A novel modular approach to triazole-functionalized phthalocyanines using click chemistry

Article abstract of DOI:10.1021/jo802078f

(Chemical Equation Presented) A novel, elegant, and significantly improved protocol for the synthesis of a protected octaacetylene phthalocyanine is described. Inexpensive, mild, and environmentally benign iodination of 1,2-dibromobenzene and subsequent optimized chemoselective palladium-catalyzed cyanation are employed to effectively build up the key intermediate 4,5-dibromophthalonitrile in two steps. Introduction of the tert- butyldimethylsilyl-protected acetylene moieties via a Sonogashira cross-coupling provides the desired phthalonitrile precursor that, after cyclization, yielded the protected octaacetylene phthalocyanine. Subsequently, in situ deprotection and "clicking" are employed as a highly efficient and quantitative route to a novel class of octatriazole-functionalized phthalocyanines. The ability of such triazole-derived phthalocyanines to form well-defined supramolecular structures upon doping with zinc(II) triflate is demonstrated.

Full text of DOI:10.1021/jo802078f

A Novel Modular Approach to Triazole-Functionalized
Phthalocyanines Using Click Chemistry
Michal Jur´ıcˇek,† Paul H. J. Kouwer,† Juraj Reha´k,† Joseph Sly,‡ and Alan E. Rowan*,†,§
Institute for Molecules and Materials, Radboud UniVersity Nijmegen, ToernooiVeld 1, 6525 ED Nijmegen,
The Netherlands, and IBM Almaden Research Center, 650 Harry Road, San Jose, 95120 California
a.rowan@science.ru.nl
ReceiVed September 19, 2008
A novel, elegant, and significantly improved protocol for the synthesis of a protected octaacetylene
phthalocyanine is described. Inexpensive, mild, and environmentally benign iodination of 1,2-
dibromobenzene and subsequent optimized chemoselective palladium-catalyzed cyanation are employed
to effectively build up the key intermediate 4,5-dibromophthalonitrile in two steps. Introduction of the
tert-butyldimethylsilyl-protected acetylene moieties via a Sonogashira cross-coupling provides the desired
phthalonitrile precursor that, after cyclization, yielded the protected octaacetylene phthalocyanine.
Subsequently, in situ deprotection and “clicking” are employed as a highly efficient and quantitative
route to a novel class of octatriazole-functionalized phthalocyanines. The ability of such triazole-derived
phthalocyanines to form well-defined supramolecular structures upon doping with zinc(II) triflate is
demonstrated.
Introduction
analogues of nature’s porphyrins have recently attracted an
increasing interest as building blocks for the construction of
molecular devices such as organic field effect transistors,6,7
optical switching and limiting devices,8,9 sensors,6,7 organic
light-emitting devices,10 low band gap molecular solar cells,11,12
Phthalocyanines (Pcs)1-5 belong to a “magic pool” of com-
pounds that are an inevitable part of modern science. Man’s
† Radboud University Nijmegen.
‡ IBM Almaden Research Center.
§ Phone: +31-(0)24-36-52323. Fax: +31-(0)24-36-52929.
(1) Phthalocyanines: Properties and Applications; Leznoff, C. C., Lever,
A. B. P., Eds.; VCH: Weinheim, 1989; Vol. 1, 1993; Vols. 2 and 3, and 1996;
Vol. 4.
(6) Bouvet, M. Anal. Bioanal. Chem. 2006, 384, 366–373.
(7) Mabeck, J. T.; Malliaras, G. G. Anal. Bioanal. Chem. 2006, 384, 343–
353.
(8) O’Flaherty, S. M.; Hold, S. V.; Cook, M. J.; Torres, T.; Chen, Y.; Hanack,
M.; Blau, W. J. AdV. Mater. 2003, 15, 19–32.
(9) Dini, D.; Barthel, M.; Schneider, T.; Ottmar, M.; Verma, S.; Hanack, M.
Solid State Ionics 2003, 165, 289–303.
(2) Phthalocyanine Materials. Synthesis, Structure and Function; McKeown,
N. B., Ed.; Cambridge University Press: Cambridge, 1998.
(3) de la Torre, G.; Nicolau, M.; Torres, T. In Supramolecular PhotosensitiVe
and ElectroactiVe Materials; Nalwa, H. S., Ed.; Academic Press: New York,
2001; pp 1-111.
