Synthesis and characterization of heteroleptic iron(II) thiolate complexes with weak iron-arene interactions

Article abstract of DOI:10.1016/j.jorganchem.2007.06.027

Selective preparation and characterization of a series of heteroleptic thiolate complexes of iron(II) are described. The compounds were synthesized by treatment of iron bis-amide Fe{N(SiMe₃)₂}₂ (1) with 1 equiv. of terphenyl thiols HS(2,6-(aryl)₂C₆H₃) followed by addition of another equivalent of different thiol. An amide-thiolate intermediate [{(Me₃Si)₂N}Fe]₂(μ-SDpp)₂ (2; Dpp = 2,6-Ph₂C₆H₃) was isolated from the 1:1 reaction of 1 and HSDpp. The X-ray crystal structures of all new thiolate complexes have been determined. The compounds crystallize as monomers or dimers, dependent on the substituents. They consist of distorted tetrahedral or trigonal-planar iron centers with weak interactions between the aromatic rings of thiolate ligands, where the Fe-C(arene) contact is 2.272(2) A? at shortest. The stronger iron-arene interaction appears to induce more pyramidalized geometry at the iron center.

Full text of DOI:10.1016/j.jorganchem.2007.06.027

Journal of Organometallic Chemistry 692 (2007) 4792–4799
www.elsevier.com/locate/jorganchem
Synthesis and characterization of heteroleptic iron(II)
thiolate complexes with weak iron–arene interactions
*
Shun Ohta, Yasuhiro Ohki, Yohei Ikagawa, Rie Suizu, 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
Received 12 May 2007; received in revised form 19 June 2007; accepted 19 June 2007
Available online 24 June 2007
Dedicated to Professor Gerhard Erker, my friend, on the occassion of his 60th birthday.
Abstract
Selective preparation and characterization of a series of heteroleptic thiolate complexes of iron(II) are described. The compounds were
synthesized by treatment of iron bis-amide Fe{N(SiMe3)2}2 (1) with 1 equiv. of terphenyl thiols HS(2,6-(aryl)2C6H3) followed by addi-
tion of another equivalent of different thiol. An amide–thiolate intermediate [{(Me3Si)2N}Fe]2(l-SDpp)2 (2; Dpp = 2,6-Ph2C6H3) was
isolated from the 1:1 reaction of 1 and HSDpp. The X-ray crystal structures of all new thiolate complexes have been determined.
The compounds crystallize as monomers or dimers, dependent on the substituents. They consist of distorted tetrahedral or trigonal-pla-
˚
nar iron centers with weak interactions between the aromatic rings of thiolate ligands, where the Fe–C(arene) contact is 2.272(2) A at
shortest. The stronger iron–arene interaction appears to induce more pyramidalized geometry at the iron center.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Iron; Thiolate; Heteroleptic complexes; Iron–arene interaction; Terphenyl group; Experimental methods
1. Introduction
ride and thiolate anions in polar solvents [1]. In such an
ion-exchange reaction, as many thiolates as possible attach
to the iron center and it generally ends up with tetrakis-
thiolate dianions. On the other hand, an acid–base reaction
between iron–amide complex Fe{N(SiMe3)2}2 [3] and thi-
ols in non-polar solvents produces non-ionic compounds
and limits the number of thiolate ligands incorporated.
This method also appears to be suitable for the preparation
of heteroleptic thiolate complexes, as demonstrated for the
synthesis of Fe3{N(SiMe3)2}2(l-STip)4 (Tip = 2,4,6-iPr3-
C6H2) [4]. The importance of heteroleptic thiolate com-
plexes is in their potential as precursors for unprecedented
types of iron–sulfur clusters, which are relevant to the
metal centers in proteins. We have previously succeeded
to reproduce the [8Fe–7S] core of nitrogenase P-cluster
from the reaction of a heteroleptic amide–thiolate complex
Fe3{N(SiMe3)2}2(l-STip)4 with HSTip, elemental sulfur,
and tetramethylthiourea [5]. More recently, a heterolep-
tic iron–thiolate complex [(TipS)Fe]2(l-SDmp)2 (Dmp =
Synthetic studies on iron thiolate complexes initiated in
mid 1970s in relation to the rubredoxin (Rd) center. The
model compounds, in which oxidation state is FeII in
[Fe(SR)4]2ꢀ or FeIII in [Fe(SR)4]ꢀ, have been prepared
and their structures and spectroscopic properties have been
compared with those for Rd to provide useful insights [1].
