Kinetics of the reaction of arylethanediylidene-bis-dithiocarbazonoate Ni complexes with morpholine in benzene: Substituent and temperature effects

Article abstract of DOI:10.1002/kin.20587

[1-Arylethanediylidene-bis(methyl dithiocarbazonoate) NN′SS′ (-2)]Ni(II) complexes were prepared by condensation of arylglyoxals with methyl dithiocarbazoate to give the corresponding hydrazonoates. The chelation of nickel(II) with these hydrazonoates gave square planar Ni complexes. The k ₃ values for the substitution of -SCH₃ close to the aryl group with morpholine (Mo) in benzene were found to increase steadily (20-35°C) followed by a sudden drop after 35°C. A continuous decrease in k₃ values was observed by further elevation in the temperature. The Arrhenius plot showed a convex curve at the whole temperatures 20-55°C, and negative ΔH^# values for the reactions were obtained at 40-55°C. The Hammett plots at the temperature ranges 20-35° and 40-55°C exhibited good straight lines with ρ values of 1.44-0.73 and 1.18-1.25, respectively. The proposed mechanism is a nucleophilic aromatic substitution-like, in which the rate-determining step is the proton transfer process in the temperature range 20-35°C whereas the mechanism in the range 40-55°C passes through the attack of Mo on the carbon carrying the SCH ₃ group followed by the addition of the second Mo molecule on Ni to form an intermediate, which undergoes elimination of Mo and CH₃SH to give a monosubstitution complex.

Full text of DOI:10.1002/kin.20587

Kinetics of the Reaction of
Arylethanediylidene-bis-
dithiocarbazonoate Ni
Complexes with Morpholine
in Benzene: Substituent
and Temperature Effects
AZIZA K. SHEHATA,1 MAGDA F. FATHALLA,2 HEBA M. A. HEADER,1 EZZAT A. HAMED2
1Chemistry and Physics Department, Faculty of Education, Alexandria University, Alexandria 21526, Egypt
2Chemistry Department, Faculty of Science, Alexandria University, Alexandria 21321, Egypt
Received 24 February 2011; revised 30 May 2011, 9 June 2011; accepted 10 June 2011
DOI 10.1002/kin.20587
Published online 1 September 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: [1-Arylethanediylidene-bis(methyl dithiocarbazonoate) NNꢀSSꢀ (−2)]Ni(II)
complexes were prepared by condensation of arylglyoxals with methyl dithiocarbazoate to
give the corresponding hydrazonoates. The chelation of nickel(II) with these hydrazonoates
gave square planar Ni complexes. The k3 values for the substitution of SCH3 close to the aryl
group with morpholine (Mo) in benzene were found to increase steadily (20–35◦C) followed
by a sudden drop after 35◦C. A continuous decrease in k3 values was observed by further
elevation in the temperature. The Arrhenius plot showed a convex curve at the whole tem-
peratures 20–55◦C, and negative ꢀH# values for the reactions were obtained at 40–55◦C.
The Hammett plots at the temperature ranges 20–35◦ and 40–55◦C exhibited good straight
lines with ρ values of 1.44–0.73 and 1.18–1.25, respectively. The proposed mechanism is a nu-
cleophilic aromatic substitution-like, in which the rate-determining step is the proton transfer
process in the temperature range 20–35◦C whereas the mechanism in the range 40–55◦C passes
through the attack of Mo on the carbon carrying the SCH3 group followed by the addition of the
second Mo molecule on Ni to form an intermediate, which undergoes elimination of Mo and
ꢁ
C
CH3SH to give a monosubstitution complex. 2011 Wiley Periodicals, Inc. Int J Chem Kinet
44: 27–40, 2012
INTRODUCTION
The metal complexes synthesized by chelating of tran-
sition and nontransition metals with dithiocarbazonate
derivatives have received much attention for the
Correspondence to: Magda F. Fathalla; e-mail: mffathalla@
hotmail.com.
2011 Wiley Periodicals, Inc.
c
ꢀ

28
SHEHATA ET AL.
following reasons: First, they provide an interesting
series of compounds, whose properties can be greatly
modified by introducing different organic substituents,
thereby causing a variation in the ultimate donor
properties. Second, the interaction of these donors
with metal ions gave complexes of different geome-
tries and properties [1–6]. Third, these complexes are
known to have some biological activity [7–9]. Fourth,
these types of complexes underwent transmetalation
[10–12], ligand substitution [13,14], displacement of
ligand from a substrate M-L (where L is a ligand) [15],
or displacement of a leaving group from the ligand
complex by various reagents [16]. The reactions of
some α-diketones and α-keto aldehydes with methyl
dithiocarbazoate to give the corresponding mono- and
bishydrazones were also reported. [3,16,17]. The se-
ries of Zn(II), Cd(II), Ni(II), Cu(II), and Pd(II) com-
plexes of these hydrazones was obtained from the
reaction of monohydrazones and bishydrazones with
the corresponding metal(II) acetate or chloride [3,17].
Nickel(II) was found to form many complexes with oc-
tahedral, square planar, and tetrahedral geometries, as
well as a number of five-coordinate compounds [18].
The magnetic moments of Ni complexes are tempera-
ture dependent, and equilibrium occurred between their
dia- and paramagnetic forms [19,20].
brant. The effective magnetic moments were calculated
after a diamagnetic correction for ligand’s component
using Pascal’s constant.
Preparation of Methyl Dithiocarbazoate
This compound was prepared from methylation of am-
monium dithiocarbazoate with methyl iodide [22] or
with dimethyl sulfate [23].
Preparation of Arylglyoxal Monohydrate
1a–1f
General Procedure. Selenium dioxide solid (SeO2;
11.1 g, 0.14 mol) in 50 mL dioxane and 2 mL H2O was
heated at 50–55◦C and stirred until the solid was dis-
solved. Then, the mixture was added to an equivalent
amount of acetophenone or acetophenone containing
4-NO2, 4-Cl, 4-Br, 4-CH3, and 4-OCH3, and the re-
sulting mixture was refluxed with stirring for 48 h. The
solid part of the resulting suspension was separated,
and the solution was concentrated under vacuum. The
residue was extracted by a mixture of ethyl acetate
and water. The organic layer was dried over anhydrous
Na2SO4, concentrated and filtered, and the separated
solid was crystallized from benzene–petroleum ether
[24–27].
The present work characterizes the nickel(II) com-
plexes derived from arylglyoxals and methyl dithiocar-
bazoate, as well as their monosubstitution complexes
obtained by their reactions with morpholine (Mo) in
benzene. In continuation in the field of nucleophilic
substitution reactions [21], the study suggests a plausi-
ble mechanism for the title reaction and discusses the
effects of substituent and temperature.
Phenyl Glyoxal Monohydrate 1a. Yield 65.6%, mp
78–80◦C, UV (DMSO) λ nm (ε, M−1 cm) =
247(12,640); 213 (3810) [24].
4-Methyl Phenyl Glyoxal Monohydrate 1b. Yield
23%, mp 80–82◦C; Anal. Calcd. for C9H10O3: C,
65.06; H, 6.02; Found: C, 65.26; H, 5.91. UV (DMSO)
λ nm (ε M−1 cm) = 259 (6460); 214 (5320). IR (KBr)
1
ν (cm−1) 3404, 3355 (OH); 1685 (C O). H NMR
EXPERIMENTAL
(DMSO-d6), δ (ppm): 7.94–7.92 (d, 2H, H2,6, J =
10 Hz,); 7.27–7.25 (d, 2H, H3,5, J = 10 Hz,); 5.64 (s,
1H, CH); 6.69 (s, br, OH); 12.74 (s, br, OH).
