In search of fullerene-based superacids: synthesis, X-ray structure, and DFT study of C60(C2F5)(5)H

Simply super! The perfluoroalkylfullerene C(60)(C(2)F(5))(5) H is the first structurally characterized perfluoroalkylated fullerene-based acid and is also predicted to be the first gas-phase fullerene-based superacid.     

An Isomer of C60Cl10 Free of Skew‐Pentagonal‐Pyramidal C60Cl6 Substructure

Chlorination is an effective approach for understanding the feature of multiple additions on fullerene cages. The chlorofullerenes obtained are versatile synthons for further derivatization. However, chlorofullerenes used for chemical reaction studies are mainly based on the skew‐pentagonal‐pyramidal (SPP) C₆₀Cl₆. In this work, a new isomer of C₆₀Cl₁₀ that does not contain an SPP‐C₆₀Cl₆ substructure was identified. Its electrochemical properties give it unexpected cyclic voltammetric behavior at more negative potentials relative to other chlorofullerenes. Friedel–Crafts arylation shows good reactivity of this compound. These new findings challenge opinions of fullerene addition patterns and will break the monopoly of C₆₀Cl₆ as a precursor for fullerene modifications.     

Alumina-catalyzed cyclodimerization of 4-hydroxymethyl derivatives of 1,8-bis(dimethylamino)- and 1,8-dimethoxynaphthalenes to symmetrical spiro compounds

4-Hydroxymethyl derivatives of 1,8-bis(dimethylamino)- and 1,8-diiiiethoxynaphthalenes undergo cyclodirnerization on alumina to form symmetrical spir0, compounds of the head-to-tail type. The reaction is considered to be a two-step electrophilic substitution with the participation of naphthyhiiethyl carbocations.Translated fromIzvestiya Akademii Nauk, Seriya Khitnicheskaya, No. 4, pp, 1016–1018, April, 1996.     

The Interaction of C60, C70, and C60(CN)2 radical anions with cobalt(II) tetraphenylporphyrin in solid multicomponent complexes

A method for the synthesis of the multicomponent ionic complexes: [Cr(I)(C(6)H(6))(2) (.+)][Co(II)(tpp)(fullerene)(-)].C(6)H(4)Cl(2), comprising bis(benzene)chromium (Cr(C(6)H(6))(2)), cobalt(II) tetraphenylporphyrin (Co(II)(tpp)), fullerenes (C(60), C(60)(CN)(2), and C(70)), and o-dichlorobenzene (C(6)H(4)Cl(2)) has been developed. The monoanionic state of the fullerenes has been proved by optical absorption spectra in the UV/vis/NIR and IR ranges. The crystal structures of the ionic [[Cr(I)(C(6)H(6))(2)](.+)](1.7)[[Co(II)(tpp)(C(60))](2)](1.7-). 3.3 C(6)H(4)Cl(2) and [[Cr(I)(C(6)H(6))(2)] (.+)](2)[Co(II)(tpp)[C(60)(CN)(2)]](-)[C(60)(CN)(2) (.-)]).3 C(6)H(4)Cl(2) are presented. The essentially shortened Co.C(fullerene) bond lengths of 2.28-2.32 A in these complexes indicate the formation of sigma-bonded [Co(II)(tpp)][fullerene](-) anions, which are diamagnetic. All the ionic complexes are semiconductors with room temperature conductivity of 2 x 10(-3)-4 x 10(-6) S cm(-1), and their magnetic susceptibilities show Curie-Weiss behavior. The neutral complexes of Co(II)(tpp) with C(60), C(60)(CN)(2), C(70), and Cr(0)(C(6)H(6))(2), as well as the crystal structures of [Co(II)(tpp)](C(60)).2.5 C(6)H(4)Cl(2), [Co(II)(tpp)](C(70)). 1.3 CHCl(3).0.2 C(6)H(6), and [Cr(0)(C(6)H(6))(2)][Co(II)(tpp)] are discussed. In contrast to the ionic complexes, the neutral ones have essentially longer Co.C(fullerene) bond lengths of 2.69-2.75 A.     