Later, they became also valuable as the precursors for a
number of iron–sulfur clusters. Preparations of [2Fe–2S],
[3Fe–4S], [4Fe–4S], and [6Fe–6S] clusters have been accom-
plished by treatment of iron–thiolate complexes with ele-
mental sulfur [1a,2]. Notably, iron–thiolates used for
cluster synthesis have been mostly limited to anionic and
homoleptic compounds [Fe(SR)4]2ꢀ, and the common
pathway to produce them is the reaction between iron chlo-
*
Corresponding author.
E-mail address: i45100a@nucc.cc.nagoya-u.ac.jp (K. Tatsumi).
2,6-(mesityl)2C6H3) appeared to serve as a suitable
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.06.027

S. Ohta et al. / Journal of Organometallic Chemistry 692 (2007) 4792–4799
4793
Dmp
i) S8
i) BuLi, -78 °C
MgBr
Tol
SH
ii) LiAlH4
iii) H+
S
Cl
Cl
Tol
Tol
Tol
ii) 2 TolMgBr
Fe
Fe
S
S
S
S
S
8 S
S
S
Dmp
(Tol = 4-CH3-C6H4)
S
Fe S
Fe
Fe
Fe
Fe
4
Fe
Fe
S
S
DtpSH
S
Fe
Dmp
Dmp
S
S
S
Scheme 2.
Tip
[(TipS)Fe]2(μ-SDmp)2
Scheme 1.
M(SAr*)2 (M = Cr, Mn, Fe, Co, Ni, Zn) [8]. In this
regard, various ortho-substituted aryl thiols were used
to provide a certain steric bulk around the sulfur atom.
One of bulky thiols in this study, DtpSH (Dtp = 2,6-(4-
CH3C6H4)2C6H3), was prepared by lithiation of 1,3-
dichlorobenzene with n-BuLi and the subsequent addition
of p-tolyl Grignard reagents to generate 1-MgBr-2,6-(p-
tolyl)2-benzene, followed by treatment with elemental
sulfur (Scheme 2). The method to generate terphenyl
anion from 1,3-dichlorobenzene has been established by
Saednya and Hart [9].
Dmp
Dxp
Dpp
(2,6-di(phenyl)phenyl)
(2,6-di(mesityl)phenyl)
(2,6-di(xylyl)phenyl)
Si
Si
Btp
(2,4,6-tri(isopropyl)phenyl) (2,6-bis(trimethylsilyl)phenyl)
Dtp
p-tolyl)phenyl)
Tip
(2,6-di(
2.2. Synthesis of Fe(II)thiolate complexes
Chart 1. Bulky aryl substituents used in this study.
Acid–base reactions between an iron–amide complex
Fe{N(SiMe3)2}2 (1) and various bulky thiols were
attempted, since an amide ligand on iron is known to
serve as a base to deprotonate from added thiols. An
important step to accomplish the formation of heterolep-
tic thiolate complexes is the selective generation of
mono-thiolate species of iron, which is denoted as
[{(Me3Si)2N}Fe(SR)]n or its solvent adducts. As reported
by Power and co-workers, the reaction of 1 with one
equiv of DmpSH produces monomeric {(Me3Si)2N}-
Fe(SDmp) [7a]. We and Henkel et al. have also demon-
strated that the reactions of 1 with one equiv of
HS(SiPh3) or HSBtp (Btp = 2,6-bis(trimethylsilyl)phenyl)
give rise to dinuclear thiolate complexes [{(Me3Si)2N}-
Fe]2(l-SR)2 (R = SiPh3 or Btp) [10]. In a similar manner,
relevant reactions with bulky thiols DxpSH (Dxp = 2,6-
(2,6-Me2C6H3)2C6H3) [11], DppSH (Dpp = 2,6-Ph2C6H3)
[12], and DtpSH are expected to produce [{(Me3Si)2N}-
Fe(SAr)]n (n = 1 or 2). Indeed, a dimeric compound
[{(Me3Si)2N}Fe]2(l-SDpp)2 (2) was isolated in 70% yield
from the 1:1 reaction between 1 and HSDpp. Assuming
that similar mono-thiolate complexes are generated in
the reactions with DxpSH and DtpSH, another equiva-
lent of different thiol was added to the 1:1 mixture of 1
and these thiols. As summarized in Scheme 3 and Table
1, five heteroleptic thiolate complexes 3–7 were synthe-
sized according to this pathway. Additionally, three new
homoleptic thiolate complexes 8–10 were also prepared
by addition of 2 equiv. of bulky thiols to 1. These
reactions smoothly underwent and provided the products
in high yields as crystals under mild conditions. All com-
pounds are sensitive to air and moisture and need to be
handled under inert conditions, while they are thermally
stable even after several days in boiling toluene.
precursor for an [8Fe–7S] cluster, [Fe8S7(SDmp)2]-
(l-SDmp)2(l-STip), the structure of which is topologically
similar to the FeMo-cofactor of nitrogenase (Scheme 1) [6].
