Para-benzihemiporphyrazine and its expanded [3 + 3]-type analogue

Article abstract of DOI:10.1246/cl.2012.702

A novel para-benzihemiporphyrazine was synthesized from a stepwise reaction of 1,3-diiminoisoindoline and para-phenylenediamine via a linear [2 + 1]-type compound, whereas its ring-expanded [3 + 3]-type analogue was obtained from a onepot condensation reaction of the same starting materials.

Full text of DOI:10.1246/cl.2012.702

doi:10.1246/cl.2012.702
702
Published on the web June 23, 2012
para-Benzihemiporphyrazine and Its Expanded [3 + 3]-type Analogue
Soji Shimizu,* Yuta Sato, and Nagao Kobayashi*
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578
(Received March 4, 2012; CL-120186; E-mail: ssoji@m.tohoku.ac.jp)
A novel para-benzihemiporphyrazine was synthesized from
depend on angles between two C-Namino bonds in the aromatic
diamines. Recently our group and Torres’s group independently
reported that a ring-expanded [3 + 3]-type hemiporphyrazine
analogue (Chart 1) was formed in a similar condensation
reaction of 2,5-diamino-1,3,4-thiadiazole and 1,3-diiminoisoin-
doline,10 whereas a ring-expanded [4 + 2]-type hemiporphyr-
azine analogue can be synthesized from a stepwise reaction
using a linear [2 + 1]-type compound comprising nitrogen-
bridged isoindole and triazole units.11 Our continuing research in
this field aiming for novel hemiporphyrazine analogues using
another aromatic diamine led to syntheses of para-benzihemi-
porphyrazine and its ring-expanded [3 + 3]-type analogue under
different reaction conditions.
A condensation reaction of para-phenylenediamine and
5,6-bis(p-tert-butylphenyl)-1,3-diiminoisoindoline in ethanol at
60 °C for 48 h provided a linear [2 + 1]-type compound 1 in
73% yield, which was further reacted with an equimolar amount
of para-phenylenediamine in 1-chloronaphthalene at 250 °C for
30 min to give para-benzihemiporphyrazine 2 in 17% yield
(Scheme 1). On the other hand, a one-pot condensation reaction
of these starting materials in 2-ethoxyethanol at 150 °C provided
a novel [3 + 3]-type hemiporphyrazine analogue 3 in 6.8% yield
instead of para-benzihemiporphyrazine (Scheme 2).
a stepwise reaction of 1,3-diiminoisoindoline and para-phenyl-
enediamine via a linear [2 + 1]-type compound, whereas its
ring-expanded [3 + 3]-type analogue was obtained from a one-
pot condensation reaction of the same starting materials.
Hemiporphyrazine comprising nitrogen-bridged isoindole
units (A) and pyridine units (B) arranged in an ABAB manner is
one of the most accessible Schiff base macrocycles obtained
from a simple condensation reaction of 2,6-diaminopyridine and
1,3-diiminoisoindolines.1,2 With respect to the component B, a
variety of aromatic ring units, such as benzene, naphthalene,
and triazole,3,4 have been utilized in place of pyridine. These
hemiporphyrazine analogues have been generally referred to as
(aromatic)hemiporphyrazines, in which the name of the aromatic
ring unit is introduced as a prefix. For example, an analogue
comprising isoindole and meta-phenylene units is named meta-
benzihemiporphyrazine (Chart 1).5
Since the first synthesis by Linstead and Elvidge in 1952,1
the coordination chemistry of hemiporphyrazines has been
intensively investigated,2,6 and their conductivity and unique
nonlinear optical properties has been demonstrated.7,8 Recently
Ziegler and Durfee have further developed the coordina-
tion chemistry of hemiporphyrazine and meta-benzihemipor-
phyrazine to reveal facile protonation at meso-imino nitrogen
atoms during metalation and side-on agostic-type interactions
between metal ions and C-H bonds of meta-phenylene moie-
ties.9 Another intriguing feature of hemiporphyrazines from a
synthetic point of view is that ring sizes of macrocycles obtained
from 1,3-diiminoisoindoline and aromatic diamines largely
High-resolution MALDI-TOFMS analysis revealed 2 and 3,
respectively, to be nitrogen-bridged [2 + 2]-type and [3 + 3]-
type macrocycles of isoindole and para-phenylene units; 2: m/z
found 967.5419, calcd for C68H67N6 967.5427 ([M+ + H]),
and 3: m/z found 1450.8110, calcd for C102H100N9 1450.8102
([M+ + H]).
1H NMR spectra in CDCl3 exhibited two singlet signals of
