Molecular Metal Research Articles

Structure-Reactivity Relationship of Zeolite-Confined Rh Catalysts for Hydroformylation of Linear α-Olefins.

Substituting the molecular metal complexes used in the industrial olefin hydroformylation process is of great significance in fundamental research and practical application. One of the major difficulties in replacing the classic molecular metal catalysts with supported metal catalysts is the low chemoselectivity and regioselectivity of the supported metal catalysts because of the lack of a well-defined coordination environment of the metal active sites. In this work, we have systematically studied the influences of key factors (crystallinity, alkali promoters, etc.) of the Rh-MFI zeolite catalysts on their performances for the hydroformylation of long-chain α-olefins (LAOs). With the help of comprehensive spectroscopy and electron microscopy characterization results, we can correlate the structural features of various Rh-MFI catalysts and their catalytic performances. The resultant structure-reactivity relationship guides us to prepare a nanosized Rh-MFI catalyst, which exhibits about a 3-fold improvement in specific activity compared to the Rh-MFI catalyst with conventional crystallite sizes and maintains very high regioselectivity for hydroformylation of LAOs.

Design and engineering of microenvironments of supported catalysts toward more efficient chemical synthesis.

Catalytic species such as molecular catalysts and metal catalysts are commonly attached to varieties of supports to simplify their separation and recovery and accommodate various reaction conditions. The physicochemical microenvironments surrounding catalytic species play an important role in catalytic performance, and the rational design and engineering of microenvironments can achieve more efficient chemical synthesis, leading to greener and more sustainable catalysis. In this review, we highlight recent works addressing the topic of the design and engineering of microenvironments of supported catalysts, including supported molecular catalysts and supported metal catalysts. Six types of materials, including oxide nano/microparticle, mesoporous silica nanoparticle (MSN), polymer nanomaterial, reticular material, zeolite, and carbon-based nanomaterial, are widely used as supports for the immobilization of catalytic species. We summarize and discuss the synthesis and modification of supports and the positive effects of microenvironments on catalytic properties such as metal-support interaction, molecular recognition, pseudo-solvent effect, regulating mass transfer, steric effect, etc. These design principles and engineering strategies allow access to a better understanding of structure-property relationships and advance the development of more efficient catalytic processes.

Electrochemical exfoliation of graphite using aqueous ammonium hydrogen carbonate solution and the ability of the exfoliated product as a hydrogen production electrocatalyst support

Electrochemical exfoliation of graphite has attracted much attention as a practical mass production of two-dimensional graphene-like materials. There is an increasing desire to find new and improved methods to create unique exfoliated products with excellent functionality. We used aqueous ammonium hydrogen carbonate solution as a new electrolyte for anodic oxidative exfoliation of graphite. The exfoliated product has a porous two-dimensional structure, and it can be dispersed in water for over five years. The oxidized and defected porous surface serves as an ideal support for molecular metal complexes, effectively functioning as heterogeneous electrocatalysts for hydrogen production.

Photocatalytic CO2 Reduction to Formic Acid (HCOOH) By an Organocobalt Catalyst - Two Different Mechanisms with Temporal Evolution of Catalysis, Effectuated by Second Coordination Sphere Interactions

The photocatalytic reduction of CO2 to formic acid (HCOOH) using molecular transition metal complexes as catalysts is believed to proceed via two mechanisms: CO2 insertion into metal hydride bonds, or hydrogenation of CO2. We present herein CO2 reduction photocatalysis by a mononuclear organocobalt catalyst with second coordination sphere interactions, which uniquely demonstrates both pathways for the conversion of CO2 to HCOOH. This dual functionality is attributed to distinct active forms of the catalyst at different temporal stages of irradiation. We employ in-situ NMR spectroscopy to monitor potential catalytic intermediates during irradiation. These observed states align closely with the kinetic profiles of product evolution, proving to be a valuable method for an informed design of molecular photocatalytic CO2 reduction catalysts. Figure 1

Application of Molecular Silver Complexes for Efficient Electrochemical CO2 Reduction in Zero-Gap Electrolyzers

