Cycloplatinated(II) complex bearing 2-vinylpyridine and monodentate phosphine ligands: Optical properties and kinetic study

Article abstract of DOI:10.1016/j.jorganchem.2015.12.005

The 2-vinylpyridinate complex [PtMe(Vpy)(DMSO)], C, is successfully prepared from dimeric platinum(II) complex cis,cis-[Me₂Pt(μ-SMe₂)₂PtMe₂], B, in the presence of DMSO and 2-vinylpyridine ligand. The DMSO molecule in complex C can be readily substituted by methyldiphenylphosphine (PPh₂Me), allowing synthesis of [PtMe(Vpy)(PPh₂Me)], 1, which has been fully characterized spectroscopically. Complex 1 is emissive in solid state and solution at room temperature and at 77 K. This complex displays an intense phosphorescence emission (with a significantly long lifetime) which is originated from mixed ³ILCT/³MLCT excited state. Additionally, complex 1 undergoes oxidative addition with alkyl halide (MeI) bearing [PtMe₂I(Vpy)(PPh₂Me)], 2, after 2 h. Kinetic studies suggest that the latter reaction (oxidative addition) proceed by a classical S_N2 mechanism. The rate of oxidative addition reaction at different temperatures is measured and high negative ΔS^# value is obtained for the reaction which supported the proposed mechanism. On the basis of NMR spectroscopy, when complex 1 reacts with MeI under extended time (5 days), complex 2 gradually converts to a mixture of platinum complexes trans-[PtMeI(PPh₂Me)₂], 3, [{PtMe₂(Vpy)₂(μ-I)₂], 4, and a free ligand Z/E-[C₈H₉N], 5, based on the carbon-carbon bond coupling.

Full text of DOI:10.1016/j.jorganchem.2015.12.005

Journal of Organometallic Chemistry 803 (2016) 82e91
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Cycloplatinated(II) complex bearing 2-vinylpyridine and monodentate
phosphine ligands: Optical properties and kinetic study
Maryam Niazi, Hamid R. Shahsavari*
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), No. 444, Yousef Sobouti Blvd., P. O. Box 45195-1159, Zanjan 45137-6731,
Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 July 2015
The 2-vinylpyridinate complex [PtMe(Vpy)(DMSO)], C, is successfully prepared from dimeric platinum(II)
complex cis,cis-[Me2Pt(m-SMe2)2PtMe2], B, in the presence of DMSO and 2-vinylpyridine ligand. The
Received in revised form
20 October 2015
Accepted 4 December 2015
Available online 12 December 2015
Dedicated to Professor Elena Lalinde on the
occasion of her 60th birthday.
DMSO molecule in complex C can be readily substituted by methyldiphenylphosphine (PPh2Me),
allowing synthesis of [PtMe(Vpy)(PPh2Me)], 1, which has been fully characterized spectroscopically.
Complex 1 is emissive in solid state and solution at room temperature and at 77 K. This complex displays
an intense phosphorescence emission (with a significantly long lifetime) which is originated from mixed
3ILCT/3MLCT excited state. Additionally, complex 1 undergoes oxidative addition with alkyl halide (MeI)
bearing [PtMe2I(Vpy)(PPh2Me)], 2, after 2 h. Kinetic studies suggest that the latter reaction (oxidative
addition) proceed by a classical SN2 mechanism. The rate of oxidative addition reaction at different
Keywords:
temperatures is measured and high negative DS
# value is obtained for the reaction which supported the
proposed mechanism. On the basis of NMR spectroscopy, when complex 1 reacts with MeI under
extended time (5 days), complex 2 gradually converts to a mixture of platinum complexes trans-
2-Vinylpyridine
Cycloplatinated
Photophysical properties
Oxidative addition
Kinetics
[PtMeI(PPh2Me)2], 3, [{PtMe2(Vpy)2(
ecarbon bond coupling.
m
-I)2], 4, and a free ligand Z/E-[C8H9N], 5, based on the carbon
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
chemistry of such complexes is undiscovered against 2-
phenylpyridinate and/or benzoquinolate complexes (I and II,
respectively, in Scheme 1) [2,50,51]. In such ligand, platinum metal
Growing interest in organometallic complexes containing
cyclometalated ligands [1e3] is conditioned by their highly versa-
tile applications in myriad of fields such as biology [4e8], organic
synthesis [9e11], catalysts [12e14] and optoelectronic materials
[15e19] with useful potential application in organic light-emitting
diode (OLED) devices [20e25] or molecular sensors [26e29]. In the
midst of these cyclometalated compounds, mono alkyl or mono
aryl cycloplatinated complexes bearing a labile leaving group such
as SMe2 [30e32], DMSO [27,32e34], CH3COCH3 [35] have been
extensively studied on account of their different reactivities toward
fundamental organometallic reactions [36e46].
Several C^N cyclometalating ligands have been utilized in the
above mentioned cycloplatinated complexes as these ligands pro-
vide a five-membered chelate which induces chemical stability to
metal complexes (Scheme 1). 2-vinylpyridinate ligand (V in Scheme
1) [47e49] is a new type of ligand in cycloplatination and the
center is bound to the b carbon atom in the vinyl group instead of to
aromatic ring through a vinylic CeH bond activation [48].
