Novel mixed-ligands Pt(II) complexes: Synthesis, multinuclear magnetic resonance and crystal structures of cis- and trans-Pt(sulfoxide)(pyrimidine)Cl2

Article abstract of DOI:10.1016/S0020-1693(01)00441-8

New types of mixed-ligands Pt(II) complexes, cis- and trans-Pt(R₂SO)(pyrimidine)Cl₂, were synthesized and characterized by IR and multinuclear magnetic resonance spectroscopies and by crystallographic methods. Compounds with R₂SO = dimethylsulfoxide (DMSO), tetramethylenesulfoxide (TMSO), di-n-propylsulfoxide (DPrSO), di-n-butylsulfoxide (DBuSO), dibenzylsulfoxide and diphenylsulfoxide were studied. The aqueous reaction of K[Pt(R₂SO)Cl₃] with pyrimidine (pm) in a 1:1 ratio produced trans-Pt(R₂SO)(pm)Cl₂, which can isomerize to the cis isomer in an organic solvent. The ¹⁹⁵Pt NMR resonances of the trans complexes were observed at higher field (ave. -3079 ppm) than the cis analogues (ave. -2932 ppm). The ¹⁹⁵Pt coupling constants with the pyrimidine atoms ³J(¹⁹⁵Pt-¹H) and ³J(¹⁹⁵Pt-¹³C) are larger in the cis configuration ( ～ 40 Hz) than in the trans analogues ( ～ 30 Hz). One v(Pt-Cl) vibration was observed for the trans compounds, while two such bands were observed for the cis isomers. The crystal structures of cis-Pt(R₂SO)(pm)Cl₂ (R₂SO = DMSO, TMSO, DPrSO and DBuSO) and of trans-Pt(TMSO)(pm)Cl₂ were determined. The trans influence of the three different ligands was compared.

Full text of DOI:10.1016/S0020-1693(01)00441-8

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Inorganica Chimica Acta 319 (2001) 95–108
Novel mixed-ligands Pt(II) complexes: synthesis, multinuclear
magnetic resonance and crystal structures of cis- and
trans-Pt(sulfoxide)(pyrimidine)Cl2
Nicolas Ne´de´lec, Fernande D. Rochon *
De´partement de Chimie, Uni6ersite´ du Que´bec a` Montre´al, C.P. 8888, Succ. Centre-6ille, Montre´al, Canada H3C 3P8
Received 15 December 2000; accepted 19 March 2001
Abstract
New types of mixed-ligands Pt(II) complexes, cis- and trans-Pt(R2SO)(pyrimidine)Cl2, were synthesized and characterized by IR
and multinuclear magnetic resonance spectroscopies and by crystallographic methods. Compounds with R2SO=dimethylsul-
foxide (DMSO), tetramethylenesulfoxide (TMSO), di-n-propylsulfoxide (DPrSO), di-n-butylsulfoxide (DBuSO), dibenzylsulfoxide
and diphenylsulfoxide were studied. The aqueous reaction of K[Pt(R2SO)Cl3] with pyrimidine (pm) in a 1:1 ratio produced
trans-Pt(R2SO)(pm)Cl2, which can isomerize to the cis isomer in an organic solvent. The 195Pt NMR resonances of the trans
complexes were observed at higher field (ave. −3079 ppm) than the cis analogues (ave. −2932 ppm). The 195Pt coupling
3
3
constants with the pyrimidine atoms J(195Ptꢀ1H) and J(195Ptꢀ13C) are larger in the cis configuration (ꢀ40 Hz) than in the trans
analogues (ꢀ30 Hz). One w(PtꢀCl) vibration was observed for the trans compounds, while two such bands were observed for the
cis isomers. The crystal structures of cis-Pt(R2SO)(pm)Cl2 (R2SO=DMSO, TMSO, DPrSO and DBuSO) and of trans-
Pt(TMSO)(pm)Cl2 were determined. The trans influence of the three different ligands was compared. © 2001 Elsevier Science B.V.
All rights reserved.
Keywords: Platinum complexes; Sulfoxide complexes; Pyrimidine complexes; Crystal structures
NMR, although they were not able to isolate the
compound [7].
1. Introduction
Pyrimidine and its derivatives are of great interest,
since they play an important role in many biological
processes. The nature of the Pt–pyrimidine bond has
not yet been studied in the literature. We have recently
undertaken a study on a new type of mixed-ligands
platinum(II) complexes containing pyrimidine and sulf-
oxide ligands. Our research group has been involved in
Pt–sulfoxide complexes for several years. These ligands
have interesting behaviors, especially because of their
p-back electron accepting properties. Sulfoxides are
bonded to Pt(II) (soft metal) through their S atom.
Most of the studies on Pt–sulfoxides complexes were
done with the most common ligand, DMSO. Marzilli
and coworkers made a comparative study of the com-
pounds cis- and trans-Pt(DMSO)(py)Cl2 (py=pyridine
and its derivatives) [8]. A few other mixed-ligands com-
plexes with DMSO are known. Published results on
other sulfoxides are much less common. Our laboratory
Platinum complexes with nitrogen-donor ligands
have been the object of numerous reports for the last 40
years and several studies have shown that some of these
complexes have an antitumor activity [1–3]. The disub-
stituted platinum(II) compounds with pyridine ligands
were first prepared in the 1960s by Kauffman [4].
However, only three papers were published on platinum
compounds with non-substituted pyrimidine (pm).
Fazakerley and Koch [5] synthesized and characterized
cis-[Pt(NH3)2(pm)2](ClO4)2 by 13C NMR spectroscopy
while Rochon and coworkers [6] prepared cis- and
trans-Pt(pm)2X2 (X=Cl and Br) and determined the
structure of the two trans isomers. Kaufmann et al.
characterized trans-Pt(PEt3)(pm)Cl2 by 31P and 1H
* Corresponding author. Tel.: +1-514-987 3000, ext. 4896; fax:
+1-514-987 4054.
E-mail address: rochon.fernande@uqam.ca (F.D. Rochon).
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00441-8

