Kinetics and mechanism of oxidative addition of MeI to binuclear cycloplatinated complexes containing biphosphine bridges: Effects of ligands

Article abstract of DOI:10.1016/j.jorganchem.2012.05.026

The binuclear complex [Pt₂Me₂(bhq) ₂(μ-dppf)], 1a, in which bhqH = benzo{h}quinoline and dppf = 1,1′-bis(diphenylphosphino)ferrocene, was synthesized by the reaction of [PtMe(SMe₂)(bhq)] with 0.5 equiv of dppf at room temperature. The reaction of Pt(II)-Pt(II) complex 1a with excess MeI gave the Pt(IV)-Pt(IV) complex [Pt₂I₂Me₄(bhq)₂(μ-dppf)], 2a. The complexes were fully characterized using multinuclear (¹H, ³¹P and ¹⁹⁵Pt) NMR spectroscopy and elemental analysis. The kinetic and mechanism of the reaction of complex 1a with MeI was investigated in CHCl₃ and based on the data, obtained from UV-vis and low temperature ³¹P NMR spectroscopies, a mechanism involving stepwise oxidative addition of MeI to the two Pt(II) centers is suggested. Reaction rates concerning the complex 1a, having bhq ligand, are almost 1.4 times slower than those involving the ppy complex [Pt₂Me ₂(ppy)₂(μ-dppf)], ppyH = 2-phenylpyridine, reported previously (Inorg. Chem. 2008, 47, 5441). This is attributed to the stronger donor ability of the ppy ligand as compared to that of the bhq ligand as is further confirmed using density functional theory (DFT) calculations through finding approximate structures for the described complexes. A comparative kinetic study of reaction of the dimeric platinum(II) complex [Pt ₂Me₂(bhq)₂(μ-dppm)], 1b, where dppm = bis(diphenylphosphino)methane, with MeI was also performed to investigate the effect of bridging biphosphine ligand on the kinetic and mechanism of the dimeric complexes with MeI. A double MeI oxidative addition was observed for which the classical S_N2 mechanism for both steps, as well as the possible intermediates, is suggested.

Full text of DOI:10.1016/j.jorganchem.2012.05.026

Journal of Organometallic Chemistry 715 (2012) 73e81
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Kinetics and mechanism of oxidative addition of MeI to binuclear cycloplatinated
complexes containing biphosphine bridges: Effects of ligands
,
a
a
a,
S. Masoud Nabavizadeh a , Marzieh Dadkhah Aseman , Behnaz Ghaffari , Mehdi Rashidi
,
*
*
Fatemeh Niroomand Hosseini b, Gholamhassan Azimi c
a Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454, Iran
b Department of Chemistry, Shiraz Branch, Islamic Azad University, Shiraz 71993-37635, Iran
c Department of Chemistry, Arak University, Arak 38156-879, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
The binuclear complex [Pt2Me2(bhq)2(
m
-dppf)], 1a, in which bhqH
¼
benzo{h}quinoline and
dppf ¼ 1,10-bis(diphenylphosphino)ferrocene, was synthesized by the reaction of [PtMe(SMe2)(bhq)]
Received 15 March 2012
Received in revised form
12 May 2012
with 0.5 equiv of dppf at room temperature. The reaction of Pt(II)ePt(II) complex 1a with excess MeI
gave the Pt(IV)ePt(IV) complex [Pt2I2Me4(bhq)2(m-dppf)], 2a. The complexes were fully characterized
Accepted 24 May 2012
using multinuclear (1H, 31P and 195Pt) NMR spectroscopy and elemental analysis. The kinetic and
mechanism of the reaction of complex 1a with MeI was investigated in CHCl3 and based on the data,
obtained from UVevis and low temperature 31P NMR spectroscopies, a mechanism involving stepwise
oxidative addition of MeI to the two Pt(II) centers is suggested. Reaction rates concerning the complex
1a, having bhq ligand, are almost 1.4 times slower than those involving the ppy complex [Pt2Me2(p-
Keywords:
Organodiplatinum
Cyclometalated
Oxidative addition
Kinetics
py)2(
m
-dppf)], ppyH ¼ 2-phenylpyridine, reported previously (Inorg. Chem. 2008, 47, 5441). This is
attributed to the stronger donor ability of the ppy ligand as compared to that of the bhq ligand as is
further confirmed using density functional theory (DFT) calculations through finding approximate
structures for the described complexes. A comparative kinetic study of reaction of the dimeric plati-
Mechanism
num(II) complex [Pt2Me2(bhq)2(
m
-dppm)], 1b, where dppm ¼ bis(diphenylphosphino)methane, with
MeI was also performed to investigate the effect of bridging biphosphine ligand on the kinetic and
mechanism of the dimeric complexes with MeI. A double MeI oxidative addition was observed for
which the classical SN2 mechanism for both steps, as well as the possible intermediates, is suggested.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
observed for isopropyl iodide [13]. In all of these, the addition
product has the halide and organic group bound to the same metal
Oxidative addition is a fundamental reaction which is the base
for many applications of organometallic compounds in many
homogeneous catalytic processes and organic synthesis [1e3].
Oxidative addition of carbon-halide or other bonds to monomeric
organoplatinum(II) complexes, especially those containing diimine
ligands, has been extensively studied [4e10]. The most common
mechanism of oxidative addition of alkyl halides is the classical SN2
mechanism involving a second-order rate law (rate ¼ k2[complex]
[halide]), although in some relatively rare cases, the reactions
proceed by concerted addition via a threeecenter transition state
(mostly for aryl halides) [5,11,12] or by radical mechanisms, e.g. as
atom, increasing the oxidation state of the metal by 2. Despite
these, examples of the related oxidative addition to binuclear
complexes are much rarer [14e18]. The oxidative addition to the
binuclear complexes is interesting because cooperative electronic
or steric effects between the two adjacent metal centers can give
rise to reaction pathways or products not possible in the mono-
nuclear analogous [19e23]. In some cases, increased steric
hindrance in binuclear complexes are thought to decrease the
reactivity of systems [16], but in other cases, cooperative effects
between the two metal centers lead to an increase in reactivity
[24,25].
