Hexachloroantimonate salts

The ready separation of the hexachloroantimonate salts of various cation radicals is possible owing to their insolubility in diethyl ether (or hexane) under conditions in which the reduced antimony(III) chloride is highly soluble. In the case of EA+ SbClg", the isolated product is quite pure as determined by iodometric titration. However in many other cases, the Lewis acid SbCl5 effects... 

The triethyloxonium cation is an effective oxidant for the production of aromatic cation-radicals, but only as the hexachloroantimonate salt. The analogous EtjO BE or Bu4N SbClg cannot be used to prepare any cation-radical. This is consistent with the previously described function of SbClg as an oxidant. The slow release of SbClj forms the basis for the efficacy of EtjO SbClg. Kochi s group describes this slow release as follows (Rathore et al. 1998a) ... 

The tris(4-bromophenyl)ammoniumyl hexachloroantimonate salt is not a rare reactant. It is available commercially. It can be readily prepared quantitatively from the recovered tris(4-bromophenyl)amine (Bell et al. 1969). It is also probably the most shelf stable of all the stable cation-radical salts. 

Table 5. Ion pair dissociation data of quaternary ammonium hexachloroantimonate salts...

Ion pair dissociation constants for a wide variety of hexachloroantimonate salts in methylene chloride are shown in Table 4, together with that for the highly symmetric salt tri-isoamyl-n-butyl>ammonium tetraphenylborate. 

The novel arenium ion 95 was synthesized266 by one-electron oxidation of the triphenylene-based starting compound to form a radical cation which abstracted a chlorine atom with a concomitant rearrangement to yield the hexachloroantimonate salt. The arenium ion character is apparent from the 13C spectrum (three signals at 813C 212.9, 187.6, and 173.6) and from the bond distances, which are very close to those shown for ion 91. Cation 95 can be stored at room temperature for months. This exceptional stability was attributed to the annelation to the two bicyclo[2.2.2]octane units and the spiroconjugation effect of the fluorenyl moiety.267... 

Other Substituted Diazonium Ions. A series of aminodiazonium ions have been prepared under superacidic conditions [Eq. (4.141)]. Schmidt495 described the preparation and IR spectra of protonated hydrazoic acid 212 and methylazide as their hexachloroantimonate salts. Olah and co-workers496 have carried out a comprehensive study on aminodiazonium ions (protonated azides) by H, 13C, and 15N NMR spectroscopy. Even the electrophilic aminating ability of aromatics of 212 has been explored.496 The tetrachloroaluminate salt of 212 has also been prepared496... 

Strahle and co-workers971 were the first to report the synthesis of the dichloroni-tronium ion [Eq. (4.226)]. According to X-ray crystal structure analysis of the hexachloroantimonate salt, which shows a remarkable stability up to 145°C, the cation is almost planar (maximum deviation from the plane is 0.038 A) and has Cs symmetry. The N—O bond distance is 1.31 A, that is, lies between the length of a NO single bond (1.151 A) and a NO double bond (1.47 A). This is indicative of a decreased Tt-bond contribution, which is also reflected in the IR spectrum (stretching vibration at 1650 cm 1 as compared to 1827 cm-1 of phosgene). 

The cyclization reactions of chloro-substituted 2-azonioallene hexachloroantimonate salts with dimethylbarbituric acid (204) give highly substituted pyrimido[5,4-e][l,3]oxazinium hexachloroantimonate salts (205) and (207). Some of them could be converted into pyrimido[4,5-c/]pyrimidines (206) (Scheme 35) <92S59i>. 

Structures of thietanium tetrafluoroborate and hexachloroantimonate salts of 107, formed by anionotropic rearrangement of corresponding thiiranium salts, were obtained by X-ray crystallography and by calculation at the RHF/6-31G //RHF/6-31G level <2001HCA860>. 

In a special reaction mode alkenediazonium hexachloroantimonate salts (312) are converted into 1,2,3-triazoles (313) with amines (sila7, 81CB3456). 

Although many of the substituted cyclopropenyl ions are marvels of stability, salts of the parent ion darken rather rapidly on heating and exposure to atmospheric moisture causes rapid decomposition. The hexachloroantimonate salt is stable for a long period at — 20° C and for a few hours at room temperature. As might be expected, the cyclopropenyl salts are soluble in polar solvents such as acetonitrile and dimethylformamide, but are insoluble in non-polar solvents. They, of course, react with protic solvents as described earlier. In aqueous solution the equilibrium of equation 24 is established. The pH required to... 

Unsubstituted cyclopropenone was prepared by hydrolysis of the di- and trichloro-cyclopropenes obtained from the reduction of tetrachlorocyclopropene " . Treatment of the trichlorides 37 and 38 with SbCls affords the hexachloroantimonate salt of... 

