Substitution and cyclometallation reactions on Pt(II) phosphite complexes

Article abstract of DOI:10.1016/j.jorganchem.2016.04.028

This paper describes the formation of newseries of platinum(II) complexes with phosphite and phosphine ligands. Treatment of cis,cis-[Me₂Pt(μ-SMe₂)₂PtMe₂] with 2 equimolar of L, L = P(OⁱPr)₃

Full text of DOI:10.1016/j.jorganchem.2016.04.028

Journal of Organometallic Chemistry 814 (2016) 8e15
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Substitution and cyclometallation reactions on Pt(II) phosphite
complexes
Mahboubeh Jamshidi, Hamidreza Samouei, Ahmad R. Esmaeilbeig*
Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71467-13565 Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
This paper describes the formation of newseries of platinum(II) complexes with phosphite and phos-
phine ligands. Treatment of cis,cis-[Me2Pt(
m
-SMe2)2PtMe2] with 2 equimolar of L, L ¼ P(OiPr)3orP(OPh)3,
Received 18 January 2016
Received in revised form
17 April 2016
Accepted 21 April 2016
Available online 23 April 2016
then adding 2 equimolar of L0, L0 ¼ PPh3 or 4-MePy, gavecis-[Me2PtLL0] complexes,1ae4a, with some side
products. Otherwise, reaction of cis,cis-[Me2Pt(m-SMe2)2PtMe2] with 4 equimolar of Me2SO, then adding
2 equimolar of PPh3, gavecis-[Me2Pt(Me2SOꢀ S)(PPh3)]. Addition of 1 equimolar of L, L ¼ P(OPh)3
k
andP(OiPr)3 and substitution of Me2SO occurred to givecis-[Me2PtLL0]complexes, 2a and 4a with more
selectivity. In order tocontrol steric and electronic effects of the ligands, 2 and 4 equimolar of P(OPh)3
Keywords:
Platinum
Phosphite
Phosphine
Orthometallation
were added to cis,cis-[Me2Pt(
m
-SMe2)2PtMe2] during refluxing and complexes 1b, [MePt(C^P))SMe2)] and
2b, [MePt(C^P){P(OPh)3}],(C^P ¼ {(
k
2-C,P)P(OPh)2(OC6H4)})were formed respectively. With adding 1
equimolar of L, L ¼ PPh3, 4-MePy to complex 1b, the products of substitution reactions were [MePt(C^P)
L], 3b and4b.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
complexes [14], might be helpful. The second restrictive reason in
synthesizing [L2Pt(PR3){P(OR)3}] complexes refers to different size
Chemists are interested in phosphines and phosphites due to
the effects of their wide varieties of steric and electronic properties
on manipulating the chemical behavior of complexes by changing
the substitutions at the phosphorus atom [1e3]. Organo-
metallicphosphite complexes are employed in a variety of metal
catalyzed processes such as hydrogenation, hydroformylation, and
hydrocyanation [4e6], but owing to the ability of phosphites to do
Arbuzov-rearrangment [7] they are more reactive than phosphine
analogues and also high solubility of their platinum complexes in
organic solvents [8], made them to be less investigated in com-
parison with phosphine complexes.
of phosphorous ligands which makesteric hindrance for entering
the second ligand during the substitution.
In the present work Pt(II) complexes containing two different p-
acceptor phosphorus ligands were synthesized such as [Me2PtLL0]
in which L ¼ P(OPh)3 or P(OiPr)3, L0 ¼ P(OiPr)3, PPh3 or 4-MePy from
different precursors to examine their effect on substitution mech-
anism. Besides, in order to control electronic and steric effects of
phosphorus ligands; some orthometallated complexes such as
[MePt(C^P)L] in which C^P
¼
{(k
2-C,P)P(OPh)2(OC6H4)} and
L ¼ P(OPh)3, PPh3, SMe2 and 4-MePy were synthesized by CeH
activation of triphenylphosphite ligand.
Platinum complexes containing both phosphine and phosphite
ligands have been rarely reported [9,10], besides, there are some
examples of these complexes with other metals [11e13]. The first
reason for this is difficulty of finding a suitable precursor which can
decrease the electronic competition between phosphorus ligands
during the reaction. So using a starting material with possibility of
dissociating a coordinated ligand as a result of possessing the
fragments and also inducing potential catalytic activity to the
2. Experimental section
The 1HNMR spectra were recorded on BrukerAvance DPX
250 MHz and BrukerAvance500 MHz Ultrashield spectrometers.
31PNMR spectra were recorded on a BrukerAvance DRX 500 MHz
and BrukerAvance400 MHz Ultrashield spectrometers. References
were TMS (1H) and H3PO4 (31P). All the chemical shifts and coupling
constants are in ppm and Hz, respectively. The phosphite
complexes are usually oily and very soluble in organic solvents such
as acetone, n-hexane and diethylether, therefore complete removal
of solvent at the end of work up stage was not easy and this has
* Corresponding author.
