Revisiting the synthesis of trans-[Pt(dmso)2ClMe] and cis-[Pt(dmso)2Me2]: Experimental and DFT studies

Article abstract of DOI:10.1016/j.jorganchem.2019.06.002

The preparation of trans-[Pt(dmso)₂ClMe] (2) and cis-[Pt(dmso)₂Me₂] (3) from cis-[Pt(dmso)₂Cl₂] (1) and SnMe₄ has been reexamined (dmso = dimethyl sulfoxide). The information obtained from experimental and DFT studies has permitted the improvement of previously reported methods for the synthesis of both complexes in terms of reaction times, reaction yields, and atom economy. These studies show that complex 1 reacts with a first equiv of SnMe₄ to form trans-[Pt(dmso)₂ClMe] (2) as an intermediate that quickly reacts with a second equiv of SnMe₄ to yield cis-[Pt(dmso)₂Me₂] (3). When only 1 equiv of the organostannane reagent is added, the comproportionation of 3 with the excess of unreacted 1 leads the reaction back to the formation of trans-[Pt(dmso)₂ClMe] (2). The mechanism of this comproportionation has been studied using DFT calculations.

Full text of DOI:10.1016/j.jorganchem.2019.06.002

Accepted Manuscript
Revisiting the synthesis of trans-[Pt(dmso) ClMe] and cis-[Pt(dmso) Me ]:
2
2
2
Experimental and DFT studies
Edwin A. Baquero, Ana Rodríguez-Zúñiga, Juan C. Flores, Manuel Temprado,
Ernesto de Jesús
PII:
S0022-328X(19)30233-5
DOI:
https://doi.org/10.1016/j.jorganchem.2019.06.002
JOM 20814
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 30 April 2019
Revised Date: 27 May 2019
Accepted Date: 4 June 2019
Please cite this article as: E.A. Baquero, A. Rodríguez-Zúñiga, J.C. Flores, M. Temprado, E. de
Jesús, Revisiting the synthesis of trans-[Pt(dmso) ClMe] and cis-[Pt(dmso) Me ]: Experimental
2
2
2
and DFT studies, Journal of Organometallic Chemistry (2019), doi: https://doi.org/10.1016/
j.jorganchem.2019.06.002.
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ACCEPTED MANUSCRIPT
Revisiting the synthesis of trans-[Pt(dmso) ClMe] and
2
cis-[Pt(dmso) Me ]: experimental and DFT studies
2
2
a,b
a
a,
c
Edwin A. Baquero, Ana Rodríguez-Zúñiga Juan C. Flores, * Manuel Temprado, Ernesto de
a,
Jesús *
a
Departamento de Química Orgánica y Química Inorgánica, Instituto de Investigación Química
"Andrés M. del Río", Universidad de Alcalá, Campus Universitario, 28871 Alcalá de Henares,
Madrid, Spain
b
Departamento de Química, Facultad de Ciencias, Universidad Nacional de Colombia Sede Bogotá,
Carrera 30 No. 45-03, 111321 Bogotá, Colombia
c
Departamento de Química Analítica, Química Física e Ingeniería Química, Instituto de
Investigación Química "Andrés M. del Río", Universidad de Alcalá, Campus Universitario, 28871
Alcalá de Henares, Madrid, Spain
*
Corresponding Authors
Email addresses: juanc.flores@uah.es (J.C.F.), ernesto.dejesus@uah.es (E.d.J).
Keywords
Platinum. Alkyl complexes. Synthesis. DFT calculations.
Dedication
Dedicated to the memory of Professor Pascual Royo and his outstanding contribution to
organometallic chemistry.
1

