Interaction of pyridineplatinum(II) complexes with alkyl sulfoxides

Article abstract of DOI:10.1134/S0036023608080159

Interaction of pyridineplatinum(II) complexes with dimethyl sulfoxide and diethyl sulfoxide is studied by NMR spectroscopy. The interaction products are pyridinesulfoxide and bissulfoxide platinum(II) complexes. Cis-trans isomerization of the products is

Full text of DOI:10.1134/S0036023608080159

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2008, Vol. 53, No. 8, pp. 1238–1241. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © D.A. de Vekki, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 8, pp. 1331–1334.
COORDINATION
COMPOUNDS
Interaction of Pyridineplatinum(II) Complexes
with Alkyl Sulfoxides
D. A. de Vekki
St. Petersburg State Technological Institute (Technical University), Moskovskii pr. 26, St. Petersburg, 198013 Russia
Received August 3, 2007
Abstract—Interaction of pyridineplatinum(II) complexes with dimethyl sulfoxide and diethyl sulfoxide is
studied by NMR spectroscopy. The interaction products are pyridinesulfoxide and bissulfoxide platinum(II)
complexes. Cis–trans isomerization of the products is observed along with the substitution reaction and deter-
mines the final configuration of the complexes.
DOI: 10.1134/S0036023608080159
1ç NMR spectrum of cis-[Pt(Py)2Cl2] (δç, ppm):
Interaction of sulfoxide platinum(II) complexes
7.53 t (2çβ, Py, J 6.8 Hz), 8.04 t (1çγ, Py, J 7.9 Hz),
8.90 dt (2çα, Py, J 5.6, J 20.3 Hz).
with nitrogen-containing ligands is well studied [1–4],
whereas the inverse process—exchange of coordinated
nitrogen-containing ligands for alkyl sulfoxides—has
not been described. However, we recently demon-
strated [5] that dissolution of pyridineplatinum(II)
complexes in dimethyl sulfoxide (DMSO) is accompa-
nied by a partial alteration of their inner coordination
spheres. Therefore, it was of interest to go further in this
direction using dimethyl and diethyl sulfoxides and di-
and tetrapyridine platinum(II) complexes.
1ç NMR spectrum of trans-[Pt(Py)2Cl2] (δç, ppm):
7.55 t (2çβ, Py, J 6.7 Hz), 8.05 t (1çγ, Py, J 8.0 Hz),
8.90 dt (2çα, Py, J 55, J 16.5 Hz).
1ç NMR spectrum of [Pt(Py)4]Cl2 (δç, ppm): 7.53 t
(2çβ, Py, J 6.4 Hz), 8.04 t (1çγ, Py, J 7.3 Ha), 8.90 dt
(2çα, Py, J 5.8, J 16.8 Hz).
EXPERIMENTAL
RESULTS AND DISCUSSION
1H NMR spectra were recorded on Bruker AC-200
and WM-400 instruments in (CD3)2CO at a working fre-
quency of 220.13 and 400.14 MHz, respectively. Mea-
surements were carried out without additional refer-
ences with frequencies related to the signal of the deu-
terated solvent. A Leco CHN-932 element analyzer was
used.
Control over the reaction of trans-[Pt(Py)2Cl2] with
excess DMSO showed that
a
mixture of
[Pt(Me2SO)(Py)Cl2] geometric isomers is formed as soon
as during dissolution; δç, ppm: cis, 3.53 t, JPtH 24.2 Hz;
trans, 3.46 t, JPtH 20.8 Hz. After 13 h at 80°C, the
trans-[Pt(Me2SO)(Py)Cl2] conversion is 34%; the ratio
cis-[Pt(Me2SO)(Py)Cl2] : trans-[Pt(Me2SO)(Py)Cl2] = 5 : 7.
Further exposure of the isomer mixture in DMSO pro-
gressively decreases the trans-[Pt(Me2SO)(Py)Cl2] con-
centration; after 18.5 h, the ratio cis-
[Pt(Me2SO)(Py)Cl2] : trans-[Pt(Me2SO)(Py)Cl2] = 7 : 1.
A rise in the reaction temperature to 100°ë enhances
isomerization: after 18 h, only cis-[Pt(Me2SO)(Py)Cl2]
In a flask equipped with a refluxer, pyridineplatinum
complex ((5–15) × 10–5 mol) was dissolved in alkyl sul-
foxide (0.5–1 mL) at 70–100°C. The reaction was inter-
rupted at an arbitrary moment, cooled, water or diethyl
ether (15–20 mL) was added, the precipitate was fil-
1
tered and analyzed using H NMR. A decrease in the
signal intensity from the γ-hydrogen atom of coordi-
nated pyridine and the appearance of a signal from the is observed in the products. The ultimate formation of
coordinated sulfoxide methyl group were monitored.
the cis-complex is due to the well known tendency of
pyridinesulfoxide trans-complexes to isomerize in the
presence of trace free sulfoxide [1, 7].
Pyridine, DMSO, diethyl sulfoxide (DESO), and
diethyl ether of chemically pure grade were used in
experiments. cis-[Pt(Me2SO)(Py)Cl2] and trans-
[Pt(Me2SO)(Py)Cl2] were prepared as described in [2];
cis-[Pt(Et2SO)(Py)Cl2] and trans-[Pt(Et2SO)(Py)Cl2] as
in [3]; cis-[Pt(Py)2Cl2], trans-[Pt(Py)2Cl2], and
[Pt(Py)4]Cl2 were prepared using the general synthesis
procedure for aminoplatinum(II) complexes [6].
When trans-[Pt(Py)2Cl2] is dissolved in DESO,
pyridine substitution occurs more slowly (after 16 h,
conversion is 88% against 94% for DMSO); the major
product is cis-[Pt(Et2SO)(Py)Cl2]. The higher activity
of DMSO compared to DESO is due to its stronger
binding with platinum [8].
1238

