Spin-adducts of radicals ·P(O)(OPri)2 and ·CMe3 with pyrrolidino[60]fullerenes studied by ESR spectroscopy

The addition of the ^·Bu^t (R¹) and ^·P(O)(OPrⁱ)₂ (R²) radicals to pyrrolidino[60]fullerenes C₆₀CH₂NMeCHX (X = C₆H₄N(CH₂CH₂Cl)₂, 2,6-(Bu^t)₂C₆H₂OH, PhC₆H₄, and indol-3-yl) was studied by ESR spectroscopy. The rate constants of R¹ radical addition to these compounds and dimerization of spin-adducts of the R¹ radicals with pyrrolidino[60]fullerenes were determined. Pyrrolidino[60]fullerenes manifest considerably higher reactivity toward the R¹ radicals than fullerene C₆₀ and methanofullerenes C₆₀CX¹X² (X¹ = X² = CO₂Et; X¹ = CO₂Me, X² = OP(OMe)₂, X¹ = X² = OP(OEt)₂).     

Addition of carbon-centered radicals to C60. Determination of the rate constants by the spin trap method

The rate constants of addition of the^.CMe₃,^.CH₂Me,^.CH₂(CH₂)₃Me,^.CH₂Ph,^.CH₂CH=CH₂, and^.CH(Me)Et radicals to fullerene C₆₀ were determined by the method of competitive addition of free radicals to spin traps. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp 2369–2372, December, 1999.     

Influence of the nature of ligands in iridium complexes with C60 fullerene and ·P(O)(OPri)2, ·CMe3, and ·CCl3 radicals on regioselectivity of addition and stability of spin-adducts formed: an EPR study

The addition of ^·P(O)(OPrⁱ)₂ (R¹), ^·CMe₃ (R²), and ^·CCl₃ (R³) radicals to metallofullerenes (η²-C₆₀)IrH(CO)(CNBu^t)₂(o-HCB₁₀H₉CCH₂PPh₂-B,P) (1), (η²-C₆₀)IrH(CO)(DIOP) (DIOP is (4R,5R)-(+)-4,5-bis(diphenylphosphinomethyl)-2,2-dimethyl-1,3-dioxolane, 2), and (η²-C₆₀)IrH(CO)(PPh₃)₂ (3) was studied by EPR spectroscopy. A stability study of spin adducts (SAs) of R¹ radicals with complexes 1 and 2 showed that when the reactions are initiated by illumination with 366-nm light, the EPR spectra exhibit only signals of those isomers that are formed upon attack of the R¹ radicals on the carbon atoms of the cis-1 and cis-2 bonds (i.e., carbon atoms of the fullerene hemisphere to which the metallofragment is attached). Investigations of the reactions of R² and R³ radicals with complexes 1–3 initiated with 366-nm light made it possible to detect (i) regioisomers formed by adding these radicals to carbon atoms of the cis-n bonds and (ii) SAs formed by adding the radicals to carbon atoms of other bonds in complexes 1–3. The hyperfine structure of the EPR spectrum essentially depends on the spatial structure of substituents at the metal atom and allows individual regioisomers of not only phosphoryl radicals, but also carbon-centered radicals R² and R³ with metallofullerenes 1–3 to be identified. The rate constants for addition of R² and R³ radicals to complexes 2 and 3 were determined. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1302–1309, July, 2007.     

ESR study of adducts of diisopropylphosphoryl radicals with C60C[P(O)(OEt)2]2 2 isomers

The radical adducts of the P^·(O)(OPrⁱ)₂ (R^·) radicals with C₆₀C[P(O)(OEt)₂]_{2 2} fullerene derivatives were studed by ESR spectroscopy. The number of stable regioisomers of phosphorylfullerenyl radicals formed by addition of the phosphoryl radicals to the C₆₀C[P(O)(OEt)₂]_{2 2} isomers depends on the mutual position of the organophosphorus groups and decreases in the series trans-2 > trans-3 trans-4 > e. The rate constants for addition of the R^· radicals to the trans-3 regioisomer (k = 1.7·10⁸ L mol^–1 s^–1) were determined.     

An ESR study of the products of multiple addition of diisopropoxyphosphoryl radicals to C60

The ESR spectra of the radicals resulting from the multiple addition of diisopropoxyphosphoryl radicals to C₆₀ have been studied. The formation of six different types of radical adducts was detected. A structure for the stable product, characterized by hyperfine coupling of the unpaired electron with two phosphorus nuclei, was proposed. The unpaired electron in C₆₀P(O)(OPrⁱ)₂ is delocalized in the same way as in alkylfullerenyl radicals,i.e., mainly over the two six-membered rings adjacent to the C-CP(O)(OPrⁱ)₂ bond.Translated fromIzvestiya Akademii Nauk. Seriva Khimicheskaya, No. 11, pp. 2679–2682, November, 1996.     

