Common Radical Cation Intermediates in Cage Hydrocarbon Activations

Abstract

The oxidation of 3,6‐dehydrohomoadamantane (1) was achieved under chemical (NO+BF4–/EtOAc, NO+OAc–/Ac2O, and NO+BF4–/CH3CN), photochemical (photoexcited 1,2,4,5‐tetracyanobenzene), and electrochemical (Pt anode, CH3CN, NH4BF4) conditions. Supporting ab initio [density functional theory (BLYP) and Møller–Plesset perturbation theory (MP2)] computations utilizing standard basis sets, 6–31G* (optimizations) and 6–311+G* (single‐point energy evaluations), agree with the experimental results implicating the involvement of the same radical cation intermediates in the activation processes. Isomeric radical cations formed from different precursors can equilibrate with low barriers (2.0–11.7 kcal mol–1) and lead to common products. The computed and experimental adiabatic ionization potential of adamantane shows that activation with NO+BF4– is also likely to occur through the adamantyl radical cation. Hence, the bonds need not be attacked directly by the electrophile in the C–H or C–C activation of alkanes with relatively low ionization potentials.

The Protoadamantane Radical Cation

“…Our recent computational and experimental studies on the halogenation mechanisms of adamantane demonstrated that the 3°CϪH regiospecificities can only be understood in terms of the adamantane moiety being largely radical cationic in the transition structures {the adamantane radical cation (C 3v ) displays a half-broken 3°C ϪH bond}. [33] CϪH activations with weakly electrophilic oxidants (such as Hal n ϩ or Hal nϪ1 H ϩ ) are best visualized as concerted H-coupled electron transfer (HCET) involving linear [R···H···E] ϩ fragments in the transition structures for hydrogen abstraction.…”

Photochemistry of Cyclobutanes: Synthesis and Reactivity

“…Similar products are obtained from the pinenes. The photo-NOCAS procedure has also been carried out on the adamantane derivative 506 illustrated in Scheme 15 330 . Here again the radical cation 507 is formed and ring opening followed by trapping by the tetracyanobenzene affords the cation 508.…”

Influence of molecular vibrations on the valence electron momentum distributions of adamantane

“…. This carbocation and the JT effect on adamantane have been thoroughly investigated from a theoretical and experimental point of view 9,10,[65][66][67][68][69][70][71] . The presence of this molecular species has been inferred from the strong asymmetric broadening in the ionization band of the 7t 2 orbital from both photoelectron (PES) 18,[72][73][74] and Penning ionization (PIES) spectroscopy 18 .…”