Insertion Reactions Research Articles

Elucidating ligand effects in rhodium(III)-catalyzed arene–alkene coupling reactions

Rhodium(III)-catalyzed CH couplings of arenes with alkenes are among the most powerful methods for CC bond formation. For these transformations, subtle manipulation of ancillary ligands can lead to dramatic changes in reactivity and selectivity. However, detailed mechanistic studies concerning the ligand effects are rare. In this study, we investigated the origin of ligand-controlled product-selectivity in rhodium(III)-catalyzed CH couplings of arenes with alkenes, using a series of well-defined [CpXRhIII] complexes that feature electronically or sterically distinct CpX (Cp (η5-C5H5), CpCF3 (η5-C5Me4CF3) and Cp* (η5-C5Me5)) ligands. A combination of experimental and theoretical investigations showed that (i) rhodium hydride species containing the electron rich Cp* ligand can undergo reinsertion of the alkene, thereby allowing rhodium-walking, (ii) rhodium hydride species involving the electron-deficient Cp or CpCF3 ligands prefer reductive elimination rather than alkene insertion. These findings offer valuable insights on future rational catalyst design for selective arene–alkene cross coupling reactions.

Transition-Metal-Free Insertion of Diazo Compounds, N-Arylsulfonylhydrazones or Ylides into Organoboronic Acids or Their Derivatives

AbstractInsertion reactions of carbenes or ylides with organoboronic acids or their derivatives have emerged as valuable methods for coupling or homologation of organoboron compounds under metal-free conditions. The crucial steps of these reactions are coordination of the electron-rich carbon centers of the carbene precursors or ylides to the electron-poor boron center, followed by 1,2-migration of the corresponding tetracoordinated boron intermediates. This type of unique transformation provides an efficient method for the construction of C–C or C–X (X = H, B) bonds. Moreover, the C–B bonds generated by such transformations can be utilized as a handle for further derivatization or iterative homologations. In this Account, we summarize the developments in this arena according to the reactive diazo compound, N-arylsulfonylhydrazone or ylide species involved.1 Introduction2 Reactions with Diazo Compounds3 Reactions with N-Arylsulfonylhydrazones4 Reactions with Ylides5 Conclusion

Experimental and Computational Studies on RuII -Catalyzed C7-Allylation of Indolines with Allyl Bromide.

The selective C7-allylation of indolines with allyl bromide under ruthenium catalysis has been revealed here. Under established reaction conditions, C7-allylation of various indolines, including drug compounds, was accomplished with good selectivity and yields. Based on combined experimental and density functional theory (DFT) studies, the olefin insertion route was energetically favorable among four possible pathways. Experimental and DFT studies further revealed that the C-H activation is a reversible rate-limiting step.

Transition Metal-catalyzed Regioselective Direct C-H Arylations Using Quinone Diazide as Arylating Agent: A Mini Review

Abstract: Quinone diazides are a class of diazo compounds, having a planar six-membered ring system with diazo, carbonyl and al-kene groups in conjugation. Earlier it was used in optical, electronic, polymer materials etc. In the last few years, various rearrangements reactions and insertion reactions were explored by these diazo compounds via the formation of metallo-carbenoids. Recently, it has been used to incorporate phenol moieties to hydrocarbons or arene/heteroarenes systems via transition metal-catalyzed C-H bond activation. The reactions proceed via C-H bond insertion or migratory insertion of metal-carbenes. In many cases, the site-selectivities were obtained by the guidance of various directing groups (remova-ble or non-removable). At the same time, several asymmetric approaches were also studied to incorporate phenol deriv-atives to arenes/heteroarenes furnishing compounds showing axial chirality with high stereoselectivity. In this review, we will mainly focus on directed regioselective arylation with quinone diazides under transition metal catalysis through C-H bond activation.

Effect of Cations on the Electrochemical Properties of Insertion Reactions Using Prussian Blue Analogues

Effect of Cations on the Electrochemical Properties of Insertion Reactions Using Prussian Blue Analogues

Chemo- and Diastereoselective Entries into All-Carbon α-Quaternary Aldehydes via C-C Insertion of 4-Diazoisoquinolin-3-ones into C-CHO Bonds.

Herein, we describe a chemo- and diastereoselective formal C-C insertion reaction of 1,2-disubstituted 4-diazo-3(2H)-isoquinolones and 4-diazoisochroman-3-one into C-CHO bonds of aldehydes, delivering all-carbon α-quaternary aldehydes bearing medicinally important 1,4-dihydro-3(2H)-isoquinolone scaffold. Our protocol is enabled by the preferential 1,2-carbon migration over more common 1,2-H shift. The corresponding reaction tolerates a wide range of functionalities in both aldehyde and diazo components, giving the target homologated aldehydes in generally high yields. The synthetic utility of this method has been further showcased by some transformations of the formyl moiety.

