Simple Ligand Exchange Reaction Research Articles

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.

Synthesis and characterization of volatile liquid Mo precursors for vapor phase deposition of thin films containing molybdenum

Volatile molybdenum precursors in liquid phase for vapor phase deposition of thin films containing molybdenum have been successfully synthesized. Heteroleptic liquid molybdenum precursors were prepared by treating MoCl5 with bidentate β-ketonate ligands such as 2,2,6,6-Tetramethyl-3,5-heptanedione (thdH) at different stoichiometric ratios (1:1 and 1:2). Molybdenum precursors in liquid phases also have been obtained via simple ligand-exchange reactions of Mo(thd)xCl4-x (x = 1 or 2) with LiNR2 (R = Et(C2H5), iPr(C3H7), SiMe3(Si(CH3)3)). The newly synthesized molybdenum precursors are readily miscible (soluble) in most organic solvents, such as acetonitrile, diethyl ether, and hexane. The chemical composition of these precursors has been characterized using Fourier-transform infrared analysis and nuclear magnetic resonance spectroscopy. The volatility and thermal stability of precursor compounds have also been investigated using thermogravimetric analysis and vapor pressure measurement. The strategy used in this experiment, which introduces bidentate ligands to the coordination sphere of the central molybdenum atom in MoCl5, improves the volatility and transferability of molybdenum precursors in gas-phase deposition processes by making them in a liquid phase.

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.

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.

Fe-doped Co-N/C as effective electrocatalyst for oxygen reaction

The development of cost-effective bifunctional electrocatalysts for metal-air batteries with high electrocatalytic activity and stability is crucial for the conversion of clean and renewable energy. In this work, Fe doped nitrogen-enriched porous carbon derived from ZIF-67 was synthesized via a simple ligand exchange reaction with subsequent calcination and acid leaching treatment. The catalysts pyrolysis at 700 °C (CoFe@NC-700) exhibited high electrocatalytic activity and superior stability toward oxygen reaction. Larger surface area and abundant mesopores structure are advantageous for charge transportation and exposure of active sites. More importantly, the synergistic effect of Co–N and Fe–N active sites and the increased number of active sites by modulating the local electronic structure further enhance the electrocatalytic performance of the as-prepared CoFe@NC-700.

Bisphosphonate Polymeric Ligands on Inorganic Nanoparticles

The design and synthesis of anchoring groups of bisphosphonate-amine (BP-NH2) are presented for the preparation of polymeric ligands on luminescent nanoparticles (NPs). Such ligands serve as overcoatings to impart colloidal stability and conjugation chemistries. These ligands were placed on quantum dots (QDs), gold nanoparticles (AuNPs), gold nanourchins (AuNUs), and iron oxide NPs (IONPs). The BP-NH2 anchoring groups were coupled to copolymers comprised of amine-terminated poly(ethylene glycol) (NH2-PEG) and poly(isobutylene-alt-maleic anhydride) (PIMA) units via aza-Michael coupling. In all cases, polymer synthesis was done as a one-pot reaction of amine-containing precursors with PIMA. The BP-NH2 anchoring groups provided similar colloidal stability as monophosphonate-amine (MP-NH2) anchoring groups on AuNPs. QDs were found to be more optically stable when coated with BP-NH2 vs MP-NH2 functionalized polymers in high-ionic-strength buffers, such as 5× phosphate-buffered saline (PBS). The versatility of BP–PIMA–PEG as universal NP overcoating chemistry was demonstrated through successful application onto IONPs and AuNUs of various sizes (50, 60, 80, and 100 nm in diameter) via simple ligand exchange reactions. Polymers that were functionalized with azide groups were prepared as substrates suitable for copper-free click chemistry addition of alkyne dyes. Successful coupling of dyes to the azide-copolymer-coated nanoparticles was verified by spectroscopic investigations of near-field resonance energy transfer (RET) interactions. Thus, a series of surface coordinating polymers with affinity to multiple materials were synthesized that yielded nanoparticles exhibiting good colloidal stability and that were amenable to subsequent conjugation reactions.

Synthesis of Chloro(phenyl)trifluoromethyliodane and Catalyst-Free Electrophilic Trifluoromethylations.

The present work deals with a challenge in the synthesis of aryltrifluoromethyliodanes (ArICF3X) and develops a direct route to PhICF3Cl via a simple ligand-exchange reaction of PhI(OCOCF3)2, Me3SiCF3, and NaCl for the first time. The I-Cl bond length in PhICF3Cl supports its iodonium character, which enables an enhanced CF3-transfer capability in electrophilic S-, O-, N-, and C-trifluoromethylations as well as in catalyst-free trifluoromethylation-cyclizations of arylisonitriles.

