Salts dimeric ammonium

In the Park-Jew group s systematic investigation, two types of catalyst - the 1,3-phenyl- and 2,7-naphthyl-based dimeric ammonium salts - were selected as an efficient skeleton of chiral PTCs for the catalytic asymmetric phase-transfer alkylation... 

Porco and coworkers [56] reported the use of the Cinchona alkaloid-derived dimeric ammonium salt 92 to catalyze an alkylative dearomatization/annula-tion process to build up the highly functionalised adamantane core of... 

Uninhibited chloroprene suitable for polymerisation must be stored at low temperature (<10° C) under nitrogen if quaUty is to be maintained. Otherwise, dimers or oxidation products are formed and polymerisation activity is unpredictable. Insoluble, autocatalytic "popcorn" polymer can also be formed at ambient or higher temperature without adequate inhibition. For longer term storage, inhibition is required. Phenothiasine [92-84-2] / fZ-butylcatechol [2743-78-17, picric acid [88-89-17, and the ammonium salt of /V-nitroso-/V-pheny1hydroxy1 amine [135-20-6] have been recommended. 

Slow, except in presence of alkalis products formed are complex polymeric quaternary ammonium salts dimerizes fairly rapidly in water. 

Cyanuric chloride reacts vigorously and exothermically with DMF after a deceptively long induction period. The 1 1 adduct initially formed decomposes above 60° C with evolution of carbon dioxide and formation of a dimeric unsaturated quaternary ammonium salt. Dimethylformamide is appreciably basic and is not a suitable solvent for acyl halides. 

Alkynes react with haloethenes [38] to yield but-l-en-3-ynes (55-80%), when the reaction is catalysed by Cu(I) and Pd(0) in the presence of a quaternary ammonium salt. The formation of pent-l-en-4-ynes, obtained from the Cu(I)-catalysed reaction of equimolar amounts of alk-l-ynes and allyl halides, has greater applicability and versatility when conducted in the presence of a phase-transfer catalyst [39, 40] although, under strongly basic conditions, 5-arylpent-l-en-4-ynes isomerize. Symmetrical 1,3-diynes are produced by the catalysed dimerization of terminal alkynes in the presence of Pd(0) and a catalytic amount of allyl bromide [41]. No reaction occurs in the absence of the allyl bromide, and an increased amount of the bromide also significantly reduces the yield of the diyne with concomitant formation of an endiyene. The reaction probably involves the initial allylation of the ethnyl carbanion and subsequent displacement of the allyl group by a second ethynyl carbanion on the Pd(0) complex. 

A study of the use of room temperature ionic liquids as a new class of nonaqneous solvents for 2-phase catalytic hydrocarbon transformations. The liquids investigated were mixtures of quartemary ammonium salts and organo-aluminum componnds. They were found to be very effective solvents for metal-catalyzed olefin dimerization and metathesis reactions. Their complexing ability and acidity can be tuned as re-... 

Chloroprene is available commercially on a restricted basis in the United States as crude P-chloroprene with a minimum purity of 95% (Lewis, 1993 DuPont Dow Elastomers, 1997). The principal impurities are dichlorobutene and solvents, with smaller amounts of 1-chlorobutadiene (a-chloroprene), chlorobutenes and dimers of both chloroprene and butadiene. Due to its reactivity, chloroprene is stored at 0°C or below under nitrogen and contains significant quantities of inhibitors, such as phenothiazine, tert-butylcatechol, picric acid and the ammonium salt of A -nitroso-N-phenylhydroxy lamine, to prevent degradation and polymerization (Stewart, 1993). Generally within six weeks of manufacture, crude chloroprene is distilled to produce polymerization grade, which is used within approximately 24 h of distillation. 

Dimeric carbonato-bridged complexes A4[Cr2(C03)4(H20)2] (A = NH4, Li, Na, K, Rb, Cs A2 = Mg) can be precipitated166 from aqueous suspensions of the acetate, and the ammonium salt (or CrC03)157 suspended in ether will react with the stronger acids CF3C02H164 and CF2HC02H167 to give dinuclear carboxylates (equation 17). 

The latter transformation requires the use of a small amount of an acid or its ammonium salt. By using [Cp2TiMe2] as the catalyst, primary anilines as well as steri-cally hindered tert-alkyl- and sec-alkylamines can be reacted.596 Hydroamination with sterically less hindered amines are very slow. This was explained by a mechanism in which equlibrium between the catalytically active [L1L2Ti=NR] imido complex and ist dimer for sterically hindered amines favors a fast reaction. Lantha-nade metallocenes catalyze the regiospecific addition of primary amines to alkenes, dienes, and alkynes.598 The rates, however, are several orders of magnitude lower than those of the corresponding intramolecular additions. 

