Ruthenium salts as hydrogenation catalysts

In the early nineteen-sixties Halpem, James and co-workers studied the hydrogenation of water-soluble substrates in aqueous solutions catalyzed by ruthenium salts [6], RuC13 in 3 M HC1 catalyzed the hydrogenation of Fe(III) to Fe(II) at 80 °C and 0.6 bar H2. Similarly, Ru(IV) was autocatalytically reduced to Ru(III) which, however, did not react further. An extensive study of the effect of HC1 concentration on the rate of such hydrogenations revealed, that the hydrolysis product, [RuCln(OH)(H20)5. ]3 n was a catalyst of lower activity. It was also established, that the mechanism involved a heterolytic splitting of H2. In accordance with this suggestion, in the absence of reducible substrates, such as Fe(III) there was an extensive isotope exchange between the solvent H20 and D2 in the gas phase. 

In aqueous hydrochloric add solutions, ruthenium(II) chloride catalyzed the hydrogenation of water-soluble olefins such as maleic and fumaric acids [6], After learning so much of so many catalytic hydrogenation reactions, the kinetics of these simple Ru(II)-catalyzed systems still seem quite fascinating since they display many features which later became established as standard steps in the mechanisms of hydrogenation. The catalyst itself does not react with hydrogen, however, the mthenium(II)-olefin complex 

These meticulous kinetic studies laid the foundations of our understanding of hydrogen activation. For more details the reader is referred to [3], 

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