Regioselective bromination of palladium tetraphenyltetrabenzoporphyrin to benzo-rings. Synthesis of mono- and octabromotetrabenzoporphyrins and their properties

Article abstract of DOI:10.1142/S1088424610002653

Bromination of palladium meso-tetraphenyl tetrabenzoporphyrin (Pd Ph ₄TBP, 1) by Me₄NBr₃ or Me₄NBr/ Br₂ was shown to proceed regioselectively to the benzo-rings annelated to main porphyrin macrocycle.

Full text of DOI:10.1142/S1088424610002653

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2010; 14: 815–824
DOI: 10.1142/S1088424610002653
Published at http://www.worldscinet.com/jpp/
Regioselective bromination of palladium
tetraphenyltetrabenzoporphyrin to benzo-rings.
Synthesis of mono- and octabromotetrabenzoporphyrins
and their properties‡
Denis Chumakov, Anna Moiseeva, Alexander Anisimov, Boris Uzhinov and
Andrey Khoroshutin*
Department of Chemistry, M.V. Lomonosov Moscow State University, Moscow 119991, Russia
Received 29 January 2010
Accepted 19 August 2010
ABSTRACT: Bromination of palladium meso-tetraphenyl tetrabenzoporphyrin (Pd Ph4TBP, 1) by
Me4NBr3 or Me4NBr/Br2 was shown to proceed regioselectively to the benzo-rings annelated to main
porphyrin macrocycle. Conditions for preferential mono- and octa-bromination have been established.
The respective mono- and octa-bromide (Pd Ph4TBP(Br), 2 and Pd Ph4TBP(Br)8, 3) have been isolated
and characterized by UV-vis, NMR and LDI-TOF spectroscopy. Changes of electrochemical properties
of tetrabenzoporphyrins induced by Br atoms were found to follow the same trends as the changes in
analogous non-extended porphyrins. Room temperature phosphorescence is not substantially influenced
by the substitution.
KEYWORDS: palladium meso-tetraphenyltetrabenzoporphyrin, benzo-rings bromination, palladium
meso-tetraphenyltetrabenzoporphyrin monobromide, palladium meso-tetraphenyltetrabenzoporphyrin
octabromide, phosphorescence, redox properties.
[14, 15]. Recently developed general methods of synthe-
INTRODUCTION
sis of π-extended porphyrins, with low-temperature con-
Tetrabenzoporphyrins (TBPs) are an important class
densation being the key step ([16] and references cited
of tetrapyrroles with π-extended aromatic system. They
possess unique photophysical properties which make
therein; [17–19]), make it possible to construct TBPs
with a variety of substituents in meso-aryl rings. How-
them attractive for such applications as organic light-
ever selection of substituents in benzo-rings is limited.
emitting diodes [1], photomedicine [2–4], biomedical
Substituents introduced so far include alkyls: alkoxy,
sensing systems [5–10], and components of field tran-
phenyl, and alkoxycarbonyl [20, 21].
sistors [11, 12]. In spite of the recent growth of interest
In this paper we explore bromination of Pd tetraphe-
in tetrabenzoporphyrins their chemistry is only starting
nyltetrabenzoporphyrin (Pd Ph4TBP), the Pd complex of
to be developed. The least explored are modifications
the simplest representative of meso-tetraarylated TBPs.
of pre-formed TBPs by different substitution reactions.
Ph4TBP can also be obtained, although in low yields, by a
Existing examples include electrophilic sulfonation [3],
simple one-step high-temperature condensation reaction
nitration [13] and nucleophilic substitution reaction
([22, 23] and references cited therein) as opposed to more
versatile but multi-step reaction schemes. Bromination of
the pre-formed Ph4TBP could provide a entry point to
SPP full member in good standing
*Correspondence to: Andrey Khoroshutin, email: khorosh@
petrol.chem.msu.ru, tel: +7 (495)-939-2448
a variety of functionalized TBP derivatives by way of
various Pd-catalyzed reactions [24].
