Trifluoromethylation of [AuF3(SIMes)]: Preparation and Characterization of [Au(CF3)xF3−x(SIMes)] (x=1–3) Complexes

Trifluoromethylation of [AuF₃(SIMes)] with the Ruppert–Prakash reagent TMSCF₃ in the presence of CsF yields the product series [Au(CF₃)_xF_3−x(SIMes)] (x=1–3). The degree of trifluoromethylation is solvent dependent and the ratio of the species can be controlled by varying the stoichiometry of the reaction, as evidenced from the ¹⁹F NMR spectra of the corresponding reaction mixtures. The molecular structures in the solid state of trans-[Au(CF₃)F₂(SIMes)] and [Au(CF₃)₃(SIMes)] are presented, together with a selective route for the synthesis of the latter complex. Correlation of the calculated SIMes affinity with the carbene carbon chemical shift in the ¹³C NMR spectrum reveals that trans-[Au(CF₃)F₂(SIMes)] and [Au(CF₃)₃(SIMes)] nicely follow the trend in Lewis acidities of related organo gold(III) complexes. Furthermore, a new correlation between the Au−C_carbene bond length of the molecular structure in the solid state and the chemical shift of the carbene carbon in the ¹³C NMR spectrum is presented.     

Polymorphism and Phonon Dynamics of α‐Quaterthiophene

Two 4T: Low‐frequency micro‐Raman spectroscopy coupled with lattice dynamics calculations is an invaluable tool for investigating polymorphism in organic semiconductors. The Raman spectra of the low‐temperature (LT) and high‐temperature (HT) polymorphs of α‐quaterthiophene (4T) are presented and interpreted (see picture). Raman mapping is applied to investigate the phase purity.

     

A perturbation solution of Michaelis–Menten kinetics in a “total” framework

In this paper we expand the equations governing Michaelis–Menten kinetics in a total quasi-steady state setting, finding the first order uniform expansions. Our results improve previous approximations and work well especially in presence of an enzyme excess.     

Porosity development in chars from thermal decomposition of poly(p-phenylene terephthalamide)

The main objective of this work was to investigate the development of porosity in solid residues from the thermal decomposition of the polymer, poly(p-phenylene terephthalamide) (PPTA). PPTA chars were prepared at different temperatures and characterized by X-ray diffraction and physical adsorption of CO₂ at 0 °C. The carbonization temperatures were selected on the basis of thermogravimetric analysis results. The effect of introducing an isothermal treatment at 500 °C on the characteristics of the resulting chars was also studied. It was found that this pre-treatment lowers the decomposition temperature of PPTA and yields a somewhat less ordered material than in the case of pyrolysis under a constant heating rate. The micropore volume increases with increasing heat treatment temperature for both series of samples. The mean micropore size decreases for the two series of chars until the 700-800 °C interval; above these temperatures, this evolution is reversed. The micropore volume of the samples submitted to the isothermal treatment is higher than when PPTA is treated under a constant heating rate. Likewise, the pore size distribution is more heterogeneous when the intermediate isothermal treatment at 500 °C is introduced during PPTA pyrolysis. Some differences between porosity development in chars from PPTA and other high thermal stability polymers were explained on the basis of different mechanistic features in polymer pyrolysis.     

Intramolecular and intermolecular OH…O and OH…F interactions in perfluoropolyethers with polar end groups: IR spectroscopy and first-principles calculations

Perfluoropolyether (PFPE) fluids constitute a class of polymers that fulfil a wide range of requirements for hi-tech applications, due to their pefluorinated backbone. For some of these applications they are requested to bear polar end groups, and the combination of a chemical inert backbone and a reactive end group can produce peculiar conformations and supramolecular structures. The molecular structure and the vibrational properties of the ethoxyl-terminated PFPE FLUOROLINK®E10H in solution are here investigated by means of IR spectroscopy. It is shown that the complex spectral features of the OH-stretching region cannot be explained without a thorough computational study, involving the investigation of the conformational space of an isolated model molecule by means of semiempirical AM1 calculations and DFT calculations. The most relevant conformers were singled out, showing a high degree of conformational disorder for FLUOROLINK®E10H. Furthermore, it is shown that intra- and intermolecular H-bonding affects significantly the molecular structure and the vibrational spectrum. Several interactions are shown to be relevant, such as OH^…F interactions and complexes with residual water. Theoretical values of the absolute intensities of OH stretching IR bands, relevant for the analytical applications, are obtained.     

Neutral p-cymene ruthenium complexes with P-stereogenic monophosphines. New catalytic precursors in enantioselective transfer hydrogenation and cyclopropanation

A family of eight neutral, pseudotetrahedral piano-stool ruthenium complexes C, of the type [RuCl₂(p-cymene)(PArPhR)] (Ar = 1-naphthyl, 9-phenanthryl and 2-biphenylyl; R = Me, i-Pr, OMe, –CH₂SiMe₃ and –CH₂SiPh₃) have been prepared and characterised, including the X-ray crystal structure for C6 (Ar = 2-biphenylyl; R = i-Pr). These complexes catalyse the asymmetric hydrogen transfer reaction of acetophenone in refluxing 2-propanol in the presence of potassium tert-butoxyde, reaching full conversions and up to 45% ee after 24 h towards the S enantiomer of 1-phenylethanol. Cationic complexes formed upon treatment of C with one equivalent of AgSbF₆ or (Et₃O)PF₆ are active in the cyclopropanation reaction of styrene and α-methylstyrene by ethyl diazoacetate. Low to moderate conversions (up to 58%), diastereoselectivities (up to 40% de), and moderate enantioselectivities (up to 69% ee) have been found. For both reactions, bulky complexes and C6 in particular lead to the best results.