Synthesis of a new trans-A2B2 phthalocyanine motif as a building block for rodlike phthalocyanine polymers

Article abstract of DOI:10.1021/jo052122l

Polyphthalocyanines have potential application in the development of electronic materials. One-dimensional polyphthalocyanines are accessible through monomers having a trans-A₂B₂ structure, but the preparation of a truly linear polyphthalocyanine is challenging because of limitations imposed by the geometry of phthalocyanines and the methodology for their synthesis. Benzimidazoporphyrazines are a known class of extra-annulated phthalocyanines. A trans-A₂B₂ benzimidazoporphyrazine is geometrically suitable for the preparation of rodlike polymers. A new synthesis of benzimidazoporphyrazines is presented as a stepping stone to the synthesis of trans-A₂B₂ benzimidazoporphyrazines.

Full text of DOI:10.1021/jo052122l

Synthesis of a New trans-A2B2 Phthalocyanine Motif as a Building
Block for Rodlike Phthalocyanine Polymers
W. Justin Youngblood*
Department of Chemistry, North Carolina State UniVersity, Raleigh, North Carolina 27695-8204
wjy2@psu.edu
ReceiVed October 10, 2005
Polyphthalocyanines have potential application in the development of electronic materials. One-dimensional
polyphthalocyanines are accessible through monomers having a trans-A2B2 structure, but the preparation
of a truly linear polyphthalocyanine is challenging because of limitations imposed by the geometry of
phthalocyanines and the methodology for their synthesis. Benzimidazoporphyrazines are a known class
of extra-annulated phthalocyanines. A trans-A2B2 benzimidazoporphyrazine is geometrically suitable for
the preparation of rodlike polymers. A new synthesis of benzimidazoporphyrazines is presented as a
stepping stone to the synthesis of trans-A2B2 benzimidazoporphyrazines.
Introduction
routes to ordered Pc materials can vary widely. These routes
include sublimation of phthalocyanines into crystalline layers,10-12
Langmuir-Blodgett film formation,13,14 mesomorphism,15,16 and
backbone polymerization.17-22
Phthalocyanine dyes are explored for use in diverse applica-
tions such as textile colorants,1 nonlinear optical generation and
limiting,2,3 photodynamic therapy,4 photovoltaics,5,6 sensors,7
electrochromic displays,8 and information storage.9 In the field
of molecular electronics, ordered phthalocyanine (Pc) materials
are generally preferred over disordered Pc materials, and the
(9) (a) Li, J.; Gryko, D.; Dabke, R. B.; Diers, J. R.; Bocian, D. F.; Kuhr,
W. G.; Lindsey, J. S. J. Org. Chem. 2000, 65, 7379-7390. (b) Gryko, D.;
Li, J.; Diers, J. R.; Roth, K. M.; Bocian, D. F.; Kuhr, W. G.; Lindsey, J. S.
J. Mater. Chem. 2001, 11, 1162-1180. (c) Gross, T.; Chevalier, F.; Lindsey,
J. S. Inorg. Chem. 2001, 40, 4762-4774. (d) Schweikart, K.-H.; Mali-
novskii, V. L.; Diers, J. R.; Yasseri, A. A.; Bocian, D. F.; Kuhr, W. G.;
Lindsey, J. S. J. Mater. Chem. 2002, 12, 808-828. (e) Schweikart, K.-H.;
Malinovskii, V. L.; Yasseri, A. A.; Li, J.; Lysenko, A. B.; Bocian, D. F.;
Lindsey, J. S. Inorg. Chem. 2003, 42, 7431-7446. (f) Wei, L.; Padmaja,
K.; Youngblood, W. J.; Lysenko, A. B.; Lindsey, J. S.; Bocian, D. F. J.
Org. Chem. 2004, 69, 1461-1469.
* Current address: Department of Chemistry, Penn State University, Uni-
versity Park, Pennsylvania 16802.
(1) Christie, R. M. Colour Chemistry; Royal Society of Chemistry:
Cambridge, UK, 2001.
(2) de la Torre, G.; Vazquez, P.; Agullo-Lopez, F.; Torres, T. J. Mater.
Chem. 1998, 8, 1671-1683.
(3) Calvete, M.; Yang, G. Y.; Hanack, M. Synth. Met. 2004, 141, 231-
243.
(4) Allen, C. M.; Sharman, W. M.; Van Lier, J. E. J. Porphyrins
Phthalocyanines 2001, 5, 161-169.
(5) Nazeeruddin, M. K.; Humphry-Baker, R.; Gra¨tzel, M.; Wo¨rhle, D.;
Schnurpfeil, G.; Hirth, A.; Trombach, N. J. Porphyrins Phthalocyanines
1999, 3, 230-237.
(6) Petritsch, K.; Friend, R. H.; Lux, A.; Rozenberg, G.; Moratti, S. C.;
Holmes, A. B. Synth. Met. 1999, 102, 1776-1777.
(7) Zhou, R.; Josse, F.; Gopel, W.; Ozturk, Z. Z.; Bekaroglu, O. Appl.
Organomet. Chem. 1996, 10, 557-577.
(8) Jiang, J.; Kasuga, K.; Arnold, D. P. In Supramolecular PhotosensitiVe
and ElectroactiVe Materials; Nalwa, H. S., Ed.; Academic Press: San Diego,
CA, 2001, 188-189 and references therein.
(10) Hassan, A. K.; Gould, R. D. Phys. Stat. Sol. A 1992, 132, 91-101.
(11) Nespurek, S.; Podlesak, H.; Hamann, C. Thin Solid Films 1994,
249, 230-235.
(12) Rajesh, K. R.; Menon, C. S. Mater. Lett. 2002, 53, 329-332.
(13) Xia W.; Minch, B. A.; Carducci, M. D.; Armstrong, N. R. Langmuir
2004, 20, 7998-8005.
(14) Oshiro, T.; Backstrom, A.; Cumberlidge, A. M.; Hipps, K. W.;
Mazur, U.; Pevovar, S. P.; Bahr, D. F.; Smieja, J. J. Mater. Res. 2004, 19,
1461-1470.
(15) Piechocki, C.; Simon, J. J. Am. Chem. Soc. 1982, 104, 5245-5247.
(16) McKeown, N. B.; Painter, J. J. Mater. Chem. 1994, 4, 1153-6.
(17) (a) Gu¨rek, A. G.; Bekaroglu, O. J. Porphyrins Phthalocyanines 1997,
1, 67-76. (b) Gu¨rek, A. G.; Bekaroglu, O. J. Porphyrins Phthalocyanines
1997, 1, 227-237.
10.1021/jo052122l CCC: $33.50 © 2006 American Chemical Society
Published on Web 03/30/2006
J. Org. Chem. 2006, 71, 3345-3356
3345

Youngblood
Backbone polymerized phthalocyanines are distinguished
from axially connected or “shish-kebab” phthalocyanines.23 The
advantages of backbone polymerized phthalocyanines relative
to noncovalently assembled phthalocyanines are (1) improved
thermal and chemical stability of the short and long-range
structure, (2) reproducible preparation of materials without
expensive or delicate instrumentation, and sometimes (3) the
addition of through-bond electronic communication between the
component monomers as a complement to through-space transfer
mechanisms for energy and/or electrons. Backbone polymeri-
zation of phthalocyanines is difficult because typical methods
of Pc synthesis allow little control over the number and geometry
of substituents and because the poor solubility of most phtha-
locyanines hinders their use in polymerization chemistries.
Backbone Pc polymers exist as either two-dimensional or one-
dimensional materials. Most efforts at preparing two-dimen-
sional backbone polyphthalocyanines have utilized the Pc
macrocyclization reaction as the material-forming step, with
bilateral or bridged building blocks such as 1,2,4,5-tetracy-
anobenzene or bis-dicyanobenzenes linked by alkyl chains or
other intermediary groups.17,18 Polyphthalocyanine sheets have
also been prepared by the polymerization of square oligomers
of four fused phthalocyanines, each bearing polymerizable end
groups.19,20 One-dimensional polymers are prepared from trans-
A2B2 Pc monomers. Hanack and co-workers have prepared one-
dimensional ladder oligomers and polymers based on phthalo-
cyanines and hemiporphyrazines.21 However, the stepwise
synthesis used for such oligomers is not well suited to the
preparation of polymers bearing many phthalocyanine macro-
cycles. Kingsborough and Swager prepared a thiophene-linked
metallophthalocyanine polymer by electropolymerization of
thiophene end groups.22 The resulting polymer chains are
described as “nearly linear”; however, they are unlikely to hold
a rodlike shape due to the natural substituent geometry of
phthalocyanines (vide infra).
The optoelectronic properties of a polyphthalocyanine mate-
rial may differ from monomeric phthalocyanine properties
according to the nature of the linking groups. The electroactive
thiophene linking groups in Kingsborough’s polyphthalocyanine
play a large role in the electronic character of the resulting
polymer,22 such that it is not the equivalent of an all-
phthalocyanine polymer. The fused linkages in the ladder
oligomers and phthalocyanine sheets have a significant effect
on the photochemical and electrochemical properties of the
individual chromophores of the resulting material, resulting in
broadening and red-shifting of the native Pc UV-vis absorption
spectra.17-20 In some cases, the perturbations that are caused
by the nature of the linkages between phthalocyanines may be
beneficial and intentional. Theoretical study of fused polyph-
thalocyanines using molecular orbital theory has led to the
FIGURE 1. Structures of two disubstituted phthalocyanines. The N-N
axis bisects two inner nitrogen atoms and two opposing benzo rings.
The axis equally can be displayed bisecting the NH-NH atoms.
prediction that such materials should exhibit intrinsic metallic
conductivities.24 As a complement to this type of beneficial
perturbation, researchers may also seek access to polyphthalo-
cyanines that exhibit properties very similar to the constituent
monomer precursors.
Backbone polymerization of porphyrins has been achieved
without perturbation of the monomeric pigment properties.
Lindsey and co-workers have prepared backbone polymers of
diethynylporphyrins by chemical as well as thermal polymer-
ization of ethyne end groups.25,26 The chemically polymerized
porphyrin “light-harvesting rods” are of interest in the capture
of solar energy,25 whereas the thermally polymerized porphyrins
have been examined as electroactive films for information
storage.26 In the light-harvesting rods the linkages between
porphyrins are made by Glaser coupling and are phenylbutadiy-
nylphenyl groups, which allow for through-bond communication
(excited-state energy, ground-state hole/electron transfer) without
perturbing the electronic properties of the linked porphyrins.25,27
A one-dimensional Pc polymer that could retain the native
electronic properties of the Pc subunits while engaging in
through-bond communication would be a useful counterpart to
the porphyrin-based rods.
The inherent geometry of phthalocyanines plays a major role
in the design of a linear phthalocyanine polymer. In Figure 1,
two possible ABAB phthalocyanines are shown, having 2,16-
and 2,17-substitution patterns. The substituents of the 2,16-
isomer are parallel but not collinear, while the substituents of
the 2,17-isomer are at a 120° angle with respect to each other.
These geometries result from the fact that each of the peripheral
(18) Wo¨rhle, D.; Benters, R.; Suvorova, O.; Schurpfeil, G.; Trombach,
N.; Bogdahn-Rai, T. J. Porphyrins Phthalocyanines 2000, 4, 491-497.
(19) Achar, B. N.; Fohlen, F. M.; Parker, J. A. J. Polym. Sci. Polym.
Chem. Ed. 1982, 20, 1785-1790.
(20) Venkatachalam, S.; Rao, K. V. C.; Manoharan, P. T. J. Polym. Sci.
Part B 1994, 32, 37-52.
(21) (a) Hauschel, B.; Ruff, D.; Hanack, M. J. Chem. Soc., Chem.
Commun. 1995, 2449-2451. (b) Hanack, M.; Stihler, P. Eur. J. Org. Chem.
2000, 303-311. (c) Rack, M.; Hanack, M. Angew. Chem., Int. Ed. Engl.
1994, 33, 1646-1648.
(22) Kingsborough, R. P.; Swager, T. M. Angew. Chem., Int. Ed. 2000,
39, 2897-2900.
(23) Hanack, M.; Hees, M.; Stihler, P.; Winter, G.; Subramanian, L. R.
In Handbook of Conducting Polymers; Skotheim, T. A., Elsenbaumer, R.
L., Reynolds, J. R., Eds.; Marcel Dekker: New York, 1998; p 381.
(24) Gomez-Romero, P.; Lee, Y.-S.; Kertesz, M. Inorg. Chem. 1988,
27, 3672-3675.
(25) Loewe, R. S.; Tomizaki, K.; Youngblood, W. J.; Bo, Z.; Lindsey,
J. S. J. Mater. Chem. 2002, 12, 3438-3451.
(26) Liu, Z.; Schmidt, I.; Thamyongkit, P.; Loewe, R. S.; Syomin, D.;
Diers, J. R.; Zhao, Q.; Misra, V.; Lindsey, J. S.; Bocian, D. F. Chem. Mater.
2005, 17, 3728-3742.
(27) Youngblood, W. J.; Gryko, D. T.; Lammi, R. K.; Bocian, D. F.;
Holten, D.; Lindsey, J. S. J. Org. Chem. 2002, 67, 2111-2117.
3346 J. Org. Chem., Vol. 71, No. 9, 2006

