A2B corrole with a meso-[PtII(bipy)Cl2]-substituent: Synthesis, electronic structure and highly efficient electrocatalyzed hydrogen evolutions

Article abstract of DOI:10.1016/j.ica.2019.119067

Synthesis and electronic structure of meso-2,2′-bipyridine substituted H₃corrole and its Pt(II) complex were described. This study demonstrates that A₂B type corrole contianing meso-[Pt^II(bipy)Cl₂] substituents are highly efficient catalysts for hydrogen evolutions with low overpotential (50 mV vs RHE), low Tafel slope (59 mV/dec) and robust catalytic behaviors. The efficient catalytic properties can be readily enhanced by charge transfer between bridging conjugated aromatic ring (corrole) and meso-[Pt^II(bipy)Cl₂] catalytic center.

Full text of DOI:10.1016/j.ica.2019.119067

Inorganica Chimica Acta 496 (2019) 119067
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
II
A B corrole with a meso-[Pt (bipy)Cl ]-substituent: Synthesis, electronic
2
2
structure and highly efficient electrocatalyzed hydrogen evolutions
Yingxin Guoa,1, Tingting Gub,1, Pengfei Li , Bo Fua,d, Lei Suna,d, Weihua Zhu , Haijun Xua,d,⁎
Xu Liang
a
a
b,c
,
b,c,⁎
Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Chemical Engineering, Nanjing Forestry University, Nanjing 210037,
PR China
b
School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China
State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing 210000, PR China
Jiangsu Key Lab of Biomass-based Green Fuels and Chemicals, Nanjing Forestry University, Nanjing 210037, PR China
c
d
A R T I C L E I N F O
A B S T R A C T
Keywords:
3
Synthesis and electronic structure of meso-2,2′-bipyridine substituted H corrole and its Pt(II) complex were
described. This study demonstrates that A B type corrole contianing meso-[Pt (bipy)Cl ] substituents are highly
2 2
efficient catalysts for hydrogen evolutions with low overpotential (50 mV vs RHE), low Tafel slope (59 mV/dec)
II
Platinum corrole
Electronic structure
Hydrogen evolution
Spectroscopy
and robust catalytic behaviors. The efficient catalytic properties can be readily enhanced by charge transfer
II
between bridging conjugated aromatic ring (corrole) and meso-[Pt (bipy)Cl
2
] catalytic center.
Electrochemistry
1
. Introduction
complexes and composites have revealed outstanding catalytic beha-
viors including low overpotential, low Tafel slope and stable for large
number of cycles [19–21], but the platinum contained metallocorroles
have never been described before in the same system. This is because of
the lack of research of platinum corrole. Till now as our best knowl-
edge, platinum(IV) corroles, of which there has been only few reports
accessible via a low yielding, but are particularly intriguing because of
their potential for axial reactivity [22,23]. In addition, to introduce 2nd
ligand at the meso-positions are also the effective strategies to stabilize
platinum atom at the corrole system at novel that could be applied in a
wide range of applications, such as biochemistry [24]. On the other
hand, platinum coordinated complexes also have several advantages in
the field molecular engineering and their applications in various cata-
lytic fields [25–27]. In this paper, 2,2′-bipyridine was used as a func-
The frontier research of hydrogen for energy storage so that supply
from renewable sources can be balanced with demand through the use
of fuel cells has many advantages to rationally replace the use of fossil
fuels in many contexts [1–3]. Within in this aim, there has been in-
creased interests in hydrogen evolution reactions (HERs) that involve
the reduction of protons, due to the straight forward procedures that
are involved and the availability of catalytic materials to convert
electrical energy to chemical energy through the generation of H
2
gas
[
4–6]. In addition to investigate the tunable catalytic behaviors through
chemical catalysis, photocatalysis and electrocatalysis [7–9], to rational
design and prepare of highly efficient catalysts are the key points
[
10–12]. On the other hand, recent researches have indicated that
molecular electrochemical catalysis exhibit various advantages, in-
cluding highly efficient, tunable and stable catalytic behaviors that
afforded further perspectives [13,14]. Corroles, porphyrin analogues
with a direct pyrrole-pyrrole bond and an extra NH proton on the inner
ligand perimeter, have applied as functional catalysts in several dif-
ferent types of reactions including organic synthesis, the removal of
environmental harmful pollutants [15], and efficient energy conver-
sions (such as HERs) [1,16–18]. Moreover, platinum coordinated
tional meso-substitutes to facilely synthesize and characterize meso-
II
[Pt (bipy)Cl
2 3
]-substituted H corrole that corrole will play the effective
electron transfer media to construct the rGO supported Pt(II)corrole
system for stably and electrochemically catalyzed hydrogen evolutions,
and the electronic structure investigations will also be described.
