Synthesis, protonation and electrochemical properties of trinuclear NiFe2 complexes Fe2(CO)6(μ3-S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, Ph) with an internal pendant nitrogen base as a proton relay

Article abstract of DOI:10.1016/j.ica.2008.04.011

Two trinuclear NiFe₂ complexes Fe₂(CO)₆(μ₃-S)₂[Ni(Ph₂PCH₂)₂NR] (R = n-Bu, 1; Ph, 2) containing an internal base were prepared as biomimetic models for the active sites of FeFe and NiFe hydrogenases. Treatment of complex Fe₂(CO)₆(μ₃-S)₂[Ni(Ph₂PCH₂)₂N(n-Bu)] (1) with HOTf gave an N-protonated complex [Fe₂(CO)₆(μ₃-S)₂{Ni(Ph₂PCH₂)₂NH(n-Bu)}][OTf] ([1H][OTf]). The structures of complexes 1, 2 and [1H][OTf] were determined by X-ray crystallography, which shows that the proton held by the N atom of [1H][OTf] lies in an equatorial position. Cyclic voltammograms of complexes 1 and [1H][OTf] were studied and compared with that of Fe₂(CO)₆(μ₃-S)₂[Ni(dppe)].

Full text of DOI:10.1016/j.ica.2008.04.011

Inorganica Chimica Acta 362 (2009) 372–376
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Inorganica Chimica Acta
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Synthesis, protonation and electrochemical properties of trinuclear NiFe2
complexes Fe2(CO)6(l3-S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, Ph) with an internal
pendant nitrogen base as a proton relay
a
a
a
a,b,
*
Lele Duan a, Mei Wang a, , Ping Li , Ning Wang , Fujun Wang , Licheng Sun
*
a State Key Laboratory of Fine Chemicals, DUT-KTH Joint Education and Research Centre on Molecular Devices, Dalian University of Technology,
Zhongshan Road 158-46, Dalian 116012, PR China
b KTH School of Chemical Science and Engineering, Organic Chemistry, Stockholm 10044, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history:
Two trinuclear NiFe2 complexes Fe2(CO)6(l3-S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, 1; Ph, 2) containing an inter-
nal base were prepared as biomimetic models for the active sites of FeFe and NiFe hydrogenases. Treat-
ment of complex Fe2(CO)6(l3-S)2[Ni(Ph2PCH2)2N(n-Bu)] (1) with HOTf gave an N-protonated complex
Received 27 November 2007
Received in revised form 7 April 2008
Accepted 8 April 2008
[Fe2(CO)6(l3-S)2{Ni(Ph2PCH2)2NH(n-Bu)}][OTf] ([1H][OTf]). The structures of complexes 1,
2 and
Available online 12 April 2008
[1H][OTf] were determined by X-ray crystallography, which shows that the proton held by the N atom
of [1H][OTf] lies in an equatorial position. Cyclic voltammograms of complexes 1 and [1H][OTf] were
studied and compared with that of Fe2(CO)6(l3-S)2[Ni(dppe)].
Keywords:
Electrochemistry
Heteronuclear complex
Hydrogenase
Ó 2008 Elsevier B.V. All rights reserved.
Diphosphine ligand
Protonation
1. Introduction
FeFe and NiFe hydrogenases. Considering the important role of the
internal base in enzymatic hydrogen uptake and production, we
Hydrogenases can catalyze the reduction of protons and the oxi-
dation of molecular hydrogen. According to the metals contained in
the enzymes, hydrogenases can be classified into two major fami-
lies: FeFe hydrogenases and NiFe hydrogenases. The structures of
both FeFe and NiFe hydrogenases have been determined by X-ray
crystallography with high resolution. Fig. 1a depicts the active site
of the FeFe hydrogenase from Desulfovibrio desulfuricans and Fig.
1b shows the active site of NiFe hydrogenase from Desulfovibrio gigas
in the oxidized form [1–4]. Density functional calculations relevant
to the theoretical models of FeFe and NiFe hydrogenase active sites
suggest that an internal base near the catalytically active metal
centers in both FeFe and NiFe hydrogenases could facilitate the
enzymatic H–H bond formation or the heterolyticcleavage of molec-
ular hydrogen in an intramolecular proton–hydride form [5–7].
