Cp2TiCl2/BuiMgBr/THF体系还原二芳基二硒醚

有机硒化合物具有生物活性[14],将硒基团引入到有机分子的一般方法是使亲核性的硒金属盐与亲电试剂反应 .二芳基二硒醚是制备有机硒化合物的重要中间体 .当它被还原时转化为硒负离子 ,被卤素等氧化时转化为亲电的硒试剂 .还原二硒醚通常使用ＮａＢＨ4[5 ],最近报道一些新的方法 ,如使用水合肼 /甲醇钠体系[6 ],Ｓｍ/ＨｇＣｌ2 体系[7].本文报道Ｃｐ2 ＴｉＣｌ2 /ＢｕｉＭｇＢｒ/ＴＨＦ体系还原二芳基二硒醚 .1　结果与讨论Ｃｐ2 ＴｉＣｌ2 与ＢｕｉＭｇＢｒ反应产生的钛氢化物是一种强的还原剂[8].在室温下 ,钛氢化物很容易与二硒醚反应生成…     

Titanium-catalyzed hydrosilylation of olefins: A comparison study on Cp2TiCl2/Sm and Cp2TiCl2/LiAlH4 catalyst system

Hydrosilylation of olefins catalyzed by Cp₂TiCl₂/Sm (Cp?=?cyclopentadienyl) under solvent free conditions have been investigated. By using Cp₂TiCl₂/Sm as catalyst system, β-adducts and hydrogenation products were detected. Hydrosilylation of olefins catalyzed by Cp₂TiCl₂/LiAlH₄ under room temperature has also been studied. The influence of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) on Cp₂TiCl₂/Sm and Cp₂TiCl₂/LiAlH₄, respectively, indicated that hydrosilylation of olefins catalyzed with Cp₂TiCl₂/Sm went through a free radical reaction pathway while a coordination mechanism was applied for Cp₂TiCl₂/LiAlH₄ catalyst system.     

Cp2TiCl2/i-BuMgBr还原断裂Se—Csp键反应研究

Cp₂TiCl₂/i-BuMgBr体系形成的钛氢化试剂与炔硒醚反应生成端炔与深蓝色钛硒化物, 后者在空气中被氧化为二醚, 与酰氯反应, 高产率地形成对应的硒代酯.     

双（环戊二烯基）二氯化锆载体催化剂催化乙烯／α—烯烃共聚合

合成了３种Ｚｒ／甲基铝氧烷（ＭＡＯ）／ＳｉＯ２型载体催化剂，考察了不同ＭＡＯ投料量对载锆反应及催化活性的影响，研究了乙烯聚合及乙烯／α－烯烃共聚合，结果表明，该催化剂对己烯和辛烯有很强的共聚作用，而对癸烯的共聚能力较弱，解释了α－烯烃碳链增长对乙烯／α－烯烃共聚催化活性的影响，ＳＥＭ分析表明，α－烯烃的加入有利于聚合物形态原改善。     

Cp2TiCl2/助催化剂体系催化异戊二烯齐聚反应的研究

过渡金属催化剂催化异戊二烯齐聚反应, 因其重要的应用背景及学术研究价值而受到人们的关注. 其中研究得最多的是镍催化体系, 采用不同的镍催化体系可以选择性地得到各种线性或环状的二聚物或齐聚物[1,2].     