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N. Ne´de´lec, F.D. Rochon / Inorganica Chimica Acta 319 (2001) 95–108
recently published a study on cis- and trans-Pt-
(DPhSO)(RꢀCN)Cl2 complexes [9].
tored for every 97 reflections to check the stability of
the crystals. The coordinates of the Pt atoms were
determined from a Patterson map calculation using the
Siemens SHELXTL system [11]. All the other non-hydro-
gen atoms were found by the usual Fourier methods.
The refinement of the structures was done on F2 by
full-matrix least-squares analysis using all reflections.
Hydrogen atom positions were fixed in their calculated
position with Ueq=1.2Ueq (or 1.5 for methyl group) of
the carbon to which they are bonded. Corrections were
made for absorption (Gaussian integration), Lorentz
The aqueous reaction of K2[PtCl4] with an excess of
sulfoxide produces the trans disubstituted isomer, which
rapidly isomerizes to cis-Pt(R2SO)2Cl2, unless the lig-
and is very sterically demanding. The greater stability
of the cis-disulfoxide complexes has been explained by
the enhanced (d–d) p-bonding, which is more effective
in the cis configuration [10]. It appeared interesting to
determine if a mixed-ligand complex containing sulfox-
ide and pyrimidine, which can theoretically form
p-bonding with Pt, would also isomerize to the cis
compound. We have therefore undertaken a systematic
study of the reaction of K[Pt(R2SO)Cl3] with pyrim-
idine. Six sulfoxides with different steric hindrance were
used: dimethylsulfoxide (DMSO), tetramethylenesulfox-
ide (TMSO), di-n-propylsulfoxide (DPrSO), di-n-butyl-
sulfoxide (DBuSO), dibenzylsulfoxide (DBzSO) and
diphenylsulfoxide (DPhSO). We have now developed
methods to synthesize the cis- and trans-Pt(R2SO)-
(pm)Cl2 complexes, which were characterized by in-
frared and multinuclear magnetic resonance (1H, 13C
and 195Pt) spectroscopies. The structure of four cis
complexes and one trans isomer are also reported.
and polarization effects. The residual peaks were below
−3
,
1.66 e A
and located in the close environment of the
platinum atom. Disorder was observed on the Cb and
Cg of one alkyl chain of the DPrSO crystal (III) and on
a terminal C atom of one butyl chain in the DBuSO
crystal (IV). Two positions were refined for each disor-
dered C atom with occupancy factors of 0.5. The final
refinement converged to the R1 and wR2 values shown
in Table 1.
The K[Pt(R2SO)Cl3] complexes were synthesized ac-
cording to the method described by Kukushkin et al.
[12]. The cis-Pt(R2SO)2Cl2 compounds were prepared
according to published methods [10,13].
2.1. cis-Pt(R2SO)(pm)Cl2 (R2SO=DMSO, TMSO,
DPrSO, DBuSO and DBzSO)
2. Experimental
K2[PtCl4] was obtained from Johnson Matthey Inc.
and was recrystallized in water before use. Pyrimidine,
CD2Cl2 and the sulfoxide ligands were purchased from
Aldrich except dipropylsulfoxide, which was bought
from Phillips Petroleum Company.
The K[Pt(R2SO)Cl3] compound (ꢀ100 mg) was dis-
solved in methanol (ꢀ5 ml) and pyrimidine in a 1:1
ratio (dissolved in 1 ml of CH3OH) was added slowly
with stirring at room temperature (r.t.). After several
days, a white precipitate was formed. The solution was
evaporated to dryness and the residue washed with
water and dried under vacuum. It was then washed
with ether and dried again. cis-Pt(DMSO)(pm)Cl2 (I):
Yield 89%, m.p. (dec.) 162 to \300°C. IR (cm−1): pm
(vibration no. [14,15]): 1596s and 1561m (9, 10), 1472m
(22), 1407s (23), 1229m (3), 1183sh (17), 1072w and
1058w (14), 1028s (1), 980m (5), 830s (12), 736m (13),
697s (4), 642s (6); w(SꢀO) 1136s; w(PtꢀS) 440s; w(PtꢀCl)
A Fisher–Johns instrument was used to determine
the melting and decomposition points, which are not
corrected. The IR spectra were measured in KBr pellets
on a Perkin–Elmer 783 spectrometer between 4000 and
280 cm−1. All the NMR spectra were measured in
CD2Cl2 on a Varian Gemini 300BB spectrometer oper-
ating at 300.075, 75.462 and 64.335 or 64.270 MHz for
1H, 13C and 195Pt, respectively. The dichloromethane
peaks (5.32 and 53.80 ppm) were used as references for
1
343s, 317s. H NMR (ppm): l=9.418 (s, H2), 8.857
1
the H and 13C NMR spectra. The external reference
(dd, H4), 7.487 (ddd, H5), 8.996 (ddd, H6), 3.502 (s, Ha).
13C NMR (ppm): l=161.64 (C2), 159.39 (C4), 122.88
(C5), 160.42 (C6), 45.13 (Ca). cis-Pt(TMSO)(pm)Cl2 (II):
Yield 66%, m.p. (dec.) 150–250°C. IR (cm−1): pm:
1595s and 1559m (9, 10), 1472m (22), 1410s (23), 1228w
(3), 1175w (17), 1076s and 1059sh (14), 1028m (1), 978w
(5), 821m (12), 698s (4), 640m (6); w(SꢀO) 1151s,
1134sh; w(PtꢀS) 448w; w(PtꢀN) 523w; w(PtꢀCl) 343m,
for 195Pt was K[Pt(DMSO)Cl3] (in D2O adjusted at
−2998 ppm from Na2[PtCl6]) and K2[PtCl4] (in D2O
with KCl adjusted at −1628 ppm from Na2[PtCl6]).
The crystallographic studies were done on a Siemens
P4 diffractometer using graphite-monochromatized Mo
,
Ka (u=0.71073 A). The crystals were selected after
examination under a polarizing microscope for homo-
geneity. The cell dimensions were determined at room
temperature, from a least-squares refinement of the
angles 2q, ꢀ and  obtained for a minimum of 25-well-
centered reflections. The data collections were made by
the 2q/ꢀ scan technique using the XSCANS program
[11]. Intensities of three standard reflections were moni-
1
321m. H NMR (ppm): l=9.443 (s, H2), 8.849 (dd,
H4), 7.477 (ddd, H5), 9.021 (ddd, H6), 4.180, 3.428 (ddd,
Ha), 2.376, 2.221 (m, Hb). 13C NMR (ppm): 161.80
(C2), 159.29 (C4), 122.81 (C5), 160.52 (C6), 59.24 (Ca),
26.44 (Cb). cis-Pt(DPrSO)(pm)Cl2 (III): Yield 74%,
m.p. (dec.) 130 to \300°C. IR (cm−1): pm: 1594s and

N. Ne´de´lec, F.D. Rochon / Inorganica Chimica Acta 319 (2001) 95–108
97
1560m (9, 10), 1467sh (22), 1410s (23), 1224w (3),
2.2. trans-Pt(R2SO)(pm)Cl2 (R2SO=DMSO, TMSO,
DBuSO and DPhSO)
1173w (17), 1084sh and 1061m (14), 1032w (1), 826m
(12), 733w (13), 704s (4), 640m (6); w(SꢀO) 1130s;
w(PtꢀS) 450w; w(PtꢀN) 527m; w(PtꢀCl) 349m; 321m.
1H NMR (ppm): l=9.358 (s, H2), 8.851 (dd, H4),
7.476 (ddd, H5), 8.931 (ddd, H6), 3.757, 3.153 (ddd,
Ha), 2.368, 2.041 (dddq, Hb), 1.201 (t, Hg). 13C NMR
(ppm): l=161.65 (C2), 159.28 (C4), 122.86 (C5),
160.31 (C6), 56.78 (Ca), 17.09 (Cb), 12.93 (Cg). cis-Pt-
(DBuSO)(pm)Cl2 (IV): Yield 56%, m.p. 110°C. IR
(cm−1): pm: 1597s and 1563m (9, 10), 1469m (22),
1420s (23), 1233m (3), 1182m (17), 1082w and 1057w
(14), 1034w (1), 831m (12), 745w (13), 702m (4), 644m
(6); w(SꢀO) 1136s; w(PtꢀS) 459w; w(PtꢀN) 502w,
The complex K[Pt(R2SO)Cl3] and pm were mixed in
a 1:1 ratio in water at r.t. for TMSO, DBuSO and
DPhSO and at about 3°C for DMSO. A pale yellow
precipitate appeared rapidly depending on the steric
hindrance of the sulfoxide ligand. The mixture was
stirred until the solution became colorless except for the
DMSO complex which was stopped after ꢀ2 min. The
precipitate was then filtered, dried, washed with ether
and dried in vacuum. The 195Pt NMR spectrum of the
product with DBuSO showed that it contained five
species which will be discussed later in the text. trans-
Pt(DMSO)(pm)Cl2: Yield 27%, m.p. 96°C. IR (cm−1):
pm: 1594s and 1559m (9,10), 1472m (22), 1408s (23),
1224m (3), 1173sh (17), 1072w and 1062m (14), 1033s
(1), 979w (5), 811m (12), 733m (13), 699s (4), 648m (6);
1
w(PtꢀCl) 344m, 321m. H NMR (ppm): l=9.362 (s,
H2), 8.854 (dd, H4), 7.478 (ddd, H5), 8.933 (ddd, H6),
3.783, 3.166 (ddd, Ha), 2.324, 1.961 (m, Hb), 1.620,
1.597 (dtq, Hg), 1.030 (t, Hd). 13C NMR (ppm): 161.63
(C2), 159.26 (C4), 122.83 (C5), 160.28 (C6), 54.95 (Ca),
25.14 (Cb), 21.83 (Cg), 13.80 (Cd). cis-Pt-
(DBzSO)(pm)Cl2: Yield 50%, m.p. (dec.) 200–290°C.
IR (cm−1): pm: 1596s and 1559m (9,10), 1456m (22),
1411s (23), 1230w (3), 1172m (17), 1082w and 1071m
(14), 1030w (1), 812w (12), 763m (13), 697s (4), 640w
(6); w(SꢀO) 1117s; w(PtꢀS) 459w; w(PtꢀN) 485w;
1
w(SꢀO) 1138s, w(PtꢀS) 444s; w(PtꢀCl) 346s. H NMR
(ppm): 9.459 (s, H2), 8.887 (dd, H4), 7.526 (ddd, H5),
9.007 (ddd, H6), 3.448 (s, Ha). 13C NMR (ppm):
l=160.44 (C2), 158.93 (C4), 122.60 (C5), 159.99 (C6),
44.65 (Ca). trans-Pt(TMSO)(pm)Cl2 (V): Yield 84%,
m.p. 121°C. IR (cm−1): pm: 1595s and 1561m (9,10),
1471m (22), 1413s (23), 1233m (3), 1176sh (17), 1071s
(14), 1028m (1), 817m (12), 696s (4), 641s (6); w(SꢀO)
1
w(PtꢀCl) 343m, 323m. H NMR (ppm): l=8.091 (s,
1
H2), 8.572 (dd, H4), 7.066 (ddd, H5), 7.659 (ddd, H6),
5.189, 4.446 (d, Ha), 7.683 (m, Hortho), 7.500 (m,
Hmeta,para). 13C NMR (ppm): d=160.88 (C2), 158.72
(C4), 122.40 (C5), 159.44 (C6), 60.02 (Ca), others
128.28–132.51.
1150s; w(PtꢀS) 445w; w(PtꢀCl) 348s. H NMR (ppm):
l=9.472 (s, H2), 8.885 (dd, H4), 7.524 (ddd, H5), 9.024
(ddd, H6), 3.990, 3.573 (ddd, Ha), 2.358, 2.196 (m, Hb).
13C NMR (ppm): l=160.40 (C2), 158.86 (C4), 122.60
(C5), 159.98 (C6), 57.24 (Ca), 24.86 (Cb). trans-Pt-
Table 1
Crystallographic data for the complexes Pt(R2SO)(pm)Cl2
Sulfoxide
cis-DMSO (I)
cis-TMSO (II)
cis-DPrSO (III)
cis-DBuSO (IV)
12H22Cl2N2OSPt
trans-TMSO (V)
Chemical formula
MW
C6H10Cl2N2OSPt C8H12Cl2N2OSPt C10H18Cl2N2OSPt
424.21
C
C8H12Cl2N2OSPt
450.25
450.25
480.31
508.37
Space group
P21/c (no. 14)
P21/c (no. 14)
P21/c (no. 14)
P21/c (no. 14)
P21/n (no. 14)
Unit cell dimensions
,
a (A)
8.273(2)
16.193(4)
9.288(2)
112.040(10)
1153.3(5)
4
2.443
12.775
784
9.898(2)
15.278(4)
8.639(2)
107.850(13)
1243.6(5)
4
2.405
11.856
840
9.502(2)
16.237(4)
10.042(2)
92.640(10)
1547.7(6)
4
2.061
9.533
912
7.4590(10)
19.977(6)
12.387(3)
95.48(2)
1837.3(8)
4
1.838
8.036
976
11.9465(14)
8.5850(8)
13.466(2)
113.897(11)
1262.7(2)
4
2.369
11.677
840
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
zcalcd (g cm−3
)
v(Mo Ka) (mm−1
F(000)
)
Independent reflections (Rint
)
2395 (0.0373)
1769
0.0386
0.0829
1.040
3631 (0.0277)
2626
0.0395
0.0895
1.038
4511 (0.0606)
3459
0.0429
0.0904
1.054
3231 (0.0477)
1963
0.0555
0.1050
1.046
3664 (0.0202)
2900
0.0345
0.0935
1.021
Reflections observed [I\2|(I)]
a
R1 [I\2|(I)]
b
wR2 (all data)
c
S
a R1=ꢀ(ꢁFo−Fcꢁ)/ꢀꢁFoꢁ.
b wR2=[ꢀ(w(Fo 2−Fc 2)2)/ꢀ(w(Fo 2)2)]1/2
.
c S=[ꢀ(w(Fo 2−Fc 2)2)/(n−p)1/2
.

