Substitution reactions of NN chelating atoms of organoplatinum (II) complexes with phosphorous donor reagents

Article abstract of DOI:10.1016/j.jorganchem.2012.11.042

Substitution reactions of the chelate 2,2′-bipyridine ligand in the organoplatinum(II) complexes of general formula [PtR₂(NN)] (NN = 2,2′-bipyridine, and R = CH₃, 1, or R = p-CH₃C ₆H₄, 1′) by the P donor reagents L, L = P(O- ⁱPr)₃ or PPh₃ or L₂ = dppm, bis(diphenylphosphino)methane, to form the complexes cis-[R₂PtL ₂] were studied. Each of the complexes 1 and 1′ has an MLCT band in the visible region which was used to easily follow kinetics of the related ligand substitution reactions by UV-Vis spectroscopy. Although the complex 1 or 1′ contains two cis Pt-C bonds, the involved substitution reaction followed a normal associative mechanism. The reaction rates were found to be dependent on concentration and nature of the entering group, while independent of the presence of excess free NN leaving group. Reaction of the complex 1 with P(O-ⁱPr)₃ proceeded some 20 times faster than similar reaction with the complex 1′. The ΔH ^?/ΔS^? compensation plot gives a straight line suggesting operation of the same mechanism involving all the entering nucleophiles.

Full text of DOI:10.1016/j.jorganchem.2012.11.042

Journal of Organometallic Chemistry 725 (2013) 22e27
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Substitution reactions of NN chelating atoms of organoplatinum (II)
complexes with phosphorous donor reagents
,
a
b
b,
S. Jafar Hoseini a , Hasan Nasrabadi , S. Masoud Nabavizadeh , Mehdi Rashidi
*
**
a Department of Chemistry, Faculty of Sciences, Yasouj University, Yasouj 74831, Iran
b Department of Chemistry, Faculty of Sciences, Shiraz University, Shiraz 71454, Iran
a r t i c l e i n f o
a b s t r a c t
Substitution reactions of the chelate 2,20-bipyridine ligand in the organoplatinum(II) complexes of
general formula [PtR2(NN)] (NN ¼ 2,20-bipyridine, and R ¼ CH3, 1, or R ¼ p-CH3C6H4, 10) by the P donor
reagents L, L ¼ P(OeiPr)3 or PPh3 or L2 ¼ dppm, bis(diphenylphosphino)methane, to form the complexes
cis-[R2PtL2] were studied. Each of the complexes 1 and 10 has an MLCT band in the visible region which
was used to easily follow kinetics of the related ligand substitution reactions by UVeVis spectroscopy.
Although the complex 1 or 10 contains two cis PteC bonds, the involved substitution reaction followed
a normal associative mechanism. The reaction rates were found to be dependent on concentration and
nature of the entering group, while independent of the presence of excess free NN leaving group.
Reaction of the complex 1 with P(OeiPr)3 proceeded some 20 times faster than similar reaction with the
Article history:
Received 24 August 2012
Received in revised form
26 November 2012
Accepted 30 November 2012
Keywords:
Organoplatinum complex
Kinetic
Substitution reaction
Phosphorous donor
D D
complex 10. The Hz/ Sz compensation plot gives a straight line suggesting operation of the same
mechanism involving all the entering nucleophiles.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
or 1,2-(diphenylphosphino)ethane, have been investigated and
shown to occur through a dissociative path [11]. The ligand disso-
ciation step is facilitated by the strong trans-influence of the alkyl or
aryl group, which weakens the MeL bonds, while the alternative
associative mechanism is less favored because the electron-rich
platinum center is resistant to nucleophilic attack [11]. Previously,
we have investigated the substitution reactions involving the binu-
Organoplatinum complexes propose extensive scope fordifferent
studies including design of catalysis for organic synthesis and
exploring new therapeutic agents, in which substitution reactions
play an important role. Thus, for example a key concept in designing
anticancer complexes is optimization of their chemical reactivity in
ligand substitution reactions to allow facile attack on the target site
(e.g., DNA) yet avoid attack on other sites associated with unwanted
side effects [1,2]. Ligand substitution reactions on square planar
platinum(II) complexes have been extensively studied [2e8] and are
usually interpreted in terms of an associative process, which
implies the formation of 18e five-coordinated intermediates [9,10].
