甲醇羰基化制乙酸反应的理论研究

采用有效核势能近似(ECP)从头算方法, 在LANL2DZ基组下研究了铑碘络合物催化剂催化甲醇羰基化制乙酸的反应机理. 优化得到了反应基态势能面的反应物、过渡态和产物的几何构型. 理论计算结果说明, 该催化反应循环中CH₃I氧化加成、羰基插入和CH₃COI还原消除基元反应步骤的活化位垒分别为216.03, 128.10和126.56 kJ/mol, CH₃I氧化加成是整个反应的决速步骤.     

改性羰基钴催化氢甲酰化反应系列基元反应的理论研究

在HF/LANL2DZ水平下,采用有效核势能近似(ECP)从头算方法,研究了有机膦配体改性羰基钴催化的氢甲酰化反应循环中部分基元反应步骤的微观反应机理.优化了基态势能面上诸反应中间体、过渡态和产物的几何构型.计算了反应活化位垒.结果表明,羰基插入、加氢氧化和脱氢还原的基元反应步骤的活化位垒分别为54.02,134.02和43.44kJ/mol.     

羟基钴催化氢甲酰化反应的理论研究

采用有效核势能近似(ECP)从头算方法,在HF/LANL2DZ水平下研究了羰基钴催化的氢甲酰化反应循环中的羰基插入、H2 氧化加成和脱氢还原系列基元反应步骤的反应机理.优化得到了反应基态势能面的中间体、过渡态和产物的几何构型.计算了反应活化位垒,并对各过渡态进行了振动分析以确认.理论计算结果表明,羰基插入、H2 氧化加成、脱氢还原的基元反应步骤的活化位垒分别为67.79、139.11和44.78kJ·mol-1.     

螯合型羰基铑配合物催化甲醇羰基化反应的机理研究

报道了螯合型正方平面羰基铑配合物催化甲醇羰基化反应的机理研究. 通过含有两种与铑具有不同配位能力的授体的配体, 与四羰基二氯二铑形成螯合型正方平面阳离子配合物. 研究证明, 该类配合物在催化甲醇羰基化反应过程中, 其活性物种区别于文献报道的[Rh(CO)2I2]－阴离子. 配合物中铑与吡啶环上共轭N形成的N→Rh配键, 在羰基化反应过程中并非通常认为的断裂而是形成新的活性物种, 即配体与铑作为整体参与了CH3I的氧化加成及CH3COI的生成过程. 通过对相应的聚合物配体铑催化剂的研究, 进一步证实了这个反应机理. 这一结果, 对该类催化剂分子设计, 以及克服其工业使用中的催化剂沉淀失活等现象均有重要意义.     

铑碘催化剂催化甲醇羰基化反应的IRC解析

在HF/LANL2DZ水平上, 采用能量梯度法, 研究了铑碘催化剂催化甲醇羰基化反应循环中各基元反应的反应物、中间体、过渡态、产物的几何结构, 并计算了它们势能面的变化. 通过对各基元反应过渡态的IRC解析, 证实了所得各类几何结构是甲醇羰基化铑碘催化循环反应途径上的驻点, 完整给出了循环反应过程中分子沿极小能量途径在各基元反应过程中的构型变化, 并提出了中间体构型转换在循环反应过程中的作用. 通过结构分析, 提出了顺式和反式催化循环反应两种途径之间除催化活性物顺反异构关联外, 还可以通过中间体构型转换关联, 其活化能为49.79 kJ/mol, 并且在还原消除基元反应步骤有既非顺式也非反式的情况, 证明该循环反应可能经历多个途径实现, 但无论何种途径, 碘甲烷氧化加成基元反应是整个循环反应过程的速控步骤.     

