Thiiranium Ions as Reaction Intermediates

The addition of sulfenvl chlorides or sulfur dichloride to unsaturated compounds proceeds via thiiranium ions. The present article reviews the electronic and steric factors influencing the nature of these ions and their effects on subsequent ring opening and product formation. For the purpose of this discussion results primarily from electrophilic ring opening have been chosen to illustrate these factors. Solvent and temperature effects have been disregarded.     

Addition Reactions of Sulfenyl and Sulfinyl Chlorides with 3‐Phenyl‐1‐azabicyclo[1.1.0]butane

The reactions of 3‐phenyl‐1‐azabicyclo[1.1.0]butane with α‐chlorosulfenyl chlorides and sulfinyl chlorides lead to the corresponding sulfenamides and sulfinamides, respectively, which possess an azetidine ring. It is proposed that a two‐step mechanism occurs involving an intermediate carbenium ion, which is formed by the addition of the electrophile at the N‐atom and cleavage of the N(1)? C(3) bond. The structures of 9b and 10b are established by X‐ray crystallography.     

Overview: The Potential of silanes for chromate replacement in metal finishing industries

Trialkoxysilanes (or silanes) have emerged as a very promising alternative for chromates in metal finishing industries. Compared to the conventional chromating processes, the major merits of silane-based surface treatments include: eco-compliance, easy-control processing, comparable corrosion protection of metals as well as paint adhesion to a variety of topcoats. In this overview paper, we report the recent status of silane studies including results of corrosion performance tests, the mechanism of corrosion protection of metals by silanes and the themal stabilities of silane films. We also address the new fields that we are beginning to explore such as nano-structured silane films, “self-healing” silane films, and “super-primers”.     

Facile synthesis and reactions of some olefin-substituted acetylacetonate complexes

Synthesis of transition metal complexes of olefin-substituted acetylacetones has been effected by reaction of nonaqueous solutions of substituted acetylacetones with the metal salt in the presence of Zn or Mg. 3-Allylacetylacetonates of Be(II), Cu(II), Ni(II), Fe(III), Co(II), Pd(II) and Zn(II) have thus been synthesized in quantitative yields. 3-Propylideneacetylacetone, which exists mainly in the keto form, afforded the corresponding 3-propenylacetylacetonates in which 3-propylideneacetylacetone has rearranged to 3-propenylacetylacetone which has a greater probability of existing in the enol form, thus making its reaction with metal ions favorable. Metal–metal exchange reactions of transition metal salts with olefin-substituted Zn or Mg acetylacetonates provide yet another route for the synthesis of transition metal olefin-substituted acetylacetonates. The homogeneous catalytic hydrogenation of the olefin moiety in olefin-substituted metal acetylacetonates could be achieved by a Pt/Sn catalyst.     

Studies of adsorption and solution of acetylacetonates of Cr(III), Co(III) and Al(III) by gas chromatography

Summary Specific retention volumes, adsorption isotherms, molar heats of solution and changes of the entropy were determined from chromatographic data, which was obtained by the gas chromatographic separation of metal acetylacetonates. The retention data for Cr(III), Co(III) and Al(III) acetylacetonates were measured at different temperatures and different flow rates. From the retention data other values associated with adsorption and solution phenomena were calculated.     

Combination of transition metal carbonyls and silanes: New photoinitiating systems

The recently developed silyl radical chemistry is used in combination with transition metal carbonyls MC (dimanganese(0) decacarbonyl; dirhenium decacarbonyl; cyclopentadienyl iron(II) dicarbonyl dimer) for both free radical promoted cationic photopolymerization (FRPCP) and free radical photopolymerization (FRP). The newly developed photoinitiating systems (MC/silane and MC/silane/iodonium salt) are highly efficient under air. Photopolymerization profiles obtained upon a visible light irradiation delivered by a xenon lamp show that high conversion can be easily achieved after a 400 s exposure. Sunlight irradiations under air can also lead to tack free coatings. The processes associated with the metal carbonyl radical/silane interactions are investigated by Laser Flash Photolysis (LFP) and ESR‐Spin Trapping (ESR‐ST) experiments. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1830–1837, 2010     

Rapid conversion of cellulose to 5-hydroxymethylfurfural using single and combined metal chloride catalysts in ionic liquid

Direct conversion of cellulose into 5-hydroxymethylfurfural(HMF) was performed by using single or combined metal chloride catalysts in 1-ethyl-3-methylimidazolium chloride(Cl) ionic liquid.Our study demonstrated formation of 2-furyl hydroxymethyl ketone(FHMK),and furfural(FF) simultaneously with the formation of HMF.Various reaction parameters were addressed to optimize yields of furan derivatives produced from cellulose by varying reaction temperature,time,and the type of metal chloride catalyst.Catalytic reaction by using FeCl3 resulted in 59.9% total yield of furan derivatives(HMF,FHMK,and FF) from cellulose.CrCl3 was the most effective catalyst for selective conversion of cellulose into HMF(35.6%) with less concentrations of FHMK,and FF.Improving the yields of furans produced from cellulose could be achieved via reactions catalyzed by different combinations of two metal chlorides.Further optimization was carried out to produce total furans yield 75.9% by using FeCl3/CuCl2 combination.CrCl3/CuCl2 was the most selective combination to convert cellulose into HMF(39.9%) with total yield(63.8%) of furans produced from the reaction.The temperature and time of the catalytic reaction played an important role in cellulose conversion,and the yields of products.Increasing the reaction temperature could enhance the cellulose conversion and HMF yield for short reaction time intervals(5~20 min).     

