Homoleptic cyclometalated iridium complexes with highly efficient red phosphorescence and application to organic light-emitting diode

Phosphorescence studies of a series of facial homoleptic cyclometalated iridium(III) complexes have been carried out. The complexes studied have the general structure Ir(III)(C-N)(3), where (C-N) is a monoanionic cyclometalating ligand: 2-(5-methylthiophen-2-yl)pyridinato, 2-(thiophen-2-yl)-5-trifluoromethylpyridinato, 2,5-di(thiophen-2-yl)pyridinato, 2,5-di(5-methylthiophen-2-yl)pyridinato, 2-(benzo[b]thiophen-2-yl)pyridinato, 2-(9,9-dimethyl-9H-fluoren-2-yl)pyridinato, 1-phenylisoquinolinato, 1-(thiophen-2-yl)isoquinolinato, or 1-(9,9-dimethyl-9H-fluoren-2-yl)isoquinolinato. Luminescence properties of all the complexes at 298 K in toluene are as follows: quantum yields of phosphorescence Phi(p) = 0.08-0.29, emission peaks lambda(max) = 558-652 nm, and emission lifetimes tau = 0.74-4.7 micros. Bathochromic shifts of the Ir(thpy)(3) family [the complexes with 2-(thiophen-2-yl)pyridine derivatives] are observed by introducing appropriate substituents, e.g., methyl, trifluoromethyl, or thiophen-2-yl. However, Phi(p) of the red emissive complexes (lambda(max) > 600 nm) becomes small, caused by a significant decrease of the radiative rate constant, k(r). In contrast, the complexes with the 1-arylisoquinoline ligands are found to have marked red shifts of lambda(max) and very high Phi(p) (0.19-0.26). These complexes are found to possess dominantly (3)MLCT (metal-to-ligand charge transfer) excited states and have k(r) values approximately 1 order of magnitude larger than those of the Ir(thpy)(3) family. An organic light-emitting diode (OLED) device that uses Ir(1-phenylisoquinolinato)(3) as a phosphorescent dopant produces very high efficiency (external quantum efficiency eta(ex) = 10.3% and power efficiency 8.0 lm/W at 100 cd/m(2)) and pure-red emission with 1931 CIE (Commission Internationale de L'Eclairage) chromaticity coordinates (x = 0.68, y = 0.32).     

Determination of trace amounts of vanadium in air samples with 2-(8-quinolylazo)-5-N,N-diethylaminophenol by reversed-phase liquid chromatography

A reversed-phase liquid chromatographic method for the determination of trace amounts of vanadium is described. Metal ions are converted into 2-(8-quinolylazo)-5-N,N-diethylaminophenol chelates in an off-line system. The chelates are injected onto a Zorbax CN column and separated with an aqueous acetonitrile mobile phase containing no chromogenic reagent. Unter these conditions, only vanadium(V) is spectrophotometrically detected at 540 nm among the metal ions Al(III), Ba(II), Ca(II), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Ga(III), Hg(II), Mg(II), Mn(II), Ni(II), Pb(II), V(V) and Zn(II). Amounts of 8.0–200 pg of vanadium(V) in 100-μl injections can be determined without interference from 10-fold molar excesses of many cations. At 0.001 a.u.f.s., the detection limit (twice the peak-to-peak noise) for vanadium(V) is 8.0 pg in 100 μl of injected solution and the relative standard deviation at 120 pg of vanadium(V) in a 100-μl injection is 3.5%. The proposed method is applied to the determination of vanadium in rain water and airborne particulates.     

1,2-silyl-migrative cyclization of vinylsilanes bearing a hydroxy group: stereoselective synthesis of multisubstituted tetrahydropyrans and tetrahydrofurans(1)

Acid-catalyzed intramolecular addition of a hydroxy group to alpha-alkylated vinylsilanes has been studied. Treatment of (Z)-5-alkyl-5-silyl-4-penten-1-ols 1 (R = alkyl) with 5 mol % TiCl(4) in CHCl(3) gave trans-2-alkyl-3-silyltetrahydropyrans 2 exclusively (trans/cis = >99/1 to 97/3). The cyclization efficiency and rate strongly depended on the geometry of the C-C double bond and the silyl group. The use of (E)-vinylsilanes resulted in lower yields with poor cis-selectivity. In the cyclization of (Z)-1 (R = Bu), the silyl group used, the reaction time, and the yield of 2 were as follows: SiMe(2)Ph, 9.5 h, 75%; SiMe(3), 7.5 h, 66%; SiMePh(2), 24 h, 58%; SiMe(2)-t-Bu, 0.75 h, 85%; SiMe(2)Bn, 1.5 h, 78%. This 1,2-silyl-migrative cyclization could be applied to stereoselective synthesis of trisubstituted tetrahydropyrans. The acid-catalyzed reaction of 1-, 2-, or 3-substituted (Z)-5-silyl-4-nonen-1-ols 8 gave r-2,t-3,c-6-, r-2,t-3,t-5-, or r-2,t-3,c-4-trisubstituted tetrahydropyrans with high diastereoselectivity, respectively. (Z)-4-Alkyl-4-silyl-3-buten-1-ols 5 as well as 1 underwent the 1,2-silyl-migrative cyclization to give 2-alkyl-3-silyltetrahydrofurans 6 with high trans-selectivity. This silicon-directed cyclization was also available for the stereoselective synthesis of tri- and tetrasubstituted tetrahydrofurans.     