However, to the best of our knowledge, such reactions have not been
studied on reactions during which a neutral chelate ring opening
is taken place in organoplatinum complexes. On the other hand,
chelate ring closure reactions in the complexes [Pt(bph)(S(CH3)2)2]
clear organoplatinum(II) complex cis,cis-[(CH3)2Pt(
meNN)(me
dppm)Pt(CH3)2], in which dppm bis(diphenylphosphino)
¼
methane and NN ¼ phthalazine, with different phosphorus nucle-
ophiles L, L ¼ P(OeiPr)3 or PPh3, or L2 ¼ dppm, using UVeVis spec-
troscopy, suggesting to proceed via the normal associative pathway
[5]. In this work, we present substitution reactions of the chelate
ligand NN of [PtR2(NN)] (NN ¼ 2,20-bipyridine, and R ¼ CH3, 1, or
R ¼ p-CH3C6H4,10) by monodentate and bidentate phosphine ligands
using UVeVis spectroscopy.
The phosphine reagent PPh3 has a higher s-donor ability than
(bph
¼
2, 20-biphenyl dianion) and [PtPh2(S(CH3)2)2], each
the phosphite reagent P(OeiPr)3, and therefore when the lone pair
of electrons of PPh3 entering ligand is binding to the low lying
platinum 6 pz orbital to form the initial transition state containing
the squareepyramidal metallic center, it is better able to cope with
the electron density already present in the same direction from the
filled metal 5dz2 orbital [4]. In contrast, however, PPh3 has a Tolman
angle (145ꢀ) greater than that of P(OeiPr)3 (130ꢀ) making nucleo-
philic attack of the former on the metallic center harder than that of
P(OeiPr)3. Both these steric and electronic effects would influence
bearing two PteC bonding, with reagents potentially having
bidentate chelate donor abilities such as bipyridine, phenanthroline
* Corresponding author. Tel.: þ98 741 2223048; fax: þ98 741 3342172.
** Corresponding author. Tel.: þ98 711 228 4822; fax: þ98 711 228 6008.
E-mail addresses: jhosseini@yu.ac.ir, sjhoseini54@yahoo.com (S.J. Hoseini),
rashidi@chem.susc.ac.ir (M. Rashidi).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.11.042

S.J. Hoseini et al. / Journal of Organometallic Chemistry 725 (2013) 22e27
23
H3C
H3C
N
N
H3C
H3C
L
L
+2 L
Pt
Pt
-NN
1
+2 dppm
L
-NN
P(O-iPr)3 2a
PPh3
2b
H3C
H3C
P
P
P
H3C
H3C
P
P
Pt
dppm
+
Pt
P
2c
p-CH3C6H4
p-CH3C6H4
p-CH3C6H4
P(O-iPr)3
P(O-iPr)3
N
N
+2 P(O-iPr)3
Pt
Pt
-NN
p-CH3C6H4
1'
2'a
N
N
P
=
N
N
dppm = Ph2PCH2PPh2
=
P
Scheme 1.
rate of the substitution reactions of these monodentate phosphines
with Pt(II) complexes [3,5]. Besides, it has previously been described
for the reaction of [Pt(p-CH3C6H4)(ppy)S(CH3)2] with PPh3 or dppm
[8] that the complex reacted faster with PPh3 than with dppm. This
has been attributed to the domination of electronic factor over steric
factor. Thus, although cone angle of the attacking part of dppm, i.e.