Mechanistic investigation of vinylic carbon-fluorine bond activation of perfluorinated cycloalkenes using Cp*2ZrH2 and Cp*2ZrHF

Cp*₂ZrH₂ (1) (Cp*: pentamethylcyclopentadienyl) reacts with cyclic perfluorinated olefins to give Cp*₂ZrHF (2) and hydrodefluorinated products under very mild conditions. Initial C-F bond activation occurs selectively at the vinylic positions of the cycloolefin to exchange fluorine for hydrogen. Several mechanisms are discussed for this H/F exchange: (a) olefin insertion/β-fluoride elimination, (b) olefin insertion/α-fluoride elimination, and (c) hydride/fluoride σ-bond metathesis. Following H/F σ-bond metathesis exchange of both vinylic C-F bonds of perfluorocyclobutene, 1 then reacts with allylic C-F bonds by insertion/β-fluoride elimination. A similar sequence is observed with perfluorocyclopentene. Cp*₂ZrHF reacts selectively with vinylic C-F bonds of perfluorocyclobutene to give 3,3,4,4-tetrafluorocyclobutene and Cp*₂ZrF₂ without further hydrodefluorination occurring. In the presence of excess 1 and H₂, perfluorocyclobutene and perfluorocyclopentene are reduced to cyclobutane and cyclopentane in 46% and 16% yield, respectively. DFT calculations exclude the pathway by way of the olefin insertion/α-fluoride elimination and suggest that the pathway by way of hydride/fluoride σ-bond metathesis is preferred.     

Cp2ZrCl2/异丁基铝氧烷催化乙烯聚合动力学

均相茂金属催化烯烃聚合体系大多采用甲基铝氧烷(MAO)为助催化剂,但对MAO的作用机理尚不清楚。据文献报道,乙基铝氧烷(EAO)和异丁基铝氧烷(BAO)也有类似的助催化作用,但聚合活性远低于MAO体系。     

Lithium nitride reduction of Cp2TiCl2 and CpTiCl3: The synthesis of (Cp2TiCl2), Cp2TiCl2)n,Cp2Ti(CO)2 and chlorotetratitanium and nitridohexatitanium complexes

Stoichiometric reactions of Cp₂TiCl₂ or CpTiCl₃ with Li₃N in various molar ratios result in reduction to (Cp₂TiCl)₂, (CpTiCl₂)_n and (CpTiCl)₄ and provide useful synthetic routes. Further reduction produces hexanuclear nitrido titanium clusters, Cp₈Ti₆N and Cp₈Ti₆N₃, characterised from mass spectral evidence. The nitrido clusters react with HCl to form (Cp₂TiCl)₂ and Cp₂TiCl₂. (Cp₂TiCl₂ is also obtained by reaction with Me₃SiCl. Cp₂Ti(CO)₂ is formed by the reaction between Cp₂TiCl₂ and Li₃ N in THF in the presence of CO.     

Die Struktur von Cp2TiMe2

The structure of dimethyltitanocene, Cp₂TiMe₂, has been determined: monoclinic, space group P2₁/n, lattice constants (at −100°C) a = 6.818(2), b = 11.571(2), c = 13.387(3) Å, β = 92.36(2)°, and Z = 4. It is isostructural with Cp₂ZrMe ₂ and Cp₂HfMe₂. The Ti-C(σ) bond lengths are 2.170(2) and 2.181(2) Å and the C(σ)-Ti-C(σ) angle is 91.3(1 )°.     

ESR Study of the Reaction Between Cp2Ti(CO)2 and Cp2TiBr2

Introduction Floriani and Fachinetti have proposed that (Cp_2TiCl)_2 can be prepared by the reaction between Cp_2TiCl_2 and Cp_2Ti(CO)_2. We extended the method to the preparation of (Cp_2TiBr)_2 and characterized an active intermediate by ESR method.     

A Facile Reduction Procedure for Nitroarenes with Cp2TiCl2/Sm System

Nitroarenes can be reduced to the corresponding primary amines in good yields with Cp₂TiCl₂/Sm system under mild and neutral conditions.     

