Synthesis, characterization and electrocatalytic H2 production of base-containing Fe/S and Fe/Se clusters

Article abstract of DOI:10.1016/j.ica.2018.05.018

Reaction of base-containing diphosphine ligand NP^S₂ (NP₂[dbnd](Ph₂PCH₂)₂NCH₃) with [Fe₃(CO)₁₂] in THF at room temperature forms [{Fe₂(CO)₆(μ-PPh₂)}₂(μ₄-S₂)] (1) and [Fe₃(CO)₈(μ₃-S)₂{kP-PPh₂CH₂N(CH₃)CH₂P([dbnd]S)Ph₂}] (2) resulting from P[dbnd]S bond cleavage and P–Fe bond formation. Similarly, NP^Se₂ reacts with Fe₃(CO)₁₂ to provide [{Fe₂(CO)₆(μ-PPh₂)}₂(μ₄-Se₂)] (3) and [Fe₃(CO)₇(μ₃-Se)₂{k²P,P-(PPh₂CH₂)₂NCH₃}] (4). All the compounds have been completely characterized by elemental analyses, IR, ¹H NMR, ¹³C NMR and ³¹P NMR spectroscopy and structurally determined by X-ray crystallography. Electrochemical studies reveal that when using HOAc or TFA as a proton source, 2 and 4 exhibit catalytic H₂ production.

Full text of DOI:10.1016/j.ica.2018.05.018

Accepted Manuscript
Research paper
Synthesis, Characterization and Electrocatalytic H2 Production of Base-con-
taining Fe/S and Fe/Se Clusters
Jin-Ping Li, Yao-Cheng Shi
PII:
S0020-1693(18)30126-9
https://doi.org/10.1016/j.ica.2018.05.018
ICA 18269
DOI:
Reference:
Inorganica Chimica Acta
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Revised Date:
Accepted Date:
26 January 2018
12 April 2018
14 May 2018
Please cite this article as: J-P. Li, Y-C. Shi, Synthesis, Characterization and Electrocatalytic H2 Production of Base-
containing Fe/S and Fe/Se Clusters, Inorganica Chimica Acta (2018), doi: https://doi.org/10.1016/j.ica.2018.05.018
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Synthesis, Characterization and Electrocatalytic H2
Production of Base-containing Fe/S and Fe/Se Clusters
Jin-Ping Li, Yao-Cheng Shi
College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, P. R. China
Abstract: Reaction of base-containing diphosphine ligand NPS (NP2 = (Ph2PCH2)2NCH3) with
2
[Fe3(CO)12] in THF at room temperature forms [{Fe2(CO)6(µ-PPh2)}2(µ4-S2)] (1) and [Fe3(CO)8(µ3-
S)2{kP-PPh2CH2N(CH3)CH2P(=S)Ph2}] (2) resulting from P=S bond cleavage and P-Fe bond
Se
2
formation. Similarly, NP2 reacts with Fe3(CO)12 to provide [{Fe2(CO)6(µ-PPh2)}2(µ4-Se2)] (3) and
[Fe3(CO)7(µ3-Se)2{k2P,P-(PPh2CH2)2NCH3}] (4). All the compounds have been completely
characterized by elemental analyses, IR, 1H NMR, 13C NMR and 31P NMR spectroscopy and structurally
determined by X-ray crystallography. Electrochemical studies reveal that when using HOAc or TFA as a
proton source, 2 and 4 exhibit catalytic H2 production.
Keywords: Fe/S Cluster; Fe/Se Cluster; Cyclic voltammetry; H2 production
1. Introduction
The development of renewable energy is nowadays one of the most important challenges as global
energy consumption is rising significantly. Molecular hydrogen is a carbon-free fuel that could become
the energy carrier of the future, thus making the reversible interconversion of protons to molecular
hydrogen a key process for future energy schemes. Nature is able to catalyze this process by a class of
1

enzymes called hydrogenases (H2ases), one of which being the [FeFe] H2ases [1]. The X-ray
crystallographic structure determination of the enzymes has revealed their active site and allowed the
mechanistic understanding of the catalytic process. Inspired by these insights, many diiron model
complexes of the [FeFe] H2ase active site have been synthesized [2-4]. However, the complexes
generally exhibit large overpotentials and low turnover rates for electrocatalytic proton reduction [5].
Therefore, novel structural and chemical models are still necessary to provide a better understanding of
the protonation mechanisms implied at the molecular level. In this context, we have recently initiated a
project developing synthetic methodologies toward iron-sulfur and iron-selenium clusters as model
compounds [6-10]. Because of the active site containing the noncoordinating amine, this functionality
has inspired the exploration of the role of pendant amines in the electrocatalytic production and
oxidation of H2. Flexible base-containing diphosphine ligands such as PR NR' ((R2PCH2)2NR’) and
2
cyclic PR NR'2 and their mononuclear and dinuclear complexes have been widely developed by Talarmin,
2
DuBois and Rakowsky DuBois [11-15]. Accordingly, their results have prompted us to synthesize
trinuclear or multinuclear complexes with pendant bases. Herein we wish to report the syntheses and
electrocatalytic H2 production of trinuclear Fe/S and Fe/Se clusters with pendant bases.
2. Results and discussion
2.1. Syntheses
Condensation of HPPh2, H2NMe and HCHO generated (Ph2PCH2)2NCH3 [16]. As expected,
(Ph2PCH2)2NCH3 reacted with En (E = S, n = 8; E = Se, n = 8) to give the corresponding derivatives
(E=PPh2CH2)2NCH3 (namely NPE ) in high yields (Equation 1). From the view of energetics,
2
Ph2PR(=S) and Ph2PR(=Se) can be utilized as sulfur and selenium transfer agents [17]. In view of NP2-
type ligands being applied to design new catalysts for H2 evolution [18], we would like to know whether
diphosphine sulfides and diphosphine selenides can be used to synthesize clusters with NP2-type
ligands. The reaction of NPS with Fe3(CO)12 at room temperature affords [{Fe2(CO)6(µ-PPh2)}2(µ4-S2)]
2
*To whom correspondence should be addressed. E-mail: ycshi@yzu.edu.cn
2