Powered by renewable sources the electrochemical conversion of CO2 can be a sustainable opportunity to generate fuels. In the past various molecular complexes have been studied in homogeneous, lab-scale systems for the electrochemical CO2 reduction. Lately the field of incorporating molecular metal complexes in heterogenous electrocatalysis emerged. This approach offers distinct advantages, such as well-defined and easily tunable environments around the active metal centers and enabling a deeper understanding of the structural features necessary for efficient catalysis. Factors like the presence of donor atoms and hydrophobicity play pivotal roles in influencing catalytic activity. Another advantage of using molecular complexes is the possibility of lower metal loadings per square centimeter compared to the usage of i.e. nanoparticles while maintaining the same activity level.[1] In recent years, our group has been focused on the integration and optimization of silver-based complexes in heterogenized systems and gas diffusion electrodes. Herein, we present our progress across two readily synthesized silver-based complexes: the Ag(tetraphenylporphyrin) and Ag(dithiacyclam)[2] complex. Although these complexes exhibited low to moderate performance in homogeneous electrocatalytic CO2 reduction, their integration into gas diffusion electrodes with a carbon black support led to a remarkable increase in faradaic efficiency for CO formation when used in scalable zero-gap electrolyzers. Performing lab scale screenings at current densities of 100 mA/cm2 with catalyst loadings of 0.5 mg/cm2 every complex exhibited a faradaic efficiency for CO formation above 90 %. Remarkably, even at a tenfold reduction in catalytic loading to 0.05 mg/cm2 the complexes’ performance was not decreased significantly. Further, these complexes also showed a high activity towards the formation of CO at elevated current densities of 300 mA/cm2, opening the gate towards electrolysis in application-orientated relevant conditions namely: even higher current densities over 500 mA/cm2, elevated temperatures of 60 °C and long-term measurements up to 100 hours.[1] Pellumbi, K.; Krisch, D.; Rettenmaier, C.; Awada, H.; Sun, H.; Song, L.; Sanden, S.; Hoof, L.; Messing, L.; junge Puring, K.; Siegmund, D.; Roldán Cuenya, B.; Schöfberger, W.; Apfel, U.-P Cell Reports Physical Science 4 2023, 101746.[2] Johnson, A.; Iffland, L.; Singh, K.; Apfel, U.-P.; Suntharalingam, K. A Dalton transactions 2021, 50 (17), 5779–5783. Figure 1

(Digital Presentation) Investigate the Reaction Mechanism in the C3H7OH Electrochemical Reduction Reaction from CO2 Using Dinuclear Cuprous Molecular Catalyst

The urgent global challenge of climate change and the depletion of energy resources have spotlighted the technology of converting carbon dioxide (CO2) into valuable carbon-based products. The CO2 reduction reaction (CO2RR) via metal complex molecules is expected to improve and enhance the electronic/chemical environment of the catalytic active sites through control with freely modulable organic ligands. The selectivity for the formation of formic acid and carbon monoxide from CO2 in organic solvents has been successfully controlled in some molecular catalysts by small structural differences in the ligands. For catalytic reactions in organic solvents, NMR and other common analytical methods can be used to follow structural changes and reaction intermediates during the reaction of unimolecular molecular catalysts. The study of detailed reaction processes has led to ligand design guidelines that contribute to higher reaction rates and improved selectivity.However, analytical methods still need to be developed for heterogeneous molecular catalysts used in water on electrodes. Catalysts capable of producing C2 products, such as ethylene and ethanol, require methods to detect intermediates in multi-electron reduction processes involving C-C coupling reactions. Current C2 producing molecular catalysts are known to decompose during reactions, turning into metals and not fully utilizing their precisely controlled active sites. Therefore, developing structurally stable molecular catalysts during reactions is critical to understanding these mechanisms.In this study, we have demonstrated a Br-bridged copper dinuclear molecular catalyst with high robustness for CO2/CO reduction reactions, producing C3+ products including C3H7OH beyond C2 products. Operando XAFS and various spectroscopic analyses show that the dinuclear molecular catalyst maintains a stable Cu(I) state during the reduction reaction, preventing decomposition. Operando spectroscopic analysis using localized surface plasmon resonance identifies key C2 and C3 coupling intermediates essential for C3 production. Reaction intermediates obtained by 13CO2-labeled operando analysis were also corroborated. DFT calculations propose a mechanism where the reaction proceeds at room temperature to form C3 coupling species. The transition state structures resulting from this mechanistic analysis suggest that the progression of C-C coupling in the Cu dinuclear molecular metal complex is facilitated by the formation of a CO2/CO-reduced intermediate species that bridges the two Cu active sites. The bridging intermediate can adjust the Cu-Cu distance during the reaction, attracting reducing species to one Cu side and accepting substrate to the other Cu side. C3H7OH is formed through C-C coupling at the bridging site in flexible Cu binuclear structures. The discovery of a robust molecular catalyst for C3+ production provides a molecular design guideline for developing next-generation catalysts for multicarbon CO2 reduction products.

