The conversion of C-H bonds into amines by nitrene insertion is an attractive transformation since it is both atom- and step-economical, and provides a direct route to functionalizing hydrocarbons. Using an iron catalyst [{( (tBu)pyrr)(2)pyr}Fe(OEt2)] (1-OEt2) (((tBu)pyrr)(2)pyr(2-) = 3,5-Bu-t(2)-bis(pyrrolyl)pyridine), we recently demonstrated the catalytic conversion of weak C-H bonds into secondary amines using aryl azides as the nitrene source [. Here, we describe detailed mechanistic studies of this intermolecular C-H amination reaction under catalytic conditions. We find by Variable Time Normalization Analysis (VTNA) that the conversion of xanthene (2-H-2) and 2,4,6-trimethyl-phenyl azide ( (Me)3) catalyzed by 1-OEt2 is an overall 3/2 order process, being 1st order in 2-H-2 and half order in (Me)3. A kinetic isotope effect study (KIE) using 2-d(2) results in a significant decrease in the rate (KIE = 61(15)), which clearly implicates the C-H insertion step as rate-determining. Furthermore, treatment of 1-OEt2 with one equivalent of N3-2,6- i Pr2-C6H3 yields the mixed-valence C-N coupled product [((tBu)pyrr)2pyrFe-N=C(2,6 i Pr-2-Ph)=N-(2,6(i)Pr2-Ph))Fe(tBu)pyrrpyr(2-H-pyrr)] (5 iPr). Quantum chemical calculations confirm the electronic structure of the mixed-valence dimer in 5(iPr) and rationalize the Hammett correlation by a delicate balance in the dinuclearization of the catalytically active monomers. Calculations further indicate significant tunneling for the pivotal H atom abstraction by the iron-imidyl complex. Combining all these results allows us to propose a mechanism consisting of imido formation in equilibrium with a radical-coupled diiron system, followed by stepwise C-H insertion via a linear H atom abstraction transition state and subsequent radical rebound.

Zinc is widely regarded as redox-inactive, yet how it may directly participate in oxygen chemistry remains unclear. Here, we show how a dinuclear zinc complex bearing a redox-active 20 bis(hydroquinone) ligand can activate O2 and oxidize 2,6-di-tert-butylphenol. The dinuclear scaffold is essential: one Zn site stabilizes superoxide while the second supports ligand oxidation, enabling cooperative O2 reduction inaccessible to mononuclear analogues. The generated superoxo–Zn–semiquinone triad mediates hydrogen atom abstraction from the phenol. Spectroscopy, mass spectrometry, kinetics, and DFT calculations establish the reaction mechanism 25 and support radical rebound to a kinetically trapped Zn2 adduct that channels reactivity toward selective C–C coupling. The branched network allows limited regeneration but also leads to framework degradation, yielding a self-limiting turnover-capable system. These findings expand zinc’s role in redox chemistry and redefine its potential biological relevance.

Mitochondria are attractive anticancer targets, but selective targeting remains challenging. We report a Cu2+-mediated strategy for mitochondria-directed activity based on intracellular metal coordination. Aminoferrocene drugs were functionalized with Cu2+-binding ligands to exploit elevated copper levels in cancer cells. Among these, the bipyridine conjugate AFb-L4 displays pronounced Cu2+-dependent cytotoxicity, with an IC50 of 29 nM in ovarian carcinoma cells (∼500-fold enhancement upon Cu2+ addition). Spectroscopic, magnetic, and mass spectrometric analyses confirm formation of a 1:1 AFb-L4-Cu2+ complex without electronic coupling between the Cu2+ and ferrocene centers. Intracellular Cu2+ coordination converts AFb-L4 into a cationic species that accumulates in mitochondria, inducing loss of membrane potential, mitochondrial remodeling, and mitochondrial ROS generation. Structure-activity relationships show that stabilization of Cu2+ is critical, as a sterically hindered isomer with reduced Cu2+ binding is largely inactive. These results establish intracellular Cu2+ coordination as a trigger for mitochondrial targeting.

