Allylpalladium(II) chloride dimer (APC) is a

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 ...

with the formula η³-C₃H₅)PdCl.html" ;"title="hapticity.html" ;"title="hapticity">η³-C₃H₅)PdCl">hapticity.html" ;"title="hapticity">η³-C₃H₅)PdClsub>2. This yellow air-stable compound is an important catalyst used in organic synthesis.Tatsuno, Y.; Yoshida, T.; Otsuka, S. "(η³-allyl)palladium(II) Complexes" Inorganic Syntheses, 1990, volume 28, pages 342-345. It is one of the most widely used

transition metal allyl complex Transition-metal allyl complexes are coordination complexes with allyl and its derivatives as ligands. Allyl is the radical with the connectivity CH2CHCH2, although as a ligand it is usually viewed as an allyl anion CH2=CH−CH2−, which is usual ...

es.

Structure

The compound has a dimeric structure that is

centrosymmetric In crystallography, a centrosymmetric point group contains an inversion center as one of its symmetry elements. In such a point group, for every point (x, y, z) in the unit cell there is an indistinguishable point (-x, -y, -z). Such point g ...

. Each allyl group lies in a plane at an angle of about 111.5° to the square formed by the palladium and carbon atoms, and the Pd–C distances are all equal. Its unit cell is monoclinic.

Synthesis

The compound is prepared by purging

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 ...

through a methanolic aqueous solution of

sodium tetrachloropalladate Sodium tetrachloropalladate is an inorganic compound with the chemical formula Na2PdCl4. This salt, and the analogous alkali metal salts of the form M2PdCl4, may be prepared simply by reacting palladium(II) chloride with the appropriate alkali meta ...

(prepared from

palladium(II) chloride Palladium(II) chloride, also known as palladium dichloride and palladous chloride, are the chemical compounds with the formula PdCl2. PdCl2 is a common starting material in palladium chemistry – palladium-based catalysts are of particular value ...

and sodium chloride), and

allyl chloride Allyl chloride is the organic compound with the formula C H2=CHCH2 Cl. This colorless liquid is insoluble in water but soluble in common organic solvents. It is mainly converted to epichlorohydrin, used in the production of plastics. It is a chl ...

. :2 Na₂PdCl₄ + 2 CH₂=CHCH₂Cl + 2 CO + 2 H₂O → η³-C₃H₅)PdClsub>2 + 4 NaCl + 2 CO₂ + 4 HCl Another method is the reaction of

propene Propylene, also known as propene, is an unsaturated organic compound with the chemical formula CH3CH=CH2. It has one double bond, and is the second simplest member of the alkene class of hydrocarbons. It is a colorless gas with a faint petro ...

with palladium(II)

trifluoroacetate Trifluoroacetic acid (TFA) is an organofluorine compound with the chemical formula CF3CO2H. It is a structural analogue of acetic acid with all three of the acetyl group's hydrogen atoms replaced by fluorine atoms and is a colorless liquid with a ...

, followed by

ion exchange Ion exchange is a reversible interchange of one kind of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid with the reaction being used especially for softening or making water demineralised, ...

with chloride: :2 (CF₃COO)₂Pd + 2 CH₂=CHCH₃ → η³-C₃H₅)Pd(CF₃COO)sub>2 : η³-C₃H₅)Pd(CF₃COO)sub>2 + 2 Cl⁻ → η³-C₃H₅)PdClsub>2 + 2 CF₃COO⁻

Reactions

APC reacts with sources of

cyclopentadienyl anion In chemistry, the cyclopentadienyl anion or cyclopentadienide is an aromatic species with a formula of and abbreviated as Cp−. It is formed from the deprotonation of the molecule cyclopentadiene. Properties The cyclopentadienyl anion i ...

to give the corresponding 18e⁻ complex

cyclopentadienyl allyl palladium Cyclopentadienyl allyl palladium is an organopalladium compound with formula (C5H5)Pd(C3H5). This reddish solid is volatile with an unpleasant odor. It is soluble in common organic solvents. The molecule consists of a Pd centre sandwiched betwee ...

: : η³-C₃H₅)PdClsub>2 + 2 NaC₅H₅ → 2 η⁵-C₅H₅)Pd(η³-C₃H₅) + 2 NaCl The dimer reacts with a variety of Lewis bases (:B) to form adducts ( η³-C₃H₅)PdCl:B. Its reaction with

pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a ...

and the corresponding enthalpy are: :1/2 η³-C₃H₅)PdClsub>2 + :NC₅H₅ → (η³-C₃H₅)PdCl:NC₅H₅ Δ''H''=−30.1 kJ.mol⁻¹ This enthalpy corresponds to the enthalpy change for a reaction forming one mole of the product, ( η³-C₃H₅)PdCl:NC₅H₅, from the acid dimer. The dissociation energy for the Pd dimer, which is an energy contribution prior to reaction with the donor, : η³-C₃H₅)PdClsub>2 → 2 (η³-C₃H₅)PdCl has been determined by the ECW model to be 28 kJ.mol⁻¹. APC catalyzes many organic reactions, such as

cross-coupling In organic chemistry, a cross-coupling reaction is a reaction where two fragments are joined together with the aid of a metal catalyst. In one important reaction type, a main group organometallic compound of the type R-M (R = organic fragment, M = ...

, nucleophilic addition to

dienes Dienes may refer to: * Dienes (surname), including a list of people with the name * the plural of diene In organic chemistry a diene ( ) (diolefin ( ) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon at ...

, and decomposition of

diazo compounds The diazo group is an organic moiety consisting of two linked nitrogen atoms ( azo) at the terminal position. Overall charge neutral organic compounds containing the diazo group bound to a carbon atom are called diazo compounds or diazoalkanes ...

to reactive

carbenes In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms. The term "carbene" m ...

. It is also a useful precursor of other Pd catalysts.

References

{{Palladium compounds Palladium compounds Metal halides Dimers (chemistry) Chloro complexes Allyl complexes