Synthesis of transition metal complexes with aza-crown substituted unsymmetrical salicylaldimine bis-Schiff base ligands and metal Schiff base complex catalysed oxidation of p-xylene to p-toluic acid

Article abstract of DOI:10.3184/174751912X13377751456987

Four unsymmetrical, salicylaldimine bis-Schiff bases with pendant benzo-10-aza-15-crown-5- or morpholino-groups and their 1:1 (ligand/metal) complexes with cobalt, copper and manganese have been synthesised and studied as catalysts in the aerobic oxidatio

Full text of DOI:10.3184/174751912X13377751456987

JOURNAL OF CHEMICAL RESEARCH 2012
RESEARCH PAPER 425
JULY, 425–428
Synthesis of transition metal complexes with aza-crown substituted
unsymmetrical salicylaldimine bis-Schiff base ligands and metal Schiff
base complex catalysed oxidation of p-xylene to p-toluic acid
Jian-zhang Lia*, Zhu-zhu Yanga, Xi-yang Hea, Jun Zeng and Jin Zhangb
aKey Laboratory of Green Catalysis of Higher Education Institutes of Sichuan, School of Chemistry and Pharmaceutical Engineering,
Sichuan University of Science & Engineering, Zigong, Sichuan, 643000, P. R. China
bDepartment of Chemistry and Environment Science, Chongqing University of Arts and Science, Yongchuan, Chongqing, 402160,
P. R. China
Four unsymmetrical, salicylaldimine bis-Schiff bases with pendant benzo-10-aza-15-crown-5- or morpholino-groups
and their 1:1 (ligand /metal) complexes with cobalt, copper and manganese have been synthesised and studied as
catalysts in the aerobic oxidation of p-xylene to p-toluic acid. Significant selectivity (up to –90%) and conversion
levels (up to –70%) were obtained. The effects of the pendant aza-crown ether group in Mn(III) Schiff base complexes
on the oxidation of p-xylene were also investigated by comparison with analogues having pendant morpholino-
groups.
Keywords: synthesis, benzo-10-aza-15-crown-5, unsymmetrical bis-Schiff base transition metal complexes, oxidation of p-xylene
base half unit.18 Other reagents were of analytical grade and were used
Schiff bases and their metal complexes have been applied
widely in the fields of coordination chemistry,1 analytical
without further purification.
chemistry,2 catalytic chemistry,3 liquid crystals and photochro-
Synthesis of unsymmetrical bis-Schiff base ligands 6H2–9H2
mism.4,5 In recent years, there has been considerable interest
Schiff base ligand 6H2: A solution of the precursor half unit (5H)
in salicylaldimine Schiff base transition-metal complexes as
(3.23g,10mmol)andN-(2-hydroxy-3-formyl-5-chlorobenzyl)morpho-
oxygen carriers6 and enzyme catalysis mimetics.7,8 Many
Schiff base ligands containing crown ether substituents
line (1) (4.36 g, 10 mmol) in anhydrous EtOH (30 mL) was stirred for
4h under N2 at 80 °C, then the mixture was cooled. The yellow pre-
possess different recognition sites for both alkali and transition
cipitate was filtered and washed with EtOH. After recrystallisation
metal guest cations;9 for example, the Na(I)– or K(I)–Co(II)
from EtOH, yellow crystals (3.58 g, yield 64%) were obtained, m.p.
199–200 °C. 1H NMR (CDCl3) δ: 12.92 (s, 1H, OH, D2O exchange),
10.35 (s, 1H, OH, D2O exchange), 8.24 (s, 1H, CH=N), 7.20–6.87 (m,
14H, ArH), 3.72–3.66 (m, 6H, OCH2, NCH2Ar), 2.72 (t, 4H, NCH2);
IR (KBr, film) vmax: 3442, 3235, 2927, 2852, 1613, 1601, 1278, 1114,
1040 cm−1; ESIMS m/z: 560(M++1). Anal. Calcd for C31H27N3O3Cl2:
C, 66.43; H, 4.86; N, 7.50; Cl, 12.65. Found: C, 66.31; H, 5.02; N,
7.35; Cl, 12.79%.
Ligand 7H2: Prepared as described for 6H2 except that the starting
material was N-(2-hydroxy-3-formyl-5-bromobenzyl)morpholine
(2) instead of 1, to give a yellow solid, yield 74%, m.p. 206–207 °C.
