The Protoadamantane Radical Cation

Abstract

Keywords: C-H activation / Density functional calculations / Electron transfer / Electrophilic additions / Radical ions DFT (B3LYP) and MP2 computations with a 6-31G* basis set show that a unique protoadamantane radical cation (1 ·+ ) structure with an elongated, half-broken C 6 −H bond prevails both in the gas phase and in solution. This is in agreement with the observed regioselectivity of the single electrontransfer oxidation of protoadamantane (1) with photoexcited 1,2,4,5-tetracyanobenzene, which only gives 5-(6-protoadamantyl)-1,2,4-tricyanobenzene (5), for which the X-ray crys-

Hydrocarbon σ‐radical cations

“…In complete agreement with the above computations, the SET oxidation of 20 in presence of photoexcited TCB in solution gave 21 as the only product (Scheme ), as a result of hydrogen loss from the C 6 H position of 20 •+ 138…”

Hydrocarbon σ‐radical cations

“…In complete agreement with the above computations, the SET oxidation of 20 in presence of photoexcited TCB in solution gave 21 as the only product (Scheme ), as a result of hydrogen loss from the C 6 H position of 20 •+ 138…”

Reactivity of [1(2,3)4]Pentamantane (Td-Pentamantane): A Nanoscale Model of Diamond

“…Photoexcited 1,2,4,5-tetracyanobenzene (TCB) is among the most powerful organic single electron acceptors and is often used 21,38,40 for the generation of hydrocarbon radical cations via an outer sphere ET. Oxidation of 5 with TCB in acetonitrile gave a single oxidation product 16 with the aromatic substituent at the apical position of the cage.…”

“…33 As we have shown previously, 31,[34][35][36] the transition structures for the reactions with oxidizing electrophiles are characteristic for inner-sphere ET and thus resemble the structures of the respective hydrocarbon radical cations. 34,35,37,38 Since Jahn-Teller-active 39 [1(2,3)4]pentamantane 5 distorts upon single ET ionization to the C 3V -form 5 •+ (Scheme 3), 25 with two axial tertiary C-H bonds in hyperconjugation with parallel C-C bonds, it is not surprising that two different substitution products form in reactions with electrophilesoxidizers.…”

Carbon‐rich Compounds: Computational Considerations

“…With the structures depicted in Scheme 8.11, one can therefore predict the CaH bond that will be broken from the optimized geometry of the respective diamondoid radical cation. This subsequent deprotonation usually produces the respective hydrocarbon radicals much more selectively than through direct radical H-abstractions [130,137,139]. Although the higher diamondoids are only slightly strained, they display remarkably low adiabatic IPs (177-184 kcal mol À1 ) hence, SET oxidations with conventional single-electron chemical oxidants are predicted to be practically valuable.…”

“…Despite common suspicions about the selectivities of reactions involving hydrocarbon radical cations, these reactions are often the most selective relative to cationic and radical transformations [130,136,137]. Single-electron transfer (SET) oxidations of hydrocarbons to radical cations require strong oxidants as the oxidation potentials of saturated hydrocarbons are rather high.…”

Hydrocarbon σ‐radical cations

“…In complete agreement with the above computations, the SET oxidation of 20 in presence of photoexcited TCB in solution gave 21 as the only product (Scheme ), as a result of hydrogen loss from the C 6 H position of 20 •+ 138…”

Reactivity of [1(2,3)4]Pentamantane (Td-Pentamantane): A Nanoscale Model of Diamond

“…Photoexcited 1,2,4,5-tetracyanobenzene (TCB) is among the most powerful organic single electron acceptors and is often used 21,38,40 for the generation of hydrocarbon radical cations via an outer sphere ET. Oxidation of 5 with TCB in acetonitrile gave a single oxidation product 16 with the aromatic substituent at the apical position of the cage.…”

“…33 As we have shown previously, 31,[34][35][36] the transition structures for the reactions with oxidizing electrophiles are characteristic for inner-sphere ET and thus resemble the structures of the respective hydrocarbon radical cations. 34,35,37,38 Since Jahn-Teller-active 39 [1(2,3)4]pentamantane 5 distorts upon single ET ionization to the C 3V -form 5 •+ (Scheme 3), 25 with two axial tertiary C-H bonds in hyperconjugation with parallel C-C bonds, it is not surprising that two different substitution products form in reactions with electrophilesoxidizers.…”

Carbon‐rich Compounds: Computational Considerations

“…With the structures depicted in Scheme 8.11, one can therefore predict the CaH bond that will be broken from the optimized geometry of the respective diamondoid radical cation. This subsequent deprotonation usually produces the respective hydrocarbon radicals much more selectively than through direct radical H-abstractions [130,137,139]. Although the higher diamondoids are only slightly strained, they display remarkably low adiabatic IPs (177-184 kcal mol À1 ) hence, SET oxidations with conventional single-electron chemical oxidants are predicted to be practically valuable.…”

“…Despite common suspicions about the selectivities of reactions involving hydrocarbon radical cations, these reactions are often the most selective relative to cationic and radical transformations [130,136,137]. Single-electron transfer (SET) oxidations of hydrocarbons to radical cations require strong oxidants as the oxidation potentials of saturated hydrocarbons are rather high.…”

Hydrocarbon σ‐radical cations

“…In complete agreement with the above computations, the SET oxidation of 20 in presence of photoexcited TCB in solution gave 21 as the only product (Scheme ), as a result of hydrogen loss from the C 6 H position of 20 •+ 138…”

Reactivity of [1(2,3)4]Pentamantane (Td-Pentamantane): A Nanoscale Model of Diamond

“…Photoexcited 1,2,4,5-tetracyanobenzene (TCB) is among the most powerful organic single electron acceptors and is often used 21,38,40 for the generation of hydrocarbon radical cations via an outer sphere ET. Oxidation of 5 with TCB in acetonitrile gave a single oxidation product 16 with the aromatic substituent at the apical position of the cage.…”

“…33 As we have shown previously, 31,[34][35][36] the transition structures for the reactions with oxidizing electrophiles are characteristic for inner-sphere ET and thus resemble the structures of the respective hydrocarbon radical cations. 34,35,37,38 Since Jahn-Teller-active 39 [1(2,3)4]pentamantane 5 distorts upon single ET ionization to the C 3V -form 5 •+ (Scheme 3), 25 with two axial tertiary C-H bonds in hyperconjugation with parallel C-C bonds, it is not surprising that two different substitution products form in reactions with electrophilesoxidizers.…”

Carbon‐rich Compounds: Computational Considerations

“…With the structures depicted in Scheme 8.11, one can therefore predict the CaH bond that will be broken from the optimized geometry of the respective diamondoid radical cation. This subsequent deprotonation usually produces the respective hydrocarbon radicals much more selectively than through direct radical H-abstractions [130,137,139]. Although the higher diamondoids are only slightly strained, they display remarkably low adiabatic IPs (177-184 kcal mol À1 ) hence, SET oxidations with conventional single-electron chemical oxidants are predicted to be practically valuable.…”

“…Despite common suspicions about the selectivities of reactions involving hydrocarbon radical cations, these reactions are often the most selective relative to cationic and radical transformations [130,136,137]. Single-electron transfer (SET) oxidations of hydrocarbons to radical cations require strong oxidants as the oxidation potentials of saturated hydrocarbons are rather high.…”