Synthesis of 2,3,9,10,16,17,23,24-octasubstituted phthalocyaninatozinc(II) complexes mediated by reductive agents

Article abstract of DOI:10.1055/s-0029-1216809

N-Butyl-N-(4,5-dicyano-2-methylbenzyl)butanamide (6) was synthesized in 69% yield from the corresponding 4,5-dibromo derivative 5. Treatment of 6 with zinc acetate in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene gave the octasubstituted zinc(II) pht

Full text of DOI:10.1055/s-0029-1216809

PAPER
1975
Synthesis of 2,3,9,10,16,17,23,24-Octasubstituted Phthalocyaninatozinc(II)
Complexes Mediated by Reductive Agents
O
ctasubstituted Ph
a
thalocyanin
b
a
tozinc
C
om
r
plexes iela A. Gauna, Ana Clara Monsalvo, Josefina Awruch*
Departamento de Química Orgánica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires,
Junín 956, 1113 Buenos Aires, Argentina
Fax 54(11)45083645; E-mail: jawruch@ffyb.uba.ar
Received 7 January 2009; revised 25 February 2009
pheral positions of the phthalocyanines. We report the
synthesis and spectroscopic properties of three novel
2,3,9,10,16,17,23,24-octasubstituted phthalocianinato-
zinc(II) complexes that are highly soluble in polar organic
Abstract: N-Butyl-N-(4,5-dicyano-2-methylbenzyl)butanamide (6)
was synthesized in 69% yield from the corresponding 4,5-dibromo
derivative 5. Treatment of 6 with zinc acetate in the presence of 1,8-
diazabicyclo[5.4.0]undec-7-ene gave the octasubstituted zinc(II)
phthalocyanine 7, which was reduced with diborane to the give solvents.
phthalocyanine 8. Quaternization of 8 with iodomethane gave the
cationic dye 9.
As shown in Scheme 1, the sequence began with the reac-
tion of 2-(4,5-dibromo-2-methylbenzyl)-1H-isoindoline-
1,3(2H)-dione6 (1) with hydrazine in refluxing ethanol to
give 1-(4,5-dibromo-2-methylphenyl)methanamine (2)
quantitatively. Treatment of amine 2 with butanoyl chlo-
ride gave the amide 3, which was reduced with diborane
in tetrahydrofuran at room temperature to give N-(4,5-di-
bromo-2-methylbenzyl)butan-1-amine (4). Acylation of
this compound with butanoyl chloride gave the corre-
sponding amide 5, treatment of which with copper(I) cya-
nide in 1-methylpyrrolidin-2-one (NMP) as a solvent gave
the phthalonitrile 6 in 69% yield; the use of a 5:1 molar
excess of copper(I) cyanide gave the best yield.
Key words: octasubstituted phthalocyaninatozinc, reduction, nu-
cleophilic aromatic substitution, phthalocyanine, zinc complexes
Phthalocyanines play a major role in modern technology,1
including medicine.2 Because phthalocyanines are barely
soluble, considerable efforts have been made to prepare li-
pophilic derivatives by the introduction of peripheral
alkyl chains.3 Most octasubstituted phthalocyanines are
symmetrical compounds and contain two substituents on
each of the benzene rings.1a As single symmetrical com-
pounds, octasubstituted phthalocyanines are generally
less soluble in organic solvents than are the corresponding
tetrasubstituted phthalocyanines.1a Because synthesis of
octasubstituted zinc(II) phthalocyanines that have four
identical substituents in the 2-, 9-, 16-, and 23-positions,
and a different group of identical substituents at the 3-, 10-,
17-, and 24-positions affords a mixture of positional iso-
mers, these compounds could be expected to have a great-
er solubility than those with eight identical substituents.
