Synthesis, structure, and properties of phosphorus-containing bis(amidrazones)

Article abstract of DOI:10.1134/S107036320608007X

Previously unknown ethenylphosphonic derivatives of bis(amidrazones) were prepared. According to spectroscopic data and quantum-chemical calculations, these compounds exist as phosphonium salts of a symmetrical linear structure with trans arrangement of the amidrazone fragments. In alkaline solutions, they are unstable and decompose to form triarylphosphine oxides. In contrast to ordinary amidrazones, their phosphorus-containing derivatives do not tend to form complexes with transition metals. Nauka/Interperiodica 2006.

Full text of DOI:10.1134/S107036320608007X

ISSN 1070-3632, Russian Journal of General Chemistry, 2006, Vol. 76, No. 8, pp. 1219 1225.
Pleiades Publishing, Inc., 2006.
Original Russian Text L.D. Popov, I.N. Shcherbakov, Yu.N. Tkachenko, S.A. Borodkin, V.A. Kogan, 2006, published in Zhurnal Obshchei Khimii, 2006,
Vol. 76, No. 8, pp. 1269 1275.
Synthesis, Structure, and Properties
of Phosphorus-Containing Bis(amidrazones)
L. D. Popov, I. N. Shcherbakov, Yu. N. Tkachenko,
S. A. Borodkin, and V. A. Kogan
Rostov State University, ul. Zorge 7, Rostov-on-Don, 344090 Russia
e-mail: saborod@list.ru
Received March 24, 2006
Abstract Previously unknown ethenylphosphonic derivatives of bis(amidrazones) were prepared. Accord-
ing to spectroscopic data and quantum-chemical calculations, these compounds exist as phosphonium salts of
a symmetrical linear structure with trans arrangement of the amidrazone fragments. In alkaline solutions, they
are unstable and decompose to form triarylphosphine oxides. In contrast to ordinary amidrazones, their phos-
phorus-containing derivatives do not tend to form complexes with transition metals.
DOI: 10.1134/S107036320608007X
Amidrazones form a class of organic compounds
whose structure and composition are represented by
the formulas R C(NH2)=N NH2 or R C(NH2)=N
NH R . Amidrazones with various R and R substi-
tuents have been described in the literature [1, 2], but
there are no data on phosphorus-containing amidra-
zones. Due to the presence of several donor centers
and acidic protons in the NH2 groups, amidrazones are
good complexants, in particular, for transition metal
ions [3 7]. Amidrazones and amidrazone complexes
exhibit high biological activity [8 10]. It seemed
interesting to introduce a phosphorus-containing
group into the amidrazone molecule and to reveal its
effect on the amidrazone structure and properties,
including complexation. For this purpose we syn-
thesized amidrazones IIIa and IIIb.
Ph
Ph
Cl
P+
O
H
CH2
C
N
NH2
N
H2N
2
X
NH2
H2N
Ia, Ib
II
Cl
CH CH
X
+
P
NH2
N
HN
N
Ph
P+
Ph
Ph
Ph
NH
H2N
HC
CH
Cl
X
IIIa, IIIb
X = H (a), OCH3 (b).
1
The H NMR spectra of IIIa and IIIb in DMSO-d6
(25 C) contain signals of aromatic ring protons at
7.20 7.86 ppm; the spectrum of IIIb also contains a
singlet of OCH3 protons at 3.66 ppm. The signals of
the NH and NH2 protons appear as two broad singlets
at 10.9 11.4 (2H) and 6.9 7.0 ppm (4H); the signals
decrease on adding D2O to the sample. The CH NH
protons give a two-proton doublet of triplets at
1219

1220
POPOV et al.
Table 1. Electronic absorption spectra of compounds IIIa
and IIIb
arrangement of ethylene protons in the Ar3P+CH=
CHNN fragment [11, 12].
1
Thus, the H NMR data show that at room tem-
Comp.
no.
Medium
Neutral
, nm
log
perature compounds IIIa and IIIb have a symmetrical
linear structure with amidrazone fragments in the
trans position.
IIIa
263 sh
269
276
348
267
385
269
355
268 sh
275 sh
293
340
285
8640
9510
9510
28100
12900
10150
13700
13820
6520
3.94
3.98
3.98
4.45
4.11
4.01
4.14
4.14
3.81
3.91
4.03
4.38
4.05
4.35
4.14
The UV spectrum of IIIa (in methanol) contains a
shoulder at
bands of
263 nm (log
3.94), two strong
max* transition (E bands),
276 nm (both with log
269 and
max
max
+ KOH
+ HCl
Neutral
= 3.98), and one band of
348 nm (log
max
* transition (K band),
4.45). On acidification (HCl) ofmaaxsolution of IIIa,miatsx
UV spectrum changes insignificantly: a 7-nm batho-
chromic shift of the long-wave band, accompanied by
a hypochromic effect ( max decreses by 14000 units),
is observed. Similar pattern is observed with IIIb
(Table 1), suggesting similarity of the structures of
both phosphonium salts.
