Metal Complexes of 5,15-Porphyrinquinones: Systematic Study of Crystal Structure, Electronic Structure, and Lewis Acidity

Article abstract of DOI:10.1002/ejic.202000527

We conducted the first systematic study on the synthesis, structure, and properties of various divalent metal complexes (Ni^II, Cu^II, Zn^II, Pd^II, Pt^II, and Pb^II) of 5,15-porphyrinquinone (PQ, a quinone compound of porphyrin) for diversifying the chemistry of traditional quinone-metal complexes. Similar to electron-accepting nature of PQ, the metal complexes studied here also exhibit it. Ni^II, Pd^II, and Pt^II complexes favor face-to-face stacked structures in the crystals, thus inducing effective Pt^II–Pt^II interaction, which has not been observed in the porphyrin analogues to date. Ultraviolet-visible (UV/Vis) absorption spectra of the metal complexes vary widely depending on the metal ion and owing to the effective d(metal)–π(PQ) coupling in their molecular orbitals. Quantitative analyses of the axial ligation on the central metal ions (Ni^II and Cu^II) revealed significantly larger binding constants than those of the porphyrin analogues, indicating significant enhancement of their Lewis acidities due to the strong electron-withdrawing nature of PQ.

Full text of DOI:10.1002/ejic.202000527

European Journal of Inorganic Chemistry
Accepted Article
Title: Metal complexes of 5,15-porphyrinquinones: Systematic study of
crystal structure, electronic structure, and Lewis acidity
Authors: Ken-ichi Yamashita, Daisuke Hirano, and Ken-ichi Sugiura
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202000527
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01/2020

10.1002/ejic.202000527
European Journal of Inorganic Chemistry
FULL PAPER
Metal complexes of 5,15-porphyrinquinones: Systematic study of
crystal structure, electronic structure, and Lewis acidity
Ken-ichi Yamashita,*[a,b] Daisuke Hirano,[a] and Ken-ichi Sugiura*[a]
Abstract: We conducted the first systematic study on the synthesis,
can bind the metal ion to their center. In fact, MgII,[3] MnIII,[4] FeIII,[5]
[3,8–12]
[3]
structure, and properties of various divalent metal complexes (NiII, CuII, NiII,[6–8] ZnII,
and TlIII
complexes have been reported to
ZnII, PdII, PtII, and PbII) of 5,15-porphyrinquinone (PQ, a quinone
compound of porphyrin) for diversifying the chemistry of traditional
quinone-metal complexes. Similar to electron-accepting nature of PQ,
the metal complexes studied here also exhibit it. NiII, PdII, and PtII
complexes favor face-to-face stacked structures in the crystals, thus
inducing effective PtII-PtII interaction, which has not been observed in
the porphyrin analogues to date. Ultraviolet–visible (UV–vis)
absorption spectra of the metal complexes vary widely depending on
the metal ion, and owing to the effective d(metal)–(PQ) coupling in
their molecular orbitals. Quantitative analyses of the axial ligation on
the central metal ions (NiII and CuII) revealed significantly larger
binding constants than those of the porphyrin analogues, indicating
significant enhancement of their Lewis acidities due to the strong
electron-withdrawing nature of PQ.
date. Although these metal complexes are also expected to have
characteristics typical of quinone-metal complexes, the properties
of those complexes have not been adequately explored except for
[9–12]
FeIII,[5] NiII,[6,7], and ZnII
complexes, or the complexes with
analogous ligands.[13,14] For example, NiII-PQ complexes exhibit
axial ligation of two pyridine ligands and the corresponding
diamagnetic-to-paramagnetic change.[6,7] This feature is induced
by the strong electron-withdrawing nature of the PQ ligand, and is
thus not observed in typical porphyrin analogues like
tetraphenylporphyrin.[15–21] However, quantitative analyses of this
axial ligation on NiII-PQ complexes have not yet been explored
while that on ZnII-PQ reported by Sanders revealed its 100-times
higher binding constant than that of the corresponding
porphyrin.[9]
Introduction
Quinones are one of the oxidized nonaromatic form of aromatic
compounds and an important class of -conjugated organic
compounds.[1] Typically, quinones are strong electron acceptors
and are readily converted to dihydroxyarenes via reversible and
stepwise 2e reduction. According to coordination chemistry, this
redox behavior has drawn considerable research attention lately
because quinones (typically o-quinones) are representative
redox-non-innocent ligands, which have strong capacities to
electronically communicate with metal ions.[2]
Porphyrinquinones (PQs), which are also called
dioxoporphodimethenes or dioxoporphyrins, are one of the
quinone compounds of 18-aromatic porphyrins (Figure 1a). PQs
have two representative structural isomers: 5,15-PQ and 5,10-PQ,
both of which were first synthesized in 1973 by oxidizing
octaethylporphyrin with TlIII(OCOCF3)3.[3] Like porphyrins, PQs
Figure 1. (a) Chemical structures of porphyrin and two representative isomers
of porphyrinquinones (PQs). (b) Chemical structure of [MII(PQ1)].
[a]
Dr. K. Yamashita, D. Hirano, Prof. Dr. K. Sugiura
Department of Chemistry, Graduate School of Science and
Engineering
Recently, we reported the facile preparation of 10,20-diaryl-
5,15-PQ (2H-PQ1, Figure 1b) through the oxidation of the
corresponding 5,15-diarylporphyrin by PhI(OAc)2, and its efficient
conversion to 10,20-diaryl-5,15-dialkoxyporphyrin.[22] As a result,
we obtained a large amount of PQ1, allowing for their systematic
study along that of relevant compounds. Herein, we report the first
systematic study of the synthesis, structure, and properties of a
series of divalent metal complexes of porphyrinquinone [MII(PQ1)]
(M = Ni, Cu Zn, Pd, Pt and Pb). We also quantitatively study the
axial ligation of [NiII(PQ1)] and [CuII(PQ1)].
Tokyo Metropolitan University
1-1 Minami-Osawa, Hachioji, Tokyo 192-0397 (Japan)
E-mail: yamashita-k@chem.sci.osaka-u.ac.jp, sugiura@porphyrin.jp
http://www.comp.tmu.ac.jp/chem/coord/english.html
Dr. K. Yamashita
Department of Chemistry, Graduate School of Science
Osaka University
[b]
1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan)
https://researchmap.jp/ken1-yamashi?lang=en
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejic.202000527
European Journal of Inorganic Chemistry
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Results and Discussion
Syntheses
The metal complexes [MII(PQ1)] (M = Ni, Cu Zn, Pd, Pt, and Pb)
were obtained almost quantitatively through the same method as
that of the preparation of the porphyrin analogues (Table 1). Each
complex was characterized by APCI HR-MS, NMR (for
diamagnetic complexes), and elemental analysis. All obtained
complexes were stable under ambient conditions.
Table 1. Synthetic condition of the metalation reactions of 2H-PQ1 and the
product yields for [MII(PQ1)].
M
metal salt (equiv)
solvent
temp
/ °C
time /
h
yield
/ %
Ni
NiII(acac)2 (5)
Toluene
reflux
r.t.
3
1
93
90
Cu
CuII(OAc)2·(H2O) (5)
CHCl3/MeOH
(10:1)
Zn
Pd
Pt
ZnII(OAc)2·(H2O)2 (5)
PdII(OAc)2 (1.5)
CHCl3/MeOH
(10:1)
r.t.
1
quant
.
CHCl3/MeOH
(10:1)
r.t.
