PtCl2-catalyzed benzannulation of nickel(II) 2,3-dialkynylporphyrins to form unusual phenanthroporphyrins

Article abstract of DOI:10.1016/j.jorganchem.2011.07.008

Reaction of Ni(II) 2,3-dibromo-5,10,15,20-tetraphenylporphyrin with substituted stannyl alkynes generates substituted 2,3-dialkynylporphyrins in good yields. Thermolysis of these motifs with stoichiometric or even catalytic equivalents of PtCl₂

Full text of DOI:10.1016/j.jorganchem.2011.07.008

Journal of Organometallic Chemistry 696 (2011) 4152e4157
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Journal of Organometallic Chemistry
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PtCl2-catalyzed benzannulation of nickel(II) 2,3-dialkynylporphyrins to form
unusual phenanthroporphyrins
*
Mahendra Nath, Maren Pink, Jeffrey M. Zaleski
Department of Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, IN 47405, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of Ni(II) 2,3-dibromo-5,10,15,20-tetraphenylporphyrin with substituted stannyl alkynes gener-
ates substituted 2,3-dialkynylporphyrins in good yields. Thermolysis of these motifs with stoichiometric
or even catalytic equivalents of PtCl2 yields unusual phenanthroporphyrins with only small amounts of
the established picenoporphyrin or other side products.
Received 2 June 2011
Received in revised form
7 July 2011
Accepted 8 July 2011
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Pt-catalysis
Extended porphyrin frameworks
Photodynamic therapy
Solar energy conversion
Bergman cyclization
Alkyne
1. Introduction
a series of substituted, trimethyl(ethynyl)tin reagents [21,22]
(Scheme 1). In the case of 2a, subsequent removal of the R ¼ TMS
The synthesis of
p
-extended porphyrins and their corresponding
protecting group with K2CO3 in THF/MeOH, produces nickel(II) 2,3-
diethynyl-5,10,15,20-tetraphenylporphyrin 2b in 75% yield [23].
The thermal Bergman cyclization of compounds such as 2c
occurs only at high temperatures (w190 ꢀC) [17], but the thermal
barrier can be reduced by decreasing the steric bulk of the R-group
[24], introducing electron withdrawing functionality at the alkyne
termini [25], or enhancing the formation of the final product
through intermediate oxidation [23]. Although picenporphyrin
product can be obtained in this manner by direct heating, lower
temperature cyclization strategies that introduce new architectures
would be advantageous.
electro-optical properties are pertinent to the development of novel
hybrid organic-inorganic materials for applications such as photo-
dynamic therapy and solar energy conversion [1e5]. Here, effective
macrocycle periphery modification is paramount to the synthesis of
unusual chromophores, and efficient organometallic strategies for
such functionalization are onlynowemerging [6e10]. In general, the
successof thesesynthetic methodsrequiresincorporation ofspecific
functionality at either the meso- or
b,b
0-pyrrole positions. Like
several established organometallic coupling strategies (e.g., Stille,
Suzuki, Sonogashira), transformations of alkyne functionalities are
extremely versatile for formation of cyclized hydrocarbon
Heating of 2b at 130 ꢀC in toluene for 8 h yields the fully cyclized
picenoporphyrin 3b product in 68% yield (Scheme 2). This product
is proposed to be formed by 1,4-radical addition across the adjacent
meso-phenyl rings [17]. In marked contrast, heating of 2b
(85e90 ꢀC) in the presence of PtCl2 (1 equiv) for 1 h, leads to 100%
consumption of starting material and formation of the unusual
phenanthroporphyrin 4b (68%) and benzoporphyrin 5 (6%) (entry 1,
Table 1). The absence of picenoporphyrin products suggests that
constructs [11], and thus can serveas an effective route tounusual p-
extended porphyrinic structures [12,13]. Within this theme, we
report the preparation of Ni(II) 2,3-dialkynylporphyins and the
PtCl2-catalyzed cyclization of the diyne-ene motif [14,15] to form
unusual phenanthroporphyrin constructs [16].
