氯化锌催化下C60与枞酸的反应

拟利用枞酸分子中的非同环共轭二烯在氯化锌作用下异构化成具有同环共轭二烯的海松酸结构, 再与C₆₀进行Diels-Alder加成反应, 预测可以得到Diels-Alder加成产物. C₆₀、枞酸及氯化锌在邻二氯苯溶剂中, 在氮气保护下于175～180 ℃反应8 h, 将反应物洗涤后进行硅胶柱层析分离, 采用FT-IR, ¹³C NMR, ¹H NMR和MALDI-TOF-MS等分析方法对反应主要产物进行结构测定, 却意外发现得到C₆₀与枞酸的加成过程中发生了脱羧脱氢反应且产物含有芳环的化学结构.     

Algebraic expressions of irreducible bases for molecules C20H20, C80, and C240

Using the symmetrized boson representation technique, concise algebraic expressions of the irreducible bases symmetry adapted to the group chain I_h⊃C₅ for the fullerene molecules C₂₀H₂₀, C₈₀, and C₂₄₀ are derived for the most general cases and those for any specific case can be derived from them easily without a projection procedure. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 283–297, 1999     

Density Functional Study of Two Seven-Membered Unconventional Fullerenes C58F17CF3 and C58F18

The density functional method is used to study the structure, electronic properties, static linear polarizabilities, and optical absorption spectra of two seven‐membered unconventional fullerene derivatives C₅₈F₁₇CF₃ and C₅₈F₁₈. It is calculated that three sites chosen to locate the CF₃ are isoenergetic. The energy gaps of C₅₈F₁₈ and C₅₈F₁₇CF₃ are much larger than that of C₅₈, indicating the fluorination and trifluoromethylation of C₅₈ can remarkably enhance the kinetic stability. The density of states explore that the influence of CF₃ to the energy levels is mainly distributed in the energy range from ?10 to ?2 eV. However, when the CF₃ substitutes for F in C₅₈F₁₈, the bond lengths, energy gaps, static linear polarizabilities, and optical absorption spectra all show small variety.     

Catalytic Reduction of CN−, CO,and CO2 by Nitrogenase Cofactors in Lanthanide‐Driven Reactions

Nitrogenase cofactors can be extracted into an organic solvent to catalyze the reduction of cyanide (CN⁻), carbon monoxide (CO), and carbon dioxide (CO₂) without using adenosine triphosphate (ATP), when samarium(II) iodide (SmI₂) and 2,6‐lutidinium triflate (Lut‐H) are employed as a reductant and a proton source, respectively. Driven by SmI₂, the cofactors catalytically reduce CN⁻ or CO to C₁–C₄ hydrocarbons, and CO₂ to CO and C₁–C₃ hydrocarbons. The C C coupling from CO₂ indicates a unique Fischer–Tropsch‐like reaction with an atypical carbonaceous substrate, whereas the catalytic turnover of CN⁻, CO, and CO₂ by isolated cofactors suggests the possibility to develop nitrogenase‐based electrocatalysts for the production of hydrocarbons from these carbon‐containing compounds.     

Water‐Promoted Generation of a Diazairida Homobarrelene by C?C Coupling Between an Iridacyclic Alkylidene and Acetonitrile

The stable cationic iridacyclopentenylidene [Tp^Me2Ir(CHC(Me)C(Me)C H₂(NCMe)]PF₆ ( A ; Tp^Me2=hydrotris(3,5‐dimethylpyrazolyl)borate) has been obtained by α‐hydride abstraction from the iridacyclopent‐2‐ene [Tp^Me2Ir(CH₂C(Me)C(Me)C H₂)(NCMe)]. Complex A exhibits Brønsted–Lowry acidity at the Ir CH₂ and proximal (relative to Ir CH₂) methyl sites. The coordination of an extra molecule of acetonitrile to the iridium center initiates the reversible isomerization of the chelating carbon chain of A to the monodentate butadienyl ligand of complex [Tp^Me2Ir(CHC(Me)C(Me)CH₂)(NCMe)₂]PF₆, which is capable to engage in a water‐promoted C C coupling with the MeCN co‐ligands. The product is an aesthetically appealing bicyclic structure that resembles the hydrocarbon barrelene.     