0.5
3
98
Figure 2. Crystal structure of [NiII(PQ1)] (C = black, H = white, N = blue, O =
red, and Ni = green). Thermal ellipsoids are drawn at 40% probability level. Two
crystallographically independent molecules with similar structural parameters
are found in the asymmetric unit, and only one molecule (Molecule A) is
illustrated. (a) Top view, (b) side view, (c) top and (d) side views of the dimeric
structure. t-Butyl groups on the phenyl groups are omitted for clarity.
PtIICl2(PhCN)2 (2)
PhCl
reflux
r.t.
quant
.
Pb
PbII(OAc)2·(H2O)3
(10)
CHCl3/MeOH
(10:1)
1.5
95
The Cmeso=O bond lengths in all compounds are within the
range of those of the typical C=O double bonds, and Cmeso–C
bond lengths are considerably longer than those of the C–C
bonds in the macrocycles. These are typical of the nonaromatic
quinoidal compounds. Notable structural features are 1) group-8-
metal complexes exhibited considerably ruffled conformations
and formed -stacked dimers (Figures 2, and S1−S4), which are
found in the crystals of 2H-PQ1[22]; and 2) for [CuII(PQ1)] and
[ZnII(PQ1)], both or one carbonyl oxygen atom were coordinated
to the central metal of the neighboring molecules to form the 1D-
chains successively (Figure 3).
[NiII(PQ1)] and [PdII(PQ1)] crystallized in the orthorhombic
Ibca space group with almost the same crystallographic
parameters while [PtII(PQ1)] crystallized in the orthorhombic
crystal system with the Pccn space group. The crystals of NiII and
PdII contained two crystallographically independent but
structurally similar molecules (A and B) in the asymmetric unit.
[NiII(PQ1)] exhibited severely ruffled conformations with a
mean deviation of 0.40 Å from the 24-atom mean plane (Figure
S7). This is typically observed in the NiII porphyrins because of
the small ion radii of the NiII ion. It is worth noting that [PdII(PQ1)]
and [PtII(PQ1)] also exhibit considerably ruffled conformation
whereas the conformation of typical PdII and PtII porphyrins is
almost planar. The geometry-optimized structures of [PdII(PQ)]
and [PdII(PQ)] according to the density functional theory (DFT)
calculation (vide infra) exhibit relatively more planar conformation.
1H NMR analyses
In the 1H NMR spectra of the obtained diamagnetic complexes (M
= Ni, Zn, Pd, Pt, and Pb), two doublet signals assigned for -
protons of the PQ1 ligand were observed within the range of 7.4
to 6.5 ppm. These are characteristic to nonaromatic quinone
compounds.
In the reported PbII porphyrin complexes, PbII ion is situated
off center from the mean plane of the macrocycles because of its
large ion radius.[23,24] This translates to reduced symmetry of the
complexes, resulting in the splitting of the NMR signals of the aryl
substituents, which are orthogonal to the porphyrin plane. This
behavior was also observed in the 1H NMR signals for tBu protons
and Aro protons of [PbII(PQ1)].
X-ray Crystallography
The molecular structures of [MII(PQ1)] (M = Ni, Cu Zn, Pd, and Pt)
were successfully elucidated by the X-ray diffraction
measurements but suitable crystals of [PbII(PQ1)] were not
obtained. Selected crystallographic and structural data are
summarized in Tables S1 and 2, respectively.
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Table 2. Selected structural data for the structure of [MII(PQ1)]
MII
Ni A
Ni B
Cu
Zn
Pd A
Pd B
Pt
2H[b]
O=Cmeso / Å
1.237(4),
1.234(4)
1.227(4),
1.232(4)
1.242(5)
1.229(5),
1.251(5)
1.218(9),
1.237(9)
1.228(9),
1.248(9)
1.228(6),
1.240(7)
1.231(5)
(Cmeso–C)av / Å
(M–N)av / Å
conformation
mpd / Å[a]
1.453
1.925
ruffle
0.40
1.461
1.927
ruffle
0.41
1.463
2.021
planar
0.06
1.467
2.072
dome
0.05
1.463
2.019
ruffle
0.31
1.461
2.009
ruffle
0.32
1.462
2.027
ruffle
0.22
planar
0.08
[a] Mean plane deviation defined by 24 core atoms. [b] Data from reference [22].
Therefore, this deformation may be attributable to intermolecular
interactions.
In the crystals, NiII, PdII, and PtII complexes formed -stacked
dimers (Figures 2c and 2d), whose selected structural data are
summarized in Table S3. The two molecules in the dimer are
twisted against the M−M axis by approximately 66° with respect
to each other. The distances between two metal centers are ca.
3.2−3.5 Å. It is worth noting that the PtII−PtII distances for
[PtII(PQ1)] (3.3618(6) Å) is shorter than twice the van der Waals
radius of PtII ion (ca. 3.5 Å). This indicates PtII−PtII electronic
interaction,[25,26] which is not observed in the PtII porphyrins
probably because of the strong  repulsion between the
porphyrins. As far as we know, these are the first PtII complexes
with porphyrinoid ligands to exhibit PtII−PtII interaction.
In the crystal of [ZnII(PQ1)], one of the oxygen atoms of the
PQ1 is coordinated to the ZnII ion of the other molecule to form
1D zigzag-chains (Figure 3a). The dihedral angle between two
neighboring PQ1 macrocycles is 88°. Due to the axial
coordination, the Zn ion is placed 0.32 Å above the PQ plane
(Figure S7g), and the PQ macrocycle is slightly dome-distorted,
but almost planar (mpd; 0.05).
Figure 3. 1D chains of (a) [ZnII(PQ1)] and (b) [CuII(PQ1)] in the crystals (C =
black, H = white, N = blue, O = red, Zn = purple, and Cu = brown). Thermal
ellipsoids are drawn at 40% probability level. Solvated molecules and t-butyl
groups on the phenyl groups are omitted for clarity.
On the other hand, [CuII(PQ1)] forms partially stacked 1D
chains in the crystal (Figure 3b). Unlike [ZnII(PQ1)], the two
neighboring molecules are in a perfectly parallel orientation. The
two oxygen atoms of PQ1 are placed above the almost planar
mean plane, defined by the 24 core atoms of the PQ ligand
(Figure S7f), and close to the CuII ion of other molecules. The
CuII···O distance (2.878 Å) is slightly larger than the typical bond
length between the axial ligand and the CuII ion in the CuII-
porphyrin complexes.[27–31] The C=O bond length (1.242(5) Å) is
larger than those of the other complexes (M= 2H, Ni, Pd, and Pt).
These results suggest an associative interaction between the
oxygen atom in the PQ ligand and the CuII ion.
Electrochemistry
Cyclic voltammograms and half-wave potentials of [MII(PQ1)]
determined through cyclic voltammetry are shown in Figure 4 and
Table 3, respectively. The PQ1 ligand and all the metal complexes
yield one irreversible oxidation wave and two reversible reduction
waves in CH2Cl2 containing 0.1 M TBAPF6. Both oxidation and
reduction potentials for [MII(PQ1)] are significantly higher than
those of the corresponding porphyrin complexes, which clearly
indicates the strong electron-accepting nature of [MII(PQ1)]. Both
first and second reduction potentials exhibited relationships that
were almost linear with Pauling’s electronegativity of the central
metal ions, as is the case with porphyrin analogues[32] (Figure 5).
It is worth noting that both first and second reduction potentials of
[NiII(PQ1)] are slightly abnormal. This may reflect its large saddle
distortion of [NiII(PQ1)] as described in the crystallography section.
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-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
Pt
Pd
Ni
Cu
Pb
Zn
1.5
1.7
1.9
2.1
2.3
Electronegativity
Figure 5. Plot of the first (black circle) and second (blue triangle) reduction
potentials versus Pauling’s electronegativity of the central metal ion (M) for
[MII(PQ1)].
