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1.
Artigo em Inglês | MEDLINE | ID: mdl-33651910

RESUMO

Rhodium-electrocatalyzed arene C-H oxygenation by weakly O- coordinating amides and ketones have been established by bimetallic electrocatalysis. Likewise, diverse dihydrooxazinones were selectively accessed by the judicious choice of current, enabling twofold C-H functionalization. Detailed mechanistic studies by experiment, mass spectroscopy and cyclovoltammetric analysis provided support for an unprecedented electrooxidation-induced C-H activation by a bimetallic rhodium catalysis manifold.

2.
Org Lett ; 23(7): 2760-2765, 2021 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-33730508

RESUMO

Asymmetric ruthenium-catalyzed C-H alkylations were enabled by a chiral C2-symmetric carboxylic acid. The mild cooperative ruthenium(II) catalysis set the stage for the assembly of chiral tetrahydrocarbazoles and cyclohepta[b]indoles with high levels of enantioselectivity at room temperature. Mechanistic studies by experiment and computation identified a fast C-H ruthenation, along with a rate- and enantio-determining proto-demetalation. The asymmetric induction was governed by weak attractive secondary dispersion interactions as found in NCI analysis of the key transition states.

3.
Angew Chem Int Ed Engl ; 60(12): 6419-6424, 2021 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-33471952

RESUMO

Electrooxidative annulations involving mild transition metal-catalyzed C-H activation have emerged as a transformative strategy for the rapid construction of five- and six-membered heterocycles. In contrast, we herein describe the first electrochemical metal-catalyzed [5+2] cycloadditions to assemble valuable seven-membered benzoxepine skeletons by C-H/O-H activation. The efficient alkyne annulation featured ample substrate scope, using electricity as the only oxidant. Mechanistic studies provided strong support for a rhodium(III/I) regime, involving a benzoxepine-coordinated rhodium(I) sandwich complex as the catalyst resting state, which was re-oxidized to rhodium(III) by anodic oxidation.

4.
Angew Chem Int Ed Engl ; 59(31): 12842-12847, 2020 Jul 27.
Artigo em Inglês | MEDLINE | ID: mdl-32329560

RESUMO

The chemical use of CO2 as an inexpensive, nontoxic C1 synthon is of utmost topical interest in the context of carbon capture and utilization (CCU). We present the merger of cobalt catalysis and electrochemical synthesis for mild catalytic carboxylations of allylic chlorides with CO2 . Styrylacetic acid derivatives were obtained with moderate to good yields and good functional group tolerance. The thus-obtained products are useful as versatile synthons of γ-arylbutyrolactones. Cyclic voltammetry and in operando kinetic analysis were performed to provide mechanistic insights into the electrocatalytic carboxylation with CO2 .

5.
Angew Chem Int Ed Engl ; 59(32): 13451-13457, 2020 Aug 03.
Artigo em Inglês | MEDLINE | ID: mdl-32243685

RESUMO

Asymmetric pallada-electrocatalyzed C-H olefinations were achieved through the synergistic cooperation with transient directing groups. The electrochemical, atroposelective C-H activations were realized with high position-, diastereo-, and enantio-control under mild reaction conditions to obtain highly enantiomerically-enriched biaryls and fluorinated N-C axially chiral scaffolds. Our strategy provided expedient access to, among others, novel chiral BINOLs, dicarboxylic acids and helicenes of value to asymmetric catalysis. Mechanistic studies by experiments and computation provided key insights into the catalyst's mode of action.

6.
Angew Chem Int Ed Engl ; 59(27): 10955-10960, 2020 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-32154625

RESUMO

The merger of cobalt-catalyzed C-H activation and electrosynthesis provides new avenues for resource-economical molecular syntheses, unfortunately their reaction mechanisms remain poorly understood. Herein, we report the identification and full characterization of electrochemically generated high-valent cobalt(III/IV) complexes as crucial intermediates in electrochemical cobalt-catalyzed C-H oxygenations. Detailed mechanistic studies provided support for an oxidatively-induced reductive elimination via highly-reactive cobalt(IV) intermediates. These key insights set the stage for unprecedented cobaltaelectro two-fold C-H/C-H activation.

7.
Chemistry ; 25(71): 16382-16389, 2019 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-31658385

RESUMO

Despite major advances, organometallic C-H transformations are dominated by precious 5d and 4d transition metals, such as iridium, palladium and rhodium. In contrast, the unique potential of less toxic Earth-abundant 3d metals has been underexplored. While iron is the most naturally abundant transition metal, its use in oxidative, organometallic C-H activation has faced major limitations due to the need for superstoichiometric amounts of corrosive, cost-intensive DCIB as the sacrificial oxidant. To fully address these restrictions, we describe herein the unprecedented merger of electrosynthesis with iron-catalyzed C-H activation through oxidation-induced reductive elimination. Thus, ferra- and manganaelectro-catalyzed C-H arylations were accomplished at mild reaction temperatures with ample scope by the action of sustainable iron catalysts, employing electricity as a benign oxidant.

