Synthesis, spectroscopic characterization, thermal studies, catalytic epoxidation and biological activity of chromium and molybdenum hexacarbonyl bound to a novel N2O2 Schiff base

Article abstract of DOI:10.1016/j.molstruc.2010.06.004

Complexes of M(CO)₆ (M = Cr and Mo) with novel Schiff base N,N′-bis(salicylidene)4,5-dichloro-1,2-phenylenediamine (H₂L) were prepared in benzene in two different conditions: (i) under reduced pressure resulting the dicarbonyl precursors [Cr(CO)₂(H₂L)] and [Mo(CO)₂(L)] and (ii) in air resulting the oxo complex [Cr(O)(L)] and the dioxo complex [Mo(O)₂(L)]. The complexes were characterized by elemental analysis, IR, ¹H NMR, mass spectrometry, and magnetic measurement. Thermal behaviors of the complexes were also studied by using thermogravimetric analysis (TGA). The catalytic activity of the novel complexes in the epoxidation of cyclooctene, cyclohexene, 1-octene and 1-hexene with tert-butyl-hydroperoxide (TBHP) in methylene chloride was investigated. The antimicrobial activities of the ligand and their complexes have been screened against various strains of bacteria and fungi and the results have been compared with some known antibiotics.

Full text of DOI:10.1016/j.molstruc.2010.06.004

Journal of Molecular Structure 979 (2010) 77–85
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, spectroscopic characterization, thermal studies, catalytic epoxidation
and biological activity of chromium and molybdenum hexacarbonyl bound to
a novel N O Schiff base
2
2
Ayman A. Abdel Aziz *
Chemistry Department, Faculty of Science, Ain Shams University, Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
0
Article history:
Complexes of M(CO)6 (M = Cr and Mo) with novel Schiff base N,N -bis(salicylidene)4,5-dichloro-1,2-
phenylenediamine (H L) were prepared in benzene in two different conditions: (i) under reduced pres-
sure resulting the dicarbonyl precursors [Cr(CO) (H L)] and [Mo(CO) (L)] and (ii) in air resulting the
oxo complex [Cr(O)(L)] and the dioxo complex [Mo(O) (L)]. The complexes were characterized by ele-
Received 15 March 2010
Received in revised form 1 June 2010
Accepted 1 June 2010
2
2
2
2
2
Available online 20 June 2010
mental analysis, IR, 1H NMR, mass spectrometry, and magnetic measurement. Thermal behaviors of
the complexes were also studied by using thermogravimetric analysis (TGA). The catalytic activity of
the novel complexes in the epoxidation of cyclooctene, cyclohexene, 1-octene and 1-hexene with tert-
butyl-hydroperoxide (TBHP) in methylene chloride was investigated. The antimicrobial activities of the
ligand and their complexes have been screened against various strains of bacteria and fungi and the
results have been compared with some known antibiotics.
Keywords:
Metal carbonyls
Schiff base
Spectral and thermal studies
Catalytic epoxidation
Biological activity
Ó 2010 Elsevier B.V. All rights reserved.
1
. Introduction
A large number of Schiff bases and their complexes are of signif-
and cyclohexene oxides are valuable organic intermediates used in
the synthesis of products such as chiral pharmaceuticals, pesti-
cides, epoxy paints, rubber promoters and dyestuffs.
icant interest and attention because of their biological activity
including anti-tumor, antibacterial, fungicidal and anti-carcino-
genic properties [1,2]. Schiff bases having donor atoms such as
Schiff bases metal carbonyl complexes have continued to
attract attention in part because of the different possible coordina-
tion geometries which the ligand may adopt [11–13]. Their low
energy metal-to-ligand charge transfer (MLCT) transitions make
these molecules attractive for luminescence and electron transfer
reactions [14]. The reactions of chromium and molybdenum
hexacarbonyls with the Schiff bases bis-(2-hydroxyacetophe-
2 2 4
N O and N around the metal ion have received more attention,
mainly because of their extensive applications as catalysts for car-
bonylation, hydrogenation, hydroformylation and epoxidation, nu-
cleic acid modification, electrochemical reduction, alkane
hydroxylation, Diels–Alder transformations, carboxylic acid decar-
boxylation, amines oxidation and medicinal studies as models for
mimicking the superoxide dismutase [3–8].
none)ethylenediimine (hapenH
propylimine (happramH) [16], N-salicylidene-2-hydroxyaniline
(shaH ) and bis-(salicylaldehyde) phenylenediimine (salphenH
2
) [15], 2-hydroxylacetophenone-
2
2
)
Partial oxidation of alkenes to epoxides and reaction products
based on epoxides are both of academic and industrial interest.
Various epoxides are among the most widely used intermediates
in organic synthesis, pharmaceuticals as well as polymer produc-
tion, acting as precursors for complex molecules due to the
strained oxirane ring [9]. They react to provide industrially impor-
tant products such as surfactants, detergents, antistatic agents and
corrosion protection agents, lubricating oils, textiles and cosmetics
in THF were investigated [17,18], however such work was limited
to synthesis and characterization of the complexes without no
application. bis-(Salicylaldehyde)-1,3-propylenediimine [19] and
Schiff bases derived from ethanolamine with acetylacetone and
benzoylacetone [20] have been also reported.
The present work reports the synthesis and characterization
of chromium and molybdenum complexes obtained by the reac-
tions between Cr and Mo hexacarbonyls with a novel Schiff
0
[
10]. Besides the epoxidation is an important step in the syntheses
base N,N -bis(salicylidene)4,5-dichloro-1,2-phenylenediamine (H
2
L),
of various biologically active compounds. In particular, cyclooctene
Scheme 1. Catalytic activities of the reported complexes were
investigated in the epoxidation of some cyclic and terminal olefins.
The reported Schiff base ligand and their complexes were tested for
antibacterial and antifungal activities.
