A new route to the synthesis of phosphine-substituted diiron azaand oxadithiolate complexes

Article abstract of DOI:10.1021/acs.organomet.7b00040

Diiron dithiolate complexes have received special attention because of their structural similarity to the active site of [FeFe]-hydrogenases, which are the most efficient and fastest catalysts for the generation of dihydrogen in nature. Recently, we established a novel and efficient way to prepare phosphine-substituted diiron aza- and oxadithiolate complexes. Reaction of Fe₂(μ-SCH₂OH)₂(CO)₆ and several phosphine ligands L (L = PPh₃, PPh₂(2-C₅H₄N), P(C₆H₄-4-CH₃)₃) affords the intermediate Fe₂(μ-SCH₂OH)₂(CO)₅L, while the intermediate in situ reacts with primary amines RNH₂ (R = CH₂CH₂CH(CH₃)₂, CH₂CH₂CH₂SCH₃, C₆H₄-4-CH₃) to produce the target phosphine- substituted diiron azadithiolate complexes Fe₂[(μ- SCH₂)₂NCH₂CH₂CH(CH₃)₂](CO)₅(PPh₃) (1), Fe₂[(μ-SCH₂)₂NCH₂CH₂CH(CH₃)₂](CO)₅[PPh₂(2-C₅H₄N)] (2), Fe₂[(μ- SCH₂)₂NCH₂CH₂CH(CH₃)₂](CO)₅[P(C₆H₄-4-CH₃)₃] (3), Fe₂[(μ-SCH₂)₂NCH₂CH₂CH₂SCH₃](CO)₅(PPh₃) (4), Fe₂[(μ- SCH₂)₂NCH₂CH₂CH₂SCH₃](CO)₅[PPh₂(2-C₅H₄N)] (5), Fe₂[(μ-SCH₂)₂NCH₂CH₂CH₂SCH₃](CO)₅[P(C₆H₄-4-CH₃)₃] (6), Fe₂[(μ-SCH₂)₂N C₆H₄-4-CH₃](CO)₅[PPh₂(2-C₅H₄N)] (7), and Fe₂[(μ-SCH₂)₂N C₆H₄-4-CH₃](CO)₅[P(C₆H₄-4-CH₃)₃] (8) in moderate yields. A novel complex Fe₂[(μ-SCH₂)₂NCH₂CH₂PPh₂](CO)₅ (9) can be obtained by reaction of Fe₂(μ- SCH₂OH)₂(CO)₆ and Ph₂PCH₂CH₂NH₂. In addition, according to the same strategy, phosphine-substituted diiron oxadithiolate complexes Fe₂[(μ-SCH₂)₂O](CO)₅[P(C₆H₄-4-F)₃] (10), Fe₂[(μ-SCH₂)₂O](CO)₅[P(C₆H₄-4-CH₃)₃] (11), and Fe₂[(μ-SCH₂)₂O](CO)₅(Ph₂PCH₂CH₃) (12) have been successfully synthesized. All of the new complexes 1-12 were fully characterized by elemental analysis, IR, and NMR spectroscopy, and particularly for 1-4, 6, 7, and 9-11 by X-ray single diffraction analysis. Moreover, complexes 1 and 10 were found to be catalysts for H₂ production under electrochemical conditions.

Full text of DOI:10.1021/acs.organomet.7b00040

Article
pubs.acs.org/Organometallics
A New Route to the Synthesis of Phosphine-Substituted Diiron Aza-
and Oxadithiolate Complexes
Jiao He,† Cheng-Long Deng,† Yao Li,† Yu-Long Li,*,† Yu Wu,† Li-Ke Zou,† Chao Mu,† Qiang Luo,†
Bin Xie,† Jian Wei,† Jing-Wen Hu,† Pei-Hua Zhao,*,‡ and Wen Zheng†
†College of Chemistry and Environmental Engineering, Sichuan University of Science & Engineering, Zigong 643000, P. R. China
‡School of Materials Science and Engineering, North University of China, Taiyuan 030051, P. R. China
S
* Supporting Information
ABSTRACT: Diiron dithiolate complexes have received special
attention because of their structural similarity to the active site of
[FeFe]-hydrogenases, which are the most efficient and fastest
catalysts for the generation of dihydrogen in nature. Recently, we
established a novel and efficient way to prepare phosphine-
substituted diiron aza- and oxadithiolate complexes. Reaction of
Fe2(μ-SCH2OH)2(CO)6 and several phosphine ligands L (L =
PPh3, PPh2(2-C5H4N), P(C6H4-4-CH3)3) affords the intermediate
Fe2(μ-SCH2OH)2(CO)5L, while the intermediate in situ reacts
with primary amines RNH2 (R = CH2CH2CH(CH3)2,
CH2CH2CH2SCH3, C6H4-4-CH3) to produce the target phos-
phine-substituted diiron azadithiolate complexes Fe2[(μ-
SCH2)2NCH2CH2CH(CH3)2](CO)5(PPh3) (1), Fe2[(μ-SCH2)2NCH2CH2CH(CH3)2](CO)5[PPh2(2-C5H4N)] (2), Fe2[(μ-
SCH2)2NCH2CH2CH(CH3)2](CO)5[P(C6H4-4-CH3)3] (3), Fe2[(μ-SCH2)2NCH2CH2CH2SCH3](CO)5(PPh3) (4), Fe2[(μ-
SCH2)2NCH2CH2CH2SCH3](CO)5[PPh2(2-C5H4N)] (5), Fe2[(μ-SCH2)2NCH2CH2CH2SCH3](CO)5[P(C6H4-4-CH3)3] (6),
Fe2[(μ-SCH2)2N C6H4-4-CH3](CO)5[PPh2(2-C5H4N)] (7), and Fe2[(μ-SCH2)2N C6H4-4-CH3](CO)5[P(C6H4-4-CH3)3] (8)
in moderate yields. A novel complex Fe2[(μ-SCH2)2NCH2CH2PPh2](CO)5 (9) can be obtained by reaction of Fe2(μ-
SCH2OH)2(CO)6 and Ph2PCH2CH2NH2. In addition, according to the same strategy, phosphine-substituted diiron
oxadithiolate complexes Fe2[(μ-SCH2)2O](CO)5[P(C6H4-4-F)3] (10), Fe2[(μ-SCH2)2O](CO)5[P(C6H4-4-CH3)3] (11), and
Fe2[(μ-SCH2)2O](CO)5(Ph2PCH2CH3) (12) have been successfully synthesized. All of the new complexes 1−12 were fully
characterized by elemental analysis, IR, and NMR spectroscopy, and particularly for 1−4, 6, 7, and 9−11 by X-ray single
diffraction analysis. Moreover, complexes 1 and 10 were found to be catalysts for H2 production under electrochemical
conditions.
INTRODUCTION
■
In recent years, diiron dithiolate complexes have received
special attention because of their structural similarity to the
active site of [FeFe]-hydrogenases, which are the most efficient
and fastest catalysts for the generation of dihydrogen in
nature.1−5 The study of the structure and functionality of the
active site of the [FeFe]-hydrogenases is significant, since it is
helpful for the design and synthesis of new low-cost and
O).
efficient catalysts for H2 production and a pathway for solving
Figure 1. Active site structure of [FeFe] hydrogenase (X = CH2, NH,
the problem of energy crisis.6 Crystallographic analyses of the
[FeFe]-hydrogenase enzymes were reported by Peters as well
as Fontecilla-Camps et al., demonstrating that the active site of
[FeFe]-hydrogenases consists of a butterfly [2Fe2S] cluster
linked to a cubane-like [4Fe4S] cluster through a cysteine
bridge (Figure 1).7−13 The Fe atoms of the [2Fe2S] cluster are
coordinated by CO and CN− ligands, as shown by FTIR
spectroscopy studies;7 meanwhile, the bridging dithiolate unit is
proposed to be SCH2XCH2S (X = CH2, NH, O).8−12 It is
generally accepted that the [2Fe2S] cluster is the catalytic
center,13 resulting in the synthesis of the diiron dithiolato
carbonyl complexes.
