Reactivity of geometric isomers of (-)-dichloropyridine(methyl-para-tolylsulfoxide)platinum(II) by optical rotatory dispersion

Article abstract of DOI:10.1023/A:1011357929566

The reactions of the optically active geometric isomers of the platinum(II) complex (-)-[Pt(Me-p-TolSO)(Py)Cl₂] with several nucleophilic reagents (Py, Ph₃PS, Ph₃P, Ph₃As, and Me₂SO) were studied by optical rotatory dispersion, IR spectroscopy, and ¹H and ³¹P NMR spectroscopy. A mechanism for the reaction is proposed.

Full text of DOI:10.1023/A:1011357929566

Russian Journal of Coordination Chemistry, Vol. 27, No. 8, 2001, pp. 579–584. Translated from Koordinatsionnaya Khimiya, Vol. 27, No. 8, 2001, pp. 617–624.
Original Russian Text Copyright © 2001 by de Vekki, Spevak, Skvortsov.
Reactivity of Geometric Isomers
of (–)-Dichloropyridine(methyl-para-tolylsulfoxide)platinum(II)
by Optical Rotatory Dispersion
D. A. de Vekki, V. N. Spevak, and N. K. Skvortsov
St. Petersburg Technological Institute (Technical University), Moskovskii pr. 26, St. Petersburg, 198013 Russia
Received October 30, 2000
Abstract—The reactions of the optically active geometric isomers of the platinum(II) complex (–)-[Pt(Me-p-
TolSO)(Py)Cl2] with several nucleophilic reagents (Py, Ph3PS, Ph3P, Ph3As, and Me2SO) were studied by opti-
cal rotatory dispersion, IR spectroscopy, and 1H and 31P NMR spectroscopy. A mechanism for the reaction is
proposed.
Organic sulfoxides R1R2SO are ambident ligands tion of (–)-trans-[Pt(Me-p-TolSO)(Py)Cl2] measured in
containing a soft (sulfur) and a hard (oxygen) electron- dichloromethane is –22°C, and that of the cis-isomer is
donating center. Therefore, they can be coordinated by –117°).
both hard and soft acids through the oxygen and the sul-
fur atoms, respectively. Due to this versatility, ligands
of this type form complex compounds with virtually all
metals of the periodic table [1, 2]; the number of known
Since almost all natural sulfoxides occurring in
onion, garlic, and other vegetable foodstuff contain
chiral sulfur atoms [4], the ORD method can be pro-
posed as a tool for investigating the reactions of various
metals with biologically active compounds.
In this study, we demonstrate that ORD measure-
ments can be applied when examining the chemical
behavior of the geometric isomers of (–)-[Pt(Me-p-
TolSO)(Py)Cl2] toward nucleophiles (Py, Ph3PS, Ph3P,
Ph3As, and Me2SO) in dichloromethane. IR and NMR
spectroscopy were used to more precisely elucidate the
stages of ligand substitution.
sulfoxide-containing
compounds
continuously
increases, and these compounds now constitute a sepa-
rate section of coordination chemistry.
The reactivity of sulfoxide-containing compounds
1
is usually studied by NMR spectroscopy (at ç, 13ë,
and 31P and at the complex-forming metal nuclei).
However, the spin properties of neither sulfur nor oxy-
gen enable NMR studies at their nuclei; therefore, in
practice, the 1H signals from the R1 and R2 substituents
are normally used.
EXPERIMENTAL
In this work, we demonstrate that the reactivity of
coordination compounds containing a chiral electron-
donating atom can be effectively studied by optical
rotatory dispersion (ORD). Previously [3], it was found
that coordinaion of (+)-methyl-para-tolyl sulfoxide
(Me-p-TolSO) through the sulfur atom is accompanied
by inversion of the sign of rotation, whereas coordina-
tion through oxygen does not change the sign of rota-
tion. This fact can be used as an analytical tool for rapid
and easy determination of the mode of coordination of
the ambident ligand using simple polarimetric mea-
surements.