‡This work has been partly presented at the Sixth International
Conference on Porphyrins and Phthalocyanines, New Mexico,
USA, 2010
Bromination has been widely used for modifica-
tion of regular non-extended porphyrins [25, 26]. Bro-
minated porphyrins are valuable as building blocks for
Copyright © 2010 World Scientific Publishing Company

816
D. ChumakOv et al.
complete absence of the reaction, e.g. in the case of
CuPh4TBP.
Further studies [34] have shown that two consequent
bromination reactions performed on the same sample of
1 made it possible to obtain octabromide 3 in 88% yield,
although the product was contaminated by heptabromide
and traces of hexabromide.
N
N
Pd
N
Br
N
Pd
N
N
N
N
Pd Ph4TBP(Br)8. In this study we extended the search
for the optimal conditions for the formation of pure octa-
bromide 3. NMe4Br was used in excess to make saturated
solution at the solvent reflux temperature, whereas Br2
amount varied. Pure NMe4Br3 was also tested as bromi-
nating agent. Besides CHCl3 used earlier, lower-boiling
CH2Cl2 was employed as a solvent, as well as higher-
boiling CHBr3. Reaction time was chosen so that neither
starting compound nor Pd Ph4TBP(Brn) (n = 1–4) were
seen on TLC. These spots are distinguishable from the
mixture Pd Ph4TBP(Brn) (n = 5–8), which appeared as
one spot.
1
2
Br
N
Br
N
Pd
N
Br
Br
Br
Br
N
Br
Br
3
Chart 1.
Identification of reaction products was performed by
Laser Desorption Ionization Time-of-Flight (LDI-TOF)
mass spectroscopy. No matrix was added, as LDI-TOF
can be successfully used for porphyrin analysis [35].
Moreover, porphyrins can serve as matrices themselves,
as shown in the analysis of B12-related compounds [36].
Variation of the number of Br2 equivalents was found
to strongly influence the outcome of the reaction (Table 1,
entries 1–2, 4–5). The concentration of Pd Ph4TBP also had
a considerable effect (Table 1, entries 4–5, 9–10). On the
other hand, carrying the reaction in inert atmosphere (argon
or nitrogen), as opposed to air, did not have noticable effect
(entries 3–4, 7–8). These results show good reproduc-
ibility of product distribution that allows one to consider
this method as a possible route to the whole spectrum of
brominated derivatives of 1, provided adequate methods of
separation of individual derivatives can be established.
Bromination at higher concentrations of both 1
and bromine lead to formation of Pd Ph4TBP(Br)7(Cl)
(Fig. 1). Similar results were obtained in the case of non-
extended porphyrins [37]. However, the increase in reac-
tion temperature by way of refluxing in CHBr3 leads to
appearance of nona-brominated product Pd Ph4TBP(Br)9,
by analogy with CHCl3 brominations at high substrate
concentrations (Table 1, entries 5, 6, 11). LDI-TOF spec-
tra additionally illustrate the reliability of determining
the number of bromine and chlorine atoms in Pd-con-
taining porphyrins. For example, isotope multiplet cor-
responding to PdBr9 was reproducibly different from that
to PdClBr8 (note intensity difference between 1625 and
1626 peaks (inset b) and respective peaks in (inset a) in
Fig. 1). Relative intensities of isotope peaks in the experi-
ment coincide with calculated ones.
complex macromolecular systems containing porphyrin
rings (for a few recent examples, see [27–32]). To our
knowledge, no direct attempts to carry out bromination
of TBPs have been disclosed. Herein, we report bromi-
nation of Pd Ph4TBP (1) and properties of the mono-
and octa-bromo derivatives Pd Ph4TBP(Br) (2) and
Pd Ph4TBP(Br)8 (3).
RESULTS AND DISCUSSION
Synthesis
In our preliminary studies we found that bromina-
tion of 1 using classic SE systems (Br2-AlBr3, Br2-FeBr3
(in situ)) resulted in unresolvable mixtures of bromides,
presumably benzo- and aryl-substituted derivatives [33].
Milder agents, such as Br2-NMe4Br, permitted bromi-
nation exclusively into the benzo-rings, with the forma-
tion of mixtures of tetra- to hepta-substituted bromides
(Scheme 1). Attempts to apply these conditions to
other metalated Ph4TBPs lead to demetalation of the
macrocycle, such as in the case of ZnPh4TBP, or to
Br
N
.
