Is oxidative addition indeed the rate-determining step of the Suzuki–Miyaura reaction with less-reactive aryl chlorides under “ligand-free” conditions?

Schmidt, Alexander F.; Kurokhtina, A. A.; Larina, E. V.; Vidyaeva, Elena V.; Lagoda, N. A.

doi:10.1016/j.jorganchem.2020.121571

Cited by 10 publications

(9 citation statements)

References 14 publications

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“…The oxidative addition of aryl halides to Pd(0) in the reaction mixture in both the dissolved and solid states becomes much more reversible in the Suzuki-Miyaura reaction with aryl chlorides than with aryl bromides and iodides. This conclusion is based on the data obtained under real catalytic conditions and is in agreement with the results of model stoichiometric experiments with phosphine-containing Pd complexes, indicating that the reversibility of the oxidative addition (characterized by the value of the equilibrium constant) increased by several orders of magnitude when moving from aryl Pd(II) complexes with iodide and bromide counterions to the complexes with chloride ions. , A similar conclusion was drawn using computational results . If the elementary steps that determine the rate ratio of aryl halide addition to dissolved or solid Pd compounds, i.e., determining if the reaction proceeds through a homogeneous or heterogeneous mechanism, become substantially reversible, the rate ratio of the homogeneous and heterogeneous reactions is influenced by the rates of the steps in the inverse direction and the rates of the steps following the reversible steps .…”

Section: Resultssupporting

confidence: 82%

Section: Scheme 2 Competing Suzuki-miyaura Reaction With Two Arylboro...supporting

confidence: 75%

“…Considering the hypothesis that the Suzuki-Miyaura reaction is possibly catalyzed by several active forms of Pd simultaneously in accordance with the concept of “catalytic cocktail”, the true reason for the sharp decrease in the contribution of heterogeneous Pd into the formation of the products using aryl chlorides needs to be studied. However, lower reactivity of aryl chlorides cannot be explained by the low rate of their oxidative addition, because this step was established to be relatively fast and even reversible . Therefore, the retarded Suzuki-Miyaura reaction proceeding with aryl chlorides can possibly result from both the insufficiency of heterogeneous catalysis mechanism and a sharp drop in the Pd concentration in solution …”

Section: Discussionmentioning

confidence: 99%

“…The results presented in the abovementioned paper 30 about lowering Pd concentration in solution using aryl chlorides instead of aryl bromides and especially aryl iodides also pointed to insufficient dissolution or rather low stability of dissolved Pd species. The experimentally revealed substantial reversibility of the oxidative addition of aryl chlorides in the Suzuki-Miyaura reaction 44 can be just one factor that decreases the stability of ArPdX intermediates by reverse reductive elimination, leading to the formation of Pd(0), which is highly unstable in the solution phase. This process can indeed be the main reason for the reduced Pd concentration in solution, thereby rendering it the key factor for the decrease in catalytic activity in the Suzuki-Miyaura reaction performed with aryl chlorides as compared to that with aryl iodides and aryl bromides.…”

Section: Scheme 2 Competing Suzuki-miyaura Reaction With Two Arylboro...mentioning

confidence: 99%

“…However, lower reactivity of aryl chlorides cannot be explained by the low rate of their oxidative addition, because this step was established to be relatively fast and even reversible. 44 Therefore, the retarded Suzuki-Miyaura reaction proceeding with aryl chlorides can possibly result from both the insufficiency of heterogeneous catalysis mechanism and a sharp drop in the Pd concentration in solution. 30…”

Section: ■ Conclusionmentioning

confidence: 99%

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Activation of Aryl Chlorides in the Suzuki-Miyaura Reaction by “Ligand-Free” Pd Species through a Homogeneous Catalytic Mechanism: Distinguishing between Homogeneous and Heterogeneous Catalytic Mechanisms

Lagoda

Larina

Vidyaeva

et al. 2021

Org. Process Res. Dev.

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A distinction between the homogeneous and heterogeneous catalytic mechanisms of a myriad of Pd catalytic systems for the Suzuki-Miyaura reaction has been made based on soluble metal complexes or heterogenized Pd compounds. To date, hypotheses that concern whether the reaction proceeds in the solution phase or on the surface of solid particles, including nanosized ones, have been based on experimental results obtained under different reaction conditions. Moreover, convincing evidence was obtained for reactions proceeding simultaneously through homogeneous and heterogeneous catalytic mechanisms. However, most of the experimental evidence was obtained for relatively reactive aryl bromides and aryl iodides, while insufficient data exists for nonreactive aryl chlorides to make any well-grounded conclusions regarding the homogeneous or heterogeneous nature of the active species. Here, we report the use of “ligand-free” conditions, which excludes the need to add strong organic ligands, such as phosphines, amines, and carbenes, for the activation of aryl chlorides in the Suzuki-Miyaura reaction. The results suggest that the reaction proceeds in the solution phase through a homogeneous mechanism even when heterogeneous precursors are used. The main reason for this conclusion is the independence of the reaction differential selectivity under the competition of two aryl chlorides or two arylboronic acids, which is based on numerous parameters that only influence the nature of the possible heterogeneous Pd forms when the homogeneous mechanism is realized.

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