Oxoiron(<scp>v</scp>) mediated selective electrochemical oxygenation of unactivated C–H and CC bonds using water as the oxygen source

Chandra, Bittu; Hellan, K M; Pattanayak, Santanu; Gupta, Sayam Sen

doi:10.1039/d0sc03616a

Cited by 34 publications

(35 citation statements)

References 56 publications

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“…During these catalytic reactions, the products formed parallel those that have been found under homogeneous conditions using Fe-bTAML analogs and NaOCl. We have previously demonstrated 40 41,42 Such regioselectivity could be due to the total shutdown of the free-radical pathway since the hydrophobic scaffold of the COF nano-spheres creates an appropriate binding pocket for both the anionic macrocyclic catalyst (via ionic interactions) and the substrate (via predominantly hydrophobic interactions). Consequently, the carbon-centered radical formed upon C-H abstraction does not escape to the bulk to react with O 2 , thereby initiating a freeradical process that would signi cantly reduce the selectivity.…”

Section: Resultsmentioning

confidence: 99%

“…The products formed during these catalytic reactions parallel those that have been found under homogeneous conditions using Fe-bTAML analogues and NaOCl. We have previously demonstrated that (Et 4 N) 2 [Fe III (Cl)bTAML] reacts with NaOCl to form the active oxoiron(V) intermediate, which is responsible for substrate oxidation. For the [Fe III (Cl)bTAML] 2– @2X TpDPP COF nanospheres, the X-band EPR spectrum at 100 K (Figure S36) manifested a rhombic S = 1/2 species with g = 2.00, 1.96, and 1.72, which indicated that the same oxoiron(V) intermediate was generated inside the COF nanospheres.…”

Section: Results and Discussionmentioning

confidence: 99%

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Heterogeneous C–H Functionalization in Water via Porous Covalent Organic Framework Nanofilms: A Case of Catalytic Sphere Transmutation

et al. 2021

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Heterogeneous catalysis in water has not been explored beyond certain advantages like recyclability and recovery of the catalysts from the reaction medium. In doing so, they often fail to address other authentic pitfalls of homogeneous catalysis. Moreover, poor yield, extremely low selectivity, and active catalytic sites' deactivation further underrate the heterogeneous catalysis in water. On the other hand, most of the synthetically useful homogeneous catalysts are either water intolerant or remain catalytically inactive in water. Considering these facts, we have rationally designed and synthesized solution dispersible porous covalent organic framework (COF) nano-spheres to utilize their distinctive morphology and dispersibility to bridge between homogeneous and heterogeneous catalysis. The success has further been extended in fabricating catalyst immobilized COF thin-lms via covalent self-assembly for the very rst time. We have used these catalyst immobilized COF thin-lms to develop a general methodology for the C-H functionalization of organic substrates in water. This unique covalent self-assembly occurs through the protrusion of the bers/threads at the interface of two nano-spheres, transmuting the catalytic spheres into lms without any leaching of catalyst molecules, which was hitherto unheard of. The catalyst immobilized porous COF thin-lms' chemical functionality and hydrophobic environment stabilizes the high valent transient active oxoiron(V) intermediate in water and restricts the active catalytic site's deactivation. An elevated catalytic yield and high selectivity (3°:2°) have been achieved in open-air conditions at room temperature, accompanying the elemental feature of heterogeneous catalysis, i.e., the recyclability. These COF lms functionalized the unactivated C-H bonds in water with a high catalytic yield (45-99%) and with a high degree of selectivity (cis:trans=155:1; 3°:2°=257:1 in case of cis-1,2dimethylcyclohexane). To establish the "practical implementation" of this approach, we conducted the in ow catalysis (Turnover Number = 355±5) using catalyst immobilized COF lms fabricated on a macroporous polymeric support.

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Section: Resultsmentioning

confidence: 99%

Section: Results and Discussionmentioning

confidence: 99%

Heterogeneous C–H Functionalization in Water via Porous Covalent Organic Framework Nanofilms: A Case of Catalytic Sphere Transmutation

et al. 2021

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“…In 2020, Gupta and coworkers reported an efficient electrochemical method for the selective oxidation of C–H bonds of unactivated alkanes. ( Gupta et al, 2020 ) Figure 1B . using a biomimetic iron complex, as the redox mediator in an undivided electrochemical cell with inexpensive carbon and nickel electrodes, a natural product derivative of cedrol, having a rigid structure with tertiary C-H bonds, affords a single hydroxylated product in 52% yield.…”

Section: C-h Oxidations For Natural Product Diversificationmentioning

confidence: 99%

Novel Strategies in C-H Oxidations for Natural Product Diversification—A Remote Functionalization Application Summary

et al. 2021

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Selectively activating the distal inactive C-H bond for functionalization is one of the on-going challenge in organic synthetic chemistry. In recent years, benefiting from the development of selective synthesis methods, novel methodologies not only make it possible to break non-traditional chemical bonds and attain more diversity in inactive sites, but also provide more possibilities for the diversification of complex natural products. Direct C-H bond functionalization approaches make it feasible to explore structure-activity relationship (SAR), generate metabolites and derivatives, and prepare biological probes. Among them, direct oxidation of inert C-H bonds is one of the most common methods for natural product diversification. In this review, we focus on the application of remote functionalization of inert C-H bonds for natural products derivatization, including the establishment of oxidation methods, the regulation of reaction sites, and the biological activities of derivatives. We highlight the challenges and opportunities of remote functionalization of inert C-H bonds for natural product diversification through selected and representative examples. We try to show that inert C-H bond oxidation, properly regulated and optimized, can be a powerful and efficient strategy in both synthetic and medicinal chemistry.

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“…23 The electrochemical generation of the Fe V (O) intermediate allowed us to perform selective electrochemical alkane hydroxylation and epoxidation. 24 The electrochemical oxidations were carried out in a simple undivided cell using inexpensive electrodes made from carbon and nickel. In this procedure, we have effectively oxidized sp 3 C-H bonds with BDE >97 kcal mol À1 using water as the oxygen source.…”

Section: Introductionmentioning

confidence: 99%

Electrocatalytic alcohol oxidation by a molecular iron complex

Kuiry

Das

et al. 2022

Faraday Discuss.

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Oxoiron(v) mediated selective electrochemical oxygenation of unactivated C–H and CC bonds using water as the oxygen source

Abstract: An efficient electrochemical method for the selective oxidation of C-H bonds of unactivated alkanes (BDE ≤97 kcal/mol) and C=C bonds of alkenes using biomimetic iron complex, [(bTAML)FeIII-OH2]-, as the redox...

Cited by 34 publications

References 56 publications

Heterogeneous C–H Functionalization in Water via Porous Covalent Organic Framework Nanofilms: A Case of Catalytic Sphere Transmutation

Heterogeneous C–H Functionalization in Water via Porous Covalent Organic Framework Nanofilms: A Case of Catalytic Sphere Transmutation

Novel Strategies in C-H Oxidations for Natural Product Diversification—A Remote Functionalization Application Summary

Electrocatalytic alcohol oxidation by a molecular iron complex

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