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A New Series ofBiologically Potent cis-Dioxomolybdenum(VI)Complexes of FluoroiminesR. V. Singh a , S. C. S. Jadon a & Neeti Gupta aa Department of Chemistry , University ofRajasthan , Jaipur, 302 004, IndiaPublished online: 20 Aug 2006.

To cite this article: R. V. Singh , S. C. S. Jadon & Neeti Gupta (1997) A New Series ofBiologically Potent cis-Dioxomolybdenum(VI) Complexes of Fluoroimines, Synthesisand Reactivity in Inorganic and Metal-Organic Chemistry, 27:5, 759-773, DOI:10.1080/00945719708000225

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SYNTH. REACT. INORG. MET.-ORG. CHEM., 27(5), 759-773 (1997)

A NEW SERIES OF BIOLOGICALLY POTENT

c~s-DIOXOMOLYBDENUM(VI)

COMPLEXES OF FLUOROIMINES

R. V. Singh", S. C. S. Jadon and Neeti Gupta Department of Chemistry, University of Rajasthan,

Jaipur-302 004, India

ABSTRACT

The modern physico-chemical, spectroscopic and biochemical

methods have proved an important tool t o elucidate the constitution

of reactive transition metal compounds. This article presents a brief

account of the synthesis and stereochemistry of dioxomolybdenum(V1)

complexes of fluoroimines. The mononuclear complexes were obtained

by bimolar reactions of dioxobis(2,4-pentanedionato-O,O')molybdenum(VI)

with the monobasic bidentate fluoroimines containing N"S and N"0

as the binding sites. Based on chemical analyses, IR and NMR spectra,

conductance measurements and molecular weight determinations an

octahedral geometry has been assigned to the newly synthesized

products. The possibility of potential uses of these complexes as

fungicides and bactericides, studied in vitro are also discussed.

759

Copyright 0 1997 by Marcel Dekker, Inc.

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760 SINGH, JADON, AND GUPTA

INTRODUCTION

Much attention has been focussed recently on the fascinating

chemistry of oxomolybdenum complexes with ligands containing hard-

soft donor atoms, e.g. , nitrogen, sulfur and/or oxygen because of their

relevance to the active sites of molybdoenzymes1~2. The ligands with

the general formula F"N"XH (where n=1-5 and X=O/S) chosen for

the present communication behave as potential bidentate ligands. The

biological activity of molybdenum mostly involves the molybdenum(V1)

state3, the chemistry of which is centred around the dioxomolybdenum(V1)

group. In these complexes, the structural and electronics demands of

the cis-M00,2' group dominate the detailed ~tereochemistry~. The

valency of molybdenum varies depending on the nature of the enzyme,

and the function of some redox enzymes is dependent on variable

valence molybdenum cofactorsJ. The fluoroimines used are strong

donors and this property induces interesting reactivity patterns in the

dioxomolybdenum(V1) complexes. Minor changes in the structures of

fluoroimines markedly affected the activity of the compounds6. Since

MOO," invariably attaches to four donor atoms to produce an octahedral

geometry around molybdenum, the binding of these bidentate ligands

(F"N"XH) would engage two coordination positions leaving the other

two sites for another similar ligand (1:2 reaction). The interaction of

fluoroimines with dioxomolybdenum(V1) ion is, therefore, of interest.

The Fluoroimines used during these studies are shown in Fig.1.

RESULTS AND DISCUSSION

The bimolar reactions o f dioxobis(2,4-pentanedionato-

O,O')molybdenum(VI) with monobasic bidentate fluoroimines (F"N"XH)

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761 c~s-DIOXOMOLYBDENUM(VI) COMPLEXES

Fig. 1.

in perfectly dry methanol produced MoO,(F"N"X), type mononuclear

coloured solids with sharp melting points (Table I).

MeOH MOO, (acac), + F"N"XH ,:2 > MOO, (F"N"x), + 2 C,H,O,

These are non-electrolytes in dry DMF (molar conductance values

ranging between 10-14 ohm-' cm2 mol-I) and are diamagnetic, as

expected for molybdenum(V1) with a 4d" configuration.

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4

m

h)

TA

BL

E I

Ph

ysi

cal

Pro

per

ties

an

d A

naly

ses

of

Met

al

Com

ple

xes

Com

plex

and

Col

our a

nd S

tate

Em

oiric

al F

orm

ula

Yie

ld

(%)

M.P

. A

naly

sis (“A)

Mol

ecul

ar

(“)

Mo

N

S W

eigh

t .

.

..

Foun

d Fo

und

Foun

d Fo

und

(Cal

cd.)

(Cal

cd.)

(Cal

cd.)

(Cal

cd.)