INTERACTION OF PYRIDINEPLATINUM(II) COMPLEXES
1239
The rate of the reaction between cis-[Pt(Py)2Cl2] and
alkyl sulfoxides is slightly higher than for
trans-[Pt(Py)2Cl2]. After 14 h at 80°ë, cis-[Pt(Py)2Cl2]
conversion in DMSO is 58% against 50% in DESO. In
this case, the reaction mixture also contains both geo-
metric isomers of the pyridinesulfoxideplatnium(II)
complex; the ratio between the cis- and trans-isomers is
about 5 : 2. Further exposure of the reaction mixture
displaces equilibrium toward cis-[Pt(Alk2SO)(Py)Cl2],
but the cis-isomer of the disulfoxideplatinum(II) com-
plex is formed in parallel. For example, cis-[Pt(Py)2Cl2]
conversion after 16 h in DMSO is 93%; the ratio
cis-[Pt(Me2SO)(Py)Cl2] : trans-[Pt(Me2SO)(Py)Cl2] :
In turn, heating of trans-[Pt(Me2SO)(Py)Cl2] and
trans-[Pt(Et2SO)(Py)Cl2] in proper sulfoxides first
results in the 90–99% isomerization of the starting
complex; then the disulfoxide product is gradually
formed (after 9 h at 100°ë, ~80% cis-[Pt(Alk2SO)2Cl2]
is formed); cis-pyridinesulfoxide complexes under sim-
ilar conditions do not isomerize, and the ligand
exchange reaction occurs at higher rates (after 8 h at
100°ë, ~85% cis-[Pt(Alk2SO)2Cl2] is formed). The
absence of trans-[Pt(Alk2SO)2Cl2] in the reaction mix-
ture (as monitored by 1H NMR spectra) is likely due to
release of thermodynamic constraints.
cis-[Pt(Me2SO)2Cl2]
cis-[Pt(Me2SO)2Cl2], δç, ppm: 3.58 t, JPt-H 23.2 Hz).
=
10
:
3
:
1; for
From the above, we suggest the following scenario
for the substitution of alkyl sulfoxide for pyridine:
+
Cl
N
Cl
N
Alk2SO
Cl–
Pt
Pt
Alk
N
Cl
N
S
Alk
O
I
Cl–
Py
Py
Cl–
Cl
Cl
Cl
Cl
Pt
Cl
Pt
N
Alk
Alk
Alk2SO
Py
∆
O
Alk
Alk
N
(Alk2SO)
S
Pt
S
S
Alk
Alk
O
Alk
Alk
O
Cl
S
O
Cl–
Py
Alk2SO
Py
+
Cl
Cl
N
N
Alk2SO
Cl–
Pt
Pt
O
N
Cl
N
S
Alk
Alk
II
First, alkyl sulfoxide substitutes for chloride anion tion mixture, pyridine in the cis-position to sulfoxide is
preferably substituted.
in
cis-[Pt(Py)2Cl2],
which
generates
[Pt(Alk2SO)(Py)2Cl]+ (I). Further transformation of
intermediate I can follow two routes: the return to the
starting complex or the substitution of pyridine. The
latter produces cis- or trans-[Pt(Alk2SO)(Py)Cl2];
The first step of the reaction of alkyl sulfoxide
with trans-[Pt(Py)2Cl2] is competitive ligand exchange.
In the
former
case
(pyridine
substitution),
trans-[Pt(Alk2SO)(Py)Cl2] is the product; in the latter
because trans-[Pt(Alk2SO)(Py)Cl2] prevails in the reac- (chloride anion substitution), [Pt(Alk2SO)(Py)2Cl]+ (II).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 53 No. 8 2008

