Novel pyrimidine-bridged platinum(II) complexes: Multinuclear magnetic resonance spectroscopy and crystal structures of (NR4)2[(PtCl3)2(μ-pyrimidine)] and cis- and trans-{Pt(R2SO)Cl2}2(μ-pyrimidine)

Article abstract of DOI:10.1021/ic001392d

Two new types of pyrimidine-bridged Pt(II) complexes, (NR₄)₂[(PtCl₃)₂(μ-pm)] and cis- and trans-{Pt(R₂SO)-Cl₂}₂(μ-pm) where pm = pyrimidine, were synthesized and characterized by IR and multinuclear magnetic resonance spectroscopies and by crystallographic methods. Compounds with dimethylsulfoxide, tetramethylene-sulfoxide, di-n-propylsulfoxide (DPrSO), di-n-butylsulfoxide (DBuSO), dibenzylsulfoxide (DBzSO), and diphenylsulfoxide were studied. The aqueous reaction of K₂PtCl₄ with pyrimidine produced the [(PtCl₃)₂(μ-pm)]^2-ions, which can be precipitated with a NR₄⁺ salt. The aqueous reaction of K[Pt(R₂SO)Cl₃] with pyrimidine in a 2:1 ratio produced the dinuclear species trans-{Pt(R₂SO)Cl₂}₂(μ-pm). With DBuSO and DBzSO, the analogous cis isomers were also obtained. The ¹⁹⁵Pt NMR resonances of the trans dimeric complexes were observed at higher field (av -3088 ppm) than the cis compounds (av -2948 ppm). The ¹⁹⁵Pt coupling constants with the atoms of pyrimidine ³J(¹⁹⁵Pt-¹H) and ³J(¹⁹⁵Pt-¹³C) are larger in the cis configuration than in the trans analogues. The crystal structures of two ionic complexes, (NR₄)₂[(PtCl₃)₂(μ-pm)] (R = Me and n-Bu), and of three mixed-ligands dimers, trans-{Pt(R₂SO)Cl₂}₂(μ-pm) (R₂SO = DMSO, DPrSO) and cis-{Pt(DBuSO)Cl₂}₂(μ-pm), were determined.

Full text of DOI:10.1021/ic001392d

5236
Inorg. Chem. 2001, 40, 5236-5244
Novel Pyrimidine-Bridged Platinum(II) Complexes: Multinuclear Magnetic Resonance
Spectroscopy and Crystal Structures of (NR4)2[(PtCl3)2(µ-pyrimidine)] and cis- and
trans-{Pt(R2SO)Cl2}2(µ-pyrimidine)
Nicolas Ne´de´lec and Fernande D. Rochon*
De´partement de Chimie, Universite´ du Que´bec a` Montre´al, C. P. 8888,
Succ. Centre-ville, Montre´al, Canada, H3C 3P8
ReceiVed December 8, 2000
Two new types of pyrimidine-bridged Pt(II) complexes, (NR4)2[(PtCl3)2(µ-pm)] and cis- and trans-{Pt(R2SO)-
Cl2}2(µ-pm) where pm ) pyrimidine, were synthesized and characterized by IR and multinuclear magnetic
resonance spectroscopies and by crystallographic methods. Compounds with dimethylsulfoxide, tetramethylene-
sulfoxide, di-n-propylsulfoxide (DPrSO), di-n-butylsulfoxide (DBuSO), dibenzylsulfoxide (DBzSO), and diphe-
nylsulfoxide were studied. The aqueous reaction of K2PtCl4 with pyrimidine produced the [(PtCl3)2(µ-pm)]2-
+
ions, which can be precipitated with a NR4 salt. The aqueous reaction of K[Pt(R2SO)Cl3] with pyrimidine in a
2:1 ratio produced the dinuclear species trans-{Pt(R2SO)Cl2}2(µ-pm). With DBuSO and DBzSO, the analogous
cis isomers were also obtained. The 195Pt NMR resonances of the trans dimeric complexes were observed at
higher field (av -3088 ppm) than the cis compounds (av -2948 ppm). The 195Pt coupling constants with the
atoms of pyrimidine 3J(195Pt-1H) and 3J(195Pt-13C) are larger in the cis configuration than in the trans analogues.
