Transition metal complexes of 5-bromosalicylidene-4-amino-3-mercapto-1,2,4- triazine-5-one: Synthesis, characterization, catalytic and antibacterial studies

Article abstract of DOI:10.2298/JSC100212136R

Transition metal complexes of 5-bromosalicylidene-4-amino-3-mercapto-1,2,4- triazine-5-one with metal precursors, such as Cu(II), Ni(II), Co(II) and Pd(II), were synthesized and characterized by physico-chemical and spectroscopic techniques. All the compl

Full text of DOI:10.2298/JSC100212136R

J. Serb. Chem. Soc. 76 (1) 75–83 (2011)
JSCS–4101
UDC 547–304.9+542.9+547.571+547.551+
66.094.3.097:615.281
Original scientific paper
Transition metal complexes of 5-bromosalicylidene-4-amino-3-
-mercapto-1,2,4-triazine-5-one: Synthesis, characterization,
catalytic and antibacterial studies
AYALOOR SUBRAMANIAN RAMASUBRAMANIAN, BADEKAI RAMACHANDRA
*
BHAT , RAMAKRISHNA DILEEP and SANDYA RANI
Department of Chemistry, National Institute of Technology Karnataka,
Surathkal, Srinivasnagar – 575025, Karnataka State, India
(Received 12 February, revised 1 June 2010)
Abstract: Transition metal complexes of 5-bromosalicylidene-4-amino-3-mer-
capto-1,2,4-triazine-5-one with metal precursors, such as Cu(II), Ni(II), Co(II)
and Pd(II), were synthesized and characterized by physico–chemical and spec-
troscopic techniques. All the complexes are of the ML type. Based on analyti-
cal, spectral data and magnetic moments, the Co(II) and Ni(II) complexes were
assigned octahedral geometries, while the Cu (II) and Pd(II) complexes square
planar. A study on the catalytic oxidation of benzyl alcohol, cyclohexanol, cin-
namyl alcohol, 2-propanol and 2-methyl-1-propanol was performed with N-
methylmorpholine-N-oxide (NMO) as co-oxidant. All the complexes and their
parent organic moiety were screened for their biological activity on several
pathogenic bacteria and were found to possess appreciable bactericidal pr-
operties.
Keywords: triazine; Schiff base; catalytic oxidation; antibacterial studies.
INTRODUCTION
Catalytic oxidation of alcohols is an important industrial process due to the
wide variety of products synthesized by this route. Many systems have been re-
ported for the oxidation of alcohols, mainly involving catalysts containing transi-
1
2
3
4
tion metals such as bivalent Co, , Pd, Ni and Ru. The ability of transition
metals to assume a wide range of oxidation states and coordination geometries
provides unique opportunities for catalysis. The development of highly efficient
transition metals-based catalysts is also driven by their tolerance towards func-
tional groups, their ease of synthesis and their versatility. Schiff bases and their
transition metal complexes are still found to be of great interest in inorganic
*Corresponding author. E-mail: chandpoorna@yahoo.com
doi: 10.2298/JSC100212136R
75
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RAMASUBRAMANIAN et al.
5,6
chemistry, although this subject has been studied extensively. Schiff bases and
their metal complexes show biological activity as antibiotics, antiviral and anti-
7,8
tumour agents because of their specific structures.
Triazole chemistry is becoming more important due to its excellent biolo-
gical activity. The triazole antifungal drugs include fluconazole, isavuconazole,
itraconazole, voriconazole, pramiconazole and posaconazole. The triazole plant
protection fungicides include epoxiconazole, triadimenol, propiconazole, metco-
nazole, cyproconazole, tebuconazole, flusilazole and paclobutrazol. Studies have
been reported on the synthesis and characterization of metal complexes of Schiff
base involving 1,2,4-mercapto triazoles with salicylaldehyde, p-nitrobenzalde-
9–11
hyde, o-nitrobenzaldehyde, p-toluylaldehyde and cimmamaldehyde.
Transi-
tion metal complexes of polydentate ligands involving five donor atoms have
12
also been reported. These ligands were reported to coordinate through depro-
tonated oxygen, thio-enolic sulphur and azomethine nitrogen atoms.