Rauchfuss and co-workers first prepared the parent
azadithiolate Fe2[(μ-SCH2)2NH](CO)6 by treatment of
Fe2(μ-SH)2(CO)6 with a mixture of paraformaldehyde and
(NH4)2CO3.10 Afterward, the azadithiolate complexes of the
type Fe2[(μ-SCH2)2NR](CO)6 can be prepared by the
Received: January 17, 2017
© XXXX American Chemical Society
A
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Scheme 1. Synthesis of the Phosphine-Substituted Diiron Azadithiolate Complexes 1−8 via One-Pot Reaction
alkylation of Fe2(μ-SLi)2(CO)6 using (ClCH2)2NR or the
reaction of Fe2(μ-SH)2(CO)6 with formaldehyde in the
presence of amines.14−25 Following these earlier studies, the
investigation on the modification of the bridge head group or
substitution of carbonyl ligands with Lewis bases have been
under intense scrutiny.26 These Lewis bases include phos-
phines, cyanide, N-hetrocyclic carebenes, thioethers, and
others.27−32 Notably, in the chemistry of preparation of
phosphine-substituted diiron azadithiolate complexes, usually
the first key step is to synthesize the diiron azadithiolate
complexes Fe2[(μ-SCH2)2NR](CO)6, then the second step is
to replace the CO ligand by a phosphine ligand in the presence
of a decarbonylation agent Me3NO, refluxing, or photoly-
sis.33−35 Although the aforementioned method has been widely
used, such a traditional route is complicated.
(CH3 )2 ](CO)5 [P(C6 H4 -4-CH3 )3 ] (3), Fe2 [(μ-
SCH2)2NCH2CH2CH2SCH3](CO)5(PPh3) (4), Fe2[(μ-
SCH2)2NCH2CH2CH2SCH3](CO)5[PPh2(2-C5H4N)] (5),
Fe2[(μ-SCH2)2NCH2CH2CH2SCH3](CO)5[P(C6H4-4-CH3)3]
(6), Fe2[(μ-SCH2)2NC6H4-4-CH3](CO)5[PPh2(2-C5H4N)]
(7), and Fe2[(μ-SCH2)2NC6H4-4-CH3](CO)5[P(C6H4-4-
CH3)3] (8) in moderate yields. In addition, according to
Scheme 2, reaction of Fe2(μ-SCH2OH)2(CO)6 and
Scheme 2. Synthesis of the Phosphine-Substituted Diiron
Azadithiolate Complex 9
Recently, we have succussfully established a novel and
efficient way to prepare phosphine-substituted diiron azadi-
thiolate complexes.14,36 Inspired by the new finds and in
continuation of our research on [FeFe]-hydrogenase model
complexes, our strategy is to prepare this kind of the
phosphine-substituted diiron azadithiolate complexes by
reaction of Fe2(μ-SCH2OH)2(CO)6 and phosphine ligand,
followed by addition of amine. According to the above one-pot
reaction, a series of new phosphine-substituted diiron
azadithiolate complexes have been successfully synthesized in
satisfactory yield. In addition, according to the same strategy,
phosphine-substituted diiron oxadithiolate complexes have also
been prepared via reaction of Fe2(μ-SCH2OH)2(CO)6 and
phosphine ligands, followed by treatment with H2SO4. The
electrochemical properties of these diiron aza- and oxadithiolate
complexes were studied by cyclic voltammetry (CV), some of
which were further found to be catalysts for H2 production
under electrochemical conditions. Herein, we report the
synthesis, structural characterization, and electrochemical
properties of 12 new diiron aza- and oxadithiolate complexes
containing different phosphine ligands.
Ph2PCH2CH2NH2 affords a novel phosphine-substituted diiron
azadithiolate complex Fe2[(μ-SCH2)2NCH2CH2PPh2](CO)5
(9). Furthermore, according to Scheme 3, reaction of Fe2(μ-
Scheme 3. Synthesis of the Phosphine-Substituted Diiron
Oxadithiolate Complexes 10−12
SCH2OH)2(CO)5L (L = P(C6H4-4-F)3, P(C6H4-4-CH3)3, and
Ph2PCH2CH3) with H2SO4 in CH2Cl2 produces phosphine-
substituted diiron oxadithiolate complexes Fe2[(μ-SCH2)2O]-
(CO)5[P(C6H4-4-F)3] (10), Fe2[(μ-SCH2)2O](CO)5[P(C6H4-
4-CH3)3] (11), and Fe2[(μ-SCH2)2O](CO)5[PPh2(CH2CH3)]
(12). It is worthy to note that compared with the traditional
way to prepare diiron dithiolate complexes containing
phosphine ligands, our one-pot reaction is simpler and more
efficient. For example, as shown in Table 1, complexes 1−8 can
be obtained in 31−57% yields using our one-pot reaction
(Method A). Comparatively, we tried to synthesize complexes
1−8 by two-step reactions (Method B) in the followings: (i)
the reaction of Fe2(μ-SCH2OH)2(CO)6 and RNH2 (R =
CH2CH2CH(CH3)2, CH2CH2CH2SCH3, C6H4-4-CH3) to
obtain the purified complex Fe2[(μ-SCH2)2NR](CO)6; and
(ii) the treatment of the as-prepared Fe2[(μ-SCH2)2NR](CO)6
with L (L = PPh3, PPh2(2-C5H4N), P(C6H4-4-CH3)3) in the
RESULTS AND DISCUSSION
■
In order to explore a simple and high efficient way to synthesize
the phosphine-substituted diiron dithiolate complexes, new
complexes 1−8 were prepared as shown in Scheme 1.
Treatment of Fe2(μ-SCH2OH)2(CO)6 with several phosphine
ligands L (L = PPh3, PPh2(2-C5H4N), P(C6H4-4-CH3)3)
affords the intermediate Fe2(μ-SCH2OH)2(CO)5L, followed
by the in situ addition of amines RNH2 (R = CH2CH2CH-
(CH3)2, CH2CH2CH2SCH3, C6H4-4-CH3) to produce the
target complexes Fe2[(μ-SCH2)2NCH2CH2CH(CH3)2]-
(CO)5(PPh3) (1), Fe2[(μ-SCH2)2NCH2CH2CH(CH3)2]-
(CO)5[PPh2(2-C5H4N)] (2), Fe2[(μ-SCH2)2NCH2CH2CH-
B
DOI: 10.1021/acs.organomet.7b00040
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Article
give two typical kinds of proton signals at ca. 4.00 and ca. 3.00
ppm for the N(CH2S)2 groups. This is possibly due to the
different substituent attached to the bridge head N atom, where
complexes 1−6 contain the alkyl-substituted N atom, but
Table 1. Yields of Complexes 1−8 Derived From Fe2(μ-
SCH2OH)2(CO)6 by Methods A and B
Method A: Fe2(μ-
SCH2OH)2(CO)5L + RNH2 Method B: Fe2(μ-SCH2OH)2(CO)6
1
complexes 7 and 8 have the aryl-linked N atom. In the H
complex
(yield)
+ RNH2 + Me3NO + L (yield)
spectrum of complex 9, the characteristic proton signals of the
dithiolate bridging correspond to a multiplet in the range of
3.77−3.90 ppm. Furthermore, the 13C NMR spectra of
complexes 1−12 display a doublet at ca. 213 ppm for the
coordinated Fe-carbonyls in PFe(CO)2groups and a singlet at
ca. 209 ppm for the terminal Fe-carbonyls in Fe(CO)3 moieties,
respectively. Additionally, the 31P NMR spectra of complexes
1−12 exhibit only a sharp singlet at 64.82, 66.75, 62.37, 64.85,
66.61, 62.44, 65.40, 62.07, 54.39, 61.83, 61.23, and 57.56 ppm
attributed to the respective phosphorus atoms of the
coordinated phosphine ligands, which are consistent with the
X-ray analysis results.
