Studies on 2-benzenesulphonamidomethyl benzimidazole as a metal chelating agent

J. inorg,nucl. Chem., 1973,Vol.35, pp. 517-522. PergamonPress. Printedin Great Britain

STUDIES ON 2-BENZENESULPHONAMIDOMETHYL BENZIMIDAZOLE AS A METAL CHELATING AGENT N. N. G H O S H and A. B H A T T A C H A R Y Y A Inorganic Chemistry Laboratory, University College of Science, 92 Acharyya Prafulla Chandra Road, Calcutta-9, India (Received 15 ,/anuary 1972)

Abstract--2-Benzenesulphonamidomethyl benzimidazole has been synthesised and studied as a metal complexing agent. Cu(II), Ni(II) and Co(II) chelates and physico-chemical properties of the ligand and its metal chelates are reported. INTRODUCTION

THE BENZE~ESULPHOZ~AMIOOderivatives of benzimidazoles have been investigated mainly for their physiological activity[I-4]. However, properly substituted

derivatives may be of considerable importance as chelating agents. With this in view, 2-benzenesulphonamidomethyl benzimidazole (RH) has been synthesised and studied as a metal complexing agent. Various physico-chemical properties of the ligand (R H) as well as of its metal chelates have been recorded. EXPERIMENTAL The compound (RH) was prepared following the method developed by Phillips [5], i.e. condensation of o-phenylene diamine and organic carboxylic acid in presence of bioling 4N hydrochloric acid and also by method of fusion [6]. Method I

o-Phenylene diamine (0.02 mole), N-benzenesuiphonyl glycine (0.03 mole) and 20 ml 4N hydrochloric acid were bioled under reflux for 30-40 rain. On neutralisation of the filtered solution with ammonia, the benzimidazole separated; it was filtered, washed thoroughly with water and recrystallised from warm aqueous ethanol. White shining crystals were obtained (m.p. 183°C). Method !1

An intimate mixture of equimolar quantities (0-02 moles) of N-benzenesuiphonyl glycine and ophenylene diamine was fused for 10 min, maintaining the temperature at 130°- 135°C. The fused mass was extracted with 25 ml hot 4N hydrochloric acid. On neutralisation of the cooled extract with ammonia (pH ~ 6) a white compound separated. It was filtered and recrystallised from warm aqueous ethanol (m.p. 183°C). (Found: C, 58.03; H, 4.72; N, 14.25. C14HjzO2N3S requires C, 58-53; H, 4.53; N, 14.63%.) On crystallisation of the hydrochloric acid solution of the reagent (ph = 2) white shining crystals I. T. R. Castles and H. E. Williamson, J. Pharm. Sci. 53, 1128 (1963). 2. M. Itaya, Yakugaku Zasshi 82, 469 (1962), C.A. 58, 3413d. 3. K. Otaki, J. Inoue, Z. Yamazaki, M. Itaya, Y. Takai, M. Yasue and D. Mizuno, Yakugaku Zasshi 85, 926 (1965); C.A. 64, 243f. 4. J. Tamm, R. Bablanian, T. M. Nemes, C. H. Shunk, F. M. Rombinson and K. A. Folkers, ,/. expt. Med. 113,625 (1961). 5. M. A. Phillips,,/. chem. Soc. 2393 (1928). 6. J. K. Hughes and F. Lions, J. Proc. R. Soc. N.S.W. 71,209 (1938). 517

518

N.N.

G H O S H and A. B H A T I ' A C H A R Y Y A

of its hydrochloride (RH, HCi) separated (m.p. 229°C). (Found: Eqv. wt., 321"0; CI, 10"79. Calc. Eqv. wt., 323.5; Cl, 10.97%.) Electronic spectra in ethanolic and in dimethylformamide solutions of R H and its hydrochloride were measured at room temperature. Data are stated in Table I. I.R. spectra of them in a KBr matrix were also recorded and assignments [7-9] of some of the vibrations were made. By potentiometric titration of RH, HCI in aqueous solution at constant ionic strength (/z = 0.25) at 25°(2 a p l ~ value ofRH2 + was obtained. The value ofpKo was obtained by Bjerrum's half-t~-method and found to be 4.82 _ 0-02. Table 1. Electronic spectral data of (RH), (RH, HCI) and some of the metal chelates and magnetic moments of the metal chelates EtOH ~"m a x

Species RH

RH, HCI CUR2, H~O CuR2

NiR~

(nm)

DMF

270 3.48 264 3.59 220 3.75 265 3.65 221 3.78 630 360 271 265 220 > 1000 750 660 550 390 271 265 221

