Low-Coordinate Iron(II) Amido Half-Sandwich Complexes with Large Internal Magnetic Hyperfine Fields

The half-sandwich complex [Cp'Fe{N(dipp)(SiMe3)}] (Fe-dipp; Cp' = 1,2,4-tri-tert-butylcyclopentadienyl and dipp = 2,6-diisopropylphenyl) and the mixed metallocene [Cp'Fe{(eta(5)-(C6H3Pr2)-Pr-i)=N(SiMe3)}] (Fe-chd) formed in the reaction between [{Cp'Fe(mu-I)}(2)] and [Li{N(dipp)(SiMe3)}](2) were characterized by NMR spectroscopy and X-ray diffraction analysis. Fe-dipp complements the series of low-coordinate, quasi-linear iron amido half-sandwich complexes [Cp'Fe{N(Bu-t)(SiMe3)}](2) (Fe-Bu-t) and [Cp'Fe{N(SiMe3)(2)}] (Fe-tms) reported earlier, and all three compounds were characterized in the solid state by zero-field Fe-57 Mossbauer spectroscopy and magnetic susceptibility measurements, confirming their S = 2 electronic ground state. Moreover, the MCissbauer absorption spectra reveal slow paramagnetic relaxation at low temperatures with large internal magnetic hyperfine fields of B-hf = 96.4 T (Fe-dipp, 20 K), B-hf = 101.3 T (Fe-Bu-t, 15 K), and B-hf = 96.9 T (Fe-tms, 20 K). The magnetic measurements further confirm that the presence of significant axial zero-field splitting and slow relaxation of magnetization is detected, which is revealed even in the absence of a static magnetic field in the case of Fe-Bu-t. Supplementary ab initio and density functional theory calculations were performed and support the experimental data.

Automated summary

In this study, the properties of a half-sandwich complex and a mixed metallocene were characterized using NMR spectroscopy, X-ray diffraction analysis, and magnetic measurements. The experimental data and theoretical calculations corroborate each other.