Simple Ligand Exchange Research Articles

Ruthenium(II) complexes of a tripodal phosphite ligand: Synthesis, characterization, and applications in catalytic dehydrogenation

The scaffold tris(8-quinolinyl)phosphite, (P(Oquin)3), can bind to metal centers as a bi- or a tridentate tripodal ligand, depending on the synthetic conditions and characteristics of the metal atom. Here the study of the coordinating properties of such chelate was extended to the synthesis and characterization of well-defined Ru(II)-halide complexes. The compound [κ3(N,P,N){P(Oquin)3}RuCl2(PPh3)] was obtained by simple ligand exchange on the precursor [(PPh3)3RuCl2]. Two isomers were observed by means of 31P{1H} NMR spectroscopy, and were partially separated by recrystallization in refluxing solvents, thus allowing their structure elucidation. X-ray diffraction analysis revealed that the two crystalline isomers have the formula [κ3(N,P,N){P(Oquin)3}RuCl2(PPh3)] with the phosphite ligand coordinated to the Ru(II) center either in a meridional or in a facial disposition. The mixture [κ3(N,P,N){P(Oquin)3}RuCl2(PPh3)] undergoes phosphine dissociation at temperatures over 100 °C, leading to the formation of [κ4(P,N3){P(Oquin)3}RuCl2]. This compound displays a tetradentate P(Oquin)3 chelate and is a suitable catalyst for the dehydrogenation of formic acid and the dehydrocoupling of methylphenylsilane.

Phenylethylammonium bromide-assisted solution-phase ligand exchange in CsPbBr3 quantum dot solar cells

CsPbBr3 quantum dots (QDs) have excellent optical properties and good phase stability, but the long-chain ligands on their surfaces affect the charge transfer between QDs. Here, we propose a simple ligand exchange strategy: solution-phase ligand exchange. By adding an acetone solution of phenylethylammonium bromide to the purification process of CsPbBr3 QDs, the long-chain ligands were effectively replaced and the electric coupling between QDs was improved. As a result, the power conversion efficiency of the solar cell was increased from 1.95% to 2.83%. Meanwhile, the stability of the devices was significantly improved in the unencapsulated case.

Palladium Complexes Derived from Waste as Catalysts for C-H Functionalisation and C-N Bond Formation

Three-way catalysts (TWCs) are widely used in vehicles to convert the exhaust emissions from internal combustion engines into less toxic pollutants. After around 8–10 years of use, the declining catalytic activity of TWCs causes them to need replacing, leading to the generation of substantial amounts of spent TWC material containing precious metals, including palladium. It has previously been reported that [NnBu4]2[Pd2I6] is obtained in high yield and purity from model TWC material using a simple, inexpensive and mild reaction based on tetrabutylammonium iodide in the presence of iodine. In this contribution, it is shown that, through a simple ligand exchange reaction, this dimeric recovery complex can be converted into PdI2(dppf) (dppf = 1,1′-bis(diphenylphosphino)ferrocene), which is a direct analogue of a commonly used catalyst, PdCl2(dppf). [NnBu4]2[Pd2I6] displayed high catalytic activity in the oxidative functionalisation of benzo[h]quinoline to 10-alkoxybenzo[h]quinoline and 8-methylquinoline to 8-(methoxymethyl)quinoline in the presence of an oxidant, PhI(OAc)2. Near-quantitative conversions to the desired product were obtained using a catalyst recovered from waste under milder conditions (50 °C, 1–2 mol% Pd loading) and shorter reaction times (2 h) than those typically used in the literature. The [NnBu4]2[Pd2I6] catalyst could also be recovered and re-used multiple times after the reaction, providing additional sustainability benefits. Both [NnBu4]2[Pd2I6] and PdI2(dppf) were also found to be active in Buchwald–Hartwig amination reactions, and their performance was optimised through a Design of Experiments (DoE) study. The optimised conditions for this waste-derived palladium catalyst (1–2 mol% Pd loading, 3–6 mol% of dppf) in a bioderived solvent, cyclopentyl methyl ether (CPME), offer a more sustainable approach to C-N bond formation than comparable amination protocols.

