Transfer Catalyst Research Articles

Disparity between rate and selectivity in the controlled synthesis of gradient conjugated copolymers

In this report, a one-pot synthesis of gradient copolymers is attempted employing Kumada catalyst transfer condensative polymerization (KCTCP). The hypothesis that a more reactive monomer is preferentially being built into the chain at the beginning, while the slower reacting monomer is only being built into the chain at the end due to it being in excess, is investigated. The monomer rate constants are influenced by the usage of differently sized sidechains (octyl versus 3-octyldodecyl) and nucleophilicity of the monomers (thiophene versus selenophene). Nonetheless, while the rate constants differ by a factor 2, no selectivity is obtained. The cause thereof is further investigated by increasing the sterical crowdedness around the catalyst-complex by employing a 4-substituted monomer, the polymerization of which also gave rise to random copolymers. Accompanied by density functional theory calculations of the geometry and Gibbs free energy, it is concluded that the distance between the nickel catalyst and the polymer chain is much smaller compared to the distance between the catalyst and the incoming monomer. This results in different polymerization rates (depending on the polymer-nickel complex), while having no selectivity for one incoming monomer over the other.

Advances in Combined Asymmetric Catalysis of Transition Metal/Phase Transfer Catalysts

Phase‐transfer catalysts (PTCs) are chemical agents that facilitate the transfer of molecules or ions between different reaction phases, thereby accelerating heterogeneous reaction processes. Transition metal catalysts are renowned for their versatility in breaking inert chemical bonds and forming new carbon‐carbon bonds. Over the past two decades, integrating metal catalysts with phase‐transfer catalysts has emerged as a highly valuable and adaptable strategy in modern organic synthesis. This combined catalytic approach highlights the enhanced synthetic capabilities and demonstrates the benefits of merging these two catalytic systems. This review provides an overview of recent advancements in asymmetric catalysis that utilize the synergy between metal and phase‐transfer catalysts, focusing on their role in the rapid and efficient synthesis of complex organic molecules with precise stereochemistry.

A design kinetic and hydrodynamic study of a coupled dual fluidized bed MTO reactor-regenerator system

The methanol-to-olefin (MTO) process, employing a dual-fluidized bed system, has introduced a new and reliable route for producing light olefins. This study intends to employ a comprehensive approach to simultaneously design and evaluate the reactor and regenerator performance. Namely, an inclusive design for a pilot-scale MTO system, encompassing the reactor, regenerator, interconnected catalyst transfer pipelines, and other critical operational aspects, is presented. The computational fluid dynamics (CFD) method using the Eulerian-Eulerian model was used to evaluate hydrodynamics, while the coupled reactor-regenerator kinetic model was developed by combining reaction kinetics with the two-phase model. The models were validated against experimental data and demonstrated a promising agreement. More importantly, an innovative procedure was devised to apply these modelling techniques to design this dual-fluidized bed system—the final design for the 10 kg catalyst inventory in the reactor at the pilot scale. The system achieves methanol conversion of 98.87 %, with ethylene and propylene product mass fractions of 45.51 % and 37.79 %, respectively.

Highly efficient nanosized MoS2/MoP heterocatalyst for enhancing hydrogen evolution reaction over a wide pH range

Energy consumption associated with the catalysts contributes partly to the high ohmic resistance arising from the low conductivity of the catalyst and poor charge transfer between nanoparticles, which has been difficult to study due to the complicated nanostructured framework of the catalysts. We constructed a novel heterostructure electrocatalyst (MoS2/MoP@NC) composed of nanosized MoS2/MoP heterostructures anchoring on hierarchical N-doped carbon for smoothing electron transfer in boosting hydrogen evolution reaction (HER). With the merits of large surface area, rapid charge transfer, and optimized electronic structure induced by charge transfer across the sufficient interface, the optimal MoS2/MoP@NC (MoSP) catalyst shows a competitive overpotential of 140 (0.5 M H2SO4), 76 (1.0 M KOH), and 103 mV (0.5 M NaCl &1.0 M KOH) at 10 mA cm−2, respectively. Raman experiment and Density functional theory (DFT) calculations reveal the formation of Mo-S-Mo bonds between MoS2 and MoP, which favor enhancing the Femi level to facilitate the electron transfer, therefore regulating the electronic structure for the optimization of adsorption energy of hydrogen intermediate. Based on the experimental results, we constructed an energy consumption model of catalysts, where energy consumption comes from three aspects. The heterostructure design decreases the energy consumption of the catalysts greatly compared to the single-phase Mo-based catalyst of MoS2 (78.0%) and MoP (45.2%) in alkaline electrolytes.

