<figure><img src="image_59.png" /><figcaption>Scheme 14. Syntheses of Various Metal Teflate Complexes Containing Organometallic Ligands</figcaption></figure>

<figure><img src="image_60.png" /></figure>

$$ \begin{aligned} & [NEt_4]_2[\mathrm{Ni}(\mathrm{OTeF}_5)_4] \xrightarrow{\mathrm{bpyMe}_2} [NEt_4][[\mathrm{Ni}(\mathrm{OTeF}_5)_3](\mathrm{bpyMe}_2)] \end{aligned} \quad (85) $$

As part of the investigation of the Lewis acidity of Au(OTeF₅)₃, the Gutmann-Beckett method was applied by addition of OPPh₃ to the Lewis acid (see Scheme 13). This led to the selective formation of [Au(OPPh₃)(OTeF₅)₃], which allowed the first structural investigation of an Au(OTeF₅)₃ adduct in the solid state via XRD.²⁴ Interestingly, the molecular structure in the solid state shows that the coordination around the gold(III) center is slightly distorted from the typical square planar geometry (τ₄ = 0.10).

The only mixed teflate compounds for group 12 can be prepared as reported by Strauss et al. by reacting ZnEt₂ with teflic acid in toluene and subsequent treatment with PhNO₂ or MeNO₂ (see Scheme 13). The initially formed [Zn-(OTeF₅)₂ tol)ₙ] (n = 1.5–2.0) rapidly exchanges the toluene ligands by PhNO₂ or MeNO₂ units. The molecular structure in

the solid state with PhNO₂ shows either the dimer [Zn-(PhNO₂)₂(OTeF₅)₂] or the monomer [Zn(PhNO₂)₃-(OTeF₅)₂]. Interestingly, the first example shows that PhNO₂ can act as either a bidentate (O,O') or monodentate (O) ligand.²⁶³

Using Hg(OTeF₅)₂, donor-acceptor adducts are formed at 0 °C between the Lewis acidic Hg(II) center and NSF₃ yielding [Hg(OTeF₅)₂·NSF₃]∞, [Hg(OTeF₅)₂·2NSF₃]₂, and [Hg₃(OTeF₅)₆·4NSF₃], as reported by Schrobilgen et al. At room temperature, a nucleophilic attack of a teflate group at the sulfur(VI) atom under elimination of TeF₆ occurs and leads to the structurally related F₂OSN derivatives. These complexes provide the first examples of NSF₃ coordination to mercury.²⁶⁴

Mixed metal complexes of the lighter teflate homologue pentafluorooxosulfate have also been reported. The addition of 2,2'-bipyridine or 4,4'-di-tert-butyl-2,2'-bipyridine (bpy(tBu)₂) to an AgOSF₅ solution in MeCN leads to the formation of [Ag(bpy)₂(OSF₅)] or [Ag(bpy(tBu)₂)(OSF₅)]. In contrast to the aforementioned AgOSF₅ solution in MeCN, the bipyridine
complexes are stable at room temperature under inert conditions. Similarly, the addition of 2,2'-bipyridine to CuOSF₅ leads to the stable complex [Cu(bpy)₂(OSF₅)]. In a metathesis reaction starting from divalent metal chlorides (CuCl₂ and NiCl₂) and AgOSF₅ under the addition of 2,2'-bipyridine, the respective complexes [M(bpy)₂(OSF₅)₂] (M = Cu, Ni) are formed. [Ni(bpy)₂(OSF₅)₂] can also be synthesized by the addition of OSF₄ to a solution of NiF₂ and 2,2'-bipyridine in MeCN. The NMR analysis of the metal OSF₅ complexes indicates that the [OSF₅]⁻ anion acts as a weakly coordinated ligand, which readily dissociates in MeCN. The molecular structure in the solid state of [Cu(bpy)₂(OSF₅)₂] shows two different types of OSF₅ moieties: one is attached to the five-coordinate copper center via its oxygen atom, while the other lies in the cavities of the [Cu(bpy)₂(OSF₅)]⁺ units and shows several H-F contacts for stabilization. The five-coordinate copper center shows a rather rare geometry for Cu(II) compounds and can be considered as a distorted trigonal bipyramid (τ₅ = 0.68).¹¹⁰

