Equilibrium Study of Pd(dba)2 and P(OPh)3 in the Pd-Catalyzed Allylation of Aniline by Allyl Alcohol

Reaction of Pd­(dba)2 and P­(OPh)3 shows a unique equilibrium where the Pd­[P­(OPh)3]3 complex is favored over both Pd­(dba)­[P­(OPh)3]2 and Pd­[P­(OPh)3]4 complexes at room temperature. At a lower temperature, Pd­[P­(OPh)3]4 becomes the most abundant complex in solution. X-ray studies of Pd­[P­(OPh)3]3 and Pd­(dba)­[P­(OPh)3]2 complexes show that both complexes have a trigonal geometry with a Pd–P distance of 2.25 Å due to the π-acidity of the phosphite ligand. In solution, pure Pd­(dba)­[P­(OPh)3]2 complex equilibrates to the favored Pd­[P­(OPh)3]3 complex, which is the most stable complex of those studied, and also forms the most active catalytic species. This catalyst precursor dissociates one ligand to give the reactive Pd­[P­(OPh)3]2, which performs an oxidative addition of nonmanipulated allyl alcohol to generate the π-allyl-Pd­[P­(OPh)3]2 intermediate according to ESI-MS studies.