B,B-diporphyrinbenzyloxy-BODIPY dyes: Synthesis and antenna effect

Article abstract of DOI:10.1021/jo3000833

B,B-Diporphyrinbenzyloxy-BODIPY derivatives have been prepared in high yields, and the photophysical properties are reported. Singlet energy transfers from BODIPY to the porphyrin units have been analyzed.

Full text of DOI:10.1021/jo3000833

Note
pubs.acs.org/joc
B,B-Diporphyrinbenzyloxy-BODIPY Dyes: Synthesis and Antenna
Effect
Bertrand Brizet,†,‡ Antoine Eggenspiller,† Claude P. Gros,*,† Jean-Michel Barbe,† Christine Goze,†
Franck Denat,† and Pierre D. Harvey*,‡
†Universite
́
de Bourgogne, ICMUB (UMR 6302), 9, Avenue Alain Savary, BP 47870, 21078 Dijon Cedex France
de Sherbrooke, Sherbrooke, Quebec, Canada J1K 2R1
‡Dep
́
artement de Chimie, Universite
́
́
S
* Supporting Information
ABSTRACT: B,B-Diporphyrinbenzyloxy-BODIPY derivatives
have been prepared in high yields, and the photophysical
properties are reported. Singlet energy transfers from BODIPY
to the porphyrin units have been analyzed.
he B−F bonds of BODIPY are convenient functions for
ionic patterns undoubtedly confirms the structure of 3 and 4
(see the Supporting Information). For example, the calculated
mass for the monosodium adduct of 4 (C121H99BN10NaO4Zn2)
is equal to 1917.6436 Da, in agreement with the experimental
value found at 1917.6396 Da ([M + Na]+).
T
the design of light-harvesting devices based on this dye.1
Despite numerous efforts, there are only a few examples
reported so far including the 4,4-dialkoxy- or 4,4-diaryloxydiaza-
S-indacene(BODIPY)-containing antennas.1u,2 In this respect,
some B-methoxy (B-OMe) BODIPYs were successfully
prepared by reacting the corresponding BF2 compound with
sodium methoxide in methanol.2a The absorption and emission
spectra of the corresponding alkoxy products reveal no change
compared to the BODIPY itself, indicating that the
introduction of substituents on the B-atom had little effect
on the electronic states of the boroindacene core.2a B-OR
BODIPYs systems have also been obtained via the treatment of
the corresponding BODIPY with various alcohols in the
presence of aluminum trichloride.2b Furthermore, a difluor-
oboron dipyrrin was subsequently converted into dioxyboron
dipyrrin derivatives by treatment with dihydroxy benzaldehyde
in the presence of aluminum trichloride and provided access to
donor−acceptor−acceptor and antenna−donor−acceptor type
triads.1u We report here the synthesis and characterization of
B,B-diporphyrinbenzyloxy-BODIPY derivatives (Chart 1).
Evidence for singlet energy transfer from BODIPY to the
porphyrin unit is provided.
Table 1 summarizes the UV−vis data for all compounds in
THF. Compound 1 exhibits two bands characteristic of
BODIPY; the S0−S1 band at 526 and the S0−S2 band at 382
nm, both assigned to spin-allowed π−π* transitions. The UV−
vis spectrum of the free base porphyrin 2 and Zn(TPP) (TPP =
5,10,15,20-tetraphenylporphyrin) are characterized by one
Soret band, two Q bands for Zn(TPP), and five Q bands for
2. It appears that absorption spectra of the multichromophoric
species 3 and 4 correspond to the sum of the absorption
spectra of the individual components, 1 and 2 for compound 3,
and 1 and Zn(TPP) for compound 4 (Figures S6 and S7,
Supporting Information) indicating that the interchromophoric
interactions are minimal. The positions of the absorption
spectra of compound 1 and Zn(TPP) indicate that BODIPY
and the porphyrin units are the S1 energy donor and acceptor,
respectively.
The photophysical data are summarized in Table 2. One
example of the fluorescence spectra is provided in Figure 1.
BODIPY 1 shows an intense fluorescence at 544 nm with a
quantum yield, ΦF, of 0.62 and a lifetime, τF, of 3.7 ns. The
emission spectra of the porphyrin subunits exhibit two
characteristic bands respectively at 653 and 718 nm for
compound 2 (τF = 11.0 ns), and 605 and 655 nm for Zn(TPP)
(τF = 1.9 ns).