**11.2.4. Organometallic Teflate Complexes.** There are metal teflate complexes with five different organometallic ligands known: cyclopentadienyl (Cp), CO, N-heterocyclic carbene (NHC), alkene and alkyl ligands. Complexes bearing Cp and teflate ligands are accessible via halide-teflate metathesis reactions of the chloride (M = Ti, Zr, Hf, Mo, W) or fluoride (M = Ti) precursors with an excess of teflic acid, yielding the corresponding M(Cp)₂(OTeF₅)₂ (M = Ti, Zr, Hf, Mo, W) species (see Scheme 14). Since the molybdenum and tungsten fluoride complexes M(Cp)₂F₂ (M = Mo, W) are unknown, Mo(Cp)₂(OTeF₅)₂ and W(Cp)₂(OTeF₅)₂ represent additional examples of metal teflate complexes without metal fluoride counterparts. The high-frequency chemical shifts observed for the Cp protons suggest a strong M-Cp interaction, which together with the significant differences in the pπ-dπ (pseudo)-halide-metal interaction between the teflate and fluoride ligands could explain the failure to isolate the fluoride analogues.²⁶⁵ The mixed compound [FeCp(CO)₂(OTeF₅)] can be prepared in the reaction of [FeCp(CO)₂Me] with teflic acid under the formation of CH₄ (see Scheme 14).²⁶⁶ A second method to prepare [FeCp(CO)₂(OTeF₅)] involves the reaction of the bromide precursor [FeCp(CO)₂Br] with AgOTeF₅ as the teflate transfer reagent. However, this route is not superior neither in terms of yield nor of purity in comparison to the first method. The more abundant carbonyl complexes can be produced in the same manner with [M(CO)₅Me] as starting material in the cases of manganese and rhenium yielding [M(CO)₅(OTeF₅)] (M = Mn, Re) (see Scheme 14).²⁶⁶,²⁶⁷ The recorded IR spectra of these compounds show that the metal-oxygen bond has a large degree of ionic character. This high ionic character of the teflate ligands can be confirmed by the long Mn-O bond in the molecular structure of [Mn-(CO)₅(OTeF₅)] (see Figure 27).

Additionally, [M(CO)₅(THF)] precursors (M = Mo, W) react with [N(nBu₄)][OTeF₅] to form [N(nBu₄)][M-(CO)₅(OTeF₅)], which were only stable for short periods of time in THF. [Mn(CO)₅(OTeF₅)], [Re(CO)₅(OTeF₅)] and [FeCp(CO)₂(OTeF₅)] are stable indefinitely in the solid state but [Mn(CO)₅(OTeF₅)] slowly releases CO in a dichloromethane solution.²⁶⁶ The synthesis of [M(CO)₅(OEF₅)] (M = Mn, Re; E = Se, Te) complexes is also possible by oxidation of M₂(CO)₁₀ with Xe(OEF₅)₂ at room temperature in dichloromethane (see Scheme 14).²⁶⁷ Here, similar reactions with XeF₂ result in an uncharacterizable mixture of products for manganese

<figure><img src="image_61.png" /><figcaption>**Figure 27.** Molecular structure in the solid state of [Mn-(CO)₅(OTeF₅)].²⁶⁷ Thermal ellipsoids are set at 25% probability.</figcaption></figure>

and in the mixed valence [Re(CO)₅(μ-F)ReF₅] complex for rhenium, which shows the better bridging properties of fluoride in comparison to the teflate ligand. However, this route is not applicable for other low-valent metal complexes like Ru₃(CO)₁₂, Os₃(CO)₁₂, Ir₄(CO)₁₂ or M(CO)₃(PPh₃)₂ (M = Ru, Os).¹⁰⁸

As mentioned above, in several cases the addition of HOTeF₅ to a metal methyl complex results in the formation of the corresponding metal teflate upon release of CH₄. However, cis-[Os(CO)₄Me₂] in combination with HOTeF₅ does not lead to cis-[Os(CO)₄(OTeF₅)₂], but to the formation of cis-[Os-(CO)₄(OTeF₅)Me] (see eq 86).²⁶¹ This underlines the boundaries of the introduction of teflate ligands with this method. Interestingly, teflic acid can be used not only for the introduction of teflate groups to the coordination sphere of a metal compound, but also for the protonation of metal complexes. This way, [HM(CO)₃(PPh₃)₂][OTeF₅] (M = Fe, Ru, Os) could be obtained from their [M(CO)₃(PPh₃)₂] precursors and showed the first use of HOTeF₅ as a protic acid (see eq 87).²⁶⁸

$$ cis-[Os(CO)₄Me₂] \xrightarrow[\text{-CH₄}]{\text{HOTeF₅}} cis-[Os(CO)₄(OTeF₅)Me] \qquad (86) $$

$$ [M(CO)₃(PPh₃)₂] \xrightarrow[\text{M = Fe, Ru, Os}]{\text{HOTeF₅}} [HM(CO)₃(PPh₃)₂][OTeF₅] \qquad (87) $$

The abundance of compounds of the other aforementioned organometallic metal teflate complex classes is scarce. For the alkene ligands only one complex bearing two teflates and a norbonadienyl (NBD) ligand, namely [Pt(NBD)(OTeF₅)₂], was synthesized by reacting [PtCl₂(NBD)] with AgOTeF₅ (see Scheme 14).