CH2O+H→CHO+H2反应途径和变分速率常数计算研究

采用QCISD/6-311G^** 从头算方法,优化了吸氢反应CH2O+H→CHO+H2的反应物、过渡态、产物几何结构,得出该反应的正、逆反应活化位垒分别是35.4kJ/mol和98.8kJ/mol。沿IRC分析指出该反应是一个C—H键断裂和H—H键生成协同进行的反应,而且在反应途径上存在一个引导反应进行的振动模式,这一反应模式引导反应进行的区间在—0.4～0.55(amu)^1/2之间。在300～3200K温度范围内,运用变分过渡态理论(CVT),计算了该反应的速率常数。     

Murai反应中芳香酮邻位C–H键活化的区域选择性的理论研究

钌催化剂RuH_2(CO)(PPh_3)_3使Murai反应中芳香酮β位C–H键的催化活化反应具有极高的产率与选择性.本文采用密度泛函(DFT)方法研究了钌配合物催化芳香酮邻位C–H键活化的反应机理,剖析了芳香酮C–H键活化反应中产生区域选择性的原因.计算结果表明,C–H键的活化位垒为1.1 kcal/mol,从反应动态学角度很好地解释了该反应的区域选择性.通过路径a与路径b的比较,发现C=C双键更容易插入到Ru–H键而不是Ru–C键中.另外,无论C–C键形成(C–C活化过程)出现在路径a的烯烃插入基元反应,还是出现在路径b的还原消除基元反应,C–C键形成步骤都是整个催化反应的决速步骤.与路径a和b比较,反应路径c中C–C键形成过程的空间位阻较大,能垒也更高.     

烷基氟化物热消除反应的理论研究-1

用RHF从头计算法研究了氟代乙烷消除氟化氢反应的取代基效应．对所有构型均采用能量梯度法在3-21G基级水平上进行了优化，过渡态的构型用振动分析确认．计算结果表明，对所讨论的基团-F，-CH_3，－CN，－NH_2，在α位和β位取代，均对过渡态的结构有一定的影响，电荷分布表明，标题反应的过渡态为部分极化的四元环过渡态．－F在α位和β位的取代均使氟代烷1－2消除氟化氢反应的活化位垒升高，且前者的活化位垒高于后者；－CN在α位的取代使反应的活化位垒升高，在β位的取代使反应的活化位垒降低．－CH_3和-NH_2在α位的取代使反应的活化位垒降低，在β位的取代使反应的活化位垒升高，只是-NH_2的效应强于-CH_3．这些结果与由实验结果推测的结论一致表明，本消除反应与其它卤代烷的消除反应有显著的差别．     

三苯膦(胂、胅、胇)配位次苄基九羰基三钴的合成及其催化活性

金属钴簇配合物的合成及其催化活性的研究一直引起人们极大的兴趣 . 1 958年 ,Markby等[1] 首先合成出烷川九羰基三钴体系的第 1个配合物 CH3CCo3(CO) 9. 1 978年 ,傅宏祥等 [2 ] 合成了甲川族金属簇配合物 YCCo3(CO) 9(Y=H、Cl、Ph、Et OO) ,并在低压下 ,对 1 -己烯、二异丁烯等烯烃的醛化、异构化反应作了研究 .Ryan[3] 等用Ph CCo3(CO) 9对 1 -戊烯的醛化反应作了研究 ,显示出较好的结果 ,并且指出 :此催化剂具有容易制备、活性高、对空气稳定、价格低廉等优点 .鉴于羰基铑以膦、三苯基膦、胺配位的配合物反应活性比羰基铑更高…     

