Enhancing the reactivity of nickel(II) in hydrogen evolution reactions (HERs) by β-hydrogenation of porphyrinoid ligands

Article abstract of DOI:10.1039/c7sc02073b

Fine-tuning of the porphyrin β-periphery is important for naturally occurring metal tetrapyrroles to exert diverse biological roles. Here we describe how this approach is also applied to design molecular catalysts, as exemplified by Ni(ii) porphyrinoids catalyzing the hydrogen evolution reaction (HER). We found that β-hydrogenation of porphyrin remarkably enhances the electrocatalytic HER reactivity (turnover frequencies of 6287 vs. 265 s^-1 for Ni(ii) chlorin (Ni-2) and porphyrin (Ni-1), and of 1737 vs. 342 s^-1 for Ni(ii) hydroporpholactone (Ni-4) and porpholactone (Ni-3), respectively) using trifluoroacetic acid (TFA) as the proton source. DFT calculations suggested that after two-electron reduction, β-hydrogenation renders more electron density located on the Ni center and thus prefers to generate a highly reactive nickel hydride intermediate. To demonstrate this, decamethylcobaltocene Co(Cp?)₂ was used as a chemical reductant. [Ni-2]^2- reacts ca. 30 times faster than [Ni-1]^2- with TFA, which is in line with the electrocatalysis and computational results. Thus, such subtle structural changes inducing the distinctive reactivity of Ni(ii) not only test the fundamental understanding of natural Ni tetrapyrroles but also provide a valuable clue to design metal porphyrinoid catalysts.

Full text of DOI:10.1039/c7sc02073b

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alternative to traditional fossil fuels.9a, 9b, 9c, 9d On the road of
seeking earth-abundant metals to replace noble metals,10a, 10b,
10c, 10d, 10e, 10f
nickel(II) complexes of porphyrins have attracted
increasing attentions for the combination of the pivotal role of
Ni(II) in [NiFe] hydrogenases11a,
11b
and the sophisticate
Recently Cao and co-
12b, 12c, 12d, 12e
porphyrin chemistry.12a,
workers proposed a one-electron reduction and bimetallic
homolysis mechanism based on Ni(II) porphyrin with meso-
pentafluorophenyl substituents.13 Nocera and co-workers
constructed a “2nd coordination sphere” around Ni(II) center
using
a hangman type porphyrin, which demonstrated
hydrogen bond facilitating proton coupled electron transfer
process.14 More importantly, the same group found a Ni(II)
phlorin intermediate during HER, in which a proton was added
to meso-carbon appended to the hangman moiety.15 The
appearance of phlorin intermediate implies the necessary to
investigate the hydroporphyrin with interrupted conjugation.
thus tend to form active nickel hydride intermediates. This is
supported by the titration of trifluoroacetic acid (TFA) to two-
2-
electron reduced nickel complexes, in which [Ni-
30 times faster than [Ni-
demonstrated that such subtle structural modification
2]
reacts ca.
1
]2-. Therefore, this work
As our continued effort to unravel the roles of
β-
modification on the functions of porphyrins,16a, 16b, 16c, 16d in the
present study, we reported the synthesis, electrochemical
characterization and HER reactivity of nickel complexes of
a
inspired by nature is instrumental to the observation and
investigation of catalytic properties of metal porphyrinoid
complexes.
