Synthesis and characterization of novel bis(diphenylphosphino)-oxalyl and (substituted) malonyl dihydrazones: P,N,N,P-tetradentate complexes of an oxalyl derivative with Cu(II), Pd(II), and Mn(II)

Article abstract of DOI:10.1007/s00706-013-1122-4

Novel ligands of bis(diphenylphosphino)-oxalyl, malonyl, and methyl- and ethyl-malonyl dihydrazones were synthesized by condensation of oxalyl, malonyl, methyl-malonyl, and ethyl-malonyl dihydrazide with o-(diphenylphosphino) benzaldehyde in different conditions. The dihydrazones exhibit three different tautomeric structures detected by NMR and IR spectra. The ³¹P NMR spectrum demonstrates four different singlet signals, i.e., chemical shifts, of the three respective tautomers. Complexes of the oxalyl ligand with Pd ²⁺, Cu²⁺, and Mn²⁺ ions are formed in 1:1 molar ratio. Their structures were characterized by IR, NMR, EPR, MS, EA, and TGA, in which the oxalyl ligand acts as a neutral P,N,N,P-tetradentate chelate. The pH stability of the complexes is in the region of ca. 4.5-7.5 and their activation energy was calculated from the conductivity measurements. Graphical abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s00706-013-1122-4

Monatsh Chem (2014) 145:435–445
DOI 10.1007/s00706-013-1122-4
ORIGINAL PAPER
Synthesis and characterization of novel bis(diphenylphosphino)-
oxalyl and (substituted) malonyl dihydrazones: P,N,N,P-
tetradentate complexes of an oxalyl derivative with Cu(II), Pd(II),
and Mn(II)
•
Mohamed Shaker S. Adam Ahmad Desoky M. Mohamad
•
Omar M. El-Hady
Received: 17 January 2013 / Accepted: 13 November 2013 / Published online: 14 December 2013
Ó Springer-Verlag Wien 2013
Abstract Novel ligands of bis(diphenylphosphino)-oxa-
lyl, malonyl, and methyl- and ethyl-malonyl dihydrazones
were synthesized by condensation of oxalyl, malonyl,
methyl-malonyl, and ethyl-malonyl dihydrazide with
o-(diphenylphosphino)benzaldehyde in different condi-
tions. The dihydrazones exhibit three different tautomeric
structures detected by NMR and IR spectra. The 31P NMR
spectrum demonstrates four different singlet signals, i.e.,
chemical shifts, of the three respective tautomers. Com-
plexes of the oxalyl ligand with Pd2?, Cu2?, and Mn2?
ions are formed in 1:1 molar ratio. Their structures were
characterized by IR, NMR, EPR, MS, EA, and TGA, in
which the oxalyl ligand acts as a neutral P,N,N,P-tetra-
dentate chelate. The pH stability of the complexes is in the
region of ca. 4.5–7.5 and their activation energy was cal-
culated from the conductivity measurements.
phthaloyldihydrazones (di-Schiff bases) are polyfunctional
N,O,O,N-type ligands [4, 5] which form mono-, di-, and
polynuclear complexes involving ligand bridging and oxo-
bridging [6, 7]. Metal complexes of dihydrazones are of
interest in studies related to homogeneous catalysis, multi-
electron-transfer processes, and oxygen-atom-transfer
reactions [8–10].
Recently, extensive fundamental research into phos-
phine chemistry has highlighted the synthesis of new series
of phosphine ligands with alternative donor atoms besides
phosphorus, e.g., N and/or O atoms [11–15] (the electronic
asymmetry or electronic differentiation and hemilability
[16–20]). One group of hemilabile phosphine ligands
involving the combination of phosphorus and other donor
heteroatoms as chelate agents for complexation [21] are of
particular interest because of their applications in catalysis.
Such ligands can display quite different coordination
modes as multidentate ligands [22–43]. Moreover, phos-
phine–Schiff base chelates of P,N and P,N,O types form
fairly effective catalysts with transition metals, e.g.,
Cu(I) [44, 45] and Pd(II) [46, 47]. They are highly enan-
tioselective in various reactions, e.g., hydroboration,
hydrosilylation, epoxidation, aziridination of olefins, the
Henry reaction, and allylic substitutions [46, 47]. Morris
et al. developed the synthesis and applications of a new
series of P,N,N,P-tetradentate ligands complexed to iro-
n(II) as precatalysts for asymmetric transfer hydrogenation
of ketones or carbonyl compounds [22–35].
Keywords Aldehyde ꢀ Tautomerism ꢀ Carbonyl–enols ꢀ
Metal(II) complexes
Introduction
Synthesis, structural investigation, and reactions of transi-
tion metal complexes with N-donor ligands, e.g., Schiff
base hydrazones, have gained attention in research because
of their biological activities [1–3]. Acyl-, aroyl-, and
Schiff bases have been extensively studied as they
possess many interesting features, including photochromic
and thermochromic properties [48], proton transfer tauto-
meric equilibria [49], and suitability for analytical
applications [50]. Some Schiff bases are unstable in solu-
tion and involved in various equilibria like carbonyl–enol
or in ring–chain tautomeric interconversion, hydrolysis, or
Electronic supplementary material The online version of this
article (doi:10.1007/s00706-013-1122-4) contains supplementary
material, which is available to authorized users.
M. S. S. Adam (&) ꢀ A. D. M. Mohamad ꢀ O. M. El-Hady
Department of Chemistry, Faculty of Science, Sohag University,
ˆ
Sohag 82534, Egypt
e-mail: shakeradam61@yahoo.com
123

436
M. S. S. Adam et al.
Scheme 1
some others [51]. Therefore, their successful application
requires a detailed study of their characteristics, i.e., the
electronic and structural properties of the ligands play an
important role in their catalytic properties [52].
Table 1 Yield of products 6 and 7a–7c
Entry
Catalyst/media
Yield/%a
6
7a
7b
7c
To the best of our knowledge, there is no report on the
synthesis and characterization of o-(diphenylphos-
phino)benzaldehyde dihydrazones, despite the importance
of such polydentate ligands, e.g., in catalysis. For this
reason, we present here the synthesis and characterization
of novel bis(diphenylphosphino)dihydrazones via conden-
sation of oxalyl, malonyl, and substituted malonyl
dihydrazides with o-(diphenylphosphino)benzaldehyde.
