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Photochemical reactions of [M[(CO).sub.6]] (M = Cr, Mo & W) with di & tri-dentate Schiff bases.


Schiff bases are compounds that are easily synthesized and many of Schiff bases in general are found to possess physiological biological and pharmaceutical activities such as antibacterial, antidiabetic, antihelmintic and antidepressant [1-5]. Monodentate Schiff bases are not known to form stable complexes, probably due to the insufficient basic strength of imino nitrogen of the C = N group. Polydentate Schiff bases with phenolic OH or nitrogen or sulphur of the ring, suitably near to the imino nitrogen may stabilize the metal-nitrogen bond through the formation of chelate rings [6a]. Bromhexine is a mucolytic agent used in the treatment of respiratory disorders associated with viscid or excessive mucus. In addition, bromhexine has antioxidant properties[6b]. However, from literature survey it appears that no G-6 metal carbonyl complexes, with these Schiff bases have yet been reported. In search of more biologically effective agent and industrial utility lead to explore a variety of chemical entities with biological properties.

In this paper we have used five Schiff bases (I) namely 2,4-dibromo-6-{[cyclohexyl(methyl)amino]methyl}-N-(-4- methoxyphenyl methylidene)aniline (BROM-ANIS), 2,4-dibromo-6-{[cyclohexyl(methyl)amino]methyl}-N-(-2,4-dimethylphenyl methylidene)aniline (BROM-DMB), 2,4-dibromo-6-{[cyclohexyl(methyl)amino]methyl}-N-(-2-methylphenyl methylidene)aniline (BROM-MB), 2,4-dibromo-6-{[cyclohexyl(methyl)amino]methyl}-N-(-2-hydroxyphenyl methylidene)aniline (BROM-HB) and 2,4-dibromo-6-{[cyclohexyl(methyl)amino]methyl}-N-(-3-methoxy-2-hydroxyphenyl methylidene)aniline (BROM-o-VANI) as ligands in the CO displacement reactions of M[(CO).sub.6] (where M = Cr, Mo and W) have been investigated. We describe the preparation and characterization of new complexes {M[(CO).sub.4][BROM-ANIS]}; {M[(CO).sub.4][BROM-DMB]}; {M[(CO).sub.4][BROM-MB]}; {M[(CO).sub.3][BROM-HB]} & {M[(CO).sub.3][BROM-o-VANI]} where (M= Cr, Mo & W), which are prepared by photochemical reaction between M(CO)6 with (BROM-ANIS), (BROM-DMB), (BROM-MB), (BROM-HB) and (BROM-o-VANI). The complexes were characterized by physical, elemental and infrared analyses. The spectroscopic studies suggest bidentate coordination of ligands in {M[(CO).sub.4][BROM-ANIS]}, {M[(CO).sub.4][BROM-DMB]} and {M[(CO).sub.4][BROM-MB]} and tridentate coordination of ligands in {M[(CO).sub.3][BROM-HB]} and {M[(CO).sub.3][BROM-o-VANI]} where (M = Cr, Mo and W).


1. (BROM-ANIS; [R.sub.1] = OC[H.sub.3]; [R.sub.2] = H; [R.sub.3] = H)

2. (BROM-DMB; [R.sub.1] = C[H.sub.3]; [R.sub.2] = H; [R.sub.3] = C[H.sub.3])

3. (BROM-MB; [R.sub.1] = H; [R.sub.2] = H; [R.sub.3] = C[H.sub.3])

4. (BROM-HB; [R.sub.1] = H; [R.sub.2] = H; [R.sub.3] = OH)

5. (BROM-o-VANI; [R.sub.1] = H; [R.sub.2] = OC[H.sub.3]; [R.sub.3] = OH) (1)


Reactions were carried out under dry argon or in vacuo. All solvents were dried and degassed prior to use. Infrared spectra were recorded on a Perkin-Elmer spectrophotometer (Model-577) in KBr discs. All the melting points were determined cryoscopically in benzene.

The Schiff bases were prepared by the method given in the literature [1]. Chromium hexacarbonyl, Molybdenum hexacarbonyl and Tungsten hexacarbonyl (Aldrich) was used as supplied.

