Aluminum carbenoids in the cyclopropanation of fulvenes

Aluminum carbenoid Et₂AlCH₂I reacts with 6-substituted fulvenes to give tricyclopropanes in high yields. Calculations at the B3LYP/6-31G(d) level of theory show that coplanar arrangement of the double bonds facilitates cyclopropanation due to conjugation in the transition state. Aluminum carbenoid Et₂AlCH₂I was generated by either the reaction of equimolar amounts of Et₃Al and CH₂I₂ in hexane or treatment of Et₂AlI with CH₂N₂ in dichloromethane.     

Ethylaluminum oxide catalysts from Et2AlOLi–Et2AlCl binary system in relation to species of AlEt3–water catalyst

Equimolar reaction of Et₂AlOLi and Et₂AlCl gave Et₂AlOAlEt₂. The catalyst behavior for polymerization of acetaldehyde, propylene oxide, and epichlorohydrin was compared with that of the AlEt₃–H₂O (1:0.5) catalyst system. The thermal disproportionation product of Et₂AlOAlEt₂ derived from Et₂AlOLi–Et₂AlCl had the structure, ? (EtAlO)_n? , and it showed catalyst behavior quite similar to that of the product obtained by the same treatment of AlEt₃–H₂O (1:0.5). These ethylaluminum oxides can be regarded as species predominating in AlEt₃–H₂O (1:0.5) and AlEt₃–H₂O (1:1), respectively. Stereospecific or high molecular weight polymerizations of these species were investigated.     

The reactions of nickel(II) carboxylates with a series of ethylaluminum chlorides

The distribution of nickel in the reaction products from the reactions of nickel(II) stearate with diethylaluminum chloride (Et₂AlCl), ethylaluminum sesquichloride (Et₃Al₂Cl₃), and ethylaluminum dichloride (EtAlCl₂) in benzene was investigated as a function of the Al/Ni reaction stoichiometry. The products consist of benzene-soluble nickel complexes and a precipitate from which can be extracted NiCl₂ and metallic nickel. The percentage of each product is seen to be dependent upon the Al/Ni reaction ratio and the aluminum compound employed in the reaction. It was found that in each case six alkylaluminums are required for complete reaction with one nickel(II) stearate molecule. The compunds Et₂AlCl, Et₃Al₂Cl₃, and EtAlCl₂ were all found to have greater reducing ability than Et₃Al at room temperature. Alternative interpretations of the chloro compounds' greater reducing abilities are discussed.     

Influence of H2O on alternating copolymerization with the EtnAlCl3-n-VOCl3 catalyst system

The effect of the catalytic amount of H₂O was investigated with the Et_nAlCl_3-n-VOCl₃ catalyst system on the alternating copolymerization of acrylic monomers with diolefins and styrene. The presence of the catalytic amount of H₂O produced an improvement in the yield and in the molecular weight as well as the structure of copolymer with the Et_nAlCl_3-n-VOCl₃ catalyst system. The efficiency of the aluminum components in the Et_nAlCl_3-n-VOCl₃ system appears with AlEt₃ and especially with Et_1.5AlCl_1.5. The catalytic activity was found to depend upon the H₂O Et_nAlCl_3-n molar ratio and was also affected by the order of mixing of the catalyst components and the monomers. Effective catalyst could be prepared when the catalyst components (except VOCl₃) were premixed without presence of monomers. The possible catalytic behavior of H₂O was discussed.     

