Design, Synthesis And Characterization Of Metal Porphyrins As Biomimetic Catalysts

Porphyrin-like compounds have special structures and unique characters. They are widely used in many fields, especially as biomimetic catalysts that catalyze the selective oxidation functionalization of saturated hydrocarbons, aromatic hydrocarbons and their side chains with dioxygen. Because of the significant effects of different central metal ions, substituents at phenyl rings of porphyrin, axial ligands and the introduction of oxygen-bridge on porphyrin's catalytic activity, their catalytic activity can be improved by adjusting central metal ions, introducing various substituents on phenyl rings and axis ligands.Based on the results of our earlier molecular modeling and the above ideas, tetra-(o/p>-nitrophenyl) iron, cobalt, copper, zinc porphyrins, porphineiron(III) choloride, -oxo-bisporphieiron(III) were designed and synthesized. And the structures of these compounds were characterized and confirmed by 1R, UV-Vis spectra and MS. -oxo-bis (tetra- (o/p-nitrophenyl) porphieiron (III)) are two new compounds, which have not been reported in literatures.Catalytic activity of these compounds was investigated by dioxygen liquid-phase oxidation of p-nitrotoluene (PNT) to p-nitrobenzoic acid (PNBA) as the model reaction. The results showed that the fourteen porphyrins had notable catalytic activity. And generally, the catalytic activity of iron porphyrins was better than that of other metal porphyrins, and the yields of PNBA are all more than 75%. The best catalyst was tetra-(o-nitrophenyl)porphineiron(III) choloride, and the yield of PNBA is up to 83.2%.In order to explain the above experimental results and explore the relationship between the structure and catalytic activity of metal porphyrins, the above fourteen catalysts were modeled by Molecular Mechanics Force Field and PM3 methods of Hyperchem software. Based on the results of molecular modeling and experiments, it showed that catalytic activity of porphyrins was directly affected by the character of center mental ions, withdrawing- electron capability of substituted groups, axes-directing ligand, -oxo bond and spatial hindrance.In addition, the methods for synthesizing tetra- (o-chlorophenyl) cobalt porphyrin, which was proved as an excellent catalyst in our earlier work, were studied. The two-step method had higher yield and was more convenient than one-step method. And the first step reaction, the yield- determining step of the two-step method was mainly investigated. The optimum synthetic conditions were 165癈, 2hr, 0.075mol/L, and 4 I 6 of mole ratio between anhydrous aluminium chloride and pyrrole.