Fabian Dielmann

Installing N‐heterocyclic olefins (NHOs) at the 4,4′‐positions converts 2,2′‐bipyridine into a donor‐flexible, proton‐switchable platform. A straightforward late‐stage synthesis from fluoroimidazolium salts and 4,4′‐dimethylbipyridine affords two ligands ( 3 , 4 ) that are exceptionally strong neutral σ donors by the Huynh electronic parameter (HEP2), with donor strength dictated by the NHO backbone (unsaturated > saturated). DFT places the HOMOs on the NHO units and the LUMOs on the bipyridine, accounting for cathodically shifted reductions and NHO‐centered oxidations. Protonation converts the exocyclic C═C into an azolium–CH ₂ spacer, electronically resetting donor strength to that of the parent bipyridine while leaving the bipyridine coordination site available. The combination of backbone‐tunable donor power and donor flexibility positions NHO‐bipyridines as promising ligands for proton‐responsive applications, including (photo)functional materials and catalysis.

N-heterocyclic olefin functionalization of a bipyridine ligand creates an intense intraligand charge-transfer excited state in a heteroleptic Ir( iii ) photosensitizer while introducing proton-responsive behavior.

An acyclic alkyl-imino phosphenium cation stabilized by an N-heterocyclic imine is reported, revealing how scaffold modification unlocks reactivity inaccessible to classical phosphenium platforms.

Phosphonioacetylides are rod-shaped, neutral carbon donors with ambiphilic character at the terminal carbon. Despite their analogy to CO and isocyanides, they remain underexplored due to their high reactivity, and only one isolable free phosphonioacetylide has been reported. Here, we describe two new isolable, room-temperature-persistent examples stabilized either by two N-heterocyclic imines (NHIs) bearing bulky, flexible tert-octyl groups or by a single dipp-substituted NHI combined with alkyl substituents. Comprehensive characterization (SCXRD, NMR, IR, MS, DFT) confirms their strong donor properties and the accessibility of the reactive C₂ unit. DFT analysis quantify how the substituents at phosphorus modulate the frontier molecular orbital energies, spanning a wide range of σ and π-donor strengths and π-acceptor abilities, with trends that mirror those of the corresponding phosphines. Both phosphonioacetylides readily form Au^I complexes, whereas the less electron-rich compound shows the tendency to eliminate its C₂ moiety thermally or upon hydrolysis. These results establish design principles for stabilizing and tuning phosphonioacetylides and open avenues for their use in coordination chemistry and catalysis.

We report the design, synthesis, and comprehensive photophysical characterization of a new class of heteroleptic Ir ^III complexes featuring a strongly electron‐donating 4,4′‐bis(N‐heterocyclic imine)‐2,2′‐bipyridine (bpy‐NHI) ligand. The bpy‐NHI ligand was synthesized on a multigram scale via a seven‐step sequence and fully characterized. Reaction with the dimer [Ir(ppy) ₂ Cl] ₂ afforded the target complex [Ir(ppy) ₂ (bpy‐NHI)] ⁺ , whose electronic structure was probed by (spectro)electrochemistry as well as by steady‐state and time‐resolved spectroscopy. Compared to the parent [Ir(ppy) ₂ (bpy)] ⁺ complex, the new complex exhibits a significantly altered redox profile, including a novel irreversible oxidation at 0.4 V vs Fc ⁺ /Fc and the absence of the typical bpy‐centered reduction, consistent with the strongly electron‐donating nature of the NHI substituents. The high basicity of the NHI substituents enabled modulation of the excited‐state properties via protonation, leading to unusual excited‐state dynamics where the metal‐to‐ligand charge‐transfer state switches between bpy‐ and ppy‐based character. In the protonated form, the complex is able to bind chloride ions, which was qualitatively detected by changes in the ground‐state absorption of the complex. These findings establish bpy‐NHI as a powerful and sensitive electron‐rich ligand platform for modulating the photophysical and electrochemical properties of Ir(III) complexes, opening new opportunities for the design of photosensitizers with tailored excited‐state properties.

Sulfur hexafluoride (SF ₆ ) is a persistent, highly potent greenhouse gas that is accumulating in the atmosphere at an increasing rate, exacerbating climate change. Whereas current degradation methods rely on forcing conditions to dissociate the inert molecule and additionally require post-treatment with basic solution to obtain harmless products, we show that SF ₆ is mineralized in a single step at ambient temperature using potassium hydroxide in water/isopropyl alcohol mixtures under UV irradiation. The reaction proceeds via an autocatalytic mechanism, where in situ-generated acetone acts as a photosensitizer, leading to the selective formation of potassium sulfite and fluoride salts. Compared to existing methods, this approach eliminates the need for extreme temperatures, hazardous catalysts, or post-treatment, providing a scalable and easy-to-apply strategy for SF ₆ degradation.

The synthesis and reactivity of secondary phosphines carrying two N-heterocyclic imine substituents are reported. These highly electron-rich phosphines feature a polarized P-H bond, with computational studies revealing their dual nature as excellent hydride donors and superbasic phosphorus nucleophiles. Experimental investigations demonstrated their ability to transfer a hydride, proton, or hydrogen atom, depending on the reaction partner, as well as their reactivity in hydrophosphination reactions. The hydrophosphination of nonactivated alkynes proceeded under mild, metal-free conditions, yielding alkenylphosphine intermediates that partly rearranged into azaphosphole heterocycles.

Rod-shaped neutral carbon ligands such as carbon monoxide and isocyanides play a central role in organometallic chemistry but are relatively weak electron donors compared to N-heterocyclic carbenes. Phosphonioacetylides (R₃PCC) have been proposed as promising candidates for stronger electron donation within the class of sp-hybridized carbon ligands. However, their high reactivity has significantly limited their exploration and isolation. In this study, we report the synthesis and characterization of a novel phosphonioacetylide, MeR₂PCC (R = 1,3-di-tert-butylimidazolidin-2-ylidenamino). While it is highly labile at ambient temperature, the compound is stable at −40 °C and can be isolated and stored in the form of alkali metal complexes. The latter undergo efficient transmetallation reactions with a variety of electrophiles, enabling the formation of Lewis base adducts with both main group elements and transition metals, including tungsten(0), nickel(0), and rhodium(I). These results demonstrate that alkali metal phosphonioacetylides serve as versatile precursors for introducing this highly donating and structurally unique ligand into coordination complexes.

The reaction of phosphine (tmg) ₃ P with C ₆₀ leads to isolable zwitterionic phosphonium fullerides with reversible P–C dative bonds and increased negative charge on the C ₆₀ core, enabling further electrophilic functionalization.

A new electron-rich 1,10-phenanthroline ligand with bulky NHI groups forms a well-structured coordination cavity, showing selective coordination of Lewis acids at phenanthroline nitrogen atoms and tunable electronic and photophysical properties.