Synthesis of phthalocyanine fused with bicyclo[2.2.2]octadienes and thermal conversion into naphthalocyanine

Article abstract of DOI:10.3987/com-07-s(w)75

Mg complex of phthalocyanine fused with bicyclo[2.2.2]octadiene (BCOD) units is prepared by the reaction of BCOD-fused phthalonitrile with Mg(OPr)₂ in PrOH at 100 °C overnight in 42% yield. Subsequent heating the product at 250 °C results in clean formation naphthalocyanine via the retro Diels-Alder reaction. An attempt to the synthesis of BCOD-fused tetraazaporphyrin by the similar cyclization of the Diels-Alder adduct of dicyanoacetylene with 1,3-cyclohexadiene was unsuccessful.

Full text of DOI:10.3987/com-07-s(w)75

HETEROCYCLES, Vol. 74, 2007
835
HETEROCYCLES, Vol. 74, 2007, pp. 835 - 842. © The Japan Institute of Heterocyclic Chemistry
Received, 26th September, 2007, Accepted, 26th October, 2007, Published online, 30th October, 2007. COM-07-S(W)75
SYNTHESIS
OF
PHTHALOCYANINE
FUSED
WITH
BICYCLO[2.2.2]OCTADIENES AND THERMAL CONVERSION INTO
NAPHTHALOCYANINE
a
a
a
a,b
Taiji Akiyama, Atsuko Hirao, Tetsuo Okujima, Hiroko Yamada,
c
a,
Hidemitsu Uno, and Noboru Ono *
a
Department of Chemistry and Biology, Graduate School of Science and
Engineering,
Ehime
University,
Matsuyama,
790-8577,
Japan,
b
ononbr@dpc.ehime-u.ac.jp; PRESTO, Japan Science and Technology Agency,
c
Japan; Department of Molecular Science, Integrated Center for Science, Ehime
University, Matsuyama 790-8577, Japan
Abstract – Mg complex of phthalocyanine fused with bicyclo[2.2.2]octadiene
(
BCOD) units is prepared by the reaction of BCOD-fused phthalonitrile with
Mg(OPr) in PrOH at 100 ºC overnight in 42% yield. Subsequent heating the
2
product at 250 ºC results in clean formation naphthalocyanine via the retro
Diels-Alder reaction. An attempt to the synthesis of BCOD-fused
tetraazaporphyrin by the similar cyclization of the Diels-Alder adduct of
dicyanoacetylene with 1,3-cyclohexadiene was unsuccessful.
th
Dedicated to Prof. Dr. Ekkehard Winterfeldt on the occasion of his 75 birthday.
INTRODUCTION
Phthalocyanines (Pcs) and their homologues exhibit a remarkable range of optical and electronic
properties that lend them to applications in electro photography, CD-Rs, sensors, optical limiters and
1
photodynamic therapy. As parent Pcs are generally insoluble in organic solvents, solubilizing groups
such as alkyl or alkoxy groups are required to increase their solubility. However, these groups can not be
removed after purification by column chromatography or recrystallization. Thus, it is extremely difficult
to get pure samples of unsubstituted Pcs by the usual procedures of purification such as column
chromatography. We have developed a simple solution of this problem by the introduction of thermally
2
removal groups into porphyrins. For example, soluble precursors of tetrabenzoporphyrin (TBP) or
tetranaphthoporphyrin (TNP) are available by fusing BCOD rings into porphyrins, which are readily

