Oxido-bridged di-, tri-, and tetra-nuclear iron complexes bearing bis(trimethylsilyl)amide and thiolate ligands

Article abstract of DOI:10.1021/ic2025928

A series of di-, tri-, and tetra-nuclear iron-oxido clusters with bis(trimethylsilyl)amide and thiolate ligands were synthesized from the reactions of Fe{N(SiMe₃)₂}₂ (1)with 1 equiv of thiol HSR (R = C₆H₅ (Ph), 4-tBuC₆H4, 2,6-Ph2C₆H₃ (Dpp), 2,4,6-iPr₃C₆H2 (Tip))and subsequent treatment with O₂. The trinuclear clusters [{(Me₃Si)₂N}Fe]₃(μ₃-O) {μ-S(4-RC₆H4)}3 (R = H (3a), tBu (3b))were obtained from the reactions of 1 with HSPh or HS(4-tBuC₆H4)and O₂, while we isolated a tetranuclear cluster [{(Me₃Si)₂N} ₂Fe2(μ-SDpp)]2(μ₃-O)₂ (4)as crystals from an analogous reaction with HSDpp. Treatment of a tertrahydrofuran (THF)solution of 1 with HSTip and O₂ resulted in the formation of a dinuclear complex [{(Me₃Si)₂N}(TipS)(THF)Fe]2(μ-O)(5). The molecular structures of these complexes have been determined by X-ray crystallographic analysis.

Full text of DOI:10.1021/ic2025928

Article
pubs.acs.org/IC
Oxido-Bridged Di-, Tri-, and Tetra-Nuclear Iron Complexes Bearing
Bis(trimethylsilyl)amide and Thiolate Ligands
Shun Ohta, Saori Yokozawa, Yasuhiro Ohki, and Kazuyuki Tatsumi*
Department of Chemistry, Graduate School of Science, and Research Center for Materials Science, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya 464-8602, Japan
S
* Supporting Information
ABSTRACT: A series of di-, tri-, and tetra-nuclear iron-oxido
clusters with bis(trimethylsilyl)amide and thiolate ligands were
synthesized from the reactions of Fe{N(SiMe3)2}2 (1) with 1
equiv of thiol HSR (R = C6H5 (Ph), 4-tBuC6H4, 2,6-Ph2C6H3
(Dpp), 2,4,6-iPr3C6H2 (Tip)) and subsequent treatment with
O2. The trinuclear clusters [{(Me3Si)2N}Fe]3(μ3-O){μ-S(4-
t
RC6H4)}3 (R = H (3a), Bu (3b)) were obtained from the
reactions of 1 with HSPh or HS(4-tBuC6H4) and O2, while we
isolated a tetranuclear cluster [{(Me3Si)2N}2Fe2(μ-SDpp)]2(μ3-O)2 (4) as crystals from an analogous reaction with HSDpp.
Treatment of a tertrahydrofuran (THF) solution of 1 with HSTip and O2 resulted in the formation of a dinuclear complex
[{(Me3Si)2N}(TipS)(THF)Fe]2(μ-O) (5). The molecular structures of these complexes have been determined by X-ray
crystallographic analysis.
INTRODUCTION
■
Iron-thiolate complexes have been commonly used as
precursors for iron-sulfur clusters structurally analogous to
those found in proteins. For example, anionic iron-thiolate
complexes [Fe(SR)4]2− (R = alkyl or aryl group), which are
formed from FeCl2 and thiolate anions in polar organic
solvents, react with elemental sulfur to afford various iron-sulfur
clusters with [Fe2S2], [Fe3S4], [Fe4S4], [Fe6S6], and [Fe6S9]
cores.1,2 Non-charged iron-thiolate complexes with or without
amide ligands, such as [Fe(SR)2], [Fe(SR){N(SiMe3)2}], and
their oligomers, are available from the reactions of an iron bis-
amide complex Fe{N(SiMe3)2}2 (1) with thiols in non-polar
organic solvents,3−8 and they also serve as good precursors for
iron-sulfur clusters.4a,c,d,7 For example, the reaction of Fe3(μ-
STip)4{N(SiMe3)2}2 (Tip = 2,4,6-iPr3C6H2) with HSTip,
SC(NMe2)2, and elemental sulfur leads to the formation of
an [Fe8S7] cluster [{(Me3Si)2N}{(Me2N)2CS}Fe4S3]2(μ6-S){μ-
N(SiMe3)2}2 (A) reproducing the inorganic core of the
nitrogenase P-cluster (Figure 1).4a,d Another notable example
is the reaction of a dinuclear iron-thiolate complex Fe2(μ-
SDmp)2(STip)2 (Dmp = 2,6-(mesityl)2C6H3) with elemental
sulfur to afford [(DmpS)Fe4S3]2(μ6-S)(μ-SDmp)2(μ-STip)
(B), whose framework is topologically analogous to the
FeMo-cofactor of nitrogenase.4c In these reactions, elemental
sulfur serves not only as a sulfurization agent but also as an
oxidant. The oxidation states of A and B with partial ferric
character, Fe(II)6Fe(III)2 and Fe(II)5Fe(III)3, respectively,
result from oxidation of the Fe(II) precursors with elemental
sulfur. Similarly, one can suggest the use of O2 instead of
elemental sulfur, to synthesize iron-oxido clusters carrying
thiolates.
