Oxidative dehydrogenation of N-(2-hydroxy-3,5-R1,R 2-benzyl)-4-aminoantipyrines in the complexation reaction

Article abstract of DOI:10.1134/S1070328412010071

Reactions of N-(2-hydroxy-3,5-R¹,R²-benzyl)-4- aminoantipyrines with copper acetate in ethanol gave complexes with Schiff bases (SBs) rather than the expected complexes with reduced SBs; i.e., the starting ligands undergo oxidative d

Full text of DOI:10.1134/S1070328412010071

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2012, Vol. 38, No. 2, pp. 126–133. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.A. Medzhidov, P.A. Fatullaeva, S.M. Peng, R.G. Ismaiylov, G.H. Lee, S.R. Garaeva, 2012, published in Koordinatsionnaya Khimiya, 2012, Vol. 38,
No. 2, pp. 132–140.
Oxidative Dehydrogenation of Nꢀ(2ꢀHydroxyꢀ3,5ꢀR1,R2ꢀBenzyl)ꢀ4ꢀ
Aminoantipyrines in the Complexation Reaction
,
A. A. Medzhidova *, P. A. Fatullaevaa, S. M. Pengb, R. G. Ismaiylova,
G. H. Leeb, and S. R. Garaevaa
a Nagiev Institute of Chemical Problems, National Academy of Sciences of Azerbaijan, Baku, Azerbaijan
*eꢀmail: ajdarmedjidov@gmail.com
b Taiwan National University, Taiwan
Received December 20, 2010
Abstract—Reactions of Nꢀ(2ꢀhydroxyꢀ3,5ꢀR1,R2ꢀbenzyl)ꢀ4ꢀaminoantipyrines with copper acetate in ethaꢀ
nol gave complexes with Schiff bases (SBs) rather than the expected complexes with reduced SBs; i.e., the
starting ligands undergo oxidative dehydrogenation during the complexation reaction. The corresponding
complexes with reduced SBs were obtained from sodium salts of the ligands and cupric sulfate in aqueous
solutions. Kinetic measurements showed that oxidative dehydrogenation occurs in the heteroleptic comꢀ
plexes Cu(Li)(CH3COO)(X) (LiH are derivatives of Nꢀ(2ꢀhydroxyꢀ3,5ꢀR1,R2ꢀbenzyl)ꢀ4ꢀaminoantipyrines;
i
= 6–10; X = H2O, CH3OH, CH3CH2OH) but does not occur in the complexes CH3OH, CH3CH2OH. The
absence of oxidative dehydrogenation of the ligands in Cu(Li)2
H2O can be explained by the octahedral enviꢀ
⋅
ronment of the Cu2+ ion and, accordingly, the absence of the coordination site for molecular oxygen. The
molecular structures of two Cu(II) complexes with SBs were determined by Xꢀray diffraction.
DOI: 10.1134/S1070328412010071
4ꢀAminoantipyrine derivatives (in particular,
Schiff bases (SBs)) and their metal complexes exhibit
antimicrobial [1], fungicidal [2], analgesic, and antiꢀ
inflammatory properties [3] and catalytic activity [4].
Complexes with various SBs (derived from 4ꢀamiꢀ
noantipyrine, 2ꢀhydroxyarenecarbaldehydes, furanꢀ
2ꢀcarbaldehyde, thiopheneꢀ2ꢀcarbaldehyde, pyrroleꢀ
2ꢀcarbaldehyde, etc.) have been obtained and examꢀ
In this study, we found that the synthesis of Cu(II)
complexes with Nꢀ(2ꢀhydroxyꢀ3,5ꢀR1,R2ꢀbenzyl)ꢀ4ꢀ
aminoantipyrines (L6H–L10H) in ethanol is accomꢀ
panied by their oxidative dehydrogenation leading to
Cu(II) complexes with the ligands L1H–L5H. Two of
these complexes were examined by Xꢀray diffraction.