The present study introduce a new method for preparation of 2-
vinylpyridinate complex [PtMe(Vpy)(DMSO)], C [48], from dimeric
methyl platinum complex B in high yield [52,53]. In addition, the
possibility of substitution reaction of the DMSO solvent with a
phosphine ligand (L ¼ PPh2Me) is investigated. Characterization,
photophysical behavior and systematic temperature dependence
kinetic study involving oxidative addition reaction of MeI with the
new corresponding phosphine complex [PtMe(Vpy)(PPh2Me)], 1,
are also studied. Our results moreover indicate that Pt(IV) complex
[PtMe2I(Vpy)(PPh2Me)], 2, is not stable in solution and is converted
to a mixture of compounds.
2. Result and discussion
Among various platinum precursors, monomeric or dimeric
organoplatinum(II) derivatives containing labile leaving groups
* Corresponding author.
E-mail address: shahsavari@iasbs.ac.ir (H.R. Shahsavari).
http://dx.doi.org/10.1016/j.jorganchem.2015.12.005
0022-328X/© 2015 Elsevier B.V. All rights reserved.

M. Niazi, H.R. Shahsavari / Journal of Organometallic Chemistry 803 (2016) 82e91
83
N
N
O
N
N
N
N
N
I
II
III
IV
V
Scheme 1. Different cyclometalating ligands.
with general formula cis-[PtMe2(DMSO)2], A [54e56], or cis,cis-
[Me2Pt( -SMe2)2PtMe2], B [52,53,57], respectively, are convenient
(L ¼ PPh2Me) in a 1:1.2 ratio gave the corresponding complex
[PtMe(Vpy)(PPh2Me)], 1, as presented in Scheme 4. This complex
was isolated as a stable orange solid and characterized by 1H and
31P {1H} NMR spectroscopy (Figs. S3 and S4, respectively). In the 1H
NMR spectrum of 1, the MePt resonance appeared as a doublet with
m
and notable starting materials for CeH bond activation. Using these
precursors, different neutral methyl cycloplatinated(II) complexes
[PtMe(C^N)S], in which S ¼ DMSO or SMe2 and C^N ¼ different
deprotonated cyclometalating ligands such as 2-phenylpyridine
(ppy) [30,32,58], 7,8-benzoquinoline (bzq) [37,59,60], rollover of
2,20-bypiridyne (N0-bpy-H), have been prepared [34,40,42].
platinum satellite at
d
¼ 0.98 ppm (2JPtH ¼ 84.3 Hz), due to coupling
with phosphorus and platinum center. The signal was observed as a
doublet accompanied with platinum satellite at
d
¼ 2.03 ppm can
Recently, 2-vinylpyridine (VpyH) [33,48,61e64] has been used
in cyclometalation reaction with precursor A in different reaction
be attributed to Me group bound to phosphorus atom and this
resonance has a low coupling constant with 195Pt (3JPtH ¼ 23.1 Hz).
31P {1H} NMR confirms only one phosphorus was bound to plat-
inum center and this phosphorus donor atom was indicated as
conditions and yielded complex [PtMe(Vpy)(DMSO)],
C [48],
(Scheme 2). In this study, in an attempt, the complex B was used as
starting material to obtain complex C (Scheme 3).
singlet with platinum satellite at
d
¼ 13.0 ppm (1JPtP ¼ 1976 Hz).
A new promising way was suggested for preparation of the
complex [PtMe(Vpy)(DMSO)], C, from the dimeric complex B
(Scheme 3). Complex B was dissolved in acetone, and then DMSO
(4.5 equiv.) was added and then the mixture was stirred for 1 h at
room temperature. VpyH ligand (2.2 equiv.) was then added to the
in situ formed complex A mixture (isolated compound was char-
acterized by 1H NMR, Fig. S1) and the resulting mixture was
refluxed for 18 h. After removing the solvent, complex C was iso-
lated as a yellow solid (confirmed by 1H NMR [48], Fig. S2). This new
synthetic route alleviated the difficulty in preparation of complex A
from [PtCl2(DMSO)2] and SnMe4 (toxic and flammable) because this
reaction requires harsh reaction condition and complex A was ob-
tained in a low yield [54,56].
This value of coupling constant between platinum and phosphorus
was ascribable to the phosphorus coordinated trans to a group
having strong trans influence [37,39].
4. Photophysical properties
Complex 1 is stable and soluble in organic solvents such as
acetone or dichloromethane (CH2Cl2). Photophysical properties of 1
was explored in solid state and fluid solution for obtaining the
absorption and luminescence spectra.
4.1. Absorption spectra
The UVevis absorption spectrum of 1 shows various bands with
different energy positions at room temperature (Fig. 1). The more
intense transitions are in range of 230e340 nm with high extinc-
tion coefficients (ε > 104 Mꢀ1 cmꢀ1) which can be attributed to
3. Ligand substitution
In complex C, carbon (Cb) of 2-vinylpyridinate ligand has a
higher trans influence in respect with other cyclometalating ligands
like ppy [32] or N0-bpy-H [34] which is caused by the lower
inductive effect of vinyl substituent compared with phenyl group in
the later ligands. Therefore, DMSO is considered as a good leaving
group and it can be readily substituted in reaction with two elec-
tron donors like phosphine ligand [48]. Reaction of complex C
(isolated or in situ formed) with the phosphorous nucleophile
spin-allowed
p-p
* intraligand transitions (1IL) [64]. According to
the previous assignments [35,51], less intense transitions
(ε > 103 Mꢀ1 cmꢀ1) at 395 nm and 418 nm are assigned to a mixture
of 1IL and/or 1MLCT (metal to ligand charge transfer). These lower
energy bands demonstrate a notable solvatochromatic property,
shifting to higher energies in acetone solvent (ca. 10 nm) as
compared with CH2Cl2 (see kinetic study section), indicating that
Me
Me
DMSO
DMSO
Me
∆, 2h (Toluene)
isolated
or
in situ prodcut
or
+
Pt
Pt
∆, 24h (Acetone)
N
N
DMSO
A
C
Scheme 2. Synthetic route for preparation of complex C.

