Showing papers on "Reactivity (chemistry) published in 1988"

Chemical modification of alkoxide precursors

Abstract: The chemical reactivity of metal alkoxides offers a broad range of possibilities for chemical modification of these molecular precursors. The whole hydrolysis-condensation process may then be completely different leading to new products. An analysis is presented concerning some of the most common chemical additives used in the sol-gel process. Their role is explained in terms of chemical reactivity. The most important parameters appear to be the reactivity of the new ligand towards hydrolysis, the charge distribution in the new molecular precursor and the coordination numbers of the metal atom.

Synthesis and reactivity toward acyl chlorides and enones of the new highly functionalized copper reagents RCu(CN)ZnI

Abstract: Les composes du titre sont prepares par transmetallation a partir d'iodures d'alkyl zinc et du sel CuCN•2LiX. Ils reagissent sur des chlorures d'acyle et des enones pour donner des cetones et des produits d'addition 1,4

Local softness and chemical reactivity in the molecules CO, SCN− and H2CO

Abstract: Fukui functions (softnesses) are calculated for three species - formaldehyde, the thiocyanate ion and carbon monoxide. The fukui function for a molecule has been defined as the derivative of electron density with respect to the change of number of electrons, keeping the positions of nuclei unchanged; this differentiation is performed by finite difference. Local softness and fukui function are proportional. The calculated results, expressed in terms of contour maps and condensed values of fukui functions, substantiate the previous argument that fukui functions serve as reactivity indices for chemical reactions. Particularly, it is confirmed that: (1) a nucleophilic reagent approaches the carbon atom in formaldehyde from the direction perpendicular to the molecular plane, while an electrophilic reagent approaches the oxygen atom in the molecular plane; (2) the sulphur end is softer than the nitrogen end in the thiocyanate ion; and (3) carbon monoxide behaves like a Lewis acid in bonding with transition metals.

Reactivity of the carbonate radical with aniline derivatives

Abstract: Carbonate radicals generated by the photolysis of H2O2 at 313 nm in aqueous sodium bicarbonate (pH 8.3) or carbonate (pH 11.6) solution reacted with substituted aromatic amine derivatives. Particularly fast reactions (second-order rate constants of 5 × 108 to 2 × 109) were observed with anilines bearing electron-donating substituents, either on the ring or at the nitrogen atom. The results suggest that carbonate radicals may play a significant role in the removal of some aromatic amines from the aquatic environment, particularly in carbonate-rich waters.

Aluminum clusters: ionization thresholds and reactivity toward deuterium, water, oxygen, methanol, methane, and carbon monoxide

Abstract: Using the pulsed cluster beam flow reactor technique, the authors have measured the reactivity of aluminum clusters toward several molecules under thermal conditions. For each different molecule they observe that the reactivity exhibits a unique dependence on the number of aluminum atoms in the cluster. The overall reactivity of aluminum clusters toward different molecules is ordered roughly as O/sub 2/ > CH/sub 3/OH > CO > D/sub 2/O > D/sub 2/ > CH/sub 4/ with CH/sub 4/ showing no reaction under these experimental conditions. In addition, they are able to place upper and lower bounds on the ionization thresholds for the smaller aluminum clusters.

CO chemisorption on free gas phase metal clusters

Abstract: Pulsed fast flow reactor techniques have been used to study the reactivity of CO toward clusters of many different transition metals; V, Fe, Co, Ni, Cu, Nb, Mo, Ru, Pd, W, Ir, and Pt as well as Al, for clusters containing up to 14 atoms. Clusters are produced by pulsed laser vaporization of metal substrates, injected into the reactor, formed into a molecular beam, and detected by photoionization time of flight mass spectrometry. Our results show that CO is readily chemisorbed on most transition metal clusters containing five or more metal atoms, and that the reactivity for larger clusters varies by a factor of 2 or 3, depending on both cluster size and metal type. Depending on the metal, certain atoms, dimers, trimers, and tetramers exhibit little evidence of reactivity toward CO. This observation is explained in terms of a competition between unimolecular decomposition and collisional stabilization, and leads to a prediction of the ordering of the metal–CO bond strengths.

Synthetic, structural, and reactivity studies of the reduction and carbon monoxide derivatization of azobenzene mediated by divalent lanthanide complexes

Abstract: Etude de l'addition de (C 5 Me 5 ) 2 Sm(THF) 2 a l'azobenzene, suivie de la reaction avec le monoxyde de carbone. Structure cristalline des divers complexes formes

New Transition Metal Clusters with Ligands from Main Groups Five and Six

Abstract: In both physics and chemistry, increased attention is being paid to metal clusters. One reason for this attitude is furnished by the surprising results that have been obtained from studies of the preparation, structural characterization and physical and chemical properties of the clusters. Whereas investigations of cluster reactivity are at present generally limited to three- or four-membered clusters, successful syntheses of clusters with many more metal atoms have recently been designed. These substances occupy an intermediate position between solid state chemistry and the chemistry of metal complexes. This review presents a versatile method for synthesizing metal clusters: the reaction of complexes of transition metal halides with silylated compounds such as E(SiMe3)2 (E = S, Se, Te) and E′R(SiMe3)2 (R = Ph, Me, Et; E′ = P, As, Sb). Although some of the compounds thus formed have already been prepared by other routes, the method affords ready access to both small and large transition metal clusters with unusual structures and valence electron concentrations; a variety of reactions in the ligand sphere are also possible.

Dioxygen−copper reactivity: generation, characterization, and reactivity of a hydroperoxo−dicopper(II) complex

Abstract: Preparation et proprietes du complexe [Cu 2 (XYL-O-)(OOH)] 2+ structure cristalline de [Cu 2 (XYL-OH) (PPh 3 ) 2 ] (ClO 4 ) 2

The chemistry of α-haloketones, α-haloaldehydes and α-haloimines

Abstract: Synthesis and reactivity of alpha-halogenated ketones alpha-halogenated imines synthesis and reactivity of alpha-halogenated aldehydes.

A convenient synthesis of alkali metal selenides and diselenides in tetrahydrofuran and the reactivity differences exhibited by these salts toward organic bromides. Effect of ultrasound

Abstract: Synthese des composes du titre a partir de Li, Na ou K et de selenium; les composes du titre reagissent avec des hydrocarbures halogenes pour conduire a des seleniures et des diseleniures organiques

Preparation and reactivity of 16-electron ‘half-sandwich’ ruthenium complexes; X-ray crystal structure of (η5-C5Me5)Ru(PPri3)Cl

Abstract: The new 16-electron ruthenium compounds (η5-C5Me5)Ru(L)Cl [(1), L = PPri3; (2), L = PCy3](Cy = cyclohexyl) were prepared from [(η5-C5Me5)RuCl]4 and PPri3 or PCy3, respectively, and the X-ray crystal structure of (1) has been determined; reactions of the title compounds with CO, C2H4, pyridine, and PhSiH3 are described.

Synthesis and reactivity of a family of copper monooxygenase model systems

Abstract: Synthese d'une serie de complexes dinucleaires de Cu(I) avec des bis(imines). Etude de la reaction des complexes avec O 2 en solution. Cette reaction reproduit la reactivite de la monooxygenase tyrosinase de Cu

Synthesis and reactivity of cobalt(III) complexes bearing primary- and secondary-side cyclodextrin binding sites. A tale of two CD's

Abstract: Synthese de 2 complexes cyclen-Co(III) positionnes alternativement sur les parties primaires et secondaires de la β-cyclodextrine. Reactivite