Synthesis and electrochemistry of phenyl-functionalized diiron propanedithiolate complexes with bidentate phosphine ligands

Article abstract of DOI:10.1007/s11243-014-9810-4

Carbonyl substitution reactions of [μ-(SCH₂) ₂CHC₆H₅]Fe₂(CO)₆ with bidentate phosphine ligands, cis-1,2-bis(diphenylphosphine)ethylene (cis-dppv) and N,N-bis(diphenylphosphine)propylamine [(Ph₂P)₂N-Pr-n], yielded an asymmetrically substituted chelated complex [(μ-SCH ₂)₂CHC₆H₅]Fe₂(CO) ₄(k ²-dppv) and a symmetrically substituted bridging complex [(μ-SCH₂)₂CHC₆H₅]Fe ₂(CO)₄[μ-(PPh₂)₂N-Pr-n] under different reaction conditions. Both complexes were fully characterized by spectroscopic methods and by X-ray crystallography. Their electrochemical behaviors were observed by cyclic voltammetry, and the catalytic electrochemical reduction of protons from acetic or trifluoroacetic acid to give dihydrogen mediated by complex [(μ-SCH₂)₂CHC₆H ₅]Fe₂(CO)₄(k ²-dppv) was investigated.

Full text of DOI:10.1007/s11243-014-9810-4

Transition Met Chem
DOI 10.1007/s11243-014-9810-4
Synthesis and electrochemistry of phenyl-functionalized diiron
propanedithiolate complexes with bidentate phosphine ligands
•
•
•
Chang-Gong Li Yong-Fang Li Jing-Yan Shang
Tian-Jun Lou
Received: 9 December 2013 / Accepted: 18 February 2014
Ó Springer International Publishing Switzerland 2014
Abstract Carbonyl substitution reactions of [l-(SCH2)2-
CHC6H5]Fe2(CO)6 with bidentate phosphine ligands, cis-1,
2-bis(diphenylphosphine)ethylene (cis-dppv) and N,N-bis
(diphenylphosphine)propylamine [(Ph2P)2N-Pr-n], yielded an
asymmetrically substituted chelated complex [(l-SCH2)2-
CHC6H5]Fe2(CO)4(k2-dppv) and a symmetrically substituted
bridging complex [(l-SCH2)2CHC6H5]Fe2(CO)4[l-(PPh2)2-
N-Pr-n] under different reaction conditions. Both complexes
were fully characterized by spectroscopic methods and by
X-ray crystallography. Their electrochemical behaviors were
observed by cyclic voltammetry, and the catalytic electro-
chemical reduction of protons from acetic or trifluoroacetic
acid to give dihydrogen mediated by complex [(l-SCH2)2-
CHC6H5]Fe2(CO)4(k2-dppv) was investigated.
in which one of the two iron atoms of the [2Fe2S] butterfly
cluster is linked to a cubic [4Fe4S] cluster bythesulfuratomof
a cysteine ligand, while a dithiolate cofactor (SCH2XCH2S;
X = N, C or O) bridges the two iron atoms, which are also
coordinated by CO and CN- ligands. Therefore, much atten-
tion has been directed to butterfly- and cubane-like Fe/S
cluster complexes in view of their structural and functional
similarity with the active sites of FeFe-hydrogenases [10,
11]. Since both iron and sulfur are widely available and
relatively abundant elements in the crust of our planet, it is
hoped that an exploration of the biomimetic chemistry of
FeFe-hydrogenases may lead to cheap and efficient iron-
based hydrogen production catalysts, instead of precious
metal platinum or palladium catalysts [12–14]. During the
investigation of the bioinspired chemistry of FeFe-hydrog-
enases, the classical diiron dithiolate complexes, [(l-pdt)
Fe2(CO)6] (pdt = SCH2CH2CH2S) [15] and [(l-adt)Fe2
(CO)6] (adt = SCH2NHCH2S) [16], became the focus
of much research [17–20]. A theoretical study by Tye,
Darensbourg and Hall concluded that ‘‘asymmetric substi-
tution of strong donor ligands is the most viable method of
making better synthetic diiron complexes that will serve as
both structural and functional models’’ of the active site of
iron-only hydrogenase [21]. As part of our ongoing research
centered on phenyl-functionalized diiron propanedithiolate
complexes [22], in this paper we describe asymmetrical and
symmetrical model complexes corresponding to replace-
ment of carbonyls by bidentate phosphine ligands, namely
cis-1,2-bis(diphenylphosphine)ethylene (cis-dppv) and N,N-
bis(diphenylphosphine)propylamine [(Ph2P)2N-Pr-n]. The
two complexes were formulated as [(l-SCH2)2CHC6H5]
Fe2(CO)4(k2-dppv) (1) and [(l-SCH2)2CHC6H5]Fe2(CO)4
[l-(PPh2)2N-Pr-n] (2). The electrochemical behaviors of
both complexes and the electrochemical reduction of protons
catalyzed by complex 1 were investigated.
