Tetrakis(triphenylphosphine)palladium(0) (sometimes called quatrotriphenylphosphine palladium) is the
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 ...
d(P(C6H5)3)4 often abbreviated
Pd(
PPh3)
4, or rarely PdP
4. It is a bright yellow
crystalline solid that becomes brown upon decomposition in
air.
Structure and properties
The four
phosphorus
Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...
atoms
Atoms are the basic particles of the chemical elements. An atom consists of a nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished from each other ...
are at the corners of a
tetrahedron
In geometry, a tetrahedron (: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex (geometry), vertices. The tet ...
surrounding the palladium(0) center. This structure is typical for four-coordinate
18 e− complexes. The corresponding complexes Ni(PPh
3)
4 and Pt(PPh
3)
4 are also well known. Such complexes reversibly dissociate PPh
3 ligands
In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's ...
in solution, so reactions attributed to Pd(PPh
3)
4 often in fact arise from Pd(PPh
3)
3 or even Pd(PPh
3)
2.
Preparation
Tetrakis(triphenylphosphine)palladium(0) was first prepared by Lamberto Malatesta et al. in the 1950s by reduction of sodium chloropalladate with
hydrazine
Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly hazardous unless handled in solution as, for example, hydraz ...
in the presence of the
phosphine
Phosphine (IUPAC name: phosphane) is a colorless, flammable, highly toxic compound with the chemical formula , classed as a pnictogen hydride. Pure phosphine is odorless, but technical grade samples have a highly unpleasant odor like rotting ...
. It is commercially available, but can be prepared in two steps from Pd(II) precursors:
:PdCl
2 + 2 PPh
3 → PdCl
2(PPh
3)
2
:
PdCl2(PPh3)2 + 2 PPh
3 +
N2H4 → Pd(PPh
3)
4 + N
2 + 2 N
2H
5Cl
Both steps may be carried out in a
one-pot reaction, without isolating and purifying the PdCl
2(PPh
3)
2 intermediate.
Reductants other than hydrazine can be employed, including
ascorbic acid
Ascorbic acid is an organic compound with formula , originally called hexuronic acid. It is a white solid, but impure samples can appear yellowish. It dissolves freely in water to give mildly acidic solutions. It is a mild reducing agent.
Asco ...
. The compound is sensitive to air, but can be purified by washing with
methanol
Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...
to give the desired yellow powder. It is usually stored cold under
argon
Argon is a chemical element; it has symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as abu ...
.
Applications
Pd(PPh
3)
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(PPh
3)
4 + ArBr → PdBr(Ar)(PPh
3)
2 + 2 PPh
3
References
{{Palladium compounds
Palladium compounds
Reagents for organic chemistry
Triphenylphosphine complexes
Homogeneous catalysis