A 5,000-fold increase in the HAT reactivity of a nonheme Fe<sup>IV</sup>=O complex simply by replacing two pyridines of the pentadentate N4Py ligand with pyrazoles.
basic_science · Level V
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- Record sourced from PubMed, PMID 39899716.
- Also identified by DOI 10.1073/pnas.2414962122 and PMC identifier 11831173.
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Abstract
A pentadentate [N5] ligand (N2Py2Pz) based on the classic N4Py (<i>N,N</i>-bis(2-pyridylmethyl)-<i>N</i>-bis(2-pyridyl)methylamine) framework has been synthesized by replacing the two pyridylmethyl arms with corresponding (<i>N</i>-methyl)pyrazolylmethyl units to form [<i>N-</i>bis(1-methyl-2-pyrazolyl)methyl-<i>N</i>-(<i>bis</i>-2-pyridylmethyl)amine] (L1). The oxidation of the iron(II) precursor (N2Py2Pz)Fe<sup>II</sup>(OTf)<sub>2</sub> (<b>1</b>) with (<sup>t</sup>BuSO<sub>2</sub>)C<sub>6</sub>H<sub>4</sub>IO at 298 K leads to the formation of the [Fe<sup>IV</sup>(O)(N2Py2Pz)]<sup>2+</sup> intermediate (<b>2</b>) with a near-IR band at 750 nm (ε<sub>M</sub> = 250 M<sup>-1</sup>cm<sup>-1</sup>) and a t<sub>1/2</sub> ~ 2 min at 298 K. The introduction of the less basic pyrazolylmethyl ligands in place of two pyridylmethyl units generates Fe<sup>IV</sup>=O intermediate <b>2</b> that exhibits a cyclohexane oxidation rate of 0.29 s<sup>-1</sup> at 298 K, which is 5,000-fold faster than that observed for the classic Fe<sup>IV</sup>(O)N4Py parent complex and 40,000-fold more reactive than the least reactive Fe<sup>IV</sup>(O)N2Py2Q' complex in this series (Py = pyridine, Q' = isoquinoline) recently reported by Nordlander.