2. Results and discussion
initial p- and subsequent s-bonding of Pt(II) to the alkyne carbons
is operative in the mechanism as proposed for simple enediyne
motifs [15]. Reaction of 2b with 0.5 equiv of Pt(II) generates nearly
identical results (entry 2, Table 1). Decreasing catalyst concentra-
tion to 0.1 equiv and subsequent reaction over 4 h still produces 4b
in 56% (entry 3, Table 1). Formation of 4b is even competent with
Ni(II) 2,3-dialkynylporphyrins 2aee are prepared by Stille cross-
coupling [17e19] of the dibromoporphyrin [20] precursor with
* Corresponding author. Tel.: þ1 812 855 2134; fax: þ1 812 855 8300.
E-mail addresses: zaleski@indiana.edu, esilvers@indiana.edu (J.M. Zaleski).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.07.008

M. Nath et al. / Journal of Organometallic Chemistry 696 (2011) 4152e4157
4153
Table 1
Yields for Pt(II)-catalyzed cycloaromatization of 2b.
Entry
Reaction conditions
Conversiona
2bb
3b
4b
5
(%)
(%)
(%)
(%)
1
2
3
4
PtCl2 (1 equiv),
100%
100%
95%
e
e
5
e
e
5
68
65
56
35
e
6
toluene, 85e90 ꢀC, 1 h.
PtCl2 (0.5 equiv),
5
5
2
e
toluene, 85e90 ꢀC, 1 h.
PtCl2 (0.1 equiv),
toluene, 85e90 ꢀC, 4 h.
PtCl2 (0.1 equiv),
80%
20
e
e
68
toluene, 40 ꢀC, 72 h.
Toluene, 130 ꢀC, 8 h.
5
100%
a
Conversion is based on consumption of 2b.
Recovered starting material.
Scheme 1. Stille coupling of the Ni(II) 2,3-dibromoporphyrin with select stannyl
alkynes produces the corresponding dialkynylporphyrins in good yields.
b
0.1 equiv of Pt(II) at 40 ꢀC over 72 h, generating 4b in 35% yield
(entry 4, Table 1), albeit with considerable unreacted starting
material.
In addition to catalytically decreasing the thermal barrier to
alkyne cyclization, and generating the unusual phenan-
throporphyrin skeleton for R ¼ H, the reaction is even viable for the
thermally very stable R ¼ TMS (2a) [24], as well as R ¼ Ph, Pr, i-Pr
(2cee) (Scheme 3).
yields to 4c and 3c, respectively, they could not be isolated in pure
form despite multiple purification steps. However, their presence is
clearly distinguishable by the NMR signatures of their
protons and equally downfield-shifted meso-phenyl protons (
8.5e9.7 ppm). Picenoporphyrins typically exhibit two downfield
doublets ( w9.65 and 8.9 ppm) and one singlet ( w8.5 ppm) with
small J (w5.2 Hz) for the -pyrrolic protons, and one doublet (
b-pyrrolic
d
d
d
b
d
w9.35) with larger J (w7.6 Hz) for two meso-phenyl protons. In
contrast, the asymmetric phenanthroporphyrins are characterized
by six doublets with small J (w4.8 Hz) between 8.5e9.6 ppm and
For 2a, stoichiometric reaction with PtCl2 at 125 ꢀC results in
deprotection of one or both of the eTMS functional groups and
subsequent cyclization to yield phenanthroporphyrins 6 (5%) and
doubly deprotected 4b (45%). This reaction is intriguing in that 2a is
extremely stable to cyclization, but can be activated via an in situ
deprotection/cyclization step with the same reagent. Additionally,
reaction of 2cee under analogous conditions affords 4cee with
smaller amounts of the picenoporphyrin derivatives 3cee, as well
as reduced alkyne and benzoporphyrin products 7 (10%) and 8 (5%),
respectively, from reaction of 2e (see Supplementary material).
