Oxidative cage opening in the C70 fullerene facilitated by preceding trifluoromethylation.

Two novel derivatives of the C70 fullerene with 9- and 10-membered cage openings were obtained by means of oxidation and decarbonylation of C70(CF3)8. The major product, C70(O)(CF3)8O2, features a cleaved C-C bond transformed into two carbonyl functions plus an ether bridge. The second product, C69O(CF3)8O, has one of the carbonyls replaced with another ether bridge. We provide a DFT analysis of the possible formation pathways to give the oxidized compounds under the action of pyridine N-oxide.

Dimeric and 1D polymeric low-chlorinated C60 fullerenes, (C60Cl5)2 and (C60Cl4)∞.

Low-chlorinated fullerenes, dimeric (C60Cl5)2 and one-dimensional, polymeric (C60Cl4)∞, were obtained by high-temperature (270 °C) chlorination of C60 with a SbCl5/SbCl3 mixture, as revealed by X-ray crystallography. The compounds were characterized by IR and Raman spectroscopy and theoretical calculations. This is the first observation of a fullerene polymer with single C-C bonding and neutral building blocks.

Structural Chemistry of Pentagon-Fused C82 Fullerene Derivatives #39173C82(CF3)14,16,18 and #39173C82Cl28.

High-temperature chlorination of the most stable Isolated-Pentagon-Rule (IPR) isomer of fullerene C82, C2-C82(3), invariably produces non-IPR #39173C82Cl28, containing one pentagon-pentagon fusion in the carbon cage. High-temperature trifluoromethylation of #39173C82Cl28 followed by HPLC separation resulted in the isolation and structure elucidation of eight #39173C82(CF3)n (n = 14, 16, 18) compounds. Structural chemistry of #39173C82(CF3)14,16,18 and #39173C82Cl28 is characterized by the variation of the addition patterns in the region of a pentagon-pentagon fusion. The regiochemistry of CF3 addition in the remaining cage region is similar to that of the known IPR C82(3)(CF3)n compounds. Theoretical calculations revealed that #39173C82(CF3)n possess lower thermodynamic stability than isomeric IPR derivatives.

Fused-Pentagon Carbon Cages in Chloro and Trifluoromethyl Derivatives of C60: Non-IPR 1809C60Cl8, 1806C60(CF3)14, and Nonclassical C60(NC)Cl14.

High-temperature chlorination of conventional IPR C60 can produce chloro derivatives of non-IPR C60 by skeletal transformations via Stone-Wales rearrangements (SWRs) of the carbon cage. We report the synthesis and structure elucidation of non-IPR 1809C60Cl8 and nonclassical C60(NC)Cl14. The present isolation of 1809C60Cl8 hints at the possibility that the same product in the previously reported chlorine-doped arc-discharge synthesis could have, likewise, resulted from the initially formed IPR C60. C60(NC)Cl14 is the first chloride containing a nonclassical carbon cage with one heptagon and 13 pentagons known previously only in a CF3 derivative. Additionally, trifluoromethylation of non-IPR chlorides revealed the formation of 1806C60(CF3)14 with a new non-IPR carbon cage and unusual trifluoromethylation pattern. Thereby, the number of different, structurally confirmed non-IPR carbon cages of C60 now reaches eight.

Two Isolated-Pentagon-Rule Isomers C98(110) and C98(111) Isolated as Trifluoromethylfullerenes C98(CF3)22.

The fullerene C98 has 259 topologically possible isomers that obey the isolated-pentagon rule (IPR). In this work, a family of experimentally confirmed IPR isomers of C98 fullerene is extended by the high-performance liquid chromatography isolation and X-ray structural characterization of two trifluoromethyl derivatives, C1-C98(110)(CF3)22 and C1-C98(111)(CF3)22. The carbon cages of isomers Cs-C98(110) and Cs-C98(111) differ by a Stone-Wales rotation of only one C-C bond, which results in very similar addition patterns of 22 CF3 groups in the C98(CF3)22 molecules. The stabilizing substructures in both C98(CF3)22 molecules include six benzenoid rings and four isolated C═C bonds. Both Cs-C98(110) and Cs-C98(111) belong to the isomers of moderate relative stability among altogether seven IPR isomers of C98 fullerene with experimentally confirmed cage structures.

