Streamlining Thionyl Tetrafluoride (SOF4) and Pentafluoro-Oxosulfate [OSF5]– Anions Syntheses

Johanna S Sturm, Alexandre Millanvois, Carlota Bahri, Paul Golz, Niklas

Limberg, Anja Wiesner, Sebastian Riedel

► To cite this version:

Johanna S Sturm, Alexandre Millanvois, Carlota Bahri, Paul Golz, Niklas Limberg, et al. Streamlining Thionyl Tetrafluoride (SOF4) and Pentafluoro-Oxosulfate [OSF5]– Anions Syntheses. Chemistry - A European Journal, 2024, 10.1002/chem.202403365. [https://doi.org/10.1002/chem.202403365](https://doi.org/10.1002/chem.202403365) [This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.](https://creativecommons.org/licenses/by/4.0/)

HAL Id: hal-04781715

https://hal.science/hal-04781715v1

Submitted on 13 Nov 2024

**HAL** is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

# Streamlining Thionyl Tetrafluoride (SOF₄) and Pentafluoro-Oxosulfate [OSF₅]⁻ Anions Syntheses

Johanna S. Sturm,[a] Alexandre Millanvois,[*a] Carlota Bahri,[a] Paul Golz,[a] Niklas Limberg,[a] Anja Wiesner,[a] and Sebastian Riedel*[a]

A one pot room temperature synthesis of thionyl tetrafluoride (SOF₄) from elemental fluorine (F₂) and thionyl fluoride (SOF₂) is reported. The selective decagram scale process (100 mmol) allows a quantitative preparation of SOF₄ with high purity. The solid-state structure has also been elucidated and compared with the reported gas phase one. The use of this reagent for the

formation of the emerging pentafluorooxosulfate [cat][OSF₅] anions led to the preparation of multiple ion-pairs (cat = Ag, NEt₃Me, PPN, PPh₄) in different organic solvents. The SuFEx reservoir ability of this anion was studied and by tuning the solvent system, the reactivity of pure thionyl tetrafluoride was observed using Ag[OSF₅] in THF and acetone.

## Introduction

The Sulfur<sup>VI</sup> fluoride exchange (SuFEx) is an efficient tool for the synthesis of sulfur containing molecules that uses the high S–F bond(s) reactivity.[1] Most SuFEx-related synthetic routes rely on the sequential formation of stable but reactive S(VI)-F intermediates acting as sulfuryl(VI) connectors (Figure 1.a).[2] Numerous examples were previously described from gaseous counterparts such as sulfuryl fluoride (SO₂F₂) that appeared as a promising reagent towards the formation of sulfonyl fluorides and fluorosulfates.[3] These monofluorinated connectors are easily isolated and able to undergo the addition of a supplementary organic moiety.

Accessing structural diversity required oxyfluoride intermediates obtained from versatile polyfluorinated connectors such as thionyl tetrafluoride[4,5] (SOF₄) or the poorly explored thiazyl trifluoride (NSF₃).[6] The lack of modern methodology involving thionyl tetrafluoride (SOF₄) can be explained by the absence of suppliers, synthetic difficulty (Figure 1.b) combined with the fading away of gas handling in organic laboratory. However, recent examples showed the versatility of SOF₄ as reagent for the preparation of valuable intermediates.[7] In addition, modern perfluorooxosulfate salts and complexes were recently brought up to date by Haupt from SOF₄[8] as well as the gas free equivalent by Demaerel and co-workers (Figure 1.c).[9] Furthermore, these salts also found their place as SuFEx

<figure><img src="image_4.png" /><figcaption>**Figure 1.** a) Examples of sulfuryl connectors; b) Reported synthesis of thionyl halide; thionyl tetrafluoride and our work; c) Preparation of OSF₅; d) SuFEx example from OSF₅.</figcaption></figure>

reagents acting as SOF₄ reservoirs from an equilibrium displacement (Figure 1.d).

