New chemical synthesis of functionalized arylzinc compounds from aromatic or thienyl bromides under mild conditions using a simple cobalt catalyst and zinc dust

A new chemical method for the preparation of arylzinc intermediates is described in acetonitrile, on the basis of the activation of aryl bromides by low-valent cobalt species arising from the reduction of cobalt halide by zinc dust. This procedure allows for the synthesis of a variety of functionalized aryl- and thienylzinc species in good to excellent yields. The versatility and the simplicity of that original method represent an alternative to most known procedures.     

New and simple one-step cobalt-catalyzed preparation of functionalized arylstannanes from the corresponding aryl bromides or iodides

A variety of functionalized arylstannanes are obtained in moderate to excellent yields by a one-step chemical procedure from corresponding halides and tributylstannyl chloride via cobalt catalysis.     

APW-Xα Compton profiles in crystalline rare gases

Augmented Plane Wave, local exchange (APW-Xα) one-electron wave functions have been used to calculate Compton profiles for crystalline Ne at three different lattice constants for two values of the local exchange parameter. Some results for Ar, Kr, and Xe are also presented. The impulse approximation is used. The crystalline calculations are little different from the isolated atom results. A variety of difficulties, primarily due to the energy-dependent nature of the APW basis, are explored. A translational symmetry restriction that is particularly severe for APW calculations of Compton profiles is studied. In all, it is concluded that the APW scheme is ill-suited to the computation of the sort of non-energy quantity represented by a Compton profile.     

Site-selective electron nuclear double resonance in the exchange-narrowed regime of the ESR in conducting solids

Electron nuclear magnetic double resonance on conduction electrons reveals the hyperfine interaction hidden by the fast electron spin exchange. We used the Overhauser shift technique to investigate the electron spin density of the conduction band of gallium oxide, beta-Ga(2)O(3). Due to the monoclinic structure, the conduction band of beta-Ga(2)O(3) is anisotropic and it is dominated by contributions from the two nonequivalent Ga sites. The large quadrupole couplings of the two gallium isotopes (69)Ga and (71)Ga (both with I = 3/2) are completely resolved in our double-resonance experiments. This resolved quadrupole interaction allows the determination of the electric field gradients at both gallium sites with high precision and high sensitivity. The resolved quadrupole splitting is the key to the site-selected determination of the hyperfine interaction. The concepts behind these double-resonance techniques are rather general and should be applicable in similar semiconductor systems.     

Iron oxide chemistry. From molecular clusters to extended solid networks

This overview features the chemical background on condensation phenomena of iron cations in aqueous solution. The formation of molecular clusters or nanosized solid phases is interpreted with illustrative mechanisms building a bridge between solution chemistry and solid state chemistry. Iron chemistry gives a very nice example of chemical versatility.     

Cobalt(I)-mediated [2 + 2 + 2] cyclization of allenediynes toward a diastereoselective approach to 11-aryl steroid skeletons

[reaction: see text] An 11-aryl steroid skeleton has been built in one step with a simultaneous introduction of the substituents at both C11 and C10 in 48% overall yield from a trans-allenediyne, whereas a formal Alder ene reaction leading to a bicyclic yne-trienic compound becomes the major process from the cis-allenediyne.     

Photochemical behavior of a new long-chain UV absorber derived from 4-tert-butyl-4'-methoxydibenzoylmethane

A new UV filter, the 1-(4-tert-butylphenyl)-2-decanyl-3-(4'-methoxyphenyl)-propane-1,3-dione, called C10-DBM, was prepared by grafting a 10-carbon aliphatic chain to the alpha-carbonyl position of 4-tert-butyl-4'-methoxydibenzoylmethane (BM-DBM), a well-known and often used UV filter. The UV-A absorption efficiency of organic solutions containing the new filter was tested and compared with identical solutions containing BM-DBM with or without irradiation (xenon lamp). The originality of this new filter is that its UV-A absorbance appeared during irradiation of the molecule. Although the molar absorption coefficient of C10-DBM in the UV-A domain was lower than that of BM-DBM, the solutions absorption exhibited a much more photostable behavior under irradiation. In this study, we first demonstrated that C10-DBM was a precursor of BM-DBM (enol isomer) by means of high-performance liquid chromatography followed by mass spectrometry. Indeed, we showed that the UV-A absorption of C10-DBM solutions appearing during the irradiation of the molecule was due to a Norrish-II reaction (beta-cleavage), which induced the release of the BM-DBM enol form and 1-decene. Then, we established a kinetic model for the photochemistry of C10-DBM and fitted the variation of UV absorption spectra to confirm the proposed mechanism.     

Optical and electrochemical cations recognition and release from N-azacrown carbazoles

Two azacrown derivatives of carbazole have been prepared and their dipole moments in the excited state were estimated from solvatochromism. Their complexation constant K with calcium and sodium cations have been determined from the absorption spectra, the fluorescence spectra and, independently, from the first oxidation potential shift, as a function of the concentration in sodium and calcium perchlorates, when K is lower than 10⁵. The fluorescence spectra of the calcium and sodium complexes in acetonitrile show two bands different from the fluorescence of the free probes, one from the excited complex similar to the fluorescence of the protonated probes and the other one from the nitrogen decoordinated cation complexes. These results are typical for moderatly polar crowned merocyanines with the ionophore acting as an electron-donor substituent. The stepwise decoordination rate of the calcium and sodium cations from the nitrogen atom of the fluorophore is competitive with the rate constant of fluorescence which accounts for the multiple fluorescence but does not allow a distant diffusion of the cations. From the study of the longer lived radical-cation of the azacrown carbazoles, generated electrochemically, the metal cations are completely released from the azacrown receptor as revealed by the unsensitivity of the second oxidation potential to the perchlorate salts. From the probe-cation pair with the higher association constant (log K > 6) the oxidation peak for the complex allows to estimate the decrease of K upon the oxidation of the probe to be a value of K ?⁺/K = 8 × 10^-4.