Triarylmethanes and 9-arylxanthenes as prototypes amphihydric compounds for relating the stabilities of cations, anions and radicals by C-H bond cleavage and electron transfer

4-Ferrocenylphenyl-Substituted Tritylium Dyes with Open and Interlinked C+Ar2Entities: Redox Behavior, Electrochromism, and a Quantitative Study of the Dimerization of Their Neutral Radicals

“…The particular stabilization of the methylium center on its incorporation into the (thio)xanthylium scaffold is also evident from the observation that the δ C+ values of complexes 3 + −5 + closely resemble those of 172.4, 172.3, and 164.8 ppm for the phenylthioxanthylium and the p-tolyl-and p-anisylxanthylium cations, respectively, 51 indicating the absence of an extra stabilizing effect by the 4-ferrocenylphenyl residue. The electron-donating effect of the 4-ferrocenylphenyl substituent becomes, however, manifest in derivatives that lack other, stronger donors.…”

“…Particularly indicative is the resonance signal of carbon atom C9 (cf. Scheme ), which changes during this conversion from a tetrahedral, neutral trityl carbinol to a trivalent methylium center. ,,− The corresponding resonance was unambiguously assigned with the aid of 2D-HMBC spectra (e.g., Figure S31 in the Supporting Information) and found to shift by roughly 100 ppm to lower field: e.g., from 78.9 ppm in 1-OH to 180.9 ppm in 1 + . Downfield shifts of 0.13 ppm (for 5 + ) to 0.35 ppm (for 2 + ) for protons H4 at the unsubstituted Cp decks of the ferrocenyl pendants signal that the electronic perturbation of the system is transmitted via the phenylene linker to the remote ferrocenyl substituent.…”

Isotopic Fractionation as a Mechanistic Probe in Light-Driven C–H Bond Exchange Reactions

“…In entry 5, the unsymmetric diarylmethane substrate ( E p/2 = 1.23 V vs Fc + /Fc) cannot be oxidized by the excited state of Ir-1 . However, its weak C–H bond can engage in HAT with the thiyl radical derived from thioacetic acid (Δ G ° = −5 kcal/mol). The thermodynamic driving force for this HAT step renders the reverse HAT process unfavorable.…”

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

“…Since the triphenylmethyl cations are so stable, evident by their spontaneous formation from the halide precursors, we sought to controllably synthesize and reduce them. Previously reported electrochemical measurements found that some carbocations exhibit reversible one-electron reduction waves. − Therefore, outer-sphere electron transfer by a homogeneous reagent with the appropriate reduction potential should enable stoichiometric formation of the radical from the carbocation. We decided to target a set of trityl substrates, ranging from electron-rich (R = Me 2 N, MeO, t Bu, and Ph) to electron-deficient (R = Cl and CF 3 ).…”