184
S. Chohan et al. / Inorganica Chimica Acta 447 (2016) 183–191
complex was transferred onto the electrode surfaces which were
then dried for 1 h at 100 °C. The CMEs were rinsed with DCM,
ethanol (EtOH) and ultrapure water prior to use. A 1 mM solution
2. Experimental
2.1. Materials
of L-cysteine was prepared in pH 4 buffer for electrocatalysis.
Tetra-4-(7-oxy-4-trifluoromethylcoumarin phthalocyaninato)Co
(II) (CoPc-cou, 5) used in the preparation of CMEs was synthesized
as previously reported [31].
4-Nitrophthalonitrile, tetrahydropyran-2-methanol, 2-furan-
methanethiol, potassium carbonate, cobalt(II) chloride, 1,8-diaz-
abicyclo[5.4.0]undec-7-ene (DBU) and electrochemical analysis
grade tetrabutylammoniumtetrafluoroborate (TBABF4) were pur-
chased from Sigma–Aldrich and used without further purification.
Organic solvents, phosphorus pentoxide (P2O5), molecular sieves
(4 Å), aluminum oxide (alumina), silicon dioxide (silica) for column
chromatography and silica plates for thin layer chromatography
were purchased from Merck SA. Dimethylformamide (DMF) used
in ligand syntheses, UV–Vis spectroscopy and electrochemical
experiments was dried and stored over molecular sieves. All metal
complexes and ligands were stored over P2O5. Ultrapure water was
obtained from an ElgaPurelab Ultra system.
2.4. Synthesis of 4-(tetrahydropyran-2-methoxy)phthalonitrile (1)
A
mixture of 4-tetrahydropyran-2-methanol (0.653 cm3,
5.78 mmol) and potassium carbonate (2.30 g, 16.64 mmol) was
stirred in anhydrous dimethylformamide (DMF) (30.0 cm3) at
room temperature under N2 for 1 h. Thereafter, to the resultant
reaction mixture, 4-nitrophthalonitrile (1.00 g, 5.78 mmol) was
added. The reaction mixture was removed after 48 h and poured
into 300 cm3 of a water–ice slurry. The resulting precipitate was
filtered and purified via column chromatography using a 1:1 (v:v)
ethyl acetate:hexane solvent system to produce a white com-
2.2. Equipment
pound. Yield: 20%; m.p (°C): 62.3–62.9; FT-IR (
(C„N) 2240, (CAOAC) 1252, 1090, 1027; UV–Vis (DMF, kmax (e,
m m
max/cmꢀ1):
m
FTIR spectra were recorded using a Bruker Alpha FTIR spectrom-
eter equipped with an ATR platinum Diamond 1 reflectance acces-
sory. NMR experiments were conducted in d6-DMSO using a
400 MHz Bruker NMR spectrometer. UV–Vis spectroscopy was car-
ried out using a Perkin-Elmer Spectrum 25 containing quartz cuv-
ettes having a path length of 1 cm. All UV–Vis spectra were
recorded in N,N0-dimethylformamide. Melting points were
recorded using a Stuart SMP3 melting point apparatus. Elemental
analysis was carried out using a CHNS-O Flash 2000 Organic Ele-
mental Analyser. Mass spectrometry (MS) was conducted in both
the positive and negative modes via direct injection of the samples
into a Waters Micromass LCT Premier MS instrument equipped
with an electrospray ionization (ESI) source and a time-of-flight
(TOF) mass analyzer. Single crystal X-ray diffraction (XRD) studies
were conducted using a Bruker Apex Duo equipped with an Oxford
Instruments Cryojet operating at 120( 2) or 100( 2) K and an
Incoatec microsource operating at 30 W. The XRD experimental
parameters, refinement details of the solid-state structures as well
as their descriptions can be found in the online supporting infor-
mation documents. Voltammetric studies were conducted using
an Autolab Potentiostat equipped with a three-electrode system:
a Pt or glassy carbon working electrode, a pseudo Ag|AgCl refer-
ence electrode and a Pt counter electrode. The Autolab Nova 1.7
software was used for operation of the potentiostat and data anal-
ysis. A GCE was used for all electrocatalytic experiments. Spectro-
electrochemical experiments were undertaken using a Specac
optically transparent thin-layer electrochemical (OTTLE) cell.
