Ruthenium-catalyzed tandem cross-metathesis/Wittig olefination: generation of conjugated dienoic esters from terminal olefins

[reaction: see text] In the presence of ruthenium-based olefin metathesis catalysts and triphenylphosphine, alpha,beta-unsaturated aldehydes can be olefinated with diazoacetates. This ruthenium-catalyzed transformation has been employed in tandem with olefin cross-metathesis to convert terminal olefins into 1,3-dienoic esters in a single operation.     

Improved hydrogen generation from formic acid

The ruthenium-catalyzed generation of hydrogen from formic acid was investigated in the presence of amines and halide additives. While amidines and halide additives increase the production of hydrogen with [RuCl₂(p-cymene)]₂, >330 mL hydrogen/h is generated in the presence of [RuCl₂(benzene)]₂/dppe and N,N-dimethyl-n-hexylamine.     

iso-PsE, a new pseudopterosin

We describe the discovery of a new member of the pseudopterosin class of marine natural products. Its structure is isomeric with that of pseudopterosin E and has therefore been given the name iso-PsE.     

Polyoxometalates-engineered hydrogen generation rate and durability of Pt/CNT catalysts from ammonia borane

Heterogeneously catalyzed hydrolytic dehydrogenation of ammonia borane is a remarkable structure sensitive reaction. In this work, a strategy by using polyoxometalates(POMs) as the ligands is proposed to engineer the surface and electronic properties of Pt/CNT catalysts toward the enhanced hydrogen generation rate and durability. Three kinds of POMs, i.e., silicotungstic acid(STA), phosphotungstic acid(PTA)and molybdophosphoric acid(PMA), are comparatively studied, among which the STA shows positive effects on the catalytic activity and durability. A catalyst structure-performance relationship is established by a combination of kinetic and isotopic analyses with multiple characterization techniques, such as HAADF-STEM, EDS, Raman spectroscopy and XPS. It is shown that the STA compared to the other two POMs can increase the Pt binding energy and thus promote the reaction. The insights demonstrated here could open a new avenue for boosting the reaction by employing the POMs as the ligands to engineer the catalyst electronic properties.     

连续式超临界水反应器中褐煤制氢过程影响因素的研究

建立了煤处理量为1kg/h的连续式超临界水反应装置并实现稳定运行,考察了反应温度（500℃～650℃）、反应压力(20MPa～30MPa)、水煤浆浓度(20%~50％)以及KOH添加量对小龙潭褐煤在超临界水中连续化制氢的影响。实验结果表明,反应进行20min后连续装置达到稳定运行状态。反应温度和KOH添加量是影响超临界水中褐煤制氢的关键因素。随着反应温度从500℃提高到650℃,氢气的体积分数与产率分别由11%和25mL/g增加到29%和110mL/g。添加0.5%KOH可明显提高碳气化率以及氢气的产率,但随着KOH加入量进一步增加,氢气产率增加的幅度减小。随着压力增加,甲烷产率有升高的趋势,氢气产率变化不大,提高水煤浆的浓度,碳气化率降低。     

光催化分解水制氢研究新进展

众所周知化石燃料储量有限,而经济的高速发展带来的能源的快速消耗最终会使这些有限的资源消耗殆尽.人们期望通过提高替代能源,包括生物质能、风能和太阳能在内的可再生能源在整个能源结构中的比例,缓解这种危机和压力.实际上,只要我们能够利用辐射到地球表面上太阳能的一小部分,就可以满足我们目前的能源消耗.用太阳能从水中制氢是最吸引人的一条太阳能利用与储存路线.我们的地球3/4的区域被水覆盖,其中蕴藏着丰富的氢源.氢能以其清洁、无污染、热值高且贮存和运输方便而被视为最理想的替代能源,同时氢气又是现代化学工业最基础的原料.1972…     

Biological generation of hydrogen

Microorganisms are capable of evolving hydrogen. Such microbiologic processes can be divided into dark anaerobic hydrogen evolution, light-dependent hydrogen evolution without oxygen evolution, and light-dependent hydrogen evolution accompanied oxygen evolution (biophitolysis). The review describes recent advances in biohydrogen production from whole-cell microorganisms.     

Ruthenium-catalyzed reduction of N-alkoxy- and N-hydroxyamides

A ruthenium-catalyzed reduction of N-alkoxy- and N-hydroxyamides was found to afford corresponding amides in good to high yields. A simple RuCl₃/Zn-Cu/alcohol system, without the addition of any other ligands, exhibited a high catalytic activity, and therefore the present reaction does not require a stoichiometric amount of metals or metal complexes as reductants. When β-substituted-α,β-unsaturated N-methoxyamides were employed as substrates, concurrent hydrogenation of the olefin moiety proceeded slowly with deprotection of the methoxy group. In the reduction of N-hydroxyamides, the alcoholic solvent was found to function as a hydrogen donor.     

Expeditious synthesis of 1,1-diarylethylenes related to isocombretastatin A-4 (isoCA-4) via palladium-catalyzed arylation of N-tosylhydrazones with aryl triflates

A quick and efficient entry to 1,1-diarylethylenes via the reaction of polyoxygenated aryl N-tosylhydrazones with aryl triflates is described. The reaction employs the catalytic system Pd(OAc)₂/XPhos, tBuOLi as the base and dioxane as the solvent. A variety of substituents on both the coupling partners’ hydrazones and triflates are tolerated. This procedure provides a complementary route to the existing methods for the access to 1,1-diarylethylenes of biological interest.     