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HETEROCYCLES, Vol. 74, 2007
purified by column chromatography. Heating these soluble precursors gives TBP and TNP in quantitative
yields accompanying by eliminating four ethylene units. TBP and TNP are pure enough without further
purification, if the precursors are pure. This method is useful not only as a synthetic method but also as a
3
4
fabrication method of the electronic devices such as organic thin film transistors (OTFTs) or solar cells.
In this paper we report the synthesis of Pcs fused with BCOD rings and its thermal conversion into
naphthalocyanines (Ncs). This is the first report of the Nc pigment from its soluble precursor (dye), which
may be useful as a method to get pure Ncs and for fabrication of electronic devices as demonstrated in the
3
case of TBP in applications for OTFTs.
RESULTS AND DISCUSSION
Synthesis of Mg-Pc fused with BCOD is shown in Scheme 1. Diels-Alder reaction of dicyanoacetylene
with 5,6-dimethylenebicyclo[2.2.2]oct-2-ene (1) proceed at room temperature to give the adduct 2 in 55%
yield. Compound 2 was oxidized to the corresponding phthalonitrile 3 by DDQ in 96% yield. Treatment
2
of 3 with Mg(OPr) in PrOH at 100 ºC overnight gives Mg salt of phthalocyanine (Mg-4) fused with
BCOD in 42% yield. Purification of Mg-4 was carried out by column chromatography on alumina with
THF.
Scheme 1. Synthesis of Mg-Pc (Mg-4) fused with BCOD and Thermal Conversion into Mg-5

HETEROCYCLES, Vol. 74, 2007
837
Thermogravimetric analysis (TGA) of Mg-4 verified the expected retro Diels-Alder reaction (Figure 1).
0 % loss of the total mass, corresponding to a loss of four ethylene units and 2H O, initiates at 200 ºC
2
2
and is complete by 250 ºC. The retro Diels-Alder reaction was also monitored by MALDI TOF showing
the expected mass loss upon heating the sample Mg-4 (Figure 2). Elimination of ethylene units takes
places stepwise under conditions of measurement of MALDI TOF MS. MALDI TOF MS shows one peak
of Mg-5 after heating Mg-4 at 250 ºC for 20 min which suggests that clean retro Diels-Alder reaction
takes place at 250 ºC to give pure Mg-5. The UV-Vis spectra of Mg-4 and Mg-5 in DMF are shown in
Figure 3, which are in good agreement of those of Pcs and Ncs. As byproduct of this thermal conversion
is only ethylene, Mg-5 obtained from purified Mg-4 is pure enough without further purification. This is
the first success of preparing Ncs from a soluble precursor.
Figure 1. TG analysis of Mg-4 heating at 10 ºC/min. The expected loss of the mass occurs between 200
and 250 ºC.
Figure 2. MALDI TOF MS of Mg-4 (a) before heating (calc MW = 848.3226) and (b) after heating at
2
50 ºC for 20 min (calc MW = 736.1974)

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HETEROCYCLES, Vol. 74, 2007
Figure 3. UV-Vis spectra of Mg-4 (solid line) and Mg-5 (bold line)
Scheme 2. Attempts to prepare soluble precursor 7 for Pcs.
The present method is not limited to the preparation of Mg-4, but it is applicable to metal free or other
metal complexes of 4. For example, heating of 3 with PrOLi in PrOH at reflux overnight gave metal free
4
in 25% yield. TGA and MALDI TOF of metal free 4 exhibits completely same behaviors as those of
Mg-4 to indicate the clean retro Diels-Alder reaction of 4. Other metals can be introduced into 4 by the
1
reaction of 4 with appropriate metal salts. Application of this thermal conversion to a fabrication of solar
cells or OTFTs using Ncs as semiconductors by a solution process is now under progress in our
laboratory.

