Fullerenyl boronic esters: ferric perchlorate-mediated synthesis and functionalization

Fullerenyl boronic esters have been prepared by a ferric perchlorate-promoted reaction of [60]fullerene with various arylboronic acids. The obtained fullerenyl boronic esters could undergo further functionalization with diols to afford C(60)-fused dioxane/dioxepane derivatives. A possible reaction mechanism for the formation of fullerenyl boronic esters has been proposed.     

Novel cycloaddition reaction of [60]fullerene with carbonyl ylides generated from epoxides

The thermal reaction of [60]fullerene (C60) with the carbonyl ylides generated in situ from trans-epoxides to give C60-fused tetrahydrofuran derivatives has been investigated. The reaction of C60 with trans-2-benzoyl-3-aryloxiranes afforded only cis-products, while the reaction of C60 with 2-cyano-2-ethoxycarbonyl-3-aryloxiranes gave exclusively or predominantly cis isomers. The isomeric distributions of the latter reactions were drastically affected by the substituent on the phenyl ring.     

Arbuzov chemistry with chlorofullerene C(60)Cl(6): a powerful method for selective synthesis of highly functionalized [60]fullerene derivatives

We report Arbuzov-type reactions of chlorofullerene C(60)Cl(6) with trialkyl phosphites producing highly functionalized fullerene derivatives C(60)[P(O)(OR)(2)](5)H with high yields. The designed family of [60]fullerene phosphonic acids and their esters showed unusual properties which might find valuable material science applications.     

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.     

Electrospray Ionization Mass Spectral Characterization of Transient Iron Species of Bioinorganic Relevance

Strategies have been developed to obtain electrospray ionization mass spectral data on short-lived intermediates derived from the reactions of non-heme iron complexes with peroxides. The molecular composition of a transient green intermediate generated from [Fe(2)O(5-Me(3)-TPA)(2)(OH)(H(2)O)](ClO(4))(3) with H(2)O(2) in CH(3)CN at -40 degrees C was determined by introducing the solution via a precooled syringe to the inlet of the mass spectrometer. The observation of prominent ion clusters in both positive and negative mass regions, together with isotope distribution patterns characteristic of the number of associated ClO(4) ions, allows its formulation as [Fe(2)(O)(2)(5-Me(3)-TPA)(2)](ClO(4))(3). The molecular composition of a transient blue species derived from the reaction of [Fe(2)O(TPA)(2)(H(2)O)(ClO(4))](ClO(4))(3) with excess benzyl alcohol and (t)BuOOH at -40 degrees C was also determined. Due to its limited stability even at -40 degrees C, the blue intermediate was generated in a cooled mixing tee from its precursor components and directly introduced into the mass spectrometer. Its formulation as {[Fe(TPA)(OO(t)Bu)(ROH)](ClO(4))}(+) (R = H or CH(2)Ph) is based on the masses observed, isotope distribution patterns, the observation of expected shifts in the mass values by appropriate substitutions, and tandem mass spectral data. These transient species relate to possible intermediates of non-heme iron enzymes.     

Approaches to open fullerenes: synthesis and thermal stability of cis-1 bis(isobenzofuran) Diels-Alder adducts of C60

In a quest to form wider openings within the cage of the fullerene C60 through controlled bond-breaking reactions, we have examined the double saturation of adjacent C=C bonds within a six-membered ring of C60. We have investigated the double Diels-Alder cycloaddition of two tethered isobenzofurans to the fullerene C60. We obtained cis-1 adducts in good yields after reacting the methylene- or quinoxaline-tethered bis(isobenzofuran) precursors 2a-k with parent 3,6-dihydro-1,2,4,5-tetrazine (3b). The X-ray structure of the methylene-tethered bis(isobenzofuran)-C60 adduct 4b has been obtained; four-eclipsed substituents are held rigidly by the bicyclic addends. The cis-1 bis(isobenzofuran) bisadducts 4b and 4e-j are kinetically far more stable toward thermal retro-Diels-Alder fragmentation than are mono(isobenzofuran) adducts of C60, in solution and in the solid state as determined by 1H NMR spectroscopy or thermogravimetric analysis. A methodology for the reversible solubilization of other fullerene derivatives based on this work is also presented.     

Structural reassignment of the mono- and bis-addition products from the addition reactions of N-(Diphenylmethylene)glycinate esters to [60]fullerene under Bingel conditions

The addition of N-(diphenylmethylene)glycinate esters (Ph2C=NCH2CO2R) to [60]fullerene under Bingel conditions gives [60]fullerenyldihydropyrroles and not methano[60]fullerenyl iminoesters [C60C(CO2R)(N=CPh2)] as previously reported. Unequivocal evidence for the structure of C60C(CO2Et)(N=CPh2) was provided by INADEQUATE NMR studies on 13C enriched material. New mechanistic details are proposed to account for the formation of [60]fullerenyldihydropyrroles and their reductive ring-opening reactions.     