84
M. Niazi, H.R. Shahsavari / Journal of Organometallic Chemistry 803 (2016) 82e91
Me2
S
N
Me
Me
Me
DMSO
DMSO
Me
Me
Me
Me
DMSO
Pt
Pt
Pt
Pt
N
DMSO
S
Me2
C
A
B
Scheme 3. New method for preparation of complex C.
Me
Me
Me
Me
Excess MeI
Me
Me
PPh2Me
trans-cis
isomeration
PPh2Me
Pt
I
Pt
Pt
Pt
N
N
PPh2Me
N
DMSO
N
I
PPh2Me
1
C
2a
2b
isolated
or
in situ formed
Scheme 4. The route for preparation of platinum(IV) complex.
the transitions have a certain degree of charge transfer character
[31].
and 2b, respectively (Fig. S7). In the aliphatic region of 1H spectrum
of complex 2, four PtMe signals appeared as doublet with platinum
coupling (Fig. 2 and Fig. S8) and two deshielded doublet resonances
with low Pt coupling were assigned to PPh2Me protons. Integration
of these peaks were used to estimate the isomer ratios (trans:
4.2. Emission spectra
cis
¼
2:1) (Fig. S8). In trans isomer 2a, signals at 0.50
Upon photoexcitation, 1 is intensely emissive at 298 K and ex-
hibits similar emission profile in solution and solid state. It displays
a structured emission band with a maximum at 550 nm accom-
panied with the feature of vibronic progression spacing ca.
1400 cmꢀ1, which is characteristic of the cyclometalated ligands
(Fig. 1) [31]. The structured emission profile and long luminescent
(2JPtH ¼ 70.1 Hz), 1.17 (2JPtH ¼ 69.0 Hz) for PtMe and 2.39 ppm
(3JPtH ¼ 11.7 Hz) for PPh2Me ligand, whereas in the cis isomer 2b,
resonances at 0.92 (2JPtH ¼ 59.1 Hz), 1.56 (2JPtH ¼ 69.3 Hz) for PtMe
and 2.19 ppm (3JPtH ¼ 11.7 Hz) for PPh2Me ligand.
Additionally, kinetics and mechanism studies of oxidative
addition of MeI to the cycloplatinated(II) complexes, such as 1, is
known to be very slow [37,40,44,46,67]. Generally, this kinetic
investigation is followed by pseudo-first-order conditions and
UVevis absorption spectroscopy is used to measure the rate of
reaction. 1 exhibited an intense MLCT band in visible region as
responsible for its orange color (see Photophysical properties sec-
lifetimes at room temperature (10.1 ms, in solid state), which are
characteristics of triplet states. Furthermore, the intensity of this
orange emission diminishes in presence of O2 molecule (Fig. S5)
since oxygen acts as a powerful quencher of the long-lived triplet
excited state [65]. Therefore, 1 exhibits a normal phosphorescence
and this can be assigned to a typical mixed spin-forbidden
3ILCT/3MLCT excited state. While the temperature is lowered to
77 K, the preliminary orange emission of 1 becomes more intense
and it is similar to emission profile which was observed at 298 K
(Fig. S6). Also, by cooling the temperature, the luminescence band
shifts to the blue (~10 nm). This hypsochromic shift could be
assigned to the increased rigidity in the glassy state, which has
usually been defined as rigidochromism [66].
tion). The fade away of this band (MLCT) at
l
¼ 387 nm (in acetone)
by addition of excess MeI ([MeI]0 >> [Pt complex 1]) under pseudo
first order kinetic conditions was selected to monitor this reaction
(Fig. 3). By fitting of absorbance versus time plot (Fig. 3) in the
monophasic first order equation (Eq. (1)), in which At ¼ absorption
at time t, A0 ¼ initial absorption and A∞ ¼ infinity absorption,
pseudo-first order rate constants (kobs) were calculated.
At ¼ (A0 ꢀ A∞) exp(ꢀkobst) þ A∞.
(1)
5. Oxidative addition reactions and kinetic study
Plots of kobs against MeI concentration was linear with no in-
tercepts (no solvolytic or no sign of any involvement of dissociative
pathway) and slope of each line gave the second order rate constant
(k2) (Fig. 4). The same method was used for different temperatures
and activation parameters were obtained from the Eyring equation
(Fig. S9 and Eq. (2)), in which T ¼ temperature in Kelvin unit,
kB ¼ Boltzmann constant, h ¼ Planck constant, R ¼ universal gas
Reaction of electron rich 1 with excess MeI yielded a mixture of
trans and cis platinum(IV) after 2 h, concomitant with a color
change to pale yellow (Scheme 4). As it is well established from
other reports [37,40e42,46], due to the restriction of 2-
vinylpyridine cyclometalated ring and high trans influence of
methyl groups, only two isomers can be formed and others may be
ignored [41]. In this case, trans isomer 2a was formed very fast as a
kinetic isomer and progressively it changed to cis isomer 2b
constant,
D
S# ¼ entropy and
D
H# ¼ enthalpy of activation, and the
(thermodynamic isomer). On the basis of NMR characterization, 31
P
results are collected in Table 1.
