Tandem Dearomatization/Enantioselective Allylic Alkylation of Pyridines

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(22), P. 11907 - 11913

Published: May 22, 2023

Herein, we report a multistep one-pot reaction of substituted pyridines leading to N-protected tetrahydropyridines with outstanding enantioselectivity (up 97% ee). An iridium(I)-catalyzed dearomative 1,2-hydrosilylation enables the use N-silyl enamines as new type nucleophile in subsequent palladium-catalyzed asymmetric allylic alkylation. This telescoped process overcomes intrinsic nucleophilic selectivity synthesize enantioenriched, C-3-substituted tetrahydropyridine products that have been otherwise challenging access.

Language: Английский

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Cross-Electrophile Silylation of Aryl Carboxylic Esters with Hydrochlorosilanes by SiH-Directed and Cr-Catalyzed Couplings

ACS Catalysis, Journal Year: 2023, Volume and Issue: 13(18), P. 12062 - 12073

Published: Aug. 29, 2023

The formation of silicon–carbon bonds through the selective coupling two strong electrophilic has been less developed. We report here silylation reactions that proceed by Si–Cl/C–O in a process is promoted chromium catalysis via α-agostic SiH → Cr interactions, allowing Si–C under ambient conditions. occur inexpensive hydrochlorosilanes with unactivated aryl carboxylic esters to give arylated hydrosilanes, while suppressing side hydride-mediated reduction achieving high chemoselectivity. In addition monosilylation, both geminal Si–Cl hydrodichlorosilanes couple C–O smoothly afford and achieve double silylations. disilanes diesters also described. Experimental theoretical studies suggest initiates reaction hydrochlorosilane Cr, which interaction group stabilizes related intermediate transition state, leading cleavage bond low barrier silachromate. Further breaking an occurs along agostic interaction, may serve as rate-determining step silylation. observation normal second-order kinetic isotope effect indicates on rates coupling. Because reactive groups are retained silylation, approach provides viable strategy access tetraorganosilane motifs late-stage hydrofunctionalization.

Language: Английский

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An Iridium-Stabilized Borenium Intermediate

Journal of the American Chemical Society, Journal Year: 2022, Volume and Issue: 144(40), P. 18359 - 18374

Published: Sept. 29, 2022

Exploration of new organometallic systems based on polyhedral boron clusters has the potential to solve challenging chemical problems such as stabilization reactive intermediates and transition-state-like species postulated for E-H (E = H, B, C, Si) bond activation reactions. We report facile clean B-H a hydroborane by iridium cluster complex. The product this reaction is an unprecedented fully characterized transition metal-stabilized cation or borenium. Moreover, intermediate bears unusual intramolecular B···H interaction between hydrogen originating from activated cyclometallated metal-bonded atom cluster. This proposed be arrested insertion into Bcage-metal initiation step "cage-walking" around upper surface process supported hydrogen-deuterium exchange observed at cluster, mechanism basis theoretical methods with special focus role noncovalent interactions. All compounds were isolated NMR spectroscopy elemental analysis. Key studied single crystal X-ray diffraction photoelectron spectroscopy.

Language: Английский

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Small molecule binding versus stabilization of coordinatively unsaturated ruthenium-pincer complex by N2/solvent

Journal of Organometallic Chemistry, Journal Year: 2025, Volume and Issue: unknown, P. 123656 - 123656

Published: April 1, 2025

Language: Английский

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Challenges and opportunities in catalytic hydrogenolysis of oxygenated plastics waste: polyesters, polycarbonates, and epoxy resins

Green Chemistry, Journal Year: 2024, Volume and Issue: unknown

Published: Jan. 1, 2024

This review comprehensively explores various homogeneous and heterogeneous catalytic systems for the hydrogenolysis of oxygenated polymeric wastes (OXPs), presenting an adaptable solution to plastic pollution generating valuable feedstock.

Language: Английский

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Mechanism Insights into the Iridium(III)- and B(C₆F₅)₃-Catalyzed Reduction of CO₂ to the Formaldehyde Level with Tertiary Silanes

Inorganic Chemistry, Journal Year: 2022, Volume and Issue: 61(50), P. 20216 - 20221

Published: Dec. 6, 2022

The catalytic system [Ir(CF3CO2)(κ2-NSiMe)2] [1; NSiMe = (4-methylpyridin-2-yloxy)dimethylsilyl]/B(C6F5)3 promotes the selective reduction of CO2 with tertiary silanes to corresponding bis(silyl)acetal. Stoichiometric and studies evidenced that species [Ir(CF3COO-B(C6F5)3)(κ2-NSiMe)2] (3), [Ir(κ2-NSiMe)2][HB(C6F5)3] (4), [Ir(HCOO-B(C6F5)3)(κ2-NSiMe)2] (5) are intermediates process. structure 3 has been determined by X-ray diffraction methods. Theoretical calculations show rate-limiting step for 1/B(C6F5)3-catalyzed hydrosilylation bis(silyl)acetal is a boron-promoted Si-H bond cleavage via an iridium silylacetal borane adduct.

