Transition metal tetrapentafluorophenyl porphyrin catalyzed hydrogen evolution from acetic acid and water

Article abstract of DOI:10.1007/s11243-017-0185-1

The performance of Cu (1), Co (2) and Zn (3) complexes of meso-tetrakis(pentafluorophenyl)porphyrin in the electrocatalyzed evolution of hydrogen has been investigated. In acetic acid media, hydrogen evolution turnover frequency (TOF) values for complexes 1, 2 and 3 were 22.1, 19.8 and 18.1?h^?1, respectively, at an overpotential of 942?mV versus Ag/AgNO₃. In buffer solution at pH 7.0, the corresponding hydrogen evolution TOF values increased dramatically, to 266, 234, 218?h^?1 at a similar overpotential of 878?mV versus SHE. The Faradaic yields of 1, 2, and 3 for sustained proton reduction in catalytic experiments at a glassy carbon electrode over 72?h were 89.7, 90.4 and 91.0%, respectively, with no observable catalyst decomposition.

Full text of DOI:10.1007/s11243-017-0185-1

Transit Met Chem (2017) 42:773–782
DOI 10.1007/s11243-017-0185-1
Transition metal tetrapentafluorophenyl porphyrin catalyzed
hydrogen evolution from acetic acid and water
Dong-Xu Zhang1 Hui-Qing Yuan1 Hua-Hua Wang1 Atif Ali1 Wei-Hong Wen1
•
•
•
•
•
An-Na Xie1 Shu-Zhong Zhan1 Hai-Yang Liu1
•
•
Received: 5 July 2017 / Accepted: 11 September 2017 / Published online: 19 September 2017
Ó Springer International Publishing AG 2017
Abstract The performance of Cu (1), Co (2) and Zn (3)
complexes of meso-tetrakis(pentafluorophenyl)porphyrin
in the electrocatalyzed evolution of hydrogen has been
investigated. In acetic acid media, hydrogen evolution
turnover frequency (TOF) values for complexes 1, 2 and 3
were 22.1, 19.8 and 18.1 h-1, respectively, at an overpo-
tential of 942 mV versus Ag/AgNO3. In buffer solution at
pH 7.0, the corresponding hydrogen evolution TOF values
increased dramatically, to 266, 234, 218 h-1 at a similar
overpotential of 878 mV versus SHE. The Faradaic yields
of 1, 2, and 3 for sustained proton reduction in catalytic
experiments at a glassy carbon electrode over 72 h were
89.7, 90.4 and 91.0%, respectively, with no observable
catalyst decomposition.
great interest because of its potential to reduce dependence
on fossil fuels [4]. One of the common approaches to
generate H2 is water splitting by electrochemical catalysis
[5]. In nature, hydrogenase enzymes can efficiently cat-
alyze the production of hydrogen. However, these enzymes
are difficult to obtain in adequate amounts for commercial
applications, and furthermore, their stability is often lim-
ited outside of living systems [6, 7]. Some platinum-based
catalysts can very efficiently catalyze H2 production from
water, but cannot be widely applied for commercial
development due to the low natural abundance and high
cost of this metal [8, 9]. However, much progress has been
made in searching for hydrogen evolution catalysts based
on earth-abundant metals. Thus, transition metal com-
plexes of iron [10–12], copper [13–15], cobalt [16–19] and
nickel [20] have been found be capable of electrocatalytic
H2 evolution. It is well known that metalloporphyrins can
catalyze many reactions due to their suitable redox prop-
erties [21]. In particular, metalloporphyrins have been
investigated as electrocatalysts for H2 generation in
homogeneous solution [22], or adsorbed onto an electrode
surface [23]. Cobalt tetraphenylporphyrin (CoTPP) Nafion
membrane coated on a Pt electrode can be used for proton
reduction in aqueous solution [24]. Recently, it was
reported that water-soluble anionic cobalt(II) tetrakis(p-
sulfonatophenyl)porphyrin (CoTPPS) is an efficient cata-
lyst for electrocatalytic H2 generation in neutral aqueous
solution [25]. Others tested metalloporphyrin electrocata-
lysts for hydrogen evolution include nickel [26] and iron
[27] complexes of meso-tetrakis(pentafluorophenyl)por-
phyrin (TFPP) and, Cu, Co, Zn, Ru, Fe and Ni complexes
of octaethylporphyrin [28]. Previously, we have focused on
electron-deficient manganese corrole [29] or porphyrin [30]
complexes for the catalytic oxidation of organic substrates.
More recently, we found that electron-deficient cobalt
Introduction
With the rapid depletion of fossil fuels, humankind faces
critical energy and environmental crises. On the basis of
current consumption levels of fossil fuels, all the available
resources on our planet will be inadequate to supply the
global energy demand in a century or two [1–3]. As a
source of clean and renewable fuel, hydrogen has attracted
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-017-0185-1) contains supplementary
material, which is available to authorized users.
& Hai-Yang Liu
chhyliu@scut.edu.cn
1
Department of Chemistry, Key Laboratory of Functional
Molecular Engineering of Guangdong Province, South China
University of Technology, Guangzhou 510641, China
123

