Diiron hexacarbonyl complexes bearing naphthalene-1,8-dithiolate bridge moiety as mimics of the sub-unit of [FeFe]-hydrogenase: Synthesis, characterisation and electrochemical investigations

Article abstract of DOI:10.1039/c5nj02074c

Eight diiron hexacarbonyl complexes bearing a 1,8-dithionaphthalenyl bridging linkage as mimics of the diiron subunit of [FeFe]-hydrogenase are reported. Reaction of Fe₃(CO)₁₂ with naphtha[1,8-cd][1,2]dithiole-n-carbaldehyde (n = 2: 2a or 4: 2b) gave two complexes, [Fe₂(μ-S)₂R(CO)₆] (-SRS- = n-formylnaphthalene-1,8-bis(thiolate), n = 2: 3a, 4: 3b), which were further used as precursors to prepare six other complexes by manipulating the formyl groups. Converting the corresponding formyl group into a hydroxymethyl group (CH₂OH) led to complexes 4a and 4b. Their reactions with halobutanoyl chloride formed complexes 5a and 5b (halo group = Cl), and 6a and 6b (halo group = Br), respectively. Among the complexes, 3a, 3b, 4b, 5b, and 6a were crystallographically analysed. Electrochemical investigations into these complexes revealed that the formyl group exerts profound electronic influence on the electrochemistry, and thus catalysis of proton reduction, due to its involvement in the conjugation of the bridging linkage. DFT calculations indicate that the formyl group influences the electrochemistry and catalysis by significantly altering the composition of the LUMOs.

Full text of DOI:10.1039/c5nj02074c

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Diiron hexacarbonyl complexes bearing
naphthalene-1,8-dithiolate bridge moiety as
mimics of the sub-unit of [FeFe]-hydrogenase:
synthesis, characterisation and electrochemical
investigations†
Cite this:DOI: 10.1039/c5nj02074c
Guifen Qian,a Wei Zhong,b Zhenhong Wei,a Hailong Wang,b Zhiyin Xiao,b Li Longb
and Xiaoming Liu*ab
Eight diiron hexacarbonyl complexes bearing a 1,8-dithionaphthalenyl bridging linkage as mimics of the diiron
subunit of [FeFe]-hydrogenase are reported. Reaction of Fe3(CO)12 with naphtha[1,8-cd][1,2]dithiole-n-
carbaldehyde (n = 2: 2a or 4: 2b) gave two complexes, [Fe2(m-S)2R(CO)6] (–SRS– = n-formylnaphthalene-1,8-
bis(thiolate), n = 2: 3a, 4: 3b), which were further used as precursors to prepare six other complexes by
manipulating the formyl groups. Converting the corresponding formyl group into a hydroxymethyl group
(CH2OH) led to complexes 4a and 4b. Their reactions with halobutanoyl chloride formed complexes 5a
and 5b (halo group = Cl), and 6a and 6b (halo group = Br), respectively. Among the complexes, 3a, 3b,
4b, 5b, and 6a were crystallographically analysed. Electrochemical investigations into these complexes
revealed that the formyl group exerts profound electronic influence on the electrochemistry, and thus
catalysis of proton reduction, due to its involvement in the conjugation of the bridging linkage. DFT
calculations indicate that the formyl group influences the electrochemistry and catalysis by significantly
altering the composition of the LUMOs.
Received (in Montpellier, France)
5th August 2015,
Accepted 29th September 2015
DOI: 10.1039/c5nj02074c
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1. Introduction
Due to the relevance of hydrogen, which may be a favourable
potential substituent of fossil fuels in the future, the structural
revelation of [FeFe]-hydrogenase more than a decade ago has
greatly inspired synthetic chemists to mimic the metal centre.1,2
In the past decade, a large number of diiron complexes of a core
‘‘Fe2(CO)6ꢀx’’ (x = 1 or 2) as mimics of the diiron subunit (Fig. 1)
of the enzyme have been reported.3–8 Among the reported diiron
mimics, some of the models nicely replicate the key features of
Fig. 1 Schematic view of the H-cluster of [FeFe]-hydrogenase.
the diiron subunit of the metalloenzyme, for example, showing replicating the proton transferring role of the azo-bridging
a vacant binding site at one of the metals in the diiron core,9 group in hydrogen oxidation and hence reducing overpotential via
possessing mixed oxidation states for the diiron centre,10–14 the PCET (proton coupled electron transfer) mechanism.15–18 The
azo character has recently been firmly confirmed by incorporating
a mimic with the azo linkage into an apo enzyme.19 Otherwise,
a School of Chemistry, Nanchang University, Nanchang, Jiangxi 330031, China
the constructed artificial enzyme does not have activity at all.
As an electrocatalyst for proton reduction, electrochemical
investigations of those mimics have been one of the main
concerns in the mimetic chemistry of this enzyme, particularly
the mechanism of election transfer of the diiron mimics.
There is no doubt about the nature of two-electron transfer
for diiron mimics.5,6,20–22 For the electron transfer involving
two electrons, the electron transfer process falls, in theory, into
b College of Biological, Chemical Sciences and Engineering, Jiaxing University,
Jiaxing, Zhejiang 314001, China. E-mail: xiaoming.liu@mail.zjxu.edu.cn;
Fax: +86(0)573 83643937; Tel: +86(0)573 83643937
† Electronic supplementary information (ESI) available: IR and UV/vis spectra of
diiron hexacarbonyl complexes, CVs of 2a and 2b, CVs of diiron hexacarbonyl
complexes at various scanning rates in DCM, current functions of diiron
hexacarbonyl complexes in MeCN and catalytic reduction of protons in MeCN–
acetic acid. CCDC 895027–895029 and 895031–895033. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c5nj02074c
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Ideally, a mimic should exhibit robustness upon reduction
for decent catalytic performance in catalysing proton reduction.
