Synthesis of aminyl biradicals by base-induced Csp³–Csp³ coupling of cationic azo dyes

Abstract

The synthesis of the industrially important polymer parylene is achieved by polymerization of <i>p</i>-quinodimethane (<i>p</i>-QDM). The polymerization is thought to proceed <i>via</i> a biradical <i>p</i>-QDM dimer, but isolation or characterization of such a biradical has remained elusive. Here, we describe the synthesis of an aza-analogue of this <i>p</i>-QDM dimer. The biradical is formed by base-induced dimerization of an azoimidazolium dye. Due to the presence of sterically shielded aminyl radicals instead of terminal H₂Ċ groups, the stability of this dimer is sufficient for analyses by ESR spectroscopy and X-ray crystallography. A similar Csp³-Csp³ coupling was observed for an azotriazolium dye, suggesting that base-induced C-C coupling reactions can be realized for different types of azo dyes.