Structural Chemistry of Fluorides and Oxide Fluorides of Nonmetals

The structural features of the nonmetal fluorides and oxide fluorides can now be explained and useful predictions can be made. The same applies in part to the chemistry of this class of compounds. Statements concerning structures can easily be made on the basis of the elctron pair repulsion model (VSEPR theory). Some rules for the number of ligands provide structural predictions for larger units than isolated molecules or ions. This is important for the fluorides and oxide fluorides of the heavier elements. This class of compounds has its limits in the lighter noble gases which, even with fluorine, form only weak bonds or no bonds at all.     

Fluorides of Copper,Silver, Gold,and Palladium

Fluorine, by far the most reactive of the non-metals, is capable of forming a large number of compounds with nearly all other elements (exceptions (so far): He, Ne, and Ar), even under comparatively “mild” reaction conditions. These compounds usually differ markedly from those of the heavier halogens in composition, structure, and chemical and physical properties. Thus, for example, it is generally quite easy to prepare fluorides containing elements in high oxidation states (often their maximum), as in AgF₂, CsAgF₄, PdF₃, CsAuF₆ etc., whereas the corresponding chlorides, bromides or iodides are in many cases (still) unknown. Conversely, the synthesis of fluorides containing these elements in middle or low oxidation states often meets with considerable difficulty, even where it is possible at all, as, e.g., in the case of CuF, AuF, PtF₂, SeF₂. Finally, there are also some examples of compounds MX_n, which with X = F are stable, but with X = Cl are unstable or decompose easily (e.g. CoF₃/CoCl₃, VF₄/VCl₄, PbF₄/PbCl₄, AsF₅/AsCl₅). Consequently, fluorine compounds are of great general interest.     

Solid State Chemistry of Ionic Fluorides

The results of intensive pure research into the chemistry and physics of fluorides can be pieced together to give an overall picture whose discernible outlines hold promise of numerous new compounds having unusual and in some cases unique properties. Modern technology is called upon to exploit them.     

氮之琐谈

氮元素是空气的主要成分,也是构成有机化合物的重要元素;生命离不开氮元素,化学工业也需要众多含氮化合物作为基础的工业原料。地球上氮元素的循环起始于闪电或生物固氮,而发展节能高效的固氮方法依然是化学家的长期任务。氮氧化物如一氧化氮和二氧化氮等是重要的空气污染源,控制其排放是治理空气污染的重要途径。对含氮有机化合物如氨基酸与蛋白质的研究至关重要,有望为人类揭示生命的奥秘或提供重要的材料如尼龙等。     

First-principles Study on Neutral Nitrogen Impurities in Zinc Oxide

The atomic geometries, electronic structures, and formation energies of neutral nitrogen im-purities in ZnO have been investigated by first-principles calculations. The nitrogen impuri-ties are always deep acceptors, thus having no contributions to p-type conductivity. Among all the neutral nitrogen impurities, nitrogen substituting on an oxygen site has the lowest formation energy and the shallowest acceptor level, while nitrogen substituting on a zinc site has the second-lowest formation energy in oxygen-rich conditions. Nitrogen interstitials are unstable at the tetrahedral site and spontaneously relax into a kick-out configuration. Though nitrogen may occupy the octahedral site, the concentrations will be low for the high formation energy. The charge density distributions in various doping cases are discussed, and self-consistent results are obtained.     

Copper-Catalyzed Asymmetric Acylboration of 1,3-Butadienylboronate with Acyl Fluorides

We report herein a Cu-catalyzed regio-, diastereo- and enantioselective acylboration of 1,3-butadienylboronate with acyl fluorides. Under the developed conditions, the reactions provide (Z)-β,γ-unsaturated ketones bearing an α-tertiary stereocenter with high Z-selectivity and excellent enantioselectivities. While direct access to highly enantioenriched E-isomers was not successful, we showed that such molecules can be synthesized with excellent E-selectivity and optical purities via Pd-catalyzed alkene isomerization from the corresponding Z-isomers. The orthogonal chemical reactivities of the functional groups embedded in the ketone products allow for diverse chemoselective transformations, which provides a valuable platform for further derivatization.     

