Catalytic Chemoselective Sulfimidation with an Electrophilic [CoIII(TAML)]−-Nitrene Radical Complex**

The cobalt species PPh₄[Co^III(TAML^red)] is a competent and stable catalyst for the sulfimidation of (aryl)(alkyl)-substituted sulfides with iminoiodinanes, reaching turnover numbers up to 900 and turnover frequencies of 640 min⁻¹ under mild and aerobic conditions. The sulfimidation proceeds in a highly chemoselective manner, even in the presence of alkenes or weak C−H bonds, as supported by inter- and intramolecular competition experiments. Functionalization of the sulfide substituent with various electron-donating and electron-withdrawing arenes and several alkyl, benzyl and vinyl fragments is tolerated, with up to quantitative product yields. Sulfimidation of phenyl allyl sulfide led to [2,3]-sigmatropic rearrangement of the initially formed sulfimide species to afford the corresponding N-allyl-S-phenyl-thiohydroxylamines as attractive products. Mechanistic studies suggest that the actual nitrene transfer to the sulfide proceeds via (previously characterized) electrophilic nitrene radical intermediates that afford the sulfimide products via electronically asynchronous transition states, in which SET from the sulfide to the nitrene radical complex precedes N−S bond formation in a single concerted process.     

KINETICS AND MECHANISM OF CATALYSIS BY FERRIHAEMS IN THE CHEMILUMINOGENIC OXIDATION OF LUMINOL BY HYDROGEN PEROXIDE

The kinetics of catalysis by deuteroferrihaem (deuterohaemin) were studied in the chemiluminogenic oxidation of luminol by hydrogen peroxide. The results imply that two distinct catalytic mechanisms operate to yield chemiluminescence from excited aminophthalate emitter in this system. The first mechanism involves initial one-electron oxidation of luminol by an oxidised derivative of deuteroferrihaem with well-established peroxidatic oxidant properties. The second mechanism involves a concerted pathway very similar to that which has been proposed [Olsson, T., L. Ewetz and A. Thore (1983), Photochem. Photobiol. 38 , 223–229] to explain protoferrihaem (haemin) catalysis in luminol oxidation. Deuteroferrihaem is a much more effective catalyst than protoferrihaem on a mole-for-mole basis and could be used with advantage in chemiluminescence analyses.     

In Silico Partial N2 to NH3 Conversion with a Light Atom Molecule

N₂ can be stepwise converted in silico into one molecule NH₃ and a secondary amide with a bond activator molecule consisting only of light main group elements. The proposed N₂-activating pincer-related compound carries a silyl ion (Si⁽⁺⁾) center as well as three Lewis acidic (−BF₂) and three Lewis basic (−PMe₂) sites, providing an efficient binding pocket for gaseous N₂ within the framework of intramolecular frustrated Lewis pairs (FLP). In addition, it exhibits supportive secondary P−B and F⋅⋅⋅B contacts, which stabilize the structure. In the PSi⁽⁺⁾−N−N−BP environment the N≡N triple bond is extended from 1.09 Å to remarkable 1.43 Å, resembling a N−N single bond. The strongly activated N−N-fragment is prone to subsequent hydride addition and protonation steps, resulting in the energy efficient transfer of two hydrogen equivalents. The next hydride added causes the release of one molecule NH₃, but leaves the ligand system as poisoned R₃Si⁽⁺⁾−NH₂−PMe₂ or R₃Si⁽⁺⁾−NH₃ dead-end states behind. The study indicates that approximately tetrahedral constrained SiBP₂-pockets are capable to activate N₂, whereas the acid-rich SiB₃- and SiB₂P-pocktes, as well as the base-rich SiP₃-pockets fail, hinting towards the high relevance of the acid-base proportion and relative orientation. The electronic structure of the N₂-activated state is compared to the corresponding state of a recently published peri-substituted bond activator molecule featuring a PSi⁽⁺⁾−N−N−Si⁽⁺⁾P site (S. Mebs, J. Beckmann, Physical Chemistry Chemical Physics 2022 , 24, 20953–20967).     

