Pitfalls in bromination reactions of zinc porphyrins: Two-sided ring opening of the porphyrin macrocycle

Article abstract of DOI:10.1021/ic500468r

Reaction of [Zn^II(TTP)] (1) (TTP = dianion of 5,10,15,20-meso-tetrakis(p-tolyl)porphyrin) with 16 equiv of N-bromosuccinamide (NBS) in methanol at reflux led to the unexpected two-sidedd open-ring brominated product [Zn^II(C₂₆H₂₀N ₂O₂Br₅)₂] (2). Similar observations have been made with other meso-substituted zinc porphyrins as well [Zn ^II(por)] {por = dianion of 5,10,15,20-meso-tetrakis(aryl)porphyrin; aryl = phenyl (TPP), p-^tBu-phenyl (TBPP), m-Cl-phenyl (TClPP)}. The respective products [Zn^II(C₂₄H₁₆N ₂O₂Br₅)₂] (3), [Zn ^II(C₃₂H₃₂N₂O₂Br ₅)₂] (4), and [Zn^II(C₂₄H ₁₄N₂O₂Cl₂Br₅) ₂] (5) have been isolated in good to moderate yields and characterized by elemental analysis and UV-vis, ¹H NMR, and mass spectrometry. Additional bromination reaction of 1 with 8 equiv of NBS in a chloroform/methanol mixture led (after the two-sided ring opening) to nonmetalated brominated bi(pyrrole) product, C₃₆H₃₄N ₂O₄Br₄ (6). The detailed structures of complexes 1, 2, 3, and 6, available in a single crystal form, have been confirmed by X-ray diffraction analysis.

Full text of DOI:10.1021/ic500468r

Article
pubs.acs.org/IC
Pitfalls in Bromination Reactions of Zinc Porphyrins: Two-Sided Ring
Opening of the Porphyrin Macrocycle
Goutam Nandi,* Hatem M. Titi, and Israel Goldberg*
School of Chemistry, Sackler Faculty of Exact Sciences, Tel-Aviv University, Ramat-Aviv, 6997801 Tel-Aviv, Israel
S
* Supporting Information
ABSTRACT: Reaction of [ZnII(TTP)] (1) (TTP = dianion
of 5,10,15,20-meso-tetrakis(p-tolyl)porphyrin) with 16 equiv of
N-bromosuccinamide (NBS) in methanol at reflux led to the
unexpected two-sidedd open-ring brominated product
[ZnII(C26H20N2O2Br5)2] (2). Similar observations have been
made with other meso-substituted zinc porphyrins as well
[ZnII(por)] {por = dianion of 5,10,15,20-meso-tetrakis(aryl)-
porphyrin; aryl = phenyl (TPP), p-tBu-phenyl (TBPP), m-Cl-
phenyl (TClPP)}. The respective products [ZnII(C24H16N2O2-
Br5)2] (3), [ZnII(C32H32N2O2Br5)2] (4), and [ZnII(C24H14-
N2O2Cl2Br5)2] (5) have been isolated in good to moderate
yields and characterized by elemental analysis and UV−vis, 1H
NMR, and mass spectrometry. Additional bromination reaction of 1 with 8 equiv of NBS in a chloroform/methanol mixture led
(after the two-sided ring opening) to nonmetalated brominated bi(pyrrole) product, C36H34N2O4Br4 (6). The detailed structures
of complexes 1, 2, 3, and 6, available in a single crystal form, have been confirmed by X-ray diffraction analysis.
architectures.7b,11 At the next stage, this work was expanded
to explore whether similar effects can be achieved with halogen
atom(s) introduced at β-pyrrolic positions of the porphyrin
macrocycle. Our initial intention was to synthesize the β-
INTRODUCTION
■
The synthesis of different kinds of bromine-substituted
porphyrins or metalloporphyrins deserved a considerable
attention over the years, because of their wide range of use
in cross-coupling reactions.1−4 These porphyrins have also been
Br8Zn(TTP) by using NBS as the brominating agent in
methanol.10c Surprisingly, the reaction of [Zn(TTP)] (1) with
NBS in methanol gave the unexpected two-sided ring-opening
structure [Zn(C26H20Br5N2O2)2] (2).12 In nature, the degra-
dation of plant pigment chlorophyll occurs by the loss of
magnesium from the center of the macrocycle along with some
structural changes in the macrocycle.13 The animal pigment
heme degradation leads to biliverdin, which is an open-chain
tetrapyrrolic moiety, and the reaction is catalyzed by heme
oxygenase.14 The initial process of degradation involves the
introduction of a hydroxyl group in one of its meso positions.15
Balch et al. have studied in detail some model heme complexes
in the context of the related natural heme-degradation
process.16 In the present study, we observe the two-sided
ring opening of the Zn-porphyrins where the two bipyrrolic
entities are held together through coordination to the central
zinc ion in the final product(s) (Scheme 1). Further details of
this interesting reaction are presented below, including
spectroscopic and structural characterizations of the ring-
opening products. To the best of our knowledge, such two-
sided ring opening of metalloporphyrins has not been reported
earlier.
subjects of investigation for their electrochemical and optical5
as well as antitumor6 characteristics. They are also found to be
involved in the construction of supramolecular and chiral
architectures reported by our group.7
Several methodologies have been reported in the literature to
synthesize the bromo-substituted porphyrins.8 The meso-
substituted bromo-porphyrins or metalloporphyrins are gen-
erally achieved by using NBS as the brominating
agent.9,1c,2a,3g,4e Sometimes, N-bromoacetamide is also used
instead of NBS.3c For bromination of β-pyrrolic positions, both
molecular bromine and NBS are commonly applied; the latter
has appeared to be the favorable and more convenient
brominating reagent, as molecular bromine has substantial
limitations.10 Condensation of aldehyde with 3-bromo- or 3,4-
dibromo-substituted pyrrole can also lead to the β-brominated
porphyrins, but this methodology is generally avoided as it
involves a tedious workup.8a
Our recent interest in the field of metalloporphyrin chemistry
involves crystal engineering efforts to construct supramolecular
porphyrin assemblies directed by halogen bonding interactions.
