On the Preparation of Nickel Porphyrins Bearing Two to Four Nitro Groups at β‐Positions

Abstract

The preparation, isolation, and identification of dinitro, trinitro, and tetranitro metalloporphyrins bearing nitro groups on pyrrole rings—desirable intermediates that enable fundamental changes in the chemico‐physical properties of the porphyrin core—were studied. All six possible dinitro‐Ni‐TPP isomers were formed; three were isolated as pure substances using column chromatography, while the remaining three were inseparable. All possible trinitro‐Ni‐TPP isomers were prepared and isolated, except for the 2,7,13 isomer. Attempts to synthesize tetranitro‐Ni‐TPP either through direct nitration of metalloporphyrin or via direct condensation of the nitropyrrole building blocks were unsuccessful. The molecular structures were unambiguously identified using 2D NMR experiments. Some experimental observations, though not all, were consistent with quantum chemical calculations performed on the geometry, energy, Fukui indices, dipole moments of nitroporphyrins, and the energy of nitration intermediates.