Nickel-phosphine complex-catalyzed Grignard coupling—II : Grignard coupling of heterocyclic compounds

A general, versatile method for alkylation and arylation of haloheterocyclic compounds is reported. In the presence of a catalytic quantity of [NiCl₂(dppp)], where dppp stands for Ph₂P(CH₂)₃PPh₂, bromothiophenes, halopyridines, haloquinoline, and haloisoquinolines reacted with alkyl and aryl Grignard reagents at room temperature or at ether refluxing temperature to give the cross-coupling products. The coupling reaction has been applied to the synthesis of isoquinoline alkaloids. Reactivities of 2-thienyl and 2-pyridyl Grignard reagents have also been examined.     

Bismuth triflate-chiral bipyridine complexes as water-compatible chiral Lewis acids

[reaction: see text] Catalytic asymmetric hydroxymethylation of silicon enolates with an aqueous formaldehyde solution has been developed using a chiral bismuth complex. This is the first example of highly enantioselective reactions using a chiral bismuth catalyst in aqueous media. In this paper, we have added Bi(OTf)(3)-1 complex as a "water-compatible Lewis acid". Bi(OTf)3 is unstable in the presence of water but is stabilized by the basic ligand.     

Synthesis of molybdenocene(IV) and tungstenocene(IV) tropolonato complexes: Its derivative containing calix[4]arene moiety

The cationic di-μ-hydroxo dinuclear complexes of molybdenocene and tungstenocene [Cp₂M(μ-OH)₂MCp₂]⁺ (Cp = η-C₅H₅; M = Mo or W) react with tropolone to afford corresponding tropolonato complexes [Cp₂M(trop)]⁺ (trop = C₇H₅O₂). The products were investigated by IR, ¹H NMR, and ¹³C NMR spectroscopy as well as by X-ray crystallography (M = W). The structure shows that the central metal is surrounded by a distorted tetrahedral array of the two centers of cyclopentadienyl ligands and the two oxygen atoms of tropolonato ligand. The reaction has been extended to the synthesis of calix[4]arene receptor functionalized at the 1,3-positions of the upper rim with two tropolonato-molybdenocene centers.     

pi-Electron interaction of PAHs with anion-exchange silica gels modified with anionic metal-porphine and -phthalocyanine derivatives as HPLC stationary phase for preparative column in organic solvents

To develop easy-to-prepare stationary phases for HPLC, we investigated anion-exchange silica gels, Nucleosil 5SB (Nuc), modified with metal-porphines and -phthalocyanines (M-P). The modified silica gels (M-P_N) were evaluated for the availability as a stationary phase of HPLC for the separation of π-electron-rich polyaromatic hydrocarbons (PAHs) in polar and non-polar eluents. Separation ability of silica gels modified with Cu-phthalocyanine derivative (Cu-PCS_N) was comparable to that of the silica gels binding Cu-PCS through sulfonamide bonds; however, the latter requires troublesome procedures for the preparation. The PAHs tested interact with Cu-PCS_N in non-polar organic eluents through their π-electrons similarly as in the case of the PYE column^®, in which interaction with PAHs was reported to be only the π-π-electron interaction.     

Influence of the precipitation rate on the seasonal variation in the specific radioactivity of short-lived222Rn daughters in precipitation

Data of variations in the RaB/²¹⁴Pb/ and RaC/²¹⁴Bi/activities in precipitation obtained from observations made for a period of almost 5 years are given together with data on changes in precipitation rate measured simultaneously. It is concluded from analysis of these data that the precipitation rate variation contributes to approximately 40% to the seasonal variation in the specific activity of precipitation.     

Isolation and Structure Determination of a Missing Endohedral Fullerene La@C70 through In Situ Trifluoromethylation

D_5h‐symmetric fullerene C₇₀ (D_5h‐C₇₀) is one of the most abundant members of the fullerene family. One longstanding mystery in the field of fullerene chemistry is whether D_5h‐C₇₀ is capable of accommodating a rare‐earth metal atom to form an endohedral metallofullerene M@D_5h‐C₇₀, which would be expected to show novel electronic properties. The molecular structure of La@C₇₀ remains unresolved since its discovery three decades ago because of its extremely high instability under ambient conditions and insolubility in organic solvents. Herein, we report the single‐crystal X‐ray structure of La@C₇₀(CF₃)₃, which was obtained through in situ exohedral functionalization by means of trifluoromethylation. The X‐ray crystallographic study reveals that La@C₇₀(CF₃)₃ is the first example of an endohedral rare‐earth fullerene based on D_5h‐C₇₀. The dramatically enhanced stability of La@C₇₀(CF₃)₃ compared to La@C₇₀ can be ascribed to trifluoromethylation‐induced bandgap enlargement.     

A Cationic Metal Glue Strategy for Expanding Paramagnetic Hetero-Multinuclear Metal-Oxo Clusters within Polyoxometalate Ligands

Precise structural design of large hetero-multinuclear metal-oxo clusters is crucial for controlling their large spin ground states and multielectron redox properties for application as a single-molecule magnet (SMM), molecular magnetic refrigeration, and efficient redox catalyst. However, it is difficult to synthesize large hetero-multinuclear metal oxo clusters as designed because the final structures are unpredictable when employing conventional one-step condensation reaction of metal cations and ligands. Herein, we report a “cationic metal glue strategy” for increasing the size and nuclearity of hetero-multinuclear metal-oxo clusters by using lacunary-type anionic molecular metal oxides (polyoxometalates, POMs) as rigid multidentate ligands. The employed method enabled the synthesis of {(FeMn₄)Mn₂Ln₂(FeMn₄)} oxo clusters (Ln=Gd, Tb, Dy, and Lu), which are the largest among previously reported paramagnetic hetero-multinuclear metal-oxo clusters in POMs and showed unique SMM properties. These clusters were synthesized by conjugating {FeMn₄} oxo clusters with Mn and Ln cations as glues in a predictable way, indicating that the “cationic metal glue strategy” would be a powerful tool to construct desired large hetero-multinuclear metal clusters precisely and effectively.     

Diverse Synthetic Transformations Using 4-Bromo-3,3,4,4-tetrafluorobut-1-ene and Its Applications in the Preparation of CF2CF2-Containing Sugars,Liquid Crystals,and Light-Emitting Materials

Organic molecules with fluoroalkylene scaffolds, especially a tetrafluoroethylene (CF₂CF₂) moiety, in their molecular structures exhibit unique biological activities, or can be applied to functional materials such as liquid crystals and light-emitting materials. Although several methods for the syntheses of CF₂CF₂-containing organic molecules have been reported to date, they have been limited to methods using explosives and fluorinating agents. Therefore, there is an urgent need to develop simple and efficient approaches to synthesize CF₂CF₂-containing organic molecules from readily available fluorinated substrates using carbon-carbon bond formation reactions. This personal account summarizes the simple and efficient transformation of functional groups at both ends of 4-bromo-3,3,4,4-tetrafluorobut-1-ene and discusses its synthetic applications to biologically active fluorinated sugars and functional materials, such as liquid crystals and light-emitting molecules.     

Asymmetric electrochemical oxidation of 1,2-diols, aminoalcohols, and aminoaldehydes in the presence of chiral copper catalyst

Asymmetric oxidation of 1,2-diols, aminoalcohols, and aminoaldehydes in the presence of copper(II) triflate and (R,R)-Ph-BOX was accomplished by electrochemical method using Br⁻ as a mediator. This oxidation was applicable to kinetic resolution of racemic cis-cycloalkane-1,2-diols, aminoalcohols, and aminoaldehydes to afford optically active compounds with good to high enantioselectivity.