Complete deconstruction of SF6 by an aluminium(I) compound

Routes to Pt Derivatives of High-Valent Sulfur Oxofluorides S(═O)2F, S(═O)F2, and S(═O)F3 by Fluorination and Oxygenation

Metal derivatives of high-valent sulfur fluorides and oxofluorides can provid e fluorinated building blocks for materials science and bioactive compounds, but so far, such building blocks are elusive. The paper describes routes to access remarkable metal derivatives of S(═O)2F, S(═O)F2, and S(═O)F3 by oxygenation or fluorination steps. The Pt(II) fluorido complex trans-[Pt(F)(SOF)(PCy3)2] (2) reacts with the Davis reagent (3-phenyl-2-(phenylsulfonyl)-1,2-oxaziridine) to yield the sulfuryl fluorido complex trans-[Pt(F)(SO2F)(PCy3)2] (4). Notably, the electrophilic fluorinating agent NFSI (N-fluorobenzenesulfonimide) reacts with 2 to form trans-[Pt(F)(SOF2)(PCy3)2][NFSO2Ph] (5a). By nucleophilic fluorination with TMAF (Me4NF) it is possible to fluorinate the sulfur center once more to give the complex trans-[Pt(F)(SOF3)(PCy3)2] (6) bearing an unprecedented SOF3 ligand. Above 283 K, complex 6 shows a decomposition of the SOF3 moiety to form trans-[Pt(F)2(PCy3)2] (7) and SOF2. The described complexes could represent a previously unknown class of transfer reagents for high-valent sulfur fluoride units.

Boron, Aluminum, and Gallium Fluorides as Catalysts for the Defluorofunctionalization of Electron-Deficient Arenes: The Role of NaBArF4 Promoters

A series of boron, aluminum, and gallium difluoride complexes [{(ArNCMe)2CH}MF2] (M = B, Al, Ga) are reported as catalysts for the defluorofunctionalization of electron-deficient arenes. Thiodefluorination reactions between TMS-SPh and poly(fluorinated aromatics) proceed under forcing conditions. Evidence is presented for the fluoride entering the catalytic cycle through a metathesis reaction with TMS-SPh to form metal thiolate intermediates, e.g., [{(ArNCMe)2CH}MF(SPh)], which are then nucleophiles for addition to the aromatic substrate, likely through a concerted SNAr mechanism. Attempts to expand the scope of reactivity to include the hydrodefluorination of electron-deficient arenes met with limited success. Activity could, however, be recovered through the addition of NaBArF4 as a catalytic additive (ArF = 3,5-C6H3(CF3)2). NMR titrations suggest that NaBArF4 is capable of coordinating with aluminum and gallium fluoride complexes, most likely through weak M-F---Na interactions (M = Al, Ga), and can play a role in lowering the barrier of metathesis between [{(ArNCMe)2CH}MF2] and Et3SiH to form the group 13 hydrido fluoride [{(ArNCMe)2CH}M(H)F], facilitating catalytic turnover. DFT calculations indicate that this weak interaction leads to a polarization of the M-F bond. The discovery of this additive effect has potentially broad implications in developing new reactivity and applications of thermodynamically stable metal fluorides.

Anionic Reactions Degrading SF6 Using Metals: Insights From the Gas Phase

Alkali metals have been used to degrade SF6 in liquid ammonia. The products include metal fluorides. In this study, we reacted K- and Ag- with SF6 in a triple quadrupole mass spectrometer. The atomic metal anions were formed by in-source collision-induced dissociation (CID) of their respective oxalate salts as previously described by our group. The only two reaction products observed were SF6 - and SF5 -. At low collision energy, the latter was deduced to be formed via an abstraction by the metal of F from SF6 - formed by electron transfer in the encounter complex between the metal anion and neutral SF6. As the collision energy was increased, there was evidence of a CID contribution to SF5 - directly from SF6 -.

Phosphonium SF5 - Salts Derived from Sulfur Hexafluoride as Deoxyfluorination Reagents

Sulfur based deoxyfluorination reagents are usually derived from the corrosive gas SF4. Herein, we report the synthesis and properties of an easily accessible phosphonium salt [(tmg)3PF]+SF5 - (1) which was obtained from the reaction of sulfur hexafluoride (SF6) with tris(tetramethylguanidinyl)phosphine. The performance of this crystalline SF5 - salt as a reagent in deoxyfluorination reactions was investigated together with a second SF5 - salt [(R1)3PF]+SF5 - (2) containing bulky substituents (R1=1,3-di-tert-butylimidazolidin-2-ylidenamino). Both reagents proved to be effective for the deoxyfluorination of various functional groups including alcohols, anhydrides, and amides.

