Synthesis of unsymmetrical benzoporphyrazines in functional ionic liquids and formation of self-aggregates of zinc(II) pyridino[3,4]tribenzoporphyrazines in solutions

Article abstract of DOI:10.1016/j.tet.2009.01.046

Unsymmetrically substituted metal-free and metallated benzoporphyrazines including pyridino[3,4]tribenzoporphyrazinic macrocycles have been synthesized in good yields by ring expansion reactions of boron(III) subphthalocyanines with phthalonitriles in functional ammonium ionic liquids in the presence of 1,8-diazabicyclo-[5,4,0]-undec-7-ene (DBU) under different reaction conditions. The concentration dependent UV/vis, fluorescence, NMR and ESI-MS spectroscopic data indicate that zinc(II) pyridino[3,4]tribenzoporphyrazines exist as head-to-tail self-aggregates in the solution phase.

Full text of DOI:10.1016/j.tet.2009.01.046

Tetrahedron 65 (2009) 2518–2524
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of unsymmetrical benzoporphyrazines in functional ionic liquids
and formation of self-aggregates of zinc(II) pyridino[3,4]tribenzoporphyrazines
q
in solutions
*
S.M.S. Chauhan , Pratibha Kumari
Department of Chemistry, University of Delhi, Delhi 110007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 April 2008
Received in revised form 10 January 2009
Accepted 14 January 2009
Available online 20 January 2009
Unsymmetrically substituted metal-free and metallated benzoporphyrazines including pyridino[3,4]-
tribenzoporphyrazinic macrocycles have been synthesized in good yields by ring expansion reactions of
boron(III) subphthalocyanines with phthalonitriles in functional ammonium ionic liquids in the presence
of 1,8-diazabicyclo-[5,4,0]-undec-7-ene (DBU) under different reaction conditions. The concentration
dependent UV/vis, fluorescence, NMR and ESI-MS spectroscopic data indicate that zinc(II) pyr-
idino[3,4]tribenzoporphyrazines exist as head-to-tail self-aggregates in the solution phase.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Unsymmetrical benzoporphyrazines
Subphthalocyanines
Ionic liquids
Assembly
Thermal heating
Ring enlargement
Complexes
1. Introduction
ring expansion reaction of subphthalocyanine though is a selective
3
method for the synthesis of A B type benzoporphyrazines, it suffers
Tetrabenzoporphyrazines, particularly the unsymmetrically
substituted benzoporphyrazines with their special chemical,
from various drawbacks ranging from slow reaction rate, low yields,
tedious workups and the formation of other unwanted substituted
benzoporphyrazines, resulting from the statistical condensation of
the ring opening fragments from subphthalocyanine. Usually these
ring expansion reactions are widely carried out at an elevated
temperatures with high boiling solvents like dimethylsulfoxide
1
physical and optical properties have gained importance for its
2
potential application in non-linear optical materials, photody-
3
4
5
namic therapy agents, antimicrobials and other newer materials.
The applications of metallated benzoporphyrazines in materials
chemistry as semiconductors, Langmuir–Blodgett thin films and
artificial light harvesting systems are often sensitive to molecular
(DMSO),
DMSO/1-chloronaphthalene,
DMSO/chlorobenzene,
DMSO/o-dichlorobenzene and N,N-dimethylaminoethanol. In this
work we have overcome many of the above-mentioned drawbacks
and offered simple purification process for the synthesis of un-
symmetrically substituted benzoporphyrazines with high selec-
tivity. In comparison to many of the organic solvents used in the
synthesis of benzoporphyrazines, ionic liquids can be thought of as
a greener alternative. Ionic liquids as solvents find their application
6
stacking in their aggregates. The self-assembly via metal co-
7
ordination has been well constructed for porphyrin systems and
II
8
Zn –salpyr complex. In comparison to other macrocyclic systems,
few such works have been reported on such assemblies in metal-
9
lated benzoporphyrazines.
Different methods are available for the preparation of non-
10
12
centrosymmetric benzoporphyrazines and the most common one
being the ring expansion reaction of boron(III) subphthalocyanines
in various chemical and biochemical transformations. In our
previous work, we have explored the usefulness of functional
ammonium, pyridinium and imidazolium ionic liquids in the syn-
2
,11
1b
with various 1,3-diiminoisoindolines
or phthalonitriles. The
13
thesis of various metal-free and metallated phthalocyanines. As
an emphasize on ionic liquids as a greener solvent in our ongoing
12a,13,14
work,
we report a simple and efficient method to synthesize
q
The part of this work has been presented at Second International Conference on
Heterocyclic Chemistry, Jaipur, India, December 16–19, 2006.
unsymmetrically substituted metal-free and metallated benzopor-
phyrazines by the ring expansion reaction of corresponding bor-
on(III) subphthalocyanines with phthalonitriles in functional
*
Corresponding author. Tel./fax: þ91 11 27666845.
E-mail address: smschauhan@chemistry.du.ac.in (S.M.S. Chauhan).
0
040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.01.046

S.M.S. Chauhan, P. Kumari / Tetrahedron 65 (2009) 2518–2524
2519
ammonium ionic liquids in the presence of 1,8-diazabicyclo-[5,4,0]-
R1
N
R3
Br
R4
undec-7-ene (DBU) under different reaction conditions. We also
report the formation of self-aggregates of zinc(II) pyridino[3,4]-
tribenzoporphyrazines in solution via metal–nitrogen coordination
involving the pyridyl nitrogen atom of one molecule and the metal
ion of a second molecule.
