Noble Metal Complexes Research Articles

Photoinduced Metal-Free Decarboxylative Fluoroalkylation of Alkenes for the Synthesis of N-Arylbutanamides and Oxindoles.

The visible light-induced decarboxylative cascade reaction of fluoroalkyl carboxylic acids has been achieved for the efficient synthesis of fluorinated compounds. However, most of the transformations rely on noble iridium metal complex. Herein, a visible light-induced metal-free decarboxylative cascade reaction of fluoroalkyl carboxylic acids has been realized. This protocol features simple operation, transition metal, and good functional group tolerance.

Facile Synthesis of Ultra-Small Silver Nanoparticles Stabilized on Carbon Nanospheres for the Etherification of Silanes.

The dehydrocoupling reaction between alcohols and hydrosilanes is considered to be one of the most atom-economical ways to produce Si-O coupling compounds because its byproduct is only hydrogen (H2), which make it extremely environmentally friendly. In past decades, various kinds of homogeneous catalysts for the dehydrocoupling of alcohols and hydrosilanes, such as transition metal complexes, alkaline earth metals, alkali metals, and noble metal complexes, have been reported for their good activity and selectivity. Nevertheless, the practical applications of these catalysts still remain unsatisfactory, which is mainly restricted by environmental impact and non-reusability. A facile and recyclable heterogeneous catalyst, ultra-small Ag nanoparticles supported on porous carbon (Ag/C) for the etherification of silanes, has been developed. It has high catalytic activity for the Si-O coupling reaction, and the apparent activation energy of the reaction is about 30 kJ/mol. The ultra-small Ag nanoparticles dispersed in the catalyst through the carrier C have an enrichment effect on all reactants, which makes the reactants reach the adsorption saturation state on the surface of Ag nanoparticles, thus accelerating the coupling reaction process and verifying that the kinetics of the reaction of the catalyst indicate a zero-grade reaction.

Microenvironment-Responsive Targeted Nanomedicine for a Collaborative Integration of Tumor Theranostics and Bone Defect Repair.

Despite advancements in breast cancer treatment, bone metastases remain a significant concern for patients with advanced breast cancer. Current theranostics strategies face challenges in integrating tumor theranostics and bone formation. Herein, we developed an activatable targeted nanomedicine AuMnCO@BSA-N3 (AMCBN) to enable a novel collaborative integration of second near-infrared (NIR-II) fluorescence imaging guided precise theranostics for breast cancer bone metastases and osteogenic microenvironment remolding. This strategy employed a chemical coordination between noble metal complex and metal carbonyl (MnCO). The surface modification of azide groups for enhanced tumor affinity through passive and active targeting. The initiated respondent behavior of AMCBN by tumor microenvironment (H2O2/acidity) accelerate the degradation of coordinated MnCO, resulting in a rapid release of multifunctional agents for efficient chemodynamic therapy (CDT)/gas synergistic therapy. Meanwhile, the exceptional bone-binding properties enable the efficient and controlled release of Mn2+ ions and CO in the bone microenvironment, thereby facilitating the expression of osteogenesis-related proteins and establishing a novel synchronous theranostics process for tumor-bone repair. This article is protected by copyright. All rights reserved.

Synergistic Effects of MOFs and Noble Metals in Photocatalytic Reactions: Mechanisms and Applications.

Photocatalytic technology can efficiently convert solar energy to chemical energy and this process is considered as one of the green and sustainable technology for practical implementation. In recent years, metal-organic frameworks (MOFs) have attracted widespread attention due to their unique advantages and have been widely applied in the field of photocatalysis. Among them, noble metals have contributed significant advances to the field as effective catalysts in photocatalytic reactions. Importantly, noble metals can also form a synergistic catalytic effect with MOFs to further improve the efficiency of photocatalytic reactions. However, how to precisely control the synergistic effect between MOFs and noble metals to improve the photocatalytic performance of materials still needs to be further studied. In this review, the synergistic effects of MOFs and noble metal catalysts in photocatalytic reactions are firstly summarized in terms of noble metal nanoparticles, noble metal monoatoms, noble metal compounds, and noble metal complexes, and focus on the mechanisms and advantages of these synergistic effects, so as to provide useful guidance for the further research and application of MOFs and contribute to the development of the field of photocatalysis.

