Palladium(II) chloride, also known as palladium dichloride, are the chemical compounds with the formula PdCl₂. PdCl₂ is a common starting material in palladium chemistry – palladium-based catalysts are of particular value in organic synthesis. It is prepared by chlorination of palladium.

Structure

Two forms of PdCl₂ are known. In both forms, the palladium centres adopt the square-planar coordination geometry that is characteristic of Pd(II). Furthermore, in both forms, the Pd(II) centres are linked by μ₂-chloride bridges. The α-form of PdCl₂ is a polymer, consisting of "infinite" slabs or chains. The β-form of PdCl₂ is molecular, consisting of an octahedral cluster of six Pd atoms. Each of the twelve edges of this octahedron is spanned by Cl^-. PtCl₂ adopts similar structures, whereas NiCl₂ adopts the CdCl₂ motif, featuring hexacoordinated Ni(II).

Uses

Palladium(II) chloride is a common starting point in the synthesis of other palladium compounds. It is not particularly soluble in water or non-coordinating solvents, so the first step in its utilization is often the preparation labile but soluble Lewis base adducts, such as those derived from acetonitrile or benzonitrile.

The acetonitrile complex is prepared by treating PdCl₂ in refluxing acetonitrile:

PdCl₂ + 2 MeCN → PdCl₂(MeCN)₂

Although occasionally recommended, inert-gas techniques are not necessary if the complex is to be used in situ.

Even when dry, palladium(II) chloride is able to rapidly stain stainless steel. Thus, palladium(II) chloride solutions are sometimes used to test for the corrosion-resistance of stainless steel. Palladium(II) chloride is sometimes used in carbon monoxide detectors.

Safety

The related nickel and platinum compounds are known to be irritants of the skin and the respiratory system and, in some cases, carcinogenic, and its is generally accepted as prudent to assume that palladium compounds share these risks.

References