We studied their spectroscopic characteristics and tauto-
meric properties. Moreover, the coordination behavior of
the oxalyl hydrazone ligand with Cu(II), Pd(II), and Mn(II)
was also studied as representative compounds.
1
2
3
a
63
91
52
50
93
41
42
85
40
38
75
28
AcONa or TEA
Dilute HCl (pH 4–5)
Yield reported after purification by column chromatography
diphenylchlorophosphine
afforded
o-(diphenylphos-
phino)bromobenzene (2) in 81 % yield. The latter
underwent a second bromine–lithium exchange with
n-butyl lithium at -78 °C followed by addition of freshly
dried DMF at -78 °C and workup with HCl (3.0 M) at
room temperature to give product 3 in 72 % yield after
purification by column chromatography [53]. Oxalyl and
malonyl dihydrazides 4 and 5a–5c were synthesized by
using published methods [48, 54], by mixing diethyl oxa-
late and diethyl malonates with excess hydrazine
monohydrate in ethanol at room temperature for the oxalyl
dihydrazide 4 and under reflux for the malonyl dihydraz-
ides 5a–5c.
Results and discussion
Synthesis of bis(diphenylphosphino)dihydrazones 6
and 7a–7c
The synthesis of tetra- or hexadentate novel P,N and/or O
ligands 6 and 7a–7c started in situ by standard condensa-
tion of oxalyl, malonyl, methyl-malonyl, and ethyl-malonyl
dihydrazides (4 and 5a–5c) with 2 equivalents of
o-(diphenylphosphino)benzaldehyde (3) under different
conditions. o-(Diphenylphosphino)benzaldehyde (3) was
prepared according to a reported procedure [53]. Thus,
bromine–lithium exchange of o-dibromobenzene (1) with
n-butyl lithium at -100 °C followed by treatment with
Condensation of 4 or 5a–5c (1 molar equivalent) with 3
(2 molar equivalents) under reflux in the absence and pre-
sence of different reagents was attempted in ethanol
(Scheme 1). White solid precipitates of 6 and 7a–7c were
collected and purified by column chromatography (Table 1).
The yields of 6 and 7a–7c were low in the absence of
anhydrous sodium acetate or TEA (Table 1, entry 1),
whereas in their presence the yields were the highest (entry
123

Synthesis and characterization
437
2). Other attempts to improve the yield of the current
ligands were tested in various conditions (highly aqueous
basic media, highly aqueous acidic media, piperidine;
discussed in the Supplementary Material), e.g., diluted HCl
(Table 1, entry 3).
It was observed that the substituent (R = H, Me, Et) in
5a–5c has a remarkable impact on the yield of 7a–7c. The
yield of 7 was the highest when R = H (7a) and the lowest
when R = Et (7c) (Table 1). Clearly, the electron-donating
nature of the alkyl group tends to reduce the reactivity of
5a–5c towards condensation with 3.
Characterization and tautomeric behavior
of 6 and 7a–7c
Many reports highlighted the isomerization of Schiff base
dihydrazone ligands (staggered–anti cis isomers) [4, 5, 55];
however, we focused here only on the tautomeric behavior
evidenced by the NMR spectral results, especially the 31P
NMR spectra. The structures of 6 and 7a–7c were con-
firmed by various spectroscopic techniques including IR,
1H, 13C, and 31P NMR, and low and high resolution mass
spectroscopy. Attempts to produce single crystals of 6 and
7a–7c were not successful. Ligands 6 and 7a–7c are very
sparingly soluble in polar solvents, e.g., methanol, acetone,
and acetonitrile, and highly soluble in more hydrophobic
solvents, e.g., chloroform and diethyl ether.
Fig. 1 31P NMR spectral signals of the tautomers of compounds 6
and 7a–7c
C=O, and C=N, respectively. The 31P NMR spectra of 6
showed a signal at -11.6 ppm (Fig. 1).
Ligands 6 and 7a–7c are air stable in the solid state but
in solution they underwent oxidation after 3 days maxi-
mum. The diphenylphosphino group was oxidized in air to
a diphenylphosphine oxide group. The structures of the
oxidized products were confirmed by the shift of the
phosphorus signal in the 31P NMR spectra, namely from -
16.0 ppm in 7b and and -16.6 ppm in 7c (in CDCl3) to
31.0 and 25.6 ppm, respectively, after oxidation in air.
On the other hand, 7a–7c have three tautomeric struc-
tures which coexist in solution (Scheme 2) as clearly
1
observed by NMR and IR. The H NMR spectrum of 7a
showed that the methylene protons of the malonyl scaffold
resonated as three singlet signals at 3.97, 3.80, and
3.31 ppm as a result of three tautomers. The NH proton
appears as two broad signals at 10.58 and 10.70 ppm due to
the dicarbonyl and carbonyl–enol forms (see Supplemen-
tary Material). The strong downfield shifted NH proton
could be attributed to the intermolecular hydrogen bonds.
In the 13C NMR spectrum of 7a, the methylene carbon
resonated as three singlet signals at 29.7, 38.4, and
39.3 ppm due to the three tautomers (dienol, carbonyl–
NMR and IR spectra of 6 and 7a–7c
NMR spectra of 6 and 7a–7c were recorded in CDCl3 and
DMSO-d6. The NMR spectra showed very little evidence
for the tautomeric behavior of 6 which is consistent with
reported salicylaldehyde benzoylhydrazone ligands and
their metal complexes [48–51, 54]. Dienol, carbonyl–enol,
and dicarbonyl forms were observed by NMR spectros-
copy. The absence of any tautomeric behavior in 6 could be
attributed to the intramolecular hydrogen bonding between
the NH protons and C=O oxygens (Scheme 1) which sta-
bilizes the dicarbonyl form. The intramolecular hydrogen
bonds in 6 could be detected by the downfield shift of the
1
enol, and dicarbonyl forms). The H NMR spectra of 7b
reports two doublet signals of the methyl group at 1.46 and
1.61 ppm and two quaternary signals of the CH-methylene
at 4.23 and 4.55 ppm. Moreover, for 7c, the 1H NMR
spectra recorded two triplets for the methyl protons of the
ethyl derivative which resonated at 0.94 and 1.07 ppm and
two triplets for the CH proton of the malonyl scaffold at
4.24 and 4.65 ppm (Fig. 2).