Ph2PCH2ꢁ, is smaller than that of PPh3, when one of the dppm
phosphorus atoms is reacting with the complex to form the
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
(a)
(b)
1.4
1.2
1
0.8
0.6
0.4
0.2
0
400
450
500
550
wavelength (nm)
0
2
4
6
time (min)
8
10
Fig. 1. Changes in the UVeVis spectrum during the reaction of complex [Me2Pt(NN)], 1,
(3 ꢂ 10ꢁ4 M) and P(OeiPr)3 (0.015 M) in acetone at T ¼ 25 ꢀC: (a) initial spectrum
(before adding P(OeiPr)3) and (b) spectrum at t ¼ 10 s; successive spectra were
recorded at intervals of 1 min.
Fig. 2. Absorbanceetime curves for the reaction of complex 1 with P(OeiPr)3 (0.015e
0.116 M, [P(OeiPr)3] increases reading downward) in acetone at 25 ꢀC.

24
S.J. Hoseini et al. / Journal of Organometallic Chemistry 725 (2013) 22e27
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
-5
T= 35 °C
-5.5
(a)
(b)
T= 30 °C
-6
(c)
T= 25 °C
-6.5
T= 15 °C
-7
0
0.02
0.04
0.06
0.08
0.1
0.12
i
[P(O-Pr) ] / M
3
-7.5
3.2
3.25
3.3
3.35
1000/T (K )
3.4
3.45
3.5
Fig. 3. Plots of first-order rate constants (kobs/sꢁ1) for the reaction of complex 1 with
P(OeiPr)3 in acetone at different temperatures vs. concentration of P(OeiPr)3.
-1
Fig. 4. Eyring plots for the reaction of complex 1 with: (a) PPh3; (b) dppm; (c) P(Oe
related penta-coordinate intermediate [Pt(p-CH3C6H4)(ppy)
S(CH3)2(h1edppm)], the other rather electronegative free phos-
phorus atom withdraws electron from the connecting phosphorus
iPr)3 in acetone.
atom making it having a lower s-donor ability than PPh3.
displacement of the chelate bipyridine ligand to give the final
complexes 2. The complexes 1 and 10 contain a band in the visible
region which is ascribed to the 5dp(Pt)
p*(imine) MLCT band
2. Results
and is believed to be responsible for the color of the complex [5,8].
This was used to monitor the reactions of complexes with donor
nucleophiles in order to investigate the kinetics of reactions by
using UVeVis spectroscopy, as will be described below. Typically,
the reaction of complex [Pt(CH3)2(NN)], 1, and P(OeiPr)3 is
described. As can be seen in Fig. 1, the complex 1 has a maximum
absorption band at 475 nm and upon reaction of the reddish
complex 1 with the phosphorus donors, L, the color is gradually
faded away and eventually an almost colorless solution is obtained.
Thus, an excess of L was used at 25 ꢀC and the disappearance of the
2.1. Reaction of the organoplatinum(II) complexes with P-donor
ligands
Reactions of the diorganoplatinum(II) complexes [PtR2(NN)]
(NN ¼ 2,20-bipyridine, and R ¼ CH3, 1, or R ¼ p-CH3C6H4, 10) with 2
equiv of
L2
L
nucleophile (L
¼
P(OeiPr)3 or PPh3, or
¼
bis(diphenylphosphino)methane, dppm) proceeded as
described in Scheme 1 by displacement of the NN chelating ligand
in each case with L to form the complexes 2, almost quantitatively
in pure form. In the reaction involving substitution of dppm, it is
suggested that the intermediate product [Pt(CH3)2(h1edppm)2] is
formed first and then it would dissociate rapidly in solution to give
the final product, identified as complex 2c [12]. When the
complexes 1 and 10 were reacted with a large excess of L or L2, the
MLCT band at
l
¼ 475 nm in acetone solution was used to monitor
the reaction. The timeedependence curves of the spectra of the
reaction in acetone are shown in Fig. 2. Thus, the pseudo-first order
rate constants kobs were evaluated by nonlinear least-squares fitting
of the absorbanceetime profiles to the monophasic first order
equation (Eq. (1)):
same products
reactions.
