Substitution reactions involving cyclometalated platinum(II) complexes: Kinetic investigations

Article abstract of DOI:10.1016/j.jorganchem.2011.08.005

Substitution reaction of the labile SMe₂ ligand in the cyclometalated platinum(II) complexes of general formula [PtAr(ppy)(SMe ₂), 1, in which ppy = deprotonated 2-phenylpyridyl and Ar = p-MeC₆H₄ or p-MeOC₆H₄, by several N or P donor reagents were studied; the N-donors, N, are pyridine (Py) and substituted pyridines, N = 4-MePy, Py, Py-d₅, 2-MePy, 3-PhPy, 3,4-Me₂Py, 4-^tBuPy or 3-C(O)OMePy, and the P-donors, L, are phosphines or phosphites, L = P(OPh)₃, P(O-ⁱPr) ₃, PPh₃, PPh₂Me and L₂ = Ph ₂PCH₂PPh₂, bis(diphenylphosphino)methane (dppm). The products were identified by multinuclear NMR studies as [PtAr(ppy)(N), 2, or [PtAr(ppy)(L), 3, respectively. Complexes 1 have a MLCT band in the visible region which was used to easily follow the kinetics of the ligand substitution reactions by UV-vis spectroscopy. Although the complexes 1 contain two cis Pt-C bonds, the substitution reactions followed a normal associative mechanism. The rates of reactions were depended on the concentration and the nature of the entering group. The ΔH^?/ ΔS^? compensation plot gave a straight line suggesting the operation of the same mechanism for all entering nucleophiles.

Full text of DOI:10.1016/j.jorganchem.2011.08.005

Journal of Organometallic Chemistry 696 (2011) 3564e3571
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Substitution reactions involving cyclometalated platinum(II) complexes: Kinetic
investigations
*
*
S. Masoud Nabavizadeh , Hamid R. Shahsavari, Masoud Namdar, Mehdi Rashidi
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
Article history:
Substitution reaction of the labile SMe2 ligand in the cyclometalated platinum(II) complexes of general
formula [PtAr(ppy)(SMe2)], 1, in which ppy ¼ deprotonated 2-phenylpyridyl and Ar ¼ p-MeC6H4 or p-
MeOC6H4, by several N or P donor reagents were studied; the N-donors, N, are pyridine (Py) and
substituted pyridines, N ¼ 4-MePy, Py, Py-d5, 2-MePy, 3-PhPy, 3,4-Me2Py, 4-tBuPy or 3-C(O)OMePy, and
Received 6 July 2011
Received in revised form
7 August 2011
Accepted 12 August 2011
the P-donors, L, are phosphines or phosphites,
L
¼
P(OPh)3, P(O-iPr)3, PPh3, PPh2Me and
L2 ¼ Ph2PCH2PPh2, bis(diphenylphosphino)methane (dppm). The products were identified by multinu-
clear NMR studies as [PtAr(ppy)(N)], 2, or [PtAr(ppy)(L)], 3, respectively. Complexes 1 have a MLCT band
in the visible region which was used to easily follow the kinetics of the ligand substitution reactions by
UVevis spectroscopy. Although the complexes 1 contain two cis PteC bonds, the substitution reactions
followed a normal associative mechanism. The rates of reactions were depended on the concentration
Keywords:
Cyclometalation
Organoplatinum
Substitution
Kinetics
and the nature of the entering group. The
operation of the same mechanism for all entering nucleophiles.
Ó 2011 Elsevier B.V. All rights reserved.
D D
Hz/ Sz compensation plot gave a straight line suggesting the
Mechanism
1. Introduction
potentially having bidentate donor abilities such as bipyridine,
phenanthroline or 1,2-(diphenylphosphino)ethane, have been
shown to occur through a dissociative path [12].
Ligand substitution reaction involving
a transition metal
complex is usually considered as a key step in many catalytic reac-
tions [1]. The related reactions on square planar platinum(II)
complexes have been extensively studied [2e7] and shown to
proceed usually via an associative process, implying direct attack of
the entering nucleophile on substratewith the formation of 18e five-
coordinated intermediates [8e10]. However, to the best of our
knowledge, such reactions have rarely been studied on cyclo-
metalated platinum complexes [11e16]. Kinetic studies of ligand
substitution on the cyclometalated platinum(II) complexes
[Pt(NeNeC)Cl] (NeNeCH ¼ 6-(1-methylbenzyl)-2,20-bipyridine)
[13] and [Pt(NeC)(N)(H2O)] (NeCH ¼ N,N-dimethylbenzylamine,
Transition metal cyclometalated complexes, in particular those
involving platinum, are of interest due to their potential applications
in many areas, such as chemosensors [17,18], photocatalysts [19,20],
and luminescent [21,22]. Square planar cyclometalated platinum
complexes have also been used as “building blocks” for complex
systems such as self-assembly [23], and dendrimers [24,25]. As such
we prompted to study the kinetics and mechanism of the ligand
substitution reactions concerning the lability of sulfur-bonded
dimethylsulfide in the cyclometalated platinum(II) complexes of
general formula [PtAr(ppy)(SMe2)], 1, in which ppy ¼ deprotonated
2-phenylpyridyl and Ar ¼ p-MeC6H4 or p-MeOC6H4, with different
nitrogen and phosphorous-donors. Despite the presence of two cis-
PteC bondings in the starting complexes 1, the kinetic investigations
comply with the substitution reactions proceeding via an associa-
tive mechanism.
N
¼
pySO3-3) [14,15] and on the cationic complex
[Pt(NeCeN)(H2O)]þ (NeCHeN ¼ 2,6-bis((dimethylamino)methyl)
phenyl) [16], each containing only one monodentate ligand for
substitution, have shown that the activation mode is associative in
nature. On the other hand, SMe2 substitution reactions in the
complexes [Pt(bph)(SMe2)2] (bph ¼ 2,20-biphenyl dianion) and
[PtPh2(SMe2)2], each bearing two PteC bondings, with reagents
2. Results and discussion
2.1. Synthesis and characterization of the complexes
* Corresponding authors. Tel.: þ98 711 228 4822; fax: þ98 711 228 6008.
E-mail addresses: nabavi@chem.susc.ac.ir(S. M. Nabavizadeh), rashidi@chem.susc.
ac.ir (M. Rashidi).
