Dimerization of 9-Phenyl-ferroceno[2,3]indenylmethyl Radicals: Electrochemical and Spectroelectrochemical Studies.

We report on three new 9-phenyl-substituted ferroceno[2,3]indenylmethylium dyes - with electron-donating (OMe, Me) or electron-withdrawing (CF) substituents. Complexes - exist as racemic mixtures of and enantiomers. Pyramidalization at the methyl C atom in the precursor carbinol species - or the corresponding one-electron reduced radicals induces a second stereocenter, as the 9-phenyl substituent may reside in an or an position. Indeed, alcohol crystallizes as a racemate of , and , isomers. Cationic complexes - are of deep green color and show intense electronic absorption in the visible. The oxidation and reduction processes are thoroughly investigated by means of cyclic voltammetry and UV/vis/NIR spectroelectrochemistry, the latter showing their electrochromic behavior. -dependent EPR spectroscopy, EPR spin counting at 20 °C, as well as the UV/vis/NIR spectra of the reduced samples suggest that the one-electron reduced, neutral radicals dimerize nearly quantitatively (≥99.98%). Chemical reduction of furnished an isomeric mixture of dimeric -. As was shown by cyclic voltammetry and UV/vis/NIR spectroelectrochemistry, the latter dimer redissociates to monomers upon oxidation, thereby closing a reversible cycle of redox-induced C-C bond making and breaking.