Binding of exogenous cyanide reveals new active-site states in [FeFe] hydrogenases.

[FeFe] hydrogenases are highly efficient metalloenyzmes for hydrogen conversion. Their active site cofactor (the H-cluster) is composed of a canonical [4Fe-4S] cluster ([4Fe-4S]) linked to a unique organometallic di-iron subcluster ([2Fe]). In [2Fe] the two Fe ions are coordinated by a bridging 2-azapropane-1,3-dithiolate (ADT) ligand, three CO and two CN ligands, leaving an open coordination site on one Fe where substrates (H and H) as well as inhibitors ( O, CO, HS) may bind.

Theory-guided development of homogeneous catalysts for the reduction of CO to formate, formaldehyde, and methanol derivatives.

The stepwise catalytic reduction of carbon dioxide (CO) to formic acid, formaldehyde, and methanol opens non-fossil pathways to important platform chemicals. The present article aims at identifying molecular control parameters to steer the selectivity to the three distinct reduction levels using organometallic catalysts of earth-abundant first-row metals. A linear scaling relationship was developed to map the intrinsic reactivity of 3d transition metal pincer complexes to their activity and selectivity in CO hydrosilylation.

Spectroscopic Identification of Active Sites of Oxygen-Doped Carbon for Selective Oxygen Reduction to Hydrogen Peroxide.

The electrochemical synthesis of hydrogen peroxide (H O ) via a two-electron (2 e ) oxygen reduction reaction (ORR) process provides a promising alternative to replace the energy-intensive anthraquinone process. Herein, we develop a facile template-protected strategy to synthesize a highly active quinone-rich porous carbon catalyst for H O electrochemical production. The optimized PCC material exhibits remarkable activity and selectivity, of which the onset potential reaches 0.

Dynamic effects on ligand field from rapid hydride motion in an iron(ii) dimer with an = 3 ground state.

Hydride complexes are important in catalysis and in iron-sulfur enzymes like nitrogenase, but the impact of hydride mobility on local iron spin states has been underexplored. We describe studies of a dimeric diiron(ii) hydride complex using X-ray and neutron crystallography, Mössbauer spectroscopy, magnetism, DFT, and calculations, which give insight into the dynamics and the electronic structure brought about by the hydrides. The two iron sites in the dimer have differing square-planar (intermediate-spin) and tetrahedral (high-spin) iron geometries, which are distinguished only by the hydride positions.

A Cooperative Rhodium/Secondary Phosphine Oxide [Rh/P(O)nBu ] Template for Catalytic Hydrodefluorination of Perfluoroarenes.

The selective activation of C-F bonds under mild reaction conditions remains an ongoing challenge of bond activation. Here, we present a cooperative [Rh/P(O)nBu ] template for catalytic hydrodefluorination (HDF) of perfluoroarenes. In addition to substrates presenting electron-withdrawing functional groups, the system showed an exceedingly rare tolerance for electron-donating functionalities and heterocycles.

Synthesis, Isolation, and Characterization of Two Cationic Organobismuth(II) Pincer Complexes Relevant in Radical Redox Chemistry.

Herein, we report the synthesis, isolation, and characterization of two cationic organobismuth(II) compounds bearing N,C,N pincer frameworks, which model crucial intermediates in bismuth radical processes. X-ray crystallography uncovered a monomeric Bi(II) structure, while SQUID magnetometry in combination with NMR and EPR spectroscopy provides evidence for a paramagnetic = 1/2 state. High-resolution multifrequency EPR at the X-, Q-, and W-band enable the precise assignment of the full - and Bi -tensors.

Bimolecular Reductive Elimination of Ethane from Pyridine(diimine) Iron Methyl Complexes: Mechanism, Electronic Structure, and Entry into [2+2] Cycloaddition Catalysis.

The application of bimolecular reductive elimination to the activation of iron catalysts for alkene-diene cycloaddition is described. Key to this approach was the synthesis, characterization, electronic structure determination, and ultimately solution stability of a family of pyridine(diimine) iron methyl complexes with diverse steric properties and electronic ground states. Both the aryl-substituted, (PDI)FeCH and (PDI)FeCH (PDI = 2,6-(2,6-R-CHN═CMe)CHN), and the alkyl-substituted examples, (APDI)FeCH (APDI = 2,6-(CHN═CMe)CHN), have molecular structures significantly distorted from planarity and = 3/2 ground states.

Data-Centric Heterogeneous Catalysis: Identifying Rules and Materials Genes of Alkane Selective Oxidation.

