Electrochemical, Spectroelectrochemical, Mößbauer, and EPR Spectroscopic Studies on Ferrocenyl‐Substituted Tritylium Dyes

Abstract

Four monoferrocenyl tritylium derivatives with donor-substituted (OMe, NMe ) aryl rings are reported, along with their spectroscopic and electrochemical properties. All the complexes show a one-electron reduction and a quasi-reversible ferrocene oxidation at a very positive potential. Small quadrupole splittings, ΔE , in Mößbauer spectra agree with highly electron-deficient ferrocenes. Comparison of the experimental half-wave potentials for ferrocene oxidation, E (Fc/Fc ), with those estimated from established correlations of E (Fc/Fc ) with ΔE indicates that the E values of the anisyl-substituted congeners FcOMe and FcMeOMe are affected by Coulombic repulsion between the positive charges at the Fe ion and the neighboring methylium site. Electronic spectra are recorded and interpreted with the aid of quantum chemical calculations. UV/Vis spectroelectrochemical measurements as well as chemical reduction provide insight into the redox-induced color changes upon ferrocene oxidation or upon reduction to the neutral trityl radicals. The neutral radicals reversibly form EPR-silent dimers. This process is studied by temperature-dependent EPR spectroscopy, and thermodynamic data for their dimerization are determined. Experimental and quantum chemical data suggest that the dimers assume classical hexaarylethane structures as opposed to normal or "offset" Jacobson-Nauta-type structures.

Extremely Electron‐Poor Bis(diarylmethylium)‐Substituted Ferrocenes and the First Peroxoferrocenophane

“…Such odd behavior was already observed for reduced samples of triarylmethylium-substituted ferrocenes 2a + to 2c + and traced to the formation of hexaarylethane-type dimers. [6] The same obviously applies here. We however note that the reduction in signal intensity upon cooling is less pronounced for cationic 1a •+ as compared to 2a • , which is reasonably expected as a consequence of electrostatic repulsion between the positively charged CAr 2…”

“…On addition of BrookhartЈs acid H(OEt 2 ) + [B{C 6 H 3 (CF 3 ) 2 -3,5} 4 ] -, [10] an instantaneous color change to blue (1a 2+ ), dark green (1b 2+ ), or dark yellow (1c 2+ ) was observed. The so-dubbed BAr F24 anion, which was first reported by Kobayshi in 1984, [11] is very weakly nucleophilic and has only little ion-pairing capabilities, [6,12] which is both crucial for the stabilization of strong electrophiles such as the present ones. After solvent removal, the corresponding dicationic bis(triarylmethylium)-substituted ferrocenes were obtained as intensely blue, red, or vividly purple solids.…”

“…The same behavior is observed on reduction of the tritylium entity to a trityl radical, which essentially removes its electron‐accepting capabilities. Neutral ferrocenyl(diaryl)methyl radicals FcC • Ar 2 are prone to dimerize, and an authentic hexaarylethane structure was proposed for these dimers …”

Facile Synthesis of a Stable Side‐on Phosphinyne Complex by Redox Driven Intramolecular Cyclisation

“…The optically transparent thin-layer electrochemical (OTTLE) cell followed the design of Hartl and Winter. [38,39] Details on the X-ray diffraction experiments, on the EPR measurement and the quantum chemical calculations are given in the Supporting Information.…”

“…This observation can be explained by dimerization of the biradical species as in the case of the Gomberg radical. [37,38] The observation of ap ure tungsten based S = 1/2 system in the EPR experiment does not exclude the existence of am onomer/dimer equilibrium, since ar eal triplet state should be largelyE PR silentdue to zero field splitting.…”