Electrochemical synthesis of carbonyl- and phosphoryl-containing methano[60]fullerenes

The combined electrochemical reduction of fullerene C₆₀ in the presence of p-bromo-benzoyldibromomethane or bis(diisopropoxyphosphoryl)dibromomethane at a brass electrode in a mixed solvent o-dichlorobenzene-MeCN (3:1 v/v)/0.05 M Bu₄NBF₄ at room temperature affords 61-(p-bromobenzoyl)methano[60]fullerene or 61,61-bis(diisopropoxyphosphoryl)methano[60]fullerene, respectively, in 50% yields.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2681–2685, December, 2004.     

Methanofullerene Molecular Scaffolding: Towards C60-substituted poly(triacetylenes) and expanded radialenes,preparation of a C60–C70 hybrid derivative,and a novel macrocyclization reaction

The synthesis of (E)-hex-3-ene-l, 5-diynes and 3-methylidenepenta-1, 4-diynes with pendant methano[60]-fullerene moieties as precursors to C₆₀-substituted poly(triacetylenes) (PTAs, Fig. 1) and expanded radialenes (Fig. 2) is described. The Bingel reaction of diethyl (E)-2, 3-dialkynylbut-2-ene-1, 4-diyl bis(2-bromopropane-dioates) 5 and 6 with two C₆₀ molecules (Scheme 2) afforded the monomeric, silyl-protected PTA precursors 9 and 10 which, however, could not be effectively desilylated (Scheme 4). Also formed during the synthesis of 9 and 10 , as well as during the reaction of C₆₀ with thedesilylated analogue 16 (Scheme 5 ), were the macrocyclic products 11, 12 , and 17 , respectively, resulting from double Bingel addition to one C-sphere. Rigorous analysis revealed that this novel macrocyclization reaction proceeds with complete regio- and diastereoselectivity. The second approach to a suitable PTA monomer attempted N, N′-dicyclohexylcarbodiimide(DCC)-mediated esterification of (E)-2, 3-diethynylbut-2-ene-l, 4-diol ( 18 , Scheme 6) with mono-esterified methanofullerene-dicarboxylic acid 23 ; however, this synthesis yielded only the corresponding decarboxylated methanofullerene-carboxylic ester 27 (Scheme 7). To prevent decarboxylation, a spacer was inserted between the reacting carboxylic-acid moiety and the methane C-atom in carboxymethyl ethyl 1, 2-methano[60]fullerene-61, 61-dicarboxylate ( 28 , Scheme 8), and DCC-mediated esterification with diol 18 afforded PTA monomer 32 in good yield. The formation of a suitable monomeric precursor 38 to C₆₀-substituted expanded radialenes was achieved in 5 steps starting from dihydroxyacetone (Schemes 9 and 10), with the final step consisting of the DCC-mediated esterification of 28 with 2-[1-ethynyl(prop-2-ynylidene)]propane-1, 3-diol ( 33 ). The first mixed C₆₀-C₇₀ fullerene derivative 49 , consisting of two methano[60]fullerenes attached to a methano[70]fullerene, was also prepared and fully characterized (Scheme 13). The C_s-symmetrical hybrid compound was obtained by DCC-mediated esterification of bis[2-(2-hydroxy-ethoxy)ethyl] 1, 2-methano[70]fullerene-71, 71-dicarboxylate ( 46 ) with an excess of the C₆₀-carboxylic acid 28 . The presence of two different fullerenes in the same molecule was reflected by its UV/VIS spectrum, which displayed the characteristic absorption bands of both the C₇₀ and C₆₀ mono-adducts, but at the same time indicated no electronic interaction between the different fullerene moieties. Cyclic voltammetry showed two reversible reduction steps for 49 , and comparison with the corresponding C₇₀ and C₆₀ mono-adducts 46 and 30 indicated that the three fullerenes in the composite fullerene compound behave as independent redox centers.     