R2
1
a
R = R = R = R = n-Bu, X= Br; [Bu N][Br]
1 2 3 4 4
1b
R = R = Me, R = C H OH, R = n-Bu, X= Br; [bhyeda][Br]
1 3 2 2 4 4
Figure 1. Structure of functional ionic liquids.
2
. Results and discussion
amount of DBU (Table 1, entry 4). The use of 1 to 1.5 equiv of ionic
liquid 1b in the ring enlargement reaction was found to be sufficient
to proceed the reaction, however, reaction was fast and yield was
high when ionic liquid was taken in excess (results not shown). The
sequence of addition of phthalonitriles, subphthalocyanines and
DBU in the reaction is not very specific to yield benzoporphyrazines
except in the case of 5b due to the tendency of the formation of DBU–
The cyclotrimerization of dry phthalonitrile (2a) with boron
trichloride (1 M solution in p-xylene) at reflux temperature under
nitrogen atmosphere gave chloro[subphthalocyaninato]boron(III)
(
3a) in 75% yield (Scheme 1). The UV/vis spectrum of 3a showed
15
characteristic absorption pattern, a Soret band at 304 nm and an
ꢀ
1
intense Q band at 564 nm. The appearance of a band at 950 cm
for –B–Cl stretching in the IR spectrum and two multiplets at
17
phthalonitrile adduct in the reaction.
1
8
.91 ppm and 7.96 ppm in the H NMR spectrum of 3a indicated the
The reaction of 3b with 3,4-dicyanopyridine in presence of DBU
and in absence of metal salt in ionic liquid 1b gave metal-free
benzoporphyrazine 5b in 41% yield. Unlike zinc metallated benzo-
porphyrazine 4b, the UV/vis spectrum of 5b showed two distinct Q
bands at 687 and 659 nm, and –NH stretching band appeared at
formation of a cyclotrimerized product of 2a in the reaction. The
þ
presence of a peak at m/z 454.36 corresponding to [MþNa ] in ESI-
MS spectrum further confirmed the structure of 3a. Similarly,
chloro[2,9,16(17)-trimethylsubphthalocyaninato]boron(III)
(3b),
ꢀ
1
chloro[2,9,16(17)-tri-tert-butylsubphthalocyaninato]boron(III) (3c)
and chloro[2,9,16(17)-trinitrosubphthalocyaninato]boron(III) (3d)
were synthesized in good yields and their structures were identi-
fied by different spectroscopic analyses. The nucleophilic attack of
polarized –CN to another cyano group and subsequent formation of
open trimer intermediate followed by template directed cyclization
3393 cm in the IR spectrum. It is noteworthy that the presence of
metal ion is not crucial to yield benzoporphyrazines although its
presence affords benzoporphyrazines in short time and better
yields. The present method can be utilized for the synthesis of
various metallated benzoporphyrazines using different metal salts
such as cobalt acetate.
16
is responsible for the formation of boron(III) subphthalocyanine.
The recyclability of ionic liquid 1b was examined in ring ex-
pansion reaction of 3a with 3,4-dicyanopyridine. The ionic liquid 1b
was recovered from the reaction mixture and was reused three
times for the synthesis of 4a. In second run, 4a was obtained in 48%
yield that reduced to 41% in third run. The ionic liquid 1b could be
used for conducting further runs.
The ring expansion of 3a with 3,4-dicyanopyridine in tetrabutyl-
ammonium bromide ionic liquid (1a) (Fig. 1) in presence of zinc
acetate and DBU gave tribenzo[b.g.l]pyrido[3,4,q] porphyr-
azinatozinc(II) (4a) in 51% yield (Scheme 1, Table 1, entry 1). The
similar reaction of 3a in butyl-(2-hydroxyethyl)dimethylammonium
bromide ionic liquid (1b) afforded 4a in relatively high yield (59%)
To investigate the mode of transformation of boron(III) sub-
phthalocyanine into benzoporphyrazine, UV/vis spectroscopic
analysis of the reaction was carried out. The UV/vis spectra of 3c on
(
Table 1, entry 2). The ring expansion reactions of 3b and 3c were also
compared in 1a and 1b ionic liquids. Interestingly, the yields of 4b
and 4c were found to be better in ionic liquid 1b than 1a under the
condition of experiment (Table 1, entries 3, 4, 6 and 7). The yield of 4b
and the rate of ring expansion reaction of 3b with 3,4-dicyanopyr-
idine were affected greatly by reducing the reaction temperature and
ꢁ
heating in ionic liquid 1b for 5 min at 140 C exhibited absorption
spectrum similar to that observed in chloroform with a Q band at
569 nm and a Soret band at 298 nm (see Supplementary data,
Fig. S1). On addition of 3,4-dicyanopyridine, DBU and zinc acetate
R
R
N
CN
N
N
N
N
N
[
N
M
N
CN
Zn(OAc)2]
R
N
N
R
(a-c): M = Zn, 5b: M = 2H
4
CN
CN
IL (1a-1b)
DBU
BCl3
N
N
B
N
Cl
R
N
N
R
R
CN
CN
2
(a-d)
N
N
R
R
N
N
N
N
3
(a-d)
R'
M
N
N
[
Zn(OAc)2]
a R= -H
N
b R= -CH
3
c R= -C(CH )
3
3
R'
R
d R= -NO2
6c: R' = H, M = 2H; 7d: R' = OC8H17, M = Zn
Scheme 1. Ring expansion of boron(III) subphthalocyanines 3a–3d in ionic liquids 1a,1b.

