Herein, we report a cascade process that is initiated by radical Brook rearrangement and promoted by 1,5-hydrogen atom transfer. A series of α-fluoroalkyl alkyl secondary alcohols were synthesized with unactivated terminal olefins and α-fluoroalkyl-α-silyl methanols. The strategy features mild reaction conditions and broad substrate scope. The diversified down-stream transformations demonstrated the synthetic potential of the reaction.
Monthly Archives: September 2023
Upcycling of Polypropylene Wastes via Catalytically C‐H Modification with Polar Olefins
While polypropylene (PP) is one of the most widely used polyolefin materials, its post-functionalization has been a continuously researched topic in the polymer field since it could significantly improve physical and chemical properties by introducing polar groups, beneficial for development of the next generation of polyolefin materials. In this work, we describe the development of a visible-light promoted, environmentally friendly iron-catalyzed strategy and establishing of the reaction scope for C−H alkylated modification of polypropylene. Under our conditions, various polypropylenes could be functionalized with diverse polar alkenes with good levels of functionalization (LOF). The properties of the resulting polymers were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and tensile testing. Polypropylene wastes could also be upcycled. While the incorporation of the polyglycol groups enhanced hydrophilicity, the installation of the ester groups increased the miscibility with other polymers by acting as a compatibilizer for polystyrene and polyethylene.
Single‐Site Ni‐Grafted TiO2 with Diverse Coordination Environments for Visible‐Light Hydrogen Production
Solar hydrogen production at a high efficiency holds the significant importance in the age of energy crisis, while the micro-environment manipulation of active sites on photocatalysts plays a profound role in enhancing the catalytic performance. In this work, a series of well-defined single-site Ni-grafted TiO2 photocatalysts with unique and specific coordination environments, 2,2'-bipyridine-Ni-O-TiO2 (T-Ni Bpy) and 2-Phenylpyridine-Ni-O-TiO2 (T-Ni Phpy), were constructed with the methods of surface organometallic chemistry combined with surface ligand exchange for visible-light-induced photocatalytic hydrogen evolution reaction (HER). A prominent rate of 33.82 μmol•g-1•h-1 and a turnover frequency of 0.451 h-1 for Ni are achieved over the optimal catalyst T-Ni Bpy for HER, 260-fold higher than those of Ni-O-TiO2. Fewer electrons trapped oxygen vacancies and a larger portion of long-lived photogenerated electrons (> 3 ns, ~ 52.9%), which were demonstrated by the electron paramagnetic resonance and femtosecond transient IR absorption, are corresponding to the photocatalytic HER activity over the T-Ni Bpy. The number of long-lived free electrons injected from the Ni photoabsorber to the conduction band of TiO2 is one of the determining factors for achieving the excellent HER activity.
Organometallic N‐acylhydrazones of 5‐nitrofuran and 5‐nitrothiophene based: Synthesis, electrochemical, antiparasitic evaluation, and computational study
We reported the synthesis, electrochemical, and antiparasitic properties and the structure–activity relationship (SAR) study of new organometallic N-acylhydrazones of general formula [R1-CH=N-NH-C(O)-(R2)] with (R1 = ferrocenyl or cyrhetrenyl; R2 = 5-nitrofuryl or 5-nitrothienyl).
In searching for new therapeutic agents for treating American trypanosomiasis and Human African trypanosomiasis, four nitroheterocyclic acylhydrazones of general formulae [R1-CH=N-NH-C(O)-(5-C4H2X)] (where R1 = ferrocenyl or cyrhetrenyl, and X = O or S) have been synthesized and characterized by spectroscopic techniques. Comparative studies of their stability by 1H-NMR and UV–Vis experiments were reported. Single-crystal X-ray diffraction confirmed the molecular structures of NF-1 and NT-2. Their X-ray crystal structures reveal that both adopt an E-configuration on the C=N moiety. Regarding the -NH-C(O)- bond, the structure of NF-1 confirmed a trans conformation, while NT-2 exhibited a cis-amide conformation. The cyclic voltammetry and electron spin resonance (ESR) experiments were conducted to study the electrochemical behavior of N-acylhydrazones. The antiparasitic activities of compounds against Trypanosoma cruzi (epimastigotes) and Trypanosoma brucei (trypomastigotes) revealed that cyrhetrenyl complexes were more effective than their ferrocenyl analogs. The cyrhetrenyl derivative NT-2 (EC50 = 2.25 μM) showed activity against T. brucei comparable to the standard drug nifurtimox (Nfx, EC50 = 3.56 μM). The ferrocenyl compound NT-1 (>200 μM) was at least two times less cytotoxic than the Nfx (88.7 μM) against the L6 rat skeletal myoblast cell line and exhibited a selectivity like Nfx toward T. brucei. Density functional theory (DFT) calculations were utilized as an approximation to explain the impact of organometallic and heterocyclic rings on antiparasitic activities. This study supported the experimental results, confirming that the cyrhetrenyl fragment in N-acylhydrazone derivatives plays a significant role in the antitrypanosomal activity, which can be attributed to an increase in positive charge on the metal.
AOMadillo: A program for fitting angular overlap model parameters
Abstract
The angular overlap model (AOM) is an established parameterization scheme within ligand field theory (LFT). In principle, its application is fairly straightforward, but can be tedious and involve a trial-and-error approach to identify and judge the best set of parameters. With the availability of quantum chemical methods to predict d-d transitions in transition metal complexes, a rich source of computational spectroscopic data with unambiguous assignments to electronic states is available. Herein, we present AOMadillo, a software package that is designed to interface the output of ab initio LFT calculations from the ORCA suite of programs and performs a least-squares fit for a chosen AOM parameterization. Many steps of the AOM parameterization are automated, so that scans of geometric parameters and evaluations of sets of similar complexes are convenient. The fitting routine is highly configurable, allowing the efficient evaluation of different parameter sets.
