Synthesis of V/Fe/S clusters using vanadium(III) thiolate complexes bearing a phenoxide-based tridentate ligand

Article abstract of DOI:10.1021/ic4030603

Vanadium(III) thiolate complexes carrying a phenoxide-based tridentate ligand were prepared from the reactions of V(NMe₂)₄ with the protonated forms of tridentate ligands (H₂(O,P,O) = bis(3,5-di-tert-butyl-2-hydroxyphenyl)phenylphosphine or H₂(O,O,O) = bis(3,5-di-tert-butyl-2-hydroxyphenyl)phenylphosphineoxide) and thiols (HSR; R = mesityl (Mes), 2,4,6-ⁱPr₃C₆H₂ (Tip)). The vanadium-thiolate complexes were subjected to the V/Fe/S cluster synthesis via treatment with an Fe(II) thiolate complex [(TipS)Fe] ₂(μ-SDmp)₂ (4, Dmp = 2,6-(mesityl)₂C ₆H₃) and elemental sulfur in toluene, leading to the formation of two new V/Fe/S clusters. One is an edge-bridged double-cubane-type [VFe₃S₄]-[VFe₃S₄] cluster [(O,P,O)VFe₃S₄(SDmp)(HNMe₂)]₂ (5) having face-capping tridentate (O,P,O) ligands on vanadium atoms. The other is a [VFe₃S₄-Fe] cluster [(μ-O,O,O)VFe₃S ₄(SDmp)(STip)Fe(μ-SDmp)] (6), the core of which consists of a cubane-type [VFe₃S₄] unit and an external iron atom. The external iron is bound to an SDmp ligand and two oxygen atoms of the tridentate (O,O,O) ligand. Cluster 6 is structurally relevant to the active site of nickel-dependent CO dehydrogenase, and their common structural features include a cubane-type unit with a heterometal, one more iron atom besides the cubane unit, and a bridging ligand between the external iron and the heterometal of the cubane unit.

Full text of DOI:10.1021/ic4030603

Article
pubs.acs.org/IC
Synthesis of V/Fe/S Clusters Using Vanadium(III) Thiolate Complexes
Bearing a Phenoxide-Based Tridentate Ligand
Nobuhiro Taniyama, Yasuhiro Ohki, and Kazuyuki Tatsumi*
Department of Chemistry, Graduate School of Science and Research Center for Materials Science, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya 464-8602, Japan
S
* Supporting Information
ABSTRACT: Vanadium(III) thiolate complexes carrying a phenoxide-based
tridentate ligand were prepared from the reactions of V(NMe2)4 with the protonated
forms of tridentate ligands (H2(O,P,O) = bis(3,5-di-tert-butyl-2-hydroxyphenyl)-
phenylphosphine or H2(O,O,O) = bis(3,5-di-tert-butyl-2-hydroxyphenyl)phenyl-
phosphineoxide) and thiols (HSR; R = mesityl (Mes), 2,4,6-iPr3C6H2 (Tip)). The
vanadium−thiolate complexes were subjected to the V/Fe/S cluster synthesis via
treatment with an Fe(II) thiolate complex [(TipS)Fe]2(μ-SDmp)2 (4, Dmp = 2,6-
(mesityl)2C6H3) and elemental sulfur in toluene, leading to the formation of two new
V/Fe/S clusters. One is an edge-bridged double-cubane-type [VFe3S4]-[VFe3S4] cluster [(O,P,O)VFe3S4(SDmp)(HNMe2)]2
(5) having face-capping tridentate (O,P,O) ligands on vanadium atoms. The other is a [VFe3S4-Fe] cluster [(μ-
O,O,O)VFe3S4(SDmp)(STip)Fe(μ-SDmp)] (6), the core of which consists of a cubane-type [VFe3S4] unit and an external
iron atom. The external iron is bound to an SDmp ligand and two oxygen atoms of the tridentate (O,O,O) ligand. Cluster 6 is
structurally relevant to the active site of nickel-dependent CO dehydrogenase, and their common structural features include a
cubane-type unit with a heterometal, one more iron atom besides the cubane unit, and a bridging ligand between the external
iron and the heterometal of the cubane unit.
Chart 1. Nitrogenase FeMo-Cofactor and the Active Site of
Ni-Dependent CO Dehydrogenase. Cys = Cysteine, His =
Histidine
INTRODUCTION
■
Metal−sulfur clusters are abundant in living organisms,
mediating electron transfer and chemical transformations.1−3
While the majority of these clusters are iron−sulfur clusters,
some clusters with two transition elements have been found in
the active sites of metalloenzymes involved in small molecule
activation. Representative examples include the FeMo-cofactor
of nitrogenase, which catalyzes the reduction of N2 into NH3,4
the FeV-cofactor of vanadium-dependent nitrogenase,5 and the
[NiFe4S4] cluster active site of nickel-dependent CO
dehydrogenase, which catalyzes the interconversion between
CO and CO2 (Chart 1).3b,6 The complicated structures and the
reducing activities of these clusters have been attracting
interests, and hence, they have been important synthetic targets
for inorganic chemists. Thus far, Holm and co-workers have
synthesized a series of M/Fe/S (M = Mo, V) clusters
topologically analogous to the nitrogenase P-cluster,7 and
they have also prepared [NiFe3S4] cubane-type clusters
mimicking the active site of CO dehydrogenase.8 Coucouvanis
et al. have reported some incomplete cubane-type [MoFe3S3]
clusters carrying a catecholate and a pyridine ligand on
molybdenum, which can be seen as a fragment of the FeMo-
cofactor.9 Notably, for the assembly of these cluster cores, polar
organic solvents (i.e., CH3CN and CH3OH) have been
commonly used to dissolve the ionic reactants, such as
tetrathio-molybdates, thiolates, and iron chlorides.
and high-potential iron−sulfur proteins.11 As shown in Scheme
1, the reaction of an Fe(II) thiolate complex with elemental
sulfur in toluene was found to give an [Fe8S7] cluster
[Fe4S3(SDmp)]2(μ-SDmp)2(μ-STip)(μ6-S) (A; Tip =
2,4,6-iPr3C6H2, Dmp = 2,6-(mesityl)2C6H3).10b In contrast to
We have developed a synthetic method to prepare iron−
sulfur clusters in toluene and have successfully synthesized a
series of clusters mimicking the metalloclusters in nitrogenase10
Received: December 13, 2013
Published: May 19, 2014
© 2014 American Chemical Society
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complex V(NMe2)4 (1) was used as the precursor to synthesize
new vanadium−thiolate complexes. Complex 1 was treated
with the protonated forms of tridentate ligands H2(O,P,O) or
H2(O,O,O) and then with 2 equiv of thiols, resulting in the
formation of the V(III)−thiolate complexes bearing a tridentate
ligand and a dimethylamine ligand, (O,P,O)V(SR)(HNMe2)
(2a, R = (mesityl) Mes; 2b, R = 2,4,6-iPr3C6H2 (Tip)) or
(O,O,O)V(SR)(HNMe2) (3a, R = Mes; 3b, R = Tip) (Scheme
2). The first step of the reaction sequence of Scheme 2 involves
Scheme 1
Scheme 2
ordinary synthetic iron−sulfur clusters with four or less than
four iron atoms, cluster A contains eight iron atoms and has an
intriguing structural relevance to the FeMo-cofactor in that two
[M4S3] incomplete cuboidal units (M = metals) are connected
by a central μ6 atom and three bridging sulfur donors. The
successful synthesis of FeMo-cofactor mimic A prompted us to
expand the scope of this reaction for the synthesis of V/Fe/S
clusters, by incorporating vanadium complexes into the reaction
mixture. As our cluster synthesis is carried out in toluene, a
series of new vanadium−thiolate precursors were prepared in
this study from the reactions of V(NMe2)4 (1)12 with tridentate
ligands and thiols. Chart 2 shows the phenoxide-based
the replacement of two amide ligands with a tridentate ligand
via proton transfer to generate a putative intermediary complex
(O,E,O)V(NMe2)2 (E = O, P), in which amide ligands take up
protons from thiols in the following step. These proton transfer
reactions provide dimethylamine, which serves as a ligand in
complexes 2a−2b and 3a−3b. Whereas the replacement of
amide ligands in (O,E,O)V(NMe2)2 with thiolates is expected
to give a V(IV) complex (O,E,O)V(SR)2, the products in
Scheme 2 are V(III) complexes with one thiolate ligand.
