Iron(II)-mediated reductive cleavage of disulfide and diselenide bonds: Iron(III) complexes of mixed O,X,O and O,X (X = S, Se) donor ligands

Article abstract of DOI:10.1002/ejic.201100674

The syntheses and characterization of a methoxo-bridged diiron(III) complex, [Fe₂L^Se₂(μ-OCH₃) ₂(CH₃OH)₂] (1), and three mononuclear iron(III) complexes Bu₄N[FeL^Se

Full text of DOI:10.1002/ejic.201100674

FULL PAPER
DOI: 10.1002/ejic.201100674
Iron(II)-Mediated Reductive Cleavage of Disulfide and Diselenide Bonds:
Iron(III) Complexes of Mixed O,X,O and O,X (X = S, Se) Donor Ligands
Tapan Kanti Paine,[a] Debobrata Sheet,[a] Thomas Weyhermüller,[b] and
Phalguni Chaudhuri*[b]
Dedicated to Acharya Prafulla Chandra Ray[‡]
Keywords: Disulfide / Diselenide / Cleavage reactions / Thiophenolate / Selenophenolate / Iron
The syntheses and characterization of a methoxo-bridged di-
iron(III) complex, [Fe2LSe2(μ-OCH3)2(CH3OH)2] (1), and three
mononuclear iron(III) complexes Bu4N[FeLSe2] (2), Bu4N-
reaction of a tridentate O,X,O ligand (X = S, Se) with iron(II)
salts in the presence of either the H2LSe–Se or H2LS–S ligand
[H2LSe–Se
= 2,2Ј-diselenobis(4,6-di-tert-butylphenol), and
[FeLSeЈLSe] (3) and Bu4N[FeLSЈLS] (4) [H2LSe = 2,2Ј-sele- H2LS–S = 2,2Ј-dithiobis(4,6-di-tert-butylphenol)] in an inert
nobis(4,6-di-tert-butylphenol), H2LS = 2,2Ј-thiobis(4,6-di-tert-
butylphenol), H2LSeЈ = 3,5-di-tert-butyl-2-hydroxyselenophe- disulfide or diselenide bonds are reductively cleaved. The
nol, and H2LSЈ = 3,5-di-tert-butyl-2-hydroxythiophenol] are
temperature-independent magnetic moment values of 3 and
discussed. The single crystal structure of 1·7CH3OH, as de- 4 indicate that the complexes contain mononuclear high spin
atmosphere, whereby iron(II) is oxidized to iron(III) and the
termined by XRD, reveals an asymmetric Fe2O2 core in
which the two iron and two methoxo oxygen atoms constitute
a perfect planar atomic arrangement. Complex 1 exhibits a
iron(III) centers. The crystal structure of 3 confirms that a re-
ductive Se–Se bond cleavage with concomitant formation of
a five coordinate trigonal bipyramidal anionic iron(III) com-
plex, [FeLSeЈLSe]–, has occurred. It is proposed that the iron(II)
ions take part in the electron-transfer reaction associated
with the reductive cleavage of the disulfide and diselenide
bonds.
moderate antiferromagnetic exchange coupling (J
=
–13.2 cm–1) that operates between the two high spin iron(III)
centers (SFe = 2.5) with a resulting St = 0 ground state, while
2 is a six coordinate mononuclear high spin iron(III) complex.
The mixed ligand complexes 3 and 4 are formed during the
ium hydride, and sodium borohydride.[4] Several metal ions
can easily oxidize thiols, a process that can then be followed
by the complexation of the metal with the resulting disul-
fide.[5] On the other hand, reductive cleavage of disulfide
bonds normally takes place in the presence of low valent
metal ions.[6] In spite of the rich coordination chemistry of
organodisulfides,[7] reports of the reductive cleavage of di-
sulfide bonds by metal ions are rare.[8]
We have been exploring the transition metal complexes
of thio- and selenobisphenol ligands and studying their re-
activity.[9] As a natural progression to our earlier work, we
have initiated a project to study the coordination chemistry
of two new ligands, dithio- and diselenobisphenol
(Scheme 1). Herein, we report the syntheses, characteriza-
tion and crystal structures of iron(III) complexes of a sele-
nobisphenol ligand (H2LSe) and compared their chemistry
with those of iron complexes containing dithio- and dis-
elenobisphenol ligands. We also describe the reductive
cleavage of the S–S bond of H2LS–S during its reaction with
an iron(II) salt in the presence of H2LS. The iron(II) is oxid-
ized to iron(III) during the reaction, which is preformed in
an argon atmosphere, with the concomitant formation of a
Introduction
The reversible cleavage of disulfide bonds is an important
reaction in biological processes such as protein folding, re-
dox reactions and cell signaling.[1] In proteins, the disulfide
linkage also acts as a binding site for metals like copper and
nickel.[2] The conversion between disulfides and thiolate has
been used as a reversible redox process for the development
of functional materials. In addition, thio- and seleno-pro-
teins are good catalysts for many redox reactions in bio-
logical systems.[1f] Thiols are oxidized to disulfides by oxid-
izing agents[3] and disulfide bonds are normally cleaved by
reducing agents such as borohydrides and alkali metals.
Similarly, diselenides can be reductively cleaved with reduc-
ing agents like sodium in liquid ammonia, lithium alumin-
[a] Department of Inorganic Chemistry, Indian Association for the
Cultivation of Science,
2A&2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032,
India
[b] Max-Planck-Institut für Bioanorganische Chemie,
Stiftstrasse 34–36, 45470 Mülheim an der Ruhr, Germany
E-mail: chaudh@mpi-muelheim.mpg.de
[‡] Founder-President of the Indian Chemical Society, on the
occasion of the 150th anniversary of his birth
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Fe-Mediated Reductive Cleavage of Disulfide and Diselenide Bonds
five coordinate mononuclear iron(III) complex, [FeLSЈLS]–.
