A.C. Durrell et al. / Journal of Catalysis 310 (2014) 37–44
39
was in good agreement with the data previously reported in the lit-
erature [30].
combined, dried over sodium sulfate, and filtered, and the solvent
was evaporated under reduced pressure. Column chromatography
(SiO2, CH2Cl2–1% MeOH) was conducted. Due to the very small dif-
ference in polarity between the staring material (traces), the de-
sired compound, and a degradation product, small fractions were
collected and the purity of each fraction was determined using
1H NMR. Combination of the pure fractions gave the p-carboxy-
phenyl acac 5 as an off-white solid. Yield: 205 mg (0.93 mmol,
23%). The low yield reported here is due to important loss of the
material during the column chromatography purification step.
Furthermore, due to its thermal instability, compound 5 was
strictly stored at ꢀ20 °C. 1H NMR spectrum was in good agreement
with the data previously reported in the literature [20,31].
1H NMR (400 MHz, CDCl3): 16.73 (s, 1H), 8.16–8.13 (m, 2H),
7.35–7.31 (m, 2H), 1.91 (s, 6H).
1H NMR (400 MHz, CD3CN): 8.75 (s, 2H), 8.75–8.72 (m, 2H),
8.69 (d, J = 8.0 Hz, 2H), 8.37 (d, J = 8.8 Hz, 2H), 8.05 (td,
J1 = 7.7 Hz, J2 = 1.8 Hz, 2H), 7.39 (ddd, J1 = 7.4 Hz, J2 = 4.8 Hz,
J3 = 1.1 Hz, 2H).
2.1.4. Synthesis of 40-(4-nitrophenyl)-2,20:60,200-terpyridine (3)
This compound was prepared following the procedure reported
by Das et al. with minor modification [30]. A 250-mL round-bot-
tom flask was charged with 2.2 g of 1 (6.7 mmol), 1.7 g of 2
(6.7 mmol), 3.6 g of ammonium acetate (46.8 mmol), and 100 mL
of methanol. The mixture was purged with argon for 15 min then
refluxed under argon for 4 h, during which time an off-white solid
precipitated. After cooling down the mixture to room temperature,
the precipitate was collected by vacuum filtration and washed
with cold methanol (3 ꢁ 50 mL) to give the desired nitrophenyl
terpyridine 3 as a white solid. Yield: 1.85 g (5.2 mmol, 78%). 1H
NMR spectrum was in good agreement with the data previously re-
ported in the literature [30].
2.1.7. Synthesis of 40-(N-(4-(2,4-dioxopentan-3-
yl)phenyl)benamide)2,20:60,200-terpyridine (L)
This compound was prepared following the procedure reported
by McNamara et al. with minor modification [20]. A 100-mL
Schlenk tube was charged with 143 mg of p-carboxyphenyl acac
5 (0.65 mmol), 435 mg of DMAP on beads (3 mmol/g, 1.3 mmol),
126 mg of EDC (0.66 mmol), and 10 mL of dry dichloromethane.
The mixture was stirred at 0 °C for 15 min under argon. A solution
of 177 mg of aminophenylterpyridine 4 (0.55 mmol) in 4 mL of dry
DMF was added, and the reaction mixture was allowed to be stir-
red at room temperature under argon. The progression of the reac-
tion was monitored by 1H NMR. After 12 h at room temperature, a
conversion of 60% was reached, and no further evolution could be
observed. A solution of 100 mg of 5 (0.45 mmol) activated with
98 mg of EDC (0.51 mmol) in 2 mL of dry dichloromethane was
added to the reaction mixture, and the medium was further stirred
at room temperature, under argon, for 12 h. 1H NMR analysis indi-
cated that the conversion then reached 85%. A second aliquot of
100 mg of 5 (0.45 mmol) activated with 98 mg of EDC (0.51 mmol)
in 2 mL of dry dichloromethane was added to the reaction mixture,
and the medium was further stirred at room temperature for 12 h
after which time no traces of the starting aminophenylterpyridine
4 could be observed by 1H NMR. The reaction mixture was filtered,
and the beads washed thoroughly with 50 mL of dichloromethane.
The combined organic phases were extracted with water
(5 ꢁ 50 mL), NaHCO3 (5% aqueous, 1 ꢁ 50 mL), and saturated NH4-
Cl (1 ꢁ 50 mL). The organic layer was collected, dried over sodium
sulfate, filtered, and the solvent was evaporated. Successive recrys-
tallization from CH2Cl2–hexanes and CH2Cl2–diethyl ether yielded
the desired ligand L as a white solid. Yield: 65 mg (0.12 mmol,
22%). Due to the thermal instability of L, this compound was
strictly stored at ꢀ20 °C. 1H NMR spectrum was in good agreement
with the data previously reported in the literature [20].