Highlights
ACCEPTED MANUSCRIPT
•
•
•
•
The methylation of [Pt(dmso) Cl ] (1) with SnMe has been reexamined.
2 2 4
Improved synthesis of trans-[Pt(dmso) ClMe] (2) and cis-[Pt(dmso) Me ] (3).
2
2
2
Reaction kinetics favors the formation of dimethyl complex 3.
Subsequent comproportionation of 1 and 3 yields to the formation of monomethyl 2.
Abstract
The preparation of trans-[Pt(dmso) ClMe] (2) and cis-[Pt(dmso) Me ] (3) from cis-
2
2
2
[
Pt(dmso) Cl ] (1) and SnMe has been reexamined (dmso = dimethyl sulfoxide). The information
2 2 4
obtained from experimental and DFT studies has permitted the improvement of previously reported
methods for the synthesis of both complexes in terms of reaction times, reaction yields, and atom
economy. These studies show that complex 1 reacts with a first equiv of SnMe to form trans-
4
[
Pt(dmso) ClMe] (2) as an intermediate that quickly reacts with a second equiv of SnMe to yield
2 4
cis-[Pt(dmso) Me ] (3). When only 1 equiv of the organostannane reagent is added, the
2
2
comproportionation of 3 with the excess of unreacted 1 leads the reaction back to the formation of
trans-[Pt(dmso) ClMe] (2). The mechanism of this comproportionation has been studied using DFT
2
calculations.
1. Introduction
The synthesis of the methyl platinum complexes trans-[Pt(dmso) ClMe] (2) and cis-
2
[
Pt(dmso) Me ] (3) (dmso = dimethyl sulfoxide) was first reported by Eaborn and coworkers in
2 2
1979,[1, 2] and described in more detail for 2 by Romeo and Monsù Scolaro two decades later
(Scheme 1).[3] These complexes are suitable precursors for the preparation of a wide range of
organoplatinum compounds by substitution of the labile dmso ligand with N-heterocyclic
carbenes,[4, 5] phosphanes,[6-10] thioxamides,[11, 12] CN-chelates,[13-16] CNN-[17] or CNC-
2

pincers,[18, 19] N-, S-, or P-chelates,[20] imines,[21] and other ligands. Other valuable [PtL ClMe]
2
ACCEPTED MANUSCRIPT
and [PtL Me ] precursors, typically 1,5-cyclooctadiene[22-24] or dimethyl sulfide complexes,[25]
2
2
are prepared by methods that are less convenient due to the use of very reactive methylating reagents
Li,[24, 25] Al,[22] or Mg [23]) or the involvement of synthetic steps that have to be carefully
performed.
(
Scheme 1 here
Scheme 1. Reported synthesis for complexes (a) 2 [1-3] and (b) 3 [1, 2] from cis-[Pt(dmso) Cl ] (1)
2
2
and SnMe4.
The procedure described by Eaborn for the synthesis of organoplatinum complexes is
appealing due to the availability of a wide range of organotin compounds.[26] In addition, the
method is simple, makes use of stable and easy to handle Pt and Sn reagents, and leads to the
targeted Pt complexes in a single step in warm dmso. However, the reported yields are poor in the
case of the methyl derivatives 2 and 3 (around 55%, Scheme 1).[2, 3] The method works better with
more reactive SnMe R derivatives (e.g., R = aryl), which are also able to react with [Pt(cod)Cl ] in
3
2
chlorinated solvents.[27] Nevertheless, the organoplatinum complexes are formed faster and tend to
be more stable in dimethyl sulfoxide, probably because the coordinated dmso molecules are less
prone to dissociate in this solvent.[2] At this point, it is worth to mention that Vrieze and coworkers
have described the preparation of [Pt(cod)ClMe] from [Pt(cod)Cl ] and SnMe (1:1), in
2
4
CH Cl /MeOH (1:1) at room temperature during 24 h, with 79% yield after work up.[28]
2
2
We have studied with some detail the formation of 2 and 3 from cis-[Pt(dmso) Cl ] and SnMe
4
2
2
in the context of our recent research interests in these complexes as starting materials.[29, 30] The
results presented here have not only allowed the optimization of the procedures, but also revealed
that the monomethyl complex 2 is only isolatable after the consumption of SnMe in the conversion
4
of half of the starting cis-[Pt(dmso) Cl ] into 3, and subsequent comproportionation of the dichloro
2
2
and dimethyl complexes.
3