However, among the numerous mimics reported in the litera-
ture,3–8 most of the diiron complexes exhibit an irreversible
reduction. Since the diiron mimics with the naphthalenyl
bridging linkage are one of the limited systems showing
reversibility upon reduction,34–39 we are interested in exploring
positions 2 and 4 on the aromatic system for diiron mimics
bearing a variety of substituents. The substituents on these
positions exert both steric and electronic effects not only on the
bridging linkage, but also provide possibilities for further
functionalising the mimics. Herein, we report the synthesis,
characterisation, and electrochemical investigation of eight
diiron hexacarbonyl complexes (3a, 3b, 4a, 4b, 5a, 5b, 6a and
6b) to be supplementary to our work reported recently.30 These
complexes were fully characterised using a variety of techniques
(FTIR, NMR, elemental analysis). The structures of most of
Scheme 1 The pathways of electron transfer involved in the reduction of
diiron mimics of [FeFe]-hydrogenase. Please note that (a) pathway iii is the
combination of i and ii, and (b) [Fe2] refers to the diiron mimics.
three categories (Scheme 1). If the monoanion is thermodyna- these complexes (3a, 3b, 4b, 5b and 6a) were determined using
mically stable enough, normal two sequential one-electron X-ray single crystal diffraction analysis. The electrochemistry of
processes (pathway i) are expected with peak potential separation these diiron complexes, as well as the naphthalenyl compounds
over 400 mV. However, so far there is no precedent example of containing a formyl group (2a and 2b), was investigated. It was
diiron mimics following this mechanism. Increasing the instability found that the influence on the electrochemistry and catalysis
of the monoanion will positively shift the second reduction of these mimics towards proton reduction exerted by the
potential. Therefore, the separation of the two peak potentials will substituents on the naphthalene ring depended mainly on
decrease and in an extreme situation become a perfect two- whether the conjugation of the naphthalene cycles is disturbed
electron process; that is, the two electron processes appear as or not. However, the formyl group showed the most profound
one single reduction wave. This can be defined as an EE process influence compared with other substituents due to it taking
(pathway i). A classic example is the oxidation of Zn into Zn2+.23 For part in the conjugation. To probe the molecular mechanism of
diiron mimics, due to the instability of the monoanion, a chemical its effect, DFT calculations for complexes 3a, 3b, 4a and 4b were
reaction is followed that is an isomerisation, likely decoordinating also performed.
one of the four Fe(I)–S bonds to lower the electron density on the
dimetal centre.24,25 The coupled reaction generates such a species
that its reduction occurs at a potential not more negative than
2. Experimental
2.1 General procedures
the first one. This is generally called potential inversion, that is,
the so-called ECE process.5,6,20,21 When the coupled reaction
is extremely fast, a perfect two-electron process is expected All solvents were distilled prior to use and stored under an argon
(pathway ii). A typical example is the diiron complex derived atmosphere. Unless otherwise stated, all syntheses and manipula-
from 1,2-dithiobenzene and its derivatives.22,26–29
tions were performed using the Schlenk technique. NaBH4 and
Recently, we investigated in detail the electrochemistry of 4-halobutanoyl chloride (4-Cl(CH2)3COCl and 4-Br(CH2)3COCl)
a diiron hexacarbonyl complex bearing a bridging linkage of were purchased from either Alfa Aesar or Sigma-Aldrich and used
(1,8-dithionaphthalen-2-yl)methyl ferrocenylcarboxylate and as received. Fe3(CO)1240 and ferrocenecarbonyl chloride (FcCOCl)41
found that the complex adopts essentially the mechanism iii were synthesised following the literature processes. Naphtho[1,8-
shown in Scheme 1 and further found by DFT calculations that cd][1,2]dithiole (1) and naphtha[1,8-cd][1,2]dithiole-n-carbaldehyde
the dianion ([Fe2]2ꢀ) generated from the two sequential one- (n = 2: 2a and n = 4: 2b) were synthesised as described in the
electron transfer isomerises to the other dianion ([Fe2]02ꢀ) result- literature.42
2ꢀ
ing from the ECE processes.30 The species [Fe2]0 is supposedly
FTIR spectra were recorded on a Scimitar 2000 (Varian).
made more stable by decoordinating one of the four Fe–S bonds NMR spectra were collected on an Avance DRX 400 (Varian) in
to lower the electron density on the diiron centre. In other words, CDCl3. Elemental analysis was carried out on a Vario ELIII
for this complex, the two pathways co-exist to compete with each elemental analyzer. Electrochemistry was performed in 0.5 mol Lꢀ1
other. Such a mechanism was also found in other systems without [NBu4]BF4-CH2Cl2 or 0.1 mol Lꢀ1 [NBu4]BF4-MeCN by using a
conjugation, like naphthalene and benzene.31,32 In the two com- vitreous carbon disc (f = 1 mm) as the working electrode, a
peting processes, which one will prevail is mainly dictated by the vitreous carbon strip as the counter electrode and Ag/AgCl,
nature of the bridging linkage and thus the thermodynamic against which the potential of the ferrocenium/ferrocene couple is
stability of the monoanion right after accepting the first electron. 0.55 V.43 A scanning rate of 0.1 V sꢀ1 was routinely used unless
Interestingly, the mechanism seems to apply to diiron complexes otherwise stated. All potentials were quoted against a ferrocenium/
of various oxidation states.33
ferrocene couple.
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2.2 Crystallographic data collection
Naph). Micro-analysis for 3b (C17H6Fe2O7S2, MW = 498.05), calc.
(found): C%, 41.00 (40.37), H%, 1.21 (1.38).
Crystals suitable for X-ray analysis were obtained by the slow
evaporation of a solution in hexane/dichloromethane. Diffrac-
tion data were collected on a Bruker SMART CCD diffractometer
with graphite-monochromated Mo-Ka radiation (l = 0.71073 Å).
The crystal structures were solved using direct methods in
the SHELXS program and refined by full-matrix least-squares
routines, based on F2, using the SHELXL package.44 CCDC
numbers are 895027–895029 and 895031–895033 for the com-
plexes 3a, 3b, 4b, 5b, 6a and 7.
2.4.2 Preparation of [Fe2((l-S)2C10H5-n-CH2OH)(CO)6] (n = 2:
4a, 4: 4b). To a solution of 3a (148 mg, 0.297 mmol) in dry THF
(30 mL) was added NaBH4 (10 mg, 0.266 mmol) at ice temperature.
The reaction mixture was stirred for about 2 h under Ar. After the
completion of the reaction (monitored by TLC), the solution was
evaporated under reduced pressure to give crude product. Purifica-
tion on a silica-gel column using a mixture of dichloromethane/
petroleum ether (3/2) as eluent produced a dark red solid (4a,
100 mg, 67%). The crude product was recrystallised in hexane–
dichloromethane. Infrared spectral bands for complex 4a
(DCM, cmꢀ1): n(CO), 2075.4, 2040.2, 2000.2, (KBr) n(OH),
3437.6. 1H NMR (CDCl3, ppm): d 8.26 (1H, d, J = 8.4 Hz, Naph),
8.00 (2H, m, Naph), 7.74 (1H, d, J = 8.4 Hz, Naph), 7.39 (1H, t,
J = 7.8 Hz, Naph), 5.32 (2H, d, J = 6.4 Hz, CH2), 2.15 (1H, t, J =
6.2 Hz, OH). 13C NMR (CDCl3, ppm): 144.07, 135.89, 133.74,
133.18, 132.28, 131.42, 125.85, 125.05, 64.31. Micro-analysis for
4a (C17H8Fe2O7S2, MW = 500.06), calc. (found): C%, 40.83
(40.51), H%, 1.61 (1.69).
