Pendant bases as proton transfer relays in diiron dithiolate complexes inspired by [Fe-Fe] hydrogenase active site

Article abstract of DOI:10.1016/j.jorganchem.2008.06.001

Three dinuclear iron complexes containing pendant nitrogen bases in phosphine ligands with general formular (μ-pdt) [Fe₂(CO)₅L] (where pdt is SCH₂CH₂CH₂S, L = PPh₂NH(CH₂)₂

Full text of DOI:10.1016/j.jorganchem.2008.06.001

Journal of Organometallic Chemistry 693 (2008) 2828–2834
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Journal of Organometallic Chemistry
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Pendant bases as proton transfer relays in diiron dithiolate complexes inspired
by [Fe–Fe] hydrogenase active site
a
a
c
a,d,
*
Zhen Wang a, Wenfeng Jiang b, Jianhui Liu a, , Weina Jiang , Yu Wang , Björn Åkermark , Licheng Sun
*
a State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT),
158 Zhongshan Road, Box 40, Dalian, Liaoning 116012, PR China
b Department of Chemistry, Dalian University of Technology (DUT), 110024 Dalian, PR China
c Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, 10691 Stockholm, Sweden
d Department of Chemistry, Organic Chemistry, Royal Institute of Technology (KTH), 10044 Stockholm, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history:
Three dinuclear iron complexes containing pendant nitrogen bases in phosphine ligands with general for-
mular -pdt) [Fe2(CO)5L] (where pdt is SCH2CH2CH2S, L = PPh2NH(CH2)2N(CH3)2 (5), PPh2NH-
Received 10 April 2008
Received in revised form 2 June 2008
Accepted 3 June 2008
(
l
(2-NH2C6H4) (6), PPh2[2-N(CH3)2CH2C6H4] (7)), were prepared as the models of the [Fe–Fe] hydrogenase
active site. The molecular structures of 5–7 were characterized by X-ray crystallography. The secondary
amine in 6 has weak intramolecular hydrogen bonding with both the terminal nitrogen and sulfur atom,
which may suggest a proton transfer pathway from amine in phosphine ligand to the sulfur atom of
active site. Protonation of complexes 5 and 6 only occurred at the terminal nitrogen atom. Electrochem-
ical properties of the complexes were studied in the presence of triflic acid by cyclic voltammetry.
Ó 2008 Published by Elsevier B.V.
Available online 7 June 2008
Keywords:
Pendant base
Phosphine ligand exchange
Proton transfer
[Fe–Fe] hydrogenase
1. Introduction
Other experimental and theoretical studies of these model com-
plexes also indicate that bridging hydride may be involved in the
The Fe–Fe hydrogenases, the more efficient enzymes in hydrogen
production than other types of hydrogenases, have inspired chem-
ists in the bioinorganic community to synthesize close mimics of
their active sites in the search for hydrogen production catalysts.
The latest spectroscopic, crystallographic and theoretical studies
suggest that the active sites consist of bimetallic iron complexes
bridged by a 1,3-azadithiolate ligand (Fig. 1) [1–5], although the nat-
ure of the bridging ligand could not be solved from X-ray data of the
enzymes. DFT calculations have shown that the amine functionality
in this dithiolate is the potential position for protonation, which pro-
vides a low energy pathway for hydrogen evolution in the natural
system [4]. Based on these significant research findings, the struc-
tural and functional models of the Fe–Fe hydrogenases active site
have been intensively studied in recent years [6–8]. There have been
some reports regarding the synthesis and electrochemistry of azadi-
catalytic cycle of hydrogenase enzymes and there are other possible
pathways as the proton transfer relays that do not require a nitrogen
of the azadithiolate ligand [17–20].
Studies on organometallic complexes have shown that pendant
nitrogen bases play an important role in proton/hydride exchange
reactions [21–23]. An understanding of proton transfer precess will
be necessary for developing efficient hydrogen production/hydro-
gen oxidation catalysts. Recently, DuBois and co-workers reported
that trans Fe(II) complexes containing the diphosphine ligand with
a pendant nitrogen base as the potential model of the iron–iron
hydrogenase enzymes can be successively protonated in two steps
using increasingly strong acids and a nitrogen atom in a six-mem-
bered chelate ring can promote very rapid intra- and intermolecular
proton/hydride exchange in octahedral Fe(II) PNP complexes and
function as a proton relay for oxidized Fe(III) hydrides as well
[24]. Incorporating good donor ligands (cyanide, tertiary phos-
phines and isonitrile) to the propanedithiolato-bridged dinuclear
thiolate diiron derivatives (l-SCH2)2NR [Fe2(CO)6] (R = H, –CH3, 4-
NO2C6H4, 4-BrC6H4CH2, 2-BrC6H4, 2-CH2C4H3O) [9–16]. However,
the distance between the nitrogen atom in the dithiolated chelate
and the iron atom of the active site is comparatively changeless.
complex [(l-pdt)Fe2(CO)6] (1) that bears remarkable structural
similarities with the active site of Fe–Fe hydrogenase renders the
iron atoms more electron-rich and more protophilic [17,25–28].