(1) and [Fe3(CO)8(µ3-S)2{kP-PPh2CH2N(CH3)CH2P(=S)Ph2}] (2), in respective yield of 12% and 23%.
However, the reaction of NPSe with Fe3(CO)12 at room temperature leads to [{Fe2(CO)6(µ-PPh2)}2(µ4-
2
Se2)] (3) and [Fe3(CO)7(µ3-Se)2{k2P,P-(PPh2CH2)2NCH3}] (4), in respective yield of 15% and 20%
(Scheme 1). Notably, 1 can be generated from the reaction of Fe(CO)5 with Ph2PSCMe3 under harsh
conditions in 3% yield [19] and the reaction of Fe3(CO)12 with Ph2PSH at room temperature in 15%
yield [unpublished results]. Via a usual route to Fe3(μ3-S)2(CO)9-xLx, Liu and coworkers have obtained
Fe3(μ3-S)2(CO)7(µ-dppf) from the reaction of Fe3(μ3-S)2(CO)9 with dppf [20]. Recently, Kaiser and
Knör have reported that the reactions of Fe3(CO)12 with dppmS2 and dppfS2 afford Fe3(μ3-S)2(CO)7(µ-
L2) clusters (L2 = dppm, dppf) [21]. Several Fe3(μ3-Se)2(CO)9 derivatives such as Fe3(μ3-Se)2(CO)7(μ-
(Ph2P)2R), Fe3(μ3-Se)2(CO)7(μ-dpmb) and Fe3(μ3-Se)2(CO)7(PPh3)2 have been produced by Tiripicchio
and coworkers [17,22]. Schollhammer and coworkers [11b] have carried out the reaction of
(Ph2PCH2)2NCH3 with [(µ-S2)Fe2(CO)6] at room temperature to afford [Fe2(CO)4(µ-k1:k1-SPPh2){µ-
k2:k1-SCH2N(Me)CH2PPh2}] via an intermediate species [Fe2(CO)5(µ-k1:k1-SPPh2){µ-k2:k1-
SCH2N(Me)CH2PPh2}]. Thus, our methodology has opened up an unprecendented route to multinuclear
clusters with pendant bases.
En
[Ph2P(=E)CH2]2NCH3
[Ph2PCH2]2NCH3
(NPS2, E = S, n = 8; NPSe2, E = Se, n = 8)
Equation 1. Syntheses of NPE
2
3

Ph
(OC)3Fe
Ph
Fe(CO)3
Fe(CO)3
P
S
[Ph2P(=S)CH2]2NCH3
S
+
Ph2P
S
S
CO
N
CH3
Fe
(OC)3Fe
P
Ph2
2
OC
(2)
(1)
Fe3(CO)12
(OC)3Fe
Se
Fe(CO)3
Fe(CO)3
[Ph2P(=Se)CH2]2NCH3
Se
+
Ph2
Ph2P
Se
P
N
Fe
(OC)3Fe
CH3
P
Ph2
2
OC
(3)
(4)
Scheme 1. Syntheses of complexes 1-4
2.2. X-ray structures of compounds
The molecular structures of NPS , NPSe and 1-4 shown in Figs. 1-6 were determined by using X-ray
2
2
diffraction methods. Crystal data, selected bond lengths and angles (Å, °) are listed in Tables 1-4. For
NPS , two Ph2PS show a staggered conformation. The P1-S1 [1.9489(10) Å] and P2-S2 [1.9520(11) Å]
2
bond distances are almost equal to the literature value [1.9523(8) Å, 8a; 1.944(3) Å, dppfS2, 23], the P-C
bond of the CH2P distances are 1.829(2) and 1.830(2) Å, but the PhP bond distances vary from 1.801(2)
to 1.814(3) Å . In NPSe , two Ph2PSe units display a similar conformation, and the P1-Se1 [2.1059(11)
2
Å] and P2-Se2 [2.1048(12) Å] bond distances are actually equal to the related value of dppfSe2 [2.103(6)
Å; 23], the P-C bond of the CH2P distances are 1.836(4) and 1.837(4) Å whereas the PhP bond distances
vary from 1.809(4) to 1.828(4) Å. Interestingly, NPS and NPSe have similar cell parameters shown in
2
2
Table 1, thus indicating that they are isomorphous.
Complex 1 (Fig. 3) is a tetrairon cluster, its molecule has been characterized by Mays et al [19].
Similarly to 1, 3 contains a butterfly Fe2PSe skeleton with a 81.90(7)° dihedral angle between Fe2P and
Fe2Se planes (Fig. 5). The Se2 ligand bridges two (μ-PPh2)Fe2(CO)6 subclusters via an equatorial Se-Sei
single bond of 2.4103(11) Å [2.3905(6) Å, (μ-k2C,N-PhC=NCH2Ph)Fe2(CO)6(µ4-Se2)Fe2(CO)6(μ-
k2C,N-PhC=NCH2Ph); 7b]. Fe atoms each show a distorted octahedral geometry and obey the 18-e rule.
4

