Reduction of an amido zinc(II) phthalocyanine by diborane

Article abstract of DOI:10.1055/s-2006-926336

1,2-Dicyano-4,5-di[(N,N-dimethylaminocarbonyl)methoxy]benzene (5) was synthesized in 80% yield from the corresponding 1,2-dibromo derivative 4. Octa(peripheral-amide)substituted zinc(II) phthalocyanine 6 was obtained from 5 and zinc acetate in the presenc

Full text of DOI:10.1055/s-2006-926336

PAPER
799
Reduction of an Amido Zinc(II) Phthalocyanine by Diborane
R
eduction of an
A
r
mido
Z
i
inc(II)
s
Phthalocy
t
anine ian A. Strassert,a Lelia E. Dicelio,b Josefina Awruch*a
a
Departamento de Química Orgánica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires,
Junín 956, 1113 Buenos Aires, Argentina
INQUIMAE, Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y Naturales,
Universidad de Buenos Aires, Ciudad Universitaria, Pabellón II, 1428 Buenos Aires, Argentina
Fax +54(11)45083645; E-mail: jawruch@ffyb.uba.ar
b
Received 22 August 2005
forded the corresponding diacyl chloride, which, after
treatment with N,N-dimethylamine, gave the desired
amide 4.
Abstract: 1,2-Dicyano-4,5-di[(N,N-dimethylaminocarbonyl)meth-
oxy]benzene (5) was synthesized in 80% yield from the correspond-
ing 1,2-dibromo derivative 4. Octa(peripheral-amide)substituted
zinc(II) phthalocyanine 6 was obtained from 5 and zinc acetate in
the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene. Phthalocya-
nine 7 was prepared via reduction of 6 with diborane. Treatment of
7 with methyl iodide afforded cationic dye 8.
As 1-methyl-2-pyrrolidinone (NMP) has favorable sol-
vent properties for several aromatic nucleophilic displace-
ment reactions under very smooth conditions,11 the
reaction of 4 was carried out with cuprous cyanide em-
ploying the above solvent. Phthalonitrile 5 was obtained
Key words: nucleophilic aromatic substitution, reduction, phthalo-
cyanines
O
BrCH2CO2Et
DMF, K2CO3
60 °C, 120 h
Br2, CH2Cl2
r.t., 48 h
O
O
OH
OH
O
O
Phthalocyanines and their metal complexes are important
dyes employed in the technological1 and medicinal2 field.
Phthalocyanines are prepared from phthalonitriles or
phthalic acid analogues, such as phthalimides, phthalic
anhydrides, and phthalic acids.1a,3 Owing to the chemical
characteristics of the molecules, only a limited number of
reactions with the peripheral substituents of the macrocy-
cle can be achieved to modulate the solubility properties
as well as to enable the dye to conjugate with other mole-
cules for different purposes. This effect is even greater in
the case of metallophthalocyanines, where we run the risk
of losing the complexed metal.1a
73%
quantitative
yield
2
1
O
1) NaOH, H2O, MeOH
2) HCl
N
3) SOCl2
4) Me2NH⋅HCl,
Py/CH2Cl2
r.t., 24 h
O
O
Br
O
Br
Br
O
O
O
N
80%
Br
O
O
4
3
O
O
In general, quaternizations towards cationic alkylammo-
nium phthalocyanines4 and pyridinum porphyrazines5 are
frequent reactions of metallophthalocyanines.6 Quite re-
cently, pure metal(II) tetraamine phthalocyanines of co-
balt, nickel, and copper complexes were synthesized via
reduction of the metal tetranitrophthalocyanines with so-
dium sulfide.7 Also, deprotection of the phthalimido
group was reported for zinc(II) phthalocyanines.8,9 This
synthetic approach allowed us to prepare an extremely li-
pophilic and strongly hydrophilic zinc(II) phthalocyanine
substituted in its periphery with 3-phthalimidopropyloxy
and 3-aminopropyloxy groups.10
N
Zn(AcO)2, DBU,
BuOH
reflux, 1.5 h
O
O
CuCN, NMP
200 °C, 6 h
NC
O
O
20%
80%
N
NC
5
R
R
N
6: R = O
O
B2H6, THF
reflux, 48 h
The synthesis of phthalocyanines 6, 7, and 8 is depicted in
Scheme 1. The sequence begins with the reaction of pyro-
catechol (1) with ethyl bromoacetate to give 1,2-
di[(ethoxycarbonyl)methoxy]benzene (2). The reaction of
compound 2 with bromine in dichloromethane at room
temperature afforded dibromo derivative 3. Saponifica-
tion of 3, followed by treatment with thionyl chloride, af-
N
N
N
N
94%
N
N
Zn
N
R
R
R
N
R
7: R = O
N
CH3I,
DMF
60 °C,
48 h
quan-
titative
yield
+ I–
R
R
N
SYNTHESIS 2006, No. 5, pp 0799–0802
x
x
.