Dissociation of an −SR group from the tentative intermediate
(O,E,O)V(SR)2 accounts for the reduction from V(IV) to
V(III), while the possible byproduct RS-SR has not been
detected.
The V(III) oxidation state of complexes 2a−2b and 3a−3b
was supported by the EPR spectra and the magnetic
susceptibility measurements. The room-temperature EPR
spectra of complexes 2a−2b (in THF) and 3a−3b (in toluene)
were silent, as the V(III) complexes with low symmetry are
known to become EPR-silent at conventional frequencies and
fields.15 The silent EPR spectra are inconsistent with the EPR-
active V(IV) state (d1 configuration), which is expected to give
an S = 1/2 signal. Temperature-dependent magnetic
susceptibilities of complexes 2a−2b and 3a−3b were measured
by the SQUID magnetometer (Supporting Information, Figure
S2). The effective magnetic moments of these complexes are
nearly constant in the range of 50−300 K, μeff = 2.76−2.94 μB
(2a), 2.51−2.74 μB (2b), 2.54−2.55 μB (3a), and 2.46−2.65 μB
(3b). In agreement with the V(III) state (d2 configuration),
these magnetic moments are similar to the spin-only value for
the S = 1 state (2.83 μB). The cyclic voltammograms (CVs) for
2a−2b and 3a−3b were measured in THF at room
Chart 2. Tridentate Ligands Used in This Study
tridentate ligands, whose protonated forms are denoted as
H2(O,P,O) and H2(O,O,O) in this paper (H2(O,P,O) =
bis(3,5-di-tert-butyl-2-hydroxyphenyl)phenylphosphine, H2-
(O,O,O) = bis(3,5-di-tert-butyl-2-hydroxyphenyl)phenyl-
phosphineoxide).13 The (O,P,O) ligand has been demonstrated
to coordinate to Ti, V, Ta, Co, and Rh as a facial tridentate
ligand,13,14 and the (O,O,O) ligand is available via oxidation of
H2(O,P,O) with H2O2.13 Herein, we report the reactions of
new vanadium−thiolate complexes with an Fe(II) thiolate
complex and elemental sulfur in toluene, leading to the
formation of two new V/Fe/S clusters. One of the new clusters
is an edge-bridged double-cubane-type [VFe3S4]-[VFe3S4]
cluster, and the other is a [VFe3S4-Fe] cluster that is structurally
relevant to the active site of nickel-dependent CO dehydrogen-
ase.
RESULTS AND DISCUSSION
Synthesis of V(III)−Thiolate Complexes Having a
Tridentate Ligand. In this study, vanadium(IV) amide
■
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temperature using [nBu4N][PF6] as an electrolyte, where some
irreversible oxidation and reduction waves appeared (Figure S3,
Supporting Information). The common features are the
reduction waves at Epc = −2.08 to −2.27 V, and the oxidation
waves of the corresponding species after reducing V(III)
complexes appearing at Epa = −1.33 to −1.37 V. These
reduction/oxidation waves are coupled, and therefore, the
oxidation waves at −1.33 to −1.37 V were not found in the
CVs measured in the range of 0 to −2.0 V. In the CVs of 2a−
3b scanning toward positive potentials up to 1.0 V, large
irreversible oxidation waves were observed at Epa = 0.18−0.35
V. These waves would be assigned as the oxidation from V(III)
to V(IV), and one of the possibilities accounting for the
irreversibility is the dissociation of an −SR group from
vanadium as 1/2 RS-SR.
shown in the Supporting Information). The vanadium center is
five-coordinate in these V(III)−thiolate complexes, with a
tridentate ligand occupying two equatorial and one axial
position. The dimethylamine ligand is located at the axial
position, while the thiolate ligand is on the equatorial plane.
The atoms in axial positions are linearly aligned with vanadium
(P−V−N 166.28(6)° for 2a and O−V−N 178.06(6)° for 3a).
The sums of S−V−O and O−V−O angles in the equatorial
plane are 359.76(17)° (2a) and 359.92(16)° (3a). The V−S
bond distances of 2a (2.2931(8) Å) and 3a (2.3136(8) Å) are
close to those in a trigonal-bipyramidal V(III) complex
V(STip)3(THF)2 (2.308(1)−2.334(1) Å).16 The V−N(amine)
distances of 2.178(3) Å (2a) and 2.2008(19) Å (3a) are also
analogous to those in V(III)−amine complexes (2.146(7)−
2.290(2) Å).17
Reactions of V(III) Thiolate Complexes with an Fe(II)
Thiolate Complex and Elemental Sulfur. (O,P,O)V
Complex. The V(III)−thiolate complexes were incorporated
into a mixture of 4 and S8 for the synthesis of V/Fe/S clusters.
Considering the rapid reaction of 2a with elemental sulfur, we
mixed the reactants in the order of 4, elemental sulfur, and 2a
in toluene. From the reaction of 4 with S8 and 2a in the ratio of
V:Fe:S = 1:3:4, an edge-bridged double-cubane-type [VFe3S4]-
[VFe3S4] cluster [(O,P,O)VFe3S4(SDmp)(HNMe2)]2 (5) was
obtained in 22% yield as black needles (Scheme 3). While some
edge-bridged double-cubane-type [VFe3S4]-[VFe3S4] clusters
have been reported,18 the [V2Fe6S8]6+ state of 5 is much higher
than the known [V2Fe6S8]2+ clusters. The unique oxidation
state of 5 shows the accessibility of a wide range of oxidation
states in the edge-bridged double-cubane clusters. The effective
magnetic moment of 5 in the solid state gradually decreases
upon lowering the temperature, from 3.10 μB at 300 K to 0.89
μB at 2 K (Figure S5, Supporting Information), and the
moment at 2 K is lower than the spin-only value for the S = 1/2
state (1.73 μB). On the other hand, the EPR spectrum of 5 in
frozen toluene at 8 K19 exhibited an S = 1/2 signal at g = 2.01
with multiple lines due to the nuclear spin of vanadium (Figure
S6, Supporting Information). This result is inconsistent with
the even number of electrons present in the centrosymmetric
cluster 5, as the odd number of electrons are required for the
appearance of the S = 1/2 signal. We speculate two possible
reasons: (i) partial contamination of the 1e-oxidized species
with one missing hydrogen atom in one of the HNMe2 ligands
or the 1e-reduced species with an additional hydrogen atom on
one of the oxygen/sulfur atoms in the same crystals, and (ii)
partial decomposition of 5 in solution. The reason remains
unclear, while the magnetic moment of 0.89 μB at 2 K for
crystal samples is in between the S = 0 and 1/2 states. In the
cyclic voltammogram of 5 in THF, an irreversible reduction
wave was observed at −1.06 V vs Ag/AgNO3 (Figure S7,
Supporting Information). The possible reasons for the
irreversibility of the reduction wave include the dissociation
of HNMe2 from iron and the splitting of the [VFe3S4]-[VFe3S4]
cluster into two [VFe3S4] clusters upon reduction. Therefore,
the measurement was also carried out in the presence of
dimethylamine (2−4 equiv), but the reduction wave remained
The molecular structures of complexes 2a−2b and 3a−3b
were determined by X-ray crystallographic analysis, and
perspective views of 2a and 3a are shown in Figure 1 (others
Figure 1. Molecular structures of 2a and 3a with thermal ellipsoids at
the 30% probability level. Selected distances (Å) and angles (deg): 2a:
V1−S1 = 2.2931(8), V1−P1 = 2.4624(7), V1−O1 = 1.8911(17), V1−
O2 = 1.8976(16), V1−N1 = 2.178(3); S1−V1−P1 = 102.44(3), S1−
V1−O1 = 119.51(6), S1−V1−O2 = 125.12(6), S1−V1−N1 =
91.28(6), P1−V1−O1 = 81.09(6), P1−V1−O2 = 80.78(5), P1−
V1−N1 = 166.28(6), O1−V1−O2 = 115.13(7), O1−V1−N1 =
91.94(8), O2−V1−N1 = 91.67(8). 3a: V1−S1 = 2.3136(8), V1−O1 =
1.9026(13), V1−O2 = 1.8921(16), V1−O3 = 2.0332(15), V1−N1 =
2.2008(19); S1−V1−O1 = 130.65(5), S1−V1−O2 = 122.67(5), S1−
V1−O3 = 91.53(5), S1−V1−N1 = 88.40(5), O1−V1−O2 =
106.60(6), O1−V1−O3 = 89.57(6), O1−V1−N1 = 89.01(6), O2−
V1−O3 = 91.66(6), O2−V1−N1 = 90.01(7), O3−V1−N1 =
178.06(7).