Reaction of hydroxyfullerene with metal salts: a route to remediation and immobilization

Hydroxylated fullerene reacts rapidly and irreversibly (across a wide pH range) with Fe(NO3)3, Al(NO3)3, CaCl2, CoCl2, CuCl2, KMnO4, Ag(NO3), and ZnCl2 under ambient aqueous conditions to produce insoluble metal-hydroxyfullerene cross-linked polymers (M-fullerenol). Materials have been characterized by SEM, TEM, AFM, XPS, and UV-visible spectroscopy. Molecular mechanics calculations on the model systems, [Fe(C60O2)2] and [Fe(C60O2)3], show that both tetrahedral and octahedral coordination are possible. The rate of precipitation reaction is proportional to the concentration of both reagents. The interaction of hydroxyfullerenes with metals is an important issue with regard to waste treatment, fullerene exposure in the environment, and fullerene-based pharmaceutical agents.     

Reactivity of a (mu-oxo)(mu-hydroxo)diiron(III) diamond core with water, urea, substituted ureas, and acetamide

A series of iron(III) complexes of the tetradentate ligand BPMEN (N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine) were prepared and structurally characterized. Complex [Fe(2)(mu-O)(mu-OH)(BPMEN)(2)](ClO(4))(3) (1) contains a (mu-oxo)(mu-hydroxo)diiron(III) diamond core. Complex [Fe(BPMEN)(urea)(OEt)](ClO(4))(2) (2) is a rare example of a mononuclear non-heme iron(III) alkoxide complex. Complexes [Fe(2)(mu-O)(mu-OC(NH(2))NH)(BPMEN)(2)](ClO(4))(3) (3) and [Fe(2)(mu-O)(mu-OC(NHMe)NH)(BPMEN)(2)](ClO(4))(3) (4) feature N,O-bridging deprotonated urea ligands. The kinetics and equilibrium of the reactions of 1 with ligands L (L = water, urea, 1-methylurea, 1,1-dimethylurea, 1,3-dimethylurea, 1,1,3,3-tetramethylurea, and acetamide) in acetonitrile solutions were studied by stopped-flow UV-vis spectrophotometry, NMR, and mass spectrometry. All these ligands react with 1 in a rapid equilibrium, opening the four-membered Fe(III)(mu-O)(mu-OH)Fe(III) core and forming intermediates with a (HO)Fe(III)(mu-O)Fe(III)(L) core. The entropy and enthalpy for urea binding through oxygen are DeltaH degrees = -25 kJ mol(-1) and DeltaS degrees = -53.4 J mol(-1) K(-1) with an equilibrium constant of K(1) = 37 L mol(-1) at 25 degrees C. Addition of methyl groups on one of the urea nitrogen did not affect this reaction, but the addition of methyl groups on both nitrogens considerably decreased the value of K(1). An opening of the hydroxo bridge in the diamond core complex [Fe(2)(mu-O)(mu-OH)(BPMEN)(2)] is a rapid associative process, with activation enthalpy of about 60 kJ mol(-1) and activation entropies ranging from -25 to -43 J mol(-1) K(-1). For the incoming ligands with the -CONH(2) functionality (urea, 1-methylurea, 1,1-dimethylurea, and acetamide), a second, slow step occurs, leading to the formation of stable N,O-coordinated amidate diiron(III) species such as 3 and 4. The rate of this ring-closure reaction is controlled by the steric bulk of the incoming ligand and by the acidity of the amide group.     

Cu(II) acetate- and Mn(III) acetate-mediated radical reactions of [60]fullerene with ketonic compounds

The copper(II) acetate monohydrate- or manganese(III) acetate dihydrate-mediated reaction of [60]fullerene with beta-keto esters 1a-1c or with beta-diketones 1d,1e in the presence of 4-dimethylaminopyridine afforded only dihydrofuran-fused C60 derivatives 2a-2e. However, aromatic methyl ketones 3a-3c gave two kinds of products: methanofullerenes 4a-4c and dihydrofuran-fused C60 derivatives 5a,5b. Possible reaction mechanisms are proposed.     

