Synthesis of bridging hydrides of phenyl-functionalized diiron propanedithiolate complexes with 1,2-bis(diphenylphosphine)ethylene or 1,2-bis(diphenylphosphine)ethane ligands

Article abstract of DOI:10.1007/s11243-015-9937-y

Abstract Reaction of 2-phenyl-1,3-dibromopropane with in situ generated (μ-SLi)₂Fe₂(CO)₆ yielded a known complex [(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₆ (A). Displacement of two carbonyls from complex A by cis-1,2-bis(diphenylphosphine)ethylene (dppv) or 1,2-bis(diphenylphosphine)ethane (dppe) in the presence of Me₃NO·2H₂O gave two chelate complexes [(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₄(κ ²-dppv), [A(κ ²-dppv)] and [(μ-SCH₂)₂CHC₆H₅]Fe₂(CO)₄(κ ²-dppe), [A(κ ²-dppe)], respectively. Protonation of the diiron centers of [A(κ ²-dppv)] and [A(κ ²-dppe)] using an excess of HBF₄·Et₂O in dichloromethane at room temperature gave the bridging hydrides [(μ-H)A(κ ²-dppv)]BF₄ and [(μ-H)A(κ ²-dppe)]BF₄. The complexes [(μ-H)A(κ ²-dppv)]BF₄, [A(κ ²-dppe)] and [(μ-H)A(κ ²-dppe)]BF₄ were characterized by elemental analysis and spectroscopic methods, and [(μ-H)A(κ ²-dppv)]BF₄ and [(μ-H)A(κ ²-dppe)]BF₄ were also characterized by X-ray crystallography. The electrochemical behavior of [(μ-H)A(κ ²-dppv)]BF₄ was investigated by cyclic voltammetry, and the catalytic electrochemical reduction in protons from trifluoroacetic acid or p-methylbenzene sulfonic acid to give hydrogen was investigated.

Full text of DOI:10.1007/s11243-015-9937-y

Transition Met Chem
DOI 10.1007/s11243-015-9937-y
Synthesis of bridging hydrides of phenyl-functionalized diiron
propanedithiolate complexes with 1,2-bis(diphenylphosphine)
ethylene or 1,2-bis(diphenylphosphine)ethane ligands
1
1
1
1
•
Chang-Gong Li
Jing-Yan Shang
•
Gao-Feng Zhang
1
•
Yong Zhu
Tian-Jun Lou
•
Feng Xue
1
2
•
Mao-Jin Cui
•
Received: 28 January 2015 / Accepted: 30 March 2015
Ó Springer International Publishing Switzerland 2015
Abstract Reaction of 2-phenyl-1,3-dibromopropane with
in situ generated (l-SLi) Fe (CO) yielded a known complex
Introduction
2
2
6
[
(l-SCH ) CHC H ]Fe (CO) (A). Displacement of two
In nature, the evolution and oxidation of hydrogen are
2
2
6
5
2
6
carbonyls from complex A by cis-1,2-bis(diphenylphos-
phine)ethylene (dppv) or 1,2-bis(diphenylphosphine)ethane
primarily carried out by hydrogenase (H ase) enzymes [1].
2
According to the metal compositions of their active sites,
(
dppe) in the presence of Me NOÁ2H O gave two chelate
distinct [NiFe], [FeFe] and [Fe] H ases have been identi-
2
3
2
2
2
complexes [(l-SCH ) CHC H ]Fe (CO) (j -dppv), [A(j -
dppv)] and [(l-SCH ) CHC H ]Fe (CO) (j -dppe), [A(j -
dppe)], respectively. Protonation of the diiron centers of
2
[
fied, among which [FeFe] H ase is usually committed to
2
2
2
6
5
2
4
2
2
the catalytic production of hydrogen [2–4]. For example,
6000–9000 hydrogen molecules per second are evolved
2
2
6
5
2
4
2
A(j -dppv)] and [A(j -dppe)] using an excess of HBF ÁEt O
from [FeFe] H ase under fermentation conditions [2]. Such
2
4
2
in dichloromethane at room temperature gave the bridging
2
hydrides [(l-H)A(j -dppv)]BF and [(l-H)A(j -dppe)]BF .
The complexes [(l-H)A(j -dppv)]BF , [A(j -dppe)] and [(l-
H)A(j -dppe)]BF were characterized by elemental analysis
and spectroscopic methods, and [(l-H)A(j -dppv)]BF and
[
high performance is of considerable interest from the point
of view of gaining insights into the mechanism of [FeFe]
2
4
4
2
2
H ase and eventually designing robust catalysts for evo-
2
4
2
lution or uptake of hydrogen [5–8]. Indeed, a large amount
of investigations have been devoted to structural and
4
2
4
2
(l-H)A(j -dppe)]BF were also characterized by X-ray
functional H ase mimics, especially following the charac-
2
4
crystallography. The electrochemical behavior of [(l-
terization of the active sites of [FeFe] H ase by X-ray
2
2
H)A(j -dppv)]BF was investigated by cyclic voltammetry,
crystallography (Fig. 1) [9–11]. The active site is com-
posed of a [2Fe2S] core, in which two iron atoms are linked
by a dithiolate cofactor (SCH XCH S; X = NH, CH or O)
4
and the catalytic electrochemical reduction in protons from
trifluoroacetic acid or p-methylbenzene sulfonic acid to give
hydrogen was investigated.