(Invited) Photocatalytic and Electrochemical CO2 Reduction By Semiconductors, Metal Complexes, and the Combinations

The establishment of so-called artificial photosynthetic reactions that use solar energy to drive the synthesis of organic matter using CO2 and H2O as raw materials is significant for reducing CO2 emissions and realizing carriers of abundant solar energy in an environmentally friendly way. Our primary approach to artificial photosynthetic reactions is the combinatorial technologies that effectively utilize the excellent properties of solid semiconductor photocatalysts and molecular metal complex catalysts. 1 We have realized the low overpotential CO2 reduction reaction (CO2RR) combined with the H2O oxidation reaction (WOR), a pair reaction for artificial photosynthesis, in a single aqueous solution at near neutral pH (Figure 1). Simultaneous operation of the CO2RR and the WOR in a single solution is one of the concepts necessary to construct a simplified form of an artificial photosynthetic system that does not require a setup for separation of sites like the thylakoid membrane existing in natural photosynthetic process for CO2RR and WOR. We will explain a photocatalytic system functioning by a two-step photoexcitation (Z-scheme) mechanism in a self-organized manner using a mixture of particulate (CuGa)0.3Zn1.4S2, BiVO4, and Co complex ([Co(4,4’-dimethyl-2,2’-bipyridine)3]2+, ([Co-dmbpy])) having bipyridine ligands. Under visible light irradiation (λ > 420 nm), a photocatalytic reaction produces O2, and yields CO with a product selectivity of 98 % by suppressing competitive H2 generation in an aqueous NaHCO3 solution bubbled with gaseous CO2. 2 3 Experimental studies and DFT calculations suggest that the Co complex acts dual-functionally in synergy with (CuGa)0.3Zn1.4S2 and BiVO4: it behaves as an efficient ionic electron mediator, and also acts as a highly selective CO2RR cocatalyst after a structural change following the acceptance of photoexcited electrons from (CuGa)0.3Zn1.4S2.We have also constructed a PV-powered electrolyzer system by using catalysts and a photo absorber without precious metal elements toward the future realization of a low-cost and low-lifecycle CO2 emission system. Mn(I) complex polymer cathode4 and β-FeOOH:Ni hyperfine nanorod anode5, 6 were set in a gas diffusion flow reactor. The system demonstrated electrochemical CO2 to CO conversion with 94% selectivity at a very low cell voltage of 1.35 V, originating from a very low overpotential of CO2 reduction approaching the theoretical lower limit at the Mn(I) polymer catalyst. 7 A direct connection of the cathode and anode with a conventional Si solar cell achieved a solar-to-CO conversion efficiency of > 20% using an aqueous alkaline media.The stability and versatility of molecular catalysts is always a topic of debate. Long-term stability, high energy efficiency, and synthesis of high carbon chemicals by molecular metal complex catalysts will also be presented. In a gas diffusion electrode (GDE)-based gas flow system, a Co-tetrapyridino-porphyrazine complex supported on carbon black together with K salt promoted electrocatalytic CO2 reduction with a current density of 100 mA/cm2 and generated CO over at least one week with a selectivity of approximately 95%. The optimal catalyst gave a turnover number of 3,800,000 and an energy conversion efficiency of more than 62% at 200 mA/cm2. 8 A Br-bridged dinuclear Cu(I) complex electrochemically yielded high-value-added C3 products, C3H7OH, with high robustness during the reaction. 9 T. Morikawa, S. Sato, K. Sekizawa, T. M. Suzuki and T. Arai, Accounts of Chemical Research, 2022, 55, 933-943.T. M. Suzuki, S. Yoshino, K. Sekizawa, Y. Yamaguchi, A. Kudo and T. Morikawa, Applied Catalysis B: Environmental, 2022, 316, 121600.T. M. Suzuki, K. Nagatsuka, T. Nonaka, Y. Yamaguchi, N. Sakamoto, T. Uyama, K. Sekizawa, A. Kudo and T. Morikawa, Chemical Communications, 2023, 59, 12318-12321.S. Sato, K. Saita, K. Sekizawa, S. Maeda and T. Morikawa, ACS Catalysis, 2018, 8, 4452-4458.T. M. Suzuki, T. Nonaka, K. Kitazumi, N. Takahashi, S. Kosaka, Y. Matsuoka, K. Sekizawa, A. Suda and T. Morikawa, Bulletin of the Chemical Society of Japan, 2018, 91, 778–786.T. Arai, S. Sato, K. Sekizawa, T. M. Suzuki and T. Morikawa, Chemical Communications, 2019, 55, 237-240.K. Sekizawa, S. Sato, N. Sakamoto, T. M. Suzuki and T. Morikawa, ChemRxiv, 2024, DOI: 10.26434/chemrxiv-2024-brj46 DOI: 10.26434/chemrxiv-2024-brj46.S. Sato, K. Sekizawa, S. Shirai, N. Sakamoto and T. Morikawa, Science Advances, 2023, 9.N. Sakamoto, K. Sekizawa, S. Shirai, T. Nonaka, T. Arai, S. Sato and T. Morikawa, Nature Catalysis, 2024, in press., https://doi.org/10.1038/s41929-024-01147-y Figure 1