In the present study, the synthesis and characterization of transition metal
complexes of 5-bromosalicylidene-4-amino-3-mercapto-1,2,4-triazine-5-one
(BrSAMT) were undertaken and their applications as catalysts for the oxidation
of benzyl alcohol, cyclohexanol, cinnamyl alcohol, 2-propanol and 2-methyl-1-
-propanol. Their possible anti-bacterial activity was also explored.
EXPERIMENTAL
Methods
The metal content of these complexes were estimated using a Varian AA 55B atomic
absorption spectrometer. The infrared spectrum was recorded on an ABB BOMEM FT-IR
spectrophotometer. Carbon, hydrogen, nitrogen and sulphur were analyzed using a Thermo
Flash EA 1112 series CHN analyzer. The magnetic susceptibilities were determined using a
Sherwood Scientific magnetic susceptibility meter (Cambridge, UK). The electronic spectra of
the complexes in DMF were recorded on a GBC model UV–Vis spectrophotometer. Thermo-
gravimetric analysis was realised using an SII Exstar 6000 model TGA analyzer. Gas chroma-
tographic analysis was performed on a Shimadzu 2014 model instrument. The 1H-NMR spec-
tra were recorded on a Bruker AV 400 instrument using TMS as the internal standard. The
conductivity measurements were performed on an Elico 32 model instrument.
Synthesis of the ligand
The ligand was synthesized in two steps. In the first step, 4-amino-3-mercapto-1,2,4-
triazine-5-one was synthesized according to a literature procedure.13 In the second step, a so-
lution of 0.10 mol of 4-amino-3-mercapto-1,2,4-triazine-5-one in 10 ml of ethanol and 0.10
mol of 5-bromo salicylaldehyde was refluxed for 4 h, cooled, filtered, washed with water,
dried and then recrystallized from absolute alcohol. The yellow coloured 5-bromosalicyli-
dene-4-amino-3-mercapto-1,2,4-triazine-5-one (BrSAMT) was dried in a desiccator.
Synthesis of the complexes
To a hot solution of 40 mmol of BrSAMT in 20 ml alcohol, 0.002 mol of the respective
transition metal chlorides in water (minimum quantity 2 ml) was added and the mixture re-
fluxed for 2 h and then cooled. The different coloured complexes were filtered, washed with
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TRANSITION METAL COMPLEXES OF 5-BROMOSALICYLIDENE-4-AMINO-3-MERCAPTO-1,2,4-TRIAZINE-5-ONE
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water, ethanol, diethyl ether and dried in a desiccator. The resultant complexes were brown
coloured for the Cu(II) and Co(II) complexes, orange brown for the Pd(II) complex and
reddish orange for the Ni(II) complex.
Catalytic oxidation experiments with N-methyl morpholine-N-oxide (NMO)
To a solution of the required alcohol (0.060–0.12 mL, 1.0 mmol) in dichloromethane (20
mL), NMO (0.35 g, 3.0 mmol) and the required metal-complex (0.01 mmol) were added and
the solution was heated under reflux for 2 h. The mixture was then filtered and the filtrate was
dried over anhydrous Na2SO4. It was then evaporated to dryness and extracted with diethyl
ether. The diethyl ether extract was filtered and evaporated to give the corresponding
aldehyde.14,15 The products were identified using gas chromatography by comparing their
retention time with those of authentic samples.
Biological tests
The synthesized complexes of BrSAMT were screened for their in vitro antibacterial
activity against pathogenic strains of gram-negative bacteria, i.e., Escherichia Coli, Pseudo-
monas aeruginosa, Salmonella typhi and Shigella flexneri using the plate technique. The bac-
teria were cultured in previously sterilized Mueller Hinton agar medium in a petri dish. So-
lutions of the ligand and its complexes in DMF were plated onto the cultured agar medium
and incubated for a period of 24 h at 37 °C. Solutions of the ligand and its complexes in DMF
were plated on cultured agar medium and incubated for a period of 24 h at 37 °C. The com-
ponents to be tested were dissolved in DMF to a final concentration of 0.5 and 1% and soaked
in filter paper discs of 5 mm diameter and 1 mm thickness. Nicotinic acid was used as
reference material. After the incubation period the plates were observed for zones of inhibition
(in cm).
