718
M. Ulusoy et al.
catalysts for the catalytic conversion of CO2 into valuable
organic products were published in recent years [20–22].
This study aims at obtaining new coordinative com-
pounds with similar properties. Therefore, the present
manuscript describes the synthesis, structural character-
ization and the catalytic activity of three new steric
hindered Schiff base ligands (L1H=N-[allylamine]-3,5-di-t-
butyl salicylaldimine, L2H=N-[2-amino-5-methyl pyridine]
-3,5-di-t-butyl salicylaldimine and L3H=N-[2-amino-6-
methyl pyridine]-3,5-di-t-butyl salicylaldimine) involving
nitrogen and oxygen donor sites and their Cu(II) metal
complexes derivatives with general formula presented
Scheme 2.
time a yellow solid precipitated from solution which was
isolated by filtration, washed with cold methanol and dried
vacuum. Then, the products were recrystallized from eth-
anol. The products are soluble in common solvents such as
CHCl3, CH3CH2OH, DMF and DMSO.
For (L1H) ligand: Color: Yellow; m.p: 102 ꢁC; Yield
(%): 88; Anal. Calc. for C18H27NO (F.W: 273.4 g/mol): C,
79.07; H, 9.95; N, 5.12. Found: C, 79.12; H, 9.89; N,
5.15%. 1H NMR (400 MHz, CDCl3, Me4Si, ppm):
d = 13.62 (s, 1H, –OH, D-exchangeable), d = 8.21 (s, 1H,
HC=N), d = 7.41 (s, 1H, Ar–CH), d = 7.19 (s, 1H,
Ar–CH), d = 6.04–5.98 (m, 1H, C=CH), d = 5.28–5.17
(m, 2H, C=CH2), d = 4.22 (s, 2H, N–CH2), d = 1.43 (s,
9H, C–CH3) and d = 1.26 (s, 9H, C–CH3). IR (KBr pellets,
t
max/cm-1): 3520–2480 t(OH…N), 3044 t(Ar–CH), 2955-
2 Experimental
2785 t(Alip–CH), 1630 t(C=N), 1458–1432 t(C=C), 1174
t(C–O). UV–Vis (kmax, nm, * = shoulder peak): 240, 264,
331 and 417* (in CHCl3).
2.1 Materials and Measurements
For (L2H) ligand: Color: Yellow; m.p: 144 ꢁC; Yield
(%): 91; Anal. Calc. for C21H28N2O (F.W: 324.5 g/mol):
C, 77.74; H, 8.70; N, 8.63. Found: C, 77.72; H, 8.64; N,
8.57%. 1H NMR (400 MHz, CDCl3, Me4Si, ppm):
d = 13.94 (s, 1H, –OH, D-exchangeable), d = 9.48 (s, 1H,
HC=N), d = 8.32 (s, 1H, Ar–CH), d = 7.59–7.56 (d, 1H,
J=12, Ar–CH), d = 7.47 (s, 1H, Ar–CH), d = 7.34 (s, 1H,
Ar–CH), d = 7.21 (s, 1H, Ar–CH), d = 2.41 (s, 3H,
Ar–CH3), d = 1.46 (s, 9H, C–CH3) and d = 1.28 (s, 9H,
C–CH3). IR (KBr pellets, tmax/cm-1): 3629 t(OH), 3052
t(Ar–CH), 2958–2742 t(Alip–CH), 1613 t(C=N),
1471–1458 t(C=C), 1170 t(C–O). UV–Vis (kmax, nm,
* = shoulder peak): 241, 281, 317, 368, 484* (in CHCl3).
For (L3H) ligand: Color: Yellow; m.p: 106 ꢁC; Yield
(%): 93; Anal. Calc. for C21H28N2O (F.W: 324.5 g/mol):
C, 77.74; H, 8.70; N, 8.63. Found: C, 77.68; H, 8.67; N,
8.66%. 1H NMR (400 MHz, CDCl3, Me4Si, ppm):
d = 13.96 (s, 1H, –OH, D-exchangeable), d = 9.81 (s, 1H,
HC=N), d = 7.81–7.79 (d, 1H, J = 12, Ar–CH), d = 7.60
(s, 1H, Ar–CH), d = 7.47 (s, 1H, Ar–CH), d = 7.35 (s, 1H,
Ar–CH), d = 7.22 (s, 1H, Ar–CH), d = 2.38 (s, 3H,
Ar–CH3), d = 1.47 (s, 9H, C–CH3) and d = 1.29 (s, 9H,
C–CH3). IR (KBr pellets, tmax/cm-1): 3580–2528 t(OHꢀꢀꢀN),
3048 t(Ar–CH), 2954–2749 t(Alip–CH), 1612 t(C=N),
1550–1457 t(C=C), 1171 t(C–O). UV–Vis (kmax, nm,
* = shoulder peak): 241, 279, 317, 368, 480* (in CHCl3).
All reagents and solvents were of reagent-grade quality and
obtained from commercial suppliers (Aldrich or Merck).
The elemental analyses were carried out in the Laboratory
of the Scientific and Technical Research Council of Turkey
(TUBITAK). IR spectra were recorded on a Perkin Elmer
Spectrum 100 FT-IR Spectrometer as KBr pellets. 1H-NMR
spectra were recorded on a Varian AS-400 MHz instrument
CDCl3 at room temperature. Chemical shifts were given in
parts per million from tetramethylsilane. Magnetic Sus-
ceptibilities were determined on a Sherwood Scientific
Magnetic Susceptibility Balance (Model MK1) at room
temperature (20 ꢁC) using Hg[Co(SCN)4] as a calibrant;
diamagnetic corrections were calculated from Pascal’s
constants [23]. Electronic spectral studies were conducted
on a Varian Carry 100 model UV–visible spectrophotom-
eter at the wavelength range of 200–1100 nm. Melting
points were measured in open capillary tubes with an
Electrothermal 9100 melting point apparatus and uncor-
rected. Catalytic tests were performed in a PARR 4843
50 mL stainless pressure reactor.
2.2 Synthesis of Ligands (L1H, L2H and L3H):
N-[allylamine]-3,5-di-t-butyl salicylaldimine (L1H), N-[2-
amino-5-methyl pyridine]-3,5-di-tert-butyl salicylaldimine
(L2H) and N-[2-amino-6-methyl pyridine]-3,5-di-tert-butyl
salicylaldimine (L3H) ligands were synthesized by the
reaction of 4.3 mmol (1.0 g) 3,5-di-tert-butyl-2-hydro-
xybenzaldehyde in 30 mL absolute methanol with
4.3 mmol (0.25 g) allylamine for L1H, 4.3 mmol (0.46 g)
2-amino-5-methyl-pyridine for L2H and 4.3 mmol (0.46 g)
2-amino-6-methyl-pyridine for L3H in 15 mL absolute
methanol. Also, 3–4 drops of formic acid were added as
catalyst. The mixtures were refluxed for 3 h. During this
2.3 Synthesis of the Cu(II) Metal Complexes
0.50 g, 1.84 mmol ligand (L1H), 0.50 g, 1.54 mmol ligand
(L2H) or 0.50 g, 1.54 mmol ligand (L3H) was dissolved in
methanol (30 cm3). A solution of 0.16 g, 0.92 mmol of the
metal salt [CuCl2ꢀ2H2O] for mononuclear [Cu(L1)2] com-
plex and 0.26 g, 1.54 mmol of the metal salt [CuCl2ꢀ2H2O]
for multinuclear [Cu3(L2,3)4]Cl2ꢀCuCl2 complexes in
123