1H NMR (CDCl3) δ: 12.95 (s, 1H, OH, D2O exchange), 10.41 (s, H,
OH, D2O exchange), 8.25 (s, 1H, CH=N), 7.21–6.87 (m, 14H, ArH),
3.73–3.63 (m, 6H, OCH2, NCH2Ar), 2.78 (t, 4H, NCH2); IR (KBr,
film) vmax: 3439, 3237, 2932, 2859, 1615, 1601, 1276, 1112, 1039 cm−
1; ESIMS m/z: 605 (M++1). Anal. Calcd for C31H27N3O3ClBr: C, 61.55;
H, 4.50; N, 6.95; Cl, 5.86; Br, 13.21. Found: C, 61.69; H, 4.37; N,
7.09; Cl, 5.71; Br, 13.38%.
heteronuclear complexes of crowned Schiff bases can bind O2
to form stable solid dioxygen adducts.10,11 Our recent work
has shown that dioxygen affinities and biomimetic catalytic
performance of crown ether substituted salicylaldimine Schiff
base transition-metal complexes are better than those of their
crown-free analogues.12 To the best of our knowledge, there
are few previous studies on Schiff base complexes with
pendant aza-crown groups as catalysts in aerobic oxidation of
p-xylene to p-toluic acid.13,14 In connection to our research on
the effect of the bonded aza-crown ether ring in a Schiff base
ligand on biomimetic catalytic properties of transition-metal
complexes, we now report the synthesis of unsymmetrical
salicylaldimine bis-Schiff bases with pendant benzo-10-aza-
15-crown-5- or morpholino-groups and their transition metal
complexes, and the homogeneous catalytic oxidation of p-
xylene to p-toluic acid by air in the presence of the Schiff base
complexes under mild conditions. The route for the synthesis
and the structure of the unsymmetrical Schiff base complexes
is shown in Fig. 1.
Ligand 8H2: A solution of the precursor half unit 5H (3.23 g, 10 mmol)
and N-(2-hydroxy-3-formyl-5-chlorobenzyl)benzo-10-aza-15-crown-
5 (3) in anhydrous EtOH (30 mL) was stirred for 5h under an N2
atmosphere at 80 °C. The solvent was removed by evaporation and the
residual mass was chromatographed on a silica gel column using
CH3COOC2H5 as an eluent to give the pure product as a yellow solid,
Experimental
Melting points were determined on a MP-500 micro-melting point
apparatus and are uncorrected. IR spectra were recorded on a Nicolet-
6700 spectrometer. 1H NMR spectra were recorded on a Bruker
AC-200MHz spectrometer using Me4Si as the internal standard.
Mass spectra were obtained on a Finnigan LCQ−DECA spectrometer.
The metal ion content was measured using an IRIS-Advantage ICP
emission spectrometer. Halogen analyses were measured using the
mercury titration method15,16 and other elementary analyses were per-
formed on a Vario EL cube elemental analyser. Molar conductances
were obtained on a DDS-11A conductivity meter.
The following compounds were prepared according to the litera-
ture:17 (1) N-(2-hydroxy- 3-formyl-5-chlorobenzyl)morpholine; (2)
N-(2-hydroxy-3-formyl-5-bromobenzyl)morpholine;(3)N-(2-hydroxy-
3-formyl-5-chlorobenzyl)benzo-10-aza-15-crown-5; (4) N-(2-hydroxy-
3- formyl-5-bromobenzyl)benzo-10-aza-15-crown-5; and (5H) Schiff
1
yield 61%, m.p.187–188 °C. H NMR (CDCl3) δ: 12.11 (s, 1H, OH,
D2O exchange), 10.79 (s, 1H, OH, D2O exchange), 8.29 (s, 1H,
N=CH), 7.55–6.68 (m, 18H, ArH), 4.12–3.33 (m, 14H, OCH2,
NCH2Ar), 2.85 (t, 4H, NCH2); IR (KBr, film) vmax: 3447, 3242, 2938,
2861, 1616, 1601, 1255, 1125, 1049, 928 cm−1; ESIMS m/z: 741
(M++1). Anal. Calcd for C41H39N3O6Cl2: C, 66.49; H, 5.31; N, 5.67;
Cl, 9.57. Found: C, 66.31; H, 5.48; N, 5.79; Cl, 9.68%.
