Tetrazo[1,2-b]indazoles: Straightforward Access to Nitrogen-Rich Polyaromatics from s-Tetrazines.

The straightforward access to a new class of aza-polyaromatics is reported. Starting from readily available fluorinated s-tetrazine, a cyclization process with azide leads to the formation of an unprecedented tetrazo[1,2-b]indazole or a bis-tetrazo[1,2-b]indazole (cis and trans conformers). Based on the new nitrogen core, further N-directed palladium-catalyzed ortho-C-H bond functionalization allows the introduction of halides or acetates. The physicochemical properties of these compounds were studied by a joint experimental/theoretical approach. The tetrazo[1,2-b]indazoles display solid-state π-stacking, low reduction potential, absorption in the visible range up to the near-infrared, and intense fluorescence, depending on the molecular structure.

Stepwise Oxidative C-C Coupling and/or C-N Fusion of Zn(II) meso-Pyridin-2-ylthio-porphyrins.

The synthesis and characterization of zinc(II) meso-pyridin-2-ylthio-porphyrins are presented in this manuscript. The (electro)chemical oxidation of [5-(pyridin-2-ylthio)-10,20-bis(p-tolyl)-15-phenylporphyrinato] zinc(II) or [5,15-bis(pyridin-2-ylthio)-10,20-bis(p-tolyl)porphyrinato] zinc(II) leads to the formation of one or two C-N bond(s) by intramolecular nucleophilic attack of the peripheral thiopyridinyl fragment(s) on the neighboring ß-pyrrolic position(s) (C-N fusion reaction). In addition, the chemical oxidation of [5-(pyridin-2-ylthio)-10,20-bis(p-tolyl)porphyrinato] zinc(II), i.e., bearing one free meso position, mainly affords the meso,meso-dimer. Further stepwise electrochemical oxidation selectively produces the mono and bis C-N fused meso,meso-dimer. The resulting pyridinium derivatives exhibit important changes in their physicochemical properties (NMR, UV-vis, CV) as compared to their initial unfused precursors. Also, the X-ray crystallographic structures of three unfused monomers, one unfused meso,meso-dimer, and two C-N fused monomers are presented.

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.

Synthesis of meso,ß-Fused Thiazinamine-Porphyrins via Oxidative C-N Fusion of Pyrimidinyl-Substituted Porphyrins.

5,15-Bis(pyrimidin-2-ylthio)porphyrins have been synthesized. Their electrochemical oxidation leads to the formation of mono- and bis-C-N-fused thiopyrimidinium intermediates depending on the applied charge and potential. These latter undergo nucleophilic attack with water during workup that drives the ring opening of the pyrimidinium moiety. When piperidine is added before or after workup, the neutral fused porphyrinthiazin-2-amines are generated, and they exhibit a significant bathochromic shift of their Soret and Q bands.

Regioselective C-H amination of free base porphyrins via electrogenerated pyridinium-porphyrins and stabilization of easily oxidized amino-porphyrins by protonation.

Four free base aminoporphyrins were synthesized in two steps via regioselective anodic nucleophilic substitution with pyridine followed by ring opening of the electrogenerated pyridinium with piperidine. The X-ray crystallographic structure of the unstable 2-aminotetraphenylporphyrin was solved. Protonation of this latter compound leads to the stable diiminium porphyrin salt.

Oxidative C-N fusion of pyridinyl-substituted porphyrins.

The mild (electro)chemical oxidation of pyridin-2-ylthio-meso substituted Ni(ii) porphyrins affords C-N fused cationic and dicationic pyridinium-based derivatives. These porphyrins are fully characterized and the molecular structure of one of them was confirmed by X-ray crystallography. A mechanism for the intramolecular oxidative C-N coupling is proposed based on theoretical calculations and cyclic voltammetry analyses.