Synthesis, characterization and electrocatalytic H2 production of phosphine-substituted CpFe complexes

Article abstract of DOI:10.1016/j.poly.2018.06.009

Reaction of Ph₂P(Se)CSNHPh with Cp₂Fe₂(CO)₄ in refluxing toluene affords complexes CpFe(CO)(k²P,S-Ph₂PC(S)[dbnd]NPh) (1) and CpFe(CO)₂(kP-P([dbnd]Se)Ph₂) (2). Further, reactions of 2 with 1 equiv of PPh₂R in the presence of Me₃NO generate complexes CpFe(CO)(kSe-SeP([dbnd]Se)Ph₂)(L) (3, L = PPh₃; 4, L = PPh₂Py). Unlike 2, reactions of CpFe(CO)₂(kP-P([dbnd]S)Ph₂) with PPh₂R under the same conditions give the corresponding phosphine-substituted complexes CpFe(CO)(kP-P([dbnd]S)Ph₂)(L) (5, L = PPh₃; 6, L = PPh₂Py). All the new compounds have been characterized by elemental analyses, IR, ¹H NMR, ¹³C NMR and ³¹P NMR spectroscopy and structurally determined by X-ray crystallography. Electrochemical studies indicate that using HOAc or TFA as a proton source complexes 1–6 can catalyze H₂ evolution.

Full text of DOI:10.1016/j.poly.2018.06.009

Polyhedron 152 (2018) 94–101
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, characterization and electrocatalytic H2 production of
phosphine-substituted CpFe complexes
Jin-Ping Li a, Su-Ping Luo b, Shu-Zhong Zhan b, Yao-Cheng Shi a,
⇑
a College of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, China
b College of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China
a r t i c l e i n f o
a b s t r a c t
Reaction of Ph2P(Se)CSNHPh with Cp2Fe2(CO)4 in refluxing toluene affords complexes CpFe(CO)(k2P,S-
Ph2PC(S)@NPh) (1) and CpFe(CO)2(kP-P(@Se)Ph2) (2). Further, reactions of 2 with 1 equiv of PPh2R in
the presence of Me3NO generate complexes CpFe(CO)(kSe-SeP(@Se)Ph2)(L) (3, L = PPh3; 4, L = PPh2Py).
Unlike 2, reactions of CpFe(CO)2(kP-P(@S)Ph2) with PPh2R under the same conditions give the corre-
sponding phosphine-substituted complexes CpFe(CO)(kP-P(@S)Ph2)(L) (5, L = PPh3; 6, L = PPh2Py). All
the new compounds have been characterized by elemental analyses, IR, 1H NMR, 13C NMR and 31P
NMR spectroscopy and structurally determined by X-ray crystallography. Electrochemical studies indi-
cate that using HOAc or TFA as a proton source complexes 1–6 can catalyze H2 evolution.
Ó 2018 Published by Elsevier Ltd.
Article history:
Received 13 March 2018
Accepted 5 June 2018
Available online 12 June 2018
Keywords:
CpFe complex
Iron carbonyl
Phosphine substitution
Cyclic voltammetry
H2 production
1. Introduction
2. Experimental
Nowadays the development of renewable energy is 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 enzymes called hydrogenases. To date, three classes of
hydrogenases, namely, the [FeFe]-, [FeNi]-, and [Fe]-hydrogenases,
have been reported. The X-ray crystallographic structure determi-
nations of the enzymes have revealed their active sites and allowed
the mechanistic understanding of the catalytic process. Inspired by
these insights, many FeFe and FeNi model complexes of the hydro-
genase active sites have been synthesized [1–4]. However, because
of the [Fe]-hydrogenase being a recent discovery, only a few small
molecule mimics of [Fe]-hydrogenase have been reported [5–8]. In
view of this reason, we have initiated a project for mimicking the
[Fe]-hydrogenase [9]. As part of this ongoing work, herein we
report syntheses and electrocatalytic H2 production of CpFe
complexes (Scheme 1).
2.1. Materials and methods
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. Ph2PCSNHPh [10], Cp2Fe2(CO)4 [11] and CpFe(CO)2
(kP-P(@S)Ph2) [12] were prepared according to literature methods.
The progress of all reactions was monitored by TLC. 1H NMR, 13C
NMR measurements were carried out on an Aglient 400 and 31P
NMR with the Bruker Avance 600 spectrometer. IR spectra were
recorded on a BrukerTensor 27 spectrometer as KBr disks in the
range 400–4000 cmÀ1. Electrochemical measurements were made
using a CHI660E potentiostat. Controlled potential coulometry
experiments on 0.5 mM 1 (2) in 0.1 M nBu4NPF6/CH3CN in the pres-
ence of 25 mM HOAc or TFA were conducted to confirm the cat-
alytic production of hydrogen. Gas chromatography (GC) analysis
of H2 was conducted with an Agilent Technologies 7890A 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.