On the other hand, transition metal cyclometalated complexes,
in particular those involving platinum, are of interest because of
their potential applications in many areas, such as chemosensors
[26,27], photocatalysts [28,29], and optoelectronic devices [30,31].
Square planar cyclometalated platinum complex species have also
* Corresponding authors. Tel. þ98 711 2284822; fax: þ98 711 2286008.
E-mail
addresses:
nabavi@chem.susc.ac.ir,
nabavizadeh@yahoo.com
(S.M. Nabavizadeh), 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.2012.05.026

74
S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 715 (2012) 73e81
been used as “building blocks” for complex systems such as den-
drimers [32].
2.2. [Pt2I2Me4(bhq)2(m-dppf)], 2a
Although oxidative addition reactions on mononuclear square
planar platinum(II) complexes, as a key step in many catalytic
reactions, have been extensively studied, to the best of our
knowledge, such reactions have rarely been studied on binuclear
platinum complexes, especially complexes having two cyclo-
platinated centers [18]. Cyclometalated platinum(II) complexes can
be highly reactive via oxidative addition to give the corresponding
platinum(IV) products.
An excess of MeI (50
m
L) was added to a solution of complex 1a
(100 mg in 20 mL of chloroform) at room temperature. The mixture
was stirred at this condition for 1 h, then the solvent was removed
under reduced pressure and the residue was triturated with ether
(2 ꢂ 3 mL). The product was dried under vacuum. Yield: 84 mg,
70%. Anal. Calcd for C64H56I2FeN2P2Pt2: C, 47.6; H, 3.5; N,1.7; Found:
C, 47.2; H, 3.7; N, 1.6. NMR data in CDCl3:
d
(1H) 1.03 (d, 6H,
3
2JPtH ¼ 60.5 Hz, JPH ¼ 7.6 Hz, 2 Me ligands trans to P), 1.55 (d, 3H,
3
A series of cycloplatinated complexes containing bridging
2JPtH ¼ 71.2 Hz, JPH ¼ 2.9 Hz, 1 Me ligand trans to N), 1.59 (d, 3H,
biphosphine ligands of the types [Pt2R2(CeN)2(
m-dppf)],
2JPtH ¼ 72.6 Hz, 3JPH ¼ 2.9 Hz, 1 Me ligand trans to N), 2.51, 2.63, 2.96
[Pt2R2(CeN)2(
m
-dppm)] and [Pt2R2(CeN)2(
m
-dppe)], in which,
(each a br s,1H, 1H, 2H, respectively, b, b
0 Cp protons), 3.44 (br s, 4H,
dppf ¼ 1,10- bis(diphenylphosphino)ferrocene (R ¼ Me or aryl),
a,
a0 Cp protons), aromatic protons: 6.6e8.2 (overlapping multi-
dppm
¼
bis(diphenylphosphino)methane
(R
¼
aryl),
plets), 9.55 (d, 1H, JHH ¼ 5.1 Hz, 3JPtH ¼ 9 Hz, CH group adjacent to
3
dppe ¼ bis(diphenylphosphino)ethane (R ¼ Me or aryl) and
CeN ¼ ppy (ppyH ¼ 2-phenylpyrine) or bhq (bhqH ¼ benzo{h}
quinoline) ligands have recently been prepared [18,33e36]. In
continuation of our interest in oxidative addition reactions of
cyclometalated Pt(II) complexes, in this study, we attempted to
investigate influence of the nature of biphosphine bridges on the
kinetic and mechanism of oxidative addition of MeI to binuclear
coordinated N atom), 9.56 (d, 1H, JHH ¼ 5.2 Hz, JPtH ¼ 9 Hz, CH
group adjacent to coordinated
N
atom);
d
(
31P) ꢁ13.1(s,
1JPtP ¼ 1012 Hz, 1P), -13.0 (s, 1JPtP ¼ 992 Hz, 1P).
2.3. Kinetic study
In a typical experiment, a solution of complex 1a or 1b in CHCl3
(3 ml, 3 ꢂ 10ꢁ4 M) in a cuvette was thermostated at 25 ꢀC and
a known excess of MeI was added using a micro syringe. After rapid
stirring, the absorbance at corresponding wavelength was moni-
tored with time.
cyclometalated methylplatinum(II) complexes [Pt2Me2(bhq)2(
dppf)], 1a, and [Pt2Me2(bhq)2( -dppm)], 1b. By comparing the data
to those reported previously for the corresponding reaction
involving the ppy analogous [Pt2Me2(ppy)2( -dppf)] [18], it was
m-
m
m
possible to describe the effect of cycloplatinated rings on rate of the
related reactions.
3. Results and discussion
3.1. Synthesis and characterization of the new binuclear complexes
2. Experimental
As is depicted in Scheme 1, the reaction of a solution of
[PtMe(SMe2)(bhq)] in acetone, with 0.5 equiv of dppf at room
temperature gave in good yield the new binuclear cyclometalated
The NMR spectra were recorded on a Bruker Avance DRX
500 MHz spectrometer. The operating frequencies and references,
respectively, are shown in parentheses as follows: 1H (500 MHz,
TMS), 31P (202 MHz, 85% H3PO4) and 195Pt (107 MHz, aqueous
Na2PtCl4). All the chemical shifts and coupling constants are in ppm
and Hz, respectively. Kinetic studies were carried out by using
a PerkineElmer Lambda 25 spectrophotometer with temperature
control using an EYELA NCB-3100 constant-temperature bath.
Benzo{h}quinoline and 1,10-bis(diphenylphosphino)ferrocene were
purchased from commercial sources. [PtMe(bhq)(SMe2)] [34] and
Pt(II)ePt(II) complex [Pt2Me2(bhq)2(m-dppf)], 1a, in which
bhq ¼ deprotonated benzo{h}quinoline or dppf ¼ 1,10-bis(diphe-
nylphosphino)ferrocene, by replacement of SMe2 ligands with the P
ligating atoms of dppf. Complex 1a is an air-stable yellow solid
which is stable in acetone or chloroform solution for several hours.
Reaction of the complex 1a with excess methyl iodide at room
temperature led to formation of the binuclear Pt(IV)ePt(IV)
complex [Pt2I2Me4(bhq)2(m-dppf)], 2a.
[Pt2Me2(bhq)2(
m
-dppm)] [36] were prepared as reported.