irreversible and one more reduction wave appeared at Epc
=
−1.14 V. The second wave may come from the monomeric
[VFe3S4] species, which is possibly generated via the splitting of
the [VFe3S4]-[VFe3S4] cluster and the coordination of HNMe2
to iron. The addition of a large excess (>20 equiv) of
dimethylamine resulted in the disappearance of the reduction
wave, indicating the degradation of the cluster.
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Scheme 3
The molecular structure of 5 was determined by crystallo-
graphic analysis, as shown in Figure 2, whereas the insufficient
ligand, three irons, and four sulfurs. The two [VFe3S4] units are
connected through one of the Fe−S edges of cubes, defining an
Fe2S2 rhomb in the middle. In analogy to the precedent edge-
bridged double-cubane-type [VFe3S4]-[VFe3S4] clusters,18 the
intracubane Fe−S distance within the rhomb (Fe2−S4,
2.357(5) Å) is longer than the intercubane Fe−S distance
(Fe2−S4′, 2.280(5) Å). In contrast to the precedent [VFe3S4]-
[VFe3S4] clusters with peripheral vanadium atoms, the (O,P,O)
V groups in 5 are located next to the central Fe2S2 rhomb.
Another notable difference between the [V2Fe6S8]6+ cluster 5
and the precedent [V2Fe6S8]2+ clusters is the oxidation state,
and the oxidation states of metals in 5 would be assigned as
V(III)2Fe(II)2Fe(III)4 or V(IV)2Fe(II)4Fe(III)2. Although the
higher oxidation state of 5 is expected to lead to the shorter V−
S and V−Fe distances due to the smaller radius of metals, the
V−S distances ranging from 2.385(5) to 2.436(4) Å are longer
than those of the known [VFe3S4]-[VFe3S4] clusters (2.35(2)−
2.372(2) Å), and the V−Fe distances of 5 (2.789(4)−3.165(6)
Å) are also longer than those of precedent clusters (2.702(2)−
2.831(2) Å). Among the V−Fe distances of 5, V−Fe1
(3.165(6) Å) is particularly long possibly because the phenyl
group of the (O,P,O) ligand is orienting toward the thiolate
ligand on Fe1, causing a steric congestion.
(O,O,O)V Complex. Encouraged by the preparation of a
double-cubane-type cluster 5, the V/Fe/S cluster synthesis was
also examined with the (O,O,O)V−thiolate complex 3b. When
complex 3b was mixed with an iron−thiolate complex 4 and
then with elemental sulfur in the ratio of V:Fe:S = 1:4:4, black
crystals of a cubane-type cluster carrying an external iron atom,
[(μ-O,O,O)VFe3S4(SDmp)(STip)Fe(μ-SDmp)] (6), was ob-
tained in 10% yield (Scheme 4). An analogous reaction using
3a (bearing an −SMes ligand) also gave rise to the same cluster
6 in 8% yield, indicating that the thiolate ligands in the
vanadium precursors readily dissociate upon treatment with
elemental sulfur. The magnetic moment of 6 was observed to
be similar in the range of 50−300 K, μeff = 4.38−4.80 μB
(Figure S8, Supporting Information), which is close to the spin-
Figure 2. Molecular structure of 5 with thermal ellipsoids at the 30%
probability level. Selected distances (Å) and angles (deg): V1−S1 =
2.385(5), V1−S2 = 2.436(4), V1−S4 = 2.420(5), V−O1 = 1.925(7),
V1−O2 = 1.891(10), V1−P1 = 2.388(5), V1−Fe2 = 2.789(4), V1−
Fe3 = 2.837(4), Fe1−Fe2 = 2.703(3), Fe1−Fe3 = 2.730(4), Fe2−Fe3
= 2.561(5), Fe2−Fe2′ = 2.716(4), Fe1−S1 = 2.293(4), Fe1−S2 =
2.276(5), Fe1−S3 = 2.210(5), Fe1−S5 = 2.194(4), Fe2−S1 =
2.218(5), Fe2−S3 = 2.281(5), Fe2−S4 = 2.357(5), Fe2−S4′ =
2.280(5), Fe3−S2 = 2.212(5), Fe3−S3 = 2.277(5), Fe3−S4 =
2.312(4); Fe2−S4−Fe2′ = 71.69(13), S4−Fe2−S4′ = 108.31(13).
quality of thin needle crystals enables limited discussion on the
structure. Cluster 5 consists of two cubane-type units, each
consisting of one vanadium carrying a face-capping (O,P,O)
Scheme 4
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only value for the S = 2 state (4.90 μB). There was no
significant signal in the EPR spectrum of 6 in frozen toluene at
4−15 K,19 while a few [Fe(SR)4]2− compounds in the S = 2
system are known to exhibit EPR signals at around g = 10.20
The cyclic voltammogram of 6 in THF was almost featureless,
exhibiting very weak waves at Epc = −0.84 V and Epa = −0.73
and −0.45 V (Figure S9, Supporting Information). This may be
due to the degradation of 6 in THF in the presence of
electrolyte [nBu4N][PF6]. The external iron atom in 6
supported by the flexible (O,O,O) ligand and the bridging
SDmp ligand may be released in an electrolyte solution of
THF, and the four-coordinate vanadium would accommodate
THF or fluoride ions from a PF6 anion.
The molecular structure of [VFe3S4-Fe] cluster 6 was
determined by X-ray crystallographic analysis, and an ORTEP
drawing is shown in Figure 3. Cluster 6 consists of a cubane-
type [VFe3S4] unit and an external iron atom (Fe4), which is
linked to the cubane unit through a thiolate sulfur and two
oxygen atoms of the (O,O,O) ligand. Although the external
iron (Fe4) looks three-coordinate, there is a weak interaction
between Fe4 and one of the mesityl rings of SDmp, completing
the distorted tetrahedral geometry. The shortest Fe4−C42
contact of 2.480(4) Å is within the range of Fe−C(arene)
interaction found for the Fe−SDmp complexes (2.389(2)−
2.599(2) Å).10b,e,21 The Fe4−S5 distance (2.3327(12) Å) is
also comparable to those of Fe(II) complexes having μ-SDmp
ligands,10b,e,21 indicating the Fe(II) state for Fe4. The external
Fe4 atom reveals no direct metal−metal interaction, and the
shortest intermetallic distance is 3.6866(9) Å (Fe4−Fe1).