Synthesis of Janus-like gold nanoparticles with hydrophilic/hydrophobic faces by surface ligand exchange and their self-assemblies in water.

This study aims at the synthesis of Janus gold nanoparticles (Janus GNPs) with hydrophilic/hydrophobic faces by a simple ligand exchange reaction in an homogeneous system and at the elucidation of the self-assembled structures of the Janus GNPs in water. As hydrophilic surface ligands, we synthesized hexaethylene glycol (E6)-terminated thiolate ligands with C3, C7, or C11 alkyl chains, referred to as E6C3, E6C7, and E6C11, respectively. As a hydrophobic ligand, a butyl-headed thiolate ligand C4-E6C11, in which a C4 alkyl was introduced on the E6C11 terminus, was synthesized. The degree of segregation between the two ligands on the GNPs (5 nm in diameter) was examined by matrix-assisted laser desorption/ionization time-of fright mass spectrometry (MALDI-TOF MS) analysis. We found that the choice of immobilization methods, one-step or two-step addition of the two ligands to the GNP solution, crucially affects the degree of segregation. The two-step addition of a hydrophilic ligand (E6C3) followed by a hydrophobic ligand (C4-E6C11) produced a large degree of segregation on the GNPs, providing Janus-like GNPs. When dispersed in water, these Janus-like GNPs formed assemblies of ∼160 nm in diameter, whereas Domain GNPs, in which the two ligands formed partial domains on the surface, were precipitated even when the molar ratio of the hydrophilic ligand and the hydrophobic ligand on the surface of the NPs was almost 1:1. The assembled structure of the Janus-like GNPs in water was directly observed by pulsed coherent X-ray solution scattering using an X-ray free-electron laser, revealing irregular spherical structures with uneven surfaces.

Sequential surface modification of au nanoparticles: from surface-bound Ag(I) complexes to Ag(0) doping.

Gold nanoparticles (Au NPs) with tailor-made structures and properties are highly desirable for applications in catalysis and sensing. In this context, surface modifications of Au NPs are of particular relevance. Herein, we present a sequential surface modification of Au NPs with Ag(I) coordination complexes, which can be converted into Ag(0)-doped Au NPs by simple ligand-exchange reaction. The key innovative element of this surface modification is a multifunctional bioxazoline-based ligand that brings coordinated Ag(I) into close proximity to the particle surface.

Simple Ligand Exchange Reactions Enabling Excellent Dispersibility and Stability of Magnetic Nanoparticles in Polar Organic, Aromatic, and Protic Solvents

The use of magnetic nanoparticles (MNPs) in real-world applications is often limited by the lack of stable solutions of monodisperse NPs in appropriate solvents. We report a facile one-pot ligand exchange reaction that is fast, efficient, and thorough for the synthesis of hydrophilic MNPs that are readily dispersed in polar organic and protic solvents (polarity index = 3.9-7.2) including alcohols, THF, DMF, and DMSO for years without precipitation. We emphasize the rational selection of small-molecule ligands such as 4-hydroxybenzoic acid (HBA), 3-(4-hydroxyphenyl)propionic acid (HPP), and gallic acid (GAL) that provide strong bonding with the MNP (FePt and FeOx) surfaces, hydrophilic termini to match the polarity of target solvents, and offer the potential for hydrogen-bonding interactions to facilitate incorporation into polymers and other media. Areal ligand densities (Σ) calculated based on the NP core size from transmission electron microscopy (TEM) images, and the inorganic fractions of NPs derived from thermogravimetric analysis (TGA) indicated a significant (2-4 times) increase in the ligand coverage after the exchange reactions. Fourier transform infrared spectrometry (FTIR) and (1)H nuclear magnetic resonance (NMR) studies also confirmed anchoring of carboxyl groups on NP surfaces. In addition, we demonstrate a facile one-step in situ synthesis of FePt NPs with aromatic ligands for better dispersibility in solvents of intermediate polarity (polarity index = 1.0-3.5) such as toluene, chlorobenzene, and dichloromethane. The creation of stable dispersions of NPs in solvents across the polarity spectrum opens up new applications and new processing widows for creating NP composites in a variety of host materials.

