With a 1:2 stoichiometric ratio of palladium atoms and acetate ligands, the compound exists as molecular and polymeric forms. Pd achieves approximate square planar coordination in both forms. As prepared by Wilkinson and coworkers in 1965 and later characterized by Skapski and Smart in 1970 by single crystalX-ray diffraction, palladium acetate is a red-brown solid that crystallizes as monoclinic plates. It has a trimeric structure, consisting of an equilateral triangle of Pd atoms each pair of which is bridged with two acetate groups in a butterfly conformation. Palladium acetate can also be prepared as a pale pink form. According to X-ray powder diffraction, this form is polymeric.
Preparation
Palladium acetate, in trimeric form, can be prepared by treating palladium sponge with a mixture of acetic acid and nitric acid. An excess of palladium sponge metal or nitrogen gas flow are required to prevent contamination by the mixed nitrito-acetate. Relative to the trimeric acetate, the mixed nitrate-acetate variant has different solubility and catalytic activity. Preventing, or controlling for the amount of, this impurity can be an important aspect for reliable use of palladium acetate. Palladium propionate is prepared analogously; other carboxylates are prepared by treating palladium acetate with the appropriate carboxylic acid. Likewise, palladium acetate can be prepared by treating other palladium carboxylates with acetic acid. This ligand exchange starting with a purified other carboxylate is an alternative way to synthesize palladium acetate free from the nitro contaminant. When warmed with alcohols, or on prolonged boiling with other solvents, palladium acetate decomposes to palladium.
Catalysis
Palladium acetate is a catalyst for many organic reactions, especially alkenes, dienes, and alkyl, aryl, and vinyl halides to form reactive adducts. Reactions catalyzed by palladium acetate:
Vinylation: An example is the Heck reaction and related processes.
Wacker process: the oxidation of ethylene by water to acetaldehyde.
Buchwald-Hartwig amination of aryl halides/pseudohalides with alkyl an aryl amines.
conversion of aryl bromides into the trimethylsilanes, a functional group in many organic compounds including the fungicide "Latitude".
Pd2 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 compounds. For example, phenylpalladium acetate, used to isomerize allyl alcohols to aldehydes, is prepared by the following reaction: Palladium acetate reacts with acetylacetone to produce Pd2. . Light or heat reduce palladium acetate to give thin layers of palladium and can produce nanowires and colloids.