1
The IR spectra of 7a and 7b gave broad absorption
bands at 3,463 and 3,460 cm-1, respectively, which orig-
inated from the –OH vibration in the dienol and carbonyl–
enol forms. The tautomeric absorption band of the NH
NH protons in the H NMR spectra (d = 10.2 ppm) [56].
Furthermore, the IR spectra of 6 showed no absorption
bands for –OH groups and showed a set of bands at 3,454,
1,687, and 1,505 cm-1 due to vibrations of amide NH,
123

438
M. S. S. Adam et al.
Scheme 2
1,571, and 1,560 cm-1 for 6 and 7a and 7b, respectively,
owing to the impact of the neighboring amido (NH–C=O)
group and the tautomerism.
The ratio of the three coexisting tautomers in 7a–7c was
determined by their integration factors in the 1H NMR
spectra. For example, in 7a, the ratio of dienol to carbonyl–
enol to dicarbonyl was 8:1:2. In particular, the most
abundant and stable tautomer in solution in different polar
solvents is the dienol form as observed previously [55].
The intermolecular hydrogen bonding in the dienol tauto-
mer between the hydrogen atom of the –OH group and the
nitrogen atom of the CH=N group of another molecule
could be the reason for the higher stability of the dienol
form than the other forms. The intermolecular hydrogen
bonding in the dienol reduces the steric repulsion between
the carbonyl groups especially in the less polar solvents
[58]. The 31P NMR spectra showed four signals for the
three aforementioned tautomers (Fig. 1).
The electronic spectral bands for 6 and 7a–7c are
summarized in Table 2, along with their characteristic
molar extinction coefficients. All ligands exhibit two bands
within the region of 220–243 and 274–306 nm which arise
due to p ? p* and n ? p* electronic transitions within
dihydrazone, respectively [48].
Fig. 2 Expansion of the 1H NMR spectra (0–5 ppm) of the CHR
group (R = H, Me, and Et) of compounds 7a–7c
Theoretical calculations of 6 and 7a–7c
Semiempirical calculations were carried out using the AM1
method with the MOPAC 6.0 program as an experiential
study [59]. Energy minimum geometries were found by
minimizing the energy, with respect to all geometrical
coordinates without any symmetry constraints [60]. Ligand
7a assembled in a dense, hydrogen-bonded network with
all six geometrically possible hydrogen bonds realized. All
group of the secondary amide group appears conspicuous at
3,421 cm-1 for 6a, whereas it was a broad band for 7b. In
the IR spectrum of 7a, the C=O and C=N amido groups
appear as an overlapped broad band at 1,660 cm-1 and the
C=N tautomeric group appears at 1,390 cm-1. The char-
acteristic C=O appears at 1,680 cm-1 for 7b and the C=N
bands of the amide tautomeric structure appear at 1,560
˚
hydrogen bonds have a length of 2.94 0.2 A. Calculated
and 1,452 cm-1
.
The characteristic C=N stretching
heats of formation of the optimized structures of both
compounds revealed that 7a is more stable than 6 (see
Supplementary Material).
absorption band appears within the 1,620–1,640 cm-1
region for Schiff bases [57], whereas these appear at 1,687,
123

Synthesis and characterization
439
Synthesis of Cu(II), Pd(II), and Mn(II) acetate
[ML](OAc)2S, where L is 6 and S is the solvent, particu-
larly H2O or MeOH (Scheme 3).
complexes 8, 9, and 10
The stoichiometry of the current complexes was deter-
mined by the widely used spectrophotometric continuous
variation method [62] in which the molar ratios of the indi-
vidual components of the tested complexes varied
continuously in solution, whereas the total concentration
remained constant. The continuous variation plots (see
Supplementary Material) reveal maximum absorbance val-
ues at kmax corresponding to molar ratios of 0.98–1.01 of the
oxalyl ligand in the studied complexes. This suggests that the
metal ion formed a 1:1 complex with 6 (Scheme 3). In par-
ticular, 6 coordinated to the central metal ion through the a-
nitrogen of the diimino group and the two phosphorus atoms
of the bis(diphenylphosphino) group. Complex 8 is olive-
brown, whereas 9 and 10 are pale brown. The complexes are
air stable in the solid state and also in solution (in polar
solvents, e.g., MeOH, EtOH, and MeCN).
Ligand 6 acts as a tetradentate chelate, whereas ligands 7a–
7c may act as hexadentate ligands as dibasic anions in the
dienolic forms and as tetrabasic moieties in the dicarbonyl
forms under suitable conditions [61] that will be studied
and presented in future work. We tested the coordination
chemical behavior of 6 only as a model towards Cu(II),
Pd(II), and Mn(II) ions. The novel complexes were syn-
thesized by mixing 6 with Cu(II), Pd(II), and Mn(II)
acetate in equimolar ratio in methanol at room temperature.
The general formula of the current complexes is
Table 2 Electronic spectra and the activation energy for compounds
6–10
Product Electronic spectraa
Activation
energyb
E 9 10-3
/
k
max/nm 104 emax
/
Assignment
dm3 mol-1 cm-1
kJ mol-1
Characterization of complexes 8–10
6
222
6.04
1.11
7.10
3.70
5.23
3.45
6.37
3.21
5.68
2.42
4.91
7.18
2.57
5.95
6.61
2.37
5.34
p ? p*
n ? p*
p ? p*
n ? p*
p ? p*
n ? p*
p ? p*
n ? p*
p ? p*
LMCT
d–d
1
The complexes 8–10 were characterized by IR, H NMR,
274
13C NMR, 31P NMR, EPR, MS, and UV–Vis spectra, and
EA. The electronic spectral data of 8–10 and 6 are sum-
marized in Table 2. The elemental analyses were in good
agreement with the calculated values after purification. The
complexes are single species as confirmed by TLC tests.