The target model compound 1 and the dyad system 3 were
readily obtained in only one step from benzyl alcohol and
porphyrin 2 (obtained by reduction of 5-(4-(carboxy)phenyl)-
10,15,20-tritolylporphyrin zinc)) in 61 and 86% yield,
respectively (Scheme 1). The zinc insertion into the free base
3 followed by purification by column chromatography over
silica with dichloromethane as the solvent gave the diporphyrin
biszinc complex 4 in an almost quantitative yield. The
experimental conditions and spectroscopic data for 1−4 are
provided in the Supporting Information and Experimental
Section. The HR-MS data of 3 and 4 reveal the presence of
only one ion attributed to the monosodium adduct. In both
cases, the perfect match between experimental and simulated
When dyad 3 is irradiated at 530 nm where the BODIPY
chromophore absorbs the most, almost exclusively the
fluorescence of the porphyrin unit is observed. The excitation
Received: January 27, 2012
Published: March 1, 2012
© 2012 American Chemical Society
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The Journal of Organic Chemistry
Note
Chart 1
Table 1. UV−vis Absorption Data in THF at 298 K
λmax (nm) (ε × 10−3 M−1 cm−1
)
porphyrin chromophore BODIPY chromophore
compd
Soret band
417 (312)
Q bands
S2 band
S1 band
1
2
382 (3.3)
526 (32.5)
649 (3.4)
593 (4.1)
550 (7.5)
515 (14.0)
484 (3.2)
648 (8.6)
592 (10.3)
546 (27.8)
559 (36.7)
598 (15.9)
594 (7.1)
555 (21.7)
3
4
418 (816)
526 (69.1)
528 (60.0)
423 (104)
423 (606)
Zn(TPP)
spectrum exhibits a perfect match with the absorption (Figure 2
and Supporting Information). These two properties indicate
clearly an efficient S1 energy transfer from BODIPY to
porphyrin, following excitation of the BODIPY subunit.
The τF data were used to extract the S1 energy transfer rates,
kET. Again, compounds 3 and 4 exhibit two fluorophores,
BODIPY and porphyrins (as a free base or a zinc(II) complex),
again assigned as the S1 energy donor and acceptor,
respectively. The ΦF data of the acceptor remain relatively
the same regardless the presence or the absence of the S1
energy donor at 298 and 77 K. This observation indicates that
the anchoring of the porphyrin unit onto BODIPY does not
Scheme 1
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The Journal of Organic Chemistry
Note
Table 2. Fluorescence Lifetimes, τF, in 2MeTHF at 298 and 77 K
2MeTHF
298 K
77 K
a
compd
ΦF 298 K
λem (nm)
λexc (nm)
τF (ns)
kET (s−1
)
λexc (nm)
τF (ns)
kET (s−1
)
1
2
3
0.62
544
530
548
530
590
530
560
563
3.7
11.0
c
530
548
530
590
530
560
563
8.1
13.6
4.5
0.089
653, 718
653
b
c
0.068
1 × 108
1 × 108
12.6
3.3
1.9
1.9
14.5
4.6
b
4
0.039
655
3 × 107
2.3
Zn(TPP)
0.037
605, 655
2.6
a
Quantum yields were measured in 2MeTHF at 298 K, using Rhodamine 6G as reference3 (ΦF = 0.94 in MeOH, λexc = 488 nm). All Φ are corrected
for changes in refractive index.4 Total quantum yield (BODIPY and porphyrins). Not measured.
b
c
orientation of the transition moments between the donor and
the acceptor according to a Forster mechanism6 (see the
̈
graphical abstract which corresponds to a minimized geometry
of 4; PC Model). In line with a Forster mechanism,6 the fact
̈
that the kET data is strongly temperature dependent (kET ∼3 ×
107 s−1 at 298 K) is consistent with this explanation where a
relative change in conformation occurs via the rotation about
the B−O and O−C single bonds upon changing the
temperature.
In conclusion, the good spectral overlap between the donor
fluorescence (BODIPY) and acceptor absorption (porphyrin)
leading to a notable quenching of the former is observed and
clearly demonstrates the BODIPY dye as a good chromophore
for the antenna effect. However, the current dyad design can be
improved from a gain in appropriate relative orientation of the
transition moments between the donor and acceptor.
Figure 1. Emission spectra of compounds 2 (red, λexc = 500 nm), 3
(green) and 1 (blue, λexc = 530 nm) in 2MeTHF at 298 K.
