Pentakis anion

A valence bond isomer of pentakis-(trifluoromethyl)-l, 3-diazepine (44) was prepared from (43) (81TL1113) (44) can be transformed thermally or photochemically to a 2,4-diazabicyclo(3.2.0)hepta-2,6 diene (45), which was subsequently photolysed to an imidazole in an anionic process. Compound (45) is highly acidic arising out of the bishomoaromaticity of the anion and forms a salt with Et3N (81TL1369). 

The related pentakis-TTF derivatives 41, synthesized by Becher et al. by reaction of tetraiodide 39 with four equivalents of the thiolate anion liberated upon treatment of 40 with cesium hydroxide (Scheme 9), displayed qualitatively similar redox behavior to 38 with noninteracting TTF units. The attachment of branched multiredox wedges (e.g. 32) to the tetrathio-TTF core should provide interesting systems in which a central TTF unit may be shielded by the outer layers and should oxidize more readily. 

However, the results of a 125Te-NMR spectroscopic investigation of a mixture containing tellurium tetrakis[trifluoroethoxide] and potassium trifluoroethoxide in benzene suggested that only the pentakis[trifluoroethoxy]tellurate(IV) anion is formed3. 

Pentakis(methoxycarbonyl)cyclopentadiene, which is a strong protic acid, reacts with bistributyltin oxide in benzene at room temperature to give a salt between the diaquotri-butyltin cation and the cyclopentadienide anion as shown in equation 9-48.109 The cation has a trigonal bipyramidal structure, with the water molecules in the apical positions, and these can be replaced by other ligating molecules such as HMPT and DMF. 

The reaction of the l-(diaminocyclopropenyliumyl)pyridinium dication 30 with two equivalents of potassium pentakis(methoxycarbonyl)cyclopentadienide (31) also afforded the ionic salt 32 of 1 2 composition, whose structure was determined by X-ray crystallography. On the other hand, the reaction of 30 with the lithium salt of the 7,7,8,8-tetracyanoquinodimethane adical anion 33 resulted in covalent bond formation giving the substituted bis(cyclo-propenylium) dication 34. °... 

On the other hand, the example of the pentakis(tri luoromethyl)cyclopentadie-nide anion demonstrates impressively that this type of reaction can also be employed highly selectively to supplant a previous complex multi-step synthesis [39] by a one-pot procedure [40] (Scheme 2.115). 

Anionic pentakis tropolonato complexes, M [M (trop)s], are known for M = Th (M = Li, Na or K), M = Pa or U (M = Li). TTie thorium compounds are prepared by heating Th(trop)4 with H trop and M OH in a mixture (1 1 2 by volume) of ethanol, water and methyl cyanide. Li[Pa(trop)s] has been obtained from Pa(trop)4 in the presence of Li(trop) in DMF, and Li[U(trop)5] has been prepared by both of the above methods. Sodium salts, Na[ThLs], are also known for HL = a- and y-isopropyltropolone. 

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