Due to our deep interest in the OSFₓ (x = 4, 5) chemistry, we herein report a safe and selective large-scale preparation of thionyl tetrafluoride to improve the reported procedure. Indeed, preparation of SOF₄ was previously described from thionyl dihalide and involved the handling of highly reactive bromide pentafluoride (BrF₅) or chlorine trifluoride (CIF₃, Figure 1.b).[10] If the use of elemental fluorine (F₂) appears as an excellent candidate, the direct reaction with thionyl fluoride (SOF₂) was previously highlighted only by means of catalyst such as silver(II) fluoride (AgF₂) at high temperature and strong overpressure (Figure 1.b).[11] We also found a forgotten industrial synthesis by Ruff in 1964 with a moderate pressure but at room temperature that was not reproduced by their academic peer.[4] Finally, electrochemical fluorination of SO₂[12] and an interesting

<footnote>[a] J. S. Sturm, A. Millanvois, C. Bahri, P. Golz, N. Limberg, A. Wiesner, S. Riedel Fachbereich Biologie, Chemie, Pharmazie Institut für Chemie und Biochemie - Anorganische Chemie Freie Universität Berlin, Fabeckstr. 34/36, 14195 Berlin, Germany
E-mail: alexm1@zedat.fu-berlin.de
s.riedel@fu-berlin.de</footnote>

<footnote>Supporting information for this article is available on the WWW under https://doi.org/10.1002/chem.202403365</footnote>

<footnote>© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.</footnote>
<figure><img src="image_5.png" /></figure>

fluorine free synthesis from sulfur tetrafluoride (SF₄) and oxygen (O₂) using nitrogen dioxide (NO₂) as catalyst were also reported for the synthesis of SOF₄.[13] Moreover, all these experimental conditions led to a mixture of gases that proved hard to separate.

## Results and Discussion

We began our investigation by attempting a new fluorine (F₂) free synthesis of thionyl tetrafluoride 3 from the commercially available thionyl fluoride (SOF₂) and xenon difluoride (Scheme 1).

As the direct fluorination of SOF₂ in MeCN did not proceed, we then attempted to perform the direct oxidation of thionyl fluoride in DCM and observed dynamic processes by ¹⁹F NMR but poor conversion in SOF₄ 3 and SO₂F₂ 4. Increasing the temperature for several days led to the full decomposition and observation of a mixture of chlorofluorocarbon species from DCM. Therefore, we examined a sequential strategy using chlorine (Cl₂) generated from triethylmethylammonium chloride ([NET₃Me]Cl) decomposition with XeF₂ (Scheme 2). Indeed, the oxidative chlorination of S⁴V to S⁶I and subsequent Cl/F exchange with fluoride ions was already reported on sulfoxide and more recently with sulfinylamine.[14] Surprisingly, these experimental conditions led to a large amount of the interesting synthon sulfur chloride pentafluoride (6, SF₅Cl) and a small amount of pentafluorooxosulfate ammonium salt (5, [NET₃Me][OSF₅]). This salt was obtained from the reaction of [NET₃Me]F and generated SOF₄. The experimental and simulated

<figure><img src="image_6.png" /><figcaption>Scheme 1. Attempted formation of SOF₄ using XeF₂.</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Scheme 2. Direct fluorination of SOF₂ in fluorine (F₂) free manner.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>Scheme 3. Synthesis of thionyl tetrafluoride SOF₄ (3, CCDC 2380907) and molecular structure. Thermal ellipsoids are drawn at 50% probability level. Selected bond lengths [Å] and angle [°]: S1-O2 1.390(3), S1-F3 1.583(2), S1-F4 1.5204(19); O2-S1-F3 97.02(9), O2-S1-F4 122.96(7), F4-S1-F3 86.19(5).</figcaption></figure>

¹⁹F NMR spectrum of 3 can be found in the SI (Figure S5). Further attempts for OSF₅ preparation from CISF₅ or oxidation/ fluorination of thionyl chloride 1 are also reported in the SI.

As a fluorine free synthesis of SOF₄ using XeF₂ appears delicate to setup, due to the over oxidation or fluorination (formation of [OSF₅]⁻ and CISF₅) we decided to re-investigate the direct room temperature fluorination of thionyl fluoride at even lower pressure.[4]

Our designed reaction for the synthesis of thionyl tetrafluoride 3 (Scheme 3) was conducted in a passivated 3 L stainless steel reactor at 100 mmol scale. This allowed us the handling of thionyl fluoride 2 and a slight excess of fluorine (F₂) with a relative pressure of 1 bar (corresponding to an absolute pressure of 2 bar).