Synthesis of a New trans-A2B2 Phthalocyanine Motif
SCHEME 1
substituents is offset with respect to one of the central N-N
axes by a 30° angle (see Figure 1 for definition of the N-N
axis). A polymer prepared from a mixture of these isomers could
not be expected to afford a linear alignment. Even a polymer
produced solely from the 2,16-isomer would be unlikely to hold
a 180° alignment over long range due to rotation about the bonds
between the phthalocyanines and their linkages.
utility of dicyanophenylenediamine 3 (Scheme 1) as a precursor
to 2-alkyl-5,6-dicyanobenzimidazoles.30 Their synthesis of 3
required seven steps, with an overall yield of ∼7%.31 The best
reported route to 3 is the preparation by Mitzel and co-workers,
with a 14% yield over four steps.32,33 Scheme 1 shows a new
synthesis of 3, with a 14% yield over three steps.
The iodination of dinitrobenzene uses I3+, formed by mixing
To produce rodlike phthalocyanine polymers, the core pig-
ment scaffold must be modified such that substituents are
collinear with the N-N axes of the macrocycles. Such
architecture can be achieved with phthalocyanines bearing five-
membered outer rings, either in place of the standard benzo
rings, or by extra-annulation. A five-membered all-carbon ring
would break the aromaticity of the macrocycle, so the outermost
ring must be heterocyclic. There are reported syntheses for
phthalocyanines bearing diverse five-membered heterocyclic
outer rings.28 Some are prepared from heterocyclic building
blocks, whereas others are achieved by peripheral modification
of phthalocyanines. Examples that permit substitution at the
outermost position include pyrrole, indole, imidazole, and
thiophene. From this list, the extra-annulated imidazole is the
most accessible in terms of numbers and types of synthetic steps.
Phthalocyanines bearing this motif have been previously termed
imidazophthalocyanines,28 as well as benzimidazoloporphyra-
zines (note that a tetrabenzoporphyrazine is synonymous with
a phthalocyanine.).29 The general form of this compound class
is shown below, with regard to the examples known in the
literature (note that up to four regioisomers are possible based
on the placement of the Nimidazo substituents).
iodine with oleum.34 The reconstitution of I2 as a product of
+
the ensuing iodination reaction allows the I3 intermediate to
reform continuously and, thus, makes atom-economic use of
the halogen starting material. However, the previously reported
yield of 56% for diiodination when using only 0.5 equiv of I2
seems unreasonable in view of the reaction stoichiometry.
Attempts to repeat the reaction as reported consistently gave
yields of 19-20%. The yield was improved to 39% by lowering
the temperature of the reaction from 170 to 120 °C, shortening
the time from 105 to 75 min, and increasing the iodine to the
stoichiometric requirement (1 equiv of I2 for diiodination). The
reduction of 1 to the corresponding diamino compound 2 using
Sn/HCl has been reported by Whitesides and co-workers,
although no specific procedure or yield was provided.35 The
use of Fe/HCl gave the compound in 66% yield and avoids the
voluminous tin salts which are typical of Sn reductions.
Compared to the cyanation of the corresponding dibromophe-
nylenediamine,32 the cyanation of 2 proceeds at lower temper-
ature (120 vs 140 °C) more quickly (3 vs 15 h) and in greater
yield (55 vs 25%). Complexation of products 2 and 3 with the
metal salts left over at the end of each reaction is avoided by
treatment of the hot crude mixtures with aqueous EDTA.
Dicyanobenzimidazoles have previously been prepared by
dehydrative cyclization of 3 with low molecular weight car-
boxylic acids (e.g., formic to hexanoic acid).30 The reactions
were conducted neat, with the carboxylic acids serving as
reagent, solvent, and Bronsted acid catalyst. Scheme 2 shows
(28) Stuzhin, P. A.; Ercolani, C. In The Porphyrin Handbook; Kadish,
K. M., Smith, K. M., Guilard, R., Eds.; Academic Press: San Diego, 2003;
Vol. 15, pp 263-364.
(29) Pardo, C.; Yuste, M.; Elguero, J. J. Porphyrins Phthalocyanines
2000, 4, 505-509.
(30) (a) Kudrik, E. V.; Shaposhnikov, G. P. MendeleeV Commun. 1999,
85-86. (b) Kudrik, E. V.; Shaposhnikov, G. P.; Balakirev, A. E. Russ. J.
Gen. Chem. 1999, 69, 1321-1324. (c) Balakirev, A. E.; Kudrik, E. V.;
Shaposhnikov, G. P. Russ. J. Gen. Chem. 2002, 72, 1616-1619.
(31) For syntheses leading to the starting material 3 used in ref 29, see:
(a) Zharnikova, M. A.; Balakirev, A. E.; Maizlish, V. E.; Kudrik, E. V.;
Shaposhnikov, G. P. Russ. J. Gen. Chem. 1999, 69, 1870-1871. (b)
Shishkina, O. V.; Maizlish, V. E.; Shaposhnikov, G. P.; Lyubimtsev, A.
V.; Smirnov, R. P.; Baran’ski, A. Russ. J. Gen. Chem. 1997, 67, 842-845.
(c) Elvidge, J. A.; Golden, J. H.; Linstead, R. P. J. Chem. Soc. 1957, 2466-
2469; Levy, L. F.; Stephen, H. J. Chem. Soc. 1931, 79-82.
(32) Mitzel, F.; Fitzgerald, S.; Beeby, A.; Faust, R. Chem. Eur. J. 2003,
9, 1233-1241.
(33) For syntheses leading to the starting material used in ref 31, see:
(a) Cheeseman, G. W. H. J. Chem. Soc. 1962, 1170-1176. (b) Acheson,
R. M. J. Chem. Soc. 1956, 4731-4735. Elderfield, R. C.; Meyer, V. B. J.
Am. Chem. Soc. 1954, 1887-1891. (c) Mørkved, E. H.; Neset, S. M.; Bjørlo,
O.; Kjøsen, H.; Hvistendahl, G.; Mo, F. Acta Chem. Scand. 1995, 49, 658-
662.
This report uses the term benzimidazoporphyrazines, a slight
abbreviation of a previous name, and still unambiguous with
respect to the motif. The work described herein has produced a
linear, trans-substituted phthalocyanine analogue, based on the
benzimidazoporphyrazine scaffold. The development of new
synthetic methodology for benzimidazoporphyrazines (BzIm-
PAs) is presented as a stepping-stone toward the desired trans-
BzImPA(s). The structural properties and photochemical be-
havior are compared with those of well-known phthalocyanines.
Results and Discussion
(34) Arotsky, J.; Butler, R.; Darby, A. C. J. Chem. Soc. C 1970, 1480-
Synthesis. All of the published reports of benzimidazopor-
phyrazines have employed 5,6-dicyanobenzimidazoles as the
key building blocks.29,30 Kudrik and co-workers showed the
1485.
(35) Schwiebert, K. E.; Chin, D. N.; MacDonald, J. C.; Whitesides, G.
M. J. Am. Chem. Soc. 1996, 118, 4018-4029.
J. Org. Chem, Vol. 71, No. 9, 2006 3347