E-mail address: esmaeilbeig@chem.susc.ac.ir (A.R. Esmaeilbeig).
http://dx.doi.org/10.1016/j.jorganchem.2016.04.028
0022-328X/© 2016 Elsevier B.V. All rights reserved.

M. Jamshidi et al. / Journal of Organometallic Chemistry 814 (2016) 8e15
9
usually been reflected in the microanalytical results. The dimeric
precursor cis,cis-[Me2Pt( -SMe2)2PtMe2] [15] and cis-[Me2P(Me2
SOꢀ S)(PPh3)] [16] were prepared by the literature methods. Tri-
phenylphosphite P(OPh)3, triisopropylphosphite
P(OIPr)3,
triphenylphosphine (PPh3), 4-methylpyridine (4-MePy) and sol-
vents were used as commercially available chemicals without any
purification.
2.5. [MePt(C^P)(SMe2)], 1b
mixture of cis,cis-[Me2Pt(
0.0174 mmol) and P(OPh)3 (0.035 mmol, 2equimolar) in 5 mL of
toluene was refluxed at 70 ꢁC for 1 h under Ar. Removal of all the
volatiles under reduced pressure gave an oily yellow mixture,
which was washed three times with diethylether (3*1 mL). The oily
product was soluble in many organic solvents. Yield:75%. NMRdata
m
-
k
A
m-SMe2)2PtMe2], (10 mg,
2.1. Cis-[Me2Pt{P(OPh)3}(4-MePy)], 1a
in CDCl3:
d
(1H) ¼ 0.72 [d, 2J(PtH) ¼ 65.7 Hz, 3J(PH) ¼ 10.2 Hz, 3H,
Me ligand], 2.33 [s, 3J(PtH) ¼ 28.8 Hz, 6H, 2Me of SMe2 ligand],
6.80e7.40 [Ph groups on P(OPh)3 ligand], 7.80 [dd,
3J(PtH) ¼ 70.6 Hz, 4J(PH) ¼ 7.6 Hz,3J(HH) ¼ 1.5Hz, H, CH group
To
a
solution of cis,cis-[Me2Pt(m-SMe2)2PtMe2], (10 mg,
0.0174 mmol) in acetone (5 mL) 9.5
mL (0.035 mmol, 2 equimolar) of
P(OPh)3 was added. After stirring at room temperature for 1 h, the
product was cis-[Me2Pt{P(OPh)3}(SMe2)]. To the latter solution,
adjacent to C atom of C^P];
on P(OPh)3 ligand].
d
(
31P) ¼ 151.5 [s, 1J(PtP) ¼ 3105.0 Hz, P
3.5
mL 4-MePy (0.035 mmol, 2 equimolar) was added. This was
stirred at room temperature for 1 h. The solvent was removed
under vacuum. The yellow oily product was obtained. Yiel-
d:60%.Anal. Calc. for C26H28O3NPPt: C, 49.7; H, 4.5; N,2.2%. Found:
2.6. [MePt(C^P){P(OPh)3}], 2b
Cis,cis-[Me2Pt( -SMe2)2PtMe2], (10 mg, 0.0174 mmol) was
m
C,49.0; H,4.5; N, 2.4%. NMR data in CDCl3:
d
(1H) ¼ 0.25 [d,
added to the solution of P(OPh)3 (0.070 mmol, 4 equimolar) in
toluene (5 mL). The reaction mixture was refluxed for 30 h at 105 ꢁC
under Ar. Next, the solvent was evaporated in vacuo and then the
mixture was washed three times with diethylether (3*1 mL) and
gave an oily colorless product. Yield: 98.5%. Anal. Calc. for
2J(PtH) ¼ 66.6 Hz, 3J(PH) ¼ 11.5 Hz, 3H, Me ligand trans to P(OPh)3],
0.79 [d, 2J(PtH) ¼ 86.3 Hz, 3J(PH) ¼ 8.9 Hz, 3H, Me ligand cis to
P(OPh)3], 2.24 [s, 3H, methyl group of 4-methylpyridine], 7.81
[d,3J(PtH) ¼ 22.5 Hz, 3J(HH) ¼ 5.3 Hz, 2H, H2 and H6 of 4-
methylpyridine], 8.30 [d, 2H, H3 and H5 of 4-methylpyridine],
C
37H32O6P2Pt: C, 53.6; H, 3.9%. Found: C,52.8; H,4.0%. NMR data in
6.50e7.50 [Ph groups on P(OPh)3 ligand];
d
(
31P) ¼ 117.4 [s,
CDCl3:
d
(1H) ¼ 0.31 [dd, 2J(PtH) ¼ 67.7 Hz, 3J(PtransH) ¼ 9.7 Hz,
1J(PtP) ¼ 3357.0 Hz, P on P(OPh)3 ligand].
