Well-defined aqueous nanoassemblies from amphiphilic meta-terphenyls and their guest incorporation

Spherical molecular assemblies with diameters of ∼2 nm were quantitatively formed in water from new amphiphilic meta-terphenyls with two hydrophilic pendants at the central benzene ring. Whereas intermolecular interactions between small aromatic rings are typically weak, the obtained nanoassemblies are stable enough at wide-ranging concentrations and mostly remain intact even in the presence of similar nanoassemblies with polyaromatic frameworks. The nanoassembly with pentamethyl-substituted terminal benzene rings provides superior host capability for fluorescent dyes in water.     

Redox-active polyiron complexes with tetra(ethynylphenyl)ethene and [2,2]paracyclophane spacers containing ethynylphenyl units: extension to higher dimensional molecular wire

Redox active polyiron complexes with higher dimensional spacers, the tetrairon complex with the two-dimensional tetra(ethynylphenyl)ethene spacer, (C=C)[p-C(6)H(4)-C triple bond C-FeCp*(dppe)](4), and the diiron complex with the three-dimensional spacer (pseudo-m-[2,2]paracyclophane)[C triple bond C-FeCp*(dppe)](2), are prepared, and their performance as molecular wires is evaluated on the basis of their comproportionation constants for the mixed valence state.     

Site-sensitive X-ray photoelectron spectroscopy of Fe3O4 by photoelectron diffraction

Fe 2p core-level photoelectron spectra of magnetite were measured using soft X-ray and hard X-ray, and its emission angle dependence was investigated. The photoelectron diffraction pattern from different atomic sites differs because the atomic arrangement surrounding each site is different. By selecting the forward-focusing-peak (FFP) directions characteristic to each atomic site and measuring the kinetic energy dependence of the FFP intensities at the Fe 2p core-level range, we succeed in detecting the variation of the peak intensity of Fe 2p core-level spectra at different emission directions. This result, consistent with recent results, suggests that the lower-binding-energy peak of the Fe 2p core-level spectrum may be assigned as the B site component.     

Coordinatively unsaturated organometallic system based on Tp ligand: tetrahedral TpM-R′ and TpM-M′Ln species

Chemistry of the highly coordinatively unsaturated, tetrahedral hydrocarbyl and dinuclear complexes bearing a hydrotris(pyrazolyl)borate (Tp^R) ligand, Tp^RM-R′ and Tp^RM-M′L_n, is reviewed. The organometallic Tp^R complexes are prepared by salt elimination between the corresponding halide and Grignard reagents or metalates and fully characterized by spectroscopic and crystallographic methods. Although the number of the valence electrons of the resultant species is much shorter than that expected for a coordinatively saturated species (for mononuclear species: 14-15e vs. 18e; for dinuclear species: 29-32e vs. 34e), they turn out to be thermally stable. In particular, the ethyl complexes Tp^iPr2M-CH₂CH₃ (M = Fe, Co) are stable with respect to β-hydride elimination. The tetrahedral structures of the obtained organometallic species cause a small ligand field splitting of the frontier orbitals to lead to a high spin configuration, which leaves no vacant coordination site, and this should be the origin of the thermal stability of the electron deficient species. Upon interaction with donors they are incorporated into the organometallic system via switching of the spin state, and selective reactions dependent on the nature of the donor molecules are observed for the dinuclear complexes. Thus the high spin species can be regarded as masked forms of coordinatively unsaturated intermediates, which are regarded as key intermediates of organometallic transformations.     

First asymmetric total synthesis of synerazol, an antifungal antibiotic, and determination of its absolute stereochemistry

[reaction: see text] By synthesizing two possible diastereomers, the first asymmetric total synthesis of synerazol, an antifungal antibiotic, has been accomplished, allowing determination of its absolute stereochemistry. A more practical second generation route was also established. The key steps are racemization-free deprotection of a TIPS group and introduction of a methyl ether by DMD oxidation of the benzylidene moiety in a substrate having a small protecting group.     

Amine-based organic high-spin systems; a room-temperature-stable one-dimensional oligoaryl triamine-based trication

A triamine, 2,2′,4,4′-tetrabromo-3″,4″-dimethyl-5,5′-bis(di(4-methylphenyl)amino)triphenylamine, was designed and synthesized as a model precursor for purely organic cationic high-spin systems. Cyclic voltammetry measurements revealed that the triamine gives stable mono-, di-, and tricationic states at ambient temperature. Novel electron transfer stopped-flow (ETSF) methods were invoked for characterizing the absorption spectra of the corresponding mono- and oligo-cationic states. The triamine-based trication was generated by chemical oxidation at room temperature, and the triamine was quantitatively recovered upon reduction. The electronic ground state of the trication is discussed.     

Photochromic metal complexes: photoregulation of both the nonlinear optical and luminescent properties

A series of dithienylethene (DTE)-containing 2,2'-bipyridine ligands and their zinc(II) diacetate, zinc(II) dichloro, rhenium(I) tricarbonyl bromo, and ruthenium(II) bis(bipyridine) complexes have been designed and synthesized, and their photochromic, photophysical, and quadratic nonlinear optical properties have been studied. Upon UV irradiation at 350 nm, the ligands and complexes undergo ring closure of the DTE units, with a good to excellent photocyclization yield. In the case of the Re(I) and Ru(II) complexes, the photocyclization of the DTE units can also be triggered using visible light, upon excitation into the metal-to-ligand charge-transfer (MLCT) bands at 400 and 490 nm, respectively. Molecular quadratic nonlinear optical (NLO) responses of the complexes have been determined by using either the electrical field induced second harmonic generation (EFISH) or harmonic light scattering (HLS) technique at 1910 nm. These studies reveal a large increase of the second-order NLO activity after UV irradiation and subsequent formation of the ring-closed isomers. This efficient enhancement clearly reflects the delocalization of the π-electron system and the formation of strong push-pull chromophores in the closed forms. The combination of the photochromic DTE-based bipyridine ligand with luminescent Re(I) and Ru(II) fragments also allows the photoregulation of the emission, leading to an efficient quenching of the ligand-based 77 K luminescence and demonstrating that the photocontrol of two optical properties, linear and nonlinear, could be achieved by using the same photochromic ligand.     

Three-component Oxytrifluoromethylation of Alkenes: Highly Efficient and Regioselective Difunctionalization of CC Bonds Mediated by Photoredox Catalysts

Here comes the sun: A facile vicinal difunctionalization of alkenes, oxytrifluoromethylation, was established by visible-light-driven photoredox catalysis. Judicious choice of the CF(3) source is key. Nucleophiles such as water, alcohols, and carboxylic acids can be used in this highly efficient (2-4?h) and regioselective (100?%) transformation using light-emitting diode (LED) lamps and natural sunlight. SET=single-electron transfer.     

Determination of the absolute configuration of marine oxylipin topsentolide A1 by the synthesis of the enantiomer of the natural product

Two possible stereoisomers of topsentolide A₁, a cytotoxic oxylipin against human solid tumor cell lines, were prepared in order to determine the stereochemistry of natural product. That is, the enantiomer of topsentolide A₁, (8S,11S,12R)-isomer, and its diastereomer was efficiently synthesized in a stereoselective manner. The stereochemistry of topsentolide A₁ was determined to be 8R,11R,12S by comparing NMR spectra and specific rotations of the synthetic isomers and the natural product.