Youngblood
SCHEME 2
the Experimental Section). Due to the poor solubility of
compounds 5b and 5c, the cyclization reaction mixture was
carried forward directly to alkylation at the 1-position, giving
6b and 6c.
Alkylation of the 1-position of these dicyanobenzimidazoles
with the relatively small propyl group was predicated on the
intent to use the resulting benzimidazoporphyrazines as com-
ponents in materials where the macrocycles would be closely
packed. Larger alkyl groups, although perhaps helpful for the
solubility of the benzimidazoporphyrazines, would prohibit the
close packing of the macrocycles. Benzimidazoles 5a and 5d
proved unreactive to iodopropane in the absence of a base, even
at elevated temperature. Deprotonation could be effected with
DBU, and subsequent alkylation with iodopropane (bp 101 °C)
succeeds at 80 °C in acetonitrile or NMP (N-methyl pyrrolidi-
none). Propyldicyanobenzimidazoles 6a-d were obtained in
35-76% yield from diamine 3. The swallowtail benzimidazole
5a gave better results in the alkylation reaction (94%) compared
to the 2-arylbenzimidazoles, suggesting some influence of the
2-substituent on the basicity/nucleophilicity of the benzimida-
zole.
The swallowtail- and phenylbenzimidazoles 6a and 6b were
chosen as benchmark motifs for tetrasubstituted (A4) 2-alkyl-
and 2-aryl-5,6-benzimidazoporphyrazines, respectively (Scheme
3). In principle, a wide variety of aldehyde-bearing groups can
be installed at the 2-position. This versatility is limited by the
stability of a given aldehyde-bearing group under the conditions
of the oxidative cyclization and alkylation reactions. Groups
that might interfere with or be affected by these two steps, such
as ferrocenyl or pyridyl, can be transformed to dicyanobenz-
imidazoles by cross-coupling to the p-iodophenyl-benzimidazole
6c. The protected ethynylphenylbenzimidazole 6d was prepared
as a building block for trans-diethynylbenzimidazoporphyrazines.
The previous reports of A4-type benzimidazoporphyrazines
report UV-vis absorption spectra in DMF and sulfuric acid.29,30
Fb-7 and Fb-8 (Scheme 3), as well as the their zinc and
magnesium chelates, were prepared to investigate the photo-
chemical properties of these macrocycles (ꢀ, λabs, λem, Φf) in
common organic solvents. Such photochemical studies provide
a comparison of the extra-annular imidazole ring with the
corresponding benzo rings of naphthalocyanine (see the Sup-
porting Information for a discussion of the photochemistry of
BzImPAs). The yields of the DBU-mediated reactions of 6a
increase according to the presence and type of metal salt in the
order Fb < Mg < Zn, in accord with known results for
phthalocyanine formation using DBU with and without metal
salts.40 The corresponding reactions with 6b do show an
improvement in the yields for the metallo-derivatives compared
to the free base, but the yields of Mg-8 and Zn-8 are essentially
equivalent within experimental variation. Surprisingly, the yield
of Fb-8 in the DBU-mediated reaction was slightly better than
that using lithium pentoxide.
the conversion of 3 to various benzimidazoles via oxidative
cyclization with selected aldehydes 4a-d. Originally developed
by Weidenhagen using Cu(OAc)2 as the oxidant,36 this method
has evolved in recent years to the more environmentally benign
use of O2, with FeCl3 as a catalytic oxidant.37,38 The oxidative
cyclization is a comparatively mild alternative to the dehydrative
condensation of phenylenediamines with substituted benzoic
acids, which typically requires strong hygroscopic acids such
as concd HCl and polyphosphoric acid.39 Yields of 58% and
81% were obtained for benzimidazoles 5a and 5d, respectively.
Benzimidazole 5d was also prepared directly from 2, taking
advantage of the copper salts left over from the cyanation
reaction (Scheme 1), by adding aldehyde 4d and bubbling O2
through the crude reaction mixture containing 3. This procedure
was considerably faster than the FeCl3 method, due to the large
quantity of copper salts present, and gave 5d in 41% yield (see
The 1H NMR spectrum of Fb-8 shows the usual evidence of
the aromatic ring current, with the core protons found at -3.13
1
ppm. The H NMR spectrum of Fb-7 shows no signal for the
core protons in the negative ppm region, even as far as -8 ppm.
The core protons of Fb-7 were assigned to an otherwise
unaccountable broad signal at 0.30-0.50 ppm that bears a
correct integration for the two NH protons and is absent from
(36) (a) Weidenhagen, R. Chem. Ber. 1936, 69, 2263-2272. (b)
Weidenhagen, R.; Weedon, U. Chem. Ber. 1938, 71, 2347-2360.
(37) Coville, N. J.; Neuse, E. W. J. Org. Chem. 1977, 42, 3485-491.
(38) Singh, M. P.; Sasmal, S.; Lu, W.; Chatterjee, M. N. Synthesis 2000,
1380-1390.
(39) Grimmett, M. R. Imidazole and Benzimidazole Synthesis; Academic
Press: New York, 1997; pp 71-94.
(40) (a) Tomoda, H.; Saito, S.; Ogawa, S.; Shiraishi, S. Chem. Lett. 1980,
1277-1280. (b) Tomoda, H.; Saito, S.; Shiraishi, S. Chem. Lett. 1983, 313-
316.
3348 J. Org. Chem., Vol. 71, No. 9, 2006

Synthesis of a New trans-A2B2 Phthalocyanine Motif
SCHEME 3
SCHEME 4
exclusion chromatography. The smaller macrocycles were then
separated from one another by adsorption chromatography. The
larger macrocycles were not individually isolated. Compound
6d appeared to be slightly more reactive than 1,2-dicyanoben-
zene, and a 1:1 ratio of the two reactants, respectively, gave a
product mixture favoring the AB3 and B4 products. A corre-
sponding ratio of 1:1.5 (6d/dicyanobenzene) gave a more even
distribution of the possible products. The recovered samples of
the trans-diethynylbenzimidazoporphyrazine Zn-13 and the cis-
1
isomer Zn-12 displayed similar H NMR and LD-MS spectra,
but were easily distinguished by their respective UV-vis
absorption spectra (see the Supporting Information). Zn-11 was
easily separated in the initial size-exclusion column. Zn-11 is
a blue solid, but takes on a blue-green color in solution. The
A2B2 compounds are also blue solids, but appear green in
solution.
Dicyanobenzimidazole 6d was transformed into the corre-
sponding diiminoisoindoline 14 in 76% yield using a well-
known procedure (Scheme 5).43 The product did not fully
crystallize from the reaction, but the quantity of recovered solid
could be amplified by concentrating the mixture using a stream
of argon. The crystals obtained were greenish-white needles that
turned deep green upon melting. The melted sample was
recovered from the capillary and was found to exhibit a UV-
vis absorption profile analogous to that of Fb-8 (see the
Supporting Information).
the 1H NMR spectra in the metalated analogues Mg-7 and Zn-
7. It is not known whether the appearance of the core protons
of Fb-7 at relatively higher ppm could be due to a steric or
electronic effect. The general structure shown in Scheme 3
depicts a macrocycle having C4h symmetry, but the A4 benz-
imidazoporphyrazines can have up to four regioisomers resulting
1
from the placement of the propyl groups. As a result, the H
NMR spectra of the zinc and free base forms of 7 and 8
exhibited broad signals for most of the expected resonances.
1
The H NMR signatures for Mg-7 and Mg-8, however, were
far less complex, indicating a possibly monodisperse product.
The effect of metal templating on the distribution of regioiso-
mers in phthalocyanine-forming reactions has been previously
detailed.41 All of the A4 benzimidazoporphyrazines are green
in solid form as well as in solution.
Diiminoisoindoline 14 was reacted with boron subphthalo-
cyanine (15) to prepare the A3B compound Fb-11 (Scheme 5).
The initial attempt to prepare a trans-diethynylbenzimida-
zoporphyrazine used a mixture of 6a and 6b in a macrocycliza-
tion reaction. This reaction gave an inseparable product mixture.
The same problem was encountered for the reaction between
6d and diheptylphthalonitrile (10).42 The reaction of 6d with
dicyanobenzene (Scheme 4) gave a separable mixture of
products. The smaller macrocyclic products (A4, A3B, and A2B2)
were separated from the larger ones (AB3 and B4) by size-
(41) Rager, C.; Schmid, G.; Hanack, M. Chem. Eur. J. 1999, 5, 280-
288.
(42) (a) Nishi, H.; Azuma, N.; Kitahara, K. J. Heterocycl. Chem. 1992,
29, 475-477. (b) Hanack, M.; Haisch, P.; Lehmann, H.; Subramanian, L.
R. Synthesis 1993, 387-390.
(43) Brach, P. J.; Grammatica, S. J.; Ossanna, O. A.; Weinberger, L. J.
Heterocycl. Chem. 1970, 7, 1403-1405.
J. Org. Chem, Vol. 71, No. 9, 2006 3349

Youngblood
SCHEME 5
SCHEME 6
dropped to 4% when ZnCl2 was used as a templating agent in
the reaction. The compound Zn-13 was more accessible by
metalation of Fb-13 using Zn(OAc)2‚2H2O. There are two
possible regioisomers of the trans-A2B2 structure, of C2V and
C2h symmetries, because of the position of the respective Nimidazo
substituents. For Fb-13 these regioisomers were not separable
by chromatography on silica gel.
1
The H NMR spectra of the isolated sample of Fb-13 had
The subPc 15 had to be employed at four times the stoichio-
metric ratio in order to suppress the formation of products having
more than one benzimidazole moiety. Fb-11 exhibits poor
solubility but is marginally more soluble than the large quantity
of unsubstituted phthalocyanine that is also formed. Fb-11 could
be largely separated from the unsubstituted phthalocyanine by
Soxhlet extraction of the product mixture using chloroform,
followed by size-exclusion chromatography. The yield is modest
(25%), but the alternative route to Fb-11 would be the
demetalation of Zn-11, which is not possible under mild
conditions. (Zinc porphyrins can be demetalated in the presence
of TFA at room temperature, but this is ineffective for zinc
phthalocyanines.) There is no published report of the demeta-
lation of a zinc phthalocyanine. Fb-11 is blue in solid form
and greenish-blue in solution.
duplicate signals for each expected resonance, including the
protons within the macrocycle (see the Supporting Information).
Compounds Fb-8 and Fb-11 have slightly broadened signals
for the inner protons, but not the twinned peaks that are seen
for Fb-13. Hanack and co-workers attributed the split appearance
of the inner proton resonance of their trans-A2B2 phthalocyanine
to the different environments encountered by the NH protons
in the tautomers of the structure.45 A variable-temperature H
1
NMR experiment in THF-d8 showed that the signals for the
various duplicated resonances of Fb-13 did approach one
another at high temperatures (up to 55 °C), but the signals never
merged, and the usual broadening associated with exchange-
equilibrium behavior was not observed. Given the rather low-
temperature limit of the solvent, this result is not conclusive as
to the origin of the twinned resonances.
The trans-diethynylbenzimidazoporphyrazine Fb-13 was
prepared in 9% yield by cross-condensation of diiminoisoin-
doline 14 with trichloroisoindolenine 16 (Scheme 6), following
the procedure reported by Young and Onyebuagu.44 A trace
quantity of an AB3 byproduct was formed in the reaction, as
previously observed.45 The yield of the trans-A2B2 product
1
The H NMR spectrum of a sample of Zn-13 having both
regioisomers was far less complex than the corresponding
(44) Young, J. G.; Onyebuagu, W. J. Org. Chem. 1990, 55, 2155-2159.
(45) Stihler, P.; Hauschel, B.; Hanack, M. Chem. Ber. 1997, 130, 801-
806.
3350 J. Org. Chem., Vol. 71, No. 9, 2006

