Synthesis of coordinatively unsaturated mesityliron thiolate complexes and their reactions with elemental sulfur

Article abstract of DOI:10.1021/ic100692v

The reactions of Fe₂Mes₄ (1; Mes = mesityl) with bulky thiols, namely, HSDmp (Dmp = 2,6-dimesitylphenyl), HSDxp (Dxp = 2,6-dixylylphenyl), and HSBtip [Btip = 2,6-(2,4,6-ⁱPr ₃C₆H₂)₂C₆H₃], provided a series of iron(II) mesityl complexes bearing bulky thiolate ligands. These iron complexes are the thiolate-bridged dinuclear complexes Fe ₂Mes₂(μ-SAr)(μ-Mes) (2a, Ar = Dmp; 2b, Ar = Dxp), the 1,2-dimethoxyethane (DME) adducts (DME)Fe(SAr)(Mes) (3a, Ar = Dmp; 3b, Ar = Dxp), the mixed-valence Fe^I?Fe^II dinuclear complexes (Mes)Fe(μ-SAr)(μ-SAr)Fe (4a, Ar = Dmp; 4b, Ar = Dxp), and a low-coordinate mononuclear complex (BtipS)Fe(Mes) (5). An [Fe₈S₇] cluster [Fe₄S₃(SDmp)]₂(μ-SDmp) ₂(μ-SMes)(μ₆-S) (6), the core structure of which is topologically relevant to that of the FeMo-cofactor of nitrogenase, was obtained from the reaction of 3a or 4a with S₈. The μ-SMes ligand in 6 is formed via insertion of a sulfur atom into the Fe?C(Mes) bond. The formation of cluster 6 from 3a or 4a demonstrates that organoiron complexes are applicable as precursors for iron?sulfur clusters.

Full text of DOI:10.1021/ic100692v

6102 Inorg. Chem. 2010, 49, 6102–6109
DOI: 10.1021/ic100692v
Synthesis of Coordinatively Unsaturated Mesityliron Thiolate Complexes and Their
Reactions with Elemental Sulfur
Takayoshi Hashimoto, 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
Received April 12, 2010
The reactions of Fe2Mes4 (1; Mes = mesityl) with bulky thiols, namely, HSDmp (Dmp = 2,6-dimesitylphenyl), HSDxp (Dxp =
2,6-dixylylphenyl), and HSBtip [Btip = 2,6-(2,4,6-iPr3C6H2)2C6H3], provided a series of iron(II) mesityl complexes bearing
bulky thiolate ligands. These iron complexes are the thiolate-bridged dinuclear complexes Fe2Mes2(μ-SAr)(μ-Mes) (2a,
Ar = Dmp; 2b, Ar = Dxp), the 1,2-dimethoxyethane (DME) adducts (DME)Fe(SAr)(Mes) (3a, Ar = Dmp; 3b, Ar = Dxp), the
mixed-valence FeI-FeII dinuclear complexes (Mes)Fe(μ-SAr)(μ-SAr)Fe (4a, Ar=Dmp;4b, Ar=Dxp), and a low-coordinate
mononuclear complex (BtipS)Fe(Mes) (5). An [Fe8S7] cluster [Fe4S3(SDmp)]2(μ-SDmp)2(μ-SMes)(μ6-S) (6), the core
structure of which is topologically relevant to that of the FeMo-cofactor of nitrogenase, was obtained from the reaction of 3a or
4a with S8.Theμ-SMes ligand in 6is formed via insertion of a sulfur atom into the Fe-C(Mes) bond. The formation of cluster 6
from 3a or 4a demonstrates that organoiron complexes are applicable as precursors for iron-sulfur clusters.
Introduction
of thiolates.1,2 While the use of iron chlorides has been useful
for providing a variety of iron-sulfur clusters containing
[Fe2S2], [Fe3S4], [Fe4S4], and [Fe6S6] cores,2 we and others
have developed the synthesis of iron-sulfur clusters in
toluene,3,4 using an iron(II) amide complex, Fe{N(SiMe3)2}2,5
as the precursor. This approach led us to discover the
[Fe8S7] cluster,3a,e which reproduces the core of a nitrogenase
P-cluster.6 From the same iron amide complex, we have
also synthesized another class of [Fe8S7] clusters, [Fe4S3(SD-
mp)]2(μ-SDmp)2(μ-STip)(μ6-S) [A; Dmp=2,6-(mesityl)2C6H3
and Tip=2,4,6-iPr3C6H2) and [Fe4S3(SDmp)]2(μ-SDmp)2{μ-
N(SiMe3)2}(μ6-S),3c whose core structures are topologically
analogous to the FeMo-cofactor7 of nitrogenase (Chart 1). In
this work, we extended our synthetic method to that using an
organoiron complex Fe2Mes4 (1; Mes=2,4,6-Me3C6H2).8 The
reactions of 1 with bulky thiols gave a series of coordinatively
unsaturated mesityliron complexes having thiolate ligands,
which were subjected to cluster synthesis by reactions with
Synthetic iron-sulfur clusters, which are analogous to the
active sites in proteins, have been obtained from homogeneous
solutions containing iron precursors and sulfur reagents.1 The
structures and yields of the clusters are sensitive to the reaction
conditions, and therefore the choices of iron precursors and
solvents are important factors to be considered. Thus far, iron
chlorides have been commonly used as iron sources, and polar
organic solvents such as CH3CN and CH3OH have usually
been chosen to dissolve iron chlorides and alkaline metal salts
*To whom correspondence should be addressed. E-mail: i45100a@
nucc.cc.nagoya-u.ac.jp.
