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Palladium(II) acetate is a
Light or heat reduce palladium acetate to give thin layers of palladium and can produce
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
of palladium
Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself na ...
described by the formula d(O2CCH3)2sub>n, abbreviated d(OAc)2sub>n. It is more reactive than the analogous platinum compound. Depending on the value of n, the compound is soluble in many organic solvents and is commonly used as a catalyst for organic reactions.
Structure
With a 1:2 stoichiometric ratio of palladium atoms and acetateligand
In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elec ...
s, the compound exists as molecular and polymeric forms with the trimeric form being the dominant form in the solid state and in solution. Pd achieves approximate square planar coordination in both forms.
As prepared by Geoffrey Wilkinson
Sir Geoffrey Wilkinson FRS (14 July 1921 – 26 September 1996) was a Nobel laureate English chemist who pioneered inorganic chemistry and homogeneous transition metal catalysis.
Education and early life
Wilkinson was born at Springside, Todm ...
and coworkers in 1965 and later characterized 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. 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(II) 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 andnitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
. An excess of palladium sponge metal or nitrogen gas flow are required to prevent contamination by the mixed nitrito-acetate (Pd3(OAc)5NO2).
:Pd + 4 HNO3 → Pd(NO3)2 + 2 NO2 + 2 H2O
:Pd(NO3)2 + 2 CH3COOH → Pd(O2CCH3)2 + 2 HNO3
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(II) acetate.
Palladium(II) propionate is prepared analogously; other carboxylates are prepared by treating palladium(II) acetate with the appropriate carboxylic acid. Likewise, palladium(II) acetate can be prepared by treating 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.
Palladium(II) acetate is prone to reduction to Pd(0) in the presence of reagents which can undergo beta-hydride elimination such as primary and secondary alcohols as well as amines
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...
. 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, especiallyalkenes
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
, diene
In organic chemistry a diene ( ) (diolefin ( ) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms. They thus contain two alk''ene'' units, with the standard prefix ''di'' of systematic nomenclature. ...
s, and alkyl, aryl, and vinyl halides to form reactive adducts.Suggs, J W. "Palladium: Organometallic Chemistry." Encyclopedia of Inorganic Chemistry. Ed. R B. King. 8 vols. Chichester: Wiley, 1994.
Reactions catalyzed by palladium(II) acetate:
* Vinylation: An example is the Heck reaction and related processes.
*Rearrangement of acyclic dienes: An example is the Cope rearrangement
The Cope rearrangement is an extensively studied organic reaction involving the ,3sigmatropic rearrangement of 1,5-dienes. It was developed by Arthur C. Cope and Elizabeth Hardy. For example, 3-methyl-hexa-1,5-diene heated to 300 °C yield ...
*Carbonylation
Carbonylation 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. The term carbony ...
reactions: for example, the formation of esters from aryl iodides, carbon monoxide
Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
, an alcohol or phenol.
*Reductive amination
Reductive amination (also known as reductive alkylation) is a form of amination that involves the conversion of a carbonyl group to an amine via an intermediate imine. The carbonyl group is most commonly a ketone or an aldehyde. It is considered ...
of aldehydes or ketones by potassium formate.
* Wacker process: the oxidation of ethylene by water to acetaldehyde (precursor to poly(vinyl acetate).
* Buchwald-Hartwig amination of aryl halide In organic chemistry, an aryl halide (also known as haloarene) is an aromatic compound in which one or more hydrogen atoms, directly bonded to an aromatic ring are replaced by a halide. The haloarene are different from haloalkanes because they exhi ...
s/pseudohalides with alkyl an aryl amines.
*conversion of aryl bromides into the trimethylsilanes, a 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.Gooben, L J. "Research Area "New Pd-Catalyzed Cross-Coupling Reactions"" 28 Feb. 2006Precursor to other Pd compounds
Palladium acetate is used to produce other palladium(II) compounds. For example, phenylpalladium acetate, used to isomerize allyl alcohols toaldehydes
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...
, is prepared by the following reaction:
:Hg(C6H5)(OAc) + Pd(OAc)2 → Pd(C6H5)(OAc) + Hg(OAc)2
Palladium(II) acetate reacts with acetylacetone (the "acac" ligand) to produce Pd(acac)2.
Light or heat reduce palladium acetate to give thin layers of palladium and can produce nanowire
A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre (10−9 metres). More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less ...
s and colloids.
See also
* Saegusa–Ito oxidationReferences
{{Acetates Palladium compounds Acetates