Transit Met Chem
A few studies on the utilization of iron-based catalysts
for the coupling reaction of epoxids and carbon dioxide
have been reported [31–33]. Rieger and co-workers
recently described the successful application of an octa-
hedral iron(II) complex of a tetradentate nitrogen ligand,
([N,N-bis(quinolin-2-ylmethylene)-1,2-cyclohexanedi-
amine]iron(II) chloride, for the conversion of propylene
oxide and CO2 to cyclic propylene carbonate in relatively
high yields (82–100%, at 100 °C and 15 bar of CO2) [34].
Furthermore, Repo et al. reported on the application of
bis(phenoxyiminato)Fe(III)-based complexes as catalysts
for coupling of CO2 with different epoxides using DMF as
spectrophotometer. GC–MS data were obtained on a Var-
ian CP-3800 GC instrument with a Varian Saturn 2100 T
mass spectrometer.
Synthesis of free ligands
N,N0-o-phenylenebis(salicylideneimine) [37] (7), N,N0-o-
phenylenebis(5-chlorosalicylideneimine) (8), N,N0-o-phe-
nylenebis(4-diethylaminesalicylideneimine) (9), N,N0-4,5-
dichloro-o-phenylenebis(salicylideneimine) (10) and N,N0-
4,5-dimethyl-o-phenylenebis(salicylideneimine) (11) were
obtained by a common procedure, as follows.
solvent.
The
bis(N-methylsalicylidene-2-phenylethy-
A solution of salicylaldehyde (1), 5-chlorosalicylalde-
hyde (2) or 4-(diethylamino)-salicylaldehyde (3) (16 mmol)
in ethanol (10.0 ml) was added dropwise to a solution of the
desired amine (4–6) (8 mmol) in the same solvent
(10.0 ml). The mixture was stirred at room temperature for
3 h, during which time a precipitate was formed. The pro-
duct was filtered out, washed with ethanol (2 9 10 ml) and
petroleum ether (3 9 10 ml) and dried in vacuum.
lamine)iron(III)chloride-based catalyst gave cyclic styrene
carbonate with high conversion (70%) under optimized
reaction conditions (solvent, DMF; time, 7 h; 145 °C and
10 bar of CO2) [35].
We recently reported on the utilization of iron(III)
complexes containing bis(salicylaldimine) ligands for the
coupling reactions of carbon dioxide and styrene epoxide
[36]. The salicylidene-based iron(III) complexes (TON up
to 1767) were found to be the most active toward the
catalytic reaction compared with the corresponding Cr(III)-
and Co(III)-based catalyst systems.
7: Yield: 3.42 g (50%). Color: yellow. Mp: 162–164 °C.
EA: found (calcd.)(%): C, 75.87 (75.93); H, 4.77 (5.10); N,
.
8.90 (8.86). IR (t C=N), 1636 cm-1 1H NMR(dppm)
(DMSO-d6, 300 MHz): d6.95(m, 2H), 7.07(d, 2H), 7.27
(m, 2H)., 7.38 (m, 6H), 13.05 (s, 2H). 13C-{H1} NMR
(DMSO-d6, 75 MHz): d = 163.8 (HC=N) [38].
8: Yield: 0.45 g (36%). Color: yellow. Mp: 148–150 °C.
EA: found (calcd.)(%): C, 63.09 (62.35); H, 3.26 (3.66); N,
7.47 (7.27). IR (tC=N) 1616 cm-1. 1H NMR (dppm)
(CDCl3, 300 MHz): d = 3.38(m, 5H), 3, 42(m, 5H), 6.25
(m, 2H), 7.18(m, 4H), 7.21 (m, 4H), 13.65 (s, 1H). 13C-
{H1} NMR (CDCl3, 75 MHz): d = 164.5 (HC=N).
9: Yield: 0.89 g (77%). Color: dark yellow. Mp:
128–130 °C. EA: found (calcd.) (%): C, 73.38 (73.33); H,
7.90 (7.47); N, 11.01 (12.22). IR (tC=N) 1624 cm-1. 1H
NMR (d ppm) (CDCl3, 300 MHz): d = 7.02(d, 2H),
7.25(m, 3H), 7.37 (m, 2H), 7.41(m, 4H), 8.59 (s, 2H), 13.01
(s, 1H).13C-{H1} NMR (CDCl3, 75 MHz): d = 162.5
(HC=N).
In the present work, we describe the synthesis of new
iron(III) complexes (12–15) bearing tetradentate Schiff
base ligands and their application as catalyst precursors for
the coupling of styrene oxide with carbon dioxide. For the
sake of comparison, the corresponding Co(III) complexes
(16–18) were also prepared. The electronic effects of the
substituents on the activities of the catalysts were evalu-
ated. In addition, the catalytic coupling of the epoxides,
1-butene oxide, cyclohexene oxide and propylene oxide
with CO2 was investigated.
Experimental
The starting materials iron(II) acetate, cobalt(II) acetate,
4,5-dimethyl-o-phenylenediamine,
4,5-dichloro-o-
10: Yield: 1.78 g (81%). Color: green. Mp: 190–192 °C.
EA: found (calcd.)(%): C, 61.52 (62.35); H, 3.97 (3.66); N,
6.07 (7.27). IR (tC=N) 1615 cm-1. 1H NMR (d ppm)
(CDCl3, 300 MHz): d = 6.97(s, 4H), 7.07(d, 4H), 7.28 (s,
4H), 7.36 (s, 4H), 7.42 (s, 4H), 8.68 (s, 2H), 12.63 (s,
1H). 13C-{H1} NMR (CDCl3, 75 MHz): d = 164.7
(HC=N).
phenylenediamine, 5-chlorosalicylaldehyde and 4-(diethy-
lamino)-salicylaldehyde, the epoxides and tetrabutylam-
monium bromide (Bu4NBr) were purchased from Aldrich.
o-Phenylenediamine was purchased from ACROS and
salicylaldehyde (98%) from Alfa Aesar. All chemicals
were used as received without further purification.
Elemental analysis was performed using a EURO EA
3000 instrument at the Hashemite University. 1H NMR
spectra were recorded on a Bruker spectrometer operating
at 300 MHz using CDCl3 as solvent with TMS as an
internal standard. 13C NMR spectra were obtained on a
Bruker spectrometer operating at 75 MHz. Infrared spectra
(KBr) were measured on a Nicolet Magna-IR 560
11: Yield: 2.01 g (79%). Color: yellow. Mp:
139–141 °C. EA: found (calcd.)(%): C, 77.22 (76.72); H,
5.30 (5.85); N, 8.05 (8.13). IR (tC=N) 1610 cm1. 1H NMR
(d ppm) (CDCl3, 300 MHz): d = 6.93(m, 2H), 7.06(d,
4H), 7.28 (s, 4H)., 7.35 (m, 4H), 7.40 (s, 4H), 8.65 (s, 2H),
13.19 (s, 1H).13C-{H1} NMR (CDCl3, 75 MHz):
d = 162.8 (HC=N).
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