Construction of an organoruthenium complex (–[biphRuCp]PF6–) within a biphenylene-bridged inorganic–organic hybrid mesoporous material, and its catalytic activity in the selective hydrosilylation of 1-hexyne

An organoruthenium complex (–[biphRuCp]PF6–; biph = –(C6H4)2–, Cp = C5H5), constructed within a biphenylene-bridged inorganic–organic hybrid mesoporous material (HMM–biph) by use of a simple ligand-exchange reaction, has been used as a heterogeneous catalyst. UV–visible and X-ray absorption fine structure (XAFS) studies furnished evidence that the structure of the complex is closely similar to that of [(C6H6)RuCp]PF6, suggesting that the biphenylene moiety within HMM–biph directly coordinates the metal center of the organoruthenium complex. The –[biphRuCp]PF6– complex constructed within the HMM–biph (HMM–biphRuCp) catalyzes hydrosilylation of 1-hexyne with triethylsilane in a solid–gas heterogeneous system and gives α-vinylsilane as a main product. Moreover, HMM–biphRuCp has higher catalytic activity than the –[phRuCp]PF6– (ph = –C6H4–) complex constructed within phenylene-bridged HMM (HMM–phRuCp). The high catalytic performance of HMM–biphRuCp can be attributed to the high loading of the HMM–biph with the Ru complex, because of the electron-donating ability of the biphenylene moieties.

Solvent dependent mechanistic pathways for η-O2CCH3 substitution from the [Mo3(μ3-O)2(μ-O2CCH3)6(η-O2CCH3)3]− anion

Rate coefficients for terminal acetate (η-O2CCH3) substitution from the [Mo3(μ3-O)2(μ-O2CCH3)6(η-O2CCH3)3]− anion were examined in polar protic (D2O and methanol-d4), polar aprotic (DMSO-d6 and DMF-d7) and acidic solvents (acetic acid-d4). Reaction rates were determined using variable-temperature 1H NMR and found to span orders of magnitude depending on the solvent (k298 K (s−1)=7.2×10−6 for D2O, 2.6×10−5 for methanol-d4, 3.7×10−4 for acetic acid-d4; no reaction for DMSO-d6 and DMF-d7). Unlike D2O and methanol-d4, little to no reaction occurs in DMSO-d6 and DMF-d7 most likely because the aprotic solvent is not able to solvate the leaving acetate ligand through hydrogen bonding. Activation parameters show that acetate substitution in polar protic solvents follows a dissociative pathway (D2O: ΔH‡=126 (±6) kJmol−1 and ΔS‡=80 (±18) Jmol−1K−1; methanol-d4: ΔH‡=115 (±3) kJmol−1 and ΔS‡=52 (±9) Jmol−1K−1) while parameters for acetate exchange in acetic acid-d4 are markedly different and suggest a mechanism more complex than a simple ligand exchange reaction (ΔH‡obs=63 (±12) kJmol−1 and ΔS‡obs=−97 (±40) Jmol−1K−1).

Solvent dependent anion dissociation limits copper(i) catalysed atom transfer reactions

Atom transfer radical addition (ATRA) and polymerisation (ATRP) reactions are commonly catalyzed by copper(I) complexes which react, reversibly, with a dormant alkyl halide initiator (RX) releasing a reactive organic radical R˙. The copper catalyst bears a multidentate N-donor ligand (L) and the active catalyst is simply Cu(I)L. The role of the catalyst in these reactions is to abstract a halogen atom from RX forming the corresponding higher oxidation state species Cu(II)LX. However, in order to perform its catalytic function (in multiple turnovers) the halido ligand must be released from the copper ion en route to regenerating the active catalyst Cu(I)L. In this work we investigate the kinetics of the Cu(I)LX/Cu(I)L equilibrium where L is the tridentate N,N,N',N'',N''-pentamethyl-diethylenetriamine (PMDETA). Using electrochemical analysis we find that the rate of formation of the active catalyst Cu(I)L is strongly dependent on solvent. We demonstrate that both the kinetics and thermodynamics of this simple ligand exchange reaction are critical in the overall reaction pathway.

A Two‐Coordinate Palladium Complex with Two Dialkylphosphinyl Ligands

Navy blue crystals of a two-coordinate homoleptic palladium complex with two phosphinyl radical ligands was synthesized by a simple ligand-exchange reaction. Significant π interactions between orbitals of Pd and the SOMO of phosphinyl radicals are responsible for the diamagnetic character, the intense blue color, and short PPd distances. Hydrogenation of the complex gave the corresponding bis(dialkylhydrophosphine)palladium complex.