2.2. Syntheses
2.2.1. Syntheses of 1and 2
⇑
To a stirred solution of Ph2PCSNHPh (6.428 g, 20 mmol) in
CH2Cl2 (50 mL) was added elemental Se (1.896 g, 24 mmol). The
Corresponding author.
E-mail address: ycshi@yzu.edu.cn (Y.-C. Shi).
https://doi.org/10.1016/j.poly.2018.06.009
0277-5387/Ó 2018 Published by Elsevier Ltd.

J.-P. Li et al. / Polyhedron 152 (2018) 94–101
95
Scheme 1. Syntheses of complexes 1–6.
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 that was dried
under vacuum (6.165 g, yield 77%; mp, 98.7–100.4 °C). Anal. Calcd.
for C19H16NPSSe (%): C, 57.00; H, 4.03; N, 3.50. Found: C, 56.87; H,
4.12; N, 3.62. IR (KBr disk): 3150 (m), 3104 (w), 2997 (w), 2957
(w), 1593 (m), 1537 (s), 1485 (m), 1436 (m), 1384 (s), 1311 (w),
1180 (m), 1090 (m), 975 (w), 899 (w), 801 (w), 751 (s), 685 (s),
128.43, 127.96, 127.85 (2C6H5), 89.20 (C5H5) ppm. 31P NMR
(243 MHz, CDCl3, 85% H3PO4): d 75.89 (s) ppm.
2.2.2. Synthesis of 3
The solution of 0.441 g (1 mmol) 2 and 0.262 g (1 mmol) PPh3 in
30 mL of THF in the presence of 0.111 g (1 mmol) Me3NOÁ2H2O was
stirred for 3 h at room temperature. After the solvent was removed
under reduced pressure, the residue was subjected to TLC separa-
tion. Elution with petroleum ether/ethyl acetate (v/v, 4:1) afforded
one orange-red band of 3 in yield of 18% (0.136 g). For 3, mp, 164.8–
165.6 °C. Anal. Calcd. for C36H30FeOP2Se2 (%, 3): C, 57.32; H, 4.01.
Found: C, 57.24; H, 4.17. IR (KBr disk): 3052 (w), 1933 (s), 1639
(s), 1464 (m), 1430 (m), 1377 (w), 1269 (w), 1180 (w), 1090 (m),
1023 (w), 993 (w), 890 (w), 826 (m), 745 (s), 691 (vs), 624 (w),
550 (s), 496 (m), 429 (w) cmÀ1 1H NMR (400 MHz, CDCl3, TMS):
.
d 12.01 (d, J = 7.6 Hz, 1H, NH), 8.10, 8.02–7.97, 7.55, 7.49–7.42,
7.31 (d, J = 8.0 Hz, 2H, m, 4H, t, J = 7.6 Hz, 2H, m, 6H, t, J = 7.6 Hz,
1H, 3C6H5) ppm. 13C NMR (100 MHz, CDCl3, TMS): d 186.72,
186.14 (C@S), 138.64, 138.51, 133.36, 133.26, 132.25, 132.22,
130.02, 129.21, 129.05, 128.42, 128.29, 127.59, 121.02 (3C6H5)
ppm. 31P NMR (243 MHz, CDCl3, 85% H3PO4): d 45.44 (s) ppm.
Ph2P(Se)CSNHPh (1.201 g, 3 mmol) and Cp2Fe2(CO)4 (0.708 g, 2
mmol) were added to 15 mL of toluene. The solution was refluxed
for 12 h, volatile components were removed in vacuo. The crude
product was purified by TLC (silica gel, petroleum ether/ethyl acet-
ate, v/v, 4:1), two orange-yellow bands in the decreasing order of Rf
values offering 1 and 2 in respective yield of 23% (0.324 g) and 26%
(0.344 g). For 1, mp, 161.5–162.7 °C. Anal. Calcd. for C25H20FeNOPS
(%, 1): C, 63.98; H, 4.30; N, 2.98. Found: C, 63.84; H, 4.21; N, 3.13. IR
(KBr disk): 3070 (w), 1944 (vs), 1547 (s), 1478 (m), 1430 (m), 1308
(w), 1242 (w), 1194 (w), 1099 (m), 997 (w), 924 (m), 826 (m), 745
596 (m), 557 (s), 508 (s), 446 (w) cmÀ1 1H NMR (400 MHz, CDCl3,
.
TMS): d 8.32, 7.75–7.70, 7.60–7.55, 7.50–7.45, 7.34, 7.17, 6.88,
6.77 (t, J = 9.6 Hz, 2H, m, 5H, m, 2H, m, 8H, t, J = 6.8 Hz, 2H, t,
J = 6.8 Hz, 2H, t, J = 6.4 Hz, 1H, t, J = 7.2 Hz, 2H, 5C6H5), 4.44 (s, 5H,
C5H5) ppm. 13C NMR (100 MHz, CDCl3, TMS): d 220.91, 220.77,
220.61, 218.37 (CO), 147.57, 147.21, 141.08, 140.74, 134.72,
134.27, 133.85, 133.75, 132.69, 132.59, 132.10, 131.60, 131.57,
131.33, 130.96, 130.88, 130.86, 130.78, 129.91, 129.89, 128.59,
128.47, 128.01, 127.98, 127.82, 127.72, 127.26, 127.16, 127.05,
126.90, 126.87 (5C6H5), 89.14 (C5H5) ppm. 31P NMR (243 MHz,
CDCl3, 85% H3PO4): d 76.61 (s), 53.06 (s) ppm.