{1H} showed two resonances as singlet with platinum satellite at
d
¼ ꢀ22.0 (1JPtP ¼ 1252 Hz) and ꢀ22.9 (1JPtP ¼ 1127 Hz) ppm for 2a

M. Niazi, H.R. Shahsavari / Journal of Organometallic Chemistry 803 (2016) 82e91
85
Fig. 1. Photographs showing the luminescence color change under UV light irradiation (365 nm) a) in solid state; b) in CH2Cl2 solution; c) Absorption (solid line), excitation (dotted
line) and emission (dashed line) spectral of complex 1 in CH2Cl2 solution (5 ꢁ 10ꢀ5 M) at 298 K. (For interpretation of the references to color in this figure legend, the reader is
referred to the web version of this article.)
incorporating in tpy ligand and it made the tpy to be slightly
ꢀ
ꢁ
ꢀ
ꢁ
electronegative (weaker donor) than Vpy. Therefore, it reduces
electron density on platinum center and subsequently the rate
constants, complying with the larger coupling constant between
platinum and phosphorus in tpy complex (1JPtP ¼ 2042 Hz) [37]
than complex 1 (1JPtP ¼ 1976 Hz).
k2
T
kB
h
DSz
R
DHz
RT
ln
¼ ln
þ
ꢀ
(2)
This reaction was followed as a simple second order rate law (Eq.
(3)), 1st order in both the corresponding 1 and MeI.
In order to obtain pure cis isomer 2b, reaction mixture of trans-
cis was stirred for 5 days at room temperature. Interestingly,
extending reaction time resulted in formation of monomeric plat-
inum(II) complex trans-[PtMeI(PPh2Me)2], 3 [53,68], the binuclear
ꢀd[complex 1]/dt ¼ k2[complex 1][MeI]
(3)
D
S# value suggested
These observations and highly negative
platinum(IV) complex [{PtMe2(Vpy)}2(m-I)2], 4 [30,69,70], and a
that a typical of oxidative addition was involved and reaction
started with the nucleophilic attack of the cycloplatinated complex
1 at MeI in an SN2 fashion [37,40,41].
To gain further insight into effect of 2-vinylpyridinate ligand on
the rate of oxidative addition reaction, the complex [PtMe(t-
py)(PPh2Me)] [37] (tpy ¼ 2-(p-tolyl)pyridinate) was selected.
Interestingly, rate constants of reaction between MeI and complex
[PtMe(tpy)(PPh2Me)] is smaller than those of 1 (Table 1). This
observation may be due to inductive effect of phenyl group which is
free ligand Z/E-[C8H9N], 5 [71,72], 2-propenyl-pyridine (Scheme 5).
It is to be noted that 3 and ligand 5 were characterized by
comparing their 1H and/or 31P {1H} NMR spectra with those of the
authentic samples used to characterize products (Figs. 5 and 6).
1H NMR spectrum was invaluable in the structural character-
ization of the products (Fig. 5). A triplet with satellite as coupling by
platinum center and two equivalent phosphorus (
d
¼ ꢀ0.02 ppm,
2JPtH ¼ 78.3 Hz and 3JPH ¼ 6.9 Hz) could be attributed to PtMe group

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M. Niazi, H.R. Shahsavari / Journal of Organometallic Chemistry 803 (2016) 82e91
Fig. 2. 1H NMR spectrum of PtMe region in the mixture of trans and cis isomer of complex 2 in Acetone-d6.
Fig. 4. Plots of first-order rate constants (kobs/sꢀ1
) for the reaction of [PtMe(V-
py)(PPh2Me)], 1, with MeI in acetone at different temperatures versus [MeI] (R2 (R-
squared) ¼ 0.99836, 0.99614, 0.99757, 0.99198, 0.9915 for T ¼ 10, 15, 20, 25 and 30 ꢂC,
respectively).
Fig. 3. Changes in the absorbance spectra of complex [PtMe(Vpy)(PPh2Me)], 1, with an
excess of MeI in acetone at T ¼ 20 ꢂC as function of wavelength; successive spectra
recorded at intervals of 45 s. Inset is the variation of absorbance at
time.
l
¼ 387 nm over
4. It is worth mentioning that the formation of the compound 5
proceeded through a CeC bond formation between a Me group and
Cb of Vpy ligand rather than the coupling reaction between two Me
groups for formation of ethane (the signal not observed in NMR
spectrum) [73,74]. This was confirmed by presence of two doublet
in complex 3 [68]. Meanwhile, another triplet resonance at
d
¼ 2.51
with significantly lower value of platinum coupling constant
2
(3JPtH ¼ 31.0 Hz and JPH ¼ 6.6 Hz), which appeared as a second
order AA0XX0 spin system through coupling between H and P
atoms, could be assigned to Me group in PPh2Me in 3 [68]. For the
methyl groups on the Pt(IV) centers in the complex 4, two singlet
of doublet signals [71], appearing at
d
¼ 1.97 with JHH ¼ 7.2, 1.5 Hz
(assigned to isomer Z) and
d
¼ 1.85 with JHH ¼ 6.8, 1.2 Hz (assigned
signals with platinum satellite at
d
¼ 1.08 (2JPtH ¼ 74.5 Hz, MePt
to isomer E) and these isomers were in different ratio (Z:E ¼ 6:1).
