Metallocorroles as sensing components for gas sensors: Remarkable affinity and selectivity of cobalt(III) corroles for CO vs. O2 and N 2

Article abstract of DOI:10.1039/b316706b

Most commercially available CO detectors are based upon metal oxides or electrochemical cell technologies. None of these approaches use the selective adsorption of CO gas on a molecular complex. Conversely, cobalt(III) corroles can bind small gaseous molecules allowing them for an application as sensing components for gas detectors. Here we describe the ability of cobalt corroies to selectively coordinate carbon monoxide vs. dinitrogen and dioxygen. The coordination properties were determined in the solid state and the adsorption characteristics were compared to those of the reference compound (To-PivPP)Fe(1,2-Me₂Im), known for its remarkable CO binding properties. The adsorption data evidence that the selectivity, affinity and capacity of the cobalt(III) corroies for CO are larger than those of the porphyrin complex. However, from a chemical point of view, the selectivity of cobalt(III) corroies for CO vs. O₂ is infinite since these derivatives do not bind O₂ while (To-PivPP)Fe(1,2-Me₂Im) does with an M value (P_1/2^O2/ P_1/2 ^Co) equal to 51. In this manuscript we also show that the affinity of cobalt(III) corroies for CO is closely related to the Lewis acid character of the central cobalt(III) ion and therefore to the nature of the substituents at the periphery of the corrole macroring.

Full text of DOI:10.1039/b316706b

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Metallocorroles as sensing components for gas sensors:
remarkable affinity and selectivity of cobalt(III) corroles for
CO vs. O2 and N2 †
Jean-Michel Barbe,* Gabriel Canard, Stéphane Brandès, François Jérôme,‡ Géraud Dubois§
and Roger Guilard*
Laboratoire d’Ingénierie Moléculaire pour la Séparation et les Applications des Gaz (LIMSAG),
UMR 5633, Faculté des Sciences, “Gabriel”, 6, Bd Gabriel, 21100, Dijon, France.
E-mail: Roger.Guilard@u-bourgogne.fr; Fax: ϩ33 380 39 61 17; Tel: ϩ33 380 39 61 11
Received 19th December 2003, Accepted 24th February 2004
First published as an Advance Article on the web 23rd March 2004
Most commercially available CO detectors are based upon metal oxides or electrochemical cell technologies. None
of these approaches use the selective adsorption of CO gas on a molecular complex. Conversely, cobalt() corroles
can bind small gaseous molecules allowing them for an application as sensing components for gas detectors. Here
we describe the ability of cobalt corroles to selectively coordinate carbon monoxide vs. dinitrogen and dioxygen.
The coordination properties were determined in the solid state and the adsorption characteristics were compared to
those of the reference compound (To-PivPP)Fe(1,2-Me2Im), known for its remarkable CO binding properties. The
adsorption data evidence that the selectivity, affinity and capacity of the cobalt() corroles for CO are larger than
those of the porphyrin complex. However, from a chemical point of view, the selectivity of cobalt() corroles for CO
O2
vs. O2 is infinite since these derivatives do not bind O2 while (To-PivPP)Fe(1,2-Me2Im) does with an M value (P1/2
/
P1/2CO) equal to 51. In this manuscript we also show that the affinity of cobalt() corroles for CO is closely related to
the Lewis acid character of the central cobalt() ion and therefore to the nature of the substituents at the periphery
of the corrole macroring.
also well-developed leading to highly CO sensitive detectors but
Introduction
exhibiting low lifetimes (6–24 months).19,20
Corrole chemistry has been extremely well developed over the
Here we report on the high affinity, capacity and selectivity
past few years due to the finding of several new versatile
of cobalt() corroles for carbon monoxide vs. N2 and O2 in the
syntheses.1–6 Many substitution variations have been introduced
solid state.21 We also show in this paper how the reversibility of
on the structure of the corrole macrocycle and it is now
the CO adsorption can be tuned by the electronic properties of
relatively easy to obtain a large variety of rings upon function-
the substituents at the periphery of the corrole skeleton. This
alization at the meso and/or the β-pyrrole positions.7 Further-
more, several different metals have been inserted into the
easy modification of the adsorption properties of the Co()
complex is of main interest for an application of corroles as a
corrole ring8 and some applications of the metallocorroles have
sensing component for a CO detector.
