Diazonium Tetrafluoroborate Research Articles

Synthesis of 2‐Aryl‐2H‐1,2,3‐triazoles via P(OMe)3‐Promoted Intramolecular Transannulation of 4‐Diazenylisoxazol‐5(4H)‐ones

AbstractTrimethyl phosphite promotes the synthesis of 2,4,5‐trisubstituted 2H‐1,2,3‐triazoles. The protocol developed affords a two‐step method towards triazoles from available reagents. 3,4‐Disubstituted isoxazolones are initially coupled with diazonium tetrafluoroborates. The subsequent reaction is triggered by a single electron transfer from the phosphite to the diazenylisoxazolone under heating or blue LED irradiation at room temperature. The radical anion cascade proceeds via a ring opening/decarboxylation/cyclization sequence. The synthesized triazoles show promising fluorescence in the region from 340 nm to 450 nm with a quantum yield up to 81.6%. The emission energy depends slightly on the substituent nature at the triazole carbon atoms. If an electron‐donor group is introduced into the N2 substituent of the triazole ring, it results in a bathochromic shift of the luminescence energy.

Rhodium(III)-Catalyzed B(4)-Azo Coupling of o-Carboranes with Aryl Diazonium Tetrafluoroborates.

Rh(III)-catalyzed B(4)-azo coupling reactions of o-carborane acids with aryl diazonium tetrafluoroborates have been developed, leading to the regioselective formation of B(4)-azo-coupled o-carboranes. Moreover, B(4)-azo-coupled o-carboranes can be further functionalized by introducing a second azo group, producing B(4)-C(1)-di(arylazo) o-carborane. The B(4)-azo group as an efficient directing group enables catalytic C-H amidation reactions, providing a new synthetic route for complex o-carborane derivatives.

Facile synthesis of Ti3C2Tx MXene nanosheets using aryl diazonium tetrafluoroborate for multiple applications

The development of an HF-free and environmentally benign method for etching the middle aluminum layer (Al) from the Ti3AlC2-MAX phase is a challenging task in titanium carbide (Ti3C2Tx) MXene synthesis. Herein, we designed a diazonium salt-based ultrasonic method to prepare MXene. We have explored 4-carboxy benzene diazonium tetrafluoroborate (4-CBDF) as a delaminating agent, which can dissolve the Al layer directly from the MAX phase. 4-carboxy benzene diazonium (4-CBD+) ion promotes the intercalation as well as exfoliation simultaneously during the etching of the MAX phase and directly results in Ti3C2Txnanosheets without undergoing any additional delamination process. Synthesized MXene nanosheets show excellent photothermal performance with a conversion efficiency of 59 %. This MXene-coated GC electrode exhibits the highest capacitance of 1133 F/g at a current density 1 A/g, which maintains a retention capacitance of 91% even after 10,000 GCD cycles. The present method provides a fundamental insight into the development of MXene-based next-generation photothermal materials and supercapacitors.

Accessing meta-Enone-Substituted Anisoles using ArN2BF4 as Precatalyst via Rearrangement of Alkyne-Tethered Cyclohexadienones

AbstractA method for the rearrangement of alkyne-tethered cyclohexadienone to furnish meta-enone-substituted anisoles using arene diazonium tetrafluoroborate salts as precatalyst was developed. The reaction proceeds via intramolecular 1,6-enyne cyclization-aromatization and oxetene ring opening. The same protocol was also employed to obtain phthalide-substituted anisoles. The reactions are atom economic, have a broad substrate scope and amenable to gram-scale synthesis. Further synthetic transformations of the products were also performed.

In situ Diazonium Salt Formation and Photochemical Aryl-Aryl Coupling in Continuous Flow Monitored by Inline NMR Spectroscopy.

A novel class of diazonium salts is introduced for the photochemical aryl-aryl coupling to produce (substituted) biphenyls. As common diazonium tetrafluoroborate salts fail, soluble and safe aryl diazonium trifluoroacetates are applied. In this mild synthesis route no catalysts are required to generate an aryl-radical by irradiation with UV-A light (365 nm). This reactive species undergoes direct C-H arylation at an arene, forming the product in reasonable reaction times. With the implementation of a continuous flow setup in a capillary photoreactor 13 different biphenyl derivatives are successfully synthesized. By integrating an inline 19F-NMR benchtop spectrometer, samples are reliably quantified as the fluorine-substituents act as a probe. Here, real-time NMR spectroscopy is a perfect tool to monitor the continuously operated system, which produces fine chemicals of industrial relevance even in a multigram scale.