However, 2,3,9,10,16,17,23,24-octasubstituted phthalo-
cyanines prepared from phthalonitriles with two different
substituents in the 4- and 5- positions have received rela-
tively little study, and only few derivatives have been re-
ported.4 Similar metallophthalocyanines octasubstituted
in the 1-, 3-, 8-, 10-, 15-, 17-, 22-, and 24-positions have,
however, been described more extensively in the litera-
ture.5
We recently showed that zinc(II) phthalocyanine deriva-
tives carrying amido substituents on the macrocycle can
be effectively reduced by diborane under relatively mild
conditions to give the corresponding amino phthalocya-
nines in good yields.7 Phthalocyanine 7 was readily pre-
pared by cyclotetramerization of phthalonitrile 6 in the
presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)
and zinc(II) acetate in 36% yield; lower yields were ob-
tained when hexan-1-ol was used as the solvent, and the
use of butan-1-ol as the solvent failed to give the desired
dye 7. Also, the reaction time was reduced from 30 min to
5 min when the reaction was carried out in the absence of
a solvent. Phthalocyanine 8 was synthesized in 38% yield
by the reduction of phthalocyanine 7 with diborane. Treat-
ment of phthalocyanine 8 with iodomethane at 60 °C gave
cationic phthalocyanine 9 in 81% yield.
Dyes 7–9 were characterized by means of electrospray
ionization time-of-flight (ESI-TOF) mass spectrometry,
and intermediates 2–5 were characterized by means of
electron ionization (EI) mass spectrometry at 70 eV. The
ion–molecule signal of phthalonitrile 6 was not observed
by EI mass spectrometry, but could be observed by ESI-
TOF mass spectrometry. The UV-visible absorption spec-
tra of phthalocyanines 7–9 showed Soret and Q band at
around 360 and 677 nm, respectively. The molar absorp-
tion coefficients for the monomeric forms of 7–9 in N,N-
dimethylformamide are 87890 M–1 cm–1 (lmax = 678 nm),
84660 M–1 cm–1 (lmax = 678 nm), and 66290 M–1 cm–1
A few years ago, we showed that zinc phthalocyanine de-
rivatives functionalized with both methyl and phthalimi-
domethyl or methyl and aminomethyl units on the
benzenoid rings are moderately soluble in organic sol-
vents but insoluble in water.6 To improve the amphiphilic-
ity of these compounds, we incorporated substituents
derived from the (dibutylamino)methyl group, instead of
a phthalimidomethyl or aminomethyl group, in the peri-
SYNTHESIS 2009, No. 12, pp 1975–1978
x
x.
x
x
.
2
0
0
9
Advanced online publication: 12.05.2009
DOI: 10.1055/s-0029-1216809; Art ID: M00109SS
© Georg Thieme Verlag Stuttgart · New York

1976
G. A. Gauna et al.
PAPER
tained with a TRIO 2 (EI, 70 eV) spectrometer. ESI-TOF mass
spectroscopy was used to characterize phthalocyanines 7–9. Elec-
tronic absorption spectra were recorded on a Shimadzu UV-3101
PC spectrophotometer. Fluorescence spectra were recorded on a
QuantaMaster Model QM-1 PTI spectrofluorometer. IR spectra
were recorded on a Perkin-Elmer Spectrum One FT-IR spectrome-
ter. Microanalyses were carried out by using a Carlo Erba EA 1108
elemental analyzer. Chromatography columns were prepared with
TLC Kieselgel (Merck), and aluminium oxide 90 standardized
(Merck). DMF was dried over 3-Å molecular sieves for 72 h, then
filtered and freshly distilled before use.8
O
N
Br
Br
Br
Br
a
b
NH2
O
O
1
3
2
Br
Br
Br
N
N
H
c
d
H
Br
4
1-(4,5-Dibromo-2-methylphenyl)methanamine (2)
A mixture of isoindolinedione 1 (1.0 g, 2.45 mmol) and N2H4·H2O
(0.5 mL) in EtOH (50 mL) was stirred and refluxed for 6 h, then
cooled. 1 M HCl (5 mL) was added and the mixture was heated at
100 °C for 8 h, then cooled. The precipitate was filtered off and
washed with H2O. The filtrate was evaporated in vacuo to eliminate
the solvent, and the residue was dissolved in 10% aq NaOH (20
mL), filtered, and extracted with Et2O (4 × 20 mL). The extracts
were dried (Na2SO4) and then evaporated to dryness in vacuo to
give a highly viscous oil; yield: 0.682 g (quant).
