Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 11 de 11
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
J Phys Chem Lett ; : 3490-3496, 2021 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-33792315

RESUMO

In light of the current energy requirements, the conversion of CO2 and N2 into useful C-N bond-containing products under mild conditions has become an area of intense research. However, the inert nature of N2 and CO2 renders their coupling extremely challenging. Herein, nitrogen and carbon atoms originating from N2 and CO2, respectively, are fixed sequentially by NbH2- anions in the gas phase at room temperature. Isocyanate and NbO2CN- anions were formed under thermal collision conditions, thus achieving the formation of new C-N bonds directly from simple N2 and CO2. The anion structures and reaction details were studied by mass spectrometry, photoelectron spectroscopy, and quantum chemical calculations. A novel N2 activation mode (metal-ligand activation, MLA) and a related mechanism for constructing C-N bonds mediated by a single non-noble metal atom are proposed. In this MLA mode, the C atom originating from CO2 serves as an electron reservoir to accept and donate electrons.

2.
Org Lett ; 22(17): 7034-7040, 2020 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-32816494

RESUMO

A secondary phosphine oxide (SPO)-nickel catalyst allowed the activation of otherwise inert C-F bonds of unactivated arenes in terms of challenging couplings with primary and secondary alkyl Grignard reagents. The C-F activation is characterized by mild reaction conditions and high levels of branched selectivity. Electron-rich and electron-deficient arenes were suitable electrophiles for this transformation. In addition, this strategy also proved suitable to heterocycles and for the activation of C-O bonds under slightly modified conditions.

3.
Artigo em Inglês | MEDLINE | ID: mdl-32700444

RESUMO

Ruthenium(II)biscarboxylate complexes enabled the selective alkylation of C-H and C-C bonds at the ortho- or meta-position. ortho-C-H Alkylations were achieved with 4-, 5- as well as 6-membered halocycloalkanes. Furthermore, the judicious choice of the directing group allowed for a full control of ortho-/meta-selectivities. Detailed mechanistic studies by experiment and computation were performed and provided strong support for an oxidative addition/reductive elimination process for ortho-alkylations, while a homolytic C-X cleavage was operative for the meta-selective transformations.

4.
J Am Chem Soc ; 142(30): 13102-13111, 2020 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-32536163

RESUMO

The iron-catalyzed hydroarylation of allenes was accomplished by weak phenone assistance. The C-H activation proceeded with excellent efficacy and high ortho-regioselectivity in proximity to the weakly coordinating carbonyl group for a range of substituted phenones and allenes. Detailed mechanistic studies, including the isolation of key intermediates, the structural characterization of an iron-metallacycle, and kinetic analysis, allowed the sound elucidation of a plausible catalytic working mode. This mechanistic rationale is supported by detailed computational density functional theory studies, which fully address multi-spin-state reactivity. Furthermore, in operando nuclear magnetic resonance monitoring of the catalytic reaction provided detailed insights into the mode of action of the iron-catalyzed C-H alkylation with allenes.

5.
Angew Chem Int Ed Engl ; 59(30): 12534-12540, 2020 07 20.
Artigo em Inglês | MEDLINE | ID: mdl-32485007

RESUMO

C7-H-functionalized indoles are ubiquitous structural units of biological and pharmaceutical compounds for numerous antiviral agents against SARS-CoV or HIV-1. Thus, achieving site-selective functionalizations of the C7-H position of indoles, while discriminating among other bonds, is in high demand. Herein, we disclose site-selective C7-H activations of indoles by ruthenium(II) biscarboxylate catalysis under mild conditions. Base-assisted internal electrophilic-type substitution C-H ruthenation by weak O-coordination enabled the C7-H functionalization of indoles and offered a broad scope, including C-N and C-C bond formation. The versatile ruthenium-catalyzed C7-H activations were characterized by gram-scale syntheses and the traceless removal of the directing group, thus providing easy access to pharmaceutically relevant scaffolds. Detailed mechanistic studies through spectroscopic and spectrometric analyses shed light on the unique nature of the robust ruthenium catalysis for the functionalization of the C7-H position of indoles.

6.
Chem Commun (Camb) ; 56(50): 6886-6889, 2020 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-32435789

RESUMO

While activation of tungsten bis(imido) complexes [WCl2(NAr)2(dme)] with EtAlCl2 affords active, and moderately selective ethylene dimerization catalysts, addition of Et3N or Oct4NCl leads to a doubling in productivity and activity, along with increased selectivity (e.g., >93% C4, >99% 1-C4). The performance of the resulting tungsten-based catalyst package is competitive with that of Axens' commercialised Ti-based AlphaButol process and exemplifies the wide potential of similar additives in selective oligomerization.