Mꢀ1cmꢀ1)): 306 nm (13081), 299 (12647); 1H NMR (ppm): 8.04
(d, 1H, H14), 7.78 (d, 1H, H13), 7.47 (d, 1H, H12), 4.06–4.14 (m,
2H, H10, H11), 3.85–3.92 (m, 1H, H8), 3.62–3.70 (m, 1H, H9),
3.35–3.42 (m, 1H, H7), 1.78–1.87 (m, 1H, H4), 1.59–1.67 (m, 1H,
H2), 1.42–1.59 (m, 3H, H3, H5, H6), 1.26–1.38 (m, 1H, H1); 13C
NMR (ppm): 22.92, 25.87, 27.67, 67.74, 72.57, 75.41, 106.38,
116.20, 116.69, 116.74, 120.57, 120.83, 136.20, 162.48. Molecular
mass (m/z): Calc.: 242.27. Found: 265.10 [M+Na]+. Anal. Calc. for
C14H14N2O2: C, 69.41; H, 5.82; N, 11.56. Found: C, 64.32; H, 4.91;
N, 10.73%.
2.5. Synthesis of 4-(furan-2-methylthio)phthalonitrile (2)
A mixture of 4-nitrophthalonitrile (1.00 g, 5.78 mmol), 2-furan-
methanethiol (0.583 cm3, 5.78 mmol) and potassium carbonate
(2.30 g, 16.64 mmol) was added to anhydrous DMF (30.0 cm3).
The reaction mixture was stirred at 90 °C under N2 for 48 h after
which it was cooled to room temperature and poured into
300 cm3 of a water–ice slurry. The resulting white precipitate
was filtered and recrystallized from hot methanol (MeOH). Yield:
80%; m.p (°C): 127.8–128.5; FT-IR (
(CAOAC) 1249, 1061; UV–Vis (DMF, kmax
m
max/cmꢀ1):
, Mꢀ1cmꢀ1)): 323 nm
m(C„N) 2228, m
(e
(76752), 295 (137469); 1H NMR (ppm): 8.15 (d, 1H, H7), 8.01 (d,
1H, H8), 7.85 (d, 1H, H6), 7.62–7.59 (m, 1H, H3), 6.42–6.38 (m,
2H, H1, H2), 4.56 (s, 2H, H4, H5); 13C NMR (ppm): 28.10, 109.37,
110.73, 111.23, 115.52, 116.07, 116.49, 131.40, 131.47, 131.19,
143.58, 145.85, 149.77. Molecular mass (m/z): Calc.: 240.28.
Found: 263.03 [M+Na]+. Anal. Calc. for C13H8N2OS: C, 64.98; H,
3.36; N, 11.66; S, 13.34. Found: C, 65.10; H, 3.36; N, 11.64; S,
13.05%.
2.3. Electrochemical methods
All electrochemical studies on the metal complexes were
conducted in deoxygenated DMF solutions containing 0.1 M
equivalents of tetrabutylammoniumtetrafluoroborate (TBABF4) as
a supporting electrolyte. The Pt electrode surface was regenerated
between voltammetric scans by polishing over a slurry of alumina
and ultra-pure water on a diamond polishing pad followed by
rinsing with ultra-pure water and anhydrous DMF. The GCE was
polished over alumina on Buehler and diamond polishing pads,
rinsed in Millipore water and ultrasonicated in methanol (MeOH)
for 2 min prior to use. Square wave voltammetry (SWV) was con-
ducted by setting the step potential at 4 mV, the amplitude at
20 mV and the frequency at 25 Hz.
2.6. Synthesis of tetra-4-(tetrahydropyran-2-methoxyphthalocyaninato)
Co(II) (CoPc-thp, 3)
A
mixture of 1 (0.125 g, 0.516 mmol), CoCl2 (0.0167 g,
0.129 mmol) and DBU was heated with stirring in n-pentanol
(20.0 cm3) at 160 °C under nitrogen for 16 h. The reaction mixture
was then cooled to room temperature and n-hexane was added
drop-wise to induce precipitation. The precipitate was filtered off
using a millipore filtration setup and then washed with water,
MeOH, EtOH, hexane and acetonitrile. The desired product was
thereafter recovered via column chromatography using a 1:10 (v:
v) tetrahydrofuran (THF):CHCl3 solvent system. Yield: 15%; IR
Adsorption of the MPcs onto a GCE was achieved via the drop-
dry method. Concentrated solutions of the metal complexes were
prepared in dichloromethane (DCM) and a drop of each metal
(
m
max/cmꢀ1):
(DMF, kmax
m
e
(C@N) 1601,
m(CAOAC) 1232, 1123, 1088; UV–Vis
(
, Mꢀ1cmꢀ1)): 667 nm (285321), 330 nm (189512),