In the 1H NMR spectrum of complex 1a (see Fig. 1), the two
equivalent methyl ligands, being trans to imine N atoms, are reso-
3
nated as a doublet signal at
d
1.17 with JPH ¼ 8.1 Hz which is
2.1. [Pt2Me2(bhq)2(m-dppf)], 1a
coupled to the platinum center to give satellites with
2JPtH ¼ 85.9 Hz. The 4 equivalent
a
and 4 equivalent
b
protons of the
1,10-Bis(diphenylphosphino)ferrocene (275 mg, 0.5 mmol) was
added to a solution of [Pt(Me)(bhq)(SMe2)], (450 mg, 1.0 mmol) in
acetone (20 ml). The mixture was stirred at room temperature for
2 h. After removal of the solvent by evaporation, a yellow residue
was obtained which was further purified by repeated washing with
ether and cold acetone. Yield 66%, mp ¼ 258 ꢀC (decomp). Anal.
cyclopentadienyl rings are appeared as two broad singlets at d 4.44
and 4.38, respectively. In the 31P NMR spectrum of complex 1a, the
two equivalent P atoms are appeared as a singlet signal at 24.1
d
which are coupled to Pt atoms to give satellites with
1JPtP ¼ 2226 Hz. Consistent with this, in the 195Pt NMR spectrum of
1
1a, a doublet is observed at
d
ꢁ2588 with JPtP ¼ 2225 Hz. The
Calcd for C62H50FeN2P2Pt2: C, 56.0; H, 3.8; N, 2.1; Found: C, 55.6; H,
equivalency of the P atoms suggests that dppf is acting as a spacer
ligand between the two PtMe(bhq) moieties and thus each P atom
is coordinated to a Pt atom in a trans disposition to coordinating C
atom of the phenyl ring of bhq ligand and each Me ligand is ought
to be located trans to one of the coordinated N atom of bhq ligand.
In the 1H NMR spectrum of complex 2a (see Fig. 1), the relative
intensity of Me ligands protons to cp protons of the dppf ligand is
12:8, confirming that the complex is a dimer. The two Me ligands
2
4.0; N, 2.4. NMR data in CDCl3:
d
(1H) 1.17 (d, 6H, JPtH ¼ 85.9 Hz,
3JPH ¼ 8.1 Hz, 2 Me), 4.38 (br s, 4H,
b
,
b
0 Cp protons), 4.44 (br s, 4H,
a
,
3
a0 Cp protons), (aromatic protons): 6.81 (m, 2H, JPtH ¼ 7.7 Hz,
3JHH ¼ 2.5 Hz, CH groups adjacent to coordinated C atoms), 7.3e8.1
3
(m, 32H, overlapping multiplets), 8.18 (m, 2H, JPtH ¼ 49.2, 2 CH
groups adjacent to coordinated
N
atoms);
d
(
13C) ꢁ14.5 (d,
1JPtC ¼ 735 Hz, 2JPC ¼ 7 Hz, Me ligands), 73.8 (d, 3JPC ¼ 10 Hz,
b, b
0 Cp
2
carbons), 75.8 (d, JPC ¼ 12.5 Hz,
a
,
a0 Cp carbons), 76.6 (d,
locating trans to P are observed as overlapping doublets at d 1.03
1JPC ¼ 46 Hz, JPtC ¼ 31 Hz, ipso Cp carbons),
d(
31P) 24.1
with 3JPH ¼ 7.6 Hz and 2JPtH ¼ 61.5 Hz. However, the two Me ligands
2
1
(1JPtP ¼ 2226 Hz, 2P of dppf);
d
(
195Pt) ꢁ2588 (d, JPtP ¼ 2225 Hz,
locating trans to N ligating atoms are appeared as two different
2Pt).
doublets at
d
1.55 (3JPH ¼ 2.9 Hz) and 1.59 (3JPH ¼ 2.9 Hz), each with

S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 715 (2012) 73e81
75
N
Ph2
P
Pt
C
Me
N
C
SMe2
Fe
+ 0.5 dppf
Me
Pt
P
C
Pt
Me
Ph2
N
1a
dppf = 1,1'-bis(diphenylphosphino)ferrocene
+ Excess MeI
C
N
Ph2
P
Me
I
Pt Me
Fe
Me
P
I
Me Pt
Ph2
C
N
2a
Scheme 1. Synthesis of complexes 1a and 2a.
a considerably higher 2JPtH value of close to 72 Hz, complying with
the trans influence of N atom being lower than that of P atom. The 4
1JPtP z 1000 Hz, a value much smaller than the corresponding value
of around 2226 Hz observed in the spectrum of the Pt(II) complex
1a. Similar to what has previously been reported for the analogous
a
protons (as a broad singlet at
d 3.44) and 4 b protons (as 3 broad
singlets at 2.51, 2.63, and 2.96, with relative intensity 1:1:2) of the
d
Pt(IV)ePt(IV) complex [Pt2I2Me4(ppy)2(m-dppf)] [18], in which the
cyclopentadienyl rings are appeared at significantly higher field as
compared with those involving in the starting complex 1a
(described above), with the effect being more pronounced for the
CeN ligand is ppy ¼ deprotonated 2-phenylpyridyl (rather than
bhq in complex 2a). Although the data would well establish the
relative disposition of the different ligands on each Pt center as
indicated in Scheme 1 (with chirality at each Pt center), it is
impossible to use the present data to actually propose any “frozen”
conformer(s) for complex 2a resulting from rotation around one or
two of the PteP bonds. Yet again, as twice the “expected” number of
signals is observed in the NMR spectra of complex 2a, the formation
b
protons than for the a protons. We believe that the conversion
from square planar to octahedral geometry moves the Cp groups
into the shielding region of the aromatic bhq ligand. In the 31P NMR
spectrum of complex 2a, the two P ligating atoms are appeared as
two different signals at
d
ꢁ13.0 and ꢁ13.1, each with
Fig. 1. 1H NMR spectra of complexes 1a (top) and 2a (bottom) in the cp rings of dppf ligand (left) and Me ligands (right) regions.

76
S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 715 (2012) 73e81
of a statistical 1:1:2 mixture of three stereoisomers (the first two
being enantiomers that are not distinguishable by NMR spectros-
copy) may be a reasonable explanation.