(m), 694 (s), 638 (w), 568 (m), 522 (m), 476 (w), 442 (w) cmÀ1 1H
.
NMR (400 MHz, CDCl3, TMS): d 8.00–7.96, 7.58–7.44, 7.37–7.31,
7.09 (m, 2H, m, 8H, m, 4H, t, J = 6.8 Hz, 1H, 3C6H5), 4.50 (s, 5H,
C5H5) ppm. 13C NMR (100 MHz, CDCl3, TMS): d 218.97, 218.70
(CO), 148.12 (C@N), 136.24, 135.90, 134.00, 133.89, 131.29,
131.26, 130.79, 130.70, 130.21, 130.18, 128.94, 128.84, 128.61,
128.38, 128.28, 124.70, 122.25 (3C6H5), 81.09 (C5H5) ppm. 31P
NMR (243 MHz, CDCl3, 85% H3PO4): d 53.20 (s) ppm. For 2, mp,
184.1–185.4 °C. Anal. Calcd. for C19H15FeO2PSe (%, 2): C, 51.74; H,
3.43. Found: C, 51.59; H, 3.54. IR (KBr disk): 3054 (m), 2026 (vs),
1974 (vs), 1582 (w), 1475 (w), 1428 (m), 1359 (w), 1306 (w),
1272 (w), 1157 (w), 1118 (w), 1081 (m), 1000 (w), 929 (w), 847
2.2.3. Synthesis of 4
The solution of 0.441 g (1 mmol) 2 and 0.263 g (1 mmol) PPh2Py
in 30 mL of THF in the presence of 0.111 g (1 mmol) Me3NOÁ2H2O
was stirred for 3 h at room temperature. After the solvent was
removed in vacuo, the residue was subjected to TLC separation.
Elution with petroleum ether/ethyl acetate (v/v, 4:1) afforded
one orange-red band of 4 in yield of 17% (0.128 g). For 4, mp,
166.3–167.7 °C. Anal. Calcd. for C35H29FeNOP2Se2 (%, 4): C, 55.65;
H, 3.87; N, 1.85. Found: C, 55.59; H, 3.77; N, 1.95. IR (KBr disk):
3052 (w), 1935 (s), 1571 (s), 1460 (s), 1378 (w), 1284 (vs), 1126
(m), 1074 (m), 1021 (w), 962 (w), 802 (w), 744 (m), 694 (s), 624
(m), 749 (m), 693 (s), 621 (m), 574 (s), 508 (m), 421 (w) cmÀ1
.
(w), 596 (w), 562 (m), 511 (m) cmÀ1 1H NMR (400 MHz, CDCl3,
.
1H NMR (400 MHz, CDCl3, TMS): d 7.92–7.87, 7.37–7.33 (m, 4H,
m, 6H, 2C6H5), 4.93 (s, 5H, C5H5) ppm. 13C NMR (100 MHz, CDCl3,
TMS): d 212.41, 212.18 (2CO), 143.19, 142.75, 137.19, 137.08,
133.79, 133.60, 130.95, 130.84, 129.50, 129.48, 128.68, 128.50,
TMS): d 8.38, 8.23, 7.73, 7.57, 7.37–7.30, 7.23–7.13, 6.89, 6.78
(d, J = 4.0 Hz, 1H, t, J = 9.6 Hz, 2H, t, J = 8.4 Hz, 2H, t, J = 8.8 Hz,
4H, m, 7H, m, 4H, s, 1H, t, J = 6.8 Hz, 1H, t, J = 7.2 Hz, 2H, 4C6H5,
2-C5H4N), 4.52 (s, 5H, C5H5) ppm. 13C NMR (100 MHz, CDCl3,

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J.-P. Li et al. / Polyhedron 152 (2018) 94–101
TMS): d 220.93, 220.64, 220.34 (CO), 158.36, 149.56, 147.80 (d, J =
69.0 Hz, d, J = 17.0 Hz, d, J = 37.0 Hz, C@N), 142.22, 141.89, 135.30,
134.86, 134.79, 134.73, 134.16, 134.07, 133.89, 133.80, 133.34,
132.92, 132.80, 131.13, 131.03, 130.95, 130.85, 130.12, 130.10,
129.93, 129.90, 128.82, 128.64, 128.17, 128.07, 127.95, 127.93,
127.82, 127.72, 127.29, 127.19, 127.08, 126.98, 126.95, 126.92,
123.44, 123.42 (4C6H5, 2-C5H4N), 88.92 (C5H5) ppm. 31P NMR
(243 MHz, CDCl3, 85% H3PO4): d 75.98 (s), 52.99 (s) ppm.
