Oxidative Decarboxylation of Benzilic Acid by a Biomimetic Iron(II) Complex: Evidence for an Iron(IV)–Oxo–Hydroxo Oxidant from O<sub>2</sub>

Paria, Sayantan; Que, Lawrence; Paine, Tapan Kanti

doi:10.1002/anie.201103971

Cited by 72 publications

(107 citation statements)

References 22 publications

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“…Although none of the proposed intermediates were characterized spectroscopically, the Fe IV (O) oxidant was intercepted with a number of external substrates such as fluorene, cyclohexene and thioanisole. 131 A subsequent study on the interception reactions with sulfides and cyclohexene revealed a nucleophilic reactivity profile for the oxidant, which was confirmed by a Hammett analysis (Scheme 12). 130 The possibility of an Fe II OOH or an Fe IV (O)–OH species was implicated in the absence of direct spectroscopic evidence.…”

Section: Dioxygen Activation By Nonheme Iron Complexesmentioning

confidence: 79%

Activation of Dioxygen by Iron and Manganese Complexes: A Heme and Nonheme Perspective

2016

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The rational design of well-defined, first-row transition metal complexes that can activate dioxygen has been a challenging goal for the synthetic inorganic chemist. The activation of O2 is important in part because of its central role in the functioning of metalloenzymes, which utilize O2 to perform a number of challenging reactions including the highly selective oxidation of various substrates. There is also great interest in utilizing O2, an abundant and environmentally benign oxidant, in synthetic catalytic oxidation systems. This Perspective brings together recent examples of biomimetic Fe and Mn complexes that can activate O2 in heme or nonheme-type ligand environments. The use of oxidants such as hypervalent iodine (e.g., ArIO), peracids (e.g., m-CPBA), peroxides (e.g., H2O2) or even superoxide is a popular choice for accessing well-characterized metal–superoxo, metal–peroxo, or metal–oxo species, but the instances of biomimetic Fe/Mn complexes that react with dioxygen to yield such observable metal–oxygen species are surprisingly few. This Perspective focuses on mononuclear Fe and Mn complexes that exhibit reactivity with O2 and lead to spectroscopically observable metal–oxygen species, and/or oxidize biologically relevant substrates. Analysis of these examples reveals that solvent, spin state, redox potential, external co-reductants, and ligand architecture can all play important roles in the O2 activation process.

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Section: Dioxygen Activation By Nonheme Iron Complexesmentioning

confidence: 79%

Activation of Dioxygen by Iron and Manganese Complexes: A Heme and Nonheme Perspective

2016

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“…Each complex features the tris(3,5-diphenylpyrazol-1-yl)borate(1-) supporting ligand ( Ph2 Tp), as substituted Tp ligands are well-known to faithfully mimic the coordination environment of the 2-His-1-carboxylate facial triad. 21 We found that inclusion of bulky phenyl groups at the 3-positions of the pyrazole rings generally discourages formation of the diiron(II)μ-hydroquinonate(2-) complexes, although dinuclear species were generated with certain HQs. As shown in Scheme 2, two types of HQ ligands were employed in this study: i) bidentate (or “tethered”) ligands that feature an ortho substituent capable of metal coordination (H 2 L A–E ), and (ii) the monodentate (or “untethered”) ligand 2,6-dimethylhydroquinone (H 2 L F ).…”

Section: Introductionmentioning

confidence: 91%

Structural, spectroscopic, and electrochemical properties of nonheme Fe(ii)–hydroquinonate complexes: synthetic models of hydroquinone dioxygenases