.
NBu4Br, Br2
CHCl3, reflux
Br
Pd
N
N
N
1
Br
.
.
Reaction at lower temperature in refluxing CH2Cl2
yielded almost unchanged starting compounds.
Thus, considering all data, the following conclusions
can be made. Despite very close properties of polybro-
minated Pd Ph4TBP containing 6- to 9-bromine atoms
. .
Br
Scheme 1. Bromination of 1 by NMe4Br-Br2 yielding mixture
of bromides Ph4TBP(Br)n, n = 4–7. Sites of substitution are
marked with dots
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RegIOSeleCtIve bROmInatIOn Of PallaDIum tetRaPhenyltetRabenzOPORPhyRIn tO benzO-RIngS
817
Table 1. Bromination products distribution as the result of reaction conditions variationsa
d
Entry
1
Agent
Eq.b
9
C (1)
t, h
2
nc
%
Reference
[34]
Br2/Me4NBr
1.5 × 10-2
4
5
6
63
34
3
2
Br2/Me4NBr
15
1.5 × 10-2
2
0
5
6
7
8
2
2
24
55
17
[34]
3
Br2/Me4NBr
Br2/Me4NBr
160
160
1.5 × 10-2
1.5 × 10-2
15
15
6
7
8
5
16
74
this study
this study
4e
6
7
8
5
17
66
5
6
Br2/Me4NBr
Br2/Me4NBr
400
400
5 × 10-2
5 × 10-2
4
4
8
9
97
3
this study
this study
7
8
9
16
78
6
7
8e
9f
Me4NBr3
Br2/Me4NBr
Br2/Me4NBr
16
16
11
8.4 × 10-3
8.4 × 10-4
8.4 × 10-4
8
2
3
4
44
6
7
1.7
5.5
20
this study
this study
this study
5
22
3
8
2
3
4
5
6
7
1.9
4.2
31
44
15
0.9
8
6
5
8
7
8
3.9
22
57
10f
11f
Br2/Me4NBr
Br2/Me4NBr
15
1.5 × 10-2
1.7 × 10-5
6
6
7
8
1
11
88
[34]
100
12
7
8
6
23
59
this study
9
15
1
12f
13f
Br2/Me4NBr
Br2/Me4NBr
160
200
5 × 10-1
8
93
this study
this study
1.4 × 10-3
6
7
8
10
19
71
a Earlier results are included for clarity. b Number of equivalents of brominating agent (Br2 or Me4Br3) relative
to Pd Ph4TBP. c n-bromosubstituted component and d its percentage in the resulting mixture (minor unidentified
e
f
Pd-containing peaks were not taken into account). Reactions were carried out in argon. Reactions were
carried out with mixtures of Pd Ph4TBP(Br)4-7 as starting material.
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818
D. ChumakOv et al.
that preclude their chromatographic isolation, conditions
can be established leading to the octabromide product of
97% purity. Best results are obtained for 50 mg load 1.
Repetitive bromination improves the octabromide purity
(entries 10–13). Highest purity of the octabromide 3 can
be achieved by high porphyrin and bromine concentra-
tions, and 3 can be isolated in 46% yield.
Pd Ph4TBP(Br). During the course of the above stud-
ies we have determined that mono-, di-and tri-bromo
derivatives of 1 can be distinguished by TLC on silica gel
from each other and from derivatives containing a higher
number of bromine atoms. This prompted us to develop a
method of synthesis of mono-bromo derivative 2.
