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Fulleroid Addition Regiochemistry Is Driven by π-Orbital Misalignment

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journal contribution
posted on 29.12.1998, 00:00 authored by Brad R. Weedon, R. C. Haddon, H. Peter Spielmann, Mark S. Meier
This article reports the first investigation into the regiochemistry of addition to the fulleroid C61H2 by Zn(Cu) reduction and hydroboration. Two major isomers of C61H4 are formed by the reduction with Zn(Cu) while only one major isomer is formed by hydroboration. The structures of the major isomers formed by reduction with Zn(Cu) were identified as 1,2-C61H4 and 3,4-C61H4. The 1,2-C61H4 isomer is the only dominant isomer formed by hydroboration with no indications of the 3,4-C61H4 isomer being formed. The regiochemistry observed in the formation of 1,2-C61H4 is the same regiochemistry seen in the further reactivity of azafulleroids (C60NR). Strain energies (calculated at the B3LYP-6-31G* level of theory) show that the relief of strain is greater for the hydrogenation of the fulleroid C61H2 than it is for the hydrogenation of C60 itself. This indicates that the twisted, anti-Bredt's rule, double bonds of the fulleroid are a source of greater localized strain than the pyramidalization of the carbons in the rest of the molecule. Thus, the regiochemistry observed for the fulleroid is due to π-orbital misalignment and not pyramidalization.