Syntheses, Properties, and Catalytic Activities of Metal(II) Complexes and Free Bases of Redox-Switchable 20π, 19π, and 18π 5,10,15,20-Tetraaryl-5,15-diazaporphyrinoids

Article abstract of DOI:10.1002/chem.201703664

In spite of significant advances in redox-active porphyrin-based materials and catalysts, little attention has been paid to 20π and 19π porphyrins because of their instability in air. Here we report the meso-modification of 5,10,15,20-tetraarylporphyrin with two nitrogen atoms, which led to redox-switchable 20π, 19π, and 18π 5,10,15,20-tetraaryl-5,15-diazaporphyrinoids (TADAPs). Three kinds of metal(II) complexes and free bases of TADAP were prepared by the metal-templated annulation of the corresponding metal-bis(dipyrrin) complexes. The inductive and resonance effects of the meso-nitrogen atoms on the aromatic, optical, electrochemical, and magnetic properties of the entire TADAP π-systems were assessed by using various spectroscopic measurements and density functional theory calculations. The aromaticity and π–π* electronic transition energies of the TADAPs varied considerably, and were shown to be dependent on the oxidation states of the π-systems. In contrast to the isoelectronic 5,10,15,20-tetraarylporphyrin derivatives, the 20π and 19π TADAPs were chemically stable under air. In particular, the 19π TADAP radical cations were extremely stable towards dioxygen, moisture, and silica gel. This reflected the low-lying singly occupied molecular orbitals of their π-systems and the efficient delocalization of their unshared electron spin. The capability of MgTADAP to catalyze aerobic biaryl formation from aryl Grignard reagents was demonstrated, which presumably involved a 19π/20π redox cycle.

Full text of DOI:10.1002/chem.201703664

A Journal of
Accepted Article
Title: Syntheses, Properties, and Catalytic Activities of Metal(II)
Complexes and Free Bases of Redox-Switchable 20π, 19π, and
18π 5,10,15,20-Tetraaryl-5,15-diazaporphyrinoids
Authors: Keisuke Sudoh, Takaharu Satoh, Toru Amaya, Ko Furukawa,
Mao Minoura, Haruyuki Nakano, and Yoshihiro Matano
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Syntheses, Properties, and Catalytic Activities of Metal(II)
Complexes and Free Bases of Redox-Switchable 20, 19, and
1
8 5,10,15,20-Tetraaryl-5,15-diazaporphyrinoids
[b]
[b]
[c]
[d]
[e]
Keisuke Sudoh, Takaharu Satoh, Toru Amaya,* Ko Furukawa,* Mao Minoura, Haruyuki
[f]
[a]
Nakano, and Yoshihiro Matano*
Dedication ((optional))
Abstract: In spite of significant advances in redox-active porphyrin-
based materials and catalysts, little attention has been paid to 20
and 19 porphyrins, because of their instability in air. Here we report
the meso-modification of 5,10,15,20-tetraarylporphyrin with two
nitrogen atoms, which led to redox-switchable 20, 19, and 18
demonstrated, which presumably involved a 19–20 redox cycle.
Introduction
5
,10,15,20-tetraaryl-5,15-diazaporphyrinoids (TADAPs). Three kinds
Porphyrins are well known as redox-active macrocyclic ligands
and 18-electron aromatic molecules. The redox properties of
of metal(II) complexes and free bases of TADAP were prepared by
the metal-templated annulation of the corresponding metal–
bis(dipyrrin) complexes. The inductive and resonance effects of the
meso-nitrogen atoms on the aromatic, optical, electrochemical, and
magnetic properties of the entire TADAP -systems were assessed,
using various spectroscopic measurements and density functional
theory calculations. The aromaticity and –* electronic transition
energies of the TADAPs varied considerably, depending on the
oxidation states of the -systems. The 20 and 19 TADAPs were
chemically stable under air, in contrast to the isoelectronic
porphyrins control
a
variety of electron/energy transfer
processes in nature and industry. There is therefore
considerable interest in the aromatic, optical, and magnetic
properties of the resulting oxidized/reduced macrocyclic -
systems.[
1,2]
One-electron and two-electron reductions of a
neutral 18 porphyrin ring produce the 19 radical anion and
0 dianion, respectively. In general, these anionic porphyrins
2
are extremely air sensitive because of their high-lying singly
occupied molecular orbital (SOMO) and highest occupied
molecular orbital (HOMO). Such sensitivity hampers their
isolation and characterization in air. Three strategies for isolating
5,10,15,20-tetraarylporphyrin derivatives. In particular, the 19
TADAP radical cations were extremely stable towards dioxygen,
moisture, and silica gel. This reflected the low-lying singly occupied
molecular orbitals of their -systems, and the efficient delocalization
of their unshared electron spin. The capability of MgTADAP to
catalyze aerobic biaryl formation from aryl Grignard reagents was
20 porphyrins in neutral form have so far been reported;
modification of the core nitrogen atoms (core modification),
metal complexation at the core, and peripheral substitution with
appropriate functional groups.[3–13] Selected examples prepared
according to these strategies are shown in Chart 1. Vogel and
co-workers reported the first examples of core-modified 20
porphyrins (isophlorins) P1 and tetraoxaisophlorin.[ Similarly, N-
alkyl-,[4] O-,[5] S-,[6] O,N-,[7] O,S-,[5] and P,S-containing[8]
isophlorins have been reported by other groups. Vaid and co-
3]
[a]
[b]
[c]
[d]
Prof. Dr. Y. Matano
Department of Chemistry, Faculty of Science,
Niigata University, Nishi-ku, Niigata 950-2181 (Japan)
E-mail: matano@chem.sc.niigata-u.ac.jp
K. Sudoh, T. Satoh
Department of Fundamental Sciences, Graduate School of Science
and Technology,
Niigata University, Nishi-ku, Niigata 950-2181 (Japan)
Prof. Dr. T. Amaya
Department of Applied Chemistry, Graduate School of Engineering,
Osaka University, Suita, Osaka 565-0871 (Japan)
E-mail: amaya@chem.eng.osaka-u.ac.jp
Prof. Dr. K. Furukawa
workers
germanium(IV) complexes of 5,10,15,20-tetraphenylporphyrin
(TPP) P2[9] and phthalocyanine,[10] in which the N
-macrocycles
synthesized
six-coordinate
silicon(IV)
and
4
were coordinated to the metal center as −4 ligands with 20-
electrons. Brothers et al. used the same strategy to obtain the
4
+
2
0 TPP-type porphyrin by inserting a diboron (B
2
) unit into the
[
11]
core. We reported the combined use of core modification and
metal complexation to obtain the air stable palladium(II) complex
-isophlorin.[12] Chen et al. isolated the free base of
of P,S,N
2
isophlorin P3 by appending four trifluoromethyl and four phenyl
groups at the periphery of the porphyrin.[13] However, these
approaches often cause severe distortion of the 20 framework
because of steric repulsion of the substituents at the core or
Center for Coordination of Research Facilities, Institute for Research
Promotion, Niigata University, Nishi-ku, Niigata 950-2181 (Japan)
E-mail: kou-f@chem.sc.niigata-u.ac.jp
[
e]
f]
Prof. Dr. M. Minoura
Department of Chemistry, College of Science,
Rikkyo University, Toshima-ku, Tokyo 171-8501 (Japan)
Prof. Dr. H. Nakano
Department of Chemistry, Graduate School of Science,
Kyushu University, Nishi-ku, Fukuoka 819-0395 (Japan)
periphery. This distortion impedes
a
comprehensive
[
understanding of properties associated with the 20–18 redox
processes. Kobayashi et al. reported the first synthesis of an air-
stable 19 tetraazaporphyrin P4, which included a six-coordinate
phosphorus(V) atom at the core.[ However, to our knowledge
there have been few reported air-stable 19 porphyrins and their
potential as redox-active catalysts and materials has not yet
14]
Supporting information (including experimental details) and the
ORCID identification numbers for the authors of this article can
be found under http://dx.doi.org/10.1002/XXXX.