Solution UV spectra and kinetic measurements were
recorded on a Shimadzu 160 A spectrophotometer in
conjunction with a thermo-bath (TB-85) temperature
control ( 0.2). The infrared (IR) spectra were obtained
using a FTIR-8400S Fourier transform infrared spec-
trophotometer (Shimadzu, Japan) using potassium bro-
4-Methoxy Phenyl Glyoxal Monohydrate 1c. Yield
70%; mp 110–112◦C; Anal. Calcd. for C9H10O6: C,
59.34; H, 5.49; Found: C, 59.54; H, 5.20. UV (DMSO)
λ nm (ε M−1 cm) = 283 (15,900); 222 (10,500). IR
1
mide pellets. H NMR spectra were carried out on
1
(KBr) ν (cm−1) 3423 (OH); 1681 (C O). H NMR
a Bruker 500-MHz spectrophotometer. Nickel analy-
ses were carried out in our laboratory by the standard
method, and the results were checked by further mea-
surements using an atomic absorption technique. The
elemental analyses of the reaction products were car-
ried out in the Microanalytical Laboratories at Cairo
National Research Center (Cairo, Egypt). Magnetic
susceptibility measurements were carried out by em-
ploying Gouy’s balance using Hg[Co(SCN)4] as a cali-
(DMSO-d6), δ (ppm) 8.03–8.01 (d, 2H, H2,6, J =
10 Hz,); 6.99–6.97 (d, 2H, H3,5, J = 10 Hz,); 5.96
(d, 1H, CH); 3.43 (s, br, OH); 12.63 (s, br, OH) [25].
4-Chlorophenyl Glyoxal Monohydrate 1d. Yield
64%, mp 90–92◦C; Anal. Calcd. for C8H7O3Cl: C,
51.47; H, 3.75; Found: C, 51.67; H, 3.58.UV (DMSO)
λ nm (ε M−1 cm) = 257 (12,360); 214(7070). IR (KBr)
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETICS OF ARYLETHANEDIYLIDENE-BIS-DITHIOCABAZONOATE NI COMPLEXES WITH MORPHOLINE
29
1
ν (cm−1): 3446, 3392 (OH); 1687 (C O). H NMR
(DMSO-d6), δ (ppm) : 8.06–8.041 (d, 2H, H2,6, J =
8.5 Hz,); 7.55–7.53 (d, 2H, H3,5, J = 8.5 Hz,); 5.90 (d,
1H, CH); 6.92 (s, br, OH); 13.09 (s, br, OH) [25].
IR (KBr) ν (cm−1): 3199, 3116 (NH); 1438 (C S);
1504 (C N). H NMR (DMSO-d6), δ (ppm): 7.12,
8.34 (s, 1H, CH; nonsymmetric); 7.87, 7.83 (d, 2H,
H3,5); 7.62, 7.61; 7.33, 7. 22 (d, 2H, H2,6, nonsym-
metric); 2.54, 2.53; 1.93, 1.92 (s, 3H, S CH3, non-
symmetric); 13.60, 13.52; 12.98, 12.17 (s, 1H, NH,
nonsymmetric);.
1
4-Bromophenyl Glyoxal Monohydrate 1e. Yield
40%, mp160–162◦C; Anal. Calcd. for C8H7O3Br: C,
41.55; H, 3.03; Found: C, 41.23; H, 3.52.UV (DMSO)
λ nm (ε M−1 cm) = 260 (16,020); 214 (8900). IR (KBr)
1-(4-Methoxyphenyl)ethanediylidene-bis(methyl di-
thiocarbazonoate) 2c. Yield 48%, mp 172–174◦C;
Anal. Calcd. for C13H14N4 S4O: C, 42.16; H, 3.78; N,
15.13; S, 34.59, Found: C, 42.47; H, 3.92; N, 15.51; S,
34.88. UV (DMSO) λ nm (ε M1 cm) = 441 (5230); 368
(7380); 306 (7690); 217 (7590). IR (KBr) ν (cm−1):
3178, 3093 (NH); 1450 (C S); 1512 (C N). 1H NMR
(DMSO-d6), δ (ppm): 7.34, 8.34 (s, 1H, CH, nonsym-
metric); 7.03, 7.01; 7.32, 7.28 (d, 2H, H3,5, nonsym-
metric); 7.69, 7.67; 7.55, 7.52 (d, 2H, H2,6,); 2.55,
2.52; 1.95, 1.93 (s, 3H, S CH3, nonsymmetric); 13.48,
13.47; 11.94 (s, 1H, NH, nonsymmetric).
1
ν (cm−1): 3429, 3375 (OH); 1687 (C O). H NMR
(DMSO-d6), δ (ppm) 7.97–7.95 ppm (d, 2H, H2,6, J =
10 Hz,); 7.83–7.81 (d, 2H, H3,5, J = 10 Hz,); 5.59 (s,
1H, CH); 3.43 (s, br, OH); 13.17 (s, br, OH).
4-Nitrophenyl Glyoxal Monohydrate 1f. Yield 24%,
mp 128–130◦C; Anal. Calcd. for C8H7O5N: C, 48.73;
H, 3.55; N, 7.1 Found: C, 48.61; H, 3.75; N, 7.3.UV
(DMSO) λ nm (ε M−1 cm) = 266 (10,380); 213 (4640).
IR (KBr) ν (cm−1) 3332, 3251 (OH); 1703 (C O);
1
1529, ( NO2 asym), 1350 (−NO2, sym). H NMR
(DMSO-d6), δ (ppm) 8.18–8.16 (d, 2H, H2,6, J =
10 Hz,); 7.78–7.76 (d, 2H, H3,5, J = 10 Hz,); 6.58
(s, 1H, CH); 6.87 (s, br, OH).
1-(4-Chlorophenyl)ethanediylidene-
bis(methyl dithiocarbazonoate) 2d
Yield 58%, mp 170◦C; Anal. Calcd. for C12H11N4S4Cl:
C, 38.24; H, 2.92; N, 14.87; S, 33. 99, Found: C, 38.47;
H, 3.23; N, 14.98; S, 34.18. UV (DMSO) λ nm (ε
M1 cm) = 465 (18,840); 360 (22,600); 309 (30,060);
218 (20,700). IR (KBr) ν (cm−1): 3178, 3091 (NH);
1413 (C S); 1496 (C N). H NMR (DMSO-d6), δ
(ppm): 8.33, 7.99 (s, 1H, CH, nonsymmetric); 7.74,
7.72; 7.53, 7.51 (d, 2H, H3,5, nonsymmetric); 7.55,
7.537.34, 7.32 (d, 2H, H2,6, nonsymmetric); 2.53; 2.36
(s, 3H, S CH3, nonsymmetric); 13.55; 13.49 (s, 1H,
NH, nonsymmetric).
Preparation of Aryl Ethandiylidene-
bis(methyl dithiocarbazonoate) 2a–2f
General Procedure. A solution of arylglyoxal mono-
hydrate 1a–1f (0.1 mol) in absolute methanol (20 mL)
was added to 2 mol of methyl dithiocarbazoate
(0.2 mol) in absolute methanol (30 mL) and refluxed
for 30 min. The resulting solution was left to cool, and
the orange precipitate was filtered off, washed with
methanol, and crystallized from methanol.
1
1
1-Phenyl-ethanediylidene-bis(methyl dithiocarbazo-
noate) 2a. Yield 59%, mp 180◦C; Anal. Calcd. for
C12H12N4S4: C, 42.10; H, 3.50; N, 16.37; S, 37.42
Found: C, 42.20; H, 3.83; N, 16.44; S, 37.68. UV
(DMSO) λ nm (ε M1 cm) = 459 (10,640); 303
(17,190); 218 (11.810). IR (KBr) ν (cm−1): 3204, 3164
(NH); 1434 (C S); 1490 (C N),1H NMR (DMSO-
d6), δ (ppm): 8.01, 8.36 (s, 1H, CH, nonsymmet-
ric); 7.46–7.33 (d, 5H, H3,5,4,2,6); 2.54, 2.36 (s, 3H,
S−CH3, nonsymmetric); 14.72; 13.55 (s, 1H, NH,
nonsymmetric).