The synthesis and crystallographic structure of trinuclear com-
plex Fe2(CO)6(l3-S)2[Ni(dppe)] (dppe = Ph2PCH2CH2PPh2) have
been reported by Seyferth et al. and Lozano et al. [8,9], but the redox
property of the trinuclear complex was not reported. This complex,
containing a butterfly Fe2S2 center and a thiolate-bridged NiFe cen-
ter, possesses the characteristics of the structural features of both
tried to introduce an internal basic site to such an interesting trinu-
clear NiFe2 complex. Dubois et al. described the important role of
the bridging-N atom of the Et2PCH2N(Me)CH2PEt2 (PNP) ligand in
the reaction of [Ni(PNP)2](BF4)2 with molecular hydrogen to form
[HNi(PNP)(PNHP)](BF4)2, in which a hydride is bound to the Ni cen-
ter and a proton is bound to the pendant N atom of a PNP ligand [10].
This result motivated us to introduce the ligands (Ph2PCH2)2NR
(R = n-Bu, Ph) as a proton relay to the nickel center of the trinuclear
complex, aiming at preparing biomimetic models for the active site
of FeFe and NiFe hydrogenases. Herein, we report the synthesis
and molecular structures of trinuclear complexes Fe2(CO)6(l3-
S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, 1; Ph, 2) and an N-protonated com-
plex [Fe2(CO)6(l3-S)2{Ni(Ph2PCH2)2NH(n-Bu)}][OTf] ([1H][OTf]). In
addition, the electrochemical properties of complexes 1, [1H][OTf]
and Fe2(CO)6(l3-S)2[Ni(dppe)] were investigated.
2. Results and discussion
2.1. Preparation and spectroscopic characterization of complexes 1, 2
and [1H][OTf]
* Corresponding authors. Tel.: +86 411 88993886; fax: +86 411 83702185 (M.
Wang).
Ligands (Ph2PCH2)2NR (R = n-Bu, Ph) were prepared according
E-mail address: symbueno@dlut.edu.cn (M. Wang).
to the literature procedure [11,12]. Compound (Ph2PCH2)2NPh
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.04.011

L. Duan et al. / Inorganica Chimica Acta 362 (2009) 372–376
373
n-Bu
R
N
H
P
S
+
N
1
Cys S
S Cys
X
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
P
P
S
P
Cys
[Fe S ]
Ni
X
Ni
Ni
S
S
S
4
4
L
2
S
S
S Cys
CN
Cys S
OC
Fe
Fe
CO
CO
OC
CN
CO
OC
OC
NC
C
O
Fe
Fe
Fe
Fe
Fe
CO
CO
OC
CO
CO
OC
CN
OC
OC
+
a
b
[1H]
R = n-Bu, 1; Ph, 2
Fig. 1. Structures of the hydrogenase active sites from (a) Desulfovibrio desulfuricans (X1 = NH or CH2), (b) Desulfovibrio gigas in the oxidized form (X2 = OHꢁ or O2ꢁ), as well as
complexes 1, 2 and [1H]+.
is a solid at room temperature and can be easily purified by
recrystallization, while (Ph2PCH2)2N(n-Bu) is an oil. Complex
NiCl2(Ph2PCH2)2NR (R = n-Bu, Ph) could be readily obtained by
the reaction of NiCl2 ꢀ 2H2O with the corresponding diphosphine
ligands. Complexes 1 and 2 were prepared from the reactions of
(l-LiS)2Fe2(CO)6 and NiCl2(Ph2PCH2)2NR (R = n-Bu, Ph) in moderate
yields. Treatment of a dark red solution of complex 1 in dichloro-
methane with HOTf gave a light red solution. Protonated species
[1H][OTf] of 1 was precipitated upon addition of hexane. Complex
1 is scarcely soluble in acetonitrile, while its protonated species
[1H][OTf] has a good solubility in acetonitrile. Therefore it is easy
to distinguish complex 1 from its protonated species according to
their solubility in acetonitrile. The in situ IR spectra show there
is no reaction between complex 1 and molecular hydrogen under
H2 atmosphere.
