3(5)-Pyrazolyl substituted triphenylphosphines as ligands for the palladium catalyzed Heck reaction

3(5)-Pyrazolyl substituted triphenylphosphines have been investigated as ligands for the palladium catalyzed Heck reaction of aryl halides with styrene. Catalysts formed in situ from those phosphines and Pd^II(OAc)₂ are comparable in activity and selectivity with the corresponding pre-synthesized Pd(II) complexes, while Pd₂(dba)₃ has turned out to be a less suitable palladium source. Among the ligands investigated, the bidentate P,N-ligand 2-[3(5)-pyrazolylphenyl]diphenylphosphine has shown the highest activities for the coupling of bromobenzene with styrene in the presence of Pd^II(OAc)₂. In the presence of 1 equiv. of nBu₄NI as the additive, unreactive 4-chloroacetophenone also undergoes Heck coupling with styrene.