423720-04-1

Upstream product

• 950994-76-0 [iron(II)(N-benzyl-N,N',N''-tris(2-pyridylmethyl)-1,2-diaminoethane)(acetonitrile)]⁽²⁺⁾ 
• 536-80-1 iodosylbenzene 
• 79-21-0 peracetic acid 

Downstream Products

• 905575-09-9 oxido(1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)iron(IV) 
• 312321-65-6 [Fe(N-benzyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine)]⁽²⁺⁾ 

Relevant academic research and scientific papers

Nonheme oxoiron(iv) complexes of pentadentate N5 ligands: Spectroscopy, electrochemistry, and oxidative reactivity

Oxoiron(iv) species have been found to act as the oxidants in the catalytic cycles of several mononuclear nonheme iron enzymes that activate dioxygen. To gain insight into the factors that govern the oxidative reactivity of such complexes, a series of five synthetic S = 1 [FeIV(O)(L N5)]2+ complexes has been characterized with respect to their spectroscopic and electrochemical properties as well as their relative abilities to carry out oxo transfer and hydrogen atom abstraction. The FeO units in these five complexes are supported by neutral pentadentate ligands having a combination of pyridine and tertiary amine donors but with different ligand frameworks. Characterization of the five complexes by X-ray absorption spectroscopy reveals FeO bonds of ca. 1.65 A in length that give rise to the intense 1s → 3d pre-edge features indicative of iron centers with substantial deviation from centrosymmetry. Resonance Raman studies show that the five complexes exhibit ν(FeO) modes at 825-841 cm-1. Spectropotentiometric experiments in acetonitrile with 0.1 M water reveal that the supporting pentadentate ligands modulate the E1/2(iv/iii) redox potentials with values ranging from 0.83 to 1.23 V vs. Fc, providing the first electrochemical determination of the E1/2(iv/iii) redox potentials for a series of oxoiron(iv) complexes. The 0.4 V difference in potential may arise from differences in the relative number of pyridine and tertiary amine donors on the LN5 ligand and in the orientations of the pyridine donors relative to the FeO bond that are enforced by the ligand architecture. The rates of oxo-atom transfer (OAT) to thioanisole correlate linearly with the increase in the redox potentials, reflecting the relative electrophilicities of the oxoiron(iv) units. However this linear relationship does not extend to the rates of hydrogen-atom transfer (HAT) from 1,3-cyclohexadiene (CHD), 9,10-dihydroanthracene (DHA), and benzyl alcohol, suggesting that the HAT reactions are not governed by thermodynamics alone. This study represents the first investigation to compare the electrochemical and oxidative properties of a series of S = 1 FeIVO complexes with different ligand frameworks and sheds some light on the complexities of the reactivity of the oxoiron(iv) unit.

Combined experimental and theoretical study on aromatic hydroxylation by mononuclear nonheme iron(IV)-oxo complexes

The hydroxylation of aromatic compounds by mononuclear nonheme iron(IV)-oxo complexes, [FeIV(Bn-tpen)(O)]2+ (Bn-tpen = N-benzyl-N,N′,N′-tris(2-pyridylmethyl)ethane-1,2-diamine) and [FeIV(N4Py)(O)]2+ (N4Py = N,N-bis(2-pyridylmethyl)-N- bis(2-pyridyl)methylamine), has been investigated by a combined experimental and theoretical approach. In the experimental work, we have performed kinetic studies of the oxidation of anthracene with nonheme iron(IV)-oxo complexes generated in situ, thereby determining kinetic and thermodynamic parameters, a Hammett ρ value, and a kinetic isotope effect (KIE) value. A large negative Hammett ρ value of -3.9 and an inverse KIE value of 0.9 indicate that the iron-oxo group attacks the aromatic ring via an electrophilic pathway. By carrying out isotope labeling experiments, the oxygen in oxygenated products was found to derive from the nonheme iron(IV)-oxo species. In the theoretical work, we have conducted density functional theory (DFT) calculations on the hydroxylation of benzene by [FeIV(N4Py)(O)]2+. The calculations show that the reaction proceeds via two-state reactivity patterns on competing triplet and quintet spin states via an initial rate determining electrophilic substitution step. In analogy to heme iron(IV)-oxo catalysts, the ligand is noninnocent and actively participates in the reaction mechanism by reshuttling a proton from the ipso position to the oxo group. Calculated kinetic isotope effects of C6H6 versus C6D6 confirm an inverse isotope effect for the electrophilic substitution pathway. Based on the experimental and theoretical results, we have concluded that the aromatic ring oxidation by mononuclear nonheme iron(IV)-oxo complexes does not occur via a hydrogen atom abstraction mechanism but involves an initial electrophilic attack on the π-system of the aromatic ring to produce a tetrahedral radical or cationic σ-complex.