porphyrin (Ni-
hydroporpholactone (Ni-
hydrogenation, Ni- and Ni-
1
), chlorin (Ni-
2
), porpholactone (Ni-
3
) and
β
β
-
-
4
). Importantly, as a results of
2
4
exhibited significantly enhanced
Results and discussion
electrocatalytic HER reactivity (determined by turnover
frequencies, TOFs) of 24 and 5 times than the corresponding
Synthesis and Characterization. In this work, free-base
porphyrinoids
1
-
4
were synthesized in good yeilds according to
17
Nickel complexes (Scheme 1.) were
porphyrin (Ni-
importantly, DFT calculation suggests that,
renders more electron rich Ni centers in two-electron reduced
[Ni-
]2- and [Ni- 2- than the analogues [Ni- 2- and [Ni- ]2-, and
1
) and porpholactone (Ni-
3
) respectively. More
the literatures.16c,
β
-hydrogenation
prepared by refluxing excess nickel(II) acetate (30 equiv.) with
2
4
]
1]
3
1
2
3
4
5
Fig. 2 ORTEP drawings of Ni-2, Ni-3 and Ni-4.The hydrogen atoms and solvent molecules are omitted for clarity. Thermal ellipsoids are drawn with 50% probability. The
lactone ring in Ni-3 shows disorder at the oxazolone and the opposite position while the Ni-4 and Ni-2 show disorder at all four -periphery
β
.
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the corresponding porphyrinoid ligands in dimethylformamide
(DMF) under N2 atmosphere. Four nickel complexes were fully
characterized by UV-vis absorption, 1H, 19F, 13C-NMR and HR
ESI-MS spectroscopes and spectrometers (Supporting
information). Ni-2 and Ni-4 were diamagnetic for the low spin
d8 electronic structure and showed the proton signals at 3.93
and 3.77-3.65 ppm, respectively, assigned to the hydropyrrole
moiety. Compared to Ni-1 and Ni-3, β-hydro-analogues Ni-2
and Ni- exhibited two bathochromic Q-bands centered at 576
4
or 565 and 617 or 613 nm in acetonitrile, which is also the
characteristic absorption of metal chlorins arising from the
lower molecular symmetry.
Crystal of Ni-2, Ni-
evaporation of a dichloroethane/n-hexane solution. As shown
in Fig. 2, the crystal structure of Ni- (CCDC: 1528290)
3 and Ni-4 were obtained by slow
2
displayed the typical ruffling distortion with Ni atom centered
at N4 planar squares. Although it is difficult to distinguish the
hydropyrrole ring from the other ones due to the symmetry
condition of the I
bond length (C2-C3, 1.383 Å) of Ni-
of Ni-
(C11-C13, 1.346 Å)13. Similarly, the hydropyrrole ring on
Ni- (CCDC: 1554494) can be distinguished through
comparison of the C-C bond length with Ni- (CCDC:1554445)
(C1-C(O)2, 1.338 Å and C3-C4, 1.341 Å for Ni- and C1-C(O)2,
1.404 Å for Ni- ). In addition, Ni- display a typical ruffling
distortion with Ni-N bond of 1.921 Å, however, Ni- displays a
planar construction with Ni-N bond of 1.950 Å. The shorter Ni-
N bond induces steric strain to Ni- , the release of which is the

42d space group, the average pyrrole C-C
2
is 0.04 Å longer than that
were shown in Fig. S18. Both Ni-
1 and Ni-2 displayed two
1
distinct reversible one-electron diffusion controlled reductions
3
(-1.27 and -1.83 V for Ni-1, -1.28 and -1.77 V for Ni-2),
referenced to the standard reduction potential of Fc+/Fc.
According to the previous reports,18a,
4
3
18b
the insertion of
4
4
electron deficient oxazolone moiety lowers the energy levels
of ligand LUMOs and thus we could observe the positive shift
3
of reduction potentials of Ni-
more negative reduction potentials than Ni-
V for Ni- , -1.14 and -1.74 V for Ni-
3
to Ni-
1
. However, Ni-
(-0.99 and -1.59
), indicating β-
4 displayed
4
driving force for easier reduction of the nickel complexes.1b
Electrochemistry. Cyclic voltammograms of Ni complexes in
acetonitrile using 0.10 M nBu4NPF6 as supporting electrolyte
3
3
4
hydrogenation increases the energy levels of LUMOs in
porpholactones.