Synthesis of a New trans-A2B2 Phthalocyanine Motif
FIGURE 2. Absorption and emission spectra for Zn-13a in THF.
SCHEME 7
signature of the free base compound. Only the aromatic region
showed more complexity than would be expected for a
monodisperse sample. The regioisomers of Zn-13 were sepa-
rable by chromatography on silica gel and exhibited distinct
patterns in the aromatic region of the 1H NMR spectrum,
enabling assignment. The first eluting species, Zn-13a, exhibits
an ABCD splitting pattern for the protons on the benzo rings,
consistent with the assignment of C2h symmetry. The second
eluting species, Zn-13b, shows multiplets that resemble typical
AA′BB′ splitting patterns, corresponding to the structure as-
signed to C2V symmetry. COSY NMR analyses were performed
to confirm the coupling patterns that support these assignments
of the regioisomers (see Supporting Information). As with the
A2B2 products from the reaction of 6d with dicyanobenzene,
all of the trans-A2B2 compounds are blue in solid form but
deeply green in solution. The UV-vis spectrum of compound
Zn-13a is shown in Figure 2. The lowered symmetry of the
macrocycle results in a split Q-band structure, but the photo-
chemical behavior of the sample is otherwise similar to typical
zinc-phthalocyanines. A detailed presentation of the photo-
chemistry of the benzimidazoporphyrazines prepared for this
report can be found in the Supporting Information.
The deprotection of Zn-13a and Zn-13b proceeded smoothly
using TBAF in dichloromethane, but the compounds proved to
be surprisingly polar during chromatography (Scheme 7). Loss
of the triisopropylsilyl groups also adversely affected the
solubility of the resulting diethynyl compounds. Zn-13a and
Zn-13b are soluble in chlorinated solvents and very soluble in
THF, whereas Zn-17a and Zn-17b slowly precipitated after
chromatographic purification. Pure samples of Zn-17a and Zn-
17b are weakly soluble in chlorinated solvents and moderately
soluble in THF.
been prepared as precursors to rodlike phthalocyanine polymers.
The quantities of the isolated diethynyl-trans-benzimidazopor-
phyrazines were small (<10 mg), but sufficient for their full
characterization and testing in exploratory polymerizations. The
procedures developed for this route typically gave moderate to
low yields but are each amenable to higher scale.
Conclusion
Experimental Section
Noncommercial Compounds. Compounds 4a,46 4d,47 9,42 15,48
and 1649 were prepared according to the literature.
The substituent geometry of benzimidazoporphyrazines makes
them useful for constructs that require a controlled alignment
of phthalocyanine macrocycles. A new basic route to 2-substi-
tuted dicyanobenzimidazoles via the oxidative cyclization of 3
with various aldehydes gives access to benzimidazoporphyra-
zines bearing useful substituents for elucidation into supramo-
lecular complexes and/or materials. Free base and metalloben-
zimidazoporphyrazines of A4, A3B and trans-A2B2 substitution
patterns can be prepared in useful quantities. Linear, trans-
diethynylbenzimidazoporphyrazines (Zn-17a and Zn-17b) have
(46) Kato, M.; Komoda, K.; Namera, A.; Sakai, Y.; Okada, S.; Yamada,
A.; Yokoyama, K.; Migita, E.; Minobe, Y.; Tani, T. Chem. Pharm. Bull.
1997, 45, 1767-1776.
(47) Rao, P. D.; Dhanalekshmi, S.; Littler, B. J.; Lindsey, J. S. J. Org.
Chem. 2000, 65, 7323-7344.
(48) Claessens, C. G.; Gonzalez-Rodriguez, D.; del Rey, B.; Torres, T.;
Mark, G.; Schuchmann, H. P.; von Sonntag, C.; MacDonald, J. G.; Nohr,
R. S. Eur. J. Org. Chem. 2003, 14, 2547-2551.
(49) Farbenfabriken Bayer, U. S. Patent 2,701,252; Feb. 1, 1955.
J. Org. Chem, Vol. 71, No. 9, 2006 3351

Youngblood
1,2-Diiodo-4,5-dinitrobenzene (1). A three-necked, 100 mL
round-bottom flask was charged with oleum (38 mL of a 20%
solution, 0.18 mol SO3) and a magnetic stirring bar. The flask was
fitted with a condenser and a bubbler, and the spare necks were
closed with glass stoppers. The flask was placed in an oil bath
heated to 120 °C. Iodine (6.86 g, 27.0 mmol) was added, after 20
min, o-dinitrobenzene (4.54 g, 27.0 mmol) was added, and the
reaction was heated for 75 min and then removed from heat and
immediately poured into a 1 L conical flask filled with ice. The
crude mixture was quenched with NaOH pellets until it was slightly
alkaline to pH paper, with more ice added to keep the mixture cold.
The mixture was then filtered through filter paper, and the filtrate
was extracted with CHCl3. The organic layer of the extraction was
washed with aqueous Na2S2O5, water, and brine, dried over Na2-
SO4, filtered, and concentrated to dryness. The dark brown filter
cake was stirred with 200 mL of hot water to which Na2S2O5 was
added until no further bubbling was observed. The mixture was
then filtered and the filtrate was discarded. The filter cake and the
residue from the extraction were recrystallized (EtOH/water)
yielding dark brown crystals (4.47 g, 39%): mp 183-184 °C (lit.34
mp 184 °C); 1H NMR (CDCl3) δ 8.31 (s, 2H); 13C NMR δ 114.6,
134.8. Anal. Calcd for C6H2I2N2O4: C, 17.16; H, 0.48; N, 6.67;
Found: C, 17.44; H, 0.41, 6.61.
Scale-up. The above procedure was followed with the following
quantities of reagents: oleum (200 mL), iodine (37.80 g), o-
dinitrobenzene (25.0 g). To quench the large volume of SO2
produced by the reaction, the evolved gas was bubbled through a
solution of aqueous NaOH (5 M, 1 L), which was later used to
quench the acidic crude reaction mixture over ice, along with an
additional 125 g of NaOH, followed by Na2S2O5 (18.5 g). The
CHCl3 extraction of the initial crude filtrate was omitted. Yield:
32%. Characterization data were consistent with the smaller scale
reaction.
5,6-Dicyano-2-(undec-7-yl)benzimidazole (5a). A 100 mL
round-bottom flask was charged with 3 (1.32 g, 8.37 mmol),
pentanol (42 mL), 2-hexyl-1-octanal46 (1.77 g, 8.37 mmol), and a
magnetic stirring bar. The flask was fitted with a Hickman still
and placed in an oil bath heated to 120 °C. NMP (4.0 mL) was
added to fully dissolve the solid material. The mixture was heated
and stirred for 2 h. Then FeCl3‚6H2O (113 mg, 0.42 mmol) was
added to the reaction vessel, and oxygen was bubbled through the
mixture as it was heated and stirred for an additional 12 h. The
reaction mixture was then removed from heat and added to 200
mL of diethyl ether. The ether solution was washed three times
with water, then washed with brine, dried over Na2SO4, filtered,
and concentrated to dryness. The residue was chromatographed
(silica, CHCl3), yielding a tan solid (2.37 g, 81%): mp 148-149
1
°C; H NMR (CDCl3) δ 0.82 (t, J ) 7.6 Hz, 6H), 1.10-1.30 (m,
16H), 1.77-1.87 (m, 2H), 2.90-3.04 (m, 1H), 8.07 (br s, 2H),
10.36 (br s, 1H); 13C NMR δ 14.2, 22.8, 27.7, 29.4, 31.8, 34.9,
41.3, 108.4, 117.0, 165.3; FAB-MS obsd 351.2551, calcd 351.2549
(C22H30N4).
5,6-Dicyano-2-(4-(triisopropylsilylethynyl)phenyl)benz-
imidazole (5d). The same procedure was followed as for 5a, with
the following quantities: 3 (468 mg, 2.96 mmol), NMP (15 mL),
4d (847 mg, 2.96 mmol), and FeCl3‚6H2O (296 µL of a 100 mM
solution, 30 µmol). The product was isolated by chromatography
(silica, CHCl3, 2% ethyl acetate) as a colorless solid (732 mg,
1
58%): mp 347-348 °C; H NMR (acetone-d6) δ 1.15-1.18 (m,
21H), 7.05 (d, J ) 8.4 Hz, 2H), 8.24-8.28 (m, 4H); 13C NMR
(acetone-d6) δ 11.5, 18.5, 93.5, 106.7, 108.4, 116.7, 118.4, 122.1
(br), 126.3, 127.6, 128.7, 132.7, 142.0 (br), 156.4; FAB-MS obsd
425.2161, calcd 425.2083 [(M + H), M ) C26H28N4Si].
Synthesis of 5d Directly from 2.: A two-necked 25 mL flask
was charged with 2 (577 mg, 1.60 mmol), CuCN (573 mg, 6.40
mmol), and NMP (2 mL). The vessel was fitted with a bubbler,
and the second neck was capped with a septum. The mixture was
heated at 120 °C for 2 h, and then more NMP (8 mL) and 4d (458
mg, 1.60 mmol) were added and O2 was bubbled through the
mixture. After 40 min, TLC (silica, CHCl3, 4% 2-propanol) showed
the desired product and no remaining 3 or 4d, so the mixture was
transferred to a 500 mL conical flask containing a hot solution of
aqueous EDTA (4.87 g, 12.8 mmol, in 200 mL), and the mixture
was heated and stirred for 30 min and then filtered. The filter cake
was dried in vacuo and chromatographed (silica, CH2Cl2, 2% ethyl
acetate), giving a colorless solid (280 mg, 41%). Characterization
data were identical with the preparation from 3 above.
5,6-Dicyano-1-propyl-2-(undec-7-yl)benzimidazole (6a). A 10
mL round-bottom flask was charged with 5a (743 mg, 2.12 mmol)
and CH3CN (2.0 mL). The flask was capped with a septum and
placed in an oil bath heated to 80 °C. DBU (317 µL, 2.12 mmol)
was added, and the mixture was stirred for 2 min. Then iodopropane
(207 µL, 2.12 mmol) was added, and the mixture was stirred for
20 min. A second dose of DBU (317 µL, 2.12 mmol), followed by
iodopropane (207 µL, 2.12 mmol), was added, and 20 min later, a
third round of DBU and iodopropane was added. HPLC analysis
of the reaction mixture (C-18 reverse phase, CH3CN as eluent)
indicated that the yields of the reaction after the first, second, and
third round of reagents were 60%, 78%, and 97%, respectively.
After the third round of reagents was added, and the mixture was
stirred for 20 min, the reaction mixture was removed from heat
and added to 200 mL diethyl ether. The ether solution was washed
three times with water, then washed with brine, dried over Na2-
SO4, filtered, and concentrated to dryness. The residue was
chromatographed (silica, hexanes/ethyl acetate 7:1, then hexanes/
ethyl acetate 6:1), yielding a tan solid (786 mg, 94%): mp 52-53
°C; 1H NMR (CDCl3) δ 0.81 (t, J ) 6.8 Hz, 6H), 1.02 (t, J ) 7.2
Hz, 3H), 1.05-1.13 (m, 16H), 1.72-1.82 (m, 6H), 2.88-2.98 (m,
1H), 4.15 (t, J ) 7.6 Hz, 2H); 13C NMR δ 11.6, 14.2, 14.2, 22.8,
23.8, 27.8, 29.5, 31.8, 35.2, 38.3, 45.9, 107.8, 108.4, 116.2, 116.9,
117.0, 125.8, 137.0, 145.3, 165.5. Anal. Calcd for C25H36N4: C,
76.49; H, 9.24; N, 14.27. Found: C, 76.38; H, 9.36; N, 14.18.
1,2-Diamino-4,5-diiodobenzene (2). Following a literature
procedure, a sample of 1 (17.42 g, 41.5 mmol) and a magnetic
stirring bar were added to a 500 mL conical flask fitted with a
jacketed condenser. EtOH (95%, 150 mL) and concd aqueous HCl
(68.6 mL, 0.83 mol) were added, and the mixture was stirred and
heated to boiling. Fe powder (18.59 g, 0.332 mol) was added in
portions, resulting in foaming of the mixture and accelerated
refluxing of the EtOH, which subsided within a few minutes of
each addition. The reaction was heated for 45 min beyond the final
addition of Fe. A hot solution of EDTA (156 g, 0.411 mol, in 300
mL H2O) was added to the mixture, and KOH pellets were added
until the solution was alkaline to pH paper. The hot mixture was
extracted twice with ethyl acetate, and the extracts were combined,
washed with water and then with brine, dried over Na2SO4, filtered,
and concentrated to dryness. The residue was recrystallized (EtOH/
1
water), giving tan needles (9.92 g, 66%): mp 135-136 °C; H
NMR (THF-d8) δ 4.21 (br s, 4H), 7.03 (s, 2H); 13C NMR (THF-
d8) δ 91.1, 124.5, 137.6. Anal. Calcd for C6H6I2N2: C, 20.02; H,
1.68; N, 7.78; Found: C, 20.19; H, 1.59, 7.71.
1,2-Diamino-4,5-dicyanobenzene (3). A 50 mL round-bottom
flask was charged with 2 (6.94 g, 19.3 mmol), CuCN (6.91 g, 77.2
mmol, 4 equiv), and a magnetic stirring bar. The vessel was capped
with a septum and flushed with Ar for 10 min, and NMP (20 mL)
was added. The vessel was heated to 120 °C for 3 h, then diluted
with DMF (20 mL) and added to a hot aqueous solution of EDTA
(88 g, 232 mmol, in 500 mL H2O) in a 1 L conical flask. Oxygen
was bubbled through the mixture as it was stirred and heated for 2
h. After 2 h, the dark heterogeneous mixture turned to a homoge-
neous green solution. The hot green solution was extracted twice
with ethyl acetate, and the extracts were washed with water, then
with brine, dried over Na2SO4, filtered, and concentrated to dryness.
The residue was recrystallized (EtOH/water), giving tiny tan needles
(1.66 g, 55%): mp 262-264 °C (lit.30b,32 mp 193-195 or 272-
275 °C); 1H NMR (acetone-d6) δ 5.40 (br s, 4H), 7.04 (s, 2H); 13
C
NMR (acetone-d6) δ 103.8, 117.1, 117.4, 139.4; FAB-MS obsd
158.0591, calcd 158.0592 (C6H6N4).
3352 J. Org. Chem., Vol. 71, No. 9, 2006

