Organoplatinum(II) complexes with phosphite ligands

Article abstract of DOI:10.1016/j.jorganchem.2008.04.034

The phosphite complexes cis-[PtMe₂L(SMe₂)] in which L = P(OⁱPr)₃, 1a, or L = P(OPh)₃, 1b, were synthesized by the reaction of cis,cis-[Me₂Pt(μ-SMe₂)₂PtMe₂] with 2 equiv. of L. If 4 equiv. of L was used the bis-phosphite complexes cis-[PtMe₂L₂] in which L = P(OⁱPr)₃, 2a, or L = P(OPh)₃, 2b, were obtained. The reaction of cis-[Pt(p-MeC₆H₄)₂(SMe₂)₂] with 2 equiv. of L gave the aryl bis-phosphite complexes cis-[Pt(p-MeC₆H₄)₂L₂] in which L = P(OⁱPr)₃, 2a′, or L = P(OPh)₃, 2b′. Use of 1 equiv. of L in the latter reaction gave the bis-phosphite complex along with the starting complex in a 1:1 ratio. The complexes failed to react with MeI. The reaction of cis,cis-[Me₂Pt(μ-SMe₂)₂PtMe₂] with 2 equiv. of the phosphine PPh₃ gave cis-[PtMe₂(PPh₃)₂] and cis-[PtMe₂(PPh₃)(SMe₂)] along with unreacted starting material. Reaction of cis-[PtMe₂L(SMe₂)], 1a and 1b with the bidentate phosphine ligand bis(diphenylphosphino)methane, dppm = Ph₂PCH₂PPh₂, gave [PtMe₂(dppm)], 8, along with cis-[PtMe₂L₂], 2. The reaction of cis-[PtMe₂L(SMe₂)] with 1/2 equiv. of the bidentate N-donor ligand NN = 4,4′-bipyridine yielded the binuclear complexes [PtMe₂L(μ-NN)PtMe₂L] in which L = P(OⁱPr)₃, 3a, or L = P(OPh)₃, 3b. The complexes were fully characterized using multinuclear NMR (¹H, ¹³C, ³¹P, and ¹⁹⁵Pt) spectroscopy.

Full text of DOI:10.1016/j.jorganchem.2008.04.034

Journal of Organometallic Chemistry 693 (2008) 2519–2526
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Organoplatinum(II) complexes with phosphite ligands
*
Ahmad R. Esmaeilbeig , Hamid R. Samouei, Mehdi Rashidi
Chemistry Department, College 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
The phosphite complexes cis-[PtMe2L(SMe2)] in which L = P(OiPr)3, 1a, or L = P(OPh)3, 1b, were synthe-
sized by the reaction of cis,cis-[Me2Pt(l-SMe2)2PtMe2] with 2 equiv. of L. If 4 equiv. of L was used the
bis-phosphite complexes cis-[PtMe2L2] in which L = P(OiPr)3, 2a, or L = P(OPh)3, 2b, were obtained. The
reaction of cis-[Pt(p-MeC6H4)2(SMe2)2] with 2 equiv. of L gave the aryl bis-phosphite complexes cis-
[Pt(p-MeC6H4)2L2] in which L = P(OiPr)3, 2a0, or L = P(OPh)3, 2b0. Use of 1 equiv. of L in the latter reaction
gave the bis-phosphite complex along with the starting complex in a 1:1 ratio.
Article history:
Received 13 March 2008
Received in revised form 21 April 2008
Accepted 23 April 2008
Available online 30 April 2008
Keywords:
The complexes failed to react with MeI. The reaction of cis,cis-[Me2Pt(l-SMe2)2PtMe2] with 2 equiv. of the
phosphine PPh3 gave cis-[PtMe2(PPh3)2] and cis-[PtMe2(PPh3)(SMe2)] along with unreacted starting
material. Reaction of cis-[PtMe2L(SMe2)], 1a and 1b with the bidentate phosphine ligand bis(diphenyl-
phosphino)methane, dppm = Ph2PCH2PPh2, gave [PtMe2(dppm)], 8, along with cis-[PtMe2L2], 2. The reac-
tion of cis-[PtMe2L(SMe2)] with 1/2 equiv. of the bidentate N-donor ligand NN = 4,40-bipyridine yielded
the binuclear complexes [PtMe2L(l-NN)PtMe2L] in which L = P(OiPr)3, 3a, or L = P(OPh)3, 3b.
The complexes were fully characterized using multinuclear NMR (1H, 13C, 31P, and 195Pt) spectroscopy.
Ó 2008 Elsevier B.V. All rights reserved.
Organoplatinum(II) complexes
Phosphite ligands
Multinuclear NMR
1. Introduction
2. Results and discussion
Phosphorus(III) ligands, especially phosphines and phosphites,
have extensively been used as auxiliary ligands in forming transi-
tion metal complexes. These ligands are very useful as they present
wide varieties of steric effects and electronic properties when coor-
dinated to transition metals. Thus, by changing the substituents at
the phosphorus atom, it is possible to greatly manipulate the
chemical behavior of their complexes.
Although organoplatinum complexes with phosphines, PR3, as
ligands are widely studied and the complexes have been involved
in many chemical transformations, the related organoplatinum
complexes with phosphite ligands, P(OR)3, have been far less
investigated [1]. One important reason for this disparity is that
the phosphites usually perform the ‘‘classical” Arbuzov rearrange-
ment during which a phosphonate molecule is formed, and this
property is often retained when they are coordinated to a transi-
tion metal [2]. Secondly, the platinum–phosphite complexes are
usually very soluble in organic solvents and easily form oils [3].
