3
2
G. Romanazzi et al. / Molecular Catalysis 446 (2018) 31–38
hydride, that is a cheap, easy-handling and ready available reducing
agent with extensive applications in organic synthesis [18].
lyzed by STEM image analysis using the ImageJ software (freeware
2.2. Catalyst preparation
2
. Experimental section
The supported catalyst (Ni-pol) was prepared by calci-
2.1. General considerations
nation under nitrogen of a polymer supported Ni(II) com-
plex (Ni(AAEMA) -pol), which in turn was obtained by co-
2
Tap water was de-ionized by ionic exchange resins (Millipore)
polymerization of the polymerizable complex Ni(AAEMA)2.
before use. All other chemicals were purchased from commercial
sources and used as received. Nickel content in Ni-pol was assessed
after sample mineralization by atomic absorption spectrometry
using a Perkin–Elmer 3110 instrument. The experimental error on
the nickel percentage was ± 0.3. Mineralization of Ni-pol prior to Ni
analyses was carried by microwave irradiation with an ETHOS E-
TOUCH Milestone applicator, after addition of HCl/HNO3 (3:1 v/v)
solution (12 mL) to each weighted sample. Microwave irradiation
2.2.1. Ni(AAEMA)2
To a solution of KOH (579 mg, 10.3 mmol) in ethanol (10 mL), 2-
(acetoacetoxy)ethyl methacrylate (HAAEMA) (2.211 g, 10.3 mmol)
was added and left under stirring at room temperature for 5 min.
The resulting solution was added to a solution of Ni(NO ) · 6 H O
3
2
2
(1.5 g, 5.16 mmol) in ethanol (15 mL), causing the sudden precip-
itation of Ni(AAEMA)2 as a pale green solid. After 1 h stirring,
the solid was filtrated and washed with water (3 × 5 mL), ethanol
(3 × 5 mL) and pentane (3 × 5 mL), and dried overnight under vac-
up to 1000 W was used, the temperature being ramped from rt to
◦
2
20 C in 10 min and the sample being held at this temperature for
1
0 min. After cooling to room temperature, the digested Ni-pol was
uum. Anal. Calc. for NiC20H O : C, 45.00; H, 4.92; Ni, 19.97. Found:
26 10
diluted to 1000 mL before submitting to Graphite Furnace Atomic
Absorption Spectrometric nickel determination.
GC–MS data (EI, 70 eV) were acquired on a HP 6890 instru-
ment using a HP-5MS cross-linked 5% pphenyl methyl siloxane
C, 44.50; H, 4.99; Ni, 19.76. HRMS: (ESI, CH OH, positive ion mode)
3
m/z: calcd. for NiC20H27O10 [M + H]+ 485.0952; found 485.0954. IR
−
1
(cm ): 1720 (s), 1635 (s), 1623 (s), 1521 (s), 1385 (vs), 1259 (vs),
1161 (vs), 977 (m), 785 (m). UV-vis (CH Cl ): 280 nm ( = 10660
2
2
−
1
−1
−1
−1
◦
(
30.0 m × 0.25 mm × 0.25 m) capillary column coupled with a
mol L cm ), 227 nm ( = 4800 mol L cm ). m.p. = 120.3± 0.4 C.
mass spectrometer HP 5973. The products were identified by com-
parison of their GC–MS features with those of authentic samples.
Reactions were monitored by GLC or by GC–MS analyses. GLC anal-
ysis of the products was performed using a HP 6890 instrument
equipped with a FID detector and a HP-1 (Crosslinked Methyl Silox-
ane) capillary column (60.0 m × 0.25 mm × 1.0 m). Conversions
and yields were calculated by GLC analysis by using biphenyl as
internal standard, or by column chromatography using silica gel
and n-hexane/ethyl acetate as the eluent.
Yield: 2.01 g, 80%.