Synthesis of a New trans-A2B2 Phthalocyanine Motif
5,6-Dicyano-2-phenyl-1-propylbenzimidazole (6b). A 25 mL
round-bottom flask was charged with 3 (316 mg, 2.00 mmol), NMP
(10 mL), benzaldehyde, (202 µL, 2.00 mmol), and a magnetic
stirring bar. The flask was fitted with a Hickman still, placed in an
oil bath heated to 120 °C, and stirred for 1 h. Then FeCl3‚6H2O
(27 mg, 0.10 mmol) was added to the reaction vessel, and oxygen
was bubbled through the mixture as it was heated and stirred for
an additional 20 h. The reaction mixture was then removed from
heat and added to ethyl acetate. The mixture was washed three
times with water, then with brine, dried over Na2SO4, filtered, and
concentrated to dryness. The residue (458 mg, 1.88 mmol) was
dissolved in NMP (2 mL) and heated to 80 °C. Then DBU (280
µL, 1.88 µmol) was added, the mixture was stirred for 2 min, and
iodopropane (183 µL, 1.88 mmol) was added. After 20 min, the
mixture was treated with a second round of DBU and iodopropane,
and after an additional 20 min, a third round of reagents was added.
After a final 20 min of heating, the mixture was transferred to ethyl
acetate and washed three times with water, then with brine, dried
over Na2SO4, filtered, concentrated to dryness, and chromatographed
(silica, CH2Cl2, 3% ethyl acetate, 1% 2-propanol), yielding an off-
white solid (253 mg, 44%): mp 183-185 °C; 1H NMR (CDCl3) δ
0.90 (t, J ) 7.6 Hz, 2H), 1.81-1.92 (m, 2H), 4.29 (t, J ) 7.6 Hz,
2H), 7.56-7.62 (m, 3H), 7.70-7.73 (m, 2H), 7.89 (s, 1H), 8.20
(s, 1H); 13C NMR (CDCl3) δ 11.4, 23.5, 47.3, 108.7, 109.0, 116.7,
116.8, 116.9, 126.6, 128.8, 129.5, 129.5, 131.4, 137.8, 145.4, 159.5;
FAB-MS obsd 287.1302, calcd 287.1297 [(M + H)+; M )
C18H14N4].
5,6-Dicyano-2-(4-iodophenyl)-1-propylbenzimidazole (6c). A
25 mL round-bottom flask was charged with 3 (340 mg, 2.15
mmol), NMP (10 mL), 4-iodobenzaldehyde, (499 mg, 2.15 mmol),
and a magnetic stirring bar. The flask was fitted with a Hickman
still, placed in an oil bath heated to 120 °C, and stirred for 1 h.
Then FeCl3‚6H2O (29 mg, 0.11 mmol) was added to the reaction
vessel, and oxygen was bubbled through the mixture as it was
heated and stirred for an additional 24 h. The reaction mixture was
then removed from heat and added to ethyl acetate. The ethyl acetate
solution was washed three times with water, then washed with brine,
dried over Na2SO4, filtered, and concentrated to dryness. The residue
(603 mg, 1.63 mmol) was suspended in CH3CN and heated to 80
°C. Then DBU (243 µL, 1.63 µmol) was added, the mixture was
stirred for 2 min, and iodopropane (159 µL, 1.63 mmol) was added.
After 20 min, the mixture was treated with a second round of DBU
and iodopropane, and after an additional 20 min, a third round of
reagents was added. After a final 20 min of heating, the mixture
was transferred to ethyl acetate and washed three times with water,
followed by brine. After the organic layer was dried over Na2SO4,
the mixture was filtered, concentrated to dryness, and chromato-
graphed (silica, CHCl3, 5% ethyl acetate), giving a white solid (440
mg, 50%): mp 208-209 °C; 1H NMR (CDCl3) δ 0.91 (t, J ) 7.6
Hz, 3H), 1.80-1.91 (m, 2H) 4.26 (t, J ) 7.6 Hz, 2H), 7.46 (d, J )
8.0 Hz, 2H), 7.87 (s, 1H), 7.95 (d, J ) 8.0 Hz, 2H), 8.22 (s, 1H);
13C NMR (CDCl3) δ 11.4, 23.6, 47.4, 98.4, 109.0, 109.3, 116.55,
116.62, 116.9, 126.7, 128.2, 130.9, 137.8, 138.7, 145.3, 158.4. Anal.
Calcd for C18H13IN4: C, 52.45; H, 3.18; N, 13.59. Found: C, 52.40;
H, 3.06; N, 13.40.
Tetrakis(2-tridec-7-yl-1-propylbenzimidazo[5,6-b:5′,6′-g:5′′,6′′-
l:5′′′,6′′′-q])porphyrazine (Fb-7). A 5 mL reaction vial was charged
with 6a (150 mg, 382 µmol), pentanol (1.90 mL), and a magnetic
stirring bar. The vial was capped and heated in a heating block set
at 145 °C, and then DBU (57 µL, 382 µmol) was added. Heating
and stirring continued for 18 h. The vial was then removed from
heat, and upon cooling to room temperature, the mixture was diluted
with 18 mL of MeOH, and then centrifuged. The supernatant was
removed, and the pellet was resuspended in MeOH and centrifuged
again. After the supernatant was removed a second time, the pellet
was redissolved in THF (2 mL) and precipitated by addition of
MeOH (18 mL). The mixture was centrifuged, and upon removal
of the supernatant, the pellet was dried in vacuo, revealing a green
solid (17 mg, 11%): 1H NMR (THF-d8) δ 0.30-0.50 (br s, 2H),
0.80-1.00 (m, 24H), 1.17-1.60 (m, 76H), 1.80-2.10 (m, 8H),
2.10-2.42 (m, 16H), 3.10-3.25 (m, 2H), 3.30-3.40 (m, 2H),
4.30-4.50 (m, 4H), 4.70-4.84 (m, 4H), 9.30-9.70 (m, 8H); LD-
MS obsd 1570.8; FAB-MS obsd 1571.2178, calcd 1571.1916
(C100H146N16); λabs (nm) 309, 342, 376, 640, 676, 713, 737; λem
742 nm; Φf ) 0.59.
Preparation of Fb-7 Using Lithium Pentoxide. A 5 mL
reaction vial was charged with a magnetic stirring bar, pentanol
(1.0 mL), and Li ribbon (23 mg, 3.3 mmol). The vial was capped,
vented, and warmed to 90 °C. After all of the Li was consumed
(40 min), the vial was removed from heat and allowed to cool to
room temperature. Then a sample of 6a (150 mg, 0.382 mmol) in
pentanol (1.0 mL) was added, and the vial was capped and heated
to 140 °C for 4 h. The vial was then removed from heat, and upon
cooling to room temperature, the mixture was diluted with 18 mL
of MeOH (2% CH3CO2H) and centrifuged, and the supernatant was
removed. The pellet was resuspended in MeOH and centrifuged
again. After the supernatant was removed a second time, the pellet
was redissolved in THF (2 mL) and precipitated by addition of
MeOH (18 mL). The mixture was centrifuged, and upon removal
of the supernatant, the pellet was dried in vacuo, giving a green
solid (74 mg, 49%). Characterization data were consistent with the
material produced from the DBU-mediated reaction (vide supra).
Tetrakis(2-tridec-7-yl-1-propylbenzimidazo[5,6-b:5′,6′-g:5′′,6′′-
l:5′′′,6′′′-q])porphyrazinatomagnesium(II) (Mg-7). A 5 mL reac-
tion vial was charged with 6a (150 mg, 382 µmol), MgCl2 (13 mg,
96 µmol), pentanol (1.90 mL), and a magnetic stirring bar. The
vial was capped and heated in a heating block set at 145 °C, and
then DBU (57 µL, 382 µmol) was added. Heating and stirring
continued for 18 h. The vial was then removed from heat, and upon
cooling to room temperature, the mixture was diluted with 16 mL
of MeOH and 2 mL of water and then centrifuged. The supernatant
was removed, and the pellet was resuspended in MeOH/water (8:
1) and centrifuged again. After the supernatant was removed a
second time, the pellet was redissolved in THF (2 mL) and
precipitated by addition of MeOH (16 mL) and water (2 mL). The
mixture was centrifuged, and upon removal of the supernatant, the
pellet was dried in vacuo, giving a green solid (41 mg, 27%): 1H
NMR (THF-d8) δ 0.82-0.96 (m, 24H), 1.16-1.58 (m, 76H), 1.87-
2.02 (m, 8H), 2.18-2.36 (m, 16H), 3.24-3.34 (m, 4H), 4.66-
4.74 (m, 8H), 9.40 (s, 2H), 9.47 (s, 2H), 9.65 (s, 2H), 9.68 (s, 2H);
LD-MS obsd 1592.7; FAB-MS obsd 1593.1650, calcd 1593.1610
(C100H144MgN16); λabs (nm) 310, 363, 640, 680, 713; λem 720 nm;
Φf ) 0.69.
5,6-Dicyano-2-(4-(triisopropylsilylethynyl)phenyl)-1-propyl-
benzimidazole (6d). The same procedure was followed as for 6a,
with the following quantities: 5d (763 mg, 1.79 mmol), NMP (10
mL), DBU (267 µL, 1.79 mmol per dose), and iodopropane (175
µL, 1.79 mmol per dose). The product was isolated by chroma-
tography (silica, CHCl3) as a colorless solid (506 mg, 61%): mp
Tetrakis(2-tridec-7-yl-1-propylbenzimidazo[5,6-b:5′,6′-g:5′′,6′′-
l:5′′′,6′′′-q])porphyrazinatozinc(II) (Zn-7). A 5 mL reaction vial
was charged with 6a (150 mg, 382 µmol) and a magnetic stirring
bar. The vial was then introduced into a glovebox under argon
atmosphere, and ZnCl2 (13 mg, 96 µmol) was added. The vial was
capped and removed from the glovebox, and pentanol (1.90 mL)
was added. The vial was heated to 140 °C in a heating block, and
then DBU (57 µL, 382 µmol) was added. The temperature of the
heating block was raised to 145 °C and continued for 18 h. The
vial was then removed from heat, and upon cooling to room
temperature, the mixture was diluted with 16 mL of MeOH and 2
1
242-243 °C; H NMR (acetone-d6) δ 0.89 (t, J ) 7.2 Hz, 3H),
1.17-1.19 (m, 21H), 1.86-1.96 (m, 2H), 4.53 (t, J ) 7.6 Hz, 2H),
7.75 (d, J ) 8.0 Hz, 2H), 7.91 (d, J ) 8.0 Hz, 2H), 8.36 (s, 1H),
8.50 (s, 1H); 13C NMR (acetone-d6) δ 10.5, 11.3, 18.4, 23.2, 47.1,
93.1, 106.6, 108.1, 108.3, 116.8, 116.9, 118.3, 125.8, 126.3, 129.6,
129.9, 132.5, 138.5, 145.4, 158.4. Anal. Calcd for C29H34N4Si: C,
74.63; H, 7.34; N, 12.01. Found: C, 74.75; H, 7.32; N, 12.01.
J. Org. Chem, Vol. 71, No. 9, 2006 3353