1
2
3
4
5
6
7
8
56%
43%
51%
42%
45%
41%
31%
33%
23%
21%
24%
20%
20%
19%
16%
17%
presence of decarbonylating agent Me3NO to afford the target
complexes 1−8 in low yields (16−24%, calculated by Fe2(μ-
S)2(CO)6)). Moreover, the intermediate Fe2(μ-
SCH2OH)2(CO)5(PPh3), which was monitored by IR spec-
troscopy, displays three absorption bands in the region 1928−
2041 cm−1 for νCO. This observation is consistent with those
observed in the coordination of phosphine ligand PPh3 to the
Fe core of the diiron carbonyl complexes.28
Red single crystals of complexes 1−4, 6, 7, and 9−11 suitable
for XRD analysis were obtained by slow vapor diffusion of
hexane into the concentrated CH2Cl2 solution at 0 °C. As
shown in Figures 2−4, the molecular structures of complexes
Complexes 1−12 have been fully characterized by elemental
1
analysis, IR, H NMR, 13C NMR, and 31P NMR spectroscopy.
The IR spectra of complexes 1−12 display three or four strong
absorption bands in the range of 1924−2052 cm−1 for their
terminal carbonyls (Table 2), which are shifted toward lower
Table 2. IR Data of the Carbonyl Stretching Frequencies for
Complexes 1−12
complex
νCO (KBr disk, cm−1
)
Fe2[(μ-SCH2)2NCH2CH2CH(CH3)2]
2040/1984/1976/1932
2038/1987/1970/1955
2038/1988/1969/1955
2043/1992/1971/1926
2042/1992/1970/1933
2042/1980/1928
(CO)5(PPh3)
Fe2[(μ-SCH2)2NCH2CH2CH(CH3)2]
(CO)5[PPh2(2-C5H4N)]
Figure 2. Molecular structure of complex 1. Hydrogens are omitted
for clarity. Selected bond lengths [Å] and angels [°]: Fe1−Fe2
2.5304(7), P1−Fe2 2.2377(7), Fe2−Fe1−P1 151.963(17), C6−N1−
C7 110.90(14).
Fe2[(μ-SCH2)2NCH2CH2CH(CH3)2]
(CO)5[P(C6H4-4-CH3)3]
Fe2[(μ-SCH2)2NCH2CH2CH2SCH3]
(CO)5(PPh3)
Fe2[(μ-SCH2)2NCH2CH2CH2SCH3]
(CO)5[PPh2(2-C5H4N)]
1−3 all feature a butterfly [2Fe2S] cluster with five carbonyl
ligands, an azadithiolate unit [(SCH2)2NCH2CH2CH(CH3)2],
and a phosphine ligand. In addition, two six-membered rings
are formed in a chair-shaped and a boat-shaped configuration. It
is interesting to note that the substituent of −CH2CH2CH-
(CH3)2 groups in complexes 1−3 are all attached to the bridge
head N1 via the sterically favored equatorial bond, which are
very similar to those reported in the diiron azadithiolate
analogues Fe2[(μ-SCH2)2NCH2CH2OCH3](CO)6,37 Fe2[(μ-
SCH2)2NCH2CH2O2CCH2CO2CH2CH3](CO)5(PPh3),38 and
Fe2[(μ-SCH2)2NC6H11](CO)4(PMe3)2.39 Moreover, the phos-
phorus atoms of the phosphine ligands (PPh3, PPh2(2-C5H4N),
P(C6H4-4-CH3)3) are all bound in apical positions. The Fe1−
Fe2 bond lengths in 1 (2.5304(7) Å, Figure 2), 2 (2.5330(5) Å,
Figure 3), and 3 (2.5159(6) Å, Figure 4) are slightly shorter
than the corresponding lengths (2.55−2.62 Å) in the natural
enzymes.7 Meanwhile, the order of the Fe−P bond lengths for
complexes 1−3 is shown as follows: 1 (P1−Fe2, 2.2377(7) Å)
> 3 (P1−Fe2, 2.2366(6) Å) > 2 (P1−Fe2, 2.2328(5) Å),
indicating the electron-donating ability of PPh2(2-C5H4N) >
P(C6H4-4-CH3)3 > PPh3, which is consistent with the results
observed in the IR spectra of complexes 1−3. The Fe−Fe−P
bond angles in 3 (Fe2−Fe1−P1 155.228°) are bigger than the
corresponding angles in 1 (Fe2−Fe1−P1 151.963°) and 2
Fe2[(μ-SCH2)2NCH2CH2CH2SCH3]
(CO)5[P(C6H4-4-CH3)3]
Fe2[(μ-SCH2)2NC6H4-4-CH3](CO)5[PPh2(2-
2041/1993/1969/1924
2044/1985/1930
C5H4N)]
Fe2[(μ-SCH2)2N C6H4-4-CH3](CO)5[P(C6H4-4-
CH3)3]
Fe2[(μ-SCH2)2NCH2CH2PPh2](CO)5
Fe2[(μ-SCH2)2O](CO)5[P(C6H4-4-F)3]
Fe2[(μ-SCH2)2O](CO)5[P(C6H4-4-CH3)3]
Fe2[(μ-SCH2)2O](CO)5[PPh2(CH2CH3)]
2041/1981/1951/1932
2052/1987/1940
2049/1988/1971/1935
2046/1981/1929
frequency than those observed in the analogues Fe2[(μ-
SCH2)2NR](CO)6.10 This indicates that the phosphine ligands
(PPh3, PPh2(2-C5H4N), P(C6H4-4-CH3)3, P(C6H4-4-F)3,
PPh2(CH2CH3), and −CH2CH2PPh2) are stronger electron
donors than CO. Meanwhile, it can be seen from the first CO
frequency of these different phosphine ligands in Table 2 that
the electron-donating ability is described in the following:
PPh2(2-C5H4N) > P(C6H4-4-CH3)3 > PPh3; PPh2(CH2CH3) >
P(C6H41-4-CH3)3 > P(C6H4-4-F)3.
The H NMR spectra of 1−6 show two similar types of
proton signals at ca. 2.80 and ca. 2.00 ppm assigned to the
bridging dithiolate units (N(CH2S)2), whereas those of 7 and 8
C
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Figure 6. Molecular structure of complex 6. Hydrogens are omitted
for clarity. Selected bond lengths [Å] and angels [°]: Fe1−Fe2
2.5305(4), Fe1−P1 2.2371(6), P1−Fe1−Fe2 153.843(19), C6−N1−
C7 111.75 (16), C6−N1−C8 108.69(16), C7−N1−C8 109.21(16).