Kinetic energy release of C70(+) and its endohedral cation N@C70(+): activation energy for N extrusion

Unimolecular decomposition of C70(+) and its endohedral cation N@C70(+) were studied by high-resolution mass-analyzed ion kinetic energy (MIKE) spectrometry. Information on the energetics and dynamics of these reactions was extracted. C70(+) dissociates unimolecularly by loss of a C2 unit, whereas N@C70(+) expels the endohedral N atom. Kinetic energy release distributions (KERDs) in these reactions were measured. By use of finite heat bath theory (FHBT), the binding energy for C2 emission from C70(+) and the activation energy for N elimination from N@C70(+) were deduced from KERDs in the light of a recent finding that fragmentation of fullerene cations proceeds via a very loose transition state. The activation energy measured for N extrusion from N@C70(+) was found to be lower than that for C2 evaporation, higher than the value from its neutral molecule N@C70 obtained on the basis of thermal stability measurements, and coincident with the theoretical value. The results provide confirmation that the proposed extrusion mechanism in which the N atom escapes from the cage via formation of an aza-bridged intermediate is correct.     

Boratabenzene Anions C5B(CN)6− and C5B(CF3)6− and the Superacidic Properties of their Conjugate Acids

Designing superacids: A computational study of protonated boratabenzenes and the gas‐phase acidity of their conjugate acids is presented. Conjugate acids of boratabenzenes substituted with CN or CF₃ groups (see figure) are highly acidic species; the protonated hexacyanoboratabenzene and hexakis(trifluoromethyl)boratabenzene have computational gas‐phase acidities of 250.5 and 276.8 kcal mol^?1, respectively.

     

Reductive Hydrogenation of Cs‐C70(CF3)8 and C1‐C70(CF3)10

CF₃‐derivatized fullerenes prove once again to be promising scaffolds for regioselective fullerene functionalization: now with the smallest possible addends—hydrogen atoms. Hydrogenation of C_s‐C₇₀(CF₃)₈ and C₁‐C₇₀(CF₃)₁₀ by means of reduction with Zn/Cu couple in the presence of water proceeds regioselectively, yielding only one major isomer of C₇₀(CF₃)₈H₂ and only two for C₇₀(CF₃)₁₀H₂, whose addition patterns are combined in the only abundant isomer of C₇₀(CF₃)₁₀H₄. The observed selectivity is governed by the electronic structure of trifluoromethylated substrates. Interestingly, we discovered that Clar's theory can be utilized to predict the regiochemistry of functionalization, and we look forward to testing it on forthcoming cases of derivatization of pre‐functionalized fullerene building blocks.     

Unusual Chlorination Patterns of Three IPR Isomers of C88 Fullerene in C88(7)Cl12/24, C88(17)Cl22, and C88(33)Cl12/14

High‐temperature chlorination of three IPR isomers of fullerene C₈₈, C₂‐C₈₈(7), C_s‐C₈₈(17), and C₂‐C₈₈(33), resulted in the isolation and X‐ray structural characterization of C₈₈(7)Cl₁₂, C₈₈(7)Cl₂₄, C₈₈(17)Cl₂₂, and C₈₈(33)Cl_12/14. Chlorination patterns of C₈₈(7) and C₈₈(33) isomers are unusual in that one or more pentagons remain free from chlorination while some other pentagons are occupied by two or three Cl atoms. The addition patterns of the isolated chlorides are discussed in terms of the distribution of twelve pentagons on the carbon cages and the formation of stabilizing isolated C=C bonds and benzenoid rings.     

Electron Donor–Acceptor Interactions in Regioselectively Synthesized exTTF2–C70(CF3)10 Dyads

The decakis(trifluoromethyl)fullerene C₁‐C₇₀(CF₃)₁₀, in which the CF₃ groups are arranged on a para⁷‐meta‐para ribbon of C₆(CF₃)₂ edge‐sharing hexagons, and which has now been prepared in quantities of hundreds of milligrams, was reacted under standard Bingel–Hirsch conditions with a bis‐π‐extended tetrathiafulvalene (exTTF) malonate derivative to afford a single exTTF₂–C₇₀(CF₃)₁₀ regioisomer in 80 % yield based on consumed starting material. The highly soluble hybrid was thoroughly characterized by using 1D ¹H, ¹³C, and ¹⁹F NMR, 2D NMR, and UV/Vis spectroscopy; matrix‐assisted laser desorption ionization (MALDI) mass spectrometry; and electrochemistry. The cyclic voltammogram of the exTTF₂–C₇₀(CF₃)₁₀ dyad revealed an irreversible second reduction process, which is indicative of a typical retro‐Bingel reaction; whereas the usual phenomenon of exTTF inverted potentials (${E{{1\hfill \atop {\rm ox}\hfill}}}$ >${E{{2\hfill \atop {\rm ox}\hfill}}}$ ), resulting in a single, two‐electron oxidation process, was also observed. Steady‐state and time‐resolved photolytic techniques demonstrated that the C₁‐C₇₀(CF₃)₁₀ singlet excited state is subject to a rapid electron‐transfer quenching. The resulting charge‐separated states were identified by transient absorption spectroscopy, and radical pair lifetimes of the order of 300 ps in toluene were determined. The exTTF₂–C₇₀(CF₃)₁₀ dyad represents the first example of exploitation of the highly soluble trifluoromethylated fullerenes for the construction of systems able to mimic the photosynthetic process, and is therefore of interest in the search for new materials for photovoltaic applications.     