x
x
.2
0
0
6
8: R = O
Advanced online publication: 07.02.2006
DOI: 10.1055/s-2006-926336; Art ID: M05605SS
© Georg Thieme Verlag Stuttgart · New York
Scheme 1

800
C. A. Strassert et al.
PAPER
in 80% yield, without requiring chromatographic purifica-
tion. Attempts to obtain 5 employing N,N-dimethylform-
amide as solvent failed, thus including long reaction times
that only led to the decomposition of compound 4. The ef-
fectiveness of the reaction in 1-methyl-2-pyrrolidinone
could also be attributed to the solubility of the cuprous cy-
anide in this solvent that led to a homogeneous-phase re-
action apart from the higher temperature attainable when
compared with N,N-dimethylformamide. Phthalocyanine
6 was readily prepared by cyclotetramerization of phtha-
lonitrile 5 employing 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU) in butanol and zinc acetate. Reduction of 6 with
diborane in tetrahydrofuran at reflux temperature gave
phthalocyanine 7 in quantitative yields. The stability of
both the precursor and the product under these reaction
conditions is noteworthy, as it shows their usefulness for
the peripheral macrocyclic amido-group reduction. Cat-
ionic phthalocyanine 8 was obtained by treatment of 7
with methyl iodide in N,N-dimethylformamide.
Except for phthalocyanine 8, the dyes were characterized
by HR-MALDI-TOF mass spectrometry. Besides, the
UV-visible absorption spectra of phthalocyanines 6–8
showed the Soret and the Q band around 360 nm and 670
nm, respectively, and typical fluorescence emission spec-
tra of zinc phthalocyanines were also observed (Figure 1).
With regard to solubility, it should be pointed out that 6, a
non-charged phthalocyanine, is soluble in protic solvents
including water and organic solvents containing small
amounts of methanol. Phthalocyanine 7 is soluble in most
organic solvents, such as dichloromethane, tetrahydrofu-
ran, and N,N-dimethylformamide. As expected, quater-
nization of 7 led to the extremely hydrophilic compound
8.
Melting points were determined on an Electrothermal 9100 capil-
lary melting point apparatus. 1H NMR and 13C NMR were recorded
1
on a Bruker MSL 300 spectrometer. The H NMR of phthalocya-
nines 6, 7, and 8 were recorded on a Bruker AM 500. Mass spectra
were obtained with a TRIO 2 (electronic ionization 70 eV) spec-
trometer. Phthalocyanines HR-MALDI-TOF mass spectra were
measured with a Mod 4700 Applied Biosystems spectrometer. Elec-
tronic absorption spectra were determined with a Shimadzu UV-
3101 PC spectrophotometer. Fluorescence spectra were monitored
with a QuantaMaster Model QM-1 PTI spectrofluorometer. Infra-
red spectra were performed with a Perkin Elmer Spectrum One FT-
IR spectrometer. Microanalyses were carried out using a Carlo Erba
EA 1108 elemental analyzer. Chromatography columns were pre-
pared with TLC Kieselgel (Merck) and Aluminium Oxide 90 stan-
dardized (Merck). N,N-Dimethylformamide was dried over 3Å
molecular sieves for 72 hours, then filtered, and freshly distilled be-
fore utilization.12
Figure 1 Absorption and fluorescence spectra of 6, 7, and 8 in DMF
IR (KBr): 2983, 2938, 1758 (CO), 1595, 1502, 1457, 1443, 1379,
1271, 1188, 1135, 1119, 1069, 1029, 751 cm–1.