The general route used to prepare the cyclometalated organo-
platinum complexes are described in Scheme 1. The reaction of 2-
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.08.005

S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 696 (2011) 3564e3571
3565
N
N
Pt
Ar
+N
2a: Ar = p-MeOC6H4, N = 4-MePy;
2b: Ar = p-MeOC6H4, N = Py;
2c: Ar = p-MeOC6H4, N = Py-d5;
2d: Ar = p-MeOC6H4, N = 2-MePy;
2e: Ar = p-MeOC6H4, N = 3-PhPy;
2f: Ar = p-MeOC6H4, N = 3,4-Me2Py;
2g: Ar = p-MeOC6H4, N = 4-tBuPy;
2h: Ar = p-MeOC6H4, N = 3C(O)OMePy;
2i: Ar = p-MeC6H4, N = 4-MePy
N
SMe2
Ar
Ar
Ar
SMe2
SMe2
refluxe, 4 h
acetone
-SMe2
Pt
+
Pt
N
Ar = p-MeC6H4, p-MeOC6H4
1a: Ar = p-MeOC6H4;
1b: Ar = p-MeC6H4
+L
N
L
Pt
Ar
3a: Ar = p-MeC6H4, L = PPh3;
3b: Ar = p-MeC6H4, L = PPh2Me;
3c: Ar = p-MeC6H4, L = dppm;
3d: Ar = p-MeC6H4, L = P(OPh)3;
3e: Ar = p-MeC6H4, L = P(O-iPr)3;
3f: Ar = p-MeOC6H4, L = PPh3
Scheme 1.
phenylpyridine (ppyH) with the starting complexes [PtAr2(SMe2)2]
(Ar ¼ p-MeC6H4 or p-MeOC6H4) led to formation of the mono-
arylplatinum complexes [PtAr(ppy)(SMe2)], 1, believed to occur by
coordination of the nitrogen atom of the pyridyl group followed by
subsequent cyclometalation, as described elsewhere for other
similar reactions involving CeH bond activation and formation of
a new metalecarbon bond [26e30].
Reaction of the complexes [PtAr(ppy)(SMe2)], 1 (Ar ¼ p-MeC6H4
or p-MeOC6H4), with 1 equiv of either the nitrogen nucleophiles N
(N ¼ 4-MePy, Py, Py-d5, 2-MePy, 3-PhPy, 3,4-Me2Py, 4-tBuPy or
3-C(O)OMePy) or the phosphorous nucleophiles L (L ¼ PPh3,
PPh2Me, P(OPh)3, P(O-iPr)3, or L2 ¼ Ph2PCH2PPh2, dppm) proceeded
via displacement of the labile SMe2 ligand to give the complexes
[PtAr(ppy)(N)] or [PtAr(ppy)(L)], as depicted in Scheme 1.
the complexes 2 should be oriented perpendicular to the square
planar geometry of the platinum centers.
The complexes [Pt(p-MeC6H4)(ppy)(L)], 3, were characterized
using NMR (1H, 31P, 195Pt) spectroscopy as typically described for
[Pt(p-MeC6H4)(ppy)(PPh3)], 3a. In the 31P NMR spectrum of
complex 3a, the phosphorous atom appeared as a singlet signal at
d
¼ 31.8 which was coupled to platinum atom to give satellites with
1JPtP ¼ 2041 Hz. Consistent with this, in the 195Pt NMR spectrum of
3a, a doublet at ꢀ2435 with 1JPtP ¼ 2035 Hz was observed. In the 1H
NMR spectrum of complex 3a, a singlet signal was observed at
2.10 ppm for the Me group of the para-tolyl ligand. The ortho and
meta protons of the para-tolyl ligand appeared as two doublets at
m
o
d
¼ 6.43 and 6.99, respectively, each with 3JH
¼ 7.5 Hz; the ortho
H
protons further coupled to platinum to give satellites with
The complexes [Pt(p-MeOC6H4)(ppy)(N)], 2, were characterized
by 1H NMR spectroscopy. Typically, in the 1H NMR spectrum of
complex [Pt(p-MeOC6H4)(ppy)(4-MePy)], 2a, the methyl groups on
3JPtH ¼ 65.0 Hz. A doublet signal at
d
¼ 6.50, accompanied by
3
3
platinum satellites, with JHH ¼ 1.5 Hz and JPtH ¼ 12.5 Hz was
attributed to the hydrogen atom of CeH group adjacent to the
coordinated C atom of ppy ligand.
4-MePy and anisole ligands were observed at
d
¼ 2.30 and 3.70,
m o
respectively. A doublet signal at
d
¼ 8.61 (with 3JH
¼ 6.0 Hz), that
o
H
3
is accompanying by platinum satellites with JPtH ¼ 24.6 Hz, is
2.2. Kinetics and mechanism of the reactions
assigned to the two equivalent Ho protons of the 4-MePy ligand.
m
o
Notice that a similar doublet signal at
d
¼ 8.87 (with 3JH
¼ 6.3 Hz)
As was mentioned above, reactions of the complexes [PtAr(p-
py)(SMe2)], 1, with 1 equiv of either of the nitrogen or phosphorus
nucleophiles proceeded via displacement of the labile SMe2 ligand
to give the final complexes 2 or 3, respectively. This was typically
demonstrated by monitoring the reaction of complex [Pt(p-
MeOC6H4)(ppy)(SMe2)], 1a, with 3-PhPy in CDC13 by using 1H NMR
spectroscopy and the results are shown in Fig. 1S. Thus the singlet
signal at 2.20 ppm with platinum satellites with 3JPtH ¼ 25.0 Hz due
to coordinated dimethylsulfide protons was disappeared while the
corresponding signal for the free SMe2 ligand at 2.05 ppm was
appeared.
H
is assigned to the two equivalent Ho protons of the Py ligand in the
1H NMR spectrum of the complex [Pt(p-MeOC6H4)(ppy)(Py)], 2b,
which as expected was missed in the spectrum of related deuter-
ated complex [Pt(p-MeOC6H4)(ppy)(Py-d5)], 2c. This indicates that
the Ho of the N ligand in complexes 2 is expected to appear close to
d
¼ 8.70 and this should not be misassigned with the signal for
ortho hydrogen of ppy ligand (i.e. proton of CeH group locating
adjacent to coordinated nitrogen atom) which seems to be over-
lapped under the aromatic protons. The equivalency of the two Ho
of the N ligand in complexes 2 confirms that the pyridine ligands in

3566
S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 696 (2011) 3564e3571
The complexes 1 contain a band in the visible region which is
ascribed to the 5dp(Pt) / *(imine) metal-to-ligand charge-
The above results led us to propose an associative mechanism. A
p
second-order rate law (Eq. (3)), k2, was clearly obtained with
solvolytic path, k1, but no sign of any involvement of dissociative
transfer (MLCT) absorption and is believed to be responsible for the
color of the complex [5,31]. 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.
processes was observed. The rather large negative values of D
Sz (see
Table 1) for all the reactions strongly confirm the associative nature
of the ligand displacement.