Ligand 9H2: Prepared as described for 8H2 except that the starting
material was N-(2-hydroxy-3-formyl-5-bromobenzyl)benzo-10-aza-
15-crown-5 (4) instead of 3, to give a yellow solid, yield 63%, m.p.
195–197 °C. 1H NMR (CDCl3) δ: 12.17 (s, 1H, OH, D2O exchange),
10.86 (s, 1H, OH, D2O exchange), 8.31 (s, 1H, N=CH), 7.56–6.69
(m, 18H, ArH), 4.15–3.35 (m, 14H, OCH2, NCH2Ar), 2.83 (t, 4H,
NCH2); IR (KBr, film) vmax: 3443, 3235, 2952, 2861, 1614, 1601,
1259, 1127, 1052, 925 cm−1; ESIMS m/z: 785(M++1). Anal. Calcd for
C41H39N3O6ClBr: C, 62.72; H, 5.01; N, 5.35; Cl, 4.52; Br, 10.18.
Found: C, 62.91; H, 4.82; N, 5.49; Cl, 4.35; Br, 10.02.
* Correspondent. E-mail: sichuanligong2006@hotmail.com

426 JOURNAL OF CHEMICAL RESEARCH 2012
Fig. 1 The synthetic route and structure of unsymmetrical salicylaldimine Schiff base transition complexes with pendant benzo-10-
aza-crown- or morpholino-groups.
Synthesis of Schiff base transition metal complexes; general
procedure
Calcd for C31H25BrClCuN3O3: C, 55.87; H, 3.78; N, 6.31; Cl, 5.32; Br,
11.99; Cu, 9.53. Found: C, 55.99; H, 3.89; N, 6.19; Cl, 5.46; Br, 12.11;
Cu, 9.34%. Λm(S·cm2·mol−1), 9.93.
A
solution of unsymmetrical salicylaldimine bis-Schiff base
(10 mmol) and transition metal salt [MnCl2.4H2O, Co(OAc).4H2O or
Cu(OAc).4H2O] (10 mmol) in EtOH (15 mL) was stirred for 2 h under
N2 at 80 °C, and then the mixture was cooled, filtered, and washed
with EtOH to give the complexes. The pure product was obtained by
recrystallisation from EtOH.
Mn6Cl: Light yellow solid, yield 74%, m.p. 255–256 °C; IR (KBr,
film) vmax: 2930, 2854, 1604, 1277, 1115cm−1; ESIMS m/z: 649
(M++1). Anal. Calcd for C31H25MnN3O3Cl3: C, 57.38; H, 3.88; N,
6.48; Cl, 16.39; Mn, 8.47. Found: C, 57.46; H, 3.99; N, 6.59; Cl,
16.24; Mn, 8.64%. Λm(S·cm2·mol−1), 99.64.
Mn8Cl: Brown solid, yield 69%; m.p. >300 °C; IR (KBr, film) vmax
:
2937, 2861, 1608, 1598, 1257, 1129, 1055, 928 cm−1; ESIMS m/z: 829
(M++1). Anal. Calcd for C41H37N3O6Cl3Mn: C, 59.40; H, 4.50; N,
5.07; Cl, 12.83; Mn, 6.63. Found: C, 59.17; H, 4.66; N, 5.22; Cl,
12.65; Mn, 6.51%. Λm (S·cm2·mol−1), 102.23.
Co8: Crimson solid, yield 68%; m.p. 252–253 °C; IR (KBr, film)
vmax: 2939, 2864, 1607, 1601, 1256, 1126, 1056, 926 cm−1; ESIMS
m/z: 798 (M++1). Anal. Calcd for C41H37N3O6Cl2Co: C, 61.74; H, 4.68;
N, 5.27; Cl, 8.89; Co, 7.39%. Found C, 61.55; H, 4.79; N, 5.15; Cl,
8.74; Co, 7.52%. Λm (S·cm2·mol−1). 10.64.
Co6: Purple solid, yield 76%; m.p. 247–249 °C; IR (KBr, film) vmax
:
2928, 2852,1605, 1597, 1278, 1116 cm−1; ESIMS m/z: 617 (M++1).
Anal. Calcd for C31H25N3O3Cl2Co: C, 60.31; H, 4.08; N, 6.81; Cl,11.48;
Co, 9.55. Found: C, 60.48; H, 4.25; N, 6.63; Cl, 11.38; Co, 9.70%.