Each Se atom behaving as a three-electron donor spans a (μ-PPh2)Fe2(CO)6 subcluster, with Fe1-Se1
and Fe2-Se1 bond lengths of 2.3686(10) and 2.3762(11) Å. The Fe1-Fe2 bond of 2.5799(11) Å is
slightly shorter than that [2.5972(18) Å] of 1.
As shown in Fig. 4, 2 contains an open triangle of Fe atoms capped by two S atoms above and below,
with an Fe2-Fe3-Fe1 angle of 80.11(4)º. The S2Fe3 core adopts a distorted square-pyramidal geometry
similar to the previously reported cluster (μ3-S)2Fe3(CO)9 [6a,24] and some derivatives [25-27]. Each of
the three Fe atoms satisfies the 18-electron rule. 2 may be viewed as involving formal replacement of the
one equatorial carbonyl ligand on one of the iron centers on the square base in (μ3-S)2Fe3(CO)9 by a
phosphine ligand, with Fe1-P1 = 2.2554(18) Å and Fe1-P1-C21 = 114.7(2)°. The phosphine ligand leads
to small structural effects, namely a slight decrease in the triiron bond angle compared with (μ3-
S)2Fe3(CO)9 [81.13(2)°; 2.5903(9) and 2.5946(9) Å], and a difference in the Fe-Fe bond lengths, with
Fe1-Fe3 = 2.6803(14) and Fe2-Fe3 = 2.5569(14) Å.
Complex 4 (Fig. 6) includes an open triangle of Fe atoms capped by two Se atoms above and below,
with an Fe3-Fe2-Fe1 angle of 82.50(3)º. The Se2Fe3 core adopts a distorted square-pyramidal geometry
analogous to (μ3-Se)2Fe3(CO)9 [6a,28] and some related clusters [17,22]. In (μ3-Se)2Fe3(CO)9, each
selenium on the square base triply bridges the two basal Fe(CO)3 units on the same base and the third
Fe(CO)3 group at the apex of the pyramid, and each of the three Fe atoms obeys the 18-electron rule.
Accordingly, 4 may be regarded as a derivative of (μ3-Se)2Fe3(CO)9 generated from substitution of the
two equatorial carbonyl ligands on one of the iron centers in (μ3-Se)2Fe3(CO)9 by a diphosphine ligand,
with Fe1-P1 = 2.2274(11) Å and P1-Fe1-P1i = 92.19(6)°. The FeP2C2N metallacycle adopts a chair
conformation, with the methyl substituent of N1 in an equatorial position [16]. The chelating
diphosphine causes structural effects, namely a slight change in the triiron bond angle compared with
(μ3-Se)2Fe3(CO)9 [83.21(3)º, 2.6569(10) and 2.6448(10) Å; 6a], and an obvious difference in the Fe-Fe
bond lengths, with Fe1-Fe3 = 2.8120(10) and Fe2-Fe3 = 2.5827(11) Å. For comparison, the
corresponding bond lengths and angles of Fe3(μ3-S)2(CO)7(µ-dppm) Fe3(μ3-S)2(CO)7(µ-dppf) are listed
as follows: Fe3-Fe1, 2.607(1), 2.568(6) Å; Fe3-Fe2, 2.615(1), 2.576(6) Å; Fe1-Fe3-Fe2, 80.3(4) º,
5

85.4(2) º [21].
Figure 1. PLATON view of NPS
2
6

Figure 2. PLATON view of NPSe
2
7

Figure 3. PLATON view of 1
8

Figure 4. PLATON view of 2
Figure 5. PLATON view of 3
9

Figure 6. PLATON view of 4
2.3. Spectroscopies of complexes
1
13
31
The above-described complexes have been further characterized by IR, H NMR, C NMR and P
NMR (Supplementary data, Fig. S1-S24). In the IR spectra, the terminal carbonyl groups show four
strong absorptions at 2055, 2031, 2006 and 1969 cm-1 for 1, 2071, 2030, 2003 and 1979 cm-1 for 2,
2049, 2010, 1980 and 1920 cm-1 for 4. However, those of 3 exhibit three strong absorptions at 2029,
2003 and 1967 cm-1. The highest-energy band of 1 is larger than that of 3, indicating that an Se complex
is more electron-rich than its S-analogue. Generally, phosphine ligands are strongly σ-donate electron
density along the Fe-P bonds, causing a more electron-rich iron core. At the same time this leads to a
significant deshielding of the phosphorus atoms, and a characteristic downfield shift of the 31P
resonance signals occurs upon coordination. Compared with (μ3-S)2Fe3(CO)9, Fe3(μ3-S)2(CO)7(µ-dppm)
is more electron-rich [2041, 2004, 1979, 1954, 1937 cm-1; 21]. Therefore, as for this aspect, 4 is close to
Fe3(μ3-S)2(CO)7(µ-dppm). Free ligands NPE , in the 31P NMR spectra, each show one singlet at 35.030
2
ppm for NPS and 24.156 ppm for NPSe whereas free (Ph2PCH2)2NCH3, namely NP2, occurs at -26.9
2
2
10