MoO

,(C,H

,N,S

F),

Yel

low

ish g

reen

C,

,HI4

N6O

,S,F

,Mo

solid

MoO

,(C,H

,N,O

F),

Gre

en s

olid

16

H,4

N60

4F2M

o

MoO

,(C,H

,N,S

F),

Gre

en so

lid

C18

H18

N60

2S2F

2Mo

MoO

,(C,H

,N,O

F),

Gre

en so

lid

1 gHI

8N

604F

2Mo

MoO

,(C,,H

,,N,S

,F),

Gre

en so

lid

C3oH

z4N4

O,S4

F,Mo

75

208

18.7

1 (1

8.44

)

76

>30

0 19

.76

(19.

65)

75

>30

0 17

.16

(1 7.

49)

75

>3 0

0 18

.76

(18.

58)

77

248

12.8

7 (1

3.05

)

15.9

9 (1

6.14

)

16.9

8 ( 1

7.20

)

15.1

1 ( 1

5.32

)

16.1

3 (1

6.27

)

17.9

7 (1

7.45

)

12.4

6 (1

2.32

)

11.8

2 (1

1.69

)

7.36

(7

.62)

0

c

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cis-DIOXOMOLYBDENUM(V1) COMPLEXES 763

IR Spectra

In the IR spectra of all the ligands broad and strong bands in

the region 3250-3100 cm" may be attributed to the vNH vibrations.

These disappear completely in the spectra of the complexes, indicating

deprotonation of this group on complexation. The spectra of ligands

do not show bands in the region 2570 cm-' due t o vSH, indicating

ketonic form in the solid state. However, the solution spectra show

bands due to vSH as well as vNH', indicating the presence of an

enolic tautomeric form in equilibrium with the ketonic form. The (C=N)

and (C=C) stretching vibrations are partially overlapping' and these

bands appear in the region 1620-1580 cm-I. These shift t o lower

frequency by 10-20 cm-' in the complexes, indicating the coordination

of the azomethine nitrogen to the metal atom. Strong bands appearing

around 1050 cm-' in the ligands are assigned to v(C=S)~. In the metal

complexes these bands diappear, indicating the coordination of the

ligands through the thiolosulfur. Similarly, a strong band in the ligands

around 1660 cm-' due to v(C=O)~ also disappears in the spectra of

the metal complexes, indicating the formation of C-0-M type of

bonding. The bands observed in the region 3430-3350 cm-' in ligands

attributed to asymmetric and symmetric modes of the NH, group remain

at nearly the same position in the complexes, indicating the non-

involvement of this group in complexation. In the spectra of the ligand

(F5NnSH) a doublet at 2900 and 2956 cm", attributed to symmetric

and asymmetric vibrations of the S-CH,-C,H, grouping lo, is reduced

to a weak doublet in the spectra of the complexes. Some new bands

in the complexes appear at -650 cm", -430 cm-' and 360 cm-I, attributed

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764 SINGH, JADON, AND GUPTA

to v(Mo-O)", v ( M o t N ) I 2 and v(Mo-S)I3, respectively. A doublet in

the spectra of the complexes in the region -900 cm-I, which may be

assigned to vSy,(O=Mo=O) and v,,~(O=MO=O), respectively, indicates

the cis-MOO, s t r ~ c t u r e ' ~ .

'H NMR Spectra

The bonding pattern discussed above is further supported by

comparing the 'H NMR spectra of the ligands with the

dioxomolybdenum(V1) complexes (Table 11). The spectra of the ligands

F"N"XH (where n = 1-5, X = S/O) display a broad signal due to

NH protons which disappear in the metal complexes, indicating the

deprotonation of this group and leading t o the bond formation between

Mo-N and Mo-S/Mo-0 atoms. The azomethine protons and the

azomethine methyl protons undergo deshielding in the dioxomolybdenum

complexes, in case of aldehydic and ketonic ligands, respectively,

substantiating the presence of the Mo-N bond. The appearence of NH,

protons at almost the same place in the ligands F N"XH to F4NN"XH

and the corresponding metal complexes, confirms the non-participation

of this group in chelation. The spectra of the ligand F5N"SH also

show an additional peak at 61.76 ppm due to S-CH,-Ph protons and

this peak appears at 61.84 ppm in the corresponding metal complex.

1

I3C NMR Spectra

The 13C NMR spectra of the ligand FIN"SH and F4N"OH and

their corresponding metal complexes have been recorded in dry

methanol (Table 111). The chemical shift values of the carbon atoms

attached to the azomethine nitrogen, thiolic sulfur or amido oxygen,

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TA

BL

E I1

'H

NM

R S

pec

tral

Data

(8

p

pm

) of

Lig

an

ds

an

d t

hei

r C

orr

esp

on

din

g

Met

al

Co

mp

lex

es

I C

ompo

und

-NH

-SH

H

~=

N H,C

-C=N

A

rom

atic

-9 S

-CH

,-Ph

~

F'N

"SH

11

.24

8.33

7.

