Preparation and characterisation of an equatorial para-adduct of (PhCH2)HC70 from the reaction of C702− with benzyl bromide and H2O: addition effects in the polar and equatorial regions of C70

Abstract

Benzyl(hydro)[70]fullerene regioisomers with the addends in both the equatorial and polar regions of C₇₀ have been prepared via the reaction of dianionic C₇₀ with benzyl bromide and H₂O. HRMS, UV-vis, ¹H, ¹³C, HMQC (heteronuclear multiple quantum coherence) and HMBC (heteronuclear multiple bond coherence) NMR characterisations have shown that the addition in the equatorial region of C₇₀ affords a new (PhCH₂)HC₇₀ regioisomer with para-positioned addends across a six-membered ring, which is different from the “polar” regioisomers where the addends have an ortho-addition pattern. ¹H NMR characterisations have shown a much stronger shielding effect for the addends in the equatorial region with respect to the counterparts in the polar region of C₇₀, while cyclic voltammetry study has shown a surprising positive shift for the first reduction potential of the equatorial regioisomer with respect to those of the polar regioisomer and pristine C₇₀, suggesting that the equatorial region of C₇₀ is rather electropositive than electronegative. D₂O experiment has shown a significant difference of the deuterated product distribution between the equatorial and polar regioisomers, which can be justified by the different acidity of the (PhCH₂)HC₇₀ regioisomers. Computational calculations have been carried out to rationalize the formation of the C₇₀HR regioisomers.