*
Tel.: +20 20101300155.
E-mail address: aymanaziz31@gmail.com
0
022-2860/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2010.06.004

7
8
A.A. Abdel Aziz / Journal of Molecular Structure 979 (2010) 77–85
H
O
H
O
and the solvent was evaporated on a vacuum line. The brown res-
idue was washed several times with hot petroleum ether (40–60)
and recrystallized from hot ethanol. The brown crystals were dried
under vacuum for few hours to give a yield of 74%.
2.3.3. Synthesis of [Cr(O)(L)] complex
N
N
2 2
Similar procedure was used as employed for [Cr(CO) (H L)]
with a reaction period of 9 h in air under reflux condition. Brown
crystals was obtained with a yield of 53%.
2
.3.4. Synthesis of [Mo(CO)
In analogous reactions treatment of Cr(CO)
.38 mol) dissolved in dry benzene (20 mL) and H
.38 mmol) were mixed. The mixture was degassed in a sealed
2
(L)] complex
6
, Mo(CO)
6
(0.10 g,
0
0
2
L (0.15 g,
Cl
Cl
tube and heated for 3 h at 80 °C. The reaction afforded brown crys-
tals with a yield of 79%.
0
Scheme 1. Structural formula of N,N -bis(salicylidene)4,5-dichloro-1,2-phenylene-
diamine (H L).
2
2
2.3.5. Synthesis of [Mo(O) (L)] complex
2
. Experimental
.1. Reagents
6
Cr(CO) , Mo(CO) , 4,5-dichloro-1,2-phenylendiammine, cyclo-
Similar procedure was used as employed for [Mo(CO) (L)] with
a reaction period of 5 h in air under reflux. Brown crystals with a
yield of 63% were obtained.
Unfortunately, suitable X-ray quality crystals of these com-
plexes were not obtained despite numerous attempts.
2
2
6
octene, cyclohexene, 1-octene, 1-hexene and tert-butyl-hydroper-
oxide (TBHP) (5.5 M in decane) were purchased from Aldrich. All
solvents were of analytical grade.
2.4. General procedure for catalytic epoxidation of olefins
Epoxidation of cyclooctene, cyclohexene, 1-octene and 1-hex-
ene catalyzed by the reported Schiff base complexes with TBHP
in methylene chloride was carried out according to the following
general procedure: to a 25 mL round bottomed flask equipped with
a magnetic stirring bar and immersed into water thermostated
bath, was added 10 mL methylene chloride, 1.0 mmol TBHP,
2
.2. Instruments
Elemental analyses were carried out on a Perkin–Elmer 2400
CHN elemental analyzer. IR measurements (KBr Pellets) were car-
ried out on a Unicam-Mattson 1000 FT-IR. Mass spectra of the solid
complexes were performed on a JEOL JMS-AX500 mass spectrom-
eter. H NMR measurements were performed on JEOL-270 MHz
6
NMR DMSO-d as a solvent and TMS as an internal reference. Elec-
tronic absorption spectra were measured on a Unicam UV2-300
UV–Vis spectrophotometer. Molar conductivities of complexes
were measured by using Jenway 4010 conductivity meter. Thermo-
gravimetric analysis (TGA) was carried out using a Shimadzu DT-
0
.01 mmol catalyst and1.0 mmol olefin. The mixture was refluxed
1
with vigorous stirring for 2 h at an appropriately chosen tempera-
ture. The progress of the reaction was monitored by carefully with-
drawing aliquots of the sample at different time intervals to
determine concentrations of the products by GC analysis, using
n-hexane as an internal standard and was left to proceed until near
complete conversion of TBHP. The concentration of the TBHP was
determined by iodometric titration method [22]. The yield of epox-
ide (%) was calculated according to the starting amount of olefin.
Assignments of the products were made by comparison with
authentic samples. All the reactions were run at least in triplicates.
Control experiments showed that no epoxide was formed in a mea-
surable extent in the absence of catalyst.
5
0 thermal analyzer under nitrogen atmosphere with a heating
rate of 10 °C/min. Magnetic moments were determined on a Sher-
wood Scientific magnetic moment balance (Model N0: MK1) at
room temperature (25 °C) using Hg[Co(SCN)
magnetic corrections were calculated from Pascal’s constants
21]. Dani 1000 gas chromatograph equipped with an FID detector
was used for analysis of catalytic epoxidation reactions.
4
] as a calibrant: dia-
[
2.5. Antimicrobial screening
2
2
.3. Syntheses
The in vitro antimicrobial activity of the free ligand and their
complexes were tested against the bacteria: Staphylococcus aureus
0
.3.1. Synthesis of N,N -bis(salicylidene)4,5-dichloro-1,2-
L)
(
gram +ve) and Escherichia coli (gram ꢀve) in Mueller Hinton-agar
phenylenediamine (H
2
medium and fungi: Aspergillus flavus and Aspergillus niger in YPD-
To a hot methanolic solution containing 20 mmol of 4,5-di-
chloro-1,2-phenylenediammine (7.7 g, 20 mL) 4.3 mL (40 mmol)
of salicylaldehyde was added drop wise. The yellow solution ob-
tained was refluxed for 2 h. After cooling, the precipitate Schiff
base was collected by filtration and recrystallized from methanol.