Youngblood
mL of water and then centrifuged. The supernatant was removed,
and the pellet was resuspended in MeOH and centrifuged again.
After the supernatant was removed a second time, the pellet was
redissolved in THF (2 mL) and precipitated by addition of MeOH
(16 mL) and water (2 mL). The mixture was centrifuged, and upon
removal of the supernatant, the pellet was dried in vacuo, giving a
green solid (72 mg, 46%): 1H NMR (THF-d8) δ 0.82-0.95 (m,
24H), 1.20-1.60 (m, 76H), 1.88-2.05 (m, 8H), 2.17-2.35 (m,
16H), 3.20-3.35 (m, 4H), 4.60-4.80 (m, 8H), 9.45 (s, 2H), 9.50
(s, 2H), 9.64-9.74 (m, 4H); LD-MS obsd 1633.0; FAB-MS obsd
1633.1111, calcd 1633.1051 (C100H144N16Zn); λabs (nm) 309, 357,
640, 681, 713; λem 724 nm; Φf ) 0.47.
Tetrakis(2-phenyl-1-propylbenzimidazo[5,6-b:5′,6′-g:5′′,6′′-l:
5′′′,6′′′-q])porphyrazine (Fb-8). The same procedure was followed
as for Fb-7 using DBU, with the following quantities: 6b (50.0
mg, 0.175 µmol), pentanol (875 µL), and DBU (26 µL, 175 µmol).
The product was a green solid (19 mg, 38%). Due to the presence
of regioisomers, some 1H NMR resonances have noninteger
integrations: 1H NMR (THF-d8) δ -3.13 (br s, 2H), 1.02-1.25
(m, 12H), 2.04-2.34 (m, 8H), 4.18-4.56 (m, 8H), 7.50-7.70 (m
12H), 7.90-8.08 (m, 8H), 8.12-8.22 (br s, 1H), 8.28-8.77 (m,
5H), 8.90-8.96 (m, 0.5H), 9.00-9.12 (m, 1.5H); LD-MS obsd
1146.7; FAB-MS obsd 1147.5127, calcd 1147.5109 [(M + H)+;
M ) C72H58N16]; λabs (nm) 316, 382, 648, 679, 718, 740; λem 744
nm; Φf ) 0.70.
Preparation of Fb-8 Using Lithium Pentoxide. The same
procedure was followed as for Fb-7 using Li, with the following
quantities: pentanol (875 µL), Li ribbon (10.0 mg, 1.44 mmol),
and 6b (50 mg, 175 µmol). The product was isolated as a green
solid (14 mg, 28%). Characterization data were consistent with the
material produced from the DBU-mediated preparation of Fb-8
(vide supra).
Tetrakis(2-phenyl-1-propylbenzimidazo[5,6-b:5′,6′-g:5′′,6′′-l:
5′′′,6′′′-q])porphyrazinatomagnesium(II) (Mg-8). The same pro-
cedure was followed as for Mg-7, with the following quantities:
6b (50.0 mg, 0.175 µmol), MgCl2 (4.2 mg, 44 µmol), pentanol
(875 µL), and DBU (26 µL, 175 µmol). The product was isolated
as a green solid (33 mg, 65%): 1H NMR (THF-d8) δ 1.12-1.22
(m, 12H), 2.22-2.34 (m, 8H), 4.83-4.92 (m, 8H), 7.59-7.72 (m,
12H), 8.06-8.12 (m, 8H), 9.55 (br s, 2H), 9.63 (br s, 2H), 9.76-
9.84 (m, 4H); LD-MS obsd, 1168.8; FAB-MS obsd 1168.4695,
calcd 1168.4724 (C72H56MgN16); λabs (nm) 314, 364, 643, 684, 717;
λem 724 nm; Φf ) 0.84.
residue was then dissolved in THF, eluted through a short plug of
silica gel in THF, and chromatographed over a column of Bio-
Beads SX-3 in THF. The mixture separated into three bands. The
first band (green) appeared (by HPLC-SEC analysis) to contain
compounds containing two or more benzimidazoles. The second
band (blue) contained Zn-11. The third band (blue) contained Zn-
10. The fractions containing Zn-10 and Zn-11 were set aside, and
the first band of green material was reconcentrated and chromato-
graphed over a column of Bio-Beads SX-1 in THF. The mixture
separated into two broad green bands. The first band, containing
pigments having three and four benzimidazoles, could not be further
purified by any chromatographic method and was therefore
discarded. The second green band contained a mixture of Zn-12
and Zn-13. The mixture was separated by chromatography (silica,
CHCl3, 2% 2-propanol).
Zinc Phthalocyanine (Zn-10, A4). The compound was isolated
as a blue band from chromatography on Bio-Beads SX-3 (vide
supra). The THF solution was concentrated, and the residue was
chromatographed over a short column (silica, CHCl3, 2% 2-pro-
panol). Fractions containing the product were concentrated, giving
a blue solid (10 mg, 4%): 1H NMR (THF-d8) δ 8.17-8.23 (m,
8H), 9.45-9.50 (m, 8H); LD-MS obsd, 576.3; FABMS obsd
576.0813, calcd 576.0789 (C32H16N8Zn); λabs 666 nm.
Tribenzo[g,l,q]-(2-{4-(2-triisopropylsilylethynyl)phenyl}-1-
propylbenzimidazo[5,6-b])porphyrazinatozinc(II) (Zn-11, A3B).
The compound was isolated as a blue band from chromatography
on Bio-Beads SX-3 (vide supra). The THF solution was concen-
trated, and the residue was chromatographed over a short column
(silica, CHCl3, 2% 2-propanol). Fractions containing the product
were concentrated, giving a blue solid (86 mg, 22%): 1H NMR
(THF-d8) δ 1.14 (t, J ) 7.2 Hz, 3H), 1.27 (s, 21H), 2.16-2.26 (m,
2H), 4.75 (t, J ) 7.6 Hz, 2H), 7.82 (d, J ) 8.0 Hz, 2H), 8.00-8.15
(m, 8H), 9.09 (s, 1H), 9.13 (d, J ) 7.6 Hz, 1H), 9.22-9.34 (m,
5H), 9.37 (s, 1H); LD-MS obsd, 914.7; FAB-MS obsd 914.2986,
calcd 914.2968 (C53H46N10SiZn); λabs (nm) 340, 611, 674; λem 692
nm; Φf ) 0.47.
Dibenzo[l,q]-(2-{4-(2-triisopropylsilylethynyl)phenyl}-1-pro-
pylbenzimidazo[5,6-b:5′,6′-g])porphyrazinatozinc(II) (Zn-12, cis-
A2B2). The compound was isolated from silica gel chromatography
as the first green band and concentrated to give a green solid (74
mg, 14%): 1H NMR (THF-d8) δ 1.09-1.20 (m, 6H), 2.15-2.30
(m, 4H), 4.81 (t, J ) 7.6 Hz, 4H), 7.76-7.84 (m, 4H), 8.06-8.19
(m, 8H), 9.12-9.50 (m, 5H), 9.63 (s, 1H), 9.70 (s, 1H); LD-MS
obsd 1252.6; FAB-MS obsd 1252.5148, calcd 1252.5146 (C74H76N12-
Si2Zn); λabs (nm) 340, 623, 693; λem 701 nm; Φf ) 0.44.
Dibenzo[g,q]-(2-{4-(2-triisopropylsilylethynyl)phenyl}-1-pro-
pylbenzimidazo[5,6-b:5′,6′-l])porphyrazinatozinc(II)-C2W (Zn-
13b, trans-A2B2). The compound was isolated from chromatography
as the second green band and concentrated to give a green solid (4
mg, 1%). Characterization data were consistent with the compound
Tetrakis(2-phenyl-1-propylbenzimidazo[5,6-b:5′,6′-g:5′′,6′′-l:
5′′′,6′′′-q])porphyrazinatozinc(II) (Zn-8). The same procedure was
followed as for Zn-7, with the following quantities: 6b (50.0 mg,
0.175 µmol), ZnCl2 (6.0 mg, 44 µmol), pentanol (875 µL), and
DBU (26 µL, 175 µmol). The product was isolated as a green solid
(33 mg, 62%). The sample was found to be a regioisomeric mixture
1
of products, which resulted in some H NMR resonances having
noninteger integrations: 1H NMR (THF-d8) δ 1.11-1.21 (m, 12H),
2.20-2.33 (m, 8H), 4.72-4.86 (m, 8H), 7.60-7.71 (m, 12H),
8.05-8.12 (m, 8H), 9.30-9.43 (m, 4H), 9.49 (s, 0.5H), 9.59, (br
s, 1.5H), 9.66 (s, 0.5H), 9.71-9.74 (m, 1.5H); LD-MS obsd, 1208.6;
FAB-MS obsd 1208.4205, calcd 1208.4165 (C72H56N16Zn); λabs
(nm) 315, 357, 643, 685, 717; λem 724 nm; Φf ) 0.43.
Zn-13b isolated from the metalation of Fb-13 (vide infra): H NMR
1
(THF-d8) δ 1.15 (t, J ) 7.2 Hz, 6H), 1.25 (s, 42H), 2.20-2.28 (m,
4H), 4.81 (t, J ) 7.2 Hz, 4H), 7.79 (d, J ) 8.4 Hz, 4H), 8.09 (d,
J ) 8.4 Hz, 4H), 8.12-8.17 (m, 2H), 8.17-8.22 (m, 2H), 9.37 (s,
2H), 9.37-9.42 (m, 2H), 9.43-9.48 (m, 2H), 9.60 (s, 2H); LD-
MS obsd 1252.6, calcd 1252.5 (C74H76N12Si2Zn); λabs (nm) 335,
679, 708; FAB-MS and fluorescence data were not separately
obtained for this sample, but were obtained for the sample reported
from the metalation of Fb-13.
Tribenzo[g,l,q]-(2-{4-(2-triisopropylsilylethynyl)phenyl}-1-
propylbenzimidazo[5,6-b])porphyrazine (Fb-11, A3B). A 20 mL
reaction vial was charged with 14a (40.0 mg, 83 µmol), boron
subphthalocyanine 1548 (143 mg, 332 µmol, 4 equiv), DMAE (4
mL), and a magnetic stirring bar. The vial was capped and heated
in an oil bath at 100 °C. Periodically, a few microliters of the
reaction mixture were removed, diluted into THF, and analyzed
by UV-vis spectroscopy. After the reaction had proceeded for 10
h, 15 could not be observed in the UV-vis spectrum. The reaction
was then cooled to room temperature and diluted with MeOH (50
Preparative-Scale Macrocyclization Reaction Using 6d and
1,2-Dicyanobenzene. A two-necked, 25 mL round-bottom flask
was charged with 6d (317 mg, 0.679 mmol), dicyanobenzene (130
mg, 1.02 mmol, 1.5 equiv), and a magnetic stirring bar. The flask
was fitted with a condenser and a bubbler and a septum for the
second neck. The apparatus was flushed for 20 min with a stream
of argon and then briefly opened to add ZnCl2 (58 mg, 0.43 mmol).
Then pentanol (8.5 mL) was added, and the mixture was gradually
heated to reflux. When the mixture was homogeneous, DBU (254
µL, 1.70 mmol) was added. The mixture was refluxed overnight
(12 h). The mixture was then cooled to room temperature and
diluted into MeOH (300 mL) and water (50 mL). The resulting
precipitate was filtered, rinsed with EtOH, and dried in vacuo. The
3354 J. Org. Chem., Vol. 71, No. 9, 2006