To a greater or lesser degree the spectra of all C-6 ionic salts, whether they are substituted with a covalent group at C-2 or not, are comprised of a mixture of the spectra of C-6 ionic and C-6 covalent forms. Differences among the spectra of the compounds result from secondary effects on the structure of the bare anions such as hydrogen bonding and dimerization due to hydrophobic dye/dye molecular interactions. This is particularly obvious when the fluorescence spectra of the ammonium salts at room temperature of the C-2, C-6 bis trimethylammonium salt shows a triad of broad peaks centered at 583 nm. At reduced temperature the same compound shows three sharper peaks at 538, 583, and 605 nm. The shortest wavelength of these... 

Scheme 4.2 General synthetic scheme for cinchona-derived dimeric quaternary ammonium salts, (a) bis(Bromomethyl)-linkers (0.5 equiv.), EtOH-DMF-CHCI3 (5 6 2), r.t. or reflux, (b) Allyl bromide or benzyl bromide (6.0 equiv.), 50% KOH (10.0 equiv.), CH2CI2, r.t.

The alkaloid content of curare is from 4% to 7%. The most important constituent in menispermaceous curare is the bis-benzyltetrahydroisoquinoline alkaloid (+)-tubocurarine (Figure 6.48). This is a monoquaternary ammonium salt, and is water soluble. Other main alkaloids include non-quaternary dimeric structures, e.g. isochondrodendrine and curine (bebeerine) (Figure 6.48), which appear to be derived from two molecules of (R)-N-methylcoclaurine, with the former also displaying a different coupling mode. The constituents in loganiaceous curare (from calabash curare, i.e. Strychnos toxifera) are even more complex, and a series of 12 quaternary dimeric strychnine-like alkaloids has been identified, e.g. C-toxiferine (toxiferine-1) (see page 359). 

Dimeric phase-transfer catalysts were also reported by Najera et al., who used cinchonidine- and cinchonine-derived ammonium salts bearing a dimethyl-anthracenyl bridge as a spacer [32]. In the presence of these catalysts high enantioselectivity of up to 90% ee was obtained. 

Reduction of 3 -iodopropionitrile at the potential of the first polarographic (1 e) wave yields Hg (CH2 CH2 CN)2, Sn2 (CH2 CH2CN)6, Pb(CH2 CH2 CN)4 and T1(CH2CH2CN)2I at Hg, Sn, Pb, or T1 cathodes 481 When ethyl or butyl iodide is reduced at platinum or copper cathodes in DMF dimers R2 and disproportionation products, RH, RH(-H2), are formed 482,483,48S Formation of these are attributed to radicals originating both from tire cathodic cleavage of the R-I and the R2-N(CH3)2 bond 482 The ammonium salt is formed by alkylation of DMF. 

Cathodic reduction of ammonium salts RR 3N+ in aprotic media, e.g., DMF, yields dimers R-R, for e.g., R=benzyl, fluorenyl, in moderate yields (15-30%) s03l Free radicals are assumed as intermediates, as inactive dimers were obtained from optically active ammonium salts RR 3N+. This rules out a conceivable S t2 reaction between cathodically generated R and RR 3N+ as products with partially inverted configuration should be obtained this way. Reduction of quaternary ammonium salts R4N+ in hexamethylphosphortriamide yields hydrocarbons RH and olefins RH(-H2) as main products and dimers R-R as minor side products, whose formation is rationalized by assuming radicals R as intermediates... 

The diisopropyldithiophosphate complex, made by reaction of the ammonium salt of the ligand with [OsCl5]2-, has a dimeric structure with two bidentate (PriO)2PS2" groups per metal atom and two bridging Pr P—S—S ligands, according to a preliminary X-ray study.732... 

The greater size mismatch between Li+ and Br makes aggregation less pronoimced in LiBr complexes. Simple ring dimers, for example, (LiBr TMEDA)2, are common. The complex LiBr-PMDETA is dimeric in the solid state with 5-coordinate lithium, but in benzene solution this rather asymmetric dimer is in equilibrium with a monomeric form. An unusual dimeric LiBr complex which may be considered as two monomers of LiBr connected only by bridging HMPA ligands is also known. This complex, [LiBr-(HMPA)i.5)2 (12), was synthesized by the in situ ammonium salt route . 

A number of fluoride complexes have been made, both by crystallization for the ammonium salts like (NH4)4CeFg, which has square-antiprismatic coordination of cerium, also found in the (CeF6 )oo chains in (NH4)2CeF6, its thermal decomposition product. (NH4)3CeF7-H20 acquires dodecahedral eight-coordination by dimerization. (NH4)4[CeFg] can... 

---