Room temperature ionic liquids based on cationic porphyrin derivatives and tetrakis(pentafluorophenyl)borate anion

Article abstract of DOI:10.1142/S1088424611003471

A series of 11 low melting ionic liquids based on meso-substituted A ₃B-porphyrins and A₂B₂-porphyrins containing one or two pyridyl substituents have been synthesized in high yields. Three of them are liquids at room temp

Full text of DOI:10.1142/S1088424611003471

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2011; 15: 560–574
DOI: 10.1142/S1088424611003471
Published at http://www.worldscinet.com/jpp/
Room temperature ionic liquids based on cationic porphyrin
derivatives and tetrakis(pentafluorophenyl)borate anion
Hai-Jun Xua, Claude P. Grosa, Stéphane Brandèsa, Pei-Yu Geb, Hubert H. Giraultb
andJean-Michel Barbe*a
a Université de Bourgogne, ICMUB (UMR 5260), 9, Avenue Alain Savary, BP 47870, 21078 Dijon Cedex, France
b Laboratoire d’Electrochimie Physique et Analytique, Station 6, Ecole Polytechnique Fédérale de Lausanne,
Station 6, CH-1015 Lausanne, Switzerland
Dedicated to Professor Karl M. Kadish on the occasion of his 65th birthday
Received 15 April 2011
Accepted 16 May 2011
ABSTRACT: A series of 11 low melting ionic liquids based on meso-substituted A3B-porphyrins and
A2B2-porphyrins containing one or two pyridyl substituents have been synthesized in high yields. Three
1
of them are liquids at room temperature. All these porphyrinic salts were characterized by H NMR,
19F NMR, MALDI-TOF mass spectrometry, elemental analysis and UV-visible spectroscopy. The
thermal properties and conductivity values of these salt derivatives have been also measured. A specific
conductivity value of up to 4 mS.cm-1 could be obtained for a compound having the counter-anion
B(C6F5)4-.
KEYWORDS: RT ionic liquids, A3B-porphyrins, A2B2-porphyrins, conductivity, tetrakis(pentafluoro-
phenyl)borate anion, DSC, TGA.
extractions [11, 12], catalysis, electrochemical reactions
INTRODUCTION
[13, 14] as well as green solvents for lithium ion batteries
Ionic liquids (ILs) are a group of organic salts that
[15–18] and for various reactions [19–21]. Up to now,
possess low melting point and usually afford liquids at
most of the reported ILs are mainly based on 1,3-dial-
temperatures below 100 °C [1]. Generally, ionic liquids
kylimidazolium cations, 1-alkylpyridinium cations and
consist completely of an organic cation and an anion (inor-
quaternary ammonium salts, whereas anions are mainly
ganic or organic). The ionic liquids which are free-flowing
focused on [BF4]-, [PF6]-, [CF3SO3]-, [(CF3SO2)2N]- and
liquids at room temperature, can be called Room Tem-
perature Ionic Liquids (RTILs) [1]. In recent years, ionic
[RCO2]- [1, 22–26]. However, there are only few exam-
ples where tetrakis(pentafluorophenyl)borate anion has
liquids have attracted much attention in many fields due to
been used in ILs [27], despite the fact that it can decrease
their unique chemical and physical properties such as air
the melting point of the salts due to its weak anion coordi-
and moisture stability, high thermal stability, good elec-
nation properties, bulkiness and benefit to a good charge
trical conductivity, high solubility, and no vapor pressure
distribution [1].
[1–9]. The ILs have been successfully used in many appli-
In addition, porphyrins have also aroused remarkable
cations, including replacing traditional organic solvents
and extensive interest for many years due to their wide-
in organic and inorganic syntheses [10], liquid-liquid
ranging applications in photophysics [28], coordination
chemistry [29], liquid crystals [30], solar cells [31, 32],
catalysis [33, 34], photovoltaic devices [35], photody-
SPP full member in good standing
namic therapy (PDT) [36] and artificial light-harvesting
*Correspondence to: Jean-Michel Barbe, email: jean-michel.
antennas [37]. The excellent properties of ionic liquids
and porphyrins stimulated us to develop ionic liquid
barbe@u-bourgogne.fr, tel: +33 (0)3-80-39-61-19, fax: +33
(0)3-80-39-61-17
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ROOm temPeRatuRe IOnIC lIquIDS baSeD On CatIOnIC PORPhyRIn DeRIvatIveS
561
porphyrin derivatives based on tetrakis(perfluorophenyl)-
monitored by thin-layer chromatography and UV-vis
spectroscopy. The 4-(dodecyloxy)benzaldehyde (2a)
[40, 41] and 5-(4-pyridyl)-dipyrromethane [42] were
synthesized according to the respective reported litera-
ture methods.
borate salts and cationic porphyrins. The room tempera-
ture liquid state was attained by introducing long alkoxy
chains on the meso phenyl groups of the porphyrins.
During the progress of our work, Gryko and coworkers
reported the synthesis of meso-substituted liquid por-
phyrins [38]. Concomitantly, Maruyama and coworkers
independently reported the synthesis of room tempera-
ture liquid porphyrins [39]. Here, we report the first trial
way to synthesize one of the most versatile ionic liquids.
These ionic liquid porphyrins (Chart 1) have been exam-
ined by 1H and 19F NMR, MALDI-TOF mass spectrom-
etry, elemental analysis, DSC, TGA and UV-visible
spectroscopy. Room temperature conductivity measure-
ments have also been performed.
3,4,5-tris(dodecyloxy)benzaldehyde (2b). A mix-
ture of 3,4,5-trihydroxybenzaldehyde (1.54 g, 10 mmol),
1-bromododecane (14.95 g, 60 mmol), K2CO3 (4.16 g,
30 mmol), and KI (100 mg) in DMF (60 mL) was stirred
at 70 °C for 16 h. The reaction mixture was cooled to
room temperature and mixed with water. The resulting
aqueous layer was extracted three times with chloroform.
The organic layers were combined, then washed with
brine and dried over Na2SO4. The solvent was removed
under reduced pressure and the resulting crude product
was purified by column chromatography (silica gel, elu-
ent CHCl3/heptane 2/3) followed by recrystallization
from CHCl3/MeOH. The product was obtained as a white
solid (6.26 g, yield: 95%). 1H NMR (300 MHz, CDCl3):
δ, ppm 9.85 (s, 1H, -CHO), 7.10 (s, 2H, phenyl-H), 4.06
(m, 6H, OCH2-), 1.87 (m, 6H, OCH2-CH2-), 1.47 (m, 6H,
OCH2-CH2-CH2-), 1.29 (m, 48H, -(CH2)9-), 0.90 (t, 9H,
J = 6 Hz).
EXPERIMENTAL
Instrumentation
1H and 19F NMR spectra were recorded with a Bruker
DRX-300 AVANCE transform spectrometer at the
“Plateforme d’Analyse Chimique de l’Université de
Bourgogne” (PACSMUB); chemical shifts are expressed
in ppm relative to chloroform. UV-vis spectra were
recorded with a Varian Cary 1 spectrophotometer. Mass
spectra and accurate mass measurements (HRMS) were
obtained with a Bruker Daltonics Ultraflex II spectrom-
eter in the MALDI/TOF reflectron mode by using dithra-
nol as a matrix. Accurate mass measurements (HRMS)
were carried out under the same conditions as before by
using the PEG-ion series as an internal calibrant. Both
measurements were made at the PACSMUB.
Thermogravimetric (TGA) measurements were per-
formed on a Netzsch STA 409 PC Luxx analyzer at the
ICMUB Institute. Samples were purged in an Ar (30
mL.min-1)/O2 (10 mL.min-1) stream during analysis and
heated to 900 °C in alumina crucibles with a heating
rate of 10 K.min-1. Differential Scanning Calorimetry
(DSC) measurements were performed on a Perkin Elmer
Diamond DSC instrument. The DSC measurements
were carried out under nitrogen at atmospheric pres-
sure in a sealed Al pan with a heating rate of 5 K/min
or 10 K/min at the “Ecole Polytechnique Fédérale de
Lausanne, EPFL”. Resistance of ionic liquid porphyrin
was detected by an on-chip conductivity sensor con-
nected to an AutoLab PGSTAT 12 potentiostat at EPFL.