Spectroscopic Properties
[MII(PQ1)], except for [PdII(PQ1)], yield a brown color in solution
while [PdII(PQ1)] yield a green color (Figure 6). UV–vis absorption
spectra of [MII(PQ1)] in toluene are shown in Figure 7. All
[MII(PQ1)] have roughly three absorption bands: at ca. 400–500
nm (band I), at ca. 500–600 nm (band II), and at ca. 600– and
quite weak with Log() ca. 2~3 (band III). The shape and intensity
of each band strongly depend on the central metal. For band II,
only PdII have significantly broad and split bands while those of
the others are sharp. This is the main cause of the difference in
the color of [PdII(PQ1)]. For band III, Log() of NiII and PtII is
considerably higher than those of the others.
Figure 4. Cyclic voltammogram of [MII(PQ1)] in CH2Cl2 containing 0.1 M
TBAPF6. M = (a) 2H,[22] (b) Ni, (c) Cu, (d) Zn, (e) Pd, (f) Pt, and (g) Pb.
Table 3. Half-wave potentials (V vs. Fc/Fc+) of [MII(PQ1)] in CH2Cl2
containing 0.1
voltammetry.
M TBAPF6. Potentials were determined by cyclic
M
ERed2
ERed1
EOx
ERed1 − ERed2
0.35
2H[a]
Ni
−1.24
−1.19
−1.23
−1.50
−1.08
−0.97
−1.39
−0.89
−0.69
−0.76
−0.98
−0.66
−0.58
−0.90
(1.18) [c]
(0.96) [c]
(0.95) [c]
(1.14) [c]
(1.16) [c]
(1.04) [c]
(0.92) [c]
0.50
Cu
Zn[b]
Pd
Pt
0.47
0.52
Figure 6. Photographs of the solution of [MII(PQ1)] in toluene. M = (a) Cu, (b)
Ni, (c) Pd, and (d) Pt.
0.42
0.39
Pb
0.49
[a] Data from reference [22]. [b] To dissolve the complex completely, the
measurement was performed in CH2Cl2–pyridine (99:1). [c] Irreversible
peak.
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Figure 8. MO Energy diagram of [MII(PQ1′)]. Blue: ligand-centered MOs, red:
metal-centered MOs (dz2), green: mixed MOs.
Figure 7. UV–vis absorption spectra of [MII(PQ1)] in toluene. M = (a) 2H,[22] (b)
Ni, (c) Cu, (d) Zn, (e) Pd, (f) Pt, and (g) Pb.
Pd: HOMO−2
Pd: HOMO−3
Theoretical calculation
To gain further insight into the electronic state and physical
properties of [MII(PQ)], DFT calculations were performed. For
simplicity, all t-butyl groups on the aryl substituents were removed
from the model structures to allow calculation ([MII(PQ1′)]).
Obtained molecular orbital (MO) energy diagrams are shown in
Figure 8. For group-8 element complexes (M = Ni, Pd, and Pt),
the orbital energies of HOMO−2 and HOMO−3 are quite different
from the those of the rest; and are generated by mixing PQ -
orbitals, which correspond to HOMO−4 and HOMO−5 of
[ZnII(PQ1′)], with metal dyz or dzx orbitals (Figures 9 and S10–S16).
Time-dependent density functional theory (TDDFT) calculation
suggests that the contribution of these orbitals to electronic
transitions is the dominant factor affecting the characteristic
colors and absorption spectra of group-8-element complexes
(Tables S5–S10, and Figures S17–S22).
Zn: HOMO−4
Zn: HOMO−5
Figure 9. Selected MO of [PdII(PQ1′)] and [ZnII(PQ1′)].
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The order of the orbital energy of HOMO and LUMO is
approximately consistent with those of the experimental redox
potentials except for [PbII(PQ)], which may be due to the
incomplete treatment of the relativistic effects.
UV–vis absorption spectra of [NiII(PQ1)] in various solvents
were measured and are shown in Figure S23. Those in 1-
methylimidazole/toluene (1:26), DMF, THF, and MeOH/toluene
(1:3) are similar with that in toluene/pyridine, indicating the axial
coordination of these solvents. It is worth noting that the axial
coordination of these oxygen-based ligands is quite rare in the
case of Ni-porphyrins.[33] On the other hand, that in acetone is
similar to that in toluene, indicating no axial coordination of
acetone. That in acetonitrile/toluene (3:1) shows both
characteristic peaks, indicating that both 4-coordinate and 6-
coordinate species exist in this condition.
Axial coordination behavior of [NiII(PQ1)]
Nickel(II) complexes of porphyrins with electron-withdrawing
substituents undergo axial ligand coordination, which induces a
change in the spin state from S = 0 (diamagnetic) to S = 1
(paramagnetic).[16–21,33] In other word, electron-withdrawing
substituents enhances the Lewis acidity of the central nickel ion.
Due to the strong electron accepting character of PQ ligand, their
nickel complexes are expected to have strong ligation, and this
was qualitatively examined in the previous study using pyridine as
an axial ligand.[6][7] We conducted quantitative analyses of the
axial ligand coordination behavior of [NiII(PQ1)] (Scheme 1).
Strong axial coordination behavior of [NiII(PQ1)] was indicated by
the difference in color and UV–vis absorption spectra in the
presence/absence of axial ligand. A solution [NiII(PQ1)] in toluene
displayed brown color whereas that in toluene/pyridine (3:1)
displayed red color (Figure 10 inset). UV–vis absorption spectra
of [NiII(PQ1)] in both solvents are shown in Figure 10. The shape
of both spectra was quite similar with that of the reported analog
in CH2Cl2 and pyridine.[6] Two sharp bands at 450 nm and 526 nm
and a severely broadened peak around 650 nm were observed in
toluene whereas the characteristic broad peak disappeared along
with the new peak at 580 nm with a shoulder at 525 nm.
NMR studies clearly indicate a change in the spin state of NiII
ion upon axial ligand coordination.[34–37] In the 1H NMR spectrum
of [NiII(PQ1)] in CDCl3, all proton signals for [NiII(PQ1)] were
observed within the range of typical diamagnetic compounds
(Figure 12a); e.g., two doublet signals assigned for  protons of
PQ ligand were observed at 6.58 and 6.25 ppm. On the other
1
hand, the H NMR spectrum of [NiII(PQ1)] in CDCl3/pyridine-d5
(1:1) showed two significantly broadened and downfield-shifted
signals for  protons of PQ1 ligand around 50 ppm (Figure 2b).
That strongly indicates the formation of the paramagnetic nature
of the 6-coordinated complex [NiII(PQ1)(pyridine-d5)2]. Thus, we
identified a paramagnetic susceptibility (m) and an effective
magnetic moment (eff) of [NiII(PQ1)(pyridine-d5)2] in
CDCl3/pyridine-d5 (1:1) at 298 K through the Evans NMR
method.[38–42] The obtained values of m and eff were 3.2510-3
emu mol-1 and 2.79 B, respectively. These values are within the
range observed for 6-coordinate paramagnetic NiII complexes (S
= 1).
Scheme 1. Axial ligation on [NiII(PQ1)].
Figure 11. 1H NMR spectra (500 MHz, 298 K) of [NiII(PQ1)] in (a) CDCl3 (4-
coordinate, diamagnetic), and (b) CDCl3/[D5]pyridine (1:1) (6-coordinate,
paramagnetic). * solvent signals.
Direct evidence of axial coordination was obtained from X-ray
structural analyses. Although Balch reported the crystal structures
of OEP analogues, the relative orientation of the two oxo
substituents could not be ascertained because of the disorder of
the macrocycle.[6] This resulted in uncertainty in their structural
information such as bond lengths.
