Isolating Fe-O2 Intermediates in Dioxygen Activation by Iron Porphyrin Complexes

Abstract

Dioxygen (O2) is an environmentally benign and abundant oxidant whose utilization is of great interest in the design of bioinspired synthetic catalytic oxidation systems to reduce energy consumption. However, it is unfortunate that utilization of O2 is a significant challenge because of the thermodynamic stability of O2 in its triplet ground state. Nevertheless, nature is able to overcome the spin state barrier using enzymes, which contain transition metals with unpaired d-electrons facilitating the activation of O2 by metal coordination. This inspires bioinorganic chemists to synthesize biomimetic small-molecule iron porphyrin complexes to carry out the O2 activation, wherein Fe-O2 species have been implicated as the key reactive intermediates. In recent years, a number of Fe-O2 intermediates have been synthesized by activating O2 at iron centers supported on porphyrin ligands. In this review, we focus on a few examples of these advances with emphasis in each case on the particular design of iron porphyrin complexes and particular reaction environments to stabilize and isolate metal-O2 intermediates in dioxygen activation, which will provide clues to elucidate structures of reactive intermediates and mechanistic insights in biological processes.

Experimental and Theoretical Study on Crown Ether-Appended-Fe(III) Porphyrin Complexes and Catalytic Oxidation Cyclohexene with O2

“…Metalloporphyrin complexes exhibit exceptional catalytic properties for various chemical transformations, including O-O bond heterolysis [1][2][3][4], H-H bond formation [5,6], O 2 adsorption [4,7,8], and catalytic oxidation [9][10][11][12] due to high activity, stability, clear molecular structure, and the ability to mimic the cytochrome enzyme [13,14]. Previous studies have shown that changing the meso-position substituents of metalloporphyrins to modulate their redox properties can alter metal ions' activities, stability, and selectivity in catalytic processes [15][16][17][18][19][20][21].…”

Catalytic Degradation of Triphenylmethane Dyes with an Iron Porphyrin Complex as a Cytochrome P450 Model

“…However, because natural enzymes cannot be extracted, their application in industrial production is also limited. Porphyrins consist of four pyrrole methylene α-carbon atoms connected to each other by a methylene bridge (=CH-) [ 15 ]. There are two pyrrole protons (N-H) in the porphyrin ring.…”

Iron Porphyrin as a Cytochrome P450 Model for the Degradation of Dye

“…However, due to their high cost, highly restricted catalytic conditions and fragile nature, the practical applications of enzymes have been hindered. To overcome these problems of enzymes for practical applications, biomimetic systems have subsequently emerged as an effective approach to synthesize highly efficient biomimetic catalysts via mimicking certain key features of enzymes [31,32].…”