774
Transit Met Chem (2017) 42:773–782
corrole shows good performance for catalytic hydrogen
evolution [31]. TFPP is a typical electron-deficient por-
phyrin [32], and so far its nickel [26] and iron [27] com-
plexes as well as the free base [33] have been tested for
catalytic hydrogen evolution. The potential at which H2
evolution occurs can be controlled by modulation of the
electronic properties of the ligand, with less electron
donating ligands giving rise to a more easily reduced
complex that catalyzes H2 evolution at a more positive
potential [34]. For metalloporphyrins, the attachment of
strongly electron-withdrawing substituents like meso-C6F5
allows for catalysis at lower overpotentials and thus pro-
motes H2 evolution, despite the fact that such groups
decrease the basicity of the metal center so make it less
reactive toward protons [26]. Nevertheless, electron-rich
metal centers can still allow catalysis at low overpotentials,
provided they are sufficiently basic. Another advantage of
fluorinated substituents is their ability to increase the
resistance toward oxidative destruction of porphyrin
ligands. Thus, more effective metalloporphyrin-based
hydrogen production electrocatalysts may be developed by
the combination of tuning the electron-withdrawing capa-
bility of the porphyrin ligand together with the basicity of
the central metal. To extend the application of transition
metal complexes of TFPP in this aspect, we here wish to
report on our investigation of catalytic hydrogen evolution
by Cu(II), Co(II), and Zn(II) complexes of TFPP
(Scheme 1). We found that water could be successfully
used as a proton source in an acetonitrile/water (V/V = 2/
3) solvent system, and CuTFPP had the best catalytic
activity among these three metalloporphyrins.
Experimental
Materials and measurements
All reagents were purchased from commercial sources and
used as received without further purification. High resolution
mass (HRMS) spectra were recorded with a Bruker Maxis
impact mass spectrometer equipped with an electrospray
ionization (ESI) source. 1H NMR spectra were recorded with
a Bruker Avance III 400 MHz spectrometer in CDCl3
(d = 7.26 ppm) solution. UV–visible spectra were recorded
with a Hitachi U-3010 spectrophotometer. Cyclic voltam-
mograms (CVs) were obtained with a CHI-660E electro-
chemical analyzer under nitrogen using a three-electrode cell
in which a glassy carbon electrode (1 mm in diameter) was
the working electrode, saturated Ag/AgNO3 (in DMF solu-
tion) and Ag/AgCl (in buffer solution) provided the refer-
ence electrode, and a platinum wire was the auxiliary
electrode. The ferrocene/ferrocenium (1?) couple was used
as an internal standard. The supporting electrolyte was 0.1 M
[(n-Bu)4N]ClO4. Controlled potential electrolysis (CPE)
experiments in aqueous media were conducted using an
airtight glass double-compartment cell separated by a glass
frit. The working compartment was fitted with a glassy car-
bon plate and an Ag/AgCl reference electrode. The auxiliary
compartment was fitted with a platinum gauze electrode. The
working compartment was filled with 40 ml of 0.25 M
buffer solution (acetonitrile–water (2:3 V/V) as solvent) at
various pH values containing 0.1 M KCl as the supporting
electrolyte, while the auxiliary compartment was filled with
40 ml of phosphate buffer solution (pH = 7). Both com-
partments were sparged for 60 min with nitrogen. CPE
experiments were conducted immediately after addition of
the appropriate complex. After electrolysis, CH4 was added
as a standard to the reactor, and the gas mixture was assayed
using an Agilent Technologies 7890A GC chromatograph.
TFPP was synthesized according to the described
method [35]: UV–Vis (CH2Cl2) kmax (relatively intensity):
412 (1.000), 507 (0.081), 583 (0.024) nm. 1H NMR
(400 MHz, CDCl3): d 8.92 (s, 8H), - 2.92 (s, 2H).19F
NMR (376 MHz, CDCl3): d - 136.51 (dd, J = 23.1,
7.8 Hz), - 151.22 (t, J = 20.9 Hz), - 161.33 (dt,
J = 22.5, 7.4 Hz). HRMS, calcd for C44H10F20N4:
975.0659, found for C44H10F20N4: 975.0656.
Preparation of the complexes
TFPP (60 mg, 61.6 lmol) was dissolved in DMF (30 mL).
Cu(OAc)2ÁH2O (200 mg, 1 mmol) was added, and the
solution was heated to reflux for 1 h, then left to cool. The
solution was extracted with dichloromethane (DCM)/water
(V/V = 1/2), and the organic phase was collected and
washed 6–7 times with water. Solvent was evaporated to
Scheme 1 Chemical formulae of metal complexes of TFPP (1: M//
Cu; 2: M//Co; 3: M//Zn)
123

