In chemistry phosphines are L-type ligands. They are used as ligands for many metal complexes. Perhaps the most popular phosphine ligand used is triphenylphosphine, a shelf-stable solid that undergoes oxidation in air relatively slowly. Unlike most metal ammine complexes, metal phosphine complexes tend to be lipophilic, displaying good solubility in organic solvents. They also are compatible with metals in multiple oxidation states. Because of these two features, metal phosphine complexes are useful in homogeneous catalysis. Prominent examples of metal phosphine complexes include Wilkinson's catalyst (Rh(PPh₃)₃Cl), Grubbs' catalyst, and tetrakis(triphenylphosphine)palladium(0).