The ligand was dried in a desiccator over anhydrous CaCl under
2
vacuum. The resultant product was washed with ethanol and the
purity of the ligand was checked by TLC (Yield 63%).
agar medium. The compounds to be tested were dissolved in DMSO
3
3
at a final concentration of 50 lg/0.1 cm and 100 lg/0.1 cm . At
General procedure [23], 25 mL of molten agar was added into ster-
ile petri dishes and allowed to solidify for 1 h. Then 50 mL of the
4 h culture of a test organism was spread evenly onto the agar
plate with the sterile cotton swab. 6-mm wide bores were made
on the agar using a borer. The solutions of the reported compounds
were added into each of the bores using a sterile tip with micropi-
pette. These plates were incubated for 24 h for bacteria and 48 h
for fungi at 35 ± 2 °C. The growth of the microorganisms was inhib-
ited by diffusion of the test solutions and then the inhibition zones
developed on the plates were measured [24]. The antibacterial
2
2
.3.2. Synthesis of [Cr(CO)
To Cr(CO) (0.10 g, 0.45 mmol) dissolved in dry benzene
20 mL), (H L) (0.17 g, 0.45 mmol) was added. The mixture was de-
2 2
(H L)] complex
6
(
2
gassed in a sealed tube and heated for 5 h at 80 °C. The color of the
activity of the ligand H
2
L and its complexes determined by disc dif-
solution was changed to brown. The reaction mixture was cooled
fusion method [25]. The effectiveness of an antimicrobial agent in

A.A. Abdel Aziz / Journal of Molecular Structure 979 (2010) 77–85
79
sensitivity is based on the zones of inhibition. The diameter of the
their tentative assignments for the ligand H
complexes are listed in Table 2.
2
L and the reported
zone is measured to the nearest millimeter (mm). The standard
drugs streptomycin and chlorotrimazole were also tested for their
antibacterial and antifungal activity at the same concentration un-
der the conditions similar to that of the test compounds concentra-
tion. DMSO alone was used as a control under the same conditions
for each organism. The diameter of inhibition zone resulting with
DMSO was subtracted from each case [26]. Finally the activity re-
sults are calculated as a mean of triplicates.
Schiff bases are capable of forming coordinate bonds with many
metal ions through both azomethine group and phenolic group or
via its azomethine or phenolic groups [29–32]. The band at
ꢀ1
1616 cm characteristic of the azomethine nitrogen atom present
in the free ligand, was shifted to lower wave number region (1599–
ꢀ1
1610 cm ) after complexation, indicating that the involvement
the azomethine nitrogen atom in coordination [33,34]. The band
ꢀ1
at 1279 cm in the IR spectrum of ligand is ascribed to the pheno-
lic C–O stretching vibration in the case of salicylideneanilines [33].
3
. Results and discussion
ꢀ
1
This band is found in the region 1280–1288 cm in the IR spectra
of the complexes. These changes suggest that the o-OH group of
this Schiff base moiety has taken part in complex formation.
Physical characteristics, elemental analysis, mass spectral and
magnetic susceptibility data of the free ligand and its complexes
are given in Table 1. The analytical data are in good agreement
with the proposed molecular formula.
ꢀ1
The free ligand exhibit a broad band at 3444 cm , which may
be assigned to the (OH) was shifted to lower wave number in
complex 1, which indicates the participation of the OH in bonding
35], however this band is missed in case of complexes 2, 3 and 4,
m
[
3.1. Molar conductivities
conferring the deprotonation of the ligand prior to coordination,
and indicating that the ligand coordinating oxidatively to the metal
All the complexes described herein are amorphous powder,
[
36,37]. Further evidence of the bonding is also shown by the
insoluble in water but soluble in CHCl
3
, CH
2 2 3
Cl , CH CN, DMF and
observation that new bands in the IR spectra of the metal com-
ꢀ3
DMSO. The molar conductivity (
K
m
) of 1 ꢁ 10 M solutions of
ꢀ1
ꢀ1
plexes appear at 451–467 cm
and 524–530 cm
assigned to
the complexes in DMSO (Table 1), indicates that all the metal com-
plexes have conductivity values in the range characteristics for the
non-electrolytic nature [27,28].
(
MAN) and (MAO) stretching vibrations that are not observed in
the spectrum of the ligand [37]. The IR spectrum of the chromium
complex (2) showed a strong band at 851 cm due to the Cr@O
ꢀ1
[
38]. The molybdenum complex (4) exhibits two absorption bands
ꢀ1
3
3
.2. Spectroscopic studies
at 925 and 940 cm , attributed, respectively, to
asym Mo@O of cis-MoO unit [39–44].
The IR spectra of the complexes 1 and 3 exhibit two terminal
msym Mo@O and
m
2
.2.1. FT-IR spectra
The IR spectra of chromium and molybdenum complexes were
compared with that of the free Schiff base ligand (H L) in order to
2
ascertain the binding mode of the Schiff base ligand to the metal in
the complexes. The most characteristic vibrational frequencies and
carbonyl stretching bands which are attributed to symmetric and
asymmetric frequencies of two CO groups [37]. The number of car-
bonyl bands provides important clues to the environment of the
metal center [45]. The presence of two CO bands in the IR spectrum
Table 1
2
Elemental analyses and some physical properties of the Schiff base ligand (H L) and the reported complexes.
ꢀ
1
mol cm2)
ꢀ1
Compound
Yield (%)
Color
M.wt
(Calculated) found (%)
K
m
(
X
leff (BM)
UV–Vis kmax (nm) (DMSO)
C
H
N
Cl
a
H
2
L
H
63
74
53
79
63
Yellow
Brown
Brown
Brown
Brown
385.25
493.26
451.23
535.19
511.17
(62.35)
62.28
(53.57)
53.42
(53.23)
53.10
(49.37)
49.02
(3.66)
3.59
(2.86)
2.76
(2.68)
2.55
(2.26)
2.01
(7.27)
7.18
(5.68)
5.49
(6.21)
6.07
(5.23)
5.13
(18.40)
18.28
(14.37)
14.23
(15.71)
15.55
(13.25)
12.99
–
–
–
283 , 375b
C
20
14
N
2
O
(H
2
Cl
L)] (1)
H N O Cl )
14 2 2 2
2
a
b
c
[
Cr(CO)
Cr(CO)
Cr(O)(L)] (2)
Cr(O)(C20
Mo(CO)
Mo(CO)
Mo(O)
2
2
9.7
278 , 408 , 542
2
(C20
a
b
d
c
[
10.2
8.8
2.79
4.87
–
268 , 378 , 534
12 2 2 2
H N O Cl )
a
b
[
2
(L)] (3)
(C20
(L)] (4)
(C20
261 , 388 , 551
2
H
12
N
2
O
2
Cl
2
)
a
b
d
[
2
(46.99)
46.87
(2.36)
2.25
(5.48)
5.34
(13.87)
13.68
12.7
264 , 419 , 527
Mo(O)
2
H
12
N
2
O
2
Cl
2
)
a
b
c
ꢂ
p
n–
–
p
p
transition.
transition.