Although compounds 4dee and 3dee are formed in comparable
a single doublet (
phenyl proton.
d w8.7 ppm) of larger J (w7.2 Hz) for one meso-
X-ray quality crystals of 2cee, 3c, 4b, and 5e8 have all been
obtained by slow diffusion, with a subset of structures shown in
Fig. 1. The Ni(II) 2,3-dialkynylporphyrins 2c and 2e exhibit the
typical ruffle distortion due to the relatively small size of the Ni(II)
ion in the macrocycle core. In marked contrast, the picenopor-
phyrin derivative 3c has a planar piceno unit resulting from meso-
phenyl ring addition, that is oriented at w38ꢀ relative to the ruffled
porphyrin plane. Unlike these two types of structures, phenan-
throporphyrin 4b is strongly saddled, with the phenanthro unit
participating in the distortion analogously to the remaining meso-
phenyl groups. The structural deviation of 4b from 3c indicates that
Scheme 2. Thermal Bergman and Pt(II)-catalyzed cyclization of 2,3-
Scheme 3. Pt(II)-catalyzed cyclization of substituted dialkynylporphyrins to yield
diethynylporphyrin to form piceno- and phenanthroporphyrin products, respectively.
phenanthroporphyrins.

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M. Nath et al. / Journal of Organometallic Chemistry 696 (2011) 4152e4157
Fig. 1. Representative X-ray structures of 2,3-dialkynylporphyrins 2c,e, as well as thermally cyclized picenoporphyrin 3c, and Pt(II)-cyclized phenanthroporphyrin 4b.
addition to both meso-phenyl rings is required to override the
structural preference of base Ni(II) porphyrin scaffolds, within
which ruffled and saddled conformations are common.
demonstrations of how organometallic strategies are coincident
with the development of novel macrocyclic architectures possess-
ing unusual chemical features.
The electronic absorption spectra of 2be4b(Fig. 2) show sharp
Soret features between l w 420e450 nm (2b: 430 nm; 3b: 451 nm;
4b: 443 nm), and a set of three weaker Q-bands (2b: 542, 582,
630 nm; 3b: 539, 580, 629 nm; 4b: 524, 561, 610 nm). The
appearance of three Q-bands in the spectrum reflects reduction in
the symmetry of the macrocycle core and lifting of the degeneracy
of the traditional eg (p*) Goutermann LUMO [26]. The consequen-
tial bathochromic shift of the Soret and Q-bands, and hyperchromic
shift of the low-energy Q-band, derive from the extended conju-
gation and intensity borrowing from the Soret band components
due to the reduced symmetry [27e30]. These differences in elec-
tronic structure can be used to readily distinguish each compound
via the red-shifted Soret and Q-region energy/intensity
distribution.
3. Conclusions
Thermal activation of Ni(II) 2,3-dialkynylporphyins in the
presence of stoichiometric-to-catalytic quantities of PtCl2 promotes
cyclization of the enediyne unit to form fused phenanthro-
(primary product) or picenoporphyrin (secondary product) scaf-
folds at moderate temperatures and in good yields. Both the
methodology for macrocycle periphery modification, and the
extended aromatic porphyrinoids themselves, are intriguing
Fig. 2. Electronic absorption spectra of dialkynylporphyrin 2b (—), picenoporphyrin 3b
(/), and Pt-cyclized phenanthroporphyrin 4b (d). Inset: Magnification of the Q-band
region.