98
N. Ne´de´lec, F.D. Rochon / Inorganica Chimica Acta 319 (2001) 95–108
(DBuSO)(pm)Cl2: Yield B10%. 1H NMR (ppm):
l=9.477 (s, H2), 8.879 (dd, H4), 7.515 (ddd, H5), 9.029
(ddd, H6). 13C NMR (ppm): l=160.42 (C2), 158.90
very bulky ligands. In the preparation of the bis-sulfox-
ide complexes, the first product is the trans compound,
which then isomerizes to the cis isomer. For DMSO,
the trans compound cannot be isolated, but trans-Pt(D-
PrSO)2Cl2 has been isolated after a few minutes of
reaction [16]. The rapid isomerization in water has been
explained by the enhanced (d–d) p-bonding which is
more effective in the cis configuration [10]. For the
Pt(R2SO)(pm)Cl2 complexes, the isomerization seems to
be slower in water, because pyrimidine cannot accept
p-electrons as effectively as sulfoxides. The reaction
with the least bulky sulfoxide (DMSO) was done at
cooler temperature (about 3°C) and the pale yellow
precipitate was filtered very rapidly (ꢀ2 min) in order
to prevent its isomerization. No isomerization was ob-
served with the other sulfoxides at room temperature in
aqueous media.
(C4),
122.47
(C5),
159.83
(C6).
trans-Pt-
(DPhSO)(pm)Cl2: Yield 82%, m.p. (dec.) 195– \300°C.
IR (cm−1): pm: 1593s and 1556m (9,10), 1467m (22),
1408s (23), 1229m (3), 1180m (17), 1073s and 1061sh
(14), 1028m (1), 994m (5), 811s (12), 739s (13), 698s (4),
640m (6); w(SꢀO) 1147s; w(PtꢀS) 450w; w(PtꢀCl) 349m.
1H NMR (ppm): d=9.538 (s, H2), 8.884 (dd, H4), 7.527
(ddd, H5), 9.081 (ddd, H6), 7.952 (m, Hortho), 7.558 (m,
Hmeta,para). 13C NMR (ppm): l=160.50 (C2), 159.06
(C4), 122.56 (C5), 160.00 (C6), 141.66 (Ca), 127.53 (Cb),
129.06 (Cg), 133.15 (Cd).
2.3. trans-Pt(R2SO)(pm)Cl2 (R2SO=DPrSO and
DBzSO)
A few methods were studied to prepare the cis-
Pt(R2SO)(pm)Cl2 complexes. In the first method, cis-
Pt(R2SO)2Cl2 reacted with pyrimidine in a 1:1 ratio in
dichloromethane. However, the products contained a
small quantity of the initial disubstituted complexes,
which could not be completely separated from cis-
Pt(R2SO)(pm)Cl2. Thus, a second method was devel-
oped, where K[Pt(R2SO)Cl3] reacted with pyrimidine
(1:1 ratio) in methanol. After evaporating the solvent,
the separation of the mixed-ligand complex from the
starting material (soluble in water) is then easy. Again,
the trans compound is first formed. The reaction can be
stopped rapidly if the trans analogue is desired (method
used to synthesize the trans DPrSO and DBzSO com-
plexes). If the reaction in methanol is stirred for a few
days, the color of the mixture gradually changed from
yellow (trans isomer) to almost white (cis analogue). If
the sulfoxide has a large steric hindrance, the isomeriza-
tion is much slower and might not be complete. With
the most bulky ligand, DPhSO, there was no isomeriza-
tion and only trans-Pt(DPhSO)(pm)Cl2 was formed in
These two compounds were prepared exactly as the
equivalent cis isomer, but the reactions were done in
methanol at low temperature (3°C) for DPrSO and at
r.t. for DBzSO. A yellow precipitate appeared after 1 h.
It was filtered, washed with ether and dried in vacuum.
trans-Pt(DPrSO)(pm)Cl2: Yield 21%, m.p. 83°C. IR
(cm−1): pm: 1595s and 1562m (9, 10), 1465sh (22),
1415s (23), 1231m (3), 1176w (17), 1076m and 1060w
(14), 1028w (1), 820m (12), 737m (13), 701m (4), 640m
(6); w(SꢀO) 1131s; w(PtꢀS) 454m; w(PtꢀN) 515m;
w(PtꢀCl) 348m. 1H NMR (ppm): l=9.474 (s, H2),
8.877 (dd, H4), 7.511 (ddd, H5), 9.025 (ddd, H6), 3.655,
3.241 (ddd, Ha), 2.241, 2.114 (dddq, Hb), 1.211 (t, Hg).
13C NMR (ppm): 160.43 (C2), 158.91 (C4), 122.47 (C5),
159.84 (C6), 56.80 (Ca), 16.96 (Cb), 13.04 (Cg). trans-
Pt(DBzSO)(pm)Cl2: Yield 60%, m.p. 150°C. IR (cm−1):
pm: 1592s and 1556m (9, 10), 1467m (22), 1409s (23),
1223w (3), 1186m (17), 1072m and 1059m (14), 1028m
(1), 820m (12), 694s (4), 637m (6); w(SꢀO) 1132s;
w(PtꢀCl) 350m. 1H NMR (ppm): l=9.370 (s, H2),
8.866 (dd, H4), 7.445 (ddd, H5), 8.900 (ddd, H6), 5.088,
4.535 (d, Ha), 7.650 (m, Hortho), 7.485 (m, Hmeta,para).
13C NMR (ppm): 160.24 (C2), 158.79 (C4), 122.56 (C5),
159.86 (C6), 60.57 (Ca), 128.41, 129.25, 129.67, 132.16
(Cphenyl).
1
all these reactions, although the H NMR spectrum of
an old solution of trans-Pt(DPhSO)(pm)Cl2 in CD2Cl2
has shown (after a few weeks) the presence of a small
quantity of a different compound which was assumed
to be the cis isomer. The trans compounds can isomer-
ize much faster in dichloromethane than in water. For
example, the crystal cis-Pt(TMSO)(pm)Cl2 (II) which
was studied by crystallographic methods was isolated
from a dichloromethane solution of the trans isomer.
All the synthesized compounds were characterized by
3. Results and discussion
1
IR and multinuclear (195Pt, 13C and H) magnetic reso-
3.1. Preparation of the complexes
nance spectroscopies. A few selected compounds which
gave adequate crystals were studied by X-ray diffrac-
tion methods.
The aqueous reaction of K[Pt(R2SO)Cl3] with pyrim-
idine in a 1:1 proportion produced trans-Pt(R2SO)-
(pm)Cl2 as expected, since the trans effect of the sulfox-
ide ligands is much larger than the one of chlorides.
The time of reaction depends on the steric hindrance of
the sulfoxide ligand. Disubstituted Pt(R2SO)2Cl2 com-
pounds have been shown to be cis isomers except for
3.2. 195Pt NMR spectroscopy
The complexes cis- and trans-Pt(R2SO)(pm)Cl2 were
studied by 195Pt NMR spectroscopy in dichloro-