A Rational Approach Towards Determination of Optical Ionicity and Non-covalent Interactions in Fullerene-Calix[4]arene Host-Guest Complexes

The present article reports the host-guest complexation of a calix[4]arene derivative, namely 4-iso-propyl-calix[4]arene (1), with fullerenes (both C₆₀ and C₇₀) in toluene and benzonitrile solutions. It is observed that the charge-transfer (CT) absorption bands are located in the ground state for the C₆₀ and C₇₀ complexes of 1. By utilizing the CT absorption bands, various important physicochemical parameters like the oscillator strength, resonance energy, transition dipole moment, electronic coupling element and solvent reorganization energies have been estimated for the C₆₀-1 and C₇₀-1 complexes. The CT transition energy is very helpful for determining the vertical ionization potential of 1 in solution. Jobs method of continuous variation was used to establish 1:1 stoichiometry for the fullerene complexes of 1. The most fascinating feature of the present study is that 1 binds C₇₀ preferentially compared to C₆₀ as obtained from binding constant (K) data. The effect of solvent on the complexation of fullerenes (C₆₀ and C₇₀) with 1 is clearly observed from the trend in the K values: in toluene and whereas in benzonitrile, and . Molecular mechanics force field (MMMF) calculations reveal fascinating features regarding the binding pattern of fullerenes towards 1 in vacuo in terms of enthalpy of formation. MMMF calculations establish that during C₇₀-1 complexation, C₇₀ is directed in an end-on manner rather than the traditional side-on pattern.     

Yttrium complexes derived from 5,11,17,23-tetra-tert-butyl-25,27-dihydroxy-26,28-dimethoxycalix[4]arene (LH2). Synthesis,properties, and structures of the [LY(thf)(μ-Cl)]2 and [LY(thf)3]+[L2Y]– complexes

5,11,17,23-Tetra-tert-butyl-25,27-dihydroxy-26,28-dimethoxycalix[4]arene (1, LH₂) was deprotonated with two equivalents of potassium naphthalenide in THF at room temperature. The reaction of a dipotassium derivative of 1 prepared in situ with anhydrous YCl₃ in a THF medium afforded the corresponding yttrium alkoxychloride [LY(thf)(-Cl)]₂·4thf (2·4thf) in 71% yield. According to the X-ray diffraction data, complex 2 has a dimeric structure. The reaction of equimolar amounts of [(Me₃Si)₂N]₃Y and compound 1 in a THF—toluene mixture at 60 °C was accompanied by the complete replacement of the bis(trimethylsilyl)amide ligands to form the homoligand ionic complex [LY(thf)₃]⁺[L₂Y]^– (3). The structure of the latter was established by X-ray diffraction analysis.     

Phosphorylated methano[60]fullerenes containing nitroxyl radicals: synthesis,structures, and electrochemical behavior

Phosphorylated methano[60]fullerenes containing one or two nitroxyl radicals were synthesized for the first time. Their structures were established from spectroscopic data and their compositions, by MALDI-TOF mass spectrometry. Their electrochemical reduction in a system o-dichlorobenzene-DMF/0.1 M Bu₄NBF₄ was studied by cyclic voltammetry, preparative electrolysis, and ESR spectroscopy in combination with in situ electrolysis. Both compounds were found to undergo four-step reduction of the fullerene sphere, reduction of nitroxyl, opening of the three-membered ring, and elimination of addends as carbanions stabilized by protonation and rearrangement into phosphate ions and substituted acetylene, which are accompanied by the formation of free fullerene and dihydrofuranofullerene. The rates of the ring opening and the addend elimination increased with an increase in the negative charge on the fullerene sphere. These reactions are fast in the case of transfer of three electrons. With the use of model compounds, heterogeneous electron transfer to the nitroxyl radical at the potentials of the transfer of the third electron to the fullerene sphere and homogeneous intramolecular electron transfer from the dianion of the fullerene sphere were revealed. The mechanisms of the observed transformations are discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1594–1607, July, 2005.     

Molecular complex of C60 fullerene with an organic π-donor,bis(methylenedithiotetrathiafulvalene): synthesis,crystal structures,and properties

A new molecular complex based on [60]fullerene, namely, (BMDT-TTF)·C₆₀·2CS₂ (1) (where BMDT-TTF is bis(methylenedithiotetrathiafulvalene)) was synthesized. The molecular and crystal structures of 1 were established by X-ray diffraction analysis. Complex 1 has a layered structure, layers of C₆₀ molecules alternating with those formed by BMDT-TTF molecules and CS₂ molecules located between them. In complex 1, there are short contacts between C₆₀ and the donor molecules, which results in a changed BMDT-TTF geometry. The donor molecules in 1 form in addition short S...S contacts. The data of IR spectroscopy indicate that the charge transfer to the fullerene molecule is insignificant if at all present. The conductivity of a single crystal of 1 measured at 20 °C using a four-contact method is 2·10^–5 ( cm)^–1.     

