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Syntheses, structures and electronic properties of zwitterionic iron(II) and cobalt(II) complexes featuring ambidentate tris(pyrazolyl)methanide ligands.

Authors
  • Kuzu, Istemi1
  • Krummenacher, Ivo
  • Hewitt, Ian J
  • Lan, Yanhua
  • Mereacre, Valeriu
  • Powell, Annie K
  • Höfer, Peter
  • Harmer, Jeffrey
  • Breher, Frank
  • 1 Institut für Anorganische Chemie, Universität Karlsruhe (TH), Engesserstr. 15, 76131 Karlsruhe, Germany. , (Germany)
Type
Published Article
Journal
Chemistry - A European Journal
Publisher
Wiley (John Wiley & Sons)
Publication Date
2009
Volume
15
Issue
17
Pages
4350–4365
Identifiers
DOI: 10.1002/chem.200802317
PMID: 19248069
Source
Medline
License
Unknown

Abstract

By deprotonation of the corresponding tris(pyrazolyl)methane ((Me)Tpm) precursor complexes [M((Me)Tpm)(2)][(OTf)(2)] (1 and 2), the zwitterionic tris(pyrazolyl)methanide iron(II) (3) and cobalt(II) (4) "sandwich" complexes of the general formula [M((Me)Tpmd)(2)] are easily accessible. The structurally characterised complexes 3 and 4 are the first such homoleptic 3d transition metal species to feature two "naked", outward pointing pyramidal carbanions. Density functional theory calculations show metal-centred HOMOs and LUMOs with the destabilised carbanion orbitals in the energy region of the filled transition-metal-centred frontier orbitals. The electronic structures of these complexes have been investigated in detail by various spectroscopic techniques such as NMR, EPR, SQUID, Mössbauer, etc. Both complexes adopt a high-spin (HS) configuration at room temperature in solution and in the solid state. A thermally induced high-spin to low-spin (HS-LS) transition is observed for the iron(II) complex 3. The HS-LS transition temperature of 3 in solution differs from that in the solid state, which in turn strongly depends on the amount of solvent molecules in the crystal lattice. Electrochemical studies on the corresponding cobalt(II) complex 4 provide evidence for a HS-Co(II) <==> LS-Co(III) transition upon oxidation, which was confirmed by preliminary synthetic oxidation reactions. Overall, it can be concluded that the related kappa(3)N-donor ligands tris(pyrazolyl)hydroborates (Tp(R)) and (R)Tpmd ligands have similar bonding properties and that the metal cations experience more or less the same ligand environment.

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