Bis (pyrazolyl) palladium (II) complexes as catalysts for Mizoroki–Heck cross-coupling reactions

Recent progress in carbon–carbon cross-coupling reactions has resulted in the discovery of highly active<br>catalysts for carrying out such transformations. However, due to the wide array of applications of the<br>products from cross-coupling reactions, there is the need to design suitable catalysts that permit the<br>practical and economical synthesis of the cross-coupled products. Palladium complexes with bulky<br>and electron-donating ligands have served as excellent (pre)catalysts for the Mizoroki–Heck cross-coupling<br>reaction. By using bulky pyrazole-based ligands, we have prepared palladium(II) complexes with<br>controlled steric and electronic properties of the metal center. We have used these bulky bis(pyrazolyl)-<br>palladium(II) complexes as (pre)catalysts for the Mizoroki–Heck cross-coupling reaction. The (pre)catalysts<br>displayed high activity and selectivity, giving high catalytic conversions at a low (pre)catalyst<br>loading and short reaction times. A mercury poisoning test confirmed that the (pre)catalysts promoted<br>the Mizoroki–Heck cross-coupling homogenously and do not decompose into palladium black during<br>the reactions. The catalytic systems were also tolerant to the presence of functional groups, such as 4-<br>CF3, 4-CH3, 4-CO2Me and 4-CO2Et, on the alkene substrates.