7.
Angew Chem Int Ed Engl ; 59(27): 11130-11135, 2020 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-32129528

RESUMO

A ruthenium-catalyzed electrochemical dehydrogenative annulation reaction of imidazoles with alkynes has been established, enabling the preparation of various bridgehead N-fused [5,6]-bicyclic heteroarenes through regioselective electrochemical C-H/N-H annulation without chemical metal oxidants. Novel azaruthenabicyclo[3.2.0]heptadienes were fully characterized and identified as key intermediates. Mechanistic studies are suggestive of an oxidatively induced reductive elimination pathway within a ruthenium(II/III) regime.

8.
Angew Chem Int Ed Engl ; 59(8): 3184-3189, 2020 Feb 17.
Artigo em Inglês | MEDLINE | ID: mdl-31777143

RESUMO

The catalytic generation of hypervalent iodine(III) reagents by anodic electrooxidation was orchestrated towards an unprecedented electrocatalytic C-H oxygenation of weakly coordinating aromatic amides and ketones. Thus, catalytic quantities of iodoarenes in concert with catalytic amounts of ruthenium(II) complexes set the stage for versatile C-H activations with ample scope and high functional group tolerance. Detailed mechanistic studies by experiment and computation substantiate the role of the iodoarene as the electrochemically relevant species towards C-H oxygenations with electricity as a sustainable oxidant and molecular hydrogen as the sole by-product. para-Selective C-H oxygenations likewise proved viable in the absence of directing groups.

9.
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.

10.
Eur J Mass Spectrom (Chichester) ; 24(1): 74-80, 2018 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-29233000

RESUMO

A novel method has been developed that enables chemical compounds to be transferred from an inert atmosphere glove box and into the atmospheric pressure ion source of a mass spectrometer whilst retaining a controlled chemical environment. This innovative method is simple and cheap to implement on some commercially available mass spectrometers. We have termed this approach inert atmospheric pressure solids analysis probe ( iASAP) and demonstrate the benefit of this methodology for two air-/moisture-sensitive chemical compounds whose characterisation by mass spectrometry is now possible and easily achieved. The simplicity of the design means that moving between iASAP and standard ASAP is straightforward and quick, providing a highly flexible platform with rapid sample turnaround.

11.
Dalton Trans ; 41(18): 5502-11, 2012 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-22246518

RESUMO

In combination with EtAlCl(2) (Mo : Al = 1 : 15) the imido complexes [MoCl(2)(NR)(NR')(dme)] (R = R' = 2,6-Pr(i)(2)-C(6)H(3) (1); R = 2,6-Pr(i)(2)-C(6)H(3), R' = Bu(t) (3); R = R' = Bu(t) (4); dme = 1,2-dimethoxyethane) and [Mo(NHBu(t))(2)(NR)(2)] (R = 2,6-Pr(i)(2)-C(6)H(3) (5); R = Bu(t) (6)) each show moderate TON, activity, and selectivity for the catalytic dimerisation of ethylene, which is influenced by the nature of the imido substituents. In contrast, the productivity of [MoCl(2)(NPh)(2)(dme)] (2) is low and polymerisation is favoured over dimerisation. Catalysis initiated by complexes 1-4 in combination with MeAlCl(2) (Mo : Al = 1 : 15) exhibits a significantly lower productivity. Reaction of complex 5 with EtAlCl(2) (2 equiv.) gives rise to a mixture of products, while addition of MeAlCl(2) affords [MoMe(2)(N-2,6-Pr(i)(2)-C(6)H(3))(2)]. Treatment of 6 with RAlCl(2) (2 equiv.) (R = Me, Et) yields [Mo({µ-N-Bu(t)}AlCl(2))(2)] (7) in both cases. Imido derivatives 1 and 3 react with Me(3)Al and MeAlCl(2) to form the bimetallic complexes [MoMe(2)(N{R}AlMe(2){µ-Cl})(NR')] (R = R' = 2,6-Pr(i)(2)-C(6)H(3) (8); R = 2,6-Pr(i)(2)-C(6)H(3), R' = Bu(t) (10)) and [MoMe(2)(N{R}AlCl(2){µ-Cl})(NR')] (R = R' = 2,6-Pr(i)(2)-C(6)H(3) (9); R = 2,6-Pr(i)(2)-C(6)H(3), R' = Bu(t) (11)), respectively. Exposure of complex 8 to five equivalents of thf or PMe(3) affords the adducts [MoMe(2)(N-2,6-Pr(i)(2)-C(6)H(3))(2)(L)] (L = thf (12); L = PMe(3) (13)), while reaction with NEt(3) (5 equiv.) yields [MoMe(2)(N-2,6-Pr(i)(2)-C(6)H(3))(2)]. The molecular structures of complexes 5, 9 and 11 have been determined.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...