Palladium compounds

forms a variety of ionic, coordination, and organopalladium compounds, typically with oxidation state Pd⁰ or Pd²⁺. Palladium compounds have also been reported. Palladium compounds are frequently used as catalysts in cross-coupling reactions such as the Sonogashira coupling and Suzuki reaction.

Ionic compounds

Most ionic compounds of palladium involve the Pd²⁺ oxidation state. Palladium chloride is a starting point in the synthesis of other palladium compounds and complexes. Palladium acetate plus triphenylphosphine is used as a catalyst in organic synthesis.

Coordination compounds

Coordination compounds of palladium contain ligands coordinated to a central Pd⁰ or Pd²⁺ center. They are typically synthesized by adding ligands to an ionic palladium compound. For example, acetonitrile, benzonitrile, or triphenylphosphine may be coordinated to palladium chloride to form bispalladium dichloride, bispalladium dichloride, or bispalladium chloride, respectively. Many other more exotic ligands form a large variety of palladium-phosphine catalysts, such as 1,1'-bisferrocene to form palladium dichloride|palladium dichloride.
Another precursor to coordination compounds of palladium is sodium tetrachloropalladate, to which dibenzylideneacetone and acetylacetonate may be coordinated to form trisdipalladium and palladium bis, respectively.
Bispalladium chloride, which contains palladium as Pd²⁺, may be reduced using hydrazine in the presence of triphenylphosphine to form tetrakispalladium, which contains Pd⁰.

Organopalladium compounds

Catalysis

Both ionic and coordination palladium compounds are frequently used to catalyze cross-coupling reactions. The catalytic ability is due to palladium's ability to switch between the Pd⁰ and Pd²⁺ oxidation states. An organic compound adds across Pd⁰ to form an organic Pd²⁺ complex. After transmetalation with an organometallic compound, two organic ligands to Pd²⁺ may exit the palladium complex and combine, forming a coupling product and regenerating Pd⁰.
For the Suzuki reaction, commonly used catalysts include Tetrakispalladium|, Bispalladium chloride|, palladium dichloride|, as well as Palladium acetate| plus triphenylphosphine. A large variety of phosphine-based ligands may be used in palladium-phosphine catalysts. Bulky, electron-rich ligands such as trisphosphine result in catalysts that are more reactive in the oxidative addition step and can catalyze the coupling of aryl chlorides, which are typically unreactive.