Solvolytic Generation of Antiaromatic Cyclopentadienyl Cations

Abstract

Solvolysis of 1,3-di-tert-butyl-5-methyl-5-cyclopenta-1,3-dienyl trifluoroacetate (15a) occurs with a strong dependence on solvent ionizing power (m = 0.97), and gives products of substitution, allylic and skeletal rearrangement with substitution, and elimination. These results are characteristic of a process involving an intermediate carbocation, and provide the first measurements of the kinetics of formation of a cyclopentadienyl cation, the prototypical 4π-electron carbocation destabilized by antiaromaticity. The reactivity of 15a in 2,2,2-trifluoroethanol at 25 °C is calculated to be lower than those of analogous fluorenyl and indenyl derivatives by factors of 3 × 104 and 4 × 102, and is exceeded by that calculated for 1,3-dimethyl-3-cyclopentenyl trifluoroacetate by a factor of 1014, showing the large carbocation destabilizing effects of antiaromaticity.

Electrochemical Exfoliation of Pillared‐Layer Metal–Organic Framework to Boost the Oxygen Evolution Reaction

“…After electrolysis,t he catalyst still contains the organic ligand (m/z (MÀH) 197) only,b ut new species (m/z (M+ +H) 169 and 185) were found in the electrolyte solution ( Figure S23). [19] In this context, the peak at m/z (M+ +H) 169 can be assigned to 2oxocyclopenta-3,5-diene-1,3-dicarboxylic acid ( Figure 5). An obvious peak at m/z (M+ +H) 169 appeared after bubbling O 2 into the solution, and another peak at m/z (M+ +H) 185 appeared after 1day ( Figure S24), indicating that the two species are initial and subsequent oxidized products.I ti sw ell known that catechol can be easily oxidized to o-quinone in alkaline solution under O 2 atmosphere,which then undergoes aclassical benzilic acid rearrangement reaction and further decarboxylation and oxidation processes to form cyclopenta-2,4-dienone.…”

“…An obvious peak at m/z (M+ +H) 169 appeared after bubbling O 2 into the solution, and another peak at m/z (M+ +H) 185 appeared after 1day ( Figure S24), indicating that the two species are initial and subsequent oxidized products.I ti sw ell known that catechol can be easily oxidized to o-quinone in alkaline solution under O 2 atmosphere,which then undergoes aclassical benzilic acid rearrangement reaction and further decarboxylation and oxidation processes to form cyclopenta-2,4-dienone. [19] In this context, the peak at m/z (M+ +H) 169 can be assigned to 2oxocyclopenta-3,5-diene-1,3-dicarboxylic acid ( Figure 5).…”

[Co2(CO)6(Alkynyl)] Complexes of Dibenzosuberyl and Dibenzosuberenyl Carbocations: Dibenzotropylium or Dibenzoheptafulvene?

“…5-Ethynyl-5H-dibenzo[a,d]cyclohepten-5-ol and its hexacarbonyldicobalt complex 28 were prepared as described elsewhere. [33] Preparation of 5-phenylethynyl-5H-dibenzo[a,d]cycloheptan-5-ol (20) In at ypical procedure, nBuLi (22.5 mL, 36 mmol) was added dropwise at 0 8Ct oas olution of phenylacetylene (3.30 mL, 30 mmol) in dry THF (250 mL). After stirring for 15 min, dibenzosuberone (6.25 g, 30 mmol) was added.…”

“…[19] This is in accord with the relative rates of solvolysis of fluorenyl, indenyl and cyclopentadienyl trifluoroacetates, which were found to be 310 4 ,3 .5 10 2 and 1, respectively. [20] These data suggest that the cations with more antiaromatic character have the greatest need for charged elocalisation onto the cluster and are more strongly bonded to am etal.…”

Bondpseudorotation, Jahn‐Teller, and pseudo‐Jahn‐Teller effects in the cyclopentadienyl cation and its pentahalogeno derivatives

“…CPC has been the target of several experimental investigations,6–9 which because of its peculiar electronic structure and chemical behavior triggered extended computational studies 9–14. CPC was identified in the mass spectrum15, 16 and its solvolytic generation was reported by Tidwell and coworkers,17 who also summarized the early synthetic work on CPC. The ground state of CPC was identified to be a triplet with D 5h ‐symmetry ( X̃ 3 A ) and the adiabatic singlet–triplet splitting was determined to be 4.38 kcal/mol 9.…”