ꢀd½complex1aꢂ=dt ¼ kobs½complex1aꢂ;kobs ¼ k1 þk2½Nꢂ
(3)
2.2.1. Kinetics of the reaction of complex 1a with N-donor
nucleophiles
The kinetic investigation using 1H NMR spectroscopy in CDCl3
was also performed typically for the reaction of complex [Pt(p-
MeOC6H4)(ppy)(SMe2)], 1a, with N ¼ 3-PhPy at 27 ꢁC (see Fig. 1S
and the above description) and the k2 value was obtained as
6.1 ꢃ10ꢀ2 L molꢀ1 sꢀ1, which is related to rate of replacement of the
labile SMe2 ligand with 3-PhPy. This value is very close to the value
of k2 ¼ ¼ 5.8 ꢃ 10ꢀ2 L molꢀ1 sꢀ1, measured for the same reaction in
CH2Cl2 solvent by using UVevis technique at 27 ꢁC and the value
k2 ¼ 6.5 ꢃ 10ꢀ2 L molꢀ1 sꢀ1 obtained at the same condition (at
27 ꢁC, in CHCl3) using UVevis spectroscopy (see Table 1).
Typically, the reaction of complex [Pt(p-MeOC6H4)(ppy)(SMe2)],
1a, and 4-MePy is described. As can be seen in Fig. 2S, the complex
1a has a maximum absorption band at 367 nm (spectrum 2b), while
the N-donor reagent 4-MePy contains no absorption band at this
point (spectrum 2a). The product complex [Pt(p-MeC6H4)(ppy)(4-
MePy)], 2a, has a maximum absorption band at 380 nm (spectra
2c and 2d). Thus, an excess of 4-MePy was used at 25 ꢁC and the
change of the MLCT band at
used to monitor the reaction. The change in the spectrum during
a typical run is shown in Fig. 1.
l
¼ 380 nm in a CH2Cl2 solution was
Rates of the reactions proceeding by an associative mechanism
must somehow be dependent on the nature of the entering group.
The rate of addition of N-donor ligands to [Pt(p-MeOC6H4)(p-
py)(SMe2)], 1a, is expected to be governed by both electronic and
steric effects [32]. Plot of the rate constants, k2, versus basicity of N-
donor nucleophile (each in logarithm scale), shown in Fig. 2, is
almost linear suggesting that increasing the basicity of entering
group has caused increasing the rate of reaction. Consistently when
the donor is 2-MePy, the related point is significantly off, con-
firming that the steric factor of Me group in ortho position of 2-
MePy is greatly influential in decreasing the rate of reaction.
Therefore, although the nucleophilicity of 2-MePy is greater than
that of Py, the rate of reaction of complex 1a with Py is more than 7
times faster than that with 2-MePy at the same condition (see
Table 1). Besides, the rate of the reaction of complex 1a with 4-
MePy, for example, at 10 ꢁC is more than 2 times faster than the
corresponding rate with Py at the same condition, confirming that
the dominating factor should be basicity of the 4-MePy (see Fig. 2).
The time-dependence curves of the spectra of the reaction in
CH2Cl2 at this condition are shown in Fig. 3S. 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)):
At ¼ AN þ ðA0 ꢀ ANÞ½expðꢀkobstÞꢂ
(1)
Plots of the first-order rate constants, kobs, versus [N-donor
ligands] was linear (Fig. 4S), showing a first-order dependence of
the rate on the concentration of N-donor ligands. The slope in each
case gave the second-order rate constant, and the results are
collected in Table 1. Therefore, the reaction obeys a simple second-
order rate law, first order in both the corresponding complex and
N-donor ligands. The same method was used at other tempera-
tures, and activation parameters were obtained from the Eyring
equation (see Eq. (2) and Fig. 5S). The data are collected in Table 1.
The D D
Hz/ Sz compensation plot for reactions of complex 1a with
ꢀ
ꢁ
ꢀ
ꢁ
k2
T
kB
h
D
R
Sz
D
RT
Hz
N-donor ligands in dichloromethane is shown in Fig. 3. A good
straight line is obtained that could probably be taken as an evidence
for operation of the same (associative, second-order) mechanism in
this series of reactions [33].
ln
¼ ln
þ
ꢀ
(2)
1.4
1.2
1
2.2.2. Kinetics of the reaction of complex 1b with P-donor
nucleophiles
The rates of reactions of complex 1b with phosphorus donor
reagents were found to be rather fast and it was not convenient to
measure the rates by common pseudo-first order technique.
Therefore, an equal molar of L was used at 25 ꢁC and the change of
the MLCT band at
l
¼ 364 nm in dichloromethane solution was
0.8
0.6
0.4
0.2
0
used to monitor the reaction; see Fig. 4 for a typical example of the
reaction of complex [Pt(p-MeC6H4)(ppy)SMe2], 1b, with dppm. The
reactions followed good second-order kinetics and the rate
constants, k2, were evaluated from the time-dependence curves of
the spectra of the reaction by fitting of the absorbanceetime
profiles to Eq. (4) [34,35]. The activation parameters were also
determined from measurement at different temperatures (see Eq.
(2) and Fig. 6S) and the data are given in Table 2. These reactions
followed good second-order kinetics, first order in both the cyclo-
metalated complex and the attacking nucleophile.
(a)
(b)
340
360
380
400
420
440
À
Á
λ / nm
A ¼ AN þ ðA0 ꢀ ANÞ= 1 þ ½complexꢂ0ꢃk ꢃ t
(4)
Fig. 1. Changes in the UVevis spectrum during the reaction of complex [Pt(p-
MeOC6H4)(ppy)SMe2], 1a (2 ꢃ 10ꢀ4 M) and 4-MePy (0.1 M) in CH2Cl2 at T ¼ 25 ꢁC: (a)
initial spectrum (before adding 4-MePy) and (b) spectrum at t ¼ 30 s; successive
spectra were recorded at intervals of 1 min.
The compensation between the enthalpic and entropic contri-
butions for reactions of complex 1b with P-donor reagents in
dichloromethane gave a good straight line as shown in Fig. 5. This

S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 696 (2011) 3564e3571
3567
Table 1
a
Second-order rate constants (L molꢀ1 sꢀ1
dichloromethane.
)
and activation parametersb for reaction of the complex [Pt(p-MeOC6H4)(ppy)(SMe2)], 1a, with the N-donor nucleophiles, N, in
Hs kJ molꢀ1 Ss J Kꢀ1 molꢀ1
N
pKa
102 k2 (105 k1) at different temperatures
D
D
10 ꢁC
15 ꢁC
20 ꢁC
25 ꢁC
30 ꢁC
35 ꢁC
3,4-Me2Py
4-MePy
6.46
5.94
2.9 (0.07)
3.6
5.1 (0.05)
5.2
8.1 (0.06)
7.6
10.5 (0.18)
10.8
57.1 ꢄ 0.7
54.2 ꢄ 0.3
ꢀ71 ꢄ 2
ꢀ81 ꢄ 1
11.9c
4-tBuPy
2-MePy
3C(O)OMePy
Py
5.8
5.9
3.13
5.23
4.85
4.5 (0.06)
6.8 (0.11)
0.5 (0.13)
3.1 (0.07)
4.2 (0.13)
5.3 (0.07)
8.9 (0.24)
0.9 (0.18)
4.1 (0.18)
6.3 (0.21)
6.4 (0.22)
6.5d (0.24)
14.1 (0.36)
1.2 (0.40)
5.4 (0.35)
8.6 (0.39)
9.9 (0.37)
50.5 ꢄ 0.4
82.3 ꢄ 0.9
48.8 ꢄ 0.6
53.8 ꢄ 0.5
44.2 ꢄ 0.6
ꢀ95 ꢄ 1
ꢀ7.4 ꢄ 2
ꢀ107 ꢄ 2
ꢀ87 ꢄ 2
3.3 (0.55)
8.7 (0.64)
1.7
3.2 (0.12)
3.6 (0.02)
3-PhPy
ꢀ118 ꢄ 2
a
Values in parentheses are k1, estimated errors in rate constants values are ꢄ5%.
