Efficient hydroxycarbonylation of aryl iodides using recoverable and reusable carbon aerogels doped with palladium nanoparticles as catalyst

Electron-rich and electron-poor aryl iodides are converted, in high to excellent yields, into the corresponding carboxylic acids through a hydroxycarboxylation reaction catalyzed by a recoverable and reusable phosphine free palladium-carbon aerogel catalyst using lithium formate and acetic anhydride as an internal condensed source of carbon monoxide. The catalyst system can be reused several times without any appreciable loss of activity.     

High performance parallel numerical methods for Volterra equations with weakly singular kernels

Non-stationary discrete time waveform relaxation methods for Abel systems of Volterra integral equations using fractional linear multistep formulae are introduced. Fully parallel discrete waveform relaxation methods having an optimal convergence rate are constructed. A significant expression of the error is proved, which allows us to estimate the number of iterations needed to satisfy a prescribed tolerance and allows us to identify the problems where the optimal methods offer the best performance. The numerical experiments confirm the theoretical expectations.     

A novel simple and efficient bromination protocol for activated arenes

An efficient, high yielding, and environmentally benign bromination using an alkali metal bromide as the bromine source is disclosed. Investigation of the protocol revealed that the method operates for activated arenes producing the corresponding monobrominated products in good to excellent yields.     

Theoretical prediction of linear free energy relationships using proton nucleomers

Values of σ and σ⁺, for use in linear free energy relationships, are determined for para hydrogen atoms having nuclear charges other than 1 (nucleomers). Hammett ρ values for a variety of free energies of activation, reaction, and other extrathermodynamic properties (e.g., vibrational frequencies) are computed therefrom and compared to those computed using typical para functional groups. The nucleomer correlations show excellent qualitative agreement with standard correlations but the quantitative agreement is less good, typically underestimating the standard ρ‐value by 10–60%. Copyright © 2007 John Wiley & Sons, Ltd.     

Self-assembly of water cluster in iron(III) oxalate-bridged complexes

The synthesis and crystal structural characterization of the compound of formula {[Fe^II(phen)₃]₂[Fe₂^IIIox₅]}·11H₂O (1) has been reported. The most interesting feature of the solid state structure of 1 consists in the occurrence of decanuclear water clusters made up of self-assembled cyclic hexameric water clusters with a quasi-planar conformation, unclosed trinuclear clusters and individual water molecules. The decanuclear water clusters are connected to the host lattices via an extensive net of strong hydrogen bonds that finally lead to an extended 3D supramolecular organization, wherein hexameric water clusters interconnected with dodecameric hybrid water–O_oxalate clusters can be identified. The comparison of this supramolecular architecture with that found in the already known compound of formula [Fe(bpm)₃]₂[Fe₂(ox)₅]·8H₂O (2) allows some preliminary observations on the design and control of water cluster nuclearity and conformation.     

Synthesis of new materials based on polythiophenes substituted with mesogen groups

A new family of conjugated polymers formed by 3-alkyloximethylthiophenes substituted with a biphenyl group was synthesised by a route involving first the coupling of a functionalised alkyl chain, from 8 to 12 carbon atoms, to 3-methanolthiophene, and then the attachment of the mesogen group. The monomer was characterised by conventional techniques, and thermal studies were also achieved. The polymerisation of these units was carried out via oxidative polymerisation with FeCl₃. The resultant polymers were characterised by FT-IR, elemental microanalysis and XPS. Subsequently, these materials were doped with I₂ and characterised by the above techniques and conductivity measurements, which indicated that these materials are in the semiconductor range. The polymerisation of these monomers was also carried out via electrochemical methods, and it was found that, together with the oxidation of the thiophene ring, the oxidation of the biphenyl group is also produced, for which an over-oxidised material is obtained, as demonstrated by XPS analysis and theoretical calculations.     

A comparison between the absorption properties of the regular and F<Subscript><Emphasis Type="Italic">s</Emphasis></Subscript>-defected MgO (100) surface

The electron density, the electrostatic potential and the electric field of the MgO (100) surface, both regular and containing an oxygen vacancy (F _s center), are compared in order to understand the modifications induced in the surface-absorbate interaction by the presence of the defect, with particular attention to the metal-oxide case. The spin-density for a gold atom absorbing on the most characteristic sites of the regular and F _s -defected surface is also shown. It is found that in the defected surface the electron pair in the vacancy protrudes appreciably out of the surface, thus shifting the electrostatic potential to negative values (but producing a similar electric field) and being able to chemically interact with neighboring absorbed species. These results rationalize the rotational invariance and double frustration effects previously described for the metal/F _s -defected MgO (100) surface.