Lewis Base Activation of Silicon Lewis Acids

Rossi, Sergio; Denmark, Scott E.

doi:10.1002/9783527814787.ch10

Cited by 3 publications

(6 citation statements)

References 257 publications

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“…While the attack of the Lewis basic phosphine on the silicon center seems natural, the Lewis acidity of the negatively charged silicon center in 2 is unclear. Such a behavior would be described as the Lewis base activation of silicon Lewis acids, and was suggested in particular by Oestreich and Denmark for the activation of silanes with fluoride and carbonate ions [4,38] …”

Section: Resultsmentioning

confidence: 93%

“…All these observations are coherent with a mechanism, showed in Figure 6, during which the phosphine PR 3 interacts with the silane 1 with the lone pair of the phosphorus, in order to form a penta ‐valent silicate 2 , with partial charges δ+ and δ‐ developed on respectively the phosphorus and the silicon atom. A reorganization of the electronic density occurs in penta ‐valent silicon species leading to a lengthening of the bonds between Si and the peripheral ligands (H − here) and an enhancement of the nucleophile character of these last ones [4,38] . The first step is therefore followed by an attack of the activated hydride H − on the aldehydic carbon of benzaldehyde to form the ion pair 3 which further reacts to form 4 .…”

Section: Resultsmentioning

confidence: 99%

“…A reorganization of the electronic density occurs in ChemPlusChem penta-valent silicon species leading to a lengthening of the bonds between Si and the peripheral ligands (H À here) and an enhancement of the nucleophile character of these last ones. [4,38] The first step is therefore followed by an attack of the activated hydride H À on the aldehydic carbon of benzaldehyde to form the ion pair 3 which further reacts to form 4. A concerted mechanism of the attack of the hydride and of the formed alkoxide on the silicon center to yield the compound 4 directly from 2 cannot be ruled out, especially considering the high reactivity of the hypothetically formed silylium cation.…”

Section: Chempluschemmentioning

confidence: 99%

“…Such a behavior would be described as the Lewis base activation of silicon Lewis acids, and was suggested in particular by Oestreich and Denmark for the activation of silanes with fluoride and carbonate ions. [4,38]…”

Section: Chempluschemmentioning

confidence: 99%

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Phosphine‐Catalyzed Activation of Phenylsilane for Benzaldehyde Reduction

et al. 2023

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Hydrosilylation reactions are commonly used for the reduction of carbonyl bonds in fine chemistry, catalyzed by transition metal complexes. The current challenge is to expand the scope of metal-free alternative catalysts, including in particular organocatalysts. This work describes the organocatalyzed hydrosilylation of benzaldehyde with a phosphine, introduced at 10 mol%, and phenylsilane at room temperature. The activation of phenylsilane was highly dependent on the physical properties of the solvent such as the polarity, and the highest conversions were obtained in acetonitrile and propylene carbonate with yields of 46 % and 97 %, respectively. The best results of the screening over 13 phosphines and phosphites were obtained with linear trialkylphoshines (PMe 3 , P n Bu 3 , POct 3 ), indicating the importance of their nucleophilicity, with yields of 88 %, 46 % and 56 %, respectively. With the help of heteronuclear 1 HÀ 29 Si NMR spectroscopy, the products of the hydrosilylation (PhSiH 3-n (OBn) n ) were identified, allowing a monitoring of the concentration in the different species, and thereby of their reactivity. The reaction displayed an induction period of ca. 60 min, followed by the sequential hydrosilylations presenting various reaction rates. In agreement with the formation of partial charges in the intermediate state, we propose a mechanism based on a hypervalent silicon center via the Lewis base activation of the silicon Lewis acid.

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Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Section: Chempluschemmentioning

confidence: 99%

Section: Chempluschemmentioning

confidence: 99%

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Phosphine‐Catalyzed Activation of Phenylsilane for Benzaldehyde Reduction

et al. 2023

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“…The Lewis acidity of silicon can also be increased by: 1) strong electron-withdrawing substituents and 2) incorporation of silicon in strained cycles. 87,92,93 Structures that incorporate these aspects can also enhance the reactivity of the silane allowing for a potentially more active silane catalyst. There must be at least one labile group on the silicon to be replaced with the -OH of the silanol.…”

Section: Designing a Catalytic Organosilanementioning

confidence: 99%

Synthesis of Organosilanes and Investigation of Their Catalytic Activity for Direct Amide Bond Formation

D'Amaral

2024

Preprint

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<p>Amide synthesis is a fundamental reaction in synthetic chemistry due to the abundance of amides in biologically active molecules, synthetic polymers, and commercial products. Coupling reagents that activate the carboxylic acid have become the most well-studied method to direct amide bond formation. Amongst these, carbodiimides, uronium and phosphonium salts, and benzotriazoles are the most common. These reactions, however, are often limited by poor atom economy, and toxic and expensive reagents. Therefore, synthetic chemists need a better method to form amides safely and efficiently. Organosilanes have been reported as greener, efficient alternative amide coupling reagents. Current work in this field often requires a stoichiometric (or more) amount of the silane. While stoichiometric amide coupling reactions are generally the methods of choice for their efficiency and practicality, catalytic amide coupling can present a new step toward greener methodologies to make amides. This thesis explores novel organosilanes that are investigated as catalysts for direct amidation. The silane catalysts are designed to have enhanced reactivity by incorporating a hydrogen bond donor (HBD) to facilitate the formation of a silyl ester intermediate and nucleophilic attack at the carbonyl by the amine coupling partner. The synthesis of various organosilanes have been investigated, including silanes that have an amide or urea, hydroxy, or protonated amine as a HBD. The silanes that have been successfully synthesized were tested as catalysts in direct amidation. Aryl and alkyl silanes, and di- and trisubstituted silanes were used in stoichiometric silane-mediated amide synthesis to study how the substitution on the silicon effects amidation.</p>

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