were shifted to lower field by ca. 0.74 and 0.36 ppm for the NCH2P
and NCH2C groups, respectively. These results strongly support the
protonation of the bridging-N atom. The 8.4 ppm upfield shift in
the 31P NMR spectrum of [1H][OTf] was possibly caused by the ste-
ric effect. The similar phenomena can be observed in other bridg-
ing-N protonated diiron complexes containing phosphine ligands
[13,14]. In terms of different 31P chemical shifts for complex 1
and [1H][OTf], the reversibility of protonation/deprotonation pro-
cess was explored in dichloromethane. Upon addition of an equiv
of aniline to the solution of [1H][OTf], the signal at d 1.9 for the
N-protonated species quickly disappeared, and at the same time
the signal at d 10.2 for complex 1 appeared as only one in the 31P
NMR spectrum, indicating a reversible protonation/deprotonation
process between 1 and [1H]+.
Complexes 1, 2 and [1H][OTf] were characterized by IR, 1H and
31P NMR spectroscopy and elemental analysis. Four strong m(CO)
bands in the region of 2045–1940 cmꢁ1 were observed in the IR
spectra of complexes 1 and 2 (Table 1). A quite broad resonance
was detected in the 31P NMR spectra of 1 and 2 in CDCl3. Compared
with complex 1, the average value of the m(CO) absorptions for
[1H][OTf] is shifted to higher energy by ca. 7 cmꢁ1. When complex
1 was protonated, the methylene resonances in 1H NMR spectra
2.2. Molecular structures of complexes 1, 2, and [1H][OTf]
The molecular structures of complexes 1, 2 and [1H][OTf] were
determined by X-ray diffraction of single crystals (Fig. 2). Selected
bond lengths and angles are listed in Table 2. The [2Fe2S] skeleton
of these three complexes has a well-known butterfly configuration,
and each iron atom is approximately coordinated in a square-pyra-
midal geometry. The nickel atom is coordinated in an almost pla-
nar geometry by two P and two S atoms. The dihedral angles
defined by the planes of the S–Ni–S and the P–Ni–P are 8.14°,
8.86° and 3.57° for complexes 1, 2 and [1H][OTf], respectively,
which are similar to the 3.74° reported for Fe2(CO)6(l3-
S)2[Ni(dppe)] [9]. The six-membered rings formed by nickel and
diphosphine ligand in complexes 1, 2 and [1H][OTf] are all in the
chair conformation. After protonation of 1, the Ni–Fe distance is
shortened by ca. 0.06 Å. The P–Ni–P angle increases from
81.22(3)° for 1 to 98.63(5)° for [1H][OTf]. On the contrary, the
Table 1
The m(CO) bands of complexes 1, 2, and [1H][OTf]
Complex
m(CO) (KBr, cmꢁ1
)
1
2
2044 s, 2004 s, 1975 s, 1940 s
2045 s, 2005 s, 1977 s, 1940 s
2051 s, 2010 s, 1982 s, 1950 s, 1932 s
[1H][OTf]
Fig. 2. Molecular structures of 1 (left), 2 (middle) and [1H]+ (right). Hydrogen atoms are omitted for clarity except for the one on the N atom in [1H]+.