Electrochemically Induced Dimerization of p9mp-C70(CF3)12 Trifluoromethylated Fullerene.

We report a comprehensive study of a novel isomer of C70(CF3)12, p9mp-C70(CF3)12, whose electrochemical behavior differs from most of the other trifluoromethylated fullerenes. The addition pattern of p9mp-C70(CF3)12 is established by means of 19F-19F COSY NMR spectroscopy and DFT calculations. Like p7mp-C70(CF3)10, the new isomer p9mp-C70(CF3)12 undergoes dimerization to the [C70(CF3)12]22- upon single-electron reduction. The electrochemical observations are supported by the DFT calculations of dimerization energy and the temperature dependence of the CW X-band EPR spectroscopy data. Experimentally determined dimerization energies of p9mp-C70(CF3)12-• and p7mp-C70(CF3)10-• in solution are ca -8 and -26 kJ mol-1, respectively, in good correspondence with DFT data.

Trifluoromethyl derivatives of pentagon-fused C60: 1809C60(CF3)n (n = 10, 12, 14, 16).

The carbon cage of buckminsterfullerene Ih-C60, obeying the Isolated-Pentagon Rule (IPR), can be transformed to the non-IPR C2v-1809C60 cage by a single Stone-Wales rearrangement (SWR) in the course of high-temperature chlorination of C60 with SbCl5. The following high-temperature trifluoromethylation of the chlorination products with CF3I afforded non-IPR CF3 derivatives, 1809C60(CF3)n. X-ray diffraction studies of 1809C60(CF3)n (n = 10, 12, 14, 16) revealed that the sites of pentagon-pentagon fusions on the carbon cage are preferentially occupied by CF3 groups. The addition patterns of 1809C60(CF3)n and related 1809C60Cln are compared, demonstrating a prevailing role of pentagon-pentagon fusions in the stability and structural chemistry of these compounds. Further SWR skeletal transformations of 1809C60 are discussed and compared with the experimental data available.

Chloro- and Trifluoromethyl Derivatives of a Pentagon-Fused C60: 1810C60Cl24, 1810C60Cl20, and 1810C60(CF3)14.

The carbon cage of Ih-C60, obeying the isolated-pentagon rule (IPR), can be transformed to the non-IPR D2h-1810C60 cage via two successive Stone-Wales rearrangements in the course of high-temperature chlorination of C60 with SbCl5. Two chloro derivatives, C2v-1810C60Cl24 and C2v-1810C60Cl20, have been isolated by high-performance liquid chromatography (HPLC). High-temperature trifluoromethylation of the chlorination products with CF3I, followed by HPLC separation, afforded a non-IPR CF3 derivative, Cs-1810C60(CF3)14. Structural elucidation of the isolated compounds revealed that all eight sites of pentagon-pentagon fusions on the carbon cage are preferentially occupied by Cl atoms or CF3 groups. According to density functional theory calculations, chloro and CF3 derivatives of 1810C60 are more stable than the isomeric derivatives of 1809C60 or IPR 1812C60, possessing respectively four or no sites of pentagon fusion in their carbon cages.

Three Isolated-Pentagon-Rule Isomers of C96 Fullerene Isolated as Trifluoromethyl Derivatives.