In complex 2b, the “soft” Pt-Cb bond of the 2-vinylpyridinate
chelate is trans to a “soft” iodine ligand which labilize the later
bond. Therefore, they exhibit antisymbiotic behavior [75].
Inversely, the PtMe group which is positioned trans to the nitrogen
trans to I) and
d
¼ 1.91 (2JPtH ¼ 71.7 Hz, MePt trans to N) were
observed. Besides, there is a resolved coupling between 195Pt nu-
cleus and H6 proton of the py ring of 2-vinylpyridinate ligand
3
3
(d
¼ 9.81 ppm, JHH ¼ 4.8 Hz, JPtH ¼ 13.1 Hz), indicating that Vpy
ligand was bonded to the platinum center via nitrogen in complex

M. Niazi, H.R. Shahsavari / Journal of Organometallic Chemistry 803 (2016) 82e91
87
Table 1
Second-order rate constantsa and activation parametersb for reaction of [PtMe(Vpy)(PPh2Me)], 1, and [PtMe(tpy)(PPh2Me)]c with MeI in acetone.
Complex
102 k2/L molꢀ1 sꢀ1 at different temperatures
D
H#/kJ molꢀ1
D
S#/JKꢀ1molꢀ1
10 ꢂC
15 ꢂC
20 ꢂC
25 ꢂC
30 ꢂC
1
2.80
2.38
3.63
3.05
4.38
3.82
5.57
4.91
7.16
6.14
30.5 0.1
31.4 0.1
ꢀ166
ꢀ165
1
1
[PtMe(tpy)(PPh2Me)]
a
Estimated errors in k2 values are 3%.
b
c
Activation parameters were calculated from the temperature dependence of the second-order rate constant in the usual way using Eyring equation (Eq. (2)).
From Ref. [37].
Fig. 5. 1H NMR spectrum of reaction of complex [PtMe(Vpy)(PPh2Me)], 1, with MeI after 5 days in Acetone-d6, Aliphatic region. Dotted line (‥‥) signals for complex 3, Solid line (─)
signals for complex 4 and Dashed line (┄) signals for compound 5.
donor of 2-vinylpyridinate ligand (N is considerably harder than
iodine ligand) [76] did not exhibit such behavior. This concept
suggested that Pt-Cb bond is more bowed to be involved in CeC
bond coupling reaction rather than the PtMe ligand [43].
The reaction of complex 1 with excess MeI was monitored using
31P {1H} NMR spectroscopy in Acetone-d6 in an NMR tube at 25 ꢂC
(Fig. 6). Immediately after the addition of MeI, singlet resonance for
1 disappeared and two singlet signals with platinum satellite at
These would suggest that this reaction completely depended on the
nature of cyclometalating and phosphine ligands. In this circum-
stance for extending the role of cyclometalating ligand, [PtMe(t-
py)(PPh2Me)] [37] was selected as a complex with different
cyclometalated ligand and its reaction with excess of MeI was fol-
lowed up by NMR spectroscopy. The kinetically isomer changed
very fast to cis isomer and thermodynamically isomer was very
stable in solution by elapse of time and did not change to any new
product(s) (Fig. S10).
Moreover, changes in the absorbance spectra of the reaction
mixture was followed up by UVevis spectroscopy during 5 days.
The result showed that when MeI was added to 1, the absorbance
decreased quickly and Pt(IV) was formed, and over time the
absorbance did not display any changes and similar plot (like Fig. 3)
was obtained. Therefore, we were not able to track formation of
new compounds from platinum(IV) complex 2 and study the
mechanism, because newly formed products did not exhibit any
absorption in visible region [68,71].
d
¼ ꢀ22.0 and ꢀ22.9 in different ratio were detectable in shielded
region which could be assigned to trans 2a and cis 2b isomers,
respectively. Over time, signals of trans isomer 2a gradually started
to fade away while the signal of cis isomer 2b was growing. As this
reaction progressed, the signal with large Pt coupling constant
appearing at
d
¼ 9.4 (1JPtP ¼ 2950 Hz) [68] could be assigned to 3,
which is in Pt(II) region, and the resonance of cis isomer 2b dis-
appeared slowly. As aforementioned, after 5 days 3 was merely
obtained that is containing the phosphine ligand.
These observations from NMR spectra suggested that we cannot
prepare a pure cis isomer 2b and it is converted to a mixture of
products (Scheme 5). Therefore, for describing a proper mechanism
on this transformation reaction, based on our preliminary studies
and similar previous reports like reaction of [PtMe(bpy-H)(L)], in
which L ¼ PPh3 [42], PPh2Me [40], PMe3 [48], with MeI yielded in
different geometrical Pt(IV) isomer as a stable complex in solution.
Further studies on similar 2-vinylpyridinate complexes with
different phosphine ligands like PPh3 and PPhMe2 are currently in
progress for the understanding of the role of the phosphine ligand
as well as the formed trans isomer in this reaction for a better
mechanism assumption.

