Palladium-catalysed dimerization of vinylarenes using indium triflate as an effective co-catalyst

A palladium-indium triflate catalyst was found to be much more active for the dimerization of vinylarenes compared with generally used cationic palladium(II) catalysts.     

Photophysical and (photo)electrochemical properties of a coumarin dye

A new coumarin dye, cyano-{5,5-dimethyl-3-[2-(1,1,6,6-tetramethyl-10-oxo-2,3,5,6-tetrahydro-1H,4H,10H-11-oxa-3a-aza-benzo[de]anthracen-9-yl)vinyl]cyclohex-2-enylidene}-acetic acid (NKX-2753), was prepared and characterized with respect to photophysical and electrochemical properties. It was employed as a dye sensitizer in dye-sensitized solar cells and showed efficient photon-to-electron conversion properties. The photocurrent action spectrum exhibited a broad feature with a maximum incident photon-to-electron conversion efficiency (IPCE) of 84% at 540 nm, which is comparable to that for the famous red dye RuL2(NCS)2 (known as N3), where L stands for 2,2'-bipyridyl-4,4'-dicarboxylic acid. The sandwich-type solar cell with NKX-2753, under illumination of full sun (AM1.5, 100 mW cm(-2)), produced 16.1 mA cm(-2) of short-circuit photocurrent, 0.60 V of open-circuit photovoltage, and 0.69 of fill factor, corresponding to 6.7% of overall energy conversion efficiency using 0.1 M LiI, 0.05 M I2, 0.1 M guanidinium thiocyanate, and 0.6 M 1,2-dimethyl-3-n-propyl-imidazolium iodide in dry acetonitrile as redox electrolyte. In comparison with its analogue NKX-2586 (Langmuir 2004, 20, 4205), NKX-2753 with an extra side ring on the alkene chain produced much higher IPCE values at the same conditions. The side ring acted as a spacer to efficiently prevent dye aggregation when adsorbed on the TiO2 surface, resulting in significant improvements of short-circuit photocurrent, open-circuit photovoltage, and fill factor compared with NKX-2586 that aggregated on the TiO2 surface.     

Thermal behavior of ternary Sm2Fe17Nx magnets

The Mössbauer spectra of Sm₂Fe₁₇N_x, prepared by the nitrogenation of Sm₂Fe₁₇ powders in an ammonia and hydrogen atmosphere, were observed at elevated temperatures to shed light on the thermal behavior of nitrogen in the compounds Sm₂Fe₁₇N_x. It was found that there were large differences in thermal behavior between the starting Sm₂Fe₁₇, crystalline Sm₂Fe₁₇N_x (x≈1.7) and amorphous Sm₂Fe₁₇N_x(x～7). The thermal decomposition behavior of Sm₂Fe₁₇N_3.2, developed as one of the most promising hard magnetic materials, was found to be different under different atmospheres.     

Highly diastereoselective chemoenzymatic synthesis of (2′R)- and (2′S)-2′-deoxy[2′-H]guanosines

In an effort to develop an efficient synthetic method of highly diastereoselective (2′R)- and (2′S)-2′-deoxy[2′-²H]guanosines, chemoenzymatic conversion was investigated. The synthesis of (2′R > 98% de)-2′-deoxy[2′-²H]guanosine was achieved by biological transdeoxyribosylation using (2′R > 98% de)-2′-deoxy[2′-²H]uridine, 2,6-diaminopurine, and Enterobacter aerogenes AJ-11125, followed by treatment with adenosine deaminase. (2′S > 98% de)-2′-Deoxy[2′-²H]guanosine was synthesized from (2′S > 98% de)-2′-deoxy[2′-²H]uridine and 2,6-diaminopurine using thymidine phosphorylase and purine nucleoside phosphorylase instead of E. aerogenes AJ-11125.     

all-Z-Tetrabenzo

Crystal structures of the silver complexes derived from tetrabenzo[16]annulene with AgOTf and AgClO(4) are different, although these two complexes show similar (1)H NMR spectra reflecting a similar clathrate structure in solution. The silver complex of pentabenzo[20]annulene with AgClO(4) adopts a clathrate structure both in the solid state and in solution.     