Interestingly, the vanadium atom of 6 is four-coordinate, with
three sulfido ligands and a phenoxide oxygen of the tridentate
(O,O,O) ligand. This is in contrast to the precedent V/Fe/S
clusters in which vanadium atoms are five- or six-coordi-
nate.18,22 Thus, the vanadium in 6 is more electron-deficient,
resulting in the relatively short V−(μ3-S) (2.2112(13)−
2.2466(12) Å) and V−Fe (2.6422(9)−2.6873(10) Å) distances
compared to those reported for the [VFe3S4] and [VFe3S4]-
[VFe3S4] clusters (V−S, 2.303(1)−2.387(2) Å; V−Fe,
2.691(2)−2.8363(6) Å).18,22 On the other hand, the Fe−Fe
(2.6896(8)−2.7409(7) Å) and Fe−(μ3-S) (2.2447(11)−
2.2843(11) Å) distances in the [VFe3S4] core of 6 are
comparable to those reported for the [VFe3S4] clusters (Fe−Fe,
2.569(2)−2.757(2) Å; Fe−(μ3-S), 2.205(2)−2.326(2) Å).22
The cubic core is rigid, and thus, distances and angles within
the cubic core do not vary significantly by the oxidation state of
metals. Further, metal−metal interactions lead to charge
delocalization, hampering the assignments to specific oxidation
states of metals. Nevertheless, the cubane unit of 6 is in the
[VFe3S4]3+ state, for which a tentative assignment of V(III)-
Fe(II)Fe(III)2 would be applied.
It is notable that the [VFe3S4-Fe] core of cluster 6 has
structural relevance to the [NiFe3S4-Fe] cluster active site of
nickel-dependent CO dehydrogenase. As shown in Figure 4,
Figure 3. Molecular structure of 6 with thermal ellipsoids at the 30%
probability level. Selected distances (Å) and angles (deg): V1−S1 =
2.2112(13), V1−S2 = 2.2384(12), V1−S4 = 2.2466(12), V−O1 =
1.786(3), V1−Fe1 = 2.6422(9), V1−Fe2 = 2.6873(10), V1−Fe3 =
2.6581(9), Fe1−Fe2 = 2.7409(7), Fe1−Fe3 = 2.6896(8), Fe2−Fe3 =
2.7330(8), Fe1−S1 = 2.2843(11), Fe1−S2 = 2.2486(13), Fe1−S3 =
2.2525(11), Fe1−S5 = 2.3118(11), Fe2−S1 = 2.2447(11), Fe2−S3 =
2.2577(11), Fe2−S4 = 2.2710(12), Fe2−S6 = 2.2243(13), Fe3−S2 =
2.2686(11), Fe3−S3 = 2.2510(13), Fe3−S4 = 2.2674(10), Fe3−S7 =
2.2232(13), Fe4−S5 = 2.3327(12), Fe4−O2 = 1.911(3), Fe4−O3 =
2.001(3), Fe4−C42 = 2.480(4); S1−V1−S2 = 107.09(5), S1−V1−S4
= 104.80(5), S1−V1−O1 = 113.10(10), S2−V1−S4 = 106.11(5), S2−
V1−O1 = 110.53(10), S4−V1−O1 = 114.65(9), S1−Fe1−S2 =
104.29(4), S1−Fe1−S3 = 102.79(4), S1−Fe1−S5 = 88.43(4), S2−
Fe1−S3 = 105.05(4), S2−Fe1−S5 = 118.49(5), S3−Fe1−S5 =
130.73(5), S1−Fe2−S3 = 103.89(4), S1−Fe2−S4 = 102.91(4), S1−
Fe2−S6 = 96.32(5), S3−Fe2−S4 = 103.51(4), S3−Fe2−S6 =
122.25(5), S4−Fe2−S6 = 123.80(5), S2−Fe3−S3 = 104.44(5), S2−
Fe3−S4 = 104.41(4), S2−Fe3−S7 = 114.23(5), S3−Fe3−S4 =
103.84(5), S3−Fe3−S7 = 114.69(5), S4−Fe3−S7 = 114.01(5), S5−
Fe4−O2 = 125.53(10), S5−Fe4−O3 = 115.83(8), O2−Fe4−O3 =
96.62(12).
Figure 4. Structures of 6 and the active site of Ni-dependent CO
dehydrogenase (CODH), emphasizing their structural relevance.
Protein structural data is taken from PDB entry 3B51.6b
their common structural features include a cubane-type
[MFe3S4] core with a heterometal (M = V or Ni), one more
iron atom besides the cubane core, and a bridging ligand
between the external iron and the heterometal. The structure of
6 also reveals the flexibility of the tridentate (O,O,O) ligand,
which appears to be important to accommodate the external
iron atom. Cluster 6 incorporates vanadium as a heterometal;
however, synthesis of nickel precursors bearing a flexible
(O,O,O) ligand and their reactions with iron−thiolate
complexes and elemental sulfur in toluene may provide
[NiFe3S4-Fe] clusters modeling the active site of CO
dehydrogenase.
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of PhPCl2 (6.0 mL, 44 mmol) was added slowly at −50 °C. The
reaction mixture was gradually warmed to 10 °C and stirred overnight.
A diethyl ether solution of HCl (90.0 mL of 1.0 M solution, 90.0
mmol) was added to the mixture at 0 °C, and the mixture was stirred
at room temperature for 2 h. The solution was centrifuged to remove
LiCl. After removal of the solvent under vacuum, the residue was
dissolved in acetonitrile (50 mL). The solution was stored at −40 °C
to give a white powder of H2(O,P,O) (18.4 g, 80%). 1H NMR
(CDCl3): δ 7.35−7.25 (m, 7H, aromatic H), 6.90 (dd, J = 6.5, 2.1 Hz,
CONCLUDING REMARKS
■
In this study, we have developed a new synthetic route to V/
Fe/S clusters in toluene. A series of precursor vanadium(III)
thiolate complexes 2a−2b and 3a−3b bearing a phenoxide-
based tridentate ligand were synthesized from the reactions of
vanadium(IV) amide complex 1 with H2(O,P,O) or H2-
(O,O,O) and thiols. These vanadium(III) complexes were
found to react with [(TipS)Fe]2(μ-SDmp)2 and elemental
sulfur, producing two new V/Fe/S clusters 5 and 6. Cluster 5 is
an edge-bridged double-cubane-type [VFe3S4]-[VFe3S4] cluster,
and the position of (O,P,O)V units in 5 next to the central
Fe2S2 rhomb is different from the known [VFe3S4]-[VFe3S4]
clusters in which vanadium atoms occupy the peripheral
positions. Cluster 6 consists of a cubane-type [VFe3S4] core
and an external iron atom. Two oxygen atoms of the (O,O,O)
ligand in 6 coordinate the external iron, leaving one phenoxide
oxygen terminally bound to vanadium. One of the thiolate
ligands is also bound to the external iron with its sulfur atom
and an aromatic ring. The synthetic protocol demonstrated in
this study would be applicable to the synthesis of Mo/Fe/S and
Ni/Fe/S clusters in toluene, providing potential routes to
structural mimics of the nitrogenase FeMo-cofactor and the
active site of Ni-dependent CO dehydrogenase. In this regard,
the successful preparation of 6 is particularly encouraging, as
this cluster has structural relevance to the active site of CO
dehydrogenase.
t
2H, aromatic H), 6.27 (d, J = 8.3 Hz, 2H, OH), 1.42 (s, 18H, Bu),
t
1.14 (s, 18H, Bu). 31P{1H} NMR (CDCl3): δ −50.5.