HETEROCYCLES, Vol. 74, 2007
839
Next, we have extended the present strategy to prepare Pcs from soluble precursors as shown in Scheme 2.
The Diels-Alder adduct 6 between dicyanoacetylene and 1,3-cyclohexadiene was treated with a base
under various conditions to get tetraazaporphyrin 7 or its metal complexes. However, the retro
Diels-Alder reaction of 6 takes place at 100 ºC to give phthalonitrile exclusively, which gives Pcs under
2
cyclization conditions (PrOLi in PrOH or Mg(OPr) in PrOH at 100 ºC). It was very difficult to get 7
from 6 without formation of Pcs. Cyclization of 6 at lower temperature or protection of the double bond
in 6 is crucial to get 7 from 6. Now we are trying to find such conditions, but we have not yet succeeded
in preparing 7 from 6 or related compounds without formation of Pcs.
EXPERIMENTAL
General. Melting points were determined on a Yanaco micro melting point apparatus MP500D and are
uncorrected. Mass spectra were measured on JEOL JMS-700 usually at 70 eV. MALDI TOF mass spectra
were measured on an Applied Biosystems Voyager de Pro. UV-Vis spectra were measured on a JASCO
1
13
V-570 spectrophotometer. H NMR spectra (and C NMR spectra) were recorded on JEOL GSX-270 at
70 MHz (67.5 MHz) and AL-400 at 400 MHz (100 MHz). Elemental analyses were performed at
2
Integrated Center for Sciences, Ehime University. Dicyanoacetylene was prepared by dehydration of the
5
corresponding amide with P
2
O
5
. The requisite amide is commercially available, but it is very expensive.
5
It can be prepared by the reaction of dimethyl acetylenedicarboxylate with NH
4
OH. Diene 1 was
6
prepared according to the literature procedure as shown in Scheme 3.
Scheme 3. Synthesis of 5,6-dimethylenebicyclo[2.2.2]oct-2-ene (1)
5
,8-Ethano-1,4,5,8-tetrahydronaphthalene-2,3-dicarbonitrile (2)
A solution of 1 (3.07 g, 23.2 mmol) in dry CH Cl (20 mL) was poured into dicyanoacetylene (1.5 g, 20
mmol) at 0 ºC. The reaction mixture was stirred under N atmosphere at rt for 12 h. The solvent was
2
2
2
removed under reduced pressure. The residue was purified by column chromatography on silica gel with
1
CHCl
3
to give 2 as a white solid (2.24 g, 55%). mp 155 ºC (decomp); H NMR (CDCl
3
, 270MHz) δ 6.31
1
3
(
m, 2H), 3.36 (m, 2H), 3.18 (s, 4H),1.28-1.35 (m, 4H); C NMR (CDCl
3
, 67.5 MHz) δ 133.79, 131.01,