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been elucidated. Developing a conceptually new molecular
design for precisely tuning the redox properties of porphyrin-
regenerate the parent DAPs under air.[20] These findings indicate
that N-aryl groups in NiTADAPs provide substantial stability to
the three -systems, 1Ni, 2Ni, and 3Ni. Encouraged by our
preliminary results, we decided to investigate the effects of the
central metals and meso-substituents on the fundamental
properties of TADAP -systems. We anticipated that a precisely
designed TADAP could be used as a redox-active catalyst for
the oxidative coupling of organomagnesium compounds under
molecular oxygen as a terminal oxidant, which is challenging
because a possible side reaction of the organomagnesium
compounds with molecular oxygen makes this reaction more
complicated.[ Herein, we report our comprehensive study of
three kinds of metal(II) complexes and free bases of 20, 19,
and 18 TADAPs. The syntheses and aromatic, optical,
electrochemical, and magnetic properties of the TADAPs are
discussed based on both experimental and theoretical results.
Preliminary results on the catalytic application of TADAP in the
oxidative homo-coupling of organomagnesium compounds are
also reported.
based 19 and 20-systems is
a challenge, both from
fundamentally and from an application perspective.
21]
Chart 1. Selected examples of 20 and 19 porphyrins.
It is well known that partial replacement of the meso-methine
(
CR; R = H, aryl, etc.) units of a porphyrin with nitrogen atoms
lowers its molecular symmetry, and stabilizes the HOMO and
lowest unoccupied molecular orbital (LUMO) energies of its -
system. For example, the redox properties of 5,15-
diazaporphyrins (DAPs) differ substantially from those of their
porphyrin counterparts;[15–17] DAPs are less readily oxidized and
more readily reduced than porphyrins. By contrast, little attention
has been paid to the meso modification of porphyrins with amine
Scheme 1. Interconversion among three oxidation states of TADAP.
Results and Discussion
Synthesis. Scheme 2 illustrates the syntheses of zinc(II)
complexes of TADAP derivatives (ZnTADAPs). Treatment of 3-
(
NR) units. We envisioned that replacing two CR units at the 5
and 15 positions of TPP-type porphyrins with two NR units
would be a promising strategy for obtaining redox-switchable
chloro-5-arylamino-8-mesityldipyrrins 4a–d (mesityl
= 2,4,6-
trimethylphenyl) with a half equiv. of zinc(II) acetate afforded the
corresponding zinc(II)–bis(dipyrrin) complexes 5Zn-a–d. When
the Zn-templated annulation reaction of 5Zn-a was conducted
20, 19, and 18 azaporphyrins (Scheme 1). Our design
concept is based on the idea that the unshared electron pairs of
the two meso-N atoms would be involved in the -circuit, and
alter its net charge for two electrons. Thus, 5,10,15,20-tetraaryl-
2 3
using K CO and DMF, which were used in the synthesis of
NiTADAPs,[ the desired 20 ZnTADAP 1Zn-a was formed in
18]
5
,15-diaza-5,15-dihydroporphyrin (TADAP) 1M, its radical cation
low yield because of the partial demetalation of 5Zn-a. When
NaOtBu and toluene were used instead of K CO and DMF, the
2 3
•+
2+
(
TADAP ) 2M, and its dication (TADAP ) 3M would be
2
−
•−
isoelectronic forms of 20 TPP , 19 TPP , and 18 TPP,
respectively. The net charges of these TADAP -systems are
more positive than those of the parent porphyrin -systems,
implying that the 20 and 19 TADAP derivatives would be more
resistant to oxidation than their porphyrin counterparts. This
concept was demonstrated in the first syntheses of 20, 19,
expected annulation, namely intramolecular double nucleophilic
substitution reaction of 5Zn-a occurred smoothly to afford 1Zn-a.
Similarly, 1Zn-b–d were obtained from 5Zn-b–d. The almost
exclusive formation of 1Zn from 5Zn was confirmed by NMR
spectroscopy and high-resolution mass (HRMS) spectrometry.
However, 1Zn-a–d were slowly oxidized in solution in the
and 18 nickel(II) complexes of TADAP derivatives
presence of air. Therefore, crude 1Zn-a–d were subsequently
oxidized to 18 ZnTADAP2+ 3Zn-a–d, by treatment with 2 equiv.
18]
(
NiTADAPs).[ All NiTADAPs are isolable as air-stable solids,
and exhibit reversible redox processes among the 20–19–18
oxidation states. Shinokubo and co-workers independently
reported the synthesis of the nickel(II) complex and free base of
of AgPF
recrystallization from CH
of 3Zn-a–d with NaBH
CoCp ) at room temperature afforded the corresponding 19
ZnTADAP 2Zn-a–d, which were isolated as greenish yellow
6
. Dications 3Zn were isolated as purple solids, by
Cl –Et O. The one-electron reduction
or bis(cyclopentadienyl)cobalt(II)
2
2
2
4
2
0 10,20-diaryl-5,15-diaza-5,15-dihydroporphyrin from the
(
2
corresponding 18 DAPs.[
19]
However, these meso-NH
•+
derivatives readily underwent dehydrogenative oxidation to
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solids by silica-gel column chromatography and subsequent
recrystallization from CH Cl –hexane.
2 2
solution of 2Zn-a quickly changed the color from yellow to red.
The 1H NMR and HRMS spectra of the reaction mixture were
consistent with the formation of the 20 magnesium(II) complex
of TADAP (MgTADAP) 1Mg-a. However, this complex could not
be isolated because of its extremely high sensitivity to air (vide
infra). After 10 min of stirring under nitrogen atmosphere, the
reaction mixture was treated with excess CF
cleaved the Mg–N bonds of 1Mg-a to afford 20 H
a in 34% overall yield from 2Zn-a. Alternatively, 1H
3
CO
TADAP 1H
-a was
2
H, which
2
2
-
2
prepared from 5Zn-a in a one-pot procedure via 1Zn-a, which
underwent the Zn-to-Mg exchange reaction to give 1Mg-a. One-
electron and two-electron oxidation reactions of 1H
2
-a with
-a,
AgPF gave 19 H -a and 18 H
6
2
TADAP•+ 2H TADAP2+ 3H
2
2
2
respectively. New NiTADAPs 1Ni-a, 2Ni-a, and 3Ni-a were
prepared according to reported methods.[18] Notably, all of the
radical cations 2M are rare examples of 19 porphyrins with high
stability toward dioxygen, moisture, and silica gel.
Scheme 2. Synthesis of ZnTADAPs.
