Low-Coordinate Iron Hydride Chemistry at an N,N,C-Heteroscorpionate Platform

Locally high-spin iron hydrides are proposed to play
a critical
role as intermediates in iron–molybdenum cofactor (FeMoco)-catalyzed
N2 fixation. Inspired by these biological systems, we report
herein our initial investigations into low-coordinate iron hydride
chemistry supported by our N,N,C-heteroscorpionate ligands. Those
ligands with smaller steric profiles are unable to completely suppress
the formation of a binuclear [Fe(μ2-H)]2 complex; however, the incorporation of more substantial steric bulk
allows for the isolation of a rare example of a terminal, high-spin
(S = 2) Fe2+ hydride. Fourier transform
infrared spectroscopy suggests an unusually weak Fe–H bond
in the latter molecule. Mössbauer spectroscopies, coupled with
density functional theory calculations, highlights the substantial
influence of the terminal hydride ligand on 57Fe isomer
shift.