⁎
Corresponding authors at: Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, College of Chemical Engineering, Nanjing
Forestry University, Nanjing 210037, PR China (H. Xu). School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China (X. Liang).
E-mail addresses: xuhaijun@njfu.edu.cn (H. Xu), liangxu@ujs.edu.cn (X. Liang).
1
These authors were contributed equally.
https://doi.org/10.1016/j.ica.2019.119067
Received 9 June 2019; Received in revised form 24 July 2019; Accepted 8 August 2019
Available online 09 August 2019
0020-1693/ © 2019 Elsevier B.V. All rights reserved.

Y. Guo, et al.
Inorganica Chimica Acta 496 (2019) 119067
II
2 2
Scheme 1. A B Corrole with a meso-bipyridine 4 and meso-[Pt (bipy)Cl ]-substituent 5.
2. Experimental section
NaHCO3 to neutralized value and the mixture was extracted by CH
2 2
Cl
(
50 mLX3). The target compound was finally obtained after distillation
1
2.1. General
to give the white solid compound in a 44% yield (870.2 mg). H NMR
CDCl , 600 MHz, ppm) δ 10.21 (1H), 8.92 (d, J = 12 Hz, 2H), 8.61 (s,
1H), 8.31 (s, 1H), 8.74 (s, 1H), 2.49 (s, 3H).
(
3
1H NMR spectra were recorded on a Bruker AVANCEIII 600 M
spectrometer. UV–Vis spectra were recorded on Shimadzu UV-2600
spectrophotometer at ambient temperature with a 1 cm quarts cell. ESI-
MS was performed in a Bruker Daltonik, GmbH (Bremen), mass spec-
trometer equipped with an electrospray ionization (ESI) source. Cyclic
voltammetry was performed with a three-electrode-compartment cell in
2
.4. Synthesis of 3
Potassium hexachloroplatinate (1.0 g) was slowly dissolved in
0 mL and DMSO (0.6 mL) was added. The light-yellow crystals were
1
4 4
o-dichlorobenzene (o-DCB) solutions with 0.1 M [n-Bu N](ClO ) as
slowly observed over 3 h, and all solid compounds were collected. After
washing by water, ethanol and ether, the target compound cis-[Pt
supporting electrolyte using CHI-730D electrochemistry workstation. A
glassy carbon electrode of diameter 3 mm was used as the working
electrode while platinum wire and Ag/AgCl electrodes were used as the
counter and reference electrodes respectively.
(
Me
.5. Synthesis of 4
The general synthetic procedure was followed literature reported
2 2 2
SO) Cl ] 3 was finally obtained in an 89% yield (89.7 mg).
2
2.2. Preparation of modified electrodes
procedure whereas arylaldehyde 2 was used instead, and the target
compound was successfully isolated from silica gel column chromato-
1.0 mg rGO was mixed with 1 mL isopropyl alcohol containing 0.2%
nafion and the mixture sonicated in ultrasonic bath for 30 min to pro-
duce a homogeneous mixture of concentration 1 mg/mL. The surface of
the glassy carbon electrode (GCE) was polished with 0.05 µm alumina
and rinsed with doubly distilled water in ultrasonic bath to remove any
graphy in an 19% yield (87.5 mg). HR-ESI-mass, m/z = 797.1418
Calcd. [M]+ = 798.1447); H NMR (CDCl
1
, 600 MHz, ppm) δ 9.23 (s,
(
3
1
H), 9.04–9.11 (m, 3H), 8.73 (s, 4H), 8.57 (s, 2H), 8.51 (s, 1H), 8.46 (d,
J = 6 Hz, 1H), 7.17 (d, J = 6 Hz, 1H), 2.53 (s, 3H); UV–vis (CH Cl ),
max/nm[ɛ × 10 /(L·mol ·cm )]: 413 (1.1793); FNMR (CDCl
ppm) δ 137.7, −152.5, −161.6.