We have shown that halogen atoms (−Br, −I), when placed
either at the meso-substituted phenyl groups or on the axial
ligands, readily take part in interactions with complementary
electron-rich heterosubstituents (N, O) of neighboring
porphyrin species, formulating halogen-bonded network
Received: February 27, 2014
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ic500468r | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Scheme 1. Two-Sided Ring-Opening Reaction of [Zn(por)]
Scheme 2. Proposed Mechanism for Formation of the Open-Ring Product from the [Zn-Tetraarylporphyrins]
effects and to optimize the precision of the structural results. These
structures were solved by direct methods and refined by full-matrix
least-squares (SIR-97, SHELXTL-2013 and SHELXL-97).18,19 All
non-hydrogen atoms were refined anisotropically. The hydrogen
atoms were located in idealized/calculated positions and were refined
using a riding model.
Synthesis. Synthesis of 2. A 14.6 mg (0.02 mmol) portion of 1
was taken in 15 mL of methanol in a 50 mL round-bottom flask. Then,
57 mg (0.32 mmol) of NBS was added to it and the solution was
refluxed for 2 h. The solvent was evaporated in a rotary evaporator to
give a pale red solid. The solid was dissolved in a minimum amount of
CHCl3/hexane (1:1) and passed through a column (20 × 3 cm)
packed with Silica 60. The pinkish red solution was collected and
evaporated to dryness to give a red solid. The solid was recrystallized
from DCM and petroleum ether (60−80 °C) to give pink needle-
shaped crystals. Yield: 72%. The synthesis of 1 is described in the
Supporting Information.
EXPERIMENTAL SECTION
■
Materials. Pyrrole, p-tolualdehyde, benzaldehyde, p-tert-butylben-
zaldehyde, and m-chlorobenzaldehyde were obtained from Sigma-
Aldrich. Solvents like propionic acid, chloroform, dichloromethane
(DCM), methanol, and hexane were obtained from Bio-Lab Ltd.,
Israel. Petroleum ether (60−80 °C) was obtained from Frutarom Ltd.,
Israel. Zinc chloride, silica gel 60, and NBS were obtained from Merck.
Free-base porphyrins were prepared following the method of Adler et
al.17
Physical Measurements. Elemental analyses for carbon, hydro-
gen, and nitrogen were obtained with a PerkinElmer 2400 micro-
analyzer. IR spectra were recorded on a Bruker Tensor 27 system
spectrophotometer in ATR mode. Electronic absorption spectral
measurements were carried out with an SP-1900 UV−vis spectropho-
tometer. Electron spray ionization mass spectrometry (ESI-MS)
spectra were recorded on a SYNAPT spectrometer. The ESI-MS
capillary was set at 3.5 kV, and the cone voltage was 10 V. The mass
spectral peaks were composed of isotopic distribution, and only the
Molecular formula C52H40N4O4Br10Zn. Elem. Anal. Calcd (found)
for C52H40Br10N4O4Zn: C, 37.87 (37.52); H, 2.44 (2.46); N, 3.40
(3.44). UV−vis [CH2Cl2; λmax (relative ε)]: 394 (15.50), 518 (100).
ESI-MS (m/z): 1647.38 ([M]+); 1H NMR (CDCl3): δ 2.85 (12H, s),
2.39 (12H, s); aromatic protons signals are overlapped between δ 6.8−
7.3.
1
central strong line is reported. H NMR spectroscopic measurements
of the complexes were recorded with a Bruker UltraShield 400 MHz
NMR spectrometer.
The X-ray measurements (Bruker-ApexDuo diffractometer, MoKα
Iμ microfocus X-ray source) were carried out at ca. 110(2) K on
crystals coated with a thin layer of amorphous oil to minimize crystal
deterioration, possible structural disorder, and related thermal motion
Syntheses of 3, 4, and 5. Syntheses of these complexes were made
by following a similar methodology as that described for 2, using
B
dx.doi.org/10.1021/ic500468r | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
by demetalation of the pyrrolic compound.22 Similar results
were obtained in a 10:1 CHCl3/MeOH mixture, but in such
conditions, the ring-breaking reaction takes longer (12 h), most
probably due to poor solubility of NBS in chloroform. The
isolation and structural characterization of this brominated
bipyrrolic derivative, C36H34N2O4Br4 (6), is in line with the
assumed nucleophilic attack of the methoxide ion at the meso
position after octabromination of the zinc porphyrins (Scheme
2). The molecular structure of 6 is shown below.