After shaking the reaction vessel for 3 days at room temperature, the absolute pressure decreased to 1.25 bar. The excess of fluorine was removed and thionyl tetrafluoride 3 was obtained quantitatively as a colourless gas. These unique synthetic conditions being in great contrast with the previously harsh reported methodology, we questioned the influence of the metal wall or perhaps the passivation layer of our stainless-steel reactor. A control experiment (30 mmol, V = 1260 mL) using a quartz reaction vessel was performed and we concluded that the passivated layer does not catalyse this reaction.[15] Therefore, a practical and direct synthesis of thionyl tetrafluoride in larger amounts is now available. Indeed, the previous complex gas separation is finally avoided.

The molecular structure of 3 is depicted in Scheme 3 and a suitable crystal of 3 was obtained by in-situ crystallization on the diffractometer in a capillary tube at 100 K. The SOF₄ structure is now fully elucidated and agrees with the determined gas phase structure (gas phase electron-diffraction with distances (GED, reported as *d*<sub>gas</sub>)) [16] as it was recently achieved for SF₄.[17] Here, for 3 the S1-F3 (apical or axial) distance is similar to the gas phase structure (1.583(2); *d*<sub>gas</sub> 1.583 Å) when the equatorial distance S1-F4 is shorter (1.5204(19); *d*<sub>gas</sub> 1.550 Å) similarly for S=O bond (1.390(3); *d*<sub>gas</sub> 1.413 Å). In the solid-state structure, angles are different from the reported gas phase one. Indeed, the F4-S1-F4' angle is 114.08(15)°, the F3-S1-F3' angle is 165.95(18)° and the O2-S1-F3 97.02(9)° in solid-state versus respectively 110, 178 and 90° in the gas phase. As expected, we herein observed a significant distortion from the ideal trigonal bipyramidal structure (TBP) suggesting a stronger repulsion from the S=O bond in solid-state than in the gas phase. Our quantum-chemical calculations at the DFT level (B3LYP/def2-TZVP) support this distorted trigonal bipyramidal arrangement, where the corresponding angles (F4-S1-F4', F3-S1-F3', O2-S1-F3) have been computed to be 112.9, 164.2 and 97.9° respectively. More information can be found in the supplementary Table S4.

Further characterization of 3 was performed by gas phase IR and by ¹⁹F NMR spectroscopy and are in agreement with the literature.[18] Furthermore, DFT calculations have been performed to simulate and examine the resulting IR spectrum (Figure 2).[19] Based on this the experimental bands are assigned to ν₅(SF₅) 571 cm⁻¹, ν₅(SF₅) 820 cm⁻¹ and ν₅(SF₆) 797 cm⁻¹, ν₅(SF₆) 927 cm⁻¹. The S=O stretching mode is found at 1380 cm⁻¹ and the wagging (ω) probably overlaps with the
<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /><figcaption>**Figure 2.** Experimental IR spectrum of SOF₄ (3, black) in comparison to the calculated spectrum (B3LYP/def2-TZVP, red).</figcaption></figure>

band at 571 cm⁻¹. In the ¹⁹F NMR spectrum, the fluorine atoms appear equivalent displaying a singlet at δ = 79.5 ppm, this being explained by the Berry-pseudorotation in a TBP system.

We then prepared the silver pentafluorooxosulfate (7, Ag-[OSF₅]) salt by condensing 1 equivalent of SOF₄ 3 into silver fluoride (AgF) in acetonitrile (Scheme 4a). We also conducted this experiment in propionitrile and were able to isolate the resulting silver salt (Scheme 4.b). From the solution containing the silver salt 4, we then performed several cation exchange reactions. Firstly, the solution was added on triethylmethylammonium chloride ([NET₃Me]Cl) leading to the precipitation silver chloride (AgCl). After filtration, the desired ammonium salt (5, [NET₃Me][OSF₅]) was obtained quantitatively and is in accordance with the observed ion-pair obtained in the XeF₂ experiment (Scheme 2).