Introduction
FeFe-hydrogenases can efficiently catalyze the reduction of
protons to dihydrogen or vice versa in a variety of microor-
ganisms [1–3]. The active site structures of FeFe-hydroge-
nases (H-cluster) have been revealed by X-ray
crystallographic [4–6] and FTIR spectroscopic [7–9] studies,
C.-G. Li (&) Á Y.-F. Li Á J.-Y. Shang
College of Chemistry and Chemical Engineering, Henan
Institute of Science and Technology, Xinxiang 453003, People’s
Republic of China
e-mail: lichanggong@sohu.com
T.-J. Lou
Xinxiang Municipal Key Laboratory of Functional Organic
Molecular, Xinxiang 453003, People’s Republic of China
123

Transition Met Chem
Experimental
Table 1 Crystal data and structural refinements for complexes 1 and 2
1
2
Materials and methods
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
C39H32Fe2O4P2S2
802.41
C40H37Fe2NO4P2S2
833.47
All reactions and operations were carried out under a dry,
oxygen-free argon atmosphere using standard Schlenk and
vacuum line techniques. CH2Cl2 and MeCN were distilled
from CaH2, while n-hexane, xylene and toluene were
purified by distillation from sodium/diphenylmethanone
under argon. Me3NOÁ2H2O and cis-dppv were commer-
cially available and used as received. (Ph2P)2N-Pr-n [23]
and [l-(SCH2)2CHC6H5]Fe2(CO)6 [22] were prepared
according to literature methods. Preparative TLC was
carried out on glass plates (25 cm 9 20 cm 9 0.25 cm)
coated with silica gel G (10–40 lm). IR spectra were
recorded on a Bruker TENSOR 27 FTIR spectrometer. 1H,
13C and 31P NMR spectra were obtained on a Bruker
Avance 400 MHz spectrometer. Elemental analyses were
performed on an Elementar Vario EL III analyzer.
291.15
291.15
Monoclinic
P21/n
Monoclinic
P21/n
˚
a/A
10.98620(11)
10.90100(9)
30.9101(3)
90.00
15.2539(3)
17.5816(4)
16.7714(3)
90.00
˚
b/A
˚
c/A
a/°
b/°
c/°
90.5358(8)
90.00
99.3578(19)
90.00
3
˚
V/A
3701.65(6)
4
4438.02(17)
4
Z
D/g mm-3
l/mm-1
F(000)
1.440
1.247
8.477
7.094
1,648.0
1,720.0
Crystal size/mm3
0.25 9 0.2 9 0.17
5.72–134.16
0.22 9 0.2 9 0.2
7.26–134.12
2h Range for data
collection/°
Index ranges
Electrochemistry
-12 B h B 13
-13 B k B 8
-36 B l B 34
13,886
-12 B h B 18
-18 B k B 20
-20 B l B 19
15,966
Electrochemical measurements were carried out using a
CHI 620 Electrochemical Workstation (CH Instruments,
Chenhua, Shanghai, China). A solution of 0.1 M n-Bu4-
NPF6 in CH3CN was used as the electrolyte, degassed by
bubbling with dry nitrogen for 10 min before measure-
ment. CV scans were obtained in a three-electrode cell with
a glassy carbon electrode (3 mm diameter) as the working
electrode, successively polished with 3 and 1 lm diamond
pastes and sonicated in ion-free water for 1 min, a platinum
wire as counter electrode, and a nonaqueous Ag/Ag?
electrode (1.0 mM AgNO3 and 0.1 M n-Bu4NPF6 in
CH3CN) as reference. The potential scale was calibrated
against the Fc/Fc? couple and reported versus this refer-
ence system.