b
c
Activation parameters were calculated from the temperature dependence of the second-order rate constant in the usual way using Eyring equation.
k2 for the reaction of complex [Pt(p-MeC6H4)(ppy)(SMe2)], 1b, with 4-MePy in CH2Cl2 at 25 ꢁC.
k2 at 27 ꢁC.
d
may be taken as an evidence for operation of the same (associative,
second-order) mechanism in this series of reactions.
The available experimental data support a rate law of the form
given in Eq. (5) for the substitution reactions involving complex 1b,
where [L] represents the concentration of the nucleophile and [M]
that of the cyclometalated platinum complex.
process suggested for the present ligand substitution reactions of
complex 1b, one might expect a lower rate for the larger entering
group. The fact that PPh3 is reacted faster than P(OPh)3 (see Table 2)
indicates that the dominating factor should be by far electronic. The
nucleophile P(O-iPr)3 has a lower
s-donor ability and Tolman cone
angle (130ꢁ) [36] than PPh3 and the related rate concerning
P(O-iPr)3 at different temperatures is rather faster than that of the
PPh3 (see Table 2), suggesting that the dominating factor should be
by far steric (see Table 2).
rate ¼ k2½Lꢂ½Mꢂ
(5)
The rate constant k2 corresponds to a direct SN2 substitution by
the nucleophile, with no any contribution from the solvent path, k1.
D
Sz (see Table 2) for all the reactions
3. Conclusions
The large negative values of
strongly confirm the associative nature of the ligand displacement.
Consistent with the proposed associative mechanism, the reactions
are dependent on the nature of the entering group (see Table 2).
Thus, for example the rate of the reactions of complex 1b with PPh3
at different temperatures is more than two times faster than those
Substitution reaction of the cyclometalated complex [Pt(p-
MeOC6H4)(ppy)SMe2], 1a, with pyridine and some other
substituted pyridine reagents, as revealed by using UVevis spec-
troscopy, is suggested to proceed by an associative SN2 mechanism,
and therefore the reaction rates should be dependent on the nature
of the entering nucleophile. As summarized in Table 1 and indi-
cated in Fig. 2, the rate of reactions involving N-donors are corre-
lated rather well with the basicity (pKa) of the entering group with
the following trend:
with P(OPh)3. PPh3 has a higher s-donor ability than P(OPh)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 square-pyramidal metallic center, it
is better able to cope with the electron density already present in
the same direction from the filled metal 5d2z orbital [3]. It is inter-
esting to note that the Tolman cone angle of PPh3 (145ꢁ) is signif-
icantly greater than that of P(OPh)3 (128ꢁ) [36]. In the associative
t
4 ꢀ MePyz3; 4 ꢀ Me2Py>4 ꢀ BuPy>3 ꢀ PhPy>Py>3
ꢀ CðOÞOMePy
-0.8
2-MePy
3,4-Me2Py
80
4-MePy
-1
3-PhPy
4-tBuPy
-1.2
70
Py
-1.4
-1.6
-1.8
-2
3-C(O)OMePy
60
3,4-Me2Py
Py
4-MePy
4-tBuPy
50
3-C(O)OMePy
2-MePy
6
3-PhPy
40
3
3.5
4
4.5
5
5.5
6.5
-120
-100
-80
-60
-40
-20
0
ΔS# / JK-1 mol-1
pk
a
Fig. 2. The plot of log k2 versus pka of entering ligand. 2-MePy was omitted form the
linear fit.
Fig. 3. The D DS
Hz/ z compensation plots of reaction of complex 1a with nucleophiles N
in CH2Cl2.

3568
S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 696 (2011) 3564e3571
significantly higher than those involving PPh3 despite of the fact
that P(O-iPr)3 has a lower
-donor ability than PPh3, indicating that
2
1.5
1
s
here the steric factor has been quite dominating. The reaction rates
involving P(O-iPr)3 nucleophile are significantly higher than those
involving P(OPh)3, with both having almost similar Tolman cone
angles. The reason here ought to be electronic; it is reasonable to
(a)
(b)
believe that the P(O-iPr)3 has a stronger
s-donor ability than
P(OPh)3, due to electron donating ability of iPr groups in the former
in contrast to electron withdrawing nature of Ph groups in the
latter. The reaction rates involving PPh3 nucleophile are nearly 2
times faster than those concerning the biphosphine nucleophile
bis(diphenylphosphino)methane, dppm, although it is reasonable
to assume that cone angle of the attacking part of dppm, i.e.
Ph2PCH2-, is smaller than that of PPh3. It is possible that when one
of the dppm phosphorus atoms is reacting with the complex 1b to
form the penta-coordinate intermediate containing a dangling
0.5
0
dppm ligand [Pt(p-MeC6H4)(ppy)(SMe2)(
rather electronegative free phosphorus atom withdraws electron
from the connecting phosphorus atom making it having a lower
h
1-dppm)], the other
340
360
380
400
420
440
λ / nm
s
-
donor ability than PPh3, indicating that the electronic factor has
been dominating.
Fig. 4. Changes in the UVevis spectrum during the reaction of complex [Pt(p-
MeC6H4)(ppy)SMe2], 1b (2.6 ꢃ 10ꢀ4 M) and dppm, under second-order 1:1 stoichio-
metric conditions, in CH2Cl2 at T ¼ 25 ꢁC: (a) initial spectrum (before adding dppm)
and (b) spectrum at t ¼ 30 s; successive spectra were recorded at intervals of 1 min.
In order to compare the abilities of the complexes [Pt(p-
MeOC6H4)(ppy)SMe2],1a, and [Pt(p-MeC6H4)(ppy)(SMe2)],1b, with
each other in terms of the above mentioned substitution reactions,
kinetics of reaction of the latter complex with 4-MePy was also
studied at 25 ꢁC (see Table 1). The results indicate that although the
metallic center of complex 1a is expected to be more electrophilic
as compared with that of the complex 1b, the reaction rates of both
complexes with 4-MePy at 25 ꢁC are almost the same within the
experimental errors. It is therefore concluded that the nature of
aromatic ligand, Ar, in complexes [PtAr(ppy)(SMe2)], 1, does not
seem to be significantly effective in the rates of their reactions with
the nitrogen donor entering reagents N. However, the related
reactions involving phosphine entering groups act differently. Thus,
complex 1b reacts some 70% faster (as compared to complex 1a)
with PPh3 at 25 ꢁC (see Table 2). The metallic center in complex 1b
is expected to be more electron rich as compared to that in complex
1a; the p-MeC6H4 ligand is considerably more electron donating
than the p-MeOC6H4 ligand. Therefore, in the penta-coordinate
intermediate formed through associative attack by the entering
ligand, PPh3, the extent of back donation from the filled d orbitals of
platinum is expected to be bigger in the reaction involving the
starting complex 1b (as compared with complex 1a). This is sug-
gested to make the related intermediate more stable and thus
causing its reaction rate faster than that for the related reaction
involving the starting complex 1a.