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Chem. Rev. 2004, 104, 527–559.
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pubs.acs.org/IC
Published on Web 06/07/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 13, 2010 6103
Chart 1
degrade gradually into the mixed-valence FeI-FeII dinuclear
complexes (Mes)Fe(μ-SAr)(μ-SAr)Fe (4a, Ar = Dmp; 4b,
Ar = Dxp), which were crystallized in 61% (4a) and 67%
(4b) yield, respectively. Consistent with the odd number of d
electrons, complexes 4a and 4b are EPR-active and show
isotropic S=1/2 signals at g = 2.077 (4a) and 2.079 (4b) in
toluene at room temperature. These g values are out of the
range of organic radicals, indicating that the unpaired spin is
metal-centered. The S=1/2 spin state was also supported by
their magnetic moments in solution, μeff=1.86 μB (4a) and
1.82 μB (4b) at 295 K. Whereas the reaction pathway from 3
to 4 was unclear, bimesityl (Mes-Mes) was formed in 43%
yield during the degradation process.
The reaction of 1 with 2 equiv of HSBtip [Btip =
2,6-(2,4,6-iPr3C6H2)2C6H3] in either Et2O or DME pro-
vided (BtipS)Fe(Mes) (5) in 64% yield. In contrast to
complexes 3a and 3b, the iron center of 5 does not add
DME, probably because of the steric hindrance of the
SBtip ligand. The bulky Btip group also prevents the
formation of sulfur-bridged di- or multinuclear complexes,
and indeed most of the precedent SBtip complexes of transi-
tion metals are monomeric.14,15 It is notable that 2a, 2b, and
5 are a unique class of heteroleptic and low-coordinate iron
complexes,9,10,13 whereas there have been several low-coor-
dinate, homoleptic iron complexes having amides, thiolates,
aryloxides, alkyls, or aryls.3,8,10,13,14,16
Structures of Mesityl/Thiolate Complexes. The mesityl/
thiolate complexes 2a, 2b, 3a, 3b, 4a, 4b, and 5 were
structurally identified based on the crystallographic anal-
ysis. The molecular structures of 2a, 3a, 5, and 4a are
shown in Figures 1-4, respectively, with selected bond
distances and angles in the captions.
elemental sulfur. The insertion of a sulfur atom into the
Fe-C(mesityl) bond occurred upon treatment with elemen-
tal sulfur, and as a result, an [Fe8S7] cluster similar to A,
[Fe4S3(SDmp)]2(μ-SDmp)2(μ-SMes)(μ6-S) (6), was obtained.
Results and Discussion
Synthesis of Iron Mesityl Complexes Having Bulky
Thiolates. The mesityl group in 1 is susceptible to proton-
ation, and the reaction with HO(2,4,6-tBu3C6H2) is known
to give the dinuclear mesityl/phenoxide complex Fe2Mes(μ-
Mes)2{O(2,4,6-tBu3C6H2)}.9 Similarly, protonation of the
mesityl group with bulky thiols, namely, HSDmp,10 HSDxp
[Dxp = 2,6-(xylyl)2C6H3],11 and HSBtip [Btip = 2,6-(2,4,
6-iPr3C6H2)2C6H3],12 took place to provide iron mesityl
complexes having bulky thiolate ligands (Scheme 1).
Treatment of an Et2O solution of 1 with 1 equiv of HSD-
mp or HSDxp led to the formation of a dark-red solution,
from which the thiolate-bridged dinuclear complexes Fe2-
Mes2(μ-SAr)(μ-Mes) (2a, Ar=Dmp; 2b, Ar=Dxp) wereob-
tained in 72% (2a) and 57% (2b) yield, respectively. Analo-
gous reactions of 1 with 2 equiv of HSDmp or HSDxp in
Et2O afforded a mixture that contained the dinuclear com-
plexes 2a or 2b and the known bis(thiolate) complexes
Fe(SAr)2 (Ar=Dmp or Dxp).10,13 On the other hand, the
same reactions in 1,2-dimethoxyethane (DME) gave rise to
the monomeric complexes, which were isolated as the DME
adducts(DME)Fe(SAr)(Mes) (3a, Ar=Dmp; 3b,Ar=Dxp)
in 66% yield for both. While complexes 3a and 3b are
thermally stable in DME, these complexes dissolved in
Et2O were found to release DME at room temperature to
The thiolate ligand and one of the mesityl ligands in 2a
bridge two iron atoms, and both iron atoms are formally
three-coordinate (Figure 1). Whereas the SDmp ligand often
forms an additional metal-Dmp interaction,3c,10,13,17 the
˚
long Fe-C(Dmp) distances [g3.3933(14) A] are indicative
of no direct interaction between the Dmp group and iron
atoms. The mesityl groups terminally bound to iron are bent
from the Fe-Fe axis, with the Fe-Fe-C angles of 152.25(4)
and 153.49(4)°. This is probably caused by the steric hin-
drance between the mesityl groups and the SDmp ligand.
(14) Nguyen, T.; Panda, A.; Olmstead, M. M.; Richards, A. F.; Stender,
M.; Brynda, M.; Power, P. P. J. Am. Chem. Soc. 2005, 127, 8545–8552.
(15) Groysman, S.; Holm, R. H. Inorg. Chem. 2009, 48, 621–627.