Complexes {M[(CO).sub.4][BROM-ANIS]}(M = Cr, Mo and W), (1a)-(1c), [(1a), M = Cr; (1b), M = Mo; (1c), M = W]; {M[(CO).sub.4][BROM-DMB]}(M = Cr, Mo and w), (2a)-(2c), [(2a), M = Cr; (2b), M = Mo; (2c), M = W]; {M[(CO).sub.4][BROM-MB]}(M = Cr, Mo and w), (3a)-(3c), [(3a), M = Cr; (3b), M = Mo; (3c), M = W]; {M[(CO).sub.3][BROM-HB]}(M = Cr, Mo and W), (4a)-(4c), [(4a), M = Cr; (4b), M = Mo; (4c), M = W]; & {M[(CO).sub.3][BROM-o-VANI]}(M = Cr, Mo and W), (5a)-(5c), [(5a), M = Cr; (5b), M = Mo; (5c), M = W] were prepared by photochemical reactions of M[(CO).sub.6] where (M = Cr, Mo & W), with Schiff bases (BROM-ANIS), (BROM-DMB), (BROM-MB), (BROM-HB) and (BROM-o-VANI) were obtained in 50-64% yields by similar methods described below. Details of representative compound only are given below. Other compounds and their characterization data are given in Table-1.

Preparation of complex (1a), Tetra carbonyl 2,4-dibromo-6-{[cyclohexyl(methyl)amino] methyl}-N-(-4-methoxyphenyl methylidene)aniline chromium (0) {M[(CO).sub.4][BROM-ANIS]}

Hexacarbonyl Chromium (0) (0.440g, 2mmole) and 2,4-dibromo-6-{[cyclohexyl (methyl)amino]methyl}-N-(-4-methoxyphenyl methylidene)aniline (0.986g, 2mmole) were dissolved in benzene (25[cm.sup.3]) and the mixture was irradiated for 5h using a 400Watt medium pressure mercury lamp in a quartz bulb. During irradiation yellow precipitate formed. It was filtered, washed with n-pentane several times to remove unreacted reactants. Product was recrystallised in dioxane and dried in vacuo to give microcrystals of {M[(CO).sub.4][BROM-ANIS]} (0.28g 64%).

The other 14 complexes (1b-5c) were prepared according to same procedure as described for the preparation of above complex by using appropriate G-6 metal hexacarbonyl {Cr[(CO).sub.6] or Mo[(CO).sub.6] or W[(CO).sub.6]}.


Results and Discussion

Complexes (1a)-(5c) were prepared by a photochemical reaction as shown is Scheme I-V. Analytical data for {M[(CO).sub.4][BROM-ANIS]}; {M[(CO).sub.4] [BROM-DMB]}; {M[(CO).sub.4][BROM-MB]}; {M[(CO).sub.3][BROM-HB]} & {M[(CO).sub.3][BROM-o-VANI]} where (M = Cr, Mo & W); complexes are given in Table-2. The photogeneration of M[(CO).sub.5] from M[(CO).sub.6] (M = Cr, Mo & W) has been extensively studied. These 16-electron M[(CO).sub.5] fragments react quickly with any available donor atom to yield a M[(CO).sub.5]L species; and where L is a chelating bidentate ligand, rapid continuation to the chelating M[(CO).sub.4]L or bridging [M.sub.2][(CO).sub.10] ([micro]-L) products may occur [7-10]. In this study, photochemical reactions of M[(CO).sub.6] (M = Cr, Mo & W) with (BROM-ANIS), (BROM-DMB) and (BROM-MB) Schiff base ligands occurs in this expected manner, and gave hither to unknown series of complexes (1a)-(1c); (2a)-(2c) and (3a)-(3c) and however the formation of (4a)-(4c) and (5a)-(5c) occur via the co-ordination of metal atom via phenolic-O, imine-N and amine-N donor atoms. Important IR spectral bands M[(CO).sub.4]L (L = (BROM-ANIS); (BROM-DMB) and (BROM-MB) and M = Cr, Mo & W) and M[(CO).sub.3]L (L = (BROM-HB) and (BROM-o-VANI); M = Cr, Mo & W) are presented in Table-4.

