Synthesis of new azole phosphonate precursors for fuel cells proton exchange membranes

Article abstract of DOI:10.1002/hc.21254

Herein we present the synthesis and characterization of new phosphonate-, bisphosphonate- and hydroxybisphosphonatebenzimidazole derivatives substituted at the N-1 position and new regioisomers phosphonate-, bisphosphonate-, and hydroxybisphosphonatebenzo

Full text of DOI:10.1002/hc.21254

Heteroatom Chemistry
Volume 00, Number 0, 2014
Synthesis of New Azole Phosphonate
Precursors for Fuel Cells Proton Exchange
Membranes
Fa´tima C. Teixeira,1 C. M. Rangel,1 and Anto´nio P. S. Teixeira2,3
1Laborato´rio Nacional de Energia e Geologia, I.P., Estrada do Pac¸o do Lumiar, 22, 1649-038,
Lisboa, Portugal
2
´
Departamento de Qu´ımica, Escola de Cieˆncias e Tecnologia, Centro de Qu´ımica de Evora,
´
Instituto de Investigac¸a˜o e Formac¸a˜o Avanc¸ada, Universidade de Evora, R. Roma˜o Ramalho, 59,
7000-671, Evora, Portugal
´
3Centro de Qu´ımica Estrutural, IST, Universidade de Lisboa, Av. Rovisco Pais, 1, 1049-001,
Lisboa, Portugal
Received 23 July 2014; revised 17 October 2014
INTRODUCTION
ABSTRACT: Herein we present the synthe-
sis and characterization of new phosphonate-,
bisphosphonate- and hydroxybisphosphonatebenzim-
idazole derivatives substituted at the N-1 position and
new regioisomers phosphonate-, bisphosphonate-,
and hydroxybisphosphonatebenzotriazole deriva-
tives substituted at N-1 or N-2 positions. The
compounds were characterized by NMR and IR
spectroscopies, and mass spectrometry (low and
high resolution) allowing the assignment of their
structure, including the identification of regioisomers.
These new azole monomers will be precursors for a
mesoporous silica host to produce novel membrane
materials with high proton conductivity for interme-
diate temperature proton exchange membrane fuel
In an energy scenario that increasingly demands
cleaner and more efficient energy sources, fuel cells
are considered promising electrochemical devices
since they can provide electric energy with high ef-
ficiency and low environmental impact, converting
the energy stored in fuels with zero pollution levels.
The proton exchange membrane fuel cells (PEMFC)
are considered one of the most promising sources
among the various kinds of existing fuel cells due to
their high power density and high power-to-weight
ratio. One of the drawbacks of current cells is related
to the electrolytes currently in use, limiting their use
to temperatures below 100°C when operating under
water-assisted proton conduction.
ꢀC
cells.
2014 Wiley Periodicals, Inc. Heteroatom
The temperature operation above 100°C could
increase the performance of PEMFC due to a faster
electrode reaction without CO poisoning of the Pt
electrocatalyst, easier heating, and high energy effi-
ciency [1–8].
Chem. 00:1–13, 2014; View this article online at
wileyonlinelibrary.com. DOI 10.1002/hc.21254
The proton exchange membrane is a key com-
ponent for the operation of PEMFC. During re-
cent years, the study of membrane materials have
been focused in obtaining high proton conductiv-
ity, low electrical conductivity, low permeability to
fuel and oxidant, good chemical and thermal stabili-
ties, good mechanical properties, and low cost [1–8].
Correspondence to: Fa´tima C. Teixeira; e-mail: fatima.
teixeira@lneg.pt.
Supporting Information is available in the online issue at
www.wileyonlinelibrary.com.
ꢀC
2014 Wiley Periodicals, Inc.
1

2
Teixeira, Rangel, and Teixeira
Generally, they are made of organic polymers con-
taining acidic functionalities (e.g., NafionꢀR ), but
the limitations of current membranes have fos-
tered the research and development of alternative
membranes, including doped polybenzimidazole, a
composite of Nafion and metal oxides, sulfonated
polymers based on aromatic hydrocarbons, and
organosiloxane based on inorganic–organic hybrids
with various acidic species [1–11].
FIGURE 1 General bridged silsesquioxane precursors of the
type (RO)3Si-R’-Si(RO)3.
Usually, some degree of hydration is required to
conducting ions. There are new materials combin-
ing acceptor and donor ion carrier capabilities of
several groups [8]. Phosphonic acids are considered
one of the groups that have good proton donor and
acceptor properties, with higher proton conductivi-
ties, oxidation resistance, and better thermal stabil-
ity than the sulfonic acid groups. The properties of
polymers with phosphonate groups allow their oper-
ation at elevated temperatures [12–17]. Heterocycles
can act as a proton-conducting species, due to their
nitrogen amphoteric behavior and can be used ei-
ther as dopant or pendant groups in PEMFC without
the need of external humidification. The properties
of many heterocycles, including benzimidazole and
triazole, enable them to be used in materials working
above 100°C [1,9,18–26].
Facing the importance of developing new ma-
terials for fuel cell applications, and taking into ac-
count the properties of heterocycles and phosphonic
acid groups, it can be conceived that molecules bear-
ing both of these groups can present good properties
for PEMFC. Also, the physicochemical and proton
conductivity properties of the membranes can be
fine-tuned by adjusting the chemical structure and
functional groups present at the monomeric units.
Based on the properties of periodic meso-
porous silica functionalized with acid groups, in-
cluding high proton conductivities and high rela-
tive humidity [27–29], we envisaged the synthesis of
new monomers for the preparation of novel mem-
branes for application in high-temperature PEMFC.
These monomers will be used to prepare organic-
functionalized materials, including mesoporous sil-
ica materials. These materials will be prepared from
bridged organosilicon precursors of the general for-
mula (RO)3Si-R’-Si(RO)3, where R represents alkyls
groups and R’ is a bridge with organic groups, such
as benzimidazole or benzotriazole, functionalized
with phosphonate or bisphosphonate groups, ob-
tained in this work (Fig. 1). Varying the organic
spacer group of the organosilicon precursors al-
lows the fine-tuning of chemical and physical prop-
erties of the mesoporous organosilica materials.
These types of hybrid compounds can combine
the high-temperature stability of polysilsesquiox-
SCHEME 1
anes with the proton conductivity of benzimidazole
or benzotriazole derivatives and phosphonic groups.
Herein, we report the synthesis and charac-
terization of the new monomers phosphonate-,
bisphosphonate-, and hydroxybisphosphonate de-
rived from benzimidazole or benzotriazole and their
characterization, including the assignment of regio-
siomers.
RESULTS AND DISCUSSION
The new phosphonate monomers were synthe-
sized from 4,7-dibromobenzimidazole 4 and 4,7-
dibromobenzotriazole 5 following several strategies
and different kinds of reagents and conditions.
The precursor 4,7-dibromobenzimidazole 4 was
prepared from 2,1,3-benzothiodiazole 1 in three
synthetic steps, modified from literature proce-
dures (Scheme 1). Compound 2 was prepared in
high yield by bromination of commercially avail-
able 2,1,3-benzothiadiazole 1 [30]. The reduction
of 2 with NaBH4 or by an alternative method us-
ing NaBH4/CoCl2·6H2O (catalytic amount) gave 1,2-
diamine 3 in moderated yield [31–34]. Cyclization of
1,2-diamine 3 to 4,7-dibromobenzimidazole 4 was
performed by the reaction with trimethylorthofor-
mate in acid conditions, using ( )-camphorsulfonic
acid [35].
Benzimidazole phosphonates and bisphospho-
nates were prepared in good yields using several
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Synthesis of New Azole Phosphonate Precursors for Fuel Cells Proton Exchange Membranes
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Analysis of crude by 1H NMR shows the char-
acteristic signals of the expected compounds as
three multiplets at 3.42, 4.07–4.22, and 4.94–5.08
ppm, consistent with the presence of a methine
proton (CH(PO3Et2)2) and two methylene groups
(POCH2CH3 and NCH2CHP), respectively, coupling
with phosphorous atoms of 2 equiv phosphonate
groups attached to the same carbon. The proton-
decoupled 31P NMR spectra of bisphosphonate 7
showed a single signal at 18.8 ppm, which confirmed
that two phosphorus atoms are magnetically equiv-
alent. The signals of these spectra are in agreement
with the presence of the desired compound 7, with
the proposed structure. However, purification of
the crude by column chromatography led to the
decomposition of compound 7, due to a retro-
Michael reaction [37], with the regeneration of
starting material 4 and a mixture of unidentified
compounds.
The most common procedures for the synthe-
sis of hydroxybisphosphonates start from carboxylic
acid derivatives, using a classical method with phos-
phoric or phosphorous acids [38, 39] or by an
Arbuzov reaction of a silylphosphite reagent, fol-
lowed by methanol hydrolysis [40,41].