(16) Amide complex:(a) Chen, H.; Bartlett, R. A.; Dias, H. V. R.;
Olmstead, M. M.; Power, P. P. J. Am. Chem. Soc. 1989, 111, 4338–4345.
(b) Reiff, W. M.; Schulz, C. E.; Whangbo, M.-H.; Seo, J. I.; Lee, Y. S.; Potratz,
G. R.; Spicer, C. W.; Girolami, G. S. J. Am. Chem. Soc. 2009, 131, 404–405.
Thiolate complex:(c) Hauptmann, R.; Kliβ, R.; Schneider, J.; Henkel, G. Z.
Anorg. Allg. Chem. 1998, 624, 1927–1936.Aryloxide complex:(d) Bartlett,
R. A.; Ellison, J. J.; Power, P. P.; Shoner, S. C. Inorg. Chem. 1991, 30, 2888–
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2894.Alkyl or aryl complex:(e) M€uller, H.; Seidel, W.; Gorls, H. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 325–327. (f) Wehmschulte, R. J.; Power, P. P.
Organometallics 1995, 14, 3264–3267. (g) Viefhaus, T.; Schwarz, W.; H€ubler,
K.; Locke, K.; Weidlein, J. Z. Anorg. Allg. Chem. 2001, 627, 715–725.
(h) LaPointe, A. M. Inorg. Chim. Acta 2003, 345, 359–362. (i) Kays, D. L.;
Cowley, A. R. Chem. Commun. 2007, 1053–1055.
(17) (a) Ohki, Y.; Sadohara, H.; Takikawa, Y.; Tatsumi, K. Angew.
Chem., Int. Ed. 2004, 43, 2290–2293. (b) Ohki, Y.; Takikawa, Y.; Sadohara, H.;
Kesenheimer, C.; Engendahl, B.; Kapatsina, E.; Tatsumi, K. Chem. Asian J.
2008, 3, 1625–1635. (c) Ohki, Y.; Sakamoto, M.; Tatsumi, K. J. Am. Chem. Soc.
2008, 130, 11610–11611. (d) Sakamoto, M.; Ohki, Y.; Tatsumi, K. Organome-
tallics 2010, 29, 1761–1770. (e) Ohki, Y.; Yasumura, K.; Ando, M.; Shimokata,
S.; Tatsumi, K. Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 3994–3997.
€
€
(9) Muller, H.; Seidel, W.; Gorls, H. Z. Anorg. Allg. Chem. 1996, 622,
1968–1974.
(10) Ellison, J. J.; Rhulandt-Senge, K.; Power, P. P. Angew. Chem., Int.
Ed. Engl. 1994, 33, 1178–1180.
(11) Luening, U.; Baumgartner, H. Synlett 1993, 8, 571–572.
(12) Niemeyer, M.; Power, P. P. Inorg. Chem. 1996, 35, 7264–7272.
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met. Chem. 2007, 692, 4792–4799.

6104 Inorganic Chemistry, Vol. 49, No. 13, 2010
Hashimoto et al.
Scheme 1
Figure 1. Molecular structure of 2a with thermal ellipsoids at the 50%
˚
probability level. Selected bond distances (A) and angles (deg): Fe1-Fe2
2.7419(2), Fe1-S 2.3253(4), Fe2-S 2.3340(4), Fe1-C1 2.0195(13), Fe1-
C10 2.1139(13), Fe2-C10 2.1243(15), Fe2-C19 2.0135(15); Fe1-S-Fe2
72.098(13), Fe1-C10-Fe2 80.62(5), S-Fe1-C10 103.27(4), S-Fe2-C10
102.65(3), Fe2-Fe1-C1 152.25(4), Fe1-Fe2-C19 153.49(4).
Figure 2. Molecular structure of 3a with thermal ellipsoids at the 50%
˚
probability level. Selected bond distances (A) and angles (deg): Fe-C1
2.0482(19), Fe-S 2.3218(5), Fe-O1 2.1473(13); S-Fe-C1 142.28(5),
S-Fe-O1 98.41(4), C1-Fe-O1 116.64(6), O1-Fe-O2 75.27(4).
It is notable that the iron mesityl groups are nearly parallel to
the Dmp mesityl groups, with interplane angles of 3.71(6)
and 8.32(6)° and with the shortest ring-to-carbon distances
larger than the S-Fe-O angles [96.96(4) and 98.41(4)°] and
the O-Fe-C angles [104.73(5) and 116.64(6)°]. The large
S-Fe-C angle is probably due to the steric congestion bet-
ween the SDmp and Fe-mesityl groups, and this congestion
may also lead to elongation of the Fe-S distance [2.3218(5)
˚
of 3.235(3) and 3.372(3) A. As indicated by these distances
and interplane angles, π-π interactions probably exist
between the iron mesityl and the Dmp mesityl groups. The
˚
Fe-Fe distance of 2.7419(2) A is longer than that of 1
[2.617(1) A].8b One of the possible reasons for the elongation
˚
˚
A], which is slightly longer than those of the reported iron(II)
of the Fe-Fe distance is the longer Fe-S(bridge) distances
complexes having terminal SDmp ligands [Fe-S = 2.2497-
10,13
˚
˚
[2.3253(4) and 2.3340(4) A] in 2a than the Fe-C(bridge)
(6)-2.314(2) A].
