The iridium‐catalyzed asymmetric hydrogenation of several N‐sulfonyl allyl amines is reported. All substrates can be easily obtained by the Ir‐catalyzed isomerization of N‐tosylaziridines reported previously. The commercially available threonine‐derived phosphinite (UbaPHOX) iridium complex has been found to be the best catalyst for this catalytic application, affording β‐methyl amines with good to excellent ee values (up to 94%). The synthetic potential of this novel methodology was demonstrated by the formal synthesis of Lorcaserin and LY‐404187.
Intramolecular addition of an O‐methyl C(sp3)−H bond across a carbon‐carbon double bond occurs in the iridium‐catalyzed reaction of methyl 2‐(propen‐2‐yl)phenyl ethers. The Ir/(S)‐DTBM‐SEGPHOS catalyst promotes the reaction efficiently in toluene at 110–135 °C to afford 3,3‐dimethyl‐2,3‐dihydrobenzofurans. Enantioselective C(sp3)−H addition is achieved in the reaction of methyl 2‐(1‐siloxyethenyl)phenyl ethers, affording enantioenriched 3‐hydroxy‐2,3‐dihydrobenzofuran derivatives with up to 96% ee.
In the present study, fatigue and fracture characteristics of sensitized marine grade Al‐Mg (AA 5754) alloy are experimentally evaluated. Received alloy is sensitized at temperatures of 150°C (SENS50) and 175°C (SENS75) for 100 hours. Fracture parameters, KIc and JIc, are experimentally evaluated. Slow strain rate tensile tests at a crosshead speed of 0.004, 0.006, and 0.01 mm/min; fatigue crack growth tests at load ratios (R = Pmin/Pmax) of 0.1, 0.2, and 0.5; and low cycle fatigue tests at four strain amplitudes of (0.3‐0.6)% are performed for SENS50 and SENS75 alloys. Relatively lower magnitude of fracture toughness values are observed for SENS75 specimen. Severe degradation in tensile properties, fatigue crack growth characteristics, and low cycle fatigue lives are observed for SENS75 samples. Extended finite element method is adopted to simulate the elasto‐plastic crack growth during fracture toughness evaluation. Scanning electron microscopy (SEM) is used to understand the failure mechanism of sensitized alloys. 相似文献
Ir‐based binary and ternary alloys are effective catalysts for the electrochemical oxygen evolution reaction (OER) in acidic solutions. Nevertheless, decreasing the Ir content to less than 50 at% while maintaining or even enhancing the overall electrocatalytic activity and durability remains a grand challenge. Herein, by dealloying predesigned Al‐based precursor alloys, it is possible to controllably incorporate Ir with another four metal elements into one single nanostructured phase with merely ≈20 at% Ir. The obtained nanoporous quinary alloys, i.e., nanoporous high‐entropy alloys (np‐HEAs) provide infinite possibilities for tuning alloy's electronic properties and maximizing catalytic activities owing to the endless element combinations. Particularly, a record‐high OER activity is found for a quinary AlNiCoIrMo np‐HEA. Forming HEAs also greatly enhances the structural and catalytic durability regardless of the alloy compositions. With the advantages of low Ir loading and high activity, these np‐HEA catalysts are very promising and suitable for activity tailoring/maximization. 相似文献
A conductive SnO2 layer and small quantities of IrO2 surface cocatalyst enhance the catalytic efficiency of nanoporous Fe2O3 electrodes in the oxygen evolution reaction at neutral pH. Anodic alumina templates are therefore coated with thin layers of SnO2, Fe2O3, and IrO2 by atomic layer deposition. In the first step, the Fe2O3 electrode is modified with a conductive SnO2 layer and submitted to different postdeposition thermal treatments in order to maximize its catalytic performance. The combination of steady‐state electrolysis, electrochemical impedance spectroscopy, X‐ray crystallography, and X‐ray photoelectron spectroscopy demonstrates that catalytic turnover and e− extraction are most efficient if both layers are amorphous in nature. In the second step, small quantities of IrO2 with extremely low iridium loading of 7.5 µg cm−2 are coated on the electrode surface. These electrodes reveal favorable long‐term stability over at least 15 h and achieve maximized steady‐state current densities of 0.57 ± 0.05 mA cm−2 at η = 0.38 V and pH 7 (1.36 ± 0.10 mA cm−2 at η = 0.48 V) in dark conditions. This architecture enables charge carrier separation and reduces the photoelectrochemical water oxidation onset by 300 mV with respect to pure Fe2O3 electrodes of identical geometry. 相似文献
Deep‐blue emitting Iridium (Ir) complexes with horizontally oriented emitting dipoles are newly designed and synthesized through engineering of the ancillary ligand, where 2′,6′‐difluoro‐4‐(trimethylsilyl)‐2,3′‐bipyridine (dfpysipy) is used as the main ligand. Introduction of a trimethylsilyl group at the pyridine and a nitrogen at the difluoropyrido group increases the bandgap of the emitter, resulting in deep‐blue emission. Addition of a methyl group (mpic) to a picolinate (pic) ancillary ligand or replacement of an acetate structure of pic with a perfluoromethyl‐triazole structure (fptz) increases the horizontal component of the emitting dipoles in sequence of mpic (86%) > fptz (77%) > pic (74%). The organic light‐emitting diode (OLED) using the Ir complex with the mpic ancillary ligand shows the highest external quantum efficiency (31.9%) among the reported blue OLEDs with a y‐coordinate value lower than 0.2 in the 1931 Commission Internationale de L'Eclairage (CIE) chromaticity diagram. 相似文献