The family of experimentally confirmed isolated-pentagon-rule (IPR) isomers of C96 fullerene is extended by trifluoromethylation of a C96 fraction of the fullerene soot, high-performance liquid chromatography separation of CF3 derivatives, and a single-crystal X-ray diffraction study of C96(CF3)n compounds with the use of synchrotron radiation. New cage isomers were revealed in C96(94)(CF3)18/20 and C96(182)(CF3)18 compounds, whereas isomer C96(181), previously known in the adduct with nickel porphyrinate, was confirmed in C96(181)(CF3)18/20 derivatives. Common and special features of the addition patterns of CF3 groups on C96 carbon cages are discussed in more detail. The investigated isomers belong to the most stable C2-C96(181) and slightly less stable C1-C96(94) and C2-C96(182) among the altogether 15 experimentally confirmed IPR isomers of C96 fullerene.

Fused-Pentagon C70Cl6 and C70Cl8 Obtained via Chlorination-Promoted Skeletal Transformation of IPR C70.

The isolated-pentagon-rule (IPR) D5h-C70 fullerene is least susceptible to skeletal transformations in comparison with higher fullerenes and even C60. A cage transformation in IPR C70 via a one-step Stone-Wales rearrangement was accomplished by high-temperature (440 °C) ampule chlorination with SbCl5. Subsequent dechlorination at 450 °C, followed by high-performance liquid chromatography separation, allowed the isolation of non-IPR C70Cl6 and C70Cl8. X-ray diffraction study revealed the presence of an unprecedented C70 carbon cage, possessing two pairs of fused pentagons and the chlorination patterns located on one cage hemisphere. A high energetic and thermal stability of both non-IPR chlorides was also confirmed by theoretical calculations of formation energies. Pathways of skeletal transformations of IPR C70 in comparison with those in C60 are discussed.

Trifluoromethyl Derivatives of Elusive Fullerene C98.

Data concerning the isomeric composition of C98 and the chemistry of C98 derivatives are scarce due to very low abundance of C98 in the fullerene soot. Trifluoromethylation of C98 -containing mixtures followed by HPLC separation of CF3 derivatives and single crystal X-ray diffraction study resulted in structural characterization of four compounds C98 (248)(CF3 )18/20 , C98 (116)(CF3 )18 , and C98 (120)(CF3 )20 . To date, these compounds represent the largest fullerenes isolated as CF3 derivatives with experimentally determined molecular structures. The addition patterns of C98 (CF3 )18/20 are discussed in detail revealing the stabilizing factors, such as isolated double C=C bonds and benzenoid rings on C98 fullerene cages. A detailed comparison with the addition patterns of the known C98 Cln allowed us to contribute to the better understanding the chemistry of elusive C98 fullerene.

Chlorination-Promoted Cage Transformation of IPR C92 Discovered via Trifluoromethylation under Formation of Non-classical C92 (NC)(CF3 )22.

High-temperature trifluoromethylation of isolated-pentagon-rule (IPR) fullerene C92 chlorination products followed by HPLC separation of C92 (CF3 )n derivatives resulted in the isolation and X-ray structural characterization of IPR C92 (38)(CF3 )18 and non-classical C92 (NC)(CF3 )22 . The formation of C92 (38)(CF3 )18 as the highest CF3 derivative of the known isomer C92 (38) can be expected. The formation of C92 (NC)(CF3 )22 was interpreted as chlorination-promoted cage transformation of C92 (38) followed by trifluoromethylation of non-classical C92 (NC) chloride. Noticeably, C92 (NC)(CF3 )22 shows the highest degree of trifluoromethylation among all known CF3 derivatives of fullerenes. The addition patterns of C92 (38)(CF3 )18 and C92 (NC)(CF3 )22 are discussed and compared to the chlorination patterns of C92 (38)Cln compounds.

Stable C92(26) and C92(38) as Well as Unstable C92(50) and C92(23) Isolated-Pentagon-Rule Isomers As Revealed by Chlorination of C92 Fullerene.