1H NMR (400 MHz, DMSO-d6): 8.71 (ddd, J1 = 4.8 Hz, J2 = 1.8 Hz,
J3 = 0.9 Hz, 2H), 8.67 (s, 2H), 8.60 (td, J1 = 8.0 Hz, J2 = 1.0 Hz, 2H),
8.35–8.31 (m, 2H), 8.14–8.10 (m, 2H), 8.02–7.97 (m, 2H), 7.49
(ddd, J1 = 7.5 Hz, J2 = 4.8 Hz, J3 = 1.2 Hz, 2H).
2.1.5. Synthesis of 40-(4-aminophenyl)-2,20:60,200-terpyridine (4)
This compound was prepared following the procedure reported
by Das et al. with minor modification [30]. In a 500-mL round-bot-
tom flask, 0.95 g of nitrophenyl terpyridine 3 (2.7 mmol), 250 mg
of palladium on carbon (5% Pd-loading), and 200 mL of absolute
ethanol were added. The resulting suspension was purged with ar-
gon for 15 min and brought to reflux under argon. 3.4 mL of hydra-
zine monohydrate (3.5 g, 70 mmol) was added, and the mixture
further refluxed under argon for 2 h, during which time the nitro-
phenyl terpyridine 3 dissolved completely. After cooling down the
medium to room temperature, the catalyst was removed by vac-
uum filtration over a Celite short plug and washed with dichloro-
methane (3 ꢁ 100 mL). The filtrate was concentrated under
reduced pressure until white needles started to crystallize out of
the medium (ꢂ75 mL). The saturated solution was then stored at
4 °C overnight. The grown crystals were recovered by vacuum fil-
tration and washed with cold ethanol (3 ꢁ 50 mL). The aminophe-
nyl terpyridine 4 was obtained as white needles. Yield: 547 mg
(1.7 mmol, 63%). 1H NMR spectrum was in good agreement with
the data previously reported in the literature [30].
1H NMR (400 MHz, DMSO-d6): 8.73 (ddd, J1 = 4.8 Hz, J2 = 1.8 Hz,
J3 = 0.9 Hz, 2H), 8.63 (td, J1 = 8.0 Hz, J2 = 1.0 Hz, 2H), 8.61 (s, 2H),
8.02–7.98 (m, 2H), 7.69–7.63 (m, 2H), 7.49 (ddd, J1 = 7.5 Hz,
J2 = 4.8 Hz, J3 = 1.2 Hz, 2H), 6.74–6.71 (m, 2H), 5.60 (s, 2H).
1H NMR (400 MHz, CDCl3): 16.72 (s, 1H), 8.75 (s, 2H), 8.74 (ddd,
J1 = 4.8 Hz, J2 = 1.8 Hz, J3 = 0.9 Hz, 2H), 8.68 (td, J1 = 8.0 Hz,
J2 = 1.0 Hz, 2H), 7.99–7.93 (m, 5H), 7.91–7.87 (m, 2H), 7.85–7.82
(m, 2H), 7.38–7.34 (m, 4H), 1.92 (s, 6H).
2.1.6. Synthesis of 3-[4-Benzoic acid]pentane-2,4-dione (5)
This compound was prepared following the procedure reported
by Jiang et al. with minor modification [31]. In a 100-mL Schlenk
tube, 1.0 g of 4-iodobenzoic acid (4.0 mmol), 90 mg of L-proline
(0.78 mmol), 3.3 g of cesium carbonate (10.1 mmol), and 15 mL
of anhydrous dimethylsulfoxide were added. The suspension was
purged with argon for 30 min, and 1.5 mL of 2,4-pentadione
(1.2 g, 12 mmol) was added. The mixture was further purged with
argon for 5 min, and 75 mg of freshly recrystallized copper iodide
(0.4 mmol) was added. The mixture was stirred at 85 °C under ar-
gon for 12 h. After cooling down to room temperature, the reaction
mixture was poured into 100 mL of water. The aqueous phase was
washed with ethyl acetate (3 ꢁ 50 mL, discarded). The pH of the
aqueous phase was then adjusted to pH ꢂ 2 with the slow addition
of 12 M hydrochloric acid, and the medium was further extracted
with ethyl acetate (3 ꢁ 50 mL). The latter organic layers were
2.1.8. Synthesis of 20,70-Dihydrodichlorofluorescein (H2DCF)
The compound was prepared following a modification of the
procedure reported by Brandt and Keston [32]. To a 250-mL
round-bottom flask, 1 g of 20,70-dichlorofluorescein (2.5 mmol)
was added to 40 mL of MeOH. The flask was heated to reflux and
20 mL glacial HOAc was added. Zinc dust was added to the solution
in five 0.6 g portions over 10 min. The solution was filtered to re-
move the solid, the filtrate was returned to reflux, five additional
0.6 g portions of zinc dust were added, and the solution was heated
at reflux for an additional 1 h, during which time the solution be-
came colorless. Following reflux, the solution was filtered and al-
lowed to cool. To the filtrate, 300 mL DI H2O was added, forming