Dinuclear Gold Catalysis: Are Two Gold Centers Better than One?

A common golden thread: The exact role of dinuclear gold species in catalysis has recently attracted considerable attention. Such well-defined complexes can now be isolated and fully characterized and may assist in elucidating the exact action of gold centers in gold-catalyzed reactions. In view of the latest developments in this area, possibilities now abound in terms of mechanistic exploration and novel catalyst design.     

Cyclophanes or Cyclodextrins: What is the Best Host for Aromatic Volatile Organic Compounds?

The first results of the complexing ability of cyclobis-(paraquat-p-phenylene) as supramolecular host with different aromatic volatile organic compounds are presented. The formation constants of cyclobis(paraquat-p-phenylene) with toluene and halogenobenzenes were determined in aqueous solution by static headspace associated with gas chromatography and compared with the ones obtained by cyclodextrins. The data indicated the formation of 1:1 inclusion compounds in both cases. The results underlined a greater complexation ability for cyclobis(paraquat-p-phenylene) which was confirmed by a theoretical study.     

Phosphate Diester Hydrolysis by Dinuclear Tb(III) Complexes with BDBPH in Second-order Dependence

In the past decade, many lanthanide metal complexes with polyazamacrocycle, Schiff base, and glycol ligands have been shown to enhance the rate of DNA-phosphate hydrolysis by seven orders of magnitude1-3. This efficiency results from the conjunction of hi…     

A Porphyrin Iron(III) π-Dication Species and its Relevance in Catalyst Design for the Umpolung of Nucleophiles

Isoporphyrins have recently been identified as remarkable species capable of turning the nucleophile attached to the porphyrin ring into an electrophile, thereby providing umpolung of reactivity (Inorg. Chem. 2022 , 61, 8105–8111). They are generated by nucleophilic attack on an iron(III) π-dication, a class of species that has received scant attention. Here, we explore the effect of the porphyrin meso-substituent and report a iron(III) π-dication bearing the meso-tetraphenylporphyrin (TPP) ligand. We provide an extensive study of the species by UV/Vis absorption, ²H NMR, EPR, applied field Mössbauer, and resonance Raman spectroscopy. We further explore the system's highly dynamic and tunable properties and address the nature of the axial ligands as well as the conformation of the porphyrin ring. The insights presented are essential for the rational design of catalysts for the umpolung of nucleophiles. Such catalytic avenues could for example provide a novel method for electrophilic chlorinations. We further examine the importance of electronic tuning of the porphyrin by nature of the meso-substituent as a factor in catalyst design.     

Pd–Porphyrin Oligomers Sensitized for Green‐to‐Blue Photon Upconversion: The More the Better?

A series of directly meso‐meso‐linked Pd–porphyrin oligomers (PdDTP‐M, PdDTP‐D, and PdDTP‐T) have been prepared. The absorption region and the light‐harvesting ability of the Pd–porphyrin oligomers are broadened and enhanced by increasing the number of Pd–porphyrin units. Triplet–triplet annihilation upconversion (TTA‐UC) systems were constructed by utilizing the Pd–porphyrin oligomers as the sensitizer and 9,10‐diphenylanthracene (DPA) as the acceptor in deaerated toluene and green‐to‐blue photon upconversion was observed upon excitation with a 532 nm laser. The triplet–triplet annihilation upconversion quantum efficiencies were found to be 6.2 %, 10.5 %, and 1.6 % for the [PdDTP‐M]/DPA, [PdDTP‐D]/DPA, and [PdDTP‐T]/DPA systems, respectively, under an excitation power density of 500 mW cm^?2. The photophysical processes of the TTA‐UC systems have been investigated in detail. The higher triplet–triplet annihilation upconversion quantum efficiency observed in the [PdDTP‐D]/DPA system can be rationalized by the enhanced light‐harvesting ability of PdDTP‐D at 532 nm. Under the same experimental conditions, the [PdDTP‐D]/DPA system produces more ³DPA* than the other two TTA‐UC systems, benefiting the triplet–triplet annihilation process. This work provides a useful way to develop efficient TTA‐UC systems with broad spectral response by using Pd–porphyrin oligomers as sensitizers.     