5-(4-pyridyl)-10,15,20-tris(4-dodecyloxyphenyl)-
porphyrin (3a) and 5,15-di(4-pyridyl)-10,20-bis(4-
dodecyloxyphenyl)porphyrin (4a). 4-(dodecyloxy)-
benzaldehyde (2.35 mmol, 1.548 g) and 4-pyridine-
dipyrromethane (2.35 mmol, 0.524 g) were dissolved in
propionic acid (30 mL) in a 100 mL round-bottom flask
equipped with a magnetic stirring bar and a water-cooled
reflux condenser. The mixture was then allowed to reflux
for 2.5 h under air in the dark. After cooling, the reaction
mixture was slowly poured into a 1/1 (v/v) mixture of
methanol (60 mL) and cold (<5 °C) aqueous NH4OH (60
mL) was added. Filtration and washing with cold water
gave a black solid. The resulting residue was purified by
silica-gel column chromatography repeatedly with 100%
CH2Cl2, 2% MeOH/CH2Cl2 to afford 5,10,15,20-tetra-
[4-(dodecyloxy)phenyl]porphyrin as the first band (very
small amount), the porphyrin 3a (130 mg, yield: 14%
based on dipyrromethane) as the second band and the
porphyrin 4a (175 mg, yield: 15%) as the third band.
5-(4-pyridyl)-10,15,20-tris(4-dodecyloxyphenyl)-
1
porphyrin (3a). H NMR (CDCl3): δ, ppm 9.05 (d,
2H, J = 6 Hz, pyridyl-H), 8.93 (m, 6H, pyridyl-H and
β-pyrrole-H), 8.80 (d, 2H, J = 6 Hz, β-pyrrole-H), 8.19
(d, 2H, J = 6 Hz, β-pyrrole-H), 8.13 (d, 6H, J = 9 Hz,
phenyl-H), 7.30 (d, 6H, J = 9 Hz, phenyl-H), 4.27 (t, 6H,
J = 6 Hz, O-CH2-), 1.99 (m, 6H, O-CH2-CH2-), 1.64 (m,
6H, -O-CH2-CH2-CH2-), 1.43 (m, 48H, -(CH2)8-), 0.92
(m, 9H, -CH3), -2.75 (s, 2H, NH). HR-MS (MALDI-
TOF): m/z 1168.8084 [M + H]+ 1168.7977 calcd. for
C79H102N5O3. UV-vis (CH2Cl2): λmax, nm (ε × 10-3 M-1.
cm-1) 421 (1769), 517.0 (71), 555.0 (46), 592.1 (26),
650.0 (27).
Chemicals and reagents
Unless otherwise noted, all chemicals and solvents
were of analytical reagent grade and used as received.
Absolute dichloromethane (CH2Cl2) was obtained from
Carlo Erba. Silica gel (Merck; 70–120 mm) was used
for column chromatography. Analytical thin-layer chro-
matography was performed with Merck 60 F254 silica
gel (precoated sheets, 0.2 mm thick). Reactions were
5,15-di(4-pyridyl)-10,20-bis(4-dodecyloxyphenyl)-
porphyrin (4a). 1H NMR (CDCl3): δ, ppm 9.06 (d, 4H,
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h.-J. Xu et al.
OC12H25
OC12H25
OC12H25
C12H25
O
C12H25
O
O
OC12H25
OC12H25
OC12H25
N
HN
N
N
HN
N
C12H25
O
OC12H25
C12H25
O
NH
NH
C12H25
N+
CH3
N+
X-
X-
CH3
5a: X- = I-
5b: X- = I-
-
-
6a: X- = B(C6F5)4
6b: X- = B(C6F5)4
CH3
N+
OC12H25
X-
C12H25
O
OC12H25
C12H25
O
O
OC12H25
OC12H25
OC12H25
N
HN
N
HN
N
C12H25
O
C12H25
O
OC12H25
NH
N
NH
C12H25
N+
C12H25
N+
X-
X-
CH3
7: X- = Br-
9a: X- = I-
-
8: X- = B(C6F5)4
CH3
N+
C12H25
N+
X-
X-
C12H25
O
OC12H25
OC12H25
OC12H25
C12H25
O
OC12H25
OC12H25
OC12H25
N
N
HN
HN
N
C12H25
O
C12H25
O
N
NH
NH
C12H25
O
C12H25O
N+
CH3
N+
X-
X-
C12H25
9b: X- = I-
10: X- = B(C6F5)4
11: X- = Br-
-
-
12: X- = B(C6F5)4
Chart 1. Structures of compounds 5–12
Copyright © 2011 World Scientific Publishing Company
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ROOm temPeRatuRe IOnIC lIquIDS baSeD On CatIOnIC PORPhyRIn DeRIvatIveS
563
J = 6 Hz, pyridyl-H), 8.97 (d, 4H, J = 6 Hz, pyridyl-H),
poured into the mixture. The precipitate was then filtered
and washed with cold chloroform. The precipitate was
further purified by column chromatography on silica gel
with 10% CH3OH in CH2Cl2. Yield: 55 mg, 98%. mp
181–182 °C. 1H NMR (CDCl3): δ, ppm 9.42 (d, 2H, J = 6
Hz, pyridyl-H), 8.89 (d, 2H, J = 6 Hz, pyridyl-H), 8.85 (d,
2H, J = 6 Hz, β-pyrrole-H), 8.78 (m, 4H, β-pyrrole-H),
8.63 (d, 2H, J = 6 Hz, β-pyrrole-H), 8.06 (d, 2H, J = 9 Hz,
phenyl-H), 7.88 (d, 4H, J = 9 Hz, phenyl-H), 7.29 (d, 2H,
J = 9 Hz, phenyl-H), 7.11 (d, 4H, J = 9 Hz, phenyl-H),
4.93 (s, 3H, N-CH3), 4.26 (t, 2H, 3JHH = 6.6 Hz, 3JHH = 6.6
Hz, O-CH2-), 4.11 (t, 4H, JHH = 6.6 Hz, JHH = 6.6 Hz,
O-CH2-), 2.01–1.91 (m, 6H, O-CH2-CH2-), 1.68–1.33
(m, 54H, -(CH2)9-), 0.94–0.89 (m, 9H, -CH3), -2.74 (s,
2H). MS (MALDI-TOF): m/z 1182.72 [M - I]+, 1182.81
calcd. for C80H104N5O3. UV-vis (CH2Cl2): λmax, nm (ε ×
10-3 M-1.cm-1) 422.0 (143), 522.0 (11), 584.0 (13), 663.0
(0.8). Anal. calcd. for C80H104IN5O3: C 73.31; H 8.00; N
5.34. Found: C 72.77; H 7.96; N 5.58.
5-(N-methylpyridinium-4-yl)-10,15,20-tris[3,4,5-
tris(dodecyloxy)phenyl]porphyrin iodide (5b). To a
solution of 3b (0.022 mmol, 50 mg) dissolved in 40 mL
chloroform and 5 mL of DMF was added 1.5 mL of
methyl iodide slowly, and the mixture was then stirred
under an argon atmosphere at room temperature over-
night. The solvent was removed under reduced pressure.
The solid residue was purified by column chromatog-
raphy on a silica gel with 10% CH3OH in CHCl3. The
product was recrystallized from CHCl3/methanol mixture
layered by hexane. Yield: 52 mg, 96%. Liquid. 1H NMR
(CDCl3): δ, ppm 9.68 (d, 2H, J = 6.0 Hz, pyridyl-H), 9.13
(d, 2H, J = 6 Hz, pyridyl-H), 8.99 (m, 4H, β-pyrrole-H),
8.93 (t, 2H, J = 3 Hz, β-pyrrole-H), 8.84 (d, 2H, J = 6
Hz, β-pyrrole-H), 7.43 (s, 6H, phenyl-H), 5.10 (s, 3H,
N-CH3), 4.33 (t, 6H, J = 6 Hz, O-CH2-), 4.12 (t, 12H,
J = 6 Hz, O-CH2-), 2.02-1.85 (m, 18H, O-CH2-CH2-),
1.70 (m, 6H, O-CH2-CH2-CH2-), 1.49 (m, 12H, O-CH2-
CH2-CH2-), 1.32–1.23 (m, 144H, -(CH2)8-), 0.92–0.83
(m, 27H, -CH3), -2.71 (s, 2H, NH). HR-MS (MALDI-
TOF): m/z 2287.8661 [M - I]+, 2287.9096 calcd. for
C152H248N5O9. UV-vis (CH2Cl2): λmax, nm (ε × 10-3 M-1.
cm-1) 428.0 (122), 522.0 (12), 589.0 (1.1), 659.0 (0.6).