Slow diffusion of methanol vapor into a solution of [NiII(PQ1)]
in 4-picoline (4-methylpyridine) afforded a single crystal, and X-
Figure 10. UV–vis absorption spectra of [NiII(PQ1)] in toluene and toluene–
pyridine (3:1). Inset shows the photographs of the solutions.
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ray analysis for this crystal revealed the nondisordered structure
[NiII(PQ1)] in toluene upon a titration with pyridine at 298 K is
of the 6-coordinate complexes, [NiII(PQ1)(4-picoline)2] (Figure 12). shown in Figure 13a. There are no clear isosbestic points,
The PQ1 ligand is almost planar with an average mean Ni−NPQ1
bond length of 2.07 Å and a mean deviation from the mean plane
of 0.07 Å.
implying the formation of a 5-coordinated complex as an
intermediate product (Scheme 1). Thus, nonlinear curve fitting
was performed using the change in the absorption at 659 nm to
determine the first and second binding constants, K1 and K2
(Figure 13b). To determine the binding constants successfully, we
assumed that the 5-coordinate and 6-coordinate complexes have
the same value in  at 659 nm as similar manners with porphyrin
analogues.[19,20] K1 and K2 were determined to be 78 ± 2 M−1 and
(4.1 ± 0.2)  102 M−1, and thus  (= K1K2) value is determined to
be (3.2 ± 0.2)  104 M−2. The results of titration with 1-
methylimidazole are shown in Figure S24. In a similar manner, K1,
K2, and  values between [NiII(PQ1)] and 1-methylimidazole were
also determined to be (3.3 ± 0.2)  104 M−1, (6.9 ± 0.7)  104 M−1,
and (2.2 ± 0.4)  107 M−2, respectively. Table 4 summarizes
binding constants for [NiII(PQ1)] and the representative NiII
porphyrin analogues.[16,17,20] Those values are significantly higher
than those of Ni-porphyrins. These results clearly indicate the
stronger Lewis acidity of nickel ion incorporated in the electron
deficient porphyrinquinone ligand.
Figure 12. Crystal structure of [NiII(PQ1)(4-picoline)2] (C = black, H = white, N
= blue, O = red, and Ni = green). Thermal ellipsoids are drawn at 40% probability
level.
Table 4. Binding constants for [MII(PQ1)] (M = Ni and Cu) and the
representative Ni porphyrin analogues.
Compd.[a]
[Ni(PQ1)]
Ligand[
K1 / M-1
K2 / M-1
 / M-2
b]
py
78±2
(4.1±0.2)
×102
(3.2±0.2) ×104
[Ni(TFPP)] [c]
[Ni(TMAFPP)] [d]
[Ni(PQ1)]
py
8.2
22.4
1.8×102
py
33±5
50±10
1.7×103
MeIm
(3.3±0.2)
×104
(6.9±0.7)
×104
(2.2±0.4) ×107
[Ni(TMAFPP)] [d]
MeIm
(5.5±0.5)
×102
(1.1±0.2)
×102
3.9×105
[Ni(TPP)] [e]
[Cu(PQ1)]
[Cu(PQ1)]
[Cu(TPP)] [f]
pyrro
py
1.08
3.79
4.1±0.4
12±2
–
4.09
13.2±0.4
181±4
55±5
MeIm
py
(2.1±0.4)×103
0.05±0.02
–
[a] TFPP = tetrakis(pentafluorophenyl)porphyrinato, TMAFPP = tetrakis(4-
(trimethylammonium)-2,3,5,6-tetrafluorophenyl)porphyrinato, TPP
=
tetraphenylporphyrinato. [b] py = pyridine, MeIm = 1-methylimidazole,
pyrro=pyrrolidine. [c] Data from reference [20]. In [D8]toluene. [d] Data from
reference [16]. In CH3CN. [e] Data from reference [17]. In CH2Cl2. [f] Data
from reference [27]. In benzene. Only formation of the 5-coordinated
complex is considered.
Figure 13. (a) UV-vis spectral change of [NiII(PQ1)] upon the addition of pyridine
(0–80 mM) in toluene at 298 K. (b) Titration curve of [NiII(PQ1)] with pyridine
monitored at 659 nm. The solid line represents the best fitting curve.
To determine the binding constants between [NiII(PQ1)] and
axial ligand L (L = pyridine, 1-methylimidazole), UV–vis titration
experiments were carried out. Change in the UV–vis spectrum of
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Axial coordination behavior of [CuII(PQ1)]
crystallographically independent molecules in the asymmetric unit
(Figure 15 and S8). The conformation of A is saddle shaped while
that of B is ruffled. The coordination environment around Cu ions
is similar between A and B; the bond length of Cu−Npicoline is ca.
0.34 Å longer than that of Cu–NPQ1. Contrary to the Ni analogue,
the difference between the bond lengths of Cu–NPQ1 for 4-
coordinated and 5-coordinated complexes was quite small. In the
crystal, A and B are stacked to form a dimeric structure, which is
observed in the crystals of [MII(PQ1)] (M = 2H, Ni, Pd, and Pt) as
shown above. These results suggest that the driving force of the
dimerization of PQ macrocycles is considerably strong. This and
the small K2 value of [CuII(PQ1)] may be the main factor
influencing crystallization as a 5-coordinated, and not a 6-
coordinated complex.
The results of [NiII(PQ1)] prompted us to evaluate the axial
coordination behavior of
a
copper(II) complex [CuII(PQ1)]
because the 5- or 6-coordinate Cu(II) porphyrin complexes are
still rare owing to their significantly lower binding constants
compared to NiII.[27–31]
UV-vis titration experiments with pyridine and 1-
methylimidazole were carried out for [CuII(PQ1)] (Figures 14 and
S25). The spectrum of [CuII(PQ1)] in the absence of pyridine
exhibits peaks at 568 nm and 458 nm. Upon the addition of
pyridine, a new peak is attained at a relatively shorter wavelength.
Initially, an unsuccessful attempt at curve fitting of the spectral
changes, assuming the 5-coordinate complex as the sole product,
was made because this assumption was generally applied for the
reported analyses of the CuII porphyrin complexes. There are no
clear isosbestic points at the late-stage of titration, implying the
formation of a 6-coordinated complex via the intermediate 5-
coordinated complex. By assuming 5- and 6-coordinate
complexes similar with the case of [NiII(PQ1)], the spectral
changes were fitted appropriately. Therefore, we concluded that
the 6-coordinated complex was the final product, even though the
inconsistent X-ray diffraction study described below. The obtained
K1, K2, and  values are summarized in Table 4. These values are
lower than those of [NiII(PQ1)], but significantly higher than that of
CuII-tetraphenylporphyrin with pyridine (0.05 ± 0.02 M−1, only
considering 5-coordinated complexes).[27–31]
Figure 15. (a) Top, and (b) side views of crystal structure of [CuII(PQ1)(4-
picoline)] (C = black, H = white, N = blue, O = red, Cu = brown). Thermal
ellipsoids are drawn at 40% probability level. Two crystallographically
independent molecules are found in the asymmetric unit, and only one molecule
(Molecule A) is illustrated.