2520
S.M.S. Chauhan, P. Kumari / Tetrahedron 65 (2009) 2518–2524
Table 1
Synthesis of unsymmetrically substituted metal-free and metallated benzopor-
type of intermediate (9). The nucleophilic attack of 9 on highly
strained imine core of subphthalocyanines (3a–3c) results in an
open tetrameric intermediate (10), which on cyclization gives
metal-free benzoporphyrazines. However, in the presence of metal
ion 10 cyclizes rapidly and efficiently to yield metal-
lobenzoporphyrazines, indicating the template effect of metal ion
ꢁ
a
phyrazines (4–7) using functional ammonium ionic liquids (1a,1b) at 140
C
Entry
SubPc
Porphyrazine
Ionic liquid
Time
Yieldb (%)
1
2
3
4
5
6
7
8
9
3a
3a
3b
3b
3b
3c
3c
3c
3d
4a
4a
4b
4b
5b
4c
4c
6c
7d
1a
1b
1a
1b
1b
1a
1b
1b
1b
10 h
5 h
51
59, 48, 41c
c
30 min
20 min
35 min
25 min
20 min
25 min
20 min
49
58
(Scheme 2). Consequently, selective ring opening of 3a–3d by 9 in
d
ionic liquid 1b could be accountable for the formation of desired
unsymmetrically substituted benzoporphyrazines (4–7) in good
41
53
58
45
47
21
yields. Further, nucleophilicity, high moisture and thermal sta-
22
bility of ionic liquid 1b offer an additional advantage and act as
a promising promoter for the ring enlargement reaction of bor-
on(III) subphthalocyanines. These results justify the versatility of
ionic liquid 1b in ring expansion reaction of different sub-
phthalocyanines bearing electron withdrawing as well as electron
donating groups with various phthalonitriles affording different
unsymmetrically substituted metal-free and metallated benzopor-
phyrazines in good yields. Ionic liquid 1b can be used in statistical
condensation of two different phthalonitriles affording different
unsymmetrically substituted benzoporphyrazines in good yields
a
Reaction condition: subphthalocyanine, phthalonitrile and DBU in 1:1:1 molar
$2H O for 4a–4c and 7d in equimolar amount. Functional ammonium
ratio. Zn(OAc)
2
2
ionic liquids (1a,1b): 1.5 g for 300 mg of subphthalocyanine.
b
Isolated yields.
c
The same recovered ionic liquid 1b was used for each of the three runs. The
reaction time for second and third run was 10 h.
d
The product 4b was isolated in 42% after 2 h when the reaction was performed in
absence of DBU and only 21% yield was recorded when the reaction was carried out
at 100 C after 24 h.
ꢁ
(please refer Supplementary data, Scheme S1, Fig. S2).
in the reaction mixture, the optical spectra exhibited clear ap-
pearance of absorption bands for 4c with the concomitant gradual
disappearance of bands for 3c, indicating the ring expansion of 3a–
The self-aggregation behaviour of unsymmetrically substituted
zinc(II) benzoporphyrazines (4a–4c) in solutions were analyzed by
1
UV/vis, fluorescence, H NMR and ESI-MS spectroscopic analyses.
ꢀ
5
3
d via ring opening by nucleophilic attack of a species generated by
The UV/vis spectrum of 4c (2.54ꢂ10 M) in chloroform showed
a Soret band at 345 nm, a splitted Q band at 685 (Q ) and 667 nm
(Q ) with two vibronic satellites at 632 and 608 nm (see Supple-
phthalonitriles under the experimental conditions. This is in ac-
cordance with the nucleophilic attack of selected anionic species
x
y
ꢀ5
such as fluoride and cyanide on the
framework of subphthalocyanine macrocycle. The theoretical
calculations and studies on ring expansion of boron(III) sub-
phthalocyanines also support the above observations. As sub-
phthalocyanines do not exhibit any fluoro-chromogenic sensing
ability for bromide ion and metal ions such as Zn
p
-delocalized polyimine
mentary data, Fig. S3). At high concentrations (61.38ꢂ10 M), the
form and position of peaks in the spectrum changed, Soret band
being red shifted to 356 nm and split Q band to 695 and 664 nm.
This red shift in the spectrum is ascribed to generation of head-to-
tail self-aggregates of 4c in solution as the formation of their ag-
gregates cause significant spectral perturbations, owing to coupling
between the electronic states of individual monomeric benzopor-
18
19
2
þ 18,20
, their attack
on imine type core and involvement in ring opening of sub-
phthalocyanines has been ruled out. Rather, metal template effect
may play an important role in cyclization leading to give final
2
3
phyrazine units. It is worth mentioning that the ratio of in-
tensities of Q and Q bands was found to be sensitive to the
x
y
13b
benzoporphyrazines products.
