High-spin and low-spin iron(ii) complexes with facially-coordinated borohydride ligands

Abstract

Rare examples of monometallic high-spin and low-spin L₃Fe(H₃BH) complexes have been characterized, where the two L₃ ligands are [Tp^Ph2] and [PhBP₃] ([Tp^Ph2] = [HB(3,5-Ph₂pz)₃]⁻ and [PhBP₃] = [PhB(CH₂PPh₂)₃]⁻). The structures are reported wherein the borohydride ligand is facially coordinated to the iron center in each complex. Density functional methods have been employed to explain the bonding in these unusual iron(II) centers. Despite the differences in spin states, short Fe–B distances are observed in both complexes and there is significant theoretical evidence to support a substantial bonding interaction between the iron and boron nuclei. In light of this interaction, we suggest that these complexes can be described as (L₃)Fe(η⁴-H₃BH) complexes.