[Zn(TPP)], [Zn(TBPP)], and [Zn(TClPP)], respectively, instead of
[Zn(TTP)] by taking the starting materials in a similar stoichiometric
ratio. The corresponding yields are 73, 53, and 64%. In all cases, the
ring-opening reactions are associated with a sharp color change from
the deep purple color of the zinc porphyrin reactant to a pink color of
the products 2−5.
Data for 3: Molecular formula C48H32N4O4Br10Zn. Elem. Anal.
Calcd (found) for C48H32N4O4Br10Zn: C, 36.18 (36.41); H, 2.02
(2.09); N, 3.52 (3.64). UV−vis [CH2Cl2; λmax (relative ε)]: 382
(10.87), 520 (100). ESI-MS (m/z): 1593.40 ([M]+).
Data for 4: Molecular formula C64H64N4O4Br10Zn. Elem. Anal.
Calcd (found) for C64H64N4O4Br10Zn: C, 42.29 (42.31); H, 3.55
(3.61); N, 3.08 (3.04). UV−vis [CH2Cl2; λmax (relative ε)]: 396
(13.15), 520 (100). ESI-MS (m/z): 1817.65 ([M]+).
Data for 5: Molecular formula C48H28N4O4Cl4Br10Zn. Elem. Anal.
Calcd (found) for C48H28N4O4Cl4Br10Zn: C, 33.30 (33.31); H, 1.63
(1.68); N, 3.24 (3.28). UV−vis [CH2Cl2; λmax (relative ε)]: 392
(11.23), 520 (100). ESI-MS (m/z): 1731.20 ([M]+).
Crystal Structures. The starting material (1), as well as
products 2, 3, and 6 available in crystalline form (single crystals
obtained by slow evaporation of DCM/petroleum ether
solution of the corresponding product), have been structurally
characterized by single-crystal X-ray diffraction analysis.
Compounds 2 and 3 crystallized as DCM solvates. Crystals
of 3 were of somewhat lower quality due solvent disorder
therein, which affected the precision of the crystallographic
determination. No crystals of 4 and 5 suitable for X-ray
diffraction analysis could be obtained. The crystallographic data
for 1−3 and 6 are as follows:
1: C48H36N4Zn, M = 734.18, monoclinic, space group P21/n,
a = 9.5745(5) Å, b = 9.2610(5) Å, c = 21.0029(11) Å, β =
99.734(2)°, V = 1835.5(2) Å3, Z = 2, T = 110(2) K, Dc = 1.328
Mg/m3, μ = 0.71 mm−1. 17 498 reflections measured, of which
4570 were unique (Rint = 0.037) and 3717 with I > 2σ(I) to
2θmax = 56.6°. Final R1 = 0.037 and wR2 = 0.092 for the 3717
data above the intensity threshold, and R1 = 0.051 and wR2 =
0.099 for all data. CCDC 988944. Structure description of 1 is
given in the Supporting Information.
RESULTS AND DISCUSSION
■
Synthesis. The reaction of [Zn(TTP)] (1) with 16 equiv of
NBS in methanol at reflux yielded a pink/red solution. TLC of
the crude solution shows the complete loss of 1 and only one
colored (pink) band, suggesting exclusive formation of a new
compound. Subsequent work up, followed by crystallization
from DCM/hexane solution, gave needle-shaped crystals of 2.
Similar observations have also been made with different meso-
substituted zinc porphyrins [Zn(TPP)], [Zn(TBPP)], and
[Zn(TClBP)], and the respective products 3, 4, and 5 have
been isolated in good to moderate yields. It has been reported
that Br atoms at the β-pyrrolic positions have a profound
influence on the redox potentials and cause a severe distortion
of the porphyrins from a flat conformation to a saddle-shaped
conformation.10a,e,20 In the present case, however, the [Zn-
(por)] after bromination at eight β-pyrrolic positions over-
comes the steric repulsions by ring opening at two opposite
meso positions in the presence of excess MeOBr.21
2: 2(C52H40Br10N4O4Zn)·3(CH2Cl2), M = 3553.48, mono-
clinic, space group P21/n, a = 16.8255(5) Å, b = 18.3237(5) Å,
c = 19.8035(6) Å, β = 95.885(1)°, V = 6073.3(3) Å3, Z = 2, T =
110(2) K, Dc = 1.943 Mg/m3, μ = 7.16 mm−1. 42 426
reflections measured, of which 10754 were unique (Rint
=
0.031) and 8886 with I > 2σ(I) to 2θmax = 50.2°. Final R1 =
0.029 and wR2 = 0.073 for the 8886 data above the intensity
threshold, and R1 = 0.041 and wR2 = 0.078 for all data. CCDC
988945.
The nucleophilic attack by the methoxide ion at the meso
position, followed by electrophilic substitution at the α-position
of the pyrrols by bromine, leads to the formation of two sp3-
carbon atoms with the loss of aromaticity as well as destruction
of the porphyrin macrocycle (Scheme 1). The proposed
mechanism for such a process is shown in Scheme 2. The use of
more NBS up to 32 equiv and prolonged reflux (around 6 h)
did not lead to further destruction of the molecules (no
electronic spectral change), suggesting that the incorporation of
additional bromine to the products is difficult in this type of
ring-opening reaction.