Deconstructive diversification of cyclic 1,3-diketones for accessing hydrazonylated 1,n-ketoesters

A mild base-promoted three-component deconstructive functionalization reaction of cyclic 1,3-diketones with aryl diazonium tetrafluoroborates in the presence of alcohols is reported, enabling direct ring-opening of unstrained cyclic ring systems to produce three types of skeletally diverse 1,n-ketoesters, namely, linear 1,5- and 1,4-ketoesters and ortho-ketobenzoates, with moderate to good yields. The methodology has the potential to be widely used throughout organic synthesis due to the use of easily accessible substrates, such as cyclic 1,3-diketones and aryl diazonium tetrafluoroborates, with different substitution patterns and mild reaction conditions.

Inhibiting Metal Galvanic and Carbon Corrosion in Aluminum Alloy-Carbon Fiber Reinforced Composite Joints by Spontaneous Deposition of Diazonium Adlayers on Exposed Carbon Fibers

The spontaneous formation of a diazonium molecular adlayer on the exposed fibers of a carbon fiber reinforced polymer (CFRP) composite was investigated as a surface treatment. The purpose of the surface treatment is to reduce the extent of galvanic corrosion on a trivalent chromium process (TCP) conversion-coated aluminum alloy when the two materials are mechanically joined as is common in aircraft structures. The adlayer functions to reduce the rate of dissolved oxygen reduction on the more noble carbon thereby reducing the rate of galvanic corrosion on the more active metal alloy. The formation of the adlayer (4-nitrophenyl (NP), 4-nitroazobenzene (NAB), or 2-fluorene diazonium tetrafluoroborate (FL)) was achieved by immersing the CFRP composite specimen in a solution of 5 mM diazonium salt dissolved in acetonitrile for a specified time (1–24 h) under open circuit conditions (so-called spontaneous deposition). Cyclic voltammetry (CFRP composite) and rotating disk voltammetry (glassy carbon) were used to investigate the oxygen reduction reaction kinetics in naturally aerated 0.5 M Na2SO4 (pH 5–6). The oxygen reduction reaction current was suppressed by greater than 90% by the NP and NAB adlayers and 80% by the FL adlayer. The surface treatment (24 h immersion) with NAB significantly reduced the galvanic corrosion damage on TCP conversion-coated aluminum alloy during a 14-day continuous neutral salt spray (NSS) exposure. The mass loss (mg/cm2) and corrosion intensity (g/m2y) were reduced by over 10×. The spontaneously formed NAB adlayers are stable during the salt-spray exposure and provide better inhibition of galvanic corrosion on the aluminum alloy and resistance to carbon corrosion than do NAB adlayers formed by an electrochemically assisted process reported on previously.

Oxygen-Promoted 6-endo-trig Cyclization of β,γ-Unsaturated Hydrazones/Ketoximes with Diazonium Tetrafluoroborates for Pyridazin-4(1H)-ones/Oxazin-4(1H)-ones.

An oxidative 6-endo-trig cyclization and [2 + 2] cycloaddition of β,γ-unsaturated hydrazones/ketoximes and diazonium tetrafluoroborates for a synthetic strategy to pyridazin-4(1H)-ones/oxazin-4(1H)-ones under metal-free conditions is presented in a one-pot procedure. This protocol features excellent functional group tolerance and remarkable regioselectivity. A mechanistic study has been verified via 18O labeling and the H218O labeling method, in which O2 acts as both a reaction component and an oxidant.

Improved adhesion and charge transfer between PEDOT:PSS and the surface of a platinum electrode through a diazonium chemistry route

Due to the high applicability of poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS) in organic electronics, current research is focused on providing new ways to further improve its functionality. In this paper, we have described a one-step process of electrochemical grafting of commercially available diazonium salts to the surface of a Pt electrode as a method to increase mechanical stability of PEDOT:PSS, simultaneously decreasing its charge transfer resistance and increasing capacitance. Pretreatment of Pt electrodes with electrografted layers of 4-nitrobenzene-, 4-methoxybenzene-, and 3,5-dichlorophenyl diazonium tetrafluoroborates is shown to improve charge storage capacity (235 mC/cm2 at the scan rate of 10 mV/s), decrease charge transfer resistance (15.0 ± 0.5 Ω) and enhance capacitance (13.3 ± 0.8 mF). The described method is also efficient in providing coatings with better affinity to the electrode and higher adhesion force.

