N-Alkyl substituted triazenide-bridged homoleptic iron(ii) dimers with an exceptionally short Fe–Fe bond

Abstract

Dinuclear transition metal complexes with direct metal–metal interactions have the potential to generate unique reactivities and properties. Using asymmetric triazine ligands HN₃^tBuR (R = Et, ⁱPr, ⁿBu) featuring different alkyl substituents at 1,3-N centers, we report here the first rational synthesis of ‘tetragonal lantern’ type Fe(II) triazenides [Fe₂(N₃^tBuR)₄] [R = Et (1), ⁱPr (2), ⁿBu (3)] having an exceptionally short Fe–Fe distance (2.167–2.174 Å). Unlike the previously reported lantern structures with related amidinate or guanidinate ligands, highly air-sensitive 1–3 show a lower spin ground state, as indicated by Mössbauer, ¹H NMR and DFT studies.