Λm (S·cm2·mol−1), 9.24.
Cu8: Grey solid, yield 72%; m.p. >300 °C; IR (KBr, film) vmax
:
2938, 2864, 1609, 1601, 1257, 1128, 1054, 927 cm−1; ESIMS m/z: 802
(M++1). Anal. Calcd for C41H37N3O6Cl2Cu: C, 61.39; H, 4.65; N, 5.24;
Cl, 8.84; Cu, 7.92%. Found: C, 61.53; H, 4.50; N, 5.11; Cl, 8.66; Cu,
8.09%. Λm (S·cm2·mol−1), 9.26.
Cu6: Grey solid, yield 72%; m.p.>300 °C ; IR(KBr, film) vmax
:
2926, 2851, 1604, 6001, 1276, 1117 cm−1; ESIMS m/z: 622 (M++1).
Anal. Calcd for C31H25N3O3Cl2Cu: C, 59.86; H, 4.05; N, 6.76; Cl,
11.40; Cu, 10.22. Found: C, 59.71; H, 4.23; N, 6.63; Cl, 11.59; Cu,
10.03%. Λm (S·cm2·mol−1), 9.83.
Mn9Cl: Brown solid, yield 66%; m.p. >300 °C; IR (KBr, film) vmax
:
2949, 2858, 1605, 1600, 1256, 1128, 1048, 927 cm−1; ESIMS m/z: 838
(M++1). Anal. Calcd for C41H37N3O6Cl2BrMn: C, 56.38; H, 4.27; N,
4.81; Cl, 8.12; Br, 9.15; Mn, 6.29. Found: C, 56.22; H, 4.45; N, 4.67;
Cl, 8.28; Br, 9.30; Mn, 6.11%. Λm (S·cm2·mol−1), 98.36.
Mn7Cl: Light yellow solid, yield 70%; m.p. 260–261 °C; IR (KBr,
film) vmax: 2930, 2860, 1606, 1600, 1274, 1114 cm−1. ESIMS m/z: 658
(M++1). Anal. Calcd for C31H25N3O3Cl2 BrMn: C, 53.70; H, 3.63; N,
6.06; Cl, 10.23; Br, 11.53; Mn, 7.92. Found C, 53.84; H, 3.54; N, 6.19;
Cl, 10.11; Br, 11.39; Mn, 7.76%. Λm (S·cm2·mol−1), 101.83.
Co9: Crimson, yield 69%; m.p. 257–259 °C; IR (KBr, film) vmax
:
2952, 2859, 1604, 1599, 1258, 1129, 1053, 928 cm−1; ESIMS m/z 842
(M++1). Anal. Calcd for C41H37N3O6ClBrCo: C, 58.48; H, 4.43; N,
4.99; Cl, 4.21; Br, 9.49; Co, 7.00. Found: C, 58.65; H, 4.32; N, 5.16;
Cl, 4.38; Br, 9.35; Co, 6.90%. Λm (S·cm2·mol−1), 10.51.
Co7: Purple solid, yield 74%; m.p. 222–224 °C; IR (KBr, film) vmax
:
2928, 2861, 1605, 1600, 1275, 1115 cm−1; ESIMS m/z: 662(M++1).
Anal. Calcd for C31H25N3O3BrClCo: C, 56.26; H, 3.81; N, 6.35; Cl,
5.36; Br, 12.07; Co, 8.90. Found: C, 56.11; H, 3.97; N, 6.19; Cl, 5.48;
Br, 11.99; Co, 9.19%. Λm (S·cm2·mol−1). 10.91.
Cu9: Grey solid, yield 71%; m.p. >300 °C; IR (KBr, film) vmax
:
2951, 2860, 1606, 1601, 1255, 1125, 1052, 926 cm−1; ESIMS m/z: 847
(M++1). Anal. Calcd for C41H37N3O6ClBrCu: C, 58.16; H, 4.40; N,
4.96; Cl, 4.19; Br, 9.44; Cu, 7.51. Found: C, 58.33; H, 4.22; N, 4.78;
Cl, 4.31; Br, 9.58; Cu, 7.39%. Λm(S·cm2·mol−1), 9.86.