1
2
3
Fig. 4 Successive cyclic voltammograms of 1.0 mM Ni-1 (a) Ni-2 (b) Ni-3 (d) and Ni-4 (e) in CH3CN (0.10 M nBu4NPF6) at increasing concentrations of TFA from 20 mM to
140 mM. Conditions: 3 mm glassy-carbon working electrode; 25 °C; scan rate 100 mV/s. (c) and (f) TOFs vs. concentrations of TFA.
4
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Fig. 6 (a) Free energy diagram for the formation of [Ni-1-H]- (black line) and [H-Ni-2]- (red line) intermediates during the HER process. Free-energy values are given in
kcal/mol. The geometric conformation of [Ni-1-H]- (b) and [H-Ni-2]- (c) active intermediates during the HER process.
wave with stronger acid such as methylsulfonic acid (MsOH) above spectroelectrochemistry results. Additionally, singly
2-
2-
1] and [Ni-3] also
(Fig. S28). In this situation, the acid might be strong enough to occupied molecular orbital (SOMO) of [Ni-
hydrogenate [Ni-P]- to [H-Ni-P]0 which then be reduced to [H-
Ni-P]- and react with anther proton to yield hydrogen (pathway
B). This phenomenon has been reported by Nocera15 and Cao13
respectively. In addition, at low acid concentration, we can
observe another catalytic plateau after the catalytic current
showed the electron density almost located on porphyrin β-
periphery (Fig. 5a and 5c). However, Nocera and his
2-
coworker’s report an analogue of [Ni-1] ( meso-chlorine
atoms were used to replace meso-pentafluorophenyl
substituents of nickel porphyrin in his work) is a flat triplet
species with a Mulliken spin density of almost 1 on the Ni
center and almost 1 on the ligands.15 As shown in Fig. S34, we
find that meso-substitutional group would affect the
calculation results. In addition, five different DFT functionals
have been used (B3LYP, B3P86, BP86, BLYP and M06L) to
confirm our results. This indicated that using 6-31+G(d) as
raised up at the second reduction peak in Ni-3. In this
situation, the [H-Ni-P]- might be further reduced to [H-Ni-P]2-
and then react with a proton to release H2 and be back to [Ni-
P]- (pathway C), as Savéant and co-workers previously
reported.26
Electronic Structures of Ni-1 to Ni-4. To understand the effect
of
complexes, DFT calculations were carried out to optimize the functional is resonable.
electronic structures (See more computation details in In sharp contrast, two-electron reduced [Ni-
supporting information). The most stable form of [Ni-
]0, [Ni- possess the most stable flat triplet with the Mulliken spin
]0 are all saddle-shaped closed-shell singlet, and density on nickel center of ρNi = 1.22 and 0.95 (Table S10 and
]0 is in flat closed-shell singlet, in accordance with the 1H- S12 ), indicating that one unpaired electron is localized on
NMR spectra and crystal structures. One-electron reduced nickel center and another on the macrocycle. Calculated
β-hydrogenation on porphyrins on the reactivity of Ni basis set and LAN2DZ as pseudopotential and B3LYP as
2-
2-
2
] and [Ni-4]
1
0
2
] and [Ni-4
[Ni-
3
2-
nickel complexes have the most stable doublet flat geometries SOMOs of [Ni-
2]
2- and [Ni-
4
]
also showed that one unpaired
) orbital of Ni center, and
with an Mulliken spin density (ρNi) of approximate 1.0 on Ni electron is localized on the σ*(ºÎ ͯÏ
̋
̋
center, indicating a formally Ni(I) specie. Interestingly, two-
another delocalized on the porphyrin, indicating
porphyrin radical (Fig. 5b and 5d).
a Ni(I)
electron reduced nickel complexes have different electronic
]2-, the flat
2-
]
DFT Calculated formations of [Ni-1-H]- and [H-Ni-2]-. Since
structures as shown in Fig. 5. For [Ni-
1
and [Ni-
3
triplet is lower in energy than the closed-shell bent singlet and
two unpaired electron localized on the porphyrin macrocycle.