1-(4-Bromophenyl)ethonediyildene-bis(methyl dithi-
ocarbazonoate) 2e. Yield 46.66%, mp 188; Anal.
Calcd. for C12H11N4S4Br, C, 34.20; H, 2.61; N, 13.30;
S, 30.41, Found:, C, 34.47; H, 2.72; N, 13.55; S,
30.78. UV (DMSO) λ nm (ε M1 cm) = 456 (14,360);
360 (22,600); 311 (23,540); 217 (18,500) .IR (KBr) ν
(cm−1): 3159, 3097 (NH); 1438 (C S); 1504 (C N).
1H NMR (acetone-d6), δ (ppm) : 8.10, 7.92 (s, 1H, CH,
nonsymmetric); 7.77, 7.76; 7.73, 7.70 (d, 2H, H3,5
nonsymmetric); 7.68, 7.66; 7.43, 7.41 (d, 2H, H2,6
,
,
nonsymmetric); 2.80; 2.43 (s, 3H, S CH3, nonsym-
metric); 13.66; 12.30 (s, 1H, NH, nonsymmetric).
1-(4-Methylphenyl)ethanediylidene-bis(methyl dithi-
ocarbazonoate) 2b. Yield 52%; mp 196–198, Anal.
Calcd. for C13H14N4 S4: C, 43.82; H, 3.93; N, 15.73; S,
35.95, Found: C, 43.67; H, 4.21; N, 15.95; S, 36.23.UV
(DMSO) λ nm (ε M1 cm) = 446 (14,060); 363
(16,660), 344 (20,190); 303 (21,520); 220 (13,670).
1-(4-Nitropheyl)ethanediylidene-bis(methyl dithio-
carbazonoate) 2f. Yield 58%, mp 180; Anal. Calcd.
for C12H11N5O2S4, C, 37.20; H, 2.84; N, 18.08;
S, 33.07, Found: C, 37.55; H, 3.11; N, 18.37; S,
International Journal of Chemical Kinetics DOI 10.1002/kin

30
SHEHATA ET AL.
33.38.UV (DMSO) λ nm (ε M1 cm) = 455 (14,660);
348 (23,780); 218 (18,620); 365 (23,420). IR (KBr)
ν cm−1): 3161, 3103 (NH); 1502 (C S); 1583
δ (ppm): 7.84 (s, 1H, CH,); 7.59 (br, 2H, H3,5); 6.91(br,
2H, H2,6); 2.58, 2.44 (s, 3H, S CH3).
[1-(4-Chlorophenyl)ethanediylidene-bis(methyl di-
thiocarbazonoate)NNꢀSSꢀ (−2)]Ni(II) Complex 3d.
Yield 97.8%, mp 230◦C; Anal. Calcd. for
C12H11N4S4ClNi, C, 33.24; H, 2.53; N, 12.92; S,
29.54; Ni, 13.55. Found: C, 32.91; H, 2.25; N, 12.61;
S, 29.68; Ni, 13.42. UV (CHCl3) λ nm (ε M1 cm) =
696 (4380); 462 (8180), 376 (15,200); 293 (34,640);
261 (38,200). IR (KBr) ν (cm−1): 1598 (C N); 1377
(C S), 590 (Ni N).1H NMR (CDCl3), δ (ppm): 7.82
(s, 1H, CH,); 7.56–7.25 (d, 4H, H3,5, H2,6); 2.57, 2.45
(s, 3H, S−CH3).
1
(C N). H NMR (acetone-d6), δ (ppm): 7.21, 7.34;
8.32, 8.31 (s, 1H, CH, (d, 2H, H3,5, nonsymmet-
ric); 8.28, 8.23; 8.21, 8.18 (d, 2H, H2,6, nonsym-
metric); 2.49, 2.46; 2.06, 2.03 (s, 3H, S CH3, non-
symmetric); 13.76, 13.38; 11.96, 10.14 (s, 1H, NH,
nonsymmetric).
Preparation of [Arylethanediylidene-
bis(methyl dithiocarbazonoate) NNꢀSSꢀ
(−2)]Ni(II) Complex 3a–3f
General Procedure. A hot solution of aryl etha-
nediylidene-bis-methyl dithiocarbazonoate (0.2 mol)
in methanol (30 mL) was treated with a hot solution of
nickel(II) acetate (0.2 mol) in methanol (20 mL), and
the reaction mixture was refluxed for 2 h. The isolated
Ni(II) complex was filtered while hot and recrystallized
from chloroform.
[1-(4-Bromophenyl)ethanediyledene-bis(methyl di-
thiocarbazonoate)NNꢀSSꢀ(−2)]Ni(II) Complex 3e.
Yield 92.89%, mp 210–212◦C; Anal. Calcd. for
C12H11N4S4Br Ni, C, 30.15; H, 2.30; N, 11.72; S,
26.80; Ni, 12.29. Found: C, 29.87; H, 1.99; N, 11.54;
S, 26.45; Ni, 12.22. UV (CHCl3) λ nm (ε M1 cm) =
696 (4260); 462 (7980), 383 (15,160), 293 (33,600),
261 (37,460). IR (KBr) ν (cm−1): 1581 (C N); 1398
(C S), 576(Ni N). 1H NMR (CDCl3), δ (ppm): 7.84
(s, 1H, CH,); 7.25 (br, 2H, H3,5); 7.54, 7.51(d, 2H,
H2,6); 2.59, 2.52 (s, 3H, S CH3).
[1-(Phenyl)ethanediylidene-bis(methyl
dithiocar-
bazonoate) NNꢀSSꢀ (−2)]Ni(II) Complex 3a. Yield
85%, mp 150–152◦C; Anal. Calcd. for C12H12N4S4
Ni, C, 36.11; H, 3.01; N, 14.04; S, 32.10; Ni, 14.72.
Found: C, 36.08; H, 2.99; N, 13.89; S, 31.81; Ni,
14.55. UV (CHCl3) λ nm (ε M1 cm) = 693 (3080);
556 (2380); 456 (7420);372 (11.420); 288 (28,700);
263 (32,280). IR (KBr) ν (cm−1): 1559 (C N); 1483
(C S) 561; (Ni N). 1H NMR (CDCl3), δ (ppm): 7.86
(s, 1H, CH,); 7.62–7.25 (d, 4H, H3,5, H2,6); 2.57, 2.44
(s, 3H, S CH3).
[1-(4-Nitrophenyl)ethanediylidene-bis(methyl dithi-
ocarbazonoate)NNꢀSSꢀ(−2)]Ni(II) Complex 3f.
Yield 98%, mp 226–228◦C; Anal. Calcd. for
C12H11N5S4O2Ni, C, 32.45; H, 2.47; N, 15.77; S,
28.84; Ni, 12.33. Found: C, 32.31; H, 2.27; N, 15.36;
S, 28.54; Ni, 12.77. UV (CHCl3) λ nm (ε M1 cm) =
710 (3440); 468 (6360), 369 (19,800); 269 (26,340).
IR (KBr) ν (cm−1): 1591 (C N); 1396 (C S),
582(Ni N). 1H NMR (CDCl3), δ (ppm): 7.84 (s, 1H,
CH,); 8.38, 8.28 (dd, 2H, H3,5); 7.84, 7.81 (d, 2H,
H2,6); 2.94, 2.58 (s, 3H, S CH3).