These results promoted us to study the role of a pendant base of
phosphine ligand in proton/hydride exchange in diiron complexes.
In this paper, we report the preparation of three phosphine ligands
containing pendant nitrogen bases, and their monosubstituted
* Corresponding authors. Address: State Key Laboratory of Fine Chemicals, DUT-
KTH Joint Education and Research Center on Molecular Devices, Dalian University of
Technology (DUT), 158 Zhongshan Road, Box 40, Dalian, Liaoning 116012, PR China.
Tel.: +86 411 88993886; fax: +86 411 83072185 (J. Liu).
complexes
(l-pdt) [Fe2(CO)5L] (L = PPh2NH(CH2)2N(CH3)2 (5),
E-mail address: liujh@dlut.edu.cn (J. Liu).
0022-328X/$ - see front matter Ó 2008 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2008.06.001

Z. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 2828–2834
2829
NH
S4Fe
4
NH
NH
PPh2
HN
N
2 OC
S
S
S
S
S
S
N
OC
OC
S
S
PPh2
CO
S
Cys
OC
NC
PPh2
H2O
CO
Fe
Fe
Fe
Fe
Fe
Fe
OC
OC
OC
OC
CO
OC
OC
CO
Fe
Fe
CO
CO
CO
5
6
7
C
CN
O
Chart 1. The structures of complexes 5, 6 and 7.
Fig. 1. The Hox state of the Fe-only hydrogenase.
PPh2NH(2-NH2C6H4) (6), PPh2[2-N(CH3)2CH2C6H4] (7) by the CO-
ligand exchange reaction (see structures in Chart 1). The nitrogen
atom of the phosphine ligand in complexes 5–7 can adopt the posi-
tion closer to the catalytically active site in space than that of the
azadithiolated bridgehead in the complexes (l-SCH2)2NR[Fe2-
(CO)6]. As desired, the protonation of the basic nitrogen atom in-
are listed in Table 1. Each complex shows three bands in the
(CO) stretching region (1890–2080 cmꢁ1), the same as that of
complex ( -pdt)[Fe2(CO)5PPh3] [29]. In comparison to all carbonyl
complex 1, the average value of the bands for monosubstituted
complex 5–7 are lowered by 50, 52 and 49 cmꢁ1, respectively. It
indicates that the electron-donating capability of phosphine
ligands 2–4 is similar.
m
l
stead of Fe–Fe bond has been observed in the presence of triflic acid.
2. Results and discussion
2.2. Molecular structures of complexes 5–7
2.1. Synthesis and spectroscopic characterization
The crystallographic structures of 5–7, which are depicted as
solvate-free forms and given as an ORTEP diagram in Fig. 2, belong
to the P2(1)/n, Pbca and P2(1)/c space groups, respectively. Selected
bond lengths and bond angles are listed in Table 2. The Fe2S2 skel-
eton of 5–7 has the well-known butterfly structure found in related
The monosubstituted 2Fe2S complex (l-pdt)[Fe2(CO)5PMe3]
was chosen as the substrate in our initial studies, based on the con-
sideration that the ligand PMe3 can increase the electron-density
of Fe atom. However, we were unable to obtain the disubstituted
products via intermolecular CO-displacement by the phosphine li-
gand 2–4 in the presence of CO-removing reagent Me3NO or in
refluxing toluene. Therefore we turned our attention to all carbonyl
substrate 1, hoping to obtain monosubstituted 2Fe2S complexes 5–
7 and to study the role of a pendant base of phosphine ligand in
proton transfer process. By treatment with Me3NO ꢀ 2H2O as
decarbonylation reagent, we obtained the monosubstituted com-
plexes in yield 55–61% (Scheme 1), which is similar to that of
PPh3 monosubstituted complex [29]. All of the three complexes
5–7, are air and thermally stable in the solid state.
diiron complexes (l-SR)2[Fe2(CO)6ꢁnLn] [25–29]. Each iron center
displays approximately square–pyramidal coordination geometry.
The Fe–Fe distances in 5 (2.5029(8) Å), 6 (2.5010(10) Å) and 7
(2.5267(18) Å) are somewhat different compared to the structural
data of Fe–Fe bonds (2.5103(11) Å) of complex 1 [29]. Both 31P
NMR and X-ray crystallographic analyses of 5–7 suggest that one
CO-displacement by tertiary phosphine in 1 affords only an apical
isomer, as shown in Fig. 2.
