Palladium-catalysed regioselective addition reaction of ethyl phenylphosphinate with terminal acetylenes: ligand- and solvent-dependent regioselectivity

Palladium-1,2-bis(diphenylphosphino)ethane complex catalyses regioselective Markovnikov addition of ethyl phenylphosphinate to terminal alkynes in toluene, while the use of tri-tert-butylphosphine as the ligand or ethanol as the solvent leads to regioselectivity reversal.     

Host-guest effect on chirality transfer from a binaphthyl derivative to a host nematic liquid crystal

A novel dichiral compound possessing both an asymmetric axis and a chiral centre induces opposite twist senses and distinct helical pitches in different host nematic liquid crystals; the host-guest effect on chirality transfer is discussed in terms of molecular recognition.     

Development of a general route to periphery-functionalized azaborines and ladder-type azaborines by using common intermediates

Azaborines and ladder-type azaborines bearing various functional groups can be synthesized starting from common dibromo derivative intermediates, and among several substituents, the carbazol-9-yl group was shown to enhance the photo-luminescence quantum yield of the azaborines up to a value of unity.     

Reverse photochromic behavior of an iron-magnesium complex

We have obtained a novel heterobimetallic iron-magnesium complex, (THF)4Mg(mu-Br)2FeBr2 (THF = tetrahydrofuran), which showed reverse photochromism in THF. The response exhibited in this system is associated with d-orbital splitting of the Fe atom and a change in the molecular aggregation state (dimerization).     

Linear metal-metal-bonded tetranuclear M-Mo-Mo-M complexes (M = Ir and Rh): oxidative metal-metal bond formation in a tetrametallic system and 1,4-addition reaction of alkyl halides

Reaction of Mo2(pyphos)4 (1) with [MCl(CO)2]2 (M = Ir and Rh) afforded linear tetranuclear complexes of a formula Mo2M2(CO)2(Cl)2(pyphos)4 (2, M = Ir; 3, M = Rh). X-ray diffraction studies confirmed that two "MCl(CO)" fragments are introduced into both axial sites of the Mo2 core in 1 and coordinated by two PPh2 groups in a trans fashion, thereby forming a square-planar geometry around each M(I) metal. Treatment of 2 and 3 with an excess amount of tBuNC and XylNC induced dissociation of the carbonyl and chloride ligands to yield the corresponding dicationic complexes [Mo2M2(pyphos)4(tBuNC)4](Cl)2 (5a, M = Ir; 6a, M = Rh) and [Mo2M2(pyphos)4(XylNC)4](Cl)2 (7, M = Ir; 8, M = Rh). Their molecular structures were characterized by spectroscopic data as well as X-ray diffraction studies of BPh4 derivatives [Mo2M2(pyphos)4(tBuNC)4](BPh4)2 (5b, M = Ir; 6c, M = Rh), which confirmed that there is no direct sigma-bonding interaction between the M(I) atom and the Mo2 core. The M(I) atom in 5 and 6 can be oxidized by either 2 equiv of [Cp2Fe][PF6] or an equimolar amount of I2 to afford Mo(II)2M(II)2 complexes, [Mo2M2(X)2(tBuNC)4(pyphos)4]2+ in which two Mo-M(II) single bonds are formed and the bond order of the Mo-Mo moiety has been decreased to three. The Ir(I) complex 5a reacted not only with methyl iodide but also with dichloromethane to afford the 1,4-oxidative addition products [Mo2Ir2(CH3)(I)(tBuNC)4(pyphos)4](Cl)2 (13) and [Mo2Ir2(CH2Cl)(Cl)(tBuNC)4(pyphos)4](Cl)2 (15), respectively, although the corresponding reactions using the Rh(I) analogue 6 did not proceed. Kinetic analysis of the reaction with CH3I suggested that the 1,4-oxidative addition to the Ir(I) complex occurs in an SN2 reaction mechanism.     

Investigation of molecular chain orientation change of polymer crystals in phase transitions by friction anisotropy measurement

Direct observation of the molecular orientation change in polymer crystals provides us visible information for understanding their structural phase-transition mechanisms. In this letter, we successfully identified the main-chain orientation of poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) crystals over all directions using friction anisotropy measured by lateral-modulation friction force microscopy (LM-FFM). This technique made possible our investigation of molecular orientation changes caused by a ferroelectric phase transition and also a fabrication process for artificial nanometer-scale structures. These results give us visual information that is directly connected to the transition mechanisms.     

An efficient oxidative lactonization of 1,4-diols catalyzed by Cp*Ru(PN) complexes

[reaction: see text] An efficient oxidative lactonization of 1,4-diols in acetone is accomplished by the well-defined ruthenium catalyst, whose bifunctional nature underlies the high efficiency as well as unique chemo- and regioselectivity of the reaction which provides a rapid access to gamma-butyrolactones including flavor lactones hinokinin, and muricatacin.     

Mass yield distributions of target fragments from the reactions of iron with 135 MeV/nucleon 12C and 80 MeV/nucleon 16O ions

Cross sections for the production of target fragments in the reactions of iron with 135 MeV/nucleon ¹²C and 80 MeV/nucleon ¹⁶O ions have been measured by off-line γ-ray spectroscopy. Through these data, the mass yield distributions have been obtained. The result of the experiment for the reaction with 135 MeV/nucleon ¹²C ions is compared with theoretical calculations using the fusion-fragmentation model and the GEMINI code for sequential binary decay, following a calculation with the fireball model. Reveived: 24 March 1999 / Revised version: 16 July 1999     

Hydrogen removal by annealing from C-doped InGaAs grown on InP by metalorganic chemical vapor deposition

Hydrogen removal from C-doped InGaAs grown on InP substrate by metalorganic chemical vapor deposition is discussed based on the dependence of hole concentration on various annealing conditions. It is revealed that the hydrogen removal rate becomes higher as the annealing temperature is higher and the activation energy of hydrogen removal is about 1.9 eV regardless of C-doped layer thickness. The hydrogen removal rate is also found to be inversely proportional to C-doped layer thickness, suggesting that the hydrogen removal reaction is mainly governed by hydrogen diffusion.