About Solid Phase vs. Liquid Phase in Suzuki-Miyaura Reaction

Abstract

A critical review of conclusions about the putative heterogeneous mechanism in the Suzuki-Miyaura coupling by supported Pd solids is reported. In the first section, the turnover frequencies (TOF) of 20 well-established homogeneous catalysts are shown to be in the range 200 to 1,000,000,000 h − 1 . The evidences used to prove a heterogeneous mechanism are discussed and another interpretation is proposed, hypothesizing that only the leached species are responsible for the catalytic reaction, even at ppb levels. Considering more than 40 published catalytic systems for which liquid phase Pd content have been reported, activities have been computed based on leached Pd concentrations and are shown to be in the range TOF 150 to 70,000,000 h − 1 . Such values are compatible with those found for the well-established homogeneous catalysts which questions the validity of the conclusions raised by many papers about the heterogeneous (solid) nature of Suzuki-Miyaura catalysis. Last, a tentative methodology is proposed which involves the rational use of well-known tests (hot-filtration test, mercury test…) to help to discriminate between homogeneous and heterogeneous mechanisms.

Kinetic Study of the Herrmann–Beller Palladacycle-Catalyzed Suzuki–Miyaura Coupling of 4-Iodoacetophenone and Phenylboronic Acid

“…The Suzuki-Miyaura (SM) reaction, and more generally Pd carbon-carbon (C-C) cross-coupling reactions, have been the subject of numerous and prolific research in organic chemistry and catalysis [1] crowned by the 2010 Nobel Prize for Chemistry [2][3][4][5], awarded to Richard Heck, Ei-ichi Negishi, and Akira Suzuki. In the last decades, many authors have shown an interest in the mechanism [6][7][8][9][10][11][12][13][14], proposing different mechanisms that have the same basic elementary steps, but with detailed discussions about several key points such as the nature of the active species [7,12,15], the role of the base [16][17][18], the missing links in the transmetallation step [19], the rate-limiting step, and the solvent effect [14]. Despite the interest devoted to the mechanism and, more generally, to the reaction [1], very few publications provide global kinetic data and/or rate laws.…”

Synthesis of fish scale derived hydroxyapatite silica propyl bis aminoethoxy ethane cuprous complex (HASPBAEECC) as a novel hybrid nano-catalyst for highly efficient synthesis of new benzimidazole-1,2,3-triazole hybrid analogues as antifungal agents

“…The hot-filtration test (also known as split test) is one of the most extensively used methods to confirm the heterogeneous nature of the catalyst. It works based on removing the solid mass from the reaction mixture at the reaction temperature and continuing the reaction on the filtrate [40]. The hot-filtration test using a glass frit was carried out after 1 h on the sample reaction that revealed no further progress of the reaction.…”

Prospects in Engineering Congested Molecular Diffusion at the Stabilizer Layer of Metal Nanocrystals for Ultrahigh Catalytic Activity

“…Similarly during hydrogenation of alkynes, too, the reactivity of the catalyst was found directly related to the shell thickness . In some reactions, such as Suzuki–Miyaura coupling, leached-out metal species were considered to be active species for catalysis. − In those cases, the active metal species leaches out only after interacting with reactant molecule. , Therefore, the diffusion of reactant molecules toward the catalyst surface will be important for the heterogeneous catalyst as well as for those catalysts that act as a reservoir to supply active metal species to allow the reaction in a homogeneous fashion. However, the estimation of the contribution of the molecular diffusivity alone to overall catalyst activity has not been possible yet, since the previous studies were not designed to confirm that the metal nanoparticles inside the different types of ligand shells were catalytically identical in nature.…”