Copper(II) complexes with Nꢀ(2ꢀhydroxybenzyl)ꢀ
ined to date. The results obtained in the synthesis of 4ꢀaminoantipyrine (L6H) and Nꢀ(2ꢀhydroxyꢀ5ꢀbroꢀ
mobenzyl)ꢀ4ꢀaminoantipyrine (L7H) were obtained
by reactions of copper salts with sodium salts of these
ligands in aqueous solutions.
metal complexes with 4ꢀaminoantipyrine derivatives
and the study of their structures and properties have
been reviewed in [5]. However, the preparation of
metal complexes with Nꢀ(2ꢀhydroxybenzyl)ꢀ4ꢀamiꢀ
noantipyrines, which can be regarded as reduced anaꢀ
logs to the corresponding SBs, has not been docuꢀ
mented.
We also performed kinetic measurements of the
oxidative dehydrogenation of L6H in ethanol in the
presence of Cu(II) acetate.
R1
R1
H3C
H3C
N CH
HO
H3C
H3C
NH CH2
HO
R2
R2
N
N
N
O
N
O
Ph
Ph
L1H: R1 = R2 = H;
L6H: R1 = R2 = H;
L2H: R1 = Br, R2 = H;
L7H: R1 = Br, R2 = H;
L3H: R1 = OCH3, R2 = H;
L4H: R1 = tetrꢀC4H9, R2 = H;
L5H: R1 = R2 = tetrꢀC4H9;
L8H: R1 = OCH3, R2 = H;
L9H: R1= tetrꢀC4H9, R2 = H;
L10H: R1= R2 = tertꢀC4H9.
126

OXIDATIVE DEHYDROGENATION
127
Table 1. Crystallographic parameters and the data collection statistics for structures
I
and II
Value
Parameter
I
II
M
852.51
982.73
Crystal system
Space group
Triclinic
Monoclinic
P
21/c
P
1
a
b
, Å
, Å
9.9663(4)
15.11376)
15.5579(7)
82.180(1)
73.066(1)
76.303(1)
2172.40(16); 2
1.303
11.7055(7)
14.9925(10)
31.564(2)
90
90.347(1)
90
c
α
, Å
, deg
, deg
, deg
, Å3;
β
γ
V
Z
5539.3(6); 4
1.178
ρcalcd, g/cm3
Molar absorption coefficient
0.000558
902
0.000447
2110
F
(000)
Crystal dimensions, mm
scan range, deg
0.38
×
0.33
×
0.27
0.50
×
0.25 0.25
×
θ
1.37–27.50
ω
1.29–25.00
ω
Scan mode
Number of measured reflections
Number of independent reflections
28879
28953
Rint = 0.0496)
9960 (
R
int = 0.0269)
9747 (
R
R
factor (
factor (for all reflections)
I
> 2
σ
(
I
))
R
R
1 = 0.0482, Rw2 = 0.1363
1 = 0.0598, Rw2 = 0.1469
1.052
R1 = 0.0997, Rw2 = 0.2597
R
1 = 0.1203, Rw2 = 0.2729
1.171
GOOF
Residual electron density Δρmax
/
Δρmin
,
e
Å3
0.456/–0.889
0.750/–0.693
EXPERIMENTAL
Atomic coordinates and other structural parameꢀ
ters for complexes and II have been deposited with
the Cambridge Crystallographic Data Collection (nos.
776110 and 776111, respectively; deposit@ccdc.cam.
ac.uk or http://www.ccdc.cam.ac.uk/data_request/
cif).
The Schiff bases L1H and L2H were prepared as
described in [8]. The ligands L3H–L5H were prepared
according to the same procedure: by mixing solutions
containing equimolar amounts of an aromatic aldeꢀ
hyde and 4ꢀaminoantipyrine.
I
IR spectra were recorded on an Mꢀ80 spectrometer
in the 400–4000 cm–1 range (KBr pellets or Nujol).
Electronic absorption spectra were recorded on
Specord Mꢀ40 and UVꢀVIS 240 spectrophotometer.
1H NMR spectra were recorded on Bruker radio specꢀ
trometer (400 MHz) in DMSOꢀd6. Mass spectra were
measured on a JMS 700 HF mass spectrometer.