Temperature /~en

~" m a x

log •

1.38 1.89 3.86 3.98 4.12 0.73 1.16 0.94 2.22 3.81 3-93 4.09

(nm)

log •

270 265 221 264 221

3-51 3-62 3"80 3.63 3"77

645 350 270 264 221 > 1000 750 650 550 380 271 265 220

1.36 1.90 3-85 3.96 4.10

> 1000 920 0.12 580 1.23 500 1.81 271 3.80 264 3.95 221 4.06

PREPARATION

(BM)

303 303

2.10 2-11

303

3.33

303 303

3"34 5-03

0.72 1.18 0.90 2.19 3.80 3.98 4.08

NiR~Py2

CoR2

(*K)

> 1000 910 0"13 580 1.24 490 1-83 271 3.83 265 3.92 221 4.12

OF THE METAL CHELATES

Cu(ll) complexes: CuR~, H~O and CuR2 The reagent (RH) and copper acetate in the ratio (2: 1) were dissolved in ethanol. A deep green solution was obtained. On keeping shining green crystals separated. They are insoluble in water but highly soluble in ethanol, pyridine and dimethyiformamide. (Found: Cu, 9.76; N, 12.64. CuRzH20 requires Cu, 9.73; N, 12-85%.) 7. L.J. Bellamy, The Infrared Spectra of Complex Molecules. Methuen, London (1954). 8. D.J. Robigs and M. M. Joullie, J. org: Chem. 29, 476 (1964). 9. D. H. Williams and J. Flemming, Spectroscopic Methods in Organic Chemistry. McGraw-Hill, New York (1966).

2-benzenesulphonamidomethyl benzimidazole

519

On dehydration at 110°C its loss in weight corresponded to one molecule of water and its colour changed to botflegreen. (Found: Cu, 9.98; N, 13.01. CuR2 requires Cu, 10.00; N, 13.22%.) N i( l l ) complexes: N iR2 and N iR2Py2 A mixture of the reagent (RH) and nickel acetate in aqueous ethanol in the ratio (2 : 1) was warmed on a waterbath, pH being adjusted to about 6.0 with dilute ammonia. The dull-red nickel complex separated, was filtered and washed with ethanol. It is insoluble in water, sparingly soluble in ethanol but fairly soluble in pyridine and dimethylforrnamide. (Found: Ni, 9.34; N, 13.54. NiR2 requires Ni, 9-31; N, 13.32%.) The deep blue pyridine solution of NiR2 was mixed with aqueous ethanol (1:1) and kept overnight. Blue crystals separated. They were collected, washed with ethanol and dried in a desiccator over N a O H in a pyridine atmosphere. (Found: Ni, 7.31; N, 13.76. NiR2Py~ requires Ni, 7.44; N, 14.20%.) On heating at 110°C for several hours, there was loss in weight corresponded to 2 molecules of pyridine (loss found, 20.01 : Calc., 20.04%) and the original dull-red colour of NiRz reappeared.

Co(ll ) complex: CoR2 Vermilion red crystals were obtained from a mixture of the reagent (RH) and cobalt acetate in the (2: 1) in ethanol. (Found: Co, 9.33; N, 12.78. CoR2 requires Co, 9.34; N, 13-31%.) Magnetic susceptibility measurements on all the complexes were made at room temperature. Results are included in Table 1. The electronic spectra in ethanolic and in dimethylformamide solutions of the complexes were measured at room temperature. Data are recorded in Table 1. I.R. spectra in KBr matrices of the complexes were recorded and assignments [7-10] of some of the vibrations were made. DISCUSSION