2.5
2
T= 308 K
T=303 K
T= 298 K
3.2. Kinetic and mechanistic study of reaction of [Pt2Me2(bhq)2(m-
dppf)], 1a, with MeI
1.5
1
The binuclear complex 1a contains an MLCT band in the visible
region that could be used to monitor its reaction with MeI and
study the kinetics of the reaction by using UVevis spectroscopy.
Thus, an excess of MeI was used at 25 ꢀC and the disappearance of
T= 293 K
T= 288 K
the MLCT band at
l
¼ 345 nm in a CHCl3 solution was used to
monitor the reaction. The change in the spectrum during a typical
run is 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 following monophasic first-order
equation:
0.5
0
0
0.2 0.4 0.6 0.8
[MeI] / M
1
1.2 1.4
Abst ¼ AbsN þ ðAbs0 ꢁ AbsNÞexpðꢁkobstÞ
(1)
Plots of the first-order rate constants, kobs, versus [MeI] was
linear with no intercepts (Fig. 3), showing a first-order dependence
of the rate on the concentration of MeI. 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 dimer and MeI. The
reproducibility of the data was remarkable (4%). The same method
was used at other temperatures, and activation parameters were
obtained from the Eyring equation. The data are collected in Table 1.
Fig. 3. Plots of first-order rate constants for the reaction of complex 1a, with MeI at
different temperatures versus the concentration of MeI in CHCl3.
form Pt(IV)ePt(IV) complex C. Occurrence of the second transecis
isomerization converted complex C to the final Pt(IV)ePt(IV)
complex, 2a. All the related intermediates have been character-
ized by monitoring of the reaction at low temperatures by 1H and
31P NMR spectroscopy (see next section and Fig. 4).
The large negative value of
D
Sz obtained for the reaction of
complex 1a with MeI is typical of oxidative addition by a common
SN2 mechanism which involves nucleophilic attack of the metallic
center at the methyl group of MeI and strongly confirms the asso-
ciative nature of the reaction.
3.3. Monitoring the reaction by variable temperature 31P NMR
spectroscopy
The reaction of complex 1a with MeI was also monitored by 31P
NMR spectroscopy (see next section and Fig. 4) and on the basis of
the gathered data and the data obtained from the above kinetic
investigations, a mechanism depicted in Scheme 2 is suggested.
Thus, after the addition of MeI, complex B, which is supposed to be
the result of SN2 addition of MeI to one of the Pt(II) centers of the
starting complex 1a (i.e. complex A) followed by a rapid transecis
isomerization of the resulting Pt(IV) center, was mainly appeared.
Then, the second MeI was added to Pt(II) center of complex B to
In order to investigate the details of mechanism, the reaction of
complex 1a with excess MeI was monitored by 31P NMR spectros-
copy at low temperatures, as shown in Fig. 4. Based on the results,
the complexes and intermediates suggested for the reaction
sequence, described in Scheme 2, were assigned. Note that
complexes 1a and 2a are characterized as described in the main
text and so their characteristic 31P NMR data were used to indicate
the complexes. Thus, immediately after the addition of MeI
at ꢁ20 ꢀC, apart from complex 1a, a Pt(II)ePt(IV) species assigned
as intermediate A, was detected. Two singlet signals, one at
d 23.3
1
2.5
2
(with JPtP ¼ 2166 Hz), which is located in the Pt(II) region and its
1JPtP value is close to that of the Pt(II)ePt(II) starting complex 1a,
and another one at
d
ꢁ10.3, located in the Pt(IV) region with
1JPtP ¼ 1275 Hz, were observed. The latter value is typical for
Pt(IV)eP coupling, but is significantly higher than the corre-
sponding value found for Pt(IV)ePt(IV) complex 2a; this is probably
due to higher trans influence of Me as compared to that of the bhq-
C ligand. Although the data provide a reasonable support for the
relative disposition of the different ligands on both Pt(II) and Pt(IV)
centers as indicated in Scheme 2 for A, by the limited available data
it is not possible to suggest any specific conformation for the
intermediate A. As the time was passing on and the temperature
was raised up, the signals due to the starting material 1a was dis-
appearing while those due to the intermediate A were growing and
then later started to fade away and meanwhile comparatively weak
signals due to complex B were also observed in the first stages. For
1.5
1
0.5
0
340 360 380 400 420 440 460
λ / nm
intermediate B, two singlet signals, one at
d 23.0 (with
1JPtP ¼ 2085 Hz, located in the Pt(II) region) and another one at
Fig. 2. Changes in the UVevis spectrum during the reaction of complex 1a,
(1.5 ꢂ 10ꢁ4 M) with MeI (0.53 M) in CHCl3 at T ¼ 25 ꢀC; successive spectra were
recorded at intervals of 35 s.
1
d
ꢁ10.4, located in the Pt(IV) region with JPtP ¼ 1255 Hz, were
observed. In the meantime the suggested intermediate C was

S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 715 (2012) 73e81
77
Table 1
Rate constants and activation parameters for the reaction of the diplatinum(II) complexes with MeI in CHCl3.