Figure 3. Molecular structure of complex 2. Hydrogens are omitted
for clarity. Selected bond lengths [Å] and angels [°]: Fe1−Fe2
2.5330(5), P1−Fe2 2.2328(5), Fe1−Fe2−P1 151.131(17), C6−N1−
C7 110.46(13).
ligand lies in the apical site. It is worth noting that the
substituent of the −CH2CH2CH2SMe group in complexes 4
and 6 is attached to the bridge head N1 via the sterically
favored equatorial bond.
As shown in Figure 7, complex 7 exhibits a typical butterfly
[2Fe2S] core, whereas the geometry around each iron atoms
Figure 4. Molecular structure of complex 3. Hydrogens are omitted
for clarity. Selected bond lengths [Å] and angels [°]: Fe1−Fe2
2.5159(6), P1−Fe2 2.2366(6), Fe2−Fe1−P1 155.228(18), C27−N1−
C28 110.88(15).
Figure 7. Molecular structure of complex 7. Hydrogens and slolvents
are omitted for clarity. Selected bond lengths [Å] and angels [°]: Fe1−
Fe2 2.5104(4), Fe2−P1 2.2373(6), P1−Fe2−Fe1 156.870(19), C23−
N2−C24 113.24(17), C23−N2−C25 121.93(17), C24−N2−C25
118.83(17).
(Fe2−Fe1−P1 151.131°), which demonstrated that the steric
hindrance between the bridge-N substituent (NCH2CH2CH-
(CH3)2) and the phosphine ligand (P(C6H4-4-CH3)3) in 3 is
bigger relative to those in 1 and 2 as observed in Figures 2−4.
As shown in Figures 5 and 6, the Fe1−Fe2 distances in 4 and
6 are 2.5277(4) Å (Figure 5) and 2.5305 (4) Å (Figure 6)
respectively, which are also shorter than that observed in the
active site of [FeFe] hydrogenase. As shown in Figures 5 and 6,
the stereochemistry of the two Fe(CO)2P sites exhibits that two
CO groups occupy the basal site and the Lewis basic phosphine
can be described as a distorted square pyramidal. It is worth
noting that the sum of angles around N1 atom is 354°,
demonstrating that the amine is planar. This is good agreement
with the fact that p-Π conjugation with the p-orbital of the
nitrogen is reflected by short N−C distance, which is very
similar to those reported in the corresponding analogues
Fe2[(μ-SCH2)2NC6H4-4-CF3](CO)5(PPh3),28 Fe2[(μ-
SCH2)2NC6F4-4-CF3](CO)5(PPh3),28 and Fe2[(μ-
SCH2)2NC6H4SO3Na](CO)5(PPh3).40
As shown in Figure 8, the crystal structure of complex 9
reveals that phosphorus atom is coordinated to one Fe(1) core,
which is consistent with the corresponding carbonyl
frequencies observed in the IR data of complex 9. The Fe1−
Fe2 bond and Fe1−P1 bond lengths in 9 (2.5113(3) and
2.2155(5) Å) are very close to those of complexes 1−4 and 6.
However, in contrast to complexes 1−4 and 6, the substituent
of the −CH2CH2PPh2 group attached to the bridge head N1
resides in an axial position due to the formation of the seven-
membered ring (FeSCNCCP). It is worth pointing out that
complex 9 is structurally similar to the known [2Fe3S] complex
Fe2[(μ-SCH2)2NCH2CH2SCH3](CO)5.33
Figure 5. Molecular structure of complex 4. Hydrogens are omitted
for clarity. Selected bond lengths [Å] and angels [°]: Fe1−Fe2
2.5277(4), P1−Fe1 2.2398(5), P1−Fe1−Fe2 153.632(17), C6−N1−
C7 111.70(14), C6−N1−C8 109.33(14), C7−N1−C8 108.63(14).
As shown in Figures 9 and 10, both complexes 10 and 11
feature a butterfly [2Fe2S] cluster with five carbonyl ligands, an
oxadithiolate unit (CH2OCH2), and a phosphine ligand
D
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are bigger than the corresponding angles in 1 (Fe2−Fe1−P1
151.963°) and 11 (Fe2−Fe1−P1 155.464(19)o).
Electrochemical Studies of Complexes 1−6 and 10.
The electrochemical properties of complexes 1−6 were studied
by CV in DCM solution. The electrochemical data of
complexes 1−6 and 10 are listed in Table 3. The CV curve
Table 3. Electrochemical Data of Complexes 1−6 and 10
complex
Epc1[V]
Epa[V]
1
−2.04
−2.08
−2.10
−2.05
−2.06
−2.10
−1.94
+0.26
+0.18
+0.22
+0.25
+0.17
+0.23
+0.54
2
Figure 8. Molecular structure of complex 9. Hydrogens and slolvents
are omitted for clarity. Selected bond lengths [Å] and angels [°]: Fe1−
Fe2 2.5113(3), Fe1−P1 2.2155(5), P1−Fe1−Fe2 1145.898(16),
C18−N1−C19 115.63(14), C18−N1−C20 120.65(14), C19−N1−
C20 118.30(14).
3
4
5
6
10
Figure 9. Molecular structure of complex 10. Hydrogens and slolvents
are omitted for clarity. Selected bond lengths [Å] and angels [°]: Fe1−
Fe2 2.5174(7), Fe2−P1 2.2470(10), P1−Fe2−Fe1 157.08(3), C24−
O6−C25 112.6(2).
Figure 11. Cyclic voltammogram of complex 1 (1.0 mM) in 0.1 M n-
Bu4NPF6/DCM at a scan rate of 100 mV s−1.
of complex 1 is shown in Figure 11, whereas the CV curves of
complexes 1 and 10 are displayed in Figures 12 and 13. As
shown in Figure 11, complex 1 displays one irreversible
reduction process at −2.04 V and one irrversible oxidation
process at +0.26 V, which can be ascribed to the reduction of
Figure 10. Molecular structure of complex 11. Hydrogens and
slolvents are omitted for clarity. Selected bond lengths [Å] and angels
[°]: Fe1−Fe2 2.5261(5), Fe1−P1 2.2462(7), P1−Fe1−Fe2
155.464(19), C27−O6−C28 113.9(2).
(P(C6H4-4-F)3, P(C6H4-4-CH3)3). Two six-membered rings
are formed in a chair-shaped and a boat-shaped configuration.
The phosphorus atoms of the phosphine ligands are both
bound in apical positions, which are very similar to the reported
diiron oxadithiolate complexes such as Fe2[(μ-SCH2)2O]-
(CO)5(Ph2PCl) and Fe2[(μ-SCH2)2O](CO)5(Ph2PNMe2).41
In addition, the Fe−P bond lengths for complexes 10 and 11
are 2.2470(10) Å) and 2.2462(7) Å), indicating that the
electron-donating ability of P(C6H4-4-F)3 < P(C6H4-4-CH3)3.
The Fe−Fe−P bond angles in 10 (Fe2−Fe1−P1 157.08(3)o)
Figure 12. Cyclic voltammogram of complex 1 (1.0 mM) with HOAc
(0−10 mM) in 0.1 M n-Bu4NPF6/DCM at a scan rate of 100 mV s−1.
E
DOI: 10.1021/acs.organomet.7b00040
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Article
electrode as the reference electrode. The potential scale was calibrated
against the Fc/Fc+ couple and reported versus this reference system.
