The Fast Formation of a Highly Active Homogeneous Catalytic System upon the Soft Leaching of Pd Species from a Heterogeneous Pd/C Precursor

Abstract

Understanding the interface between soluble metal complexes and supported metal particles is important in order to reveal reaction mechanisms in a new generation of highly active homogeneous transition metal catalysts. In this study, we show that, in the case of palladium forming on a carbon (Pd/C) catalyst from a soluble Pd(0) complex Pd2dba3, the nature of deposited particles on a carbon surface turns out to be much richer than previously assumed, even if a very simple experimental procedure is utilized without the use of additional reagents and procedures. In the process of obtaining a heterogeneous Pd/C catalyst, highly active “hidden” metal centers are formed on the carbon surface, which are leached out by the solvent and demonstrate diverse reactivity in the solution phase. The results indicate that heterogeneous catalysts may naturally contain trace amounts of molecular monometallic centers of a different nature by easily transforming them to the homogeneous catalytic system. In line with a modern concept, a heterogenized homogeneous catalyst precursor was found to leach first, leaving metal nanoparticles mostly intact on the surface. In this study, we point out that the previously neglected soft leaching process contributes to high catalyst activity. The results we obtained demand for leaching to be reconsidered as a flexible tool for catalyst construction and for the rational design of highly active and selective homogeneous catalytic systems, starting from easily available heterogeneous catalyst precursors.

4D Catalysis Concept Enabled by Multilevel Data Collection and Machine Learning Analysis

“…Recently, our research group conducted a study of a specific site of the catalyst at the level of nanoparticles and individual atoms before and after the reaction in cross-coupling. 18,56 The results made it possible to reveal the previously unknown key role of single palladium atoms in C−C cross-coupling reactions; in addition, the study surprisingly suggested that metal nanoparticles can act as catalyst poisons rather than active centers.…”

“…Typically used approaches to study random areas of a catalyst before and after a reaction may lead to “random” results, leaving inaccessible the most useful information for researchers about the behavior of particular catalytic centers in the reaction. Recently, our research group conducted a study of a specific site of the catalyst at the level of nanoparticles and individual atoms before and after the reaction in cross-coupling. , The results made it possible to reveal the previously unknown key role of single palladium atoms in C–C cross-coupling reactions; in addition, the study surprisingly suggested that metal nanoparticles can act as catalyst poisons rather than active centers.…”

Palladium(ii)/N-heterocyclic carbene (NHC) catalyzed direct C–H arylation of heteroarenes with different aryl bromides and chlorides

“…115,116 Reliably distinguishing the nature of the active centers and the type of catalyst (homogeneous or cluster/nanoparticle) is of great significance for tuning the reaction conditions and designing new generations of highly efficient, stable, and sustainable catalysts. 117 Among the various methods, the mercury test (''Hg test'', ''mercury poisoning test'', ''Hg poisoning test'', or ''Hg drop test'') is one of the most frequently used rapid methods for distinguishing between truly homogeneous molecular catalysis and cluster/nanoparticle catalysis. 118 The method is based on the assumption that metallic mercury will poison M0 clusters/ nanoparticles that are acting as catalytically active centers but is inert toward molecular metal complexes.…”