Based on above facts, it is believed that the alkoxide ion of ionic
concentration of 4c in solution, which may be due to head-to-tail
self-organization tendency of 4c. Similar effect has been reported
for dimerization of triazole-functionalized phthalocyaninatozinc(II)
13
liquid 1b (8), generated by proton abstraction with DBU, attacks
2
4
on phthalonitrile leading to the formation of an imidoisoindoline
complex in the solution phase. Additionally, the concentration
Me
Me
H-DBU
N
O
OH
+
DBU
+
Bu
Bu
Me
N
Br
Br
Me
8
1b
N
N
C
C
R
R
R
R
N
O
N
N
NH
N
N
N
N
N
N
N
M
N
N
N
R
HN
N
N
O
HN
Cl
9
R
R
N
N
B
N
4
-7
10
N
N
N
R
R
Scheme 2. Proposed mechanism for ring expansion of subphthalocyanines 3a–3d in ionic liquid 1b.

S.M.S. Chauhan, P. Kumari / Tetrahedron 65 (2009) 2518–2524
2521
dependent UV/vis spectra of zinc(II) tetrapyridinoporphyrazine
see Supplementary data, Fig. S4), showed a great change in the
ratio of intensities of split Q bands at 672 and 662 nm in DMF,
which could be attributed to higher order zinc-coordinated self-
aggregates of the macrocycle in the solution phase.
addition of disruptor methanol or pyridine, a slight red shift with
a substantial increase in fluorescence intensity at 687 nm was ob-
served (see Supplementary data, Fig. S11). Similar changes were
observed in the fluorescence spectrum of 4b on addition of meth-
anol or pyridine (see Supplementary data, Fig. S12). However, the
concentration dependent fluorescence spectrum of 5b did not
show such changes in the spectrum. These results support the
formation of self-aggregates via pyridine-to-zinc metal co-
(
To investigate the de-aggregation of 4c, a coordinating solvent,
methanol was added, which caused a substantial increase in ab-
sorption concomitant a blue shift in the spectrum (Q band ab-
sorptions from 695 and 664 nm to 686 and 664 nm, and Soret band
absorption from 355 to 352 nm) (see Supplementary data, Fig. S5).
In addition, the vibrational satellites corresponding to monomeric
species became more distinct. The appearance of isosbestic points
at 700, 650, 625 and 375 nm further suggested the existence of
molecular self-aggregates in the solution phase. Similar results
were obtained on addition of pyridine in solution of 4c, indicating
the destruction of self-coordination from pyridyl nitrogen atom of
one molecule to central zinc ion of a second molecule, owing to
ligation of pyridine or methanol with central zinc ion. Similar
concentration dependent absorption spectrum with red shift was
recorded for 4b (see Supplementary data, Fig. S6), which exhibited
similar blue shift with distinct isosbestic points in the spectrum on
addition of methanol or pyridine (see Supplementary data, Figs. S7
6
f
ordination in 4a–4c as reported in porphyrinic systems.
Further confirmation of the formation of self-aggregates by 4a–
1
1
4c was obtained by the H NMR spectroscopy. The H NMR spec-
trum of 4c in CDCl showed broad signals with two upfield signals
for -pyridyl protons at 5.20 and 3.90, and no signal downfield of
9.32 was observed (see Supplementary data, Fig. S13). Upon ad-
dition of pyridine-d the spectrum simplified and in particular, the
-pyridyl protons of 4c now appeared at 10.71. It is believed that
3
a
d
d
5
a
d
higher oligomers may be present at the higher solution concen-
trations used in the NMR experiment. No such aggregation studies
were possible for 4a and 4b as their poor solubility in CDCl
3
makes
it difficult to record their well-resolved H NMR spectra and addi-
tion of coordinating solvents such as DMSO-d , pyridine-d in order
1
6
5
to solubilize them may disrupt their self-coordinate assemblies.
1
and S8). The change in the ratio of intensities of Q
x
and Q
y
bands in
However, the H NMR spectrum of monomeric 4a and 4b in DMSO-
the absorption spectrum of 4b in o-dichlorobenzene was more
apparently observed on addition of pyridine (see Supplementary
data, Fig. S9). No such concentration and disrupting effects were
observed in metal-free benzoporphyrazine 5b on increasing the
concentration, and thus suggesting the involvement of metal ion in
the self-assembly generation. Recently, the interaction of pyridine
and other coordinating solvents with central metal ion in tetra-
d
6
exhibited the pyridyl protons at
The existence of self-assembled molecular species of 4a–4c was
d 9.95 and 10.08, respectively.
also detected by ESI-MS analysis. The solutions of 4a–4c were
injected for mass analysis, which showed the presence of mono-
meric species at high cone voltage (>50 V) as the peaks appeared at
m/z 579.96, 621.99, 748.26, respectively, in the ESI-MS spectra. At
moderate cone voltage with tuning of other parameters like reso-
lution gas flow, capillary voltage, dissolution temperature and
source temperature, the peaks corresponding to dimeric species of
4a–4c were observed at m/z 1158.86, 1242.98 and 1495.46, re-
spectively (see Supplementary data, Figs. S14, S15 and S16). Further,
no peaks corresponding to monomeric and dimeric species of 4a–
2
5
benzoporphyrazines have been reported.
