Abstract
The present review examines catalytic systems which activate molecular hydrogen. Particular attention is paid to catalysis by compounds of transition metals. These systems are discussed in the following order: catalysis by salts of transition metals; catalysis by salts of transition metals in the presence of reducing agents (complex-forming reagents); and catalysis by individual complexes. General problems relating to the activation of hydrogen and the mechanism of the hydrogenation of organic compounds are also discussed. A separate section is devoted to the activation of molecular hydrogen by enzymatic systems. The bibliography contains 282 references.