The angles of C(6)–S(1)–Fe(1) [114.8 (2)°] and C(8)–S(2)–Fe(1)
[114.7(2)°] in 6 are a little wider than the corresponding angles
of C(6)–S(1)–Fe(2) [111.0(2)°] and C(8)–S(2)–Fe(2) [111.6(2)°]. It
shows that the six-membered ring of the propanedithiolate in 6
is pushed away from the site occupied by an apical phosphine
The products obtained were characterized by IR, 1H and 31P
NMR spectroscopy and elemental analysis. Their IR data of m(CO)
P
P
N
H
H2N
3
P
N
N
N
H
2
4
NH
N
S
S
OC
PPh2
2
Fe
Fe
CH3CN, 1h OC
OC
CO
CO
5
NH2
PPh2
HN
S
S
S
S
OC
3
CO
CO
OC
Me3NO
CH3CN, 30min
Fe
Fe
Fe
Fe
CH3CN, 1h
OC
OC
OC
OC
CO
CO
CO
1
6
S
S
N
OC
OC
4
PPh2
CO
Fe
Fe
CH3CN, 1h
OC
CO
7
Scheme 1. The synthetic procedure of complexes 5–7.

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Z. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 2828–2834
Table 1
sum of the van der Waals radii for two nitrogen atoms (3.0 Å),
The IR data of complexes 1, 5–7
therefore it easily forms the stable N–HꢀꢀꢀN intramolecular hydro-
gen bond. As shown in Fig. 2b, a particularly attractive aspect is
that the hydrogen atom of N(1) has weak intramolecular hydrogen
bond with both N(2) and sulfur atom. The distances and angles of
the two kinds of H-bonds in the crystals of complex 6 are given in
Table 3. The two intramolecular hydrogen bond might suggest a
proton transfer pathway from amine of phosphine ligand to the
sulfur atom of active site. Although the SꢀꢀꢀH distance for the intra-
molecular is longer than that of typically sulfur hydrogen bond
[30,31], it may influence the skeleton of 2Fe2S whose distance
(3.049 Å) of non-bonded two sulfur atoms for 6 is slightly longer
than that of two sulfur atoms for 5 (3.03 Å) and for 7 (3.042 Å).
Complex
m )
(CO) (cmꢁ1
1
5
6
7
2073
2053
2041
2046
2032
1974
1979
1981
1989
1928
1919
1930
ligand, leading to the lean of the propanedithiolate ring towards
the Fe(CO)3 site, as its analogue ( -pdt) [Fe2(CO)5PPh3] [29]. The
l
compounds 5 and 7 show a similar structure feature. The angle
of P–Fe(1)–Fe(2) for 5 is 3.66° wider than that of C(3)–Fe(2)–
Fe(1) for 7. However, the difference of corresponding two angles
is only 1.52(33)° and 0.51(31)° for 5 and 6, respectively. The Fe–
P bond lengths of 2.2160(13) Å in 5, 2.2139(14) Å in 6 and
2.269(2) Å in 7 are similar to the values of Fe–P bond lengths re-
ported for PR3 coordinating diiron complexes [29]. The average
Fe(2)–C(CO) bonds, 1.796(6)–1.772(7) Å for 5–7, are slightly short-
er than those in 1 [av. 1.800(3) Å], and the average Fe(1)–C(CO)
distance [1.757(9) Å] of 5–7 is considerably shortened by ca.
0.022–0.032 Å after coordination of phosphine to Fe(1). Another
notable fact is that the Fe–C bond lengths in apical positions are
decreased in the monosubstituted complexes. A reasonable expla-
nation is that the displacement of CO by the electron-donating
phosphine ligand increases the electron-density on one of the iron
centers of the diiron dithiolate complex, to give stronger back
donation to the CO ligands and weaken the CO bonds.
2.3. Protonation of model complexes 5 and 6
Protonation of 5 and 6 to form corresponding 5H+ and 6H+ pro-
tonated species occurs in an acetonitrile solution upon addition of
triflic acid. The 1H NMR spectra monitor the protonation processes
(Figs. 3 and 4). As 4 equiv. of triflic acid were added to the CD3CN
solution of 5, the signal of N(CH3)2 at d 2.09 ppm shifts to d
2.60 ppm, and the signal of N(CH2)2N at 2.24 and 2.74 ppm shift
to d 2.87 and 3.10 ppm, respectively, whereas the peak of the sec-
ondary amine, the two phenyl and propanedithiolate bridge have
no changes. All of these features indicate the protonation only oc-
curred at terminal tertiary amine. This was also verified by IR. The
m
(CO) band pattern of the protonated derivative for 5 is identical to
that of compound 1 with the
m
(CO) values shifting by only 5 cmꢁ1
on average. The smaller shift is consistent with ligand-based pro-
tonation as expected for the exposed tertiary nitrogen atoms on
the phosphine ligand [17].
In the crystalline solid state of complex 5, the chain N(1)–
C(21)–C(22)–N(2) takes the gauche form. The nonbonding
N(1)ꢀꢀꢀN(2) distance (2.781 Å) for 5 is apparently shorter than the
5
6
7
Fig. 2. ORTEP (ellipsoids at 30% probability level) view of 5, 6 and 7.