2
2
2
-
and coordinated by CN ligands and terminal, bridged or
semi-bridged CO ligands. A cubane [4Fe4S] cluster, which
relays electrons from and to the [2Fe2S] active site, is
tethered to the Fep (Fe atom proximal to the [4Fe4S]
cluster) of the [2Fe2S] core by the sulfur atom of a cysteine
ligand, whereas Fed (Fe atom distal from the [4Fe4S]
cluster) has an open site at an apical position, where sub-
strates can be combined [12, 13]. During the course of
investigations on the synthesis and reactivity of iron
hydrides pertinent to the processes of evolution or uptake
&
Chang-Gong Li
lichanggong@sohu.com
1
of hydrogen by [FeFe] H ase, many terminal or bridg-
2
College of Chemistry and Chemical Engineering, Henan
Institute of Science and Technology, Xinxiang 453003,
People’s Republic of China
ing hydrides have been synthesized [14–21]. In con-
tinuation of research into phenyl-functionalized diiron
propanedithiolate complexes [22–24], in this paper, we
report two bridging hydrides containing chelating 1,2-
2
Xinxiang Municipal Key Laboratory of Functional Organic
Molecular, Xinxiang 453003, People’s Republic of China
123

Transition Met Chem
2
2
H)A(j -dppv)]BF or [(l-H)A(j -dppe)]BF at 5 °C. For
4
4
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
[
27], the structures were solved with the ShelXS structure
solution program using direct methods and refined with the
ShelXL refinement package using least-squares minimiza-
À
tion [28]. The F atoms of the BF anions were disordered
4
over two sets of sites with occupancies of 0.54:0.46 for [(l-
2
2
H)A(j -dppv)]BF
dppe)]BF , respectively. Bond (DFIX) and thermal
and 0.74:0.26 for [(l-H)A(j -
4
4
Fig. 1 Structure of the active sites of [FeFe] H
2
ase
(EADP) restraints were placed on these F atoms. Details of
crystal data, data collections, and structure refinement of
2
2
bridging hydrides [(l-H)A(j -dppv)]BF and [(l-H)A(j -
4
bis(diphenylphosphine)ethylene or 1,2-bis(diphenylphos-
phine)ethane ligands.
dppe)]BF are summarized in Table 1.
4
Preparation of complex A
Experimental
A solution of [(l-S) Fe (CO) ] (0.292 g, 0.85 mmol) in
2
2
6
THF (10 ml) was cooled to -78 °C with a liquid nitrogen/
Materials and methods
alcohol bath. LiBEt H (1 M in THF, 1.70 ml, 1.70 mmol)
3
was added dropwise to this solution by syringe. At the
midpoint of the addition, the reaction solution turned from
red to dark emerald green and remained green for the rest of
addition. After stirring at -78 °C for ca. 15 min, a solution
of 2-phenyl-1,3-dibromopropane (0.237 g, 0.85 mmol) in
THF (5 ml) was transferred to the reaction solution by a
canula. The coolant bath was removed, and the reaction
solution was stirred at room temperature for about 3 h.
During this period, the color of the solution changed back to
red. The solvent was removed on a rotary evaporator, and the
residue was subjected to preparative TLC separation using
CH Cl /petroleum ether (v/v = 1:6) as the eluent. From the
All manipulations were performed using standard Schlenk line
and syringe/rubber septa techniques under an argon atmo-
sphere. Solvents were of reagent grade and purified as follows:
dichloromethane and acetonitrile were distilled over CaH2,
while n-hexane and THF were purified by distillation from
2
sodium/diphenylmethanone. (l-S )Fe (CO) [25] and [A(j -
2
2
6
dppv)] [26] were prepared according to literature methods.
