Synthesis and Self-Assembly of β-Octa[(4-Diethoxyphosphoryl)phenyl]porphyrins

The beta-substituted porphyrinoids commonly used to form functional assembled systems in nature yet are still scarcely used in material chemistry probably due to the laborious synthesis of these compounds. In this work, beta-octa[(4-diethoxyphosphoryl)phenyl]porphyrin (2HOPPP) and its metal (Zn(II), Cd(II), Cu(II), and Ni(II)) complexes were prepared in good yields. These highly soluble chromophores were characterized in solution using spectroscopic (NMR, UV-vis, fluorescence), electrochemical, and spectroelectrochemical methods. Attachment of the electron-deficient residue (ArP(O)(OEt)(2)) to the porphyrin macrocycle leads to easier reductions and harder oxidations of the macrocycle for all complexes studied as compared to corresponding meso-tetra[4-(diethoxyphosphoryl)phenyl]porphyrin derivatives reported previously. We demonstrated that the strong electron-deficient character of the MOPPP porphyrins results principally from the increase in the number of electronwithdrawing groups at the periphery of the tetrapyrrolic macrocycle. Electron-deficient porphyrins are highly required in supramolecular and material chemistry in part due to their ability to form supramolecular assemblies via the coordination of axial ligands to the central metal atom. According to single-crystal X-ray data, ZnOPPP forms in the crystalline phase dimers in which each of the two tetrapyrrolic macrocycles is connected through an unusual combination of hydrogen bonding of two phosphoryl groups and the water molecules axially coordinated to the zinc atom of the partner molecule. The involvement of water molecules in porphyrin binding allows for an increase of distance between two porphyrin mean N-4 planes, up to 4.478 angstrom. The offset of phosphoryl groups attached to the macrocycle through a 1,4-phenylene spacer withdraws the whole porphyrin macrocycle of one molecule from spatial overlap with the macrocycle of a partner molecule and increases the Zn-Zn distance up to 10.372 angstrom. This still unknown type of porphyrin dimers allows one to get deeper insights into the organization of naturally occurring tetrapyrrolic macrocycles. ZnOPPP also forms a labile dimeric complex in 5.3 x 10(-7)-5.8 x 10(-5) M chloroform solutions. In contrast, other complexes prepared in this work exist as monomeric species under these experimental conditions. The self-association constant of ZnOPPP has been determined by electronic absorption spectroscopy.

Automated summary

This study synthesized a series of new β-phosphorylporphyrin compounds with different metal ions and characterized their spectral, electrochemical, and spectroelectrochemical properties. It was found that these compounds have strong electron-deficient properties and can form supramolecular assemblies through coordination with axial ligands by the central metal atom. The zinc ion complex formed a novel dimeric structure in the crystal phase, providing deeper insights into the organization of naturally occurring tetrapyrrolic macrocycles.