Synthesis and Characterization of (R)- and (S)-1,1′-Bi-2-Naphtholato Coordinated Gallium(III) Porphyrins and Their Chiroptical Properties

In the course of research aimed at reproducing the functions of naturally occurring porphyrins, ongoing efforts have been directed toward introducing chirality—characteristic of many natural products—in order to mimic biological functions. Traditionally, chiral centers have been incorporated into the porphyrin framework through multistep, synthetically demanding procedures involving covalent bond formation. A more straightforward approach is proposed that utilizes a stable metal coordination bond, which was previously developed, to introduce a chiral source in a single step via axial ligation. Specifically, a novel compound is synthesized by coordinating 1,1′-bi-2-naphtholato (BINOL)—an easily accessible molecule with broad applications in asymmetric catalysis and chiroptical chemistry—to gallium porphyrin. As expected, the resulting complex exhibited high stability, with the molecular ion peak confirmed by atmospheric-pressure chemical ionization mass spectrometry. Furthermore, the structure of the compound is thoroughly characterized by single-crystal X-ray diffraction and various nuclear magnetic resonance techniques. Its chiroptical properties are also investigated using electronic circular dichroism and vibrational circular dichroism spectroscopy. This study is expected to serve as a foundation for future developments in chiroptical chemistry and asymmetric catalysis involving chiral porphyrins.