[1-(4-Methylphenyl)ethanediylidene-bis(methyl di-
thiocarbazonoate) NNꢀSSꢀ (−2)]Ni(II) Complex 3b.
Yield 87.8%, mp 188–190◦C; Anal. Calcd. for
C13H14N4S4 Ni, C, 37.79; H, 3.39; N, 13.56; S, 31.01;
Ni, 14.22, Found: C, 37.41; H, 3.02; N, 13.33; S, 30.98;
Ni,14.08.UV (CHCl3) λ nm (ε M1 cm) = 688 (2800);
458 (5340); 384 (10,340); 263 (26,140). IR (KBr) ν
Preparation of [Arylethanediylidene-
(S-methyl-N-morpholino methyl
dithiocarbazonoate)NNꢀSSꢀ (−2)]Ni(II)
Complex, 4a–4f
1
(cm−1): 1546 (C N); 1604 (C S), 551 (Ni N). H
NMR (CDCl3), δ (ppm) : 7.83 (s, 1H, CH,); 7.61, 7.53
(d, 2H, H3,5); 7.25, 7.22 (d, 2H, H2,6); 2.45, 2.37 (s,
3H, S−CH3).
General Procedures. A solution of the Ni(II) com-
plex (0.2 mol) in a smallest amount of benzene was
treated with Mo (molar ratio 1:10) at room temperature.
The reaction mixture was followed by thin-layer chro-
matography until a precipitate was formed, filtered,
and crystallized from chloroform.
[1-(4-Methoxyphenyl)ethanediylidene-bis(methyl di-
thiocarbazonoate) NNꢀSSꢀ (−2)]Ni(II) Complex 3c.
Yield 89.2% mp 180◦C; Anal. Calcd. for C13H14N4S4O
Ni, C, 36.38; H, 3.26; N, 13.06; S, 29.85; Ni, 13.69,
Found: C, 35.98; H, 2.87; N, 12.96; S, 29.34; Ni,
13.39. UV (CHCl3) λ nm (ε M1 cm) = 689 (2600);
404 (12,040); 264 (25,140). IR (KBr) ν (cm−1): 1595
(C N); 1471 (C S), 565 (Ni N). 1H NMR (CDCl3),
[1-Phenylehtanediylidene-(S-methyl-N-morpholino
methyl dithiocarbazonoate)NNꢀSSꢀ (−2)]Ni (II)
Complex 4a. Yield 54%, mp 180–184◦C; Anal.
Calcd. for C15H17N5S3ONi, C, 41.12; H, 3.88; N,
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETICS OF ARYLETHANEDIYLIDENE-BIS-DITHIOCABAZONOATE NI COMPLEXES WITH MORPHOLINE
31
15.99; S, 21.93; Ni, 13.41, Found: C, 41.43; H, 3.52;
N, 15.66; S, 21.72; Ni, 13.24. UV (CHCl3) λ nm
(ε M1 cm) = 644 (2760); 436 (5980); 413 (5540);
294 (22,140); 255 (28,460). IR (KBr) ν (cm−1): 1548
(C N); 1429 (C S). 1H NMR (CDCl3), δ (ppm):
8.08 (s, 1H, CH,); 7.39–7.25, (d, 4H, H3,5, H2,6); 2.60
(s, 3H, S CH3); 4.68, 3.79–3.73 (s, 2H, α-CH2; 2H,
β-CH2).
13.55; S, 18.58; Ni, 11.36, Found: C, 34.97; H, 3.21;
N, 13.25; S, 18.34; Ni, 11.26. UV (CHCl3) λ nm
(ε M1 cm) = 648 (3540); 440 (7260); 358 (9280);
296 (28,660); 255 (34,520). IR (KBr) ν (cm−1): 1546
1
(C N); 1417 (C S), 663(Ni N). H NMR (CDCl3),
δ (ppm): 7.94 (s, 1H, CH,); 7.52–7.50 (d 2H, H3,5, J
= 10 Hz); 7.34 (br, 2H, H2,6); 2.58 (s, 3H, S CH3);
4.65 (br, 2H, α-CH2); 3.80–3.73, (m, 6H, β-CH2).
[1-(4-Methylphenyl)ethanediylidene-(S-methyl-N-
morpholinomethyldithiocarbazonoate)NNꢀSSꢀ(−2)]-
Ni(II) Complex 4b. Yield 26%, mp 196◦C; Anal.
Calcd. for C16H19N5S3ONi, C, 42.50; H, 4.20; N,
15.49; S, 21.25; Ni, 12.99, Found: C, 42.82; H, 4.42;
N, 15.26; S, 21.58; Ni, 12.65. UV (CHCl3) λ nm
(ε M1 cm) = 641 (3380); 436 (6900), 410 (6800);
361 (9340); 293 (27,020); 256 (32,880). IR (KBr) ν
[1-(4-Nitrophenyl)ethanediylidene(S-methyl-N-mor-
pholinomethyldithiocarbazonoate)NNꢀSSꢀ(−2)]Ni-(II)
Complex 4f. Yield 44%, mp 222◦C; Anal. Calcd.
for C15H16N6S3O3Ni, C, 37.29; H, 3.31; N, 17.40;
S, 19.88; Ni, 12.16, Found: C, 37.47; H, 3.49; N,
17.55; S, 19.53; Ni, 11.92. UV (CHCl3) λ nm (ε M1
cm) = 656 (2940); 445 (6480); 359 (16,520); 262
(25,720). IR (KBr) ν (cm−1): 1539 (C N); 1404
(C S), 559(Ni N). 1H NMR (CDCl3), δ (ppm): 8.26
(s, 1H, CH,); 7.35–7.25 (d, 4H, H3,5, H2,6); 2.60 (s,
3H, S CH3); 4.66 (br, 2H, α-CH2); 3.93–3.76, (m,
6H, β-CH2).
1
(cm−1): 1550 (C N); 1421 (C S), 563 (Ni N). H
NMR (CDCl3), δ (ppm): 7.90 (s, 1H, CH,); 7.37–7.35,
7.52, 7.51 (d 2H, H3,5, J = 10 Hz); 7.20–7.18 (d, 2H,
H2,6, J = 10 Hz); 2.58 (s, 3H, S CH3); 4.69–4.67,
3.80–3.79 (d, 2H, α-CH2, J = 10 Hz); 3.77–3.76,
3.76–3.72 (d, 2H, β-CH2, J = 10 Hz).
Kinetic Measurements
The reaction of [1-arylethanediylidene-bis(methyl
dithiocarbazonoate) NNꢀSSꢀ (−2)] nickel(II) com-
plexes (1 × 10−4 mol dm−3) with different concen-
trations of Mo (10 × 10−4 to −30 × 10−4) mol dm−3
was followed spectrophotometrically in benzene. The
kinetic runs were performed by following the disap-
pearance of the reactant at λ = 700 nm. The recorded
spectra at the end of the reaction were identical to the
spectra of the corresponding authentic sample of the
monomorpholino complex derivatives in the same sol-
vent. The pseudo-first-order rate constant, kψ , is given
by the following equation:
[1-(4-Methoxyphenyl)ethanediylidene-(S-methyl-N-
morpholinomethyldithiocarbazonoate)NNꢀSSꢀ(−2)]-
Ni(II) Complex 4c. Yield 80%, mp 176–178◦C; Anal.
Calcd. for C16H19N5S3ONi, C, 41.05; H, 4.20; N,
14.96; S, 20.52; Ni, 12.55, Found: C, 41.27; H,4.31;
N, 14.75; S, 20.33; Ni, 12.33. UV (CHCl3) λ nm (ε
M1 cm) = 643 (4200); 377 (13,640); 255 (39,040).