M. Nath et al. / Journal of Organometallic Chemistry 696 (2011) 4152e4157
4155
4. Experimental section
(24.02); IR (cmꢂ1): 3050, 2956, 2220, 1598, 1490, 1440, 1365, 1346,
1271, 1198, 1177, 1071, 1006, 967, 835, 793, 748, 716, 698; 1H NMR
4.1. Materials and general procedures
(CDCl3):
d
8.68 (d, J ¼ 5.1 Hz, 4H, -pyrrolic H), 8.63 (d, J ¼ 5.1 Hz,
b
2H, -pyrrolic H), 7.99e7.96 (m, 4H, meso-ArH), 7.92e7.88 (m, 4H,
b
All of the chemicals and solvents were obtained from Aldrich
and Fluka. Reactions were carried out under nitrogen atmosphere
with the use of Schlenk and dry box techniques. Solvents used in
the reactions were dried and degassed by standard procedures. The
products were purified by flash chromatography using silica gel
(200e400 mesh) or activated neutral aluminum oxide (w150
mesh). UVevisible spectra were obtained using Perkin Elmer
Lamba 19 spectrophotometer using UV Winlab software. 1H NMR
and 13C NMR spectra were recorded on Gem 300 MHz or VXR
400 MHz NMR spectrometer and referenced to the proton or
carbon resonances resulting from incomplete deuteration of
deuterated solvents. IR spectra were recorded from KBr pellets on
a Nicolet 510P FT IR spectrometer. FD mass data were obtained from
University of Illinois with a micro mass Quatto-I mass spectrometer
and MALDI-TOF, FAB and EI-HRMS data were recorded on Bruker
Biglex III MALDI-TOF and Thermo Finnigan MAT 95 XP high reso-
lution mass spectrometer, respectively.
Trimethyl(trimethylsilylethynyl)tin, trimethyl(propylethynyl)
tin and trimethyl-(isopropylethynyl)tin were synthesized by
following the literature procedures [21,22]. Trimethyl(phenyle-
thynyl)tin was used as received from Aldrich. Nickel(II) 2,3-
bis(trimethylsilylethynyl)-5,10,15,20-tetraphenylporphyrin 2a was
prepared by cross-coupling reaction [17e19] of nickel(II) 2,3-
dibromo-5,10,15,20-tetraphenylporphyrin 1 [20] with trimethyl(-
trimethylsilylethynyl)tin in the presence of Pd(PPh3)4, which on
subsequent deprotection of trimethylsilyl group with K2CO3 in THF/
meso-ArH), 7.68e7.64 (m, 6H, meso-ArH), 7.61e7.59 (m, 6H, meso-
ArH), 2.19 (t, J ¼ 7.2 Hz, 4H, 2CH2), 1.52e1.44 (m, 4H, 2CH2), 0.99 (t,
J ¼ 7.5 Hz, 6H, 2CH3); MALDI-TOF-MS m/z 802 (Mþ), EI-HRMS calcd.
for C54H40N4Ni (Mþ): 802.2600. Found: 802.2586.
4.4. Nickel(II) 2,3-bis(isopropylethynyl)-5,10,15,20-
tetraphenylporphyrin (2e)
To
a
mixture
of
nickel(II)
2,3-dibromo-5,10,15,20-
tetraphenylporphyrin (0.30 g, 0.36 mmol) and (Ph3P)4Pd (0.045 g,
0.04 mmol) in dry THF (25 mL), a solution of trimethyl(isopropy-
lethynyl)tin (0.25 g, 1.08 mmol) in THF (10 mL) was added. The
reaction mixture was stirred at 70e80 ꢀC for 5 h under nitrogen
atmosphere. The reaction mixture was cooled to room temperature
and evaporated to dryness under reduced pressure. The crude
compound was purified on Si-gel column by using CH2Cl2:hexane
(1:4) as eluent. Yield: 80%. UVevis (CH2Cl2): lmax
(
3
ꢁ 10ꢂ4) ¼ 579
(0.87), 542 (1.86), 428 (25.09); IR (cmꢂ1): 3047, 2967, 2215, 1598,
1576, 1481, 1440, 1365, 1346, 1310, 1190, 1178, 1147, 1073, 1005, 947,
836, 794, 749, 716, 698; 1H NMR (CDCl3):
d
8.67 (s, 2H,
b-pyrrolic H),
8.64 (d, J ¼ 5.1 Hz, 2H,
b
-pyrrolic H), 8.62 (d, J ¼ 5.1 Hz, 2H,
b-
pyrrolic H), 7.99e7.96 (m, 4H, meso-ArH), 7.90e7.87 (m, 4H, meso-
ArH), 7.69e7.58 (m, 12H, meso-ArH), 2.60e2.54 (m, 2H, 2CH), 1.13
(d, J ¼ 6.9 Hz, 12H, 4CH3); MALDI-TOF-MS m/z 802 (Mþ), FAB-HRMS
calcd. for C54H41N4Ni (MHþ): 803.2684. Found: 803.2721.