The oxidative dehydrogenation rate was deterꢀ
mined by measuring the optical densities of solutions
at 415 nm. The concentration of the reaction product
Cu(L1)(CH3COO) was found from a calibrating curve
of the optical density plotted versus the concentration
of the heteroleptic complex. Calibrating solutions of
the heteroleptic complex were prepared by mixing
L3H. The yield was 82%,
1H NMR (
, ppm): 2.40 (s, 3H, C–CH3), 3.20 (s,
3H, OCH3), 6.86–6.82 (t, 1H, Ar phenyl, = 8.0 Hz),
7.05–7.02 (m, 2H, Ar phenyl), 7.40–7.36 (m, 3H, Ar
phenyl), 7.55–7.51 (t, 2H, Ar phenyl, = 7.8 Hz),
9.67 (s, 1H, CH=N), 13.01 (s, 1H, OH).
IR (KBr,
cm–1): 3450–2600 br.w (OH), 1656
(C=O), 1592 (C=N).
MS (
, %)): 338 (100) [M]+.
Tm = 200
°
C.
δ
J
solutions of Cu(L1)2 and Cu(CH3COO)2
⋅
H2O
.
J
4
An Xꢀray diffraction study of the complexes Cu(L )
⋅
2
and Cu(L5)2
⋅
ЕtOH
⋅
H2O (II) was
ν
,
ЕtOH
performed on a Bruker Smart Apex CCD diffractomeꢀ
ter (Мо radiation, = 0.71073 Å) at 295 K. Strucꢀ
and II were solved by the direct methods with
⋅
H2O (
I)
K
λ
m/e (I
α
tures
I
the SHELXSꢀ97 program [6] and refined by the fullꢀ
matrix leastꢀsquares method on F2 [7]. Crystalloꢀ
graphic parameters and the data collection statistics
for structures
Selected bond lengths and bond angles are given in
Table 2.
For C19H19N3O3
anal. calcd, %:
Found, %:
C, 67.64;
C, 67.60;
H, 5.68;
H, 5.57;
N, 12.64.
N, 12.43.
I and II are summarized in Table 1.
L4H. The yield was 78%,
Tm = 180 C.
°
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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2012

128
MEDZHIDOV et al.
Synthesis of L6Н–L10Н The ligand L1H–L5H
.
Table 2. Selected bond lengths and bond angles in strucꢀ
tures and II
I
(0.01 mol) was dissolved in ethanol (20 mL). Then
NaBH4 (~0.015 mol) was added in portions with vigꢀ
orous stirring until the yellow color of the solution disꢀ
appeared completely. The reaction mixture was
diluted with water (100 mL) and acidified with 1 N
HCl to pH 7. The white crystals that formed were isoꢀ
lated, dried, and recrystallized from an appropriate
solvent.
Bond
d
, Å
Bond
d, Å
I
II
Cu–O(3)
Cu–O(1)
Cu–N(4)
Cu–N(1)
1.8819(15) Cu–O(1)
1.8834(15) Cu–O(3)
1.9525(17) Cu–N(4)
1.9560(18) Cu–N(1)
1.888(4)
1.889(3)
1.952(4)
1.955(4)
L6H. The yield was 84%,
T
m = 123
°
C.
IR (
(C=O).
MS (
ν
, cm–1): 3340 (OH), 3360 (NH), 1630
m/e (I
, %)): 309 (100) [M]+.
Angle
ω
, deg
Angle
ω
, deg
For C18H19N3O2
anal. calcd, %:
Found, %:
I
II
O(1)CuO(3)
O(1)CuN(4) 147.2(2)
C, 69.68;
C, 69.92;
H, 6.19;
H, 6.30;
N, 10.58.
N, 13.62.
O(3)CuO(1)
O(3)CuN(4)
O(1)CuN(4)
O(3)CuN(1)
O(1)CuN(1)
N(4)CuN(1)
C(1)O(1)Cu
90.28(7)
93.54(7)
150.72(8)
148.43(8)
93.85(7)
97.85(7)
90.00(17)
L7H. The yield was 80%,
Tm = 163 C.
°
O(3)CuN(4)
O(1)CuN(1)
93.81(16)
94.09(17)
IR (
(C=O).
MS (
ν
, cm–1): 3480 (OH), 3184 (NH), 1640
m/e (I
, %)): 389 (100) [M]+.
O(3)CuN(1) 146.6(2)
N(4)CuN(1) 100.26(17)
For C18H18N3O2Br
anal. calcd, %:
Found, %:
C, 55.61;
C, 55.75;
H, 4.68;
H, 4.57;
N, 10.82.
N, 10.46.
