- The rearrangement of the cubane radical cation in solution
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The rearrangement of the cubane radical cation (1.+) was examined both experimentally (anodic as well as (photo)chemical oxidation of cubane 1 in acetonitrile) and computationally at coupled cluster, DFT, and MP2 [BCCD(T)/cc-pVDZ//B3LYP/6-31G* + ZPVE as well as BCCD(T)/cc-pVDZ//MP2/6-31G* + ZPVE] levels of theory. The interconversion of the twelve C2v degenerate structures 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 cation (2.+) and for the C-C bond fragmentation to the secocubane-4,7-diyl radical cation (10.+) are virtually identical (ΔH0? = 7.8 and 7.9 kcal mol-1, respectively). The low-barrier rearrangement of 10.+ to the more stable syn-tricyclooctadiene radical cation 3.+ favors the fragmentation pathway that terminates with the cyclooctatetraene radical cation 6.+. Experimental single-electron transfer (SET) oxidation of cubane in acetonitrile with photoexcited 1,2,4,5-tetracyanobenzene, in combination with back electron transfer to the transient radical cation, also shows that 1.+ preferentially follows a multistep rearrangement to 6.+ through 10.+ and 3.+ rather than through 2.+. This was confirmed by the oxidation of syn-tricyclooctadiene (3), which, like 1, also forms 6 in the SET oxidation/rearrangement/electron-recapture process. In contrast, cuneane (2) is oxidized exclusively to semibullvalene (9) under analogous conditions. The rearrangement of 1.+ to 6.+ via 3.+, which was recently observed spectroscopically upon ionization in a hydrocarbon glass matrix, is also favored in solution.
- Schreiner, Peter R.,Wittkopp, Alexander,Gunchenko, Pavel A.,Yaroshinsky, Alexander I.,Peleshanko, Sergey A.,Fokin, Andrey A.
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- THE DEOXYGENATION OF EPOXIDES WITH PHOSPHINES. II. THE FORMATION OF THE SYN-DIMER OF CYCLOBUTADIENE FROM FURAN
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In contrast to the known photochemical reaction of furan with triphenylphosphine (which leads to the anti-dimer of cyclobutadiene and triphenylphosphineoxide) the irradiation of a solution of furan and tri-n-butylphosphine in acetone affords the syn-dimer of cyclobutadiene, together with the corresponding phosphineoxide.
- Condeiu, Cristian,Marton, George,Dinulescu, Ilie G.,Oniciu, Daniela-Carmen,Badea, Florin
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p. 855 - 857
(2007/10/02)
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- 3,4-DIAZABENZVALENE, THE AZOALKANE PRECURSOR TO TETRAHEDRANE. SYNTHESIS AND REACTIVITY.
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The title diazene 1 has been synthesized and shown to decompose thermally to cyclobutadiene over a surprisingly small barrier.
- Kaisaki, David A.,Dougherty, Dennis A.
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p. 5263 - 5266
(2007/10/02)
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