Indium-mediated beta-allylation,beta-propargylation,and beta-allenylation onto alpha,beta-unsaturated ketones: reactions of in-situ-generated 3-tert-butyldimethylsilyloxyalk-2-enylsulfonium salts with in-situ-generated organoindium reagents

3-tert-Butyldimethylsilyloxyalk-2-enylsulfonium salts, generated in situ from the reaction of alpha,beta-enones with dimethyl sulfide in the presence of TBSOTf, underwent a novel nucleophilic substitution with allylindiums to give silyl enol ethers of delta,epsilon-alkenyl ketones in good yields, which correspond to formal Michael addition products. In a similar manner, 1,4-propargylation of propargylindiums onto the sulfonium salts produced the corresponding silyl enol ethers of delta,epsilon-alkynyl ketones in good yields. Organoindium reagents derived from gamma-substituted propargyl bromide and indium afforded the corresponding silyl enol ethers of beta-allenyl ketones in good yields. The reaction proceeds via an addition-substitution mechanism involving the formation of allylic sulfonium salts. The presence of the intermediate sulfonium salt was confirmed by observation of the low-temperature (1)H NMR spectra.     

Stereoblock poly(lactic acid): synthesis via solid-state polycondensation of a stereocomplexed mixture of poly(L-lactic acid) and poly(D-lactic acid)

Stereoblock poly(lactic acid) consisting of D- and L-lactate stereosequences can be successfully synthesized by solid-state polycondensation of a 1:1 mixture of poly(L-lactic acid) and poly(D-lactic acid). In the first step, melt-polycondensation of L- and D-lactic acids is conducted to synthesize poly(L-lactic acid) and poly(D-lactic acid) with a medium-molecular-weight, respectively. In the next step, these poly(L-lactic acid) and poly(D-lactic acid) are melt-blended in 1:1 ratio to allow formation of their stereocomplex. In the last step, this melt-blend is subjected to solid-state polycondensation at temperature where the dehydrative condensation is allowed to promote chain extension in the amorphous phase with the stereocomplex crystals preserved. Finally, stereoblock poly(lactic acid) having high-molecular-weight is obtained. The stereoblock poly(lactic acid) synthesized by this way shows a higher melting temperature in consequence of the controlled block lengths and the resulting higher-molecular-weight. The product characterization as well as the optimization of the polymerization conditions is described. Changes in M(w) of stereoblock poly(lactic acid) (sb-PLA) as a function of the reaction time.     

Broad spectrum and mode of action of an antibiotic produced byScytonema sp. TISTR 8208 in a seaweed-type bioreactor

A photobioreactor was constructed using anchored polyurethane foam strips (1 x 1 x 40 cm) fixed onto a stainless-steel ring to prevent flotation, as a biomass support material (BSM). This type of reactor was named a seaweed-type bioreactor. A filamentous cyanobacterium, Scytonema sp. TISTR 8208, which produces a novel cyclic dodecapeptide antibiotic, was immobilized in seaweed-type photobioreactor and cultivated with air containing 5% CO₂ sparged at a gas flow rate of 250 mL/min under illumination at a light intensity of 200 μmol photon m^-2s^-1. The antibiotic produced in the seaweed-type photobioreactor was purified by HPLC and examined regarding its spectrum and mode of action. The antibiotic effectively inhibited the growth of Gram-positive bacteria, pathogenic yeasts, and filamentous fungi, but it had only a weak effect on Gram-negative bacteria. Scanning electron micrograph analysis showed that the most characteristic change was swelling of the cells after exposure to the antibiotic. The antibiotic seems to alter the conformation of the microbial cell membrane, thereby changing its permeability, leading to osmotic shock.     

Cross-coupling of alkenyl,aryl or allylic selenides and grignard reagents catalyzed by nickel-phosphine complexes

Alkenyl, aryl or allylic selenides smoothly couple with Grignard reagents in the presence of Ni(II)-phosphine complexes as catalysts to afford the corresponding unsaturated compounds in good yields. The reactivity order of coupling reaction with BuMgBr catalyzed by NiCl₂ [Ph₂PCH₂CH₂CH₂PPh₂] was found to be PhSeMe « PhCl > PhSMe by the competitive reactions.     

Absorption Spectra of Sodium Aluminate Solutions

The absorption spectra of sodium aluminate solutions have been examined at different concentrations. As a result, it was found that the characteristic absorption band due to aluminate ion shows a λ_max at 265–270 mm?.     

Meerwein-Ponndorf-Verley alkynylation of aldehydes: essential modification of aluminium alkoxides for rate acceleration and asymmetric synthesis

A novel carbonyl alkynylation has been accomplished based on utilization of the Meerwein-Ponndorf-Verley (MPV) reaction system. The success of the MPV alkynylation crucially depends on the discovery of the remarkable ligand acceleration effect of 2,2'-biphenol. For example, the alkynylation of chloral (2c) with the aluminium alkoxide 6(R = Ph), prepared in situ from Me(3)Al, 2,2'-biphenol and 2-methyl-4-phenyl-3-butyn-2-ol (1a) as an alkynyl source, proceeded smoothly in CH(2)Cl(2) at room temperature to give the desired propargyl alcohol 3ca in almost quantitative yield after 5 h stirring. The characteristic feature of this new transformation involving no metal alkynides can be visualized by the fact that the alkynyl group bearing keto carbonyl was transferred successfully to aldehyde carbonyl without any side reactions on keto carbonyl. Although the use of (S)-1,1[prime or minute]-bi-2-naphthol and its simple analogues was found to be unsuitable for inducing asymmetry in this reaction, design of new chiral biphenols bearing a certain flexibility of the biphenyl axis led to satisfactory results in terms of enantioselectivity as well as reactivity.