Quest for Zinc Methoxyisoporphyrin Molecules: Experimental and Theoretical Studies

Abstract

AbstractThis study describes the synthesis, characterization and theoretical studies of two new zinc isoporphyrin compounds, [5‐(methoxy)‐5,10,15,20‐tetrakis(4‐hydroxy)‐5,15H‐porphinato]zinc(II) 1 b, and [5‐(methoxy)‐5,10,15,20‐tetrakis(4‐methyl)‐5,15H‐porphinato]zinc(II) 2 b. Meso‐tetra(4‐hydroxyphenyl)zinc porphyrin, [ZnT(4‐OH)PP], 1 a and, meso‐tetra(4‐methylphenyl)zinc porphyrin, [ZnT(4‐CH3)PP] 2 a were used as a parent porphyrins to synthesize the respective isoporphyrin complexes in the presence of ceric ammonium nitrate (CAN) in methanol medium. The synthesized isoporphyrin compounds are characterized using all standard spectroscopic techniques like UV‐Visible, IR, 1HNMR, and ESI‐Mass spectrometric method. Theoretical calculations at the DFT level was performed to understand the properties and reactivity of the isoporphyrins. To get some insight into the mechanism of isoporphyrin formation via zinc porphyrin dication, the geometry of zinc porphyrin dication [ZnT(4‐OH)PP]++ was optimized and the distribution of Mulliken charge in the dication ring was calculated. The higher positive charge at the meso C‐atoms of the zinc porphyrin dication with respect to other ring carbon atoms supports the proposed nucleophilic attack at the meso carbon of the dication. The DFT calculations studied here is suitable to understand the mechanism of formation of isoporphyrins in the presence of nucleophiles, unique electronic spectra, and redox properties of isoporphyrins.