The crystal structures of two ionic complexes, (NR4)2[(PtCl3)2(µ-pm)] (R ) Me and n-Bu), and of three mixed-
ligands dimers, trans-{Pt(R2SO)Cl2}2(µ-pm) (R2SO ) DMSO, DPrSO) and cis-{Pt(DBuSO)Cl2}2(µ-pm), were
determined.
Introduction
compound was isolated and characterized by IR and 13C NMR,
while the P(n-Bu)3 complex was not isolated. It was only
synthesized directly in the NMR tube and characterized by 1H
and 31P NMR.
Pyrimidine and its derivatives are of biological interest, since
they play an important role in many biological processes.
However, there are very few papers in the literature on platinum
compounds with nonsubstituted pyrimidine (pm). Fazakerley
and Koch1 synthesized and characterized cis-[Pt(NH3)2(pm)2]-
(ClO4)2 by 13C NMR spectroscopy, while Rochon and co-
workers2 prepared cis- and trans-Pt(pm)2X2 (X ) Cl and Br)
and determined the crystal structures of the two trans isomers.
Kaufmann et al. characterized trans-Pt(PEt3)(pm)Cl2 by 1H and
31P NMR, although they were not able to isolate the compound.3
These authors have also prepared the dimer {PtCl2(PR3)}2(µ-
pm). The nature of the platinum-pyrimidine bond has not been
investigated yet.
In an attempt to prepare the ionic complex [Pt(pm)Cl3]-, we
have studied the reaction of K2[PtCl4] with pyrimidine in water.
The isolated crystals were identified by X-ray diffraction
methods as the pyrimidine-bridged dinuclear species [(PtCl3)2-
(µ-pm)]-2, which had not been reported yet. Only one paper
has been published on a pyrimidine-bridged dimer, {PtCl2-
(PR3)}2(µ-pm), where R ) Et and n-Bu.3 Although the crystal
structures of the compounds were not determined, the authors
suggested a trans configuration, because of the large trans effect
of phosphines. The complexes were synthesized from the
reaction of Pt2Cl4(PR3)2 with pyrimidine in CDCl3. The PEt3
Our research group has been involved in Pt-sulfoxide
complexes for many years. These molecules have interesting
behaviors, since they can accept π electron density from the
metallic center. Most of the studies on Pt-sulfoxide complexes
were done with the most common ligand, DMSO. The aqueous
reaction of K2[PtCl4] with an excess of sulfoxide produces trans-
Pt(R2SO)2Cl2, which radiply isomerizes to the cis isomer, unless
the ligand is very sterically demanding. The greater stability of
the cis-disubstituted complexes has been explained by the
enhanced (d-d)π bonding, which is more effective in the cis
configuration than in the trans geometry.4 In the Pt-amine
system, where π bonding is absent, the trans isomers are more
stable than the cis compounds.
We have recently undertaken a study on a new type of mixed-
ligand Pt(II) complexes with pyrimidine and sulfoxide ligands.
It appeared interesting to determine if a trans mixed-ligand
complex containing sulfoxide and pyrimidine would also
isomerize to the cis compound. Pyrimidine contains empty π
antibonding orbitals, which could accept electron density from
Pt. The reactions of K[Pt(R2SO)Cl3] with pyrimidine were
studied with different types of sulfoxides and in different
experimental conditions. In the first part of this project, we have
recently reported the synthesis and characterization of complexes
the types cis- and trans-Pt(R2SO)(pm)Cl2.5 These compounds
were prepared from the reaction of K[Pt(R2SO)Cl3] with
* Corresponding author. Tel: (514) 987-3000, 4896#. Fax: (514) 987-
4054. E-mail: rochon.fernande@uqam.ca.
(1) Fazakerley, G. V.; Koch, K. R. Inorg. Chim. Acta 1979, 36, 13-25.