Since its formation is simply achieved by addition of
elemental sulfur to a solution of thiolate complex [(TipS)-
Fe]2(l-SDmp)2, variety of thiolate in the precursor likely
makes an influence on the structure of resultant iron–sulfur
clusters. While some relevant homoleptic thiolate com-
plexes have been reported with bulky thiolates [7,8], we
examined the selective preparation of a series of heterolep-
tic thiolate complexes of iron. Some of bulky thiolates used
in this study are able to weakly coordinate to the metal cen-
ter with their ortho-aryl substituents (Chart 1), and stabilize
the products as monomeric or dimeric forms.
2. Results and discussion
2.1. Synthesis of ortho-substituted thiols
Iron(II) thiolate complexes with a general formulae
{Fe(SR)2}n readily become polymeric (n ꢁ 1) via forma-
tion of sulfur bridges between iron centers that satisfy the
tetrahedral coordination of each iron center. Since the
formation of coordination polymers hampers the subse-
quent use in reactions, this needs to be avoided to main-
tain homogeneous conditions in organic solvents. An
effective way to retard the bridging mode of thiolates is
to incorporate a bulky substituent on the sulfur atom.
For instance, a bulky SDmp thiolate has been shown
to stabilize low-coordinate organometallic and inorganic
compounds as monomeric forms [7], and more bulky
SAr* (Ar* = 2,6-(2,4,6-iPr3C6H2)2C6H3) is able to produce
a series of divalent, quasi-two-coordinate complexes

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S. Ohta et al. / Journal of Organometallic Chemistry 692 (2007) 4792–4799
[(Ar'S)Fe]2(μ-SAr)2(3-6)
or
HSAr
HSAr'
Si
Si
Si
Si
N
Fe N
Fe(SDmp)(SBtp)(7)
or
1
[Fe(SAr)2]1or2(8-10)
Si
N
Fe
S
Si
HSAr
HSAr'
Ar
(Ar = Dmp)
or
Ar
S
Si
Si
Si
Si
N Fe
Fe N
S
Ar
(Ar = Dpp (2), Btp)
Fig. 1. Molecular structure of [{(Me3Si)2N}Fe]2(l-SDpp)2 (2), showing
50% probability ellipsoids. Hydrogen atoms are omitted for clarity.
Scheme 3.
Table 1
Substituents and yields of complexes 3–10
3
4
5
6
7
8
9
10
Ar
Dpp
Btp
85
Dpp Dtp Dxp Dmp Dpp Dtp Dxp
Ar0
Tip
94
Tip
62
Tip
89
Btp
56
Dpp Dtp Dxp
75 89 95
Yield
2.3. X-ray crystal structures of Fe(II) thiolate complexes
All new thiolate complexes 2–10 have been identified by
means of X-ray crystallography. The structures of 2–6 and
8–9 are dimeric, whereas 7 and 10 are monomers. Selected
bond distances and angles are given in Table 2. Molecular
structures of representative complexes 2, 5, 7, and 10 are
shown in Figs. 1–4. The structures of dimeric complexes
2–6 and 8 have a crystallographically required center of
symmetry at the midpoint between two iron centers. Thus
the Fe2S2 rings in these complexes are planar and there
are two independent Fe–Sbridge distances. Whereas complex
9 was analyzed as an entire molecule without symmetric
center between iron atoms, the Fe2S2 ring is planar with
torsion S(1)–Fe(1)–Fe(2)–S(2) angle of 178.89(9)ꢁ and the
bond distances and angles around two iron centers are
Fig. 2. Molecular structure of [(TipS)Fe]2(l-SDtp)2 (5), showing 50%
probability ellipsoids. Hydrogen atoms are omitted for clarity.
almost identical. As expected, the Fe–Sbridge bond lengths
are significantly longer than the Fe–Sterminal distances.
