Electrochemical oxidation and reduction of rhodium and iridium complexes with fullerenes C60 and C70

The electrochemical behavior of rhodium and iridium complexes with fullerences C₆₀ and C₇₀ was studied by cyclic voltammetry in a THF—toluene mixture. The complexes were found to be capable of oxidation and reduction. It was demonstrated that thein situ generation of metallofullerene complexes in the electrochemical cell by the interaction of C₆₀ and C₇₀ with hydridocarbonylphosphine complexes of rhodium and iridium, HM(CO)(PPh₃)₃, is possible. The influence of structural factors and the action of CO₂ on changes in the redox properties of fullerene complexes was considered.     

Heterobimetallic Coinage Metal-Ruthenium Complexes Supported by Anionic N-Heterocyclic Carbenes

The lithium complexes [(WCA-NHC)Li(toluene)] of anionic N-heterocyclic carbenes with a weakly coordinating borate moiety (WCA-NHC, WCA=B(C₆F₅)₃, NHC=IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were used for the preparation of silver(I) or copper(I) WCA-NHC complexes. While the reactions in THF with AgCl or CuCl afforded anionic mono- and dicarbene complexes with solvated lithium counterions [Li(THF)_n]⁺ (n=3, 4), the reactions in toluene proceeded with elimination of LiCl and formation of the neutral phosphine and arene complexes [(WCA-NHC)M(PPh₃)] and [(WCA-NHC)M(η²-toluene)] (M=Ag, Cu). The latter were used for the preparation of chlorido- and iodido-bridged heterobimetallic Ag/Ru and Cu/Ru complexes [(WCA-NHC)M(μ-X)₂Ru(PPh₃)(η⁶-p-cymene)] (M=Ag, Cu, X=Cl; M=Ag, X=I). Surprisingly, these complexes resisted the elimination of CuCl, AgCl, or AgI, precluding WCA-NHC transmetalation.     

Intramolecular dehydrofluorinative coupling of η-arene and fluoroarylphosphine ligands in ruthenium complexes

NMR studies of reactions between a series of arene ruthenium(II) fluoroarylphosphine complexes and Proton Sponge have revealed the necessary conditions for intramolecular dehydrofluorinative ligand coupling. The complex must be cationic, and the phosphine need have only one fluoroaryl substituent. The reaction is rapid and clean for [(η⁶-toluene)RuCl(dfppe)]BF₄, [(η⁶-mesitylene)RuCl{(C₆F₅)₂PC₆H₄SMe}]BF₄ and the diastereomer of [(η⁶-toluene)RuCl{Ph₂PC₂H₄PPh(C₅F₄N-4)}]BF₄ in which the tetrafluoropyridyl substituent is close to the η⁶-arene. [(η⁶-p-cymene)RuCl(dfppe)]BF₄ reacts in the presence of Proton Sponge to give a mixture of unidentified compounds. The neutral complex [(η⁶-toluene)RuCl₂{Ph₂P(C₆F₅)}] and the diastereomer of [(η⁶-toluene)RuCl{Ph₂PC₂H₄PPh(C₅F₄N-4)}]BF₄ in which the tetrafluoropyridyl substituent is distant to the η⁶-arene do not undergo reaction.     

Morphological features of C60 and C70 microcrystals obtained from C6H5CH3 and CCl4 solutions

Fullerene C₆₀ and C₇₀ microcrystals of different morphologies obtained by crystallization from toluene and carbon tetrachloride solutions were investigated using scanning electron microscopy and diffuse reflectance IR Fourier transform spectroscopy. The obtained results are discussed with regard to the features of fullerenes clusterization processes in solutions.     

Quenching of electronically excited Ln3+* ions by C60 fullerene

Quenching of electronically excited states of Ln^3+* ions generated upon photoexcitation of toluene solutions of Ln(acac)₃·H₂O (Ln = Tb, Eu) complexes by C₆₀ fullerene at 293 K was detected and investigated. The dependences of quenching efficiency on C₆₀ concentration obtained from data on the decrease in the photoluminescence intensity and Ln^3+* lifetimes obey the Stern-Volmer law. Quenching is due to inductive-resonant energy transfer from Ln^3+* to C₆₀ fullerene. The bimolecular rate constants for quenching, the overlap integrals of the Ln^3+* photoluminescence spectra with the C₆₀ absorption spectra, and the critical energy transfer distances were determined. No sensitized luminescence of C₆₀ in the system studied was detected. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 921–925, June, 2006.     