3J(PcisH) ¼ 7.6 Hz, 3H, Me ligand], 6.50e7.20 [Ph groups on P(OPh)3
ligand], 7.70 [ddd, 3J(PtH)
¼
56.7 Hz, 4J(PcisH)
¼
7.7 Hz,
2.2. Cis-[Me2Pt{P(OPh)3}(PPh3)], 2a
4J(PtransH) ¼ 9.4 Hz,3J(HH) ¼ 1.6Hz, H, CH group adjacent to C atom
of C^P];
d
(
31P) ¼ 120.8 [d, 1J(PtP) ¼ 3606.7 Hz, 2J(PP) ¼ 25.3, P on
To
a
solution of cis-[Me2Pt(Me2SOꢀ
k
S)(PPh3)] (10 mg,
P(OPh)3 ligand], 155.0 [d, 1J(PtP) ¼ 2852.4 Hz, 2J(PP) ¼ 25.3, P on C^P
0.0177 mmol) in CH2Cl2 (5 mL) 4.8
m
L (0.0177 mmol,1 equimolar) of
ligand].
P(OPh)3 was added. After stirring at room temperature for 2 h, the
solvent was removed under vacuum to yield a white residue and
then washed with 2 mL of diethylether. Yield:66.7%. Anal. Calc. for
2.7. [MePt(C^P)(PPh3)], 3b
C
38H36O3P2Pt: C, 57.2; H, 4.6%. Found: C,57.9; H,4.7%. NMR data in
To a solution of [MePt(C^P)(SMe2)] (20 mg, 0.035 mmol) in
toluene (5 mL) was added PPh3 (9.15 mg, 0.035 mmol). The mixture
was stirred at room temperature for 1 h. The solvent was removed
under reduced pressure and the oily yellow product was obtained.
CDCl3:
d
(1H) ¼ 0.24 [dd, 2J(PtH) ¼ 68.5 Hz, 3J(PH) ¼ 10.1 Hz,
3J(PH) ¼ 9.1 Hz, 3H, Me ligand trans to P(OPh)3], 0.72 [dd,
2J(PtH) ¼ 71.8 Hz, 3J(PH) ¼ 8.7 Hz, 3J(PH) ¼ 6.9Hz, 3H, Me ligand cis
to P(OPh)3], 6.60e7.70 [Ph groups on P(OPh)3 and PPh3 ligands];
Yield:75%. NMRdata in CDCl3:
d
(1H) ¼ 0.63 [dd, 2J(PtH) ¼ 66.5 Hz,
d
(
31P) ¼ 31.4 [d, 1J(PtP) ¼ 1775.5 Hz, 2J(PP) ¼ 14.9, P on PPh3 ligand],
3J(PtransH) ¼ 9.6 Hz, 3J(PcisH) ¼ 7.6 Hz, 3H, Me ligand], 6.80e7.80 [Ph
groups on P(OPh)3 and PPh3 ligands], 7.90 [t, 3J(PtH) ¼ 56.6 Hz,
4J(PcisH) ¼ 4J(PtransH) ¼ 6.0Hz, H, CH group adjacent to C atom of
120.2 [d, 1J(PtP) ¼ 3269.4 Hz, 2J(PP) ¼ 14.9, P on P(OPh)3 ligand].
2.3. Cis-[Me2Pt{P(OiPr)3}(4-MePy)],3a
C^P];
d
(
31P) ¼ 31.6 [d, 1J(PtP) ¼ 1867.0 Hz, 2J(PP) ¼ 17.8, P on PPh3
ligand], 150.8 [d, 1J(PtP) ¼ 3058.0 Hz, 2J(PP) ¼ 17.8, P on P(OPh)3
Complex 3a was made similarly using method for
ligand].
