium cations, esters of phosphoric or sulphuric acid with alcohols with long alkyl chains) ... 

Abstract The term Lewis acid catalysts generally refers to metal salts like aluminium chloride, titanium chloride and zinc chloride. Their application in asymmetric catalysis can be achieved by the addition of enantiopure ligands to these salts. However, not only metal centers can function as Lewis acids. Compounds containing carbenium, silyl or phosphonium cations display Lewis acid catalytic activity. In addition, hypervalent compounds based on phosphorus and silicon, inherit Lewis acidity. Furthermore, ionic liquids, organic salts with a melting point below 100 °C, have revealed the ability to catalyze a range of reactions either in substoichiometric amount or, if used as the reaction medium, in stoichiometric or even larger quantities. The ionic liquids can often be efficiently recovered. The catalytic activity of the ionic liquid is explained by the Lewis acidic nature of then-cations. This review covers the survey of known classes of metal-free Lewis acids and their application in catalysis. 

In the phosphonium iodide and chloride salt catalyzed TMSCN addition on aldehydes and ketones, a double activation should exist. Not only the activation of the ketones or aldehydes with the phosphonium cation is necessary, but also the activation of the TMSCN by the soft Lewis base [I] or the harder Lewis base [Cl], which can form a pentavalent silicon intermediate [121]. 

Phosphonitrilic halides (continued) primary amines and, 1 360-362 secondary amines and, 1 350-362 tertiaiy amines and, 1 362-363 structural theory further aspects of, 1 375 structure, 1 365-366 high polymer and, 1 372 medium polymers and, 1 368-372 spectroscopic data and, 1 369-372 structural theory and, 1 372-375 tetrameric compounds and, 1 367-368 trimeric compounds and, 1 366-367 Phosphonium cations, 9 243-250 halogenated, 9 243-249 salts... 

Lopes, J. N. C. and Padua, A. A. H., Molecular force field for ionic liquids III Imidazolium, pyridinium, and phosphonium cations chloride, bromide, and dicyanamide anions, /. Phys. Chem. B, 110,19586, 2006. 

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