EXPERIMENTAL SECTION
Instrumentation. H NMR spectra were recorded on a 300 MHz
■
1
spectrometer at the Po
̂
le Chimie Molec
́
ulaire (Universite
́
de
Bourgogne); chemical shifts are expressed in ppm relative to
chloroform. 13C NMR spectra were recorded on a 300 MHz
́
spectrometer at the Universite de Sherbrooke. Mass spectra were
obtained in the MALDI/TOF reflectron mode using dithranol as a
matrix or by ESI on an Orbitrap spectrometer. The measurements
̂ ́ ́
were made at the Pole Chimie Moleculaire (Universite de Bourgogne).
UV−vis spectra were recorded on a diode array apparatus. Emission
and excitation spectra were obtained using a double monochromator
instrument. Fluorescence and phosphorescence lifetimes were
measured on a apparatus incorporating a nitrogen laser as the source
and a high-resolution dye laser (fwhm = 1.4 ns). Fluorescence lifetimes
were obtained from high-quality decays and deconvolution or
distribution lifetime analysis. The uncertainties ranged from 20 to 40
ps on the basis of multiple measurements. Phosphorescence lifetimes
were determined using an apparatus incorporating a 1 μs tungsten
flash lamp (fwhm ∼1 μs). Flash photolysis spectra and transient
lifetimes were measured using the 355 nm line of a YAG laser from
Continuum (Serulite; fwhm =13 ns).
Quantum Yield Measurements. For measurements at 298 K, all
samples were prepared in a glovebox, under argon (O2 < 12 ppm), by
dissolution of the compounds in 2MeTHF, using 1 cm3 quartz cells
with a septum. Three different measurements (i.e., different solutions)
were performed for each set of photophysical data (quantum yield).
The sample concentrations were chosen to correspond to an
absorbance of ∼0.05 at the excitation wavelength. Each absorbance
value was measured three times for better accuracy in the
measurements of emission quantum yields. Tetraphenylporphyrin
(0.10 in THF)7 or tetraphenylporphyrin zinc(II) (0.033 in THF) was
used as reference.8
Figure 2. Absorption and excitation spectra of compound 4 (λexc
653 nm).
=
increase the rates for the nonradiative processes internal
conversion, kic, and intersystem crossing, kisc. On the other
hand, a decrease in τF of the donor is noted, particularly at 77 K
(by a factor of approximately 2). Using the equation kET
=
1/τF(donor) − 1/τF°(donor) where τF and τF° are the fluorescence
lifetimes of the donor in the presence and absence of acceptor,
respectively, then the approximate kET is ∼1 × 108 s−1 for both
3 and 4. Despite the obvious decrease in total ΦF (going from
0.62 for 1 to 0.068 and 0.039 for 3 and 4, respectively, at 298
K), the through space energy transfer rates of 1 × 108 s−1 are
considered modest with respect to other dyads (∼109−1010
s−1).5 The reason for this is most likely due to the nonparallel
Chemicals and Reagents. Unless otherwise noted, all chemicals
and solvents were of analytical reagent grade and used as received.
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Note
Silica gel (70−120 μm) was used for column chromatography.
Analytical thin-layer chromatography was performed with 60 F254 silica
gel (precoated sheets, 0.2 mm thick). Reactions were monitored by
thin-layer chromatography, UV/vis spectroscopy, and MALDI/TOF
mass spectrometry.
Mp > 300 °C. UV/vis (CH2Cl2): λmax (nm) (ε × 10−3 L mol−1 cm−1)
= 416.0 (330), 514.0 (13), 550.0 (8), 590.0 (4), 646.0 (3). H NMR
1
(pyridine-d5, 298 K): δ (ppm) = −2.27 (s, 2H), 2.61 (s, 9H), 5.36 (s,
2H), 7.60 (d, J = 7.6 Hz), 8.07 (d, J = 7.9 Hz, 2H), 8.27 (d, J = 7.6 Hz,
6H), 8.47 (d, J = 7.9 Hz, 2H), 9.14 (m, 8H). 13C NMR (CDCl3, 75
MHz, 298 K): δ (ppm) = 14.1, 21.5, 29.7, 30.3, 65.4, 120.2, 125.3,
127.4, 131.0, 134.5, 137.3, 139.3. MS (MALDI-TOF): m/z = 686.3122
[M]+•, 686.3040 calcd for C48H38N4O.