Conclusions
Varieties of divalent metal complexes of 5,15-porphyrinquinone
[MII(PQ1)] were almost quantitatively synthesized. In the crystals,
the complexes tend to form stacked dimers (M = Ni, Pd, and Pt)
or 1D-infinite chains via the coordination of the oxygen atom of
the ligand to the central metal ions (M = Cu and Zn). The
dimerization effectively induces PtII–PtII interaction, which has not
been observed in the porphyrin analogues to date. The high
reduction potentials of [MII(PQ1)] indicate their strong electron
accepting nature. UV-vis absorption spectra of the complexes
vary widely depending on the metal ion. Especially, longer
absorption bands of the complexes with d8 metal ions are quite
different from one another and from those of the other metal
complexes. Theoretical studies suggest that this is caused by the
effective d- coupling in the MO of the complexes. The strong
electron-withdrawing nature of PQ enhances the Lewis acidity of
the central metal ions, thus inducing the significantly strong axial
ligation of the various ligands on the central metals. We anticipate
that the revealed basic properties of the metal-PQ complexes
could contribute to the new design of catalysts or advanced
Figure 14. (a) UV-vis spectral change of [CuII(PQ1)] upon the addition of
pyridine (0–0.78 M) in toluene at 298 K. (b) Titration curve of [NiII(PQ1)] with
pyridine monitored at 554 nm.
A single crystal of [CuII(PQ1)] grown in the presence of 4-
picoline was analyzed through X-ray diffractometry. The revealed
structure was not a 6-, but a 5-coordinated structure, i.e.,
[CuII(PQ1)(4-picoline)].
The
crystal
contained
two
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10.1002/ejic.202000527
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temperature for 1 h. The reaction mixture was directly poured on top of a
basic alumina column packed with CHCl3, then eluted with CHCl3. The
solvent was removed under reduced pressure. The crude product was
recrystallized from toluene–octane to give [CuII(PQ1)] as dark red
microcrystals (28.2 mg, 0.036 mmol, 90%). m.p.: >300 ºC; IR (ATR): ν˜ =
2960, 2904, 2867, 1592, 1552, 1490, 1393, 1349, 1320, 1264, 1232, 1206,
1054, 1015, 969, 897, 851, 832, 811, 760, 727, 714, 587, 492, 452, 421
cm-1; UV/Vis (toluene): max (Log) = 309 (4.42), 365 (4.50), 421 (4.49),
458 (4.51), 529 (4.08), 568 nm (4.67); HRMS(APCI): m/z calcd for
C48H51N4O2Cu: 778.3303 ([M+H]+), found 778.3293; elemental analysis
calcd (%) for C48H50N4O2Cu: C, 74.06; H, 6.47; N, 7.20; found: C, 73.99;
H, 6.47; N, 7.10.
materials. For this purpose, we are currently performing further
experiments to reveal the catalytic or redox-non-innocent
behavior of the complexes.
Experimental Section
Instrumentation and Materials
The porphyrinquinone ligand (2H-PQ1) was synthesized using the
procedure developed by our group.[22] Toluene, CH2Cl2, pyridine, and 1-
methylimidazole were distilled from CaH2. All the other chemicals were of
reagent grades and used without further purification. Analytical thin layer
chromatography (TLC) was performed on silica gel 60 F254 plates. Flash
column chromatography was performed using silica gel 60N (spherical,
neutral, 40–50 m). All NMR spectral data were recorded on a Bruker AV-
500 (500 MHz) spectrometer. These data were collected at ambient
temperature (25 °C) unless otherwise noted. 1H NMR spectra were
internally referenced to tetramethylsilane as a standard. 13C NMR spectra
were internally referenced to solvent signals ( = 77.0 ppm for CDCl3). ESI
HRMS data were measured on a Bruker micrOTOF II. APCI HRMS data
were measured on a Bruker micrOTOF II equipped with the DirectProbe
assembly. IR spectral data were recorded on a PerkinElmer Spectrum Two
spectrometer equipped with an ATR unit. UV–Vis spectral data were
recorded on a HITACHI U-3500 spectrometer or Shimadzu UV-3600
spectrometer. Melting points were determined on a Yanaco MP-S3 melting
point apparatus. Cyclic voltammetry (CV) measurements were carried out
using ALS 650C electrochemical analyzer in argon-saturated CH2Cl2
solutions containing 0.1 M tetrabutylammonium hexafluorophosphate as a
supporting electrolyte at ambient temperature (298 K). A conventional
three-electrode cell was used with a glassy carbon working electrode, a
platinum wire counter electrode, and an Ag/AgCl reference electrode.
Ferrocene was used as the internal standard in all electrochemical
experiments.
[ZnII(PQ1)]
A mixture of 2H-PQ1 (28.6 mg, 0.040 mmol) and Zn(OAc)2·2H2O (44.0 mg,
0.20 mmol) in CHCl3 (2 mL) and MeOH (0.2 mL) was stirred at room
temperature for 1 h. The reaction mixture was directly poured on top of a
basic alumina column packed with CHCl3, then eluted with CHCl3. The
solvent was removed under reduced pressure to give [ZnII(PQ1)] as dark
red powder (31.53 mg, 0.040 mmol, quant.). The product was further
recrystallized from butyronitrile–toluene to give [ZnII(PQ1)]·(PrCN) as dark
red microcrystals (23.6 mg, 0.027 mmol, 68%). m.p.: >300 ºC; 1H NMR
(500 MHz, CDCl3)  = 7.43 (br, 2H, HAr-p), 7.08 (d, J = 1.5 Hz, 4H, HAr-o),
7.04 (d, J = 4.4 Hz, 4H, H), 6.23 (d, J = 4.4 Hz, 4H, H), 1.22 ppm (s, 36H,
t-Bu); 13C NMR (125 MHz, CDCl3/[D5]pyridine (19:1))  = 177.6 (Cq), 157.7
(Cq), 156.2 (Cq), 149.7 (Cq), 146.6 (Cq), 137.6 (Cq), 133.4 (CH), 124.6
(CH), 122.9 (CH), 121.2 (CH), 34.7 (Cq), 31.3 ppm (CH3); IR (ATR): ν˜ =
2958, 2904, 2870, 1592, 1528, 1496, 1480, 1395, 1347, 1313, 1246, 1225,
1201, 1052, 1007, 964, 896, 852, 832, 808, 760, 727, 582, 562, 488, 452,
409 cm-1; UV/Vis (toluene/pyridine (99:1)): max (Log) = 357 (4.59), 453
(4.86), 505 (4.21), 542 nm (4.86); HRMS(APCI): m/z calcd for
C48H51N4O2Zn: 779.3298 ([M+H]+), found 779.3285; elemental analysis
calcd (%) for C48H50N4O2Zn·(C4H7N): C, 73.53; H, 6.76; N, 8.24; found: C,
73.54; H, 6.89; N, 8.19.
[NiII(PQ1)]
[PdII(PQ1)]
A mixture of 2H-PQ1 (81.3 mg, 0.11 mmol) and Ni(acac)2 (146.1 mg, 0.57
mmol) in toluene (5 mL) was refluxed for 3 h. The reaction mixture was
directly poured on top of a silica gel column packed with CHCl3, then eluted
with CHCl3. The solvent was removed under reduced pressure. The crude
product was purified by flash column chromatography (silica gel,
hexane:CH2Cl2 = 1:1), and then recrystallized from toluene–octane to give
[NiII(PQ1)] as dark brown microcrystals (87.1 mg, 0.01 mmol, 93%).