1
The H and 31P NMR spectra of solutions of the
compounds in (CD3)2CO and CDCl3 were recorded on
a Bruker AC-200 instrument operating at 200.13 and
81.01 MHz for H and 31P, respectively. The chemical
1
shifts (in ppm) were expressed with respect to TMS. No
standards were used in the measurements; the signal
positions were related to the positions of the signals
from the deuterated solvents.
IR spectra were recorded on IKS-29 (4200–400 cm–1)
and Hitachi FIS-3 (400–100 cm–1) spectrometers using
KBr pellets.
Optical rotatory dispersion was measured on a Per-
kin Elmer 241MC polarimeter in dichloromethane in
the 450–610 nm range using 10 cm-long quartz cells
maintained at a constant temperature. The concentra-
tion of the complex was varied from 10–4 to 10–5 mol/l.
Since coordination of sulfoxides to platinum group
metals occurs, as a rule, through the sulfur atom, evolu-
tion of free sulfoxide sharply changes the observed
angle of optical rotation (OR) of the reaction mixture
up to complete inversion of the OR sign (the specific
rotation of (+)-Me-p-TolSO in dichloromethane is
The degree of conversion of (–)-[Pt(Me-p-
equal to +142°). Thus, the replacement of sulfoxide by TolSO)(Py)Cl2] was calculated from the polarimetry
another ligand can be easily monitored by polarimetry data. It is known [5] that the observed OR of a chiral
in both geometric isomers obtained (the specific rota- compound can be expressed in terms of specific OR,
1070-3284/01/2708-0579$25.00 © 2001 åÄIä “Nauka /Interperiodica”

580
DE VEKKI et al.
concentration, and optical path. Assuming that the
Reagent pure grade pyridine, dimethyl sulfoxide,
observed OR of a mixture of noninteracting compounds and commercial dichloromethane (Merck) were used in
is the sum of the optical rotations of components and the work.
using molar concentrations in place of the weight con-
centrations, one can express the observed OR for a mix-
ture of n components in the following way:
(–)-trans-[Pt(Me-p-TolSO)(Py)Cl2]. (–)K[Pt(Me-
p-TolSO)Cl3] (81.3 mg, 0.164 mmol) was dissolved in
water (3 ml). A 0.163 M aqueous solution of pyridine
(1 ml) was slowly added under stirring at 15°ë. This
immediately gave a fine light yellow precipitate. The
reaction mixture was stirred for another 20 min, and the
precipitate was filtered off and dried in a thermostat at
50°ë. The yield was 72.7 mg (0.145 mmol, 88.6%).
[α]589 = –22° (5 g in 100 ml of CH2Cl2).
1ç NMR (CDCl3, δ, ppm): 2.48 (s, 3H, Ph-CH3);
3.47 (t, 3 H, S-CH3, JPt-H 20 Hz); 7.40 (d, 2 H, Ph, JH-H
8 Hz); 7.43 (t, 2 H, Py, JPt-H 18 Hz); 7.88 (t, 1 H, Py, JPt-H
16 Hz); 7.97 (d, 2 H, Ph, Jç-ç 8 Hz); 8.78 (t, 1 H, Py, JPt-H
33 Hz); 8.81 (t, 1 H, Py, JPt-H 32 Hz).
n
αΣ = 103l [α j]TcjMj,
(1)
λ
∑
j = 1
where αΣ is the observed rotation of n components in a
mixture at wavelength λ (nm) and solution temperature
T(°ë), [αj] is the specific rotation of a j-th component
(g/mol), and l is the optical path (dm).
If the reaction
(–)[Pt(Me-p-TolSO)PyCl2] + L
(2)
IR (ν, cm–1): 1644 νPy, 1473, 1434 δ(ëç3), 1144
ν(S=O), 1093, 1078 δ(ëç)Py, 969 τ(ëç3), 824
δ(ëç)Ph, 776 δ(CH)Py, 729 ν(ë–S), 700 δ(ëç)Py, 353
ν(Pt–Cl).