The distances between the iron atom
distances in 1 (2.103-2.105 A),8b while the Fe-S-Fe angle
˚
˚
and the carbon atoms of the SDmp ligand (g3.5348(16) A)
are too long to form an interaction between the Dmp group
and iron. In contrast to 3a, the iron center of 5 is stabilized
with an additional Fe-arene interaction (Figure 3). The Fe-
[72.098(13)°] is narrower than the Fe-C-Fe angles of 1
[76.1(2)°] and 2 [80.62(5)°].
The iron center of 3a is in a distorted tetrahedral geometry
(Figure 2), and the S-Fe-C angle [142.28(5)°] is notably
˚
C(arene) distance is 2.432(2) A, and similar Fe-C(arene)

Article
Inorganic Chemistry, Vol. 49, No. 13, 2010 6105
Scheme 2
Figure 3. Molecular structure of 5 with thermal ellipsoids at the 50%
˚
probability level. Selected bond distances (A) and angles (deg): Fe-C1
2.038(2), Fe-S 2.2778(7), Fe-C16 2.432(2); C1-Fe-S 125.07(6).
˚
group [Fe1-C40=2.599(2) A] indicates a weak Fe1-mesityl
˚
interaction. The Fe-Fe distance [2.6390(5) A] is shorter than
that in 2a and is indicative of a direct bonding interaction
between FeI-FeII centers.
Reactions of Mesityliron Thiolate Complexes with S8.
Having a series of mesityl/thiolate complexes of iron, we
attempted their reactions with elemental sulfur (S8) in
toluene to synthesize iron-sulfur clusters. These reac-
tions gave black solids after evaporation, and the color
was similar to those of iron-sulfur clusters that we had
previously reported.3 However, characterization of the
products has been difficult because of the lack of single
crystals suitable for X-ray diffraction. After several at-
tempts, an [Fe8S7] cluster, [Fe4S3(SDmp)]2(μ-SDmp)2(μ-
SMes)(μ6-S) (6), was found to crystallize from the cyclo-
hexane extracts of 3a þ S8 or 4a þ S8 in 17% or 5% yield,
respectively (Scheme 2). Whereas some other iron-sulfur
complexes may be present in the mother liquor, we have
only been successful in crystallizing 6. It is interesting to
note that the μ-SMes ligand in 6 is formed via insertion of
a sulfur atom into the iron-mesityl bonds of the pre-
cursors. This is a rare example of sulfur atom insertion
into an Fe-C σ bond, while analogous sulfur insertion
reactions are known for Grignard reagents, alkyl- or
aryllithium compounds,18 and a Cu-Btip complex.15
The molecular structure of 6 was determined by crystal-
lographic analysis (Figure 5), and the selected bond
distances and angles are listed in Table 1. Two crystal-
lographic mirror planes run through the molecule. One of
the planes involves the central sulfur atom (μ6-S) and the
sulfur atoms of the μ-SDmp and μ-SMes ligands. The
Figure 4. Molecular structure of 4a with thermal ellipsoids at the 50%
˚
probability level. Selected bond distances (A) and angles (deg): Fe1-Fe2
2.6390(5), Fe1-C1 2.050(2), Fe1-S1 2.4974(6), Fe1-S2 2.3738(8),
Fe2-S1 2.2339(8), Fe2-S2 2.2769(6), Fe2-C16 2.041(2), Fe1-C40
2.599(2); S1-Fe1-S2 86.53(2), S1-Fe2-S2 95.53(2), Fe1-S1-Fe2
67.54(2), Fe1-S2-Fe2 69.11(2).
interactions are found in some bulky thiolate complexes
10
˚
of iron such as Fe(SDmp)2 [2.470(3) and 2.535(3) A],
14
Fe(SBtip)2 [2.427(1) A], and Fe(SDmp){SC6H3-2,6-(Si-
˚
Me3)2} [2.389(2) A].13 Considering this weak Fe-arene inte-
˚
raction, the iron center in 5 is three-coordinate.
In complex 4a (Figure 4), both thiolate sulfur atoms are
bridging two iron atoms, and one of the thiolate ligands
also uses its o-mesityl group to cover one of the iron centers
(Fe2) as an η6-arene ligand. The Fe2-C(η6-arene) distances
1
6
˚
are 2.041(2)-2.129(2) A. Such a tethered η (S):η (arene)-
coordination mode for the SDmp ligand is known for some
ruthenium complexes.17b While the Fe1 atom is formally
three-coordinate with two thiolate ligands and a mesityl
ligand, one of the Dmp mesityl groups is oriented toward
Fe1. The shortest contact between Fe1 and the mesityl
(18) Patai, S. The Chemistry of the Thiol Group, Part 1; John Wiley & Sons:
New York, 1974.

6106 Inorganic Chemistry, Vol. 49, No. 13, 2010
Hashimoto et al.
Figure 5. Molecular structure of 6 with thermal ellipsoids at the 50% probability level. Only one of the disordered μ-SMes groups is shown for clarity.