1a.Yield:65%.NMR data in CDCl3:
d
(1H)
¼
0.28[d,
2J(PtH) ¼ 63.2 Hz,3J(PH) ¼ 10.5 Hz, 3H, Me ligand trans to
P(OiPr)3],0.61 [d, 2J(PtH) ¼ 85.0 Hz,3J(PH) ¼ 7.9 Hz, 3H, Me ligand cis
to P(OiPr)3],1.19 [d, 3J(HH) ¼ 6.2 Hz, 12H, 4Me of iPr groups], 1.35 [d,
3J(HH) ¼ 6.2 Hz, 6H, 2Me of iPr groups],2.33 [s, 3H, methyl group of
4-methylpyridine], 4.80[m, 3H, CH of iPr groups], 7.77
[d,3J(PtH) ¼ 18.2 Hz, 3J(HH) ¼ 6.3 Hz, 2H, H2 and H6 of 4-
methylpyridine], 8.36 [d, 2H, H3 and H5 of 4-methylpyridine].
2.8. [MePt(C^P)(4-MePy)], 4b
This complex was prepared following a synthetic procedure
similar to 3b, described above. Yield:75%. NMR data in CDCl3:
d
(1H) ¼ 0.53 [d, 2J(PtH) ¼ 67.0 Hz, 3J(PH) ¼ 10.7 Hz, 3H, Me ligand],
2.21 [s, 3H, methyl group of 4-methylpyridine], 7.80e7.10 [Ph
groups on P(OPh)3 ligand],7.60 [d, 3J(PtH) ¼ 70.2 Hz, 4J(PH) ¼ 7.3Hz,
H, CH group adjacent to C atom of C^P], 7.85 [d, 3J(PtH) ¼ 26.1 Hz,
3J(HH) ¼ 7.3 Hz, 2H, H2 and H6 of 4-methylpyridine], 8.35 [d, 2H, H3
2.4. Cis-[Me2Pt{P(OiPr)3}(PPh3)], 4a
and H5 of 4-methylpyridine;
d
(
31P) ¼ 148.5 [s, 1J(PtP) ¼ 3059.0 Hz,
Complex 4a was made similarly using method for 2a. Yield:%80.
P on C^P ligand].
NMR data in CDCl3:
d
(1H)
¼
0.04 [t, 2J(PtH)
¼
64.4 Hz,
3J(PH)
¼
9.3 Hz, 3H, Me ligand trans to PPh3], 0.67 [t,
3. Results and discussion
2J(PtH) ¼ 70.8 Hz, 3J(PH) ¼ 8.4 Hz, 3H, Me ligand cis to PPh3], 0.93
[d, 3J(HH) ¼ 6.2 Hz, 12H, 4Me of iPr groups], 1.26 [d, 3J(HH) ¼ 6.3 Hz,
6H, 2Me of iPr groups], 4.60 [m, 3H, CH of iPr groups], 7.00e7.70 [Ph
3.1. Synthesis and substitution reactions of P-donor complexes
groups on PPh3 ligand];
d
(
31P) ¼ 32.9 [d, 1J(PtP) ¼ 1757.0 Hz,
Since synthesized platinum(II) complexes containing both
phosphine and phosphite ligands have been rarely reported, some
efforts for producing such complexes is tabloid in current paper.
2J(PP) ¼ 22.5, P on PPh3 ligand], 128.6 [d, 1J(PtP) ¼ 3153.0 Hz,
2J(PP) ¼ 22.5, P on P(OiPr)3 ligand].

10
M. Jamshidi et al. / Journal of Organometallic Chemistry 814 (2016) 8e15
Starting from synthesis of monophosphite complexes, cis-
[Me2PtL(SMe2)], L ¼ P(OiPr)3, P(OPh)3, as precursors [17] followed
by in situ adding of 1 equimolar of L0 ligand (L0 ¼ PPh3, 4-MePy) to
produce cis-[Me2PtLL0] does not act 100% selective. As depicted in
Scheme 1, after 1 h stirring reaction at room temperature, not only
the predicted monosubstituted complex cis-[Me2PtLL0], is formed,
but also two disubstituted complexes cis-[Me2PtL2] and cis-
[Me2PtL02] are seen in the mixture of the reaction. Repeating the
reaction in three solvents, tetrahydrofuran, acetone, and toluene
makes the same results. For more investigation, it was decided to
examine the formation of the precursors more carefully. It was
shown in Scheme 3 [21,22].
In addition, high electron density at the metal prevents the
approach of the axially incoming nucleophile and forming penta-
coordinated intermediate [16]. It seems that in cis,cis-[Me2Pt(m-
SMe2)2PtMe2] precursor, two bridged SMe2 can not produce
enough electron density on two platinum center, thus associative
substitution is preferred.