O
O
Br
Br
NC
N
N
e
f
NC
5
6
R
O
7 R =
N
N-(4,5-Dibromo-2-methylbenzyl)butanamide (3)
A soln of PrCOCl (0.6 mL, 5.78 mmol) in anhyd CH2Cl2 (20 mL)
was added dropwise to a stirred cold soln of amine 2 (0.682 g, 2.44
mmol) in anhyd pyridine (10 mL). The mixture was then stirred for
12 h at r.t. CH2Cl2 (30 mL) was added and the mixture was washed
sequentially with 1 M aq HCl (4 × 30 mL) and H2O (1 × 30 mL).
The organic phase was washed again with 5% aq NaHCO3 (2 × 30
mL) and H2O (1 × 30 mL), then dried (Na2SO4) and evaporated to
dryness in vacuo. The solid residue was dissolved in a small volume
of CH2Cl2–MeOH (9.5:0.5) and the soln was filtered through a sili-
ca gel column that had been packed and washed with the same sol-
vent. After evaporation of the solvent, the solid residue was
crystallized (MeOH–H2O); yield: 0.470 g (55%); mp 104–106 °C.
g
N
N
N
Zn
N
R
N
N
R
N
N
8 R =
N
h
R
IR (KBr): 3910, 3876, 3860, 3844, 3827, 3807, 3786, 3718, 3696,
3680, 3660, 3286, 3065, 2961, 2928, 2872, 1636, 1548, 1463, 1378,
1364, 1334, 1315, 1283, 1247, 1219, 1183, 1157, 1121, 1056, 1004,
984, 907, 894, 878, 807, 698, 652, 623, 569, 495, 462 cm–1.
1H NMR (300 MHz, CDCl3): d = 0.97 (t, J = 7.2 Hz, 3 H, CH3), 1.70
(m, 2 H, CH2CH3), 2.22 (t, J = 7.6 Hz, 2 H, CH2CH2CH3), 2.25 (s,
3 H, CH3), 4.36 (d, J = 5.7 Hz, 2 H, CH2NHCO), 7.43 (s, 2 H, Ar).
+
I–
N
9 R =
Scheme 1 Reagents and conditions: (a) H2NNH2, EtOH, reflux, 6
h, quant; (b) PrCOCl, py, r.t., 12 h, 55%; (c) B2H6, THF, r.t.,72 h,
51%; (d) PrCOCl, i-Pr2NEt, r.t., 48 h, 75%; (e) CuCN, NMP, 200 °C,
6 h, 69%; (f) Zn(OAc)2, DBU, 158 °C, 5 min, 36%; (g) B2H6, THF,
reflux, 48 h, 38%; (h) MeI, 60 °C, 48 h, 81%.
MS (EI, 70 eV): m/z (%) = 349 (17.84) [M+], 351 (7.70) [M+ + 2],
347 (8.33) [M+ – 2], 262 (100).
(lmax = 676 nm) respectively. When excited at 610 nm,
compounds 7–9 showed fluorescence emission spectra
typical of zinc phthalocyanines; at a concentration of 10–6
M in N,N-dimethylformamide the emission maxima oc-
curred at 683, 686 and 682 nm for 7–9, respectively.
Anal. Calcd for C12H15Br2NO: C, 41.29; H, 4.33; N, 4.01. Found: C,
41.15; H, 4.34; N, 4.00.
N-(4,5-Dibromo-2-methylbenzyl)butan-1-amine (4)
BF3·Et2O (25 mL) was slowly dropped into a suspension of NaBH4
(7.5 g) in diglyme (5 mL), and the resulting B2H6 was bubbled
through a suspension of amide 3 (1 g, 2.86 mmol) in anhyd THF (25
mL). The mixture was stirred for 72 h at r.t., cooled, acidified with
1 M HCl soln, poured into CH2Cl2 (30 mL), washed with H2O
(2 × 25 mL), dried (Na2SO4), and evaporated to dryness in vacuo.