˚
Table 1. Selected Bond Distances (A) and Angles (deg) for Cluster 6
Fe1-Fe1A
Fe1-Fe1B
Fe1-Fe2
Fe1-Fe3
Fe2-Fe3
Fe3-Fe3A
Fe1-S1
2.9212(7)
3.6506(6)
2.7626(7)
2.8527(7)
2.7257(8)
2.9714(9)
2.4335(9)
2.2785(9)
2.2769(10)
2.3142(7)
2.2810(9)
2.2537(9)
2.2220(12)
2.2956(11)
2.2667(10)
2.367(2)
S1-Fe1-S2
S1-Fe1-S3
S1-Fe1-S4
S2-Fe1-S3
S2-Fe1-S4
S3-Fe1-S4
S2-Fe2-S2A
S2-Fe2-S3
S2-Fe2-S5
S3-Fe2-S5
S1-Fe3-S2
S1-Fe3-S6
S2-Fe3-S2A
S2-Fe3-S6
S2A-Fe3-S6
99.48(4)
101.84(3)
76.81(3)
Fe1-S1-Fe1A
Fe1-S1-Fe1B
Fe1-S1-Fe1C
Fe1-S1-Fe3
Fe1-S1-Fe3A
Fe3-S1-Fe3A
Fe1-S2-Fe2
Fe1-S2-Fe3
Fe2-S2-Fe3
Fe1-S3-Fe1A
Fe1-S3-Fe2
Fe1-S4-Fe1B
Fe1-S4-C14
Fe2-S5-C1
73.77(2)
97.18(4)
147.72(5)
74.12(2)
134.22(5)
80.69(4)
74.59(2)
77.73(3)
73.63(3)
79.80(3)
75.14(3)
104.12(4)
122.24(5)
113.94(14)
77.79(7)
112.3(3)
103.41(3)
135.38(4)
121.00(4)
104.10(3)
104.08(3)
117.35(3)
108.35(4)
104.09(4)
98.33(5)
Fe1-S2
Fe1-S3
Fe1-S4
Fe2-S2
Fe2-S3
Fe2-S5
105.03(4)
105.38(6)
136.10(7)
Fe3-S1
Fe3-S2
Fe3-S6-Fe3A
Fe3-S6-C29
Fe3-S6
other plane contains the μ6-S atom, the peripheral iron
atoms [denoted as Fe(outer)], and the ipso- and p-carbon
atoms of the central phenyl ring of the SDmp ligand on
Fe(outer). The sulfur atom of the μ-SMes ligand is
disordered over two positions within the former plane,
and the mesityl group is disordered over four positions.
For clarity, Figure 5 shows only one of the disordered
μ-SMes groups. The core geometry of 6 is almost identical
with that of the previously reported A (Chart 1),3c which
has the μ-STip bridge instead of the μ-SMes ligand in 6.
Similarity between 6 and A is also found in the Fe-S and
while the Fe-μ-SR-Fe angles for these groups are com-
parable [77.79(7)° (6) and 77.87(3)° (A)]. These differences
may be due to either a steric effect or a packing effect.
The oxidation state of iron centers in 6 is FeII5FeIII
3
with an odd number of d electrons, and thus 6 is expected
to be EPR-active. The EPR spectrum in frozen toluene at
8 K exhibited a rhombic S=1/2 signal at g=2.209, 2.074,
and 1.952 (Figure 6, top), the values of which are similar
to those for A (g = 2.185, 2.068, and 1.957). The S=1/2
ground state for 6 is also supported by the temperature-
dependent magnetic susceptibility in the solid state
(Figure 6, bottom). The effective magnetic moment at
2 K is 1.84 μB, which is close to the spin-only value with
one unpaired electron (1.73 μB). It is notable that the μeff
value of 6 changes gradually as a function of the tem-
perature, and we have reported an analogous behavior
in the magnetic susceptibility of the [Fe8S7] model com-
plex of the P-cluster.3a,e Whereas elucidation of the
˚
Fe-Fe distances, such as Fe(inner)-μ6S, av. 2.388 A (6)
˚
˚
and 2.386 A (A), and Fe(inner)-Fe(outer), av. 2.750 A (6)
˚
and 2.759 A (A). Nevertheless, the Fe-SMes distance
˚
[2.367(2) A] and the Fe-Fe distance along with the
˚
μ-SMes bridge [2.9714(9) A] in 6 are slightly longer than
˚
the Fe-STip distances [2.3015(12) and 2.3296(11) A] and
˚
the corresponding Fe-Fe distance [2.9103(10) A] in A,

Article
Inorganic Chemistry, Vol. 49, No. 13, 2010 6107
Thus, one of the important advances to be made in future
studies is encapsulation of X at the center of the metal-sulfur
clusters.
Experimental Section
General Procedures. All reactions were carried out using
standard Schlenk techniques and a glovebox under a nitrogen
or argon atmosphere. Toluene, diethyl ether, tetrahydrofuran,
hexane, and 1,2-dimethoxyethane (DME) were purified by the
method of Grubbs,20 where the solvents were passed over columns
of activated alumina and a supported copper catalyst supplied by
Hansen & Co. Ltd. Solvents, degassed and distilled from sodium
benzophenone ketyl, were also used. C6D6 and toluene-d8 were
dried by sodium and distilled prior to use. The 1H NMR spectrum
was recorded on a JEOL ECA-600. The signals were referenced to
the residual proton peak of C6D6. UV-vis spectra were measured
on a Jasco V560 spectrometer. Elemental analyses were performed
on a LECO CHNS-932 microanalyzer, where the samples were
sealed into silver capsules in a glovebox. The EPR spectrum was
recorded on a Bruker EMX-plus spectrometer at X-band frequen-
cies. X-ray diffraction data were collected on a Rigaku AFC8 or
RA-Micro7 equipped with a CCD area detector using graphite-
monochromated Mo KR radiation. The magnetic susceptibility was
measured using a Quantum Design MPMS-XL SQUID-type mag-
netometer, and the crystalline samples were sealed in quartz tubes.