Infrared spectra of all the Schiff bases show a new band in the range 1630-1635 [cm.sup.-1], attributable to the formation of an imino group which was shifted to a lower frequency region about 1610-1615 [cm.sup.-1] in complexes (1a)-(5c) indicating that the v(C-N) group is taking part in coordination to M[(CO).sub.4] fragment [10,11]. This may be due to a decrease in the bond order of v (C = N) or weakening of the C=N bond resulting from the loss of electron density from the nitrogen to the metal atom (Cr, Mo and W) [6,10.11]. Which is further supported by the appearence of a new band in the range 380-390 [cm.sup.-1] (s) in the far-IR spectra of the complexes which may be assigned to the v (M-N) mode [12]. The OH stretching vibration, v(OH), found as a medium band at 3210 [cm.sup.-1] in the Schiffbases (BROM-Hb) and (BROM-o-VANI) disappeared in the spectra of the complexes (3a)-(5c) in the range ~420-[425cm.sup.-1], which may be assigned to the v(M-O) mode [13].

The characteristics frequency of a C-N bond of the type -C[H.sub.2]-N-(C[H.sub.3])([C.sub.6][H.sub.10]) was observed in the range 1300-1306 [cm.sup.-1] (s)in all Schiff bases shift to a lower wave number in the range 1280-1286 [cm.sup.-1] in complexes (1a)-(5c), which indicate the donation of a lone pair of nitrogen atom as expected [14]. This fact is further supported by the appearance of a new low frequency band in the range 380-390 [cm.sup.-1](s) assigned to metal-nitrogen (M-N) bond formation [15,16]. Further evidence about this interaction can be correlated with the decrease in v(CO) modes of (1a)-(5c) complexes move to lower wave numbers in comparision with the starting M[(CO).sub.6] (M = Cr, Mo & W) molecules [2,7]. This decrease in the frequency of CO absorption is because of the accumulation of charge density on metal atom (Cr, Mo and W) which stabilizes itself by transferring it back to the nearby CO (a n-acceptor ligand) [14]. The sharp peak observed in the range 2851-2857 [cm.sup.-1] assigned to C-H stretching of benzene ring. The bond observed in the range 1590-1592[cm.sup.-1] can be assigned to C-C stretching [15-17].

Four bands in the range (2001-2010 [cm.sup.-1]), (1896-1906 [cm.sup.-1]), (1865-1876 [cm.sup.-1]) and (1820-1832 [cm.sup.-1]) arising from v (CO) vibrations are seen which presumably have local Ca, symmetry of M[(CO).sub.4] unit in {M[(CO).sub.4][BROM-ANIS]}; {M[(CO).sub.4][BROM-DMB]} and {M[(CO).sub.3][BROM-MB]} (M = Cr, Mo and W) complexes (Scheme I-III). These values are in close resemblance to the values of v (CO) vibration for other nitrogen containing disubstituted group-6 metal carbonyls [13, 16, 18, 19]. While infrared spectra of the tricarbonyl metal complexes {M[(CO).sub.3][BROM-HB]} and {M[(CO).sub.3][BROM-o-VANI]}(M = Cr, Mo and W) (Scheme IV-V) showed three bands in the carbonyl stretching region (2001-2015 [cm.sup.-1]), (1895-1912 [cm.sup.-1]) and (1865-1887 [cm.sup.-1]) as expected [8, 20-23]. The presence of normal Schiff base bands indicated that these bands were intact in the complexes. The nature and number of CO bands resemble closely to the bands of other known di and trisubstituted metal carbonyls [18,23].

Antibacterial Activity

All the synthesized Schiff bases were screened for their antibacterial activity by using agar diffusion method [24] against S. aureus, B. subtile gram positive and E. coli, S. paralyphi gram negative bacteria in nutrient agar medium. Ciprofloxacin was used as standard drug for comparison.

With the help of activity data it could be observed that Schiff base BROM-DMB showed good activity against E.coli. Schiff bases BROM-o-VANI, BROM-MB exhibited good activity against S. paratyphi-B. While the remaining Schiff bases BROM-ANIS & BROM-HB are less or inactive against all bacteria.


In summary (BROM-ANIS), (BROM-DMB) and (BROM-MB) behave as bidentate ligands via N-imine donor atom and amine nitrogen atom (attached with cyclohexyl ring of ligand) in complexes (1a)-(1c), (2a)-(2c) and (3a)-(3c) but (BROM-HB) and (BROM-o-VANI) behave as tridentate ligands via phenolic-O, imine-N and amine-N donor atoms in complexes (4a)-(4c) and (5a)-(5c).


