Carbon radical generation by d0 tantalum complexes with α-diimine ligands through ligand-centered redox processes

High-valent tantalum complexes having redox-active α-diimine ligands, (α-diimine)TaCl(n) (n = 3, 4), are prepared by the reaction of TaCl(5), α-diimine ligands, and an organosilicon-based reductant, 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene. Reductive cleavage of the C-Cl bond of polyhaloalkanes is accomplished by trichlorotantalum complexes having dianionic α-diimine ligands via electron transfer from the dianionic ligands, whereas oxidative decomposition of tetraphenylborate is observed using tetrachlorotantalum complexes with monoanionic α-diimine ligands through electron transfer to the monoanionic ligands. Chemically oxidized or reduced complexes of (α-diimine)TaCl(4) are isolated as ligand-centered redox products, [Cp(2)Co][(α-diimine)TaCl(4)] and [(α-diimine)TaCl(4)][WCl(6)], where the α-diimine ligand coordinates to the metal center as a dianionic or neutral ligand, respectively. On the basis of EPR measurements of (α-diimine)TaCl(4) complexes (which are key intermediates for reductive cleavage of C-Cl bond and oxidative decomposition of tetraphenylborate), two redox isomers--a tantalum-centered radical and ligand-localized radical--are present in solution.     

Homological mirror symmetry for Brieskorn�CPham singularities

We prove that the derived Fukaya category of the Lefschetz fibration defined by a Brieskorn–Pham polynomial is equivalent to the triangulated category of singularities associated with the same polynomial together with a grading by an abelian group of rank one. Symplectic Picard-Lefschetz theory developed by Seidel is an essential ingredient of the proof.     

SrTiO3(100) − √5 × √5 − R26.6 surface observed by high-resolution scanning tunneling microscopy

SrTiO₃(100) – (√5 × √5) – R26.6 surfaces were studied by means of high-resolution scanning tunneling microscopy (STM) under ultrahigh vacuum conditions. By varying the bias voltage in the occupied state, it was possible to observe the arrangement of titanium and oxygen atoms in the unit cells of a (√5 × √5) surface superstructure, which revealed that the TiO₂ layer is the terminating plane of the (√5 × √5) surface. In the STM images, peculiar protrusions were seen at the oxygen fourfold hollow site responsible for √5 × √5 periodicity. The protrusions are asymmetrical in contrast, which would be an important consideration in proposing accurate structural models for (√5 × √5) surface superstructures.     

Rational synthesis of supramolecular assemblies based on tetraplatinum units: synthesis, characterization, and selective substitution reactions of four different Pt4 clusters

Four different types of square‐planar Pt₄ clusters, trans‐[Pt₄(μ‐OCOCH₃)₆(μ‐ArNCHNAr)₂] ( 2 : ArNCHNAr=N,N′‐diarylformamidinate), [Pt₄(μ‐OCOCH₃)₇(μ‐ArNCHNAr)] ( 8 ), cis‐[Pt₄(μ‐OCOCH₃)₆(κ⁴‐N₄‐DArBp)] ( 9 : DArBp=1,3‐bis(arylbenzamidinate)propane), and [Pt₄Cl₂(μ‐OCOCH₃)₅(κ⁴‐N₂,P₂‐dpfam)] ( 13 : dpfam=N,N′‐bis[(2‐diphenylphosphino)phenyl]formamidinate), were successfully prepared by using selective substitution reactions of in‐plane acetate ligands of [Pt₄(μ‐OCOCH₃)₈] ( 1 ), which has four in‐plane and four out‐plane acetate ligands, with appropriate capping ligands. Fundamental substitution reactions of the remaining in‐plane acetates with benzoic acid derivatives were also investigated. All newly prepared complexes were characterized from spectral and physical data and combustion analysis. X‐ray crystallographic studies of some of the clusters were also performed. Electrochemical measurements of amidinate‐modified Pt₄ clusters revealed stepwise oxidation processes of the Pt₄ core due to Pt₄⁹⁺/Pt₄⁸⁺ and Pt₄¹⁰⁺/Pt₄⁹⁺. Based on the lability of the in‐plane acetate ligands of the modified Pt₄ clusters, reactions of cis‐[Pt₄(μ‐OCOCH₃)₆(κ⁴‐N₄‐DArBp)] ( 9 c : Ar=C₆H₄tBu‐4) with ferrocenedicarboxylic acid and p‐phenylenedipropionic acid resulted in the selective formation of cyclic dimers 17 and 18 and the reaction of 13 with 4,4′‐biphenyldicarboxylic acid afforded a linear dimer 20 . The dimers were characterized by spectral data, as well as X‐ray analyses for 17 and 18 . The finding of two Fe³⁺/Fe²⁺ redox couples in the electrochemical measurement of dimer 17 indicated that two ferrocenyl units in dimer 17 communicated electronically.     