[Pt2Me2(ppy)2
-dppf)]a
Complex 1a
Complex 1bb
(
m
102 k2 /Lmolꢁ1sꢁ1
102 k2 /Lmolꢁ1sꢁ1
first step 102 k2/L molꢁ1sꢁ1
second step 102 k20/Lmolꢁ1sꢁ1
c / Lmolꢁ1
0
Keq [or Keq ]
(102
k
/sꢁ1
)
(102
k
ꢁ2
/sꢁ1
)
0
ꢁ2
T ¼ 10 ꢀC
T ¼ 15 ꢀC
T ¼ 20 ꢀC
T ¼ 25 ꢀC
T ¼ 30 ꢀC
1.11 ꢃ 0.02
1.57 ꢃ 0.02
2.17 ꢃ 0.03
3.00 ꢃ 0.05
3.79 ꢃ 0.06
41.8 ꢃ 1.2
ꢁ134 ꢃ 4
0.79 ꢃ 0.01
4.84 ꢃ 0.04d
1.56 ꢃ 0.02
2.15 ꢃ 0.01
3.39 ꢃ 0.05
49.9 ꢃ 2.4
0.89 ꢃ 0.05 (0.064 ꢃ 0.003)
0.15 ꢃ 0.01 (0.02 ꢃ 0.01)
13.90 ꢃ 1.02 [7.50 ꢃ 3.78]
1.58 ꢃ 0.09 (0.24 ꢃ 0.05)
2.09 ꢃ 0.02 (0.39 ꢃ 0.08)
2.71 ꢃ 0.03 (0.63 ꢃ 0.10)
37.4 ꢃ 0.2 (79.5 ꢃ 3.7)
ꢁ152 ꢃ 1 (ꢁ23 ꢃ 12)
ꢁ42.2 ꢃ 3.7
0.29 ꢃ 0.06 (0.06 ꢃ 0.01)
0.38 ꢃ 0.07 (0.08 ꢃ 0.02)
0.54 ꢃ 0.05 (0.18 ꢃ 0.05)
43.6 ꢃ 1.3 (72.5 ꢃ 7.8)
ꢁ144 ꢃ 4 (ꢁ59 ꢃ 37)
ꢁ29.8 ꢃ 6.5
6.58 ꢃ 1.42 [4.83 ꢃ 1.28]
5.36 ꢃ 1.10 [4.75 ꢃ 1.47]
4.30 ꢃ 0.68 [3.00 ꢃ 0.88]
D
D
D
D
H
z e/kJ molꢁ1
Sze /JKꢁ1 molꢁ1
Hꢀ /kJ molꢁ1
ꢁ109 ꢃ 8
Sꢀ /JKꢁ1 molꢁ1
ꢁ127 ꢃ 13
ꢁ88 ꢃ 22
a
b
c
Data from ref. [18].
Values in parenthesis are parameters for reverse reactions (see Scheme 3; D / 1b and F / E).
0
Keq and Keq are equilibrium constants for first and second steps, respectively.
d
e
At 35 ꢀC.
Standard errors of
D
H
z and
DS
z correlate as
s(
D
Sz) ¼ (1/Tav
) s(D
Hz) [37].
started to show up. For the intermediate C we observed two signals
in the Pt(IV) regions with expected JPtP values (one signal at
[PtMe(dppf)(ppy-
for the corresponding reaction involving the bhq analog complex
studied in the present work, i.e. [Pt2Me2(bhq)2( -dppf)], 1a. Thus,
k
1C)]. However, no such scenario was observed
1
1
d
ꢁ11.0, with JPtP ¼ 1234 Hz, another signal at
d
ꢁ12.5, with
m
1JPtP ¼ 1032 Hz). As the reaction was progressed, the Pt(IV)ePt(IV)
intermediates C was quickly being disappeared and the final
Pt(IV)ePt(IV) complex 2a started to appear. After 70 min (room
temperature) all the signals were completely disappeared and the
final Pt(IV)ePt(IV) product 2a was purely obtained.
as is depicted in Scheme 2, the latter reaction proceeded more
straightforward than the former one. We believe that as a result of
the bhq ligand being more rigid than the ppy ligand, formation the
related side product [PtMe(dppf)(bhq-
during the latter reaction. Consistently, attempts to prepare the
complex [PtMe(dppf)(bhq- with the reaction of
1C)]
k
1C)] has not been favorable
k
[PtMe(bhq)(SMe2)] with 1 equiv of dppf was unsuccessful. These
observations indicate that the rigid ligand bhq, as compared to the
more flexible ppy ligand, is less prone to bind as the k1 form [34].
Besides, as is clear from Table 1, the reaction rates of complex
3.4. Effect of ligands
By comparing the above kinetic results with those of the
previously reported reaction of MeI with the ppy analogous
complex [Pt2Me2(ppy)2(m-dppf)] [18] (see Table 1), we now find
that the nature of CeN ligand has significant impact on rate and
mechanism of the reaction of MeI with the studied complexes
containing dppf as spacer ligand. In the suggested mechanism for
[Pt2Me2(bhq)2(m-dppf)], 1a, with MeI in CHCl3 at different
temperatures, are at least 1.3 times slower than the corresponding
reaction involving ppy. For example, MeI at 25 ꢀC reacted nearly 1.5
times faster with [Pt2Me2(ppy)2(
m
-dppf)] (k2 ¼ 3.00 ꢂ 10ꢁ2
Lmolꢁ1sꢁ1) than with 1a (k2 ¼ 2.15 ꢂ 10ꢁ2 Lmolꢁ1sꢁ1). This
confirms the stronger donor ability of the ppy ligand as compared
to that of the bhq ligand and shows that the platinum center in the
the reaction of binuclear complex [Pt2Me2(ppy)2(m-dppf)] with
excess MeI [18], a side reaction has been detected during which the
cyclometalated CeN ligand is opened up from the N site at the
expense of dppf ligand becoming chelated forming the complex
ppy complex [Pt2Me2(ppy)2(m-dppf)] is more electron rich than the
Fig. 4. Reaction of complex 1a with excess methyl iodide as monitored by 31P NMR spectroscopy at low temperatures. Left view: Pt(II) region. Right view: Pt(IV) region. (a) Pure 1a
(253 K), (b) immediately after addition of excess MeI (253 K), (c) 20 min after addition (265 K), (d) 34 min after addition (275 K), (e) 46 min after addition (285 K), (f) 55 min after
addition (285 K) and (g) 70 min after the temperature was raised up to room temperature. Peak assignments are shown; platinum satellites are observed and shown for all involved
species including intermediates A, B and C.