Initially the reaction conditions were optimized to
maximize the amount of monobromide in the reaction
mixture (Table 2). It was found that pure NMe4Br3 leads
to the mixture of mono- and di-bromides (Table 1, entries
7–8). Thus, we varied Pd Ph4TBP concentration, reagent-
substrate mole ratio, and reaction time. An additional
parameter to change was mode of the reagent addition,
i.e. simultaneous or in small portions during the reaction,
as organic tribromide salts at elevated temperatures are
Fig. 1. LDI-TOF spectra of (a) 3 contaminated with Pd
Ph4TBP(Br)7(Cl), (b) 3 contaminated with Pd Ph4TBP(Br)9
Table 2. Optimization of bromination conditions for maximum contents of 2 in the mixture
c
Entry
1
Solvent
CHCl3
Eq.a
0.7
C (1), M
4.5 × 10-4
Addition mode
simultaneous
t, h
15
nb
%
0
1
2
57
39
2.5
2
3
4
5
6d
7
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CH2Cl2
CH2Cl2
1.2
2
4.5 × 10-4
1.65 × 10-3
1.65 × 10-3
3.3 × 10-4
1.5 × 10-2
1.65 × 10-3
1.08 × 10-2
-”-
6
11
8
0
1
2
44
48
8
in portion
0
1
2
4
62
30
2.5
4
-”-
0
1
2
18
67
15
-”-
dropwise (Br2)
dropwise (Me4NBr3)
-”-
9
0
1
2
19
67
14
6.6
2
3
1
2
3
14
34
25
5.5
15
0
1
2
52
21
5
8
16
0
1
TLC main spot
TLC traces
a
b
Number of equivalents of brominating agent (Br2 or Me4Br3) relative to Pd Ph4TBP. n-bromosubstituted
c
d
component and its percentage in the resulting mixture. Br2 in the presence of Me4NBr was used as
brominating agent.
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RegIOSeleCtIve bROmInatIOn Of PallaDIum tetRaPhenyltetRabenzOPORPhyRIn tO benzO-RIngS
819
known to be unstable [38]. It was assumed that portion-
wise mode of addition would diminish the fraction of the
decomposed reagent.
As seen in Table 2, addition of reagent in small por-
tions together with long reaction time gives the best
results. Pd Ph4TBP(Br) 2 is isolated from this mixture in
63% yield.
to Type C benzo-rings ratio approximately 1:1 in this
mixture.
Finally, only signal of Type C benzo-ring (that of HC)
1
is present in the spectrum of 3. Thus, H NMR spectra
of 1, 2 and 3, together with that of the bromides mixture
are consistent with each other. Substitution pattern of a
benzo-ring does not influence the chemical shifts of other
benzo rings present in the molecule.
NMR spectra
Signals corresponding to the phenyl rings show some
complicated shape when the number of susbtitutents
increases, but, in the case of symmetrical octabromide 3,
they are simplified again, the spectra resembling unsub-
stituted Pd Ph4TBP.
1H NMR spectra of 1, 2 and 3, together with that of the
bromides Pd Ph4TBP(Br)5-7 mixture (Chart 3), exhibit the
following features, which are reproduced for molecules
with different numbers of substituents.
Analyzing the 1H NMR spectrum in the region corre-
sponding to the protons of benzo rings, one can conclude
that the presence of the following structural fragments
accounts for the shape and multiplicity of 1H signals, i.e.
non-substituted benzo-rings (Type A), mono-substituted
benzo-rings (Type B) and di-substituted benzo-rings
(Type C). Structures of 1, 2, 3 and that of hexabromide
[39] with marked protons for spectral assignments are
shown in Chart 2.
In mono-substituted bromide 2 (Chart 3b), one can
see AA’BB’ multiplets with changed BB’ part for Type
A benzo-ring having approximately the same chemical
shifts as protons of Type A benzo-ring in 1. Signals of
AMX spin system can be assigned due to their multiplic-
ity, whereas H4 proton is hidden within HO protons of
Type A ring (Type B benzo ring).
Spectrum of mixture of Pd Ph4TBP(Br)5-7 (Chart 3c)
exhibits two sets of AMX multiplets (corresponding to
Type B benzo-rings), referred to as minor and major
according to their integral intensities. Also, there are two
sets of singlets corresponding to Type C benzo-rings.