SCHEME 2
The first step to synthesize hydroxybisphospho-
nates 10a–b (n = 1 and 2) involved the preparation of
ester derivatives, followed by their hydrolysis to af-
ford the corresponding carboxylic acids. So, starting
from 4,7-dibromobenzimidazole 4, the benzimida-
zole ester derivatives 8a–b (n = 1 and 2) were ob-
tained by the nucleophilic substitution reaction of
bromo esters (Br(CH2)nCO2Et, n = 1–2), in good to
excellent yields. The hydrolysis of the ester deriva-
tives 8a–b (n = 1 and 2) allowed the synthesis of
the corresponding carboxylic acids 9a–b (n = 1 and
2) in excellent yield (Scheme 2). The basic hydrol-
ysis of ester derivative 8a (n = 1) gave the desired
carboxylic acid 9a (n = 1) in 99% yield, but these
hydrolysis conditions for ester derivative 8b (n = 2)
gave a mixture of the carboxylic acid 9b (n = 2) and
the starting material 4,7-dibromobenzimidazole 4,
in the ratio of 1.4:1. The hydrolysis of ester deriva-
tive 8b (n = 2) was done in acidic conditions, using
HCl (1 M) in acetone, to provide the carboxylic acid
9b (n = 2) in 99% yield.
strategies described in Scheme 2. Compounds 6–
10 were fully characterized by NMR (including
bidimensional techniques), IR spectroscopy, and
mass spectrometry (low and high resolution). The
phosphonate and bisphosphonate structure of com-
pounds 6, 7, and 10a–b (n = 1 and 2) was easily
identified by analysis of NMR data. Electron impact
ionization (EI) (compounds 6 – 9) and electrospray
ionization (ESI) (compounds 10a–b) Mass spec-
trometry techniques were used to show the molec-
ular ion of compounds and confirmed the proposed
molecular formulae.
The reaction of 4,7-dibromobenzimidazole 4
with potassium carbonate, in EtOH, followed by the
addition of diethyl 2-bromoethylphosphonate gave
phosphonate 6 in excellent yield (Scheme 2). The 13C
NMR spectrum of phosphonate 6 shows a doublet at
29.2 ppm (JCP = 139 Hz), consistent with a methy-
lene carbon coupling with one phosphorous nuclei,
which supported the proposed structure. Also, the
proton-decoupled 31P NMR spectrum of 6 shows a
singlet at 25.8 ppm.
Bisphosphonates 10a–b (n = 1 and 2) were syn-
thesized in good yield by the reaction of carboxylic
acids 9a–b (n = 1 and 2) with SOCl2, to produce in
situ the corresponding acyl chloride, followed by the
reaction with tris(trimethylsilyl)phosphite and sub-
sequent methanolysis (Scheme 2).
The synthesis of bisphosphonate 7 substituted
at the N-1 position was performed by the reaction
of 4,7-dibromobenzimidazole 4 with tetraethyl
1
The H NMR spectrum of 10a (n = 1) shows a
ethylidene-1,1-bisphosphonate
[36]
in
THF
triplet at 5.19 (JHP = 10 Hz) ppm for the protons
on carbon NCH2 due to the coupling with 2 equiv
(Scheme 2), by a Michael addition reaction [37].
Heteroatom Chemistry DOI 10.1002/hc

4
Teixeira, Rangel, and Teixeira
phosphorous nuclei. The 13C NMR spectra of com-
pounds 10a (n = 1) and 10b (n = 2) show a triplet
at 73.9 ppm (JCP = 139 Hz) and 71.3 ppm (JCP
= 142 Hz), respectively, consistent with a quater-
nary carbon (disappearing in DEPT 135 13C NMR
mode) coupling with the 2 equiv phosphorous nu-
clei, which support the proposed structures with
two phosphonate groups attached to the same car-
bon. The proton-decoupled 31P NMR spectra of com-
pounds 10a (n = 1) and 10b (n = 2) show a singlet at
17.4 and 18.6 ppm, respectively, in agreement with
two chemically and magnetically equivalent phos-
phorus atoms.
Like benzimidazole, the benzotriazole is also
a planar and rigid aromatic heterocycle, with one
more nitrogen atom, replacing the C-2 methine
group of benzimidazole, presenting a moderate
electron-deficient character [42]. Since previous
studies showed that triazole [19] enhances the pro-
ton conductivity with respect to imidazole, it is
expected that benzotriazole also presents higher
proton conductivity than benzimidazole. Also, the
presence of a pendant group bonded to a nitro-
gen atom of benzotriazole ring create two N-1 and
N-2 regioisomers, which present different optical
and electrochemical behavior [43]. Moreover, small
structural variations at the monomers should be
considered since they can fine-tune the electron
and proton conductivity properties of the resulting
materials.
carbonate, in DMF gave regioisomers 11 and 12,
with the N-2 derivative 12 as a major regioisomer
(70% yield) and the N-1 derivative 11 with lower
yield (17% yield) (Scheme 3). Compounds 11 and 12
were separated by column chromatography to pro-
vide the pure phosphonate regioisomers.
The regioisomers of 4,7-dibromobenzotriazoles
11 and 12 present qualitative differences in the NMR
spectra, according to their molecular symmetry. The
unambiguous assignment of benzotriazole deriva-
tives substituted at N-1 and N-2 was carried out
by 1H and 13C NMR spectroscopy, including two-
dimensional NMR techniques. The NMR spectra of
compound 12 show only one signal for the two
5-H and 6-H protons, and only one signal for each
pair: C4 and C7, C5 and C6, and C3a and C7a, show-
ing that the atoms of these pairs are magnetically
equivalents, and the compound present molecular
symmetry, consistent with the N-2 benzotriazole re-
gioisomer. Spectra of compound 11 present differ-
ent chemical shifts for each proton or carbon atoms,
according to a nonsymmetric molecular structure
of N-1 regioisomer. These spectroscopic data are in
agreement with the 13C NMR spectra of N-1 and N-2
substituted benzotriazole regioisomers reported in
the literature [45–49].
The Michael addition reaction of 4,7-
dibromobenzotriazole 5 with tetraethyl ethylidene-
1,1-bisphosphonate [36], in THF afforded the
bisphosphonate 13 substituted at the N-2 position
and unreacted starting material 5 [37]. After column
chromatography, compound 13 was isolated in 37%
yield (Scheme 3). The NMR spectra of compound
13 are in agreement with a symmetric molecular
structure, according to a N-2 benzotriazole re-
gioisomer. Only the N-2 derivative was observed
as a product of this reaction probably due to the
steric hindrance caused by bromine atoms at 4
and 7 positions of benzotriazole, in contrast with
the reaction between benzotriazole and tetraethyl
ethylidene-1,1-bisphosphonate already reported,
which also afforded the N-1 derivative [50].
The precursor 4,7-dibromobenzotriazole 5 was
prepared using a different synthetic procedure
for cyclization of 1,2-diamine 3 (Scheme 1), in
the presence of sodium nitrite in acetic acid in
good yield [44]. The synthesis of phosphonate-
and bisphosphonate derivatives substituted at N-
1 or N-2 positions, starting from the precur-
sor 4,7-dibromobenzotriazole 5, is presented at
Scheme 3.
The reaction of 4,7-dibromobenzotriazole 5 with
diethyl 2-bromoethylphosphonate and potassium
Similar to benzimidazolebisphosphonates, for
the synthesis of hydroxybenzotriazolebisphos-
phonate was necessary to prepare the cor-
responding esters and carboxylic acids. The
4,7-dibromobenzotriazole 5 reacted with a base, fol-
lowed by addition of the corresponding bromo es-
ters with one or two methylene groups chain length
(Br(CH2)nCO2Et, n = 1–2). Under these conditions, a
mixture of N-1 or N-2 substituted regioisomers ben-
zotriazole esters 14a–b (n = 1 and 2) and 15a–b
(n = 1 and 2) were obtained in different yields and
ratios (Table 1). Compounds 14a–b (n = 1 and 2)
and 15a–b (n = 1 and 2) were separated by column
SCHEME 3
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Synthesis of New Azole Phosphonate Precursors for Fuel Cells Proton Exchange Membranes
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TABLE 1 Synthesis of Benzotriazole Ester Derivatives Substituted at N-1 and N-2 (14 and 15)
Br
Br
Br
N
N
N
N
i) Base
ii) Br(CH2)nCO2Et
N
N
+
N
(CH2)nCO2Et
N
N
H
(CH2)nCO2Et
Br
Br
Br
15
14
5
n
Base (solvent)
Compound 14 (%)
Compound 15 (%)
15a 53
14 + 15 (%)
1
KOtBu (EtOH)
K2CO3 (DMF)
KOtBu (THF)
K2CO3 (DMF)
14a
14b
37
90
78
28
19
37
50
25
48
2
15b
44a
85
a56% of starting material 5 remained unreacted.
chromatography to provide pure regioisomers. The
identification of the different N-1 and N-2 regioiso-
mers were done according to the observed molecular
symmetry or asymmetry, for N-2 derivatives or N-1
derivatives, respectively, at NMR spectra, and are in
agreement with NMR data reported in the literature
for N-1 and N-2 substituted benzotriazole regioiso-
mers [45–49].
pairs, in agreement with the molecular symmetry of
N-2 regioisomers 19a–b (n = 1 and 2). The spectra of
compounds 18a–b (n = 1 and 2) present distinctive
signals to all proton and carbon atoms, in agreement
with an asymmetric molecular structure of the N-1
regioisomer.