Z. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 2828–2834
2831
Table 2
Selected bond lengths (Å) and angles (°) for 5–7
Complex
5
6
7
Bond lengths
Fe(1)–Fe(2)
Fe(1)–S(1)
Fe(1)–S(2)
Fe(2)–S(1)
Fe(2)–S(2)
Fe(1)–P
Fe(1)–C(1)
Fe(1)–C(2)
Fe(2)–C(3)
Fe(2)–C(4)
Fe(2)–C(5)
P–N(1)
2.5029(8)
2.2532(14)
2.2482(13)
2.2757(14)
2.2550(13)
2.2160(13)
1.755(6)
1.764(6)
1.796(6)
1.772(7)
1.778(7)
2.5010(10)
2.2603(14)
2.2650(15)
2.2673(15)
2.2653(14)
2.2139(14)
1.766(6)
1.766(6)
1.778(6)
1.785(6)
1.781(6)
2.5267(18)
2.269(2)
2.279(3)
2.266(3)
2.269(3)
2.269(2)
1.776(8)
1.767(10)
1.778(10)
1.779(10)
1.793(12)
1.653(5)
1.684(4)
Bond angles
P–Fe(1)–S(1)
P–Fe(1)–S(2)
P–Fe(1)–C(1)
P–Fe(1)–C(2)
104.49(5)
106.59(5)
97.42(18)
94.13(17)
87.55(19)
161.20(17)
155.91(18)
87.65(17)
56.88(4)
56.36(3)
108.6(2)
151.9(2)
86.79(19)
102.00(18)
87.23(18)
158.8(2)
103.60(5)
108.13(5)
97.28(17)
97.09(18)
88.34(17)
159.22(18)
154.56(17)
87.02(17)
56.60(4)
109.23(9)
105.71(9)
95.7(2)
96.7(2)
155.0(2)
86.8(2)
Fig. 4. The 1H NMR spectra of complexes 6 and 6H+.
S(1)–Fe(1)–C(1)
S(1)–Fe(1)–C(2)
S(2)–Fe(1)–C(1)
S(2)–Fe(1)–C(2)
S(1)–Fe(1)–Fe(2)
S(2)–Fe(1)–Fe(2)
S(1)–Fe(2)–C(3)
S(1)–Fe(2)–C(4)
S(1)–Fe(2)–C(5)
S(2)–Fe(2)–C(3)
S(2)–Fe(2)–C(4)
S(2)–Fe(2)–C(5)
88.0(3)
complex. The
m
(CO) value of the protonated derivative 6H+ are
157.5(2)
56.09(7)
56.07(7)
102.3(3)
159.9(3)
88.3(3)
107.4(3)
87.3(3)
152.6(3)
shifted by only 6 cmꢁ1 on average. Due to the extremely poor sol-
ubility of complex 7 in MeCN, we were unfortunately unable to
study its protonation.
56.50(4)
105.16(18)
157.60(19)
86.92(18)
105.75(19)
87.84(17)
155.19(19)
2.4. Electrochemistry of model complexes 5–7
In order to get an estimate of the capability to catalyze hydro-
gen production, cyclic voltammetry (CV) of the complexes 5, 6
and 7 (Fig. 5) was performed. Compared with the electrochemical
data of the analogous complexes (l-pdt){Fe2(CO)5L} (L = PPh3,
PMe2Ph, PMe3) [29], the reductive peaks at the range of ꢁ1.8 to
Table 3
Distances (Å) and angles (°) for the H-bonds in the crystals of 6
ꢁ1.9 V are ascribed to the one-electron process Fe(I)Fe(I)/Fe(0)Fe(I)
,
H-bond
dDꢀꢀꢀA
dHꢀꢀꢀA
DꢀꢀꢀH–A angle
112.30
134.81
and the oxidation peaks at the range of 0.6–0.8 V versus Fc/Fc+
are assigned to the Fe(I)Fe(I)/Fe(II)Fe(I) process [13,32,33]. In the cyc-
lic voltammograms of 5 and 6, the oxidation peaks at 0.348 V and
0.259 V, which is not observed in the cyclic voltammogram of 7, is
presumably due to the oxidation of the NH group of 5 and 6.
According to the literature [13], the oxidative peak of the NH2
group of 6 is covered by the peak at 0.259 V. Compared to the all
carbonyl complex 1 (Ered = ꢁ1.67 V vs. Fc/Fc+) [14], the first reduc-
tive potential is shifted towards more negative potential by 194,
179 and 173 mV for 5–7, respectively. The core iron atom of com-
plex 5 is harder to reduce due to the better electron-donating capa-
bility of ligand 2.