A comparative study of the bond strengths of the second row transition metal hydrides,fluorides, and chlorides

Summary Correlated calculations have been performed for the diatomic second row transition metal hydrides, fluorides, and chlorides. The ground states have been determined for the entire second row from yttrium to palladium. It is found that the halide binding energies vary much more across the row than the hydride binding energies. The results are analyzed in terms of ionic and covalent contributions to the bonding. The two main factors responsible for the large variation of the halide binding energies are differences in ionization energies and differences in the interactions between the halide lone-pairs and the metal 4d-orbitals for the atoms to the left and to the right. To the left the lone-pair interaction is attractive through electron donation to empty 4d-orbitals, whereas to the right the interaction is repulsive.     

Synthesis of Functional Monosilanes by Disilane Cleavage with Phosphonium Chlorides

The Müller–Rochow direct process (DP) for the large-scale production of methylchlorosilanes Me_nSiCl_4−n (n=1–3) generates a disilane residue (Me_nSi₂Cl_6−n, n=1–6, DPR) in thousands of tons annually. This report is on methylchlorodisilane cleavage reactions with use of phosphonium chlorides as the cleavage catalysts and reaction partners to preferably obtain bifunctional monosilanes Me_xSiH_yCl_z (x=2, y=z=1; x,y=1, z=2; x=z=1, y=2). Product formation is controlled by the reaction temperature, the amount of phosphonium chloride employed, the choice of substituents at the phosphorus atom, and optionally by the presence of hydrogen chloride, dissolved in ethers, in the reaction mixture. Replacement of chloro by hydrido substituents at the disilane backbone strongly increases the overall efficiency of disilane cleavage, which allows nearly quantitative silane monomer formation under comparably moderate conditions. This efficient workup of the DPR thus not only increases the economic value of the DP, but also minimizes environmental pollution.     

Reactions of dodecamethylcyclohexasilane and polydimethylsilane with metal chlorides

The reactions of dodecamethylcyclohexasilane and high-molecular-weight polydimethylsilane with chlorides of I, II, IV-VI and VIII Group metals at high temperature in the absence of a solvent were studied. The interaction of (Me₂Si)₆ with metal chlorides proceeds with the cleavage of SiSi and SiC bonds with the formation of chloro derivatives of linear and cyclic permethyloligosilanes. The reactions of polydimethylsilane with metal chlorides afford mixtures of α,ω-dichlorooligosilanes, Cl(Me₂Si)_nCl (n=2-9). The influence of the reaction conditions (temperature, reaction time and the reagent ratio) on the composition and yields of the reaction products was examined.     

Capillary gas chromatography of some metal acetylacetonates

Summary The retention and resolution of simple mixture of Al(III), Cr(III), Co(III), and Fe(III) acetylacetonates were investigated on capillary columns coated with methyl and methyl phenyl silicones (OV-1 or OV-17) used as the stationary phase, at different column temperatures and carrier gas flow rates. Successful elution and good resolution were obtained only for the Al(III) and Cr(III) complexes, both under isothermal and programmed-temperature conditions; better resolution was observed on the column coated with OV 17.     

Syntheses of Transition Metal Complexes of Pentafluorophenylhydrazine

By reaction of pentafluorophenylhydrazine with metal chlorides the complexes M(NH₂NHC₆F₅)₄Cl₂ (M = Co, Ni), M(NH₂NHC₆F₅)₂Cl₂ (M = Mn, Fe, Pd, Zn, Cd), Cu(NH₂NHC₆F₅)Cl, and Hg(NH₂NHC₆F₅)₂Cl were obtained. From Cr(CO)₆ and pentafluorophenylhydrazine the complex Cr(CO)₅(NH₂NHC₆F₅) was synthesized.     

Methane conversion by various metal, metal oxide and metal carbide catalysts

The progress in the field of methane conversion into higher hydrocarbons including aromatics and oxygenated compounds in the recent five years will be reviewed shortly, together with a new type of the methane conversion reaction with carbon monoxide at lower temperatures (600–700 K) by supported group VIII metal catalysts. Benzene was formed selectively among hydrocarbons in the CH₄–CO reaction over silica-supported Rh, Ru, Pd and Os catalysts under atmospheric pressure. Both CH₄ and CO were required for benzene formation, and only ethane and ethylene were formed besides benzene. The amount of C₃–C₅ hydrocarbons was negligible, which suggests that a completely different mechanism from the CO–H₂ reaction may be operating over these catalysts despite of the similarity in the reaction conditions with the CO–H₂ reaction. The mechanism of benzene formation was studied deeply by means of kinetical investigation as well as infrared spectroscopy and isotopic tracer method in connection with that of CO hydrogenation.     