Chitosan/Nitrogen Doped Reduced Graphene Oxide Modified Biosensor for Impedimetric Detection of microRNA

The development of a low‐cost and disposable biosensor platform for the sensitive and rapid detection of microRNAs (miRNAs) is of great interest for healthcare, pharmaceuticals, and medical science. We designed an impedimetric biosensing platform using Chitosan (CHIT)/nitrogen doped reduced graphene oxide (NRGO) conductive composite to modify the surface of pencil graphite electrodes (PGE) for the sensitive detection of miRNAs. An initial optimisation protocol involved investigation of the effect of NRGO concentration and miR 660 DNA probe concentration on the response of the modified electrode. After the optimization protocol, the sequence‐selective hybridization between miR 660 DNA probe and its RNA target was evaluated by measuring changes on charge transfer resistance, R_ct values. Moreover, the selectivity of impedimetric biosensor was tested in the presence of non‐complementary miRNA (NC) sequences, such as miR 34a and miR 16. The hybridization process was examined both in phosphate buffer (PBS) and in PBS diluted fetal bovine serum (FBS:PBS) solutions. The biosensor demonstrated a detection limit of 1.72 μg/mL in PBS and 1.65 μg/mL in FBS:PBS diluted solution. Given the easy, quick and disposable attributes, the proposed conductive nanocomposite biosensor platform shows great promise as a low‐cost sensor kit for healthcare monitoring, clinical diagnostics, and biomedical devices.     

Rhodium-Catalyzed Asymmetric Synthesis of 1,2-Disubstituted Allylic Fluorides

Although there are many methods for the asymmetric synthesis of monosubstituted allylic fluorides, construction of enantioenriched 1,2-disubstituted allylic fluorides has not been reported. To address this gap, we report an enantioselective synthesis of 1,2-disubstituted allylic fluorides using chiral diene-ligated rhodium catalyst, Et₃N ⋅ 3HF as a source of fluoride, and Morita Baylis Hillman (MBH) trichloroacetimidates. Kinetic studies show that one enantiomer of racemic MBH substrate reacts faster than the other. Computational studies reveal that both syn and anti π-allyl complexes are formed upon ionization of allylic substrate, and the syn complexes are slightly energetically favorable. This is in contrast to our previous observation for formation of monosubstituted π-allyl intermediates, in which the syn π-allyl conformation is strongly preferred. In addition, the presence of an electron-withdrawing group at C2 position of racemic MBH substrate renders 1,2-disubstituted π-allyl intermediate formation endergonic and reversible. To compare, formation of monosubstituted π-allyl intermediates was exergonic and irreversible. DFT calculations and kinetic studies support a dynamic kinetic asymmetric transformation process wherein the rate of isomerization of the 1,2-disubstituted π-allylrhodium complexes is faster than that of fluoride addition onto the more reactive intermediate. The 1,2-disubstituted allylic fluorides were obtained in good yields, enantioselectivity, and branched selectivity.     

Recent Advances in the Synthesis and Transformation of Carbamoyl Fluorides,Fluoroformates, and Their Analogues

Carbamoyl fluorides, fluoroformates, and their analogues are a class of important compounds and have been evidenced as versatile building blocks for the preparation of useful molecules in organic chemistry. While major achievements were made in the synthesis of carbamoyl fluorides, fluoroformates, and their analogues in the last half of 20^th century, an increasing number of reports have focused on using O/S/Se=CF₂ species or their equivalents as the fluorocarbonylation reagents for the direct construction of these compounds from the parent heteroatom-nucleophiles in recent years. This review mainly summarizes the advances in the synthesis and typical application of carbamoyl fluorides, fluoroformates, and their analogues by the halide exchanges and fluorocarbonylation reactions since 1980.     

