Oxidation of Olefins with Hydrogen Peroxide Catalyzed by Bismuth Salts: A Mechanistic Study

Defect Engineered Bi2Te3 Nanosheets with Enhanced Haloperoxidase Activity for Marine Antibiofouling

Defective bismuth telluride (Bi2Te3) nanosheets, an artificial nanozyme mimicking haloperoxidase activity (hPOD), show promise as eco-friendly, bactericidal, and antimicrofouling materials by enhancing cytotoxic hypohalous acid production from halides and H2O2. Microscopic and spectroscopic characterization reveals that controlled NaOH (upto X = 250 µL) etching of the nearly inactive non-transition metal chalcogenide Bi2Te3 nanosheets creates controlled defects (d), such as Bi3+species, in d-Bi2Te3-X that induces enhanced hPOD activity. d-Bi2Te3-250 exhibits approximately eight-fold improved hPOD than the as-grown Bi2Te3 nanosheets. The antibacterial activity of d-Bi2Te3-250 nanozymes, studied by bacterial viability, show 1, and 45% viability for Staphylococcus aureus and Pseudomonas aeruginosa, respectively, prevalent in marine environments. The hPOD mechanism is confirmed using scavengers, implicating HOBr and singlet oxygen for the effect. The antimicrofouling property of the d-Bi2Te3-250 nanozyme has been studied on Pseudomonas aeruginosa biofilm in a lab setting by multiple assays, and also on titanium (Ti) plates coated with the nanozyme mixed commercial paint, exposed to seawater in a real setting. All studies, including direct microscopic evidence, exhibit inhibition of microfouling, up to ≈73%, in the presence of nanozymes. This approach showcases that defect engineering can induce antibacterial, and antimicrofouling activity in non-transition metal chalcogenides, offering an inexpensive alternative to noble metals.

Methodological Development and Applications of Tryptamine-Ynamide Cyclizations in Synthesizing Core Skeletons of Indole Alkaloids

Over the past two decades, synthetic strategies for synthesizing the skeletons of various indole alkaloids based on tryptamine-ynamide have been continuously developed and applied to the total syntheses or formal total syntheses of related molecules. In this synopsis, we summarized the cyclization pathways of tryptamine-ynamide under different catalytic conditions, emphasizing the reaction mechanism and applications in the syntheses of indole alkaloids.

Organoantimony Dihydroperoxides: Synthesis, Crystal Structures, and Hydrogen Bonding Networks

Despite growing interest in the potential applications of p-block hydroperoxo complexes, the chemistry of inorganic hydroperoxides remains largely unexplored. For instance, single-crystal structures of antimony hydroperoxo complexes have not been reported to date. Herein, we present the synthesis of six triaryl and trialkylantimony dihydroperoxides [Me₃Sb(OOH)₂, Me₃Sb(OOH)₂·H₂O, Ph₃Sb(OOH)₂·0.75(C₄H₈O), Ph₃Sb(OOH)₂·2CH₃OH, pTol₃Sb(OOH)₂, pTol₃Sb(OOH)₂·2(C₄H₈O)], obtained by the reaction of the corresponding dibromide antimony(V) complexes with an excess of highly concentrated hydrogen peroxide in the presence of ammonia. The obtained compounds were characterized by single-crystal and powder X-ray diffraction, Fourier transform infrared and Raman spectroscopies, and thermal analysis. The crystal structures of all six compounds reveal hydrogen-bonded networks formed by hydroperoxo ligands. In addition to the previously reported double hydrogen bonding, new types of hydrogen-bonded motifs formed by hydroperoxo ligands were found, including infinite hydroperoxo chains. Solid-state density functional theory calculation of Me₃Sb(OOH)₂ revealed reasonably strong hydrogen bonding between OOH ligands with an energy of 35 kJ/mol. Additionally, the potential application of Ph₃Sb(OOH)₂·0.75(C₄H₈O) as a two-electron oxidant for the enantioselective epoxidation of olefins was investigated in comparison with Ph₃SiOOH, Ph₃PbOOH, t-BuOOH, and H₂O₂.

Mechanistic Details of the Sharpless Epoxidation of Allylic Alcohols—A Combined URVA and Local Mode Study

