Tris(dibenzylideneacetone)dipalladium: Structure, CAS Number, Properties and Uses

Tris(dibenzylideneacetone)dipalladium, Pd2(dba)3 (CAS 51364-51-3, PubChem CID 9811564), is a dinuclear palladium(0) complex that is 23.2% palladium by weight, with the formula C51H42O3Pd2. Chemists use it as a ligand-tunable source of Pd(0), adding a phosphine or N-heterocyclic carbene ligand at the point of use rather than buying a pre-ligated catalyst outright. Its identity, structure, palladium content, physical properties, preparation, catalytic role, commercial form and hazard classification follow below, section by section.

What Is Tris(dibenzylideneacetone)dipalladium?#

Tris(dibenzylideneacetone)dipalladium is a dinuclear palladium(0) complex sold as a ligand-tunable catalyst precursor, commonly written as Pd2(dba)3 or abbreviated Pd2dba3. Its formula, C51H42O3Pd2, and CAS number, 51364-51-3, identify a discrete molecular complex, not a mixture: two palladium atoms, the "bis(palladium)" of its PubChem IUPAC name, held together by three dibenzylideneacetone ligands, the "tris" of the common name, with each palladium in the zero oxidation state. PubChem catalogs the compound under CID 9811564 with the systematic name tris((1E,4E)-1,5-diphenylpenta-1,4-dien-3-one);bis(palladium) and a molecular weight of 915.7 g/mol. TCI America's registry entry establishes 51364-51-3 as the primary CAS for the unsolvated complex; PubChem's synonym list also carries 60748-47-2, a number some suppliers associate with the chloroform-solvate adduct Pd2(dba)3.CHCl3 rather than the parent compound described here.

Tris(dibenzylideneacetone)dipalladium is one of the platinum group metal compounds and catalysts cataloged with a dedicated CAS registry entry on this site.

Tris(dibenzylideneacetone)dipalladium Structure and Bonding#

Tris(dibenzylideneacetone)dipalladium has a dinuclear, ligand-bridged structure: two palladium(0) centers held together by three dibenzylideneacetone (dba) ligands binding through their terminal alkene groups. Pierpont and Mazza solved the crystal structure by X-ray diffraction in 1974 (Pierpont & Mazza, Inorganic Chemistry, 13(8), 1891-1895, DOI 10.1021/ic50138a020), reporting a triclinic unit cell in space group P1 with dimensions a = 12.400(5) A, b = 15.149(5) A and c = 12.956(5) A. In that structure the two palladium atoms sit 320 pm (3.20 A) apart, bridged by the three dba ligands, two of which adopt an s-cis,trans conformation and the third an s-cis,cis conformation. Each palladium center is formally palladium(0), a d10 configuration, and because the dba ligands hold on only weakly through those alkene termini, the complex behaves as a "naked" Pd(0) synthon that releases dba as soon as a phosphine or N-heterocyclic carbene ligand, or an oxidative-addition substrate, is introduced.

Wikipedia's entry on the compound, fetched this session, describes Pd2(dba)3 as more air-stable than tetrakis(triphenylphosphine)palladium, Pd(PPh3)4, the other major Pd(0) source used in cross-coupling chemistry. That air stability, rather than a hindered coordination sphere, is why Pd2(dba)3 tolerates ordinary weighing and storage in air better than Pd(PPh3)4, even though both are zero-valent palladium complexes.

PGM Content of Tris(dibenzylideneacetone)dipalladium#

Tris(dibenzylideneacetone)dipalladium is 23.2 wt% palladium, computed from its two palladium atoms against the compound's 915.7 g/mol molecular weight. Palladium's standard atomic weight, 106.42 g/mol, multiplied by the two palladium atoms in the formula C51H42O3Pd2 and divided by the compound's 915.7 g/mol molecular weight (PubChem CID 9811564), gives (2 x 106.42) / 915.7 = 0.2324, or 23.2 wt% Pd. Three dibenzylideneacetone ligands, each a comparatively heavy C17H14O unit, make up most of the remaining mass, which is why a bulky organometallic source like this one carries a lower palladium fraction than a simple palladium salt of similar molecular size. That 23.2% figure is the basis for pricing a batch of catalyst against its contained-palladium value rather than a flat per-gram catalog number, since palladium is the metal whose market the compound's cost tracks. Current pricing for the metal itself is on DailyPlatinum's palladium price today page.