Charge Storage Mechanism in Electrospun Spinel-Structured High-Entropy (Mn0.2 Fe0.2 Co0.2 Ni0.2 Zn0.2 )3 O4 Oxide Nanofibers as Anode Material for Li-Ion Batteries.

High-entropy oxides (HEOs) have emerged as promising anode materials for next-generation lithium-ion batteries (LIBs). Among them, spinel HEOs with vacant lattice sites allowing for lithium insertion and diffusion seem particularly attractive. In this work, electrospun oxygen-deficient (Mn,Fe,Co,Ni,Zn) HEO nanofibers are produced under environmentally friendly calcination conditions and evaluated as anode active material in LIBs. A thorough investigation of the material properties and Li+ storage mechanism is carried out by several analytical techniques, including ex situ synchrotron X-ray absorption spectroscopy. The lithiation process is elucidated in terms of lithium insertion, cation migration, and metal-forming conversion reaction. The process is not fully reversible and the reduction of cations to the metallic form is not complete. In particular, iron, cobalt, and nickel, initially present mainly as Fe3+ , Co3+ /Co2+ , and Ni2+ , undergo reduction to Fe0 , Co0 , and Ni0 to different extent (Fe < Co < Ni). Manganese undergoes partial reduction to Mn3+ /Mn2+ and, upon re-oxidation, does not revert to the pristine oxidation state (+4). Zn2+ cations do not electrochemically participate in the conversion reaction, but migrating from tetrahedral to octahedral positions, they facilitate Li-ion transport within lattice channels opened by their migration. Partially reversible crystal phase transitions are observed.

Vanillin and organosilicon functionalized graphene oxide modified ester resin composite coatings with excellent anti-corrosion properties

Epoxy vinyl ester resin is widely used in the field of corrosion protection because of its excellent corrosion resistance and mechanical properties. However, due to the ease of hydrolysis of the ester group in the ester resin, the barrier ability of the coating is reduced, which will accelerate metal corrosion. The existing literature shows that the use of nano-sheet materials such as graphene oxide (GO) can effectively enhance the barrier properties of the coating. In order to solve the poor compatibility and electrical corrosion phenomenon of GO, in this work, renewable vanillin and silicone with excellent anti-corrosive properties were grafted to GO (APGO) by insertion reaction and D-A reaction. Subsequently, a series of new APGO-based epoxy vinyl ester resin composites with excellent mechanical properties and anti-corrosion properties were prepared by thermal crosslinking polymerization. The results showed that when the additive amount of APGO was 0.1 wt%, the comprehensive performance of the composite was the best: the conductivity (1.9 × 10−13–5.6 × 10−13 S/cm) of the composite was far lower than the critical electrical insulation value (10−9 S/cm), the breaking strength was improved by 38.0 %, the contact angle was increased by 65.7 %, and its anti-corrosion efficiency was up to 99.03 %. After 70 days of immersion in 3.5 wt% salt water, the impedance modulus of the composite at low frequency (Zf = 0.01 Hz) remained 2.23 × 1010 Ω cm2, which was 2 orders of magnitude higher than that of pure epoxy vinyl ester resin (2.43 × 108 Ω cm2). The above results were not only related to the maze effect formed by APGO, but also related to the increased crosslinking density of the system. This work provided a novel strategy for preparing GO-based composites with excellent comprehensive properties.

Process Development of Heterogeneous Rh Catalyzed Carbene Transfer Reactions Under Continuous Flow Conditions.

A very simple Rh-based catalyst operates under heterogeneous flow conditions for the carbene transfer of methyl diazoacetate (MDA) with several substrates. Two different methods for heterogenizing the catalyst in a column reactor have been applied. Different X-H (X=O, S, Si, CH2 ) were successfully functionalized by the carbene and cyclopropenation was performed under very mild continuous flow conditions. Following these promising results, catalyst recycling experiments using both methodologies were conducted in which up to 5 catalytic cycles have been achieved for the carbene O-H insertion reaction and interestingly, a sequential transformation of different substrates with up to 10 consecutive runs per reactor were achieved with no loss in the catalytic activity, thus allowing the production of families of compounds.

