Hans_Bauer96

We present the use of microwave radiation to lithium chemistry, specifically in the kinetically hindered deprotonation of a tertiary amine at high temperatures without polar additives. The amine acts as substrate and deaggregation agent as shown by a solid-state structure. The lithium compounds remain stable at the harsh conditions and the deprotonated amine is storage-stable, facilitating diverse follow-up chemistry.

Abstract

Deprotonation reactions with lithium alkyls exhibit a high temperature dependency. However, the reactivity of lithium alkyls with conventionally used Lewis bases limits their deprotonation capability of more challenging substrates like tertiary amines. Therefore, we have focused on the use of high but exactly set reaction temperatures by usage of microwave radiation in the deprotonation reaction of a tertiary amine in the absence of polar additives. Our study proves the robustness of lithium alkyls, like t-butyllithium and α-metalated tertiary amines under microwave conditions. A solid-state structure of the prelithiation aggregate and quantum chemical calculations offer an insight into the mechanism, revealing that the substrate amine performs as Lewis base for deaggregation itself. By our method, N-methylpiperidine was deprotonated without any intermediate or possibly toxic reaction steps, solvents, or additives, solely with t-butyllithium in the microwave with 56% yield. By using design of experiments we identified the most important factors for a successful deprotonation, revealing the closed reaction conditions under pressure and an excess of amine to be crucial. This investigation proves the high potential of microwave radiation in lithium chemistry, as it provides high but exact energy and introduces new possibilities for deprotonation reactions to overcome high kinetic reaction barriers.

Publication date: 15 January 2026

Source: Chem, Volume 12, Issue 1

Author(s): Fairoosa Poovan, Rajenahally V. Jagadeesh, Matthias Beller

We report stable and isolable difluoromethylene transition metal complexes, synthesized by reaction of free difluorocarbene with organogold(I) precursors. Difluorocarbene insertion reactions occurs with alkyl- or aryl-gold(I) complexes, whereas the difluorocarbene cycloaddition reaction occurs with alkynylgold(I) complex.

Abstract

The gem-difluoromethylene functional group is an important motif in medicinal chemistry, and development of new fluoroalkyl-metal systems has been crucial to enable new syntheses of gem-difluoromethylenes. However, well-defined and isolable examples of either nucleophilic RCF₂M or difluorocyclopropenyl transition metal complexes are rare. The Au(I) platform has been useful for the synthesis of isolable transition-metal complexes bearing reactive ligands. Herein we utilize reactions of difluorocarbene with organogold(I) complexes, analogous to reactions of difluorocarbene with organic substrates, to access novel examples of gem-difluoromethylene organometallics. First, difluorocarbene insertion into the R─Au(I) bond of organogold(I) species with free difluorocarbene was demonstrated for the first time, forming alkyl-CF₂-Au(I) and aryl-CF₂-Au(I) species. Second, via a difluorocarbene cycloaddition reaction we isolate for the first time a κ¹-difluorocyclopropenyl-transition metal complex, formed by reaction of alkynylAu(I) complex with free difluorocarbene. Subsequent study of these reaction systems by density functional theory calculations facilitated study of the difluorocarbene insertion reactions, and a comparison of difluorocarbene insertion and cycloaddition pathways in the reaction of difluorocarbene and alkynylAu(I).

Nature Reviews Chemistry, Published online: 13 August 2025; doi:10.1038/s41570-025-00732-4

Die Reaktion eines Dihydro-Dialans, das von einem Hybridliganden (DNI) koordiniert wird, mit organischen Aziden ergibt strukturell unterschiedliche Aluminiumspezies mit Aluminium in niedriger Oxidationsstufe: das erste Diazido-Dialan, ein Aluminium-Tetrazol und Produkte der Azid-Aluminierung. Spektroskopische Untersuchungen zeigen ein dynamisches Verhalten in Lösung mit einer Pendeluhr-ähnlichen Bewegung eines Benzylazids und N_α-Oszillation zwischen zwei Aluminiumatomen.

