Solvent separated complexes

In the first step the hydrated ion and ligand form a solvent-separated complex this step is believed to be relatively fast. The second, slow, step involves the readjustment of the hydration sphere about the complex. The measured rate constants can be approximately related to the constants in Scheme IX by applying the fast preequilibrium assumption the result is k = Koko and k = k Q. However, the situation can be more complicated than this. - °... 

Lanthanide complexes with inorganic ligands such as Cl, Br, I, SCN, N03 and sulphate can be either inner sphere LnX2+ or outer sphere or solvent separated complexes, Ln(H20)2+X In the case of halides the complexes are thought to be outer sphere Ln(H20) X2+, although there is evidence for the existence of anionic complexes like LnCl. Similarly EuSCN2+ is supposed to have both inner sphere and outer sphere character [23]. 

Solvent coordination number, 134, 403 Solvent effects, 385, 418 initial and transition state, 418 kinetic measures of, 427 Solvent ionizing power parameter, 430 Solvent isotope effects, 272, 300 Solvent nucleophilicity, 431 Solvent participation, covalent, 429 Solvent polarity, 399, 425 Solvent polarity parameter, 436 Solvent properties, 389 Solvent-separated complex, 152 Solvent sorting, 404 Solvent structure, 402 Solvophobic interaction, 395 Solvophobicity parameter, 427 Sound absorption chemical, 145 classical, 145... 

To evaluate conclusively the hypotheses presented here, additional solution and solid-state studies are needed, particularly for trisolvated organolithium compounds, solvent-separated complexes, and unsaturated complexes of the heavier alkali metals. The results do, however, furnish the first glimpse of the stereochemistry of a chemically important class of compounds and should also provide working models for understanding the role of Group la metals in polymerization reactions and in their reactions with electrophilic reagents. 

Fig. 6 Heterobimetallic solvent-separated complex [(thf)3Ca(p-Ph)3Ca(thf)3]-" [(thf)2CaI (p-Ph)3MnPh] with bridging phenyl groups between two metal centers (color code Mn violet)...

The clay-cataly2ed iatermolecular condensation of oleic and/or linoleic acid mixtures on a commercial scale produces approximately a 60 40 mixture of dimer acids and higher polycarboxyUc acids) and monomer acids (C g isomerized fatty acids). The polycarboxyUc acid and monomer fractions are usually separated by wiped-film evaporation. The monomer fraction, after hydrogenation, can be fed to a solvent separative process that produces commercial isostearic acid, a complex mixture of saturated fatty acids that is Hquid at 10°C. Dimer acids can be further separated, also by wiped-film evaporation, iato distilled dimer acids and trimer acids. A review of dimerization gives a comprehensive discussion of the subject (10). 

Consequently, due to preferred cis-cis orientation a dimeric structure is observed for the indium complex and an unprecedented cis-trans arrangement in the thallium structure leads to a polymeric aggregate. Further N-NMR spectroscopic studies show that the aluminum and gallium complexes are stable contact ion pairs even in solution whereas the indium and thallium compounds are solvent-separated ion pairs in THE solution. 

The first example of a tetrakisimido analogue of the orthophosphate ion, PO, the solvent-separated ion pair [(THF)4Li][(THF)4Li2P(Nnaph)4] (16), was reported by Russell et al. [21]. This complex was isolated in low yield from the reaction of P2I4 with a-naphthylamine in THF/NEt3, followed by the addition of "BuLi. The mechanism of this remarkable redox process is not understood. 

Eigen Tamm (1962a,b) and Atkinson Kor (1965, 1967) envisage a more complex situation and consider that there are two kinds of solvent-separated ion-pairs those with one intervening molecule of solvent and others where the ion-pair is fully solvated (Wilson Crisp, 1977). 

