Despite the earth abundance and easy availability of silicon, only few examples of isolable neutral silicon centered Lewis superacids are precedent in the literature. To approach the general drawbacks of limited solubility and unselective deactivation pathways, we introduce a Lewis superacid, based on perfluorinated pinacol substituents. The compound is easily synthesized on a gram-scale as the corresponding acetonitrile mono-adduct 1•(MeCN) and was fully characterized, including single crystal X-ray diffraction analysis (SC-XRD) and state-of-the-art computations. Lewis acidity investigations by the Gutmann-Beckett method and fluoride abstraction experiments indicate a Lewis superacidic nature. The challenging SiÀF bond activation of Et 3 SiF is realized and promising catalytic properties are demonstrated, consolidating the potential applicability of silicon centered Lewis acids in synthetic catalysis.

The Lewis superacid bis(perchlorocatecholato)silane catalyzes C−O bond metathesis of alkyl ethers with an efficiency outperforming all earlier reported systems. Chemoselective ring contractions of macrocyclic crown ethers enable substrate‐specific transformations, and an unprecedented ring‐closing metathesis of polyethylene glycols allows polymer‐selective degradation. Quantum chemical computations scrutinize a high Lewis acidity paired with a simultaneous low propensity for polydentate substrate binding as critical for successful catalysis. Based on these mechanistic insights, a second‐generation class of silicon Lewis superacid with enhanced efficacy is identified and demonstrated.

Given its earth abundance, silicon is ideal for constructing Lewis acids of use in catalysis or materials science. Neutral silanes were limited to moderate Lewis acidity, until halogenated catecholato ligands provoked a significant boost. However, catalytic applications of bis (perhalocatecholato)silanes were suffering from very poor solubility and unknown deactivation pathways. In this work, the novel per(trifluoromethyl)catechol, H 2 cat CF3 , and adducts of its silicon complex Si(cat CF3 ) 2 (1) are described. According to the computed fluoride ion affinity, 1 ranks among the strongest neutral Lewis acids currently accessible in the condensed phase. The improved robustness and affinity of 1 enable deoxygenations of aldehydes, ketones, amides, or phosphine oxides, and a carbonyl-olefin metathesis. All those transformations have never been catalyzed by a neutral silane. Attempts to obtain donor-free 1 attest to the extreme Lewis acidity by stabilizing adducts with even the weakest donors, such as benzophenone or hexaethyl disiloxane.

Catechols occupy a unique role in the structural, bio-, and geochemistry of silicon. Although a wealth of knowledge exists on their hypercoordinate complexes, the structure of tetracoordinate bis­(catecholato)­silane, Si­(catH)2 1, has been enigmatic since its first report in 1951. Indeed, the claim of a planar-tetracoordinated silicon in 1 triggered a prominent debate, which is unsettled to this day. Herewith, we present a comprehensive structural study on 1 and derivatives in the gas phase by electron diffraction, in a neon matrix by IR spectroscopy, in solution by diffusion NMR spectroscopy, and in the solid-state by X-ray diffraction and MAS NMR spectroscopy, complemented by high-level quantum-chemical computations. The compound exhibits unprecedented phase adaptation. In the gas phase, the monomeric bis­(catecholato)­silane is tetrahedral, but in the condensed phase, it is metastable toward oligomerization up to a degree controllable by the type of catechol, temperature, and concentration. For the first time, spectroscopic evidence is obtained for a rapid Si–O σ-bond metathesis reaction. Hence, this study sorts out a long-lasting debate and confirms dynamic covalent features for our Earth’s crust’s most abundant chemical bond.

The heterolytic cleavage of dihydrogen constitutes the hallmark reaction of frustrated Lewis pairs (FLP). While being well‐established for planar Lewis acids, such as boranes or silylium ions, the observation of the primary H2 splitting products with non‐planar Lewis acid FLPs remained elusive. In the present work, we report bis(perfluoro‐N‐phenyl‐ortho‐amidophenolato)silane and its application in dihydrogen activation to a fully characterized hydridosilicate. The strict design of the Lewis acid, the limited selection of the Lewis base, and the distinct reaction conditions emphasize the narrow tolerance to achieve this fascinating process with a tetrahedral Lewis acid.

Obwohl Silicium ein einfach zugängliches und häufig vorkommendes Element der Erdkruste ist, gibt es bisher nur wenige Beispiele isolierbarer Lewis-Supersäuren auf der Basis von neutralen Siliciumverbindungen. Um Lçslichkeitsproblemen und unselektiven Deaktivierungsmechanismen entgegenzuwirken, stellen wir in dieser Arbeit eine Lewis-Supersäure mit perfluorierten Pinakolat-Substituenten vor. Die Titelverbindung wird auf einfachstem Weg im Gramm-Maßstab als das Acetonitril-Monoaddukt 1•(MeCN) synthetisiert und inklusive modernster Berechnungen vollständig charakterisiert. Untersuchungen der Lewis-Azidität mittels Gutmann-Beckett-Methode und weiterführende Experimente zur Fluorid-Abstraktion bestätigen den Charakter einer Lewis-Supersäure. Die Aktivierung der SiÀF-Bindung von Et 3 SiF sowie vielversprechende Katalyse-Experimente demonstrieren das hohe Potenzial Silicium-basierter Lewis-Säuren in der katalytischen Synthese.

Stable metal-free diradicaloids are fascinating compounds, typically based on covalent polycyclic or nitrogen-containing π-conjugated frameworks. Unfortunately, their preparation and the modulation of their diradical character require substantial synthetic efforts. The present work introduces a synthetic approach to diradicaloids by the ease and modularity of Lewis pair formation. Binding redoxactive bis(catecholato)silane Lewis acids to ditopic tetraox-olene Lewis bases yields adducts with varying spin ground states. Computational analyses disclose that the diradical character increases with the electron donor ability of the catechols and the electron accepting ability of the tetraoxolene. Hence, this protocol grants access to diradicaloids with rationally adjustable diradical character of high potential for numerous applications in a single step.

Lewis acids (LAs) play a prominent role in all domains of chemistry. The present contribution deals with a “super” class of LAs. As a starting point for a meaningful discussion, a more general treatise of the concept of Lewis acidity is required. Lewis acidity is a multi‐dimensional property that depends on a delicate interplay of steric and electronic factors during the interaction with a reference Lewis base or a substrate. Accordingly, various methods that gauge the strength and effectiveness of LAs on various grounds have been developed, as will be discussed in the first part of this work. Different scaling methods do not necessarily show the same trend. In turn, there is no reason to believe that one single parameter is sufficient to describe the full character of a LA. Based on the nature of the Lewis acidity scaling methods and the factors that cause the computed or measured output, a classification into “global”, “effective”, and “intrinsic” groups is made. With this framework in mind, the fluoride ion affinity (FIA) is chosen as a firm “global” parameter to discuss a broad range of LAs within the second part of this contribution. LAs that exceed the FIA of SbF 5 are termed Lewis superacids (LSAs). Accordingly, LAs that reach or exceed this threshold are collected and discussed. The clear focus is on neutral LAs of the p‐block elements, but reference will also be given for cationic Lewis acidic compounds. The majority of those compounds can be found in group 13 and for the heavier group 15 elements. Beyond, this summary touches strong Lewis acidity of d‐block metals and Lewis acidity in alternative media.