been reported in catalysis9–13 as well as in various volatile
organic molecules detection.14,15
When compared to porphyrins, a peculiar property of
corroles is their ability to coordinate metals in higher oxidation
Results
Our approach is different from the preceding sensor tech-
nologies since we use a molecular complex which can directly
and selectively coordinate carbon monoxide in an ambient
atmosphere. We demonstrate in this paper that Co() corroles
states. In the particular case of cobalt, porphyrins stabilize the
ϩ oxidation state while cobalt() corroles are obtained even
when metalated with a cobalt() salt. This difference is at the
origin of the specific coordination properties of the cobalt()
coordinate CO at the cobalt() centre with no interference with
corroles. For example, cobalt() corroles are able to bind many
donor molecules and particularly carbon monoxide16,17 while
Co() porphyrins cannot, thus allowing the use of the former
O2 since no coordination of this gas can occur at the Co() ion.
There are many reports on molecules able to coordinate
carbon monoxide. For example, hemoglobin, myoglobin and
derivatives for gas sensing purposes.
their model compounds coordinate CO and O2 in solution.22–29
CO detection is a crucial point for industry and domestic
The selectivity of these derivatives for CO is given in eqn. (1)
purposes. Detectors are currently available and two main
O2
CO
where P1/2 and P1/2 represent the half-saturation pressures
technologies are used. The metal oxide technology is based on
the conductivity variation of an oxide upon contact with the
gas at high temperature. The involved oxides comprise metals
such as Zn, Ti, W, Ga, . . . but mostly Sn. Mixed oxides of
perovskite structure are also used.18 The sensitivity of such
detectors is generally high but the selectivity for the detected gas
(i.e. CO) is relatively low. The electrochemical cell technology is
of O2 and CO, respectively.
O2
CO
M = P1/2 /P1/2
(1)
The larger the M value, the larger is the relative affinity for
CO. M Values for myoglobin and hemoglobin range from 20 to
150, while a model compound, (To-PivPP)Fe(1,2-Me2Im),
(Scheme 1) exhibits a much larger affinity for CO than O2
in solution at room temperature (M = 4280).22 In the same
solution conditions, the cobalt() corroles do not interact with
O2 but with CO and therefore the selectivity CO/O2 can be
considered as infinite.16 Moreover, they are stable under an air
atmosphere containing O2 and H2O, while the former iron
complex slowly transforms into an inactive Fe() derivative.
† Electronic supplementary information (ESI) available: Adsorption
isotherms of corroles 5 and 6, IR spectra of the corrole/CO species
(corroles 3–5) (Figs. S1–S3). See http://www.rsc.org/suppdata/dt/b3/
b316706b/
‡ Present address: LACCO-ESIP, UMR 6503 CNRS, Université de
Poitiers, 40, Avenue du Recteur Pineau, 86022 Poitiers, France.
§ Present address: IBM Almaden Research Center, 650 Harry Road,
San Jose, CA 95120, USA.
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Adsorption experiments
The affinity for CO of the six investigated metallocorroles does
not only depend on the presence of a cobalt() ion but also on
the Lewis acid character of the cobalt() centre. The larger
the electron density on the metal, the lower the Lewis acid
character, the lower is the affinity of the complex for CO. There-
fore simple modifications of the molecular framework will
tune the affinity for CO. This is true for corrole 1 which does
not adsorb carbon monoxide in the solid state (in the con-
ditions used here) due to the electron donating properties of the
β-substituents on the corrole ring and therefore to the resulting
weak Lewis acid character of the central cobalt() ion.
The carbon monoxide adsorption curves in the solid state for
corroles 2–5 shown in Figs. 1–4 were compared to dinitrogen
adsorption which was regarded as a blank due to non-selective
adsorption of this gas on the solid derivative. Moreover,
dioxygen adsorption data allowed defining the CO/O2 selectiv-
ity for each corrole complex. It is well-known, in the case of
Scheme 1 Structure of (To-PivPP)Fe(1,2-Me2Im).
For CO detection purposes, the adsorption properties of six
Co() corroles were determined in the solid state (Scheme 2).
All values were compared to those obtained for (To-PivPP)-
Fe(1,2-Me2Im) in the same conditions.
Fig. 1 Adsorption isotherms for corrole 2 at 293 K: (᭹ CO, * N2 and
ꢀ O ) and calculated isotherms with components 1 (- - -), 2 (- -) and 3
ؒ
(---)2for CO adsorption.