Water-soluble, SDS-functionalized CdSe/CdS/ZnS quantum dots for uranium detection in aqueous environments

Water-soluble fluorescent probes for conveniently and rapidly monitoring the hazardous uranyl ions (UO22+) in nuclear wastewater are crucial for public nuclear security. Herein, we demonstrated a water-soluble CdSe/CdS/ZnS QDs probe by substituting hydrophilic dodecyl sodium sulfate (SDS) ligands for the original hydrophobic oleic acid ligands toward the rapid and accurate detection of trace UO22+ in aqueous environments. From this simple ligand exchange mothed, the as-prepared QDs probe exhibited a narrow full width at half maximum (FWHM) of 53 nm with an emission peak at 666 nm. Benefiting from dynamic and static fluorescence quenching interaction, this probe represented a high sensitivity (a detect limit of 15.4 nM), a high selectivity with comparison of presettable eight metal ions), a high environmental stability (a recovery rate of 81–94 %) and a rapid inspection ability (on the order of a few minutes). Therefore, this work provided a new approach for the determination of UO22+ in aqueous environments and then for the assurance of public nuclear security.

Reversible Assembly of Conductive Supragel Building Blocks by Metallo‐Complexes

AbstractThe design of multicomponent, building block‐based assemblies of polymer materials has gained tremendous interest due to the ability to combine functional variety and materials inside one integrated object. One such type of building blocks are polymer hydrogels that assemble into so‐called supragels. For that, it is necessary to implement reliable intra‐ and innerparticle cross‐linking methods that ensure mechanical stability and the supragels' adaptiveness over its life cycle, e.g., via selective assembly and disassembly. Here, a facile method for reversible interparticle cross‐linking of vinylimidazole‐based polymer hydrogel particles is presented. The method is based on supramolecular cross‐linking via transition metal complexation. Supragels consisting of four to 27 individual 3 × 3 × 3 mm particles are successfully obtained. By swelling the preassembled hydrogels inside aqueous solutions of Zn2+, Cu2+, and Fe2+ ions, stable interparticle linkage is achieved within 15 min. These supragels resist mechanical forces, but can be quantitatively disassembled into their corresponding building blocks by simple ligand exchange with ethylenediaminetetraacetic acid (EDTA). With this method, it is possible to quickly build hydrogel macrostructures of any shape and complexity, which exemplarily also exhibit electrical conductivity due to the introduction of metal ions for cross‐linking.

Selective Dehydrogenation of Formic Acid Catalyzed by Air‐Stable Cuboidal PN Molybdenum Sulfide Clusters

AbstractFormic acid is considered as a promising hydrogen storage material in the context of a green hydrogen economy. In this work, we present a series of aminophosphino and imidazolylamino Mo3S4 cuboidal clusters which are active and selective for formic acid dehydrogenation (FAD). Best results are obtained with the new [Mo3S4Cl3(ediprp)3](BPh4) (4(BPh4)) (ediprp=(2‐(diisopropylphosphino)ethylamine)) cluster, which is prepared through a simple ligand exchange process from the Mo3S4Cl4(PPh3)3(H2O)2 precursor. Under the conditions investigated, complex 4+ showed significantly improved performance (TOF=4048 h−1 and 3743 h−1 at 120 °C in propylene carbonate using N,N‐dimethyloctylamine as base after 10 min and 15 min, respectively) compared to the other reported molybdenum compounds. Mechanistic investigations based on stoichiometric and catalytic experiments show that cluster 4+ reacts with formic acid in the presence of a base to form formate substituted species [Mo3S4Cl3‐x(OCOH)x(ediprp)3]+ (x=1–3) from which the catalytic cycle starts. Subsequently, formate decarboxylation of the partially substituted [Mo3S4Cl3‐x(OCOH)x(ediprp)3]+ (x=1, 2, 3) catalyst through a β‐hydride transfer to the metal generates the trinuclear Mo3S4 cluster hydride. Dehydrogenation takes place through protonation by HCOOH to form Mo−H⋅⋅⋅HCOOH dihydrogen adducts, with regeneration of the Mo3S4 formate cluster. This proposal has been validated by DFT calculations.