Highly efficient circularly polarized electroluminescence based on chiral manganese(ii) complexes.

Currently reported circularly polarized luminescent devices are primarily based on rare earth and noble metal complexes or lead perovskite materials. Reports on electroluminescent devices employing eco-friendly luminescent materials are notably scarce. In this study, we strategically designed and synthesized manganese complexes featuring Binapo as the chiral ligand. The complex structure reveals a tetrahedral coordination configuration, with the R/S configurations exhibiting a mirror relationship. Leveraging the strong ligand field and chiral structural characteristics of Binapo, the enantiomers display red emission and exhibit significant circularly polarized luminescence with a circularly polarized luminescence asymmetric factor (g lum) of 5.1 × 10-3. The circularly polarized electroluminescent performance was investigated by using a solution processing method and host-guest doping strategy. Our efforts resulted in device performance with an external quantum efficiency (EQE) exceeding 4%, and its electroluminescent asymmetric factor (g EL) reached an impressive -8.5 × 10-3. This surpasses the performance of most devices relying on platinum (Pt) and iridium (Ir) metal complexes and perovskite related materials. Our work establishes a pathway for the development of cost-effective and environmentally friendly chiral electroluminescent materials and devices.

Single-electron transfer reactions on surface-modified gold plasmons

Photoredox catalysis's relevance in organic synthesis research and innovation will increase in the coming decades. However, the processes rely almost exclusively on expensive noble metal complexes, most notably iridium complexes, to absorb light and transfer a single charge to a substrate or a catalyst to initiate cascade transformations. Light-triggered plasmon resonances generate a non-Fermi-Dirac energy distribution with many hot carriers that decay in ∼1 ps. Their ultrafast relaxation makes performing single electron transfer (SET) transformations challenging. Herein, a novel photosystem is proposed based on surface-modified gold nanoparticles (aka plasmon "molecularization"), which improved charge separation and, more importantly, enabled SET reactions, expanding the portfolio of photocatalysts available for photoredox catalysis. The photosystem was made into an electrode, permitting its use in photoelectrochemical arrangements that leverage electro- and photo-chemical approaches' benefits and chemical engineering solutions, helping the synthetic chemistry efforts towards greener synthesis and synthesis of more complex structures on a scale.

A Rising Star: Luminescent Carbene-Metal-Amide Complexes.

Coinage metal (gold, silver, and copper) complexes are attractive candidates to substitute the widely studied noble metal complexes, such as, iridium(III) and platinum(II), as luminescent materials in organic light-emitting diodes (OLEDs). However, the development of coinage metal complexes exhibiting high emission quantum yields and short exciton lifetimes is still a formidable challenge. In the past few years, coinage metal complexes featuring a carbene-metal-amide (CMA) motif have emerged as a new class of luminescent materials in OLEDs. Thanks to the coinage metal-bridged linear geometry, coplanar conformation, and the formation of excited states with dominant ligand-to-ligand charge transfer character and reduced metal d-orbital participation, most CMA complexes have high radiative rates via thermally activated delayed fluorescence. Currently, the family of CMA complexes have rapidly evolved and remarkable progresses in CMA-based OLEDs have been made. Here, a Concept article on CMA complexes is presented, with a focus on molecular design principles, the correlation between molecular structure/conformation and optoelectronic properties, as well as OLED performance. The future prospects of CMA complexes are also discussed.

Reactive Deposition Versus Strong Electrostatic Adsorption (SEA): A Key to Highly Active Single Atom Co-Catalysts in Photocatalytic H2 Generation.