Complexes with NHC and teflate ligands could be prepared for the late d-block metals nickel and gold. The nickel NHC complex was obtained by reaction of trans-[NiBr₂(iPrIm)₂] (iPrIm = 1,3-diisopropylimidazolium) with AgOTeF₅ upon precipitation of AgBr (see Scheme 14). In contrast to the starting complex with the bromide ligands trans to each other, cis-[Ni(iPrIm)₂(OTeF₅)₂] was formed and is a rare example of Ni(II) NHC complexes with the two carbene ligands coordinated in cis-position to each other.²⁶²,²⁶⁹ Another relevant NHC complex with a teflate ligand is trans-[AuF₂(OTeF₅)]
<table><caption>Table 11. Overview of Heteroleptic Transition Metal Teflates</caption><thead><tr><th>Element</th><th>Ox</th><th>Compound</th><th>Refs</th><th>Element</th><th>Ox</th><th>Compound</th><th>Refs</th></tr></thead><tbody><tr><td rowspan="2">Ti</td><td rowspan="2">IV</td><td>TiCp<sub>2</sub>(OTeF<sub>5</sub>)<sub>2</sub></td><td>265</td><td rowspan="2">Os</td><td rowspan="2">±0</td><td>[HOs(CO)<sub>3</sub>(PPh<sub>3</sub>)<sub>2</sub>][OTeF<sub>5</sub>]</td><td>268</td></tr><tr><td>TiCl<sub>4-n</sub>(OTeF<sub>5</sub>)<sub>n</sub> (n = 1–3)</td><td>243</td><td>[Os(PPh<sub>3</sub>)(CO)<sub>4</sub>(OTeF<sub>5</sub>)]</td><td>261</td></tr><tr><td rowspan="2">Zr</td><td rowspan="2">IV</td><td rowspan="2">ZrCp<sub>2</sub>(OTeF<sub>5</sub>)<sub>2</sub></td><td>265</td><td rowspan="2">II</td><td>II</td><td>[OsMe(CO)<sub>4</sub>(OTeF<sub>5</sub>)]</td><td>261</td></tr><tr><td></td><td>VI</td><td>OsO(OTeF<sub>5</sub>)<sub>4</sub></td><td>145</td></tr><tr><td>Hf</td><td>IV</td><td>HfCp<sub>2</sub>(OTeF<sub>5</sub>)<sub>2</sub></td><td>265</td><td rowspan="2">Ni</td><td rowspan="2">II</td><td>OsO(OTeF<sub>5</sub>)<sub>5</sub></td><td>254</td></tr><tr><td>V</td><td>V</td><td>VO(OTeF<sub>5</sub>)<sub>3</sub></td><td>145</td><td></td><td></td></tr><tr><td></td><td></td><td>VO(OSeF<sub>5</sub>)<sub>3</sub></td><td>42</td><td></td><td></td><td>[Ni(Hacac)<sub>2</sub>(OTeF<sub>5</sub>)<sub>2</sub>]</td><td>262</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td>[Ni(<sup>IPr</sup>Im)<sub>2</sub>(OTeF<sub>5</sub>)<sub>2</sub>]</td><td>262</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td>[NEt<sub>4</sub>]<sub>2</sub>[Ni(Et<sub>2</sub>O)<sub>2</sub>(OTeF<sub>5</sub>)<sub>4</sub>]</td><td>34</td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td>[NEt<sub>4</sub>][Ni(bpyMe<sub>2</sub>)(OTeF<sub>5</sub>)<sub>3</sub>]</td><td>34</td></tr><tr><td>Cr</td><td>VI</td><td>CrO<sub>2</sub>(OTeF<sub>5</sub>)<sub>2</sub></td><td>145</td><td></td><td></td><td>[Ni(bpy)<sub>2</sub>(OSF<sub>5</sub>)<sub>2</sub>]</td><td>110</td></tr><tr><td></td><td></td><td>CrO<sub>2</sub>(OSeF<sub>5</sub>)<sub>2</sub></td><td>42</td><td></td><td></td><td></td><td></td></tr><tr><td rowspan="4">Mo</td><td rowspan="4">±0</td><td rowspan="4">[N(nBu)<sub>4</sub>][Mo(CO)<sub>5</sub>(OTeF<sub>5</sub>)]</td><td>266</td><td