Non-symmetrical, potentially redox non-innocent imino NHC pyridine ‘pincers’ via a zinc ion template-assisted synthesis

Abstract

New non-symmetrical, redox-active imino NHC pyridine pincer ligands, 2-(R¹-imidazol-2-ylidene)-6-(R²NCH)-pyridine (R¹ = 2,6-diisopropylphenyl (DiPP), R² = 2,4,6-trimethylphenyl (Mes), 4B; R¹ = R² = DiPP, 4C), have been accessed by a Zn^II-promoted modular synthesis involving the quaternization of R¹-imidazole by [Zn(κN^imineκN^pyridine)(2-(R²NCH)-6-bromo-pyridine)Cl₂], followed by Zn^II removal and deprotonation of imidazolium pro-ligands. Redox active forms of 4B were implicated in the two complexes obtained by its reaction with FeBr₂/KC₈; metrical data analysis pointed to the occurrence of radical anionic and dianionic redox states of 4B.