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. 2023 Jul 21;88(14):9893-9901.
doi: 10.1021/acs.joc.3c00658. Epub 2023 Jul 5.

A Guide to Tris(4-Substituted)-triphenylmethyl Radicals

Abigail M Heuer  1 , Scott C Coste  1 , Gurjot Singh  1 , Brandon Q Mercado  1 , James M Mayer  1
Affiliations

A Guide to Tris(4-Substituted)-triphenylmethyl Radicals

Abigail M Heuer et al. J Org Chem. .

Abstract

Triphenylmethyl (trityl, Ph3C•) radicals have been considered the prototypical carbon-centered radical since their discovery in 1900. Tris(4-substituted)-trityls [(4-R-Ph)3C•] have since been used in many ways due to their stability, persistence, and spectroscopic activity. Despite their widespread use, existing synthetic routes toward tris(4-substituted)-trityl radicals are not reproducible and often lead to impure materials. We report here robust syntheses of six electronically varied (4-RPh)3C•, where R = NMe2, OCH3, tBu, Ph, Cl, and CF3. The characterization reported for the radicals and related compounds includes five X-ray crystal structures, electrochemical potentials, and optical spectra. Each radical is best accessed using a stepwise approach from the trityl halide, (RPh)3CCl or (RPh)3CBr, by controllably removing the halide with subsequent 1e- reduction of the trityl cation, (RPh)3C+. These syntheses afford consistently crystalline trityl radicals of high purity for further studies.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. 4-Substituted Trityl Radicals ([R]•) and Related Compounds
Scheme 2
Scheme 2. Routes to Trityl Radicals: Conventional Synthesis with Heterogeneous Reductants (Red) vs the Recommended Two-Step Synthesis (Blue)
Figure 1
Figure 1
(a) Molecular structures of the trityl radicals determined by single-crystal X-ray diffraction; thermal ellipsoids are shown at 50% probability (one of the CF3 groups is disordered). Cl and F, green; O, red; C, gray; H, white. (b) Side-on view of radical stacking in [Cl]• (left) and [Ph]• (right) structures showing possible intermolecular interactions. The purple ball in the structure for [Ph]• represents the ring centroid.
Figure 2
Figure 2
UV–visible spectra of [(4-RPh)3C]+/•/– measured at room temperature. (a) Absorbance spectra of radicals plotted as molar extinction coefficient (εM) in M–1 cm–1. Each radical spectrum is reported in toluene, except [Me2N]•, which is reported in MeCN. (b) Absorbance spectra of the carbocations in DCM, plotted as εM, generated from the reaction of the triarylmethyl halide with AgOTf except for crystal violet. (c) Absorbance spectra of the carbanions in THF, plotted as εM, generated from reduction of the triarylmethyl halide with KC8 or from deprotonation with TBAOH. Estimated εM values for the carbocations and carbanions are presented in Table S1.
Figure 3
Figure 3
Cyclic voltammograms of carbocations or radicals (5–15 mM) in MeCN at room temperature, 0.1 M [Bu4N][PF6], internally referenced after the scan with Fc/Fc+, and with iR compensation; scan rates, 100 mV/s.
See this image and copyright information in PMC

References

    1. Roberts J. D.; Caserio M. C.. Basic principles of organic chemistry; 2nd ed.; W. A., Benjamin: Menlo Park: Calif., 1977; pp. 350–409.
    1. Darcy J. W.; Koronkiewicz B.; Parada G. A.; Mayer J. M. A Continuum of Proton-Coupled Electron Transfer Reactivity. Acc. Chem. Res. 2018, 51, 2391–2399. 10.1021/acs.accounts.8b00319. - DOI - PMC - PubMed
    1. Darcy J. W.; Kolmar S. S.; Mayer J. M. Transition State Asymmetry in C-H Bond Cleavage by Proton-Coupled Electron Transfer. J. Am. Chem. Soc. 2019, 141, 10777–10787. 10.1021/jacs.9b04303. - DOI - PMC - PubMed
    1. Pitre S. P.; Weires N. A.; Overman L. E. Forging C(sp3)-C(sp3) Bonds with Carbon-Centered Radicals in the Synthesis of Complex Molecules. J. Am. Chem. Soc. 2019, 141, 2800–2813. 10.1021/jacs.8b11790. - DOI - PMC - PubMed
    1. Bonjoch J.; Diaba F. Radical Reactions in Alkaloid Synthesis: A Perspective from Carbon Radical Precursors. Eur. J. Org. Chem. 2020, 2020, 5070–5100. 10.1002/ejoc.202000391. - DOI