Synthesis and Electrochemical Properties of Tetrasubstituted Tetraphenylethenes

Tetrakis(4‐acetoxyphenyl and 4‐benzoyloxyphenyl)ethenes 1f and 1g were obtained by acylation of tetrakis(4‐hydroxyphenyl)ethene 1b . Ullmann etherification of 4,4′‐dihydroxybenzophenone 2b and subsequent McMurry coupling yielded tetrakis(phenoxyphenyl)ethene 1i . The tetrakis(acetamidophenyl)ethene 1h was prepared in three steps from tetraphenylethene 1c by nitration, Raney‐Ni reduction and subsequent acetylation. Alternatively, trifluoroacetamide 1j , 2‐methylhexanamide 1k and 2,4‐dimethylbenzamide 1l , with less tendency to form 2D hydrogen bonding networks and thus increased solubility as compared to 1h , were prepared by acylation of 4,4′‐diaminobenzophenone 2a and subsequent McMurry coupling. Compounds 1f – l were investigated by cyclic voltammetry. While the phenyl ether derivative 1i displays single‐electron processes during oxidation, a two‐electron process was discovered for trifluoroacetamide 1j as was also supposed for the esters 1f and 1g . In addition, comproportionation constants were shown to be dependent on the solvent. In situ IR spectroelectrochemistry provided evidence for quinoidal type substructures in the dioxidized forms of tetraphenylethenes 1 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)