Mechanism of Heterolytic Hydrogen Splitting by Frustrated Lewis Pairs: Comparison of Static and Dynamic Models

Daru, János; Bakó, Imre; Stirling, András; Pápai, Imre

doi:10.1021/acscatal.9b01137

Cited by 32 publications

(28 citation statements)

References 108 publications

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“…Indeed, this charge‐separated state lies much higher in energy (54.4 kcal mol −1 ) than the neutral donor‐acceptor pair [PMes 3 , B(C 6 F 5 ) 3 ] and undergoes rapid back‐electron transfer (lifetime=237 ps) as determined by transient absorption spectroscopy to regenerate the FLP, [10] thus preventing build‐up of a concentration of radicals large enough to influence the reaction kinetics. This leads to the conclusion that the splitting of dihydrogen by PMes 3 and B(C 6 F 5 ) 3 proceeds via a two‐electron, heterolytic pathway, even when the reaction is performed in ambient light [2e–g] …”

Section: Resultsmentioning

confidence: 99%

Single‐Electron Transfer in Frustrated Lewis Pair Chemistry

et al. 2020

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Frustrated Lewis pairs (FLPs) are well knownf or their ability to activate small molecules.R ecent reports of radical formation within such systems indicate single-electron transfer (SET) could play an important role in their chemistry. Herein, we investigate radical formation upon reacting FLP systems with dihydrogen, triphenyltin hydride,o rt etrachloro-1,4-benzoquinone (TCQ) both experimentally and computationally to determine the nature of the single-electron transfer (SET) events;that is,being direct SET to B(C 6 F 5) 3 or not. The reactions of H 2 and Ph 3 SnH with archetypal P/B FLP systems do not proceed via ar adical mechanism. In contrast, reaction with TCQ proceeds via SET,w hichi so nly feasible by Lewis acid coordination to the substrate.Furthermore,SET from the Lewis base to the Lewis acid-substrate adduct may be prevalent in other reported examples of radical FLP chemistry, which provides important design principles for radical maingroup chemistry.

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Section: Resultsmentioning

confidence: 99%

Single‐Electron Transfer in Frustrated Lewis Pair Chemistry

et al. 2020

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“…The geometries of all species discussed in this work have been optimized at the B3LYP/6‐31G* level of theory [26–27] . The B3LYP hybrid functional have been shown to give accurate geometries and energies for FLP chemistry by previous computational studies, [28–30] and previous benchmark calculations [19,31] revealed that the computed ΔG for FLP reactions are somehow independent on the selected functional (i. e. B97D, M062X) and basis set (i. e. 6‐31G* and 6‐31+G**). Moreover, the adopted computational approach is not to produce accurate Gibbs energies for direct comparison with the experimentally measured quantities, but to provide qualitative trends for predicting FLP′s thermochemistry.…”

Section: Computational Detailsmentioning

confidence: 88%

Effects of Ionic Liquids on the Thermodynamics of Hydrogen Activation by Frustrated Lewis Pairs: A Density Functional Theory Study**

et al. 2021

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Nowadays, hydrogen activation by frustrated Lewis pairs (FLPs) and their applications are one of the emerging research topics in the field of catalysis. Previous studies have shown that the thermodynamics of this reaction is determined by electronic structures of FLPs and solvents. Herein, we investigated systems consisting of typical FLPs and ionic liquids (ILs), which are well known by their large number of types and excellent solvent effects. The density functional theory (DFT) calculations were performed to study the thermodynamics for H2 activation by both inter‐ and intra‐molecular FLPs, as well as the individual components. The results show that the computed overall Gibbs free energies in ILs are more negative than that computed in toluene. Through the thermodynamics partitioning, we find that ILs favor the H−H cleavage elemental step over the elemental steps of proton attachment, hydride attachment and zwitterionic stabilization. Moreover, the results show that these effects are strongly dependent on the type of FLPs, where intra‐molecular FLPs are more affected compared to the inter‐molecular FLPs.

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“… 17 − 30 In addition, the flexibility and dynamical behavior of FLP systems, including in transition-state (TS) geometries, have been subjected to several molecular dynamics investigations. 31 − 34 …”

Section: Introductionmentioning

confidence: 99%

Optimizing the Energetics of FLP-Type H₂ Activation by Modulating the Electronic and Structural Properties of the Lewis Acids: A DFT Study

Heshmat

Ensing

2020

J. Phys. Chem. A

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The great potential of frustrated Lewis pairs (FLPs) as metal-free catalysts for activation of molecular hydrogen has attracted increasing interest as an alternative to transition-metal catalysts. However, the complexity of FLP systems, involving the simultaneous interaction of three molecules, impedes a detailed understanding of the activation mechanism and the individual roles of the Lewis acid (LA) and Lewis base (LB). In the present work, using density functional theory (DFT) calculations, we examine the reactivity of 75 FLPs for the H 2 splitting reaction, including a series of experimentally investigated LAs combined with conventional phosphine-based ( t Bu 3 P) and oxygen-based (i.e., ethereal solvent) Lewis bases. We find that the catalytic activity of the FLP is the result of a delicate balance of the LA and LB strengths and their bulkiness. The H 2 splitting reaction can be changed from endergonic to exergonic by tuning the electrophilicity of the LA. Also, a more nucleophilic LB results in a more stable ion pair product and a lower barrier for the hydrogen splitting. The bulkiness of the LB leads to an early transition state to reduce steric hindrance and lower the barrier height. The bulkiness of the fragments determines the cavity size in the FLP complex, and a large cavity allows for a larger charge separation in the ion pair configuration. A shorter proton–hydride distance in this product complex correlates with a stronger attraction between the fragments, which forms more reactive ion pairs and facilitates the proton and hydride donations in the subsequent hydrogenation process. These insights may help with rationalizing the experimentally observed reactivities of FLPs and with designing better FLP systems for hydrogenation catalysis and hydrogen storage.

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Mechanism of Heterolytic Hydrogen Splitting by Frustrated Lewis Pairs: Comparison of Static and Dynamic Models

Cited by 32 publications

References 108 publications

Single‐Electron Transfer in Frustrated Lewis Pair Chemistry

Single‐Electron Transfer in Frustrated Lewis Pair Chemistry

Effects of Ionic Liquids on the Thermodynamics of Hydrogen Activation by Frustrated Lewis Pairs: A Density Functional Theory Study**

Optimizing the Energetics of FLP-Type H₂ Activation by Modulating the Electronic and Structural Properties of the Lewis Acids: A DFT Study

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Mechanism of Heterolytic Hydrogen Splitting by Frustrated Lewis Pairs: Comparison of Static and Dynamic Models

Cited by 32 publications

References 108 publications

Single‐Electron Transfer in Frustrated Lewis Pair Chemistry

Single‐Electron Transfer in Frustrated Lewis Pair Chemistry

Effects of Ionic Liquids on the Thermodynamics of Hydrogen Activation by Frustrated Lewis Pairs: A Density Functional Theory Study**

Optimizing the Energetics of FLP-Type H2 Activation by Modulating the Electronic and Structural Properties of the Lewis Acids: A DFT Study

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Optimizing the Energetics of FLP-Type H₂ Activation by Modulating the Electronic and Structural Properties of the Lewis Acids: A DFT Study