Synthesis and characterization of new schiff base metal complexes and their use as catalysts for olefin cyclopropanation

Article abstract of DOI:10.1080/10426500902967904

New transition metal complexes of CoII, CuII, NiII, and FeIII of the ligands 2N,2-bis((7- hydroxy-5-methoxy-2-methyl-4-oxo-4H-chromen-6-yl)methylene) hydrazinecarbo-thioamide H3L1 and (E)-2-((7-hydroxy-5-methoxy-2-methyl-4-oxo-4H- chromen-6-yl)methylene)-

Full text of DOI:10.1080/10426500902967904

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Synthesis and Characterization of
New Schiff Base Metal Complexes
and Their Use as Catalysts for Olefin
Cyclopropanation
Nabil S. Youssef a , Eman A. El-Zahany a & Ahmed M. A. El-Seidy a
a Inorganic Chemistry Department , National Research Centre ,
Dokki, Giza, Egypt
Published online: 23 Mar 2010.
To cite this article: Nabil S. Youssef , Eman A. El-Zahany & Ahmed M. A. El-Seidy (2010) Synthesis
and Characterization of New Schiff Base Metal Complexes and Their Use as Catalysts for Olefin
Cyclopropanation, Phosphorus, Sulfur, and Silicon and the Related Elements, 185:4, 785-798, DOI:
10.1080/10426500902967904
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Phosphorus, Sulfur, and Silicon, 185:785–798, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902967904
SYNTHESIS AND CHARACTERIZATION OF NEW SCHIFF
BASE METAL COMPLEXES AND THEIR USE
AS CATALYSTS FOR OLEFIN CYCLOPROPANATION
Nabil S. Youssef, Eman A. El-Zahany,
and Ahmed M. A. El-Seidy
Inorganic Chemistry Department, National Research Centre, Dokki, Giza, Egypt
New transition metal complexes of CoII, CuII, NiII, and FeIII of the ligands 2N,2-bis((7-
hydroxy-5-methoxy-2-methyl-4-oxo-4H-chromen-6-yl)methylene)hydrazinecarbo-thioamide
H3L1 and (E)-2-((7-hydroxy-5-methoxy-2-methyl-4-oxo-4H-chromen-6-yl)methylene)-N-
phenylhydrazinecarbothioamide H2L2 have been prepared and characterized. Mass spectra
and NMR assignments for the ligands, using COSY, NOESY homonuclear, and HMQC and
HMBC heteronuclear correlation techniques were carried out. Electronic and magnetic mo-
ments of the complexes indicate that the geometries of the metal centers are either distorted
square pyramidal or octahedral. The structures are consistent with the IR and UV-VIS, as
well as conductivity and magnetic moments measurements. Cyclopropanation reactions of
unactivated olefins by ethyldiazoacetate (EDA) in the presence of H3L1Cu2.Cl4.H2O as
catalyst proceed with excellent turn over numbers (TON: up to 12556).
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords Condensation reactions; cyclopropanation reactions; homogeneous catalysis; metal
complexes; Schiff bases; thiosemicarbazide
INTRODUCTION
A large number of Schiff base compounds are often used as ligands in coordination
chemistry as they readily form stable complexes. Metal complexes with these Schiff bases
have the ability to reversibly bind oxygen in epoxidation reactions,1 catalytic activity
in hydrogenation of olefins2,3 and photochromic properties.4 Moreover, the chemistry of
metal complexes of Schiff base ligands having nitrogen, oxygen, and sulfur at their donor
sites has been extensively studied in the last decades.5–31 Also, these complexes have
numerous applications, such as, in the treatment of cancer,32 as antibactericide agents,33
as antiviral agents,34 as fungicide agents,35 and for their other biological properties.36
All these advantages make Schiff bases very good candidates in the effort to synthesize
metal complexes of interest in bioinorganic chemistry, catalysis, encapsulation, transport
Received 23 October 2008; accepted 14 April 2009.
