Photoswitchable electrochemical behaviour of a [FeFe] hydrogenase model with a dithienylethene derivative

Article abstract of DOI:10.1039/c2dt31507f

A diiron dithiolate complex 1o with a dithienylethene (DTE) phosphine ligand has been elaborately designed and fully investigated by spectroscopic and DFT computational studies. Upon irradiation with UV light, the DTE moiety in complex 1o undergoes an exc

Full text of DOI:10.1039/c2dt31507f

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2012, 41, 11813
www.rsc.org/dalton
PAPER
Photoswitchable electrochemical behaviour of a [FeFe] hydrogenase model
with a dithienylethene derivative†
Hui-Min Wen, Jin-Yun Wang, Ming-Qiang Hu, Bin Li, Zhong-Ning Chen* and Chang-Neng Chen*
Received 9th July 2012, Accepted 2nd August 2012
DOI: 10.1039/c2dt31507f
A diiron dithiolate complex 1o with a dithienylethene (DTE) phosphine ligand has been elaborately
designed and fully investigated by spectroscopic and DFT computational studies. Upon irradiation with
UV light, the DTE moiety in complex 1o undergoes an excellent photocyclization reaction to attain
ring-closed state 1c in high yield (>95%), accompanied by a colour change from orange to deep blue.
On the other hand, upon irradiation with visible light (>460 nm), ring-closed form 1c in CH3CN solution
reverts perfectly into ring-open form 1o. Both 1o and 1c were characterised by IR, 1H, 31P, 19F NMR
and electrochemical spectroscopy. The electrochemical behaviours of both the open and closed forms
were investigated by cyclic voltammetry. Upon photocyclization reaction, a 290 mV (from −2.29 V to
−2.00 V) positive shift is induced in the potential of electrochemical catalytic proton reduction, due to
the electron-withdrawing effect of the ring-closed DTE moiety. Consequently, complex 1 can reversibly
photoswitch the potential of proton reduction on the [FeFe] moiety.
more positive than that of the excited state of the photosensitizer,
Introduction
making the photoinduced electron transfer from the photosensiti-
zer to the catalyst thermodynamically feasible.5–7 Today, one of
Hydrogen gas is regarded as a promising clean and renewable
energy source for the future. [FeFe] hydrogenase has received
intensive attention because of its high efficiency in reversible H2
production and/or H2 oxidation in nature under mild conditions:
2H+ + 2e ⇄ H2 1. The X-ray crystallographic analyses of the
[FeFe] hydrogenase enzymes from Desulfovibrio desulfuricans
Hildenborough and Clostridium pasteurianum I have revealed
that the active site is a novel dithiolate bridged di-iron cluster
which shares a structural resemblance with the di-iron dithiolate
carbonyl organometallic complexes.2 In order to mimic the
structure and behavior of the active site, extensive researches
have been devoted to find catalyst candidates for biomimetic
hydrogen production and uptake. In the past decades, numerous
catalyst models based on [2Fe2S] complexes have been syn-
thesized, and most of them have shown inspiring electro-
catalytic3,4 and photocatalytic activities.5,6 Generally, the most
economical catalysts are supposed to be those having a low
reduction potential and a remarkable increase in the intensity of
the reduction current with the addition of acid.8 Recently, the
di-iron complex with a less negative reduction potential is high-
lighted for photo-catalytic hydrogen production, because the
reduction potential of the dinuclear iron complex needs to be
the most prominent ways to reduce the reduction potential is to
introduce electron-withdrawing chloro substituents onto the
dithiolate bridge of diiron dithiolate hexacarbonyl complexes, as
reported by Ott and co-workers.9 Sun et al. reported another
approach to adjust the reduction potentials and improve the
photostability of the [2Fe2S] model complexes by using weak
electron donating phosphine ligands to displace carbonyls.10
We report herein a novel [2Fe2S] model compound to tune the
potential of hydrogen production by introducing a photochromic
dithienylethene (DTE) unit into the [FeFe] hydrogenase subsite
mimic.
As we know, the combination of the photochromic ligands
with other functional systems can change reversibly not only the
absorption spectra, but also their geometrical and electronic
structures,11 which eventually switch the physicochemical pro-
perties such as fluorescence, electrical conductivity and magnet-
ism.12,13 Since dithienylethenes (DTEs) are a class of efficient
photochromic compounds because of their excellent photochro-
mic properties such as fast response, fatigue resistance and facile
color-control,11–12 they can undergo a reversible change between
the ring-open and ring-closed states upon irradiation with proper
UV/Vis light, resulting in the conversion of both the color and
the electronic structure of the whole molecule. Considering that
the ring-closed isomer of the DTE moiety is a stronger π-electron
accepter than its ring-open counterpart,13,14 it is expected that
the incorporation of a dithienylethene ligand into the [FeFe]
hydrogenase model would modulate the reduction potential of
the [FeFe] moiety. In order to achieve this target, we elaborately
designed and prepared compound 1o (Scheme 1) that
State Key Laboratory of Structural Chemistry, Fujian Institute of
Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou, Fujian 350002, China. E-mail: ccn@fjirsm.ac.cn;
Tel: (+86) 591-8379-2395
†Electronic supplementary information (ESI) available: Spectral data;
optimized geometries; and computational details. See DOI:
10.1039/c2dt31507f
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 11813–11819 | 11813

View Article Online
Scheme 1 Synthetic routes to 1o. (a) (i) n-BuLi, THF; (ii) I2; (b) (μ-pdt)Fe2(CO)6, Me3NO·2H2O, CH3CN; (c) [PdCl2(PPh3)2], CuI, TEA, toluene,
40 °C.