Fig. 2 Adsorption isotherms for corrole 3 at 293 K (᭹ CO) and
Scheme 2 Structures of the investigated cobalt() corroles.
calculated isotherms with components 1 (- - -), 2 (- -) and 3 (---) for CO
ؒ
adsorption.
Syntheses
Corrole 1 and 2 free-bases were synthesized according to
previously described procedures.16,30 The corrole 4 free-base was
prepared by the 1ϩ2 method involving the condensation
of one eq. of 2,4,6-trimethoxybenzaldehyde with 2 eq. of
5-mesityldipyrromethane in dichloromethane in the presence of
a catalytic amount of trifluoroacetic acid (TFA).6 Corrole 3
free-base was obtained via a step-wise reaction involving first
the synthesis of the 5,15-dimesityl-10-(4-nitrophenyl)corrole
as described for corrole 4 (see Experimental section), then
reduction of the nitro group to an amino group by H2 on Pd/C
in THF, and finally reaction with chloracetyl chloride in THF.
The insertion of the cobalt in each of the six corroles was
then performed in a classical way by reaction of the free-base
corrole with an excess of cobalt() acetate tetrahydrate in a
chloroform–methanol mixture.
Fig. 3 Adsorption isotherms for corrole 4 at 293 K (᭹ CO, * N2 and ꢀ
O ) and calculated isotherms with components 1 (- - -), 2 (- -) and 3
ؒ
(-2--) for CO adsorption.
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hybrid silica materials,31,32 that the equilibrium constants for
gas binding affinity, Ki, and adsorption capacity, Vi, can be
calculated assuming that the gas adsorption results from two
different processes: the chemisorption of carbon monoxide on
the cobalt centre and a non-selective adsorption (physisorption)
due to dissolution and diffusion of the gas in the non-porous
solid. Thus, the isotherms were analyzed here using a multiple-
site adsorption process based on a multiple Langmuir-type
adsorption model first described for carbonaceous and zeolitic
solids.33–35 Several equilibria, as given in eqn. (2), can be
involved in the adsorption process and the summation (eqn. (3))
of two Langmuir-type components (1 and 2) with a Henry
mode (component 3) gave satisfactory calculated isotherms.
CorroleCo(s) ϩ CO(g)
CorroleCo(CO)(s)
(2)
(3)
This three-equilibrium model accurately describes the
reactivity between a gas and a non-porous solid with hetero-
geneous energetic interactions, such as diffusion of the gas in
the microcrystalline solid (low energetic) and binding on the
metal centre with a higher energetic interaction. A similar
two-site model was also required to describe the heterogeneous
energetic interactions of organic compounds with MFI
zeolite36 and cations with chelating mesoporous silica.37 The Vi
and Ki values were calculated using a non-linear least-square
minimisation. The two Langmuir-type components correspond
to the chemisorption of carbon monoxide on metallocorroles
on the surface of the solid with a high K1 affinity and on the less
accessible inner solid cobalt sites leading to a lower binding K2
constant. The physisorption of carbon monoxide was well
described with a simple Henry-type isotherm leading to a
straight line with a slope K3. Process 1 is the major contribution
at low pressures (<30 Torr) due to the high binding constant of
the accessible sites while the two others predominate at higher
pressures. Only one Langmuir-type isotherm was considered
for dioxygen and dinitrogen adsorption because these two gases
do not coordinate on the metal centre. Moreover, adsorption
capacity and gas binding affinity are very low for each corrole
complex. The thermodynamic data calculated for corroles 2–6
are given in Table 1 and experimental isotherms with data fits
are illustrated in Figs. 1–3. Considering a two Langmuir-type
model for CO binding on cobalt(), the percentage of active
sites was calculated by adding V1 and V2 capacities (Table 1).
Nevertheless, only the highest binding constant (lower (P1/2CO)1)
corresponding to the first process of the isotherm model was
considered to estimate the selectivity of the corrole complexes.
The CO adsorption isotherms given in Fig. 1 evidence that
the corrole 2 adsorbs the carbon monoxide at a maximum of
4.04 cm3 gϪ1 at atmospheric pressure (760 Torr) and 14% of the
cobalt sites are accessible if one considers that only one CO
molecule can be bound to the metal.16
This result is in agreement with a low accessibility of the
CO
cobalt sites inside the solid. Two P1/2 values (components
1 and 2) equal to 11.8 and 472 Torr were respectively obtained.