Address correspondence to Nabil S. Youssef, Inorganic Chemistry Department, National Research Centre,
Dokki, Giza, Egypt. E-mail: nabilyoussef@hotmail.com
785

786
N. S. YOUSSEF ET AL.
H
2O
X
N
X
Cl
N
H
O
M
Cl
S
O
H
O
M
O
O
O
H
S
O
O
O
O
O
H
N
N
X
X
N
N
H
H
H
O
O
M
Cl
Cl
O
H
O
H2
O
M
H
O
H
H2O
H2
O
Complex 2: H3L1Co2Cl4.(H2O)3, X=Cl
Complex 3 : H3L1Ni2Cl4.(H2O)3,X=Br
Complex 5:H3L1Cu2Cl4H2
O
Complex H3L1Co2Br4.(H2O)3,X=Cl
4:
H3
C
H3
C
O
O
O
H
C
H
N
H
N
O
O
O
H
C
H
N
H
N
N
N
(Z)
(Z)
S
S
Co
M
H3C
O
H3C
O
H
H2
O
X
H2
O
Cl
Cl
Cl
2
8:
Complex L Ni.Cl(H2O)2, X=H2O
Complex 7: H2L2CoCl2.H2O
Complex 10: L2FeCl2.H2O, X=Cl
H3C
O
O
O
H
C
H
N
H
N
N
S
H3
C
O
Ni
CH3
O
O
H2
O
S
N
C
N
N
H
O
O
H
H
CH3
2
9:
Complex [(L )2Ni]H2O
Figure 1 The proposed structures of metal complexes.
and separation processes, magnetochemistry,37,38 and heterogeneous and homogeneous
catalysis for oxidation and polymerization of organic compounds.39–42 Cyclopropanation
of olefins with diazo reagents catalyzed by metal complexes has attracted great research
interest because of its fundamental and practical importance.43–46 Carbene intermediates can
beeasily generated starting fromdiazoalkanederivatives, inthe presence of different metals.
Copper,47–49 rhodium,50–52 and ruthenium53,54 complexes have proven to be among the most
effective and with general applicability.55,56 The resulting cyclopropanes are of biological
and industrial importance and serve as versatile precursors in organic synthesis.44–46,57–60
In view of the above facts and in continuation of our recent research61 on the
synthesis and characterization of new Schiff bases complexes and their use as catalysts
for cyclopropanation of olefins, we report in this article the synthesis and identification
of the Schiff base ligands 2N,2-bis((7-hydroxy-5-methoxy-2-methyl-4-oxo-4H-chromen-
6-yl)methylene)hydrazi necarbothioamide H3L1 and (E)-2-((7-hydroxy-5-methoxy-2-
methyl-4-oxo-4H-chromen-6-yl)methylene)-N-phenylhydrazine-carbothioamide H2L2 and
their CoII, CuII, NiII, and FeIII complexes. 13C NMR spectra were also obtained to
determine the structure of the ligands and some of their complexes. The catalytic activity of
complexes H3L1Cu2.Cl4.H2O (5) toward the decomposition of ethyl diazoacetate (EDA) in
the presence of olefins to yield cyclopropane products has also been investigated. Although
various methodologies are available today, the cycloaddition of carbenoids to C C double
bonds is the most practical one to construct this class of compounds. Stereochemical
control of these reactions, such as differentiation of the enantiotopic faces of the double

NEW SCHIFF BASE METAL COMPLEXES
787
bond or cis-trans selectivity imposed on the cyclopropanation reaction by the presence of a
substituent at the carbenoid carbon, are the main issues.62,63 However, another issue of the
cyclopropanation is the chemoselectivity of the reaction: Very often catalysts that are fast in
the activation of the approaching carbenoid, namely diazoacetates, give olefins derived by
coupling reactions as major byproducts. Rarely, metal complexes can give high selectivities
in cyclopropanation reactions together with high turnover number (TON). We report in
this article that H3L1Cu2Cl4H2O (5) is a competent catalyst for the cyclopropanation
of olefins, even the underlying examination of the copper complex prepared from the
ligand that was prepared from a (1:1) condensation of hydrazinecarbothioamide and
7-hydroxy-5-methoxy-2-methyl-4-oxo-4H-chromene-6-carbaldehyde showed similar
activity (Schemes 1 and 2).
CH3
O
O
O
O
H3C
HO
H
O
CH3
S
C
O
O
H
S
C
H2N
reflux
H
N
N
H
NH2
2
N
N
H
H3C
OH
O
O
H3C
O
OH
CH3
Scheme 1 Schematic representation for the formation of the Schiff base ligand H3L1.
