Nature has chosen high-spin iron(IV)=O oxidants for nonheme iron enzymes with mononuclear active sites to cleave strong substrate C–H bonds. In our efforts to mimic such enzyme active sites and understand the properties of their biomimetic analogs, a new S = 1 FeIV=O complex has been synthesized with oxidative properties superior to those of the FeIV=O complexes in the N4Py family reported thus far. The new pentadentate ligand (N2Py2Pz) is based on the classic N4Py (N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework and has been synthesized by replacing the two pyridylmethyl arms with corresponding (N-methyl)pyrazolylmethyl units to form [N-bis(1-methyl-2-pyrazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L1). The oxidation of the iron(II) precursor (N2Py2Pz)FeII(OTf)2 (1) with (tBuSO2)C6H4IO at 298 K leads to the formation of the [FeIV(O)(N2Py2Pz)]2+ intermediate (2) with a near-IR band at 750 nm (EM = 250 M-1cm-1) and a t1/2 ~ 2 min at 298 K. The introduction of the less basic pyrazolylmethyl ligands in place of two pyridylmethyl units generates FeIV=O intermediate 2 that exhibits a cyclohexane oxidation rate of 0.29 s-1 at 298 K, which is 5000-fold faster than that observed for the classic FeIV(O)N4Py parent complex and 40,000-fold more reactive than the least reactive FeIV(O)N2Py2Q’ complex in this series (Py = pyridine, Q’ = isoquinoline). This significant enhancement in reactivity derives from the distinct electronic and steric properties of the pyrazolylmethyl units.
The paper has been published today in Proceedings of the National Academy of Sciences (PNAS)
N. Pal, J. Xiong, M. Jahja, S. Mahri, V.G. Young, Y. Guo, M. Swart and L. Que, Jr.
“A 5000-fold Increase in the HAT Reactivity of a Nonheme FeIV=O Complex Simply by Replacing Two Pyridines of N4Py Ligand with Pyrazoles”
Proc. Natl. Acad. Sci. USA 2025, 122, e241496212
http://doi.org/10.1073/pnas.2414962122
Girona, February 4th, 2025
For more info: ges.iqcc@udg.edu