Integral intensities of these peaks correspond to actual
numbers of the unsubstituted protons, making Type B
UV-vis spectra
The number of bromine substituents (Table 3) has
little effect on UV-vis bands maxima positions, slightly
changing B- to Q-intensity ratio. In comparison,
β-pyrrole substitution for bromine in non-extended por-
phyrins leads to significant red shift in their absorption
spectra. For both unsubstituted and meso-tetraphenyl-
substituted porphyrins “each bromine substitution con-
tributes a shift of 6 nm” [40, 41]. An overall band shift
in Pd Ph4TBP system in octabromide is 6–8 nm to the
red region.
A possible explanation of such difference in the behav-
iour is that introduction of beta-pyrrolic bromines into
Pd TPP drastically changes its conformation, bringing flat
Pd TPP 4 to saddle-shaped octabromide 5 [42–44] due to
the steric overlap of the bromine atoms with meso-aryl
substituents. Such overlap is absent or negligibly small
in the case of 3. Optimized geometries (see Supplemen-
tary material) of 1 and 3 show approximately the same
distortion, i.e. N(1)-N(2)-N(3)-N(4) dihedral angles are
8.6 and 8.3 degrees, respectively, which is close to the
distortion observed in 5 [44].
Br
Br Br
(a)
A
A
B
N
C
N
Pd
N
N
N Pd N
N
N
N Pd N
N
Br
Br
Br
Br
Br
Br
Br
Br
A
A
A
N
N
B
C
N
C
C
C
Pd N
Br
N
A
A
B
C
Br
Br
Br
1
2
PdPh4TBP(Br)6
3
C
H
H1
B
(b)
H2
Br
Br
Br
N
N
N
C
A
o-
m-
H
H
H4
H
Chart 2. (a) Designation of distinct structural fragments of 1 and brominated porphyrins 2 and 3 as marked in Chart 3. Hexabromide
was shown for Pd Ph4TBP(Br)5-7 mixture. (b) designation of the protons types of different benzo rings
Copyright © 2010 World Scientific Publishing Company
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820
D. ChumakOv et al.
Chart 3. 1H NMR spectra of (a) 1(CDCl3 + acetone-d6); (b) 2; (c) mixture of Pd Ph4TBP(Br)n (n = 5–7); (d) 3 (all - CDCl3). Phenyl
part is on the left; benzo- part is on the right. Chemical shifts can be seen in Experimental section. See Chart 2 for assignment
designations
Table 3. UV-vis (CH2Cl2) spectra of the studied compounds
Electrochemical measurements
and their phosphorescence (DMF) data (cf. Fig. 3)a
Electrochemical properties of porphyrins 1–3 were
studied by the cyclic voltammetry and the rotating disk
electrode methods. Combined results of electrochemical
studies are presented in Table 1; the cyclic voltammetry
curves CV curves for 1 and 2 are shown in Fig. 2.
First reduction and oxidation processes are found to be
reversible for all three compounds, whereas second redox
processes are quasi-reversible for 1 and 2.
λmax, abs
λmax, abs
λmax, phos
φphos
Soret (log ε) Q band (log ε)
nm
1b
2
441 (5.48)
442 (5.31)
449 (5.45)
627 (5.04)
628 (4.85)
633 (5.07)
803
799
791
0.09 0.01
0.09 0.01
0.11 0.01
3
a
For the sake of clarity of representation data on emission of
the studied compounds are also included in this table. Discussion
is given below. b Although UV-vis spectrum of Pd Ph4TBP in
DMF is reported [5], no such measurements in CH2Cl2 have
been made.
Electrochemical properties of β-brominated porphy-
rins were extensively studied previously. Kadish et al. [26]
performed systematic research on the series of metalated
Br
N
Br
N
Pd
N
N
Pd
N
Br
Br
Br
Br
N
N
N
Br
Br
PdTPP, 4
PdTPPBr8, 5
Chart 4.