1.2Ueq(C). PLATON views of compounds are drawn using the
PLATON software [14].
2.4. Electrochemistry of 1–6
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 (0.01 M AgNO3/0.1 M nBu4NPF6 in MeCN) electrode and
the counter electrode a Pt wire. The electrolyte was 0.1 M nBu4NPF6
in MeCN. 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 experi-
ment. All CV’s reported are background-corrected, i.e. the scan with
only electrolyte present was subtracted from the raw data. All back-
ground scans confirmed sufficient removal of O2 as seen by the
absence of a reduction peak at ca. À1.2 V. CV data were collected
under flow of N2 gas. The electrolyte solution was degassed by bub-
bling 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.
2.2.4. Synthesis of 5
The solution of 0.394 g (1 mmol) CpFe(CO)2(kP-P(@S)Ph2) and
0.262 g (1 mmol) PPh3 in 30 mL of THF in the presence of 0.111 g
(1 mmol) Me3NOÁ2H2O was stirred for 3 h at room temperature.
After the solvent was removed under vacuum, the residue was sub-
jected to TLC separation. Elution with petroleum ether/ethyl acet-
ate (v/v, 4:1) afforded one orange-red band of 5 in yield of 24%
(0.151 g). For 5, mp, 173.4–174.7 °C. Anal. Calcd. for C36H30FeOP2S
(%, 5): C, 68.80; H, 4.81. Found: C, 68.63; H, 4.68. IR (KBr disk):
3051 (w), 1929 (vs), 1657 (w), 1578 (vs), 1466 (m), 1430 (w),
1374 (w), 1284 (s), 1127 (w), 1077 (m), 996 (w), 850 (w), 829
(w), 741 (m), 692 (s), 625 (w), 596 (m), 559 (m), 515 (m), 478
(w), 416 (w) cmÀ1 1H NMR (400 MHz, CDCl3, TMS): d 8.00, 7.56–
.
7.45, 7.33, 7.10 (s, 2H, m, 10H, s, 12H, t, J = 6.0 Hz, 1H, 5C6H5),
4.50 (s, 5H, C5H5) ppm. 13C NMR (100 MHz, CDCl3, TMS): d
219.00, 218.73 (CO), 137.17, 137.12, 137.10, 134.04, 133.93,
133.82, 133.65, 133.64, 131.35, 130.80, 130.71, 130.26, 128.99,
128.89, 128.71, 128.65, 128.49, 128.43, 128.33, 124.75, 122.28
(5C6H5), 81.14 (C5H5) ppm. 31P NMR (243 MHz, CDCl3, 85%
H3PO4): d 76.12 (s), 73.95 (s) ppm.
3. Results and discussion
3.1. Syntheses
The reaction of Ph2P(Se)CSNHPh, generated from the reaction of
Ph2PCSNHPh and elemental selenium in dichloromethane, with
Cp2Fe2(CO)4 in refluxing toluene affords CpFe(CO)(k2P,S-Ph2PC
(S)@NPh) (1) and CpFe(CO)2(kP-P(@Se)Ph2) (2). Further reactions
of 2 with 1 equiv of PPh2R in the presence of Me3NO lead to com-
plexes CpFe(CO)(kSe-SeP(@Se)Ph2)(L) (3, L = PPh3; 4, L = PPh2Py).
Some modified FeCp(CO)2 complexes such as CpFe(CO)2X (X =
SeSO2R, SeCO2R), CpFe(CO)(k2S,E-ECS2Ph) [15], CpFe(CO)(EPh3)
SeCOAr and CpFe(CO)(PPh3)SCO2Ar [16] have been reported by
El-khateeb. Unlike 2, reactions of CpFe(CO)2(kP-P(@S)Ph2) with
PPh2R under the same conditions lead to the corresponding phos-
phine-substituted complexes CpFe(CO)(kP-P(@S)Ph2)(L) (5, L =
PPh3; 6, L = PPh2Py). Also, it should be mentioned that several CpFe
complexes such as CpFe(CO)(PPh3)TePh, CpFe(CO)(PPh3)R [17] and
2.2.5. Synthesis of 6
The solution of 0.394 g (1 mmol) CpFe(CO)2(kP-P(@S)Ph2) and
0.263 g (1 mmol) PPh2Py in 30 mL of THF in the presence of
0.111 g (1 mmol) Me3NOÁ2H2O was stirred for 3 h at room temper-
ature. After the solvent was removed in vacuo, the residue was
subjected to TLC separation. Elution with petroleum ether/ethyl
acetate (v/v, 4:1) afforded one orange-red band of 6 in yield of
21% (0.132 g). For 6, mp, 176.8–178.5 °C. Anal. Calcd. for C35H29
-
FeNOP2S (%, 6): C, 66.78; H, 4.64; N, 2.23. Found: C, 66.59; H,
4.71; N, 2.29. IR (KBr disk): 3054 (m), 1935 (s), 1573 (m), 1461
(vs), 1376 (m), 1282 (vs), 1185 (w), 1126 (m), 1075 (m), 1038
(w), 965 (w), 840 (m), 742 (vs), 697 (vs), 647 (w), 595 (w), 552
[CpFe(PR3)(CO)(BNCAr2)]+[BAr4X À
[18] have been synthesized by
Pasynskii and Niemeyer.