incorporated the dithienylethenederivative L1 into the [FeFe]
hydrogenase model.
Results and discussion
Synthesis and characterization
Ott and co-workers have synthesized a dyad in which the photo-
sensitizer was linked to a model of the [FeFe] hydrogenase
active site by a phosphine ligand.15 We chose a similar phos-
phine ligand to prepare complex 1 by reaction of L1 (1-(5-
methyl-2-(2-phenyl)-4-thienyl)-2-(2-methyl-5-ethynyl-3-thienyl)-
perfluorocyclopentene) with the complex 2 [(μ-pdt)Fe2(CO)5-
(PPh2C6H4I-4)] (pdt = propanedithiolate = –SCH2CH2CH2S–)
moiety through Sonogashira cross coupling reaction in the
presence of Pd(PPh3)2Cl2 and CuI in TEA–toluene solution
(Scheme 1). The IR spectrum of complex 1o in CH3CN exhibits
three major bands in the CO region at 2044, 1984, 1931 cm−1
,
which is comparable to that of triphenylphosphine mono-
substituted di-iron dithiolate complexes, indicating similar
skeletal and electronic structures for these complexes.15 After
the photocyclization reaction, no distinguishable shift is observed
in 1c.
The photochromic reaction has been monitored by 1H, 31P and
19F NMR spectra in CD2Cl2.16 Upon irradiation with UV light,
the two thienyl proton signals of 1o at 7.30 (H1o) and 7.26 (H2o)
ppm show a high field shift to 6.69 (H1c) and 6.51 (H2c) ppm
due to the formation of the ring-closed form 1c, indicating a
higher electron density in both DTE thiophene rings than in the
ring-open counterparts (Fig. 1a).16 The 31P NMR signal of the
open form 1o at 65.06 ppm is shifted slightly to the low-field at
65.38 ppm in the closed form (Fig. 1b).16 In the 19F NMR
spectra, the open form 1o exhibits one signal at −132.2 ppm,
two signals at −110.3 and −110.4 ppm with an intensity ratio of
1 : 1 : 1 (Fig. S1†).16 Upon photocyclization, the signal at
−132.2 ppm is gradually reduced, a high-field shifted signal is
observed at −133.8 ppm due to the conversion of 1o → 1c.
Meanwhile, the two signals at −110.3 and −110.4 ppm are pro-
gressively decreased, whereas four sets of doublets are detected
at high-field from −112.0 to −115.1 ppm, indicating higher
1
Fig. 1 The (a) H and (b) 31P NMR spectral changes of 1o in CD2Cl2
upon irradiation with 313 nm, showing the conversion of 1o → 1c.
electron density in DTE perfluorocyclopentene after photocycli-
zation (Fig. S1†).14 The conversion percentage of 1o → 1c at the
photostationary state (PSS) is >95%, as revealed from 1H,
31P and 19F NMR spectral studies.
Electronic absorption and photochromic properties
Photochromic conversions of complex 1 are depicted in
Scheme 2. Upon irradiation at 313 nm within 80 s, 1o in
11814 | Dalton Trans., 2012, 41, 11813–11819
This journal is © The Royal Society of Chemistry 2012

View Article Online
CH3CN turns from orange to deep blue (Scheme 2), followed by
the UV-Vis absorption spectral changes (Fig. 2). The absorption
bands of ring-open 1o in CH3CN are located at 271 nm and
321 nm. Based on the TD-DFT calculations, the high-energy
absorption band at 271 nm is mainly composed of IL [π → π*-
(DTE)] intraligand transition and CLCT [3d(Fe) → π*(DTE)]
clusters to ligand charge transfer transition (Table 1). The absorp-
tion at 321 nm is primarily ascribed to the intracluster tran-
sitions (IC) within the Fe2S2 cluster mixed with some IL [π →
π*(DTE)] character based on TD-DFT calculations (Table 1).