Synthesis of (O,P,O)V(SMes)(HNMe2) (2a). A toluene (10 mL)
solution of H2(O,P,O) (342 mg, 0.66 mmol) was slowly added to a
toluene (10 mL) solution of 1 (150 mg, 0.66 mmol) at −80 °C. The
reaction mixture was gradually warmed to room temperature. The
color of the reaction mixture turned from dark green to dark red. After
stirring for 2.5 h, a toluene (5 mL) solution of HSMes (201 mg, 1.32
mmol) was added at room temperature. The color of the solution
turned to dark yellow. The reaction mixture was stirred for 3.5 h, and
the solvent was removed under reduced pressure to give a dark yellow
oily material. The residue was washed with pentane (10 mL) to afford
an orange powder of 2a (400 mg, 79%). Single crystals suitable for
crystallography were obtained from a THF/pentane solution at −40
°C. UV−vis (THF): λmax = 313 nm (sh, ε 12 000 M−1 cm−1), 335 nm
1
(sh, ε 9600 M−1 cm−1). H NMR (C6D6): δ 13.7, 11.5, 6.33, 2.26
(tBu), 1.23 (tBu), −3.94, −6.12 (Mes). Cyclic voltammogram (2 mM
in THF, potential vs Ag/Ag+): Epc = 0.55, 0.12, −2.24, −2.65 V, Epa
=
0.67, 0.35, 0.18, −1.37 V (irreversible). EPR (microwave power, 1.00
mW; microwave frequency, 9474.082 MHz; modulation width, 0.4
mT; 1 mM in THF): Silent at room temperature. Magnetic
susceptibility (B.M.): μeff = 2.21 (2 K), 2.94 (300 K). Anal. Calcd
for C45H63NO2PSV: C, 70.74; H, 8.31; N, 1.83; S, 4.20. Found: C,
71.06; H, 8.18; N, 1.71; S, 4.22.
EXPERIMENTAL SECTION
■
General Procedures. All reactions were carried out using standard
Schlenk techniques and a glovebox under a nitrogen atmosphere.
Acetonitrile, diethyl ether, hexane, pentane, tetrahydrofuran, and
toluene were purified by the method of Grubbs et al.,23 where the
solvents were passed over columns of activated alumina and a
supported copper catalyst supplied by Hansen & Co. Ltd. The 1H and
31P{1H} NMR spectra were recorded on a JEOL ECA-600. The
Synthesis of (O,P,O)V(STip)(HNMe2) (2b). Complex 2b was
prepared from complex 1 (150 mg, 0.66 mmol), H2(O,P,O) (342 mg,
0.66 mmol), and HSTip (312 mg, 132 mmol) in a similar manner to
that used for 2a. Crystallization from pentane at −40 °C yielded 2b
(213 mg, 39%) as orange crystals. UV−vis (THF): λmax = 326 nm (sh,
1
ε 10 000 M−1 cm−1). H NMR (C6D6): δ 13.7, 6.44, 2.42 (tBu), 1.24
(tBu), 1.03 (iPr of Tip), −1.99, −4.0. Cyclic voltammogram (2 mM in
proton signals were referenced to the residual signals of deuterated
solvents. The 31P{1H} NMR chemical shifts are relative to the external
reference of 85% H3PO4. The 31P NMR of complexes 2a−2b and 3a−
3b were measured in C6D6, but paramagnetism of these complexes led
us to observe no assignable 31P signals. In other words, detection
sensitivity of the 31P NMR is not good enough to clearly show the
broadened paramagnetic signals. UV−vis spectra were measured on a
JASCO V560 spectrometer. Elemental analyses were performed on a
LECO CHNS-932 microanalyzer, where the crystalline samples were
sealed into silver capsules in a glovebox. Cyclic voltammograms (CVs)
were recorded in THF at room temperature using glassy carbon as the
working electrode with 0.2 M [nBu4N][PF6] as the supporting
electrolyte. The potentials were referenced to Ag/AgNO3. The solid-
state magnetic susceptibility was measured using a Quantum Design
MPMS-XL SQUID-type magnetometer, and the samples were sealed
in quartz tubes. The EPR spectrum was recorded on a Bruker EMX-
plus spectrometer at X-band frequencies. X-ray diffraction data were
collected on a Rigaku AFC8 or RA-Micro7 equipped with a CCD area
detector using graphite monochromated Mo Kα radiation. V(NMe2)4
(1),12a [(TipS)Fe]2(μ-SDmp)2 (4),10b HSMes,24 HSTip,25 and
bis(3,5-di-tert-butyl-2-hydroxyphenyl)phenylphosphine oxide (H2-
(O,O,O))13 were prepared according to literature procedures. 2-
Bromo-4,6-di-tert-butylphenol and PhPCl2 were purchased and used as
received.
THF, potential vs Ag/Ag+): Epc = 0.52, 0.06, −0.75, −2.27 V, Epa
=
0.71, 0.34, −0.66, −1.36 V (irreversible). EPR (microwave power, 1.00
mW; microwave frequency, 9474.082 MHz; modulation width, 0.4
mT; 1 mM in THF): Silent at room temperature. Magnetic
susceptibility (B.M.): μeff = 2.15 (2 K), 2.51 (300 K). Anal. Calcd
for C51H75NO2PSV: C, 72.22; H, 8.91; N, 1.65; S, 3.78. Found: C,
72.70; H, 8.57; N, 1.66; S, 4.05.
Synthesis of (O,O,O)V(SMes)(HNMe2) (3a). Complex 3a was
prepared from complex 1 (150 mg, 0.66 mmol), H2(O,O,O) (353 mg,
0.66 mmol), and HSMes (201 mg, 132 mmol) in a similar manner to
that used for 2a. Washing the residue with pentane (10 mL) leaves a
yellow powder of 3a (353 mg, 69%). Single crystals suitable for
crystallography were obtained from a toluene solution at −40 °C.
UV−vis (THF): λmax = 321 nm (ε 12 000 M−1 cm−1). 1H NMR
(C6D6): δ 9.90, 7.97, 6.55, 1.76 (tBu), 1.23, 1.09 (tBu), 0.28, −3.34,
−7.74 (Mes). Cyclic voltammogram (2 mM in THF, potential vs Ag/
Ag+): Epc = 0.53, 0.12, −2.08, −2.63 V, Epa = 0.70, 0.34, 0.19, −0.57,
−1.37 V (irreversible). EPR (microwave power, 1.00 mW; microwave
frequency, 9474.082 MHz; modulation width, 0.4 mT; 1 mM in
toluene): Silent at room temperature. Magnetic susceptibility (B.M.):
μeff = 1.88 (2 K), 2.55 (300 K). Anal. Calcd for C45H63NO3PSV: C,
69.29; H, 8.14; N, 1.80; S, 4.11. Found: C, 69.79; H, 8.08; N, 1.71; S,
3.74.
Synthesis of (O,O,O)V(STip)(HNMe2) (3b). Complex 3b was
prepared from complex 1 (150 mg, 0.66 mmol), H2(O,O,O) (353 mg,
0.66 mmol), and HSTip (312 mg, 132 mmol) in a similar manner to
that used for 2a. Washing the residue with pentane (10 mL) leaves a
yellow powder of 3b (228 mg, 40%). Single crystals suitable for
crystallography were obtained from a toluene solution at −40 °C.