Study of the reactions of 3-chloro-4-cyanobenzo[b][1,6]naphthyridine with nucleophilic reagents

The reactions of 3-chloro-4-cyanobenzo[b][1,6]naphthyridine (4) with S-, C-, and N-nucleophiles afford stable s-adducts at position 10. In the base-catalyzed reactions of compound 4 with thiols, the resulting -complexes are rearranged into sulfides 14a—c. Sulfides 14b,c undergo the Thorpe—Ziegler cyclization to give 1-aminobenzo[b]thieno[2,3-h][1,6]naphthyridine derivatives 15a,b. The reaction of naphthyridine 4 with aniline affords a mixture of -adducts of the C—N and C—C types, while those with aliphatic amines yield 3-amino derivatives 17a—c. In the presence of H₂O₂, benzonaphthyridine 4 adds peroxycarboxylic acids to give compounds 8a,b. In alkaline medium, adduct 8a is rearranged into 4-aminopyridine-3-carbaldehyde derivative 10.     

Synthesis of new condensed heterocyclic systems

Two new diamines — [1,3-bis(5-phenyl-1,2,4-triazol-3-yl)-4,6-diamino]benzene and [1,3-di-(2-benzimldazolyl)-4,6-diamino]benzene — were synthesized from 4,6-dinitroisophthalic acid. Newheterocyclic systems — 3,5,9,11-tetraphenyl[benzo[1,2-a; 4,5-a]bis(1,2,4-triazolo[4,3-c]pyrimidine)] and 2,16-diphenyl[benzo[1,2-a;4,5-a']bis(pyrimido[1,6-a]benzimidazole)]—were obtained by reaction of the diamines with benzoyl chloride and subsequent cyclization.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1274–1277, September, 1977.     

Ring-opening reaction of cyclopropanated [60]fullerenes: unexpected transformation of methano[60]fullerenes having an electron-donating group on the methano-bridge carbon

A series of novel transformations of [60]fullerene derivatives were found, starting from methano[60]fullerenes with an electron-donating group on the methano-bridge carbon. Aminomethano[60]fullerenes, in situ generated by the treatment of their trifluoromethanesulfonic acid salts with a base, were readily converted into 1-acyl-1,2-dihydro[60]fullerenes via the ring opening of the cyclopropane moiety. The aldehyde/ketones thus obtained were easily hydrolyzed to give 1,2-dihydro[60]fullerene in the presence of hydroxide anions.     

Binuclear and polynuclear transition metal complexes with macrocyclic ligands 1. Synthesis and the structure of an antiferromagnetic binuclear nickel complex prepared by the reaction of o-phenylenediamine with pyrrole-2,5-dicarbaldehyde and nickel pivalate

The reaction of pyrrole-2,5-dicarbaldehyde (1) with o-phenylenediamine (2) in anhydrous EtOH afforded a [1+1]-condensation product, viz., Schiff"s base. The structure of the latter was established by NMR spectroscopy and X-ray diffraction analysis. The reaction of this product or a mixture of 1 and 2 with Ni₉(_n-OOCBu^t)₁₂(HOOCBu^t)₄(₄-OH)₃(₃-OH)₃ in MeCN in the presence of AcOH gave rise to an antiferromagnetic binuclear complex. According to the X-ray diffraction data, the macrocycle in the latter complex is a [2+2]-condensation product of compounds 1 and 2, _eff ranging from 0.569 to 2.614 B (2—301 K), –2J = 360 cm^–1. The Ni₂(OAc)₂ fragment is located in the central cavity of the macrocycle. The structures of the condensation products are discussed based on the results of DFT quantum-chemical calculations.     

Inclusion of methano[60]fullerene derivatives in cavitand-based coordination cages

The X-ray study of self-assembled coordination cage 1, constituted of two tetrapyridyl-substituted resorcin[4]arene cavitands coupled through four square-planar palladium complexes is reported. The coordination cage, embracing an internal cavity of ca. 840 Å³, reveals to have the right size for the inclusion of large molecules such as fullerenes. Cage 1 forms 1:1 complexes with methano[60]fullerene derivatives 3 and 4 bearing a dimethyl and a diethyl malonate addend, respectively. Evidence for inclusion complexation was provided by ¹H NMR spectroscopic studies and ESI-MS investigations, which unambiguously showed the formation of 1:1 fullerene-cage complexes. The association constants (K_a) were experimentally determined to be ca. 150 M⁻¹ at 298 K in CD₂Cl₂. In both complexes 1·3 and 1·4, the malonate residue is threaded through one of the four lateral portals, as clearly shown by docking simulations.     

