Bulky guanidinato nickel(I) complexes: Synthesis, characterization, isomerization, and reactivity studies

Cameron Jones, Christian Schulten, Lea Fohlmeister, Andreas Stasch, Keith S. Murray, Boujemaa Moubaraki, Stuart Kohl, Mehmed Z. Ertem, Laura Gagliardi, Christopher J. Cramer

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Reactions of lithium complexes of the bulky guanidinates [{(Dip)N} 2CNR2]- (Dip=C6H3iPr 2-2,6; R=C6H11 (Giso-) or iPr (Priso-), with NiBr2 have afforded the nickel(II) complexes [{Ni(L)(Iμ-Br)}2] (L=Giso- or Priso -), the latter of which was crystallographically characterized. Reduction of [{Ni(Priso)(Iμ-Br)}2] with elemental potassium in benzene or toluene afforded the diamagnetic species [{Ni(Priso)} 2(Iμ-C6H5R)] (R=H or Me), which were shown, by X-ray crystallographic studies, to possess nonplanar bridging arene ligands that are partially reduced. A similar reduction of [{Ni(Priso)(Iμ-Br)} 2] in cyclohexane yielded a mixture of the isomeric complexes [{Ni(Iμ-κ1-N-,ν2-Dip-Priso)}2] and [{Ni(Iμ-κ2-N,N′-Priso)}2], both of which were structurally characterized. These complexes were also formed through arene elimination processes if [{Ni(Priso)}2(Iμ-C6H 5R)] (R=H or Me) were dissolved in hexane. In that solvent, diamagnetic [{Ni(Iμ-κ1-N-,ν2-Dip-Priso)} 2] was found to slowly convert to paramagnetic [{Ni(Iμ- κ2-N,N′-Priso)}2], suggesting that the latter is the thermodynamic isomer. Computational analysis of a model of [{Ni(Iμ-κ2-N,N′-Priso)}2] showed it to have a NiNi bond that has a multiconfigurational electronic structure. An analogous copper(I) complex [{Cu(Iμ-κ2-N, N′-Giso)}2] was prepared, structurally authenticated, and found, by a theoretical study, to have a negligible Cua⋯Cu bonding interaction. The reactivity of [{Ni(Priso)}2(Iμ-C 6H5Me)] and [{Ni(Iμ-κ2-N,N′- Priso)}2] towards a range of small molecules was examined and this gave rise to diamagnetic complexes [{Ni(Priso)(Iμ-CO)}2] and [{Ni(Priso)(Iμ-N3)}2]. Taken as a whole, this study highlights similarities between bulky guanidinate ligands and the β-diketiminate ligand class, but shows the former to have greater coordinative flexibility.

Original languageEnglish (US)
Pages (from-to)1294-1303
Number of pages10
JournalChemistry - A European Journal
Issue number4
StatePublished - Jan 24 2011


  • guanidinate
  • low oxidation state
  • metal-metal interactions
  • nickel
  • small-molecule activation
  • structure elucidation


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