The selenium analogue of the disulfide ligand shows Se–
Se bond cleavage under similar reaction conditions to yield
[FeLSeЈLSe]–. The roles of the ligands and of the iron salt in
the reductive cleavage of the disulfide and diselenide bonds
are discussed.
Scheme 3. Reductive cleavage of disulfide and diselenide bonds.
The IR spectra for complexes 1–4 confirmed the presence
of the ligands in these complexes, as indicated by strong
peaks in the 3000–2800 cm–1 regions due to ν(C–H)
stretches of the tert-butyl groups of the ligands, together
with other ν(C–H, C=C, C–O) vibrations that were found
in the normal wavenumber ranges for these types of link-
ages.[10] The bands due to the ν(OH) vibrations in the spec-
tra of the free ligands are replaced by broad peaks in the
3200–3400 cm–1 regions of the spectra of 1–4, indicating the
loss of phenol character of the ligands upon complexation.
Two weak but sharp bands at around 1050 cm–1, corre-
sponding to ν(OMe) vibrations, are present in the spectra
of 1, but are absent in the IR spectra of the mononuclear
complexes. Except for the μ-methoxo complex 1, mass spec-
trometry in the electron impact (EI) and ESI mode was
found to be a useful analytical tool for the characterization
of the complexes. Mass spectroscopic data recorded in ESI
mode for 2, 3 and 4 do not leave any doubt about the com-
positions of 2, 3 and 4. Two single peaks, one at m/z = 242.2
(in positive mode) and the second at m/z = 1030.5, 827.5
and 732.4 (in negative mode) with the expected isotope dis-
tribution pattern calculated for [Bu4N]+ and [FeLSe2]– (2),
[FeLSeLSeЈ]– (3) and [FeLSLSЈ]– (4) species, respectively.
The optical spectra for complexes 1–4 in CH2Cl2 have
been measured in the range of 300–1000 nm. The bands are
of charge-transfer origin, as evident from their high absorp-
tion coefficient values.[11] The 450–500 nm regions of the
optical spectra for complexes 1–4 are dominated by phenol-
ate-to-iron(III) charge-transfer bands.
Scheme 1. Ligands used in this study.
Results and Discussion
Ligand H2LSe–Se was synthesized by reacting 2,4-di-tert-
butylphenol with selenium and selenium dioxide in a mix-
ture of concd. HCl and concd. H2SO4. Ligand H2LS–S was
prepared by reacting 2,4-di-tert-butylphenol with S2Cl2 in
toluene. Both the ligands were characterized by different
spectroscopic and analytical techniques (see Exp. Section).
The iron(III) complexes were synthesized readily by the re-
action of the iron salts with the ligands, as shown in
Scheme 2. Reaction, in CH3OH, of the ligand H2LSe with
FeCl2 produces the bis(μ-methoxo)diiron(III) complex 1.
Addition of excess nBu4NOCH3, which acts as a base, to a
mixture of CH2Cl2, CH3OH, and 1 yields the homoleptic
bisligand mononuclear iron(III) complex 2. Complex 2 can
also be synthesized by reaction, in a nitrogen atmosphere,
of the ligand H2LSe with FeCl2 (2:1) in CH3CN in the pres-
ence of excess nBu4NOH, followed by exposure of the reac-
tion solution to air.
Single Crystal X-ray Diffraction Studies
Molecular Structure of [Fe2LSe (μ-OCH3)2(CH3OH)2]·
2
7CH3OH (1·7CH3OH)
The crystal structure of 1·7CH3OH reveals the presence
of the discrete dinuclear molecule shown in Figure 1. Each
molecule consists of two iron(III) centers that are related
Scheme 2. Syntheses of iron(III) complexes.
Interestingly, ligands H2LSe and H2LS react with FeCl2 in by a crystallographic inversion center. Each iron is coordi-
CH3OH solution under argon and in the presence of their nated in a facial manner by two cis-phenolate oxygen atoms
respective diheterobis analogues, H2LSe–Se and H2LS–S, to and one selenium atom of the tridentate ligand, and the
yield the mononuclear iron(III) complexes 3 and 4, respec- octahedral environment of each metal center is completed
tively. During the reaction, cleavage of the Se–Se and S–S by a pair of methoxy groups that asymmetrically bridge the
bonds occurs to generate the new ligands H2LSeЈ and H2LSЈ two iron(III) ions, and one oxygen atom of a coordinated
and thus affording five coordinate mononuclear iron(III) methanol molecule. Two iron and two methoxo oxygen
complexes, as shown in Scheme 3. The reductive cleavage of atoms constitute a perfect planar atomic arrangement.
the disulfide and diselenide bonds could not be observed in
The bridging angles Fe(1)–O(30)–Fe(1)# [106.11(11)°]
the absence from the reaction mixture of either the metal and Fe(1)–O(30)#–Fe(1)# are equal, as are the O(30)–
ion or H2LX ligand.