(+)Me-p-TolSO + D,
(where (–)-[Pt(Me-p-TolSO)(Py)Cl2] and (+)-Me-p-
TolSO are compounds with a chiral center and L and D
are compounds without a chiral center) takes place in
the solution, the observed OR of the solution can be
expressed in the following way:
(–)-cis-[Pt(Me-p-TolSO)(Py)Cl2].
K[Pt(Py)Cl3]
(79.6 mg, 0.190 mmol) was dissolved in water (4 ml).
(+)-Me-p-TolSO (29.3 mg, 0.190 mmol) was slowly
added under stirring. The reaction mixture was kept for
24 h at room temperature, and the white flaky precipi-
tate formed was filtered off and dried in a thermostat at
50°C. The yield was 85.6 mg (0.171 mmol, 90.4%).
[α]589 = –117° (5 g in 100 ml of CH2Cl2).
αΣ = 103l([αA]cAMA + [αB]cBMB),
(3)
where [αA] and [αÇ] are the specific rotations of (–)-
[Pt(Me-p-TolSO)(Py)Cl2] (A) and (+)-Me-p-TolSO
(B), respectively, MÄ and MÇ are the molar masses, and
cA and cB are the molar concentrations of A and B,
respectively.
1ç NMR (CDCl3, δ, ppm): 2.46 (s, 3H, Ph–CH3),
3.59 (t, 3H, S–CH3, JPt–H 23 Hz), 7.30 (t, 2H, Py, JPt–H
6
Hz), 7.37 (d, 2H, Ph, JH–H 8 Hz), 7.82 (t, 1H, Py, JPt–H
15 Hz), 7.96 (d, 24, Ph, JH–H 8 Hz), 8.61 (t, 1H, Py, JPt–H
41 Hz), 8.64 (t, 1H, Py, JPt–H 40 Hz).
If only (–)-[Pt(Me-p-TolSO)(Py)Cl2] is present in
the solution at the initial instant of time (t = 0) and its
concentration is equal to [Ä]0, then, having designated
the (+)-Me-p-TolSO concentration at time t by x(t), we
can find cÄ at time t as cA=[Ä]0 – x(t). In view of this
fact, Eq. (3) takes the form
IR (ν, cm–1): 1624 νPy, 1460 δ(ëç3), 1144 ν(S=O),
1082 δ(ëç)êy, 967, 953 τ(ëç3), 810, 762 δ(ëç)Py,
720ν (C–S), 692 δ(ëç)Py, 391 γ (CSO), 339, 324, 318
ν(Pt–Cl), 277 ν(Pt–Py).
cis-[Pt(Ph3P)(Py)Cl2],
cis-[Pt(C2H5)SO(Py)Cl2]
α (t)
(71.3 mg, 0.158 mmol) was dissolved in acetone (4 ml).
PPh3 (41.4 mg, 0.158 mmol) was added under stirring.
The white precipitate was immediately formed which was
filtered off and washed on the filter with alcohol (4 ml)
and ether (5 ml). The yield was 66.7 mg (0.110 mmol,
70%).
(4)
= 103l{([A0] – x(t))[αA]MA + x(t)[αB]MB},
where α(t) is the observed rotation of a mixture of opti-
cally active substances A and B at time t.
Transformation of Eq. (4) with respect to the degree
of conversion of (–)-[Pt(Me-p-TolSO)(Py)Cl2] (the
complex concentration is expressed in terms of the
sample weight) gives the relation
1ç NMR (CDCl3, δ, ppm): 6.88 (t, 2 H, Py, JPt–H
12 Hz); 7.32 (m, 9 H, Ph and Py, JH–H 25 Hz); 7.62 (m,
8 H, Ph, JH–H 19 Hz); 8.37 (t, 1 H, Py, JPt–H 44 Hz); 8.40
(t, 1 H, Py, JPt–H 42 Hz).
31P NMR (CDCl3, δ, ppm): 7.51 (JPt-P 3900 Hz).