128.91(14) C(1)O(1)Cu 128.9(4)
C(23)O(3)Cu 126.45(14) C(27)O(3)Cu 129.1(3)
L8H. The yield was 66%,
IR (KBr, cm–1): 3450 (OH), 3240 (NH), 1640
(C=O).
MS (
T
m = 155
°
C.
1H NMR (
3H, C–CH3), 3.21 (s, 3H, N–CH3), 6.86–6.82 (t,
1H, Ar phenyl, = 7.6 Hz), 7.28–7.24 (t, 2H, Ar pheꢀ
nyl, = 7.4 Hz), 7.40–7.36 (t, 3H, Ar phenyl, = 8.6 Hz),
7.55–7.51 (t, 2H, Ar phenyl, = 7.6 Hz), 9.67 (s, 1H,
CH=N), 13.92 (s, 1H, OH).
IR (KBr,
cm–1): 3480–2600 br.w (OH), 1664
(C=O), 1600 (C=N).
MS (
, %)): 364 (100) [M]+.
δ
, ppm): 1.41 (s, 9H, tertꢀBu), 2.42 (s,
m/e (I
, %)): 339 (100) [M]+.
J
J
J
For C19H21N3O3
anal. calcd, %:
Found, %:
J
C, 67.24;
C, 67.32;
H, 6.24;
H, 6.12;
N, 12.38.
N, 12.45.
ν
,
L9H. The yield was 82%,
T
m = 156
°
C.
m/e (I
IR (
(C=O).
MS (
ν
, cm–1): 3480 (OH), 3210 (NH), 1630
For C22H25N3O3
m/e (I
, %)): 365 (100) [M]+.
anal. calcd, %: C, 72.70;
H, 6.93;
H, 6.90;
N, 11.56.
N, 11.44.
Found, %:
C, 72.62;
For C22H27N3O2
anal. calcd, %:
Found, %:
C, 72.05;
C, 72.22;
H, 7.45;
H, 4.52;
N, 11.58.
N, 11.42.
L5H. The yield was 85%,
1H NMR (
T
m = 205 C.
°
δ
, ppm): 1.27 (s, 9H, tertꢀBu), 1.41 (s,
9H, tertꢀBu), 2.41 (s, 3H, C–CH3), 3.21 (s, 3H,
CH3), 7.40–7.21 (m, 5H, Ar phenyl), 7.55–7.51
(t, 2H, Ar phenyl, = 8.0 Hz), 9.68 (s, 1H, CH=N),
13.70 (s, 1H, OH).
IR (KBr,
, cm–1): 3450–2700 br.w (OH), 1660
(C=O), 1595 (C=N).
MS (
, %)): 420 (100) [M]+.
L10H. The yield was 83%,
IR (
, cm–1): 3500–2900 (OH), 3320 (NH), 1648
Tm = 170
°
C.
N
⎯
ν
J
(C=O).
MS (
m/e (I
, %)): 421 (100) [M]+.
ν
For C26H35N3O2
anal. calcd, %:
Found, %:
m/e (I
C, 74.04;
C, 74.35;
H, 8.37;
H, 8.51;
N, 9.97.
N, 9.83.
For C26H33N3O2
anal. calcd, %:
Found, %:
C, 74.43;
C, 74.33;
H, 7.93;
H, 7.76;
N, 10.02.
N, 10.27.
Synthesis of complex I. A solution of the ligand L4H
(0.01 mol) and Сu(CH3COO)2 H2O (0.01 mol) in
⋅
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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2012

OXIDATIVE DEHYDROGENATION
129
ethanol was stirred with a magnetic stirring bar at 50–
60 C for 20 min, concentrated to 1/3 of its initial volꢀ (930), 670, 750 (20).
ume, and left for 24 h. The resulting dark green crystals
of complex were suitable for Xꢀray diffraction. The
yield was 57%, m = 310 C.
IR (
, cm–1): 1645 (C=O), 1580 (C=N).
UVꢀVIS (λmax, nm (
, dm3 mol–1 cm–1)): 374
UVꢀVIS (λmax, nm (
ε
, dm3 mol–1 cm–1)): 440
°
I
For C36H36Cu N6O6Br2
T
°
anal. calcd, %:
Found, %:
C, 50.51
;
H, 4.24
;
;
N, 9.80.