In the present study, using suitable starting materials, we have
synthesized some primary organoplatinum(II) complexes contain-
ing the phosphite ligands L = P(OiPr)3 or P(OPh)3, of formula cis-
[PtMe2L(SMe2)], cis-[PtMe2L2], or cis-[Pt(p-MeC6H4)2L2]. Some
reactions of the complexes, including reactions with the bidentate
N-donor, 4,40-bipyridine, were also investigated.
2.1. Synthesis and reactions of the complexes
The synthetic methods used to prepare the desired complexes
are described in Scheme 1. The reaction of organoplatinum(II) pre-
cursors cis-[PtR2(SMe2)2] (R = p-MeC6H4) or cis,cis-[R2Pt(l-SMe2)2-
PtR2] (R = Me) with 2 equiv. or 4 equiv., respectively, of the
phosphite ligand L, L = P(OiPr)3 or P(OPh)3, in benzene gave cis-
[PtR2L2], 2. When cis,cis-[Me2Pt(l-SMe2)2PtMe2] was reacted with
2 equiv. of L, the monosubstituted complexes cis-[PtMe2L(SMe2)],
1, were formed. Note that reaction of the starting complex cis-
[PtR2(SMe2)2] (R = p-MeC6H4) with 1 equiv. of L did not give the
expected monosubstituted complexes cis-[PtR2L(SMe2)] and
instead the corresponding complexes 2 were obtained along with
the unreacted starting complex, in a 1:1 ratio. When 2 equiv. of
PPh3 was reacted with 1 equiv. of cis,cis-[Me2Pt(l-SMe2)2PtMe2],
the di-substituted complex cis-[PtMe2(PPh3)2] was formed along
with the monosubstituted complex, cis-[PtMe2(PPh3)(SMe2)] in
an approximately 1:2 ratio, and small amount of the starting
complex.
All these observations could be explained in terms of the
p-acceptor ability or nucleophilicity of the phosphorus ligand. In
all these substitution reactions, it is known that they normally
proceed via a penta-coordinated intermediate involving bonding
of the incoming phosphorus ligand with the empty 6pz orbital of
the square-planar starting complex to form a square-pyramidal
species [5]. As such, the dimethylplatinum complexes
* Corresponding author.
E-mail address: esmaeilbeig@chem.susc.ac.ir (A.R. Esmaeilbeig).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.04.034

2520
A.R. Esmaeilbeig et al. / Journal of Organometallic Chemistry 693 (2008) 2519–2526
Me2
S
Me
Me
Me
R
R
SMe2
SMe2
Pt
Pt
Pt
0.5 equiv
+ L
1 equiv
Me
S
Me2
+ 2 L
- 2 SMe2
R = Me
+ 2 L
- 2 SMe2
R
- SMe2
p-MeC6H4
R =
L
Me
L
- SMe2
+ L;
Pt
Pt
R = Me
L
R
SMe2
Me
L
R
L
P(OiPr)3
P(OPh)3
P(OiPr)3
P(OPh)3
Me
2a
2b
P(OiPr)3
1a
1b
Me
P(OPh)3
p-MeC6H4
p-MeC6H4
2a'
2b'
Scheme 1.
cis-[PtMe2L(SMe2)], 1a and 1b, are stable enough to be separated
under normal condition; high p-acceptor ability of the phosphite
ligands L has stabilized the complexes. However, the related tolyl
analogues cis-[Pt(p-MeC6H4)2L(SMe2)] were not formed at the
same condition. We believe that in the latter species, the additional
p-acceptance implemented by the aryl ligands, as compared to the
Me ligands in complexes 1, has made the metallic center more
electrophilic and therefore more prone to attack by the second
nucleophile L, i.e. the rate of the substitution of the first L is com-
parable to that of the second substitution by L. In addition, it has
previously been shown that the trans influence of tolyl ligand is
greater than that of Me ligand [4], and this would further facilitate
the displacement of the second SMe2 labile ligand in the tolyl
complexes.
[PtMe2(PPh3)2]. We attributed this to the lower p-acceptor ability
of PPh3, as compared to that of phosphites, in stabilizing the mon-
osubstituted complex. Besides, it has been shown [5,6] that in this
type of substitution reaction involving the attack of a phosphorus
donor on a square-planar platinum(II) complex, PPh3 has a higher
r-donor ability than P(OiPr)3, and therefore when the lone pair of
electrons on PPh3 is bound to the low lying platinum 6pz 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 filled metal 5dz2 orbital [5].
We found that the SMe2 ligand in complexes cis-[PtMe2L-
(SMe2)], 1, could be substituted with N-donor ligands. Thus, as
shown in Scheme 2, when each of the complexes 1 was reacted
with 1/2 equiv. of the bidentate N-donor, 4,40-bipyridine(NN), the
bimolecular complex [PtMe2L(l-NN)PtMe2L], 3, was obtained.
