Mixed tetradentate NHC/1,2,3-triazole iron complexes bearing cis labile coordination sites as highly active catalysts in Lewis and Brønsted acid mediated olefin epoxidation

Schlagintweit, Jonas F.; Dyckhoff, Florian; Nguyen, Ly; Jakob, Christian; Reich, Robert M.; Kühn, Fritz E.

doi:10.1016/j.jcat.2020.01.011

Cited by 24 publications

(10 citation statements)

References 51 publications

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“…Other catalysts that do not contain an aminopyridine tetradentate ligand can also promote the selective oxidation of organic substrates in combination with H 2 O 2 or other oxidants. − However, the well-defined first coordination sphere and the efficient H 2 O 2 activation mechanism of Mn and Fe complexes with tetradentate ligands make them a privileged platform to tune the oxidation selectivity, and most notably the enantioselectivity, via rational modulation of the catalyst structure.…”

Section: Enzymes and Synthetic Modelsmentioning

confidence: 99%

Rational Design of Bioinspired Catalysts for Selective Oxidations

2020

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Recognizing Nature’s unique ability to perform challenging oxygenation reactions with exquisite selectivity parameters at iron-dependent oxygenases, chemists have long sought to understand and mimic these enzymatic processes with artificial systems. In the last two decades, replication of the reactivity of non-heme iron oxygenases has become feasible even with simple coordination complexes of iron and manganese. A bona fide minimalistic functional model was the tetradentate-N4 ligand based iron complex [Fe(tpa)(CH3CN)2]2+(Fe(tpa), tpa = tris(2-methylpyridyl)amine), which activates H2O2 via a mechanism that mirrors key steps of enzymatic O2 activation processes at mononuclear iron centers: controlled O–O bond cleavage, generation of a high-valent FeO oxidant, and promotion of almost the full spectrum of its oxidative reactivity (C–H hydroxylation, olefin epoxidation, syn-dihydroxylation, and desaturation). These landmark discoveries set the mechanistic framework to use iron coordination complexes with nitrogen-rich ligands as catalysts for oxidizing organic substrates under synthetically relevant conditions. Due to proof-of-concept demonstrations of the potential of these catalysts in organic synthesis, this chemistry has flourished over the past decade. In parallel to the realization of the potential of this class of catalysts in diverse organic transformations, effort has been spent to manipulate the catalyst structure with the aim of tuning both the reactivity and selectivity of the oxidation reactions. This perspective provides an overview of the progress of this research. Some key features of the archetypical Fe(tpa) catalyst have stayed surprisingly true throughout this evolution, but a series of alterations that modulate its electronic, steric, or binding properties allowed a rational elicitation of a specific reactivity or selectivity. In some cases, the replacement of iron by manganese has also proven beneficial. Overall, the rational optimization of the catalyst structure has enabled the development of highly asymmetric olefin epoxidation, syn-dihydroxylation, and site-selective and even enantioselective C–H oxidation reactions.

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Section: Enzymes and Synthetic Modelsmentioning

confidence: 99%

Rational Design of Bioinspired Catalysts for Selective Oxidations

2020

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“…In terms of the extremely low catalysts activities, a temperature of 0 °C instead of À 10 °C or À 20 °C as for other known high performance catalysts is chosen (Figure 4). [4,24] Figure 2. Comparison of the mono-and bis(tert-butylisocyanide) substituted derivatives 2 a and 2 b with an already existing and in epoxidation catalysis tested system 3.…”

Section: Catalytic Olefin Epoxidationmentioning

confidence: 99%

“…Concerning this matter, a divergent behavior pattern of 2 a and 2 b referring to other cyclic substrates like cyclohexene (entry 1) is basically recognizable when compared to other non-heme catalysts. [4,[24][25] Usually, cyclic olefins are considered as favored substrates in epoxidation reactions as the electron donating effect of the neighboring CH 2 -groups. Contrary to the assumptions, the oxidation products of the catalyzed cyclohexene are not just limited to the formation of cis-diol, but also arise from oxidation of existing CÀ H bonds and can be assigned by NMR spectroscopy to several ketone (2-cyclohexen-1-one) and alcohol (2-cyclohexen-1-ol) species nearby located to the double bond.…”