The methanolic solutions of 8–10 show uniform spots on a
TLC plate covered with silica gel and developed using a
mixture of acetone and methanol (2:1).
7a
7b
7c
8
234
296 br
236
300 br
243
306 br
221
2.14
1.35
1.57
312
351 br
229
IR, NMR, and EPR spectra of complexes 8–10
9
p ? p*
LMCT
d–d
317
The IR spectra of 8–10 illustrated that most bands are
almost in the same position as those of the uncoordinated
ligand 6 but considerably reduced in their intensity. No
observed changes were seen for the NH and C=O bands
after complexation with Cu(II), Pd(II), or Mn(II) ions. The
bands of the HC=N group coordinated to the central metal
ion show a strong shift of its stretching vibrations from
1,505 cm-1 in 6 to 1,636, 1,685, and 1,564 cm-1 in 8–10,
respectively.
445 br
222
10
p ? p*
LMCT
d–d
320
425 br
LMCT ligand–metal charge transfer band
a
Electronic spectra were recorded in methanol
b
Activation energies were measured for each complex at a concen-
tration of 2.0 9 10-5 mol dm-3 at 298 K
Scheme 3
123

440
M. S. S. Adam et al.
Complexes 8 and 10 are paramagnetic, whereas 9 is
1
diamagnetic. In the H NMR spectra of 9, the proton res-
free electron g value (2.0023). The complex gave an EPR
spectrum containing six lines due to hyperfine interaction
[68–70] between the unpaired electrons and the 55Mn
nucleus (I = 5/2). The nuclear magnetic quantum numbers
MI corresponding to the lines are -5/2, -3/2, -1/2, ?1/2,
?3/2, and ?5/2 from low to high field (Fig. 4).
onances of the methyl group of the acetate ion and of the
coordinated methanol appear at 1.84 and 5.97 ppm as
singlets, respectively. A little downfield shift of the HC=N
proton resonance is observed from 8.99 (in 6) to 9.01 ppm
(in 9) which appears as a doublet with higher coupling
from 5.7 (in 6) to 11.2 Hz (in 9) which is attributable to the
coordination through the nitrogen atom to the Pd2? ion. In
the 13C NMR spectra, the acetate ion shows two signals at
22.0 and 175.5 ppm corresponding to CH3 and C=O car-
bons, respectively. The other 13C NMR spectral signals do
not have observed shift after complexation.
Electronic spectra of complexes 8–10
The electronic absorption spectra are often very helpful in
the evaluation of results furnished by other methods of
structural investigation. Moreover, the electronic spectral
measurements were used to assign the stereochemistries of
metal ions in the complexes on the basis of the positions
and number of d $ d transition peaks.
The EPR spectra of the Cu(II) complex were recorded in
methanol at 115 K (Fig. 3). The X-band EPR spectra of the
Cu(II) complex, particularly 8, show one intense absorption
band in the high field region. This band is isotropic owing
to the tumbling motion of the molecules. However, this
complex in the frozen state shows five well-resolved peaks
in the low field region. It exhibits anisotropic signals with
The electronic spectra of the synthesized complexes
compared to their corresponding ligand 6 show three bands
in the region 222–229 (p ? p*), 312–320 (LMCT), and
351–425 nm (d $ d) in methanol (Table 2). The appear-
ance of bands in the regions 221–229 and 312–320 nm in
the complexes suggests that the ligand (222 and 274 nm in
6, respectively) undergoes splitting and shows blue shift as
well as red shift. This feature associated with the ligand
indicates an effect of complexation on the ligand. The
complexes show another strong broad band in the region of
351–425 nm in the visible region, cf. Table 2. Since 6 is
not expected to be chromophoric in the visible region,
these bands have been assigned as ligand–metal charge
transfer (LMCT) transitions on the basis of their high
intensity [70]. They may be associated, most probably,
with a ligand-to-metal charge transfer originating from an
electronic excitation from the HOMO of bis(diphenyl-
phosphino) to the LUMO of the complexes as reported
before [48]. Also, the broad bands appearing as moderately
intense peaks in the region 351–445 nm of the complexes
g values (g = 2.066 and g\ = 2.009) which are charac-
k
teristic of axial symmetry [63]. Since the g\ and g values
k
are closer to 2 and g [ g\, this suggests a square-planar
k
geometry around the Cu(II) ion corresponding to elonga-
tion along the fourfold symmetry Z-axis [64, 65]. In
addition, exchange coupling interaction between two
Cu(II) ions of two complex cations was explained by
Hathaway’s expression G = (g - 2)/(g\ - 2). The
k
G value of 7.33 indicated negligible exchange interaction
coupling of Cu–Cu within two complex cations [66, 67],
see Fig. 3. The EPR spectrum of the Mn(II) complex 10
was measured in DMSO as a polycrystalline sample at
311 K (Fig. 4), giving two main signals with g = 1.887
k
and g\ = 2.123. The polycrystalline samples gave one
broad isotropic signal centered approximately at around the
Fig. 3 EPR analysis of Cu(II) complex 8 at 115 K in MeOH
Fig. 4 EPR analysis of Mn(II) complex 10 at 115 K in DMSO
123

Synthesis and characterization
441
Activation energy and pH stability of complexes 8–10
are assigned to the d $ d transition [71] and the position
of these bands indicates that the chelate ligand coordinated
to the central metal ion in a square-planar structure. The
broad band observed at 351 nm in the electronic spectrum
The activation energy (E/kJ mol-1) of the studied com-
plexes 8–10 could be calculated from Eq. (1) as shown in
Fig. 5. Equation (1) shows the linear relation between log s
(observed conductance) versus 1/T (the reciprocal of tem-
perature from 298 to 333 K) [73]. The observed
conductance of the current complexes is tabulated at var-
ious temperatures (from 25 to 60 °C) in the Supplementary
Material.
2
of the Cu(II) complex was assigned to the 2Eg ? T2g
transition which is consistent with octahedral geometry
including the two acetate anions [72].
