Synthesis of Thiophene-Substituted Spiropyrans and Spirooxazines,Precursors of Photochromic Polymers

The synthesis of spiropyrans 11 and 12 and spirooxazines 13–17 containing a thiophene moiety is described. Two different synthetic approaches were used. The spectrokinetic properties of these new compounds are reported.     

Electrochemistry of Mono- through Hexakis-adducts of C60

The first systematic electrochemical study by cyclic voltammetry (CV) and rotating-disk electrode (RDE) of the changes in redox properties of covalent fullerene derivatives ( 2 – 11 ) as a function of increasing number of addends is reported. Dialkynylmethanofullerenes 2 – 4 undergo multiple, fullerene-centered reduction steps at slightly more negative potentials than C₆₀ ( 1 ; see Table and Fig. 1). The two C-spheres in the dumbbell-shaped dimeric fullerene derivative 4 show independent, identical redox characteristics. This highlights the insulating character of the sp³-C-atoms in methanofullerenes which prevent through-bond communication of substituent effects from the methano bridge to the fullerene sphere. In the series of mono- through hexakis-adducts 5 – 11 , formed by tether-directed remote functionalization, reductions become increasingly difficult and more irreversible with increasing number of addends (see Table and Fig. 2). Whereas, in 0.1M Bu₄NPF₆/CH₂Cl₂, the first reduction of mono-adduct 5 occurs reversibly at ?1.06 V vs. the ferrocene/ferricinium couple (Fc/Fc⁺), hexakis-adduct 11 is reduced irreversibly only at ? 1.87 V. Hence, with incremental functionalization of the fullerene, the LUMO of the remaining conjugated framework is raised in energy. Reduction potentials are also dependent on the relative spatial disposition of the addends on the surface of the fullerene sphere. Observed UV/VIS spectral changes and changes in the chemical reactivity along the series 5 – 11 are in accord with the results of electrochemical measurements. Further, with increasing number of addends, the oxidation of derivatives 5 – 11 becomes more reversible. Whereas oxidations are increasingly facilitated upon going from mono-adduct 5 (+1.22 V) to tris-adduct 7 (+0.90 V), they occur at nearly the same potential (+0.95 to +0.99 V) in the higher adducts 8 – 11 . This indicates that the oxidations occur in these compounds at a common sub-structural element, for which a ‘cubic’ cyclophane is proposed (see Fig. 3). This sub-structure is fully developed in hexakis-adduct 11 .     

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.     

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.