In recent years, the use of single atoms (SAs) has become of a rapidly increasing significance in photocatalytic H2 generation; here SAnoble metals (mainly Pt SAs) can act as highly effective co-catalysts. The classic strategy to decorate oxide semiconductor surfaces with maximally dispersed SAs relies on "strong electrostatic adsorption" (SEA) of suitable noble metal complexes. In the case of TiO2 - the classic benchmark photocatalyst - SEA calls for adsorption of cationic Pt complexes such as [(NH3 )4 Pt]2+ which then are thermally reacted to surface-bound SAs. While SEA is widely used in literature, in the present work it is shown by a direct comparison that reactive attachment based on the reductive anchoring of SAs, e.g., from hexachloroplatinic(IV) acid (H2 PtCl6 )leads directly to SAs in a configuration with a significantly higher specific activity than SAs deposited with SEA - and this at a significantly lower Pt loading and without any thermal post-deposition treatments. Overall, the work demonstrates that the reactive deposition strategy is superior to the classic SEA concept as it provides a direct electronically well-connected SA-anchoring and thus leads to highly active single-atom sites in photocatalysis.

(η5‐CpR)Ge:]+[BArF4]−/O2 – A Sustainable and Efficient Catalytic System for the Hydrosilylation of Selected Olefins

AbstractThe cationic Ge(II) borates [(η5‐CpR)Ge:]+[BArF4]− (CpR=substituted cyclopentadienyl) efficiently catalyze the anti‐Markovnikov hydrosilylation of alkenes in the presence of oxygen which is investigated using the examples of α‐methylstyrene and 1‐hexene. Full conversion is achieved with a minimal amount of 0.01 mol % of the cationic Ge(II) borate even at rt. The effect of oxygen is investigated and quantified by kinetic measurements which demonstrate that oxygen is an activator which interacts directly with the germanium complex. Solvent‐free hydrosilylation conditions are realized by the introduction of a more lipophilic silylated borate counteranion. Thus, the novel catalytic system is an efficient, sustainable and air‐stable catalyst alternative for the established hydrosilylation catalysts based on noble metal complexes.

Recent Development of Single-Atom Catalysis for the Functionalization of Alkenes

The functionalization of alkenes is one of the most important conversions in synthetic chemistry to prepare numerous fine chemicals. Typical procedures, such as hydrosilylation and hydroformylation, are traditionally catalyzed using homogeneous noble metal complexes, while the highly reactive and stable heterogeneous single-atom catalysts (SACs) now provide alternative approaches to fulfill these conversions by combining the advantages of both homogeneous catalysts and heterogeneous nanoparticle catalysts. In this review, the recent achievement in single-atom catalyzed hydrosilylation and hydroformylation reactions are introduced, and we highlight the latest applications of SACs for additive reactions, constructing new C-Y (Y = B, P, S, N) bonds on the terminal carbon atoms of alkenes, and then mention the applications in single-metal-atom catalyzed hydrogenation and epoxidation reactions. We also note that some tandem reactions are conveniently realized in one pot by the concisely fabricated SACs, facilitating the preparation of some pharmaceutical compounds. Lastly, the challenges facing single-atom catalysis for alkene conversions are briefly mentioned.

Heteroleptic Square Planar Cobalt(I/II) Complexes

AbstractReduction of the cobalt(II) chloride complex, Ph2B(tBuIm)2Co(THF)Cl (1) in the presence of tBuN≡C affords the diamagnetic, square planar cobalt(I) complex Ph2B(tBuIm)2Co(C≡NtBu)2 (2). This is a rare example of a 16‐electron cobalt(I) complex that is structurally related to square planar noble metal complexes. Accordingly, the electronic structure of 2, as calculated by DFT, reveals that the HOMO is largely dz2 in character. Complex 2 is readily oxidized to its cobalt(II) congener [Ph2B(tBuIm)2Co(C=NtBu)2]BPh4 (3‐BPh4), whose EPR spectral parameters are characteristic of low‐spin d7 with an unpaired electron in an orbital of dz2 parentage. This is also consistent with the results of DFT calculations. Despite its 16‐electron configuration and the dz2 parentage of the HOMO, the only tractable reactions of 2 involve one electron oxidation to afford 3.