An effective metallohydrolase model with a supramolecular environment: structures, properties, and activities

A supramolecular inclusion complex, [Zn(L1)(H2O)2(beta-CD)](ClO4)2.9.5 H2O (1) was synthesized and characterized structurally and its first-order active species for hydrolysis of esters, [Zn(L1)(H2O)(OH)(beta-CD)](ClO4) (2), was isolated (L1=4-(4'-tert-butylbenzyl)diethylenetriamine; beta-CD=beta-cyclodextrin). The apparent inclusion stability constant of the host and the guest measured in aqueous solution was (5.91+/-0.03)x10(3) for 1. The measured values of the first- and second-order pK(a) values of coordinated water molecules were 8.20+/-0.08 and 10.44+/-0.08, respectively, and were assigned to water molecules occupying the plane and remaining axial positions in a distorted trigonal bipyramid of the [Zn(L1)(H2O)2(beta-CD)]2+ sphere according to the structural analysis of [Zn(L2)(H2O)}2(mu-OH)](ClO4)3 (3) (L2=4-benzyldiethylenetriamine). p-Nitrophenyl acetate (pNA) hydrolysis catalyzed by 1 at pH 7.5-9.1 and 25.0+/-0.1 degrees C exhibited a first-order reaction with various concentrations of pNA and 1, but the pH profile did not indicate saturated kinetic behavior. Second-order rate constants of 0.59 and 24.0 M(-1) s(-1) were calculated for [Zn(L1)(H2O)(OH)(beta-CD)]+ and [Zn(L1)(OH)2(beta-CD)], respectively; the latter exhibited a potent catalytic activity relative to the reported mononuclear and polynuclear Zn(II) species.     

Addition Reaction of Fe（CO）_n （n = 3～5） on Fullerene C_（50）, C_（60）, and C_（70）： A Density Functional Theory Study

The electronic structure and reactivities of Fe(CO)n (n = 3~5) addition to different fullerenes have been investigated through the first-principles calculations, and the results indicate that Fe(CO)3 and Fe(CO)4 can be adsorbed to the outside network of fullerene via hollow and bridge sites, respectively. Both of them have larger binding energy, but when Fe(CO)5 is adsorbed via the top site, the binding energy is relatively smaller. According to the directional curvature theory, the reactivities of Fe(CO)3 addition to the fullerenes are determined by KM of the ring center, and those of Fe(CO)4 addition by KD of the C-C bond curvature; while for Fe(CO)5, it presents weak reactivities in the addition reaction because of the larger volume effect. No matter whether the addition reaction takes place on the hollow or bridge site, the binding energies show a linear relationship with KD. This work further enriched the directional curvature theory and applied the isolobel analogy theory in the fullerene addition reactions.     

Addition of tetrahydrofuran to [60]fullerene through C-H bond activation induced by arylzinc reagents

The reaction of [60]fullerene with an arylzinc halide in a mixture of THF and DMF produces a mono(2-tetrahydrofuranyl) adduct of [60]fullerene C60(C4H7O)H instead of the expected arylated fullerene. The reaction involves a C-H bond activation at the 2-position of THF that probably takes place through a radical mechanism. In the presence of a copper(I) complex, the reaction does not stop at the stage of mono-addition, with the aryl group of the zinc reagent adding four times regioselectively to the mono(2-tetrahydrofuranyl) adduct to produce a penta-adduct C60Ar4(C4H7O)H. This product can be converted further to the corresponding buckyferrocene Fe[C60Ar4(C4H7O)]Cp and its derivatives.     

Molecular photoelectric switch using a mixed SAM of organic [60]fullerene and [70]fullerene doped with a single iron atom

We describe a photoswitch fabricated on indium tin oxide (ITO) as a self-assembled monolayer (SAM) of two fullerene molecules, a purely organic [60]fullerene that generates an anodic current and a [70]fullerene doped with a single iron atom. This device generates a bidirectional photocurrent upon irradiation at 340 and 490 nm. The new [70]fullerene iron complex bearing three rigid carboxylic acid legs, Fe[C(70)(C(6)H(4)C(6)H(4)COOH)(3)]Cp, generates only a cathodic current upon photoexcitation between 350 and 700 nm, whereas the organic [60]fullerene absorbs at wavelengths shorter than 500 nm. The quantum efficiency of the photocurrent generation by the mixed SAM is comparable to that of a single-component SAM, indicating that the individual diode molecules on ITO generate photocurrents independently with little cross talk.     