2‐(o‐Tolyl) Pyridine as Ligand Improves the Efficiency in Ketone Directed ortho‐Arylation
In this work, we explore how adding a catalytic amount of an NC-type ligand improves ketone-directed ortho C−H arylation, whereas a full equivalent shuts down the transformation. Increased catalytic activity stems from the formation of a cyclometallated complex containing the NC-type ligand to provide an intermediate which accelerates the ortho-arylation of the ketone substrate.
Abstract
Herein, we report a ruthenium-catalyzed ketone directed ortho-arylation wherein the addition of a bidentate NC-type ligand, most effectively 2-(o-tolyl) pyridine, significantly enhances the C−H arylation reaction. Various aryl-alkyl ketones, including cyclic, aliphatic, and heterocyclic ones, are competent substrates, and arylboronic acid esters were used as aryl sources. However, substitution with OMe and CF3 in the aromatic ring of the ketone substrates is not tolerated, while such residues on the benzoic ester are possible. Notably, this study provides valuable insights into ketone-directed ortho arylation in the presence of 2-(o-tolyl) pyridine and adds additional options for catalyst and ligand optimization in ruthenium-catalyzed C−H functionalization.
Geopolymer Based Electrodes as New Class of Material for Electrochemical CO2 Reduction
The Front Cover illustrates a chimney made of Sn-modified geopolymer-bricks. Functionalized geopolymers can be applied as hybrid material for construction and as an electrode for CO2 electrolysis to formate. The cover was designed by one of the authors Jürgen Schuster and the designer Verena Stöckl. More information can be found in the Research Article by J. Schuster et al.
Electrochemical Approach for Advanced Flow Reactors via Additive Manufacturing of High Surface Area Ti‐6Al‐4V Anode
Noble-free 3D anode: 3D-printed Ti-6Al-4V electrode was evaluated for its anodic behavior in alkaline solutions with a novel electrochemical approach. According to the ECSA results from voltammetry, 3D Ti-6Al-4V provides 42 times more active surface area than flat plate anodes. It enables effective charge transfer of 911 mA cm−2 from almost non-conductive anodic behavior of a plate structure.
Abstract
Electrochemical processes use expensive noble metal-based anodes which limit industrial implementation. In this study, a noble-metal-free Ti-6Al-4V anode is introduced in an advanced flow reactor. We demonstrate that the 3D additively manufactured electrode can provide a more projected surface area and facilitate anodic reactions under controlled electrolyte conditions. Alkaline NaOH and KOH electrolytes act as anodic electrolytes that are toxic compounds-free and enable corrosion control. Impedance and voltammetry responses to electrochemical reactions are studied. The electrochemical active surface area of the 4 rods scaffold geometry is 42 times higher than a flat plate anode. Therefore, improved charge transfer is achieved in the flow reactor incorporating the 3D Ti-6Al-4V electrode due to the increased surface area and wettability. The structure of almost non-conductive passivation on a flat plate anode is changed to unstable passivation due to the 3D scaffold structure. This enables effective charge transfer of 911 mA cm−2 at higher potentials up to 5 V for 1.5 m KOH in a non-flow condition. Furthermore, a 1 m KOH solution delays metal ion dissolution from the anode surface by acting as a corrosion-controlling medium. 3D Ti-6Al-4V is likely to be an affordable alternative anode in alkaline environmentally friendly electrochemical applications.
Radiation‐Induced Transfer of Charge, Atoms, and Energy within Isolated Biomolecular Systems
In this review, we survey mainly experimental but also theoretical work, focusing on radiation-induced intra- and inter-molecular transfer of charge, atoms, and energy within biomolecular systems in the gas phase. Building blocks of DNA, proteins, and saccharides, but also antibiotics are considered. The emergence of general processes as well as their timescales and mechanisms are highlighted.
Abstract
In biological tissues, ionizing radiation interacts with a variety of molecules and the consequences include cell killing and the modification of mechanical properties. Applications of biological radiation action are for instance radiotherapy, sterilization, or the tailoring of biomaterial properties. During the first femtoseconds to milliseconds after the initial radiation action, biomolecular systems typically respond by transfer of charge, atoms, or energy. In the condensed phase, it is usually very difficult to distinguish direct effects from indirect effects. A straightforward solution for this problem is the use of gas-phase techniques, for instance from the field of mass spectrometry. In this review, we survey mainly experimental but also theoretical work, focusing on radiation-induced intra- and inter-molecular transfer of charge, atoms, and energy within biomolecular systems in the gas phase. Building blocks of DNA, proteins, and saccharides, but also antibiotics are considered. The emergence of general processes as well as their timescales and mechanisms are highlighted.
Metal‐Free Photoinduced Defluorinative Carboxylation of Trifluoromethylalkenes with Formate
In this work, we have described an efficient protocol for the photoinduced defluorocarboxylation of α-trifluoromethylstyrene using formate as the CO2 radical anion precursor, which successfully yields a wide variety of gem-difluorovinylacetic acids with excellent functional group tolerance.
Abstract
Herein, we report an efficient protocol in which formate is used as a precursor of the CO2 radical anion for the photoinduced defluorocarboxylation of α-trifluoromethylstyrene. A wide range of gem-difluorovinylacetic acids bearing a variety of functional groups were successfully obtained in the absence of metal catalysts. The synthetic value of this protocol was highlighted by successful gram-scale synthesis and late-stage modification for complex biologically active molecules. This protocol provides a complementary method that extends the range of currently available methodologies for accessing the structurally versatile gem-difluoroalkenes.