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M. Niazi, H.R. Shahsavari / Journal of Organometallic Chemistry 803 (2016) 82e91
Fig. 6. The reaction of complex [PtMe(Vpy)(PPh2Me)], 1, with an excess of MeI (30 folds) as monitored by 31P {1H} NMR spectroscopy in Acetone-d6 at room temperature. (I): Pt(II)
region. (II): Pt(IV) region. (a) pure complex 1, (b) immediately, (c) 30 min (d) 2 h, (e) 6 h, (f) 12 h, (g) 1 day, (h) 2 days, (i) 3 days, (j) 4 days and (k) 5 days after addition of excess MeI.
The signal assignments are depicted.
Me
Me
Pt
Me
Pt
Me
Pt
I
I
Me
PPh2Me
I
Me
I
Me
Me
Pt
+
+
N
MePh2P
N
N
N
PPh2Me
2b
3
4
5
Scheme 5. Transformation of complex 2b by passing of time.
6. Conclusion
oxidative addition reaction followed a second order kinetic, first
order in each reagent and occurred by a typical SN2 mechanism. The
stability of 2 was checked with NMR spectroscopy (up to 5 days)
and we found that this complex is converted to a mixture of
compounds exhibiting CeC bond coupling. Furthermore, pre-
liminary results indicated that this transformation depends on the
cyclometalated ligand and nature of phosphine ligand [77].
Herein, cycloplatinated(II) complex C has been synthesized
through dimeric methyl platinum complex B in existence of DMSO,
when 2-vinylpyridine was used as the cyclometalating ligand. On
the other hand, this labile leaving group (DMSO) was allowed to be
replaced by a phosphine ligand (PPh2Me) for preparation of novel
emissive complex [PtMe(Vpy) (PPh2Me)], 1. Complex 1 exhibited a
low energy absorption band around 400 nm tentatively attributed
to transitions having mixed configurations (1LC/1MLCT). Upon
photoexcitation at 298 K and 77 K in this wavelength,1 exhibited an
intense orange emission profile with the lifetime being in order of
7. Experimental
All NMR spectra (1H and 31P{1H}) were recorded on a Brucker
Avance DPX 400 MHz instrument and are referenced to the residual
m
s. This emission is arising from spin forbidden triplet state with
peak of the solvent, i.e. CDCl3 or CD3COCD3, the chemical shifts (
being reported as ppm and coupling constants (J) expressed in Hz.
The microanalyses were performed using vario EL CHNS
d)
mixing origin (3LC/3MLCT). By reaction of 1 with excess MeI this
band disappeared quickly and this was used to readily follow ki-
netics of formation of corresponding cycloplatinated(IV) complex
[PtMe2I(Vpy)(PPh2Me)], 2. According to our kinetic data, the
a
elemental analyzer. Mass spectra were recorded on an Agilent 7000
triple quad spectrometer. Kinetic studies were carried out by using

M. Niazi, H.R. Shahsavari / Journal of Organometallic Chemistry 803 (2016) 82e91
89
3
an Ultrospec 4000 Pro, UVeVis spectrometer with temperature
control using a Pharmacia Biotech constant-temperature bath.
Excitation and emission spectra were obtained on Varian Cary
Eclips instrument and/or PerkinElmer LS45 fluorescence spec-
trometer with the lifetimes measured in phosphorimeter mode. 2-
vinylpyridine (VpyH) and methyldiphenylphosphine (PPh2Me)
were purchased from Acros and Aldrich, respectively. The starting
ArH Vpy and PPh2Me ligands), 7.51 (t, JHH ¼ 8.0 Hz, 1H, H4 Vpy
ligand), 7.70e7.76 (m, overlapping 4H, ArH Vpy and PPh2Me li-
gands), 7.67 (t, 3JHH ¼ 8.9 Hz, 2JPtH ¼ 159.2 Hz, 1H, Hb Vpy Ligand);
d
(
31P) 13.0 (s, 1JPtP ¼ 1976 Hz, 1P of PPh2Me ligand).
7.1.1.2. Method II. PPh2Me (57
mL, 0.306 mmol, 1.2 equiv.) was
added to solution of [PtMe(Vpy) (DMSO)], C, (100 mg,
a
materials cis-[Pt(Me)2(DMSO)2],
A
[54e56], cis,cis-[Me2Pt(
m-
0.255 mmol) in acetone (20 mL) under an Ar atmosphere. The
mixture was stirred at room temperature for 1 h. The deep orange
solution was evaporated and concentrated to a small volume
(2 mL), and n-haxene was added (5 mL) to give an orange solid
identified as 1. The solid was dried in vacuum.
