Cobaltacarborane-phthalocyanine conjugates: Syntheses and photophysical properties

Article abstract of DOI:10.1016/j.jorganchem.2008.11.037

Syntheses of two new cobaltacarborane-phthalocyanine conjugates, one anionic (Pc 6) and one zwitterionic (Pc 7), were accomplished via cyclotetramerization of the corresponding cobaltacarborane-substituted phthalonitriles (4 or 5) with excess phthalonitri

Full text of DOI:10.1016/j.jorganchem.2008.11.037

Journal of Organometallic Chemistry 694 (2009) 1607–1611
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Cobaltacarborane–phthalocyanine conjugates:
Syntheses and photophysical properties
*
Hairong Li, Frank R. Fronczek, M. Graça H. Vicente
Department of Chemistry, Louisiana State University, 433 Choppin Hall, Baton Rouge, LA 70803, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Syntheses of two new cobaltacarborane–phthalocyanine conjugates, one anionic (Pc 6) and one zwitter-
ionic (Pc 7), were accomplished via cyclotetramerization of the corresponding cobaltacarborane-substi-
tuted phthalonitriles (4 or 5) with excess phthalonitrile in quinoline. X-ray structures of two
phthalonitrile precursors (2 and 3) were obtained and are discussed, and the absorption and emission
properties of the two cobaltacarborane–phthalocyanine conjugates in several solvents were investigated.
The anionic conjugate 6 exists mainly as a monomer in polar organic solvents and has fluorescence quan-
tum yields in the region 0.2–0.3. The zwitterionic conjugate 7 aggregates in solution and displays lower
quantum yields ꢀ0.1 in organic solvents.
Received 10 September 2008
Received in revised form 4 November 2008
Accepted 5 November 2008
Available online 27 November 2008
Keywords:
Cobaltacarborane
Phthalocyanine
BNCT
Ó 2008 Elsevier B.V. All rights reserved.
PDT
1. Introduction
vents [10]. Herein we report the syntheses of two new cobaltacar-
borane–phthalocyanine conjugates, one anionic and the other
Phthalocyanines (Pcs) containing boron-10 are attractive dual
sensitizers for the photodynamic therapy (PDT) and the boron neu-
tron capture therapy (BNCT) of tumors, due to their strong absorp-
tions in the near-IR, their ability for generating singlet oxygen with
high quantum yields and their tendency for selective accumulation
within tumor tissues [1–4]. BNCT [5] and PDT [6] are localized can-
cer treatment modalities that involve the irradiation of sensitizer-
rich tumors with low energy neutrons (in BNCT) or light (in PDT).
The use of a single drug for both the BNCT and PDT of cancer has
several advantages, since a dual treatment approach might lead
to increased therapeutic efficacy due to the targeting of different
cellular components and/or mechanisms of tumor cell destruction.
We have recently reported the synthesis of boron-containing chlo-
rins [7,8], tetrabenzoporphyrins [9] and phthalocyanines [10] for
application as dual sensitizers in BNCT and PDT. Of these classes
of compounds cobaltacarborane-containing Pcs show the strongest
near-IR absorptions (>670 nm), which are able to utilize light hav-
ing a deeper penetration power into most human tissues [11]. Sev-
eral phthalocyanine-based molecules, for example AlPcS4 and Pc4,
are currently undergoing clinical investigations for application in
PDT [12]. On the other hand, only a few boron-containing phthal-
ocyanines have been reported to date, because of their difficult
syntheses and purification procedures. We have recently synthe-
sized a series of anionic cobaltacarboranyl–phthalocyanines that
show high solubility and exist as monomers in polar organic sol-
zwitterionic, and compare their solubility and photophysical
properties.