N, 9.65.
ν
C, 50.80
;
H, 4.32
ε
(6700), 425 (4800), 520 sh, 730 (45).
RESULTS AND DISCUSSION
Reactions of L6H–L10H with Cu(II) acetate in
methanol–ethanol (1 : 1) were accompanied by oxidaꢀ
tive dehydrogenation of the ligands, giving the comꢀ
plexes Cu(L6)2–Cu(L10)2 rather than the expected
complexes Cu(L1)2–Cu(L5)2. The overall oxidation of
the ligand L6H can be represented by the following
scheme:
For C46H56N6O6
anal. calcd, %:
Found, %:
C, 64.81;
C, 64.65;
H, 6.62;
H, 6.73;
N, 9.86.
N, 9.46.
Complex II was obtained from L5H as described
above for the synthesis of complex . The yield was
81%, m = 335 C.
IR (
, cm–1): 1640 (C=O), 1600 (C=N).
UVꢀVIS (λmax, nm (
, dm3 mol–1 cm–1)): 378
I
2L6H + Cu CH COO + O → Cu L6
T
°
(
)
(
)
3
2
2
2
ν
+ 2CH3COOH + H2O2.
ε
The complexes Cu(L1)2–Cu(L5)2 can also be
obtained immediately from copper acetate and L1H–
L5H in methanol–ethanol mixtures.
(7200), 440 (5300), 550 sh, 750 (60).
For C52H74Cu N6O7
The electronic absorption spectra of the complexes
Cu(L1)2–Cu(L5)2 show bands at 26800–27300 and
23400–24400 cm–1 (ligand–metal charge transfer
bands) and a lowꢀintensity wide band at 19000–
anal. calcd, %:
Found, %:
C, 69.09;
C, 69.15;
H, 7.57;
H, 7.42;
N, 9.85.
N, 9.80.
20000 cm–1
(
d–d transition).
The IR spectra of these complexes contain intense
bands at 1640–1650 (
(C=O)) and ~1580–1600 cm–1
(С=N)).
The sodium salts of the ligands L6H and L7H react
with copper(II) sulfate or copper(II) chloride to give
Reactions of Nꢀ(2ꢀhydroxyꢀ3,5ꢀR1,R2ꢀbenzyl)ꢀ4ꢀ
aminoantipyrines (L6H–L10H) with copper acetate in
ethanol gave complexes with SBs L1H–L5H rather
than the expected complexes with reduced SBs. This
transformation is described below with L9H as an
example.
ν
(
ν
the complexes Cu(Li)2
Н2О (i = 6 and 7). Copper(II)
⋅
A solution of Cu(CH3COO)2
⋅
H2O (0.199 g,
C to a stirred
complexes with L8H–L10H were not obtained because
of the poor solubilities of these ligands and the high
rate of their oxidative dehydrogenation.
0.001 mol) in methanol was added at 50
°
solution of L9H (0.706 g, 0.002 mol) in ethanol
(20 mL).The resulting solution was concentrated to
The IR spectra of the complexes Cu(L6)2
⋅
Н2О and
1/3 of its initial volume to produce dark crystals, Tm
310 C.
The IR and UVꢀVIS spectra of the crystals formed
are fully identical with those of the complex Cu(L4)2
obtained from L4H
=
Cu(L7)2
⋅
Н2О show absorption bands at 3250 and
°
3240 cm–1, respectively (NH). In the IR spectra of the
free ligands, these bands appear at 3336 and 3200 cm–1,
respectively. This indicates the coordination of the amino
group to the metal ion. The band at ~1640 cm–1 due to
the carbonyl group at the antipyrine ring is shifted to
the lower frequencies (1630 cm–1) upon the complexꢀ
ation.
.
Synthesis of the complex Cu(L6)2
⋅ Н2О. The ligand
L6Н (0.307 g, 0.001 mol) and NaOH (0.040 g,
0.001 mol) were dissolved in water (100 mL). Then a
solution of CuSO4 5H2O (0.125 mg, 0.5 mmol) in
⋅
The visible range of the UVꢀVIS spectrum of
water (50 mL) was added. The light green crystals that
formed were isolated and dried in vacuo. The yield was
91%, m = 201 C.
