Ruth M. Gschwind

Photoinduced transformations of pyridine-BCl ₃ Lewis adducts revealed by in-situ NMR spectroscopy show photoinduced hydrolysis versus ring contraction in protic and aprotic media inverse to literature.

We report the synthesis of hexafluorophosphate (PF6–) salts directly from white phosphorus (P4) and simple fluorides MF (M = Li, Na, K, Cs, NMe4) in a single step. The utilization of p-quinones, such as 2,3-dichloro-4,5-dicyano-1,4-benzoquinone (DDQ) offers a selective fluorination pathway, which affords MPF6 salts in up to 95% yield in acetonitrile (MeCN). NMR investigations of the DDQ-mediated P4 fluorination reaction revealed the formation of PF3 and PF5·MeCN as key reaction intermediates. Donor–acceptor interactions between DDQ and fluoride are critical, effectively increasing the fluoride concentration and enabling efficient fluorination to PF6–. Tetraethylene glycol (TEG) selectively stops the reaction at the adduct K[PF5·TEG]. In contrast, noncoordinating dichloromethane (DCM) favors PF3 formation by suppressing EDA interactions through low fluoride solubility, possibly via the tris(hydroquinonyl)phosphite P(DDQH)3, underscoring the critical role of fluoride solubility. This work demonstrates that quinone–fluoride interactions can be exploited for oxidative fluorination chemistry, establishing a new conceptual framework for P4 fluorination.

Chiral phosphoric acids (CPAs) have emerged as versatile catalysts for asymmetric catalysis, capable of transforming a wide selection of substrates with high stereoselectivities. However, the mechanistic role of higher aggregates in CPA-catalyzed reactions remains poorly understood, although increasing evidence suggests that dimeric and trimeric CPA species can promote challenging transformations. This work provides comprehensive experimental evidence demonstrating that special [CPA/imine]₂ species critically enhance the reactivity and selectivity in CPA-catalyzed Mannich-type reactions with imines bearing an N-2-hydroxyphenyl moiety. Using low-temperature NMR spectroscopy, diffusion-ordered spectroscopy (DOSY), and molecular dynamics (MD) simulations, we revealed that imines with a N-2-hydroxyphenyl moiety promote the formation of dimeric [CPA/imine]₂ aggregates, while monomeric CPA/imine complexes dominate, with imines lacking this moiety. [CPA/imine]₂ formation is favored under low-temperature and high-concentration conditions. Dimers with sufficient structural flexibility provide enhanced reactivity, acidity, and selectivity. In contrast, at higher temperatures, where no [CPA/imine]₂ aggregates are formed, the Mannich-type reaction proceeds inefficiently. A nonlinear effect analysis provided evidence of asymmetric amplification in the present Mannich-type reaction, proving the participation of aggregated species in the reaction pathway. Together, these results highlight the importance of controlling catalyst aggregation as a strategy to optimize the reactivity and selectivity in asymmetric organocatalysis.

We demonstrate a method for complex reaction monitoring that combines two approaches: time-resolved non-uniform sampling and time-resolved diffusion NMR. The new approach was demonstrated in the study of the photodegradation of retinyl acetate.

The activation of white phosphorus with inorganic Grignard reagents enables the selective synthesis of diverse polyphosphorus compounds.