Photosensitization of Nanocrystalline TiO2 Electrode Modified with C60 Carboxylic Acid Derivatives

C₆₀ carboxylic acid derivatives can be readily adsorbed on the surface of nanocrystalline TiO₂ film. The C₆₀ carboxylic acids adsorbed on nanocrystalline TiO₂ films act as charge‐transfer sensitizer. The electron transport from TiO₂ to the C₆₀ derivatives results in the generation of the cathodic photocurrent. The short‐circuit photocurrent of a C₆₀ tetracarboxylic acid is 0.45 μA/cm² under 464 nm light illumination. The photoelectric behaviour of ITO electrodes modified by the same C₆₀ carboxylic acids is different from that of the modified TiO₂ electrodes, and shows anodic photocurrent.     

Unexpected C–C Bond Formation with a Ferrocenyl Fischer Carbene Complex

Thermolysis of (OC)₅Cr(C(OEt)(Fc)) ( 1 ) gives 2,N-diferrocenyl acetamide Fc–CH₂–CO–NH–Fc ( 2 ) in the presence of amino ferrocene Fc-NH₂. In the absence of a nucleophile, 4-ethoxy-2,3,4-triferrocenyl-cyclobut-2-enone ( 3 ) forms from 1 under thermal activation. Single crystal X-ray diffraction, NMR spectroscopy and mass spectrometry unambiguously confirm the structure of both unexpected products. Quantum chemical calculations and kinetic experiments by mass spectrometry and IR spectroscopy help to propose conceivable pathways to their formation.     

Solar Hydrocarbons: Single-Step,Atmospheric-Pressure Synthesis of C2−C4 Alkanes and Alkenes from CO2

Cobalt ferrite (CoFe₂O₄) spinel has been found to produce C₂−C₄ hydrocarbons in a single-step, ambient-pressure, photocatalytic hydrogenation of CO₂ with a rate of 1.1 mmol g⁻¹ h⁻¹, selectivity of 29.8 % and conversion yield of 12.9 %. On stream the CoFe₂O₄ reconstructs to a CoFe−CoFe₂O₄ alloy-spinel nanocomposite which facilitates the light-assisted transformation of CO₂ to CO and hydrogenation of the CO to C₂−C₄ hydrocarbons. Promising results obtained from a laboratory demonstrator bode well for the development of a solar hydrocarbon pilot refinery.     

Proton chemical shifts in NMR: Part 17. Chemical shifts in alkenes and anisotropic and steric effects of the double bond

The ¹H NMR spectra of a number of alkenes of known geometry were recorded in CDCl₃ solution and assigned, namely ethylene, propene, 4-methylcyclohexene, 1,4-dimethylcyclohexene, methylene cyclohexane (in CFCl₃–CD₂Cl₂ at 153 K), 5-methylene-2-norbornene, camphene, bicyclopentadiene, styrene and 9-vinylanthracene. These results together with literature data for other alkenes, i.e. 1,3- and 1,4-cyclohexadiene, norbornene, norbornadiene, bicyclo[2.2.2]oct-2-ene and α- and β-pinene, and other data allowed the determination of the olefinic shielding in these molecules. The shielding was analysed in terms of the magnetic anisotropy and steric effects of the double bond together with a model (CHARGE7) for the calculation of the two- and three-bond electronic effects. For the aromatic alkenes ring current and π-electron effects were included. This analysis showed that the double bond shielding arises from both anisotropic and steric effects. The anisotropy is due to the perpendicular term only with a value of Δχ(CC) of −12.1 × 10⁻⁶cm³mol⁻¹. There is also a steric deshielding term of 82.5/r⁶ (r in Å). The shielding along the π-axis changes sign from shielding at long range (>2.5 Å) to deshielding at short range (<2 Å). The model gives the first comprehensive calculation of the shielding of the alkene group. For the data set considered (172 proton chemical shifts) ranging from δ=0.48 to 8.39, the r.m.s. error of observed vs calculated shifts was 0.11 ppm. Copyright © 2001 John Wiley & Sons, Ltd.     