2 were isolated with effectively no further
The complexes 2 and 20a were identified by comparison of their
At ¼ AN þ ðA0 ꢁ ANÞðexpðꢁkobstÞÞ
(1)
1H NMR spectra with those of the authentic samples [6,12].
The reactions followed good first order kinetics (Fig. 2). Graphs
of these first-order rate constants against the concentration of the
nucleophile L gave good straight line plots passing through origin,
showing a first-order dependence of the rate on the concentration
of L (Fig. 3). The slope in each case gave the second-order rate
constant, and the results are collected in Table 1. The same method
2.2. Kinetic study of the substitution reactions
As was mentioned above, reactions of the complexes [PtR2(NN)],
1 or 10, with 2 equiv of phosphorus nucleophiles proceeded via
Table 1
Second-order rate constants (102 k2/L molꢁ1 sꢁ1
)
a and activation parameters (
D
Hz in kJ molꢁ1
,
D
Sz in J Kꢁ1 molꢁ1
)
b for reaction of the complex [PtR2(2,20-bipyridine)], (R ¼ Me,1
and R ¼ p-CH3C6H4, 10) with the nucleophile L (L ¼ PPh3 and P(OeiPr)3) or L2 ¼ dppm) in acetone.
Reagent
Complex
15 ꢀC
25 ꢀC
30 ꢀC
35 ꢀC
D
Hz
D
Sz
P(OeiPr)3
PPh3
1
1
1
10
21.0(0.0)
27.0(0.2)
22.2(0.1)
0.93(0.01)
38.7(0.1)
56.3(0.4)
46.0(0.4)
1.9(0.0)
50.9(0.2)
76.1(0.7)
61.4(0.3)
2.4(0.0)
66.4(0.3)
110.2(0.5)
88.3(0.5)
3.3(0.0)
40.2(0.5)
49.0(1.1)
48.1(1.2)
50.0(1.3)
ꢁ118(1.8)
ꢁ85(3.8)
ꢁ90(4.2)
ꢁ127(4.3)
dppm
P(OeiPr)3
a
Second-order rate constant values, and associated errors, are given based on 95% confidence limits from least-squares regression analysis.
Obtained from the Eyring equation.
b

S.J. Hoseini et al. / Journal of Organometallic Chemistry 725 (2013) 22e27
25
bond lengthening
L
L
H3C
H3C
N
N
H3C
H3C
N
N
N
+ L
Pt
Pt
H3C
Pt
k2
N
CH3
4
1
3
trigonal bipyramide
Pt center
square pyramide
Pt center
PtN bond PtL bond
breaking strenghtening
(fast)
H3C
H3C
L
H3C
Pt
H3C
L
L
+L
-NN
fast
Pt
N
N
2
5
Scheme 2.
was used at other temperatures, and activation parameters were
obtained from the Eyring equation (see Eq. (2) and Fig. 4) and
the data are given in Table 1. In Eq. (2), kB is the Boltzmann constant,
h is the Planck constant, R is the gas constant and ln(kB/h) has
a value of 23.76.
center, which will decrease the electron density on the metal center
and make it more electrophilic to enable an associative attack by
the entering ligands. We therefore suggest that as shown in Scheme
2, the first mole of L has an associative nucleophilic attack on the
platinum(II) center of complex 1, and so the first step, which is rate
determining, is proceeded via the usual five coordinated transition
states with a square pyramid and a trigonal bipyramid geometries,
3 and 4, respectively, to give the intermediate 5. The second mole of
L completely replaces the NN ligand by a rate which is much faster
than the rate of replacement of the first L.
lnðk2=TÞ ¼ lnðkB=hÞ þ
D
Sz=R ꢁ
D
Hz=RT
(2)
We also measured the rate constant of the reactions in the
presence of excess free bipyridine (NN) and found no change in the
rate constants. Thus, for example, rate constant (k2) for the reaction
of [Pt(CH3)2(NN)], 1, with excess P(OeiPr)3 at 25 ꢀC is
38.7(0.1) ꢂ 10ꢁ2 L molꢁ1 sꢁ1 (see Table 1), and that for the same
reaction in the presence of excess NN was measured to be
The D D
Hz/ Sz compensation plot for reactions of complex 1 with
P-donor nucleophiles in acetone is shown in Fig. 5. A good straight
line is obtained and this may be taken as an evidence for operation
of the same mechanism (associative, second-order) in this series of
reactions.