Synthesis of Complex Fe2[(μ-SCH2)2NCH2CH2CH(CH3)2]-
(CO)5(PPh3) (1). Method A. The reaction was carried out under
nitrogen atmoshpere by use of standard Schlenk techniques. A red
solution of Fe2(μ-S)2(CO)6 (0.344 g, 1.0 mmol) in THF (15 mL) was
cooled to −78 °C and then treated dropwise with LiHBEt3 (2 mL, 2.0
mmol) to give a green solution. After stirring for 10 min, CF3CO2H
(0.16 mL, 2.0 mmol) was added to cause an immediate color change
from green to red. The mixture was stirred for 10 min, and then 37%
aqueous formaldehyde (0.17 mL, 2.0 mmol) was added. The new
mixture was allowed to warm up to room temperature and stirred for 2
h. Then PPh3(0.262 g, 1.0 mmol) was added to cause an immediate
color change from red to dark red. After stirring for 4 h,
NH2CH2CH2CH(CH3)2 (0.12 mL, 1.0 mmol) was added, and the
resulting solution was stirred for additional 12 h. Volatiles were
removed under vacuum, and the residue was subjected to TLC using
CH2Cl2/petroleum ether (v/v = 1:4) as eluent. From the main red
band, complex 1 (0.221 g, 56%) was obtained as a dark red solid. Anal.
calcd for C30H30Fe2NO5PS2: C, 52.12; H, 4.37; N, 2.03. Found: C,
51.87; H, 4.51; N, 1.98. IR (KBr disk): νCO 2040 (vs), 1984 (vs),
1976 (vs), 1932 (m) cm−1.1H NMR (δ, ppm, 500 MHz, CDCl3): 7.68
(s, 6H, 3m-PhH), 7.42 (s, 9H, 3o, p-PhH), 2.79 (s,2H, 2NCHaHeS),
2.38 (s, 2H, NCH2CH2), 1.98 (s, 2H, NCHaHeS), 1.25 (s, 1H, CH),
0.83 (s, 2H, NCH2CH2), 0.71 (s, 6H, 2CH3).13CNMR (δ, ppm, 126
MHz, TMS): 22.43 (CH3), 26.09 (NCH2CH2), 34.72 (CH), 50.80
(NCH2CH2), 57.01 (NCH2S), 128.35, 129.97, 133.51, 136.00
Figure 13. Cyclic voltammogram of complex 10 (1.0 mM) with
HOAc (0−10 mM) in 0.1 M n-Bu4NPF6/DCM at a scan rate of 100
mV s−1.
FeIFeI to FeIFe0 and the oxidation of FeIFeI to FeIFeII,42−44
respectively. In addition, complexes 1 and10 have been found
to have the catalytic ability for proton reduction to H2 in the
presence of HOAc under CV conditions. As shown in Figures
12 and 13, upon addition of the first 2 mM HOAc to the
solutions of complexes 1 and 10, the reduction peaks at −2.04
V and −1.94 V increased markedly and continued to increase
with increasing concentration of HOAc. These observations
imply that complexes 1 and 10 have the ability to the
electrocatalytic reduction of proton to dihydrogen. In addition,
according to the above-mentioned electrochemical observations
of complexes 1 and 10, a 2E2C (E = electrochemical; C =
chemical) catalytic mechanism can be proposed for this
electrocatalytic H2 production. We suggest that complexes 1
and 10 may be completed via the ECEC or ECCE catalytic
mechanism, although more evidence is still needed for an
accurate mechanism.
2
(PhCH), 209.78 (s, FeCO), 213.61 (d, JPC = 8.9 Hz, PFeCO). 31P
NMR (202 MHz, CDCl3, 85% H3PO4): 64.82 (s).
Method B. (i) A red solution of Fe2(μ-S)2(CO)6 (0.344 g, 1.0
mmol) in THF (15 mL) was cooled to −78 °C and then treated
dropwise with LiHBEt3 (2 mL, 2.0 mmol) to give a green solution.
After stirring for 10 min, CF3CO2H (0.16 mL, 2.0 mmol) was added
to cause an immediate color change from green to red. The mixture
was stirred for 10 min, and then 37% aqueous formaldehyde (0.17 mL,
2.0 mmol) was added. The new mixture was allowed to warm up to
room temperature and stirred for 2 h. Then NH2CH2CH2CH(CH3)2
(0.12 mL, 1.0 mmol) was added, and the resulting solution was stirred
for additional 6 h. Volatiles were removed under vacuum, and the
residue was subjected to TLC using CH2Cl2/petroleum ether (v/v =
1:8) as eluent. From the main red band, complex Fe2[(μ-
SCH2)2NCH2CH2CH(CH3)2](CO)6 (0.200 g) was obtained as a
red solid. IR (KBr disk): νCO 2073 (vs), 2030 (vs), 1995 (vs) cm−1.
1H NMR (δ, ppm, 500 MHz, CDCl3): 3.47 (s, 4H, 2NCH2S), 2.63 (s,
2H, NCH2CH2), 1.46 (s, 1H, CH), 1.18 (s, 2H, NCH2CH2), 0.85 (s,
6H, 2CH3). 13C NMR (δ, ppm, 126 MHz, TMS): 22.43 (CH3), 25.75
(NCH2CH2), 36.29 (CH), 52.98 (NCH2CH2), 55.67 (NCH2S),
207.81 (s, FeCO). (ii) To a solution of complex Fe2[(μ-
SCH2)2NCH2CH2CH(CH3)2](CO)6 (0.200 g, 0.44 mmol) in
CH3CN (15 mL) was added decarbonylation reagent Me3NO·2H2O
(0.049 g, 0.44 mmol). The mixture was stirred at room temperature
for 15 min, and then PPh3 (0.116 g, 0.44 mmol) was added. The
resulting mixture was stirred for additional 2 h to give a dark red
solution. Solvents were removed under vacuum, and the residue was
subjected to TLC using CH2Cl2/petroleum ether (v/v = 1:4) as
eluent. From the main red band, complex 1 (0.160 g, 23%, calculated
by Fe2(μ-S)2(CO)6)) was obtained as a dark red solid.
EXPERIMENTAL DETAILS
■
Reactions were performed using standard Schlenk techniques. Solvents
were distilled under nitrogen over an appropriate drying agent.
LiHBEt3 (1.0 M in THF), HCHO (37%), NH2CH2CH2CH(CH3)2,
NH2CH2CH2CH2SCH3, NH2C6H4-4-CH3, Ph2PCH2CH2NH2, PPh3,
PPh2 (2-C5 H4 N), P(C6 H4 -4-CH3 )3 , P(C6 H4 -4-F)3 , and
PPh2(CH2CH3) were obtained commercially and used as received.