EPR study on the charge-transfer photochemistry of the bromide mixed-ligand dithiocarbamate complex of copper(II)

The EPR technique has been used to study the photolysis of the mixed-ligand complex Cu^II(Et₂dtc)Br in a 1:1 solvent mixture of chloroalkane and alcohol, where the chloroalkane is CCl₄, CHCl₃ or CH₂Cl₂ and the alcohol is MeOH, EtOH, i-PrOH or i-BuOH, in comparison with Cu^II(Et₂dtc)Cl photolysis in CHBr₃:ROH. It was found that while Cu^II(Et₂dtc)Br photolysis in chloroalkane:ROH yielded Cu^II(Et₂dtc)Cl as an intermediate, the opposite conversion of Cu^II(Et₂dtc)Cl to Cu^II(Et₂dtc)Br proceeded via Cu^II(Et₂dtc)Cl photolysis in CHBr₃:ROH. The final photolytic products in both cases were tetraethylthiuramdisulphide and the corresponding copper(II) salt (CuCl₂ or CuBr₂, respectively). The results obtained by EPR allowed to get some insight into the behaviour of the primary photolytic products towards both components of the mixed solvent.     

Activation of CS2 and CO2 by Silylium Cations

The hydride-bridged silylium cation [Et₃Si−H−SiEt₃]⁺, stabilized by the weakly coordinating [Me₃NB₁₂Cl₁₁]⁻ anion, undergoes, in the presence of excess silane, a series of unexpected consecutive reactions with the valence-isoelectronic molecules CS₂ and CO₂. The final products of the reaction with CS₂ are methane and the previously unknown [(Et₃Si)₃S]⁺ cation. To gain insight into the entire reaction cascade, numerous experiments with varying conditions were performed, intermediate products were intercepted, and their structures were determined by X-ray crystallography. Besides the [(Et₃Si)₃S]⁺ cation as the final product, crystal structures of [(Et₃Si)₂SMe]⁺, [Et₃SiS(H)Me]⁺, and [Et₃SiOC(H)OSiEt₃]⁺ were obtained. Experimental results combined with supporting quantum-chemical calculations in the gas phase and solution allow a detailed understanding of the reaction cascade.     

Electrolytic partial fluorination of organic compounds. Part 51: Electrochemical fluorination of 1-methylpyrroles having electron-withdrawing groups at the 2-position: Effect of supporting fluoride salts on the fluorinated product selectivity

Anodic fluorination of 1-methylpyrroles having electron-withdrawing groups at the 2-position was comparatively studied using Et₃N•3HF and Et₃N•2HF as a supporting electrolyte and a fluorine source. The use of Et₃N•3HF gave trifluorinated products predominantly or selectively depending on solvents used while the use of Et₃N•2HF provided the corresponding monofluorinated pyrrole derivatives in considerable amount along with the trifluorinated products regardless of the solvents. This is the first successful example of selective anodic fluorination of pyrroles. The effects of supporting electrolyte on product selectivity are discussed.     

Mechanochemical Synthesis of Tri-μ2-Disulfido-μ3-Thio-Tris(Diethyldithiocarbamato)-S,S"-triangular- Trimolybdenum Diethyldithiocarbamate {Mo3(μ3-S)(μ2-S2)3[(C2H5)2NCS2]3}+[(C2H5)2NCS2]–

The mechanoactivated solid-state reaction of [Et₄N]₂[Mo₃S₇Br₆] with Na(Et₂NCS₂) in a vacuum vibration ball mill yields the [Mo₃S₇(Et₂NCS₂)₃]⁺[Et₂NCS₂]^–complex. The product was studied by IR and Raman spectroscopy and differential thermal analysis.     

Solvent Effect on the Ligand Exchange between Bis(diethyldithiocarbamato)copper(II) and Bis(diethyldiselenocarbamato)copper(II)

