Bulky bis(carbene) borate ligands can stabilize high-valent iron (+4 oxidation state and higher) and form complexes with multiple metal-ligand bonds that have potential applications in catalysis. Researchers from Indiana University reported the first crystal structure of a stable Fe(VI) bis(imido) complex. They also structurally and spectroscopically characterized several four-coordinate Fe(V) and Fe(VI) bis(imido) complexes in seesaw geometry. Calculations on their electronic structures were performed in order to elucidate the reasons of the uncommon seesaw geometry. These findings provide the basis for the design of new high valent iron complexes.

Jorge L. Martinez, Sean A. Lutz, Hao Yang, Jiaze Xie, Joshua Telser, Brian M. Hoffman, Veronica Carta, Maren Pink, Yaroslav Losovyj, Jeremy M. Smith.  Structural and spectroscopic characterization of an Fe(VI) bis(imido) complex.  Science, 2020, 370, 356-359 DOI: 10.1126/science.abd3054 abstract