38.1(0.1) ꢂ 10ꢁ2 L molꢁ1 sꢁ1
.
The kinetic of the substitution reaction involving the chelate
ring opening of [(p-CH3C6H4)2Pt(NN)], 10, with P(OeiPr)3 was
investigated similarly at different temperatures. The reaction fol-
lowed a second order rate law (Fig. 6). This reaction occurs nearly
20 times slower than the similar reaction for complex 1, due to
3. Discussion
The above studies led us to propose the associative mechanism
shown in Scheme 2. A simple second-order rate law (Eq. (3)) was
clearly obtained with absolutely no sign of any dissociative or
solvolytic paths.
50
ꢁd½complex 1ꢃ=dt ¼ kobs½complex 1ꢃ; kobs ¼ k2½Lꢃ
(3)
Sz (see Table 1) for all the
dppm
PPh3
The rather large negative values of
D
48
46
44
42
40
38
36
reactions strongly confirm the associative mechanism. A further
support for the proposed associative mechanism comes from the
fact that the rate of the reactions is dependent on the nature of the
entering group (see Table 1), but independent of presence of excess
free NN leaving group. The following trend was observed for rates
of reactions of the phosphorus donors with complex
1:PPh3 > dppm > P(OeiPr)3. Rate of the reaction of complex 1 with
PPh3 in acetone at 25 ꢀC is 1.5 times faster than the corresponding
rate with P(OeiPr)3 at the same condition due to lower n0Pt value of
P(OeiPr)3 as compared with that of the PPh3 [5]. This trend is
P(O–iPr)3
similar to that observed for the reaction of cis,cis-[(CH3)2Pt(
me
NN)( edppm)Pt(CH3)2] with corresponding phosphorus nucleo-
m
philes [5]. An opposite trend has been seen for the substitution
reactions of the complex [Pt(p-CH3C6H4)(ppy)(S(CH3)2)], with
phosphorus nucleophiles [8]. The complex 1 has two PteC bonds
that should labilize the PteC bond significantly to enable a disso-
ciative substitution mechanism. However, the in plane bipyridine
-120
-110
-100
-90
-80
‡
ΔS / J K
-1
Fig. 5. The
nucleophiles in acetone.
D D
Hz/ Sz compensation plots of reaction of complex 1 with the P-donor
ligand can cause a significant
p-back bonding with the metal

26
S.J. Hoseini et al. / Journal of Organometallic Chemistry 725 (2013) 22e27
0.014
0.012
0.01
i) The types of ancillary ligands present in the complexes, i.e. 2
N ligands in the complex 10 as compared to one N and one S
ligands in the cyclometalated complex [Pt(p-CH3C6H4)(ppy)
S(CH3)2]. S-donor ligand has weaker
donor ligand and also the former ligand forms a better
s
-donor ability than N-
-back
p
T = 35 °C
bonding, as compared to N-donor ligand, with the metallic
center. Both these effects would significantly increase the
positive charge density on the platinum center in the
complex [Pt(p-CH3C6H4)(ppy)S(CH3)2] as compared to that in
the complex 10 causing the former complex being signifi-
cantly more prone to substitution reactions than the latter
complex.
0.008
0.006
0.004
0.002
0
T = 30 °C
T = 25 °C
ii) The lower steric influence around the Pt center of the
complex [Pt(p-CH3C6H4)(ppy) S(CH3)2], as compared to that
in the complex [(p-CH3C6H4)2Pt(NN)], 10, would also help in
increasing the related rates of the former complex. Both
complexes have one p-CH3C6H4 ligand, but the other
aromatic ligand in complex [Pt(p-CH3C6H4)(ppy)S(CH3)2] is
involved in cyclometalation and so is expected to be
oriented coplanar with the squareeplanar geometry,
creating less steric influence when compared with
the aromatic ligand p-CH3C6H4 in complex 10, that is ex-
pected to be perpendicular to plane of the squareeplanar
geometry.