(10) Hohnholz, D.; Steinbrecher, S.; Hanack, M. J. Mol. Struct. 2000, 521,
231–237.
(4) The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guillard, R.,
Eds.; Academic Press: San Diego, 2003; Vols. 15-20.
(5) de la Torre, G.; Claessens, C. G.; Torres, T. Chem. Commun. 2007, 2000–
2015.
(11) Claessens, C. G.; Hahn, U.; Torres, T. Chem. Rec. 2008, 8, 75–97.
(12) (a) Cid, J.-J.; Yum, J.-H.; Jang, S.-R.; Nazeeruddin, M. K.; Mart´ınez-
Ferrero, E.; Palomares, E.; Ko, J.; Gra¨tzel, M.; Torres, T. Angew. Chem., Int.
Ed. 2007, 46, 8358–8362. (b) And references cited therein.
10.1021/jo802078f CCC: $40.75
Published on Web 11/26/2008
2009 American Chemical Society
J. Org. Chem. 2009, 74, 21–25 21

Jur´ıcˇek et al.
SCHEME 1. Postmodification of Octaacetylene Pc 1 via Click Chemistry Using Dodecylazide as a Model Substrate: Traces
Yielding Clicking of 1a (Right) and Efficient in Situ Deprotection and Clicking of 1b (Left)
SCHEME 2. Three-Step Harsh Original Procedure (Top)
and a New Two-Step Route (Bottom) Affording the Key
Intermediate 3
nonlinear optical materials,8,13 etc. This is due to their outstand-
ing dye properties and the ability to self-assemble, by means
of π-π interactions, into highly ordered arrays that can be tuned
by careful design of their periphery (e.g., equipping them with
specific molecular-recognition sites). These arrays exhibit unique
photophysical and (opto)electronic properties as a result of
excitonic interactions between adjacent dye units.14
In spite of their enormous potential, the synthesis of large
Pcs bearing sensitive functional groups remains a challenge.
This drawback arises from the fact that cyclic rearrangement
of the corresponding precursors (e.g., phthalonitriles, phthal-
imides, etc.) to form Pcs usually requires high reaction tem-
peratures (>140 °C) and a presence of a strong nucleophile.
Moreover, yields of functionalized Pcs obtained in such a way
are in many cases unsatisfactory and purifications cumbersome.
Another frequently overlooked drawback is that the synthetic
routes toward substituted phthalonitrilessthe most commonly
used precursors to Pcssare limited to few reactions only, and
these are exclusively indelicate. Most often they are synthesized
by cyanation of corresponding ortho-substituted aryl halides
requiring the use of highly toxic (NaCN, KCN) or heavy metal
containing (CuCN, Zn(CN)2) cyanide sources and/or high
temperatures (150-250 °C) to obtain reasonably good yields.
This significantly lowers an overall efficiency when cyanation
cannot be employed prior to incorporation of sensitive functional
groups.15
In order to overcome these problems, we have been looking
for an alternative: a general and relatively easily applicable route
toward functionalized Pcs that would also be suitable for
sensitive groups. The recently discovered copper(I)-catalyzed
modification of the 1,3-dipolar cycloaddition of azides and
alkynes leading to 1,2,3-triazole derivatives,16 belonging to the
pool of “click chemistry” reactions,17 is an excellent candidate
for efficient postmodification. Moreover, the synthesis of
octaacetylene Pc 1a and its protected analogue 1b,18 as well as
an example of application of click chemistry in phthalocyanine
postmodification19 have recently been reported. Here, we would
like to describe our recently developed approach to octatriazole-
functionalized Pcs using copper(I)-catalyzed cycloaddition of
azides to octaacetylene Pc 1 (Scheme 1). A novel and sig-
nificantly improved protocol for the preparation of 1 is also
reported.
Results and Discussion
In the previously reported original synthesis of 1, Leznoff et
al. introduced 4,5-diiodophthalonitrile (3a) as a key intermediate
to attach acetylene moieties.18,20 Since the original three-step
proceduresstarting from phthalimidesinvolved a harsh iodi-
nation step (reflux in fuming sulfuric acid) and a multistep
poorly reproducible crystallization procedure of the correspond-
ing product (from a mixture containing hydrolysis products of
the phthalimide moiety), we have designed and optimized a
novel two-step route to the analogous 4,5-dibromophthalonitrile
(3b), starting from a commercially available 1,2-dibromoben-
zene and using the cheapest iodination method to date followed
by subsequent chemoselective cyanation (Scheme 2).
