Ruthenium-Catalyzed Selective Hydro<i>boronolysis</i> of Ethers

Kaithal, Akash; Kalsi, Deepti; Krishnakumar, Varadhan; Pattanaik, Sandip; Bordet, Alexis; Leitner, Walter; Gunanathan, Chidambaram

doi:10.1021/acscatal.0c04269

Cited by 17 publications

(15 citation statements)

References 46 publications

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“…On the basis of experimental observations, DFT calculations, and our previous reports on catalytic hydroboration and hydrosilylation of different functional groups, − the plausible reaction mechanism for regioselective 1,2-hydrosilylation of N -heteroaromatic compounds is proposed in Scheme . DFT studies indicate the dissociation of phosphine ligand from the catalyst 1 , leading to the formation of dichloro ruthenium intermediate 20 , which upon reaction with phenylsilane generates 7 .…”

Section: Resultsmentioning

confidence: 99%

“…Using phosphine-ligated mononuclear ruthenium catalyst 1 , we have developed an efficient regioselective 1,4-hydroboration of pyridines . Very recently, our group demonstrated the ruthenium-catalyzed selective hydroboronolysis of ethers . In continuation of our interest in hydroelementation and selective dearomatization reactions, herein, we report the ruthenium-catalyzed regioselective 1,2-hydrosilylation of N -heteroaromatic compounds (Scheme ).…”

Section: Introductionmentioning

confidence: 98%

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Ruthenium(II)-Catalyzed Regioselective 1,2-Hydrosilylation of N-Heteroarenes and Tetrel Bonding Mechanism

et al. 2021

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An efficient regioselective dearomatization of N-heteroarenes using a ruthenium precatalyst [Ru-(p-cymene)(PCy 3 )Cl 2 ] 1 is achieved. Reactions were performed under mild and neat conditions. A wide variety of N-heteroarenes undergo the addition of silanes in the presence of precatalyst 1, leading to exclusive N-silyl-1,2-dihydroheteroarene products. This catalytic method displays a broad substrate scope; quinolines, isoquinolines, benzimidazoles, quinoxalines, pyrazines, pyrimidines, and pyridines undergo highly selective 1,2-dearomatization. Both electron-donating and electronwithdrawing substituents on N-heteroaromatics are well tolerated in this protocol. Mechanistic studies indicate the presence of [Ru-(p-cymene) (PCy 3 )HCl] 4 in the reaction mixture, which may be the resting state of the catalyst. The complete catalytic cycle as revealed from density functional theory (DFT) studies show that the product formation is governed by N → Si tetrel bonding. Initially, PCy 3 dissociates from 1, and further reaction of [(p-cymene)RuCl 2 ] 20 with silane generates the catalytically active intermediate [(p-cymene)RuHCl] 7. Heteroarene coordinates with 7, and subsequent dearomative 1,3-hydride transfer to the C2 position of the heteroaryl ligand generates an amide-ligated intermediate in which the reaction of silane occurs through a tetrel bonding and provides a selective pathway for 1,2-addition. DFT studies also revealed that ruthenium-catalyzed 1,4-hydroboration of pyridines is a facile process with a free energy barrier of 3.2 kcal/mol, whereas a pathway for the 1,2-hydroboration product is not observed due to the steric effects exerted by methyl groups on pinacolborane (HBpin) and p-cymene. Notably, enabled by the amine−amide inter-conversion of the coordinated heteroarene ligand, the +2 oxidation state of ruthenium intermediates remains unchanged throughout the catalytic cycle.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Ruthenium(II)-Catalyzed Regioselective 1,2-Hydrosilylation of N-Heteroarenes and Tetrel Bonding Mechanism

et al. 2021

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“…Silyl, Bpin, amine,e ther, and alkyl substituents were tolerated at the arene.Reaction of 4-methoxytoluene gave minor amounts of CÀOMe cleavage product (27 %). [14] Very electron-rich benzyl diboronates were sensitive to protodeborylation and oxidation. Thec rude mixture of benzyl diboronates and benzyl monoboronates (95/5 to 80/20 ratio) could be converted to the stable benzyl monoboronates in high yields by protolysis with NEt 3 /SiO 2 (isolated yields given).…”

Section: Resultsmentioning

confidence: 99%

Selective Benzylic CH‐Borylations by Tandem Cobalt Catalysis

2021

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Metal-catalyzed C À Ha ctivations are environmentally and economically attractive synthetic strategies for the construction of functional molecules as they obviate the need for pre-functionalized substrates and minimizew aste generation. Great challenges reside in the control of selectivities,the utilization of unbiased hydrocarbons,a nd the operation of atom-economical dehydrocoupling mechanisms.Anespecially mild borylation of benzylic CH bonds was developed with the ligand-free pre-catalyst Co[N(SiMe 3 ) 2 ] 2 and the bench-stable and inexpensive borylation reagent B 2 pin 2 that produces H 2 as the only by-product. Af ull set of kinetic, spectroscopic,a nd preparative mechanistic studies are indicative of at andem catalysis mechanism of CH-borylation and dehydrocoupling via molecular Co I catalysts.

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“…Borylation of C(sp 3 )-H bond produces value-added alkyl boronates that can be further converted to other functional groups 4,[7][8][9][10][11] , but requires catalysts based on noble metals such as Ir [12][13][14][15][16][17][18] and Ru [19][20][21][22][23][24] and tailor-made ligands [25][26][27][28] . Noble-metal-free alkane borylation has only been achieved recently by photochemistry 29,30 .…”

Section: Full Textmentioning

confidence: 99%

A noble-metal-free metal-organic framework for alkane borylation

Zeng

Cao

et al. 2022

Preprint

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Catalytic borylation of unactivated C(sp3)‒H bond is of great interest but quite challenging. Reported catalysts mostly contain noble metals such as iridium and ruthenium. Here, we report an earth-abundant zirconium-based metal-organic framework (MOF) catalyst with zirconium hydride (Zr‒H) active sites for methane borylation. Isotope exchange experiment and spectroscopic evidence confirm methane activation by Zr‒H active sites to generate Zr‒CH3 and H2, possibly via σ-bond metathesis. Theoretical calculations suggest another σ-bond metathesis step for C‒B bond formation. The MOF catalyst selectively borylates end methyl group in alkanes and other compounds. For example, the MOF catalyst mono-borylated the end methyl group of n-pentane in 87% yield with > 98% selectivity. The selectivity of primary C‒H bond over secondary C‒H bond is attributed to the steric effect around the Zr‒H site in the MOF, as Zr‒H sites on supports with less stringent steric control have poorer selectivity. This work provides new insights into developing catalysts for alkane functionalization.

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Ruthenium-Catalyzed Selective Hydroboronolysis of Ethers

Cited by 17 publications

References 46 publications

Ruthenium(II)-Catalyzed Regioselective 1,2-Hydrosilylation of N-Heteroarenes and Tetrel Bonding Mechanism

Ruthenium(II)-Catalyzed Regioselective 1,2-Hydrosilylation of N-Heteroarenes and Tetrel Bonding Mechanism

Selective Benzylic CH‐Borylations by Tandem Cobalt Catalysis

A noble-metal-free metal-organic framework for alkane borylation

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