As Romeo et al. investigated the kinetic parameters of reaction
of cis-[Me2Pt(Me2SOꢀ
kS)(PPh3)], with 1 equimolar of py ligand in
CHCl3 solution and found that this reaction proceed via a disso-
ciative mechanism [16], it is likely that the reaction of 1 equimolar
found that the reaction of
1
equimolar of cis,cis-[Me2Pt(
m-
of nucleophiles (L ¼ P(OiPr)3 or P(OPh)3) with cis-[Me2Pt(Me2
-
SMe2)2PtMe2] complex with 2 equimolar of the phosphite ligand L,
L ¼ P(OiPr)3 or P(OPh)3, produces ~80%cis-[Me2PtL(SMe2)] and
~20% cis-[Me2PtL2] with small amount of the unreacted complex
that sometimes can be seen in cis-[Me2Pt(SMe2)2] form [18]. So in
the next step adding 2equimolar of L0, caused formation of a
mixture of products. Even by adding 1.5 equimolar of L, the same
trend can be seen.
SOꢀ
kS)(PPh3)], may also obey the dissociative mechanism due to
low p-acceptor ability of PPh3 as compared to L and high s-donor
ability of PPh3 that induces high electron density at the metal
center. As mentioned, synthesis of a complex holding one cis
acceptor ligand (Me2SO, P(OiPr)3, P(OPh)3, 4-MePy)with one
stronger -donor ligand (SMe2, PPh3) in a dimethylplatinum(II)
p
-
s
complex, caused stability of complex, as well as, making the reac-
tion proceed with high selectivity.
For getting more selectivity, another dimethylplatinum pre-
cursor,cis-[Me2Pt(Me2SOꢀ
k
S)2]was chosen to react with 1 and 2
1He31P Heteronuclear Multiple Bond Correlation(HMBC)NMR
spectrum of 2a in CDCl3 is depicted in Fig. 1. In the 1H NMR spec-
trum of 2a, two 1:1 triplets (each further coupled with the Pt
equimolar of PPh3. The monosubstituted complex cis-[Me2Pt(Me2
-
SOꢀ
kS)(PPh3)], and disubstituted complex cis-[Me2Pt(PPh3)2]were
formed respectively, as Romeo et al. have pointed out [16]. Note
center) at
d
¼ 0.24, for Me ligand trans to P(OPh)3, and at
d
¼ 0.72,
that reaction of the starting complex cis-[Me2Pt(Me2SOꢀ
k
S)2] with
for Me ligand trans to PPh3, are observed. The 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 PPh3. In the 31P NMR
1 equimolar. ofL (L ¼ P(OiPr)3,P(OPh)3)gives approximately 60% cis-
[Me2Pt(Me2SOꢀ
kS)L], 20% cis-[Me2PtL2] with 20% starting complex,
as can be seen in Scheme 2.
spectrum, two doublets at
PPh3 ligand and at
d
¼ 31.4 ppm with 1J(PtP) ¼ 1775.5 Hz for
All these observations could be explained in terms of the asso-
ciative and dissociative substitution mechanisms which can be
determined according to different nucleophilic discrimination of
precursor and intermediate complexes and also diversity in leaving
groups and nucleophilicity of entering groups which affect on
electron density and steric hindrance of the complexes. In cis-
d
¼ 120.2 with 1J(PtP) ¼ 3269.4 Hz and
2J(PP) ¼ 14.9 Hz for P(OPh)3 ligand are observed. Two most
important variables determining 31P NMR chemical shifts and
coupling constants are the electronegativity of substituents on
phosphorus and the cone angle [23,24].
The complex 4a, is similarly identified. In 1H NMR spectrum in
addition of two methyl groups coordinated to platinum, there can
[Me2Pt(Me2SOꢀ
kS)2], trans influence of strong s-donors, i.e.,
methyl groups can induce bond weakening at the leaving group,
PteS bond, leading to formation of a three coordinated interme-
diate. Moreover, the stabilization by the remaining set of three in
plane ligands of 14-electron intermediate without changing the
singlet ground state plays an important role in promoting reaction
via a dissociative pathway [19,20]. Unlike [Me2Pt(Me2S)], three-
be seen two doublets in 2:1 ratio at
resulting from the four methyl groups of two Pr groups directed
d
¼ 0.93 [3J(HH) ¼ 6.2 Hz]
i
away from phosphorus lone pair, and at
d
¼ 1.26 [3J(HH) ¼ 6.3 Hz]
resulting from two methyl groups of the third iPr group, taking up
position toward the lone pair. Also the corresponding CH groups of
iPr, each appeared as two sets with relative intensity 2:1 at
4.60 ppm shows sufficient evidence of conformation of P(OiPr)3 in
this complex [25,26].