Reflections collected
Independent
6,604 (0.0225)
7,904 (0.0496)
reflections (Rint
)
Data/restraints/
parameters
Goodness-of-fit on F2 1.031
6,604/0/442
7,904/0/461
1.029
Final R indexes
[I [ 2r (I)]
R1 = 0.0352;
wR2 = 0.0883
R1 = 0.0495;
wR2 = 0.1210
Final R indexes [all
data]
R1 = 0.0410;
wR2 = 0.0919
R1 = 0.0728;
wR2 = 0.1296
Largest diff. peak/
-3
˚
0.32/-0.43
0.64/-0.34
hole/e A
X-ray structure determination
Synthesis of complex 1
Single crystals of both complexes suitable for X-ray dif-
fraction analysis were grown by slow evaporation of the
CH2Cl2/hexane solutions at 5 °C. For each complex, a
suitable crystal was selected and analyzed on an Xcalibur,
Eos, Gemini diffractometer. The crystal was kept at
291.15 K during data collection. Using Olex2 [24], the
structure was solved with the ShelXS structure solution
program using direct Methods and refined with the ShelXL
refinement package using least-squares minimization [25].
The program SQUEEZE was employed to squeeze out
hexane, which was disordered beyond recognition. Details
of crystal data, data collections and structure refinement are
summarized in Table 1.
[l-(SCH2)2CHC6H5]Fe2(CO)6 (0.08 g, 0.17 mmol) was
dissolved in toluene (10 mL) under argon, and Me3-
NOÁ2H2O (0.02 g, 0.18 mmol) in MeCN (5 mL) was
added. The red solution became brown immediately. After
stirring at room temperature for ca. 10 min, a solution of
cis-dppv (0.075 g, 0.19 mmol) in toluene (10 mL) was
added and the mixture was stirred at room temperature for
3 h. The solvent was removed on a rotary evaporator, and
the residue was subjected to preparative TLC separation
using CH2Cl2/petroleum ether (v/v = 1:2) as eluent. From
the brown band, complex 1 was obtained as a brown-black
solid (0.122 g, 90 %). IR (KBr disk, cm-1): mC:O 2,014
123

Transition Met Chem
(vs), 1,941 (vs), 1,930 (vs), 1,905 (vs). 1H NMR
(400 MHz, CDCl3, ppm): 1.777–1.927 (m, 3H, 2 SCHaHe,
PhCH), 2.414 (m, 2H, 2 SCHaHe), 6.152 (d, 2H, 2 = CH,
3J = 2.8 Hz), 7.033–7.867 (m, 25H, PhH). 13C NMR
(400 MHz, CDCl3, ppm): 207.8 (s, FeCO), 132.8, 132.7,
130.4, 130.0, 128.7, 128.5, 128.3, 126.4 (s, PhC), 48.7 (s,
CH), 31.1 (s, SCH2). 31P NMR (161.9 MHz, CDCl3, 85 %
H3PO4, ppm): 90 (s, 92 %, basal–apical), 78 (s, 8 %,
basal–basal). Anal. Calc. for C39H32Fe2O4P2S2: C, 58.4; H,
4.0. Found: C, 58.6; H, 3.8 %.
for complex 2 is consistent with substitution of the two
carbonyls with diphosphine in a bridging coordination
geometry [27]. In the 1H NMR spectra, compared with the
chemical shifts of the propanedithiolate bridge protons of
the precursor complex [l-(SCH2)2CHC6H5]Fe2(CO)6,
those of complex 1 showed upfield shifts, whereas those of
complex 2 were little changed. These observations imply
that coordination of phosphine ligands not only increases
the electron density of the diiron centers, but also indirectly
affects other ligands depending on the nature of the coor-
dination sphere. The upfield shift signals of the n-Pr pro-
tons in complex 2 are due to the shielding effect of the
benzene rings [28]. The 13C NMR spectra showed weak
resonances from the carbonyl carbon atoms at ca. 210 ppm,
strong olefin carbon signals in the range of 126–148 ppm
and alkane carbon signals in the range of 11–54 ppm. The
31P NMR spectra showed two singlets at 90 and 78 ppm for
the phosphorus atoms of the cis-dppv ligand in complex 1
with a ratio of ca. 92:8, corresponding to apical–basal and
basal–basal chelating coordination patterns, whereas that of
complex 2 displayed one singlet at 119 ppm, consistent
with symmetrical coordination of the two nitrogen-binding
phosphine atoms to two iron atoms in a basal–basal coor-
dination manner.