Multicomponent Annulative SO2 Insertion of Heteroatom‐Linked 1,7‐Diynes for Accessing Tricyclic Sulfones

AbstractA metal‐free radical multicomponent bicyclization of heteroatom‐linked 1,7‐diynes with aryl diazonium tetrafluoroborates and DABCO‐bis(sulfurdioxide) (DABSO) is reported, enabling annulative SO2 insertion access to produce two types of skeletally diverse tricyclic sulfones, namely, thieno[3,4‐c]quinoline 2,2‐dioxides and thieno[3,4‐c]chromene 2,2‐dioxides, with moderate to good yields by simply tuning the linkers of the 1,7‐diynes. This protocol demonstrates remarkable compatibility regarding N‐ and O‐linked 1,7‐diynes with different substitution patterns and aryl diazonium tetrafluoroborates.magnified image

Organophotoredox-mediated Formal [3+2]-Cycloaddition of 2H-Azirines with Aryldiazonium Salts: Direct Access to Trisubstituted 1,2,4-Triazoles.

The present work documents an organophotoredox-mediated formal [3+2]-cycloaddition of 2H-azirines with aryl diazonium tetrafluoroborate salts to furnish 1,3,5-trisubstituted 1,2,4-triazoles. The reaction furnishes a regioisomeric mixture of 1,2,4-triazoles in case of unsymmetrically substituted azirines. It is noteworthy that aryl radical generation from diazonium salt under visible light photoredox conditions could be successfully avoided by carefully selecting the reaction conditions.

Arene Diazonium Tetrafluoroborate Salts: Novel Lewis Acid Catalysts for Friedel‐Crafts Alkylation of Indoles with α,β‐Unsaturated Ketones

AbstractIn this study, the Friedel crafts alkylation of indole with α, β‐unsaturated ketones catalyzed by arene diazonium tetrafluoroborate salts is reported for the first time, and the optimal conditions of this reaction were explored. The experimental results show that the optimal conditions employed 10 mol % 2‐(2‐bromophenoxy)phenyl diazonium fluoborate (2) as a catalyst, CH3OH as a solvent, 60 °C as reaction temperature, and 24 h as reaction time. Under these optimized conditions, the reaction of indoles with various α,β‐unsaturated ketones can proceed smoothly to obtain aimed products (8). Yields of these reactions ranged from 60 % to 92 %. The reaction conditions are mild and the reaction operation is simple.

A Scalable Balz-Schiemann Reaction Protocol in a Continuous Flow Reactor.

The demand for aromatic fluorides is steadily increasing in the pharmaceutical and fine chemical industries. The Balz-Schiemann reaction is a straightforward strategy for preparing aryl fluorides from aryl amines, via the preparation and conversion of diazonium tetrafluoroborate intermediates. However, significant safety risks exist in handling the aryl diazonium salts when scaling up. In order to minimize the hazard, we present a continuous flow protocol that has been successfully performed at a kilogram scale that eliminates the isolation of aryl diazonium salts while facilitating efficient fluorination. The diazotization process was performed at 10 °C with a residence time of 10 min, followed by a fluorination process at 60 °C with a residence time of 5.4 s with about 70% yield. The reaction time has been dramatically reduced by introducing this multi-step continuous flow system.

Highly diastereoselective Heck–Matsuda reaction with pyrazolyl diazonium salts

Novel pyrazolyl-derived diazonium tetrafluoroborate salts were used in the palladium-catalyzed Heck–Matsuda reaction for the diastereoselective synthesis of highly substituted cyclopenten-ols/-amines.

Pyridine-promoted diazotization of P[sbnd]H bonds with aryl diazonium tetrafluoroborates: Synthesis of azo organophosphorus compounds

A pyridine-promoted diazotization of PH bonds with aryl diazonium tetrafluoroborates is established. The reported method is simple and efficient for the synthesis of azo organophosphorus compounds with excellent yields, which avoids the adoption of complex and harsh reaction conditions and the addition of oxides, tolerating various kinds of functional groups. The synthesized azo organophosphorus compounds may have potential applications in organic chemistry and drug design.

Transition Metal Catalyst, Solvent, Base Free Synthesis of Diaryl Diselenides under Mechanical Ball Milling.

Synthesis of diaryl diselenides was restricted into only few Cu-catalyzed C-Se Cross coupling protocol where use of ligands, high reaction temp, long reaction time were required. To achieve a sustainable protocol for the synthesis of diaryl diselenides Method: Reaction of aryl diazonium fluoroborate with KSeCN was successfully performed under ball milling in absence of any ransition metal catalyst, ligands, base and external heating to get diaryl diselenides. A library of diaryl diselenides were obtained in good yields with different functional groups. First transition metal free protocol for the synthesis of diaryl diselenides has been developed successfully.