(2) Rochon, F. D.; Kong, P.-C.; Melanson, R. Can. J. Chem. 1981, 59,
195-198.
(3) Kaufmann, W.; Venanzi, L. M.; Albinati, A. Inorg. Chem. 1988, 27,
1178-1187.
(4) Price, J. H.; Williamson, A. N.; Schramm, R. F.; Wayland, B. B. Inorg.
Chem. 1972, 11, 1280-1284.
(5) Ne´de´lec, N.; Rochon, F. D. Inorg. Chim. Acta 2001, 319, 95-108.
10.1021/ic001392d CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/30/2001

Novel Pyrimidine-Bridged Pt(II) Complexes
Inorganic Chemistry, Vol. 40, No. 20, 2001 5237
Table 1. Experimental Details of the Crystallographic Studies of (NR4)2[(PtCl3)2(µ-pm)] (R ) CH3 (I) and C4H9 (II)),
trans-{Pt(R2SO)Cl2}2(µ-pm) (R2SO ) DMSO (III) and DPrSO (IV)), and cis-{Pt(DBuSO)Cl2}2(µ-pm) (V)
I
II
III
IV
V
formula
fw
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
C12H28N4Cl6Pt2
831.28
P1h
C36H76N4Cl6Pt2
1167.89
P21/c
14.511(3)
16.316(3)
20.571(9)
C8.5H17N2O2S2Cl5Pt2
810.79
Pccn
14.474(2)
30.108(4)
9.1560(10)
C16H32N2O2S2Cl4Pt2
880.54
C2/c
22.965(2)
7.3390(10)
32.585(3)
C20H40N2O2S2Cl4Pt2
936.64
I1/a
15.059(3)
15.059(3)
28.372(10)
8.406(4)
11.728(10)
12.890(10)
102.49(7)
101.02(6)
93.13(6)
1211.7(14)
2
99.62(3)
108.37(1)
4802(3)
4
3990.0(9)
8
5212(1)
8
6434(3)
8
F(000)
772
2.278
12.324
5559
3975 (F>4σ(F))
0.037 (F>4σ(F))
0.047
2312
1.615
6.181
8460
4447
0.0613
0.0975
0.971
2968
3312
3568
1.934
9.168
2824
855
0.0661
0.1184
0.991
F
calc (Mg/m3)
2.699
14.890
3883
2.244
11.310
4594
µ(Mo KR) (mm-1
)
ind reflns
obs reflns (I>2σ(I))
R1 (I>2σ(I))a
wR2 (all data)b
S
1338
2894
0.0638
0.1182
0.992
0.0576
0.1079
1.090
1.29
b
2
2
a R1 ) ∑(|Fo - Fc|)/∑|Fo|. wR2 ) [∑(w(Fo - Fc2)2)/∑(wFo )2]1/2
.
ø obtained for well-centered reflections. The data collections were made
by the 2θ/ω scan technique using the XSCANS6 program (except for
crystal I). The coordinates of the Pt atoms were determined from
Patterson map calculations. All the other non-hydrogen atoms were
found by the usual Fourier methods. The refinement of the structures
was done on F2 (F for I) by full matrix least-squares analysis. The
hydrogen atom positions were fixed in their calculated position with
Ueq ) 1.2Ueq (or 1.5 for methyl groups) of the carbon to which they
are bonded (for I, Ueq ) 0.076 Å2). Corrections were made for
absorption (Gaussian integration except for V (empirical)), Lorentz,
and polarization effects. In crystal II, three C atoms of one butyl chain
of the cation were found disordered. Crystal III did not diffract very
well. It was also measured with Cu KR radiation, but the results did
not improve. Attempts to prepare crystals of better quality were not
successful. It contained 0.5 molecule of CH2Cl2 per dinuclear species
(the C atom is located on a 2-fold axis). In crystal V the two butyl
chains of the DBuSO ligands were found very disordered and the
different components intermingle. The H atoms of the disordered C
atoms were neglected. The residual peaks were located in the close
environment of the platinum atoms. The calculations were done using
the Siemens SHELXTL6 system (except for crystal I7). The pertinent
data are summarized in Table 1.
pyrimidine in water for the trans isomer and in methanol for
the cis compound. The first product is the trans complex, which
then isomerizes to the cis isomer. The isomerization is quite
slow in water especially with more bulky ligands, but much
faster in an organic solvent.