ppm in CDCl3 [16]. One singlet at 133.381 ppm for 1 and 140.214 ppm for 3 is consistent with the
bridging mode of PPh2 [7-10]. Two doublets at 58.559, 32.124 (d, d, J = 10.7 Hz, J = 10.9 Hz, FeP,
P=S) ppm for 2 and one singlet at 43.623 ppm for 4, indicating the presence of two coordination modes,
viz. unidentate in 2 and bidentate in 4 [75.4 ppm in CDCl3, Fe3(μ3-S)2(CO)7(µ-dppm); 68.4 ppm in
1
CDCl3, Fe3(μ3-S)2(CO)7(µ-dppf); 21], are in accordance with their crystal structures. In the H NMR
spectra, the phenyl group shows a multiplet in the region of 7.743-7.137 ppm for 1 and 7.595-7.159 ppm
for 3 and 7.789-7.397 ppm for 2 and 7.700-7.421 ppm for 4. Moreover, the methylene group shows four
singlets at 4.498, 4.332, 3.899, 3.797 ppm for 2 whereas that of 4 exhibits one singlet at 3.529 and one
doublet at 2.669 (d, J = 9.6 Hz) ppm, the methyl group occurs as two singlets at 2.252, 2.075 ppm for 2
and one singlet at 2.481 ppm for 4. In the 13C NMR spectra, the terminal carbonyls as one singlet occur
at 210.31 ppm for 1, 210.46 ppm for 3, 210.26 ppm for 2 and 210.40 ppm for 4, indicating that they are
fluxional in CDCl3. Two methylene groups diplay two doublets at 60.95, 58.77 (d, d, J = 43.0 Hz, J =
38.0 Hz) ppm for 2 whereas those of 4 exhibit two triplets at 60.61, 51.13 (t, t, J = 20.0 Hz, J = 12.0 Hz)
ppm, the methyl group appears as one singlet at 44.17 ppm for 2 and 53.40 ppm for 4.
2.4. Electrochemistry
Cyclic voltammetry of 2 and 4 has been investigated to evaluate the capability of the new triiron
complexes to catalyze H2 evolution (Figs. 7-8) [29]. In MeCN, CV of 2 in the absence of acetic acid
shows one irreversible oxidation at 0.52 V and two irreversible reductions at -1.26 and -2.48 V. Using
HOAc as a proton source (pKa, 23.51, in MeCN, direct reduction at -2.36 V) [30], the second reduction
peak at -2.48 V satisfactorily exhibits catalytic behavior, the reduction current increase with increasing
concentration of acetic acid added. In CH2Cl2 (4 being insoluble in MeCN), CV of 4 in the absence of
TFA shows one irreversible oxidation at 0.51 V and two irreversible reductions at -1.31 and -1.85 V.
Using TFA as a proton source (CF3CO2H, pKa, 12.65, in MeCN, direct reduction at -1.81 V) [30], the
first reduction peak at -1.31 V displays catalytic behavior. According to the defination of catalytic
efficiency proposed by Evans et al. [2d], CE = (icat/id)/(CHA/Ccat) (icat, catalytic current; id, current for
reduction of the catalyst in the absence of acid; CHA, acid concentration; Ccat, catalyst concentration), CE
11

is calculated to be 0.59 for 2 and 0.74 for 4, indicating that 2 and 4 can catalyze H2 production.
400
2
350
300
250
HOAc mM
12
10
8
6
4
200
2
0
150
100
50
0
-50
-100
-0.75
-1.00
-1.25
-1.50
-1.75
-2.00
-2.25
-2.50
-2.75
+
E/V versus Fc /Fc
Figure 7. Cyclic voltammograms of 2 (1.0 mM) with HOAc (0-12 mM) in 0.1 M nBu4NPF6/MeCN at a
scan rate of 100 mV s-1
400
4
350
TFA mM
12
10
8
6
4
300
250
200
150
100
50
2
0
0
-50
-0.25
-0.50
-0.75
-1.00
-1.25
-1.50
-1.75
-2.00
-2.25
-2.50
+
E/V versus Fc /Fc
Figure 8. Cyclic voltammograms of 4 (1.0 mM) with TFA (0-12 mM) in 0.1 M nBu4NPF6/CH2Cl2 at a
scan rate of 100 mV s-1
12

-175
-150
-125
-100
-75
-50
-25
0
HOAc mM
12
10
8
6
4
2
0
25
50
-0.50 -0.75 -1.00 -1.25 -1.50 -1.75 -2.00 -2.25 -2.50 -2.75
+
E/V versus Fc /Fc
Figure 9. Cyclic voltammograms of HOAc (0-12 mM) in 0.1 M nBu4NPF6/MeCN at a scan rate of 100
mV s-1
-350
-300
-250
-200
-150
-100
-50
TFA mM
12
10
8
6
4
2
0
0
50
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
+
E/V versus Fc /Fc
Figure 10. Cyclic voltammograms of TFA (0-12 mM) in 0.1 M nBu4NPF6/MeCN at a scan rate of 100
mV s-1
3. Conclusions
Reaction of NPS with Fe3(CO)12 affords 1, [{Fe2(CO)6(µ-PPh2)}2(µ4-S2)] and 2, [Fe3(CO)8(µ3-
2
S)2{kP-PPh2CH2N(CH3)CH2P(=S)Ph2}]. Reaction of NPSe with Fe3(CO)12 offers 3, [{Fe2(CO)6(µ-
2
13