Upon irradiation at 313 nm, the two intense UV absorptions
gradually decrease, while two new absorption bands at 380 nm
and 600 nm appear due to the photocyclization reaction of 1o to
1c (Fig. 2a). The shoulder peak at 380 nm of the closed form 1c
arises from IC transition of the Fe2S2 cluster mixed with some
CLCT charge transfer transition from Fe2S2 cluster to
PPh2PhCuC/DTE (Table 2). The low energy absorption at
600 nm is mainly contributed by the IL [π → π*(DTE)] tran-
sition of the ring-closed isomer. On the other hand, upon
irradiation with visible light (>460 nm) for 12 min, ring-closed
complex 1c in CH3CN solution reverts into the open form
(Fig. 2b). As shown in Fig. S2,† this complex shows excellent
reversibility in its photochromic behavior, with no apparent loss
in its photochromic reactivities over at least six repeating cycles.
The quantum yields for the photocyclization and photocyclo-
reversion of the complex are 0.45 (Φo-c) and 0.017 (Φc-o
)
respectively.
Electrochemistry
The cyclic voltammograms (CV) of 1o and 1c were monitored
under N2 with stepwise addition of HOAc in CH3CN solution.
Complex 1o exhibits two obvious irreversible reductive peaks at
−1.78 and −1.95 V in the absence of HAcO vs. Fc–Fc+. The
first irreversible reduction at −1.78 V due to the diiron portion is
quite similar to PPh3 mono-substituted complexes.15 With refer-
ence to previous works on many phosphine ligand mono-substi-
tuted diiron analogues, the first reduction is assigned to [FeIFeI]
→ [FeIFe0].17,18 Controlled-potential electrolysis of complex 1o
(1 mM in the absence of acid in CH3CN at −1.45 V vs. Ag/
AgCl ≈ −1.85 V vs. Fc+–Fc) requires a net consumption of
about 0.9 F mol−1, which supports the assignment of the one-
electron reduction process under these conditions. As a result,
the one-electron reduced product could be unambiguously
Scheme 2 Photochromic behaviour of complex 1.
Fig. 2 (a) The UV-Vis absorption spectral changes of the complex 1o (2 × 10−5 M) in CH3CN at 298 K upon irradiation at 313 nm. (b) The UV-Vis
absorption spectral changes of the complex 1c (2 × 10−5 M) in CH3CN at 298 K upon irradiation at >460 nm.
Table 1 Absorption transitions and singlet excited states for 1o in CH3CN, calculated by TD-DFT method
E/nm (eV)
Transition
Contrib. (%)
O.S.
Assignment
Exp./nm
321
S13
S31
342.89 (3.62)
HOMO → LUMO + 2
HOMO − 1 → LUMO + 1
HOMO → LUMO
HOMO − 1 → LUMO + 3
HOMO → LUMO + 3
35.80
28.62
25.30
47.42
37.76
0.7568
IC/IL
IL/IC/CLCT/LLCT
IC/IL/CLCT
IL/CLCT/LLCT
CLCT/IL/LLCT
283.79 (4.37)
0.3965
271
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 11813–11819 | 11815

View Article Online
Table 2 Absorption transitions and singlet excited states for 1c in CH3CN, calculated by TD-DFT method
E, nm (eV)
Transition
Contrib. (%)
O.S.
Assignment
Exp (nm)
S1
S7
641.90 (1.93)
387.74 (3.20)
HOMO → LUMO
HOMO − 1 → LUMO + 1
HOMO → LUMO + 1
79.51
34.24
0.6272
0.3472
0.2615
IL
600
380 Sh
IC/CLCT/IL
LCCT/IL/LLCT
Fig. 3 Cyclic voltammograms of complex 1o (black line) and 1c (gray
line), 1.0 mM in 0.1 M nBu4NPF6–CH3CN at a scan rate of 100 mV s−1
vs. Fc+–Fc.
observed in electrochemistry as that described in the previous
literature.10,18–23 The middle peak at −1.95 V exhibits a slightly
positive shift compared to that of free ligand L1o (Ered = −2.03 V),
implying that this reduction process is localized on the DTE
unit (Fig. 3). In the presence of HOAc, a new reduction peak at
−2.29 V is involved in electrocatalysis of H2 production as evi-
denced by the increase in current with acid concentration
(Fig. 4a). This electrocatalytic behavior of 1o is comparable to
the typical electrocatalytic reduction of weak acid in the phos-
phine ligand mono-substituted or all-carbonyl diiron models
(Table 3).18,22,23
When the solution of complex 1o without acid was irradiated
by a UV lamp, the reduction wave due to the ring-open DTE
moiety at −1.95 V converts to two new reduction peaks at −1.23
and −1.55 V (Fig. 3) with the conversion of 1o to 1c. The reduc-
tive potential of 1o at −1.78 V shifts slightly to −1.75 V after
photocyclization, which is similar to other aryl phosphine mono-
substituted complexes (Fig. S3†).10,15 On the other hand, the
wave (−2.29 V in 1o) involved in the electrocatalytic proton
reduction process is shifted to the less negative region at −2.00 V
upon photo-induced ring closure (Fig. 4b), possibly with the
same electrocatalytic mechanism as 1o because of their similar
molecular structure and voltammograms. Consequently, 290 mV
(from −2.29 V to −2.00 V) positive shift is achieved for the
hydrogen production through photocyclization, because the ring-
closed DTE is a stronger π-acid than its ring-open counterpart
which draws more electron density via backbonding from diiron
dithiolate cluster.13,14 Nevertheless, the electrocatalytic efficiency
is apparently reduced as concluded from the process that the cata-
lytic current is less sensitive to [H+] (Fig. S4†). To investigate
the stability of the system, the electrochemical behaviour of
complex 1 in CH3CN with 10 equivalents of acetic acid was
monitored under repeated irradiation with UV and visible light
by cyclic voltammetry, and the cyclic voltammograms can revert
Fig. 4 Cyclic voltammograms of 1o (a) and 1c (b), 1.0 mM in 0.1 M
nBu4NPF6–CH3CN at a scan rate of 100 mV s−1 vs. Fc+–Fc, upon
addition of HOAc (0–11 mM).