Transit Met Chem (2017) 42:773–782
775
dryness to obtain the crude product CuTFPP. This was
purified by column chromatography using DCM/MeOH
(V/V = 100/5). Recrystallization from DCM/hexane
afforded complex 1 as a red solid (63 mg, yield 95%).
Complexes 2 and 3 were synthesized by the same proce-
dure, but replacing Cu(OAc)2ÁH2O with Co(OAc)2Á4H2O
and Zn(OAc)2Á2H2O, respectively. HRMS of the com-
plexes and given in the Supplementary Materials.
CuTFPP: UV–Vis (CH2Cl2) kmax (relatively intensity):
409 (1.000), 535 (0.049), 570 (0.022) nm. HRMS, calcd for
C44H8CuF20N4: 1035.9798, found for C44H8CuF20N4:
1035.9795.
ZnTFPP: UV–Vis (CH2Cl2) kmax (relatively intensity):
415 (1.94), 545 (0.073), 569 (0.012) nm. 1H NMR
(400 MHz, CDCl3): d 8.98 (s, 2H). 19F NMR (376 MHz,
CDCl3): d - 136.83 (dd, J = 23.8, 8.3 Hz), - 152.02 (t,
J = 20.9 Hz), - 161.78 (td, J = 23.5, 8.2 Hz). HRMS,
calcd for C44H8ZnF20N4: 1036.9794, found for C44H8-
ZnF20N4: 1036.9795.
Results and discussion
Cyclic voltammetry studies
CoTFPP: UV–Vis (CH2Cl2) kmax (relatively intensity):
406 (1.000), 534 (0.132), 570 (0.063) nm. HRMS, calcd for
C44H8CoF20N4: 1030.9756, found for C44H8CoF20N4:
1030.9767.
CVs of each complex in DMF in the presence of 0.1 M [n-
Bu4N]ClO4 as supporting electrolyte are shown in Fig. 1.
As observed in Fig. 1a, the CV of complex 1 exhibits two
Fig. 1 CVs of complexes 1 (a), 2 (b), 3 (c) (2.4 lM) in 0.1 M [n-Bu4N]ClO4 DMF solution at a glassy carbon electrode and a scan rate of
100 mV s-1. Ferrocene internal standard (*)
123