The Q band in UV/vis spectra of tetrabenzoporphyrazines cor-
2
6
responds to the lowest energetic
bands can be influenced by both the metal centre and the axial li-
gands. In metallotetrabenzoporphyrazines there is a -back-do-
nation of electrons from the metal d orbitals to the macrocycle
ligand transition energy, and therefore the Q
orbitals.27 The
band, is strongly influenced by this
troduction of axial ligands modifies the
macrocycle, and therefore the transition energy is affected.
p–
p
*
ligand transition. The Q
p
ꢀ7
4c could be recorded with their very dilute solutions (w10 M)
even by changing any parameter. Using w10 M solutions of 4a–
ꢀ5
p
*
p–
p
*
2
8
p
-back-donation. The in-
4c, the peaks corresponding to their dimeric species were recorded
in the ESI-MS spectra in the solution phase. These dimeric species
could exist in the form as shown in Scheme 3. On the other hand,
the ESI-MS spectrum of 5b (see Supplementary data, Fig. S17)
exhibited the peak at m/z corresponding to its monomeric form at
equivalent concentration by adjusting any parameter.
Further, the zinc metallated benzoporphyrazine 7d bearing an
octyloxy substituent also exhibited similar type of aggregation
behaviour in the solution phase. A blue shift in the absorption
spectrum of 7d in chloroform was observed on addition of co-
ordination disruptor methanol (see Supplementary data, Fig. S18).
It is believed that oxygen atom of alkoxy substituent coordinates
p
-back-donation to the
2
9
p
–p
*
Owing to this effect, the generation of self-coordinating assemblies
in 4a–4c via coordination of nitrogen with zinc metal caused the
changes in Q band absorbance. This suggested the existence of
metal-directed self-assembled molecular species of 4a–4c in
solution.
The fluorescence spectrum of 4c in chloroform showed maxi-
mum fluorescence intensity at 687 nm, which shifted to 681 nm
with a great intensity loss as the concentration was varied from
ꢀ
6
ꢀ5
1.47ꢂ10
to 1.205ꢂ10 M (see Supplementary data, Fig. S10).
9
c,d
These changes are in accordance with the existence of an aggregate
of zinc(II) tetrabenzoporphyrazines in solution. Upon gradual
with zinc metal in 7d as reported in the literature.
methanol disrupts the metal-directed self-assembly of 7d by
Addition of
9
c
R
R
N
N
N
N
Zn
R
N
R
N
N
N
N
N
N
R
N
N
N
N
in solution
R
N
N
M
N
N
N
N
N
N
Zn
N
N
N
R
N
R
R
Scheme 3. Possible interactions in 4a–4c in the solution phase.

2522
S.M.S. Chauhan, P. Kumari / Tetrahedron 65 (2009) 2518–2524
forming coordination bond with zinc metal, which results in im-
proved solubility of 7d in chloroform.
3.2.2. Chloro[2,9,16(17)-trimethylsubphthalocyaninato]-
3
2
boron(III) (3b)
Yield: 60%; purple solid, UV/vis (CHCl
307 (3.93), 512 (3.71), 547 (4.02), 566 nm (4.23); IR (Nujol,
1724, 1614, 1461, 1217, 1170, 1128, 1044, 960, 820, 783, 722 cm . H
NMR (300 MHz, CDCl
In conclusion, the ring enlargement of subphthalocyanines with
phthalonitriles in presence of DBU (and metal salt) yielding various
unsymmetrically substituted metal-free and metallated benzopor-
phyrazines, in hydroxylated ammonium based ionic liquid (1b), is
simple and efficient. Moreover, hydroxylated ammonium ionic
liquids are biodegradable, cost-effective and UV/vis transparent
making the study of the reaction convenient by UV/vis spectro-
scopic analysis. The present method offers various advantages such
as short reaction time, less side products, easy isolation, good yield
of products, survival of a variety of substituents and recyclability of
ionic liquid. Different substituted zinc(II) pyridino[3,4]-
tribenzoporphyrazines exist in the form of head-to-tail self-ag-
gregates generated by nitrogen-to-zinc metal coordination in
solutions.
3
,
lmax/log
3): 261 (4.02),
n
): 3062,
ꢀ1 1
3
)
d
: 8.43 (d, J¼8.1 Hz, 3H, ArH), 8.37 (m, 3H,
ArH), 7.58 (d, J¼7.8 Hz, 3H, ArH), 2.67 (s, 9H, CH
3
). ESI-MS (m/z):
þ
found (MþK ) 511.26; C27
6
H18BClN requires 472.74.
3.2.3. Chloro[2,9,16(17)-tri-tert-butylsubphthalocyaninato]-
3
3
boron(III) (3c)
Yield: 58%; purple solid; UV/vis (CHCl
514 (3.17), 548 (4.41), 568 nm (3.62); IR (Nujol,
1462, 1409, 1365, 1306, 1257, 1119, 1083, 1042, 975, 749, 721 cm
3
,
lmax/log
3): 301 (3.80),
n
): 3144, 1749, 1619,
ꢀ
1
.
1
3
H NMR (300 MHz, CDCl ) d: 8.87–8.86 (m, 3H, ArH), 8.81–8.80 (m,
3H, ArH), 8.01 (m, 3H, ArH), 1.54 (s, 27H, t-Bu). ESI-MS (m/z): found
þ
(
MþNa ) 621.98; C36
6
H36BClN requires 598.97.
