Molecular and electronic structure of a nonheme iron(II) model complex containing an iron-carbon bond

The synthesis and molecular structure of a novel iron(II) complex of an acyclic non-NHC bis(2-pyridylthio)carbene ligand containing a S-N-C facial triad are discussed. The iron carbene complex is formed in situ during the reaction of tris(2-pyridylthio)methane with an iron(II) salt. In the six-coordinate iron(II) complex, a strong Fe-C interaction (1.776 A) is observed crystallographically and the complex exhibits a singlet-spin ground state. Density functional theory calculations that reproduce the geometry as well as the spin ground state indicate that the electronic structure of the complex is best described as an iron(II) carbene. The carbene center is stabilized by extensive back-bonding from iron(II) and delocalization into the adjacent thiopyridine units.