¡-benzo protons and phenylene protons at 8.12 and 6.90 ppm for
2 and at 8.09 and 7.14 ppm for 3, while a set of doublet signals
due to the p-tert-butylphenyl substituents was observed for both
compounds between 7.14 and 7.26 ppm. These simple NMR
spectral patterns indicate their thermally equilibrated symmetric
structures in solution. Finally the structure of 2 was unambig-
Scheme 1. Synthesis of para-benzihemiporphyrazine 2. Re-
action conditions: a) ethanol, 60 °C, 2 days, b) para-phenylene-
diamine, 1-chloronaphthalene, 250 °C, 30 min. See Supporting
Information (SI) for details.14
Chart 1. Hemiporphyrazine (top, left), meta-benzihemipor-
phyrazine (top, right), and [3 + 3]-type hemiporphyrazine
analogue (bottom).
Chem. Lett. 2012, 41, 702-704
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703
Figure 2. UV-vis absorption spectra of 2 (solid line) and 3
(dashed line) in CHCl3.
Scheme 2. Synthesis of the [3 + 3]-type hemiporphyrazine
analogue 3. Reaction conditions: a) 2-ethoxyethanol, 150 °C,
20 h. See SI for details.14
Figure 3. UV-vis absorption spectra of 3 in various solvents,
CHCl3 (solid line), toluene (dashed line), and THF (dotted line).
In summary, the stepwise and the one-pot condensation
reactions of para-phenylenediamine and 1,3-diiminoisoindoline
provided para-benzihemiporphyrazine and its [3 + 3]-type
hemiporphyrazine analogue, respectively. Despite the nonaro-
matic character of both 2 and 3, which was shown by NMR and
absorption spectroscopic analyses, solvent-dependent changes in
the absorption of 3 probably due to its flexible structure in
solution are of great interest. These compounds can be utilized
as metal-coordinating ligands, in which interactions between
metal ions and ³-electrons as well as multimetal coordination
is strongly expected. Research along these lines is currently
underway.
Figure 1. X-ray crystal structure of 2, top view (top) and side
views (bottom). The thermal ellipsoids are scaled to the 50%
probability level. p-tert-Butylphenyl substituents and hydrogen
atoms are omitted for clarity in the side views.
uously elucidated by single-crystal X-ray analysis on crystals
obtained from slow diffusion of methanol into a toluene solution
of 2 (Figure 1).12 In the solid state, the phenylene moieties are
largely tilted by 61° from the mean-plane defined by the
isoindole moieties. An apparent bond-length alternation was
observed for the C-N-C bonds at the meso-positions (1.28 and
1.43 ¡), which infers a nonaromatic character of 2. The
phenylene moieties are slightly skewed in a boat-like confor-
mation with a bent-angle of 6.6°, which is similar to that of
[3.3]-cyclophane.13
2 exhibits two broad absorptions at 278 and 322 nm in
CHCl3 (Figure 2), which can be interpreted in terms of its
nonaromatic character. 3 also shows similarly broad absorptions
at 280 and 379 nm in CHCl3 (Figure 2), whereas the longer-
wavelength absorption shifts to the red in toluene (401 nm) and
THF (424 nm, Figure 3). The spectral shape becomes quite
structured in THF with absorptions at 424 and 407 nm and two
less intense bands at around 500 and 540 nm, which is similar
to the absorption spectra of [3 + 3]-type analogues comprising
isoindole and 1,3,4-thiadiazole units (Chart 1).10 Assuming
solvent-dependent changes in the spectral shapes are insignif-
icant in the case of 2, it can be inferred that a degree of rotational
freedom of the phenylene moieties in 3 is larger than that of 2
due to the ring-expanded structure of 3.
This work was partly supported by a Grant-in-Aid for
Scientific Research (C) (No. 23550040) from Japan Society for
the Promotion of Science (JSPS) and a Grant-in-Aid for
Scientific Research on Innovative Areas (No. 20108007, “pi-
Space”) from the Ministry of Education, Culture, Sports,
Science and Technology (MEXT). The authors thank Prof.
M. Hirama and Dr. S. Yamashita at Tohoku University for
MALDI-TOF mass measurement and Prof. T. Iwamoto and Dr.
S. Ishida in Tohoku University for X-ray measurement.
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ꢀ
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Chem. Lett. 2012, 41, 702-704
© 2012 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/