However, when complex 1b was reacted with 1 equiv. of NN, then
the complex 4, in which the NN acts as a monodentate ligand,
In contrast to complexes cis-[PtMe2L(SMe2)], 1, the related
phosphine complex cis-[PtMe2(PPh3)(SMe2)] could not be sepa-
rated and it quickly reacted with the second PPh3 to form cis-
Me
L
N
N
Me
Me
Pt
L
Pt
+ 1 equiv NN
- 2 SMe2
Me
Me
L
Me
L
2
Pt
P(OiPr)3
3a
3b
P(OPh)3
SMe2
+ 2 equiv NN
L = P(OPh)3
L
P(OiPr)3
1a
1b
Me
Pt
P(OPh)3
+ Complex 3b
N
N
Me
L
NN = 4, 4'- bipyridine
4
Scheme 2.

A.R. Esmaeilbeig et al. / Journal of Organometallic Chemistry 693 (2008) 2519–2526
2521
was formed along with the corresponding binuclear complex
3b.
has displaced the SMe2 ligand of the unreacted complex 1 to form
complex 2.
The reaction of complexes 1 with the bidentate phosphine li-
gand bis(diphenylphosphino)methane, dppm = Ph2PCH2PPh2, was
also studied and the results are summarized in Scheme 3. The
bidentate ligand dppm has a strong tendency to act both as a che-
late or bridging ligand [7], although in some cases it acts as a
monodentate (dangling) ligand [8]. As has been reported before
[9], when the binuclear complex cis,cis-[Me2Pt(l-SMe2)(l-dppm)-
PtMe2], 5, is reacted with 2 equiv. of P(OiPr)3, then the bridging
SMe2 ligand is displaced and the binuclear complex cis,cis-[Me2-
{P(OiPr)3}Pt(l-dppm)Pt{P(OiPr)3}Me2], 6, was obtained (see
Scheme 3). As can be seen, upon this reaction, the binuclear integ-
rity of the complex in retained. In contrast, in the present work
when we started from the mononuclear complex 1 and reacted it
with 0.5 equiv. of dppm, the binuclear complex 6 was not formed
and instead the known dppm chelate complex [PtMe2(dppm)]
[4d], 8, was obtained along with an equivalent amount of the
mononuclear complex cis-[PtMe2L2], 2. The complex 1 has proba-
bly reacted with dppm and by replacing SMe2, the dppm monoden-
tate intermediate 7 has formed first as a mixture with 1 equiv. of
the unreacted complex 1. The chelate effect has probably resulted
in displacement of L by the dangling phosphorus end of the dppm
ligand to form the chelate complex 8 and meanwhile the released L
The phosphite complexes 1 and 2 resisted reaction with MeI,
even in the presence of excess reagent and long reaction times.
We believe that this is related to strong p-acceptor ability of the
phosphite ligands, making the complexes poor nucleophiles for
an attacking Me group in the oxidative addition reagent MeI, via
the usual SN2 type process. Although steric hindrances are also
influential in this kind of reactions, its importance in the reactions
involving the present phosphite complexes are ruled out. Note that
for example although the Tolman cone angle of P(OiPr)3, 130°, is
smaller than that of PMePh2 (136°), the corresponding dimethyl
complex of the latter, cis-[PtMe2(PMePh2)2], is known to have
reacted with MeI to give the Pt(IV) complex [PtMe3I(PMePh2)2]
[4d].
2.2. Characterization of the complexes
The complexes were fully characterized using multinuclear
NMR (1H, 31P, 13C and 195Pt) spectroscopy. The phosphite com-
plexes 1 and 2 are very soluble in organic solvents and therefore
complete removal of solvent at the end of work up stage was not
always possible and this has usually been reflected in the microan-
alytical results.
H2
C
H2
C
Ph2
P
Pt
Ph2
PPh2
Pt
P
P Ph2
Pt
Me2
S
- SMe2
+ 2L;
L
Me
L = P(OiPr)3
Pt
Me
Me
Me
L
Me
Me
Me
Me
5
6
- 2 SMe2
Me
SMe2
2
Pt
H2
C
+ 1 dppm
Ph2
Me
L
L
Me
P
PPh2
SMe2
L
Me
- SMe2
Pt
Pt
+
P(OiPr)3
P(OPh)3
1a
1b
Me
Me
L
1
7
- SMe2
dppm = Ph2PCH2PPh2
Ph2
P
Me
Me
L
L
Pt
Pt
CH2
+
P
Me
Me
Ph2
2
8
Scheme 3.

2522
A.R. Esmaeilbeig et al. / Journal of Organometallic Chemistry 693 (2008) 2519–2526
In the 1H NMR spectrum of cis-[PtMe2{P(OPh)3}(SMe2)], 1b,
In the 1H and 13C NMR spectra of 1a, both the Me groups of
P(OiPr)3 ligand, and the corresponding CH groups, each appeared
as two sets with relative intensity 2:1. It has been shown [10] that
P(OR)3 ligands can take up four different conformations resulting
from the relative positions of the R groups. It is also indicated that
one of the possibilities in which two of the R groups direct away
from phosphorus lone pair and the third R group take up position
toward the lone pair, as indicated in Scheme 4, is more likely.