N. Ne´de´lec, F.D. Rochon / Inorganica Chimica Acta 319 (2001) 95–108
99
Table 2
ꢀ94°) because of its rigid four-membered ring. It is
interesting to note that in a series of cis- and trans-Pt-
(DPhSO)(RꢀCN)Cl2 complexes [9], the chemical shift
variations (trans–cis) are not affected by the R group
on the nitrile ligand (the Dl values varied from 134 to
138 ppm), probably because the nitrile ligand is linear
and the R group is far from the binding N atom.
In order to obtain more information on the multi-
plicity of the Pt–pyrimidine bond, we have synthesized
cis- and trans-Pt(pm)2Cl2 and measured the 195Pt NMR
spectra. The chemical shift of the trans isomer was
observed at −2061 ppm in CDCl3, while that of the cis
compound appeared at −2043 ppm in deuterated
DMF (the cis analogue is not soluble in chloroform or
dichloromethane, but the l(Pt) are usually very similar
in these three solvents). Contrary to the diamine com-
plexes, the resonance of trans-Pt(pm)2Cl2 is found at
higher field (Dl=18 ppm) as observed in our
Pt(R2SO)(pm)Cl2 complexes, although the Dl value is
much smaller. The fact that trans-Pt(pm)2Cl2 is ob-
served at higher field than the cis analogue, might be an
indication of the presence of electronic back-donation
(Pt“pm) in the Pt–pyrimidine bond. These results
could be compared to those reported for Pt(py)2Cl2
(py=pyridine derivative) complexes, where the trans
isomers were observed at lower fields than the cis
compounds. The authors came to the conclusion that
p-bonding in Pt–py complexes is not very important
[20]. Our results seem to indicate that p-bonding is
slightly more important in Pt–pm compounds.
195Pt chemical shifts (ppm) of the cis- and trans-Pt(R2SO)(pm)Cl2
complexes (in CD2Cl2)
R2SO
cis
trans
Dl
DMSO
TMSO
DPrSO
DBuSO
DBzSO
DPhSO
−2917
−2864
−2951
−2954
−2975
−3070
−3056
−3059
−3060
−3078
−3148
153
192
108
106
103
methane-d2. The chemical shifts of the complexes are
shown in Table 2. Except for trans-Pt(DBuSO)(pm)Cl2,
only one signal was observed in the 195Pt NMR spectra.
The cis compounds were observed between −2864 and
−2975 ppm while the trans analogues were found at
higher field, between −3056 and −3148 ppm. These
values are in agreement with the values published for
Pt(DMSO)(NH3)Cl2 (−3045 (cis) and −3067 (trans)
ppm) [17,18], and Pt(DMSO)(L)Cl2 (L=pyridine
derivative, −2856 to −3043 ppm [8,17]), which were
all measured in DMSO-d6 or DMF-d7 and those pub-
lished for Pt(DPhSO)(RꢀCN)Cl2 (−3041 to −3186
ppm in CDCl3) [9].
The cis compounds were observed at lower fields
than the trans analogues contrary to diamine com-
pounds, where the cis complexes were found at slightly
higher
fields.
For
example,
cis-Pt(1-adaman-
tanamine)2Cl2 was reported at −2184 ppm, while the
trans analogue was observed at −2141 ppm [19]. The
difference could be explained by the presence of
p-bonding in the sulfoxide complexes, while the amine
ligands cannot accept p-backbonding from the metal.
For Pt(amine)2X2 complexes, the trans isomers are usu-
ally more stable than the cis compounds because of
steric effects, while for Pt(R2SO)2X2, the cis compounds
are the most stable (except for very bulky ligands),
because of the more effective (d–d) p-bonding in the cis
configuration [10]. The p-bond decreases the electron
density on the Pt atom. Therefore in the cis compound,
the electronic density on the Pt atom will be reduced
compared to the one in the trans isomer, causing a
deshielding of the cis compound. The group of Marzilli
[8] has observed for Pt(DMSO)(pyridine)Cl2 a Dl
(ltrans−lcis) value of 162 ppm (in DMSO-d6), which is
close to our value for the DMSO–pm complexes (153
ppm in CD2Cl2). These results suggest that the PtꢀN
bonds in pyridine and pyrimidine complexes are not too
different. For sulfoxides other than DMSO, the Dl are
slightly different (Table 2). The values are larger for
TMSO (192 ppm) and smaller for DPrSO (108 ppm),
DBuSO (106 ppm) and DBzSO (103 ppm). This Dl
value seems to vary with the bulkiness of the sulfoxide
close to the binding site. TMSO is the least bulky
around the S binding site (angle CꢀSꢀC reduced to
The complex trans-Pt(DPhSO)(pm)Cl2 is the most
shielded compound of the series. Two explanations
were examined. The observed shielding of the DPhSO
complex could be caused by the presence of two aro-
matic phenyl groups on the S atom. The phenyl groups
might account for a stronger s-bond and/or a weaker
p-bond. Inversed polarization of the p-electrons of the
SꢁO bond has been suggested [21] to explain an in-
creased electronic density on the sulfoxide ligand when
bonded to Pt. This inverse polarization would be more
important in sulfoxides containing aromatic groups and
might change the strength of the PtꢀS bond. The
DBzSO complex, which also contains aromatic groups,
although they are farther away from the S atom was
observed in the same region as the complexes with
sulfoxides containing only alkyl groups. The second
explanation for the difference observed for the DPhSO
complex is related to its much greater bulkiness around
the binding atom. All the other sulfoxides contain
ꢀCH2 or ꢀCH3 groups attached to the S atom. For
Pt(amine)2Cl2 compounds, deshielding effects have been
observed for Pt complexes containing secondary amines
compared to primary amines [19]. For our complexes
Pt(R2SO)(pm)Cl2, we have observed opposite effects.
Again the presence of p-bonding in our compounds
might lead to different results. We intend to continue