1240
DE VEKKI
Further transformation of intermediate II can follow occur in stages, as observed for [Pt(Py)2Cl2] geometri-
two routes: return to the starting complex or yield cis-
[Pt(Alk2SO)(Py)Cl2].
cal isomers. The reaction mixture always contains
cis-[Pt(Alk2SO)PyCl2] in addition to both
Given that the reaction mixture contains free alkyl
sulfoxide, trans-[Pt(Alk2SO)(Py)Cl2] gradually isomer-
izes to cis-[Pt(Alk2SO)(Py)Cl2], which in turn interacts
with a new alkyl sulfoxide molecule and generates
[Pt(Alk2SO)2Cl2].
[Pt(Alk2SO)2Cl2] isomers; for example, after 18 h at 80°ë,
the ratio between cis-[Pt(Me2SO)PyCl2], trans-
[Pt(Me2SO)2Cl2], and cis-[[Pt(Py)4]Cl2] is 3 : 13 : 4.
The first stage of the reaction between [Pt(Py)4]C
The reaction between alkyl sulfoxides and tet- and alkyl sulfoxides is substitution of one inner-sphere
rapyridineplatnum(II) chloride [Pt(Py)4]Cl2 does not
pyridine ligand.
2+
2+
2+
N
N
N
N
N
N
Alk2SO
Py
Alk2SO
Py
Pt
Pt
Pt
O
Alk
Alk
Alk
Alk
S
S
N
S
N
N
Alk
Alk
O
O
Cl–
III
IV
Py
Cl–
Py
+
+
Cl
N
N
N
2Cl–
2Py
Pt
Pt
Alk
Alk
Alk
Alk
S
S
N
Cl
O
O
V
VI
Cl–
Py
Cl–
Cl–
Py
Py
Cl
Cl
Cl
Cl
Cl
N
Alk2SO
Py
∆
Pt
Pt
Pt
(Alk2SO)
Alk
Alk
Alk
Alk
Alk
O
S
S
N
S
S
Cl
Alk
O
O
Alk
Alk
O
Further transformation of intermediate III involves
Having analyzed the data on substitution of pyridine
the following routes: (a) the return to the initial com- for alkyl sulfoxides obtained in this work and borrowed
plex (unlikely in excess sulfoxide), (b) substitution of from the literature, we notice that ligand exchange of
alkyl
sulfoxide
for
pyridine
to
yield pyridine for sulfoxide in platinum(II) complexes has
[Pt(Alk2SO)2(Py)2]2+ (IV), and (c) dissociation/pyridine
substitution resulting in intermediates V and VI. Argu-
ments in favor of the occurrence of stage (b) are the
existence of cis-[Pt(Alk2SO)2Cl2] even at the initial
stage (it is easily generated from IV as a result of sub-
stitution of chloride anion for two pyridine molecules)
and the familiar ability of sulfoxides to form tet-
rakissulfoxide platinum(II) complexes [9, 10]. The
occurrence of stage (c) explains the existence of mix-
tures of cis- and trans-[Pt(Alk2SO)(Py)Cl2] in the
products.
lower rates and occurs under more severe conditions
than the inverse process.
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