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Amines are extremely important intermediates and end products of the chemical industry and are often obtained by hydrogenation of the corresponding nitro compounds or imines. | 98 Previous Page Chapter 3 MoH T 5-C5H5 CO 2 PCy3 was more active 2 turnovers h . Similar but water soluble tungsten and molybdenum complexes are known 223-226 which would allow the use of water as solvent for such reactions. It is noteworthy though that ionic hydrogenation of ketones by dihydrogen complexes has so far been observed only in non-aqueous solutions 223 227 perhaps the coordination of a ketone is disfavoured in water due to competition by H2O. HYDROGENATION OF MISCELLANEOUS ORGANIC SUBSTRATES Hydrogenation of nitro compounds and imines Amines are extremely important intermediates and end products of the chemical industry and are often obtained by hydrogenation of the corresponding nitro compounds or imines. A search of the literature reveals that hydrogenation of nitro compounds catalyzed by well-defined molecular complexes in aqueous solutions is rare. One reason may line in the fact that reduction of the -NO2 function proceeds in one-electron steps while many soluble hydrogenation catalysts act in the oxidative addition of H2 -reductive elimination of the product cycles in which the central metal ion formally looses or gains two electrons at a time. It is not surprising therefore that the catalysts of nitro-hidrogenations are either metal centered radicals themselves CoH CN 5 3- or are capable of delocalizing the temporary surplus of electron s on their large conjugated 7t-electron system Pd QS 2 or on a cluster framework Rhs CO i6 . Catalysts operating through formation of intermediate monohydrides which does not require the change of the oxidation state of the metal are good candidates of nitroreduction see also on reductions with CO H2O . Unfortunately other functional groups in a molecule are usually even more reactive towards hydrogenation than the nitro functionality - therefore selective reduction of -NO2 groups is not an easy task. Hydrogenations of nitro compounds catalyzed by CoH CN 5 3 are briefly mentioned in . Some