Identification of Alkoxy Radicals as Hydrogen Atom Transfer Agents in Ce-Catalyzed C–H Functionalization

Journal of the American Chemical Society, Journal Year: 2022, Volume and Issue: 145(1), P. 359 - 376

Published: Dec. 20, 2022

The intermediacy of alkoxy radicals in cerium-catalyzed C–H functionalization via H-atom abstraction has been unambiguously confirmed. Catalytically relevant Ce(IV)–alkoxide complexes have synthesized and characterized by X-ray diffraction. Operando electron paramagnetic resonance transient absorption spectroscopy experiments on isolated pentachloro Ce(IV) alkoxides identified as the sole heteroatom-centered radical species generated ligand-to-metal charge transfer (LMCT) excitation. Alkoxy-radical-mediated hydrogen atom (HAT) verified kinetic analysis, density functional theory (DFT) calculations, reactions under strictly chloride-free conditions. These experimental findings establish critical role Ce-LMCT catalysis definitively preclude involvement chlorine radical. This study also reinforced necessity a high relative ratio alcohol vs Ce for selective alkoxy-radical-mediated HAT, seemingly trivial changes can lead to drastically different mechanistic pathways. Importantly, previously proposed radical–alcohol complex, postulated explain alkoxy-radical-enabled selectivities this system, examined scrutiny ruled out regioselectivity studies, experiments, high-level calculations. Moreover, peculiar selectivity generation LMCT homolysis heteroleptic analyzed back-electron (BET) may regulated efficiency formation ligand-centered radicals.

Language: Английский

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Anti-Markovnikov hydro- and deuterochlorination of unsaturated hydrocarbons using iron photocatalysis

Nature Synthesis, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 2, 2025

Language: Английский

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Electrophotocatalytic Si–H Activation Governed by Polarity-Matching Effects