Anal. calcd. for C152H248IN5O9: C 75.55; H 10.34; N 2.90.
Found: C 75.90; H 10.30; N 2.85.
8.83 (d, 4H, J = 3 Hz, β-pyrrole-H), 8.18 (d, 4H, J = 6 Hz,
β-pyrrole -H), 8.12 (d, 4H, J = 9 Hz, phenyl-H), 7.31 (d,
4H, J = 6 Hz, phenyl-H), 4.27 (t, 4H, J = 6.0 Hz, O-CH2-),
2.04 (m, 4H, O-CH2-CH2-), 1.66 (m, 4H, -O-CH2-CH2-
CH2-), 1.44 (m, 32H, -(CH2)8-), 0.93 (t, 6H, J = 6 Hz,
-CH3), -2.79 (s, 2H). MS (MALDI-TOF): m/z 985.61 [M +
H]+, 985.61 calcd. for C66H77N6O2. UV-vis (2%CH3OH in
CH2Cl2): λmax, nm (ε × 10-3 M-1.cm-1) 420.0 (1622), 515.0
(72), 552.0 (37), 591.0 (23), 650.0 (18).
5-(4-pyridyl)-10,15,20-[3,4,5-tris(dodecyloxy)phe-
nyl]porphyrin (3b) and 5,15-dipyridyl-10,20-bis[3,4,5-
tris(dodecyloxy)phenyl]porphyrin (4b). The reaction
was carried out using the same procedure as for 3a and
4a starting from 3,4,5-tris(dodecyloxy)benzaldehyde
(2.35 mmol, 1.548 g) and 4-pyridinedipyrromethane
(2.35 mmol, 0.524 g). The resulting residue was puri-
fied by silica-gel column chromatography three times
with 100% CH2Cl2, 25% CHCl3-75% CH2Cl2 to afford
the purple porphyrin 3b as the second red band and the
purple porphyrin 4b as the third red band which were
both recrystallized from chloroform/methanol to give
the pure porphyrin 3b (143 mg, yield: 8%, according to
the dipyrromethane) and the pure porphyrin 4b (182 mg,
yield: 9%) respectively.
3
3
5-(4-pyridyl)-10,15,20-tris[3,4,5-tris(dodecyloxy)
phenyl]porphyrin (3b). 1H NMR (CDCl3): δ, ppm 9.00
(m, 8 H, pyridyl-H, β-pyrrole-H), 8.79 (d, 2H, J = 6 Hz,
β-pyrrole-H), 8.16 (d, 2H, J = 6 Hz, β-pyrrole-H), 7.45
(s, 6H, phenyl-H), 4.33 (t, 6H, JHH = 6 Hz, O-CH2-), 4.12
(t, 12 H, 3JHH = 6.6 Hz, 3JHH = 6.3 Hz, O-CH2-), 2.07 (m,
6H, O-CH2-CH2-), 1.88 (m, 12H, O-CH2-CH2-), 1.72–
1.25 (m, 162H, -(CH2)9-), 0.90 (m, 27H, -CH3), -2.80 (s,
2H, NH). MS (MALDI-TOF): m/z 2273.75 [M + H]+,
2273.89 calcd. for C151H246N5O9. UV-vis (CH2Cl2): λmax
,
nm (ε × 10-3 M-1.cm-1) 421.0 (350), 516.0 (18), 552.0
(8.7), 591.0 (4.8), 649.0 (4.2).
5,15-di-(4-pyridyl)-10,20-bis[3,4,5-tris(dodecyl-
oxy)phenyl]porphyrin (4b). 1H NMR (CDCl3): δ,
ppm 9.06 (m, 8 H, pyridyl-H), 8.83 (d, 4H, J = 3 Hz,
β-pyrrole-H), 8.19 (d, 4H, J = 6 Hz, β-pyrrole-H), 7.45
(s, 6H, phenyl-H), 4.33 (t, 4H, J = 6 Hz, O-CH2-), 4.12 (t,
8H, J = 6 Hz, O-CH2-), 2.01 (m, 4H, O-CH2-CH2-), 1.90
(m, 8H, O-CH2-CH2-), 1.25–1.67 (m, 108 H, -(CH2)9-),
0.95–0.85 (m, 18H), -2.82 (s, 2H). HR-MS (MALDI-
TOF): m/z 1722.3385 [M + H]+, 1722.3411 calcd. for
C114H173N6O6. UV-vis (CH2Cl2): λmax, nm (ε × 10-3 M-1.
cm-1) 421.0 (448.9), 516.0 (22.7), 550.0 (8.8), 591.0
(7.0), 646.0 (4.6).
5-(N-methylpyridinium-4-yl)-10,15,20-tris(4-do-
decyloxyphenyl)porphyrin iodide (5a). 50 mg of 3a
(0.042 mmol) was dissolved in 40 mL of chloroform and
5 mL of DMF, 2 mL of methyl iodide was added to the
solution of 3a, and the mixture was then stirred under
argon at room temperature overnight and monitored by
TLC. After the end of the reaction, the solution was con-
centrated to about 3 mL and then 50 mL of ether was
5-(N-methylpyridinium-4-yl)-10,15,20-tris(4-dode-
cyloxyphenyl)porphyrin tetrakis(pentafluorophenyl)-
borate(6a).Toa3mLCH2Cl2 solutionofNaB(C6F5)4·Et2O
(46.4 mg, 0.067 mmol) was added a 5 mL CH2Cl2 solu-
tion of 5a (80 mg, 0.067 mmol). The reaction mixture
was stirred for 48 h under argon before filtration to
remove NaI. The filtrate was concentrated under reduced
pressure to give a crude product, which was washed with
heptane and sonicated for 1 h. The product was puri-
fied by recrystallization (CHCl3/hexane). Any remaining
volatile components were removed under reduced
pressure to afford a purple-black solid. Yield: 101 mg,
1
80%. mp 128–129°C. H NMR (CDCl3): δ, ppm 8.98
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h.-J. Xu et al.
(d, 2H, J = 6 Hz, pyridyl-H), 8.93–8.89 (m, 4H, pyri-
dyl-H, β-pyrrole-H), 8.61 (d, 2H, J = 9 Hz, β-pyrrole-H),
8.51 (m, 4H, β-pyrrole-H), 8.08 (m, 6H, phenyl-H),
7.31 (m, 6H, phenyl-H), 4.44 (s, 3H, N-CH3), 4.25 (m,
6H, O-CH2-), 1.99 (m, 6H, O-CH2-CH2-), 1.64–1.28
(m, 54H, -(CH2)9-), 0.92 (m, 9H, -CH3), -2.51 (s, 2H,
NH). 19F NMR (CDCl3): δ, ppm -132.6 (d, 2F), -162.2
(t, 1F), -166.3 (t, 2F). MS (MALDI-TOF): m/z 1182.77
[M - B(C6F5)4]+, 1182.81 calcd. for C80H104N5O3. UV-vis
(CH2Cl2): λmax, nm (ε × 10-3 M-1.cm-1) 419.0 (131), 590.0
(1.6), 661.0 (1.1). Anal. calcd. for C104H104BF20N5O3: C
67.06; H 5.63; N 3.76. Found: C 67.07; H 6.03; N 3.83.
