Redox-Active Lewis Pairs Yield Diradicaloids and Enable Modular Control of the Diradical Character.

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.

Silicon Carbamates by CO Fixation: Brønsted Acid Labile Precursor of a Lewis Superacid.

Treatment of Lewis superacidic Si(cat)(MeCN) and tetramethylpiperidine (TMP) or hexahydropyrimidopyrimidine (hppH) with CO leads to an FLP-type formation of silicon carbamates. The employed Lewis base determines the hapticity at silicon and the reactivity of the carbamates in subsequent transformations. Upon treatment with a Brønsted acid, the carbamates liberate CO and reactivate the Lewis superacidic behavior of .

Dihydrogen Activation with a Neutral, Intermolecular Silicon(IV)-Amine Frustrated Lewis Pair.

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 H 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.

Synthesis and Characterization of Hypercoordinated Silicon Anions: Catching Intermediates of Lewis Base Catalysis.

Anionic hypercoordinated silicates with weak donors were proposed as key intermediates in numerous silicon-based reactions. However, their short-lived nature rendered even spectroscopic observations highly challenging. Here, we characterize hypercoordinated silicon anions, including the first bromido-, iodido-, formato-, acetato-, triflato- and sulfato-silicates.

Calix[4]pyrrolato Aluminate Catalyzes the Dehydrocoupling of Phenylphosphine Borane to High Molar Weight Polymers.

High molar weight polyphosphinoboranes represent materials with auspicious properties, but their preparation requires transition metal-based catalysts. Here, calix[4]pyrrolato aluminate is shown to induce the dehydropolymerization of phosphine boranes to high molar mass polyphosphinoboranes (up to M =43 000 Da). Combined GPC and P DOSY NMR spectroscopic analyses, quantum chemical computations, and stoichiometric reactions disclose a P-H bond activation by the cooperative action of the square-planar aluminate and the electron-rich ligand framework.

The Structure of Bis(catecholato)silanes: Phase Adaptation by Dynamic Covalent Chemistry of the Si-O Bond.

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(cat) , has been enigmatic since its first report in 1951. Indeed, the claim of a planar-tetracoordinated silicon in triggered a prominent debate, which is unsettled to this day.

Bis(perchlorocatecholato)silane and heteroleptic bidonors: hidden frustrated Lewis pairs resulting from ring strain.

Bis(perchlorocatecholato)silane and bidentate N,N- or N,P-heteroleptic donors were reacted to form hexacoordinated complexes. Depending on the ring strain and hemilability in the adducts, frustrated Lewis pair (FLP) reactivity with aldehydes and catalytic ammonia borane dehydrocoupling was enabled. All reactions were analyzed using density functional theory.

[Si(O C F ) ] : Self-Assembly of a Giant Perfluorinated Macrocyclic Host by Low-Barrier Si-O Bond Metathesis.

The dynamic covalent self-assembly of 14 units of bis(perfluorocatecholato)silane leads to [Si(O C F ) ] -the first giant perfluorinated macrocycle. The oligomerization process is monitored spectroscopically, and the macrocycle analyzed by single-crystal X-ray diffraction. The molecule forms a rigid cavity that can host two o-closo-dodecacarboranes.

An Air-Stable, Neutral Phenothiazinyl Radical with Substantial Radical Stabilization Energy.

The vital effect of radical states on the pharmacological activity of phenothiazine-based drugs has long been speculated. Whereas cationic radicals of N-substituted phenothiazines show high stability, the respective neutral radicals of N-unsubstituted phenothiazines have never been isolated. Herein, the 1,9-diamino-3,7-di-tert-butyl-N ,N -bis(2,6-diisopropylphenyl)-10H-phenothiazin-10-yl radical (SQH ) is described as the first air-stable, neutral phenothiazinyl free radical.

Bis(catecholato)silanes: assessing, rationalizing and increasing silicon's Lewis superacidity.

Although bis(catecholato)silanes have been known for several decades, their substantial Lewis acidity is not yet well described in the literature. Herewith, the synthesis and characterization of multiple substituted bis(catecholato)silanes and their triethylphosphine oxide, fluoride and chloride ion adducts are reported. The Lewis acidity of bis(catecholato)silanes is assessed by (Gutmann-Beckett, catalytic efficiency), (theoretical and relative experimental fluoride (FIA) and chloride (CIA) ion affinities) and (electrophilicity index) scaling methods.