374
L. Duan et al. / Inorganica Chimica Acta 362 (2009) 372–376
Table 2
Selected bond lengths (Å) and angles (°) for complexes 1, 2 and [1H][OTf]
Complex
1
2
[1H][OTf]
Ni(1)ꢀ ꢀ ꢀFe(1)
Ni(1)ꢀ ꢀ ꢀFe(2)
Fe(1)–Fe(2)
Ni(1)–P(1)
Ni(1)–P(2)
Ni(1)–S(1)
Ni(1)–S(2)
Fe(1)–S(1)
Fe(1)–S(2)
Fe(2)–S(1)
Fe(2)–S(2)
3.1206(10)
3.2209(6)
2.5009(6)
2.1542(7)
2.1612(7)
2.1804(7)
2.1902(7)
2.2722(8)
2.2745(8)
2.2704(9)
2.2759(8)
3.1102(14)
3.2476(15)
2.5072(15)
2.1577(19)
2.165(2)
2.1916(19)
2.183(2)
2.277(2)
3.0608(9)
3.2621(9)
2.5190(11)
2.1622(13)
2.1734(12)
2.1776(12)
2.1800(12)
2.2758(15)
2.2750(14)
2.2767(14)
2.2768(13)
2.278(2)
2.275(2)
2.281(2)
S(1)–Ni(1)–S(2)
P(1)–Ni(1)–P(2)
93.81(3)
81.22(3)
81.04(7)
94.62(7)
81.00(4)
98.63(5)
S–Ni–S angle decreases from 93.81(3)° to 81.00(4)°. Compared
with the structural data reported for the hydrogenase from Desulf-
ovibrio gigas in the oxidized form (Fe–S(68), 2.2 Å; Ni–S(68), 2.6 Å;
Niꢀ ꢀ ꢀFe, 2.9 Å) [4], complexes 1, 2 and [1H][OTf] possess similar Fe–
S bond lengths (2.27–2.28 Å), significantly shorter Ni–S bonds
(2.18–2.19 Å), and somewhat longer Niꢀ ꢀ ꢀFe distances (3.06–
3.12 Å). The Fe–Fe bond lengths are 2.5009(6), 2.5072(15) and
2.5190(11) Å for 1, 2 and [1H][OTf], respectively, which are shorter
than the Fe–Fe bond length reported for the [2Fe2S] H-cluster in
the enzyme structure (ca. 2.6 Å) [1,2]. The X-ray studies show that
protonation of 1 has almost no influence on the framework of the
molecule except for the spatial orientation of the n-Bu on the N
atom of the NCPNiPC chair conformation. The position of the n-
Bu group changes from equatorial in 1 to axial in [1H][OTf]. In
the structure of [1H][OTf], the proton on the bridging-N atom lies
in an equatorial position. The result indicates that the bridging-N
atom of the ligand (Ph2PCH2)2N(n-Bu) in complex 1 can play a role
of the proton relay.
Fig. 4. CVs of 1 (0.5 mM) under Ar and CO in CH3CN at a scan rate of 0.1 V sꢁ1
.
in acetonitrile. A good CV of complex 2 could not be obtained be-
cause of the poor solubility of 2 in acetonitrile.
The redox potentials of three trinuclear complexes are summa-
rized in Table 3. Under Ar atmosphere, complex 1 displays two oxi-
dation peaks and two reduction peaks. The oxidation peaks are
assigned to the iron centers as the nickel(II) in complex 1 cannot
be further oxidized. Compared with the electrochemical data of
other reported diiron dithiolate complexes [15,16], the first oxida-
tion peak at +0.18 V is attributed to the FeIFeI/FeIIFeI process and
the second one at +0.52 V is assigned to the further oxidation pro-
cess of FeIIFeI to FeIIFeII. Nickel complexes with P2S2 or N2S2 coordi-
nation modes reported previously did not show redox potentials
within the window of CH3CN [17]. In the light of this experimental
fact, the first reduction peak is ascribed to the FeIFeI/Fe0FeI process
instead of the NiII/NiI process. A typical phenomenon for multi-car-
bonyl diiron dithiolate complexes is that the second reduction
peak close to the first one disappears when CV is measured in
CH3CN under a CO atmosphere [15,16,18], due to the depression
of the CO-displacement by solvent. The CV control study of com-
plex 1 showed that the second reduction peak of 1 at ꢁ2.00 V dis-
appeared (Fig. 4) when the measurement was carried out under
CO. Therefore, the second reduction peak is attributed to the reduc-
tion process of FeIFeI to Fe0FeI for a CH3CN substituted species of
complex 1. Similarly, the first oxidation peak at +0.19 V and the
first reduction peak at ꢁ1.68 V for Fe2(CO)6(l3-S)2[Ni(dppe)] are
attributed to the FeIFeI/FeIIFeI process and the FeIFeI/Fe0FeI process,
respectively. When the bridging-N atom of complex 1 is proton-
ated, the electron density of the iron centers is somewhat de-
creased. Upon addition of two equivalent acid (HOTf) to the
solution of 1 in CH3CN, a new reduction peak was observed at ca.