Thermodynamic Features of the Complexation of Neodymium(III) and Americium(III) by Lactate in Trifluoromethanesulfonate Media

The protonation of lactate has been studied in a variety of electrolyte solutions using microcalorimetry to reveal a distinct medium influence imposed on the thermochemistry of the equilibrium. The thermochemistry of lactate protonation, when studied directly in 1.0 mol⋅L⁻¹ sodium lactate, agreed well with the studies performed in trifluoromethanesulfonate (triflate). This thermodynamic agreement suggests that the physical chemistry of lactate in the solutions applicable to the TALSPEAK process—a solvent extraction method for separating trivalent actinides from trivalent lanthanides within the scope of used nuclear fuel processing efforts—may be simulated in triflate solutions. Potentiometry, spectrophotometry and microcalorimetry have been subsequently used to study the thermodynamic features of neodymium and americium complexation by lactate using triflate as a strong background electrolyte. Three successive mononuclear lactate complexes were identified for Nd(III) and Am(III). The stability constants for neodymium, β ₁₀₁=2.60±0.01, β ₁₀₂=4.66±0.02 and β ₁₀₃=5.6±0.1, and for americium, β ₁₀₁=2.60±0.06, β ₁₀₂=4.7±0.1 and β ₁₀₃=6.2±0.2, were found to closely agree with the thermodynamic studies reported in sodium perchlorate solutions. Consequently, the thermodynamic medium effect, imposed on the TALSPEAK-related solution equilibria by the presence of strong background electrolytes such as NaClO₄ and NaNO₃, does not significantly impact the speciation in solution.     

Is the enthalpy of fusion of tris(acetylacetonato)metal(III) complexes affected by their potential energy in the crystal state?

In this Article we present enthalpies of fusion and melting points obtained from new thermochemical measurements of tris(acetylacetonato)metal(III), M(acac)(3), complexes (M = Fe, Al, Cr, Mn, Co) using differential scanning calorimetry (DSC) and evaluate them in relation to their different values found in the literature. An enthalpy of fusion of 27.67 kJ mol(-)(1) was derived for Mn(acac)(3) from a symmetrical DSC thermogram captured for the first time. The enthalpy value was indirectly confirmed with the solubility measurements of Mn(acac)(3) in acetylacetone. A hypothesis has been stated that the enthalpy of fusion and the potential energy of M(acac)(3) in the crystal state may be related. To calculate molecular in-crystal potential energy, in this Article we proposed a molecular mechanics model for the M(acac)(3) class of compounds. Nine X-ray crystal structures of M(acac)(3) complexes (M = Fe, Al, V, Mn, Co, Cr, Sc) were included in the modeling. The conformational potential energy was minimized for a molecule surrounded by other molecules in the crystal lattice. The partial charges from two schemes, the electrostatic potential (ESP) fit and the natural population analysis (NPA), were used to construct two types of force fields to examine which force field type would yield a better fit with the experimental thermal properties. The final force fields were named FF-ESP and FF-NPA. Both force field sets reproduced well the experimental crystal data of nine M(acac)(3) complexes as well as of tris(3-methyl-2,4-pentanedionato-O,O')cobalt(III). Only in-crystal potential energies derived by FF-NPA yielded a significant correlation (correlation coefficient R = -0.71) with the measured enthalpies of fusion. The enthalpy of fusion for Co(acac)(3) could not be determined experimentally because of simultaneous decomposition and fusion, and it is predicted to be 33.2 kJ mol(-)(1) from the correlation regression line.     

Thermodynamic Quantities for the Different Steps Involved in the Oxidation of the Drug Ketorolac by Copper(III) Periodate Complex in Aqueous Alkaline Medium: A Mechanistic Approach

The oxidation of ketorolac (KET) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.10 mol⋅dm⁻³ was studied spectrophotometrically at 298 K. The reaction is of first order in [DPC] and has less than unit order in both [KET] and [alkali], and negative fractional order in [periodate]. The oxidation reaction in alkaline medium has been shown to proceed via a DPC-ketorolac complex, which decomposes slowly in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test, IR and GC-MS spectral studies. The reaction constants involved in the different steps of the mechanism were calculated at different temperatures, which yielded thermodynamic quantities for different steps of the reaction scheme. The activation parameters with respect to the slow step of the mechanism were computed and discussed; thermodynamic quantities were also determined.     

Asymmetric oxidative dearomatizations promoted by hypervalent iodine(III) reagents: an opportunity for rational catalyst design?

The use of and λ³- and λ⁵-iodanes in the oxidative dearomatization of phenols is a well-established and general procedure for the construction of cyclohexadienone structures. However, their use in asymmetric dearomatization reactions is quite underdeveloped and, despite work by several research groups over the past several years, a general chiral aryl iodide catalyst has yet to emerge. This Letter will serve to highlight the significant progress that has been made in this area and will reveal some of deficiencies in the literature that the author believes may be hindering further progress.     