Complex Fe2(μ-S)2(CO)6 was prepared according to the literature
procedures.45 Preparative TLC was carried out on glass plates (26 ×
20 × 0.25 cm) coated with silica gel H (10−40 μm). 1H NMR spectra
(500 MHz) were referenced to residual solvent relative to
tetramethylsilane. 31P NMR (202 MHz) spectra were referenced to
external 85% H3PO4. IR spectra were recorded at room temperature
on a Bruker Vector 22 infrared spectrophotometer. Elemental analyses
were performed on an Elementar Vario EL analyzer. Crystallographic
data for complexs 1−4, 6, 7, and 9−11 were collected using a Bruker
SMART diffractometer equipped with a Mo Kα source (λ = 0.71073
Å). Data collection, reduction, and absorption corrections were
performed by Bruker SMART and Bruker SAINT. The structures were
solved by direct methods using the SHELXS-97program and refined
by full-matrix least-squares techniques (SHELXL-97) on F2.46,47
Hydrogen atoms were located using the geometric method. Electro-
chemical measurements were carried out under nitrogen using a CHI
620 Electrochemical Workstation. As the electrolyte, n-Bu4NPF6 was
recrystallized multiple times from a CH2Cl2 solution by the addition of
hexane. CV scans were obtained in a three-electrode cell with a glassy
carbon electrode (3 mm diameter) as the working electrode, a
platinum wire as the counter electrode, and a nonaqueous Ag/Ag+
Synthesis of Complex Fe2[(μ-SCH2)2NCH2CH2CH(CH3)2]-
(CO)5[PPh2(2-C5H4N)] (2). Complex 2 was prepared in a fashion
similar to that of complex 1 (Methods A and B) using PPh2(2-C5H4N)
as the phosphine ligand. Yields: 43% (Method A) and 21% (Method
B), dark red solid. Anal. calcd for C29H29Fe2N2O5PS2: C, 50.31; H,
4.22; N, 4.05. Found: C, 50.25; H, 4.39; N, 3.86. IR (KBr disk): νCO
1
2038 (vs), 1987 (vs), 1970 (vs), 1955 (vs) cm−1. H NMR (δ, ppm,
500 MHz, CDCl3): 7.44−8.81 (m, 14H, 2PhH, C5H4N), 2.79 (s, 2H,
2NCHaHeS), 2.54 (s, 2H, NCH2CH2), 2.03 (s, 2H, 2NCHaHeS), 1.26
(s, 1H, CH), 0.82 (s, 2H, NCH2CH2), 0.72 (s, 6H, 2CH3). 13C NMR
(δ, ppm, 126 MHz, TMS): 21.44 (CH3), 25.10 (NCH2CH2), 33.87
(CH), 50.08 (NCH2CH2), 55.92 (NCH2S), 122.29, 126.38, 127.25,
129.13, 133.08, 133.91, 134.41, 148.97, 160.87 (PhCH, C5H4N),
F
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208.89 (s, FeCO), 212.33 (d, 2JPC = 10.2 Hz, PFeCO). 31P NMR (202
MHz, CDCl3, 85% H3PO4): 66.75 (s).
51.99; H, 3.75; N, 3.91. IR (KBr disk): νCO 2041 (vs), 1993 (vs),
1
1969 (vs), 1924 (m) cm−1. H NMR (δ, ppm, 500 MHz, CDCl3):
Synthesis of Complex Fe2[(μ-SCH2)2NCH2CH2CH(CH3)2]-
(CO)5[P(C6H4-4-CH3)3] (3). Complex 3 was prepared in a fashion
similar to that of complex 1 (Methods A and B) using P(C6H4-4-
CH3)3 as the phosphine ligand. Yields: 51% (Method A) and 24%
(Method B), dark red solid. Anal. calcd for C33H36Fe2NO5PS2: C,
54.04; H, 4.95; N, 1.91. Found: C, 53.95; H, 5.12; N, 1.95. IR (KBr
6.47−8.82 (m, 18H, 2PhH, C6H4, C5H4N), 3.99 (d, J = 7.0 Hz, 2H,
2NCHaHeS), 3.29 (br s, 2H, 2NCHaHeS), 2.24 (s, 3H, CH3). 13C
NMR (δ, ppm, 126 MHz, TMS): 20.33 (CH3), 47.92 (NCH2S),
115.87, 118.17, 123.50, 128.53, 128.31, 130.16, 134.14, 144,54,150.01
2
(C6H5, C5H4N), 208.99 (s, FeCO), 212.78 (d, JPC = 10.6
Hz,PFeCO). 31P NMR (202 MHz, CDCl3, 85% H3PO4): 65.4 (s).
Synthesis of Complex Fe2[(μ-SCH2)2NC6H4-4-CH3](CO)5[P-
(C6H4-4-CH3)3] (8). Complex 8 was prepared in a fashion similar to
that of complex 3 using NH2C6H4-4-CH3 as the amine. Yields: 33%
(Method A) and 17% (Method B), dark red solid. Anal. calcd for
C35H32Fe2NO5PS2: C, 55.80; H, 4.28; N, 1.86. Found: C, 55.70; H,
4.44; N, 1.81. IR (KBr disk): νCO 2044 (vs), 1985 (vs), 1930 (m)
1
disk): νCO 2038 (vs), 1988 (vs), 1969 (vs), 1955 (vs) cm−1. H
NMR (δ, ppm, 500 MHz, CDCl3): 7.55 (s, 6H, 3m-PhH), 7.21 (s, 6H,
3o-PhH), 2.80 (d, J = 10 Hz, 2H, 2NCHaHeS), 2.37 (s, 11H, 3CH3,
NCH2CH2), 2.04 (s, 2H, 2NCHaHeS), 1.26 (s, 1H, CH), 0.82 (s, 2H,
NCH2CH2), 0.71 (d, J = 5 Hz, 6H, 2CH3). 13C NMR (δ, ppm, 126
MHz, TMS): 21.30 (CH2CH3), 22.43 (CH3), 26.06 (NCH2CH2),
34.83 (CH), 50.77 (NCH2CH2), 56.99 (NCH2S), 129.03, 133.47,
1
cm−1. H NMR (δ, ppm, 500 MHz, CDCl3): 7.63 (t, J = 8.5 Hz, 6H,
2
140.04 (PhCH), 210.02 (s, FeCO), 213.88 (d, JPC = 10.9 Hz,
3m-PhH), 7.20 (d, J = 6.5 Hz, 6H, 3o-PhH), 7.03 (d, J = 7.0 Hz, 2H,
2o-NC6H4-4-CH3), 6.51 (d, J = 7.5 Hz, 2H, 2m-NC6H4-4-CH3), 4.00
(d, J = 12.5 Hz, 2H, 2NCHaHeS), 3.04 (br s, 2H, 2NCHaHeS), 2.42 (s,
9H, 3C6H4-4-CH3), 2.26 (s, 3H, NC6H4-4−CH3). 13C NMR (δ, ppm,
126 MHz, TMS): 20.33 (NC6H4-4-CH3), 21.31 (C6H4-4-CH3), 47.45
(NCH2S), 115.81, 129.26, 129.91, 132.39, 132.72, 133.52, 140.38,
PFeCO). 31P NMR (202 MHz, CDCl3, 85% H3PO4): 62.37 (s).
Synthesis of Complex Fe2[(μ-SCH2)2NCH2CH2CH2SCH3]-
(CO)5(PPh3) (4). Complex 4 was prepared in a fashion similar to
that of complex 1 (Methods A and B) using NH2CH2CH2CH2SCH3
as the amine. Yields: 42% (Method A) and 20% (Method B), dark red
solid. Anal. calcd for C29H28Fe2NO5PS3: C, 49.10; H, 3.98; N, 1.97.
Found: C, 48.81; H, 4.22; N, 1.91. IR (KBr disk): νCO 2043 (vs),
2
144.49 (PhCH), 209.07 (s, FeCO), 213.24 (d, JPC = 11.3 Hz,
PFeCO). 31P NMR (202 MHz, CDCl3, 85% H3PO4): 62.07 (s).
Synthesis of Complex Fe2[(μ-SCH2)2NCH2CH2PPh2](CO)5 (9).