Fe2Mes4 (1),8c HSDmp [Dmp = 2,6-(mesityl)2C6H3],10 HSDxp
[Dxp = 2,6-(xylyl)2C6H3],11 and HSBtip [Btip = 2,6-(2,4,6-iPr3-
C6H2)2C6H3]12 were prepared according to literature procedures.
Synthesis of Fe2Mes2(μ-SDmp)(μ-Mes) (2a). An Et2O (40 mL)
solution of HSDmp (380 mg, 1.10 mmol) was added slowly to
an Et2O (20 mL) solution of Fe2Mes4 (646 mg, 1.10 mmol) at
-80 °C. The mixture was gradually warmed to room temperature
and stirred overnight, during which an orange crystalline powder
of 2a appeared. The crystalline powder was collected, washed
with hexane, and dried under vacuum (645 mg, 72%). Single
crystals suitable for crystallography were obtained from a toluene
solution at room temperature. 1H NMR (600 MHz, C6D6): δ 38.8
(2H), 33.8 (4H), 30.5 (3H), 25.1 (6H), 24.3 (6H) 13.0 (2H), 8.84
(6H), 5.79 (4H), 1.87 (1H), -6.42 (12H), -11.0 (12H). Anal.
Calcd for C51H58Fe2S: C, 75.18; H, 7.18; S, 3.94. Found: C, 75.39;
H, 7.08; S, 4.07.
Figure 6. EPR spectrum at 8 K (top) and the temperature-dependent
magnetic susceptibility (bottom) of cluster 6.
spin structure of the [Fe8S7] core is difficult because the
core is a strongly correlated multispin system, we have
previously reproduced the μeff curve of the [Fe8S7] model
of the P-cluster, based on the exchange interactions (J values)
of magnetic models calculated from the hybrid density
functional theory method.19 An analogous approach could
be applied to analyze the spin structure of 6 in future
studies.
Concluding Remarks
Synthesis of Fe2Mes2(μ-SDxp)(μ-Mes) (2b). An Et2O (30 mL)
solution of HSDxp (272 mg, 0.85 mmol) was added slowly to
an Et2O (30 mL) solution of Fe2Mes4 (500 mg, 0.85 mmol) at
-80 °C. The mixture was gradually warmed to room tempera-
ture and stirred overnight. The resulting dark-red solution was
evaporated until dryness, and the red residue was extracted with
toluene (10 mL). After centrifugation, the extract was evapo-
rated under reduced pressure, and the residue was washed with
hexane to afford an orange powder of 2b (382 mg, 57%). Single
crystals suitable for crystallography were obtained from a
toluene solution at -40 °C. 1H NMR (600 MHz, C6D6): δ
36.2 (2H), 32.8 (4H), 30.2 (3H), 25.3 (6H), 18.2 (6H) 12.6 (2H),
9.98 (2H), 6.24 (4H), 1.07 (1H), -3.54 (12H), -8.42 (12H).
Anal. Calcd for C49H54Fe2S: C, 74.81; H, 6.92; S, 4.08. Found:
C, 74.80; H, 7.00; S, 3.79.
The iron mesityl complex 1 was found to serve as a
precursor for a series of mesityl/thiolate complexes of iron,
including a mixed-valence FeI-FeII complexes 4a and 4b and
a low-coordinate heteroleptic complex 5. The incorporated
bulky thiolate ligands, SDmp, SDxp, and SBtip, contribute
to the stabilization of the products by steric congestion and
by an additional iron-arene interaction in 4a, 4b, and 5.
Anew[Fe8S7] cluster6was obtained from the reactions of 3a
or 4a with S8, demonstrating that iron-aryl complexes are
applicable as precursors for iron-sulfur clusters. The forma-
tion of 6 involves the insertion of a sulfur atom into the Fe-
C(Mes) bond. Such an insertion reaction would be used as a
synthetic protocol because thiolate ligands constitute impor-
tant fragments of metal-sulfur clusters. As suggested in the
previous study on A, cluster 6 possesses the topology of the
FeMo-cofactor of nitrogenase (Chart 1 and Scheme 2). The
arrangement of iron and sulfur atoms in 6 reveals an analogy
with the arrangement of metals and sulfur atoms in the FeMo-
cofactor. However, there are substantial differences between
these cores, and one of the major the differences is the element
of the central atom in 6 (μ6-S) and the FeMo-cofactor (μ6-X).
Synthesis of (DME)Fe(SDmp)(Mes) (3a). A DME (45 mL)
solution of HSDmp (577 mg, 0.85 mmol) was added slowly to a
DME (30 mL) solution of Fe2Mes4 (500 mg, 0.85 mmol) at
-50 °C. The resulting dark-yellow solution was evaporated
under reduced pressure, and the residue was extracted with
Et2O (30 mL). After centrifugation, the extract was evaporated
until dryness. Complex 3a was isolated as light-yellow crystals
(680 mg, 66%) from a mixture of DME (3 mL) and Et2O (10 mL)
at -40 °C. UV-vis (Et2O): a shoulder was observed at 400 nm.
(19) Shoji, M.; Koizumi, K.; Kitagawa, Y.; Yamanaka, S.; Okumura, M.;
Yamaguchi, K.; Ohki, Y.; Sunada, Y.; Honda, M.; Tatsumi, K. Int. J.
Quantum Chem. 2006, 106, 3288–3302.
(20) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518–1520.

6108 Inorganic Chemistry, Vol. 49, No. 13, 2010
Hashimoto et al.
