Novel synthesis of phthalocyanines from phthalonitriles under mild conditions

Article abstract of DOI:10.1055/s-2002-34237

A convenient preparation of phthalocyanines from phthalonitriles was accomplished by treatment with metal salts and hexamethyldisilazane (HMDS) in DMF at 100 °C. This reaction provides a new preparative method under mild conditions for phthalocyanines having a variety of metals and substituted phthalocyanines as well as Zn-naphthalocyanine.

Full text of DOI:10.1055/s-2002-34237

LETTER
1649
Novel Synthesis of Phthalocyanines from Phthalonitriles under Mild
Conditions
N
ovel Synthesis of
i
Phtha
t
o
ne
s
from Pht
s
halonitrile
h
s
unde
r
Mild
i
Conditions Uchida, Hirokazu Tanaka, Hideyuki Yoshiyama, Paidi Yella Reddy,1 Shuichi Nakamura, Takeshi Toru*
Department of Applied Chemistry, Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466-8555, Japan
Fax +81(52)7355217; E-mail: toru@ach.nitech.ac.jp
Received 26 July 2002
First, we examined the preparation of phthalocyanine un-
der several reaction conditions (Scheme 1). The results
obtained in reactions of phthalonitrile 1 with ZnBr2 are
shown in Table 1 (entries 1–7). The reaction without
Abstract: A convenient preparation of phthalocyanines from
phthalonitriles was accomplished by treatment with metal salts and
hexamethyldisilazane (HMDS) in DMF at 100 °C. This reaction
provides a new preparative method under mild conditions for
phthalocyanines having a variety of metals and substituted phthalo- HMDS did not afford Zn-phthalocyanine 2a at all (entry
cyanines as well as Zn-naphthalocyanine.
1). Yields of Zn-phthalocyanine are dependent on the mo-
lar equivalents of HMDS (entries 2–4), the concentration
of 1 in DMF (not shown in Table 1), the reaction temper-
ature (entries 3, 5 and 6), and the reaction time (entries 3
and 7). The reaction in the presence of HMDS gave 2a, re-
sulting in the highest yield with 2 equivalents of HMDS.
DMF was the best solvent among the aprotic polar sol-
vents examined (entries 8 and 9). Thus, to a 4 mol/L DMF
solution of 1 were added 0.25 equivalents of ZnBr2 and 2
equivalents of HMDS, and the mixture was heated at
100 °C for 10 hours. Zn-Phthalocyanine 2a was obtained
in 78% yield after removing the impurities by extraction
with chloroform using Soxhlet’s extractor (entry 3).
Key words: phthalocyanine, naphthalocyanine, phthalonitrile,
hexamethyldisilazane, dye
Phthalocyanines are extremely stable blue dyes. Recently,
a number of their derivatives have been prepared for de-
veloping functional dyes2 useful for optical information
recording media, organic semiconductors for laser beam
5,6
printers,3 agents for photodynamic therapy,4 NOx and
halogen6 gas sensors, and pH sensors.7 Preparation of a
wide range of phthalocyanine derivatives should require
an efficient preparative method performed under mild
conditions. For this purpose, the method starting from
phthalonitrile derivatives has been often adopted, since
another well-known preparative method starting from
phthalimides with urea needs temperature higher than
200 °C.2,8 However, the preparative methods from
phthalonitriles still meet with some limitations including
treatment, often on heating, with a strong base such as
DBN,9 DBU,9,10 lithium alkoxides,11 sodium alkoxides,12
or heating at high temperature with ammonia gas13 or
urea.14 We herein report a convenient synthesis of phtha-
locyanines on treatment of phthalonitriles with metal salts
and hexamethyldisilazane (HMDS) under mild condi-
tions.
This procedure was compatible with a variety of metal
salts such as ZnCl2, Zn(OTf)2, Zn(OAc)2, Zn(acac)2,
MgBr2, CuBr2, and InCl3, giving the corresponding
phthalocyanines in good yields (entries 10–16), where the
reaction with FeBr2 and CoBr2 gave the corresponding
phthalocyanines in low yields (entries 17 and 18). The Zn-
phthalocyanines having a variety of substituents were also
produced in good yields from 4-t-Bu-, 4-n-propyloxy-, 4-
phenyloxy-, and 4-octylthiophthalonitriles (Scheme 2 and
Table 2). These phthalocyanine derivatives 7–10 were
obtained as a mixture of regioisomers which were not
separated. Zn-Naphthalocyanine 12 could also be pre-
pared in good yield (Scheme 3). In this case, the reaction
N
metal salt (0.25 equiv)
CN
N
N
N
N
HMDS
N
N
M
N
DMF
CN
1
2
Scheme 1
Synlett 2002, No. 10, Print: 01 10 2002.
Art Id.1437-2096,E;2002,0,10,1649,1652,ftx,en;U04702ST.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0936-5214