Artificial intelligence (AI) can accelerate catalyst design by identifying key physicochemical descriptive parameters correlated with the underlying processes triggering, favoring, or hindering the performance. In analogy to genes in biology, these parameters might be called "materials genes" of heterogeneous catalysis. However, widely used AI methods require big data, and only the smallest part of the available data meets the quality requirement for data-efficient AI.

Pd(II)-catalyzed carboxylation of aromatic C─H bonds with CO.

The carboxylation of nonactivated C─H bonds provides an attractive yet hitherto largely elusive chemical process to synthesize carboxylic acids by incorporation of CO into the chemical value chain. Here, we report on the realization of such a reaction using simple and nonactivated arenes as starting materials. A computationally designed Pd(II) complex acts as organometallic single-component catalyst, and apart from a base, necessary for thermodynamic stabilization of the intermediates, no other additives or coreagents are required.

Sulfur-Ligated [2Fe-2C] Clusters as Synthetic Model Systems for Nitrogenase.

Metal clusters featuring carbon and sulfur donors have coordination environments comparable to the active site of nitrogenase enzymes. Here, we report a series of di-iron clusters supported by the dianionic yldiide ligands, in which the Fe sites are bridged by two μ-C atoms and four pendant S donors.The [LFe] (L = {[PhP(S)]C}) cluster is isolable in two oxidation levels, all-ferrous Fe and mixed-valence FeFe.

Catalytic Hydrogenation of CO to Formate Using Ruthenium Nanoparticles Immobilized on Supported Ionic Liquid Phases.

Ruthenium nanoparticles (NPs) immobilized on imidazolium-based supported ionic liquid phases (Ru@SILP) act as effective heterogeneous catalysts for the hydrogenation of carbon dioxide (CO ) to formate in a mixture of water and triethylamine (NEt ). The structure of the imidazolium-based molecular modifiers is varied systematically regarding side chain functionality (neutral, basic, and acidic) and anion to assess the influence of the IL-type environment on the NPs synthesis and catalytic properties. The resulting Ru@SILP materials contain well-dispersed Ru NPs with diameters in the range 0.

Molecular elucidation of drug-induced abnormal assemblies of the hepatitis B virus capsid protein by solid-state NMR.

Hepatitis B virus (HBV) capsid assembly modulators (CAMs) represent a recent class of anti-HBV antivirals. CAMs disturb proper nucleocapsid assembly, by inducing formation of either aberrant assemblies (CAM-A) or of apparently normal but genome-less empty capsids (CAM-E). Classical structural approaches have revealed the CAM binding sites on the capsid protein (Cp), but conformational information on the CAM-induced off-path aberrant assemblies is lacking.

Stepwise assembly of the active site of [NiFe]-hydrogenase.

[NiFe]-hydrogenases are biotechnologically relevant enzymes catalyzing the reversible splitting of H into 2e and 2H under ambient conditions. Catalysis takes place at the heterobimetallic NiFe(CN)(CO) center, whose multistep biosynthesis involves careful handling of two transition metals as well as potentially harmful CO and CN molecules. Here, we investigated the sequential assembly of the [NiFe] cofactor, previously based on primarily indirect evidence, using four different purified maturation intermediates of the catalytic subunit, HoxG, of the O-tolerant membrane-bound hydrogenase from Cupriavidus necator.

Manifestation of Hydrogen Bonding and Exciton Delocalization on the Absorption and Two-Dimensional Electronic Spectra of Chlorosomes.

Chlorosomes are supramolecular aggregates that contain thousands of bacteriochlorophyll molecules. They perform the most efficient ultrafast excitation energy transfer of all natural light-harvesting complexes. Their broad absorption band optimizes light capture.

Experimental assignment of long-range magnetic communication through Pd & Pt metallophilic contacts.

Record-breaking magnetic exchange interactions have previously been reported for 3d-metal dimers of the form [M(Pt(SAc))(pyNO)] (M = Ni or Co) that are linked in the solid state metallophilic Pt⋯Pt bridges. This contrasts the terminally capped monomers [M(Pt(SAc))(py)], for which neither metallophilic bridges nor magnetic exchange interactions are found. Computational modeling has shown that the magnetic exchange interaction is facilitated by the pseudo-closed shell d⋯d metallophilic interaction between the filled Pt 5d orbitals.

Probing a Hydrogen-π Interaction Involving a Trapped Water Molecule in the Solid State.