PPh2)}2(µ4-Se2)] and 4, [Fe3(CO)7(µ3-Se)2{k2P,P-(PPh2CH2)2NCH3}]. Electrochemical studies of 2 and
4 have demonstrated that using HOAc or TFA as a proton source 2 and 4 can catalyze H2 production.
4. Experimental section
4.1. General procedures and materials
All reactions were carried out under N2 atmosphere with standard Schlenk techniques. All solvents
employed were dried by refluxing over appropriate drying agents and stored under N2 atmosphere.
(Ph2PCH2)2NCH3), namely NP2, was prepared according to the literature method [15]. The progress of
1
all reactions was monitored by TLC. H NMR, 13C NMR and 31P NMR measurements were carried out
on an Aglient 400 (1H N NMR, 13C NMR) and Bruker Avance 600 spectrometer (31P NMR). IR spectra
were recorded on a BrukerTensor 27 spectrometer as KBr disks in the range 400-4000 cm-1.
Electrochemical measurements were made using a CHI660E potentiostat. Gas chromatography (GC)
analysis of H2 was conducted with a Shimadzu GC-8A equipped with a thermal conductivity detector.
Analyses for C, H and N were performed on an Elementar Vario EL analyzer. Melting points were
measured on an X-4B apparatus and uncorrected.
4.2. Syntheses
4.2.1 Syntheses of NPE
2
To a stirred solution of NP2 (8.549 g, 20 mmol) in CH2Cl2 (50 mL) was added S (1.346 g, 42 mmol).
The reaction mixture was stirred for 3 h at room temperature, then the solvent was removed under
reduced pressure, and the residue was recrystallized by acetonitrile to give a powdery solid dried under
vacuum (8.14 g, yield 82.9%, mp, 117.3-118.4 ˚C). Anal. Calcd. for C27H27NP2S2 (%): C, 65.97; H,
5.54; N, 2.85. Found: C, 66.13; H, 5.64; N, 2.71. IR (KBr disk): 3050 (m), 2943 (m), 2823 (w), 2776
(m), 1583 (w), 1478 (m), 1434 (s), 1309 (m), 1230 (w), 1180 (w), 1089 (s), 1039 (m), 996 (w), 855 (s),
1
740 (s), 704 (vs), 609 (s), 522 (s), 479 (m), 438 (w) cm-1. H NMR (400 MHz, CDCl3, TMS): δ 7.883-
7.834, 7.484-7.448, 7.420-7.377 (m, m, m, 8H, 4H, 8H, 4C6H5), 4.118 (s, 4H, 2CH2), 2.548 (s, 3H,
NCH3) ppm. 13C NMR (100 MHz, CDCl3, TMS): δ 132.30, 131.62, 131.58, 131.53, 131.50, 131.46,
14

2
128.57, 128.55, 128.49, 128.43 (4C6H5), 61.82, 61.77, 61.19, 61.14 (d, d, J = 5.0 Hz, 2CH2), 46.29
(NCH3) ppm. 31P NMR (243 MHz, CDCl3, 85% H3PO4): 35.030 (s) ppm.
To a stirred solution of NP2 (8.549 g, 20 mmol) in CH2Cl2 (50 mL) was added Se (3.316 g, 42 mmol).
The reaction mixture was stirred for 3 h at room temperature. After the solvent was removed in vacuo,
the resulting residue was recrystallized by acetonitrile to afford a powdery solid that was dried under
vacuum (8.65 g, yield 73.9%, mp, 86.7-87.4 ˚C). Anal. Calcd. for C27H27NP2Se2 (%): C, 55.40; H, 4.65;
N, 2.39. Found: C, 55.53; H, 4.52; N, 2.31. IR (KBr disk): 3048 (m), 2929 (m), 2786 (m), 1581 (w),
1479 (m), 1434 (s), 1309 (m), 1182 (w), 1096 (s), 1030 (m), 996 (w), 854 (s), 740 (s), 691 (vs), 530 (vs),
473 (m), 426 (w) cm-1. 1H NMR (400 MHz, CDCl3, TMS): δ 7.879-7.830, 7.481-7.388 (m, m, 8H, 12H,
4C6H5), 4.329 (s, 4H, 2CH2), 2.458 (s, 3H, NCH3) ppm. 13C NMR (100 MHz, CDCl3, TMS): δ 132.22,
132.18, 132.13, 132.08, 132.03, 131.57, 131.00, 130.33, 128.66, 128.62, 128.56, 128.50, 128.46
2
31
(4C6H5), 61.54, 61.52, 61.00, 60.98 (d, d, J = 2.0 Hz, 2CH2), 45.63 (CH3) ppm. P NMR (243 MHz,
CDCl3, 85% H3PO4): 24.156 (s) ppm.
4.2.2 Syntheses of 1 and 2
NPS (0.982 g, 2 mmol) and Fe3(CO)12 (1.007 g, 2 mmol) were added to 30 mL of THF. The solution
2
slowly turned to dark brown. After 12 h stirring at room temperature, volatile components were removed
in vacuo. The crude product was purified by TLC (silica gel, petroleum ether/ethyl acetate, v/v, 10:1),
the one orange-yellow band and the other dark-brown band in the decreasing order of Rf values offering
1 and 2 in respective yield of 12.1% and 23.0%. For 1, mp, 93.4-95.1 °C. Anal. Calcd. for
C36H20Fe4O12P2S2 (%, 1): C, 43.50; H, 2.03. Found: C, 43.74; H, 1.95. IR (KBr disk): 3057 (w), 2922
(m), 2852 (w), 2055 (s), 2031 (vs), 2006 (vs), 1969 (vs), 1573 (w), 1546 (w), 1476 (w), 1433 (m), 1130
1
(w), 1091 (w), 1040 (w), 1019 (w), 995 (w), 747 (w), 694 (m), 592 (m), 560 (m), 514 (w) cm−1. H
NMR (400 MHz, CDCl3, TMS): δ 7.743-7.137 (m, 20H, 4C6H5) ppm. 13C NMR (100 MHz, CDCl3,
TMS): δ 210.31 (12CO), 134.08, 134.00, 133.32, 133.23, 130.42, 130.39, 130.09, 128.66, 128.56,
31
128.17, 128.07 (4C6H5) ppm. P NMR (243 MHz, CDCl3, 85% H3PO4): 133.381 (s) ppm. For 2, mp,
120.9-122.4 °C. Anal. Calcd. for C35H27Fe3NO8P2S3 (%, 2): C, 45.93; H, 2.97; N, 1.53. Found: C,
15