Synthesis and Chemical Behavior of N-(2-Chloroethyl)O-alkyl-3-methyl-1,2-butadienephosphoniates

Abstract

The synthesis and reactivity of the titled compounds towards electrophilic reagents have been discussed.     

Carbonyldinitrosyltris(fluorosulfato)tungstate(II) and ‐Molybdate(II) Anions: Synthesis,Spectroscopy, and Density Functional Theory Calculations

Carbonyldinitrosyltris(fluorosulfato)tungstate(II) and ‐molybdate‐(II) anions, [fac‐M(CO)(NO)₂(SO₃F)₃]^? (M=W, Mo), which are novel weakly coordinating anions that contain a metal carbonyl/nitrosyl moiety, have been generated in fluorosulfonic acid and completely characterized by multinuclear NMR, IR, and Raman spectroscopy as well as ESI mass spectrometry. ESI MS measurements performed for the first time on a superacidic solution system unambiguously reveal the formation of the monoanionic, mononuclear W and Mo complexes formulated as [M(CO)(NO)₂(SO₃F)₃]^? (M=W, Mo). Multinuclear NMR spectroscopic studies at natural abundance and ¹³C and ¹⁵N enrichment clearly indicate the presence of one CO ligand, two equivalent NO ligands, and two types of nonequivalent SO₃F^? groups in a 2:1 ratio. The IR and Raman spectra reveal that the two equivalent NO ligands have a cis conformation, thus indicating a fac structure. Density functional calculations at the B3LYP level of theory predict that these anions have a singlet ground state (¹A′) with a C_s symmetry along with C–O and N–O vibrational frequencies that are in agreement with the experimental observations. Mulliken population analysis shows that the monovalent negative charge is dispersed on the bulky sphere, the surface of which is covered by all the negatively charged O and F atoms with charge densities much lower than SO₃F^?, suggesting that [fac‐M(CO)(NO)₂(SO₃F)₃]^? (M=W, Mo) are weakly nucleophilic and poorly coordinating anions.     

Structures and electronic properties of C(56)Cl(8) and C(56)Cl(10) fullerene compounds.

Stimulated by the recent observation of the first C(56)Cl(10) chlorofullerene (Science, 2004, 304, 699), we performed a systematic density functional study of the structures and properties of C(56)Cl(10) and related compounds. The fullerene derivatives C(56)Cl(8) and C(56)Cl(10) based on the parent fullerene C(56)(C(2v):011), rather than those from the most stable C(56) isomer with D(2) symmetry, are predicted to possess the lowest energies, and they are highly aromatic. Further investigations show that the heats of formation of the C(56)Cl(8) and C(56)Cl(10) fullerene derivatives are highly exothermic, that is, -48.59 and -48.89 kcal mol(-1) per Cl(2) (approaching that of C(50)Cl(10)), suggesting that adding eight (or ten) Cl atoms releases much of the strain of pure C(56)(C(2v):011) fullerene and leads to highly stable derivatives. In addition, C(56)Cl(8) and C(56)Cl(10) possess large vertical electron affinities, especially for C(56)Cl(8) with value of 3.20 eV, which is even larger than that (3.04 eV) of C(50)Cl(10), indicating that they are potential good electron acceptors with possible photonic/photovoltaic applications. Finally, the (13)C NMR chemical shifts and infrared spectra of C(56)Cl(8) and C(56)Cl(10) are simulated to facilitate future experimental identification.