Table 3 The electrochemical data of L1o, L1c, 1o and 1c
Ered a/V
DTE
Fe2S2 centerb
Fe2S2 centerc
L1o
L1c
1o
−2.03
—
—
−1.78
−1.75
—
—
−2.29
−2.00
−1.30, −1.65
−1.95
1c
−1.23, −1.55
a All potentials were recorded in 1.0 mM in 0.1 M nBu4NPF6–CH3CN at
a scan rate of 100 mV s−1 vs. Fc+–Fc. b The reduction potential of
[FeIFeI] → [FeIFe0]. c The potential of hydrogen production.
between the two states over at least four repeating cycles in 12 h
(Fig. S5†).
11816 | Dalton Trans., 2012, 41, 11813–11819
This journal is © The Royal Society of Chemistry 2012

View Article Online
1
as the eluent to give 2 (252 mg, 67%) as a dark-red solid. H
Conclusion
NMR (CDCl3, ppm): 1.37–1.53 (m, 4H), 1.73–1.78 (m, 2H),
7.38–7.44 (m, 8H), 7.64–7.68 (m, 4H), 7.77 ppm (d, J =
7.56Hz, 2H). 31P NMR (CDCl3, ppm): 65.01. ESI-MS (m/z):
634.7 [M − 4CO + H]+. Elemental analysis calcd (%) for
C26H20Fe2IO5PS2: C, 41.85; H, 2.70. Found: C, 41.88; H, 2.63.
IR (CH3CN, cm−1): 2046, 1984, 1931.
We report for the first time a fairly photo-stable model of iron-
only hydrogenases with a photochromic dithienylethene–phos-
phine ligand. The UV-Vis absorptions of 1 are ascribed reason-
ably, based on DFT calculation. The electrochemical catalytic
proton reduction behavior of the open and closed forms have
been investigated, both of which show electrocatalytic hydrogen
production. The reductive potential of H2 production shows a
290 mV anodic shift compared with that of the ring-open form
due to the electron-withdrawing performance of the ring-closed
DTE moiety upon photocyclization reaction. Consequently, the
potential of hydrogen production can be photoswitchable in one
molecular system by irradiation with UV/Vis, based on the fact
that the distribution of electron density is altered between the
ring-open and closed states.
1o. [PdCl2(PPh3)2] (23 mg, 0.032 mmol) and CuI (2.5 mg,
0.0125 mmol) were added to a degassed solution of [(μ-pdt)-
Fe2(CO)5{PPh2(p-C6H4I)}] (240 mg, 0.32 mmol) and L1o
(150 mg, 0.32 mmol) in triethylamine–toluene (1 : 1, 20 mL)
solution at 40 °C. After stirring in the dark for 3 h at this temp-
erature, the solution was concentrated in vacuo and the black
residue was subjected to column chromatography using CH2Cl2–
hexane (2 : 1 v/v) to give 1o (146 mg, yield: 42%) as a dark-red
solid. 1H NMR (CD2Cl2, ppm): 1.41–1.51 (m, 4H, CH2),
1.72–1.77 (m, 2H, CH2), 1.94 (s, 3H, Me), 1.95 (s, 3H, Me),
7.26 (s, 1H, thiophene), 7.27–7.31 (m, 1H, Ph), 7.31 (s, 1H,
thiophene), 7.37 (t, 2H, J = 7.48 Hz, Ph), 7.46 (m, 6H, Ph), 7.54
(d, 4H, J = 7.48 Hz, Ph), 7.62–7.70 (m, 6H, Ph). 31P NMR
(CD2Cl2, ppm): 65.06. 19F NMR (CD2Cl2, ppm): −110.3 (s,
2F), −110.4 (s, 2F), −132.2 (s, 2F). ESI-MS (m/z) 1031
Experimental section
General procedures and materials
All reactions were carried out under a dry argon atmosphere by
using Schlenk techniques and vacuum-line systems unless other-
wise specified. The solvents were dried, distilled, and degassed
prior to use except that those for spectroscopic measurements
were of spectroscopic grade. The ligands L1o,24 (4-bromophe-
[M
− 2CO +
H]+. Elemental analysis calcd (%) for
C49H33F6Fe2O5PS4: C, 54.16; H, 3.06. Found: C, 55.21; H,
3.12. IR (CH3CN, cm−1): 2044, 1984, 1931.
nyl)diphenylphosphine25 and (μ-pdt)Fe2(CO)6 were prepared
26
by the synthetic procedures described in the literature. Other
chemicals were purchased from commercial sources and used
without further purification.
