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53 cm, Ø=1 mm) as the counter electrode, and a saturated calo-
mel electrode as the reference electrode. The Devarda working
electrode was prepared by co-deposition of Ni and Devarda alloy
particles on a stainless-steel grid (3 cm4 cm).[40] Electrolyses were
followed by TLC and UV/Vis absorption measurements.
a well-behaved electrochemical response, which indicates that
the porphyrin structure is retained. Although further character-
ization will be necessary to obtain a formal proof, a direct
bonding of the porphyrin to the electrode surface (with no
linker between them) has been achieved. The specific elec-
trode properties that are anticipated from such a particularity
might be essential for developments in sensing and electro-
catalysis.
Synthesis
Magnesium(II)
5,15-ditolyl-10-phenylporphyrin
(Mg(PDTP)):
H2(PDTP) (200 mg, 0.35 mmol) and MgBr2 (2.60 g) were dissolved in
CH2Cl2 (50 mL) that contained triethylamine (4 mL, 80 equiv). The
reaction mixture was stirred for 10 min at room temperature. The
solution was then washed five times with distilled water (250 mL).
After evaporation of the solvent, purification by column chroma-
tography (alumina, 0 to 1% MeOH in CH2Cl2), and recrystallization
from MeOH/H2O, Mg(PDTP) was obtained in 80% yield (166 mg).
Experimental Section
Reagents and instrumentation
Tetraethylammonium hexafluorophosphate (TEAPF6; Fluka puriss.,
electrochemical grade, ꢀ99.0%) and 2,6-lutidine (Aldrich, ꢀ99%)
were used as received. Tetraethylammonium tetrafluoroborate
(TEABF4) was synthesized by the following method. Typically, in
a 500 mL Erlenmeyer flask, tetrafluoroboric acid (84.28 g; HBF4;
Sigma Aldrich, 48% H2O) was mixed with a solution of tetraethy-
lammonium hydroxide (193.84 g; TEAOH; Alfa Aesar, 35% H2O).
The reaction mixture was continuously stirred under an atmos-
phere of air. Then, a white precipitate formed after cooling the
flask in an ice bucket and was filtered using a Buchner apparatus.
Finally, the residue was crystallized from MeOH under reflux condi-
tions, then cooled in a freezer at À188C, filtered on a Buchner, and
dried at 110 8C in the stove for at least two days before use. CH2Cl2
(Carlo Erba 99.5%), CH3CN (SDS, Carlo Erba, HPLC gradient 99.9%),
and triethylamine (99%, Acros) were distilled from P2O5, CaH2, and
CaH2 respectively. H2(PDTP) was prepared as described in the
literature.[4a,14]
3
1H NMR (CD2Cl2, 300 MHz, 298 K): d=2.73 (s, 6H; CH3), 7.59 (d, J=
7.8 Hz, 4H; m-tol), 7.71–7.79 (m, 3H; m-and p-Ph), 8.12 (d, 3J=
3
7.8 Hz, 4H; o-tol), 8.20–8.23 (m, 2H; o-Ph), 8.88 (d, J=4.5 Hz, 2H;
3
3
b-Pyrr), 8.93 (d, J=4.5 Hz, 2H; b-Pyrr), 9.03 (d, J=4.3 Hz, 2H; b-
3
Pyrr), 9.35 (d, J=4.3 Hz, 2H; b-Pyrr), 10.19 ppm (s, 1H; b-Pyrr); UV/
Vis (CH2Cl2): lmax =420 (100), 558 (4.03), 595 nm (1.73); MALDI-TOF
+
C
MS (dithranol): m/z: 587.97 [M]
.
Electrosynthesis
Magnesium(II)
5-nitro-10,20-ditolyl-15-phenylporphyrin
(Mg(PDTPÀNO2)): The electrolysis was carried out under argon at
room temperature in CH3CN (170 mL) that contained TEAPF6
(0.1m), Mg(PDTP) (100 mg, 0.17 mmol), 2,6-lutidine (200 mL,
10 equiv), and NaNO2 (40 mg, 0.58 mmol) under vigorous stirring
(w=1350 rpm). The applied potential was Eapp =0.70 V versus SCE.