Catalytic N‐H Insertion Reactions with α‐Diazoacetates: An Efficient Method for Enantioselective Amino Acid Synthesis

AbstractAs the monomers of proteins, amino acids are critical in chemistry and biology, playing important roles in multiple fields such as synthetic chemistry, medicinal chemistry, and materials chemistry. Unlike proteinogenic amino acids, unnatural amino acids can be difficult to obtain from living organisms and generally are synthesized chemically. Recently, a method involving the asymmetric N−H bond carbene insertion reaction with α‐diazoacetates as the carbene precursor has shown high enantioselectivity and good functional group tolerance, allowing for the facile synthesis of natural and unnatural amino acids and the introduction of new concepts in catalysis.

Oxidation of chlortetracycline and its isomers by Botrytis aclada laccase in the absence of mediators: pH dependence and identification of transformation products by LC-MS.

Tetracyclines are antibiotics considered emerging pollutants and currently, wastewater treatment plants are not able to remove them efficiently. Laccases are promising enzymes for bioremediation because they can oxidize a wide variety of substrates. The aim of this study was to evaluate the Botrytis aclada laccase for the oxidation of chlortetracycline and its isomers in the absence of a mediator molecule, at a pH range between 3.0 to 7.0, and to characterize the transformation products by LC-MS. Chlortetracycline and three isomers were detected in both, controls and reaction mixtures at 0h and in controls after 48h of incubation but in different proportions depending on pH. An additional isomer was also detected, but only in the presence of BaLac. Based on the transformation products identified in the enzymatic reactions and information from literature, we assembled a network of transformation pathways starting from chlortetracycline and its isomers. The spectrometric analysis of the products indicated the probable occurrence of oxygen insertion, dehydrogenation, demethylation and deamination reactions. Four new products were identified, and we also described a novel transformation product without the chloro group. We observed that increasing pH led to higher diversity of main products. This is the first study using the laccase from fungi Botrytis aclada to oxidate chlortetracycline and its isomers and it can be considered as an ecological alternative to be used in bioremediation processes such as wastewater.

Cu(I)-Catalyzed Highly Diastereo- and Enantioselective Constructions of Boron/Carbon Vicinal Stereogenic Centers via Insertion Reaction

Cu(I)-Catalyzed Highly Diastereo- and Enantioselective Constructions of Boron/Carbon Vicinal Stereogenic Centers via Insertion Reaction

Density Functional Theory Calculations for Multiple Conformers Explaining the Regio- and Stereoselectivity of Ti-Catalyzed Hydroaminoalkylation Reactions.

Hybrid Density Functional Theory (DFT) calculations for multiple conformers of the insertion reactions of a methylenecyclopropane into the Ti-C bond of two differently α-substituted titanaaziridines explain the experimentally observed differences in regioselectivity between catalytic hydroaminoalkylation reactions of methylenecyclopropanes with α-phenyl-substituted secondary amines and corresponding stoichiometric reactions of a methylenecyclopropane with titanaaziridines, which can only be achieved with α-unsubstituted titanaaziridines. In addition, the lack of reactivity of α-phenyl-substituted titanaaziridines as well as the diastereoselectivity of the catalytic and stoichiometric reactions can be understood.

Atroposelective Synthesis of N-N Axially Chiral Bipyrroles via Rhodium-Catalyzed C-H Insertion Reaction.

An atroposelective synthesis of bipyrroles with an axially chiral N-N bond has been established via a rhodium-catalyzed C-H bond insertion reaction to provide the desired atropisomers in good yields (up to 97% yield) with good to excellent enantioselectivities (up to 99% ee).

Electrochemical Exploration of Layered Cu-Based Oxychalcogenides Obtained Topochemically via Anionic Redox and Displacement Reaction

Li-rich oxides, operating partially on high-voltage anionic redox, permit energy densities larger than electrode materials relying solely on transition-metal redox. On the contrary, Li-rich sulfides present a lower hysteresis but operate at a lower voltage. Oxysulfide electrodes, if adequately designed, can bridge this gap and offer high energy density with a minor penalty of hysteresis or capacity. Tetragonal-layered CuMOX (M = Bi/La, X = S/Se) chalcogenides are explored in this direction, and we found that Cu can be extracted at room temperature both electrochemically and chemically with different outcomes, some of which lead to new layered monoclinic bismuth “oxyperchalcogenide” oxidized phases, BiOX*, with dimerized S/Se. Moreover, we show that these new BiOX* phases can insert lithium to form new tetragonal-layered LiBiOX phases, isostructural to pristine CuBiOX. Both the CuBiOX and BiOX* phases are shown to insert four lithium ions via conversion and intercalation–conversion reactions, respectively. Further, we demonstrate the importance of the host cation on the above insertion reactivity by replacing Bi with La to produce a new layered tetragonal phase Cu1–xLixLaOS. The encountered different reaction pathways are rationalized by theoretical calculations. This work shows that Cu-based layered oxychalcogenides can offer rich hunting grounds for new metastable electrochemically active layered materials.

