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 In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

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 complexes.

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 grou ...

. 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 poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

through a methanolic

aqueous solution An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, also known as sodium chloride (NaCl), in water ...

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 me ...

(prepared from palladium(II) chloride and

sodium chloride Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...

), 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 c ...

. :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 . 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 petroleum-like od ...

with palladium(II) trifluoroacetate, followed by

ion exchange Ion exchange is a reversible interchange of one species of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid. Ion exchange is used in softening or demineralizing of water, purification of ch ...

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 Sodium cyclopentadienide is an organosodium compound with the formula C5H5Na. The compound is often abbreviated as NaCp, where Cp− is the cyclopentadienide anion. Sodium cyclopentadienide is a colorless solid, although samples often are pin ...

to give the corresponding 18e⁻ complex cyclopentadienyl allyl palladium: : 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 (chemistry), basic heterocyclic compound, 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, weak ...

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 In chemistry, the ECW model is a semi-quantitative model that describes and predicts the strength of Lewis acid–Lewis base interactions. Many chemical reactions can be described as acid–base reactions, so models for such interactions are of pot ...

to be 28 kJ.mol⁻¹. APC catalyzes many organic reactions, such as cross-coupling,

nucleophilic addition In organic chemistry, a nucleophilic addition (AN) reaction is an addition reaction where a chemical compound with an electrophilic double or triple bond reacts with a nucleophile, such that the double or triple bond is broken. Nucleophilic addit ...

to dienes, and decomposition of diazo compounds to reactive carbenes. It is also a useful precursor of other Pd catalysts.

References

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