ꢁ1.42 V, resulting from the formation of [1H][OTf] in situ. The first
reduction peak of the isolated [1H][OTf] salt appeared at ꢁ1.40 V,
shifted to anodic direction by ca. 330 mV as compared to that of
1. It is noticeable that the intensity of the peaks at +0.36 and
ꢁ1.40 V for [1H][OTf] is relatively weak, and in addition to the
2.3. Electrochemistry of complexes 1, [1H][OTf] and Fe2(CO)6(l3-S)2-
[Ni(dppe)]
The cyclic voltammograms (CV) of complexes 1, [1H][OTf] and
Fe2(CO)6(l3-S)2[Ni(dppe)] are shown in Fig. 3. To compare the elec-
trochemical property of 1 with other [2Fe2S] complexes that were
detected in acetonitrile [15], the CV of complex 1 was also per-
formed in acetonitrile even though complex 1 is not very soluble
Table 3
Redox potentials of 1, [1H][OTf] and Fe2(CO)6(l3-S)2[Ni(dppe)] vs. Ag/Ag+
Complex
Epa (V)
Epa (V)
Epc (V)
FeIIFeI/FeIIFeII
FeIFeI/FeIIFeI
FeIFeI/Fe0FeI
1
+0.52
+0.18
+0.36
+0.19
ꢁ1.73
ꢁ1.40
ꢁ1.68
[1H][OTf]
Fe2(CO)6(l3-S)2[Ni(dppe)]
Fig. 3. CVs of complexes 1 (0.5 mM), [1H][OTf] (0.5 mM) and Fe2(CO)6(l3-S)2[Ni(-
dppe)] (1.0 mM) in CH3CN under Ar at a scan rate of 0.1 V sꢁ1
.

L. Duan et al. / Inorganica Chimica Acta 362 (2009) 372–376
375
peaks of [1H][OTf], weak redox peaks for complex 1 at +0.18 and
ꢁ1.73 V were also observed. It indicates the partial deprotonation
of [1H][OTf] in acetonitrile. In the presence of aniline, the peaks at
+0.36 and ꢁ1.40 V quickly disappeared and the peaks at +0.18 and
ꢁ1.73 V for 1 was quantitatively recovered.
on a rotary evaporator, the crude product was purified by column
chromatography on silica gel using dichloromethane/hexane (2/1,
v/v) as eluent. Complex 1 was obtained as brown solid. Yield:
1.56 g (62%). IR (KBr): m(CO) 2044 s, 2004 s, 1975 s, 1940 s cmꢁ1
.
1H NMR (CDCl3): d 7.77 (s br, 8H, PPh), 7.42 (s br, 12H, PPh), 3.16
(s br, 4H, NCH2P), 2.48 (s br, 2H, NCH2C), 1.25 (s br, 2H,
CH2CH2CH2). 1.04 (s br, 2H, CH2CH3), 0.78 (s br, 3H, CH2CH3).
31P{1H} NMR (CDCl3): d 10.2. Anal. Calc. for C36H33Fe2NNiO6P2S2
(Mr = 872.11): C, 49.58; H, 3.81; N, 1.61. Found: C, 49.51; H, 3.76;
N, 1.60%.
3. Conclusion
An internal base was introduced to the NiFe2 trinuclear com-
plexes, which possess structural characters of the active sites of
Complex Fe2(CO)6(l3-S)2[Ni(Ph2PCH2)2NPh] (2) was prepared in
70 % yield with the essentially identical procedure for complex 1.
FeFe and NiFe hydrogenases. The
N atom in Fe2(CO)6(l3-
S)2[Ni(Ph2PCH2)2N(n-Bu)](1) can readily catch a proton from acid
to form N-protonated species [1H]+, which quickly and quantita-
tively regenerates 1 in the presence of aniline. The X-ray studies
show that the n-Bu group of the (Ph2PCH2)2N(n-Bu) ligand changes
from the equatorial position in 1 to the axial position in [1H]+,
resulting in an equatorial position for the proton held by the N
atom of [1H]+. Complex 1 displays similar IR and CV data to those
of the reported [2Fe2S] complexes [15,16,18], indicating that the
nickel unit gives rise to no significant influence on the redox prop-
erty of the [2Fe2S] complex.