1H NMR (300 MHz, CDCl3): d = 1.26 (t, 6 H, J = 7.3 Hz, CH3),
4.23 (q, 4 H, J = 7.3 Hz, CH2), 4.69 (s, 4 H, CH2), 6.9 (m, 4 H, Ar).
13C NMR (75 MHz, DMSO-d6): d = 14.06 (CH3), 60.62
[OCH2(CH3)], 65.64 [OCH2(CO2)], 114.77 [CH(CCO), Ar], 121.86
[CH(CO), Ar], 147.60 (CO, Ar), 168.88 (CO2).
MS (EI, 70 eV): m/z (%) = 282 (1.47) [M+], 254 (17.03) [M+ – 28],
236 (1.56), 226 (3), 210 (8.62), 109 (100).
1,2-Di[(ethoxycarbonyl)methoxy]benzene (2)
A mixture of pyrocatechol (4.4 g, 40 mmol), ethyl bromoacetate
(21.1 g, 126 mmol), and K2CO3 (12 g, 87 mmol) in anhyd DMF (40
mL) was stirred and heated at 60 °C for 120 h under Ar and then
poured into H2O (100 mL) and extracted with CH2Cl2. The com-
bined extracts were washed with 5% NaHCO3 soln (3 × 50 mL) and
H2O (50 mL), dried (Na2SO4), and evaporated in vacuo. Highly vis-
cous oil; yield: 11.5 g (100%).
Anal. Calcd. for C14H18O6: C, 59.57; H, 6.43. Found: C, 59.50; H,
6.24.
1,2-Dibromo-4,5-di[(ethoxycarbonyl)methoxy]benzene (3)
Br2 (10.0 mL, 195 mmol), dissolved in CH2Cl2 (10 mL), was added
dropwise to an ice-cold solution of 2 (11.5 g, 40 mmol) dissolved in
CH2Cl2 (10 mL). After addition, stirring was continued for 48 h at
Synthesis 2006, No. 5, 799–802 © Thieme Stuttgart · New York

PAPER
Reduction of an Amido Zinc(II) Phthalocyanine
801
r.t., 5% NaHCO3 soln was added to neutralize the acidic medium,
followed by the addition of 5% Na2S2O3 soln to reduce the excess
Br2. The reaction mixture was extracted with CH2Cl2 (3 × 30 mL),
then washed with 5% NaHCO3 (3 × 30 mL) and H2O (1 × 30 mL).
The organic phase was dried over Na2SO4 and evaporated in vacuo,
and the solid residue was recrystallized twice from EtOH. Yield: 13
g (73%); mp 93–95 °C (lit.13 97–99 °C).
Anal. Calcd. for C16H18N4O4: C, 58.17; H, 5.49; N, 16.96. Found:
C, 58.20; H, 5,52; N, 16.91.
2,3,9,10,16,17,23,24-Octakis[(N,N-dimethylaminocarbon-
yl)methoxy]phthalocyaninatozinc(II) (6)
A mixture of 5 (0.14 g, 0.42 mmol), anhyd Zn(OAc)2 (0.14 g, 0.70
mmol), and 0.14 mL (0.94 mmol) DBU in anhyd BuOH (14 mL)
was stirred and heated at reflux temperature for 1.5 h under Ar. Af-
ter evaporation in vacuo, the residue was treated with CH2Cl2 (5
mL) and centrifuged to eliminate the excess Zn(OAc)2. The organic
solution was evaporated in vacuo leaving a blue-green solid, that
was then dissolved in CH2Cl2 and filtered through a column with
Al2O3 packed and prewashed with the same solvent. The title com-
pound was eluted with CH2Cl2–MeOH (5:1). After evaporation, the
dye was recrystallized from CH2Cl2–hexane. Yield: 0.030 g (20%).