2.3 DFT calculations
All calculations were carried out by using the Gaussian 03
package.45 DFT calculations were carried out using the BP86
functional46,47 and a valence triple-z basis set with polarization on
all atoms (TZVP).48 Geometry optimizations of the investigated
complexes were performed without any symmetry constraints
in the ground state and the initial geometries are derived from
the crystallographic data. Frequency calculations were carried
out to ensure that the obtained geometries are at a minimum
on the potential energy surface with no imaginary frequencies.
Based on the optimized geometries, the orbital energies and
compositions of the HOMOs and LUMOs of the studied com-
plexes were calculated.
4b was analogously prepared as a dark red solid (101 mg,
68%). Infrared spectral bands for complex 4b (DCM, cmꢀ1):
n(CO), 2074.9, 2039.3, 1999.5. 1H NMR (CDCl3, ppm): d 8.32
(1H, d, J = 8.4 Hz, Naph), 8.27 (1H, d, J = 7.6 Hz, Naph), 8.23
(1H, d, J = 7.6 Hz, Naph), 7.47 (2H, m, Naph), 5.14 (2H, d, J =
5.6 Hz, CH2), 1.88 (1H, t, J = 5.8 Hz, OH). 13C NMR (CDCl3,
ppm): 207.63, 140.26, 132.79, 132.46, 132.38, 127.40, 126.96,
2.4 Synthesis
2.4.1 Preparation of [Fe2((l-S)2C10H5-n-CHO)(CO)6] (n = 2: 125.80, 125.60, 125.00, 124.62, 63.56. Micro-analysis for 4b
3a, 4: 3b). A mixture of 2a (130 mg, 0.596 mmol) and [Fe3(CO)12] (C17H8Fe2O7S2, MW = 500.06), calc. (found): C%, 40.83 (40.67),
(331 mg, 0.656 mmol) in toluene (25 mL) was refluxed at 110 1C H%, 1.61 (1.56).
for 1.5 h. The reaction was allowed to cool to room temperature
2.4.3 Preparation of [Fe2((l-S)2C10H5-n-CH2O2C(CH2)3Cl)
before filtration was carried out to remove any insoluble solids. (CO)6] (n = 2: 5a, 4: 5b). To a solution of 4a (32 mg, 0.064 mmol)
The filtrate was concentrated under reduced pressure before in DCM (10 mL) was added Et3N (0.01 mL) and 4-chloro-
being purified using flash column chromatography (silica gel, butanoylchloride (0.008 mL, 0.071 mmol), respectively, at ice
eluent: petroleum ether/DCM = 2/3). The product was collected temperature. The reaction mixture was stirred for 30 min under
as a dark-red powder (178 mg, 60%). Recrystallisation was Ar. When the reaction was completed (monitored by TLC), the
performed in a mixture of DCM and hexanes at ꢀ20 1C to give solvent was evaporated under reduced pressure. Purification on a
single crystals suitable for X-ray diffraction analysis. Infrared silica column using dichloromethane/petroleum ether (1 : 1) as
spectral absorption bands for complex 3a (DCM, cmꢀ1): n(CO), eluent gave a dark red solid (5a, 35 mg, 91%). Infrared spectral
1
2078.4, 2043.6, 2004.4, (KBr) n(CHO), 1690.6. H NMR (CDCl3, bands for complex 5a (DCM, cmꢀ1): n(CO), 2075.8, 2040.6, 2000.8.
ppm): d 11.29 (1H, s, CHO), 8.23 (1H, d, J = 6.8 Hz, Naph), 7.95 1H NMR (CDCl3, ppm): d 8.27 (1H, d, J = 7.2 Hz, Naph), 7.99
(3H, d, J = 5.2 Hz, Naph), 7.44 (1H, t, J = 7.6 Hz, Naph). 13C NMR (2H, m, Naph), 7.58 (1H, d, J = 8.4 Hz, Naph), 7.41 (1H, m, Naph),
(CDCl3, ppm): 207.27, 191.40, 133.86, 132.41, 131.47, 127.81, 5.75 (2H, s, PhCH2O), 3.64 (2H, t, J = 6.2 Hz, ClCH2), 2.65 (2H, t,
127.23, 123.97. Microanalysis for complex 3a (C17H6Fe2O7S2, J = 7.4 Hz, COCH2), 2.17 (2H, m, CH2CH2CH2). 13C NMR (CDCl3,
MW = 498.05), calc. (found): C%, 41.00 (40.33), H%, 1.21 (1.37). ppm): 207.43, 172.27, 138.83, 134.02, 133.28, 132.21, 131.24,
The relatively large discrepancy between the calculated and the 127.15, 126.79, 125.50, 125.01, 124.37, 65.51, 44.04, 31.13, 27.58.
determined values may result from the involvement of moisture Micro-analysis for 5a (C21H13ClFe2O8S2, MW = 604.60), calc.
during the operation, since the addition of 0.46 equivalent of (found): C%, 41.72 (41.33), H%, 2.17 (2.07).
H2O to the complex gave a decent result, calc. (found): C%,
40.33 (40.33), H%, 1.38 (1.39).
5b (dark-red solid, 33 mg, 85%) was prepared analogously to
5a. Infrared spectral absorption bands for complex 5b (DCM,
3b was analogously prepared as a dark red solid (202 mg, cmꢀ1): n(CO), 2075.4, 2040.2, 2000.2. 1H NMR (CDCl3, ppm):
68%). Infrared spectral bands for complex 3b (DCM, cmꢀ1): d 8.28 (1H, d, J = 7.6 Hz, Naph), 8.21 (2H, m, Naph), 7.48 (2H, t,
n(CO), 2077.5, 2042.5, 2003.3, (KBr) n(CHO), 1689.7. 1H NMR J = 6.6 Hz, Naph), 5.55 (2H, s, PhCH2O), 3.58 (2H, t, J = 6.2 Hz,
(CDCl3, ppm): d 10.29 (1H, s, CHO), 9.39 (1H, d, J = 8.4 Hz, ClCH2), 2.59 (2H, t, J = 7.0 Hz, COCH2), 2.12 (2H, m, CH2CH2CH2).
Naph), 8.37 (1H, d, J = 7.6 Hz, Naph), 8.22 (1H, d, J = 7.6 Hz, Micro-analysis for 5b (C21H13ClFe2O8S2, MW = 604.60), calc.
Naph), 7.81 (1H, d, J = 7.6 Hz, Naph), 7.50 (1H, t, J = 7.8 Hz, (found): C%, 41.72 (41.78), H%, 2.17 (2.28).
