Pentaisopropylcyclopentadienyl: singlet anion, doublet radical, and triplet cation of a carbocyclic .pi. system

Sitzmann, Helmut; Bock, H.; Boese, Roland; Dezember, Thomas; Havlas, Zdeněk; Kaim, Wolfgang; Moscherosch, Michael; Zanathy, L.

doi:10.1021/ja00078a043

“…1), so that the two halves of the molecule are orthogonal to one another. This nonplanar unit prevents the formation of a one-dimensional structural chain (4,5), thus obviating the occurrence of a Peierls transition to an insulating ground state (6). A variety of alkyl (C n H 2n ϩ 1 ) groups can be attached to the nitrogen atoms to modify the crystal packing; the first phenalenyl-based neutral radical to be crystallized [1, with a hexyl group (n ϭ 6) attached to nitrogen] is a resonance-stabilized carbon-based free radical (7).…”

mentioning

confidence: 99%

“…A variety of alkyl (C n H 2n ϩ 1 ) groups can be attached to the nitrogen atoms to modify the crystal packing; the first phenalenyl-based neutral radical to be crystallized [1, with a hexyl group (n ϭ 6) attached to nitrogen] is a resonance-stabilized carbon-based free radical (7). The existence of the monomeric, neutral carbonbased free radical 1 in the crystalline state is unprecedented; all prior structures have required steric hindrance to inhibit dimerization (4,5,8,9). Furthermore, the hexyl radical 1 shows the highest conductivity of any neutral organic molecular solid, despite the fact that all intermolecular contacts are outside of the van der Waals spacing (7).…”

mentioning

confidence: 99%

Magneto-Opto-Electronic Bistability in a Phenalenyl-Based Neutral Radical

Itkis

¹

,

Chi

²

,

Cordes

³

et al. 2002

Science

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A new organic molecular conductor, based on a spiro-biphenalenyl neutral radical, simultaneously exhibits bistability in three physical channels: electrical, optical, and magnetic. In the paramagnetic state, the unpaired electrons are located in the exterior phenalenyl units of the dimer, whereas in the diamagnetic state the electrons migrate to the interior phenalenyl units and spin pair as a pi-dimer. Against all expectations, the conductivity increases by two orders of magnitude in the diamagnetic state, and the band gap decreases. This type of multifunctional material has the potential to be used as the basis for new types of electronic devices, where multiple physical channels are used for writing, reading, and transferring information.

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“…The parent cyclopentadienyl cation [18], its pentachloro derivative [19], and the pentaisopropyl-substituted compound [20], have all been generated at low temperatures (78 and 115 K), respectively, and shown by electron spin resonance (ESR) spectroscopy to exist as triplet species [21]. The singlet-triplet gap is significantly lowered for [4]Rotane and its radical cation.…”

Section: The Quest For Pentacyclopropylcyclopentadienyl Cationmentioning

confidence: 99%

New structurally interesting cyclopropane derivatives. A world of wonders and surprises

Meijere

¹

,

Kozhushkov

²

,

Fokin

³

et al. 2003

Pure and Applied Chemistry

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The structurally intriguing [4]-and [5]triangulanes have been prepared in enantiomerically pure form. Their surprisingly high specific rotations are well reproduced by DFT/SCI computations and stem from the fact that these hydrocarbons essentially are σ-helicenes (i.e., rigidly held helical arrangements of σ-bonds). Some light is shed on the properties of radical cations derived from [3]-and [4]rotanes. While the former adopts C s or C 2v symmetry, the latter retains the D 4h symmetry of the neutral hydrocarbon, according to highlevel computations. Experimental and computational evidence is also presented that the antiaromatic cyclopentadienyl cation is stabilized as a singlet ground state by five cyclopropyl substituents. Yet, the three cyclopropyl groups in tricyclopropylamine do not favor the formation of its radical cation, because they are not in the proper orientation. When this amine radical cation is generated by cobalt γ-irradiation in a Freon matrix, evidence for a significant conformational change is obtained by EPR spectroscopy. Finally, the conformational dynamics of the newly prepared crowded molecules tetracyclopropyl-and tetraisopropylmethane are discussed.

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“…The parent cyclopentadienyl cation [18], its pentachloro derivative [19], and the pentaisopropyl-substituted compound [20], have all been generated at low temperatures (78 and 115 K), respectively, and shown by electron spin resonance (ESR) spectroscopy to exist as triplet species [21]. The singlet-triplet gap is significantly lowered for the pentaarylcyclopentadienyl cations, especially for those with donor-substitued aryl groups, so that the singlet species become detectable at -40°C [22].…”

Section: The Quest For Pentacyclopropylcyclopentadienyl Cationmentioning

confidence: 99%

New Structurally Interesting Cyclopropane Derivatives: A World of Wonders and Surprises

Meijere

¹

,

Kozhushkov

²

,

Fokin

³

et al. 2003

View full text Add to dashboard Cite

The structurally intriguing [4]-and [5]triangulanes have been prepared in enantiomerically pure form. Their surprisingly high specific rotations are well reproduced by DFT/SCI computations and stem from the fact that these hydrocarbons essentially are σ-helicenes (i.e., rigidly held helical arrangements of σ-bonds). Some light is shed on the properties of radical cations derived from [3]-and [4]rotanes. While the former adopts C s or C 2v symmetry, the latter retains the D 4h symmetry of the neutral hydrocarbon, according to highlevel computations. Experimental and computational evidence is also presented that the antiaromatic cyclopentadienyl cation is stabilized as a singlet ground state by five cyclopropyl substituents. Yet, the three cyclopropyl groups in tricyclopropylamine do not favor the formation of its radical cation, because they are not in the proper orientation. When this amine radical cation is generated by cobalt γ-irradiation in a Freon matrix, evidence for a significant conformational change is obtained by EPR spectroscopy. Finally, the conformational dynamics of the newly prepared crowded molecules tetracyclopropyl-and tetraisopropylmethane are discussed.

show abstract

Pentaisopropylcyclopentadienyl: singlet anion, doublet radical, and triplet cation of a carbocyclic .pi. system

Cited by 76 publications

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Magneto-Opto-Electronic Bistability in a Phenalenyl-Based Neutral Radical

Magneto-Opto-Electronic Bistability in a Phenalenyl-Based Neutral Radical

New structurally interesting cyclopropane derivatives. A world of wonders and surprises

New Structurally Interesting Cyclopropane Derivatives: A World of Wonders and Surprises

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