In the second part of the research project, we have isolated
and characterized a new type of pyrimidine-bridged dinuclear
complexes with sulfoxide ligands. Six sulfoxides with different
steric hindrance were studied: dimethylsulfoxide (DMSO),
tetramethylenesulfoxide (TMSO), di-n-propylsulfoxide (DPrSO),
di-n-butylsulfoxide (DBuSO), dibenzylsulfoxide (DBzSO), and
diphenylsulfoxide (DPhSO). We have now developed methods
to synthesize cis- and trans-Pt(R2SO)Cl2(µ-pm)Pt(R2SO)Cl2,
which were characterized by infrared and multinuclear magnetic
resonance (1H, 13C, and 195Pt) spectroscopies. The crystal
structures of two trans compounds and one cis isomer were
determined.
We also report in this paper the crystal structures of two ionic
complexes of the type (NR4)2[PtCl3(µ-pm)PtCl3] (R ) Me and
n-Bu).
The K[Pt(R2SO)Cl3] complexes were synthesized according to the
method described by Kukushkin et al.8 The DBzSO complex was
obtained in small quantities due to the great insolubility of the ligand
and the very favorable formation of the cis-disubstituted compound.
trans-{Pt(R2SO)Cl2}2(µ-pm). The K[Pt(R2SO)Cl3] compounds and
pyrimidine were dissolved in water in 2:1 proportions at room
temperature. A yellow precipitate appeared rapidly, but the stirring of
the solution was pursued until it became colorless. After filtration, the
precipitate was dried, washed with ether, and dried in a vacuum. For
the DPrSO and DBuSO complexes, the reactions were done in a 2:1
H2O-CH3OH mixture, while for the DBzSO, the reaction was done
only in CH3OH. trans-{Pt(DMSO)Cl2}2(µ-pm) (III): yield 93%, mp
171 °C. IR (cm-1): pm (vibration number9,10) 1614s (9,10), 1469m
(22), 1416s (23), 1234w (3), 1198w (17), 1040s (1), 987w (5), 819m
(12), 742w (13), 704m (4); ν(S-O) 1156s, ν(Pt-S) 445m, ν(Pt-Cl)
Experimental Section
K2[PtCl4] was obtained from Johnson Matthey Inc., and it was
purified by recrystallization in water before use. The NR4Cl salts, CD2-
Cl2, pyrimidine, and the sulfoxide ligands were purchased from Aldrich
except dipropylsulfoxide, which was bought from Phillips Petroleum.
The melting and decomposition points were measured on a Fischer-
Johns instrument and were not corrected. The IR spectra were recorded
in the solid state (KBr pellets) on a Perkin-Elmer 783 spectrometer
between 4000 and 270 cm-1. All the NMR spectra were measured in
CD2Cl2 on a Varian Gemini 300BB spectrometer operating at 300.075,
75.462, 64.400, or 64.335 MHz for H, 13C, and 195Pt, respectively.
1
The dichloromethane peaks were used as an internal standard for the
1H (5.32 ppm) and 13C (53.80 ppm) NMR spectra. For 195Pt, the external
references were K2[PtCl4] (-1628 ppm in D2O with KCl) or K[Pt-
(DMSO)Cl3] (in D2O, adjusted at -2998 ppm from Na2[PtCl6]). The
195Pt NMR spectra were measured between -1000 and -2500 ppm
for (NBu4)2[(PtCl3)2(µ-pm)] or between -2500 and -4000 ppm for
the sulfoxide complexes.
(6) XSCANS and SHELXTL (PC, version 5) programs; Bruker Analytical
X-Ray Systems: Madison, WI, 1995.
