Azadithiolates cofactor of the iron-only hydrogenase and its PR3-monosubstituted derivatives: Synthesis, structure, electrochemistry and protonation

Article abstract of DOI:10.1016/j.jorganchem.2007.08.026

The core structure (μ-SCH₂)₂NH[Fe₂(CO)₆] (5) of Fe-only hydrogenases active site model has been synthesized by the condensation of iron carbonyl sulfides, formaldehyde and silyl protected amine. Its monosubstituted complexes (μ-SCH₂)₂NH[Fe₂(CO)₅PR₃] (R = Ph (6), Me (7)) were accordingly prepared. The coordination configurations of 5 and 6 were characterized by X-ray crystallography. Protonation of complex 7 to form the N-protonated product occurs in an acetonitrile solution upon addition of triflic acid. The redox properties of these model complexes were studied by cyclic voltammetry.

Full text of DOI:10.1016/j.jorganchem.2007.08.026

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Journal of Organometallic Chemistry 692 (2007) 5501–5507
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Note
Azadithiolates cofactor of the iron-only hydrogenase and its
PR3-monosubstituted derivatives: Synthesis, structure,
electrochemistry and protonation
a
a,
a
a
b
˚
Zhen Wang , Jian-Hui Liu *, Cheng-Jiang He , Shi Jiang , Bjo¨rn Akermark ,
a,c,
*
Li-Cheng Sun
a
State Key Laboratory of Fine Chemicals, Dalian University of Technology, Zhongshan Road 158-40, Dalian 116012, PR China
b
Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm, Sweden
c
KTH Chemistry, Organic Chemistry, Royal Institute of Technology, 10044 Stockholm, Sweden
Received 29 March 2007; received in revised form 20 August 2007; accepted 23 August 2007
Available online 29 August 2007
Abstract
The core structure (l-SCH2)2NH[Fe2(CO)6] (5) of Fe-only hydrogenases active site model has been synthesized by the condensation of
iron carbonyl sulfides, formaldehyde and silyl protected amine. Its monosubstituted complexes (l-SCH2)2NH[Fe2(CO)5PR3] (R = Ph (6),
Me (7)) were accordingly prepared. The coordination configurations of 5 and 6 were characterized by X-ray crystallography. Protonation
of complex 7 to form the N-protonated product occurs in an acetonitrile solution upon addition of triflic acid. The redox properties of
these model complexes were studied by cyclic voltammetry.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Azapropanedithiolate; Phosphine ligand exchange; Iron-only hydrogenase
1. Introduction
carbonyl, cyanide and aqua ligands and the non-proteic
dithiolate connects to a tether [1,5]. The groups of Pickett,
Rauchfuss and Darensbourg have synthesized a number of
propyldithiolate diiron analogue and these complexes can
produce hydrogen in an electrochemical cell, giving a sup-
ply of protons and electrons [6–9]. Certain structural and
spectroscopic features of the enzyme have suggested that
the structure of this tether is –SCH2NHCH2S– (azadithiol-
ate, ADT) or the N-protonated equivalent (see Fig. 1) [10].
In addition, DFT calculations have shown that the amine
functionality in this dithiolate is the potential position for
protonation, which provides a low energy pathway for
hydrogen evolution in the natural system. The protonation
at this N atom is much more favorable than that with other
basic site such as terminal CN or bridging S atom [11].
Although there have been numerous reports regarding
the synthesis and electrochemistry of tertiary amine
azadithiolate diiron derivatives (l-SCH2)2NR[Fe2-
(CO)6] (R = –CH3, 4-NO2C6H4, 4-BrC6H4CH2, 2-BrC6H4,
Iron hydrogenases (Fe–H2ase) are highly efficient
enzymes that catalyze the reversible reduction of protons
to molecular hydrogen [1,2]. Since high-quality structures
of the Fe–H2ase isolated from Desulfovibrio desulfuricans
and Clostridium pasteurianum have been revealed [3,4],
the structural and functional models of the Fe-only
hydrogenase active site (H-cluster) have turned out to be
a fascinating topic due to the potential value of molecular
hydrogen as a clean energy carrier. The active site of
Fe–H2ase is comprised of one unusual low-valent diiron
disulfide that is linked by a cysteine-ligand to a [Fe4S4] clus-
ter, with one bridging carbonyl and additional terminal
*
Corresponding authors. Address: State Key Laboratory of Fine
Chemicals, Dalian University of Technology, Zhongshan Road 158-40,
Dalian 116012, PR China. Tel.: +86 411 88993886; fax: +86 411 83072185.