The first value corresponds to the chemisorption of CO on
the accessible Co() sites while the second one accounts for
the diffusion and adsorption on less available sites. For the
comparison of the adsorption properties of all the studied
complexes, we will consider afterwards only the first Langmuir
isotherm because it represents the adsorption at very low CO
partial pressures, which is a condition required for a gas sensor
application. It is noteworthy that the adsorbed volumes of O2
and N2 are very low compared to the CO adsorption, especially
at low pressure. This clearly demonstrates that the involved
process, for these latter gases, is physisorption. In order to defin-
itely discriminate between chemisorption and physisorption of
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CO, we carried out adsorption experiments on corrole 2 where
the cobalt coordination sites were blocked by two imidazole
molecules. This complex did not adsorb carbon monoxide even
at pressure beyond 760 Torr. This result confirms that CO is
effectively bound to the cobalt ion of the corrole.
carbon monoxide and dioxygen are given in Table 1. The fits
of the CO adsorption isotherm as well as O2 and N2 adsorption
isotherms for corrole 5 are given as ESI.†
Discussion
For an application of the cobalt complex as a gas-sensing
device, the reversibility of the CO adsorption should be a
prerequisite. After degassing the previous corrole 2/CO com-
plex (12 h at 10Ϫ3 Torr), the second CO adsorption isotherm
is strictly identical to the first one, thus demonstrating the
reversibility of the system. Another proof of the reversibility of
the system is obtained by the FT/IR analysis, which shows that
the spectrum of the corrole 2/CO derivative, recorded in the
transmittance mode, exhibits a strong absorption band at 2045
cmϪ1, accounting for the binding of the CO molecule on the
cobalt() ion. When the complex is left under air, this band
decreases in intensity and totally disappears with degassing
under vacuum (5 min at 3 Torr) (vide infra).
Fig. 2 shows the adsorption isotherms of CO for corrole 3.
O2 and N2 adsorptions are not illustrated because they are
negligible. The maximum CO adsorbed volume is equal to 8.28
cm3 gϪ1 and an occupation ratio of available sites of 23% is
calculated. The two P1/2CO values are equal to 0.8 and 117 Torr,
respectively, showing that the CO affinity of corrole 3 is
higher than that of corrole 2, with more accessible sites. The
CO stretching band appears at lower wavenumbers than for
corrole 2 (2041 cmϪ1, Table 1). Moreover, the high CO binding
constant and the lack of O2 adsorption leads to an infinite
theoretical selectivity.
For the sake of comparison, CO and O2 binding experiments
were performed in the same experimental conditions on
(To-PivPP)Fe(1,2-Me2Im). The corresponding isotherms are
given in Fig. 5 and half-saturation pressure values are reported
in Table 1. Two Langmuir isotherms were used to fit with
experimental values of the CO adsorption, leading to a first
CO
P1/2 of 0.67 Torr. Surprisingly, no Henry-type isotherm was
used in the adsorption model to obtain a well-adjusted
isotherm, which is attributable to negligible physisorption of
the gas in the solid powder. The ratio of available coordination
sites occupied by a carbon monoxide molecule is slightly
higher (50%) than for corroles 4 and 5, and the adsorbed CO
volume is 9.3 cm3 gϪ1 at 760 Torr. Similarly, the characteristics
of the dioxygen adsorption have been determined and V760
,
O2
occupation ratio and P1/2 are equal to 9 cm3 gϪ1, 58% and 34.1
Torr, respectively. It should be noticed that these values are
somewhat different than those obtained in a preliminary
experiment;38 this is certainly due to the use of another prox-
imal axial base (1-MeIm) in this latter case and to different
experimental conditions.
The same behaviour is observed for corrole 4 which exhibits a
low O2 adsorbed volume at 760 Torr (2.1 cm3 gϪ1) and a very
O2
weak binding constant (P1/2 = 2880 Torr) while still not
adsorbing dinitrogen in the same pressure conditions (Fig. 3).