46.12; H, 2.84; N, 1.63. IR (KBr disk): 3056 (w), 2924 (w), 2853 (w), 2070 (s), 2029 (vs), 2003 (vs),
1979 (vs), 1569 (w), 1481 (w), 1433 (m), 1322 (w), 1307 (w), 1165 (w), 1096 (m), 1050 (w), 996 (w),
1
859 (w), 831 (w), 749 (w), 725 (w), 693 (m), 572 (m), 509 (w), 479 (w) cm-1. H NMR (400 MHz,
CDCl3, TMS): δ 7.789-7.739, 7.500-7.397 (m, m, 4H, 16H, 4C6H5), 4.498, 4.332, 3.899, 3.797 (s, s, s, s,
2H, 2H, 2CH2), 2.252, 2.075 (s, s, 3H, NCH3) ppm. 13C NMR (100 MHz, CDCl3, TMS): δ 210.26
(8CO), 133.24, 133.19, 133.16, 133.02, 132.88, 132.82, 132.31, 131.52, 131.49, 131.15, 131.05, 130.80,
128.83, 128.73, 128.62, 128.54, 128.45 (4C6H5), 61.17, 60.74, 58.96, 58.58 (d, d, J = 43.0 Hz, J = 38.0
Hz, 2CH2), 44.17 (NCH3) ppm. 31P NMR (243 MHz, CDCl3, 85% H3PO4): 58.581, 58.537, 32.147,
32.102 (d, d, J = 10.7 Hz, J = 10.9 Hz, FeP, P=S) ppm.
4.2.3 Syntheses of 3 and 4
NPSe2 (1.170 g, 2 mmol) and Fe3(CO)12 (1.007 g, 2 mmol) were added to 30 mL of THF. The solution
slowly turned to dark brown. After 12 h stirring at room temperature, volatile components were removed
in vacuo. The crude product was purified by TLC (silica gel, petroleum ether/ethyl acetate, v/v, 20:1),
the one orange-yellow band and the other dark-brown band in the decreasing order of Rf values offering
3 and 4 in respective yield of 14.6% and 19.5%. For 3, mp, 147.5-149.2 °C. Anal. Calcd. for
C36H20Fe4O12P2Se2 (%, 3): C, 39.75; H, 1.85. Found: C, 39.87; H, 1.79. IR (KBr disk): 3059 (w), 2920
(w), 2852 (w), 2029 (vs), 2003 (vs), 1967 (vs), 1570 (w), 1475 (m), 1432 (w), 1366 (w), 1183 (w), 1089
1
(w), 997 (w), 746 (m), 694 (m), 594 (m), 562 (s), 517 (m), 445 (w) cm−1. H NMR (400 MHz, CDCl3,
13
TMS): δ 7.595-7.586, 7.369, 7.173-7.159 (m, s, m, 5H, 10H, 5H, 4C6H5) ppm. C NMR (100 MHz,
CDCl3, TMS): δ 210.46 (12CO), 133.79, 133.75, 133.71, 133.09, 133.05, 133.00, 130.39, 130.38,
130.15, 128.68, 128.62, 128.58, 127.96, 127.91, 127.86 (4C6H5) ppm. 31P NMR (243 MHz, CDCl3,
85% H3PO4): 140.214 (s) ppm. For 4, mp, 212.3-213.5 °C. Anal. Calcd. for C34H27Fe3NO7P2Se2 (%, 4):
C, 43.03; H, 2.87; N, 1.48. Found: C, 43.25; H, 2.76; N, 1.56. IR (KBr disk): 3053 (w), 2944 (w), 2826
(w), 2048 (vs), 2009 (vs), 1979 (vs), 1920 (vs), 1570 (w), 1480 (w), 1433 (m), 1365 (w), 1307 (w), 1187
1
(w), 1090 (w), 877 (w), 846 (w), 732 (m), 692 (m), 573 (m), 504 (m), 476 (w), 440 (w) cm-1. H NMR
(400 MHz, CDCl3, TMS): δ 7.700, 7.577, 7.421 (s, s, s, 5H, 5H, 10H, 4C6H5), 3.529, 2.681, 2.657 (s, d,
16