Synthesis of a New trans-A2B2 Phthalocyanine Motif
mL) and water (30 mL). The mixture was filtered through paper,
and the solid residue was rinsed with MeOH and air-dried. The
filter paper containing the solid residue was then loaded into a
Soxhlet thimble, and the thimble was extracted with CHCl3 for 20
h. Upon the apparatus was cooled, most of the extracted pigment
precipitated out of the filtrate. The solvent was removed from the
filtrate under reduced pressure and the solid material was resus-
pended in THF (20 mL) with sonication. The mixture was filtered
through a cotton-plugged pipet and chromatographed over a column
of Bio-Beads SX-3 in THF. The desired compound was recovered
from the column as a dark blue-green band that eluted just after a
faint green band and before a purple band. The faint green band
was identified by UV-vis as a mixture of benzimidazoporphyra-
zines having more than one benzimidazole, and was discarded. The
purple band was identified by UV-vis as a mixture of remaining
subPc 15 and unsubstituted phthalocyanine and was discarded. The
fractions containing the desired compound were concentrated and
chromatographed over silica gel (CH2Cl2, 2% 2-propanol, 2.5%
THF, 2.5% ethyl acetate). Fractions containing the desired com-
pound were concentrated, giving a blue solid (18 mg, 25%): 1H
NMR (THF-d8) δ -3.29 (br s, 2H), 1.17 (t, J ) 7.6 Hz, 3H), 1.32
(s, 21H), 2.10-2.25 (m, 2H), 4.45-4.60 (m, 2H), 7.68 (t, J ) 7.2
Hz, 1H), 7.75-7.94 (m, 4H), 7.87 (d, J ) 8.0 Hz, 4H), 8.11 (d, J
) 8.0 Hz, 4H), 8.24-8.32 (m, 1H), 8.52-8.66 (m, 3H), 8.68-
8.82 (m, 4H); LD-MS obsd 852.5; FAB-MS obsd 853.3945, calcd
853.3911 [(M + H)+; M ) C53H48N10Si]; λabs (nm) 337, 622, 649,
669, 695; λem (nm) 700, 714; Φf ) 0.68.
Dibenzo[g,q]-(2-{4-(2-triisopropylsilylethynyl)phenyl}-1-pro-
pylbenzimidazo[5,6-b:5′,6′-l])porphyrazine (Fb-13, trans-A2B2).
An oven-dried, three-necked, 300 mL round-bottom flask was
charged with 14 (465 mg, 0.96 mmol) and a magnetic stirring bar.
The vessel was flushed with argon for 10 min and immersed in an
ice bath. Freshly dried THF (70 mL) and freshly dried TEA (269
µL, 1.92 mmol, 2 equiv) were added to the flask. A sample of 1649
(212 mg, 0.96 mmol) was dissolved in dry THF (10 mL) and slowly
added to the reaction vessel. The mixture was kept at 0-5 °C for
1 h and then allowed to warm to room temperature overnight. Then
the triethylammonium salt that had formed was removed by
filtration of the mixture into an oven-dried, two-necked, 250 mL
round-bottom flask. The vessel was flushed with argon for 5 min,
and a sample of hydroquinone (106 mg, 0.96 mmol) in THF (10
mL) was added, followed by NaOMe (658 µL of a 25 wt % solution
in MeOH, 2.88 mmol, 3 equiv). The mixture was refluxed for 6 h,
then cooled to room temperature and poured into MeOH (20 mL),
to which water (100 mL) was added. After standing for 1 h, the
mixture was filtered and the solid residue was air-dried, dissolved
in CH2Cl2, and chromatographed (silica, CH2Cl2, 1% 2-propanol,
5% ethyl acetate, 5% THF). The first green band (faint) was
identified by LD-MS as the AB3 macrocycle (LD-MS m/z 1526.0).
The product was collected as the second (dark) green band (49
mg, 9%): 1H NMR (THF-d8) δ -4.32 (br s, 1H), -4.22 (br s,
1H), 1.02 (t, J ) 6.8 Hz, 3H), 1.10 (t, J ) 6.8 Hz, 3H), 1.34 (s,
42H), 1.82-2.10 (m, 4H), 4.10-4.38 (m, 4H), 7.29-7.37 (m, 1H),
7.47-7.64 (m, 4H), 7.74-7.83 (m, 4H), 7.83-7.90 (m, 1H), 7.91
(d, J ) 7.6 Hz, 2H), 7.95 (d, J ) 8.4 Hz, 2H), 7.99-8.15 (m, 4H),
8.17-8.24 (m, 1H), 8.29-8.47 (m, 1H); LDMS obsd 1190.7;
FABMS obsd 1190.6040, calcd 1190.6011 (C74H78N12Si2); λabs (nm)
340, 610, 631, 662, 681, 703, 732; λem (nm) 711, 739; Φf ) 0.66.
Dibenzo[g,q]-(2-{4-(2-triisopropylsilylethynyl)phenyl}-1-pro-
pylbenzimidazo[5,6-b:5′,6′-l])porphyrazinatozinc(II) (Zn-13, trans-
A2B2). From Cross-Condensation Reaction. An oven-dried 20
mL reaction vial was charged with 14 (48 mg, 99 µmol) and a
magnetic stirring bar. The vial was capped with a septum flushed
with argon for 10 min and immersed in an ice bath. Freshly dried
THF (8 mL) and freshly dried TEA (28 µL, 0.20 mmol, 2 equiv)
were added to the vial. A sample of 1649 (22 mg, 99 µmol) was
dissolved in dry THF (2 mL) and slowly added to the reaction vial.
The mixture was kept at 0-5 °C for 1 h and then allowed to warm
to room temperature overnight. The triethylammonium salt that had
formed was removed by filtration of the mixture into an oven-
dried, 25 mL round-bottom flask. Hydroquinone (11 mg) was added,
and the vessel was flushed with argon for 5 min, and NaOMe (69
µL of a 25 wt % solution in MeOH, 0.30 mmol, 3 equiv) was added.
The mixture was refluxed for 6 h, then cooled to room temperature
and poured into MeOH (50 mL), to which water (2 mL) was added.
After standing for 1 h, the mixture was filtered, and the solid residue
was air-dried, dissolved in CH2Cl2, and chromatographed (silica,
CH2Cl2, 1% 2-propanol, 2.5% ethyl acetate, 2.5% THF). The first
green band (faint) was identified by LD-MS as the ZnAB3
macrocycle (LD-MS m/e 1591.0). The product was collected as
the second (dark) green band (5.0 mg, 4%): 1H NMR (THF-d8) δ
1.15 (t, J ) 7.6 Hz, 6H), 1.28 (s, 42H), 2.13-2.25 (m, 4H), 4.69
(t, J ) 7.6 Hz, 4H), 7.80 (d, J ) 8.0 Hz, 4H), 8.02-8.20 (m, 4H),
8.09 (d, J ) 8.0 Hz, 4H), 9.06-9.13 (m, 1H), 9.18-9.24 (m, 2H),
9.29-9.43 (m, 5H); LD-MS obsd 1252.8; FAB-MS obsd 1252.5242,
calcd 1252.5146 (C74H76N12Si2Zn); λabs (nm) 338, 614, 648, 679,
709. Fluorescence data were not collected from this sample but
were collected for the separated regioisomers (vide infra).
From Zinc Metalation of Fb-13. A 20 mL reaction vial was
charged with Fb-13 (20 mg, 17 µmol), Zn(OAc)2‚2H2O (7.4 mg,
34 µmol, 2 equiv), dioxane (2.0 mL), DMF (0.5 mL), and a
magnetic stirring bar. The vial was kept in an oil bath heated to
100 °C for 2 h, upon which the UV-vis absorbance analysis of a
removed sample showed a spectrum for Zn-13 with no evidence
of remaining starting material. The reaction mixture was cooled
and diluted to 20 mL with MeOH. The mixture was filtered, and
the solid was air-dried, then dissolved through the filter with THF,
and concentrated to dryness. The residue was chromatographed
(silica, toluene, 10% THF) to separate a trace of remaining Fb-13
that was too small to be detected in the mixture by UV-vis analysis.
The product eluted as the first (dark) green band (19 mg, 90%). A
second chromatography (silica, CH2Cl2, 1% 2-propanol, 5% ethyl
acetate, 5% THF) separated the two regioisomeric products. The
first green band was assigned as Zn-13a. Fractions containing the
second green band were rechromatographed twice to separate all
trace of the first eluting isomer. The second eluting species was
assigned as Zn-13b. These two isomers, Zn-13a and Zn-13b, were
determined by their COSY NMR data to be the C2h and C2V
symmetric structures, respectively (see the Results and Discussion).
1
Data for Zn-13a (C2h): yield ) 10.0 mg (47%); H NMR (THF-
d8) δ 1.16 (t, J ) 8.0 Hz, 6H), 1.28 (s, 42H), 2.14-2.26 (m, 4H),
4.71 (t, J ) 8.0 Hz, 4H), 7.81 (d, J ) 8.0 Hz, 4H), 8.02-8.14 (m,
4H), 8.08 (d, J ) 8.0 Hz, 4H), 8.88 (s, 2H), 9.13 (d, J ) 7.2 Hz,
2H), 9.22 (s, 2H), 9.23 (d, J ) 7.2 Hz, 2H); LD-MS obsd 1253.0;
FAB-MS obsd 1252.5214, calcd 1252.5146 (C74H76N12Si2Zn); λabs
(nm) 338, 614, 648, 679, 709; λem 717 nm; Φf ) 0.32.
Data for Zn-13b (C2W): yield ) 9.0 mg (43%); 1H NMR (THF-
d8) δ 1.15 (t, J ) 7.6 Hz, 6H), 1.28 (s, 42H), 2.13-2.25 (m, 4H),
4.69 (t, J ) 7.6 Hz, 4H), 7.79 (d, J ) 7.6 Hz, 4H), 8.13 (d, J ) 7.6
Hz, 6H), 8.10-8.19 (m, 2H), 8.95 (s, 2H), 9.09-9.20 (m, 2H),
9.21-9.35 (m, 4H); LD-MS obsd 1252.4; FAB-MS 1252.5172,
calcd 1252.5146 (C74H76N12Si2Zn); λabs (nm) 338, 614, 648, 679,
709; λem 717 nm; Φf ) 0.26.
2-(4-(2-(Triisopropylsilyl)ethynyl)phenyl)-1-propylimidazo-
[4,5-f]isoindole-1,3-diimine (14). Following a literature proce-
dure,43 a 25 mL round-bottom flask was charged with 6d (606 mg,
1.30 mmol) and a magnetic stirring bar. The vessel was sealed with
a condenser, a bubbler, and a septum for the second neck. The
apparatus was flushed with argon for 15 min, and then anhydrous
MeOH (14 mL), freshly dried THF (7 mL), and NaOMe (30 µL of
a 25 wt % solution in MeOH, 130 µmol) were added. The reaction
flask was heated in an oil bath at 70 °C, and the mixture became
homogeneous. The argon line was removed, and ammonia gas was
bubbled through the mixture as it refluxed for 6 h. The flask was
then removed from heat and allowed to cool under ammonia
atmosphere. When the mixture reached room temperature, the
ammonia gas flow was stopped and the mixture was allowed to
stand overnight under a slowly flowing stream of argon, during
J. Org. Chem, Vol. 71, No. 9, 2006 3355

