Palladium(II) acetate
Encyclopedia
Palladium 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 nitric acid
. An excess of palladium sponge is used to prevent contamination by PdNO3·OAc.
Palladium(II) propionate is prepared analogously; other carboxylates are prepared by reacting palladium(II) acetate with the appropriate carboxylic acid.
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:
Pd(O2CCH3)2 converts aryl bromides into aryltrimethylsilanes, an important functional group in many organic compounds including the fungicide "Latitude".
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.
Palladium(II) acetate reacts with acetylacetone
to produce Pd(acac)2, a precursor to Pd(0).
Light or heat reduce palladium acetate to give thin layers of palladium and can produce nanowires and colloids.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
of palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...
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.
Structure
Palladium(II) acetate is 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.Preparation
Palladium acetate can be prepared by refluxing palladium sponge with hot glacial acetic acidAcetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
and nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
. An excess of palladium sponge is used to prevent contamination by PdNO3·OAc.
- Pd + 4 HNO3 → Pd(NO3)2 + 2 NO2 + 2 H2O
- Pd(NO3)2 + 2 CH3COOH → Pd(O2CCH3)2 + 2 HNO3
Palladium(II) propionate is prepared analogously; other carboxylates are prepared by reacting palladium(II) acetate with the appropriate carboxylic acid.
Reactions
When warmed with alcohols, or on prolonged boiling with other solvents, palladium(II) acetate decomposes to palladium.Catalysis
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-allylAllyl
An allyl group is a substituent with the structural formula H2C=CH-CH2R, where R is the connection to the rest of the molecule. It is made up of a methylene , attached to a vinyl group . The name is derived from the Latin word for garlic, Allium sativum. Theodor Wertheim isolated an 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 reactionHeck reactionThe Heck reaction is the chemical reaction of an unsaturated halide with an alkene and a base and palladium catalyst to form a substituted alkene. Together with the other palladium-catalyzed cross-coupling reactions, this reaction is of great importance, as it allows one to do substitution...
- Rearrangement of Acyclic Dienes: An example is the Cope reactionCope reactionThe Cope reaction or Cope elimination, developed by Arthur C. Cope, is an elimination reaction of an amine oxide to form an alkene and a hydroxylamine. The reaction mechanism involves an intramolcular 5-membered cyclic transition state, leading to a syn elimination product...
- CarbonylationCarbonylationCarbonylation refers to reactions that introduce carbon monoxide into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry.-Organic chemistry:...
reactions: for example, the formation of esters from aryl iodides by addition of carbon monoxide and an alcohol or phenol. - Reductive aminationReductive aminationReductive amination is a form of amination that involves the conversion of a carbonyl group to an amine via an intermediate imine...
of aldehydes or ketones using potassium formate. - Wacker processWacker processThe Wacker process or the Hoechst-Wacker process originally referred to the oxidation of ethylene to acetaldehyde by oxygen in water in the presence of a tetrachloropalladate catalyst...
: the oxidation of ethylene in water to form acetaldehyde (precursor to poly(vinyl acetate), a common glue). - Buchwald-Hartwig synthesis of aryl amines from aryl halides/pseudohalides and primary or secondary 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
Palladium(II) acetate reacts with acetylacetone
Acetylacetone
Acetylacetone is an organic compound that famously exists in two tautomeric forms that rapidly interconvert. The less stable tautomer is a diketone formally named pentane-2,4-dione. The more common tautomer is the enol form. The pair of tautomers rapidly interconvert and are treated as a single...
to produce Pd(acac)2, a precursor to Pd(0).
Light or heat reduce palladium acetate to give thin layers of palladium and can produce nanowires and colloids.