Comparative Analysis of Tetravalent Actinide Schiff Base Complexes: Influence of Donor and Ligand Backbone on Molecular Geometry and Metal Binding.

A series of isostructural early actinide AnIV complexes was synthesized in order to investigate the influence of a conjugated framework in the ligand backbone on An bonding. Therefore, the AnIV complexes [An(pyrophen)2] (An = Th, U, Np, and Pu) with the pure N-donor ligand bis(2-pyrrolecarbonylaldehyde)-o-phenylenediamine referred to as pyrophen, were synthesized and characterized. Solid state analysis via single-crystal X-ray diffraction (SC-XRD) reveals two sets of ligands binding in an almost orthogonal arrangement to the actinide center. For the larger actinides Th and U, the coordination sphere allows for additional coordination by a solvent molecule. Nuclear magnetic resonance spectroscopy (NMR) studies show the presence of highly symmetrical complexes in solution in good agreement with the solvent-free solid structures. While SC-XRD suggests mainly ionic binding, an analysis of paramagnetic NMR contributions and quantum chemical bond analysis hint towards significant covalency in the U, Np, and Pu compounds. This series of An complexes allowed for a thorough structural and theoretical comparison of a conjugated system to a closely related N-donor ligand (pyren)[1] as well as to the mixed N,O Schiff base ligands salophen (conjugated) and salen (non-conjugated).

Redox Self-Equilibration in Molecular Vanadium Oxide Mixtures Enables Multi-Electron Storage.

Polyoxometalates (POMs) are ideal components for reversible multi-electron storage in energy technologies. To-date, most redox-applications employ only single, individual POM species, which limits the number of electrons that can be stored within a given potential window. Here, we report that spontaneous redox self-equilibration during cluster synthesis leads to the formation of two structurally related polyoxovanadates which subsequently aggregate into co-crystals. This results in systems with significantly increased redox reactivity. The mixed POM system was formed by non-aqueous self-assembly of a vanadate precursor in the presence of Mg2+, resulting in two mixed-valent (VIV/V) species, [(MgOH)V13O33Cl]4- (={MgV13}) and the di-vanadium-functionalized species [V14O34Cl]4- (={V14}), which co-crystallize in a 1 : 1 molar stoichiometry. Experimental data indicate that in the native state, {MgV13} is reduced by three electrons, and {V14} is reduced by five electrons. Electrochemical studies in solution show, that the system can reversibly undergo up to fourteen redox transitions (tentatively assigned to twelve 1-electron processes and two 2-electron processes) in the potential range between -2.15 V to +1.35 V (vs Fc+/Fc). The study demonstrates how highly redox-active, well-defined molecular mixtures of mixed-valent molecular metal oxides can be accessed by redox-equilibration during synthesis, opening new avenues for molecular energy storage.