IR (KBr): m(CO) 2045 s, 2005 s, 1977 s, 1940 s cmꢁ1 1H NMR
.
(CDCl3): d 7.80 (m, 8H, PPh), 7.50 (t, 4H, PPh), 7.44 (t, 8H, PPh),
7.16 (t, 2H, NPh), 6.96 (t, 1H, NPh), 6.61 (d, 2H, NPh). 3.80 (s, 4H,
NCH2P). 31P{1H} NMR (CDCl3): d 11.0. Anal. Calc. for C38H29Fe2N-
NiO6P2S2 (Mr = 892.10): C, 51.16; H, 3.28; N, 1.57. Found: C,
51.11; H, 3.26; N, 1.55%.
4.3. Synthesis of Fe2(CO)6(l3-S)2[Ni(Ph2PCH2)2NH(n-Bu)](OTf)
([1H][OTf])
The acid HOTf (12 lL) was added to the solution of Fe2(CO)6(l3-
S)2[Ni(Ph2PCH2)2N(n-Bu)] (100 mg, 0.11 mmol) in CH2Cl2 (5 mL)
with stirring. Hexane (15 mL) was added to the solution after
5 min, and a brown solid was precipitated, which was isolated by
filtration, washed with hexane, and dried in vacuo to give the pure
product. Yield: 0.11 g (89%). IR (KBr): m(CO) 2051 s, 2010 s, 1982 s,
4. Experimental
All reactions and operations related to organometallic com-
plexes were carried out under an atmosphere of dinitrogen using
standard Schlenk techniques. The solvent THF was pre-dried
with KOH and distilled prior to use over sodium/benzophenone
ketyl under a nitrogen atmosphere. Compounds Fe2(CO)6(l3-S)2-
[Ni(dppe)] [9], (l-S)2Fe2(CO)6 [8], (Ph2PCH2)2N(n-Bu) [11], and
(Ph2PCH2)2NPh [12] were prepared according to literature meth-
ods. All other commercially available reagents were used as
received.
1950 s, 1932 s cmꢁ1 1H NMR (CD3CN): d7.89, 7.58 (2s br, 20H,
.
PPh), 5.43 (s, 1H, NH), 3.90 (s br, 4H, NCH2P), 2.84 (s br, 2H, NCH2C),
1.38 (s br, 2H, CH2CH2CH2). 1.04 (s br, 2H, CH2CH3), 0.76 (t, 3H,
CH2CH3). 31P{1H} NMR (CD3CN): d 1.9. Anal. Calc. for C37H34F3Fe2N-
NiO9P2S3 (Mr = 1022.19): C, 43.47; H, 3.35; N, 1.37. Found: C, 43.41;
H, 3.34; N, 1.32%.
Infrared spectra were recorded on a JASCO FT/IR 430 spectro-
photometer using KBr discs. 1H and 31P NMR spectra were recorded
on a Varian INOVA 400 NMR spectrometer. Elemental analyses
were performed with a Thermoquest-Flash EA 1112 apparatus.
4.4. Crystal structure determination of complexes 1, 2 and [1H][OTf]
Single crystals of Fe2(CO)6(l3-S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, 1;
Ph, 2) and Fe2(CO)6(l3-S)2[Ni(Ph2PCH2)2NH(n-Bu)](OTf) ([1H][OTf])
were obtained from saturated CH2Cl2 solutions of complexes by
diffusion of hexane. Crystallographic data were collected on a Bru-
ker Smart APEXII diffractometer for 1 and [1H][OTf], and on a Bru-
ker P4 diffractometer for 2 with graphite monochromated Mo Ka
radiation (k = 0.71073 Å). Data processing was accomplished with
the SAINT processing program [19]. Intensity data were corrected
for absorption by the SADABS program [20]. The structures were
solved by direct methods and refined on F2 against full-matrix
least-squares methods using the SHELXTL97 program package [21].
