Nickel-catalyzed hydrosilylation/cyclization of difluoro-substituted 1,6-enynes

Ni-catalyzed hydrosilylative cyclization of difluoro-substituted 1,6-enynes can be carried out. The presence of a geminal-difluoromethylene group at an alkene terminus in enynes is essential for the reaction to proceed.     

Electrochemically stable fluorohydrogenate ionic liquids based on quaternary phosphonium cations

Fluorohydrogenate ionic liquids of quaternary phosphonium cations, tri-n-butylmethylphosphonium (P₄₄₄₁) fluorohydrogenate, tetra-n-butylphosphonium (P₄₄₄₄) fluorohydrogenate, and tri-n-butyl-n-octylphosphonium (P₄₄₄₈) fluorohydrogenate, have been synthesized by the metatheses of anhydrous hydrogen fluoride and the corresponding phosphonium chloride precursors. All the obtained salts have melting points below room-temperature with a vacuum-stable composition of P_444m(FH)_2.3F (m = 1, 4, and 8) and were characterized by density, conductivity, and viscosity measurements. Linear sweep voltammetry with a glassy carbon working electrode shows that the P_444m(FH)_2.3Fs have wide electrochemical windows exceeding 5.2 V. In particular, P₄₄₄₁(FH)_2.3F has an electrochemical window of 6.0 V, which is the widest among fluorohydrogenate ionic liquids reported to date. The thermal stability of these ionic liquids is also improved compared to the salts of N-heterocyclic ammonium cations.     

Trichlorosilyl triflate for enantioselective direct-type aldol reaction with chiral phosphine oxide

Trichlorosilyl triflate, in the presence of a chiral Lewis base catalyst, provides an effective method for the enantioselective direct-type aldol reaction of aldehydes and ketones. A chiral Lewis base induces both the production and activation of trichlorosilyl enol ether, yielding an aldol product in good yield and with high diastereo- and enantioselectivities.     

Enantioselective reductive aldol reaction using tertiary amine as hydride donor

An efficient method was developed for the enantioselective reductive aldol reaction of α,β-unsaturated ketones with aldehydes in the presence of a Lewis base catalyst; conjugate reduction using a tertiary amine and trichlorosilyl triflate, followed by an aldol reaction with BINAP dioxide (BINAPO) as an organocatalyst, gave the corresponding product in high yield with high stereoselectivity.     

Transfer efficiency in ballistic electron emission microscopy taking diffraction of emitted hot electrons into account

We have analyzed the transfer efficiency of ballistic electron emission microscopy (BEEM), taking the finite spot size of the emitted electron beam from scanning probes into account. Three-dimensional diffraction from an aperture at a surface-metal/air interface is introduced to model an effect caused by the finiteness of spot size. As a general trend, the diffraction decreases BEEM transfer efficiency. The diffraction effect increases as the spot size decreases and the air-gap distance increases. In a Au/GaAs sample, BEEM transfer efficiency markedly deteriorates down to 6% of the value derived from a conventional planar tunneling theory when a spot size of 0.2 nm, an air-gap distance of 0.6 nm, and an electron energy of 0.2 eV, measured from the bottom of the GaAs conduction band, are assumed. BEEM transfer efficiency is markedly dependent on the spot size of the emitted hot electron. This result indicates that the BEEM current depends on the spatial resolution of the scanning probe, that is, the condition of the tip apex.     

Nickel-catalyzed reductive cleavage of aryl alkyl ethers to arenes in absence of external reductant

The reductive cleavage of the C–O bonds of aryl ethers has great potential in organic synthesis. Although several catalysts that can promote the reductive cleavage of aryl ethers have been reported, all such systems require the use of an external reductant, e.g., hydrosilane or hydrogen. Here, we report the development of a new nickel-based catalytic system that can cleave the C–O bonds of ethers in the absence of an external reductant. The hydrogen atom required in this new reductive cleavage reaction is provided by the alkoxy group of the substrate, which serves as an internal reductant. The absence of an external reductant enables the unique chemoselectivity, i.e., the selective reduction of an alkoxy group over alkenes and ketones.     

Striking Differences in Properties of Geometric Isomers of [Ir(tpy)(ppy)H]+: Experimental and Computational Studies of their Hydricities,Interaction with CO2, and Photochemistry

We prepared two geometric isomers of [Ir(tpy)(ppy)H]⁺, previously proposed as a key intermediate in the photochemical reduction of CO₂ to CO, and characterized their notably different ground‐ and excited‐state interactions with CO₂ and their hydricities using experimental and computational methods. Only one isomer, C‐trans‐[Ir(tpy)(ppy)H]⁺, reacts with CO₂ to generate the formato complex in the ground state, consistent with its calculated hydricity. Under photocatalytic conditions in CH₃CN/TEOA, a common reactive C‐trans‐[Ir(tpy)(ppy)]⁰ species, irrespective of the starting isomer or monodentate ligand (such as hydride or Cl), reacts with CO₂ and produces CO with the same catalytic efficiency.