Non-Dissociative Activation of Chemisorbed Dinitrogen on One or Two Vanadium Atoms Supported by a Mo6S8 Cluster

Adsorption of N₂ on Mo₆S₈^q_V_x clusters (x=0, 1, 2; q=0, ±1) were systematically studied by density functional theory calculations with dispersion corrections. It was found that the N₂ can be chemisorbed and undergo non-dissociative activation on single or double metal atoms. The adsorption and activation are influenced by metal types (V or Mo), N₂ coordination modes and charge states of the clusters. Particularly, anionic Mo₆S₈⁻_V₂ clusters have remarkable ability to fix and activate N₂. In Mo₆S₈⁻_V₂, two V atoms prefer to adsorb on two adjacent S−Mo−S hollow sites, leading to the formation of a supported V…V unit. The N₂ is bridged side-on coordinated with these two V atoms with high adsorption energy and significant charge transfer. The bond order, bond length and vibration frequency of the adsorbed N₂ are close to those of a N−N single bond.     

Determination of Melamine in Dairy Products and Melamine Tableware by Inhibition Electrochemiluminescent Method

An electrochemiluminescent (ECL) method has been developed for the determination of melamine based on the inhibition of luminol ECL. A significant luminol ECL can be found at 1.47 V in the phosphate buffer solution at high pHs and low potential scan rates, this ECL signal can be inhibited obviously by melamine. The decrease of ECL intensity was linearly proportional to the logarithm of melamine concentration in the range of 1–100 ng/mL (R²=0.9911) and with the detection limit of 0.1 ng/mL. The method has been applied successfully to determine melamine in dairy products and melamine tableware, the recoveries were in the range of 98.5%–103.7% and 95.5%–106.0%, respectively. The mechanism of the inhibition effect was also proposed, the active oxygen (O₂^{· −}) generated from the electrooxidation of OH⁻ reacted with luminol anion (L^{· −}) to generate light emission, and the present of melamine can eliminate the active oxygen, which cause the decrease of the ECL intensity.     

Direct Observation of Dynamic Bond Evolution in Single-Atom Pt/C3N4 Catalysts

Single-atom catalysts are promising platforms for heterogeneous catalysis, especially for clean energy conversion, storage, and utilization. Although great efforts have been made to examine the bonding and oxidation state of single-atom catalysts before and/or after catalytic reactions, when information about dynamic evolution is not sufficient, the underlying mechanisms are often overlooked. Herein, we report the direct observation of the charge transfer and bond evolution of a single-atom Pt/C₃N₄ catalyst in photocatalytic water splitting by synchronous illumination X-ray photoelectron spectroscopy. Specifically, under light excitation, we observed Pt−N bond cleavage to form a Pt⁰ species and the corresponding C=N bond reconstruction; these features could not be detected on the metallic platinum-decorated C₃N₄ catalyst. As expected, H₂ production activity (14.7 mmol h⁻¹ g⁻¹) was enhanced significantly with the single-atom Pt/C₃N₄ catalyst as compared to metallic Pt-C₃N₄ (0.74 mmol h⁻¹ g⁻¹).     

Micellar complexes of energy transfer

In micellar solutions of cationic surfactants the rate of oxidation and electrooxidation of luminol, quantum recovery of the fluorescence of anionic fluorescer, and the probability of electron excitation energy transfer are enhanced. Owing to these facts, the intensity of chemiluminescence and electrochemiluminescence of luminol in the presence of cetyltrimethylammonium bromide and fluorescein is from 10 to 100 times higher compared with that of pure solutions free of surfactants.The intensity of the emitted radiation is proportional to the concentrations of micellar complexes, which allows the introduction of the idea of a complex of electron excitation energy transfer in which the excited oxidation product of luminol (aminophthalate ion) plays the role of the donor and the fluorescer the role of the acceptor of energy. The substrate-binding constants are of an order of magnitude of 10⁴ up to 10⁵M⁻¹.From the formal point of view, the intensity of chemiluminescence obeys the same laws as the kinetics of enzymatic and micellar catalysis, respectively.     

