Axial ligand exchange reactions of meso-aryl subporphyrins - Axially fluoro-substituted subporphyrin and a μ-oxo dimer and trimer of subporphyrins

High reactivity of the boron atom of mesoaryl subporphyrins enables the introduction of a broad range of functional groups to its axial position. Axially fluoro-substituted subporphyrins were easily synthesized upon treatment of axially hydroxyl-substituted subporphyrins with BF₃· OEt₂. Homogeneous μ-oxo dimers of subporphyrins were formed by heating monomers in the presence of triethylamine under a high vacuum. A heterogeneous subporphyrin - phthalocyanine-subporphyrin trimer was selectively formed from the respective monomers under similar reaction conditions. Structures of these molecules were elucidated by ¹H NMR spectra and a single-crystal X-ray diffraction analysis, and the interactions between neighboring chromophores in the dimeric systems were estimated from absorption and magnetic circular dichroism spectra.