Ligandless, Anionic, Arylpalladium Halide Intermediates in the Heck Reaction

Abstract

We report the isolation and reactivity of a series of “ligandless,” anionic arylpalladium complexes of the general structure [Pd(Ar)Br2]22- by the reaction of (tBu3P)Pd(Ar)(Br) and bromide. These anionic complexes insert olefins at room temperature, and these fast insertions indicate that the anionic complexes are kinetically competent as intermediates in Heck-Mizoroki reactions conducted under “ligandless” conditions (lacking added dative ligand). Kinetic studies showed that the anionic complexes insert olefins much faster than the corresponding neutral, P(t-Bu)3-ligated complexes. Addition of halide to the reaction of the neutral complex (tBu3P)Pd(Ar)(Br) and styrene led to a significant rate acceleration, suggesting that the anionic complex forms rapidly and reversibly in situ from the neutral species prior to migratory insertion. These data, along with studies on the regioselectivity for reaction of aryl halides with butyl vinyl ether in the presence of the different starting catalysts, are consistent with the intermediacy of the same anionic, arylpalladium intermediates in Heck reactions catalyzed by palladium complexes containing bulky trialkylphosphine ligands as in reactions conducted under ligandless conditions.

General Olefin Synthesis by the Palladium‐Catalyzed Heck Reaction of Amides: Sterically Controlled Chemoselective NC Activation

“…[6] Significant advances in the development of new catalytic systems [7] and mechanistic studies have been reported. [8] However,d espite the reported advances,t he use of amides as electrophilic coupling partners in the Heck reaction remains unknown. [1][2][3][4][5][6][7][8] There is little doubt that the successful application of bench-stable amide building blocks as olefination precursors would significantly broaden the scope of electrophilic partners for the Heck reaction and represent an attractive opportunity for the development of new activation modes of inert NÀCb onds.…”

Studies on the Amination of Aryl Chlorides with a Monoligated Palladium Catalyst: Kinetic Evidence for a Cooperative Mechanism

“…be catalytically active; [13,26,31] in particular, the effect of chloride anions cannot be disregarded. [28] The first cycle includes oxidative addition of 2, binding of 3, and reductive elimination of 4.…”

DFT Investigation of the Palladium‐Catalyzed Ene–Yne Coupling

“…This is in line with our earlier suggestions of low-ligated states in Pd-catalyzed reactions, [12] and also with recent experimental studies by Hartwig and co-workers. [13] The solvato complex 2 b and TS 3 b prefer a geometry in which the small, weak DMF ligand is cis to the alkyne and trans to the very strongly influencing hydride ligand. The alternative geometry (not shown) is higher in energy.…”