2. Results and discussion
ACCEPTED MANUSCRIPT
Our initial attempts to prepare complex 2 from cis-[Pt(dmso) Cl ] (1) and SnMe following the
2
2
4
method reported in ref [3] (Scheme 1a) afforded monomethyl complex 2 in very low yields (9% at
best). The reagents were heated at 80 ºC in dimethyl sulfoxide under an inert atmosphere using, as
reported, a flask equipped with a condenser. Nevertheless, the reaction outcome might be influenced
by subtle experimental variables due to the low boiling point of tetramethyltin (74–75 °C). For this
reason, the reaction was next performed in a closed ampoule tube under otherwise the reported
conditions (i.e., dmso, 80 ºC, 24 h, 1:1.8 Pt/Sn molar ratio). The outcome of the reaction was in this
case a mixture of the starting dichloride 1 and the dimethyl complex 3, instead of the expected
monomethyl complex 2 (Scheme 2). When the concentration of tetramethyltin was decreased to a
Pt/Sn molar ratio of 1:1, the result of the reaction barely changed except for the larger amounts of
unreacted 1 observed. In consequence, an eventual formation of 3 caused by the excess of SnMe4
(
i.e., 0.8 equiv) can be ruled out. These observations suggest that the intermediate trans-
Pt(dmso) ClMe] (2) reacts much faster with SnMe than the starting reagent cis-[Pt(dmso) Cl ] (1).
[
2
4
2
2
This interpretation is consistent with the large trans effect of the methyl group opposite to the Pt–Cl
bond in 2 compared to that of dmso in dichloride 1.[31] Under this hypothesis, the formation of 2
and 3 was further examined.
Scheme 2 here
Scheme 2. The reaction between 1 and SnMe in a closed vessel.
4
1
We first monitored the formation of the dimethyl complex 3 in dmso-d by H NMR
6
spectroscopy. The reaction mixture was heated at 80 °C in an NMR tube equipped with a J. Young
valve. Surprisingly, the transformation of 1 into 3 was complete in just 3 h using only a slight excess
of tetramethyltin (Pt/Sn = 1:2.5). The monomethyl complex 2 was detected as an intermediate in
concentrations always below those of the dimethyl complex 3 (for instance, the ratio 2/3 was ≈0.2
after 1 h of reaction). Further optimization of the reaction at a 1.5-g synthetic scale showed that a
stoichiometric amount of tin reagent is enough to reach almost quantitative yields (91% after
4

isolation, Scheme 3a). Under these conditions, a colorless solution is observed at the end of the
ACCEPTED MANUSCRIPT
reaction without evidences of formation of Pt(0) colloids or precipitates.
Scheme 3 here
Scheme 3. Optimized conditions for the synthesis of (a) 3 and (b) 2.
Eaborn and coworkers reported much lower yields for 3 (55% vs. 91%) in spite of the large
excess of tetramethyltin and the longer reaction times that they employed (Scheme 1b vs. 3a). They
suggested that the yields obtained in the synthesis of 3 and other organoplatinum derivatives were
reflecting the efficiency of isolation of purified compounds rather than the efficiency of the reactions
themselves.[2] Our observations show, however, that a long reaction time and a large excess of
SnMe are both counterproductive in the synthesis of 3 since both together promote the
4
decomposition of the reaction product. Thus, a gradual darkening of the solutions due to the
formation of Pt(0) colloids or precipitates was observed when the reactions were prolonged for 24 h.
Darkening was also perceptible in a solution of 3 in dmso-d after 10 h at 80 ºC in the presence of 3
6
equiv of SnMe , but the same solution was stable after 48 h at the same temperature in the absence
4
of the organotin reagent. The isolation step poses an additional problem because complex 3
decomposes quicker in concentrated solutions. Therefore, a good control of temperature and a
system assuring an efficient evacuation of dmso is important for attaining high yields. It is worth to
note here that all our attempts to replace dimethyl sulfoxide with a more volatile solvent were
unsuccessful.[32]
We have highlighted above that the monomethyl complex 2 was only a transient and minor
intermediate in the transformation of 1 into 3 in dmso at 80 °C. Nevertheless, complex 2 was
isolated by Romeo et al. in reasonable yields (56%) in the same solvent and at the same temperature
(
Scheme 1a).[3] As they used an open vessel and a relatively low excess of SnMe , we can consider
4
highly probable the initial formation of a mixture of 1 and 3 under Romeo's conditions. Then, the
isolation of the chloridomethyl complex 2 at the end of the reaction could be the result of a
subsequent comproportionation of the dichlorido (1) and the dimethyl (3) complexes. Ligand
5