Aggregation control by homologous tripodal tetradentate amino acid ligands in oxo-bridged diiron(III) aquo complexes

Isoelectronic oxo-bridged diiron(III) aquo complexes of the homologous tripodal tetradentate amino acid ligands, N,N'-bis(2-pyridylmethyl)-3-aminoacetate (bpg(-)) and N,N'-bis(2-pyridylmethyl)-3-aminopropionate (bpp(-)), containing [(H(2)O)Fe(III)-(mu-O)-Fe(III)(H(2)O)](4+) cores, oligomerise, respectively, by dehydration and deprotonation, or by dehydration only, in reversible reactions. In the solid state, [Fe(2)(O)(bpp)(2)(H(2)O)(2)](ClO(4))(2) (1(ClO(4))(2)) exhibits stereochemistry identical to that of [Fe(2)(O)(bpg)(2)(H(2)O)(2)](ClO(4))(2) (2(ClO(4))(2)), with the ligand carboxylate donor oxygen atoms and the water molecules located cis to the oxo bridge and the tertiary amine group trans to it. Despite their structural similarity, 1(2+) and 2(2+) display markedly different aggregation behaviour in solution. In the absence of significant water, 1(2+) dehydrates and dimerises to give the tetranuclear complex, [Fe(4)(O)(2)(bpp)(4)](ClO(4))(4) (3(ClO(4))(4)), in which the carboxylate groups of the four bpp(-) ligands act as bridging groups between two [Fe(2)(O)(bpp)(2)](2+) units. Under similar conditions, 2(2+) dehydrates and deprotonates to form dinuclear and trinuclear oligomers, [Fe(2)(O)(OH)(bpg)(2)](ClO(4)) (4ClO(4)) and [Fe(3)(O)(2)(OH)(bpg)(3)](ClO(4)) (5(ClO(4))), related by addition of 'Fe(O)(bpg)' units. The trinuclear 5(ClO(4)), characterised crystallographically as two solvates 5(ClO(4)).3H(2)O and 5(ClO(4)).2MeOH, is based on a hexagonal [Fe(3)(O)(2)(OH)(bpg)(3)](+) unit, formally containing one hydroxo and two oxo bridges. The different aggregation behaviour of 1(ClO(4))(2) and 2(ClO(4))(2) results from the difference of one methylene group in the pendant carboxylate arms of the amino acid ligands.     

Synthesis of α-Arylthioalkyl Esters: The Addition Reactions of Vinyl Esters with Arylthiols Catalyzed by Lipase

α-Arylthioalkyl esters can be prepared by the addition reactions of vinyl esters with arylthiols in the presence of Pseudomonas lipase (PSL) as catalyst. In the toluene, the reaction mixtures were stirred at 60 °C for three days, the chemical yields up to 85% were obtained.     

Synthesis and characterization of mono- and bis-methano[60]fullerenyl amino acid derivatives and their reductive ring-opening retro-bingel reactions

The addition of N-(diphenylmethylene)glycinate esters (Ph2C=NCH2CO2R) 3-6 to [60]fullerene under Bingel conditions gives, respectively, the methano[60]fullerenyl iminoesters 7-10. Upon treatment of 7-9 with sodium cyanoborohydride, in the presence of a protic or a Lewis acid, a novel reductive ring-opening reaction occurred to give the corresponding 1,2-dihydro[60]fullerenyl glycine derivatives 11-13. Using tethered bis-N-(diphenylmethylene)glycinate esters 33 and 34derived from m- and p-benzenedimethanol scaffolds, the corresponding bis-methano[60]fullerenyl iminoesters 35-38 were synthesized under double Bingel reaction conditions. The m-benzenedimethanol derivative 33 gave the trans-4 (35) and cis-3 (36) regioisomeric bisadducts in a ratio of 80:20. The analogous para-tethered derivative 34 afforded the trans-3 (37) and trans-4 (38) regioisomers in a 80:20 ratio. The regiochemistry of the major bisadducts 35 and 37 (via the trans-esterified 39) were unequivocally determined using 2D INADEQUATE and C-C TOCSY NMR experiments. The regiochemistry of these bis-additions were unexpected on the basis of literature precedents. These results unequivocally show that the regiochemistry of tethered bis-additions is not solely dependent on the nature of the tether. A mixture of the trans-4 and cis-3 nonsymmetrical bisadducts 45 and 46 was obtained from the double-Bingel cyclopropanation of a bis-N-(diphenylmethylene)glycinate tether based on a 1,3-naphthyldimethanol scaffold. The regiochemistry of these compounds (45 and 46) was identified by correlation with the diethyl esters 40 and 47, prepared by trans-esterification of 35/45 and 36/46, respectively. The INADEQUATE and molecular modeling experiments allowed topological mapping of the fullerene surfaces of the bis-methano[60]fullerenes 38 and 42. Reductive ring-opening reactions on the tethered bis-methano[60]fullerenes 35-37, 45, and 46 gave none of the expected bis-fullerenylglycinates rather the reductive ring-opening-retro-Bingel products, the 1,2-dihydro[60]fullerenylglycinates 48, 49, 52, and 53. These compounds resulted from the reductive ring-opening of one methanoimino ester moiety and a retro-Bingel reaction of the other. Under analogous reductive ring-opening-retro-Bingel conditions, the nontethered bis-methano[60]fullerene 40 afforded the 1,2-dihydro[60]fullerenylglycinate 12. Thus, it was concluded that the tether was not the driving force for the reductive elimination of one of the methano groups.     

