Hydrogenations are among the most important reaction class in the production of both bulk and fine chemicals. By adding hydrogen atoms to an organic compound, double or triple bond functionality is reduced, forming single bonds. In a single step, a hydrogenation reaction allows the formation of C-C simple bonds from alkenes and alkynes, C-O bonds from ketones, and aldehyde or esters, and C-N (amines) from imines or nitriles, etc.
Metal catalysts are often used in hydrogenation reactions to reduce the high energy barrier to the transformation. For example, in the case of transforming alkenes and alkynes into alkanes, nickel, palladium or platinum catalysts are required. Hydrogenations can either be homogenous or heterogenous, using metals adsorbed on various substrates. In the former case, for example, rhodium and iridium metal catalysts that are coordinated with specific ligands are used to achieve asymmetric synthesis hydrogenation. In the latter case, alkanes are formed from double or triple bond carbon moieties. In all cases the choice of the catalyst greatly influences a hydrogenation reaction, as well as the catalyst concentration, solvent, substrate purity, temperature, and pressure.