E-mail address: liujh@dlut.edu.cn (J.-H. Liu).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.08.026

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Z. Wang et al. / Journal of Organometallic Chemistry 692 (2007) 5501–5507
triisopropylsilyl, which was treated as the alternative
NH
S4Fe4
amino protective groups. Alkylsilylamine as starting mate-
rial can react with paraformaldehyde to form the
bis(hydromethyl) derivative 2a–c (Scheme 1). Treatment
of thiol complex 3 with 2a–c afforded diiron azadithiolates
4a–c. The alkylsilyl groups were simultaneously removed
by the excess CF3COOH existing in the solution to afford
5 in isolated yields of 10% for 1a, 32% for 1b and 36%
for 1c (Scheme 1). But we did not obtain the stable nitro-
gen-protective complex 4a–c, probably due to unstable
Si–N bond in the presence of trace acid. Comparing with
the isolated yield for 1b (32%) and 1c (36%), the yield for
1a (10%) is quite low. Under the same experimental condi-
tion, the unisolated yield of our method is obviously higher
than that of Rauchfuss’ method.
S
S
S
Cys
H2O
CO
Fe
Fe
OC
NC
C
CN
O
Fig. 1. The active site of Fe-only hydrogenase.
2-CH2C4H3O) [12–16], less work has been done to the
construction of this parent core structure, i.e., (l-SCH2)2-
NH[Fe2(CO)6]. Recently, Rauchfuss et al. reported the first
synthesis of this model complex by a three-component con-
densation starting from iron carbonyl sulfides, formalde-
hyde, and amines. However, the yield in this reaction was
low (37%) and no crystal structure was reported [17]. The
synthetic difficulty may probably be attributed to the
unstability of the azadithiolate-bridged complex in which
the central atom of the chelate is a secondary amine. We
decided to assess whether organosilicon reagent could be
applied to such reaction as a N-protection reagent. To this
end, alkylsilyl chloride was chosen and subjected to ami-
nating with NH3 or KNH2, followed by treating with form-
aldehyde, and finally reacted with Fe–S complex to achieve
the condensation. In addition, since the electron-donating
characteristics of tertiary phosphine ligands towards the
Fe atom are similar to those of CNÀ ligands and the com-
plicated protonation on the cyanide nitrogen atom can be
avoided, the PR3-monosubstituted complexes (l-
SCH2)2NH[Fe2(CO)5PR3] (R = Ph (6), Me (7)) were pre-
pared for a study of the influence of phosphine ligands
on the coordination structures and the protonation ability.
In this paper, we would like to report this modified proto-
col for the synthesis of (l-SCH2)2NH[Fe2(CO)6] (5), the
conversion to its PR3-coordinated products as well as their
electrochemical properties.
Monosubstituted complexes (l-SCH2)2NH[Fe2(CO)5L]
(L = PPh3 (6), PMe3 (7)) were readily prepared in moder-
ate to reasonable yields by treating 5 with PR3, according
to literature procedures (see Scheme 2) [18,19]. Considering
the different solubility and coordination ability of the ter-
tiary phosphine, different solvents were used for the indi-
vidual reactions, with hexane for trimethylphosphine and
toluene for triphenylphosphine. While the reaction of 5
with 1 equiv of trimethylphosphine, which has a good
coordinated ability, can be controlled at the monosubsti-
tuted stage, the reaction to form complex 6 required
2 equiv of PPh3 in refluxing toluene.
1
The products 5–7 were characterized by IR, H and 31P
NMR spectra and elemental analyses. The IR spectra of
these three complexes in KBr show three strong CO bands
in the region of 1910–2080 cmÀ1, identical to the carbonyl
stretching pattern for terminal CO bonds. In comparison
with all carbonyl complex 5, the average value of the bands
for monosubstituted complex 6 and 7 are lowered by 36
and 60 cmÀ1, respectively.