The Fe–Fe distances which vary between 2.9086(4) and
˚
3.2093(4) A are indicative of no direct Fe–Fe interaction,
although the Fe–S–Fe angles are acute (76.09(2)–
84.342(15)ꢁ). The substituents on bridging sulfur atoms
are mutually trans to each other with respect to the Fe2S2
ring. It is notable that terphenyl thiolates occupy the bridg-
ing positions, and one of aryl substituents in the bridging
Table 2
Selected data for [{(Me3Si)2N}Fe]2(l-SDpp) (2) and [Fe(SAr)(SAr0)]n, (3–10, n = 1 or 2)
Compound
Ar
Ar0
Yield (%)
Fe–C(arene)
Fe–S–Fe
(l-S)–Fe–(l-S)
Fe–Sbridge
Fe–Sterminal
Fe–Fe
2
3
4
5
6
7
8
9
Dpp
Dpp
Dpp
Dtp
Dxp
Dmp
Dpp
Dtp
–
70
85
94
62
89
56
75
89
2.589(2)
2.579(2)
2.341(3)
2.272(2)
2.438(4)
2.389(2)
2.417(3)
2.335(9)
2.315(9)
2.437(4)
84.342(15)
80.37(2)
79.39(3)
76.09(2)
80.38(3)
–
78.13(2)
77.49(10)
77.36(9)
–
95.658(19)
99.63(2)
100.61(3)
103.91(2)
99.62(3)
–
101.87(2)
102.60(11)
102.54(11)
–
2.3790(6), 2.4013(4)
2.3404(10), 2.3689(7)
2.3682(10), 2.3631(11)
2.3498(6), 2.3698(6)
2.3749(10), 2.3898(10)
–
2.3396(7), 2.3686(6)
2.364(2), 2.378(2)
2.376(3), 2.368(2)
–
–
3.2093(4)
3.0389(6)
3.0218(8)
2.9086(4)
3.0747(7)
–
Btp
Tip
Tip
Tip
Btp
Dpp
Dtp
2.2851(8)
2.2593(10)
2.2504(6)
2.2730(12)
2.2782(7), 2.2497(6)
2.2794(6)
2.9673(5)
2.966(2)
2.265(2), 2.268(3)
10
Dxp
Dxp
95
2.2497(9), 2.2905(13)
–

S. Ohta et al. / Journal of Organometallic Chemistry 692 (2007) 4792–4799
4795
interact with one of the ortho-aryl groups where the Fe–
˚
C(arene) distances are 2.389(2) (7) and 2.437(4) (10) A. Sim-
ilar Fe–C(arene) interactions are found in relevant mono-
˚
meric complexes Fe(SDmp)2 (2.470(3), 2.535(3) A) and
˚
{(Me3Si)2N}Fe(SDmp) (2.422–2.459 A) [7a]. The Fe–S
˚
bond lengths are 2.2782(7) and 2.2497(6) A (7) and
˚
2.2497(9) and 2.2905(13) A (10), which are comparable to
˚
those observed in Fe(SDmp)2 (2.275(2) and 2.277(2) A).
2.4. Properties
The iron–thiolate complexes 2–10 are paramagnetic and
1
their H NMR spectra exhibited dramatically shifted sig-
nals from the diamagnetic values for free thiols. For
instance, five signals for the Dpp group in 2 were observed
at d 8.8, 0.3, ꢀ2.6, ꢀ9.9, and ꢀ15.8, while the SiMe3 reso-
nance appeared at d 16.6. Whereas satisfactory assignments
for complexes 3–8 were not successful, the complexity of
the NMR spectra of 4–6 and 8 indicated that the dimeric
framework is retained in solution. Interestingly, the 1H
NMR spectrum of 10 shows equivalent Dxp groups, indi-
cating the reversible coordination of xylyl groups to iron
on the NMR time scale.
Fig. 3. Molecular structure of Fe(SDmp)(SBtp) (7), showing 50%
probability ellipsoids. Hydrogen atoms are omitted for clarity.
In the light of paramagnetic nature of 2–10, the mag-
netic moments in solution were determined by the Evans
method [14]. The monomeric complexes 7 and 10 afforded
magnetic moments 5.3 and 5.1 lB, respectively, which are
consistent with four unpaired electrons and a quintet
ground state for d6 high-spin configuration (spin only
value: 4.89 lB). The magnetic moments for dimeric com-
plexes 2–6, 8, and 9 are lower and between 2.3 and
4.6 lB, owing to antiferromagnetic coupling between the
metal centers. The UV–Vis spectra of the iron–thiolate
complexes are almost featureless, and their major charac-
teristic is a gradual rise in absorption toward the higher
energy region of the spectrum.
Fig. 4. Molecular structure of Fe(SDxp)2 (10), showing 50% probability
ellipsoids. Hydrogen atoms are omitted for clarity.
thiolate ligands is oriented toward the vacant site of each
iron center. The weak iron–arene interaction is also
indicated by the slightly pyramidalized geometry of iron
centers, with the sum of S–Fe–S angles in the range of
330.4–335.0ꢁ for 4–6 and 8–9 that exhibit close contact
3. Conclusion
˚
between arene and iron (<2.5 A). This supplementary
The use of ortho-aryl thiols in acid–base reactions with
Fe{N(SiMe3)2}2 appeared to generate iron amide–thiolate
species [{(Me3Si)2N}Fe(SAr)]n (n = 1 or 2), and the subse-
quent treatment with different thiols allowed the selective
synthesis of a series of heteroleptic thiolate complexes.