exchanges between dimethyl and dichlorido platinum complexes have been previously applied to the
ACCEPTED MANUSCRIPT
preparation of other [PtL ClMe] complexes.[25, 27, 33, 34] Thus, we have examined the reaction
2
1
between equimolar amounts of 1 and 3 in dmso-d by H NMR spectroscopy. The reaction starts
6
only at 80 °C and the conversion into trans-[Pt(dmso) ClMe] (2) is complete after 24 h of reaction.
2
Regrettably, yields achieved at a preparative scale under these conditions were below 30%. Once
more, these low yields were associated to the formation, also noticed in the Romeo's report,[3] of
platinum colloids and precipitates during workup (i.e., upon removal of the solvent under vacuum at
80 ºC). After isolation of the compound, the samples of 2 dissolved in dimethyl sulfoxide are stable
at least for 48 h at 80 ºC. Therefore, decomposition of 2 seems to be favored in warm dmso under
the specific conditions of the concentration step, in parallel to the behavior noted above for 3. Due to
this drawback, we tested the preparation of 2 in alternative solvents. In CH Cl , the reaction
2
2
proceeded smoothly at room temperature affording complete conversions after 24 h, and complex 2
could be isolated in a 65% yield.
Scheme 4 summarizes the main points of the above discussion. The dimethyl complex 3 is the
main product observed in the course of the reaction because the intermediate 2 reacts faster with
SnMe than the starting dichloride 1. In the presence of substoichiometric amounts of alkylating
4
agent (due to the addition of a lower stoichiometry or to the volatility of SnMe ), the excess of cis-
4
[
Pt(dmso) Cl ] (1) comproportionates with the dimethyl complex 3 in a slow reaction that selectively
2 2
leads back to the monomethyl complex 2.
Scheme 4 here
Scheme 4. A general scheme of the reactions involved in the formation of cis-[Pt(dmso) ClMe] (2)
2
from cis-[Pt(dmso) Cl ] (1) and SnMe .
2
2
4
In the last part of this work, we studied the mechanism involved in the comproportionation of
1
and 3. This reaction progresses at room temperature in CH Cl but requires heating in dimethyl
2
2
sulfoxide. A slower reaction in the last solvent suggests that one of the steps of the reaction
mechanism probably involves the dissociation of coordinated dmso. Dissociation and exchange of
6