Charge transfer in complexes of C60 and C70 in solutions and solid state

Electronic absorption spectra of complexes of C₆₀ and C₇₀ fullerenes with donors, tetrathiafulvalene and pyranylidene derivatives, were studied in solutions and in the solid state. Charge transfer bands were found in the 680–1300 nm range. The charge transfer energies (hv _ct) for the C₆₀ and C₇₀ complexes in solutions are close and almost independent of the solvent polarity. For the C₆₀ complexes in the solid state, the dependence ofhv _ct on the ionization potential (IP) of donors was found to behv _ct=0.82IP–3.93 eV. In the C₆₀ complexes in the solid state, thehv _ct values are 0.15–0.20 eV lower than those in the solution. The linear dependences ofhv _ct onIP of donors for the C₆₀ complexes lie 0.6–0.7 eV higher than those in the complexes with tetracyanoethylene (TCNE). This is associated with lower values of the electron affinity of C₆₀ and the energy of the electrostatic interaction in the fullerene complexes as compared to those of the TCNE complexes. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 478–483, March, 1999.     

Molecular complexes of C60 with tetrasulfur tetranitride

Compounds C₆₀(S₄N₄)_2−x (C₆H₆) _x (1a-d) withx=0.67 (a), 1.0 (b), 1.1 (c), and 1.2 (d), in which isomorphous replacement of S₄N₄ with benzene takes place, were obtained by the reaction of fullerence C₆₀ with tetrasulfur tetranitride in benzene. Complexes C₆₀·S₄N₄ (2) and C₆₀(S₄N₄)₂ (3) containing no solvent were isolated from toluene. The compositions of the compounds were established by elemental and thermogravimetric analyses. The data of IR and X-ray photoelectron (XP) spectroscopies show that in the complexes studied the transfer of electron density occurs mainly from the nitrogen atoms of S₄N₄. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 37–40. January 1977.     

Synthesis and identification of bromofullerenes C70Br8 and C70Br10 and their solubility in some aromatic solvents

Bromofullerenes C₇₀Br₈ and C₇₀Br₁₀ were synthesized and identified by electronic absorption and infrared spectroscopy. Their solubility in aromatic solvents (benzene, toluene, o-xylene, and o-dichlorobenzene) was studied in the temperature range from 20 to 60°C.     

Carbonyl compounds of cobalt(II) and nickel(II). Reversible arene-carbon monoxide exchange and similarities to analogous η6-arene complexes

Displacement of η⁶-arene in (C₆F₅)₂Co(η⁶-toluene), (Cl₃Si)₂Ni(η⁶-toluene), and (F₃Si)₂Ni(η⁶-toluene) by CO yielded very labile (C₆F₅)₂Co(CO)₃, (Cl₃Si)₂Ni(CO)₃, and (F₃Si)₂Ni(CO)₃, which are rare examples of isolated, characterized, simple carbonyl complexes of cobalt(II) and nickel(II). According to infrared ν(CO) studies the cobalt(II) tricarbonyl and the nickel(II) tricarbonyl derivatives are trigonal bipyramidal with the CO ligands in the axial positions. These η⁶-arene substitutions with CO are reversible under mild conditions. However, the cobalt system slowly degrades to cobalt(I) while the nickel system degrades to nickel(0) carbonyl compounds.     

ESR spectra of C60 in concentrated sulfuric acid

On dissolution of C₆₀ in concentrated sulfuric acid, ESR spectra of paramagnetic species, which were identified as dimers (C₁₂₀ ⁺) or oligomers (nC₆₀)⁺, were recorded. The ESR spectra recorded upon the reaction of a toluene solution of C₆₀ with sulfuric acid were assigned to the radical cation C₆₀ ⁺. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2373–2376, November, 1998.     

Annealing Temperature Dependence of the Size of C60 Clusters in C60-Doped Silicon Oxide Films

C₆₀-doped silicon oxide thin films were prepared by spin-coating a viscous solution formed upon soaking at 40°C an acidic toluene/ethanol solution of C₆₀, phenyltriethoxysilane, and tetraethoxysilane with a C₆₀–to–Si molar ratio of 2.5 × 10^–3. The films were submitted to annealing at 300–500°C in Ar to investigate variation in the size of C₆₀ clusters embedded in the films by photoluminescence spectroscopy. The film before annealing was found to contain the clusters consisting of ca. 60 C₆₀ molecules, suggesting that C₆₀ is present well-dispersed in the film. The molecules in the film aggregated to increase the size with increasing annealing temperature, indicating that the molecules diffuse easily in the film upon heating and therefore the size of the clusters is controllable with the annealing temperature.     