High-temperature chlorination of C92 fractions, followed by single-crystal X-ray diffraction, resulted in the structure determination of C92(38)Cl18, C92(38)Cl22, C92(26)Cl24, nonclassical C90( NC)Cl22, and non-isolated-pentagon-rule C90Cl26. Two latter chloro derivatives were obtained by chlorination-promoted cage transformations via a single C2 loss from C92(50) and a combination of a C2 loss from C92(23) and three Stone-Wales rearrangements. The chlorination patterns are stabilized by the formation of isolated C═C bonds and aromatic substructures on carbon cages. The presence of C92 isomer numbers 23, 26, and 50 in the arc-discharge fullerene soot has been confirmed for the first time.

Rebuilding C60: Chlorination-Promoted Transformations of the Buckminsterfullerene into Pentagon-Fused C60 Derivatives.

In recent years, many higher fullerenes that obey the isolated pentagon rule (IPR) were found capable of rearranging into molecules with adjacent pentagons and even with heptagons via chlorination-promoted skeletal transformations. However, the key fullerene, buckminsterfullerene I h-C60, long seemed insusceptible to such rearrangements. Now we demonstrate that buckminsterfullerene yet can be transformed by chlorination with SbCl5 at 420-440 °C and report X-ray structures for the thus-obtained library of non-IPR derivatives. The most remarkable of them are non-IPR C60Cl24 and C60Cl20 with fundamentally rearranged carbon skeletons featuring, respectively, four and five fused pentagon pairs (FPPs). Further high-temperature trifluoromethylation of the chlorinated mixture afforded additional non-IPR derivatives C60(CF3)10 and C60(CF3)14, both with two FPPs, and a nonclassical C60(CF3)15F with a heptagon, two FPPs, and a fully fused pentagon triple. We discuss the general features of the addition patterns in the new non-IPR compounds and probable pathways of their formation via successive Stone-Wales rearrangements.

Synthesis, Isolation and Structures of Trifluoromethylated Fullerenes D2 -C76 , C76 (1)(CF3 )10-18.

High-temperature trifluoromethylation of fullerene C76 chlorination products followed by HPLC separation of C76 (CF3 )n derivatives resulted in the isolation and X-ray structural characterization of thirteen C76 (1)(CF3 )n compounds including nine new isomers such as one isomer of C76 (1)(CF3 )10 , two C76 (1)(CF3 )12 , three C76 (1)(CF3 )14 , one C76 (1)(CF3 )16 , and two isomers of C76 (1)(CF3 )18 . Depending on their addition patterns, C76 (1)(CF3 )n isomers are divided into three subgroups and discussed in terms of trifluoromethylation pathways and relative formation energies.

Chlorination-promoted skeletal transformation of IPR C76 discovered via trifluoromethylation under the formation of non-IPR C76(CF3)nFm.

High-temperature chlorination of an Isolated-Pentagon Rule (IPR) D2-C76 fullerene followed by high-temperature trifluoromethylation of non-IPR C76 chlorides with CF3I unexpectedly resulted in a series of non-IPR C76(CF3)nFm compounds. X-ray diffraction study with the use of synchrotron radiation revealed the mixed CF3/F structures of non-classical, non-IPR C76(CF3)14, C76(CF3)14F2, and C76(CF3)16F6.

Facile Separation, Spectroscopic Identification, and Electrochemical Properties of Higher Trifluoromethylated Derivatives of [70]Fullerene.