Figure 1.
Iron-oxido clusters with sulfur ligands have potential
relevance to metal centers in proteins. For example, the active
site of the hybrid-cluster protein (HCP) is an iron-oxido-sulfido
cluster supported by cysteinyl thiolates, glutamates, and a
histidinyl imidazole (Figure 2).9,10 Iron clusters with one oxido
Received: December 1, 2011
Published: February 2, 2012
© 2012 American Chemical Society
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the iron-amide-thiolate complexes [Fe(SAr){N(SiMe3)2}2]n.
For instance, it was reported that the mono- and di-nuclear
complexes [Fe(SDmp){N(SiMe3)2}], [{(Me3Si)2N}Fe]2(μ-
SDpp)2 (Dpp = 2,6-Ph2C6H3), and [{(Me3Si)2N}Fe]2[μ-
S{2,6-(Me3Si)2C6H3}]2 were synthesized in high yields by the
1:1 reactions of 1 and corresponding thiols.3b,4b,5 An iron-
amide-thiolate complex with less hindered mesityl thiolates has
also been isolated as a tetrahydrofuran (THF) adduct,
[{(Me3Si)2N}(THF)Fe]2(μ-SMes)2 (Mes = mesityl).8 In an
attempt to isolate an analogous iron-amide-thiolate complex for
SPh or S(4-tBuC6H4), 1 was treated with 1 equiv of HSPh or
HS(4-tBuC6H4) in toluene to give a dark reddish-brown
suspension. From the reaction of 1 and HSPh, it was possible
to obtain crystals of [{(Me3Si)2N}Fe2(μ-SPh){μ-N-
(SiMe3)2}]2(μ-SPh)2 (2) in 20% yield. According to the X-
ray analysis, complex 2 has a linear Fe−Fe−Fe−Fe array, and
an inversion center resides at the midpoint of Fe2 and Fe2* as
shown in Figure 3. The inner iron atoms (Fe2 and Fe2*) are
Figure 2. Active site structure of the HCP. X1 and X2 have been
interpreted as an oxygen atom in two alternate positions.9
ligand may also constitute useful synthons toward synthetic
analogues of the FeMo-cofactor, which consists of a
[MoFe7S9X] (X = O, N, or C) core featuring an iron-bound
interstitial atom X.11 In this study, we present a new class of
iron-oxido clusters having amide and thiolate ligands,
synthesized by the reactions of iron-amide-thiolate complexes
with O2. The number of iron atoms in the products varies
dependent on the thiolate ligands, and di-, tri-, and tetra-nuclear
clusters were obtained.
RESULTS AND DISCUSSION
■
We have examined reactions of the iron bis-amide Fe{N-
(SiMe3)2}2 (1) with various thiols with subsequent addition of
O2. Scheme 1 summarizes the results.
Scheme 1
Figure 3. Molecular structure of 2 with thermal ellipsoids at the 50%
probability level. Selected bond distances (Å) and angles (deg): Fe1−
Fe2 = 2.7875(5), Fe2−Fe2* = 3.6352(6), Fe1−N1 = 1.9148(18),
Fe1−N2 = 2.0483(15), Fe1−S1 = 2.3836(7), Fe2−N2 = 2.0544(19),
Fe2−S1 = 2.3484(6), Fe2−S2 = 2.3536(7), Fe2−S2* = 2.3819(7),
N1−Fe1−N2 = 144.11(8), N1−Fe1−S1 = 115.27(6), N2−Fe1−S1 =
100.59(6), N2−Fe2−S1 = 101.58(5), N2−Fe2−S2 = 115.80(5), N2−
Fe2−S2* = 134.90(5), S1−Fe2−S2 = 110.54(3), S1−Fe2−S2* =
112.25(3), S2−Fe2−S2* = 79.71(2), Fe1−N2−Fe2 = 85.60(7), Fe1−
S1−Fe2 = 72.18(2), Fe2−S2−Fe2* = 100.29(2).
four-coordinate and are bound to three bridging thiolate sulfurs
and one bridging amide nitrogen, while the outer iron atoms
(Fe1 and Fe1*) are three-coordinate with one terminal amide,
a bridging amide, and a bridging thiolate. The Fe1−Fe2
distance of 2.7875(5) Å is notably shorter than the Fe2−Fe2*
distance of 3.6352(6) Å. The short Fe1−Fe2 distance is
accompanied by the acute Fe1−S1−Fe2 angle of 72.18(2)°,
while the Fe2−S2−Fe2* angle is large (100.29(2)°), indicating
a weak Fe1−Fe2 interaction. The molecule may be viewed as a
dimer of the [{(Me3Si)2N}(PhS)Fe2(μ-SPh){μ-N(SiMe3)2}].