2.2. Molecular structures of complexes 5 and 6
2. Results and discussion
Single-crystal X-ray diffraction analysis of 5 and 6
(Fig. 2) shows the usual distorted square-pyramidal geom-
etry around the iron centers. The Fe–Fe distances of the
two complexes are somewhat shorter than those in the
structures of H2-uptake enzyme from DdHase (Desulfovib-
rio desulfuricans) and H2-evolving enzyme from CpHase
2.1. Synthesis and spectroscopic characterization
Rauchfuss and co-workers have synthesized the core
structural molecule (l-SCH2)2NH[Fe2(CO)6] (5) by the
treatment of 3 with a premixed solution of paraformalde-
hyde and (NH4)2CO3 or hexamethylenetetramine in yield
of 37% [17]. However, the isolated yield for the target com-
plex is very low (<20%) when we repeated their work. We
reasoned that the bridge N could be protected to increase
the stabilities. Many amine protective groups such as acyl
chloride and carbamate are usually removed by treatment
with strong base. In contrast, the silyl group can be
removed quite easily by treatment with trace acid or in a
mild, natural conditions, for instance by using TBAF.
Thus, considering the unstability of the Fe2S2 skeleton in
basic conditions, we choose some silyl reagents as the
amino protective groups to achieve the transformation to
complex 5, including triethylsilyl, t-butyldimethylsilyl and
˚
(Clostridium pasteurianum) (ca. 2.6 A) [3,4,10], but still in
good agreement with the structural data of Fe–Fe bonds
˚
(2.49–2.51 A) found in other diiron azadithiolates com-
plexes [12,15,17]. The CO displacement by one molecule
of triphenylphosphine ligand has only a small effect on
˚
the Fe–Fe distance [2.519(8) A in 6] as compared to that
˚
of 5 [2.505(1) A]. Similar to (l-SCH2)2NH[Fe2(CO)4
(CN)2] [17], the N–H of 5 and 6 are all axial as anticipated
[11] and the bridging-N atoms are of sp3-hybridization. In
the solid state, the nonbonding Fe–H distance between the
H atom at the bridging-N atom and the nearest Fe atom of
˚
5 is almost consistent with 6 (3.34 and 3.38 A, respectively),
which is significantly longer than that of dicyanide substi-

Z. Wang et al. / Journal of Organometallic Chemistry 692 (2007) 5501–5507
5503
NH3
Si
Cl
Si
NH2
15-20 , benzene
1a
R2
NH3
-78 , pentane
R1
R1
Si
N
Si
Cl
(HCHO)n
THF, 4h
Si
NH2
1b
OH OH
KNH2
R1 = R2 = Et,
R1 = Me, R2 = t -Bu, 2b
R1 = R2 = i -Pr,
2a
Si
Cl
Si
NH2
1c
-50 , NH3
2c
R2
R1
Si
R1
S
H
S
H
S
2a
2b
2c
NH
N
CO
CO
OC
OC
OC
+
r.t, 10h
Fe
Fe
H+
S
S
CO
CO
OC
OC
OC
S
CO
CO
Fe
Fe
OC
OC
OC
Fe
Fe
3
CO
CO
CO
5
R1 = R2 = Et,
4a
R1 = Me, R2 = t -Bu, 4b
R1 = R2 = i -Pr, 4c
Scheme 1. The synthetic procedure of complexes 5.
NH
NH
NH
S
S
S
S
S
S
PPh3
toluene
P
PMe3
hexane
OC
OC
OC
CO
CO
P
OC
OC
OC
OC
OC
OC
Fe
Fe
Fe
Fe
Fe
Fe
CO
CO
CO
CO
CO
6
5
7
Scheme 2. The transformation of 5 to complexes 6 and 7.
a
b
˚
Fig. 2. Molecular structures of 5 (a) and 6 (b), hydrogen atoms omitted for clarity. Selected bond lengths [A] and angles [ꢁ] for complexes 5: Fe(1)–Fe(2)
2.505(1), Fe–C 1.796(1)–1.803(1), C(8)–N(1)–C(7) 119.7(1), C(7)–N(1A)–C(8) 117.1(1), Sum of angles at N 338.7, 341.1; for complexes 6: Fe(1)–Fe(2)
2.519 (1), Fe(1)–P(1) 2.244 (1), Fe–C 1.766(2)–1.801(0), C(6)–N(1)–C(7) 116.3(2), Sum of angles at N 336.3.
