[6,6]-Open and [6,6]-closed isomers of C70(CF2): synthesis, electrochemical and quantum chemical investigation

Difluoromethylenation of fullerene C70 provides isomeric diversity and availability of equatorial [5,6]-homofullerene C70(CF2)

We report synthesis, isolation, and spectroscopic characterization of the novel [5,6]-open C70(CF2) isomer III along with the already known [6,6]-closed and [6,6]-open C70(CF2) isomers I and II. The compounds were...

Regioselective CF2 functionalization of Sc3N@D3h(5)-C78

We report the first synthesis and computational study of Sc₃N@C₇₈(CF₂) - an analog of the previously reported Sc₃N@C₈₀(CF₂) with a less common carbon cage whose chemical properties presently remain far less studied. Sc₃N@C₇₈ appears to be considerably more reactive toward CF₂ addition than Sc₃N@C₈₀ and somewhat more reactive than C₆₀. Even though the less symmetric D_3h(5)-C₇₈ carbon cage offers far broader opportunities for isomerism than I_h-C₈₀, CF₂ addition to Sc₃N@C₇₈ proceeds regioselectively, similarly to other common fullerene reactions. A DFT survey of the thermodynamic and kinetic aspects of CF₂ addition demonstrates that the regioselectivity is controlled kinetically.

Addition of CF2 group to endohedral fullerene Sc3N@Ih-C80

We report the first successful synthesis of a CF₂ derivative of the stable endohedral fullerene Sc₃N@I_h-C₈₀. Reaction with CF₂ClCOONa yields a single C_s-symmetric Sc₃N@C₈₀(CF₂) adduct where the CF₂ group is inserted into a [6,6]-bond and opens it to 2.3 Å between the bridgehead carbon atoms. As evidenced by absorption and fluorescence spectroscopy as well as cyclic voltammetry, both the HOMO and the LUMO level of Sc₃N@C₈₀(CF₂) are slightly (ca. 0.1 eV) downshifted with respect to the parent Sc₃N@I_h-C₈₀, so the HOMO-LUMO gap remains essentially unchanged. The DFT calculations suggest that the reaction mechanism is not the previously assumed [2 + 1]-cycloaddition of :CF₂ carbene but rather nucleophilic addition of CF₂Cl^- anion followed by elimination of Cl^- and closing of the CF₂ bridge via intramolecular nucleophilic substitution. Selective formation of the [6,6]-Sc₃N@C₈₀(CF₂) turns out to be kinetically controlled and promoted by a particular orientation of the endohedral Sc₃N cluster with respect to the CF₂Cl^- addition site. In its turn, the CF₂ addend partly hampers the rotation of Sc₃N the endohedral cluster compared to its quasi-free reorientations in the parent Sc₃N@I_h-C₈₀.

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.