Polymeric Molecular Design Towards Horizontal Zn Electrodeposits at Constrained 2D Zn2+ Diffusion: Dendrite‐Free Zn Anode for Long‐Life and High‐Rate Aqueous Zinc Metal Battery

AbstractAqueous zinc metal batteries have garnered unprecedented attention owing to their high theoretical specific capacity, appropriate redox potential, and remarkable sustainability. Nevertheless, the intractable issues induced by the notorious Zn dendrite growth and serious interfacial side reactions significantly impede their large‐scale utilization. Inducing Zn to electrodeposit through parallel arrangement mode is critical to realizing dendrite‐free Zn metal anodes (ZMAs). To realize this purpose, a unique polymeric molecular design strategy through chemically grafting a thin polyanthraquinone (PAQ) overlayer on the Zn surface in the manner of spontaneous polymerization reaction of anthraquinone diazonium tetrafluoroborate (AQN2+BF4−) is proposed firstly. Impressively, thus‐derived PAQ overlayer as an artificial protective layer can constrain the Zn2+ ions 2D diffusion and homogenize the electric field and Zn2+ ions concentration distribution, further guiding preferential growth along the Zn(002) plane. Assisted by the PAQ overlayer, the dendrite growth, H2 evolution reaction, and Zn corrosion on ZMAs are suppressed effectively. Accordingly, such polymeric molecular modified ZMAs ensure a remarkably high Coulombic efficiency of 99.7% at 4 mA cm−2 and achieve a long cycling lifespan up to 1750 h at 1 mA cm−2 and superior rate capability. This work provides a new insight into designing an interface protective layer for achieving highly stable ZMAs.

3-Arylsulfonylquinolines from N-Propargylamines via Cascaded Oxidative Sulfonylation Using DABSO.

We report a cascaded oxidative sulfonylation of N-propargylamine via a three-component coupling reaction using DABCO·(SO2)2 (DABSO). 3-Arylsulfonylquinolines were obtained by mixing diazonium tetrafluoroborate, N-propargylamine, and DABSO under argon atmosphere in dichloroethane (DCE) for 1 h. In a radical pathway, DABSO was utilized as the sulfone source and an oxidant in this radical-mediated cascaded reaction.

Fluorine‐Free Nanoporous Low‐k Dielectric Film Covalently Grafted on Si via Aryldiazonium Chemistry

AbstractFluorine‐free nanoporous low‐k dielectric film containing polyhedral oligomeric silsesquioxanes (POSS) cage nanostructure is covalently grafted onto a p‐Si(100) surface via aryldiazonium chemistry, in an open environment without any inert gas protection. The method is based on two‐step reduction of aryldiazonium salts. First, 4‐nitrobenzene diazonium tetrafluoroborate (NBD) is reduced and a polynitrophenyl (PNP) passivation layer is formed on the p‐Si(100) surface, in an aqueous media with hydrofluoric acid being added. Second, NBD is reduced by electrons provided by external pulse power supply, and initiates octavinylsilsesquioxane polymerizing to form the film, which is composed of PNP and massive POSS cage, leading to a low k value. The average dielectric constant of the film is 2.12 at the range of 600 to 1700 nm wavelength, much lower than some low‐k materials reported by recent literature and traditional materials. The prepared films completely cover the Si substrate and are compact and thickness controllable. In particular, the k value can be controlled though the concentration of NBD. The low‐k properties imply they will be suitable to be utilized as high‐performance dielectric materials in future higher frequency communication field.

In situ Bi/carboxyphenyl-modified glassy carbon electrode as a sensor platform for detection of Cd2+ and Pb2+ using square wave anodic stripping voltammetry.

Herein, a sensor platform, Bi/carboxyphenyl-modified glassy carbon electrode (Bi/CP/GCE), is presented for the detection of Cd2+ and Pb2+ using square wave anodic stripping voltammetry (SWASV). The sensor was obtained through electrografting of the GCE using 4-carboxybenzene diazonium tetrafluoroborate (4-CBD) and in situ electrodeposition of Bi3+. The stability of the grafted layer and the proposed mechanism of interaction between the metal ions and the grafted layer is supported by DFT calculations. Under the optimized conditions, Pb2+ had a linear working range of 25–500 μg L−1 with LOD of 10 μg L−1 (S/N = 3) and Cd2+ provided linear range of 50–500 μg L−1 and LOD of 25 μg L−1. The fabricated electrode presented good repeatability and reproducibility. The applicability of the electrode was tested for determination of Cd2+ and Pb2+ in tap water resulting in recoveries of 96.2–101% for Cd2+ and 98.1–104% for Pb2+.