Asymmetric Hydrogenation of Aryl Perfluoroalkyl Ketones Catalyzed by Rhodium(III) Monohydride Complexes Bearing Josiphos Ligands

The asymmetric hydrogenation of 2,2,2-trifluoroacetophenones and aryl perfluoroalkyl ketones was developed using a unique, well-defined chloride-bridged dinuclear rhodium(III) complex bearing Josiphos-type diphosphine ligands. These complexes were prepared from [RhCl(cod)]₂, Josiphos ligands, and hydrochloric acid. As catalyst precursors, they allow for the efficient and enantioselective synthesis (up to 99 % ee) of chiral secondary alcohols with perfluoroalkyl groups. This system does not require an activating base for the hydrogenation of 2,2,2-trifluoroacetophenones. Additionally, the enantioselective C=O hydrogenations of 2-phenyl-3-(haloacetyl)-indoles, a class of privileged structures in medicinal chemistry, is reported for the first time.     

On-chip micellar electrokinetic chromatographic separation of phenolic chemicals in waters

This paper describes on-chip micellar electrokinetic chromatography (MEKC) separation of bisphenol A and 3 kinds of alkylphenols, which have been recently recognized as endocrine disrupting chemicals for fish by the Japanese government, using microchip capillary electrophoresis with UV detection. We successfully obtained high-speed separation of the phenolic chemicals within 15 s as optimizing in microfluidic controls and MEKC separation conditions. We obtained fairly good linearity with correlation coefficient of over 0.98 from 0 to 50 mg/l phenolic chemicals except for 4-nonylphenol, which sample is the mixture of many geometrical isomers (r = 0.86). The values of the relative standard deviation for peak height in 50 mg/l phenolic chemicals were less than 8% except for bisphenol A (11.0%). The limits of detection obtained at a signal-to-noise ratio of 3 were from 5.6 to 20.0 mg/l. To realize on-site monitoring, we described strategy for on-chip MEKC analysis of the phenolic chemicals in waters using a portable analyzer based on microfluidic devices.     

One-step preparation of manganese-, iron-, and aluminum-promoted sulfated zirconias for reaction of butane to isobutane

Highly active superacids of Mn-, Fe-, and Al-sulfated ZrO₂'s for the isomerization of butane to isobutane were obtained by exposing zirconia gel to aqueous solutions of 0.05 M MnSO₄, 0.25 M FeSO₄, and 0.5 M Al₂(SO₄)₃ followed by calcining in air at 700, 600, and 675°C, respectively. The catalysts were much more active than the superacid of sulfated zirconia, the temperature difference to show the same conversion (20%) between the catalysts and sulfated zirconia being 85, 77, and 85°C for the Mn-, Fe-, and Al-catalysts, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermodynamic investigation of the charge-ordered insulating state of the quasi-one-dimensional organic system (DI-DCNQI)2Ag

Heat capacity measurements of a charge-ordered organic conductor (DI-DCNQI)2Ag have been performed in a temperature range between 0.3 and 14 K. We found no thermal anomaly at the Néel temperature ( T(N) = 5.5 K) but instead a T-linear term suggestive of the spin excitations of one-dimensional character in the charge-ordered insulating state. The analysis of the T-linear term and the excess entropy indicates that the charge fluctuations in the charge-ordered state influence the growth of spin excitations at elevated temperatures, which seems to be a peculiar aspect of a 1D charge-ordered system.     

Unusual hydration behavior of dielectric loss in KA zeolite

Two relaxations measured in dehydrated KA zeolite showed different hydration behaviors; the higher frequency relaxation shifted to higher frequency with increasing hydration whereas the lower frequency relaxation shifted to lower frequency; the latter behavior being contrary to present theory.     

Analysis of spurious bulk waves in ball surface wave device

We analyzed the acoustic waves propagating in a sphere to establish a useful guideline for the design of NDE apparatus and ball surface acoustic wave (SAW) device exploiting the diffraction-free propagation of SAW on a sphere. First, we calculated the laser-generated acoustic displacements both under ablation condition and under thermoelastic condition and verified experimentally the validity of the calculation. Next, the acoustic waves excited by out-of-plane stress and those excited by in-plane stress were compared. The results showed that when the out-of-plane stress was applied, the relative amplitudes of the bulk waves to that of the SAW were larger and the number of bulk waves was larger than that when the in-plane stress was applied, while the SAW had similar waveforms in each case. The ratio of the relative amplitude of the bulk waves for the out-of-plane stress and the in-plane stress was 3.1:1 at phi(1)=90 degrees and 1.67:1 at phi(1)=0 degrees. The large amplitude for the out-of-plane stress can be explained by wide directivities of bulk waves. Consequently, we found that it is necessary for ball SAW device to select a piezoelectric material and form of interdigital transducer so that the in-plane stress becomes dominant.