Redox‐Selbstequilibrierung in molekularen Vanadiumoxid‐ Mischungen ermöglicht Multi‐ Elektronenspeicherung

AbstractPolyoxometallate (POM) sind ideale Komponenten für die reversible Multielektronenspeicherung in der Energietechnik. Bislang werden in den meisten Redox‐Anwendungen nur einzelne POM‐Spezies verwendet, was die Anzahl der Elektronen, die innerhalb eines bestimmten Potenzialfensters gespeichert werden können, begrenzt. Hier berichten wir, dass eine spontane Redox‐ Selbstequilibrierung während der Clustersynthese zur Bildung von zwei strukturell verwandten Polyoxovanadaten führt, die anschließend zu Ko‐Kristallen aggregieren. Dies führt zu Systemen mit deutlich erhöhter Redox‐Reaktivität. Das gemischte POM‐System wurde durch nichtwässrige Selbstassemblierung einer Vanadat‐Vorstufe in Gegenwart von Mg2+ gebildet, was zu zwei gemischtvalenten (VIV/V) Spezies führte, [(MgOH)V13O33Cl]4− (={MgV13}) und der Di‐Vanadium‐funktionalisierten Spezies [V14O34Cl]4− (={V14}), die in einer 1 : 1‐Molstöchiometrie ko‐kristallisieren. Experimentelle Daten zeigen, dass {MgV13} im nativen Zustand um drei Elektronen und {V14} um fünf Elektronen reduziert ist. Elektrochemische Untersuchungen in Lösung zeigen, dass das System reversibel bis zu vierzehn Redoxübergänge (vorläufig zwölf 1‐Elektronen‐Prozesse und zwei 2‐Elektronen‐Prozessen zugeordnet) im Potenzialbereich zwischen −2,15 V und +1,35 V (gegen Fc+/Fc) durchlaufen kann. Die Studie zeigt, wie hochgradig redoxaktive, wohldefinierte Mischungen aus gemischtvalenten molekularen Metalloxiden durch Redox‐ Selbstequilibrierung während der Synthese zugänglich gemacht werden können, was neue Möglichkeiten für die molekulare Energiespeicherung eröffnet.

Structural Phase Transitions of Mg2NiH4 Induced by NiH4 Molecular Ion Distortion and Metal Lattice Deformation under High Pressures.

Experimental observations indicate that pressure treatments transform the monoclinic and orthorhombic low-temperature phases of Mg2NiH4 into an unresolved pseudocubic phase even at room temperatures, resembling the temperature-induced phase transformation of the material. This pressure-induced phase transformation is anticipated to involve deformations of the tetrahedrally bonded NiH4 molecular ion and the metal lattice. However, the precise mechanism underlying this transformation remains unclear. To elucidate this behavior, this study adopted first-principles density functional theory calculations to investigate the effect of applied pressure on the observed phase transition. The results revealed that the phase transition from the low-temperature phases to the pseudocubic phase occurs at approximately 8-9 GPa. Furthermore, at this pressure, the metal lattice deforms into an antifluorite-like structure, and the NiH4 molecular ion undergoes substantial distortion, resulting in the alignment of hydrogen atoms along the crystal axes of the metal lattice. Furthermore, through a comprehensive structural exploration, we successfully identified several tetragonal and orthorhombic models that are energetically more stable than the low-temperature phases at low pressures. These models are potential candidates for elucidating the pseudocubic phase observed in experiments. Overall, our findings are anticipated to enhance the current understanding of the structural changes occurring during pressure and temperature-induced phase transitions.