IIIb
8180
10760
24240
11330
22500
13790
+ KOH
+ HCl
390
276
Insofar as molecules of IIIa and IIIb contain
several donor centers and functional groups connected
by a system of multiple bonds, they can exist as
several relatively stable tautomers. The tautomerism
within one amidrazone fragment can be represented as
follows (Nam is amide nitrogen, Nh1 and Nh2 are the
nitrogen atoms of hydrazone fragment):
6.4 ppm (JCHNH = 4, JCHCH = JCHP = 14 Hz), and
CHP protons, a two-proton doublet of doublets at 5.7
6.0 ppm (JCHP = 16.5, JCHCH = 14 Hz, exchanges with
D2O). The P H coupling constants suggest the trans
H2Nam
+
Nh2 Nh1
H2Nam
H2Nam
H
H
Nh2 Nh1
Nh2 Nh1
H
H
A
B
C
Table 2. Caculated [B3LYP, 6-31G(d,p)] total energies
Etot and energies relative to the most stable tautomer Erel
for various isomeric forms of IV
To assess the relative stability of alternative
molecular structures of IIIa and IIIb, we performed a
quantum-chemical calculation of various structures of
molecular dication IV. To reduce the computing time,
the triphenylphosphonium fragments in III were re-
placed by trimethylphosphonium fragments.
Comp.
no.
Erel,
kcal mol
Tautomer
Etot, au
1
IVa
IVb
IVc
IVd
IVe
IVf
IVg
A
A
A
B
C
1484.897325
1484.897741
1484.874523
1484.867412
1484.846792
1484.856461
1484.878314
0.0
0.3
CH=CH
+
14.6
19.0
32.0
25.9
12.2
NH2
HN
N
(CH3)3P
H2N N NH +P(CH3)3
HC=CH
C
A, B
The geometries of the optimized structures are
shown in the figures below; their total and relative
energies are listed in Table 2.
Each tautomer can exist in the form of various
conformers differing in the steric repulsion of their
fragments and in the number and strength of intra-
molecular H bonds.
The most preferable are the conformations corre-
sponding to tautomers A (IVa IVc). Among them, the
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SYNTHESIS, STRUCTURE, AND PROPERTIES
1221
2.242
1.367
2.607
1.765
1.361
1.491
1.381
1.299
1.357
2.446
IVa
2.241
1.374
1.488
1.379
1.363
1.297
2.402
1.765
1.353
IVb
2.239
1.400
1.292
1.491
1.377
1.386
1.354
1.303
1.363
2.026
1.351
1.364
1.365
1.766
1.772
IVc
Fig. 1. Geometric structures of isomers IVa IVc.
most stable are structures IVa and IVb with trans
configuration of the bonds relative to the central C C
bond, which is stabilized by four relatively strong H
bonds Nam H Nh1 (2.242
) and Nh2 H Nam
(2.446 ). Conformation IVa is slightly more pre-
1
ferable (by 0.3 kcal mol ) due to additional stabiliza-
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1222
POPOV et al.
1.382
1.509
1.359
1.769
1.360
1.389
1.275
2.526
2.181
IVd
1.770
1.754
1.343
1.478
1.336
1.338
1.372
1.377
IVe
2.237
2.508
1.443
1.365
1.349
1.374
1.330
1.343
1.757
IVf
2.182
2.387
1.273 1.365
1.500
2.488
1.399
1.383
1.299
1.383
1.350
1.358
1.360
1.364
2.263
1.763
1.769
IVg
Fig. 2. Geometric structures of isomers IVd IVg.
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SYNTHESIS, STRUCTURE, AND PROPERTIES
1223
tion by the attracting interaction of the amidine nirtro-
gen atom Nh1 and a proton in the ethylene group (the
Nh2 H Nam H-bond length increases from 2.402 in
Table 3. Calculated [B3LYP/6-31G(d,p)] parameters of
vibrations of IVa in comparison with the experimental
vibration frequencies of IIIa
IVb to 2.446
in IVa, but owing to additional
1
C H Nh1 H bonding an energy gain is achieved). The
central fragment of the molecule is essentially planar;
the amide and Nh2 nitrogen atoms are noticeable
pyramidal.
