Molecular hydrogen, activation

Molecular hydrogen activation occurs at the metal centre, eventually resulting in cyclopentane and HML i. 

Garland M, Pino P (1990) Kinetics of molecular hydrogen activation by cobaltrhodium heptacarbonyl. Organometallics 9(6) 1943-1949... 

In contrast to the situation with the alternative nitrogenases, but with the notable exception of the C. pasteurianum proteins, the component proteins from aU. Mo-based nitrogenases interact as heterologous crosses to form catalyticaHy active enzymes (52). Carbon monoxide, CO, is a potent inhibitor of aU. nitrogenase-cataly2ed substrate reductions, with the exception of reduction (126). Molecular hydrogen has a unique involvement with Mo-nitrogenase... 

Both reactions were carried out under two-phase conditions with the help of an additional organic solvent (such as iPrOH). The catalyst could be reused with the same activity and enantioselectivity after decantation of the hydrogenation products. A more recent example, again by de Souza and Dupont, has been reported. They made a detailed study of the asymmetric hydrogenation of a-acetamidocin-namic acid and the kinetic resolution of methyl ( )-3-hydroxy-2-methylenebu-tanoate with chiral Rh(I) and Ru(II) complexes in [BMIM][BF4] and [BMIM][PFg] [55]. The authors described the remarkable effects of the molecular hydrogen concentration in the ionic catalyst layer on the conversion and enantioselectivity of these reactions. The solubility of hydrogen in [BMIM][BF4] was found to be almost four times higher than in [BMIM][PFg]. 

This enzyme is of wide occurrence in bacteria where it is concerned with the reduction of nitrate and CO2 as well as sulphur. Methods for its estimation depend on measuring some activity of hydrogenase by (a) dye reduction (benzyl viologen or methylene blue), (b) isotopic exchange and (c) evolution of molecular hydrogen. Interpretation of quantitative results is difficult due to the complex relationship between the enzyme cell structure and the particular method selected. ... 

Activation of Molecular Hydrogen by Homogeneous Catalysts S. W. Weller and G. A. Mills Catalytic Syntheses of Ketones... 

PdClJ , Rh(III) and Ru(III) act as homogeneous catalysts for reduction of FeClj by molecular hydrogen ° °. The kinetics of all three activation reactions fall into Class I. The Arrhenius parameters are... 

Promotion of molecular hydrogen on solid acid cracking activity... 

It has been revealed that the formation of protonic acid sites from molecular hydrogen is observable for the catalysts other than Pt/S042--Zr02, and the protonic acid sites thus formed act as catalytically active sites for acid-catalyzed reaction. We propose the concept "molecular hydrogen-originated protonic acid site" as a widely applicable active sites for solid acid catalysts. 

The Rh-NHC complexes, with or without phosphine co-ligands, have been stndied as hydrogenation catalysts of alkenes with molecular hydrogen, with the aim to develop more active, selective (and/or enantioselective) and thermally stable catalysts. 

Corma, A., Boronat, M., Conzalez, S. and Illas, F. (2007) On the activation of molecular hydrogen by gold a theoretical approximation to the nature of potential active sites. Chemical Communications, (23), 3371-3373. 

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