5-(4-Carboxyphenyl)-10,15,20-tritolylporphyrin Zinc. To a
solution of 4-carboxybenzaldehyde (2.20 g, 14.6 mmol) in 250 mL of
CHCl3 were added 4.56 g (19.3 mmol) of 5-p-tolyldipyrromethane
and 590.0 mg (5.0 mmol) of 4-methylbenzaldehyde. The solution was
degassed under nitrogen bubbling for 15 min, shielded from light.
Boron difluoride diethyl etherate (325 μL, 2.5 mmol) was added
dropwise, and the reaction mixture was stirred at room temperature for
1 h 30 min p-chloranil (2.40 g, 9.7 mmol) was then added under
stirring. After 2 h, the solvent was evaporated under reduced pressure.
The residue thus obtained was chromatographed on silica gel using
CH2Cl2/MeOH (100/5), and the first purple fraction was isolated.
After evaporation of the solvent under vacuum, the residue was
redissolved in 250 mL of chloroform, and the solution was treated with
100 mL of a methanolic solution of Zn(OAc)2·2H2O (2.40 g, 30.0
mmol) in the presence of sodium acetate (2.40 g, 30.0 mmol). The
mixture was heated at 75 °C, and the reaction was monitored by TLC,
UV−vis, and MALDI/TOF mass spectrometry. After 2 h and cooling
to room temperature, the reaction mixture was washed three times
with water (750 mL), dried over magnesium sulfate, and concentrated.
The residue obtained was chromatographed on silica gel (CH2Cl2/
MeOH, 100/5). The red-pink fraction was isolated, and the solvent
was removed under reduced pressure to give the title compound in
27% yield (2.00 g, 2.67 mmol) Mp > 300 °C. UV/vis (CH2Cl2): λmax
(nm) (ε × 10−3 L mol−1 cm−1) = 422.0 (135), 551.0 (6), 588.0 (3).
1H NMR (CDCl3, 298 K): δ (ppm) = 2.61 (s, 9H), 7.54 (d, J = 7.8
B,B-Bis(1-benzyloxy-10,15,20-tritolylporphyrinyl)-1,3,7,9-
tetramethyl-2,8-diethyl-5-(p-methylbenzoyl)-BODIPY (3). To a
solution of BODIPY ester (23.0 mg, 52 μmol) in dry THF (50 mL)
was added, under nitrogen, aluminum trichloride (55.0 mg, 412 μmol).
The solution was heated to 40 °C for 30 min (the color of the solution
turned from pale-orange to red) and then cooled to room temperature.
5-(4-(Hydroxymethyl)phenyl)-10,15,20-tritolylporphyrin 2 (170.0 mg,
250 μmol) was then added, and the reaction mixture was stirred at
room temperature for 1 h 30 min. After filtration over alumina in order
to remove AlCl3, all of the volatiles were evaporated under reduced
pressure. After purification by chromatography on silica (EtOAc/
heptane, 30/70), the compound was crystallized in a CH2Cl2/heptane
mixture to afford the title compound 3 as a purple solid in 84% yield
(78.0 mg, 44 mmol). Mp > 300 °C. UV/vis (CH2Cl2): λmax (nm) (ε ×
10−3 L mol−1 cm−1) = 418.0 (880), 525.0 (77), 592.0 (10), 649.0 (10).
1H NMR (CDCl3, 298 K): δ (ppm) = −2.77 (s, 4H), 1.05 (t, J = 7.4
Hz, 6H), 1.42 (s, 6H), 2.42 (q, J = 7.4 Hz, 4H), 2.68 (s, 18H), 2.88 (s,
6H), 3.98 (s, 3H), 4.57 (s, 4H), 7.54 (d, J = 7.9 Hz, 12H), 7.64 (d, J =
8.4 Hz, 2H), 7.67 (d, J = 8.0 Hz, 4H), 8.08 (d, J = 7.9 Hz, 12H), 8.10
(d, J = 8.0 Hz, 4H), 8.24 (d, J = 8.4 Hz, 2H), 8.83 (s, 16H). 13C NMR
(CDCl3, 75 MHz, 298 K): δ (ppm) = 12.1, 13.2, 14.9, 17.3, 21.5, 29.7,
52.4, 64.8, 120.0, 120.3, 126.2, 127.4, 129.1, 130.3, 130.9, 131.8, 133.3,
134.3, 134.5, 155.1. HR-MS (ESI): m/z = 886.4219 [M + 2H]2+,
886.4209 calcd for C121H103BN10O4.