Synthesis of complex 2
A
xylene (15 mL) solution of [l-(SCH2)2CHC6H5]
Fe2(CO)6 (0.143 g, 0.31 mmol) and (PPh2)2N-Pr-
n (0.133 g, 0.31 mmol) was refluxed for 3 h. After
removing the solvent under reduced pressure, the crude
product was purified by chromatography on silica gel using
CH2Cl2/petroleum ether (v/v = 1:1) as eluent. Complex 2
was obtained as a red solid (0.077 g, 30 %). IR (KBr disk,
1
cm-1): mC:O 1,994 (vs), 1,961 (vs), 1,924 (vs). H NMR
(400 MHz, CDCl3, ppm): 0.053 (s, 3H, NCH2CH2CH3),
0.292 (m, 2H, NCH2CH2CH3), 1.803 (s, 2H, NCH2CH2-
CH3), 2.529–2.677 (m, 5H, SCH2CHCH2S), 7.079–7.718
(m, 25H, PhH). 13C NMR (400 MHz, CDCl3, ppm): 216.1
(s, FeCO), 148.0, 133.2, 132.3, 132.0, 130.4, 128.6, 128.0,
127.7, 127.0 (s, PhC), 54.4, 53.5, 50.1, 31.6, 22.9, 11.0 (s,
CH, CH2, CH3). 31P NMR (161.9 MHz, CDCl3, 85 %
H3PO4, ppm): 119 (s). Anal. Calc. for C40H37Fe2NO4P2S2:
C, 57.6; H, 4.5, N, 1.7. Found: C, 57.5; H, 4.2, N, 1.9 %.
X-ray crystal structures
The molecular structures of both complexes were unam-
biguously confirmed by X-ray crystallography (Figs. 1, 2),
and crystal data, selected bond lengths and angles are listed
in Tables 1 and 2. Both complexes each have a butterfly
[2Fe2S] core in which their two iron atoms are bridged by a
2-phenyl-1, 3-propanedithiolate ligand. One of the two Fe
atoms and the propanedithiolate bridge form a six-mem-
bered ring in chair conformation, with the phenyl group in
an equatorial position. The Fe–Fe bond length of complex
Results and discussion
Synthesis and spectroscopic characterization
˚
1 (2.5517(5) A) is much longer than that of complex 2
˚
(2.4851(9) A) and close to those found in the reduced
As shown in Scheme 1, the reaction of the precursor
complex [l-(SCH2)2CHC6H5]Fe2(CO)6 with ca. 1 equiva-
lent of the decarbonylating agent Me3NOÁ2H2O followed
by addition of 1.1 equivalent of cis-dppv at room temper-
ature gave the chelated complex 1, while refluxing a xylene
solution of the precursor complex [l-(SCH2)2CHC6H5]
Fe2(CO)6 with 1 equiv of (Ph2P)2N-Pr-n yielded the
bridged complex 2. Compared with the IR absorption
bands of the terminal carbonyls of the precursor complex
(2,071, 2,022, 2,008, 1,970 cm-1), those of complexes 1
and 2 were considerably shifted by about 60–80 cm-1
toward lower energy. This is apparently due to two CO
ligands being replaced by stronger electron-donating
diphosphine ligands [26]. The biggest absorption band of
the terminal carbonyls at 2,014 cm-1 for complex 1 cor-
responds to substitution of the two carbonyls by the che-
lating diphosphine, while the band observed at 1,994 cm-1
active site of FeFe-hydrogenases [6]. The two phosphine
atoms of cis-dppv chelate one of the two iron atoms with an
apical–basal coordination geometry, whereas the two
phosphine atoms of (Ph2P)2N-Pr-n coordinate two iron
atoms with a bridging basal–basal manner. The bite angle
P2–Fe2–P1 is 87.83(5)° for complex 1, close to those of
[(l-SCH2)2]Fe2(CO)4(j2-dppv) [29, 30]. Two phosphine
atoms and two carbon atoms of cis-dppv ligand, and the
Fe2 atom in complex 1 constitute a five-membered ring
with dihedral angle of 15.2 (1)° between the plane (P2,
Fe2, P1) and the plane (P1, C26, C27), and a torsion angle
of 3.6 (8)° between P2 and P1. In the five-membered ring
of complex 2, the dihedral angle between planes (P1, N1,
P2) and (N1, P1, Fe1) is 10.8 (7)°, and four atoms, P2, P1,
Fe1 and Fe2, are almost co-planar.