The bulky substituents efficiently stabilize the compounds
as monomers or dimers with weak Fe–arene interactions,
which in turn make the compounds highly soluble in
organic solvents. While the iron centers are covered by
bulky thiolate ligands, the compounds are air-sensitive
and highly reactive. This feature would be useful for fur-
ther reactions with elemental sulfur, donor molecules,
and protic reagents.
Fe–C(arene) interaction efficiently stabilizes the dimeric
form of thiolate complexes, with varying the degrees of
interaction. The strongest interaction can be seen in 5
˚
where the Fe–C(arene) distance is as short as 2.272(2) A
(Fe–C(19)). This is slightly longer than those in iron–arene
˚
compounds (1.92–2.27 A) in which iron center interacts
with g2–g6 p-systems [13]. The Fe–C(arene) distances
appeared to be correlated to the (l-S)–Fe–(l-S) angles,
since stronger Fe–C(arene) interaction leads to more pyra-
midalized geometry at the iron center that requires wider
(l-S)–Fe–(l-S) angles.
In contrast to dimers, both compounds 7 and 10 are sta-
bilized as monomers, which is due to larger steric require-
ments of the bulky substituents. The differences between 7
and 10 are the ortho-substituents in one of thiolates, which
are SiMe3 in 7 and xylyl in 10. The structural features
observed in 7 and 10 are common, and both iron centers
4. Experimental
All manipulations were carried out under nitrogen
atmosphere using standard Schlenk techniques and glove

4796
S. Ohta et al. / Journal of Organometallic Chemistry 692 (2007) 4792–4799
boxes. THF, hexane, and toluene were purified by the
method of Grubbs, where the solvents were passed over
columns of activated alumina and supported copper
catalyst supplied by Hansen & Co. Ltd. Degassed and
distilled solvents from sodium benzophenone ketyl (hex-
ane and toluene) were also used. 1H NMR (600 MHz)
and 13C{1H} NMR (151 MHz) were recorded on a JEOL
ECA600 spectrometer. 1H NMR chemical shifts are
given in ppm relative to the residual protons of
deuterated solvents. 13C{1H} NMR chemical shifts are
referenced to signals of C6D6. UV–Vis spectra were
measured on a JASCO V560 spectrometer. Elemental
analyses were performed on a LECO CHNS-932 micro-
analyzer where the samples were sealed into silver
capsules in a glovebox. FAB mass spectra were obtained
on a JEOL JMS-LCMATE mass spectrometer under a
stream of high energy Xe gas, where m-nitrobenzyl
alcohol was used as the matrix. Iron(II) bis-amide
Fe{N(SiMe3)2}2 [3], DmpSH [7a], DxpSH [11], DppSH
[12], BtpSH [15], and TipSH [16] were prepared accord-
ing to the literature procedures. Other chemicals were
used as received.
4.2. Synthesis of [{(Me3Si)2N}Fe]2(l-SDpp)2 (2)
To a solution of Fe{N(SiMe3)2}2 (0.500 g, 1.33 mmol) in
15 mL of toluene was added a solution of DppSH (0.348 g,
1.33 mmol) in 15 mL of toluene. The reaction mixture was
left stirring for 2 h and then evaporated. The residue was
extracted with toluene (5 mL) and centrifuged. The solu-
tion was layered with hexane (20 mL) to afford
[{(Me3Si)2N}Fe]2(l-SDpp)2 (2) (0.444 g, 0.465 mmol,
70%) as yellow crystals. 1H NMR (600 MHz, C6D6): d
16.6 (SiMe3), 8.8 (Dpp), 0.3 (Dpp), ꢀ2.6 (Dpp), ꢀ9.9
(Dpp), ꢀ15.8 (Dpp). UV–Vis (cyclohexane, kmax, nm (e,
M
ꢀ1 cmꢀ1)): 347 (1600), 298 (sh, 5100). Anal. Calc. for
C48H62N2Fe2S2Si4: C, 60.36; H, 6.54; N, 2.93; S, 6.71.
Found: C, 59.90; H, 6.05; N, 2.85; S, 6.72%. leff (Evans
method, 296 K): 4.6 lB.