Cu7: Grey solid, yield 73%; m.p. >300 °C ; IR (KBr, film) vmax
:
2932, 2856, 1605, 1278, 1118 cm−1; ESIMS m/z: 666 (M++1). Anal.

JOURNAL OF CHEMICAL RESEARCH 2012 427
Oxidation of p-xylene to p-toluic acid(PTA) with air; general
procedure
The oxidation of p-xylene was carried out in a general gas–liquid
reactor. Fresh air was bubbled at 120 °C with a flow rate of 0.05 L h−1
into a mixture of p-xylene (1.21 x 10−1 mol, 15 cm3) and Schiff base
complex (1.5 x 10−5 mol). The oxidation products were analysed at
regular intervals by HPLC (Afilent 1100LC, Hypersil ODS 100 mm x
4.6 mm, 5mm). Authenticated standard samples were used to confirm
the identity of products. The oxidation was stopped on reaching the
maximum value of accumulated content of PTA, and the total conver-
sion and product distribution were evaluated by using calibration
curves, which were obtained by injecting a known amount of authen-
ticated standard samples. Conversions and selectivity were calculated
based on the amount of p-xlene reacted and oxidation products formed
by HPLC.
Results and discussion
The unsymmetrical bis-Schiff base ligands (6H2–9H2) were
conveniently prepared by the reaction of the Schiff base
half unit with crown ether-functionalised salicylaldehyde or
morpholino-functionalised salicylaldehyde (Fig. 1) and char-
Fig. 2 The effect of central metal of Schiff base complexes on
catalytic oxidation of p-xylene to p-toluic acid.
1
acterised by IR, H NMR, mass spectroscopy and elemental
analysis. In the IR spectra of 6H2–9H2, the characteristic
absorbtions of Ar-OH at 3447–3439 cm−1 and 3242–3235 cm−1
were observed, as was that for CH=N at 1616–1613cm−1.
1H NMR spectra of 6H2–9H2 show the aromatic protons as
multiplets in the range 7.56–6.69 ppm, the chemical shifts
of the O–H protons of the phenolic groups are in the range
12.95–12.11 ppm and 10.86–10.35 ppm, respectively.
Compared with the IR spectrum of the free ligands, those of
the Schiff base transition metal complexes are almost at the
same frequencies, except for the C=N stretching vibration
which is shifted 7–10 cm−1 to a lower frequency and also shows
an intensity greater than the free ligand. The absence of an
OH stretching vibration (–3440 cm−1 and –3230 cm−1) in the
complexes indicates deprotonation of OH in the ligand upon
complex formation, suggesting the formation of a N–O–M
coordination bond (M=Co, Cu or Mn). The C–O–C stretching
vibrations in the crown ether ring for the complexes are at
almost the same frequency as for the free ligand. These facts
suggest that the cobalt only interacts with the Ar-OH and
CH=N groups.12 The observed molar conductances of the
complexes in DMF solution (1.0×10−3 mol L−1) at 25 °C show
that these unsymmetrical bis-Schiff base cobalt and copper
complexes are non-electrolytes, whereas the unsymmetrical
bis-Schiff base manganese complexes are electrolytes.19 The
ESI-MS mass spectra and elemental analysis of the complexes
indicate that 6H2–9H2 formed 1:1(metal/ligand) complexes.
We therefore suggest structural formulae for these Schiff base
transition metal complexes as shown in Fig. 1.
Fig. 3 The effect of aza-crown ether group on catalytic oxida-
tion for p-xylene of p-toluic acid.
microenvironment of the active centre owing to the hydropho-
bicity of its outer ethylene groups and orderly arrangement
of the inner oxa-atoms, which facilitate the approach of the
oxygen molecule to the coordination centre of the aza-crown
Schiff base Mn(III) complexes.
From Fig. 4, an obvious relationship exists between the
catalytic oxidation activity and the electronic properties of the
Oxidation of p-xylene to PTA
In order to investigate the effect of the central metal of the
Schiff base complexes on the catalytic oxidation of p-xylene to
PTA, Mn9Cl, Co9 and Cu9 are used as examples. The results
of oxidation of p-xylene to PTA are shown in Fig. 2. From
Fig. 2, the catalytic oxidation activity of the Mn(III) Schiff
base complexes is higher than that of Co(II)- or Cu(II)-Schiff
base complex analogues using the same ligand, due to the
differences in 3d electronic structure of the central metal ion,
which leads to a different capacity of Schiff base complexes to
activate dioxygen in the reaction system.