LiBEt H (1 M in THF) and Me NOÁ2H O were available
3
3
2
commercially and used as received. 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
2
2
1
31
on a Bruker TENSOR 27 FTIR spectrometer. H and P NMR
spectra were obtained on a Bruker Avance 400 MHz spec-
trometer. Elemental analyses were obtained on an Elementar
Vario EL III analyzer.
second red band, complex A was obtained as a red solid
1
-
(0.181 g, 46 %). IR (KBr disk, cm ): mC:O 2071 (vs), 2021
(vs), 2006 (vs), 1970 (vs). H NMR (400 MHz, CDCl ,
1
3
2
ppm): 1.82 (t, 2 H, J
3
= J
= 13.4 Hz, 2 SCH H ),
HaHa’ a e
HaHe
3
2.35 (m, 1 H, CH), 2.70, 2.74 (dd, 2 H, J
Electrochemical measurements were carried out under dry
nitrogen using a CHI 620 Electrochemical Workstation (Chen-
Hua instrument co., Shanghai, China). n-Bu NPF (0.1 M in
= 3.5 Hz,
HeHa’
2
JHeHa = 13.2 Hz, 2 SCH H ), 7.10–7.31 (m, 5 H, C H ).
a
e
6 5
4
6
Anal. Calc. for C H Fe O S : C, 39.0; H, 2.2. Found: C,
15 10 2 6 2
CH CN) was used as the electrolyte. CV scans were obtained in
3
38.8; H, 2.3 %.
a three-electrode cell with a glassy carbon electrode (3 mm
diameter) as the working electrode, successively polished with
2
Preparation of [A(j -dppe)]
3- and 1-lm diamond pastes and sonicated in ion-free water for
1
min, a platinum wire as counter electrode, and a nonaqueous
To a solution of complex A (0.092 g, 0.20 mmol) and dppe
(0.080 g, 0.20 mmol) in MeCN (10 ml) was added Me3-
?
Ag/Ag electrode (1.0 mM AgNO and 0.1 M n-Bu NPF in
3
4
6
CH CN) as reference. The potential scale was calibrated against
3
NOÁ2H O (0.022 g, 0.20 mmol), and the resulting solution
2
?
the Fc/Fc couple and is reported versus this reference system.
was stirred at 80 °C for 15 h. After removing the solvent
on a rotary evaporator, the residue was subjected to pre-
parative TLC separation using CH Cl /petroleum ether (v/
X-ray structure determination
2
2
v = 1:1) as the eluent. From the green band, the complex
2
Single crystals for X-ray diffraction analysis were grown
[A(j -dppe)] was obtained as a deep green solid (0.040 g,
-
1
by slow evaporation of CH Cl /hexane solutions of [(l-
25 %). IR (KBr disk, cm ): mC:O 2007 (s), 1929 (vs),
2
2
1
23

Transition Met Chem
Table 1 Crystal data and
structural refinements for [(l-
2
2
[
(l-H)A(j -dppv)]BF
Fe
4
[(l-H)A(j -dppe)]BF
4
2
Empirical formula
Formula weight
Temperature/K
Crystal system
Space group
C
39
H
33BF
4
2
O
4
P
2
S
2
C
39
H35BF
Fe O P S
4 2 4 2 2
H)A(j -dppv)]BF
H)A(j -dppe)]BF
4
and [(l-
2
890.22
291.15
Triclinic
P¯ı
892.24
291.15
Triclinic
P¯ı
4
˚
a/A
10.9839(7)
14.4739(9)
10.2201(6)
˚
b/A
14.5303(10)
27.750(2)
91.727(6)
98.427(6)
104.930(6)
3928.9(5)
4
˚
c/A
26.4000(17)
87.738(5)
87.482(5)
70.628(6)
3954.3(4)
4
a/°
b/°
c/°
3
˚
Volume/A
Z
3
q
calcmg/mm
1.495
1.508
-
1
l/mm
8.141
8.194
F(000)
Crystal size/mm
h range for data collection
1816.0
1824.0
3
0.14 9 0.12 9 0.08
6.48 to 127.74°
0.14 9 0.1 9 0.05
6.32 to 134.16
-12 B h B 12
-17 B k B 14
-22 B l B 33
27,019
2
-
12 B h B 12
-10 B k B 16
30 B l B 30
Index ranges
-
Reflections collected
24,812
Independent reflections (Rint
Data/restraints/parameters
)
12,798 [0.0453]
12,798/14/1007
1.024
13,829 [0.0484]
13,829/2/981
1.016
2
Goodness-of-fit on F
Final R indexes [I C 2r (I)]
Final R indexes [all data]
R
R
1
1
= 0.0557, wR
= 0.1023, wR
2
2
= 0.1044
= 0.1244
R
R
1
1
= 0.0645, wR
= 0.1122, wR
2
2
= 0.1470
= 0.1744
-
3
˚
Largest difference in peak/hole/e A
0.50/-0.36
0.72/-0.39
1
898 (s). H NMR (400 MHz, CDCl , ppm): 1.74 (t, 2 H,
1
1 ml) and diethyl ether (ca. 10 ml) was added dropwise.
