Donor hydrogenation, reactions during

Pertinent reviews published during 1980 cover cyclometallation of P-donor ligands, CO insertion into metal-carbon o-bonds, mechanistic features of catalytic CO hydrogenation reactions, and stoicheiometric reactions of transition-metal carbene complexes. Other articles of interest deal with the stability of metal-carbon bonds, " transition-state geometry for insertion of metals into C-H bonds, organic synthesis using Group VIII metal complexes, and C-H bond activation by transition metals. " Molecular orbital calculations on the interconversion of metal bis(olefin) and metallocyclo-pentane complexes have been reported. ... 

The presence of an electron donor causes the equiHbrium to shift to the left. The acidity represented by this mechanism is important in hydrocarbon conversion reactions. Acidity may also be introduced in certain high siHca zeoHtes, eg, mordenite, by hydrogen-ion exchange, or by hydrolysis of a zeoHte containing multivalent cations during dehydration, eg,... 

One aldehyde molecule has transferred its aldehyde hydrogen during course of the reaction onto another aldehyde molecule, which is why the reactants are called donor and acceptor (see below). 

The transfer of hydrogen from donors to the coal substrate during liquefaction occurs by concerted pericyclic reactions of the type termed group transfers by Woodward and Hoffman (1 ). ... 

The preceding experiments offer preliminary support to our notion that pericyclic pathways might be intimately involved in the mechanism of coal liquefaction. More specifically, the results indicate that pericyclic group transfer reactions constitute a plausible pathway for the transfer of hydrogen from donor solvents to coal during liquefaction. 

In the reaction of luminol, hydrogen peroxide, and horse radish peroxidase 122> the chemiluminescence intensity is proportional to the square of luminol radical concentration. The lifetime of these luminol radicals was found by ESR techniques to be about 10 sec. Titration studies revealed that luminol acts as two-electron donor during the reduction of a hydrogen peroxide-horseradish peroxidase complex. The enzyme is not involved in the reaction step leading directly to light emission. This step is formulated as... 

Alcohols will serve as hydrogen donors for the reduction of ketones and imi-nium salts, but not imines. Isopropanol is frequently used, and during the process is oxidized into acetone. The reaction is reversible and the products are in equilibrium with the starting materials. To enhance formation of the product, isopropanol is used in large excess and conveniently becomes the solvent. Initially, the reaction is controlled kinetically and the selectivity is high. As the concentration of the product and acetone increase, the rate of the reverse reaction also increases, and the ratio of enantiomers comes under thermodynamic control, with the result that the optical purity of the product falls. The rhodium and iridium CATHy catalysts are more active than the ruthenium arenes not only in the forward transfer hydrogenation but also in the reverse dehydrogenation. As a consequence, the optical purity of the product can fall faster with the... 

Other salts of formic acid have been used with good results. For example, sodium and preferably potassium formate salts have been used in a water/organic biphasic system [36, 52], or with the water-soluble catalysts discussed above. The aqueous system makes the pH much easier to control minimal COz is generated during the reaction as it is trapped as bicarbonate, and often better reaction rates are observed. The use of hydrazinium monoformate salts as hydrogen donors with heterogeneous catalysts has also been reported [53]. 

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