Fe(1)–O(30)# [73.89(11)°] and O(30)–Fe(1)#–O(30)#
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FULL PAPER
Figure 1. Molecular structure of 1·7CH3OH.
angles (Table 1). The dimethoxo bridge is asymmetric, Table 1. Selected bond lengths [Å] and angles [°] for 1·7CH3OH.
d[Fe(1)–O(30)] = d[Fe(1)#–O(30)#] = 2.010(2) Å, d[Fe(1)–
Fe(1)–O(1)
Fe(1)–O(2)
Fe(1)–O(30)
Fe(1)–O(30)#
Fe(1)–O(40)
Fe(1)–Se(1)
C(1)–O(1)
C(15)–O(2)
1.940(3)
1.927(3)
2.010(2)
1.979(2)
2.070(3)
2.6476(8)
1.321(4)
1.333(4)
3.188(3)
96.33(11)
165.37(11)
93.15(10)
95.99(11)
166.87(10)
73.89(11)
92.45(11)
92.36(11)
98.29(10)
91.65(11)
82.46(8)
82.59(8)
87.76(7)
94.54(7)
172.35(8)
106.11(11)
O(30)#] = d[Fe(1)#–O(30)] = 1.979(2) Å; Δd = 0.031 Å. A
similar asymmetric Fe2O2 core has been described earlier
by Walker, Poli, and Palaniandavar et al.[12] The bridging
Fe–OCH3, Fe–O(phenolate) [Fe(1)–O(1), 1.940(3) Å; Fe(1)–
O(2), 1.927(3) Å] and Fe(1)–O(40) [2.070(3) Å] (where O40
is within a methanol molecule) distances are within the nor-
mal range.[13] Both the angles involving the bridging oxygen
atoms [106.11(11)°] are equal, as are those involving the
iron centers [73.89(11)°], and are typical for an Fe–O–Fe–
O ring.[14] The preference of the Fe–O–Fe–O ring for an O–
Fe–O angle close to 76° leads to distortions in the remain-
ing angles in the iron coordination sphere altering it from
an ideal octahedron. An increase or decrease from the ideal
value of 90° occurs for the angles O(40)–Fe(1)–O(30)
[98.29(10)°], Se(1)–Fe(1)–O(30) [87.76(7)°], O(40)–Fe(1)–
O(30)# [91.65(11)°], and a decrease from 180° is seen for
the O(2)–Fe(1)–O(30) [165.37(11)°] and O(1)–Fe(1)–O(30)#
[166.87(10)°] angles, making the coordination geometry of
the iron a distorted octahedron.
The oxygen of the methanol molecule coordinated to
Fe(1), O40, is hydrogen bonded to a noncoordinated meth-
anol molecule. There is a hydrogen bonding network be-
tween three other methanol molecules of solvation. The
long Fe(1)–O(30) bond is relatively weak because it is trans
to the stronger, and hence shorter, Fe–O(phenolate) bond,
which mitigates the Lewis acidity of the iron center and
decreases its affinity for the methoxide bridge. The asym-
metry of the Fe–O–Fe–O bridge originates from the cis-
phenolate coordination of the ligand.
Fe(1)···Fe(1)#
O(2)–Fe(1)–O(1)
O(2)–Fe(1)–O(30)
O(1)–Fe(1)–O(30)
O(2)–Fe(1)–O(30)#
O(1)–Fe(1)–O(30)#
O(30)–Fe(1)–O(30)#
O(2)–Fe(1)–O(40)
O(1)–Fe(1)–O(40)
O(30)–Fe(1)–O(40)
O(30)#–Fe(1)–O(40)
O(2)–Fe(1)–Se(1)
O(1)–Fe(1)–Se(1)
O(30)–Fe(1)–Se(1)
O(30)#–Fe(1)–Se(1)
O(40)–Fe(1)–Se(1)
Fe(1)–O(30)–Fe(1)#
O,Se,O donor sets bind to the metal in a facial manner.
Two phenolate groups and two selenium atoms from two
ligands form the equatorial plane in which atoms of the
same type occupy cis positions. The remaining two phenol-
ate groups are trans to each other, and satisfy the hexacoor-
dinate sites. The O(2)–Fe(1)–O(4) and O(1)–Fe(1)–Se(2)
bond angles of 156.75(7)° and 171.91(7)°, respectively, are
in accord with the distorted nature of the complex, which
deviates from an ideal octahedral geometry.
Molecular Structure of Bu4N[FeLSe2] (2)
The crystal lattice of 2 consists of discrete [Bu4N]+ and
The average Fe–O(phenolate) bond length is 1.912 Å,
[FeLSe2]– ions. An ORTEP diagram of the anion with the which is within the range for normal FeIII–O bond lengths.
atom labelling scheme is shown in Figure 2. The central The Fe(1)–O(2) and Fe(1)–O(4) bonds [1.929(2) and
metal ion, iron(III), is in a distorted octahedral FeO4Se2 1.934(2) Å, respectively] are a little longer than the upper
coordination environment. Two tridentate ligands with limit for the range of corrected values (Table 2). This may
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Fe-Mediated Reductive Cleavage of Disulfide and Diselenide Bonds
Table 2. Selected bond lengths [Å] and angles [°] for 2.
Fe(1)–O(1)
Fe(1)–O(3)
Fe(1)–O(2)
Fe(1)–O(4)
Fe(1)–Se(1)
Fe(1)–Se(2)
C(1)–O(1)
C(15)–O(2)
1.892(2)
1.893(2)
1.929(2)
1.934(2)
2.7966(5)
2.7797(5)
1.330(3)
1.324(3)
1.324(3)
1.321(3)
102.17(7)
100.77(8)
93.28(8)
93.82(8)
101.28(8)
156.75(7)
171.91(6)
79.98(5)
86.83(5)
78.09(5)
79.69(5)
170.82(6)
77.54(5)
87.49(5)
99.43(2)
C(31)–O(3)
C(45)–O(4)
O(1)–Fe(1)–O(3)
O(1)–Fe(1)–O(2)
O(3)–Fe(1)–O(2)
O(1)–Fe(1)–O(4)
O(3)–Fe(1)–O(4)
O(2)–Fe(1)–O(4)
O(1)–Fe(1)–Se(2)
O(3)–Fe(1)–Se(2)
O(2)–Fe(1)–Se(2)
O(4)–Fe(1)–Se(2)
O(1)–Fe(1)–Se(1)
O(3)–Fe(1)–Se(1)
O(2)–Fe(1)–Se(1)
Figure 2. ORTEP representation of 2.