dmso ligands have been evidenced for [Pt(dmso) ClR] and [Pt(dmso) R ] compounds (R = Me,
2
2 2
ACCEPTED MANUSCRIPT
aryl),[2] and in phosphane-dmso substitution reactions.[7] Likewise, a SMe dissociative pathway
2
was proposed in the synthesis of [Pt(SMe ) ClMe] by a similar comproportionation approach.[21]
2
2
DFT calculations were performed to confirm this hypothesis and to elucidate the full mechanism of
the comproportionation reaction. The optimized structures of all complexes studied are collected in
the Supplementary Information (SI). Good agreement between the computed and the X-ray structure
of cis-[Pt(dmso) Cl ] (1) has been observed (see Table S1 in the SI).
2
2
As it can be seen in Figure 1, the transformation studied is computed to be thermodynamically
favorable and occurs with a moderate kinetic barrier in agreement with experimental observations.
Figure 1 here
Figure 1. Gibbs Energy diagram showing the most representative minima and transition state
computed at the PBE0-D3(PCM,CH Cl )/Def2TZVP level of theory for the methyl-chloro exchange
2
2
process observed to occur between cis-[Pt(dmso) Me ] (1) and cis-[Pt(dmso) Cl ] (3). Two
2
2
2
2
additional intermediates corresponding to the two minima connected through TS1-2 are not shown in
the figure for simplicity purposes (see Figures S1 and S2 for more details).
The first step is the decoordination of a dmso ligand from complex 1 to give the corresponding
cis-[Pt(dmso)Me ] reactive T-shaped intermediate, T in Figure 1. This dissociative process is
2
0
thermochemically uphill (∆H (298 K, CH Cl ) = 25.5 kcal/mol) but entropically favored. As
2
2
expected, the alternative decoordination of dmso from the starting cis-[Pt(dmso) Cl ] complex is
2
2
0
about 5 kcal/mol more disfavored (∆H (298 K, CH Cl ) = 30.8 kcal/mol). Once the T-shaped
2
2
intermediate, T, is formed, it would quickly react with an appropriate partner being the solvent the
most reasonable one. Thus, when dmso is used as solvent, high temperatures are needed to achieve
the desired conversion since the starting products are regenerated after recoordination of an
additional dmso molecule. On the other hand, when the reaction is performed in dichloromethane, a
molecule of solvent immediately adds to the unsaturated T-shaped intermediate cis-[Pt(dmso)Me2]
yielding the corresponding square planar complex [Pt(dmso)Me (CH Cl )]. However, the
2
2
2
7

0
stabilization obtained with this coordination is much lower (∆H (298 K,CH Cl ) = −6.4 kcal/mol)
2
2
ACCEPTED MANUSCRIPT
than that acquired with the dmso binding (i.e., −25.5 kcal/mol) and consequently, at room
temperature, the dissociation of the labile CH Cl ligand occurs easily but, similarly, is quickly
2
2
replaced by a different solvent molecule located in the surroundings. Alternatively, the T-shaped
intermediate can react bimolecularly with cis-[Pt(dmso) Cl ] to form cis-[(Pt(dmso) Cl)(µ-
2
2
2
Cl)(Pt(dmso)Me )], Int1 in Figure 1, with a chloride ligand bridging the two Pt(II) atoms. After that,
2
a second dmso ligand is released and then, in the crucial step, TS1-2 (see Figure 1) must be overcome
to achieve the methyl-chloro exchange between the two metal centers through the inversion of the
configuration of the methyl bridging ligand. The optimized structure of this transition state is shown
in Figure 2 and presents an almost planar methyl ligand with a C1–H1–H2–H3 dihedral angle of
C1–H1–H2–H3 = 16.4º.[35] Once this transition state has surmounted, two dmso ligands
subsequently add to yield the bimolecular species Int2 and, finally, two molecules of product 2. Two
additional intermediates, not shown in Figure 1, were located corresponding to the two minima
connected through TS1-2 (see Figures S1 and S2 the SI for more details).
Figure 2 here
Figure 2. Optimized structure of TS . Selected distances (in Å) and angles (in degrees): Pt1–Cl1 =
1
-2
2
.346, Pt1–S1 = 2.185, Pt1–C1 = 2.214, Pt1–Cl2 = 2.409, Pt1–Pt2 = 3.507, Pt2–Cl2 = 2.591, Pt2–C1
2.127, Pt2–C2 = 2.027, Pt2–S2 = 2.234, Pt1–Cl2–Pt2 = 89.0, Pt1–C1–Pt2 = 107.8, C1–Pt1–Cl2 =
9.2, C1–Pt2–Cl2 = 76.7, C1–Pt1–S1 = 95.2, S1–Pt1–Cl1 = 92.2, Cl1–Pt1–Cl2 = 93.5, Cl2–Pt2–S2
98.3, S2–Pt2–C2 = 91.2, C2–Pt2–C1 = 93.8, Pt1–Cl2–Pt2–C1 = 19.0, C1–H1–H2–H3 = 16.4.
=
7
=
3
. Conclusions
In this work, we have looked for solutions to several issues associated with the methylation of
Pt(dmso) Cl ] (1) with SnMe (low yields, low reproducibility, the need of large excesses of the
[
2
2
4
organostannane, etc.). We have observed that the kinetics favors the preferential formation of cis-
Pt(dmso) Me ] (3), independently of the stoichiometric ratio of the reagents. Subsequent
[
2
2
comproportionation between 1 and 3 permits the selective formation of the chloromethyl derivative
8