776
Transit Met Chem (2017) 42:773–782
reversible redox waves (E1/2) at - 1.32 and - 0.84 V
versus Ag/AgNO3, which can be assigned to the CuI/0 and
CuII/I couples, respectively. Figure 1b, c for complexes 2
and 3 displays assigned similar trends, respectively. As
shown in Fig. S1, the current responses of the redox events
at the two peak potentials display a linear dependence on
the square root of the scan rate in each figure, which is
indicative of diffusion-controlled processes [36], with
electrochemically active species freely diffusing in solu-
tion. Based on these observations, we proceeded to explore
the activities of this series of complexes as electrocatalysts
for hydrogen evolution at such distinctive potentials.
Scheme 2 Possible mechanistic pathways for H2 evolution electro-
catalyzed by metal complexes of TFPP
Catalytic hydrogen evolution in DMF
also be from a metal-hydride H-M? intermediate, formed
by the reduction of higher valent metal-hydride H-M2?
species. Thus, there might be two hydrogen evolution
pathways A and B in the current catalytic system
(Scheme 2). Similar behavior was observed for the cobalt
porphyrin 2 (Fig. S2(a)). However, path B was not
observed for Zn porphyrin 3, which exhibited no catalytic
wave growing after the M(0) state. This is consistent with
the properties of Zn2? as a hard acid with stable d10
electronic configuration.
For the purpose of determining their possible electrocat-
alytic activities, CVs of all three complexes were recorded
in the presence of acetic acid in DMF. For complex 1,
addition of varying amounts of HOAc triggers catalytic
currents at potentials near the CuI/Cu0 couple (Fig. 2). The
scans show a systematic increase in icat near - 1.36 V with
increasing acid concentrations from 0.00 to 18.00 lM. This
rise in current can be attributed to the catalytic generation
of H2 from acetic acid [37]. The reduction potential of
complex 1 remains almost constant and the onset of the
catalytic wave moves slightly to more anodic values with
sequential increments of acid concentration. Interestingly,
a new intense hydrogen evolution peak at icat near -1.81 V
could be observed upon addition of HOAc. Similar
observations have been reported for other catalytic systems
[19, 27, 34]. As in these examples, hydrogen evolution may
To confirm that the complexes are responsible for
catalysis, a number of controlled potential experiments
were also carried out under the same conditions, including
the metal-free TFPP, M(OAc)2ÁH2O and the mixture of the
free ligand and M(OAc)2ÁH2O (M = Cu, Co and Zn). As
observed in Fig. S3–S9, the catalytic waves observed for
free TFPP, M(OAc)2ÁH2O, or the mixtures of the TFPP and
M(OAc)2ÁH2O, did not match that obtained for complex 1.
To further validate the electrocatalytic activities of these
complexes, we conducted a series of electrolyses in DMF
solution with acetic acid at variable applied potential in a
double-compartment cell. Figure 3a, c, e shows the total
charge for bulk electrolysis of solutions containing com-
plexes 1, 2 and 3 in the presence of acetic acid. The charge
increased significantly when the applied potential was
made more negative. Another evaluation of good catalytic
efficiency is that catalysis could occur with relatively low
overpotential. The overpotential is defined by Eq. (1) [38];
from Fig. 3a, we can see when the overpotential was
542 mV versus Ag/AgNO3, catalysis occurred. Further-
more, when the applied potential was - 1.45 V versus Ag/
AgNO3 (overpotential 942 mV versus Ag/AgNO3), the
maximum charge reached 13.2 mC during 2 min of
electrolysis.
Fig. 2 CVs of complex 1 (1.14 mM) in the absence of acid (black
trace), and with varying concentrations of acid in DMF. Conditions:
room temperature, 0.1 M [n-Bu4N]ClO4 as supporting electrolyte,
scan rate = 100 mV s-1, GC working electrode (1 mm diameter), Pt
wire counter electrode, Ag/AgNO3 reference electrode, Ferrocene
internal standard
Overpotential ¼ Applied potential À EHꢀ A
EHꢀ A ¼ EHꢀ þ À ð2:303RT=FÞpKa;HA
ð1Þ
123

Transit Met Chem (2017) 42:773–782
777
Fig. 3 a, c, e Charge buildup versus time from electrolysis of
complexes 1, 2, 3 (0.01 lM) in DMF (0.1 M [n-Bu4N]ClO4) under
various overpotentials. All data have been processed by blank
subtraction. b, d, f Turnover frequency (mol H2/mol catalysts/h) for
electrocatalytic hydrogen production by complexes 1, 2, 3 (0.01 lM)
under overpotentials (mV versus Ag/AgNO3)
123

