CO2 anion-radical in organic carboxylations

This letter shows a first approximation to the use of CO₂ anion-radical in the obtention of α-methyl and α-ethylcyanoacetic acids from propionitrile and butyronitrile, respectively, through a paired electrochemical reaction with CO₂. The electrosynthesis of α-chloro-phenylacetic acid from benzyl chloride and phenylacetic acid from toluene by another proposed pathway is also discussed.     

Dicyclopentadienyl-niobium(iii) and -niobium(iv) complexes

The reduction of (η-C₅H₅)₂NbCl₂ (I) under various conditions gives the dimer (η-C₅H₅)₄Nb₂Cl₃ (II) containing niobium(III) and niobium(IV). Reaction of II with AgClO₄ gives [(η-C₅H₅)₄Nb₂Cl₂]⁺ ClO₄^- (III). FeCl₃ and (C₆F₅)₂ TlBr displace I from II to give (η-C₅H₅)₂Nb(μ-Cl)(μ-X)MY₂, where MFe, XYCl(IV) and MTl, XBr, YC₆F₅ (V). Reactions of I with metal halides MXY₂ give (η-C₅H₅)₂ClNb(μ-Cl)MXY₂ where XYCl, MAl (VI), Fe (VII), Tl (VIII) and XBr, YC₆F₅, MTl (IX). The chemical behaviour of all these compounds is described.     

In situ FTIR spectroscopy study of the break-in phenomenon observed for PPy/PVS films in acetonitrile

The in situ Fourier transform infrared (in situ FTIR) technique was used for the first time to investigate the break-in phenomenon observed for polypyrrole/poly(vinyl sulfonate) (PPy/PVS) films in acetonitrile containing 0.1 M LiClO(4). Consecutive potential scans provided a continuous increase of the infrared band intensities, simultaneous to an increase observed in the charge involved in the voltammetric peaks, suggesting a rise in the number of the polymeric chains participating in the infrared signal at the same time as the electroactive participants increase in the redox process. Moreover, in situ FTIR spectra evidence that the new infrared-activated chains in each voltammetric cycle adopt the same polymeric structure achieved by the chains activated in the initial cycles. However, if we achieve a cathodic potential limit of -2.1 V (vs Ag/AgCl), a restructuring of the polymeric morphology is observed. In situ FTIR spectra obtained for PPy/ClO(4) films under the same conditions pointed to a steady-state behavior from the very early voltammetric scans. Moreover, the intensities of FTIR bands obtained for PPy/ClO(4) films in the early voltammetric cycles are much higher than those obtained for PPy/PVS films after several potential scans. Only when high cathodic and high anodic potential limits were used for the consecutive cycles did the FTIR band intensities from PPy/PVS become similar to those obtained from PPy/ClO(4), indicating that in both films a similar number of polymeric chains were infrared active. Polarization at a high anodic potential (+1.3 V vs Ag/AgCl) produced overoxidation of the polymer appearing characteristic 1725 cm(-1) band assigned to the formation of carbonyl groups. Furthermore, the approximately 1540 cm(-1) band shifted to higher wavenumbers, indicating that overoxidation reduced the length of conjugated chains in the polypyrrole.     

Carbene formation in its lower singlet state from photoexcited 3H-diazirine or diazomethane. A combined CASPT2 and ab initio direct dynamics trajectory study

The potential energy surfaces of the ground and valence excited states of both 3H-diazirine and diazomethane have been studied computationally by mean of the CASSCF method in conjunction with the cc-pVTZ basis set. The energies of the critical points found on such surfaces have been recomputed at the CASPT2/cc-pVTZ level. Additionally, ab initio direct dynamic trajectory calculations have been carried out on the S(1) and S(2) surfaces, starting each trajectory run at the region dominated by the conformational molecular rearrangement of diazomethane. It is found that both isomers are interconnected along a C(s)() reaction coordinate on each potential surface. Radiationless deactivation of the corresponding S(1) state of each isomer occurs through the same point on the surface, an S(1)/S(0) conical intersection. Thereafter, the system has enough energy to surmount the barrier which leads to dissociation products (CH(2) + N(2)) on S(0) state. Therefore, photoexcitation to S(1) state of either diazirine of diazomethane produces methylene in its lower singlet state on a very short time scale (ca. 100 fs). Furthermore, both isomers can generate excited singlet carbene when they are excited onto the S(2) surface; in this case, they lose the activation energy passing through another common S(2)/S(1) conical intersection and then proceed to dissociation into carbene and N(2) on the S(1) surface. For the special case of methylene, it rapidly experiences deexcitation to S(0) state.     