In this work, we investigated the catalytic effects of a Sharpless dimeric titanium (IV)–tartrate–diester catalyst on the epoxidation of allylalcohol with methyl–hydroperoxide considering four different orientations of the reacting species coordinated at the titanium atom (reactions R1–R4) as well as a model for the non-catalyzed reaction (reaction R0). As major analysis tools, we applied the URVA (Unified Reaction Valley Approach) and LMA (Local Mode Analysis), both being based on vibrational spectroscopy and complemented by a QTAIM analysis of the electron density calculated at the DFT level of theory. The energetics of each reaction were recalculated at the DLPNO-CCSD(T) level of theory. The URVA curvature profiles identified the important chemical events of all five reactions as peroxide OO bond cleavage taking place before the TS (i.e., accounting for the energy barrier) and epoxide CO bond formation together with rehybridization of the carbon atoms of the targeted CC double bond after the TS. The energy decomposition into reaction phase contribution phases showed that the major effect of the catalyst is the weakening of the OO bond to be broken and replacement of OH bond breakage in the non-catalyzed reaction by an energetically more favorable TiO bond breakage. LMA performed at all stationary points rounded up the investigation (i) quantifying OO bond weakening of the oxidizing peroxide upon coordination at the metal atom, (ii) showing that a more synchronous formation of the new CO epoxide bonds correlates with smaller bond strength differences between these bonds, and (iii) elucidating the different roles of the three TiO bonds formed between catalyst and reactants and their interplay as orchestrated by the Sharpless catalyst. We hope that this article will inspire the computational community to use URVA complemented with LMA in the future as an efficient mechanistic tool for the optimization and fine-tuning of current Sharpless catalysts and for the design new of catalysts for epoxidation reactions.

Homogeneous oxidation of C–H bonds with m-CPBA catalysed by a Co/Fe system: mechanistic insights from the point of view of the oxidant

A Co/Fe system efficiently catalyses the oxidation of C–H bonds with m-CPBA. The nitric acid promoter hampers the m-CPBA homolysis, suppressing the free radical activity. Experimental and computational data evidence a concerted oxidation mechanism.

Ionic-caged heterometallic bismuth-platinum complex exhibiting electrocatalytic CO2 reduction

An air-stable heterometallic Bi-Pt complex with the formula [BiPt(SAc)5]n (1; SAc = thioacetate) was synthesized. The crystal structure, natural bond orbital (NBO) and local orbital locator (LOL) analyses, localized orbital bonding analysis (LOBA), and X-ray absorption fine structure (XAFS) measurements were used to confirm the existence of Bi-Pt bonding and an ionic cage of O atoms surrounding the Bi ion. From the cyclic voltammetry (CV) and controlled potential electrolysis (CPE) experiments, 1 in tetrahydrofuran reduced CO2 to CO, with a faradaic efficiency (FE) of 92% and a turnover frequency (TOF) of 8 s-1 after 30 min of CPE at -0.79 V vs. NHE. The proposed mechanism includes an energetically favored pathway via the ionic cage, which is supported by the results of DFT calculations and reflectance infrared spectroelectrochemistry data.

Efficient synthesis of novel pyrazole-linked 1,2,4-triazolidine-3-thiones using bismuth on zirconium oxide as a recyclable catalyst in aqueous medium

The Bi₂O₃ loading on ZrO₂ as heterogeneous catalyst was established as an extremely efficient catalyst for the synthesis of a series of novel 5-(1-(2,4-dinitrophenyl)-3-substituted-phenyl-1H-pyrazol-4-yl)-1,2,4-triazolidine-3-thione derivatives (3a-o) with high yields (90-96%) by reaction of 1-(2,4-dinitrophenyl)-3-substituted-phenyl-1H-pyrazole-4-carbaldehydes and thiosemicarbazide using water as a greener solvent at 80 °C within 30-45 min. Materials with different percentages of Bi₂O₃ on ZrO₂ were prepared by simple wet impregnation method. The synthesized material has been characterized by various techniques (XRD, TEM, SEM, BET). 2.5% Bi₂O₃/ZrO₂ proved superior catalyst. The Bi₂O₃/ZrO₂ catalyst is easily recoverable and reused up to sixth run with no loss of activity. Excellent yields, short reaction time, avoidance of hazardous solvents, and no need for chromatographic purifications are the proven advantages.

Heterometallic CoIIIZnII Schiff Base Catalyst for Mild Hydroxylation of C(sp3)–H Bonds of Unactivated Alkanes: Evidence for Dual Mechanism Controlled by the Promoter

The novel Schiff base complex [CoIIIZnIIL3Cl2]·CH3OH (1) was synthesized by interaction of zinc powder, cobalt(II) chloride and methanol solution of the pre-formed HL in air (HL is the product of condensation of o-vanillin and methylamine) and characterized by IR, UV-Vis and NMR spectroscopy, ESI-MS and single crystal X-ray diffraction analysis. In the heterometallic core of 1 the two metal centers are bridged by deprotonated phenoxy groups of the L− ligands with the cobalt-zinc separation of 3.123 Å. Catalytic investigations demonstrated a pronounced activity of 1 towards mild alkane oxidation with m-chloroperbenzoic acid (m-CPBA) as an oxidant and cis-1,2-dimethylcyclohexane (cis-1,2-DMCH) as the model substrate. The influence of the nature of different promoting agents of various acidities (from HOTf to pyridine) on the catalytic process was studied in detail and a pronounced activity of 1 in the presence of nitric acid promoter was found, also showing a high retention of stereoconfiguration of the substrate (>99% for cis-1,2-DMCH). The best achieved yield of tertiary cis-alcohol based on the oxidant was 61%, with a turnover number (TON) of 198 for nitric acid as promoter. The 18O-incorporations into the alcohols when the reactions were performed under 18O2 atmosphere using acetic and nitric acid promoters, suggest that the cis-1,2-DMCH hydroxylation proceeds by two distinct pathways, a non-stereoselective and a stereoselective one (with and without involvement of a long-lived free carbon radical, respectively). The former dominates in the case of acetic acid promoter and the latter is realized in the case of HNO3 promoter.