The systematic nucleophilic functionalisation of the cationic pentaphosphole ligand complex [Cp*Fe(eta 4-P5Me)][OTf] ([OTf]- = [SO3CF3]-) (A) with sterically demanding CpR derivatives is reported. This newly developed protocol turned out to be a highly reliable method for the synthesis of end-deck cyclo-P5 ligand complexes bearing bulky CpR substituents. By the reaction of A with anionic CpR salts, complexes of the type [Cp*Fe(eta 4-P5MeCpR)] (Cp* = eta 5-C5Me5; CpR = Cp ' (1), Cp '' (2), Cp & tprime; (3), CpMe (4); Cp ' = eta 5-C5H4tBu, Cp '' = eta 5-1,3-tBu2C5H3, Cp & tprime; = eta 5-1,3,4-tBu3C5H2, CpMe = eta 5-C5Me4H) are obtained. All products feature a selective 1,1 '-disubstitution at the cyclo-P5 ligand. Further reactivity studies of these complexes with FeBr2 enabled the formation of novel, sterically demanding ferrocene derivatives [{Cp*Fe(eta 4-P5Me(eta 5-Cp ''))}2Fe] (5) and [Cp*Fe(eta 4-P5Me(eta 5-Cp ''))FeCp ''] (6), featuring three different Fe atoms in a ferrocene-like environment. Oxidation of 5 yielded the dicationic complex [{Cp*Fe(eta 4-P5Me(eta 5-Cp ''))}2Fe][FAl]2 (7). EPR, zero-field 57Fe M & ouml;ssbauer, as well as DFT investigations on 7 showed a symmetric distribution of the positive charges on the outer Fe atoms.

Mitochondria are attractive anticancer targets, but selective targeting remains challenging. We report a Cu2+-mediated strategy for mitochondria-directed activity based on intracellular metal coordination. Aminoferrocene drugs were functionalized with Cu2+-binding ligands to exploit elevated copper levels in cancer cells. Among these, the bipyridine conjugate AFb-L4 displays pronounced Cu2+-dependent cytotoxicity, with an IC50 of 29 nM in ovarian carcinoma cells (similar to 500-fold enhancement upon Cu2+ addition). Spectroscopic, magnetic, and mass spectrometric analyses confirm formation of a 1:1 AFb-L4-Cu2+ complex without electronic coupling between the Cu2+ and ferrocene centers. Intracellular Cu2+ coordination converts AFb-L4 into a cationic species that accumulates in mitochondria, inducing loss of membrane potential, mitochondrial remodeling, and mitochondrial ROS generation. Structure-activity relationships show that stabilization of Cu2+ is critical, as a sterically hindered isomer with reduced Cu2+ binding is largely inactive. These results establish intracellular Cu2+ coordination as a trigger for mitochondrial targeting.

N-anchored tripodal N-heterocyclic carbene ligands, satTIMMNMes and Me2TIMMNMes, were synthesized and used to stabilize a series of mid-valent Fe(IV) and high-valent Fe(V) and Fe(VI) nitrides. The Fe(IV) and Fe(V) species adopt trigonal-pyramidal and trigonal-bipyramidal geometries, respectively, whereas the Fe(VI) nitrides exhibit octahedral coordination, representing rare examples of structurally characterized iron(VI) nitrido complexes. All complexes were characterized by single-crystal X-ray diffraction, multinuclear (1H, 13C, 15N, and 19F) NMR, zero- and applied-field 57Fe Mössbauer, electron paramagnetic resonance, as well as vibrational and electronic absorption spectroscopy. Combined spectroscopic, electrochemical, and computational studies examined how systematic variation in the NHC backbone modulates the electronic structures of the [Fe≡N]n+ and Fe-CNHC moieties. Structural and spectroscopic parameters of Me2TIMMNMes-based Fe(IV-VI) nitrides closely resemble those of parent TIMMNMes analogues, while more pronounced deviations are observed for satTIMMNMes derivatives. 57Fe Mössbauer spectroscopy at 80 K revealed an unusually negative isomer shift for the tetravalent (d4, S = 0) [(satTIMMNMes)FeIV≡N]+ (δ = -0.45 mm s-1), distinct from Me2TIMMNMes and TIMMNMes analogues (δ = -0.36 and -0.35 mm s-1), attributable to enhanced Fe-CNHC covalency in satTIMMNMes ligand. Cyclic voltammetry, supported by theoretical calculations, quantifies relative ligand π-donation in the Fe(IV) nitrido complexes, complementary to established NHC σ-donor descriptors, yielding the trend satTIMMNMes < TIMMNMes < Me2TIMMNMes. Consistent with this trend, structural and EPR data indicate differing degrees of Jahn-Teller distortion among the paramagnetic Fe(V) nitrides (d3, S = 1/2). In contrast, the structural and spectroscopic differences are relatively diminished in highly covalent Fe(VI) nitrides (d2, S = 0).