However, when the donor is 2-MePy, the steric factor of Me
group in ortho position of 2-MePy is greatly influential in
decreasing the rate of reaction.
The substitution reactions of the complex [Pt(p-MeC6H4)(p-
py)(SMe2)], 1b, with phosphorus nucleophiles are generally pro-
ceeded much faster than those involving the nitrogen nucleophiles.
This observation complies well with the phosphorus donors being
soft (as compared with the nitrogen donors that are hard) when
they react with the platinum center of complex that is soft. Thus,
rates of the related substitution reactions involving phosphorus
donors, using UVevis spectroscopy, were too fast to be studied by
more traditional pseudo-first order method and so second-order
technique was used to measure the rate constants by employing
1:1 molar ratio of the complex: reagent. The following trend was
observed for rates of reactions of the phosphorus donors with
complex 1b:
i
PðO ꢀ PrÞ3>PPh3>PðOPhÞ3zdppm
Steric and electronic effects have been responsible for the trend.
The reaction rates of complex 1b with PPh3 at different tempera-
tures are more than two times faster than those with P(OPh)3,
having a rather lower Tolman cone angle (128ꢁ) as compared to that
of PPh3 with its Tolman cone angle being considerably bigger
(145ꢁ). Here the electronic effect has been dominating as PPh3 has
The complexes 1 have two PteC bonds that should labilize the
PteS bond significantly to enable a dissociative substitution
mechanism. However, the in plane pyridine ligand can cause
a significant pi-back bonding with the metal 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.
a higher s-donor ability (enabling it to better coping with the filled
metal 5dz2 orbital of the platinum center) than P(OPh)3. In contrast,
the reaction rates involving P(O-iPr)3 nucleophile (having a Tolman
cone angle of 130ꢁ, which is smaller than that of PPh3) are
Table 2
Second-order rate constantsa and activation parametersb for reaction of the complex [Pt(p-MeC6H4)(ppy)(SMe2)], 1b, with the P-donor nucleophiles, L, in dichloromethane.
L
k2(L molꢀ1 sꢀ1) at different temperatures
D
Hs kJ molꢀ1
D
Ss J Kꢀ1 molꢀ1
5
ꢁC
10 ꢁC
100.8
15 ꢁC
122.0
20 ꢁC
147.8
25 ꢁC
30 ꢁC
186.4
35 ꢁC
204.6
PPh3
84.6
169.8
104.3c
101.8
94.6
19.1 ꢄ 0.1
ꢀ139 ꢄ 1
dppm
31.2
37.0
96.7
42.2
46.5
114.6
59.8
58.3
137.6
78.1
75.7
163.5
122.6
108.7
233.1
140.3
124.7
263.2
34.2 ꢄ 0.2
27.3 ꢄ 0.1
22.0 ꢄ 0.1
ꢀ92 ꢄ 1
ꢀ116 ꢄ 1
ꢀ127 ꢄ 1
P(OPh)3
P(O-iPr)3
197.7
a
Estimated errors in k2 values are ꢄ3%.
b
c
Activation parameters were calculated from the temperature dependence of the second-order rate constant in the usual way using Eyring equation.
k2 from reaction of the complex [Pt(p-MeOC6H4)(ppy)(SMe2)], 1a, with PPh3 in CH2Cl2 at 25 ꢁC.

S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 696 (2011) 3564e3571
3569
a green solid was dried under vacuum. Yield 18 mg; 84%,
40
35
30
25
20
15
mp ¼ 218 ꢁC (decomp.). Anal. Calcd. for C24H22N2OPt: C, 52.5; H, 4.0;
N, 5.1; Found: C, 52.8; H, 4.0; N, 5.2.1H NMR data in CDCl3:
Me group on the 4-MePy ligand,1 Me), 3.68 (s, OMe group on the p-
d
¼ 2.30 (s,
dppm
m
o
anisol ligand, 1 Me), 6.58 (d, 3JH
¼ 8.6 Hz, Hm of p-anisol ligand, 2
H
m
o
H), 7.12 (d, 3JH
¼ 6.0 Hz, Hm of 4-MePy ligand, 2 H), 7.34 (d,
H
o
m
o
3JH H ¼ 8.6 Hz, 3JPtH ¼ not resolved, Ho of p-anisol ligand, 2 H), 7.62
3
3
P(OPh)
(d, JHH ¼ 5.3 Hz, JPtH ¼ 19.1, CH group adjacent to coordinated N
atom of ppy ligand, 1 H), 6.91e7.73 (aromatic protons), 8.61 (d,
3
o
m
o
3JH H ¼ 6.0 Hz, 3JPtH ¼ 24.6 Hz, Ho of 4-MePy ligand, 2 H).
The following complexes were made similarly by using the
appropriate N-donor nucleophiles:
P(O-iPr)
3
4.1.1.1. [Pt(p-MeOC6H4)(ppy)(Py)],
2b. Yield
16
mg;
77%,
PPh
mp ¼ 225 ꢁC (decomp.). Anal. Calcd. for C23H20N2OPt: C, 51.6; H, 3.8;
3
N, 5.2; Found: C, 52.0; H, 3.9; N, 5.4. 1H NMR data in CDCl3:
d
¼ 3.76
m
o
(s, OMe group on the p-anisol ligand, 1 Me), 6.66 (d, 3JH
¼ 8.3 Hz,
H
-150 -140 -130 -120 -110 -100 -90
-80
m
o
H
m of p-anisol ligand, 2 H), 7.23 (dd, 3JH
¼ 6.3 Hz, Hm of Py ligand,
H
ΔS# / JK-1 mol-1
o
m
o
2 H), 7.41 (d, 3JH H ¼ 8.3 Hz, 3JPtH ¼ 69.7, Ho of p-anisol ligand, 2 H),
7.01e7.65 (aromatic protons), 7.80 (d, 3JHH ¼ 6.1 Hz, 3JPtH ¼ 18.6, CH
group adjacent to coordinated N atom of ppy ligand, 1 H), 8.87 (d,
Fig. 5. The
D D
Hz/ Sz compensation plots of reaction of complex 1b with the P-donor
nucleophiles L in CH2Cl2.
o
m
o
3JH H ¼ 6.3 Hz, 3JPtH ¼ 23.1 Hz, Ho of Py ligand, 2 H).