One-Step Catalyst-Transfer Macrocyclization: Expanding the Chemical Space of Azaparacyclophanes.

In this paper, we report on a one-step catalyst-transfer macrocyclization (CTM) reaction, based on the Pd-catalyzed Buchwald-Hartwig cross-coupling reaction, selectively affording only cyclic structures. This route offers a versatile and efficient approach to synthesize aza[1n]paracyclophanes (APCs) featuring diverse functionalities and lumens. The method operates at mild reaction temperatures (40 °C) and short reaction times (∼2 h), delivering excellent isolated yields (>75% macrocycles) and up to 30% of a 6-membered cyclophane, all under nonhigh-dilution concentrations (35-350 mM). Structural insights into APCs reveal variations in product distribution based on different endocyclic substituents, with steric properties of exocyclic substituents having minimal influence on the macrocyclization. Aryl-type endocyclic substituents predominantly yield 6-membered macrocycles, while polycyclic aromatic units such as fluorene and carbazole favor 4-membered species. Experimental and computational studies support a proposed mechanism of ring-walking catalyst transfer that promotes the macrocycle formation. It has been found that the macrocyclization is driven by the formation of cyclic conformers during the oligomerization step favoring an intramolecular C-N bond formation that, depending on the cycle size, hinges on either preorganization effect or kinetic increase of the reductive elimination step or a combination of the two. The CTM process exhibits a "living" behavior, facilitating sequential synthesis of other macrocycles by introducing relevant monomers, thus providing a practical synthetic platform for chemical libraries. Notably, CTM operates both under diluted and concentrated regimes, offering scalability potential, unlike typical macrocyclization reactions usually operating in the 0.1-1 mM range.

Intramolecular catalyst transfer on silylene group between benzene rings in Suzuki–Miyaura coupling reaction: synthesis of σ−π conjugated cyclic polymers

Intramolecular catalyst transfer on silylene group between benzene rings in Suzuki–Miyaura coupling reaction: synthesis of σ−π conjugated cyclic polymers

Synthesis and end-group control of soluble, high-molecular-weight hyperbranched poly(phenylene thienylene)s by non-stoichiometric A2 + B3 Suzuki-Miyaura polycondensation without gelation

Non-stoichiometric Suzuki-Miyaura polycondensation of tribromo monomer 1, containing a thienylene group, with diboronic acid (ester) monomer 7 in the presence of tBuPPd catalyst, which has a propensity for intramolecular catalyst transfer on a π-electron face, was investigated. We anticipated that the presence of thienylene groups in the obtained hyperbranched polymer would increase the detection sensitivity in matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry and enable the analysis of the polymer end groups up to the high-molecular-weight region. We first conducted Suzuki-Miyaura reaction of several kinds of 1 with phenylboronic acid 2 in the presence of tBuPPd precatalyst 3. The reaction of tris(5-bromo-4-hexylthien-2-yl)benzene 1c with 2 afforded exclusively tri-substituted product 4c, indicating that the tBuPPd catalyst undergoes intramolecular catalyst transfer on 1c after the first and second substitutions of 1c with 2. The polycondensation of equimolar 1c and pinacol phenylenediboronate 7a (reaction site ratio of Br:BPin = 1.5:1.0 (BPin = pinacol boronate)) was then carried out in the presence of 3 for 3 h, affording hyperbranched polymer with Mn = 37500 without gelation. The product was purified by precipitation. The degree of polymerization (DP) was calculated from the absolute molecular weight, determined by multi-angle light scattering (MALLS) analysis, to be 200, which is a far higher than would be predicted from the Flory-Stockmayer theory at the critical gel point (DP = 6.6). Furthermore, the MALDI-TOF mass spectra showed two series of peaks due to polymer with boronate ends and boronate ends along with one cyclic unit up to m/z of about 7500, as we had expected. The absence of peaks due to polymer with Br ends indicates that the degree of branching (DB) of this hyperbranched polymer is 100 %.

Photoinduced Radical Borylation of Alkyl Chlorides

AbstractThe traditional method for the preparation of alkylboronic esters involves transition metal catalysis or transition metal‐free methods relying on single electron transfer. Each method relies on the suitable choice of catalyst or electron transfer mediator. In this study, we have developed a new method for the synthesis of alkylboronic esters from alkyl chlorides and diboron(4) compounds, without the need for additional metal or non‐metal catalysts. We discovered that under 400 nm visible light irradiation, alkyl chlorides can be activated in the presence of bis(neopentyl glycolato)diboron and an alkoxide base to form alkyl radical intermediates, which then react with diboron(4) compounds, resulting in high yields of alkylboronic esters. The reaction is applicable to both primary and secondary alkyl chlorides. The simplicity of operation and the broad substrate scope of this method make it practical for the synthesis of valuable alkylboronic ester intermediates.