ꢂ
MLCT.
LCMT.
d
Table 2
The infrared spectral data (cmꢀ1) of the Schiff base ligand (H
2
L) and the reported complexes.
(CAO) (C@O)
Compound
m(OH)
m
(C@N)
m
m
m(MAO)
m
(MAN)
m
(Cr@O)
m
s
(Mo@O)
mas(Mo@O)
H
2
L
3444(m,b)
3409(m,b)
1616(s)
1602(s)
1279(m)
1285(m)
–
–
–
–
–
–
–
–
–
[
Cr(CO)
2
(H
2
L)] (1)
1940(m)
530(w)
457(w)
1
–
842(m)
[
[
Cr(O)(L)] (2)
Mo(CO) (L)] (3)
–
–
1610(s)
1599(s)
1280(m)
1288(m)
526(w)
524(w)
451(w)
460(w)
851(s)
–
–
–
–
–
2
1939(m)
1
–
862(m)
[
Mo(O)
2
(L)] (4)
–
1601(s)
1286(m)
525(w)
467(w)
–
925(s)
940(s)
ꢂ
s, strong; m, medium; w, weak; b, broad.

8
0
A.A. Abdel Aziz / Journal of Molecular Structure 979 (2010) 77–85
suggested that they were bound to the metal in cis-position [38].
Also the CO modes in complexes 1 and 3 moves to lower wave
numbers when compared with the starting carbonyl complexes
46,47].
molybdenum may have +6 formal oxidation state with d0 elec-
tronic configuration.
m
Depending on The IR and 1H NMR spectra and magnetic mea-
surements, the proposed structural formula of the reported chro-
mium and molybdenum complexes are given in Scheme 3.
[
1
3
.2.2. Magnetic moment and H NMR spectra
The effective magnetic moment ( eff) of complex (2) and (3)
measured at 25 °C, were 2.79 and 4.87 BM (Table 1), respectively.
l
3
.2.3. Electronic spectra
Electronic absorption spectra of the ligand and the reported
Therefore the chromium oxo complex (2) has Cr(IV) with a high
ꢀ3
complexes were obtained in 1 ꢁ 10 M DMSO solutions at room
2
spin d configuration and the dicarbonyl molybdenum complex
temperature is included in Table 1. The electronic absorption spec-
4
(
3) has Mo(II) with a high spin d configuration [18,48].
tra of H
are assigned for the
complexation with chromium and molybdenum a bathochromic
shifts were exerted in the
2
L ligand displayed two bands at 283 and 375 nm, which
1
Investigation of the complexes (2) and (3) by H NMR spectros-
ꢂ
ꢂ
p–p and n–p transitions, respectively. Upon
copy gave no signal due to their paramagnetism. The chemical
shifts of the different types of protons in the 1H NMR spectra of
ꢂ
p–p
electronic transitions. On the other
the symmetric Schiff base H
and (4) are listed in Table 3. The H NMR spectrum of the parent
Schiff base ligand H L shows a singlet signal at 12.47, attributed
2
L and its diamagnetic complexes (1)
ꢂ
hand, the n–
p
electronic transitions exhibited hypsochromic
1
shifts. The electronic spectra of the complexes 1–4 showed a new
band in the visible region (534–551 nm). These bands could be
attributed to metal-to-ligand charge transfer (MLCT) in case of
the complexes 1 and 3 [52]. In case of complexes 2 and 4, these
bands may be assigned as charge transfer transitions of the type
LMCT [53].
2
to two phenolic AOH protons. The ligand also showed one singlet
at 8.89 ppm which is attributed to two azomethine (ACH@NA)
1
protons. The H NMR spectrum of the ligand revealed a multiplet
at 6.87–7.74 ppm corresponding to aromatic protons.
Coordination of both nitrogen atoms of the ligand to metal cen-
ter in complexes (1) and (4) is indicated by a shift of the signal for
the imine carbon protons from 8.89 ppm for the free ligand to 8.72
and 8.50, respectively. The presence of only one azomethine reso-
nance for the complexes (1) and (4) is consistent with the presence
3.3. Thermogravimetric and mass spectra analysis
The thermal studies of the reported chromium and molybde-
num complexes provided further insight into the proposed struc-
tures. The reported complexes were found to be air stable and
have high thermal stability to use as catalysts in epoxidation reac-
tions [54]. The thermal studies were carried out using thermo-
gravimetric analysis (TGA) and derivative thermogravimetry
of only
a-cis isomer in solution. This is because the a-cis isomer
possesses a twofold axis which bisects the NACHRACHRAN chain,
and therefore the two CHAN protons are expected to be equivalent
[
49,50]. The b-cis isomer is less symmetrical and compounds with
1
this structure usually give at least two signals in the H NMR spec-
trum, (Scheme 2).
(
DTG) techniques. The decomposition mass losses were found in
1
agreement with the formula weight of each complex proposed
from the elemental analysis. The decomposition patterns were fur-
ther confirmed from the mass spectral peaks, Table 4.