78
S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 715 (2012) 73e81
Me
N
N
Ph2
Ph2
P
Pt
I
C
Me
P
Pt
C
Me
Fe
Ph2
P
Me
Fe
Ph2
P
Me
+ MeI
C
Pt
C
Pt
k
2
N
trans-cis isomerization
of Pt(IV) center
N
(A)
1a
C
N
C
Ph2
N
P
Pt Me
Me
Ph2
P
Me
+ MeI
Fe
Me
Pt Me
Ph2
Me
Me
I
C
Pt
P
Fe
Ph2
I
C
Pt
N I
P
N
(B)
(C)
trans-cis isomerization of
the second Pt(IV) center
C
N
Ph2
Me
P
Pt Me
I
Fe
Me
Ph2
P
I
Me Pt
C
N
2a
Scheme 2. Suggested mechanism for reaction of complex 1a with MeI.
platinum center in complex 1a toward nucleophilic attacks. This is
3.5. Kinetic and mechanistic study of reaction of
[Pt2Me2(bhq)2( -dppm)], with MeI
1
consistent with the trends found for JPtP values in the 31P NMR
m
spectra of the analogous complexes [Pt2Me2(ppy)2(
m-dppf)]
(2090 Hz) and [Pt2Me2(bhq)2( -dppf)] (2226 Hz). These results also
m
As has been reported previously [36], on the basis of 31P NMR
suggest that the trans influence of metalated C atom of ppy ligand
should be greater than that of bhq ligand [35]. This was further
confirmed using density functional theory (DFT) calculations
through finding approximate structures for the described
complexes and charge on the involved platinum center. The DFT-
studies, reaction of the binuclear Pt(II)ePt(II) complex
[Pt2Me2(bhq)2(m-dppm)], 1b, in which dppm, bis(diphenylphos-
phino)methane, acts as a bridging ligand, with excess MeI first
gives a Pt(II)ePt(IV) intermediate which is finally converted to
a mixture of two Pt(IV)ePt(IV) binuclear complexes. In this work in
an attempt to shed some light on mechanism of the reaction, we
investigated kinetics of the reaction using UVevis spectroscopy.
The binuclear complex 1b contains an MLCT band in the visible
region that could be used to monitor its reaction with MeI and
study the kinetics of the reaction by using UVevis spectroscopy.
Thus, an excess of MeI was used at 25 ꢀC and the disappearance of
optimized structures for complexes [Pt2Me2(bhq)2(
m-dppf)] and
[Pt2Me2(ppy)2( -dppf)] at B3LYP level along with the calculated
m
bond distances are shown in Fig. 5.
As is clear from Fig. 5, the charge on the platinum atom in
[Pt2Me2(ppy)2(m-dppf)] complex (ꢁ0.034) is lower than that on the
platinum atom in the analog bhq complex (ꢁ0.026). This lower
charge (meaning higher electron density) at the platinum center,
complies with the higher reaction rates of the ppy complex as
compared with that of the analogs bhq complex toward their
nucleophilic attack on MeI operating by an SN2 mechanism. Also
PteP bond length for the complex having ppy ligand (Pt-
P ¼ 2.413 Å) is longer than that involving the bhq ligand (Pt-
the MLCT band at
monitor the reaction. The change in the spectrum during a typical
run is shown in Fig. 6.
l
¼ 425 nm in a CHCl3 solution was used to
The timeedependence curves of the spectra of the reaction in
CHCl3 at this condition are shown in Fig. 7. As is clear from this
figure, low concentration of MeI did not allow the reaction to shift
to completion and equilibrium has been established, but under
a large excess of MeI, the reaction was completed. The data failed to
fit properly in the monophasic first-order equation (Eq. (1)).
However, the data were successfully fitted in Eq. (2) with two
exponentials, showing a clear biphasic kinetic behavior. Thus, the
1
P ¼ 2.408 Å) complying with the smaller JPtP value in the ppy
complex as compared with that in the bhq complex. These results
suggest again the higher trans influence of the metalated C atom of
ppy as compared to that of the bhq analog, and the stronger donor
ability of the ppy ligand as compared with that of the bhq ligand.

S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 715 (2012) 73e81
79
Fig. 5. DFT calculated structures of (a) [Pt2Me2(bhq)2(
m
-dppf)] and (b) [Pt2Me2(ppy)2(
m
-dppf)]. Selected bond distances (Å) and Pt charges are shown. The H atoms are omitted for
more clarity.
0
pseudo-first-order rate constants kobs and kobs for the two steps of
the reaction were evaluated by nonlinear least-square fitting of the
absorbanceetime profiles to the biphasic first-order equation
(Eq. (2)).
the corresponding temperature data by applying a linear ln Keq
least-squares analysis according to the van’t Hoff equation (see
Table 1).
On the basis of the NMR and kinetic data, we suggest that, as is
indicated in Scheme 3, MeI first performs an electrophilic attack on
one of the electron-rich platinum(II) centers of diplatinum(II)
complex 1b with an SN2-type mechanism with the rate constant k2
and the mixed-valence Pt(II)ePt(IV) binuclear intermediate D is
formed. The reaction followed by a rapid transecis isomerization of
the resulting Pt(IV) center to form complex E. Intermediate E is
then reacted with MeI in step 2, again by an SN2-type mechanism,
Â
À
ÁÃ
At ¼ AN
þ
a
½expðꢁkobstÞꢄ þ
b
exp ꢁk0obs
t
(2)
Plots of the first-order rate constants, kobs and kobs0, versus [MeI]
was linear with a two-term rate law for both steps of the reaction
(see Fig. 8 and Scheme 3):
ꢁd½1bꢄ=dt ¼ kobs½1ꢄ; where kobs ¼ kꢁ2 þ k2½MeIꢄ
ꢁd½Eꢄ=dt ¼ k0obs½Eꢄ; where ko0 bs ¼ kꢁ0 2 þ k02½MeIꢄ
0
with the rate constant k2 that is nearly 5e6 times smaller than the
corresponding value for k2 (see Table 1) to give the Pt(IV)ePt(IV)
intermediate F. A rapid transecis isomerization of the second
Pt(IV) center in F is then occurs to give an almost 1:1 mixture of two
isomeric Pt(IV)ePt(IV) complexes, suggested to have structures 2b
and 2b0.
0
The slope and intercept of the kobse[MeI] and kobs e[MeI] plots
0
in each case gave the second-order 0rate constants (k2 and k2 ) and
reverse rate constants (k and kꢁ2 ), respectively and the results
ꢁ2
As shown above, the step 2 of MeI addition (i.e. E / F) is slower
than the step 1 (1b / D). It is suggested that in a two-step
oxidative addition reaction of this type in which none of the
components of the reaction contains any metalemetal bond and
yet the metallic centers are not too far from each other, the first
addition occurs faster than the second [23,38]. In the present work,
we believe that this has actually been the case. In the first step, MeI
are collected in Table 1. Therefore, the reaction obeys a simple
second-order rate law, first order in both the corresponding dimer
and MeI. The reproducibility of the data was remarkable (4%). The
same method was used at other temperatures, and activation
parameters were obtained from the Eyring equation (see Fig. 9) and
reported in Table 1. Equilibrium constants (Keq ¼ k2/k
and
ꢁ2
0
0
0
Keq ¼ k2 /kꢁ2 ) at different temperatures have also been calculated
and reported in Table 1.
