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The H* transfer rate constants for a series of group 6 molybdenum and tungsten pyrazolyl borate complexes are described. The rate constants for these complexes were found to span a range over 1 magnitude. Analysis of the H* transfer rate constants suggests that a combination of steric, electronic, and enthalpic factors are important in these reactions. Further analysis of the components suggests that the generated 17 [e.sup.-] radicals of these complexes are less electrophilic than the more commonly used CpCr[(CO).sub.3]H complexes. General implications for H* transfer reactions are discussed. Key words: hydrogen atom transfer, metal hydride complex. Nous decrivons les constantes de vitesse du transfert de H* pour une serie de complexes de pyrazolylborate avec des metaux du groupe 6 (le molybdene et le tungstene). Nous avons observe que les constantes de vitesse de ces complexes s'etendaient sur plus d'un ordre de grandeur. Selon l'analyse des constantes de vitesse du transfert de H*, une combinaison de facteurs steriques, electroniques et enthalpiques serait importante dans ces reactions. Une analyse plus approfondie des composants semble indiquer que les radicaux a 17 [e.sup.-] generes a partir de ces complexes sont moins electrophiles que ceux des complexes CpCr[(CO).sub.3]H, plus communement employes. Nous discutons des implications generales de ces resultats pour les reactions de transfert de H*. Mots-cles: transfert d'atome d'hydrogene, complexe d'hydrure metallique., Introduction Group 6 hydride complexes are important catalysts for a variety of organic and organometallic H* transformations. (1-2) These include hydrogenation of epoxides, (3-4) olefins, (5-6) alkynes, (7) and the [...]

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Tandem catalysis involving simultaneous dihydrogen generation from a hydrogen carrier and substrate reduction on a heterogeneous catalyst provides unique opportunities for green chemistry synthesis under mild reaction conditions. However, in traditional batch conditions for nitro reductions, excess hydrogen is often necessary to achieve full conversion and thermal management on scale-up is a safety issue due to large heats of reaction and adiabatic temperature rise. Herein, we report a continuous-flow strategy to maximize hydrogen utilization efficiency (HUE) and improve reaction safety in tandem nitro-reduction reactions, using stoichiometric amounts of ammonia borane (AB) in methanol as the hydrogen source with Pd/C catalyst. This strategy provides a full conversion of nitrobenzene to highly pure aniline in 15 s, with only air cooling needed. In comparison, a batch reaction with stoichiometric AB only reaches a 42% yield of aniline over Pd/C after 30 min. The space–time yield of aniline in a flow system (92.07 g L−1 min−1) is substantially higher than that in a batch reaction (0.13 g L−1 min−1). The tandem reaction set in a flow configuration was simulated with commercial software (Aspen Plus v8.8) enabling scale-up, safe operation, and optimization of energy use. Our tandem flow system with a full HUE, good thermal management, and excellent catalytic efficiency provides a practical way for the green chemistry synthesis of anilines. [ABSTRACT FROM AUTHOR]

CpRu(P-P) H carries out a study on the scope and mechanism of the catalysis of the ionic hydrogenation of an iminium cation (where P-P is a chelating diphosphine). This catalysis reaction involves the transfer of H(super -) to form an amine, the coordination of H(sub 2) to the resulting Ru cation, and the transfer of H(super +) from the coordinated dihyrodgen to the amine formed.

The kinetics and thermodynamics of the reactions of (eta (super 5)-C5R5)Cr(CO)3H (2a) (R = Ph, Me, H) with methyl methacrylate (MMA) and styrene are examined to assess the ability of different metalloradicals to catalyze chain transfer. The heating of a solution of 2a with MMA results in commencement of polymerization along with the slow conversion of the hydride to the metalloradical

Research has been conducted on the silylated alpha-amino acid esters. The preparation of these esters from zirconaaziridines has been investigated and the results have demonstrated the effectiveness of the zirconaaziridine route in preparation of the silylated alpha-amino acid esters.

Research has been conducted on the ribonucleotide reductase apoprotein. The second-order rate constant for the iron(II) uptake by this apoprotein has been measured in investigating ribonucleotide reductase activation and the details are reported.

Synthesis of oxo complexes from 2,7-nonadiyne and rhenium compounds is described. Protonation kinetics analyses by Low temperature NMR technique reveal that the rhenium oxo complexes exhibit two second-order rate constants. Two doubly protonated intermediates that give rise to the rhenium diyne ligand by an acid-independent process.