金刚石附氢(100)面脱氢势垒的量子化学研究

采用MNDO（UHF）方法计算了金刚石（100）－（1×1）：2H双氢化表面和（100）－（2×1）：H单氢化表面的脱氢势垒，论证了决定金刚石附氢表面脱氢势垒大小的主要因素是气相－表面吸附氢原子间的相互排斥大小，得出（100）面两种表面结构脱氢势垒的理论预言值分别为71和59kJ·mol-1，均大于（111）面脱氢势垒的理论预言值42kJ·mol-1．揭示了在同等生长条件下金刚石（111）面可供成核和生长的反应基多于（100）面，与实验上得到的同等生长条件下（111）面的相对生长率大于（100）面的结论是一致的。     

Generation of cationic [Zr-[tert-butyl enolate]] reactive species: methyl abstraction versus hydride abstraction

Treatment of the neutral methyl-Zr-enolate [Cp(2)Zr(Me)[O(tBuO)C=CMe(2)]] (1) with one equivalent of B(C(6)F(5))(3) or [HNMe(2)Ph][B(C(6)F(5))(4)] as a methyl abstractor in THF at 0 degrees C leads to the selective formation of the free ion pair complex [Cp(2)Zr(THF)[O(tBuO)C=CMe(2)]](+) [anion](-) (2) (anion=MeB(C(6)F(5))(3) (-), B(C(6)F(5))(4) (-)), which is relevant to the controlled polymerization of methacrylates. Cation 2 rapidly decomposes at 20 degrees C in THF with release of one equivalent of isobutene to form the cationic Zr-carboxylate species [Cp(2)Zr(THF)(O(2)CiPr)](+) (3), through a proposed intramolecular proton transfer process from the tert-butoxy group to the enolate. The reaction of 1 with one equivalent of B(C(6)F(5))(3) or [HNMe(2)Ph][B(C(6)F(5))(4)] in CH(2)Cl(2) leads to the direct, rapid formation of the dimeric micro-isobutyrato-Zr dicationic species [[Cp(2)Zr[micro-(O(2)CiPr)]](2)](2+) (4), which gives 3 upon dissolution in THF. Contrastingly, when [Ph(3)C][B(C(6)F(5))(4)] is used to generate the cationic Zr-enolate species from 1 in CD(2)Cl(2), a 15:85 mixture of dicationic complexes 4 and [[Cp(2)Zr[micro-(O(2)C-C(Me)=CH(2))]](2)](2+)[B(C(6)F(5))(4)]]2-(5-[B(C(6)F(5))(4)](2)) is obtained quantitatively. The formation of 5 is proposed to arise from initial hydride abstraction from a methyl enolate group by Ph(3)C(+), as supported by the parallel production of Ph(3)CH, and subsequent elimination of methane and isobutene. In addition to standard spectroscopic and analytical characterizations for the isolated complexes 2-5, complexes 4 and 5 have also been structurally characterized by X-ray diffraction studies.     

Polar and solvation effects in reactions of oxygen atoms and hydroxyl and alkoxyl radicals with oxygen-containing compounds

Experimental data on the activation energies of reactions of H-abstraction from oxygencontaining compounds by oxygen atoms and hydroxyl and alkoxyl radicals in the gas and liquid phases have been analyzed by means of the parabolic model of the transition state. The contribution of polar interaction to the activation energies of the reactions has been calculated. The contribution of solvation to the activation energy has been calculated by comparison of the reaction parameters of the respective reaction in the liquid and gas phases.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 38–42, January, 1994.     

Characterization and Reactivity Studies of a Terminal Copper–Nitrene Species

High‐valent terminal copper–nitrene species have been postulated as key intermediates in copper‐catalyzed aziridination and amination reactions. The high reactivity of these intermediates has prevented their characterization for decades, thereby making the mechanisms ambiguous. Very recently, the Lewis acid adduct of a copper–nitrene intermediate was trapped at ?90 °C and shown to be active in various oxidation reactions. Herein, we describe for the first time the synthesis and spectroscopic characterization of a terminal copper(II)–nitrene radical species that is stable at room temperature in the absence of any Lewis acid. The azide derivative of a triazamacrocyclic ligand that had previously been utilized in the stabilization of aryl–Cu^III intermediates was employed as an ancillary ligand in the study. The terminal copper(II)–nitrene radical species is able to transfer a nitrene moiety to phosphines and abstract a hydrogen atom from weak C?H bonds, leading to the formation of oxidized products in modest yields.     

A Radical Tricationic Rhomboid Tetraborane(4) with Four‐Center,Five‐Electron Bonding

The red‐colored tetraborane(4) [B₄(hpp)₄]^3+. ( 3 ; hpp=1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidinate) with a rhomboid B₄ skeleton stabilized by four N donors, was synthesized by the reaction of the strong hydride abstraction reagent [(acridine)BCl₂][AlCl₄] with the electron‐rich diborane(4) [HB(hpp)]₂ ( 1 ). The salt 3 [AlCl₄]₃ was structurally characterized and the presence of unpaired electrons proven by EPR measurements. The unprecedented radical tricationic 3 is distinguished by a high positive charge and boron atoms in a low oxidation state (less than two).     