Thus in the 13C NMR spectrum of the latter complex, the Me
groups of P(OiPr)3 ligand appeared as two doublets at d = 23.6
and d = 24.2 and the corresponding CH groups were located at
d = 68.8 and d = 68.9, respectively. Consistently, in the 1H NMR
spectrum two doublets (2:1) at d = 1.26 and d = 1.30, respectively,
were observed for Me groups of P(OiPr)3 ligand and the related
CH groups appeared as multiplet at d = 4.80. These data support
the suggestion that the conformation of phosphite ligand in 1a is
as suggested in Scheme 4.
shown in Fig. 1, two doublets (each further coupled with the Pt
center) at d = 0.36 [2J(PtH) = 65.4 Hz, 3J(PH) = 10.8 Hz], for Me li-
gand trans to P(OPh)3, and at d = 0.80 [2J(PtH) = 85.8 Hz,
3J(PH) = 8.9 Hz], for Me ligand trans to SMe2, were observed. The
considerably lower 2J(PtH) value for the first signal, as compared
to that of the second one, is due to the higher trans influence of
P(OPh)3 than SMe2. A singlet at 1.89 accompanied by Pt satellites
with 3J(PtH) = 23.9 Hz was assigned to 2 equiv. Me groups of the
terminal SMe2 ligand. The observation of this 1:4:1 pattern for
SMe2 as well as the overall 2:1:1 relative intensity of the three dif-
ferent Me groups, strongly confirms the monomeric nature of the
complex 1b and rules out the possibility of formation of any binu-
clear species of type cis,cis-[{P(OPh)3}Me2Pt(l-SMe2)PtMe2-
{P(OPh)3}], for which the Me groups would be expected to give
similar patterns.
Consistent with the 1H NMR data, is the 13C NMR spectrum of
cis-[PtMe2{P(OPh)3}(SMe2)], 1b, shown in Fig. 2. A doublet signal
at d = ꢀ9.8 with 2J(CP) = 9 Hz and 1J(PtC) = 695 Hz was assigned
to the Me ligand trans to SMe2 and cis to P(OPh)3]. The second
Me ligand which is trans to P(OPh)3 appeared at d = 8.3 with a
much higher value of 2J(CP) = 165 Hz, but a lower value of
1J(PtC) = 637 Hz.
The 1H NMR spectrum of cis-[PtMe2{P(OPh)3}2], 2b, is shown in
Fig. 3. The signal at d = 0.14 due to the 2 equiv. Pt–CH3 groups
which are trans to two P ligands, has a complicated pattern [4d],
and the Pt satellites gave 2J(PtH) = 70.6 Hz. The 2 equiv. phospho-
rus atoms in complex 2b appeared as a singlet at d = 120 in the
31P NMR spectrum with platinum satellites with 1J(PtP) = 3036 Hz.
Due to a very high solubility of complex 2b, it was possible to ob-
tain a very well resolved signal in its 1H coupling 195Pt NMR spec-
trum, as shown in Fig. 4. This is interesting since the Pt signal,
appeared at d = ꢀ2899 and has coupled to 6 equiv. protons of the
2Me ligands to give a septet with 2J(PtH) = 71 Hz, a value almost
identical to the value of 70.6 Hz obtained from the corresponding
1H NMR spectrum, discussed below. The septet is further coupled
with 2 equiv. P atoms to give a triplet with a 1J(PtP) value of
3025 Hz, close to the 1J(PtP) value of 3036 Hz, obtained in the re-
lated 31P NMR spectrum. The complex cis-[PtMe2{P(OiPr)3}2], 2a,
was similarly identified and the data are summarized in the exper-
imental. Both di-methyl complexes 2a and 2b were also identified
by 13C NMR spectroscopy. Typically, as shown in Fig. 2, a doublet of
doublets at d = 0.8 with 1J(PtC) = 552 Hz, 2J(CPtrans) = 142 Hz and
2J(CPcis) = 14 Hz was observed for the two Pt–Me groups trans to
P(OiPr)3 in complex cis-[PtMe2{P(OiPr)3}2], 2a.
In the 31P NMR spectrum of cis-[PtMe2{P(OPh)3}(SMe2)], 1b, a
singlet at d = 116 with 1J(PtP) = 3343 Hz was observed for the phos-
phite ligand. Observation of a doublet at ꢀ2677 in the 195Pt NMR
spectrum of complex 1b with 1J(PtP) = 3352 Hz (very close to the
value of 1J(PtP) = 3343 Hz, obtained from the 31P NMR spectrum)
clearly indicated the presence of only one phosphite ligand in the
complex. The complex cis-[PtMe2{P(OiPr)3}(SMe2)], 1a, was simi-
larly identified and the data are summarized in Section 3.
31
In the P NMR spectrum of cis-[Pt(p-MeC6H4)2{P(OiPr)3}2], 2a0,
a singlet at d = 121.8 with 1J(PtP) = 3119 Hz was observed for the
2 equiv. phosphorous ligands and this is consistent with the obser-
vation of a triplet at d = ꢀ2940 in the corresponding 195Pt NMR
spectrum with 1J(PtP) = 3114 Hz. A similar trend was also observed
for the analogous complex cis-[Pt(p-MeC6H4)2{P(OPh)3}2], 2b0. The
13C NMR spectra of these di-tolyl complexes gave useful informa-
tion about the tolyl ligands. The region of C atoms of tolyl ligands
directly connected to the platinum center in complex cis-[Pt(p-
MeC6H4)2{P(OiPr)3}2], 2a0, is shown in Fig. 2. The observation of a
doublet of doublets at d = 154.4 with 2J(CPtrans) = 169 Hz and
2J(CPcis) = 20 Hz was assigned to the 2 equiv. C atoms of tolyl li-
gands (Ci) that further coupled to platinum center to give
1J(PtC) = 796 Hz. It is interesting to note that this latter coupling
is nearly 30% lower than 1J(PtC) = 552 Hz observed for Me ligands
trans to P(OiPr)3 in cis-[PtMe2{P(OiPr)3}2], 2a, discussed above
(see also Fig. 2). This is obviously due to the fact that the C atom
of tolyl ligand (Ci) has used sp2 hybrid orbital to bind to the plati-
num center, as compared with sp3 hybrid orbital used by C of Me in
complex 2a. This behavior has also been reflected on the 2J(CPtrans
)
values and as is expected based on hybrid orbitals. The value for
the tolyl complex 2a0 is some 16% greater than the corresponding
value for the Me complex 2a (169 vs. 142). A similar trend, a 30%
change in the 2J(CPcis) values (20 vs. 14) is observed for the com-
plexes 2a and 2a0. Consistently, the 1J(PtP) value in the 31P NMR
spectrum of complex cis-[PtMe2{P(OiPr)3}2], 2a, 3177 Hz, is higher
than the value for the complex cis-[Pt(p-MeC6H4)2{P(OiPr)3}2], 2a0,
Fig. 1. 1H NMR spectrum of cis-[PtMe2{P(OPh)3}(SMe2)], 1b.

