8318 Inorganic Chemistry, Vol. 48, No. 17, 2009
Popescu et al.
the vast literature detailing low-spin organoiron complexes
that obey the 18-electron rule, the electronic structure of
high-spin organoiron complexes has remained largely unex-
plored. One notable exception is the spectroscopic and
theoretical study of a trigonal methyliron(II) complex sup-
ported by a β-diketiminate ligand, LFe(Me) (L = β-dike-
timinate).18 Andres et al. explored the electronic structure
and bonding in this complex by Mossbauer, electron para-
¨
magnetic resonance (EPR), and theoretical studies. Their
results revealed large unquenched orbital angular momen-
tum in one spatial direction (namely, on the axis perpendi-
cular to the β-diketiminate plane) due to the presence of low-
lying excited orbital states. A closer examination, by the same
group, of the electronic structure of additional two- and
planar three-coordinate Fe(II) and Fe(I) compounds estab-
lished that the unquenched orbital angular momentum is a
common feature of this family of iron compounds. This
unquenching phenomenon generates ground states, which
are pseudodoublets for Fe(II) and Kramers doublets for Fe(I),
that exhibit uniaxial magnetic behavior with large effective g
values (geff ≈ 11.4 for the [(β-diketiminate)Fe(II)Me])18 and
large internal magnetic fields along the spin quantization
axis.19,20 Another unusual feature of the planar ferrous β-
diketiminate complexes is their small quadrupole splitting
(1.11<|ΔEQ|<1.74 mm/s, for the [(β-diketiminate)Fe(II)L]
series, L = NHtBu, NHTol, Cl, CH3), shown to be caused by
ligandcontributions to the electric field gradients (EFGs) and
associated with the planarity of the complex, rather than the
coordinated alkyl.18,21
Figure 1. Molecular structure of [PhTttBu]Fe(Me) (1) with thermal
ellipsoids drawn to 30% probability (H atoms not shown). Inset: A
molecular model (truncated for clarity) showing the z axis used for
spectroscopic and DFT calculations.
activated alumina22 with oxygen subsequently removed via a
nitrogen purge.
a. Synthesis of 1. MeMgBr (3.0 M in ethyl ether, 55 μL, 0.15
mmol) was added to a vial via syringe. This solution was diluted
with 10 mL of ethyl ether, and 1,4-dioxane was added dropwise
precipitating MgCl2. The cloudy mixture was added dropwise to
23
a stirring 1,4-dioxane solution (30 mL) of {[PhTttBu]FeCl}2
(0.075 g, 0.15 mmol), producing a cloudy yellow solution. The
mixture was stirred for 10 min and then filtered through Celite.
The solvent was removed in vacuo, affording a light brown solid
that was extracted with pentane (2 ꢀ 3 mL) and dried under a
vacuum, yielding a yellow solid. Yellow blocks of 1 were grown
by slow evaporation of a concentrated pentane solution. Yield:
We report the synthesis and characterization of the C3-
symmetric complex [PhTttBu]Fe(Me), 1 (PhTttBu =C6H5B-
(CH SC(CH ) ) ), including crystallographic, Mossbauer,
¨
2
3 3 3
and EPR spectroscopic studies. To our knowledge, this
is the first report of a sulfur-ligated, organoiron complex
with a high-spin configuration. According to the data pre-
sented here, 1 is a 14-electron, high-spin ferrous complex, in
which the symmetry and alkyl coordination produce an
orbital ground state (consisting predominantly of dxy
assuming the z axis along the Fe-C bond, Figure 1) that
mixes through spin-orbit coupling with the next state
(dx2-y2-like), generating a relatively large and negative
zero-field splitting (ZFS), a large magnetic moment along
the z axis, and a ground spin state with uniaxial magnetic
properties.
1
0.041 g, 72%. H NMR (C6D6): δ 42.9 (s, m-(C6H5)B), 20.2
(s, o-(C6H5)B), 18.7 (s, p-(C6H5)B), -26.4 (br, (CH3)3S). UV-
vis (THF), λmax (ε, M-1 cm-1): 323 (1100). Anal. Calcd for
C22H41BFeS3: C, 56.41; H, 8.82. Found: C, 56.04; H, 8.89. The
magnetic moment of 1 was measured in solution by the Evans
method,24 μeff (C6D6)=5.1(2) μB.
b. X-Ray Diffraction. Crystal data collection and refinement
parameters are given in Table 1. Yellow blocks of 1 were grown
by slow evaporation of a concentrated pentane solution. Cry-
stals were mounted using viscous oil on glass fibers and cooled to
the data collection temperature. Data were collected on a
Bruker-AXS APEX CCD diffractometer with graphite-mono-
˚
chromated Mo KR radiation (λ = 0.71073 A). Unit cell para-
meters were obtained from 60 data frames, 0.3ꢀ ω, from three
different sections of the Ewald sphere. The systematic absences
in the diffraction data are uniquely consistent with the mono-
clinic space group, P21/n. The data sets were treated with
SADABS absorption corrections based on redundant multiscan
data.25 The structure was solved using direct methods and
refined with full-matrix, least-squares procedures on F2. All
non-hydrogen atoms were refined with anisotropic displace-
ment parameters. All hydrogen atoms were treated as idealized
contributions. Structure factors are contained in the SHELXTL
6.12 program library.25
2. Materials and Experimental Methods
Due to the air and moisture sensitivity of complex 1, all
manipulations were performed under a nitrogen atmosphere
employing solvents predried via passage through columns of
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¨
c. Mossbauer and EPR Spectroscopy. Mossbauer samples
were prepared in a Vacuum Atmospheres glovebox by stirring
¨
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