EPR and spectrophotometric study on the products of ligand‐exchange taking place on mixing bis(diethyldiselenocarbamato)copper(II), [Cu(Et₂dsc)₂], and bis(diethyldithiocarbamato)copper(II), [Cu(Et₂dtc)₂], solutions is reported. EPR spectra monitored at room temperature for one month period reveal a stable equilibrium among the parents (chromophores CuS₄ and CuSe₄) and the obtained mixed‐chelate [Cu(Et₂dtc)(Et₂dsc)] complex (chromophore CuS₂Se₂) in heptane, hexane, benzene, toluene, acetone, DMFA, DMSO and dichloromethane. In CCl₄ and CHCl₃ two new additional EPR spectra appear attributed to the mixed‐chelate complexes with the chromophores CuSSe₃ and CuS₃Se which are not observed with electronic spectroscopy. The intensities of all five EPR spectra decrease with the time. It is assumed that the new mixed‐chelates observed in CCl₄ and CHCl₃ are obtained in a reaction of [Cu(Et₂dtc)(Et₂dsc)] or [Cu(Et₂dtc)₂] with the ester of diselenocarbamic acid which is formed in a parallel reaction of [Cu(dsc)₂]with CCl₄ or CHCl₃.     

Synthesis and x‐ray crystal structures of hypervalent hexacoordinate antimony compounds without halogen ligands

Hypervalent hexacoordinate antimony‐ate complex { 2‐Et₄N : Rf₃Sb⁻Et₄N⁺ (Rf: o‐C₆H₄C(CF₃)₂O‐)} was synthesized by the reaction of Rf₂SbCl with lithium 1,1,1,3,3,3‐hexafluoro‐2‐(2‐lithiophenyl)‐2‐propoxide followed by countercation exchange. Reaction of 2‐Et₄N with triethyloxonium tetrafluoroborate gave the O‐ethylated adduct ( 3 ). X‐ray crystallographic analysis of 2‐Et₄N and 3 showed distorted octahedral structures of these compounds. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:33–37, 2001     

Cyclopropanation of alkenes with CH2I2/Et3Al by the phase-vanishing method based on fluorous phase screen

Phase-vanishing (PV) method using perfluorohexanes as a screen phase was applied to cyclopropanation reactions with CH₂I₂/Et₂Zn and CH₂I₂/Et₃Al. When Et₃Al was used as a carbenoid generator, the reaction proceeded smoothly and desired cyclopropane derivatives were obtained in high yield. The PV cyclopropanation took 2 or 3 days to complete, however, reduction of reaction time by a factor of 2-3 was also achieved by vigorous stirring after the bottom CH₂I₂ layer disappeared.     

Stereoregular polymerization of 1-vinylnaphthalene, 2-vinylnaphthalene,and 4-vinylbiphenyl

1-Vinylnaphthalene, 2-vinylnaphthalene, 4-vinylbiphenyl, and styrene were polymerized with Et₃Al–TiCl₄, Et₂AlCl–TiCl₃, and Et₃Al–TiCl₃ catalyst systems. The latter catalyst system gave polymers in 75–95% conversion which were at least 90% isotactic. Extraction with 2-butanone (MEK) separated the atactic from the isotactic fractions. The polymers were characterized by infrared and nuclear magnetic resonance spectroscopy.     

Neue nitridoverbrückte Dreikernkomplexe des Rheniums

New Trinuclear Rhenium Complexes with Bridging Nitrido Ligands Trinuclear complexes with bridging nitrido ligands between the rhenium atoms are formed when [ReN(Et₂dtc)₂ · (Me₂PhP)] (Et₂dtc^– = N,N‐diethyldithiocarbamate) reacts with TlCl or Pr(O₃SCF₃)₃. [Cl(Me₂PhP)₂(Et₂dtc)Re≡N–Re(N) · Cl₂(Me₂PhP)–N≡Re(Et₂dtc)(Me₂PhP)₂Cl] and [(Et₂dtc)₂ · (Me₂PhP)Re≡N–Re(N)(Et₂dtc)(Me₂PhP)–N≡Re(Me₂PhP) · (Et₂dtc)₂]⁺ contain two almost linear, asymmetric nitrido bridges. Additional, terminal nitrido ligands are located at the middle rhenium atoms.     