A.R. Esmaeilbeig et al. / Journal of Organometallic Chemistry 693 (2008) 2519–2526
2523
Fig. 2. 13C NMR spectra of complexes: bottom view, the Pt–Me region of cis-[PtMe2{P(OPh)3}(SMe2)], 1b; middle view, the Pt–Me region of cis-[PtMe2{P(OiPr)3}2], 2a; top
view, C atoms of tolyl ligands directly connected to Pt center in cis-[Pt(p-MeC6H4)2{P(OiPr)3}2], 2a0. The assignments are shown.
3119 Hz. The difference, although modest (ꢁ2%), reflects the high-
er trans influence of tolyl ligand as compared to that of Me ligand
[4]. A similar trend of ꢁ2% difference was observed for the P(OPh)3
complexes 2b and 2b0.

2524
A.R. Esmaeilbeig et al. / Journal of Organometallic Chemistry 693 (2008) 2519–2526
observed for the di-methyl complexes 2a and 2b. The phosphite li-
O
R
O
gands P(OR)3 are r-donors as well as rather strong p-acceptors
i
R
when forming bond with platinum atom. The alkyl group Pr in
P
P(OiPr)3, as compared to the aryl group Ph in P(OPh)3, would obvi-
ously make P(OiPr)3 a stronger r-donor and a weaker p-acceptor
than P(OPh)3. As such it would seem that the r-donor ability plays
a dominating role in forming a bond between platinum and the
phosphites. Consistently, the 13C NMR data for P(OiPr)3 indicates
a higher trans influence than P(OPh)3. Thus, the 1J(PtC) value of
552 Hz observed for the Pt–Me group in the 13C NMR spectrum
of complex cis-[PtMe2{P(OiPr)3}2], 2a, is some 4% lower than that
of the corresponding value of 1J(PtC) = 575 Hz in complex cis-
[Me2Pt{P(OPh)3}2], 2b. A similar ‘‘4% decrease” trend was also ob-
served for the 1J(PtC) coupling between the platinum atom and
the C atom of the tolyl ligand directly connected to platinum in
di-aryl complexes 2a0 and 2b0.
O
R
Scheme 4.
The binuclear complexes 3a and 3b, containing bridging NN li-
gand were characterized using 1H and 31P NMR spectroscopy.
Typically in the 1H NMR spectrum of [Me2{P(OiPr)3}Pt(l-NN)Pt-
{P(OiPr)3}Me2], 3a, a doublet at d = 0.32 with 2J(PtH) = 64.7 Hz
and 3J(PH) = 10.3 Hz was assigned to the 2 equiv. Pt–Me groups
trans to P(OiPr)3] while the doublet at d = 0.76 with 3J(PH) = 8.0 Hz
and a considerably higher 2J(PtH) value of 87.9 Hz was assigned to
the 2 equiv. Pt–Me groups cis to P(OiPr)3 and trans to N. The 2J(PtH)
values are consistent with a higher trans influence of the phosphite
ligand than that of the N ligating atom. In the 31P NMR spectrum of
[Me2{P(OPh)3}Pt(l-NN)Pt{P(OPh)3}Me2], 3b, shown in Fig. 5, the
observation of a singlet with Pt satellites at d = 117.5 with
1J(PtP) = 3341 Hz indicates that each of the two P atoms are situ-
ated on one platinum center to give a symmetrical geometry as
shown in Scheme 2. A relatively low intensity singlet was observed
at d = 119.5 with 1J(PtP) = 3043 Hz, which is assigned to a very
small amount of the monomeric complex [Me2Pt(NN-N)-
{P(OPh)3}],4, (NN-N = monodentate 4,40-bipyridine). As mentioned
in the previous section (see also Scheme 2), a higher concentration
of the complex 4 could be obtained when 2 equiv. of NN are
reacted with complex 1b. In the 1H NMR spectrum, two doublets
Fig. 3. 1H NMR spectrum of cis-[PtMe2{P(OPh)3}2], 2b, in Me region.
The above data also suggest that the phosphite P(OiPr)3, as com-
pared to P(OPh)3, forms a stronger bond to the platinum center.