SMe2)2PtMe2], [52,53,57], [PtMe(Vpy)(DMSO)],
B
C
[48,78],
[PtMe(tpy)(PPh2Me)] [37] and [PtMe2I(tpy)(PPh2Me)] [37] were
prepared according to known procedures. The NMR labeling for the
Vpy ligand for clarifying the chemical shift assignments is shown in
Scheme 6. For complex C, 1H NMR data in CD3COCD3:
d 0.68 (s,
2JPtH ¼ 83.4 Hz, 3H, PtMe), 3.12 (s, 3JPtH ¼ 17.1 Hz, 6H, Me of DMSO),
6.92 (d, 3JHH ¼ 8.8 Hz, 3JPtH ¼ 107.6 Hz, 1H, Ha Vpy ligand), 7.17e7.20
7.1.2. [PtMe2I(Vpy)(PPh2Me)], 2
3
(m, 1H, H5 Vpy ligand), 7.28 (d, JHH ¼ 7.8 Hz, 1H, H3 Vpy ligand),
At room temperature, to a solution of [PtMe(Vpy)(PPh2Me)], 1,
(60 mg, 0.117 mmol) in acetone (10 mL) was added 220 mL (excess,
7.43 (d, 3JHH ¼ 8.8 Hz, 2JPtH ¼ 170.2 Hz, 1H, Hb Vpy Ligand), 7.86 (td,
4
3JHH ¼ 7.7 Hz, JHH ¼ 1.6 Hz, 1H, H4 Vpy ligand), 9.37 (d,
30 folds) of MeI. The solution was stirred for 2 h at room temper-
ature, then diethyl ether was added to give a precipitate which was
filtered, washed with diethyl ether to give the product as a pale
yellow solid identified as 2 (cis and trans mixture). The product was
dried in vacuum. Yield: 73%, mp ¼ 110 ꢂC. Anal. Calcd. For
3
3JHH ¼ 5.6 Hz, JPtH ¼ 12.3 Hz, 1H, H6 Vpy ligand).
7.1. Synthesis of complexes
C
22H25INPPt; C, 40.26; H, 3.84; N, 2.13. Found: C, 40.09; H, 3.69; N,
7.1.1. [PtMe(Vpy)(PPh2Me)], 1
2.20. Mass data: m/z 657.1 [M]þ; 530.3 [MꢀI]þ. NMR data in
7.1.1.1. Method I. To a solution of cis,cis-[Me2Pt(
(100 mg, 0.174 mmol) in acetone (15 mL) was added DMSO (55.7
0.783 mmol, 4.5 equiv.) under an Ar atmosphere and reaction
mixture stirred for 1 h. Then, 2-vinylpyridine (41.3 L, 0.383 mmol,
2.2 equiv.) was added to the solution and refluxed for 18 h, then
heating was turned off and the PPh2Me (77.8 L, 0.418 mmol, 2.4
m-SMe2)2PtMe2], B,
3
CD3COCD3: (trans isomer, 2a)
d
(1H) 0.50 (d, JPH
¼
7.2,
m
L,
2JPtH ¼ 70.1 Hz, 3H, Me ligand trans to I, PtMe), 1.17 (d, JPH ¼ 8.4,
2JPtH ¼ 69.0 Hz, 3H, Me ligand trans to N, PtMe), 2.39 (d, 2JPH ¼ 8.7,
3JPtH ¼ 11.7 Hz, 3H, Me group of the PPh2Me ligand), 8.35 (d,
3
m
3JHH ¼ 5.0 Hz, JPtH ¼ 14.5 Hz, 1H, H6 Vpy ligand), 6.65e8.10
3
m
(overlapping multiplets, ArH Vpy and PPh2Me ligands for both trans
equiv.) added. The solution was stirred for 1 h, then concentrated to
a small volume (2 mL) and treated with n-hexane (5 mL). The
formed precipitate was filtered off, washed with n-hexane to give
the product as an orange solid. The precipitate was dried in vac-
uum. Yield: 87%, mp ¼ 120 ꢂC (decomp.). Anal. Calcd. For
1
and cis isomer);
d
(
31P) ꢀ22.0 (s, JPtP ¼ 1252 Hz, 1P of PPh2Me
ligand). (cis isomer, 2b)
d
(1H) 0.92 (d, 3JPH ¼ 7.9, 2JPtH ¼ 59.1 Hz, 3H,
Me ligand trans to P, PtMe), 1.56 (d, 3JPH ¼ 8.2, 2JPtH ¼ 69.3 Hz, 3H,
Me ligand trans to N, PtMe), 2.19 (d, 2JPH ¼ 9.0, 3JPtH ¼ 11.7 Hz, 3H,
3
Me group of the PPh2Me ligand), 9.04 (d, JHH
¼
5.1 Hz,
C
21H22NPPt; C, 49.02; H, 4.31; N, 2.72. Found: C, 49.30; H, 4.02; N,
3JPtH ¼ 14.9 Hz, 1H, H6 Vpy ligand), 6.65e8.10 (overlapping multi-
2.84. Mass data: m/z 513.1 [M]þ; 499.1 [M-Me]þ. NMR data in
plets, ArH Vpy and PPh2Me ligands for both trans and cis isomer);
3
2
CD3COCD3:
d
(1H) 0.84 (d, JPH ¼ 8.2, JPtH ¼ 85.05 Hz, 3H, PtMe),
d
(
31P) ꢀ22.9 (s, 1JPtP ¼ 1127 Hz, 1P of PPh2Me ligand).