Aromatic iodides are widely used in organic synthesis, and
many different synthetic methods have been reported for their
effective preparation. However, direct iodination methods of
deactivated arenes are less numerous and include use of
expensive (silver salts, triflic acid) or hazardous (fuming sulfuric
(13) de la Torre, G.; Va´zquez, P.; Agullo´-Lo´pez, F.; Torres, T. Chem. ReV.
2004, 104, 3723–3750.
(14) Elemans, J. A. A. W.; van Hameren, R.; Nolte, R. J. M.; Rowan, A. E.
AdV. Mater. 2006, 18, 1251–1266.
(15) Sly, J.; Kasa´k, P.; Gomar-Nadal, E.; Rovira, C.; Go´rriz, L.; Thodarson,
P.; Amabilino, D. B.; Rowan, A. E.; Nolte, R. J. M. Chem. Commun. 2005,
1255–1257.
(16) (a) Tornøe, C. W.; Christensen, C.; Meldal, M. J. Org. Chem. 2002,
67, 3057–3062. (b) Rostovtsev, R. R.; Green, L. G.; Fokin, V. V.; Sharpless,
K. B. Angew. Chem. 2002, 114, 2708-2711; Angew. Chem., Int. Ed. 2002, 41,
2596-2599.
(17) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed. 2001,
40, 2004–2021.
(19) Campidelli, S.; Ballesteros, B.; Filoramo, A.; D´ıaz D´ıaz, D.; de la Torre,
G.; Torres, T.; Rahman, G. M. A.; Ehli, C.; Kiessling, D.; Werner, F.; Sgobba,
V.; Guldi, D. M.; Cioffi, C.; Prato, M.; Bourgoin, J.-P. J. Am. Chem. Soc. 2008,
130, 11503–11509.
(18) Leznoff, C. C.; Li, Z.; Isago, H.; d’Asciano, A. M.; Terekhov, D. S. J.
Porphyrins Phthalocyanines 1999, 3, 406–416.
(20) Terekhov, D. S.; Nolan, K. J. M.; McArthur, C. R.; Leznoff, C. C. J.
Org. Chem. 1996, 61, 3034–3040.
22 J. Org. Chem. Vol. 74, No. 1, 2009

Modular Approach to Triazole-Functionalized Pcs
SCHEME 3. Iodination of 1,2-Dibromobenzene Using
Strongly Electrophilic I+ Intermediates
negative effect on the yield of the desired product (entries 2, 3,
and 4), which is in agreement with the observations reported in
the literature,22 where a higher concentration of the cyanides
in the solution led to the formation of palladium(II) cyanide
species which are almost inactive in a cyanation reaction. Thus,
only a slight excess (2.4 equiv/2.8 equiv in the case of multiple
additions) of cyanide species was used for further experiments.
Crucial parameters for cyanation of ortho-substituted aryl
halides are the reaction time and temperature. Typically, longer
reaction times (>1 day) and higher temperatures (>120 °C)
are required for effective cyanation. However, the cyclic
rearrangement of phthalonitriles to form phthalocyanines (or
polymerization) that occurs under similar conditions makes the
reaction very delicate. We investigated the influence of the
reaction time on the yield of the desired product (entries 5, 7,
and 9). We found that prolongation of the reaction time after
48 hswhen maximum (73%) efficiency was achievedsled to
partial decomposition of the product, and in the final case (entry
11) no product could be isolated at all.
To further increase the yield of 3b we applied stepwise
addition of the catalyst and cyanide source (entries 8 and 10).
This, however, led to the decrease of the reaction yield of 3b
probably due to contamination of the system with oxygen during
the addition. A significant effect of an additive was observed.
Addition of 1 equiv of pyridine to the reaction mixture led to
an 18% increase of the yield of 3b as a result of the increased
reactivity of the Zn(CN)2/pyridine complex (entries 6 and 7).