The residue was dissolved in a small volume of CH2Cl2 and the soln
was filtered through a silica gel column that had been packed and
washed with the same solvent. After evaporation of the solvent, the
solid residue was crystallized (MeOH–H2O); yield: 0.493 g (51%);
mp 72–73 °C.
With regard to solubility, note that 7 and 8 are soluble in
most organic solvents. Quaternization of 8 gave com-
pound 9, which was partially soluble in dichloromethane,
methanol, and water.
To summarize, we prepared and characterized three novel
octasubstituted zinc(II) phthalocyanines. We are currently
attempting to improve the yields of the syntheses and con-
ducting photobiological studies on 7–9.
IR (KBr): 3732, 3703, 3626, 3601, 3448, 3196, 3048, 2959, 2926,
2870, 2346, 2274, 1728, 1582, 1470, 1427, 1384, 1352, 1322, 1302,
1264, 1245, 1228, 1209, 1194, 1162, 1127, 1111, 1071, 1015, 959,
918, 895, 877, 866, 826, 809, 797, 730, 687, 668, 654, 652, 606,
576, 545, 502, 454 cm–1.
Melting points were determined on an Electrothermal 9100 capil-
lary melting-point apparatus. 1H NMR spectra were recorded on a
Bruker MSL 300 spectrometer. The 1H NMR of phthalocyanines 7,
8, and 9 were recorded on a Bruker AM 500. Mass spectra were ob-
Synthesis 2009, No. 12, 1975–1978 © Thieme Stuttgart · New York

PAPER
Octasubstituted Phthalocyaninatozinc Complexes
1977
1H NMR (300 MHz, CDCl3): d = 0.87 (t, J = 7.4 Hz, 3 H, CH3), 1.25
(m, 2 H, CH2CH3), 1.62 (m, 2 H, CH2CH2CH3), 2.32 (s, 3 H, CH3),
2.71 (m, 2 H, CH2CH2CH2CH3), 3.26 (s, 1 H, NH), 3.65 (m, 2 H,
CH2NH), 7.44 (s, 1 H, Ar), 7.51 (s, 1 H, Ar).
dissolved in CH2Cl2–MeOH (5:1) and filtered through an Al2O3 col-
umn that had been packed and washed with the same solvent. Evap-
oration of the solvent gave a solid residue that was crystallized
(CH2Cl2–hexane); yield: 0.014 g (36%).
MS (EI, 70 eV): m/z (%) = 335 (2.69) [M+], 337 (1.32) [M+ + 2],
IR (KBr): 2926, 2852, 1643, 1446, 1384, 1262, 1199, 1081, 597
cm–1.
333 (1.34) [M+ – 2].
Anal. Calcd for C12H17Br2N: C, 43.01; H, 5.11; N, 4.18. Found: C,
42.90; H, 5.09; N, 4.19.
1H NMR (500 MHz, CDCl3): d = 0.90–1.05 (m, 24 H, CH3), 1.24–
1.32 (m, 8 H, CH2CH3), 1.55–1.61 (br, 8 H, CH2CH2CH3), 1.64–
1.78 (br, 8 H, CH2CH3), 2.36–2.48 (m, 8 H, CH2CH2CH3), 2.50–
2.62 (br, 12 H, CH3), 3.20–3.60 (m, 8 H, CH2CH2CH2CH3), 4.51–
4.71 (m, 8 H, CH2N), 7.32–8.23 (m, 8 H, Ar).
N-Butyl-N-(4,5-dibromo-2-methylbenzyl)butanamide (5)
A soln of PrCOCl (0.1 mL, 0.96 mmol) in anhyd CH2Cl2 (1.5 mL)
was added dropwise to a stirred cold soln of amine 4 (0.100 g, 0.30
mmol) in CH2Cl2 (1.5 mL) containing i-Pr2NEt (0.1 mL). The mix-
ture was stirred for 48 h at r.t., then CH2Cl2 (40 mL) was added and
the mixture was washed with H2O (2 × 30 mL). The organic phase
was dried (Na2SO4) and evaporated to dryness in vacuo. The residue
was dissolved in a small volume of CH2Cl2–MeOH (9:1) and the
soln was filtered through a silica gel column that had been packed
and washed with the same solvent. Evaporation of the solvent gave
a viscous oil; yield: 0.091 g (75%).