100
N. Ne´de´lec, F.D. Rochon / Inorganica Chimica Acta 319 (2001) 95–108
the work with more bulky alkyl sulfoxides, to determine
if bulkiness can be partly responsible for the higher field
chemical shift observed for the DPhSO complex.
We were not able to prepare the cis isomer with
DPhSO, probably because of the bulkiness of the li-
gand. Furthermore, pyrimidine is a weaker p-back elec-
tron acceptor than sulfoxides, which would decrease the
stability of the cis isomer (compared to the bis-sulfoxide
complex) and partially account for the unsuccessful
preparation of the cis DPhSO-pm isomer.
−3079 ppm has not been assigned yet with certainty.
The H NMR spectrum has shown that it contains the
1
pyrimidine ligand. The possibility of the presence of
rotamers was examined. Since it was not observed in
the spectrum of cis-Pt(DBuSO)(pm)Cl2, where it should
be mostly present, the hypothesis was rejected. The
presence of K[Pt(DBuSO)Cl3] was also rejected, since
its resonance should be found at lower field. It might be
caused by the presence of unsymmetric pyrimidine-
bridged dimers, which would show two different sig-
nals. The resonance at −3079 ppm would account for
one segment with the trans configuration, while the cis
segment would be hidden under the cis dimers observed
at −2940 ppm. This hypothesis will be further dis-
cussed in a subsequent publication on the synthesis and
characterization of pyrimidine-bridged dimeric species.
As mentioned above, the synthesized complexes were
pure, since only one resonance was observed in 195Pt
1
NMR (also confirmed by H NMR), except for trans-
Pt(DBuSO)(pm)Cl2, whose spectrum showed the pres-
ence of five different species. The trans compound
(ꢀ5%) was assigned to the signal at −3060 ppm,
while the cis isomer (ꢀ12%) was observed at −2954
ppm. Two other species observed at −2940 (ꢀ41%)
and −3069 ppm (ꢀ8%) were assigned, respectively, to
the pyrimidine-bridged dimers cis- and trans-
{Pt(DBuSO)Cl2}2(m-pm), which have been partially
characterized and will be discussed in a subsequent
publication. The fifth signal (ꢀ34%) observed at
1
3.3. H and 13C NMR spectroscopies
The signals of free pyrimidine and bonded pyrim-
1
idine in the complexes will be first discussed. The H
and 13C chemical shifts of the complexes are presented
in Section 2, while the Dl (lcomplex−lligand) of the
Table 3
1H NMR Dl (lcomplex−lligand) (ppm) and 3J(195Ptꢀ1H) (Hz) of the pyrimidine ligand in the cis- and trans-Pt(R2SO)(pm)Cl2 complexes
R2SO
H2
H4
H5
H6
Dlave
3J(195Ptꢀ1H2)
3J(195Ptꢀ1H6)
DMSO
TMSO
DprSO
DBuSO
DBzSO
DPhSO
cis
trans
cis
trans
cis
trans
cis
trans
cis
trans
cis
trans
0.241
0.282
0.267
0.295
0.181
0.298
0.185
0.300
−1.086
0.193
0.229
0.361
0.138
0.169
0.131
0.167
0.132
0.159
0.135
0.161
−0.146
0.148
0.113
0.166
0.160
0.199
0.150
0.197
0.149
0.184
0.150
0.188
−0.261
0.118
0.150
0.200
0.277
0.288
0.302
0.306
0.212
0.308
0.215
0.311
−1.059
0.182
0.276
0.362
0.204
0.235
0.213
0.241
0.169
0.237
0.171
0.240
−0.638
0.160
0.192
0.272
24
20
23
20
22
19
24
44
31
42
31
39
32
40
a
22
20
23
b
20
a Hidden under the phenyl signals.
b Values obtained from an old solution of the trans isomer in CD2Cl2, which contained a small quantity of cis isomers.
Table 4
13C NMR Dl (lcomplex−lligand) (ppm) and 3J(195Ptꢀ13C) (Hz) of the pyrimidine ligand in the cis- and trans-Pt(R2SO)(pm)Cl2 complexes
R2SO
C2
C4
C5
C6
Dlave
3J(195Ptꢀ13C5)
DMSO
TMSO
DPrSO
DBuSO
DBzSO
DPhSO
cis
trans
cis
trans
cis
trans
cis
trans
cis
trans
trans
2.30
1.10
2.46
1.06
2.31
1.08
2.29
1.08
1.52
0.90
1.16
2.17
1.71
2.06
1.64
2.06
1.69
2.03
1.68
1.52
1.57
1.84
0.95
0.67
0.87
0.67
0.92
0.54
0.90
0.54
0.47
0.63
0.63
3.20
2.77
3.30
2.76
3.09
2.61
3.06
2.61
2.22
2.64
2.78
2.16
1.56
2.17
1.53
2.10
1.48
2.07
1.48
1.43
1.44
1.60
39
30
37
29
40
29
39
30

N. Ne´de´lec, F.D. Rochon / Inorganica Chimica Acta 319 (2001) 95–108
101
Dlave is slightly higher (0.272 ppm) for DPhSO than for
the other trans isomers (ꢀ0.240 ppm, excluding
DBzSO). In this configuration, the bulkiness is less
important than in the cis analogues. Since the DPhSO
compound was observed at higher field in 195Pt NMR,
the signals of its ligands should be more deshielded in
1H or 13C NMR. The cis complex with DBzSO is
drastically different from the other complexes. The
preparation of the compound was repeated several
times in order to certify our results. For this compound,
Scheme 1.
1
all the pyrimidine H signals were observed at higher
field than those of free pyrimidine.
pyrimidine ligand and coupling constants with plat-
inum-195 are summarized in Tables 3 and 4. Free
pyrimidine is a symmetric molecule, which shows three
The variation of Dlave with the different sulfoxides
should be more important in the cis isomers, where the
bulkiness of the sulfoxide becomes an important factor.
In the trans compounds, the rotation of the pyrimidine
ligand around the PtꢀN bond is less limited (p-bonding
is not very strong), but not in the cis isomers, especially
for more bulky sulfoxides. In the latter compounds, the
rotation of the pyrimidine ligand will be more limited
and the pyrimidine ring will be predominantly perpen-
dicular to the platinum plane. The results on the cis
compounds in Table 3 show that the Dlave are slightly
smaller for more bulky ligands, although it is difficult
to compare these values. The rotation around the PtꢀN
bond will be more important in the TMSO complex
(angle CꢀSꢀC is the smallest) and the observed value
will be an average value of the different conformations
of the molecule, while in the more bulky ligand like
DBuSO, it might correspond to only one conformation.
Therefore, the chemical shifts of H4 and H5, which are
far from the cis sulfoxide ligand do not vary very much,
but the ones of H2 and H6 depend on the sulfoxide. The
Dlave values decrease (0.213–0.169 ppm) with an in-
crease in the bulkiness of the sulfoxide, TMSO\
DMSOꢁDPrSOꢀDBuSO (omitting the ligands
containing aromatic rings). It is interesting to note that
the 195Pt chemical shift variations Dl (Table 2) follow
the same order. The relation Dl(H2 or H6) versus
l(195Pt) is linear for these four cis compounds.
signals in H or 13C NMR. The most deshielded signal
1
is H2 observed at 9.177 ppm (in CD2Cl2), then H4 and
H6 (8.718 ppm, 3J=4.9 Hz) while H5 (7.327 ppm,
3J=4.9 Hz, 5J=1.5 Hz) is the most shielded. No
coupling of H2 can be observed because of its proximity
to two N atoms. The shielding order is the same in 13C
NMR. These results are similar to those reported for
pyrimidine in other solvents [22,23].
Pyrimidine bonded to Pt(II) is no longer symmetric
(Scheme 1) and four different signals are expected. The
proton H6 is more influenced by Pt binding than H4
and the deshielding order is H2, H6, H4 and H5. All
protons should couple to each other, but the couplings
on H2 are not observed. The signals of H5 and H6
consist of a doublet of doublets of doublets (ddd) with
normal aromatic coupling constants, except for
4J(H6ꢀH2) (1.1 Hz) which is slightly low, close to the
coupling constant 5J(H5ꢀH2). Castellano et al. have
also noted smaller coupling constants for protons in
meta position close to the nitrogen atom in the pyridine
ring [24]. No coupling of H4 was observed with H2, and
the signal of H4 appears as a doublet of doublets. The
absence of couplings on H2 can be explained by the
presence of the two neighboring N atoms. The coupling
of H2 with the two 14N nuclei, which possesses a large
quadrupolar moment, leads to the broadening of the
signal.
1
The H signals of all the cis compounds were ob-
The binding of pyrimidine to platinum leads to a
served at higher field (Dlave= −0.638 to 0.213 ppm)
deshielding of the ligand signals in H and 13C NMR
1
than those of the corresponding trans isomers (Dlave
=
0.160–0.272 ppm), in agreement with the 195Pt NMR
spectroscopic results. Since the trans isomers were ob-
served at higher fields in 195Pt NMR, the pyrimidine
spectroscopies, as indicated by the positive Dl values
(Tables 3 and 4), except for the H NMR signals of the
1
cis-DBzSO compound. The protons close to the bind-
ing site are more affected by coordination to the metal
as expected. An average value of Dl has been calcu-
lated in order to compare the results shown in Table 3.
All the complexes containing no aromatic groups have
similar chemical shifts. The trans diphenylsulfoxide
(DPhSO) compound is slightly different, with H2 and
H6 at slightly lower field. This ligand is the most bulky,
but it is also different from the other ligands, since it
contains aromatic groups directly on the binding atom,
which could produce different electronic effects. The
1
signals will be observed at lower fields in H NMR.
Binding of pyrimidine to the Pt atom reduces the
electronic density on pyrimidine (except for cis-Pt-
(DBzSO)(pm)Cl2) but increases it on the Pt atom. The
presence of p-bonding between the metal center and the
ligand will produce the opposite effect. The results on
195Pt NMR described above for cis- and trans-
Pt(pm)2Cl2 seem to indicate that p-bonding is present to
a small extent in Ptꢀpm complexes, contrary to Pt–
amine compounds.