Fig. 2. CVA redox curves for 1 (a) and 2 (b)
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RegIOSeleCtIve bROmInatIOn Of PallaDIum tetRaPhenyltetRabenzOPORPhyRIn tO benzO-RIngS
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Table 4. Redox potentials for Pd Ph4TBP 1, Pd Ph4TBP(Br) 2
and Pd Ph4TBP(Br)8 3 in DMF vs. Ag/AgCl, 0.1 M of TBAP
(number of electrons in the electrode process are given in
parentheses)
Compound
E1/2 II red
E1/2 I red
E1/2 I ox
E1/2 II ox
1
2
3
-1.60(1)qrev -1.15(1)rev 0.80(1) rev 1.21(1)rev
-1.54(1)qrev -1.09(1)rev 0.83(1)rev
-1.27(1)qrev -0.83(1)rev 0.80qev
1.22(1)qrev
1.03irr
(Fe(III), Mn(III), Co, Zn) mono- to octabrominated por-
phyrins, whereas Bhyrappa et al. [41] investigated elec-
trochemistry of β-octabromo-meso-tetraphenylporphyrin
and some of its metal derivatives, including Pd.
Direct comparison of the results of this and earlier
studies of the influence of bromination on potentials is
difficult, because the latter were done in other solvent
[41, 45–48].
However, the trends found for ring-originated redox
potentials can be compared. Our results show similar
behavior as those for MTPPBrx (x = 0 to 8) [26], includ-
ing anode shift of first two reduction potentials, stabil-
ity (within experimental error) of first oxidation one and
cathode shift of second oxidation one with increase of the
number of bromine substituents.
Fig. 3. Room-temperature (25 °C) phosphorescence spectra of
DMF solutions of (a) Pd Ph4TBP; (b) Pd Ph4TBP(Br1); (c) Pd
Ph4TBP(Br8), normalized for the quantum yield of the standard
and OD of the studied solution. lexc = 635 nm. Other details of
the measurements can be found in the Experimental section
comparative studies of the emissive properties of 3 vs. 1
at 77 K reveal much higher emission of the former (see
Supplementary material).
According to reference 49, halogen atoms in the
porphyrin molecule, appearing in addition to central
metal atom, can either enhance or reduce phosphores-
cence quantum yield due to a number of reasons. The
quantum yield, being virtually independent of the num-
ber of bromine substituents for the new compounds, is
to be the subject of future detailed studies, as well as tem-
perature dependence of these compounds phosphores-
cence.
At this stage we are unable to obtain individual
Pd Ph4TBPBr2-7 due to the statistical character of bromine
substitution and products separation problem. Hence,
more detailed trends of the potential changes, similar to
non-extended porphyrin bromides, are to be studied for
TBP series.
EXPERIMENTAL
All solvents and commercial reagents were obtained
from Aldrich, Khimmed and Reachim. Deuterated sol-
vents were purchased from “Applied Chemistry” SciTech
Plant, St. Petersburg. 1 was synthesized according to the
literature procedures [18].
Phosphorescence studies
Halogenation of porphyrins and chlorins is known to
have dramatic effects on their photophysical properties
[49]. In Pd tetrabenzoporphyrins intersystem crossing
results in rapid depopulation of singlet-excited states,
resulting in nearly quantitative formation of emissive
triplet states [50]. Introduction of heavy atoms, such as
bromine, could further influence the rates of intersystem
crossings, leading to both formation and deactivation of
the triplet state, as well as the radiative rate of the triplet
emission. Since phosphorescence of Pd tetrabenzopor-
phyrins is important for several applications (vide supra),
it was interesting to examine triplet emissivity of the bro-
minated derivatives of 1.
Phosphorescence spectra of 1, 2 and 3, studied in
DMF solution at room temperature showed the features
presented in Fig. 3. Although the sensitivity range of our
detector did not cover full emission bands, these mea-
surements can provide initial information about rela-
tive emissivity of the Pd porphyrins. Phosphorescence
maxima proved to gradually shift to the blue region as
the number of substituents increase, whereas maxima
increase. On the other hand, phosphorescence quantum
yields (Table 3) remain approximately constant. However,
1H NMR spectra were measured on Bruker Avance
400 spectrometer in CDCl3, unless stated otherwise. LDI-
TOF spectra on Bruker Autoflex II mass spectrometer.