The
D D
Hꢀ and Sꢀ values for the first and second equilibrium
0.8
0.7
0.6
0.5
steps of the reaction of complex 1b with MeI were evaluated from
1.4
1.2
1
To equilibrium
0.4
0.8
0.6
0.4
0.2
0
0.3
0.2
0.1
To completion
0
2
4
6
8
10 12 14
time / min
400
450
500
550
600
650
λ / nm
Fig. 7. The plots show the time course of absorbance for the reaction of complex 1b
with MeI (0.26e0.80 M) in CHCl3 at 20 ꢀC. The three top curves show the approach to
equilibrium; the other one, the reaction drawn to completion. The biexponential fit for
the reaction of 1b with MeI (0.37 M) is shown.
Fig. 6. Changes in the UVevis spectrum during the reaction of complex 1b,
(3 ꢂ 10ꢁ4 M) with MeI (0.66 M) in CHCl3 at T ¼ 25 ꢀC; successive spectra were recorded
at intervals of 30 s.

80
S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 715 (2012) 73e81
-9
kobs = 0.0024 + 0.0158 [MeI]
0.015
0.01
0.005
0
-10
-11
-12
-13
-14
-15
(a)
(b)
(c)
kobs ' = 0.0006 + 0.0029 [MeI]
(d)
0.0032 0.0033 0.0034 0.0035 0.0036
0
0.2
0.4
0.6
0.8
1
T -1 / K -1
[MeI]
Fig. 8. Plots of first-order rate constants [(a) first step, kobs/sꢁ1, and (b) second step,
kobs0/sꢁ1] for the reaction of complex 1b with MeI at 20 ꢀC versus the concentration of
MeI in CHCl3.
Fig. 9. Eyring plots for the reaction of complex 1b with MeI (0.26e0.80 M) in CHCl3:
(a) first step, forward reaction; (b) second step, forward reaction; (c) first step, reverse
reaction; (d) second step, reverse reaction.
attacks the platinum(II) center of a Pt(II)ePt(II) complex, 1b, while
in the second step, MeI reacts with the platinum(II) center of
a Pt(II)ePt(IV) species (complex E). As such, the reaction should be
slower in the second step because, in contrast to complex 1b, in
species E the adjacent Pt(IV) moiety not only creates a more severe
steric hindrance for the attacked Pt(II) center but also reduces its
nucleophilicity through the bridging biphosphine ligand. This
assignment has also been confirmed by Espenson’s approach [39]
as the value of extinction coefficient of complex E at 425 nm is
found to be almost 1.95 ꢂ 103 Mꢁ1 cmꢁ1. This value lies close to the
value of extinction coefficient of complex 1b (2.20 ꢂ 103 Mꢁ1 cmꢁ1),
in which both of the related complexes have MLCT bands, and far
from
3
p
(0.90 ꢂ 103 Mꢁ1 cmꢁ1), as one would expect for the final
products 2b and 2b0 with no MLCT band in the visible region.
Ph2
P
Ph2
Me
C
N
P
Me
Me
N
+ MeI, k
Ph2 Me
P
2
Pt
N
C
Pt
C
Pt
C
k-2
P
Pt
N
Ph2
(D)
Me
1b
I
C
N
=
trans-cis isomerization
of Pt(IV) center
C
N
Me
Me
P
C
N
Me
P
C
Ph2
P
C
N
Pt
I
N
+ MeI, k '
2
C
Pt
I
Ph2
P
Pt
N
k-2'
Pt
I
Ph2
Me
Ph2
(E)
Me
(F)
Me
Me
trans-cis isomerization of
the second Pt(IV) center
C
C
N
Me
Me
N
Me
Me
C
Ph2
P
Pt
I
C
Ph2
P
N
Pt
I
N
+
P
Pt
I
P
Pt
I
Ph2
Ph2
Me
Me
Me
Me
(2b')
(2b)
Scheme 3. Suggested mechanism for reaction of complex 1b with MeI.

S.M. Nabavizadeh et al. / Journal of Organometallic Chemistry 715 (2012) 73e81
81
[7] M. Rashidi, S.M. Nabavizadeh, R. Hakimelahi, S. Jamali, J. Chem. Soc. Dalton
Trans. (2001) 3430e3434.
4. Conclusion
[8] M. Rashidi, N. Shahabadi, S.M. Nabavizadeh, Dalton Trans. (2004) 619e622.
[9] M. Rashidi, S.M. Nabavizadeh, A. Akbari, S. Habibzadeh, Organometallics 24
(2005) 2528e2532.
[10] V. De Felice, B. Giovannitti, A. De Renzi, D. Tesauro, A. Panunzi, J. Organomet.
Chem. 593-594 (2000) 445e453.
On the basis of UVevis and 31P NMR spectroscopy studies,
reaction of the Pt(II)ePt(II) binuclear complex [Pt2Me2(bhq)2(m-
dppf)], 1a, in which bhqH ¼ benzo{h}quinoline and dppf ¼ 1,10-
bis(diphenylphosphino)ferrocene, with excess MeI, to give the
[11] C.M. Anderson, R.J. Puddephatt, G. Ferguson, A.J. Lough, J. Chem. Soc. Chem.
Commun. 568 (1998) 53e61.
Pt(IV)ePt(IV) complex [Pt2I2Me4(bhq)2(m-dppf)], 2a, in CHCl3, is
[12] C.M. Anderson, M. Crespo, M.C. Jennings, A.J. Lough, G. Ferguson,
R.J. Puddephatt, Organometallics 10 (1991) 2672e2679.
[13] R.H. Hill, R.J. Puddephatt, J. Am. Chem. Soc. 107 (1985) 1218e1225.
[14] R.G. Finke, G. Gaughan, C. Pierpont, J.H. Noordik, Organometallics 2 (1983)
1481e1482.
[15] S. Shyu, A. Wojcicki, Organometallics 4 (1985) 1457e1459.