2
3
2.04 (d, JPH ¼ 7.8, JPtH ¼ 23.1 Hz, 3H, Me group of the PPh2Me
ligand, this signal has overlap with CD3COCD2H NMR solvent), 6.59
(t, 3JHH ¼ 7.1 Hz,1H, H5 Vpy ligand), 7.21 (d, 3JHH ¼ 8.1 Hz,1H, H3 Vpy
ligand), 7.25 (dd, 3JHH ¼ 9.3 Hz, 4JPH ¼ 15.1 Hz, 3JPtH ¼ 90.1 Hz,1H, Ha
Vpy ligand), 7.46e7.50 (m, overlapping 7H, ArH Vpy and PPh2Me
ligands), 7.67 (dd, 3JHH ¼ 9.1 Hz, 3JPH ¼ 7.7 Hz, 2JPtH ¼ 159.5 Hz, 1H,
Hb Vpy Ligand), 7.70e7.76 (m, overlapping 5H, ArH Vpy and PPh2Me
If stirring was prolonged for 5 days at room temperature and
then solvent was removed, and the resulting residue was dried to
form a yellowish solid as a mixture of 3, 4 and 5 in 2:1:2 ratios
(Scheme 5). Selected NMR result for this mixture in CD3COCD3:
(Complex 3)
d
(1H) ꢀ0.02 (t, 3JPH ¼ 6.9 Hz, 2JPtH ¼ 78.3 Hz, 3H, PtMe),
2.51 (t, 2JPH ¼ 6.6 Hz, 3JPtH ¼ 31.0 Hz, 6H, Me group of the PPh2Me
1
ligands);
d
(
31P) 9.4 (s, JPtP ¼ 2950 Hz, 2P of PPh2Me ligands).
ligands);
data in CDCl3:
d
(
31P) 12.4 (s, 1JPtP ¼ 1981 Hz, 1P of PPh2Me ligand). NMR
(Complex 4)
d
(1H) 1.08 (s, 2JPtH ¼ 74.5 Hz, 6H, Me trans to I, PtMe),
d
(1H) 0.98 (d, 3JPH ¼ 8.6, 2JPtH ¼ 84.3 Hz, 3H, PtMe),
2
1.91 (s, JPtH ¼ 71.7 Hz, 6H, Me trans to N, PtMe), 9.81 (d,
2
3
2.03 (d, JPH ¼ 7.6, JPtH ¼ 23.1 Hz, 3H, Me group of the PPh2Me
3JHH ¼ 4.8 Hz, JPtH ¼ 13.1 Hz, 2H, H6 Vpy ligands). (Compound 5)
3
ligand), 6.45 (t, JHH ¼ 7.2 Hz, 1H, H5 Vpy ligand), 7.10 (d,
3
d
(1H) 1.85 (dd, JHH ¼ 6.8, 1.2 Hz, 3H, (% 15), Me (isomer E)), 1.97 (dd,
3JHH ¼ 8.0 Hz, 1H, H3 Vpy), 7.36 (dd, JHH ¼ 9.4 Hz, JPH ¼ 14.9 Hz,
3
4
JHH ¼ 7.2,1.5 Hz, 3H, (% 85), Me (isomer Z)), 9.05 (d, 3JHH ¼ 4.6 Hz,1H
(15%), pyridine H6 (E)), 9.22 (d, 3JHH ¼ 4.6 Hz, 1H (85%), pyridine H6
(E)).
3JPtH ¼ 90.5 Hz, 1H, Ha Vpy ligand), 7.38e7.46 (m, overlapping 7H,
4
7.2. Kinetic study
5
3
A solution of complex [PtMe(Vpy)(PPh2Me)],1, in acetone (3 mL,
5 ꢁ 10ꢀ4 M) in a cuvette was thermostated at 20 ꢂC and a known
Hα
6
excess of MeI (15 mL, 160 folds) was added using a microsyringe.
N
After rapid stirring, the absorbance at
l
¼ 387 nm was collected
with time. The absorbance-time curves were analyzed by pseudo
first order method (Eq. (1)). The same method was used at other
temperatures (10, 15, 25, and 30 ꢂC) and activation parameters ( S#
D
Pt
Hβ
and
the full data are collected in Table 1.
D
H#) were obtained from the Eyring equation [79] (Eq. (2)) and
Scheme 6. Representation of Vpy ligand with position labeling.

90
M. Niazi, H.R. Shahsavari / Journal of Organometallic Chemistry 803 (2016) 82e91
D.N. Kozhevnikov, H. Yersin, Brightly luminescent Pt(II) pincer complexes
with a sterically demanding carboranyl-phenylpyridine ligand: a new mate-
rial class for diverse optoelectronic applications, J. Am. Chem. Soc. 136 (2014)
9637e9642.
7.2.1. Reaction of [PtMe(Vpy)(PPh2Me)], 1, with MeI
This reaction was monitored by 31P NMR spectroscopy at room
temperature in an NMR tube. To
py)(PPh2Me)], 1, (10 mg) in CD3COCD3 (0.5 mL), an excess of MeI
(30 L, 30 folds) was added. The NMR spectra were recorded several
a solution of [PtMe(V-
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times at during about 120 h until the mixture was converted to
trans-[PtMeI(PPh2Me)2], 3, in solution.
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metallated 5-[small pi]-delocalized-donor-1,3-di(2-pyridyl)benzene ligands
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Acknowledgments
We thank the Institute for Advanced Studies in Basic Sciences
(IASBS) Research Council and the Iran National Science Foundation
(Grant no. 93026027) for financial support.
[22] H. Yersin, Highly Efficient OLEDs with Phosphorescent Materials, in: Highly
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complex containing dibenzo-24-crown-8: synthesis, luminescence and
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Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2015.12.005.
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