1,2-Dibromo-4,5-di[(N,N-dimethylaminocarbonyl)meth-
oxy]benzene (4)
To a solution of NaOH (17.4 g, 435 mmol) in H2O (140 mL) and
MeOH (140 mL) 3 (8.0 g, 18 mmol) dissolved in MeOH (140 mL)
was added dropwise. The mixture was stirred for 3 h at r.t. and then
adjusted to pH 2 with HCl soln. After stirring for 1 h, the precipitate
was filtered off, washed with cold H2O, and dried in vacuo; 6.8 g
(97%) of crude white solid was obtained.
IR (KBr): 2924, 2853, 1655 (CON), 1500, 1431, 1405, 1364, 1283,
1264, 1203, 1163, 1109, 1069, 906, 807, 743, 729, 643, 626, 598,
479 cm–1.
1H NMR (500 MHz, DMSO-d6): d = 3.32 (s, 24 H, CH3), 3.35 (s, 24
H, CH3), 5.49 (s, 16 H, CH2), 8.8 (s, 8 H, Ar).
This diacid (1.0 g, 2.6 mmol) was reacted with SOCl2 (6 mL, 82
mmol) and kept at reflux for 2.5 h until the solid was completely dis-
solved. Excess SOCl2 was evaporated in vacuo, leaving a solid res-
idue that was then dissolved in anhyd CH2Cl2 (10 mL) and added
dropwise to a cold Me2NH·HCl soln (1.6 g, 19.6 mmol) in anhyd
CH2Cl2 (5 mL) and anhyd pyridine (15 mL). The reaction mixture
was stirred for 24 h at r.t., poured into 1 M HCl soln (100 mL), then
stirred for 1 h, and the organic phase was decanted after addition of
CH2Cl2 (20 mL). The organic phase was washed again with 1 M
HCl soln (3 × 50 mL) and H2O (1 × 50 mL), dried over Na2SO4, and
evaporated to dryness in vacuo. The solid residue was dissolved in
a small volume of CH2Cl2–MeOH (9.5:0.5) and filtered through a
silica-gel column packed and pre-washed with the same solvent.
After evaporation of the solvent, the solid residue was recrystallized
from MeOH. Yield: 0.950 g (80%); mp 89–91 °C.
HRMS–MALDI-TOF: m/z [M+] calcd. for C64H72N16O16Zn:
1384.4644; found: [M+] 1384.4585 and [M + H]+ 1385.4694.
UV/Vis (DMF): lmax (e, M–1cm–1) = 358.5 (70300), 608.5 (26900),
645.5 (25400), 675 nm (181200).
Fluorescence emission (DMF): lmax = 680.5 nm.
Anal. Calcd. for C64H72N16O16Zn: C, 55.43; H, 5.23; N, 16.16.
Found: C, 55.50; H, 5.30; N, 16.22.
2,3,9,10,16,17,23,24-Octakis[(N,N-dimethylamino-
ethoxy)]phthalocyaninatozinc(II) (7)
IR (KBr): 3102, 3079, 3013, 2931, 1657 (CON), 1584, 1497, 1443,
1355, 1338, 1251, 1206, 1153, 1055, 914, 878, 859, 808, 788, 651,
599 cm–1.
1H NMR (300 MHz, CDCl3): d = 2.95 (s, 6 H, CH3), 3.03 (s, 6 H,
CH3), 4.73 (s, 4 H, CH2), 7.13 (s, 2 H, Ar).
13C NMR (75 MHz, CDCl3): d = 35.64 (CH3), 36.31 (CH3), 68.20
(CH2), 116.32 (CBr, Ar), 119.79 (CH, Ar), 147.99 (CO, Ar), 166.86
(CON).