Heterogenized molecular catalysts commonly rely on covalent grafting to solid supports. Cleavage of these linkages under catalytic conditions, however, can compromise structural definition and control at the interface. Here, we introduce a ligand-encoded anchoring strategy in which a platinum(II) bis(NHC) complex is immobilized on mesoporous silica (SBA-15) exclusively through directional, non-covalent F-Si interactions. The molecular pre-catalyst trans-[Pt(LF)2Cl2] was structurally characterized by single-crystal X-ray diffraction and multinuclear solution-state NMR spectroscopy. Advanced solid-state MAS NMR experiments, including 19F{29Si} REDOR, combined with molecular dynamics simulations, establish well-defined F-Si contacts with internuclear distances on the Å-scale and reveal the organization of the pre-catalyst at the silica interface. A model hydrosilylation reaction demonstrates catalytic activity and retention of the molecular species on the support during turnover. This work establishes non-covalent interface engineering as a viable strategy for structurally defined heterogenized catalysis.

The hydrodynamic size of magnetic nanoparticle clusters is a critical determinant of their in vivo behaviour and therapeutic efficacy. While alkaline co-precipitation offers a scalable route for polyacrylic acid (PAA) coated superparamagnetic iron oxide nanoparticles (SPIONs), it typically yields polydisperse agglomerates. This work establishes a predictive engineering process using controlled, post-synthesis ultrasound treatment to precisely tune SPION cluster size. Utilising a D-optimal Design of Experiments (DoE) approach, we modelled the influences of sonication parameters on the hydrodynamic diameter, identifying specific energy input as the governing factor for de-agglomeration. The resulting verified regression model (adj. R2=0.9986) enables predictable laboratory scale-up across varying volumes (1-10 ml) and concentrations (1-10 mg/ml) while maintaining material integrity. Quantitative magnetic characterisation revealed that ultrasound-induced fragmentation increases the mass-specific susceptibility, which is attributed to the magnetic de-locking of frustrated cores as inter-cluster spacing increases. Crucially, biological evaluations in B16-F10 melanoma cells demonstrate that this ultrasound-assisted size tuning directly influences cellular loading. Cellular iron mass post SPION incubation was found to follow a dual-variable dependency: while iron loading increases with cluster diameter for a fixed core size, it is significantly impacted by the primary core dimensions. SPION clusters with 12 nm cores exhibited a two-fold higher iron loading (8.23 pg Fe/cell) compared to those with 8 nm cores at equivalent hydrodynamic sizes, highlighting the importance of the magnetic payload per cluster. These findings establish a robust framework for engineering SPIONs with tailored dimensions to maximise and predict the magnetic responsiveness of loaded cells, providing a reliable foundation for future applications such as cell tracking, magnetic drug targeting, and hyperthermia.