4. Experimental
4.1.1.2. [Pt(p-MeOC6H4)(ppy)(Py-d5)], 2c. 1H NMR data in CDCl3:
d
¼ 3.69 (s, OMe group on the p-anisol ligand, 1 Me), 6.59 (d,
The 1H and 13C NMR spectra were recorded on a Bruker Avance
DPX 250 MHz spectrometer and the 31P and 195Pt NMR spectra were
recorded on a Bruker Avance DRX 500 MHz spectrometer. The
operating frequencies and references, respectively, are shown in
m o o m
3JH
¼ 8.2 Hz, Hm of p-anisol ligand, 2 H), 7.36 (d, 3JH H ¼ 8.2 Hz,
H
3JPtH ¼ 68.4, Ho of p-anisol ligand, 2 H), 6.91e7.60 (aromatic
o
3
3
protons), 7.72 (d, JHH ¼ 5.9 Hz, JPtH ¼ 18.1, CH group adjacent to
coordinated N atom of ppy ligand, 1 H).
parentheses as follows: 1H (250 MHz, TMS), 13C (69 MHz, TMS), 31
P
(202 MHz, 85% H3PO4), and 195Pt (107 MHz, aqueous Na2PtCl4). The
chemical shifts and coupling constants are in ppm and Hz, respec-
tively. The microanalyses were performed using a Thermofinigan
Flash EA-1112 CHNSO rapid elemental analyzer. Kinetic studies were
carried out by using a PerkineElmer Lambda 25 spectrophotometer
with temperature control using an EYELA NCB-3100 constant-
temperature bath. 2-phenylpyridine was purchased from Aldrich,
and the monomeric precursors cis-[PtAr2(SMe2)2] (Ar ¼ p-MeC6H4
or p-MeOC6H4) were made by the known methods [37]. The
complexes [Pt(p-MeOC6H4)(ppy)(SMe2)], 1a, [Pt(p-MeC6H4)(p-
4.1.1.3. [Pt(p-MeOC6H4)(ppy)(2-MePy)], 2d. Yield 15 mg; 71%,
mp ¼ 221 ꢁC (decomp.). Anal. Calcd. for C24H22N2OPt: C, 52.5; H, 4.0;
N, 5.1; Found: C, 52.1; H, 3.9; N, 5.4.1H NMR data in CDCl3:
d
¼ 2.95 (s,
Me group on the 2-MePy ligand, 1 Me), 3.74 (s, OMe group on the
m
o
p-anisol ligand,1 Me), 6.64 (d, 3JH
¼ 8.4 Hz, Hm of p-anisol ligand,
H
o
m
o
2 H), 7.45 (d, 3JH H ¼ 8.4 Hz, 3JPtH ¼ 67.2 Hz, Ho of p-anisol ligand, 2
3
o m
H), 7.02e7.80 (aromatic protons), 8.97 (d, JH H
¼
5.1 Hz,
o
3JPtH ¼ 21.6 Hz, Ho of 2-MePy ligand, 1 H).
4.1.1.4. [Pt(p-MeOC6H4)(ppy)(3-PhPy)], 2e. Yield 19 mg; 80%,
mp ¼ 223 ꢁC (decomp.). Anal. Calcd. for C29H24N2OPt: C, 57.0; H,
4.0; N, 4.6; Found: C, 57.4; H, 4.1; N, 4.8. 1H NMR data in CDCl3:
py)(SMe2)], 1b, and [Pt(p-MeC6H4)(ppy)(
h
1-dppm)], 3c, were
¼ 20.2 (s, Me of SMe2
prepared as reported [27]. For 1a: 13C NMR:
d
ligand, 2 C), 55.0 (s, OMe group on the p-anisol ligand, 1 C), 114.0 (s,
d
¼ 3.76 (s, OMe group on the p-anisol ligand, 1 Me), 6.68 (d,
o
m
2JPtC ¼ 83 Hz, Co of p-anisol ligand, 2 C),136.9 (s, 3JPtC ¼ 20 Hz, Cm of
p-anisol ligand, 2 C), 139.0 (s, Cp of p-anisol ligand, 1 C), 147.0 (s, C
atom of the p-anisol ligand connected to Pt atom, 1 C), ppy carbons,
123.0 (s, C atom which is connected to Pt atom, 1 C), 119.0 (s, 1 C),
122.3 (s, 1 C), 123.8 (s, 1 C), 130.0 (s, 1 C), 137.0 (s, 1 C). For 1b: 13C
m o o m
3JH
¼ 8.6 Hz, Hm of p-anisol ligand, 2 H), 7.44 (d, 3JH H ¼ 8.6 Hz,
H
o
3JPtH ¼ not resolved, Ho of p-anisol ligand, 2 H), 7.00e7.81
3
3
(aromatic protons), 7.98 (d, JHH ¼ 5.4 Hz, JPtH ¼ 19.3, CH group
adjacent to coordinated N atom of ppy ligand, 1 H), 8.83 (d,
6
5
3
6
3JH H ¼ 4.6 Hz, JPtH ¼ 20.3, H6 of 3-PhPy ligand, 1 H), 9.15 (s,
NMR:
d
¼ 20.2 (s, Me of SMe2 ligand, 2 C), 21.0 (s, Me group on the p-
2
3JPtH ¼ 21.6 Hz, Ho of 3-PhPy ligand, 1 H).
o
tolyl ligand,1 C),128.0 (s, 2JPtC ¼ 74 Hz, Co of p-tolyl ligand, 2 C),136.8
3
m
(s, JPtC ¼ 17 Hz, Cm of p-tolyl ligand, 2 C), 138.0 (s, Cp of p-tolyl
4.1.1.5. [Pt(p-MeOC6H4)(ppy)(3,4-Me2Py)], 2f. Yield 12 mg; 56%,
mp ¼ 196 ꢁC (decomp.). Anal. Calcd. for C25H24N2OPt: C, 53.3; H, 4.3;
1
ligand, 1 C), 146.7 (s, JPtC ¼ 538 Hz, C atom of the p-tolyl ligand
connected to Pt atom, 1 C), ppy carbons, 123.4 (s, 1JPtC ¼ 538 Hz, C
atom which is connected to Pt atom, 1 C), 119.0 (s, JPtC ¼ 17 Hz, 1 C),
122.3 (s, JPtC ¼ 6 Hz, 1 C), 123.8 (s, JPtC ¼ 6 Hz, 1 C), 130.2 (s,
JPtC ¼ 79.3 Hz, 1 C), 137.4 (s, JPtC ¼ 74 Hz, 1 C).