˚
tuted analogue (3.18 A) [17]. It is noticeable that the NH
group of 6 slants towards the larger electron-density
Fe(1) atom. The structural character of 6 may influence
hydrogen-evolving processes in the designed molecules.
After protonation of 6, the proton is anticipated to be in
proximity to the diiron active site. Triphenylphosphine
ligand is coordinated to an apical site on Fe(1) and roughly
trans to the Fe–Fe bond. Both 31P NMR and X-ray

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Z. Wang et al. / Journal of Organometallic Chemistry 692 (2007) 5501–5507
crystallographic analyses of 6 suggest that one CO dis-
placement by tertiary phosphine in 5 affords only an apical
isomer, as shown in Fig. 2b. The angles of C(6)–S(1)–Fe(1)
[114.5(1)ꢁ] and C(7)–S(2)–Fe(1) [114.8(1)ꢁ] in 6 are a little
wider than the corresponding angles of C(6)–S(1)–Fe(2)
[108.0(1)ꢁ] and C(7)–S(2)–Fe(2) [109.1(1)ꢁ]. It shows that
the six-membered ring of the propanedithiolate in 6 is
pushed away from the site occupied by an apical PPh3
ligand, leading to the lean of the propanedithiolate ring
towards the Fe(CO)3 site, as its analogue (l-pdt)
[Fe2(CO)5PPh3] [8].
1JNH = 58 Hz appears at d 6.01, attributing to the proton
on the bridge nitrogen of [7NHH]+ [15]. The two protons
of the CH2S group, which are on the equatorial bonds rel-
ative to the 6-membered ring [Fe(1)–S(2)–C(7)–N(1)–
C(6)–S(1), Fig. 2] and cis to the proton of the NH group,
should display higher resonances than those on the vertical
bonds and trans to the proton of the NH group. All obser-
vations in the 1H NMR spectra are consistent with the pro-
tonation of the bridging-N atom. No peaks at d < 0 exist in
the 1H NMR were observed, showing that the protonation
occurred on the N atom rather than to form l-H complex at
the Fe–Fe site. Upon addition of an excess of pyridine to the
1
2.3. Reactions of diiron derivatives with strong acid
solution of [7NHH]+ in CD3CN, a triplet with JNH
=
67 Hz emerges at d 13.56, and at the same time all signals
move back to the original. The newly-formed triplet in the
low field region is assigned to the NH of protonated pyri-
dine [21]. From Fig. 3c, we can see that the deprotonation
of [7NHH]+ occurs instantly to afford 7 and pyridinium tri-
flate in the presence of pyridine.
Attempts to protonate 5–7 were performed in an CH3CN
solution upon addition of triflic acid, but only the complex 7
was observed to be protonated. This result indicates that the
basicity of the bridging-N atom of the complexes 5 and 6 are
too weak to be protonated in the non-aqueous solution.
Protonation of 7 was performed with triflic acid in CHCl3
in order to afford an orange precipitate [(l-SCH2)2NH(H)-
{Fe2(CO)5PMe3}]+ ([7NHH]+). The IR spectra monitored
the whole processes. In CH3CN solution complex 7 displays
three m(CO) bands at 2035, 1965, 1914 cmÀ1. After 1 equiv
of triflic acid was added, the m(CO) bands shifted to higher
wavenumber by ca.18 cmÀ1, which is consistent with the
observations during the bridging-N atom protonation for
the related complexes [12,14,15,20]. With the addition of
an excess of pyridine to the CH3CN solution of [7NHH]+,
the m(CO) absorptions shifted to frequencies essentially
equivalent to those of parent 7.