arise due to the deviation of the complex from the ideal
octahedral geometry. The bond lengths and angles in the O(4)–Fe(1)–Se(1)
cation [Bu4N]+ seem to be reasonable, and are comparable
Se(2)–Fe(1)–Se(1)
with reported values.[15]
Molecular Structure of Bu4N[FeLSeЈLSe] (3)
The iron(III) center is in a distorted trigonal bipyramidal
Although the analytical and spectroscopic data for 3 FeSe2O3 coordination environment (τ = 0.77).[16] One li-
unambiguously showed that the mononuclear Bu4N- gand with an O,Se,O donor set and another with an O,Se
[FeLSeЈLSe] unit is the smallest unit within the structure, a donor set satisfy the five coordination sites of the iron. Two
single-crystal X-ray analysis was undertaken to remove any phenolate oxygen atoms from a H2LSe ligand and one sele-
doubts regarding the connectivity within the structure. The nium atom from a H2LSeЈ ligand form the equatorial plane,
structure analysis shows that the lattice consists of discrete with O(1)–Fe(1)–O(2) and O(2)–Fe(1)–Se(2) angles of
[Bu4N]+ and [FeLSeLSeЈ]– ions. The structural analysis con- 110.57(13) and 125.64(9)°, respectively. The Fe(1)–Se(1) and
firmed that reductive Se–Se bond cleavage of the H2LSe–Se Fe(1)–O(3) bonds, which are in mutually trans positions,
ligand occurred during its reaction with the iron(II) salt in form axial linkages with an O(3)–Fe(1)–Se(1) angle of
the presence of the tridentate facial ligand H2LSe. An OR- 171.70(9)°. The bond lengths are significantly shorter in 3
TEP diagram of the anion with the atom labelling scheme than those within the six coordinate complex 2. The Fe–O
is shown in Figure 3.
bond lengths are consistent with a d5 high spin electronic
Figure 3. Molecular structure of 3.
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T. Kanti Paine, D. Sheet, T. Weyhermüller, P. Chaudhuri
FULL PAPER
configuration for the iron(III) center (Table 3).[17] The C–C axial zero-field interactions (DSZ2) were accounted for if
bond lengths of the phenyl rings indicate that the aromatic necessary. The solid line in Figure 4 represents the best fit
character of the rings is retained after complexation of the to the data for 1 and was obtained with the parameters: J
ligands, and that the ligands coordinated to the iron(III) = –13.2 cm–1, gFe = 2.0, which are in accord with those for
center are dianionic in nature; this leaves an overall negative comparable complexes. A comparison of the Fe–O–Fe
charge on the iron(III) complex, which is neutralized by a bridge angles and the Fe–Obridge bond lengths for 1 with
tetrabuylammonium cation.
those reported in the literature supports the notion that no
definitive magneto-structural conclusions based only one of
the structural parameters mentioned above can be ob-
tained.[19]
Table 3. Selected bond lengths [Å] and angles [°] for 3.
Fe(1)–O(1)
Fe(1)–O(3)
Fe(1)–O(2)
Fe(1)–Se(1)
Fe(1)–Se(2)
C(1)–O(1)
C(15)–O(2)
C(31)–O(3)
O(2)–Fe(1)–O(1)
O(2)–Fe(1)–O(3)
O(1)–Fe(1)–O(3)
O(2)–Fe(1)–Se(2)
O(1)–Fe(1)–Se(2)
O(3)–Fe(1)–Se(2)
O(2)–Fe(1)–Se(1)
O(1)–Fe(1)–Se(1)
O(3)–Fe(1)–Se(1)
Se(1)–Fe(1)–Se(2)
1.886(3)
1.886(3)
1.866(3)
2.7448(7)
2.4571(8)
1.332(5)
1.345(5)
1.332(5)
110.57(13)
100.91(12)
104.98(12)
125.64(9)
119.43(9)
86.15(8)
80.86(9)
81.73(8)
171.70(9)
86.26(2)
Figure 4. Plots of μeff vs. T for solids 1 and 2; the solid lines repre-
sent the best fits to the data.
Above 10 K, complexes 2, 3 and 4 exhibit μeff values of
6.13Ϯ0.04, 5.92Ϯ0.06 and 6.01Ϯ0.10 μB, respectively (see
Figures 4 and 5). This clearly shows that the complexes con-
tain d5 high spin ions, i.e. iron(III). Simulations of the ex-
perimental magnetic moment data yield gFe = 2.074 (θ =
Magnetic Susceptibility Measurements
Magnetic measurements for polycrystalline samples of
complexes 1–4 were done in the temperature range 2–290 K
in an applied field of 1 T. The magnetic behavior of 1 is
typical for an antiferromagnetically coupled dinuclear com-
plex. At 290 K the μeff (χMT) value is 6.78 μB
(5.74 cm3 Kmol–1), but it decreases with decreasing tem-
–0.39 K) for 2, gFe
= 2.0 (θ = –0.96 K, TIP =
256ϫ10–6 cm3 mol–1) for 3 and gFe = 2.02 (θ = –0.65 K,
TIP = 290ϫ10–6 cm3 mol–1) for 4. A TIP (temperature-
independent
paramagnetism)
value
of
ca.
perature until it reaches
(0.112 cm3 Kmol–1) at 2 K, indicating the presence of ex-
change coupling between the two iron(III) centers (SFe
2.5) with a resulting St = 0 for the ground state of 1 (Fig-
a
value of 0.94 μB
300ϫ10–6 cm3 mol–1 per ion for high-spin iron(III) has
been reported in the literature.[20] The temperature-indepen-
dent μeff values indicate the mononuclear nature of 2–4.