123

Transition Met Chem
Scheme 1 Preparation of
complexes 1 and 2
Fig. 1 Molecular structure of complex 1 with thermal ellipsoids at
30 % probability
Fig. 2 Molecular structure of complex 2 with thermal ellipsoids at
30 % probability
Electrochemistry
-1.875 V, positively shifted by about 0.2 V compared
with the reduction potential at -2.106 V in the absence of
trifluoroacetic acid. With increasing concentration of tri-
fluoroacetic acid, the current intensity of the new reduction
potential at -1.875 V grew dramatically and the reduction
potential moved from -1.875 V to more negative reduc-
tion potential at -2.413 V. The current intensity of the
reduction potential at -2.106 V showed little change and
was obscured with increasing concentration of trifluoro-
acetic acid (Fig. 3). In the presence of acetic acid, the
current intensities of the two reduction potentials at -2.106
and -2.542 V increased slightly (Fig. 4, 1 and 2 mM
acetic acid), while a new reduction process at -2.355 V
was observed for 4 mM acetic acid, and its current inten-
sity grew markedly with the further increment of acetic
The cyclic voltammograms of both complexes were
recorded and are shown in Figs. 3, 4 and 5. Complex 1
displays two irreversible reduction processes at -2.106 and
-2.542 V, and one quasi-reversible oxidation process at
?0.014 V, which are assigned to the reductions of FeIFeI to
FeIFe0 and FeIFe0 to Fe0Fe0, and the oxidation of FeIFeI to
FeIFeII, respectively. The reduction potentials of complex 1
are negatively shifted by 0.46 V compared to the corre-
sponding reduction potentials of the precursor complex [l-
(SCH2)2CHC6H5]Fe2(CO)6 [22], due to its two CO ligands
being replaced by the stronger electron-donating ligand.
For complex 1, after addition of trifluoroacetic acid
(1 equiv.), a new reduction process was observed at
123

Transition Met Chem
˚
Table 2 Selected bond lengths (A) and angles (deg) for complexes 1 and 2
1
Fe(1)–Fe(2)
2.5517(5)
2.2632(7)
2.2712(7)
1.137(4)
Fe(2)–P(1)
2.1797(7)
2.2123(6)
2.2566(6)
1.132(4)
Fe(2)–S(2)
2.2459(6)
1.839(2)
1.825(2)
1.141(4)
68.743(19)
68.79(2)
C(26)–C(27)
O(4)–C(4)
1.316(4)
1.149(3)
Fe(1)–S(1)
Fe(2)–P(2)
S(1)–C(5)
Fe(1)–S(2)
Fe(2)–S(1)
S(2)–C(6)
Fe(1)–C(1)
1.796(3)
O(1)–C(1)
O(2)–C(2)
O(3)–C(3)
Fe(2)–C4
1.756(3)
S(1)–Fe(1)–S(2)
S(1)–Fe(1)–Fe(2)
P(1)–Fe(2)–P(2)
84.29(2)
S(2)–Fe(2)–S(1)
S(1)–Fe(2)–Fe(1)
85.02(2)
Fe(2)–S(1)–Fe(1)
Fe(2)–S(2)–Fe(1)
S(2)–Fe(1)–Fe(2)
S(2)–Fe(2)–Fe(1)
55.137(17)
56.075(18)
55.506(17)
87.31(2)
55.750(18)
P(1)–Fe(2)–Fe(1) 157.35(2)
P(2)–Fe(2)–S(1) 92.75(2)
C(3)–Fe(1)–Fe(2) 143.63(10)
P(1)–Fe(2)–S(1) 111.99(3)
P(2)–Fe(2)–S(2) 165.16(3)
P(1)–Fe(2)–S(2) 107.15(3)
C(4)–Fe(2)–P(2) 89.22(9)
C(3)–Fe(1)–C(1) 104.75(14)
P(2)–Fe(2)–Fe(1) 110.86(2)
C(4)–Fe(2)–P(1)
2
90.31(8)
C(1)–Fe(1)–Fe(2)
97.94(9)
Fe(1)–Fe(2)
2.4851(9)
2.2097(11)
2.2180(11)
56.41(3)
Fe(1)–S(1)
2.2580(12) Fe(1)–S(2)
2.2564(10) Fe(1)–C(1)
2.2574(12) O(1)–C(1)
2.2505(11) Fe(2)–C(4)
1.764(5)
1.148(5)
1.764(4)
66.90(3)
66.81(3)
92.37(14)
Fe(1)–P(1)
P(1)–N(1)
1.713(3)
1.719(3)
Fe(2)–S(2)
Fe(2)–P(2)