778
Transit Met Chem (2017) 42:773–782
which gave * 4.6 mL of H2 over an electrolysis period of
where E°H? is the standard potential for the solvated pro-
ton–dihydrogen couple, and Ka,HA is the dissociation con-
stant of acetic acid.
1 h with
a Faradaic efficiency of 89.7% for H2
(Fig. S12(a)). Based on Eq. (2), the TOF for complex 1 was
266 h-1 at an overpotential of 878 mV versus SHE (pH
7.0) (see equation S4 and Fig. 5b), where
Assuming that every catalyst molecule and every elec-
tron are used for the reduction of protons, in accordance
with Eq. (2) [39], we calculated TOF values for the cata-
lysts reaching a maximum of 21.6, 19.4 and 18.3 h-1 at an
overpotential of 942 mV [Eq. (S1) (S2) (S3) and Fig. 3b, d,
f)], for complexes 1, 2 and 3, respectively. Hence, the three
complexes have almost identical catalytic capacities, and
copper was a little better than the others.
Overpotential ¼ Applied potential À EðpHÞ
EðpHÞ ¼ 0:059 pH
ð3Þ
The analyses for complexes 2 and 3 can be seen in
Fig. 5c–f. Comparing the three results, we found that 1 is a
better catalyst than the other two complexes, not only in
DMF but also in acetonitrile/water solvent mixture. To the
best of our knowledge, these values (266, 234, 217 h-1) are
comparable with those for other molecular catalysts and
higher than those of some reported molecular catalysts for
electrochemical hydrogen production from neutral water,
including a dinickel complex that exhibits a turnover
number of 100 mol of H2 per mole of catalyst with a
turnover frequency of 160 mol of H2 per mole of catalyst
per hour at an overpotential of 820 mV [40] and a cobalt
complex displaying a turnover number of 5 mol of H2 per
mole of catalyst with a turnover number of 0.4 mol of H2
per mole of catalyst per hour at an overpotential of 390 mV
[41].
TOF ¼ DC=ðF Â n1 Â n2 Â tÞ
ð2Þ
where DC is the charge from the catalyst solution during
CPE minus the charge from solution without catalyst dur-
ing CPE, F is Faraday’s constant, n1 is the moles of elec-
trons required to generate 1 mol of H2, n2 is the moles of
catalyst in solution, and t is duration of electrolysis.
Catalytic hydrogen evolution in aqueous media
We have also investigated catalytic hydrogen evolution in
aqueous media, a much more attractive medium for the
sustainable generation of hydrogen. CVs were conducted in
0.25 M phosphate buffers at different pH values and con-
centrations. From Fig. 4a, we can see that, at pH 7, cat-
alytic current was not apparent until a potential of -1.5 V
versus Ag/AgCl was attained in the absence of complex 1.
With addition of complex 1, the onset of catalytic current
was observed at about -1.23 V versus Ag/AgCl, and the
current strength increased significantly with increasing
concentrations of complex 1 from 0.00 to 0.038 lM. The
potential shifted to a more positive value of about 270 mV
compared to that in the absence of complex 1. It is sug-
gested that 1 can also catalyze reduction of protons from
water to H2. Furthermore, it was found that the catalytic
current maxima for all three complexes are also dependent
on the pH values of the buffers (Fig. S10), indicating that
the catalytic current is controlled by diffusion of the sub-
stance to the electrode surface and that the catalysts are
molecular in nature.
Catalytic stabilities of the complexes
To evaluate the catalytic durabilities of the complexes, we
operated extended CPE in water while keeping the pH at
7.0 with 0.25 M buffer. A potential of -1.45 V versus Ag/
AgCl was employed for the measurement in order to ensure
a rapid turnover rate during the electrolysis. Again taking
the complex 1 as an example, as shown in Fig. S13(a), a
total of 454.8 C was passed during the electrolysis. The
catalyst affords a robust and essentially linear charge
buildup over time, with no substantial loss over the course
of 72 h. After electrolysis for 72 h, the pH of the solution
increased from 7.0 to 8.9, consistent with accumulation of
OH- by water reduction. Fig. S13(c–f) displays the cat-
alytic charge and current for complexes 2 and 3.
Catalytic hydrogen production can also be achieved with
these complexes in neutral buffer. Figure 5 shows the total
charge of bulk electrolysis of solutions containing com-
plexes 1, 2 and 3 at pH 7.0. From the CPE experiments, the
maximum charge was only 98 mC under -1.45 V versus
Ag/AgCl at pH 7.0 during 2 min of electrolysis in absence
of complex 1 (Fig. S11(a)). Upon addition of complex 1,
the charge reached 208.7 mC due the formation of H2. The
evolved H2 was analyzed by gas chromatography, Fig. 6a,
Conclusions
In conclusion, the three metal porphyrins were demon-
strated to be viable catalysts for electrochemical hydrogen
evolution. Electrocatalytic experiments indicated that this
series of complexes can not only electrocatalyze hydrogen
evolution from acetic acid but also from purely aqueous
media (pH 7.0). The copper complex proved to be the best
123