IR (ν, cm–1): 1602 νPy, 1490, 1440 δ(ëç3), 745
δ(ëç)êh, 690 δ(ëç)Py, 545 δ(ëç)Ph, 344, 297 ν(Pt–
Cl), 201, 162 ν(Pt–PPh).
α (t)V
MA -------------- – [αA]
lmA
----------------------------------------------
conv(t) =
× 100% ,
(5)
[αB]MB – [αA]MA
where conv(t) is the degree of conversion of (–)-
(+)-Me-p-TolSO was synthesized by a procedure
[Pt(Me-p-TolSO)(Py)Cl2] at time t, mÄ (g) is the mass given in [6]; (–)-K[Pt(Me-p-TolSO)Cl3] and (–)-cis-
of compound A at time t = 0, and V (ml) is the volume [Pt(Me-p-TolSO)2Cl2] were synthesized as described
of the solution containing the sample.
in [7].
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 8 2001

REACTIVITY OF GEOMETRIC ISOMERS
581
Conversion, %
1, 2
RESULTS AND DISCUSSION
reactivity of (–)-cis-[Pt(Me-p-
TolSO)(Py)Cl2]. Treatment of (–)-cis-[Pt(Me-p-
TolSO)(Py)Cl2] with Ph3P, Ph3As, Py, Ph3PS, or
Me2SO leads to an increase in the angle of OR of the
reaction mixture (the sign of rotation changes from
negative to positive) due to the replacement of (+)-Me-
p-TolSO by the corresponding ligand
The
100
80
60
40
20
3
4
(–)[Pt(Me-p-TolSO)(Py)Cl2] + L
(6)
[Pt(L)(Py)Cl2] + (+)Me-p-TolSO.
The occurrence of this reaction is confirmed by 1H
NMR spectra, which exhibit signals due to free and
coordinated (+)-methyl-p-tolyl sulfoxide and for the
initial and resulting metal complexes. The degree of
conversion of the metal complex was calculated from
Eq. (5).
5
6
The ORD monitoring of the kinetics of the ligand
exchange in (–)-cis-[Pt(Me-p-TolSO)(Py)Cl2] makes it
possible to arrange the ligands in the following
sequence in terms of their activity (Fig. 1):
7
0
50
100
150
200
250
Time, min
Ph3P > Ph3As ӷ Me2SO > Py ӷ Ph3PS.
Fig. 1. Time variation of the degree of conversion of (–)-cis-
[Pt(Me-p-TolSO)(Py)Cl ] in the reactions with nucleophilic
The reactions of the cis-complex with an equimolar
amount of Ph3P and Ph3As at 20°ë occur quantitatively
within several minutes to give cis and trans plati-
num(II) phosphine pyridine and arsine pyridine com-
plexes, respectively. The same reaction products are
formed when cis-[Pt(Et2SO)(Py)Cl2] in dichlo-
romethane is treated with Ph3P and Ph3As; however, to
attain high yields (in the case of triphenylarsine), the
reaction time should be increased (after 2 days at 20°ë,
the yield is 65%, and after ~9 h at reflux, it is 95%). The
lower reaction rate observed for the diethyl sulfoxide
complex is due to the higher lability of the bond
between the (+)methyl-p-tolyl sulfoxide molecule and
the metal atom, which is related, apparently, to steric
factors.
The traditional synthesis of phosphine amine and
arsine amine complexes makes use of either bridging
compounds or monoamine complexes; preparation of
these complexes and compounds is a fairly difficult
task. Therefore, the reaction of Ph3P and Ph3As with
sulfoxide pyridine complexes of platinum(II) can be
recommended as a preparative method for the synthesis
of these compounds.
2
reagents (1) Ph P, (2) Ph As, (3, 4) Me SO, (5, 6) Py, and
3
3
2
(7) Ph PS. The complex: L molar ratio was (1, 2, 4, 6, 7) 1 :
3
1 or (3, 5) 1 : 10; T = 20°ë.
upon gradual addition of hexane, which shifts the equi-
librium due to precipitation of the cis-complex.