CCS Chemistry, Journal Year: 2021, Volume and Issue: 4(5), P. 1796 - 1805

Published: June 29, 2021

Open AccessCCS ChemistryRESEARCH ARTICLE1 May 2022Electrophotocatalytic Si–H Activation Governed by Polarity-Matching Effects Yangye Jiang, Kun Xu and Chengchu Zeng Jiang Faculty of Environment Life, Beijing University Technology, 100124 , *Corresponding authors: E-mail Address: [email protected] https://doi.org/10.31635/ccschem.021.202101010 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Trialkylsilanes are important building blocks in organic synthesis; however, their widespread use redox chemistry is limited high oxidation potentials comparably bond dissociation energies (BDEs) α–Si–C–H bonds (>92 kcal mol−1). Herein, we report a new strategy for homolysis enabled the synergistic combination electrooxidation, photoinduced ligand-to-metal charge transfer (LMCT), radical-mediated hydrogen atom (HAT). polarity-matching effect, HAT electrophilic MeO· or [Cl-OHCH3]· from more hydridic instead C–H allows selective generation silyl radicals. This electrophotocatalytic protocol provides rapid access Si-functionalized benzimidazo-fused isoquinolinones with broad functional-group compatibility. Mechanistic studies have shown that n-Bu4NCl essential electrooxidation CeCl3 form Ce(IV) species. Download figure PowerPoint Introduction Organosilanes great interest fields medicinal chemistry,1,2 synthesis,3,4 electronics.5,6 Currently, most attractive approach Si-incorporation involves interception radicals alkenes heterocycles. In this regard, homolytic cleavage liable Si–X (X = Si,7,8 B,9 COOH,10 etc.11–13) has been identified as powerful tool obtain A practical economic alternative silicon hydrides. The classical activation relies on stoichiometric peroxide an initiator (Scheme 1a).14–18 However, limitations include harsh conditions functional group incompatibility driven identification strategies activation. Recently, photoredox catalysis19–28 emerged appealing radical formation substrates were invariably phenylsilanes (TMS)3SiH labile 1b).11,29–35 As pioneered Fagnoni et al.,36 decatungstate was found be effective (HAT) photocatalyst aromatic tertiary silanes 1c). Nevertheless, only poor selectivities observed trialkylsilanes owing mol−1).37 Wu colleagues38,39 recently developed mild generally applicable platform using quinuclidin-3-yl acetate triisopropylsilanethiol highly reagent 1d). Considering valuable synthetic utilities radicals, establishment mechanistically readily available remains desirable but synthetically challenging. Scheme 1 | (a–e) Representative produce Organic electrosynthesis utilizes electron reactive intermediates sustainable manner. Its application carbon- heteroatom-centered therefore flourishing over past decade.40–55 comparison carbon electrochemical largely unexplored. Lin coworkers56 reported elegant electroreductive Si–Cl-containing compounds Mg sacrificial anode. Aligned our ongoing electrosynthesis,57–59 intrigued possibility electrochemically generating starting trialkylsilanes. direct hydrides results compatibility selectivity, mainly due hydrides.60 Since without limitation potentials,61,62 synergy opportunities at much lower operating than those analogous electrooxidations. Among many reagents, envision should ideal following reasons: (1) Hydrogen abstraction (BDE up 96 mol−1)63 O–H: 105 mol−1)64 thermodynamically favorable; (2) electronegative (electronegativity 2.2 vs 1.9 Pauling scale), triggered would preferably occur according effect65; (3) byproduct MeOH generated process easily removed reaction mixture. success proposal hinges facile energetically challenging potential subsequently trigger afford desired Motivated seminal works Zuo66–71 who proved RO· alcohols via cerium-catalyzed herein combines LMCT, methoxyl-radical-mediated 1e). BDEs activated through polarized transition state. utility electrophotocatalytic72–79 demonstrated compatibility, which prevalent biologically active molecules advanced materials.80,81 Our working hypothesis inspired recent reports demonstrating alkoxy LMCT excitation Ce(IV)-OR complexes.66–70,82–89 2, anodically could coordinate transient Ce(IV)-OMe, can undergo give MeO·. MeO · preference situ chlorine cannot excluded moment.90 Subsequently, intercepted compound B, triggers cyclization followed proton release deliver isoquinolinone E product. two main challenges must solved realize mechanistic hypothesis. First, relatively low concentration. Otherwise, competition between during lead selectivity. Second, Ce(IV)-OMe complex quickly avoid its cathodic reduction. 2 Experimental Methods General procedure electrophotochemical synthesis: An undivided cell equipped felt anode (1.0 × 1.0 cm2) foamed nickel cathode connected current (DC) regulated power supply. To added (0.3 mmol), mL), CeCl3·7H2O (0.06 mmol, 20 mol %), CH3CN:cholorobenzene (5 mL, V/V 1:1). placed 3 cm away light-emitting diodes (LEDs) (390 nm, W). mixture electrolyzed constant (2 mA) 50 °C under magnetic stirring. When thin-layer chromatography (TLC) analysis indicated electrolysis complete (witnessed disappearance 1), solvent distillation. product then extracted dichloromethane (DCM) (3 dried Na2SO4, concentrated vacuo. residue purified column silica gel pure Further details including experimental procedures additional data Supporting Information. Results Discussion Following hypothesis, parameters established 1a triethylsilane ( 2a) model (Table 1). Ni foam catalyst, MeOH/CH3CN/chlorobenzene electrolytic solution, while being irradiated W 390 nm LEDs 9 h, polycyclic 3aa obtained 66% yield (entry Replacing graphite plate changing led decreased yields (entries 3). optimization density showed mA/cm2 optimal 4 5). Reducing amount silane Ce catalyst 6 7). Anhydrous similar efficiency compared 8). choice precursor had significant influence chemical yield. Decreasing increasing afforded 10). chlorobenzene other halogenated benzenes PhCF3 PhBr failed 11 12). Irradiation 440 white light reduced 49% 31%, respectively 13 14). series control experiments cerium MeOH, irradiation, all transformation 15–18), showcasing cooperation photocatalysis. Table Optimization Reaction Conditionsa Entry Deviation Standard Conditions Yield (%)b None 66 Graphite 43 44 I mA 5 42 Et3SiH (0.7 mL) 37 7 (0.03 mmol) 31 8 67 (0.05 39 10 (0.2 56 PhCl Trace 12 1,3-Dichlorobenzene 0 49 14 White 15 No 16 17 18 electricity aReaction conditions: 2a (1 (0.1 CH3CN:chlorobenzene (1:1, (working area: cm2), cell, mA, (20 W), °C, h. bIsolated With established, began examine substrate scope 3, excellent affording corresponding products 3a– 3f 81% yield, competitive adjacent not observed. Aromatic tolerated well, Si-products 3g– 3i 73% 1,4-bis(dimethylsilyl)benzene employed substrate, one underwent tandem furnish 3j 39% (TMS)3SiH, BDE, suitable generate 3k 72% trimethoxysilane 3l probably instability radical. unstable even electrolysis, decomposition major side these transformations. hydrosilanes. 2a–2l mL liquid hydrides, mmol solid hydrides), CH3CN: (V/V 1:1, h; isolated Having hydride scope, next focused determining N-substituted benzimidazole derivatives. 4, variety benzimidazoles reactions smoothly Si-incorporated 4– good moderate yields. For Ar1 moiety, presence electron-donating groups systems containing electron-withdrawing substituents 6). Ar2 both (OMe) -withdrawing (CN) well-tolerated 16). alkene 11), borate 13), ester 14), sulfonate 15), nitrile 16) compatible conditions, giving 67% R methyl phenyl 17). Notably, derived l-menthol, (–)-nopol, diacetone-d-glucose also 18– 64% thus preparative transformation. benzimidazoles. 2c addition benzimidazoles, indole 22 71% construction indole-based gain insight into mechanism, cyclic voltammetry (CV) conducted (Figure (curves b c), suggests might proceed simultaneously. CV did display obvious peak (curve e), 0.68 V g). tetrabutylammonium salts n-Bu4NI, n-Bu4NBr, n-Bu4NPF6 (see Information Figure S3–S5 details). These reveal exogenous chloride Ce(III) species subsequent needed reagent. information coupled reagents moiety 1a, leads us proposed cycle Ce(IV). related 0.1 M LiClO4/CH3CN/PhCl/MeOH Pt disk electrode, wire counter Ag/AgNO3 CH3CN) reference electrode: Background, mM), (4) background, (5) (6) (7) (9 mM) + mM). further demonstrate electrooxidative assisted chloride, UV–vis carried out. CH3CN/MeOH absorption band λmax 250 nm. After min, appeared 395 consistent evidence highest irradiation when replace n-Bu4NPF6, no shift after S7 spectra solution 1:1 before (black line) (red line). Conclusions We synergistically combining BDEs. scenario makes electrons clean oxidants earth-abundant salt induce turn acts activate selectively effect. entry diversified isoquinolinones. methodology basis functionalization inert currently investigation laboratory. includes general considerations, detailed procedures, spectral characterization, voltammograms, data. Conflict Interest There conflict report. Funding work supported grants National Key Technology R&D Program (no. 2017YFB0307502), Natural Science Foundation China 21871019), Municipal Education Committee Project (nos. KZ202110005003 KM202110005006). References 1. Ramesh R.; Reddy D. S.Quest Novel Chemical Entities Incorporation Silicon Drug Scaffolds.J. Med. Chem.2018, 61, 3779–3798. Google Scholar 2. Franz A. K.; Wilson S. 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Language: Английский