IR (KBr) ν (cm−1): 1550 (C N); 1425 (C S),
563(Ni N). 1H NMR (CDCl3), δ (ppm): 8.04 (s, 1H,
CH,); 6.91, (br, 2H, H3,5); 7.25 (d, 2H, H2,6); 2.56 (s,
3H, S CH3); 3.82 (br, 4H, α-CH2 and β-CH2).
[1-(4-Chlorophenyl)ethanediylidene-(S-methyl-N-
morpholino methyl dithiocarbazonoate)NNꢀSSꢀ
(−2)]Ni(II) Complex 4d. Yield 22%; mp 178–180◦C;
Anal. Calcd. For C15H16ClN5S3ONi, C, 38.11; H,
3.38; N, 14.82; S, 20.33; Ni, 12.43, Found: C, 38.37;
H, 3.51; N, 14.79; S, 20.13; Ni, 12.35. UV (CHCl3)
λ nm (ε M1 cm) = 647 (5060); 439 (10,600); 293
(40,040); 256 (43,920). IR (KBr) ν (cm−1): 1542
(C N); 1388 (C S), 570(Ni N) .1H NMR (CDCl3).
δ (ppm): 7.91 (s, 1H, CH,); 7.411 (d, 2H, H3,5, J =
10 Hz); 7.36–7.34 (d, 2H, H2,6, J = 10 Hz); 2.58 (s,
3H, S CH3); 4.67–4.65, 3.81–3.80 (d, 2H, α-CH2);
3.79–3.78, 3.73–3.72 (d, 2H, β-CH2).
−kꢀt
log (At − A ) =
+ log (Ao − A ) (1)
∞
∞
2.303
kꢀ values were calculated from the slope of the plot of
log (At − A ) versus time (in seconds), where Ao, At ,
∞
and A are the values of the absorbance at zero time,
∞
time t, and at the end of the reaction, respectively.
RESULTS AND DISCUSSION
Synthesis of Arylglyoxal Hydrate 1a–1f
Arylglyoxal hydrates 1a–1f were prepared by oxi-
dation of 4-substituted acetophenones with SeO2 in
dioxane [24,25] (Scheme 1). The FT-IR spectra of
1a–1f revealed the presence of two broad bands at ν
(cm−1) 3251–3446 corresponding to two OH groups.
[1-(4-Bromophenyl)ethanediyledene(S-methyl
N-
morpholinomethyldithiocarbazonoateNNꢀSSꢀ(−2)]-
Ni(II) Complex 4e. Yield 60%, mp 188–190◦C; Anal.
Calcd. for C15H16BrN5S3ONi, C, 34.84; H, 3.09; N,
International Journal of Chemical Kinetics DOI 10.1002/kin

32
SHEHATA ET AL.
Scheme 1
1H NMR confirmed the presence of two broad signals
at δ (ppm) 3.43–6.92 and 12.63–13.17 attributable to
two OH groups, whereas the singlet at δ (ppm) 5.59–
6.58 was attributed to the CH proton. These obser-
vations indicated that the arylglyoxals exist in the hy-
drated form.
The IR frequency of the N H band disappeared
showing thereby coordination of the sulfur to the
nickel(II) by the loss of the thiolic protons of the lig-
and. This agrees with the lack of signals due to the res-
1
onance of NH and SH protons in the H NMR study.
All isolated Ni(II) chelates 3a–3f were found to ex-
1
hibit sharp H NMR signals indicating that they are
diamagnetic, a result that infer a square planar environ-
ment around the Ni(II) ion [16,25–28]. The electronic
spectra of the complexes 3a–3f in benzene, chloro-
form, and Nujol mull showed intense bands at 691–742
nm (14471–13477 cm−1), which should be assigned to
d(M) → π*(L) transition.
Synthesis of Arylethanediylidine-bis(methyl
dithiocarbazonoate) 2a–2f
The condensation of arylglyoxal hydrates 1a–1f with
methyl dithiocarbazoate yielded the bishydrazones 2a–
2f (Scheme 1). The 1H NMR spectra of hydrazones 2a–
2f showed two singlets assigned to azomethine CH N
protons, two doublets of doublet for H3,5 and H2,6, two
signals corresponding to two different S CH3 protons,
two signals of SH protons, and other two signals in
most substituent for NH protons. These observations
can be attributed to the nonsymmetric nature of the
molecule rather thione → thiol tautomers [5] because
The green-colored complexes 3a–3f were found to
be only feebly paramagnetic (μ = 0 → 0.55 BM
at 298 K), suggesting a planar environment of lig-
and around the nickel(II) ion [20]. These complexes
showed insignificant magnetic properties when they
were measured at 55◦C meaning that the complexes
still have a square planar geometry on increasing tem-
perature [20].
1
the H NMR spectra of the corresponding symmetric
diacetyl and benzil bis(dithiocarbazone) do not exhibit
such a behavior.
Synthesis of Monosubstituation Nickel(II)
Complexes 4a–4f
Synthesis and Geometry of
Arylethanediylidene-bis(methyl
dithiocarbazonoate)Nickel Complexes
3a–3f
The complexes 3a–4f underwent either nucelophilic
attack on the Ni atom or nucleophilic substitution of the
SCH3 group or both [3,17,29]. At low concentration
of amine and because the first formed monosubstituted
product deactivated the other C SCH3 group, the mo-
mosubstituted chelates 4a–4f were isolated. The attack
of the nucleophile on the Ni atom without the release
of the SCH3 group gave a monoaddition complex 5a–
5f, whereas with the release of SCH3 a monoaddition
monosubstitution [16] was isolated. On the other hand,
Nickel(II) chelates of the hydrazone derivatives 3a–3f
were prepared either directly from the reaction of the
ligand 2a–2f with nickel acetate in a (1:1) molar ratio
or in situ from the reaction of arylglyoxal 1a–1f with
methyl dithiocarbazonoate and nickel acetate (1:2:1
molar ratio, respectively) in ethanol (Scheme 1).
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETICS OF ARYLETHANEDIYLIDENE-BIS-DITHIOCABAZONOATE NI COMPLEXES WITH MORPHOLINE
33
Figure 1 Delocalization of the lone pair on nitrogen of the morpholinyl group, and carbon carries the SCH3.
in the presence of large excess of amine, the complexes
3a–3f gave disubstitution products [16].
carbon bearing the other C−SCH3. This inhibits further
attack on that carbon, and consequently no disubstitu-
tion products are obtained under these conditions of
the reaction (Fig. 1).
In the present investigation, the reactions of [1-
arylethanediylidene-bis(methyl dithiocarbazonoate)
NNꢀSSꢀ (-2)]Ni(II) 3a–3f with Mo in benzene un-
dergo mono-morpholino-demethyl-thiolation to give
the corresponding [1-arylethanediylidene (methyl
Kinetic Studies and Mechanism for the
Reaction of Arylethanediylidine-bis(methyl
dithiocarbazonoate)Nickel(II) Complexes
3a–3f with Mo in Benzene
morpholino
dithiocarbazonoate)
NNꢀSSꢀ]Ni(II)
complex derivatives 4a–4f, as indicated by their
elemental analysis, UV, IR, and 1H NMR spectra
(Eq. (2)).
