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Although iron is a dream candidate to substitute noble metals in photoactive complexes, realization of emissive and photoactive iron compounds is demanding due to the fast deactivation of their charge-transfer states. Emissive iron compounds are scarce and dual emission has not been observed before. Here we report the FeIII complex [Fe(ImP)2][PF6] (HImP = 1,1′-(1,3-phenylene)bis(3-methyl-1-imidazol-2-ylidene)), showing a Janus-type dual emission from ligand-to-metal charge transfer (LMCT)- and metal-to-ligand charge transfer (MLCT)-dominated states. This behaviour is achieved by a ligand design that combines four N-heterocyclic carbenes with two cyclometalating aryl units. The low-lying π* levels of the cyclometalating units lead to energetically accessible MLCT states that cannot evolve into LMCT states. With a lifetime of 4.6 ns, the strongly reducing and oxidizing MLCT-dominated state can initiate electron transfer reactions, which could constitute a basis for future applications of iron in photoredox catalysis.Noble metals dominate the field of photosensitizers and luminophores. Now, an approach incorporating cyclometalating and carbene functions into FeIII complexes has been shown to enable dual emission from the opposing ligand-to-metal and metal-to-ligand charge-transfer states. The latter shows an exceptionally long lifetime of 4.6 ns and is quenched by oxygen and other quenchers.

Molecules containing multiple bonds between atoms—most often in the form of olefins—are ubiquitous in nature, commerce, and science, and as such have a huge impact on everyday life. Given their prominence, over the last few decades, frequent attempts have been made to perturb the structure and reactivity of multiply-bound species through bending and twisting. However, only modest success has been achieved in the quest to completely twist double bonds in order to homolytically cleave the associated π bond. Here, we present the isolation of double-bond-containing species based on boron, as well as their fully twisted diradical congeners, by the incorporation of attached groups with different electronic properties. The compounds comprise a structurally authenticated set of diamagnetic multiply-bound and diradical singly-bound congeners of the same class of compound. Attempts to bend and twist multiple bonds in order to alter their reactivities have thus far been met with only modest success. Here, Braunschweig and colleagues isolate double-bond-containing boron-based species and their 90°-twisted diradical analogs, thanks to their stabilization with Lewis basic units.

Bonds are at the very heart of chemistry. Although the order of carbon–carbon bonds only extends to triple bonds, metal–metal bond orders of up to five are known for stable compounds, particularly between chromium atoms. Carbometallation and especially carboalumination reactions of carbon–carbon double and triple bonds are a well established synthetic protocol in organometallic chemistry and organic synthesis. We now extend these reactions to compounds containing chromium–chromium quintuple bonds. Analogous reactivity patterns indicate that such quintuple bonds are not as exotic as previously assumed. Yet the particularities of these reactions reflect the specific nature of the high metal–metal bond orders. Extremely short quintuple bonds between chromium atoms have recently been discovered. Carboalumination reactions have now been performed to further investigate the properties of these unusual bonds, and show that they have interesting analogies to lower-order bonds, as well as revealing more about the nature of quintuple bonds.

Silylium ions, three‐coordinated as well as donor‐stabilized, have attracted the interest of chemists for many years, have paved its way into practical application as catalysts for organic reactions, and have contributed to the understanding of fundamental chemistry problems. Since the first carbenes have been isolated and characterized, they had and still have an ongoing enormous impact on organic as well as on inorganic and organometallic chemistry. Herein, the synthesis and complete characterization of silatranyl cations as their acetonitrile‐ respectively propionitrile‐coordinated hexachlorido antimonates is reported. Upon interaction of the former with 4‐dimethylaminopyridine (DMAP) conversion to an unprecedented carbene–type complex of antimony pentachloride occurred, nicely combining silylium and carbene chemistry. Reacting 1‐hydridosilatrane with triphenylcarbenium hexachloridoantimonate in acetonitrile solution and in the presence of 4‐dimethylaminopyridine combines the world of silatranes with the world of carbenes, giving an unprecedented carbene‐type antimony pentachloride complex. This finding offers a new playground for exciting new chemistry.

The reaction of the diferrocenylphosphenium ion with four terminal allenes follows two different pathways, via allyl or vinyl carbocations, which proceed with electrophilic substitution reactions at one ferrocenyl moiety to form persistent Wheland intermediates and eventually alkenyldiferrocenylphosphonium salts. The reaction of the diferrocenylphosphenium ion with 2‐(trimethylsilyl)‐2,3‐pentadiene affords a stable Wheland intermediate of ferrocene in high yields, which is isolated and fully characterized. A kinetically stable Wheland intermediate of the electrophilic aromatic substitution at ferrocene is isolated from the reaction of the diferrocenylphosphenium ion with the allene 2‐(trimethylsilyl)‐2,3‐pentadiene and fully characterized.

