Non-C2-symmetrical antimony-phosphorus ligand, (R/S)-2-diphenylphosphano-2′-di(p-tolyl)stibano-1,1′-binaphthyl (BINAPSb): preparation and its use for asymmetric reactions as a chiral auxiliary

A new non-C₂-symmetrical antimony-phosphorous ligand, (±)-2-diphenyl-phosphano-2′-di(p-tolyl)stibano-1,1′-binaphthyl (BINAPSb) 3, has been prepared from 2-bromo-2′-diphenylphosphano-1,1′-naphthyl 4 via its borane complex 6, and could be resolved by the separation of a mixture of the diastereomeric palladium complexes 8A and 8B derived from the reaction of (±)-3 with optically active palladium reagent (S)-7. The enantiomerically pure BINAPSb 3 has proved to be highly effective in the palladium-catalyzed asymmetric hydrosilylation of styrene as a chiral auxiliary.     

Simple and efficient copper-catalyzed S-arylation of diaryl disulfides with triarylbismuthanes under aerobic conditions

Novel and simple copper-catalyzed C(aryl)-S bond formation of diaryl disulfides with bismuth reagents is described. Reactions of diaryl disulfides with triarylbismuthanes in the presence of CuOAc (10 mol %) and 1,10-phenanthroline (10 mol %) under aerobic conditions led to the formation of unsymmetrical diaryl sulfides in satisfactory yields. The reaction is atom-economic and all three aryl groups of the triarylbismuthanes and both sulfanyl groups of the diaryl disulfides could be transferred to the coupling products.     

Carbon-14 dating of tree rings for tritium measurement

The carbon-14 concentration in tree-ring cellulose of an 80-year-old pine tree which has been used for tritium measurement was measured during the 1941–1987 period. This was done to determine the formation year of each tree ring in order to study the pathway of tritium uptake into the tree rings. In the 1941 to 1953 period, the Δ¹⁴C value remained slightly lower than 0%., It began to increase from 1954 to a small broad peak of 250% between 1959 and 1961, followed by rapid increase to the highest value of approximately 800% in 1964. Since 1964, it had been diminishing year by year to reach a level of 190% in 1987. The two peak years coincided with those in the known carbon-14 patterns in tree rings. However, there existed a difference in the amplitude of the Δ¹⁴C values during the period of 1963–1967.     

Temporal variation of tritium concentration in tree-ring cellulose over the past 50 years

Concentration of organically-bound tritium in the tree-ring cellulose of a pine tree grown in Shika-machi, Ishikawa prefecture, Japan (37.1°N, 136.5°E), was measured during the ring-years from 1949 to 1999. The results were compared with those of a pine tree grown in Tatsunokuchi-machi, Ishikawa prefecture, Japan (36.4°N, 136.5° E). The annual variation of tritium in tree rings demonstrated two differences between the Shika-machi tree and the Tatsunokuchi-machi tree. No secondary peak appeared in the period after the maximum peak of 1963 for the Shika-machi tree, while two peaks appeared in 1966 and 1970 for the Tatsunokuchi-machi tree. In addition, the height of the 1963 peak was 30% higher for the Shika-machi tree than for the Tatsunokuchi-machi tree. These differences are considered to be caused by the influence that the underground water in the root zone of the Tatsunokuchi-machi tree was strongly affected by water which was transported to the tree site from mountain regions as compared to the Shika-machi tree.This study was supported in part by a Grant from the Ishikawa Prefectural Institute of Public Health and Environmental Science.     

Palladium-Catalyzed C–H Arylation of Benzofurans with Triarylantimony Difluorides for the Synthesis of 2-Arylbenzofurans

Pd-catalyzed regioselective C–H arylation is a useful tool for the chemical modification of aromatic heterocycles and 2-arylbenzofuran derivatives are of interest as biologically active substances. Herein, the reaction of triarylantimony difluorides with benzofurans under aerobic conditions in 1,2-DCE, using 5 mol% Pd (OAc)₂ and 2 eq. of CuCl₂ at 80 °C, produced a variety of 2-arylbenzofurans in moderate-to-high yields. The reaction is sensitive to the electronic nature of the substituents on the benzene ring of the triarylantimony difluorides: an electron-donating group showed higher reactivity than an electron-withdrawing group. Single crystal X-ray analysis of tri(p-methylphenyl) antimony difluoride revealed that the central antimony atom exhibits trigonal bipyramidal geometry.     