Transit Met Chem (2017) 42:773–782
779
Fig. 4 a, c, e CVs of complexes 1, 2 and 3 at various concentrations
(pH = 7.0). Conditions: 0.1 M KCl as supporting electrolyte; scan
rate, 100 mV s-1; GC working electrode (1 mm in diameter); Pt
counter electrode; Ag/AgCl reference electrode. b, d, f plot of
catalytic peak current versus concentrations of complexes 1, 2 and 3
123

780
Transit Met Chem (2017) 42:773–782
Fig. 5 a, c, e Charge buildup of complexes 1, 2 and 3 (0.10 lM)
versus a series of applied potentials in 0.25 M phosphate buffer at pH
7.0. All data have been background subtracted. b, d, f Turnover
frequency (mol H2/mol catalysts/h) for electrocatalytic hydrogen
production by complexes 1, 2 and 3 (0.10 lM) under overpotentials
(mV vs. SHE) in 0.25 M phosphate buffer (pH = 7.0)
123

Transit Met Chem (2017) 42:773–782
781
Fig. 6 1 (a), 2 (b), 3 (c) GC traces after a 1 h of controlled potential electrolysis at - 1.45 V versus Ag/AgCl of 0.01 lM complexes 1, 2 and 3
in 0.25 M phosphate buffer, pH 7.0. A standard of CH4 was added for calibration purposes
7. Vignais PM, Billoud B (2007) Chem Rev 107:4206–4272
8. Dempsey JL, Brunschwig BS, Winkler JR, Gray HB (2009) Acc
Chem Res 42:1995–2004
9. Helm ML, Stewart MP, Bullock RM, Dubios MR, Dubios DL
of the three. Ongoing efforts are focused on modifying the
ligands to give related water-soluble complexes for further
functional studies, with an emphasis on chemistry relevant
to sustainable energy cycles.
(2011) Science 333:863–866
10. Rose MJ, Gray HB, Winkler JR (2012) J Am Chem Soc
134:8310–8313
11. Berggren G, Adamska A, Lambertz C, Simmons TR, Esselborn J,
Atta M, Gambarelli S, Mouesca JM, Reijerse E, Lubitz W, Happe
T, Artero V, Fontecave M (2013) Nature 499:66–69
12. Li X, Wang M, Zheng D, Han K, Dong J, Sun L (2012) Energ
Environ Sci 5:8220–8224
Acknowledgements This research was funded by National Natural
Science Foundation of China (Nos. 21371059, 21671068).
References
13. Cao JP, Fang T, Fu LZ, Zhou LL, Zhan SZ (2014) Int J Hydrog
Energy 39:13972–13978
14. Fang T, Lu HX, Zhao JX, Zhan SZ, Lv QY (2015) J Mol Catal A
Chem 396:304–309
1. Blankenship RE, Tiede DM, Barber J, Brudvig GW, Fleming G,
Ghirardi M, Gunner MR, Junge W, Kramer DM, Melis A (2011)
Science 332:805–809
2. Gust D, Moore TA, Moore AL (2009) Acc Chem Res
42:1890–1898
15. Sirbu D, Turta C, Gibson EA, Benniston AC (2015) Dalton Trans
44:14646–14655
3. Balzani V, Credi A, Venturi M (2008) ChemSusChem 1:26–58
4. Lewis NS, Nocera DG (2006) Proc Natl Acad Sci USA
103:15729–15735
5. McKone JR, Marinescu SC, Brunschwig BS, Winkler JR, Gray
HB (2014) Chem Sci 5:865–878
16. Kleingardner JG, Kandemir B, Bren KL (2013) J Am Chem Soc
136:4–7
17. Singh WM, Baine T, Kudo S, Tian SL, Ma XAN, Zhou HY,
DeYonker NJ, Pham TC, Bollinger JC, Baker DL, Yan B,
Webster CE, Zhao X (2012) Angew Chem Int Ed 51:5941–5944
18. Mondal B, Sengupta K, Rana A, Mahammed A, Botoshansky M,
Dey SG, Gross Z, Dey A (2013) Inorg Chem 52:3381–3387
6. Fontecilla-Camps JC, Volbeda A, Cavazza C, Nicolet Y (2007)
Chem Rev 107:4273–4303
123