Spectral data were consistent with the previously reported data.[8] Rf = 0.15
(hexane/CH2Cl2 1:1); m.p.: >300 ºC; 1H NMR (500 MHz, CDCl3)  = 7.50
(t, J = 1.7 Hz, 2H, HAr-p), 7.16 (d, J = 1.7 Hz, 4H, ArHAr-o), 6.58 (d, J = 4.6
Hz, 4H, H), 6.25 (d, J = 4.6 Hz, 4H, H), 1.34 ppm (s, 36H, t-Bu); 13C NMR
(125 MHz, CDCl3)  = 179.4 (Cq), 155.5 (Cq), 152.3 (Cq), 150.5 (Cq),
142.3 (Cq), 134.8 (Cq), 133.6 (CH), 124.0 (CH), 123.7 (CH), 120.9 (CH),
34.9 (Cq), 31.4 ppm (CH3); IR (ATR): ν˜ = 3112, 2961, 2866, 1623, 1558,
1554, 1490, 1394, 1346, 1327, 1267, 1235, 1206, 1052, 1018, 976, 899,
851, 839, 828, 808, 759, 727, 716, 563, 499, 443 cm-1; UV/Vis (toluene):
max (Log) = 321 (4.34), 363 (4.39), 450 (4.82), 526 nm (4.24);
HRMS(APCI): m/z calcd for C48H51N4O2Ni: 773.3360 ([M+H]+), found
773.3366; elemental analysis calcd (%) for C48H50N4O2Ni: C, 74.52; H,
6.51; N, 7.24; found: C, 74.60; H, 6.48; N, 7.15.
A mixture of 2H-PQ1 (35.6 mg, 0.050 mmol) and Pd(OAc)2 (16.5 mg, 0.075
mmol) in CHCl3 (2.5 mL) and MeOH (0.25 mL) was stirred at room
temperature for 25 min. The reaction mixture was directly poured on top of
a silica gel column packed with CHCl3, then eluted with CHCl3. The solvent
was removed under reduced pressure to give [PdII(PQ1)] as green powder
(40.4 mg, 0.049 mmol, 98%). Analytically pure product was obtained by
the recrystallization from hot toluene–hexane. Rf = 0.26 (hexane/toluene
1:1); m.p.: >300 ºC; 1H NMR (500 MHz, CDCl3)  = 7.51 (t, J = 1.7 Hz, 2H,
HAr-p), 7.19 (d, J = 1.7 Hz, 4H, ArHAr-o), 6.93 (d, J = 4.7 Hz, 4H, H), 6.36
(d, J = 4.7 Hz, 4H, H), 1.35 ppm (s, 36H, t-Bu); 13C NMR (125 MHz, CDCl3)
 = 176.7 (Cq), 155.8 (Cq), 150.5 (Cq), 150.0 (Cq), 140.4 (Cq), 136.2 (Cq),
133.7 (CH), 124.8 (CH), 123.1 (CH), 121.6 (CH), 35.0 (Cq), 31.4 ppm
(CH3); IR (ATR): ν˜ = 3108, 2962, 2866, 1611, 1542, 1476, 1394, 1349,
1342, 1271, 1234, 1205, 1052, 1023, 986, 899, 850, 839, 827, 809, 758,
725, 565, 507, 453, 438 cm-1; UV/Vis (toluene): max (Log) = 323 (4.37),
365 (4.34), 441 (4.79), 576 (3.99), 618 nm (4.16); HRMS(APCI): m/z calcd
for C48H51N4O2Pd: 821.3058 ([M+H]+), found 821.3052; elemental analysis
calcd (%) for C48H50N4O2Pd: C, 70.19; H, 6.14; N, 6.82; found: C, 70.45;
H, 6.21; N, 6.60.
[PtII(PQ1)]
[CuII(PQ1)]
Synthesis of [PtII(PQ1)] was performed as a similar manner with the facile
synthesis of PtII-porphyrin analogues reported by us.[43] A mixture of 2H-
PQ1 (14.2 mg, 0.020 mmol) and PtCl2(PhCN)2 (18.6 mg, 0.040 mmol) in
A mixture of 2H-PQ1 (28.7 mg, 0.040 mmol) and Cu(OAc)2·H2O (40.4 mg,
0.20 mmol) in CHCl3 (2 mL) and MeOH (0.2 mL) was stirred at room
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chlorobenzene (0.5 mL) was refluxed for 3 h. The solvent was removed
under reduced pressure, and the crude product was purified by
chromatography (silicagel, hexane:CH2Cl2=2:1). The solvent was removed
under reduced pressure to give [PtII(PQ1)] as black microcrystals (18.1 mg,
0.020 mmol, quant.). Analytically pure product was obtained by the
recrystallization from hot toluene–hexane. Rf = 0.13 (hexane/CH2Cl2 1:1);
m.p.: >300 ºC; 1H NMR (500 MHz, CDCl3)  = 7.49 (t, J = 1.8 Hz, 2H, HAr-
p), 7.22 (d, J = 1.8 Hz, 4H, ArHAr-o), 6.86 (d, J = 4.7 Hz, 4H, H), 6.28 (d, J
= 4.7 Hz, 4H, H), 1.35 ppm (s, 36H, t-Bu); 13C NMR (125 MHz, CDCl3) 
= 176.1 (Cq), 156.0 (Cq), 151.2 (Cq), 150.1 (Cq), 139.4 (Cq), 135.9 (Cq),
133.9 (CH), 124.6 (CH), 123.1 (CH), 121.0 (CH), 35.0 (Cq), 31.4 (CH3); IR
(ATR): ν˜ = 3107, 2962, 2866, 1615, 1543, 1475, 1349, 1337, 1271, 1234,
1205, 1051, 1024, 982, 899, 849, 839, 827, 809, 759, 726, 564, 497, 452,
439 cm-1; UV/Vis (toluene): max (Log) = 366 (4.33), 438 (4.72), 499 (3.90),
535 nm (4.51); HRMS(APCI): m/z calcd for C48H51N4O2Pt: 910.3658
([M+H]+), found 910.3675; elemental analysis calcd (%) for C48H50N4O2Pt:
C, 63.35; H, 5.54; N, 6.16; found: C, 63.43; H, 5.57; N, 6.12.
Single-crystal X-ray diffraction data for the rest were collected on a Bruker
Smart APEX CCD diffractometer using graphite-monochromated Mo K
radiation ( = 0.71073 Å) by the  scan mode. The crystal was cooled by
a stream of cooled N2 gas. The program SAINT was used for integration
of the diffraction profiles. Empirical absorption corrections were applied by
using the SADABS program.
The structures were solved by direct methods (SHELXS97)[44] or
SHELXT[45] program and refined by full-matrix least-squares calculations
on F2 (SHELXL2014).[46] All non-hydrogen atoms were modeled
anisotropically. Hydrogen atoms were fixed at calculated positions and
refined with a riding model. A summary of the crystallographic data is given
in Tables S1 and S2. CCDC 1989954 ([NiII(PQ1)]), 1989949 ([CuII(PQ1)]),
1989952 ([ZnII(PQ1)]), 1989953 ([PdII(PQ1)]), 1989955 ([PtII(PQ1)]),
1989951 ([NiII(PQ1)(4-picoline)2]), and 1989950 ([CuII(PQ1)(4-picoline)])
contain the supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif.
[PbII(PQ1)]
Determination of binding constants for [NiII(PQ1)]
First, 1.81 mg (2.34 mol) of [NiII(PQ1)] was dissolved in 20 mL of toluene.
Then 3 mL of the solution was placed in a 1 cm quartz cell, and 3 L of a
toluene solution of pyridine (0.40 M) or 1-methylimidazole (2.5 mM) was
added into the solution via a micro-syringe. The resultant solution was
stirred for 3 min at room temperature. UV–vis spectra were recorded at
room temperature after each addition. The changes in absorption at 659
nm as a function of the concentration of the axial ligand were plotted. The
first and second binding constants (K1 and K2) were determined by a
nonlinear curve fitting based on the following equation.