(b). Reaction of 1 with HSPh or HS(4-tBuC6H4) in the
Presence of O2. We observed that a dark reddish-brown
toluene suspension, which was obtained from the reaction of 1
and 1 equiv of HSPh or HS(4-tBuC6H4), turned to a dark
brown solution, upon treatment with 0.2 equiv of O2. From the
resulting solution, the trinuclear oxido complexes
[{(Me3Si)2N}Fe]3(μ3-O){μ-S(4-RC6H4)}3 were isolated in
(a). Isolation of [{(Me3Si)2N}Fe2(μ-SPh){μ-N-
(SiMe3)2}]2(μ-SPh)2 (2). The reactions of the iron bis-amide
(1) with 1 equiv of HSAr (Ar = aryl group) are known to afford
t
20% (3a; R = H) and 52% (3b; R = Bu) yields, respectively,
as dark brown crystals (Scheme 1, top). Crystals suitable for X-
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ray diffraction study were obtained from hexane for 3a and 3b.
with the corresponding thiols and elemental sulfur has been
reported.7
The oxidation state of 3a−b is Fe(II)Fe(III)2, and their cyclic
voltammograms (CVs) exhibit one quasi-reversible oxidation
and one reduction events as shown in Figure 5. The half-
Both 3a and 3b crystallize in the space group of P1 (#2) with Z
̅
= 4, so there are two crystallographically independent
molecules in an asymmetric unit. As the molecular structures
of 3a and 3b are very similar, top and side views of only one of
the independent molecules of 3a are shown in Figure 4.
Figure 5. CVs (scan rate = 0.1 V/s) of 3a (top) and 3b (bottom) in
THF.
potentials (E1/2) for the Fe(III)3/Fe(II)Fe(III)2 couple are at
E1/2 = −0.28 V (3a) and −0.33 V (3b), and those for the
Fe(II)Fe(III)2/Fe(II)2Fe(III) couple are at E1/2 = −1.20 V (3a)
and −1.25 V (3b). The redox potentials of 3b are slightly more
negative compared with the corresponding potentials of 3a,
probably because of the electron-donating property of the
t
thiolate Bu groups.
Figure 4. Molecular structure of 3a with thermal ellipsoids at the 50%
probability level. In the side view, methyl and phenyl (except ipso
carbon atom) groups have been omitted for clarity. Selected bond
distances (Å) and angles (deg): Fe1−Fe2 = 2.8745(8), Fe1−Fe3 =
2.9346(8), Fe2−Fe3 = 2.9325(8), Fe1−N1 = 1.872(2), Fe2−N2 =
1.872(2), Fe3−N3 = 1.911(2), Fe1−S1 = 2.3892(8), Fe1−S3 =
2.3399(10), Fe2−S1 = 2.4037(9), Fe2−S2 = 2.3493(10), Fe3−S2 =
2.4556(8), Fe3−S3 = 2.4692(7), Fe1−O1 = 1.895(2), Fe2−O1 =
1.899(2), Fe3−O1 = 1.984(2), Fe1−O1−Fe2 = 98.51(8), Fe1−O1−
Fe3 = 98.32(9), Fe2−O1−Fe3 = 98.07(9).
(c). Reaction of 1 with HSDpp (Dpp = 2,6-Ph2C6H3) in
the Presence of O2. A 1:1 reaction mixture of 1 and HSDpp
in toluene was treated with O2 (0.3 equiv to 1) at room
temperature resulting in a dark purple solution. The solution
color gradually turned to dark reddish brown. Recrystallization
of the crude product from toluene/hexane gave black block
crystals of the tetranuclear oxido complex [{(Me3Si)2N}2Fe2(μ-
SDpp)]2(μ3-O)2 (4) in 21% yield (Scheme 1, middle), along
with colorless crystals of the disulfide Dpp−SDpp which was
isolated in 20% yield. The formation of DppS−SDpp accounts
for the reduction of iron. Cluster 4 is formed via 4e reduction
of O2 to give two μ3-oxido ligands. Two of the required
electrons are furnished by iron oxidation from 2Fe(II)2 to the
Fe(II)2Fe(III)2 state of 4, and the formation of DppS−SDpp
supplies the other 2e−. This Fe(II)2Fe(III)2 state of 4 appears
to be stable, according to its CV, which shows only an
irreversible reduction event at −2.48 V vs Ag/AgNO3.