MeOH,
produces
nickel(II)
2,3-diethynyl-5,10,15,20-
4.5. Thermolysis of nickel(II) 2,3-diethynyl-5,10,15,20-
tetraphenylporphyrin 2b in 75% yield [23].
tetraphenylporphyrin (2b)
4.2. Nickel(II) 2,3-bis(phenylethynyl)-5,10,15,20-
tetraphenylporphyrin (2c)
A mixture of 2b (50 mg, 0.07 mmol) and toluene (1.0 mL) was
heated at 130 ꢀC in pressure tube for 8 h. After completion of the
reaction, the mixture was cooled to 25 ꢀC and then diluted with
CH2Cl2 (10 mL). The solvent was evaporated off, the crude solid was
loaded on Si-gel column and eluted with CH2Cl2:hexane (1:1) as
solvent. The major green band was collected and recrystallized
with CH2Cl2/MeOH to afford nickel(II) 10,15-diphenyl-piceno
[20,1,2,3,4,5-fghij]porphyrin 3b [23] in 68% yield.
To
a
mixture
of
nickel(II)
2,3-dibromo-5,10,15,20-
tetraphenylporphyrin (0.50 g, 0.60 mmol) and (Ph3P)4Pd (0.075 g,
0.065 mmol) in dry THF (50 mL), trimethyl(phenylethynyl)tin
(0.42 g, 1.59 mmol) was added and reaction mixture was stirred
under N2 at 75 ꢀC for 5 h. After completion of the reaction, the
reaction mixture was cooled to room temperature. The solvent was
removed under reduced pressure and crude product was purified
by Si-gel column (40% CH2Cl2 in hexane). Yield: 65%. UVevis
4.6. Thermal cycloaromatization of nickel(II) 2,3-diethynyl-
5,10,15,20-tetra-phenylporphyrin (2b) in the presence of PtCl2
(entries 1e4 in Table 1)
(CH2Cl2): lmax
(
3
ꢁ 10ꢂ4) ¼ 592 (1.60), 547 (1.74), 438 (22.39); IR
(cmꢂ1): 3049, 2928, 2191, 1597, 1492, 1441, 1366, 1344, 1254, 1230,
1176, 1073, 1003, 914, 834, 798, 752, 718, 700; 1H NMR (CDCl3):
A mixture of 2b (50 mg, 0.07 mmol) and PtCl2 (0.1e1.0 equiv) in
toluene (1.0 mL) was heated under appropriate conditions (see
Table 1). After completion of the reaction, the mixture was cooled
to 25 ꢀC and evaporated under reduced pressure. The crude product
was loaded on activated neutral aluminum oxide column and
eluted with 20% CH2Cl2 in hexane as solvent to afford phenan-
throporphyrin 4b and benzoporphyrin 5. Characterization data for
d
8.68 (d, J ¼ 5.4 Hz, 4H,
b
-pyrrolic H), 8.64 (d, J ¼ 5.1 Hz, 2H,
b-
pyrrolic H), 8.02e7.97 (m, 8H, meso-ArH), 7.71e7.62 (m, 12H, meso-
ArH), 7.34e7.31 (m, 4H, ArH), 7.28e7.25 (m, 6H, ArH); MALDI-TOF-
MS m/z 871 (MHþ), FAB-HRMS calcd. for C60H37N4Ni (MHþ):