The detection and characterization of trapped water molecules in chemical entities and biomacromolecules remains a challenging task for solid materials. We herein present proton-detected solid-state Nuclear Magnetic Resonance (NMR) experiments at 100 kHz magic-angle spinning and at high static magnetic-field strengths (28.2 T) enabling the detection of a single water molecule fixed in the calix[4]arene cavity of a lanthanide complex by a combination of three types of non-covalent interactions.

Differentiating between Acidic and Basic Surface Hydroxyls on Metal Oxides by Fluoride Substitution: A Case Study on Blue TiO from Laser Defect Engineering.

Both oxygen vacancies and surface hydroxyls play a crucial role in catalysis. Yet, their relationship is not often explored. Herein, we prepare two series of TiO (rutile and P25) with increasing oxygen deficiency and Ti concentration by pulsed laser defect engineering in liquid (PUDEL), and selectively quantify the acidic and basic surface OH by fluoride substitution.

Selective oxidation of silanes into silanols with water using [MnBr(CO)] as a precatalyst.

The development of earth-abundant catalysts for the selective conversion of silanes to silanols with water as an oxidant generating valuable hydrogen as the only by-product continues to be a challenge. Here, we demonstrate that [MnBr(CO)] is a highly active precatalyst for this reaction, operating under neutral conditions and avoiding the undesired formation of siloxanes. As a result, a broad substrate scope, including primary and secondary silanes, could be converted to the desired products.

From Divalent to Pentavalent Iron Imido Complexes and an Fe(V) Nitride via N-C Bond Cleavage.

As key intermediates in metal-catalyzed nitrogen-transfer chemistry, terminal imido complexes of iron have attracted significant attention for a long time. In search of versatile model compounds, the recently developed second-generation -anchored -NHC chelating ligand -[2-(3-mesityl-idazole-2-ylidene)-ethyl]amie (TIMMN) was utilized to synthesize and compare two series of mid- to high-valent iron alkyl imido complexes, including a reactive Fe(V) adamantyl imido intermediate en route to an isolable Fe(V) nitrido complex. The chemistry toward the iron adamantyl imides was achieved by reacting the Fe(I) precursor [(TIMMN)Fe(N)] () with 1-adamantyl azide to yield the corresponding trivalent iron imide.

Improved Itaconate Production with via Co-Metabolism of CO-Derived Formate.

In recent years, it was shown that itaconic acid can be produced from glucose with strains at up to maximum theoretical yield. The use of acetate and formate as co-feedstocks can boost the efficiency of itaconate production with Ustilaginaceae wild-type strains by reducing the glucose amount and thus the agricultural land required for the biotechnological production of this chemical. Metabolically engineered strains ( Δ Δ ↑P and Δ Δ P ↑P) were applied in itaconate production, obtaining a titer of 56.

Modulating the frontier orbitals of L(X)Ga-substituted diphosphenes [L(X)GaP] (X = Cl, Br) and their facile oxidation to radical cations.

Modulating the electronic structures of main group element compounds is crucial to control their chemical reactivity. Herein we report on the synthesis, frontier orbital modulation, and one-electron oxidation of two L(X)Ga-substituted diphosphenes [L(X)GaP] (X = Cl 2a, Br 2b; L = HC[C(Me)N(Ar)], Ar = 2,6-PrCH). Photolysis of L(Cl)GaPCO 1 gave [L(Cl)GaP]2a, which reacted with MeSiBr with halide exchange to [L(Br)GaP]2b.

Light-induced reversible reorganizations in closed Type II reaction centre complexes: physiological roles and physical mechanisms.

The purpose of this review is to outline our understanding of the nature, mechanism and physiological significance of light-induced reversible reorganizations in closed Type II reaction centre (RC) complexes. In the so-called 'closed' state, purple bacterial RC (bRC) and photosystem II (PSII) RC complexes are incapable of generating additional stable charge separation. Yet, upon continued excitation they display well-discernible changes in their photophysical and photochemical parameters.

Disentangling the Effect of Pressure and Mixing on a Mechanochemical Bromination Reaction by Solid-State NMR Spectroscopy.

Mechanical forces, including compressive stresses, have a significant impact on chemical reactions. Besides the preparative opportunities, mechanochemical conditions benefit from the absence of any organic solvent, the possibility of a significant synthetic acceleration and unique reaction pathways. Together with an accurate characterization of ball-milling products, the development of a deeper mechanistic understanding of the occurring transformations at a molecular level is critical for fully grasping the potential of organic mechanosynthesis.