Frequency, cm
Vibration mode
calculated
experimental
NH2 stretching (as)
NH2 stretching (s)
NH stretching
Ethylene C H
stretching
3528 (2.30)
3418 (1.27)
3394 (1.54)
3090 (0.2)
3380
3250
3185
3060
The cisoid conformer (relative to the central C C
bond) IVc of tautomer of type A is considerably
1
destabilized (by 14.6 kcal mol ) as compared to the
transoid conformers (IVa, IVb). There are only two H
bonds in its structure, and significant repulsion turns
the amidrazone fragments by approximately 30 to
opposite directions.
C=C, C=N stretching 1656 (0.80)
1629 (5.00)
1645
1625
1592
1597 (52.3)
The tautomer of type B (structure IVd) is still less
stable. Here the conjugation chain is the shortest,
because the peripheral fragments of the molecule are
turned by 90 around the single N N bond of the
hydrazone moiety to maintain the best conditions for
hydrogen bonding Nam H Nh2 in addition to
Nh1 H Nam.
NH2 bending
NH bending
1576 (1.20)
1493 (0.40)
1575 sh
1500
1.835
for the other bonds). This fact suggests
easiness of chemical degradation processes and can
be responsible for the observed instability of amidra-
zones IIIa and IIIb in alkaline medium.
The conformations of type C, IVe and IVf, are the
least stable. The nonplanar structure IVf with four
intramolecular H bonds (rotation by 25 around the
central C C bond) is preferable over the almost planar
structure IVe with only two intramolecular H bonds.
Thus, the calculation results and NMR data indi-
cate that structure IVa prevails for the compounds
synthesized.
The IR spectra of the compounds contain the fol-
lowing bands: band in the region of 1440 cm 1 charac-
teristic of a P C bond [13], strong band in the region
Among the possible unsymmetrical tautomers, IVg
is the most stable, due to formation of four different
H bonds. It contains one amidrazone fragment in
tautomeric form A, NH2 C=N NH, and the second
fragment in form B, NH=C NH NH. The effect of H
bonding on the stabilization in this structure is so
strong that this structure is more favorable even than
the cis conformer IVc of the type A tautomer.
1
of 1600 cm [probably due to overlapping (C=C)
and (C=N) bands], and several bands at 3200
1
3500 cm due to NH and NH2 stretching vibrations.
To interpret the IR spectra, we calculated the
frequency of the harmonic vibrations of IVa in the
B3LYP/6-31G(d,p) approximation. The results ob-
tained [an empirical factor of 0.9614 proposed by
A. Scott and L. Radom [14] is taken to correct the fre-
quency of the normal modes calculated in the frame-
work of B3LYP/6-31G(d) approach] are compared in
Table 3 with the experimental spectrum of IIIa.
Deprotonation of dication IV leads to a planar
structure of type V with four practically equivalent H
bonds formed by hydrogen atoms of NH2 groups with
the nitrogen atoms of hydrazine groups. The position
of the long-wave maximum
of V, calculated in
max
the TDDFT approximation, is 338 nm, which is
24 nm higher than that calculated for conformer IVa,
314 nm. Thus, the bathochromic shift of the maxi-
mum of the long-wave absorption band upon alkaliza-
The experimental and calculated parameters are
well consistent, confirming correctness of determina-
tion of the most stable form of IIIa and IIIb.
tion in compounds IIIa (
47 nm) and IIIb
One of our goals was the study of the complexing
ability of bisphosphonium salts IIIa and IIIb. Data
on the complextion of the related amidrazones with
transition metal salts have been published [15 20].
(
50 nm) may be due tmoaxdeprotonation of the
max
parent cation.
A structural feature of V is the preference of the
flagstaff conformation of trimethylphosphonium
fragments relative to the plane of the central part of
the molecule and significant loosening of one of the
P CH3 bonds (elongation to 1.857 , as compared to
Adding a methanolic solution of copper, nickel, or
zinc acetate to a methanolic solution of a phospho-
nium salt III results in a change in the color. How-
ever, we failed to isolate a complex after prolonged
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1224
POPOV et al.
1.835
1.857
2.277
1.483
1.397
1.425
1.302
1.700
1.300
1.370
2.272
V
Fig. 3. Geometric structure of compound V.
refluxing of the reaction solution followed by evapora-
tion. Attempted synthesis of a complex in an alkaline
medium resulted in recovery of the corresponding
triarylphosphine oxide contaminated with a metal salt.
