general method for the palladium-catalyzed formation of diaryl ethers is described. Electron-rich, bulky aryldialkylphosphine ligands, in which the two alkyl groups are either tert-butyl or 1-adamantyl, are the key to the success of the transformation. A wide range of electron-deficient, electronically neutral and electron-rich aryl bromides, chlorides, and triflates can be combined with a variety of phenols with the use of sodium hydride or potassium phosphate as base in toluene at 100 degrees C. The bulky yet basic nature of the phosphine ligand is thought to be responsible for increasing the rate of reductive elimination of the diaryl ether from palladium.
“Novel Electron-Rich Bulky Phosphine Ligands Facilitate the Palladium-Catalyzed Preparation of Diaryl Ethers”, J. Am. Chem. Soc., 1999, 121(18), 4369-4378.