X-ray analysis of 4 reveals an Fe4(μ3-O)2 framework, as
shown in Figure 6. The atoms Fe1, O, Fe1*, and O* form a
nearly perfect square face, which has an inversion center at its
middle. Fe2 and Fe2* are mutually trans with respect to the
[Fe2O2] plane, with the Fe2−O distance of 1.9358(10) Å. The
Fe1−Fe1* distance (2.7139(4) Å) is much shorter than the
Fe1−Fe2 distance (3.0223(4) Å), which is too long to be a
direct Fe−Fe interaction. The central iron atoms (Fe1 and
Fe1*) are close to tetrahedral, coordinated by two oxido
ligands, one SDpp, and one amide. Although the outer iron
atoms (Fe2 and Fe2*) seem to be three-coordinate with oxido,
SDpp, and amide ligands, an additional weak interaction
Clusters 3a and 3b consist of a nearly-equilateral triangle Fe3
frame, to which an oxygen atom caps, and three thiolate sulfur
atoms bridge the iron atoms, and one amide coordinates at
each iron from the lateral site. The coordination geometry of
each iron is tetrahedral. The μ3-O atom of 3a or 3b is displaced
by 0.934(3)−0.950(2) Å from the Fe3 plane. This is in contrast
to the known Fe3(μ3-O) clusters with octahedral Fe(II)Fe(III)2
atoms,12−14 in which the μ3-O ligand is located only ≤0.34 Å
from the Fe3 plane. In agreement with the structural difference
between 3a−b and the known Fe3(μ3-O) clusters, the Fe−(μ3-
O)−Fe angles of 3a−b (97.17(13)−98.69(13)°) are smaller
than those of the known Fe3(μ3-O) clusters (109.9(2)−
127.1(4)°).12−14 The amide nitrogens in 3a−b are planar, and
deviation of the N atom from the plane defined by the
neighboring silicon and iron atoms is ≤0.043(3) Å. The Si−N−
Si planes orient nearly perpendicular to the Fe3 plane (74.3−
98.7°) because of steric hindrance with μ-SR ligands. Synthesis
of the sulfido analogues of 3a−b, [{(Me3Si)2N}Fe]3(μ3-S)(μ-
SR)3 (R = 4-CH3C6H4, adamantyl), from the reactions of 1
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spectrum of 5 in hexane exhibited two broad absorptions at 429
nm (ε = 6100 M−1 cm−1) and 330 nm (ε = 6300 M−1 cm−1), in
addition to a shoulder at 280 nm (ε = 9200 M−1 cm−1). The
former two bands are probably ascribed to the charge-transfer
bands from amide, thiolate, and/or oxido ligands to Fe(III).
The Fe−O−Fe structure of 5 was identified by X-ray
crystallographic analysis (Figure 7). In the solid state, cluster 5
Figure 7. Molecular structure of 5 with thermal ellipsoids at the 50%
probability level. Selected bond distances (Å) and angles (deg): Fe−N
= 1.913(3), Fe−S = 2.2798(12), Fe−O1 = 1.7845(9), Fe−O2 =
2.067(2), N−Fe−S = 126.05(10), N−Fe−O1 = 117.34(12), N−Fe−
O2 = 102.62(14), S−Fe−O1 = 100.74(4), S−Fe−O2 = 105.33(9),
O1−Fe−O2 = 101.85(9), Fe−O1−Fe* = 149.3(2).
Figure 6. Molecular structure of 4·C6H14 with thermal ellipsoids at the
50% probability level. Selected bond distances (Å) and angles (deg):
Fe1−Fe1* = 2.7139(4), Fe1−Fe2 = 3.0223(4), Fe1−N1 =
1.8834(13), Fe1−S = 2.3870(5), Fe1−O = 1.9310(13), Fe1−O* =
1.8998(10), Fe2−N2 = 1.9089(15), Fe2−S = 2.4336(6), Fe2−O =
1.9358(10), Fe2−C18 = 2.9382(16), O−Fe1−O* = 89.79(5), Fe1−
N1−Si1 = 115.30(10), Fe1−N1−Si2 = 122.97(9), Si1−N1−Si2 =
121.35(8), Fe2−N2−Si3 = 116.24(8), Fe2−N2−Si4 = 119.75(11),
Si3−N2−Si4 = 123.83(10), Fe1−S−Fe2 = 77.644(17), Fe1−S−C1 =
117.19(6), Fe2−S−C1 = 119.74(7), Fe1−O−Fe2 = 102.81(6), Fe1−
O−Fe1* = 90.21(5), Fe2−O−Fe1* = 134.86(6).