et al. 2012

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Using the tris(3,5-diphenylpyrazol-1-yl)borate (Ph2Tp) supporting ligand, a series of mono- and dinuclear ferrous complexes containing hydroquinonate (HQate) ligands have been prepared and structurally characterized with X-ray crystallography. The monoiron(II) complexes serve as faithful mimics of the substrate-bound form of hydroquinone dioxygenases (HQDOs) – a family of nonheme Fe enzymes that catalyze the oxidative cleavage of 1,4-dihydroxybenzene units. Reflecting the variety of HQDO substrates, the synthetic complexes feature both mono- and bidentate HQate ligands. The bidentate HQates cleanly provide five-coordinate, high-spin Fe(II) complexes with the general formula [Fe(Ph2Tp)(HLX)] (1X), where HLX is a HQate(1-) ligand substituted at the 2-position with a benzimidazolyl (1A), acetyl (1B and 1C), or methoxy (1D) group. In contrast, the monodentate ligand 2,6-dimethylhydroquinone (H2LF) exhibited a greater tendency to bridge between two Fe(II) centers, resulting in formation of [Fe2(Ph2Tp)2(μ-LF)(MeCN)] [2F(MeCN)]. However, addition of one equivalent of “free” pyrazole (Ph2pz) ligand provided the mononuclear complex, [Fe(Ph2Tp)(HLF)(Ph2pz)] [1F(Ph2pz)], which is stabilized by an intramolecular hydrogen bond between the HLF and Ph2pz donors. Complex 1F(Ph2pz) represents the first crystallographically-characterized example of a monoiron complex bound to an untethered HQate ligand. The geometric and electronic structures of the Fe/HQate complexes were further probed with spectroscopic (UV-vis absorption, 1H NMR) and electrochemical methods. Cyclic voltammograms of complexes in the 1X series revealed an Fe-based oxidation between 0 and −300 mV (vs. Fc+/0), in addition to irreversible oxidation(s) of the HQate ligand at higher potentials. The one-electron oxidized species (1Xox) were examined with UV-vis absorption and electron paramagnetic resonance (EPR) spectroscopies.

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“…[18] High-spin biomimetic complexes remain rare with very few examples, [20][21][22][23] the set of which was very recently extended by a complex with a trigonal pyrrolide platform. [19] Que and coworkers [24] recently also reported a Fe(IV)-oxo-hydroxo species, starting from a highspin Fe II (benzilate) complex.…”

Section: Metal-oxo Species and Exchange-enhanced Reactivitymentioning

confidence: 99%

Spin states of (bio)inorganic systems: Successes and pitfalls

Swart

2012

Int J of Quantum Chemistry

106

127

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The calculation of spin-state splittings of transition-metal complexes is known to be very sensitive to the level of theory and the quality of the basis set. The performance of density functionals is in general understood, with older pure functionals overstabilizing low spin states, and Hartree-Fock and hybrid functionals doing the same for the high spin states. More recent functionals (OLYP/OPBE, TPSSh, SSB-D, M06-L) seem to improve on these, but there are still some systems that prove difficult. This Perspective describes some of the recent successes and pitfalls in the description of spin states and treats both methodology and applications such as metal-oxo complexes, exchange-enhanced reactivity, spin-state catalysis, and spin-crossover compounds.

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Oxidative Decarboxylation of Benzilic Acid by a Biomimetic Iron(II) Complex: Evidence for an Iron(IV)–Oxo–Hydroxo Oxidant from O₂

Abstract: O2‐dependent transformation: An iron(II)‐benzilate complex of a tridentate N3 donor ligand reacts with O2 to undergo oxidative decarboxylation. Cyclohexene is selectively converted into cis‐cyclohexane‐1,2‐diol in the reaction.

Cited by 72 publications

References 22 publications

Activation of Dioxygen by Iron and Manganese Complexes: A Heme and Nonheme Perspective

Activation of Dioxygen by Iron and Manganese Complexes: A Heme and Nonheme Perspective

Structural, spectroscopic, and electrochemical properties of nonheme Fe(ii)–hydroquinonate complexes: synthetic models of hydroquinone dioxygenases

Spin states of (bio)inorganic systems: Successes and pitfalls

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Oxidative Decarboxylation of Benzilic Acid by a Biomimetic Iron(II) Complex: Evidence for an Iron(IV)–Oxo–Hydroxo Oxidant from O2

Abstract: O2‐dependent transformation: An iron(II)‐benzilate complex of a tridentate N3 donor ligand reacts with O2 to undergo oxidative decarboxylation. Cyclohexene is selectively converted into cis‐cyclohexane‐1,2‐diol in the reaction.

Cited by 72 publications

References 22 publications

Activation of Dioxygen by Iron and Manganese Complexes: A Heme and Nonheme Perspective

Activation of Dioxygen by Iron and Manganese Complexes: A Heme and Nonheme Perspective

Structural, spectroscopic, and electrochemical properties of nonheme Fe(ii)–hydroquinonate complexes: synthetic models of hydroquinone dioxygenases

Spin states of (bio)inorganic systems: Successes and pitfalls

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Oxidative Decarboxylation of Benzilic Acid by a Biomimetic Iron(II) Complex: Evidence for an Iron(IV)–Oxo–Hydroxo Oxidant from O₂