CH3
O
O
O
O
H3C
S
O
O
H
O
H
N
H
N
ruflux
H
H
NH2
N
H
N
H
N
H
H3C
O
S
H3C
O
Scheme 2 Schematic representation for the formation of the Schiff base ligand H2L2.
RESULTS AND DISCUSSION
The elemental and physical data of the ligands H3L1and H2L2 and their complexes
(Table I) showed that the stoichiometry of the complexes obtained is 1:1, 1:2, or 2:1
(metal:ligand) (see Figure 1).
Mass Spectra of the Ligands
The mass spectra of the Schiff base ligands H3L1 and H2L2 revealed the molecular
ion peaks at m/e 523 and 383, which are coincident with the formula weights (523.51) and
(383.42), respectively, for these ligands support the identity of their structures. The pathway
fragmentation patterns of the mass spectra of these ligands are depicted in Schemes S1 and
S2 (available online in the Supplemental Materials).
Infrared Spectra
The IR bands for the metal complexes derived from Schiff bases H3L1 and H2L2,
which are most useful in attempting to determine the mode of coordination, are listed in

788

NEW SCHIFF BASE METAL COMPLEXES
789
Table II IR frequencies of the bands (cm−1) of ligand H3L1, H2L2, their metal complexes, and their assignments
No.
Ligand/complexes
ν(H2O)
ν(OH)
ν(NH)
ν(C O)
ν(C S)
ν(C N)
ν(N N)
1
2
3
4
5
6
H3L1
—
3295 s
3286 m
3289 m
3286 m
3282 m
3276 s
3160 m
3164 m
3166 m
3164 m
3175 m
3249 m
3150 w
3148 w
3199 w
3155 w
3172 w
—
1219
1211
1210
1212
1232
1221
886 m
880 m
879 m
881 m
883 v.w
845 s
1648 v.s
1633 m
1624 m
1628 m
1626 s
1108 m
1115 m
1116m
1119 m
1118 m
1110 m
H3L1Co2Cl4(H2O)3
H3L1Ni2Cl4(H2O)3
H3L1Co2Br4(H2O)3
H3L1Cu2Cl4 H2O
H2L2
3484 br
3380 br
3463 br
3440 br
—
1605 s
7
H2L2CoCl2(H2O)
3451 br
3270 m
1228
828 w
1600 sh
1157 m
8
9
10
L2Ni.Cl(H2O)2
[(L2)2Ni]H2O
L2FeCl2(H2O)
3450 br
3440 br
3430 br
—
—
—
1234
1225
1220
837 m
838 w
835 m
1598 sh
1597 sh
1599 sh
1174 m
1140 m
1171 m
Table II. The assignments were made by comparison with the vibrational frequencies of
the free ligand.
The most characteristic vibrational frequencies and their tentative assignments for
the ligand H3L1, H2L2 and their transition metal complexes are listed in Table II. The
assignments were made by comparison with the vibrational frequencies of the free ligand.
The IR data obtained for the ligand H3L1 showed that the ligand behaves as a neutral
pentadentate (ONSNO) ligand coordinating through C OH, C N, and C S groups. In
these complexes, the mode of coordination was suggested by the following pieces of
evidence: i) the band due to the hydroxyl group is shifted to lower wave number by 6–
13 cm−1, which is further supported by the shift in the stretching frequency of phenolic
oxygen υ(C O) in thecomplexes,64 indicating thesubsequent deprotonationof thephenolic
proton prior to coordination. ii) The imines bands are shifted to lower wave number by 15–
24 cm ,
−1 65,66 with iii) the negative shift and weakness of the band assigned to the thioketone
group; iv) the shift of υN–N band to higher wave number by 7–11 cm−1; v) the simultaneous
appearance of new bands in the 345–384, 419–455, and 500–540 cm−1 regions due to the
υ(M–S), υ(M N), and υ(M O) vibrations, respectively.67,68
On the other hand, the IR data obtained for the H2L2 ligand suggested that this ligand
can behave as either of the following:
1) Mononegative tridentate ligand coordinating through the C O, C N, and C S groups.