2.4. Cyclic voltammograms of model complexes 5–7 and
[7NHH]+
Electrochemistry of model complexes were studied to
evaluate their redox properties. The electrochemical data
are presented in Fig. 4. Complexes 5–7 each display one
irreversible oxidation peak and one irreversible reduction
peak. Compared with the electrochemical data of the
azadithiolat diiron complexes and other analogous
[13,14,21], the oxidation peaks at the range of 0.1–0.6 V
versus Fc/Fc+ are assigned to the Fe(I)Fe(I)/Fe(II)Fe(I) pro-
cess. The reductive peaks at the range of À1.5 to À1.9 V are
ascribed to the one-electron process Fe(I)Fe(I)/Fe(0)Fe(I).
Compared to the (l-pdt)Fe2(CO)6 (pdt = SCH2CH2CH2S)
(Ered = À1.67 V versus Fc/Fc+) [14], the reductive poten-
tial of 5 (À1.58 V) was less negative, which is close to the
value of the tertiary amine azadithiolate diiron derivatives
The reversible protonation of 7 and deprotonation of
1
[7NHH]+ were monitored by the H NMR (Fig. 3). As
5 equiv of triflic acid was added to a solution of 7 in
CD3CN, the signal of the CH2S at d 3.47 ppm (singlet)
shifts to d 3.34 ppm (doublet) and d 3.65 ppm (singlet) shifts
to d 3.80 ppm (doublet). Simultaneously a triplet with
Fig. 3. 1H NMR spectra of (a) 7 in CD3CN, (b) [7NHH]+ (5 equiv CF3SO3H in CD3CN), (c) [7NHH]+ + 6 equiv pyridine in CD3CN.

Z. Wang et al. / Journal of Organometallic Chemistry 692 (2007) 5501–5507
5505
Fig. 4. Cyclic voltammograms of 5 (a), 6 (b), 7(c) and [7NHH]+(d), 1.0 mmol in 0.05M [n-Bu4NPF6]/CH3CN at a scan rate of 100 mV sÀ1. Potentials are
vs. Fc/Fc+.
(l-SCH2)2NR[Fe2(CO)6] (R = 4-NH2C6H4 (À1.58 V), 4-Br
C6H4CH2 (À1.56 V), 2-CH2C4H3O (À1.55 V)) [13,14,16].
The replacement of one CO for one PR3 leads to a negative
shift of the reduction potential by ca. 0.12 and 0.3 V for 6
and 7, respectively, as compared to that of the all-carbonyl
parent complex 5. The reduction potential for 6 is obviously
less negative than that for complex 7 by 180 mV, indicative
of a considerable influence of different phosphine ligands on
the redox properties of the iron atoms of Fe-only hydroge-
nase-active-site model complexes. As addition of 2 equiv of
triflic acid to the CH3CN solution of 7, the cyclic voltam-
mogram of [7NHH]+ is observed. The first reductive peak
is shifted by 480 mV towards more positive potential com-
pared to that of complex 7, which is a result of the fact that
[7NHH]+ carries a proton, and this reductive peak is corre-
sponding to a one-electron reduction of the protonated
complex to [7NHH]+ [14].
bridging nitrogen atom can be protonated and assists the
formation of the H–H bond to produce molecular hydro-
gen during the catalytic cycle.
4. Experimental
4.1. Reagents and instruments
All manipulations related to organometallic complexes
were performed under dry, oxygen-free nitrogen gas with
standard Schlenk techniques. All solvents were purified
according to standard methods. Commercially available
chemicals, including paraformaldehyde, t-butyldimethylsi-
lyl chloride, triethylsilyl chloride, triisopropylsilyl chloride,
tertiary phosphanes and Fe(CO)5, were used without fur-
ther purification. The reagent LiEt3BH was purchased
from Aldrich. Starting compounds triethylsilylamine (1a)
[22], t-butyldimethylsilylamine (1b) [23], triisopropylsilyl-
amine (1c) [24], (l-S)2[Fe2(CO)6], (l-HS)2[Fe2(CO)6] (3)
were prepared according to literature methods [25,26]. All
other reagents were used as purchased without further
3. Conclusions
In summary, the desired diiron azadithiolate complexes
(l-SCH2)2NH[Fe2(CO)6] (5) was synthesized starting from
the alkylsilyl-protected material, and its PR3-monosubsti-
tuted derivatives (l-SCH2)2NH[Fe2(CO)5PR3] (R = Ph
(6), Me (7)) were also obtained. The crystal structure of
the complex 6 showed that the N–H bond is in axial posi-
tion and close to the higher electron-density Fe atom. This
may indicate that the hydrogen on the bridged-N atom
plays a very important role in the catalyzing the reversible
reaction of protons and electrons to molecular hydrogen.
