A range of tertiary carbanions XCH(CO2Et)2 of differing sizes have been reacted with C60F18 to assess the steric effect of X on the position of nucleophilic substitution. For X
= CO2Et, NO2, P(O)(OMe)2, SO2CH2Ph, the all trans annulenes (trannulenes) were obtained as a result of extended SN2′
(i.e. SN2″) substitution; in the case of the phosphorus compound, with reduced amounts of base (DBU) dephosphonylation of one or more P(O)(OMe)2 groups by hydrogen occurred. Trannulene formation did not occur for X
= F, CN due to the smaller size of the nucleophile, and in the latter case substitution was shown to take place by an SN2′ mechanism, resulting in the addend being adjacent to a fluorine addend. Trannulenes (X
= CO2Et, Br, Cl) exhibited reversible one-electron reductions at potentials (−0.02 to −0.09 V) significantly more positive than for fullerene. Trannulene (X
= NO2) exhibited an irreversible one-electron reduction (0.08 V); the irreversibility may be associated with fluorine loss. Conformational isomerism at temperatures below 298 K was observed for all trannulene derivatives as a result of eclipsing addend–addend interactions. Minimum energy conformations with a rotational energy barrier of 12–15 kcal mol−1 were observed when these interactions are calculated using molecular mechanics.
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