All compounds 11–19 were characterized by
NMR, IR spectroscopy, and mass spectrome-
try, which confirmed their proposed molecular
structures.
The esters isomers 14a–b (n = 1 and 2) and 15a–
b (n = 1 and 2) were subjected to the hydrolysis to
afford the corresponding carboxylic acid derivatives
16a–b (n = 1 and 2) and 17a–b (n = 1 and 2), re-
spectively. Using basic hydrolysis conditions, both
regioisomers of n = 1 derivatives (16a (n = 1) and
17a (n = 1)) were obtained in excellent yields (Ta-
ble 2). But the basic hydrolysis of compounds 14b
(n = 2) and 15b (n = 2) did not afford the desired
compounds. Instead, for compound 14b (n = 2) was
obtained a mixture of carboxylic acid 16b (n = 2) and
the 4,7-dibromobenzotriazole 5, and for compound
15b (n = 2) was recovered the starting material 15b
(n = 2) and 4,7-dibromobenzotriazole 5. For n = 2
was necessary to use acidic hydrolysis conditions to
obtain the desired carboxylic acids 16b (n = 2) and
17b (n = 2) (Table 2).
CONCLUSIONS
Several new azole phosphonate derivatives were
synthesized to become precursors of membranes
for PEMFC. From 4,7-dibromobenzimidazole
4, new phosphonate-, bisphosphonate- and hy-
droxybisphosphonatebenzimidazole
derivatives
substituted at the N-1 position were synthesized
in good yields. New regioisomers phosphonate-,
bisphosphonate- and hydroxybisphosphonateben-
zotriazole derivatives substituted at the N-1 or N-2
position were synthesized in good yields, from
4,7-dibromobenzotriazole 5. All new compounds
were fully characterized by NMR, IR spectroscopy,
and mass spectrometry. NMR spectroscopy allowed
the identification of both regioisomers due to
their molecular symmetric (N-2 regioisomers) or
asymmetric structure (N-1 regiosiomers).
After preparation of the benzotriazole carboxylic
acid derivatives, the synthesis of bisphosphonates
18a–b (n = 1 and 2) and 19a–b (n = 1 and 2)
was carried out by the reaction of the carboxylic
acids 16a–b (n = 1 and 2) and 17a–b (n = 1
and 2) with SOCl2, to produce in situ the corre-
sponding acyl chloride, followed by the reaction
with tris(trimethylsilyl)phosphite and subsequent
methanolysis (Table 3).
EXPERIMENTAL
All the reactions involving air-sensitive reagents
were performed under an atmosphere of dry ni-
trogen, and all solvents were degassed before use.
THF was distilled from sodium benzophenone ketyl.
Column chromatography was performed on silica
gel (230–400 mesh) under a positive pressure of
nitrogen.
The NMR spectra allowed the identification of
both regioisomers due to the observation of molecu-
lar symmetry or asymmetry structure of compounds.
1
The H NMR spectra show one signal for 5-H and
6-H pair of protons, and 13C NMR spectra present
one signal for each C4–C7, C5–C6, and C3a–C7a
Heteroatom Chemistry DOI 10.1002/hc

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Teixeira, Rangel, and Teixeira
TABLE 2 Hydrolysis of Benzotriazole Carboxylic Acid Derivatives Substituted at N-1 and N-2 (16 and 17)
Br
Br
N
N
N
N
Hydrolysis Conditions
N
N
(CH2)nCO2Et
(CH2)nCO2H
Br
Br
14-15
16-17
Regioisomer
Reagent
n
Hydrolysis Conditions
Product
16 or 17 (%)
N-1
14a
14b
14b
15a
15b
15b
1
2
2
1
2
2
NaOH (10 M)
NaOH (10 M)
HCl (1 M)
NaOH (10 M)
NaOH (10 M)
HCl (1 M)
16a
16b
16b
17a
17b
17b
99
a
87
N-2
99
b
99
aA mixture of carboxylic acid 16b (n = 2) and benzotriazole 5 was obtained in the ratio of 2:1.
bA mixture of starting material 15b (n = 2) and benzotriazole 5 was obtained in the ratio of 2.5:1.
TABLE
3
Synthesis of Benzotriazolebisphosphonate
(Bruker Daltonics) or APEX-Q (Bruker Daltonics) in-
struments.
Melting points were determined on a Reichert
Thermovar melting point apparatus and are not
corrected.
Derivatives Substituted at N-1 and N-2 (18 and 19)
Br
Br
Br
N
N
N
N
i) SOCl2
N
N
OH
ii) [(CH3)3SiO]3P, THF
iii) MeOH
(CH2)nCO2H
PO3H2
(
)
n
Br
PO3H2
General Procedure A:
A
mixture of 4,7-
18-19
16-17
dibromo-1H-benzimidazole 4 or 4,7-dibromo-1H-
benzotriazole 5 and K2CO3 (3 equiv) in DMF (3 mL)
was stirred at 80°C during 30 min. The correspond-
ing bromo ester (Br(CH2)nCO2Et, n = 1–2) was
added, and the reaction mixture was refluxed again.
Upon cooling, the mixture was acidified with 10%
aqueous HCl solution and the aqueous layer was ex-
tracted with EtOAc. The combined organic extracts
were washed with brine and dried over anhydrous
MgSO4. After filtration, the solvent was removed in
vacuum. The resulting oil was purified by column
chromatography.
Regioisomer
Reagent
n
Product
Yield (%)
N-1
16a
16b
17a
17b
1
2
1
2
18a
18b
19a
19b
78
83
44
48
N-2
2,1,3-Benzothiadiazole 1 is commercially avail-
able (Aldrich, 2710-901 Sintra, Portugal). 4,7-
Dibromo-1H-benzimidazole 4 was synthesized in
General Procedure B: To
4,7-dibromo-1H-benzotriazole
a
solution of
a
three-step synthesis by modifying the syn-
5
and KOtBu in
thetic procedures reported [35]. 4,7-Dibromo-1H-
benzotriazole 5 [44] and tetraethyl ethenylidenebis-
phosphonate [36] were prepared according to
literature procedures.
NMR spectra were recorded on Bruker AMX 300
and on a Bruker Avance II 300 (1H 300 MHz, 13C 75
MHz, 31P 121 MHz), on a Bruker Avance II 400 and
Bruker Avance 400 MHz Ultra-shield (1H 400 MHz,
13C 100 MHz, 31P 162 MHz) spectrometers. Chemical
shifts (δ) are reported in ppm and coupling constants
(J) in Hz.
Infrared spectra were recorded on a Perkin-
Elmer FT-IR spectrum BX Fourier transform spec-
trometer, using KBr disks or film.
Low resolution and high resolution (HRMS)
mass spectra analyses were performed at the ‘CACTI,
Unidad de Espectrometria de Masas’ at the Univer-
sity of Vigo, Spain, on a VG AutoSpect M, MicroTOF
EtOH, the proper bromo ester (Br(CH2)nCO2Et,
n = 1–2) was added and the reaction mix-
ture was refluxed. After removing the solvent
by evaporation, the residue was washed with
H2O and extracted with dichloromethane. The
organic solution was condensed by evapora-
tion, and the product was purified by column
chromatography (3:1 dichloromethane/petroleum
ether).
General Procedure C: An ester derivative (n = 1)
(8a, 14a, or 15a) in an aqueous NaOH solution (10
M) was stirred at reflux for 2 h. The reaction mix-
ture was cooled to room temperature and acidified
with 10% aqueous HCl solution, and the aqueous
layer was extracted with EtOAc. The combined or-
ganic extracts were washed with brine, dried over
anhydrous MgSO4, and filtered, and the solvent was
removed in vacuum.
Heteroatom Chemistry DOI 10.1002/hc

Synthesis of New Azole Phosphonate Precursors for Fuel Cells Proton Exchange Membranes
7
General Procedure D: To a solution of ester
derivative (n = 2) (8b, 14b, or 15b) in acetone, an
aqueous HCl solution (1 M) was added. The reaction
mixture was refluxed for 18 h. Upon cooling, the mix-
ture was concentrated in vacuum. The obtained solid
was dissolved in water, and the aqueous layer was ex-
tracted with EtOAc. The combined organic extracts
were treated as described in the general procedure C.
General Procedure E: A mixture of carboxylic acid
(1 equiv) and thionyl chloride was kept under reflux
for 2 h. The excess of thionyl chloride was removed
under reduced pressure to give the corresponding
acyl chloride, which was immediately used without
further purification. The crude acyl chloride was dis-
solved in dry THF and tris(trimethylsilyl)phosphite
(2 equiv) was added. Then, the mixture was stirred
at room temperature for 1 h. The excess of solvent
was removed under reduced pressure. Methanol was
added, and the mixture was stirred for 1 h. After sol-
vent removal under reduced pressure, the residue
was washed with ethyl ether and precipitated with
acetone.