Physical measurements
1H, 31P and 19F NMR spectra were performed on a Bruker
Avance III (400 MHz) spectrometer with SiMe4 as the internal
reference and H3PO4 as the external reference, respectively.
UV-Vis absorption spectra were measured on a Perkin-Elmer
Lambda 25 UV-Vis spectrophotometer. Infrared spectra (IR) in
CH3CN solution were recorded on a Magna 750 FT-IR spectro-
photometer. Elemental analyses (C, H and N) were carried out
on a Perkin-Elmer model 240 C elemental analyzer. Electrospray
ionization mass spectrometry (ESI-MS) was recorded on a Finni-
gan DECAX-30000 LCQ mass spectrometer using dichloro-
methane as the mobile phase. Cyclic voltammetry (CV) and
differential pulse voltammetry (DPV) were conducted with a
potentiostat/galvanostat model 263A in acetonitrile solution con-
Synthesis
PPh2(p-C6H4I). To an anhydrous THF (30 mL) solution of
(4-bromophenyl)diphenylphosphine (0.512 g, 1.5 mmol) was
slowly added n-BuLi (1.6 M in hexane, 1.0 mL, 1.6 mmol)
using a syringe. After reaction, the mixture was stirred for
40 min at −78 °C and a solution of iodine (0.5 g, 2 mmol) in
anhydrous THF (10 mL) was transferred into the reaction flask.
The reaction mixture was slowly warmed to room temperature
with stirring over 16 h before being quenched by the slow
addition of a 10 wt% solution of aqueous sodium sulfite
(50 mL). The aqueous layer was separated from the organic layer
and extracted with CH2Cl2 (3 × 50 mL). The combined organic
fractions were washed with brine (50 mL), dried over MgSO4,
filtered and evaporated to dryness under reduced pressure. The
residue was purified by crystallization from ethanol–water to
give PPh2(p-C6H4I) (332 mg, 57%) as a colorless solid. 1H
NMR (CDCl3, ppm): 7.00–7.04 (t, 2H, J = 7.64 Hz), 7.28–7.36
(m, 10H), 7.65–7.67 (d, 2H, J = 7.88 Hz). 31P NMR (CDCl3,
ppm): −6.36. ESI-MS (m/z): 389 [M + H]+.
n
taining 0.1 M Bu4NPF6 as the supporting electrolyte under N2
unless otherwise stated. DPV was performed at a rate of 20 mV s−1
with a pulse height of 40 mV. Platinum and glassy graphite
were used as the counter and working electrodes, respectively,
and the potential was measured against the Ag/AgCl reference
electrode and reported relative to the internal reference of
Fc–Fc+ = 0.00 V. UV light was irradiated using a ZF5 UV lamp
(313 nm), and visible light irradiation (>460 nm) was carried out
by using a LZG220 V500 W tungsten lamp with cutoff filters.
The quantum yields were determined by comparing the reaction
yields of the diarylethenes against 1,2-bis(2-methyl-5-phenyl-
3-thienyl) perfluorocyclo-pentene.27
(μ-pdt)Fe2(CO)5{PPh2(p-C6H4I)} (2). A solution of (μ-pdt)
Fe2(CO)6 (0.389 g, 0.5 mmol) and Me3NO·2H2O (0.111 g,
1 mmol) in CH3CN (30 mL) was stirred for 5 to 10 min at room
temperature. A solution of PPh2(p-C6H4I) (0.388 g, 0.5 mmol)
in CH3CN (10 mL) was then added with stirring for 3 h. The
solvent was evaporated, and the residue was purified by chrom-
atography on a silica gel column with CH2Cl2–hexane (2 : 1 v/v)
Theoretical methodology
The geometrical structures of compounds 1o and 1c as isolated
molecules in vacuum were optimized by density functional
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 11813–11819 | 11817

View Article Online
theory (DFT)28 methods at the gradient-corrected correlation
functional PBE1PBE level.29 During the optimization processes,
the convergent values of maximum force, root-mean-square
(RMS) force, maximum displacement, and RMS displacement
were set by default. To analyze the spectroscopic properties,
eighty simple excited states of the studied compounds were
calculated by time-dependent DFT (TD-DFT) methods30 at the
PBE1PBE level on the basis of the optimized geometrical struc-
tures. The polarizable continuum model method (PCM)31 using
acetonitrile as the solvent was employed. The self-consistent
field (SCF) convergence criteria of the RMS density matrix and
maximum density matrix were set at 10−8 and 10−6 a.u., respect-
ively, in all the electronic structure calculations. The iterations of
excited states continued until the changes on energies of states
were no more than 10−7 a.u. between the iterations, and then
convergence was reached in all the excited states. In these calcu-
lations, the SDD32 basis set consisting the effective core poten-
tials (ECP) was employed for the iron, phosphorus, and sulfur
atoms, and the 6-31G(p,d)33 basis set for the remaining atoms
were used. To describe precisely the molecular properties, one
additional f-type polarization function was implemented for iron
(αf = 2.462) atom,34 and the d-type polarization function was
implemented for phosphorus (αd = 0.34), and sulfur (αd = 0.421)
atoms.35 All calculations were performed with the Gaussian 03
program package.36 Visualization of the optimized structures and
frontier molecular orbitals were performed by GaussView. The
Ros & Schuit method37 (C-squared population analysis method,
SCPA) is used to partition orbital composition.