The maximum adsorbed carbon monoxide volume at 760
Torr is equal to 15.3 cm3 gϪ1 and 39% of the cobalt sites are
CO
accessible. As for corrole 3, the P1/2 for the first component
of the isotherm is very low (Ӷ1) and is in the same range as that
of (To-PivPP)Fe(1,2-Me2Im) measured in solution.25 The
O2
obtained P1/2 and the (P1/2CO)1 values give a selectivity beyond
108, but the exact value cannot be calculated since inaccurate
values are generally obtained for extremely high binding
constants.
The reversibility of the CO binding on corrole 5 has also been
demonstrated by a series of adsorption/desorption experiments
and Fig. 4 represents four recorded CO adsorption isotherms
with corrole 5 after desorption cycles. As shown on this figure,
the four isotherms are nearly identical thus clearly demon-
strating the reversibility of the adsorption of carbon monoxide
for this cobalt() corrole in non-drastic conditions. The
maximum CO adsorbed volume by corrole 5 is 13.6 cm3 gϪ1
(37% occupation ratio). Values for half-saturation pressure of
Fig. 5 Adsorption isotherms of ᭹ CO, and ꢀ O2 for (To-PivPP)-
Fe(1,2-Me2Im) at 293 K in the solid state.
By simply considering the data given in Table 1, the calcu-
lated M values clearly evidence the larger selectivity for carbon
monoxide vs dioxygen of four of the investigated cobalt()
corroles compared to (To-PivPP)Fe(1,2-Me2Im), the exceptions
being corroles 1 and 2. For example, corrole 4 exhibits an M
value higher than 108 vs. 51 for (To-PivPP)Fe(1,2-Me2Im).
However, as stated before, it is noteworthy that the adsorption
of O2 on the cobalt() corroles occurs via a simple physisorp-
tion phenomenon. Therefore, from a chemical point of view,
the selectivity CO/O2 of the cobalt() corroles can be con-
sidered as infinite. Furthermore, by considering the volume (V1)
for the first contribution of the isotherm model (eqn. (3)),
relative to the highest binding constant and selectivity, corrole 5
is the most efficient CO sorbent since process 1 of the isotherm
is predominant with a very low (P1/2CO)1 value and V1 ӷ V2.
CO
Finally, it is noteworthy that the P1/2
value recorded in
solution for corrole 2 (7.1 Torr)16 is very close to (P1/2
)
1
CO
obtained here in the solid state (11.8 Torr).
Nevertheless, the half-saturation CO pressures cannot allow
to definitely classify the complexes as to their affinities for CO.
Indeed, since adsorption measurements were carried out on
solid ground samples, differences in size of powder particles,
as well as packing of the molecules inside the crystal structure,
can enhance or limit the access to the cobalt() sites. Therefore,
Fig. 4 Reversibility of the CO adsorption for corrole 5: ᭹ first cycle
(degassing conditions: 10Ϫ3 Torr for 2 h at 363 K), ᭿ second cycle and
third cycle (degassing conditions: 10Ϫ3 Torr for 8 h at 295 K), ꢀ fourth
cycle (degassing conditions: identical to second and third cycles).
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P1/2CO and Vmax can be increased or decreased depending upon
the accessibility of the sites. For example, the occupation ratio
equals 23% for corrole 3 while it is close to 40% for corroles
4 and 5.
Conclusions
Six cobalt() corroles have been studied with regard to their
CO, O2 and N2 adsorption properties. We have shown that the
affinity of these derivatives for CO is infinite from a chemical
point of view and application as sensing components for a gas
sensor can be expected. Toward this objective, it is now
necessary to synthesize materials where properly functionalized
corroles could be grafted on a solid support. In this regard, our
goal is the anchoring of corroles on silica gel, mesoporous
templated silica (MTS), organic polymers and organic–
inorganic hybrid materials via the sol–gel process. Preliminary
results have been obtained in this latter domain and will be
published later.40
Conversely, correlations can be established between the
Lewis acid character of the central cobalt ion and the CO
stretching frequency in the infrared spectra. These frequencies
are given in Table 1 and they range between 2040 and 2079 cmϪ1
for the corrole derivatives and located at 1961 cmϪ1 for
(To-PivPP)Fe(1,2-Me2Im). The lower frequency observed for
the iron complex is due to an important metal carbon π
orbital back bonding. This value is close to that recorded in
solution for the same complex (1969 cmϪ1).39 It is also note-
worthy that the already reported frequencies for CO vibrations
of cobalt() corroles in solution fall in the same range (2040–
2050 cmϪ1).16 The higher wavenumbers compared to (To-
PivPP)Fe(1,2-Me2Im) can be explained by less back bonding
from the Co() ion to the empty π orbitals of the CO ligand.