Table 2. Crystal Data for 2a-6
2a
2b C7H8
3
3a
3b C4H10O
3
formula
fw
C51H58Fe2S
814.77
C56H62Fe2S
878.86
C37H46FeO2S
610.68
C39H52FeO3S
656.74
temp (°C)
cryst syst
space group
-160
-160
-100
-100
monoclinic
P21/c (No. 14)
8.4622(5)
36.244(2)
14.4677(9)
triclinic
P1 (No. 2)
8.8682(8)
11.6714(8)
24.285(3)
77.214(4)
89.527(4)
71.410(4)
2318.1(4)
2
monoclinic
P21/n (No. 14)
12.4774(16)
15.7671(19)
18.322(2)
triclinic
P1 (No. 2)
10.9948(18)
11.972(2)
15.679(2)
98.720(4)
90.870(5)
114.882(5)
1843.4(5)
2
˚
a (A)
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
105.4570(18)
106.1116(15)
3
˚
V (A )
4276.9(4)
4
3462.9(8)
4
Z
Dcalcd (g/cm3)
max 2θ (deg)
no. of data collected
no. of unique data
no. of variables
R1a
1.265
55.0
35 673
9537
545
0.0317
0.0906
1.003
1.259
55.0
28 039
10529
594
0.0333
0.0744
1.004
1.171
55.0
26 788
7919
371
0.0429
0.0810
1.002
1.183
55.0
21 803
8315
398
0.0450
0.0957
1.005
wR2b
GOFc
4a
4b
5
6 (C6H12)4.5
3
formula
fw
C57H61Fe2S2
921.92
C53H53Fe2S2
865.82
C45H60FeS
688.88
C132H165Fe8S12
2583.25
temp (°C)
cryst syst
space group
-100
-100
-100
-100
tetragonal
P42/mnm (No. 136)
24.8871(8)
monoclinic
P21/c (No. 14)
10.9617(15)
15.031(2)
28.612(4)
triclinic
P1 (No. 2)
11.436(2)
11.610(2)
16.799(3)
96.251(2)
99.877(3)
92.479(3)
2180.0(7)
2
monoclinic
P21/n (No. 14)
15.156(2)
16.5093(19)
17.497(2)
˚
a (A)
˚
b (A)
˚
c (A)
21.4512(9)
R (deg)
β (deg)
γ (deg)
94.503(2)
112.8640(15)
3
˚
V (A )
4699.7(11)
4
4034.1(9)
4
13286.2(8)
4
Z
Dcalcd (g/cm3)
max 2θ (deg)
no. of data collected
no. of unique data
no. of variables
R1a
1.303
55.0
37 669
10589
611
0.0488
0.0787
1.001
1.319
54.9
25 679
9886
515
0.0339
0.0673
1.000
1.134
55.0
32 137
9174
477
0.0450
0.0953
1.003
1.291
54.9
104 182
8036
385
0.0521
0.1217
1.007
wR2b
GOFc
P
P
P
P
P
a R1 = ||Fo| - |Fc||/ |Fo| [I > 2σ(I)]. b wR2 = [( (w(|Fo| - |Fc|)2/ wFo2))1/2 (all reflections). c GOF = [ w(|Fo| - |Fc|)2/(No - Nv)]1/2
(where No = number of observations and Nv = number of variables).
Anal. Calcd for C37H46FeO2S: C, 72.77; H, 7.59; S, 5.25. Found:
C, 72.60; H, 7.66; S, 5.38.
Formation of Bimesityl during the Degradation of 3a. Standing
an Et2O (5 mL) solution of 3a (100 mg, 0.164 mmol) at room tempe-
rature for 1 week resulted in the formation of dark-orange crystals of
4a (34 mg, 45%). The supernatant was treated with aqueous HCl.
The organic layer was extracted with Et2O, and the organic layer was
dried over MgSO4. After removal of the solvent under reduced pres-
sure, the residue was extracted with MeOH. The extract was eva-
porated under reduced pressure to afford a mixture of bimesityl and
HSDmp (13 mg). The molar ratio of bimesityl and HSDmp was
Synthesis of (DME)Fe(SDxp)(Mes) (3b). A DME (30 mL)
solution of HSDxp (540 mg, 1.70 mmol) was added slowly
to a DME (30 mL) solution of Fe2Mes4 (500 mg, 0.85 mmol)
at -50 °C. The resulting dark-yellow solution was evaporated
under reduced pressure, and the residue was extracted with Et2O
(20 mL). After centrifugation, the extract was concentrated to
ca. 10 mL under reduced pressure and was stored at -40 °C.
1
Light-yellow crystals of 3b C4H10O were obtained (740 mg,
determined by H NMR as 2:3, and the yield of bimesityl was
calculated to be 43%.
3
66%). UV-vis (Et2O): a shoulder was observed at 400 nm.
Anal. Calcd for C35H42FeO2S: C, 72.15; H, 7.27; S, 5.50. Found:
C, 72.09; H, 7.15; S, 5.27.
Synthesis of (Mes)Fe(μ-SDxp)(μ-SDxp)Fe (4b). Standing an
Et2O (3 mL) solution of 3b (44 mg, 0.076 mmol) at room tempera-
ture for 1 week resulted in the formation of dark-orange crystals of 4b
(22 mg, 67%), which were collected and dried under vacuum. UV-
vis (toluene): λmax=489 nm (ε 2100), 616 (ε 990). Evans’ method
(toluene-d8, 295 K): 1.82 μB. EPR (X-band, microwave 1.0 mW,
room temperature): g=2.079 (isotropic). Anal. Calcd for C53H53-
Fe2S2: C, 73.52; H, 6.17; S, 7.41. Found: C, 73.60; H, 6.37; S, 7.53.
