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 PdII(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 PdII(OAc)2. In the presence of 1 equiv. of nBu4NI as the additive, unreactive 4-chloroacetophenone also undergoes Heck coupling with styrene.