5-(N-methylpyridinium-4-yl)-10,15,20-tris[3,4,5-
tris(dodecyloxy)phenyl]porphyrin tetrakis(pentafluoro-
phenyl)borate (6b). To a flask containing NaB-
(C6F5)4Et2O (25 mg, 0.035 mmol) was added a solution
of 5b (60 mg, 0.025 mmol) in CH2Cl2 (5 mL). The reac-
tion mixture was stirred for 48 h under argon before
filtration to remove NaI. The filtrate was diluted with
CH2Cl2 and washed with brine, distilled water and dry
over MgSO4. The organic solution was concentrated
under reduced pressure to give a crude product, which
was purified by recrystallization (CHCl3/methanol) to
afford the oil porphyrin (51 mg, 69%). 1H NMR (CDCl3):
δ, ppm 9.09 (d, 2H, J = 6 Hz, pyridyl-H), 8.99 (m, 4H,
β-pyrrole-H), 8.85 (s, 4H, β-pyrrole-H), 8.59 (d, 2H,
J = 6 Hz, pyridyl-H), 7.42 (s, 6H, phenyl-H), 4.65 (s, 3H,
N-CH3), 4.32 (t, 6H, J = 6 Hz, O-CH2-), 4.10 (t, 12H,
J = 6 Hz, O-CH2-), 1.99 (m, 6H, O-CH2-CH2-), 1.87 (m,
12H, O-CH2-CH2-), 1.54–1.22 (m, 162H, -(CH2)9-),
0.91–0.83 (m, 27H, -CH3), -2.59 (s, 2H, NH). 19F NMR
(CDCl3): δ, ppm -132.6 (d, 2F), -162.2 (t, 1F), -166.3
(t, 2F). HR-MS (MALDI-TOF): m/z 2287.9025 [M -
B(C6F5)4]+, 2287.9097 calcd. for C152H248N5O9. UV-vis
(CH2Cl2): λmax, nm (ε × 10-3 M-1.cm-1) 421.0 (113), 589.0
(14), 633.0 (0.8). Anal. calcd. for C176H248BF20N5O9: C
71.21; H 8.42; N 2.36. Found: C 71.19; H 8.53; N 2.41.
5-(4-N-dodecanoylpyridinium-4-yl)-10,15,20-tris-
[3,4,5-tris(dodecyloxy)phenyl]porphyrin bromide (7).
Porphyrin 3b (200 mg, 0.105 mmol) was added to 1.5 g
(6 mmol) of 1-bromododecane in 100 mL of dry DMF and
the mixture was then heated to reflux for 6 h under
Ar. After evaporation of the solvent, the residual solid
was washed with ether and filtered out. Purification of
the solid by chromatography on silica gel with 10%
CH3OH-CH2Cl2 gave 217 mg product. Yield: 96%. mp
145–146 °C. 1H NMR (CDCl3): δ, ppm 9.78 (d, 2H, J =
6 Hz, pyridyl-H), 9.12 (d, 2H, J = 6 Hz, pyridyl-H), 8.99
(s, 4H, β-pyrrole-H), 8.85 (t, 4H, J = 6 Hz, β-pyrrole-H),
524.0 (13), 593.0 (13), 659.0 (0.7). Anal. calcd. for
C163H270BrN5O9·3H2O: C 76.77; H 10.29; N 2.65. Found:
C 76.90; H 10.26; N 2.80.
5-(4-N-dodecanoylpyridinium-4-yl)-10,15,20-tris-
[3,4,5-tris(dodecyloxy)phenyl]porphyrin tetrakis(penta-
fluorophenyl)borate (8). To a 3 mL CH2Cl2 solution of
NaB(C6F5)4·Et2O (30.1 mg, 0.04 mmol) was added a 5 mL
of CH2Cl2 solution of 7 (100 mg, 0.04 mmol). The reac-
tion mixture was stirred for 48 h under argon. The solu-
tion was diluted with CH2Cl2. The organic solution was
washed with distilled water, dried over MgSO4, and the
solvent was removed under reduced pressure. The prod-
uct was purified by recrystallization (CHCl3/methanol) to
afford an oily black product (104 mg, yield: 84%). Liquid.
1H NMR (CDCl3): δ, ppm 9.09 (d, 2H, J = 6 Hz, pyri-
dyl-H), 8.99 (m, 4H, β-pyrrole-H), 8.90 (d, 2H, J = 9
Hz, β-pyrrole-H), 8.84 (d, 2H, J = 6.0 Hz, β-pyrrole-H),
8.62 (d, 2H, J = 3 Hz, pyridyl-H), 7.43 (s, 6H, phenyl-H),
4.78 (t, 2H, J = 6 Hz, N-CH2-), 4.32 (t, 6H, J = 6.0 Hz,
O-CH2-), 4.10 (m, 12H, O-CH2-), 2.31 (m, 2H, N-CH2-
CH2-), 1.98 (m, 6H, O-CH2-CH2-), 1.90 (m, 12H, O-CH2-
CH2-), 1.70–1.23 (m, 180H, -(CH2)9-), 0.92–0.84 (m,
30 H, -CH3), -2.59 (s, 2H, NH). 19F NMR (CDCl3): δ,
ppm -132.5 (t, 2F), -162.4 (m, 1F), -166.52 (m, 2F). MS
(MALDI-TOF): m/z 2442.00 [M - B(C6F5)4]+, 2442.08
calcd. for C163H270N5O9. UV-vis (CH2Cl2): λmax, nm (ε ×
10-3 M-1.cm-1) 423.0 (118), 593.0 (15), 664.0 (0.9). Anal.
calcd. for C163H270BF20N5O9: C 71.92; H 8.71; N 2.24.
Found: C 72.14; H 8.82; N 2.35.
5,15-di(N-methylpyridinium-4-yl)-10,20-bis(4-do-
decyloxyphenyl)porphyrin diiodide (9a). To a solution
of 4a (50 mg, 0.05 mmol) dissolved in 45 mL of chlo-
roform and 5 mL of DMF was added 2 mL of methyl
iodide, and the reaction mixture was stirred under argon
at room temperature for two days and monitored by TLC.
The solution was then concentrated to about 3 mL and
then 50 mL of ether was poured into the mixture. The
precipitate was then filtered and washed with chloro-
form. After drying of the precipitate under vacuum, it
was recrystallized from mixed solvents of chloroform and
methanol with layered hexane. Yield: 61 mg, 96%. mp
1
235–236 °C. H NMR (DMSO-d6): δ, ppm 9.47 (d, 4H,
J = 6 Hz, pyridyl-H), 9.01 (d, 12H, J = 6 Hz, pyridyl-H
and β-pyrrole-H), 8.12 (d, 4H, J = 9 Hz, phenyl-H), 7.41
(d, 4H, J = 9 Hz, phenyl-H), 4.72 (s, 6H, N-CH3), 4.27 (t,
4H, J = 6 Hz, OCH2-), 1.91 (m, 4H, OCH2-CH2-), 1.57
(m, 4H, OCH2-CH2-CH2-), 1.47–1.21 (m, 32H, -(CH2)8-),
0.86 (m, 6H, -CH3), -2.94 (s, 2H, NH). MS (MALDI-
TOF): m/z 1015.62 [M - 2I + H]+, 1015.66 calcd. for
C68H83N6O2. UV-vis (CH2Cl2): λmax, nm (ε × 10-3 M-1.
cm-1) 438.0 (115), 526.0 (9.4), 574.0 (11), 666.0 (7.5).