We next applied a metal-templated annulation method to
synthesize copper(II) complexes of the TADAP derivatives
(
CuTADAPs). When 4b was treated with a half equiv. of
copper(II) acetate in CH Cl
2
2
–MeOH, 19 CuTADAP•+ 2Cu’-b
was unexpectedly obtained in moderate yield instead of the
copper(II)–bis(dipyrrin) complex 5Cu-b (Scheme 3). The
copper(II) salt most likely promoted the intramolecular N–C
coupling of 5Cu-b, but then also oxidized the resulting 20
CuTADAP. Indeed, when 4b was treated with 1.2 equiv. of
copper(II) acetate, 2Cu’-b was isolated in better yield. Similarly,
Scheme 3. Synthesis of CuTADAPs.
2Cu’-a,d were directly formed from 4a,d and copper(II) acetate.
At this stage, the counter anions of 2Cu’ were not characterized,
and 2Cu’ were reduced to 20 CuTADAP 1Cu by treatment with
NaBH
the corresponding 18 CuTADAP2+ 3Cu-a,b,d, after
reprecipitation from CH Cl –Et O. Furthermore, the mixing of
equimolar amounts of 1Cu and 3Cu in CH Cl quantitatively
4 6
. Oxidation of 1Cu-a,b,d with 2 equiv. of AgPF afforded
2
2
2
2
2
produced 19 CuTADAP•+ 2Cu-a,b,d as hexafluorophosphates.
In this anti-disproportionation reaction, single electron transfer
from 1Cu to 3Cu occurred to form two moles of 2Cu.
Free bases of TADAP derivatives (H
afforded by the acidolysis of 2Zn and 3Zn, which remained
intact after prolonged treatment with CF CO H. Therefore, we
2
TADAPs) were not
3
2
used the Yorimitsu–Osuka procedure for the two-step
transformation of metalloporphyrins to free bases via
magnesium(II) porphyrins;[22] step one was exchange of the
central metal from Ni/Zn/Cu/Ag to Mg, by treatment with a
Grignard reagent; step two was acidolysis. After screening
2
reaction conditions, we obtained H TADAP in moderate yield
starting from 2Zn-a (Scheme 4). The addition of 60 equiv. of
phenylmagnesium bromide (PhMgBr; THF solution) to a toluene
2
Scheme 4. Synthesis of H TADAPs.
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Characterization. MTADAPs (M = Zn, Cu, Ni, H
characterized by NMR and IR spectroscopy, HRMS, and X-ray
crystallography (for 1Cu-b and 2Ni-a). In the HRMS spectra of
2
) were
Aromaticity. As mentioned above, the unshared electron pairs
of the meso-N atoms of TADAP can be involved in the
macrocyclic -circuit. This implies that 1M and 3M are
isoelectronic with the corresponding metal complexes of the 20
TPP dianion and 18 TPP, respectively. Taking these -electron
counts into consideration, the aromatic character of 1M and 3M
is discussed. Diatropic and paratropic ring-current effects in the
1
M, 2M, and 3M, intense peaks are detected and are consistent
+
]+, and [M – 2(PF
)]z+ (z = 1, 2),
with m/z = [M] , [M – PF
6
6
respectively. In the 31P{ H} NMR spectra of 2M and 3M (M = Zn,
Ni), a characteristic septet from the hexafluorophosphate ion is
observed at  = −141 to −146 ppm (JP–F = 711 to 713 Hz).
Correlation between the ring-current effects in the 1H NMR
spectra and the aromaticity of the 20 and 18 MTADAPs (M =
1
1
H NMR spectra are a good index for evaluating aromaticity and
antiaromaticity, respectively, in terms of a magnetic criterion.
Representative 1H NMR spectra are shown in Figure 2. The
peripheral  protons (d and e) of 1Zn-c appear at  = 4.05 and
2
Zn, H ) is discussed in the following section.
The crystal structures of 1Cu-b and 2Ni-a were elucidated
by X-ray crystallography.[23] The copper center in 1Cu-b adopts
a square planar geometry, whereas the nickel center in 2Ni-a
2.81 ppm in C
and 8.25 ppm in CD
6
D
6
, whereas those of 3Zn-c appear at  = 8.64
Cl . These upfield and downfield shifts of
2
2
the peripheral protons indicate that 1Zn-c and 3Zn-c receive
considerable paratropic (20) and diatropic (18) ring currents,
respectively. The ortho-, meta-, and para-protons of the meso-
aryl groups (c, f, g, and h) of 1Zn-c and 3Zn-c also receive the
opposite ring-current effects from each other. Similar spectral
features are observed for the other 20/18 MTADAPs (M = Zn,
adopts an octahedral geometry with two THF-oxygen atoms as
−
the axial ligands. Although the counter anion (PF
6
) and axial
THF molecules of 2Ni-a showed positional disorder, the TADAP
moiety was satisfactorily refined. As shown in Figure 1 and
Figure S1 in the Supporting Information (SI), both 1Cu-b and
2
Ni-a have highly flat DAP -planes with root-mean-square
Ni, H
2
). The chemical shifts (in CDCl
3
or CD
2
Cl
2
) of the  protons
-a ( = 8.64, 8.3
deviations (drms) of 0.029 and 0.044 Å, respectively. The meso-
aryl groups are almost perpendicular to the DAP ring (dihedral
angles are 74.0–86.5° for the 10,20-mesityl groups and 82.3–
of 3Zn ( = 8.64–8.54, 8.27–8.20 ppm) and 3H
ppm) are shifted upfield compared with the corresponding
2
chemical shifts of the 18 porphyrin references 6Zn ( = 8.89,
8.78 ppm) and 6H
2
( = 8.78, 8.68 ppm).[ In contrast, the 
24]
85.4° for the 5,15-aryl groups). This suggests that -conjugation
between the meso-aryl groups and the DAP ring is very small.
The relatively short C1–N2 and C2–N2 bonds (average bond
lengths are 1.381 Å for 1Cu-b and 1.371 Å for 2Ni-a) indicate
that the unshared electron pairs in the p orbitals of the meso-N
atoms are effectively conjugated with the -orbitals in the
adjacent -pyrrolic carbon atoms (Table S1 in SI). The average
Cu–N bond length of 1Cu-b (1.986 Å) is slightly longer than the
average Ni–N bond length of 1Ni-b (1.945 Å),[18] reflecting the
different covalent radii of Cu and Ni.
protons of 1Zn ( = 2.8 to 4.1 ppm) are shifted downfield
compared with those of a ZnTPP dianion ( = −0.9 ppm in
[D
8
]THF).[ These differences may be attributed to different
2d]
charges and electron densities of the entire -systems between
1Zn/3Zn and the ZnTPP counterparts (20 dianion/18 neutral
1
molecule). The H NMR spectrum of 1H
2
-a in C
6
D
6
displays the
inner NH protons at  = 24.87 ppm (Figure S2 in SI), which is
close to the value reported for 10,20-dimesityl-5,15-diaza-5,15-
dihydroporphyrin ( = 24.5 ppm in [D
8
]THF).[19] The downfield
appearance of the NH protons of 3H
to those of 6H
may reflect a positive charge of the -system in 3H
2
-a ( = −0.54 ppm) relative
( = −2.62 ppm)[24] and 7H
( = −2.61 ppm)
-a.