The rate of interaction of the cis-compound with
dimethyl sulfoxide is somewhat lower than in the case
with Ph3P or Ph3As. Apart from the major reaction (6),
isomerization of the initial complex takes place; the
isomer ratio depends on the reaction conditions (table).
Apparently, in this case, isomerization is catalyzed by
dimethyl sulfoxide:
(–)cis-[Pt(Me-p-TolSO)(Py)Cl2]
(7)
Me2SO
(–)trans-[Pt(Me-p-TolSO)(Py)Cl2].
Treatment of the cis-isomer with a tenfold excess of
Me2SO results in 100% conversion over a period of
90 min (Fig. 1), giving isomerically pure cis-
[Pt(Me2SO)(Py)Cl2].
The products of reaction of cis-[Pt(Me-p-
TolSO)(Py)Cl2] with triphenylphosphine were charac-
The reaction of (–)-cis-[Pt(Me-p-TolSO)(Py)Cl2]
terized, in addition to other physicochemical methods, with pyridine proceeds even more slowly. With an
31
by P NMR spectroscopy. The spectrum exhibits sig- equimolar ratio of the reactants, it affords cis- and
nals of the coordinated triphenylphosphine group with trans-[Pt(Py)2Cl2] (table) without isomerization of the
δ = 7.51 ppm (ëDCl3; JPt-P = 3900 Hz) and δ = initial complex. On treatment with a tenfold excess of
20.45 ppm (ëDCl3; JPt-P = 2636 Hz), which correspond pyridine, in addition to the above-mentioned products,
to the cis- and trans-arranged phosphorus-containing [Pt(Py)4]Cl2, complex is formed which is usually pre-
and pyridine ligands in the complex, respectively. The pared through the reaction of a cis-dipyridine complex
cis-isomer predominates in the solution (table). This with excess pyridine in a boiling water bath [5]. Since
product can be isolated upon complete isomerization of the signals from protons of the pyridine rings in the 1H
the minor trans-isomer into the cis-isomer occurring NMR spectra of trans-[Pt(Py)2Cl2] and [Pt(Py)4]Cl2
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 8 2001

582
DE VEKKI et al.
Experimental (1H NMR, acetone-d6) data on the replacement of (+)-Me-p-TolSO in (–)-[Pt(Me-p-TolSO)(Py)Cl2] by other
ligands
Compound
L
Content of complexes in the reaction mixture, % (δ,a ppm)
(–)-[Pt(Me-p-TolSO)(Py)Cl2] [Pt(L)(Py)Cl2]
cis- trans-
T, °C
t, h
conv, %
isomer
complex : L
cis-
trans-
Cis-
Ph3PSb
1 : 1
40/50 30/21
27
88 (t 3.59)
25 (t 3.66)
2 (t 3.48)
34 (t 3.47)
2 (t 3.47)
10 (d 8.73)
12
75
Me2SO
7 : 1
21 (t 3.53) 20 (t 3.45)
1 : 10
20
10
49
32
1
48 (t 3.53) 50 (t 3.46) 100
39 (d 8.80) 60 (d 8.90) 99
Py
1 : 1
1 (t 3.66)
1 : 10c
1 : 1
20
20
5 (d 8.80)
8 (d 8.90) 100
100
Ph3Asb
Ph3P
100 (t 6.90)
1.5
13 (t 3.66)
4 (t 3.47)
83 (s 2.67)
83
83
1 : 1
20
1.5b
17 (t 3.59)
62d
40d
21d
60d
4
100
40
Me-p-TolSO
1 : 1
1 : 1
8 : 1
1 : 10
20
40
35
24
2.5
60 (t 3.66)
traces
40 (t 3.47)
100 (t 3.47)
91 (t 3.47)
Trans- Ph3PS
9 (t 3.45)
9
Me2SO
20
27
25
70
(t 3.53)
(t 3.46) 100
68
36 (d 8.80) 64 (d 8.90) 100
100 (t 8.12) 100
32 (t 3.65)
24 (t 3.47) 21 (d 8.80) 24 (d 8.90)
Py
1 : 1
1 : 1
20
20
traces
Ph3As
1.5
5.5b
10 (t 3.59)
41d
49d
90
90
8
Ph3P
1 : 1
1 : 1
20
20
50
5.5
4 (t 3.65)
8 (t 3.66)
46 (t 3.66)
6 (t 3.47)
92 (t 3.47)
54 (t 3.47)
90 (s 2.68)
24
Me-p-TolSO
6
46
a
Note: The δ range for determining the component ratio in the reaction mixture.
b
c
d
In CDCl .