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2.4.4 Preparation of [Fe2((l-S)2C10H5-n-CH2O2C(CH2)3Br)
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(CO)6] (n = 2: 6a, 4: 6b). 6a and 6b were produced in the same
manner as that of 5a and 5b by using 4a and 4b (408 mg,
0.816 mmol) to produce 6a (433 mg, 95%) and 6b (527 mg, 99%),
respectively. Infrared spectral bands for complex 6a (DCM, cmꢀ1):
n(CO), 2075.9, 2040.6, 2001.0. 1H NMR (CDCl3, ppm): d 8.27 (1H,
d, J = 7.6 Hz, Naph), 7.99 (2H, m, Naph),7.57 (1H, d, J = 8.4 Hz,
Naph), 7.41 (1H, t, J = 7.8 Hz, Naph), 5.75 (2H, s, PhCH2O), 3.50
(2H, t, J = 6.4 Hz, ClCH2), 20.65 (2H, t, J = 7.2 Hz, COCH2), 2.26
(2H, m, CH2CH2CH2). 13C NMR (CDCl3, ppm): d 207.34, 172.06,
138.81, 134.00, 133.23, 132.16, 131.18, 127.14, 126.75, 125.46,
125.02, 124.37, 65.47, 32.56, 32.37, 27.67. Micro-analysis for 6a
(C21H13BrFe2O8S2, MW = 649.05), calc. (found): C%, 38.86 (38.56),
H%, 2.02 (2.02). Infrared spectral bands for complex 6b (DCM,
1
cmꢀ1): n(CO), 2075.0, 2039.9, 1999.8. H NMR (CDCl3, ppm): d
8.235 (3H, m, Naph), 7.470 (2H, d, J = 7.2 Hz, Naph), 5.545 (2H, s,
PhCH2O), 3.447 (2H, t, J = 6.0 Hz, ClCH2), 2.591 (2H, t, J = 7.0 Hz,
COCH2), 2.195 (2H, t, J = 4.4 Hz, CH2CH2CH2). 13C NMR (CDCl3,
400 MHz): d 207.41, 172.24, 135.28, 132.88, 132.61, 132.27, 127.20,
126.99, 126.58, 126.16, 126.02, 125.88, 64.28, 32.60, 32.36, 27.52.
Micro-analysis for 6b (C21H13BrFe2O8S2, MW = 649.05), calc.
(found): C%, 38.86 (39.01), H%, 2.02 (2.11).
2.4.5 Preparation of [Fe2(l-S)2C10H6(CO)6] (8). Complex 8 (a
dark red solid, 246 mg, 87%) was prepared in the same manner as
complex 3a. Infrared spectral bands for complex 8 (DCM, cmꢀ1):
n(CO), 2074.6, 2038.9, 1999.1. 1H NMR (CDCl3, ppm): d 8.26
(2H, d, J = 8.0 Hz, Naph), 8.01 (2H, d, J = 8.0 Hz, Naph), 7.42 (2H,
t, J = 8.0 Hz, Naph). 13C NMR (CDCl3, ppm): d 207.62, 134.30,
132.79, 132.03, 126.55, 125.38, 124.93.
Scheme 2 Synthesis of the naphthalene derivatives, the eight diiron
complexes and 7.30
Table 1 FTIR absorption bands (CO) for diiron hexacarbonyl complexes in
DCM
Complex
n
CO/cmꢀ1
3aa
3ba
4a
4b
5a
5b
6a
6b
7c
2078.4, 2043.6, 2004.4, 1690.6b
2077.5, 2042.5, 2003.3, 1689.7b
2075.4, 2040.2, 2000.2
2074.9, 2039.3, 1999.5
2075.8, 2040.6, 2000.8, 1738.3b
2075.4, 2040.2, 2000.2, 1740.6b
2075.9, 2040.6, 2001.0, 1737.6b
2075.0, 2039.9, 1999.8, 1739.9b
2075.0, 2039.9, 2000.1, 1723.3b
2074.6, 2038.9, 1999.1
8
a
The absorption bands of the formyl groups of 2a and 2b are 1642.6
3. Results and discussion
3.1 Synthesis and characterization
and 1664.1 cmꢀ1 (KBr), respectively. Organic carbonyl group (KBr).
b
c
Quoted from ref. 30.
Naphtho[1,8-cd][1,2]dithiole (1) was prepared by following
the literature procedure.49 Its derivatives, naphthalene-1,8-
disulfide-2-carboxaldehyde (2a) and naphthalene-1,8-disulfide-
4-carboxaldehyde (2b) were prepared using modified literature
procedures (Scheme 2).42 Reaction of these disulfides with
triiron dodecacarbonyl led to two diiron complexes 3a and 3b,
respectively. The diiron core of the complexes is robust enough
to allow a reaction to be performed on the formyl group without
affecting the integrity of the diiron hexacarbonyl core. Reduction
of the formyl group by NaBH4 formed complexes 4a and 4b by
converting the formyl group into a hydroxymethyl group. The
hydroxyl group could react further with 4-halobutanoyl chloride
to form complexes 5a, 5b, 6a and 6b. In addition to the above
complex (8) derived from naphtho[1,8-cd][1,2]dithiole were also
included. The data fall into two categories. For 3a and 3b, all the
absorption bands are at higher frequencies by a few wavenumbers.
This shift is attributed to the electron-withdrawing nature of
the formyl group and its conjugation with the naphthalene
ring. For the other complexes, although the substituents on
the aromatic ring vary, electronically these groups have little
influence on the absorption bands. The UV-vis spectra of
complexes 3a and 3b showed similar characteristic features,
as found in their infrared spectra in Fig. S2 (ESI†).
3.2 Structural analysis
diiron carbonyl complexes, complex 8, bearing no substituent on The molecular structures of diiron hexacarbonyl complexes 3a, 3b,
the naphthalene ring, was also synthesised by directly reacting 4b, 5b and 6a were confirmed by X-ray analysis. It should be noted
compound 1 with Fe3(CO)12 rather than using its reduced form, that the molecular structure of complex 7 was also determined
naphthalene-1,8-dithiol.34
by X-ray crystallography, even though other characterizations
These diiron complexes exhibited characteristic infrared of this complex had been reported in our recent work.30 The
absorption bands of diiron hexacarbonyl complexes, three absorp- crystal structures are shown in Fig. 2 and crystallographic
tion bands of the bound CO ranging from 2080 to 2000 cmꢀ1, as details and selected binding parameters are listed in Tables 2
shown in Fig. S1 (ESI†). All the infrared data are tabulated in and 3, respectively. In the case of complex 7, the structure
Table 1. For comparison, the infrared absorption bands of the includes a molecule of dichloromethane solvent, with a polymorph
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iron centres are linked to three carbonyl ligands in a distorted
square-pyramidal geometry, as previously reported for the analogous
complexes.34,35,50 As indicated by the data in Table 3, the Fe–Fe bond
length (2.50–2.53 Å) as well as the Fe–S bond length between
each iron and each sulphur (2.23–2.25 Å) for these complexes
are comparable with each other. Together with some represen-
tative bond angles shown in Table 3, these parameters are not
altered very much with the different substituents or different
positions on the naphthalene moiety.