100%), 439 (MH+, 54%). HRMS (ESI) m/z calcd for
C13H18Br2N2O3P 438.9416 (Br-79 isotope) [MH]+,
found 438.9416.
Tetraethyl (2-(4,7-Dibromo-1H-benzimidazol-1-
yl)ethane-1,1-diyl)bisphosphonate (7)
A
mixture of 4,7-dibromo-1H-benzimidazole 4
(100 mg, 0.363 mmol) and tetraethylethenyli
denebisphosphonate (109 mg, 0.363 mmol) in THF
(5 mL) was stirred under reflux for 18 h. The solvent
was evaporated in vacuum to afford a yellow oil.
The NMR spectra of crude product show the start-
ing material 4, CH2 C(PO3Et2)2 and compound 7.
Purification by column chromatography led to the
decomposition of compound 7 to give the starting
material 4 and a mixture of unidentified compounds.
1H NMR spectrum of compound 7 in the crude
mixture: 1H NMR (300 MHz, CDCl3): δ (ppm) = 1.19
(t, J = 7.2, 6H, OCH2CH3), 1.28 (t, J = 7.2, 6H,
OCH2CH3), 3.42 (m, 1H, CH(PO3Et2)2), 4.07–4.22
(m, 8H, CH2CH3), 4.94–5.08 (m, 2H, NCH2), 7.31
(m, 2H, ArH, 5-H and 6-H), 8.11 (s, 1H, ArH, 2-H).
31P NMR (121 MHz, H3PO4/ CDCl3): δ (ppm) = 18.8.
Diethyl (2-(4,7-dibromo-1H-benzimidazol-1-
yl)ethyl)phosphonate (6)
A
solution of 4,7-dibromo-1H-benzimidazole 4
(300 mg, 1.087 mmol) and K2CO3 (450 mg,
3.261 mmol) in EtOH (15 mL) was refluxed dur-
ing 30 min. An excess of Br(CH2)2PO3Et2 (0.39 mL,
2.174 mmol) was added, and the reaction mixture
was refluxed for 24 h. The reaction mixture was
cooled to room temperature and filtered, and the
solvent was removed in vacuum. The resulting oil
was purified by column chromatography (1:1 ethyl
acetate/acetone) to give compound 6 (450 mg, 94%)
as white solid. mp 40–41°C. νmax (KBr) (cm−1): 3072,
2984, 2906, 1503, 1477, 1453, 1393, 1376, 1364, 1340,
1328, 1317, 1294, 1277, 1232, 1206, 1164, 1140, 1102,
1087, 1053, 1026, 975, 948, 925, 892, 865, 800, 719,
688, 652, 632, 574, 530, 518. 1H NMR (300 MHz,
CDCl3): δ (ppm) = 1.24 (t, J = 7.1, 6H, 2× OCH2CH3),
2.39 (dt, J = 18.6 and 7.2, 2H, CH2PO3Et2), 4.00–4.09
(m, 4H, 2× OCH2CH3), 4.74–4.83 (m, 2H, NCH2),
7.30 (d, J = 8.3, 1H, ArH, 5-H or 6-H), 7.33 (d, J =
8.3, 1H, ArH, 5-H or 6-H), 8.12 (s, 1H, ArH, 2-H). 13C
NMR (75 MHz, CDCl3): δ (ppm) = 16.4 (d, JCP = 6.0,
Ethyl 2-(4,7-Dibromo-1H-benzimidazol-1-
yl)acetate (8a (n = 1))
Following general procedure A, the reaction of 4,7-
dibromo-1H-benzimidazole 4 (120 mg, 0.435 mmol)
and K2CO3 (180 mg, 1.305 mmol) in DMF (3 mL),
followed by the addition of BrCH2CO2Et (0.10 mL,
0.870 mmol), was refluxed for 45 min and puri-
fied by column chromatography (ether) to give com-
pound 8a (n = 1) (144 mg, 91%) as a white solid.
mp 110–111°C. νmax (KBr) (cm−1): 3064, 2979, 1745,
1605, 1505, 1476, 1424, 1376, 1364, 1347, 1338,
1317, 1280, 1220, 1168, 1161, 1107, 1027, 975, 923,
892, 793, 777, 711, 634, 537, 426. 1H NMR (300
MHz, CDCl3): δ (ppm) = 1.26 (t, J = 7.2, 3H,
OCH2CH3), 4.24 (q, J = 7.2, 2H, OCH2CH3), 5.22
(s, 2H, NCH2), 7.26 (d, J = 8.1, 1H, ArH, 5-H or 6-H),
7.32 (d, J = 8.4, 1H, ArH, 5-H or 6-H), 7.96 (s, 1H,
ArH, 2-H). 13C NMR (75 MHz, CDCl3): δ (ppm) =
13.9 (CH3), 47.7 (NCH2), 62.2 (OCH2), 102.1, 113.2
(Ar:C4,C7), 126.4, 128.4 (Ar:C5,C6), 131.4 (Ar:C7a),
143.4 (Ar:C3a), 145.8 (Ar:C2), 169.3 (CO). MS (EI):
m/z = 364 (M+ + 4, 17%), 362 (M+ + 2, 40%), 360
(M+, 19%), 291 (364-COOEt, 35%), 289 (362-COOEt,
100%), 287 (360-COOEt, 40%). HRMS (EI) m/z calcd
for C11H10Br2N2O2 359.9109 (Br-79 isotope) [M]+,
found 359.9105.
CH3), 29.2 (d, JCP = 139.1, CH2PO3Et2), 41.2 (d, JCP
=
2.3, NCH2), 62.3 (d, JCP = 6.5, OCH2), 102.0, 113.4
(Ar:C4,C7), 126.8, 128.8 (Ar:C5,C6), 131.1 (Ar:C7a),
143.7 (Ar:C3a), 145.9 (Ar:C2). 31P NMR (121 MHz,
H3PO4/ CDCl3): δ (ppm) = 25.8. MS (ESI): m/z =
465 (MNa+ + 4, 25%), 463 (MNa+ + 2, 52%), 461
(MNa+, 26%), 443 (MH+ + 4, 54%), 441 (MH+ + 2,
Heteroatom Chemistry DOI 10.1002/hc

8
Teixeira, Rangel, and Teixeira
Ethyl 3-(4,7-Dibromo-1H-benzimidazol-1-
yl)propanoate (8b (n = 2))
3-(4,7-Dibromo-1H-benzimidazol-1-
yl)propanoic acid (9b (n = 2))
Following general procedure A, the reaction of 4,7-
dibromo-1H-benzimidazole 4 (121 mg, 0.439 mmol)
and K2CO3 (182 mg, 1.316 mmol) in DMF (3 mL), fol-
lowed by the addition of Br(CH2)2CO2Et (0.11 mL,
0.877 mmol), was refluxed for 4 h and purified by
column chromatography (ether) to give compound
8b (n = 2) (115 mg, 70%) as a white solid. mp 64–
65°C. νmax (KBr) (cm−1): 3126, 3079, 2978, 2959,
1727, 1495, 1473, 1443, 1405, 1384, 1374, 1366, 1354,
1336, 1312, 1244, 1204, 1191, 1162, 1103, 1087, 1058,
1025, 983, 946, 916, 890, 869, 852, 790, 626, 593, 572.
1H NMR (300 MHz, CDCl3): δ (ppm) = 1.23 (t, J =
7.1, 3H, OCH2CH3), 2.95 (t, J = 6.2, 2H, NCH2CH2),
4.13 (q, J = 7.1, 2H, OCH2CH3), 4.81 (t, J = 6.2, 2H,
NCH2), 7.30 (d, J = 8.7, 1H, ArH, 5-H or 6-H), 7.33 (d,
J = 8.2, 1H, ArH, 5-H or 6-H), 8.08 (s, 1H, ArH, 2-H).
13C NMR (100 MHz, CDCl3): δ (ppm) = 14.2 (CH3),
36.5 (CH2), 41.9 (NCH2), 61.3 (OCH2), 102.0, 113.7
(Ar:C4,C7), 126.5, 128.5 (Ar:C5,C6), 131.2 (Ar:C7a),
144.2 (Ar:C3a), 146.3 (Ar:C2), 170.6 (CO). MS (EI):
m/z = 378 (M+ + 4, 21%), 376 (M+ + 2, 49%), 374
(M+, 23%), 291 (378-CH2COOEt, 40%), 289 (376-
CH2COOEt, 100%), 287 (374-COOEt, 48%). HRMS
(EI) m/z calcd for C12H12Br2N2O2 373.9265 (Br-79
isotope) [M]+, found 373.9259.