TGA analysis of complexes 8–10
The thermogravimetric (TGA) analyses of 8–10 were
performed using air as the gas carrier. The complexes were
heated at rate of 10.0 °C per min from 30.0 to 600.0 °C.
The thermogram of the studied complexes shows that the
complexes decomposed in three successive steps. This is
attributed to the loss of solvent molecules, acetate ions, and
bis(diphenylphosphino) groups of the complexes for the
first, second, and third steps, respectively.
s ¼ s0 expðꢁE=2kTÞ
ð1Þ
where s is the observed conductance of the complex
solution, s0 is the specific conductance (a constant value),
and E is the activation energy of the charged complex ions
in the solution. The observed conductivities follow the
order 10 \ 9 \ 8 (Table 2). This order agrees with the
effect of the type of central metal ion and its geometry in
complexation with the title ligands on the conductivity of
the complexes for all applied temperatures [74]. The acti-
vation energies of the charged complex ions decrease in the
following direction 9 \ 10 \ 8, which parallels the
increased conductivities of these complexes.
In the thermogram of the complexes, the first endothermic
weight loss of 8 was observed between 150 and 180 °C and
ascribed to the loss of one coordinated water molecule. The
experimental mass loss value (Dmrel = 1.90 %) approxi-
mately agrees with the expected one (Dmrel = 1.08 %) in
complex 8. In complex 9, the methanol molecule was lost at
100–120 °C with an observed mass loss value
(Dmrel = 3.06 %) which agrees with the expected value
(Dmrel = 3.48 %). This suggests that the methanol molecule
was part of the lattice structure in complex 9. The complexes
8 and 9 did not show any weight loss until a temperature of
300 °C after which they decomposed without melting.
The pH stability was tested using universal buffer
solutions [74] added to an ethanolic solution of 8, 9, or 10,
followed by measuring the absorbance at kmax at room
temperature. The investigated complex ions are highly
stable within a wide range of pHs, from ca. 4.5 to 7.5 (see
Supplementary Material). The tested solutions of 8–10 in
the aforementioned pH range maintain their colors for
more than 3 days without fading. This observation shows
the extent of the stability of our studied complexes in that
pH range. But outside that range the colors of the complex
ions fade at once.
Complex
9
underwent exothermic loss at 250 °C
(Dmrel = 9.05 %) which corresponds to one acetate group as
expected theoretically (Dmrel = 9.90 %). But in complex 8,
exothermic loss occurred at 350 °C with Dmrel = 33.58 %,
which is due to the loss of the two acetate groups and two
phenyl groups of the bis(diphenylphosphino) groups
(Dmrel = 33.60 %). In both 8 and 9, the acetate group was
assumed to be lost as acetic acid. The third part of the TGA
decomposition of 8 and 9 is attributed to the loss of two
diphenylphosphino groups and the central metal ion.
2.20
complex 8
complex 9
complex 10
2.15
2.10
2.05
2.00
1.95
1.90
1.85
1.80
1.75
1.70
The second endothermic weight loss of complex 10 in
the thermogram was observed between 250 and 300 °C
owing to the loss of the coordinated methanol molecule,
two acetate anions, and two phenyl groups of the
bis(diphenylphosphino) group. The experimental mass loss
value (Dmrel = 33.91 %) approximately agrees with the
expected one (Dmrel = 35.07 %). Then the third endo-
thermic weight loss of complex 10 was observed between
450 and 500 °C which corresponds to the loss of the two
additional phenyl groups of the bis(diphenylphosphino)
1.65
2.95 3.00 3.05 3.10 3.15 3.20 3.25 3.30 3.35 3.40
1000 / (T/K)
groups.
The
experimental
mass
loss
value
(Dmrel = 54.93 %) approximately agrees with the expected
one (Dmrel = 52.84 %).
Fig. 5 Plot of logarithm of the observed conductivity of complexes
8–10 at ca. 2 9 10-4 mol dm-3 versus 1,000/T
123

442
M. S. S. Adam et al.
Experimental
values were checked using a Metrohm 695 pH/ion meter to
0.005 units with temperature control using an ultrather-
mostat (HAAKE model F3-k) within 0.2 °C.
Reactions with moisture- or air-sensitive compounds were
conducted in dried and deoxygenated solvents under a
nitrogen atmosphere using Schlenk techniques, carried out
with magnetic stirring, and held at the chosen temperature
by immersion in a thermostatted oil bath. Hydrazine
monohydrate, diethyloxalate, diethylomalonate, methyl
diethylomalonate, ethyl diethylomalonate, chlorodiphen-
ylphosphine, 1,2-dibromobenzene, n-BuLi (2.5 M in
hexane), palladium acetate, copper acetate monohydrate,
and manganese acetate dihydrate were used as received
from commercial suppliers (Sigma-Aldrich, Merck, and
Acros).
General procedure for the synthesis of oxalic
and (substituted) malonic acid dihydrazides
Under a nitrogen atmosphere in a two-necked round-bot-
tomed flask equipped with a dropping funnel 5 cm3 of
ethanolic solution of o-(diphenylphosphino)benzaldehyde
(3) was poured into 5 cm3 of an ethanolic solution of
oxalyl, malonyl, methyl-malonyl, or ethyl-malonyl dihy-
drazide and anhydrous sodium acetate or triethylamine
(TEA). The reaction mixture was refluxed for a period of
time controlled by TLC. A white precipitate was formed
which was collected by filtration, washed many times with
EtOH, and purified by column chromatography.
Oxalyl, malonyl, methyl-malonyl, and ethyl-malonyl
dihydrazides (4 and 5a–5c) were synthesized by the liter-
ature methods [48, 54]. The oxalyl, malonyl, methyl-
malonyl, and ethyl-malonyl dicarboxylic acid esters reac-
ted directly with hydrazine monohydrate in ethanolic
solution by refluxing or by stirring at room temperature to
give white precipitates of the corresponding dihydrazides.
o-(Diphenylphosphino)benyaldehyde (3) was prepared as
reported before [53].