单加成环丙烷富勒烯膦酸酯衍生物的合成与电化学性能

在Mn(OAc)₃•2H₂O催化下, C₆₀分别和亚甲基二膦酸四乙酯、氰基亚甲基膦酸二乙酯或乙氧羰基亚甲基膦酸二乙酯在氯苯中回流, 生成3个单加成环丙烷富勒烯膦酸衍生物C₆₀C(R)PO(OEt)₂ [1, R＝PO(OEt)₂; 2, R＝COOEt; 3, R＝CN]. 与以前报道的Bingel反应法相比, 该方法副产物少并且缩短了反应时间. 采用循环伏安法发现1, 2的还原电位相对于C₆₀发生负移, 而3的还原电位相对于C₆₀却正移40 mV, 表明引入象氰基一样具有很强吸电子能力的取代基团, 可以改善富勒烯球的电化学性能, 合成电子接受能力较强的富勒烯衍生物.     

Stereochemistry of planarchiral compounds,part X

2,7-Dibromo-1,6-methano[10]anulene (3) and 2,9-Dibromo-syn-1,6:8,13-diimino[14]anulene (9) were quantitatively separated into their enantiomers by chromatography on triacetylcellulose (TAC) in ethanol. X-ray structure analysis (Bijvoet technique) established the chiralities (+)(R)-3 and (+)(S)-9 for the dextrorotatory enantiomers.Comparison of the CD spectra allowed the configurational assignment to further optically active [10] and [14] anulenes which were also accessible by chromatography onTAC. Conversion of (+)(R)-2-bromo-1,6-methano[10]anulene (2) into the corresponding methylester (–)-4 confirmed its previously proposed chirality (–)(R).2,7-Dibromo-1,6-oxido[10]anulene (7) and 2,9-dibromo-syn-diimino[14]anulene (9) are in contrast to the 2,9-dibromo-syn-dioxido[14]anulene (10) optically stable until 250°C. Consequently their inversion barriers are higher than 42 kcal (176 kJ) mol^–1.The CD spectra of mono and disubstituted anulenes (with C₁ and C₂ symmetry, resp.) are compared: For the [10]anulenes theCotton effect around 330 nm seems to be specific for their configuration with a positive effect indicating (S)-chirality and vice versa. Some regularities concerning the chromatographic resolutions are discussed.

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Stereochemie planar chialer Verbindungen, 10. Mitt.: Röntgenkristallstruktur und absolute Chiralität überbrückter [10]- und [14] Anulene

Zusammenfassung 2,7-Dibrom-1,6-methano[10]anulen (3) und 2,9-Dibrom-syn-1,6:8,13-diimino[14]anulen (9) wurden durch Chromatographie an Triacetylcellulose (TAC) in Ethanol quantitativ in ihre Enantiomeren getrennt. Röntgenstruktur-analyse (Bijvoet-Technik) bewies für die rechtsdrehenden Enantiomeren die Chiralität (+)(R)-3 bzw. (+)(S)-9.Ein Vergleich der CD-Spektren ermöglichte die Konfigurationszuordnung weiterer optisch aktiver [10]- und [14]Anulene, die gleichfalls durch Chromato-graphie anTAC erhalten worden waren. Umwandlung von (+)(R)-2-Brom-1,6-methano[10]anulen (2) in den entsprechenden Methylester (–)-4 bestätigte dessen schon früher vorgeschlagene Chiralität (–)(R).Dibrom-1,6-oxido[10]anulen (7) und Dibrom-diimino[14]anulen (9) sind im Gegensatz zum Dioxido[14]anulen (10) bis 250°C optisch stabil. Ihre Inver-sionsbarrieren liegen somit über 42 kcal (176kJ) mol^–1.Die CD-Spektren von mono- und disubstituierten Anulenen (mit C₁ bzw. C₂-Symmetrie) werden verglichen: Für die [10]Anulene scheint derCottoneffekt um 330 nm konfigurationsspezifisch zu sein, wobei ein positiver Effekt (S)-Chiralität anzeigt — und vice versa. Einige Regelmäßigkeiten bezüglich der chromatographischen Enantiomerentrennung werden diskutiert.