Sonogashira cross-coupling was used to attach acetylene
moieties at positions 4 and 5 of 3b. Due to the lower reactivity
of 3b compared to 3a, reflux and a prolonged reaction time
were necessary to obtain comparable yields of 6. Moreover,
due to the fragility of the acetylenes (even those protected with
a bulky tert-butyldimethylsilyl groups) to hard nucleophilic
alkoxides that are widely used in phthalocyanine synthesis, an
alternative route using gaseous ammonia was proposed by
Leznoff et al. in the synthesis of 1a, providing after zinc
insertion its protected derivative 1b in 24% yield.18 In order to
make this route synthetically more attractive, we performed the
cyclic rearrangement of 6 in an analogous manner to the
previously described cyclizations of acetylene-containing ph-
thalonitriles23 using ZnCl2 as a template. This resulted in a
significantly improved efficiency of this reaction affording 1b
in 65% yield. Deprotection of 1b using an excess of TBAF
afforded 1a in quantitative yield24 (in overall 37% yield starting
from 1,2-dibromobenzene) (Scheme 4).
TABLE 1. Palladium-Catalyzed Cyanation of 4a
yield (%)c
entry
M
CN (equiv)
Ad.b
t (h)
t (°C)
3b
5
4
1d
2
3
4
5
6
7
8
9
K
2.0
3.0
6.0
8.0
2.4
2.4
2.4
2.8e
2.4
2.8e
2.8e
CuI
py
py
py
py
-
py
py
py
py
py
72
16
8
70
110
120
120
120
120
120
120
120
120
130
10
30
20
15
61
55
73
47
65
52
0
20
20
15
11
13
25
4
60
40
55
64
17
10
1
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
Zn
16
36
48
48
48
60
60
90
6
0
f
f
f
10
11
0
0
0
a 4 (1 equiv), Pd(PPh3)4 (0.01 equiv), and DMF. b Additive: CuI (0.01
equiv) or pyridine (1 equiv). c Isolated yield. d THF was used as a
solvent. e Catalyst (0.012 equiv) and cyanide were added in two
portions. f Yield not determined.
acid, iodine(I) chloride) reagents.21 Recently, an easy, inexpen-
sive, and effective oxidative iodination of deactivated arenes
in 90% (v/v) concentrated sulfuric acid has been described using
strongly electrophilic I+ intermediates, simply generated from
diiodine and NaIO3 as an oxidant.21a We used and optimized
these reaction conditions for diiodination of 1,2-dibromobenzene
to afford 1,2-dibromo-4,5-diiodobenzene (4) in >90% yield
(Scheme 3). We discovered that low temperature (0 °C) and
vigorous stirring were important parameters to obtain high
selectivity (iodination takes place preferably at positions 4 and
5), and the crude product could be easily separated from the
reaction mixture by filtration. Furthermore, since 2 equiv of I+
intermediates was sufficient for complete conversion (otherwise
a product of trisubstitution was formed in the reaction mixture
which complicated purification of the product), the reaction
waste only composed of the NaHSO4/H2SO4 mixture could be
disposed after dilution without a problem.
To provide the key intermediate 3b, the scope and limitations
of chemoselective cyanation of 4 were investigated. Since
aromatic iodides are significantly more reactive in transition
metal catalyzed cross-coupling reactions than bromides, pal-
ladium-catalyzed cyanation22a of 4 was chosen and optimized
for the preparation of 3b. An overview of the results is
summarized in Table 1.
Despite the poor solubility of 1a in all organic solvents, we
decided to investigate the possibility of its use as a unique
precursor for preparation of a wide spectrum of novel triazole-
functionalized Pcs via click chemistry. Not only would such
an approach represent a highly efficient, mild, and selective way
to potentially interesting Pc derivatives (including those bearing
sensitive groups) but also building in of a triazole moiety (stable
heterocyclic ligand) could open up new pathways to the
controlled self-organization of such molecules upon doping with
Lewis acids (e.g., metals) at the supramolecular level. Moreover,
plausible oxidative coupling through the carbon atoms of two
Initially, we compared two of the most commonly used
catalyzed cyanation procedures (entries 1 and 2). Prompted by
the promising result of the latter (50% conversion of 4 to the
mono- and bisubstituted products), we decided to optimize these
reaction conditions. Increasing the amount of a cyanide had a
(22) (a) Sundermeier, M.; Zapf, A.; Beller, M. Eur. J. Inorg. Chem. 2003,
3513–3526. (b) And references cited therein.
