Iron(III) 5,15-Diazaporphyrin Catalysts for the Direct Oxidation of C(sp3)-H Bonds

Dioxygen Activation by Gold(I)-Distorted Porphyrin Dinuclear Complexes

Interactions between gold-based materials and dioxygen (O2) have motivated researchers to understand reaction mechanisms for O2 activation by homo- and heterogeneous gold catalysts. In this work, gold(I) porphyrin dinuclear complexes were synthesized with a saddle-distorted porphyrin ligand. The gold(I) porphyrin complexes showed unprecedented O2 activation in the presence of protic solvents to form gold(III) tetradentate porphyrin complexes. Mechanistic insights into the O2 activation by the gold(I) center were elucidated by spectroscopic measurements and theoretical calculations, revealing that dissociation of halides on the gold(I) center by alcohol solvents and hydrogen bonding of an N-H proton in the distorted porphyrin with dioxygen played important roles in establishing the unique reactivities of gold(I) complexes.

Factors controlling the reactivity of synthetic compound-I Analogs

A high-valent iron(IV)-oxo porphyrin radical cation (FeIV(O)(porph+•) serves as a key, reactive intermediate for a range of heme enzymes, including cytochrome P450 (CYP), horseradish peroxidase (HRP), and catalase (CAT). Synthetic analogs of this intermediate, known as Compound-I (Cpd-I) in the heme enzyme literature, have been generated with different tetrapyrrolic, macrocyclic ligands, including porphyrin derivatives, and the closely related ring-contracted macrocycles, corroles and corrolazines. These synthetic analogs have been useful for assigning and understanding structural and spectroscopic features and examining the reactivity of Cpd-I-like species in controlled and well-defined environments. This review focuses on summarizing recent developments in the synthesis and reactivity of high-valent iron-oxo porphyrinoid complexes in two main classes of reactions, proton-coupled electron transfer (PCET) and oxygen atom transfer (OAT). The relationship between the structure of the complexes and their reactivity is emphasized, including the influence of axial ligation and peripheral macrocyclic substitution, as well as the effects of solvent and secondary coordination spheres on the reactivity of the Cpd-I analogs. In bringing together the latest findings on Cpd-I analogs, this review intends to broaden our current understanding of the factors that control the stability and reactivity of Cpd-I species. This new knowledge should, in turn, point toward new synthetic strategies for constructing catalysts that rely on Cpd-I-like reactive intermediates.

Stepwise N-Methylation of Ruthenium and Cobalt 5,15-Diazaporphyrins: Post-Functionalization of Porphyrinoid Catalysts

Post-functionalization of porphyrinoid catalysts provides a powerful tool for fine-tuning their electronic structure. We have succeeded in the stepwise methylation of the peripheral nitrogen atoms in ruthenium and cobalt 5,15-diazaporphyrins. The axial coordination of an anion to the metal center accelerates the second methylation through charge neutralization. N-Methylation of the diazaporphyrin complexes effectively controls their electron deficiency, Lewis acidity, and catalytic activity.

Iron hexamesityl-5,15-diazaporphyrin: synthesis, structure and catalytic use for direct oxidation of sp3 C-H bonds

Iron hexamesityl-5,15-diazaporphyrin was synthesized through the cross-coupling reaction of tetrabromodiazaporphyrin. The use of chloroiron(iii) hexamesityl-5,15-diazaporphyrin as a catalyst for oxidation of cyclooctane showed high performance with a total TON up to 731. The introduction of bulky mesityl groups at β-positions prevented the catalyst deactivation via formation of a μ-oxo dimer.