The reagent 2-benzenesulphonamidomethyl benzimidazole (RH) is an imidazole as well as a sulphonamide derivative. It has yielded water insoluble complexes with Cu(II), Co(II) and Ni(II). In view of the constitution of metal complexes with imidazole derivatives [11-13] and those of the sulphonamides [ 14] bonding through the four nitrogen atoms is to be expected. The ionisation of the imido-hydrogen of the sulphonamide group occurs on complex formation. Magneto-chemical data suggest the complexes are high spin octahedral complexes, as also do the absorption spectral studies. Copper complexes usually have a distorted octahedral stereochemistry, although a few are known which are square planar or approximately tetrahedral stereochemistry. Their magnetic moment values are ranging from 1.8 to 2-2 BM [15, 16]. Octahedral Ni(II) complexes should show magnetic moments ranging from 2.9 to 3.4 BM depending on the magnitude of the orbital contribution while the tetrahedral complexes have moments 3.5-4-2 BM [ 15, 17]. In the present case the Ni(II) complexes were found to have /~eff = 3.33 and 3.34 BM suggests an octahedral structure. In the case of the cobalt complex, the observed magnetic moment is 5.03 B M - a value expected for a high spin octahedral complex [15, 16]. 10. K. Nakamoto, Infrared spectra of Inorganic and Coordination Compounds. Wiley, New York (1963). 11. A. K. Banerjee and S. P. Ghosh, J. Ind. chem. Soc. 38, 237 ( 1961 ). 12. M. Goodgame and L. I. B. Haines, J. chem. Soc. (A), 174 (1966). 13. M. Goodgame, D. M. L. Goodgame and M. J. Weeks, J. chem. Soc. (A), 1125; 1676 (1967). 14. N. N. Ghosh and M. N. Majumdar, J. Ind. chem. Soc. 44, 559 (1967). 15. P.W. Selwood, Magnetochemistry. Interscienee, New York (1956). 16. B.N. Figgis andJ. Lewis, Prog. inorg. Chem. 6, 37 (1964). 17. N. S. Gill and R, S. Nyhlom, J. chem. Soc. 3997 (1959).

520

N.N.

G H O S H and A. B H A T T A C H A R Y Y A

The electronic spectra of the Cu(l I) complexes show characteristic band in the region 900-600 nm [ 18]. The absorption maxima at 630 nm in ethanolic solution shifts to a higher wavelength (a red shift) 645 nm in dimethylformamide solution and a blue shift from 360 to 350 nm as well has been observed. However, the Cmax values in both the solvents support distorted octahedral structure [ 19]. For Ni(II) and Co(II) complexes in both ethanolic and dimethylformamide solutions there is clear indication of a maximum at a wavelength beyond 1000 nm. The absorption maxima actually observed and corresponding Emax values support octahedral structure for the complexes. For Ni(II), the absorption bands at 750, 660, 550 and 390 nm are in accordance with the expected transitions from aA2u state to aTlo(F), lEo(D), 1AI,(G) and ZTlu(P) states respectively[20]. The cobalt complex shows absorption bands at 920, 580 and 500 nm due to known transitions for octahedral complexes, i.e. from 4Tlg ground state to 2Eg, 4A2g(F) and 4T~g(P) states respectively. In dimethylformamide solutions the absorption bands at 750, 650, 550 and 380 nm for Ni(II) complex and 910, 580 and 490 nm for Co(II) complex have been observed. In dimethylformamide solutions shifts of some of the bands to shorter wavelengths occur. However, the absorption spectra in both the solvents support a distorted octahedral structure. The red shift of the d-d band of CuR2 indicates that D M F is a more strongly coordinating axial ligand than ethanol and it is clear that the position of this band is a useful indication of the degree of tetragonal distortion [21], supporting a square planar or much greater tetragonally distorted structure for the Cu(II) complex CuRs. Similar effects have been observed with tetragonal Ni(II) complexes[22], but to a lesser degree. However, in both the Ni(II) and Co(II) complexes, blue shifts in D M F of the bands at 660 and 920 nm are observed. So it is apparent that the axial interaction already exists in NiR2 and CoR~ but it is much weaker in the Cu(II) complex. The absorption bands in both solvents at lower wavelength region are mainly due to the ligand. The log ~ values of the metal chelates and the ligand at those wavelengths are found to differ by about 0-3 in each case. This is due to the presence of two ligands in the metal chelates, apparently on chelation the molar extinction values remain almost unaltered. A similar result has also been reported in the complex compounds formed by the chelating a g e n t s - benzene-azo-(acetylacetone) and benzene-azo-(ethylaceto-acetate) [23]. Electronic spectra of the ligand and its hydrochloride in ethanolic as well as in dimethylformamide solution show a number of peaks in the u.v. region (vide Table 1). The peak at 270 nm due to ligand (I) in both solvents has disappeared in the spectra of its hydrochloride. But on complex formation it does not disappear. This may be due to immobilisation of the unshared pair on the basic nitrogen on protonation forming a benzimidazolium ion which is best represented as a symmetrical resonance hybrid (II)[8, 24]. The protonation and complex formation 18. F . A . Cotton and G. Wilkinson,,4dvancedlnorganic Chemistry. Interscience, New York (1962). 19. A. B. P. Lever, Inorganic Electronic Spectroscopy, Chap. 9. Elsevier, Amsterdam (1968). 20. J. Lewis and R. G. Wilkins (Editors), Modern Coordination Chemistry. Interscience, New York (1960). 21. A. B. P. Lever and E. Mantovani, lnorg. Chem. 10, 817 (197 I). 22. D. A. Rowley and R. S. Drago, lnorg Chem. 7, 795 0968). 23. N. N. Ghosh and S. Maulik,J. Ind. chem. Soc. 46, 675 (1969). 24. R. C. Elderfield (Editor), Heterocyclic Compounds, Vol 5, p. 194. Wiley, New York (1957).