Physical and Chemical Properties#

Tris(dibenzylideneacetone)dipalladium is a dark purple-brown solid that is modestly soluble in organic solvents such as chloroform and benzene, with no melting or decomposition point established in the sources cited for this page. Wikipedia's entry on the compound, fetched this session, also notes that the purity of commercial samples is reported to vary, which can affect catalytic performance from lot to lot. ChemicalBook's property data lists the solid as air- and moisture-sensitive, with recommended storage between 2-8 C (or below 15 C) under inert gas, in amber glass, and ChemicalBook's separate technical entry adds that the complex is air-stable as a solid but decomposes slowly once dissolved, a practical reason to prepare fresh catalyst solutions rather than store them.

How Is Tris(dibenzylideneacetone)dipalladium Made?#

Tris(dibenzylideneacetone)dipalladium is made by combining dibenzylideneacetone with sodium tetrachloropalladate, Na2PdCl4 (CAS 13820-53-6), the water-soluble palladium(II) source that supplies the metal for the complex. Commercial material is commonly recrystallized from chloroform, which is why suppliers most often ship the compound as the chloroform adduct Pd2(dba)3.CHCl3 rather than the unsolvated complex described in the identity table above, according to Wikipedia's entry on the compound, fetched this session.

What Is Tris(dibenzylideneacetone)dipalladium Used For?#

Tris(dibenzylideneacetone)dipalladium is used as a ligand-tunable source of palladium(0) for cross-coupling reactions, typically combined with an added phosphine or N-heterocyclic carbene ligand at the point of use rather than sold as a pre-ligated catalyst, according to Wikipedia's entry on the compound. That flexibility lets a chemist pair the same Pd2(dba)3 stock with whichever ligand a given Suzuki, Negishi, Heck or Buchwald-Hartwig coupling calls for, instead of stocking a separate pre-formed catalyst for each reaction. Beyond generic cross-coupling, ChemicalBook's technical entry on the compound names Suzuki and Heck coupling of aryl chlorides specifically, along with arylation of ketones, fluorination of allylic chlorides, beta-arylation of carboxylic esters and carbonylation of 1,1-dichloro-1-alkenes among its documented applications. As a dissolved, ligand-tunable catalyst precursor, it belongs to the PGM catalysts in chemistry used across pharmaceutical and fine-chemical cross-coupling synthesis.

Catalytic Cycle#

The cross-coupling cycle that tris(dibenzylideneacetone)dipalladium feeds runs through three canonical steps: oxidative addition, transmetalation or migratory insertion, and reductive elimination, the same cycle the Nobel Committee credited when it awarded the 2010 Chemistry Prize to Richard Heck, Ei-ichi Negishi and Akira Suzuki for palladium-catalyzed cross couplings.

1. Release the active catalyst: an added phosphine or NHC ligand displaces the dba ligands from Pd2(dba)3, generating the ligated Pd(0) species that enters the cycle.
2. Add an organic halide (R-X) oxidatively to the Pd(0) center, oxidizing palladium to Pd(II) and forming an R-Pd-X intermediate.
3. Transmetalate (in a Suzuki coupling, from an organoboron reagent with base) or insert an alkene followed by beta-hydride elimination (in a Heck coupling), building the new carbon-carbon bond at palladium.
4. Eliminate reductively: the two carbon fragments couple and depart together, regenerating the Pd(0) catalyst so it can re-enter the cycle.

Cross-coupling is a dissipative use of palladium: the metal ends up in waste streams and product-purification resins rather than being recovered, and residual palladium in pharmaceutical active ingredients is regulated as an elemental impurity, a commercial consequence for palladium demand.

