Elias Drösemeier

Best of both worlds: The ionic liquid [NEt₃Me][Cl(SO₂) _n ] unites the atom economy and low cost of sulfur dioxide with the safety and applicability of common surrogates, streamlining SO₂ transfer to access to 3-sulfolenes, sulfonamides, and SuFEx reagents.

ABSTRACT

Herein, the ionic liquid [NEt₃Me][Cl(SO₂) _n ] is reported as a reversible sulfur dioxide storage medium and transfer reagent for organic synthesis. Vapor pressure measurements revealed that the ionic liquid can store up to 3.66 equivalents of SO₂ at room temperature, which can be released in a controlled manner upon heating or depressurization. The physicochemical properties were investigated, and long-term stability was demonstrated, as no decomposition was observed for more than six months. Based on its solid-state structure, the bonding analysis indicated a covalent sulfur-chlorine interaction, which is consistent with conducted Raman studies and quantum chemical calculations. Atom economy and cost estimates are compared with those of commonly used SO₂ surrogates, highlighting the developed transfer reagent as an inexpensive and (atom-)economic alternative for laboratory-scale applications. The synthetic utility of [NEt₃Me][Cl(SO₂) _n ] is further demonstrated, enabling the synthesis of valuable organosulfur compounds such as 3-sulfolenes, sulfonamides, sulfones, and sulfonyl fluorides in good to excellent yields. Importantly, the incorporation of SO₂ is scalable, rendering [NEt₃Me][Cl(SO₂) _n ] as a safe and user-friendly SO₂ transfer reagent for synthetic applications.

A 9,10-dihydro-9,10-disilaanthracene platform was efficiently synthesized and features intrinsically electrophilic Si sites. Upon stepwise reductive Si─H bond cleavage, these Si sites are converted into nucleophilic centers. This controlled polarity switching also enables ambiphilic reactivity within a homo-heteroelement framework.

ABSTRACT

9,10-Dihydro-9,10-diheteroanthracenes constitute rigid molecular entities that enable cooperative reactivity between two proximal heteroatoms. While diboraanthracenes act as ditopic Lewis acids and diphosphaanthracenes as ditopic Lewis bases, ambiphilic behavior has so far largely relied on the incorporation of two different heteroelements. Herein, we demonstrate ambiphilicity within a homo-heteroelement framework based on 9,10-dihydro-9,10-disilaanthracene (DSA). Efficient cyclocondensation of 1,2-disilyl-4,5-dimethylbenzene, promoted by substoichiometric amounts of MeLi, affords DSA 1^2H featuring two SiH₂ groups. Compound 1^2H exhibits electrophilic reactivity toward magnesium anthracene, affording a double ‘butterfly’-type framework 13 reminiscent of the anthracene photodimer. Selective reductive Si–H bond cleavage using 2 equiv. KC₈ or excess elemental K enables controlled, stepwise access to the monosilanide [1^H ]⁻ or the disilanide [1]²⁻, respectively. The disilanide [1]²⁻, which was structurally characterized by SCXRD, behaves as a ditopic Lewis base toward 9,10-dihydro-9,10-diboraanthracene, forming a cyclic, 13-type double adduct K₂[10]. Notably, [1^H ]⁻ displays ambiphilic reactivity toward pTolC≡CpTol to furnish a tricyclic product containing a deprotonated 1,2-ethylenediyl bridge between the Si centers. These findings establish that controlled reduction within a homo-heteroelement platform enables polarity switching, thereby providing a versatile strategy for the design of cooperative main-group reactivity.

Unlocking gallyl nucleophiles: Counterion control enables formation of an unsupported gallyl─gold complex. Gold coordination induces a polarity switch at gallium, enabling cooperative activation of NH₃ and related N─H/O─H substrates under mild conditions.

ABSTRACT

Controlling the reactivity of low-valent main-group nucleophiles in small-molecule activation remains a significant challenge. Here, we report the synthesis of a family of charge-delocalized β-diketiminate gallyl anions, accessible across the Li–Cs series, whose aggregation and ion pairing can be tuned to furnish a cation-gated gallium(I) nucleophilic platform. Only the cesium crown-encapsulated derivative forms a truly separated ion pair (SIP) that exhibits clean nucleophilic reactivity toward (IPr)AuCl to generate an unsupported Ga─Au bimetallic complex, isolable, and structurally authenticated. Coordination at Au enhances the Lewis acidity at gallium(I), enabling cooperative N─H and O─H σ-bond activation under mild conditions via a substrate-assisted proton-shuttle pathway. This reactivity, exemplified by NH₃ and H₂O, and extended to MeNH₂ and MeOH, is inaccessible to the free gallyl anions. These findings define a new gallium-based nucleophilic platform for exploiting bimetallic cooperation in small-molecule bond activation.