78-6

.70

2.16

MO

O,(F

N^

SH),

FWO

H

Mo0

,(F4N

nO),

FSN

"SH

Mo0

,(F5N

"SH

),

8.77

7.

94-6

.84

2.24

).30

1.

88

7.52

-6.1

6 3.

08

2.23

7.

76-6

.3 1

3.12

'

1.68

4.

28

8.94

7.

92-6

.68

1.76

9.28

8.

14-6

.80

1.84

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TA

BL

E I1

1

13C

NM

R S

pec

tral D

ata

(8

pp

m)

of

Lig

an

ds

an

d t

hei

r C

orr

esp

on

din

g

Met

al

Com

ple

xes

Com

poun

d A

mid

oITh

iolo

A

zom

ethi

ne

Met

hyl

Aro

mat

ic

F'N

"SH

17

9.52

15

7.38

14

3.66

, 127

.85,

126

.54,

12

3.34

, 122

.17,

120

.33

MO

OJF

' N" s

)~

171.

36

151.

77

143.

61, 1

27.6

8, 1

26.4

3,

123.

28, 1

22.0

9, 1

20.2

8

F4N

"OH

z? z 0

14

1.29

, 129

.64,

129

.10,

z

164.

58

156.

51

15.8

8 12

6.72

, 123

.52,

123

.41

Mo0

,(F4N

nO),

156.

62

151.

61

15.3

0 14

1.02

, 129

.53,

128

.98,

z

126.

66, 1

23.5

1, 1

23.3

9

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cis-DIOXOMOLYBDENUM(V1) COMPLEXES 767

when compared with the respective fluoroimines, lends further support

to the proposed coordination in these complexes.

19F NMR Spectra

The 19F NMR spectra of F3N"SH and F4N"OH display a sharp

singlet at 6-109.00 and -108.36 ppm, respectively. The

dioxomolybdenum(V1) complexes of these ligands given sharp signals

at 6-109.44 and 6-108.59 ppm and thus support the non-involvement

of fluorine in complexation.

On the basis of the above studies, and in agreement with previous

authors", an octahedral geometry with cis-Moo, has been proposed for

the dioxomolybdenum(V1) complexes with F N"SH as an example

(Fig. 2 ) .

1

Fungicidal and Bactericidal Activities

Fungicidal and bactericidal activities of the fluoroimines and their

respective dioxomolybdenum(V1) complexes against pathogenic fungi

and bacteria are recorded in Tables IV and V. It is apparent that sulfur

containing compounds are more toxic" than the oxygen containing

compounds. It has been suggested that the ligands with the N and

S donor system might have inhibited the enzyme production, since the

enzymes which require free sulfhydryl groups for their activity appear

t o the especially susceptible to inactivation by the ions of the

complexes. The complexes facilitate their diffusion through the lipid

layer of spore membranes to the site of action ultimately killing them

by combining with -SH groups of certain cell enzymes. The variation

in the effectiveness of different biocidal agents against different

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768 SINGH. JADON, AND GUPTA

Fig.2

organism16 depends on the impermeability of the cell. The hydrocarbon

tail functions as a lipophilic group" to drive the compound through

the semipermeable membrane of the cell.

The toxicity of the dioxomolybdenum(V1) complexes can be well

understood by considering the chelation theoryI8. Chelation reduces the

polarity of the central ion mainly because of the partial sharing of

its positive charge with the donor groups and possible n-electron

delocalisation within the whole chelate ring. This chelation increases

the lipophilic nature of the central atom which favours its permeation

through the lipid layer of the membrane.

The striking feature seen in the bactericidal activity is the

remarkable potential of toxicity for the Gram(+) stain as compared to

the Gram(-) stain. The reason is the difference in the structure of the

cell walls. The walls of Gram(-) cells are more complex than those

of Gram(+) cells. The lipopolysaccharides form an outer lipid membrane

and contribute t o the complex antigenic specificity of Gram(-) cells.

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TABL

E IV

Fu

ngic

idal

Scr

een

ing D

ata

of

Lig

an

ds

an

d t

hei

r M

etal

Com

ple

xes

k?