2. Results and discussion
The synthetic route to cobaltacarborane–phthalocyanine conju-
gates 6 and 7 involves the nucleophilic attack of zwitterionic 3,30-
Co(8-C4H8O2-1,2-C2B9H10)(10,20-C2B9H10) [13] by phenoxyl or pyri-
dyl substituents situated on phthalonitriles 2 and 3, followed by
cyclotetramerization in the presence of excess phthalonitrile and
zinc acetate (Scheme 1). The (4-hydroxyphenoxyl)phthalonitrile
(2) was synthesized using two different methods: (1) by nucleo-
philic aromatic substitution of the nitro group of 1 followed by
deprotection of the methoxy group using BBr3 (in 33% overall
yield), or (2) by direct nucleophilic substitution of 3-nitrophthalo-
nitrile (1) using hydroquinone in 22% yield. 3-Pyridyloxyphthalo-
nitrile (3) was prepared in 74% yield from the reaction of
3-nitrophthalonitrile (1) and 3-hydroxypyridine. The molecular
structures of phthalonitriles 2 and 3 are shown in Fig. 1 and the
crystal data are presented in Table 1. All CN triple bond distances
fall within the range 1.147(2)–1.151(2) Å. The conformations of
the two molecules are quite similar. The dihedral angle formed
by the phthalonitrile ring and the phenol ring in 2 is 82.80(3)°,
while the corresponding angle between the phthalonitrile and pyr-
idine rings in 3 is 70.50(3)°. The phenolic OH group in 2 forms an
essentially linear intermolecular O–Hꢁ ꢁ ꢁN hydrogen bond with ni-
trile N1, having Oꢁ ꢁ ꢁN distance 2.8137(17) Å.
* Corresponding author.
E-mail address: vicente@lsu.edu (M. Graça H. Vicente).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.11.037

1608
H. Li et al. / Journal of Organometallic Chemistry 694 (2009) 1607–1611
OR
O
OH
a, b
c
N
N
NC
NC
CN
N
Zn
N
e
d
2
NO2
OR
N
N
NC
CN
NC
CN
N
N
O
1
4, 5
N
CN
3
6, 7
O
O
O
4, 6: R =
5, 7: R =
K
O
Co
CH
BH
B
O
N
Co
Scheme 1. Conditions: (a) 4-methoxyphenol, K2CO3, DMF, 90 °C (83%); (b) BBr3, CH2Cl2, ꢂ80 °C (40%); (c) 3-hydroxypyridine, K2CO3, DMF, 90 °C (74%); (d) 3,30-Co(8-C4H8O2-
1,2-C2B9H10)(10,20-C2B9H10), K2CO3, 50 °C, 24 h (94%); (e) 30 equiv. phthalonitrile, Zn(OAc)2, quinoline, 220 °C, 1 h (1–8%).
Cobaltacarborane-containing phthalonitriles 4 and 5 were syn-
thesized in 94% yield via a nucleophilic opening reaction of the
dioxane ring of 3,30-Co(8-C4H8O2-1,2-C2B9H10)(10,20-C2B9H10) in
the presence of anhydrous potassium carbonate, as previously re-
ported [10]. Cyclotetramerization of phthalonitriles 4 and 5 with
an excess (30 equiv.) of phthalonitrile in quinoline and in the pres-
ence of zinc acetate as template gave the target A3B-type phthalo-
cyanines 6 and 7 in 8% and 1% yields, respectively. The very low
yield obtained for Pc 7 is mainly due to the instability of pyr-
idyloxyphthalonitrile (5) under the high temperature reaction con-
ditions, and the lower solubility of Pc 7 in common organic
solvents due to its higher tendency for aggregation compared with
Pc 6. The observed low solubility of zwitterionic Pc 7 in comparison
with anionic Pc 6, is in agreement with our earlier investigations of
cobaltacarborane–porphyrin conjugates [14–16].
matic protons on the phenoxyl and pyridyloxyl rings are shifted
upfield to 7–8 ppm. The aliphatic and dicarbollide protons appear
in the range 3–5 ppm. Mass spectrometry (ESI) shows the mono-
negative molecular ion of Pc 6 at m/z 1095.4212 [MꢂK]ꢂ. However,
we were unable to obtain a clear mass spectrum with the expected
isotopic patterns for Pc 7 due to its poor solubility in most organic
solvents.