Zusammenfassung

Hier wird die Reaktivität eines Dihydrodialans mit organischen Aziden beschrieben. Die Umsetzung eines auf [(DNI{H}Al)₂] (I) basierenden hybriden Dialans (DNI = [3,3-dimethyl-2-2-methyl-2-(2,6-diisopropylanilin)ethenyl]-3H-indolenin) mit TMSN₃ (TMS = Trimethylsilyl) bei Zimmertemperatur ergibt das erste Diazodialan [(DNI{N₃}Al)₂] (1). Davon ausgehend erfolgt die Umwandlung in ein stabileres Aluminiumtetrazol [DNIAl(NTMS)₂N₂] (2). Andere Azide RN₃ führen zu [(DNI{H}Al)₂(κ²-N₃R)] (R = Benzyl in 3 und 1-Adamantyl in 4) mit dem Azid in einer μ-verbrückenden Position zwischen beiden Aluminiumatomen. In der ¹H-NOESY/EXSY-NMR-Spektroskopie von 2 wird ein Positionswechsel beider TMS-Gruppen durch Rotation der Tetrazoleinheit beobachtet. Im Gegensatz dazu weist 3 in Lösung eine pendeluhrartige Dynamik auf, bei der das N_α-Atom zwischen beiden Aluminiumatomen oszilliert. Die Reaktion des Dialans I mit DippN₃ (Dipp = 2,6-iPr₂-C₆H₃) führt zur Dialuminiumverbindung [{DNI(H)Al}₂(μ-NDipp)] (5).

Despite the prevalence of Ni/Al catalysts for pyridine C─H functionalization, mechanistic details of such systems remain scarce. Herein, we present the discovery of PCy₃-catalyzed bond-breaking and making processes that occur in the coordination sphere of a novel Ni─Al heterometallic complex. The reaction is 1^st order in PCy₃ and proceeds with a low KIE of 0.9–1.1. These data suggest that both C─H activation and H₂ reductive elimination steps in this system are low energy, are readily accessible, and are not rate limiting.

Abstract

Herein we present a ligand-catalyzed bond-breaking and making process that occurs with a Ni–Al heterometallic complex. While combinations of Ni pre-catalysts and Al additives are known for site-selective C─H functionalization, detailed studies of such systems are rare. Combining [Ni(COD)₂] and [(BDI)AlH₂] (1; BDI = 2,6-diisopropylphenyl-β-methyldiketiminate) results in facile formation of a Ni–Al heterometallic complex [(η ⁴-COD)Ni{(μ-H)₂Al(BDI)}] (2; COD = 1,5-cyclooctadiene). Once generated, this species can effect the C(sp²)─H activation of 4-dimethylaminopyridine (DMAP) or pyridine with concomitant H₂ evolution, a process that is accelerated through addition of PCy₃. The mechanism was studied through kinetics, kinetic isotope effects (KIEs), isotope labeling studies, and modeling. The reaction is 1^st order in PCy₃ and proceeds with a KIE of 0.9–1.1. Support is provided for a pathway involving the synergistic action of both metals, promoted by reversible coordination of the phosphine. The data suggest that both C─H oxidative addition and H₂ reductive elimination steps in this system are readily accessible and are not rate limiting. This finding has implications for future catalyst design using combinations of Ni and Al metals and suggests that control of ligand exchange steps may be the most important consideration in determining the rate of reaction.

Typically, the addition of a chemical bond to a metal centre is assumed─without question─to be an oxidative process. Here, through studies of bond addition to tin(II), we reveal a spectrum ranging from ‘oxidative’ (Cl─Cl) to ‘reductive’ (Be─Be) processes, with other bonds (B─B, B─H, H─H) falling between these two extremes.