Supported Binuclear Gold Phosphine Complexes as CO Oxidation Catalysts: Insights into the Formation of Surface‐Stabilized Au Particles

Atomically precise gold phosphine complexes as precursors for supported Au catalysts tested in CO oxidation are presented. Using a variety of analytical techniques, including in situ and operando X‐ray absorption spectroscopy, it is discovered that minor changes in the ligand of the molecular complexes result in significantly different activation behaviors of supported Au catalysts under reaction conditions. When using [Au2(μ2‐POP)2]OTf2 (POP = tetraphenylphosphoxane) as single‐source precursor, an active supported oxidation catalyst in second light‐off is obtained, outperforming a commercial Au/TiO2 and a P‐free Au/Al2O3 reference catalyst. Conversely, using [Au2(μ2‐dppe)2]OTf2 (dppe = diphenylphosphinoethane) on alumina leads to a significant decrease in CO oxidation activity. This difference is attributed to the formation of P‐containing ligand residues on the support in the case of [Au2(μ2‐POP)2]OTf2/Al2O3, which enhances the thermal stability of the Au particles and affects the particle's electronic properties through charge transfer processes. This work provides insights into the dynamic ligand decomposition of molecular gold complexes under reaction conditions and demonstrates the delicate balance between the stabilization of Au particles, clusters, and complexes using ligands and the blocking of active sites. This knowledge will pave the way for the targeted use of molecular transition metal complexes as precursors in synthesizing surface‐stabilized nanoparticles.

Impact of Manufacturing Process and Compounding on Properties and Quality of Follow-On GLP-1 Polypeptide Drugs.

The prevalence of follow-on and compounded products of glucagon-like peptide-1 analogs is increasing. We assessed glucagon-like peptide-1 analogs semaglutide and liraglutide for purity, potential immunogenicity, and expected stability, by comparing a representative selection of commercially available follow-on drug substances (DSs) and drug products (DPs) with their corresponding originators. Tests included several chromatography methods coupled with ultraviolet and mass spectrometry detectors, inductively coupled plasma optical emission spectroscopy, inductively coupled plasma mass spectrometry, nuclear magnetic resonance, dissolution analyses, in silico peptide/major histocompatibility complex II-binding prediction, and fibrillation assays. Overall, 16 injectable semaglutide, 8 oral semaglutide, and 2 injectable liraglutide follow-on products were analyzed alongside originator products. Compared with originator, follow-on injectable semaglutide DSs and DPs had new impurities and impurity patterns, including high molecular weight proteins, trace metals, anions, counterions, and residual solvents. Analyses showed that several commercialized follow-on oral semaglutide DPs had a markedly lower quantity of semaglutide than the label claim, while dissolution tests indicated different semaglutide and sodium N-(8-[2-hydroxybenzoyl] amino)caprylate (SNAC) release profiles, which may reduce bioavailability. Neoepitopes were identified in DS and DP semaglutide follow-ons, indicating potential immunogenicity. Fibrillation assays showed increased fibrillation tendency and reduced physical stability in liraglutide follow-on DP samples compared with originator. This study highlights that differences in the manufacturing processes of follow-on semaglutide and liraglutide (vs those used for originators) can result in several changes to the DSs and DPs. The impact of these changes on efficacy and safety outcomes remains unknown and should be investigated by clinical studies.

Molecular sieves hybrid metal–organic framework for efficient simultaneously capturing carbon dioxide and collecting water from air

Water scarcity and climate change associated with global warming are two common challenges facing humankind. The simultaneous removal of water and carbon dioxide (CO2) from the air has become a popular candidate strategy to address these challenges. In this paper, molecular sieve@MOF composites were synthesized in-situ for the first time by adding ZSM-5 and HZSM-5 during the preparation of Mg/DOBDC. A comprehensive review of the air capture CO2 and water harvesting properties of the novel composites was also presented. Primarily, the effects of molecular sieve category and ratio on the composite were systematically investigated. Subsequently, the crystal structure, morphological composition and textural properties of the composites were characterized. Finally, CO2/H2O co-adsorption performance, adsorption and desorption cycle stability and adsorption mechanism were investigated. The results demonstrated that the metal nodes of Mg/DOBDC interacted with the molecular sieve surface functional groups to increase the metal active sites and porosity. The obtained 0.5HZSM-5@Mg/DOBDC MOF showed the maximum CO2 uptake of 15.90 mmol/g (0.1 MPa, 25 °C), which was 3.66 times the amount of Mg/DOBDC.