13
J = 9.6 Hz, 2H, 2H, 2CH2), 2.481 (s, 3H, NCH3) ppm. C NMR (100 MHz, CDCl3, TMS): δ 210.40
(7CO), 135.23, 135.20, 135.03, 135.01, 134.99, 134.76, 133.73, 132.95, 130.22, 129.92, 128.51, 128.47,
128.42, 128.02, 127.98, 127.94 (4C6H5), 60.81, 60.61, 60.41, 51.26, 51.13, 51.01 (t, t, J = 20.0 Hz, J =
12.0 Hz, 2CH2), 53.40 (NCH3) ppm. 31P NMR (243 MHz, CDCl3, 85% H3PO4): 43.623 (s) ppm.
4.3. X-ray Structure Determinations of Compounds
Single crystals of NPS , NPSe and 1-4 suitable for X-ray diffraction analyses were grown by slow
2
2
evaporation of the CH2Cl2-petroleum ether solutions of NPS , NPSe and 1-4 at 0-4 °C. For each
2
2
compound, a selected single crystal was mounted on a Bruker D8quest CCD diffractometer using
graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å) at 295 K. The structures of NPS , NPSe and
2
2
1-4 were solved by direct methods using the SIR-2011 software and refined by full-matrix least-squares
based on F2 with anisotropic thermal parameters for all non-hydrogen using the SHELXTL program
package [31]. All H atoms were placed at geometrically idealized positions and subsequently treated as
riding atoms, with C-H = 0.93 (aromatic), 0.97 (CH2) and 0.96 (CH3) Å and Uiso(H) values of 1.2Ueq(C)
and 1.5Ueq(CMethyl). PLATON views of compounds are drawn using the PLATON software [32].
4.4. Electrochemistry of 2 and 4
Cyclic voltammetry experiments were carried out in a ca 5-mL one-compartment glass cell. The
working electrode was a glassy carbon disk (0.3 cm in diameter), the reference electrode an Ag/AgNO3
(0.01M AgNO3/0.1 M nBu4NPF6 in MeCN) electrode and the counter electrode a Pt wire. The potentials
(E) at the working electrode in all CV’s are reported with respect to the Fc+/Fc couple in electrolyte
solution. The Fc+/Fc coupling data were collected at the end of each experiment. All CV’s reported are
background-corrected, i.e. the scan with only electrolyte present was subtracted from the raw data. The
electrolyte was 0.1 M nBu4NPF6 in MeCN or CH2Cl2. The potentials (E) at the working electrode in all
CV’s are reported with respect to the Fc+/Fc couple in electrolyte solution. The Fc+/Fc coupling data
were collected at the end of each experiment. All CV’s reported are background-corrected, i.e. the scan
with only electrolyte present was subtracted from the raw data. All background scans confirmed
sufficient removal of O2 as seen by the absence of a reduction peak at ca. -1.2 V. CV data were collected
17

under flow of N2 gas. The electrolyte solution was degassed by bubbling with N2 for at least 10 min
before measurement. The typical concentration of the organometallic complex was 1 mM. The acid
concentration in the electrolyte was varied by addition of measured volumes of a solution of HOAc or
TFA in MeCN or CH2Cl2.
Acknowledgments
We are grateful to the Mao Zedong Foundation of China, Project Funded by the Priority Academic
Program Development of Jiangsu Higher Education Institutions (PAPD), Postgraduate Research &
Practice Innovation Program of Jiangsu Province (No. KYLX15_1356), Natural Science Foundation of
China (No. 21472161, No. 20572091) and Natural Science Foundation of Jiangsu Province (No.
05KJB150151) for financial support of this work.
Appendix A. Supplementary data
CCDC 1818822 (NPS ), 1818823 (NPSe ), 1818824 (1), 1818825 (2), 1818826 (3) and 1818827 (4)
2
2
contain the supplementary crystallographic data (including structure factors) for this paper. These data
can be obtained free of charge from the Cambridge Crystallographic Data Centre.
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Table 1. Crystal data and structure refinements for NPS and NPSe
2
2
NPS
NPSe
2
2
Formula
Fw
C27H27NP2S2
491.56
C27H27NP2Se2
585.36
Cryst system
Monoclinic
P21/c
Monoclinic
P21/c
Space group
a/Å
b/Å
c/Å
α/°
15.403(3)
7.8737(16)
21.459(5)
90.00
15.621(4)
7.8262(16)
21.794(5)
90.00
β/°
102.866(7)
90.00
102.640(7)
90.00
γ/°
22

V/Å3
2537.2(9)
4
2599.8(10)
4
Z
Dc/gcm-3
μ/mm-1
F(000)
Index ranges
1.287
1.495
0.352
2.983
1032
1176
-19≤h≤20
-10≤k≤8
-25≤l≤27
24672
-20≤h≤20
-9≤k≤10
-28≤l≤27
28127
Reflections measured
Unique reflections
Reflections (I>2σ(I))
Rint
5811
6109
3203
3567
0.081
0.090
θ Range/º
1.4-27.6
5811/0/290
0.0549/0.0991
0.1346/0.1199
0.99
2.1-27.9
6109/0/290
0.0515/0.1193
0.1130/0.1436
0.93
Data/restraints/parameters
R1/wR2 (I>2σ(I))
R1/wR2 (all data)
GOF
Largest diff peak and hole/e Ǻ-3
0.24/-0.24
0.79/-0.86
Table 2. Crystal data and structure refinements for 1-4
1
2
3
4
Formula
Fw
C36H20Fe4O12P2S2
C35H27Fe3NO8P2S3
C36H20Fe4O12P2Se2∙2(CH2Cl2)
C34H27Fe3NO7P2Se2∙2(CH2Cl2)
993.98
915.25
1257.63
1118.83
23