[17b]
2
2
2
Figure 1. Top views (50% probability ellipsoids) of a) 1Cu-b and b) 2Ni-a (a
part of two independent crystals). Hydrogen atoms are omitted for clarity. For
–
2
Ni-a, the counter PF
6
ion and two axial THF ligands are also omitted. Bond
Figure 2. 1H NMR spectra of a) 1Zn-c in C
Asterisks indicate residual solvent peaks.
6 6 2 2
D and b) 3Zn-c in CD Cl .
lengths (Å) except the standard deviations (0.001–0.003 Å for 1Cu-b, 0.002–
.004 Å for 2Ni-a) are shown in red.
0
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To understand the nature of –* electronic excitations of the
TADAP -systems, we carried out time-dependent density
functional theory (TD-DFT) calculations on 1Zn-m, 3Zn-m, and
6Zn-m (Figure 4 and Table 2; for the results on nickel(II)
complexes, see ref. 18). Both 1Zn-m and 3Zn-m have D
2
symmetry, and their HOMO/HOMO−1 and LUMO/LUMO+1 are
nondegenerate because of the electronic effects of the two
meso-N atoms. As shown in Figure 4, the electron distribution of
the HOMO of 1Zn-m largely corresponds to that of the LUMO of
3Zn-m. This implies that the two electrons in the HOMO of 1Zn
are removed in the oxidation leading to 3Zn.
Chart 2. MTADAP models (1Zn-m, 2M-m, 3Zn-m), porphyrin references and
models (6M, 6Zn-m), and DAP references and models (7M, 7Zn-m).
To gain deeper insight into the ring-current effects of the
TADAP -systems, we calculated nuclear independent chemical
shifts (NICS)[
25]
at three positions in the -planes of the
ZnTADAP models 1Zn-m and 3Zn-m (Chart 2). The NICS
values at the midpoints between the two adjacent pyrrole rings
(
a and b) in 1Zn-m are +8.13 and +9.32 ppm, respectively,
indicating that there are global paratropic ring currents in its 20
circuit. In contrast, the NICS value at the center of the pyrrole
ring (c) in 1Zn-m is −6.51 ppm, implying that the pyrrole ring has
local diatropic ring currents. The NICS values at the a, b, and c
positions in the -plane of 3Zn-m are −17.72, −17.11, and −7.06
ppm, respectively, which are apparently due to diatropic ring
currents derived from the 18 circuit. As a whole, the DAP -
systems in 1Zn-m and 3Zn-m have substantial antiaromatic and
aromatic character, respectively, in terms of the ring-current
effects. The NICS values of 3Zn-m are less negative than those
of the porphyrin model 6Zn-m ( = −18.76 and −9.26 ppm at a
(
= b) and c, respectively) and DAP model 7Zn-m ( = −18.93
and −19.22 ppm at a and b, respectively). This suggests that the
macrocyclic ring-current effects of 18 ZnTADAP are slightly
weaker than those of ZnTPP and ZnDAP.
Optical and Redox Properties. Table 1 summarizes the
experimentally observed optical data for the MTADAPs and
porphyrin/DAP references. The UV/vis/NIR absorption spectra of
the 5,15-p-anisyl-substituted derivatives 1M-a, 2M-a, and 3M-a
(
2
M = Zn, Cu, Ni, H ) are shown in Figure 3. In a series of metal
complexes bearing p-anisyl groups, 1M-a exhibit two intense
absorption bands with absorption maxima (max) of 444–446 and
5
19–531 nm, whereas 3M-a exhibit two intense bands with max
of 391–393 and 629–632 nm. The max of the free bases 1H -a
426 and 488 nm) and 3H -a (390 and 645 nm) differ from those
2
(
2
of their metal complexes, as is typically observed for porphyrins.
The Q-like bands of 3M-c (M = Zn, Ni) are largely red-shifted
compared with the Q bands of 6M (max = 526–551 nm; M = Zn,
Ni) and 7M (max = 571–584 nm; M = Zn, Ni). This indicates that
the HOMO–LUMO gaps of the 18 MTADAPs are considerably
smaller than those of the isoelectronic porphyrins and DAPs.
The radical cations 2M-a exhibit intense absorption bands in the
NIR region (max = 860–890 nm) together with two bands in the
UV/vis region, highlighting the characteristic optical properties of
their 19 systems. In all three kinds of TADAPs, the para-
substituents of the meso-N-aryl groups exert only small
influences on the max values.
Figure 3. UV/vis/NIR absorption spectra of MTADAPs bearing p-anisyl
groups: M = Zn (a), Cu (b), Ni (c), and H
absorption spectra of 1Zn-a and 3H -a are normalized to those of 3Zn-a and
-a, respectively, at the absorption maxima.
2 2 2
(d). Measured in CH Cl . The
2
1H
2
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Table 1. Optical data for MTADAPs and references.
4
high-lying energy levels because of the neutral, D -symmetric -
abs [nm] (log )[a]

system. From the results of the TD-DFT calculations, the
longest-wavelength bands observed for 1Zn are assigned to a
combination of the HOMO-to-LUMO+1 and HOMO−1-to-LUMO
excitations, whereas those observed for 3Zn are assigned to the
essential HOMO-to-LUMO excitation. The TD-DFT results also
clarify that the HOMO-to-LUMO excitation of 1Zn-m is
symmetrically forbidden (oscillator strength ~ 0).
Compound
1
Zn-a
Zn-b
Zn-c
444 (n.d.), 519 (n.d.)
1
445 (n.d.), 519 (n.d.)
1
443 (n.d.), 518 (n.d.)
1
Zn-d
Cu-a
443 (n.d.), 516 (n.d.)
1
444 (5.05), 522 (4.87)
The 18 ZnTADAP2+ 3Zn and H
fluorescent in CH Cl (Figure S3 in SI). The optical HOMO–
LUMO gaps of 3Zn-a and 3H -a (1.94 and 1.92 eV, respectively),
TADAP2+ 3H
2
2
-a are weakly
1
Cu-b
Cu-d
444 (5.06), 523 (4.87)
2
2
1
443 (5.09), 519 (4.94)
2
as estimated from the intersections of the absorption and
fluorescence spectra, are considerably smaller than those of the
1
Ni-a
Ni-b
Ni-c
446 (4.89), 531 (4.78)
1
446 (4.96), 532 (4.85) [b]
445 (4.94), 531 (4.81) [b]
426 (4.80), 488 (4.53)
analogous porphyrin 6Zn and DAPs 7M (M
2
= Zn, H ).
1
Accordingly, the 18 TADAPs would be promising frameworks
for cationic sensitizers that are capable of responding to long-
wavelength visible light.