Mn(iii)-mediated C-P bond activation of diphosphines: toward a highly emissive phosphahelicene cation scaffold and modulated circularly polarized luminescence.

Transition metal mediated C-X (X = H, halogen) bond activation provides an impressive protocol for building polyaromatic hydrocarbons (PAHs) in C-C bond coupling and annulation; however, mimicking both the reaction model and Lewis acid mediator simultaneously in a hetero-PAH system for selective C-P bond cleavage faces unsolved challenges. At present, developing the C-P bond activation protocol of the phosphonic backbone using noble-metal complexes is a predominant passway for the construction of phosphine catalysts and P-center redox-dependent photoelectric semiconductors, but non-noble metal triggered methods are still elusive. Herein, we report Mn(iii)-mediated C-P bond activation and intramolecular cyclization of diphosphines by a redox-directed radical phosphonium process, generating phosphahelicene cations or phosphoniums with nice regioselectivity and substrate universality under mild conditions. Experiments and theoretical calculations revealed the existence of the unusual radical mechanism and electron-deficient character of novel phosphahelicenes. These rigid quaternary bonding skeletons facilitated versatile fluorescence with good tunability and excellent efficiency. Moreover, the enantiomerically enriched crystals of phosphahelicenes emitted intense circularly polarized luminescence (CPL). Notably, the modulated CPL of racemic phosphahelicenes was induced by chiral transmission in the cholesteric mesophase, showing ultrahigh asymmetry factors of CPL (+0.51, -0.48). Our findings provide a new approach for the design of emissive phosphahelicenes towards chiral emitters and synthesized precursors.

The Side-chain design of rhodamine dye and the performance research of photocatalytic hydrogen production system by the first principles

It is very important to seek visible light photosensitizers with high catalytic activity and continuous reaction stability to promote the development of the homogeneous photocatalytic hydrogen production. The study shows that the hydrogen production activity of organic dyes is higher than that of noble metal complexes under the same experimental conditions, so the pure organic dyes can effectively reduce the hydrogen production reaction cost under the premise of ensuring the photocatalytic activity. In this work, we take rhodamine photosensitizers S150 to replace S in the xanthene ring as the prototype and modify its structure by extending side chain. We further comprehensively study the electronic and optical properties of newly designed photosensitizer molecules by density functional theory (DFT). The results indicate that both S156 and S162 molecules exhibit excellent light absorption properties, such as wide range of absorption spectrum and good visible light response. The molar extinction coefficient of S156 molecule is as high as2.65×104M-1·cm-1. And the molecules that are screened out have a larger photoinduced electron transfer drive and more negative reduction potential. The reduction potential of S162 (-0.76 V vs SCE) is 22.6 % higher than that of S150, which suggests that S162 has more outstanding photocatalytic performance of hydrogen production than S150. So the dyes extended by the 3-(methoxymethyl) Heptane side chain are very promising candidates for homogeneous photocatalytic hydrogen production photosensitizer systems.

Broadband and strong visible-light-absorbing cuprous sensitizers for boosting photosynthesis

Rational construction of broadband and strong visible-light-absorbing (BSVLA) earth-abundant complexes is of great importance for efficient and sustainable solar energy utilization. Herein, we explore a universal Cu(I) center to couple with multiplestrong visible-light-absorbing antennas to break the energy level limitations of the current noble-metal complexes, resulting in the BSVLA nonprecious complex (Cu-3). Systematic investigations demonstrate that double "ping-pong" energy-transfer processes in Cu-3 involving resonance energy transfer and Dexter mechanism enable a BSVLA between 430 and 620 nm and an antenna-localized long-lived triplet state for efficient intermolecular electron/energy transfer. Impressively, Cu-3 exhibited an outstanding performance for both energy- and electron-transfer reactions. Pseudo-first-order rate constant of photooxidation of 1,5-dihydroxynaphthalene with Cu-3 can achieve a record value of 190.8 × 10-3 min-1 among the molecular catalytic systems, over 30 times higher than that with a noble-metal photosensitizer (PS) [Ru(bpy)3]2+. These findings pave the way to develop BSVLA earth-abundant PSs for boosting photosynthesis.