2
3
2
3
JHaHe = J
= 12 Hz, 2 SCH H ), 1.82 (m, 1 H, CH),
a
After mixing, [(l-H)A(j -dppv)]BF (0.077 g, 79 %) was
HaHa’
2
.43 (d, 2 H, J
e
4
2
= 12 Hz, 2 SCH H ), 2.54 (m, 2 H, 2
a e
precipitated and isolated as a dark red solid. IR (KBr disk,
-
HeHa
1
1
PCH ), 2.68 (m, 2 H, 2 PCH ), 6.20 (s, 2 H, C H ), 7.02 (s,
2
cm ): mC:O 2102 (s), 2043 (vs), 1967 (s). H NMR
(400 MHz, CD Cl , ppm): -14.69 (t, 1 H, J = 20.1 Hz,
2
6 5
3
H, C H ), 7.37–7.51 (m, 16 H, C H ), 7.84 (s, 4 H,
6 5 6 5
2
2
PH
3
C H ). P NMR (161.9 MHz, CDCl , 85 % H PO , ppm):
1
l-H), 2.699 (m, 2 H, 2 SCH H ), 3.180 (m, 3 H, 2 SCH H ,
6
5
3
3
4
a
e
a e
9
1.1 (s, 70 %, basal–apical), 78.2 (s, 30 %, basal–basal).
CH), 7.371–7.385 (m, 23 H, C H ), 8.531 (m, 2 H, C H ).
6 5 6 5
3
1
Anal. Calc. for C H Fe O P S : C, 58.2; H, 4.3. Found:
2
P NMR (161.9 MHz, CD Cl , 85 % H PO , ppm): 83.6
2 2 3 4
3
9
34
2
4
2
C, 58.1; H, 4.3 %.
(s). Anal. Calc. for C H BF Fe O P S : C, 52.6; H, 3.7.
39 33 4 2 4 2 2
Found: C, 52.9; H, 3.5 %.
2
Protonation of [A(j -dppv)] and [A(j -dppe)]
2
2
Repetition of the above operations using [A(j -dppe)]
0.042 g, 0.053 mmol) and HBF ÁEt O (52 %, 19 lL,
(
4
2
2
2
To a dichloromethane (15 ml) solution of [A(j -dppv)]
0.13 mmol) gave [(l-H)A(j -dppe)]BF (0.033 g, 71 %)
4
-
1
(
0.090 g, 0.11 mmol) was added HBF ÁEt O (52 %, 40 lL,
as a dark red solid. IR (KBr disk, cm ): mC:O 2099 (s),
2034 (vs), 1946 (m). H NMR (400 MHz, CD Cl , ppm):
4
2
1
0
.27 mmol) at room temperature. The resulting solution
2
2
gradually changed from green to red. After stirring at room
temperature for 2 h, the solution was filtered and the
volatiles of the filtrate were removed. The resulting solid
was washed with diethyl ether (ca. 3 9 1 ml). Subse-
quently, the solid was redissolved in dichloromethane (ca.
-14.30 (t, 1 H, JPH = 21.2 Hz, l-H), 1.80 (m, 1 H), 1.90
(m, 2 H), 2.60 (m, 2 H), 3.24 (m, 2 H), 3.35 (m, 2 H),
3
1
7.38–7.85 (m, 25 H, C H ). P NMR (161.9 MHz, CDCl3,
6
5
85 % H PO , ppm): 78.1 (s). Anal. Calc. for C H BF
3
4
39 35
4-
Fe O P S : C, 52.5; H, 4.0. Found: C, 52.7; H, 3.7 %.
2 4 2 2
123

Transition Met Chem
Results and discussion
dppv ligand may assist in the displacement of the second
2
carbonyl, resulting in ready formation of [A(j -dppv)],
whereas dppe will require an internal rotation from trans to
Synthesis and spectroscopic characterization
cis before replacement of the second carbonyl, perhaps
2
The known complex A has been prepared previously by the
addition of 2-phenyl-1,3-propanedithiol to Fe (CO) in
hindering the formation of [A(j -dppe)]. Compared with
the IR spectrum of complex A (2071, 2021, 2006,
3
12
-
1970 cm ), the biggest absorption frequency of the ter-
1
high yield [22]. However, preparation of 2-phenyl-1,3-
propanedithiol from 2-phenyl-1,3-propanediol requires at
least 72 h. Thus, an alternative synthesis of complex A was
designed. 2-Phenyl-1,3-propanediol was readily trans-
formed to 2-phenyl-1,3-dibromopropane at room tem-
2
-1
minal carbonyl of complex [A(j -dppe)] (2007 cm ) was
-
1
considerably shifted by about 64 cm toward lower fre-
quency. This is consistent with two CO ligands being re-
placed by more electron-donating diphosphine ligands in
1
perature using CBr and triphenylphosphine. Subsequently,
4
chelating manner [18, 21, 30]. The H NMR spectrum of
2
[A(j -dppe)] showed that signals at 1.74, 1.82 and
2
-
using the in situ generated dianion [(l-S) Fe (CO) ] and
2
2
6
2
-phenyl-1,3-dibromopropane, complex A could be readily
prepared within 24 h from 2-phenyl-1,3-propanediol in
2.43 ppm for the propanedithiolate protons shifted upfield
compared with those of the complex A (1.82, 2.35 and