1
H
2
-a
Zn-a
Zn-b
Zn-c
2
384 (4.73), 448 (4.81), 890 (4.54)
385 (4.79), 447 (4.90), 890 (4.63)
384 (4.77), 445 (4.81), 894 (4.56)
382 (4.79), 442 (4.85), 903 (4.55)
384 (4.70), 444 (4.82), 871 (4.59)
387 (4.66), 444 (4.88), 870 (4.59)
384 (4.70), 440 (4.87), 879 (4.60)
381 (4.63), 444 (4.78), 860 (4.47)
384 (4.56), 444 (4.80), 860 (4.43) [b]
375 (4.77), 449 (4.71), 888 (4.53)
389 (4.76), 634 (4.63)
2
2
2
Zn-d
Cu-a
2
2
Cu-b
Cu-d
2
2Ni-a
2Ni-b
2
H
2
-a
Zn-a
Zn-b
Zn-c
3
3
388 (4.95), 634 (4.93)
3
392 (4.66), 632 (4.65)
3
Zn-d
Cu-a
391 (4.88), 634 (4.77)
3
392 (4.95), 631 (4.85)
3
Cu-b
Cu-d
391 (4.91), 630 (4.93)
3
394 (4.85), 628 (4.72)
3
Ni-a
Ni-b
Ni-c
393 (4.81), 629 (4.47)
3
393 (4.82), 627 (4.55) [b]
397 (4.78), 626 (4.51) [b]
390 (n.d.), 645 (n.d.)
3
3H
2
-a
Zn
Ni
Zn
Cu
6
421 (5.67), 551 (4.26)
6
413 (5.29), 526 (4.15) [b]
394 (4.92), 584 (4.86) [c]
384 (4.98), 397 (4.97), 577 (4.94) [c]
373 (4.79), 390 (4.89), 571 (4.78) [c]
393 (5.11), 541 (4.51), 627 (4.62) [c]
7
7
7
7
Ni
H
2
[
a] Measured in CH
MeOC (a), p-tBuC
b] Data from ref. 18. [c] Data from ref. 17.
2
Cl
2
. max >350 nm and log  > 4 are listed. R2 = p-
(b), Ph (c), p-CF (d). n.d. = not determined.
6
H
4
6
H
4
3 6 4
C H
[
The orbital characteristics and energies of 3Zn-m differ
Figure 4. Optimized structures and selected Kohn-Sham orbitals and their
considerably from those of 6Zn-m, whose HOMO/HOMO−1 and
energies (in eV) calculated by the DFT method with the solvent effect (PCM,
LUMO/LUMO+1 are intrinsically degenerate and are located at
2 2
CH Cl ): a) 1Zn-m, b) 3Zn-m, and c) 6Zn-m. H = HOMO; L = LUMO.
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+
Ag/Ag ]. The 21/20 and 20/19 redox processes of 1Cu-b in
Table 2. Excitation energies and oscillator strengths of 1Zn-m, 3Zn-m, and
6
Zn-m calculated by the TD-DFT method.[
a]
THF are observed at −1.88 and −0.33 V, respectively, vs.
+
Ag/Ag (Figure S4 in SI). From these values, the electrochemical
State
Excitation
energy
Oscillator
strength (f)
Excitation
Weight
[%]
HOMO–LUMO gap of 1Cu-b is determined to be 1.55 eV.
[
eV/nm]
1Zn-m
2
2.41/515
3.15/394
3.40/365
3.54/351
0.166
1.583
0.149
0.479
HOMO  LUMO+1
HOMO−1  LUMO
HOMO−1  LUMO
HOMO  LUMO+1
HOMO−5  LUMO
HOMO−2  LUMO
HOMO−2  LUMO
HOMO−5  LUMO
75.5
24.5
72.0
23.6
61.0
26.8
61.3
32.0
6
1
1
1
3
3
2
1
1
2
Zn-m
2.01/616
3.07/404
3.19/389
3.37/368
0.393
0.599
0.305
1.241
HOMO  LUMO
90.3
6
7
0
HOMO −1 LUMO+1 89.5
HOMO−4  LUMO+1 61.0
HOMO−4  LUMO+1 35.3
Figure 5. Cyclic voltammograms of a) MTADAPs bearing N-p-anisyl groups
(
M = Zn, Cu, Ni, H
2
) and b) ZnTADAPs (a–b denote para-substituents of the
HOMO  LUMO
27.8
+
N-aryl groups). Measured in CH
Bu
reference electrode; scan rate = 60 mV s
2
Cl
2
(from −0.7 to +1.0
V
vs. Ag/Ag );
(MeCN)] as a
+
−
+
N PF
6
(0.1 M) as a supporting electrolyte; Ag/Ag [AgNO
3
6Zn-m
4
–1
.
1
2.28/544
3.12/398
0.013
HOMO  LUMO+1
HOMO−1  LUMO
HOMO−1  LUMO
HOMO  LUMO
49.8
49.8
49.4
49.4
3
1.619
The electronic effects of the para-substituents of the N-aryl
groups on the redox potentials of ZnTADAPs are compared in
Figure 5b. Introducing an electron-donating group (OMe, tBu)
slightly shifts the 20/19 and 19/18 processes towards
negative potentials (E = −0.02 to −0.03 V; Zn-a,b vs. Zn-c),
[
2 2
a] B3LYP/6-311G(d,p) and Wachters–Hay(f) (PCM, CH Cl ) at the
optimized structures. Except for the lowest-energy excited state of 6Zn-m,
the states whose oscillator strengths are less than 0.1 are not included.
3
whereas introducing an electron-withdrawing CF group shifts
them towards positive potentials (E = +0.08 to +0.09 V; Zn-d vs.
Zn-c). In all the metal complexes, the para-substituents exert
small but clear influences on the HOMO and LUMO levels of the
Redox potentials of the MTADAPs were measured by cyclic
voltammetry in CH Cl or THF, with Bu NPF as a supporting
2 2 4 6
electrolyte. Selected voltammograms are shown in Figure 5.
-systems (Table 3).
Regardless of the starting materials (1M, 2M, or 3M), all the
MTADAPs exhibit two reversible redox processes, attributable to
+
2
0/19 and 19/18, in the range −0.7 to +1.0 V vs. Ag/Ag .
Table 3. Redox Potentials for MTADAPs.
For example, MTADAPs bearing the p-anisyl groups are
oxidized/reduced in two separate one-electron steps at −0.58
and +0.15 V for ZnTADAP, −0.36 and +0.31 V for CuTADAP,
M
a
b
c
d
Zn
Cu
Ni
−0.50, +0.15
−0.36, +0.31
−0.37, +0.29
−0.19, +0.44
−0.51, +0.16
−0.41, +0.27
−0.39, +0.30
n.p.
−0.48, +0.18
n.p.
−0.39, +0.26
−0.29, +0.32
n.p.
−
H
1
0.37 and +0.29 V for NiTADAP, and −0.19 and +0.44 V for
TADAP, respectively (Figure 5a). Both the 20/19 and
9/18 redox processes of ZnTADAP occur at more negative
2
−0.37, +0.30
n.p.
potentials than those of NiTADAP and CuTADAP, reflecting the
smaller electronegativity of zinc (1.65, Pauling scale) compared
with those of copper (1.90) and nickel (1.91). The more negative
redox potentials observed for the 20/19 process of ZnTADAP
explains the relatively low stability of 1Zn in air. However, the
H
2
n.p.
[a] Half-wave potentials (vs. Ag/Ag+) measured by CV in CH
Cl with
2 2
Bu N PF (0.1 M). n.p. = not prepared.
4 6
+
−
Magnetic properties. As mentioned in the Introduction, there
are currently few reported air-stable 19 porphyrins. To
understand the key factors providing the remarkable stability to
the present 19 radical cations, we measured EPR spectra of
2
0/19 redox processes of the MTADAPs occur at much more
positive potentials than those of the isoelectronic MTPP dianions
+
(
E < −2 V vs Ag/Ag ). Therefore, it can be concluded that the
high stability of 1M arise from the neutral charge of their 20-
systems.[
2d]
2Zn-a–d, 2H
2
-a, 1Cu-a, and 3Cu-a. The EPR spectrum of 2Ni-c
It should also be noted that the electron-accepting
has been reported previously.[ As shown in Figure 6a, 2Zn-a
18]
ability of 3M is considerably higher than that of 6M [e.g.