Synthesis and upconversion luminescence properties of YF3:Yb/Tm octahedral nanocrystals

YF₃:Yb³⁺(20%)/Tm³⁺(2%) octahedral nanocrystals were synthesized by a microemulsion method with NH₄HF₂. Pumped with a 980-nm diode laser, the nanocrystals emitted weak blue and intense ultraviolet light. Especially, unusual ³P₂ → ³H₆ (∼265 nm) and ³P₂ → ³F₄ (∼309 nm) emissions, coming from a five-photon excitation process, were observed. The emissions from ¹D₂ and ¹I₆ were much stronger than those from ¹G₄ and ³H₄. The upconversion mechanism was discussed in detail.     

Highly Selective Photoelectroreduction of Carbon Dioxide to Ethanol over Graphene/Silicon Carbide Composites

Using sunlight to produce valuable chemicals and fuels from carbon dioxide (CO₂), i.e., artificial photosynthesis (AP) is a promising strategy to achieve solar energy storage and a negative carbon cycle. However, selective synthesis of C₂ compounds with a high CO₂ conversion rate remains challenging for current AP technologies. We performed CO₂ photoelectroreduction over a graphene/silicon carbide (SiC) catalyst under simulated solar irradiation with ethanol (C₂H₅OH) selectivity of>99 % and a CO₂ conversion rate of up to 17.1 mmol g_cat⁻¹ h⁻¹ with sustained performance. Experimental and theoretical investigations indicated an optimal interfacial layer to facilitate the transfer of photogenerated electrons from the SiC substrate to the few-layer graphene overlayer, which also favored an efficient CO₂ to C₂H₅OH conversion pathway.     

Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity

Terminal alkyne coupling reactions promoted by rhodium(I) complexes of macrocyclic NHC-based pincer ligands—which feature dodecamethylene, tetradecamethylene or hexadecamethylene wingtip linkers viz. [Rh(CNC-n)(C₂H₄)][BAr^F₄] (n=12, 14, 16; Ar^F=3,5-(CF₃)₂C₆H₃)—have been investigated, using the bulky alkynes HC≡CtBu and HC≡CAr’ (Ar’=3,5-tBu₂C₆H₃) as substrates. These stoichiometric reactions proceed with formation of rhodium(III) alkynyl alkenyl derivatives and produce rhodium(I) complexes of conjugated 1,3-enynes by C−C bond reductive elimination through the annulus of the ancillary ligand. The intermediates are formed with orthogonal regioselectivity, with E-alkenyl complexes derived from HC≡CtBu and gem-alkenyl complexes derived from HC≡CAr’, and the reductive elimination step is appreciably affected by the ring size of the macrocycle. For the homocoupling of HC≡CtBu, E-tBuC≡CCH=CHtBu is produced via direct reductive elimination from the corresponding rhodium(III) alkynyl E-alkenyl derivatives with increasing efficacy as the ring is expanded. In contrast, direct reductive elimination of Ar'C≡CC(=CH₂)Ar’ is encumbered relative to head-to-head coupling of HC≡CAr’ and it is only with the largest macrocyclic ligand studied that the two processes are competitive. These results showcase how macrocyclic ligands can be used to interrogate the mechanism and tune the outcome of terminal alkyne coupling reactions, and are discussed with reference to catalytic reactions mediated by the acyclic homologue [Rh(CNC-Me)(C₂H₄)][BAr^F₄] and solvent effects.     

Topological Design of Unprecedented Metal-Organic Frameworks Featuring Multiple Anion Functionalities and Hierarchical Porosity for Benchmark Acetylene Separation

Separation of acetylene (C₂H₂) from carbon dioxide (CO₂) or ethylene (C₂H₄) is industrially important but still challenging so far. Herein, we developed two novel robust metal organic frameworks AlFSIX-Cu-TPBDA (ZNU-8) with znv topology and SIFSIX-Cu-TPBDA (ZNU-9) with wly topology for efficient capture of C₂H₂ from CO₂ and C₂H₄. Both ZNU-8 and ZNU-9 feature multiple anion functionalities and hierarchical porosity. Notably, ZNU-9 with more anionic binding sites and three distinct cages displays both an extremely large C₂H₂ capacity (7.94 mmol/g) and a high C₂H₂/CO₂ (10.3) or C₂H₂/C₂H₄ (11.6) selectivity. The calculated capacity of C₂H₂ per anion (4.94 mol/mol at 1 bar) is the highest among all the anion pillared metal organic frameworks. Theoretical calculation indicated that the strong cooperative hydrogen bonds exist between acetylene and the pillared SiF₆²⁻ anions in the confined cavity, which is further confirmed by in situ IR spectra. The practical separation performance was explicitly demonstrated by dynamic breakthrough experiments with equimolar C₂H₂/CO₂ mixtures and 1/99 C₂H₂/C₂H₄ mixtures under various conditions with excellent recyclability and benchmark productivity of pure C₂H₂ (5.13 mmol/g) or C₂H₄ (48.57 mmol/g).     