3.3 Electrochemistry
All the diiron complexes exhibited at least two reduction
processes and one oxidation process, as shown in Table 4, Fig. 3
and Fig. S3 (ESI†). For reference, the electrochemistry of com-
pounds 2a and 2b is also shown in Fig. S4 (ESI†). Further scanning
towards negative potential could reveal a further reduction process
Fig. 2 Structural views of complexes 3a, 3b, 4b, 5b, 6a and 7.
not including the solvent given in Fig. 2. All of the crystal which may be assigned to a dimer generated from the reaction of
structures possess a [Fe2S2] butterfly core and in which the two the dianion and its parent complex.22
Table 2 Crystallographic data for complexes 3a, 3b, 4b, 5b, 6a and 7
Complex
3a
3b
4b
5b
6a
7
Chemical formula
Fw
Temp. (K)
Radiation
Crystal system
Space group
C
17H6O7S2Fe2
C17H6O7S2Fe2
498.04
296(2)
0.71073
Triclinic
%
P1
C17H8O7S2Fe2
500.05
296(2)
0.71073
Triclinic
%
P1
C21H13O8S2Fe2Cl
604.58
296(2)
0.71073
Monoclinic
P2(1)
C21H13O8S2Fe2Br
649.04
296(2)
0.71073
Triclinic
%
P1
C29H18O8S2Fe3Cl2
797.00
296(2)
0.71073
Triclinic
%
P1
498.04
296(2)
0.71073
Triclinic
%
P1
a/Å
b/Å
c/Å
7.556(5)
9.504(7)
14.246(10)
86.686(8)
79.551(8)
66.911(8)
925.4(11)
2
7.9316(11)
8.4597(12)
14.947(2)
90.946(2)
101.791(2)
109.5740(10)
921.1(2)
2
8.0499(10)
8.5617(11)
14.8223(18)
91.110(2)
102.7310(10)
109.1460(10)
936.7(2)
2
7.9363(12)
34.734(5)
17.444(3)
90.00
94.006(2)
90.00
4796.9(13)
8
1.674
7.710(3)
11.306(4)
15.523(5)
110.397(4)
91.963(4)
107.447(4)
1195.2(7)
2
7.653(8)
14.654(15)
14.902(15)
68.932(11)
78.682(11)
84.567(12)
1529(3)
2
a/(1)
b/(1)
g/(1)
V/Å3
Z
Dc/(g cmꢀ3
)
1.787
1.796
1.773
1.803
1.732
y range (deg)
F(000)
2.33 to 25.00
496
2.57 to 26.00
496
2.53 to 25.00
500
2.41 to 25.00
2432
2.80 to 25.00
644
2.45 to 25.00
800
Reflections collected (Rint
Reflections independent
GOF
)
6692 (0.0182)
3233
1.002
7326 (0.0186)
3569
1.037
6783 (0.0187)
3288
1.026
35 686 (0.0190)
15 924
1.045
5828 (0.0202)
3784
1.037
7337 (0.0163)
4989
1.022
R1[I 4 2s(I)]
0.0263
0.0342
0.0308
0.0360
0.0485
0.0373
wR2 (all data)
0.0725
0.1059
0.0909
0.0911
0.1402
0.1029
Table 3 Selected bonding parameters of the complexes 3a, 3b, 4b, 5b, 6a and 7
Complexes
3a
3b
4b
5b
6a
7
Fe(1)–Fe(2)
Fe(1)–S(1)
Fe(1)–S(2)
Fe(2)–S(1)
Fe(2)–S(2)
S(1)–C(7)
2.5169(18)
2.2382(15)
2.2371(13)
2.2414(12)
2.2393(14)
1.772(2)
2.5100(7)
2.2509(10)
2.2422(9)
2.2444(10)
2.2436(9)
1.783(3)
2.5140(6)
2.2532(8)
2.2427(8)
2.2476(8)
2.2455(8)
1.783(3)
2.5270(10)
2.2482(14)
2.2403(14)
2.2499(14)
2.2408(15)
1.766(5)
2.5108(12)
2.2466(15)
2.2399(14)
2.2444(15)
2.2406(15)
1.784(5)
2.509(2)
2.241(2)
2.241(2)
2.239(2)
2.2405(18)
1.772(4)
1.775(3)
S(2)–C(15)
1.778(2)
1.771(3)
1.770(3)
1.738(5)
1.771(4)
S(1)–Fe(1)–Fe(2)
S(2)–Fe(1)–Fe(2)
Fe(1)–S(1)–Fe(2)
Fe(1)–S(2)–Fe(2)
S(1)–Fe(2)–Fe(1)
S(2)–Fe(2)–Fe(1)
S(1)–Fe(1)–S(2)
S(1)–Fe(2)–S(2)
55.88(2)
55.83(4)
68.37(6)
68.42(5)
55.76(5)
55.75(2)
84.02(4)
83.89(4)
55.93(3)
56.00(3)
67.88(3)
68.05(3)
56.18(3)
55.95(3)
84.14(3)
84.26(3)
55.94(2)
55.99(2)
67.92(2)
68.13(2)
56.15(2)
55.88(2)
84.17(3)
84.23(3)
55.85(4)
55.68(4)
68.36(4)
68.65(4)
55.79(4)
55.66(4)
84.22(5)
84.17(5)
55.97(4)
55.93(4)
67.98(5)
68.17(4)
56.05(4)
55.90(4)
84.28(5)
84.31(5)
55.90(7)
55.95(3)
68.11(5)
68.08(6)
55.99(4)
55.97(7)
84.02(4)
84.09(5)
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Table 4 Electrochemical data for the diiron complexes and compounds 2a and 2ba
DCM
MeCN
Reduction (E1 a/E1 c, E2
)
Reduction (E1 a/E1 c, E2
)
E1 c–E2
o30
Oxidation (Ea)
E1 c–E2
Oxidation (Ea)
c
c
c
c
3a
3ac
3b
3bc
4a
4b
5a
5b
6a
6b
7
ꢀ1.44/ꢀ1.51b (ꢀ1.48)
ꢀ1.46/ꢀ1.54b (ꢀ1.50)
0.86
ꢀ1.36/ꢀ1.46 (ꢀ1.41), ꢀ1.60
ꢀ1.28/ꢀ1.36 (ꢀ1.32), ꢀ1.63
ꢀ1.37/ꢀ1.45 (ꢀ1.41), ꢀ1.55
ꢀ1.29/ꢀ1.37 (ꢀ1.33), ꢀ1.58
ꢀ1.44/ꢀ1.53 (ꢀ1.49), ꢀ1.88
ꢀ1.46/ꢀ1.54 (ꢀ1.50), ꢀ1.87
ꢀ1.43/ꢀ1.51 (ꢀ1.47), ꢀ1.87
ꢀ1.44/ꢀ1.51 (ꢀ1.48), ꢀ1.89
ꢀ1.44/ꢀ1.51 (ꢀ1.48), ꢀ1.88
ꢀ1.44/ꢀ1.51 (ꢀ1.48), ꢀ1.90
140
270
100
210
350
330
360
380
370
390
0.75
o30
0.69
0.77
ꢀ1.52/ꢀ1.62 (ꢀ1.57), ꢀ1.88
ꢀ1.54/ꢀ1.65 (ꢀ1.60), ꢀ1.87
ꢀ1.52/ꢀ1.60 (ꢀ1.56), ꢀ1.93
ꢀ1.53/ꢀ1.63 (ꢀ1.58), ꢀ1.95
ꢀ1.52/ꢀ1.61 (ꢀ1.57), ꢀ1.93
ꢀ1.54/ꢀ1.63 (ꢀ1.59), ꢀ1.96
ꢀ1.53/ꢀ1.62 (ꢀ1.58), ꢀ1.92
ꢀ1.52/ꢀ1.61 (ꢀ1.57), ꢀ1.92
260
220
330
320
320
330
300
310
0.82
0.82
0.89
0.90
0.90
0.89
0.85d
0.94
0.79
0.81
0.85
0.84
0.82
0.82
8
2a
2b
ꢀ1.44/ꢀ1.52 (ꢀ1.48), ꢀ1.91
ꢀ1.66, ꢀ1.79
390
130
0.70
ꢀ1.52, ꢀ1.98
460
0.69
a
b
c
c c
E1/2 is placed in parentheses where applicable. The second reduction peak potential E2 overlaps with E1
E1/2 of the pendent ferrocenyl group is 0.27 V.30