A similar two-sided ring-opening product is also formed
when the reaction(s) is performed under an Ar atmosphere
(i.e., in the absence of oxygen), indicating that oxygen is not
involved in the ring-opening process, in contrast to the Fe-OEP
complex.16 The reaction was also unaffected when ethanol is
used as the solvent instead of methanol, likewise when the
solvent is a 10:1 MeOH:pyridine. Total destruction of the zinc
porphyrin is observed when excess Br2 is used as brominating
agent in methanol (or in CCl4)8a,10g at reflux, yielding a
colorless solution. Supplementary information and further
support of the proposed mechanism were obtained when the
bromination reaction of 1 was carried out in a CHCl3/MeOH
(2:1) mixture, using 8 equiv of NBS. The room-temperature
stirring of solution containing the reactants for 2 h led to the
bromination at the β-pyrrolic positions as well as ring breaking
at the meso positions. This reaction was accompanied, however,
3: 2(C48H32Br10N4O4Zn)·(1 + x)(CH2Cl2), M = 3271.31,
monoclinic, space group P21/c, a = 22.0103(9) Å, b =
21.6959(8) Å, c = 22.7148(8) Å, β = 90.858(1)°, V =
10845.9(7) Å3, Z = 4, T = 110(2) K, Dc = 2.003 Mg/m3, μ =
7.92 mm−1 (excluding the unknown fraction x of the DCM
crystallization solvent). 74 009 reflections measured, of which
19 900 were unique (Rint = 0.089) and 13 163 with I > 2σ(I) to
2θmax = 50.8°. Final R1 = 0.082 and wR2 = 0.168 for the 13 163
data above the intensity threshold, and R1 = 0.135 and wR2 =
0.186 for all data. CCDC 988946.
6: C H Br N O , M = 878.29, tetragonal, space group I42d,
̅
36 34
4
2
4
a = 26.8013(11) Å, b = 26.8013(11) Å, c = 9.6943(4) Å, V =
6963.5(5) Å3, Z = 8, T = 110(2) K, Dc = 1.676 Mg/m3, μ =
4.66 mm−1. 11 846 reflections measured, of which 3073 were
unique (Rint = 0.043) and 2632 with I > 2σ(I) to 2θmax = 50.1°.
Final R1 = 0.027 and wR2 = 0.057 for the 2632 data above the
intensity threshold, and R1 = 0.041 and wR2 = 0.062 for all
data. CCDC 988947.
The molecular structure of product 2 is illustrated in Figure
1. The asymmetric unit contains one molecule of 2 and 11/2
solvent DCM species. The crystallographic analysis reveals that
a total of 10 bromine atoms have been incorporated into the
molecule. Two trans-related meso positions of the porphyrin
ring open up and form sp3-carbon sites bearing one tolyl group
and two methoxy substituents. All the β-pyrrolic positions and
C
dx.doi.org/10.1021/ic500468r | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
one well ordered and the other severely disordered in the
crystal lattice. As in the previous case, the C48H32N4O4Br10Zn
product reveals the two-sided ring opening of the porphyrin
macrocycle, associated with substitution of 10 Br atoms on the
molecular framework. The two crystallographically independent
molecules, while differing slightly in their conformational
features, exhibit similar distorted octahedral coordination
geometries around the central zinc ions, and the corresponding
Zn−N and Zn···O distances within the zinc-coordination
spheres are within 1.983(9)−2.064(9) Å and 2.463(7)−
2.488(8) Å in one molecule and 1.993(9)−2.070(9) Å and
2.502(7)−2.545(7) Å in the other species.
The molecular structure of the ring-opening product 6 is
illustrated in Figure 3. The structural analysis revealed that the
Figure 1. Molecular structure of 2 with 50% probability atomic
displacement parameters (hydrogen atoms and DCM solvent are
omitted for clarity; only the major position of the partly disordered
Br7 is shown). Selected bond distances (Å): Zn1−N1 = 2.041(3),
Zn1−N2 = 1.989(3), Zn1−N3 = 1.998(3), Zn1−N4 = 2.050(3). Note
that O2 and O4 lie also in close proximity to Zn1, providing along
with the four N atoms a pseudo-octahedral coordination environment.
one α-position from each fragment are substituted now by
bromine atoms. The central zinc ion is strongly coordinated to
the four N(pyrrole) atoms at Zn−N bond distances in the
range of 1.989−2.050(3) Å, and weakly interacting also with
two of the methoxy O atoms, O2 and O4, at 2.536(3) and
2.501(3) Å, respectively. The zinc ion thus adopts a distorted
tetrahedral geometry with respect to the coordinated N-sites,
and a distorted octahedral geometry when the two O-sites
(occupying cis-related coordination sites) are taken into
consideration as well.
Figure 3. Ball-and-stick illustration of the molecular structure of 6 with
50% probability atomic displacement parameters, which resides in the
crystal on axes of 2-fold rotation (hydrogen atoms are omitted for
clarity).
Similar results were obtained when the bromination reaction
was repeated with the closely related [Zn(por)] complex. The
molecular structure of the product 3 is depicted in Figure 2.
The asymmetric unit of this crystal structure consists of two
molecules of the zinc complex and two DCM solvent moieties,
β-pyrrolic positions are occupied by the bromine atoms and the
α-carbons are bonded to sp3-carbon atoms that are having two
methoxy groups and one tolyl group to complete the
tetrahedral geometry. The different stoichiometric ratio of the
porphyrin and NBS reactants (along with the modified
experimental conditions), with respect to the previous
experiments, resulted in slightly different patterns of the Br-
substitution (limited this time to the β-carbons only) and
methoxy-driven (asymmetric) two-sided ring opening of the
porphyrin macrocycle.