coordinate [Me2Pt(Me2SOꢀ
kS)] complex, has a sufficient long life-
time to distinguish different nucleophiles because of the tendency
for the oxygen of the remaining sulfoxide to satiate the lack of
electron by partial interaction at the vacant coordination site, as
For better comparison, selected 1H NMR and31P{1H} NMR data
of new complexes and some analogues that have been reported
major
minor
Me
Me2
S
Me
Me
L
Me
Me
Me
Me
L
SMe2
SMe2
Me
Me
L
L
+ 2L
Pt
Pt
Pt
Pt
Pt
S
SMe2
Me
Me2
L'
+ 2L'
P(OPh)3 4-MePy
P(OPh)3 PPh3
1a
2a
3a
4a
Me
L
Me
Me
L'
L'
Me
L
P(OiPr)3
4-MePy
Pt
Pt
Pt
P(OiPr)3
PPh3
Me
L'
Me
L
major product
Scheme 1.

M. Jamshidi et al. / Journal of Organometallic Chemistry 814 (2016) 8e15
11
Me
Me
dmso
dmso
Me
Me
PPh3
Me
Me
PPh3
dmso
- Me2SO
+ Me2SO
+ PPh3
Pt
Pt
Pt
L
+L =
P(OPh)3
P(OiPr)3
+L
2a
4a
P(OPh)3
P(OiPr)3
Me
L
Me
Me
dmso
dmso
Me
PPh3
L
Me
Me
L
L
Pt
Pt
Pt
Pt
Me
dmso
60%
Me
20%
20%
Scheme 2.
M-P(OR)3 bond, so trans influence of P(OiPr)3 is more than P(OPh)3
and 2J(PtHa) of Me trans to it, is smaller. Also31P NMR chemical shift
of P(OiPr)3 is downfield compared to that of P(OPh)3. In [Me2Pt
Me
Me
Me
Pt
Me
Pt
Me
O
O
Me
Me
S
Me
Me
S
S
{P(OPh)3}L] complexes (L
¼
P(OPh)3, PPh3, SMe2, 4-MePy)
+
Me2SO
the1J(PtPa) coupling increases slightly by changing the cis ligands in
the sequence of P(OPh)3 < PPh3 < SMe2 < 4-MePy, this is the same
trend in 2J(PtHb) which shows that cis and trans influence are in the
order of P(OiPr)3 > P(OPh)3 > PPh3 > SMe2 > 4-MePy. Also the small
O
Me
Scheme 3.
Fig. 1. 1He31P HMBC NMR spectrum of cis-[Me2Pt{P(OPh)3}(PPh3)] in CDCl3.
previously [17] are collected in Table 1. According to 2J(PtHa) in
[Me2Pt{P(OPh)3}(PPh3)],2a, and [Me2Pt{P(OiPr)3}(PPh3)], 4a,
donor ability in P(OR)3 ligands plays a dominating role in forming a
magnitudes of the coupling constants, 2J(PP) (Tables 1 and 2) are
consistent with coupling between cis-phosphorus ligands [27,28].
s
-

12
M. Jamshidi et al. / Journal of Organometallic Chemistry 814 (2016) 8e15
Table 1
1H and31P{1H}NMR data of non-cyclometallated cis-[Me2PtLLʹ] complexes in CDCl3. The chemical shifts and coupling constants are in ppm and Hz, respectively.
Structure
1H NMR
31P{1H} NMR
d
(CH3)a
d
(CH3)b
d
(P)a
d
(P)b
2J(PaPb)
2J(PtH)
2J(PtH)
1J(PtP)
1J(PtP)
3J(PaH),3J(PbH)
3J(PaH), 3J(PbH)
0.36
65.4 Hz
10.8 Hz
0.80
85.8
8.9
116.1
3343.0
Ref. [11]
Ref. [11]
0.14
70.6
7.8
119.8
3036.1
0.25
66.6
11.5
0.79
86.3
8.9
117.4
3357.0
0.24
0.72
120.2
31.4
14.9
68.5
71.8
3269.4
1775.5
10.1, 9.1
6.9, 8.7
0.28
63.2
10.5
0.6
85.0
7.9
0.04
64.4
9.3
0.67
70.8
8.4
128.6
3153.0
32.9
1757.0
22.5
3.2. Synthesis and orthometallation reactions of the complexes
group vapors during the reaction with respect to high temperature
of solution and passing argon gas during the reaction that causes an
irreversible reaction. It was found that coordinated SMe2 ligand,
was easily substituted with entering ligands. So adding 1 equimolar
of L (L ¼ PPh3, 4-MePy) to complex 1b at room temperature, pro-
duced 3b and 4b.