. The data were collected in DMF.
d
Among the complexes, complexes 3a and 3b show distinct
features in their reductions from the other complexes. This is
particularly obvious in DCM. In this medium, the two reductions
are almost indistinguishable except for a slight broadening of
the wave. Increasing the scanning rate enhances the second
reduction, which becomes visible as shown in Fig. S4 (ESI†). This
indicates that the formyl group exerts much stronger electronic
influence on the diiron centre compared with other substituents.
As shown in their structures, the formyl group at either position
(2 and 4) adopts a coplanar orientation with the naphthalene
moiety (Fig. 1) and the conjugation between the aromatic ring
and the formyl group is established. This conjugation may be the
root-cause of the profound difference in their reductions as the
formyl group is of electron-withdrawing nature. This means that
expanding the conjugation with the naphthalene rings ought to
be beneficial to lowering the electron density on the metal centre
and therefore, stabilising the monoanion. In other words, a larger
potential separation for the two processes would be expected.
However, the observation is to the contrary. By considering
that the aldehydes of the bridging linkages show reduction
processes between ꢀ1.5 and ꢀ1.8 V (Fig. S4, ESI†), the observed
reduction processes may contain both metal-based and ligand-
Fig. 3 Cyclic voltammograms (CVs) of complexes 3a, 3b, 4a and 4b (C =
2.86 mmol Lꢀ1) on a vitreous carbon electrode in 0.1 mol Lꢀ1 [NBu4]BF4/
CH3CN (dotted line) or 0.5 mol Lꢀ1 [NBu4]BF4/DCM (solid line) solution at a
scan rate of 0.1 V sꢀ1 (298 K, vs. Fc+/Fc). Blue or red colour is used to
distinguish the CVs obtained within various ranges of scanning potentials.
Our previous investigation into complex 7 suggested that the based processes.
electron transfer of the complex comprises two competing pathways
To support this argument, complexes 3a and 3b, 4a and 4b
with potential inversion (pathway iii, Scheme 1).30 As suggested by were chosen for theoretical calculations and the energies and
their electrochemistry, responses to the variation in scanning rates compositions of their HOMOs and LUMOs were calculated.
and current functions (Fig. 3, Fig. S3, S5 and S6, ESI†), these Recently, we used DFT calculations to examine how a bridging
complexes, except for complexes 3a and 3b, would adopt similar linkage affects the compositions of the HOMOs and LUMOs of
mechanisms for their charge transfer. The separation of the two diiron hexacarbonyl mimics.51 It was found that the linkage has
reductions of these complexes is sensitive to solvent. The gap significant influence on the compositions of the HOMOs, and
between the two processes is widened in polar solvent, such as the LUMOs were mainly located on the diiron centre in all the
acetonitrile and DMF, compared with nonpolar solvent (DCM). This examples examined. However, the calculations (Table 5 and
indicates that in polar medium, the monoanion is somewhat Fig. 4) for the four complexes showed that there are significant
stabilised and alters the energies of the LUMOs. This can be differences between the complexes. The results for complexes
attributed to electrostatic and hydrogen bonding interactions 4a and 4b follow the trend well in that their LUMOs were
between the monoanion and the solvents. Such an interaction is mainly located on the diiron centre, but the LUMOs of com-
in agreement with what we found recently that intramolecular plexes 3a and 3b are mostly dominated by the organic motif by
interaction exerts electronic influence on the frontier orbitals.51
about two thirds (Fig. 4 and Table 5). The orbital compositions
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Table 5 The energies and compositions of the HOMOs and LUMOs of
complexes 3a and 3b, 4a and 4b
HOMO (%)
LUMO (%)
Bridging
Bridging
linkage
{Fe2} linkage
{Fe2}
Complex EHOMO
ELUMO
3a
3b
4a
4b
ꢀ6.16007 ꢀ3.97729 72.4
43.6
ꢀ6.14728 ꢀ3.68668 43.3
ꢀ6.04171 ꢀ3.55689 42.7
27.6
56.4
56.7
57.3
67.5
67.8
12.8
9.8
32.5
32.2
87.2
90.2
ꢀ6.24116 ꢀ4.0649
Fig. 5 The cyclic voltammograms of complexes 3a and 3b (C
=
2.86 mmol Lꢀ1) in acetic acid–acetonitrile (inset: the plot of catalytic
current of the first reduction peak against the concentration of acetic acid
for 3a (open circle) and 3b (solid circle). The potentials were quoted
against the Fc+/Fc couple).
rather differently from the others in their reduction processes
(Fig. 3 and Fig. S3, ESI†).