Synthesis,Structure, and Reactivity of a Gold Carbenoid Complex That Lacks Heteroatom Stabilization

Hydride abstraction from the neutral gold cycloheptatrienyl complex [( P )Au(η¹‐C₇H₇)] ( P =P(tBu)₂(o‐biphenyl)) with triphenylcarbenium tetrafluoroborate at −80 °C led to the isolation of the cationic gold cycloheptatrienylidene complex [( P )Au(η¹‐C₇H₆)]⁺ BF₄⁻ in 52 % yield, which was characterized in solution and by single‐crystal X‐ray diffraction. This cycloheptatrienylidene complex represents the first example of a gold carbenoid complex that lacks conjugated heteroatom stabilization of the electron‐deficient C1 carbon atom. The cycloheptatrienylidene ligand of this complex is reactive; it can be reduced by mild hydride donors, and converted to tropone in the presence of pyridine N‐oxide.     

Preparation of Butadienylpyridines by Iridium-NHC-Catalyzed Alkyne Hydroalkenylation and Quinolizine Rearrangement

Iridium(I) N-heterocyclic carbene complexes of formula Ir(κ²O,O’-BHetA)(IPr)(η²-coe) [BHetA=bis-heteroatomic acidato, acetylacetonate or acetate; IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-carbene; coe=cyclooctene] have been prepared by treating Ir(κ²O,O’-BHetA)(η²-coe)₂ complexes with IPr. These complexes react with 2-vinylpyridine to afford the hydrido-iridium(III)-alkenyl cyclometalated derivatives IrH(κ²O,O’-BHetA)(κ²N,C-C₇H₆N)(IPr) through the iridium(I) intermediate Ir(κ²O,O’-BHetA)(IPr)(η²-C₇H₇N). The cyclometalated IrH(κ²O,O’-acac)(κ²N,C–C₇H₆N)(IPr) complex efficiently catalyzes the hydroalkenylation of aromatic and aliphatic terminal alkynes and enynes with 2-vinylpyridine to afford 2-(4R-butadienyl)pyridines with Z,E configuration as the major reaction products (yield up to 89 %). In addition, unprecedented (Z)-2-butadienyl-5R-pyridine derivatives have been obtained as minor reaction products (yield up to 21 %) from the elusive 1Z,3gem-butadienyl hydroalkenylation products. These compounds undergo a thermal 6π-electrocyclization to afford bicyclic 4H-quinolizine derivatives that, under catalytic reaction conditions, tautomerize to 6H-quinolizine to afford the (Z)-2-(butadienyl)-5R-pyridine by a retro-electrocyclization reaction.     

Shedding Light on the Diverse Reactivity of NacNacAl with N-Heterocycles

The aluminum(I) compound NacNacAl (NacNac=[ArNC(Me)CHC(Me)NAr]⁻, Ar=2,6-iPr₂C₆H₃, 1 ) shows diverse and substrate-controlled reactivity in reactions with N-heterocycles. 4-Dimethylaminopyridine (DMAP), a basic substrate in which the 4-position is blocked, induces rearrangement of NacNacAl by shifting a hydrogen atom from the methyl group of the NacNac backbone to the aluminum center. In contrast, C−H activation of the methyl group of 4-picoline takes place to produce a species with a reactive terminal methylene. Reaction of 1 with 3,5-lutidine results in the first example of an uncatalyzed, room-temperature cleavage of an sp² C−H bond (in the 4-position) by an Al^I species. Another reactivity mode was observed for quinoline, which undergoes 2,2′-coupling. Finally, the reaction of 1 with phthalazine produces the product of N−N bond cleavage.     