Small Mulliken spin density ρNis of 0.0026 and 0.36 were
HER occurred at the second reduction peak experimentally, we
further use the relative free energies to compare the
2-
formation and reactivity of hydride intermediate from [Ni-
]2-, as shown in Fig. 6. Protonation of [Ni-
1]
2-
2-
and [Ni-
2
1
]
2– by TFA is
obtained for [Ni-
1]
and [Ni-
3]
respectively (Table S9 and
S11), suggesting a Ni(II) porphyrin diradical consistent to the
thermodynamically downhill by 7.7 kcal/mol (Fig. 6a) but
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obliquely to the pyrrolic nitrogen in porphyrin ring, and thus
indicates a metal hydride like intermediate [H-Ni-
]- (Fig. 6c).
2
Scheme 3. Proposed mechanism for HER catalyzed by a nickel
compounds.
However, in [Ni-1
]2-, the proton bonds to the pyrrolic nitrogen
and formed an N-H bond with a distance of 1.02 Å. Further
insights into bonding characteristics of proton adducts is
gained from analysis of the Mulliken atomic charges of [Ni-
H]- (0.397) and [H-Ni- ]- (-0.016). (Fig. S33) This demonstrated
that hydrogen atom of [Ni-
-H]- is more electronegative to the
hydride of [H-Ni-
]-, and might prefer to react with another
1-
Fig. 7 (a) UV-vis absorption spectra of the process of [Ni-2]2- reacting with TFA.
Inset: Plot of absorption of Soret band vs. time for the reaction of [Ni-1]2- (blue
line) and [Ni-2]2- (red line) with 100 equiv. TFA at 10 oC. (b) Plot of kobs vs.
concentration of TFA for the reaction of [Ni-1]2- (blue line) and [Ni-2]2- (red line)
with TFA.
2
2
1
TFA molecule via a heterolytic pathway.
Spectroelectrochemical TFA titration of [Ni-1]2- and [Ni-2]2-.
-
protonation of [Ni-
1
]
is thermodynamically uphill by 32.2
2–
2-
To verify the reactivity of the two intermediates, [Ni-
1
]
and
kcal/mol (Fig. S36). Thus, starting from [Ni-
1
]
is
[Ni-2
]2-, we carried out redox titration of nickel complexes in
thermodynamically preferred, which is consistent to the
acetonitrile solution using Co(Cp*)2 (Eox = -1.90 V vs. Fc+/Fc) as
a chemical reductant. The one-electron oxidation potential of
Co(Cp*)2 is lower than the two-electron reduction potential of
experimental CVs that the HER occurring at ca. -1.80V. The
resulted exothermal product [Ni-1
-H]- was formed through a
stretching vibration between H and N transition state TS1 with
energy barrier by 18.5 kcal/mol. To find the protonation
intermediate, four protonation sites have been tested: meso-
Ni-
1
and Ni-
2-
2
. Thus, addition of Co(Cp*)2 led to the formation
]2-, which is evidenced by the similar UV-vis
of [Ni-
1
]
or [Ni-
2
absorption spectra to that obtained in spectroelectrochemistry
(Fig. S29-30). The addition of excess TFA to the solution of [Ni-
carbon (metallophlorin intermediate),
β-carbon, pyrrolic
nitrogen and the nickel center (metal hydride), and we choose
the most thermodynamically favored pyrrolic nitrogen
protonated one as intermediate. In addition, for the pyrrolic
nitrogen, we can indeed find a transition state (Fig. S35c). IRC
path shows that H-atom goes through a stretching vibration
2-
] or [Ni-2] resulted in fast conversion to Ni-1 or Ni-2 (Fig.
2-
1
7a), accompanied with the formation of H2 bubble. The overall
two-step kinetics reaction mechanisms of H2 production were
shown in Scheme 2 (pathway A). The first proton adding step
might be very fast and the second step might be the rate-
and the porphyrin ring changes from the flat to ruffle. This
2-
27b, 27c
2-
determining step.27a,
As shown in Fig. 7a, [Ni-2]
2-
phenomenon indicates the protonation of [Ni-
2-
1
]
to [Ni-
1
-H]-,
displayed much larger kobs (0.27 s-1) than [Ni-
1
]
(6.2×10-3 s-1)
since [Ni-
1
]
is a triplet flat and [Ni-
-H]- can react with another TFA to release H2
1
-H]- is a bent singlet.
