Allylpalladium chloride dimer

Allylpalladium(II) chloride dimer (APC) is a chemical compound with the formula [(η3-C3H5)PdCl]2. This yellow air-stable compound is an important catalyst used in organic synthesis.[2] It is one of the most widely used transition metal allyl complexes.

Allylpalladium(II) chloride dimer
Names
IUPAC name
Allylpalladium(II) chloride dimer
Other names
Allylpalladium chloride dimer
bis(allyl)di-μ-chloro-dipalladium(II)
APC
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.031.423
EC Number
  • 234-579-8
Properties
C6H10Cl2Pd2
Molar mass 365.85 g/mol
Appearance Pale yellow, crystalline solid
Density Solid
Melting point decomp at 155-156 °C
Insoluble
Solubility in other solvents Chloroform
benzene
acetone
methanol
Structure[1]
monoclinic
P21/n, No. 14
2
Hazards
Safety data sheet http://www.colonialmetals.com/pdf/5048.pdf
GHS pictograms
GHS Signal word Warning
H302, H312, H315, H319, H332, H335
P261, P264, P270, P271, P280, P301+312, P302+352, P304+312, P304+340, P305+351+338, P312, P321, P322, P330, P332+313, P337+313, P362, P363, P403+233, P405, P501
Related compounds
Related compounds
 (η3-allyl)(η5 – cyclopentadienyl)palladium(II)
di-μ-chlorobis(crotyl)dipalladium
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Structure

The compound has a dimeric structure that is centrosymmetric. 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.[1]

Synthesis

The compound is prepared by purging carbon monoxide through a methanolic aqueous solution of sodium tetrachloropalladate (prepared from palladium(II) chloride and sodium chloride), and allyl chloride.[2]

2 Na2PdCl4   +   2 CH2=CHCH2Cl   +   2 CO   +   2 H2O   →   [(η3-C3H5)PdCl]2   +   4 NaCl   +   2 CO2   +   4 HCl

Another method is the reaction of propene with palladium(II) trifluoroacetate, followed by ion exchange with chloride:[3]

2 (CF3COO)2Pd + 2 CH2=CHCH3 → [(η3-C3H5)Pd(CF3COO)]2
[(η3-C3H5)Pd(CF3COO)]2 + 2 Cl− → [(η3-C3H5)PdCl]2 + 2 CF3COO−

Reactions

APC reacts with sources of cyclopentadienyl anion to give the corresponding 18e− complex cyclopentadienyl allyl palladium:

[(η3-C3H5)PdCl]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 and the corresponding enthalpy are:

1/2 [(η3-C3H5)PdCl]2 + :NC5H5 → (η3-C3H5)PdCl:NC5H5   ΔH = −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)PdCl]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, nucleophilic addition to dienes, and decomposition of diazo compounds to reactive carbenes. It is also a useful precursor of other Pd catalysts.[3]

References
  1. Smith, A. E. (1965). "The structure of the allylpalladium chloride complex (C3H5PdCl)2 at –140°C". Acta Crystallographica. 18 (3): 331–340. doi:10.1107/S0365110X65000774. ISSN 0365-110X.
  2. Tatsuno, Y.; Yoshida, T.; Otsuka, S. "(η3-allyl)palladium(II) Complexes" Inorganic Syntheses, 1990, volume 28, pages 342-345. ISBN 0-471-52619-3
  3. Godleski, Stephen A.; Michelet, Véronique; Genêt, Jean-Pierre (2006), "Bis(allyl)di-μ-chlorodipalladium", Encyclopedia of Reagents for Organic Synthesis, Chichester, UK: John Wiley & Sons, Ltd, doi:10.1002/047084289x.rb098s.pub2, ISBN 978-0-471-93623-7, retrieved 2020-09-06
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