MeTHF

Low-lying vacant orbitals of alkali metal cations can, consequently, accept an unpaired electron density even if it is delocalized over an extended n system of carbon chains. The anion-radical of 1,4-diphenylbutadiene can exist in i-trans and in -cis forms. The relative amounts of these geometrical isomers appear to depend highly on the counterion/solvent system. Li and K+ were studied as counterions THF, 2-MeTHF, and DME were employed as solvents (Schenk et al. 1991). Interaction between the anion-radical and the cation contributes to a stabilization of... 

Ion pairs do not conduct electricity, but triple ions (M2A+ and MA2) are conductive. Thus, the formation of triple ions is detected by conductimetric measurement. Figure 7.2 shows the log /1-log c relations for LiAsF6 and LiBF6 in 2-methyl-tetrahydrofuran (2-MeTHF) [17]. After passing a minimum, the value of log A increases again with log c, showing that a triple ion formation occurred in the solution. 

By far more is known about the UV spectra of silylene-Lewis base complexes in matrices as well as in solution. To observe silylene-Lewis base complexes in matrices, an appropriate silylene precursor, in most cases a cyclic or acyclic oligosilane, is photolyzed at low temperature in an inert hydrocarbon or noble gas matrix, which is doped with small amounts (2-5%) of the respective Lewis base. In a few cases, 2-methyltetrahydrofuran (2-MeTHF), which serves as matrix material as well as a Lewis base, is used. When a rigid matrix such as a 3-methylpentane (3-MP) or 2-MeTHF matrix is used, the formation of the silylene complexes normally requires the matrix to be annealed in order to allow the molecules to diffuse through the softening matrix. In contrast, when the silylene is generated in an a priori soft matrix,... 

Levin et al.33 recorded the decay of the UV-absorption maxima of a variety of dimethylsilylene-Lewis base complexes in cyclohexane at room temperature and found that the lifetimes of these complexes are significantly longer than that of noncoordinated dimethylsilylene (Table VI). Gillette et al.36 estimated the lifetime of complex 31d to be 1 min at -135°C in 2-MeTHF solution. 

Initiation by p-ClC6H4N3 PFjj also seemed to occur via a hydride ion abstraction. Dreyfuss and Dreyfuss (25) showed that the expected product of hydride ion abstraction, chlorobenzene, is formed in the decomposition of p-ClC6H4N PF3 in 2-MeTHF and the product of thermal decomposition, p-chlorofluorobenzene, was absent. In this case... 

Certain cyclic ethers which will not homopolymerize will copolymerize with THF (25, 52). These cyclic ethers are stable five and six-membered ring compounds such as 2-methyltetrahydrofuran (2-MeTHF), and 1,4-dioxane (DOX). It is probable that 4-phenyl-l,3-dioxane (PhDOX), tetrahydropyran (THP), and 4-methyl-l,3-dioxolane (MDOL) which do not homopolymerize but which have been reported to copolymerize with BCMO (107, 108) would also copolymerize with THF. In the copolymerizations a correlation was again found between the basicity of the attacking ether and its reactivity with the cyclic oxonium ion. The... 

TABLE 5. Photophysical Properties of Polymers 23—26 and model compound 27 in 2-MeTHF at 77 K... 

This contradiction comes from acridine contained as an impurity in the preparation of Acr+-Mes by Benniston et al., who synthesized the compound via methylation of the corresponding acridine [56]. It was confirmed that the phosphorescence maximum of 9-phenylacridine in glassy 2-MeTHF at 77 K afforded a similar spectrum to that reported by Benniston et al. [59]. In contrast to the synthetic method that Benniston et al. employed [59], we prepared Acr+-Mes by the Grignard reaction of 10-methyl-9(10H)-acridone with 2-mesitylmagnesium bro-... 

Fig. 13.20 UV-Vis absorption spectra ob- picture images of frozen PhCN solutions of tained by photoirradiation with a high-pres- Acr+-Mes before and after photoirradiation at sure mercury lamp of deaerated 2-MeTHF low temperatures and taken at 77 K [59]. glasses of Acr+-Mes at 77 K [59], Inset ...

In contrast to the photoirradiation of a purified PhCN solution of Acr+-Mes at 298 K, when the photoirradiation of the same solution was performed at low temperatures (213-243 K) with a 1000-W high-pressure mercury lamp through the UV light-cutting filter (>390 nm) and the sample was cooled to 77 K, the color of the frozen sample at 77 K was clearly changed from green to brownish, as shown in the inset in Fig. 13.20. When a glassy 2-methyltetrahydrofuran (2-MeTHF) is employed for the photoirradiation of Acr+-Mes at low temperature,... 

Ph2Ge (C6HnCl-c) Ph2Ge CIPh Ph2Ge S=C=C(Bu-/)2 Mes2Ge (2-MeTHF)... 

Pentane or hexane(s) Ethers Dichloromethane (extractions) Dichloromethane (chromatography) Heptane 2-MeTHF or methyl -butyl ether (MTBE) Ethyl acetate, MTBE, toluene, 2-MeTHF Ethyl acetate-heptane mixture... 

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