(pseudo-first-order kinetic model), as exemplified in presence
of 100 equiv. TFA at 10 oC. Secondary reaction kinetics
Then, [Ni-
1
exothermically by 22.3 kcal/mol, regenerating the neutral [Ni-
2-
2-
constants k2s for [Ni-1] and [Ni-2]
of 9.17×10-2 and 3.03 M-
-
2-
1
]0. For Ni-
thermodynamically uphill by 29.5 and 4.8 kcal/mol,
respectively, and [Ni-
2- is thermodynamically favourable (Fig.
S37). To find the protonation intermediate for Ni- , the four
2
, protonation of [Ni-
2]
and [Ni-
2]
are both
1s-1 respectively, were obtained by linearly fitting kobss vs. TFA
concentration (Fig. 7b). Similar enhancement of titration
reaction rates to electrocatalytic HER clearly demonstrated the
importance of disrupted conjugation on the electronic
structures and the reactivity of reduced Ni complexes, which is
consistent to DFT calculation results.
2]
2
protonation sites also have been tested, and the most
thermodynamically favored metal hydride was chosen. We can
also find a transition state (Fig. S35d) and IRC path shows the
generation of [H-Ni-
energy barrier by 15.2 kcal/mol which is 3.3 kcal/mol lower
2
]- is through a transition state TS2 with
Conclusion
than TS1. The reaction between [H-Ni-
2
]- with another proton
Taken together, we demonstrated for the first time,
β-
is also exothermic by 31.9 kcal/mol.
Interestingly, for [Ni-2
]2-, the proton of TFA approaches to
hydrogenation of porphyrin is important on enhancing the HER
reactivity using nickel porphyrinoids. Experimental and
the electron rich nickel center with the distance of 1.49 Å,
theoretical studies showed that β-hydrogenation significantly
affects the electronic structures of two-electron reduced Ni
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complexes and renders more electron density localized on Ni hydroporpholactone (
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4
) were synthesized according to the
2-
center in [Ni-
shown in Scheme 3., protonation of [Ni-
metal hydride intermediate [H-Ni-
]2-, while [Ni-
affords a ligand centred hydride [Ni-
-H]2-. [H-Ni- ]- prefers to refluxed with 30 equiv. of Ni(OAc)2 (1 mmol, 180 mg) in
2
]
and [Ni-
4]
2- than [Ni-
1
]
2- and [Ni-
3
]2-. Thus, as literature.16c, 17
2-
2
] leads to a typical Synthesis of Ni-1 to Ni-4:
2-
]
2
1
only Typical procedure: Porphyrin free base ligand (0.1 mmol) was
1
2
react with another proton via a quick heterolytic pathway as acetonitrile under nitrogen for 6 hours. The solvent was
demonstrated by the time course results of reacting with TFA. removed by adding 100 equivalents of water and the residue
This work also provides an opportunity to further design of was purified through silica column.
metal molecular catalysts with subtle structural changes of Ni-1: Isolated yields were over 90%. Eluent: ethyl acetate:
ligands inspired by natural metal cofactors.
petroleum ether, 1:5. 1H NMR (400 MHz, CDCl3) δ 8.81 (s, 8H).
19F NMR (377 MHz, CDCl3) δ -136.47 (dd, J = 23.2, 7.7 Hz, 8F), -
150.17 (m, 4H), -161.32 (dt, J = 22.5, 7.4 Hz, 8F). 13C NMR (101
MHz, CDCl3) δ 142.98 (s), 132.52 (s), 103.09 (s). ESI-MS m/z:
Calcd. for C44H8F20N4Ni 1029.97831, found 1029.97854. Anal.