Mechanochemical reduction of alkyl and aryl halides using mesoporous zinc oxide.

In this study, we propose a mechanochemical approach that combines mesoporous ZnO (m-ZnO) as a mechanoredox catalyst and silane-mediated atom transfer chemistry to achieve efficient hydrodehalogenation of organic halides. The reaction can be conducted under mild conditions without the use of a large amount of organic solvent. Substrates ranging from activated alkyl halides to unactivated aryl halides were converted to the corresponding debrominated hydrogenation products in moderate to excellent isolated yields (50-95%). In addition, m-ZnO can be recycled and reused without appreciable loss of catalytic activity.

Dehalogenative deuteration of alkyl and aryl bromides by thiyl radical catalysis under visible-light irradiation.

Herein, we report a mild and practical method for the deuteration of alkyl and aryl bromides by a thiyl radical catalyst and halogen-atom transfer (XAT) using disulfides and silanes under visible-light irradiation. In this study, various organic bromides such as 1°, 2°, and 3°-alkyl bromides and aryl bromides were converted to deuterated products in good to excellent yields and D-incorporation.

Graphene-wrapped yolk-shell of silica-cobalt oxide as high-performing anode for lithium-ion batteries.

Silica (SiO2) shows promise as anode material for lithium-ion batteries due to its low cost, comparable lithium storage discharge potential and high theoretical capacity (approximately 1961 mA h g-1). However, it is plagued by issues of low electrochemical activity, low conductivity and severe volume expansion. To address these challenges, we initially coat SiO2 with CoO, followed by introducing SiO2@CoO into graphene sheets to fabricate an anode composite material (SiO2@CoO/GS) with uniformly dispersed particles and a 3D graphene wrapped yolk-shell structure. The coating of CoO on SiO2 converted the negative surface charge of SiO2 to positive, enabling effective electrostatic interactions between SiO2@CoO and graphene oxide sheets, which provided essential prerequisites for synthesizing composite materials with uniformly dispersed particles and good coating effects. Furthermore, the Co-metal formed during the charge-discharge process can act as a catalyst and electron transfer medium, activating the lithium storage activity of SiO2 and enhancing the conductivity of the electrode, conclusively achieving a higher lithium storage capacity. Ultimately, due to the activation of SiO2 by Co-metal during cycling and the excellent synergistic effect between SiO2@CoO and graphene, SiO2@CoO/GS delivers a high reversible capacity of 738 mA h g-1 after 500 cycles at 200 mA g-1. The product also demonstrates excellent rate performance with a reversible capacity of 206 mA h g-1 at a high specific current of 12.8 A g-1. The outstanding rate performance of SiO2@CoO/GS may be ascribed to the pseudo-capacitive contribution at high specific current upon cycling.

Direct synthesis of π-conjugated polymers with bromoaryl groups in side chains via a chemoselective intramolecular catalyst transfer system

Poly(thienylene phenylene) with bromoaryl groups on its side chains was directly synthesized without protection via the Migita–Kosugi–Stille coupling polycondensation based on a chemoselective intramolecular catalyst transfer system.

UiO66-NH2-TiO2/NiF photoanode for photocatalytic fuel cell by towards simultaneous treatment of antibiotic wastewater and electricity generation

Environmental destruction, water crisis, and clean energy are among the very important challenges worldwide based on sustainable development goals. Photocatalytic fuel cell, a potential candidate for converting chemical energy into electrical energy through a pollution-free method, holds promise in addressing these challenges. In this regard, we investigated the response of a photoanode covered with UiO66-NH2-TiO2/NiF on a porous nickel foam as an attractive electrochemical response to remove antibiotics from aqueous solution and simultaneously produce electricity using a one-step hydrothermal synthesis. Nickel foam with its fine structure provides a suitable space for the interaction of light, catalyst, and efficient mass transfer of reactive molecules. It appears that it can be used as a competitive electrode in fuel cells. In order to investigate the properties of the photocatalyst, structural analyses including XRD, FESEM, FTIR, and UV–vis DRS were utilized. Additionally, polarization and electrochemical tests such as chronoamperometry and EIS were measured to further examine the electrochemical features of the PFC photoanode system. The obtained results under optimal conditions (SMZ concentration = 20 ppm, pH = 6, irradiation time = 120 min) were as follows: removal efficiency of 91.7%, Pmax = 16.98 μW/cm2, Jsc = 96.75 μA/cm2, Voc = 644 mV. The light-induced current flow in UiO66-NH2-TiO2/NiF exhibited prominent and reproducible photocurrent responses, indicating efficient and stable charge separation in TiO2/NiF composite materials, which is a promising strategy for pollutant removal and simultaneous electricity generation.