Following general procedure D, the hydrolysis of
compound 8b (n = 2) (43 mg, 0.114 mmol) in an
aqueous HCl solution (1 M) (0.3 mL) gave com-
pound 9b (n = 2) (40 mg, 99%) as a white solid.
mp 222–223°C. νmax (KBr) (cm−1): 3400–2300, 3119,
3057, 3032, 3012, 2943, 2913, 1684, 1547, 1497,
1466, 1449, 1418, 1389, 1379, 1362, 1250, 1218, 1190,
1166, 1109, 1089, 934, 908, 870, 820, 794, 660, 628,
610, 538, 480. 1H NMR (300 MHz, DMSO-d6): δ
(ppm) = 2.90 (t, J = 6.9, 2H, NCH2CH2), 4.74 (t,
J = 6.9, 2H, NCH2), 7.47 (s, 2H, ArH, 5-H and 6-H),
8.57 (s, 1H, ArH, 2-H). 13C NMR (100 MHz, DMSO-
d6): δ (ppm) = 35.8 (CH2), 42.1 (NCH2), 102.4, 111.9
(Ar:C4, C7), 126.5, 128.7 (Ar:C5, C6), 130.9 (Ar:C7a),
142.2 (Ar:C3a), 147.2 (Ar:C2), 171.8 (CO). MS (EI):
m/z = 350 (M+ + 4, 12%), 348 (M+ + 2, 28%),
346 (M+, 13%), 291 (350-CH2COOH, 13%), 289
(348-CH2COOH, 34%), 287 (346-CH2COOH, 16%),
278 (350-(CH2)2COO+, 42%), 276 (348-(CH2)2COO+,
100%), 274 (346-(CH2)2COO+, 52%). HRMS (EI) m/z
calcd for C10H8Br2N2O2 345.8952 (Br-79 isotope)
[M]+, found 345.8951.
(2-(4,7-Dibromo-1H-benzimidazol-1-yl)-1-
hydroxyethane-1,1-diyl)bisphosphonic acid
(10a (n = 1))
Following general procedure E, the reaction of car-
boxylic acid 9a (n = 1) (100 mg, 0.300 mmol), thionyl
chloride (2 mL), and tris(trimethylsilyl)phosphite
(0.2 mL, 0.600 mmol) gave compound 10a (n =
1) (125 mg, 87%) as a white solid. mp 214–215°C.
νmax (KBr) (cm−1): 3500–2300, 3143, 3081, 3067,
2928, 2864, 1635, 1497, 1387, 1255, 1198, 1134,
1108, 1088, 1054, 1003, 979, 922, 857, 824, 732, 670,
617, 592, 572, 559, 519, 486, 473. 1H NMR (400
MHz, DMSO-d6): δ (ppm) = 5.19 (t, JHP = 10.0, 2H,
NCH2C(OH)(PO3H2)2), 7.34 (s, 2H, ArH, 5-H and
6-H), 8.50 (s, 1H, ArH, 2-H). 13C NMR (100 MHz,
DMSO-d6): δ (ppm) = 48.6 (NCH2), 73.9 (t, JCP = 139,
C(OH)(PO3H2)2), 104.3, 112.9 (Ar:C4,C7), 126.5,
129.7 (Ar:C5,C6), 133.2 (Ar:C7a), 143.3 (Ar:C3a),
148.9 (Ar:C2). 31P NMR (121 MHz, H3PO4/ DMSO-
d6): δ (ppm) = 17.4. MS (ESI): m/z = 483 (MH+ + 4,
13%), 481 (MH+ + 2, 21%), 479 (MH+, 13%). HRMS
(ESI) m/z calcd for C9H11Br2N2O7P2 478.8403 (Br-
79 isotope) [MH]+, found 478.8418.
2-(4,7-Dibromo-1H-benzimidazol-1-
yl)acetic acid (9a (n = 1))
Following general procedure C, the hydrolysis of
compound 8a (n = 1) (135 mg, 0.327 mmol) in the
aqueous NaOH solution (10 M) (1 mL) gave com-
pound 9a (n = 1) (124 mg, 99%) as a white solid.
mp 280–281°C. νmax (KBr) (cm−1): 3500–2300, 3125,
3103, 2998, 2960, 1720, 1604, 1508, 1479, 1424, 1400,
1373, 1347, 1279, 1245, 1224, 1204, 1168, 1112, 981,
938, 894, 808, 797, 678, 644, 629, 598, 569, 540, 530,
440. 1H NMR (300 MHz, MeOD): δ (ppm) = 5.38
(s, 2H, NCH2), 7.38 (s, 2H, ArH, 5-H and 6-H), 8.27
1
(s, 1H, ArH, 2-H). H NMR (300 MHz, DMSO-d6): δ
(ppm) = 5.32 (s, 2H, NCH2), 7.38 (m, 2H, ArH, 5-H
and 6-H), 8.37 (s, 1H, ArH, 2-H). 13C NMR (75 MHz,
DMSO-d6): δ (ppm) = 47.7 (NCH2), 102.4, 112.5
(Ar:C4,C7), 126.0, 128.0 (Ar:C5,C6), 131.8 (Ar:C7a),
143.3 (Ar:C3a), 147.6 (Ar:C2), 169.9 (CO). MS (EI):
m/z = 336 (M+ + 4, 39%), 334 (M+ + 2, 81%),
332 (M+, 41%), 291 (336-COOH, 47%), 289 (334-
COOH, 100%), 287 (332-COOH, 51%). HRMS (EI)
m/z calcd for C9H6Br2N2O2 331.8796 (Br-79 isotope)
[M]+, found 331.8804.
(3-(4,7-Dibromo-1H-benzimidazol-1-yl)-1-
hydroxypropane-1,1-diyl)bisphosphonic acid
(10b (n = 2))
Following general procedure E, the reaction of car-
boxylic acid 9b (n = 2) (78 mg, 0.224 mmol), thionyl
Heteroatom Chemistry DOI 10.1002/hc

Synthesis of New Azole Phosphonate Precursors for Fuel Cells Proton Exchange Membranes
9
Compound 12: mp 54°C. νmax (KBr) (cm−1):
3061, 2979, 2930, 2907, 1498, 1476, 1448, 1391, 1366,
1311, 1256, 1239, 1219, 1198, 1162, 1136, 1099, 1054,
1018, 982, 952, 834, 814, 796, 782, 755, 719, 671, 654,
583, 552, 516. 1H NMR (300 MHz, CDCl3): δ (ppm) =
1.30 (t, J = 7.1, 6H, 2× OCH2CH3), 2.60–2.72 (m, 2H,
CH2PO3Et2), 4.08–4.18 (m, 4H, 2× OCH2CH3), 4.99–
5.07 (m, 2H, NCH2), 7.44 (s, 2H, ArH, 5-H and 6-H).
chloride (1 mL), and tris(trimethylsilyl)phosphite
(0.15 mL, 0.448 mmol) gave compound 10b (n =
2) (66 mg, 60%) as a white solid. mp 243–244°C.
νmax (KBr) (cm−1): 3500–2300, 3147, 3074, 2962,
2924, 1636, 1612, 1578, 1551, 1508, 1500, 1386,
1250, 1201, 1166, 1076, 1039, 979, 951, 928, 882,
836, 774, 755, 670, 637, 615, 593, 567, 535, 523,
481. 1H NMR (400 MHz, DMSO-d6): δ (ppm) =
2.41 (m, 2H, NCH2CH2C(OH)(PO3H2)2), 4.81 (m,
2H, NCH2CH2C(OH)(PO3H2)2), 7.39 (s, 2H, ArH, 5-
H and 6-H), 8.34 (s, 1H, ArH, 2-H). 13C NMR (100
MHz, DMSO-d6): δ (ppm) = 35.8 (CH2), 41.9 (t, JCP
= 7.6, NCH2), 71.3 (t, JCP = 142.3, C(OH)(PO3H2)2),
102.1, 112.4 (Ar:C4,C7), 125.9, 128.0 (Ar:C5, C6),
131.4 (Ar:C7a), 143.3 (Ar:C3a), 147.1 (Ar:C2). 31P
NMR (121 MHz, H3PO4/ DMSO-d6): δ (ppm) = 18.6.
13C NMR (75 MHz, CDCl3): δ (ppm) = 16.5 (d, JCP
=
6.0, CH3), 27.2 (d, JCP = 140.8, CH2PO3Et2), 51.8
(NCH2), 62.3 (d, JCP = 6.4, OCH2), 110.1 (Ar:C4, C7),
130.0 (Ar:C5, C6), 144.0 (Ar:C3a, C7a). 31P NMR (121
MHz, H3PO4/CDCl3): δ (ppm) = 24.8. MS (ESI): m/z
= 466 (MNa+ + 4, 19%), 464 (MNa+ + 2, 36%), 462
(MNa+, 17%), 444 (MH+ + 4, 51%), 442 (MH+ + 2,
100%), 440 (MH+, 53%). HRMS (ESI) m/z calcd for
C12H17Br2N3O3P 439.9369 (Br-79 isotope) [MH]+,
found 439.9357.