Oxalic acid 1,2-bis[2-[2-(diphenylphosphino)phenylmeth-
ylene]hydrazide] (6, C40H32N4O2P2)
Reaction of 0.38 g 3 (1.30 mmol) with 0.077 g 4
(0.65 mmol) and 0.10 g anhydrous sodium acetate
(1.30 mmol) or 0.09 cm3 TEA (1.30 mmol) under reflux
for 2 h. Purification of the final product by column
chromatography was carried out using 40 % ethyl ace-
tate/60 % n-hexane to afford 0.39 g (91 %) of 6. M.p.:
Some analyses of the synthesized compounds were
carried out in collaboration with Prof. Dr. Rinaldo Poli
labs, Inorganic Chemistry, Laboratoire de Chimie de
Coordination (LCC), UPR CNRS 8241 205, Route de
Narbonne, 31077 Toulouse Cedex 4, France (NMR, EA,
and PR analyses). NMR spectra were recorded at 25 °C on
a multinuclear FT-NMR spectrometer Bruker ARX300 and
ARX250 at 300 (1H), 75 (13C), and 121 (31P) MHz. The
1H, 13C, and 31P chemical shifts are given in ppm relative
to Me4Si and H3PO4 (85 %), respectively, as external
standards. Coupling constants refer to JHH in 1H and JPC in
13C NMR unless denoted otherwise. Splitting patterns for
larger and smaller coupling constants are given in the same
order as the J values. Mass spectra were recorded on a
Finnigan MAT system 8200 spectrometer, equipped with a
3-T superconducting magnet with ESI. Elemental analyses
(C, H, N, S) were conducted using a CHNS-932 analyzer
from LECO using standard conditions; their results were
found to be in good agreement with calculated values
( 0.4 %). Conductivity measurements were carried out
using Jenway conductivity meter model 4320, using an
epoxy-bodied conductivity cell (two electrodes, shiny) with
cell constant calibration (from 0.01 to 19.99) at 298 K,
which was controlled by an ultrathermostat (HAAKE
model F3-k) within 0.2 °C. The electronic spectra of
ligands 6 and 7a–7c and the complexes 8–10 were mea-
sured using 10-mm silica cells in the thermostatted cell
holder of a Jasco UV–Vis spectrophotometer (model
V-530). The thermostatted cell holder was fitted with an
ultrathermostat water circulator (HAAKE model F3-k). pH
1
248 °C; H NMR (300 MHz, CDCl3): d = 6.95 (dd, 2H,
4
3J = 4.5, J = 0.9 Hz), 7.23–7.45 (m, 24 H), 8.24 (dddd,
2H, 3J = 4.2, 3.9, 4J = 1.2, 0.9 Hz), 8.99 (d, CH=N,
4JPH = 5.7 Hz), 10.23 (s, br, 2 NH) ppm; 13C NMR
(75 MHz, CDCl3): d = 127.3, 128.7, 128.8, 129.1, 129.2,
131.1, 133.7, 134.1, 135.4, 135.6, 136.4, 136.7, 137.6,
137.9, 149.6, 150.1, 155.0 ppm; 31P NMR (121 MHz,
CDCl3): d = -11.67 (JPP = 19.6 Hz) ppm; IR (KBr):
ꢀ
m = 3,454.0 (NH), 3,059.5, 750.4 (C=CH aromatic),
1,978.2 (N–C=O), 1,687.0 (C=O), 1,505.6 (C=N, amide),
1,439.1 (C–N) cm-1; MS (ESI MS CI?, DCI/CH4): m/
z = 662.
Malonic acid 1,3-bis[2-[2-(diphenylphosphino)phenyl-
methylene]hydrazide] (7a, C41H34N4O2P2)
Reaction of 0.40 g 3 (1.37 mmol) with 0.09 g 5a
(0.68 mmol) and 0.11 g anhydrous sodium acetate
(1.37 mmol) or 0.10 cm3 TEA (1.37 mmol) under reflux
overnight. Purification of the final product by column
chromatography was carried out using 40 % ethyl acetate/
60 % n-hexane to afford 0.43 g (93 %) of 7a. M.p.:
1
198 °C; H NMR (300 MHz, CDCl3): d = 3.97 (s, 2H,
CH2), 6.88–6.93 (m, 2 H), 7.21–7.33 (m, diphenyl,
overlapped with solvent peak), 7.91 (dd, 3J = 4.2,
3.9 Hz), 8.46 (t, 2H, overlapped with the carbonyl–enol
3
1
form, J = 5.1, 3.3 Hz), 9.03 (s, CH=N) ppm; H NMR
signals which could be distinguished for the dicarbonyl
123

Synthesis and characterization
443
3
form are 3.80 (s, 2H, CH2), 8.21 (dd, J = 4.5, 3.6 Hz),
2-Ethylmalonic acid 1,3-bis[2-[2-(diphenylphosphino)phe-
nylmethylene]hydrazide] (7c, C43H38N4O2P2)
3
8.87 (t, J = 5.7 Hz), 10.70 (br s, 2 NH) ppm; H NMR
1
signals which could be distinguished for the carbonyl–enol
3
form are 3.31 (s, 2H, CH2), 8.00 (dd, J = 4.4, 3.7 Hz),
Reaction of 0.40 g 3 (1.37 mmol) with 0.11 g 5c
(0.68 mmol) and 0.11 g anhydrous sodium acetate
(1.37 mmol) or 0.10 cm3 TEA (1.37 mmol) under reflux
overnight. Purification of the final product was by
column chromatography carried out using 30 % ethyl
acetate/70 % n-hexane to afford 0.36 g (75 %) of 7c.