Cu(L6)2
⋅
2Н2О exhibit a wide absorption band at
420 nm, which can be attributed to the ligand–metal
charge transfer, and two lowꢀintensity bands at 575
and 680 nm due to the d–d transitions.
T
°
UVꢀVIS (λmax, nm (
, dm3 mol–1 cm–1)): 420
ε
For Cu(L7)2
Н2О, similar absorption bands appear
⋅
(1300), 560, 720 (20).
at 425, 560, and 675 nm.
For C36H38Cu N6O5
An Xꢀray diffraction study of similar nickel comꢀ
plexes Ni(L6)2
⋅
H2O (III
)
and Ni(L7)2
H2O (IV)
⋅
anal. calcd, %:
Found, %:
C, 61.93;
C, 61.70;
H, 5.48;
H, 5.25;
N, 12.04.
N, 12.15.
1
showed that each Ni atom has a distorted octahedral
environment made up of two N atoms of secondary
Complex Cu(L7)2
described above for the synthesis of the complex
Cu(L6)2
Н2О. The yield was 93%, m = 175 C.
⋅
Н2О was obtained from L7H as
1
The crystallographic studies performed by Samatov and superꢀ
vised by Ibragimov will be published elsewhere.
⋅
T
°
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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2012

130
MEDZHIDOV et al.
As mentioned above, the reduced SBs L6H–L10H
A
in reactions with copper acetate in ethanol undergo
oxidative dehydrogenation leading to the complexes
Cu(L1)–Cu(L5). Neither Co(II) acetate nor Ni(II)
acetate reacts with the ligands L6H–L10H under these
conditions.
1.2
1.0
0.8
0.6
0.4
0.2
0
The complexes М(Li)2 (where LiН – L6H and L7H
)
7
can be obtained from sodium salts of these ligands and
transition metal sulfates or chlorides. These comꢀ
plexes are resistant to oxidative dehydrogenation. For
instance, a solution of Cu(L6)2 in methanol–ethanol
remains unchanged at ambient temperature for several
hours (i.e., the reduced SBs undergo no oxidative
dehydrogenation).
1
6
5
At the same time, when mixing solutions of the
ligand and copper acetate in alcohols, we observed
rapid oxidative dehydrogenation because the elecꢀ
tronic absorption spectrum exhibits a band characterꢀ
istic of the coordinated azomethine group (Fig. 1).
Note that no oxidative dehydrogenation occurs in the
absence of oxygen.
4
3
2
The decomposition of the complex Cu(L6)2 is also
accompanied by oxidative dehydrogenation. For
instance, when a small amount of acetic acid is added
to a solution of Cu(L6)2 in ethanol, the wide absorpꢀ
tion band at 420 nm disappears because of the decomꢀ
position of the starting complex. Instead, the spectrum
contains a relatively narrow peak at 415 nm due to the
heteroleptic complex with the dehydrogenated ligand,
Cu(L1)(CH3COO). This peak becomes more intense
with time (Fig. 2).
300
400
500
λ
, nm
All these data suggest that the oxidative dehydroꢀ
genation of the coordinated ligand occurs in the hetꢀ
eroleptic complex Cu(L6)(CH3COO), in which the
metal : ligand ratio is 1 : 1. This process can be repreꢀ
sented by the scheme:
Fig. 1. Electronic absorption spectra of the reaction mixꢀ
6
–5
ture of L H and Cu(CH COO)
⋅
H O
;
6
= 7.5
×
10
,
cL H
3
2
2
–3
= 5
×
10 mol/L. Spectra 1–8 are
cCu CH COO
2⋅H2O
(
)
3
recorded at time intervals of 3 min.