We survey the structure and electronic properties of the family of higher trifluoromethylated C70 (CF3 )n molecules with n=14, 16, 18, and 20. Twenty-two available compounds, of which thirteen are newly obtained and characterized, demonstrate the broad diversity of π-system topologies, which enabled us to study the interplay between the CF3 addition pattern and the electronic properties. UV/Vis spectroscopic and cyclic voltammetric studies demonstrate the importance of the exact addition pattern rather than the plain number of addends. Of particular interest is the skew pentagonal pyramid (SPP) addition pattern, which enables formation of closed-shell cyclopentadienyl anions C70 (CF3 )n-1- through CF3 detachment upon electron transfer. A detailed study of the process is presented for a SPP-C70 (CF3 )16 where potentiostatic electrolysis at the second reduction potential gives C70 (CF3 )15- oxidizable to a persistent C70 (CF3 )15. radical. Together with the literature data for the lower C70 (CF3 )n compounds with n=2-12, the present results show good correlation between the experimental boundary level positions and the DFT predictions. The compounds turn out to be electron acceptor molecular semiconductors with experimental LUMO energies and HOMO-LUMO gaps within the ranges of -4.3 to -3.7 eV and 1.6 to 3.3 eV, respectively, depending on the shape of the conjugated fragments. The HOMO levels fall within the range of -5.6 to -6.9 eV and show linear correlation with the number of addends.

Steering the Geometry of Butterfly-Shaped Dimetal Carbide Cluster within a Carbon Cage via Trifluoromethylation of Y2C2@C82(6).

As one of the largest sub-branches of endohedral clusterfullerenes, dimetal carbide clusterfullerene (CCF) in the form of M2C2@C2 n is quite intriguing since an alternative structure of M2@C2 n+2 as conventional dimetallofullerene may exist as well. Herein, by using high-temperature trifluoromethylation followed by HPLC separation and single-crystal X-ray diffraction study, we report for the first time the unambiguous structural determination of yttrium (Y)-based CCF as its trifluoromethyl derivatives, Y2C2@C82(6)(CF3)16. Four isomers of Y2C2@C82(6)(CF3)16 with different addition patterns of 16 CF3 groups are successfully isolated, and two Y atoms of the butterfly-shaped Y2C2 cluster are coordinated by two cage pentagons in each isomer. The butterfly geometry of Y2C2 cluster varies significantly in the four Y2C2@C82(6)(CF3)16 isomers, with Y···Y distances ranging from 3.544 to 4.051 Å dependent on the relative positions of the two yttrium-coordinated pentagons on the carbon cage.

Synthesis, Isolation, and Trifluoromethylation of Two Isomers of C84 -Based Monometallic Cyanide Clusterfullerenes: Interplay between the Endohedral Cluster and the Exohedral Addends.

As an emerging member of endohedral fullerenes, metal cyanide clusterfullerenes (CYCF) are unique in terms of the encapsulation of a monometallic cluster. To date the reported carbon cages of CYCFs are limited to C82 and C76 , and little is known about the chemical reactivity of CYCFs. Herein, two isomers of the first C84 -based CYCFs, YCN@C84 , were isolated as trifluoromethyl derivatives, including YCN@C84 (23)(CF3 )18 and three isomers of YCN@C84 (13)(CF3 )16 , which are based on a unique chiral C2 -C84 (13) cage. As a common feature of the CF3 addition patterns, the YCN@C84 (CF3 )16/18 compounds are stabilized by the formation of isolated C=C bonds and benzenoid rings on the carbon cages. The interplay between the endohedral YCN cluster and the exhohedral CF3 addends was unveiled according to single-crystal X-ray diffraction studies, thus offering new insight into the chemical reactivity of CYCFs.

Trifluoromethyl Derivatives of a Monometallic Cyanide Cluster Fullerene, YCN@C82(6)(CF3)16/18.

Recently discovered monometallic cyanide cluster fullerenes are a novel family of endohedral molecules, whose chemical reactivity has not yet been probed. High-temperature trifluoromethylation of the yttrium cyanide cluster fullerene YCN@C82(6), followed by high-performance liquid chromatography separation and an X-ray diffraction study of the two crystallized fractions, resulted in the structural characterization of YCN@C82(6)(CF3)16/18. In both molecules, exohedrally attached CF3 groups delimit the spherical π system into localized double bonds, benzenoid rings, larger aromatic assemblies, and a conjugated fragment with the only intact pentagon that is involved in coordination to the interior Y atom. We also present theoretical results on charge distributions in the compounds reported.