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. 2022 Jul 11;61(28):e202203777.
doi: 10.1002/anie.202203777. Epub 2022 May 16.

The Tris(pentafluorophenyl)methylium Cation: Isolation and Reactivity

Kurt F Hoffmann  1 , David Battke  1 , Paul Golz  1 , Susanne M Rupf  1 , Moritz Malischewski  1 , Sebastian Riedel  1
Affiliations

The Tris(pentafluorophenyl)methylium Cation: Isolation and Reactivity

Kurt F Hoffmann et al. Angew Chem Int Ed Engl. .

Abstract

Herein, we present two different routes for the synthesis of the perfluorinated trityl cation, which allowed the handling of the free, uncoordinated species in organic solvents for the first time. The usage of the weakly coordinating anion [Al(OTeF5 )4 ]- and its derivatives allows the characterization of this species by NMR spectroscopy and most importantly by single-crystal X-ray diffraction. The high hydride ion affinity of the cation is shown by hydrogen abstraction from isobutane. Furthermore, cyclic voltammetry reveals its oxidative potential which is supported by the reaction with tris(4-bromophenyl)amine, giving rise to the formation of the ammoniumyl radical cation, also known as "magic blue".

Keywords: High Hydride Affinity; Perfluorinated Trityl Cation; Strong Oxidizer; Superacids; Weakly Coordinating Anions.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Lewis structures of the precursor tris(pentafluorophenyl)methyl chloride 1 and the product tris(pentafluorophenyl)methylium 2.
Scheme 1
Scheme 1
Synthesis of the perfluorinated trityl cation via a Brønsted acidic route.
Figure 2
Figure 2
Molecular structure of HC(C6F5)3 in the solid state. Thermal ellipsoids set at 50 % probability. Selected bond lengths [pm] and angles [°]: C1–C2 153.5(4), C1–C8 152.7(4), C1–C14 153.6(4); C2‐C1‐C14 113.5(2), C8‐C1‐C2 114.6(2), C8‐C1‐C14 113.4(2).
Figure 3
Figure 3
Molecular structure of [C(C6F5)3][Al(OTeF5)4] in the solid state. Thermal ellipsoids set at 50 % probability. Selected bond lengths [pm] and angles [°]: C1–C2 143.2(6), C1–C8 144.9(10); C2‐C1‐C8 119.8(3), C2‐C1‐C2′ 120.5(6), C2′‐C1‐C8 119.8(3).
Scheme 2
Scheme 2
Synthesis of the perfluorinated trityl cation via a Lewis acidic route.
Figure 4
Figure 4
Top: Plotted electrostatic potential of perfluorinated and non‐fluorinated trityl cations (in E H, isovalue: 0.025). Bottom: Plotted Lowest Unoccupied Molecular Orbitals of [C(C6F5)3]+ and [C(C6H5)3]+ along with the calculated difference of LUMO energy and the adiabatic ionization energy. Calculations were performed at RI‐B3LYP/def2‐TZVPP level of theory.
Scheme 3
Scheme 3
Reaction of the perfluorinated trityl cation with isobutane performed in SO2ClF.
Figure 5
Figure 5
Cyclic voltammogram of a 0.078 M solution of [C(C6F5)3][Al(OTeF5)4] in ortho‐difluorobenzene at −35 °C. Scan rate: 100 mV s−1. Irreversible oxidation wave at 1.11 V.
Scheme 4
Scheme 4
Reaction of the perfluorinated trityl cation with ferrocene (top) and tris(4‐bromophenyl)amine (bottom).
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