UV-vis spectra were obtained on Agilent 8453 spectro-
photometer. Cyclic voltammetric experiments were car-
ried out using a PI-50-1.1 potentiostat (Gomel, Belarus)
equipped with PR-8 programmable module. The system
consisted of the three-electrode assembly, glassy carbon
(GC) electrode (working electrode, disk d = 2 mm), Ag/
AgCl/KCl (aq., satur.) (reference electrode) and platinum
electrode (counter electrode, plate s = 0.5 cm2). Tetrabu-
tylammoniumperclorate (TBP) (Fluka) 0.1 M, was used
as received in acetonitrile. The anhydrous solvents had
electronic grade purity. Measurements were performed
using 1 mM concentration of porphyrins. A 1 mM solu-
tion of ferrocene along with 0.1 M TBAP was employed
during calibration. The cyclic voltammetric experiments
were carried out after deaerating the experimental solu-
tions by purging pure argon gas. All the measurements
were carried out at 22 °C. Scan rate: 200 mV/s.
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D. ChumakOv et al.
Phosphorescencespectraandquantumyieldsweremea-
sured on Fluorolog-3 instrument equipped with HORIBA
Jobin Yvon FL 1073 detector. Right-angle detection was
used in all measurements. Assemblies of quartz cuvette
with graded quatz-borosilicate seal and a side flask for
freeze-pump-thaw degassing were used. DMF solutions
of the substances with OD no more than 0.1 at the excita-
tion wavelength were placed in the flask and the assembly
attached to a vacuum (10-2 Torr) line. After 5 to 7 freeze-
pump-thaw cycles the assembly was seal-detached in
vacuum, then frozen solution was melted and poured into
the cuvette. An identical cuvette was used for the stan-
dard – tetraphenylporphyrin, which was measured in ben-
zene solution in ambient atmosphere (quantum yield 0.11
[51]). Solutions were irradiated at 635 nm, range of emis-
sion detector was 640–850 nm. Slit widths in both excita-
tion and emission channels were 3 nm. Instrument built-in
correction factors are used to obtain true emission spectra.
Phosphorescence quantum yields were determined accord-
ing to [52], correction having been applied to amount of
absorbed light and to the difference of refraction indices
of the solvents. For details of phosphorescence measure-
ments at 77 K, see Supplementary material.
400 equiv.) dissolved in of CHCl3 (3.6 mg) 1 (50 mL,
54 µmol) was added. Then the reaction mixture was
brought to reflux and the reflux continued for 4 h. Reaction
mixture was quenched and processed as for the previous
compound. 38 mg of 3 (25 µmol, 46%) was obtained.
Molecular ion isotope distribution spectrum is identical
1
with simulated one. UV-vis spectrum see in Table 3. H
NMR (400 MHz, CDCl3, HMDS, ring designation – bold
letter – see in Chart 2): δH, ppm 8.14 (8H, d, o-Ph), 8.03
(4H, t, p-Ph), 7.93 (8H, t, m-Ph), 7.28 (8H, s, H-C). LDI-
TOF mass spectrum (see Supplementary material) shows
isotope distribution identical to the calculated one.
Mixture of palladium 2,9,16,23,-tetrabromo-6,13,
20,27-tetraphenyltetrabenzo[b:g:l:q]porphyrin [53],
palladium 2,3,9,16,23,-pentabromo-6,13,20,27-tetra-
phenyltetrabenzo[b:g:l:q]porphyrin, palladium 2,3,9,
10,16,23,-hexabromo-6,13,20,27-tetraphenyl-tetra-
benzo[b:g:l:q]porphyrin, palladium 2,3,9,10,16,17,23-
heptaromo-6,13,20,27-tetraphenyltetrabenzo[b:g:l:q]
porphyrin. This mixture was obtained on according
1
to Table 1, entry 7. Spectrum is shown in Chart 3c. H
NMR (400 MHz, CDCl3, HMDS, ring designation – bold
letter – see in Chart 2): δH, ppm 8.20–8.11 (8H, m, o-Ph),
8.06–7.80 (12H, p-,m-Ph), 7.36–7.29 (2H, m, H2-Bmaj
and H1-Bmin), 7.27 (s, H-Cmaj), 7.17 (quasi-d, H-Cmin
and H4-Bmaj), 7.08 (6H(together with 7.27 and 7.17),
Geometry optimizations were performed using Gauss-
ian 03 software at B3LYP/LanL2MB level of theory.