The H NMR spectrum of the complex (1) displayed a signal at
1
1.67 ppm indicating the presence of OH groups. The signal
showed lower field shift and indicated that the ligand coordinated
to the chromium atom through the OH group. The diamagnetism of
complex (1) suggests the existence of chromium in zero oxidation
2 2
The TGA plot of Cr(CO) (H L) complex (1) was found to be ther-
mally decomposed in a well-defined two decomposition steps in
the temperature range 83–758 °C (Scheme 4). The first decomposi-
tion step occurred in the temperature range 83–316 °C with a net
weight loss of 11.35% which corresponds to the elimination of two
CO molecules. The second decomposition step occurred in the tem-
perature range 575–758 °C with a net weight loss of 71.61%. This
6
state with low spin d electronic configuration. On the other hand,
1
the H NMR spectrum of complex (4) missed the OH signal, which
supports deprotonation of the ligand prior to coordination with
molybdenum [51]. According to the proposed structure (Scheme 3),
decomposition step corresponds to the elimination of C20
H
14
N
2
Cl
2
Table 3
species to give finally a metallic oxide residue of CrO
weight of 17.02%.
2
with a net
The 1H NMR spectral data (d, ppm) of the Schiff base (H
L), chromium complex (1)
Aromatic protons
2
and molybdenum complex (4).
On the other hand the TGA plot Cr(O)(L) complex (2) displayed
two resolved and well-defined two decomposition steps in the
temperature rang 116–575 °C (Scheme 5). The first decomposition
occurred in the temperature range 116–275 °C with a net weight
loss of 26.39% which is consistent with the elimination of
Compound
OH (phenolic)
CH@N
H
2
L
12.47 (s)
11.67 (s)
–
8.89 (s, 2H)
8.72 (s, 2H)
8.50 (s, 2H)
6.87–7.74 (m, 10H)
6.34–7.65 (m, 10H)
6.42–7.70 (m, 10H)
[
[
Cr(CO)
Mo(O)
2
(H
(L)] (4)
2
L)] (1)
2
ꢂ
s, singlet; m, multiplet.
7 5
C H NO species. The second decomposition step occurred in the
temperature range 383–575 °C with a net weight loss of 62.07%.
This decomposition step corresponds to the elimination of
13 7 2 2
C H NO Cl species to give finally a metallic Cr residue with a
net weight of 11.52%.
O
N
2
The TGA plot of Mo(CO) (L) complex (3) displayed three re-
O
O
solved and well-defined steps in the temperature range 100–
733 °C (Scheme 6). The first decomposition step occurred in the
temperature range 100–316 °C with a net weight loss of 5.23%
which correspond to elimination of one CO molecule. The second
decomposition step occurred in the range 316–450 °C with a net
weight loss of 5.23% corresponds to elimination of the second CO
molecule. The third decomposition step occurred in the tempera-
ture range 452–733 °C with a weight loss of 71.60% which corre-
N
N
O
M
M
O
N
O
O
O
α-cis isomer
β-cis isomer
sponds to the elimination of
20 12 2 2 2
C H N O Cl species leaving
Scheme 2.
finally a metallic residue of Mo with a net weight of 17.92%.

A.A. Abdel Aziz / Journal of Molecular Structure 979 (2010) 77–85
81
OH
O
O
O
CO
CO
Cl
Cl
N
N
Cr
Cr
N
N
OH
Cl
Cl
(
1)
(2)
O
Mo
O
O
Mo
O
O
Cl
Cl
N
N
CO
CO
Cl
Cl
N
N
O
(
3)
(4)
Scheme 3. The proposed structural formula for the Cr and Mo complexes.
o
Table 4
Selected mass spectral data of the reported complexes.
83-316 C
Cr(CO) (C20H N O Cl )
2
14
2
2
2
Cr(C20H14N2O2Cl2)
37.25
493.26
-(2CO) (11.35 %)
4
Compound
Molar
mass
m/z Values (relative intensity)
m/z = 493; 24.3 %)
(
m/z =437; 31.5 %)
[
[
[
Cr(CO)
Cr(O)(L)] (2)
Mo(CO) (L)] (3)
2
(H
2
L)] (1)
493.26
451.23
535.19
493 (24.3%), 437 (31.5%), 84 (3.17%)
451 (43.5%), 332 (36.5%), 52 (17.2%)
535 (37.8%), 507 (16.4%), 479 (11.9%),
2
9
5 (9.8%)
[
Mo(O)
2
(L)] (4)
511.17
511 (42.5%), 408 (19.5%), 143 (16.8%)
Finally the TGA plot of Mo(O)
solved well-defined decomposition steps in the temperature range
7–712 °C (Scheme 7). The first decomposition step occurred in the
temperature range 67–400 °C with a net weight loss of 20.17%
which corresponds to loss of C N species. The second decompo-
2
L complex (4) displayed two re-
CrO2
6
8
3.99
(
m/z =84; 3.17 %)
7
H
5
sition step occurred in the temperature range 517–712 °C with a
2 2
Scheme 4. The thermal decomposition steps of Cr(CO) (H L) complex (1) and mass
weight loss of 51.66% which corresponds to the elimination of
spectra of some fragments.

8
2
A.A. Abdel Aziz / Journal of Molecular Structure 979 (2010) 77–85
o
1-hexene with TBHP and methylene chloride as a solvent at differ-
ent temperatures 25, 45 and 65 °C (Scheme 8).
1
16-275 C
Cr(O)(C H N O Cl )
Cr(C13
332.11
(m/z =332.; 36.5 %)
H
7
NO
2
Cl
2
)
2
0
12
2
2
2
-
(C H NO) (26.39 %)
4
51.23
7 5
TBHP is used as an oxidant due to it has a good thermal stability
and is relatively easy to handle [55]. Furthermore, the by-product
of the reaction, tert-butyl alcohol, is easy to separate by distillation
and can be recycled or used for other industrial processes. The
reaction was performed in methylene chloride, because it is known
that chlorinated solvents facilitate epoxidation [56] and the com-
plexes studied are stable in this solvent. The catalytic reactions
were initially performed in air (laboratory atmosphere) in order
to test the performance of the system under the easiest possible
reaction conditions. A substrate : oxidant : catalyst ratio of
m/z =451; 43.5 %)
1
00:100:1 was used. The carbonyl precursors 1 and 3 were first
stirred with THBP for ca. 2 h to be oxidized to the catalytically ac-
tive compounds (Scheme 9) before oxidation of the substrate [57].