Sincere thanks are due to Head, Dept. of Chemistry, D.P.B.S. College, Anoopshahar, Bulandshahar, for providing research facilities. Authors are also thankful to Dr. M.P. Singh, Principal, M.M.H. College, Ghaziabad for his constant encouragement to carry out such research work. Special thanks are also due to CDRI, Lucknow, Intertek, Mumbai and TIFR, Mumbai for allocation of time for various analyses.


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[2] M.J. Almond, F. Sarikahya and O.S. Senturk, Polyhedron, 16, 1101 (1997), Hiral Patel, Y. Prajapati, P. Solankee, S. Solankee, G. Patel K. Kapadia and A. Solankee, Acta ciencia Indica. Vol.XXXIV C, No.-2, 327 (2008).

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[6] a.Amar Srivastava and A.K. Shrimal, Indian Jour. Of Chem. 41 A, 785-790 (April, 2002). b.Morton, Ian; Hall, Judith (1999) Concise Dictionary of Pharmacological Agents, Spinger, p-55.

[7] F. Sarikahya and O.S. Senturk, Syn. React. Inorg. Met.,31, 1843(2001).

[8] F.A. Cotton and G. Wilkinson, Advance Inorg. Chem., 5th Edt., Wiley Interscience, New York, 1047 (1988).

[9] Sema Sert, Ozan S.S. and F.U. Sarikahya, Transition Metal Chem., 28, 133-136 (2003).

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[12] EI-Asmu AA, Mabrouk HE, AI-Ansity, Amin RR, EI-Shahat MF., Synth. React. Inorg. Met.-Org. Chem., 23, 1709, (1993).

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[22] Bailey M.F., Dahl L.F., Inorg. Chem, 4, 1298 (1965).

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[24] Barry, A.L., The antimicrobial susceptibility Test, Principal and practice, Illus Lea and Febiges, Philadelphia, Pa. U.S.A., 180-193 (1976).

Ayodhya Singh *, Munesh Kumar **, Manish Kaushik **, Seema Singh ***, Ruchi Kaushik * and Anjali Singh *

* Department of Chemistry, M.M.H. College, Ghaziabad, U.P., India 201001

** Department of Chemsitry, D.P.B.S. College, Anoopshahr, Bulandshahr, U.P., India 203001

*** Department of Chemsitry, Kishan P.G. College, Bahraich, U.P., India 271801
Table 1: Physical and analytical data of Schiff bases.

Abbrebiation            Empirical Formula          Color    Yield %
of Schiff bases

(BROM-ANIS)       [C.sub.22][H.sub.25][N.sub.2]    Light      85
                           O[Br.sub.2]             Yellow
(BROM-DMB)        [C.sub.23][H.sub.27][N.sub.2]    White      86
(BROM-MB)         [C.sub.22][H.sub.25][N.sub.2]    White      83
(BROM-HB)         [C.sub.21][H.sub.23][N.sub.2]    White      80
(BROM-o-VANI)     [C.sub.22][H.sub.25][N.sub.2]    Light      84
                       [O.sub.2][Br.sub.2]         Yellow

Abbrebiation       Melting               Found (Calculated),
of Schiff bases     Point                Found (Calculated), %

                                  C        H        N      Mol. Wt

(BROM-ANIS)          209        53.00     5.02     5.62      488
                               (53.55)   (5.07)   (5.68)    (493)
(BROM-DMB)           192        55.42     5.42     5.62      485
                               (56.21)   (5.50)   (5.70)    (491)
(BROM-MB)            185        54.89     5.20     5.70      473
                               (55.35)   (5.24)   (5.87)    (477)
(BROM-HB)            170        51.96     4.74     5.77      474
                               (52.61)   (4.80)   (5.84)    (479)
(BROM-o-VANI)        218        51.26     4.85     5.44      503
                               (51.87)   (4.91)   (5.50)    (509)

Table 2: Physical and analytical data of Complexes.

