Nadezhda B. Tamm

Fusing Pentagons in a Fullerene Cage by Chlorination: IPR D2‐C76 Rearranges into non‐IPR C76Cl24

As is well known, fullerenes obtained by conventional arcdischarge synthesis obey the isolated pentagon rule (IPR). Unless fullerene molecules are directly subjected to “fullerene surgery”, exohedral functionalization does not affect the connectivity of their carbon networks. Non-IPR fullerene isomers have been available through appropriate modifications of the arc-discharge methodology to synthesize an already chemically derivatized molecule in which the derivatization stabilizes the pentagon–pentagon junctions. In particular, non-IPR cages are quite common in endohedral metallofullerenes, as encapsulated metal atoms are likely to stabilize the fused pentagon fragments by charge-transfer binding to them. More recently, a number of unconventional exohedral fullerene derivatives, including C50Cl10, [5, 6] C56Cl10, [7] C66H4, [8] C68Cl4, [6] and non-IPR C60Cl8 and C60Cl12, [9] have been obtained by means of an arc-discharge process in presence of additives such as CCl4, Cl2, and CH4. Rare examples of more classical chemical approaches to nonIPR fullerenes are indirectly confirmed transformation of dodecahedrane into C20 [10] and synthesis of a C62 derivative with four-membered cycle in its carbon cage from C60. [11]

Isolation and Structural X‐ray Investigation of Perfluoroalkyl Derivatives of Six Cage Isomers of C84

Perfluoroalkylation of a higher fullerene mixture with CF(3)I or C(2)F(5)I, followed by HPLC separation of CF(3) and C(2)F(5) derivatives, resulted in the isolation of several C(84)(R(F))(n) (n=12, 16) compounds. Single-crystal X-ray crystallography with the use of synchrotron radiation allowed structure elucidation of eight C(84)(R(F))(n) compounds containing six different C(84) cages (the number of the C(84) isomer is given in parentheses): C(84) (23)(C(2)F(5))(12) (I), C(84) (22)(CF(3))(16) (II), C(84) (22)(C(2)F(5))(12) (III), C(84) (11)(C(2)F(5))(12) (IV), C(84) (16)(C(2)F(5))(12) (V), C(84) (4)(CF(3))(12) (VI with toluene and VII with hexane as solvate molecules), and C(84) (18)(C(2)F(5))(12) (VIII). Whereas some connectivity patterns of C(84) isomers (22, 23, 11) had previously been unambiguously confirmed by different methods, derivatives of C(84) isomers numbers 4, 16, and 18 have been investigated crystallographically for the first time, thus providing direct proof of the connectivity patterns of rare C(84) isomers. General aspects of the addition of R(F) groups to C(84) cages are discussed in terms of the preferred positions in the pentagons under the formation of chains, pairs, and isolated R(F) groups.

Synthesis, Structure, and Theoretical Study of Trifluoromethyl Derivatives of C84(22) Fullerene

Trifluoromethylation of higher fullerene mixtures with CF(3)I was performed in ampoules at 400 to 420 and 550 to 560 °C. HPLC separation followed by crystal growth and X-ray diffraction studies allowed the structure elucidation of nine CF(3) derivatives of D(2)-C(84) (isomer 22). Molecular structures of two isomers of C(84)(22)(CF(3))(12), two isomers of C(84)(22)(CF(3))(14), four isomers of C(84)(22)(CF(3))(16), and one isomer of C(84)(22)(CF(3))(20) were discussed in terms of their addition patterns and relative formation energies. DFT calculations were also used to predict the most stable molecular structures of lower CF(3) derivatives, C(84)(22)(CF(3))(2-10). It was found that the addition of CF(3) groups to C(84)(22) is governed by two rules: additions can only occur at para positions of C(6)(CF(3))(2) hexagons and no additions can occur at triple-hexagon-junction positions on the fullerene cage.

Regioselective synthesis and crystal structure of C70(CF3)10[C(CO2Et)2]

The Bingel reaction of poly(trifluoromethyl)fullerene p7mp-C70(CF3)10 with diethyl malonate and CBr4 in the presence of bases yields the C70(CF3)10[C(CO2Et)2] cycloadduct as a major product, along with two C70(CF3)10[CH(CO2Et)] isomers. An XRD study of the main compound demonstrates that a [2 + 1] cycloaddition occurs at the unoccupied pole of the p7mp-C70(CF3)10 molecule. The observed regiochemical selectivity of the [2 + 1] cycloaddition is shown to be favored from both energetic and orbital reactivity viewpoints.