All non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were placed by geometrical calculation and refined in a rid-
ing model, and the proton on the N atom of [1H][OTf] was located
by the difference Fourier map. Crystal data and parameters for data
collections and refinements of complexes 1, 2, and [1H][OTf] are
listed in Table 4.
4.1. Synthesis of NiCl2[(Ph2PCH2)2NR] (R = n-Bu, Ph)
A solution of (Ph2PCH2)2N(n-Bu) (1.5 g, 3.19 mmol) in CH2Cl2
(30 mL) was added dropwise to a solution of NiCl2 ꢀ 2H2O (0.53 g,
3.20 mmol) in ethanol (20 mL). The solution became dark red
immediately. The mixture was stirred for 30 min and the orange
precipitate was isolated by filtration, washed with diethyl ether,
and then recrystallized from ethanol to give complex
NiCl2[(Ph2PCH2)2N(n-Bu)]. Yield: 1.53 g (80%). 1H NMR (CDCl3): d
7.92 (d, 8H, PPh), 7.53 (t, 8H, PPh), 7.38 (t, 4H, PPh), 4.2–3.8 (s
br, 4H, NCH2P), 2.48 (t, 2H, NCH2C), 1.25 (m, 2H, CH2CH2CH2),
1.05 (m, 2H, CH2CH3), 0.78 (t, 3H, CH2CH3). 31P{1H} NMR (CDCl3):
d 1.4 (very br).
Starting complex NiCl2[(Ph2PCH2)2NPh] was prepared in 85%
yield with the similar procedure aforementioned. 1H NMR (CDCl3):
d 7.94 (d, 8H, PPh), 7.56 (t, 8H, PPh), 7.42 (t, 4H, PPh), 7.18 (t, 2H,
NPh), 6.96 (t, 1H, NPh), 6.61 (d, 2H, NPh). 4.9-4.2 (s br, 4H, NCH2P).
31P{1H} NMR (CDCl3): d 1.2 (very br).
4.5. Electrochemistry studies of complexes 1, [1H][OTf] and Fe2(CO)6-
(l3-S)2[Ni(dppe)]
4.2. Synthesis of Fe2(CO)6(l3-S)2[Ni(Ph2PCH2)2NR] (R = n-Bu, 1; Ph, 2)
Electrochemical measurements were recorded using a BAS-
100W electrochemical potentiostat as previously reported [15].
Cyclic voltammograms were obtained in a three-electrode cell un-
der argon. A glassy carbon disc was used as working electrode, a
non-aqueous Ag/Ag+ electrode (0.01 M AgNO3 in CH3CN) as refer-
ence electrode, and a platinum wire as auxiliary electrode. A solu-
tion of 0.05 M n-Bu4NPF6 (Fluka, electrochemical grade) in CH3CN
was used as a supporting electrolyte.