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New insight into two penta-coordinated multinuclear copper(II) single-armed salamo-based complexes

Inorganica Chimica Acta, Journal Year: 2022, Volume and Issue: 540, P. 121047 - 121047

Published: June 9, 2022

Language: Английский

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Renaissance of Homogeneous Cerium Catalysts with Unique Ce(IV/III) Couple: Redox-Mediated Organic Transformations Involving Homolysis of Ce(IV)–Ligand Covalent Bonds

Journal of the American Chemical Society, Journal Year: 2021, Volume and Issue: 143(21), P. 7879 - 7890

Published: April 27, 2021

Recent advances in the catalytic application of cerium complexes were achieved through controlling Ce(IV/III) redox couple. Although Ce(IV) have been extensively investigated as stoichiometric oxidants organic synthesis on basis their highly positive potentials, these can be used catalysts, not only by introducing supporting ligands around coordination sphere cerium, but also taking advantage photoresponsive properties and Ce(III) species. Cerium is abundant, comparable to that some first-row transition metals such copper, nickel, zinc. are new promising homogeneous catalyst candidates for a variety transformations under mild reaction conditions. They typically activate dioxygen oxidize compounds applied radical generation using character carboxylates alkoxides well electronic Ce(III), which homolysis Ce(IV)–ligand covalent bonds an important step overall cycle. In this Perspective, we first review early discovery Ce(OAc)4-mediated oxidative emphasize importance Ce(IV)–OAc bond various C–C bond-forming reactions its relation recent developments. We then focus fundamental reactivity involving thermal photoassisted developments regarding changes together with our findings cerium-based catalysis.