A red solution of Fe2(μ-S)2(CO)6 (0.344 g, 1.0 mmol) in THF (15
mL) was cooled to −78 °C and then treated dropwise with LiHBEt3
(2 mL, 2.0 mmol) to give a green solution. After stirring for 10 min,
CF3CO2H (0.16 mL, 2.0 mmol) was added to cause an immediate
color change from green to red. The mixture was stirred for 10 min,
and then 37% aqueous formaldehyde (0.17 mL, 2.0 mmol) was added.
The new mixture was allowed to warm up to room temperature and
stirred for 2 h. Then Ph2PCH2CH2NH2 (0.23 g, 1.0 mmol) was added,
and the resulting solution was stirred for 12 h. Volatiles were removed
under vacuum, and the residue was subjected to TLC using CH2Cl2/
petroleum ether (v/v = 1:2) as eluent. From the main red band,
complex 9 (0.135 g, 24%) was obtained as a dark red solid. Anal. calcd
for C21H18Fe2NO5PS2: C, 44.16; H, 3.18; N, 2.45. Found: C, 44.12; H,
3.27; N, 2.38. IR (KBr disk): νCO 2041 (vs), 1981 (vs), 1951 (s),
1932 (m) cm−1. 1H NMR (δ, ppm, 500 MHz, CDCl3): 7.50−7.81 (m,
10H, PhH), 3.77−3.90 (m, 4H, 2NCH2S), 2.79−2.89 (m, 4H,
NCH2CH2P). 13CNMR (δ, ppm, 126 MHz, TMS): 37.38
(NCH2CH2), 50.79 (NCH2CH2), 53.38 (NCH2S), 128.35, 129.97,
1
1992 (vs), 1971 (vs), 1926 (s) cm−1. H NMR (δ, ppm, 500 MHz,
CDCl3): 7.43−7.68 (m, 15H, 3PhH), 2.88 (d, J = 11 Hz,2H,
2NCHaHeS), 2.34 (brs, 2H, NCH2CH2CH2S), 2.22 (s, 2H,
NCH2CH2CH2S), 2.15 (br s, 2H, 2NCHaHeS), 1.98 (s, 3H, SCH3),
1.30 (br s, 2H, NCH2CH2CH2S). 13CNMR (δ, ppm, 126 MHz,
TMS): 15.41 (SCH3), 25.52 (NCH2CH2CH2S), 31.56
(NCH2CH2CH2S), 50.56 (NCH2CH2CH2S), 57.18 (NCH2S),
128.40, 130.05, 133.50, 135.79 (C6H5), 209.77 (s, FeCO), 213.49
2
(d, JPC = 10.2 Hz, PFeCO). 31P NMR (202 MHz, CDCl3, 85%
H3PO4): 64.85 (s).
Synthesis of Complex Fe2[(μ-SCH2)2NCH2CH2CH2SCH3]-
(CO)5[PPh2(2-C5H4N)] (5). Complex 5 was prepared in a fashion
similar to that of complex 2 using NH2CH2CH2CH2SCH3 as the
amine. Yields: 45% (Method A) and 20% (Method B), dark red solid.
Anal. calcd for C28H27Fe2N2O5PS3: C, 47.34; H, 3.83; N, 3.94. Found:
C, 47.25; H, 3.86; N, 4.01. IR (KBr disk): νCO 2042 (vs), 1992 (vs),
1
1970 (vs), 1933 (m) cm−1. H NMR (δ, ppm, 500 MHz, CDCl3):
7.44−8.81 (m, 14H, 2PhH, C5H4N), 2.89 (d, J = 10.5 Hz, 2H,
2NCHaHeS), 2.52 (d, 2H, J = 8.5 Hz,NCH2CH2CH2S), 2.21−2.24 (m,
4H, NCH2CH2CH2S, 2NCHaHeS), 1.99 (s, 3H, SCH3), 1.30 (s, 2H,
NCH2CH2CH2S). 13C NMR (δ, ppm, 126 MHz, TMS): 15.42
(SCH3), 25.61 (NCH2CH2CH2S), 31.59 (NCH2CH2CH2S), 50.85
(NCH2CH2CH2S), 57.09 (NCH2S), 123.35, 127.35, 128.31, 132.39,
134.07, 134.78, 135.66, 149.95, 161.68 (C6H5, C5H4N), 209.88 (s,
2
133.51, 136.00 (PhCH), 209.40 (s, FeCO), 212.10 (d, JPC = 6.9 Hz,
PFeCO). 31P NMR (202 MHz, CDCl3, 85% H3PO4): 54.39 (s).
Synthesis of Complex Fe2[(μ-SCH2)2O](CO)5[P(C6H4-4-F)3]
(10). A red solution of Fe2(μ-S)2(CO)6 (0.344 g, 1.0 mmol) in
THF (20 mL) was cooled to −78 °C and then treated dropwise with
LiHBEt3 (2 mL, 2.0 mmol) to give a green solution. After stirring for
15 min, CF3CO2H (0.18 mL, 2.2 mmol) was added to cause an
immediate color change from green to red. The mixture was stirred for
10 min, and then 37% aqueous formaldehyde (0.17 mL, 2.0 mmol)
was added. The new mixture was allowed to warm up to room
temperature and stirred at this temperature for 1 h. Then P(C6H4-4-
F)3 (0.316 g, 1.0 mmol) was added to cause an immediate color
change from red to dark red. After stirring for 6 h, volatiles were
removed under vacuum. The residue was washed by n-hexane (20 mL)
and reacted with H2SO4 (1.0 mL, 18 mmol) in CH2Cl2 (20 mL) at
room temperature. The resulting solution was stirred for 20 h, and
then H2O (25 mL) was added. The organic phase was collected, the
volatiles were removed, and the residue was subjected to TLC using
CH2Cl2/petroleum ether (v/v = 1:4) as eluent. From the main red
band, 10 (0.176 g, 26%) was obtained as a red solid. Anal. calcd for
C25H16F3Fe2O6PS2: C, 44.41; H, 2.39. Found: C, 44.25; H, 2.61. IR
2
FeCO), 213.20 (d, JPC = 10.5 Hz, PFeCO). 31P NMR (202 MHz,
CDCl3, 85% H3PO4): 66.61 (s).
Synthesis of Complex Fe2[(μ-SCH2)2NCH2CH2CH2SCH3]-
(CO)5[P(C6H4-4-CH3)3] (6). Complex 6 was prepared in a fashion
similar to that of complex 3 using NH2CH2CH2CH2SCH3 as the
amine. Yields: 41% (Method A) and 19% (Method B), dark red solid.
Anal. calcd for C32H34Fe2NO5PS3: C, 51.15; H, 4.56; N, 1.86. Found:
C, 50.88; H, 4.75; N, 1.83. IR (KBr disk): νCO 2042 (vs), 1980 (vs),
1928 (m) cm−1. 1H NMR (δ, ppm, 500 MHz, CDCl3): 7.54 (t, J = 9.5
Hz, 6H, 3m-PhH), 7.20 (d, J = 7.5 Hz, 6H, 3o-PhH), 2.90 (d, J = 11.5
Hz, 2H, 2NCHaHeS), 2.38 (br s, 11H, 3CH3, NCH2CH2CH2S), 2.21−
2.24 (m, 4H, NCH2CH2CH2S, 2NCHaHeS), 1.98 (s, 3H, SCH3), 1.30
(s, 2H, NCH2CH2CH2S). 13C NMR (δ, ppm, 126 MHz, TMS): 15.41
(SCH3), 21.31 (CH3), 25.76 (NCH2CH2CH2S), 31.66
(NCH2CH2CH2S), 50.68 (NCH2CH2CH2S), 57.17 (NCH2S),
2
129.08, 133.50, 140.16 (PhCH), 210.00 (s, FeCO), 213.80 (d, JPC
= 11.3 Hz, PFeCO). 31P NMR (202 MHz, CDCl3, 85% H3PO4):
62.44 (s).
