The Rearrangement of the Cubane Radical Cation in Solution

Schreiner, Peter R.; Wittkopp, Alexander; Gunchenko, Pavel A.; Yaroshinsky, Alexander I.; Peleshanko, Sergey A.; Fokin, Andrey A.

doi:10.1002/1521-3765(20010702)7:13<2739::aid-chem2739>3.0.co;2-r

Cited by 19 publications

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References 33 publications

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“…Either cuneane or syn ‐tricyclooctadiene radical cations ( 10 •+ and 11 •+ , respectively) were suggested as the key intermediates for the rearrangement of 9 •+ to octacyclooctatetraene ( 12 •+ ) radical cation in the Freon matrix117 or hydrocarbon glasses 118. Only the rearrangement trough 11 •+ was supported computationally and experimentally by the single‐electron oxidation of cubane in solution, as the independent oxidation of cuneane gave semibulvalene ( 14 ) exclusively 116…”

Section: Theoretical Methodsmentioning

confidence: 99%

Hydrocarbon σ‐radical cations

Shubina

Fokin

2011

WIREs Comput Mol Sci

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The structure and transformations of radical cations derived from saturated hydrocarbons in the gas phase and solution may be, in most cases, predicted with high‐level computational methods. The review covers so‐called sigma‐radical cations, i.e., the species with partially broken CH and CC bonds. The radical cations formed from the small acyclic (methane, ethanes, and butanes), as well as cyclic (cyclopropane, cyclobutane, and rotanes) and polycyclic hydrocarbons were analyzed. © 2011 John Wiley & Sons, Ltd. WIREs Comput Mol Sci 2011 1 661–679 DOI: 10.1002/wcms.24 This article is categorized under: Structure and Mechanism > Molecular Structures

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Section: Theoretical Methodsmentioning

confidence: 99%

Hydrocarbon σ‐radical cations

Shubina

Fokin

2011

WIREs Comput Mol Sci

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“…However, cleavage of a second CÀC bond is highly exothermic and followed by rapid rearrangements. For instance, thermolysis [16,19] and single-electron oxidation [20] of 1 leads to cyclooctatetraene. In contrast, mild radical reagents [21] lead to substitution products with conservation of the cubane cage.…”

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The Protonation of Cubane Revisited

et al. 2004

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Protonation of saturated hydrocarbons is the simplest and practically most important electrophilic reaction.[1] Small alkanes like methane, ethane, and isobutane [2] form welldefined protonated species, and their experimental proton affinities (PAs) are excellently reproduced computationally. [3][4][5] However, the current data on the protonations of strained hydrocarbons are rather controversial, and facile rearrangements are thought to account for the difficulties encountered in measuring the PAs.[6] Cyclopropane (strain energy(E str ) = 27.2 kcal mol À1 ) is an exception because the number of energetic downhill paths is very limited and the barrier for the ring opening of corner-protonated C 3 H 7 + to the 2-propyl cation is high. The experimental PA of cyclopropane (179.4 kcal mol À1 [7] ) is well reproduced computationally (179.3 kcal mol À1 at CCSD(T)/cc-pVTZ//CCSD(T)/cc-pVDZ for corner-protonated C 3 H 7 + ).[8] In contrast to cyclopropane which displays secondary CÀH bonds only, a surprisingly small range of PAs is characteristic for a number of hydrocarbons with tertiary C À H bonds. These hydrocarbons differ considerably in their strain energies, for example, dodecahedrane (PA = 201.7 kcal mol À1 , [9] E str = 65.4 kcal mol), adamantane (PA = 175.7 kcal mol À1 , [11] E str = 6.3 kcal mol À1 [12] ), and cubane [13] (PA = ca 200 kcal mol À1 , [7,9] E str = 161 kcal mol À1 [14] ). For these systems the question remains: How much does the strain energy affect the proton affinity of a saturated hydrocarbon and to what extent should isomerizations be considered? The experimental PA of cubane (1) measured by ion-cyclotron resonance spectroscopy [9] is surprisingly low and was recently questioned by Koppel et al. [15] on the basis that 1 rearranges rapidly to cuneane so that the PA is attributed to the energy change of the entire protonation/rearrangement/deprotonation process. However, cuneane is also highly strained, so where one does stop? Are there any other rearrangement paths for protonated cubane? Herein we address both computationally and experimentally the question to what extent the cubane cage is able to survive electrophilic attack [16] and what the most favorable paths for the reaction of 1 with a proton are.Despite enormous strain, cubane [15,17,18] is kinetically quite stable because breaking just one CÀC bond causes only minor structural changes and hence only little relief of strain. However, cleavage of a second CÀC bond is highly exothermic and followed by rapid rearrangements. For instance, thermolysis [16,19] and single-electron oxidation [20] of 1 leads to cyclooctatetraene. In contrast, mild radical reagents [21] lead to substitution products with conservation of the cubane cage. [22] Electrophilic cubane conversions are limited to reactions of soft electrophiles like metal ions, [18] and a number of fascinating rearrangements (e.g., to syn-tricyclooctadiene (2) with Pd 2+ and to cuneane (3) with Ag + and Li + ) are preparatively useful. [18,23] The attack of a proton on cubane i...