rowspan="4">Pd</td><td rowspan="4">II</td><td rowspan="4">[Pd(OTeF<sub>5</sub>)<sub>2</sub>(PhCN)<sub>2</sub>]</td><td rowspan="4">259</td></tr><tr><td>265</td><td></td></tr><tr><td>251</td><td></td></tr><tr><td>145,244</td><td></td></tr><tr><td rowspan="5">W</td><td rowspan="5">±0</td><td rowspan="5">[N(nBu)<sub>4</sub>][W(CO)<sub>5</sub>(OTeF<sub>5</sub>)]</td><td>266</td><td rowspan="5">Pt</td><td rowspan="5">II</td><td>[Pt(NBD)(OTeF<sub>5</sub>)<sub>2</sub>]</td><td>259</td></tr><tr><td>265</td><td></td></tr><tr><td>145,255</td><td></td></tr><tr><td>42</td><td></td></tr><tr><td>244</td><td></td></tr><tr><td rowspan="4">Mn</td><td rowspan="4">I</td><td rowspan="4">[Mn(CO)<sub>5</sub>(OTeF<sub>5</sub>)]</td><td>108,267</td><td rowspan="4">Au</td><td rowspan="4">III</td><td>[Au(OTeF<sub>5</sub>)<sub>3</sub>(OPPh<sub>3</sub>)]</td><td>24</td></tr><tr><td>108,267</td><td></td></tr><tr><td>108</td><td></td></tr><tr><td>108</td><td></td></tr><tr><td rowspan="5">Re</td><td rowspan="5">I</td><td rowspan="5">[Re(CO)<sub>5</sub>(OTeF<sub>5</sub>)]</td><td>108</td><td rowspan="5">Zn</td><td rowspan="5">II</td><td>[Zn(PhNO<sub>2</sub>)<sub>3</sub>(OTeF<sub>5</sub>)<sub>2</sub>]</td><td>263</td></tr><tr><td>108</td><td></td></tr><tr><td>254</td><td></td></tr><tr><td>254</td><td></td></tr><tr><td>145,253</td><td></td></tr><tr><td></td><td></td><td>[ReO(OTeF<sub>5</sub>)<sub>5</sub>]</td><td>253</td><td rowspan="4">Hg</td><td rowspan="4">II</td><td>HgMe(OTeF<sub>5</sub>)</td><td>11</td></tr><tr><td></td><td></td><td>[NMe<sub>4</sub>][ReO<sub>2</sub>(OTeF<sub>5</sub>)<sub>4</sub>]</td><td></td><td>[Hg(OTeF<sub>5</sub>)<sub>2</sub>·1.5XeF<sub>2</sub>]</td><td>236</td></tr><tr><td></td><td></td><td></td><td></td><td>[Hg(OTeF<sub>5</sub>)<sub>2</sub>·1.5KrF<sub>2</sub>]</td><td>236</td></tr><tr><td></td><td></td><td></td><td></td><td>[Hg(OTeF<sub>5</sub>)<sub>2</sub>·NSF<sub>3</sub>]<sub>∞</sub></td><td>264</td></tr><tr><td></td><td></td><td>[Fe(Cp)(CO)<sub>2</sub>(OTeF<sub>5</sub>)]</td><td>266</td><td></td><td></td><td>[Hg(OTeF<sub>5</sub>)<sub>2</sub>·2NSF<sub>3</sub>]<sub>2</sub></td><td>264</td></tr><tr><td></td><td></td><td>Fe(OEP)(OTeF<sub>5</sub>)</td><td>257</td><td></td><td></td><td>[Hg<sub>3</sub>(OTeF<sub>5</sub>)<sub>6</sub>·4NSF<sub>3</sub>]</td><td>264</td></tr><tr><td></td><td></td><td>Fe(TPP)(OTeF<sub>5</sub>)</td><td>257,258</td><td></td><td></td><td>[Hg(OTeF<sub>5</sub>)(NSOF<sub>2</sub>)·NSF<sub>3</sub>]<sub>∞</sub></td><td>264</td></tr><tr><td></td><td></td><td>[Fe(TPP)(OTeF<sub>5</sub>)(THF)]</td><td>257,258</td><td></td><td></td><td>[Hg<sub>3</sub>(OTeF<sub>5</sub>)<sub>5</sub>(NSOF<sub>2</sub>)·2NSF<sub>3</sub>]<sub>2</sub></td><td>264</td></tr><tr><td>Ru</td><td>±0</td><td>[HRu(CO)<sub>3</sub>(PPh<sub>3</sub>)<sub>2</sub>][OTeF<sub>5</sub>]</td><td>268</td><td>U</td><td>VI</td><td>UF<sub>6-n</sub>(OTeF<sub>5</sub>)<sub>n</sub> (n = 1–5)</td><td>17</td></tr></tbody></table>

