Effects of the counteranion on the pyrazole-nitrile coupling reaction mediated by nickel(II) ions

Chang Chih Hsieh, Chia Jung Lee, Yih Chern Horng

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The reaction of Ni(ClO4)2 with 4 equiv of pyrazole (pzH) in MeCN leads to [Ni(pzH)2(HN= C(Me)pz)2](ClO4) 2 via the intermediate [Ni(MeCN)2(pzH)4] (ClO4)2, which is the first pyrazole-nitrile coupling reaction activated by a Ni(II) complex. The reaction is also successfully conducted with other nitries RCN bearing an electron-donating group (R = Et, Bz) and is counteranion-specific. The reaction proceeds more quickly with NO 3̄ as counteranion than with ClO4̄, and BF4̄ is found to be unsatisfactory for the coupling reaction. As for the X-ray crystal structures, [Ni(MeCN) 2(pzH)4](ClO4)2 possesses stronger pyrazolyl NH... anion hydrogen-bonding interactions than does [Ni(MeCN) 2(pzH)4](BF4)2. The same trend is also observed by solution IR (pyrazolyl NH) analysis. The supramolecular structure of the complex [Ni(pzH)2(HN=C(Me)pz)2](ClO 4)2 displays a two-dimensional network dominated by cooperative face-toface π-π stacking and edge-to-face CH...π bonding interactions. In addition, a mechanism based on anion-mediated/hydrogen-bonding- driven proton transfer for the coupling reaction is proposed.

Original languageEnglish
Pages (from-to)4923-4928
Number of pages6
Issue number17
Publication statusPublished - 2009 Sep 14


All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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