3.4 Catalysis of the reduction of protons
Catalysis of proton reduction by these complexes was examined
in DCM and/or acetonitrile by using acetic acid as a proton
source (Fig. 5 and Fig. S7, ESI†). The results revealed that none
of the complexes showed sign of catalysis at the first reduction
process, except complexes 3a and 3b. Significant increases in
currents were observed at far negative potential, which is attrib-
uted to the catalysis of the diiron mimics (Fig. S8, ESI†). This
observation suggests that among the co-existing and competing EE
and ECE mechanisms we reported recently,30 the EE mechanism
prevails. This means that in the first reduction, the dianion
generated from the ECE process and with strong affinity towards
protons is not dominant. What is surprising is that complexes 3a
and 3b showed catalysis of proton reduction to some extent. As
shown in Table 4, the reduction potentials of the two complexes
are the most positive ones among the complexes, which indicates
relatively low electron density on the metal centre compared with
the other complexes. These observations are in good agreement
with their blue shift in infrared absorption bands (Table 1).
Apparently, the involvement of the formyl group in the conjuga-
Fig. 4 The HOMOs and LUMOs of complexes 3a, 3b, 4a and 4b.
suggest that the first reductions of the two complexes (3a tion played a role in reducing the electron density on the diiron
and 3b) are very much dominated by the bridging linkages. centre. Since catalytic reduction of protons involves protonation,
The involvement of the bridging linkage in their LUMOs may a catalyst of high electron density must be beneficial to the
explain why the two complexes with a formyl group behave catalysis. Evidently, the observed catalytic responses of the first
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reduction of these complexes towards proton reduction are not in Notes and references
agreement with the above argument. This abnormal behaviour
1 J. W. Peters, W. N. Lanzilotta, B. J. Lemon and L. C. Seefeldt,
Science, 1998, 282, 1853–1858.
2 Y. Nicolet, C. Piras, P. Legrand, C. E. Hatchikian and
J. C. Fontecilla-Camps, Structure, 1999, 7, 13–23.
3 X. M. Liu, S. K. Ibrahim, C. Tard and C. J. Pickett, Coord.
Chem. Rev., 2005, 249, 1641–1652.
4 J. C. Fontecilla-Camps, A. Volbeda, C. Cavazza and Y. Nicolet,
Chem. Rev., 2007, 107, 4273–4303.
5 J. F. Capon, F. Gloaguen, F. Y. Petillon, P. Schollhammer
and J. Talarmin, Coord. Chem. Rev., 2009, 253, 1476–1494.
6 F. Gloaguen and T. B. Rauchfuss, Chem. Soc. Rev., 2009, 38,
100–108.
7 C. Tard and C. J. Pickett, Chem. Rev., 2009, 109, 2245–2274.
8 T. R. Simmons, G. Berggren, M. Bacchi, M. Fontecave and
V. Artero, Coord. Chem. Rev., 2014, 270–271, 127–150.
9 N. Wang, M. Wang, Y. Wang, D. Zheng, H. Han, M. S. G.
Ahlquist and L. Sun, J. Am. Chem. Soc., 2013, 135, 13688–13691.
10 T. B. Liu and M. Y. Darensbourg, J. Am. Chem. Soc., 2007,
129, 7008–7009.
may be due to the dominant involvement of the organic moiety in
the reduction. Furthermore, the potential of the catalytic process
shifts positively over 100 mV (Fig. 5). This positive shift could be
caused by proton-coupled electron transfer (PCET), since the
reduction of the formyl group ought to involve proton transfer.
The electrochemistry and catalytic responses towards proton
reduction further support the argument that the bridging linkage
exerts profound influence on the metal centre of a diiron carbonyl
complex.32 Not surprisingly, the second reduction of all the
complexes exhibited catalysis of proton reduction, as shown in
Fig. S7 (ESI†). This catalysis supports, on the other hand, the
assignment that the second reduction process is the successive
reduction from ‘‘Fe(I)Fe(0)’’ to ‘‘Fe(0)Fe(0)’’ of the EE mecha-
nism. It must be pointed out that those peak currents increas-
ing with acid concentration can certainly be assigned to
catalysis by the reduced species of the diiron mimics, as
revealed by the control (Fig. S8, ESI†), but the exact nature of
the catalytic species is unknown.
11 A. K. Justice, L. De Gioia, M. J. Nilges, T. B. Rauchfuss, S. R.
Wilson and G. Zampella, Inorg. Chem., 2008, 47, 7405–7414.
12 A. K. Justice, M. J. Nilges, T. B. Rauchfuss, S. R. Wilson,
L. De Gioia and G. Zampella, J. Am. Chem. Soc., 2008, 130,
5293–5301.
13 C. M. Thomas, T. B. Liu, M. B. Hall and M. Y. Darensbourg,
Inorg. Chem., 2008, 47, 7009–7024.
14 M. Karnahl, S. Tschierlei, O. F. Erdem, S. Pullen,
M. P. Santoni, E. J. Reijerse, W. Lubitz and S. Ott, Dalton
Trans., 2012, 41, 12468–12477.
15 B. E. Barton, M. T. Olsen and T. B. Rauchfuss, J. Am. Chem.
Soc., 2008, 130, 16834–16835.
16 M. T. Olsen, T. B. Rauchfuss and S. R. Wilson, J. Am. Chem.
Soc., 2010, 132, 17733–17740.
17 O. F. Erdem, L. Schwartz, M. Stein, A. Silakov, S. Kaur-
Ghumaan, P. Huang, S. Ott, E. J. Reijerse and W. Lubitz,
Angew. Chem., Int. Ed., 2011, 50, 1439–1443.
18 D. Schilter and T. B. Rauchfuss, Angew. Chem., Int. Ed., 2013,
52, 13518–13520.
4. Conclusions
In this piece of work, eight diiron complexes with a naphthalene
moiety as the bridging linkage have been synthesised and fully
characterised. Their electrochemistry and behaviours of catalysis of
proton reduction suggest that, like the analogue (7) that we reported
recently,30 these complexes adopt two competing mechanisms in
their electron transfer, that is, ECE and EE mechanisms (pathway
iii, Scheme 1). Due to the conjugating effect of the naphthalene
moiety, which lowers the electron density on the diiron centre and
thus stabilises the monoanion after accepting the first electron,
of the competing mechanisms the two sequential one-electron
processes (EE mechanism) is dominant. The substituent on the
naphthalene does not significantly affect the electrochemistry and
catalysis of proton reduction if it does not significantly disturb the
conjugation of the naphthalene moiety, as it does in the cases of
complexes 3a and 3b. The involvement of the formyl group in the
conjugation of the entire naphthalene skeleton significantly altered
the electrochemical and catalytic behaviours of the two complexes.
