Synthesis of NiII porphyrin—NiII 5,15-diazaporphyrin hybrid tapes

Abstract

Ni^II porphyrin (P) and Ni^II 5,15-diazaporphyrin (DAP) hybrid tapes were synthesized by Suzuki–Miyaura cross-coupling reactions of meso- or β-borylated P with β-brominated DAP followed by intramolecular oxidative fusion reactions. Meso-β doubly linked hybrid tapes were synthesized by oxidation of singly linked precursors with DDQ-FeCl₃. Synthesis of triply linked hybrid tapes was achieved by oxidation with DDQ-FeCl₃-AgOTf with suppression of peripheral β-chlorination. In these tapes, DAP segments were present as a 20π-electronic unit, but their local antiaromatic contribution was trivial. Remarkably, these hybrid tapes were stable and exhibited extremely enhanced absorption bands in the NIR region and multiple reversible redox waves. A pentameric hybrid tape showed a remarkably sharp and red-shifted band at 1168 nm with ε = 5.75 × 10⁵ M⁻¹ cm⁻¹. Singly linked P-DAP dyads were oxidized with DDQ-FeCl₃ to give stable radicals, which were oxidized further to afford dimeric hybrid tapes possessing a nitrogen atom at the peripheral-side meso-position.