     

Protonation of ferrocene,ruthenocene, and osmocene: a density functional study

Protonated forms of the ferrocene, ruthenocene, and osmocene molecules in the gas phase were calculated using the density functional approach with the Becke—Lee—Young—Parr functional. The proton affinity energies of ferrocene, ruthenocene, and osmocene were estimated at 214.2, 220.3, and 229.7 kcal mol^–1, respectively. The addition of a proton to carbon atoms of the cyclopentadienyl ring in the ferrocene molecule and to the metal atom in the ruthenocene and osmocene molecules is more energetically favorable. No minimum corresponding to ring protonation was located on the potential energy surface of protonated osmocene. The C—H _endo bond in the ring-protonated [C₁₀H₁₁M]⁺ (M = Fe, Ru) cations is involved in agostic interaction with the metal atom. Transition states of interconversions between the ring-protonated and metal-protonated forms were identified. A specific group of protonated forms of the ferrocene and ruthenocene molecules includes four types of structures, viz., ring-protonated (1a,b) and metal-protonated (2a,b) structures, transition states of the 1 2 interconversion (3a,b), as well as ring-protonated structures with the cyclopentadiene ring folded along the C(2)—C(5) line so that the M—H _endo interaction is virtually negligible. The latter structures are required for [1,5]-sigmatropic shift of the exo-hydrogen atom in the Cp ring to occur. The results obtained were used for the interpretation of the available schemes of electrophilic substitution reactions in metallocenes and of the sigmatropic shift mechanisms.     

Syntheses,crystal structures and magnetic properties of two cyano-bridged two-dimensional assemblies [Fe(salpn)]2 [Fe(CN)5NO] and [Fe(salpn)]2[Ni(CN)4]

Two cyano-bridged assemblies, [Fe^III(salpn)]₂[Fe^II(CN)₅NO] (1) and [Fe^III (salpn)]₂[Ni^II(CN)₄] (2) [salpn = N, N-1,2-propylenebis(salicylideneiminato)dianion], have been prepared and structurally and magnetically characterized. In each complex, [Fe(CN)₅NO]^2– or [Ni(CN)₄]^2– coordinates with four [Fe(salpn)]⁺ cations using four co-planar CN^– ligands, whereas each [Fe(salpn)]⁺ links two [Fe(CN)₅NO]^2– or [Ni(CN)₄]^2– ions in the trans form, which results in a two-dimensional (2D) network consisting of pillow-like octanuclear [—M^II—CN—Fe^III—NC—]₄ units (M = Fe or Ni). In complex (1), the NO group of [Fe(CN)₅NO]^2– remains monodentate and the bond angle of Fe^II—N—O is 180.0°. The variable temperature magnetic susceptibilities, measured in the 5–300 K range, show weak intralayer antiferromagnetic interactions in both complexes with the intramolecular iron(III)iron(III) exchange integrals of –0.017 cm^–1 for (1) and –0.020 cm^–1 for (2), respectively.     

New class of neutral paramagnetic binuclear sulfur-containing iron nitrosyl complexes

Neutral paramagnetic binuclear iron nitrosyl complexes, whose structures and properties differ from those of the known Roussin"s red salt esters, were synthesized for the first time. The iron nitrosyl complexes [Fe₂(₂-SR)₂(NO)₄]·nH₂O (¹-S, ¹-N; n = 1 or 2; R is 5-amino-1,2,4-triazol-3-yl (1), 1,2,4-triazol-3-yl (2), 1-methyltetrazol-5-yl (3), or benzothiazol-2-yl (4)) were prepared by the exchange reactions of Na₂Fe₂(S₂O₃)₂(NO)₄ with heterocyclic thiols. According to the results of X-ray diffraction analysis, complex 1 has a centrosymmetrical dimeric structure in which the iron atoms are linked through the -N—C—S structural fragment. Each Fe atom is bound to the N atom of one ligand and the S atom of another ligand. The isomer shifts of complexes 1—4 have virtually equal values (_Fe = 0.291(1)—0.304(1) mm s^–1 at T = 85 K), which are twice as large as _Fe for Roussin"s red salt esters. The iron atoms in complexes 1—4 have the low-spin configuration d⁷ (Fe⁺). The ESR spectra of polycrystalline powders of complexes 1—4 consist of a single Lorentzian line with g = 2.032 and a width of 6—10 mT. The temperature dependence of the magnetic susceptibility of complex 1 in the temperature range of 80—300 K is adequately described by the Curie—Weiss law with 8 K; the effective magnetic moment per iron atom is 1.85 B.     