MS (ESI): m/z = 497 (MH+ + 4, 10%), 495 (MH+
+
2, 17%), 493 (MH+, 10%). HRMS (ESI) m/z calcd for
C10H13Br2N2O7P2 492.8559 (Br-79 isotope) [MH]+,
found 492.8566.
Tetraethyl (2-(4,7-dibromo-2H-benzotriazol-2-
yl)ethane-1,1-diyl)bisphosphonate (13)
Diethyl (2-(4,7-dibromo-1H-benzotriazol-1-yl)
ethyl)phosphonate (11) and Diethyl
(2-(4,7-dibromo-2H-benzotriazol-2-
yl)ethyl)phosphonate (12)
A mixture of compound 5 (100 mg, 0.376 mmol)
and tetraethyl ethenylidene-1,1-bisphosphonate
(113 mg, 0.376 mmol) in THF (5 mL) was stirred
under reflux for 18 h. The solvent was evaporated
in vacuum, and the crude material was purified by
column chromatography (1:3 ethyl acetate/acetone)
to give compound 13 (81 mg, 37%) as a colorless
oil. νmax (film) (cm−1): 2986, 2935, 2911, 1715, 1652,
1622, 1479, 1445, 1394, 1370, 1249, 1165, 1098,
1026, 974, 856, 802. 1H NMR (300 MHz, CDCl3):
δ (ppm) = 1.17 (t, J = 7.0, 6H, OCH2CH3), 1.26 (t,
J = 7.0, 6H, OCH2CH3), 3.72 (tt, JHP = 23.0 and
7.1, 1H, CH(PO3Et2)2), 4.07–4.22 (m, 8H, CH2CH3),
5.27 (dt, JHP = 13.8 and 7.1, 2H, NCH2), 7.43 (s,
2H, ArH, 5-H and 6-H). 13C NMR (75 MHz, CDCl3):
A
solution of 4,7-dibromo-1H-benzotriazole
5
(100 mg, 0.376 mmol) and K2CO3 (158 mg,
1.143 mmol) in DMF (3 mL) was stirred at 80°C dur-
ing 30 min. Br(CH2)2PO3Et2 (0.14 mL, 0.752 mmol)
was added, and the reaction mixture was stirred for
1 h at 80°C. Upon cooling, the reaction mixture was
filtered and the solvent was removed in vacuum The
resulting oil was purified by column chromatogra-
phy (ethyl acetate) to give compound 11 (29 mg,
17%), as a colorless oil and compound 12 (115 mg,
70%), as a white solid.
δ (ppm) = 16.2 (t, JCP = 6.9, CH3), 38.2 (t, JCP
=
Compound 11: νmax (film) (cm−1): 3063, 2983,
2931, 2909, 1486, 1446, 1394, 1369, 1252, 1200, 1163,
1124, 1098, 1054, 1026, 961, 907, 865, 828, 793, 690,
132.2, CH(PO3Et2)2), 53.3 (t, JCP = 2.9, NCH2),
63.4 (t, JCP = 7.0, OCH2), 110.1 (Ar:C4,C7), 129.9
(Ar:C5,C6), 143.7 (Ar:C3a,C7a). 31P NMR (121 MHz,
H3PO4/ CDCl3): δ (ppm) = 18.5. MS (ESI): m/z =
602 (MNa+ + 4, 46%), 600 (MNa+ + 2, 86%), 598
(MNa+, 48%), 580 (MH+ + 4, 20%), 578 (MH+ + 2,
44%), 576 (MH+, 20%). HRMS (ESI) m/z calcd for
C16H26Br2N3O6P2 575.9658 (Br-79 isotope) [MH]+,
found 575.9650.
1
648, 585, 568. H NMR (300 MHz, CDCl3): δ (ppm)
= 1.32 (t, J = 7.1, 6H, 2× OCH2CH3), 2.45–2.57 (m,
2H, CH2PO3Et2), 4.09–4.19 (m, 4H, 2× OCH2CH3),
5.19–5.27 (m, 2H, NCH2), 7.42 (d, J = 8.0, 1H, ArH,
5-H or 6-H), 7.52 (d, J = 8.0, 1H, ArH, 5-H or 6-
H). 13C NMR (75 MHz, CDCl3): δ (ppm) = 16.6 (d,
JCP = 6.0, CH3), 28.6 (d, JCP = 139.0, CH2PO3Et2),
44.4 (NCH2), 62.4 (d, JCP = 6.4, OCH2), 101.6, 113.3
(Ar:C4,C7), 128.3, 132.5 (Ar:C5, C6), 131.9 (Ar:C7a),
146.1 (Ar:C3a). 31P NMR (121 MHz, H3PO4/ CDCl3):
δ (ppm) = 24.9. MS (ESI): m/z = 466 (MNa+ + 4,
13%), 464 (MNa+ + 2, 26%), 462 (MNa+, 13%), 444
(MH+ + 4, 46%), 442 (MH+ + 2, 100%), 440 (MH+,
50%). HRMS (ESI) m/z calcd for C12H17Br2N3O3P
439.9369 (Br-79 isotope) [MH]+, found 439.9370.
Ethyl 2-(4,7-dibromo-1H-benzotriazol-1-
yl)acetate (14a (n = 1)) and Ethyl 2-(4,7-
dibromo-2H-benzotriazol-2-yl)acetate (15a
(n = 1))
1. Following general procedure B, to a mixture
of 4,7-dibromo-1H-benzotriazole 5 (150 mg,
0.561 mmol) and KOtBu (69 mg, 0.617 mmol)
Heteroatom Chemistry DOI 10.1002/hc

10 Teixeira, Rangel, and Teixeira
1.88 mmol) and KOtBu (232 mg, 2.068 mmol)
EtOH (12 mL), Br(CH2)2CO2Et (0.27 mL,
2.068 mmol) was added and refluxed for 24 h to
give compound 14b (n = 2) (176 mg, 25%) and
compound 15b (n = 2) (134 mg, 19%) and unre-
acted starting material 5.
in EtOH (6 mL), BrCH2CO2Et (0.07 mL,
0.620 mmol) was added and refluxed for 3 h to
afford compound 14a (n = 1) (75 mg, 37%) and
compound 15a (n = 1) (109 mg, 53%) as a white
solids.
2. Following general procedure A, to a mixture
of 4,7-dibromo-1H-benzotriazole 5 (100 mg,
0.376 mmol) and K2CO3 (156 mg, 1.128 mmol)
in DMF (3 mL). BrCH2CO2Et (0.045 mL,
0.414 mmol) was added and refluxed for 30 min.
to afford compound 14a (n = 1) (38 mg, 28%)
and compound 15a (n = 1) (68 mg, 50%) as white
solids.
2. Following general procedure A, to a mixture
of 4,7-dibromo-1H-benzotriazole 5 (337 mg,
1.267 mmol) and K2CO3 (350 mg, 2.534 mmol)
in DMF (3 mL), Br(CH2)2CO2Et (0.18 mL,
1.394 mmol) was added and refluxed for 3 h to
afford compound 14b (n = 2) (179 mg, 37%) as a
colorless oil and compound 15b (n = 2) (220 mg,
48%) as a white solid.
Compound 14a (n = 1): mp 79–80°C. νmax (KBr)
(cm−1): 3068, 3002, 2964, 2942, 2903, 1741, 1489,
1472, 1468, 1459, 1445, 1420, 1407, 1394, 1375, 1351,
1287, 1265, 1240, 1208, 1132, 1101, 1083, 1022, 969,
906, 875, 820, 814, 787, 711, 594, 544, 428. 1H NMR
(400 MHz, CDCl3): δ (ppm) = 1.27 (t, J = 7.1, 3H,
OCH2CH3), 4.27 (q, J = 7.1, 2H, OCH2CH3), 5.70 (s,
2H, NCH2), 7.43 (d, J = 8.0, 1H, ArH, 5-H or 6-H),
7.51 (d, J = 8.1, 1H, ArH, 5-H or 6-H). 13C NMR (100
MHz, CDCl3): δ (ppm) = 14.2 (CH3), 51.0 (NCH2),
62.7 (OCH2), 101.8, 113.4 (Ar:C4,C7), 128.4, 132.5
(Ar:C5,C6), 132.7 (Ar:C7a), 146.0 (Ar:C3a), 166.8
(CO). MS (EI): m/z = 365 (M+ + 4, 19%), 363 (M+ +
2, 40%), 361 (M+, 20%), 292 (365-COOEt, 45%), 290
(363-COOEt, 100%), 288 (361-COOEt, 45%). HRMS
(EI) m/z calcd for C10H9Br2N3O2 360.9061 (Br-79
isotope) [M]+, found 360.9056.
