User:Praseodymium-141/Palladium compounds

Palladium compounds are compounds formed by the element palladium (Pd). These compounds exist primarily in the 0 and +2 oxidation state. Other less common states are also recognized. Generally the compounds of palladium are more similar to those of platinum than those of any other element.

Palladium(II)
Palladium(II) chloride is the principal starting material for other palladium compounds. It arises by the reaction of palladium with chlorine. It is used to prepare heterogeneous palladium catalysts such as palladium on barium sulfate, palladium on carbon, and palladium chloride on carbon. Solutions of PdCl2 in nitric acid react with acetic acid to give palladium(II) acetate, also a versatile reagent. PdCl2 reacts with ligands (L) to give square planar complexes of the type PdCl2L2. One example of such complexes is the benzonitrile derivative PdX2(PhCN)2.
 * PdCl2 + 2 L → PdCl2L2 (L = PhCN, PPh3, NH3, etc)

The complex bis(triphenylphosphine)palladium(II) dichloride is a useful catalyst.



Palladium(0)
Palladium forms a range of zerovalent complexes with the formula PdL4, PdL3 and PdL2. For example, reduction of a mixture of PdCl2(PPh3)2 and PPh3 gives tetrakis(triphenylphosphine)palladium(0):
 * 2 PdCl2(PPh3)2 + 4 PPh3 + 5 N2H4 → 2 Pd(PPh3)4 + N2 + 4 N2H5+Cl−

Another major palladium(0) complex, tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3), is prepared by reducing sodium tetrachloropalladate in the presence of dibenzylideneacetone.

Palladium(0), as well as palladium(II), are catalysts in coupling reactions, as has been recognized by the 2010 Nobel Prize in Chemistry to Richard F. Heck, Ei-ichi Negishi, and Akira Suzuki. Such reactions are widely practiced for the synthesis of fine chemicals. Prominent coupling reactions include the Heck, Suzuki, Sonogashira coupling, Stille reactions, and the Kumada coupling. Palladium(II) acetate, tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)4, and tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3) serve either as catalysts or precatalysts.

Other oxidation states
Although Pd(IV) compounds are comparatively rare, one example is sodium hexachloropalladate(IV), Na2[PdCl6]. A few compounds of palladium(III) are also known. Palladium(VI) was claimed in 2002, but subsequently disproven.

Mixed valence palladium complexes exist, e.g. Pd4(CO)4(OAc)4Pd(acac)2 forms an infinite Pd chain structure, with alternatively interconnected Pd4(CO)4(OAc)4 and Pd(acac)2 units.

When alloyed with a more electropositive element, palladium can acquire a negative charge. Such compounds are known as palladides, such as gallium palladide. Palladides with the stoichiometry RPd3 exist where R is scandium, yttrium, or any of the lanthanides.