A solution of LiHBEt3 (6 mL, 1 M in THF) was added to the solu-
tion of (l-S)2Fe2(CO)6 (1.0 g, 2.90 mmol) in THF (15 mL) at ꢁ78 °C
within 15 min. The green solution was stirred for another 10 min
at ꢁ78 °C, and then NiCl2[(Ph2PCH2)2N(n-Bu)] (1.74 g, 2.90 mmol)
was added. The mixture was warmed to room temperature and
the dark red solution was stirred for 2 h. After removal of solvent

376
L. Duan et al. / Inorganica Chimica Acta 362 (2009) 372–376
Table 4
Crystallographic data and processing parameters for 1, 2, and [1H][OTf]
1
2
[1H][OTf]
Formula
Mw
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a (°)
b (°)
C36H33Fe2NNiO6P2S2
872.10
monoclinic
P21/c
11.692(2)
16.581(3)
20.084(4)
90.00
92.17(3)
90.00
3890.8(12)
4
1.489
1.448
1784
C38H29Fe2NNiO6P2S2
892.09
monoclinic
P21/c
11.896(4)
16.261(5)
20.163(6)
90.00
92.887(7)
90.00
3895(2)
4
1.521
1.448
1816
C37H34F3Fe2NNiO9P2S3 ꢀ 0.5H2O
1031.19
triclinic
ꢀ
P1
11.2601(2)
12.2963(2)
17.0799(3)
93.388(1)
93.580(1)
104.409(1)
2279.16(7)
2
c (°)
V (Å3)
Z
Dcalcd (g cmꢁ3
)
1.503
1.307
1050
l (mmꢁ1
F(000)
)
Crystal size (mm)
h Range (°)
Reflections collected
Independent reflections
Rint
0.22 ꢂ 0.15 ꢂ 0.12
2.03–27.00
28244
8379
0.0279
0.45 ꢂ 0.32 ꢂ 0.20
1.61–26.10
21543
7719
0.1222
0.26 ꢂ 0.25 ꢂ 0.09
2.51–27.56
21402
10429
0.0387
Reflections with [I > 2r(I)]
Parameters refined
Goodness-of-fit on F2
6412
479
1.038
0.0370/0.0963
0.467/ꢁ0.644
3594
469
0.969
0.0734/0.1018
0.405/ꢁ0.362
6137
536
1.015
0.0582/0.1599
1.128/ꢁ0.641
a
b
R1 [I > 2r(I)]/wR2
Residue electron density (e Åꢁ3
)
P
a
R1
¼
kFo j ꢁ j Fck.
P
P
2
2 1=2
wR2 ¼ ½ ½wðF2o ꢁ Fc2Þ ꢃ= wðF2oÞ ꢃ
.
b
[4] A. Volbeda, E. Garcin, C. Piras, A.L. de Lacey, V.M. Fernandez, E.C. Hatchikian, M.
Frey, J.C. Fontecilla-Camps, J. Am. Chem. Soc. 118 (1996) 12989.
[5] V. Artero, M. Fontecave, Coord. Chem. Rev. 249 (2005) 1518.
[6] H.-J. Fan, M.B. Hall, J. Am. Chem. Soc. 123 (2001) 3828.
[7] S. Niu, M.B. Hall, Inorg. Chem. 40 (2001) 6201.
[8] D. Seyferth, R.S. Henderson, L. Song, Organometallics 1 (1982) 125.
[9] A.A. Lozano, M.D. Santana, G. García, J.E. Barclay, S.C. Davies, D.J. Evans, Z.
Anorg. Allg. Chem. 631 (2005) 2062.
Acknowledgments
We are grateful to the Chinese National Natural Science Foun-
dation (Grant No. 20633020), the Program for Changjiang Scholars
and Innovative Research Team in University (IRT0711), the Swed-
ish Research Council and K&A Wallenberg Foundation for financial
support of this work.
[10] C.J. Curtis, A. Miedaner, R. Ciancanelli, W.W. Ellis, B.C. Noll, M.R. DuBois, D.L.
DuBois, Inorg. Chem. 42 (2003) 216.
[11] W. Wu, C. Li, Chem. Commun. (2003) 1668.
Appendix A. Supplementary material
[12] A.L. Balch, M.M. Olmstead, S.P. Rowley, Inorg. Chim. Acta 168 (1990) 255.
[13] L. Schwartz, G. Eilers, L. Eriksson, A. Gogoll, R. Lomoth, S. Ott, Chem. Commun.
(2006) 520.
[14] P. Das, J. Capon, F. Gloaguen, F.Y. Pétillon, P. Schollhammer, J. Talarmin, Inorg.
Chem. 43 (2004) 8203.
[15] 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.
[16] D. Chong, I.P. Georgakaki, R. Mejia-Rodriguez, J. Sanabria-Chinchilla, M.P.
Soriaga, M.Y. Darensbourg, Dalton Trans. (2003) 4158.
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Organometallics 12 (1993) 870.
CCDC 647078, 647079 and 647077 contain the supplementary
crystallographic data for 1, 2 and ([1H][OTf]). These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.ica.2008.04.011.
[18] P. Li, M. Wang, C. He, X. Liu, K. Jin, L. Sun, Eur. J. Inorg. Chem. (2007)
3718.
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