2.2.2. Ni(AAEMA) -pol
2
−
Ni(AAEMA)2 (4.0 mmol, 2.0 g) [AAEMA = deprotonated form
of 2-(acetoacetoxy) ethyl methacrylate] was dissolved in N,N
−dimethylformamide (DMF, 5 mL) and the resulting solution was
added of a mixture of N,N’-methylenebisacrylamide (1.2 mmol,
0.186 g) and N,N −dimethylacrylamide (43.2 mmol, 4.434 g) in DMF
◦
(6 mL) and heated at 120 C under vigorous stirring. After 1 h from
FT-IR spectra (in KBr pellets) were recorded on a Jasco FT/IR
200 spectrophotometer. Elemental analyses were obtained on a
EuroVector CHNS EA3000 elemental analyser using acetanilide as
analytical standard material. The high-resolution mass spectrom-
etry (HRMS) analysis was performed using a Bruker microTOF Q
II mass spectrometer equipped with an electrospray ion source
the addition of azaisobutyronitrile (5 mg), the green jelly solid
which formed in the reaction vessel was filtered off, washed with
acetone and diethyl ether, dried under vacuum, kept overnight in
4
◦
oven at 95 C and grinded with a mortar to give a pale green powder.
Yield: 4.04 g of polymer supported Ni(AAEMA)2 [Ni(AAEMA) -pol].
2
Elemental Analysis (found): Ni 3.69; C 57.06; H 7.94; N 9.91%. IR
−
1
operated in positive ion mode. The sample solutions (CH OH) were
(cm ): 3477 (bs), 2923 (bs), 1720 (s), 1622 (s), 1527 (s), 1256 (vs),
1144 (vs), 1355 (s), 780 (m).
3
introduced by continuous infusion with a syringe pump at a flow
−1
rate of 180 L min . The instrument was operated with end-plate
offset and capillary voltages set to −500 V and −4500 V respec-
2.2.3. Ni-pol
tively. The nebulizer pressure was 0.4 bar (N ), and the drying gas
The as-obtained Ni(AAEMA) -pol was put in a tube furnace,
2
2
−
1
◦
−1
◦
(
N ) flow rate was 4.0 L min . Capillary exit and skimmer volt-
ramped at 10 C min in flowing N to 300 C, and kept at the final
2
2
ages were 90 V and 30 V, respectively. The drying gas temperature
was set at 180 C. The calibration was carried out with a sodium
temperature for 30 min, yielding a black powder referred to as Ni-
pol. Yield: 3.83 g. Elemental Analysis (found): Ni 5.35; C 56.66; H
9.20; N 11.54%. IR (cm ): 3482 (bs), 2930 (bs), 1720 (s), 1631 (s),
1495 (m), 1402 (m), 1258 (m), 1144 (s), 1053 (m).
◦
−
1
formate solution (10 mM NaOH in isopropanol/water 1:1 (+0.2%
HCOOH)) and the software used for the simulations was Bruker
Daltonics DataAnalysis (version 4.0). Thermogravimetric analyses
−
1
(
TGA) were performed in a nitrogen flow (40 mL min ) with a
2.3. General experimental procedure for the reduction of
nitroarenes catalyzed by Ni-pol
◦
Perkin-Elmer Pyris 6 TGA in the range from 30 to 800 C with a heat-
ing rate of 10 C min . Triplicate TGA runs have been performed
to ensure reproducibility.
◦
−1
0.5 mmol of nitroarene, 10.2 mg of Ni-pol (Ni%w = 5.35, 9.3
−
3
Surface morphology was investigated on a selected piece of
Ni-supported catalyst considered to be representative of the mate-
rial. Nova NanoSEM 450 manufactured by FEI Company, USA, was
used to perform FESEM analysis on the selected samples. Tiny
plate-like of the powdered catalyst were mounted on TEM cop-
per grids, and gold-palladium sputtered (K550, Emitech Ltd, United
Kingdom). Scanning Transmission Electron Microscopy (STEM)
Detector allowed transmission images to be taken at 30 keV, lower
energy level with respect to commonly used TEM, beam voltage
10 mmol of Ni) and 10.0 mmol of sodium borohydride were
stirred under nitrogen at room temperature in 2.5 mL of double
deionized water and 2.5 mL of diethyl ether for the appropriate
amount of time, using a three-necked flask equipped by a gas bub-
bler to discharge the hydrogen excess produced during reaction.
The progress of the reaction was monitored by GLC. After com-
pletion of the reaction, the reaction mixture was centrifuged to
separate the catalyst. The solid residue was first washed with deion-
ized water and then with acetone and diethyl ether to remove any
traces of organic material. The filtrate containing the reaction mix-
ture was extracted with ethyl acetate (3 × 5 mL) and then dried
1
1
00–200keV. Resolution limits of this microscope are remarkable:
.4 nm @ 1 kV in high vacuum mode. The particle sizes were ana-