We report the synthesis and comprehensive characterization of a closed-shell iron(IV) oxo (ferryl) complex, S = 0, which is accessible through multiple methods and stabilized by a tripodal tris-N-heterocyclic carbene (NHC) ligand. Reaction of the FeI precursor [(Me2TIMMNMes)FeI(η1-N2)](PF6) (1) (Me2TIMMNMes = tris-[2-(3-mesityl-4,5-dimethyl-imidazolin-2-ylidene)methyl]amine) with an excess of N2O at -78 °C in THF yields the reactive FeIII oxo complex [(Me2TIMMNMes)FeIII(O)](PF6) (3). One-electron oxidation of the in situ generated 3 with [Cp2Fe][PF6] provides access to a rare, nonmagnetic (d 4, S = 0) FeIV oxo complex, namely [(Me2TIMMNMes)FeIV(O)](PF6)2 (4). Alternatively, tetravalent 4 could also be obtained by treatment of the divalent iron complex [(Me2TIMMNMes)FeII(THF)](PF6)2 (2-THF) with 1 equiv of trimethylamine N-oxide (TMAO) or by the photolysis reaction of the ferrous sulfoxide isotopomers [(Me2TIMMNMes)FeII(MeS(16/18O)Ph)](PF6)2 (2-16/18OSR2). Although the fleeting nature of trivalent oxide 3 precludes extensive characterization and isolation in the solid state, the one-electron oxidation product [(Me2TIMMNMes)FeIV(O)](PF6)2 (4) is isolable and was reproducibly synthesized as well as fully characterized, including CHN elemental analysis, multinuclear NMR, IR vibrational, UV/vis electronic absorption, zero- and applied-field 57Fe Mössbauer spectroscopy, and single-crystal X-ray crystallography studies. Diamagnetic 4 features a remarkably short Fe-O bond (d(Fe-O) = 1.576(1) Å) and a notably negative isomer shift (δ = -0.38 mm s-1) in the 57Fe Mössbauer spectrum. Computational analyses corroborate the + IV oxidation state and advocate an iron-oxygen triple bond, FeIV≡O. Preliminary reactivity studies show that the closed-shell iron(IV) oxo complex can mediate intermolecular oxygen-atom transfer chemistry. A reversible redox event at a half-wave potential, E1/2, of 1.25 V vs Fe(Cp)2/Fe(Cp)2+ in the cyclic voltammogram of 4 suggests the existence of an Fe(V) oxo species.

Alkenes are known to undergo successive oxidation to form alkene-derived radical cations and dications, which have found applications across various fields. As the aluminum analogues of alkenes, dialumenes likewise have the potential to lose one or two π-bonding electrons, forming dialumene-derived radical cations or dications. To date, however, these species have remained elusive, most likely due to the intrinsic electron deficiency imposed by both the positive charge and the pronounced electrophilicity of aluminum. Here, we present the synthesis of a stable aluminum-centered radical cation and dication through the combination of bulky silyl substituents and electron-donating carbene ligands. Further studies reveal that these aluminum complexes can switch between their neutral, radical cationic, and dicationic states, thus establishing a redox-reversible system. Furthermore, the dication exhibits multiple modes of reactivity, acting as a Lewis acid while also mediating both deoxygenation reactions and isocyanide homologation.