Thus, the 1J(PtP) value of 3119 Hz observed in the 31P NMR spec-
trum of the di-aryl complex cis-[Pt(p- MeC6H4)2{P(OiPr)3}2], 2a0,
is some 4% higher than the corresponding value of 2987 Hz ob-
served in the 31P NMR spectrum of the di-aryl complex cis-[Pt(p-
MeC6H4)2{P(OPh)3}2], 2b0. A similar ‘‘4% increase” trend was also
Fig. 4. 1H coupling 195Pt NMR spectrum of cis-[PtMe2{P(OPh)3}2], 2b.

A.R. Esmaeilbeig et al. / Journal of Organometallic Chemistry 693 (2008) 2519–2526
2525
6H, 2Me of SMe2 ligand], 4.80 [m, 3H, 3 CH of iPr groups]; d
(
13C) = ꢀ12.6 [d, 1J(PtC) = 688 Hz, 2J(CP) = 9 Hz, Me ligand cis to
P(OiPr)3], 6.9 [d, 1J(PtC) = not resolved, 2J(CP) = 153 Hz, Me ligand
trans to P(OiPr)3], 21.5 [d,2J(PtC) = 9 Hz, 3J(CP) = 3 Hz, Me groups
of SMe2 ligand], 23.6 [d, 3J(CP) = 5 Hz, 4Me groups of Pr], 24.2 [d,
i
3J(CP) = 4 Hz, 2Me groups of iPr], 68.8 [s, 3J(CPt) = 17 Hz, CH groups
i
i
of Pr], 68.9 [s, 3J(CPt) = 18 Hz, CH groups of Pr]; d (31P) = 128.1 [s,
1J(PtP) = 3315 Hz]; d (195Pt) = ꢀ2720 [d, 1J(PtP) = 3321 Hz].
The complex cis-[PtMe2{P(OPh)3} (SMe2)],1b, was prepared sim-
ilarly using 2 equiv. of P(OPh)3. Yield: almost quantitative. Anal.
Calc. for C22H27O3PPtS: C, 44.23; H, 4.52. Found: C, 44.59; H,
4.73%. NMR in CDCl3: d (1H) = 0.36 [d, 2J(PtH) = 65.4 Hz, 3J(PH) =
10.8 Hz, 3H, Me ligand trans to P(OPh)3], 0.80 [d, 2J(PtH) = 85.8 Hz,
3J(PH) = 8.9 Hz, 3H, Me ligand cis to P(OPh)3], 1.89 [s, 3J(PtH) =
23.9 Hz, 6H, 2Me of SMe2 ligand], 6.84–7.06 [Ph groups on
P(OPh)3 ligand]; d (13C) = ꢀ9.8 [d, 1J(PtC) = 695 Hz, 2J(CP) = 9 Hz,
Me ligand cis to P(OPh)3], 8.3 [d, 1J(PtC) = 637 Hz, 2J(CP) = 165 Hz,
Me ligand trans to P(OPh)3], 20.4 [d, 3J(CP) = 3 Hz, Me groups of
SMe2 ligand], 120.9, 121.0, 124.3, 129.5, 151.5, 151.6 [the Ph pro-
tons]; d (31P) = 116.1 [s, 1J(PtP) = 3343 Hz]; d (195Pt) = ꢀ2677.3 [d,
1J(PtP) = 3352 Hz].
3.2. cis-[PtMe2{P(OiPr)3}2], 2a
One thousand lL stock solution of P(OiPr)3 (0.348 mmol) was
Fig. 5. 31P NMR spectrum of [Me2{P(OPh)3}Pt(l-NN)Pt{P(OPh)3}Me2], 3b. The signal
together with its Pt satellites shown by asterisks is due to a small quantity of the
monomeric complex [Me2Pt(NN-N){P(OPh)3}],4, (NN-N = monodentate 4,40-
bipyridine).
added to
a solution of cis,cis-[Me2Pt(l-SMe2)2PtMe2] (50 mg,
0.087 mmol) in dried benzene (10 mL) and stirred at room temper-
ature for 1 h. The solvent was removed under reduced pressure to
yield a colorless oily product which was soluble in many organic
solvents. Yield: almost quantitative. Anal. Calc. for C20H48O6P2Pt ꢂ
0.2C6H6: C, 38.63; H, 7.52. Found: C, 38.83; H, 7.49%. NMR in CDCl3:
d (1H) = 0.46 [m, 2J(PtH) = 66.5 Hz, 3J(P-PtCH3) = 10.5 Hz, 6H, 2Me
at d = 0.26 and 0.85 with 2J(PtH) = 66.8 Hz [3J(PH) = 11.3 Hz] and
2J(PtH) = 86.9 Hz [3J(PH)=9.0 Hz] were assigned to the Me ligand
trans to P(OPh)3 and the Me ligand cis to P(OPh)3 (and trans to
N), respectively. The binuclear complexes 3a and 3b are therefore
always contaminated with at least a very small amount of the
monomeric complex of type 4 and as such the obtained CNH
microanalytical results did not properly match with the calculated
quantities.
i
ligands], 1.28 [d, 3J(HH) = 6.2 Hz, 36H, 12Me groups of Pr], 4.73
[m, 6H, 6CH groups of iPr]; d (13C) = 0.8 [dd, 1J(PtC) = 552 Hz,
2J(CPtrans) = 142 Hz, 2J(CPcis) = 14 Hz, 2Me ligands trans to P(OiPr)3],
i
24.2 [t, 3J(CP) = 4 Hz, Me groups of Pr], 68.7 [s, 3J(CPt) = 17 Hz, CH
groups of iPr]; d (31P) = 131.7 [s, 1J(PtP) = 3177 Hz]; d (195Pt) =
ꢀ2966 [t, 1J(PtP) = 3170 Hz, 2J(PtH) = 64 Hz (obtained from the 1H
coupling 195Pt NMR spectrum)].