Spectroscopy. The course of the reaction (1 to 2) was
monitored by the UV−vis spectral studies, which showed that
the reaction between 1 and NBS occurs very rapidly in the
present reaction conditions with the complete disappearance of
the Soret band of 1 within 5 min. A strong absorption band
appears at 480 nm, which then splits into two bands at 470 nm
and another at a slightly higher wavelength. The band at 470
nm is indicative of the β-Br8Zn(TTP), which shows a Soret
band at 469 nm in DCM.20 The band appearing initially at 480
nm may be composed of the β-Br8Zn(TTP) and any of the
intermediates (shown in Scheme 2). During the reaction, the
higher wavelength band starts to increase in intensity with the
shifting of its position, ending eventually as a strong peak at 519
nm for the formation of the final product 2 (Figure 4a).
A comparison of UV−visible spectra of 1 and 2 in the region
of 300−800 nm in DCM is shown in Figure 4b. The
disappearance of the Q-band (in 2) at the expected region
(580−660 nm) for octabrominated metalloporphyrins20 and
Figure 2. Perspective view of one of the molecules in 3 with 50%
probability atomic displacement parameters/ellipsoids (hydrogen
atoms and DCM solvent are omitted for clarity). Note the close
overall resemblance of the molecular structure of 3 to that of 2 shown
in Figure 1.
D
dx.doi.org/10.1021/ic500468r | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 4. (a) The electronic spectral changes in the transformation of 1 (1.1 × 10−5 M) to 2 in MeOH. The band at 470 nm is indicative of the
initial formation of β-Br8Zn(TTP) (see Results and Discussion). (b) Comparison of electronic spectra of 1 (1.2 × 10−5 M, purple) and purified 2
(2.3 × 10−4 M, pink) in DCM.
the appearance of a strong band at higher wavelength (518−
519 nm) similar to BODIPY derivatives23 are consistent with
the two-sided porphyrin ring opening. Similar spectral features
are also observed for 3, 4, and 5 (see Figures S2−S4 in the
Supporting Information).
generate at δ 2.3−2.5 ppm, and eventually it splits (see Figure
S7 in the Supporting Information).
In the ESI-MS spectrum of the complexes in DCM, the
molecular ion peak (m/Z) could be observed as an intense peak
(see in the Supporting Information) with excellent isotopic
distribution. However, in 2, 3, 4, and 5, the peak corresponding
to the m/Z value with the loss of one methoxy group has higher
intensity than the molecular ion peak. ESI-MS spectra for
compounds 1−5 are shown, respectively, in Figures S13−S17
in the Supporting Information.
1H NMR spectra of 1 and 2 in the range of δ 6−10 are
displayed in Figure 5. The spectrum of 2 revealed a
CONCLUSION
■
An unusual observation has been made in attempts to
octabrominate the zinc porphyrins using NBS in methanol at
reflux. The bromination reactions were associated with the two-
sided ring opening of the metalloporphyrin ring, leading to
unexpected products 2−5. No further degradation has been
observed under harsher conditions. The structures of
complexes 2 and 3 have been confirmed unequivocally by
single-crystal X-ray diffraction analysis. The observed results
strongly suggest that the methanol should be avoided in
bromination reactions of Zn-porphyrins using NBS as the
brominating agent. While single ring opening of the
tetraarylporphyrin macrocycle in alcoholic environments has
been observed recently,12 the two-sided opening is being
reported here for the first time. The present findings may
provide additional insight into the degradation of natural
pigments like chlorophyll and hemoglobin, which dominate the
plant and animal kingdom, respectively. The generality of this
phenomenon is currently being probed with other metal-
loporphyrin systems.
1
Figure 5. Comparison of H NMR (400 MHz) spectra of 1 and 2 in
CDCl3.
nonaromatic conjugated system. The signal for the β-pyrrolic
protons was absent as compared to 1, which shows a sharp peak
at δ 8.89 for eight protons, suggesting that those positions are
occupied by the bromine atoms in 2. The signals for the ortho
and meta positions give overlapping signals in the range of δ
6.8−7.3 for 2 compared to sharp signals in case of 1, as shown
in Figure 5. (see also Figures S8−S12 in the Supporting
Information). Monitoring of the reaction in CD3OD by
1HNMR spectroscopic analysis shows the disappearance of
the signal for pyrrolic protons within 5 min after addition of
NBS, indicating the generation of β-Br8Zn(TTP) in the
solution. The signal for other aromatic protons becomes
broader. With time, the signal for methoxy protons starts to
ASSOCIATED CONTENT
■
S
* Supporting Information
1
Synthesis and solid-state structure of 1; UV−vis, FT-IR, H
NMR, and ESI-MS spectra; and X-ray crystallographic data (in
CIF format; CCDC 988944−988947). This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: gtm.nnd@gmail.com (G.N.).
*E-mail: goldberg@post.tau.ac.il (I.G.).
■
E
dx.doi.org/10.1021/ic500468r | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
3145−3154. (f) Kachadourian, R.; Flaherty, M. M.; Alvin, L. C.; Patel,
M.; Day, B. J. J. Inorg. Biochem. 2003, 95, 240−248. (g) Spyroulias, G.
