- Synthesis and characterization of six-membered pincer nickelacycles and application in alkylation of benzothiazole
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Six-membered pincer nickelacycle complexes have been synthesized and employed for the catalytic C–H bond alkylation of benzothiazole. The pincer nickelacycle, {κP, κC, κP- (2 - iPr 2POCH 2-
- Pandiri, Hanumanprasad,Sharma, Dipesh M,Gonnade, Rajesh G,Punji, Benudhar
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- Radical Chain Reduction via Carbon Dioxide Radical Anion (CO2?-)
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We developed an effective method for reductive radical formation that utilizes the radical anion of carbon dioxide (CO2?-) as a powerful single electron reductant. Through a polarity matched hydrogen atom transfer (HAT) between an electrophilic radical and a formate salt, CO2?- formation occurs as a key element in a new radical chain reaction. Here, radical chain initiation can be performed through photochemical or thermal means, and we illustrate the ability of this approach to accomplish reductive activation of a range of substrate classes. Specifically, we employed this strategy in the intermolecular hydroarylation of unactivated alkenes with (hetero)aryl chlorides/bromides, radical deamination of arylammonium salts, aliphatic ketyl radical formation, and sulfonamide cleavage. We show that the reactivity of CO2?- with electron-poor olefins results in either single electron reduction or alkene hydrocarboxylation, where substrate reduction potentials can be utilized to predict reaction outcome.
- Hendy, Cecilia M.,Smith, Gavin C.,Xu, Zihao,Lian, Tianquan,Jui, Nathan T.
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supporting information
p. 8987 - 8992
(2021/07/01)
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- Catalytic C-H Bond Alkylation of Azoles with Alkyl Halides Mediated by Nickel(II) Complexes of Phenanthridine-Based N^ N-^ N Pincer Ligands
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Ni(II) complexes supported by tridentate N^N-^N diarylamido pincer-type ligands have been demonstrated to act as active catalysts in the carbon-carbon bond forming alkylation of azoles using unactivated alkyl halides. Here, we show that benzann
- Braun, Jason D.,Herbert, David E.,Mandapati, Pavan,Sidhu, Baldeep K.,Wilson, Gabrielle
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p. 1989 - 1997
(2020/06/08)
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- Mechanistic Aspects of Pincer Nickel(II)-Catalyzed C-H Bond Alkylation of Azoles with Alkyl Halides
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The quinolinyl-based pincer nickel complex, κN,κN,κN-{C9H6N-(μ-N)-C6H4-NMe2}NiCl [(QNNNMe2)NiCl; (1)] has recently been demonstrated to be an efficient and robust catalyst for the alkylation of azoles with alkyl halides under copper-free conditions. Herein, we report the detailed mechanistic investigation for the alkylation of azoles catalyzed by (QNNNMe2)NiCl (1), which highlights an iodine-atom transfer (IAT) mechanism for the reaction involving a NiII/NiIII process. Deuterium labeling experiments indicate reversible cleavage of the benzothiazole C-H bond, and kinetic studies underline a fractional negative rate order with the substrate benzothiazole. The involvement of an alkyl radical during the alkylation is validated by radical clock and external additive experiments. An active intermediate species (QNNNMe2)Ni(benzothiazolyl) (5a) has been isolated and structurally characterized. The complex (QNNNMe2)Ni(benzothiazolyl) (5a) is found to be the resting state of catalyst 1. Kinetic analysis of electronically different intermediates suggests that the step involving the reaction of 5a with alkyl iodide is crucial and a rate-influencing step. DFT calculations strongly support the experimental findings and corroborate an IAT process for the alkylation reaction.
- Patel, Ulhas N.,Jain, Shailja,Pandey, Dilip K.,Gonnade, Rajesh G.,Vanka, Kumar,Punji, Benudhar
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supporting information
p. 1017 - 1025
(2018/03/30)
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- Controllable assembly of the benzothiazole framework using a CC triple bond as a one-carbon synthon
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A concise and efficient protocol to assemble diverse benzothiazole derivatives in high yields was provided via copper catalyzed tandem cyclization with o-haloanilines, elemental sulfur and terminal alkynes as raw materials. In this protocol, C atoms on the CC triple bond were controllably involved in the construction of the benzothiazole framework and multiple carbon-heteroatom bonds through divergent routes.
- Huang, Yubing,Yan, Donghao,Wang, Xu,Zhou, Peiqi,Wu, Wanqing,Jiang, Huanfeng
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supporting information
p. 1742 - 1745
(2018/02/21)
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- Synthesis of Quinoline-Based NNN-Pincer Nickel(II) Complexes: A Robust and Improved Catalyst System for C-H Bond Alkylation of Azoles with Alkyl Halides
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The quinoline-based pincer nickel(II) complexes κN,κN,κN-{R2N-C6H4-(μ-N)-C9H6N}NiX ((R2NNNQ)NiCl: R = Me, 2a; R = Et, 2b) were synthesized by the reaction of the ligand precursors (R2NNNQ)H (R = Me, 1a; R = Et, 1b) with (DME)NiCl2 in the presence of Et3N. Similarly, the pincer nickel(II) derivatives (R2NNNQ)NiX (R = Me, X = Br, 3a; R = Et, X = Br, 3b; R = Me, X = OAc, 4a) were obtained by treatment of the ligands (R2NNNQ)H with the nickel precursor (THF)2NiBr2 or Ni(OAc)2. All of these complexes were characterized by 1H and 13C NMR spectroscopy as well as by elemental analysis. Further, the molecular structures of 2a and 3a,b were elucidated by X-ray crystallography. Complex 2a is found to be an efficient catalyst for the direct C-H bond alkylation of substituted benzothiazoles and oxazoles with various unactivated alkyl halides containing β-hydrogens under mild reaction conditions. The catalyst 2a is very robust and was recycled and reused five times for the alkylation reaction without a decrease in its catalytic activity. Preliminary studies reveal that the catalyst 2a acts as an active catalyst and the alkylation reaction appears to operate via a radical pathway.
- Patel, Ulhas N.,Pandey, Dilip K.,Gonnade, Rajesh G.,Punji, Benudhar
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supporting information
p. 1785 - 1793
(2016/07/06)
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- User-friendly [(diglyme)NiBr2]-catalyzed direct alkylations of heteroarenes with unactivated alkyl halides through C-H bond cleavages
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A nitrogen and phosphorus ligand-free catalytic system derived from inexpensive [(diglyme)NiBr2] allowed for efficient direct C-H bond alkylations of heteroarenes with unactivated β-hydrogen-containing alkyl halides under basic reaction conditi
- Ackermann, Lutz,Punji, Benudhar,Song, Weifeng
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supporting information; experimental part
p. 3325 - 3329
(2012/01/19)
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