1
(KBr disk): νCO 2052 (s), 1987 (vs), 1940 (s) cm−1. H NMR (δ,
ppm, 500 MHz, CDCl3): 7.13−7.7 (12H, 3C6H4), 3.76 (d, 2H,
2OCHaHeS), 3.57 (d, 2H, 2OCHaHeS). 13C NMR (δ, ppm, 126 MHz,
TMS): 67.66 (OCH2S), 116.2, 132.02, 132.35, 135.52, 163.09, 165.12
Synthesis of Complex Fe2[(μ-SCH2)2NC6H4-4-CH3]-
(CO)5[PPh2(2-C5H4N)] (7). Complex 7 was prepared in a fashion
similar to that of complex 2 using NH2C6H4-4-CH3 as the amine.
Yields: 31% (Method A) and 16% (Method B), dark red solid. Anal.
calcd for C31H25Fe2N2O5PS2: C, 52.27; H, 3.54; N, 3.93. Found: C,
2
(PhCH), 208.9 (s, FeCO), 213.52 (d, JPC = 10.1 Hz, PFeCO). 31P
NMR (200 MHz, CDCl3, 85% H3PO4): 61.83 (s).
G
DOI: 10.1021/acs.organomet.7b00040
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Article
Synthesis of Complex Fe2[(μ-SCH2)2O](CO)5[P(C6H4-4-CH3)3]
(11). Complex 11 was synthesized in a fashion similar to that of
complex 10 using P(C6H4-4-CH3)3 as the phosphine ligand. Yield:
25%, red solid. Anal. calcd for C28H25Fe2O6PS2: C, 50.63; H, 3.79.
Found: C, 50.55; H, 4.01. IR (KBr disk): νCO 2049 (vs), 1988 (vs),
1971 (vs); 1935 (s) cm−1. 1H NMR (δ, ppm, 500 MHz, CDCl3): 7.61,
7.24 (2s, 12H, 3C6H4), 3.79 (s, 2H, 2OCHaHeS), 3.44 (s, 2H,
2OCHaHeS), 2.41 (s, 9H, 3CH3). 13C NMR (δ, ppm, 126 MHz,
TMS): 21.54 (CH3), 67.08 (OCH2S), 129.33, 133.54, 140.48
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00040.
■
S
CV curves for 1−6, IR and NMR spectra for 1−12
(PDF)
Crystallographic data for 1−4, 6, 7, and 9−11 (CIF)
2
(PhCH), 209.57 (s, FeCO), 213.82 (d, JPC = 10.0 Hz, PFeCO).
31P NMR (200 MHz, CDCl3, 85% H3PO4): 61.23 (s).
AUTHOR INFORMATION
Corresponding Authors
*E-mail: yu_longli@aliyun.com.
*E-mail: zph2004@nuc.edu.cn.
Notes
Synthesis of Complex Fe2[(μ-SCH2)2O](CO)5[PPh2(CH2CH3)]-
(12). Complex 12 was synthesized in a fashion similar to that of
complex 10 using PPh2(CH2CH3) as the phosphine ligand. Yield:
22%, red solid. Anal. calcd for C21H19Fe2O6PS2: C, 43.93; H, 3.34.
Found: C, 43.83; H, 3.45. IR (KBr disk): νCO 2046 (vs), 1981 (vs),
■
1
1929 (s) cm−1. H NMR (δ, ppm, 500 MHz, CDCl3): 7.71, 7.43 (2s,
10H, 2C6H5), 3.72 (s, 4H, 2OCH2S), 2.50−2.53 (m, 2H, CH2), 1.16−
1.23 (m, 3H, CH3). 13C NMR (δ, ppm, 126 MHz, TMS): 8.69 (CH3),
27.06 (CH2), 67.85 (OCH2S), 128.56, 128.63, 130.18, 132.66
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
2
(PhCH), 209.35 (s, FeCO), 214.54 (d, JPC = 10.0 Hz, PFeCO).
Financial support for this work was provided by National
Natural Science Foundation of China (21501124, 21301160),
Science & Technology Department of Sichuan Province
(2017JY0195, 2016086), Zigong Science & Technology and
Intellectual Property Bureau (2014HX02, 2015CXM01),
Sichuan University of Science & Engineering (2014RC05),
and Material Corrosion and Protection of Key Laboratory of
Sichuan Province (2014CL14).
31P NMR (200 MHz, CDCl3, 85% H3PO4): 57.56 (s).
CONCLUSION
■
In summary, we report on the synthesis of nine new phosphine-
substituted diiron azadithiolate complexes and three new
phosphine-substituted diiron oxadithiolate complexes via an
interesting one-pot reaction. Reaction of Fe2(μ-
SCH2OH)2(CO)6 and several phosphine ligands L (L =
PPh3, PPh2(2-C5H4N), P(C6H4-4-CH3)3) affords the inter-
mediate Fe2(μ-SCH2OH)2(CO)5L, while the intermediate in
situ reacts with primary amines RNH2 (R = CH2CH2CH-
(CH3)2, CH2CH2CH2SCH3, C6H4-4-CH3) to produce the
target phosphine-substituted diiron azadithiolate complexes
Fe2[(μ-SCH2)2NR](CO)5L in moderate yields. Comparatively,
the traditional way to synthesize this kind of the diiron
azadithiolate complexes with monophosphine ligands needs
two steps. The first step is to synthesize the all-carbonyl diiron
azadithiolate complexes Fe2[(μ-SCH2)2NR](CO)6. The second
step is further treatment of the as-prepared complexes Fe2[(μ-
SCH2)2NR](CO)6 with phosphine ligand in the presence of
decarbonylating agent Me3NO affords the target phosphine-
substituted complexes Fe2[(μ-SCH2)2NR](CO)5L. Compared
with the widely used tradtional way, this novel one-pot method
is simpler and more efficient. In this paper, a series of new
phosphine-substituted diiron azadithiolate complexes 1−8 have
been successfully synthesized by the one-pot reaction in
satisfactory yield. In addition, reaction of Fe2(μ-
SCH2OH)2(CO)6 and Ph2PCH2CH2NH2 affords complex
Fe2[(μ-SCH2)2NCH2CH2PPh2](CO)5 (9). In addition, ac-
cording to the same strategy, phosphine-substituted diiron
oxadithiolate complexes Fe2[(μ-SCH2)2O](CO)5[P(C6H4-4-
F)3] (10), Fe2[(μ-SCH2)2O](CO)5[P(C6H4-4-CH3)3] (11),
and Fe2[(μ-SCH2)2O](CO)5(Ph2PCH2CH3) (12) have been
successfully synthesized. All of the new complexes 1−12 were
fully characterized by elemental analysis, IR, and NMR
spectroscopy, and particularly for 1−4, 6, 7, and 9−11 by X-
ray single diffraction analysis. Moreover, the electrochemical
properties of complexes 1−6 and 10 were investigated by CV
in DCM solution. Complexes 1 and 10 were found to be
catalysts for H2 production under electrochemical conditions.
Further study on the synthesis of diiron azadithiolate complexs
containing different diphosphine ligands is in progress in our
research group.
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