3
3
. Experimental
3
.2.4. Chloro[2,9,16(17)-trinitrosubphthalocyaninato]-
31
boron(III) (3d)
.1. General
Yield: 82%; violet solid; UV/vis (CHCl
3
,
lmax/log
3): 301 (4.14),
5
26 (3.73), 543 (3.83), 575 (4.14), 585 nm (4.14). IR (Nujol,
n
): 3207,
The IR spectra were recorded on a Perkin–Elmer 1710 FTIR
spectrometer and the nmax is expressed in cm . The electronic
1780, 1625, 1606, 1538, 1462, 1346, 1307, 1185, 1104, 1078, 1040, 976,
ꢀ1
ꢀ1 1
3
840, 801, 742, 721 cm . H NMR (300 MHz, CDCl ) d: 9.78 (m, 3H,
spectra were recorded on a Perkin–Elmer Lambda-35 UV/vis
spectrophotometer and the max are expressed in nanometers. The
H NMR and C NMR spectra were recorded on Bruker Avance-300
ArH), 9.07 (m, 3H, ArH), 8.85 (m, 3H, ArH). ESI-MS (m/z): found
l
þ
(MþH ) 566.65; C24
9 9 6
H BClN O requires 565.65.
1
13
spectrometer using TMS as internal standard (chemical shifts in
ppm). The mass spectra (ESI-MS) were recorded on Micromass LCT
KC455 using electron spray positive ion mass spectra. Elemental
analyses were obtained on GmbH Vario EL-III elemental analyzing
system [CHN analyzer laboratory, University Science In-
strumentation Centre (USIC), University of Delhi, Delhi]. Fluores-
cence spectra were recorded on Shimadzu RF-5301
spectrofluorometer. The excitation and emission bandwidths were
3
.3. General procedure for the synthesis of unsymmetrically
substituted metallated benzoporphyrazines
A sample of boron(III) subphthalocyanine (3a–3d) (2 mmol) in
functional ammonium ionic liquid (1a,1b) (1.5 g for 300 mg of 3a–
ꢁ
3d) was heated at 140 C under nitrogen atmosphere for 5 min. To
the reaction mixture, phthalonitriles (2 mmol), DBU (304
2
ml,
mmol) and zinc acetate (2 mmol) were added and heating was
set at 3 nm. The R
roform/methanol, v/v) (for 7d, 1% solution CHCl
recorded on TLC plates, Kieselgel 60 F254, 25 folien 20ꢂ20 cm,
.2 mm obtained from Merk. Phthalonitrile (2a), 4-methyl-
phthalonitrile (2b), 4-tert-butylphthalonitrile (2c), 4-nitro-
phthalonitrile (2d), 3,4-dicyanopyridine, BCl (1 M solution in
f
of products (4a–4c and 5b) (10% solution chlo-
continued for appropriate time as mentioned in Table 1. The
progress of the reaction was monitored by TLC and UV/vis spec-
troscopic analysis. After the reaction, the mixture was washed
with distilled water (2ꢂ100 ml) and filtered. The solid green
product was subjected to column chromatography on silica gel
3
/DMF) were
0
3
(230–400 mesh) eluting with chloroform/methanol (varying ratio)
p-xylene) and 1,8-diazabicyclo-[5,4,0]-undec-7-ene (DBU) were
obtained from Aldrich. Tetrabutylammonium bromide was
obtained from Spectrochem Pvt. Ltd. The butyl-(2-hydroxy-
ethyl)dimethylammonium bromide ionic liquid (1b) and zinc(II)
tetrapyridinoporphyrazine were prepared according to the
methods reported by us1 and characterized by different spec-
troscopic data that concur with published data.22a,30 All reactions
ꢁ
to yield pure products. The filtrate was collected and dried at 70 C
using a rotary evaporator to recover ionic liquid 1b, which was
reused for the synthesis of unsymmetrically substituted
benzoporphyrazines.
3b
3.3.1. Zinc(II) tribenzo[b.g.l]pyrido[3,4,q]porphyrazine (4a)
Green solid; [Found: C, 64.78; H, 3.01; N, 21.88. C31
H
15
N
9
Zn
/MeOH)
): 365 (3.15), 603 (2.95), 625 (2.94),
62 (3.57), 673 nm (3.59); IR (Nujol, ): 1620, 1463, 1380, 1248,
: 9.95
(m, 2H, ArH), 9.26–8.12 (m, 13H, ArH); C NMR (75 MHz, DMSO-
: 162.50, 158.7, 152.5, 145.0, 138.9, 137.2, 134.6, 134.2, 132.7,
130.28, 129.9, 128.8, 128.3, 126.7, 122.9. ESI-MS (m/z): found
were carried out under N
2
atmosphere except mentioned. All other
f 3
requires: C, 64.32; H, 2.61; N, 21.78%]; R (50% CHCl
solvents and reagents were used as received.
0
6
.75; UV/vis (DMF, lmax/log 3
n
ꢀ
1 1
3
.2. General procedure for the synthesis of boron(III)
1152, 1054, 884, 749 cm . H NMR (300 MHz, DMSO-d
6
)
d
13
subphthalocyanines (3a–3d)
6
d ) d
3
A solution of BCl (5 ml, 1 M solution in p-xylene) was added to
þ
þ
dry phthalonitrile (2a–2d) (5 mmol) under nitrogen atmosphere.
The reaction mixture was refluxed for 30 min with stirring. The
products were isolated and purified following the literature
procedures.
(MþH ) 579.96, [2ꢂMþH ] 1158.86;
31 15 9
C H N Zn requires
578.90.