871.23712. Found: 871.23743.
4.3. Nickel(II) 2,3-bis(propylethynyl)-5,10,15,20-
tetraphenylporphyrin (2d)
4b: UVevis (CH2Cl2): lmax
(
3
ꢁ 10ꢂ4) ¼ 610 (1.28), 560 (0.90), 444
(16.79); 1H NMR (CDCl3):
d
9.51 (d, J ¼ 4.8 Hz, 1H), 8.98 (d,
J ¼ 8.8 Hz, 2H), 8.90 (d, J ¼ 4.8 Hz, 1H), 8.88 (d, J ¼ 8.8 Hz, 1H), 8.67
(dd, J ¼ 5.6, 5.2 Hz, 2H), 8.61 (d, J ¼ 4.8 Hz, 1H), 8.54 (d, J ¼ 4.8 Hz,
1H), 8.04e7.91 (m, 8H), 7.86e7.78 (m, 4H), 7.71e7.65 (m, 6H), 7.36
To
a
suspension of nickel(II) 2,3-dibromo-5,10,15,20-
tetraphenylporphyrin (0.30 g, 0.36 mmol) and (Ph3P)4Pd (0.045 g,
0.039 mmol) in dry THF (25 mL), a solution of trimethyl(propyle-
thynyl)tin (0.25 g, 1.08 mmol) in THF (10 mL) was added. The
reaction mixture was stirred at 70e75 ꢀC for 6 h. After completion
of the reaction, the mixture was cooled to 25 ꢀC and solvent was
evaporated off under reduced pressure. The residue was purified on
Si-gel column by using 50% CH2Cl2 in hexane as solvent. Yield: 75%.
(d, J ¼ 7.6 Hz, 1H); 13C NMR (CDCl3):
d 144.91, 141.59, 141.31, 141.26,
140.40, 140.35,140.22, 139.33, 138.63, 136.89, 135.13, 134.98, 134.54,
133.51, 133.40, 133.06, 132.71, 132.46, 132.33, 131.30, 131.18, 130.66,
130.54, 130.27, 128.44, 128.34, 127.84, 127.79, 127.48, 127.36, 126.98,
126.94, 126.78, 125.51, 124.37, 123.79, 121.38, 120.86, 120.15, 115.92,
105.97; FD-MS m/z 718 (Mþ); MALDI-TOF-MS m/z 718 (Mþ); EI-
HRMS calcd. for C48H28N4Ni (Mþ): 718.1667. Found: 718.1659.
UVevis (CH2Cl2): lmax
(
3
ꢁ 10ꢂ4) ¼ 578 (0.76), 542 (1.66), 430

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M. Nath et al. / Journal of Organometallic Chemistry 696 (2011) 4152e4157
Characterization data for 5: UVevis (CH2Cl2): lmax
(0.49), 550 (0.77), 435 (12.07); 1H NMR (CDCl3):
(
3
ꢁ 10ꢂ4) ¼ 592
reaction, the mixture was cooled to 25 ꢀC and diluted with 10 mL
CH2Cl2. To this solution, neutral aluminum oxide was added and
solvent was evaporated off under reduced pressure. The resulting
powder was loaded on activated neutral aluminum oxide column
and eluted by 50% CH2Cl2 in hexane as solvent. The major green
fraction was collected, which upon evaporation affords a mixture of
compounds. Proton NMR of mixture showed the presence of cor-
responding phenanthroporphyrin 4d and picenoporphyrin 3d with
other minor products. The efforts to separate these compounds in
pure form were unsuccessful.
d
8.78 (d, J ¼ 4.8 Hz,
1H), 8.66e8.62 (m, 3H), 8.50 (d, J ¼ 5.2 Hz, 1H), 8.48 (d, J ¼ 4.8 Hz,
1H), 8.29 (d, J ¼ 4.8 Hz, 1H), 8.05 (dd, J ¼ 3.2, 2.4 Hz, 2H), 8.01e7.97
(m, 6H), 7.78e7.75 (m, 3H), 7.71e7.65 (m, 10H), 7.04 (t, J ¼ 4.5 Hz,
1H); MALDI-TOF-MS m/z 754 (Mþ); EI-HRMS calcd. for
C48H29ClN4Ni (Mþ): 754.1434. Found: 754.1470.