RESULTS AND DISCUSSION
Analytic and spectral data
Ligand. Yield: 60 %; Anal. Calcd. for C H BrN O S: C, 36.4; H 2.1; N,
10
6
4 2
–1
17.0; S 9.7 %. Found: C, 36.5, H, 2.1, N, 17.2, S, 9.7 %. IR (KBr, cm ): 1690 s
(–C=O stretching of –CO in the triazole group), 1650 (C=N– stretching of the
1
azomethine group), 1455 (thioamide group). H-NMR (200 MHz, DMSO-d , δ /
6
/ ppm): 11.20 (1H, s, –SH), 8.7 (1H, s, –CH=N–), 6.24–8.76 (3H, m, aromatic,
J = 7.8 Hz).
Ni(II) complex. Yield: 60 %; Anal. Calcd. for C H BrClN NiO S: C,
10 10
4
4
26.29; H, 2.15; N, 12.15; S, 7.01 %. Found: C, 26.32, H, 2.15, N, 12.28, S, 7.03 %.
–1
IR (KBr, cm ): 3500, 900 (–OH stretching of H O), 1730 s (–C=O stretching of
2
–CO in triazole group), 1620 (C=N– stretching of the azomethine group), 1450
1
(thioamide group), 490 (Ni–O), 440 (Ni–N). H-NMR (200 MHz, DMSO-d , δ /
6
/ ppm): 11.24 (1H, s, –SH), 8.5 (1H, s, –CH=N–), 6.24–8.76 (3H, m, aromatic,
J = 7.8 Hz). Magnetic moment, μ / μ : 2.73.
eff
B
Co(II) complex. Yield: 60 %; Anal. Calcd. for C H BrClCoN O S: C,
10 10
4 4
26.25; H, 2.20; N, 12.20; S, 7.01 %. Found: C, 26.31, H, 2.21, N, 12.27, S, 7.02
–1
%. IR (KBr, cm ): 3500, 905 (–OH stretching of H O), 1740 s (–C=O stretching
2
of –CO in the triazole group), 1610 (C=N– stretching of the azomethine group),
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RAMASUBRAMANIAN et al.
1
1445 (thioamide group), 495 (Co–O), 445 (Co–N). H-NMR (200 MHz, DMSO–
–d , δ / ppm): 11.10 (1H, s, –SH), 8.55 (1H, s, –CH=N–), 6.24–8.76 (3H, m,
6
aromatic, J = 7.8 Hz). Magnetic moment, μ / μ : 3.72.
eff
B
Cu(II) complex. Yield: 60 %; Anal. Calcd. for C H BrClCuN O S: C,
10
6
4 2
28.15; H, 1.36; N, 13.09; S, 7.41 %. Found: C, 28.25, H, 1.42, N, 13.18, S, 7.54 %.
–1
IR (KBr, cm ): 1745 s (–C=O stretching of –CO in the triazole group), 1620
(C=N– stretching of the azomethine group), 1452 (thioamide group), 490 (Cu–O),
1
440 (Cu–N). H-NMR (200 MHz, DMSO-d , δ / ppm): 11.55 (1H, s, –SH), (1H,
6
s, –CH=N–), 6.24–8.76 (3H, m, aromatic, J = 7.8 Hz). Magnetic moment, μ
/
eff
/ μ : 1.73.
B
Pd(II) complex. Yield: 60 %; Anal. Calcd. for C H BrClCuN O S: C,
10
6
4 2
25.58; H, 1.28; N, 11.75; S, 7.01 %. Found: C, 25.66, H, 1.29, N, 11.97, S, 7.02 %.
–1
IR (KBr, cm ): 1744 s (–C=O stretching of –CO in the triazole group), 1615
(C=N– stretching of the azomethine group), 1448 (thioamide group), 491 (Pd–O),
1
446 (Pd–N). H-NMR (200 MHz, DMSO-d , δ / ppm): 11.35 (1H, s, –SH), 8.45
6
(1H, s, –CH=N–), 6.24–8.76 (3H, m, aromatic, J = 7.8 Hz).