102
N. Ne´de´lec, F.D. Rochon / Inorganica Chimica Acta 319 (2001) 95–108
The 13C NMR results on the pyrimidine ligand
methylene group is closer to the oxygen atom, because
of the rigidity of the ring, and its resonance was found
at lower field than the second proton. In the DPrSO,
DBuSO and DBzSO complexes, the geminal H atoms
are also non-equivalent, except for the terminal methyl
groups. The non-equivalence is caused by limited rota-
tion around the bonds, because of the presence of the
two bulky groups. The separation between the signals
of the geminal protons decreases as the distance from
the coordination site increases. This difference is larger
in the cis compounds than in the trans isomers. The
aromatic protons of the DPhSO and DBzSO complexes
appeared as two not well-resolved multiplets, one for
the ortho and one for the meta and para protons (Table
5).
showed a deshielding of all the carbons atoms, but
contrary to the protons signals, the Dl are slightly
greater for the cis isomers. Mesomeric effects on the
pyrimidine ligand are affected to a large extent by
bonding to the Pt atom and the results are more
reflected on the electron density of the C atoms than on
the protons. This study indicates that the Pt–pyrim-
idine bond is much more complicated than expected,
especially when mixed-ligands capable of forming
p-bonds and containing aromatic rings are coordinated
to platinum. Inversed polarization of the p-electrons of
the SꢁO bond [21] probably also influence the C spec-
trum of the other ligands as observed by Cooper and
Powell, who have suggested an influence of the inversed
polarization of the CꢂO bond on the ligand located in
trans position in the complexes trans-Pt(CO)(pyX)Cl2
(where pyX is a para-substituted pyridine derivative)
[25].
The R substituent on the sulfoxide ligand does not
seem to have an important influence on the pyrimidine
carbon atoms. The value for C6 seems to depend
slightly on the bulkiness of the sulfoxide in the cis
isomers and vary in the order TMSO\DMSO\
DPrSOꢀDBuSO (excluding the ligands containing
aromatic groups). The difference of Dl between the two
isomers is the most important on C2, with average
values of 2.18 and 1.06 ppm for the cis and trans
complexes, respectively.
The sulfoxide chemical shifts are shown in Section 2,
except for trans-Pt(DBuSO)(pm)Cl2 which contained
other species and its precise assignment was not possi-
ble, because of the overlap of the signals. In the DMSO
complexes, the six methyl H atoms are found to be
equivalent and an intense single peak was observed. In
the other R2SO complexes, the H atoms close to the
binding site are more deshielded than the others (Table
5). For TMSO, the two geminal hydrogens bonded to
the a carbon (the same is true for Cb) have different
chemical environments and two separated signals were
noted in the 1H NMR spectra. One proton of each
1
Some H NMR signals were not well-resolved and
some coupling constants could not be measured. In the
complexes with TMSO, DPrSO and DBuSO, the cou-
pling constants 2J(1Hꢀ1H) between geminal H atoms
3
vary from 12.5 to 15.0 Hz, whereas J(1Haꢀ1Hb) are 5.0
or 11.0 Hz. In the TMSO compounds, the average
coupling constant 3J is 7.0 Hz. The Ha signal is a
doublet of doublets of doublets (eight peaks) but only
five peaks were observed (relative intensity 1:2:2:2:1).
For the DPrSO b hydrogens, an additional coupling
with the protons of the methyl group led to a dddq
signal. The DBuSO Hg signals consisted of eight peaks
because of the additional coupling between the two
geminal protons.
The chemical shift variations of the sulfoxides in 13C
NMR spectroscopy are listed in Table 6. The Dl values
are in agreement with those of the K[Pt(R2SO)Cl3]
compounds [21]. For the DMSO and TMSO com-
plexes, the cis compounds are found at lower fields than
the trans analogues, while for DPrSO, the chemical
shift variations are identical. For trans-Pt-
(DPhSO)(pm)Cl2, the signals of the a carbons were
observed at much higher field (Dl= −4.84 ppm). The
observed Dl values are smaller than expected as ob-
served for the ionic K[Pt(R2SO)Cl3] complexes [21]. 13C
NMR spectroscopy is very dependent on mesomeric
effects and the smaller Dl values have been assigned to
Table 5
1H NMR Dl (lcomplex−lligand) (ppm) and 3J(195Ptꢀ1H) (Hz) of the sulfoxide ligands in the cis- and trans-Pt(R2SO)(pm)Cl2 complexes
R2SO
Ha
Hb
Hg
Hd
3J(195Ptꢀ1Ha)
DMSO
TMSO
DPrSO
cis
trans
cis
trans
cis
trans
cis
cis
trans
trans
0.961
0.908
25
22
1.399, 0.647
1.208, 0.791
1.159, 0.556
1.057, 0.644
1.166, 0.548
1.29, 0.55
1.19, 0.64
0.313ortho
0.252, 0.010
0.227, −0.008
0.604, 0.277
0.477, 0.350
0.624, 0.261
0.32ortho
0.137
0.147
0.152, 0.129
0.14meta+para
0.12meta+para
DBuSO
DBzSO
0.075
0.29ortho
0.091meta+para
DPhSO

N. Ne´de´lec, F.D. Rochon / Inorganica Chimica Acta 319 (2001) 95–108
103
Table 6
13C NMR Dl (lcomplex−lligand) (ppm) and 3J(195Ptꢀ13C) (Hz) of the sulfoxide ligands in the cis- and trans-Pt(R2SO)(pm)Cl2 complexes
R2SO
Ca
Cb
Cg
Cd
2J(195Ptꢀ13Ca)
3J(195Ptꢀ13Cb)
DMSO
TMSO
DPrSO
cis
trans
cis
trans
cis
trans
cis
cis
trans
trans
3.70
3.22
4.24
2.24
2.00
2.03
2.36
2.00
2.55
59
59
63
63
47
47
48
49
53
0.69
−0.90
0.41
0.28
0.11
−0.24
−0.11
2.72
29
17
−0.64
−0.53
−0.64
1.41
1.06
−0.59
DBuSO
DBzSO
−0.04
0.30 (Co=−0.52)
0.12 (Co=−0.83)
1.86
DPhSO
−4.84
an inversed polarization of the p-electrons in the SꢁO
bond. This effect might be more important when the
ligand contains an aromatic groups, which should in-
crease the inversed polarization of the SꢁO p-bond.
of sulfoxides are identical in the two types of com-
pounds (shown in Table 6). These constants vary with
2
the sulfoxide with J values between 47 and 63 Hz and
3J between 17 and 29 Hz, in agreement with the values
determined for the K[Pt(R2SO)Cl3] complexes [21].
3.4. Coupling constants with 195Pt
3.5. Infrared spectroscopy
Several couplings between 195Pt and H2, H6 and C5 of
pyrimidine were observed and the constants are listed in
Tables 3 and 4. These coupling constants are very
important, since they can allow fast identification of the
geometry of the Pt(II) complexes. Average values of 20
The pyrimidine vibrations have been reported in the
literature and our assignments (Section 2) are based on
these studies [14,15]. Upon coordination, the pyrim-
idine vibrations in our complexes were observed at
higher or identical energies than those of free pyrim-
idine. These values are similar in the two types of
complexes for all the sulfoxides. The vibrations 9, 10,
22 and 23 [15] exhibit high intensities and involve CꢁC
and CꢁN stretching vibrations. The vibrations 1, 6 and
14 involve ring deformations, whereas the bands 3 and
17 are b(CꢀH) plane deformation of the molecule.
Finally, the vibrations 5, 12 and 13 are out of plane
CꢀH deformations, while band 4 is an out of plane ring
deformation mode.
The w(SꢀO) absorption band of free sulfoxides were
observed in the region 1020–1060 cm−1. In Pt(II)
complexes, sulfoxides are bonded to the metal by the S
atom and the vibration is expected to absorb at higher
energy [28]. An increase in frequency between 80 and
130 cm−1 were observed. The w(SꢀO) values are similar
for the two geometries, as already observed for
Pt(Et2SO)LCl2 (L=NH3 and py) [29]. For the corre-
sponding DMSO compounds, the w(SꢀO) vibration was
reported at slightly higher energy in the cis complexes
[12].
3
and 23 Hz were observed for J(195Ptꢀ1H2) in trans and
cis complexes, respectively. The study of the
3J(195Ptꢀ1H6) couplings seems particularly important,
since the difference between the two configurations is
much more significant. Values of about 31 Hz were
observed for the trans complexes, whereas much higher
values (39–44 Hz) were calculated for the cis deriva-
tives. Our results are slightly different from those re-
ported
for
trans-Pt(PEt3)(pm)Cl2,
where
the
3
3J(195Ptꢀ1H2) and the J(195Ptꢀ1H6) coupling constants
were found identical (22.3 Hz) [7]. Our J(195Ptꢀ13C5)
3
values are also geometry-dependent and are similar to
those determined with H6, 39 Hz for the cis complexes
and 30 Hz for the trans isomers. Our results are in
agreement with those published for complexes of the
types Pt(py)2Cl2 [20] and Pt(DMSO)(py)Cl2 [26] (py=
pyridine and its derivatives).
Coupling constants between 195Pt and the sulfoxide
protons could be measured only with DMSO, since in
the other complexes, the sulfoxide signals are multiplets
of lower intensity and the satellites arising from 195Pt
couplings could not be observed in our instrument. The
coupling constant in cis-Pt(DMSO)(pm)Cl2 (25 Hz)
appears to be slightly higher than the one measured in
the trans analogue (22 Hz). Similar results were pub-
lished for cis- and trans-Pt(DMSO)(py)Cl2 complexes
(average values of 24 and 21 Hz, respectively) [27]. In
The Pt(R2SO)(pm)Cl2 complexes possess Cs point
symmetries for both cis and trans configurations. From
group theory, two w(PtꢀCl) vibrations are expected for
both geometries. Our IR spectra of the cis isomers
showed two w(PtꢀCl) bands but only one vibration
mode was observed for the trans complexes (as ex-
pected for C26 and D2h symmetries). An average value
of 348 cm−1 was obtained for the trans compounds,
3
contrast to the J(195Ptꢀ13C) values observed for pyrim-
idine, the coupling constants between 195Pt and the Ca