Direct cyclopropanation of 1-alkynylphosphonates by Cp2ZrCl2/2EtMgBr/2AlCl3 to afford cyclopropylmethylphosphonates

[reaction: see text] The reagent system Cp2ZrCl2/2EtMgBr/2AlCl3 converts 1-alkynylphosphonates into cyclopropylmethylphosphonates 3 in good isolated yields. Ethers, chlorides, and other cyclopropyl groups are compatible with the reaction conditions. Deuterium labeling is consistent with the formation of stable cyclopropylmethylbimetallic phosphonates by ring contraction of the corresponding aluminacyclopentenylphosphonate. Temperature is crucial; apparently, the cyclopropylmethylbimetallic phosphonates are in equilibrium with the aluminacyclopentenylphosphonates. Low temperature favors the former. We surmise that the negative charges of the intermediate are stabilized by the phosphonate group. Thus, diphenylacetylene and 3-hexyne failed to give cyclopropyl products under the same reaction conditions.     

Condensation of Cp2TiCI2 with Tetraamines

The synthesis of titanium polyamines from tetraamines is general and rapid. Systems utilizing equimolar quantities of reactants produce linear products, whereas tri- and tetra-substitution occurs when excess Cp₂TiCl₂ is used. The products exhibit moderate high-temperature stability but poor low-temperature stability, with degradation occurring via nonoxidative routes to ca. 200°C, and by oxidative routes in air at higher temperatures.     

The Reduction of Sulfoxides and Active Halides with Cp2TiCl2/Sm System

Cp₂TiCl₂/Samarium system is used as a new reagent for reducing sulfoxides to sulfides, benzyl halides to bibenzyls and α-bromoketones to ketones respectively in good yields under mild and neutral conditions.     

Relative reactivity enhancement of (Me5Cp)2ZrCl2 in mixture with (1,2,4-Me3Cp)2ZrCl2 during ethene/1-hexene copolymerization

Dual-site ethene/1-hexene copolymerizations with MAO-activated (1,2,4-Me₃Cp)₂ZrCl₂ and (Me₅Cp)₂ZrCl₂ catalysts were performed. Copolymers with narrow molecular weight distributions and bimodal short chain branching distributions could be produced. The combined catalyst system demonstrates a number of discrepancies from an expected average behavior of the individual sites. Dual-site (1,2,4-Me₃Cp)₂ZrCl₂/(Me₅Cp)₂ZrCl₂ systems produce copolymers with lower incorporation than expected. Clear evidences for relative activity enhancement of the (Me₅Cp)₂ZrCl₂ catalyst in the mixture were observed in melting endotherms and Crystaf profiles. Molecular weights obtained by the mixture were higher than for any of the individual catalysts. A similar effect is observed for a dual-site system of the (1,2,4-Me₃Cp)₂ZrCl₂ catalyst together with the Me₄Si₂(Me₄Cp)₂ZrCl₂ catalyst as an alternative to (Me₅Cp)₂ZrCl₂.     

Comparison of the catalytic activity of Ziegler-type catalysts based on Cp2ZrCl2 and (Cp2ZrCl)2O

The rates of ethylene polymerization catalyzed by Cp₂ZrCl₂-polymethylalumoxane and (Cp₂ZrCl)₂O-polymethylalumoxane are equal. According to NMR and ESR spectral data, the same precatalyst, presumably Cp₂ZrMe₂, is formed in both systems by the action of AlMe₃. This accounts for the equal catalytic activity of the systems based on Cp₂ZrCl₂ and (Cp₂ZrCl)₂O. A scheme of reactions resulting in cleavage of the Zr-O-Zr bridge is proposed and confirmed by spectroscopic data.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2104–2107, December, 1993.     

Complexes of decamethylsilicocene: Cp2*Si(CO) and Cp2*Si(N2)

The synthesis and IR spectroscopic detection of the monocarbonyl and mononitrogen complex of decamethylsilicocen in liquid xenon (LXe) and liquid nitrogen (LN₂) is reported. The reactions were found to be highly incomplete under a few bar of CO or N₂ and reversibel when the pressure is released. Cp₂*Si(CO) is characterized by three isotopomeres and Cp₂*Si(N₂) was synthesized on two independent routes.