trans-[Pt(dmso) ClMe] (2). The choice of a closed vessel to avoid losses of the volatile
2
ACCEPTED MANUSCRIPT
tetramethyltin reagent, the addition of stoichiometric amounts of this reagent, the adequate selection
of the solvent, and the use of reaction times as short as possible are key points to achieve high and
reproducible yields. The improved procedure here reported for the synthesis of 2 and 3 affords these
compounds in shorter reaction times, in higher yields, and using stoichiometric amounts of the
tetramethyltin reagent. This will increase the interest of these complexes as useful starting materials
for the preparation of other platinum methyl complexes.
4. Experimental section
4.1. General procedures
All reactions were performed under an argon atmosphere using standard Schlenk techniques.
Unless otherwise stated, reagents and solvents were used as received from commercial sources. The
complex cis-dichlorobis(dimethyl sulfoxide)platinum(II) was prepared as described in the
literature.[3] All solvents were deoxygenated prior to use. Dimethyl sulfoxide was distilled under
argon over calcium hydride and then was passed through a basic Alumina column. NMR spectra
experiments were done in a Varian Mercury 300, Unity 300, or Unity 500 Plus spectrometer.
Compounds 2 and 3 were characterized by comparison with their previously reported NMR data.[1-
3]
4
.2. Synthesis of cis-[Pt(dmso) Me ] (3)
2
2
cis-[Pt(dmso) Cl ] (1.604 g, 3.799 mmol), SnMe (1.359 g, 1.05 mL, 7.599 mmol) and dmso
2
2
4
(6 mL) were introduced into a 25 mL ampoule fitted with a PTFE valve under an argon atmosphere.
The flask was completely submerged into an oil bath heated at 80 °C and the mixture was stirred
until formation of a colorless solution (2–4 h). Two different methods of isolation can then be used.
Method A. The solution was carefully evaporated to dryness under vacuum at a maximum
temperature of 80 °C to avoid decomposition of product. The brown solid thus obtained was washed
with Et O (3 × 20 mL), dissolved in 50 mL of CH Cl and stirred with activated charcoal (2 g) at
2
2
2
9

room temperature for 30 min. After filtration, the colorless solution was dried under vacuum (30 °C,
ACCEPTED MANUSCRIPT
00 mbar) to obtained complex 3 as a white solid (1.188 g, 82%).
3
Method B. In attempts to remove the solvent by lyophilization, we observed that complex 2
remained precipitated after unfreezing the dmso. Therefore, the solution was cooled to 40 °C,
divided in four similar fractions that are transferred each one to a different 15-mL standard
Eppendorf tube. The tubes were stored overnight at −20 °C and then allowed to reach room
temperature. After the melting of the solvent, the white precipitate was separated by filtration. The
supernatant solution can be stored again at −20 °C overnight to recover a second crop of the product.
All the portions were then combined and dissolved in dichloromethane (20 mL). The solution was
evaporated to dryness under vacuum and the residue washed with diethyl ether (3 × 30 mL), filtered,
and dried under vacuum for 1 h to afford 3 as a white solid (1.318 g, 91%).
4
.3. Synthesis of trans-[Pt(dmso) ClMe] (2).
2
cis-[Pt(dmso) Cl ] (0.650 g, 1.54 mmol) and cis-[Pt(dmso) Me ] (0.588 g, 1.54 mmol) and
2
2
2
2
CH Cl (10 mL) were introduced into a 50 mL Schlenk flask under an argon atmosphere and stirred
2
2
at room temperature for 24 h. Activated charcoal (1 g) was then added to the solution and the
mixture was stirred at room temperature during 30 minutes. After filtration, the colorless solution
was dried under vacuum (30 °C, 300 mbar), and the resulting solid was extracted with EtOH, filtered
off and dried under vacuum (30 °C, 50 mbar) to give 2 as a white solid (0.804 g, 65%).
4.4. Computational details
Electronic structure calculations were performed using the PBE0 density functional[36, 37]
with the D3 version of Grimme’s dispersion[38] and the Def2-TZVP basis set[39] for all atoms and
associated pseudopotential for Pt.[40] Geometry optimizations of all stationary points were
performed without any symmetry restrictions in CH Cl solution using the integral equation
2
2
formalism of the polarizable continuum model (IEF-PCM)[41, 42] and computing analytical energy
10