In these complexes, the mode of coordination was suggested by the following pieces
of evidence: (i) the disappearance of the band due to the hydroxyl oxygen, indicating
the subsequent deprotonation of the phenolic proton prior to coordination64; ii) the shift
of the two imine bands to lower wave number by 5–8 cm−1 with a decrease in their
intensities65,66; iii) the band due to the thioketone group is weakened and shifted to
lower wave number by 8–10 cm−1; iv) the positive shift of υN–N band by 30–64 cm−1
;
v) the simultaneous appearance of new bands in the 355–391, 420–447, and 477–519
cm−1 regions due to the υ(M–S), υ(M N), and υ(M O) vibrations, respectively.67,68
2) Neutral tridentate ligand coordinating via the C OH, C N, and C S groups in complex
7. In this complex, the mode of coordination was suggested by the following pieces of
evidence: (i) the weakness and shift of υOH band to lower wave number by 6 cm−1
;
ii) the red shift of the imine bands by 5 cm−1 with a weak appearance65,66; iii) the

790
N. S. YOUSSEF ET AL.
red shift of band due to the thioketone group by 17 cm−1 with a decrease in intensity;
iv) the blue shift of the υN–N band by 47 cm−1; v) the simultaneous appearance of new
bands in the 370, 432, and 507 cm−1 regions attributable to the υ(M–S), υ(M N), and
υ(M O) vibrations, respectively.67,68
Molar Conductance Data
The metal complexes discussed herein were dissolved in DMF or DMSO, and the
molar conductivities of their solutions (10−3 M) at room temperature were measured to
establish the charge of the metal complexes. The conductance data, reported in Table I,
indicate that all the metal complexes have conductivity values in the range characteristics
for the non-electrolytic nature of these complexes due to absence of counter ions in the
proposed structures of these complexes.
Electronic Spectra and Magnetic Moments
Cobalt (II) complexes. The electronic spectrum of the cobalt(II) complex (7) gave
three bands at 1092, 679, and 529 nm, which can be assigned to the transitions 4T1g(F) →
4
4
4T2g(F) (ν1) and 4T1g(F) → A2g(F) (ν2) and 4T1g(F) → T2g(P) (ν3), respectively, whereas
the spectra of complexes (2) and (4) showed the last two transitions at 1096–1165 and
602–672 nm, and the first transition is masked by the more intense charge transfer band,
suggesting an octahedral69–72 geometry around Co(II) ion. The magnetic moment of com-
plex (7) is 4.72 B.M. in consistent with octahedral geometry,73, while complexes (2) and
(4) show magnetic moment values in the range 2.64–3.84 B.M., which is smaller than
the calculated value for two Co(II) ions in octahedral geometries, and this may be due to
antiferromagnetism between the two ion centers (Table S1, Supplemental Materials).
Copper (II) complex. The UV-Vis spectra of the Cu complex H3L1Cu2.Cl4.H2O
showed a single band at 632 nm, which indicates a normal distorted square pyramidal
geometry at Cu(II).74
Nickel (II) complexes. The absorption spectral bands of nickel(II) complexes
3
3
3
3
(3, 8, 9) showed three spin-allowed transitions: A2g(F) → T2g(F), A2g(F) → T1g(F),
3A2g(F) → T1g(P) appearing in the ranges 1198–1100, 894–877, and 620–578 nm, consis-
3
tent with a typical Ni(II) in an octahedral environment.70,71 The magnetic moment values
for complexes 8 and 9 were found in the range 3.15–3.5 B.M.70,71 expected for octahedral
nickel complexes, but in the case of the complex (3), the value is 2.64 B.M., which indicates
antiferromagnetism between the two Ni centers.
Iron (III) complex. The electronic spectra of Fe(III) complex showed broad bands
at 766 and 527 nm. The former band may be due to the spin forbidden transition 6A1g
→
4T2g(G), which may gain intensity as a result of the vibronic mechanism in the octahedral
6
4
field around ferric ion. The second band may be attributed to A1 → T1(G) transitions.
In addition, a third absorption band with high intensity observed at 440 nm assigned for
charge transfer transition. The magnetic moment of complex is 5.14 B.M.75
Catalytic Activity
The catalytic activity of complex H3L1Cu2Cl4H2O (5) in cyclopropanation reactions
has been investigated. As a model reaction, we choose the cyclopropanation of α-methyl

NEW SCHIFF BASE METAL COMPLEXES
791
styrene by EDA (EDA = ethyl diazoacetate) (Scheme S3, Supplemental Materials). Cat-
alytic reactions were run by adding the EDA to a stirred solution containing the olefin and
the metal complex in dichloroethane under dinitrogen.