The absorption spectra of Pc 6 in acetone, DMF, DMSO and
methanol show characteristic strong Q bands typical of monomeric
Pcs with extinction coefficients larger than 105 L molꢂ1 cmꢂ1. Fig. 2
shows the absorption spectrum of Pc 6 in various solvents. As we
have previously observed [10], the kmax for the Q absorption band
in DMSO (679 nm) was red-shifted by 7 nm compared with that in
acetone (672 nm). In comparison with the anionic di-a-substituted
cobaltacarboranyl–Pcs previously reported [10], Pc 6 shows 12–
18 nm blue-shifted absorption and emission bands. In HEPES pH
7.4 solution Pc 6 showed a significant broader and weaker absorp-
tion, indicating aggregation of this compound in aqueous solution.
On the other hand, the zwitterionic Pc 7 shows broader, weaker
The 1H NMR spectra of compounds 6 and 7 in deuterated DMF
show the macrocycle protons on the three identical isoindole sub-
units in the downfield region between 8 and 10 ppm, consistent
with those observed for the di-substituted analogs [10]. The aro-
Fig. 1. Molecular structures of phthalonitriles (a) 2 and (b) 3.

H. Li et al. / Journal of Organometallic Chemistry 694 (2009) 1607–1611
1609
Table 1
yield [17] in DMSO (0.29), and the lowest in methanol (0.13). On
the other hand Pc 6 has lower fluorescence quantum yields than
Pc 7 in the corresponding solvent, the highest in DMSO and ace-
tone (0.11), and the lowest in methanol (0.09). Quantum yields
in the range 0.09–0.15 are typical for this type of compound
[10,18]. Of all the cobaltacarborane-containing Pcs that we have
tested to date, Pc 6 shows the largest fluorescence quantum yield
in DMSO. We are currently investigating the biological properties
of cobaltacarboranyl–Pcs, and their potential for application as
dual sensitizers in the PDT and BNCT treatment of tumors.
Crystal data and structure refinement.
2
3
Formula
C14H8N2O2
CCDC 699696
236.22
Orthorhombic
Pna21
C13H7N3O
CCDC 699697
221.22
Monoclinic
P21/n
CCDC deposition no.
Formula weight
Crystal system
Space group
Cell dimensions
a (Å)
17.586(2)
11.7388(15)
5.4751(5)
90
1130.3(2)
90
9.151(2)
10.401(2)
11.457(2)
108.690(10)
1033.0(4)
90
b (Å)
c (Å)
b (°)
3. Conclusions
V (Å3)
Temperature (K)
Z
Two new cobaltacarborane–phthalocyanine conjugates have
been synthesized via the cyclotetramerization of the correspond-
ing cobaltacarborane–phthalonitriles with excess phthalonitrile.
The X-ray structures of phthalonitrile intermediates 2 and 3 are
presented. While the anionic Pc 6 is highly soluble in polar organic
solvents and only shows aggregation in aqueous solution, Pc 7
shows increased aggregation behavior in both polar organic sol-
vents and in aqueous solution. Pc 6 has blue-shifted absorption
4
4
Crystal size
0.17 ꢃ 0.22 ꢃ 0.25
0.17 ꢃ 0.23 ꢃ 0.25
l
(mmꢂ1
)
0.096
0.095
hmax (°)
Data collected
Independent data
Observed (I > 2
35.0
21256
2677
2361
0.022
0.037
0.096
2677/166
0.42, ꢂ0.24
30.0
13500
3018
2311
0.028
0.040
0.097
r
(I))
[R(int)
]
R
wR2 [I > 2
Data/parameter
Residual density (e Åꢂ3
r(I)]
and emission bands compared with di-a-substituted cobaltacarb-
3018/155
0.33, ꢂ0.22
oranyl–Pcs but significantly higher fluorescence quantum yields
(0.2–0.3) in polar organic solvents, while Pc 7 has decreased quan-
tum yields of ꢀ0.1. Both Pcs 6 and 7 might have application as dual
sensitizers in the PDT and BNCT treatment of tumors.
