Azo-MICs: Redox-Active Mesoionic Carbene Ligands Derived from Azoimidazolium Dyes.

Azoimidazolium dyes were used as precursors for mesoionic carbene ligands (Azo-MICs). The properties of these ligands were examined by synthesizing RhI , AuI , and PdII complexes. Experimental (NMR, IR) and theoretical investigations show that Azo-MICs are potent σ-donor ligands. Yet, they feature a small singlet-triplet gap and very low-lying LUMO levels. The unique electronic properties of Azo-MICs allow for reversible one-electron reductions of the metal complexes, as evidenced by cyclic voltammetry.