2
2
−5
−1
−1
19
2 3
adhered Al O particles. The electrodes were rinsed with ethanol and
λ
3
,
dried under room temperature for about 5 min. Three times 3 µL of the
rGO/isopropyl alcohol/nafion suspension was drop casted on the sur-
face of the GC electrode and allowed to dry at room temperature. A
2.6. Synthesis of 5
1
0 μL of 0.2 mM THF solutions of 5 was added dropwise to three dif-
ferent rGO/nafion-coated electrodes and dried at room temperature for
H
3
corrole 4 (79.8 mg, 0.1 mmol) and cis-[Pt(Me
.1 mmol) was dissolved in 25 mL dry CH Cl and stirred at 60 °C for
h under Ar atmosphere, after removal of organic solvent, the target
Cl /EtOH) in an
8% yield (101.5 mg). HR-ESI-mass, m/z = 1063.0555 (Calcd.
2 2 2
SO) Cl ] 3 (42 mg,
1
h.
0
5
2
2
2.3. Synthesis of 2
compound 5 was obtained from recrystallization (CH
2
2
8
+
1
4,4-dimethyl-2,2′-bipyridine (10 mmol, 1.8 mg), SeO
2
(12 mmol,
3
[M] = 1063.0532); H NMR (CDCl , 600 MHz, ppm) δ 9.64 (s, 1H),
1.3 mg) and water (3 mL) were dissolved in 20 mL dioxane and stirred
9.21 (d, J = 4.2 Hz, 2H), 8.88 (d, J = 4.2 Hz, 2H), 8.81 (d, J = 4.8 Hz,
2H) 8.66 (d, J = 3.6 Hz, 2H), 8.38 (d, J = 5.4 Hz, 1H), 7.92 (s, 1H),
at 90 °C for 24 h under Ar. After cooling to the room temperature, 0.3 M
sodium pyrosulfite (Na ) solution (50 mL) was added and stirred
again at room temperature. Then, the pH value was adjusted by
2 2
S O
5
7.43 (d, J = 18 Hz, 2H), 2.55 (s, 3H); UV–vis (CH
[ɛ × 10 /(L·mol ·cm )]: 417 (0.4081). FNMR (CDCl
2
Cl
2
), λmax/nm
, ppm) δ
−5
−1
−1
19
3
2

Y. Guo, et al.
Inorganica Chimica Acta 496 (2019) 119067
137.6, −151.7, −161.3.
Moreover, 4 and 5 are also emitted with the moderate fluorescent
3
properties for H corrole 4, and significantly decreased result for 5 were
3
. Results and discussion
observed, respectively (Fig. S9 and Table 1). This significant decrease of
the fluorescent properties could be illustrated as the effective electron
II
3.1. Synthesis and characterization
transfer between meso-[Pt (bipy)Cl
2
]-substituent and the corrole aro-
matic core.
The free-base corrole compounds 4 were synthesized from a reac-
tion of dipyrromethane 1 and the appropriate aryl-aldehyde (Scheme 1)
according to the literature procedures.11 The Pt complex 5 was syn-
2 2 2
thesized from 4 and cis-[Pt(Me SO) Cl ] 3, were purified by re-
Cyclic voltammetry (CVs) and differential pulse voltammetry
(DPVs) measurements revealed that Pt-corrole 5 has two reversible
reduction curves at E1/2 = −1.15 and −1.60 V (Fig. 2), respectively.
These two reversible processes can be assigned to the 1st reduction of
the Pt to PtI and the reduction of corrole ring itself, respectively.
Moreover, a reversible curve is observed at E1/2 = 1.12 V assigned as
the corrole ring oxidation. When a comparison is made with the triar-
ylcorroles using the same electrochemical characterization methods, no
II
crystallization. High-resolution ESI-MS spectra revealed intense parent
+
peaks at m/z = 797.1418 (Calcd. [M] = 798.1447) for 4 and m/
+
z = 1063.0555 (Calcd. [M] = 1063.0532) for 5, respectively. These
3
results are providing direct evidence that the H corrole 4 and its Pt
complex 5 were successfully prepared. The proton signals for the meso-
significant shifts of the reduction and oxidation steps are consistently
1
II
substituted bipyridine and pyrrole rings in the HNMR spectra of 4 (Fig.