4.3. Synthesis of [(BtpS)Fe]2(l-SDpp)2 (3)
To a solution of Fe{N(SiMe3)2}2 (1.00 g, 2.66 mmol) in
20 mL of toluene was added a solution of DppSH (0.697 g,
2.66 mmol) in 20 mL of toluene, followed by dropwise
addition of a solution of BtpSH (0.677 g, 2.66 mmol) in
20 mL of toluene. After 2 h, the solution was concentrated
under reduced pressure to ca. 10 mL. An orange powder
formed was collected on a frit. Crystallization from toluene
4.1. Synthesis of 2,6-di-p-tolylbenzenethiol (DtpSH)
A
hexane solution of n-BuLi (1.56 M, 45.0 mL,
1
70.2 mmol) was added dropwise from a dropping funnel
to a solution of 1,3-dichlorobenzene (10.3 g, 70.1 mmol)
in THF (200 mL) at ꢀ78 ꢁC over a period of 10 min,
and the reaction mixture was stirred for 1.5 h at
ꢀ78 ꢁC. To the resulting white slurry was slowly added
a THF solution of p-tolylmagnesium bromide (1.0 M,
147 mL, 147 mmol) from a dropping funnel at ꢀ78 ꢁC
over a period of 30 min. After 1 h, the mixture was
allowed to warm to room temperature and refluxed for
2 h. It was cooled in an ice bath and elemental sulfur
(11.2 g, 350 mmol) was added to it under positive pres-
sure of nitrogen. The mixture was allowed to warm to
room temperature and stirred for 3 h. LiAlH4 (8.0 g,
210 mmol) was added to it little by little at 0 ꢁC and
the mixture was stirred overnight at room temperature.
The resulting gray slurry was quenched with dilute HCl
at 0 ꢁC. After removal of THF under reduced pressure,
the aqueous mixture was extracted with CH2Cl2
(300 mL · 4) and the organic layer was dried over
MgSO4. The solvent was removed in vacuo and crystalli-
zation of the residue from hot ethyl acetate gave DtpSH
at ꢀ20 ꢁC yielded 3 (1.29 g, 85%) as orange crystals. H
NMR (600 MHz, C6D6): major signals appeared at d
17.1, 15.9, 3.3 (SiMe3), 2.5, ꢀ4.1, ꢀ5.7. UV–Vis (cyclohex-
ane, kmax, nm (e, Mꢀ1 cmꢀ1)): 427 (2100), 298 (sh, 4600).
Anal. Calc. for C60H68Fe2S4Si4: C, 63.01; H, 6.00; S,
11.02. Found: C, 63.13; H, 6.00; S, 11.24%. leff (Evans
method, 296 K): 3.5 lB.
4.4. Synthesis of [(TipS)Fe]2(l-SDpp)2 (4)
Complex 4 was prepared from Fe{N(SiMe3)2}2 (1.00 g,
2.66 mmol), DppSH (0.697 g, 2.66 mmol), and TipSH
(0.628 g, 2.66 mmol) in a similar manner to that used for 3.
Crystallization from toluene at ꢀ20 ꢁC yielded 4 (1.38 g,
1.25 mmol, 94%) as red crystals. 1H NMR (600 MHz,
C6D6): major signals appeared at d 35.0, 18.5, 16.5, 16.1,
15.5, 8.7, 6.2, 5.0, 4.3, 2.2, ꢀ6.3, ꢀ12.1. UV–Vis (cyclohex-
ane, kmax, nm (e, Mꢀ1 cmꢀ1)): 403 (3300). Anal. Calc. for
C66H72Fe2S4: C, 71.72; H, 6.57; S, 11.61. Found: C, 71.57;
H, 6.67; S, 11.49%. leff (Evans method, 294 K): 3.8 lB.
1
(13.5 g, 46.5 mmol, 66%) as colorless crystals. H NMR
4.5. Synthesis of [(TipS)Fe]2(l-SDtp)2 (5)
(600 MHz, C6D6): d 7.32 (d, JH–H = 7.9 Hz, 4H, o- or
m-CH of p-tol), 7.13 (d, JH–H = 7.6 Hz, 2H, m-CH of
Dtp), 6.98 (d, JH–H = 7.9 Hz, 4H, o- or m-CH of p-tol),
6.97 (t, JH–H = 7.6 Hz, 1H, p-CH of Dtp), 3.62 (s, 1H,
SH), 2.10 (s, 6H, p-CH3 of p-tol). 13C{1H} NMR
(151 MHz, C6D6): d 141.4, 139.3, 137.4, 131.9, 129.8,
129.7, 129.6, 124.7, 21.2. FAB-MS (m-NBA, Xe): 290
(M+, 100). Anal. Calc. for C20H18S: C, 82.71; H, 6.25;
S, 11.04. Found: C, 82.23; H, 5.94; S, 10.61%.
Complex 5 was prepared from Fe{N(SiMe3)2}2 (0.520 g,
1.38 mmol), DtpSH (0.400 g, 1.38 mmol), and TipSH
(0.330 g, 1.40 mmol) in a similar manner to that used for
3. Crystallization from toluene at ꢀ20 ꢁC yielded 5
(0.500 g, 0.430 mmol, 62%) as red crystals. 1H NMR
(600 MHz, C6D6): major signals appeared at d 38.0, 17.6,
15.6, 14.8, 7.9, 5.9, 5.4, 5.0, 4.4, 1.8, 1.0, ꢀ5.6, ꢀ14.2.