E(18/19) = +0.30 V for 3Ni-c and −1.69 V for 6Ni-c, vs.
exhibits an EPR signal at g = 2.0039, with the fine structure
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1
4
1
derived from two meso- N and four - H atoms. The calculated
spin distribution of its model 2Zn-m supports the observed fine
structure (Figure 6b).
The other zinc(II) complexes 2Zn-b–d exhibit similar EPR
spectra, featuring small electronic effects of their para-
substituents on the electron spin distribution (Figure S5 in SI).
The free base 2H
with the fine structure derived from meso- N and - H atoms
Figure S6 in SI). Most importantly, the unshared electron spin of
2
-a exhibits an EPR spectrum at g = 2.0023,
1
4
1
(
these 19 radical cations is efficiently delocalized over the entire
DAP ring. The aryl groups attached to the meso-N/C atoms,
which have moderate spin densities, may also contribute to the
stabilization of the -radicals by steric protection. The
CuTADAPs 1Cu-a and 3Cu-a exhibit EPR signals that are
[
26,27]
characteristic of related copper(II) (diaza)porphyrins.
9
Specifically, the fine structures originating from the d copper
center and four core 14N atoms (for 1Cu-a) are observed at 30 K
(
(
Figure 7). These results clearly support that the oxidation state
+2) of the copper center does not change during the redox
conversion between 1Cu and 3Cu.[
28]
TADAP-catalyzed oxidative homo-coupling reactions. As
mentioned above, 2Zn-a was transformed to 1Mg-a by
treatment with excess PhMgBr, whereas 1Mg-a was quickly
converted to 2Mg-a (the counter anion was not characterized) in
air. These results indicate that (1) 19 MTADAP•+ can accept
one electron from organomagnesium compounds, in view of the
redox potential,[ to become the 20 MTADAP, and (2) 20
MgTADAP is readily oxidized by molecular oxygen to regenerate
29]
Figure 6. a) EPR spectra of 2Zn-a observed in toluene (blue) and simulated
9 MgTADAP•+.
1
(red). b) Spin density distribution at the optimized structure (left) and spin
With these reactivities in mind, we examined a catalytic
densities at the DAP ring (right) of 2Zn-m: calculated by the DFT method.
oxidative homo-coupling of PhMgBr under molecular oxygen to
explore the possibility of MTADAP as a redox-active catalyst.
The reaction progress was monitored by 1H NMR and EPR
spectroscopies (Figure 8) and MALDI-TOF-MS spectrometry.
Treatment of 2Zn-a (19) with PhMgBr in [D ]THF under
8
nitrogen atmosphere at room temperature stoichiometrically
afforded the desired coupling product, biphenyl, together with
1
Zn-a (20:  = 3.73 and 2.74 ppm for -H) and 1Mg-a (20:  =
.80 and 2.84 ppm for -H) (Figure 8a).[ Further addition of
30]
3
PhMgBr induced the complete substitution of Zn to MgII in
TADAP, forming 1Mg-a as the major TADAP species (Figure 8b).
These observations clearly show that the oxidative homo-
coupling of PhMgBr is faster than the metal exchange reaction.
Introducing molecular oxygen to this mixture resulted in the
disappearance of the peaks of 1Mg-a, and growth of the peaks
II
1
of biphenyl and a small amount of a phenol derivative, in the H
NMR spectrum (Figure 8c). In addition, the EPR and MALDI-
TOF-MS spectra of the resulting mixture show the generation of
2Mg-a (19, g = 2.003). Again, a sequence of the addition of
PhMgBr followed by exposure to molecular oxygen was
1
repeated. This resulted in similar behavior in the H NMR and
EPR spectra (Figure 8d,e), clearly showing the catalytic cycle of
2
0/19 MgTADAP (Scheme 5).[31]
Scheme 5. Plausible catalytic cycle for MgTADAP-catalyzed oxidative homo-
coupling reaction.
Figure 7. EPR spectra of a) 1Cu-a and b) 3Cu-a observed in CH
blue) and simulated (red).
2 2
Cl at 30 K
(
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1
Figure 8. H NMR and EPR spectra to follow the catalytic behavior of MTADAP in oxidative homo-coupling of PhMgBr in [D
8
]THF.
Encouraged by this result, we also examined the oxidative
homo-coupling of 2-naphthylmagnesium bromide in the
presence of 1 mol% of 2Zn-a in THF. As expected, 2,2’-
binaphthyl was obtained in 31% yield after 6 h, where the
catalytic turn-over number was 31 (for details, see SI). Although
there is ample room for improving the catalyst efficiency,[32] this
is the first demonstration of diazaporphyrin as a redox-active
catalyst in a C–C bond-forming redox reaction of organometallic
reagents.
the unshared electron spin can be efficiently delocalized in the
cationic -system. The antiaromatic and aromatic characters of
20 and 18 TADAPs, respectively, were confirmed by NMR
spectroscopy and DFT calculations. These three -systems
show quite different optical properties; their absorption bands
range from 500 to 900 nm, reflecting their orbital characteristics.
It is noteworthy that the redox processes among the 20-, 19-,
and 18-systems proceed reversibly in one-electron steps. We
have established an alternative approach, the meso modification
with nitrogen atoms, to intrinsically stabilize 20 and 19
porphyrin rings without introducing any specific central metals or
peripheral substituents. TADAPs can be used not only for the
fundamental study of -conjugated azamacrocycles, but also for
applied research on redox-active catalysts. This is demonstrated
by the preliminary results on the oxidative homo-coupling
reactions of organomagnesium compounds. The demonstrated
reaction is the first example showing that diazaporphyrin acts as
a redox-active catalyst in a C–C bond-forming reaction of
organometallic reagents. Further studies on developing new
meso-modified azaporphyrinoids are underway.
Conclusion
We investigated the synthesis and aromatic, optical,
electrochemical, and magnetic properties of TADAPs in the
three different oxidation states, 20, 19, and 18. The metal-
templated annulation method was effective for synthesizing the
zinc(II) and copper(II) complexes, and the metal–exchange
reaction was used to synthesize the free base. The redox
potentials and chemical stabilities of the MTADAPs strongly
depend on the central metals. The nickel(II) and copper(II)
complexes are more resistant to oxidation than the zinc(II)
counterparts, reflecting the difference in their electronegativities. Experimental Section
Because of the high electron affinity and resonance effects of
nitrogen at the meso positions, the 20 and 19 derivatives
resist air oxidation, while the 18 derivatives exhibit strong
electron-accepting properties, compared with the isoelectronic
TPP derivatives. In particular, the 19 TADAP radical cations are
extremely stable towards dioxygen, moisture, and silica gel,
irrespective of the central metal atom. This stability is because
General Remarks. All melting points were recorded on a micro melting
point apparatus and are uncorrected. NMR spectra were recorded on
7
00 MHz (Agilent) and/or 400 MHz (Agilent or JEOL JNM-ECP)
spectrometers. The 1H and C chemical shifts are reported in ppm as
13
relative values vs. tetramethylsilane (in CDCl
residual signal ( 7.16 ppm in C
), and the 31P chemical shifts are
reported in ppm vs. H PO . High-resolution mass (HRMS) spectra were
3 2 2
and CD Cl ) or a solvent
H
6 6
D
3
4
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measured on
a
Thermo Fisher Scientific EXACTIVE spectrometer
[7]
[8]
S. P. Panchal, S. C. Gadekar, V. G. Anand, Angew. Chem. Int. Ed.
2016, 55, 7797–7800; Angew. Chem. 2016, 128, 7928–7931.
a) T. Nakabuchi, M. Nakashima, S. Fujishige, H. Nakano, Y. Matano, H.