A mixture of 2H-PQ1 (28.7 mg, 0.040 mmol) and Pb(OAc)2·3H2O (151.5
mg, 0.40 mmol) in CHCl3 (2 mL) and MeOH (0.2 mL) was stirred at room
temperature for 90 min. The reaction mixture was directly poured on top of
a basic alumina column packed with CHCl3, then eluted with CHCl3. The
solvent was removed under reduced pressure, and then recrystallized
from toluene–hexane to give [PbII(PQ1)] as dark brown microcrystals (35.2
mg, 0.038 mmol, 95%). Analytically pure product was obtained by the
recrystallization from hot toluene–hexane. m.p.: >300 ºC; 1H NMR (500
MHz, C6D6)  = 7.68 (t, J = 1.6 Hz, 2H, HAr-p), 7.60 (brs, 2H, ArHAr-o), 7.56
(d, J = 4.3 Hz, 4H, H), 7.48 (brs, 2H, ArHAr-o), 6.78 (d, J = 4.3 Hz, 4H, H),
1.38 (s, 18H, t-Bu), 1.35 ppm (s, 18H, t-Bu); 13C NMR (125 MHz, CDCl3) 
= 177.3 (Cq), 157.2 (Cq), 157.0 (Cq), 150.1 (Cq), 149.9 (Cq), 144.9 (Cq),
137.5 (Cq), 135.0 (CH), 125.2 (CH), 124.8 (CH), 123.3 (CH), 122.4 (CH),
35.0 (Cq), 31.5 ppm (CH3); IR (ATR): ν˜ = 2955, 2906, 2869, 1578, 1536,
1513, 1506, 1461, 1394, 1339, 1331, 1293, 1239, 1231, 1224, 1058, 1051,
1000, 958, 843, 834, 810, 760, 737, 725, 566, 483, 448, 403 cm-1; UV/Vis
(toluene): max (Log) = 360 (4.52), 472 (4.91), 507 (4.14), 544 nm (4.74);
HRMS(APCI): m/z calcd for C48H51N4O2Pb: 923.3779 ([M+H]+), found
923.3759; elemental analysis calcd (%) for C48H50N4O2Pb: C, 62.52; H,
5.47; N, 6.08; found: C, 62.82; H, 5.62; N, 5.90.
∆휀1퐾1[퐿]0[푃]0 + ∆휀2퐾1퐾2[퐿]20[푃]0
∆퐴 =
1 + 퐾1[퐿]0 + 퐾1퐾2[퐿]02
where A is differential absorbance (A – A0), and  is the difference
between the molar extinction coefficient of [NiII(PQ1)(L)2] and that of
[NiII(PQ1)].
Evans measurements
The magnetic susceptibility of [NiII(PQ1)(pyridine-d5)2] in CDCl3/pyridine-
d5 (1:1) solution was determined through the Evans method[38–42] using
TMS as the reference. To do so, 3.00 mg of [NiII(PQ1)] was dissolved in
0.5 mL of CDCl3/pyridine-d5 (1:1) containing 1% TMS. In a special coaxial
tube, the resultant solution was placed in the outer tube and the same
solvent was placed in the inner tube. 1H NMR spectra were recorded at
298 K on a Bruker AV-500 (500.13 MHz) spectrometer. The separation of
a TMS peak from the inner and outer tubes () was determined to be 60.7
Hz. The molar magnetic susceptibility, M is calculated using the
appropriate equation for a superconducting magnet:
X-Ray crystal structure determinations
Single crystals of [NiII(PQ1)] were grown by the vapor diffusion of hexane
into its benzene solution. Single crystals of [CuII(PQ1)] were grown by the
vapor diffusion of acetonitrile into its chloroform solution. Single crystals of
[ZnII(PQ1)] were grown by the vapor diffusion of acetone into its chloroform
solution. Single crystals of [PdII(PQ1)] were grown by the vapor diffusion
of hexane into its chloroform solution. Single crystals of [PtII(PQ1)] were
grown by the vapor diffusion of hexane into its toluene solution. Single
crystals of [NiII(PQ1)(4-picoline)2] were grown by the vapor diffusion of
methanol into its 4-picoline solution. Single crystals of [CuII(PQ1)] were
grown by the vapor diffusion of hexane into its 4-picoline solution.
paraM=1000 / 0Sfc − dia
M
where 0 is the spectrometer frequency (500.13  106 Hz), Sf is the shape
factor of the magnet (4π/3 for a cylindrical sample in a superconducting
magnet), c is the molar concentration of [NiII(PQ1)(pyridine-d5)2] (7.76 
10-3 mol L−1), and diaM is the diamagnetic contribution of the complex. The
diaM value is roughly estimated using Pascal's constants.[47]
Single-crystal X-ray diffraction data for [CuII(PQ1)] were collected on a
Rigaku XtaLab P200 diffractometer using multi-layer mirror
monochromated Mo-K radiation ( = 0.71075 Å) by the  scan mode.
The crystal was cooled by a stream of cooled N2 gas. Data were collected
and processed using CrystalClear (Rigaku). The data were corrected for
Lorentz and polarization effects, and empirical absorption correction was
applied.
Computational Details
For simplicity, all t-butyl groups on the phenyl rings were removed from the
model structures (PQ1′). Geometries of all models were optimized by the
DFT method at the Becke, three-parameter, Lee−Yang−Parr (B3LYP)
exchange-correlation functional. Stuttgart RSC 1997 ECP and the
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10.1002/ejic.202000527
European Journal of Inorganic Chemistry
FULL PAPER
associated basis set (SDD)[48] were used for the metal atoms, and the 6-
311+G(d,p) basis set was used for the other light atoms. To confirm that
the optimized geometries were not in saddle points but in stable points,
frequency calculations without scaling were performed. None of the
geometry-optimized structures gave imaginary frequencies. Excitation
energies and oscillator strengths were computed with the time-dependent
density functional theory (TDDFT) method, in which the solvent effect of
toluene was included by the PCM method. All calculations were carried out
using the Gaussian 09 program package (Rev. E01).[49]
[17]
[18]
[19]
S.-L. Jia, W. Jentzen, M. Shang, X.-Z. Song, J.-G. Ma, W. R.
Scheidt, J. A. Shelnutt, Inorg. Chem. 1998, 37, 4402–4412.
H. Duval, V. Bulach, J. Fischer, R. Weiss, Inorg. Chem. 1999, 38,
5495–5501.
Y. Song, R. E. Haddad, S. L. Jia, S. Hok, M. M. Olmstead, D. J.
Nurco, N. E. Schore, J. Zhang, J. G. Ma, K. M. Smith, S. Gazeau, J.
Pécaut, J. C. Marchon, C. J. Medforth, J. A. Shelnutt, J. Am. Chem.
Soc. 2005, 127, 1179–1192.
[20]
S. Thies, C. Bornholdt, F. Köhler, F. D. Sönnichsen, C. Näther, F.
Tuczek, R. Herges, S. I. Materials, A. Fluor-, S.- Aldrich, D. Core,
Chem. - Eur. J. 2010, 16, 10074–10083.
Acknowledgements
[21]
[22]
[23]
[24]
[25]
[26]
[27]
M. Dommaschk, F. Gutzeit, S. Boretius, R. Haag, R. Herges, Chem.
Commun. 2014, 50, 12476–12478.
We thank Prof. Dr. Motoko S. Asano (Gunma University) and Prof.
Dr. Takuji Ogawa (Osaka University) for helpful discussion. The
theoretical calculations were performed by using the Research
Center for Computational Science, Okazaki, Japan.
K. Yamashita, D. Hirano, M. S. Asano, K. Sugiura, Chem. Lett.
2014, 43, 1049–1051.
M. John Plater, S. Aiken, G. Bourhill, Tetrahedron 2002, 58, 2415–
2422.