UV–Vis (cyclohexane, kmax, nm (e, Mꢀ1 cmꢀ1)): 430

S. Ohta et al. / Journal of Organometallic Chemistry 692 (2007) 4792–4799
4797
(1800). Anal. Calc. for C70H80Fe2S4: C, 72.40; H, 6.94; S,
11.04. Found: C, 72.67; H, 6.84; S, 10.74%. leff (Evans
method, 295 K): 2.5 lB.
M
ꢀ1 cmꢀ1)): 346 (1200). Anal. Calc. for C80H68Fe2S4: C,
75.70; H, 5.40; S, 10.10. Found: C, 75.43; H, 5.17; S,
10.00%. The magnetic moment of 9 was not measured
because of its low solubility.
4.6. Synthesis of [(TipS)Fe]2 (l-SDxp)2 Æ C7H8(6 Æ C7H8)
4.10. Synthesis of Fe(SDxp)2 (10)
Complex 6 was prepared from Fe{N(SiMe3)2}2 (1.00 g,
2.66 mmol), DxpSH (0.846 g, 2.66 mmol), and TipSH
(0.628 g, 2.66 mmol) in a similar manner to that used for
3. Crystallization from toluene at ꢀ20 ꢁC yielded 6 Æ C7H8
(1.55 g, 1.18 mmol, 89%) as red crystals. 1H NMR
(600 MHz, C6D6): major signals appeared at d 28.5, 19.2,
16.5, 12.6, 8.8, 7.9, 2.1, ꢀ2.0, ꢀ15.9. UV–Vis (cyclohexane,
To a solution of Fe{N(SiMe3)2}2 (0.500 g, 1.33 mmol) in
toluene (20 mL) was added a solution of DxpSH (0.846 g,
2.66 mmol) in toluene (20 mL). The reaction mixture was
left stirring for 2 h and then evaporated in vacuo. The res-
idue was extracted with toluene (5 mL) and centrifuged.
The solution was layered with hexane (20 mL) to afford
Fe(SDxp)2 (10) (0.871 g, 1.26 mmol, 95%) as red crystals.
1H NMR (600 MHz, C6D6): d 49.2 (24H, –CH3), 6.7
(4H, m-C6H3 or p-xylyl), ꢀ22.2 (8H, m-xylyl), ꢀ26.1
(2H + 4H, p-C6H3 and m-C6H3 or p-xylyl). UV–Vis (cyclo-
hexane, kmax, nm (e, Mꢀ1 cmꢀ1)): 452 (300), 395 (300), 287
(sh, 750). Anal. Calc. for C44H42FeS2: C, 76.50; H, 6.13; S,
9.28. Found: C, 76.57; H, 5.91; S, 9.41%. leff (Evans
method, 297 K): 5.1 lB.
k
max, nm (e, Mꢀ1 cmꢀ1)): 333 (430), 283 (sh, 900). Anal.
Calc. for C74H88Fe2S4 Æ C7H8: C, 74.29; H, 7.39; S, 9.79.
Found: C, 74.34; H, 7.09; S, 9.71%. leff (Evans method,
295 K): 2.4 lB.
4.7. Synthesis of Fe(SDmp)(SBtp) (7)
Complex 7 was prepared from Fe{N(SiMe3)2}2 (1.00 g,
2.66 mmol), DmpSH (0.920 g, 2.66 mmol), and BtpSH
(0.676 g, 2.66 mmol) in a similar manner to that used for
3. Crystallization from hexane at ꢀ20 ꢁC yielded 7
(0.974 g, 1.49 mmol, 56%) as orange crystals. 1H NMR
(600 MHz, C6D6): major signals appeared at d 56.1, 37.5,
9.8 (SiMe3), 3.9. UV–Vis (cyclohexane, kmax, nm (e,
4.11. X-ray structural analysis
Crystallographic data are summarized in Table 3. Crys-
tals of DtpSH and 2–10 were mounted on a loop using oil
(CryoLoop, Immersion Oil, Type B or Paraton, Hampton
Research Corp.) and set on a Rigaku AFC-8 instrument
equipped with a Mercury CCD detector, with a Saturn
CCD detector, or on a Rigaku RA-Micro007 with a Saturn
CCD detector by using graphite-monochromated Mo Ka
M
ꢀ1 cmꢀ1)): 287 (sh, 2300). Anal. Calc. for C36H46FeS2Si2:
C, 66.02; H, 7.08; S, 9.79. Found: C, 66.19; H, 7.11; S,
9.63%. leff (Evans method, 296 K): 5.3 lB.