In 1985, Eisch et al. isolated a cationic alkenyltitanium complex (55) by the insertion of an alkyne into the cationic Ti-C bond generated from titanocene dichloride and methylaluminum dichloride (Eq. 2) [77], Similarly, a mixture of Cp2TiCl(CH2SiMe3) and A1C13 afforded the solvent-separated ion pairs,... 

Aliphatic amines have been determined by a number of methods. Batley et al. [290] extracted the amines into chloroform as ion-association complexes with chromate, then determined the chromium in the complex colorimetri-cally with diphenylcarbazide. The chromium might also be determined, with fewer steps, by atomic absorption. With the colorimetric method, the limit of detection of a commercial tertiary amine mixture was 15ppb. The sensitivity was extended to 0.2 ppb by extracting into organic solvent the complex formed by the amine and Eosin Yellow. The concentration of the complex was measured fluorometrically. Gas chromatography, with the separations taking place on a modified carbon black column, was used by Di Corcia and Samperi [291] to measure aliphatic amines. 

On substitution of allyllithium with methyl groups, the structures are distorted tt complexes becoming more jj -like. The previously described allyllithiums are contact ion pairs (CIP) whose dissociation is too low to permit study of the free carbanion. However, this is not the case for a more delocalized system such as 1,3-diphenylallyl whose lithium salts can exist as solvent separated ion pairs (SSIP) in ethereal solutions for which the organic moiety could be treated essentially as a free carbanion55 Boche and coworkers studied the effect of substitution at C(2) in their 1,3-diphenylallyl lithiums on the rotational barriers... 

The counterpart to the photo-induced electron transfer is the corresponding thermal transformation of the electron donor-acceptor complex the barrier to such an adiabatic electron transfer is included in Fig. 18 as T, with the implicit understanding that solvation is an intrinsic part of the activation process (Fukuzumi and Kochi, 1983). When the rate of back electron transfer is diminished (e.g. by a reduced driving force), the dynamics for the contact ion pair must also include diffusive separation to solvent-separated ion pairs and to free D+- and A-- (Masnovi and Kochi, 1985a,b Yabe et al., 1991). 

Solvation of the lithio cation of the silylated reagents by HMPA leads to solvent-separated ion pairs (Eq. 9.5). Titration experiments indicate coordination by four HMPA molecules. These solvated complexes, including the TBS derivative, exist entirely as the propargyl structures, emphasizing the importance of the silyl group to charge stabilization. 

For instance, (kH/kD)a was 1.085 0.011 when the sodium thiophenoxide concentration was 0.0086 mol dm-3 and 1.129 0.010 when the concentration of the sodium thiophenoxide was reduced to 0.0040 mol dm-3 in DMF at 20°C. Conductivity and UV studies of sodium thiophenoxide solutions in DMF, in DMSO, in methanol and in diglyme, and reactions done in the presence of the macrocyclic polyether 15-crown-5 (Westaway and Lai, 1988), showed that the change in the secondary a-deuterium KIE was due to a change in the form of the reacting nucleophile from a solvent-separated ion-pair complex at the higher concentration (see (27)) to a free ion at the lower concentration. 

Table 26 The secondary a-deuterium KIEs for the SN2 reactions between butyl chloride and thiophenoxide ion when the nucleophile is a contact ion-pair, a solvent-separated ion-pair complex and a free ion at 200C.0...

These KIEs were measured using lithium thiophenoxide as the nucleophile. The contact ion-pair was converted into the solvent-separated ion-pair complex by adding between 1.0% and 7.5% water to dry diglyme (Fang and Westaway, 1991). 

The nucleophile in the S.v2 reactions between benzyldimethylphenylammonium nitrate and sodium para-substituted thiophenoxides in methanol at 20 °C (equation 42) can exist as a free thiophenoxide ion or as a solvent-separated ion-pair complex (equation 43)62,63. The secondary alpha deuterium and primary leaving group nitrogen kinetic isotope effects for these Sjv2 reactions were determined to learn how a substituent on the nucleophile affects the structure of the S.v2 transition state for the free ion and ion-pair reactions64. 

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