Thermolysis of 3‐alkyl‐3‐methyl‐1,2‐dioxetanes: activation parameters and chemiexcitation yields

3‐Methyl‐3‐(3‐pentyl)‐1,2‐dioxetane 1 and 3‐methyl‐3‐(2,2‐dimethyl‐1‐propyl)‐1,2‐dioxetane 2 were synthesized in low yield by the α‐bromohydroperoxide method. The activation parameters were determined by the chemiluminescence method (for 1 ΔH‡ = 25.0 ± 0.3 kcal/mol, ΔS‡ = −1.0 entropy unit (e.u.), ΔG‡ = 25.3 kcal/mol, k₁ (60°C) = 4.6 × 10⁻⁴s⁻¹; for 2 ΔH‡ = 24.2 ± 0.2 kcal/mol, ΔS‡ = −2.0 e.u., ΔG‡ = 24.9 kcal/mol, k₁ (60°C) = 9.2 × 10⁻⁴s⁻¹. Thermolysis of 1–2 produced excited carbonyl fragments (direct production of high yields of triplets relative to excited singlets) (chemiexcitation yields for 1: ϕ^T = 0.02, ϕ^S ≤ 0.0005; for 2: ϕ^T = 0.02, ϕ^S ≤ 0.0004). The results are discussed in relation to a diradical‐like mechanism. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:176–179, 2001     

In Vitro Monitoring of Picogram Levels of Captopril in Human Urine Using Flow Injection Chemiluminescence with Immobilized Reagent Technique

Abstract

A flow‐injection procedure for detection of captopril using a Co²⁺‐captopril complex formed on line based enhancement of luminol and dissolved oxygen chemiluminescence is described. The chemiluminescence reagents, luminol and Co²⁺, were both immobilized on ion exchange resin in the flow injection system. When captopril solution flowed through the immobilized Co²⁺ column, the Co²⁺‐captopril (1:2) complex formed on line could greatly enhanced the chemiluminescence intensity generated from the reaction between luminol and dissolved oxygen. The increment of chemiluminescence emission was correlated with the captopril concentration in the range from 7 to 1000 pg mL^?1, and the detection limit was 2 pg mL^?1 (3σ). One analysis cycle, including sampling and washing, could be accomplished in 0.5 min with relative standard deviations of less than 3.0% (n=11). The proposed method was applied directly in the assay of human urine without any pretreatment and it was found that the captopril concentration reached its maximum after being administrated orally for 1.5 hours, with the mean excretion ratio in 6.5 hours of 54.3% in the body of volunteers. The possible chemiluminescence mechanism was discussed.     

C−H and C−M Activation,Aromaticity Tuning,and Co⋅⋅⋅Ru Interactions Confined in the Azuliporphyrin Framework

Taking advantage of the specific properties of azuliporphyrin and the reactivity of cobalt(II), activation of an azulene C(sp²)−H bond occurred and organometallic complexes with Co−C bonding were formed. The system allowed for macrocyclic aromaticity tuning through metal coordination and oxidation. Thanks to the Co^II−C and parallel tested Cu^II−C reactivity and the affinity of metal centers to dioxygen, oxygen atom insertion into the M−C bond could be investigated. Insertion starts with an oxygen molecule coordination and leads to monomeric and dimeric complexes of specific electronic structures. Formation of unique paramagnetic σ/π-hybrid bimetallic complexes enabled spectroscopic and theoretical investigations of peculiar Co^II⋅⋅⋅Ru⁰ interactions.     

