text: Coordinated ligands display reactivity distinct from the free ligands.  For example, the acidity of the ammonia ligands in [[Cobalt(III) hexammine chloride|[Co(NH)]]] is elevated relative to NH itself.  Alkenes bound to metal cations are reactive toward nucleophiles whereas alkenes normally are not.  The large and industrially important area of catalysis hinges on the ability of metals to modify the reactivity of organic ligands.  Homogeneous catalysis occurs in solution and heterogeneous catalysis occurs when gaseous or dissolved substrates interact with surfaces of solids.  Traditionally homogeneous catalysis is considered part of organometallic chemistry and heterogeneous catalysis is discussed in the context of surface science, a subfield of solid state chemistry.  But the basic inorganic chemical principles are the same.  Transition metals, almost uniquely, react with small molecules such as CO, H, O, and CH.  The industrial significance of these feedstocks drives the active area of catalysis.  Ligands can also undergo ligand transfer reactions such as transmetalation.