N(2)ꢀꢀꢀH–N(1)
S(1)ꢀꢀꢀH–N(1)
2.709
3.460
2.263
2.799
As 4 equiv. of triflic acid were added to the CD3CN solution of 6,
the signal of –NC6H4N– at d 6.26 ppm and 6.42 ppm shift to d 7.39
and 6.77 ppm, respectively, and those at d 6.76 and 6.47 ppm shift
to d 7.08 ppm. Meanwhile, the signal of –PNH– at 5.47 ppm shift to
5.82 ppm due to the intramolecular hydrogen bond in the two
nitrogen atoms. Similar to complex 5, the protonation for 6 only
occurred at terminal nitrogen atom. An excess of triflic acid was
needed, and the behavior in the 1H NMR is the same. In the case
of complexes 5 and 6, no peaks at d < 0 exist, also showing that
The catalytic proton reduction by compound 5 and 6 was stud-
ied through cyclic voltammetry (Fig. 6) on addition of CF3SO3H in
CH3CN, with the concentration of 0–10 mM. With the increasing
amount of the acid, the first reduction peak of 5 is shifted by
around 172 mV towards more positive potential by the addition
of excess triflic acid. The reductive peak at ꢁ1.702 V corresponds
to a one-electron reduction of the protonated complex to 5H+.
The reduction current increases and the position of this peak shifts
to a more negative potential with increasing concentration of the
acid added. Compound 6 show a similar behavior in the CH3CN
solution in the presence of triflic acid (see Fig. 6b). Both of these
features seemed indicative of catalytic proton reduction, but a cyc-
lic voltammogram of blank solution indicate that they are not effi-
cient catalysts for the H2 production (complex 5 showing only
minor catalytic ability while complex 6 with no such ability, see
Supplemental material). This unfavorable catalytic ability may be
attributed to the far distance of the protonated terminal amino
groups to the Fe–Fe center of the model compounds of 5 and 6.
As described above, phosphine ligand containing pendant nitro-
gen bases in [2Fe2S] complexes could affect the reduction potential
the protonation occurred on the N atom rather than to form
l-H
Fig. 3. The 1H NMR spectra of complexes 5 and 5H+.

2832
Z. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 2828–2834
40
b
a
20
10
0
-1.874V
20
-1.859V
0
-20
-10
-20
-30
-40
0.706V
-60
0.259V
0.5
0.642V
1.0
0.348V
0.5
0.0
-0.5
E/V
-1.0
-1.5
-2.0
1.0
0.0
-0.5
E/V
-1.0
-1.5
-2.0
20
10
c
-1.853V
0
-10
-20
-30
-40
-50
0.771V
1.0
0.5
0.0
-0.5
E/V
-1.0
-1.5
-2.0
Fig. 5. Cyclic voltammogram of 5 (a), 6 (b) and 7 (c) (1.0 mM) in 0.05 M n-Bu4NPF6/CH3CN at a scan rate of 100 mV/s. Potentials are vs. Fc/Fc+.
b 200
a
00
50
00
50
0
160
120
80
40
0
50
-40
00
1.5
1.0
0.5
0.0 -0.5 -1.0 -1.5 -2.0
E/V
1.0
0.5
0.0
-0.5 -1.0
E/V
-1.5 -2.0
Fig. 6. Cyclic voltammograms of 5 (a) and 6 (b) in CH3CN in the presence of triflic acid (0, 2, 4, 6, 8, 10 equiv.).
of the iron complexes but the catalytic ability for the proton reduc-
tion still need to improve. Further work is focusing on the ligand
design with a pendant amine that can closely approach to the
Fe–Fe center to form a powerful catalytic center for the H2
production.
ods. Commercially available chemicals, including 1,3-propanedi-
thiol, diphenylchlorophosphine, dimethylethylenediamine, o-dia-
minobenzene, 2-methyl-N,N-dimethylaniline, and Fe(CO)5, were
used without further purification. Starting compounds [(l-pdt)Fe2
(CO)6] (1) [29,32], N,N-dimethyl-N-diphenylphosphinoethylenedi-
amine (2) [33], N-diphenylphosphino-o-diaminobenzene (3) and
N,N-dimethyl-o-diphenylphosphinobenzylamine (4) [34] were pre-
pared according to literature methods. All other reagents were used
as purchased without further purification. 1H and 31P NMR spectra
were recorded on a Varian INOVA 400 spectrometer. IR spectra were
recorded from KBr pellets with a JASCO FT/IR430. Elemental analy-
ses were performed with a Thermoquest-Flash EA 1112 elemental
analyzer.
3. Experimental
3.1. Reagents and instruments
All manipulations related to organometallic complexes were per-
formed under dry, oxygen-free nitrogen gas with standard Schlenk
techniques. All solvents were purified according to standard meth-

Z. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 2828–2834
2833
3.2. Procedures
3.2.1. ( -pdt)[Fe2(CO)5PPh2NH(CH2)2N(CH3)2] (5)
for C26H23Fe2N2O5PS2: C, 48.02; H, 3.57; N, 4.31. Found: C, 48.23; H,
3.82; N, 4.70%.
l
To the red solution of hexacarbonyldiiron dithiolate 1 (0.97 g,
0.25 mmol) in CH3CN (15 mL) was added Me3NO ꢀ 2H2O (111 mg,
0.1 mmol). When the color of the solution turned dark red, com-
pound 2 (136 mg, 0.5 mmol) was added to the reaction solution.
