Palladium chloride, also known as palladium dichloride, are the chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

s with the formula

Chemical formula

A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 PdCl₂. PdCl₂ is a common starting material in palladium

Palladium

Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...

 chemistry – palladium-based catalysts are of particular value in organic synthesis

Organic synthesis

Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

. It is prepared by chlorination

Chlorination

Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water...

 of palladium

Palladium

Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...

.

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 bridge

Bridging ligand

A bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually restricted to small ligands such as pseudohalides or to ligands that are...

s. 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

Octahedral cluster

Octahedral clusters are inorganic or organometallic cluster compounds composed of six metals in an octahedral array. One important class of octahedral clusters are chalcohalide clusters of the type M6X8L6 where M is a metal usually of group 6 or group 7, X is a ligand and more specifically an...

 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).

ball-and-stick model Ball-and-stick model In chemistry, the ball-and-stick model is a molecular model of a chemical substance which is to display both the three-dimensional position of the atoms and the bonds between them...  of the crystal structure of α-PdCl2	thermal ellipsoid Thermal ellipsoid Thermal ellipsoids, more formally termed atomic displacement parameters, are ellipsoids used in crystallography to indicate the magnitudes and directions of the thermal vibration of atoms in crystal structures...  model of the Pd6Cl12 molecule found in the crystal structure of β-PdCl2

Preparation

Palladium(II) chloride is prepared by dissolving palladium metal in aqua regia

Aqua regia

Aqua regia or aqua regis is a highly corrosive mixture of acids, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing concentrated nitric acid and hydrochloric acid, usually in a volume ratio of 1:3, respectively...

 or hydrochloric acid

Hydrochloric acid

Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

 in the presence of chlorine

Chlorine

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

. Alternatively, it may be prepared by heating palladium sponge with chlorine gas at 500°C.

Reactions

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 of labile but soluble Lewis base adduct

Adduct

An adduct is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components. The resultant is considered a distinct molecular species...

s, such as those derived from acetonitrile

Acetonitrile

Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...

 or benzonitrile

Benzonitrile

Benzonitrile is the chemical compound with the formula C6H5CN, abbreviated PhCN. This aromatic organic compound is colourless, with a sweet almond odour. It is prepared by the dehydration of benzamide, or by the reaction of sodium cyanide with bromobenzene....

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

PdCl₂ + 2 MeCN → PdCl₂(MeCN)₂

Although occasionally recommended, inert-gas techniques

Air-free technique

Air-free techniques refer to a range of manipulations in the chemistry laboratory for the handling of compounds that are air-sensitive. These techniques prevent the compounds from reacting with components of air, usually water and oxygen; less commonly carbon dioxide and nitrogen...

 are not necessary if the complex is to be used in situ. As an example, bis(triphenylphosphine)palladium(II) dichloride

Bis(triphenylphosphine)palladium(II) dichloride

Bispalladium dichloride is a coordination compound of palladium containing two triphenylphosphine and two chloride ligands. This yellow complex is often used for palladium-catalyzed coupling reactions, e.g. the Sonogashira–Hagihara reaction. The complex is square planar...

 may be prepared from palladium(II) chloride by reacting it with triphenylphosphine

Triphenylphosphine

Triphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...

 in benzonitrile:

PdCl₂ + 2 PPh₃ → PdCl₂(PPh₃)₂

Further reduction in the presence of more triphenylphosphine gives tetrakis(triphenylphosphine)palladium(0)

Tetrakis(triphenylphosphine)palladium(0)

Tetrakispalladium is the chemical compound Pd[P3]4, often abbreviated Pd4, or even PdP4. It is a bright yellow crystalline solid that becomes brown upon decomposition in air.-Structure and properties:...

; the second reaction may be carried out without purifying the intermediate dichloride:

PdCl₂(PPh₃)₂ + 2 PPh₃ + 2.5 N₂H₄

Hydrazine

Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...

  → Pd(PPh₃)₄ + 0.5 N₂ + 2 N₂H₅⁺Cl⁻

Alternatively, palladium(II) chloride may be solubilized in the form of the tetrachloropalladate anion, e.g. sodium tetrachloropalladate

Sodium tetrachloropalladate

Sodium tetrachloropalladate is an inorganic compound with the chemical formula Na2PdCl4. This salt, and the analogous alkali metal salts of the form M2PdCl4, may be prepared simply by reacting palladium chloride with the appropriate alkali metal chloride in aqueous solution...

, by reacting with the appropriate alkali metal chloride in water: Palladium(II) chloride is insoluble in water, whereas the product dissolves:

PdCl₂ + 2 MCl → M₂PdCl₄

This compound may also further react with phosphines to give phosphine complexes of palladium.

Palladium chloride may also be used to give heterogeneous palladium catalysts: palladium on barium sulfate

Barium sulfate

Barium sulfate is the inorganic compound with the chemical formula BaSO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs as the mineral barite, which is the main commercial source of barium and materials prepared from it...

, palladium on carbon

Palladium on carbon

Palladium on carbon, often referred to as Pd/C, is a form of palladium used for catalysis. It is usually used for catalytic hydrogenations in organic chemistry...

, and palladium chloride on carbon.

Uses

Even when dry, palladium(II) chloride is able to rapidly stain stainless steel

Stainless steel

In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

. Thus, palladium(II) chloride solutions are sometimes used to test for the corrosion

Corrosion

Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...

-resistance of stainless steel.

Palladium(II) chloride is sometimes used in carbon monoxide

Carbon monoxide

Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 detectors. Carbon monoxide reduces palladium(II) chloride to palladium:

PdCl₂ + CO + H₂O → Pd + CO₂ + 2HCl

Residual PdCl₂ is converted to red PdI₂, the concentration of which may be determined colorimetrically:

PdCl₂ + 2 KI → PdI₂ + 2 KCl