(SIMes)], which is formed in a reaction of [AuF<sub>3</sub>(SIMes)] with Me<sub>3</sub>SiOTeF<sub>5</sub> upon elimination of Me<sub>3</sub>SiF (see eq 88). Here, due to the *trans* influence of the NHC ligand, the Au–F bond in *trans* position to the carbene is elongated and thus only this fluoride is replaced by a teflate ligand, which is therefore transferred in *trans* position to SIMes.<sup>182</sup> For the case of *d*-block metal complexes containing only teflate and alkyl ligands only one example is known, i.e., HgMe(OTeF<sub>5</sub>), which is selectively formed by reaction of HgMe<sub>2</sub> and HOTEF<sub>5</sub> (see eq 89). The addition of an excess of HOTEF<sub>5</sub> or a reaction temperature up to 140 °C does not lead to Hg(OTeF<sub>5</sub>)<sub>2</sub>, similarly to the formation of cis-[Os(CO)<sub>4</sub>(OTeF<sub>5</sub>)Me].<sup>11</sup> Heteroleptic transition metal compounds are gathered in Table 11.

$$ [\text{AuF}_3(\text{SIMes})] \xrightarrow[\text{TMSO}_F_5]{\text{TMSO}_F_5} [\text{AuF}_2(\text{OTeF}_5)(\text{SIMes})] \quad (88) $$

$$ HgMe_2 \xrightarrow[\text{CH}_4]{\text{HOTeF}_5} HgMe(OTeF_5) \quad (89) $$

### 11.3. *f*-Block Metal Teflates

Whereas no lanthanide teflate species are known thus far, uranium provides the only example of an isolated and characterized actinide teflate compound and was reported by Seppelt.<sup>17,270</sup> The homoleptic neutral U(OTeF<sub>5</sub>)<sub>6</sub> is a very water-sensitive yellow crystalline solid, which melts at 160 °C with slow decomposition. In the solid state, it appears as discrete molecules with the central uranium atom octahedrally bonded to the six teflate ligands, which are also almost octahedral, leading to an overall spherically shaped molecule (see Figure 28),<sup>270</sup> quite similar to Te(OTeF<sub>5</sub>)<sub>6</sub>.<sup>22</sup> The negligible intermolecular forces between the different molecules account for the volatility of U(OTeF<sub>5</sub>)<sub>6</sub>, which can be sublimed at 60 °C despite its high molecular weight. A recent theoretical study
<figure><img src="image_62.png" /><figcaption>Figure 28. Molecular structure of U(OTeF₅)₆ in the solid state.²⁷⁰ The O atoms are depicted isotropically, the thermal ellipsoids of the U, Te and F atoms are set at 25% probability.</figcaption></figure>

assigned an oxidation state of +VI to the U center in this compound.²⁷¹

Compound U(OTeF₅)₆ can be prepared by using two different teflate transfer reagents, B(OTeF₅)₃ and F₃SiOTeF₅, in both cases starting from UF₆ and with yields higher than 95% (see eqs 90 and 91).¹⁷ Both reactions take place stepwise and all the compounds with the formula FₙU(OTeF₅)₆⁻ₙ (n = 0–6), including all possible isomers, could be detected by NMR spectroscopy when an excess of UF₆ was used. Nevertheless, none of these intermediates could be isolated from the obtained orange liquid mixture.

$$UF_6 + 2B(OTeF_5)_3 \xrightarrow[-2BF_3]{U(OTeF_5)_6} \quad (90)$$

$$UF_6 + 6F_3SiOTeF_5 \xrightarrow[-6SiF_4]{U(OTeF_5)_6} \quad (91)$$

## 12. CONCLUSION

This Review underscores the exceptional properties and chemistry of pentafluoroorthochalcogenate (OEF₅, E = S, Se, Te) compounds in comparison with fluorine-containing species, highlighting their significance in contemporary and future chemical research with a strong focus on teflates. The combination of strong electron-withdrawing effects, substantial steric effects, and reduced lone pair back-bonding renders the OTeF₅ group and its derivatives compelling substitutes for fluorine in various applications. Moreover, steric effects result in the formation of molecular structures that are more precise in comparison to fluorinated analogues, which often form oligomeric or polymeric structures. Evidently, these properties have facilitated the synthesis of a plethora of innovative compounds across the periodic table, ranging from new main group compounds to fundamental new transition metal

complexes. This observation underscores the remarkable versatility of the teflate group and its derivatives, thereby highlighting their considerable potential in expanding the frontiers of modern chemistry in different areas such as Lewis or Brønsted acids, coordination chemistry, strong oxidizers and many more. Furthermore, teflate compounds are of interest not only as a result of their sometimes unique structures and properties but also due to their potential use for the preparation and stabilization of often fragile and very reactive species, which opens novel pathways in advanced synthesis and materials design.

Nevertheless, the field continues to encounter substantial challenges. The synthetic routes to teflate compounds often require costly and difficult-to-handle reagents, which restrict their extensive utilization in conventional chemical laboratories. Furthermore, some of these compounds exhibit sensitivity to hydrolysis, necessitating cautious handling that could impede their utilization in some applications. Consequently, there is a necessity for future research efforts to concentrate on the development of more efficient, straightforward-to-prepare, cost-effective, and environmentally friendly synthetic protocols to address these limitations.