Simultaneous determination of In(III) and Cd(II) by differential pulse polarography in the presence of poly ?-cyclodextrin

The difference in the peak potentials of In(III) and Cd(II), whose reduction potentials are very close to each other, becomes large in the presence of poly -cyclodextrin in sodium perchlorate medium. The relationships between the peak currents for these two ions and their concentrations are linear, suggesting that the simultaneous determination of the ions is possible in the presence of this reagent.     

Hexaazatriphenylene (HAT) versus tri‐HAT: The Bigger the Better?

A new hexaazatriphenylene (HAT) derivative formed by the fusion of three HAT units has been prepared and its electronic and molecular structures have been fully characterized by optical and vibrational Raman spectroscopy, electrochemistry, solid-state UV and inverse photoemission spectroscopy (UPS and IPES), and by quantum-chemical calculations. A comparative HAT versus tri-HAT study was performed. The fusion of three HAT molecules causes modifications in the optical and electrochemical properties consistent with enhanced π-electron delocalization attained in a bigger planar core. Such combined experimental and theoretical studies are useful to balance chemical design with supramolecular engineering directed to find enhanced characteristics for new organic semiconductor applications.     

Single-Atom or Dual-Atom in TiO2 Nanosheet: Which is the Better Choice for Electrocatalytic Urea Synthesis?

As rising star materials, single-atom and dual-atom catalysts have been widely reported in the electro-catalysis area. To answer the key question: single-atom and dual-atom catalysts, which is better for electrocatalytic urea synthesis? we design two types of catalysts via a vacancy-anchorage strategy: single-atom Pd₁−TiO₂ and dual-atom Pd₁Cu₁−TiO₂ nanosheets. An ultrahigh urea activity of 166.67 mol_urea mol_Pd⁻¹ h¹ with the corresponding 22.54 % Faradaic efficiency at −0.5 V vs. reversible hydrogen electrode (RHE) is achieved over Pd₁Cu₁−TiO₂, which is much higher than that of Pd₁−TiO₂. Various characterization including an in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and theoretical calculations demonstrate that dual-atom Pd₁Cu₁ site in Pd₁Cu₁−TiO₂ is more favorable for producing urea, which experiences a C−N coupling pathway with a lower energy barrier compared with Pd₁ in Pd₁−TiO₂.     

Chemical modification of expanded glass aggregate with N-Benzoyl-N′-(4-methylphenyl) thiourea (TTU) for the adsorptive removal of Cr(III) ion

In this study, the silylant agent 3-aminopropyl trimethoxysilane (APTES) was anchored on expanded glass aggregate (GA) to prepare a new adsorbent. N-Benzoyl-N′-(4-methylphenyl) thiourea (TTU) bonded to amino-functionalized GA adsorbent with reflux. Developed adsorbent (GA-APTES-TTU) was characterized using thermal analysis (TGA) and scanning electron microscopy (SEM). TGA and SEM studies indicated that modification of the glass aggregate (GA) surfaces was successfully performed. The adsorption studies exhibited that the GA-APTES-TTU could be efficiently used for the removal of Cr(III) from aqueous solutions. The effects of pH, adsorbent dosage, ion concentration, time, and temperature were investigated as adsorption parameters. The maximum removal of Cr(III) was observed at pH 4. The adsorption equilibrium was achieved in 120 min and adsorption of Cr(III) followed the Langmuir isotherm model. The maximum adsorption capacity for Cr(III) was 0.4305 mmol/g with GA-APTES-TTU. Thermodynamic parameters such as the standard free energy (ΔG^o), enthalpy change (ΔH°) and entropy change (ΔS°) were calculated in order to explain the mechanism of adsorption process. The thermodynamic data showed that Cr(III) adsorption was spontaneous, endothermic, and a physisorption reaction. In addition, the adsorption kinetic data fitted to the pseudo-second order model.     

Phenol Oxidation by a Nickel(III)–Fluoride Complex: Exploring the Influence of the Proton Accepting Ligand in PCET Oxidation

In order to gain insight into the influence of the H⁺-accepting terminal ligand in high-valent oxidant mediated proton coupled electron transfer (PCET) reactions, the reactivity of a high valent nickel–fluoride complex [Ni^III(F)(L)] ( 2 , L=N,N’-(2,6-dimethylphenyl)-2,6-pyridinecarboxamidate) with substituted phenols was explored. Analysis of kinetic data from these reactions (Evans–Polanyi, Hammett, and Marcus plots, and KIE measurements) and the formed products show that 2 reacted with electron rich phenols through a hydrogen atom transfer (HAT, or concerted PCET) mechanism and with electron poor phenols through a stepwise proton transfer/electron transfer (PT/ET) reaction mechanism. The analogous complexes [Ni^III(Z)(L)] (Z=Cl, OCO₂H, O₂CCH₃, ONO₂) reacted with all phenols through a HAT mechanism. We explore the reason for a change in mechanism with the highly basic fluoride ligand in 2 . Complex 2 was also found to react one to two orders of magnitude faster than the corresponding analogous [Ni^III(Z)(L)] complexes. This was ascribed to a high bond dissociation free energy value associated with H−F (135 kcal mol⁻¹), which is postulated to be the product formed from PCET oxidation by 2 and is believed to be the driving force for the reaction. Our findings show that high-valent metal–fluoride complexes represent a class of highly reactive PCET oxidants.     