Anal. calcd. for C68H82I2N6O2·4H2O: C 60.89; H 6.76; N
6.27. Found: C 60.89; H 6.36; N 6.46.
3
3
7.43 (s, 6H, phenyl-H), 5.37 (t, 2H, JHH = 6 Hz, JHH
=
9 Hz, N-CH2-), 4.32 (t, 6H, J = 6 Hz, O-CH2-), 4.12 (t,
12H, J = 6 Hz, O-CH2-), 2.40 (m, 2H, N-CH2-CH2-), 2.00
(m, 6H, O-CH2-CH2-), 1.91-1.87 (m, 12H, O-CH2-CH2-),
1.67-1.23 (m, 180H, -(CH2)9-), 0.93-0.83 (m, 30H,
-CH3), -2.70 (s, 2H, NH). MS (MALDI-TOF): m/z
2442.15 [M - Br]+, 2442.08 calcd. for C163H270N5O9. UV-
vis (CH2Cl2): λmax, nm (ε × 10-3 M-1.cm-1) 427.0 (131),
5,15-di(N-methylpyridinium-4-yl)-10,20-bis[3,4,5-
tris(dodecyloxy)phenyl]porphyrin diiodide (9b). To
100 mg of 5,15-dipyridyl-10,20-bis(3,4,5-tris(dodecyl-
oxy)phenyl)porphyrin (0.058 mmol) dissolved in 45 mL
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565
of chloroform and 5 mL of DMF was slowly added 2.0 mL
177–179 °C. 1H NMR (CDCl3): δ, ppm 9.82 (d, 4H, J =
6 Hz, pyridyl-H), 9.03 (d, 4H, J = 6 Hz, pyridyl-H), 8.85
(s, 4H, β-pyrrole-H), 8.63 (d, 4H, J = 3 Hz, β-pyrrole-H),
of methyl iodide, and the mixture was then stirred under
an argon atmosphere at room temperature overnight. The
solvent was removed under reduced pressure. The solid
residue was purified by column chromatography on a
silica gel using 10% CH3OH-CHCl3 as eluent. The prod-
uct was recrystallized from CHCl3/methanol/hexane.
Yield: 96% (111 mg). mp 181–183 °C. 1H NMR (CDCl3):
δ, ppm 9.66 (d, 4H, J = 6 Hz, pyridyl-H), 9.12 (d, 4H, J =
3 Hz, pyridyl-H), 9.00 (s, 4H, β-pyrrole-H), 8.77 (d, 4H,
J = 6.0 Hz, β-pyrrole-H), 7.38 (s, 4H, phenyl-H), 5.08
(s, 6H, N-CH3), 4.32 (t, 4H, J = 6 Hz, O-CH2-), 4.11 (t,
8H, J = 6 Hz, O-CH2-), 2.01 (m, 4H, O-CH2-CH2-), 1.90
(m, 8H, O-CH2-CH2-), 1.72–1.20 (m, 108H, -(CH2)9-),
0.91-0.80 (m, 18H, -CH3), -3.15 (s, 2H, NH). HR-MS
(MALDI-TOF): m/z 1752.3856 [M - 2I + H]+, 1752.3881
calcd. for C116H179N6O6. UV-vis (CH2Cl2): λmax, nm (ε ×
10-3 M-1.cm-1) 441.0 (220), 526.0 (17.9), 575.1 (18.1),
663.0 (11.1). Anal. calcd. for C116H178I2N6O6: C 69.44; H
8.94; N 4.19. Found: C 69.46; H 8.75; N 4.26.
3
3
7.32 (s, 4H, phenyl-H), 5.34 (t, 4H, JHH = 9 Hz, JHH
=
6 Hz, N-CH2-), 4.32 (t, 4H, J = 6 Hz, O-CH2-), 4.09 (t,
3
3
8H, JHH = 6 Hz, JHH = 9 Hz, O-CH2-), 2.39 (m, 4H,
N-CH2-CH2-), 1.88 (m, 4H, O-CH2-CH2-), 1.75 (m, 8H,
O-CH2-CH2-), 1.53–1.22 (m, 144H, -(CH2)9-), 0.85 (m,
24H, -CH3), -3.55 (s, 2H, NH). MS (MALDI-TOF): m/z
2060.76 [M - 2Br + H]+, 2060.73 calcd. for C138H223N6O6.
UV-vis (CH2Cl2): λmax, nm (ε × 10-3 M-1.cm-1) 435.0
(166), 526 (12), 575.0 (12), 663.0 (7.7). Anal. calcd. for
C138H222Br2N6O6: C 74.62; H 10.07; N 3.78. Found: C
74.21; H 9.73; N 3.91.
5,15-di-(4-N-dodecanoylpyridinium-4-yl)-10,
20-bis[3,4,5-tris(dodecyloxy)phenyl]porphyrin
di-[tetrakis(pentafluorophenyl)borate] (12). To a 3 mL
CH2Cl2 solution of NaB(C6F5)4·Et2O (68.4 mg, 0.097 mmol)
was added a 5 mL of CH2Cl2 solution of 11 (100 mg,
0.045 mmol). The reaction mixture was stirred over-
night. The resulting solution was diluted with CH2Cl2 and
washed with brine, distilled water and then dried over
MgSO4. The organic solvent was removed under reduced
pressure. The product was purified by recrystallization
from CHCl3/methanol. Any remaining volatile compo-
nents were removed under reduced pressure to afford the
violet-black solid (134 mg, yield: 87%). mp 98–100 °C.
1H NMR (CDCl3): δ, ppm 9.06 (d, 4H, J = 6 Hz, pyri-
dyl-H), 8.97 (d, 4H, J = 6 Hz, β-pyrrole-H), 8.85 (d, 4H,
J = 6 Hz, β-pyrrole-H), 8.56 (d, 4H, J = 6 Hz, pyridyl-H),
5,15-di(N-methylpyridinium4-yl)-10,20-bis[3,4,5-
tris(dodecyloxy)phenyl]porphyrin di-[tetrakis(penta-
fluorophenyl)borate] (10). To a 3 mL CH2Cl2 solution
of NaB(C6F5)4·Et2O (70 mg, 0.1 mmol) was added a 5 mL
CH2Cl2 solution of 9b (100 mg, 0.05 mmol). The reaction
mixture was stirred for 48 h under argon before filtration
to remove NaI. The filtrate was diluted with CH2Cl2 then
washed with distilled water two times. The organic layer
was dried over MgSO4. The solvent was removed under
reduced pressure and the solid product was purified by
recrystallization (CHCl3/methanol). Any remaining vola-
tile components were removed under reduced pressure
to afford a violet-black solid. Yield: 122 mg (78%). mp
3
3
7.38 (s, 4H, phenyl-H), 4.80 (t, 4H, JHH = 9 Hz, JHH
=
3
3
6 Hz, N-CH2-), 4.27 (t, 4H, JHH = 9 Hz, JHH = 6 Hz,
O-CH2-), 3.96 (t, 8H, J = 6 Hz, O-CH2-), 2.31 (m, 4H,
N-CH2-CH2-), 1.96 (m, 4H, O-CH2-CH2-), 1.67 (m, 16H,
O-CH2-CH2-), 1.50–1.18 (m, 136H, -(CH2)9-), 0.88 (m,
24H, -CH3), -2.66 (s, 2H, NH). 19F NMR (CDCl3): δ, ppm
-132.6 (d, 2F), -162.2 (t, 1F), -166.3 (t, 2F). MS (MALDI-
TOF): m/z 2060.59 [M -2B(C6F5)4 + H]+, 2060.73 calcd.
for C138H223N6O6. UV-vis (CH2Cl2): λmax, nm (ε × 10-3
M-1.cm-1) 453.0 (153), 527.0 (12.7), 583.0 (19.4), 668.0
(12.7). Anal. calcd. for C186H222B2F40N6O6: C 65.33; H
6.54; N 2.46. Found: C 65.33; H 6.58; N 2.53.
1
65–66 °C. H NMR (CDCl3): δ, ppm 9.32 (d, 4H, J =
6.0 Hz, pyridyl-H), 9.12 (d, 4H, J = 6 Hz, pyridyl-H),
8.85 (d, 4H, J = 6.0 Hz, β-pyrrole-H), 8.76 (d, 4H, J =
3 Hz, β-pyrrole-H), 7.41 (s, 4H, phenyl-H), 4.89 (s, 6H,
N-CH3), 4.32 (t, 4H, J = 6 Hz, O-CH2-), 4.07 (t, 8H,
J = 6 Hz, O-CH2-), 2.01 (m, 4H, O-CH2-CH2-), 1.80 (m,
8H, O-CH2-CH2-), 1.76–1.18 (m, 108H, -(CH2)9-), 0.84
(m, 18H, -CH3), -2.72 (s, 2H, NH). 19F NMR (CDCl3):
δ, ppm -132.7 (d, 2F), -162.3 (m, 1F), -166.5 (m, 2F).
