Potassium chloropalladite
[CAS# 10025-98-6]

Identification

• Name: Potassium chloropalladite
• Synonyms: Dipotassium tetrachloropalladate; Potassium tetrachloropalladate(II)
• Molecular Formula: K₂PdCl₄
• Molecular Weight: 326.41
• CAS Registry Number: 10025-98-6
• EC Number: 233-049-3
• SMILES: Cl[Pd-2](Cl)(Cl)Cl.[K+].[K+]

Properties

• Density: 2.67 g/mL
• Melting point: 105 °C (dec.)
• Water solubility: SOLUBLE

Safety Data

• Hazard Symbols: GHS05;GHS06;GHS07;GHS09 Danger
• Risk Statements: H301-H315-H317-H318-H319-H335-H400-H410
• Safety Statements: P261-P264-P264+P265-P270-P271-P272-P273-P280-P301+P316-P302+P352-P304+P340-P305+P351+P338-P305+P354+P338-P317-P319-P321-P330-P332+P317-P333+P317-P337+P317-P362+P364-P391-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	3	H301
Skin sensitization	Skin Sens.	1A	H317
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Serious eye damage	Eye Dam.	1	H318
Eye irritation	Eye Irrit.	2	H319
Skin irritation	Skin Irrit.	2	H315
Specific target organ toxicity - single exposure	STOT SE	3	H335
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Acute toxicity	Acute Tox.	4	H302
Acute toxicity	Acute Tox.	4	H332
Acute toxicity	Acute Tox.	4	H312
Chronic hazardous to the aquatic environment	Aquatic Chronic	4	H413

Discovery and Applications

Potassium chloropalladite is an inorganic coordination compound with the general formula K₂PdCl₄. It consists of a palladium(II) ion coordinated by four chloride ligands to form the square planar [PdCl₄]²⁻ complex anion, with two potassium (K⁺) counterions providing charge balance. This compound is one of the most commonly used sources of palladium(II) in solution and has broad applications in synthesis, catalysis, and analytical chemistry.

The compound was first studied systematically in the 19th and early 20th centuries, as part of the growing interest in platinum group metal salts and their coordination chemistry. Potassium chloropalladite became important in the development of palladium-based catalytic systems due to its relatively high solubility in water and its ability to readily form complexes with a variety of ligands.

Potassium chloropalladite is typically prepared by dissolving metallic palladium or palladium(II) chloride (PdCl₂) in aqueous hydrochloric acid, followed by the addition of potassium chloride. This reaction produces a deep red or reddish-brown solution containing the [PdCl₄]²⁻ complex. Upon evaporation or crystallization, the red solid potassium salt can be isolated.

The [PdCl₄]²⁻ anion adopts a square planar geometry around the Pd(II) center, which is typical for d⁸ metal ions. This geometry is central to its chemical reactivity and allows for efficient ligand substitution reactions. These properties make potassium chloropalladite an effective precursor for the synthesis of a wide range of palladium(II) coordination and organometallic complexes.

A major application of potassium chloropalladite is in homogeneous catalysis. It serves as a palladium source for catalytic cycles involved in carbon-carbon and carbon-heteroatom bond-forming reactions, including Suzuki–Miyaura, Heck, and Sonogashira couplings. In these transformations, [PdCl₄]²⁻ is often reduced in situ to Pd(0), which is the catalytically active species. The ability of potassium chloropalladite to generate catalytically competent intermediates under mild conditions has led to its frequent use in laboratory-scale and industrial-scale synthesis.

In analytical chemistry, potassium chloropalladite has been employed in the determination of various organic and inorganic analytes. Its reactions with certain functional groups or elements, such as sulfur-containing compounds, can be used to detect or quantify these species by colorimetric or gravimetric methods.

The compound is also useful in electroplating and metal recovery processes. Solutions containing [PdCl₄]²⁻ can be used to deposit palladium metal onto substrates by electrochemical reduction. In recycling applications, palladium can be recovered from industrial waste streams by precipitating or reducing it from potassium chloropalladite-containing solutions.

Potassium chloropalladite is typically handled as a crystalline or powdered solid and is soluble in water, alcohols, and hydrochloric acid. Its stability in aqueous solution depends on the pH and chloride concentration; in concentrated hydrochloric acid, the [PdCl₄]²⁻ complex is stabilized, while in dilute or neutral solutions, hydrolysis or disproportionation reactions may occur over time.

Care must be taken in handling potassium chloropalladite, as palladium compounds can be toxic and irritant. Contact with skin or inhalation of dust should be avoided, and proper laboratory safety procedures, including the use of gloves, protective eyewear, and fume hoods, should be followed. Waste disposal must comply with environmental regulations concerning heavy metal compounds.

In summary, potassium chloropalladite is a well-defined palladium(II) chloride complex used extensively in coordination chemistry and catalysis. Its solubility, reactivity, and compatibility with ligand exchange make it a valuable reagent for preparing palladium complexes and facilitating palladium-catalyzed synthetic reactions.

References

2007. Palladate Salts from Chiral Pyridinium Ionic Liquids: Synthesis and Crystal Structures. Molecules (Basel, Switzerland), 12(8).
DOI: 10.3390/12081940

2007. Sodium tetrachloropalladate (Na2[PdCl4]) as an improved test salt for palladium allergy patch testing. Contact Dermatitis, 58(1).
DOI: 10.1111/j.1600-0536.2007.01259.x

2012. Sodium tetrachloropalladate for diagnosing palladium sensitization. Contact Dermatitis, 67(4).
DOI: 10.1111/j.1600-0536.2012.02061.x