On the kinetics of catalytic reduction of nitrogen oxide by alkenes in oxidizing atmosphere

A kinetic model is presented which considers the catalytic reduction of NO to N₂ by hydrocarbons in oxidizing atmosphere (NO−HC−O₂) as the sum of two simultaneous competitive reactions: the red-ox reaction between NO and hydrocarbon (NO−HC) and the hydrocarbon oxidation (O₂−HC). The model is developed for alkenes employed as reductants and noble metal catalysts. The ratio of the kinetic constants of the two reactions can be considered as a selectivity index in evaluating the ability of a catalyst to favor the desired NO reduction with respect to the undesired O₂−HC oxidation.     

Selective synthesis of conformationally restricted mono-cyclopentadienyl titanium(IV) complexes of p-tBu-calix[6]arene

Reaction of p-'Bu-calix[6]arene with potassium metal in methanol followed by [TiCp2Cl2] affords novel mononuclear and binuclear monocyclopentadienyl titanium(IV) complexes, both having the same inverted double cone conformation with a Cp in one of the cavities, in both complexes.     

Headspace solid-phase microextraction with gas chromatography and mass spectrometry in the investigation of volatile organic compounds in an ectomycorrhizae synthesis system

Ectomycorrhizae formation represents one of the most significant steps in the truffle life cycle and is determined by a complex molecular signaling between two symbionts. In order to understand the molecular pathway of ectomycorrhiza development, we focused on the signaling interaction between the ectomycorrhizal fungus Tuber borchii Vittad. and the Tilia americana L. plant roots. The medium of a pre-symbiotic (T. americana-T. borchii) in vitro system was analysed by headspace solid-phase microextraction coupled with gas chromatography and mass spectrometry. In total, 73 volatile organic compounds (VOCs) were identified. Twenty-nine of these VOCs were produced only during the interaction phase between the two partners, leading to a hypothesis that these molecules might act as molecular messengers in order to pilot the ectomycorrhizae formation.     

First synthesis of the beta-D-rhamnosylated trisaccharide repeating unit of the O-antigen from Xanthomonas campestris pv. campestris 8004

The trisaccharide repeating unit of the O-antigen of the lipopolysaccharide from Xanthomonas campestris pv. campestris 8004, a pathogen of cruciferous crops, presents some structural features that renders it a challenging synthetic target: the presence of a beta-D-rhamnosidic linkage, the steric crowd on a 1,2-cis-diglycosylated D-rhamnose, and finally the noncommercial availability of its monosaccharide constituents. The synthesis of this trisaccharide as methyl glycoside has been accomplished by exploiting a strategy whose key steps were the sequential beta-D-rhamnosylation with a 2-O-benzylsulfonyl-N-phenyltrifluoroacetimidate donor, debenzylsulfonylation, and coupling with a D-Fucp3NAc thioglycoside donor.     

Coordination networks with flexible ligands based on silver(I) salts: complexes of 1,3-bis(phenylthio)propane with silver(I) salts of PF6-, CF3COO-, CF3CF2COO-, CF3CF2)CF2COO-, p-TsO-, and CF3SO3-