HRMS (ESI-TOF): m/z [M+] Calcd for C72H92N12O4Zn: 1255.6890;
found: 1256.6963 [M + H]+.
3,10,17,24-Tetra[(dibutylamino)methyl]-2,9,16,23-tetrameth-
ylphthalocyaninatozinc(II) (8)
BF3·Et2O (6 mL) was slowly dropped into a suspension of NaBH4
(1.8 g) in diglyme (5 mL) and the resulting B2H6 was bubbled
through a solution of amide 7 (0.024 g, 0.019 mmol) in anhyd THF
(15 mL). The mixture was refluxed for 48 h, cooled, and poured into
hexane. The blue-green precipitate was separated by centrifugation,
washed several times with H2O, dried, and then applied to an Al2O3
column that had been packed and washed with CH2Cl2–MeOH
(9.5:0.5). After evaporation of the solvent, the solid residue was
crystallized (CH2Cl2–hexane); yield: 0.009 g (38%).
IR (KBr): 3437, 2959, 2930, 2872, 1647, 1466, 1379, 1305, 1281,
1250, 1210, 1122, 1093, 1007, 937, 892, 809, 751, 598 cm–1.
1H NMR (300 MHz, CDCl3): d = 0.94 (m, 6 H, CH3), 1.33 (m, 2 H,
CH2CH3), 1.53 (m, 2 H, CH2CH2CH3), 1.74 (m, 2 H, CH2CH3), 2.21
(s, 3 H, CH3), 2.43 (t, J = 7.8 Hz, 2 H, CH2CH2CH3), 3.17 (t, J = 7.8
Hz, 2 H, CH2CH2CH2CH3), 4.59 (s, 2 H, CH2N), 7.42 (s, 2 H, Ar).
IR (KBr): 2927, 2853, 1639, 1445, 1375, 1261, 1198, 1097, 1037,
977, 801, 729, 571 cm–1.
1H NMR (500 MHz, CDCl3): d = 0.88–1.07 (m, 24 H, CH3), 1.23–
1.33 (m, 16 H, CH2CH3), 1.55–1.85 (br, 16 H, CH2CH2CH3), 2.38–
2.49 (m, 12 H, CH3), 3.39–3.61 (m, 16 H, CH2CH2CH2CH3), 4.49–
4.71 (br, 8 H,CH2N), 7.59–7.61 (br, 8 H, Ar).
MS (EI, 20 eV): m/z (%) = 405 (21.28) [M+], 407 (9.18) [M+ + 2],
403 (9.57) [M+ – 2].
Anal. Calcd for C16H23Br2NO: C, 47.43; H, 5.72; N, 3.46. Found: C,
47.30; H, 5.70; N, 3.45.
N-Butyl-N-(4,5-dicyano-2-methylbenzyl)butanamide (6)
A soln of amide 5 (0.030 g, 0.07 mmol) and CuCN (0.033 g, 0.37
mmol) in NMP (1 mL) was heated at 200 °C for 6 h under argon,
then cooled, poured into 25% aq NH4OH (3 mL), and stirred for 24
h. The soln was extracted with CH2Cl2 (4 × 30 mL), and the extracts
were washed with H2O (4 × 30 mL), dried (Na2SO4), and evaporat-
ed to dryness in vacuo. The residue was dissolved in a small volume
of CH2Cl2–MeOH (9:1) and filtered through a silica gel column that
had been packed and washed with the same solvent. Evaporation of
the solvent gave a viscous oil; yield: 0.015 g (69%).
HRMS (ESI-TOF): m/z [M+] Calcd for C72H100N12Zn: 1196.7485;
found: 1197.7563 [M + H]+.