Transition metal reactions of silanes II. The reaction of cycloalkenes with various hydrosilanes and carbon monoxide catalyzed by Co2(CO)8

The reaction of cycloalkenes(cyclopentene, cyclohexene, cycloheptene, cyclooctene, 1-methylcyclohexene, and norbornene) with Et₂MeSiH and carbon monoxide in the presence of Co₂(CO)₈ gave the corresponding diethylmethylsiloxymethylenecycloalkenes. In such reactions of cyclohexene, the following hydrosilanes gave the corresponding siloxymethylenecyclohexanes: Me₃SiH, EtMe₂SiH, Et₂MeSiH, Et₃SiH, PhMe₂SiH, Ph₂MeSiH. Effects of the reaction conditions(the pressure of carbon monoxide, the temperature, and the molar ratio of cyclohexene to Et₂MeSiH) were examined. The yield of diethylmethylsiloxymethylenecyclohexane increased remarkably with increasing molar ratio of cyclohexene to Et₂MeSiH. At higher temperature, the yield of the isomerization product, 1-(diethylmethylsiloxymethyl)-cyclohex-1-ene, increased.     

Unexpected Silaazetidine Formation in the Thermolysis of thf‐Supported Silanimine Et2Si=N–SitBu3·thf

The silyl amide Et₂SiCl‐NLi‐SitBu₃ can be cleanly prepared from precursor silylamine Et₂SiCl‐NH‐SitBu₃ and Li[nBu]. The CF₃SO₃SiMe₃ induced LiCl elimination of Et₂SiCl‐NLi‐SitBu₃ in thf afforded a 2‐silaazetidine derivative by [2+2] cycloaddition of Et₂Si=N–SitBu₃ with Et₂Si(OCH=CH₂)–NH–SitBu₃. X‐ray quality crystals of this 2‐silaazetidine derivative (triclinic, space group P$\bar{1}$ ) were grown from benzene at room temperature. The starting material for this approach, Et₂SiCl–NH–SitBu₃, is water‐sensitive. Hydrolysis of Et₂SiCl‐NH‐SitBu₃ gave [tBu₃SiNH₃]Cl along with (Et₂SiO)_n oligomers. The hydro chloride [tBu₃SiNH₃]Cl could be isolated and was characterized by X‐ray crystallography (trigonal, space group P$\bar{3}$ ).     

Synthesis and Characterization of Poly(vinyl Chloride-g-α-Methylstyrene)- A New Thermoplastic Resin. 2

α-Methylstyrene was grafted on PVC using alkylaluminum Et₂AlCl, Et₃Al, and Me₃Al coinitiators and CH₂Cl₂ as solvent or suspending agent. Grafting was shown to be feasible using both solution and suspension techniques. High grafting efficiency and low monomer conversion were obtained using Et₃Al and Me₃Al, while low grafting efficiency but high conversion could be obtained using Et₃AlCl coinitiator. This paper discusses the synthesis, characterization and some mechanical properties of α-methyl-styrene grafted PVC.     

Cation-anion interactions in [Mo<Subscript>3</Subscript>S<Subscript>7</Subscript>(Et<Subscript>2</Subscript>dtc)<Subscript>3</Subscript>](Et<Subscript>2</Subscript>dtc) solutions

Quantum chemical calculations of the [Mo₃S₇(Et₂dtc)₃](Et₂dtc) complex in different solvents are performed. It is shown that the binding energy between the cluster [Mo₃S₇(Et₂dtc)₃]⁺ cation and the outersphere (Et₂dtc)^? anion exponentially decreases with increase in the solvent dielectric permittivity. By DOSY NMR it is determined that in chloroform, the cationic and anionic moieties of the complex form an associate (contact ion pair), while in strongly polar dimethyl sulfoxide these moieties move independently of one another.     