This reagent reacts in solution (CS ) at room temperature with certain hydrocarbons, for example triphenylmethane, to give hexachloroantimonate salts of carboniumions ... 

Not only free cycloprop-2-enecarboxylic acids but also esters 5 were decarbonylated in oxidizing Bronsted acids, such as 25% sulfur trioxide in sulfuric acid, chlorosulfonic acid or fluorosulfuric acid, with evolution of carbon monoxide. Nearly quantitative formation of the corresponding cyclopropenylium ions 6 in solution was demonstrated by HNMR spectroscopy, and the hexachloroantimonate salts 7 were isolated when the solutions were treated with antimony(V) chloride in aeetyl chloride. ... 

The reactivity of the trichlorocyclopropenylium ion exhibited a marked dependence on its counterion. In contrast to the tetrachloroaluminate salt, the trifluoromethanesulfonate salt 7 reacted with a large excess of benzene or fluorobenzene to give the corresponding triarylcyclo-propenylium salts 8 in good yield. By using the hexachloroantimonate salt 9, the trichlorocyclopropenylium ion underwent trisubstitution by disubstituted alkenes via the addition-elimination mechanism this reaction was not attained with the use of other counterions. ... 

Combining the hexachloroantimonate salt of the trichlorocyclopropenylium ion 13 with N-(trimethylsilyl)dimethylamine resulted in the transamination reaction, which was controlled by variation of the stoichiometry and reaction temperature. The reaction afforded the series of 1-amino-2,3-dichloro-, 1,2-diamino-3-chloro- and 1,2,3-triaminocyclopropenylium ions (14-16) in reasonable to good yield (50-100 /o). When the chloride, tetrafluoroborate or tri-fluoromethanesulfonate ion was used as a counterion, the reaction was hard to control and triamination occurred exclusively. ... 

Since the highest occupied molecular orbital of the triaminocyclopropenylium ion is greatly lowered by the conjugatively electron-donating amino groups, the ion undergoes facile one-electron oxidation either electrochemically ° or by the action of sulfuric acid ° or anti-mony(V) chloride. The produced radical dication, which is red-violet in color, is so stable that it can be directly observed by ESR ° and also isolated as the bis(hexachloroantimonate) salts 2 in more than 90% yield. " ... 

The IR spectra of all diazonium salts 2.296 exhibit an intensive absorption for the diazonio group between 2130 and 2155 cm Reactions with most nucleophiles result in either no reaction or total destruction, leading to dark oils or tars, besides loss of N2. The diazonium salts react smoothly, however, with water to give 2-(di-alkylcarbamoyl)-2-(dialkylamino)ethenediazonium salts 2.301 (2-115). Thermolysis of the solid hexachloroantimonate salt at 130 °C resulted in the l,2-bis(dialkyl-amino)-3-chloro-cyclopropenium antimonate 2.302 (25%), i.e., in a Balz-Schie-mann chloro-de-diazoniation, in addition to unidentified products. 

A hexachloroantimonate salt of the D-gluco acetoxonium ion is isolable only if the reaction is performed at low temperature (—10°) in a nonpolar solvent (such as carbon tetrachloride) from which the salt is precipitated, by virtue of its insolubility, as fast as it is formed. Under these conditions, the ion 59 has no time to undergo successive acyloxonium rearrangements to 60, 61, and 62, because the rate of precipitation is greater than the rate of rearrangement. The salt thereby obtained contains over 90% of the D-gluco derivative. ... 

The hexachloroantimonate salts of unsubstituted imidoyl halides have been converted to the corresponding azides Boron trichloride complexes of N-substituted benzimidoyl chlorides are reported by Hall and co-workers... 

Preparative Methods to an ice cooled solution of antimony(V) chloride (7.85 mmol) in anhydrous CH2CI2 (5 mL), a solution of methanesulfenyl chloride (7.85 mmol) and dimethyl disulfide (7.85 mmol) in CH2CI2 (10 mL) is added dropwise. The producf partially precipitates from the solution. Addition of /j-pentane causes corrqilete precipitation of the hexachloroantimonate salt. The product (95% yield) is isolated by filtration in a dry box and can be used without any further purification. Alternatively, to a well-stirred solution of dimethyl disulfide (0.1 mol) in dry CH2CI2 (50 mL) is dropped at 0°C a solution of SbCls (0.1 mol) in dry CH2CI2 (50 mL). After completion of the addition the salt starts crystallizing as yellowish needles. Addition of dry Et20 completes the precipitation of the product (92% yield). ... 

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