Fluorides of Silver Under Large Compression**

The silver-fluorine phase diagram has been scrutinized as a function of external pressure using theoretical methods. Our results indicate that two novel stoichiometries containing Ag⁺ and Ag²⁺ cations (Ag₃F₄ and Ag₂F₃) are thermodynamically stable at ambient and low pressure. Both are computed to be magnetic semiconductors under ambient pressure conditions. For Ag₂F₅, containing both Ag²⁺ and Ag³⁺, we find that strong 1D antiferromagnetic coupling is retained throughout the pressure-induced phase transition sequence up to 65 GPa. Our calculations show that throughout the entire pressure range of their stability the mixed-valence fluorides preserve a finite band gap at the Fermi level. We also confirm the possibility of synthesizing AgF₄ as a paramagnetic compound at high pressure. Our results indicate that this compound is metallic in its thermodynamic stability region. Finally, we present general considerations on the thermodynamic stability of mixed-valence compounds of silver at high pressure.     

Synthesis of N-Difluoromethyl Carbonyl Compounds from N-Difluoromethylcarbamoyl Fluorides

Fluorinated small molecules are commonly used in functional small-molecule chemistry, and N-difluoromethyl (N-CF₂H) compounds are particularly intriguing due to their unique and unexplored physiochemical properties. However, despite limited progress, a general methodological approach to the synthesis of N-CF₂H compounds remains elusive. Here, guided by computation, we present a simple and practical protocol to access N-CF₂H amides and related carbonyl derivatives. The protocol involves a one-pot conversion of thioformamides through desulfurization-fluorination and acylation, providing N-difluoromethylcarbamoyl fluoride building blocks that can be further diversified to a variety of unexplored N-CF₂H carbonyl compounds with rich functionality. Additionally, preliminary studies on their properties and stability showcased their potential application in pharmaceuticals and agrochemicals.     

Nickel-Copper-Catalyzed Hydroacylation of Vinylarenes with Acyl Fluorides and Hydrosilanes

The hydroacylation of vinylarenes with acyl fluorides and hydrosilanes was enabled by a synergistic bimetallic Ni/Cu-catalytic system, giving access to the corresponding branched ketone products. The reaction takes place under mild conditions at 25–80 °C and tolerates base-sensitive functional groups such as methoxycarbonyl and acetoxy groups.     

A Unified Strategy for Arylsulfur(VI) Fluorides from Aryl Halides: Access to Ar-SOF3 Compounds

A convenient protocol to selectively access various arylsulfur(VI) fluorides from commercially available aryl halides in a divergent fashion is presented. Firstly, a novel sulfenylation reaction with the electrophilic N-(chlorothio)phthalimide (Cl-S-Phth) and arylzinc reagents afforded the corresponding Ar-S-Phth compounds. Subsequently, the S(II) atom was selectively oxidized to distinct fluorinated sulfur(VI) compounds under mild conditions. Slight modifications on the oxidation protocol permit the chemoselective installation of 1, 3, or 4 fluorine atoms at the S(VI) center, affording the corresponding Ar-SO₂F, Ar-SOF₃, and Ar-SF₄Cl. Of notice, this strategy enables the effective introduction of the rare and underexplored -SOF₃ moiety into various (hetero)aryl groups. Reactivity studies demonstrate that such elusive Ar-SOF₃ can be utilized as a linchpin for the synthesis of highly coveted aryl sulfonimidoyl fluorides (Ar-SO(NR)F).     

Fluorine‐Rich Fluorides: New Insights into the Chemistry of Polyfluoride Anions

Polyfluoride anions have been investigated by matrix‐isolation spectroscopy and quantum‐chemical methods. For the first time the higher polyfluoride anion [F₅]^? has been observed under cryogenic conditions in neon matrices at 850 cm^?1. In addition, a new band for the Cs⁺[F₃]^? complex in neon is reported.     

