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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• 作者：Ulhas N. Patel ; Dilip K. Pandey ; Rajesh G. Gonnade ; Benudhar Punji
• 刊名：Organometallics
• 出版年：2016
• 出版时间：June 13, 2016
• 年：2016
• 卷：35
• 期：11
• 页码：1785-1793
• 全文大小：594K
• 年卷期：0
• ISSN：1520-6041

文摘

The quinoline-based pincer nickel(II) complexes κ^N,κ^N,κ^N-{R₂N-C₆H₄-(μ-N)-C₉H₆N}NiX ((^R2NNN^Q)NiCl: R = Me, 2a; R = Et, 2b) were synthesized by the reaction of the ligand precursors (^R2NNN^Q)H (R = Me, 1a; R = Et, 1b) with (DME)NiCl₂ in the presence of Et₃N. Similarly, the pincer nickel(II) derivatives (^R2NNN^Q)NiX (R = Me, X = Br, 3a; R = Et, X = Br, 3b; R = Me, X = OAc, 4a) were obtained by treatment of the ligands (^R2NNN^Q)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.