(7) Melanson, R.; Rochon, F. D. Can. J. Chem. 1975, 53, 2371-2374.
(Cyber 830 computer).
(8) Kukushkin, Yu. N.; Vyaz’menskii, Yu. E.; Zorina, L. I. Russ. J. Inorg.
Chem. 1968, 13, 1573-1576.
The crystallographic measurements were done on a Siemens P4
(except crystal I, which was measured on a P-1) diffractometer using
graphite-monochromatized Mo KR (λ ) 0.71073 Å) radiation. All the
crystals were selected after examination under a polarizing microscope
for homogeneity. The cell dimensions were determined at room
temperature, from a least-squares refinement of the angles 2θ, ω, and
(9) Lord, R. C.; Marston, A. L.; Miller, F. A. Spectrochim. Acta 1957, 9,
113-125.
(10) Brown, D. J. The Chemistry of Heterocyclic Compounds. The
Pyrimidines; John Wiley and Sons: New York, 1962; Chapter 13,
Vol. 16.

5238 Inorganic Chemistry, Vol. 40, No. 20, 2001
Ne´de´lec and Rochon
353m. 1H NMR (ppm): H2 9.986s, H4,6 9.329dd, H5 7.708dt, HR 3.487s.
13C NMR (ppm): C2 162.58, C4,6 161.43, C5 123.34, CR 45.09. trans-
{Pt(TMSO)Cl2}2(µ-pm): yield 89%, mp 167 °C. IR (cm-1): pm 1608s
(9,10), 1467m (22), 1409s (23), 1225w (3), 1190m (17), 1079s (14),
1046w (1), 990w (5), 820m (12), 698sh (4), 665sh (6); ν(S-O) 1149s,
ν(Pt-Cl) 347s. 1H NMR (ppm): H2 10.003s, H4,6 9.349dd, H5 7.714dt,
HR 4.016ddd, 3.627ddd, Hâ 2.387m, 2.221m. 13C NMR (ppm): C2
162.44, C4,6 161.33, C5 123.26, CR 57.66, Câ 24.83. trans-{Pt(DPrSO)-
Cl2}2(µ-pm) (IV): yield 74%, mp 164 °C. IR (cm-1): pm 1604s (9,-
10), 1466m (22), 1413m (23), 1228sh (3), 1187w (17), 1077w (14),
1041w (1), 830m (12), 738w (13), 688sh (4), 662w (6); ν(S-O) 1146s,
1066w (14), 1025w (1), 818m (12), 736m (13), 681s (4); ν(Pt-Cl)
332s. 1H NMR (ppm): H2 10.239s, H4,6 9.384dd, H5 7.167dt. 13C NMR
(ppm): C2 164.77, C4,6 160.16, C5 121.66. 195Pt NMR: -1820 ppm.
Results and Discussion
Synthesis of the Complexes. The aqueous reaction of K[Pt-
(R2SO)Cl3] with pyrimidine in a 2:1 ratio produced the dimeric
complexes trans-{Pt(R2SO)Cl2}2(µ-pm). Compounds with R2-
SO ) DMSO, TMSO, DPrSO, DBuSO, DBzSO, and DPhSO
were prepared. The quantities must be exact to avoid the
formation of trans-Pt(R2SO)(pm)Cl2, which was prepared by a
similar reaction using a 1:1 ratio. For the preparation of the
DPrSO and DBuSO complexes, the reactions were done in a
2:1 water-methanol mixture, while the DBzSO compound was
synthesized in methanol only.