Pressure-induced generation of heterogeneous electrocatalytic metal hydride surfaces for sustainable hydrogen transfer

Metal hydrides are crucial intermediates in numerous catalytic reactions. Intensive efforts have been dedicated to constructing molecular metal hydrides, where toxic precursors and delicate mediators are usually involved. Herein, we demonstrate a facile pressure-induced methodology to generate a cost-effective heterogeneous electrocatalytic metal hydride surface for sustainable hydrogen transfer. Taking carbon dioxide (CO2) electroreduction as a model system and zinc (Zn), a well-known carbon monoxide (CO)-selective catalyst, as a model catalyst, we showcase a homogeneous-type hydrogen atom transfer process induced by heterogeneous hydride surfaces, enabling direct hydrogenation pathways traditionally considered “prohibited”. Specifically, the maximal Faradaic efficiency for formate is enhanced by ~fivefold to 83% under ambient conditions. Experimental and theoretical analyses reveal that unlike the distal hydrogenation route for CO2 to CO over pristine Zn, the Zn hydride surface enables direct hydrogenation at the carbon site of CO2 to form formate. This work provides a promising material platform for sustainable synthesis.

DFT Modeling of Coordination Polymerization of Polar Olefin Monomers by Molecular Metal Complexes

Introducing polar functional groups into polyolefin chains through polar olefin monomer coordination (co)polymerization can directly and significantly improve the surface properties of polymer materials and expand their application range. Therefore, the related research has always received considerable attention from both academia and industry. Many experimental studies have been reported in this field, and molecular metal complexes have shown high catalytic activity and selectivity in polar olefin monomer polymerizations. Although considerable DFT calculations have also been conducted for better understanding of the (co)polymerization performance, the factors governing the activity, selectivity, and molecular weight of resulting polymers are still ambiguous. This review mainly focuses on the DFT studies of polar olefin monomer coordination (co)polymerization catalyzed by molecular metal complexes in recent years, discussing the chain initiation and propagation, the origin of polymerization activity and selectivity, and the specific role of additives in the (co)polymerization reactions.

Multifaceted regulation of chiroptical properties and self‐assembly behaviors of chiral fluorescent polymers

AbstractThe multifaceted regulation of the chiroptical properties and self‐assembly behaviors of chiral fluorescent polymers is of great significance yet remains challenging to achieve. Herein, a series of novel salen‐based chiral fluorescent polymers with aggregation‐induced emission and varied substitution manners were facilely and efficiently synthesized. Multiple factors were systematically investigated on the chiroptical properties and self‐assembly performance of these polymers, which include molecular structures, solvent environments, metal coordination, and liquid crystal (LC) assemblies. Sutle change in the solvent composition can lead to diverse assembly morphologies of all these chiral polymers, from single‐handed helical fibers, helical toroids or loops, to spherical structures, consequently leading to an aggregation‐reduced circular dichroism (CD) phenomenon. The polymers bearing salen units show highly selective and reversible coordination with Zn2+ and can also induce multiple responses in the absorption, luminescence, CD, and circularly polarized luminescence (CPL) of these chiral fluorescent polymers via a coordination‐ and dissociation‐initiated self‐assembly tuning. Furthermore, a small amount of the chiral fluorescent polymer in can induce achiral nematic 4‐cyano‐4′‐n‐pentylbiphenyl (5CB) to form ordered chiral nematic LC phase with significant improvement in their CD and CPL signal. The absolute absorption and luminescent dissymmetry factors of the resulting supramolecular assemblies can reach the order of 10−1.

Light-Induced Redox Dynamics in Plasmonic Nanostructures and Photosensitizer Transition Metal Compounds

