Synthesis, Structures, and Near-IR Absorption of Heterole-Fused Earring Porphyrins

Abstract

A reaction sequence of regioselective peripheral bromination, Suzuki-Miyaura coupling with 2-borylated thiophene or pyrrole, and oxidative ring-closure with FeCl₃ allowed the synthesis of heterole-fused earring porphyrins 4Pd and 9Pd from the parent earring porphyrin 1. Differently pyrrole-fused porphyrins 5H and 6H and their Pd^II complexes 5Pd and 6Pd were also synthesized. The structures of 4Pd, 5H, 6Pd, and 8Pd have been revealed by X-ray analysis to be slightly twisted owing to constraints imposed by heterole-fused structures. 5Pd exhibits an intensified band at 1505 nm, while 4Pd and 9Pd display small but remarkably red-shifted absorption bands reaching around 2200 nm.

Keywords: cyclic voltammetry; earring porphyrins; near-infrared absorption; oxidative fusion reaction; porphyrins.