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“…Trotz außerordentlich hoher Ringspannung ist Cuban15, 17, 18 kinetisch relativ stabil, weil der (thermische) Bruch von nur einer C‐C‐Bindung lediglich eine sehr geringe strukturelle Änderung bewirkt und damit auch nur wenig Ringspannung abgebaut wird. Der Bruch einer zweiten C‐C‐Bindung jedoch ist hoch exotherm und begleitet von schnellen Umlagerungen; so ergeben die Thermolyse16, 19 und die Einelektronenoxidation20 von 1 Cyclooctatetraen. Im Unterschied dazu bleibt beim Einsatz milder Radikalspezies21 der Cubankäfig bei der C‐H‐Substitution erhalten 22.…”

Section: Methodsunclassified

Protonierung von Cuban: eine Neubetrachtung

et al. 2004

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zum 70. Geburtstag gewidmet Die Protonierung gesättigter Kohlenwasserstoffe ist zwar die einfachste, aber praktisch wohl die wichtigste elektrophile Reaktion.[1] Niedere Alkane wie Methan, Ethan und Isobutan [2] bilden wohldefinierte protonierte Strukturen, deren experimentelle Protonenaffinitäten (PAs) rechnerisch hervorragend reproduziert werden. [3][4][5] Trotzdem werden die vorliegenden Daten zur Protonierung von gespannten Kohlenwasserstoffen kontrovers diskutiert, und es werden schnelle Umlagerungen für die Schwierigkeiten bei der Messung der PAs verantwortlich gemacht.[ CCSD(T)/cc-pVTZ//CCSD(T)/ccpVDZ-Niveau für eckprotoniertes C 3 H 7 +).[8] Viele Kohlenwasserstoffe mit tertiären C-H-Bindungen weisen sehr ähn-liche PAs auf, obwohl sich ihre Spannungsenergien deutlich unterscheiden. Beispiele hierfür sind Dodecahedran (PA = 201.7 kcal mol À1 , [9] E str = 65.4 kcal mol), Adamantan (PA = 175.7 kcal mol À1 , [11] E str = 6.3 kcal mol À1 [12] ) und Cuban [13] (PA % 200 kcal mol À1 , [7,9] E str = 161 kcal mol À1 [14] ). Für diese Systeme bleibt deshalb die Frage unbeantwortet, wie stark sich die Spannungsenergie auf die Protonenaffinität

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The Rearrangement of the Cubane Radical Cation in Solution

Cited by 19 publications

References 33 publications

Hydrocarbon σ‐radical cations

Hydrocarbon σ‐radical cations

The Protonation of Cubane Revisited

Protonierung von Cuban: eine Neubetrachtung

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