Neutron activation analysis of6Li isotopic abundance using a low background liquid scintillation counter

A neutron activation method based on the measurement of tritium radioactivity produced by⁶Li (n,)³H reaction was applied to determine the isotopic abundance of⁶Li in aqueous solution with known lithium concentration. Tritium radioactivity was measured with a low background liquid scintillation counter over a period of 2000 min. The present method demonstrated a good linearity between the isotopic abundance of⁶Li and tritium radioactivity produced per unit amount of lithium in a wide range of lithium concentration. A comparison of the present data with those from mass spectrometry showed agreement, though our method was 10 times less sensitive, than mass spectrometry. The present new approach should thus prove quite useful for determining the isotopic abundance of⁶Li.     

Catalytic action of triarylstibanes: oxidation of benzoins into benzyls using triarylstibanes under an aerobic condition

Benzoins are simply oxidized to benzils in excellent yields with a catalytic amount of triarylstibanes under an aerobic condition. This catalytic oxidation is heteroatom-specific in the antimony compound and no reaction take place with other group 15 reagents such as triphenylphosphane, -arsane and -bismuthane. The reaction should involve an oxidation-reduction cycle between stibane Sb(III) and stiborane Sb(V) under air.     

Intense high-energy proton beams from Petawatt-laser irradiation of solids

An intense collimated beam of high-energy protons is emitted normal to the rear surface of thin solid targets irradiated at 1 PW power and peak intensity 3x10(20) W cm(-2). Up to 48 J ( 12%) of the laser energy is transferred to 2x10(13) protons of energy >10 MeV. The energy spectrum exhibits a sharp high-energy cutoff as high as 58 MeV on the axis of the beam which decreases in energy with increasing off axis angle. Proton induced nuclear processes have been observed and used to characterize the beam.     

Long-term variation of 14C concentration in atmospheric CO2 in Japan from 1991 to 2000

The long-term variation of ¹⁴C concentrations in atmospheric CO₂ samples collected every 10 days was measured in the Ohkuwa area of Kanazawa, Ishikawa prefecture, Japan (36.3°N, 136.4°E), from April 1991 to December 2000. The ¹⁴C concentration decreased gradually by about 5‰ each year from 1991 to 2000, with a pronounced seasonal cycle which began to increase from spring and reached the maximum in late July or early August, followed by a decrease to the minimum from December to February. The appearance of large seasonal cycles and the extreme decrease of ¹⁴C concentration in winter seemed to be caused mainly by the air containing a large amount of ¹⁴C-free fossil fuel CO₂ transported across the Sea of Japan from the Asian continent, not by the influence of local fossil fuel consumption.     

Synthesis,Structural Characterization,and Optical Properties of Benzene-Fused Tetracyclic and Pentacyclic Stiboles

The expectation that antimony (Sb) compounds should display phosphorescence emissions based on the “heavy element effect” prompted our interest in the introduction of antimony to a biaryl as the bridging atom in a fused heterole system. Herein, the synthesis, molecular structures, and optical properties of novel benzene-fused heteroacenes containing antimony or arsenic atoms are described. The stiboles and arsole were prepared by the condensation of dibromo(phenyl)stibane or dichloro(phenyl)arsine with dilithium intermediates derived from the corresponding dibromo compounds. Nuclear magnetic resonance (NMR) spectroscopy and X-ray crystal analysis revealed that the linear pentacyclic stibole was highly symmetric in both the solution and crystal states. In contrast, the curved pentacyclic stibole adopted a helical structure in solution, and surprisingly, only M helical molecules were crystallized from the racemate. All synthesized compounds produced very weak or no emissions at room temperature or in the solid state. In contrast, the linear penta- and tetracyclic stiboles exhibited clear phosphorescence emissions in the CHCl₃ frozen matrix at 77 K under aerobic conditions.