8.
J Am Chem Soc ; 141(43): 17198-17206, 2019 10 30.
Artigo em Inglês | MEDLINE | ID: mdl-31549815

RESUMO

A flow-metallaelectro-catalyzed C-H activation was realized in terms of robust rhodaelectro-catalyzed alkyne annulations. To this end, a modular electro-flow cell with a porous graphite felt anode was designed to ensure efficient turnover. Thereby, a variety of C-H/N-H functionalizations proved amenable for alkyne annulations with high levels of regioselectivity and functional group tolerance, viable in both an inter- or intramolecular manner. The electro-flow C-H activation allowed easy scale up, while in-operando kinetic analysis was accomplished by online flow-NMR spectroscopy. Mechanistic studies suggest an oxidatively induced reductive elimination pathway on rhodium(III) in an electrocatalytic regime.

9.
Angew Chem Int Ed Engl ; 58(37): 12874-12878, 2019 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-31207070

RESUMO

An iron-catalyzed C-H/N-H alkyne annulation was realized by using a customizable clickable triazole amide under exceedingly mild reaction conditions. A unifying mechanistic approach combining experiment, spectroscopy, kinetics, and computation provided strong support for facile C-H activation by a ligand-to-ligand hydrogen transfer (LLHT) mechanism. Combined Mössbauer spectroscopic analysis and DFT calculations were indicative of high-spin iron(II) species as the key intermediates in the C-H activation manifold.

10.
Angew Chem Int Ed Engl ; 58(19): 6342-6346, 2019 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-30835907

RESUMO

Rapid access to structurally diversified polycyclic aromatic hydrocarbons (PAHs) in a controlled manner is of key significance in materials sciences. Herein, we describe a strategy featuring two distinct electrocatalytic C-H transformations for the synthesis of novel nonplanar PAHs. The combination of rhodaelectrooxidative C-H activation/[2+2+2] alkyne annulation of easily accessible boronic acids with electrocatalytic cyclodehydrogenation provided modular access to diversely substituted PAHs with electricity as a sustainable oxidant. The unique molecular topology as well as the photophysical and electronic properties of the thus obtained PAHs were fully analyzed. The unique power of this metallaelectrocatalysis method was demonstrated by the chemoselective assembly of synthetically useful iodo-substituted PAHs.

11.
Angew Chem Int Ed Engl ; 57(47): 15425-15429, 2018 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-30289577

RESUMO

The enantioselective cobalt(III)-catalyzed C-H alkylation was achieved through the design of a novel chiral acid. The cobalt(III)-catalyzed enantioselective C-H activation was characterized by high position-, regio- and enantio-control under exceedingly mild reaction conditions. Thereby, the robust cooperative cobalt(III) catalysis proved tolerant of valuable electrophilic functional groups, including hydroxyl, bromo, and iodo substituents. Mechanistic studies revealed a considerable additive effect on kinetics and on a negative non-linear-effect.

12.
Angew Chem Int Ed Engl ; 57(43): 14179-14183, 2018 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-30199130

RESUMO

Iridium-catalyzed electrochemical C-H activation was accomplished within a cooperative catalysis manifold, setting the stage for electrooxidative C-H alkenylations through weak O-coordination. The iridium-electrocatalyzed C-H activation featured high functional-group tolerance through assistance of a metal-free redox mediator through indirect electrolysis. Detailed mechanistic insights provided strong support for an organometallic C-H cleavage and a synergistic iridium(III/I)/redox catalyst regime, enabling the use of sustainable electricity as the terminal oxidant with improved selectivity features.

13.
Chemistry ; 24(49): 12784-12789, 2018 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-29901828

RESUMO

Catalyst- and chemical oxidant-free electrochemical azole C-H aminations were accomplished via cross-dehydrogenative C-H/N-H functionalization. The catalyst-free electrochemical C-H amination proved feasible on azoles with high levels of efficacy and selectivity, avoiding the use of stoichiometric oxidants under ambient conditions. Likewise, the C(sp3 )-H nitrogenation proved viable under otherwise identical conditions. The dehydrogenative C-H amination featured ample scope, including cyclic and acyclic aliphatic amines as well as anilines, and employed sustainable electricity as the sole oxidant.