The titled reaction is considered as a bimolecular nu-
cleophilic aromatic substitution-like, i.e., nucleophilic
(2)
The 1H NMR spectral data of these complexes
display only one signal at δ 2.58–2.60 ppm corre-
sponding to only one SCH3 group and only one
morpholinyl proton. The bands displayed at 651–655
(15,360–15,267 cm−1) in benzene, and at 641–656 nm
(15,600–15,243 cm−1) in CHCl3 can be attributed to
d(M) → π*(L) transition. The assumed square planar
geometry for these complexes was confirmed from the
zero value of their room temperature magnetic mo-
ment. The reason that the reaction of 3a–3f with Mo of
the concentration less than 30 folds gave only mono-
substitution products 4a–4f can be explained on the
basis of the delocalization of the fourth electron on the
mopholinyl nitrogen creates a negative charge on the
substitution and not ligand substitution [13]. In gen-
eral, the nucleophilic substitution reactions involv-
ing amine at sp2 carbon have been suggested to pro-
ceed through unanalyzed or amine-catalyzed mech-
anism or a mixture of them. The catalyzed mech-
anism could proceed by a dimer mechanism [30–
32], specific base (SB) [33–35], or SB-general acid
mechanism (SB-GA) [36]. The reaction conditions,
e.g., the nature of the solvent [37,38], the nature of
the amine [38,39], and the structure of the reacting
species, were used to decide which mechanism was
operating.
International Journal of Chemical Kinetics DOI 10.1002/kin

34
SHEHATA ET AL.
Table I Rate Constants and Activation Parameters for the Reaction of Substituted Ni(II) Complexes (3a–3f) with Mo
in Benzene at Temperatures 20–35◦C
k3 (×10−2 dm6 mol−2 s−1
)
R
20◦C
25◦C
30◦C
35◦C
ꢁH# (kcal mol−1
)
−ꢁS# (cal mol−1K−1
)
4-NO2
4-Cl
4-Br
H
4-CH3
4-OCH3
ρ
69.79
7.45
7.18
4.65
3.08
2.40
1.44
102.4
9/09
8.77
5.68
3.92
3.03
1.42
110.76
13.16
11.69
7.50
5.02
4.09
–
1.99
8.13
8.15
8.67
8.85
9.08
39.58
42.84
42.94
43.90
44.37
44.77
14.71
13.89
9.21
6.67
5.00
0.73
1.35
Table II Rate Constants and Activation Parameters for the Reaction of Substituted Ni(II) Complexes (3a–3f) with Mo
in Benzene at Temperatures 40–55◦C
k3 (×10−2 dm6 mol−2 s−1
)
R
35◦C
29.82
40◦C
45◦C
50◦C
55◦C
−ꢁH# (kcal mol−1
)
−ꢁS# (cal mol−1K−1
)
4-NO2
4-Cl
4-Br
H
4-CH3
4-OCH3
ρ
27.78
6.69
6.22
4.36
2.46
1.38
1.18
25.60
5.97
5.58
3.80
2.13
1.20
1.19
23.54
5.13
4.86
3.33
1.85
1.08
1.20
22.73
4.70
4.60
3.00
1.65
0.94
1.25
3.43
5.46
5.50
5.68
5.96
6.18
43.45
46.61
46.65
47.48
48.67
49.83
their plots in both ranges of temperatures 20–35◦ and
40–55◦ gave a good straight line (not shown). Surpris-
ingly, the enthalpy of activation values for the reactions
of 3a–3f with Mo in the temperature range 40–55◦C is
negative and showed a small difference with change in
the nature of the substituent [39] (Table II). These ob-
servations are presumably due to heat capacity changes
in the activated complex, temperature-induced changes
in the ground state, or a combination of both, conforma-
tional switches of the structure of the starting materials,
or finally the reaction follows the same mechanism but
with different positions in the rate-determining step
[34].
Accordingly, Scheme2maybesuggestedtoaccount
for the isolation of the monosubstitution products 4a–
4f at 20–35◦C. The mechanism shows that the first Mo
molecule attacks the electrophilic carbon that bears the
SCH3 group close to the aryl group to form the zwit-
terionic intermediate (I). As expected, the formation of
the highly ionic intermediates (I) is not favored in non-
polar solvents, and the second Mo molecule can thus
deprotonates the intermediate (I) to give an anionic
intermediate (II). Finally, this intermediate undergoes
decomposition to give the monosubstitution product
4a–4f and the reaction follows the SB mechanism.
Another suggested mechanism is that the protonated
Reactions of 3a–3f with Mo in Benzene:
Effects of Substituents and Temperature
The rate of reactions of 3a–3f with Mo obeyed the
pseudo-first-order kinetics with excess Mo, and the
plots of kψ (s−1)/[Mo] against the corresponding [Mo]
gave a straight line passing through the origin with
slopes equal to third-order rate constants, k3 (dm6
mol−2 −1), indicating that the reaction depends on
s
two amine molecules, i.e., amine-catalyzed reaction.
The third-order rate constants, the activation parame-
ters, and ρ are presented in Tables I and II.
Interestingly, the k3 values were found to increase
steadily with increasing temperature in the range 20–
35◦C followed by a sudden drop after 35◦C, then a
continuous decrease in k3 values was observed by fur-
ther elevation of the temperature in the range 40–55◦C,
whereas this behavior is observed in 4-nitro derivative
3f in the range 35–55◦C (Tables I and II).
The kinetic results with temperatures ranging be-
tween 20 and 55◦C show a convex curve for the Ar-
rhenius correlation (Fig. 2). The entropies of activation
were quite similar for both reactions in the tempera-
ture ranges 20–35◦ and 40–55◦C. Although the plots
of ꢁH# versus ꢁS# for the reactions of Mo with 3a–3f
at all temperatures 20–55◦C gave scattered correlation,
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETICS OF ARYLETHANEDIYLIDENE-BIS-DITHIOCABAZONOATE NI COMPLEXES WITH MORPHOLINE
35
(a)
(b)
3
2.9
2.8
2.7
2.6
2.5
2.4
3
2.9
2.8
2.7
2.6
2.5
2.4
3
3.05
3.1
3.15
3.2
3.25
3.3
3.35
3.4
3.45
3
3.05
3.1
3.15
3.2
3.25
3.3
3.35
3.4
3.45
3
3
1\Tx10
1\Tx10
Figure 2 Plot of log k3 versus 1/T for the reaction of 3a with Mo in benzene: (a) convex and (b) two separate series 20–35◦C
and 40–55◦C.
Mo donates a proton to the leaving SCH3 group, and
the reaction follows the SB-GA mechanism. Such a
mechanism cannot be applied in our reaction because
it is known that this mechanism actually occurs in dipo-
lar solvent especially DMSO [36]. Another investiga-
tion of the reaction is the dimer mechanism, where a
dimer amine formed in a fast and reversible process
attacks the electrophilic carbon that bears the SCH3
group close to the aryl group, and at the same time
donates a proton to the leaving group, followed by the
involvement of a third amine to give the final products
4a–4f. This mechanism is also unfavorable because
the correlation between kA and [Mo] is not curvilinear
[30–32]. The elimination of the uncatalyzed pathway
(Scheme 2) is based on the fact that the reaction is
amine catalyzed.
The kinetic expression for the reaction of 3a–3f with
Mo is derived with reference to Scheme 2, where a k2
pathway is neglected. Making the usual assumption
that the zwitterionic adduct may be treated as a steady-
state intermediate when the amine acts as both the
nucleophile and the catalyzing base, the overall rate
constant is given by the following equation:
If we assume that k1 is the rate-determining step,
Am
i.e., k−1k4 + k
k
ꢂ k3Amk4 [Am]
−1
−3
k1k3Amk4[Am]
k3Amk4[AM]
kA =
= k1
(4)
If we assume that k3 is the rate-determining step, k−1 k4
Am
ꢃ k3Amk4[Am] + k
k
3
−1
k1k3Amk4[Am]
kA =
= k3AmK1[Am]
(5)
k
−1k4
O
O
H
N
C
N
H
N
N
Ar
S
N
N
S
CH3
Ni
ꢀ
ꢁ
S
kψ
k1k3Amk4[Am]
H
kA =
=
Am
−3
k
−1k4 + kAmk4[Am] + k
k
C
[Am]
−1
3
(3)
SCH3
where kꢀ is the pseudo-first-order rate constant and kA
(kψ (s−1)/[Am] is the second-order rate constant.