9.10 (s, CH=N), 10.58 (br s, 1 NH) ppm; from the
integration factor, the ratio of dienol to dicarbonyl to
carbonyl–enol form is 1.8:1.0:0.8; 13C NMR (75 MHz,
CDCl3): d = 29.7 (CH2), 38.4 (CH2), 39.7 (CH2), 126.8
(CH), 127.2 (CH), 128.6 (CH), 129.0 (CH), 129.1 (CH),
129.9 (CH), 130.3 (CH), 130.4 (CH), 133.7 (CH), 133.9
(CH), 134.0 (CH), 135.8 (Cq), 136.0 (Cq), 136.5 (Cq), 136.8
(Cq), 137.0 (Cq), 142.3 (d, CH, J = 24.5 Hz), 144.2 (d,
CH, J = 20.5 Hz), 146.5 (d, CH, J = 28.4 Hz), 162.1 (Cq,
C=O), 169.2 (Cq, C=O), 169.8 (Cq, C=O) ppm; 31P NMR
(121 MHz, CDCl3): d = -16.55, -16.08, -14.79, -
1
M.p.: 170 °C; H NMR (300 MHz, CDCl3): d = 0.94 (t,
3
3H, CH3, J = 7.5, 7.2 Hz), 2.04 (m, 2H, CH2), 4.24 (t,
1H, CH, 3J = 7.2 Hz), 6.89–6.97 (m, 2 H), 7.09–7.45
(m, diphenyl, overlapped with solvent peak), 8.00 (dddd,
2H, 3J = 4.2, 3.7, 4J = 1.0, 0.8 Hz), 8.23 (ddd,
3J = 3.7, 4J = 1.0 Hz), 8.48 (d, 3J = 5.5 Hz), 8.63 (s,
CH=N), 8.88 (d, 3J = 5.5 Hz) ppm; 1H NMR signals
which could be distinguished for the dicarbonyl form are
1.07 (t, 3H, CH3, 3J = 7.5 Hz), 4.65 (t, 1H, CH,
3J = 7.2, 7.0 Hz), 7.94 (dddd, 2H, 3J = 4.2, 3.7,
4J = 1.0, 0.5 Hz), 8.15 (ddd, 3J = 4.0, 4J = 1.2 Hz),
8.38 (d, 3J = 4.5 Hz), 8.69 (s, CH=N), 9.22 (d,
ꢀ
14.26 ppm; IR (KBr): m = 3,463.6 (OH), 3,421.2 (NH),
3,090, 742.7 (C=CH, aromatic), 2,928.3, 694.5 (CH,
aliphatic), 1,660.9 (C=O), 1,571.3 (C=N), 1,390.8 cm-1
(C=N, tautomer), 1,369.2 (C–N) cm-1; MS (EI? 30 eV):
m/z = 677 [M?].
1
3J = 4.5 Hz), 10.38 (br s, 2 NH) ppm; H NMR signals
2-Methylmalonic acid 1,3-bis[2-[2-(diphenylphosphino)-
phenylmethylene]hydrazide] (7b, C42H36N4O2P2)
which could be distinguished for the carbonyl–enol form
are 0.99 (t, 3H, CH3, 3J = 7.2 Hz), 8.85 (d,
3J = 5.7 Hz), 10.16 (br s, 2 NH) ppm; 13C NMR
(75 MHz, DMSO-d6): d = 11.4 (CH3), 47.2 (CH), 49.4
(CH), 126.2 (CH), 126.3 (CH), 127.2 (CH), 128.5 (CH),
128.7 (CH), 129.1 (CH), 130.7 (CH), 133.7 (CH), 133.9
(CH), 134.0 (CH), 135.8 (Cq), 141.1 (CH), 171.2 (Cq,
C=O) ppm; 31P NMR (121 MHz, CDCl3): d = -16.81,
-16.66, -15.99, -14.89, -13.42 ppm; MS (EI?
30 eV): m/z = 705 ([M?1]?); HRMS: calcd 705.2504,
found 705.2548.
Reaction of 0.40 g 3 (1.37 mmol) with 0.10 g 5b
(0.68 mmol) and 0.11 g anhydrous sodium acetate
(1.37 mmol) or 0.10 cm3 TEA (1.37 mmol) under reflux
overnight. Purification of the final product by column
chromatography was carried out using 40 % ethyl acetate/
60 % n-hexane to afford 0.40 g (85 %) of 7b. M.p.:
174 °C; 1H NMR (300 MHz, CDCl3): d = 1.46 (t, 3H,
3
3
CH3, J = 7.2 Hz), 4.55 (q, 1H, CH, J = 7.5, 7.2 Hz),
6.89–7.00 (m, 2 H), 7.13–7.47 (m, 10H, diphenyl), 7.96 (m,
2H, 3J = 4.0, 3.4 Hz), 8.44 (d, 3J = 5.2 Hz), 8.59 ppm (s,
CH=N); 1H NMR signals which could be distinguished for
the dicarbonyl form are 1.61 (br, 3H, CH3), 4.23 (q, 1H,
CH, 3J = 7.2 Hz), 8.14 (m), 9.22 (d, 3J = 4.7 Hz), 8.68 (s,
[Oxalic acid 1,2-bis[2-[2-(diphenylphosphino)phenyl-
methylene]hydrazide]]copper(II) acetateꢀH2O
(8, C44H40CuN4O7P2)
1
CH=N), 10.38 (br s, 2 NH) ppm; H NMR signals which
Under nitrogen in a two-necked round-bottomed flask
5 cm3 of a methanolic solution of 0.05 g Cu(CH3-
COO)2ꢀH2O (0.25 mmol) was added dropwise to 5 cm3
of a methanolic solution of 0.17 g 6 (0.25 mmol). The
color of the reaction mixture changed to pale green just
after addition of the Cu2? solution. The reaction mixture
was stirred at room temperature for 3 h to afford an
olive-brown precipitate. The precipitate was filtrated and
washed many times with ethanol and ether and then
dried in vacuo. The complex was recrystallized from
ethanol to afford 0.14 g (64 %) of 8. M.p.: [300 °C
could be distinguished for the carbonyl–enol form are 8.17
(m), 8.36 (d, 3J = 4.2 Hz), 8.89 (d, 3J = 5.5 Hz) ppm; 13
C
NMR (75 MHz, DMSO-d6): d = 13.1 (CH3), 14.2 (CH3),
45.2 (CH), 126.4 (CH), 126.6 (CH), 126.7 (CH), 129.1
(CH), 129.3 (CH), 129.4 (CH), 129.6 (CH), 130.0 (CH),
133.6 (CH), 133.8 (CH), 133.9 (CH), 134.1 (CH), 135.8
(Cq), 136.1 (Cq), 136.1 (Cq), 136.2 (Cq), 136.4 (Cq), 138.3
(d, Cq, J = 20.7 Hz), 139.8 (d, CH, J = 28.0 Hz), 168.2
(Cq, C=O), 171.5 (Cq, C=O), 173.1 (Cq, C=O) ppm; 31P
NMR (121 MHz, DMSO-d6): d = -18.31, -17.28, -
ꢀ
ꢀ
16.73, -16.00 ppm; IR (KBr): m = 3,460.0 (br, OH and
(dec.); IR (KBr): m = 3,424.1 (NH), 3,060.0, 749.4
NH), 3,055.6, 746.5 (C=CH, phenyl), 2,929.3, 695.4 (CH,
aliphatic), 2,365.0 (weak, N–C=O), 1,680.2 (C=O), 1,560.6
(C=N, amide), 1,452.6 (C=N, tautomer), 1,366.7 (C–N)
cm-1; MS (ESI MS CI?, DCI/CH4): m/z = 691 [M?].