782
Transit Met Chem (2017) 42:773–782
19. Lei H, Han A, Li F, Zhang M, Han Y, Du P, Lao W, Cao R
(2014) Phys Chem Chem Phys 16:1883–1893
31. Yuan HQ, Wang HH, Kandhadi J, Wang H, Zhan SZ, Liu HY
(2017) Appl Organomet Chem. doi:10.1002/aoc.3773
32. Musselman BD, Watson JT, Chang CK (1986) J Mass Spectrom
21:215–219
´
20. Jacques PA, Artero V, Pecaut J, Fontecave M (2009) Proc Natl
Acad Sci USA 106:20627–20632
21. Zagal JH, Bedioui F, Dodelet JP (2006) N4—Macrocyclic Metal
Complexes. Springer Science—Business Media LLC, New York
22. Kellett RM, Spiro TG (1985) Inorg Chem 24:2373–2377
23. Kellett RM, Spiro TG (1985) Inorg Chem 24:2378–2382
24. Abe T, Taguchi F, Imaya H, Zhao F, Zhang J, Kaneko M (1998)
Polym Adv Technol 9:559–562
25. Beyene BB, Mane SB, Hung CH (2015) Chem Commun
51(81):15067–15070
26. Han YZ, Fang HY, Jing HZ, Sun HL, Lei HT, Lai WZ, Cao R
(2016) Angew Chem Int Ed 55:5457–5462
27. Alenezi K (2017) Int J Electrochem Sci 12:812–818
33. Wu YY, Villagran, Dino (2016) Abstracts of papers, 251st ACS
national meeting & exposition, San Diego, CA, United States
34. Hu XL, Brunschwig BS, Peters JC (2007) J Am Chem Soc
129:8988–8998
35. Lindsey JS, Wagner RW (1989) J Org Chem 54:828–836
36. Thoi VS, Karunadasa HI, Surendranath Y, Long JR, Chang CJ
(2012) Energy Environ Sci 5:7762–7770
37. Karunadasa HI, Chang CJ, Long JR (2010) Nature
464:1329–1333
38. Felton GA, Glass RS, Lichtenberger DL, Evans DH (2006) Inorg
Chem 45:9181–9184
´
28. Canales C, Varas-Concha F, Mallouk TE, Ramırez G (2016) Appl
Catal B Environ 188:169–176
39. Karunadasa HI, Montalvo E, Sun YJ, Majda M, Long JR, Chang
CJ (2012) Science 335:698–702
29. Wang Q, Zhang Y, Yu L, Yang H, Mahmood MHR, Liu HY
(2014) J Porphyrins Phthalocyanines 18:316–325
30. Wang HH, Yuan HQ, Mahmood MHR, Jiang YY, Cheng F, Shi
L, Liu HY (2015) Rsc Adv 5:97391–97399
40. Collin JP, Jouaiti A, Sauvage JP (1988) Inorg Chem
27:1986–1990
41. Bernhardt PV, Jones LA (1999) Inorg Chem 38:5086–5090
123