[{ReN(Me2PhP)(Et2dtc)Cl}2{ReN(Et22tc)2}2{SbCl3}2] — ein neuer vierkerniger Rheniumkomplex mit asymmetrischen Nitridobrücken

[{ReN(Me₂PhP)(Et₂dtc)Cl}₂{ReN(Et₂dtc)₂}₂{SbCl₃}₂] — a Novel Tetranuclear Rhenium Complex with Asymmetric Nitrido Bridges The reaction of [ReN(Et₂dtc)₂(Me2₂hP)] (Me₂PhP = dimethylphenylphosphine, Et₂dtc^‐ = diethyldithiocarbamate) with SbCl₃ in dichloromethane results in the formation of [{ReN(Me₂PhP)(Et2₂tc)Cl}₂{ReN(Et₂dtc)₂}₂{SbCl₃}₂]. A {Re≡N‐}₄ ring with asymmetric nitrido bridges is stabilised by the co‐ordination of SbCl₃ onto the chloro ligands and sulphur atoms of the dithiocarbamates. The compound decomposes upon heating in acetonitrile and the fragments of the tetrameric complex re‐arrange to form [ReN‐(Me₂PhP)(Et₂dtc)Cl]₄ and [ReN(Et₂dtc)₂]. The multinuclear rhenium compounds have been studied by X‐ray crystallography. The 8‐membered {Re≡N‐}₄ ring system in [{ReN(Me₂PhP)(Et₂dtc)Cl}2₂ReN(Et₂dtc)₂}₂{SbCl₃}₂] is almost planar, while that of [ReN(Me₂PhP)(Et₂dtc)Cl]₄ is clearly V‐shaped when viewed down either diagonal Re…Re axis. A dihedral angle of 47.88(2)° has been found between the contributing planes.     

枸橼酸二乙酯、枸橼酸钠和膦甲酸钠对高钙诱导小鼠血管平滑肌细胞钙化的抑制

在高钙及不同浓度枸橼酸二乙酯（Et₂Cit）、枸橼酸钠（Na₃Cit）和膦甲酸钠（PFA）存在下培养小鼠血管平滑肌细胞（MOVAS）14 d，分别通过茜素红染色、免疫荧光和annexin V染色检测细胞的分化、凋亡和细胞钙沉积量，研究了Et₂Cit、Na₃Cit和PFA对高钙诱导MOVAS细胞钙化的抑制效果及可能的作用机制。结果表明，Et₂Cit、Na₃Cit和PFA均能减少高钙诱导的MOVAS钙化，减少细胞外钙化斑块和钙沉积量。这些抑制剂均能抑制平滑肌细胞向成骨样细胞表型转化，导致向成骨细胞转化的标记物碱性磷酸酶（ALP）活性降低。抑制效果均存在浓度依赖性。当抑制剂浓度相同时，其抑制效果从大到小为：PFA > Na₃Cit > Et₂Cit。低浓度的Et₂Cit和Na₃Cit可通过减少细胞凋亡来抑制钙化，但高浓度的Et₂Cit、Na₃Cit和PFA自身具有毒性，这增加了细胞的凋亡。作为血液抗凝剂的Et₂Cit和Na₃Cit可以有效地抑制MOVAS的钙化。     

Influence of electrolyte characteristics on the electrochemical parameters of electrical double layer capacitors

Electrical double layer capacitors based on ideally polarizable nanoporous carbon electrodes in propylene carbonate with the addition of different 1 M Me₃EtNBF₄, Me₂Et₂NBF₄, MeEt₃NBF₄, Et₄NBF₄, Et₃PrNBF₄ and Et₃BuNBF₄ electrolytes have been tested by cyclic voltammetry, chronoamperometry and electrochemical impedance methods. The limits of ideal polarizability, low-frequency limiting capacitance and series resistance, time constant, Ragone plots (energy density vs. power density dependencies) and other characteristics have been discussed. The influence of the electrolyte molar mass on the electrochemical characteristics of the nanoporous carbon electrode cells has been established. The applicability limits of the Srinivasan and Weidner model have been tested.