P(2)–N(1)
Fe(2)–S(1)
S(1)–Fe(1)–Fe(2)
S(2)–Fe(1)–Fe(2)
P(1)–Fe(1)–Fe(2)
P(2)–Fe(2)–Fe(1)
S(1)–Fe(2)–Fe(1)
S(1)–Fe(2)–S(2)
P(1)–N(1)–P(2)
56.70(3)
S(2)–Fe(1)–S(1)
S(2)–Fe(2)–Fe(1)
C(1)–Fe(1)–P(1)
C(3)–Fe(2)–P(2)
84.61(4)
56.58(3)
98.86(15)
96.85(14)
Fe(2)–S(1)–Fe(1)
56.61(3)
84.76(4)
Fe(1)–S(2)–Fe(2)
C(2)–Fe(1)–P(1)
97.25(3)
118.48(18)
94.79(4)
C(4)–Fe(2)–P(2) 100.82(15)
C(4)–Fe(2)–Fe(1) 147.93(17)
Fig. 4 Cyclic voltammetry of complex 1 (1 mM) in 0.1 M n-
Bu4NPF6/MeCN with and without CH3COOH (0–12 mM) at a scan
rate of 0.1 V s-1
Fig. 3 Cyclic voltammetry of complex 1 (1 mM) in 0.1 M n-
Bu4NPF6/MeCN with and without CF3COOH (0–10 mM) at a scan
rate of 0.1 V s-1
acid (Fig. 4). The dramatic increment of the current
intensity (reduction potential at -1.875 V for complex 1 or
at -2.355 V for complex 2) with increasing concentration
of acid is indicative of a catalytic proton reduction process
[31–33]. Because protonation at the Fe–Fe center or at the
peripheral N atom of the diiron dithiolate core can posi-
tively shift the reduction potential by about 1 or 0.4 V,
respectively [34], the less negative reduction potential (at
-1.875 or -2.355 V in the presence of CF3COOH or
CH3COOH) may not result from protonation of the Fe–Fe
center. This means that the bridging or terminal hydride
intermediate in the presence of CF3COOH or CH3COOH
cannot be produced [35]. At the present stage, the exact
catalytic mechanism in the presence of CF3COOH (mod-
erate acid, pKa = 12.7 in CH3CN) or CH3COOH (weak
acid, pKa = 22.3 in CH3CN) [36, 37] cannot be inferred
with confidence. Complex 2 displays two irreversible
reduction processes at -2.154 and -2.551 V, an irrevers-
ible oxidation process at ?0.342 V, respectively (Fig. 5).
123

Transition Met Chem
2. Graf EG, Thauer RK (1981) FEBS Lett 136:165
3. Cammack R, Patil D, Aguirre R, Hatchikian EC (1982) FEBS
Lett 142:289
4. Peters JW, Lanzilotta WN, Lemon BJ (1998) Science 282:1853
5. Nicolet Y, Piras C, Legrand P, Hatchikian EC, Fontecilla-Camps
JC (1999) Structure 7:13
`
6. Nicolet Y, De Lacey AL, Vernede X, Fernandez VM, Hatchikian
EC, Fontecilla-Camps JC (2001) J Am Chem Soc 123:1596
7. Pierik AJ, Hulstein M, Hagen WR, Albracht SPJ (1998) Eur J
Biochem 258:572
8. De Lacey AL, Stadler C, Cavazza C, Hatchikian EC, Fernandez
VM (2000) J Am Chem Soc 122:11232
9. Chen Z, Lemon BJ, Huang S, Swartz DJ, Peters JW, Bagley KA
(2002) Biochemistry 41:2036
10. Wang N, Wang M, Wang Y, Zheng DH, Han HX, Ahlquist MSG,
Sun LC (2013) J Am Chem Soc 135:13688
11. Manor BC, Rauchfuss TB (2013) J Am Chem Soc 135:11895
12. Felton GAN, Vannucci AK, Chen JZ, Lockett LT, Okumura N,
Petro BJ, Zakai UI, Evans DH, Glass RS, Lichtenberger DL
(2007) J Am Chem Soc 129:12521
13. Borg SJ, Behrsing T, Best SP, Razavet M, Liu XM, Pickett CJ
(2004) J Am Chem Soc 126:16988
Fig. 5 Cyclic voltammetry of complex 2 (1 mM) in 0.1 M n-
Bu4NPF6/MeCN at a scan rate of 0.1 V s-1
14. Mejia-Rodriguez R, Chong D, Reibenspies JH, Soriaga MP,
Darensbourg MY (2004) J Am Chem Soc 126:12004
15. Wang WG, Nilges MJ, Rauchfuss TB, Stein M (2013) J Am