From Fig. 3, the catalytic oxidation activity of the aza-crown
Mn(III) Schiff base complex (Mn9Cl) is higher than that of the
Mn(III) morpholino-Schiff base complex (Mn7Cl). The time
taken for PTA to reach the maximum concentration during the
oxidation of p-xylene catalysed by the aza-crown Mn(III)
Schiff base complexes is also shorter than that for crown-free
Mn(III) Schiff base complexes. This may be due to the pres-
ence of the aza-crown ring which can control efficiently the
Fig. 4 The effect of aromatic substituents group on catalytic
oxidation of p-xylene to p-toluic acid

428 JOURNAL OF CHEMICAL RESEARCH 2012
Scheme 1 The catalytic oxidation products of p-xylene by Mn(III) Schiff base complexes.
Table 1 Schiff base Mn (III) complex catalytic oxidation of
p-xylene to p-toluic acida
conditions for the oxidation of p-xylene catalysed by aza-
crown Mn(III) Schiff base complexes are milder than for other
inorganic catalysts.20,21
Cata- Induction Conversion TOF Selectivity for productsb
lyst
period
/h
/wt%
/h−1
A
B
C
D Others
Conclusion
In this paper, four unsymmetrical salicylaldimine bis-Schiff
bases with pendant benzo-10-aza- 15-crown-5- or morpholino-
groups and their cobalt, copper and manganese complexes
have been synthesised and studied as catalysts in the aerobic
oxidation of p-xylene to p-toluic acid. Significant selectivity
(up to –90%) and conversion levels (up to –70%) have been
obtained. The study demonstrates that the catalytic oxidation
activity of Mn(III) Schiff base complexes is higher than that of
Co(II)- or Cu(II)-Schiff base complex analogues. The selective
oxidation of p-xylene to p-toluic acid can successfully occur
in the presence of Schiff base Mn(III) complexes having a
pendant aza-crown group; the catalytic oxidation activity of
the aza-crown Mn(III) Schiff base complex is higher than that
of the morpholino- Mn(III) Schiff base complex.
Mn6Cl
Mn7Cl
Mn8Cl
Mn9Cl
5
5
4
4
60
63
73
78
320 89.2 3.3 2.9 1.8 2.8
334 90.8 2.5 2.6 1.3 2.8
520 92.3 1.9 2.8 1.6 1.5
533 93.2 1.8 2.0 1.2 1.8
a Condition: p-xylene: 15 cm−3 (1.21×10−1 mol); Mn(III) Schiff
base complexes: 1.0×10−3 mol dm−3; flow rate for air: 2.4 L h−1;
Reaction temperature: 120 °C; Reaction time: 14 h.
b Legend: A = p-toluic acid; B = p-tolyl alchol; C = p-tolualde-
hyde; D = terephalic acid; TOF = Turnover frequency (mol
p-xylene converted per mol catalyst per h).
substituent group on the aromatic rings of Mn(III) Schiff base
complexes. Figure 4 shows that the catalytic oxidation activity
of Mn9Cl, containing a Br substituent group, is higher than
that of Mn8Cl, containing a Cl substituent group, when the
structure of ligand is otherwise similar. Because the electron-
donating effect of the substituent group follows the order
Br>Cl, the electron density of the central metal manganese is
enhanced by an electron-donating effect of the substituent
group on the salicyl-aromatic ring, which facilitates the Schiff
base complexes enhanced affinity for the oxygen molecule.
Comparing the catalytic oxidation activities of the Schiff
base Mn(III) complexes with a pendant aza-crown group,
the effect of the substituent group on the aromatic ring on
the oxidation of p-xylene seems to be small, and the same
phenomenon was also observed for the Schiff base Mn(III)
complexes with a pendant morpholino-group. The macrocycle
effect of the aza crown ring may be significant factor for the
catalytic oxidation performance of the Schiff base Mn(III)
complex.
The authors gratefully acknowledge financial support from
China National Natural Science Foundation (No: 20072025),
the Opening Project of Key Laboratory of Green Catalysis
of Sichuan Institutes of High Education (Nos LZJ01 and
LZJ1101) and Key Scientific and Technological Project Issued
by Ministry of Education of China (No. 208118).