Cyclic anionic intermediate (III)
International Journal of Chemical Kinetics DOI 10.1002/kin

36
SHEHATA ET AL.
Scheme 2
Consequently, Eq. (5) is consistent with a mecha-
nism in which the proton transfer process is the rate-
determining step, i.e., SB.
An alternative mechanism for the reaction of 3a–3f
with Mo in benzene to produce monosubstitution is
shown in Scheme 3. It shows that the reaction of Mo
with complexes initially proceeds either by two path-
ways: The first one is the formation of monoadduct
5a–5f followed by a further attack of the second Mo
molecule on the C SCH3 carbon of the monoadduct
5a–5f to form a zwitterionic intermediate 6a–6f (struc-
ture A). The second pathway occurred by the attack of
Mo on the carbon bearing the SCH3 close to the
aryl ring to form the zwitterionic intermediate 7a–7f
followed by the attack of the second Mo molecule
to give the same zwitterionic intermediate 6a–6f. In
this intermediate, the positive charge is located on
the nitrogen atom whereas the negative charge can be
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETICS OF ARYLETHANEDIYLIDENE-BIS-DITHIOCABAZONOATE NI COMPLEXES WITH MORPHOLINE
37
Scheme 3
accommodated either on the aryl ring (structure B)
or on the carbon atom of the other C SCH3 car-
bon through extended conjugation (structure C). Also,
the electron-releasing morpholinyl group undoubtly re-
duces the formal positive charge on the Ni(II) ion con-
taining intermediate 7a–7f, thus decreasing the Ni N
bond strength. Consequently, it seems reasonable to
assume that the formed monosubstituted monoadduct
intermediate becomes thermodynamically less stable
[16] and readily lose the axially coordinated base with
accompanying elimination of the CH3SH molecule
giving rise to the monosubstitution product 4a–4f.
Kinetics and Mechanism for the Reaction
of 3a–3f with Mo in the Temperature
Range between 20 and 35◦C
In the preceding discussion, we suggested that the re-
action of 3a–3f with Mo in benzene proceeds by the
mechanism shown in either Scheme 2 or Scheme 3. The
International Journal of Chemical Kinetics DOI 10.1002/kin

38
SHEHATA ET AL.
Hammett plots exhibited good straight lines with ρ
values of 1.42–0.73, depending on temperature and r
values of 0.93–0.98.
time the 4-OCH3 group destabilizes Ic and increases
the expulsion rates of the leaving group SCH3 (the
k4 value) from Ic. See the structure in the next section.
It was reported that the carbon carrying the SCH3
group close to the aromatic ring in the nickel com-
plex 3a possesses higher electrophilicity than the other
C SMe carbon, and thus, the nucleophilic attack of
amines will preferentially occur on the former carbon
[16]. On the other hand, the delocalization of the devel-
oped negative charge with the aromatic ring to give the
stable zwitterionic intermediate II can explain the re-
gioselectivity to give the monosubstitution 4a–4f. This
charge delocalization presumably gives stable zwit-
terionic intermediates I, whereas such delocalization
hardly occurs with the aromatic ring if Mo attacks the
C SCH3 far from the aryl group. Table I reveals that an
electron-withdrawing substituent, e.g., NO2 3f accel-
erates the rate of nucleophilic attack. We ascribed the
increase in the rate to the increase in the electrophilicity
of the carbon atom bearing the SCH3 group located
close to the aryl group, as well as the NO2 group
stabilization of the tetrahedral intermediate (If). Mean-
while, the resonance between the developed negative
charge and the –NO2 group retards the departure of the
leaving group IV.
Kinetics and Mechanism for the Reactions
of 3a–3f with Mo in the Temperature
Range of 40–55◦C
As mentioned previously, the k3 values at 40◦C suffer
from a sudden drop followed by a continuous decrease
in the k3 value for all substituents with an increase in
the temperature till 55◦C. The Hammett plots exhibited
a good linear correlation with ρ values ranged between
1.18 and 1.25 (r = 0.96–0.99; Table II). We noticed
that the ρ values have a relatively small difference
with the change in temperature, and unexpectedly it
increased with increasing temperature. However, the
calculated ρ values for the reaction with Mo in the
temperature range 40–55◦C are comparable to those
measured for the same reactions at the temperature
range 20–35◦C. As a result, the effect of substituents
on rates is similar to those for the reaction of 3a–3f
with Mo in the temperature range 40–55◦C.
In contrast, Table I shows that an electron-donating
substituent, e.g., OCH3 3c, inhibits the nucleophilic
attack. We ascribed the decrease in the rate to the de-
crease in the electrophilicity of the carbon atom bear-
ing the SCH3 group close to the aryl group due to the
resonance as found in structure V, whereas at the same
Accordingly, many mechanisms for the reactions of
3a–3f with Mo in the temperature range 40–55◦C could
be interpreted based on the following: (i) the reaction in
the two temperature ranges follows the SB mechanism
(Scheme 2); with a change in the position of the
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETICS OF ARYLETHANEDIYLIDENE-BIS-DITHIOCABAZONOATE NI COMPLEXES WITH MORPHOLINE
39
slow step, the rate-limiting step is the proton transfer
process in the temperatures 20–35◦C, whereas it may
be the departure of the SCH3 group (product forma-
tion) in the temperatures 40–55◦C. This is not possible
because ρ values in both ranges 20–35◦C and 40–55◦C
of temperatures are quite the same. (ii) The reaction
may follow a dimer-mechanism involving intermedi-
ate (III). This mechanism is rejected on the ground that
no parabolic kA – [Am] shape was observed [30–32].
(iii) A reduction in the splitting of the 3d energy level
by the ligand to produce a square-planar paramagnetic
complex [20]. And (iv) the complexes 3a–3f are sub-
jected to a fast configurational equilibrium, which is
greatly enhanced by increasing the temperature. The
comparable ρ and entropy values as well as the de-
crease in k3 values with increasing temperature may
be consistent with the fast configurational equilibrium
mechanism, where the proton transfer process is still
the rate-determining step. One might conclude that the
decrease in k3 values with increasing temperature is
due to the fact that the equilibrium is shifted contin-
uously toward the square planar structure, which may
react more slowly than the initial configuration struc-
ture with Mo [39].
when it was measured at 55◦C compared with that
at 30◦C, meaning that this complex still has a square
planar geometry with increasing temperature; (d) it is
observed that increasing the temperature from 30◦C
to 55◦C for the reaction of 3a with Mo in benzene
increases the intensity of bands and shoulders in the
range 500–660 nm (not shown). Points (a)–(c) ruled
out the formation of mono adduct 5a–5f and favor the
formation of intermediate 6a–6f.
Accordingly, the mechanism shown in Scheme 3
in which the probable pathway is the attack of Mo
on the C SCH3 close to the aryl group followed by
adding of the second Mo molecule to the Ni atom to
form an zwitterionic intermediate 6a–6f is largely con-
sistent with the previous facts. This is corroborated
on the basis that the monosubstituted monoadduct in-
termediate 7a–7f is reported to be thermodynamically
unstable [16] and consistent with the decrease in our k3
values with increasing temperature. This intermediate
undergoes elimination of Mo and CH3SH to give the
monosubstitution complex 4a–4f.
However, the last two mechanisms are not accepted
on the ground that (a) the electronic spectra of complex
3a in benzene showed no change at 30◦C and 55◦C;
(b) the addition of pyridine to a benzene solution of
3a (1:20 molar ratio) at 30◦C and 55◦C accompanied
by no change in the absorption bands characteristic of
the square planar form (SP). This observation ruled
out the formation of an octahedral bis-adduct; (c) the
complex 3a showed insignificant magnetic properties
BIBLIOGRAPHY
1. El-Sayed, L.; Iskander, M. F.; El-Toukhy, A. J Inorg
Nucl Chem 1974, 36, 1639.