3.3.2. Zinc(II) 2(3),9(10),16(17)-trimethyltribenzo[b.g.l]-
pyrido[3,4,q]porphyrazine (4b)
3
.2.1. Chloro[subphthalocyaninato]boron(III) (3a)31
Yield: 75%; purple solid; UV/vis (CH Cl max/log
85 (3.10), 522 (3.45), 546 (3.72), 564 nm (3.96); IR (Nujol,
Green solid; [Found: C, 65.92; H, 3.51; N, 20.19. C34
requires: C, 65.76; H, 3.41; N, 20.30%]; R (50% CHCl /MeOH) 0.82;
UV/vis (DMF, max/log ): 351 (4.23), 605 (3.88), 631 (3.87), 665
(4.54), 679 nm (4.56); IR (Nujol, ): 1609, 1461, 1378, 1324, 1258,
21 9
H N Zn
2
2
,
l
3
): 304 (3.74),
): 3046,
f
3
4
n
l
3
ꢀ1 1
1
730, 1687, 1604, 1444,1382,1305,1050, 950, 808, 748, 714 cm . H
NMR (300 MHz, CDCl : 8.91 (m, 6H, ArH), 7.96 (m, 6H, ArH). ESI-
MS (m/z): found (MþNa ) 454.36; C24
n
ꢀ
1 1
3
)
d
þ
1136, 1080, 924, 823, 742, 721 cm . H NMR (300 MHz, DMSO-d
6
)
H
12BClN
6
requires 430.66.
d: 10.08 (m, 2H, ArH), 9.09–7.67 (m, 10H, ArH), 2.96–2.89 (m, 9H,

S.M.S. Chauhan, P. Kumari / Tetrahedron 65 (2009) 2518–2524
2523
CH
3
); 13C NMR (75 MHz, DMSO-d
6
)
d
: 161.6, 154.7, 151.2, 143.5,
3.5. General procedure for the study of self-aggregation in
zinc(II) pyridino[3,4]tribenzoporphyrazines (4b,4c) by UV/vis
spectroscopy
138.2, 134.9, 132.1, 130.2, 128.9, 122.8, 122.1, 107.6, 102.3, 22.1–21.0.
þ
þ
ESI-MS (m/z): found (MþH ) 621.99, (2ꢂMþH ) 1242.98;
34 21 9
C H N
Zn requires 620.98.
ꢀ
4
ꢀ3
Stock solutions of 4b (7.085ꢂ10 M), 4c (1.296ꢂ10 M) and 5b
ꢀ
4
3.3.3. Zinc(II) 2(3),9(10),16(17)-tri-tert-butyltribenzo[b.g.l]-
(7.086ꢂ10 M) were prepared in chloroform. An aliquot of 50
ml
pyrido[3,4,q]porphyrazine (4c)
from the stock solution of 4b was added to 2.5 ml of chloroform
Green solid; [Found: C, 69.32; H, 5.18; N, 16.94. C43
H
39
N
9
Zn
/MeOH)
): 350 (4.00), 606 (3.57), 632
3.56), 666 (4.22), 681 nm (4.24); IR (Nujol, ): 2921, 2852,
613, 1485, 1393, 1257, 1139, 1081, 920, 833, 749 cm
300 MHz, CDCl /pyridine-d , 3:1) : 10.71 (m, 2H, ArH), 9.52–
.28 (m, 10H, ArH), 1.81 (m, 27H, t-Bu); C NMR (75 MHz,
DMSO-d : 169.5, 154.9, 148.1, 143.7, 135.1, 130.8, 129.6, 128.3,
27.2, 125.4, 122.7, 122.5, 119.3, 115.0, 20.5–18.5. ESI-MS (m/z):
solution taken in a quartz cell and its UV/vis spectrum was recor-
ded. Further, 50 ml stock solution of 4b was added in stages to the
quartz cell and the absorption spectra were recorded in each case.
To study the effect of pyridine or methanol on head-to-face as-
requires: C, 69.12; H, 5.26; N, 16.87%]; R
.85; UV/vis (DMF, max/log
f
(2.5% CHCl
3
0
(
1
(
l
3
n
ꢀ
1 1
;
H NMR
sembly of 4b, pyridine (0.72 M) or methanol (20 ml) was added in
ꢀ
4
3
5
d
stages to 1.242ꢂ10 M solution of 4b in chloroform (3 ml) in
a quartz cell and the changes in the absorption spectra were
recorded each time. Similar experiments were performed with 4c
and 5b. Further, this study was repeated for zinc(II) tetrapyr-
idinoporphyrazine in DMF and for 7d in chloroform.
13
8
6
) d
1
þ
þ
found (MþH ) 748.26, (2ꢂMþH ) 1495.46; C43
39 9
H N Zn re-
quires 747.22.