14.
J Am Chem Soc ; 140(25): 7913-7921, 2018 06 27.
Artigo em Inglês | MEDLINE | ID: mdl-29812927

RESUMO

Electrochemical oxidative C-H/N-H activations have been accomplished with a versatile cobalt catalyst in terms of [4 + 2] annulations of internal alkynes. The electro-oxidative C-H activation manifold proved viable with an undivided cell setup under exceedingly mild reaction conditions at room temperature using earth-abundant cobalt catalysts. The electrochemical cobalt catalysis prevents the use of transition metal oxidants in C-H activation catalysis, generating H2 as the sole byproduct. Detailed mechanistic studies provided strong support for a facile C-H cobaltation by an initially formed cobalt(III) catalyst. The subsequent alkyne migratory insertion was interrogated by mass spectrometry and DFT calculations, providing strong support for a facile C-H activation and the formation of a key seven-membered cobalta(III) cycle in a regioselective fashion. Key to success for the unprecedented use of internal alkynes in electrochemical C-H/N-H activations was represented by the use of N-2-pyridylhydrazides, for which we developed a traceless electrocleavage strategy by electroreductive samarium catalysis at room temperature.

15.
Angew Chem Int Ed Engl ; 57(26): 7719-7723, 2018 06 25.
Artigo em Inglês | MEDLINE | ID: mdl-29697898

RESUMO

C-H activation bears great potential for enabling sustainable molecular syntheses in a step- and atom-economical manner, with major advances having been realized with precious 4d and 5d transition metals. In contrast, we employed earth abundant, nontoxic iron catalysts for versatile allene annulations through a unique C-H/N-H/C-O/C-H functionalization sequence. The powerful iron catalysis occurred under external-oxidant-free conditions even at room temperature, while detailed mechanistic studies revealed an unprecedented 1,4-iron migration regime for facile C-H activations.

16.
Angew Chem Int Ed Engl ; 56(47): 15063-15067, 2017 11 20.
Artigo em Inglês | MEDLINE | ID: mdl-28985452

RESUMO

Chemoselective hydroarylations were accomplished by a novel synergistic Brønsted acid/manganese(I)-catalyzed C-H activation manifold. Thus, alkynes bearing O-leaving groups could, for the first time, be employed for C-H alkenylations without concurrent ß-O elimination, thereby setting the stage for versatile late-stage diversifications. Also described is the first manganese-catalyzed C-H activation in continuous flow, thus enabling efficient hydroarylations within only 20 minutes.

17.
Angew Chem Int Ed Engl ; 56(50): 15891-15895, 2017 12 11.
Artigo em Inglês | MEDLINE | ID: mdl-29065240

RESUMO

A unified strategy for nickel(0)-catalyzed C-H allylations, alkenylations, and dienylations has been realized through versatile hydroarylations of allenes with ample scope. Thus, an inexpensive nickel catalyst modified with a N-heterocyclic carbene ligand enabled the direct transformation of C-H bonds of biologically relevant imidazole and purine derivatives with full control of regio- and chemoselectivity.

18.
Angew Chem Int Ed Engl ; 56(45): 14197-14201, 2017 11 06.
Artigo em Inglês | MEDLINE | ID: mdl-28922549

RESUMO

Highly enantioselective iron-catalyzed C-H alkylations by inner-sphere C-H activation were accomplished with ample scope. High levels of enantiocontrol proved viable through a novel ligand design that exploits a remote meta-substitution on N-heterocyclic carbenes within a facile ligand-to-ligand H-transfer C-H cleavage.

19.
Chemistry ; 23(48): 11524-11528, 2017 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-28704583

RESUMO

C-H alkylations with challenging ß-hydrogen-containing alkyl halides were accomplished with sustainable MnCl2 as the catalyst under phosphine-ligand-free conditions. The proximity-induced benzamide C-H activation occurred with ample substrate scope through rate-determining C-H metalation, also setting the stage for manganese-catalyzed oxidative C-H methylations.

20.
J Phys Chem A ; 116(22): 5464-71, 2012 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-22587633

RESUMO

Specific ion effects, related to the hydration of ions and ion-solute interactions, play a fundamental part in many processes in chemistry and biology. Although intensively studied since the seminal studies of Franz Hofmeister and co-workers, their molecular origin has only recently started to be unveiled. In this work, we have investigated the interaction between halide anions and a selected set of amino acid residues in an attempt to identify the forces behind ion specificity. Two-dimensional potential energy surfaces have been calculated with the use of local second order Møller-Plesset perturbation theory (LMP2), coupled with the COSMO model to describe solvent effects. The results show in great detail the impact of dispersion interactions, in particular for the heavier anions (Br(-) and I(-)). The obtained potential energy surfaces also hint at a greater mobility of iodide in the vicinity of a residue, which correlates well with its placing in the Hofmeister series.


Assuntos
Aminoácidos/química , Modelos Químicos , Ânions/química , Simulação por Computador , Halogênios/química , Interações Hidrofóbicas e Hidrofílicas , Íons/química , Modelos Moleculares , Conformação Molecular , Proteínas/química , Solventes/química , Termodinâmica
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