Nickel(II) complexes of 3-acetyl-4,5-dihydro-1,2,4-triazole hydrazones

Transition Metal Chemistry 29: 280–283, 2004. Ó 2004 Kluwer Academic Publishers. Printed in the Netherlands.

280

Nickel(II) complexes of 3-acetyl-4,5-dihydro-1,2,4-triazole hydrazones Adel M. Awadallah* and Nabil M. El-Halabi Department of Chemistry, Faculty of Science, Islamic University of Gaza, Gaza, Palestine Abdel-Rahman S. Ferwanah Department of Chemistry, Faculty of Science, Al-Azhar University of Gaza, P.O. Box-1277, Gaza, Palestine Boshra M. Awad Department of Chemistry, University College for Women, Ain Shams University, Heliopolis, Cairo, Egypt Received 04 August 2003; accepted 24 September 2003

Abstract 3-Acetyl-1,2,4-triazole hydrazones (3b,c) and methylhydrazone (4d) were prepared by reacting triazoles (1b–d) with an excess of hydrazines at room temperature. Square planar nickel(II) complexes (8b,c) of (3b,c) were obtained from their reaction with Ni(OAc)2 in a 2:1 mol ratio in EtOH at room temperature. The spectral data suggest structures (8b,c) for the obtained complexes, which result from ring opening of the triazole ring followed by recyclization to give the 5-arylhydrazono-2,3-dihydro-4H-1,2,4-triazine ligand (7b,c). The reaction of triazole methylhydrazone (4d) with Ni(OAc)2 in EtOH resulted, however, in the formation of the starting triazole (1d). All new compounds were characterized by elemental analysis, i.r., 1H-n.m.r. 13C-n.m.r. and hrms.

Introduction Substituted 1,2,4-triazoles have many practical applications: e.g., they are currently used as fungicides, [1–3]; insecticides [4, 5], antimicrobials, [6], herbicides, [7] and against animal parasites, [8]. Many 1,2,4-triazoles having different functionalities are used as dyes and photographic chemicals, [9, 10]. Polymers derived from triazoles currently embody the most important practical application of this heterocyclic system [11]. Metal coordination compounds with 1,2,4-triazoles and its derivatives have been reviewed recently by Haasnoot [12]. A new area is the search for triazole ligands to be used in iron(II) spin-crossover systems, [13, 14]. The synthesis of 3-acetyl-4,5-dihydro-1H-1,2,4-triazoles (1a–d) from 1,3-dipolar cycloadditions of cycloalkanone oximes and hydrazonoyl halides in the presence of triethylamine at room temperature was described by our group [15]. Quite recently, we have investigated the complexation reaction of 3-acetyl-1,2,4-triazole oximes (2a) with nickel(II) acetate (Ferwanah et al., unpublished results). X-ray structure determination revealed that metallation led to unexpected ring transformation of the triazole oxime to imidazole-N-oxide intermediate (5a) which coordinated to the nickel ion nickel(II) giving the square planar complexes (6a). * Author for correspondence

This encouraged us to investigate the reaction of 3acetyl-4,5-dihydro-1H-1,2,4-triazole- hydrazones (3b,c) and -methylhydrazone (4d) with nickel(II) acetate. Such ligands can behave as good bidentate species in complexation with metals.

Experimental Melting points (uncorrected) were determined on an electrothermal Mel. Temp. apparatus. I.r. spectra were obtained using Perkin-Elmer 237 i.r. spectrometer (KBr discs) 1H- and 13C-n.m.r. spectra were recorded on a Brucker 300 MHz instrument for solutions in CDCl3 at 21 °C, using TMS as an internal reference. Chemical shifts are expressed in d(p.p.m.) downfield from TMS. Electron impact ms were run on a Finnigan Mat 8200 and 8400 series double focusing sector field spectrometer at 70 eV. Triazoles (1a–d) were prepared from hydrazonoyl halides and keto-oximes as reported by our group [14]. Synthesis of 3-acetyl-1,2,4–triazole hydrazones (3b,c) To a solution of the respective triazole (1b,c) (1 mmol) in MeOH (50 cm3) was added N2H4 Æ H2O (80%, 5 mmol). The resulting mixture was stirred overnight at room temperature. The solvent was then evaporated at room temperature and the crude product was recrystallized from EtOH or CHCl3/petroleum ether (40–60 °C).