In the same manner, we investigated the formation of the
phosphonium derivatives respectively from tetraphenylphos-
phonium chloride ([PPh₄]Cl) and

bis(triphenylphosphine)iminium bromide ([PNP]Br) with precip-
itation of the corresponding silver halide (Scheme 4).

Both phosphonium salt **8** and iminophosphonium salt **9** were obtained quantitatively and isolated. Suitable crystals of **7**, **8** and **9** for X-ray diffraction analysis were obtained by cooling down a propionitrile or acetonitrile solution to -20 °C (Scheme 4, b–d). Data of these crystals are reported in the SI. As expected for coordinating solvent, each structure displays a dissociated ion-pair which is in contrast with its reported pentafluoroorthotellurate (OTeF₅, teflate) counterpart obtained from non-coordinating solvent (i.e. DCM or Toluene).[20] For each structure, the [OSF₅]⁻ anion appears as a slightly distorted octahedron with the oxygen occupying the apical position. For most structures (7<sub>MeCN</sub> & EtCN<sup>2</sup>; 9), the bond distances can be described as *d*(S–O) < *d*(S–F<sub>eq</sub>) < *d*(S–F<sub>ap</sub>) and is explained by the O→S backbonding. In the case of **8**, the O1 and F2 atom are disordered due a symmetry element, therefore we did not include it in the structural discussion. The salts **8** and **9** display hydrogen bond interaction in the solid-state structure between the aromatic ring, two equatorial fluorine atoms and the negatively charged oxygen.

The strong ion-pair dissociation of these compounds (4–7) was also observed in solution by ¹⁹F NMR as minor chemical shift variations were observed independently from the solvent or cation. (Table S1, entry 1–2). To further investigate the coordination behaviour of the [OSF₅]⁻ salts, we then decided to prepare several stock solutions from 3 in different organic solvents with a wide range of polarity and different binding properties of the Ag⁺ cation (Figure 3 and Table S1, entry 3–8).

Surprisingly, the preparation of the desired stock solutions
can be achieved in various coordinating organic solvents
(Figure 3). This allowed us the first observation of an overall
correlation between the chemical shift difference δΔ and the
polarity of the solvent for such [OYF₅]⁻ (Y = S, Se, Te) species. To
begin, with decreased polarity and decreased δΔ, the reaction

<figure><img src="image_11.png" /><figcaption>**Scheme 4.** a) Preparation of [cat][OSF₅] (cat = NET₃Me (5); PPh₄ (8); PNP (9)) ion-pairs from the silver salt 7; For molecular structure of 7–9, the disorder of the [OSF₅]⁻ anion and hydrogen have been omitted for clarity. b) X-ray crystallographic structure (CCDC 2380906) of 7, thermal ellipsoids are drawn at 50% probability level, 35% for N and C atoms of EtCN; c,d) X-ray crystallographic structure 8 (CCDC 2380904) and (CCDC 2380905) of 9, thermal ellipsoids are drawn at 50% probability.</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>**Figure 3.** Solvent influence toward Ag[OSF<sub>5</sub>] the shift difference δΔ(F<sub>A</sub>-F<sub>X</sub>) in ppm.</figcaption></figure>

time to reach full conversion increases. With these results, we hypothesize that the shift difference δΔ(F<sub>A</sub>-F<sub>X</sub>) between the two fluorine signals could act as a fluorine probe, strongly suggesting the electronic or charge contributions for such species. Here, the solvent and possible coordination reduces the signal differences by more than 10 ppm from the acetonitrile solution versus the benzene one (Figure 3). This shift could be attributed for our S<sup>vi</sup> ion-pairs as correlated to the resulting interactions between the silver cation and [OSF<sub>5</sub>]<sup>−</sup>.