1
ν(Pt-S) 450w, ν(Pt-N) 503m, ν(Pt-Cl) 352m. H NMR (ppm): H2
10.011s, H4,6 9.331dd, H5 7.678dt, HR 3.680ddd, 3.270ddd, Hâ
2.240dddq, 2.117dddq, Hγ 1.211t. 13C NMR (ppm): C2 162.45, C4,6
161.28, C5 122.95, CR 57.21, Câ 17.00, Cγ 12.99. trans-{Pt(DBuSO)-
Cl2}2(µ-pm): yield 79%, mp 108 °C. IR (cm-1): pm 1607s (9,10),
1467m (22), 1412m (23), 1230w (3), 1192w (17), 1044w (1), 970w
(5), 814w (12), 727w (13), 698w (4), 661w (6); ν(S-O) 1149s, ν(Pt-
S) 457w, ν(Pt-N) 510 w, ν(Pt-Cl) 348m. 1H NMR (ppm): H2 10.026s,
2K[Pt(R2SO)Cl3] + pm f
trans-(R2SO)Cl2Pt(µ-pm)Pt(R2SO)Cl2 + 2KCl
H4,6 9.336dd, H5 7.683dt, HR 3.707ddd, 3.293ddd, Hâ 2.195m, 2.067m,
Hγ 1.629sextuplet, Hδ 1.037t. 13C NMR (ppm): C2 162.47, C4,6 161.28,
C5 122.94, CR 55.35, Câ 25.03, Cγ 21.89, Cδ 13.82. trans-{Pt(DBzSO)-
Cl2}2(µ-pm): yield 64%, mp 134 °C. IR (cm-1): pm 1606s (9,10), 1457s
(22), 1410s (23), 1180 m (17), 1070w (14), 1027w (1), 813w (12),
760m (13), 694s (4); ν(S-O) 1122, ν(Pt-Cl) 345m. 1H NMR (ppm):
H2 9.869s, H4,6 9.181dd, H5 7.618dt, HR 5.120d, 4.579d, Hortho 7.657m,
As expected, the trans compound is first formed, since the
trans effect of the sulfoxide ligands is much larger than that of
chlorides. The reaction time depends on the steric hindrance of
the sulfoxide ligand. The yields varied between 64 and 93%.
The same reactions in methanol produce the yellow trans
dimers. In the case of DBuSO and DBzSO, the trans compounds
isomerize completely in about 3 days to the almost white cis
dinuclear species. The trans dimers can be isolated at the
beginning of the reaction if desired. With sulfoxides other than
DBuSO and DBzSO, the trans dimers did not isomerize even
with prolonged time. The isomerization of the trans dimers
(other that DBuSO and DBzSO) was also studied in dichlo-
romethane and chloroform, but without success.
H
meta,para 7.496m. 13C NMR (ppm): C2 161.86, C4,6 160.92, C5 122.53,
CR 60.97, Cphenyl 129.21, 129.67, 130.11, 132.00. trans-{Pt(DPhSO)-
Cl2}2(µ-pm): yield 87%, mp dec 121-246 °C. IR (cm-1): pm 1606s
(9,10), 1474s (22), 1413s (23), 1230w (3), 1181sh (17), 1067s (14),
1044w (1), 997m (5), 811w (12), 744s (13), 693s (4), 640w (6); ν-
(S-O) 1147s, ν(Pt-S) 446w, ν(Pt-Cl) 348s. 1H NMR (ppm): H2
10.132s, H4,6 9.383dd, H5 7.693dt, Hortho 7.942m, Hmeta,para 7.553m. 13
C
NMR (ppm): C2 162.76, C4,6 161.55, C5 123.07, Cphenyl 142.28, 127.56,
129.18, 133.40.
cis-{Pt(R2SO)Cl2}2(µ-pm) (R2SO ) DBuSO and DBzSO). The
K[Pt(R2SO)Cl3] complex and pyrimidine (2:1 ratio) were dissolved in
a minimum quantity of methanol at room temperature. After 3 days, a
white precipitate was observed and the solvent was evaporated. The
residue was mixed with water, and the solution was filtered to remove
the soluble K[Pt(R2SO)Cl3] and KCl. The cis dimer was then dried,
washed with ether, and finally dried in a vacuum. cis-{Pt(DBuSO)-
Cl2}2(µ-pm) (V): yield 33%, mp 165 °C. IR (cm-1): pm 1613s (9,10),
1467m (22), 1415m (23), 1233w (3), 1189w (17), 1087sh (14), 1053w
(1), 820m (12), 732w (13), 681m (4), 663w (6); ν(S-O) 1137s, ν-
(Pt-S) 460w, ν(Pt-N) 505w, ν(Pt-Cl) 353m, 322m. 1H NMR
(ppm): H2 9.851s, H4,6 9.089dd, H5 7.565dt, HR 3.766ddd, 3.198ddd,
Hâ 2.299m, 1.950m, Hγ 1.609dtq, 1.602dtq, Hδ 1.028t. 13C NMR
(ppm): C2 165.06, C4,6 162.14, C5 123.19, CR 54.77, Câ 25.05, Cγ 21.84,
Cδ 13.78. cis-{Pt(DBzSO)Cl2}2(µ-pm): yield 53%, dec 193-230 °C.