Imahori, J. Org. Chem. 2010, 75, 375–389; b) Y. Matano, H. Nakabuchi,
H. Imahori, Pure Appl. Chem. 2010, 82, 583–593.
(
electron spray–quadrupole), and MALDI-TOF mass spectra were
recorded on a BRUKER AUTOFLEX III mass spectrometer. UV/Vis/NIR
absorption spectra were measured on a JASCO V-530 spectrometer in
the range of 300–1100 nm. The IR spectra were obtained on
a
PerkinElmer Spectrum GX spectrometer using KBr pellets.
Electrochemical redox potentials were measured using a glassy carbon
working electrode, a platinum wire counter electrode, and an Ag/Ag+
[9]
a) J. A. Cissell, T. P. Vaid, A. L. Rheingold, J. Am. Chem. Soc. 2005,
127, 12212–12213; b) J. A. Cissell, T. P. Vaid, G. P. A. Yap, J. Am.
Chem. Soc. 2007, 129, 7841–7847.
[
0.01 M AgNO
fluorescence spectra were measured on an FP-8300 spectrometer.
Fluorescence quantum yields were measured on Hamamatsu
3
, 0.1 M Bu
4
NPF
6
(MeCN)] reference electrode. UV-vis
[10] a) J. A. Cissell, T. P. Vaid, A. G. DiPasquale, A. L. Rheingold, Inorg.
Chem. 2007, 46, 7713–7715; b) E. W. Y. Wong, C. J. Walsby, T. Storr,
D. B. Leznoff, Inorg. Chem. 2010, 49, 3343–3350.
a
Photonics Quantaurus-QY spectrometer. Thin-layer chromatography was
performed with Kieselgel 60 F254, and preparative column
chromatography was performed using Silica Gel 60 spherical, neutrality.
All reactions were performed under an argon or nitrogen atmosphere
unless otherwise noted. For the experimental details and characterization
data of new compounds are reported in the Supporting Information.
[11] a) A. Weiss, M. C. Hodgson, P. D. W. Boyd, W. Siebert, P. J. Brothers,
Chem. Eur. J. 2007, 13, 5982–5993; b) P. J. Brothers, Chem. Commun.
2008, 2090–2102.
[12] a) Y. Matano, T. Nakabuchi, S. Fujishige, H. Nakano, H. Imahori, J. Am.
Chem. Soc. 2008, 130, 16446–16447; b) Y. Matano, H. Imahori, Acc.
Chem. Res. 2009, 42, 1193–1204.
[
[
[
13] C. Liu, D.-M. Shen, Q.-Y. Chen, J. Am. Chem. Soc. 2007, 129, 5814–
815.
5
14] T. Yoshida, W. Zhou, T. Furuyama, D. B. Leznoff, N. Kobayashi, J. Am.
Chem. Soc. 2015, 137, 9258–9261.
Acknowledgements
15] For selected reviews, see: a) K. Ishii, N. Kobayashi, in The Porphyrin
Handbook Vol 16 (Eds.: K. M. Kadish, K. M. Smith, R. Guilard),
Academic Press, San Diego, 2003, pp. 1–42; b) J. Mack, N. Kobayashi,
Chem. Rev. 2011, 111, 281–321; c) Y. Matano, Chem. Rev. 2017, 117,
This work was supported by JSPS KAKENHI (15H00931 to YM,
24109008, 15K05663 to KF, 15H00962 to MM, and 15K05392 to
HN) and the Naito Foundation (YM).
3138–3191.
[
16] H. Ogata, T. Fukuda, K. Nakai, Y. Fujimura, S. Neya, P. A. Stuzhin, N.
Keywords: porphyrinoids • redox chemistry • dyes/pigments •
aromaticity • EPR spectroscopy
Kobayashi, Eur. J. Inorg. Chem. 2004, 1621−1629.
[17] a) Y. Matano, T. Shibano, H. Nakano, H. Imahori, Chem. Eur. J. 2012,
8, 6208−6216; b) Y. Matano, T. Shibano, H. Nakano, Y. Kimura, H.
1
Imahori, Inorg. Chem. 2012, 51, 12879−12890.
[
1]
16 porphyrins: a) Y. Yamamoto, A. Yamamoto, S.-y. Furuta, M. Horie,
M. Kodama, W. Sato, K.-y. Akiba, S. Tsuzuki, T. Uchimaru, D.
Hashizume, F. Iwasaki, J. Am. Chem. Soc. 2005, 127, 14540–14541;
b) J. A. Cissell, T. P. Vaid, G. P. A. Yap, Org. Lett. 2006, 8, 2401–2404;
c) Y. Yamamoto, Y. Hirata, M. Kodama, T. Yamaguchi, S. Matsukawa,
K. Akiba, D. Hashizume, F. Iwasaki, A. Muranaka, M. Uchiyama, P.
Chen, K. M. Kadish, N. Kobayashi, J. Am. Chem. Soc. 2010, 132,
[
18] T. Satoh, M. Minoura, H. Nakano, K. Furukawa, Y. Matano, Angew.
Chem. Int. Ed. 2016, 55, 2235–2238; Angew. Chem. 2016, 128, 2275–
2
278.
19] M. Horie, Y. Hayashi, S. Yamaguchi, H. Shinokubo, Chem. Eur. J. 2012,
8, 5919−5923.
[
[
[
1
20] A. Yamaji, H. Tsurugi, Y. Miyake, K. Mashima, H. Shinokubo, Chem.
Eur. J. 2016, 22, 3956–3961.
12627–12638; d) T. Kakui, S. Sugawara, Y. Hirata, S. Kojima, Y.
21] a) A. Krasovskiy, A. Tishkov, V. del Amo, H. Mayr, P. Knochel, Angew.
Chem. Int. Ed. 2006, 45, 5010–5014; Angew. Chem. 2006, 118, 5132–
Yamamoto, Chem. Eur. J. 2011, 17, 7768–7771; e) S. Sugawara, M.
Kodama, Y. Hirata, S. Kojima, Y. Yamamoto, J. Porphyrins
Phthalocyanines 2011, 15, 1326–1334; f) S. Hiramatsu, S. Sugawara,
S. Kojima, Y. Yamamoto, J. Porphyrins Phthalocyanines 2013, 17,
5136; b) G. Cahiez, A. Moyeux, J. Buendia, C. Duplais, J. Am. Chem.
Soc. 2007, 129, 13788–13789; c) W. Liu, A. Lei, Tetrahedron Lett. 2008,
49, 610–613; d) M. S. Maji, T. Pfeifer, A. Studer, Angew. Chem. Int. Ed.