Infrared spectra
–1
The ligands showed an infrared band at 2900 cm , indicating the absorp-
tions ν(C–H). The ligand also showed the presence of four thioamide bands I, II,
–1
III and IV at 1500–1600, 1270, 900, and 800 cm , respectively, indicating the
presence of the thioamide moiety in the ligand molecule. No systematic shifts of
–1
these bands in the complexes were observed. The band at around 1700 cm ,
corresponding to ν(C=O) of the carbonyl group in the ligand, was altered in the
complexes. This shows the possibility of carbonyl group participation in the
–1
bonding. The bands at 1650 and 1600 cm in the ligand and the complexes cor-
16
respond to ν(C=N) of the azomethine linkage and the shift in frequency to
lower wave numbers indicates the coordination of the nitrogen of this group with
–1
the metal ions. In the complexes, the band at 1300 cm , due to the phenolic
group, was shifted to higher wave numbers, indicating the involvement of the
phenolic oxygen in the coordination with the metal. The broad band at around
–1
3500 and 890 cm , corresponding to ν(O–H) in cases of the Co(II) and Ni(II)
complexes indicates the presence of coordinated water molecules in these com-
–1
plexes. The presence of a band at 669 cm in the spectrum of the BrSAMT li-
gand and its complexes, due to C–Br stretching, remained unchanged, indicating
that the bromo group was not involved in the bonding.
Electronic spectra
In the case of six coordinated octahedral and pseudo-octahedral Ni(II) com-
3
3
3
plexes, the three spin allowed transitions from A (F) to T (F), T (F) and
2g
2g
1g
3
–1
–1
T (P) generally fall within the regions 7000–13000 cm , 11000–20000 cm
1g
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TRANSITION METAL COMPLEXES OF 5-BROMOSALICYLIDENE-4-AMINO-3-MERCAPTO-1,2,4-TRIAZINE-5-ONE
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–1
and 19000–27000 cm , respectively. The ratio of the frequencies of the second
17
to the first transitions would be around 1.8. The first transition, corresponding
3
3
to A (F) to T (F) was not recorded in the electronic spectra. For high spin
2g
2g
octahedral complexes of Co(II), three transitions are expected in the electronic
4
4
4
4
4
4
spectra and they are T (F) → T (F), T (F) → A and T (F) → T (P)
1g
2g
1g
2g
1g
1g
in order of increasing energy. The first transition was not recorded but the po-
sition was calculated from the second transition. For the complexes of Cu (II),
only one transition was observed, assigned to E (F) → T (F).
2
2
1g
2g
1H-NMR Spectra
1
The H-NMR spectra of the free ligand and the complexes were recorded in
DMSO. The ligand exhibit a singlet at 11.24. This signal in the spectra of the
complexes remained as such, suggesting the non-participation of sulphur in the
coordination. The singlet at 8.7 ppm in the ligand due to the azomethine proton
was shifted to 8.5 ppm in the complexes. In the spectrum of the ligand, multiplets
due to aromatic protons appeared in the range δ 6.24–8.76 ppm. These resonance
signals remain unchanged in the spectra of the complexes, suggesting their non-
involvement in bonding. The peak corresponding to –OH at 10.8 ppm in the free
ligand was not observed in the spectra of the complexes. This clearly shows
deprotonation of –OH during complex formation.
Magnetic susceptibility
The magnetic susceptibility results indicate that the complexes of Co(II),
Ni(II) and Cu(II) are paramagnetic, while the Pd(II) complex is diamagnetic in
8
nature. Ni(II) being a d in an octahedral field contains two unpaired electrons
and hence shows paramagnetism. The value of 2.73 μ is close to the theoretical
B
7
value of 2.83 for octahedral Ni(II) complexes. Co(II) is a d system, thus its com-
plexes show paramagnetism equivalent to three unpaired electrons in octahedral
geometry. Since the orbital contribution of tetrahedral Co(II) is much less than
that of octahedral complexes, tetrahedral Co(II) complexes generally have lower
values of magnetic moments, as compared to that of octahedral complexes. This
high degree of orbital contribution for octahedral complexes is due to the three-
4
-fold degeneracy of the T ground state. The observed value of 3.72 μ is close
1g
B
to the theoretically calculated values of 3.83 μ for octahedral Co(II) complexes.