ESR study of radical adducts of dialkoxyphosphoryl radicals with (η2-C60)lrH(CO)(PPh3)2 and (η2-C60IrH(8H12)(PPh3)

The reaction of phosphoryl radicals with (η²-C₆₀)lrH(CO)(PPh₃)₂ and (η²-C₆₀IrH(₈H₁₂)(PPh₃) was shown (ESR) to result in the formation of isomers differing in the constants of hyperfine interaction (HFI) with³¹P nuclei,g-factors, and linewidths. It is likely that the addition of phosphoryl radicals at a distance of two-three bond lengths from the metallofragment is predominant. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 870–872, April, 1997.     

ESR‐Vis/NIR Spectroelectrochemical Study of C70(CF3)2−. and C70(C2F5)2−. Radical Anions

A spectroelectrochemical study of the two isostructural asymmetric perfluoroalkyl derivatives C₁‐7,24‐C₇₀(CF₃)₂ and C₁‐7,24‐C₇₀(C₂F₅)₂ is presented. Reversible formation of their stable monoanion radicals is monitored by cyclic voltammetry and by in situ ESR‐Vis‐NIR spectroelectrochemistry. The ESR spectrum of the C₇₀(CF₃)₂^?. radical is a 1:3:3:1 quartet with a ¹⁹F hyperfine coupling constant (a(F)) of 0.323(4) G, demonstrating that the unpaired spin is coupled to only one of the two CF₃ groups. The ¹³C satellites are assigned to specific carbon atoms. The ESR spectrum of the C₇₀(C₂F₅)₂^?. radical is an apparent octet with an apparent a(F) value of 0.83(2) G. DFT calculations suggest that this pattern is due to the superposition of spectra for four nearly isoenergetic C₇₀(C₂F₅)₂^?. conformers. Time‐dependent DFT calculations suggest that the NIR band at 1090 nm exhibited by both C₇₀(R_f)₂^?. radical anions is assigned to the SOMO→LUMO+3 transition. The analogous NIR band exhibited by the closed‐shell C₇₀(CF₃)₂^2? dianion was blue‐shifted to 1000 nm.     

Addition of Me2·CCN,Me2·CPh,and CCl3CH2·CHPh radicals to fullerene C60

The rate constants for addition of the Me₂ ^·CCN, Me₂ ^·CPh, and CCl₃CH₂ ^·CHPh radicals to fullerene C₆₀ at 22 °C were determined by ESR spectroscopy using spin trapping technique.     

ESR spectroscopic investigation of steric and polar factors in the addition of radicals to unsaturated compounds

The rate constants of the addition of CCl₃CH₂ClCH₃(R⁶) radicals to -methyl-styrene, styrene, methyl methacrylate, methyl acrylate, and acrylonitrile and of CCl₃CH₂(CH₃)₂(R⁷) radicals to styrene, methyl acrylate, and acrylonitrile were determined by ESR spectroscopy. It was shown that the radicals R⁶ and R⁷ possess approximately equal reactivity in addition to unsaturated compounds, despite the difference in the donor-acceptor properties of the substituents at the vinyl group. In a comparison of the reactivity of radicals R⁶ and R⁷ with the reactivity of radicals CCl₃CH₂H₂(R¹), CCl₃CH₂HCH₃(R³), CCl₃CH₂HCl(R⁴), and ClCH₂CH₂Cl₂(R⁵) [1] in addition reactions, it was shown that polar and steric effects of the substituents situated in the -position to the radical site of the above-mentioned radicals, as well as the donor-acceptor properties of the substituents at the vinyl group in the unsaturated compounds, lead to appreciable changes in reactivity.A. N. Nesmeyanov Institute of Heteroorganic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 136–141, January, 1992.     

ESR study of formation of allylic radicals in simultaneous photochemical generation of phosphoryl and carbon-centered radicals in the presence of C60 fullerene

Allylic radicals resulting upon simultaneous photochemical generation of phosphoryl [^.P(O)(OPrⁱ)₂] and carbon-centered [^.C(O)OMe,^.CH₃,^.CCl₃] radicals in saturated toluene solutions of C₆₀ have been studied by the ESR method. The donor-acceptor properties of carbon-centered radicals determine the positions of phosphoryl groups in the allylic system.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2422–2424, December, 1995.This work was performed under terms of the Russian Interdisciplinary Scientific and Technical Program Fullerenes and Atomic Clusters and was financially supported by the Russian Foundation for Basic Research (Project Nos. 93-03-18725 and 93-03-4101) and the International Scientific and Technical Center (Grant No. 079 (B)).     

Distribution of C60 and C70 fullerenes in the extraction system (C60 + C70)-α-pinene-ethanol-H2O

The distribution of C₆₀ and C₇₀ fullerenes in the extraction system (C₆₀ + C₇₀)-α-pinene-ethanol-H₂O was studied at constant C₆₀ to C₇₀ ratio and variable total fullerene concentration at 25°C. The relationship between the C₆₀ and C₇₀ content in ethanol (I) and α-pinene (II) phases is nonlinear over the entire fullerene concentration range.     