Moreover, as the Lewis acid character of the cobalt ion increases
with the presence of electron withdrawing substituents at the
periphery of the macrocycle, the d π back bonding again
decreases and the CO stretching frequency increases. The
exception in these results, is the CO vibration of the corrole 2
which appears at a higher value than expected for such a basic
ligand (see Table 1). A similar trend can be proposed for the
affinity of the corrole complex for CO which roughly increases
with the Lewis acid character of the cobalt (Scheme 3). It is
noteworthy that in solution a good correlation can also be
established between the IR frequency of the CO stretching
band and the electron density at the cobalt centre.16
Experimental
Chemicals
For the syntheses, commercially available chemicals and
solvents were used as received without further purification.
Basic alumina (MERCK 90, standardized) and silica gel (SDS
2100027, 70–200 µm) were used for column chromatography.
Physical methods
1H NMR spectra were recorded on a Bruker AVANCE 300 or a
Bruker DRX-500 AVANCE spectrometer at the “Centre de
Spectrométrie Moléculaire de l’Université de Bourgogne”;
chemical shifts are expressed in ppm relative to chloroform
(7.25 ppm). UV-visible spectra were recorded on a Varian Cary
50 spectrophotometer. Mass spectra were obtained on a Bruker
ProFLEX III MALDI/TOF spectrometer using dithranol
as a matrix. IR spectra were recorded on a Bruker IFS 66v
FTIR spectrophotometer and samples were prepared as 1%
dispersions in KBr pellets. Gaseous uptake measurements at
293 K were performed on a Micromeritics ASAP 2010 analyser
equipped with 1, 10 and 1000 Torr transducers, employing
a 20-point pressure table ranging from 1 to 850 Torr. The
experimental isotherms were analysed by using eqn. (3). The
thermodynamic values were calculated from the experimental
data with the Microsoft Excel 2000 program using a nonlinear
regression least-squares method with a conjugate-gradient or
Newton algorithm. The samples were degassed for 2 h under
vacuum (10Ϫ3 Torr) at 80 ЊC prior to gas adsorption analysis.
Microanalyses were performed at the Université de Bourgogne
on a Fisons EA 1108 CHNS instrument.
Scheme 3
The classification proposed in Scheme 3, established only on
the basis of IR data, is corroborated by CO desorption experi-
ments. The CO molecule bound to corroles 2, 3 and 4 is totally
removed by degassing the complex for 2 h at room temperature
under 10Ϫ3 Torr. An example of the easy decoordination of the
CO molecule from the cobalt() corrole is given in Fig. 6. In
this figure are reproduced the IR spectra of corrole 2/CO
recorded under an air atmosphere (spectra 1–5) and under
vacuum (5 min under 3 Torr, spectrum 6). The slow desorption
of CO from the complex is clearly evidenced in spectra 1–5 and
the initial corrole 2 is fully recovered when degassed for 5 min
under 3 Torr. By contrast, CO can only be removed from
corrole 5 by degassing at least 8 h under 10Ϫ3 Torr. This is in
agreement with the higher (P1/2CO)1 value of corrole 2 compared
to those of corroles 3–6. Finally, corrole 6 exhibits the largest
affinity for carbon monoxide since the total removal is only
obtained at 50 ЊC under 10Ϫ3 Torr for 12 h. This confirms the
classification given in Scheme 3.
Synthesis
(2,3,8,12,17,18-Hexaethyl-7,13-dimethylcorrolato)cobalt()
(corrole 1),30 (7,8,12,13-tetramethyl-2,3,10,17,18-pentaphenyl-
corrolato)cobalt() (corrole 2),16 5,15-dimesityl-10-(4-nitro-
phenyl)corrole,6
5,10,15-tris(2,6-dichlorophenyl)corrole,41
(5,10,15-trispentafluorophenylcorrolato)cobalt() (corrole 6),42
and 5-mesityldipyrromethane43 were synthesized as reported in
the literature.