Chem Soc 135:3633
16. Liu XF, Xiao XW, Shen LJ (2011) Transit Met Chem 36:465
17. Darensbourg MY, Lyon EJ, Smee JJ (2000) Coord Chem Rev
206–207:533
18. Evans DJ, Pickett CJ (2003) Chem Soc Rev 32:268
19. Fontecilla-Camps JC, Volbeda A, Cavazza C, Nicolet Y (2007)
Chem Rev 107:4273
20. Gloaguen F, Rauchfuss TB (2009) Chem Soc Rev 38:100
21. Tye JW, Darensbourg MY, Hall MB (2006) Inorg Chem 45:1552
22. Li CG, Zhu Y, Jiao XX, Fu XQ (2014) Polyhedron 67:416
23. Ewart G, Lane AP, McKechnie J, Payne DS (1964) J Chem Soc
1543
Conclusions
Substitution of two carbonyls of the all-carbonyl diiron
propanedithiolate complex [l-(SCH2)2CHC6H5]Fe2(CO)6
with bidentate phosphine ligands, namely cis-dppv and
(Ph2P)2N-Pr-n, yielded an asymmetrically substituted
complex 1 and a symmetrically substituted complex 2
under different reaction conditions. In the solid state, the
two phosphine atoms of cis-dppv chelate one of the two
iron atoms of complex 1 with a basal–apical coordination
geometry, whereas the two phosphine atoms of (Ph2P)2N-
Pr-n coordinate the two iron atoms of complex 2 in a
bridging basal–basal manner. Moderate acid (trifluoroace-
tic acid) or weak acid (acetic acid) positively shifted the
reduction potential of complex 1 by ca. 0.2 V. Complex 1
can catalyze reduction of protons to dihydrogen under
electrochemical conditions.
24. Dolomanov OV, Bourhis LJ, Gildea RJ, Howard JAK, Pusch-
mann H (2009) J Appl Cryst 42:339
25. Sheldrick GM (2008) Acta Cryst A64:112
26. Collman JP, Hegedus LS (1980) Principles and applications of
organotransition metal chemistry. University Science Books, Mill
Valley, pp 81–89
27. Crabtree RH (2005) The organometallic chemistry of the transi-
tion metals, 4th edn. Wiley, New York
28. Yam VWW, Fung WKM, Wong MT (1997) Organometallics
16:1772
29. Justice AK, Zampella G, Gioia LD, Rauchfuss TB, van der Vlugt
JI, Wilson SR (2007) Inorg Chem 46:1655
Supporting data
30. Adam FI, Hogarth G, Richards I (2007) J Organomet Chem
692:3957
31. Chong D, Georgakaki IP, Mejia-Rodriguez R, Sanabria-Chin-
chilla J, Soriaga MP, Darensbourg MY (2003) Dalton Trans 4158
32. Borg SJ, Behrsing T, Best SP, Razavet M, Liu X, Pickett CJ
(2004) J Am Chem Soc 126:16988
33. Gloaguen F, Lawrence JD, Rauchfuss TB (2001) J Am Chem Soc
123:9476
34. Felton GAN, Mebi CA, Petro BJ, Vannucci AK, Evans DH, Glass
RS, Lichtenberger DL (2009) J Organomet Chem 694:2681
CCDC 974591 (complex 1) and 974593 (complex 2)
contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
Acknowledgments This work is financially supported by the Chi-
nese National Natural Science Foundation (No. 21072046) and the
Chinese National Training Programs of Innovation and Entrepre-
neurship for Undergraduates (No. 201210467022).
´
35. Ezzaher S, Capon JF, Gloaguen F, Petillon FY, Schollhammer P,
Talarmin J (2007) Inorg Chem 46:3426
36. Felton GAN, Glass RS, Lichtenberger DL, Evans DH (2006)
Inorg Chem 45:9181
37. Wang M, Chen L, Sun LC (2012) Energy Environ Sci 5:6763
References
1. Albracht SP (1994) J Biochim Biophys Acta Bioenerg 1188:167
123