Hz, 6H), 8.08 (d, J = 7.8 Hz, 6H), 8.32 (d, J = 8.1 Hz, 2H), 8.47 (d, J
= 8.1 Hz, 2H), 8.91 (m, 8H). MS (MALDI-TOF): m/z = 762.18
[M]+•, 762.19 calcd for C48H34N4O2Zn.
B,B-Bis(zinc(II)-1-benzyloxy-10,15,20-tritolylporphyrinyl)-
1,3,7,9-tetramethyl-2,8-diethyl-5-(p-methylbenzoyl)-BODIPY
(4). To a solution of BODIPY-diporphyrin 3 (50.0 mg, 28 μmol) in 10
mL of CH2Cl2 was added a methanolic solution of Zn(OAc)2·2H2O
(24.0 mg, 109 μmol) and sodium acetate (20.0 mg, 243 μmol), and
the mixture was heated under reflux for 2 h. The reaction was
monitored by TLC, UV−vis, and MALDI/TOF mass spectrometry.
After cooling to room temperature, the reaction mixture was washed
three times with water (10 mL), dried over magnesium sulfate, and
filtered. The title compound 4 was obtained in almost quantitative
yield as a purple solid (53.0 mg, 28 μmol) after recrystallization in a
CH2Cl2/heptane mixture. Mp > 300 °C. UV/vis (CH2Cl2): λmax (nm)
B,B-Bisbenzoyl-1,3,7,9-tetramethyl-2,8-diethyl-5-(p-methyl-
benzoyl)-BODIPY (1). To a solution of BODIPY ester (70.0 mg, 160
μmol) in dry CH2Cl2 (25 mL) was added, under nitrogen, aluminum
trichloride (175.0 mg, 1.31 mmol). The solution was heated to 40 °C
for 30 min (the color of the solution turned from pale-orange to red)
and then cooled to room temperature. Benzyl alcohol (85 μL, 820
μmol) was then added, and the reaction mixture was stirred at room
temperature for 1 h. After filtration over alumina in order to remove
AlCl3, all the volatiles were evaporated under reduced pressure. After
purification by chromatography on silica (EtOAc), the title compound
was isolated as a red oil in 61% yield (60.0 mg, 97 mmol). UV/vis
(CH2Cl2): λmax (nm) (ε × 10−3 L mol−1 cm−1) = 418.0 (880), 525.0
1
1
(ε × 10−3 L mol−1 cm−1) = 422.0 (810), 529.0 (56), 590.0 (6). H
(77), 592.0 (10), 649.0 (10). H NMR (CDCl3, 298 K): δ (ppm) =
0.87 (t, J = 7.4 Hz, 6H), 1.17 (s, 6H), 2.15 (q, J = 7.4 Hz, 4H), 2.42 (s,
6H), 4.02 (s, 3H), 4.49 (s, 4H), 7.15 (m, 10H), 7.40 (d, J =8.4 Hz,
2H), 8.13 (d, J =8.4 Hz, 2H). 13C NMR (CDCl3, 75 MHz, 298 K): δ
(ppm) = 11.9, 12.7, 14.7, 17.1, 29.7, 30.2, 31.4, 52.4, 64.5, 124.5, 126.3,
127.5, 127.7, 129.0, 130.2, 136.2, 141.5, 154.9. HR-MS (ESI): m/z =
637.3178 [M + Na]+, 637.3214 calcd for C39H43BNaN2O4.
NMR (CDCl3, 298 K): δ (ppm) = 1.07 (t, J = 7.4 Hz, 6H), 1.44 (s,
6H), 2.44 (q, J = 7.4 Hz, 4H), 2.69 (s, 18H), 2.90 (s, 6H), 3.97 (s,
3H), 4.58 (s, 4H), 7.54 (d, J = 7.9 Hz, 12H), 7.64 (d, J = 8.4 Hz, 2H),
7.67 (d, J = 8.0 Hz, 4H), 8.09 (d, J = 7.9 Hz, 12H), 8.11 (d, J = 8.0 Hz,
4H,), 8.23 (d, J = 8.4 Hz, 2H), 8.94 (s, 16H). 13C NMR (CDCl3, 75
MHz, 298 K): δ (ppm) = 12.1, 13.2, 14.9, 17.3, 21.5, 29.7, 52.4, 64.8,
121.1, 126.1, 127.3, 129.1, 131.8, 134.1, 137.0, 139.9, 140.1, 150.3. MS
(MALDI-TOF): m/z = 1895.28 [M + H]+, 1895.66 calcd for
C121H100BN10O4Zn2. HR-MS (ESI): m/z = 1917.6396 [M + Na]+,
1917.6436 calcd for C121H99BN10NaO4Zn2.
