Formation Labile Cations

Complex Formation Labile Cations. Solvent effects on reactivity in the formation of complexes of metal(n) cations with unidentate ligands have been reviewed, with special reference to magnesium(n) and to the solvents methanol, acetonitrile, DMF, and DMSO. There has been controversy over the mechanism of reaction of thiocyanate with nickel(n) in DMSO, with supporters of the usual Eigen-Wilkins la mechanism and of a D mechanism. The most recent investigators of this reaction report rate constants and activation parameters and favour the la mechanism. There has been further discussion of the mechanism of the reaction between nickel(n) and bipy in DMSO an earlier suggestion that the rate-determining step is ring closure is not supported by recent observations. Rate constants for the reaction of acetate, of other carboxylates, and of pada with nickel(ii) in several non-aqueous solvents have been determined. 

Isomerization. Differences between kinetic parameters for intramolecular rearrangement within organotin j5-diketonates of the [Sn(acac)2Ph2] type in bromoform, chloroform, and dichloromethane are small.  

Rates of cis- trans isomerization for [PtClR(PEt3)a] in methanol and propan-2-ol are consistent, from a qualitative Grunwald-Winstein analysis, with rate-determining chloride loss and generation of a three-co-ordinate intermediate. The solvent must also play a vital role in cis trans isomerizations involving five- or six-co-ordinate intermediates, as for example for [Pd(N3)2(PPh3)a].  

Miscellaneous. Rates of palladium-carbene complex formation in reaction (2) depend on solvent nature, increasing in the order acetone dioxan 1,2-dichloro- 

The majority of studies cited so far have been concerned with normal solvents at temperatures around ambient. Kinetic studies at considerably higher temperatures can be conducted in molten salts. Recent examples include pyrophosphate degradation in molten nitrates, where a first-order reaction in pyrophosphate is reported in the presence of Li+, and a radiochemical investigation of rates of sulphur migration in thiosulphate in potassium thiocyanate melts. Here the sulphur can move intramolecularly within the thiosulphate and can undergo exchange with the thiocyanate. 

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Boomer, J. A., Thompson, D. H., and Sullivan, S. M. Formation of plasmid-based transfection complexes with an acid-labile cationic lipid Characterization of in vitro and in vivo gene transfer. Pharm Res 19(9) 1292-1301. 2002. 

Above 4-6 nmol cationic lipid/pg DNA, small particles were obtained containing compacted DNA. The formation of complexes between DNA and pH labile cationic lipids thus obeys similar rules as those observed with classical nonlabile cationic lipids. 

Several acid-labile linker systems have been developed that rely on the property of silicon to stabilize the formation of cations on a carbon two atoms away. For instance, linkers 42 [92] and 43 [93] release acids and amides upon treatment with TFA, respectively. 

This topic can be conveniently, if rather arbitrarily, divided into two parts, viz. formation of complexes of inert cations and formation of complexes of labile cations. The latter aspect ranges from the simplest examples through to biochemical systems this whole range is covered in a unified discussion in Part III of this Report. Formation reactions at kinetically inert centres will be discussed in this present section, in which references will be grouped according to the nature of the cation. Two general and comprehensive reviews of the formation of complexes have appeared the formation of complexes of sp elements has also been reviewed. ... 

Halogen addition is characterized by stereospecificity. For example, the addition of bromine to acetylenedicarboxylic acid is accompanied by the predominant formation of dibromofumaric acid, that is, occurs in the trans-position. Therefore, the formation of labile cations with the bridged structure is assumed... 

Formation reactions of mixed aquo-ligand as well as of hexa-aquo-complexes are included. Formation reactions at labile cations are discussed in Chapter 4 of this Part. 

These observations illustrate that there are two transformations open to metallocarboxylic acid intermediates reversible loss of OH" accompanied by oxygen exchange, and metal-hydride formation with expulsion of C02. Our entry into this area of chemistry was in 1975 when extensive studies of oxygen lability in metal carbonyl cations were initiated (10). These... 

The easier nucleophilic addition to 2-benzopyrylium salts, compared with monocyclic analogs, leads to loss of selectivity by the cation towards nucleophiles present in the mixture when they possess approximately equal nucleophilicity (NH3, H20, ROH). This forms stable adducts 109 (R = Aik), under these conditions, and labile pseudobases 109 (R = H) which undergo ring opening to diketones 29. The benzo[c ]annelation also plays its role in the easy formation of anhydrobases 119, which are stabilized by two aryl rings. 

In the literature, the simultaneous formation of the major NMMO degradation products N-methylmorpholine, morpholine and formaldehyde [20] is always attributed to the disproportionation of the primary aminyl radical 3, as a - not further defined - redox process between two molecules of 3, in which one is reduced to N-methylmorpholine (2) and the other oxidized to N-(methylene)morpholinium cation (17), which upon addition of water, forms morpholine and formaldehyde. Also this disproportionation can be rationalized as a radical coupling reaction which proceeds through recombination of N-centered 3 and C-centered 4, via the ammonium aminal intermediate 16 as the actual recombination product (Scheme 6). The intermediacy of this species was indeed confirmed by isolation from the reaction mixture and full characterization [17]. Compound 16 is quite labile and immediately de-... 

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