Effect of type of peroxide on cross-linking of poly(l-lactide)

Poly(l-lactide) (PLLA) was cross-linked with various types of peroxides under constant mole ratios of peroxide-derived radicals to PLLA during reactive extrusion. Peroxides were classified into three groups according to their decomposition rates (Group I: fast, Group II: moderate and Group III: slow) and comparisons were performed within each group. Cross-linking behavior was readily understood in terms of free radical efficiency and hydrogen abstraction ability of radicals. In the case of Groups II and III, the weight-average molecular weight (M_w) of cross-linked PLLA increased with overall hydrogen abstraction ability, because slow decomposition caused uniform cross-linking in molten PLLA. In Group I, M_w and gel fraction were higher than other groups despite Group I's lower hydrogen abstraction ability, leading to the conclusion that peroxide decomposition localized in solid PLLA caused partial cross-linking because of rapid decomposition. Furthermore, the efficiency of peroxide-induced cross-linking was investigated using the Charlesby-Pinner equation.     

含氮药物分子中氮a-位碳氢键离解能的理论研究

本文利用G3B3 和CBS-Q高精度理论方法检验了一系列胺类有机化合物中α-碳氢键离解能的实验测量值,在此基础上筛选出(U)BHandH/6-311++G(2df, 2p)//(U)B3LYP/6-31G(d)方法,发现其可以准确快速的预测氮α-碳氢键离解能。运用该方法研究了若干含氮药物分子,发现氮α-碳氢键离解能随药物分子结构发生明显变化。为了阐明其变化规律,系统研究单取代和双取代基效应,并解释了不同取代基效应的来源。     

Electrochemically Driven C−H Hydrogen Abstraction Processes with the Tetrachloro‐Phthalimido‐N‐Oxyl (Cl4PINO) Catalyst

The radical redox mediator tetrachloro‐phthalimido‐N‐oxyl (Cl₄PINO) is generated at a glassy carbon electrode and investigated for the model oxidation of primary and secondary alcohols with particular attention to reaction rates and mechanism. The two‐electron oxidation reactions of a range of primary, secondary, and cyclic alcohols are dissected into an initial step based on C−H hydrogen abstraction (rate constant k₁, confirmed by kinetic isotope effect) and a fast radical‐radical coupling of the resulting alcohol radical with Cl₄PINO to give a ketal that only slowly releases the aldehyde/ketone and redox mediator precursor back into solution (rate constant k₂). In situ electrochemical EPR reveals Cl₄PINO sensitivity towards moisture. DFT methods are applied to confirm and predict C−H hydrogen abstraction reactivity.     

Chlorine-atom abstraction and cluster fragmentation in the reaction of H3Re3(CO)10(MeCN)2 with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd): X-ray diffraction structure of fac-ClRe(CO)3(bpcd)

Treatment of the activated trirhenium cluster H₃Re₃(CO)₁₀(MeCN)₂ with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) in CH₂Cl₂ does not afford the expected cluster product H₃Re₃(CO)₁₀(bpcd) but rather the mononuclear complex fac-ClRe(CO)₃(bpcd). The identity of fac-ClRe(CO)₃(bpcd) was determined in solution by IR and NMR (¹H and ³¹P) spectroscopies and the solid-state structure was established by X-ray diffraction analysis. fac-ClRe(CO)₃(bpcd) crystallizes in the triclinic space P-1, a = 9.958(2) Å, b = 11.991(3) Å, c = 13.676(3) Å, α = 73.230(4)°, β = 73.806(4)°, γ = 77.409(4)°, V = 1484.6(6) ų, Z = 2, and d _calc = 1.723 Mg/m³; R = 0.0367, R _w  = 0.0857 for 4253 reflections with I > 2σ(l).     

Reactions of mono- and bimolecular hydrogen transfer in alkyl radicals: analysis using the parabolic model and density functional calculations

Experimental data on monomolecular hydrogen transfer in the reactions of the type RC^·H(CH₂)_nCH₂R¹ RCH₂(CH₂)_nC^·HR¹ (n = 2—4, R and R¹ are alkyl substituents) were analyzed using the parabolic model (PM). The parameters characterizing this class of reactions were calculated. Isomerization of alkyl radicals via cyclic transition states (TS) is characterized by the following energy barriers to thermoneutral reaction E _e0: 53.5, 65.4, and 63.2 kJ mol^–1 for the six-, five-, and seven-membered TS, respectively. The E _e0 energy and the strain energy change in parallel in the series of cycloparaffins C_nH_2n. Density functional calculations of intramolecular hydrogen transfer in the n-butyl and n-pentyl radicals and of the bimolecular hydrogen abstraction from the ethane molecule by the ethyl radical were performed. The activation energies of the intra- and intermolecular hydrogen transfer were compared. The parameters of the PM were compared with the interatomic distances in the reaction center of the TS calculated by the density functional method.