Stereoselective synthesis of (Z)-2-fluoro-1-alkenyl(phenyl)iodonium tetrafluoroborates

[reaction: see text] (Z)-2-Fluoro-1-alkenyl(phenyl)iodonium salts were stereoselectively prepared by the reaction of alkynyl(phenyl)iodonium salts with aqueous HF in good yields. The method is applicable to the synthesis of fluoroalkenyliodonium salts having functional groups such as ketone, ester, and chloride. (Z)-2-Fluoro-1-alkene, (Z)-2-fluoro-2-alkenoate, and (Z)-beta-fluoroenyne could be stereoselectively prepared from the fluoroalkenyliodonium salt.     

An iron reservoir model based on ferrichrome: iron(III)-binding and metal(III)-exchange properties of tripodal monotopic and ditopic hydroxamate ligands with an L-alanyl-L-alanyl-N-hydroxy-beta-alanyl sequence

To gain knowledge about biological iron mobilization, tripodal monotopic and ditopic hydroxamate ligands (1 and 2) are prepared, and their iron-chelating properties are investigated. Ligands 1 and 2 contain three Ala-Ala-beta-(HO)Ala units and three [Ala-Ala-beta-(HO)Ala](2) units connected with tris(alanylaminoethyl)amine, respectively, and form six-coordinate octahedral complexes with iron(III) in aqueous solution. Ligand 1 and 1 equiv of iron give Fe-1, and ligand 2 and 1 or 2 equiv of iron produce Fe(1)-2, or Fe(2)-2. These complexes exhibit absorptions at lambda(max) 425 nm of epsilon 2800-3000/Fe, characteristic of tris(hydroxamato)iron(III) complexes, and preferentially assume the Delta-cis configuration. Loading of Fe(III) on 1, 2, and M(III)-loaded ligands (M-1 and M(1)-2, M = Al, Ga, In) with ammonium ferric oxalate at pH 5.4 is performed, and the second-order rate constants of loading with respect to Fe(III) and the ligand or M(III)-loaded ligands are determined. The rates of loading of Fe(III) on M-1 increase in the order Al-1 < Ga-1 < In-1, and those on M(1)-2 in the order Al(1)-2 < Ga(1)-2 < Fe(1)-2 < In(1)-2, indicating that the dissociation tendency of M(III) ions from the hydroxamate ligand is an important factor. The iron complexes formed with 2 are subjected to an iron removal reaction with excess EDTA in aqueous pH 5.4 solution at 25.0 degrees C, and the collected data are analyzed by curve-fitting using appropriate first-order kinetic equations, providing the rate constants for the upper site and the lower site of 2. Similar analysis for FeM-2 affords removal rate constants for Fe(up)-2, M(up)-2, and Fe(low)-2, and the iron residence probability at each site. The protonation constants of the hydroxamate groups for 1 and 2 (pK(1,) pK(2), pK(3), and pK(1,) pK(2)., pK(6)) are determined, and the proton-independent stability constants for Fe-1, the upper site of Fe(2)-2, and the lower site of Fe(1)-2 are 10(28), 10(29), and 10(28.5), respectively.     

Polyhydrazides. III. N-methylated polyhydrazides by ring-opening of poly-p-phenylene-1,3,4-oxadiazole

A new ring-opening reaction of 1,3,4-oxadiazole by methylating reagents was developed in fuming sulfuric acid or polyphosphoric acid and then, by applying this reaction to poly-p-phenylene-1,3,4-oxadiazole, a high molecular weight poly-N-methylterephthalylhydrazide was obtained. Various methylating reagents were investigated as ring-opening reagents. The degrees of ring-opening in polymers were estimated and related to the properties of the polymers.     

Palladium(0)-catalyzed stereoselective cyclization of allenenes: divergent synthesis of pyrrolidines and 3-azabicyclo[3.1.0]hexanes from single allenenes

Two novel palladium(0)-catalyzed cyclizations of allenenes are described. Treatment of allenenes such as N-(1-alkyl-2,3-butadienyl)-N-allylsulfonamide with an aryl halide and K(2)CO(3) in the presence of a catalytic amount of Pd(PPh(3))(4) in dioxane affords 2,3-cis-pyrrolidines in a stereoselective manner. In sharp contrast, cyclization of the same allenenes using catalytic Pd(2)(dba)(3) x CHCl(3) in the presence of allyl methyl carbonate in CH(3)CN leads to stereoselective formation of a 3-azabicyclo[3.1.0]hexane framework in moderate yields.