=
ˆ
ure 4). Using the Heisenberg spin-Hamiltonian, H = –2J
ˆ
ˆ
S1·S2, for an isotropic exchange coupling between two spins
S1 and S2, the experimental magnetic data were simulated
with a least square fitting procedure[18] with diagonalization
Conclusions
The synthesis and characterization of two new bisphenol
of the full exchange coupling matrix, Zeeman splitting and ligands and their reactivity towards an iron salt are re-
Figure 5. Plots of μeff vs. T for solids 3 and 4; the solid lines represent the best fits to the data.
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Fe-Mediated Reductive Cleavage of Disulfide and Diselenide Bonds
Pascal’s constants. 1H NMR experiments were carried out on a
Bruker ARX spectrometer (400 MHz).
ported. The reductive S–S and Se–Se bond cleavage of di-
thio- and diselenobisphenols by iron(II) in the presence of
tridentate O,X,O donor ligands (X = S, Se) with the con-
comitant formation of iron(III) complexes, [FeLXLXЈ]–, is
discussed. The reactions with the iron(II) salt were per-
formed in an inert atmosphere, but the isolated products
are iron(III) complexes, which was established by various
spectroscopic analyses. The single crystal structure of the
selenium analogue, 1·7CH3OH, confirmed that cleavage of
the diselenide bond had occurred. It is proposed that the
iron(II) takes part in this electron-transfer process, reducing
the disulfide and diselenide groups to thiolate and sele-
nolate, respectively. The results described herein have shown
the roles of the metal and ligand in the reductive cleavage
of disulfide and diselenide bonds. The reactivity of diseleno-
and dithiobisphenol ligands with other metal ions is cur-
rently being investigated in our laboratory.
X-ray Crystallographic Data Collection and Refinement of the Struc-
tures: Dark red single crystals of 1·7CH3OH, 2, 3 were coated with
perfluoropolyether, picked up with glass fibers, and mounted on a
Siemens SMART diffractometer (1·7CH3OH and 2) and a Nonius
Kappa-CCD diffractometer (3) equipped with cryogenic nitrogen
cold streams operating at 100(2) K. Graphite monochromated Mo-
Kα radiation (λ = 0.71073 Å) was used. Intensity data were cor-
rected for Lorentz and polarization effects. The faces of the crystals
of 1·7CH3OH and 2 were determined, and the intensity data for
these complexes were corrected for absorption with the Gaussian
absorption correction method embedded in ShelXPREP,[21a]
whereas data for 3 were corrected with SADABS.[21b] The program
SHELXL97[21c] was used for the refinement of the structures. All
structures were solved and refined by direct methods and difference
Fourier techniques. Non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were placed at calculated positions in the
models and refined as riding atoms with isotropic displacement
parameters. Details of the data collections and structure refine-
ments are summarized in Table 4.
Experimental Section
Materials and Physical Measurements: All chemicals were pur-
chased from commercial sources and used without further purifica-
tion. Solvents were distilled and dried before use. Fourier transform
infrared spectroscopy with KBr pellets was performed on a Perkin–
Elmer 2000 FTIR instrument. Solution electronic spectra were
measured on a Perkin–Elmer Lambda 19 spectrophotometer. Mass
spectra were recorded either in the EI or ESI (in CH2Cl2) mode
with a Finnigan MAT 95 or 8200 spectrometer. Magnetic suscep-
tibilities of the polycrystalline samples were recorded on a SQUID
magnetometer (MPMS, Quantum Design) in the temperature range
2–290 K with an applied field of 1 T. The resulting volume magne-
tization values for the samples had their diamagnetic contributions
compensated for and were recalculated as volume susceptibilities.
Diamagnetic contributions were estimated for each compound with
Crystals of 3 appeared to be of low quality. The structure refine-
ment revealed that the unit cell contains large volumes filled with
extremely disordered solvent, most probably methanol and water
molecules, which account for of 22% of the total crystal volume.
Attempts to find a reasonable disorder model for the solvent in
3 were not successful. The SQUEEZE[21d] routine in the program
PLATON was therefore used to remove diffuse solvent contri-
butions from the data for 3. The [NBu4]+ cation and two tert-butyl
groups of the ligand were also found to be disordered. Two split
atoms positions were refined for these moieties, the bond lengths
were restrained and equal displacement parameters were applied
for the related atoms with the SAME, SADI and EADP instruc-
tions of ShelXL97. A total of 172 restraints were used in the refine-
ment of the crystal structure.
Table 4. Crystallographic data for 1·7CH3OH, 2 and 3.