5-(4-(Hydroxymethyl)phenyl)-10,15,20-tritolylporphyrin (2).
To a suspension of LiAlH4 (75.0 mg, 1.97 mmol) in dry
tetrahydrofuran (35 mL) was added dropwise at −80 °C a solution
of 5-(4-carboxyphenyl)-10,15,20-tritolylporphyrin zinc (500.0 mg,
0.65 mmol) in dry tetrahydrofuran (35 mL). The mixture was stirred
at −80 °C for 10 min, warmed to room temperature for 1 h, and then
quenched with water (5 mL). After evaporation of the solvent in
vacuum, the residue was extracted with CHCl3, washed three times
with water (10 mL), dried over magnesium sulfate, filtered, and
evaporated. The residue obtained was chromatographed on silica
(CH2Cl2/MeOH, 100/2). The fractions were collected, and the
solvent was evaporated under reduced pressure. The solid was
dissolved in CH2Cl2 (100 mL), and 2.0 mL of trifluoroacetic acid was
added dropwise under stirring. After 2 h, the reaction mixture was
washed with saturated hydrogen carbonate solution and two times
with water (100 mL) and then dried over magnesium sulfate. After all
volatiles were removed under reduced pressure, the title compound 2
was isolated in 57% yield (254.0 mg, 0.37 mmol) as a purple powder.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra and mass spectra (HR-MS) of
compounds 1−4 (Figures S1−S12). Absorption spectra of 1,
ZnTPP, and 4 in MeTHF at 298 K (Figure S13). Absorption
spectra of 1−3 in MeTHF at 298 K (Figure S14). Emission
spectra of 4, 1, and ZnTPP in MeTHF at 298 K (Figure S15).
Emission spectra of 2, 3, and 1 in MeTHF at 298 K (Figure
S16). This material is available free of charge via the Internet at
http://pubs.acs.org.
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The Journal of Organic Chemistry
Note
(4) Schafer, F. P. In Topics in Applied Physics: Structure and Properties
̈
AUTHOR INFORMATION
■
of Laser Dyes; Springer-Verlag: Berlin, 1990; Vol. 1, Dye Lasers.
(5) (a) Harvey, P. D. In The Porphyrin Handbook; Kadish, K. M.,
Smith, K. M., Guilard, R., Eds.; Academic Press: Boston, 2003; Vol. 18,
p 63. (b) Harvey, P. D.; Stern, C.; Guilard, R. In Handbook of
Porphyrin Science With Applications to Chemistry, Physics, Materials
Science, Engineering, Biology and Medicine; Kadish, K. M., Smith, K. M.,
Guilard, R., Eds.; World Scientific Publishing: Singapore, 2011; pp 1−
179.
Corresponding Author
*E-mail: pierre.harvey@usherbrooke.ca; claude.gros@u-
bourgogne.fr.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(6) (a) Forster, T. Naturwissenschaften 1946, 33, 166−175.
̈
■
(b) Forster, T. Ann. Phys. 1948, 2, 55−73.
̈
The Centre National de la Recherche Scientifique (ICMUB,
UMR CNRS 6302) is gratefully thanked for financial support.
(7) Li, B.; Li, J.; Fu, Y.; Bo, Z. J. Am. Chem. Soc. 2004, 126, 3430−
3431.
Support was provided by the CNRS, the Universite
Bourgogne and the Conseil Regional de Bourgogne through
the 3MIM integrated project (Marquage de Molecules par les
Metaux pour l’Imagerie Medicale). P.D.H. thanks the Natural
́
de
(8) (a) Aly, S. M.; Ayed, C.; Stern, C.; Guilard, R.; Abd-El-Aziz, A. S.;
Harvey, P. D. Inorg. Chem. 2008, 47, 9930−9940. (b) Loutfy, R. O.;
Law, K. Y. J. Phys. Chem. 1980, 84, 2803−2808.
́
́
́
́
Sciences and Engineering Research Council of Canada
(NSERC) for financial support. We are thankful to Normand
Pothier for the registration of 13C NMR spectra.
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