Cationic Silicon‐Based Lewis Acids in Catalysis

Shaykhutdinova, Polina; Keeß, Sebastian; Oestreich, Martin

doi:10.1002/9783527814787.ch5

Cited by 12 publications

(10 citation statements)

References 86 publications

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“…Catalytic C–F bond activation is the main area of application for silylium ions. − ,,− The reason for this is, aside from Lewis acidity, silicon’s affinity for fluoride. Hence, silylium-ion-promoted conversion of C(sp 3 )–F bonds into C(sp 3 )–H bonds employing hydrosilanes as stoichiometric hydride sources is thermodynamically driven, with the resulting Si–F bond being stronger than the C–F bond .…”

Section: Applications Of Silylium Ions In Synthesis and Catalysismentioning

confidence: 99%

“…Although carbenium (R 3 C + ) and silylium ions (R 3 Si + ) are closely related based on the positions of carbon and silicon in the periodic table, their historic development could not be more different. − Silylium ions are, compared to their lower homologues, truly late bloomers, and their existence in the condensed phase has been the subject of controversial debates. − The targeted synthetic uses of silylium ions as reactive intermediates and even catalysts have begun to boom just recently. − Part of reason why silylium ions had such a slow start nearly four decades ago was their difficult isolation in free form and their characterization in the condensed phase. Silylium ions are three-coordinate cations with an enormously Lewis-acidic silicon atom.…”

Section: Introductionmentioning

confidence: 99%

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Silylium Ions: From Elusive Reactive Intermediates to Potent Catalysts

et al. 2021

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The history of silyl cations has all the makings of a drama but with a happy ending. Being considered reactive intermediates impossible to isolate in the condensed phase for decades, their actual characterization in solution and later in solid state did only fuel the discussion about their existence and initially created a lot of controversy. This perception has completely changed today, and silyl cations and their donor-stabilized congeners are now widely accepted compounds with promising use in synthetic chemistry. This review provides a comprehensive summary of the fundamental facts and principles of the chemistry of silyl cations, including reliable ways of their preparation as well as their physical and chemical properties. The striking features of silyl cations are their enormous electrophilicity and as such reactivity as super Lewis acids as well as fluorophilicity. Known applications rely on silyl cations as reactants, stoichiometric reagents, and promoters where the reaction success is based on their steady regeneration over the course of the reaction. Silyl cations can even be discrete catalysts, thereby opening the next chapter of their way into the toolbox of synthetic methodology.

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Section: Applications Of Silylium Ions In Synthesis and Catalysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Silylium Ions: From Elusive Reactive Intermediates to Potent Catalysts

et al. 2021

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“…This significantly affected the development of entirely new synthesis methods and stimulated progress in the design of novel silicon-based Lewis acid catalysts . Now, the scope of catalytic applications using silylium ions covers a wide range of transformations …”

Section: Introductionmentioning

confidence: 99%

Structural and Electronic Effects on Phosphine Chalcogenide Stabilized Silicon Centers in Four-Membered Heterocyclic Cations

Falk

Bauer

2022

Inorg. Chem.

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Understanding the interplay of structural and electronic parameters in the stabilization of Lewis acidic silicon centers is crucial for stereochemical questions and applications in bond activation and catalytic transformations. Phosphine chalcogenide functionalized (Ch = O, S, and Se) hydrosilanes having tert-butyl and 2,4,6-trimethoxyphenyl (TMP) substituents on the silicon atom were synthesized, and the ring-closing reactions to afford the heterocyclic four-membered CPChSi cations were investigated. Synthetic access was only achieved for the sulfur-and selenium-based cations. A thorough study by means of single-crystal X-ray structure determination, NMR spectroscopic data, and density functional theory (DFT) calculations provided insight into important electronic and structural parameters affecting the stability of the intramolecularly stabilized cations. Detailed structural considerations were made on the contributions to the ring strain (angular strain and steric repulsion). Thermochemical investigations showed that the substituents on the silicon and phosphorus atoms play an important role for the stability of the cationic heterocycles. In the absence of large steric repulsions through bulky substituents (methyl groups on silicon and tert-butyl groups on phosphorus), an intrinsic stability sequence of the intramolecular Ch−Si coordination depending on the chalcogen atom in the direction Se ≤ S < O can be observed. However, the order is reversed (O < S < Se) in the case of strong repulsions between sterically demanding substituents (tert-butyl groups on both silicon and phosphorus atoms). Natural bond orbital (NBO) analysis supported the explanations for the observed deshielding trends in 31 P NMR spectroscopy and revealed that the O−Si bond is more ionic in nature compared to the S−Si and Se−Si bonds, with the latter exhibiting higher covalent character due to a more efficient charge transfer through a σ-type n Ch → p Si interaction.

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“…Since the generation of a silylium ion, R 3 Si + , is intrinsically linked to the proposed mechanism, we became interested if the use of a silylium ion as a catalyst would lead to the same catalytic outcome. We took into account that R 3 Si + is isolobal with the borane (F 5 C 6 ) 3 B but is more electrophilic . The application of silylium ions in catalysis is much more limited in comparison with that of boranes and is primarily focused on C–F bond activation and Lewis acid catalysis, such as the Diels–Alder reaction .…”

Section: Introductionmentioning

confidence: 99%

“…We took into account that R 3 Si + is isolobal with the borane (F 5 C 6 ) 3 B but is more electrophilic . The application of silylium ions in catalysis is much more limited in comparison with that of boranes and is primarily focused on C–F bond activation and Lewis acid catalysis, such as the Diels–Alder reaction . The literature on silylium ion catalyzed hydrosilylation is particularly scarce.…”

Section: Introductionmentioning

confidence: 99%