The copper complex H3L1Cu2.Cl4.H2O (5) exhibited an interesting catalytic capabil-
ity toward the decomposition of ethyl diazoacetate and the subsequent transfer of the carbene
moiety to the C C double bond. To evaluate the catalytic activity of H3L1Cu2.Cl4.H2O (5),
we used the complex as a catalyst in our model reaction. Conditions of the catalytic reaction
were examined by varying the temperature and relative ratio of 5/EDA/olefin. Results are
summarized in Table S2 (Supplemental Materials).
The copper complex H3L1Cu2Cl4H2O (5) exhibited excellent catalytic capability
toward the decomposition of ethyl diazoacetate, and the subsequent transfer of the carbene
moiety to the C C double bond.
According to the results (Table S2), it can be seen that H3L1Cu2Cl4.H2O (5) is a
very active catalyst for cyclopropanation reactions. The catalyst was examined with 1:1.1,
1:2, and 1:5 ratios of EDA/olefin, and it was found that a large excess of the olefin is not
required for the reaction to proceed: even if equimolar amounts of EDA and olefin were
used, the cyclopropane products were obtained in reasonable yields (70–78%); the rest of
the starting EDA is consumed to form the well-known coupling byproducts (maleate and
fumarate) normally obtained in cyclopropanation reactions (Table S2). The temperature
plays an important role in these reactions: the catalyst at room temperature is inactive
(Table S2, entry 5), but as soon as the temperature is increased to 65◦C it becomes active
(Table S2, entry 6). Reaction times can be almost reduced to a half just by increasing the
temperature at 75◦C (Table S2, entry 7). After complete consumption of the starting EDA,
the catalytic cycle can be restored just by addition of both reactants. In the second and third
runs, we observed even shorter reactions times (see later in this section). The cis:trans ratio
is not affected to a large extent by changing the conditions, and nearly equal amounts of
both cyclopropanes have always been obtained. The best result in terms of cyclopropane
yield (93% based on EDA) was obtained at 65◦C at a 5/EDA/olefin ratio of 1:500:2500
(Table S2, entry 6). In contrast to the prolonged EDA addition time generally required to
reduce the formation of coupling products in cyclopropanation, we found complex 5 to be
very active: a loading of 0.01 mol% of the catalyst and one pot addition of EDA completely
consumed all the EDA and afforded cyclopropane products with good selectivity (76%
based on converted EDA) in less than 100 min (TON 1000, Table S2, entry 9). The turnover
number (TON) reached 12556 at a 5/EDA/olefin ratio of 1:20000:40000 at 75◦C; in this
case we observed a 73% conversion based on converted EDA in just 5 h, 20 min (Table S2,
entry 10). Although, the catalyst H3L1Cu2Cl4.H2O (5) has shown a very high selectivity
(93%, Table S2, entry 6), it showed a low diastereoselectivity (cis:trans = 41:59, Table S2,
entries 5 and 8).
To examine the generality of the complex H3L1Cu2Cl4H2O (5) as a cyclopropa-
nation catalyst, several alkenes were employed to determine the substrate scope of the
complex H3L1Cu2Cl4H2O (5). At a 5/EDA/olefin ratio of 1:1000:2000 at 75◦C, the com-
plex catalyzed the cyclopropanation of a range of substrates with quantitative conversion
in short reaction times and with selectivities ranging from good to excellent. The results
are summarized in Table S3 (Supplemental Materials).
When styrene is employed as substrate, we observed a slight decrease in the quanti-
tative conversion of the starting EDA to what was observed in the case of α-methyl styrene
with an increase of the conversion rate. However, in this case, the diastereoselectivity is
improved (cis:trans = 29:71, compare entry 1, Table S3 and entry 4, Table S2). Slightly

792
N. S. YOUSSEF ET AL.
better yields in cyclopropane products, although with slightly longer reaction times, are
obtained when electron-donating substituents are present in the para position of the aro-
matic ring (entry 2, Table S3). If 4-chloro-α-methylstyrene is employed as substrate, the
catalytic rate increases with a slight decrease in the yield (entry 3, Table S3). It can be seen
that in the absence of an α substituent on the styrene derivative, the formation of the trans
cyclopropane is slightly favored. Steric hindrance at the α position does not hamper the
reaction, and good yields are obtained even with 1,1-diphenyl ethylene (entry 4, Table S3).