(C=C–H, aromatic), 2,926.4, 694.5 (C–H aliphatic),
2,364.1 (N–C=O), 1,698.5 (C=O), 1,636.8 (C=N, amide),
1,495.0 (C=N, tautomer), 1,376.4 (C–N) cm-1; MS (ESI
in CH3Cl/MeOH–CH3COO-): m/z = 725 [M?].
123

444
M. S. S. Adam et al.
2. Sridhar SK, Pandeya SN, Stables JP, Ramesh A (2002) Eur J
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6. Lal K, Gupta SP, Sahni SK (1986) Polyhedron 5:1499
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[Oxalic acid 1,2-bis[2-[2-(diphenylphosphino)phenyl-
methylene]hydrazide]]palladium(II) acetateꢀMeOH
(9, C45H42N4O7P2Pd)
Under nitrogen in a two-necked round-bottomed flask
5 cm3 of a methanolic solution of 0.033 g Pd(CH3COO)2
(0.15 mmol) was added dropwise to 5 cm3 of a methanolic
solution of 0.10 g 6 (0.15 mmol). The reaction mixture was
kept under stirring at room temperature for 4 h to afford a
brown precipitate. The precipitate was filtrated and washed
many times with ethanol and ether and then dried in vacuo.
The complex was recrystallized from methanol to afford
1
0.14 g (60 %) of 9. M.p.: [300 °C; H NMR (300 MHz,
CDCl3): d = 1.84 (s, 3H, CH3, acetate), 5.97 (br s, 1H,
CH3, MeOH), 6.97 (m, 4 H), 7.26–7.61 (m, 10H,
3
overlapped with solvent peak), 7.51 (t, 1H, J = 7.7 Hz),
9.01 (d, 1H, CH=N, 3J = 11.2 Hz) ppm; 13C NMR
(75 MHz, CDCl3): d = 22.0 (CH3, acetate), 123.3, 123.8,
124.2, 127.5, 128.7, 128.9, 130.9, 131.8, 132.5, 133.4,
133.6, 136.1, 156.0, 169.0, 175.5 (C=O of acetate) ppm;
31P NMR (101.25 MHz, CDCl3): d = 31.47 ppm (contam-
inated with very small signals of the reactant, 16.1, 33.16,
14. Garralda MA, Hernandez R, Ibarlucea L, Pinilla E, Torres MR
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17. Nardelli M, Pelizzi C, Pelizzi G, Tarasconi P (1985) J Chem Soc
Dalton Trans 321–415
ꢀ
35.68 ppm); IR (KBr): m = 3,421.2 (br, interfering of
MeOH and NH), 3,053.7, 745.6 (C=C–H, aromatic),
2,938.9, 693.5 (C–H aliphatic), 1,685.0 (C=O), 1,523.0
(C=N, amide), 1,431.4 (C=N, tautomer), 1,359.7 (C–N)
cm-1; MS (ESI in MeOH): m/z = 886 [M?].
18. Cingolani A, Effendy, Pellei M, Pettinari C, Santini C, Skelton
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[Oxalic acid 1,2-bis[2-[2-(diphenylphosphino)phenyl-
methylene]hydrazide]]manganese(II) acetateꢀMeOH
(10, C45H42MnN4O7P2)
Under nitrogen in a two-necked round-bottomed flask
5 cm3
23. Tollabi M, Framery E, Goux-Henry C, Sinou D (2003) Tetra-
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´
31. del Campo O, Carbayo A, Cuevas JV, Garcıa-Herbosa G, Mun˜oz
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of
a
methanolic
solution
of
0.05 g
Mn(CH3COO)2ꢀ2H2O (0.23 mmol) was added dropwise
to 5 cm3 of a methanolic solution of 0.15 g 6 (0.23 mmol).
The reaction mixture was kept under stirring at room
temperature for 4 h to afford a brown precipitate. The
precipitate was filtrated and washed many times with
ethanol and ether and then dried in vacuo. The complex
was recrystallized from methanol to afford 0.045 g (69 %)
ꢀ
of 10. M.p.: [300 °C (dec.); IR (KBr): m = 3,420.2 (br,
interfering of MeOH and NH), 3,056.0, 716.6 (C=C–H,
aromatic), 2,929.3 (C–H aliphatic), 1,564.5 (strong br,
C=O, C=N, amide), 1,423.6 (C=N, tautomer), 1,312.7 (C–
N) cm-1; MS (ESI in MeOH): m/z = 835 [M?].
Acknowledgments The authors greatly thank Prof. Dr. Rinaldo Poli,
Laboratoire de Chimie de Coordination (LCC), UPR CNRS 8241 205,
Route de Narbonne, 31077 Toulouse Cedex 4, France, for his continued
and precious advice and encouragement to produce this work.
32. Sui-Seng C, Haque FN, Hadzovic A, Pu¨tz A-M, Reuss V, Meyer
N, Lough AJ, De Iuliis MZ, Morris RH (2009) Inorg Chem
48:735
33. Meyer N, Lough AJ, Morris RH (2009) Chem Eur J 15:5605
34. Mikhailine A, Lough AJ, Morris RH (2009) J Am Chem Soc
131:1394
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