Heavy alkaline earth metal pyrazolates: Synthetic pathways, structural trends, and comparison with divalent lanthanoids

Julia Hitzbleck, Anna Y. O'Brien, Craig M. Forsyth, Glen B. Deacon, Karin Ruhlandt-Senge

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Two series of heavy alkaline earth metal pyrazolates, [M(Ph 2pz)2(thf)4] 1a-c (Ph2pz: = 3,5-diphenylpyrazolate, M = Ca, Sr, Ba; THF = tetrahydrofuran) and [M(Ph 2pz)2(dme)n] (M = Ca, 2a, Sr, 2b, n = 2; M = Ba, 2c, n = 3; DME = 1,2-di-methoxyethane) have been prepared by redox transmetallation/ligand exchange utilizing Hg(C6F5) 2. Compounds 1a and 2b were also obtained by redox transmetallation with Tl(Ph2pz). Alternatively, direct reaction of the alkaline earth metals with 3,5-diphenylpyrazole at elevated temperatures under solventless conditions yielded compounds 1a-c and 2a-c upon extraction with THF or DME. By contrast, [M(Me2pz)2(Me2pzH)4] 3a-c (M = Ca, Sr, Ba; Me2pzH = 3,5-dimethylpyrazole) were prepared by protolysis of [M{N(SiMe3)2}2(thf)2] (M = Ca, Sr, Ba) with Me2pzH in THF and by direct metallation with Me2pzH in liquid NH3/THF. Compounds 1a-c and 2a-c display η2-bonded pyrazolate ligands, while 3a,b exhibit η1-coordination. Complexes 1a-c have transoid Ph2pz ligands and an overall coordination number of eight with a switch from mutually coplanar Ph2pz ligands in 1a,b to perpendicular in 1c. In eight coordinate 2a,b the pyrazolate ligands are cisoid, whilst 2c has an additional DME ligand and a metal coordination number of ten. By contrast, 3a,b have octahedral geometry with four η1-Me2pzH donors, which are hydrogen-bonded to the uncoordinated nitrogen atoms of the two trans Me 2pz ligands. The application of synthetic routes initially developed for the preparation of lanthanoid pyrazolates provides detailed insight into the similarities and differences between the two groups of metals and structures of their complexes.

Original languageEnglish (US)
Pages (from-to)3315-3323
Number of pages9
JournalChemistry - A European Journal
Issue number13
StatePublished - Jul 5 2004


  • Alkaline earth metals
  • Coordination modes
  • Lanthanides
  • N ligands
  • Structure elucidation
  • Synthetic methods

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry


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