Cyclopropenylium salts 197 —

Another convenient approach to the azapentatriafulvalene system is given by the in situ formation of cyclopropenylium salts from cyclo-propenones and dry HCl gas followed by their electrophilic attack on various indoles. Tire corresponding heterofulvalenium salts of type 35 were isolated as chlorides, which were somewhat photosensitive and thermally labile (68TL5537). 

Isolation of 3-cyclopropenyl metal compounds by this method has been achieved so far for iron and rhenium metals only. Thus, the reaction of Na[CpFe(CO)J (NaFp) with cyclopropenylium salts at -70 °C, in THF, gave 3-Fp-cyclopropene complexes (equation 194)2 267. The X-ray crystal structure of the most stable iron complex 3-Fp-C3Ph3 exhibits a regular cyclopropene C—C single and double bond distances (151 and 129 pm), and a characteristic distance of 208 pm for the Fe—C (T-bond267. The H NMR (CS2) spectrum of the 3-Fp-C3Ph,H complex displays a singlet at S = 2.63 ppm, of the cyclopropen yl proton at the 3-position. ... 

The major route to -cyclopropenylium complexes L M(C3R3) (metallatetrahedranes) is by oxidative addition reactions of cyclopropenylium salts to transition metal complexes of groups 5 (V), 6 (Mo, W), 8 (Fe, Ru), 9 (Co, Rh, Ir) and 10 (Ni, Pd, Pt). The addition is frequently accompanied by loss of one or more carbonyl, olefin or halogen auxiliary ligand. Concurrent formation of oxocyclobutenyl complexes by carbonyl insertion into the cyclopropenyl ring is often observed in reactions with group 9 cobalt triad and early transition metal complexes. 

TABLE 6. 13C NMR spectra of palladium cyclopropenylidene complexes [Cl2Pd(C3R2)]2 and cu-Cl2(Bu3P)Pd(C3R2), and cyclopropenylium salts [tranj-Cl(Bu3P)2Pd(C3R2)]C104... 

T-Bound cyclopropenylium cation complexes of palladium 4 were formed upon reaction of 1,1-dichlorocyclopropenes with palladium metal. Protonolysis resulted in decomplexation to give the free cyclopropenylium salt 5. ... 

A related reaction leads directly from cyclopropenylium salts to allenes without the isolation of a cyclopropene. ... 

Reaction of tris(tert-butylsulfanyl)cyclopropenylium salt with anhydrous sodium hydrogen carbonate in refluxing ethyl acetate gave the thione 5 in 90% yield. This reaction has not been used for the preparation of other cyclopropenethiones. 

In the presence of a mineral acid, the reaction of bis(isopropylamino)cyclopropencthiones with acrylamide or 1,4-benzoquinone afforded [2-(aminocarbonyl)ethylsulfanyl]bis(diisopropyl-amino)cyclopropenylium bromide (using HBr, EtOH) and (2,5-dihydroxyphenylsulfanyl)-bis(diisopropylamino)cyclopropenylium perchlorate (using HCIO4, EtOH), respectively. Reaction of bis(diisopropyl)cyclopropenethionc with chlorobis(diisopropyl)cyclopropenylium salts in chloroform afforded a sulfur bridged dication 3. °" ... 

The reaction of disubstitutcd acetylenes 1 with arylchlorocarbenes, which were generated by the action of strong base upon (dichloromethyl)benzcnes 2, afforded the cyclopropenyl halides 3. The halides, or the cyclopropenyl alkoxides obtained therefrom, were readily converted to the cyclopropenylium salts 4 upon treatment with Bronsted acids. ... 

Substituted halocarbenes, generated either thermally or photochemically from substituted halodiazirines 10, added to disubstituted acetylenes 9 to give the 3-halocyclopropenes 11, which ionized into the cyclopropenylium salts either spontaneously" or under the action of Bronsted acids." Tritylium salts were also employed for ionization of the halides. ... 

When 3-halocyclopropenes 1 were treated with Lewis acids, the halide ion was abstracted to give the cyclopropenylium salts 2 with metalated anions as the counter-ion. 

Similarly, l-aryl-2,3,3-trichlorocyclopropenes 16 were converted to the 3-aryl-l,2-bis(di-methylamino)cyclopropenylium salts 17.34.44-46... 

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