2012, 5, 6763–6778; F. Wang, W. G. Wang, H. Y. Wang, G. Si,
C. H. Tung and L. Z. Wu, ACS Catal., 2012, 2, 407–416; P. Du and
R. Eisenberg, Energy Environ. Sci., 2012, 5, 6012–6021.
6 A. P. S. Samuel, D. T. Co, C. L. Stern and M. R. Wasielewski, J. Am.
Chem. Soc., 2010, 132, 8813–8815; L. C. Song, X. F. Liu, J. B. Ming,
J. H. Ge, Z. J. Xie and Q. M. Hu, Organometallics, 2010, 29, 610–617;
D. Streich, Y. Astuti, M. Orlandi, L. Schwartz, R. Lomoth,
L. Hammarstrom and S. Ott, Chem.–Eur. J., 2010, 16, 60–63; F. Wang,
W. G. Wang, X. J. Wang, H. Y. Wang, C. H. Tung and L. Z. Wu, Angew.
Chem., Int. Ed., 2011, 50, 3193–3197; W. G. Wang, T. B. Rauchfuss,
L. Bertini and G. Zampella, J. Am. Chem. Soc., 2012, 134, 4525–4528.
7 H. M. Wen, Y. H. Wu, Y. Fan, L. Y. Zhang, C. N. Chen and Z. N. Chen,
Inorg. Chem., 2010, 49, 2210–2221; H. M. Wen, Y. H. Wu, L. J. Xu,
L. Y. Zhang, C. N. Chen and Z. N. Chen, Dalton Trans., 2011, 40, 6929–
6938.
8 G. A. N. Felton, R. S. Glass, D. L. Lichtenberger and D. H. Evans,
Inorg. Chem., 2006, 45, 9181–9184; V. Fourmond, P. A. Jacques,
M. Fontecave and V. Artero, Inorg. Chem., 2010, 49, 10338–10347.
9 L. Schwartz, P. S. Singh, L. Eriksson, R. Lomoth and S. Ott, C. R. Chim.,
2008, 11, 875–889; S. Kaur-Ghumaan, L. Schwartz, R. Lomoth, M. Stein
and S. Ott, Angew. Chem., Int. Ed., 2010, 49, 8033–8036.
10 Y. Na, M. Wang, J. X. Pan, P. Zhang, B. Akermark and L. C. Sun, Inorg.
Chem., 2008, 47, 2805–2810; P. Li, M. Wang, L. Chen, J. H. Liu,
Z. B. Zhaoa and L. C. Sun, Dalton Trans., 2009, 1919–1926; F. W. Huo,
J. Hou, G. C. Chen, D. M. Guo and X. J. Peng, Eur. J. Inorg. Chem.,
2010, 3942–3951.
11 M. Irie and M. Mohri, J. Org. Chem., 1988, 53, 803–808; M. Irie and
K. Uchida, Bull. Chem. Soc. Jpn., 1998, 71, 985–996; M. Irie, Chem.
Rev., 2000, 100, 1685–1716.
12 K. Matsuda and M. Irie, J. Photochem. Photobiol., C, 2004, 5, 169–182;
H. Tian and S. J. Yang, Chem. Soc. Rev., 2004, 33, 85–97.
13 P. H.-M. Lee, C.-C. Ko, N. Zhu and V. W.-W. Yam, J. Am. Chem. Soc.,
2007, 129, 6058–6059; M. T. Indelli, S. Carli, M. Ghirotti, C. Chiorboli,
M. Ravaglia, M. Garavelli and F. Scandola, J. Am. Chem. Soc., 2008,
130, 7286–7299; V. W.-W. Yam, J. K.-W. Lee, C.-C. Ko and N. Zhu,
J. Am. Chem. Soc., 2009, 131, 912–913.
14 M. N. Roberts, C. J. Carling, J. K. Nagle, N. R. Branda and M. O. Wolf,
J. Am. Chem. Soc., 2009, 131, 16644–16645.
15 J. Ekstrom, M. Abrahamsson, C. Olson, J. Bergquist, F. B. Kaynak,
L. Eriksson, S. C. Licheng, H. C. Becker, B. Akermark, L. Hammarstrom
and S. Ott, Dalton Trans., 2006, 4599–4606.