Youngblood
which time some greenish-white crystals formed in the vessel. The
supernatant was drained off with a pipet, and the crystals were
washed with a few milliliters of anhydrous MeOH and then dried
in vacuo, yield 479 mg, 76%; mp 248-250 °C, upon which the
sample melted and turned deep green. The melting capillary was
broken and the residue taken up in THF and analyzed by UV-vis
spectroscopy, which showed a spectrum similar to that of Fb-8.
Due to the presence of tautomeric forms of the product, the NH
signals do not all integrate to integers: 1H NMR (THF-d8) δ 0.86
(t, J ) 7.2 Hz, 3H), 1.19 (s, 21H), 1.80-1.92 (m, 2H), 3.14 (br s,
0.5H), 4.30-4.44 (m, 2H), 7.48 (br s, 0.5H), 7.65 (d, J ) 8.0 Hz,
2H), 7.83 (d, J ) 8.0 Hz, 2H), 7.80-8.60 (m, 4H); due to poor
solubility, 13C NMR spectroscopy was not performed; IR (film)
3260, 3201, 2941, 2861, 2161, 1666, 1547, 1460, 1410, 1345, 1144,
1109, 1081, 1054, 994, 916, 882; FAB-MS obsd 484.2876, calcd
484.2896 [(M + H)+; M ) C29H37N5Si] Anal. Calcd for C29H37N5-
Si: C, 72.01; H, 7.71; N, 14.48. Found: C, 69.90; H, 7.86; N,
13.91 (consistent with crystal inclusion of one molecule MeOH
per molecule compound..
Dibenzo[g,q]-(2-{4-ethynylphenyl}-1-propylbenzimidazo[5,6-
b:5′,6′-l])porphyrazinatozinc(II)-C2h (Zn-17a, trans-A2B2). A 20
mL vial was charged with Zn-13a (9.5 mg, 7.6 µmol), CH2Cl2 (4
mL), and a magnetic stirring bar. Then TBAF (17 µL of a 1 M
solution in THF, 17 µmol) was added, and the mixture was stirred
at room temperature for 1.5 h. TLC analysis (silica, CH2Cl2, 1%
2-propanol, 5% ethyl acetate, 5% THF) indicated that neither
starting material nor intermediate remained, so the mixture was
directly added to a short (15 cm) silica gel column packed in CH2-
Cl2. The product proved to be very polar, and the eluent (CH2Cl2,
1% 2-propanol, 5% ethyl acetate, 5% THF) was changed to
increasing amounts of THF (final eluent: CH2Cl2/THF, 1:4) to elute
the product as a dark blue-green band (6.2 mg, 87%): 1H NMR
(THF-d8) δ 1.17 (t, J ) 7.2 Hz, 6H), 2.18-2.28 (m, 4H), 3.84 (s,
2H), 4.74 (t, J ) 8.0 Hz, 4H), 7.70 (d, J ) 8.4 Hz, 4H), 8.02-8.12
(m, 4H), 8.05 (d, J ) 8.4 Hz, 2H), 9.04 (br s, 2H), 9.21 (d, J ) 6.4
Hz, 2H), 9.26-9.32 (m, 4H); LD-MS obsd 940.6; FAB-MS obsd
940.2510, calcd 940.2477 (C56H36N12Zn).
Dibenzo[g,q]-(2-{4-ethynylphenyl}-1-propylbenzimidazo[5,6-
b:5′,6′-l])porphyrazinatozinc(II)-C2v (Zn-17b, trans-A2B2). The
same procedure was followed as for Zn-17a, with the following
quantities: Zn-13b (8.2 mg, 6.5 µmol), CH2Cl2 (4 mL), and TBAF
(14 µL of a 1 M solution in THF, 14 µmol). The chromatography
procedure was followed similarly (final eluent: CH2Cl2, 30% THF),
and the product eluted as a dark blue-green band (4.4 mg, 72%):
1H NMR (d8-THF) δ 1.15 (t, J ) 6.8 Hz, 6H), 2.16-2.27 (m, 4H),
3.85 (s, 2H), 4.72 (t, J ) 7.6 Hz, 4H), 7.77 (d, J ) 7.6 Hz, 4H),
8.04 (d, J ) 7.6 Hz, 6H), 8.12-8.17 (m, 2H), 9.04 (s, 2H), 9.16-
9.22 (m, 2H), 9.29-9.35 (m, 4H); LD-MS obsd 940.9; FAB-MS
obsd 940.2490, calcd 940.2477 (C56H36N12Zn).
Acknowledgment. I thank Prof. Jonathan S. Lindsey for
helpful advice on this work. This research was supported by a
grant to Prof. Jonathan S. Lindsey from the Division of
Chemical Sciences, Office of Basic Energy Sciences, Office of
Energy Research, U.S. Department of Energy. W.J.Y. was also
supported by a GAANN-ELMAT fellowship from the Depart-
ment of Education. Mass spectra were obtained at the Mass
Spectrometry Laboratory for Biotechnology at North Carolina
State University. Partial funding for the NCSU Facility was
obtained from the North Carolina Biotechnology Center and
the NSF.
Supporting Information Available: A detailed presentation of
the photochemical behavior of the benzimidazoporphyrazines
prepared for this report, as well as general experimental information
and characterization data (NMR, LD-MS, UV-vis, fluorescence)
for selected compounds. This material is available free of charge
via the Internet at http://pubs.acs.org.
JO052122L
3356 J. Org. Chem., Vol. 71, No. 9, 2006