The derivatization of the OTeF₅ group, as reviewed in Section 2.6, represents an area of significant interest. Beyond improving synthetic protocols, there remains considerable room for exploring broader applications of pentafluoroortho-chalcogenate-based compounds (OEF₅, E = S, Se, Te). These compounds demonstrate considerable potential in a number of intriguing fields of chemistry, including catalysis, the study of weakly coordinating anions, and the production of functional materials, as well as the stabilization of otherwise elusive chemical species. The OSF₅ group in particular could be of importance in the future as a promising PFAS (per- and polyfluoroalkyl substances) substituent, e.g. in pharmaceuticals or agrochemicals.

Overall, the pentafluoroorthotellurate group and its derivatives are of significant interest within the field of chemical science, yet their potential remains largely untapped. With ongoing innovation in their synthesis, characterization, and application, these compounds have the potential to play crucial roles in solving emerging challenges and driving discoveries in many fields of chemistry. This comprehensive review not only summarizes the current state of knowledge in the field but also serves as a call to action for further exploration of this promising class of compounds.

## AUTHOR INFORMATION

### Corresponding Author

Sebastian Riedel - Department of Chemistry and Biochemistry, Freie Universität Berlin, 14195 Berlin, Germany;

● orcid.org/0000-0003-4552-5719; Email: s.riedel@fu-berlin.de

### Authors

Julia Bader - Department of Chemistry and Biochemistry, Freie Universität Berlin, 14195 Berlin, Germany; ● orcid.org/0009-0007-5543-9765

Lukas Fischer - Department of Chemistry and Biochemistry, Freie Universität Berlin, 14195 Berlin, Germany;

● orcid.org/0000-0002-3141-9088

Kurt F. Hoffmann - Department of Chemistry, University of British Columbia, V6T 1Z1 Vancouver, BC, Canada;

● orcid.org/0000-0002-5419-1741
**Niklas Limberg** - Department of Chemistry and Biochemistry,
Freie Universität Berlin, 14195 Berlin, Germany;
● orcid.org/0000-0003-3130-9978

**Alexandre Millanvois** - Department of Chemistry and
Biochemistry, Freie Universität Berlin, 14195 Berlin,
Germany; ● orcid.org/0000-0002-0527-2123

**Friederike Oesten** - Department of Chemistry and
Biochemistry, Freie Universität Berlin, 14195 Berlin,
Germany; ● orcid.org/0009-0005-1451-0129

**Alberto Pérez-Bitrián** - Institut für Chemie, Humboldt-
Universität zu Berlin, 12489 Berlin, Germany; ● orcid.org/
0000-0003-2260-676X

**Johanna Schlögl** - Department of Chemistry and Biochemistry,
Freie Universität Berlin, 14195 Berlin, Germany;
● orcid.org/0000-0001-7265-954X

**Ahmet N. Toraman** - Department of Chemistry and
Biochemistry, Freie Universität Berlin, 14195 Berlin,
Germany; ● orcid.org/0000-0002-3074-1665

**Daniel Wegener** - Department of Chemistry and Biochemistry,
Freie Universität Berlin, 14195 Berlin, Germany;
● orcid.org/0000-0003-4302-0952

**Anja Wiesner** - Department of Chemistry and Biochemistry,
Freie Universität Berlin, 14195 Berlin, Germany;
● orcid.org/0000-0001-5300-2059

Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.chemrev.5c00075

## Author Contributions

Section 1 was written by K.F.H. and A.W.; Section 2 by K.F.H., D.W., and A.W.; Sections 3 and 4 by J.S.; Section 5 by K.F.H., D.W., and A.W.; Section 6 by A.M. and F.O.; Sections 7 and 8 by L.F.; Sections 9 and 10 by A.N.T.; and Section 11 by A.P.-B. and N.L. The manuscript was conceptualized by A.W., J.B., and S.R. and revised by all authors.

## Notes

The authors declare no competing financial interest.

## Biographies

Julia Bader was born in Bonn (Germany) in 1982 and studied chemistry at the University of Cologne. She obtained her Ph.D. in inorganic chemistry at the Universität Bielefeld in 2010 and continued her research in fluorine chemistry as a postdoc in Bielefeld, until she joined the Riedel group at the Freie Universität Berlin in 2019. She has been working in the Department of Occupational Safety and Environmental Protection at the University of Cologne since 2024.

Lukas Fischer, born in 1994 in Oldenburg in Holstein (Germany), studied chemistry at Freie Universität Berlin, where they received their master's degree in 2020. For their Ph.D., under the supervision of Prof. Sebastian Riedel, they focused on the synthesis and reactivity of novel Lewis superacids, as well as fluorinated halonium and noble gas cations.