2. Ali, M. A.; Livingstone, S. E.; Philips, D. J. Inorg Chim
Acta 1973, 7, 179.
3. Iskander, M. F.; Al-Toukhy, A.; Mishrikey, M. M. J Inorg
Chem 1980, 42, 361.
International Journal of Chemical Kinetics DOI 10.1002/kin

40
SHEHATA ET AL.
4. Ali, M. A.; Majumder, S. M. M.; Butcher, R. J.; Janiski,
J. P.; Jasinki, J. M. Polyhedron 1997, 16, 2749.
5. Singh, H. L.; Varshney, A. K. Appl Organometal Chem
2001, 15, 762.
6. Singh, H. L.; Varshney, A. K. Bioinorgchem Appl 2006,
23245.
7. Livingstone, S. E.; Dasbrit, M. J Cancer 1978, 37, 466.
8. Maiti, A.; Guha, A. K.; Gosh, S. J Inorg Biochem 1988,
33, 57.
9. Ali, M. A.; Livingotone, S. E. Coord Rev B, 1974, 101.
10. El-Toukhy, A.; Cai, G. Z.; Davies, G.; Gilbert, T. R.;
Onan, K. D.; Veidis, M. J Am Chem Soc 1984, 106,
4596.
11. Davies, G.; El-Sayed, M. A.; El-Toukhy, A.; Henary,
M.; Onan, K. D. Inorg Chem 1986, 25, 2373.
12. Davies, G.; El-Sayed, M. A.; El-Toukhy, A. Comments
Inorg Chem 1989, 8, 203.
13. Schumann, M.; Elias, H. Inorg Chem 1985, 24, 3187.
14. Fayyaz, M. U.; Grant, M. W. Aust J Chem 1979, 32,
2159.
26. (a) Demir, I.; Bayrakci, M.; Mutlu, K.; Pekacar, I. Acta
Chem Solv 2008, 55, 120; (b) Anacona, J. R.; Bastardo,
E. Transition Metal Chem 1999, 24, 478; (c) Shakir,
M. O.; Nasman, S. M.; Varkey, S. P. Polyhedron 1996,
15, 309.
27. (a) Ramana, N.; Mitub, L.; Sakthivela, A.; Pandia, M.
S. S. J Iran Chem Soc 2009, 6, 738; (b) Anacona, J.
R.; Bastardo, E. Transition Met Chem 1999, 24, 1478;
(c) Chande, S.; Sharma, S. D. Transition Met Chem
2002, 27, 732; (d) Lodeiro, C.; Basitida, R.; Bertolo, E.;
Macias, A.; Rodriq-uez, A. Transition Met Chem 2003,
28, 388.
28. (a) Tarafder, M. T. H.; Ali, M. A. Cand J Chem 1978, 56,
2000; (b) Ali, M. A.; Mirza, A. H.; Wei, L. K.; Bernhardt,
P. V.; Atchade, O.; Song, X.; Eng, G.; May, L. J. Coord
Chem 2010, 63, 1194, and references cited therein; (c)
Ali, M. A.; Mirza, A. H.; Bujang, F. H.; Haniti, M.;
Hamid, M. S. A.; Bernhardt, P. V. Polyhedron 2006,
25(17), 3245; Abou-Melha, K. S.; Faruk, H. J Iran Chem
Soc 2008, 5(1), 122.
15. Cattalini, L.; Ugo, R.; Orio, A. J Am Chem Soc 1968,
90, 4800.
16. Iskander, M. F.; El-Sayed, L.; El-Toukhy, A.; Shehata,
A. K. Inorg Chim Acta 1986, 123, 19.
17. Iskander, M. F.; El-Dessouky, M. A. Sallam, S. A.
J Inorg Nucl Chem 1976, 38, 2201.
18. Muetterties, E. L.; Schusen, R. A. Quart Rev Chem Soc
1966, 20, 245.
29. Shazly, R. M.; Al-Hazmi, G. A. A.; Ghazy, S. E.; El-
Shahawi, M. S.; El-Asmy, A. A. Spectrochim Acta A
2005, 61, 243.
30. Klayman, D. L.; Scovill, J. P.; Bartosevich, J. F. J Med
Chem 1979, 22,1367.
31. Massoud, S. S. Bull Chem Soc Ethiop 1987, 1, 27.
32. Chamberlain, R. A.; Crampton, M. R. J Chem Soc,
Perkin Trans 2 1995, 1831.
19. Clark, H. C.; Odell, A. L. J Chem Soc 1956, 520.
20. Mukherjee, J. Indian J Chem A 2008, 47, 207.
21. (a) Hamed, E. A. Int J Chem Kinet 1997, 29, 599;
(b) Hamed, E. A.; El-Bardan, A. A.; Gohar; G. A.; Has-
san, G. M. J Chem Soc, Perkin Trans 1997, 2, 2415;
(c) El-Hegazy, F. M.; Abdel-Fattah, S. Z.; Hamed, E.
A.; Sharaf, S. M. J Phys Org Chem 2000, 13, 549; (d)
Al-Howsaway, H. O. M.; Fathalla, M. F.; El-Bardan, A.
A.; Hamed, E. A. Chem Res 2007, 509; (e) Asghar, B.
H. M.; Fathalla, M. F.; Hamed, E. A. Int J Chem Kinet
2009, 41, 777.
33. Smith, M. B.; March, J. March’s Advanced Organic
Chemistry. 5th ed.; Wiley: New York, 2001.
34. (a) Isanbor, C.; Emokpae, T. A.; Crampton, M. R. J
Chem Soc, Perkin Trans 2 2002, 2019; (b) Crampton,
M. R.; Emokpae, T. A.; Isanbor, C.; Batsanov, A. S.;
Howard, J. A. K.; Mondal, R. Eur J Org Chem 2006,
1222; (c) Crampton, M. R.; Emokpae, T. A.; Isanbor,
C. Eur J Org Chem 2007, 1378 ; (d) Alvaro, C. E. S.;
Nudelman, N. S. Arkivoc 2003, 95; (e) Banjoko, O.;
Babatunde, I. A. Tetrahedron 2004, 60, 4645; (f) Harati,
M.; Gholami, M. R. Int J Chem Kinet 2005, 37, 90; (g)
Terrier, F. Nucleophilic Aromatic Displacement; VCH:
New York, 1991.
22. Audrieth, L. F.; Scott, E. S.; Skippur, P. J Org Chem
1953, 19, 733.
23. Brand, U.; Rombach, M.; Seebacher, J.; Vahrenkamp,
H. Inorg Chem 2001, 40, 6151.
35. Akinycle, E. T.; Onyido, I. J. J Chem Soc, Perkin Trans
2 1988, 1859.
24. Furnis, A. J.; Hannaord, A. J.; Smith, P. W. G.; Tatchell,
A. R. Vogel. Textbook of Practical Chemistry, 5th ed.
Longman: London, 1989.
36. Alvaro, C. E. S.; Nudelman, N. S. Arkiv 2003, 95, 106.
37. Jouanne, J. V.; Heidberg, J. J Am Chem Soc 1973, 95,
487.
25. Shinkai, S.; Yamashita, T.; Kusano, Y.; Manable, O.;
J Am Chem Soc 1981, 103, 2070.
38. Hirst, J.; Bankole, T. O. J Chem Soc B 1969, 848.
39. Bunnett, J. F. Quart Rev 1958, 12, 1.
International Journal of Chemical Kinetics DOI 10.1002/kin