On the other hand, steric hindrance at the β-position of the styrene greatly affected the
reactivity. In case of cis-stilbene a dramatic drop in the cyclopropanation products was
observed (entry 6, Table S3).
Even aliphatic double bonds that are generally less reactive towards cyclopropana-
tion gave excellent results. Though the time of the cyclopropanation reaction for these
substrates increased slightly if compared to what is observed for styrenic derivatives, very
good yields were always obtained (entries 8–11, Table S3). Even in these cases, trans cyclo-
propane compounds are obtained as major products, and a remarkable diastereoselectivity
(trans:cis = 10.1) has been observed in the case of cyclohexene (entry 9, Table S3). With
2,5-dimethyl-2,4-hexadiene, an important precursor to chrysanthemic acid,76 the catalytic
reaction yielded the desired cyclopropanes in very good yields (84%) and with reasonable
diastereoselectivities (entry 10, Table S3), without the need of a large excess of the olefin.
Copper(I) complexes are known to be more efficient cyclopropanation catalysts than
copper(II) compounds. It has been observed that Cu(II) complexes are reduced to Cu(I)
derivatives by the diazo compound under the reaction conditions. This has led to general
agreement that the active catalyst is a Cu(I) species, irrespective of the oxidation state of
the copper complex used as the precatalyst. It is also generally accepted that transition
metal-catalyzed cyclopropanation reactions proceed via a metal–carbene complex, which
is formed by association of the diazo compound and the catalyst with concomitant extrusion
of nitrogen.77 A detailed mechanistic study of the cyclopropanation reaction catalyzed by
complex H3L1Cu2Cl4H2O (5) has not been undertaken yet due to the very high reactivity of
this complex; any attempt to isolate it met with failure. We can anyway note the following:
(i) all the catalytic reactions tested need an induction period before the nitrogen evolution
due to the EDA decomposition was observable. All the reactions were also followed by
IR spectroscopy to monitor the disappearance of the band due to the stretching of the N2
moiety of the EDA (ν = 2114 cm−1). The consumption of the diazoacetate always started
after an induction period. This explains why the catalytic cycle is faster in the second
and third runs. This induction period depends also on the concentration of the olefin and
increases with increasing the olefin concentration. (ii) When the EDA conversion reached
completion, it was possible to restore the catalytic cycle just by adding new EDA and
olefin to the reaction. In this case, no induction period was necessary to the system and the
reactions always proceeded to give cyclopropanes with almost identical yields. (iii) During
the reaction, the color of the solution, due to the dissolved copper complex, changed from
green (due to copper(II) complex) to light yellow. The time needed for the change in
color was always coincident with the induction period. (iv) The induction period observed
depends also on the olefin employed, and longer times are observed for trans-β-methyl
styrene or non conjugated double bonds. All this data, together with the data reported in
literature,78 suggest that the catalyst is activated during the induction period and that the
initial reduction of copper(II) to copper(I) is necessary for the catalysis to take place.
Usually, good catalysts give TON around 400,79–92 and excellent ones give TON
around 10.000.61,93–102 If we compare our catalyst activity to some other catalysts reported

NEW SCHIFF BASE METAL COMPLEXES
793
in literature, we will find that our catalyst lies in the range reported for catalysts with
excellent TON (up to 12556).
CONCLUSIONS
Two new tridentate and pentadentate Schiff base ligands [H3L1] and [H2L2] containing
the ONS and ON-ONS donor set and their corresponding CoII, CuII, NiII, and FeIII complexes
have been synthesized and spectrally characterized. The study revealed octahedral geometry
around Ni(II), Co(II), and Fe(III) complexes. However, distorted square pyramidal geometry
is suggested for copper ion in the binuclear Cu(II) complex. In all H2L2 complexes, the
ligand acts either as monobasic, neutral, or tridentate ligand coordinating through ONS
coordination sites. Olefins cyclopropanation reactions by ethyldiazoacetate (EDA) in the
presence of H3L1Cu2Cl3.H2O as catalyst proceed with excellent TON (up to 12556).