)
and red-shifted Q absorptions in acetone and DMSO compared
with Pc 6, due to its higher tendency for aggregation. Pc 7 has a
major absorption at 681 nm in acetone and a corresponding
14 nm red-shifted absorption in DMSO. In HEPES pH 7.4 solution
Pc 7 showed even a broader and weaker absorption. The emission
spectra of Pcs 6 and 7 in acetone and DMSO show the same trend
as their absorption spectra, as seen in Fig. 3. The spectroscopic
properties of Pc 6 and 7 are summarized in Table 2. While Pc 6
emits at 684 nm in DMSO Pc 7 emits at 701 nm, a value similar
4. Experimental
4.1. General
All reagents and solvents were purchased from commercial
sources and used directly without further purification. Silica gel
60 (230 ꢃ 400 mesh, Sorbent Technologies) and alumina gel (50–
200 lm, neutral, standard activity I, Sorbent Technologies) were
to those observed for the anionic di-a-substituted cobaltacarbora-
used for column chromatography. Analytical thin-layer chroma-
tography (TLC) was carried out using polyester backed TLC plates
254 (precoated, 200 lm) from Sorbent Technologies. NMR spectra
nyl–Pcs [10]. However, Pc 7 shows decreased intensity of emission
in acetone and DMSO compared with Pc 6. On the other hand Pc 6
has Stokes’ shifts of 3–4 nm in polar organic solvents such as ace-
tone, methanol and DMSO, while Pc 7 has larger Stokes’ shifts of 8–
10 nm in these solvents. Pc 6 has the largest fluorescence quantum
were recorded on a DPX-250 or AV-400 Bruker spectrometers
(250 MHz or 400 MHz for 1H, 63 MHz or 100 MHz for 13C). The
chemical shifts are reported in d ppm using the following deuter-
ated solvents as internal references: CD3COCD3 2.04 ppm (1H),
29.92 ppm (13C); d-DMF 2.92 ppm (1H), 34.89 ppm (13C); CD2Cl2
5.32 ppm (1H), 54.00 ppm (13C); CDCl3 7.24 ppm (1H), 77.23 ppm
(
13C). Electronic absorption spectra were measured on a Perkin–El-
mer Lambda 35 UV–Vis spectrometer. MALDI-TOF mass spectra
were recorded on a Bruker ProFlex III mass spectrometer using
dithranol as the matrix, and high resolution ESI mass spectra were
obtained on an Agilent Technologies 6210 Time-of-Flight LC/MS.
HPLC purification was carried out on a Dionex system equipped
with a P680 pump and a UVD340U detector with a multi-step gra-
dient elution; A: H2O, B: acetonitrile; 85% B (0 min)–95% B
(10 min)–100% B (20 min)–100% B (37 min) 85% B (40 min). A
semi-preparative column Luna C18 100 Å, 5
Phenomenex, USA, was used.
lm, 10 ꢃ 250 mm from
4.2. Phthalonitrile (2)
4.2.1. Method A
3-Nitrophthalonitrile (1) (1.5 g, 8.7 mmol) and 4-methoxyphe-
nol (1.6 g, 12.9 mmol) were dissolved in dry DMF (30 mL). Potas-
sium carbonate (20 g, 14.5 mmol) was added in five portions. The
reaction was heated at 90 °C for 2 h. The reaction mixture was
cooled to room temperature, poured into ice water (500 mL), and
the resulting precipitate was collected. The crude product was
purified by alumina column chromatography using dichlorometh-
Fig. 2. UV–Vis spectra of Pcs 6 (black) and 7 (red) at 4.5 lM concentration in
acetone (full line), DMSO (dash line), and HEPES pH 7.4 (dot line). (For interpre-
tation of the references to colour in this figure legend, the reader is referred to the
web version of this article.)

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H. Li et al. / Journal of Organometallic Chemistry 694 (2009) 1607–1611
Table 2
gon. The solution was heated to 50 °C. 3-Nitrophthalonitrile (1 g,
5.8 mmol) dissolved in DMF (2 mL) was added via syringe. The
reaction mixture was kept at 50 °C for 2 h and stirred at room tem-
perature for two days. After evaporation of the solvent under vac-
uum, 1 N HCl (30 mL) was added to the residue and the precipitate
was filtered and washed with water. The precipitate was dissolved
in acetone (50 mL) and dried over anhydrous sodium sulfate. The
crude product was purified by chromatography on a silica gel col-
umn using dichloromethane/methanol 95:5 for elution to afford a
white solid (0.3 g, 22%). 1H NMR (acetone-d6, 250 MHz): d 8.75 (br,
1H, OH), 7.79 (t, J = 4.3 Hz, 1H, Ar-H), 7.68–7.65 (m, 1H, Ar-H),
7.20–7.16 (m, 1H, Ar-H), 7.10–7.07 (m, 2H, Ar-H), 6.96–6.92 (m,
2H, Ar-H). 13C NMR (acetone-d6, 63 MHz): d 162.59, 156.44,
147.18, 136.16, 127.83, 122.64, 121.14, 117.60, 117.38, 116.22,
113.87, 105.63 (Ar-C, CN). HRMS-ESI m/z 237.0655 [M+H]+, calcd.