3
The reaction products contain 87% [Pt(Py) ]Cl .
4
2
31
Found from P NMR data (CDCl , δ, ppm): 7.51 (cis) and 20.45 (trans).
3
coincide, it is impossible to determine their ratio in this change significantly, whereas the rate of isomerization
way. To determine the amount of tetrapyridine complex increases up to a certain limiting value (the angle of OR
obtained, it was extracted with water, the water was of the mixture increases, see Fig. 2). Subsequently, the
evaporated, and the resulting precipitate was washed exchange rate either starts to increase or remains con-
with dichloromethane to remove (+)-Me-p-TolSO; this stant (the angle of the OR of the mixture decreases),
gave 43% of the weight of the whole precipitate.
while the isomerization rate apparently decreases.
When the equilibrium concentration of isomers under
the given conditions is attained, and such isomer ratio
is subsequent by maintained, the rate of isomerization
does not have a substantial effect on the OR of the mix-
ture. The maximum in the curves (Fig. 2) corresponds
to a situation when the rate of exchange reaction has
already become greater than the isomerization rate.
The addition of a solution of Ph3PS to a solution of
the chiral cis-complex at 20°ë does not change the
observed optical rotation of the mixture, thus indicating
that the platinum–sulfoxide ligand bond is not cleaved.
An increase in temperature to 40 to 50°ë brings about
the appearance of reaction products (the degree of con-
version is only several percent) and isomerization of the
starting compound (table).
Heating of (–)-trans-[Pt(Me-p-TolSO)(Py)Cl2] with
The
reactivity
of
(–)-trans-[Pt(Me-p- Ph3PS entails only isomerization of the initial complex
TolSO)(Py)Cl2]. On mixing of (–)-trans-[Pt(Me-p- (table). This behavior of the trans-isomer can be
TolSO)(Py)Cl2] with an equimolar amount of Py, geo- accounted for by the low activity of Ph3PS (caused by
metric isomerization of the complex takes place, as its low σ-donor and π-acceptor capacities) and also by
1
indicated by H NMR data (table). This can be seen the fact that the trans-isomer is less reactive in ligand
most clearly when a tenfold excess of pyridine is used. exchange reactions than the cis-isomer because of the
The rate of the exchange reaction does not appear to severe shielding of the reaction center by the ligands.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 8 2001

REACTIVITY OF GEOMETRIC ISOMERS
583
Treatment of the trans-complex with Ph3P and
However, when equimolar amounts of the (–)-cis-
Ph3As induces replacement of (+)-Me-p-TolSO by the complex and (+)-Me-p-TolSO are kept in dichlo-
corresponding ligand; in the case of triphenylphos- romethane, slow isomerization of the initial complex
phine, both cis- and trans-complexes are finally formed
and with triphenylarsine, only the trans-isomer is
formed (table).
The reaction of (–)-trans-[Pt(Me-p-TolSO)(Py)Cl2]
with Me2SO gives the same product as the reaction of
the cis-isomer (table).
Side processes hamper determination of the true
activity of the (–)-cis- and (–)-trans-[Pt(Me-p-
TolSO)(Py)Cl2] isomers in the ligand exchange reac-
tion; nevertheless, an important conclusion is that the
relative rate of substitution is higher in the cis-isomer.
takes place even at 20°C (table). This prompts the idea
that one variant of isomerization of the cis-complex
during any ligand exchange is the isomerization
induced by the evolved (+)-Me-p-TolSO.