3,10,17,24-Tetra{[dibutyl(methyl)aminiumato)methyl]-
2,9,16,23-tetramethylphthalocyaninatozinc(II) Tetraiodide (9)
MeI (1.5 mL, 25 mmol) was added to phthalocyanine 8 (0.008 g,
0.006 mmol), and the mixture was stirred for 48 h at 60 °C then
cooled to r.t. CH2Cl2 (5 mL) was added and the mixture was washed
several times with H2O. The organic phase was evaporated in vacuo
to give a blue-green solid; yield: 0.009 g (81%).
IR (KBr): 3437, 3242, 2961, 2930, 2873, 2739, 2230 (CN), 1765,
1721, 1667, 1646, 1631, 1460, 1384, 1303, 1263, 1212, 1180, 1098,
1036, 990, 946, 900, 793, 746, 725, 644, 522, 472 cm–1.
1H NMR (300 MHz, CDCl3): d = 0.94 (m, 6 H, CH3), 1.30 (m, 2 H,
CH2CH3), 1.56 (m, 2 H, CH2CH2CH3), 1.74 (m, 2 H, CH2CH3), 2.39
(t, J = 8.2 Hz, 2 H, CH2CH2CH3), 2.84 (s, 3 H, CH3), 3.39 (t, J = 7.2
Hz, 2 H, CH2CH2CH2CH3), 4.60 (s, 2 H, CH2N), 7.45 (s, 2 H, Ar),
7.63 (s, 1 H, Ar).
IR (KBr): 2929, 1741, 1647, 1457, 1261, 1100, 844, 801, 732, 700
cm–1.
1H NMR (500 MHz, CDCl3): d = 0.83–1.06 (m, 24 H, CH3), 1.28 (s,
16 H, CH2CH3), 1.60 (br, 16 H, CH2CH2CH3), 2.38–2.57 (m, 12 H,
CH3), 3.27–3.33 (br, 12 H, NCH3), 3.41–3.72 (m, 16 H,
CH2CH2CH2CH3), 4.52–4.68 (m, 8 H,CH2N), 7.45–7.80 (br, 8 H,
Ar).
HRMS (ESI-TOF): m/z [M+] Calcd for C76H112I4N12Zn: 1764.4606;
HRMS (ESI-TOF): m/z [M+] Calcd for C18H23N3O: 297.1841;
found: 1765.4681 [M + H]+.
found: 298.1914 [M + H]+.
Anal Calcd for C18H23N3O: C, 72.70; H, 7.80; N, 14.13. Found: C,
72.50; H, 7.77; N, 14.18.
Acknowledgment
This work was supported by grants from the Universidad de Buenos
Aires, Consejo Nacional de Investigaciones Científicas y Técnicas
(CONICET), and the Agencia Nacional de Promoción Científica y
Tecnológica. We wish to thank Ms Juana Alcira Valdez for techni-
cal assistance with chromatography, Mr. Diego Cobice for assis-
tance with the ESI-TOF mass spectrometry, and Prof. Rex Davis for
help with the English language.
3,10,17,24-Tetra{[butyryl(butyl)amino]methyl}-2,9,16,23-tet-
ramethylphthalocyaninatozinc(II) (7)
A mixture of 6 (0.037 g, 0.12 mmol), anhyd Zn(OAc)2 (0.037 g,
0.20 mmol), and DBU (0.4 mL, 2.68 mmol) was stirred and heated
at 158 °C for 5 min under argon, then cooled. CH2Cl2 (15 mL) was
added and the soln was washed with H2O (3 × 15 mL). The organic
phase was evaporated in vacuo to give a blue-green solid that was
Synthesis 2009, No. 12, 1975–1978 © Thieme Stuttgart · New York

1978
G. A. Gauna et al.
PAPER
(3) Strassert, C. A.; Rodriguez, M. E.; Dicelio, L. E.; Awruch, J.
J. Porphyrins Phthalocyanines 2005, 9, 361; and references
cited therein.
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Synthesis 2009, No. 12, 1975–1978 © Thieme Stuttgart · New York