[16] S.S.M. Ling, I.R. Jobe, L.M. Muir, K.W. Muir, R.J. Puddephatt, Organometallics 4
(1985) 1198e1202.
[17] S. Jamali, S.M. Nabavizadeh, M. Rashidi, Inorg. Chem. 44 (2005) 8594e8601.
[18] S. Jamali, S.M. Nabavizadeh, M. Rashidi, Inorg. Chem. 47 (2008) 5441e5452.
[19] A.L. Gavrilova, C.J. Qin, R.D. Sommer, A.L. Rheingold, B.J. Bosnich, Am. Chem.
Soc. 24 (2002) 1714e1722.
[20] M. Konard, S. Wuth, F. Meyer, E. Kaifer, Eur. J. Inorg. Chem. (2001) 2233e2240.
[21] M.A. Casado, J.J. Perez-Torrenet, M.A. Ciriano, I.T. Dobrinovitch, F.J. Lahoz,
L.A. Oro, Inorg. Chem. 42 (2003) 3956e3964.
suggested to occur through stepwise oxidative addition of MeI to
the two Pt(II) centers by the classical SN2 mechanism. The reaction
rates at different temperatures are almost 1.4 times slower than
those involving the ppy analogous complex [Pt2Me2(ppy)2(m-
dppf)], ppyH ¼ 2-phenylpyridine, reported previously to proceed
by similar mechanism [18]. This is attributed to the stronger donor
ability of the ppy ligand as compared to that of the bhq ligand as
was further confirmed using density functional theory (DFT)
calculations through finding approximate structures for the
described complexes. The higher rate of the latter reaction is dis-
cussed to be enthalpy driven.
In the above two-step reaction, after each trans MeI addition,
a trans to cis isomerization is observed. We believe that this is most
probably due to higher trans influence of the ligating C atom of
either ppy or bhq ligand, as compared to that of Me ligand, that
prefers to stay trans to I ligand, which has a lower trans influence
than P ligand (see Scheme 2 and 3).
[22] C. Tejel, M.A. Ciriano, J.A. Lopez, F.J. Lahoz, L.A. Oro, Organometallics 19 (2000)
4977e4984.
[23] T.G. Schenck, C.R.C. Milne, J.F. Sawyer, B. Bosnich, Inorg. Chem. 24 (1985)
2338e2344.
[24] J.P. Fackler Jr., H.H. Murray, J.D. Basil, Organometallics 3 (1984) 821e823.
[25] K.A. Azam, M.P. Brown, R.H. Hill, R.J. Puddephatt, R.J. Yavari, Organometallics 3
(1984) 697e702.
[26] M. Albrecht, R.A. Gossage, U. Frey, A.W. Ehlers, E.J. Baerends, A.E. Merbach,
G. van Koten, Inorg. Chem. 40 (2001) 850e855.
Acknowledgments
[27] M. Albrecht, R.A. Gossage, M. Lutz, A.L. Spek, G. van Koten, Chem. Eur. J. 6
(2000) 1431e1445.
[28] D. Zhang, L.-Z. Wu, L. Zhou, X. Han, Q.-Z. Yang, L.-P. Zhang, C.-H. Tung, J. Am.
Chem. Soc. 126 (2004) 3440e3441.
[29] M. Hissler, J.E. McGarrah, W.B. Connick, D.K. Geiger, S.D. Cummings,
R. Eisenberg, Coord. Chem. Rev. 208 (2000) 115e137.
[30] R.C. Evans, P. Douglas, C. Winscom, Coord. Chem. Rev. 250 (2006) 2093e2126.
[31] W. Sun, H. Zhu, P.M. Barron, Chem. Mater. 18 (2006) 2602e2610.
[32] P.A. Chase, R.J.M. Klein Gebbink, G. van Koten, J. Organomet. Chem. 689 (2004)
4016e4054.
We thank the Iran National Science Foundation (Grant No.
90005392) and the Shiraz University Research Council for financial
support. We also thank Dr. S. Jamali for helpful discussions and Ms.
S. Nikahd and Ms. M. Asadi for assistance with the initial
experiments.
References
[33] S.M. Nabavizadeh, M.G. Haghighi, A.R. Esmaeilbeig, F. Raoof, Z. Mandegani,
S. Jamali, M. Rashidi, R.J. Puddephatt, Organometallics 299 (2010) 4893e4899.
[34] M.G. Haghighi, M. Rashidi, S.M. Nabavizadeh, S. Jamali, R.J. Puddephatt, Dalton
Trans. 39 (2010) 11396e11402.
[35] S.M. Nabavizadeh, H. Amini, H.R. Shahsavari, M. Namdar, M. Rashidi, R. Kia,
B. Hemmateenejad, M. Nekoeinia, A. Ariafard, F. Niroomand Hosseini,
A. Gharavi, A. Khalafi-Nezhad, M.T. Sharbati, F. Panahi, Organometallics 30
(2011) 1466e1477.
[36] S. Jamali, R. Czerwieniec, R. Kia, Z. Jamshidi, M. Zabel, Dalton Trans. 40 (2011)
9123e9130.
[37] G. Lente, I. Fábián, A.J. Poë, New J. Chem. 29 (2005) 759e760.
[38] J.D. Scott, R.J. Puddephatt, Organometallics 5 (1986) 2522e2529.
[39] M. Shimura, J.H. Espenson, Inorg. Chem. 23 (1984) 4069e4071.
[1] J.P. Collman, L.S. Hegedus, J.R. Norton, R.J. Fink, Principles and Applications of
Organotransition Metal Chemistry, University Science Books, Mill Valley, CA,
1987.
[2] R.H. Crabtree, Organometallic Chemistry of the Transition Metals, third ed..
John Wiley & Sons, New York, 2001.
[3] J.D. Atwood, Inorganic and Organometallic Reaction Mechanism, second ed..
Wiley-VCH, New York, 1997.
[4] L.M. Rendina, R.J. Puddephatt, Chem. Rev. 97 (1997) 1735e1754.
[5] S.J. Hoseini, H. Nasrabadi, S.M. Nabavizadeh, M. Rashidi, R.J. Puddephatt,
Organometallics 31 (2012) 2357e2366.
[6] M. Rashidi, B.Z. Momeni, J. Organomet. Chem. 574 (1999) 286e293.