C−H Activation from Iron(II)‐Nitroxido Complexes

Kleinlein, Claudia; Bendelsmith, Andrew J.; Zheng, Shao‐Liang; Betley, Theodore A.

doi:10.1002/ange.201706594

Cited by 5 publications

(3 citation statements)

References 38 publications

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“…The solid state molecular structure shows that the potassium counterion is coordinated to two of the dipyrrin-flanking phenyl rings (Figure S-25). 7 Reaction of 3 with a just-thawed solution of silver tetrafluoroborate (1 equiv) in THF precipitates a silver mirror over the course of 10 min. The solid byproducts were removed by repeated filtration, and the remaining product was purified via recrystallization from benzene/hexanes to afford orange-red crystals of ( Ar L)Fe(O t Bu) 2 ( 6) in 65% yield.…”

Section: Methodsmentioning

confidence: 99%

Ground State and Excited State Tuning in Ferric Dipyrrin Complexes Promoted by Ancillary Ligand Exchange

2017

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Three ferric dipyrromethene complexes featuring different ancillary ligands were synthesized by one electron oxidation of ferrous precursors. Four-coordinate iron complexes of the type (ArL)FeX2 [ArL = 1,9-(2,4,6-Ph3C6H2)2-5-mesityldipyrromethene] with X = Cl or tBuO were prepared and found to be high-spin (S = 5/2), as determined by superconducting quantum interference device magnetometry, electron paramagnetic resonance, and 57Fe Mössbauer spectroscopy. The ancillary ligand substitution was found to affect both ground state and excited properties of the ferric complexes examined. While each ferric complex displays reversible reduction and oxidation events, each alkoxide for chloride substitution results in a nearly 600 mV cathodic shift of the FeIII/II couple. The oxidation event remains largely unaffected by the ancillary ligand substitution and is likely dipyrrin-centered. While the alkoxide substituted ferric species largely retain the color of their ferrous precursors, characteristic of dipyrrin-based ligand-to-ligand charge transfer (LLCT), the dichloride ferric complex loses the prominent dipyrrin chromophore, taking on a deep green color. Time-dependent density functional theory analyses indicate the weaker-field chloride ligands allow substantial configuration mixing of ligand-to-metal charge transfer into the LLCT bands, giving rise to the color changes observed. Furthermore, the higher degree of covalency between the alkoxide ferric centers is manifest in the observed reactivity. Delocalization of spin density onto the tert-butoxide ligand in (ArL)FeCl(OtBu) is evidenced by hydrogen atom abstraction to yield (ArL)FeCl and HOtBu in the presence of substrates containing weak C–H bonds, whereas the chloride (ArL)FeCl2 analogue does not react under these conditions.

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Section: Methodsmentioning

confidence: 99%

Ground State and Excited State Tuning in Ferric Dipyrrin Complexes Promoted by Ancillary Ligand Exchange

2017

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“…15 Related studies in nonheme chemistry have been carried out recently by us and others for Fe, Cu, and Ni. [16][17][18][19][20][21][22][23] Synthetic, heme-based catalysts are also known to proceed through a mechanism similar to that shown in Scheme 1. In the synthetic systems, metals other than iron can be employed, and manganese porphyrins were employed successfully to carry out challenging C-H hydroxylation and halogenation reactions.…”

Section: Introductionmentioning

confidence: 99%

Hydroxyl Transfer to Carbon Radicals by Mn(OH) vs Fe(OH) Corrole Complexes

et al. 2020

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The transfer of OH• from metal-hydroxo species to carbon radicals (R•) to give hydroxylated products (ROH) is a fundamental process in metal-mediated heme and nonheme C-H bond oxidations. This step, often referred to as the hydroxyl "rebound" step, is typically very fast, making direct study of this process challenging if not impossible. In this report, we describe the reactions of the synthetic models M(OH)(ttppc) (M = Fe (1), Mn (3); ttppc = 5,10,4,6

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“…Int I , an iron- N -peroxo analogue, likely undergoes N–O bond lysis to generate Int II , the active species responsible for N -transfer reactivity. Betley and co-workers have reported high-spin Fe(II)-nitroxido species which are stable in the absence of weak C–H bonds, but decay via N–O bond homolysis undergoing C–H activation . So far from our experimental results, spectroscopic analyses and theoretical calculations, it is evident that Int I converts to Int II , an Fe(III)-NH • radical species [high-spin Fe(III)-iminyl radical species].…”

Section: Implications For the Reaction Mechanismmentioning

confidence: 61%

A Combined Spectroscopic and Computational Study on the Mechanism of Iron-Catalyzed Aminofunctionalization of Olefins Using Hydroxylamine Derived N–O Reagent as the “Amino” Source and “Oxidant”

et al. 2022

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Herein, we study the mechanism of iron-catalyzed direct synthesis of unprotected aminoethers from olefins by a hydroxyl amine derived reagent using a wide range of analytical and spectroscopic techniques (Mössbauer, Electron Paramagnetic Resonance, Ultra-Violet Visible Spectroscopy, X-ray Absorption, Nuclear Resonance Vibrational Spectroscopy, and resonance Raman) along with high-level quantum chemical calculations. The hydroxyl amine derived triflic acid salt acts as the “oxidant” as well as “amino” group donor. It activates the high-spin Fe(II) ( S t = 2) catalyst [Fe(acac) 2 (H 2 O) 2 ] ( 1 ) to generate a high-spin ( S t = 5/2) intermediate ( Int I ), which decays to a second intermediate ( Int II ) with S t = 2. The analysis of spectroscopic and computational data leads to the formulation of Int I as [Fe(III)(acac) 2 - N -acyloxy] (an alkyl-peroxo-Fe(III) analogue). Furthermore, Int II is formed by N–O bond homolysis. However, it does not generate a high-valent Fe(IV)(NH) species (a Fe(IV)(O) analogue), but instead a high-spin Fe(III) center which is strongly antiferromagnetically coupled ( J = −524 cm –1 ) to an iminyl radical, [Fe(III)(acac) 2 -NH·], giving S t = 2. Though Fe(NH) complexes as isoelectronic surrogates to Fe(O) functionalities are known, detection of a high-spin Fe(III)- N -acyloxy intermediate ( Int I ), which undergoes N–O bond cleavage to generate the active iron–nitrogen intermediate ( Int II ), is unprecedented. Relative to Fe(IV)(O) centers, Int II features a weak elongated Fe–N bond which, together with the unpaired electron density along the Fe–N bond vector, helps to rationalize its propensity for N -transfer reactions onto styrenyl olefins, resulting in the overall formation of aminoethers. This study thus demonstrates the potential of utilizing the iron-coordinated nitrogen-centered radicals as powerful reactive intermediates in catalysis.

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C−H Activation from Iron(II)‐Nitroxido Complexes

Cited by 5 publications

References 38 publications

Ground State and Excited State Tuning in Ferric Dipyrrin Complexes Promoted by Ancillary Ligand Exchange

Ground State and Excited State Tuning in Ferric Dipyrrin Complexes Promoted by Ancillary Ligand Exchange

Hydroxyl Transfer to Carbon Radicals by Mn(OH) vs Fe(OH) Corrole Complexes

A Combined Spectroscopic and Computational Study on the Mechanism of Iron-Catalyzed Aminofunctionalization of Olefins Using Hydroxylamine Derived N–O Reagent as the “Amino” Source and “Oxidant”

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