The set of the obtained data suggests that the mech-
anism of ligand exchange depends on the nature of the
attacking ligand. To elucidate the mechanism of reac-
tion of these attacking ligands with (–)-cis- and (–)-
trans-[Pt(Me-p-TolSO)(Py)Cl2] in detail, we studied
the behavior of these complexes in the presence of a
1
tenfold excess of C5D5N or (CD3)2SO by H NMR
The polarimetric monitoring of the course of inter-
action of (–)-trans-[Pt(Me-p-TolSO)(Py)Cl2] with an
equimolar amount of (+)-Me-p-TolSO in dichlo-
romethane shows that keeping the reaction mixture at
20–40°C does not change the OR. Therefore, “sulfox-
ide-catalyzed” isomerization of (–)-trans-[Pt(Me-p-
TolSO)(Py)Cl2] similar to that observed for trans-
[Pt(Me2SO)(Py)Cl2] in dimethyl sulfoxide [8] appears
unlikely; thus, the formation of the opposite isomer of
spectroscopy. As the ligand exchange advances, signals
from (+)-Me-p-TolSO incorporated in both isomers
appear in the spectrum. This confirms the fact of
isomerization of the initial complexes during the reac-
tion and explains the presence of both isomers in the
reaction products.
The data presented above concerning the ligand
exchange involving Me2SO, Py, Ph3P, and Ph3As allow
the initial complex is due to the replacement of (+)-Me- one to compose the following scheme of transforma-
p-TolSO by other ligands via the formation of a com- tions of the geometric isomers of (–)-[Pt(Me-p-
mon intermediate.
TolSO)(Py)Cl2].
Me
O
+
Me
Tol
Cl
O
S
L
Cl
S
(MeTolSO)
L
Tol
Cl
Pt
Cl–
Pt
N
N
Cl–
–MeTolSO
Cl
L
Pt
+
Cl
N
L = Me2SO, Py, Ph3P, Ph3As
N
O
L
Cl–
Me
Tol
Pt
–MeTolSO
Me2SO
(Py)
S
S
Cl
L
(MeTolSO)
Cl–
+
N
O
Cl
Cl
N
Cl
N
O
Cl–
L
Cl–
Cl
Me
Pt
Pt
Me
Tol
–MeTolSO
Pt
S
Cl
L
L
Tol
The primary chemical event is the substitution of the tion of this intermediate depends on the nature and
potential ligand (L) for the halogen atom (Cl) to give amount of ligand L and can follow three pathways: (a)
[Pt(R1R2SO)(Py)(L)Cl]+. The subsequent transforma- return to the initial complex; (b) the formation of an
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 8 2001

584
DE VEKKI et al.
isomeric complex (isomerization); or (c) elimination of
The mechanism of interaction of pyridine sulfoxide
the sulfoxide (formation of the substitution product). complexes with weak-field ligands (Ph3PS) differs
appreciably from that given above. In this case, isomer-
ization processes predominate and no transformations
of the trans-complex are observed.
The reaction pathway (b) accounts for the presence of
both cis- and trans-isomers of the final complex
[Pt(L)(Py)Cl2], irrespective of the configuration of the
initial complex.
N
O
Cl
Cl
Ph3PS
Cl–
Me
Pt
S
+
Tol
Cl
N
O
S=PPh3
S=PPh3
Cl–
Me
Pt
Pt
–MeTolSO
MeTolSO
S
Cl
Cl
N
Tol
Me
O
S
Cl
Ph3PS
Tol
Cl
Pt
N
Thus, we found that treatment of the complex with geometric isomers of the final complex; the isomer
ratio depends on the nature of the attacking ligand.
a ligand stronger than (+)-Me-p-TolSO, the direct
ligand exchange is accompanied by isomerization of
the initial complex, resulting in the formation of both
ACKNOWLEDGMENTS
This work was supported by the Ministry of Educa-
tion of the Russian Federation (project no. 97-9.4-171)
and by the Russian Foundation for Basic Research
(project no. 00-03-32670a).
α, deg
1
–0.14
–0.12
–0.10
–0.08
–0.06
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comp
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