is in a C2v symmetry, with a C2 axis running through the μ-
oxido ligand. A THF molecule is bound to each iron atom, and
the iron atom has a slightly distorted tetrahedral Fe(N)(O)2(S)
geometry. The Fe−O−Fe* angle (149.3(2)°) and the Fe−O
distance (1.7845(9) Å) are within the ranges of those reported
for FeIII−O−FeIII complexes, 131.7−180° for Fe−O−Fe and
1.7266(4)−1.792(1) Å for Fe−O.17−19 The Fe−S distance of 5
(2.2798(12) Å) is comparable to those of [(PhS)3Fe−O−
Fe(SPh)3]2− (2.287(2)−2.305(2) Å).20 The N−Fe−O angles
(102.62(14)−117.34(12)°) and the N−Fe−S angle
(126.05(10)°) are larger than the S−Fe−O angles
(100.74(4)−105.33(9)°) and the O−Fe−O angle (101.85(9)
°), probably because of the steric hindrance of the amide ligand.
between Fe2 and one of the phenyl groups of the SDpp ligand
with a shortest Fe−C distance of 2.9382 (16) Å is not
negligible. This weak iron-phenyl interaction leads to a slight
pyramidalization of Fe2, and Fe2 deviates by 0.2962(3) Å from
the least-square plane defined by amide nitrogen (N2), thiolate
sulfur (S), and oxygen (O) atoms. Similar weak Fe−C(arene)
interactions have been found in iron complexes having S(2,6-
Ar2C6H3) ligands,3b,c,4b,c,15 but usually their closest Fe−
C(arene) distances (2.272(2)−2.589(2) Å) are shorter than
that of 4. Cluster 4 contains two kinds of iron sites Fe1/Fe1*
and Fe2/Fe2* with a Fe(II)2Fe(III)2 mixed oxidation state, and
notably the Fe1−N (1.8834 (13) Å), Fe1−S (2.3870(5) Å),
and Fe1−O distances (1.8998(10) and 1.9310(13) Å) are
shorter than the Fe2−N (1.9089(15) Å), Fe2−S (2.4336(6)
Å), and Fe2−O (1.9358(10) Å) distances. This difference may
indicate that Fe1/Fe1* are ferric sites and Fe2/Fe2* are ferrous
sites. Thus far, several Fe4(μ3-O)2 clusters have been reported,
and most of the precedent clusters consist of octahedral
Fe(III)4 centers with bridging carboxylate ligands.16 Cluster 4 is
a unique type of Fe4(μ3-O)2 cluster because of its tetrahedral
iron atoms in the mixed Fe(II)2Fe(III)2 oxidation state and the
presence of thiolate ligands.
CONCLUDING REMARKS
■
The reactions of complex 1 with thiols and O2 provide a new
class of iron-oxido clusters carrying amide and thiolate ligands,
and the number of iron atoms in the clusters varies dependent
on the thiolate ligands. This work offers a new synthetic route
to iron-oxido clusters carrying sulfur ligands; however further
work will be required to model some metal clusters in biology.
For example, the reactions of iron-thiolate-amide complexes
with a mixture of O2 and elemental sulfur are probably
important to provide synthetic analogues of the active site of
the HCP. The reactions of 3a−b with iron and molybdenum
compounds together with elemental sulfur may provide Mo/
Fe/S/O clusters relevant to the FeMo-cofactor. These studies
are currently on going in our group.
EXPERIMENTAL SECTION
■
(d). Reaction of 1 with HSTip (Tip = 2,4,6-iPr3C6H2) in
the Presence of O2. The reaction of 1 with 1 equiv of HSTip
in THF at room temperature followed by treatment with 0.3
equiv of O2 at −40 °C resulted in the formation of an Fe(III)2
μ-oxido complex [{(Me3Si)2N}(TipS)(THF)Fe]2(μ-O) (5),
which crystallized as red needles in 11% yield (Scheme 1,
bottom). In the CV of 5 in THF, only an irreversible reduction
process was observed at −1.65 V vs Ag/AgNO3. The UV−vis
General Procedures. All reactions except for the synthesis of
DppS−SDpp were carried out using standard Schlenk techniques and
a glovebox under a nitrogen atmosphere. Hexane, hexamethyldisilox-
