Electronic Structure of an Iron-Porphyrin—Nitrene Complex.

Middle and late transition metal imido complexes (which may also be viewed as metal—nitrene adducts) are rather rare, especially for square-pyramidal and octahedral coordination geometries. However, an iron(ll) porphyrin aminonitrene adduct, denoted here as Fe(Por)(NN), has been known for almost a quarter of a century. Unlike the corresponding S= 1 oxene and S = 0 carbene adducts, Fe(Por)(NN) exhibits an S = 2 ground slate. DFT calculations reported herein provide a molecular orbital description of this unusual species as well as a rationale for its S = 2 ground stale. The electronic configuration of Fe(Por)(NN) may be described as dπ2dxy1dze1dxe-yedπ'1, where the z direction corresponds to the Fe—NN axis. The stability and double occupancy of one of the dπ orbitals may be attributed to a π-backbonding interaction with the N-N π* orbital. The weak a-donor ability of the aminonitrene ligand results in a relatively low-energy dze orbital and an overall d orbital splitting pattern that engenders a high-spin ground state. [ABSTRACT FROM AUTHOR]