UV−vis (THF): λmax = 321 nm (ε 11 000 M−1 cm−1). 1H NMR
Modified Synthesis of Bis(3,5-di-tert-butyl-2-hydroxy-
phenyl)phenylphosphine (H2(O,P,O)). The yield of H2(O,P,O)
(40% in the literature)13 has been improved to 80%, mainly due to the
scale-up. A hexane solution of nBuLi (111 mL of 1.59 M solution, 176
mmol) was added slowly to a diethyl ether (180 mL) solution of 2-
bromo-4,6-di-tert-butylphenol (25.2 g, 88.3 mmol) at −35 °C. After
stirring at room temperature for 6 h, a diethyl ether solution (60 mL)
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Table 1. Crystal Data for 2a−2b, 3a−3b, 5 and 6
2a
2b
3a·C7H8
3b·(C7H8)2.5
formula
C45H63NO2PSV
763.97
C51H72NO2PSV
845.11
C52H71NO3PSV
872.11
C68.50H75NO3PSV
1074.33
formula wt (g mol−1
crystal system
space group
a (Å)
)
orthorhombic
P212121 (No. 19)
11.9681(13)
13.640(2)
triclinic
monoclinic
P21/c (No. 14)
16.251(5)
monoclinic
P21/n (No. 14)
17.059(3)
P1 (No. 2)
̅
12.868(3)
13.695(3)
14.623(3)
91.954(3)
103.666(3)
97.180(3)
2478.9(8)
2
b (Å)
21.181(6)
17.444(3)
c (Å)
26.614(9)
16.277(5)
21.669(4)
α (deg)
β (deg)
114.506(4)
94.454(2)
γ (deg)
V (Å3)
4344.4(9)
4
5098(3)
4
6429(2)
4
Z
Dcalcd (g/cm3)
1.168
55.0
1.132
1.136
54.7
1.110
54.9
max 2θ (deg)
54.9
no. of reflections measured
no. of data used (I > 2.00σ(I))
no. of parameters refined
35 477
9950
30 009
40 691
11 471
536
51 636
14 385
723
11 253
481
527
a
R1
0.0457
0.1056
1.071
0.0591
0.0493
0.1286
1.074
0.0806
0.2645
1.056
b
wR2
0.1691
c
GOF
1.066
5·(C4H8O·C7H8)0.5
6·(C5H12)2
formula
C71H88Fe3NO3PS5V
1413.24
C107H106Fe4O3PS7V
1969.74
formula wt (g mol−1
crystal system
space group
a (Å)
)
triclinic
triclinic
P1 (No. 2)
̅
P1 (No. 2)
̅
14.50(3)
16.41(3)
17.69(3)
102.80(2)
93.233(9)
114.94(2)
3667(10)
2
15.978(3)
16.111(3)
22.370(4)
87.810(6)
82.923(5)
79.975(5)
5627(2)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
Dcalcd (g/cm3)
1.280
1.163
max 2θ (deg)
51.0
55.0
no. of reflections measured
no. of data used (I > 2.00σ(I))
no. of parameters refined
32 174
13 319
709
69 808
25 680
1078
a
R1
0.1629
0.4614
1.097
0.0640
0.1992
1.011
b
wR2
c
GOF
a
b
c
2
I > 2σ(I), R1 = ∑||Fo| − |Fc||/∑|Fo|. Refined with all data, wR2 = [{∑w(Fo2 − Fc2)2}/∑w(Fo )2]1/2. GOF = [{∑w(Fo2 − Fc2)2}/(N0 − Np)]1/2
,
where N0 and Np denote the numbers of reflection data and parameters.
(C6D6): δ 11.4, 9.81, 8.00, 6.63, 1.71 (tBu), 1.25, 1.20, 1.09 (tBu), 0.97,
0.86 (iPr of Tip), 0.28, −1.44. Cyclic voltammogram (2 mM in THF,
potential vs Ag/Ag+): Epc = 0.54, 0.14, −1.53, −2.16 V, Epa = 0.72,
0.35, 0.20, −0.48, −1.37 V (irreversible). EPR (microwave power, 1.00
mW; microwave frequency, 9474.082 MHz; modulation width, 0.4
mT; 1 mM in toluene): Silent at room temperature. Magnetic
susceptibility (B.M.): μeff = 1.98 (2 K), 2.46 (300 K). Anal. Calcd for
C51H75NO3PSV: C, 70.88; H, 8.75; N, 1.62; S, 3.71. Found: C, 70.98;
H, 8.57; N, 1.68; S, 3.91.
Synthesis of [(O,P,O)VFe3S4(SDmp)(HNMe2)]2 (5). A toluene
(10 mL) solution of S8 (25.2 mg, 0.784 mmol) was added to a toluene
(15 mL) solution of 4 (375 mg, 0.588 mmol) at room temperature.
After stirring for 2.5 h, a toluene (10 mL) solution of 2a (150 mg,
0.196 mmol) was added to the solution at room temperature. The
reaction mixture was stirred for 3 days, and the solvent was removed
under reduced pressure to give a black oily material. The residue was
extracted with pentane (10 mL), and the extract was filtered to remove
a small amount of insoluble black material. Upon standing at room
temperature, black needles of 5 (110 mg, 22%) were obtained. UV−vis
(THF): λmax = 326 nm (sh, ε 22 000 M−1 cm−1), 442 nm (sh, ε 15 000
M−1 cm−1), 559 nm (sh, ε 13 000 M−1 cm−1). Cyclic voltammogram
(2 mM in THF, potential vs Ag/Ag+): Epc = −1.06 V (irreversible).
EPR (microwave power, 1.00 mW; microwave frequency, 9474.082
MHz; modulation width, 0.4 mT; 5 mM in toluene, 8 K): a signal with
multiple lines appeared at g = 2.01. Magnetic susceptibility (B.M.): μeff
= 0.89 (2 K), 3.10 (300 K). Anal. Calcd for C120H154Fe6N2O4P2S10V2:
C, 57.46; H, 6.19; N, 1.12; S, 12.79. Found: C, 57.77; H, 5.73; N, 1.33;
S, 12.43.
Synthesis of [(μ-O,O,O)VFe3S4(SDmp)(STip)Fe(μ-SDmp)] (6).
Method A. A toluene (3 mL) solution of 4 (442 mg, 0.694 mmol) was
added to a toluene (2 mL) solution of 3b (150 mg, 0.174 mmol) at
room temperature. After stirring for 10 min, a toluene (5 mL) solution
of S8 (22.3 mg, 0.694 mmol) was added at room temperature. The
reaction mixture was stirred for 3 days, and the solvent was removed
under reduced pressure to give a black oily material. The residue was
extracted with pentane (5 mL), and the extract was filtered to remove
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a small amount of insoluble black material. Upon standing at room
temperature, black plates of 6 (32 mg, 10%) were obtained. UV−vis
(toluene): λmax = 314 nm (ε 24 000 M−1 cm−1), 385 nm (sh, ε 7700
Dr. Yoshiaki Syuku (Nagoya Univ.) for aiding us with a
SQUID-type magnetometer.
M
−1 cm−1), 420 nm (sh, ε 3600 M−1 cm−1). Cyclic voltammogram (2
REFERENCES
mM in THF, potential vs Ag/Ag+): Epc = −0.84 V, Epa = −0.45, −0.73
V (irreversible). EPR (microwave power, 1.00 mW; microwave
frequency, 9474.082 MHz; modulation width, 0.4 mT; 5 mM in
toluene): Silent in the range of 4−15 K. Magnetic susceptibility
(B.M.): μeff = 2.00 (2 K), 4.80 (300 K). Anal. Calcd for
C97H118Fe4O3PS7V: C, 62.57; H, 6.39; S, 12.06. Found: C, 62.39;
H, 5.97; S, 12.20.
