The discovery of a new chemical reaction often leads to new applications and new chemical principles. Low-valent ruthenium and iridium hydride complexes are highly useful redox Lewis acid and base catalysts. Nitriles are activated by these catalysts and undergo reactions with either nucleophiles or electrophiles under neutral conditions. Hydration of nitriles, esterification of nitriles with alcohols, and amidation of nitriles with amines can be performed catalytically together with formation of ammonia. The catalytic reactions of pronucleophiles such as nitriles and carbonyl compounds with electrophiles such as alkenes, alkynes, carbonyl compounds, imines, and nitriles take place generally.