B2H6 from BF3·Et2O (5 mL) was slowly dropped into a suspension
of NaBH4 (1.5 g) in diglyme (5 mL) and this mixture was bubbled
through a suspension of 6 (0.020 g, 0.014 mmol) in anhyd THF. The
mixture was refluxed for 48 h until 6 was completely dissolved and
was then poured into hexane and the blue-green precipitate was cen-
trifuged, dried, and then applied to an Al2O3 column packed and
prewashed with toluene. After washing with toluene and CH2Cl2,
the title compound was eluted with CH2Cl2–MeOH (8:2). Due to
addition of hexane, 7 precipitated, and was isolated by centrifuga-
tion. Yield: 0.016 g (94%).
MS (EI, 70 eV): m/z (%) = 438 (3.23) [M+], 440 (1.8) [M+ + 2], 436
(1.63) [M+ – 2], 366 (17.35), 352 (2.62), 86 (100), 72 (39.63).
IR (KBr): 3001, 2946, 1609, 1496, 1461, 1394, 1351, 1281, 1200,
1170, 1099, 1053, 1007, 931, 869, 805, 745, 669, 621, 580 cm–1.
1H NMR (500 MHz, DMSO-d6): d = 3.31 (br s, 48 H, CH3), 3.47 (br
s, 16 H, CH2N), 5.01 (br s, 16 H, OCH2), 8.99 (br s, 8 H, Ar).
Anal. Calcd for C14H18Br2N2O4: C, 38.38; H, 4.14; N, 6.39. Found:
C, 38.40; H, 4,18; N, 6.41.
1,2-Dicyano-4,5-di[(N,N-dimethylaminocarbonyl)meth-
oxy]benzene (5)
HRMS–MALDI-TOF: m/z [M+] calcd. for C64H88N16O8Zn:
1272.6262; found: [M+] 1272.6291 and [M + H]+ 1273.6328.
A solution of 4 (0.30 g, 0.68 mmol) and CuCN (0.300 g, 3.35 mmol)
of in NMP (10 mL) was heated at 200 °C for 6 h under Ar. After
cooling, it was poured into 25% NH4OH soln (20 mL) and stirred
for 24 h. The solution was extracted with CH2Cl2 (3 × 40 mL),
washed with H2O (1 × 40 mL), dried over Na2SO4, and then evapo-
rated to dryness in vacuo. The solid residue was recrystallized twice
from MeOH. Yield: 0.183 g (80%); mp 206–208 °C.
UV/Vis (DMF): lmax (e, M–1cm–1) = 360.5 (89400), 607 (35100),
644 (33400), 672 nm (241400).
Fluorescence emission (DMF): lmax = 677.5 nm.
Anal. Calcd. for C64H88N16O8Zn: C, 60.29; H, 6.96; N, 17.58.
Found: C, 60.25; H, 6.94; N, 17.54.
IR (KBr): 3588, 3481, 3121, 3040, 2963, 2667, 2232 (CN), 1651
(CON), 1589, 1521, 1298, 1262, 1234, 1158, 1096, 1032, 810, 538
cm–1.
1H NMR (300 MHz, CDCl3): d = 2.99 (s, 6 H, CH3), 3.06 (s, 6 H,
CH3), 4.50 (s, 4 H, CH2), 7.16 (s, 2 H, Ar).
13C NMR (75 MHz, CDCl3): d = 35.74 (CH3), 36.13 (CH3), 67.31
(CH2), 109.41 [C(CN), Ar], 115.53 (CN), 118.11 (CH, Ar), 151.54
(CO, Ar), 165.69 (CON).
MS (EI, 70 eV): m/z (%) = 330 (0.86) [M+], 258 (8.68), 102 (2.84),
86 (48.64), 72 (100).
2,3,9,10,16,17,23,24-Octakis[(N,N,N-trimethylammoni-
um)ethoxy]phthalocyaninatozinc(II) Octaiodide (8)
MeI (1.0 mL, 16 mmol) was added to a solution of phthalocyanine
7 (0.005 g, 0.004 mmol) in DMF (3 mL) and the solution was stirred
for 48 h at 60 °C. After cooling to r.t., CH2Cl2 (5 mL) was added and
the blue-green powder was centrifuged, suspended in CH2Cl2 (5
mL), and centrifuged again.