■
(1) (a) Bertini, I.; Sigel, A.; Sigel, H. Handbook on Metalloproteins;
Marcel Dekker: New York, 2001; Chapter 10. (b) Messerchmidt, A.;
Huber, R.; Poulos, T.; Wiehardt, K. Handbook of Metalloproteins; John
Wiley & Sons: Chichester, U. K., 2001; Vol. 1, pp 543−552, 560−609.
(2) (a) Vignais, P. M.; Billoud, B. Chem. Rev. 2007, 107, 4206−4272.
(b) Fontecilla-Camps, J. C.; Volbeda, A.; Cavazza, C.; Nicolet, Y.
́
Chem. Rev. 2007, 107, 4273−4303. (c) De Lacey, A. L.; Fernandez, V.
Method B. A toluene (3 mL) solution of 4 (375 mg, 0.589 mmol)
was added to a toluene (2 mL) solution of 3a (150 mg, 0.196 mmol)
at room temperature. After stirring for 10 min, a toluene (5 mL)
solution of S8 (25.2 mg, 0.694 mmol) was added at room temperature.
The reaction mixture was stirred for 3 days, and the solvent was
removed under reduced pressure to give a black oily material. The
residue was extracted with pentane (5 mL), and the extract was filtered
to remove a small amount of insoluble black material. Upon standing
at room temperature, black plates of 6 (29 mg, 8%) were obtained.
X-ray Crystal Structure Determination. Crystallographic data
and refinement parameters for 2a−2b, 3a−3b, 5, and 6 are
summarized in Table 1. Single crystals were coated with oil
(immersion oil, type B: Code 1248, Cargille Laboratories, Inc.) and
mounted on loops. Diffraction data were collected at −100 °C under a
cold nitrogen stream on a Rigaku RA-Micro7 equipped with a
Saturn70 CCD detector, using graphite-monochromated Mo Kα
radiation (λ = 0.710690 Å). Six preliminary data frames were measured
at 0.5° increments of ω, to assess the crystal quality and preliminary
unit cell parameters. The intensity images were also measured at 0.5°
intervals of ω. The frame data were integrated using the CrystalClear
program package, and the data sets were corrected for absorption
using a REQAB program. The calculations were performed with the
CrystalStructure program package. All structures were solved by direct
methods and refined by full-matrix least-squares. Anisotropic refine-
ment was applied to all non-hydrogen atoms except for disordered
atoms (refined isotropically), and all hydrogen atoms were put at
calculated positions. Crystals of cluster 5 appear as thin needles, and
the quality of their diffraction data was not sufficient. Therefore, some
alerts A and B appear in the checking-program of crystallographic data
(CIF-check). In 2b, one tert-butyl group is disordered over two
positions in a 3:7 ratio. In 5, a methyl group of toluene (crystal
solvent) is disordered over two positions in a 2:3 ratio. In 6, one tert-
butyl group is disordered over two positions in a 1:1 ratio.
M.; Rousset, M.; Cammack, R. Chem. Rev. 2007, 107, 4304−4330.
(d) Tard, C.; Pickett, C. J. Chem. Rev. 2009, 109, 2245−2274.
(3) (a) Ragsdale, S. W.; Kumar, M. Chem. Rev. 1996, 96, 2515−2539.
(b) Ragsdale, S. W. Crit. Rev. Biochem. Mol. Biol. 2004, 39, 165−195.
(c) Hegg, E. L. Acc. Chem. Res. 2004, 37, 775−783. (d) Messerchmidt,
A. Handbook of Metalloproteins; John Wiley & Sons: Chichester, U. K.,
2011; Vol. 4, pp 387−396, 397−412.
(4) (a) Howard, J. B.; Rees, D. C. Chem. Rev. 1996, 96, 2965−2982.
(b) Burgess, B. K.; Lowe, D. J. Chem. Rev. 1996, 96, 2983−3012.
(c) Einsle, O.; Tezcan, F. A.; Andrade, S. L. A.; Schmid, B.; Yoshida,
M.; Howard, J. B.; Rees, D. C. Science 2002, 297, 1696−1700.
(d) Spatzal, T.; Aksoyoglu, M.; Zhang, L.; Andrade, S. L. A.;
Schleicher, E.; Weber, S.; Rees, D. C.; Einsle, O. Science 2011, 334,
940. (e) Lancaster, K. M.; Roemelt, M.; Ettenhuber, P.; Hu, Y.; Ribbe,
M. W.; Neese, F.; Bergmann, U.; DeBeer, S. Science 2011, 334, 974−
977.
(5) (a) Eady, R. R. Chem. Rev. 1996, 96, 3013−3030. (b) Eady, R. R.
Coord. Chem. Rev. 2003, 237, 23−30. (c) Fay, A. W.; Blank, M. A.; Lee,
C. C.; Hu, Y.; Hodgson, K. O.; Hedman, B.; Ribbe, M. W. J. Am.
Chem. Soc. 2010, 132, 12612−12618.
(6) (a) Lindahl, P. A. Biochemistry 2002, 41, 2097−2105. (b) Jeoung,
J.-H.; Dobbek, H. Science 2007, 318, 1461−1464.
(7) (a) Osterloh, F.; Sanakis, Y.; Staples, R. J.; Munck, E.; Holm, R.
̈
H. Angew. Chem., Int. Ed. 1999, 38, 2066−2070. (b) Osterloh, F.;
Achim, C.; Holm, R. H. Inorg. Chem. 2001, 40, 224−232. (c) Zhang,
Y.; Zuo, J.-L.; Zhou, H.-C.; Holm, R. H. J. Am. Chem. Soc. 2002, 124,
14292−14293. (d) Zhang, Y.; Holm, R. H. J. Am. Chem. Soc. 2003,
125, 3910−3920. (e) Zhang, Y.; Holm, R. H. Inorg. Chem. 2004, 43,
674−682. (f) Berlinguette, C. P.; Miyaji, T.; Zhang, Y.; Holm, R. H.
Inorg. Chem. 2006, 45, 1997−2007. (g) Berlinguette, C. P.; Holm, R.
H. J. Am. Chem. Soc. 2006, 128, 11993−12000. (h) Hlavinka, M. L.;
Miyaji, T.; Staples, R. J.; Holm, R. H. Inorg. Chem. 2007, 46, 9192−
9200.
(8) (a) Ciurli, S.; Yu, S.-B.; Holm, R. H.; Srivastava, K. K. P.; Munck,
̈
ASSOCIATED CONTENT
■
E. J. Chem. Soc. 1990, 112, 8169−8171. (b) Ciurli, S.; Ross, P. K.;
S
* Supporting Information
Scott, M. J.; Yu, S.-B.; Holm, R. H. J. Am. Chem. Soc. 1992, 114, 5415−
An X-ray crystallographic information file (CIF) for the
structures of 2a−6; molecular structures of 2b and 3b;
temperature-dependent magnetic susceptibility and cyclic
5423. (c) Zhou, J.; Scott, M. J.; Hu, Z.; Peng, G.; Munck, E.; Holm, R.
̈
H. J. Am. Chem. Soc. 1992, 114, 10843−10854. (d) Panda, R.; Zhang,
Y.; McLauchlan, C. C.; Rao, P. V.; Tiago de Oliveira, F. A.; Munck, E.;
̈
1
Holm, R. H. J. Am. Chem. Soc. 2004, 126, 6448−6459. (e) Panda, R.;
Berlinguette, C. P.; Zhang, Y.; Holm, R. H. J. Am. Chem. Soc. 2005,
127, 11092−11101. (f) Sun, J.; Tessier, C.; Holm, R. H. Inorg. Chem.
2007, 46, 2691−2699.
voltammograms of 2a−2b, 3a−3b, 5, and 6; H NMR spectra
of 2a−2b and 3a−3b; and EPR spectrum of 5. This material is
available free of charge via the Internet at http://pubs.acs.org.