Complexes              Empirical Formula              Color    Yield %

1a          [C.sub.26][H.sub.25][N.sub.2][O.sub.5]    Yellow     64
1b          [C.sub.26][H.sub.25][N.sub.2][O.sub.5]    Yellow     58
1c           [C.sub.26][H.sub.25][N.sub.2][O.sub.5    Yellow     50
2a          [C.sub.27][H.sub.27[].sub.N2][O.sub.4]    Light      62
                         [Br.sub.2]Cr                 Yellow
2b          [C.sub.27][H.sub.27][N.sub.2][O.sub.4]    Light      57
                         [Br.sub.2]Mo                 Yellow
2c          [C.sub.27][H.sub.27][N.sub.2][O.sub.4]    Light      49
                          [Br.sub.2]W                 Yellow
3a          [C.sub.26][H.sub.25][N.sub.2][O.sub.4]    Brown      60
3b          [C.sub.26][H.sub.25][N.sub.2][O.sub.4]    Brown      59
3c          [C.sub.26][H.sub.25][N.sub.2][O.sub.4]    Brown      52
4a          [C.sub.24][H.sub.23][N.sub.2][O.sub.4]     Deep      58
                         [Br.sub.2]Cr                 Yellow
4b          [C.sub.24][H.sub.23][N.sub.2][O.sub.4]     Deep      61
                         [Br.sub.2]Mo                 Yellow
4c          [C.sub.24][H.sub.23][N.sub.2][O.sub.4]     Deep      54
                          [Br.sub.2]W                 Yellow
5a          [C.sub.25][H.sub.25][N.sub.2][O.sub.5]    Brown      55
5b          [C.sub.25][H.sub.25][N.sub.2][O.sub.5]    Brown      58
5c          [C.sub.25][H.sub.25][N.sub.2][O.sub.5]    Brown      56

Complexes   Melting Point            Found (Calculated), %

                               C        H        N      Mol. Wt

1a               201         47.13     3.78     4.23      653
                            (47.49)   (3.80)   (4.26)    (657)
1b               205         43.94     3.52     3.94      698
                            (44.51)   (3.57)   (3.99)    (701)
1c               207         39.25     3.14     3.52      784
                            (39.54)   (3.17)   (3.55)    (789)
2a               195         49.09     4.09     4.24      652
                            (49.46)   (4.12)   (4.27)    (655)
2b               190         45.63     3.80     3.94      693
                            (46.35)   (3.86)   (4.01)    (699)
2c               192         40.75     3.40     3.52      784
                            (41.17)   (3.43)   (3.56)    (787)
3a               230         48.00     3.85     4.31      637
                            (48.67)   (3.90)   (4.37)    (641)
3b               235         45.22     3.62     4.06      680
                            (45.55)   (3.65)   (4.09)    (685)
3c               237         40.00     3.20     3.59      769
                            (40.36)   (3.23)   (3.62)    (773)
4a               190         46.08     3.68     4.48      611
                            (46.83)   (3.74)   (4.55)    (615)
4b               195         43.31     3.46     4.21      654
                            (43.70)   (3.49)   (4.25)    (659)
4c               193         38.15     3.05     3.71      743
                            (38.55)   (3.08)   (3.75)    (747)
5a               175         46.15     3.85     4.31      642
                            (46.51)   (3.88)   (4.34)    (645)
5b               178         43.16     3.60     4.03      684
                            (43.54)   (3.63)   (4.06)    (689)
5c               180         38.22     3.18     3.57      772
                            (38.61)   (3.22)   (3.60)    (777)

Table 3: Selected I.R. bands ([cm.sup.-1]) of Schiff bases.

Schiff bases    C = N   C-H    C-N Aromatic   C-N Cyclohexyl

(BROM-ANIS)     1635    2857       1306            1194
(BROM-DMB)      1630    2851       1300            1188
(BROM-MB)       1631    2853       1304            1185
(BROM-HB)       1630    2854       1302            1190
(BROM-o-VANI)   1634    2855       1306            1193

Table 4: Selected I.R. bands ([cm.sup.-1]) of Complexes.

Complexes       v(CO) [cm.sup.-1]

1a          2003   1898   1868   1823
1b          2005   1900   1870   1825
1c          2008   1904   1875   1828
2a          2001   1896   1865   1820
2b          2003   1897   1866   1821
2c          2009   1906   1877   1830
3a          2005   1902   1872   1827
3b          2008   1904   1874   1827
3c          2010   1906   1876   1832
4a          2001   1895   1865    -
4b          2003   1897   1867    -
4c          2010   1907   1880    -
5a          2009   1905   1876    -
5b          2012   1907   1882    -
5c          2015   1912   1887    -
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Author:Singh, Ayodhya; Kumar, Munesh; Kaushik, Manish; Singh, Seema; Kaushik, Ruchi; Singh, Anjali
Publication:International Journal of Applied Chemistry
Article Type:Report
Geographic Code:9INDI
Date:May 1, 2010
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