Digestion of Insoluble Fluorides in Geochemical Samples by Ammonium Fluoride

The ability of ammonium fluoride attacking insoluble fluorides was studied. Ammonium fluoride was used to digest some geochemical certified reference materials instead of hydrofluoric acid. Inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry were employed to determined major, minor, and trace elements, respectively. By testing CRMs and a large number of real samples, it was determined that the effects on those elements, which easily formed insoluble fluorides, were better by ammonium fluoride than by hydrofluoric acid. Furthermore, it was more secure for operators using ammonium fluoride than hydrofluoric acid. A possible mechanism was also proposed.     

Metal-Free Visible-Light Synthesis of Arylsulfonyl Fluorides: Scope and Mechanism

The first metal-free procedure for the synthesis of arylsulfonyl fluorides is reported. Under organo-photoredox conditions, aryl diazonium salts react with a readily available SO₂ source (DABSO) to afford the desired product through simple nucleophilic fluorination. The reaction tolerates the presence of both electron-rich and -poor aryls and demonstrated a broad functional group tolerance. To shed the light on the reaction mechanism, several experimental techniques were combined, including fluorescence, NMR, and EPR spectroscopy as well as DFT calculations.     

Microwave Assisted Synthesis of Sodium Sulfonates Precursors of Sulfonyl Chlorides and Fluorides

We describe the use of a microwave reaction for the conversion of various bromides to sodium sulfonates that have been further elaborated to sulfonyl chlorides. This new approach leads to much improved yields and shorter reaction times. Representative sulfonyl chlorides serve as precursors for the respective sulfonyl fluorides that are potent inhibitors of the fatty acid amide hydrolase.     

Enantioselective Synthesis of Tertiary Allylic Fluorides by Iridium‐Catalyzed Allylic Fluoroalkylation

Few allylic electrophiles containing two different substituents at a single allyl terminus and none in which one of the two substituents is a heteroatom, have been shown previously to react with iridium catalysts to form substitution products. We report that iridium‐catalysts are uniquely suited to form tertiary allylic fluorides enantioselectively by the addition of a diverse range of carbon‐centered nucleophiles at the fluorine‐containing terminus of 3‐fluoro‐substituted allylic esters. The products contain tertiary stereogenic centers bearing a single fluorine, which are isosteric with common tertiary stereocenters containing a single hydrogen. Computational studies reveal the principal steric interactions influencing the stability of endo and exo π‐allyl intermediates formed from 3,3‐disubstituted allylic electrophiles.     

Perovskite Oxide as A New Platform for Efficient Electrocatalytic Nitrogen Oxidation

Electrocatalytic nitrogen oxidation reaction (NOR) offers an efficient and sustainable approach for conversion of widespread nitrogen (N₂) into high-value-added nitrate (NO₃⁻) under mild conditions, representing a promising alternative to the traditional approach that involves harsh Haber–Bosch and Ostwald oxidation processes. Unfortunately, due to the weak absorption/activation of N₂ and the competitive oxygen evolution reaction, the kinetics of NOR process is extremely sluggish accompanied with low Faradaic efficiencies and NO₃⁻ yield rates. In this work, an oxygen-vacancy-enriched perovskite oxide with nonstoichiometric ratio of strontium and ruthenium (denoted as Sr_0.9RuO₃) was synthesized and explored as NOR electrocatalyst, which can exhibit a high Faradaic efficiency (38.6 %) with a high NO₃⁻ yield rate (17.9 μmol mg⁻¹ h⁻¹). The experimental results show that the amount of oxygen vacancies in Sr_0.9RuO₃ is greatly higher than that of SrRuO₃, following the same trend as their NOR performance. Theoretical simulations unravel that the presence of oxygen vacancies in the Sr_0.9RuO₃ can render a decreased thermodynamic barrier toward the oxidation of *N₂ to *N₂OH at the rate-determining step, leading to its enhanced NOR performance.