In addition, orthoplatinated complex 2b, is prepared by reflux-
ing cis-[Me2Pt{P(OPh)3}2], for 30 h in toluene in 105 ꢁC. For further
examination, we followed the progression of the reaction of cis-
[Me2Pt{P(OPh)3}2] in closed NMR tube in toluene-d8 by 1HNMR and
31P{H} NMR which is shown in Fig. 2. During rising the temperature
from 25ꢁCto 100 ꢁC in 8 h, 1HNMR shows one triplet signal at
As part of continuing investigation of phosphorus complexes of
the platinum metal, the results on the orthometallation reactions of
triphenylphosphite in dimethylplatinum(II) complexes are re-
ported in this section. Orthometallated complexes containing the
unit M{(
k
2-C,P)P(OPh)2(OC6H4)} are commonly made by heating
complexes of triphenylphosphite in high boiling aromatic solvent
since the process of intramolecular CeH activation is usually slow
at room temperature [12,29,30] and strong tendency to afford
sterically favoured, five-membered chelate rings is observed. The
synthetic methods used to prepare the desired complexes are
described in Scheme 4. Treatment of cis,cis-[Me2Pt(
m
-
d
¼ 0.91 ppm for methyl group in aliphatic region and three signal
SMe2)2PtMe2], with 2 equimolar of P(OPh)3 ligand in toluene at
in aromatic region due to three kinds of hydrogens in phenyl ring,
in 1:2:2 ratio, Fig. 2a. When the temperature of the sample is
gradually raised from 100 ꢁCe105 ꢁC, conversion of cis-[Me2Pt
{P(OPh)3}2] to orthometallatedC^P complex 2b,starts. During the
course of the reaction, methane (CH4) is formed and its signal is
70 ꢁC for 1 h gives orthometallated complex 1b, cis-[MePt(SMe2)
{(k
2-C,P)P(OPh)2(OC6H4)}]. Start of cyclometallation reaction is
predictable by observing a color change in solution from colorless
to some yellow. This metal-carbon bond formation reaction in-
volves activation of ortho-CH group of a phenyl moiety of triphe-
nylphosphite and gives rise to a product with sterically favoured
five-membered chelate rings in a good yield. SMe2 as a leaving
observed at
d
¼ 0.21 Hz, with no evidence for deuterated methane.
Also a downfield signal with Pt satellites appears at 7.99 ppm for
Hm0 (CH group adjacent to C atom of C^P) with coupling with

M. Jamshidi et al. / Journal of Organometallic Chemistry 814 (2016) 8e15
13
Table 2
1H and31P{1H}NMR data of orthometallated cis-[XPt(C^P)L] complexes in CDCl3.The chemical shifts and coupling constants are in ppm and Hz, respectively.
Structure
1H NMR 31P{1H} NMR
d
(CH3)a
d
(Hm'
)
d
(P)a
d
(P)b
2J(PaPb)
2J(PtH)
3J(PtH)
1J(PtP)
1J(PtP)
3J(PaH),3J(PbH)
4J(PaH), 3J(PbH)
12.0
100.5
112.8
29.0
6371.0
3229.0
Ref. [27]
0.72
65.7
10.2
7.80
70.6
7.6
151.5
3105.0
0.31
67.7
9.7, 7.6
7.70
56.3
7.7, 9.4
155.0
2852.4
120.8
3606.7
25.3
17.8
0.63
7.90
150.8
31.6
66.5
56.6
3058.0
1867.0
9.6, 7.6
6.0, 6.0
0.53
67.0
10.7
7.60
70.2
7.3
148.5
3059.5
O
1b
O
P(OPh)2
P(OPh)2
+2 L
r.t.
2 P(OPh)3
Pt
Pt
+ CH4
Me
SMe2
Me
L
Me2
L
Me
Me
S
Me
Me
O
2b
reflux
3b
4b
PPh3
4 P(OPh)3
Pt
Pt
P(OPh)2
4-MePy
+ CH4
Pt
S
Me2
Me
P(OPh)3
i
2 or 4
2 or 4
P(O Pr)
3 No cyclometallation occured
PPh3
Scheme 4.
phosphorus through four bonds and having 1:3 ratio relative to
methyl ligand. These are conspicuous evidences of forming new
orthometallated complex 2b (Fig. 2b).