Preparation strategy of bimetallic MOF hollow photocatalysts for hydrogen evolution

Hollow structure materials have been proved to be excellent photocatalysts due to their advantages in the separation of electron-hole pairs. However, the synthesis of such materials is complex, time-consuming, and poor versatility. In this study, Cu-DHTP/ZIF-67 (DHTP = 2,5-dihydroxyterephthalic acid) hollow materials containing both Co and Cu were designed and synthesized by a simple one-step etching and ligand exchange strategy. It is worth noting that the bimetallic hollow catalyst can be synthesized in the presence of both Cu(Ⅱ) and DHTP within 5 min at room temperature. The synthesized hollow bimetallic catalyst has improved photoresponse performance and electron-hole pair separation ability, which results in the best catalytic performance compared with DHTP/ZIF-67, Cu/ZIF-67, and ZIF-67 when used in the photocatalytic water splitting reaction. The hydrogen evolution yield of Cu-DHTP/ZIF-67 can reach 39.7 mmol g−1, which is 6 times than that of pure ZIF-67. This study demonstrates the promising potential of Cu-DHTP/ZIF-67 photocatalyst in the field of photocatalytic water reduction and hydrogen evolution, and provides a new idea for designing and preparing more hollow structure bimetallic photocatalysts with excellent performance.

High temperature flow synthesis of iron oxide nanoparticles: Size tuning via reactor engineering

Batch thermal decomposition syntheses of iron oxide nanoparticles (IONPs) provide precise control of particle properties, but their scalability and reproducibility is challenging. This is addressed in this work via a versatile high temperature flow reactor with adjustable temperature profiles through three individual stages operated between 180 °C and 280 °C. The tuneable temperature profiles in combination with self-seeded growth methods made it possible to synthesise IONPs between 2 and 17 nm (a size increase that corresponds to a >600 fold particle volume increase) at production rates of several gIONP per day. The precursor solutions contained only iron(III) acetylacetonate in a polyol solvent and no nucleation or growth inhibitors, oxidation or reducing agents, ligands or any other additives . This broad size range covers most biomedical applications and is of special interest for T1 MRI contrast agents (2–5 nm), as well as for magnetic hyperthermia cancer therapy (>10 nm). The potential of the IONPs produced was demonstrated by their high longitudinal relaxivity >16 mM−1s−1 at a transversal/longitudinal relaxivity ratio <2.5 (small IONPs) and specific absorption rates increasing with the IONP size up to180 W/gFe. In addition, the polyol method employed allowed for simple ligand exchange with biocompatible sodium tripolyphosphate to make the IONPs stable in water, thus rendering them suitable for biomedical applications. The continuous high temperature process presented shows how to control the particle size not via the chemistry (e.g., chemical additives affecting the particle size through the surface chemistry), but engineering parameters, i.e., reactor temperature profiles, reagent addition sequences and seeded growth strategies.

A reliable upconversion nanoparticle-based immunochromatographic assay for the highly sensitive determination of olaquindox in fish muscle and water samples

Olaquindox residues in food from its illegal use has received great attention. Here, an immunoassay strategy integrating an upconversion nanoparticle (UCNP)-based immunochromatographic strip with a fluorescence reader was proposed for the highly selective and sensitive detection of olaquindox. Polyacrylic acid-functionalized UCNPs were synthesized using a simple ligand exchange process and combined with an olaquindox polyclonal antibody to form a fluorescent probe. This approach achieved a sensitive response and specific recognition of olaquindox. A convenient upconversion fluorescence reader was introduced to implement accurate and sensitive quantitative analysis of olaquindox based on the fluorescence intensity of control and test lines on a strip. Under optimal conditions, the method demonstrated a favorable linear range (0–50 ng/mL) and sensitive detection (1.42 ng/mL, S/N = 3). This method was applied successfully to determine olaquindox in fish muscle and water samples, and results were consistent with an HPLC approach, and considered a promising strategy for monitoring olaquindox residuals.

Air-Stable and Environmentally Friendly Full Color-Emitting ZnSeTe/ZnSe/ZnS Quantum Dots for Display Applications

We have developed a nontoxic method of synthesizing blue-emitting ZnSeTe/ZnSe/ZnS quantum dots (QDs), which can be employed to realize QD-based electroluminescent displays. By introducing excessive metal halides without highly toxic hydrofluoric acid, we achieved a very high photoluminescence quantum yield reaching 94%. Furthermore, for the first time, air-stable ZnSeTe/ZnSe/ZnS QDs were demonstrated by employing simple surface ligand exchange performed both in solution and solid states. Various spectroscopic studies revealed that initial carboxylate ligands could be very effectively replaced by our simple ligand exchange at room temperature. In addition, we significantly broadened the spectral range of QDs by increasing the Te ratio of the core; therefore, green- and red-emitting ZnSeTe/ZnSe/ZnS QDs were demonstrated. The air-stable Zn-based QDs with full color emission developed in our study can be used as superior emitters in displays.