Cryst system
Triclinic
P-1
Triclinic
P-1
Monoclinic
P21/c
Orthorhombic
Pnma
Space group
a/Å
b/Å
c/Å
α/°
β/°
10.209(4)
10.612(4)
11.452(4)
102.236(13)
102.759(12)
118.027(12)
993.7(7)
1
9.579(3)
12.108(3)
18.665(5)
102.816(9)
99.150(11)
107.273(10)
1956.0(10)
2
15.512(3)
10.0336(16)
17.148(4)
90.00
23.401(3)
21.583(2)
8.7346(8)
90.00
116.440(6)
90.00
90.00
γ/°
90.00
V/Å3
Z
2389.8(8)
2
4411.5(8)
4
Dc/gcm-3
μ/mm-1
1.661
1.554
1.748
1.685
1.677
1.389
3.059
2.983
F(000)
498
928
1236
2216
Index ranges
-12≤h≤12
-13≤k≤13
-14≤l≤14
11613
-12≤h≤12
-15≤k≤15
-23≤l≤24
27232
-19≤h≤20
-12≤k≤13
-22≤l≤21
25366
-30≤h≤29
-28≤k≤26
-11≤l≤11
49783
Reflections measured
Unique reflections
Reflections (I>2σ(I))
Rint
3766
8586
5487
5211
2013
4248
3714
3716
0.101
0.112
0.081
0.065
θ Range/º
2.4-26.0
3766/0/253
0.0596/0.1664
0.1689/0.2425
1.04
2.3-27.6
8586/0/470
0.1337/0.1318
0.2324/0.1515
1.14
1.4-27.6
5487/0/280
0.0671/0.1795
0.1024/0.2075
1.01
2.0-27.5
5211/0/265
0.0426/0.1157
0.0739/0.1307
1.00
Data/restraints/parameters
R1/wR2 (I>2σ(I))
R1/wR2 (all data)
GOF
Largest diff peak and hole/e Ǻ-3
1.01/-1.26
0.44/-0.57
1.34/-1.23
0.78/-0.66
24

Table 3. Selected bond lengths and angles (Å, °) for NPS and NPSe
2
2
NPS
NPSe
2
2
C1-P1
1.813(3)
C1-P1
1.809(4)
C13-N1
P1-S1
1.463(3)
C13-N1
1.461(5)
1.9489(10)
105.30(11)
112.23(9)
117.00(16)
P1-Se1
2.1059(11)
105.78(17)
111.78(14)
116.9(3)
C7-P1-C1
C1-P1-S1
N1-C13-P1
C7-P1-C1
C1-P1-Se1
N1-C13-P1
Table 4. Selected bond lengths and angles (Å, °) for 1-4
1
2
3
4
C1-Fe1
C7-P1
Fe1-P1
Fe1-S1
Fe1-Fe2
Fe2-S1
Fe2-P1
S1-S1i
1.774(11)
1.817(7)
2.228(2)
2.244(2)
2.5972(18)
2.234(2)
2.238(2)
2.110(4)
Fe1-S1
Fe1-S2
Fe1-P1
Fe1-Fe3
Fe2-S1
Fe2-S2
Fe2-Fe3
Fe3-S1
Fe3-S2
P2-S3
2.236(2)
2.212(2)
2.256(2)
2.6803(14)
2.248(2)
2.242(2)
2.5569(14)
2.253(2)
2.258(2)
1.955(2)
C1-Fe1
C7-P1
1.790(8)
C1-Fe1
C5-Fe3
C6-P1
1.712(6)
1.815(6)
1.794(6)
Fe1-P1
Fe1-Se1
Fe1-Fe2
Fe2-P1
Fe2-Se1
Se1-Se1i
2.2257(16)
2.3686(10)
2.5799(11)
2.2114(16)
2.3762(11)
2.4103(11)
1.826(4)
Fe1-P1
Fe1-Se1
Fe1-Fe3
Fe2-Se1
Fe2-Fe3
Fe3-Se1
2.2275(11)
2.3379(7)
2.8121(10)
2.3708(8)
2.5827(11)
2.3713(7)
P1-Fe1-S1
P1-Fe1-Fe2
S1-Fe1-Fe2
S1-Fe2-P1
S1-Fe2-Fe1
P1-Fe2-Fe1
Fe1-P1-Fe2
S1i-S1-Fe2
76.52(8)
54.60(6)
54.37(6)
76.54(8)
54.74(6)
54.28(6)
71.12(7)
110.13(13)
P1-Fe1-Se1
P1-Fe1-Fe2
Se1-Fe1-Fe2
P1-Fe2-Se1
P1-Fe2-Fe1
Se1-Fe2-Fe1
Fe2-P1-Fe1
Fe1-Se1-Fe2
77.24(5)
54.19(4)
57.20(3)
77.35(5)
54.71(4)
56.92(3)
71.10(5)
65.88(3)
P1-Fe1-Se1
P1-Fe1-Fe3
91.94(3)
113.12(3)
53.88(2)
57.01(2)
82.50(3)
98.28(2)
Fe2-Fe3-Fe1
Fe1-S1-Fe2
Fe1-S2-Fe2
S1-Fe1-S2
S2-Fe3-S1
80.11(4)
97.52(7)
98.41(7)
80.79(7)
79.41(7)
Se1-Fe1-Fe3
Se1-Fe2-Fe3
Fe2-Fe3-Fe1
Fe1-Se1-Fe2
25

S1i-S1-Fe1
Fe2-S1-Fe1
110.23(13)
70.89(7)
S1-Fe2-S2
79.88(7)
Fe1-Se1-Se1i
Fe2-Se1-Se1i
108.99(4)
108.55(4)
Fe1-Se1-Fe3
Fe2-Se1-Fe3
73.33(2)
66.00(3)
P1-Fe1-Fe3
115.25(6)
26

.Reaction of (Ph2P(=S)CH2)2NCH3 with Fe3(CO)12 forms Fe/S clusters
.Reaction of (Ph2P(=Se)CH2)2NCH3 with Fe3(CO)12 provides Fe/Se clusters
.Clusters have been characterized by spectroscopy and cyclic voltammetry
27

Ph
(OC)3Fe
Ph
P
S
S
S
CO
N
CH3
Fe
(OC)3Fe
P
Ph2
[Ph2P(=E)CH2]2NCH3
- [Ph2PFe2(CO)6]2E2
OC
Fe3(CO)12
(OC)3Fe
Se
Ph2
P
Se
Fe
N
(OC)3Fe
CH3
P
OC
Ph2