Photoactive Copper Complexes: Properties and Applications.

Photocatalyzed and photosensitized chemical processes have seen growing interest recently and have become among the most active areas of chemical research, notably due to their applications in fields such as medicine, chemical synthesis, material science or environmental chemistry. Among all homogeneous catalytic systems reported to date, photoactive copper(I) complexes have been shown to be especially attractive, not only as alternative to noble metal complexes, and have been extensively studied and utilized recently. They are at the core of this review article which is divided into two main sections. The first one focuses on an exhaustive and comprehensive overview of the structural, photophysical and electrochemical properties of mononuclear copper(I) complexes, typical examples highlighting the most critical structural parameters and their impact on the properties being presented to enlighten future design of photoactive copper(I) complexes. The second section is devoted to their main areas of application (photoredox catalysis of organic reactions and polymerization, hydrogen production, photoreduction of carbon dioxide and dye-sensitized solar cells), illustrating their progression from early systems to the current state-of-the-art and showcasing how some limitations of photoactive copper(I) complexes can be overcome with their high versatility.

Modulating the Surface and Photophysical Properties of Carbon Dots to Access Colloidal Photocatalysts for Cross-Couplings

Photoredox-mediated Ni-catalyzed cross-couplings are powerful transformations to form carbon–heteroatom bonds and are generally photocatalyzed by noble metal complexes. Low-cost and easy-to-prepare carbon dots (CDs) are attractive quasi-homogeneous photocatalyst alternatives, but their applicability is limited by their short photoluminescence (PL) lifetimes. By tuning the surface and PL properties of CDs, we designed colloidal CD nano-photocatalysts for a broad range of Ni-mediated cross-couplings between aryl halides and nucleophiles. In particular, a CD decorated with amino groups permitted coupling to a wide range of aryl halides and thiols under mild, base-free conditions. Mechanistic studies suggested dynamic quenching of the CD excited state by the Ni co-catalyst and identified that pyridinium iodide (pyHI), a previously used additive in metallaphotocatalyzed cross-couplings, can also act as a photocatalyst in such transformations.

A Theoretical Investigation into the Homo- and Hetero-leptic Cu(I) Phosphorescent Complexes Bearing 2,9-dimethyl-1,10-phenanthroline and bis [2-(diphenylphosphino)phenyl]ether Ligand.

Cu(I) complexes have received widespread attention as a promising alternative to traditional noble-metal complexes. Herein, we systematically study the properties of Cu(I) complexes from homo- to hetero-ligands, and found the following: (1) hetero-ligands are beneficial to regulate phosphorescent efficiency; (2) when the hetero-ligands in a tetracoordinated Cu(I) complex are 1:1, the ligands coordinate along the dx2-y2 direction of Cu(I) ion, which can observably suppress structural deformation; (3) unlike the P^P ligand, the N^N ligand can enhance the participation of Cu(I) during the transition process; (4) the addition of an appropriate amount of P^P ligand can effectively raise the energy level of HOMO (highest occupied molecular orbital), enhance the proportion of LLCT (ligand–ligand charge transfer), and thereby increase the available singlet emission transition moments which can be borrowed, thus promoting the radiative decay process. As a result, this work provides a detailed understanding of the effects of different ligands in Cu(I) complexes, and provides a valuable reference and theoretical basis for regulating and designing the phosphorescent properties of Cu(I) complexes in the future.

