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. 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
CAS Number	12012-95-2 Y
3D model (JSmol)	Interactive image
ChemSpider	21171401 Y
ECHA InfoCard	100.031.423
EC Number	234-579-8
PubChem CID	61538
CompTox Dashboard (EPA)	DTXSID10897423
InChI InChI=1S/2C3H5.2ClH.2Pd/c2*1-3-2;;;;/h2*3H,1-2H2;2*1H;;/q;;;;2*+1/p-2 Y Key: TWKVUTXHANJYGH-UHFFFAOYSA-L Y InChI=1/2C3H5.2ClH.2Pd/c2*1-3-2;;;;/h2*3H,1-2H2;2*1H;;/q;;;;2*+1/p-2/r2C3H5ClPd/c2*1-2-3-5-4/h2*2H,1,3H2 Key: TWKVUTXHANJYGH-NNVIZEFPAF
SMILES Cl[Pd]CC=C.C=CC[Pd]Cl
Properties
Chemical formula	C6H10Cl2Pd2
Molar mass	365.85 g/mol
Appearance	Pale yellow, crystalline solid
Melting point	decomp at 155-156 °C
Solubility in water	Insoluble
Solubility in other solvents	Chloroform benzene acetone methanol
Structure
Crystal structure	monoclinic
Space group	P21/n, No. 14
Formula units (Z)	2
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H312, H315, H319, H332, H335
Precautionary statements	P261, P264, P270, P271, P280, P301+P312, P302+P352, P304+P312, P304+P340, P305+P351+P338, P312, P321, P322, P330, P332+P313, P337+P313, P362, P363, P403+P233, P405, P501
Safety data sheet (SDS)	http://www.colonialmetals.com/pdf/5048.pdf
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). N verify (what is YN ?) 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.

Synthesis

sample of allyl palladium chloride dimer

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 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:

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.