for [C14H9N2O2]+ 237.0658.
Spectroscopic properties of phthalocyanine conjugates 6 and 7.
Solvent
DMSO
Methanol
Acetone
HEPES
6a Absorption max (nm) 679 (m), 612 673(m), 608 672(m), 606 634(b)
Emission max (nm)
Stokes shift (nm)
Q.Y.c
684
4
0.29
678
3
0.13
677
4
0.24
–
–
–
7b Absorption max (nm) 693(m), 625
684(m), 621 681(m), 616 678(b)
694
10
Emission max (nm)
Stokes shift (nm)
Q.Y.c
701
8
0.11
691
10
0.11
–
–
–
0.09
a
b
c
Excited at 610 nm.
Excited at 620 nm.
Fluorescence quantum yield determined using ZnPc in 1-chloronaphthalene as
standard; m, major; b, broad.
ane for elution to afford a white solid (1.8 g, 83%). 1H NMR (CDCl3,
250 MHz): d 7.54 (t, J = 8.2 Hz, 1H, Ar-H), 7.39 (d, J = 7.6 Hz, 1H, Ar-
H), 7.02–6.90 (m, 5H, Ar-H), 3.80 (s, 3H, Ar-H). 13C NMR (CDCl3,
4.3. Phthalonitrile (3)
63 MHz):
d 161.53, 157.51, 146.70, 134.43, 126.47, 121.60,
119.69, 116.86, 115.34, 115.13, 112.78, 105.11 (Ar-C, CN), 55.59
(OCH3). MS (MALDI-TOF) m/z 250.934 [M+H]+, calcd. for
[C15H11N2O2]+ 251.082. The methoxy-protected phthalonitrile
(1.0 g, 4 mmol) was dissolved in freshly distilled dichloromethane
(25 mL) and the solution stirred at ꢂ80 °C. Boron tribromide
(0.4 mL, 4.2 mmol) in dichloromethane (10 mL) was added drop-
wise over 10 min via an addition funnel. The reaction solution
was kept at ꢂ80 °C for 1 h and then stirred at room temperature
for 24 h. The reaction solution was slowly poured into 100 mL of
ice water. The precipitate was collected, dissolved in 150 mL of
ethyl acetate and extracted with 50 mL of 2 N NaOH solution. After
neutralization with 1 N HCl and extraction with 150 mL ether, the
organic layer was dried over anhydrous sodium sulfate. The crude
product was purified by chromatography on a silica gel column
using methanol/dichloromethane 1:9 for elution to afford a yellow
solid (0.4 g, 40%).
3-Nitrophthalonitrile (1) (1.5 g, 8.7 mmol) and 3-hydroxypyri-
dine (1.5 g, 15.8 mmol) were dissolved in dry DMF (30 mL). Potas-
sium carbonate (20 g, 14.5 mmol) was added to the solution in five
portions. The reaction was heated at 90 °C for 4 h. The mixture was
cooled down to room temperature, poured into ice water (500 mL),
and the resulting precipitate was collected. The crude product was
purified by column chromatography on alumina using methanol/
dichloromethane 5:95 for elution to afford a pink solid (1.4 g,
74%). 1H NMR (CD2Cl2, 250 MHz): d 8.54–8.48 (m, 2H, Ar-H),
7.70–7.44 (m, 4H, Ar-H), 7.15–7.12 (m, 1H, Ar-H). 13C NMR (CD2Cl2,
63 MHz): d 160.16, 151.10, 147.58, 142.71, 135.29, 128.30, 127.86,
125.10, 121.16, 117.67, 115.43, 112.91, 106.84 (Ar-C, CN). MS
(MALDI-TOF) m/z 221.946 [M+H]+, calcd. for [C13H8N3O]+ 222.067.