2.72 ppm), reflecting the increased electron density on the
1
spite of a medium yield [29]. The IR and H NMR spectra
2
of complex A closely matched those of the reported com-
plex [(l-SCH ) CHC H ]Fe (CO) [22]. In the presence of
ca. one equivalent of the decarbonylating agent Me
diiron center in [A(j -dppe)]. Two signals at 2.54 and
2.68 ppm were assigned to the methylene protons of the
2
2
6
5
2
6
3
1
2
dppe ligand. The P NMR spectrum of [A(j -dppe)]
showed two signals at 91.1 and 78.2 ppm with different
intensities, indicating alternate basal–apical and basal–
basal conformations of the diphosphine in solution. Addi-
3
-
2
NOÁ2H O, the chelate complex [A(j -dppv)] was synthe-
2
sized in 90 % yield from complex A (Scheme 1) [26]. For
2
the preparation of [A(j -dppe)], continuous heating at
8
0 °C for about 15 h was required but the yield was only
5 % [18, 21]. The inherent cis-configuration of the cis-
tion of excess HBF
2
4
ÁEt
O to a dichloromethane solution of
2
2
2
either [A(j -dppv)] or [A(j -dppe)] at room temperature
Scheme 1 Preparation of [(l-
2
2
H)A(j -dppv)]BF
4
, [A(j -
2
dppe)] and [(l-H)A(j -
dppe)]BF
4
1
23

Transition Met Chem
resulted in a color change of the solution from green to red.
2
2
Protonation of the diiron center of [A(j -dppv)] or [A(j -
-
1
dppe)] is indicated by the deserved shifts of 96 or 91 cm
,
respectively, in the IR absorption frequencies of the ter-
minal carbonyls to higher wavenumbers, as those observed
2
for the protonation of (l-pdt)Fe (CO) (j -dppe) [18], (l-
2
4
2
2
pdt)Fe (CO) (j -dppp) [21], (l-pdt)Fe (CO) [j -Ph
PN(allyl)PPh2] [20] and (l-pdt)Fe(CO) Fe(CO)(j -
2
4
2
4
2-
2
3
IMeCH IMe) [30]. Protonation of the diiron center or the
2
1
bridging hydride was further confirmed by the H NMR
spectra, which showed a triplet at d -14.69 or
-
14.30 ppm, respectively, at high field as those of analo-
2
gous bridging hydrides, [(l-H)(l-pdt)Fe (CO) (j -
2
4
2
dppe)]BF and [(l-H)Fe (CO) (j -dppp)(l-pdt)]BF [18,
4
2
4
4
3
1]. The P NMR spectra displayed changes from the two
1
2
2
signals of the precursor [A(j -dppv)] at 96.0 and 82.1 ppm
to one signal for [(l-H)A(j -dppv)]BF at 83.6 ppm or
from the two signals of [A(j -dppe)] at 91.1 and 78.2 ppm
to one signal for [(l-H)A(j -dppe)]BF4 at 78.1 ppm,
consistent with the chemical equivalence of the phosphines
2
4
2
2
2
2
of [(l-H)A(j -dppv)]BF or [(l-H)A(j -dppe)]BF in a
4
4
basal–basal conformation.
X-ray crystal structures
2
2
Single crystals of [(l-H)A(j -dppv)]BF and [(l-H)A(j -
2
4
Fig. 2 Molecular structure of [(l-H)A(j -dppv)]BF
ellipsoids at 30 % probability
4
with thermal
dppe)]BF suitable for X-ray diffraction were grown by
4
slow evaporation of hexanes/dichloromethane solutions of
2
2
[
(l-H)A(j -dppv)]BF or [(l-H)A(j -dppe)]BF , while all
4
4
2
attempts to grow crystals of [A(j -dppe)] were unsuc-
from the plane S1-S2-O2-O3. The biggest structural
2
change during the protonation of [A(j -dppv)] is the ex-
change of positions between a basal carbonyl ligand and an
2
cessful. The molecular structures of [(l-H)A(j -dppv)]BF
and [(l-H)A(j -dppe)]BF were unambiguously confirmed
4
2
4
by X-ray crystallography (Figs. 2, 3) and crystal data, se-
lected bond lengths and angles are listed in Tables 1 and 2.
The metric parameters of the [2Fe2S] cluster in the [(l-
apical phosphine ligand coordinated to atom Fe , forming a
2
2
basal–basal diphosphine complex [(l-H)A(j -dppv)]BF .
4
The other structural changes are an increase in the bond
angles of Fe2–Fe1–C2 and Fe2–Fe1–C3 by about 6°, and a
simultaneous decrease in the bond angles of Fe2–Fe1–C1
by about 4.5°, in order to make room for the hydride. The
2
?