]
(w), 515 (s) cmÀ1 1H NMR (400 MHz, CDCl3, TMS): d 8.72, 7.98,
.
7.55, 7.36, 7.18, 7.08 (s, 2H, s, 2H, s, 4H, s, 12H, s, 2H, s, 2H,
4C6H5, 2-C5H4N), 4.50 (s, 5H, C5H5) ppm. 13C NMR (100 MHz,
CDCl3, TMS): d 219.01, 218.73 (CO), 150.28, 148.50 (d, J = 13.0 Hz,
d, J = 22.0 Hz, C@N), 136.22, 135.87, 135.73, 134.28, 134.08,
134.01, 133.90, 131.33, 131.30, 131.11, 130.79, 130.69, 130.24,
130.21, 129.06, 128.97, 128.87, 128.64, 128.58, 128.40, 128.30,
124.72, 122.25, 122.21 (4C6H5, 2-C5H4N), 81.12 (C5H5) ppm. 31P
NMR (243 MHz, CDCl3, 85% H3PO4): d 76.14 (s), 74.30 (s) ppm.
3.2. X-ray structures
The molecular structures of Ph2P(Se)CSNHPh and 1–3, 5 and 6
shown in Figs. 1–6 were determined by using X-ray diffraction
2.3. X-ray structure determinations
Single crystals of Ph2P(Se)CSNHPh and 1–3, 5 and 6 suitable for
X-ray diffraction analyses were grown by slow evaporation of their
CH2Cl2-petroleum ether solutions at 0–4 °C. For each compound, a
selected single crystal was mounted on a Bruker D8quest CCD
diffractometer using graphite-monochromated Mo-K
a radiation
(k = 0.71073 Å) at 295 K. Their structures 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 [13].
All H atoms attached to C atoms were placed at geometrically
idealized positions and subsequently treated as riding atoms, with
C–H = 0.93 (Phenyl), 0.98 (Cyclopentadienyl) and Uiso(H) values of
Fig. 1. PLATON view of Ph2P(Se)CSNHPh.

J.-P. Li et al. / Polyhedron 152 (2018) 94–101
97
Fig. 4. PLATON view of 3.
Fig. 2. PLATON view of 1.
Fig. 5. PLATON view of 5.
Fig. 3. PLATON view of 2.
methods. Crystal data, selected bond lengths and angles (Å, °) are
listed in Tables 1–2. Complex 1 adopts the geometry of a three-
legged piano-stool, with Cp as the base and the one carbonyl and
the Ph2PC(S)@NPh ligand as the legs. The cyclopentadienyl ring
Fig. 6. PLATON view of 6.
(Cp) ligand is bonded to the Fe atom in an
g
5-fashion with FeAC
bond distances ranging from 2.036(4) to 2.079(3) Å. The Fe-car-
bonyl bond distance of 1.744(3) Å is shorter than those (1.768(4),
1.780(4) Å) of CpFe(CO)2SCO2Et [19]. The deprotonated ligand as
PS donors is coordinated to the Fe atom, with the C7–N1 bond
distance being 1.264(3) Å. The four-membered ring Fe1P1S1C7 is
puckered, with the distance of Fe1 to plane P1S1C7 being 0.4331
(3) Å. The FeAP bond distance is 2.1770(7) Å. The FeAS bond
distance of 2.3124(8) Å is larger than that (2.2675(10) Å) of CpFe
(CO)2SCO2Et [19].
As shown in Figs. 3, 2 also contains the geometry of a three-
legged piano-stool. The Cp ligand in an
5-mode is coordinated
g
to the Fe atom, with FeAC bond distances ranging between 2.087
(4) and 2.107(5) Å. The Fe-carbonyl bond distances are 1.767(4)
and 1.772(4) Å. The SePPh2 ligand as a monoanion is linked to
the Fe atom. The FeAP bond length is 2.2577(10) Å with the PASe
bond distance of 2.1436(9) Å, indicating that the bond is a single
bond [20].

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J.-P. Li et al. / Polyhedron 152 (2018) 94–101
Table 1
Crystal data, data collections and structure refinements for Ph2P(Se)CSNHPh, 1–3 and 5–6.
