Equilibrium study of Pd(dba)2 and P(OPh)3 in the Pd-catalyzed allylation of aniline by allyl alcohol

摘要

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 A˚ 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.

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