Calcd for C44H8F20N4Ni: C, 51.25; H, 0.78; N, 5.43, found C,
51.29; H, 0.92; N, 5.38.
Experimental Section
General Procedures. Commercially available solvents were
used after being purified by the Mbraun SPS-800 Solvent
Purification System. Deuterium solvents were stored with 4 Å
molecular sieves. Manipulations of air and moisture sensitive
materials were performed in glove box in an atmosphere of
argon. CH3CN and dimethylformamide was distilled and
Ni-2. Isolated yields were 75%. Eluent: ethyl acetate:
petroleum ether, 1:10. 1H NMR (400 MHz, CDCl3) δ=8.29 (d, J =
4.9 Hz, 2H), 8.14 (s, 2H), 7.95 (d, J = 5.0 Hz, 2H), 3.93 (s, 4H). 19
F
NMR (377 MHz, CDCl3) δ = -136.94 (dd, J=23.2, 7.7Hz, 4F), -
137.89 (dd, J=23.8, 8.3Hz, 4F), -151.88 (t, J=20.9Hz, 2F), -
152.10 (t, J=20.9Hz, 2F), -160.66 (dt, J=23.3, 8.0Hz, 4F), -161.57
(dt, J=22.6, 7.4Hz, 4F). 13C NMR (101 MHz, CDCl3) δ 169.03 (s),
152.66 (s), 140.39 (s), 135.31 (s), 132.27 (s), 128.22 (s), 123.62 (s),
106.31 (s), 96.83 (s), 35.31 (s, -CH2-). ESI-MS m/z: Calcd. For
C44H10F20N4Ni 1031.99396, found 1031.98981. Anal. Calcd for
C44H10F20N4Ni: C, 51.15; H, 0.98; N, 5.42, found C, 51.16; H,
1.14; N, 5.31.
degassed
before
use.
Tetrabutylammonium
hexafluorophosphate (nBu4NPF6) was recrystallized from
absolute ethanol. Other reagents were purchased from
commercial suppliers and used without purification. UV/Vis
spectra were recorded on an Agilent 8453 UV/Vis
spectrometer equipped with a Agilent 89090A thermostat
(±0.1 oC). ESI-MS were recorded on Bruker APEX IV Fourier
Transform Ion Cyclotron Resonance Mass Spectrometer using
electrospray ionization. 1H, 19F and 13C NMR spectra were
recorded on Bruker-400 MHz NMR. All 1H NMR experiments
were reported in δ units, parts per million (ppm), all coupling
constants were in Hz and measured relative to the signal for
residual chloroform (7.26 ppm) in the deuterated solvent
CDCl3. For 19F NMR spectra, CF3COOH was used as an external
reference at 0 ppm. Transmission electron microscopy were
determined by JEM-2100F(JEOL). DLS measurements were
performed by using a Laser Light Scattering Spectrometer
(ALV/Laser Vertriebsgesellschaft m.b.H), which can detect
particle sizes ranging from 1.0 nm-1.0 μm. SEM and EDX were
performed by using Hitachi S-4800 field emission scanning
electron microscope at an accelerating voltage of 5 and 15 kV,
respectively. Elemental analyses were done on Elementar
Vario EL CUBE (Germany). Cyclic voltammetry experiments
were recorded on Shanghai Chenhua CHI660C electrochemical
workstation work, glassy carbon electrode was selected as
working electrode, auxiliary electrode was platinum wire
electrode and Ag/AgCl was reference electrode. All samples
were recorded in acetonitrile with 0.1M tBu4NPF6 as
electrolyte, the scan rate was 0.1 V s−1 and E1/2 were calculated
Ni-3. Isolated yields were over 90%. Eluent: ethyl acetate:
1
petroleum ether, 1:5. H NMR (400 MHz, CDCl3) δ 8.67 (d, J =
5.1 Hz, 1H), 8.65 – 8.61 (m, 2H), 8.58 (d, J = 5.1 Hz, 1H), 8.55 (d,
J = 4.9 Hz, 2H). 19F NMR (377 MHz, CDCl3) δ -136.69 – -136.96
(m), -138.17 – -138.39 (m), -150.28 – -150.62 (m), -151.20 (q, J
= 20.9 Hz), -160.27 – -160.87 (m), -161.37 (qd, J = 22.1, 6.8 Hz).