281 The following compounds were synthesized using this method. 3-Acetyl-1-(4-chlorophenyl)-1,2,4-triazaspiro[4.5]dec-2ene hydrazone (3b) From 0.29 g (1 mmol) of (1b): yield: 0.21 g (68%); m.p. 127–8 °C; 1H-n.m.r. 7.2–7.1 (m, 4H, aromatic protons), 5.52 (s, 2H, NH2), 5.35 (s, 1H, NAH), 2.1 (s, 3H, CH3C@N), 1.9–1.1 (m, 10H, cyclohexane protons); 13Cn.m.r.: 149.8 (C@NNH2), 143.8 (C@N), 138.7, 128.9, 127.0, 121.0 (aromatic carbons), 86.6 (C-5 ring spiro carbon), 35.8, 25.3, 23.8 (cyclohexane carbons), 9.9 (CH3); MS: m/z 305 (M+), 262 (M+-C3H7), 125 (ClC6H4N+), 111 (C6H4Cl+); HRMS (M+ found ¼ 305.140444; calcd. ¼ 305.140723; mass difference for C15H20ClN5 ¼ 0.90); i.r. cm)1 ¼ 3416, 3318, 3228 (3 NAH), 1628, 1595 (2 C@N) (Calcd.: C, 58.9; H, 6.6; N, 22.9. Found: C, 59.4; H, 6.8; N, 23.3%). 3-Acetyl-1-(4-chlorophenyl)-1,2,4-triazaspiro[4.6] undec-2-ene hydrazone (3c)

deep brown solid product was collected by suction filtration, washed with cold EtOH (5 cm3), and dried in vacuum. The following complexes were prepared using this method. Bis{3-methyl-4-(4-chlorophenylhydrazono)-1,2,5-triazaspiro[5,5]undec-2-ene}nickel(II) (8b) From 0.26 g (0.8 mmol) of (3b): yield: 0.10 g (35%); m.p. 233–235 °C; 1H-n.m.r.: 9.1, 7.0 (2d, 8H, aromatic protons), 5.9 (s, 2H, 2NH), 2.3 (s, 6H, 2CH3C@N), 2.2– 1.2 (m, 20H, 2cyclohexane protons); 13C-n.m.r.: 165.57 (C@NNH), 149.78 (C@N), 143.89, 133.63, 128.03, 120.84 (aromatic carbons), 74.17 (C-3 ring spiro carbon), 37.10/36.06, 25.08, 22.40/22.17 (cyclohexane carbons), 17.70 (CH3); MS: m/z 664 (M+); i.r. cm)1: 3245, 1476 (Calcd.: C, 54.1; H, 5.4; N, 21.0. Found: C, 54.4; H, 5.7; N, 20.7%). Bis{3-methyl-4-(4-chlorophenylhydrazono)-1,2,5-triazaspiro[5,6]dodec-2-ene}nickel(II) (8c)

From 0.31 g (1 mmol) of (1c): yield: 0.24 g (74%); m.p. 147–8 °C; 1H-n.m.r. 7.2–7.1 (m, 4H, aromatic protons), 5.48 (s, 2H, NH2), 5.27 (s, 1H, NH), 2.1 (s, 3H, CH3C@N), 2.0–1.1 (m, 12H, cycloheptane protons); 13 C-n.m.r.: 149.2 (C@NNH2), 143.5 (C@N), 138.7, 129.0, 126.1, 119.5 (aromatic carbons), 89.3 (C-5 ring spiro carbon), 39.3, 28.5, 22.7 (cycloheptane carbons), 9.9 (CH3); MS: m/z 319 (M+), 262 (M+-C4H9), 125 (ClC6H4N+), 111 (C6H4Cl+); HRMS (M+. found ¼ 319.156307; calcd. ¼ 319.156373; mass difference for C16H22N5Cl ¼ 0.19); i.r. cm)1 ¼ 3417, 3316, 3229 (3 NAH), 1627, 1592 (2 C@N) (Calcd.: C, 60.1; H, 6.9; N, 21.9. Found: C, 60.5; H, 7.1; N, 22.3%).

From 0.20 g (0.65 mmol) of (3c): yield: 0.07 g (33%); m.p. 235–237 °C; 1H-n.m.r.: 9.1 , 7.1 (2d, 8H, aromatic protons), 5.7 (s, 2H, 2NH), 2.3 (s, 6H, 2CH3C@N), 2.2– 1.3 (m, 24H, 2cycloheptane protons); 13C-n.m.r.: 165.25(C@NNH), 149.45 (C@N), 143.15, 133.63, 128.18, 121.09 (aromatic carbons), 78.83 (C-3 ring spiro carbon), 40.75/38.63, 30.87/30.74, 21.99/21.81 (cycloheptane carbons), 17.81 (CH3); MS: m/z 692 (M+); HRMS (M+ found ¼ 692.216402; calcd. ¼ 692.216788; mass difference for C32H40N10Cl2Ni ¼ )0.55); i.r. cm)1 ¼ 3247, 1478. (Calcd.: C, 55.4; H, 5.8; N, 20.2. Found: C, 55.6; H, 6.1; N, 19.8%).