Herein we disclose a novel route to redox-active vanadacyclobutadiene (VCBD) and vanadatetrahedrane (VTd) complexes, which circumvents a vanadium alkylidyne precursor ([VV][triple bond, length as m-dash]CR). [VV] VCBD salts and VTd's are prepared through an unusual, non-classical oxidative addition reaction via the addition of electrophiles to a low-spin [VIII] deprotiovanadacyclobutadiene (dVCBD). The microscopic reverse reaction, a reductive elimination, reverts the [VV] VCBD and VTd scaffolds back to the low-spin [VIII] dVCBD species via the addition of a Brønsted base. The interconversion of the [VV] VCBD salts and VTd's is mediated through anion exchange, which promotes a change in the spin-state and geometry of the organometallic species, highlighting the redox active nature of the allene ligand (C3) bound to vanadium (V). Single electron reduction of the [VV] VCBD or VTd with cobaltocene (CoCp2) led to the formation of neutral and radical-based [VIV] VCBDs. Oxidation of the [VIV] VCBDs with ferrocenium based salts ([FeCp2][X], X = BArF20 -, BArF24 -, OTf-) or chloride-delivering oxidants (i.e. triphenylmethyl chloride (Ph3CCl) or lead(ii) chloride (PbCl2)) regenerates the discrete [VV] VCBD salts or VTd's, respectively. Cyclic voltammetry studies reveal quasi-reversible one electron redox couples, while X-band electron paramagnetic resonance (EPR) spectroscopic studies confirms the presence of a paramagnetic [VIV], d1 system in the VCBD. Computational analysis of the dVCBD, VTd, and VCBD complexes affords detailed insight into the structure and bonding of this unusual class of molecules and delineates the role of the anion in their interconversion. Further examination of the reaction of dVCBD with electrophiles corroborates the nonclassical character of the oxidative addition sequence involving metal-ligand cooperation, with ligand-centered redox activity, rather than a formal two-electron oxidation at the metal center. The present work demonstrates how these rare dVCBD, VCBD, and VTd scaffolds can all be interconverted via reversible C-C bond formation and splitting pathways using the right combination of anion exchange, redox, and Brønsted acid-base chemistry.

An all‐uranium‐based electrochemical cell consisting of simple [U IV/V ( t Bu acac) 4 ] 0/+ and [U III/IV (N(SiMe 3 ) 2 ) 4 ] −/0 complexes as anolyte and catholyte species was constructed with a cell voltage of 2.2 V. The [U IV ( t Bu acac) 4 ] ( 1 ) and [U IV (N(SiMe 3 ) 2 ) 4 ] ( 2 ) complexes have favorable properties for redox‐flow‐battery applications, including reversible redox chemistry, relatively high stability toward electrochemical cycling, and high solubility in common organic solvents. The [U III/IV (N(SiMe 3 ) 2 ) 4 ] −/0 complexes were first isolated and characterized by Schelter et al., and performed well in electrochemical studies due to the comparably low reduction potential of −2.05 V vs. Fc/Fc + to the reduced uranium(III) species. Treatment of conveniently accessible 1 with AgSbF 6 allowed the isolation of [U V ( t Bu acac) 4 ][SbF 6 ] ( 3 ), which is the active catholyte species generated during cell charging. Galvanostatic cycling with charging and discharging at currents of 20 and 5 μA, respectively, was performed in a two‐compartment static H‐cell with high‐surface‐area carbon fiber electrodes to achieve a potential of 2.2 V. The success of this 1 || 2 cell‐provides a promising entry point to a potential future class of uranium‐based, nonaqueous redox‐flow‐battery electrolytes, not for use in personal devices but incorporated into underground energy storage systems, where weight and radioactivity levels are not an issue and where this abundant waste material could find new application.