Compound 15a (n = 1): mp 140–142 °C. νmax
(KBr) (cm−1): 3066, 3010, 2978, 2934, 1743, 1498,
1464, 1446, 1408, 1396, 1374, 1348, 1321, 1310, 1283,
1239, 1198, 1174, 1168, 1108, 1095, 1020, 1002, 974,
948, 874, 820, 788, 711, 656, 552, 534. 1H NMR
(400 MHz, CDCl3): δ (ppm) = 1.29 (t, J = 7.1, 3H,
OCH2CH3), 4.28 (q, J = 7.1, 2H, OCH2CH3), 5.58
(s, 2H, NCH2), 7.49 (s, 2H, ArH, 5-H and 6-H). 13C
NMR (100 MHz, CDCl3): δ (ppm) = 14.1 (CH3),
57.6 (NCH2), 62.7 (OCH2), 110.3 (Ar:C4,C7), 130.3
(Ar:C5,C6), 144.3 (Ar:C3a,C7a), 146.0 (Ar:C3a), 165.4
(CO). MS (EI): m/z = 365 (M+ + 4, 34%), 363 (M+ + 2,
100%), 361 (M+, 43%), 292 (365-COOEt, 15%), 290
(363-COOEt, 35%), 288 (361-COOEt, 16%). HRMS
(EI) m/z calcd for C10H9Br2N3O2 360.9061 (Br-79
isotope) [M]+, found 360.9056.
Compound 14b (n = 2): νmax (film) (cm−1): 3084,
2981, 2935, 2905, 1738, 1732, 1599, 1562, 1487, 1446,
1393, 1379, 1355, 1319, 1297, 1252, 1192, 1124, 1103,
1087, 1019, 1008, 980, 943, 907, 858, 815, 694, 666,
644. 1H NMR (400 MHz, CDCl3): δ (ppm) = 1.22
(t, J = 7.2, 3H, OCH2CH3), 3.08 (t, J = 7.3, 2H,
NCH2CH2), 4.15 (q, J = 7.2, 2H, OCH2CH3), 5.24
(t, J = 7.3, 2H, NCH2),7.40 (d, J = 8.0, 1H, ArH, 5-
H or 6-H), 7.49 (d, J = 8.1, 1H, ArH, 5-H or 6-H).
13C NMR (100 MHz, CDCl3): δ (ppm) = 14.2 (CH3),
35.5 (CH2), 45.4 (NCH2), 61.3 (OCH2), 101.7, 113.2
(Ar:C4,C7), 128.2, 132.4 (Ar:C5,C6), 132.0 (Ar:C7a),
146.0 (Ar:C3a), 169.9 (CO). MS (ESI): m/z = 380
(MH+ + 4, 48%), 378 (MH+ + 2, 100%), 376 (MH+,
41%). HRMS (ESI) m/z calcd for C11H12Br2N3O2
375.9291 (Br-79 isotope) [MH]+, found 375.9288.
Compound 15b (n = 2): mp 70–72°C. νmax (KBr)
(cm−1): 3066, 2989, 2940, 2910, 1727, 1691, 1420,
1397, 1382, 1355, 1311, 1282, 1263, 1210, 1194, 1152,
1115, 1065, 1041, 1020, 952, 868, 821, 703, 670, 653,
588, 552, 464. 1H NMR (400 MHz, CDCl3): δ (ppm) =
1.24 (t, J = 7.2, 3H, OCH2CH3), 3.19 (t, J = 7.2, 2H,
NCH2CH2), 4.17 (q, J = 7.2, 2H, OCH2CH3), 5.07
(t, J = 7.2, 2H, NCH2), 7.42 (s, 2H, ArH, 5-H and
6-H). 13C NMR (100 MHz, CDCl3): δ (ppm) = 14.2
(CH3), 34.2 (CH2), 52.6 (NCH2), 61.3 (OCH2), 110.1
(Ar:C4,C7), 129.9 (Ar:C5,C6), 143.9 (Ar:C3a,C7a),
169.9 (CO). MS (ESI): m/z = 402 (MNa+ + 4, 7%),
400 (MNa+ + 2, 13%), 398 (MNa+, 7%), 380 (MH+
+ 4, 51%), 378 (MH+ + 2, 100%), 376 (MH+, 48%).
HRMS (ESI) m/z calcd for C11H12Br2N3O2 375.9291
(Br-79 isotope) [MH]+, found 375.9289.
Ethyl 3-(4,7-dibromo-1H-benzotriazol-1-
yl)propanoate (14b (n = 2)) and Ethyl
3-(4,7-dibromo-2H-benzotriazol-2-yl)propanoate
(15b (n = 2))
2-(4,7-Dibromo-1H-benzotriazol-1-yl)acetic acid
(16a (n = 1))
Following general procedure C, the hydrolysis of
compound 14a (n = 1) (73 mg, 0.201 mmol) in
the aqueous NaOH solution (10 M) (2 mL) gave
compound 16a (n = 1) (67 mg, 99%) as a white
1. Following general procedure B, to a mixture
of 4,7-dibromo-1H-benzotriazole 5 (500 mg,
Heteroatom Chemistry DOI 10.1002/hc

Synthesis of New Azole Phosphonate Precursors for Fuel Cells Proton Exchange Membranes 11
solid. mp 191–193°C. νmax (KBr) (cm−1): 3550–3100,
3317, 3237, 3089, 3070, 3009, 2956, 1720, 1647, 1492,
1415, 1401, 1359, 1290, 1264, 1252, 1215, 1188, 1138,
1113, 1090, 1004, 974, 943, 907, 829, 812, 685, 660,
(Ar:C5,C6), 133.4 (Ar:C7a), 146.7 (Ar:C3a), 173.5
(CO). MS (ESI): m/z = 352 (MH+ + 4, 50%), 350
(MH+ + 2, 100%), 348 (MH+, 49%). HRMS (ESI)
m/z calcd for C9H8Br2N3O2 347.8978 (Br-79 isotope)
[MH]+, found 347.8977.
1
645, 598, 541, 526. H NMR (400 MHz, MeOD): δ
(ppm) = 5.80 (s, 2H, NCH2), 7.53 (d, J = 8.0, 1H,
ArH, 5-H or 6-H), 7.65 (d, J = 8.1, 1H, ArH, 5-H
or 6-H). 13C NMR (100 MHz, CDCl3): δ (ppm) =
51.9 (NCH2), 103.5, 113.3 (Ar:C4,C7), 129.7, 133.8
(Ar:C5,C6), 134.0 (Ar:C7a), 146.6 (Ar:C3a), 170.3
(CO). MS (EI): m/z = 337 (M+ + 4, 43%), 335 (M+ +
2, 95%), 333 (M+, 47%), 292 (337-COOH, 50%), 290
(335-COOH, 100%), 288 (333-COOH, 50%). HRMS
(EI) m/z calcd for C8H5Br2N3O2 332.8748 (Br-79 iso-
tope) [M]+, found 332.8748.
Ethyl 3-(4,7-dibromo-2H-benzotriazol-2-
yl)propanoate (17b (n = 2))
Following general procedure D, the hydrolysis of
compound 15b (n = 2) (189 mg, 0.501 mmol) in
an aqueous HCl solution (1 M) (0.35 mL) gave com-
pound 17b (n = 2) (174 mg, 99%) as a white solid.
mp 152–155°C. νmax (KBr) (cm−1): 3550–2500, 3134,
3127, 2990, 2928, 1743, 1696, 1692, 1497, 1452, 1443,
1414, 1389, 1376, 1349, 1312, 1293, 1281, 1262, 1226,
1193, 1183, 1154, 1078, 1062, 1044, 1014, 953, 816,
796, 687, 654, 620, 560, 552, 480, 459, 407. 1H NMR
(400 MHz, MeOD): δ (ppm) = 3.23 (t, J = 6.8, 2H,
NCH2CH2), 5.05 (t, J = 6.8, 2H, NCH2), 7.49 (s, 2H,
ArH, 5-H and 6-H). 13C NMR (100 MHz, MeOD): δ
(ppm) = 34.2 (CH2), 53.7 (NCH2), 110.9 (Ar:C4,C7),
131.0 (Ar:C5,C6), 144.8 (Ar:C3a,C7a), 173.6 (CO).
MS (ESI): m/z = 352 (MH+ + 4, 49%), 350 (MH+
+ 2, 100%), 348 (MH+, 49%). HRMS (ESI) m/z calcd
for C9H8Br2N3O2 347.8978 (Br-79 isotope) [MH]+,
found 347.8975.
2-(4,7-Dibromo-2H-benzotriazol-2-yl)acetic acid
(17a (n = 1))
Following general procedure C, the hydrolysis of
compound 15a (n = 1) (60 mg, 0.165 mmol) in the
aqueous NaOH solution (10 M) (2 mL) gave com-
pound 17a (n = 1) (55 mg, 99%) as a white solid.
mp 215–216°C. νmax (KBr) (cm−1): 3550–3200, 3514,
3377, 3070, 3006, 2962, 1727, 1648, 1542, 1501,
1468, 1416, 1351, 1312, 1285, 1260, 1200, 1168,
1104, 1010, 985, 952, 900, 833, 822, 697, 653, 589,
552, 534. 1H NMR (400 MHz, MeOD): δ (ppm) =
5.67 (s, 2H, NCH2), 7.54 (s, 2H, ArH, 5-H or 6-
H). 13C NMR (100 MHz, MeOD): δ (ppm) = 58.5
(NCH2), 111.0 (Ar:C4,C7), 131.4 (Ar:C5,C6), 145.3
(Ar:C3a,C7a), 169.0 (CO). MS (EI): m/z = 337 (M+
+ 4, 43%), 335 (M+ + 2, 90%), 333 (M+, 47%), 293
(337-COO+, 46%), 291 (335-COO+, 100%), 289 (333-
COO+, 50%). HRMS (EI) m/z calcd for C8H5Br2N3O2
332.8748 (Br-79 isotope) [M]+, found 332.8743.