A.; Despotopoulos, A. P.; Raptopoulou, C. P.; Terzis, A.; de
Montauzon, D.; Poilblanc, R.; Coutsolelos, A. G. Inorg. Chem. 2002,
41, 2648−2659. (h) Tagliatesta, P.; Li, J.; Autret, M.; Van
Caemelbecke, E.; Villard, A.; D’Souza, F.; Kadish, K. M. Inorg.
Chem. 1996, 35, 5570−5576. (i) Kadish, K. M.; Li, J.; Caemelbecke, E.
V.; Ou, Z.; Guo, N.; Autret, M.; D’Souza, F.; Tagliatesta, P. Inorg.
Chem. 1997, 36, 6292−6298. (j) Kadish, K. M.; D’Souza, F.; Villard,
A.; Autret, M.; Van Caemelbecke, E.; Bianco, P.; Antonini, A.;
Tagliatesta, P. Inorg. Chem. 1994, 33, 5169−5170. (k) Reddy, D.;
Ravikanth, M.; Chandrashekar, T. K. J. Chem. Soc., Dalton Trans. 1993,
3575−3580.
Funding
This research was supported by the Israel Science Foundation
− Grant No. 108/12.
Notes
The authors declare no competing financial interest.
REFERENCES
■
(1) (a) Minnetian, O. M.; Morris, I. K.; Snow, K. M.; Smith, K. M. J.
Org. Chem. 1989, 54, 5567−5574. (b) Suzuki, A. J. Organomet. Chem.
1999, 576, 147−168. (c) DiMagno, S. G.; Lin, V. S. Y.; Therien, M. J.
J. Org. Chem. 1993, 58, 5983−5993. (d) DiMagno, S. G.; Lin, V. S.-Y.;
Therien, M. J. J. Am. Chem. Soc. 1993, 115, 2513−2515. (e) Chan, K.
S.; Zhou, X.; Au, M. T.; Tam, C. Y. Tetrahedron 1995, 51, 3129−3136.
(f) LeCours, S. M.; Guan, H.-W.; DiMagno, S. G.; Wang, C. H.;
Therien, M. J. J. Am. Chem. Soc. 1996, 118, 1497−1503. (g) Zhou, X.
A.; Tse, M. K.; Wan, T. S. M.; Chan, K. S. J. Org. Chem. 1996, 61,
3590−3593. (h) Liu, C. J.; Yu, W. Y.; Peng, S. M.; Mak, T. C. W.; Che,
C. M. J. Chem. Soc., Dalton Trans. 1998, 1805−1812. (i) Blake, I. M.;
Anderson, H. L.; Beljonne, D.; Bredas, J. L.; Clegg, W. J. Am. Chem.
Soc. 1998, 120, 10764−10765.
(6) Brunner, H.; Scheller, K. M.; Treittinger, B. Inorg. Chim. Acta
1997, 264, 67−79.
(7) (a) Titi, H. M.; Karmakar, A.; Goldberg, I. J. Porphyrins
Phthalocyanines 2011, 15, 1250−1257. (b) Titi, H. M.; Patra, R.;
Goldberg, I. Chem.Eur. J. 2013, 19, 14941−14949.
(8) (a) Chumakov, D. E.; Khoroshutin, A. V.; Anisimov, A. V.;
Kobrakov, K. I. J. Heterocycl. Chem. 2009, 45, 259−283. (b) Wijesekera,
T.; Dupre, D.; SR Cader, M.; Dolphin, D. Bull. Soc. Chim. Fr. 1996,
133, 765−775.
(2) (a) Arnold, D. P.; Healy, P. C.; Hodgson, M. J.; Williams, M. L. J.
Organomet. Chem. 2000, 607, 41−50. (b) Sugiura, K.; Yoshinobu, F.;
Yoshiteru, S. Chem. Commun. 2000, 1105. (c) Shanmugathasan, S.;
Edwards, C.; Boyle, R. W. Tetrahedron 2000, 56, 1025−1046.
(d) Sharman, W. M.; van Lier, J. E. J. Porphyrins Phthalocyanines
2000, 4, 441−453. (e) Shanmugathasan, S.; Johnson, C. K.; Edwards,
C.; Matthews, E. K.; Dolphin, D.; Boyle, R. W. J. Porphyrins
Phthalocyanines 2000, 4, 228−232. (f) Tse, M. K.; Zhou, Z. Y.; Mak,
T. C. W.; Chan, K. S. Tetrahedron 2000, 56, 7779−7783. (g) Aratani,
N.; Osuka, A. Org. Lett. 2001, 3, 4213−4216. (h) Screen, T. E. O.;
Lawton, K. B.; Wilson, G. S.; Dolney, N.; Ispasoiu, R.; Goodson, T.,
III; Martin, S. J.; Donal, D. C. J. Mater. Chem. 2001, 11, 312−320.
(3) (a) Fletcher, J. T.; Therien, M. J. J. Am. Chem. Soc. 2002, 124,
4298−4311. (b) Loewe, R. S.; Tomizaki, K.; Youngblood, W. J.; Bo, Z.