The synthesis and characterization of nine coordination networks based on 1,3-bis(phenylthio)propane, L(3), and silver(I) salts of PF(6)(-) (1), CF(3)COO(-) (2), CF(3)CF(2)COO(-) (3), CF(3)CF(2)CF(2)COO(-) (4), p-TsO(-) (5, 6), and CF(3)SO(3)(-) (7-9) are reported. Only 1 and other "isostructural" complexes with weakly coordinating anions such as ClO(4)(-) and SbF(6)(-) are of the host-guest type. In all the other complexes, the anions and the acetone molecules, when present, are coordinated to the metal. Most of the complexes studied here form a 2D-coordination network. Only 4 and 5 adopt a polymer-like chain structure. The packing of the chains of 4 is pseudohexagonal compact, while that of 5 is of the centered type. In complex 1, the silver atom is tetrahedrally coordinated to the sulfur atoms of four different ligands. The PF(6)(-) anions and acetone molecules, sandwiched between silver-ligand cationic sheets, are held through van der Waals interactions. In each of the three perfluorocarboxylates (2-4), two silver atoms are joined by the anions in a diatomic bridging mode. The Ag...Ag distances are sufficiently short to indicate weak metal...metal interactions. The dimeric units in 2 and 3 are interconnected through the ligands, thereby generating a 2D-network of neutral sheets, while, in 4, the dimeric units are bound to four ligands and a 1D-coordination polymer is generated. In the case of the sulfonate anions (p-TsO(-) and CF(3)SO(3)(-)), the crystallization solvent influences the structure adopted. Thus, in 5, 7, and 9 obtained from petroleum ether, or other nonpolar solvents, two silver atoms are bound in a double-bridge fashion, while a monobridge mode is noted for 6 and 8, both recrystallized from diethyl ether. In 8, both bridging types are observed. The thermogravimetric investigation, in the room temperature-450 degrees C interval, of complexes 1, 3, and 7, which incorporate acetone molecules in their crystal structures, reveals a two-step weight loss for 1 (the acetone molecules are lost first followed by the ligands, leaving behind the silver salt), while complexes 3 and 7 decompose in a single step to metallic silver.     

Synthesis of spiro polymers,

Synthesis of the first totally organic spiro polymer was accomplished by the reaction of 1,4-cyclohexanedione and pentaerythritol in benzene plus a trace of p-toluenesulfonic acid to produce the polyspiroketal. The polymer did not melt, but began to decompose at 350°C. Although it was insoluble in most common solvents, it was found to be soluble in hexafluoroisopropanol. The x-ray diffraction indicated the polymer was very highly crystalline. A series of lower molecular weight related polymers were prepared by carrying out a similar condensation with a mixture of 1,4-cyclohexanedione containing 5–50 mole-% of cyclohexanone. In order to prepare a material with greater solubility, a polyspiroketal was prepared from 1,10-cyclooctadecanedione plus pentaerythritol. This polymer was soluble not only in hexafluoroisopropanol, but to a limited extent in dimethyl sulfoxide.     

Redox reactions with bis(η-arene) derivatives of early transition metals

The reactivity of M(η⁶-arene)₂ derivatives of early transition metals (M = Ti, Cr, Mo, arene = MeC₆H₅; M = V, Nb, arene = 1,3,5-Me₃C₆H₃) has been investigated and the syntheses of new and known compounds are described. The derivatives M(CH₃COO)₃, M = Ti, V, Nb, Cr; M(CF₃COO)₃, M = Ti, Nb, Cr; M(acac)₃, M = Ti, V, Mo, acac = acetylacetonato, and M(F₆acac)₃, F₆acac = hexafluoroacetylacetonato, M = V, Nb have been prepared by reaction of the metal bis(arene) derivatives with the appropriate Lewis acid. The crystal and molecular structure of V(F₆acac)₃ has been determined. Hydrogen halides or halogens react with M(η⁶-arene)₂ with formation of metal halides, a highly reactive form of VCl₃ being obtained from V(η⁶-1,3,5-Me₃C₆H₃)₂ and hydrogen chloride in heptane. TiCl₄ oxidizes Ti(η⁶-arene)₂ with complete loss of the arene ligands. An electron transfer process affording ionic derivatives of formula [M(η⁶-MeC₆H₅)₂][TiCl₄(THF)₂], M = Cr (structurally characterized), Mo, has been observed between the THF-adduct of TiCl₄ and the appropriate metal-arene derivative of Group 6.     

Adducts of copper(II) acetate with amines in ethanolic solution

Copper(II) acetate was calorimetrically titrated with pyridine, 2-, 3- and 4-methylpyridine in absolute ethanol. The enthalpy of reaction and the equilibrium constant were determined for the adduct formation in solution for each ligand. The amines react with copper(II) acetate without breaking the dimeric structure at least in the limit of the concentration ratio|ligand|/|(CH₃CO₂)₄Cu₂|<2.