(2-(4,7-Dibromo-1H-benzotriazol-1-yl)-1-
hydroxyethane-1,1-diyl)bisphosphonic acid
(18a (n = 1))
Following general procedure E, the reaction of car-
boxylic acid 16a (n = 1) (50 mg, 0.149 mmol), thionyl
chloride (1 mL), and tris(trimethylsilyl)phosphite
(0.10 mL, 0.299 mmol) gave compound 18a (n =
1) (56 mg, 78%) as a white solid. mp 155–156°C.
νmax (KBr) (cm−1): 3600–2300, 3398, 3180, 3032,
2984, 1672, 1485, 1396, 1262, 1179, 1152, 1131,
1088, 1032, 1011, 956, 931, 921, 864, 818, 687, 670,
662, 590, 571, 554, 539, 509, 460. 1H NMR (400
MHz, DMSO-d6): δ (ppm) = 5.52 (JHP = 9.6, 2H,
NCH2C(OH)(PO3H2)2), 7.54 (d, J = 8.0, 2H, ArH, 5-
H or 6-H), 7.66 (d, J = 7.9, 2H, ArH, 5-H or 6-H). 13C
NMR (100 MHz, DMSO-d6): δ (ppm) = 51.1 (NCH2),
72.8 (t, JCP = 141.6, C(OH)(PO3H2)2), 103.3, 111.5
(Ar:C4,C7), 127.6, 132.8 (Ar:C5,C6), 133.0 (Ar:C7a),
144.5 (Ar:C3a). 31P NMR (161 MHz, H3PO4/ DMSO-
3-(4,7-Dibromo-1H-benzotriazol-1-yl)propanoic
acid (16b (n = 2))
Following general procedure D, the hydrolysis of
compound 14b (n = 2) (110 mg, 0.291 mmol) in
an aqueous HCl solution (1 M) (0.35 mL) gave com-
pound 16b (n = 2) (98 mg, 97%) as a white solid.
mp 178–180°C. νmax (KBr) (cm−1): 3500–2500, 3086,
3063, 2958, 2930, 1734, 1493, 1482, 1440, 1406, 1388,
1353, 1302, 1261, 1233, 1213, 1184, 1132, 1040, 976,
950, 938, 905, 831, 782, 717, 670, 640, 566, 548, 536,
521, 493. 1H NMR (400 MHz, MeOD): δ (ppm) =
3.12 (t, J = 7.1, 2H, NCH2CH2), 5.26 (t, J = 7.1,
2H, NCH2), 7.51 (d, J = 8.0, 1H, ArH, 5-H or 6-
H), 7.65 (d, J = 8.1, 1H, ArH, 5-H or 6-H). 13C
NMR (100 MHz, MeOD): δ (ppm) = 35.7 (CH2),
47.0 (NCH2), 103.2, 113.2 (Ar:C4,C7), 129.6, 133.9
d6): δ (ppm) = 15.3. MS (ESI): m/z = 506 (MNa+
+
4, 8%), 504 (MNa+ + 2, 17%), 502 (MNa+, 8%), 484
(MH+ + 4, 50%), 482 (MH+ + 2, 100%), 480 (MH+,
49%). HRMS (ESI) m/z calcd for C8H10Br2N3O2P2
479.8355 (Br-79 isotope) [MH]+, found 479.8352.
Heteroatom Chemistry DOI 10.1002/hc

12 Teixeira, Rangel, and Teixeira
0.287 mmol), thionyl chloride (2 mL), and
tris(trimethylsilyl)phosphite (0.19 mL, 0.573 mmol)
gave compound 19b (n = 2) (68 mg, 48%) as a white
powder. mp 204–205°C. νmax (KBr) (cm−1): 3600–
2300, 3386, 2962, 2926, 2854, 1640, 1498, 1458, 1312,
1183, 1097, 1059, 1008, 955, 817, 789, 761, 682,
(2-(4,7-Dibromo-2H-benzotriazol-2-yl)-1-
hydroxyethane-1,1-diyl)bisphosphonic acid
(19a (n = 1))
Following general procedure E, the reaction
of carboxylic acid 17a (n
=
1) (100 mg,
0.275 mmol), thionyl chloride (1 mL), and
tris(trimethylsilyl)phosphite (0.18 mL, 0.551 mmol)
gave compound 19a (n = 1) (58 mg, 44%) as a
white powder. mp 200–201°C. νmax (KBr) (cm−1):
3550–2400, 3422, 3020, 2964, 2923, 1685, 1499, 1356,
1314, 1306, 1282, 1261, 1191, 1162, 1081, 1045,
1017, 958, 943, 900, 819, 804, 689, 656, 647, 592,
552, 538, 510, 454. 1H NMR (400 MHz, MeOD):
δ (ppm) = 5.41 (t, JHP = 10.0, 2H, NCH2C(OH)
(PO3H2)2), 7.55 (s, 2H, ArH, 5-H and 6-H). 13C NMR
(100 MHz, MeOD): δ (ppm) = 60.2 (NCH2), 74.2
(t, JCP = 146.5, C(OH)(PO3H2)2), 111.0 (Ar:C4,C7),
131.3 (Ar:C5,C6), 144.8 (Ar:C3a,C7a). 31P NMR (121
MHz, H3PO4/ MeOD): δ (ppm) = 14.7. MS (ESI): m/z
= 506 (MNa+ + 4, 24%), 504 (MNa+ + 2, 50%), 502
(MNa+, 21%), 484 (MH+ + 4, 50%), 482 (MH+ + 2,
100%), 480 (MH+, 63%). HRMS (ESI) m/z calcd for
C8H10Br2N3O2P2 479.8355 (Br-79 isotope) [MH]+,
found 479.8375.
1
655, 585, 549, 514. H NMR (400 MHz, DMSO-d6):
δ (ppm) = 2.82–2.92 (m, 2H, NCH2CH2), 5.19–5.23
(m, 2H, NCH2CH2), 7.52 (s, 2H, ArH, 5-H and 6-H).
13C NMR (100 MHz, MeOD): δ (ppm) = 35.2 (CH2),
54.2 (t, JCP = 7.6, NCH2CH2), 72.8 (t, JCP = 146.5,
C(OH)(PO3H2)2), 110.9 (Ar:C4,C7), 131.0 (Ar:C5,C6),
144.9 (Ar:C3a,C7a). 31P NMR (121 MHz, H3PO4/
DMSO-d6): δ (ppm) = 18.0. MS (ESI): m/z = 498
(MH+ + 4, 49%), 496 (MH+ + 2, 100%), 494 (MH+,
48%). HRMS (ESI) m/z calcd for C9H12Br2N3O7P2
493.8512 (Br-79 isotope) [MH]+, found 493.8507.
ACKNOWLEDGEMENTS
We thank to Fundac¸a˜o para a Cieˆncia e a Tecnologia
(FCT) and Fundo Europeu de Desenvolvimento Re-
gional (FEDER) (Quadro de Refereˆncia Estrate´gica
Nacional (QREN)-Programa Operacional Factores
de Competitividade (COMPETE)) for the provision
of funding (PTDC/CTM-CER/109843/2009) and to
Portuguese NMR Network (IST-UTL Center) (FCT
project RECI/QEQ-QIN/0189/2012) for providing ac-
cess to the NMR facilities.
(3-(4,7-Dibromo-1H-benzotriazol-1-yl)-1-
hydroxypropane-1,1-diyl)bisphosphonic acid
(18b (n = 2))
Following general procedure E, the reaction of car-
boxylic acid 16b (n = 2) (50 mg, 0.143 mmol), thionyl
chloride (1 mL), and tris(trimethylsilyl)phosphite
(0.1 mL, 0.286 mmol) gave compound 18b (n = 2)
(59 mg, 83%) as a white powder. mp 204–205°C. νmax
(KBr) (cm−1): 3550–2300, 3377, 3068, 2957, 2936,
2869, 1639, 1508, 1490, 1458, 1322, 1304, 1261, 1210,
1173, 1136, 1080, 1045, 1000, 980, 965, 951, 882,
824, 813, 790, 766, 682, 670, 660, 644, 586, 570, 556,
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541, 524, 456, 428. H NMR (400 MHz, DMSO-d6):
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Heteroatom Chemistry DOI 10.1002/hc

Synthesis of New Azole Phosphonate Precursors for Fuel Cells Proton Exchange Membranes 13
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Heteroatom Chemistry DOI 10.1002/hc