A SNAr‐Active External Initiator that Enables Heterobifunctional Clickable Polythiophenes

AbstractPoly(3‐hexylthiophene) (P3HT) is a well‐studied conjugated polymer; however, the end‐group functionalization of these polymers is limited by fundamental synthetic challenges. Generally, end‐capping agents are used to terminate the Kumada catalyst transfer polycondensation (KCTP) to install functional end‐groups at the propagating chain end. In this work, it is shown that P3HT can be prepared with a novel SNAr‐active external initiator, followed by end capping to afford heterobifunctional end‐groups that exhibit orthogonal chemical reactivity. This orthogonal chemistry can be leveraged in sequential “click”‐type reactions to ultimately achieve the synthesis of triblock copolymers. More specifically, it is shown that the synthesis of a new pentafluorophenyl initiator allows one to append this readily functionalized group at the initiating end during P3HT synthesis. After reaching the desired degree of polymerization, an ethynyl group is incorporated at the polymer terminus using an end‐capping Grignard reagent. Critically, this heterobifunctional P3HT allows for both orthogonal para‐fluoro thiol reactions, a subset of nucleophilic aromatic substitution (SNAr), and copper‐catalyzed alkyne‐azide cycloadditions (CuAAC). The efficacy of this heterobifunctional polymer design is demonstrated by assessing sequential “click” reactions with different nonconjugated polymer blocks to either end of the P3HT polymer block.

Reviews and syntheses: Iron – a driver of nitrogen bioavailability in soils?

Abstract. An adequate supply of bioavailable nitrogen (N) is critical to soil microbial communities and plants. Over the last decades, research efforts have rarely considered the importance of reactive iron (Fe) minerals in the processes that produce or consume bioavailable N in soils compared to other factors such as soil texture, pH, and organic matter (OM). However, Fe is involved in both enzymatic and non-enzymatic reactions that influence the N cycle. More broadly, reactive Fe minerals restrict soil organic matter (SOM) cycling through sorption processes but also promote SOM decomposition and denitrification in anoxic conditions. By synthesizing available research, we show that Fe plays diverse roles in N bioavailability. Fe affects N bioavailability directly by acting as a sorbent, catalyst, and electron transfer agent or indirectly by promoting certain soil features, such as aggregate formation and stability, which affect N turnover processes. These roles can lead to different outcomes in terms of N bioavailability, depending on environmental conditions such as soil redox shifts during wet–dry cycles. We provide examples of Fe–N interactions and discuss the possible underlying mechanisms, which can be abiotic or microbially meditated. We also discuss how Fe participates in three complex phenomena that influence N bioavailability: priming, the Birch effect, and freeze–thaw cycles. Furthermore, we highlight how Fe–N bioavailability interactions are influenced by global change and identify methodological constraints that hinder the development of a mechanistic understanding of Fe in terms of controlling N bioavailability and highlight the areas of needed research.

Correlating Molar Mass, π-Conjugation, and Optical Properties of Narrowly Distributed Anionic Polythiophenes in Aqueous Solutions.

Polythiophene-based conjugated polyelectrolytes (CPE) are attracting increasing attention as sensor or interface materials in chemistry and biology. While cationic polythiophenes are better understood, limited structural information is available on their anionic counterparts. Limited access to well-defined polymers has made the study of structure-property relationships difficult and clear correlations have remained elusive. By combining controlled Kumada catalyst transfer polymerization with a polymer-analog substitution, regioregular and narrowly distributed poly(6-(thiophen-3-yl)hexane-1-sulfonate)s (PTHS) with tailored chain length are prepared. Analysis of their aqueous solution structures by small-angle neutron scattering (SANS) revealed a cylindrical conformation for all polymers tested, with a length close to the contour length of the polymer chains, while the estimated radii remain too small (<1.5nm) for extensive π-stacking of the chains. The latter is particularly interesting as the longest polymer exhibits a concentration-independent structured absorption typical of crystalline polythiophenes. Increasing the ionic strength of the solution diminishes these features as the Coulomb repulsion between the charged repeat units is shielded, allowing the polymer to adopt a more coiled conformation. The extended π-conjugation, therefore, appears to be a key parameter for these unique optical features, which are not present in the corresponding cationic polythiophenes.

