Reactions of C702– with Organic Halides Revisited: Unusual Magnetic Equivalence for the Diastereotopic Methylene Protons in 2,5-(PhCH2)2C70

Regioselective Mono- and Dialkylation of [6,6]-open C60 (CF2 ): Synthetic and Kinetic Aspects

Alkylation of homofullerene [6,6]-C₆₀ (CF₂ )^2- dianion with the set of alkyl halides, RX, was established to demonstrate an effect of RX nature on the conversion, product composition, and regioselectivity. The respective C₆₀ (CF₂ )RH, C₆₀ (CF₂ )R₂ and C₆₀ (CF₂ )R'R'' compounds were obtained in the reaction with sterically unhindered RX, isolated by HPLC and unequivocally characterized. The kinetic studies evidenced S_N 2 mechanism for both alkylation steps, yielding mono- and dialkylated C₆₀ (CF₂ ), respectively, and indicated the negative charge localization at the bridgehead carbon atoms as well as a steric hindrance of the CF₂ moiety likely to be a key factors for the S_N 2 reaction mechanism and observed regioselectivity. The significant difference in the rate constants of the first and the second steps is attributed to the different activation barriers predicted by DFT calculations which makes possible to develop synthetic methods for the regioselective preparation of monoalkylated C₆₀ (CF₂ )RH and heterodialkylated C₆₀ (CF₂ )R'R'' derivatives.

Synthesis of (MeO)2Bn2C70: Regiochemistry of 2-fold Additions to C70 with Addends That Are Preferential for Ortho Addition and Capable of Para Addition

Three C₇₀ tetraadducts, 2,10-(MeO)₂-5,9-Bn₂C₇₀ (6), 1,56-Bn₂-2,57-(MeO)₂C₇₀ (7, 2 o'clock isomer), and 1,41-Bn₂-2,58-(MeO)₂C₇₀ (8, 12 o'clock isomer), were obtained from the reaction of C₇₀ with MeO^- and BnBr (benzyl bromide). The structures of 6-8 were resolved via single-crystal X-ray diffraction and spectroscopic characterizations. Computational calculations on the electrophilic Fukui functions f_k⁺, the stability of reaction intermediates, and activation barriers for the key processes of the reaction were performed to rationalize the regioselectivity of the reaction. A conversion of the 5 and 12 o'clock intermediates to the 2 o'clock intermediate was proposed to account for the regioselectivity related to the 2-fold additions at the two distinctive polar regions of C₇₀. Electrochemical study showed a similar electron deficiency for the 2 and 12 o'clock isomers, while the 2,5,9,10-tetraadduct was more electron deficient with respect to the 2 and 12 o'clock isomers.

Regioisomer-specific electron affinities and electronic structures of C70para-adducts at polar and equatorial positions with (bromo)benzyl radicals: photoelectron spectroscopy and theoretical study

Negative ion photoelectron spectroscopy shows interesting regioisomer-specific electron affinities (EAs) of 2,5- and 7,23-para-adducts of C70 [(ArCH2)2C70] (Ar = Ph, o-, m-, and p-BrC6H4). Their EA values are larger than that of C70 by 5-150 meV with the 2,5-polar adducts' EAs being higher than their corresponding 7,23-equatorial counterparts, exhibiting appreciable EA tunable ranges and regioisomeric specificity. Density functional theory (DFT) calculations reproduce both the experimental EA values and EA trends very well.

Electronic vs steric effects on the stability of anionic species: a case study on the ortho and para regioisomers of organofullerenes

The stability of the anionic species of the ortho and para regioisomers of (MeO)BnC(2n) (Me = methyl, Bn = benzyl, n = 30 or 35) has been examined. The results show that the ortho adducts (electronically favored regioisomers) are stable upon receiving one or two electrons, while the para ones (sterically favored adducts) decompose by removing the methoxy group under similar conditions. Computational calculations indicate that the stability of the anionic species is significantly affected by the electronic structure, where the [5,6]-double bond is responsible for the instability of the reduced species of the para adducts. Further study with 1,15-(MeO)2-2,4-Bn2C60, an adduct with both the ortho and para positioned methoxy, shows that the reduced species is stable, indicating that the 1,2,4,15-configuration is an electronically preferential structure even though it has a [5,6]-double bond.