NH
NH
H2C
R
H2C
R
amino groups, two phenolate Ophen atoms, and two
Oant atoms of the antipyrine fragment. The Ni–Oant
bonds (2.167 Å) are substantially longer than the Ni–
Ophen and Ni–NH bonds (2.036 and 2.120 Å, respecꢀ
tively). Since the diffraction patterns of complexes III
+ O2
Cu
Cu
O
O
O
O2
X
X
O
C CH3
C CH3
O
O
and IV and Со(L7)2
of Сu(L6)2 H2O and Сu(L7)2
⋅
H2O are fully identical with those
NH
Cu
CH
O
R
X
⋅
⋅
H2O, these complexes
+ H2O2
are isostructural. Thus, Cu(II) complexes with
reduced SBs are sixꢀcoordinate entities
k
O
C CH3
CH2 NH
CH3
O
N CH3
O
O
N
CH3
R =
X = H2O, CH3OH, C2H5OH
Ph
M
Ph
N
N
CH3
O
N
O
O
CH3
CH3
N
Ph
NH CH2
Our kinetic studies of the reaction of L6Н with copꢀ
per acetate in methanol–ethanol (1 : 1) showed that
as distinct from fourꢀcoordinate complexes with unreꢀ
duced analogs.
the reaction rate at [Cu(CH3COO)2 ]
H O] [L6H
ӷ
2
⋅
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
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2012

OXIDATIVE DEHYDROGENATION
131
A
ln(A∞ – A)
0
1.2
1.0
0.8
0.6
0.4
0.2
0
–0.2
7
1
–0.4
–0.6
–0.8
–1.0
6
5
4
3
2
10
20
30
40
, min
τ
Fig. 3. Time dependence of ln(A –A
)
for a mixture of
–5
∞
6
L H and Cu(CH COO)
⋅
H O
;
6
= 7.5
×
10
,
cL H
3
2
–3
2
⋅H O = 5 × 10 mol/L.
cCu CH COO
2
(
)
3
2
300
400
500
λ
, nm
6
Fig. 2. Electronic absorption spectra of (
1)
Cu(L )
⋅ H O
2
2CuL1CH COO ꢀ Cu L1 + Cu CH COO
. (4)
(
)
and (2–6) its mixture with acetic acid in ethanol;
(
)
3
3
2
2
–4
⋅H O = 10 mol/L;
= 0.1 mol/L. Specꢀ
cCu L6
c
CH3COOH
(
)
2
trum 22is recorded immediately upon the addition of acetic
When the ligand concentration is low and the conꢀ
centration of copper acetate is high, equilibrium (2)
can be ignored. Experimental data suggest that the
acid. Spectra 3–6 are recorded at time intervals of ~6 min.
obeys the firstꢀorder equation in the concentration of ligand L6H is found in the heteroleptic complex only
L6H (Fig. 3). At equal concentrations of the reaction
components or for [Cu(CH3COO)2
H2O] < [L6H],
(i.e.,
k
1 ӷ
k–1).
Under the assumption that the reaction of
CuL6CH3COO with oxygen is the rateꢀlimiting step of
the overall process, the reaction rate for
⋅
the oxidative dehydrogenation is strongly inhibited
and stopped by the formation of the inactive complex
Cu(L6)2.
[
Cu(CH3COO)2
⋅
H O] [L6H] and
k
1 ӷ
k
–1
can be
ӷ
2
written as
The overall kinetic scheme of the reaction includꢀ
ing complexation equilibria (1), (2), and (4) and oxiꢀ
dative dehydrogenation (3) can be written as follows:
w = k[CuL6 CH3COO
⋅ H2O][O2] = k
[L6H][O2]
or w = k = k[O2].
'
[L6H], where
k'
Thus, we obtain the pseudofirstꢀorder equation of the
reaction rate in the concentration of the starting
ligand, which is confirmed experimentally.
Cu CH COO ⋅H O + L6H
(
)
3
6
2
2
(1)
(2)
k1
⎯⎯⎯→
←⎯⎯⎯
k−1
Cu(L )CH COO +CH COOH,
3
3
The pseudofirstꢀorder reaction rate constant deterꢀ
mined from a plot of logw vs. logc (Fig. 4) is k' = 1.1 ≈
10–1 s–1. Note that the pseudofirst order in the ligand
6
6
CuLCH3COO+LH
concentration under the aforementioned stipulations
k2
←⎯⎯⎯
H O] [L6H] and
k
1 ӷ
k–1) holds
6
([Cu(CH3COO)2
⋅
ӷ
⎯⎯⎯→
2
Cu L +CH COOH,
(
)
3
k−2
2
with Eq. (1) as the rateꢀlimiting step. However, the
substantial increase in the oxidative dehydrogenation
6
1
k
(3) rate of L8H–L10H, which are stronger electron donors
CuL CH3COO + O2 ⎯⎯→CuL CH3COO + H2O2,
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 2
2012

132
MEDZHIDOV et al.
droxysalicylaldiminate. Note that a similar complex with
a dichlorinated ligand has a trans structure [9].
log
1.2
w + 6
The central Cu2+ ion has a square planar environꢀ
ment with a tetrahedral distortion. The environment
consists of two O atoms and two N atoms of two
ligands L4 (Fig. 5). The average distances Cu–N and
Cu–O (1.954(2) and 1.882(2) Å, respectively) are
close to the values found for similar complexes [9].
