ME and ME complexes of iron and cobalt that emphasize three-fold symmetry (E = O, N, NR)

Mid-to-late transition metal complexes that feature terminal, multiply bonded ligands such as oxos, imides, and nitrides have been invoked as intermediates in several catalytic transformations of synthetic and biological significance. Until about ten years ago, isolable examples of such species were virtually unknown. Over the past decade or so, numerous chemically well-defined examples of such species have been discovered. In this context, the present review summarizes the development of 4- and 5-coordinate Fe(E) and Co(E) species under local three-fold symmetry.

Research highlights
► Mid-to-late transition metal complexes that feature terminal, multiply bonded ligands.
► Review of 4- and 5-coordinate L3M(E) and L′L3M(E) species (E = oxo, imide, nitride, M = Fe or Co).
► FeNx triple bond across five oxidation states.
► Atom and group transfer reactions to install multiply bonded ligands.