Commercial Forms, Purity and Price#

Tris(dibenzylideneacetone)dipalladium is sold commercially as the chloroform solvate, Pd2(dba)3.CHCl3, a dark purple-brown solid available from Strem, TCI, Sigma-Aldrich, Colonial Metals and Ottokemi, among others, according to Strem Chemicals' product listing. Commercial assay is quoted against the compound's contained-palladium content rather than a flat per-gram catalog rate: Strem's catalog #46-3000 basis lists around 20 wt% Pd, a J&K Scientific listing of the same Strem material states at least 22.7 wt% Pd, and both sit below the 23.2 wt% theoretical figure for the unsolvated complex computed above. ChemicalBook specifies technical/reagent grade at 97% or higher purity, while American Elements separately offers ultra-high-purity material from 99% up to 99.9999%; Strem also sells the chloroform solvate as its own distinct catalog item, #46-3010, apart from the unsolvated complex. Suppliers price all of these per gram in laboratory quantities rather than by the troy ounce used for bullion PGMs.

Safety and Hazard Classification#

PubChem records no GHS signal word and no hazard statement codes on file for tris(dibenzylideneacetone)dipalladium under CID 9811564. GHS classification reported to PubChem: no signal word, no hazard statement codes, zero notifications on file. That absence on PubChem is not the full hazard picture: TCI's safety data sheet, a single-sourced record cross-checked against Wikipedia, lists these hazard statements:

• H315, skin irritation
• H317, allergic skin reaction
• H319, eye irritation
• H335, respiratory irritation
• H411, toxic to aquatic life, long-lasting effects

The same TCI record carries the precautionary statement P403+P233 (store in a well-ventilated place, keep the container tightly closed). No US occupational exposure limit specific to this compound is established in the sources cited for this page, so handlers follow the supplier safety data sheet's control measures, gloves, eye protection and fume-hood practice, with its dust not inhaled.

Where Tris(dibenzylideneacetone)dipalladium Chemistry Stops: Medical and Pharmaceutical Platinum#

This page covers tris(dibenzylideneacetone)dipalladium as a laboratory and industrial catalyst precursor only, not as a component of any medical or pharmaceutical product. Palladium-catalyzed cross-coupling reactions of the kind this compound enables build carbon-carbon bonds during active pharmaceutical ingredient synthesis, but the resulting drug's dosing, side effects and clinical use are a separate subject that this site covers elsewhere, without dosing or clinical detail, on its platinum and palladium compound pages. Jewelry and catalytic-converter repair also fall outside this page's scope: tris(dibenzylideneacetone)dipalladium has no jewelry or automotive-catalyst use.

Related PGM Compounds#

Tris(dibenzylideneacetone)dipalladium shares its palladium(0) cross-coupling chemistry with tetrakis(triphenylphosphine)palladium, the other major Pd(0) source cataloged among this site's palladium compounds, and its "tris" naming convention with a ruthenium complex from an unrelated metal family.

History#

Tris(dibenzylideneacetone)dipalladium was first reported in 1970 by Takahashi, Ito, Sakai and Ishii in the Journal of the Chemical Society, according to Wikipedia's entry on the compound, fetched this session. It has since become one of the standard commercial sources of unligated palladium(0) for cross-coupling chemistry, valued for the air stability its bulkier dba ligands provide relative to Pd(PPh3)4.

Frequently Asked Questions#

What is Pd2 DBA 3? Pd2 DBA 3 is the common shorthand for tris(dibenzylideneacetone)dipalladium(0), a dinuclear palladium(0) complex, CAS 51364-51-3, used as a ligand-tunable catalyst precursor for cross-coupling reactions.

What is the structure of Pd2(dba)3? Pd2(dba)3 has a dinuclear structure in which two palladium(0) centers, 320 pm apart, are bridged by three dibenzylideneacetone ligands, as solved by Pierpont and Mazza's 1974 X-ray crystal structure (triclinic, space group P1).

What is tris(dibenzylideneacetone)dipalladium(0)? It is a dark purple-brown, 23.2 wt% palladium(0) complex, formula C51H42O3Pd2, sold as a source of unligated Pd(0) for downstream cross-coupling catalysis after a phosphine or NHC ligand is added.

What is the CAS number of Pd2(dba)3? 51364-51-3, the CAS number TCI America and other major suppliers use for the unsolvated complex; PubChem's synonym list also carries 60748-47-2, associated with the chloroform-solvate adduct rather than the parent compound.

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