0.8
0.4
The crystal structure of Cu(L5)2 in complex II is
shown in Fig. 6. The coordination environment of the
copper atom is also a cisꢀsquare with a tetrahedral disꢀ
tortion, which is made up of two azomethine N atoms
and two nonprotonated phenolate O atoms of two
ligands L5. The average distances Cu–O and Cu–N
(1.888(4) and 1.955(4) Å, respectively) are close to
those in Cu(L4)2
.
Thus, oxidative dehydrogenation in Cu(L6)2 is preꢀ
1.2
1.6
2.0 log
c + 5
cluded by the absence of a coordination site for atmoꢀ
6
Fig. 4. Plot of log
w vs. logc of the ligand L H for its oxidaꢀ
tive dehydrogenation.
spheric oxygen since the Cu2+ ion in Cu(L6)2
⋅ H2O is
hexacoordinated. However, this reaction readily
occurs in heteroleptic complexes in which the C.N. of
the metal ion is lower.
It should also be noted that the oxidative dehydroꢀ
genation rates of coordinated reduced Schiff bases
derived from 4ꢀaminoantipyrine are higher than those
of similar coordinated Nꢀsubstituted 2ꢀhydroxybenꢀ
than L6H, suggests that the rateꢀlimiting step has a
redox character, thus corresponding to Eq. (2).
According to Xꢀray diffraction data, the ligands L4
in the crystal structure I are cis to each other, much the
same as in copper(II) Nꢀ(4ꢀaminoantipyrine)ꢀ3,6ꢀdihyꢀ zylamines [10, 11]. This is probably due to the presꢀ
C(4)
C(5)
C(3)
C(19)
C(16)
C(6)
C(15)
O(2)
C(2)
C(7)
N(1)
N(2)
C(1)
O(1)
C(8)
C(9)
C(14)
C(17)
C(18)
C(11)
C(22)
C(12)
C(21)
C(20)
C(41)
C(10)
N(6)
N(3)
C(44)
C(13)
C(37)
C(38)
C(32)
Cu
C(43)
O(4)
O(3)
C(39)
N(4)
C(40)
C(36)
N(5)
C(31)
C(29)
C(23)
C(33)
C(30)
C(24)
C(42)
C(28)
C(34)
C(35)
C(25)
C(27)
C(26)
4
Fig. 5. Molecular structure of Cu(L )
.
2
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 2
2012

OXIDATIVE DEHYDROGENATION
133
C(49)
C(48)
C(47)
C(50)
C(30)
C(31)
C(32)
C(41)
C(29)
C(28)
C(43)
C(42)
C(46)
C(40)
O(4)
C(33)
C(34)
C(27)
C(35)
N(4)
C(39)
C(37)
N(6)
C(45)
C(44)
O(3)
O(1)
C(38)
C(18)
N(5)
C(36)
C(52)
C(26)
C(25)
C(51)
C(10)
Cu
N(2)
C(19)
C(20)
C(17)
N(3)
C(11)
C(12)
N(1)
C(1)
C(13)
C(14)
C(9)
C(2)
C(3)
C(8)
C(7)
O(2)
C(6)
C(16)
C(5)
C(4)
C(15)
C(23)
C(21)
C(24)
C(22)
Fig. 6. Molecular structure of Cu(L )
5
.
2
6. Sheldrick, G.M., SHELXSꢀ97. Program for Solution of
Crystal Structures, Göttingen (Germany): Univ. of Götꢀ
tingen, 1997.
ence of the double bond at the secondary amino
group.
7. Sheldrick, G.M., SHELXLꢀ97. Program for Refinement
of Crystal Structures, Göttingen (Germany): Univ. of
Göttingen, 1997.
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RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 38
No. 2
2012