Iridium-Catalyzed Silylation of Five-Membered Heteroarenes: High Sterically Derived Selectivity from a Pyridyl-Imidazoline Ligand

Karmel, Caleb; Rubel, Camille; Kharitonova, Elena; Hartwig, John F.

doi:10.26434/chemrxiv.10046525

Cited by 2 publications

(2 citation statements)

References 8 publications

(11 reference statements)

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“…This origin of selectivity contrasts with that we reported recently for the silylation of fivemembered ring heteroarenes. 6 In our study of H/D exchange between the silane and these heteroarenes, the selectivity for H/D exchange at the least hindered C-H bond was lower than the selectivity for silylation at the least sterically hindered C-H bond. These data imply that the high selectivity for reactions of these less hindered substrates results from a slower rate for reductive elimination from a more hindered arylsilane than from a less hindered arylsilane.…”

Section: Origin Of Selectivitymentioning

confidence: 59%

Mechanism of the Iridium-Catalyzed Silylation of Aromatic C–H Bonds

Karmel

Hartwig

2020

J. Am. Chem. Soc.

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Phenanthroline ligands and [Ir(cod)(OMe)] 2 form complexes that catalyze the silylation of aromatic and aliphatic C-H bonds. However, no experimental data on the identity of complexes related to the mechanism of this process or the mechanisms by which they react to functionalize C-H bonds have been reported. Herein, we describe our studies on the mechanism of the iridiumcatalyzed silylation of aryl C-H bonds. The resting state of the catalyst is an iridium disilyl hydride complex (phenanthroline)Ir(SiMe(OTMS) 2 ) 2 (H)(L), in which L varies with the arene and additives. An iridium disilyl hydride complex was isolated, characterized, and allowed to react with arenes to form aryl silanes. The kinetics of the reactions of electron-rich and electron-poor arenes showed that the rate-limiting step varies with the electronic properties of the arene. Computational studies on related iridium silyl complexes revealed that the high activity of iridium complexes containing sterically encumbered phenanthroline ligands is due to a change in the number of silyl groups bound to iridium between the resting state of the catalyst containing the hindered phenanthroline and that containing less-hindered phenanthroline.

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Section: Origin Of Selectivitymentioning

confidence: 59%

Mechanism of the Iridium-Catalyzed Silylation of Aromatic C–H Bonds

Karmel

Hartwig

2020

J. Am. Chem. Soc.

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“…Heteroarylsilanes are considered as an important and versatile intermediates for the construction of complex molecules, since silyl groups can be easily transferred into a wide varieties of substituents [21][22][23] . Thus, C-H silylation of heteroarenes have extensively been employed for the preparation of highly important silylated heteroarenes [24][25][26][27][28][29] . Due to the presence of multiple C-H bonds in heteroaromatic compounds, the site-selective C-H bond functionalization is represents a key challenge in this arena.…”

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confidence: 99%

Phosphorus(III)-assisted regioselective C–H silylation of heteroarenes

et al. 2021

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Heteroarenes containing carbon–silicon (C–Si) bonds are important building blocks that play an important role in the construction of natural products, pharmaceuticals, and organic materials. In this context, the C–H silylation of heteroarenes is a topic of intense interest. Indole C–H silylation can preferentially occur at the nucleophilic C3 and C2 position (pyrrole core), while accessing the C4-C7 positions (benzene core) of the indole remains highly challenging. Here, we show a general strategy for the regioselective C7-H silylation of indole derivatives. Mainly, the regioselectivity is determined by strong coordination of the palladium catalyst with phosphorus (III) directing group. Using this expedient synthetic strategy, the diverse C7-silylated indoles are synthesized effectively which exhibits the broad functional group compatibility. Moreover, this protocol also been extended to other heteroarenes such as carbazoles. The obtained silylated indoles have been employed in various transformations to enable the corresponding differently functionalized indole derivatives. Significantly, a cyclopalladated intermediate is successfully synthesized to test the hypothesis about the P(III)-directed C–H metalation event. A series of mechanistic experiments and density functional theory (M06-2X) calculations has shown the preferred pathway of this directed C–H silylation process.

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Iridium-Catalyzed Silylation of Five-Membered Heteroarenes: High Sterically Derived Selectivity from a Pyridyl-Imidazoline Ligand

Cited by 2 publications

References 8 publications

Mechanism of the Iridium-Catalyzed Silylation of Aromatic C–H Bonds

Mechanism of the Iridium-Catalyzed Silylation of Aromatic C–H Bonds

Phosphorus(III)-assisted regioselective C–H silylation of heteroarenes

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