Optimized geomeries showed no imaginary frequencies
in vibrational analyses.
s H4-Bmin), 6.97 (d, JH H -Bmaj
(2H(together with 6.97), dd, JH H -Bmin
2.0, H2-Bmin).
1
2
= 8.8, H1-Bmaj), 6.87
Bromination of Pd Ph4TBP. Synthesis of palladium
2-bromo-6,13,20,27-tetraphenyltetrabenzo[b:g:l:q]-
porphyrin (2). Amount of Pd Ph4TBP relevant to concen-
tration specified in Table 2 was dissolved in the mentioned
solvent. Then reflux and stirring was begun, and Me4NBr3
added by equal portions in equal time periods (or added
dropwise if CH2Cl2 usedasathesolvent). Refluxandreagent
addition was continued until TLC showed mainly the for-
mation of the target porphynate.At the end reaction mixture
was washed by 10% aq. Na2SO3 and brine. Organic layer
wasdriedoverNa2SO4.Thenthesolventwasevaporatedand
the residue was analysed by LDI-TOF. For preparative pur-
poses (Table 2, entry 4) 1(50 mg, 54.4 µmol) were dissolved
in CHCl3 (3.3 mL) and NMe4Br3 (44 mg, 0.14 mmol) were
added in portions for specified time. After workup, residue
was chromatographed on silica, eluent CCl4/hexanes. Yield
33 mg, 63%. Molecular ion isotope distribution spectrum
is identical with simulated one. UV-vis spectrum see in
Table 3. 1H NMR (400 MHz, CDCl3, HMDS, ring designa-
tion – bold letter – see in Chart 3): δH, ppm8.25–8.20(8H, m,
1
2
= 8.9, JH H -Bmin
2
4
=
SUMMARY AND CONCLUSION
Bromination of Pd Ph4TBP 1 yields mono- and octa-
bromoderivative 2 and 3. These derivatives were isolated
and characterized. UV-vis, redox and phosphorescence
properties have been studied. Bromination was found to
exert little influence on UV-vis data. Reduction potentials
showed anode shift upon bromination, whereas at first
oxidation one remained unchanged; for second oxidation
one moved to cathode region. Unlike the results at 77 K,
octabromosubstitution did not give rise to increased
phophorescence quantum yield at room temperature.
Acknowledgements
Grant from Russian Foundation for Basic Research
(10-03-01071a) is gratefully acknowledged. Authors are
grateful to Mr. MizerevAA. for careful reading the manu-
script, Dr. Fedorov Yu. V. for assisting room temperature
phosphorescence measurements and to Prof. Vinogradov
S.A. (University of Pennsylvania) for helpful and stimu-
lating discussion.
o-Ph), 7.98–7.81 (12H, p-, m-Ph), 7.28 (1H, dd, JH1H -B
8.7, JH2H -B
= 1.7 Hz, H2-B), 7.21–7.19 (7H, m(quasi-AA’
part of AA’BB’), o-A, H2-B)), 7.10 (6H, m, m-A), 6.89
(1H, d, JH1H -B
= 8.7, H1-B). LDI-TOF mass spectrum
2
=
4
2
(see Supplementary material) shows isotope distribution
identical to the calculated one.
Bromination of Pd Ph4TBP. Synthesis of palladium
2,3,9,10,16,17,23,24-octabromo-6,13,20,27-tetraphenyl-
tetrabenzo[b:g:l:q]porphyrin (3). To the mixture of
NMe4Br (17 mg, 54 µmol) and Br2, (3.5 g, 22 mmol,
Supporting information
Figures S1–S5 are given in the supplementary mate-
rial. This material is available free-of-charge via the
Internet at http://www.worldscinet.com/jpp/jpp.shtml.
Copyright © 2010 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2010; 14: 822–824

RegIOSeleCtIve bROmInatIOn Of PallaDIum tetRaPhenyltetRabenzOPORPhyRIn tO benzO-RIngS
823
24. Negishi E.-I. Handbook of Organopalladium Chem-
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