A rare example of an equatorially bound terminal uranium(V) oxo complex in a chelating sulfur-based ligand environment, namely [(mes(Me,AdArS)3)UV(Oeq)(THF)] (2), is presented. Octahedrally coordinated 2 is obtained by reaction of the mesitylene-anchored tris-thiophenolate-coordinated uranium(III) complex [UIII((SArAd,Me)3mes)] (1) with the oxygen-atom transfer reagent N2O. The observed, equatorially bound oxo ligand in 2 is in stark contrast to its known tris-aryloxide analog, [(mes(Me,AdArO)3)UV(Oax)(THF)] (A), where the oxo ligand occupies the typically observed axial coordination site. Complexes 1 and 2 are characterized by single-crystal X-ray diffraction analyses and spectroscopic and magnetochemical methods, including 1H NMR, UV/vis/NIR electronic absorption, as well as EPR spectroscopy and SQUID magnetometry, thus confirming the CS symmetry and the pentavalent oxidation state of 2. Encompassing quantum chemical calculations (DFT and CASPT2) on 2 and its tris-phenolate analog A, support and rationalize the structural and electronic differences. The molecular orbital pictures show that a stabilizing σ-bonding interaction arising from the U-Oeq inverse trans influence (ITI) is present in 2 but missing in A. In 2, the sulfur 3p orbitals are closer in energy to the uranium 5f manifold than the arene π-system, leading to an ITI, while U-arene σ- or δ-bonding is not observed. Although the arene orbitals remain separated from the uranium 5f orbitals in A, the absence of an ITI allows the arene a2u orbital to engage in a σ-type interaction with the metal. Thus, incorporating a tris-thiophenolate to an arene anchor introduces a new design concept in molecular f-element chemistry. This approach stabilizes an equatorially bound U(V) oxo center, contrasting with its tris-phenolate counterpart, where oxo coordination is axial. The observed geometric divergence, driven by competing ITI and U-arene interactions, not only tunes electronic structure but also leads to differentiated reactivity: only the phenolate analogs activate H2O, while the thiolates do not.

When talking about homogeneous catalyst systems, it has long been assumed that the system at hand consists of a transition metal complex in solution with the liquid interface representing the composition of the bulk solution. Now, in light of considerable developments in the study of metal complexes dissolved in ionic liquids with their negligible vapor pressures, more detailed studies of the composition at the liquid/gas interface became possible. These investigations revealed pronounced surface enrichment and segregation effects of high relevance for practical applications. This article reviews recent advancements in tailoring the interfacial composition of ionic liquid-based catalytic systems. A particular focus is dedicated to surface enrichment phenomena, and a variety of parameters are presented for deliberate control of the local concentration of the complexes at the surface, that is, the nature of the ligands, the bulk concentration, the temperature, and the nature of the IL solvent. As experimental methods, angle-resolved X-ray photoelectron spectroscopy (ARXPS) and vacuum-based pendant-drop surface tension measurements were applied. The reviewed results are intended to provide the basis for the advancement of catalytic systems with high surface areas, such as in supported ionic liquid phase (SILP) catalysis, where the interface design is directly interconnected with catalytic performance.

Nanoclusters are nanometer-sized molecular compounds characterized by significant metal-metal bonding and low average oxidation states, and they exhibit unique properties distinct from those of small metal complexes or nanoparticles. Unlike noble metals stable in metallic forms, the synthesis of nanometer-sized iron clusters has been precluded by the relatively weak iron-iron bonds and the high reactivity of low oxidation state iron, despite the extensive history of molecular iron compounds. Here, we report the synthesis and characterization of a cationic 55-atom iron cluster with a 1.2 nm icosahedral core. Its 12 vertices are occupied by tri-tert-butylphosphines, while multiple hydrides cover the surface. This core can be viewed as a substructure of the face-centered cubic (fcc), in contrast to the body-centered cubic (bcc) for the stable bulk phase. This work reveals a stable structure and fundamental properties of a nanometer-sized iron cluster, which have remained elusive for decades, and the simple synthetic protocol provides a route to explore molecular nanochemistry.