The reaction of these reactions has been reported previously [58].
The epoxide yield was higher for cyclic olefins than those for
terminal olefins, in accordance with the known higher reactivity
of cyclic olefins in these reactions [59]. Based on the epoxidation
mechanism suggested earlier [60,61], higher electron donating
ability of olefin double bond is expected to facilitate the reaction
rate. Inspection of the results reveals that both olefin and catalyst
structures affect the catalyst activity. As seen in Table 5, the order
of increasing reactivity based on yield% are as cyclooctene > cyclo-
hexene > 1-hexene > 1-octene. To explain this trend, two deter-
mining parameters of electronic and steric effects should be
Cr
1.99
m/z =52; 17.2 %)
5
(
Scheme 5. The thermal decomposition steps of [Cr(O)(L)] complex (2) and mass
spectra of some fragments.
C
13
7
H NOCl
2 3
species leaving finally a metallic oxide residue MoO
with a net weight of 28.15%.
3.4. Catalytic activity
Catalytic activities of the reported complexes 1–4 were investi-
gated in the epoxidation of cyclooctene, cyclohexene, 1-octene and
o
1
00-316 C
Mo(CO) (C H N O Cl )
Mo(CO)(C20
507.18
(m/z = 507; 37.8 %)
H N O Cl )
12 2 2 2
2
20 12
2
2
2
535.19
- (CO) (5.23 %)
(
m/z = 535; 37.8 %)
o
4
52-733 C
Mo
Mo(C H N O Cl )
2
0
12
2
2
2
9
5.94
- (C H N O Cl ) (71.60 %)
20 12 2 2 2
479.17
m/z = 479; 16.4 %)
(
m/z = 95; 9.8 %)
(
Scheme 6. The thermal decomposition steps of [Mo(CO)
2
(L)] complex (3) and mass spectra of some fragments.
o
6
7-400 C
Mo(O) (C H N O Cl )
Mo(O) (C H NO Cl )
2 13 7 2 2
408.05
(m/z = 408; 19.5 %)
2
20 12
2
2
2
-
(C H N) (20.17 %)
7 5
5
11.17
(m/z = 511; 42.5 %)
MoO3
43.94
m/z =143; 16.8 %)
1
(
2
Scheme 7. The thermal decomposition steps of [Mo(O) (L)] complex (4) and mass spectra of some fragments.

A.A. Abdel Aziz / Journal of Molecular Structure 979 (2010) 77–85
83
O
taken into consideration. The higher electronic density of the dou-
ble bond is expected to show more epoxidation reactivity. There-
fore, cyclooctene and cyclohexene with double bonds driven
from secondary carbons should exhibit more activities in compar-
ison with 1-hexene and 1-octene which contain double bonds be-
tween secondary and primary carbons. On the other hand,
cyclooctene is more reactive than cyclohexene due to the presence
Catalyst, t-BuOOH
CH Cl2
2
Scheme 8. Olefin epoxidation with tert-BuOOH catalyzed by chromium and
molybdenum complexes.
2 6
of more electron donating (CH ) cyclic bridge connected to the
double bond. 1-Octene is epoxidized slower than 1-hexene can
be inferred since larger hexyl group connected to double bond ste-
rically hinders it in approaching to the catalyst metal center with
respect to 1-hexene which its double bond carries a smaller butyl
group.
The results (Table 5) showed that the reported molybdenum
complexes 3 and 4 have higher catalytic activity than chromium
complexes. Also the epoxide yield increase with the rise in
temperature.
O
O
O
CO
N
N
TBHP/CH Cl2
N
N
2
M
O
M
O
CO
O
Epoxidation mechanism (Scheme 10) can be rationalized as di-
rect oxygen atom transfer from the metal complex derived by coor-
Scheme 9. Conversion of the carbonyl precursors into catalytically active species.
ꢀ
dination of t-BuOO anion to metal center to the olefin [60,62].
Therefore, reaction of an olefin as a nucleophile with oxygen as
an electrophile easily explains the observation that electron rich
olefins react faster than electron poor olefins.
Table 5
Results of catalytic epoxidation of some olefins with TBHP in the presence of catalysts
(the reported complexes).
Catalysta
Substrate
Epoxide yieldb (%)
2
5 °C
45 °C
65 °C
3.5. Biological activity
[
[
[
[
Cr(CO)
2
(H
2
L)] (1)
Cyclooctene
Cyclohexene
54
32
24
15
72
66
58
33
88
75
70
49
2
The Schiff base ligand H L and their chelates (1–4) were tested
1
1
-Hexene
-Octene
for their inhibitory effects on the growth of bacteria: S. aureus and
E. coli and fungi: A. flavus and A. niger fungi because such organisms
can achieve resistance to antibiotics through biochemical and mor-
phological modification [63]. The antimicrobial activity was tested
by the agar well-diffusion method. The antibacterial and antifungal
activities of the new compounds are presented in Table 6. The re-
sults indicate that the complexes show more activity than the par-
ent ligand against the same microorganisms under identical
experimental conditions and the activity increase with increase
in concentration of test solution containing the new complexes.