The reaction mixture was stirred for 0.5 h and the color turned
red. After the solvent was removed in vacuum, the crude product
was purified by column chromatography on neutral Al2O3 with
CH2Cl2/hexane (2:1) as eluent to give 5 as red solid (96 mg, 61%).
The crystal suitable for X-ray analysis was obtained from a solution
of CH2Cl2 in hexane atmosphere at 2 °C. 1H NMR (CDCl3) d 7.65–
7.70 (m, 4H, Ph), 7.40 (s, 6H, Ph), 3.33–3.37 (m, 1H, PNHC), 2.72–
7.72 (m, 2H, NCH2C), 2.26 (s, 2H, NCH2C), 2.12 (s, 6H, NCH3),
1.84–1.92 (m, 2H, SCH2C), 1.66–1.70 (m, 2H, SCH2C), 1.60–1.63
3.2.3. (
Complex 7 was prepared by a procedure similar to that of 5. To
the red solution of hexacarbonyldiiron dithiolate (0.97 g,
l-pdt){Fe2(CO)5PPh2[2-N(CH3)2CH2C6H4]} (7)
1
0.25 mmol) in CH3CN (15 mL) was added Me3NOꢀ2H2O (111 mg,
0.1 mmol). When the color of the solution turned dark red, com-
pound 4 (159 mg, 0.5 mmol) was added to the reaction solution.
The reaction mixture was stirred for 0.5 h and the color turned
red. After the solvent was removed in vacuum, the crude product
was purified by column chromatography on silica gel with
CH2Cl2/hexane (1:5) as eluent to give 7 as red solid (96 mg, 57%).
The crystal suitable for X-ray analysis was obtained from a solution
of hexane/CH2Cl2 (1/1) at 2 °C. 1H NMR (CDCl3) d 8.00 (s, 1H, Ph),
7.88–7.92 (m, 4H, Ph), 7.59–7.64 (m, 2H, Ph), 7.54 (s, 6H, Ph),
7.34 (t, 1H, Ph, J = 7.2 Hz), 3.47 (s, 2H, PhCH2N), 3.46 (s, 2H, PhNH2),
1.99 (s, 6H, NCH3), 1.79–1.84 (m, 2H, SCH2C), 1.48 (s, 1H, SCH2C),
1.24–1.29 (m, 3H, SCH2C, CCH2C), 31P NMR (CDCl3) d 62.72; IR
(m, 2H, CCH2C), 31P NMR (CDCl3) d 100.06; IR (KBr):
m(CO) 2053,
1974, 1928 cmꢁ1. Anal. Calc. for C24H27Fe2N2O5PS2: C, 45.74; H,
4.32; N, 4.44. Found: C, 45.76; H, 4.29; N, 4.59%.
(Film):
m
(CO) 2046, 1981, 1930 cmꢁ1. Anal. Calc. for C29H28Fe2-
3.2.2. (
Complex 6 was prepared by a procedure similar to that of 5. To
the red solution of hexacarbonyldiiron dithiolate (0.97 g,
l
-pdt)[Fe2(CO)5PPh2NH(2-NH2C6H4)] (6)
NO5PS2: C, 51.42; H, 4.17; N, 2.07. Found: C, 51.94; H, 3.98; N,
2.31%.
1
0.25 mmol) in CH3CN (15 mL) was added Me3NO ꢀ 2H2O (111 mg,
0.1 mmol). When the color of the solution turned dark red, com-
pound 3 (159 mg, 0.5 mmol) was added to the reaction solution.
The reaction mixture was stirred for 0.5 h and the color turned
red. After the solvent was removed in vacuum, the crude product
was purified by column chromatography on silica gel with
CH2Cl2/hexane (2:1) as eluent to give 6 as red solid (89 mg, 55%).
The crystal suitable for X-ray analysis was obtained from a solution
of hexane/CH2Cl2 (1/10) at 2 °C. 1H NMR (CDCl3) d 7.77 (s, 4H, Ph),
7.41 (s, 6H, Ph), 6.71 (s, 2H, Ph), 6.41 (t, 1H, Ph, J = 7.2 Hz), 6.34 (d,
1 H, Ph, J = 2 Hz), 5.25 (d, 1H, J = 15.6 Hz, PNHPh), 3.46 (s, 2H,
PhNH2), 1.95 (s, 2H, SCH2C), 1.65 (s, 4H, SCH2C, CCH2C), 31P NMR
3.3. Crystal structure determinations of complexes 5–7
The single crystal X-ray diffraction data were collected with a
Siemens Smart CCD diffractometer equipped with graphite mono-
chromated Mo Ka radiation (k = 0.71073 Å) for 5–7. Complete crys-
tal data and parameters for data collection and refinement are
listed in Table 4. The structure was solved by direct methods and
subsequent difference Fourier syntheses, and refined on F2 against
full-matrix least-squares methods by using the SHELXTL-97 program
package. All non-hydrogen atoms were refined anisotropically. The
hydrogen atoms located by geometrical calculation, but their posi-
tions and thermal parameters were fixed during the structure
refinement.
