Synthesis and structure of five or six-coordinate manganese deuteroporphyrin-niacin dyads with intramolecular axial pyridine

Deuteroporphyrin-niacin dyads with different chain lengths have been synthesized by modification of the propionate side chains of hemin. When a manganese ion was inserted into the porphyrin core, the UV spectral shift of manganese deuteroporphyrin-niacin dyads were experimentally demonstrated to mainly originate from the intramolecular coordination. In order to elaborate the intramolecular coordination, the spectra of single manganese porphyrin complexes in CH2Cl2 solution were measured and compared to that of the addition of axial ligands (pyridine and methyl nicotinate). Among all the synthetic dyads, the compounds of 2,7,12,18-tetramethyl-13,17-di(3-hydroxypropyl nicotinate) porphyrin and 2,7,12,18-tetramethyl-13,17-di(3-aminoethyl nicotinate) porphyrin manganese bearing the short chains did not show intramolecular coordination of the terminal base on the metal ion. Other three compounds of the niacin moiety indirectly bonded to the propionate side chains of manganese porphyrin through the diols linkage exhibited optical spectra characteristic of five or six-coordinate manganese complexes. These results indicate that the niacin groups' access to the Mn(III) center depended on the chain lengths.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A general method has been outlined by modification of the hemin-propionate chains. ► A series of deuteroporphyrin-niacin dyads have been prepared and characterized. ► The behavior of intramolecular binding of these days depends on the chain lengths. ► Six-coordinate Mn-porphyrin with intramolecular axial pyridine was synthesized.