Bis(dibenzylideneacetone)palladium
[CAS# 32005-36-0]

Identification

• Classification: Organic raw materials >> Organometallic compound >> Organic palladium
• Name: Bis(dibenzylideneacetone)palladium
• Synonyms: Pd(dba)2
• Molecular Formula: C₃₄H₂₈O₂Pd
• Molecular Weight: 575.01
• CAS Registry Number: 32005-36-0
• EC Number: 608-691-6
• SMILES: C1=CC=C(C=C1)/C=C/C(=O)/C=C/C2=CC=CC=C2.C1=CC=C(C=C1)/C=C/C(=O)/C=C/C2=CC=CC=C2.[Pd]

Properties

• Melting point: 150 °C (Expl.)
• Solubility: Slightly soluble (CH2Cl2, CHCl3, benzene) (Expl.)

Safety Data

• Hazard Symbols: GHS02;GHS07 Danger
• Risk Statements: H228-H302-H312-H315-H319-H332
• Safety Statements: P210-P240-P241-P261-P264-P264+P265-P270-P271-P280-P301+P317-P302+P352-P304+P340-P305+P351+P338-P317-P321-P330-P332+P317-P337+P317-P362+P364-P370+P378-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin sensitization	Skin Sens.	1B	H317
Eye irritation	Eye Irrit.	2	H319
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	4	H332
Skin sensitization	Skin Sens.	1	H317
Acute toxicity	Acute Tox.	4	H312
Acute toxicity	Acute Tox.	4	H302
Flammable solids	Flam. Sol.	2	H228
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Specific target organ toxicity - single exposure	STOT SE	3	H335

Discovery and Applications

Bis(dibenzylideneacetone)palladium, commonly abbreviated as Pd(DBA)2, is a well-known organopalladium complex that has significant applications in organic synthesis, particularly in catalysis. The compound is composed of a palladium center coordinated to two dibenzylideneacetone (DBA) ligands, which are bidentate ligands that help stabilize the palladium metal and facilitate its catalytic activity.

The discovery of bis(dibenzylideneacetone)palladium can be traced back to the development of palladium-catalyzed reactions in the 20th century. The complex is recognized for its utility in various organic transformations, especially in the context of carbon-carbon bond formation. Its widespread use is primarily due to its effectiveness as a catalyst in coupling reactions, including the Heck reaction, which involves the coupling of aryl halides with alkenes.

In particular, Pd(DBA)2 is a key catalyst in the Heck reaction, where it facilitates the formation of substituted alkenes by coupling aryl or vinyl halides with olefins. This reaction is highly valuable in organic synthesis, as it allows for the construction of complex carbon-carbon bonds, a crucial step in the preparation of various organic compounds, including pharmaceuticals, agrochemicals, and materials. The use of Pd(DBA)2 in this context has been pivotal in advancing the field of synthetic chemistry, enabling the production of a wide range of molecules that are difficult to synthesize through other methods.

The mechanism of catalysis in the Heck reaction typically involves the oxidative addition of the aryl or vinyl halide to the palladium(0) species, followed by the insertion of the alkene into the palladium-carbon bond. After the product is formed, the palladium complex is reduced back to its palladium(0) state, allowing the cycle to repeat. The dibenzylideneacetone ligands in Pd(DBA)2 serve to stabilize the palladium center, making it more effective in catalyzing these reactions. These ligands also help prevent the formation of palladium(II) species, which would be less active as catalysts.

Beyond the Heck reaction, Pd(DBA)2 has also been used in other important transformations such as the Suzuki coupling and Stille coupling reactions. Both of these reactions are essential in the synthesis of complex organic molecules and materials, and Pd(DBA)2 plays a crucial role in enabling these processes by facilitating the coupling of organoboron and organostannane compounds with aryl or vinyl halides.

Another advantage of Pd(DBA)2 is its ability to catalyze reactions under relatively mild conditions, which can be important when working with sensitive substrates or when aiming for high selectivity. This has made it a popular catalyst in both laboratory research and industrial applications. Furthermore, the use of Pd(DBA)2 in catalytic processes often allows for the reuse of the catalyst, which is advantageous from both an economic and environmental standpoint.

The use of Pd(DBA)2 is not limited to cross-coupling reactions. It has also been employed in other types of catalysis, including reactions that form carbon-nitrogen bonds, such as Buchwald-Hartwig amination. In these reactions, Pd(DBA)2 enables the coupling of amines with halides to form primary, secondary, and tertiary amines, which are key intermediates in the synthesis of pharmaceuticals and fine chemicals.

In summary, bis(dibenzylideneacetone)palladium is a versatile and highly effective catalyst with a wide range of applications in organic synthesis. Its discovery has significantly advanced the field of palladium-catalyzed reactions, particularly in the formation of carbon-carbon and carbon-nitrogen bonds. Pd(DBA)2 continues to be an important catalyst in both academic and industrial settings, enabling the efficient and selective synthesis of complex molecules used in the development of a variety of chemical products.

References

2024. Palladium-catalyzed cyclization of N-(2-iodophenyl)acrylamides and hydrophosphoryl compounds in the presence of (R,R)-DIOP and (S)-Monophos ligands. Russian Chemical Bulletin, 73(9).
DOI: 10.1007/s11172-024-4383-7

1983. Biphasic and phase transfer catalyzed carbonylation of vinylic bromides. Transition Metal Chemistry, 8(5).
DOI: 10.1007/bf00620866