Solar energy harvesting is a nuanced scientific field that involves precise control across energy, time, and nanometer length scales. The understanding of how to harness sunlight to promote chemical reactions is vital for the advancement of renewable energy applications and a sustainable future. Limited knowledge of the precise chemical mechanisms underlying solar energy harvesting restricts widespread technological use and the development of photovoltaic devices that utilize light-harvesting biodegradable materials. My research focuses on developing a fundamental understanding of visible light-activated excited state chemistry that is of great importance in elucidating the mechanisms, structures, and design features for catalysis. In this talk, we will examine excited-state chemical structure dynamics in nanomaterials that use light-matter interactions to drive interfacial or intramolecular charge transfer. Steady-state and time-resolved optical/X-ray spectroscopy allow for the observation of these dynamics across an expansive timescale—from the seconds timescale of oxygen-evolving reactions to the ultrafast timescales of electronic and vibrational motion. Novel light-matter interactions in plasmonic nanostructures, biomimetic metal oxides, and molecular transition metal complexes will be discussed. The talk will conclude with future opportunities for expanding the scope of nanoscale photocatalysis and for designing enhanced localized control over excited-state chemistry.[1] E. A. Sprague-Klein*, X. He, M. W. Mara, B. J. Reinhart, S. Lee, L. M. Utschig, K. L. Mulfort, L. X. Chen*, D. M. Tiede*. “Photo-Electrochemical Effect in the Water Oxidation Catalyst Cobalt-Phosphate (CoPi),” ACS Energy Letters, 2022, 7, 9, 3129–3138. [2] N. L. Warren, U. Yunusa, A. B. Singhal, E. A. Sprague-Klein*. "Facilitating Excited-State Plasmonics and Photochemical Reaction Dynamics," Chemical Physics Reviews, (Accepted December 2023).[3] U. Yunusa, N. Warren, D. Schauer, P. Srivastava, E. Sprague-Klein*. "Plasmon resonance dynamics and enhancement effects in Tris(bipyridine)ruthenium(II) gold nanosphere oligomers," Nanoscale, (Under Review).

Understanding Ligand Effects on Bielectronic Transitions: Chemo‐ and Electroreduction of Rhodium Bis(Diphosphine) Complexes to Low Oxidation States

AbstractRhodium complexes in the −I and 0 oxidation states are of great potential interest in catalytic applications. In contrast to their rhodium +I congeners, however, the structural and electronic parameters governing their access and stability are far less understood. Herein, we investigate the two‐electron reduction of a parameterized series of bis(diphosphine) Rh complexes [Rh(dxpy)2]NTf2 (x=P‐substituent, y=alkanediyl bridging P atoms). Through (electro)reductions from the RhI parents, Rh−I d10‐complexes were obtained and characterized spectroscopically, including 103Rh NMR data. The reductive steps convolute with structural rearrangements from square planar to tetrahedral coordination. We found that the extent of these reorganisations defines whether the first E0(RhI/0) and second E0(Rh0/−I) reduction potentials are normally ordered, leading to monoelectronic stepwise transitions, or inverted, giving bielectronic events. Reductionist approaches based on Hammett parameters or the P−Rh‐P bite angles provide only partial correlations with the redox potentials. However, we identified the C−O stretch of analogue diphosphine complexes as an expedient computational parameter that enables these correlations through both electronic and geometric features, even in a predictive manner. Gaining control over two‐electron reduction behaviors through rationalized ligand effects has potential impact beyond Rh complexes, for molecular and enzymatic metal sites commonly exhibiting bielectronic transitions.

Understanding Ligand Effects on Bielectronic Transitions: Chemo- and Electroreduction of Rhodium Bis(Diphosphine) Complexes to Low Oxidation States.

Rhodium complexes in the -I and 0 oxidation states are of great potential interest in catalytic applications. In contrast to their rhodium +I congeners, however, the structural and electronic parameters governing their access and stability are far less understood. Herein, we investigate the two-electron reduction of a parameterized series of bis(diphosphine) Rh complexes [Rh(dxpy)2]NTf2 (x=P-substituent, y=alkanediyl bridging P atoms). Through (electro)reductions from the RhI parents, Rh-I d10-complexes were obtained and characterized spectroscopically, including 103Rh NMR data. The reductive steps convolute with structural rearrangements from square planar to tetrahedral coordination. We found that the extent of these reorganisations defines whether the first E0(RhI/0) and second E0(Rh0/-I) reduction potentials are normally ordered, leading to monoelectronic stepwise transitions, or inverted, giving bielectronic events. Reductionist approaches based on Hammett parameters or the P-Rh-P bite angles provide only partial correlations with the redox potentials. However, we identified the C-O stretch of analogue diphosphine complexes as an expedient computational parameter that enables these correlations through both electronic and geometric features, even in a predictive manner. Gaining control over two-electron reduction behaviors through rationalized ligand effects has potential impact beyond Rh complexes, for molecular and enzymatic metal sites commonly exhibiting bielectronic transitions.