EXPERIMENTAL
Materials
All the reagents employed for the preparation of the ligand and its complexes were of
analytical grade and used without further purification. Unless otherwise stated, all catalytic
tests were carried out under an atmosphere of purified dinitrogen using modified Schlenk
techniques. Solvents employed were dried and distilled before use by standard methods.103
Benzene, cyclohexene, and 1-octene were distilled over sodium; styrene and α-methyl
styrene were distilled over calcium hydride and stored under dinitrogen.
Physical Measurements
The ligands and their metal complexes were analyzed for C, H, N, and M contents at
the Microanalytical Laboratory, Faculty of Science, Cairo University, Egypt. Analytical and
physical data of the ligand H3L1, H2L2 and their metal complexes are reported in Table I. The
metal ion contents of the complexes were also determined104–106 by the previously reported
methods.107,108 IR spectra of the ligands and their metal complexes were measured using
KBr discs with a Jasco FT/IR 300E Fourier transform infrared spectrophotometer covering
the range 400–4000 cm−1 and in the 500–100 cm−1 region using polyethylene-sandwiched
1
Nujol mulls on a Perkin Elmer FT-IR 1650 spectrophotometer. H and 13C NMR spectra
were obtained on Bruker Avance 300-DRX or Avance 400-DRX spectrometers. Chemical
shifts (ppm) are reported relative to TMS. The mass spectra were run at 70 eV with HP
Model MS 5988A and/or GCMS Cap 1000 EX SHIMADZU spectrometer using Electron
Impact Technique. The electronic spectra of the ligands and their complexes were obtained
in Nujol mulls and in saturated DMSO solutions using a Shimadzu UV-240 UV-Visible
recording spectrophotometer. Molar conductivities of the metal complexes in DMSO (10−3
M) were measured using a dip cell and a Bibby conductimeter MC1 at room temperature.
The resistance measured in ohms and the molar conductivities were calculated according to
the equation: ꢀ = V × K × Mw/g × ꢁ, where ꢀ, molar conductivity (ohm−1 cm2 mol−1);
V, volume of the complex solution (mL); K, cell constant 0.92 cm-1; Mw, molecular weight
of the complex; g, weight of the complex; and ꢁ, resistance measured in ohms. Magnetic
moments at 298 K were determined using the Gouy method with Hg[Co(SCN)4] as a
calibrant. Mass spectra of the solid ligand were recorded using a JEUL JMS-AX-500 mass
spectrometer.

794
N. S. YOUSSEF ET AL.
Synthesis of the Schiff Base Ligands
Synthesis of the Schiff base ligand H3L1. The solid hydrazinecarbothioamide
(0.194 g, 2.13 mmol) was added to a hot solution (75◦C) containing 7-hydroxy-5-methoxy-
2-methyl-4-oxo-4H-chromene-6-carbaldehyde (chromone) (0.500 g, 2.13 mmol) in ethanol
(60 mL). A few drops of acetic acid were added to the reaction mixture, which was then
refluxed for 10 h. The reaction was then followed by TLC using ethylacetate/n-hexane as
an eluent until the disappearance of the chromone spot. A hot (75◦C) solution of chromone
(0.500 g, 2.13 mmol) in methanol (60 mL) was then added to the reaction mixture and
refluxed for a further 85 h. The reaction mixture was then again followed by TLC (same
condition) until the disappearance of the spot of chromone. The reaction is very sensitive to
temperature (maximum 80◦C) and also to the quantity of acetic acid (adjust the pH to 5.5),
as exceeding these conditions leads to the formation of undesired product. The mixture
was then concentrated to 25 mL, and the yellow product was then filtered off, washed
with cold methanol, recrystallized from ethanol, and dried under vacuum over anhydrous
1
CaCl2 (65% yield). H NMR (300 MHz, DMSO): δ = 11.95 and 11.50 [s, broad, H(45)
and H(46)], 10.60 [s, broad, H(40)], 10.26 and 8.59 [S, 2H, H(22) and H(39)], 6.79 [d, 2H,
H(42), H(43)], 6.08 and 6.03 [S, 2H, H(41), H(44)], 3.93 and 3.80 [S, 6H, OCH3(20)
and OCH3(37)], 2.31 [d, 6H, CH3(19) and CH3(36)]. 13C NMR (300 MHz, DMSO, 300
K): C(3) 175.39, C(21) and C(38) 142.70 and 142.76, C(15) and C(32) 111.32 and 111.47,
C(6) and C(23) 100.62 and 100.70, C(20) and C(37) 63.52 and 64.70, C(19) and C(36)
19.69 and 19.73. (See Scheme 1 and Figure S for numbering.)