N, 5.0; Found: C, 53.8; H, 4.4; N, 5.2.1H NMR data in CDCl3:
Me group on the 3,4-MePy ligand in para postion, 1 Me), 2.32 (s, Me
group on the 3,4-MePy ligand in meta postion, 1 Me), 3.63 (s, OMe
d
¼ 2.20 (s,
group on the p-anisol ligand, 1 Me), 6.39 (d, 3JH
¼ 8.1 Hz, Hm of p-
m
o
H
o
m
o
anisol ligand, 2 H), 7.62 (d, 3JH H ¼ 8.1 Hz, 3JPtH ¼ not resolved, Ho of
4.1. Synthesis
p-anisol ligand, 2 H), 6.83e8.14 (aromatic protons), 8.32
3
3
(d, JHH ¼ 6.1 Hz, JPtH ¼ 18.1, CH group adjacent to coordinated N
3
2
4.1.1. Preparation of the complex [Pt(p-MeOC6H4)(ppy)(4-MePy)], 2a
To a solution of [Pt(p-MeOC6H4)(ppy)(SMe2)], 1a, (20 mg,
atom of ppy ligand, 1 H), 8.66 (s, JPtH ¼ 19.4 Hz, H2 of 3,4-MePy
3
6
5
3
6
ligand, 1 H), 9.90 (d, JH H ¼ 5.6 Hz, JPtH ¼ 20.8 Hz, H6 of 3,4-
0.04 mmol) in acetone (20 ml) was added 4-MePy (4
m
L, 0.04 mmol),
MePy ligand, 1 H).
and the solution was stirred for 3 h. A green solution was formed,
then the solvent was removed under reduced pressure and the
residue was triturated with cold acetone (2 ꢃ 3 mL). The product as
4.1.1.6. [Pt(p-MeOC6H4)(ppy)(4-tBuPy)], 2g. Yield 17 mg; 75%,
mp ¼ 238 ꢁC (decomp.). Anal. Calcd. for C27H28N2OPt: C, 54.9; H, 4.8;

3570
S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 696 (2011) 3564e3571
N, 4.7; Found: C, 55.0; H, 4.8; N, 4.6.1H NMR data in CDCl3:
d
¼ 1.33 (s,
p-tolyl ligand, 2 H), 7.16e7.87 (aromatic protons), 9.24 (d,
3
tBu group on the 4-tBuPy ligand, 3 Me), 3.81 (s, OMe group on the
3JHH ¼ 4.5 Hz, JPtH ¼ 17.8 Hz, CH group adjacent to coordinated N
m
o
p-anisol ligand,1 Me), 6.65 (d, 3JH
¼ 8.5 Hz, Hm of p-anisol ligand,
atom, 1 H); 31P NMR:
d
¼ 116.0 (s, 1JPtP ¼ 3517 Hz, 1 P).
m
o
2 H), 7.36 (d, 3JH
¼ 5.1 Hz, HmHof 4-tBuPy ligand, 2 H), 7.43 (d,
H
o
m
o
3JH H ¼ 8.5 Hz, 3JPtH ¼ 63.4 Hz, Ho of p-anisol ligand, 2 H), 7.54 (d,
3JHH ¼ 5.6 Hz, 3JPtH ¼ 18.4, CH group adjacent to coordinated N atom
of ppy ligand, 1 H), 7.00e7.80 (aromatic protons), 8.74 (d,
4.1.2.3. [Pt(p-MeC6H4)(ppy)[P(O-iPr)3], 3e. Yield (as yellowish oil),
almost quantitative. NMR data in CDCl3: 1H NMR:
d
¼ 1.23[d,
3JHH ¼ not resolved, 12Me groups of iPr, 36H], 2.28 (s, Me group on
o
m
o
i
3JH H ¼ 5.1 Hz, 3JPtH ¼ 22.3 Hz, Ho of 4-tBuPy ligand, 2 H).
the p-tolyl ligand, 1 Me), 4.82 [m, 6CH groups of Pr, 6H], 6.87 (d,
m
o
3 o m
3JH
¼ 7.2 Hz, Hm of p-tolyl ligand, 2 H), 7.38 (d, JH H ¼ 7.2 Hz,
H
o
4.1.1.7. [Pt(p-MeOC6H4)(ppy)(3C(O)OMePy)], 2h. Yield 19 mg; 83%,
mp ¼ 232 ꢁC (decomp.). Anal. Calcd. for C25H22N2O3Pt: C, 50.6; H, 3.7;
3JPtH ¼ 66.5 Hz, Ho of p-tolyl ligand, 2 H), 7.06e7.90 (aromatic
protons), 9.33 (d, 3JHH ¼ 4.8 Hz, 3JPtH ¼ 18.3 Hz, CH group adjacent
N, 4.7; Found: C, 50.1; H, 3.6; N, 4.5.1H NMR data in CDCl3:
d
¼ 3.75 (s,
to coordinated N atom, 1 H); 31P NMR:
d
¼ 125.6 (s, 1JPtP ¼ 3485 Hz,
s, OMe group on the p-anisol ligand, 1 Me), 3.96 (s, OMe group of
1 P); 195Pt NMR:
d
¼ ꢀ2429 (d, 1JPtP ¼ 3476 Hz, 1 Pt).
m
o
3C(O)OMePy ligand, 1 Me), 6.66 (d, 3JH
¼ 8.6 Hz, Hm of p-anisol
H
o
m
o
ligand, 2 H), 7.50 (d, 3JH H ¼ 8.6 Hz, 3JPtH ¼ 62.6 Hz, Ho of p-anisol
ligand, 2 H), 7.81 (d, 3JHH ¼ 5.5 Hz, 3JPtH ¼ 18.1, CH group adjacent to
coordinated N atom of ppy ligand, 1 H), 7.00e8.44 (aromatic
4.1.2.4. [Pt(p-MeOC6H4)(ppy)(PPh3)], 3f. Yield 22 mg; 82%,
mp ¼ 233 ꢁC (decomp.). Anal. Calcd. for C36H30NOPPt: C, 60.2; H, 4.2;
N, 2.0; Found: C, 60.6; H, 4.3; N, 2.1. NMR data in CDCl3: 1H NMR:
6
5
6
protons), 8.98 (d, 3JH H ¼ 4.3 Hz, 3JPtH ¼ 21.3 Hz, H6 of 3C(O)OMePy
d
¼ 3.67 (s, OMe group on the p-anisol ligand, 1 Me), 6.30 (d,
2
m
3JH
o
3
ligand, 1 H), 9.56 (s, 3JPtH ¼ 22.7 Hz, H2 of 3C(O)OMePy ligand, 1 H).
¼ 8.6 Hz, Hm of p-tolyl ligand, 2 H), 6.50 (d, JHH ¼ 2.4 Hz,
H
3JPtH ¼ 13.7 Hz, CH group adjacent to coordinated C atom,1 H), 7.01 (d,
3JH H ¼ 8.6 Hz, 3JPtH ¼ 65.8 Hz, Ho of p-tolyl ligand, 2 H), 7.08e7.85
o
m
o
4.1.1.8. [Pt(p-MeC6H4)(ppy)(4-MePy)], 2i. Yield 17 mg; 80%,
mp ¼ 238 ꢁC (decomp.). Anal. Calcd. for C24H22N2Pt: C, 54.0; H, 4.2;
(aromatic protons); 31P NMR:
d
¼ 30.7 (s, 1JPtP ¼ 2029 Hz, 1 P).