In our opinion, the low complexing ability of IIIa and
IIIb is due to the presence in the ligand molecules of
positive charges which decrease the donor power of
the nitrogen lone pairs. Adding alkali to a solution
of phosphonium salt IIIa or IIIb leads to its decom-
position; therefore, it is impossible to prepare a com-
plex with such a ligand in an alkaline medium. Thus,
addition of the positively charged phosphonium group
to the amidrazone fragment does not promote the
complex formation.
6.43 d.t (2H, H C=C HtransN, JPH 14, JCHCH
14, JCHNH 3.7 Hz), 6.92 br.s (4H, NH2), 7.67
7.86 m (30H, C6H5), 10.93 br.s (2H, NH). Found, %:
C 65.78; H 5.33; N 11.22; P 8.02; Cl 8.92. C42H40
N6P2Cl2. Calculated, %: C 66.23; H 5.29; N 11.03;
P 8.13; Cl 9.31.
(1Z,2Z)-N 1, N 2-Bis[(E)-2-{(2-methoxyphenyl)di-
phenyl}phosphonio]oxamidrazone chloride IIIb.
To a hot solution of 0.002 mol of (formylmethyl)(2-
methoxyphenyl)diphenylphosphonium chloride Ib
(prepared by the same procedure as Ia) in 10 ml of
ethanol, a hot solution of 0.001 mol of dihydrazine II
in 10 ml of ethanol was added, and the mixture was
refluxed for 5 h. Then the mixture was evaporated to
1/3 of the initial volume, and 15 ml of ethyl acetate
was added. The precipitate of IIIb was filtered off,
washed with ethyl acetate, and recrystallized from
methanol ethyl acetate, 1:3. Yield 58%, mp >300 C.
1H NMR spectrum (DMSO-d6), , ppm: 3.66 s (6H,
OCH3), 5.73 d.d (2H, P+HC=, JPH 16.7, JCHCH
14.1 Hz), 6.38 d.t (2H, H C=C HtransN, JPH 14,
JCHCH 14.1, JCHNH 4.3 Hz), 7.01 br.s (4H, NH2),
7.20 7.82 m (28H, Ar), 11.38 br.s (2H, NH). Found,
%: C 64.78; H 5.43; N 9.75; P 7.72; Cl 8.42.
C44H44N6P2P2Cl2. Calculated, %: C 64.31; H 5.40;
N 10.23; P 7.54; Cl 8.63.
EXPERIMENTAL
The IR spectra were recorded on a Unicam-SP1200
1
spectrophotometer from mulls in mineral oil. The H
NMR spectra were taken on a Bruker AM-300 in-
strument with internal TMS. The electronic spectra
were measured on an SF-200 spectrophotometer in the
range 220 500 nm from ethanolic solutions.
Oxamidrazone II. A mixture of 2.6 g of dithio-
oxamide (hydrorubeanic acid), 12 ml of ethanol, and
3 ml of 95% hydrazine hydrate was heated on a water
bath for 30 min. The precipitate was filtered off,
washed with ethanol, and recrystallized from aqueous
methanol. Yield 75%, mp >300 C.
Quantum-chemical calculations. Geometry opti-
mization and calculation of the electronic structure
and vibration spectra of the conformers were per-
formed in the framework of density functional theory
(DFT) with B3LYP hybrid functional [20 22] in the
6-31G(d,p) basis set. All the calculations were per-
formed using PCGAMESS package [23, 24]. Input
data preparation, presentation of structures, and vis-
ualization of the calculation results were made using
ChemCraft program [25]. The optical spectra of
model compounds were calculated in the TDDFT
approximation [26 28].
(1Z,2Z)-N 1, N 2-Bis[(E)-2-triphenylphosphonio]-
oxamidrazone chloride IIIa. To a hot solution of
0.002 mol of (formylmethyl)triphenylphosphonium
chloride Ia [18] in 10 ml of ethanol, a hot solution of
0.001 mol of dihydrazide II [19] in 10 ml of ethanol
was added, and the mixture was refluxed for 5 h. The
precipitate of IIIa was filtered off, washed with etha-
nol, and recrystallized from methanol. Yield 75%,
1
mp >300 C. H NMR spectrum (DMSO-d6), , ppm:
5.98 d.d (2H, P+HC=, JPH 16.4, JCHCH 14 Hz),
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SYNTHESIS, STRUCTURE, AND PROPERTIES
1225
All the considered structures correspond to minima
on the potential energy surface (no imaginary vibra-
tion frequencies).
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Acad. Republicii Socialiste Romania, 1965.
ACKNOWLEDGMENTS
14. Scott, A.P. and Radom, L., J. Phys. Chem., 1996,
The authors are grateful to G. Zhurko for the li-
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