Photo-thermal Cooperative Carbonylation of Ethanol with CO2 on Cu2O-SrTiCuO3-x

Carbonylation of ethanol with CO₂ as carbonyl source into value-added esters is of considerable significance and interest, while remains of great challenge due to the harsh conditions for activation of inert CO₂ in that the harsh conditions result in undesired activation of α-C−H and even cleavage of C−C bond in ethanol to deteriorate the specific activation of O−H bond. Herein, we propose a photo-thermal cooperative strategy for carbonylation of ethanol with CO₂, in which CO₂ is activated to reactive CO via photo-catalysis with the assistance of *H from thermally-catalyzed dissociation of alcoholic O−H bond. To achieve this proposal, an interfacial site and oxygen vacancy both abundant SrTiCuO_3-x supported Cu₂O (Cu₂O-SrTiCuO_3-x) has been designed. A production of up to 320 μmol g⁻¹ h⁻¹ for ethyl formate with a selectivity of 85.6 % to targeted alcoholic O−H activation has been afforded in photo-thermal assisted gas-solid process under 3.29 W cm⁻¹ of UV/Vis light irradiation (144 °C) and 0.2 MPa CO₂. In the photo-driven activation of CO₂ and following carbonylation, CO₂ activation energy decreases to 12.6 kJ mol⁻¹, and the cleavage of alcoholic α-C−H bond has been suppressed.     

Highly Bright Near-Infrared Chemiluminescent Probes for Cancer Imaging and Laparotomy

Near-infrared (NIR) chemiluminescence imaging holds potential for sensitive imaging of cancer due to its low background; however, few NIR chemiluminophores are available, which share the drawback of low chemiluminescence quantum yields (Φ_CL). Herein, we report the synthesis of NIR chemiluminophores for cancer imaging and laparotomy. Molecular engineering of the electron-withdrawing group at the para-position of the phenol-dioxetane leads to a highly bright NIR chemiluminophore (DPT), showing the Φ_CL (4.6×10⁻² Einstein mol⁻¹) that is 3 to 5-fold higher than existing NIR chemiluminophores. By caging the phenol group of DPT with a cathepsin B (CatB) responsive moiety, an activatable chemiluminescence probe (DPT_CB) is developed for real-time turn-on detection of deeply buried tumor tissues in living mice. Due to its high brightness, DPT_CB permits accurate chemiluminescence-guided laparotomy.     

Thermolysis of disubstituted 1,2-dioxetanes: Activation parameters and chemiexcitation yields

trans-3-Methyl-4-(p-anisyl)-1,2-dioxetane 1, trans-3-methyl-4-(o-anisyl)-1,2-dioxetane 2 , 3-methyl-3-benzyl-1,2-dioxetane 3 , and 3-methyl-3-p-methoxybenzyl-1,2-dioxetane 4 were synthesized in low yield by the β-bromo hydroperoxide method. The activation parameters were determined by the chemiluminescence method (for 1 ΔG≠ = 22.8 ± 0.3 kcal/mol, Δ≠ = 22.2, ΔS≠ = −1.7 e.u., k₆₀ = 7.6 × 10⁻³s⁻¹; for 2 ΔG≠ + 23.6 ± 0.3 kcal/mol, ΔH≠ = 22.8, ΔS≠ = −2.2 e.u., k₆₀ = 2.5 × 10⁻³S⁻¹; for 3 ΔG≠ = 24.0 ± 0.4 kcal/mol, ΔH≠ = 23.1, ΔS≠ = −2.7 e.u., k₆₀ = 1.2 × 10⁻³S⁻¹; for 4 ΔG≠ = 24.0 ± 0.2 kcal/mol, ΔH≠, = 23.2, ΔS≠, = −2.4 e.u., k₆₀ = 1.2 × 10⁻³s⁻¹). Thermolysis of 1–4 produced excited carbonyl fragments (direct production of high yields of triplets relative to excited singlets) [chemiexcitation yields ϕ^T, ϕ^S, respectively: for 1 0.02, 0.0001; for 2 0.02, 0.0001; for 3 0.03, 0.0002; for 4 0.02, 0.0001]. The effect of paramethoxyaryl substitution was consistent with electronic effects. The ortho substitution in 2 resulted in an increase in stability of the dioxetane, opposite that observed for an electronic effect. The results are discussed in relation to a diradical-like mechanism.     