ane (HMDSO), toluene, and THF were purified by the method of
Grubbs et al.,21 where the solvents were passed over columns of
activated alumina and a supported copper catalyst supplied by Hansen
& Co. Ltd. Dry cyclohexane was purchased from Kanto Chemical Co.,
Inc., and was used as received. UV−vis spectra were measured on a
JASCO V560 spectrometer. Elemental analyses were recorded on a
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Table 1. Crystal Data for 2, 3a−b, 4·C6H14, 5, and DppS−SDpp
2
3a
3b
4·C6H14
5
DppS−SDpp
formula
fw
C48H92Fe4N4S4Si8
1301.59
C36H69Fe3N3OS3Si6
992.19
C48H93Fe3N3OS3Si6
1160.51
C66H112Fe4N4O2S2Si8
1505.82
C50H98Fe2N2O3S2Si4
1063.49
C36H26S2
522.72
temperature
crystal system
space group
a (Å)
−100
triclinic
−100
triclinic
−100
triclinic
−100
triclinic
−100
−100
monoclinic
C2/c (#15)
34.823(8)
10.771(2)
19.696(5)
monoclinic
P21/a (#14)
17.587(3)
13.356(3)
23.862(5)
P1 (#2)
P1 (#2)
P1 (#2)
P1 (#2)
̅
̅
̅
̅
9.3519(14)
12.756(2)
14.818(2)
82.532(6)
78.884(5)
81.637(5)
1706.6(5)
1
14.621(2)
15.555(3)
23.629(4)
82.513(5)
87.754(7)
77.228(5)
5195.9(16)
4
15.234(3)
19.699(3)
22.889(4)
73.301(6)
80.481(7)
89.422(7)
6483.7(18)
4
12.6761(12)
13.1696(8)
13.2939(10)
65.161(4)
81.878(4)
84.077(5)
1991.4(3)
1
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
122.306(3)
103.347(3)
6244(2)
4
5453.5(17)
8
Dcalc (g cm−3
μ(MoKα) (cm−1
2θmax (deg)
)
1.266
1.268
1.198
1.256
1.131
6.437
55.0
1.273
2.191
55.0
)
11.273
55.0
11.133
55.0
9.019
9.269
55.0
55.0
no. of data collected
no. of unique rflns
no. of variables
13633
41948
78261
23932
24801
7134
334
42906
12251
685
7431
22741
29422
9048
307
938
1123
388
a
R1
0.0325
0.0873
1.041
0.0643
0.1975
1.152
0.0792
0.2348
1.044
0.0289
0.0626
0.1868
0.0626
0.1702
1.106
b
wR2
0.0860
c
GOF
1.058
1.004
a
b
c
2
2
2
I > 2σ(I), R1 = ∑||Fo| − |Fc||/∑|Fo|. Refined with all data, wR2 = [{∑w(Fo − Fc2)2}/∑w(Fo )2]1/2. GOF = [{∑w(Fo −Fc2)2}/(No − Np)]1/2
,
where No and Np denote the numbers of reflection data and parameters.
LECO-CHNS-932 elemental analyzer where the crystalline samples
were sealed in silver capsules under nitrogen. CVs were recorded in
THF at room temperature using gold as the working electrode with
0.2 M [nBu4N][PF6] as the supporting electrolyte. The potentials are
referenced to Ag/AgNO3. The 1H NMR (600 MHz) and the 13C{1H}
NMR (151 MHz) were recorded on a JEOL ECA600 spectrometer.
H), −22.1 (6H, o- or m-H). UV−vis (hexane): λmax = 241 nm (ε =
22000 M−1 cm−1). Anal. Calcd for C36H69Fe3N3OS3Si6: C, 43.58; H,
7.01; N, 4.24; S, 9.70. Found: C, 43.34; H, 6.78; N, 3.92; S, 9.75. CV
(20 mM in THF): E1/2 = −0.28, −1.20 V (quasi-reversible).
Synthesis of [{(Me3Si)2N}Fe]3(μ3-O){μ-S(4-tBuC6H4)}3 (3b).
Complex 3b was synthesized from 1 (5.09 g, 13.5 mmol),
HS(4-tBuC6H4) (2.25 g, 13.5 mmol), and O2 (66 mL, 2.69 mmol),
in a similar manner to that used for 3a. Crystallization from hexane at
−30 °C yielded dark brown blocks of 3b (2.72 g, 52%). 1H NMR (600
MHz, C6D6): δ 17.5 (6H, o- or m-H), 7.9 (54H, SiMe3), 1.1 (27H,
tBu), −22.1 (6H, o- or m-H). UV−vis (hexane): λmax = 241 nm (ε =
30000 M−1 cm−1). Anal. Calcd for C48H93Fe3N3OS3Si6: C, 49.68; H,
8.08; N, 3.62; S, 8.29. Found: C, 49.40; H, 7.74; N, 3.63; S, 7.95. CV
(20 mM in THF): E1/2 = −0.33, −1.25 V (quasi-reversible).
1
The H and the 13C{1H} NMR chemical shifts are given in parts per
million (ppm) relative to the residual signals of the deuterated
solvents. Fe{N(SiMe3)2}2 (1),22 HSDpp,23 and HSTip24 were
prepared according to literature procedures. HSPh and HS-
(4-tBuC6H4) were purchased and used as received.
