title: Synthesis of 18pi annulenic fluorofullerenes from tertiary carbanions: size matters!
abstract: 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 S(N)2' (i.e. S(N)2'') 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 S(N)2' 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 [60]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.
authors.affiliation: School of Chemistry, Physics and Environmental Sciences, University of Sussex, Brighton, UK BN1 9QJ. G.Burley@sussex.ac.uk
authors.forename: Glenn A
authors.initials: GA
authors.lastname: Burley
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Avent
authors.forename: Olga V
authors.initials: OV
authors.lastname: Boltalina
authors.forename: Thomas
authors.initials: T
authors.lastname: Drewello
authors.forename: Ilya V
authors.initials: IV
authors.lastname: Goldt
authors.forename: Massimo
authors.initials: M
authors.lastname: Marcaccio
authors.forename: Francesco
authors.initials: F
authors.lastname: Paolucci
authors.forename: Demis
authors.initials: D
authors.lastname: Paolucci
authors.forename: Joan M
authors.initials: JM
authors.lastname: Street
authors.forename: Roger
authors.initials: R
authors.lastname: Taylor