|Molar mass||1,155.56 g mol−1|
|Appearance||Bright yellow crystals|
|Melting point||decomposes around 115 °C|
|Solubility in water||Insoluble|
|four triphenylphosphine unidentate
ligands attached to a central Pd(0)
atom in a tetrahedral geometry
|Dipole moment||0 D|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Tetrakis(triphenylphosphine)palladium(0) is the chemical compound Pd[P(C6H5)3]4, often abbreviated Pd(PPh3)4, or even PdP4. It is a bright yellow crystalline solid that becomes brown upon decomposition in air.
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 18e complexes. 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.
Tetrakis(triphenylphosphine)palladium(0) was first prepared by Lamberto Malatesta and his group in Milan in the 1960s by reduction of sodium chloropalladate with hydrazine in the presence of the phosphine. It is commercially available, but can be prepared in two steps from Pd(II) precursors:
- PdCl2 + 2 PPh3 → cis-PdCl2(PPh3)2
- cis-PdCl2(PPh3)2 + 2 PPh3 + 2.5 N2H4 → Pd(PPh3)4 + 0.5 N2 + 2 N2H5+Cl-
Both steps may be carried out in a one-pot reaction, without isolating and purifying the cis-PdCl2(PPh3)2 intermediate. Reductants other than hydrazine can be employed. 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.
Pd(PPh3)4 is widely used as a catalyst for palladium-catalyzed coupling reactions. 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
- C. Elschenbroich, A. Salzer ”Organometallics : A Concise Introduction” (2nd Ed) (1992) Wiley-VCH: Weinheim. ISBN 3-527-28165-7
- L. Malatesta and M. Angoletta, "Palladium(0) compounds. Part II. Compounds with triarylphosphines, triaryl phosphites, and triarylarsines" J. Chem. Soc., 1186 (1957). doi:10.1039/JR9570001186
- D. R. Coulson; Satek, L. C.; Grim, S. O. (1972). "Tetrakis(triphenylphosphine)palladium(0)". Inorg. Synth. Inorganic Syntheses 13: 121. doi:10.1002/9780470132449.ch23. ISBN 978-0-470-13244-9.
- P. W. van Leeuwen (2005). Homogeneous Catalysis: Understanding the Art. Springer. ISBN 1-4020-3176-9.