Turning the Inert Element Zinc into an Active Single-Atom Catalyst for Efficient Fenton-Like Chemistry

Amongst various Fenton-like single-atom catalysts (SACs), the zinc (Zn)-related SACs have been barely reported due to the fully occupied 3d¹⁰ configuration of Zn²⁺ being inactive for the Fenton-like reaction. Herein, the inert element Zn is turned into an active single-atom catalyst (SA−Zn−NC) for Fenton-like chemistry by forming an atomic Zn−N₄ coordination structure. The SA−Zn−NC shows admirable Fenton-like activity in organic pollutant remediation, including self-oxidation and catalytic degradation by superoxide radical (O₂⋅⁻) and singlet oxygen (¹O₂). Experimental and theoretical results unveiled that the single-atomic Zn−N₄ site with electron acquisition can transfer electrons donated by electron-rich pollutants and low-concentration PMS toward dissolved oxygen (DO) to actuate DO reduction into O₂⋅⁻ and successive conversion into ¹O₂. This work inspires an exploration of efficient and stable Fenton-like SACs for sustainable and resource-saving environmental applications.     

Electrode/Electrolyte Synergy for Concerted Promotion of Electron and Proton Transfers toward Efficient Neutral Water Oxidation

Neutral water oxidation is a crucial half-reaction for various electrochemical applications requiring pH-benign conditions. However, its sluggish kinetics with limited proton and electron transfer rates greatly impacts the overall energy efficiency. In this work, we created an electrode/electrolyte synergy strategy for simultaneously enhancing the proton and electron transfers at the interface toward highly efficient neutral water oxidation. The charge transfer was accelerated between the iridium oxide and in situ formed nickel oxyhydroxide on the electrode end. The proton transfer was expedited by the compact borate environment that originated from hierarchical fluoride/borate anions on the electrolyte end. These concerted promotions facilitated the proton-coupled electron transfer (PCET) events. Due to the electrode/electrolyte synergy, Ir−O and Ir−OO⁻ intermediates could be directly detected by in situ Raman spectroscopy, and the rate-limiting step of Ir−O oxidation was determined. This synergy strategy can extend the scope of optimizing electrocatalytic activities toward more electrode/electrolyte combinations.     

Chemiluminescence quantum yield in permanganate reduction reactions in acid medium

Chemiluminescence quantum yields for the reactions of permanganate with oxalic, tartaric, and citric acids; hydrazine; KBr; and FeSO₄ in aqueous solutions of sulfuric acid have been measured. The maximum quantum yield reaches 1.2 × 10^?5 einstein/mol with the chemiexcitation yield being 2%. Hence, the relatively low chemiluminescence quantum yield is due to a low yield of light emission by chemiexcited particles, rather than the low chemiexcitation yield.     

Bonding Energetics of Palladium Amido/Aryloxide Complexes in DMSO: Implications for Palladium-Mediated Aniline Activation

Thermodynamic knowledge of the metal–ligand (M−L) σ-bond strength is crucial to understanding metal-mediated transformations. Here, we developed a method for determining the Pd−X (X=OR and NHAr) bond heterolysis energies (ΔG_het(Pd−X)) in DMSO taking [(tmeda)PdArX] (tmeda=N,N,N′,N′-tetramethylethylenediamine) as the model complexes. The ΔG_het(Pd−X) scales span a range of 2.6–9.0 kcal mol⁻¹ for ΔG_het(Pd−O) values and of 14.5–19.5 kcal mol⁻¹ for ΔG_het(Pd−N) values, respectively, implying a facile heterolytic detachment of the Pd ligands. Structure-reactivity analyses of a modeling Pd-mediated X−H bond activation reveal that the M−X bond metathesis is dominated by differences of the X−H and Pd−X bond strengths, the former being more influential. The ΔG_het(Pd−X) and pK_a(X−H) parameters enable regulation of reaction thermodynamics and chemoselectivity and diagnosing the probability of aniline activation with Pd−X complexes.     