Synergistic Effects in the Europium(III)–Thenoyltrifluoroacetone–1,10-Phenanthroline System in Micelles of Block Copolymers of Nonionic Surfactants and Their Analytical Applications

The effect of micelles of block copolymers of nonionic surfactants (NIS) on the fluorescence properties of the Eu³⁺–thenoyltrifluoroacetone (TTA)–1,10-phenanthroline (Phen) system was studied. It was shown that the introduction of micelles of nonionic surfactants increases the chelate fluorescence intensity by an order of magnitude. The limit of detection of europium using the TTA–Phen–NIS system depends on the hydrophobicity of nonionic surfactants. The sensitization of Eu³⁺luminescence by the gadolinium ion leads to a further decrease in DL by two orders of magnitude (1 × 10^–11g/mL). The procedure of europium determination developed in this work was approved using samples of biological (sea fish) and inorganic (CaSO₄preparation) origin.     

Selective Hydrogenation of CO2 Dictated by Isomers in Au28(SR)20 Nanoclusters: Which One is Better?

It is a challenge to make clear how isomerism in a heterogeneous catalyst induces distinct differences in catalytic properties, as attainment of the structural isomerism in a conventional catalyst is difficult. By successfully identifying the isomerism in the atomically precise Au nanoclusters, an exciting opportunity for unravelling catalysis of isomeric catalysts is opened up. Herein, we report that the isomerism in the Au₂₈(SR)₂₀ nanoclusters with different surface atom arrangements can indeed render different catalytic behaviors in the selective hydrogenation of CO₂. We anticipate that our studies will serve as a starting point for fundamental investigations about how to control the catalytic activity and selectivity by the isomerism-induced catalysis.     

Annulative π-Extension by Rhodium(III)-Catalyzed Ketone-Directed C−H Activation: Rapid Access to Pyrenes and Related Polycyclic Aromatic Hydrocarbons (PAHs)

Annulative π-extension (APEX) reaction has become a powerful tool for the precise synthesis of well-defined polycyclic aromatic hydrocarbons (PAHs) such as nanographene, graphene, and other PAHs possessing unique structure. Herein, an APEX reaction has been realized at the masked bay-region for the efficient and rapid synthesis of valuable PAH, pyrene, bearing substitutions at the most challenging K-region. Rh^III-catalyzed ketone-directed C−H activation at the peri-position of a naphthyl-derived ketone, alkyne-insertion, intramolecular nucleophilic attack at the carbonyl-group, dehydration, and aromatization steps occurred in one-pot to effectuate the protocol. Employing this strategy, a two-fold APEX reaction on enantiopure BINOL-derived ketones provided access to axially-chiral bipyrene derivatives. The detailed DFT study to support proposed mechanism, and synthesis of helical PAHs like dipyrenothiophene and dipyrenofuran are other highlights of the present study.     

Iridium(III) Catalysts with an Amide-Pendant Cyclopentadienyl Ligand: Double Aromatic Homologation Reactions of Benzamides by Fourfold C−H Activation

The synthesis, characterization, and catalytic performance of iridium(III) catalysts that bear an amide-pendant cyclopentadienyl ligand ([Cp^AIrI₂]₂) is reported. These [Cp^AIrI₂]₂ catalysts were obtained from the complexation of a Cp^A ligand precursor with [Ir(cod)OAc]₂ followed by oxidation. Double aromatic homologation reactions of benzamides with alkynes by fourfold C−H activation proceeded in good to high yield with these [Cp^AIrI₂]₂ catalysts, demonstrating their superior catalytic performance in this challenging transformation.     

Cerium(III) Chloride: A Highly Efficient Reagent for the Synthesis of α‐Aminonitriles

We report a highly efficient, one‐pot, three‐component condensation of carbonyl compounds, amines, and TMSCN in MeCN; the reaction is significantly promoted by the catalytic amount of cerium(III) chloride at ambient temperature in excellent yields without any adverse effect on the other substituents. The method afforded an elegant alternative to the synthesis of α‐aminonitriles. The reactions are fast and clean, and the products obtained are of high purity.