镍配合物催化N-烯丙基酰胺异构化反应机理

采用密度泛函理论(DFT)方法,对镍配合物Ni(PPh3)2催化N-烯丙基酰胺异构化生成N-丙烯基酰胺的微观反应机理进行了计算.反应涉及了C—H键活化、异构化及还原消除生成新的C—H键等步骤.对C—H键活化和异构化步骤,分别考虑了Ni(PPh_3)_2和Ni(PPh_3)的催化活性,发现均为前者对应的能垒更低;对异构化步骤,分别考虑了π-烯丙基和σ-烯丙基机理,发现前者能垒更低.在整个反应路径中,生成产物E异构体的决速能垒为141.8 kJ/mol,与生成Z异构体的决速能垒(141.1 kJ/mol)仅差0.7 kJ/mol,与实验上E/Z选择性不高(56/44)一致.Pd(PPh_3)_2催化的决速中间体和过渡态的计算表明,生成E和Z异构体的决速能垒较高,均超过175 kJ/mol,与实验上Pd(PPh_3)_4没有催化活性一致.Ni(PPh_3)_2和Pd(PPh_3)_2催化活性不同,可由Ni的d电子对烯丙基阴离子π*反键的反馈作用较Pd更强来解释.此外,通过反应物中不同取代基对产物E/Z选择性影响的分析,发现E/Z选择性不同是由各取代基在生成E和Z异构体的决速过渡态中所受空间位阻不同所导致.     

TiCl4-mediated reduction of 1,3-diketones with BH3-pyridine complex: a highly diastereoselective method for the synthesis of syn-1,3-Diols

[reaction: see text] 1,3-Diketones can be reduced in high yields and with excellent diastereoselectivity to the corresponding syn-1,3-diols by carrying out the reaction with BH3-pyridine complex in CH2Cl2 at -78 degrees C in the presence of an equivalent of TiCl4 and 0.1 equiv of pyridine. This protocol shows a general character: excellent results are obtained when the groups bound to the carbonylic functions are linear or branched carbon chains and aromatic or benzylic frameworks as well.     

A unique six-membered chelated iridium complex

The reaction of 2-(3-methylbiphenyl-2-yl)pyridine with IrCl(3).nH(2)O in the presence of water incorporates a tightly bonded CO at the iridium center; in the subsequent reaction with picolinic acid a complex revealing an unusual CH activation of a methyl group is formed.     

Synthesis and characterization of diorganohydrazido(2-) tungsten complexes

Diorganohydrazido(2-) complexes of tungsten (L)Cl4W(NNR2) [R2=Me2, Ph2, -(CH2)5-; L=CH3CN, pyridine] were synthesized by reacting the corresponding 1,1-diorganohydrazine with WCl6, followed by reaction with acetonitrile or pyridine. Crystallographic structure determination of (CH3CN)Cl4W(NNMe2) and (CH3CN)Cl4W(NNPh2) allows a comparison of the structural features of the diorganohydrazido(2-) functionality with varying substituents. Mass spectrometry, thermogravimetric analysis, and preliminary chemical vapor deposition experiments were performed to determine the viability of these complexes as single-source precursors for deposition of WNx and WNxCy films.     

Kinetics and mechanism of oxygen transfer to methyloxo(dithiolato)rhenium(V) complexes

The kinetics and mechanism of the reactions of the dimeric and monomeric methyloxo(dithiolato)rhenium(V) complexes [(o-SC6H4CH2S)Re(O)CH3]2 and [(o-SC6H4CH2S)PyRe(O)CH3] (Py = pyridine) with XO, sulfoxides, and pyridine N-oxides are studied. In these reactions, an oxygen atom from XO is transferred to rhenium, from which it later removed. A reaction scheme is proposed to interpret the kinetic data. This scheme features the formation of a monomeric (sulfoxide)- or (pyridine N-oxide)(dithiolato)methyloxorhenium(V) complex followed by its bimolecular oxidation in a rate-controlling step. Several sulfoxides (methyl, methyl phenyl, and substituted diphenyl) all react at similar rates. Activation parameters are determined for dimethyl sulfoxide and di-4-tolyl sulfoxide from temperature-dependent studies. The reactions with pyridine N-oxides show autocatalysis in which the catalyst is confirmed to be pyridine formed in the reactions.     