Yield: 0.009 g (100%).
IR (KBr): 2929, 2710, 1631, 1609, 1496, 1461, 1396, 1449, 1281,
1199, 1110, 1055, 988, 956, 930, 863, 815, 745, 729, 579 cm–1.
Synthesis 2006, No. 5, 799–802 © Thieme Stuttgart · New York

802
C. A. Strassert et al.
PAPER
(2) (a) Hasrat, A.; van Lier, J. E. Chem. Rev. 1999, 99, 2379.
1H NMR (500 MHz, DMSO-d6): d = 3.34 (br s, 72 H, NCH3), 4.15
(br s, 16 H, CH2N), 5.18 (br s, 16 H, OCH2), 9.15 (br s, 8 H, Ar).
UV/Vis (DMF): lmax (e, M–1cm–1) = 367.5 (88300), 607 (33600),
644.5 (32000), 672.5 nm (225400).
(b) Pandey, R. K. J. Porphyrins Phthalocyanines 2000, 4,
368. (c) MacDonald, I. J.; Dougherty, T. J. J. Porphyrins
Phthalocyanines 2001, 5, 105:. (d) Detty, M. R.; Gibson, S.
L.; Wagner, S. J. J. Med. Chem. 2004, 47, 3897.
(3) Uchida, H.; Reddy, P. Y.; Nakamura, S.; Toru, T. J. Org.
Chem. 2003, 68, 8736; and references cited therein.
(4) (a) Leznoff, C. C.; Vigh, S.; Svirskaya, P. I.; Greenberg, S.;
Drew, D. M.; Ben-Hur, E.; Rosenthal, I. Photochem.
Photobiol. 1989, 49, 279. (b) Fernández, D. A.; Awruch, J.;
Dicelio, L. E. J. Photochem. Photobiol., B 1997, 41, 227.
(c) De Filippis, M. P.; Dei, D.; Fantetti, L.; Roncucci, G.
Tetrahedron Lett. 2000, 41, 9143. (d) Sugimori, T.; Nojima,
J.; Ozawa, T.; Handa, M.; Kasuga, K. Chem. Lett. 2004, 33,
1014.
Fluorescence emission (DMF): lmax = 678 nm.
Anal. Calcd. for C72H112I8N16O8Zn: C, 35.88; H, 4.68; N, 9.30.
Found: C, 35.82; H, 4.62; N, 9.24.
Acknowledgment
This work was supported by grants from the University of Buenos
Aires, the Consejo Nacional de Investigaciones Científicas y Técni-
cas (CONICET), and the Agencia Nacional de Promoción Científi-
ca y Tecnológica. We wish to thank Ms. Juana Alcira Valdez for
technical assistance regarding chromatography. HR-MALDI-TOF
mass spectrometry assistance of Dr. Fernando Lafont is also appre-
ciated, as well as language supervision by Prof. Rex Davis.
(5) Ramirez, C.; Antonacci, C.; Ferreira, J.; Sheardy, R. D.
Synth. Commun. 2004, 34, 3373.
(6) Anderson, M. E.; Barret, A. G. M.; Hoffman, B. M. Inorg.
Chem. 1999, 38, 6143.
(7) Achar, B. N.; Lokesh, K. S. J. Organomet. Chem. 2004, 689,
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(8) Fernández, D. A.; Dicelio, L. E.; Awruch, J. J. Heterocycl.
Chem. 1995, 32, 519.
(9) Rodriguez, M. E.; Strassert, C. A.; Dicelio, L. E.; Awruch, J.
J. Heterocycl. Chem. 2001, 38, 387.
(10) Strassert, C. A.; Rodriguez, M. E.; Dicelio, L. E.; Awruch, J.
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(11) (a) Encyclopedia of Reagents for Organic Synthesis, Vol. 5;
Paquette, L. A., Ed.; John Wiley and Sons: Chichester, 1999,
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Synthesis 2006, No. 5, 799–802 © Thieme Stuttgart · New York