Predominant 1,2-insertion of styrene in the Pd-catalyzed alternating copolymerization with carbon monoxide.

The regioselectivity of styrene insertion to an acyl-Pd bond was studied by NMR in (i) a stoichiomeric reaction and (ii) a copolymerization with CO. In the stoichiometric reaction of styrene with [(CH(3)CO)Pd(CH(3)CN)[(R,S)-BINAPHOS]].[B[3,5-(CF(3))(2)C(6)H(3)](4)], both 1,2- and 2,1-products were given. To mimic the real polymerization conditions, a polyketone-substituted complex [[CH(3)(CH(2)CHCH(3)CO)(n)]Pd[(R,S)-BINAPHOS]].[B(3,5-(CF(3))(2)C(6)H(3))(4)] (n approximately 14) was prepared. When this polymer-attached Pd species was treated with styrene, the 1,2-insertion product was the only detectable species. Thus, exclusive 1,2-insertion is demonstrated to be responsible for the styrene-CO copolymerization, in sharp contrast to the predominant 2,1-insertion with conventional nitrogen ligands. Chain-end analysis revealed that beta-hydride elimination took place from the 2,1-complex but not from the 1,2-complex. Thus, once 2,1-insertion occurs, rapid beta-hydride elimination proceeds to terminate the polymerization, as is common to the other phosphorus-ligand systems. The resulting Pd-H species re-initiates the copolymerization, as was proven by MALDI-TOF mass analysis of the product copolymers.     

Synthesis of fully conjugated aromatic polyazomethine from AB-type monomer using soluble precursor method

A new AB-type monomer, N,N-bistrimethylsilylated p-aminobenz-aldehyde diethyl acetal was prepared via three steps from p-bromoaniline as a starting material. The two-stage polymerization involving a soluble precursor polymer process gave a poly(p-phenylenevinylene)-type polyazomethine, poly(1,4-phenylene-nitrilomethylidyne). The first stage of polymerization was carried out in tetrahydrofuran or hexamethylphosphoramide containing water at room temperature. In the second stage, the polymer was thermally converted into the final polyazomethine by heating over 300°C to form a free-standing film. The film was reddish brown and insoluble in common organic solvents. The investigation of the first-stage products by means of MALDI-TOF mass spectroscopy proved the oligomers with 4-11 repeating units per molecule. From the ¹H-NMR analysis of the model reaction, the polymerization mechanism was found to be a stepwise polycondensation of 4-diethoxymethylaniline which was formed by removal of two silyl groups of the monomer.     

Improved stability of molecular organic EL devices

Influence of emission sites on emission efficiency and running durability of molecular organic electroluminescent devices was investigated. When fluorescent dye rubrene was doped into TPD diamine hole transport layer, rubrene molecule emitted bright yellow light with a max. luminance of 61 000 cd/m². The device had the highest efficiency of 9.8 Im/W at 100 cd/m². Half-decay time of the device from initial luminance of 530 cd/m² under constant direct current was 3 600 h. On the other hand, when rubrene was doped into BeBq₂ complex electron transport layer, the efficiency was 4.4 Im/W and the half-decay time was 110 h. Thus doping site is found to exert significant influence both on the emission efficiency and the running durability.     

Unusual Disordered Crystal Structure of a Racemate Exhibiting a Novel Enantiomeric Resolution: Preferential Enrichment

Simple recrystallization of racemic (±)-NC leads to preferential enrichment of one enantiomer in the mother liquor, which allows the efficient resolution of the two enantiomers. In the unique disordered crystal structure of the racemate, the two enantiomers form centrosymmetric dimers as the major component.     

In situ and ex situ studies on thermal decomposition process of hydromagnesite Mg5(CO3)4(OH)2·4H2O

Journal of Thermal Analysis and Calorimetry - We investigated crystal structure and the local structure changes during the thermal decomposition of hydromagnesite by using in situ high-temperature...     

Signal-source estimation from magnetic field image obtained using atomic magnetometer and digital micro-mirror device

Optical Review - Visualization of an electromagnetic field distribution is helpful for spatial evaluation of field leakage and can aid in solving inverse problems of signal-source estimation....     

Short synthesis of epi-cytoxazone via oxazoline formation through intramolecular benzylic substitution of a bis-trichloroacetimidate

A short and efficient method for synthesizing epi-cytoxazone via the corresponding oxazoline intermediate was developed. The formation of the oxazoline ring, which proceeds through an S_N1 mechanism to ensure that the trans-oxazoline stereochemistry is retained, was induced by intramolecular benzylic substitution of a 1,2-bis-trichloroacetimidate, starting from the known enantiomerically pure diol.