H)A(j -dppv)] cation vary only slightly from those found
2
in the precursor [A(j -dppv)]. For example, the bond
˚
lengths of Fe–P (2.2223(14) and 2.2382(15) A) and the bite
˚
˚
angle of P1–Fe –P2 (87.03(5)°) are almost the same as
Fe1–H (1.644 A) and Fe2–H (1.722 A) distances are
comparable to those of other bridging hydrides [30]. The
2
2
those of the precursor [A(j -dppv)] (2.1797(7) and
2
?
˚
2
.21235(6) A, 87.31(2)°). Protonation occurs as expected
across the Fe–Fe bond and leads to a shortening of this
framework of the [(l-H)A(j -dppe)] cation is similar to
2
?
that of the [(l-H)A(j -dppv)] cation with the diphosphine
of dppe coordinating atom Fe2 in a basal–basal confor-
mation and a hydrogen atom bridging two iron atoms in a
2
˚
˚
vector by ca. 0.03 A (from 2.6090(5) A in [A(j -dppv)] to
2
˚
2
.5832(10) A in [(l-H)A(j -dppv)]BF ), similar to the
4
2
shortening of the Fe–Fe bond during the protonation pro-
2
geometry close to that of the [Fe (l-pdt)(CO) (j -dppe)(l-
2
4
?
cesses of (l-pdt)Fe (CO) )(j -dppe) [18], (l-pdt)Fe
H)] cation [18]. The main difference between [(l-
2
5
2
2
2
2
?
2
?
(
CO) (j -IMeCH IMe) [30] and [Fe (CO) (j -Ph PN
H)A(j -dppv)] and [(l-H)A(j -dppe)] cations is the
bond length of C26–C27, which is a single bond of
2
2
2
4
2
(
allyl)PPh )(l-pdt)] [20]. Both iron centers in the [(l-H)
2
2
?
2
˚
A(j -dppv)] cation display distorted octahedral geome-
tries, similar to previously reported bridging hydrides [18,
1.5339(9) A in [(l-H)A(j -dppe)]BF and double bond of
1.310(3) A in [(l-H)A(j -dppv)]BF . Correspondingly, the
bond angle of P1–Fe2–P1 (87.57(6) °) in [(l-H)A(j -
dppe)]BF4 is slightly larger than that of P1–Fe2–P1
4
2
˚
4
2
2
0, 31]. Each iron atom is displaced from its pyramidal
˚
base toward the apical direction, by 0.320(1) A for Fe2
˚
from the plane S1-S2-P1-P2 and by 0.215(1) A for Fe1
2
(87.03(5)°) in [(l-H)A(j -dppv)]BF .
4
123

Transition Met Chem
2
2
Fig. 4 CVs of [(l-H)A(j -dppv)]BF
.1 M n-Bu NPF
4
and [A(j -dppv)] (1 mM) in
-1
0
4
6
/MeCN at a scan rate of 0.1 V s
Fe–Fe bond and the concomitant reduction in electron
density in the diiron center [32]. The oxidation peaks at
-
0.382, -0.201 and ?0.088 V may be ascribed to the in-
termediate species generated from the reduction processes
2
of [(l-H)A(j -dppv)]BF , as these peaks disappeared when
4
the CVs were conducted toward the anode from the initial
potential at -0.50 V. On addition of one equivalent of tri-
fluoroacetic acid (pK = 12.7 in MeCN), the current height
a
2
Fig. 3 Molecular structure of [(l-H)A(j -dppe)]BF
ellipsoids at 30 % probability
4
with thermal
at -1.305 V increased slightly, whereas further increases of
acid did not show obvious increases in the current heights.