Acknowledgements
We thank financial support from the National Natural Science
Foundation China (Grant Nos. 20973172, 21071145 and
21101153), the National Basic Research Program of China (no.
2009CB220009), and the Provincial Natural Science Foundation
of Fujian (no. 2011J01063).
16 B. Li, Y. H. Wu, H. M. Wen, L. X. Shi and Z. N. Chen, Inorg. Chem.,
2012, 51, 1933–1942.
17 R. Mejia-Rodriguez, D. S. Chong, J. H. Reibenspies, M. P. Soriaga and
M. Y. Darensbourg, J. Am. Chem. Soc., 2004, 126, 12004–12014;
Z. Wang, J. H. Liu, C. J. He, S. Jiang, B. Akermark and L. C. Sun,
J. Organomet. Chem., 2007, 692, 5501–5507; W. M. Gao, J. Ekstrom,
J. H. Liu, C. N. Chen, L. Eriksson, L. H. Weng, B. Akermark and
L. C. Sun, Inorg. Chem., 2007, 46, 1981–1991.
18 G. Si, W. G. Wang, H. Y. Wang, C. H. Tung and L. Z. Wu, Inorg. Chem.,
2008, 47, 8101–8111; W. G. Wang, H. Y. Wang, G. Si, C. H. Tung and
L. Z. Wu, Dalton Trans., 2009, 2712–2720; X. H. Zeng, Z. M. Li and
X. M. Liu, Electrochim. Acta, 2010, 55, 2179–2185; L. J. Wang,
Z. Y. Xiao, X. Ru and X. M. Liu, RSC Adv., 2011, 1, 1211–1219;
N. Wen, F. F. Xu, Y. A. Feng and S. W. Du, J. Inorg. Biochem., 2011,
105, 1123–1130.
19 F. Gloaguen, J. D. Lawrence, M. Schmidt, S. R. Wilson and
T. B. Rauchfuss, J. Am. Chem. Soc., 2001, 123, 12518–12527; L. C. Song,
Z. Y. Yang, H. Z. Bian, Y. Liu, H. T. Wang, X. F. Liu and Q. M. Hu, Orga-
nometallics, 2005, 24, 6126–6135; S. Gao, J. L. Fan, S. Sun, X. J. Peng,
X. Zhao and J. Hou, Dalton Trans., 2008, 2128–2135; F. F. Xu, S. W. Du,
Y. P. Liu, J. Hassan, J. Zhang and A. M. Bond, Dalton Trans., 2011, 40,
10907–10917; C. Gimbert-Suriñach, M. Bhadbhade and S. B. Colbran,
Organometallics, 2012, 31, 3480–3491.
20 Y. T. Si, C. B. Ma, M. Q. Hu, H. Chen, C. C. Chen and T. Q. Liu, New
J. Chem., 2007, 31, 1448–1454; M. Q. Hu, H. M. Wen, C. B. Ma, N. Li,
Q. Y. Yan, H. Chen and C. N. Chen, Dalton Trans., 2010, 39, 9484–
9486.
References
1 M. W. W. Adams and E. I. Stiefel, Science, 1998, 282, 1842–1843;
R. Cammack, Nature, 1999, 397, 214–215; M. Frey, ChemBioChem,
2002, 3, 153–160.
2 J. W. Peters, W. N. Lanzilotta, B. J. Lemon and L. C. Seefeldt, Science,
1998, 282, 1853–1858; B. J. Lemon and J. W. Peters, Biochemistry,
1999, 38, 12969–12973; Y. Nicolet, C. Piras, P. Legrand,
C. E. Hatchikian and J. C. Fontecilla-Camps, Structure, 1999, 7, 13–23.
3 M. Schmidt, S. M. Contakes and T. B. Rauchfuss, J. Am. Chem. Soc.,
1999, 121, 9736–9737; M. Y. Darensbourg, E. J. Lyon and J. J. Smee,
Coord. Chem. Rev., 2000, 206–207, 533–561; L. C. Song, Acc. Chem.
Res., 2005, 38, 21–28; J. F. Capon, F. Gloaguen, P. Schollhammer and
J. Talarmin, Coord. Chem. Rev., 2005, 249, 1664–1676; J. F. Capon,
F. Gloaguen, F. Y. Petillon, P. Schollhammer and J. Talarmin, Coord.
Chem. Rev., 2009, 253, 1476–1494; F. Gloaguen and T. B. Rauchfuss,
Chem. Soc. Rev., 2009, 38, 100–108.