At the end of the electrolysis, 2 Faraday per mole of Mg(PDTP)
were transferred. The solution mixture was then evaporated to dry-
ness under reduced pressure. The resulting crude solid was dis-
solved in a minimum of CH2Cl2, and this solution was washed five
times with distilled water (750 mL) to remove the supporting elec-
trolyte. The organic phase was evaporated to dryness. The crude
product was then purified by column chromatography (alumina, 0
to 2% MeOH in CH2Cl2) and recrystallized from MeOH/H2O to give
Mg(PDTPÀNO2) in 91% yield (98 mg). 1H NMR (CD2Cl2, 300 MHz,
UV/Vis absorption spectra were recorded using a Varian Cary UV/
Vis spectrophotometer 50 scan using quartz cells (Hellma). In the
spectroelectrochemical experiments, a UV/Vis immersion probe
(Hellma, l=2 mm) was connected through a fiber optic to the
same spectrophotometer.
Mass spectra were obtained using a Bruker ProFLEX III spectrome-
ter (MALDI-TOF) with dithranol as a matrix or using a Bruker Micro-
ToF Q instrument in ESI mode.
3
NMR spectra were measured using a Bruker 300 MHz spectrometer
(Avance III Nanobay, Avance III, Avance II, respectively). The refer-
ence was the residual non-deuterated solvent.
298 K): d=2.72 (s, CH3; 6H), 7.59 (d, J=7.7 Hz, 4H; m-tol), 7.71–
3
7.81 (m, 3H; m-and p-Ph), 8.08 (d, J=7.4 Hz, 4H; o-tol), 8.16–8.20
3
(m, 2H; o-Ph), 8.82 (s, 4H; b-Pyrr), 8.98 (d, J=4.5 Hz, 2H; b-Pyrr),
All electrochemical manipulations were performed using Schlenk
techniques under an atmosphere of dry oxygen-free argon at
room temperature (T=(20Æ3)8C). The supporting electrolyte was
degassed under vacuum before use. Voltammetric analyses were
carried out in a standard three-electrode cell using an Autolab
PGSTAT 302N potentiostat connected to an interfaced computer
that employed Electrochemistry Nova software. A double-junction
SCE with background electrolyte between the two frits was used
as reference electrode. The auxiliary electrode was a platinum wire
in an independent compartment filled with the background elec-
trolyte and separated from the analyzed solution by a sintered
glass disk. For all voltammetric measurements, the working elec-
trode was a platinum disk electrode (Ø=2 mm). Under these con-
ditions, when operating in CH3CN (0.1m TEAPF6) or in CH2Cl2 (0.1m
TEABF4), the formal potential for the Fc+/Fc couple was found to
be +0.40 or +0.52 V versus SCE, respectively.
9.25 ppm (d, 3J=4.5 Hz, 2H; b-Pyrr); UV/Vis (CH2Cl2): lmax =426
+
C
(100), 565 (7.97), 619 nm (6.12); MS (ESI-MS): m/z: 634.21 [M+1]
.
5-Amino-10,20-ditolyl-15-phenylporphyrin (H2(PDTPÀNH2)): The
synthesis protocol was inspired by the work of J. Lessard et al.[21d]
In practice, the activated Devarda electrode (3 cm4 cm) was
placed in the cell that contained MeOH (170 mL) with H2O (1.5%)
and KOH (0.27m) under argon. The electrolysis was carried out
under argon at room temperature under vigorous stirring (w=
1350 rpm). The applied potential was Eapp =À1.20 V versus SCE to
generate hydrogen at the surface of the electrode for at least
20 min. After the addition of Mg(PDTPÀNO2) (70 mg) in one por-
tion, 6 Faradays per mole of Mg(PDTPÀNO2) were transferred at
À0.96 V versus SCE. At the end of the electrolysis, concentrated hy-
drochloric acid (5 mL) was added, and this mixture was stirred for
1 min. After evaporation of the solvent, the colored residue was
dissolved in CH2Cl2. The precipitated KCl was then removed by fil-
tration. The green filtrate was evaporated to dryness and neutral-
ized with saturated sodium acetate solution (100 mL). The mixture
was extracted with CH2Cl2. The organic phase was washed twice
Bulk electrolyses were performed in a three-compartment cell sep-
arated by glass frits of medium porosity using an Amel 552 poten-
tiostat coupled with an Amel 721 electronic integrator. A platinum
grid was used as the working electrode, a platinum wire spiral (l=
Chem. Eur. J. 2015, 21, 8281 – 8289
8287
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