Our results show also that the diiron complexes possessing
the naphthalene moiety exhibited decent tolerance towards
chemical manipulation under relatively mild conditions. The
tolerance offers possibilities of accessing novel diiron complexes
starting from complexes such as 3a and 3b to achieve mimics of
additional functionalities.
19 G. Berggren, A. Adamska, C. Lambertz, T. R. Simmons,
J. Esselborn, M. Atta, S. Gambarelli, J. M. Mouesca,
E. Reijerse, W. Lubitz, T. Happe, V. Artero and
M. Fontecave, Nature, 2013, 499, 66–69.
20 G. A. N. Felton, C. A. Mebi, B. J. Petro, A. K. Vannucci, D. H.
Evans, R. S. Glass and D. L. Lichtenberger, J. Organomet.
Chem., 2009, 694, 2681–2699.
21 X. H. Zeng, Z. M. Li, Z. Y. Xiao, Y. W. Wang and X. M. Liu,
Electrochem. Commun., 2010, 12, 342–345.
22 J. Zhao, Z. H. Wei, X. H. Zeng and X. M. Liu, Dalton Trans.,
2012, 41, 11125–11133.
Acknowledgements
23 A. J. Bard and L. R. Faulkner, Electrochemical methods:
fundamentals and applications, Wiley, New York, 2nd edn,
2001.
24 G. A. N. Felton, B. J. Petro, R. S. Glass, D. L. Lichtenberger
and D. H. Evans, J. Am. Chem. Soc., 2009, 131, 11290–11291.
We thank the National Natural Science Foundation of China
(Grant No. 21171073, 20871064), Ministry of Science and Technology
(China) (973 program, Grant No. 2009CB220009), and the
Government of Zhejiang Province (Qianjiang professorship
for XL) for supporting this work.
New J. Chem.
This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2015

View Article Online
NJC
Paper
25 A. K. Vannucci, S. H. Wang, G. S. Nichol, D. L. Lichtenberger, 42 E. W. Miller, S. X. Bian and C. J. Chang, J. Am. Chem. Soc.,
D. H. Evans and R. S. Glass, Dalton Trans., 2010, 39, 3050–3056. 2007, 129, 3458–3459.
26 G. A. N. Felton, A. K. Vannucci, J. Chen, L. T. Lockett, 43 X. H. Zeng, Z. M. Li and X. M. Liu, Electrochim. Acta, 2010,
N. Okumura, B. J. Petro, U. I. Zakai, D. H. Evans, R. S. Glass and
D. L. Lichtenberger, J. Am. Chem. Soc., 2007, 129, 12521–12530.
27 F. Gloaguen, D. Morvan, J. F. Capon, P. Schollhammer and
J. Talarmin, J. Electroanal. Chem., 2007, 603, 15–20.
28 L. Schwartz, P. S. Singh, L. Eriksson, R. Lomoth and S. Ott,
C. R. Chim., 2008, 11, 875–889.
29 D. Streich, M. Karnahl, Y. Astuti, C. W. Cady, L. Hammarstrom,
R. Lomoth and S. Ott, Eur. J. Inorg. Chem., 2011, 1106–1111.
30 G. F. Qian, H. L. Wang, W. Zhong and X. M. Liu, Electrochim.
Acta, 2015, 163, 190–195.
31 Y. W. Wang, Z. M. Li, X. H. Zeng, X. F. Wang, C. X. Zhan,
Y. Q. Liu, X. R. Zeng, Q. Y. Luo and X. M. Liu, New J. Chem.,
2009, 33, 1780–1789.
32 Y. Tang, Z. H. Wei, W. Zhong and X. M. Liu, Eur. J. Inorg.
Chem., 2011, 1112–1120.
33 Z. Y. Xiao, Z. H. Wei, L. Long, Y. L. Wang, D. J. Evans and
X. M. Liu, Dalton Trans., 2011, 40, 4291–4299.
34 R. J. Wright, C. Lim and T. D. Tilley, Chem. – Eur. J., 2009,
15, 8518–8525.
35 A. P. S. Samuel, D. T. Co, C. L. Stern and M. R. Wasielewski,
J. Am. Chem. Soc., 2010, 132, 8813–8815.
36 C. Figliola, L. Male, P. N. Horton, M. B. Pitak, S. J. Coles,
55, 2179–2185.
44 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.,
2008, 64, 112–122.
45 M. J. T. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery Jr., T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi,
V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega,
G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth,
P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz,
Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov,
G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin,
D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara,
M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez and J. A. Pople, Gaussian 03
(Revision E.01), 2003.
S. L. Horswell and R. S. Grainger, Organometallics, 2014, 33, 46 J. P. Perdew, Phys. Rev. B: Condens. Matter Mater. Phys., 1986,
4449–4460. 33, 8822–8824.
37 C. Topf, U. Monkowius and G. Knor, Inorg. Chem. Commun., 47 A. D. Becke, Phys. Rev. A: At., Mol., Opt. Phys., 1988, 38,
2012, 21, 147–150. 3098–3100.
38 L. Chen, M. Wang, F. Gloaguen, D. H. Zheng, P. L. Zhang 48 F. Weigend and R. Ahlrichs, Phys. Chem. Chem. Phys., 2005,
and L. C. Sun, Chem. – Eur. J., 2012, 18, 13968–13973. 7, 3297–3305.
39 L. Chen, M. Wang, F. Gloaguen, D. H. Zheng, P. L. Zhang 49 A. J. Ashe, J. W. Kampf and P. M. Savla, Heteroat. Chem.,
and L. C. Sun, Inorg. Chem., 2013, 52, 1798–1806. 1994, 5, 113–119.
40 H. Wang, Y. Xie, R. B. King and H. F. Schaefer, J. Am. 50 P. Li, S. Amirjalayer, F. Hartl, M. Lutz, B. d. Bruin, R. Becker,
¨
Chem. Soc., 2006, 128, 11376–11384.
S. Woutersen and J. N. H. Reek, Inorg. Chem., 2014, 53,
41 T. Kojima, D. Noguchi, T. Nakayama, Y. Inagaki, Y. Shiota,
5373–5383.
K. Yoshizawa, K. Ohkubo and S. Fulkuzumi, Inorg. Chem., 51 H. L. Wang and X. M. Liu, Inorg. Chim. Acta, 2013, 406,
2008, 47, 886–895. 113–118.
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