Kurt F. Hoffmann studied chemistry at the Freie Universität Berlin, where he completed his Ph.D. in 2022 under the supervision of Prof. Sebastian Riedel in the department of inorganic chemistry. After an appointment as a postdoctoral associate with Asst. Prof. Marcus Drover at Western University in London, Ontario (Canada) in 2023, he joined the group of Prof. Derek Gates in 2024 as a Walter Benjamin Postdoctoral Fellow at the University of British Columbia in Vancouver.

Niklas Limberg, born in 1997 in Karlsruhe (Germany), studied chemistry at Freie Universität Berlin, where he earned his M.Sc. degree in 2022. Following his master's studies, he joined the research group of

Prof. Sebastian Riedel in 2022 to pursue a Ph.D. in inorganic fluorine chemistry, focusing on transition metals in high oxidation states and fluorinated ligands.

Alexandre Millanvois received his Bachelor (UPMC) and master's degree at Sorbonne Université (SU, ex UPMC) with honors. He did a joint Ph.D. under the supervision of Prof. Louis Fensterbank, Prof. Tan Choon Hong and Dr. Cyril Ollivier between Sorbonne Université (France) and Nanyang Technological University (NTU, Singapore). He then joined the Riedel lab within the Rising Star fellowship, and his current research interests are focused on the development of reagents and catalytic methods toward the synthesis of organic compounds bearing the bio(inorganic) OSF₅ moiety.

Friederike Oesten studied chemistry at Université de Haute-Alsace (France) and Albert-Ludwigs-Universität Freiburg (Germany) where she received her M.Sc. in 2021. During her studies she completed a research stay at Lunds Universitet (Sweden) as well as at Kwame Nkrumah University of Science and Technology (Ghana). After her master's studies she joined the group of Prof. Dr. Sebastian Riedel in 2022 to pursue her Ph.D. researching group IV Lewis (super)acids.

Alberto Pérez-Bitrián was born in Huesca (Spain) in 1992. He studied Chemistry and the Master in Molecular Chemistry and Homogeneous Catalysis at the Universidad de Zaragoza, where he also obtained his Ph.D. in inorganic chemistry in 2020. Directly afterwards, he joined the group of Prof. Dr. Sebastian Riedel at the Freie Universität Berlin as an Alexander von Humboldt postdoctoral fellow. In summer 2023 he started his independent career funded by a Liebig fellowship of the Fonds der Chemischen Industrie (FCI) at the Humboldt-Universität zu Berlin, where he is now an Emmy Noether fellow of the Deutsche Forschungsgemeinschaft (DFG).

Johanna Schlögl was born in Berlin (Germany) in 1997. She obtained both her bachelor's and master's degrees at the Freie Universität Berlin and is currently working on her Ph.D. in the group of Prof. Riedel investigating Lewis superacids and reactive cations.

Ahmet N. Toraman was born in Ankara (Turkey) in 1994. He studied chemistry at the Middle East Technical University and earned his master's degree from Freie Universität Berlin in 2023. He is currently pursuing a Ph.D. under the supervision of Prof. Riedel, focusing on main group teflate species and reactive cations stabilized by weakly coordinating anions.

Daniel Wegener, born in 1996 in Lippstadt and grown up in Oelde, North Rhine-Westphalia (Germany), studied chemistry at the University of Bielefeld and received his master's degree in 2021. Afterward he started his Ph.D. thesis at the Freie Universität Berlin under the supervision of Prof. Sebastian Riedel. There he investigates the synthesis of new organotellurium-based ligand systems for the generation of strong Lewis acids and weakly coordinating anions.

Anja Wiesner was born in Görlitz (Germany) in 1988 and studied chemistry at the Technische Universität Dresden. She did her Ph.D. under the supervision of Prof. Riedel at the Freie Universität Berlin investigating group 13 teflates. After one year working at the Bundesanstalt für Materialforschung and -prüfung (BAM), she is a senior scientist in the Riedel lab.

Sebastian Riedel was born in Groß-Gerau (Germany) in 1975 and was trained as a chemistry laboratory technician at Siemens and Degussa in Hanau-Wolfgang. He then studied chemistry at the Universities of Siegen and Würzburg and obtained his Ph.D. in theoretical chemistry at the institute of inorganic chemistry in 2006. As a Humboldt postdoctoral fellow, he joined the groups of Räsänen and Pyykkö and afterwards carried out a postdoctoral stay in the group of Schrobilgen. Having finished his habilitation at Universität Freiburg in 2013, he
became a full professor of inorganic chemistry at the Freie Universität Berlin where he was appointed in 2021 as Einstein-Professor.