(CDCl3) d 96.80; IR (KBr): m
(CO) 2041, 1979, 1919 cmꢁ1. Anal. Calc.
Table 4
Crystallographic data and processing parameters for complexes 5–7
5
6 ꢀ 0.5C6H14
7 ꢀ CH2Cl2
Empirical formula
Formula weight
Crystal system
C24H27Fe2N2O5PS2
630.27
Monoclinic
P2(1)/n
C29H30Fe2N2O5PS2
693.34
Orthorhombic
Pbca
C30H30Cl2Fe2NO5PS2
762.24
Monoclinic
P2(1)/c
Space group
0
a (AÅ)
9.7103(5)
18.4200(8)
16.5942(7)
90.00
20.4923(14)
7.9571(5)
37.192(2)
90.00
18.168(11)
9.223(6)
22.164(13)
90.00
0
b (AÅ)
0
c (AÅ)
a
(°)
b (°)
104.830(3)
90.00
2869.2(2)
4
90.00
90.00
6064.6(7)
8
1.519
113.199(16)
90.00
3414(4)
c
(°)
0
Volume (AÅ)3
Z
4
Dcalc. (Mg/m3)
1.459
1.483
F(000)
1296
2856
1560
Crystal size (mm)
Range for data collection (°)
Reflections collected
Independent reflections (Rint
Completeness to h
Data/restraints/parameters
Goodness-of-fit on F2
0.25 ꢂ 0.32 ꢂ 0.3
2.21–26.08
5656
3996 (0.0351)
26.08°, 99.6%
5656/30/329
1.044
0.37 ꢂ 0.2 ꢂ 0.2
1.99–22.72
4065
3114 (0.0622)
22.72°, 99.4%
4065/9/370
1.061
0.2 ꢂ 0.15 ꢂ 0.22
1.89–22.66
4511
2987 (0.0632)
22.66°, 99.2%
4511/0/388
1.024
)
Final R indices (I > 2
r
(I))
R1 = 0.0544
wR2 = 0.1425
R1 = 0.0803
wR2 = 0.1614
0.600 and ꢁ0.582
R1 = 0.0468
wR2 = 0.0982
R1 = 0.0679
wR2 = 0.1073
0.328 and ꢁ0.396
R1 = 0.0632
wR2 = 0.1580
R1 = 0.1039
wR2 = 0.1827
1.110 and ꢁ1.005
R indices (all data)
0
Largest difference in peak and hole (e ÅAꢁ3
)
(1) R1 = (
(2) wR2 = [
R
||Fo| ꢁ |Fc||)/(
R
R
|Fo|).
w(F2o)2]1/2
.
R
w(F2o ꢁ F2c)2/

2834
Z. Wang et al. / Journal of Organometallic Chemistry 693 (2008) 2828–2834
3.4. Protonation of complexes 5–6
References
[1] Y. Nicolet, A.L. de Lacey, X. Vernède, V.M. Fernandez, E.C. Hatchikian, J.C.
Fontecilla-Camps, J. Am. Chem. Soc. 123 (2001) 1596.
[2] J.W. Peters, W.N. Lanzilotta, B.J. Lemon, L.C. Seefeldt, Science 282 (1998) 1853.
[3] Y. Higuchi, H. Ogata, K. Miki, N. Yasuoka, T. Yagi, Structure 7 (1999) 549.
[4] H.-J. Fan, M.B. Hall, J. Am. Chem. Soc. 123 (2001) 3828.
[5] A. Volbeda, J.C. Fontecilla-Camps, J. Chem. Soc., Dalton Trans. 21 (2003)
4030.
[6] X.-M. Liu, S.K. Ibrahim, C. Tard, C.J. Pickett, Coord. Chem. Rev. 249 (2005)
1641.
[7] I.P. Georgakaki, L.M. Thomson, E.J. Lyon, M.B. Hall, M.Y. Darensbourg, Coord.
Chem. Rev. 238 (2003) 255.
A small amount of 5 (2–3 mg) was dissolved in CD3CN (0.5 mL)
in an NMR-tube, and then 1 mL of triflic acid were added directly to
the solution for in situ 1H NMR analysis. Complex 6 was protonated
in a similar way.
3.5. Crystal data for 5–7
See Table 4.
[8] T.B. Rauchfuss, Inorg. Chem. 43 (2004) 14.
[9] H.-X. Li, T.B. Rauchfuss, J. Am. Chem. Soc. 124 (2002) 726.
[10] Z. Wang, J.-H. Liu, C.-J. He, S. Jiang, B. Åkermark, L.-C. Sun, J. Organomet. Chem.
692 (2007) 5501.