HR-MS (MALDI-TOF): m/z 1752.3809 [M - 2B(C6F5)4 +
H]+, 1752.3881 calcd. for C116H179N6O6. UV-vis (CH2Cl2):
λ
max, nm (ε × 10-3 M-1.cm-1) 445.0 (153.3), 526.0 (11.9),
581.0 (16.1), 668.0 (10.1). Anal. calcd. for C164H178
RESULTS AND DISCUSSION
-
B2F40N6O6: C 63.32; H 5.77; N 2.70. Found: C 64.88; H
6.90; N 3.25.
Synthesis and characterization
5,15-di-(4-N-dodecanoylpyridinium-4-yl)-10,20-
bis[3,4,5-tris(dodecyloxy)phenyl]porphyrin dibromide
(11). Porphyrin 4b (200 mg, 0.116 mmol) was added to
2.0 g (8 mmol) of 1-bromododecane in 100 mL of dry
DMF and the mixture was then heated to reflux for 6 h.
After evaporation of the solvent, the residual solid was
washed with ether and filtered out. Purification of the
solid by chromatography on silica gel with 10% CH3OH-
CH2Cl2 gave the title product in 97% yield (250 mg). mp
The synthetic approach in order to access to free
base porphyrin precursors 3a–4b is shown in Scheme 1.
4-(dodecyloxy)benzaldehyde and 3,4,5-tris(dodecyloxy)-
benzaldehyde were prepared according to the litera-
ture [40, 41]. The free-base porphyrins (3a, 3b, 4a, 4b)
were successfully synthesized from the propionic acid-
catalyzed condensation of 5-(4-pyridyl)dipyrromethane
[42] with the corresponding aldehyde under reflux in the
dark for 2.5 h. The solvent was removed under reduced
Copyright © 2011 World Scientific Publishing Company
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566
h.-J. Xu et al.
OH
respectively. The phenyl and pyridyl
meso substituents of the free-base por-
phyrin have signals located at 7.45 and
9.04 ppm, respectively. In the aliphatic
area, relative to the long alkyl chains,
two triplet signals at 4.33 (4H) and 4.12
(8H) ppm are respectively accounting
for the methylene protons (α-CH2) 1′
and 1 linked to the oxygen atoms. The
resonances of the β-methylene pro-
tons 2′ and 2 appear as muliplets at
2.01 (4H) and 1.90 (8H) ppm, respec-
tively. The methyl protons have signals
located between 0.85–0.95 ppm. Other
protons of the alkyl chains are less well
resolved with resonances in the region
1.25–1.70 ppm. 3a, 3b and 4a exhibit
similar proton NMR spectra as for
4b. The low-field signals (7.29–9.07
ppm) correspond to the protons of the
pyridyl groups, β-pyrrole and phenyl
groups. The high-field signals (singlet
at about -2.80 ppm, 2H) are assigned
to the NH protons. The resonances
for the α-methylene and β-methylene
protons appear at around 4.11 and
2.01 ppm as triplets, respectively. The
resonances of the remaining protons of
the methylene and methyl groups are
located between 0.91 and 2.06 ppm.
1H NMR data of these derivatives are
given in the Experimental Section and
spectra are shown in the Supporting
information.
R1
R1
N
1a. R1 = H
1b. R1 = OH
CHO
CHO
RBr, KI,
K2CO3,DMF
85 ˚C
N
H
N
OR2
R3
R3
+
CHO
NH HN
2a. R2 = C12H25, R3 = H
2b. R2 = C12H25, R3 = OC12H25
Propionic acid
reflux
R4
R4
R5
R5
R5
R5
R5
R5
NH
N
NH
N
N
N
R4
N
+
N
N
HN
HN
R5
R5
R5
R5
R4
R4
3a. R4 = OC12H25, R5 = H
3b. R4 = R5 = OC12H25
4a. R4 = OC12H25, R5 = H
4b. R4 = R5 = OC12H25
The synthetic routes used for the
preparation of the ionic porphyrin deriv-
atives are shown in Schemes 2 and 3.
Scheme 1. Synthetic scheme of porphyrins 3 and 4
The bromide salts (7 and 11) were synthesized by reac-
tion of 1-bromododecane with the corresponding neutral
porphyrin in DMF at 70 °C followed by purification by
column chromatography and recrystallization in nearly
quantitative yields. Similarly, compounds 3 and 4 were
methylated in a dimethylformamide/chloroform mixture
under reflux by using CH3I to afford compounds 5 and 9 in
97% yield (Schemes 2 and 3). Tetrakis(perfluorophenyl)-
borate salts were prepared by anionic exchange of bro-
mide or iodide porphyrins with a little excess of sodium
tetrakis(perfluorophenyl)borate (NaB(C6F5)4) in dichlo-
romethane at room temperature. The insoluble, inorganic
salts, NaBr and NaI, were removed by filtration under
vacuum and the organic solutions were washed with dis-
tilled water. The porphyrin salts were finally isolated in
relatively high yields (69–87%). However, the reaction of
9a with sodium tetrakis(perfluorophenyl)borate was not
successful using the similar synthetic method described
for 9b, probably due to the poor solubility of the precur-
sor 9a in the organic solvent. All these porphyrin salts
pressure and the residues were purified by column chro-
matography on silica gel by using a 0–5% CH3OH in
CH2Cl2 mixture as the eluent. Recrystallization of the
resulting solid with CHCl3/CH3OH, afforded the cor-
responding porphyrins 3 and 4 in 8–15% yields. Several
different condensation conditions were also explored
in order to optimize the reaction conditions leading to
compounds 3 and 4. Trifluoroacetic acid (TFA) or boron
trifluoride etherate as catalysts in chloroform or dichlo-
romethane at room temperature were not suitable for any
of the present reactions: no expected porphyrin derivative
could be obtained from the reactions in the presence of
these two catalysts. All these new porphyrin compounds
1
were characterized by H NMR, UV-vis spectroscopy
and MALDI-TOF mass spectrometry.
1
The H NMR spectrum of the porphyrin 4b is shown
in Fig. 1a as a representative example. The porphyrin 4b
displays resonances peaks at 8.83, 8.18 and -2.81 ppm,
which are assigned to the β-pyrrole and NH protons
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ROOm temPeRatuRe IOnIC lIquIDS baSeD On CatIOnIC PORPhyRIn DeRIvatIveS
567
R4
R5
R5
R4
R5
R5
R5
NH
N
N
3a. R4 = OC12H25, R5 = H
3b. R4 = R5 = OC12H25
R4
N
HN
R5
R4
CH3I, rt
DMF-CHCl3
R4
BrC12H25, DMF
70 ˚C
R4
R5
R5
R5
R5
R5
R5
R5
NH
N
N
NH
N
N
H3C N+
I-
C12H25 N+
Br-
R4
HN
HN
R5
R5
R5
R5
R5
R4
R4
7. R4 = R5 = OC12H25
5a. R4 = OC12H25, R5 = H
5b. R4 = R5 = OC12H25
CH2Cl2,
NaB(C6F5)4·Et2O
CH2Cl2,
NaB(C6F5)4·Et2O
rt
rt
R4
R4
R5
R5
R5
R5
R5
R5
NH
N
N
HN
NH
N
N
HN
H3C N+
C12H25 N+
R4
R4
-
B(C6F5)4
-
B(C6F5)4
R5
R5
R5
R5
R5
R5
R4
R4
8. R4 = R5 = OC12H25
6a. R4 = OC12H25, R5 = H
6b. R4 = R5 = OC12H25
Scheme 2. Synthetic scheme of cationic porphyrins 5a–8
Copyright © 2011 World Scientific Publishing Company
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568
h.-J. Xu et al.