The result of the protonation of 5–7 showed that only by
coordinating of a strong electron-donating ligand, the
1
purification. H and 31P NMR spectra were recorded on
a Varian INOVA 400 spectrometer. IR spectra were
recorded from KBr pellets with a JASCO FT/IR430. Ele-
mental analyses were performed with a Thermoquest-Flash
EA 1112 elemental analyzer.
4.2. Procedures
4.2.1. (l-SCH2)2NH [Fe2(CO)6] (5)
A mixture of triethylsilylamine (393 mg, 3.00 mmol),
paraformaldehyde (304 mg, 0.01 mol) and THF (25 mL)

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Z. Wang et al. / Journal of Organometallic Chemistry 692 (2007) 5501–5507
Table 1
was stirred for ca. 4 h. Then it was treated with a THF solu-
tion (25 mL) of 3 (0.59 mmol) and stirred for further 10 h.
After removing THF under vacuum, the crude product
was purified by flash chromatography on silica gel eluting
with hexane/CH2Cl2 (8:1) to give 5 as a red solid (24 mg,
10%). The crystal suitable for X-ray analysis was obtained
Crystallographic data and processing parameters for complexes 5 and 6
5
6
Empirical formula
Formula weight
Crystal system
Space group
C8H5Fe2NO6S2 C25H20Fe2NO5PS2
386.95
621.22
Monoclinic
P2(1)/n
7.8127(4)
15.1218(9)
11.7395(5)
90.00
99.902(2)
90.00
1366.27(12)
4
Monoclinic
P2(1)/c
9.1382(18)
17.286(4)
16.651(3)
90.00
102.44(3)
90.00
2568.4(9)
32
1
from a solution of hexane at 2 ꢁC. H NMR (CDCl3) d
˚
a (A)
3.56 (s, 4H, NCH2S), IR (KBr, mCO): m = 2073, 2031,
1994 cmÀ1. Anal. Calc. for C8H5Fe2NO6S2: C, 24.83; H,
1.30; N, 3.62. Found: C, 24.79; H, 1.31; N, 3.65%.
The synthetic procedure of complexes 5 started from
t-butyldimethylsilylamine (1b) and triisopropylsilylamine
(1c) is similar to that of triethylsilylamine (1a). The yield
is, respectively, 32% for 1b and 36% for 1c.
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z
Dcalc (Mg/m3)
F(000)
1.881
768
1.606
1264
Crystal size (mm)
Range for data collection (ꢁ)
Reflections collected
0.35 · 0.22 · 0.2 0.3 · 0.25 · 0.22
4.2.2. (l-SCH2)2NH [Fe2(CO)5PPh3] (6)
2.22–25.08
1.72–27.43
To the red solution of hexacarbonyldiiron dithiolate 5
(50 mg, 0.129 mmol) in toluene (10 mL) was added triphenyl-
phosphine (135 mg, 0.258 mmol). The reaction mixture was
refluxed for 4 h and the color turned to dark red. After the
solvent was removed in vacuum, the crude product was puri-
fied by column chromatography on silica gel with hexane/
CH2Cl2 (4:1) as eluent to give 6 as red solid (32 mg, 40%).
The crystal suitable for X-ray analysis was obtained from a
solution of hexane/CH2Cl2 (10/1) at 2 ꢁC. 1H NMR (CDCl3)
2400
5538
Independent reflections (Rint
)
2034 (0.0219)
25.08ꢁ, 98.9%
2400/2/188
1.068
4350 (0.0416)
27.43ꢁ, 94.5%
5538/0/329
0.980
Completeness to h
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices (I > 2r(I))
R1 = 0.0440
wR2 = 0.0892
R1 = 0.0573
wR2 = 0.0987
0.457 and
À0.389
R1 = 0.0272
wR2 = 0.0655
R1 = 0.0412
wR2 = 0.0773
0.507 and À0.400
R indices (all data)
Largest difference in peak and
À3
˚
d 7.72 (s, 9H, Ph), 7.46 (s, 6H, Ph), 3.18 (s, 4H, SCH2N), 31
P
hole (e A
)
NMR (CDCl3) d 65.52; IR (KBr, mCO): m = 2035, 1985,
1974 cmÀ1. Anal. Calc. for C25H20Fe2NO5PS2: C, 48.33; H,
3.25; N, 2.25. Found: C, 48.91; H 3.24; N 2.22%.