% In

hibi

tion

afte

r 96

hour

s (C

onc.

in p

pm)

Com

poun

d 50

10

0 20

0 50

10

0 20

0 50

10

0 20

0 z

Col

leto

tric

hum

caps

ici

Peni

cilli

um n

otat

um

Scel

erot

ium

rorf

sii

C

Bav

istin

90

10

0 10

0 88

10

0 10

0 87

10

0 10

0

F~N

"SH

79

89

94

84

90

96

m

CA

83

90

98

F4N

"OH

60

69

79

61

68

80

58

66

78

MO

O,(

F~N

~O),

74

83

90

70

79

91

76

86

92

F5N

"SH

72

80

88

78

86

88

78

82

90

Mo0

,(F5N

"S),

80

92

100

84

92

100

82

94

100

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TA

BL

E V

An

tib

act

eria

l S

cree

nin

g D

ata

of

Lig

an

ds

an

d t

hei

r M

eta

l C

om

ple

xes

% I

nhib

ition

afte

r 24

hou

rs

Com

poun

d 50

0 10

00

500

1000

50

0 10

00

Esc

heri

chia

coli(

-)

Stap

hylo

cocc

us aw

eus(

+)

Kle

bsie

lla a

erog

enou

s(-)

Stre

ptom

ycin

95

10

0 88

10

0 25

42

F~

N"S

H

34

50

42

53

59

84

MO

O,(F

"9),

39

56

53

65

75

100

F4N

nOH

E

28

50

36

47

42

59

Mo0

,(F4N

nO),

39

62

47

59

65

84

F5N

"SH

39

56

59

83

84

10

0 P

Z u

Mo0

,(F5N

"S),

50

67

71

94

92

100

0 5 2

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cis-DIOXOMOLYBDENUM(V1) COMPLEXES 77 1

Overall, bactericidal results were appreciable when compared with a

standard.

In the fungicidal activity, although the bioactivity increased on

undergoing complexation, but did not reach the efficacy of the

conventional fungicide Bavistin at lower cencentration. However, at

higher ppm concentration the results achieved were satisfactory. The

aforesaid studies are clearly worthy of further investigation.

EXPERIMENTAL

All reactions were carried out under strictly anhydrous conditions

and chemicals of AR grade were used. All the physico-chemical

techniques employed during the study have been reported ear lie^'^.

Dioxobis(2,4-pentanedionato-O,O')molybden~m(VI)'~ and fluoroimines6

were also prepared by the reported methods.

Synthesis of Dioxomolybdenum(V1) Complexes

Dioxobis(2,4-pentanedionato-O,O')molybdenum(VI) (1.08-2.14 g,

3.31-6.56 mmol) and the ligands (1.25-2.14 g, 2.40-4.11 mmol) were

mixed in 1:2 molar ratio in 60 mL dry methanol. The mixture was

refluxed for 12-15 h on a fractionating column. After the completion

of the reaction, excess of the solvent was distilled off and the product

was dried in vacuo. It was repeatedly washed with dry n-hexane and

again dried for 2 h t o obtain the purified product

Physical Measurements and Analytical Methods

The IR spectra were recorded as KBr pellets or Nujol mulls

on a Perkin-Elmer 577 Grating Spectrophotometer. 'H NMR Spectra

were recorded on a Jeol Fx 90Q Spectrometer in DMSO-d, using TMS

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772 SINGH, JADON, AND GUPTA

as the internal standard. 13C NMR spectra were recorded in methanol

at 22.89 MHz. Elemental analyses were carried out by standard

methods20. Molecular weights were determined by an osmotic pressure

osmometer. The purity of the compounds was checked by TLC.

Biochemical Aspects

The Fluoroimines and their dioxomolybdenum(V1) complexes

were tested for the in vitro growth inhibitory activity against pathogenic

fungi, viz., Colletotrichum capsici, Penicillium notatum and

Scelerotium rolfsii and bacteria, Escherichia coli, Staphylococcus

aureus and Klebsiella aerogenous. Aseptic techniques were employed

to prepare the cultures of fungi and bacteria2'. The Radial Growth

Method was employed to evaluate the antimycotic activity and Paper-

Disc Plate Method used for antibacterial activities and % inhibition

has been calculated among the bacterial speciesz2.

ACKNOWLEDGEMENTS

The authors are thankful t o Department of Science and

Technology, Government of Rajasthan, Jaipur, for financial support.

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cis-DIOXOMOLYBDENUM(V1) COMPLEXES 773

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G. J. J. Chen, J. W. McDonald and W. E. Netwon, Inorg. Chem., - 15, 2612 (1976).

A. I . Vogel, "Text book of Quantitative Inorganic Analysis", ELBS and Longman, London (1985).

E. R. Rawlins, "Bentray's Text book of Pharmaceuticals", 8th Ed. Boilliere Tindall, London (1977).

C. Saxena, D. K. Sharma and R. V. Singh, Phosphorus, Sulfur, and Silicon, 9, 85 (1993).

Received: 29 August 1996 Referee I: J. M. Boncella Accepted: 1 March 1997 Referee II: K. Moedritzer

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