˚
4.8. Synthesis of [(DppS)Fe]2(l-SDpp)2 (8)
radiation (k = 0.710690 A) under a cold nitrogen stream.
The frame data were integrated and corrected for absorp-
tion with the Rigaku/MSC CrystalClear package. The
structures were solved by direct methods and standard dif-
ference map techniques, and were refined with full-matrix
least-square procedures on F by a Rigaku/MSC Crystal-
Structure package. Anisotropic refinement was applied to
all non-hydrogen atoms except for the disordered groups.
Methyl groups bound to Si(2) in 2 and 7, the ortho-iPr
groups of STip ligand in 4 and 6 Æ C7H8, one of the xylyl
groups in 6 Æ C7H8, and one of the mesityl groups in 7 are
disordered over two positions with 50:50 occupancy fac-
tors. The para-iPr group of STip ligand in 4 is disordered
over two positions with 60:40 occupancy factors. The crys-
tal solvent toluene is disordered in 3 Æ C7H8 and 6 Æ C7H8
over two positions with 50:50 occupancy factors. All
hydrogen atoms were placed at calculated positions. Addi-
tional crystallographic data are given in the Supporting
Information.
To a solution of Fe{N(SiMe3)2}2 (1.00 g, 2.66 mmol) in
toluene (20 mL) was added a solution of DppSH (1.39 g,
5.31 mmol) in toluene (40 mL). The reaction mixture gave
a red suspension over the course of a few hours. The suspen-
sion was concentrated in vacuo to ca. 10 mL. The red pow-
der was collected on a frit and washed with hexane.
Crystallization from toluene at ꢀ20 ꢁC gave 8 (1.15 g,
0.994 mmol, 75%) as red crystals. 1H NMR (600 MHz,
C6D6): major signals appeared at d 37.6, 18.0, 13.9, 4.9,
3.2, ꢀ3.2, ꢀ7.0, ꢀ8.6, ꢀ13.2. UV–Vis (cyclohexane, kmax
,
nm (e,
M
ꢀ1 cmꢀ1)): 423 (3300). Anal. Calc. for
C72H52Fe2S4: C, 74.73; H, 4.53; S, 11.08. Found: C, 74.72;
H, 4.51; S, 11.09%. leff (Evans method, 295 K): 4.2 lB.
4.9. Synthesis of [(DtpS)Fe]2(l-SDtp)2 (9)
To a solution of Fe{N(SiMe3)2}2 (2.36 g, 6.27 mmol) in
toluene (150 mL) was added a solution of DtpSH (3.65 g,
12.6 mmol) in toluene (20 mL). The reaction mixture gave
an orange suspension over the course of a few hours. The
solution was decanted, and the orange microcrystals were
washed with hexane and dried to give 9 (3.56 g, 2.80 mmol,
4.12. Magnetic moments
The magnetic moments in solution were measured by
the method originally described by Evans [14]. A reference
is used by placing a sealed capillary containing a mixture of
C6D6/cyclohexane (90/10 v/v) and dropped into an NMR
1
89%). H NMR analysis was not successful due to its low
solubility in C6D6. UV–Vis (cyclohexane, kmax, nm (e,

4798
S. Ohta et al. / Journal of Organometallic Chemistry 692 (2007) 4792–4799
tube containing the solution of the complex (ꢁ10 mg) in a
mixture of C6D6/cyclohexane (90/10 v/v). The chemical
shift difference of the cyclohexane signal between the inner
and the outer tubes was measured. From this difference in
the chemical shift the molar susceptibility vM and the mag-
netic moment leff can be calculated with Eqs. (1) and (2)
(given in S.I. units)
3 ꢂ Df
vM
¼
ð1Þ
1000 ꢂ f ꢂ c
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
pffiffiffiffiffiffiffiffiffiffiffiffi
3k
leff
¼
ꢂ T ꢂ vM ¼ 798 T ꢂ vM
ð2Þ
NA ꢂ l0 ꢂ l2B
v
M is the molar susceptibility of the complex in m3 mol, Df
the difference in the chemical shift in Hz, f the frequency of
operation of the spectrometer in Hz, c the concentration of
the complex in mol dmꢀ3, and T is the temperature in K.
Acknowledgements
This research was financially supported by a Grant-in-
Aid for Scientific Research (Nos. 18GS0207 and
18064009) from the Ministry of Education, Culture,
Sports, Science and Technology, Japan.
Appendix A. Supplementary material
CCDC 643482, 643483, 643484, 643485, 643486,
643487, 643488, 643489, 643490, and 643491 contain the
supplementary crystallographic data for this paper. These
data can be obtained free of charge via http://www.ccdc.
cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit
@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.jorganchem.2007.06.027.
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