5,15-Dimesityl-10-(4-aminophenyl)corrole. To 0.30 g of Pd/C
(5% w) was added a solution of 1.13 g (1.72 mmol) of 5,15-
dimesityl-10-(4-nitrophenyl)corrole and 1 mL of triethylamine
in 240 mL of THF. The mixture was stirred under dihydrogen at
atmospheric pressure for 24 h and then filtered on Celite®. The
filtrate was evaporated and the resulting solid chromatographed
on silica gel using CH2Cl2–heptane (4 : 1, v/v) as eluent to remove
impurities and then pure CH2Cl2 to collect as the next fraction
the expected compound. After recrystallization from CH2Cl2–
MeOH, 0.97 g of pure compound was isolated (90% yield). 1H
NMR (300 MHz, CDCl3): δ Ϫ1.92 (br s, 3H), 1.92 (s, 12H), 2.60
(s, 6H), 3.91 (br s, 2H), 7.01 (d, J = 7.92 Hz, 2H), 7.25 (s, 4H),
7.93 (d, J = 7.92 Hz, 2H), 8.31 (d, J = 3.86 Hz, 2H), 8.47 (d,
J = 4.52 Hz, 2H), 8.54 (d, J = 4.52 Hz, 2H), 8.88 (d, J = 3.86 Hz,
Fig. 6 Infrared spectra recorded during CO desorption experiments
carried out on corrole 2.
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2H). MS (MALDI/TOF): m/z 625.55 [Mϩ ], calc. for C43H39N5:
CH3OH C 69.91, H 5.23, N 8.86; found C 70.42, H 5.15, N
8.89%.
ؒ
625.32. UV-Vis (CH2Cl2): λmax/nm (10Ϫ3ε/molϪ1 L cmϪ1) 408
(92.9), 427 (69.7), 567 (14.3), 606 (10.4), 637 (6.9). Anal. calc.
for C43H39N5ؒCH3OH: C 80.33, H 6.59, N 10.65; found C 80.24,
H 6.14 N 10.71%.
[5,15-Dimesityl-10-(2,4,6-trimethoxyphenyl)corrolato]-
cobalt(III) (corrole 4). Corrole 4 was obtained as described
above from 0.69 g (0.98 mmol) of 5,15-dimesityl-10-(2,4,6-
trimethoxyphenyl)corrole and 0.74 g (2.75 mmol) of cobalt()
5,15-Dimesityl-10-(4-chloroacetamidophenyl)corrole. A solu-
tion of 0.45 g of chloroacetyl chloride (4.00 mmol, 1.2 eq.) in
5 mL of THF was added dropwise to a solution of 2.1 g of
5,15-dimesityl-10-(4-aminophenyl)corrole (3.35 mmol) in
400 mL of THF. The reaction mixture was stirred for 1 h and
then 0.40 g of triethylamine (4.00 mmol, 1.2 eq.) was added.
After 15 more min of stirring, the solvent was removed under
vacuum and the solid taken up in dichloromethane. The organic
layer was washed with water, dried over magnesium sulfate and
evaporated. The solid was then chromatographed on silica gel
with CH2Cl2–heptane (1 : 1, v/v) as eluent. The second eluted
fraction was collected and the solid obtained after evaporation
recrystallized from CH2Cl2–heptane yielding 1.76 g of 5,15-
dimesityl-10-(4-chloroacetamidophenyl)corrole (75%). 1H
NMR (300 MHz, CDCl3) δ Ϫ1.87 (br s, 3H), 1.91 (s, 12H), 2.59
(s, 6H), 4.31 (s, 2H), 7.25 (s, 4H), 7.90 (d, J = 8.2 Hz, 2H), 8.15
(d, J = 8.2 Hz, 2H), 8.32 (d, J = 4.21 Hz, 2H), 8.46 (d, J = 4.76
Hz, 2H), 8.49 (d, J = 4.76 Hz, 2H), 8.53 (s, 1H), 8.88 (d, J = 4.21
1
acetate tetrahydrate (41% yield, 0.31 g). H NMR (500 MHz,
C5D5N) δ 1.95 (s, 12H), 2.57 (s, 6H), 3.30 (s, 6H), 4.01 (s, 3H),
6.84 (s, 2H), 7.31 (s, 4H), 8.75 (d, J = 4.00 Hz, 2H), 8.89 (d,
J = 4.61 Hz, 2H), 9.02 (d, J = 4.61 Hz, 2H), 9.36 (d, J = 4.00 Hz,
2H). MS (MALDI/TOF): m/z 756.80 [Mϩ ], calc. for C46H41-
ؒ
CoN4O3 756.79. UV-Vis (CH2Cl2): λmax/nm (10Ϫ3ε/molϪ1
L
cmϪ1) 389 (66.1). Anal. calc. for C46H41CoN4O3: C 73.0, H 5.46,
N 7.40; found C 72.47, H 5.43, N 7.36%.