The synthesis of aromatic amines, especially anilines, is crucial in organic chemistry because of their significance in pharmaceuticals and high‐value chemicals. However, traditional methods for producing aniline involve pre‐functionalization and/or several high‐energy‐demanding steps. Therefore, the development of direct protocols towards aniline has attracted significant interest. We introduce a direct photocatalytic method for synthesizing aniline using hydroxylamine and vanadium complexes. While previous studies describe vanadium complexes and hydroxylamine in thermally driven reactions, our research utilizes photochemistry, providing milder reaction conditions for the efficient benzene amination. Mechanistic investigations using ⁵¹ V‐NMR support coordination of hydroxylamine to vanadium and the multifaceted role of acetic acid as solvent, acid, and ligand. X‐band EPR and ⁵¹ V‐NMR demonstrated the time‐dependent reduction of vanadium by hydroxylamine. The same excess experiments and ¹⁵ N‐NMR coordination studies identified product inhibition by aniline. ¹ H‐NMR kinetic experiments, enabled through a broad peak suppression, suggest a paramagnetic V ⁺⁴ ‐hydroxylamine complex as the key intermediate, and ⁵¹ V‐NMR kinetics support the photocatalyst's role in maintaining the redox cycle and reducing the active V ⁺⁴ ‐hydroxylamine intermediate. Our direct photocatalytic method not only enables the selective synthesis of aniline under mild conditions, but also allows easy scaling through its compatibility with flow systems.

Kurzzusammenfassung: Die dehydrierende Kupplung (DHC) von Hydridosilanen mit Silanolen unter metallfreien Bedingungen bietet einen nachhaltigen Zugang zur Si─O‐Bindungsbildung. Der mechanistische Ursprung der Wasserstofffreisetzung in solchen Systemen blieb jedoch bislang unklar. Hier zeigen wir, dass die dynamische Permutationsisomerie pentakoordinierter Siliciumintermediate eine entscheidende Voraussetzung für die Si─H‐Aktivierung und H ₂ ‐Freisetzung darstellt. Unter Verwendung sterisch maßgeschneiderter Diaminohydridosilane demonstrieren wir, dass nur Liganden, die den Zugang zu axialen Hydridkonfigurationen ermöglichen, eine Si─O‐Kupplung mit produktiver H ₂ ‐Eliminierung vollziehen. Im Gegensatz dazu fixiert eine N‐ tert ‐Butylsubstitution das Hydrid in der äquatorialen Position und lenkt die Reaktivität in Richtung Si─N‐Bindungsspaltung. Multinukleare variable‐Temperatur‐NMR‐Spektroskopie, kombiniert mit quantenchemischen Berechnungen, offenbart ein Gleichgewicht zwischen äquatorialen und axialen Hydridkonfigurationen, das Berry‐Pseudorotation und Wasserstoffentwicklung ermöglicht. Diese Ergebnisse liefern eine mechanistische Grundlage für die H ₂ ‐Freisetzung in Hydridosilicaten und etablieren die ligandengesteuerte Isomerie als allgemeines Konstruktionsprinzip für die selektive, metallfreie Si─H‐Aktivierung.

Dehydrogenative coupling (DHC) of hydridosilanes with silanols under metal‐free conditions provides a sustainable route to Si─O bond formation. Yet, the mechanistic origin of hydrogen release in such systems has remained unclear. Here, we show that dynamic permutational isomerism of pentacoordinate silicon intermediates is a key prerequisite for Si─H activation and H ₂ release. Using sterically tailored diaminohydridosilanes, we demonstrate that only ligands enabling access to axial hydride configurations facilitate Si─O coupling with productive H ₂ elimination. In contrast, N– tert ‐butyl substitution locks the hydride in the equatorial position and diverts reactivity toward Si─N bond cleavage. Multinuclear variable‐temperature NMR spectroscopy, combined with quantum chemical calculations, reveals an equilibrium between equatorial and axial hydride configurations, enabling Berry pseudorotation and hydrogen evolution. These findings provide a mechanistic rationale for H ₂ release in hydridosilicates and establish ligand‐directed isomerism as a general design principle for selective, metal‐free Si─H activation.

The development of a low-cost fiber-based setup to perform in-situ illuminated NMR-spectroscopy is presented. A high-power diode laser module is used instead of LEDs and the sample is illuminated via a sandblasted NMR tube (NMRtorch tube) rather than a sandblasted fiber end. The design of the setup for 450 nm illumination is described, as well as promis-ing initial performance tests to compare it with a currently used LED-NMR based setup.