Ph2P(Se)CSNHPh
19H16NPSSe
1
2
3
5
6
Formula
Fw
C
C25H20FeNOPS
469.30
C19H15FeO2PSe
441.09
C36H30FeOP2Se2
754.31
C36H27FeOP2S
625.43
C35H29FeNOP2S
629.44
400.32
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Orthorhombic
Pbca
11.9718(5)
8.7806(4)
34.2265(16)
90.00
Monoclinic
P21/c
15.0798(10)
10.2845(6)
14.7903(10)
90.00
Monoclinic
P21/n
11.0062(6)
12.1643(5)
13.5707(6)
90.00
Monoclinic
P21/c
18.4204(15)
11.571(1)
18.1814(15)
90.00
Monoclinic
P21/c
10.7723(4)
11.9828(6)
22.9556(11)
90.00
Monoclinic
P21
11.2159(4)
30.0279(11)
11.8440(5)
90.00
a
(°)
b (°)
90.00
90.00
3597.9(3)
8
1.478
105.955(2)
90.00
2205.4(2)
4
1.413
0.868
93.470(2)
90.00
1813.55(15)
4
1.615
2.934
117.515(2)
90.00
3436.9(5)
4
1.458
2.676
93.102(1)
90.00
2958.8(2)
4
1.404
0.717
116.480(1)
90.00
3570.5(2)
4
1.171
0.595
c
(°)
V (Å3)
Z
Dc (gcmÀ3
)
l
(mmÀ1
)
2.290
F(000)
1616
968
880
1512
1292
1304
Index ranges
À15 ꢀ h ꢀ 15
À11 ꢀ k ꢀ 10
À44 ꢀ l ꢀ 44
52533
À18 ꢀ h ꢀ 19
À13 ꢀ k ꢀ 13
À19 ꢀ l ꢀ 16
22139
À14 ꢀ h ꢀ 12
À15 ꢀ k ꢀ 14
À14 ꢀ l ꢀ 17
13379
À23 ꢀ h ꢀ 23
À14 ꢀ k ꢀ 15
À23 ꢀ l ꢀ 23
30796
À13 ꢀ h ꢀ 13
À15 ꢀ k ꢀ 13
À26 ꢀ l ꢀ 29
30530
À12 ꢀ h ꢀ 14
À38 ꢀ k ꢀ 37
À15 ꢀ l ꢀ 12
40426
Reflections measured
Unique reflections
4144
5069
4143
7858
6783
15054
Reflections (I > 2
r
(I))
3494
3679
3244
4948
4484
12721
Rint
0.037
0.037
0.043
0.072
0.050
0.028
h Range (°)
Data/restraints/parameters
R1
2.9–27.6
4144/0/212
0.0360
2.4–27.6
5069/0/271
0.0448
2.5–27.6
4143/0/217
0.0488
2.2–27.6
7858/0/379
0.0566
2.5–27.5
6783/0/389
0.0508
1.4–27.5
15054/200/770
0.0543
wR2
0.1093
1.00
0.66/À0.74
0.1229
1.03
0.47/À0.30
0.1384
1.04
0.54/À1.36
0.1409
1.00
1.06/À0.97
0.1481
0.98
0.73/À0.35
0.1590
1.03
0.71/À0.48
Goodness-of-fit (GOF) on F2
Largest difference in peak and hole (e ÅÀ3
)
Table 2
Selected bond lengths and angles (Å, °) for Ph2P(Se)CSNHPh, 1–3 and 5–6.
Ph2P(Se)CSNHPh
1
2
3
5
6
C1–N1
C7–N1
C7–S1
C7–P1
P1–Se1
1.415(3)
1.320(3)
1.641(2)
1.878(2)
2.1077(6)
Fe1–P1
Fe1–S1
C7–N1
C7–S1
C7–P1
C8–N1
2.1770(7) Fe1–P1
2.3124(8) Fe1–C1
2.2577(10) Fe1–P2
2.2224(11) Fe1–P1
2.2720(8)
Fe1–P1
Fe1–P2
Fe1–C1
Fe1–C2
2.2660(17)
2.2168(16)
1.721(7)
2.119(7)
2.009(2)
1.767(4)
2.107(5)
1.841(3)
2.1436(9)
Fe1–Se2
Fe1–C1
Fe1–C2
2.4267(7)
1.751(5)
2.121(4)
Fe1–P2
Fe1–C1
Fe1–C2
2.2349(9)
1.752(3)
2.110(3)
2.0044(11) P1–S1
N1–C19
1.264(3)
1.759(2)
1.832(2)
1.421(3)
Fe1–C3
C8–P1
P1–Se1
P1–Se1
2.1194(12) P1–S1
2.2003(12)
P1–Se2
1.365(8)
C1–Fe1–P2
96.06(15)
N1–C7–S1
N1–C7–P1
S1–C7–P1
C7–P1–Se1
129.67(18) S1–C7–P1
111.40(17) P1–Fe1–S1 74.63(2)
118.90(14) C7–P1–Fe1 93.73(8)
98.62(12)
C1–Fe1–Se2 97.32(15)
110.64(13) P2–Fe1–Se2 88.17(3)
112.19(12) Se1–P1–Se2 118.15(5)
C1–Fe1–P2 91.63(10)
C1–Fe1–P1 93.67(10)
P2–Fe1–P1 101.19(3)
S1–P1–Fe1 114.58(4)
C1–Fe1–P2 91.3(2)
C1–Fe1–P1 94.5(2)
P2-Fe1–P1 100.34(6)
S1–P1-Fe1 115.31(8)
C8–P1–Se1
C8–P1–Fe1
Se1–P1–Fe1 111.56(4)
110.28(8)
C7–S1–Fe1 91.24(8)
P1–Se2–Fe1 108.21(4)
Besides Cp, CO and PPh3, 3 (Fig. 4) has a particular ligand Ph2-
