text: Catalysts are often based on palladium, which is frequently selected due to high functional group tolerance. Organopalladium compounds are generally stable towards water and air. Palladium catalysts can be problematic for the pharmaceutical industry, which faces extensive regulation regarding heavy metals.  Many pharmaceutical chemists attempt to use coupling reactions early in production to minimize metal traces in the product.  Heterogeneous catalysts based on Pd are also well developed.
  Copper-based catalysts are also common, especially for coupling involving heteroatom-C bonds.
  Iron-, cobalt-, and nickel-based catalysts have been investigated.