Mechanistic aspects of the metal catalyzed alternating copolymerization of epoxides and carbon monoxide

The cobalt-catalyzed alternating copolymerization of epoxides and CO is a novel, direct approach to aliphatic polyesters, such as poly(hydroxybutyrate) (PHB). This reaction was found to be catalyzed by Ph3Si[Co(CO)4] (4) and pyridine affording in a first step the stable mono-insertion product Ph3Si-O-CH(CH3)-CH2-CO-Co(CO)4 (5). However, a profound mechanistic understanding, especially of the role of pyridine as the key component for the polymerization reaction was missing. ATR-IR online monitoring under catalytic conditions and DFT calculations were used to show that an acylpyridinium cation is formed by cleavage of the cobalt-acyl bond of 5 in the presence of pyridine. The Lewis acid thus generated activates the next incoming epoxide monomer for ring opening through [Co(CO)4]-. The catalytic cycle is completed by a subsequent CO insertion in the new cobalt-alkyl bond. The calculations are used to explore the energetic hypersurface of the polymerization reaction and are complemented by extended experimental investigations that also support the mechanistic hypotheses.     

Characterization and dynamics of substituted ruthenacyclobutanes relevant to the olefin cross-metathesis reaction

The reaction of the phosphonium alkylidene [(H(2)IMes)RuCl(2)=CHP(Cy)(3))](+) BF(4)(-) with propene, 1-butene, and 1-hexene at -45 °C affords various substituted, metathesis-active ruthenacycles. These metallacycles were found to equilibrate over extended reaction times in response to decreases in ethylene concentrations, which favored increased populations of α-monosubstituted and α,α'-disubstituted (both cis and trans) ruthenacycles. On an NMR time scale, rapid chemical exchange was found to preferentially occur between the β-hydrogens of the cis and trans stereoisomers prior to olefin exchange. Exchange on an NMR time scale was also observed between the α- and β-methylene groups of the monosubstituted ruthenacycle (H(2)IMes)Cl(2)Ru(CHRCH(2)CH(2)) (R = CH(3), CH(2)CH(3), (CH(2))(3)CH(3)). EXSY NMR experiments at -87 °C were used to determine the activation energies for both of these exchange processes. In addition, new methods have been developed for the direct preparation of metathesis-active ruthenacyclobutanes via the protonolysis of dichloro(1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)(benzylidene) bis(pyridine)ruthenium(II) and its 3-bromopyridine analogue. Using either trifluoroacetic acid or silica-bound toluenesulfonic acid as the proton source, the ethylene-derived ruthenacyclobutane (H(2)IMes)Cl(2)Ru(CH(2)CH(2)CH(2)) was observed in up to 98% yield via NMR at -40 °C. On the basis of these studies, mechanisms accounting for the positional and stereochemical exchange within ruthenacyclobutanes are proposed, as well as the implications of these dynamics toward olefin metathesis catalyst and reaction design are described.     

Photochemical activation of ruthenium(II)-pyridylamine complexes having a pyridine-N-oxide pendant toward oxygenation of organic substrates