PSeÀ2 . Fe–Cp bond distances are in the range of 2.074(4)–2.121
(4) Å. The Fe-carbonyl bond distance of 1.751(5) Å is slightly
shorter than that of 2. The Fe–PPh3 bond distance of 2.2224(11)
Å is close to those found in the related iron complexes [2.230(1)
Å; 17b]. The PASe bond distances are 2.1194(12) Å for P1@Se1
and 2.2003(12) Å for P1-Se2. The FeASe bond distance is 2.4267
(7) Å, which is slightly larger than that (2.3829(8) Å) of CpFe(CO)2-
SeCO2Et [21]. Notably, the carbonyl is significantly bent, with the
O1C1Fe1 bond angle being 172.6(4)°.
Complexes 5 and 6 are the corresponding monophosphine-sub-
stituted derivatives of CpFe(CO)2[kP-P(@S)Ph2]. As shown in Figs. 5
and 6, 5 and 6 also show the geometry of a three-legged piano-
stool, with Cp as the base and CO, SPPh2 and PPh2R ligands as
the legs. Unlike 5, 6 has two different molecules in a unit cell.
The Cp ligand is bound to the Fe atom with FeAC bond distances
of 2.097(3)–2.115(3) Å for 5 and 2.073(8)–2.119(7) Å for 6. The
Fe-carbonyl bond of 1.752(3) Å for 5 and 1.721(7), 1.747(6) Å for
6 is slightly shorter than those of CpFe(CO)2[kP-P(@S)Ph2]. The
OCFe bond angle is 176.6(3)° for 5 and 175.6(6), 174.4(6)° for 6.
The FeAP bond lengths are 2.2720(8), 2.2349(9) Å for 5 and
2.2660(17), 2.2168(16) and 2.2691(16), 2.2121(16) Å for 6. The
PAS bond distance is 2.0044(11) Å for 5 and 6 and 2.009(2),
2.009(2) Å for 6. The FePS bond angle is 114.58(4)° for 5 and
115.31(8), 115.28(8)° for 6. As a comparison, the corresponding
values of CpFe(CO)2[kP-P(@S)Ph2] (CCDC: YUCLOX) are listed as
follows: FeAC, 1.770, 1.773; FeAP, 2.2605(6); P@S, 1.9906(7) Å;
OCFe, 177.74, 178.47; FePS, 111.97° [12].
3.3. Spectroscopies
The synthesized complexes have been further characterized by
IR, 1H NMR, 13C NMR and 31P NMR (see Supplementary data,
Figs. S1–S28). In the IR spectra, the terminal carbonyl group shows
one strong absorption at 1944, 1933, 1935, 1929 and 1935 cmÀ1
for 1 and 3–6 except that 2 exhibits two absorptions at 2026 and
1974 cmÀ1. In the 1H NMR spectra of 1–6, the phenyl and pyridyl
groups are multiplets ranging from 8.72 to 6.76 ppm, the Cp group
shows one singlet at 4.50, 4.93, 4.44, 4.52, 4.50 and 4.50 for 1–6,
respectively. In the 13C NMR spectra, the terminal carbonyls as a
doublet occur at 212.41, 212.18 ppm for 2 whereas those of 1
and 3–6 appear as a doublet or multiplet in the downfield range
of 220.93–218.37 ppm. The Cp group displays one singlet at
81.09, 89.20, 89.14, 88.92, 81.14 and 81.12 for 1–6, respectively.

J.-P. Li et al. / Polyhedron 152 (2018) 94–101
99
The C@N group as one singlet occurs at 148.12 for 1, but one mul-
tiplet at 158.71–147.61 ppm for 4 and two doublets at 150.28,
148.00 ppm (d, d, J = 13.0 Hz, J = 22.0 Hz) for 6. The 31P NMR spec-
tra exhibit one singlet at 49.249, 75.889 ppm for 1–2 but two sin-
glets at 76.61/53.06, 75.98/52.99, 76.12/73.95 and 76.14/74.30
ppm for 3–6.