Fluorescence spectroscopy of C60 in toluene solutions at 5 K

We have recorded the dispersed fluorescence and the fluorescence excitation spectra of C₆₀ in toluene matrices at 5 K. Upon excitation with the green Ar⁺ laser line (λ=514 nm) we obtained for the first time in this matrix well resolved visible fluorescence spectra which we have compared with those observed in other low temperature matrices. Our spectra were interpreted and assigned using theoretical assessments of vibronic activities of transitions between the three lowest excited electronic states ¹T_1g, ¹T_2g, ¹G_g and the totally symmetric ground state, and on the basis of a single 0⁰ level which has pseudo-Jahn–Teller (JT) components of the three near-degenerate excited states. The fluorescence spectra exhibit prominent JT induced h_g(1) progressions, Herzberg–Teller-induced h_u and other ungerade mode vibrations, including a very active t_1u(4) mode. Excitation wavelength independent bands are assigned to the fluorescence of C₆₀ molecules in toluene microcrystals embedded in the toluene glass whereas excitation wavelength dependent features are interpreted as originating from C₆₀ molecules isolated in the toluene glass itself. These interpretations are supported by the results of spectrally selective detected fluorescence excitation spectra.     

Fluorescent Bis-Calix[4]arene-Carbazole Conjugates: Synthesis and Inclusion Complexation Studies with Fullerenes C60 and C70

Supramolecular chemistry has become a central theme in chemical and biological sciences over the last decades. Supramolecular structures are being increasingly used in biomedical applications, particularly in devices requiring specific stimuli-responsiveness. Fullerenes, and supramolecular assemblies thereof, have gained great visibility in biomedical sciences and engineering. Sensitive and selective methods are required for the study of their inclusion in complexes in various application fields. With this in mind, two new fluorescent bis-calix[4]arene-carbazole conjugates (4 and 5) have been designed. Herein, their synthesis and ability to behave as specific hosts for fullerenes C₆₀ and C₇₀ is described. The optical properties of the novel compounds and their complexes with C₆₀ and C₇₀ were thoroughly studied by UV-Vis and steady-state and time-resolved fluorescence spectroscopies. The association constants (K_a) for the complexation of C₆₀ and C₇₀ by 4 and 5 were determined by fluorescence techniques. A higher stability was found for the C₇₀@4 supramolecule (K_a = 5.6 × 10⁴ M⁻¹; ΔG = −6.48 kcal/mol). Evidence for the formation of true inclusion complexes between the host 4 and C₆₀/C₇₀ was obtained from NMR spectroscopy performed at low temperatures. The experimental findings were fully corroborated by density functional theory (DFT) models performed on the host–guest assemblies (C₆₀@4 and C₇₀@4).     

C3-bonded hetero-β-diketonates of palladium(II)

Reactions of PdL₂ complexes, where LH = benzoylacetone, dibenzoyl methane, or dipivaloyl methane, with pyridine and neat β-diketones (L ¹H trifluoroacetylacetone, hexafluoroacetylacetone, thenoyltrifluoroacetone and pivaloyltrifluoroacetone) in toluene resulted in the formation of central carbon (C³) bonded hetero-β-diketonate complexes of the formula [Pd(L)(C³-L′)py]. These were characterized by microanalyses, IR and ¹H NMR spectral data.     

Formation and Optical Absorption of Clusters of the p-tert-butylcalix[8]arene:C60 Complex

Depending on the initial concentrations of fullerene (C₆₀) and p-tert-butyl calix[8]arene (C[8]A) in toluene, two regimes of their interaction were distinguished. The changes in optical absorption of C₆₀:C[8]A mixed solutions observed over a period of time suggest that the following consecutive processes take place upon interaction between C₆₀ and C[8]A in toluene: (1) molecular inclusion, and (2) growth and sedimentation of the insoluble C₆₀/C[8]A clusters. At increased concentrations of the components, process (2) is suppressed and stable C₆₀/C[8]A colloids can be formed. Spectral features of these colloids in different solvents clearly indicate the difference between self-aggregated C₆₀ and small clusters of the complex. A specific influence of the C[8]A cage on the entrapped C₆₀ molecules is also confirmed by IR spectroscopy of the complex in the solid state.     