[5,10,15-Tris(2,6-dichlorophenyl)corrolato]cobalt(III) (corrole
5). Corrole 5 was obtained as described above for corrole 3 from
0.40 g (0.55 mmol) of 5,10,15-tris(2,6-dichlorophenyl)corrole
and 0.40 g (1.63 mmol) of cobalt acetate tetrahydrate (87%
1
yield, 0.42 g). H NMR (500 MHz, C5D5N) δ 7.51 (t, 3H),
7.66–7.70 (m, 6H), 8.83 (d, J = 4.70 Hz, 2H), 8.86 (d, J = 4.10
Hz, 2H), 9.10 (d, J = 4.70 Hz, 2H), 9.35 (d, J = 4.10 Hz, 2H).
MS (MALDI/TOF): m/z = 785.05 [Mϩ ], calc. for C37H17-
ؒ
Hz, 2H). MS (MALDI/TOF): m/z 701.74 [Mϩ ], calc. for
Cl6CoN4 785.89. UV-Vis (CH2Cl2): λmax/nm (10Ϫ3ε/molϪ1
L
ؒ
C45H40ClN5O: 701.29. UV-Vis (CH2Cl2): λmax/nm (10Ϫ3ε/molϪ1
L cmϪ1) 407 (120.6), 427 (95.6), 567 (17.3), 604 (11.8), 635 (6.3).
Anal. calc. for C45H40ClN5O : C 76.96, H 5.74, N 9.97; found C
76.64, H 5.99, N 9.91%.
cmϪ1) 392 (85.7). Anal. calc. for C37H17Cl6CoN4: C 56.31, H
2.17, N 7.10; found C 56.40, H 1.99, N 6.96%.
Acknowledgements
This work was supported by the CNRS and Air Liquide. GC
gratefully acknowledges the ӶRégion Bourgogneӷ and Air
Liquide for a financial support.
5,15-Dimesityl-10-(2,4,6-trimethoxyphenyl)corrole. 2.1 g (8
mmol) of 5-mesityldipyrromethane and 0.78 g (4 mmol) of
2,4,6-trimethoxybenzaldehyde were dissolved in 240 mL of
CH2Cl2. The mixture was stirred at room temperature and 24
µL of TFA were added. Stirring was continued for 5 more hours
and a solution of 1.8 g (8 mmol) of DDQ in 20 mL of THF was
added. After 15 min of stirring, the reaction mixture was
chromatographed on a silica gel plug with CH2Cl2–heptane
(1 : 1, v/v) as eluent. After evaporation of the solvents, the
resulting solid was again chromatographed on a silica gel
column using CH2Cl2–heptane (1 : 1, v/v) as eluent. The second
collected fraction yielded the expected 5,15-dimesityl-10-(2,4,6-
trimethoxyphenyl)corrole which was recrystallized from
heptane (0.34 g, 12%). 1H NMR (500 MHz, CDCl3) δ Ϫ1.05 (br
s, 3H), 1.91 (s, 12H), 2.59 (s, 6H), 3.56 (s, 6H), 4.07 (s, 3H), 6.55
(s, 2H), 7.23 (s, 4H), 8.21 (d, J = 3.87 Hz, 2H), 8.35 (d, J = 4.68
Hz, 2H), 8.38 (d, J = 4.68 Hz, 2H), 8.76 (d, J = 3.87 Hz, 2H).
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ϩ
H]ϩ, calc. for
C46H44N4O3: 700.88. UV-Vis (CH2Cl2): λmax/nm (10Ϫ3ε/molϪ1 L
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ؒ
C45H37ClCoN5O 758.21. UV-Vis (CH2Cl2): λmax/nm (10Ϫ3ε/
molϪ1 L cmϪ1) 393 (49.2). Anal. calc. for C45H37ClCoN5Oؒ
D a l t o n T r a n s . , 2 0 0 4 , 1 2 0 8 – 1 2 1 4
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