1650
H. Uchida et al.
LETTER
Table 1 Preparation of Phthalocyanines 2 by Treatment of Phthalonitrile 1 with Metal Salts and HMDS in DMF
Entry
Metal Salt
HMDS
(equiv)
Reaction temp Reaction time
M
Product
Yield
(%)
(°C)
100
100
100
100
80
(h)
10
10
10
10
10
10
24
10
10
10
10
10
10
10
10
10
26
10
1
2
ZnBr2
ZnBr2
ZnBr2
ZnBr2
ZnBr2
ZnBr2
ZnBr2
–
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Mg
Cu
InCl
Fe
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2a
2b
2c
2d
2e
2f
0
1.0
2.0
3.0
2.0
2.0
2.0
1.0
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
54
78
71
33
68
77
35
41
73
73
73
55
75
74
59
43
37
3
4
5
6
120
100
100
100
100
100
100
100
100
100
100
125
100
7
a
8
ZnBr2
b
9
ZnBr2
10
11
12
13
14
15
16
17
18
ZnCl2
Zn(OTf)2
c
Zn(OAc)2
Zn(acac)2
MgBr2
CuBr2
InCl3
FeBr2
CoBr2
Co
a Dimethylacetamide was used instead of DMF.
b DMSO was used instead of DMF.
c Zn(OAc)2 H2O was used.
Table 2 Preparation of Substituted Phthalocyanines by Treatment
of Phthalonitrile Derivatives with ZnBr2 and HMDS in DMF
was carried out in a 1.0 mol/L solution, because of the
solubility of naphthalonitrile in DMF. The structures of
phthalocyanines, were confirmed by the TOF Mass, IR
and/or 1H NMR spectra as well as elemental analyses.15
Entry Phthalonitrile derivatives
Conc.
Prod- Yield
(mol/L) uct
(%)
We observed that diisopropylamine also accelerated the
formation of phthalocyanine, and Zn-phthalocyanine was
obtained in 55% yield on heating a mixture of phthalo-
nitrile and ZnBr2 with 2.0 equivalents of diisopropyl-
amine in DMF for 10 hours at 100 °C. Both HMDS
and diisopropylamine are weakly basic and the former
is weaker than the latter. HMDS apparently gives the
phthalocyanine more efficiently than the latter. Thus,
HMDS would not only act as a nucleophilic base but also
accelerate, together with a metal salt, the cyclization of
phthalonitriles and/or further consecutive reactions to
form the phthalocyanine skeleton.
1
3
4.0
7
65
2
3
4
4
4
5
4.0
6.0
4.0
8
8
9
46
63
68
In summary, we have demonstrated a new method for the
preparation of phthalocyanines from phthalonitriles using
HMDS and metal salts. Prominent among the advantages
of this method is its operation under nearly neutral, mild
conditions, operational simplicity, and high yields.
5
6
4.0
10
66
Synlett 2002, No. 10, 1649–1652 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Novel Synthesis of Phthalocyanines from Phthalonitriles under Mild Conditions
1651
R
R
N
ZnBr2 (0.25 equiv)
HMDS (2.0 equiv)
N
N
N
N
CN
CN
N
N
Zn
DMF, 100 °C, 10 h
R
3-6
N
R
R
7-10
Scheme 2
N
ZnCl2 (0.25 equiv)
HMDS (2.0 equiv)
N
N
CN
CN
N
N
Zn
N
DMF (1.0 mol/L),
100 °C, 10 h
N
N
11
55%
12
Scheme 3
(4) (a) Wagner, J. R.; Ali, H.; Langlois, E.; Brasseuseur, N.; van
Lier, J. E. Photochem. Photobiol. 1987, 45, 587.
Acknowledgement
(b) Brasseur, N.; Langlois, E.; Ali, H.; van Lier, J. E.
Photochem. Photobiol. 1987, 46, 739. (c) Paquette, B.; Ali,
H.; Langlois, R.; van Lier, J. E. Photochem. Photobiol. 1988,
47, 215. (d) Brasseur, N.; Ali, H.; Langlois, E.; van Lier,
J. E. Photochem. Photobiol. 1988, 47, 705. (e) Ali, H.;
Langlois, E.; Wagner, J. R.; Brasseur, N.; Paquette, B.; van
Lier, J. E. Photochem. Photobiol. 1988, 47, 713.
This work was partly supported by a Grant-in-Aid for Scientific Re-
search on Priority Areas (A) ‘Exploitation of Multi-Element Cyclic
Molecules’ (No. 14044040) from the Ministry of Education, Cul-
ture, Sports, Science, and Technology, Japan.
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LETTER
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(15) Representative Procedure: A mixture of phthalonitrile
(107 mg, 0.84 mmol), HMDS (0.35 mL, 1.66 mmol), ZnBr2
(50 mg, 0.22 mmol), and DMF (0.21 mL) was heated at
100 °C under Ar atmosphere. The mixture was separated
into two phases. After heating for 10 h, the reaction mixture
was subjected to evaporation under reduced pressure. The
resultant solid was washed successively with MeOH (50
mL) and with water (50 mL). The obtained crude product
was further purified by extraction with chloroform (50 mL)
using Soxhlet’s extractor, and dried under reduced pressure,
affording Zn-phthalocyanine 7a (91 mg) in 78% yield. Anal.
Found: C, 66.21; H, 2.88; N, 19.59. Calcd: C, 66.50; H, 2.79;
N, 19.39. IR (KBr):1608, 1486, 1456, 1412, 1331, 1285,
1167, 1118, 1090, 1061, 887, 778, 752, 727 cm–1. TOF MS
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Synlett 2002, No. 10, 1649–1652 ISSN 0936-5214 © Thieme Stuttgart · New York