Electrochemical Recovery and Concentration of Noble Metals

Noble metals are integral materials to chemical and electronics industries for their unmatched chemical inertness, electrical conductivity, and catalytic activity. However, the growing demand for noble metals such as Pt, Pd, and Au is outpacing the dwindling supply, and without new recycle strategies these critical noble metal resources will run out. Therefore, energy and resource efficient noble metal recycling technologies are critical to develop sustainable use of these scarce and valuable resources. Recently, electrification of chemical process units has been receiving justifiable attention as an easily scalable means of increasing energy and material sustainability in industry, particularly for chemical separations. In particular, the incorporation of redox-active materials has been met with great success for chemical energy storage and chemical separations due to enhanced charge transfer and easily tunable target ion interactions. Here, we introduce an electrochemically mediated platform for capture, release, and up-concentration of noble metal complexes from mining ore, electronic waste, and valuable elements in industrial manufacturing, where favorable charge transfer binding of noble metals to electrode bound redox sites enables selective capture of target noble metals over other common competitors – all with the flick of a switch. Highlights of our system are its high uptake (>200 mg/g), selectivity (>5 vs competing ions), energy efficiency (<5 kJ/g-PGM), cyclability (>5000 reuse cycles), and scalability to flow system. Technoeconomic analysis of our system compared to current industrial separation technologies indicates economically significant improvements in capital and operating costs with our electrochemical noble metal recycling platform. By lowering the economic barrier of noble metal recycling, these critical materials can be sustainably used and reused for years to come.

Evolution of Gold in the Oxidation Zone of the Kopto Deposit (the Republic of Tuva, Russia)

Abstract —The Kopto deposit (northeastern Tuva) is assigned to gold ore objects with a combination of the Au–Cu–skarn and superposed quartz–gold–sulfide stockwork types of mineralization. From the surface, the ores underwent intense oxidation, which formed a zone of secondary gold enrichment, containing a supergene paragenesis with gold and silver chalcogenides and newly formed gold. The depth of distribution of oxidized ores from the surface is 80–90 m. The Au content varies from fractions of ppm to 150 ppm (on average, 30.8 ppm). Using computer thermodynamic modeling, it is shown how the ore gold–sulfide–quartz association transformed under oxidizing conditions with a decrease in the pH of solutions. Gold becomes more and more high-grade; acanthite appears and disappears; limonite prevails (pH = 1.65; Eh = 0.69 V). The conditions for the stability of pyrite, iron hydroxides, and gold and silver chalcogenides (petrovskaite (AgAuS) and uytenbogaardtite (Ag3AuS2)) have been estimated. It requires weakly acidic solutions with pH = 5–6 and Eh values close to zero, which ensures the stability of thiosulfate and hydrosulfide complexes of noble metals. The main difference between solutions in equilibrium with petrovskaite and uytenbogaardtite is the Ag/Au ratios, which are maximum in the first case and approximately equal in the second. The paper is concerned with a comparative analysis of the morphologic features of gold from primary and oxidized ores of the Kopto gold deposit. The aim of this work is to identify a set of signs of the supergene nature of gold and to assess the extent of its redistribution.

Recent advances in noble metal complex based photodynamic therapy.

Photodynamic therapy (PDT) utilizes light-activated photosensitizers (PSs) to generate toxic species for therapeutics. It has become an emerging solution for cancer treatment because of its specific spatiotemporal selectivity and minimal invasiveness. Noble metal (Ru, Ir and Pt) complexes are of increasing interest as photosensitizers for their excellent photophysical, photochemical, and photobiological properties. In this review, we highlight recent advancements in the development of noble metal complex photosensitizers for PDT during the last 5 years. We will summarize the design strategies of noble metal complexes for efficient and precise PDT, including increasing the light penetration depth, reducing the oxygen-dependent nature and improving target ability. Finally, we summarize recent efforts for the development of noble-based PSs and discuss the limitations of such PSs in clinical application and future perspectives in this field, such as the combination of PDT with other treatment modalities.