Activation and Catalytic Degradation of SF6 and PhSF5 at a Bismuth Center

In this work, we report the catalytic degradation of SF6 and PhSF5 using N,C,N pincer bismuthinidene complexes (1 and 5). Exposure of SF6 and PhSF5 to 1 results in the reduction of the S(VI) substrates and concomitant formation of Bi(III) and Bi(II) compounds, which were isolated and characterized. The oxidized bismuth-based products were demonstrated to undergo reduction with PMe3, recovering the starting complex 1. Having established a synthetic redox cycle, the catalytic degradation of SF6 and PhSF5 was developed through ligand optimization to 5, leading to a 528 TON for SF6 and the first reported TON for PhSF5 (3.2).

Bis(Aluminyl)Magnesium: A Source of Nucleophilic or Radical Aluminium-Centred Reactivity

The homoleptic magnesium bis(aluminyl) compound Mg[Al(NON)]2 (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene) can be accessed from K2[Al(NON)]2 and MgI2 and shown to possess a non-linear geometry (∠Al-Mg-Al=164.8(1)°) primarily due to the influence of dispersion interactions. This compound acts a four-electron reservoir in the reductive de-fluorination of SF6, and reacts thermally with polar substrates such as MeI via nucleophilic attack through aluminium, consistent with the QT-AIM charges calculated for the metal centres, and a formal description as a Al(I)-Mg(II)-Al(I) trimetallic. On the other hand, under photolytic activation, the reaction with 1,5-cyclooctadiene leads to the stereo-selective generation of transannular cycloaddition products consistent with radical based chemistry, emphasizing the covalent nature of the Mg-Al bonds and a description as a Al(II)-Mg(0)-Al(II) synthon. Consistently, photolysis of Mg[Al(NON)]2 in hexane in the absence of COD generates [Al(NON)]2 together with magnesium metal.

Recent advances in the chemistry of isolable carbene analogues with group 13-15 elements

Carbenes (R2C:), compounds with a divalent carbon atom containing only six valence shell electrons, have evolved into a broader class with the replacement of the carbene carbon or the RC moiety with main group elements, leading to the creation of main group carbene analogues. These analogues, mirroring the electronic structure of carbenes (a lone pair of electrons and an empty orbital), demonstrate unique reactivity. Over the last three decades, this area has seen substantial advancements, paralleling the innovations in carbene chemistry. Recent studies have revealed a spectrum of unique carbene analogues, such as monocoordinate aluminylenes, nitrenes, and bismuthinidenes, notable for their extraordinary properties and diverse reactivity, offering promising applications in small molecule activation. This review delves into the isolable main group carbene analogues that are in the forefront from 2010 and beyond, spanning elements from group 13 (B, Al, Ga, In, and Tl), group 14 (Si, Ge, Sn, and Pb) and group 15 (N, P, As, Sb, and Bi). Specifically, this review focuses on the potential amphiphilic species that possess both lone pairs of electrons and vacant orbitals. We detail their comprehensive synthesis and stabilization strategies, outlining the reactivity arising from their distinct structural characteristics.

Advances in Continuous Flow Fluorination Reactions

Fluorination reactions are important in constructing organofluorine motifs, which contribute to favorable biological properties in pharmaceuticals and agrochemicals. However, fluorination reagents and reactions are associated with various problems, such as their hazardous nature, high exothermicity, and poor selectivity and scalability. Continuous flow has emerged as a transformative technology to provide many advantages relative to batch syntheses. This review article summarizes recent continuous flow techniques that address the limitations and challenges of fluorination reactions. Approaches based on different flow techniques are discussed, including gas-liquid reactions, packed-bed reactors, in-line purifications, streamlined multistep synthesis, large-scale reactions well as flow photoredox- and electrocatalysis.

Seven-Membered Cyclic Diamidoalumanyls of Heavier Alkali Metals: Structures and C-H Activation of Arenes

Like the previously reported potassium-based system, rubidium and cesium reduction of [{SiNDipp}AlI] ({SiNDipp} = {CH2SiMe2NDipp}2) with the heavier alkali metals [M = Rb and Cs] provides dimeric group 1 alumanyl derivatives, [{SiNDipp}AlM]2. In contrast, similar treatment with sodium results in over-reduction and incorporation of a formal equivalent of [{SiNDipp}Na2] into the resultant sodium alumanyl species. The dimeric K, Rb, and Cs compounds display a variable efficacy toward the C-H oxidative addition of arene C-H bonds at elevated temperatures (Cs > Rb > K, 110 °C) to yield (hydrido)(organo)aluminate species. Consistent with the synthetic experimental observations, computational (DFT) assessment of the benzene C-H activation indicates that rate-determining attack of the Al(I) nucleophile within the dimeric species is facilitated by π-engagement of the arene with the electrophilic M+ cation, which becomes increasingly favorable as group 1 is descended.