Facile and Reversible Formation of Iron(III)–Oxo–Cerium(IV) Adducts from Nonheme Oxoiron(IV) Complexes and Cerium(III)

Ceric ammonium nitrate (CAN) or CeIV(NH4)2(NO3)6 is often used in artificial water oxidation and generally considered to be an outer-sphere oxidant. Herein we report the spectroscopic and crystallographic characterization of [(N4Py)FeIII-O-CeIV(OH2)(NO3)4]+ (3), a complex obtained from the reaction of [(N4Py)FeII(NCMe)]2+ with 2 equiv CAN or [(N4Py)FeIV=O]2+ (2) with CeIII(NO3)3 in MeCN. Surprisingly, the formation of 3 is reversible, the position of the equilibrium being dependent on the MeCN/water ratio of the solvent. These results suggest that the FeIV and CeIV centers have comparable reduction potentials. Moreover, the equilibrium entails a change in iron spin state, from S=1 FeIV in 2 to S=5/2 in 3, which is found to be facile despite the formal spin-forbidden nature of this process. This observation suggests that FeIV=O complexes may avail of reaction pathways involving multiple spin states having little or no barrier.

An inverted and more oxidizing isomer of [FeIV(O)(tmc)- (NCCH3)]2+

(Chemical Equation Presented) Oxoferryl gymnastics: The oxo and CH 3CN ligands in 1-NCCH3 can swap positions in the presence of iodosobenzene and tetrafluoroborate anion leading to the generation of a more reactive isomer 2. This conversion is proposed to take place via an activated FeIV unit (1a) or a transient dioxoiron(VI) species (1b).

Evidence for an alternative to the oxygen rebound mechanism in C-H bond activation by non-heme FeIVO complexes

The hydroxylation of alkanes by heme FeIVO species occurs via the hydrogen abstraction/oxygen rebound mechanism. It has been assumed that non-heme FeIVO species follow the heme FeIVO paradigm in C-H bond activation reactions. Herein we report theoretical and experimental evidence that C-H bond activation of alkanes by synthetic non-heme Fe IVO complexes follows an alternative mechanism. Theoretical calculations predicted that dissociation of the substrate radical formed via hydrogen abstraction from the alkane is more favorable than the oxygen rebound and desaturation processes. This theoretical prediction was verified by experimental results obtained by analyzing iron and organic products formed in the C-H bond activation of substrates by non-heme FeIVO complexes. The difference in the behaviors of heme and non-heme FeIVO species is ascribed to differences in structural preference and exchange-enhanced reactivity. Thus, the general consensus that C-H bond activation by high-valent metal-oxo species, including non-heme FeIVO, occurs via the conventional hydrogen abstraction/oxygen rebound mechanism should be viewed with caution.

Structural insights into nonheme alkylperoxoiron(III) and oxoiron(IV) intermediates by X-ray absorption spectroscopy

Transient mononuclear low-spin alkylperoxoiron(III) and oxoiron(IV) complexes that are relevant to the activation of dioxygen by nonheme iron enzymes have been generated from synthetic iron(II) complexes of neutral tetradentate (TPA) and pentadentate (N4Py, Bn-TPEN) ligands and structurally characterized by means of Fe K-edge X-ray absorption spectroscopy (XAS). Notable features obtained from fits of the EXAFS region are Fe-O bond lengths of 1.78 A for the alkylperoxoiron(III) intermediates and 1.65-1.68 A for the oxoiron(IV) intermediates, reflecting different strengths in the Fe-O π interactions. These differences are also observed in the intensities of the 1s-to-3d transitions in the XANES region, which increase from 4 units for the nearly octahedral iron(II) precursor to 9-15 units for the alkylperoxoiron(III) intermediates to 25-29 units for the oxoiron(IV) species.