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

Abstract

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.

Reactions of Secondary Allylamines with Bis(η5:η1-pentafulvene)titanium Complexes: Selective Formation of Monoazabutadiene Titanium Complexes by N–H and C–H Bond Activation

“…However, the two broad signals of the N-CH 2 protons at 4.71 and 3.56 ppm are much more significant for this type of monoamide species. In clear contrast to the allylamine (3.35 ppm), 24 these signals are shifted to lower field and are split by 1.2 ppm. This signal pattern is indicative of the strong agostic interaction between the titanium center and one proton of the N-CH 2 unit.…”

Real-time analysis of Pd2(dba)3 activation by phosphine ligands

“…16 Heating of precatalyst and ligand prior to the addition of substrates has been suggested as a means to ensure reproducible reaction rates; [17][18][19] however, others question the benefits of this precaution. 2,3,20 Depending on the precatalyst and ligand used, long stirring times may be unnecessary or may even change catalyst speciation which further complicates the activation. A further complicating factor is the non-innocence of the dba ligand leading to the presence of Pd(dba) x L y type complexes.…”

“…The outcome of the activation process can depend on the source of the precatalyst, 2 order of addition, and chosen reaction conditions. 3 Recently, several reports on the activation chemistry of Pd(II) precursors have appeared, 4 but investigations regarding the activation of zero valent Pd precursors remain limited. [5][6][7][8][9][10][11][12] Pd 2 (dba) 3 is the most frequently employed source of Pd(0), 13 but despite its popularity the actual nature of the catalytically relevant species and the influence of reaction conditions on its activation are incompletely understood.…”

Palladium-Catalyzed Solvent-Free Preparation of Arylphosphonates ArP(O)(OAr)2from (ArO)3P via the Michaelis–Arbuzov Rearrangement

“…First, treatment of Pd 2 (dba) 3 with P­(OPh) 3 1a quickly generated Pd­[P­(OPh) 3 ] 3 ( 6a ) at room temperature (eq ). Then, the oxidative addition of 6a to iodobenzene produced the arylpalladium complex 7a quantitatively at room temperature (eq 3 ). This reaction can be achieved in one pot.…”