N, 5.3; Found: C, 54.3; H, 4.3; N, 5.1. 1H NMR data in CDCl3:
d
¼ 2.24
(s, Me group on the p-anisol ligand, 1 Me), 2.37 (s, Me group on the
4.2. Kinetic studies
4-MePy ligand, 1 Me), 6.83 (d, 3JH
¼ 7.2 Hz, Hm of p-tolyl ligand, 2
m
o
H
m
o
H), 7.20 (d, 3JH
¼ 5.0 Hz, Hm of 4-MePy ligand, 2 H), 7.41 (d,
H
For the reactions with N-donors: in a typical experiment,
a solution of [Pt(p-MeOC6H4)(ppy)(SMe2)], 1a, in dichloromethane
(3 ml, 2 ꢃ 10ꢀ4 M) in a cuvette was thermostated at 25 ꢁC and
3JH H ¼ 7.2 Hz, JPtH ¼ 61.9 Hz, Ho of p-tolyl ligand, 2 H), 7.78 (d,
3JHH ¼ 4.8 Hz, 3JPtH ¼ 19.6, CH group adjacent to coordinated N atom
of ppy ligand, 1 H), 6.95e7.67 (aromatic protons), 8.72 (d,
o
m
3
o
a known excess of a solution of 4-MePy in dichloromethane (30 ml,
o
m
3
o
3JH H ¼ 5.0 Hz, JPtH ¼ 22.8 Hz, Ho of 4-MePy ligand, 2 H).
1 M) was added using a microsyringe. After rapid stirring, the
absorbance at
l
¼ 380 nm was monitored with time. The same
4.1.2. Preparation of the complex [Pt(p-MeC6H4)(ppy)(PPh3)], 3a
method was used at other temperatures.
To
a solution of [Pt(p-MeC6H4)(ppy)(SMe2)], 1b, (20 mg,
For the reaction with P-donors: in a typical experiment, a solu-
tion of [Pt(p-MeC6H4)(ppy)(SMe2)], 1b, in dichloromethane (3 ml,
2.6 ꢃ 10ꢀ4 M) in a cuvette was thermostated at 25 ꢁC and a solution
0.04 mmol) in acetone (20 ml) was added PPh3 (11 mg, 0.04 mmol),
and the solution was stirred for 1 h. A green solution was formed,
then the solvent was removed under reduced pressure and the
residue was triturated with cold acetone (2 ꢃ 3 mL). The product as
a green solid was dried under vacuum. Yield 23 mg; 82%,
mp ¼ 250 ꢁC (decomp.). Anal. Calcd. for C36H30NPPt: C, 61.6; H, 4.3;
N, 2.0; Found: C, 61.8; H, 4.5; N, 1.9. NMR data in CDCl3: 1H NMR:
of dppm in dichloromethane (78
ml, 0.01 M) was added using
a microsyringe. After rapid stirring, the absorbance at
was monitored with time. The same method was used at other
temperatures.
l
¼ 364 nm
4.3. 1H NMR study of reaction of [Pt(p-MeOC6H4)(ppy)(SMe2)], 1a,
with N-donor ligand
d
¼ 2.10 (s, Me group on the p-tolyl ligand, 1 Me), 6.43 (d,
m
3JH
o
3
¼ 7.5 Hz, Hm of p-tolyl ligand, 2 H), 6.50 (d, JHH ¼ 1.5 Hz,
H
3JPtH ¼ 12.5 Hz, CH group adjacent to coordinated C atom, 1 H), 6.99
3
o
m
3
o
(d, JH H ¼ 7.5 Hz, JPtH ¼ 65.0 Hz, Ho of p-tolyl ligand, 2 H),
For the experiment using 1H NMR spectroscopy, to a sample of
complex [Pt(p-MeOC6H4)(ppy)(SMe2)], 1a, (10 mg, 0.02 mmol) in
CDCl3 (0.75 mL) in an NMR tube was added 3-PhPy ligand (30 ml,
0.02 mmol) and the disappearance of signal of the SMe2 ligand
connected to platinum center atom and the appearance of the
signal for the free SMe2 ligand were used to monitor the reaction.
7.06e7.84 (aromatic protons); 31P NMR:
d
¼ 31.8 (s, 1JPtP ¼ 2041 Hz,
1 P); 195Pt NMR:
d
¼ ꢀ2435 (d, 1JPtP ¼ 2035 Hz, 1 Pt).
The following complexes were made similarly by using the
appropriate P-donor nucleophile:
4.1.2.1. [Pt(p-MeC6H4)(ppy)(PPh2Me)], 3b. Yield 19 mg; 75%,
mp ¼ 218 ꢁC (decomp.). Anal. Calcd. for C31H28NPPt: C, 58.1; H, 4.4;
N, 2.2; Found: C, 57.6; H, 4.4; N, 1.9. NMR data in CDCl3: 1H NMR:
Acknowledgments
d
¼ 1.40 (d, 2JPH ¼ 8.8 Hz, 3JPtH ¼ 35.0 Hz, Me group of the PPh2Me
We thank the Shiraz University Research Council, Iran, for
financial support.
ligand, 1 Me), 2.24 (s, Me group on the p-tolyl ligand, 1 Me), 6.53 (d,
3JHH ¼ 1.7 Hz, JPtH ¼ 13.2 Hz, CH group adjacent to coordinated C
3
atom, 1 H), 6.79 (d, 3JH
¼ 7.5 Hz, Hm of p-tolyl ligand, 2 H), 7.31 (d,
m
o
H
Appendix. Supplementary material
o
m
o
3JH H ¼ 7.5 Hz, 3JPtH ¼ 60.0 Hz, Ho of p-tolyl ligand, 2 H), 7.08e7.82
(aromatic protons); 31P NMR:
d
¼ 14.5 (s, 1JPtP ¼ 1997 Hz, 1 P); 195Pt
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.08.005.
NMR:
d
¼ ꢀ2413 (d, 1JPtP ¼ 1990 Hz, 1 Pt).
4.1.2.2. [Pt(p-MeC6H4)(ppy)[P(OPh)3], 3d. Yield 21 mg; 73%,
mp ¼ 167 ꢁC. Anal. Calcd. for C36H30NO3PPt: C, 57.6; H, 4.0; N, 1.9;
References
Found: C, 57.2; H, 4.0; N,1.8. NMR data in CDCl3: 1H NMR:
d
¼ 2.25 (s,
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Me group on the p-tolyl ligand, 1 Me), 6.75 (d, 3JH o ¼ 7.5 Hz, Hm of
H
3
o
m
3
p-tolyl ligand, 2 H), 7.11 (d, JH H ¼ 7.5 Hz, JPtH ¼ 61.4 Hz, Ho of

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