Ruthenium(II)-acetonitrile complexes having η(3)-tris(2-pyridylmethyl)amine (TPA) with an uncoordinated pyridine ring and diimine such as 2,2'-bipyridine (bpy) and 2,2'-bipyrimidine (bpm), [Ru(II)(η(3)-TPA)(diimine)(CH(3)CN)](2+), reacted with m-chloroperbenzoic acid to afford corresponding Ru(II)-acetonitrile complexes having an uncoordinated pyridine-N-oxide arm, [Ru(II)(η(3)-TPA-O)(diimine)(CH(3)CN)](2+), with retention of the coordination environment. Photoirradiation of the acetonitrile complexes having diimine and the η(3)-TPA with the uncoordinated pyridine-N-oxide arm afforded a mixture of [Ru(II)(TPA)(diimine)](2+), intermediate-spin (S = 1) Ru(IV)-oxo complex with uncoordinated pyridine arm, and intermediate-spin Ru(IV)-oxo complex with uncoordinated pyridine-N-oxide arm. A Ru(II) complex bearing an oxygen-bound pyridine-N-oxide as a ligand and bpm as a diimine ligand was also obtained, and its crystal structure was determined by X-ray crystallography. Femtosecond laser flash photolysis of the isolated O-coordinated Ru(II)-pyridine-N-oxide complex has been investigated to reveal the photodynamics. The Ru(IV)-oxo complex with an uncoordinated pyridine moiety was alternatively prepared by reaction of the corresponding acetonitrile complex with 2,6-dichloropyridine-N-oxide (Cl(2)py-O) to identify the Ru(IV)-oxo species. The formation of Ru(IV)-oxo complexes was concluded to proceed via intermolecular oxygen atom transfer from the uncoordinated pyridine-N-oxide to a Ru(II) center on the basis of the results of the reaction with Cl(2)py-O and the concentration dependence of the consumption of the starting Ru(II) complexes having the uncoordinated pyridine-N-oxide moiety. Oxygenation reactions of organic substrates by [Ru(II)(η(3)-TPA-O)(diimine)(CH(3)CN)](2+) were examined under irradiation (at 420 ± 5 nm) and showed selective allylic oxygenation of cyclohexene to give cyclohexen-1-ol and cyclohexen-1-one and cumene oxygenation to afford cumyl alcohol and acetophenone.     

载体对Rh基催化剂上甲烷解离活性的影响

采用脉冲反应技术、原位CO吸附和吡啶吸附红外光谱,考察了Al2O3和SiO2负载的Rh基催化剂上Rh-CeO2相互作用和CH4解离活性.结果表明,载体酸性对Rh-CeO2相互作用有显著影响.Rh/Al2O3催化剂中添加CeO2增加了载体Al2O3的Lewis酸位,使Al2O3接受电子的能力增强,从而降低Rh的电子密度,有利于CH4解离活化.相反,Rh/SiO2催化剂中添加CeO2减少了载体SiO2的Lewis酸位和酸强度,使SiO2难于接受电子,导致Rh的电子密度增加,不利于CH4解离活化.     

Synthesis of mixed acid anhydrides from methane and carbon dioxide in acid solvents

[reaction: see text] The reaction of CH(4) with CO(2) has been performed in anhydrous acids using VO(acac)(2) and K(2)S(2)O(8) as promoters. NMR analysis establishes that the primary product is a mixed anhydride of acetic acid and the acid solvent. In sulfuric acid, the overall reaction is CH(4) + CO(2) + SO(3) --> CH(3)C(O)-O-SO(3)H. Hydrolysis of the mixed anhydride produces acetic acid and the solvent acid. When trifluoroacetic acid is the solvent, acetic acid is primarily formed via the reaction CH(4) + CF(3)COOH --> CH(3)COOH + CHF(3).     

Gas-phase bimolecular reactions between (.)CH(2)-(CH(2))(n)-C(+)=O distonic ions and pyridine: a combined experimental and theoretical study

The gas-phase reactivities of the well-known (.)CH(2)CH(2)C(+)=O and (.)CH(2)CH(2)CH(2)C(+)=O distonic ions towards neutral pyridine were studied both experimentally (six sector hybrid mass spectrometer) and theoretically (density functional theory and M?ller-Plesset ab initio calculations). Competitively to the charge exchange and protonation processes, both radical cations react with pyridine by an initial bonding between the positive charge site of the ion and the lone electron pair of the neutral molecule. At variance with previously reported studies in which such a nucleophilic interaction was proposed to play only a transient catalytic role, the initial C-N bond is likely to remain in the observed ion-molecule reaction products. The structures of the ion-molecule reactions products were probed by collisional activation at high kinetic energy and the reaction pathways were tentatively proposed on the basis of labeling experiments and ab initio molecular orbital calculations.