S.; Lindsey, J. S. J. Mater. Chem. 2002, 12, 3438−3451. (c) Shi, D. F.;
Wheelhouse, R. T. Tetrahedron Lett. 2002, 43, 9341−9342. (d) Arnold,
D. P.; Hartnell, R. D.; Heath, G. A.; Newby, L.; Webster, R. D. Chem.
Commun. 2002, 754−755. (e) Aratani, N.; Cho, H. S.; Ahn, T. K.;
Cho, S.; Kim, D.; Sumi, H.; Osuka, A. J. Am. Chem. Soc. 2003, 125,
9668−9681. (f) Nakamura, K.; Fujimoto, T.; Takara, S.; Sugiura, K.-i.;
Miyasaka, H.; Ishii, T.; Yamashita, M.; Sakata, Y. Chem. Lett. 2003, 32,
694−695. (g) Hasobe, T.; Imahori, H.; Yamada, H.; Sato, T.; Ohkubo,
K.; Fukuzumi, S. Nano Lett. 2003, 3, 409−412. (h) Shi, B. L.; Scobie,
M.; Boyle, R. W. Tetrahedron Lett. 2003, 44, 5083−5086.
(9) (a) Nudy, L. R.; Hutchinson, H. G.; Schieber, C. Tetrahedron
1984, 40, 2359−2363. (b) LeCours, S. M.; DiMagno, S. G.; Therien,
M. J. J. Am. Chem. Soc. 1996, 118, 11854−11864. (c) Shediac, R.;
Mike, M. H. B.; Gray, H. B.; Uyeda, H. T.; Johnson, R. C.; Hupp, J. T.;
Angiolillo, P. J.; Michael, M. J.; Therien, J. J. Am. Chem. Soc. 2000, 122,
7017−7033. (d) Garcia-Ortega, H.; Ribo, J. M. J. Porphyrins
Phthalocyanines 2000, 4, 564−568. (e) Kato, A.; Hartnella, R. D.;
Yamashitab, M.; Miyasakab, H.; Sugiurab, K.-i.; Arnold, D. P. J.
Porphyrins Phthalocyanines 2004, 8, 1222−1227. (f) Odobel, F.;
Suresh, S.; Blart, E.; Nicolas, Y.; Quintard, J.-P.; Janvier, P.; Le Questel,
J.-Y.; Illien, B.; Rondeau, D.; Richomme, P.; Haupl, T.; Wallin, S.;
Hammarstrom, L. Chem.Eur. J. 2002, 8, 3027−3046.
(10) (a) Mandon, D.; Ochsenbein, P.; Fischer, J.; Weiss, R.; Jayaraj,
K.; Austin, R. N.; Gold, A.; White, P. S.; Brigaud, O.; Battioni, P.;
Mansuy, D. Inorg. Chem. 1992, 31, 2044−2049. (b) Campestrini, S.;
Tonellato, U. J. Mol. Catal. A: Chem. 2000, 164, 263−272.
(c) Hoffmann, P.; Labat, G.; Robert, A.; Meunier, B. Tetrahedron
Lett. 1990, 31, 1991−1994. (d) Campestrini, S.; Meunier, B. Inorg.
Chem. 1992, 31, 1999−2006. (e) Turk, H.; Tay, T.; Berber, H. J. Mol.
Catal. A: Chem. 2000, 160, 323−330. (f) Gonsalves, A. M. d. A. R.;
Johnstone, R. A. W.; Pereira, M. M.; Shaw, J.; Sobrala, A. J. F. d. N.
Tetrahedron Lett. 1991, 32, 1355−1358. (g) Chorghade, M. S.;
Dolphin, D.; Dupre, D.; Hill, D. R.; Lee, E. C.; Wijesekera, T. P.
Synthesis 1996, 1320−1324.
(4) (a) Carcel, C. M.; Laha, J. K.; Loewe, R. S.; Thamyongkit, P.;
Schweikart, K.-H.; Misra, V.; Bocian, D. F.; Lindsey, J. S. J. Org. Chem.
2004, 69, 6739−6750. (b) Setsune, J.-i. J. Porphyrins Phthalocyanines
2004, 8, 93−102. (c) Taniguchi, M.; Kim, M. N.; Ra, D.; Lindsey, J. S.
J. Org. Chem. 2005, 70, 275−285. (d) Laha, J. K.; Muthiah, C.;
Taniguchi, M.; Lindsey, J. S. J. Org. Chem. 2006, 71, 7049−7052.
(e) Atefi, F.; McMurtrie, J. C.; Turner, P.; Duriska, M.; Arnold, D. P.
Inorg. Chem. 2006, 45, 6479−6489. (f) Locos, O. B.; Arnold, D. P. Org.
Biomol. Chem. 2006, 4, 902−916. (g) Fan, D.; Taniguchi, M.; Lindsey,
J. S. J. Org. Chem. 2007, 72, 5350−5357. (h) Muthiah, C.; Ptaszek, M.;
Nguyen, T. M.; Flack, K. M.; Lindsey, J. S. J. Org. Chem. 2007, 72,
7736−7749. (i) Taniguchi, M.; Ptaszek, M.; McDowell, B. E.; Lindsey,
J. S. Tetrahedron 2007, 63, 3840−3849. (j) Varamo, M.; Loock, B.;
Maillard, P.; Grierson, D. S. Org. Lett. 2007, 9, 4689−4692. (k) Gao,
G.-Y.; Ruppel, J. V.; Allen, D. B.; Chen, Y.; Zhang, X. P. J. Org. Chem.
2007, 72, 9060−9066. (l) Takanami, T.; Yotsukura, M.; Inoue, W.;
Inoue, N.; Hino, F.; Suda, K. Heterocycles 2008, 76, 439−453.