840
HETEROCYCLES, Vol. 74, 2007
-1
1
24.29, 115.59, 39.62, 30.77, 24.76; IR (KBr) νmax 2225, 1425, 846, 692, 682 (CN) cm ; MS (70 eV) m/z
+
(
rel intensity) 208 (M , 7%), 180 (100), 153 (21), 140 (20); Anal. Calcd for C14
N, 13.45. Found: C, 80.86; H, 5.98; N, 13.29.
,8-Dihydro-5,8-ethanonaphthalene-2,3-dicarbonitrile (3)
12 2
H N : C, 80.74; H, 5.81;
5
To a solution of 2 (1.61 g, 7.75 mmol) in dry 1,4-dioxane (50 mL) was added DDQ (3.5 g, 15 mmol). The
resulting mixture was stirred under N atmosphere at 60 ºC for 2 days. The solvent was removed under a
2
3
reduced pressure. The residue was dissolved in CHCl . The solution was washed with water and brine,
and dried over anhydrous Na
on alumina with CHCl
2
SO
4
. After evaporation, the residue was purified by column chromatography
1
3
to give 3 as a white solid (1.54 g, 96%). mp 129-131 ºC; H NMR (CDCl
3
, 270
MHz) δ 7.57 (s, 2H), 6.52 (dd, 2H, J = 4.4, 2.9 Hz), 4.11 (m, 2H), 1.62-1.69 (m, 2H), 1.41-1.45 (m, 2H);
1
3
C NMR (CDCl
229 (CN), 1477, 717 cm ; MS (70 eV) m/z (rel intensity) 206 (M , 6%), 178 (100); Anal. Calcd for
: C, 81.53; H, 4.89; N, 13.58. Found: C, 81.46; H, 5.07; N, 13.43.
3
, 67.5 MHz) δ 150.39, 134.07, 127.22, 116.02, 112.57,40.12, 24.63; IR (KBr disk) νmax
-1
+
2
14 10 2
C H N
BCOD-fused phthalocyanine Mg-4
A mixture of magnesium (51.4 mg, 2.11 mmol) and a small amount of iodine in propanol (74 mL) was
refluxed until magnesium was dissolved. After the solution was cooled to rt, 3 (800 mg, 3.88 mmol) was
added to it. The resulting mixture was heated at 100 ºC overnight. The solvent was removed under
reduced pressure. The residue was purified by column chromatography on alumina with THF and then
1
washed with Et
2
O to give Mg-4 (381 mg, 42%). H NMR (DMSO-d
6
, 400 MHz) δ 9.23 (m, 8H) 6.84 (m,
+
+
8
3
7
H), 4.69 (m, 8H), 1.75-1.83 (m, 16H); MS (FAB) m/z (rel intensity) 1697 (2*M +1, 8%), 849 (M +1,
1), 763 (45), 737 (100); Anal. Calcd for C56
40 8 2
H N Mg·2H O: C, 75.97; H, 5.01; N, 12.66. Found: C,
5.80; H, 4.91; N, 12.66.
Naphthalocyanine Mg-5
Mg-4 (9.3 mg 0.011 mmol) was heated in a grass tube under vacuum at 250 ºC for 20 min to give Mg-5
+
(
8.4 mg 0.011 mmol, 100%). MS (FAB) m/z (rel intensity) 737 (M +1, 100%); Anal. Calcd for
42 8 2
C H24MgN Mg·3H O: C, 72.87; H, 3.82; N, 14.16. Found: C, 73.17; H, 3.70; N, 14.07.
BCOD-fused phthalocyanine free base-4
A mixture of lithium (51.5 mg, 7.42 mmol) in butanol (8.0 mL) was refluxed until lithium was dissolved.
After the solution was cooled to rt, 3 (350 mg, 1.68 mmol) was added to it. The resulting mixture was
refluxed overnight. The solvent was removed under reduced pressure. The residue was purified by
column chromatography on silica gel with CHCl
3
and then recrystallized from hexane/CHCl
3
to give
1
Metal free-4 (87.4 mg, 25%). H NMR (5% TFA/CDCl
3
, 400 MHz) δ 9.17 (br, 8H), 6.83 (br, 8H), 4.62
+
+
(
(
2 4
br, 8H), 1.75-1.94 (br, 16H); MS (MALDI TOF) m/z (rel intensity) 827 (M +1), 799 (M +1-C H ), 770
+
+
+
M +1-2C
H
2 4
), 743 (M +1-3C
2
H
4
), 715 (M +1-4C
2
H
4
).

HETEROCYCLES, Vol. 74, 2007
841
Attempt to prepare 7
Bicyclo[2.2.2]octa-2,5-diene-2,3-dicarbonitrile 6 was prepared by stirring a solution of dicyanoacetylene
1.74 g, 22.9 mmol) and 1,3-cyclohexadiene (2.5 mL, 26 mmol) in CHCl (20 mL) at rt for 24 h. Removal
of the solvent gave 6 (2.95 g, 83%). mp 101-102 ºC [lit., mp 105 ºC]; H NMR (CDCl , 270 MHz) δ 6.40
(
3
7
1
3
1
3
(
dd, 2H, J = 4.4, 3.4), 4.04 (m, 2H), 1.54-1.58 (m, 4H); C NMR (CDCl
3
, 67.5 MHz) δ132.31, 131.86,
-1
1
13.94, 41.13, 24.06; IR (KBr disk) νmax 2221 (CN), 1585, 1342, 736, 686 cm ; MS (70 eV) m/z (rel
+
8 2
intensity) 156 (M , 8), 128 (100), 101 (10), 69 (14), 57 (13); Anal. Calcd for C10H N : C, 76.90; H, 5.16;
N, 17.94. Found: C, 76.85; H, 5.26; N, 17.61.
8
Treatment of 6 with Mg(OPr)
2
in PrOH or HMDS and Zn(OAc)
2
in DMF at 100 ºC gave MgPc or ZnPc,
respectively. The reaction using LiOR or DBU as a base at lower temperature (80 ºC) resulted in recovery
of 6.
ACKNOWLEDGEMENTS
The present work was partially supported by a Grant-in-Aid for Scientific Research from Ministry of the
Education, Culture, Sports, Science and Technology, Japan.
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