Clickable Polymer Ligand-Functionalized Iron Oxide Nanocubes: A Promising Nanoplatform for 'Local Hot Spots' Magnetically Triggered Drug Release.

Exploiting the local heat on the surface of magnetic nanoparticles (MNPs) upon exposure to an alternating magnetic field (AMF) to cleave thermal labile bonds represents an interesting approach in the context of remotely triggered drug delivery. Here, taking advantages of a simple and scalable two-step ligand exchange reaction, we have prepared iron oxide nanocubes (IONCs) functionalized with a novel multifunctional polymer ligand having multiple catechol moieties, furfuryl pendants, and polyethylene glycol (PEG) side chains. Catechol groups ensure a strong binding of the polymer ligands to the IONCs surface, while the PEG chains provide good colloidal stability to the polymer-coated IONCs. More importantly, furfuryl pendants on the polymer enable to click the molecules of interest (either maleimide-fluorescein or maleimide-doxorubicin) via a thermal labile Diels-Alder adduct. The resulting IONCs functionalized with a fluorescein/doxorubicin-conjugated polymer ligand exhibit good colloidal stability in buffer saline and serum solution along with outstanding heating performance in aqueous solution or even in viscous media (81% glycerol/water) when exposed to the AMF of clinical use. The release of conjugated bioactive molecules such as fluorescein and doxorubicin could be boosted by applying AMF conditions of clinical use (16 kAm-1 and 110 kHz). It is remarkable that the magnetic hyperthermia-mediated release of the dye/drug falls in the concentration range 1.0-5.0 μM at an IONCs dose as low as 0.5 gFe/L and at no macroscopical temperature change. This local release effect makes this magnetic nanoplatform a potential tool for drug delivery with remote magnetic hyperthermia actuation and with a dose-independent action of MNPs.

Activation Mechanism of Nickel(0) N-Heterocyclic Carbene Catalysts Stabilized by Fumarate Ligands.

Nickel(0) catalysts of N-heterocyclic carbenes (NHCs) that are stabilized by electron-deficient alkenes possess desirable properties of air tolerance and ease of handling while also retaining high catalytic activities. Since catalyst stability often comes at the expense of catalytic activity, we have undertaken a detailed study of the activation mechanism of an IMes-nickel(0) catalyst stabilized by di(o-tolyl) fumarate that converts the stable precatalyst form into a catalytically active species. Computational evaluation provided evidence against a simple ligand exchange as the activation mechanism for this catalyst, and a stoichiometric activation process that covalently modifies the stabilizing ligand was identified. A detailed computational picture for the activation process was developed, with predictive insights that elucidate an unexpected catalyst activation pathway that operates when ligand exchange is thermodynamically unfavorable.

Ligand Exchange Triggered Photosensitizers – Bodipy‐Tagged NHC‐Metal Complexes for Conversion of 3O2 to 1O2

AbstractA new imidazolium salt 3⋅HI with 8‐Bodipy as one N‐aryl substituent was synthesized from 8‐chloro‐Bodipy and imidazole followed by alkylation with iPrI. NHC‐metal complexes [CuCl(3)], [AuCl(3)], [Pd(allyl)Cl(3)] and [MCl(cod)(3)] and [MCl(CO)2(3)] (M=Rh, Ir) were synthesized and the X‐ray crystal structure of [IrCl(CO)2(3)] determined. The donation of NHC 3 was determined via IR (ν(CO) and cyclic voltammetry (Ir(I/II) redox potential). The photosensitizing properties of the complexes for the generation of 1O2 were quantified observing singlet oxygen quantum yield of up to Φs.o.=0.63. [IrCl(cod)(3)] displays poor Φs.o.=0.09, but, following a simple ligand exchange reaction of cod by two CO [IrCl(CO)2(3)], a pronounced increase to Φs.o.=0.63 is observed.