Language: Английский

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Investigations of stable penta- and hexa-coordinate polynuclear Zn(II) and Cd(II) complexes derived from a single-armed salamo-based ligand

Journal of Coordination Chemistry, Journal Year: 2022, Volume and Issue: 76(1), P. 28 - 44

Published: Dec. 26, 2022

AbstractA penta-coordinated dinuclear Zn(II) complex, [Zn2(L)(μ-PhCOO)(EtOH)] (1), and a hexa-coordinate tetranuclear Cd(II) [{Cd2(L)(EtOH)(η-OAc)}2]·2CH2Cl2 (2), have been synthesized by reactions of single-armed salamo-based ligand, H3L, two kinds transition metal salts, (Zn(NO3)2·6H2O Cd(OAc)2·2H2O), respectively. Complexes 1 2 characterized elemental analyses, single crystal X-ray diffraction, IR spectra UV-Vis spectra. Complex is composed totally deprotonated ligand (L)3- moiety, ions, one μ-PhCOO- counter-anion coordinated ethanol molecule. The unit packages the bridges adjacent ions molecule coordinates with Zn2 ion, so that both are slightly distorted trigonal bipyramidal configurations, τ5 values Zn1 0.86 0.65, consists discrete similar electroneutral tetra-nuclear units, A 2B, crystallized dichloromethane molecules. Each has symmetric structure made up completely moieties, four η-OAc- counter-anions Fluorescence properties Hirshfeld surfaces analyses studied as well.Keywords: Single-armed ligandcrystal structureHirshfeld surface analysisfluorescence property Disclosure statementNo potential conflict interest was reported authors.Additional informationFundingThis work supported Science Technology Program Gansu Province (21YF5GA057) National Natural Foundation China (21761018), which gratefully acknowledged.

Language: Английский

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Decarboxylative sulfoximination of benzoic acids enabled by photoinduced ligand-to-copper charge transfer

Chemical Science, Journal Year: 2022, Volume and Issue: 13(45), P. 13611 - 13616

Published: Jan. 1, 2022

Sulfoximines are synthetically important scaffolds and serve roles in drug discovery. Currently, there is no solution to decarboxylative sulfoximination of benzoic acids; although thoroughly investigated, limited substrate scope harsh reaction conditions still hold back traditional thermal aromatic functionalization. Herein, we realize the first acids via photo-induced ligand copper charge transfer (copper-LMCT)-enabled carbometalation. The transformation proceeds under mild conditions, has a broad scope, can be applied late-stage functionalization complex small molecules.

Language: Английский

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Iron-mediated ligand-to-metal charge transfer enables 1,2-diazidation of alkenes

Nature Communications, Journal Year: 2022, Volume and Issue: 13(1)

Published: Dec. 23, 2022

Given the widespread significance of vicinal diamine units in organic synthesis, pharmaceuticals and functional materials, as well privileged molecular catalysts, an efficient practical strategy that avoids use stoichiometric strong oxidants is highly desirable. We herein report application ligand-to-metal charge transfer (LMCT) excitation to 1,2-diazidation reactions from alkenes TMSN

Language: Английский

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Light-induced homolysis of copper(ii)-complexes – a perspective for photocatalysis

Chemical Science, Journal Year: 2023, Volume and Issue: 14(17), P. 4449 - 4462

Published: Jan. 1, 2023

A new kid on the block: Cu( ii ) offers unique possibilities in photocatalysis for generating and stabilizing radicals to promote challenging synthetic transformations.

Language: Английский

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Iron-Mediated Photochemical Anti-Markovnikov Hydroazidation of Unactivated Olefins

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(41), P. 22347 - 22353

Published: Oct. 9, 2023

Unactivated olefins are converted to alkyl azides with bench-stable NaN3 in the presence of FeCl3·6H2O under blue-light irradiation. The products obtained anti-Markovnikov selectivity, and reaction can be performed mild ambient conditions air moisture. transformation displays broad functional group tolerance, which renders it suitable for functionalization complex molecules. Mechanistic investigations conducted provide insight into hydroazidation reveal role water from iron hydrate as H atom source.

Language: Английский

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