(5) (a) Bhyrappa, P.; Purushothaman, B. J. Chem. Soc., Perkin Trans. 2
2001, 238−242. (b) Nelson, N. Y.; Medforth, C. J.; Nurco, D. J.; Jia, S.
L.; Shelnutt, J. A.; Smith, K. M. Chem. Commun. 1999, 2071−2072.
(c) Bhyrappa, P.; Krishnan, V. Inorg. Chem. 1991, 30, 239−245.
(d) D’Souza, F.; Villard, A.; Van Caemelbecke, E.; Franzen, M.;
Boschi, T.; Tagliatesta, P.; Kadish, K. M. Inorg. Chem. 1993, 32, 4042−
4048. (e) George, R. G.; Padmanabhan, M. Polyhedron 2003, 22,
(11) (a) Muniappan, S.; Lipstman, S.; Goldberg, I. Chem. Commun.
2008, 1777−1779. (b) Lipstman, S.; Muniappan, S.; Goldberg, I. Cryst.
Growth Des. 2008, 8, 1682−1688. (c) Nandi, G.; Titi, H. M.;
Goldberg, I. Cryst. Growth Des. 2014, 14, 3557−3566.
(12) Liu, C.; Shen, D.-M.; Chen, Q.-Y. Chem. Commun. 2006, 770−
772.
(13) (a) Hendry, G. A. F.; Houghton, J. D.; Brown, S. B. New Phytol.
1987, 107, 255−302. (b) Matile, P.; Hortensteiner, S.; Thomas, H.
Annu. Rev. Plant Physiol. Plant Mol. Biol. 1999, 50, 67−95.
(c) Hortensteiner, S. Annu. Rev. Plant Biol. 2006, 57, 55−77.
(d) Barry, S. Plant Sci. 2009, 176, 325−333.
(14) (a) Yoshida, T.; Migita, C. T. J. Inorg. Biochem. 2000, 82, 33−41.
(b) Ortiz de Montellano, P. R. Acc. Chem. Res. 1998, 31, 543−549.
(c) Docherty, J. C.; Schacter, A. B.; Firneisz, G. D.; Brown, S. B. J. Biol.
Chem. 1984, 259, 13066−13069.
(15) (a) Rath, S. P. J. Chem. Sci. 2006, 118, 463−474. (b) Abhilash,
G. J.; Bhuyan, J.; Singh, P.; Maji, S.; Pal, K.; Sarkar, S. Inorg. Chem.
2009, 48, 1790−1792.
́
(16) (a) Kalish, H.; Lee, H. M.; Olmstead, M. M.; Latos-Grazynski,
̇
L.; Rath, S. P.; Balch, A. L. J. Am. Chem. Soc. 2003, 125, 4674−4675.
(b) Rath, S. P.; Koerner, R.; Olmstead, M. M.; Balch, A. L. J. Am.
Chem. Soc. 2003, 125, 11798−11799. (c) Rath, S. P.; Olmstead, M. M.;
Latos-Grazyn
́
̇
F
dx.doi.org/10.1021/ic500468r | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
12679. (d) Rath, S. P.; Olmstead, M. M.; Balch, A. L. Inorg. Chem.
2004, 43, 7648−7655. (e) Rath, S. P.; Olmstead, M. M.; Balch, A. L.
Inorg. Chem. 2004, 43, 6357−6365. (f) Rath, S. P.; Kalish, H.; Latos-
́
Grazynski, L.; Olmstead, M. M.; Balch, A. L. J. Am. Chem. Soc. 2004,
̇
126, 646−654. (g) Rath, S. P.; Olmstead, M. M.; Balch, A. L. J. Am.
Chem. Soc. 2004, 126, 6379−6386. (h) Sprutta, N.; Rath, S. P.;
Olmstead, M. M.; Balch, A. L. Inorg. Chem. 2005, 44, 1452−1459.
(i) Rath, S. P.; Olmstead, M. M.; Balch, A. L. Inorg. Chem. 2006, 45,
6083−6093.
(17) Adler, A. D.; Longo, F. R.; Finarelli, J. D.; Goldmacher, J.;
Assour, J.; Korsakoff, L. J. Org. Chem. 1967, 32, 476.
(18) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27,
435.
(19) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, 64, 112−122.
(20) Hariprasad, G.; Dahal, S.; Maiya, B. G. J. Chem. Soc., Dalton
Trans. 1996, 3429−3436.
(21) (a) Talluri, S. K.; Sudalai, A. Org. Lett. 2005, 7, 855−857.
(b) Prakash, G. K. S.; Mathew, T.; Hoole, D.; Esteves, P. M.; Wang,
Q.; Rasul, G.; Olah, G. A. J. Am. Chem. Soc. 2004, 126, 15770−15776.
(22) The presence of an acidic impurity such as HCl in the
commercial chloroform solvent may be responsible for the
demetalation.
(23) (a) Kajiwara, Y.; Nagai, A.; Chujo, Y. J. Mater. Chem. 2009, 20,
2985−2992. (b) Li, Q.; Guo, Y.; Shao, S. Analyst 2012, 137, 4497−
4501. (c) Lakshmi, V.; Shaikh, M. S.; Ravikanth, M. J. Fluoresc. 2013,
23, 519−525.
G
dx.doi.org/10.1021/ic500468r | Inorg. Chem. XXXX, XXX, XXX−XXX