(23) Maya, E. M.; Haisch, P.; Va´zquez, P.; Torres, T. Tetrahedron 1998,
54, 4397–4404.
(24) Precipitation in methanol instead of column chromatography was used
as a purification technique due to restricted solubility of 1a which also prevents
characterization of the compound.
(21) (a) Kraszkiewicz, L.; Sosnowski, M.; Skulski, L. Tetrahedron 2004,
60, 9113–9119. (b) And references cited therein.
J. Org. Chem. Vol. 74, No. 1, 2009 23

Jur´ıcˇek et al.
SCHEME 4a
a (a) 3a, tert-butyldimethylsilylacetylene, Pd(PPh3)4, CuI, Et3N, r.t., 14 h,
90%.18 (b) 3b, tert-butyldimethylsilylacetylene, Pd(PPh3)4, CuI, Et3N, reflux,
36 h, 87%. (c) i NH3, DMAE, reflux, 4 h, ii Zn(OAc)2, DMF, toluene,
reflux, 12 h, 24%.18 (d) ZnCl2, DMAE, reflux, 12 h, 65%. (e) TBAF, THF,
r.t., 12 h, quantitative.18,24
triazoles in ortho position in 2 would afford a flat superconju-
gated Pc system that is expected to absorb in near-infrared.
Copper(I)-catalyzed cycloaddition of azides and alkynes is
an extremely versatile reaction that can proceed even in
heterogeneous systems (i.e., in systems where either catalyst
or substrates have restricted solubility). Unfortunately, this was
not the case when 1a was treated with dodecylazide and a
copper(I) catalyst to provide 2 (Scheme 1). The reaction
proceeded very slowly, and only traces of product were detected
even after few weeks. This could be because of extremely low
solubility of 1a which forms unreactive aggregates where the
formation of copper(I) acetylide(s) (first step in the proposed
mechanism of click cycloaddition)16b cannot occur. To prevent
this problem, we decided to use an in situ deprotection and
clicking approach where 1b (soluble protected analogue of 1a)
was treated with TBAF in the presence of a copper(I) species
so that formation of copper(I) acetylide(s) of 1a could occur
prior to aggregation and precipitation of 1a. In this case,
“activated” 1a with an unspecified number of acetylenes bearing
copper(I) instead of a proton precipitated out and quantitatively
(each acetylene of 1a underwent cycloaddition)25 reacted with
dodecylazide over a period of 24 h. Strict oxygen-free conditions
were crucial to obtain pure 2, otherwise broadening and a red
shift of UV-vis absorption maximum of 2 were observed, which
were attributed to the partial oxidative coupling of neighboring
groups in 2 extending the π conjugation of the Pc.26,27
2a was isolated by precipitation from CH2Cl2 in MeOH and
characterized by 1H NMR (significant broadening of the peaks
indicated very strong aggregation that could be suppressed by
addition of TFA),28 UV, IR (showing complete disappearance
of acetylene stretches), and MALDI-TOF mass spectrometry
techniques.
FIGURE 1. (a) UV-vis titration of 2 ([Pc]0 ) 6.76 µM) with Zn(OTf)2
in THF and (b) Job plot at absorption maximum of the complex (657 nm).
shift is indicative of a cofacial geometry, the precise architecture
of which is currently being investigated.
Conclusion
In summary, a novel improved protocol for the synthesis of
1a using mild, easy, and inexpensive iodination of 1,2-di-
bromobenzene and subsequent chemoselective cyanation has
been reported. Although 1a does not undergo copper(I)-
catalyzed click cycloadditions with azides due to solubility
restrictions, an in situ deprotection and clicking procedure of
its protected derivative 1b has been developed to overcome this
problem. Using this method, octatriazole Pc 2 was synthesized
in an excellent yield for the first time. Upon the basis of the
demonstrated versatility of click chemistry, this route is of great
potential for the highly efficient, mild, and easy construction
of novel functionalized Pcs, in particular those bearing sensitive
groups. In addition, preliminary studies show the ability of 2
to form well-defined supramolecular structures upon doping with
zinc(II) triflate.