Small and Stable Phosphorylcholine Zwitterionic Quantum Dots for Weak Nonspecific Phagocytosis and Effective Tat Peptide Functionalization

Facile surface modification of quantum dots (QDs) to make them water-soluble, small, stable, antibiofouling, and functional is crucial for their biological applications. This study demonstrates a simple ligand-exchange reaction to convert hydrophobic CdSe/ZnS QDs into water-soluble QDs using amphiphilic, zwitterionic 11-mercaptoundecylphosphorylcholine (HS-PC). The phosphorylcholine (PC)-modified QDs (QD-PC) possess several advantages, such as small hydrodynamic diameter, good resistance to pH variations and high salinity, excellent stability in 100% human plasma, and low protein adsorption. Importantly, the PC modification endows the QDs with very low, nonspecific interaction with cells, and strongly minimizes nonspecific phagocytosis of QDs by macrophages. In addition, cell penetrating Tat peptide functionalized QDs can be easily produced by mixing Tat with HS-PC with various ratios, which is proved to effectively enhance QD ability to enter cells and accumulate around perinuclear region. Compared to traditional mercaptoundecanoic acid (MUA) modification, PC modification not only makes the cell penetrating QDs more stable and brighter, but also provides the Tat- and PC-conjugated QDs with much lower nonspecific phagocytic uptake than the Tat- and MUA-conjugated ones. This research will provide insights into designing suitable ligands for surface modification of QDs and improving biofunctional QD performance in biological applications.

Highly Sensitive Gold Nanoparticle-Based Colorimetric Sensing of Mercury(II) through Simple Ligand Exchange Reaction in Aqueous Media

A strategy for the rational design of a novel colorimetric sensor based on dithioerythritol-modified gold nanoparticles for the selective recognition of Hg2+ in aqueous media is presented. This approach relies on the combination of gold nanoparticles with Hg2+ through sulfur-Hg2+-sulfur interaction. The gold nanoparticles showed high selectivity toward Hg2+ with binding-induced red shift in the absorption spectra, with no response to major interfering cations such as Pb2+, Cd2+, and Cu2+ in the presence of ethylenediamine tetraacetic acid. The system responds to Hg2+ with a detection limit of 100 nM and might open a new avenue for the development of Hg2+ sensing probes.

Proton interaction in phosphate adsorption onto goethite

The adsorption of phosphate on goethite is generally modeled by assuming a simple ligand exchange reaction with surface hydroxyl groups. This study investigates the binding forms of phosphate on goethite by evaluating the proton interaction and surface charge change during phosphate adsorption. It is found that OH − release stoichiometry increases with phosphate coverage, which suggests that different mechanisms predominate at different phosphate loadings. It demonstrates that surface binding changes from monodentate complexation to bidentate complexation with increasing surface phosphate coverage. The net OH − release accompanying this transformation is best interpreted with a 2 p K a multisite model.

Pillars, Layers, Pores and Networks from Nickeltripyrrins: A Porphyrin Fragment as a Versatile Building Block for the Construction of Supramolecular Assemblies

Sterically hindered nickel- tripyrrins [Ni(trpy)X] with different di-, tri- and tetradentate anions X have been prepared with the aim of finding coordination polymers formed by self-association. The syntheses were performed by simple ligand-exchange reactions and proceeded successfully with the pseudohalides CN(-), OCN(-), SCN(-), SeCN(-), N(CN)(2) (-) (dicyanoamido, dca) and C(CN)(3) (-) (tricyanomethanido, tcm), the cyanidometallates [Ag(CN)(2)](-) and [Ni(CN)(4)](2-) and the salicylate anion (sal(-)). X-ray crystallographic analyses revealed that the complexes with cyanido and isocyanato ligands, as well as the compound with a salicylato ligand, are prototypes for structurally distinct monomeric species in the solid state, whereas one-dimensional coordination polymers or supramolecular three-dimensional networks are formed from all other combinations. The polymeric compounds display a variety of individual pillar and network architectures with functionalised pores and clefts and with the Ni(trpy) fragments in different relative orientations. Hydrogen bonding and pi stacking were found to be additional structure-directing effects, which increased the structural complexity of the system. The Ni(trpy) subunit has thus been proven to be a versatile building block for the construction of supramolecular assemblies and metal organic frameworks (MOFs) from pentacoordinate Ni(II) ions.

Synthesis and insertion reactions of the cyclometalated palladium-alkyl complexes Pd(CH(2)CMe(2)-o-C(6)H(4))L(2). Observation of a pentacoordinated intermediate in the insertion of SO(2).

Palladacycles of the type 2, have been synthesized by treatment of the corresponding chloroalkylcomplexes Pd(CH(2)CMe(2)C(6)H(5))ClL(2) (L(2) = (PMe(3))(2), 2a, or 1,5-cyclooctadiene (cod), 2b) with suitable bases, or by simple ligand exchange reactions from the cyclooctadiene derivative 2b. The metallacycles 2 react with activated alkynes and with sulfur dioxide, giving rise to different insertion products.