Homolytic X-H Bond Cleavage at a Gold(III) Hydroxide: Insights into One-Electron Events at Gold

C(sp³)-H and O−H bond breaking steps in the oxidation of 1,4-cyclohexadiene and phenol by a Au(III)-OH complex were studied computationally. The analysis reveals that for both types of bonds the initial X−H cleavage step proceeds via concerted proton coupled electron transfer (cPCET), reflecting electron transfer from the substrate directly to the Au(III) centre and proton transfer to the Au-bound oxygen. This mechanistic picture is distinct from the analogous formal Cu(III)-OH complexes studied by the Tolman group (J. Am. Chem. Soc. 2019 , 141, 17236–17244), which proceed via hydrogen atom transfer (HAT) for C−H bonds and cPCET for O−H bonds. Hence, care should be taken when transferring concepts between Cu−OH and Au−OH species. Furthermore, the ability of Au−OH complexes to perform cPCET suggests further possibilities for one-electron chemistry at the Au centre, for which only limited examples exist.     

Outer‐Sphere 2 e−/2 H+ Transfer Reactions of Ruthenium(II)‐Amine and Ruthenium(IV)‐Amido Complexes

A diverse set of 2 e⁻/2 H⁺ reactions are described that interconvert [Ru^II(bpy)(en*)₂]²⁺ and [Ru^IV(bpy)(en‐H*)₂]²⁺ (bpy=2,2′‐bipyridine, en*=H₂NCMe₂CMe₂NH₂, en*‐H=H₂NCMe₂CMe₂NH⁻), forming or cleaving different O−H, N−H, S−H, and C−H bonds. The reactions involve quinones, hydrazines, thiols, and 1,3‐cyclohexadiene. These proton‐coupled electron transfer reactions occur without substrate binding to the ruthenium center, but instead with precursor complex formation by hydrogen bonding. The free energies of the reactions vary over more than 90 kcal mol⁻¹, but the rates are more dependent on the type of X−H bond involved than the associated ΔG °. There is a kinetic preference for substrates that have the transferring hydrogen atoms in close proximity, such as ortho ‐tetrachlorobenzoquinone over its para ‐isomer and 1,3‐cyclohexadiene over its 1,4‐isomer, perhaps hinting at the potential for concerted 2 e⁻/2 H⁺ transfers.     

Plasma-Assisted Coupling Reactions of Dinitrogen and Carbon Dioxide Mediated by Monometallic YB1–4−⋅Anions: Carbon−Nitrogen Bond Formation

Transition-metal catalyzed coupling to form C−N bonds is significant in chemical science. However, the inert nature of N₂ and CO₂ renders their coupling quite challenging. Herein, we report the activation of dinitrogen in the mild plasma atmosphere by the gas-phase monometallic YB_1–4⁻ anions and further coupling of CO₂ to form C−N bonds by using mass spectrometry and theoretical calculation. The observed product anions are NCNBO⁻ and N(BO)₂⁻, accompanied by the formation of neutral products YO and YB_0–2NC, respectively. We can tune the reactivity and the type of products by manipulating the number of B atoms. The B atoms in YB_1–4N₂⁻ act as electron donors in CO₂ reduction reactions, and the carbon atom originating from CO₂ serves as an electron reservoir. This is the first example of gas-phase monometallic anions, which are capable to realize the functionalization of N₂ with CO₂ through C−N bond formation and N−N and C−O bond cleavage.