104
N. Ne´de´lec, F.D. Rochon / Inorganica Chimica Acta 319 (2001) 95–108
whereas values of about 345 and 320 cm−1 were
measured for the cis complexes. Similar results have
also been observed for
Pt(DMSO)(L)Cl2 [17,30].
a
series of complexes
One absorption band observed around 450 cm−1 was
assigned to a w(PtꢀS) vibration, as suggested in the
literature [10,17,31–33]. This band seems independent
of the geometry of the complex. A plot of the frequency
of the vibration versus the PtꢀS bond distance was
made for the five compounds (four cis complexes and
one trans isomer) analyzed by X-ray diffraction meth-
ods and a linear relationship was obtained. The bond
distance increases as the energy of the vibration
decreases.
The w(PtꢀN) vibrations are usually difficult to iden-
tify, since these absorption bands are usually of low
intensity. A few compounds showed a band between
502 and 527 cm−1, which could be assigned to this
vibration as suggested in the literature [34,35].
Fig. 1. Labeled diagram of cis-Pt(DMSO)(pm)Cl2 (I). The ellipsoids
correspond to 40% probability.
3.6. Crystal structures
The crystal structures of four complexes cis-
Pt(R2SO)(pm)Cl2 (R2SO=DMSO (I), TMSO (II),
DPrSO (III) and DBuSO (IV)) and of trans-
Pt(TMSO)(pm)Cl2 (V) were studied by X-ray diffrac-
tion methods. Crystal IV is the first example in the
literature of a Pt–DBuSO compound. Labeled dia-
grams of the five complexes are shown in Figs. 1–5.
Selected bond distances and angles are listed in Table 7.
Crystals of the trans complexes are difficult to obtain,
since they isomerize to the cis compounds in organic
solvents.
The coordination around the Pt atom is square pla-
nar as shown by the calculation of the best planes. In
the cis compounds, the oxygen atom of the sulfoxide
ligand is almost in the Pt(II) coordination plane and it
is oriented towards the pyrimidine ligand. Therefore,
the alkyl groups of the sulfoxide are far from pyrim-
idine, in order to reduce steric hindrance. The devia-
tions of the O atom from the calculated best plane are
−0.209(9) (I), 0.038(7) (II), −0.168(7) (III) and
Fig. 2. Labeled diagram of cis-Pt(TMSO)(pm)Cl2 (II). The ellipsoids
correspond to 30% probability.
,
0.006(11) A (IV). In the trans TMSO isomer, the O
atom of TMSO is clearly out of the coordination plane
,
(deviation of −1.320(5) A). The angles around the
platinum atom are close to the expected 90 and 180°.
These results are similar to those determined in trans-
Pt(DMSO)LCl2 complexes (L=2-picoline, py, NH3)
[36–38].
The pyrimidine ring is planar in all the complexes.
The dihedral angles between the coordination and the
pyrimidine planes in the cis complexes are 79.5(3) for I,
62.6(2) for II, 65.7(2) for III and 74.0(4)° for IV. The
angle in the cis DMSO compound is larger than the
one determined in cis-Pt(DMSO)(py)Cl2 (56.8°) [39]
and not too far from the one found in cis-Pt-
Fig. 3. Labeled diagram of cis-Pt(DPrSO)(pm)Cl2 (III). The ellipsoids
correspond to 40% probability. For clarity, only one conformation is
shown for C12 and C13.

N. Ne´de´lec, F.D. Rochon / Inorganica Chimica Acta 319 (2001) 95–108
105
those found in cis-Pt(DMSO)LCl2 complexes where L
is RCN [17,43,44], 2-picoline [41] or py [39] and in the
trans analogues, where L=piperidine [42], 2-picoline
[36], ammine [38], isopropylamine [45] or pyridine [37].
These values are much smaller than PtꢀS bonds in trans
position to another sulfoxide ligand as in trans-Pt(D-
,
PrSO)2Cl2 (2.292(2) A) [16].
The PtꢀN bonds in the cis isomers, which are located
in trans position to a chloride ligand vary between
,
2.020(9) and 2.043(6) A whereas the one in trans-
,
Pt(TMSO)(pm)Cl2 is longer, 2.063(5) A. There is only
one structure in the literature on chloro Ptꢀpm com-
pounds. The PtꢀN distance in trans-Pt(pm)2Cl2 is
2.008(5) A [6] (trans to pm). Thus, it seems from these
,
results, that the trans influence on the PtꢀN bond vary
in the order R2SO\Cl−\pm. The PtꢀN bond seems
to be more sensitive to the trans ligand than the PtꢀCl
bond.
Fig. 4. Labeled diagram of cis-Pt(DBuSO)(pm)Cl2 (IV). The ellip-
soids correspond to 30% probability. For clarity, only one position
for C24 is shown.
Ligand trans to pm: pm
B Cl−
2.028(7)
B R2SO
2.063(5)
,
PtꢀN ave. bond (A) 2.008(5)
The bond distances and angles of the different lig-
ands are normal and similar in all the compounds. The
average SꢀO and SꢀC bond lengths are 1.466(6) and
,
1.790(9) A, respectively. The SꢀC bond does not seem
to depend on the lengths of the alkyl chains. The S
atom in the sulfoxide ligands is in an approximate
tetrahedral environment. The PtꢀSꢀO angles (ave.
115.2(3)°) are slightly larger than the PtꢀSꢀC angles
(ave. 112.0(4)°). The OꢀSꢀC bond angles are also
slightly larger (ave. 108.8(4)°) than the CꢀSꢀC angles
(ave. 93.8(4)° for TMSO, 102.0(5)° for others). Again,
the CꢀSꢀC angles do not seem to vary with the lengths
of the alkyl chains. It is 102.4(5)° for DMSO, 101.5(4)°
for DPrSO and 102.1(7)° for DBuSO. All these values
are similar to those observed in reported PtꢀR2SO
complexes [46].
Fig. 5. Labeled diagram of trans-Pt(TMSO)(pm)Cl2 (V). The ellip-
soids correspond to 30% probability.
(DMSO)(thiazole)Cl2 (72.8 and 65.6°) [40]. This angle is
usually related to the bulkiness of the two cis ligands.
Pyridine and pyrimidine have very similar steric re-
quirements. In cis-Pt(DMSO)(2-picoline)Cl2, the dihe-
dral angle was found to be 87° [41]. The dihedral angle
in trans-Pt(TMSO)(pm)Cl2 (78.0(3)°) is larger than the
one measured in the cis analogue. This angle can be
compared to those reported for trans-Pt(DMSO)(2-pi-
coline)Cl2 (ꢀ73°) [36], trans-Pt(DMSO)(thiazole)Cl2
(39.1°) [40], trans-Pt(pm)2X2 (X=Cl and Br) (52.5 and
54.3°) [6], trans-Pt(DMSO)(py)Cl2 (59.4°) [37], and
trans-Pt(DMSO)(piperidine)Cl2 (96(1)°) [42]. Packing
forces are important factors in the orientation of the
pyrimidine ring, when there is less steric hindrance as in
the trans compounds.
In the pyrimidine ligands, the ave. NꢀC distance is
,
1.330(13) A while the ave. CꢀC bond length is 1.348(15)
,
A. These distances are in agreement with those deter-
,
mined in free pyrimidine (1.33(1) and 1.37(1) A, respec-
tively) [47]. The ave. PtꢀNꢀC angle is 121.5(6)°. The
internal NꢀCꢀC (ave. 122.0(9)°) and NꢀCꢀN angles
(ave. 124.8(10)°) are larger than the CꢀNꢀC (ave.
116.7(9)°) and CꢀCꢀC angles (ave. 117.8(10)°). All these
angles are in agreement with those of the free ligand
[47] and the values reported in trans-Pt(pm)2X2 [6]. The
binding of N1 to the Pt atom does not change the
internal angle at the N1 atom as it does in the hy-
drochlorides of pyrimidine and pyrimidin-2-one [48,49].
The protonation at N1 in both these compounds in-
creased the ring angle at the N atom by about 6°. This
effect is not observed when Pt is the exocyclic bonded
group. Therefore, contrary to protonation, coordina-
Sulfoxides have a higher trans influence than chloride
and amine ligands. In the cis compounds, the PtꢀCl
bonds located in trans position to R2SO are longer
,
(2.305(2)–2.318(2) A) than the PtꢀCl distances located
,
in trans position to pm (2.286(2)–2.300(2) A). In trans-
Pt(TMSO)(pm)Cl2, the average PtꢀCl distance is
,
2.286(2) A. The PtꢀS bond length is identical in the five
,
complexes (ave. 2.214(2) A). This value is very close to