1·7CH3OH
2
3
Empirical formula
Formula weight
Temperature [K]
λ(Mo-Kα) [Å]
C67H122Fe2Se2O15
1437.27
100(2)
C72H116FeNO4Se2
1273.48
100(2)
0.71073
C58H96FeNSe2O3
1069.13
100(2)
0.71073
0.71073
¯
¯
Space group
P1
P21/n
R3
a [Å]
b [Å]
c [Å]
α [°]
11.3876(8)
13.16808(10)
13.7062(12)
83.28(2)o
16.1348(12)
23.824(3)
19.000(2)
27.014(2)
27.014(2)
51.115(4)
90
90
β [°]
86.92(2)o
94.23(2)o
90
γ [°]
88.08(2)o
2037.4(3)/1
1.171
1.302
764
90
120o
V [Å3]/Z
7283.6(13)/4
1.161
1.250
2724
32304(4)/18
Density (calcd.) [Mgm–3]
Absorption coeff. [mm–1]
F(000)
0.989[a]
1.257
10242
θ Range
1.79–27.50°
17597
8766 [Rint = 0.0423]
8761/0/422
0.992
R1 = 0.0550, wR2 = 0.1442
R1 = 0.0848, wR2 = 0.1570
0.93/–0.50
3.20–30.00°
24780
17789 [Rint = 0.0532]
17638/0/749
1.011
R1 = 0.0449, wR2 = 0.0953
R1 = 0.0733, wR2 = 0.1102
0.50/–0.79
1.51–23.50°
28941
10449 [Rint = 0.0608]
10449/172/664
1.019
R1 = 0.0504, wR2 = 0.1253
R1 = 0.0798, wR2 = 0.1344
0.38/–0.26
Reflections collected
Unique reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I Ͼ2σ(I)]
R indices (all data)
Largest diff. peak and hole [eÅ–3]
[a] Low density is due to solvent elimination with PLATON/SQUEEZE.[21d]
Eur. J. Inorg. Chem. 2011, 5250–5257
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5255

T. Kanti Paine, D. Sheet, T. Weyhermüller, P. Chaudhuri
CCDC-777324 (for 1·7CH3OH), -777325 (for 2) and -777326 (for 0.5 mmol) was added and the resulting red solution was refluxed
FULL PAPER
3) contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Ligand Synthesis: The ligand H2LS was synthesized according to a
literature procedure.[22] The ligand H2LSe was synthesized accord-
ing to a modified version of the method described by Pastor et
al.[23]
under nitrogen for 0.5 h. After cooling, the solution was opened to
air and stirred for another 15 min. The solution was then filtered
to remove any insoluble solid and the filtrate was kept under a slow
sweep of nitrogen gas. Deep red crystals were isolated from the
solution within 2 d; yield 0.55 g (86%). C72H116FeNO4Se2
(1273.48 gmol–1): calcd. C 67.91, H 9.18, N 1.10; found C 68.1, H
9.2, N 1.2. IR: ν = 3447 (br), 2949–2872 (s), 1429 (s), 1302 (s), 1094,
˜
835, 731, 536 cm–1. Absorption spectrum (CH2Cl2) λmax (nm), ε
(m–1 cm–1): 463, 9650. ESI-MS (CH2Cl2): m/z = 242.2 (positive,
Bu4N+), m/z = 1030.5 (negative, M–).
2,2Ј-Diselenobis(4,6-di-tert-butylphenol), H2LSe–Se: To a suspension
of metallic selenium (2.1 g, 27 mmol) and selenium dioxide (1.0 g,
9 mmol) in conc. hydrochloric acid (20 mL), conc. sulfuric acid
(2.5 mL) was added drop wise and with constant stirring over a
period of 30 min. The reaction was stirred for another 2 h to settle
a red oily liquid. Chloroform (15 mL) was added to the mixture.
Then a mixture of 2,4-di-tert-butylphenol (3.6 g, 17 mmol) in chlo-
roform (15 mL) was added drop wise with a syringe and the reac-
tion mixture was stirred for another 8 h at room temperature. The
resulting solution was filtered through a celite bed, the filtrate was
washed with brine solution, and the organic part was dried with
anhydrous sodium sulfate and concentrated in vacuo. A brown so-
lid emulsion was formed that was subjected to column chromatog-
raphy with hexane to give a brown solid. The brown solid was
recrystallized from a methanol/hexane (1:1) mixture to afford
H2LSe–Se as a yellow solid; yield 2.50 g (25%); m.p. 108 °C.
C28H42O2Se2 (568.56 gmol–1): calcd. C 59.15, H 7.45; found C 58.9,
H 7.6. ESI-MS (in positive ion mode, methanol) m/z = 593.05
Bu4N[FeLSeЈLSe] (3): H2LSe (0.5 mmol, 0.245 g) and H2LSe–Se
(0.5 mmol, 0.285 g) were dissolved in dry CH3OH (25 mL) under
nitrogen. To this mixture a light yellow solution of Bu4NOCH3
(2 mL, 20% methanolic solution) was added, which turned the re-
action solution deep yellow. After stirring the solution for 15 min
under nitrogen, FeCl2 (0.13 g, 1 mmol) was added and the solution
immediately turned pink/red. Within 1 h a deep red crystalline
complex was isolated from the solution; yield 0.29 g (55%).
C58H96FeNO3Se2 (1069.13 gmol–1): calcd. C 65.16, H 9.05, N 1.31;
found C 65.3, H 8.8, N 1.1. IR: ν = 3447 (br), 2959–2871 (s), 1425
˜
(s), 1280–1253 (s), 1095, 834, 733, 547 cm–1. Absorption spectrum
(CH2Cl2) λmax (nm), ε (m–1 cm–1): 341(sh), 10940; 504, 9650. ESI-
MS (CH2Cl2): m/z = 242.2 (positive, Bu4N+), m/z = 827.5 (negative,
M–).
Bu4N[FeLSЈLS] (4): Complex 4 was synthesized by a procedure sim-
ilar to that described for 3 except that H2LS and H2LS–S were used
instead of the selenium analogues; yield 0.41 g (84%).
C58H96FeNO3S2 (975.37 gmol–1): calcd. C 71.42, H 9.92, N 1.44,
1
(100%, [H2LSe–Se +Na]+). H NMR (300 MHz, CDCl3): δ = 1.24
(s, 9 H), 1.42 (s, 9 H), 1.63 (s, 18 H), 6.28 (s, 2 H, OH), 7.30, 7.31
(m, 4 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 29.73, 31.57,
34.45, 35.42, 117.21, 125.56, 129.81, 135.86, 143.48, 151.74 ppm.