Spectroscopic and Theoretical Investigations on Supramolecular Interaction of a Newly Designed Monoporphyrin with Fullerenes and Functionalized Fullerenes in Solution

The present paper reports the results of a photophysical investigation of a designed monoporphyrin (1) and its supramolecular complexes with C₆₀, C₇₀ and derivatized fullerenes, namely tert-butyl-(1,2-methanofullerene)-61-carboxylate (2) and [6,6]-phenyl C₇₁ butyric acid methyl ester (3) in toluene. UV–vis studies reveal appreciable ground state interaction between the fullerenes and compound 1. Steady state fluorescence studies show quenching of fluorescence of 1 in the presence of fullerenes. The binding constants of the C₆₀/1, C₇₀/1, 2/1 and 3/1 complexes are estimated to be 300, 20770, 1150 and 13170 dm³⋅mol⁻¹, respectively. Molecular mechanics calculations in vacuo evoke the stereoscopic structures of the fullerene/1 complexes and allow interpretation of the stability difference among various fullerene complexes of 1 in terms of their enthalpies of formation.     

Energies of Charge Transfer for the Supramolecular Complexes of [60]- and [70]Fullerenes with a Series of meso-Tetraphenylporphyrins in the Solution State

Supramolecular complexes of [60]- and [70]fullerenes with various meso-tetraphenylporphyrins in toluene solutions have been studied by electronic absorption spectroscopy. Charge transfer (CT) absorption bands are observed in the visible region. Vertical ionization potentials (I _D ^V) of the meso-tetraphenylporphyrins are reported from a study of EDA interaction of these porphyrins with a number of electron acceptors like o-chloranil, p-chloranil, 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) and vitamin K. The dependence of the CT transition energy on the donor ionization potential has been utilized to estimate the vertical electron affinities (E _A ^V) of [60]- and [70]fullerenes in solution. The value of E _A ^V for [60]fullerene is found to be 0.10 eV lower in magnitude than that of [70]fullerene. We have extracted degrees of CT, and oscillator and transition dipole strengths of the fullerenes/meso-tetraphenylporphyrins complexes. The experimental results show that the CT complexes studied here have a neutral character in their ground states. Electronic coupling elements have been determined for fullerene/meso-tetraphenylporphyrin complexes. Values of the solvent reorganization energy indicate that the electron transfer process takes place at a faster rate in the case of [70]fullerene/meso-tetraphenylporphyrin complexes.     

A scalable synthesis of methano[60]fullerene and congeners by the oxidative cyclopropanation reaction of silylmethylfullerene

1,2-Dihydromethano[60]fullerene and its congeners have attracted much interest, but they have been synthesized only in very low yields because of several insurmountable problems. A new three-stage synthesis involving addition of a silylmethylmagnesium chloride to [60]- and [70]fullerene and oxidation of the anionic intermediate with CuCl(2) afforded the methano[60]- and methano[70]fullerenes in 90% and 70% overall yield, respectively. The reaction with 1,4-diorgano[60]fullerene also proceeded smoothly to give a diastereomerically pure 56-π-electron fullerene that has a higher LUMO level than the parent fullerene and gave a higher open-circuit voltage and better power conversion efficiency when fabricated into an organic photovoltaic device.     

Synthesis of Fullerene-Containing Sol-Gel Glasses

Macroscopically homogeneous and visually transparent fullerene-containing glasses are fabricated from sol-gel mixtures of aminated C₆₀ derivatives and tetraethyl orthosilicate (TEOS) through physical blending and chemical reaction. The aminated fullerenes are synthesized by the amination reactions of C₆₀ with 6-amino-1-hexanol, cyclohexylamine, 2-(2-aminoethoxy)ethanol, and 3-aminopropyltriethoxysilane at 100°C under nitrogen. The amination products are purified by filtration, precipitation, and column chromatography and are isolated in good to excellent yields (32–82%). Characterization by NMR, MS, and TGA analyses reveals that the aminated fullerenes possess molecular structures H _x C₆₀[NH(CH₂)₆OH] _x , H _x C₆₀(NH-cyclo-C₆H₁₁) _x , H _x C₆₀[NH(CH₂CH₂O)₂H] _x , and H _x C₆₀[NH(CH₂)₃Si(OCH₂CH₃)₃] _x . All the aminated fullerenes except 2 are completely soluble in aqueous alcoholic solutions of TEOS and can be incorporated into silica gel networks by sol-gel process in the absence or presence of drying-control chemical additives, giving crack-free monoliths of large sizes (up to 60 mm). Electronic absorption spectrum of the fullerene glass continuously red shifts with an increase in the C₆₀ content, suggesting the formation of fullerene nanoclusters in the sol-gel process. The fullerene glasses are thermally and optically stable, resisting continuous attack of strong laser pulses of 532 nm for a prolonged period of time without losing their optical limiting power.