4.4. Cobaltacarboranyl-phthalonitrile (4)
A mixture of phthalonitrile (2) (0.1 g, 0.41 mmol) and potas-
sium carbonate (61.5 mg, 0.46 mmol) in acetone (50 mL) was re-
fluxed at 50 °C under argon. After 20 min, 3,30-Co(8-C4H8O2-1,
2-C2B9H10)(10,20-C2B9H10) (0.18 g, 0.43 mmol) [13] was added to
4.2.2. Method B
Hydroquinone (1.0 g, 9 mmol) and potassium carbonate (1.6 g,
11.6 mmol) were dissolved in anhydrous DMF (30 mL) under ar-
Fig. 3. Emission spectra of Pcs 6 (black) and 7 (red) at 0.4
lM concentration in acetone (full line) and DMSO (dash line). (For interpretation of the references to colour in this
figure legend, the reader is referred to the web version of this article.)

H. Li et al. / Journal of Organometallic Chemistry 694 (2009) 1607–1611
1611
the mixture in 3 portions. The final mixture was heated for one
4.7. Cobaltacarboranyl-phthalocyanine (7)
day, then cooled to room temperature and the solvent removed
under vacuum. The crude product was purified by silica gel chro-
matography using methanol/dichloromethane 5:95 for elution to
The synthesis of this Pc was similar to that of Pc 6 described
above and afforded a dark green solid in 1% yield. 1H NMR (DMF-
d7, 400 MHz): d 9.54–9.45 (m, 7H, Ar-H), 8.26–8.21 (m, 7H, Ar-H),
7.78 (m, 3H, Ar-H), 7.27–7.24 (m, 2H, Ar-H), 5.05 (s, 2H, OCH2),
4.50 (s, 2H, CH2), 4.39 (s, 2H, CH), 4.35 (s, 2H, CH), 4.03–4.02 (m,
afford
a
yellow solid (0.24 g, 94%). 1H NMR (acetone-d6,
400 MHz): d 7.81–7.77 (m, 1H, Ar-H), 7.68–7.66 (m, 1H, Ar-H),
7.22–7.16 (m, 3H, Ar-H), 7.09–7.07 (m, 2H, Ar-H), 4.25 (br, 4H,
OCH2), 4.16 (t, J = 4.8 Hz, 2H, OCH2), 3.82 (t, J = 4.8 Hz, 2H, OCH2),
3.59 (s, 4H, CH), 3.00–1.50 (br, 34H, BH). 13C NMR (acetone-d6,
2H, OCH2), 3.95–3.92 (m, 2H, OCH2). UV–Vis (acetone): kmax (loge)
682 (4.77), 616 (4.05) nm.
100 MHz):
d 162.39, 157.97, 148.14, 136.21, 127.94, 122.49,
121.36, 117.34, 117.13, 116.20, 113.83, 105.72 (Ar-C, CN), 72.85,
70.12, 69.27, 68.98 (OCH2), 55.15, 47.22 (CH). HRMS-ESI m/z
646.3819 [MꢂK]ꢂ, calcd. for [C22H36B18CoN2O4]ꢂ 646.3812.
4.8. X-ray structures
The crystal structures of phthalonitriles
determined, using data collected at low temperature with graph-
ite-monochromated Mo K radiation (k = 0.71073 Å) on a Nonius
2 and 3 were
4.5. Cobaltacarboranyl-phthalonitrile (5)
a
Kappa CCD diffractometer. Details of data collection and refine-
ment are given in Table 1. The H atoms for both structures were
visible in difference maps, and were placed in calculated positions,
except for the phenolic H atom of phthalonitrile (2), which was re-
fined. Friedel equivalents were merged for refinement of the polar
structure of 2.