B
9
Cu(II), being a d system, shows paramagnetism in square planar complexes. The
value of 1.74 μ is close to theoretical value of 1.73 BM for Cu(II) square planar
B
complexes.
Molar conductance
2
–1
The results of molar conductance, which were less than 30 μS m mol in
DMF solution, indicate that all the formed complexes were non-electrolytes,
18
electrically neutral and non-ionic in nature.
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RAMASUBRAMANIAN et al.
Thermogravimetric analysis
It was observed that the complexes of Ni(II) and Co(II) show a loss in
weight between 150–200 °C, indicating that crystal water molecules and coor-
dinated water molecules are present in the complexes. The TG curves in the 200–
–310 °C range suggest that the loss in weight for all complexes corresponds to
decomposition of the ligand. In the range above 310 °C, the loss in weight corres-
ponded to the remaining organic ligand molecules. In all cases, the remaining re-
sidues were the corresponding metal oxide. These results are in accordance with
the composition of the complexes.
Catalytic studies
The catalytic activity of the newly synthesized complexes was examined in
the presence of NMO as a co-oxidant for the oxidation of primary and secondary
alcohols in CH Cl . The results are presented in Table I. The reaction was ini-
2
2
tially conducted using molecular oxygen. Results of the present investigation
suggest that the complexes are able to react more efficiently with NMO than with
molecular oxygen, as indicated by the low product yield when molecular oxygen
was employed as the co-oxidant. This is in accordance with a previous obser-
19
vation . N-Methylmorpholine and water were the by-products during the course
of the reactions. An important characteristic of the transition metal–NMO system
TABLE I. Oxidation of alcohols by the synthesised metal(II) complexes
Complex
Substrate
Product
Yielda, %
TONb
Ni(II) BrSAMT
Benzyl alcohol
Cyclohexanol
Cinnamyl alcohol
2-Propanol
2-Methyl-1-propanol
Benzyl alcohol
Cyclohexanol
Cinnamyl alcohol
2-Propanol
2-Methyl-1-propanol
Benzyl alcohol
Cyclohexanol
Cinnamyl alcohol
2-Propanol
2-Methyl-1-propanol
Benzyl alcohol
Cyclohexanol
Cinnamyl alcohol
2-Propanol
Benzaldehyde
Cyclohexanone
Cinnamaldehyde
Acetone
2-Methylpropanal
Benzaldehyde
Cyclohexanone
Cinnamaldehyde
Acetone
2-Methylpropanal
Benzaldehyde
Cyclohexanone
Cinnamaldehyde
Acetone
2-Methylpropanal
Benzaldehyde
Cyclohexanone
Cinnamaldehyde
Acetone
85
80
88
73
76
87
92
89
76
72
90
91
85
74
79
86
88
93
77
78
87
82
89
75
77
89
93
90
78
74
92
92
87
76
81
88
89
94
78
79
Co(II) BrSAMT
Pd(II) BrSAMT
Cu(II) BrSAMT
a
2-Methyl-1-propanol
b
2-Methylpropanal
Yield based on substrate; turn-over number, moles of product per mole of catalyst
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TRANSITION METAL COMPLEXES OF 5-BROMOSALICYLIDENE-4-AMINO-3-MERCAPTO-1,2,4-TRIAZINE-5-ONE
81
results in the selective oxidation at the alcoholic group of the unsaturated cinna-
myl alcohol to cinnamaldehyde, while the double bond remained unaffected. Sa-
turated aliphatic alcohols, such as 2-propanol and 2-methyl-1-propanol, were
converted to the corresponding aldehydes with high conversion.