3. Experimental
The following complexes were made similarly using cis,cis-
[Me2Pt(l-SMe2)2PtMe2] and 4 equiv. or cis-[Pt(p-MeC6H4)2(SMe2)2]
and 2 equiv. of the corresponding L group: cis-[PtMe2{P(OPh)3}2],
2b. Yield: almost quantitative. Anal. Calc. for C38H36O6P2Pt: C,
53.84; H, 4.24. Found: C, 53.86; H, 4.24%. NMR in CDCl3: d
(1H) = 0.14 [m, 2J(PtH) = 70.6 Hz, 6H, 2Me ligands], 6.83–7.15 [Ph
groups on P(OPh)3 ligand]; d (13C) = 1.7 [dd, 1J(PtC) = 575 Hz,
2J(CPtrans) = 146 Hz, 2J(CPcis) = 15 Hz, 2Me ligands], 120.7, 124.4,
129.4, 151.3 [s, carbons in Ph groups of P(OPh)3]; d (31P) = 119.8
The 1H NMR spectra were recorded on a Bruker Avance DPX 250
MHz spectrometer. 31P, 13C and 195Pt NMR spectra were recorded
on a Bruker Avance DRX 300 MHz spectrometer. References were
TMS (1H, 13C), H3PO4 31P), and aqueous K2PtCl4 195Pt); CDCl3
( (
was used as solvent. All the chemical shifts and coupling constants
are in ppm and Hz, respectively. cis-[Pt(p-MeC6H4)2(SMe2)2] [11]
and the dimeric precursor cis,cis-[Me2Pt(l-SMe2)2PtMe2] [12] were
prepared by the literature methods. The phosphites P(OiPr)3 and
P(OPh)3 were used as purchased from Fluka without any purifica-
tion. The stock solutions of P(OR)3 were prepared by adding 474 lL
of P(OPh)3 or 444 lL of P(OiPr)3 to 5 mL dried benzene.
[s, 1J(PtP) = 3036 Hz];
d
(
195Pt) = ꢀ2899 [t, 1J(PtP) = 3025 Hz,
2J(PtH) = 71 Hz]. cis-[Pt(p-MeC6H4)2{P(OiPr)3}2], 2a0. Anal. Calc. for
C
32H56O6P2Pt ꢂ 0.5C6H6: C, 50.47; H, 7.14. Found: C, 50.49; H,
7.69%. NMR in CDCl3: d (1H) = 1.18[d, 3J(HH) = 6.2 Hz, 36H, 12Me
i
groups of Pr], 2.08 [s, 6H, 2Me groups on the p-tolyl ligands],
3.1. cis-[PtMe2{P(OiPr)3}(SMe2)], 1a
4.54 [m, 6H, 6CH groups of iPr]; 6.69 [d, 3J(HH) = 6.4Hz, 4Hm of tolyl
ligands], 7.18 [m, 3J(PtH) = 55.9 Hz, 4Ho of tolyl ligands];
d
Five hundred lL stock solution of P(OiPr)3 (0.174 mmol) was
(
13C) = 20.8 [s Me groups on the p-tolyl ligands]; 24.3 [s, Me groups
added to
a
solution of cis,cis-[Me2Pt(l-SMe2)2PtMe2] (50 mg,
of iPr], 69.5 [s, CH groups of iPr],127.6 [t, 2J(CPt) = 63 Hz,
3J(CP) = 8 Hz, Co of tolyl ligands], 129.7 [s, Cp of tolyl ligands],
136.9 [t, 3J(CPt) = 35 Hz, Cm of tolyl ligands], 154.4 [dd,
1J(PtC) = 796 Hz, 2J(CPtrans) = 169 Hz, 2J(CPcis) = 20 Hz, Ci of tolyl
ligands]; d (31P) = 121.8 [s, 1J(PtP) = 3119 Hz]; d (195Pt) = ꢀ2940 [t,
1J(PtP) = 3114 Hz]. cis-[Pt(p-MeC6H4)2{P(OPh)3}2], 2b0. NMR in
CDCl3: d (1H) = 1.82 [s, 6 H, 2Me groups on the p-tolyl ligands],
6.27 [d, 3J(HH) = 7.5 Hz, 4Hm of tolyl ligands], 6.73 [m, J(PtH);= not
resolved, 3J(HH) = 31.2 Hz, 4Ho of tolyl ligands]; 6.89–7.1 [Ph
groups on P(OPh)3 ligand]. d (13C) = 20.8[s, Me groups on the
0.087 mmol) in dried benzene (10 mL). After stirring at room tem-
perature for 1 h, the solvent was removed under vacuum. The oily
product was soluble in many organic solvents. Yield: almost quan-
titative. Anal. Calc. for C13H33O3PPtS: C, 31.52; H, 6.66. Found: C,
30.86; H, 6.97%. NMR in CDCl3: d (1H) = 0.32 [d, 2J(PtH) = 62.4 Hz,
3J(PH) = 10.2 Hz, 3H, Me ligand trans to P(OiPr)3], 0.64 [d,
2J(PtH) = 84.0 Hz, 3J(PH) = 8.1 Hz, 3H, Me ligand cis to P(OiPr)3],
1.26 [d, 3J(HH) = 6.1 Hz, 12H, 4Me of iPr groups], 1.30 [d,
3J(HH) = 6.1 Hz, 6H, 2Me of Pr groups], 2.43 [s, 3J(PtH) = 24.0 Hz,
i

2526
A.R. Esmaeilbeig et al. / Journal of Organometallic Chemistry 693 (2008) 2519–2526
p-tolyl ligands];120.8, 124.6, 129.5, 151.3 [s, aromatic carbons in
P(OPh)3]; 127.8 [t, 2J(CPt) = 65 Hz, 3J(CP) = 8 Hz, Co of tolyl ligands],
131 [s, Cp of tolyl ligands], 136 [t, 3J(CPt) = 34 Hz, Cm of tolyl
ligands], 151 [dd, 1J(PtC) = 830 Hz, 2J(CPtrans) = 175 Hz, 2J(CPcis) =
19 Hz, Ci of tolyl ligands]; d (31P) = 111.4 [s, 1J(PtP) = 2987 Hz]; d
was stirred for 3 h at room temperature. The solvent was removed
under reduced pressure and the resulting oil was washed with
n-hexane to give a white powder which was identified by 1H
NMR spectroscopy as a 1:1 mixture of [PtMe2(dppm)] and [PtMe2-
{P(OiPr)3}2].