A mixture of phthalonitrile (3) (0.1 g, 0.45 mmol) in acetone
(50 mL) was refluxed at 50 °C under argon. 3,30-Co(8-C4H8O2-1,2-
C2B9H10)(10,20-C2B9H10) [13] (0.2 g, 0.48 mmol) was added to the
reaction solution in 3 portions. The reaction mixture was heated
for one day, then cooled to room temperature and the solvent re-
moved under vacuum. The crude product was purified by silica
gel chromatography using methanol/dichloromethane 5:95 for
elution to afford the title compound as a yellow solid (0.3 g,
94%). 1H NMR (acetone-d6, 250 MHz): d 9.34–9.28 (m, 2H, Ar-H),
8.69–8.66 (m, 1H, Ar-H), 8.35–8.29 (m, 1H, Ar-H), 8.05–7.96 (m,
2H, Ar-H), 7.83–7.79 (m, 1H, Ar-H), 5.01 (t, J = 4.4 Hz, OCH2),
4.13–4.06 (m, 4H, OCH2), 3.94 (br, 2H, OCH2), 3.64 (s, 4H, CH),
Acknowledgement
The authors acknowledge the National Institutes of Health
(grant CA098902) for partially supporting the work described.
Appendix A. Supplementary material
3.00–1.50 (br, 17H, BH). 13C NMR (acetone-d6, 63 MHz):
d
158.15, 155.06, 143.84, 138.80, 137.03, 131.24, 130.21, 124.39,
118.17, 115.76, 113.03, 108.84 (Ar-C, CN), 73.32, 69.75, 69.70,
63.08, 52.73, 47.35 (OCH2, CH). HRMS-ESI m/z 631.3981 [MꢂH]ꢂ,
calcd. for [C21H36B18CoN3O3]ꢂ 631.3815.
CCDC 699696 and 699697 contain the supplementary crystallo-
graphic data for 2 and 3. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2008.11.037.
4.6. Cobaltacarboranyl-phthalocyanine (6)
Phthalonitrile (1.52 g, 12.0 mmol), anhydrous zinc(II) acetate
(0.4 g, 2.0 mmol) and phthalonitrile (4) (67 mg, 0.1 mmol) were
added to a 10 mL thick-wall Schlenk tube. The tube was dried by
purge-and-refill with argon three times. Then 1.0 mL of freshly dis-
tilled quinoline was added and the solution was heated to 220 °C.
After 1 h, the reaction mixture was cooled to room temperature.
The precipitate was filtered and washed repeatedly with acetone
and methanol. The dark green filtrate was concentrated under vac-
uum. The crude product was purified using a Sephadex LH-20 col-
umn and acetone for elution. The pure phthalocyanine was
obtained by reverse phase HPLC using a Luna C18 semi-preparative
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column and water/acetonitrile as the mobile phase, with
a
multi-step gradient method. The pure product was collected and
vacuum dried at 30 °C for 2 days to afford a dark bluish green solid
(9.0 mg) in 8% yield based on the amount of 4 used. 1H NMR (DMF-
d7, 400 MHz): d 9.37–9.12 (m, 7H, Ar-H), 8.24–8.17 (m, 7H, Ar-H),
7.71 (d, J = 7.8 Hz, 1H, Ar-H), 7.59 (d, J = 9.0 Hz, 2H, Ar-H), 7.23
(d, J = 9.0 Hz, 2H, Ar-H), 4.31 (s, 2H, CH), 4.27 (s, 2H, CH), 4.21 (t,
J = 4.7 Hz, 2H, OCH2), 3.86 (t, J = 4.7 Hz, 2H, OCH2), 3.70–3.68 (m,
2H, OCH2), 3.64–3.62 (m, 2H, OCH2). 13C NMR (DMF-d7,
100 MHz):
d 155.83, 154.38, 154.24, 154.00, 153.88, 153.53,
152.80, 152.73, 141.97, 139.38, 139.09, 131.31, 129.96, 128.41,
123.39, 123.02, 120.44, 120.26, 118.56, 116.65 (Ar-C), 72.59,
70.19, 69.23, 68.90 (OCH2), 54.22, 47.21 (CH). HRMS-ESI m/z
1095.4212 [M-K]ꢂ, calcd. for [C46H48B18CoN8O4Zn]ꢂ 1095.4231.
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UV–Vis (acetone): kmax (loge) 672 (5.33), 606 (4.53) nm.