With these data in hand, we decided to further assess the stability of these ion-pairs based on the reported methodology published by Demaerel, De Borggraeve and Ismalaj (Scheme 5).<sup>[9]</sup> From their seminal observation, the [OSF<sub>5</sub>]<sup>−</sup> anion could react as a reservoir of SOF<sub>4</sub> SuFEx reagent in presence of aniline (Equation (1)).

$$ \mathrm{Ag[OSF_5] \rightleftharpoons AgF + SOF_4} \quad (1) $$

We decided to apply our Ag[OSF<sub>5</sub>] stock solutions to compare the influence of the solvent on Ag[OSF<sub>5</sub>] stability for the formation of reactive SOF<sub>4</sub> resulting in a sulfurimidoyl fluoride compound 11 (Scheme 5).

We hypothesize that the use of less polar solvents such as acetone and THF could enhance the reaction rate as it should favor the precipitation of AgHF<sub>2</sub> by the immediate reaction of the fluoroaniline 10 with SOF<sub>4</sub>. We prepared several stock solutions (0.5 M, 0.1 M) of 7 in THF-d8, acetone-d6 and MeCN-d3. In comparison with the reported reaction (0.05–0.1 M), the reaction rate was considerably increased using a higher concentration of 7 in MeCN (50% conversion in 1 h, <sup>19</sup>F NMR). To our delight, using acetone and THF at 0.5 M led immediately

to a large amount of precipitation attributed to AgHF<sub>2</sub>, 10•HF salts and 11 was obtained (by <sup>19</sup>F NMR) in solution. Both side-products undergo glass etching and two decomposition products [Ag]<sub>2</sub>[SiF<sub>6</sub>] and 10•HBF<sub>4</sub> were also observed on standing. This observed reaction rate appears similar with the direct reaction between pure SOF<sub>4</sub> 3 and 10. The higher reaction rate in THF and acetone was confirmed as full conversion was also obtained almost immediately at 0.1 M.

## Conclusions

In summary, we report a selective synthesis of SOF<sub>4</sub> at low pressure (maximum 1 BarG), low temperature (rt) and large scale (100 mmol). A control experiment in a quartz vessel suggests a non-catalyzed process: That allows to re-investigate a convenient synthesis of thionyl tetrafluoride. Furthermore, the structure of SOF<sub>4</sub> was elucidated for the first time by SC-XRD and compared to the previous gas phase analysis (GED). Currently, we are actively working on the design of a small-scale chemical plant to optimize this reaction and to be able to efficiently provide SOF<sub>4</sub> to the community. We then studied the transformation of the reagent with silver fluoride into the silver perfluorooxosulfate ion-pair Ag[OSF<sub>5</sub>]. Cation exchanges were conducted allowing the formation of phosphonium and ammonium salts. The binding properties of these salts were studied in solid-state by SC-XRD and in solution by <sup>19</sup>F NMR. We successfully prepared and assessed the stability and binding properties of different salts in multiple solvents. This being observed by <sup>19</sup>F NMR and by its decomposition into sulfurimidoyl using perfluorinated aniline. Using THF and acetone, we were able to mimic the reactivity of pure SOF<sub>4</sub> with the stability brought by these soluble salts that nowadays can be obtained in a gas free manner. We believe that the combination of both studies could greatly expand the OSF<sub>5</sub> chemistry and perhaps allows further developments as a potential alternative to PFAS.

Further research involving the preparation of organic scaffolds bearing the perfluorooxosulfate moiety are actively ongoing in the laboratory.

## Acknowledgements

The authors would like to thank the HPC Service of ZEDAT and the Core Facility BioSupraMol supported by the DFG. This work was supported by Freie Universität Berlin, A.M. thanks the University for a postdoctoral Rising Star fellowship. C.B. thanks Erasmus<sup>+</sup>. We thank Thomas Drews for his help and useful discussions. Further support is acknowledged by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - Project-ID 387284271 - SFB 1349. We thank Solvay Fluor for providing elemental fluorine. Open Access funding enabled and organized by Projekt DEAL.

<figure><img src="image_13.png" /><figcaption>**Scheme 5.** Synthesis of sulfurimidoyl fluoride 11 from Ag[OSF<sub>5</sub>] (7).</figcaption></figure>
<figure><img src="image_14.png" /></figure>

Conflict of Interests

The authors declare no conflict of interest.

Data Availability Statement

The data that support the findings of this study are available in
the supplementary material of this article.