Access to Polysubstituted Furan Derivatives via Cascade Oxy-palladation and Hydrocarbofunctionalization of Unactivated Alkenes.

The development of an expedient strategy for the synthesis of biologically relevant multisubstituted furans is a much-desired yet challenging task. Herein, we report an efficient and versatile strategy involving two different pathways for the construction of diverse polysubstituted C3- and C2-substituted γ-furanyl carboxylic acid derivatives. The synthetic approach for C3-substituted furans involves intramolecular cascade oxy-palladation of alkyne-diols followed by the regioselective coordinative insertion of unactivated alkenes. In contrast, C2-substituted furans were obtained exclusively by performing the protocol in a tandem manner.

Effects of overvoltage and temperature on the lithium insertion kinetics of MgMn2O4

The power capability of lithium-ion batteries strongly depends on the reaction kinetics of the lithium insertion material used in the electrodes. Previously, chronoamperometry revealed that the lithium insertion reaction of MgMn2O4 differs between static and dynamic processes and that the dynamic process consists of a nucleation–growth process followed by diffusion. Herein, we present the overvoltage and temperature dependence of the reaction rate of MgMn2O4 through chronoamperometry results under different applied voltages and temperatures. The rate constant of each process is determined by fitting the measured current profile to a solid-state reaction model. The rate constant of the nucleation-growth process exhibits an Arrhenius relationship with temperature and a Tafel-like relationship with overvoltage, whereas that of diffusion exhibits an Arrhenius relationship with temperature and does not depend on overvoltage. These dependencies are different because nucleation–growth is a reaction process on the particle surface, whereas diffusion is a reaction process occurring inside the particle. Accordingly, the rate-determining step of lithium insertion under various operating conditions is discussed.

Composite cathode with low-defect NiFe Prussian blue analogue on reduced graphene oxide for aqueous sodium-ion hybrid supercapacitors

Although sodium-ion hybrid supercapacitor (Na-ion HSC) has attracted great interest, exploitation of suitable cathode materials for reversible Na+ insertion reaction remains a challenge. Herein, a novel binder-free composite cathode with highly crystallized NiFe Prussian blue analogue (NiFePBA) nanocubes in-situ grown on reduced graphene oxide (rGO) was fabricated via sodium pyrophosphate (Na4P2O7)-assisted co-precipitation and the subsequent ultrasonic spraying and chemical reduction. Profiting from the low-defect PBA framework and close interface contact of PBA and conductive rGO, the NiFePBA/rGO/carbon cloth composite electrode exhibits a high specific capacitance of 451F g−1, remarkable rate performance and satisfactory cycling stability in aqueous Na2SO4 electrolyte. Impressively, the aqueous Na-ion HSC assembled with the composite cathode and activated carbon (AC) anode manifests a high energy density of 51.11 Wh kg−1, superb power density of 10 kW kg−1 and the intriguing cycling stability. This work may open a door for scalable fabrication of binder-free PBA cathode material for aqueous Na-ion storage.

Rh(II)/Pd(0) Dual Catalysis: Interception of Ammonium Ylide with Allyl Palladium to Construct 2,2-Disubstituted Tetrahydroquinoline Derivatives.

New synthetic methods to construct 2,2-disubstituted tetrahydroquinoline derivatives are of significant value in pharmaceutical chemistry. Herein, a Rh(II)/Pd(0) dual-catalyzed diazo α-aminoallylation reaction has been developed between allylpalladium(II) and ammonium ylides derived from the Rh2(OAc)4-mediated intramolecular N-H bond insertion reaction of diazo compounds, affording various 2,2-disubstituted tetrahydroquinoline derivatives in good yields up to 93% with high chemoselectivities under mild reaction conditions. A substrate scope investigation reveals broad ester substituent tolerance, and control experiments provide the basis for a proposed reaction mechanism.

Enantioselective Hydroalkenylation and Hydroalkynylation of Alkenes Enabled by a Transient Directing Group: Catalyst Generality through Rigidification.

The catalytic enantioselective synthesis of α-chiral alkenes and alkynes represents a powerful strategy for rapid generation of molecular complexity. Herein, we report a transient directing group (TDG) strategy to facilitate site-selective palladium-catalyzed reductive Heck-type hydroalkenylation and hydroalkynylation of alkenylaldehyes using alkenyl and alkynyl bromides, respectively, allowing for construction of a stereocenter at the δ-position with respect to the aldehyde. Computational studies reveal the dual beneficial roles of rigid TDGs, such as L-tert-leucine, in promoting TDG binding and inducing high levels of enantioselectivity in alkene insertion with a variety of migrating groups.