Keywords: Lewis acids • Metal-metal interactions •
Porphyrinoids • Quinones • Transition metals
M. J. Plater, S. Aiken, T. Gelbrich, M. B. Hursthouse, G. Bourhill,
Polyhedron 2001, 20, 3219–3224.
K. M.-C. Wong, V. K.-M. Au, V. W.-W. Yam, in Compr. Inorg. Chem.
II, Elsevier, 2013, pp. 59–130.
[1]
S. Patai, Z. Rappoport, Eds. , The Quinonoid Compounds: Vol. 1
(1988), John Wiley & Sons, Inc., Chichester, UK, 1988.
W. Kaim, Inorg. Chem. 2011, 50, 9752–9765.
G. H. Barnett, B. Evans, K. M. Smith, Tetrahedron 1975, 31, 2711–
2717.
A. Aliprandi, D. Genovese, M. Mauro, L. De Cola, Chem. Lett. 2015,
44, 1152–1169.
[2]
[3]
J. R. Miller, G. D. Dorough, J. Am. Chem. Soc. 1952, 74, 3977–
3981.
[4]
D. Lahaye, K. Muthukumaran, C.-H. Hung, D. Gryko, J. S.
Rebouças, I. Spasojević, I. Batinić-Haberle, J. S. Lindsey, Bioorg.
Med. Chem. 2007, 15, 7066–7086.
[28]
[29]
P. Hambright, Chem. Commun. (London) 1967, 470–471.
G. Szintay, A. Horváth, G. Grampp, J. Photochem. Photobiol. A
Chem. 1999, 126, 83–89.
[5]
[6]
[7]
A. L. Balch, B. C. Noll, M. M. Olmstead, S. L. Phillips, Inorg. Chem.
1996, 35, 6495–6506.
[30]
[31]
G. Szintay, A. Horváth, Inorganica Chim. Acta 2001, 324, 278–285.
J. Cremers, S. Richert, D. V. Kondratuk, T. D. W. Claridge, C. R.
Timmel, H. L. Anderson, Chem. Sci. 2016, 7, 6961–6968.
J. H. Furhop, K. M. Kadish, D. G. Davis, J. Am. Chem. Soc. 1973,
95, 5140–5147.
A. L. Balch, M. M. Olmstead, S. L. Phillips, Inorg. Chem. 1993, 32,
3931–3936.
[32]
[33]
[34]
A. L. Balch, B. C. Noll, S. L. Phillips, S. M. Reid, E. P. Zovinka,
Inorg. Chem. 1993, 32, 4730–4736.
A. Yagi, T. Kondo, D. Yamashita, N. Wachi, H. Omori, N. Fukui, T.
Ikeue, H. Shinokubo, Chem. – A Eur. J. 2019, 25, 15580–15585.
F. A. Walker, in The Porphyrin Handbook, Vol. 5 (Eds.: K.M. Kadish,
K.M. Smith, R. Guilard), Academic Press, San Diego, CA, 2000, pp.
81–183.
[8]
[9]
D. M. Shen, C. Liu, X. G. Chen, Q. Y. Chen, Synlett 2009, 945–948.
D. W. J. McCallien, J. K. M. Sanders, J. Am. Chem. Soc. 1995, 117,
6611–6612.
[10]
[11]
Z. Clyde-Watson, N. Bampos, J. K. M. Sanders, New J. Chem.
1998, 22, 1135–1138.
[35]
[36]
E. Pacholska-Dudziak, L. Latos-Grażyński, Eur. J. Inorg. Chem.
2007, 2007, 2594–2608.
A. D. Bond, N. Feeder, S. J. Teat, Z. Clyde-Watson, N. Bampos, J.
K. M. Sanders, Acta Crystallogr. Sect. E Struct. Reports Online
2001, 57, m454–m456.
M. Pawlicki, L. Latos-Grażyński, in Handbook of Porphyrin Science,
Vol. 2 (Eds.: K.M. Kadish, K.M. Smith, R. Guilard), World Scientific
Publishing, Singapore, 2010, pp. 103–192.
[12]
[13]
[14]
Y. Ding, X. Li, J. P. Hill, K. Ariga, H. Ågren, J. Andréasson, W. Zhu,
H. Tian, Y. Xie, Chem. - Eur. J. 2014, 20, 12910–12916.
M. G. Derry Holaday, G. Tarafdar, A. Kumar, M. L. P. Reddy, A.
Srinivasan, Dalton Trans. 2014, 43, 7699–7703.
N. L. Bill, M. Ishida, S. Bähring, J. M. Lim, S. Lee, C. M. Davis, V. M.
Lynch, K. a Nielsen, J. O. Jeppesen, K. Ohkubo, S. Fukuzumi, D.
Kim, J. L. Sessler, J. Am. Chem. Soc. 2013, 135, 10852–10862.
F. A. Walker, E. Hui, J. M. Walker, J. Am. Chem. Soc. 1975, 97,
2390–2397.
[37]
F. A. Walker, in Handbook of Porphyrin Science, Vol. 6 (Eds.: K.M.
Kadish, K.M. Smith, R. Guilard), World Scientific Publishing,
Singapore, 2010, pp. 1–337.
[38]
[39]
[40]
[41]
[42]
[43]
D. F. Evans, J. Chem. Soc. 1959, 2003–2005.
D. Ostfeld, I. A. Cohen, J. Chem. Educ. 1972, 49, 829.
E. M. Schubert, J. Chem. Educ. 1992, 69, 62.
[15]
[16]
D. H. Grant, J. Chem. Educ. 1995, 72, 39.
C. Piguet, J. Chem. Educ. 1997, 74, 815–816.
K. Yamashita, N. Katsumata, S. Tomita, M. Fuwa, K. Fujimaki, T.
Yoda, D. Hirano, K. Sugiura, Chem. Lett. 2015, 44, 492–494.
T. La, R. A. Richards, R. S. Lu, R. Bau, G. M. Miskelly, Inorg. Chem.
1995, 34, 5632–5640.
For internal use, please do not delete. Submitted_Manuscript
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[44]
[45]
[46]
G. M. Sheldrick, Acta Crystallogr. Sect. A Found. Crystallogr. 2007,
64, 112–122.
Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, J. E.
Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N.
Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K.
G. M. Sheldrick, Acta Crystallogr. Sect. A Found. Adv. 2015, 71, 3–
8.
Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M.
Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V.
Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O.
Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L.
Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J.
J. Dannenberg, S. Dapprich, A. D. Daniels, Farkas, J. B. Foresman,
J. V Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09, Rev. E.01,
Gaussian, Inc., Wallingford CT 2009.
G. M. Sheldrick, Acta Crystallogr. Sect. C Struct. Chem. 2015, 71,
3–8.
[47]
[48]
G. A. Bain, J. F. Berry, J. Chem. Educ. 2008, 85, 532.
M. Dolg, U. Wedig, H. Stoll, H. Preuss, J. Chem. Phys. 1987, 86,
866–872.
[49]
M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.
A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F.
Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M.
Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima,
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Entry for the Table of Contents (Please choose one layout)
Key Topic: Quinone-metal complexes
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Ken-ichi Yamashita,* Daisuke Hirano,
Ken-ichi Sugiura*
Page No. – Page No.
Metal complexes of 5,15-
porphyrinquinones: Systematic study
of crystal structure, electronic
structure, and Lewis acidity
Aimed at the expansion of the chemistry of quinone-metal complexes, the
systematic study of divalent metal complexes of 5,15-porphyrinquinone revealed
their strong electron-accepting nature and metal-metal interaction (for Pt), effective
d(metal)-(ligand) coupling in their molecular orbital, and their great enhancement
of the Lewis acidity of the central metals.
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