Synthesis of [{(Me3Si)2N}Fe2(μ-SPh){μ-N(SiMe3)2}]2(μ-SPh)2
(2). A toluene (5 mL) solution of HSPh (0.3 mL, 2.93 mmol) was
added dropwise to a toluene (5 mL) solution of 1 (1.10 g, 2.92 mmol)
at 0 °C. The reaction mixture became a dark reddish-brown
suspension immediately and was allowed to warm to room
temperature. After stirring at this temperature for 12 h, the mixture
was centrifuged to remove insoluble material. Upon standing the
solution at −40 °C, dark orange plates of 2 (0.045 g, 5%) were formed.
The mother liquor was concentrated and recrystallized to give a
second crop, 0.14 g (15%). 1H NMR (600 MHz, C6D6): major signals
appeared at δ 10.3 (Ph), 7.8 (SiMe3), 5.3 (SiMe3), −2.0 (Ph), −2.7
(SiMe3), −3.8 (SiMe3), −11.1 (Ph), −11.3 (Ph), −13.2 (Ph). UV−vis
(cyclohexane): featureless with a slow rise toward the UV region. Anal.
Calcd for C48H92Fe4N4S4Si8: C, 44.29; H, 7.12; N, 4.30; S, 9.85.
Found: C, 43.89; H, 7.07; N, 3.82; S, 10.14. CV (1 mM in THF): Epc
= −1.99 V, Epa = 0.23 V (irreversible).
Synthesis of [{(Me3Si)2N}2Fe2(μ-SDpp)]2(μ3-O)2 (4). A toluene
(10 mL) solution of HSDpp (0.59 g, 2.25 mmol) was added dropwise
to a toluene (10 mL) solution of 1 (0.85 g, 2.26 mmol) at room
temperature. After stirring for 2 h, O2 (17 mL, 0.69 mmol) was
bubbled into the solution using a gas-tight syringe at room
temperature. The resultant dark purple solution was stirred for 3 h
at room temperature to afford a dark reddish brown solution. The
solvent was removed under reduced pressure to give a black solid. The
black residue was extracted with toluene (5 mL), and the extract was
centrifuged to remove a small amount of insoluble material. Hexane
(15 mL) was layered on the solution to yield black blocks of 4·C6H14
(0.18 g, 21%). Cooling the mother liquor at −40 °C resulted in the
formation of colorless crystals of DppS−SDpp (0.12 g, 20%), which
were identified by X-ray diffraction analysis. 1H NMR (600 MHz,
C6D6): major signals appeared at δ 25.5 (SiMe3), 5.1 (SiMe3), 4.4
(SiMe3), 3.5 (Dpp), 2.8 (Dpp), 2.3 (Dpp), −1.8 (SiMe3), −9.2 (Dpp),
−16.4 (Dpp). UV−vis (hexane): λmax = 419 nm (ε = 6000 M−1 cm−1).
Anal. Calcd for C60H98Fe4N4O2S2Si8: C, 50.76; H, 6.96; N, 3.95; S,
4.52. Found: C, 51.10; H, 7.19; N, 3.58; S, 4.03. CV (2 mM in THF):
Epc = −2.48 V (irreversible).
Synthesis of [{(Me3Si)2N}Fe]3(μ3-O)(μ-SPh)3 (3a). A toluene (25
mL) solution of HSPh (1.4 mL, 13.7 mmol) was added dropwise to a
toluene (30 mL) solution of 1 (5.01 g, 13.3 mmol) at room
temperature. After stirring for 1 h, O2 (65 mL, 2.65 mmol) was
bubbled into the mixture using a gas-tight syringe. The reaction
mixture became a dark brown solution immediately. The mixture was
stirred for 3 h at room temperature, and was evaporated to dryness
under reduced pressure. The black residue was extracted with hexane
(18 mL), and the extract was centrifuged to remove a small amount of
insoluble material. Upon standing at room temperature, the solution
Synthesis of DppS−SDpp. The synthetic procedure reported by
Takaguchi et al.25 was modified as follows. HSDpp (0.89 g, 3.39
mmol) was dissolved in 30 mL of CHCl3. A CHCl3 (30 mL) solution
of Et3N (0.7 mL, 5.02 mmol) was added to the CHCl3 solution of
HSDpp. A CHCl3 solution (50 mL) of I2 (0.86 g, 3.39 mmol) was
1
deposited dark brown blocks of 3a (0.87 g, 20%). H NMR (600
MHz, C6D6): δ 17.4 (6H, o- or m-H), 8.0 (54H, SiMe3), −15.6 (3H, p-
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Inorganic Chemistry
Article
added to the reaction mixture to give a brown solution. The mixture
was stirred for 3 h at room temperature, and was washed with aqueous
saturated Na2S2O3. The organic layer was dried over MgSO4, and was
evaporated until dryness. The product was isolated as colorless crystals
Ministry of Education, Culture, Sports, Science, and Technol-
ogy, Japan. We thank Roger E. Cramer for his help in X-ray
crystallographic analysis and for careful reading of the
manuscript.