The current heights at -1.792 V increased with successive
additions of trifluoroacetic acid, but appeared slightly re-
sponsive to the increment of acids and only reached 44 lA
in the presence of 10 equivalents of acid (Fig. 5). However,
under the same conditions, the current height of the pre-
Electrochemistry
2
2
The CVs of [(l-H)A(j -dppv)]BF and [A(j -dppv)] are
shown in Fig. 4. The bridging hydride [(l-H)A(j -dp-
pv)]BF displayed two reduction processes at -1.305 and
4
2
2
cursor [A(j -dppv)] reached 135 lA, larger than that of [(l-
4
2
-
1.792 V and one oxidation process at ?0.779 V. Com-
2
pared with redox potentials of [A(j -dppv)], positive shifts
of 0.75–0.80 V were observed due to protonation of the
H)A(j -dppv)]BF [26]. When using a stronger p-methyl-
4
benzene sulfonic acid (TsOH, pK = 8.7 in MeCN) as the
a
proton resource, the changes of current intensities around
2
2
˚
Table 2 Selected bond lengths (A) and angles (deg) for [(l-H)A(j -dppv)]BF
4
and [(l-H)A(j -dppe)]BF
4
2
[
(l-H)A(j -dppv)]BF
Fe(1)–Fe(2)
4
2.5832(10) Fe(1)–S(1)
2.2223(14) Fe(2)–S(2)
2.2813(15) Fe(1)–S(2)
2.2509(14) Fe(2)–P(2)
2.2718(14) Fe(2)–S(1)
2.2382(15) Fe(1)–C(1)
2.2613(14)
1.800(6)
Fe(2)–P(1)
Fe(2)–C(4)
1.757(6)
87.03(5)
91.57(17)
69.66(4)
P(1)–C(26)
1.810(5)
P(2)–C(27)
1.812(5)
O(4)–C(4)
1.142(5)
P(1)–Fe(2)–P(2)
C(4)–Fe(2)–P(2)
C(27)–P(2)–Fe(2) 107.26(18) C(26)–P(1)–Fe(2)
107.47(17) P(2)–Fe(2)–Fe(1)
148.04(17) Fe(2)–S(1)–Fe(1)
110.03(5)
69.31(4)
P(1)–Fe(2)–Fe(1)
S(1)–Fe(1)–S(2)
109.10(5)
84.12(5)
C(4)–Fe(2)–Fe(1)
S(2)–Fe(2)–S(1)
Fe(2)–S(2)–Fe(1)
2
(l-H)A(j -dppe)]BF
Fe(1)–Fe(2)
85.06(5)
C(1)–Fe(1)–Fe(2)
139.14(19)
[
4
2.5783(13) Fe(1)–S(1)
2.2398(16) Fe(2)–S(2)
2.2725(19) Fe(1)–S(2)
2.2532(16) Fe(2)–P(2)
2.2754(16) Fe(2)–S(1)
2.2523(17) Fe(1)–C(10)
2.2491(17)
1.810(8)
1.145(7)
112.48(5)
69.53(6)
Fe(2)–P(1)
Fe(2)–C(13)
1.754(7)
87.57(6)
P(1)–C(27)
1.834(6)
P(2)–C(26)
1.837(6)
105.6(2)
O(4)–C(13)
P(1)–Fe(2)–P(2)
C(27)–P(1)–Fe(2) 107.4(2)
C(26)–P(2)–Fe(2)
P(1)–Fe(2)–Fe(1)
Fe(2)–S(1)–Fe(1)
C(13)–Fe(2)–P(1) 90.5(2)
Fe(2)–S(2)–Fe(1) 69.41(5)
P(2)–Fe(2)–Fe(1)
S(1)–Fe(1)–S(2)
107.00(6)
83.75(6)
C(13)–Fe(2)–Fe(1) 148.0(2)
S(2)–Fe(2)–S(1) 84.79(6)
C(10)–Fe(1)–Fe(2) 139.0(2)
1
23

Transition Met Chem
the chelate complexes. Protonation of these precursor
2
complexes yielded the bridging hydrides [(l-H)A(j -dp-
2
pv)]BF4 and [(l-H)A(j -dppe)]BF . These protonation
4
reactions induce a change in coordination model of the
diphosphine from apical–basal to basal–basal. The CVs of
2
[
(l-H)A(j -dppv)]BF in the presence of acids indicated
4
that the bridging hydride can catalyze the electrochemical
reduction of protons, but with different efficiencies de-
pending on the strength of the acid. The relative thermo-
dynamic stability together with the basicity of the bridging
hydride may influence the catalytic process.
Supporting information
2
2
Fig. 5 CVs of [(l-H)A(j -dppv)]BF
4
(1 mM) in 0.1 M n-Bu
MeCN in the presence of CF COOH (0–10 mM) at a scan rate of
4
NPF
6
/
CCDC 1032305 ([(l-H)A(j -dppv)]BF ) and 1045156
4
2
3
(
[(l-H)A(j -dppe)]BF ) contain the supplementary crys-
4
-
1
0
.1 V s
tallographic 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 En-
trepreneurship for Undergraduates (No. 201210467022).