106
N. Ne´de´lec, F.D. Rochon / Inorganica Chimica Acta 319 (2001) 95–108
tion to the platinum atom does not affect the structure
of the pyrimidine ligand.
organic solvents. The cis complexes were observed at
lower field in 195Pt NMR spectroscopy than their trans
analogues. These results can be explained by a more
effective (d–d) p-bond in the cis isomers. Moreover, the
study of the chemical shift variations seems to indicate
the presence of p-bonding between Pt and pyrimidine,
but to a much smaller extent than in the PtꢀR2SO
bonding. The l(Pt) chemical shift of the DPhSO com-
plex was observed at higher field than those of the other
ligands, which might be explained by its greater bulki-
ness around the donor atom. In order to determine the
importance of bulkiness on the l(Pt) chemical shifts,
we intend to continue the work with more bulky alkyl
sulfoxides, but these molecules are not very easily
available.
The conformation of the TMSO ligand in cis- and
trans-Pt(TMSO)(pm)Cl2 is of the envelope type, but
they are different as seen by comparing Figs. 2 and 5.
In the cis compound, four atoms including the S atom
are almost in the same plane (deviations from 0.035 to
,
,
0.058 A), while C3 is out of the plane by 0.584 A. In
the trans isomer, the deviations are slightly more impor-
tant (deviations of C7 to C10 between 0.061 and 0.111
,
,
A), while the S atom is out of the plane by 0.716 A.
The possibility of p–p stacking was examined. It can
be observed in the crystal of trans-Pt(TMSO)(pm)Cl2
complex, but none could be found in the cis isomers.
The packing of the trans molecules is more efficient and
,
the distances between the pyrimidines rings is 3.67 A.
Inversed polarization of the p-electrons of the SꢁO
bond in the sulfoxide complexes was suggested to ex-
plain some of the NMR results. This phenomenon has
already been suggested by our group in the 13C NMR
spectroscopic interpretation of the complexes
K[Pt(R2SO)Cl3] [21] and PtL2(RCOO)2 [50]. The con-
cept was originally suggested in the literature by
Cooper and Powell [25] to explain the 13C NMR chem-
ical shifts in PtꢀCꢂO complexes.
4. Conclusions
A few methods were developed for the synthesis of
new platinum(II) mixed-ligand complexes of the types
cis- and trans-Pt(R2SO)(pm)Cl2. The compounds were
characterized by IR and multi-NMR spectroscopies
and a few by crystallographic methods. The trans com-
pounds were prepared using K[Pt(R2SO)Cl3] and pm in
1:1 proportion in water whereas methanol was used for
the preparation of the cis isomers. The trans com-
pounds can isomerize to the cis isomers, especially in
The configuration of these Pt(II) complexes can be
determined by IR spectroscopy. Two w(PtꢀCl) vibra-
tions were observed for the cis compounds and only
one for the trans complexes. The geometry can also be
determined from the coupling constants between the
Table 7
,
Selected bond distances (A) and angles (°) in the Pt(R2SO)(pm)Cl2 crystals I–V
Crystal
Cis-DMSO (I)
cis-TMSO (II)
cis-DPrSO (III)
cis-DBuSO (IV)
trans-TMSO (V)
PtꢀCl(1) (trans to pm)
PtꢀCl(2)(trans to R2SO) 2.318(2)
PtꢀS
PtꢀN
SꢀO
SꢀC
2.300(2)
2.296(2)
2.314(2)
2.214(2)
2.043(6)
1.460(5)
1.808(9), 1.822(9)
2.286(2)
2.305(2)
2.218(2)
2.025(5)
1.471(5)
1.796(8), 1.795 (7)
2.290(3)
2.311(4)
2.219(3)
2.020(9)
1.453(8)
2.285(2) (trans to Cl−
2.287(2) (trans to Cl−
2.2114(14)
2.063(5)
1.473(5)
)
)
2.209(2)
2.023(7)
1.475(7)
1.775(9), 1.771(9)
1.793(13), 1.775(12) 1.784(6), 1.784(6)
1.33(2), 1.345(14)
NꢀC
1.344(12), 1.318(11) 1.342(10), 1.353(10) 1.332(9), 1.333(10)
1.302(14), 1.339(14) 1.340(14), 1.315(12) 1.377(11), 1.334(14) 1.31(2), 1.34(2)
1.347(15), 1.380(14) 1.353(11), 1.36(2) 1.295(15), 1.328(12) 1.34(2), 1.34(2)
1.293(9), 1.331(9)
1.326(11), 1.299(11)
1.372(12), 1.367(11)
CꢀC (pm)
Cl(1)ꢀPtꢀCl(2)
SꢀPtꢀCl(1)
SꢀPtꢀCl(2)
N(1)ꢀPtꢀCl(1)
N(1)ꢀPtꢀCl(2)
N(1)ꢀPtꢀS
OꢀSꢀPt
CꢀSꢀPt
CꢀNꢀPt
OꢀSꢀC
CꢀSꢀC
91.68(10)
90.53(9)
175.10(8)
176.6(2)
87.1(2)
90.9(2)
115.6(3)
111.4(4), 109.6(4)
120.7(7), 122.7(6)
109.1(5), 107.9(5)
102.4(5)
90.44(9)
89.76(8)
177.59(8)
177.3(2)
88.5(2)
91.4(2)
116.0(2)
111.9(3), 114.5(3)
119.3(6), 122.8(5)
108.6(4), 109.2(4)
94.4(4)
124.2(9)
117.9(7), 116.6(9)
90.51(8)
90.88(7)
178.59(7)
177.2(2)
87.4(2)
91.2(2)
115.1(2)
111.6(3), 109.8(2)
122.4(5), 119.3(6)
109.0(4), 109.0(3)
101.5(4)
90.99(14)
90.02(13)
178.78(13)
177.6(3)
87.6(3)
91.4(3)
174.87(9)
94.62(7)
88.85(7)
87.6(2)
89.3(2)
174.82(14)
113.9(2)
114.0(2), 116.5(2)
122.6(5), 120.8(5)
109.1(3), 108.3(3)
93.1(3)
115.5(4)
109.9(5), 110.8(5)
124.2(9), 120.2(8)
109.0(6), 108.6(6)
102.1(7)
NꢀCꢀN
CꢀNꢀC
NꢀCꢀC
CꢀCꢀC (pm)
125.8(10)
116.6(9), 116.8(10)
121.3(10), 121.8(10) 120.3(8), 122.9(9)
117.7(10) 117.9(9)
121.1(9)
126.2(13)
126.5(8)
118.3(7), 116.6(9)
121.6(10), 122.9(8)
119.5(9)
115.5(10), 115.1(12) 116.6(6), 117.0(8)
122.9(12), 124.1(12) 120.9(8), 121.1(7)
116.1(13)
117.7(8)

N. Ne´de´lec, F.D. Rochon / Inorganica Chimica Acta 319 (2001) 95–108
107
1
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coupling constants J(195Ptꢀ1H2) are slightly larger in
3
the cis complexes than in the trans analogues, whereas
the constants J(195Ptꢀ1H6) are very different in the two
3
geometries. Values between 39 and 44 Hz were ob-
served for cis complexes, while lower values (average 31
Hz) were measured for trans compounds. The
3J(195Ptꢀ13C5) coupling constants are also geometry-de-
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were measured.
The crystal structures of four cis complexes and one
trans compound were determined. The study of these
crystals confirmed the IR and NMR results. The com-
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than the chloride ligand or pyrimidine. Our results on
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of chlorides is slightly larger than that of pyrimidine.
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chloro Pt–pyrimidine compounds are needed to
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three ligands in the trans influence series: sulfoxideꢁ
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