(9) (a) Tyson, M. A.; Coucouvanis, D. Inorg. Chem. 1997, 36, 3808−
3809. (b) Han, J.; Beck, K.; Ockwing, N.; Coucouvanis, D. J. Am.
Chem. Soc. 1999, 121, 10448−10449. (c) Coucouvanis, D.; Han, J.;
Moon, N. J. Am. Chem. Soc. 2002, 124, 216−224.
AUTHOR INFORMATION
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Corresponding Author
*E-mail: i45100a@nucc.cc.nagoya-u.ac.jp.
(10) (a) Ohki, Y.; Sunada, Y.; Honda, M.; Katada, M.; Tatsumi, K. J.
Am. Chem. Soc. 2003, 125, 4052−4053. (b) Ohki, Y.; Ikagawa, Y.;
Tatsumi, K. J. Am. Chem. Soc. 2007, 129, 10457−10465. (c) Ohki, Y.;
Imada, M.; Murata, A.; Sunada, Y.; Ohta, S.; Honda, M.; Sasamori, T.;
Tokitoh, N.; Katada, M.; Tatsumi, K. J. Am. Chem. Soc. 2009, 131,
13168−13178. (d) Ohki, Y.; Murata, A.; Imada, M.; Tatsumi, K. Inorg.
Chem. 2009, 48, 4271−4273. (e) Hashimoto, T.; Ohki, Y.; Tatsumi, K.
Inorg. Chem. 2010, 49, 6102−6109. (f) Ohta, S.; Ohki, Y.; Hashimoto,
T.; Cramer, R. E.; Tatsumi, K. Inorg. Chem. 2012, 51, 11217−11219.
(g) Ohki, Y.; Tanifuji, K.; Yamada, N.; Cramer, R. E.; Tatsumi, K.
Chem.Asian J. 2012, 7, 2222−2224.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was financially supported by Grant-in-Aids for
Scientific Research (Nos. 23000007, 23685015, 25105725,
25109522) from the Ministry of Education, Culture, Sports,
Science and Technology, Japan. We are grateful to Prof. Kunio
Awaga, Prof. Michio Matsushita, Prof. Hirofumi Yoshikawa, and
5445
dx.doi.org/10.1021/ic4030603 | Inorg. Chem. 2014, 53, 5438−5446

Inorganic Chemistry
Article
(11) (a) Ohki, Y.; Sunada, Y.; Tatsumi, K. Chem. Lett. 2005, 34,
172−173. (b) Ohki, Y.; Tanifuji, K.; Yamada, N.; Imada, M.; Tajima,
T.; Tatsumi, K. Proc. Natl. Acad. Sci. U.S.A. 2011, 108, 12635−12640.
(12) (a) Haaland, A.; Rypdal, K.; Volden, H. V.; Andersen, R. A. J.
Chem. Soc., Dalton Trans. 1992, 891−895. (b) Dubberley, S. R.;
Tyrrell, B. R.; Mountford, P. Acta Crystallogr. 2001, C57, 902−904.
(13) Siefert, R.; Weyhermuller, T.; Chaudhuri, P. J. Chem. Soc.,
̈
Dalton Trans. 2000, 4656−4663.
(14) (a) Paine, T. K.; Weyhermuller, T.; Slep, L. D.; Neese, F.; Bill,
̈
E.; Bothe, E.; Wieghardt, K.; Chaudhuri, P. Inorg. Chem. 2004, 43,
7324−7338. (b) Liang, L. C.; Chang, Y. N.; Lee, H. M. Inorg. Chem.
2007, 46, 2666−2673. (c) Carmichael, C. D.; Fryzuk, M. D. Can. J.
Chem. 2010, 88, 667−675.
(15) Krzystek, J.; Ozarowski, A.; Telser, J. Coord. Chem. Rev. 2006,
250, 2308−2324.
(16) Randall, C. R.; Armstrong, W. H. Chem. Commun. 1988, 986−
987.
(17) (a) Magill, C. P.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Inorg.
Chem. 1993, 32, 2729−2735. (b) Witte, P. T.; Meetsma, A.; Hessen, B.
Organometallics 1999, 18, 2944−2946. (c) Lee, I. S.; Long, J. R. Dalton
Trans. 2004, 3434−3436.
(18) (a) Hauser, C.; Bill, E.; Holm, R. H. Inorg. Chem. 2002, 41,
1615−1624. (b) Zuo, J.-L.; Zhou, H.-C.; Holm, R. H. Inorg. Chem.
2003, 42, 4624−4631. (c) Scott, T. A.; Holm, R. H. Inorg. Chem. 2008,
46, 3426−3432.
(19) The EPR spectra at higher than 20 K are not discussed for
clusters in this study because fast relaxation is known for iron−sulfur
clusters. See for examples: (a) Guigliarelli, B.; Bertrand, P. Adv. Inorg.
Chem. 1997, 47, 421−497. (b) Rao, P. V.; Holm, R. H. Chem. Rev.
2004, 104, 527−559.
(20) Werth, M. T.; Kurtz, D. M., Jr.; Howes, B. D.; Huynh, B. H.
Inorg. Chem. 1989, 28, 1357−1361.
(21) (a) Ellison, J. J.; Ruhlandt-Senge, K.; Power, P. P. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 1178−1180. (b) Ohta, S.; Ohki, Y.; Ikagawa, Y.;
Suizu, R.; Tatsumi, K. J. Organomet. Chem. 2007, 692, 4792−4799.
(22) (a) Do, Y.; Simhon, E. D.; Holm, R. H. Inorg. Chem. 1985, 24,
4635−4642. (b) Kovacs, J. A.; Holm, R. H. J. Am. Chem. Soc. 1986,
108, 340−341. (c) Kovacs, J. A.; Holm, R. H. Inorg. Chem. 1987, 26,
711−718. (d) Carney, M. J.; Kovacs, J. A.; Zhang, Y.-P.;
Papaefthymiou, G. C.; Spartalian, K.; Frankel, R. B.; Holm, R. H.
Inorg. Chem. 1987, 26, 719−724. (e) Ciurli, S.; Holm, R. H. Inorg.
Chem. 1989, 28, 1685−1690. (f) Cen, W.; Lee, S. C.; Li, J.;
MacDonnell, F. M.; Holm, R. H. J. Am. Chem. Soc. 1993, 115, 9515−
9523. (g) Malinak, S. M.; Demadis, K. D.; Coucouvanis, D. J. Am.
Chem. Soc. 1995, 117, 3126−3133. (h) Huang, J.; Mukerjee, S.; Segal,
B. M.; Akashi, H.; Zhou, J.; Holm, R. H. J. Am. Chem. Soc. 1997, 119,
8662−8674. (i) Deng, Y.; Liu, Q.; Chen, C.; Wang, Y.; Cai, Y.; Wu, D.;
Kang, B.; Liao, D.; Cui, J. Polyhedron 1997, 16, 4121−4128. (j) Zhang,
Y.; Liu, Q.; Deng, Y.; Zhu, H.; Chen, C.; Liao, D.; Cui, J. Polyhedron
1999, 18, 3153−3163. (k) Fomitchev, D. V.; McLauchlan, C. C.;
Holm, R. H. Inorg. Chem. 2002, 41, 958−966.
(23) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518−1520.
(24) Chisholm, M. H.; Corning, J. F.; Huffman, J. C. Inorg. Chem.
1984, 23, 754−757.
(25) Blower, P. J.; Dilworth, J. R.; Hutchinson, J. P.; Zubieta, J. A. J.
Chem. Soc., Dalton Trans. 1985, 1533−1541.
5446
dx.doi.org/10.1021/ic4030603 | Inorg. Chem. 2014, 53, 5438−5446