Die in dieser Publikation behandelten Themen sollen viele verschiedene Aspekte der Chemie vermitteln, die einen guten & Uuml;berblick & uuml;ber die grundlegenden Kenntnisse der anorganischen Chemie geben und den gr & ouml;ss ten Teil einer Erstsemestervorlesung abdecken sollen. Dennoch geht das vermittelte Wissen weit & uuml;ber das Verst & auml;ndnis grundlegender Redox- oder S & auml;ure-Base-Reaktionen hinaus. Das Demonstrieren von Versuchen geht immer Hand in Hand mit der Vermittlung des richtigen und sicheren Umgangs mit Chemikalien. In vielen dieser Experimente wurden Chemikalien verwendet, die mit & auml;u ss erster Sorgfalt behandelt werden m & uuml;ssen. Ein Chemiker muss sich immer & uuml;ber die Gefahren im Klaren sein, die mit bestimmten Chemikalien verbunden sind. Stoffe, die stark mit Wasser, Luft oder mit chlorierten L & ouml;sungsmitteln reagieren, m & uuml;ssen immer unter den richtigen Bedingungen gehandhabt werden. Alle gezeigten Experimente sind kontrollierte Explosionen und Verbrennungen. Es w & auml;re schrecklich, sich vorzustellen, welche Sch & auml;den durch Fehlkalkulationen und falsche Anwendung entstehen k & ouml;nnen. Diese Arbeit sollte auch als Mahnung verstanden werden, Chemikalien mit dem n & ouml;tigen Respekt, aber niemals mit Angst zu behandeln. Schlie ss lich sind chemische Reaktionen das t & auml;gliche Gesch & auml;ft fast aller Chemiker. Die Erkenntnisse und Erfahrungen, die man durch die Lekt & uuml;re dieses Artikels oder durch das Anschauen von Videos zu diesen chemischen Experimenten gewinnt, k & ouml;nnen gegebenenfalls den Unterricht im H & ouml;rsaal bereichern, aber sie k & ouml;nnen niemals das Gef & uuml;hl eines Live-Experiments ersetzen. The topics addressed in this publication should have taught many different aspects of chemistry, providing a good overview of the fundamental knowledge of inorganic chemistry and covering the major part of a first-semester lecture. Still, the knowledge transferred goes far beyond the understanding of basic redox or acid-base reactions. Demonstrating experiments always goes hand in hand with teaching the correct and safe handling of chemicals. In many of these experiments, chemicals were used that must be treated with extreme care. A chemist should always be aware of the dangers associated with specific chemicals. Substances that react vigorously with water, in air, or with chlorinated solvents must always be handled under the right conditions. All demonstrated experiments involved controlled explosions and combustions. It would be dreadful to imagine the damage resulting from miscalculations and improper use. This work should also serve as a reminder to treat chemicals with the appropriate respect, but never with fear. In the end, chemical reactions are the everyday business of nearly every chemist. The experience and knowledge gained from reading this text or watching a movie about one of these chemical experiments can enhance classroom teaching, if necessary, but can never replace the feeling of a live performance experiment.

AbstractIn der homogenen Katalyse geht man üblicherweise davon aus, dass sich die Konzentrationen der Übergangsmetallkomplexe an der Gas‐Flüssig‐Grenzfläche und im Volumen der Lösung nicht unterscheiden. Tatsächlich zeigen aber umfangreiche Untersuchungen an gelösten Metallkomplexen in ionischen Flüssigkeiten (Englisch: Ionic Liquids, ILs) ausgeprägte Oberflächenanreicherungs‐ und Segregationseffekte, die auch für praktische Anwendungen von großer Bedeutung sein können. Diese Untersuchungen basieren auf Methoden der Oberflächenforschung, die aufgrund der vernachlässigbaren IL‐Dampfdrücke unter wohldefinierten Vakuumbedingungen anwendbar sind. Dieser Übersichtsartikel bietet einen Überblick über die jüngsten Fortschritte bei der Steuerung der Grenzflächenzusammensetzung von katalytischen Systemen auf der Basis ionischer Flüssigkeiten. Ein besonderer Schwerpunkt liegt auf der gezielten Oberflächenanreicherung. Insbesondere werden eine Vielzahl von Parametern vorgestellt, welche die lokale Komplexkonzentration an der Oberfläche beeinflussen wie etwa die Wahl der Liganden, die Konzentration im Volumen, die Temperatur und die Natur des IL‐Lösungsmittels. Als experimentelle Methoden wurden vor allem winkelaufgelöste Röntgenphotoelektronenspektroskopie (Englisch: Angle‐Resolved X‐Ray‐Photoelectron Spectroscopy, ARXPS) und Oberflächenspannungsmessungen mit der Methode des hängenden Tropfens (Englisch: Pendant Drop Method) unter ultrareinen Vakuumbedingungen eingesetzt. Die hier zusammengefassten Ergebnisse bilden die Grundlage für die Weiterentwicklung von maßgeschneiderten katalytischen Anwendungen mit großer innerer Oberfläche, z.B. in der Katalyse mit geträgerten ionischen Flüssigphasen (Englisch: Supported Ionic Liquid Phase, SILP); bei solchen Systemen hat das Design der Grenzfläche einen erheblichen Anteil an der katalytischen Effizienz.