T = 15 °C
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
i
[P(O-Pr) ] / M
3
Fig. 6. Plots of first-order rate constants (kobs/sꢁ1
) for the reaction of [(p-
CH3C6H4)2Pt(NN)] complex with P(OeiPr)3 in acetone at different temperatures vs.
concentration of P(OeiPr)3.
more steric effect of p-CH3C6H4, indicative of associative
mechanism.
The complex [Pt(CH3)2(NN)], 1, reacted faster with PPh3 than
with bis(diphenylphosphino)methane, dppm; for example the
reaction rates involving PPh3 and dppm at 25 ꢀC are 56.3 ꢂ 10ꢁ2
L molꢁ1 sꢁ1 and 46.0 ꢂ 10ꢁ2 L molꢁ1
s
ꢁ1, respectively. This obser-
4. Conclusion
vation confirms the assumption suggested previously (see the
Introduction).
The substitution reactions of the organoplatinum(II) complexes
[PtR2(NN)], (R ¼ CH3, 1, R ¼ p-CH3C6H4, 10), with different phos-
phorus nucleophiles L, L ¼ P(OeiPr)3 or PPh3, or L2 ¼ dppm, were
investigated using UVeVis spectroscopy and suggested to proceed
via the normal associative pathway. Observation of the large
negative entropies of activation, the significant dependency of the
rate on both concentration and nature of the entering nucleophile,
L (Table 1), and independency of the rate in presence of excess free
NN leaving group, supported the proposed mechanism.
The substitution reactions of the complex [(p-CH3C6H4)2-
Pt(NN)],10, with P(OeiPr)3 are generally proceeded much slower, by
a factor of nearly 20, than those involving the complex 1; for
example the reactionꢁr2ates involving complex 1 and complex 10 at
25 ꢀC are 38.7 ꢂ 10 L molꢁ1 sꢁ1 and 1.9 ꢂ 10ꢁ2 L molꢁ1 sꢁ1
,
respectively. We believe that in this case the higher steric effect of
p-CH3C6H4 ligands in the complex 10 (considering that these
aromatic ligands stay perpendicular to the plane of the related
squareeplanar complex), as compared to that of CH3 ligands in
complex 1, is greatly influential in decreasing the rate of reactions.
All these observations comply well with the proposed associative
mechanism.
In the reaction involving the CH3 complex [Pt(CH3)2(NN)], 1, in
acetone solvent, the nucleophile PPh3 is reacted slightly faster than
P(OeiPr)3 (by a factor of nearly 1.5); for example the reaction rates
involving PPh3 and P(OeiPr)3 at 25 ꢀC are 56.3 ꢂ 10ꢁ2 L molꢁ1 sꢁ1
and 38.7 ꢂ 10ꢁ2 L molꢁ1
s
ꢁ1, respectively. Thus, it could be
concluded that in these two types of phosphorous donors the steric
and electronic effects compensate each other causing their reaction
rates with complex 1 being close to each other. Also, as has been
reported previously, the reaction rates for cyclometalated complex
[Pt(p-CH3C6H4)(ppy)S(CH3)2], in which ppy ¼ deprotonated 2-
phenylpyridyl [8], with PPh3 and P(OeiPr)3 at 25 ꢀC (in CH2Cl2) are
5. Experimental
The 1H NMR spectra of the complexes were recorded in CDCl3
solutions on a Bruker Avance DPX 250 MHz spectrometer and
TMS (0.00) was used as external reference. Kinetic studies were
carried out by using a PerkineElmer Lambda 25 spectropho-
tometer with temperature control using an EYELA NCB-3100
constant-temperature bath. The [Pt(CH3)2(NN)], 1, was made as
described in the literature [13]. The final products complexes 2
were fully identified according to their 1H NMR spectra reported
earlier [6,12].