observed except from the meso-[Pt (bipy)Cl
2
]-substituent itself. The
S5) lie beyond 7.16 ppm which is consistent with the presence of pen-
tafluorophenyl rings at the meso-positions., and the peak at
δ = 2.53 ppm for 4 could be assign as the protons from methyl units. In
the case of 5 (Fig. S7), due to the platinum(II) coordination, the protons
from all pyridine rings were shifted to the lower field region, which lie
electrochemical behavior was also characterized by checking the effect
Red
Ox
of using various scan-speeds in non-aqueous media. The i
p
and i
p
values, determined from CV measurements for 5 made at various scan-
rates from 20 to 500 mV, provides an insight into the reversibility of the
system on an experimental time-scale (Fig. S10, see ESI). The linear
correlations confirm that all of the oxidation and reduction processes
are diffusion controlled.
1
9
beyond 7.41 ppm. FNMR spectra of 4 and 5 in CDCl3 revealed similar
peaks (Figs. S6 and S8) at δ = −137, −151 and −160 ppm.
3.2. Electronic structure
3.3. Electrocatalysis
The UV–visible absorption and MCD spectra of H
3
corrole 4 and its
Stability in acidic environments is an important consideration
Pt(II)corrole 5 are measured in CH
2
Cl
2
(Fig. 1). The electronic structure
during the design of new HER catalysts. The stability of 5 was evaluated
and optical spectroscopy of porphyrinoids can be readily understood by
using Michl's perimeter model as a conceptual framework, through a
consideration of the effect of structural perturbations on the molecular
at acid media. The Pt-corrole 5 and H
2 4
SO (1:10 M ratio) were mixed in
CH CN and were kept in the dark. Electronic absorption spectra were
3
recorded at regular intervals for 4 h. Since negligible spectral changes
are observed, it is safe to assume that 5 suitable for use as HER cata-
lysts. It has been reported that Pt complexes could be efficiently used as
molecular and/or single atom electrocatalysts for the electrochemically
catalyzed hydrogen evolutions (HERs). Inspired by the above studies,
2−
orbitals (MOs) of a C16
sponding to the inner ligand perimeter. When compared to the UV–-
visible absorption spectrum of the parent H -triphenylcorrole, less to no
H
16
parent hydrocarbon perimeter corre-
3
spectral changes were observed, due to the perturbation of bipyridine
ring on the electronic structure is weak. The UV–vis absorption spectra
of 4 reveals soret band absorption at λ = 418 nm, while the Q-band
absorptions were lie at λ = 568, 608, 642. When Pt atom was co-
ordinated to bipyridine, complex 5 reveal slightly blue-shifted soret
band (λ = 414 nm) and Q-band absorption (λ = 560, 610, 640 nm). It
should be pointed out here, Pt complex reveals an additional absorption
band lie at λ = 352 nm assigned as the metal-to-ligand charge transfer
from Pt atom to bipyridine ligand [28,29]. On the other hand, relatively
II
−
we prepared a A
2
B Corrole with a meso-[Pt (bipy)Cl
2
]
substituent to
explore their electrocatalytic efficiency HERs. To evaluate the catalytic
speed the conversion efficiency, linear sweep voltammetry (LSVs) of
rGO supported 5 was tested in 0.5 M H SO (Fig. 3). In the acid media,
2 4
the Pt(II)corroles was exhibited as an excellent catalyst with over-
potential E = −0.05 V (speed: 0.1 V/s; V vs RHE). More importantly,
the Tafel slope was assigned as 59 mV/dec (speed: 0.1 V/s; V vs RHE)
which was significantly lower than other transition metal-coordinated
complexes (about 100–200 mV/dec), but only slightly higher than Pt/C
0
clear Faraday B terms are observed for each of these bands in the MCD
spectrum of 4 and 5 as would normally be anticipated for metal por-
phyrinoids with four-fold symmetry due to there being orbitally non-
nanocomposites (35 mV/dec). It should be mentioned here, that
II
Pt (bipy)Cl
2
complex 6 (Figs. S11 and S12, see ESI) exhibits negative-
degenerate excited states. The introduction of the meso-bipyridine and
shifted overpotential E = −0.25 V (speed: 0.1 V/s; V vs RHE) and in-
creased Tafel slope 230 mV/dec (speed: 0.1 V/s; V vs RHE), that in-
dicated the corrole ring plays and important role for charge transfer
II
meso-[Pt (bipy)Cl
2
]-substituent of the A
2
B type corrole ligand has been
considered to weakly interact with both HOMO and LUMO orbitals.
