Speciation of Pd(OAc)₂in ligandless Suzuki–Miyaura reactions

Abstract

Generation of catalytically active Pd(0) species from Pd(OAc) 2 has been examined, in the context of Suzuki-Miyaura reactions involving substitution of aryl bromides under aerobic and ambient conditions. Using a combination of spectroscopic, microscopic and kinetic measurements, the role of each reaction component is delineated in the speciation of the palladium species. Among the key findings are the effects of O 2 , H 2 O and inorganic base, and implications for catalytic activity.

Palladium-Catalyzed Suzuki Reactions in Water with No Added Ligand: Effects of Reaction Scale, Temperature, pH of Aqueous Phase, and Substrate Structure

“…Under the reaction conditions with no added ligand when water and PhB(OH) are present, Pd(OAc) 2 can rapidly generate catalytically active Pd(0) molecules, which undergo aggregation to form nanoclusters, nanoparticles and, eventually, Pd black (Figure 2). 75 The interactions between the basic nitrogen centers and Pd(0) can also be verified by the classic mercury test, since the addition of excess of Hg(0) (relative to the Pd catalyst) will lead to the amalgamation of the surface of a Pd particle, thus poisoning it. 77,78 The resulting deactivation effect is 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 21 always obvious for a catalytic system containing heterogeneous and unprotected Pd(0) species.…”

Enhanced Catalytic Activity of High-Index Faceted Palladium Nanoparticles in Suzuki–Miyaura Coupling Due to Efficient Leaching Mechanism

“…26 When the Pd catalyst concentration is decreased to 0.1 mol%, after and rate has been associated with a homogenous mechanism. 44 Deactivation of this so-called homeopathic Pd occurs as the solubilized Pd nucleates to form Pd clusters that continue to grow. [46][47] Quenching of the catalytically active Pd atoms in solution becomes more efficient as the Pd concentration increases due to greater leaching.…”

Operando XAFS of supported Pd nanoparticles in flowing ethanol/water mixtures: implications for catalysis

“…There now exist a number of examples of this technique being applied to study various aspects of Pd catalyzed selective oxidation [17][18][19][20][21][22] and homogeneous [23][24][25][26][27][28] and heterogeneous 29,30 catalytic carboncarbon coupling. There now exist a number of examples of this technique being applied to study various aspects of Pd catalyzed selective oxidation [17][18][19][20][21][22] and homogeneous [23][24][25][26][27][28] and heterogeneous 29,30 catalytic carboncarbon coupling.…”