4 D. J. Evans and C. J. Pickett, Chem. Soc. Rev., 2003, 32, 268–275;
S. P. Best, Coord. Chem. Rev., 2005, 249, 1536–1554; X. M. Liu,
S. K. Ibrahim, C. Tard and C. J. Pickett, Coord. Chem. Rev., 2005, 249,
1641–1652; C. Tard and C. J. Pickett, Chem. Rev., 2009, 109, 2245–
2274; S. Tschierlei, S. Ott and R. Lomoth, Energy Environ. Sci., 2011, 4,
2340–2352.
21 S. J. Borg, T. Behrsing, S. P. Best, M. Razavet, X. M. Liu and
C. J. Pickett, J. Am. Chem. Soc., 2004, 126, 16988–16999; S. J. Borg,
M. I. Bondin, S. P. Best, M. Razavet, X. Liu and C. J. Pickett, Biochem.
Soc. Trans., 2005, 33, 3–6; S. J. Borg, J. W. Tye, M. B. Hall and
S. P. Best, Inorg. Chem., 2007, 46, 384–394.
5 L. C. Sun, B. Akermark and S. Ott, Coord. Chem. Rev., 2005, 249,
1653–1663; R. Lomoth and S. Ott, Dalton Trans., 2009, 9952–9959;
M. Wang, L. Chen, X. Q. Li and L. C. Sun, Dalton Trans., 2011, 40,
12793–12800; M. Wang, L. Chen and L. Sun, Energy Environ. Sci.,
22 S. J. Borg, S. K. Ibrahim, C. J. Pickett and S. P. Best, C. R. Chim., 2008,
11, 852–860.
11818 | Dalton Trans., 2012, 41, 11813–11819
This journal is © The Royal Society of Chemistry 2012

View Article Online
23 D. S. Chong, I. P. Georgakaki, R. Mejia-Rodriguez, J. Samabria-Chinchilla,
M. P. Soriaga and M. Y. Darensbourg, Dalton Trans., 2003, 4158–4163.
24 M. N. Roberts, J. K. Nagle, J. G. Finden, N. R. Branda and M. O. Wolf,
Inorg. Chem., 2009, 48, 19–21.
25 J. Shin, J. Bertoia, K. R. Czerwinski and C. Bae, Green Chem., 2009, 11,
1576–1580.
26 E. J. Lyon, I. P. Georgakaki, J. H. Reibenspies and M. Y. Darensbourg,
J. Am. Chem. Soc., 2001, 123, 3268–3278.
27 M. Irie, T. Lifka, S. Kobatake and N. Kato, J. Am. Chem. Soc., 2000,
122, 4871.
28 A. D. Becke, J. Chem. Phys., 1993, 98, 5648–5652.
29 J. P. Perdew, K. Burke and M. Ernzerhof, Phys. Rev. Lett., 1996, 77,
3865–3868.
30 R. Bauernschmitt and R. Ahlrichs, Chem. Phys. Lett., 1996, 256, 454–
464; M. E. Casida, C. Jamorski, K. C. Casida and D. R. Salahub,
J. Chem. Phys., 1998, 108, 4439–4449; R. E. Stratmann, G. E. Scuseria
and M. J. Frisch, J. Chem. Phys., 1998, 109, 8218–8224.
31 V. Barone, M. Cossi and J. Tomasi, J. Chem. Phys., 1997, 107, 3210–
3221; M. Cossi, G. Scalmani, N. Rega and V. Barone, J. Chem. Phys.,
2002, 117, 43–54.
32 M. Dolg, U. Wedig, H. Stoll and H. Preuss, J. Chem. Phys., 1987, 86,
866–872; P. Schwerdtfeger, M. Dolg, W. H. E. Schwarz, G.
A. Bowmaker and P. D. W. J. Boyd, Chem. Phys., 1989, 91, 1762–1774;
D. Andrae, U. Häussermann, M. Dolg, H. Stoll and H. Preuss, Theor.
Chim. Acta, 1990, 77, 123–141.
33 M. M. Francl, W. J. Pietro, W. J. Hehre, J. S. Binkley, M. S. Gordon,
D. J. DeFrees and J. A. Pople, J. Chem. Phys., 1982, 77, 3654–3665.
34 A. W. Ehlers, M. Böhme, S. Dapprich, A. Gobbi, A. Höllwarth, V. Jonas,
K. F. Köhler, R. Stegmann, A. Veldkamp and G. Frenking, Chem. Phys.
Lett., 1993, 208, 111–114.
35 P. Pyykkő and F. Mendizabal, Inorg. Chem., 1998, 37, 3018–3025.
36 M. J. 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. 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 D.02.
Gaussian, Inc., Wallingford, CT, 2004.
37 P. Ros and G. C. A. Schuit, Theor. Chim. Acta, 1966, 4, 1–12.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 11813–11819 | 11819