As previously mentioned, 2 could serve as a model compound
for controlling the self-assembly properties of triazole-deriva-
tized Pcs upon doping with Lewis acids. To illustrate this, 2
was successfully titrated with zinc(II) triflate, and this process
was monitored using UV-vis spectroscopy. The resulting
titration curves together with the Job plot are depicted in Figure
1. To our surprise, these preliminary results showed that 2 forms
a very well-defined 1:1 complex with zinc(II) triflate as seen
by a significant blue shift of the absorption maximum (697 to
657 nm) and a precise isosbestic point. The former absorption
Experimental Section
General. All chemicals and solvents were purchased from
commercial sources and used without further purification unless
stated otherwise. Solvents were distilled prior to use: THF (Na),
CH2Cl2, 2-(dimethylamino)ethanol (DMAE), Et3N, MeOH, and
pyridine (CaH2). All cross-coupling and click reactions were
performed under an argon atmosphere using Schlenk techniques
and deoxygenated solvents (freeze-pump-thaw in three cycles,
<0.4 mbar). For more detailed instructions and instrumentation,
see Supporting Information.
(25) We believe that a certain number of molecules of dodecylazide reacted
with insoluble copper(I)x derivative of 1a and thereby solubilized it. Remaining
“free” acetylenes underwent copper(I) acetylide formation and subsequent
cycloaddition with dodecylazide in solution.
(26) Optimizing conditions for controlled and quantitative oxidative coupling
of ortho-bis(triazole) moieties in 2 are currently under intense investigation.
(27) Angell, Y.; Burgess, K. Angew. Chem., Int. Ed. 2007, 46, 3649–3651.
(28) The reduced aggregation of 2 is a result of mutual electrostatic repulsion
between the positively charged protonated Pcs.
24 J. Org. Chem. Vol. 74, No. 1, 2009

Modular Approach to Triazole-Functionalized Pcs
1,2-Dibromo-4,5-diiodobenzene (4). A mixture of a fine-
grounded I2 (3.43 g, 13.5 mmol), NaIO3 (1.34 g, 6.76 mmol), and
160 mL of 90% H2SO4 (v/v) was stirred at 40 °C for 1 h in the
dark. The resulting dark solution was then cooled to 0 °C, and 1,2-
dibromobenzene (4.00 g, 16.9 mmol) was added in one portion.
The solution was vigorously stirred at 0 °C for 4 h before it was
poured on ice (400 g). The white precipitate was filtered off and
washed with an excess of water (1 L) before it was dissolved in
chloroform (0.5 L), washed with 10% aq. NaHSO3, and dried over
Na2SO4. After filtration, the solvent was evaporated and the residue
dried under vacuum to give 8.16 g of the crude product. Crystal-
lization from chloroform/hexanes or chromatography over a short
plug of silica (hexanes) afforded pure product as a white crystalline
solid in >90% yield. Characterization was in agreement with the
literature.29
Procedure for Cyanation of 4 using KCN. 4 (1.0 g, 2.05
mmol), KCN (0.27 g, 4.10 mmol), CuI (0.039 g, 0.205 mmol),
and Pd(PPh3)4 (0.24 g, 0.205 mmol) were placed in a Schlenk tube
equipped with a stirrer, and the system was evacuated and filled
with argon in three cycles. After THF (25 mL) was added with a
syringe, the mixture was heated to reflux for 72 h under an argon
atmosphere. The reaction was quenched using 10% aq. NH3, and
the crude products were extracted with chloroform. The combined
organic layers were washed with 10% aq. NH4Cl and dried over
Na2SO4. After filtration, the solvent was evaporated, and the residue
was purified by chromatography over silica gel using hexane/
dichloromethane 4/1 and 2/1 as eluents.
General Procedure for Cyanation of 4 using Zn(CN)2. 4 (1.0
mmol), Zn(CN)2, and Pd(PPh3)4 (0.10 mmol) were placed in a
Schlenk tube equipped with a stirrer, and the system was evacuated
and filled with argon in three cycles. After DMF (20 mL, extra
dry, <0.01% H2O) and pyridine (1 mmol) were added with a
syringe, the mixture was heated under an argon atmosphere. The
reaction was quenched using 10% aq. NH3, and the crude products
were extracted with chloroform. Combined organic layers were
washed with 10% aq. NH4Cl and dried over Na2SO4. After filtration,
the solvent was evaporated, and the residue was purified by
chromatography over silica gel using hexane/dichloromethane 4/1
and 2/1 as eluents.