[11] J.D. Lawrence, H.-X. Li, T.B. Rauchfuss, M.B. Tnard, M. Rohmer, Angew. Chem.,
Int. Ed. 40 (2001) 1768.
[12] L.-C. Sun, B. Åkermark, S. Ott, Coord. Chem. Rev. 249 (2005) 1653.
[13] T.-B. Liu, M. Wang, Z. Shi, H.-G. Cui, W.-B. Dong, J.-S. Chen, B. Åkermark, L.-C.
Sun, Chem. Eur. J. 10 (2004) 4474.
3.6. Electrochemistry
A solution of 0.05 M of n-Bu4NPF6 (Fluka, electrochemical
grade) in CH3CN was used as electrolyte, which was degassed by
bubbling with dry argon for 10 min before measurement. Electro-
chemical measurements were recorded using a BAS-100 W electro-
chemical potentiostat at
a scan rate of 100 mV/s. Cyclic
[14] S. Ott, M. Kritikos, B. Åkermark, L.-C. Sun, R. Lomoth, Angew. Chem., Int. Ed. 43
(2004) 1006.
[15] F. Wang, M. Wang, X. Liu, K. Jin, W. Dong, G. Li, B. Åkermark, L. Sun, Chem.
Commun. 25 (2005) 3221.
[16] S. Jiang, J.-H. Liu, L.-C. Sun, Inorg. Chem. Commun. 9 (2006) 290.
[17] R. Mejia-Rodriguez, D. Chong, J.H. Reibenspies, M.P. Soriaga, M.Y. Darensbourg,
J. Am. Chem. Soc. 126 (2004) 12004.
[18] F. Gloaguen, J.D. Lawrence, T.B. Rauchfuss, M. Benard, M.-M. Rohmer, Inorg.
Chem. 41 (2002) 6573.
voltammograms were obtained in a three-electrode cell under ar-
gon. 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 auxiliary electrode
was a platinum wire.
[19] M. Bruschi, P. Fantucci, L. De Gioia, Inorg. Chem. 42 (2003) 4773.
[20] T. Zhou, Y. Mo, A. Liu, Z. Zhou, K.R. Tsai, Inorg. Chem. 43 (2004) 923.
[21] S. Park, A.J. Lough, R.H. Morris, Inorg. Chem. 35 (1996) 3001.
[22] H.S. Chu, C.P. Lau, K.Y. Wong, W.T. Wong, Organometallics 17 (1998) 2768.
[23] J.A. Ayllon, S.F. Sayers, S. Sabo-Etienne, B. Donnadieu, B. Chaudret, E. Clot,
Organometallics 18 (1999) 3981.
[24] R.M. Henry, R.K. Shoemaker, D.L. DuBois, M.R. DuBois, J. Am. Chem. Soc. 128
(2006) 3002.
[25] M. Schmidt, S.M. Contakes, T.B. Rauchfuss, J. Am. Chem. Soc. 121 (1999)
9736.
[26] E.J. Lyon, I.P. Georgakaki, J.H. Reibenspies, M.Y. Darensbourg, J. Am. Chem. Soc.
123 (2001) 3268.
[27] M.M. Hasan, M.B. Hursthouse, S.E. Kabir, K.M.A. Malik, Polyhedron 20 (2001)
97.
[28] J.L. Nehring, D.M. Heinekey, Inorg. Chem. 42 (2003) 4288.
[29] P. Li, M. Wang, C.-J. He, G.-H. Li, X.-Y. Liu, C.-N. Chen, B. Åkermark, L.-C. Sun,
Eur. J. Inorg. Chem. (2005) 2506.
[30] K. Baba, T. Okamura, H. Yamamoto, T. Yamamoto, M. Ohama, N. Ueyama, Inorg.
Chem. 45 (2006) 8365.
Acknowledgments
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 Program of Introduc-
ing Talents of discipline to Universities, the Swedish Energy Agency,
the K&A Wallenberg Foundation, and the Swedish Research Council
for financial supports of this work. This work was also supported by
Program for Changjiang Scholars and Innovative Research Team in
University (IRT0711).
Appendix A. Supplementary material
CCDC 628139, 624771 and 658987 contain the supplementary
crystallographic data for 5, 6 and 7. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2008.06.001.
[31] N. Ueyama, T. Okamura, A. Nakamura, J. Am. Chem. Soc. 114 (1992) 8129.
[32] F. Gloaguen, J.D. Lawrence, M. Schmidt, S.R. Wilson, T.B. Rauchfuss, J. Am.
Chem. Soc. 123 (2001) 12518.
[33] D. Chong, I.P. Georgakaki, R. Mejia-Rodriguez, J. Sanabria-Chinchilla, M.P.
Soriaga, M.Y. Darensbourg, Dalton Trans. 21 (2003) 4158.
[34] L. Brammer, J.C. Mareque Rivas, C.D. Spilling, J. Organomet. Chem. 609 (2000)
36.