Symmetrical and unsymmetrical quadruply Aza bridged closely interspaced cofacial Bis(5,10,15,20-tetraphenylporphyrin)s. 2. Synthesis, characterization, and conformational effects of solvents

Article abstract of DOI:10.1021/ja00038a065

Several water- and non-water-soluble symmetrical and unsymmetrical quadruply aza bridged closely interspaced cofacial bis(5,10,15,20-tetraphenylporphyrin)s have been synthesized and fully characterized by 2D ¹H-¹H NMR (COSY), 2D ¹³C-¹H NMR, FABMS, UV/vis, IR, and fluorescence spectral techniques. It was established, on the basis of ¹H NMR, UV/vis, and emission spectrophotometries, that tetrakis[m,m-(methylene(m-pyridinesulfonyl)imino)methylene]-strati-bis-(5,10,15, 20-tetraphenylporphyrin) (5), tetrakis[m,m-(methylene(m-pyridiniumsulfonyl)imino)methylene]-strati-bis-(5,10, 15,20-tetraphenylporphyrin) chloride (7), and tetrakis[m,m-(methylene(p-toluenesulfonyl)imino)methylene]-strati-bis(5,10,15, 20-tetraphenylporphyrin) (11) exist in more than one conformation in DMSO and in only one symmetrical conformation in CHCl₃. The biszinc and tetraprotonated 5, 7, and 11 exist in one conformation regardless of the solvent. These observations have been attributed to an interaction between DMSO and the pyrrolic N-H protons of the porphyrin cores which is inhibited by metalation (Zn²⁺) or protonation of the porphyrin moiety. Molecular dynamics calculations reveal that the intracavity interactions of 5 with DMSO are more important than the intercavity interactions which result in discrete, unsymmetrical conformations of the dimer. In contrast, tris[m,m-(methylene(m-pyridinesulfonyl)imino)methylene]-mono((((methyleneoxy) carbonyl)oxy)methylene)-strati-bis(5,10,15,20-tetraphenylporphyrin) (6), tetrakis[m,m-(methylenecyanoimino)-methylene]-strati-bis(5,10,15,20- tetraphenylporphyrin) (8), tris[m,m-(methylenecyanoimino)methylene]-mono((((methyleneoxy)carbonyl)oxy) methylene)-strati-bis(5,10,15,20-tetraphenylporphyrin) (9), and tetrakis[m,m-(methylene(formainido)imino)methylene]-strati-bis(5,10,15,20- tetraphenylporphyrin) (10) do not show any conformational changes upon switching from chloroform to DMSO. This is attributed to the long interplanar distances calculated for the porphyrin dimers which prevent any intracavity coordination of DMSO with both porphyrin moieties. ¹H NMR variable-temperature experiments of porphyrin dimer 5 in DMSO show that the conformation of the dimer is greatly affected by temperature. While at room temperature 5 exists in more than one conformation, at higher temperatures (150 °C) only one conformation is populated. It is proposed that at room temperature, the existence of a hydrogen-bonding network between DMSO and the dimer results in more than one conformation, while at higher temperatures the network is destroyed to furnish an average conformation.