Synthesis, structural investigation, and theoretical study of pentaf luoroethyl derivatives of [60]fullerene

Pentafluoroethyl derivatives of [60]fullerene C60(C2F5)n (n = 6, 8, and 10) were synthesized by the reaction of C60 with C2F5I in glass ampoules at 380–440 °C. Isomers of composition C60(C2F5)6 (one isomer), C60(C2F5)8 (five isomers), and C60(C2F5)10 (two isomers) were isolated by chromatographic separation. Their molecular structures were established by X-ray diffraction. The relative stabilities of isomers were compared by density functional theory calculations.

Synthesis, isolation, and addition patterns of trifluoromethylated D5h and I(h) isomers of Sc3N@C80: Sc3N@D5h-C80(CF3)18 and Sc3N@I(h)-C80(CF3)14.

Sc(3)N@D(5h)-C(80) and Sc(3)N@I(h)-C(80) were trifluoromethylated with CF(3)I at 400 °C, affording mixtures of CF(3) derivatives. After separation with HPLC, the first multi-CF(3) derivative of Sc(3)N@D(5h)-C(80), Sc(3)N@D(5h)-C(80)(CF(3))(18), and three new isomers of Sc(3)N@I(h)-C(80)(CF(3))(14) were investigated by X-ray crystallography. The Sc(3)N@D(5h)-C(80)(CF(3))(18) molecule is characterized by a large number of double C-C bonds and benzenoid rings within the D(5h)-C(80) cage and a fully different position of the Sc(3)N unit compared to that in the pristine Sc(3)N@D(5h)-C(80). A detailed comparison of five Sc(3)N@I(h)-C(80)(CF(3))(14) isomers reveals a strong influence of the exohedral additions on the behavior of the Sc(3)N cluster inside the I(h)-C(80) cage.

Investigations in the field of higher fullerenes

Halogenation of higher fullerene mixtures or their perfluoroalkylation with RFI followed by HPLC separation of RF derivatives and subsequent synchrotron X-ray crystallographic study made it possible to confirm cage connectivities of higher fullerenes and, in addition, to receive information concerning their reactivity in radical addition reactions. The data obtained are compared with theoretical predictions for higher fullerenes. Addition patterns of higher fullerene derivatives are discussed. Skeletal rearrangement of the D2-C76 cage during chlorination has been observed for the first time.

Preparation, crystallographic characterization and theoretical study of two isomers of C70(CF3)12

Two isomers of C70(CF3)12 have been isolated from a mixture obtained by trifluoromethylation of C70 with CF3I; their molecular structures determined by X-ray crystallography are in good agreement with the results of theoretical DFT calculations for the most stable C70(CF3)12 isomers.

Crystal and molecular structures of trifluoromethyl derivatives of fullerenes C76 and C82

Trifluoromethyl derivatives of C76 and C82 were synthesized by the reaction of a mixture of higher fullerenes with trifluoroiodomethane followed by the separation by high-performance liquid chromatography. The crystal and molecular structures of C76(CF3)16 (two isomers) and crystal solvates of C76(CF3)18, C82(CF3)16, and C82(CF3)18 were determined by single-crystal X-ray diffraction using synchrotron radiation. The addition patterns of CF3 groups in the C76(CF3)14–18 and C82(CF3)16–18 molecules are discussed.

X-ray Crystallographic Proof of the Isomer D2-C84(5) as Trifluoromethylated and Chlorinated Derivatives, C84(CF3)16, C84Cl20, and C84Cl32

Minor isomer comes forward: Minor isomer C(84)(5) has been captured by high temperature trifluoromethylation with CF(3)I and chlorination with VCl(4). The compounds C(84)(CF(3))(16), C(84)Cl(20), and C(84)(5)Cl(32) were investigated by X-ray crystallography providing the first direct proof of the cage connectivity of D(2)-C(84)(5). The D(2)-C(84)(5)Cl(32) molecule (see figure; C grey, Cl green) contains two flattened, pyrene-like substructures on opposite poles of the cage resulting in its drum-like shape.