Direct Aerobic Generation of a Ferric Hydroperoxo Intermediate Via a Preorganized Secondary Coordination Sphere

Abstract

Enzymes exert control over the reactivity of metal centers with precise tuning of the secondary coordination sphere of active sites. One particularly elegant illustration of this principle is in the controlled delivery of proton and electron equivalents in order to activate abundant but kinetically inert oxidants such as O 2 for oxidative chemistry. Chemists have drawn inspiration from biology in designing molecular systems where the secondary coordination sphere can shuttle protons or electrons to substrates. However, a biomimetic activation of O 2 requires the transfer of both protons and electrons, and molecular systems where ancillary ligands are designed to provide both of these equivalents are comparatively rare. Here, we report the use of a dihydrazonopyrrole (DHP) ligand complexed to Fe to perform exactly such a biomimetic activation of O 2 . In the presence of O 2 , this complex directly generates a high spin Fe(III)-hydroperoxo intermediate which features a DHP • ligand radical via ligand-based transfer of an H atom. This system displays oxidative reactivity and ultimately releases hydrogen peroxide, providing insight on how secondary coordination sphere interactions influence the evolution of oxidizing intermediates in Fe-mediated aerobic oxidations.

Cobalt-Catalyzed Hydrogenation Reactions Enabled by Ligand-Based Storage of Dihydrogen

“…Our laboratory has been interested in first-row transition metal complexes ligated by dihydrazonopyrrole (DHP) ligands. These complexes can reversibly transfer dihydrogen stored on the ligand framework, which enables the catalytic hydrogenation of benzoquinone in a Ni-based system. , Related Fe complexes are also able to transfer H-atoms to O 2 to generate hydroperoxo intermediates and ultimately H 2 O 2 using ligand-derived H-atom equivalents . We rationalized that striking a balance between redox and spin-state flexibility, as present with Fe complexes, and more classic organometallic metals, such as Ni, might be advantageous for new catalytic transformations. , …”

“… 9 , 10 Related Fe complexes are also able to transfer H-atoms to O 2 to generate hydroperoxo intermediates and ultimately H 2 O 2 using ligand-derived H-atom equivalents. 11 We rationalized that striking a balance between redox and spin-state flexibility, as present with Fe complexes, and more classic organometallic metals, such as Ni, might be advantageous for new catalytic transformations. 10 , 11 …”

“… 11 We rationalized that striking a balance between redox and spin-state flexibility, as present with Fe complexes, and more classic organometallic metals, such as Ni, might be advantageous for new catalytic transformations. 10 , 11 …”

Unveiling the interplay between homogeneous and heterogeneous catalytic mechanisms in copper–iron nanoparticles working under chemically relevant tumour conditions

“…57,58 The specic generation of cO 2 À was evaluated using dihydroethidium (DHE)(see Fig. ESI-6a †).…”

Generation and Aerobic Oxidative Catalysis of a Cu(II) Superoxo Complex Supported by a Redox-Active Ligand

“…We have recently been interested in using biomimetic approaches with dihydrazonopyrrole (DHP) ligand scaffolds that can support H + , e – , H-atom, or H 2 transfer similar to biological cofactors or active sites. This strategy has enabled the generation of superoxo and hydroperoxo intermediates with Ni and Fe, respectively, , but no aerobic catalysis was observed in these systems. We rationalized that the noted aerobic chemistry of Cu might enable oxidative catalysis and that the established redox activity of the DHP ligand might facilitate the observation and characterization of catalytic intermediates such as superoxo complexes.…”