Tetrakis(triphenylphosphine)palladium(0) 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. It is a high-yielding catalyst used in coupling reactions. 

Typical application it is used as the catalyst:

Palladium-Catalyzed Three-Component Reaction for the Synthesis of Imidazolidinones

Typical Procedure: Once the Schlenk tube containing K2CO3 (55 mg, 0.40 mmol) is flamed, dried, and filled with argon, Pd(PPh3)4 (12 mg, 0.010 mmol), PMB-protected 2,3-allenylamine (37 mg, 0.20 mmol), iodobenzene (58 mg, 0.28 mmol), phenyl isocyanate (36 mg, 0.30 mmol), and CH3CN (4 mL) are added sequentially. The resulting solution is heated to and stirred at 70°C. When the reaction is completed as monitored by TLC, the solvent is evaporated under reduced pressure, and the residue is purified by chromatography on silica gel (petroleum ether : ethyl acetate = 7:1) to afford the corresponding imidazolidione (72 mg, Y. 96%) as an oil.

Other examples as the catalyst:

1. Catalyst for Suzuki coupling of chiral secondary organoboronic esters.

2. Palladium-catalyzed SNAr reactions for the synthesis of heteroaryl ethers.

3. Catalyst for cross-coupling of a-diazocarbonyl compouns with arylboronic acids.

4. Diastereoselective synthesis of trans-1,2-diazetidines.

5. Palladium-catalyzed alkynyl iminium ion cyclization.

6. Widely used reagent in a variety of transformations including Heck arylation, enyne and diyne cycloisomerization.

7. Catalysts for cross-coupling.