3.4. Electrochemistry
Cyclic voltammetry of 1–6 has been investigated to evaluate the
capability of the new CpFe complexes to catalyze dihydrogen pro-
duction (Figs. 7–12). According to the results proposed by Demp-
sey et al. [22], the average acid reduction potential versus Fc+/Fc
in 0.1 M [Bu4N][PF6] of CH3CN on GC is À2.36 0.05 V for HOAc
and À1.81 0.03 V for TFA, therefore, as shown in Table 3, cyclic
voltammetry of 1–6 in the presence of acids rules out direct reduc-
tions for acids. Except for 5, all the other complexes in the absence
of acids each show one irreversible oxidation and two irreversible
reductions. Using TFA as a proton source, the second reduction
Fig. 9. Cyclic voltammograms of 3 (1.0 mM) with TFA (0–12 mM) in 0.1 M nBu4-
peak of
1 exhibits catalytic behavior, the reduction current
NPF6/MeCN at a scan rate of 100 mV sÀ1
.
increases with increasing concentration of TFA added [23]. In the
Fig. 7. Cyclic voltammograms of 1 (1.0 mM) with TFA (0–12 mM) in 0.1 M nBu4-
Fig. 10. Cyclic voltammograms of 4 (1.0 mM) with TFA (0–12 mM) in 0.1 M nBu4-
NPF6/MeCN at a scan rate of 100 mV sÀ1
NPF6/MeCN at a scan rate of 100 mV sÀ1
.
.
Fig. 8. Cyclic voltammograms of 2 (1.0 mM) with HOAc (0–12 mM) in 0.1 M nBu4-
NPF6/MeCN at a scan rate of 100 mV sÀ1
Fig. 11. Cyclic voltammograms of 5 (1.0 mM) with HOAc (0–12 mM) in 0.1 M
nBu4NPF6/MeCN at a scan rate of 100 mV sÀ1
.
.

100
J.-P. Li et al. / Polyhedron 152 (2018) 94–101
Fig. 14. GC traces after a 1 h controlled-potential electrolysis vs Ag/AgNO3 of 1 (0.5
mM) in 25 mM TFA (CH4 added for calibration purposes).
Fig. 12. Cyclic voltammograms of 6 (1.0 mM) with TFA (0–12 mM) in 0.1 M nBu4-
NPF6/MeCN at a scan rate of 100 mV sÀ1
.
Table 3
Electrochemical data of 1–6 (0.1 M nBu4NPF6/MeCN; scan rate, 100 mV sÀ1
;
E vs Fc+/Fc).
Epc1/V
Epc2/V
Epa/V
1
2
3
4
5
6
À1.60
À1.70
À1.30
À1.37
À1.65
À1.16
À2.36
À1.89
À2.17
À2.17
–
+0.53
+0.69
+0.92
+0.90
+1.12
+1.00
À1.46
presence of acetic acid, 2 with the second reduction can catalyze H2
evolution. However, using TFA as a proton source, the first reduc-
tions of the other complexes display catalytic behavior. This fact
supports that the pendent base can lower reduction potentials
[4a,24]. The electrocatalytic activity of the CpFe complexes has
been further confirmed by bulk electrolysis (Figs. 13–16). When
bulk electrolysis of a MeCN solution of 1 (0.5 mM) with excess
TFA (25 mM) or 2 (0.5 mM) with excess HOAc (25 mM) has been
carried out for 1 h, a total of 19.4 and 16.4 F molÀ1 passed, 9.7
and 8.2 turnovers are obtained. Moreover, gas chromatographic
Fig. 15. Charge buildup vs time from electrolysis of 2 (0.5 mM) in 25 mM HOAc.
Fig. 16. GC traces after a 1 h controlled-potential electrolysis vs Ag/AgNO3 of 2
(0.5 mM) in 25 mM HOAc (CH4 added for calibration purposes).
analysis shows that the yield of H2 is about 83.7% and 73.3%,
respectively. According to the defination of catalytic efficiency
proposed by Evans et al. [2d], CE = (icat/id)/(CHA/Ccat) (icat, catalytic
Fig. 13. Charge buildup vs time from electrolysis of 1 (0.5 mM) in 25 mM TFA.

J.-P. Li et al. / Polyhedron 152 (2018) 94–101
101
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acid; CHA, acid concentration; Ccat, catalyst concentration), CE is
calculated to be 0.71, 0.89 for 1–2, 0.86, 0.91, 0.85, 0.81 for 3–6,
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Six complexes of 1–6 have been synthesized by the reaction of
Ph2P(Se)CSNHPh with Cp2Fe2(CO)4 and the corresponding phos-
phine-substituted reaction of CpFe(CO)2(kP-P(@E)Ph2) (E = S, Se)
in the presence of Me3NO. Electrochemical studies (Cyclic voltam-
metry and Bulk electrolysis) confirm that these CpFe complexes
show catalytic H2-producing activity in the presence of HOAc or
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Acknowledgments
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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 &
PracticeInnovationProgramofJiangsuProvince(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.
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