Abstract

Here, the addition of H─H, Be─Be, B─B, and B─H bonds to Sn^II is studied by experimental and theoretical means. We report the first examples of B─B and Be─Be bond additions to a main group metal centre, along with the first example of borazine B─H bond addition to any element of the Periodic Table. Quantum chemical calculations suggest that the classification of these reactions as prototypical “oxidative” addition processes may be misleading and that a more nuanced description is warranted.

The potassium aluminyl K[Al(NON)] reacts with Ge[N(SiMe₃)₂]₂ by a sequential reductive deamination pathway. The initially formed aluminacyclodigermene contains Ge(I) centres and may be considered as a η ²-coordinated digermyne at aluminium. Further reduction leads to compounds containing a μ,η ²,η ²-[Ge(0)]₂ unit coordinated to two Al(NON) groups, or a Ge₄-cluster containing species with oxidation state Ge(-I). DFT analysis indicates reduced Al centres and Ge─Ge multiple bonding in both the [RGeGeR] and [Ge₂] groups.

Abstract

The reaction of the potassium aluminyl K[Al(NON)] ([NON]²⁻ = [O(SiMe₂NDipp)₂]²⁻, Dipp = 2,6-iPr₂C₆H₃) with the diaminogermylene Ge[N(SiMe₃)₂]₂ afforded [K(C₆H₆)][Al(NON){(Me₃Si)₂NGeGeN(SiMe₃)₂}] containing an AlGe₂ ring. Structural and computational analysis confirm an aluminacyclodigermene complex that can be considered as an η ²-coordinated digermyne at aluminium with Ge(I) centres. This compound is an intermediate on the reduction pathway to K₃[(Ge₄){Al(NON)}₂{N(SiMe₃)₂}], which contains a distorted tetrahedral cluster of Ge(-I) centres. Characterisation of the dialumane (NON)Al─Al(NON) from this reaction is indicative of sequential one electron redox processes initiated by the aluminyl anion. Repeating the reaction in methylcyclohexane afforded K₂[{Al(NON)}₂(Ge₂)], containing a formally digermanium(0) unit with an exceptionally long Ge═Ge double bond.

Carbenes, first named in 1951, stand as a vivid example of carbon's versatility. Once elusive, they have become powerful tools across chemistry. The isolation of the first stable, singlet carbene (a (phosphino)(silyl)carbene) in 1988 by Guy Bertrand and colleagues marked an important milestone. Today, their stereoelectronic diversity continues to fuel discovery, pushing the limits of how we deploy them. The Concept by B. Sawyer, J. L. Peltier and R. Jazzar (DOI: 10.1002/chem.202501600) explores popular strategies for their detection and structural elucidation highlighting both their capabilities and limitations.

Alkyne insertion into the Sn─Si bond of a silyl-substituted stannylene occurs regio-selectively and - in the cases of more sterically encumbered substrates - reversibly

Abstract

A range of aryl- and alkyl- substituted alkynes has been shown to insert regio-selectively into the Sn─Si bond of the electron-rich aryl(silyl)stannylene, Ar^MesSnSi(SiMe₃)₃ (Ar^Mes = 2,6-Mes₂C₆H₃, Mes = 2,4,6-Me₃C₆H₂) to generate a series of vinyl-stannylene products. In all cases, the product features a syn arrangement of Sn and Si-containing groups about the resulting carbon–carbon double bond; in the case of unsymmetrical alkynes, the more sterically bulky group is exclusively incorporated in the 1-position (i.e., proximal to Sn). Remarkably, insertion is shown to occur reversibly in the cases of 3-hexyne and trimethylsilylacetylene. The thermodynamic parameters associated with these processes have been determined by variable temperature NMR spectroscopy, and the activation barriers associated with the key mechanistic steps elucidated by quantum mechanical methods.

Die Synthese und vollständige Charakterisierung des elektronenarmen Ferrocens [Fe(C₅H₅)(C₅(CF₃)₅)] und seines Ferroceniumsalzes wird vorgestellt. Ein extremes Redoxpotential von E _1/2 = 1.35 V (vs. Fc/Fc⁺) ermöglicht den synthetischen Einsatz als starkes Oxidationsmittel.

