Tetrakis(triphenylphosphine)palladium(0)

Tetrakis(triphenylphosphine)palladium(0)

Tetrakis(triphenylphosphine)palladium(0)

Chemical compound

Tetrakis(triphenylphosphine)palladium(0) (sometimes called quatrotriphenylphosphine palladium) is the chemical compound [Pd(P(C6H5)3)4], often abbreviated Pd(PPh3)4, or rarely PdP4. It is a bright yellow crystalline solid that becomes brown upon decomposition in air.

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Structure and properties

The four phosphorus atoms are at the corners of a tetrahedron surrounding the palladium(0) center. This structure is typical for four-coordinate 18 e− complexes.[2] The corresponding complexes Ni(PPh3)4 and Pt(PPh3)4 are also well known. Such complexes reversibly dissociate PPh3 ligands in solution, so reactions attributed to Pd(PPh3)4 often in fact arise from Pd(PPh3)3 or even Pd(PPh3)2.[3]

Preparation

Tetrakis(triphenylphosphine)palladium(0) was first prepared by Lamberto Malatesta et al. in the 1950s by reduction of sodium chloropalladate with hydrazine in the presence of the phosphine.[4] It is commercially available, but can be prepared in two steps from Pd(II) precursors:

PdCl2 + 2 PPh3 → PdCl2(PPh3)2
PdCl2(PPh3)2 + 2 PPh3 + 5⁄2 N2H4 → Pd(PPh3)4 + 1⁄2 N2 + 2 N2H5Cl

Both steps may be carried out in a one-pot reaction, without isolating and purifying the PdCl2(PPh3)2 intermediate.[5] Reductants other than hydrazine can be employed, including ascorbic acid.[6] The compound is sensitive to air, but can be purified by washing with methanol to give the desired yellow powder. It is usually stored cold under argon.

Applications

Pd(PPh3)4 is widely used as a catalyst for palladium-catalyzed coupling reactions.[7] Prominent applications include the Heck reaction, Suzuki coupling, Stille coupling, Sonogashira coupling, and Negishi coupling. These processes begin with two successive ligand dissociations followed by the oxidative addition of an aryl halide to the Pd(0) center:

Pd(PPh3)4 + ArBr → PdBr(Ar)(PPh3)2 + 2 PPh3

References

  1. [1]
    "Tetrakis(triphenylphosphine)palladium". pubchem.ncbi.nlm.nih.gov.
  2. [2]
    Elschenbroich, C.; Salzer, A. (1992). Organometallics: A Concise Introduction (2nd ed.). Weinheim: Wiley-VCH. ISBN 3-527-28165-7.
  3. [3]
    Scott, Neil W. J.; Ford, Mark J.; Schotes, Christoph; Parker, Rachel R.; Whitwood, Adrian C.; Fairlamb, Ian J. S. (2019). "The Ubiquitous Cross-Coupling Catalyst System 'Pd(OAc)2'/2PPh3 Forms a Unique Dinuclear PdI Complex: An Important Entry Point into Catalytically Competent Cyclic Pd3 Clusters". Chemical Science. 10 (34): 7898–7906. doi:10.1039/C9SC01847F.
  4. [4]
    Malatesta, L.; Angoletta, M. (1957). "Palladium(0) compounds. Part II. Compounds with triarylphosphines, triaryl phosphites, and triarylarsines". J. Chem. Soc. 1957: 1186. doi:10.1039/JR9570001186.
  5. [5]
    Coulson, D. R.; Satek, L. C.; Grim, S. O. (1972). "Tetrakis(triphenylphosphine)palladium(0)". Inorganic Syntheses. Vol. 13. pp. 121–124. doi:10.1002/9780470132449.ch23. ISBN 978-0-470-13244-9.
  6. [6]
    Carrasco, Sergio; Martín-Matute, Belén (16 April 2019). "Hydrazine-Free Facile Synthesis of Palladium-Tetrakis(Triphenylphosphine)". European Journal of Inorganic Chemistry. 2019 (14): 1951–1955. doi:10.1002/ejic.201900060. S2CID 107314949. Retrieved 26 November 2023.
  7. [7]
    Van Leeuwen, P. W. (2005). Homogeneous Catalysis: Understanding the Art. Springer. ISBN 1-4020-3176-9.
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