2-benzenesulphonamidomethyl benzimidazole

521

(III) may be depicted as below:

H

H +H +

~+N/)cCHzN

HSOz~

I H+ ~/~CH2NHSO2~ H II H N ~C "

-Nh/ C C H ~ N~H S ~O 2 ~

+ ½MO'+ "

~k-.~ H

+H +

% / ~

lq2so 2 _ _ ~

Ill / The i.r. spectral data show shifts in -SO2N

stretching frequency from 1346 \ cm -~ (iigand) to lower frequencies ( - 1278 cm-') in the complexes. It is likely that these are associated with ionisation of the imido-hydrogen of the suiphonamide group, as closely comparable shifts have also been observed in the salts of the type-Na2Cu(Rt)2 where RtH2=N-p toluenesulphonyl glycine[25]. Other shifts in C=N stretching, 1665 cm-' (ligand) and heterocyclic breathing modes 860, 785 and 775 cm-' (ligand) to lower frequencies ( - 1656, 849, 766 and 755 cm-') have also been observed on complex formation. They may be regarded as evidences of bonding of the nitrogen in -SO2N / as well as the basic nitrogen in \ the imidazole ring to metal. In the complexes of benzimidazole derivatives, coordination takes place through the tertiary nitrogen as has been shown by i.r. spectral studies[26,27] and confirmed by stability studies[28]. This leads to different frequencies for the N - H vibrations in the complexes and the benzimidazole itself. But in this case such investigation is not possible because of presence of other N - H vibrations in the ligand. The M - N stretching frequencies ( - 596 cm -1) in the complexes are also observed. If the complexes are distorted / octahedral there is likelihood of intermolecular interaction. The shift in -SO~N \ 25. N. N. Ghosh and A. Bhattacharyya,J. Ind. chem. Soc. 48, 889 ( 1971). 26. W.J. Eilbeck, F. Holmes and A. E. Underhill, J. chem. Soc. (A) 757 (1967). 27. T. R. Harkins, J. L. Walter, O. E. Harris and H. Freiser, J. Am. chem. S~,,c, 78, 260 ( 19561. 28. T. 3. Lane and K. P. Quinlan, J. A m . chem. Soc. 82, 2994 (1960).

522

N . N . G H O S H and A. B H A T T A C H A R Y Y A

stretching frequency from 1164 cm -1 (ligand) to lower frequencies ( - 1148 cm -~) in the complexes may be evidence of such interactions through an O atom of / -SO~N group. \ It is also possible that ligand may form octahedral complexes of the type [MNd by intramolecular interaction. The bidentate behaviour of benzimidazole [12] and 2-methylbenzimidazole[29] has been reported. So the ligand R H may be tridentate. The i.r. spectral data of the ligand and its hydrochloride show shifts in C=N stretching, 1665cm -1 (ligand) and heterocyclic breathing modes, 860cm -1 (ligand) to higher frequencies, 1675 and 890cm -1 (hydrochloride). These are probably associated with the protonation of one nitrogen in the imidazole ring. From potentiometric titration pKa value for R H ~ + in water has been found to be 4.82 ___0.02. For a comparison pKa values reported for a number of benzimidazoles [8] with different substituents in 2-position are recorded in Table 2 along with that of RH. Table 2. pK~ values of substituted benzimidazoles Substituent in 2-position CzH5 CH3 PKa

6.20

6.19

H

CH~NHSO2CsHs

COCHa

CF3

5.53

4.82

4.61

4.51

The data in Table 2 show that the shifts in the basicity of the benzimidazoles follow the electron-attracting and electron-repelling inductive effects of the substituents and the pKa values obtained in the case of RH is in accordance with the presence of an electron-attracting benzenesulphonyl group in the furthest end 2=position. Acknowledgements-Our grateful thanks are due to Professor D. K. Banerjee, Indian Institute of Science, Bangalore for i.r. spectra. We are also indebted to University Grants Commission for financial assistance. 29. S. P. Ghosh and L. K. Mishra, J. Indian chem. Soc. 47, 1151 (1970).