Keywords: Thionyl fluoride · Thionyl tetrafluoride · Pentafluorooxosulfate Salts (OSF~5~) · Sufex · Fluorination

[1] a) J. Dong, L. Krasnova, M. G. Finn, K. B. Sharpless, *Angew. Chem. Int. Ed.* **2014**, *53*, 9430; b) J. Dong, L. Krasnova, M. G. Finn, K. B. Sharpless, *Angew. Chem.* **2014**, *126*, 9584; c) J. A. Homer, L. Xu, N. Kayambu, Q. Zheng, E. J. Choi, B. M. Kim, K. B. Sharpless, H. Zuilhof, J. Dong, J. E. Moses, *Nat. Rev. Methods Primers* **2023**, *3*, 2004; d) A. S. Barrow, C. J. Smedley, Q. Zheng, S. Li, J. Dong, J. E. Moses, *Chem. Soc. Rev.* **2019**, *48*, 4731; e) X. Zhang, F. Wang, C.-H. Tan, *JACS Au* **2023**, *3*, 700.

[2] D. Zeng, W.-P. Deng, X. Jiang, *Chem. Eur. J.* **2023**, *29*, e202300536.

[3] R. Lekkala, R. Lekkala, B. Moku, K. P. Rakesh, H.-L. Qin, *Org. Chem. Front.* **2019**, *6*, 3490.

[4] J. K. Ruff, R. Czerepinski, *Inorganic Syntheses*, John Wiley & Sons, Ltd, Wiley, **1968**.

[5] W. L. Jolly, *Inorganic Syntheses*, John Wiley & Sons, Ltd, Wiley, **1968**.

[6] a) B.-Y. Li, K. Su, L. van Meervelt, S. H. L. Verhelst, E. Ismalaj, W. M. de Borggraeve, J. Demaerel, *Angew. Chem. Int. Ed.* **2023**, *62*, 2485; b) B.-Y. Li, K. Su, L. Van Meervelt, S. H. L. Verhelst, E. Ismalaj, W. M. De Borggraeve, J. Demaerel, *Angew. Chem.* **2023**, *135*, e202305093.

[7] a) S. Li, P. Wu, J. E. Moses, K. B. Sharpless, *Angew. Chem. Int. Ed.* **2017**, *56*, 2903; b) S. Li, P. Wu, J. E. Moses, K. B. Sharpless, *Angew. Chem.* **2017**, *129*, 2949–2954; c) F. Liu, H. Wang, S. Li, G. A. L. Bare, X. Chen, C. Wang, J. E. Moses, P. Wu, K. B. Sharpless, *Angew. Chem. Int. Ed.* **2019**, *58*, 8029; d) F. Liu, H. Wang, S. Li, G. A. L. Bare, X. Chen, C. Wang, J. E. Moses, P. Wu, K. B. Sharpless, *Angew. Chem.* **2019**, *131*, 8113; e) Z. Peng, S. Sun, M.-M. Zheng, Y. Li, X. Li, S. Li, X.-S. Xue, J. Dong, B. Gao, *Nat. Chem.* **2024**, *16*, 353.

[8] a) A. Haupt, D. Duvinage, E. Lork, M. Ponomarenko, G.-V. Röschenthaler, *Angew. Chem. Int. Ed.* **2021**, *60*, 17866; b) A. Haupt, D. Duvinage, E. Lork, M. Ponomarenko, G.-V. Röschenthaler, *Angew. Chem.* **2021**, *133*, 18010.

[9] a) A. Zogu, K. Ullah, S. Spanopoulos, E. Ismalaj, W. M. De Borggraeve, J. Demaerel, *Angew. Chem. Int. Ed.* **2024**, *63*, e202403797; b) A. Zogu, K. Ullah, S. Spanopoulos, E. Ismalaj, W. M. de Borggraeve, J. Demaerel, *ChemRxiv. Preprint* **2024**; c) A. Zogu, K. Ullah, S. Spanopoulos, E. Ismalaj, W. M. De Borggraeve, J. Demaerel, *Angew. Chem.* **2024**, *136*, e202403797.

[10] K. Seppelt, Z. anorg. allg. Chem. **1971**, 386, 229.