Synthesis of Mg Alkoxide Nanowires from Mg Alkoxide Nanoparticles upon Ligand Exchange.

We report on a new synthesis pathway for Mg n-propoxide nanowires (NWs) from Mg ethoxide nanoparticles using a simple alkoxy ligand exchange reaction followed by condensation polymerization in n-propanol. In order to uncover the morphology-structure correlation in the metal alkoxide family, we employed a powerful range of state-of-the-art characterization techniques. The morphology transformation from nanoparticles to nanowires was demonstrated by time-lapse SEM micrographs. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (such as 1H NMR and solid-state 13C cross-polarization (CP)-MAS NMR) illustrated the replacement of ethyl by n-propyl and metal alkoxide condensation polymerization. We identified chemical formulas of the products also using NMR spectroscopy. The crystal structure simulation of Mg ethoxide particles and Mg n-propoxide NWs provided insights on how the ligand exchange and the associated increase in the fraction of OH groups greatly enhanced Mg alkoxide bonding and enabled a higher degree of coordination polymerization to facilitate the formation and growth of the Mg n-propoxide NWs. The discovered synthesis method could be extended for the fabrication of other metal alkoxide (nano) structures with various morphologies.

CuInSe2 quantum dots doped MAPbI3 films with reduced trap density for perovskite solar cells

The organic-inorganic halide perovskite (OIHP) materials are becoming promising, but there is still inherent defect-mediated-carrier recombination in hybrid perovskite materials, thus, leading to inefficient power conversion efficiency (PCE). The defect states, which act as the recombination centers, are usually formed during crystallization process. Here, by a hot injection method, Na2S ligand exchange is applied to synthesize copper indium selenium quantum dots (CuInSe2 QDs), which are well dispersed in N,N-dimethylformamide (DMF) and then added into perovskite precursor solution. The resulted QD-in-perovskite structure is found to be beneficial for enlarging grain size, and thus exhibits an improved crystallinity and absorption due to the passivation of trap states. Hence, the perovskite solar cell (PSC) based on the MAPbI3-CuInSe2 QD hybrid film show an improved carrier lifetime from 58.17 ns to 243.23 ns and an enhanced PCE from 16.3% to 18.4% due to higher open-circuit voltage, compared to the cell device based on the pure perovskite film. Additionally, the optimized cell device presents better stability, which can still keep 75% of the initial PCE after 20-day storage. Such a simple Na2S ligand exchange to introduce QD into perovskite provides strong potential for preparing other hybrid materials.

Heterobimetallic uranyl(VI) alkoxides of lanthanoids: formation through simple ligand exchange.

Lanthanoid and actinoid silylamides are versatile starting materials. Herein we show how a simple ligand exchange with tert-butanol leads to the formation of the first trimeric heterobimetallic uranyl(VI)-lanthanoid(III) alkoxide complexes. The μ3 coordination of the endogenous uranyl oxo atom results in a significant elongation of the bond length and a significant deviation from the linear uranyl arrangement.

Enhancing the peroxidase-like activity of MIL-88B by ligand exchange with polydopamine.

Metal-organic frameworks (MOFs) as nanozymes have been widely used in biosensing. However, MOFs have inherent defects of easy agglomeration, leading to the stacking of active surfaces. In addition, the low conductivity of MOFs is not conducive to the electron migration in the Fenton-like reaction, which leads to a further decrease in catalytic activity and severely restricts their application. In response to the above problems, it makes sense to develop a method to improve both the dispersion and conductivity of MOFs. Here, a simple ligand exchange method with polydopamine (PDA) was used to synthesize MOF PDA-MIL-88B. PDA-MIL-88B shows stronger peroxidase-like activity than MIL-88B. One reason is the good dispersibility of PDA-MIL-88B, which is conducive to exposing the active surface. In addition, the reduced electrochemical impedance of PDA-MIL-88B increases its electrical conductivity, which is favorable for electron migration in the Fenton-like reaction. As a result, PDA-MIL-88B can better catalyze 3,3',5,5'-tetramethylbenzidine to achieve redoximorphic color changes. PDA-MIL-88B can be used to detect glucose in human serum with good sensitivity and selectivity. This work can provide a strategy for MOFs to enhance the enzyme-like activity.