1183–1187.
2008, 47, 9547–9550; Angew. Chem. 2008, 120, 9690–9692; e) S.-K.
[
2]
20 porphyrin dianions: a) G. L. Closs, L. E. Closs, J. Am. Chem. Soc.
Hua, Q.-P. Hu, J. Ren, B.-B. Zeng, Synthesis 2013, 45, 518-526; f) T.
Amaya, R. Suzuki, T. Hirao, Chem. Eur. J. 2014, 20, 653–656; g) T.
Korenaga, K. Nitatori, H. Muraoka, S. Ogawa, K. Shimada, Org. Lett.
1
963, 85, 818–819; b) J. W. Buchler, L. Puppe, Liebigs Ann. Chem.
970, 740, 142–163; c) G. N. Sinyakov, A. M. Shul'ga, I. V. Filatov,
1
G. P. Gurinovich, Theor. Exp. Chem. 1988, 24, 37–44; d) R. Cosmo, C.
Kautz, K. Meerholz, J. Heinze, K. Müllen, Angew. Chem. Int. Ed. Engl.
2015, 17, 5500–5503; h) S. Murarka, J. Möbus, G. Erker, C. Mück-
Lichtenfeld, A. Studer, Org. Biomol. Chem. 2015, 13, 2762–2767; i) T.
Amaya, R. Suzuki, T. Hirao, Chem. Commun. 2016, 52, 7790–7793.
22] K. Murakami, Y. Yamamoto, H. Yorimitsu, A. Osuka, Chem. Eur. J.
1
989, 28, 604–607; Angew. Chem. 1989, 101, 638–640; e) K. M.
Kadish, E. Van Caemelbecke, G. Royal, in The Porphyrin Handbook
Vol 8 (Eds.: K. M. Kadish, K. M. Smith, R. Guilard), Academic Press,
San Diego, 2000, pp 1–114; f) K. Reddy, A. Basavarajappa, M. D.
Ambhore, V. G. Anand, Chem. Rev. 2017, 117, 3420–3443, and
references therein.
[
[
2013, 19, 9123–9126.
23] The diffraction data for several crystals of 2M and 3M (M = Zn, Cu)
indicated that their DAP rings are highly flat, although these data could
not be fully refined to a publishable level because of uncertain loss or
positional disorder of the solvent molecules included.
[
[
3]
4]
M. Pohl, H. Schmickler, J. Lex, E. Vogel, Angew. Chem. Int. Ed. Engl.
1991, 30, 1693–1697; Angew. Chem. 1991, 103, 1737–1741.
[
[
[
[
24] B. J. Littler, Y. Ciringh, J. S. Lindsey, J. Org. Chem. 1999, 64, 2864–
a) J. Setsune, K. Kashihara, K. Wada, H. Shinozaki, Chem. Lett. 1999,
2872.
28, 847–875; b) T. P. Vaid, J. Am. Chem. Soc. 2011, 133, 15838–
25] P. von R. Schleyer, C. Maerker, A. Dransfeld, H. Jiao, N. J. R. van
Eikema Hommes, J. Am. Chem. Soc. 1996, 118, 6317–6318.
15841.
[
5]
6]
a) J. S. Reddy, V. G. Anand, J. Am. Chem. Soc. 2008, 130, 3718–
26] S. P. Greiner, D. L. Rowlands, R. W. Kreilick, J. Phys. Chem. 1992, 96,
3719; b) B. K. Reddy, S. C. Gadekar, V. G. Anand, J. Am. Chem. Soc.
9132–9139.
2015, 51, 8276–8279.
27] Y. Matano, D. Fujii, T. Shibano, K. Furukawa, T. Higashino, H. Nakano,
[
M. Kon-no, J. Mack, N. Kobayashi, M. Suenaga, K. Yoza, T.
H. Imahori, Chem. Eur. J. 2014, 20, 3342−3349.
Shinmyozu, Chem. Eur. J. 2012, 18, 13361−13371.
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Chemistry - A European Journal
10.1002/chem.201703664
FULL PAPER
[
28] No X- and W-band EPR signals were observed for 2Cu-a at room
ref. H. G. Richey, Jr, Grignard Reagents: New Developments, John
Wiley & Sons Inc., New York, 2000.
temperature and 20 K, respectively, probably because the large zero-
9
field splitting interaction between the d copper center and TADAP π-
[31] The mechanism of the reaction is not clear at present. According to the
previous reports,[21a,h] the homo-coupling reaction may take place based
on the stepwise electron transfer as follows: 1) electron transfer from
PhMgBr to 2Mg-a (or 2Zn-a) (19) to form a kind of phenyl radical
species, 2) addition of PhMgBr to the radical species to give Ph-Ph
radical anion species, and 3) electron transfer from the radical anion
species to another 2Mg-a (or 2Zn-a) (19) to afford Ph-Ph.
[32] The MALDI-TOF-MS spectrum of the crude mixture in the 1H NMR
experiments shown in Figure 8 indicated the formation of a small
amount of the adduct of Grignard reagent to TADAP although the main
peak exhibited the desired 19 MgTADAP 2Mg-a. This might cause a
decrease of the catalyst efficiency.
radical induced the significant line-broadening. In addition, no NMR
signal was observed for 2Cu-a at room temperature, which may
suggest contribution of the triplet ground state. However, the detailed
discussion on the spin state of 19 CuTADAP is beyond the scope of
the present paper, and will be reported elsewhere.
[
29] T. Ramnial, S. A. Taylor, J. A. C. Clyburne, C. J. Walsby, Chem.
Commun. 2007, 2066–2068.
[
30] In the case of 1,4-benzoquinone as a typical two-electron oxidant, the
oxidative coupling product of PhMgBr is not obtained in THF. Instead,
PhMgBr attacks to the carbonyl groups to give 1,2-addition adduct. See
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Chemistry - A European Journal
10.1002/chem.201703664
FULL PAPER
Entry for the Table of Contents
FULL PAPER
]
A series of redox-switchable 20,
Keisuke Sudoh Takaharu Satoh, Toru
Amaya,* Ko Furukawa,* Mao Minoura,
Haruyuki Nakano, and Yoshihiro
Matano*
19, and 18 5,10,15,20-tetraaryl-
20π
Ar
N
19π
Ar
N
18π
Ar
N
5,15-diazaporphyrinoids (TADAPs)
+
2+
Ar
N
N
N
N
– e–
N
N
N
N
– e–
N
N
N
N
were prepared. The aromatic,
optical, electrochemical, and
Ar
M
Ar
Ar
M
Ar
Ar
M
+ e–
+ e–
N
N
N
Ar
Ar
Ar
Page No. – Page No.
magnetic properties of TADAPs are
strongly dependent on the oxidation
states of their -systems. MgTADAP
behaved as the redox-active catalyst
in a C–C bond-forming reaction of
organometallic reagents.
Application as a Redox-Active Catalyst for C–C Bond Formation
Ar
N
19p MgTADAP
20p MgTADAP
R
MgBr
N
N
N
N
Syntheses, Properties, and Catalytic
Activities of Metal(II) Complexes and
Free Bases of Redox-Switchable
0, 19, and 18 5,10,15,20-
Tetraaryl-5,15-diazaporphyrinoids
Ar
Mg
Ar
O2
N
1
/2 R
R
Ar
MgTADAP
2
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