Synthesis and Characterization of Spinel‐Type Gallia‐Alumina Solid Solutions

By precipitation with ammonia of ethanolic solutions containing the appropriate proportions of gallium and aluminium nitrate, following by calcination of the resulting gels at 773 K, mixed Ga₂O₃/Al₂O₃ oxides having Ga:Al ratios of 9:1, 4:1, 1:1, 1:4 and 1:9 were obtained. Powder X‐ray diffraction showed that these mixed metal oxides form a series of solid solutions having the spinel‐type structure; also shown by γ‐Al₂O₃ and γ‐Ga₂O₃. The specific surface area (determined by nitrogen adsorption at 77 K) was found to range from 160 m² g^?1 for the mixed oxide having Ga:Al = 9:1 up to 370 m² g^?1 for that having Ga:Al = 1:9. High resolution MAS NMR showed that Ga³⁺ and Al³⁺ ions occur at both tetrahedral and octahedral sites in the spinel‐type structure of the mixed metal oxides, although there is a preferential occupation of tetrahedral sites by Ga³⁺ ions. A proportion of penta‐coordinated Al³⁺ ions was also found. IR spectra of carbon monoxide adsorbed at 77 K showed that the mixed metal oxides have a considerable Lewis acidity, related mainly to tetrahedrally coordinated metal ions exposed at crystal surfaces. The characteristic infrared absorption band of coordinated (adsorbed) CO appears in the range 2205–2190 cm^?1, and its peak wavenumber is nearly independent of Ga:Al ratio in the mixed gallia‐alumina oxides.     

Synthesis and characterization of cyclopentadienyl/alkoxo titanium dichlorides: structural analysis of monocyclopentadienyl titanium dichlorides with ligands derived from menthol and borneol

A variety of monocyclopentadienyl alkoxo titanium dichloride and bisalkoxo titanium dichloride complexes have been prepared and characterized by spectroscopic techniques. The titanium derivatives containing both cyclopentadienyl and various alkoxo ligands [Ti(η⁵-C₅H₅)(OR)Cl₂] (1-5) have been synthesized from the reaction of [Ti(η⁵-C₅H₅)Cl₃] with 1 equivalent of the corresponding alcohol in THF in the presence of triethylamine (ROH = Adamantanol, 1R,2S,5R-(−)-menthol, 1S-endo-(−)-borneol, cis-1,3-(−)-benzylideneglycerol, 1,2:3,4-di-O-isopropylidene-α-d-galactopyranose). The bisalkoxo titanium dichloride derivatives [TiCl₂(OR)₂] (6-10) have been prepared by a redistribution reaction between Ti(OR)₄ and TiCl₄ compounds 6-8 (OR = Adamantanoxy, (1R,2S,5R)-(−)menthoxy, (1S-endo)-(−)-borneoxy) and by reaction of [Ti(OR)₂(OPrⁱ)₂]₂ with CH₃COCl compounds 9 and 10 (OR = 1,2:3,4-di-O-isopropylidene-α-d-galactopyranoxy, and 1,2:5,6-di-O-isopropylidene-α-d-glucofuranoxy). The molecular structures of 2 and 3 have been determined by single crystal X-ray diffraction studies.     

Growth of Textured Adenine Thin Films to Exhibit only Chiral Faces

The growth of adenine on Au(111) from the submonolayer up to several microns film thickness is studied by combining STM and surface X‐ray diffraction techniques. The study shows that adenine thin films are composed of highly textured crystallites with the reported α‐adenine crystal structure in such a way that they only exhibit (001)‐faces. Such faces, with chiral p2 symmetry planes, have an average size of 15 nm. Thus, the formed adenine films reported herein, which expose only chiral and biocompatible faces, might find applications such as enantioselective heterogeneous catalysts for the chemical and pharmaceutical industries.     

IR-Spectroscopic Study of the Binding Isomerism of Adsorbed Molecules

This paper discusses the use of IR spectroscopy in the studies of isomerism in the binding of adsorbed molecules with a surface when a molecule may form several different surface species at the same site. Species whose geometry does not provide minimal adsorption energy can be considered as adsorption complexes in an excited state. The spectral manifestations of such a steric excitation are compared with the electronic and vibrational excitations of surface species. The sterically excited isomeric states existing in thermodynamic equilibrium with ordinary adsorption species are found and studied in detail. Examples are CO molecules bound through C and O atoms with metal cations in zeolites or with surface hydroxyl groups, the thiophene molecule via hydrogen bonding with silanol groups, and HD molecules dissociatively adsorbed on ZnO. A possible role of sterically activated isomeric states in catalysis is discussed.