We report on the utilization of the ethylene-bridged bis[(dialkylamino)cyclopropenimine] (bisCPI) ligand, LCPI, to give access to new main-group E(II) halide complexes (E = Ge, Sn, Pb; 1, 2, 3). Subsequent reduction with Collman's reagent (Na2Fe(CO)4 • dioxane) enables the isolation of a series of zero-valent tetrylone-tetracarbonyl iron complexes, (LCPI)E(Fe(CO)4 (E = Ge (4), Sn (5), Pb (6)). Compounds 4 - 6 were reacted further with iron pentacarbonyl to yield the bis-tetracarbonyl iron complexes (LCPI)E[(Fe(CO)4]2 (E = Ge (7), Sn (8), Pb (9)). The electronic structure of these complexes was studied by 57Fe Mössbauer spectroscopy and computationally by density functional theory calculations.

Using an Earth-abundant transition metal to mediate formation and splitting of C-C σ-bonds, in response to electrical stimuli, constitutes a promising strategy to construct complex organic skeletons. Here, we showcase how [ n Bu4N][N3] reacts with an isocyanide adduct of a tetrahedral and high-spin TiII complex, [(Tp tBu,Me)TiCl] (1), to enact N-atom transfer, C-N bond formation, and C-C coupling, to form a dinuclear complex, [(Tp tBu,Me)Ti{AdN(N)C-C(N)NAd}Ti(Tp tBu,Me)] (3), with two TiIII ions bridged by a disubstituted oxalimidamide ligand ( n Bu = n-butyl, Tp tBu,Me = hydrotris(3-tert-butyl-5-methylpyrazol-1-yl)borate, Ad = 1-adamantyl). Magnetic and computational studies reveal two magnetically isolated d1 TiIII ions, and electrochemical studies unravel a reversible two-electron oxidation at -0.87 V vs. [FeCp2]0/+. Despite these observations, chemical oxidation of 3, ultimately, leads to rupture of the oxalimidamide moiety with C-C bond splitting to form [(Tp tBu,Me)Ti{1,3-μ2-AdNCN}2Ti(Tp tBu,Me)][B(C6F5)4]2 (4), which displays an antiferromagnetically coupled Ti2 III,III configuration, mediated by superexchange through its bridging carbodiimide ligands. A comparative reactivity study of isocyanide toward a transient vanadium nitride [(Tp tBu,Me)V[triple bond, length as m-dash]N(THF)] (5) gives further insight into the structure of putative intermediates involved in the coupling sequence.

Treatment of the ligand precursor H3TIMMNMesCl3 (TIMMNMes = tris-[(3-mesityl-imidazol-2-ylidene)methyl]amine) with an excess of base yields the literature-known ferrous tris-N-heterocyclic carbene (NHC) complex [(TIMMNMes)FeIICl]Cl (1-Cl). In contrast, utilizing a substoichiometric amount of base initiates a unique rearrangement of all three NHC pendant arms to yield the tripodal, all-N-bound tris-imidazole [(N-TIMMNMes)FeIICl]Cl (2-Cl sol ). Divalent 2-Cl and 2-PF 6 are fully characterized, structurally by single-crystal X-ray diffraction analysis and spectroscopically by 1H NMR and 57Fe Mossbauer spectroscopy as well as SQUID magnetization measurements, to demonstrate the influence of the change from a soft strong-field to a hard weak-field ligand. Optimized reaction conditions for the reproducible, high-yield carbene-to-imidazole rearrangement were developed in a series of experiments.