## ACKNOWLEDGMENTS

This work was funded by the European Research Council (ERC) Project HighPotOx (ID: 818862) as well as by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project-ID 387284271 – SFB 1349. The high-performance computing center at Freie Universität Berlin granted computational resources and user support. K.F.H. gratefully thanks the Deutsche Forschungsgemeinschaft for a Walter Benjamin fellowship. A.M. thanks the Freie Universität Berlin for a postdoctoral Rising Star fellowship. A.P.-B. gratefully thanks the Fonds der Chemischen Industrie for a Liebig fellowship.

## ABBREVIATIONS

<table><tr><td>aHF</td><td>anhydrous hydrogen fluoride</td></tr><tr><td>acac</td><td>acetylacetonate</td></tr><tr><td>ax</td><td>axial</td></tr><tr><td>bp</td><td>boiling point</td></tr><tr><td>bpy</td><td>2,2'-bipyridine</td></tr><tr><td>bpyMe<sub>2</sub></td><td>6,6'-dimethyl-2,2'-bipyridine</td></tr><tr><td>bpy(tBu)<sub>2</sub></td><td>4,4'-di-tert-butyl-2,2'-bipyridine</td></tr><tr><td>bz</td><td>benzene</td></tr><tr><td>Cp</td><td>cyclopentadienyl</td></tr><tr><td>DBDHM</td><td>1,3-dibromo-5,5-dimethylhydantoin</td></tr><tr><td>DCE</td><td>1,2-dichloroethane</td></tr><tr><td>DCM</td><td>dichloromethane</td></tr><tr><td>EDF</td><td>electron distribution function</td></tr><tr><td>eq</td><td>equatorial</td></tr><tr><td>ESP</td><td>electrostatic potential</td></tr><tr><td>Et</td><td>ethyl</td></tr><tr><td>F-113</td><td>1,1,2-trichloro-1,2,2-trifluoroethane, Freon-113</td></tr><tr><td>F-114</td><td>1,2-dichloro-1,1,2,2-tetrafluoroethane, Freon-114</td></tr><tr><td>FIA</td><td>fluoride ion affinity</td></tr><tr><td>HPLC</td><td>high-performance liquid chromatography</td></tr><tr><td>iBu</td><td>isobutyl</td></tr><tr><td>iPr</td><td>isopropyl</td></tr><tr><td><sup>i</sup>PrIm</td><td>1,3-diisopropylimidazolium</td></tr><tr><td>IQA</td><td>interacting quantum atoms</td></tr><tr><td>IR</td><td>infrared</td></tr><tr><td>ITC</td><td>isothermal titration calorimetry</td></tr><tr><td>m-CBA</td><td>3-chlorobenzoic acid</td></tr><tr><td>m-CPBA</td><td>3-chloroperbenzoic acid</td></tr><tr><td>Me</td><td>methyl</td></tr><tr><td>Mes</td><td>mesitylene</td></tr><tr><td>mp</td><td>melting point</td></tr><tr><td>NBD</td><td>norbonadienyl</td></tr><tr><td>nBu</td><td>n-butyl</td></tr><tr><td>Ng</td><td>noble gas</td></tr><tr><td>NHC</td><td>N-heterocyclic carbene</td></tr><tr><td>NMR</td><td>nuclear magnetic resonance</td></tr><tr><td>NPA</td><td>natural population analysis</td></tr><tr><td>nPr</td><td>n-propyl</td></tr><tr><td>OEP</td><td>2,3,7,8,12,13,17,18-octaethylporphyrinate</td></tr><tr><td>OTf</td><td>triflate</td></tr><tr><td>PFAS</td><td>per- and polyfluoroalkyl substances</td></tr><tr><td>Ph</td><td>phenyl</td></tr><tr><td>PNP</td><td>bis(triphenylphosphine)iminium</td></tr><tr><td>py</td><td>pyridine</td></tr><tr><td>QAIM</td><td>quantum theory of atoms in molecules</td></tr></table>

<table><tr><td>r.t.</td><td>room temperature</td></tr><tr><td>sBu</td><td>sec-butyl</td></tr><tr><td>SIMes</td><td>1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene</td></tr><tr><td>solv</td><td>solvent</td></tr><tr><td>tBu</td><td>tert-butyl</td></tr><tr><td>TCICA</td><td>trichloroisocyanuric acid</td></tr><tr><td>THF</td><td>tetrahydrofuran</td></tr><tr><td>THP</td><td>tetrahydropyran</td></tr><tr><td>tol</td><td>toluene</td></tr><tr><td>TPP</td><td>5,10,15,20-tetraphenylporphyrinate</td></tr><tr><td>WCA</td><td>weakly coordinating anion</td></tr><tr><td>XRD</td><td>X-ray diffraction</td></tr></table>

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