Room Temperature Defluorination of Poly(tetrafluoroethylene) by a Magnesium Reagent

Perfluoroalkyl substances (PFAS) are pervasive in the environment. The largest single use material within the PFAS compound class is poly(tetrafluoroethylene) (PTFE), a robust and chemically resistant polymer. Despite their widespread use and serious concerns about their role as pollutants, methods for repurposing PFAS are rare. Here we show that a nucleophilic magnesium reagent reacts with PTFE at room temperature, generating a molecular magnesium fluoride which is easily separated from the surface-modified polymer. The fluoride in turn can be used to transfer the fluorine atoms to a small array of compounds. This proof-of-concept study demonstrates that the atomic fluorine content of PTFE can be harvested and reused in chemical synthesis.

Repurposing of F-gases: challenges and opportunities in fluorine chemistry

Fluorinated gases (F-gases) are routinely employed as refrigerants, blowing agents, and electrical insulators. These volatile compounds are potent greenhouse gases and consequently their release to the environment creates a significant contribution to global warming. This review article seeks to summarise: (i) the current applications of F-gases, (ii) the environmental issues caused by F-gases, (iii) current methods of destruction of F-gases and (iv) recent work in the field towards the chemical repurposing of F-gases. There is a great opportunity to tackle the environmental and sustainability issues created by F-gases by developing reactions that repurpose these molecules.

Electrochemical Synthesis of Glycosyl Fluorides Using Sulfur(VI) Hexafluoride as the Fluorinating Agent

This manuscript describes the electrochemical synthesis of 17 different glycosyl fluorides in 73-98% yields on up to a 5 g scale that relies on the use of SF6 as an inexpensive and safe fluorinating agent. Cyclic voltammetry and related mechanistic studies carried out subsequently suggest that the active fluorinating species generated through the cathodic reduction of SF6 are transient under these reductive conditions and that the sulfur and fluoride byproducts are effectively scavenged by Zn(II) to generate benign salts.

Fluorination Reactions at a Platinum Carbene Complex: Reaction Routes to SF3 , S(=O)F and Fluorido Complexes

The electron-rich Pt complex [Pt(IMes)2 ] (IMes: [1,3-bis(2,4,6-trimethylphenyl)-2-imidazolinylidine]) can be used as precursor for the syntheses of a variety of fluorido ligand containing compounds. The sulfur fluoride SF4 undergoes a rapid oxidative addition at Pt0 to yield trans-[Pt(F)(SF3 )(IMes)2 ]. A photolytic reaction of SF6 at [Pt(IMes)2 ] in the presence of IMes gave the fluorido complexes trans-[Pt(F)2 (IMes)2 ] and trans-[Pt(F)(SF3 )(IMes)2 ] along with trans-[Pt(F)(SOF)(IMes)2 ] and trans-[Pt(F)(IMes')(IMes)] (IMes': cyclometalated IMes ligand), the latter being products produced by reaction with adventitious water. trans-[Pt(F)(SOF)(IMes)2 ] and trans-[Pt(F)2 (IMes)2 ] were synthesized independently by treatment of [Pt(IMes)2 ] with SOF2 or XeF2 . A reaction of [Pt(IMes)2 ] with a HF source gave trans-[Pt(H)(F)(IMes)2 ], and an intermediate bifluorido complex trans-[Pt(H)(FHF)(IMes)2 ] was identified. Compound trans-[Pt(H)(F)(IMes)2 ] converts in the presence of CsF into trans-[Pt(F)(IMes')(IMes)].

Nucleophilic Activation of Sulfur Hexafluoride by N-Heterocyclic Carbenes and N-Heterocyclic Olefins: A Computational Study

Sulfur hexafluoride (SF₆ ) is considered as a potent greenhouse gas, whose effective degradation is challenging. Here we report a computational study on the nucleophilic activation of sulfur hexafluoride by N-heterocyclic carbenes and N-heterocyclic olefins. The result shows that the activation of SF₆ is both thermodynamically and kinetically favorable at mild condition using NHOs with fluoro-substituted azolium and sulfur pentafluoride anion being formed. The Gibbs free energy barrier during the activation of SF₆ has a linear relationship with the energy of HOMO of substrates, which could be a guideline for applying those compounds that feature higher energy in HOMO to activate SF₆ in high efficiency.