Tetrakis(triphenylphosphine)palladium(0)

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.

Preparation, structure, and properties
This complex is 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-

Reductants other than hydrazine can be employed.

The four P 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, releasing the 16e M(PPh3)3. Thus, reactions attributed to Pd(PPh3)4 in fact arise from Pd(PPh3)3 or even Pd(PPh3)2.

If the tetrakis(triphenylphosphine)palladium (0) is an orange brown, triturate with methanol and filter to give the desired yellow powder. Store under nitrogen in the fridge.

Applications
Pd(PPh3)4 is widely used as a catalyst for coupling reactions. Prominent applications include the Heck reaction and Suzuki coupling. These processes begin with the oxidative addition of an aryl halide to the Pd(0) center:
 * Pd(PPh3)4 + ArBr → PdBr(Ar)(PPh3)2 + 2 PPh3