Intramolecular Palladium Catalyst Transfer on Benzoheterodiazoles as Acceptor Monomers and Discovery of Catalyst Transfer Inhibitors.

Intramolecular catalyst transfer on benzoheterodiazoles was investigated in Suzuki-Miyaura coupling reactions and polymerization reactions with tBu3PPd precatalyst. In the coupling reactions of dibromobenzotriazole, dibromobenzoxazole, and dibromobenzothiadiazole with pinacol phenylboronate, the product ratios of monosubstituted product to disubstituted product were 0/100, 27/73, and 89/11, respectively, indicating that the Pd catalyst undergoes intramolecular catalyst transfer on dibromobenzotriazole, whereas intermolecular transfer occurs in part in the case of dibromobenzoxazole and is predominant for dibromobenzothiadiazole. The polycondensation of 1.3 equivalents of dibromobenzotriazole with 1.0 equivalent of para- and meta-phenylenediboronates afforded high-molecular-weight polymer and cyclic polymer, respectively. In the case of dibromobenzoxazole, however, para- and meta-phenylenediboronates afforded moderate-molecular-weight polymer with bromine at both ends and cyclic polymer, respectively. In the case of dibromobenzothiadiazole, they afforded low-molecular-weight polymers with bromine at both ends. Addition of benzothiadiazole derivatives interfered with catalyst transfer in the coupling reactions.

Synthesis of Hyperbranched Polyphenylene with High Degree of Polymerization and 100% Degree of Branching from A2 + B3 Suzuki-Miyaura Polycondensation through Intramolecular Catalyst Transfer

Synthesis of Hyperbranched Polyphenylene with High Degree of Polymerization and 100% Degree of Branching from A₂ + B₃ Suzuki-Miyaura Polycondensation through Intramolecular Catalyst Transfer

Nonstoichiometric Migita-Kosugi-Stille Coupling Polycondensation based on Intramolecular Catalyst Transfer System

In this paper, a nonstoichiometric Migita-Kosugi-Stille coupling polycondensation based on intramolecular catalyst transfer systems has been reviewed. The achievement of those systems is significant from the viewpoints of (1) acquisition of new knowledge in the synthesis of semiconducting polymer materials, (2) unnecessary strict control in monomer feed ratios generally required for a single-phased solution polycondensation, (3) possible improvement of the monomer reactivity by varying feed ratios, and (4) possibility of controlled chain end groups and extension to the synthesis of all-conjugated block copolymers. In practice, naphthalene-diimide-, phthalimide-, and terephthalate-based π-conjugated polymers have been synthesized under imbalanced stoichiometric conditions, possessing much higher molecular weights than those based on Carothers/Flory’s theory. The results of various model reactions and DFT calculations have revealed that the origin of the intramolecular catalyst transfer phenomenon is related to the existence of carbonyl groups introduced at the ortho-position of dibromo aryl monomers used in excess as well as types of palladium catalysts/precatalysts. In the near future, the proposed nonstoichiometric Migita-Kosugi-Stille coupling polycondensation will be established by extending the adaptable monomers and further optimizing catalysts/precatalysts.

Reversible-Hydrogen-Transfer-Mediated Anomerization of Azaheterocyclyl 2-Deoxy-C-glycosides and Mechanistic Studies

Mutarotation of O-glycans and O-glycosides has long been well-established and exploited in the stereocontrolled chemical synthesis of O-glycosides, while few examples of C-glycoside anomerization are known to date. During the development of a simple iridium catalyst-promoted α-stereoselective C-glycosylation of 2-indoly-pyridine with glycal donors, we serendipitously discovered the occurrence of 2-deoxy-C-glycoside anomerization, enabling α-to-β configuration conversion. Control experiments and density functional theory calculations were performed to explore the mechanistic details of the anomerization of the C-glycosylation products, which could tolerate C-aryl and C-alkyl-glycosides. The anomerization reaction plausibly proceeds through the pathway involving the activation of the C(sp3)–H bond mediated by the iridium catalyst and reversible hydrogen transfer, rather than the classical anomerization mechanisms involving the endocyclic cleavage of the C1–O5 bond or exocyclic cleavage of the glycosidic bond.