Chemistry:Palladium compounds

Short description: Chemical compounds with at least one palladium atom

Palladium forms a variety of ionic, coordination, and organopalladium compounds, typically with oxidation state Pd⁰ or Pd²⁺. Palladium(III) 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

Palladium(II) acetate, Pd(OAc)
2

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

Coordination compounds

Bis(triphenylphosphine)palladium chloride, PdCl
2(PPh
3)
2

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(II) chloride (PdCl
2) to form bis(acetonitrile)palladium dichloride (PdCl
2(NCC
6H
5)
2), bis(benzonitrile)palladium dichloride (PdCl
2(PPh
3)
2), or bis(triphenylphosphine)palladium chloride (PdCl
2(PPh
3)
2), respectively. Many other more exotic ligands form a large variety of palladium-phosphine catalysts, such as 1,1'-bis(diphenylphosphino)ferrocene (dppf) to form [1,1'-bis(diphenylphosphino)ferrocene]palladium(II) dichloride (PdCl
2(dppf)).

Another precursor to coordination compounds of palladium is sodium tetrachloropalladate, to which dibenzylideneacetone (dba) and acetylacetonate may be coordinated to form tris(dibenzylideneacetone)dipalladium(0) (Pd
2(dba)
3) and palladium(II) bis(acetylacetonate), respectively.

Bis(triphenylphosphine)palladium chloride, which contains palladium as Pd²⁺, may be reduced using hydrazine in the presence of triphenylphosphine to form tetrakis(triphenylphosphine)palladium(0) (Pd(PPh
3)
4), which contains Pd⁰.

Organopalladium compounds

Main article: Chemistry:Organopalladium chemistry

Catalysis

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General scheme of Suzuki reaction

Mechanism of the Suzuki reaction

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 (oxidative addition). 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 (reductive elimination).

For the Suzuki reaction, commonly used catalysts include Pd(PPh
3)
4, PdCl
2(PPh
3)
2, PdCl
2(dppf), as well as Pd(OAc)
2 plus triphenylphosphine (PPh
3). A large variety of phosphine-based ligands may be used in palladium-phosphine catalysts. Bulky, electron-rich ligands such as tris(2,4,6-trimethoxyphenyl)phosphine result in catalysts that are more reactive in the oxidative addition step and can catalyze the coupling of aryl chlorides, which are typically unreactive.

See also

• Category:Palladium compounds
• Nickel compounds
• Platinum compounds