S 6.57; found C 71.1, H 9.8, N 1.5, S 6.6. IR: ν = 3447 (br), 2960–
˜
2872 (s), 1434 (s), 1288–1254 (s), 1102, 835, 741, 549 cm–1. Absorp-
tion spectrum (CH2Cl2) λmax (nm), ε (m–1 cm–1): 492, 7690. ESI–
MS (CH2Cl2): m/z = 242.2 (positive, Bu4N+), m/z = 732.4 (negative,
M–).
2,2Ј-Dithiobis(4,6-di-tert-butylphenol), H2LS–S: To a solution of 2,4-
di-tert-butylphenol (15.8 g, 76.7 mmol) in toluene (30 mL) was
added, over a period of 2 h and at room temperature, a solution of
S2Cl2 (3.42 mL, 43.3 mmol) in toluene (20 mL). The reaction mix-
ture was stirred at 80 °C for an additional 90 min. The solvent was
evaporated and the viscous, orange-brown crude product was dis-
solved in hot ethanol. The solution was cooled and the product
extracted and then recrystallized from CH3OH as a light yellow
compound; yield 5.8 g (32%); m.p. 140 °C. C28H42O2S2
(474.76 gmol–1): calcd. C 70.84, H 8.92, S 13.51; found C 70.9, H
Acknowledgments
We are grateful to the Deutsche Forschungsgemeinschaft (DFG)
and the Department of Science and Technology (DST), India for
the financial support. D. S. acknowledges the Council of Scientific
and Industrial Research (CSIR), India for a fellowship. Skilful
technical assistance of Mrs. H. Schucht, Mr. A. Göbel and Mr. B.
Mienert is thankfully acknowledged. This work was initiated by
T. K. P. during his stay in Mülheim.
1
8.7, S 12.9. H NMR (300 MHz, CDCl3): δ = 1.28 (s, 18 H), 1.41
(s, 18 H), 6.52 (s, 2 H, OH), 7.40–7.47 (m, 4 H) ppm. EI-MS: m/z
(%) = 474(44) [M+].
[Fe2LSe2(μ-OCH3)2(CH3OH)2] (1): The ligand H2LSe (0.49 g,
1 mmol) was dissolved in dry CH3OH (40 mL). To this mixture
Bu4NOCH3 (2.5 mL, 20% methanolic solution) was added and the
solution stirred under argon for 5 min. To this, a yellow solution
of FeCl2 (0.13 g, 1 mmol) was added and the resulting brown solu-
tion was refluxed under argon for 0.5 h. After cooling, the solution
was opened to air and stirred for another 15 min. A deep brown
microcrystalline compound was isolated by filtration and air-dried.
X-ray diffraction quality crystals of 1·7CH3OH were grown from
a solvent mixture of CH2Cl2 and CH3OH (1:1); yield 0.35 g (49%).
1·4CH3OH (1341.16 gmol–1): calcd. C 57.31, H 8.27; found C 57.6,
[1] a) S. Dai, C. Schwendtmayer, P. Schürmann, S. Ramaswamy,
H. Eklund, Science 2000, 287, 655–658; b) N. M. Giles, G. I.
Giles, C. Jacob, Biochem. Biophys. Res. Commun. 2003, 300, 1–
4; c) C. Jacob, Nat. Prod. Rep. 2006, 23, 851–863; d) C. Jacob,
I. Knight, P. G. Winyard, Biol. Chem. 2006, 387,1385–1397; e)
S. Raina, D. Missiakas, Annu. Rev. Microbiol. 1997, 51, 179–
202; f) C. Jacob, G. I. Giles, N. M. Giles, H. Sies, Angew. Chem.
2003, 115, 4890–4907; Angew. Chem. Int. Ed. 2003, 42, 4742–
4758.
[2] L. Banci, I. Bertini, V. Calderone, S. Ciofi-Baffoni, S. Mangani,
M. Martinelli, P. Palumaa, S. Wang, Proc. Natl. Acad. Sci.
USA 2006, 103, 8595–8600.
H 8.2. IR: ν = 3442(br), 2955–2817(s), 1433(s), 1287–1255(s), 1042,
˜
[3] See for example: a) R. Hunter, M. Caira, N. Stellenboom, J.
Org. Chem. 2006, 71, 8268–8271; b) M. Kirihara, Y. Asai, S.
Ogawa, T. Noguchi, A. Hatano, Y. Hirai, Synthesis 2007, 3286–
3289; c) A. Khazaei, M. A. Zolfigol, A. Rostami, Synthesis
2004, 2959–2961.
[4] a) D. Liotta, U. Sunay, H. Santiesteban, W. Markiewicz, J. Org.
Chem. 1981, 46, 2605–2610; b) H. Suzuki, M. Yoshinaga, K.
1014, 835, 733, 565. Absorption spectrum (CH2Cl2) λmax (nm), ε
(m–1 cm–1): 484, 3600.
Bu4N[FeLSe2] (2): The ligand H2LSe (0.49 g, 1 mmol) was dissolved
in dry CH3OH (30 mL). To this mixture Bu4NOH (3 mL, 1 m
methanolic solution) was added and the solution stirred under ar-
gon for 5 min. To this, a yellow solution of FeCl2 (0.065 g,
5256
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 5250–5257

Fe-Mediated Reductive Cleavage of Disulfide and Diselenide Bonds
Takaoka, Y. Hiroi, Synthesis 1985, 497–499; c) K. B. Sharpless,
R. F. Laura, J. Am. Chem. Soc. 1973, 95, 2697–2699.
Fleischer, S. Hawkinson, J. Am. Chem. Soc. 1967, 89, 720–721.
[14]
J. A. Thich, C. Chih Ou, D. Powers, B. Vasiliou, D. Mastropa-
olo, J. A. Potenza, H. J. Schugar, J. Am. Chem. Soc. 1976, 98,
1425–1433.