were refined anisotropically. The hydrogen atoms of the
NH group in 5 and 6 were located from Fourier difference
maps and the other H-atoms located by geometrical calcu-
lation, but their positions and thermal parameters were
fixed during the structure refinement.
4.2.3. (l-SCH2)2NH [Fe2(CO)5PMe3] (7)
To the red solution of hexacarbonyldiiron dithiolate 5
(50 mg, 0.129 mmol) in hexane (10 mL) was added trimeth-
ylphosphine (10 mg, 0.129 mmol). The reaction mixture
was refluxed for 1 h and the color turned to dark red. After
the solvent was removed in vacuum, the crude product was
purified by column chromatography on silica gel with hex-
ane/CH2Cl2 (3:1) as eluent to give 7 as a red solid (32 mg,
40%). 1H NMR (CNCD3) 3.65 (s, 2H, SCH2N), 3.47(s, 2H,
SCH2N), 1.48(d, JPH = 9.6 Hz, 9H, CH3) 31P NMR
4.4. Crystal data for 5 and 6
Crystallographic data and processing parameters for
complexes 5 and 6 are given in Table 1.
4.5. Electrochemistry
(CDCl3)
d
26.46; IR (KBr, mCO): m = 2035, 1965,
A solution of 0.05 M of n-Bu4NPF6 (Fluka, electro-
chemical grade) in CH3CN was used as electrolyte, which
was degassed by bubbling with dry argon for 10 min before
measurement. Electrochemical measurements were
recorded using a BAS-100W electrochemical potentiostat
at a scan rate of 100 mV/s. Cyclic voltammograms were
obtained in a three-electrode cell under argon. The working
electrode was a glassy carbon disc (diameter 3 mm)
successively polished with aqueous alumina powder slurry
for 10 min. The reference electrode was a non-aqueous
Ag/Ag+ electrode (0.01 m AgNO3 in CH3CN) and the aux-
iliary electrode was a platinum wire.
1914 cmÀ1. C10H14Fe2NO5PS2 (435.02): Anal. Calc. C,
27.61, H, 3.24, N, 3.22. Found: C 27.21, H 3.24, N 3.19%.
4.3. Crystal structure determinations of complexes 5 and 6
The single crystal X-ray diffraction data were collected
with a Siemens Smart CCD diffractometer equipped with
graphite monochromated Mo Ka radiation (k =
0.71073 A) for 5 and with a Rigaku R-axis rapid-IP
equipped with graphite monochromated Mo Ka radiation
´
´
(k = 0.71073 A) for 6. Complete crystal data and parame-
ters for data collection and refinement are listed in Table
1. The structure was solved by direct methods and subse-
quent difference Fourier syntheses, and refined on F2
against full-matrix least-squares methods by using the
SHELXTL-97 program package. All non-hydrogen atoms
5. Supplementary material
CCDC 239490 and 244941 contain the supplementary
crystallographic data for (l-SCH2)2NH[Fe2(CO)6] and

Z. Wang et al. / Journal of Organometallic Chemistry 692 (2007) 5501–5507
5507
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[8] P. Li, M. Wang, C.-J. He, G.-H. Li, X.-Y. Liu, C.-N. Chen, B.
(l-SCH2)2NH[Fe2(CO)5PPh3]. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223 336 033; or e-mail: deposit@ccdc.
cam.ac.uk.
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Acknowledgements
We are grateful to the Ministry of Science and
Technology of China and the Chinese National Natural
Science Foundation (Grant No. 20471013, 20633020 and
20672017), the Swedish Energy Agency, the K&A Wallen-
berg Foundation, the Program of Introducing Talents of
discipline to Universities, and the Swedish Research Coun-
cil for financial supports of this work.
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