The ESR study of the influence of fluorinated alcohols on spin-adducts of phosphoryl radicals with C60 and C70: a change of magnetic resonance parameters and exclusive formation of monoadducts

Complex formation of^.C₆₀P(O)(OPrⁱ)₂ or three isomers of^.C₇₀P(O)(OPrⁱ)₂ with fluorinated alcohols CF₃CH₂OH (1), (CF₃)₃COH (2), and (CF₃)₂CHOH (3) results in an increase in the hyperfine splitting constants with the³¹P nucleus by approximately 3–4 G. Only monoadducts are formed when alcohols1–3 are added to toluene saturated solutions of Hg[P(O)(OPrⁱ)₂]₂ and C₆₀ under photochemical conditions of multi-addition of phosphoryl radicals to C₆₀. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1869–1871, September, 1998.     

Free-radical pathways in the decomposition of ketones over polycrystalline TiO(2): the role of organoperoxy radicals.

The oxidative decomposition of various ketones (including acetone, 2-butanone, 4-heptanone, cyclopentanone and cyclohexanone) over dehydrated TiO(2) (P25) powder is investigated by electron paramagnetic resonance (EPR) spectroscopy. For the first time, a series of thermally unstable radical intermediates are observed both on the activated and reduced TiO(2) surface, depending on the adopted experimental conditions. These radical intermediates are identified as organoperoxy-based species of general formula ROO(.-) and RCO(3) (.-). They are formed by reaction of photogenerated charge carriers (either trapped electrons or trapped holes) with the adsorbed ketones in the presence of molecular oxygen. The organoperoxy intermediates are thermally unstable and decompose at temperatures in the region of 180-250 K. This work demonstrates that free-radical pathways involving both organoperoxy and superoxide radicals can be responsible for the thermal- and photodecomposition of ketones over polycrystalline TiO(2) (P25).     

Reactions of carbanions of bis(dialkoxyphosphoryl)bromomethane with fullerenes C60 and C70

The reactions of carbanions of bis(dialkoxyphosphoryl)bromomethanes with fullerenes C₆₀ and C₇₀ afforded new bis(dialkoxyphosphoryl)methanofullerenes C₆₀ and C₇₀, respectively, whose structures were established by spectroscopic methods.     

Thermal rate constant for the C(3P) + OH(X2Π) → CO(X1Σ) + H(2S) reaction using stochastic energy grained master equation method

In the present work, the kinetic mechanism of the reaction is studied. The rate constants were determined using the Master Equation Solver for Multi-Energy Well Reactions (MESMER). The master equation modeling was also employed to examine the pressure dependence for each pathway involved. The theoretical analysis shows that the overall rate coefficient is practically independent of pressure up to 100 Torr for the temperature range 125-500 K. The unusual dependence of the overall rate constant with temperature was fit with the d-Arrhenius expression , where cm³molecule⁻¹s⁻¹, , and  kJ·mol⁻¹, for 125⩽ T ⩽ 500 K. The thermal rate constant results are in relatively good agreement with other theoretical studies.     

Interaction of the iridium(III) trihydridophosphine complex with fullerene C60 under thermal and photochemical excitation

The interaction of the PPh₃-stabilized iridium trihydrido complex H₃Ir(PPh₃)₃ with fullerene C₆₀ under thermal and photochemical excitation was studied under anaerobic conditions. Heating (100 °C) or photolysis by the visible light of the H₃Ir(PPh₃)₃-C₆₀ 650 nm, which are characteristic of the ·²-coordinated C₆₀ in several fullerene-containing metal complexes. The kinetic behavior of the H₃Ir(PPh₃)₃)-C₆₀ system in benzonitrile was investigated using a Nd³⁺-YAG laser (λ=532 nm). The quenching rate constant determined from the dependence of the effective first-order quenching constant of C₆₀(T) on the concentration of H₃Ir(PPh₃)₃ is equal to 1.1·10⁹ L mol⁻¹ s⁻¹. The quenching of C₆₀(T) by the iridium hydridophosphine complex follows the reductive mechanism to form a C₆₀ monoanion. The ESR signal with g=2.000 and ΔH=0.17 mT (at room temperature) and characteristic absorption bands in the near-IR region at 940, 1004, and 1076 nm support the formation of the C₆₀ monoanion during the interaction of the triplet-excited C₆₀ with H₃Ir(PPh₃)₃. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2145–2148, December, 1997.     

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.     

Fullerenes as a tert-butylperoxy radical trap,metal catalyzed reaction of tert-butyl hydroperoxide with fullerenes,and formation of the first fullerene mixed peroxides C(60)(O)(OO(t)Bu)(4) and C(70)(OO(Bu)(10)

tert-Butylperoxy radicals generated by TBHP and Ru(PPh3)3Cl2 or other catalysts adds to C60 and C70 to form stable multiadducts, C60(O)(OOtBu)4 and C70(OOtBu)10. The four tert-butylperoxy groups in the C60 mixed peroxide are located around a pentagon, and the epoxy O occupies the remaining 6,6-bond connected to the same pentagon. The C70 decaadduct shows an unprecedented C2 symmetry with the 10 tert-butylperoxy groups added around the central part of C70 by consecutive 1,4-addition. The compounds are fully characterized by spectroscopic data.