4.7. PtCl2 induced thermal cycloaromatization of nickel(II) 2,3-
bis(trimethylsilylethynyl)-5,10,15,20-tetraphenylporphyrin (2a)
A
mixture of 2a (100 mg, 0.12 mmol) and PtCl2 (31 mg,
4.10. PtCl2 induced thermal cycloaromatization of nickel(II) 2,3-
0.12 mmol) in toluene (2.0 mL) was heated in pressure tube at
125 ꢀC for 24 h. The dark green reaction mixture was cooled to
25 ꢀC and diluted with 10 mL CH2Cl2. After evaporation of solvent
under reduced pressure, the residue was loaded on Si-gel column
and eluted with 25% CH2Cl2 in hexane to produce phenan-
throporphyrins 4b and 6 in 45% and 5% yields, respectively. Char-
acterization data for 4b: same as given above. Characterization data
bis(isopropylethynyl)-5,10,15,20-tetraphenylporphyrin (2e)
A
mixture of 2e (50 mg, 0.062 mmol) and PtCl2 (16 mg,
0.06 mmol) in toluene (1.0 mL) was heated at 115 ꢀC for 24 h. After
completion of the reaction, the mixture was cooled to 25 ꢀC and
diluted with 10 mL CH2Cl2. To this solution, neutral aluminum
oxide was added and solvent was evaporated to dryness. The
resulting powder was loaded on activated neutral aluminum oxide
column and eluted by 25e50% CH2Cl2 in hexane as solvent. The
reduced alkyne product 7 and benzoporphyrin 8 were obtained in
10% and 5% yields, respectively. Further, the column was eluted
with CH2Cl2:hexane (1:1) and major green band was collected,
which on evaporation produced an inseparable mixture of desired
phenanthroporphyrin 4e and picenoporphyrin 3e along with other
minor products on the basis of proton NMR. The purification of
these compounds were unsuccessful due to their close Rf. Charac-
for 6: UVevis (CH2Cl2): lmax
(
d
3
ꢁ 10ꢂ4) ¼ 611 (0.99), 561 (0.79), 445
(13.80); 1H NMR (CDCl3):
9.53 (d, J ¼ 4.8 Hz, 1H), 9.09 (d,
J ¼ 7.2 Hz, 1H), 9.06 (s, 1H), 9.00 (d, J ¼ 7.6 Hz, 1H), 8.89 (d,
J ¼ 4.8 Hz, 1H), 8.72 (d, J ¼ 4.8 Hz, 1H), 8.69 (d, J ¼ 5.2 Hz, 1H), 8.60
(d, J ¼ 4.8 Hz, 1H), 8.54 (d, J ¼ 4.8 Hz, 1H), 8.04e7.93 (m, 7H),
7.88e7.82 (m, 4H), 7.71e7.65 (m, 6H), 7.54 (s, 1H), 0.43 (s, 9H,
(CH3)3Si); MALDI-TOF-MS m/z 790 (Mþ); EI-HRMS calcd. for
C51H37N4NiSi (MHþ): 791.2140. Found: 791.2147.
terization data for 7: UVevis (CH2Cl2): lmax
(
3
ꢁ 10ꢂ4) ¼ 574 (0.60),
4.8. PtCl2 induced thermal cycloaromatization of nickel(II) 2,3-
bis(phenylethynyl)-5,10,15,20-tetraphenylporphyrin (2c)
539 (1.54), 424 (21.76); 1H NMR (CDCl3):
d 8.67 (s, 2H), 8.58 (d,
J ¼ 4.8 Hz, 2H), 8.53 (br s, 2H), 7.98e7.96 (m, 4H), 7.84 (br s, 4H),
7.69e7.64 (m, 6H), 7.58 (dd, J ¼ 7.6, 7.2 Hz, 2H), 7.52e7.47 (m, 4H),
5.55 (d, J ¼ 7.6 Hz, 2H, 2CH), 2.54e2.47 (m, 2H, 2CH), 1.00 (d,
J ¼ 6.0 Hz, 6H, 2CH3), 0.89 (d, J ¼ 2.4 Hz, 6H, 2CH3); EI-HRMS calcd.
