Trifluoromethylation of Fullerenes: Kinetic and Thermodynamic Control

We present a survey and theoretical interpretation of the experimental results on trifluoromethylation of fullerenes. A thermodynamic model has been developed to describe the C_60/70(CF₃)_<i>n</i> condensed phase mixtures capable of free exchange of addends and, consequently, of isomerization and changing the degrees of addition. It was found that the purely thermodynamic model affords at least satisfactory prediction of composition of products even for apparently nonequilibrium syntheses. Special cases can be identified by means of detailed kinetic modeling based on the BEP approach, which includes stepwise energetic analysis of the possible trifluoromethylation sequences. This analysis reveals two types of reactions with remarkable difference in rates: direct trifluoromethylation and rearrangements of the CF₃ groups. Whenever a particular group of compounds is interrelated through direct addition/abstraction of CF₃ groups, it is more or less safe to assume that the said group is in equilibrium describable by the thermodynamic model. In the same time, the slower migration of addends is controlled kinetically, and interference of the sublimation processes frequently prevents its equilibration. Among the most illustrative examples of hindered formation via rearrangements in absence of sufficiently favorable direct trifluoromethylation pathways are certain isomers of the <i>C</i>_3<i>v</i>–C₆₀(CF₃)₁₈, C₇₀(CF₃)₁₈, and C₇₀(CF₃)₂₀ compounds

From Corannulene to Indacenopicene: Effect of Carbon Framework Topology on Aromaticity and Reduction Limits

The electronic structure, reduction limits, and coordination abilities of a bowl-shaped polycyclic aromatic hydrocarbon, indacenopicene (C₂₆H₁₂, <b>1</b>), have been investigated for the first time using a combination of theoretical and experimental tools. A direct comparison with the prototypical corannulene bowl (C₂₀H₁₀, <b>2</b>) revealed the effects of carbon framework topology and symmetry change on the electronic properties and aromaticity of indacenopicene. The accessibility of two reduction steps for <b>1</b> was predicted theoretically and then confirmed experimentally. Two reversible one-electron reduction processes with the formal reduction potentials at −1.92 and −2.29 V vs Fc^+/0 were detected by cyclic voltammetry measurements, demonstrating the stability of the corresponding mono- and dianionic states of <b>1</b>. The products of the doubly reduced indacenopicene have been isolated as rubidium and cesium salts and fully characterized. Their X-ray diffraction study revealed the formation of tetranuclear organometallic building blocks with the [M₂(18-crown-6)]²⁺ (M = Rb (<b>3</b>) and Cs (<b>4</b>)) cations occupying the concave cavities of two C₂₆H₁₂^2– anions. The coordination of two outside <i>exo</i>-bound rubidium ions is terminated by crown ether molecules in <b>3</b> to form the discrete [Rb⁺₄(18-crown-6)₃­(C₂₆H₁₂^2–)₂] tetramer. In contrast, the larger cesium ions allow the 1D polymeric chain propagation in <b>4</b> to afford [Cs⁺₂(18-crown-6)₂­(THF)­(C₂₆H₁₂^2–)]_∞

From Corannulene to Indacenopicene: Effect of Carbon Framework Topology on Aromaticity and Reduction Limits

The electronic structure, reduction limits, and coordination abilities of a bowl-shaped polycyclic aromatic hydrocarbon, indacenopicene (C₂₆H₁₂, <b>1</b>), have been investigated for the first time using a combination of theoretical and experimental tools. A direct comparison with the prototypical corannulene bowl (C₂₀H₁₀, <b>2</b>) revealed the effects of carbon framework topology and symmetry change on the electronic properties and aromaticity of indacenopicene. The accessibility of two reduction steps for <b>1</b> was predicted theoretically and then confirmed experimentally. Two reversible one-electron reduction processes with the formal reduction potentials at −1.92 and −2.29 V vs Fc^+/0 were detected by cyclic voltammetry measurements, demonstrating the stability of the corresponding mono- and dianionic states of <b>1</b>. The products of the doubly reduced indacenopicene have been isolated as rubidium and cesium salts and fully characterized. Their X-ray diffraction study revealed the formation of tetranuclear organometallic building blocks with the [M₂(18-crown-6)]²⁺ (M = Rb (<b>3</b>) and Cs (<b>4</b>)) cations occupying the concave cavities of two C₂₆H₁₂^2– anions. The coordination of two outside <i>exo</i>-bound rubidium ions is terminated by crown ether molecules in <b>3</b> to form the discrete [Rb⁺₄(18-crown-6)₃­(C₂₆H₁₂^2–)₂] tetramer. In contrast, the larger cesium ions allow the 1D polymeric chain propagation in <b>4</b> to afford [Cs⁺₂(18-crown-6)₂­(THF)­(C₂₆H₁₂^2–)]_∞

From Corannulene to Indacenopicene: Effect of Carbon Framework Topology on Aromaticity and Reduction Limits

The electronic structure, reduction limits, and coordination abilities of a bowl-shaped polycyclic aromatic hydrocarbon, indacenopicene (C₂₆H₁₂, <b>1</b>), have been investigated for the first time using a combination of theoretical and experimental tools. A direct comparison with the prototypical corannulene bowl (C₂₀H₁₀, <b>2</b>) revealed the effects of carbon framework topology and symmetry change on the electronic properties and aromaticity of indacenopicene. The accessibility of two reduction steps for <b>1</b> was predicted theoretically and then confirmed experimentally. Two reversible one-electron reduction processes with the formal reduction potentials at −1.92 and −2.29 V vs Fc^+/0 were detected by cyclic voltammetry measurements, demonstrating the stability of the corresponding mono- and dianionic states of <b>1</b>. The products of the doubly reduced indacenopicene have been isolated as rubidium and cesium salts and fully characterized. Their X-ray diffraction study revealed the formation of tetranuclear organometallic building blocks with the [M₂(18-crown-6)]²⁺ (M = Rb (<b>3</b>) and Cs (<b>4</b>)) cations occupying the concave cavities of two C₂₆H₁₂^2– anions. The coordination of two outside <i>exo</i>-bound rubidium ions is terminated by crown ether molecules in <b>3</b> to form the discrete [Rb⁺₄(18-crown-6)₃­(C₂₆H₁₂^2–)₂] tetramer. In contrast, the larger cesium ions allow the 1D polymeric chain propagation in <b>4</b> to afford [Cs⁺₂(18-crown-6)₂­(THF)­(C₂₆H₁₂^2–)]_∞

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>I</i>_<i>h</i>-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