Synthesis of 3-acetyl-8-tert-butyl-1-(4-chlorophenyl)1,2,4-triazaspiro[4.5]dec-2-ene methylhydrazone (4d)

Results and discussion

To a solution of the triazole (1d) (0.52 g, 1.5 mmol) in MeOH (50 cm3) was added MeNHNH2 (0.2 cm3, 3 mmol) and the resulting mixture was stirred overnight at room temperature. The solvent was then evaporated at room temperature and the resulting product was recrystallized from EtOH. Yield: 0.27 g (49%), m.p. 142–143 °C. MS: m/z 375 (M+), 276 (M+-C7H15), 125 (ClC6H4N+), 111 (C6H4Cl+); HRMS (M+ found ¼ 375.219221; calcd. ¼ 375.218973; mass difference for C20H30N5Cl ¼ )0.67); i.r. cm)1 ¼ 3477, 3316 (2 NAH), 1640, 1588 (2 C@N). Synthesis of nickel(II) complexes (8b,c) To a solution of the triazole hydrazone (2 mmol) in absolute EtOH (25 cm3) was added a solution of Ni(OAc)2 (1 mmol) in absolute EtOH (25 cm3). The resulting reaction mixture was stirred overnight at room temperature, then refrigerated for 2 h. The

The hydrazones (3b,c, 4d) are readily accessible via direct reaction of acetyl triazoles with an excess of hydrazine at room temperature (Scheme 1). All new hydrazones gave satisfactory elemental analyses and exhibited consistent i.r. and n.m.r. spectra, ms and HRMS. The reaction of the respective hydrazones (3b,c) with nickel(II) acetate tetrahydrate, in a 2:1 mole ratio was conducted in ethanol at room temperature for 24 h. The black stable complexes, which formed, were insoluble in water, but soluble in acetone and chloroform. The spectral data suggested structures (8b,c) for the formed complexes, which resulted from opening of the triazole ring and recyclization to give the 5-arylhydrazono-2,3-dihydro-4H-1,2,4-triazine ligand (7b,c). This is similar to the reaction of the triazole oximes with nickel(II) ions. The 4N-donor set comprises both triazine nitrogen and arylhydrazone nitrogen. The whole process is associated with loss of one hydrogen molecule.

282 R R R R

R R HN O

HN

NH2X

N Ar N

N

X= OH, NH2

N Ar N

X CH3

CH3

HN 4d X = NHCH3

O

Ni(OAc)2 .4H2O

N Ar N

CH3

(2-4)

(1d)

(1a-d) (2a) X = OH

(3b,c) X = NH2 Ni(OAc)2.4H2O ring transformation

R

R R HN

H N Ar

H N

R

N

N

CH3

(5a)

(7b,c)

N N

R

N

N

Ar

R

Ni

R

H3C

O N

N

Cl

N

N

O

N

(8b,c)

Ar = 4-ClC6H4

CH3

N Ar

N

CH3

(6a)

R, R

Ni

NH R R

N

CH3

a

N

N

R R HN

N

N

Entry

N

CH3

H3C

R

H N Ar

N

O

Cl

H N

b

c

d

Spectral data (i.r., mass, 1H-n.m.r.) indicated that there is no NH2 group in the complexes, A signal for only one NAH group was observed, which supports the suggested structure containing two symmetric NAH groups. The i.r. spectra of the complexes (8b,c) (KBr discs) show one NH band at ca. 3246 cm)1. The electron impact (EI) mass spectra of the complexes (8b,c) display the correct molecular ions in accordance with the suggested structures. HRMS was also done for compound (8c). 1 H-n.m.r. showed one signal for the two symmetric NAH groups at ca. 5.7 p.p.m., which support the suggested structures. The signals for CH3 groups appear at ca. 2.3 p.p.m.. Signal doubling is observed for the 2R groups because they are not symmetric with respect to the metal. 13C-n.m.r. spectra display characteristic signals of the suggested structures. The signal for C3 (spiro carbon of the triazine ring) appears at ca.

76 p.p.m.; this is similar to the reported values for spiro carbons in six-membered heterocycles [16]. The two C@N signals appear at 165, 149 p.p.m. CH3 signals appear at ca. 18 p.p.m. Signal doubling is also observed for the 2R groups in the 13C-n.m.r. spectra of complexes (8b,c). The electronic spectra of the nickel(II) complexes (8b,c) display a distinct absorption band of medium intensity at ca. 18,450 cm)1 which supports the square planar diamagnetic structure of the complexes [17]. The reaction of the triazole methylhydrazone (4d) with nickel(II) acetate tetrahydrate or with Palladium(II) acetate, gave however, the starting triazole (1d).

Acknowledgements The authors thank Dr W. Schrader, Max-Planck Institut fu¨r Kohlenforschung, Mu¨lheim, Germany, for ob-

283 taining the ms spectra, and Dr Jalal Ahmed, Jordan University, Amman, Jordan, for obtaining the n.m.r. spectra. Thanks are also due to the Islamic University of Gaza, and the Union of the Arab Universities for financial support.

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