3D model (JSmol)
|Molar mass||224.50 g/mol|
|Appearance||Brown yellow solid|
|Melting point||205 °C (401 °F; 478 K) decomposes|
|Main hazards||considered nonhazardous|
|Safety data sheet|||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Palladium(II) acetate is a chemical compound of palladium described by the formula Pd(O2CCH3)2 or Pd(OAc)2. It is considered more reactive than the analogous platinum compound. It is soluble in many organic solvents, and commonly used as a catalyst for organic reactions and as a precursor for the synthesis of other palladium catalysts.
Although the compound is a 1:2 stoichiometric ratio of palladium atoms and acetate ligands as their oxidation states suggest, the actual molecular nature of the chemical depends on how it is prepared.
As prepared by Wilkinson and coworkers in 1965, and later studied by Skapski and Smart in 1970 by single crystal X-ray diffraction, palladium(II) acetate is a red-brown solid that crystallizes as monoclinic plates. Its structure was determined to be trimeric, consisting of an equilateral triangle of Pd atoms each pair of which is bridged with two acetate groups in a butterfly conformation. Each metal atom achieves approximate square planar co-ordination.
On the other hand, palladium(II) acetate prepared in a slightly different way was isolated as a pale pink powder, whose structure was determined by X-ray powder diffraction to consist of infinite chains of palladium atoms, each linked by an adjacent pair of acetate bridges to the next, in which the coordination geometry around each Pd is true square planar.
Palladium acetate, in trimeric form, can be prepared by refluxing palladium sponge with hot glacial acetic acid and nitric acid. An excess of palladium sponge metal or nitrogen gas flow is used to prevent contamination by a material that contains a nitrite ligand in place of one of the acetates (Pd3(OAc)5NO2).
- Pd + 4 HNO3 → Pd(NO3)2 + 2 NO2 + 2 H2O
- Pd(NO3)2 + 2 CH3COOH → Pd(O2CCH3)2 + 2 HNO3
The nitro variant has different solubility and catalytic activity in some reactions. Preventing, or controlling for the amount of, this impurity can be an important aspect for reliable use of palladium(II) acetate.
Palladium(II) propionate is prepared analogously; other carboxylates are prepared by reacting palladium(II) acetate with the appropriate carboxylic acid. Likewise, palladium(II) acetate can be prepared by reacting other palladium(II) carboxylates with acetic acid. This ligand exchange starting with a purified other carboxylate is an alternative way to synthesize palladium(II) acetate free from the nitro contaminant.
When warmed with alcohols, or on prolonged boiling with other solvents, palladium(II) acetate decomposes to palladium.
Palladium acetate is a catalyst for many organic reactions by combining with many common classes of organic compounds such as alkenes, dienes, and alkyl, aryl, and vinyl halides to form reactive adducts. Alkenes and π-allyl coordination to palladium(II) acetate involves sigma-type donation from the pi orbital of the alkene or π-allyl with concomitant pi-backbonding into an empty pi* orbital on the alkene or π-allyl. The greater the sigma donation to the metal is, the greater the pi-backbonding. The greater the pi-backbonding is, the greater the reduction in the bond order of the alkene or π-allyl. Reduction of the alkenes or π-allyl by coordination to palladium(II) acetate reverses the reactivity of the organic ligand allowing them to undergo reactions with nucleophiles rather than electrophiles.
Examples of palladium(II) acetate catalyzed reactions are:
- Vinylation: An example is the Heck reaction
- Rearrangement of Acyclic Dienes: An example is the Cope rearrangement
- Carbonylation reactions: for example, the formation of esters from aryl iodides by addition of carbon monoxide and an alcohol or phenol.
- Reductive amination of aldehydes or ketones using potassium formate.
- Wacker process: the oxidation of ethylene in water to form acetaldehyde (precursor to poly(vinyl acetate), a common glue).
- Buchwald-Hartwig amination of aryl halides/pseudohalides with alkyl an aryl amines.
Pd(O2CCH3)2 converts aryl bromides into aryltrimethylsilanes, an important functional group in many organic compounds including the fungicide "Latitude".
- RC6H4Br + Si2(CH3)6 → RC6H4Si(CH3)3 + Si(CH3)3Br
Pd(O2CCH3)2 is compatible with the electronic properties of aryl bromides, and unlike other methods of synthesis, this method does not require high pressure equipment.
Precursor to other Pd compounds
Palladium acetate is used to produce other palladium(II) compounds. For example, phenylpalladium acetate, used to isomerize allylic alcohols to aldehydes, is prepared by the following reaction:
- Hg(C6H5)(CH3COO) + Pd(CH3COO)2 → Pd(C6H5)(O2CCH3) + Hg(O2CCH3)2
- T. A. Stephenson; S. M. Morehouse; A. R. Powell; J. P. Heffer and G. Wilkinson (1965). "667. Carboxylates of palladium, platinum, and rhodium, and their adducts". Journal of the Chemical Society (Resumed): 3632. doi:10.1039/jr9650003632.
- Skapski, A C.; M. L. Smart (1970). "The Crystal Structure of Trimeric Palladium(II) Acetate". J. Chem. Soc. D (11): 658b–659. doi:10.1039/C2970000658b.
- Kirik, S.D.; Mulagaleev, S.F.; Blokhin, A.I. (2004). "[Pd(CH 3 COO) 2 ] n from X-ray powder diffraction data". Acta Crystallogr. C. 60 (9): m449–m450. doi:10.1107/S0108270104016129.
- Bakhmutov, V. I.,; Berry, J. F.; Cotton, F. A.; Ibragimov, S.; Murillo, C. A. (2005). "Non-Trivial Behavior of Palladium(II) Acetate". Dalton Transactions (11): 1989–1992. PMID 15909048. doi:10.1039/b502122g.
- "High Purity Homogeneous Catalyst" (PDF). Engelhard. September 2005. Archived from the original (PDF) on 17 March 2006. Retrieved 24 February 2006.
- Ritter, Stephen K. (May 2, 2016). "Chemists introduce a user's guide for palladium acetate". Chemical & Engineering News. 94 (18): 20–21.
- Toreki, R. "Allyl Ligands." The Organometallic HyperTextBook. 20 Nov. 2003. Chemglass. 01 Apr. 2006<http://www.ilpi.com/organomet/allyl.html>.
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- Basu, B., Satadru J., Mosharef H. B., and Pralay D. (2003). "A Simple Protocol for the Direct Reductive Amination of Aldehydes and Ketones Using Potassium Formate and Catalytic Palladium Acetate". ChemInform. 34 (30): 555–557. doi:10.1002/chin.200330069.
- "Buchwald-Hartwig Cross Coupling Reaction". Organic Chemistry Portal.
- Gooben, L J. "Research Area "New Pd-Catalyzed Cross-Coupling Reactions"" 28 Feb. 2006<http://www.mpi-muelheim.mpg.de/kofo/bericht2002/pdf/2.1.8_gossen.pdf> Archived July 12, 2007, at the Wayback Machine..
- Richard F. Heck. "Aldehydes from Allylic Alcohols and Phenylpalladium Acetate: 2-Methyl-3-Phenylpropionaldehyde". Org. Synth.; Coll. Vol., 6, p. 815
Salts and the ester of the acetate ion