A mononuclear tantalum catalyst with a peroxocarbonate ligand for olefin epoxidation in compressed CO2

A mononuclear tantalum complex bonded to a peroxocarbonate ligand has been proved to be particularly important in the epoxidation reactions.

Oxidative functionalization of C–H compounds induced by the extremely efficient osmium catalysts (a review)

In recent years, osmium complexes have found applications not only in thecis-hydroxylation of olefins but also very efficient in the oxygenation of C–H compounds (saturated and aromatic hydrocarbons and alcohols) by hydrogen peroxide as well as organic peroxides.

Mixed-ligand aminoalcohol-dicarboxylate copper(II) coordination polymers as catalysts for the oxidative functionalization of cyclic alkanes and alkenes

New copper(II) catalytic systems for the mild oxidative C–H functionalization of cycloalkanes and cycloalkenes were developed, which are based on a series of mixed-ligand aminoalcohol-dicarboxylate coordination polymers, namely [Cu2(μ-dmea)2(μ-nda)(H2O)2]n·2nH2O (1), [Cu2(μ-Hmdea)2(μ-nda)]n·2nH2O (2), and [Cu2(μ-Hbdea)2(μ-nda)]n·2nH2O (3) that bear slightly different dicopper(II) aminoalcoholate cores, as well as on a structurally distinct dicopper(II) [Cu2(H4etda)2(μ-nda)]·nda·4H2O (4) derivative [abbreviations: H2nda, 2,6-naphthalenedicarboxylic acid; Hdmea, N,N′-dimethylethanolamine; H2mdea, N-methyldiethanolamine; H2bdea, N-butyldiethanolamine; H4etda, N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine]. Compounds 1–4 act as homogeneous catalysts in the three types of model catalytic reactions that proceed in aqueous acetonitrile medium under mild conditions (50–60°C): (i) the oxidation of cyclohexane by hydrogen peroxide to cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone, (ii) the oxidation of cycloalkenes (cyclohexene, cyclooctene) by hydrogen peroxide to a mixture of different oxidation products, and (iii) the single-pot hydrocarboxylation of cycloalkanes (cyclopentane, cyclohexane, cycloheptane, cyclooctane) by carbon monoxide, water, and a peroxodisulfate oxidant into the corresponding cycloalkanecarboxylic acids. The catalyst and substrate scope as well as some mechanistic features were investigated; the highest catalytic activity of 1–4 was observed in the hydrocarboxylation of cycloalkanes, allowing to achieve up to 50% total product yields (based on substrate).

Rearrangements of organic peroxides and related processes

This review is the first to collate and summarize main data on named and unnamed rearrangement reactions of peroxides. It should be noted, that in the chemistry of peroxides two types of processes are considered under the term rearrangements. These are conventional rearrangements occurring with the retention of the molecular weight and transformations of one of the peroxide moieties after O-O-bond cleavage. Detailed information about the Baeyer-Villiger, Criegee, Hock, Kornblum-DeLaMare, Dakin, Elbs, Schenck, Smith, Wieland, and Story reactions is given. Unnamed rearrangements of organic peroxides and related processes are also analyzed. The rearrangements and related processes of important natural and synthetic peroxides are discussed separately.

Oxidation of olefins with H2O2 catalysed by salts of group III metals (Ga, In, Sc, Y and La): epoxidation versus hydroperoxidation

Simple soluble salts of the group III metals (Ga, In, Sc, Y and La) exhibit catalytic activity towards oxidation of olefins with H₂O₂via two competitive channels (i.e. allylic hydroperoxidation and epoxidation).

Synthesis of a BiFeO3 nanowire-reduced graphene oxide based magnetically separable nanocatalyst and its versatile catalytic activity towards multiple organic reactions

Herein, we report for the first time synthesis of a BiFeO₃ nanowire-reduced graphene oxide nanocatalyst (BFO–RGO) using a hydrothermal method.

p-Tolylimido rhenium(v) complexes with phenolate-based ligands: synthesis, X-ray studies and catalytic activity in oxidation with tert-butylhydroperoxide

The reactions of mer-[Re(p-NTol)X₃(PPh₃)₂] with phenolate-based ligands gave 16 new rhenium(v) complexes. Only a few of them exhibited high catalytic activity.