M. R. Snow, J. A. Ibers, Inorg. Chem. 1973, 12, 249–254.
A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn, G. C. Ver-
[5] For
a selective example, see: N. Roy, S. Sproules, T.
Weyhermüller, K. Wieghardt, Inorg. Chem. 2009, 48, 3783–
3791.
[6] J. M. Gonzales, D. J. Musaev, K. Morokuma, Organometallics
2005, 24, 4908–4914.
[15]
[16]
schoor, J. Chem. Soc., Dalton Trans. 1984, 1349–1356.
[7] D. Carrillo, Coord. Chem. Rev. 1992, 119, 137–169.
[8] a) S. Itoh, M. Nagagawa, S. Fukuzumi, J. Am. Chem. Soc.
2001, 123, 4087–4088; b) J. S. Figueroa, K. Yurkerwich, J. Mel-
nick, D. Buccella, G. Parkin, Inorg. Chem. 2007, 46, 9234–9244;
c) L. Han, X. Bu, Q. Zhang, P. Feng, Inorg. Chem. 2006, 45,
5736–5738.
[9] For representative examples, see: a) T. K. Paine, T.
Weyhermüller, K. Wieghardt, P. Chaudhuri, Inorg. Chem. 2002,
41, 6538–6540; b) T. K. Paine, T. Weyhermüller, L. D. Slep, F.
Neese, E. Bill, E. Bothe, K. Wieghardt, P. Chaudhuri, Inorg.
Chem. 2004, 43, 7324–7338; c) T. K. Paine, T. Weyhermüller,
K. Wieghardt, P. Chaudhuri, Dalton Trans. 2004, 2092–2101;
d) P. Chaudhuri, K. Wieghardt, T. Weyhermüller, T. K. Paine,
S. Mukherjee, C. Mukherjee, Biol. Chem. 2005, 386, 1023–
1033.
[10] M. Hesse, H. Meier, B. Zeeh, in: Spektroskopische Methode
in der Organischen Chemie, Georg Thieme Verlag, Stuttgart,
Germany, 1995.
[11] A. B. P. Lever, in: Inorganic Electronic Spectroscopy, Elsevier,
Amsterdam, 1984.
[12] a) J. D. Walker, R. Poli, Inorg. Chem. 1990, 29, 756–761; b) R.
Viswanathan, M. Palaniandavar, P. Pravakaran, P. T. Muthiah,
Inorg. Chem. 1998, 37, 3881–3884.
[17]
a) B. S. Synder, G. S. Patterson, A. J. Abrahamson, R. Holm,
J. Am. Chem. Soc. 1989, 111, 5214–5223; b) P. Chaudhuri, M.
Winter, P. Fleischhauer, W. Haase, U. Flörke, H.-J. Haupt, In-
org. Chim. Acta 1993, 212, 241–249.
E. Bill, julX Program, Max-Planck-Institut für Bioanorganis-
che Chemie, Mülheim an der Ruhr, Germany, 2008.
T. Weyhermüller, R. Wagner, P. Chaudhuri, Eur. J. Inorg. Chem.
2011, 2547–2557, and references cited therein.
a) B. Albela, E. Bill, O. Brosch, T. Weyhermüller, K. Wiegh-
ardt, Eur. J. Inorg. Chem. 2000, 139–146; b) W. Hibbs, P. J.
van Koningsbruggen, A. M. Arif, W. W. Shum, J. S. Miller, In-
org. Chem. 2003, 42, 5645–5653; c) T. Mochizuki, T. Nogami,
T. Ishida, Inorg. Chem. 2009, 48, 2254–2259.
a) ShelXTL v.6.14, Bruker AXS Inc., Madison, WI, USA,
2003; b) G. M. Sheldrick, SADABS, Bruker–Siemens Area De-
tector Absorption and Other Correction, version 2006/1, Univer-
sity of Göttingen, Germany, 2006; c) G. M. Sheldrick,
ShelXL97, University of Göttingen, Germany, 1997; d) PLA-
TON program suite: A. L. Spek, Acta Crystallogr., Sect. D
2009, 65, 148–155.
S. D. Pastor, J. D. Spivack, L. P. Steinhuebel, J. Heterocycl.
Chem. 1984, 21, 1285–1287.
a) T. Thompson, S. D. Pastor, G. Rihs, Inorg. Chem. 1999, 38,
4163–4167; b) T. K. Paine, E. Rentschler, T. Weyhermüller, P.
Chaudhuri, Eur. J. Inorg. Chem. 2003, 3167–3178; c) T. K.
Paine, T. Weyhermüller, E. Bothe, K. Wieghardt, P. Chaudhuri,
Dalton Trans. 2003, 3136–3144.
[18]
[19]
[20]
[21]
[22]
[23]
[13] a) B. Chiari, O. Piovesana, T. Tarantelli, P. F. Zanazzi, Inorg.
Chem. 1982, 21, 1396–1402; b) J. E. Davies, B. M. Gatehouse,
J. Chem. Soc., D 1970, 1166; c) J. A. Bertrand, J. L. Breece,
P. G. Eller, Inorg. Chem. 1974, 13, 927–934; d) J. A. Bertrand,
J. L. Breece, A. R. Kalyanaraman, G. J. Long, W. A. Baker Jr.,
J. Am. Chem. Soc. 1970, 92, 5233–5234; e) J. A. Bertrand, J. L.
Breece, P. G. Eller, Inorg. Chem. 1974, 13, 125–131; f) M. Ger-
loch, F. E. Mabbs, J. Chem. Soc. A 1967, 1598–1608; g) E.
Received: July 1, 2011
Published Online: November 3, 2011
Eur. J. Inorg. Chem. 2011, 5250–5257
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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