References
1
. Lubitz W, Ogata H, R u¨ diger O, Reijerse E (2014) Chem Rev
14:4081
1
2
. Fontecilla-Camps JC, Volbeda A, Cavazza C, Nicolet Y (2007)
Chem Rev 107:4273
3
4
5
6
7
. Vignais PM, Billoud B (2007) Chem Rev 107:4206
. Adams MWW (1990) Biochim Biophys Acta 1020:115
. Tard C, Pickett CJ (2009) Chem Rev 109:2245
. Gloaguen F, Rauchfuss TB (2009) Chem Soc Rev 38:100
. Capon JF, Gloaguen F, P e´ tillon FY, Schollhammer P, Talarmin J
2
Fig. 6 CVs of [(l-H)A(j -dppv)]BF
MeCN in the presence of TsOH (0–10 mM) at a scan rate of
4 4 6
(1 mM) in 0.1 M n-Bu NPF /
-
1
0
.1 V s
(
2009) Coord Chem Rev 253:1476
8
9
. Georgakaki IP, Thomson LM, Lyon EJ, Hall MB, Darensbourg
MY (2003) Coord Chem Rev 238–239:255
. Simmons TR, Berggren G, Bacchi M, Fontecave M, Artero V
-
1.305 V were very similar to those in the presence of tri-
fluoroacetic acid, but the current heights at -1.792 V in-
(
2014) Coord Chem Rev 270–271:127
creased substantially on successive additions of TsOH,
1
1
0. Liu XM, Ibrahim SK, Tard C, Pickett CJ (2005) Coord Chem Rev
249:1641
1. Capon JF, Gloaguen F, Schollhammer P, Talarmin J (2005)
Coord Chem Rev 249:1664
2. Peters JW, Lanzilotta WN, Lemon BJ (1998) Science 282:1853
3. Nicolet Y, Piras C, Legrand P, Hatchikian EC, Fontecilla-Camps
JC (1999) Structrue 7:13
4. Wang N, Wang M, Chen L, Sun LC (2013) Dalton Trans
2:12059
reaching 121 lA in the presence of 10 equivalents (Fig. 6)
2
[33, 34]. These observations imply that [(l-H)A(j -dp-
pv)]BF can catalyze the reduction in protons and the catalytic
4
1
1
efficiency is related to the strength of the acid [35–37]. Both
2
the thermodynamic stability and the basicity of [(l-H)A(j -
dppv)]BF may be relevant to the catalytic process [31].
1
1
4
4
5. Carroll ME, Barton BE, Rauchfuss TB, Patrick J (2012) J Am
Chem Soc 134:18843
Conclusions
16. Wang WG, Rauchfuss TB, Zhu LY (2014) J Am Chem Soc
36:5773
1
2
2
17. Zhao X, Georgakaki IP, Miller ML, Yarbrough JC, Darensbourg
MY (2001) J Am Chem Soc 123:9710
The complexes [A(j -dppv)] and [A(j -dppe)] have been
prepared and characterized. The inherent configuration of
diphosphine ligands has influence on the ease of access of
1
8. Ezzaher S, Capon JF, Gloaguen F, P e´ tillon FY, Schollhammer P,
Talarmin J (2007) Inorg Chem 46:3426
123

Transition Met Chem
1
2
9. Nehring JL, Heinekey DM (2003) Inorg Chem 42:4288
0. Ghosh S, Hogarth G, Hollingsworth N, Holt KB, Richards I,
Richmond MG, Sanchez BE, Unwin D (2013) Dalton Trans
30. Morvan D, Capon JF, Gloaguen F, Le Goff A, Marchivie M,
Michaud F, Schollhammer P, Talarmin J, Yaouanc JJ, Pichon R,
Kervarec N (2007) Organometallics 26:2042
4
2:6775
1. Adam FI, Hogarth G, Kabir SE, Richards I (2008) C R Chim
1:890
31. Barton BE, Zampella G, Justice AK, De Gioia L, Rauchfuss TB,
Wilson SR (2010) Dalton Trans 39:3011
32. Felton GAN, Mebi CA, Petro BJ, Vannucci AK, Evans DH, Glass
RS, Lichtenberger DL (2009) J Organomet Chem 694:2681
33. Gloaguen F, Lawrence JD, Rauchfuss TB, B e´ nard M, Rohmer
MM (2002) Inorg Chem 41:6573
2
1
2
2
2
2. Li CG, Zhu Y, Jiao XX, Fu XQ (2014) Polyhedron 67:416
3. Li CG, Xue F, Cui MJ, Shang JY (2014) J Clust Sci 25:1641
4. Li CG, Xue F, Cui MJ, Shang JY, Lou TJ (2015) Transit Met
Chem 40:47
34. Gloaguen F, Lawrence JD, Rauchfuss TB (2001) J Am Chem Soc
123:9476
2
2
2
5. Seyferth D, Henderson RS, Song LC (1982) Organometallics
1
:125
6. Li CG, Li YF, Shang JY, Lou TJ (2014) Transit Met Chem
9:373
35. Chong D, Georgakaki IP, Mejia-Rodriguez R, Sanabria-Chin-
chilla J, Soriaga MP, Darensbourg MY (2003) Dalton Trans 4158
36. Borg SJ, Behrsing T, Best SP, Razavet M, Liu X, Pickett CJ
(2004) J Am Chem Soc 126:16988
37. Felton GAN, Glass RS, Lichtenberger DL, Evans DH (2006)
Inorg Chem 45:9181
3
7. Dolomanov OV, Bourhis LJ, Gildea RJ, Howard JAK, Pusch-
mann H (2009) J Appl Cryst 42:339
8. Sheldrick GM (2008) Acta Cryst A64:112
9. Seyferth D, Henderson RS, Song LC (1980) J Organomet Chem
1
2
2
92:C1
1
23