R4
R5
R5
NH
N
N
4a. R4 = OC12H25, R5 = H
4b. R4 = R5 = OC12H25
N
N
HN
R5
R5
R4
CH3I, rt
BrC12H25, DMF
70 ˚C
DMF-CHCl3
R4
R4
R5
R5
R5
R5
NH
N
N
NH
N
N
N+ C12H25
Br-
N+ CH3
I-
C12H25 N+
Br-
H3C N+
I-
HN
HN
R5
R5
R5
R5
R4
R4
9a. R4 = OC12H25, R5 = H
9b. R4 = R5 = OC12H25
11. R4 = R5 = OC12H25
CH2Cl2,
rt
CH2Cl2,
rt
NaB(C6F5)4·Et2O
NaB(C6F5)4·Et2O
R4
R4
R5
R5
R5
R5
NH
N
NH
N
N
N
N+ CH3
B(C6F5)4
N+ C12H25
H3C N+
C12H25 N+
-
-
-
HN
HN
-
B(C6F5)4
B(C6F5)4
B(C6F5)4
R5
R5
R5
R5
R4
R4
10. R4 = R5 = OC12H25
12. R4 = R5 = OC12H25
Scheme 3. Synthetic scheme of cationic porphyrins 9a–12
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ROOm temPeRatuRe IOnIC lIquIDS baSeD On CatIOnIC PORPhyRIn DeRIvatIveS
569
1
*
Fig. 1. Representative 300 MHz H NMR spectra of porphyrins 4b (a), 9b (b) and 10 (c) in CDCl3 ( solvent: CH2Cl2)
Copyright © 2011 World Scientific Publishing Company
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570
h.-J. Xu et al.
are very immiscible with water and the hydrophobicity
of these compounds can be attributed to the high water-
repellency of the long alkyl chains of the cationic part
of the molecule and the low polarizability. This property
facilitated purification by simply washing the crude prod-
uct with distilled water in order to remove any traces of
water soluble impurities.
and 9b; 8.86 and 8.63 ppm for 5a, 9.01 ppm for 9a) and
phenyl protons (ca. 7.30 ppm for 9b and 11 as singlets,
7.43 ppm for 5b and 7 as singlets, 7.09–8.08 ppm for
5a as doublets, 8.11 and 7.40 ppm for 9a as doublets).
The medium range resonances (between 4 and 6 ppm)
are respectively attributed to –O-CH2-protons (4.27 ppm
for 9a; 4.26 and 4.11 ppm for 5a; 4.33 and 4.12 ppm
for 5b, 7, 9b and 11), N-CH2-protons (5.37 ppm for 7;
5.34 ppm for 11) and N-CH3 protons (ca. 5.10 ppm for
5b and 9b; 4.93 ppm for 5a; 4.72 ppm for 9a). Higher
field resonances (between 0.5 and 2.5 ppm) are attributed
to the remaining aliphatic protons. The last region near
-3.0 ppm corresponds to inner NH proton resonances
(-2.70 ppm for 5b and 7; -2.74 ppm for 5a; -2.94 ppm
for 9a; -3.62 ppm for 11; -3.15 ppm for 9b). By compari-
son of the proton NMR spectra of the ionic porphyrins
with that of the corresponding neutral ones, the alkylated
pyridyl rings do not induce significant shifts on proton
resonances with the exception of the pyridine α protons
which demonstrate a downfield shift. As an example,
the 1H NMR spectrum of 9b is given on Fig. 1b. For 9b,
pyridine α protons are shifted to 9.66 pm (9.04 ppm for
4b) while pyridine α protons resonances remain almost
unchanged (see Fig. 1a for comparison).
Some of the porphyrin salts that have been prepared
are solid with exception of compounds 5b, 6a, and 8
which are liquid at room temperature. All the structures
and compositions of these new porphyrin salts were
1
determined by H and 19F NMR spectroscopy, MALDI-
TOF mass spectrometry (MS and HRMS), UV-visible
spectroscopy and elemental analysis. MALDI-TOF mass
spectrometry technique was used firstly to characterize
these porphyrin compounds and their salts.All the studied
compounds exhibit one main peak (protonated molecule
for neutral derivatives or cationic part of the molecule for
ionic liquids). These data confirmed the expected struc-
tures. For example, the MALDI-TOF mass spectrum of
8 exhibits the parent-ion peak at m/z = 2442.00 for cat-
ionic part (calculated for C163H270N5O9 m/z = 2442.08)
(Fig. 2).
The well-resolved proton NMR spectra of 5a, 5b, 7,
9a, 9b and 11, shown in the Supporting information are
very well consistent with the expected structures and
exhibit similar chemical shifts. The proton resonances
occur in four distinct regions. The downfield region from
7 to ca. 10 ppm correspond to pyridine ring protons (ca.
9.80 and 9.03 ppm for 7 and 11, ca. 9.67 and 9.12 ppm
for 5b and 9b, ca. 9.44 and 9.00 ppm for 5a and 9a),
β-pyrrolic protons (ca. 9.00 and 8.70 ppm for 7, 11, 5b
The completion of the anionic exchange reaction of
bromide or iodide with tetrakis(perfluorophenyl)borate
was confirmed by mass spectrometry, 1H NMR and 19F
NMR. In the negative mode MALDI/TOF mass spectra
of these derivatives, a single ionic pattern a m/z = 679
corresponding to the B(C6F5)4- ion was detected. In con-
trast to the precursors, remarkable changes in the proton
NMR spectra take place in the pyridinium α protons, the
Fig. 2. MALDI-TOF mass spectrum of 8 (cationic part)
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ROOm temPeRatuRe IOnIC lIquIDS baSeD On CatIOnIC PORPhyRIn DeRIvatIveS
571
methylene or the methyl groups adjacent to N-pyridyl
(N-CH2-) or (N-CH3) which are shifted to higher field due
to the influence of the large B(C6F5)4- anion. The remain-
ing proton resonances do not exhibit change with respect
to the precursors. As an example, the 1H NMR spectrum
of 10 is given in Fig. 1c. When compared to the spectrum
of 9b (Fig. 1b), the pyridinium α and N-CH3 protons of
10 appear at 9.32 and 4.32 ppm, respectively (9.66 and
5.08 ppm for 9b respectively). In addition, the resonances
of the inner NH protons in 10 are shifted to lower field
(-2.72 ppm compared to 9b (-3.15 ppm)). The 19F NMR
spectra (given in Supporting information) of 6a, 6b, 8a, 10
and 12 also confirmed the presence of B(C6F5)4- ion. The
resonances of the para-, ortho- and meta-fluorine atoms
appear at -162.2, -132.6 and -166.3 ppm respectively.
The UV-vis data of the neutral porphyrins and the por-
phyrin salts are given in Table 1. The UV-vis spectra of
4b, 9b and 10 in CH2Cl2 are presented in Fig. 3. The neu-
tral porphyrin 4b shows a typical electronic spectrum of
meso-substituted porphyrins in CH2Cl2 with a sharp Soret
band at 421 nm and four Q-bands at 519, 550, 591 and
646 nm. Upon cationization of the neutral porphyrin 4b,
the number of absorption bands in 9b and 10 is reduced.
Three Q-bands appear at 526 (526), 575 (581) and 663
(668) nm for 9b (10). The most relevant feature is the
red-shift of the Soret band upon alkylation of the pyridyl
groups. For example, the Soret band of the N-methylated
porphyrin 9b is red-shifted by 20 nm from the corre-
sponding Soret bands of 4b. When I- is substituted by
B(C6F5)4-, the Soret band of 10 is further red-shifted to
445 nm (see Fig. 3). Similar trend is observed for other
derivatives (Table 1). Another interesting feature can
be observed on the UV-vis spectra. The Soret bands of
Fig. 3. UV-vis spectrum (CH2Cl2) of porphyrins 4b, 9b and 10
the porphyrin salts are significantly broadened and their
extinction coefficients are remarkably decreased relative
to those of the corresponding neutral porphyrins (Fig. 3
and Table 1).