Section: Catalyst T [°C]mentioning

confidence: 99%

“…Thus, a lower half-cell potential of the reversible Fe(II)/Fe(III) redox couple indicates a higher activity and vice versa. [4,22,24] This concept of isocyanide ligand substitution was transferred to the notably more active Fe-cCCCC complex 2 to create novel complexes with mixed catalytic properties released by axial π-acceptor ligands. [4,21b] Accordingly, the mono-(2 a) and bis(tert-butylisocyanide) derivatives (2 b) were already synthesized and characterized by NMR-spectroscopy, elemental analysis, ESI-MS, and single crystal X-ray diffraction (SC-XRD) before.…”

Section: Introductionmentioning

confidence: 99%

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The Effect oftransAxial Isocyanide Ligands on Iron(II) Tetra‐NHC Complexes and their Reactivity in Olefin Epoxidation

et al. 2021

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The performance of trans axially substituted mono‐(2 a) and bis(tert‐butylisocyanide) (2 b) complexes derived from the highly active bio‐inspired iron(II) (pre‐ )catalyst 2 containing an equatorial macrocyclic tetra N‐heterocyclic carbene in homogenous olefin epoxidation catalysis is reported. H2O2 is used as oxidant in combination with the Lewis acid Sc(OTf)3 as additive resulting in a considerable improvement of catalytic activity. In contrast to other iron epoxidation catalysts, the introduction of π‐accepting isocyanide ligands does not improve the catalytic performance of 2 a and 2 b posed by cyclic voltammetry. However, besides their lower activity, a high temperature tolerance of both compounds is found as a unique feature for iron NHC epoxidation catalysts.

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“…It has been observed that the triazole ring can coordinate with metal ions via the N2 nitrogen atom to form stable complexes when there are neighboring assisting groups. [49][50][51] It was proposed that the interaction between the chemosensor and the metal ion occurs between the coumarin carbonyl and triazole nitrogen via a stable pseudo-six-membered ring as shown in Figure 17. The complexation affinity was attributed to the N-2 nitrogen lone electron pair donation from the triazole ring to the metal ion, assisted by a lone pair of electrons from the coumarin-carbonyl group.…”

Section: Proposed Binding Site Between S1 and Fe 3+mentioning

confidence: 99%

Synthesis and application of a fluorescent “turn-off” triazolyl-coumarin-based fluorescent chemosensor for the sensing of Fe3+ ions in aqueous solutions

Mama¹,

Battison²

2020

Arkivoc

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Two coumarin derivatives containing triazole moieties have been synthesized using "click chemistry" protocol and investigated as chemosensors for the detection of metal ions. These compounds displayed a strong preference for Fe 3+ ions with complexation resulting in fluorescent quenching. The detection limit of the preferred chemosensor was determined to be 1.4 µM. The preferred triazole-coumarin compound showed greater selectivity towards Fe 3+ in the presence of competing metal cations. Binding stoichiometry between this triazole-coumarin and Fe 3+ was shown to occur in a 1:1 ratio between the chemosensor and metal cation. The binding site of Fe 3+ to the triazole-coumarin was determined using 1 H NMR, 13 C NMR and molecular modeling studies.

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Mixed tetradentate NHC/1,2,3-triazole iron complexes bearing cis labile coordination sites as highly active catalysts in Lewis and Brønsted acid mediated olefin epoxidation

Cited by 24 publications

References 51 publications

Rational Design of Bioinspired Catalysts for Selective Oxidations

Rational Design of Bioinspired Catalysts for Selective Oxidations

The Effect oftransAxial Isocyanide Ligands on Iron(II) Tetra‐NHC Complexes and their Reactivity in Olefin Epoxidation

Synthesis and application of a fluorescent “turn-off” triazolyl-coumarin-based fluorescent chemosensor for the sensing of Fe3+ ions in aqueous solutions

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