Palladium–catalyzed C–C– and C–N–coupling reactions of aryl chlorides

Abstract

In this paper we report a brief review of the palladium–catalyzed olefination and amination of aryl chlorides. Special emphasis is given on the efficiency of known catalysts. Best turnover numbers (TON up to 40,000) known to date for Heck reactions are displayed by palladacycle catalysts, e.g., 1 in the presence of salts as co–catalysts. Model studies show that the catalyst productivity is strongly influenced by the nature of the added salt. In addition, the ability of mixtures of Pd(OAc)2 and phosphines to catalyze the reaction of styrene with 1–chloro–4–trifluoromethylbenzene was studied dependent on the Pd:P ratio. It was found that apart from the palladacycle 1 a number of established phosphines permit efficient C–Cl activation. Amination of aryl chlorides is also possible in the presence of palladacycles as catalyst precursors. Crucial for the success of the C–N bond forming reaction is the use of potassium tert–butoxide as base and reaction temperatures > 120°C. Turnover numbers up to 900 and yields up to 80% have been obtained for the amination of 1–chloro–4–trifluoromethylbenzene.