The different compounds exhibit weak activity against the bacte-
rial species when compared with standard streptomycin while
they exhibit better activity against the fungi species when com-
pared with chlorometazole. Though the complexes possess activ-
ity, it could not reach the effectiveness of the standard drugs,
Cr(O)(L)] (2)
Cyclooctene
Cyclohexene
56
58
38
28
68
69
52
41
89
87
77
66
1
1
-Hexene
-Octene
Mo(CO)
2
(H
2
L)] (3)
Cyclooctene
Cyclohexene
59
48
37
23
79
67
52
44
91
90
68
67
1
1
-Hexene
-Octene
Mo(O
2
)(L)] (4)
Cyclooctene
Cyclohexene
76
58
48
32
88
81
70
55
96
94
89
78
1
1
-Hexene
-Octene
a
All reactions were carried out at with a catalyst: substrate ratio of 1:100.
Determined from GC analysis based on the initial substrate.
b
O
O
N
N
O
O
M
O
+
H
O
O
R
M
O
O
O
H
O
O
R
N
N
O
O
N
N
N
O
O
O
M
O
+ ROH +
M
O
H
O R
O
O
N
+
O
Scheme 10. Proposed mechanism for epoxidation of olefins with TBHP.

8
4
A.A. Abdel Aziz / Journal of Molecular Structure 979 (2010) 77–85
streptomycin and chlorometazole. This would suggest that chela-
tion could facilitate the ability of the complex to cross a cell mem-
brane and can be explained by Tweedy’s chelation theory [64].
Chelation considerably reduces the polarity of the metal ion be-
cause of partial sharing of its positive charge with donor groups
and possible electron delocalization over the whole chelate ring.
Such a chelation could enhance the lipophilic character of the cen-
tral metal atom, which subsequently favors its permeation through
the lipid layer of the cell membrane. The variation in the effective-
ness of different compounds against different organisms depends
on either the impermeability of the cells of the microbes or on dif-
ferences in ribosome of microbial cells [65].
4
. Conclusion
0
The interaction of the tetradentate Schiff base N,N -bis(salicylid-
ene)4,5-dichloro-1.2-phenylenediamine (H L) with M(CO) (M = Cr
and Mo) under different conditions afforded the dicarbonyl precur-
sors [Cr(CO) (H L)], [Mo(CO) (L)], the oxo complex [Cr(O)(L)]
and the dioxo complex [Mo(O )(L)]. The reported complexes were
2
6
2
2
2
2
investigated in the epoxidation of cyclooctene, cyclohexene, 1-oc-
tene and 1-hexene. The resulting epoxides are both of academic
and industrial interest. The antibacterial and antifungal activities
of the new compounds were tested for their inhibitory effects on
the growth of bacteria: S. aureus and E. coli and fungi: A. flavus
and A. niger. The different compounds exhibit weak activity against
the bacterial species when compared with standard streptomycin
and weak to good activity against the fungi species when com-
pared with standard chlorometazole.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2010.06.004.
References
[
1] S. Ren, R. Wang, K. Komatsu, P. Bonaz-Krause, Y. Zyrianov, C.E. Mckenna, C.
Csipke, Z.A. Tokes, E.J. Lien, J. Med. Chem. 45 (2002) 410.
[
[
2] N. Raman, A. Thangaraja, C. Kulandaisamy, Transition Met. Chem. 28 (2003) 29.
3] E. Dunach, A.P. Esteves, M.J. Medeiros, D. Pletcher, S. Olivero, J. Electroanal.
Chem. 566 (2004) 39.
[
[
[
4] E.G. Samsel, K. Srinivasan, J.K. Kochi, J. Am. Chem. Soc. 107 (1985) 7606.
5] C. Floriani, F. Calderazzo, J. Chem. Soc. A (1969) 946.
6] W. Zhang, J.L. Loebach, S.R. Wilson, E.N. Jacobsen, J. Am. Chem. Soc. 112 (1990)
2
801.
7] S.B. Routier, J.L. Bernier, M.P. Catteau, C. Bailly, Bioorg. Med. Chem. Lett. 7
1997) 63.
8] (a) V. Mirkhani, S. Tangestaninejad, M. Moghadam, M. Moghbel, Bioorg. Med.
Chem. 12 (2004) 903;
[
[
(
(
b) V. Mirkhani, S. Tangestaninejad, M. Moghadam, M. Moghbel, Bioorg. Med.
Chem. 12 (2004) 4673.
[
9] A.K. Yudin, Aziridines and Epoxides in Organic Synthesis, Wiley-VCH,
Weinheim, 2006.
[
[
10] G. Sienel, R. Rieth, K.T. Rowbottom, Epoxides, VCH Publishers, New York, 1985.
11] S.W. Kirtley, in: G. Wilkinson, F.G.A. Stone, E.W. Abel (Eds.), Comprehensive
Organometallic Chemistry, vol. 3, Pergamon Press, Oxford, 1982, p. 1079, 1255.
12] A.S. Cavallo, G. Solladie, E. Tsano, J. Organomet. Chem. 144 (1978) 181.
13] R. Lal De, K. Samanta (née Bera), I. Banerjee, Indian J. Chem. 40 (2001) 144.
14] W. Kaim, S. Kohlmann, Inorg. Chem. 26 (1987) 68.
[
[
[
[
[
15] R.M. Ramadan, M.S.A. Hamza, S.A. Ali, J. Coord. Chem. 43 (1998) 31.
16] S.A. Ali, A.A. Soliman, M.M. AboAli, R.M. Ramadan, J. Coord. Chem. 55 (2002)
1161.
[
[
[
[
[
17] S.M. El-Medani, O.A.M. Ali, R.M. Ramadan, J. Mol. Struct. 738 (2005) 171.
18] S.M. El-Medani, J. Coord. Chem. 57 (2004) 497.
19] T.A. Youssef, J. Coord. Chem. 61 (2008) 816.
20] A.A. Soliman, S.A. Ali, A. Orabi, Spectrochim. Acta A 65 (2006) 841.
21] A. Earnshaw, Introduction to Magnetochemistry, Academic Press, London,
1968. p. 4.