(
195Pt) = ꢀ2883 [t, 1J(PtP) = 2981 Hz,].
3.6. Attempted reaction of MeI with complexes 1 and 2
3.3. [Me2Pt{P(OiPr)3}(l-NN)Pt{P(OiPr)3}Me2], 3a
In a typical experiment, excess of MeI (1 mL) was added to
10 mg of complex [PtMe2{P(OiPr)3}2], 2a, (either as solid or in
5 mL of benzene or acetone solutions). The mixture was stirred
for 2 h. The solvent was removed and based on the 1H NMR data
of the resulting residue, no reaction had been occurred.
To
a
colorless solution of cis-[PtMe2{P(OiPr)3}(SMe2)], 1a,
(86.245 mg, 0.174 mmol) in benzene(10 mL) was added 4,40-bipyr-
idine (13.5 mg, 0.087 mmol). The mixture was stirred at room tem-
perature for 3 h, during which the color of the solution was
changed to yellow. The solvent was removed under reduced pres-
sure and the oily yellow product was washed with n-hexane (2 mL)
to give a yellow powder. NMR in CDCl3: d (1H) = 0.32 [d, 2J(PtH) =
64.7 Hz, 3J(PH) = 10.3 Hz, 6H, 2Me ligands trans to P(OiPr)3], 0.76
[d, 2J(PtH) = 87.9 Hz, 3J(PH) = 8.0 Hz, 6H, 2Me ligands cis to
Acknowledgement
We thank the Shiraz University for financial support.
P(OiPr)3], 0.97[d, 3J(HH) = 6.2 Hz, 36 H, 12Me groups of Pr], 4.85
i
[br., 6H, 6CH groups of iPr], 7.30[d, 3J(HH) = 7.5Hz, 4Hm of NN
ligand], 8.60 [m, 3J(HH) = 6.5Hz, 4 Ho of NN ligand]; d(31P) =
128.3[s, 1J(PtP) = 3367 Hz, P(OiPr)3 ligands].
References
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G.B. Young, Comprehensive Organometallic Chemistry, Pergamon Press,
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The complex [Me2{P(OPh)3}Pt(l-NN)Pt{P(OPh)3}Me2], 3b, was
prepared similarly using complex 1b. NMR in CDCl3: d (1H) = 0.32
[d, 2J(PtH) = 58.8 Hz, 3J(PH) = 12.5 Hz, 6H, 2Me ligands trans to
P(OPh)3], 0.88 [d, 2J(PtH) = 87.9 Hz, 3J(PH) = 9.0 Hz, 6H, 2Me ligands
cis to P(OPh)3], 6.9-7.5 [Ph groups on P(OPh)3 ligand], 8.0–8.75
[aromatic region of NN ligand];
3341 Hz].
d (
31P) = 117.5 [s, 1J(PtP) =
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3.4. [Me2Pt(NN-N){P(OPh)3}], 4
This was obtained as an approximately 1:1 mixture with com-
plex 3b by the above procedure used to prepare 3b, i.e. the reaction
of complex cis-[PtMe2{P(OPh)3}(SMe2)], 1b, with 2 equiv. of NN.
NMR in CDCl3: d (1H) = 0.26 [d, 2J(PtH) = 66.8 Hz, 3J(PH) = 11.3 Hz,
3H, Me ligand trans to P(OPh)3], 0.85 [d, 2J(PtH) = 86.9 Hz,
3J(PH) = 9.0 Hz, 3H, Me ligand cis to P(OPh)3], 6.8–7.2 [Ph groups
on P(OPh)3 ligand], 7.25–8.75 [aromatic region of NN ligand];
d(31P) = 119.5 [s, 1J(PtP) = 3043 Hz].
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3.5. Reaction of cis-[PtMe2L(SMe2)], 1, with dppm
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In a typical experiment, to a solution of complex cis-[PtMe2-
{P(OiPr)3}(SMe2)], 1a, (8.6245 mg, 0.0174 mmol) in 10 mL dried
benzene was added dppm (3.34 mg, 0.0087 mmol) and the mixture
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