Nature, Published online: 08 May 2026; doi:10.1038/d41586-026-01473-0

Sterically tuned N-silyl phosphinimines enable four-membered SiCPN cations. Hydride abstraction yields cyclic cations for Me and iPr substituents at silicon, while tBu gives a protonated intermediate. Multinuclear NMR spectroscopy, X-ray crystallography, thermochemical density functional theory investigations, and natural bond orbital analyses reveal how steric bulk modulates N–Si bonding, ring strain, and cationic character at silicon.

A systematic study of four-membered cationic SiCPN cycles derived from sterically tuned hydrosilyl-functionalized phosphinimines is presented. Hydride abstraction of the methyl- and iso-propyl-substituted precursors successfully affords the corresponding cyclic cations, while the tert-butyl analogue resists cyclization, yielding a protonated intermediate instead. Multinuclear NMR spectroscopy reveals significant downfield shifts in both ³¹P and ²⁹Si NMR signals, reflecting enhanced cationic character at silicon and pronounced modulation of hyperconjugative n_N → σ*_(P–C) interactions. Correlated shifts at phosphorus and silicon highlight efficient electronic communication across the R₃P–N–SiMe₃ framework, consistent with its isoelectronic analogy to disiloxane linkages. Structural data from single-crystal X-ray diffraction analysis, thermochemical density functional theory investigations, and natural bond orbital analyses show that increasing steric bulk at silicon weakens intramolecular N–Si bonding, in line with systematically reduced ring-opening Gibbs energies. These findings provide a clear picture of the interplay between steric and electronic effects in SiCPN cations and offer design principles for strained donor–acceptor silicon heterocycles.

This Review provides an overview of masked silylenes as bench-stable precursors that release silylenes (R₂Si:) under thermal activation or reversible equilibria. Precursor preparation, generation pathways, and characteristic reactivity are summarized, including trapping chemistry, reversible interconversions, insertion-type processes, and small-molecule activation enabled by controlled access to silylene species.

Silylenes (divalent silicon species) are highly reactive intermediates that are often difficult to handle directly. Although steric protection and electronic stabilization have enabled the isolation of persistent silylenes, such stabilization tends to restrict their intrinsic reactivity. Masked silylenes offer an alternative strategy in which the reactive silicon(II) center is temporarily embedded in a precursor framework or coordination environment. As a result, the precursor can be handled or even isolated, and silylene reactivity is accessed in situ by thermal activation. This review focuses on masked silylene chemistry governed by thermolysis and reversible equilibria and summarizes how precursor structure controls the generation of silylenes and their subsequent reactivity. Representative precursor classes include SiC₂-derived strained frameworks, SiC₆ arene adducts such as 7-silanorbornadienes and silepins, SiE double-bond systems (E = Si, N), as well as Lewis-base adducts and σ-bond complexes. Typical reactivity patterns and applications, including trapping reactions, small-molecule activation, and organosilicon synthesis, are highlighted.

A new iminophosphorane-based scorpionate ligand enabled the characterization of a head-to-head silylene dimer with unsupported Si─Si bonding, whereas the tetrylene species of Sn and Pb afforded head-to-tail coordination polymers in the solid state.

ABSTRACT

N,N-chelating ligands disfavor element–element bonding in heavier alkene analogs of group 13 and group 14 elements. Here, we present a series of group 14 element(II) compounds of a new sterically demanding iminophosphorane-based scorpionate ligand. The molecular structures of the Si and Ge analogs form element–element bonded interactions in the solid state in a head-to-head fashion, whereas the Sn and Pb analogs form one-dimensional coordination polymers in a head-to-tail fashion. Analysis of the Si─Si bonding by experimental, for example, X-ray diffraction, and computational methods suggests that a significant unsupported bonding interaction is present and enabled by the ligand that can be easily perturbed by the ligand sterics, including dispersion, and broken by entropic effects.