TGA measurements
TGA analyses were performed under a Ar/O2 gas
stream mixture for six porphyrins in order to correlate
their thermal stability to their structure (Fig. 4). The
less stable structures are porphyrins 9b and 5a since
their decomposition began at 183 °C and 193 °C respec-
tively and a further mass decrease occurred starting from
370 °C due to the porphyrin calcination. TGA curves
indicated a first 13.5% weight loss for 9b and 11.3% for
5a assigned to methyl iodide release during the heating
Table 1. UV-vis absorption data in CH2Cl2 for the synthesized derivatives
Compound
λ
max, nm (ε × 10-3, M-1.cm-1)
Soret band
421 (1769)
Q-bands
3a
3b
4a
4b
5a
5b
6a
6b
7
517 (71)
516 (18)
515 (72)
555 (46)
552 (8.7)
552 (37)
550 (8.8)
584 (13)
589 (1.1)
661 (1.1)
633 (0.8)
593 (13)
664 (0.9)
574 (11)
575 (18.1)
581 (16.1)
575 (12)
581 (19.4)
592 (26)
591 (4.8)
591 (23)
591 (7.0)
663 (0.8)
659 (0.6)
650 (27)
649 (4.2)
650 (18)
646 (4.6)
421 (350)
420 (1622)
421 (449)
422 (143)
428 (122)
419 (131)
421 (113)
427 (131)
423 (118)
438 (115)
441 (220)
445 (153)
435 (166)
453 (153)
516 (22.7)
522 (11)
522 (12)
590 (1.6)
589 (14)
524 (13)
593 (15)
526 (9.4)
526 (17.9)
526 (11.9)
526 (12)
527 (12.7)
659 (0.7)
8
9a
9b
10
11
12
666 (7.5)
663 (11.1)
668 (10.1)
663 (7.7)
668 (12.7)
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572
h.-J. Xu et al.
Fig. 4. TGA traces for porphyrins 5a (blue line), 6a (black line), 9a (pink line), 9b (red line), 11 (green line) and 12 (orange line)
under an Ar/O2 gas stream (30 mL.min-1/10 mL.min-1)
process. The respective theoretical values are 14.1% and
10.8%. This result demonstrates that when iodide is used
as the counter-anion, the thermal stability is quite low
compared to porphyrins 11, 12 and 6a with other coun-
ter-anions. Compound 9a is surprisingly more stable than
9b and 5a despite the presence of two iodide ions and
this is may be due to electronic effects since 9a possess
less donor atoms and is then less oxidizable. Neverthe-
less, a straightforward correlation was observed between
the thermal stability and the nature of the counter-anion
if we compared 11 vs. 12, 5a vs. 6a and 9b vs. 11. From
this result, a stability series clearly emerged: I- < Br- <<
B(C6F5)4-. Moreover, if we compare 6a and 12, the num-
ber and the length of the peripheral alkyl chains seem to
have no effect on the thermal stability of the porphyrins.
differential scanning calorimetry (DSC) upon heat-
ing and cooling down (heating and cooling rate: 10 °C.
min-1). Endothermic or exothermic peaks assigned as the
melting or crystallizing processes were observed below
300 °C. The measured data of glass transition tempera-
ture (Tg), solid-solid transition (Ts-s), and melting point
(Tm) are presented in Table 2. Porphyrin 9a has a melt-
ing point at 236 °C. 5a, 6a, 7 and 9b have melting points
below 200 °C, while 5b, 6b, 8, 10 and 12 have melting
temperatures ranging from 98 to 181 °C. More interest-
ing is the behavior of 5b, 6b, and 8 salts which can be
considered as room-temperature ionic liquids due to low
melting points observed below 25 °C. To our knowledge,
these are the first examples of porphyrins displaying ionic
liquid properties close to room temperature.
The first type of behavior is characterized by the salts
that have a melting transition (6a, 6b, 7, 9b, 10, 11 and
12 in Table 1). The second type of behavior is repre-
sented by a number of salts that exhibited one solid-solid
Phase transition
The thermal properties and solid-liquid phase tran-
sitions of these porphyrin salts were examined by
Table 2. Thermal and conductivity properties of the ionic liquid salts
Compound
Tg, °Ca
Ts-s, °Cb
91
Tm, °Cc
181
∆Hm, kJ.mol-1
∆Sm, J.mol-1.K-1 d
κ/mS.cm-1 e
5a
5b
6a
6b
7
26.61
58.09
solid
1.32
solid
4.01
solid
0.05
solid
solid
solid
solid
solid
-28
129
-23
145
-22
236
181
66
67.30
8.53
163.35
34.13
42.75
5.12
17.99
1.28
8
-39
9a
9b
10
11
12
213
27.86
37.18
21.43
31.73
88.35
54.00
81.89
49.72
70.52
236.24
177
98
a Glass transition. b Solid-solid transition. c Melting point. d Entropy of fusion (∆Sm = ∆Hm/Tm, where ∆Hm
is melting enthalpy at Tm(K)). e Specific conductivity at 22 °C.
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ROOm temPeRatuRe IOnIC lIquIDS baSeD On CatIOnIC PORPhyRIn DeRIvatIveS
573
Indeed, we were not able to measure specific conductiv-
ity values for the other salts at higher temperatures. For
the salts with the same cation, the specific conductivity
-
is much higher for the B(C6F5)4 (6a and 8) anion than
I- anion (5b). For B(C6F5)4- anion, the specific conductiv-
ity of 6b (4.01 mS.cm-1) is greatly higher than 8 (0.05
mS.cm-1). This can be explained by the bigger cation size
and molecular weight of the cation of 8 [24].
CONCLUSION
In summary, we have developed an effective synthetic
method to prepare porphyrin derivatives bearing one
pyridyl or two pyridyl groups by [2+2] aldehyde-dipyr-
romethane condensation in a one-pot reaction. Alkylation
Fig. 5. DSC traces on second cooling for porphyrin 8
of the neutral porphyrins led to mono- or di-cationic por-
phyrin salts which were fully characterized by 1H NMR,
19F NMR, MALDI-TOF mass spectrometry, elemental
analysis and UV-visible spectroscopy. DSC studies also
indicate that those new ionic liquid porphyrin exhibit
relatively low melting points. Furthermore, 5b, 6b, and
8 salts are liquid at room temperature and their melting
points are observed below 25 °C. These results show that
low symmetry of the cation and presence of large anions
play an important role in decreasing melting points of
these ionic liquid porphyrin derivatives. A specific con-
ductivity value up to 4 mS.cm-1 was obtained for a com-
pound (6b) having the coordinating anion B(C6F5)4-.
Further work on complexation of these ILs is currently
underway in our laboratory.
transition (Ts-s) before melting (compounds 5a, 8 and
9a). The third type of behavior is represented by the salt
that only exhibited a glass transition at 200 °C without
melting (5b). Figure 5 shows the DSC traces of one of
the representatives, porphyrin (8) as an example, Upon
cooling, 8 undergoes a single liquid-solid phase transi-
tion at approximately T = -22 °C, showing an exothermic
peak and exhibit afterwards a solid-solid phase transition
at -39 °C with an endothermic peak.
A comparison of the melting point values of the asym-
metric porphyrin based salts with those of the symmetric
porphyrin based ones clearly evidences the influence of the
asymmetry on the melting temperature. The melting point
values of the asymmetric porphyrin salts (mono-alkylated)
are lower than those for the corresponding symmetric salts
(di-alkylated). For the same anion, the salts with lower
symmetry porphyrins generally exhibit a lower melting
point than those with higher symmetry (see Table 2, 5a vs.
9a, 5b vs. 9b, 7 vs. 11, 6b vs. 10, 8 vs. 12). These results
suggest that the packing efficiency of the salt could be
disrupted by reducing the cation symmetry, thus lowering
the melting point. It seems that the asymmetric factor and
longer alkyl chains of the cationic porphyrin salt play a key
role in achieving the low melting points of these salts.
The nature of the anion affects also significantly the
melting point of the porphyrin salts. For these porphyrin-
based salts, the influence of tetrakis(perfluorophenyl)-
borate groups on the melting point is remarkably obvious
and tetrakis(perfluorophenyl)borate porphyrins (6a, 6b,
8, 10 and 12) display melting temperatures that are
greatly lower than that of bromide or iodide porphyrins
(5a, 5b, 7, 9b and 11) (see Table 2). This is probably due
to the effective charge distribution over the anion which
tends to reduce the crystal lattice energy of the salts, thus
resulting in low-melting salts [24].
Acknowledgements
The Centre National de Recherche Scientifique
(ICMUB, UMR CNRS 5260) is gratefully thanked for
financial support. Hai-Jun Xu also gratefully acknowl-
edges the “Région Bourgogne” and CNRS for a post-
doctoral fellowship.
Supporting information
1H and 19F NMR spectra, MALDI-TOF mass spec-
tra and thermal analyses (Figs S1–S46) are given in the
supplementary material. This material is available free of
charge via the Internet at http://www.worldscinet.com/jpp/
jpp.shtml.
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