Noble-metal-free bimetallic nanoparticle-catalyzed selective hydrogen generation from hydrous hydrazine for chemical hydrogen storage

Noble-metal-free nickel-iron alloy nanoparticles exhibit excellent catalytic performance for the complete decomposition of hydrous hydrazine, for which the NiFe nanocatalyst, with equimolar compositions of Ni and Fe, shows 100% hydrogen selectivity in basic solution (0.5 M NaOH) at 343 K. The development of low-cost and high-performance catalysts may encourage the effective application of hydrous hydrazine as a promising hydrogen storage material.     

Efficient total synthesis of iso-cladospolide B and cladospolide B

An efficient synthesis of iso-cladospolide B and cladospolide B has been achieved using Jacobsen’s hydrolytic kinetic resolution (HKR), Sharpless asymmetric dihydroxylation and Yamaguchi macrolactonization as the key steps.     

Thermochemical solar hydrogen generation

Solar direct, indirect and hybrid thermochemical processes are presented for the generation of hydrogen and compared to alternate solar hydrogen processes. A hybrid solar thermal/electrochemical process combines efficient photovoltaics and concentrated excess sub-bandgap heat into highly efficient elevated temperature solar electrolysis of water and generation of H2 fuel utilizing the thermodynamic temperature induced decrease of E(H2O) with increasing temperature. Theory and experiment is presented for this process using semiconductor bandgap restrictions and combining photodriven charge transfer, with excess sub-bandgap insolation to lower the water potential, and their combination into highly efficient solar generation of H2 is attainable. Fundamental water thermodynamics and solar photosensitizer constraints determine solar energy to hydrogen fuel conversion efficiencies in the 50% range over a wide range of insolation, temperature, pressure and photosensitizer bandgap conditions.     

Complex formation equilibria between Ag(I) and thioureas in n-propanol

Complex formation equilibria between Ag(I) and thiourea or N-alkyl-substituted thioureas have been investigated in n-propanol by potentiometry at 10 °C intervals from 5 to 50 °C. Stepwise formation of tris-coordinated AgL_n (n = 1-3) complexes has been found for the majority of the ligands. ΔH and ΔS values for the complex formation reactions have been evaluated from the dependence of ln β_n on temperature. The alkyl-substituents affect the ligand affinities in different ways in relation with the coordination level n.The reactions are exothermic with few exceptions. Enthalpy favoured complex formation with negative dependence of ΔG on temperature (ΔS > 0) have been found.The enthalpy and entropy changes for the stepwise complex formation equilibria are correlated by two linear compensative relationships with the same isoequilibrium temperature 50-51 °C.     

Supercritical thermal decompositions of normal- and iso-dodecane in tubular reactor

Thermal decompositions of a serials of normal- and iso-dodecane mixtures with different iso/normal ratios were performed in a tubular reactor under supercritical conditions (550-680 °C, 4.0 MPa). It was found that iso-dodecane has an accelerating effect on the pyrolysis of n-dodecane depending upon iso/normal ratio of the mixture, and that accelerating factor reaches up to almost 4 at iso/normal ratio of 3/1. Decomposition conversions of the mixtures show a strong dependence on the iso/normal ratio and the temperature owing to their possible effect on the radical generation mechanism and the decomposition kinetics. In addition, iso/normal ratio of the mixture also affects the formation rates and morphologies of cokes due to the variation of decomposition conversion.     

Ruthenium-catalyzed tertiary amine formation from nitroarenes and alcohols

A highly selective ruthenium-catalyzed C-N bond formation was developed by using the hydrogen-borrowing strategy. Various tertiary amines were obtained efficiently from nitroarenes and primary alcohols. The reaction tolerates a wide range of functionalities. A tentative mechanism was proposed for this direct amination reaction of alcohols with nitroarenes.     

Spectroscopic characterization of the oxidation control of the iso-pentaphyrin/pentaphyrin system

We have recently described the synthesis of two porphyrogenic macrocycles: 20-phenyl-2,13-dimethyl-3,7,8,12-tetraethyl-[24]iso-pentaphyrin (1) and 20-phenyl-2,13-dimethyl-3,7,8,12-tetraethyl-[22]pentaphyrin (2) (J. Med. Chem.2006, 49, 196-204). We found that the structure of iso-pentaphyrin is influenced by the acidity of the medium. By adjusting the TFA concentration, we solved two isomers of iso-pentaphyrin: 1 and 1A. At high TFA concentration iso-pentaphyrin is present only as 1, which is slowly oxidized into the aromatic macrocycle 2 upon exposure to air. The correlation between acidic conditions, isomer structures, and oxidation is discussed.     

Syntheses of aza-analogous iso-ergoline scaffolds using carbene mediated C-H insertion

A novel direct, flexible, and robust approach to the iso-ergoline tetracyclic system in which a five or six-membered ring is established by intramolecular carbene C-H insertion is reported. The protocol involves a two step conversion of an aromatic aldehyde to the corresponding hydrazone and without purification further conversion to the diazo-compound followed by thermal carbene formation and C-H insertion α to a nitrogen.     

Novel improved ruthenium catalysts for the generation of hydrogen from alcohols

The dehydrogenation reaction of alcohols to generate hydrogen at ambient conditions has been studied, it is shown for the first time that ruthenium in the presence of easily available amine ligands constitutes an active catalysts for this reaction: high turnover frequencies (TOF) up to 519 h(-1) (after 2 h) and catalyst stability (>250 h) were achieved for the dehydrogenation of isopropanol with a combination of [RuCl2(p-cymene)]2/TMEDA.