1
1
0
0
0
0
0
.2
.0
.8
.6
.4
.2
.0
4
18
4
5
in CH Cl2
2
in CH Cl2
2
414
5
68
608
352
5
60
642
6
10
640
700
3
00
400
500
600
800
900
λ / nm
2 2
Fig. 1. UV–Vis absorption (left) and MCD (right) spectra of 4 and 5 in CH Cl .
3

Y. Guo, et al.
Inorganica Chimica Acta 496 (2019) 119067
Table 1
Fluorescent characterizations of 4 and 5.
cpd
λex (nm)
λ
em (nm)
Φ
F
τ
f
[ns]
Δμ (nm)
K
r
[108 s−1
]
K ]
nr[108 s−1
4
5
410
410
652
655
5.04%
0.33%
3.88
0.94
242
245
0.01299
0.00351
0.2447
1.0603
Φ
F r
: Absolute quantum yield; Δμ: Stokes’s shift; K : Emission rate; Knr: Non-emission rate.
1.12
-1.60
-1.15
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
1
.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0
Potential (V vs Ag/AgCl)
Potential (V vs Ag/AgCl)
Fig. 2. CV and DPV measurements of Pt-corrole 5 in oDCB containing 0.1 M TBAP.
1
1
1
40
20
00
0
.1
.0
Tafel region
59 mV/dec
5
5
0
2
R = 1.00
after 1000 cycles
-
-
-
-
-
-
0.1
0.2
0.3
0.4
0.5
0.6
0.05
8
6
4
2
0
0
0
0
0
0.00
-
0.05
-0.10
-
1.0
-0.5
0.0
0.5
1.0
2
Log( j / mA·cm
)
-
1.0
-0.5
0.0
0.5
1.0
1.5
2.0
0.1
0.0
-0.1
-0.2
-0.3
-0.4
-0.5
2
E (V vs RHE)
Log( j / mA·cm )
Fig. 3. LSV of rGO supported 5 and after 1000 cycles in 0.5 M H
2
SO
4
(left) and the Tafel slope of rGO supported 5 in the same media (right).
between catalytic center and rGO supporters. On the other hand, the
catalytic stability was also confirmed, and negligible changes on the
LSV measurements were observed after 1000 cycles. All these results
demonstrated that the Pt-corrole 5 exhibits efficient electrocatalytic
hydrogen evolution behaviors, and the high conjugated corrole 18π
aromatic ring were played essential media of the electron transfer
process during the whole catalytic procedures.
center.
Acknowledgements
Financial support was provided by the National Scientific
Foundation of China (No. 21701058 and 21606133), NSFC of Jiangsu
province of China (no. BK20160499 and BK20160922) and the fund
from the State Key Laboratory of Coordination Chemistry (SKLCC1817),
the fund from Key Laboratory of Functional Inorganic Material
Chemistry (Heilongjiang University) of Ministry of Education, the
China post-doc foundation (No. 2018M642183), the Lanzhou High
Talent Innovation and Entrepreneurship Project (No. 2018-RC-105) and
the Jiangsu University (project 17JDG035).
4. Conclusion
In this manuscript, an A
2
B Corrole with a meso-bipyridine and meso-
II
[
Pt (bipy)Cl
2
]-substituent were synthesized and isolated. Electronic
structure was investigated by A detailed analysis of the UV–visible
absorption and MCD spectra, cyclic and differential pulse voltammetry
measurements, to identify the key trends in the redox and optical
Appendix A. Supplementary data
properties. Evidence for normally charge transfer between H
3
corrole
]-substituent was observed.
B type corrole contianing meso-
] substituents are highly efficient catalysts for hydrogen
evolutions with low overpotential (50 mV vs RHE for 5), low Tafel slope
59 mV/dec for 5) and robust catalytic behaviors. The efficient catalytic
properties can be readily enhanced by charge transfer between bridging
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.ica.2019.119067.
II
macrocyclic ring and meso-[Pt (bipy)Cl
This study demonstrates that A
2
2
II
[
Pt (bipy)Cl
2
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