A R T I C L E S
Alexander Merrill et al.
Figure 1. Thermal ellipsoid (30%) drawing of 1. Hydrogen atoms (except
N-H) are not shown. Fe---C(7),C(7)A 2.792 Å. Dashed lines indicate
possible, very weak intramolecular interactions.
Figure 2. Thermal ellipsoid (30%) drawing of 2. Hydrogen atoms (except
N-H) are not shown. Fe(1)---C(16) 2.690 Å, Fe(1)---C(31) 2.588 Å. Dashed
lines indicate weak intramolecular aryl π---Fe interactions.
ration. Investigations of the magnetic properties of the rigorously
linear Fe{C(SiMe3)3}2 have shown that it exhibits essentially
free ion magnetic behavior (µeff ) 6.8 ( 0.2 µB) and the largest
internal hyperfine fields (152 T) observed to date.19,20 In
addition, it has been shown that the almost linear Fe(NBut2)2
(N-Fe-N ) 179.45(8)°) also possesses a high magnetic
moment (µeff ) 5.55 µB) and a large internal hyperfine field
(105 T). However, there have been no studies on two-coordinate
species that feature different geometries with the same ligand
class. Such a study provides a rare opportunity to investigate
the effects of lowering the symmetry of the two-coordinate iron
environment on the orbital contribution to the magnetic moment
and internal hyperfine field while maintaining a very similar
ligand set.
We report the synthesis of the closely related iron(II) amido
complexes Fe{N(H)Ar*}2 (1) (Ar* ) C6H3-2,6-(C6H2-2,4,6-
Pri2)2) and Fe{N(H)Ar#}2 (2) (Ar# ) C6H3-2,6-(C6H2-2,4,6-
Me3)2). They were characterized by X-ray crystallography,
magnetization, zero- and applied field Mo¨ssbauer effect, and
ESR spectroscopy and DFT calculations. The complexes possess
local D∞h (1), Figure 1, and C2V (2), Figure 2, symmetry at iron.
We show that the symmetry change from strict linearity induces
dramatic effects on the magnetic properties of 2.
using a Grubbs-type22 solvent purification system or distilled from
Na/K alloy, and degassed by sparging with dry argon for 10 min.
Ar#NH2 was prepared from reduction of Ar#N3 with LiAlH4 in
Et2O,23,24 Ar#N3 having been prepared by treating Ar#Li25 with
p-toluenesulfonyl azide26 in Et2O. Ar*NH2 was prepared in an
analogous manner. Fe{N(SiMe3)2}2 was synthesized according to
a
modified literature procedure,10a using anhydrous FeCl2
(FeCl2 ·4H2O, Alfa, dehydrated at ∼250 °C under reduced pressure
for 1 d) instead of the bromide. All physical measurements were
obtained under strictly anaerobic conditions. 1H NMR spectra were
recorded on a Varian 300 MHz instrument and referenced internally
to residual silicone vacuum grease, δ 0.29 ppm in C6D6. IR spectra
were recorded as Nujol mulls between CsI plates on a Perkin-Elmer
1430 spectrophotometer. UV-vis spectra were recorded as dilute
hexane solutions in 3.5 mL quartz cuvettes using a HP 8452 diode
array spectrophotometer. Melting points were determined on a
Meltemp II apparatus using glass capillaries sealed with vacuum
grease and are uncorrected.
Fe{N(H)Ar*}2 (1). A Schlenk flask was charged with Ar*NH2
(1.403 g, 3.0 mmol), Fe{N(SiMe3)2}2 (0.678 g, 1.8 mmol), and a
stirring bar. The mixture was then shaken as it was heated to ∼200
°C, melting and codissolving as the reaction ensued. Intermittent
vacuum was applied over ∼10 min to remove the HN(SiMe3)2
byproduct as a white vapor. A deep-red solid resulted, and under
reduced pressure, the entire flask was heated from bottom to top at
∼180 °C for 5 min to to complete the reaction, removing all the
HN(SiMe3)2 as well as unreacted Fe{N(SiMe3)2}2. The resulting
solid was extracted with 40 mL of hexane, filtered on a medium
frit with Celite, and concentrated to ∼15 mL. After 2 d standing at
∼25 °C deep-red, rod-shaped crystals appeared, yield 0.350 g
Experimental Section
Synthetic Methods, Physical Measurements, and Calculations.
General Procedures. All manipulations were performed with the
use of modified Schlenk techniques under argon or in a Vacuum
Atmospheres drybox under N2. Solvents were dried and collected
1
(22%), mp 263 °C. H NMR (300 MHz, C6D6, 25 °C) δ 7.09 (br,
(11) Chen, H.; Bartlett, R. A.; Dias, H. V. R.; Olmstead, M. M.; Power,
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s, ArH), 1.21 (br, m), 0.84 (br, s), 0.19 (br, m), -13.2 (br, s), -57.2
(br, s). IR, cm-1: ν(N-H) 3350; ν(Fe-N) 400. UV-vis, nm (ε,
M-1 cm-1): 450 (2840), 424 sh (2360), 320 (12100), 310 sh (11800).
Fe{N(H)Ar#}2 (2). A Schlenk flask was charged with Ar#NH2
(0.988 g, 3.0 mmol) and [Fe{N(SiMe3)2}2] (0.678 g, 1.8 mmol),
and a stirring bar. As the solids began reacting at ∼25 °C (indicated
by a reddening of the crystalline Ar#NH2), toluene (∼10 mL) was
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