Syntheses and structural characterization of dinuclear and tetranuclear iron(III) complexes with dinucleating ligands and their reactions with hydrogen peroxide

The iron(III) complexes [Fe(2)(HPTB)(mu-OH)(NO(3))(2)](NO(3))(2).CH(3)OH.2H(2)O (1), [Fe(2)(HPTB)(mu-OCH(3))(NO(3))(2)](NO(3))(2).4.5CH(3)OH (2), [Fe(2)(HPTB)(mu-OH)(OBz)(2)](ClO(4))(2).4.5H(2)O (3), [Fe(2)(N-EtOH-HPTB)(mu-OH)(NO(3))(2)](ClO(4))(NO(3)).3CH(3)OH.1.5H(2)O (4), [Fe(2)(5,6-Me(2)-HPTB)(mu-OH)(NO(3))(2)](ClO(4))(NO(3)).3.5CH(3)OH.C(2)H(5)OC(2)H(5).0.5H(2)O (5), and [Fe(4)(HPTB)(2)(mu-F)(2)(OH)(4)](ClO(4))(4).CH(3)CN.C(2)H(5)OC(2)H(5).H(2)O (6) were synthesized (HPTB = N,N,N',N'-tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, N-EtOH-HPTB = N,N,N',N'-tetrakis(N' '-(2-hydroxoethyl)-2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, 5,6-Me(2)-HPTB = N,N,N',N'-tetrakis(5,6-dimethyl-2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane). The molecular structures of 2-6 were established by single-crystal X-ray crystallography. Iron(II) complexes with ligands similar to the dinucleating ligands described herein have been used previously as model compounds for the dioxygen uptake at the active sites of non-heme iron enzymes. The same metastable (mu-peroxo)diiron(III) adducts were observed during these studies. They can be prepared by adding hydrogen peroxide to the iron(III) compounds 1-6. Using stopped-flow techniques these reactions were kinetically investigated in different solvents and a mechanism was postulated.     

Preparation of [5,6]- and [6,6]-oxahomofullerene derivatives and their interconversion by Lewis acid assisted reactions of fullerene mixed peroxides

[60]Fullerene mixed peroxides C60(O)(OOtBu)4 exhibit chemo- and regioselective reactions under mild conditions. The epoxy moiety is opened by ferric chloride to form vicinal hydroxy chloride C60Cl(OH)(OOtBu)4. BF3 is also effective in opening the epoxy moiety. The O-O bond of the fullerene mixed peroxide is cleaved by aluminum chloride to form both [5,6]- and [6,6]-fullerene hemiketals (oxohomo[60]fullerenes). A Hock-type rearrangement is proposed for the formation of the hemiketals, in which a fullerene C-C bond is cleaved. Lewis acids and/or visible light can initiate isomerization of the hemiketal isomers. Single-crystal X-ray analysis and theoretical calculations confirmed the results.     

Electron microscopic imaging of a single Group 8 metal atom catalyzing C-C bond reorganization of fullerenes

Heating a bulk sample of [60]fullerene complexes, (η(5)-C(5)H(5))MC(60)R(5) (M = Fe, Ru, R = Me, Ph), produces small hydrocarbons because of coupling of R and C(5)H(5) via C-C and C-H bond activation. Upon observation by transmission electron microscopy, these complexes, encapsulated in single-walled carbon nanotubes, underwent C-C bond reorganization reactions to form new C-C bond networks, including a structure reminiscent of [70]fullerene. Quantitative comparison of the electron dose required to effect the C-C bond reorganization of fullerenes and organofullerenes in the presence of a single atom of Ru, Fe, or Ln and in the the absence of metal atoms indicated high catalytic activity of Ru and Fe atoms, as opposed to no catalytic activity of Ln. Organic molecules such as hydrocarbons and amides as well as pristine [60]fullerene maintain their structural integrity upon irradiation by ca. 100 times higher electron dose compared to the Ru and Fe organometallics. The results not only represent a rare example of direct observation of a single-metal catalysis but also have implications for the use of single metal atom catalysis in Group 8 metal heterogeneous catalysis.