gradients. The obtained minima were characterized by performing energy second derivatives,
ACCEPTED MANUSCRIPT
confirming them as minima by the absence of negative eigenvalues of the Hessian matrix of the
energy. Transition states were characterized by single imaginary frequency, whose normal mode
corresponded to the expected motion. Computed electronic energies were corrected for zero-point
0
energy, thermal energy and entropic effects to determine ∆H (298K,CH Cl ) and
2
2
0
∆
G (298K,CH Cl ) values. All calculations were performed with the Gaussian 09 suite of
2 2
programs.[43]
Acknowledgments
This work was supported by the Spanish Ministerio de Ciencia, Innovación y Universidades
projects CTQ2017-85203-P and CTQ2016-80600-P). E.A.B. is grateful to the Universidad de
(
Alcalá for an FPI Doctoral Fellowship.
Appendix A. Supplementary data
Supplementary data to this article containing figures, tables and cartesian coordinates of
optimizes structures can be found online at ....
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[
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1 (2002) 783-785.
[
[
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[
[
[
[
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1
53.
[
[
[
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(
(
1
[
2
2
12

[
[
[
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ACCEPTED MANUSCRIPT
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[
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D.J. Fox, Gaussian 09, Revision D.01; Gaussian, Inc., Wallingford CT, 2013.
13

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Pt/Sn
:1.8
a)
1
Cl
dmso
dmso
Me
Pt
(
2
dmso
dmso
dmso
Cl
Cl
Pt
+
SnMe4
(56%, ref. [3])
7
0-80 ºC Pt/Sn
24 h
1:6.1
b)
1
dmso
dmso
Me
Me
Pt
(
3
(55%, ref [2])

ACCEPTED MANUSCRIPT
dmso
dmso
Me
Me
Pt
3
+
dmso
dmso
dmso
Cl
Cl
Pt
+ SnMe4
Cl
dmso
Me
Pt
8
0 ºC, 24 h
dmso
1
closed vessel
2
not observed
Pt/Sn = 1 : 1 or 1.8
+
unreacted 1

ACCEPTED MANUSCRIPT
(a)
Pt/Sn = 1:2
dmso
dmso
Cl
Cl
clossed vessel
dmso
dmso
Me
Me
Pt
+ SnMe4
Pt
+ SnMe Cl
3
dmso, 80 ºC
2–4 h
3
1
(
91%)
(b)
dmso
dmso
Cl
Cl
dmso
+
dmso
Me
Me
Cl
dmso
dmso
Pt
Pt
2
Pt
Me
CH2Cl2, r. t.
24 h
3
2
1
(
65%)

ACCEPTED MANUSCRIPT
Cl
dmso
Me
2
Pt
cis-[Pt(dmso) Cl ]
2
2
dmso
1
2
SnMe4 slow
slow
1
SnMe4
dmso
dmso
Me
Me
Cl
dmso
Me
Pt
Pt
dmso
fast
2
3

ACCEPTED MANUSCRIPT
Highlights
•
•
•
•
The methylation of [Pt(dmso) Cl ] (1) with SnMe has been reexamined.
2 2 4
Improved synthesis of trans-[Pt(dmso) ClMe] (2) and cis-[Pt(dmso) Me ] (3).
2
2
2
Reaction kinetics favors the formation of dimethyl complex 3.
Subsequent comproportionation of 1 and 3 yields to the formation of monomethyl 2.