Synthesis of the Schiff base ligand H2L2. A few drops of glacial acetic
acid were added to a hot solution (75◦C) of 7-hydroxy-5-methoxy-2-methyl-4-oxo-4H-
chromene-6-carbaldehyde (1.00 g, 4.27 mmol) in ethanol (25 mL). The reaction mixture
was then added to a hot solution (75◦C) of N(4)-phenylthiosemicarbazide (0.714 g, 4.27
mmol) in dioxane (10 mL). The reaction mixture was refluxed for 15 h. After cooling, water
was added, and a yellow precipitate started to form which was filtered off, and washed with
water and then with ethanol. The product was recrystallized from ethanol and dried under
1
vacuum over anhydrous CaCl2 (75% yield). H NMR (300 MHz, DMSO): δ = 11.86 [s,
1H, H(30)], 10.19 [s, 1H, H(29)], 8.68 [S, 1H, H(28)], 7.53 [d, 2H, J = 7.6, H(32) and
H(22)], 7.38 [t, 2H, J = 7.6, H(33) and H(35)], 7.21 [t, 1H, J = 7.6, H(34)], 6.80 [S, 1H,
H(37)], 6.04 [S, 1H, H(38)], 3.83 [S, 3H, OCH3(26)], 2.30 [S, 3H, CH3(25)]. 13C NMR
(300 MHz, DMSO, 300 K): C(14) 175.41, C(27) 142.03, C(20) 125.67, C(5) 111.35, C(26)
63.58, C(21) and C(19) 128.83, C(22) and C(32) 125.27, C(7) 100.77 and C(25) 19.75.
(See Scheme 2; Figure S2 for numbering.)
Synthesis of the metal complexes. The metal complexes of the ligands were
prepared by mixing a hot methanolic solution of the metal salt with the required amount of
a hot ethanolic solution of the ligand to form 1:1, 1:2, or 2:1 M/L (metal/ligand) complexes,
as shown in Table III. The reaction mixture was then refluxed for a time depending on the
transition metal salt used. The precipitates formed were filtered off, washed with ethanol
then with diethyl ether, and dried under vacuum over anhydrous CaCl2.
Typical Procedure for the Catalytic Cyclopropanation of Olefins
by H3L1Cu2Cl4H2O (5)
EDA (see caption of Tables S2 and S3 for quantities) was added to a suspension of
H3L1Cu2Cl4 H2O (5) (5.0 mg, 1.15 × 10−2 mmol) and the olefin (see caption of Tables S2

NEW SCHIFF BASE METAL COMPLEXES
795
Table III Amounts of the reactants used in the formation of the metal complexes
Metal chloride, or bromide in
10–20 mL methanol
ligand in 10–25 mL ethanol
No. Ligand/Complexes Metal salt used Mass(g) × 10−3 mmol × 10−3 Mass(g) × 10−3 mmol × 10−3
1
2
3
4
5
6
7
8
9
H3L1
H3L1Co2Cl4(H2O)3 CoCl2.6H2O
H3L1Ni2Cl4(H2O)3 NiCl2 6H2O
H3L1Co2Br4(H2O)3 CoBr2 6H2O
H3L1Cu2Cl4 (H2O) CuCl2
H2L2
195
199
266
190
821
840
936
215
220
245
371
411
420
468
709
1417
H2L2CoCl2(H2O)
L2Ni.Cl(H2O)2
[(L2)2Ni].H2O
CoCl2.6H2O
NiCl2 6H2O
NiCl2 6H2O
FeCl3.6H2O
149
186
87
626
783
365
783
240
300
280
300
626
783
731
783
10 L2FeCl2(H2O)
211
and Tables S3 for quantities) in dichloroethane (10 mL). The resulting pale green solution
was heated at the required temperature under stirring; depending on the olefin used and its
concentration, after a few minutes, the solution turned to colorless and dinitrogen started to
evolve from the system. The reaction was followed until total consumption of the EDA (IR
absorbance, νmax = 2114 cm−1, < 0.025) was observed. The final solution was analyzed
by GC-MS after the addition of 2,4-dinitrotoluene as an internal standard.
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