Catalytic synthesis of carbon nanotubes over ordered mesoporous matrices

Pyrolytic decomposition of acetylene over the surface of nickel-, cobalt- and iron-containing ordered mesoporous MCM-41 silicas has been studied. Catalytically active matrices have been prepared by chemisorption of volatile metal acetylacetonate complexes on the silica surface. Reduction of the supported metal-containing compounds was carried out in hydrogen or acetylene atmosphere. Acetylene is used not only as a source of carbon in synthesis of the nanostructures but also as a reagent capable of reducing metal ions in the surface chemical compounds. Formation of carbon nanotubes and nanofibers is shown to depend on the pyrolysis conditions.     

热电池正极材料的研究进展

热电池是一种热激活贮备式电池,由于其优良的贮存稳定性、放电可靠性等特点,广泛应用于多种军用武器的内部电源。为了满足当前不同军用武器装备的需求,热电池的发展趋于在提高电化学性能的同时实现小型化、微型化。热电池电化学性能的提高主要取决于正极材料的发展,目前对现有正极材料的优化改性和新型正极材料的开发是提高热电池性能的主要方法。本文从合成和改性方法的角度综述了近年来硫化物、氯化物、氟化物热电池正极材料的研究进展,并对其材料特性和放电性能进行了综合评估。最后,基于热电池特殊的应用场景,从热稳定性、放电电压、电导率等方面对热电池正极材料未来的发展方向进行了总结与展望。     

Triboluminescence of lanthanide acetylacetonates

Triboluminescence of Ln(acac)₃·H₂O (Ln = Tb, Eu, Pr, Ce, Gd) was found. The UV radiation was detected for the first time as narrow bands caused by the emission of the adsorbed N₂* molecules (transitions ³∏_u → ³∏_g) in the study of triboluminescence of lanthanide compounds. The emission of Ln³⁺* (ionic triboluminescence) was observed only for Tb³⁺* (λ_max/nm: 490 (⁵D₄-⁷F₆), 545 (⁵D₄-⁷F₅), 580 (⁵D₄-⁷F₄)) and Eu³⁺* (λ?max/nm: 613, 614 (⁵D₂-⁷F₃)). The generation of N₂* occurs due to the energy of electric fields appeared upon the destruction of crystalline samples of Ln(acac)₃·H₂O. The Tb³⁺* and Eu³⁺* ions are formed due to the energy transfer from the triplet level of the ligand (acacT₁), which is excited by the light emitted from the N₂* molecule.     

新型B(C6F5)3/有机胺盐酸盐催化体系的反应研究

近年来, 受限路易斯酸碱对(FLPs: Frustrated Lewis Pairs)在小分子的活化以及在催化还原等方面所表现出的独特反应特性, 使得有关FLPs化学的研究受到了国内外广泛的关注. 设计了一种新型的FLPs催化体系, 该体系以三(五氟苯基)硼(BCF)为路易斯酸, 以多种不同取代的有机胺盐酸盐替代常规FLPs中的路易斯碱有机胺. 发现利用该体系与氢化硅烷反应, 不仅可以高产率地制备分离得到相应的伯、仲、叔硼氢化胺盐; 而且还可以这一体系作为催化剂, 以氢化硅烷作为还原剂, 在常温常压下可高选择性地部分或彻底还原大部分含羰基官能团醛酮等有机化合物. 由BCF/2,2,6,6-四甲基哌啶(TMP)盐酸盐组成的催化体系在对CO₂催化还原为甲烷的反应中, 亦较相应的BCF/TMP体系显示更高的活性. 还通过核磁共振详细地对比研究了原料有机胺盐酸盐、中间体氯代硼胺盐以及产物氢化硼胺盐中, 胺基氮上质子的核磁共振谱信息, 发现不仅胺基上取代基的位阻效应会影响到具有电四极矩性的¹⁴N磁性核的弛豫效应, 而且阴离子基团的配位强弱对胺基氮上质子的化学位移也会产生较大的影响.     

The stokes and robinson hydration theory: A modification with application to concentrated electrolyte solutions

The proposed extension to the Stokes and Robinson hydration theory is based on the premise that H₂O molecules of electrolyte solutions reside in two unique environments, the solvent environment and the hydration envelope (or sheath) environment. Changes to the chemical potential of H₂O in either environment result in redistribution of H₂O molecules between the environments; consequently hydration numbers of electrolytes decrease as the solvent activity decreases. An equation derived from the theory and containing two adjustable parameters reproduces electrolyte activity coefficients more accurately than does the original Stokes and Robinson equation.     

Regiodivergent and Stereoselective Hydrosilylation of 1,3‐Disubstituted Allenes

Methods for the highly stereoselective and regiodivergent hydrosilylation of 1,3‐disubstituted allenes have been developed. The synthesis of E allylsilanes is accomplished with palladium NHC catalysts, and trisubstituted Z alkenylsilanes are accessed with nickel NHC catalysts. Unsymmetrically substituted allenes are well tolerated with nickel catalysis and afford Z alkenylsilanes. Evidence for a plausible mechanism was obtained through an isotopic double‐labeling crossover study.