1
(0.56 g, 63%) from a mixture of CH2Cl2 and EtOH at −40 °C. H
NMR (600 MHz, CDCl3): δ 7.33 (t, JH−H = 7.6 Hz, 2H, p-CH of
Dpp), 7.27 (m, 4H, p-CH of Ph), 7.20 (m, 8H, o- or m-CH of Ph),
7.09 (d, JH−H = 7.6 Hz, 4H, m-CH of Dpp), 6.74 (m, 8H, o- or m-CH
of Ph). 13C{1H} NMR (151 MHz, CDCl3): δ 148.1, 141.7, 133.1,
130.1, 130.0, 128.4, 127.5, 126.7. UV−vis (hexane): λmax = 298 nm (ε
= 4500 M−1 cm−1), 337 nm (ε = 2100 M−1 cm−1). Anal. Calcd for
C36H26S2: C, 82.72; H, 5.01; S, 12.27. Found: C, 82.20; H, 5.41; S,
12.41. CV (4 mM in THF): Epc = −2.23 V (irreversible). Melting
point = 206−209 °C.
Synthesis of [{(Me3Si)2N}(TipS)(THF)Fe]2(μ-O) (5). A THF (15
mL) solution of HSTip (3.21 g, 13.6 mmol) was added dropwise to a
THF (15 mL) solution of 1 (5.11 g, 13.6 mmol) at room temperature.
After stirring for 1 h, O2 (100 mL, 4.08 mmol) was bubbled into the
solution using a gas-tight syringe at −40 °C. The reaction mixture
became a dark red solution immediately. The mixture was allowed to
warm to room temperature and was stirred for 6 h at room
temperature. The solvent was removed under reduced pressure to give
a dark red solid. The dark red residue was extracted with a mixture of
HMDSO (38 mL) and THF (15 mL), and the extract was centrifuged
to remove a small amount of insoluble material. Upon standing at −30
°C, red needles of 5 (0.80 g, 11%) were formed. 1H NMR (600 MHz,
C6D6): major signals appeared at δ 35.4, 29.2, 21.2, 14.3, 5.3, 2.6
(SiMe3), −3.8. UV−vis (hexane): λmax = 280 nm (ε = 9200 M−1
cm−1), 330 nm (ε = 6300 M−1 cm−1), 429 nm (ε = 6100 M−1 cm−1).
Anal. Calcd for C50H98Fe2N2O3S2Si4: C, 56.47; H, 9.29; N, 2.63; S,
6.03. Found: C, 56.84; H, 9.53; N, 2.23; S, 6.53. CV (2 mM in THF):
Epc = −1.65 V (irreversible).
X-ray Crystal Structure Determination. Crystallographic data
and refinement parameters for 2−5 and DppS−SDpp are summarized
in Table 1. Single crystals were coated with oil (immersion Oil, type B:
Code 1248, Cargille laboratories, Inc.) and mounted on loops.
Diffraction data were collected at −100 °C under a cold nitrogen
stream on a Rigaku AFC8 equipped with a Rigaku Saturn 70 CCD/
Micromax using graphite-monochromatized Mo Kα radiation (λ =
0.710690 Å). Six preliminary data frames were measured at 0.5°
increments of ω, to assess crystal quality and preliminary unit cell
parameters. The intensity images were also measured at 0.5° intervals
of ω. The frame data were integrated using the CrystalClear program
package, and the data sets were corrected for absorption using a
REQAB program. The calculations were performed with the
CrystalStructure program package. All structures were solved by
direct methods and refined by full-matrix least-squares. Anisotropic
refinement was applied to all non-hydrogen atoms except for
disordered atoms (refined isotropically), and all hydrogen atoms
were put at calculated positions. Four tBu groups in 3b are disordered
over two positions in 1:1, 1:1, 2:3, or 1:1 ratios. Six Me3Si groups in 3b
are disordered over two positions in 1:1, 7:3, 1:1, 1:1, 3:2, or 7:3 ratios.
A SIMU restraint was applied to the C71−C76 atoms in 3b.
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ASSOCIATED CONTENT
* Supporting Information
Crystallographic data in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org.
■
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AUTHOR INFORMATION
Corresponding Author
*E-mail: i45100a@nucc.cc.nagoya-u.ac.jp.
Notes
■
The authors declare no competing financial interest.
W.; Scheurer, A.; Reimann, U.; Hampel, F.; Trieflinger, C.; Buschel,
̈
M.; Daub, J.; Trautwein, A. X.; Schunemann, V.; Coropceanu, V.
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ACKNOWLEDGMENTS
This research was financially supported by the Grant-in-Aid for
Specially Promoted Research (No. 23000007) from the
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