3.6. General procedure for the study of self-aggregation in
3
.3.4. Zinc(II) 2(3),9(10),16(17)-trinitro-23(24)-octyloxytetra-
benzoporphyrazine (7d)
Green solid; [Found: C, 57.88; H, 4.23; N, 18.77. C40
requires: C, 57.12; H, 3.48; N, 18.32%]; R (50% CHCl /MeOH) 0.89;
UV/vis (DMF, max/log ): 285 (4.39), 349 (4.33), 647 (4.34), 684 nm
4.39); IR (Nujol, ): 2925, 1611, 1522, 1486, 1335, 1137, 1086, 1040,
zinc(II) pyridino[3,4]tribenzoporphyrazines (4b,4c) by
spectrofluorometry
29 11 7
H N O Zn
ꢀ
6
f
3
2.5 ml solution of 4c (1.47ꢂ10 M) in chloroform was taken in
l
3
a
quartz cell. Its concentration was slowly increased up to
ꢀ5
(
n
1.205ꢂ10 M by further addition of 4c stock solution in it. The fluo-
ꢀ
1 1
8
46, 757, 728 cm . H NMR (300 MHz, DMSO-d
), 1.73–1.29 (m, 12H, –CH
); C NMR (75 MHz, DMSO-d : 164.4, 158.7, 157.5, 155.6,
50.0, 138.7, 135.0, 133.7, 130.0, 125.0, 122.5, 119.3, 106.2, 103.7, 68.6,
1.2, 28.6, 25.3, 22.0, 13.9.
6
)
d: 8.44–7.29 (m,
rescence spectra were recorded in each case. The spectral changes on
12H, ArH), 4.10 (m, 2H, –OCH
2
2
–), 0.88 (m,
stepwise addition of pyridine solution (0.72 M) or methanol (20 ml) to
13
3
1
3
H, –CH
3
6
)
d
4c solution in chloroform were also recorded. Similar experiments
were performed with 4.97ꢂ10ꢀ M solution of 5b in chloroform.
5
3
.7. General procedure for the study of self-aggregation in
1
zinc(II) pyridino[3,4]tribenzoporphyrazine (4c) by H NMR
spectroscopy
3
.4. General procedure for the synthesis of unsymmetrically
substituted metal-free benzoporphyrazines
The benzoporphyrazine 4c (15 mg, 0.020 mmol) was dissolved
A mixture of functional ammonium ionic liquid (1b) (1.5 g for
3
in CDCl (600 ml) in a sample tube. This solution was transferred to
ꢁ
3
00 mg of 3b,3c) and DBU (304
ml, 2 mmol) was heated at 140 C
an NMR tube and aliquots of pyridine-d5 (1–3 equiv v/v) were
added to the solution in the NMR tube. The change in chemical shift
for each peak was recorded.
under nitrogen atmosphere for 5 min. To the reaction mixture,
phthalonitrile (2 mmol) followed by boron(III) subphthalocyanine
(3b,3c) (2 mmol) were added and heating was continued for
appropriate time as mentioned in Table 1. The products were
isolated and purified as mentioned above for metallobenzo-
porphyrazines.
3.8. General procedure for the study of self-aggregation in
zinc(II) pyridino[3,4]tribenzoporphyrazines (4a–4c) by ESI-MS
spectroscopy
ꢀ
ꢀ
5
3
.4.1. 2(3),9(10),16(17)-Trimethyltribenzo[b.g.l]pyrido[3,4,q]
A sample of 4c (1.64ꢂ10 M) was prepared in chloroform. The
5
ꢀ5
porphyrazine (5b)
solutions of 4a (2.43ꢂ10 M), 4b (2.49ꢂ10 M) and 5b
ꢀ5
Green solid; [Found: C, 70.75; H, 4.39; N, 21.88. C34
H
23
N
9
$H
/MeOH) 0.41;
): 340 (4.86), 606 (4.49), 635 (4.63), 659
4.97), 687 nm (4.98); IR (Nujol, ): 3393, 1618, 1032, 1099, 743,
H NMR (300 MHz, DMSO-d : 10.11–7.55 (m, 12H,
2
O
(2.23ꢂ10 M) were prepared in chloroform/methanol (99:1, v/v).
These samples were analyzed on electrospray mass spectrometer
by tuning different parameters in the instrument. The resulting
mass spectra were analyzed on the basis of m/z values.
requires: C, 70.94; H, 4.38; N, 21.90%]; R
UV/vis (THF, max/log
(
7
f 3
(50% CHCl
l
3
n
ꢀ
1
1
22 cm
;
6
) d
1
3
ArH), 2.31 (m, 9H, CH
75 MHz, DMSO-d
3
), ꢀ3.89 to ꢀ2.57 (m, 2H, –NH); C NMR
Acknowledgements
(
6
)
d
: 167.5, 148.4, 145.4, 144.8, 136.4, 134.7, 129.0,
þ
1
5
23.5, 122.9, 115.9, 113.1, 105.2, 21.4. ESI-MS (m/z): found (MþH )
P.K. and S.M.S.C. acknowledge CSIR and DST for financial support.
Supplementary data
58.63; C34
23 9
H N requires 557.61.
3
.4.2. 9(10),16(17),23(24)-Tri-tert-butyltetrabenzoporp-
34
hyrazine (6c)
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2009.01.046.
Green solid; [Found: C, 77.08; H, 6.04; N, 16.68. C44
quires: C, 77.39; H, 6.20; N, 16.41%]; UV/vis (CHCl max/log
4.98), 602 (4.45), 643 (4.64), 662 (5.04), 694 nm (5.07). IR (Film,
H
42
N
8
re-
): 337
):
419, 2957, 2919, 2850,1540,1489,1463,1394,1362,1215,1190,108,
3
,
l
3
(
n
References and notes
3
9
8
ꢀ
1 1
08, 848, 759 cm
.
H NMR (CDCl
3
)
d
: 9.12–8.32 (m, 8H, ArH),
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