Synthesis of (Mes)Fe(μ-SDmp)(μ-SDmp)Fe (4a). Standing an
Et2O (5 mL) solution of 3a (28 mg, 0.046 mmol) at room
temperature for 1 week resulted in the formation of dark-orange
crystals of 4a (13 mg, 61%), which were collected and dried
under vacuum. UV-vis (toluene): λmax = 497 nm (ε = 2200),
621 (ε 980). Evans’ method (toluene-d8, 295 K): 1.86 μB. EPR
(X-band, microwave 1.0 mW, room temperature): g = 2.077
(isotropic). Anal. Calcd for C57H61Fe2S2: C, 74.26; H, 6.67; S,
6.96. Found: C, 73.84; H, 6.39; S, 6.75.
Synthesis of (BtipS)Fe(Mes) (5). An Et2O (40 mL) solution of
HSBtp (2.62 g, 5.10 mmol) was slowly added to an Et2O (30 mL)

Article
Inorganic Chemistry, Vol. 49, No. 13, 2010 6109
solution of Fe2Mes4 (1.50 g, 2.55 mmol) at -80 °C. The mixture
was gradually warmed to room temperature and stirred over-
night. The resulting dark-yellow solution was evaporated under
reduced pressure, and the residue was extracted with Et2O
(50 mL). After centrifugation, the extract was evaporated until
dryness, and the residue was washed with hexane to afford a
yellow powder of 5 (2.26 g, 64%). Single crystals suitable for
crystallography were obtained from an Et2O solution at -40 °C.
1H NMR (600 MHz, C6D6): δ 116.1, 113.6, 44.7, 27.8, 4.8, -3.5,
-13.3, -53.1. Anal. Calcd for C45H60FeS: C, 78.46; H, 8.78; S,
4.66. Found: C, 78.08; H, 8.71; S, 4.55.
1248, Cargille Laboratories, Inc., Cedar Grove, NJ) and
mounted on loops. Diffraction data were collected at -100
or -160 °C under a cold nitrogen stream on a Rigaku AFC8
equipped with a Mercury CCD detector or on a Rigaku RA-
Micro7 equipped with a Saturn70 CCD detector, using gra-
˚
phite-monochromated Mo KR radiation (λ = 0.710 690 A).
Six preliminary data frames were measured at 0.5° increments of
ω, to assess the crystal quality and preliminary unit cell para-
meters. 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 absorp-
tion using the REQAB program. The calculations were per-
formed 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 iso-
tropically), and all hydrogen atoms were put at calculated
positions. One isopropyl group of the SBtip ligand in 5 is
disordered over two positions in a 1:1 ratio. The SMes bridging
ligand of 6 is located at the intersection of two mirror planes,
Wycoff position g, and is, therefore, 4-hold-disordered. Three
crystal solvents (cyclohexane) in 6 are disordered over two or
three positions in a 1:1, 2:3, or 3:3:4 ratio, respectively. Addi-
tional data are available as Supporting Information.
Synthesis of [Fe4S3(SDmp)]2(μ-SDmp)2(μ-SMes)(μ6-S)
(6). Method A. Complex 3a (690 mg, 1.13 mmol) and
elemental sulfur (S8; 36 mg, 0.140 mmol) were charged into
a Schlenk tube, and toluene (15 mL) was added at 0 °C to
dissolve these compounds. After stirring for 5 days at room
temperature, the solvent was removed under reduced pres-
sure to give a black oily material. The residue was extracted
with hexane (30 mL), and the solution was centrifuged.
Evaporation of the extract gave a black powder. The powder
was dissolved in cyclohexane (5 mL), and the solution was
kept standing at room temperature for several days, afford-
ing black crystals of 6 (C6H12 4.5 (63 mg, 17%). UV-vis
)
3
(toluene, rt): λmax = 450 nm (ε 17000). EPR (X-band,
microwave 1.0 mW, 8 K): g = 2.209, 2.074, and 1.952. Anal.
Calcd for C132H165Fe8S12: C, 61.37; H, 6.44; S, 14.90.
Found: C, 61.44; H, 6.04; S, 15.39.
Acknowledgment. This research was financially supported
by Grants-in-Aid for Scientific Research (Grants 18GS0207,
18064009, and 20613004) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan. We are grate-
ful to Dr. Rie Suizu and Professors Hirofumi Yoshikawa,
Michio Matsushita, and Kunio Awaga (Nagoya University)
for aiding us in the SQUID measurements.
Method B. Complex 4a (500 mg, 0.54 mmol) and elemental
sulfur (S8; 35 mg, 0.140 mmol) were dissolved in toluene (15 mL)
at 0 °C. After stirring for 5 days at room temperature, the solvent
was removed under reduced pressure. An analogous workup, as
described in method A, gave black crystals of 6 (C6H12)4.5
(18 mg, 5.1%).
3
Supporting Information Available: X-ray crystallographic
data in CIF format for the structures of 2a-6. This material is
available free of charge via the Internet at http://pubs.acs.org.
X-ray Crystal Structure Determination. Crystal data and
refinement parameters for 2a-6 are summarized in Table 2.
Single crystals were coated with oil (Immersion Oil type B: Code