for C54H42Cl2N4Ni (Mþ): 874.2140. Found: 874.2136. Characteriza-
A
mixture of 2c (50 mg, 0.06 mmol) and PtCl2 (15 mg,
0.056 mmol) in toluene (1.0 mL) was heated in pressure tube at
115 ꢀC for 40 h. After completion of the reaction, the mixture was
cooled to 25 ꢀC and diluted with 10 mL CH2Cl2. To this solution,
neutral aluminum oxide was added and solvent was evaporated off
under reduced pressure. The resulting powder was loaded on
activated neutral aluminum oxide column and eluted by 50%
CH2Cl2 in hexane as solvent. The major green fraction was collected,
which on evaporation affords a mixture of compounds. The mixture
was further repurified on Si-gel preparative TLC by using
CH2Cl2:hexane (30:70) as solvent. Only two major compounds 4c
and 3c were obtained in 35% and 10% yields, respectively. The
efforts to separate other minor products were unsuccessful due
their close Rf. Characterization data for 4c: UVevis (CH2Cl2): lmax
tion data for 8: UVevis (CH2Cl2): lmax
(
3
ꢁ 10ꢂ4) ¼ 608 (0.57), 564
(0.73), 443 (9.30); 1H NMR (CDCl3):
d
8.47e8.42 (m, 4H), 8.32 (d,
J ¼ 4.8 Hz, 1H), 8.09 (d, J ¼ 4.8 Hz, 1H), 8.00e7.90 (m, 4H), 7.84e7.79
(m, 4H), 7.67e7.58 (m, 12H), 7.52 (s, 1H), 3.47e3.42 (m, 1H, CH),
2.92e2.88 (m, 1H, CH), 1.30 (d, J ¼ 6.8 Hz, 12H, 4CH3); EI-HRMS
calcd. for C54H41ClN4Ni (Mþ): 838.2373. Found: 838.2366.
Acknowledgments
The generous support of the National Science Foundation (NSF
CHE-0956447) is gratefully acknowledged.
(
d
3
ꢁ 10ꢂ4) ¼ 611 (1.0), 562 (0.82), 448 (14.15); 1H NMR (CDCl3):
9.53 (d, J ¼ 4.8 Hz, 1H), 8.92 (d, J ¼ 4.8 Hz, 1H), 8.78 (d, J ¼ 7.2 Hz,
1H), 8.70 (d, J ¼ 4.8 Hz, 1H), 8.62 (d, J ¼ 4.8 Hz, 1H), 8.59 (d,
J ¼ 4.8 Hz, 1H), 8.55 (d, J ¼ 5.2 Hz, 1H), 8.02 (br, 6H), 7.74e7.66 (m,
10H), 7.48e7.43 (m, 6H), 7.41 (s, 1H), 7.23e7.19 (m, 4H), 7.13e7.11
(m, 2H); MALDI-TOF-MS m/z 870 (Mþ); EI-HRMS calcd. for
C60H36N4Ni (Mþ): 870.2293. Found: 870.2292. Characterization
Appendix A. Supplementary material
CCDC 804628e804635 (for 9 compounds) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Center via www.cccdc.cam.ac.uk/data-request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2011.07.008.
data for 3c: UVevis (CH2Cl2): lmax
(
3
ꢁ 10ꢂ4) ¼ 633 (2.59), 584
(0.62), 541 (0.50), 455 (15.96); 1H NMR (CDCl3):
d
9.70 (d, J ¼ 5.2 Hz,
2H), 9.43 (d, J ¼ 7.6 Hz, 2H), 8.94 (d, J ¼ 4.8 Hz, 2H), 8.48 (s, 2H),
8.08e8.06 (m, 4H), 7.96e7.91 (m, 4H), 7.74e7.70 (m, 6H), 7.58e7.56
(m, 4H), 7.51e7.44 (m, 8H); EI-HRMS calcd. for C60H34N4Ni (Mþ):
868.2136. Found: 868.2124.
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