Oxygen atom transfer mediated by an iron(IV)/iron(II) macrocyclic complex containing pyridine and tertiary amine donors

A new non-heme iron model complex containing a high-spin iron(II) complexed with N-methylated pyridine-containing macrocycle was synthesized and crystallographically characterized. The complex generates peroxo- and high-valent iron-oxo intermediates in reactions with tert-butylhydroperoxide and isopropyl 2-iodoxybenzoate, respectively, allowing to gain insight into the formation and reactivity of enzyme-like intermediates related to biological oxygen activation. The formation and reactivity of these intermediate species were investigated by the stopped-flow methodology. The mechanism of oxygen transfer to organic substrates involving reaction of oxoiron(IV) intermediate was elucidated on the basis of spectroscopic and kinetic data. Incorporation of a pyridine ring into the macrocycle increased the reactivity of the FeIVO intermediates in comparison with polyamine tetraaza macrocyclic complexes: ferryl (FeIVO) species derived from 3 demonstrated electrophilic reactivity in transferring an oxygen atom to substituted triarylphosphines and to olefins (such as cyclooctene). However, iron(III) alkylperoxo intermediate was unreactive with cyclooctene.

Graphical abstractFerryl (FeIVO) species derived from 3 demonstrated electrophilic reactivity in transferring an oxygen atom to substituted triarylphosphines and to olefins (such as cyclooctene); however, iron(III) alkylperoxo intermediate was unreactive with cycloocteneFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► N-methylated pyridine azamacrocycle (PyMAC) folds upon binding iron(II), forming a high-spin complex. ► Reaction with t-Buhydroperoxide yields an alkylperoxo intermediate that does not oxidize substrates. ► Reaction with iodine(V) yields an electrophilic Fe(IV)O intermediate that epoxidizes olefins. ► Kinetic parameters for these reactions were determined by the low temperature stopped-flow method.