which cleanly disappears when the reaction is completed. 98.5%
conversion to the orthometallated complex 2b is achieved by
refluxing the reaction mixture for 30 h. The nonequivalence of the
two phosphorus donors is indicated by the observation of two
Fig. 3 shows the31P{1H}NMR spectrum at 105 ꢁC in the middle of
reaction (after 16 h) with the expected singlet signal at
resonances as two doublet signals a t
d
¼ 120.8 [1J(PtP) ¼ 3606.7 Hz]
d
¼ 123.2 ppm showing the presence of cis-[Me2Pt{P(OPh)3}2],
and 155.0 [1J(PtP) ¼ 2852.4 Hz]. The anomalous downfield signal

14
M. Jamshidi et al. / Journal of Organometallic Chemistry 814 (2016) 8e15
Fig. 2. 1HNMR spectra of a) cis-[Me2Pt{P(OPh)3}2] at 25e100 ꢁC; b) cis-[MePt{( 2-C,P)P(OPh)2(OC6H4)}{P(OPh)3}], 2b, after 30 h heating; c) expansion of b. in toluene-d8. As-
k
signments are given on the spectra.
31
Fig. 3. P NMR spectra of 2b in the middle of the reaction, after 16 h reflux in toluene-d8at 105 ꢁC; unreacted cis-[Me2Pt{P(OPh)3}2] is shown by *. Assignments are given on the
spectrum.
observed at 155.0 ppm gives further support for the occurrence of
orthometallation of triphenylphosphite because of appreciable
differences between the electronic environment of phosphorus in
cyclometallated and non-cyclometallated phosphite ligands [31].
cyclometallation processes, determination of the exact mechanism
is far from being understood and experimental data does not pro-
vide convincing evidence.
It is reported that the ease of orthometallation of [X2Pt
{P(OPh)3}2] complexes depend on the tendency of X for acting as a
leaving group and in comparison with dihalide platinum complexes
(X ¼ Cl, Br) [32] the rate of orthometallation of dimethyl complexes
decreases due to higher methylꢀplatinum bond strength. Addi-
tionally, the smaller 2J(PtPa) observed in the cis-[MePt(C^P)
{P(OPh)3}] compound compared to that in cis-[ClPt(C^P){P(OPh)3}]
indicates the larger trans effect of Me relative to chloride ligand.
Also cis-[ClPt(C^P){P(OPh)3}] complex resonates at higher field.
These observations show trans influence in the trend of
As a result, 1J(PtPa) decreases because of decreasing
p-acceptor
ability of orthometallated phosphite and reduced electron density
of platinum center as a result of elimination of one methyl
ligandbut 1J(PtPb) increases because of changing its trans ligand and
smaller trans influence of aryl compared to methyl group.
When the reaction is monitored by 1H NMR spectroscopy, there
is no evidence for the formation of a M ꢀ H bond in ꢀ20 to 2 ppm
region in any of the spectra to assign any intermediate of oxidative
addition. However, it should be mentioned that, for most

M. Jamshidi et al. / Journal of Organometallic Chemistry 814 (2016) 8e15
J. Organomet. Chem. 797 (2015) 101e109.
15
Me > Ph > Cl which should be noticed that it may be a result for
these complexes that contain a phenyl derivative in a chelate form
and the reverse behavior (Me < Ph) in other complexes has been
reported previously [33,34]. Data of complexes 3b and 4b are
summarized in Table 2 and can be interpreted in the same manner
as above.
It is worthy of mention that attempts to form cyclometallated
complexes with two other phosphorus ligands, PPh3 and P(OiPr)3,
under the same reaction conditions were unsuccessful.
[14] J.P. Collman, L.S. Hegedus, J.R. Norton, R.C. Finke, Principles and Applications
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4. Conclusion
[19] S. Lanza, D. Minniti, R. Romeo, P. Moore, J. Sachinidis, M.L. Tobe, Dissociative
substitution in four-co-ordinate planner platinium(II) complexes. The kinetic
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Different precursors can perform reactions with different
mechanisms due to different leaving group and spectator ligands.
In order to synthesize dimethyl platinum(II) complexes containing
both phosphite and phosphine ligands with high selectivity it is
better to use some starting materials such as [Me2Pt(Me2SOꢀ
kS)2]
with possibility of dissociating a coordinated ligand. Also, the steric
and electronic factors of phosphorus ligands which influence the
reaction can be adjustable with orthometallation of P(OPh)3 ligand.
Orthometallation for formation of a five-membered chelate, leads
to both a larger downfield shift in the 31P chemical shift and also a
smaller1J(PteP) in a cyclometallated ring relative to those in the
non-cyclometallated species.
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Acknowledgment
[24] M. Crutchfield, C. Dungan, J. Letcher, V. Mark, J. Van Wazer, P3i Nuclear
Magnetic Resonance, Top. Phosphorus Chem. 5 (1967).
We thank Shiraz University for financial support.
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