Hydrogen production through water splitting is one of the most promising solutions for the storage of renewable energy. [NiFe] hydrogenases are organometallic enzymes containing nickel and iron centres that catalyse hydrogen evolution with performances that rival those of platinum. These enzymes provide inspiration for the design of new molecular catalysts that do not require precious metals. However, all heterodinuclear NiFe models reported so far do not reproduce the Ni-centred reactivity found at the active site of [NiFe] hydrogenases. Here, we report a structural and functional NiFe mimic that displays reactivity at the Ni site. This is shown by the detection of two catalytic intermediates that reproduce structural and electronic features of the Ni-L and Ni-R states of the enzyme during catalytic turnover. Under electrocatalytic conditions, this mimic displays high rates for H 2 evolution (second-order rate constant of 2.5 × 10 4  M −1  s −1 ; turnover frequency of 250 s −1 at 10 mM H + concentration) from mildly acidic solutions. [NiFe] hydrogenases are enzymes containing nickel and iron centres that catalyse hydrogen evolution with performances that rival those of platinum catalysts. Now, a NiFe model complex has been reported that mimics the structure and the Ni-centred hydrogen evolution activity found at the active site of [NiFe] hydrogenases.

The extraordinary advances in carbene (R 1 –C–R 2 ) chemistry have been fuelled by strategies to stabilize the electronic singlet state via π interactions. In contrast, the lack of similarly efficient approaches to obtain authentic triplet carbenes with appreciable lifetimes beyond cryogenic temperatures hampers their exploitation in synthesis and catalysis. Transition-metal substitution represents a potential strategy, but metallocarbenes (M–C–R) usually represent high-lying excited electronic configurations of the well-established carbyne complexes (M≡C–R). Here we report the synthesis and characterization of triplet metallocarbenes (M–C–SiMe 3 , M = Pd II , Pt II ) that are persistent beyond cryogenic conditions, and their selective reactivity towards carbene C–H insertion and carbonylation. Bond analysis reveals significant stabilization by spin-polarized push–pull interactions along both π-bonding planes, which fundamentally differs from bonding in push–pull singlet carbenes. This bonding model, thus, expands key strategies for stabilizing the open-shell carbene electromers and closes a conceptual gap towards carbyne complexes. Although strategies to stabilize the singlet state of carbenes are known, obtaining stable triplet electromers remains a challenge. Now it has been shown that transition-metal substitution enables the generation of triplet metallocarbenes stabilized by spin-polarized push–pull interactions; these compounds exhibit appreciable lifetimes beyond cryogenic temperatures.

Silylium ions, three‐coordinated as well as donor‐stabilized, have attracted the interest of chemists for many years, have paved its way into practical application as catalysts for organic reactions, and have contributed to the understanding of fundamental chemistry problems. Since the first carbenes have been isolated and characterized, they had and still have an ongoing enormous impact on organic as well as on inorganic and organometallic chemistry. Herein, the synthesis and complete characterization of silatranyl cations as their acetonitrile‐ respectively propionitrile‐coordinated hexachlorido antimonates is reported. Upon interaction of the former with 4‐dimethylaminopyridine (DMAP) conversion to an unprecedented carbene–type complex of antimony pentachloride occurred, nicely combining silylium and carbene chemistry.

The Front Cover shows a round‐bottomed flask containing a burgundy solution of diferrocenylphosphenium ion [Fc2P][B(C6F5)4], which was used in this work to activate various allenes. Dropwise addition to 2‐(trimethylsilyl) penta‐2,3‐diene yields a bright red solution of a stable Wheland intermediate of ferrocene, whose solid‐state structure is depicted as a ball‐and‐stick model. In front lies Saint Peter’s Key, a prominent feature of the City of Bremen’s coat of arms, representing the unlocked potential of highly reactive main group species. More information can be found in the Research Article by E. Hupf, J. Beckmann and co‐workers (DOI: 10.1002/ceur.202500031).

The massive worldwide use of antibiotics leads to water pollution and increasing microbial resistance. Hence, the removal of antibiotic residues is a key issue in water remediation. Here, we report the solar light-assisted oxidative degradation of ciprofloxacin (CPF), using H2O2 in aqueous solution, catalyzed by iron(III) chelated cross-linked chitosan (FeIII-CS-GLA) immobilized on a glass plate. The FeIII-CS-GLA catalyst was characterized by FTIR and 57Fe-Mössbauer spectroscopies as well as X-ray diffraction, revealing key structural motifs and a high-spin ferric character of the metal. Catalytic degradation of CPF was investigated as a function of solar light irradiation time, solution pH, concentration of H2O2 and CPF, as well as cross-linker dosage and iron(III) content in FeIII-CS-GLA. The system was found to serve as an efficient catalyst with maximum CPF degradation at pH 3. The specific ·OH scavenger mannitol significantly reduces the degradation rate, indicating that hydroxyl radicals play a key role. The mechanism of catalytic CPF degradation was evaluated in terms of pseudo-first-order and Langmuir-Hinshelwood kinetic models; adsorption of CPF onto the FeIII-CS-GLA surface was evidenced by field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. FeIII-CS-GLA can be reused multiple times with only minor loss of catalytic efficiency. Antimicrobial activity tests performed against both Gram-negative (Escherichia coli DH5α, Salmonella typhi AF4500) and Gram-positive bacteria (Bacillus subtilis RBW) before and after treatment confirmed complete degradation of CPF. These results establish the immobilized FeIII-CS-GLA as a rugged catalyst system for efficient photo-Fenton type degradation of antibiotics in aqueous solutions.