close to each other but with PPh3 (169.8 L molꢁ1
slightly slower than P(OeiPr)3 (197.7 L molꢁ1
s
ꢁ1) reacting
ꢁ1). A slight
s
discrepancy in the trends of reaction rates with PPh3 and P(OeiPr)3
in these two types of reactions can be related to the solvent effect
on these reagents. The latter reagent is expected to be more polar
than PPh3 and so its interaction, as compared to PPh3, with acetone
solvent molecules (used in the present study) is more pronounced
than that with CH2Cl2 solvent molecules (used in the reference 8)
slightly affecting the reaction rates. It is also interesting to notice
that the reactions of PPh3 and P(OeiPr)3 with the cyclometalated
complex [Pt(p-CH3C6H4)(ppy)S(CH3)2] [8], proceed some 8000e
10,000 times faster as compared to those studied at the present
work involving the complex [(p-CH3C6H4)2Pt(NN)], 10, containing
bipyridine ligand. We attribute this rather huge difference to the
following factors:
5.1. Kinetic study
In a typical experiment, a solution of complex 1 in acetone (3 ml,
3 ꢂ 10ꢁ4 M) in a cuvette with a 1 cm path length was thermostated
at 25 ꢀC and a known excess of P(OeiPr)3 (50
ml, 4.37 M) was added
using a micro syringe. After rapid stirring, the absorbance at
l
¼ 475 nm was monitored with time. The same reaction was
performed in the presence of excess NN ligand (10 equiv,
3 ꢂ 10ꢁ3 M).

S.J. Hoseini et al. / Journal of Organometallic Chemistry 725 (2013) 22e27
27
[5] S.J. Hoseini, S.M. Nabavizadeh, S. Jamali, M. Rashidi, J. Organomet. Chem. 692
(2007) 1990e1996.
Acknowledgments
[6] A.R. Esmaeilbeig, H.R. Samouei, M. Rashidi, J. Organomet. Chem. 693 (2008)
2519e2526.
We thank the Yasouj University and the Shiraz University
[7] M. Rashidi, S.M. Nabavizadeh, A. Zare, S. Jamali, R.J. Puddephatt, Inorg. Chem.
49 (2010) 8435e8443.
Research Councils, Iran, for financial support.
[8] S.M. Nabavizadeh, H.R. Shahsavari, M. Namdar, M. Rashidi, J. Organomet.
Chem. 696 (2011) 3564e3571.
References
[9] R.G. Wilkins, Kinetics and Mechanisms of Reactions of Transition Metal
Complexes, VCH, Weinheim, Germany, 1991.
[10] F. Basolo, Coord. Chem. Rev. 154 (1996) 151e161.
[11] M.R. Plutino, L.M. Scolaro, R. Romeo, A. Grassi, Inorg. Chem. 39 (2000) 2712e
2720 (and references therein).
[12] F.S.M. Hassan, D.M. McEwan, P.G. Pringle, B.L. Shaw, J. Chem. Soc. Dalton
Trans. (1985) 1501e1506.
[13] J.D. Scott, R.J. Puddephatt, Organometallics 2 (1983) 1643e1648.
[1] M. Frezza, Q.P. Dou, Y. Xiao, H. Samouei, M. Rashidi, F. Samari,
B. Hemmateenejad, J. Med. Chem. 54 (2011) 6166e6176.
[2] F. Wang, A. Habtemariam, E.P.L. vanderGeer, R. Fernandez, M. Melchart,
R.J. Deeth, R. Aird, S. Guichard, F.P.A. Fabbiani, P. Lozano-Casal, I.D.H. Oswald,
D.I. Jodrell, S. Parsons, P.J. Sadler, Proc. Natl. Acad. Sci. 102 (2005) 18269e18274.
[3] M.L. Tobe, J. Burgess, Inorganic Reaction Mechanism, Longman, Essex, UK, 1999.
[4] D.T. Richens, Chem. Rev. 105 (2005) 1961e2002.