13C NMR (101 MHz, CDCl3) δ 163.03 (s), 149.75 (s), 144.95 (s),
134.45 (s), 132.47 (d), 131.78 (s), 131.17 (s), 130.34 (s), 120.59
(s). ESI-MS m/z: Calcd. For C43H6F20N4NiO2 1048.95556, found
1048.95959. Anal. Calcd for C43H6F20N4NiO2: C, 49.23; H, 0.58;
N, 5.34, found C, 48.66; H, 0.67; N, 5.26.
Ni-4. Isolated yields were over 90%. Eluent: ethyl acetate:
1
petroleum ether, 1:5. H NMR (400 MHz, CDCl3) δ 7.97 (d, J =
4.8 Hz, 1H), 7.77 (dd, J = 20.5, 4.5 Hz, 2H), 7.54 (d, J = 4.7 Hz,
1H), 3.76 (d, J = 8.4 Hz, 2H), 3.66 (d, J = 8.4 Hz, 2H). 19F NMR
(377 MHz, CDCl3) δ -137.63 (d, J = 23.9 Hz), -137.89 (d, J = 15.5
Hz), -138.76 (d, J = 15.8 Hz), -151.16 (d, J = 34.0 Hz), -151.50
(s), -151.79 (s), -160.07 (d, J = 6.2 Hz), -160.31 (d, J = 5.9 Hz), -
160.68 (d, J = 6.1 Hz), -161.42 (d, J = 5.9 Hz). 13C NMR (101 MHz,
CDCl3) δ 165.72 (s, -C=O), 162.06 (s), 156.20 (s), 151.18 (s), 149.93
(s), 141.77 (s), 139.34 (s), 138.75 (s), 133.28 (s), 127.83 (s), 126.19
(s), 115.90 (s), 96.88 (s), 82.19 (s), 34.40 (s, -CH2-), 32.29 (s, -CH2-).
Calcd. For C43H8F20N4NiO2 [M+H]+1050.97586, found
1050.97686. Anal. Calcd for C43H8F20N4NiO2: C, 49.13; H, 0.77;
N, 5.33, found C, 48.96; H, 0.93; N, 5.20.
based on peak position for the internal standard FeCp2 (E1/2
0.45 V vs. SCE).
=
Synthesis of free base porphyrinoids 1-4. Meso-
tetrakispentafluorophenylporphyrin
tetrakispentafluorophenylchlorin
(
1
),
meso-
meso-
(2),
tetrakispentafluorophenylporpholactone
(3) and adjacent-
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Cyclic Voltammetry. Cyclic voltammetry was performed with a
CHI 660C instrument. A glassy carbon (3 mm diameter) was
used as working electrode, a platinum filament as counter
electrode, Ag/AgCl as reference electrode. Solvents were
purified by a Mbraun SPS-800 Solvent Purification System. All
samples were recorded in dichloromethane with 0.1M
nBu4NPF6 as electrolyte. Unless otherwise noted, all potentials
21571007, 21271013, 21321001). X. R. He is gratefully thanked
for help with the ESI-MS. Z.-C. Huang and H. Zhu are gratefully
thanked for help with the DFT calculation parts. T. Huang is
gratefully thanked for help with DLS. T.-T. Zuo is gratefully
thanked for help with TEM. Y.-Y. Yuan is gratefully thanked for
help with SEM and EDX.
in this study were adjusted ferrocenium/ferrocene (Fc+/0
)
Notes and references
couple as internal standard.
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Acknowledgements
We acknowledge financial support from the National Key Basic
Research Support Foundation of China (Grant 2015CB856301)
and the National Scientific Foundation of China (Grants
8 | J. Name., 2012, 00, 1-3
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