Water-soluble polyketones and esters as the main stable products of ozonolysis of fullerene C60 solutions

Stable ozonolysis products of C₆₀ solutions in CCl₄, toluene, and hexane were studied by elemental analysis, HPLC, and UV and IR spectroscopy. Polyketones and esters were established for the first time to be the main stable products, whose content increased during the whole ozonolysis time (1 h). Epoxides C₆₀O _n (n = 1—6) are accumulated within 1—3 min, and after 5 min of ozonolysis their concentration decreases to zero. Fullerene C₆₀ disappears from the reaction solution due to its conversion to oxides and mechanical capturing of C₆₀ by these oxides to form a precipitate. The oxidation of C₆₀ is completed in the solid phase by the formation of the C₆₀O₁₆ oxide in which 9.68 O atoms fall on fullerene polyketones, 6 O atoms are attributed to esters, and 0.32 O atoms fall per epoxides. The optimum medium for preparation of the C₆₀ oxides is CCl₄ rather than traditional toluene, which reacts with ozone in the side reaction to form products containing active oxygen. The C₆₀ cage is raptured during ozonolysis because of the C=C bond cleavage to form two C=O groups at the ends of the open hexagon. Ozonolysis of C₆₀ solutions in CCl₄ is efficient for synthesis of water-soluble fullerene oxides due to the high yield and solubility of polyketones and esters in water.     

Derivative des borols : II. Pentaphenylborol: Synthese,reduktion zum dianion und komplexe von kobalt und platin

Analytically pure, dark blue pentaphenylborole (PPB) can be synthesized from 1,1-dibutyl-2,3,4,5-tetraphenylstannole and C₆H₅BCl₂ in toluene in 95% yield. Reduction of PPB with elemental potassium in THF produces brownish red K₂[PPB] which is derived from the new 6π-electron anion [PPB]^2?. The new complexes (C₅H₅)Co(PPB) and (COD)Pt(PPB) (COD = 1,5-cyclooctadiene) are obtained by irradiation of a toluene solution of (C₅H₅)Co(CO)₂ and PPB and by ligand substitution reaction from Pt(COD)₂ and PPB respectively.     

The 31P NMR spectra of ArCr(CO)2P(C6H5)3 compounds in neutral and acidic media

The ³¹P NMR spectra of C₆H₅XCr(CO)₂P(C₆H₅)₃ (X = H, CH₃, OCH₃, N(CH₃)₂, COOCH₃) (I), p-C₆H₄X₂Cr(CO)₂P(C₆H₅)₃ (X = COOCH₃)(II) and C₆H₃X₃Cr(CO)₂P(C₆H₅)₃ (X = CH₃) (III) complexes in neutral and acidic media were investigated. The protonation of complexes I and III in trifluoroacetic acid results in the greater upfield shielding of ³¹P{¹H} signal. In this case the complexes I (X = H, CH₃, OCH₃) are completely protonated at the metal, complex I (X = COOCH₃)is partially protonated, while no protonation occurs in the case of complex II.Temperature-dependence of the ³¹P{¹H} NMR spectra was investigated for complexes I (X = H, OCH₃) in a 1/10 mixture of trifluoroacetic acid and toluene and for complexes I (X = COOCH₃) and II in trifluoroacetic acid. The degree of protonation was found to increase with decreasing temperature.     

ESR spectra of fullerence C70 in concentrated sulfuric acid

It was established by ESR spectroscopy that the reaction of C₇₀ with concentrated H₂SO₄ resulted in the formation of isomeric dimers C₁₄₀ ⁺, and the action of H₂SO₄ on a toluene solution of C₇₀ ⁺ gave the C₇₀ radical cation. The structure of dimers was discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 208–210, January, 1999.     

Supramolecular fullerene/porphyrin charge transfer interaction studied by absorption spectrophotometric method

A detailed UV–Vis spectrometric and thermodynamic studies were done to look insight into the nature of molecular interactions of the electron donor–acceptor complexes of C₆₀ and C₇₀ with 5,10,15,20-tetrakis(octadecyloxyphenyl)-21H,23H-porphyrin (1) in chloroform and toluene. Charge transfer (CT) absorption bands were located in the visible region and vertical ionization potential of 1 was determined utilizing CT transition energy. Low values of oscillator and transition dipole strengths suggested that the complexes were almost of neutral character in ground states. The high binding constant value for the C₇₀–1 complex indicated high selectivity of 1 molecule towards C₇₀. Experimental as well as theoretically determined of enthalpies of formation value substantiated the trend in K values for fullerene–1 complexes.