Palladium bromide
[CAS# 13444-94-5]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Metal halides and halides >> Metal bromide and salt
• Name: Palladium bromide
• Synonyms: Palladium(II) bromide
• Molecular Formula: PdBr₂
• Molecular Weight: 266.23
• CAS Registry Number: 13444-94-5
• EC Number: 236-588-2
• SMILES: Br[Pd]Br

Properties

• Density: 5.173 g/mL (25 °C) (Expl.)
• Water solubility: INSOLUBLE

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H315-H319-H335
• Safety Statements: P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335

Discovery and Applications

Palladium bromide is an inorganic compound with the formula PdBr₂. It is one of the important palladium(II) halide complexes widely used in organometallic chemistry and homogeneous catalysis. Palladium bromide generally appears as a dark red or brown crystalline solid, moderately soluble in polar solvents such as dimethylformamide and dimethyl sulfoxide, and less soluble in water. The compound features palladium in the +2 oxidation state coordinated to two bromide ions, usually adopting a square planar geometry typical of d⁸ metal centers.

The preparation of palladium bromide typically involves direct halogenation of palladium metal or palladium(II) salts with bromine or hydrobromic acid under controlled temperature and stoichiometry. Alternatively, it can be synthesized by halide exchange reactions where palladium chloride is treated with a bromide source. The solid-state structure often consists of polymeric chains or oligomers stabilized by bridging bromide ligands, which influences its physical properties and reactivity.

Historically, palladium halides have played a pivotal role in the development of palladium-catalyzed cross-coupling reactions, which revolutionized synthetic organic chemistry. Palladium bromide itself is a key precursor to various catalytic systems used in important carbon-carbon bond-forming reactions such as the Suzuki-Miyaura, Heck, and Sonogashira couplings. These transformations enable the construction of complex molecules used in pharmaceuticals, agrochemicals, and materials science.

The versatility of PdBr₂ stems from its ability to undergo ligand substitution reactions. Upon coordination with phosphines, amines, or N-heterocyclic carbenes, palladium bromide forms well-defined complexes that serve as active catalysts. The bromide ligands influence catalyst stability, electronic properties, and catalytic activity, often providing different reactivity profiles compared to the chloride analogs. For example, the presence of bromide can affect oxidative addition and reductive elimination steps in catalytic cycles, which are critical to catalytic efficiency.

Palladium bromide also finds utility as a precursor in the synthesis of palladium nanoparticles and thin films used in advanced materials and electronic applications. Its controlled decomposition and reduction facilitate the preparation of nanostructured palladium with defined size and morphology, which is essential for catalytic and sensing applications.

From a chemical safety standpoint, palladium bromide is toxic if inhaled, ingested, or absorbed through the skin, and may cause irritation to the respiratory tract and eyes. It is essential to handle the compound using appropriate personal protective equipment and in well-ventilated environments, adhering to safety protocols for transition metal salts.

In research and industrial contexts, palladium bromide is valued for its reliability and reactivity as a catalyst precursor. Its solid-state stability and solubility in organic solvents make it amenable to use in a variety of synthetic protocols. Because of its broad applicability, it remains an indispensable reagent in laboratories focused on developing new catalytic processes and complex molecule synthesis.

In summary, palladium bromide is a key palladium(II) halide compound extensively utilized as a precursor to palladium catalysts in organic synthesis and materials science. It participates in critical catalytic transformations that underpin modern synthetic chemistry, particularly cross-coupling reactions forming carbon-carbon bonds. The compound’s distinctive bromide ligands modulate its catalytic properties and contribute to its role in preparing diverse palladium complexes and nanomaterials. Proper handling and safety measures ensure its effective use across academic and industrial applications, making it an essential compound in organometallic and catalytic chemistry.

References

2023. Synthesis, Spectral Analysis and Antimicrobial Activity of New Pd (II) Complexes Involving 5,6-Dimethylbenzimidazole. Chemical Research in Chinese Universities, 39(2).
DOI: 10.1007/s40242-023-2355-3

2022. Palladium Complexes [Ph3PCH2CN]2[PdBr4], [Ph4P]2[PdBr4], [Ph3PC5H9-cyclo][PdBr3(Et2SO)], and [Ph4P]2[Pd2Br6]. Synthesis and Structure. Russian Journal of General Chemistry, 92(7).
DOI: 10.1134/s1070363222070209

2022. Palladium Complexes [Ph3PEt][PdBr3(DMSO)], [Ph3PCH2OMe][PdBr3(DMSO)], [Ph3PC5H9-cyclo][PdBr3(DMSO)], and [Ph3PCH2CH=CHCH2PPh3][PdBr3(DMSO)]2: Synthesis and Structure. Russian Journal of Coordination Chemistry, 48(9).
DOI: 10.1134/s1070328422090044