Molecular engineering of 3-arylated tetrazo[1,2-b]indazoles: divergent synthesis and structure-property relationships

The synthetic scope of 3-arylated tetrazo[1,2-b]indazoles is reported based on a Pd-catalyzed Liebeskind-Srogl cross-coupling reaction followed by an N-cyclisation process. The reactivity of the nitrogen atoms was used to further diversify these N-rich polyaromatic tetrazo[1,2-b]indazoles in a panel of reactions (protonation, selective oxidation, metallations). Selective ortho-C-H activation/functionalization on the heterocycle was also demonstrated with three transition metals (TM = Pd, Ir and Rh). The effects of all these molecular engineering strategies, particularly the N-modifications, on the optical and redox properties of the 3-arylated tetrazoindazoles were studied experimentally and theoretically. This study highlights the diversity of molecular structures and electronic properties offered by the tetrazo[1,2-b]indazole platform.