The rearrangement of the cubane radical cation in solution

The rearrangement of the cubane radical cation (1(.+)) was examined both ex perimentally (anodic as well as (photo)chemical oxidation of cubane 1 in ac etonitrile) and computationally at coupled cluster, DFT, and MP2 [BCCD(T)/c c-pVDZ//B3LYP/6-31G* + ZPVE as well as BCCD(T)/cc-pVDZ//MP2/6-31G* + ZPVE] levels of theory. The interconversion of the twelve C-2v degenerate structu res of 1(.+) is associated with a sizable activation energy of 1.6 kcal mol (-1). The barriers for the isomerization of 1(.+) to the cuneane radical ca tion (2(.+)) and for the C-C bond fragmentation to the secocubane- 4,7-diyl radical cation (10(.+)) are virtually identical (DeltaH(0)(double dagger) = 7.8 and 7.9 kcal mol(-1), respectively). The low-barrier rearrangement of 10(.+) to the more stable syn-tricyclooctadiene radical cation 3(.+) favor s the fragmentation pathway that terminates with the cyclooctatetraene radi cal cation 6(.+). Experimental single-electron transfer (SET) oxidation of cubane in acetonitrile with photoexcited 1,2,4,5-tetracyanobenzene, in comb ination with back electron transfer to the transient radical cation, also s hows that 1(.+) preferentially follows a multistep rearrangement to 6(.+) t hrough 10(.+) and 3(.+) rather than through 2(.+). This was confirmed by th e oxidation of syn-tricyclooctadiene (3), which, like 1, also forms 6 in th e SET oxidation/rearrangement/electron-recapture process. In contrast, cune ane (2) is oxidized exclusively to semibullvalene (9) under analogous condi tions. The rearrangement of 1(.+) to 6(.+) via 3(.+), which was recently ob served spectroscopically upon ionization in a hydrocarbon glass matrix, is also favored in solution.