Biological tests
The Cu(II), Co(II) and Ni(II) complexes of BrSAMT showed a greater zone
of inhibition compared to the uncomplexed Schiff base, indicating that these
complexes possess more antibacterial activity against pathogenic strains of gram
20,21
negative bacteria, such as E. Coli, P. aeruginosa, S. typhi and S. flexneri.
The results are given in Table II.
TABLE II. Antibacterial activity of the synthesised metal(II) complexes (Zone inhibition in cm)
S. Typhi
P. aeruginosa
E. Coli
S. Flexneri
Amount, µg
Compound
30
–
1.3
1.0
1.2
–
50
0.9
1.7
1.2
1.6
–
30
0.8
1.4
0.8
1.3
–
50
1.2
1.9
1.1
1.8
–
30
0.7
1.3
0.9
0.9
–
50
1.2
1.8
1.4
1.1
–
30
0.7
0.9
0.8
0.9
–
50
0.9
1.4
1.2
1.4
–
Ligand
Ni(II) BrSAMT
Co(II) BrSAMT
Cu(II) BrSAMT
Pd(II) BrSAMT
Nicotinic acid
DMF
1.8
–
2.0
–
2.4
–
2.6
–
2.4
–
2.7
–
1.3
–
1.8
–
CONCLUSIONS
Based on the above characterization data and keeping in mind the preferred
geometries, octahedral structures are proposed for the Co(II) and Ni(II) com-
plexes (Fig. 1) and square planar geometries for the Cu(II) and Pd(II) complexes
(Fig. 2). The newly synthesized complexes are good catalysts for the oxidation of
alcohols to the corresponding carbonyl compounds. The catalytic efficiency was
high when NMO was employed as the co-oxidant. The Cu(II), Ni(II) and Co(II)
complexes exhibited antibacterial activity against gram-negative bacteria, such as
E. Coli, P. aeruginosa, S. typhi and S. flexneri. Further studies on the catalytic
and biological applications are in progress.
Fig. 1. Proposed structure for the Ni(II) and Co(II)
complexes.
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82
RAMASUBRAMANIAN et al.
Fig. 2. Proposed structure for the Cu(II) and Pd(II)
complexes.
Acknowledgements. The authors are grateful to the Indian Institute of Science, Banga-
lore, for the NMR analysis.
И З В О Д
КОМПЛЕКСИ ПРЕЛАЗНИХ МЕТАЛА СА 5-БРОМОСАЛИЦИЛИДЕН-4-АМИНО-3-
-МЕРКАПТО-1,2,4-ТРИАЗИН-5-ОН ЛИГАНДОМ: СИНТЕЗА, КАРАКТЕРИЗАЦИЈА,
КАТАЛИТИЧКА И АНТИБАКТЕРИЈСКА ИСПИТИВАЊА
A.S. RAMASUBRAMANIAN, BADEKAI RAMACHANDRA BHAT, RAMAKRISHNA DILEEP и SANDYA RANI
Department of Chemistry, National Institute of Technology Karnataka, Surathkal,
Srinivasnagar – 575025, Karnataka State, India
Описана је синтеза, физичко-хемијскa и спектроскопскa карактеризација комплекса
Cu(II), Ni(II), Co(II) и Pd(II) са 5-бромосалицилиден-4-амино-3-меркапто-1,2,4-тризин-5-он
лигандом. Нађено је да су сви добивени комплекси ML-типа. На основу аналитичких пода-
така, IR спектросопије и магнетних мерења закључено је да комплекси Co(II) и Ni(II) имају
октаедарску, а комплекси Cu (II) и Pd(II) квадратно-планарне геометрију. Помоћу N-метил-
формолин-N-оксида и молекулског кисеоника као оксиданаса, у присуству наведених ком-
плекса као каталитичких агенаса, испитивана је оксидација бензил-алкохола, циклохекса-
нола, цинамил алкохола, 2-пропанола и изобутил-алкохола. Нађено је да неки од добијених
комплекса показују антибактеријске особине.
(Примљено 12. фебруара, ревидирано 1. јуна 2010)
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TRANSITION METAL COMPLEXES OF 5-BROMOSALICYLIDENE-4-AMINO-3-MERCAPTO-1,2,4-TRIAZINE-5-ONE
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