Stable Iron Oxide Nanoflowers with Exceptional Magnetic Heating Efficiency: Simple and Fast Polyol Synthesis.

Magnetically induced hyperthermia has reached a milestone in medical nanoscience and in phase III clinical trials for cancer treatment. As it relies on the heat generated by magnetic nanoparticles (NPs) when exposed to an external alternating magnetic field, the heating ability of these NPs is of paramount importance, so is their synthesis. We present a simple and fast method to produce iron oxide nanostructures with excellent heating ability that are colloidally stable in water. A polyol process yielded biocompatible single core nanoparticles and nanoflowers. The effect of parameters such as the precursor concentration, polyol molecular weight as well as reaction time was studied, aiming to produce NPs with the highest possible heating rates. Polyacrylic acid facilitated the formation of excellent nanoheating agents iron oxide nanoflowers (IONFs) within 30 min. The progressive increase of the size of the NFs through applying a seeded growth approach resulted in outstanding enhancement of their heating efficiency with intrinsic loss parameter up to 8.49 nH m2 kgFe-1. The colloidal stability of the NFs was maintained when transferring to an aqueous solution via a simple ligand exchange protocol, replacing polyol ligands with biocompatible sodium tripolyphosphate to secure the IONPs long-term colloidal stabilization.

Reversible Ligand Exchange in Atomically Dispersed Catalysts for Modulating the Activity and Selectivity of the Oxygen Reduction Reaction.

Rational control of the coordination environment of atomically dispersed catalysts is pivotal to achieve desirable catalytic reactivity. We report the reversible control of coordination structure in atomically dispersed electrocatalysts via ligand exchange reactions to reversibly modulate their reactivity for oxygen reduction reaction (ORR). The CO-ligated atomically dispersed Rh catalyst exhibited ca. 30-fold higher ORR activity than the NHx -ligated catalyst, whereas the latter showed three times higher H2 O2 selectivity than the former. Post-treatments of the catalysts with CO or NH3 allowed the reversible exchange of CO and NHx ligands, which reversibly tuned oxidation state of metal centers and their ORR activity and selectivity. DFT calculations revealed that more reduced oxidation state of CO-ligated Rh site could further stabilize the *OOH intermediate, facilitating the two- and four-electron pathway ORR. The reversible ligand exchange reactions were generalized to Ir- and Pt-based catalysts.

Water-Dispersible Fe3O4 Nanoparticles Modified with Controlled Numbers of Carboxyl Moieties for Magnetic Induction Heating

Monodisperse Fe3O4 nanoparticles (NPs) with excellent water dispersibility and stability were prepared by the introduction of the carboxyl group (−COOH) on the surface of the as-prepared oleyl-capped Fe3O4 NPs. Controlled introduction of the COOH moieties on the NP surface was carried out by a simple ligand exchange reaction using two types of phosphonic acid ligands with dodecyl moiety and the terminal COOH group. The degree of modification of the COOH group on the particle surface was controlled by tuning the molar ratios of the two phosphonic acids. During the ligand exchange reaction, no change was observed in the crystal structure and morphology of the Fe3O4 NPs. The results of Fourier transform infrared (FT-IR) spectroscopy confirmed that the two ligands were bound to the Fe3O4 NP surface through their phosphoric acid functional groups. The surface coverage and molar ratios of the two ligands were evaluated by thermal gravimetric analysis (TGA) and via proton nuclear magnetic resonance (1H NMR) measurements, respectively. Results obtained from the thermal analyses were consistent with the initial molar ratios of the ligands used in the reaction, which reflect on the efficiency of the developed ligand exchange process. Our COOH-modified Fe3O4 NPs could be dispersed in water by deprotonation for over 6 months and exhibit a typical ferrofluid behavior without the addition of other surfactants and dispersants, showing high dispersion stability. Furthermore, the magnetic induction heating performance of the Fe3O4 NPs in aqueous dispersions was evaluated and the specific absorption rate (SAR) value was estimated to be 38.3 W/g Fe. These results suggest that our COOH-modified Fe3O4 NPs with the desired number of COOH surface moieties can be advantageous for applications such as precise surface design, water-based ferrofluid, and hyperthermia treatment.