[11] a) J. K. Ruff, M. Lustig, *Inorg. Chem.* **1964**, *3*, 1422; b) H. Jonas, Z. anorg. allg. Chem. **1951**, *265*, 273; c) F. B. Dudley, G. H. Cady, D. F. Eggers, *J. Am. Chem. Soc.* **1956**, *78*, 1553.

[12] S. Nagase, T. Abe, H. Baba, *Bull. Chem. Soc. J.* **1969**, *42*, 2062.

[13] W. C. Smith, V. A. Engelhardt, *J. Am. Chem. Soc.* **1960**, *82*, 3838.

[14] a) X. Ou, A. F. Janzen, *Can. J. Chem.* **1996**, *74*, 2002; b) J. Berreur, A. Diez-Varga, A. Manel, F. R. Leroux, A. Panossian, *Chem. Eur. J.* **2022**, *28*, e202202564; c) N. Lional, F. M. Miloserdov, H. Zuilhof, *Angew. Chem. Int. Ed.* **2024**, *63*, e202406915; d) N. Lional, F. M. Miloserdov, H. Zuilhof, *Angew. Chem.* **2024**, *136*, e202406915.

[15] The control experiment was conducted with a maximum pressure of 900 mbar in the reaction flask to avoid explosion risk or fluorine leakage. Therefore, the reaction rate appears slightly lower as a small amount of SOF~2~ (~5%) was trapped with SOF~4~ after 3 days at room temperature suggesting a low influence of the pressure for the reaction rate.

[16] a) A. F. Hollemann in *Lehrbuch der anorganischen Chemie*, Berlin, Boston: De Gruyter, **1985**, 449–536; b) J. A. Tossell, *Chem. Phys.* **1991**, *154*, 211; c) K. Kimura, S. H. Bauer, *J. Chem. Phys.* **1963**, *39*, 3172; d) L. Hedberg, K. Hedberg, *J. Phys. Chem.* **1982**, *86*, 598; e) I. Hargittai, *J. Mol. Struct.* **1979**, *56*, 301; f) G. Gundersen, K. Hedberg, *J. Chem. Phys.* **1969**, *51*, 2500.

[17] a) J. T. Goettel, N. Kostiuk, M. Gerken, *Angew. Chem.* **2013**, *125*, 8195; b) J. T. Goettel, N. Kostiuk, M. Gerken, *Angew. Chem. Int. Ed.* **2013**, *52*, 8037.

[18] K. O. Christe, C. J. Schack, E. C. Curtis, *Spectrochim. Acta Part A Mol. Biomol. Spectrosc.* **1977**, *33*, 323.

[19] F. Neese, *WIREs Comput. Mol. Sci.* **2022**, *12*, 12753.

[20] a) M. R. Colsman, M. D. Noirot, M. M. Miller, O. P. Anderson, S. H. Strauss, *J. Am. Chem. Soc.* **1988**, *110*, 6886; b) S. H. Strauss, M. D. Noirot, O. P. Anderson, *Inorg. Chem.* **1985**, *24*, 4307.

Manuscript received: September 9, 2024

Accepted manuscript online: October 1, 2024

Version of record online: ■■, ■■
RESEARCH ARTICLE

**SuF-ficiently.** The preparation of 100 mmol of thionyl tetrafluoride (SOF₄) by the direct S–F bond formation from fluorine (F₂) and thionyl fluoride (SOF₂) was achieved in a quantitative and convenient manner. The solid-state structure was elucidated, and the reagent fully characterized. This efficient SuFEx reagent was transformed using a fluoride salt in pentafluorooxosulfate (OSF₅) anion that can behave as an SOF₄ storage reagent. Tuning the solvent system, the stable OSF₅ anion appears as reactive as SOF₄ for the formation of sulfurimidoyl fluorides.

<figure><img src="image_15.png" /></figure>

J. S. Sturm, A. Millanvois*, C. Bahri, P. Golz, N. Limberg, A. Wiesner, S. Riedel*

1 – 6

Streamlining Thionyl Tetrafluoride (SOF₄) and Pentafluoro-Oxosulfate [OSF₅]⁻ Anions Syntheses

<figure><img src="image_16.png" /></figure>

VIP