Darstellung und Charakterisierung der Fulleren-Kokristallisate C60 · 12 C6H12, C70 · 12 C6H12, C60 · 12 CCl4, C60 · 2 CHBr3, C60 · 2 CHCl3, C60 · 2 H2CCl2

Synthesis and Characterization of the Fullerene Co-Crystals C₆₀ · 12 C₆H₁₂, C₇₀ · 12 C₆H₁₂, C₆₀ · 12 CCl₄, C₆₀ · 2CHBr₃, C₆₀ · 2CHCl₃, C₆₀ · 2H₂CCl₂ By crystallization of fullerenes from non-polar solvents (C₆H₁₂, CCl₄, CHBr₃, CHCl₃, H₂CCl₂) compounds of the following compositions were obtained: C₆₀ · 12C₆H₁₂, C₇₀ · 12C₆H₁₂, C₆₀ · 12CCl₄, C₆₀ · 2CHCl₃, C₆₀ · 2CHBr₃ and C₆₀ · 2H₂CCl₂. Lattice parameters have been determined by X-ray diffraction of powder samples; according to single-crystal examinations on C₆₀ · 12C₆H₁₂, C₆₀ · 12CCl₄ and C₆₀ · 2CHBr₃ the fullerene is orientationally disordered. C₆₀ · 12C₆H₁₂, cubic, a = 28.167(1) Å; C₇₀ · 12C₆H₁₂, cubic, a = 28.608(2) Å; C₆₀ · 12CCl₄, cubic, a = 27.42(1) Å; C₆₀ · 2CHBr₃, hexagonal, a = 10.212(1), c = 10.209(1) Å; C₆₀ · 2CHCl₃, hexagonal, a = 10.08(1), c = 10.11(2) Å; C₆₀ · 2H₂CCl₂, tetragonal, a = 16.400(1) Å, c = 11.645(7) Å.     

Effect of Halide Anions on the Electroreduction of CO2 to C2H4: A Density Functional Theory Study**

The halide anions present in the electrolyte improve the Faradaic efficiencies (FEs) of the multi-hydrocarbon (C₂₊) products for the electrochemical reduction of CO₂ over copper (Cu) catalysts. However, the mechanism behind the increased yield of C₂₊ products with the addition of halide anions remains indistinct. In this study, we analysed the mechanism by investigating the electronic structures and computing the relative free energies of intermediates formed from CO₂ to C₂H₄ on the Cu (100) facet based on density functional theory (DFT) calculations. The results show that formyl *CHO from the hydrogenation reaction of the adsorbed *CO acts as the key intermediate, and the C−C coupling reaction occurs preferentially between *CHO and *CO with the formation of a *CHO-CO intermediate. We then propose a free-energy pathway of C₂H₄ formation. We find that the presence of halide anions significantly decreases the free energy of the *CHOCH intermediate, and enhances desorption of C₂H₄ in the order of I⁻>Cl⁻>Br⁻>F⁻. Lastly, the obtained results are rationalized through Bader charge analysis.     

Enantioselective Construction of C−SCF3 Stereocenters via Nickel Catalyzed Asymmetric Negishi Coupling Reaction

The construction of the SCF₃-containing 1,1-diaryl tertiary carbon stereocenters with high enantioselectivities is reported via a nickel-catalyzed asymmetric C−C coupling strategy. This method demonstrates simple operations, mild conditions and excellent functional group tolerance, with newly designed SCF₃-containing synthon, which can be easily obtained from commercially available benzyl bromide and trifluoromethylthio anion in a two-step manner. Further substrate exploration indicated that the reaction system could be extended to diverse perfluoroalkyl sulfide (SC₂F₅, SC₃F₇, SC₄F₉, SCF₂CO₂Et)-substituted 1,1-diaryl compounds with excellent enantioselectivities. The synthetic utility of this transformation was further demonstrated by convenient derivatization to optical SCF₃-containing analogues of bioactive compounds without an apparent decrease in enantioselectivity.     

Catalytic hydrogenation of C60 on transition metals

The catalytic hydrogenation of C₆₀ on Ru, Rh and Ir produced C₆₀H₁₈ mainly, while Pd, Pt, Co and Ni catalysts gave C₆₀H₃₆ principally. Very little activity was observed on Au and Fe. The higher hydrogenated fullerene obtained on Pd, Pt, Co and Ni was ascribed to the smaller % d-character of the metallic bond, on which the fullerene and hydrogen may more strongly be adsorbed. This revised version was published online in August 2006 with corrections to the Cover Date.