4,5-Bis(tert-butyldimethylsilylethynyl)phthalonitrile (6). 3b
(0.56 g, 1.96 mmol), tert-butyldimethylsilylacetylene (0.73 g, 5.20
mmol), CuI (0.15 g, 0.785 mmol), and Pd(PPh3)4 (0.23 g, 0.196
mmol) were placed in a Schlenk tube equipped with a stirrer, and
the system was evacuated and filled with argon in three cycles.
After Et3N (25 mL) was added with a syringe, the mixture was
heated to 60 °C for 36 h under an argon atmosphere. The reaction
was quenched using 10% aq. NH3, and the crude product was
extracted with chloroform. Combined organic layers were washed
with 10% aq. NH4Cl and dried over Na2SO4. After filtration, the
solvent was evaporated and the residue purified by chromatography
over silica gel using hexane/CH2Cl2 2/1 as eluent to afford 0.69 g
(87% yield) of the product as an off-white solid. Characterization
was in agreement with the literature.18
2,3,9,10,16,17,23,24-Octakis(tert-butyldimethylsilylethy-
nyl)phthalocyanato Zinc(II) (1b). A mixture of 6 (525 mg, 1.30
mmol), ZnCl2 (44.2 mg, 0.325 mmol), and DMAE (4 mL) was
heated to 140 °C overnight. The solvent was evaporated, and the
residue was dried under vacuum. Column chromatography over
silica (CHCl3 followed by CHCl3/EtOH 99/1) and crystallization
from CH2Cl2/MeOH afforded 355 mg (65% yield) of the product
as a dark green solid. Characterization was in agreement with the
literature.18
2,3,9,10,16,17,23,24-Octakis(1-dodecyl-1H-1,2,3-triazole-4-
yl)phthalocyanato Zinc(II) (2). 1b (17.3 mg, 0.0103 mmol),
dodecylazide (138 mg, 0.658 mmol), and CuI (62 mg, 0.329 mmol)
were placed in a Schlenk tube equipped with a stirrer, and the
system was evacuated and filled with argon in three cycles. Then
THF (10 mL) and 1,1,4,7,7-pentamethyldiethylenetriamine (114 mg,
0.658 mmol) were added with a syringe, and the mixture was
stirred until all CuI dissolved (10 min). TBAF (1 M, 0.66 mL)
was added dropwise (the first portion of 0.11 mL over 1 h and the
second portion of 0.55 mL over 1.5 h), and the reaction mixture
was stirred for 24 h under an argon atmosphere before it was
quenched with 10% aq. NH3. The crude product was extracted with
CH2Cl2, and the combined organic layers were washed with 10%
aq. NH4Cl and dried over Na2SO4. After filtration, the solvent was
evaporated, and the desired product was obtained after five
precipitations from CH2Cl2 in MeOH as a dark green solid in >90%
yield. IR (neat, cm-1) 2956, 2922, 2851, 1258, 1094, 1017, and
1
798. UV-vis (THF) 698, 665, 629, and 370 nm. H NMR (500
MHz, CDCl3 + TFA) δ 9.98 (br, 8H, CAr-H), 8.74 (br, 8H, CAr-
H), 4.72 (br, 16H, CH2), 2.16 (br, 16H, CH2), 1.45-1.30 (br, 144H,
CH2), 0.88 (br, 24H, CH3). MALDI-TOF MS m/z calcd for
C
144H216N32Zn + H+ 2458.72, found 2458.96. GPC (THF): tR
)
8.42 min, Mn ) 2566 g/mol, Mw/Mn ) 1.12.
Acknowledgment. Marie Curie Research Training Network
CHEXTAN (MRTN-CT-2004-512161), (A.E.R.) Vidi and Vici,
Nanoned Funding, and NWO Nederlands are gratefully ac-
knowledged for financial support. We thank Ja´n Lauko for the
synthesis of dodecylazide.
Supporting Information Available: Complete Experimental
Section including characterization of all compounds, copies of
1H NMR (5, 2) and 13C NMR (5) spectra, copies of IR (1b, 2),
UV-vis (1b, 2), MALDI-TOF (2) spectra, and GPC chromato-
grams (1b, 2). This material is available free of charge via the
Internet at http://pubs.acs.org.
ˇ
(29) Miljanic´, O. S.; Vollhardt, K. P. C.; Whitener, G. D. Synlett 2003, 29–
34.
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J. Org. Chem. Vol. 74, No. 1, 2009 25