An ultra-stable oxoiron(iv) complex and its blue conjugate base

England, Jason, Bigelow, J.O., Van Heuvelen, K.M. , Farquhar, E.R., Martinho, M., Meier, K.K., Frisch, J.R., Münck, E. and Que, L. (2014) An ultra-stable oxoiron(iv) complex and its blue conjugate base. Chemical Science, 5 (3). pp. 1204-1215. ISSN 2041-6520

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Treatment of [FeII(L)](OTf)2 (4), (where L = 1,4,8-Me3cyclam-11-CH2C(O)NMe2) with iodosylbenzene yielded the corresponding S = 1 oxoiron(IV) complex [FeIV(O)(L)](OTf)2 (5) in nearly quantitative yield. The remarkably high stability of 5 (t1/2 ≈ 5 days at 25 °C) facilitated its characterization by X-ray crystallography and a raft of spectroscopic techniques. Treatment of 5 with strong base was found to generate a distinct, significantly less stable S = 1 oxoiron(IV) complex, 6 (t1/2 ∼ 1.5 h at 0 °C), which could be converted back to 5 by addition of a strong acid; these observations indicate that 5 and 6 represent a conjugate acid–base pair. That 6 can be formulated as [FeIV(O)(L–H)](OTf) was further supported by ESI mass spectrometry, spectroscopic and electrochemical studies, and DFT calculations. The close structural similarity of 5 and 6 provided a unique opportunity to probe the influence of the donor trans to the FeIV=O unit upon its reactivity in H-atom transfer (HAT) and O-atom transfer (OAT), and 5 was found to display greater reactivity than 6 in both OAT and HAT. While the greater OAT reactivity of 5 is expected on the basis of its higher redox potential, its higher HAT reactivity does not follow the anti-electrophilic trend reported for a series of [FeIV(O)(TMC)(X)] complexes (TMC = tetramethylcyclam) and thus appears to be inconsistent with the two-state reactivity rationale that is the prevailing explanation for the relative facility of oxoiron(IV) complexes to undergo HAT.

Keywords:Mass spectrometry, Redox reactions, X ray crystallography, Electrochemical studies, ESI mass spectrometry, H-atom transfer, Quantitative yields, Redox potentials, Spectroscopic technique, Structural similarity, Two-state reactivity, Iron compounds
Subjects:F Physical Sciences > F120 Inorganic Chemistry
Divisions:College of Science > School of Chemistry
ID Code:51910
Deposited On:11 Oct 2022 10:09

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