Cyclopropenylium cation

The phosphirene cation (5) (with two resonance structures 5a and 5b) has been predicted to possess a Zji aromatic system for quite some time." The aromaticity of the corresponding cyclopropenylium cation (C3H3+) is well-known.Substituted derivatives of 5, however, have only recently been observed in solution and in complexed form. 5 is the global... 

Analogously, the reaction of rhenate pentacarbonyl anion [Re(CO)5] as its sodium salt, with cyclopropenylium cations [C3Ph3]X (X = BF4, PF6) in THF, at -80 °C, afforded the octahedral n-coordinated pentacarbonyl ( /-l,2,3-triphenylcyclopropenyl)rhenium complex in 60-73% yield (equation 195)26 269. The l3C NMR (acetone-, .) spectrum dis-... 

Ring enlargement to r/3-oxocyclobutenyl complexes, by carbonyl insertion into the three-membered ring, is generally observed in reactions of group 9 cobalt carbonyl anions with cyclopropenylium cations (equation 197)271 275. Formation of j/ -oxocyclobutenyl complexes also occurs with nitroso iron carbonyl anions270,275. These reactions are usually... 

X-ray structure analysis of the tris(trimethylsilyl)cyclopropenylium cation... 

In a similar reaction at the same level for the cyclopropenylium cation, the stabilization is 59 kcal mol-1 [101]. Also, the equalized CC and PC bond distances are in good accordance with the aromatic behavior of the phosphirene cation. Not only does the phosphirene cation have aromatic 2n electron delocalization, but its r 3-complexed form has similar structural characteristics as well [4],... 

The pulse radiolysis of trimethyl-(TM-)cyclopropenylium cation, TMCP+ examined by time resolved optical spectroscopy, provided evidence for the eventual formation of hexamethylbenzene cation, HMB +. Apparently TMCP+ and its one-... 

Since cobalt carbonyl anions react readily with a large variety of cyclopropenylcarbonyl chlorides to give selectively / -oxocyclobutenyl complexes (equation 198), it was suggested that reactions of cyclopropenylium cations and [Co(CO)4] involve direct electrophilic attack at the CO ligand rather than at cobalt . However, observation of ring expansion products in the -cyclopropen-3-yl rhenium complex (vide suggests that an... 

C67H , which consists of the tri(cyclopropyl)cyclopropenylium cation and Kuhn s anion, is completely ionized in the solid and in DMSO solution. However, in chloroform, tetrachloromethane, and benzene solutions at room temperature, a covalent hydrocarbon is formed from the two ions. Surprisingly, cooling the chloroform solution to -78 °C or evaporation of the solvent regenerates the original green hydrocarbon salt. 

Another hydrocarbon salt, composed of the tri(cyclopropyl)cyclopropenylium cation and Kuhn s anion, which can exist in all three types of elementary organic species i.e. as an ionic, radical, and covalent compound) in a solution equilibrium, depending on the solvent, has already been mentioned in Section 2.6 [292]. 

Heteroanalogs of cyclopropenylium cations and cyclopropenones 03CRV1371. Similarities and differences between aziridines and epoxides 02CSR247. 

Few cases of r -cyclopropenyl decomplexation have been reported. Conversion of various substituted cyclopropenylium cations with sodium dicarbonyl(cyclopentadienyl)ferrate gives (T-bound cyclopropenyliron complexes 1 which were converted to (x-cyclopropenylium complexes 2 or were decomplexed with self-coupling to form dicyclopropenylium systems 3. ... 

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. ... 

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. 

Kleinpeter and Koch have recently introduced spatial magnetic properties as a measure of homoaromaticity. These are calculated as through-space NMR shieldings (TSNMRS) and visualized as iso-chemical shielding surfaces (ICSF). The structures, the intramolecular flexibility, and the and C NMR chemical shifts are calculated on the MP2/6-311 + G level of theory. TSNMRS of benzene and the cyclopropenylium cation as prototype aromatic molecules published earlier are used as references for homoaromaticity in a number of homoaromatic carbocations. The existence and the degree of homoaromaticity are deduced from the TSNMRSs by comparing the experimental and computed H and NMR NMR chemical shifts. 

Calculations on electrophilic additions to acetylene were reported for a number of hydrocarbon cations, including CH" [129], C3H3" [130, 131], and phenylvinylium ion [132]. It was predicted that the cyclopropenylium cation, the most stable form of C3H, forms an ion-molecule complex with acetylene but does not undergo further addition [131]. The linear propargyl cation, however, reacts with acetylene without an apparent barrier, to form many different C5H5 isomers [130,131]. Wang et al. computed the AMI potential energy surfaces and carried out RRKM and microcanonical variational transition-state analysis for the rate of reaction of phenylvinylium ion with acetylene [132]. 

Trialkyloxonium salts such as Me30 BF4 are excellent reagents for the generation of cyclopropenylium cations by O-methylation of suitable cyclopropenones (eq 9). ... 

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