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Hydride-Rhodium(III)- N-Heterocyclic Carbene Catalyst for Tandem Alkylation/Alkenylation via C-H Activation

AuthorsAzpíroz, Ramón; Giuseppe, Andrea di ; Urriolabeitia, Asier; Passarelli, Vincenzo ; Polo, Víctor; Pérez-Torrente, Jesús J. ; Oro, Luis A. ; Castarlenas, Ricardo
KeywordsC−H activation
N-heterocyclic carbene
alkene isomerization
DFT calculations
rhodium catalysis
Issue Date4-Oct-2019
PublisherAmerican Chemical Society
CitationACS Catalysis 9(10): 9372-9386 (2019)
AbstractThe unsaturated hydride complex RhClH{κ-N,C-(CHN)}(IPr) {IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazolin-2-carbene} (2) has been prepared via C-H activation of 2-phenylpyridine and fully characterized by spectroscopic methods and X-ray diffraction analysis. Complex 2 efficiently catalyzes the isomerization of terminal and internal olefins under mild conditions to give preferentially the E regioisomers. Complex 2 also catalyzes the hydroarylation of terminal olefins with 2-phenylpyridine to yield selectively mono-ortho-alkylated derivatives. Tandem isomerization-alkylation processes were observed for internal olefins. In contrast to olefins, double alkenylation is operative for internal alkynes. The marked complementary reactivity of olefins and alkynes allows for a tandem alkylation/alkenylation of 2-phenylpyridine to yield substituted styrenes. These heterobiaryl compounds exhibit axial chirality. The rotational barrier has been experimentally calculated and corroborated by density functional theory (DFT) calculations. A catalytic cycle for hydroarylation reactions has been proposed based on the identification of key reaction intermediates and H/D exchange experiments. The reaction seems to proceed by initial C-H activation of 2-phenylpyridine, subsequent insertion of alkene or alkyne, and reductive elimination steps. According to experimental results, DFT calculations have shown a higher energy barrier for bis-alkylation processes than for bis-alkenylation ones that display a feasible activation energy. Moreover, it has been found that reductive elimination is the rate-limiting step for alkene hydroarylation, whereas migratory insertion is the rate-limiting step for alkyne hydroarylation processes.
Publisher version (URL)http://doi.org/10.1021/acscatal.9b01233
Identifiersdoi: 10.1021/acscatal.9b01233
e-issn: 2155-5435
Appears in Collections:(ISQCH) Artículos
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