Cyclopropenylium tetrafluoroborate

Unlike such unstable intermediates, the first, rare example of reversible dissociation of a carbon-carbon a bond into a stable carbocation and carbanion was reported for a nitro-dicyano compound (20) prepared from trimethyl- and triphenyl-cyclopropenylium tetrafluoroborate ([4" ]BF4 and [5 JBFJ) with the potassium salt of p-substituted-phenylmalononitrile anions (Arnett et al., 1983 Troughton et al., 1984 Arnett and Molter, 1985). Other ionically dissociative malononitrile derivatives have been prepared from such carbocations as the tropylium [S ] (Arnett and Troughton, 1983) and the tris(p-methoxyphenyl)methylium [93 j (Arnett and Troughton, 1983) ions. 

The reaction of tetrachlorocyclopropene (3) with thiols in the presence of silver(I) tetrafluoro-borate in acetonitrile afforded the tris(alkylsulfanyl)cyclopropenylium tetrafluoroborates... 

I,2,3-Tris(/ Tf-butylsulfanyl)cyclopropenylium Tetrafluoroborate (4, R = r-Bn) Typical Procedure - ... 

To a stirred solution of diphenylcyclopropenone (2.06 g, 10.0 mmol) in CH2CI2 (10 mL) was added triethyloxonium tetrafluoroborate (2.30 g, 12.0 mmol). After 20 min, a suspension of 1-ethoxy-2,3-diphenyl-cyclopropenylium tetrafluoroborate (6, R = = Ph) in CHjClj was formed. To this suspension was... 

To a stirred suspension of l-chloro-2,3-bis(diisopropylamino)cyclopropenylium tetrafluoroborate (1.79 g,... 

When l,2,3-tris(rf rt-butylsulfanyl)cyclopropenylium tetrafluoroborate (29) was treated with anilines, one of the tert-butyl groups was replaced by the phenylamino group to give the 1-arylamino-2,3-bis(mrr-butylsulfanyl)cyclopropenylium salts 30. The reaction with alkyl-amines of higher basicity, however, caused cleavage of the cyclopropenylium ring, giving rise to vinylazomethine-type iminium salts. 

An equimolar amount of EtjNH was added to a solution of l,2,3-tris(terr-butylsulfanyl)cyclopropenylium tetrafluoroborate in CH Clj at — 20 to — 10 C. Solvent removal was followed by repeated reprecipitation of the residue from CHCl3/Et20 yield 62% mp 105 C (dec.). 

Reactions of di- and trisubstituted cyclopropenylium tetrafluoroborates 13 with tricarbonyl-nitrosylferrate ion afforded the iron complexes 14." The structure of the l-fert-butyl-2,3-diphenyl derivative was determined by X-ray crystallography."... 

TRI- ferf-BUTYLCYCLOPROPENYL FLUOROBORATE (Cyclopropenylium, tri- er/-butyl tetrafluoroborate)... 

Hydride abstraction from 1,3-dialkyl-2-chlorocyclopropenes with one equivalent of tritylium tetrafluoroborate in dichloromethane at 0 C resulted in complete conversion to the chloro-cyclopropenylium cations. Treatment of the cation solutions with saturated sodium hydrogen carbonate afforded cydopropenones. 

Treatment of cydopropenimines with tetrafluoroboric acid produced cyclopropenylium tetra-fluoroborates. ... 

The tris(methylsulfanyl)cyclopropenylium salt 19 was also prepared from tetrachlorocyclo-propene (3) by the reaction with dirnethyl(methylsulfanyl)sulfonium tetrafluoroborate and dimethyl disulfide." ... 

The perchlorate or tetrafluoroborate salt of the trityl cation abstracted the hydride ion from trisubstituted cyclopropenes 1 bearing a tertiary hydrogen to give the corresponding cyclopropenylium salts 2. The reaction was usually conducted in polar solvents, such as acetonitrile or dichloromethane, at room temperature under protection from moisture. Addition of a nonpolar solvent such as diethyl ether resulted in precipitation of the formed cyclopropenylium salts. " ... 

The reaction of diarylcyclopropenones 1 with aryl- or cyclopropylmagnesium °° bromide and hydrolysis using aqueous potassium dihydrogen phosphate solution, followed by treatment with a strong Bronsted acid such as tetrafluoroboric - or hydrobromic acid, afforded the trisubstituted cyclopropenylium salts 26. 

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