Kurzzusammenfassung

Eine photolytisch induzierte Aren-Substitution in [Fe(C₅H₅)(oDCB)][PF₆] (oDCB = ortho-Dichlorbenzol) in Gegenwart von [NEt₄][C₅(CF₃)₅] ergab das hochfluorierte und stabile Ferrocen [Fe(C₅H₅)(C₅(CF₃)₅)]. Der perfluorierte Cp*-Ligand übt einen extremen Elektronenzug auf das Ferrocen mit E _1/2 = 1.35 V (vs. Fc/Fc⁺) aus. Dies ist das höchste Redoxpotenzial, das bisher für ein Ferrocen gemessen wurde. Der entsprechende stabile und lagerbare Ferrocenium-Komplex [Fe(C₅H₅)(C₅(CF₃)₅)][AsF₆] wurde in quantitativer Ausbeute synthetisiert und stellt nicht nur die oxidierendste Ferrocenium-Spezies dar, sondern auch das stärkste bekannte isolierbare organometallische Oxidationsmittel. Dessen Stärke wurde durch die zweifache Oxidation von [Fe(C₅(CH₃)₅)₂] zu dessen Dikation und eine oxidative C-H-Aktivierung von ortho-Terphenyl demonstriert. Diese außergewöhnliche Redoxchemie in Verbindung mit der Löslichkeit in Perfluorkohlenstoffen ermöglicht ein selektives und quantitatives Recycling des hochfluorierten Ferrocens. Zusammen mit der geringen Basizität und Inertheit von [Fe(C₅H₅)(C₅(CF₃)₅)] wird die Chemie der starken Oxidationsmittel hiermit auf Organometallverbindungen erweitert.

Displaying strong controlled metalating power, hydrocarbon-soluble sodium neopentyl can deprotonate challenging non-activated arenes and alkenes, with sodiated intermediates successfully undergoing onward functionalisation reactions. By characterising key reaction intermediates, and running computational studies on models, insight has been gained on the structure, bonding, and special reactivity of this promising new reagent.

Abstract

While recent studies have shown that organosodium reagents can offer excellent promise in organic synthesis, their widespread applications can be hindered by their limited solubility in organic solvents, lack of stability, and uncontrolled reactivity. Improving this immature area, here we report the structure of unsolvated neopentyl sodium, which exhibits a unique discrete tetrameric motif and good solubility in hexane. Combining spectroscopic and crystallographic studies with computational bonding analysis, key insights into its constitution and stability have been gained. Expanding its synthetic potential, supporting neopentyl sodium with Lewis donor PMDETA (N,N,N′,N″,N″-pentamethyldiethylenetriamine) allows for the direct metalation of challenging non-activated arenes and alkenes, including the regioselective meta-functionalisation of selected 1,3-disubstituted alkyl arenes. Shedding light on sodium-mediated metalation protocols, key organometallic intermediates have been isolated and structurally defined, which can subsequently be intercepted with CO₂ or a boron electrophile to be directly used in Pd-catalysed Suzuki cross coupling reactions.

Diazirines are 3-membered heterocycles containing two nitrogen atoms connected by a double bond. They possess a multi-faceted reactivity that holds great potential for organic synthesis. This review discusses their properties, modes of activation, and their many modern uses, underlining their underappreciated versatility: as carbene precursors, but also as electrophilic nitrogen donors, as NMR hyperpolarization probes, or as molecular tools in materials science.