Received 14 January 2012; accepted 23 April 2012
Paper 1201106 doi: 10.3184/174751912X13377751456987
Published online: 26 June 2012
References
1
2
3
S. Yamada, Coord. Chem. Rev., 1999, 190, 537.
Z. Cimernan, N. Galic and B. Bosner, Anal. Chim. Acta, 1997, 343, 145.
T. Panniyamurthy, B. Bhatia, M.M. Reddy, G.C. Maikap and J. Iqbal,
Tetrahedron, 1997, 53, 7649.
The oxidation of p-xylene to PTA was carried out using
Mn(III) Schiff base complexes as the catalyst as shown in
Scheme 1. The results of oxidation of p-xylene to PTA are
shown in Table 1. The data in Table 1 indicate that the induc-
tion periods required for initiating the oxidation of p-xylene
catalysed by Mn(III) Schiff base complexes are 4 h for Mn8Cl,
4 h for Mn9Cl, 5 h for Mn6Cl, and 5h for Mn7Cl, respectively.
This shows that the induction periods of initiating the oxida-
tion of p-xylene catalysed by the aza-crown Mn(III) Schiff
base complexes are shorter than those for the oxidation of
p-xylene catalysed by the morpholino-Mn(III) Schiff base
complex. Moreover, as shown in Table 1, the selectivity for the
oxidation product PTA, conversion and turnover frequency
(TOF) for the oxidation of p-xylene catalysed by the Schiff
base Mn(III) complexes with a pendant aza-crown group
are also excellent in comparison with those of the oxidation of
p-xylene catalysed by the morpholino-Mn(III) Schiff base
complexes analogues. Although the conversion (–78%) for the
oxidation of p-xylene catalysed by the Schiff base Mn(III)
complexes with the pendant aza-crown group is lower than
that of Co(OAc)2/NaBr/AcOH or Co(C18H35O2)2/NH4Br, the
selectivity (up to –93%) for the oxidation product PTA is
higher than that of Co(OAc)2/NaBr/AcOH, and the reaction
4
5
M.G. Xie, M.S. Peng, Q. Jiang, Z.L. Hu and X.L. Wang, Liq. Cryst., 1996,
21, 461.
V.W.W.Yam, K.M.C.Wong, K.K.W. LoandK.K. Cheung, Organometallics,
1995, 14, 4034.
D. Chen, A.E. Martell and Y. Sun, Inorg. Chem., 1989, 28, 2647.
K. Srinivasan, P. Michaud and J.K. Kochi, J. Am. Chem. Soc., 1986, 108,
2309.
N. Kim and J. Suh, J. Org. Chem., 1994, 59, 1561.
F.C.J.M. Veggel, W. Verboom and D.N. Reinhoude, Chem. Rev., 1994, 94,
279.
6
7
8
9
10 K. Salkata and T. Annoura, Inorg. Chim. Acta, 1990, 176, 123.
11 X.X. Lu, S.Y. Qin, Z.Z. Zhou and V.W.W. Yam, Inorg. Chem. Acta, 2003,
346, 49.
12 W. Zeng, J.Z. Li, Z.H. Mao, Z. Hong and S.Y. Qin, Adv. Synth. Catal.,
2004, 346, 1385.
13 W. Zeng, J.Z. Li and S.Y. Qin, Supramol. Chem., 2004, 16, 569.
14 J.Z. Li, Y. Wang and S.Y. Qin, Supramol. Chem., 2008, 20, 249.
15 D. Pitre and M. Grandi, Mikrochim. Acta, 1967, 37.
16 R.A. Lalaneette, Microchem. J., 1972, 17, 665.
17 J.Yan, J.Z. Li, K.B. Li, B. Zhou, W. Zeng and S.Y. Qin, Trans. Met. Chem.,
2006, 31, 286.
18 R. Atkins, G. Brewer, E. Kokot, G.M. Mockler and E. Sinn, Inorg. Chem.,
1985, 24, 127.
19 W.J. Geary, Coord. Chem. Rev., 1971, 7, 81.
20 C.R. Jacob, S.P. Varkey and P. Ratnasamy, Appl. Catal. A, 1999, 182, 91.
21 F. Fang, J. Sun, R. Zheng, W.W. Qiu, J. Tang and M.Y. He, Tetrahedron,
2004, 60, 1225.

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