Language: Английский

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Palladium-catalyzed C(sp³)–Si cross-coupling silylation of benzyl halides with hydrosilanes

Organic Chemistry Frontiers, Journal Year: 2023, Volume and Issue: 10(21), P. 5443 - 5450

Published: Jan. 1, 2023

An unprecedent and chemoselective Si–C(sp 3 ) bond-forming cross-coupling silylation of benzyl halides with hydrosilanes has been established by palladium catalysis B(C 6 F 5 for the facile synthesis functional silanes good yields.

Language: Английский

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Cationic Bis(hydrosilane)−Coinage Metal Complexes: Synthesis, Characterization, and Use as Catalysts for Outer‐Sphere C=O Hydrosilylation Not Involving Metal Hydrides

Angewandte Chemie International Edition, Journal Year: 2024, Volume and Issue: unknown

Published: Aug. 9, 2024

Abstract The preparation of cationic bis(hydrosilane)–coinage‐metal complexes by chloride abstraction from the neutral metal precursors with Na[BAr F 4 ] is described. Unlike previously reported hydrosilane‐stabilized copper and silver complexes, presented are feature two bidentate ( ortho ‐silylphenyl)phosphine ligands. These were fully characterized NMR spectroscopy X‐ray diffraction analysis, revealing that both Si−H bonds activated Lewis acidic center. new found to be effective in catalytic carbonyl hydrosilylation, leading corresponding silyl ethers under mild conditions without addition an external base. Combined mechanistic control experiments quantum chemical calculations support ionic outer‐sphere mechanism, which a alkoxide species instead hydride key intermediate interacts silylcarboxonium ion generate ether.

Language: Английский

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Dehydropolymerization of H₃B·NMeH₂ Mediated by Cationic Iridium(III) Precatalysts Bearing κ³-ⁱPr-PN^RP Pincer Ligands (R = H, Me): An Unexpected Inner-Sphere Mechanism

ACS Catalysis, Journal Year: 2022, Volume and Issue: 12(20), P. 13050 - 13064

Published: Oct. 12, 2022

The dehydropolymerization of H3B·NMeH2 to form N-methylpolyaminoborane using neutral and cationic catalysts based on the {Ir( i Pr-PNHP)} fragment [ Pr-PNHP = κ3-(CH2CH2P Pr2)2NH] is reported. Neutral Ir( Pr-PNHP)H3 or Pr-PNHP)H2Cl precatalysts show no, poor unselective, activity respectively at 298 K in 1,2-F2C6H4 solution. In contrast, addition [NMeH3][BArF4] (ArF 3,5-(CF3)2C6H3) immediately starts catalysis, suggesting that a catalytic manifold operates. Consistent with this, independently synthesized are active (tested between 0.5 2.0 mol % loading) producing poly(N-methylaminoborane) Mn ∼ 40,000 g/mol, Đ ∼1.5, i.e., dihydrogen/dihydride, [Ir( Pr-PNHP)(H)2(H2)][BArF4]; σ-amine-borane Pr-PNHP)(H)2(H3B·NMe3)][BArF4]; Pr-PNHP)(H)2(NMeH2)][BArF4]. Density functional theory (DFT) calculations probe hydride exchange processes two these complexes also barrier amine-borane dehydrogenation lower (22.5 kcal/mol) for system compared (24.3 kcal/mol). proceeds via an inner-sphere process without metal-ligand cooperativity, this supported experimentally by N-Me substituted Pr-PNMeP)(H)2(H3B·NMe3)][BArF4] being catalyst. Key calculated outer-sphere coordination additional N-H group ligand. Experimentally, kinetic studies indicate complex reaction shows pronounced deceleratory temporal profiles. As speciation DFT studies, key observation deprotonation Pr-NHP)(H)2(H2)][BArF4], formed upon dehydrogenation, slow situ formation NMeH2 (via B-N bond cleavage), results essentially inactive Pr-PNHP)H3, coproduct [NMeH3]+/[H2B(NMeH2)2]+. While reprotonation return cycle, it proposed, doping experiments, attenuated entrainment [NMeH3]+/[H2B(NMeH2)2]+/catalyst insoluble polyaminoborane. role [NMeH3]+/[H2B(NMeH2)]+ as chain control agents noted.

Language: Английский

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Si–H Bond Activation and Dehydrogenative Coupling of Silanes across the Iron–Amide Bond of a Bis(amido)bis(phosphine) Iron(II) Complex

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(2), P. 794 - 799

Published: Jan. 3, 2023

Despite the utility of Si–Si bonds, there are relatively few examples bond formation by base metals. In this work, a four-coordinate iron complex, (PNNP)FeII, is shown to strongly activate Si–H bonds in primary silanes across Fe–amide metal–ligand cooperative fashion. Upon treatment with excess silane, dehydrogenative homocoupling occur Fe–Namide without concomitant oxidation and spin state changes at Fe center.

Language: Английский

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