Abstract

Diazirines are 3-membered heterocycles containing two nitrogen atoms connected by a double bond. They are mostly known for their usage in photoaffinity labeling (PAL), due to their stability and their facile photolysis for on-demand carbene generation. Yet diazirines possess a multi-faceted reactivity that also holds great potential for organic synthesis. This is illustrated in the present review, which is meant to be a beginner's guide for new diazirine users. After briefly summarizing the main synthetic approaches to these derivatives (with a focus on recent improvements), we emphasize some of their most critical features and properties before describing the various modes of activation toward carbene generation, some of which were only uncovered in the past decade. We then review the many modern uses of diazirines, underlining their underappreciated versatility: as carbene precursors in synthesis, but also as electrophilic nitrogen donors, as NMR hyperpolarization probes, or as molecular tools in materials science.

Calcium salts consisting of Ca²⁺ weakly coordinated by carborate counterions have been prepared through anhydrous and aqueous methods. The Ca²⁺ center is sufficiently Lewis acidic to weakly coordinate olefins, alkynes and aromatics, and catalyze the hydrosilylation of 1-hexene and several alkynes.

Abstract

The syntheses of calcium carborates, Ca[HexCB₁₁Cl₁₁]₂, 1, Ca[HCB₁₁Cl₁₁]₂, 2, and Ca[MeCB₁₁Cl₁₁]₂·2(o-DFB), 3·2(o-DFB), (o-DFB = 1,2-difluorobenzene) including the structure of 2·4(o-DFB) are described. The large size of the Ca²⁺ cation is reflected by the coordination geometry with the Ca center being coordinated by three Cl donors from each of the carborate anions and one F donor from each of the two coordinated solvent molecules. Based on ¹¹B NMR and DOSY NMR studies, the salts 1, 2 and 2·2(o-DFB) form close ion pairs in PhBr and o-DFB solutions. The Fluoride Ion Affinities (FIA) in PhBr for the salts 1 and 2·2(o-DFB) were DFT-calculated (ωB97XD/6–31 + G**) at 211.3 kJ mol⁻¹ and 217.5 kJ mol⁻¹, respectively, which is below that of the landmark Lewis acid B(C₆F₅)₃ (241.5 kJ mol⁻¹). The Ca²⁺ center in salt 1 is sufficiently Lewis acidic to coordinate 1,5-cyclooctadiene (1,5-COD) and 2,6-octadiyne and to catalyze the hydrosilylation of 1-hexene and several alkynes, albeit slowly. Compound 1 also displays moderate activity as a catalyst for transfer hydrogenation catalysis and carbonyl-olefin metathesis (COM), a first for Ca compounds.

Following initial experimental and theoretical studies that indicated that silylboranes decompose via oxygenation, bulky silyl anions were used to synthesize silylboranes with enhanced bench stability and novel reactivity. These kinetically stabilized silylboranes are stable in air and moderately activate carbon monoxide (CO) to form spirocyclic compounds. DFT calculations suggested that the activation of CO is driven by hyperconjugation.

Abstract

Silylboranes are versatile intermediates in organic synthesis, and a wide range of structural variants of silylboranes have already been synthesized. However, the stability of silylboranes varies significantly, and their decomposition mechanism remains to be fully understood. Moreover, some silylborane motifs have not yet been applied as synthetic reagents due to their instability. To address this issue, we first investigated the decomposition mechanism of silylboranes in air and moisture using experimental and theoretical methods. We discovered that oxygenation by atmospheric oxygen is the major decomposition pathway, resulting in the formation of a borylsilylether, and that the introduction of a bulky silyl group suppresses this decomposition. Based on these results, we synthesized triisopropylsilyldimesitylborane (i-Pr₃Si–BMes₂), which exhibits high bench stability. Moreover, i-Pr₃Si–BMes₂ reacts with carbon monoxide (CO), which is the first example of a reaction between a silylborane and CO. Further computational studies revealed that electronic effects, including hyperconjugation between the Si─B σ-bond and C─O π*-bond, are crucial for CO activation. Furthermore, we prepared a bench-stable bissilylaminoborane by introducing triisopropylsilyl groups, providing a bissilylchloroborane upon hydrogen chloride treatment. These findings provide valuable insights into how steric and electronic effects can be used to optimize the balance between stability and reactivity in silylboranes.