[
[
22] W.F. Brill, J. Am. Chem. Soc. 85 (1963) 141.
23] M.J. Relezar, E.C.S. Chan, N.R. Kreig, Microbiology, fifth ed., McGraw Hill, New
York, 1998.
[
24] M. Shakiv, Y. Azim, H.T.N. Chishti, S. Parveen, Spectrochim. Acta A 65 (2006)
490.

A.A. Abdel Aziz / Journal of Molecular Structure 979 (2010) 77–85
85
[
25] C.H. Collins, P.M. Lyne, Microbial Methods, University Park Press, Baltimore,
970.
26] G.G. Mohamed, Spectrochim. Acta A 64 (2006) 188.
[46] M.J. Almond, F. Sarikahya, O.S. Sentürk, Polyhedron 16 (2001) 1843.
[47] F. Sarikahya, O.S. Sentürk, Synth. React. Inorg. Met. 31 (2001) 1843.
[48] S.M. El-Medani, J. Coord. Chem. 57 (2004) 115.
[49] W.E. Hill, N. Atabay, C.A. McAuliffe, F.P. McCullough, S.M. Razzoki, Inorg. Chim.
Acta 35 (1979) 35.
1
[
[
27] A. Golcu, M. Tumer, H. Demirelli, R.A. Wheatley, Inorg. Chim. Acta 358 (2005)
1
785.
[
[
[
[
[
[
[
[
[
28] M.S. Refat, J. Mol. Struct. 742 (2007) 24.
[50] M. Gullotti, A. Pasini, G.M. Zanderighi, G. Ciani, A. Sironi, J. Chem. Soc., Dalton
Trans. (1981) 902.
[51] T. Masanobu, O. Sachiko, N. Tomohiro, S. Genta, S. Takashi, Sakutai Kagaku
Toronkai Koen Yoshishu 50 (2000) 378.
[52] S.M.O. Quintal, H.I.S. Nogueira, H.M. Carapuca, V. Felix, M.G.B. Drew, J. Chem.
Soc., Dalton Trans. (2001) 3196.
[53] R. Hahn, U. Kusthardt, W. Scherer, Inorg. Chim. Acta 210 (1993) 177.
[54] T. Katsuki, Coord. Chem. Rev. 140 (1995) 189.
[55] J.M. B r´ egeault, J. Chem. Soc., Dalton Trans. (2003) 3289.
[56] B.C. Reichardt, Solvents and Solvent Effect in Organic Chemistry, VCH,
Weinhem, 1988.
[57] C. Freund, M. Abrantes, F.E. Kühn, J. Organomet. Chem. 691 (2006) 3718.
[58] S. Bahaduri, D. Mukesh, Homogeneous Catalysis, Mechanism and Industrial
Application, John-Wiley & Sons, Inc., Canada, 2000. p. 183.
[59] U. Arnold, R. Serpa da Cruz, D. Mandelli, U. Schuchardt, J. Mol. Catal. A 165
(2001) 149.
29] S.A. Sadeek, M.S. Refat, J. Korean Chem. Soc. 50 (2006) 107.
30] S.V. Sheat, T.V. Waters, J. Inorg. Nucl. Chem. 26 (1964) 1221.
31] R.J. Cozens, K.S. Murray, B.O. West, J. Organomet. Chem. 27 (1971) 399.
32] A. Bigotto, V. Galasso, G. Dealti, Spectrochim. Acta A 28 (1972) 1581.
33] J.E. Kovacic, Spectrochim. Acta A 23 (1967) 183.
34] B.B. Mahapatra, D.K. Das, Indian J. Chem. A 26 (1987) 173.
35] G. Bandoli, T.I. Gerber, R. Jacobs, J.G.H. Dupreez, Inorg. Chem. 33 (1994) 178.
36] J.P. Collman, L.S. Hegedus, Principles and Application of Organotransition
Metal Chemistry, University Science Book, California, 1980.
37] S.A. Ali, M.M.H. Khalil, R.M. Ramadan, Transition Met. Chem. 25 (2000) 121.
38] N. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, fourth ed., Wiley, New York, 1986.
39] W.A. Nuget, J.M. Mayer, Metal–Ligand Multiple Bonds, Wiley, New York, 1988.
pp. 113–119.
40] K. Yamanouchi, S. Yamada, Inorg. Chim. Acta 9 (1974) 83.
41] W.E. Hill, N. Attabay, C.A. McAuliffe, F.P. McCullough, S.M. Razzoki, Inorg.
Chim. Acta 35 (1979) 35.
[
[
[
[
[
[60] A.A. Valente, J. Moreira, A.D. lopes, M. Pillinger, C.D. Nunes, I.S. Goncalves, New
J. Chem. 28 (2004) 308.
[
42] M. Gullotti, A. Pasini, G.M. Zanderighi, G. Ciani, A. Sironi, J. Chem. Soc. Dalton
[61] Z. Petrovski, M. Pillinger, A.A. Valente, I.S. Goncalves, C.C. Romao, J. Mol. Catal.
A 227 (2004) 67.
(
1981) 902.
[
[
[
43] O.A. Rajan, A. Chakravorty, Inorg. Chem. 20 (1980) 660.
44] U. Sandbhor, S. Padhe, E. Sinn, Transition Met. Chem. 27 (2002) 681.
45] G.L. Miessler, D.A. Tarr, Inorganic Chemistry, second ed., Prentice Hall, New
Jersey, 2000. p. 471.
[62] M.H. Lim, A. Stein, Chem. Mater. 11 (1999) 3285.
[63] S. Mandal, K. Nag, J. Chem. Soc., Dalton Trans. (1983) 2429.
[64] B.G. Tweedy, Phytopathology 55 (1964) 910.
[65] P.G. Lawrence, P.L. Harold, O.G. Francis, Antibiot. Chemother. (1980) 1597.