IR (cm-1): pm 1609s (9,10), 1454s (22), 1418s (23), 1227w (3), 1185m
(17), 1072w (14), 1030m (1), 818m (12), 759m (13), 697s (4), 674m
(6); ν(S-O) 1120s, ν(Pt-S) 477s, ν(Pt-N) 485m, ν(Pt-Cl) 352m,
These dinuclear species were characterized by IR and
multinuclear magnetic resonance spectroscopies. The synthe-
sized complexes were pure, since only one resonance was
observed in 195Pt NMR spectroscopy (confirmed also by 1H and
13C NMR). Two trans and one cis dinuclear compound, {Pt-
(R2SO)Cl2}2(µ-pm), were also studied by X-ray diffraction
methods.
The aqueous reaction of K2[PtCl4] with pm in a 2:1 ratio
produced the ionic potassium dinuclear species. The yield of
this reaction is limited by the important precipitation of cis-Pt-
(pm)2Cl2, which has already been reported.2 The product K2-
[(PtCl3)2(µ-pm)] was transformed into the tetraalkylammonium
salt by its aqueous reaction with NR4Cl, which instantaneously
produced the insoluble salt (NBu4)2[(PtCl3)2(µ-pm)]. The latter
was prepared in order to compare its NMR spectra with those
of the mixed-ligand dimers in the same solvent, since (NBu4)2-
[(PtCl3)2(µ-pm)] is more soluble in organic solvents than the
potassium analogue. It also produced crystals of better quality.
Crystals of K2[(PtCl3)2(µ-pm)] could not be obtained.
1
320m. H NMR (ppm): H2 8.273s, H4,6 7.381dd, H5 6.733dt, J ) 5.9
Hz, HR 5.058d, 4.466d, Hortho 7.590m, Hmeta,para 7.498m. 13C NMR
(ppm): C2 163.58, C4,6 161.05, C5 122.54, CR 59.66, Cphenyl 127.73,
129.63, 130.24, 132.42.
(NR4)2[(PtCl3)2(µ-pm)] (R ) CH3 and C4H9). One millimole of
K2[PtCl4] was dissolved in water (∼8 mL), and 0.5 mmol of pyrimidine
(in 1 mL of H2O) was added to the solution at room temperature. After
1 day, the solution was filtered to remove Pt(pm)2Cl2 and evaporated
to dryness. The residue was then dissolved in acetone and filtered to
remove KCl and unreacted K2[PtCl4]. After evaporating the acetone,
the K2[(PtCl3)2(µ-pm)] compound was dried, washed with ether, and
dried in a vacuum. The potassium dimeric salt and NR4Cl were
dissolved in water (1:1 ratio), and a yellow precipitate appeared
immediately. The mixture was stirred until the solution became
colorless, and the (NR4)2[(PtCl3)2(µ-pm)] compound was filtered out,
dried, washed with ether, and dried in a vacuum. Yield: 5-10%.
(NBu4)2[(PtCl3)2(µ-pm)] (II): mp 157 °C. IR (cm-1): pm (vibration
no.9,10): 1597s (9,10), 1460s (22), 1407s (23), 1218w (3), 1176w (17),
K2[PtCl4] + pm f
K2[(PtCl3)2(µ-pm)]
V NR4Cl
(NR4)2[(PtCl3)2(µ-pm)]
+ KCl + Pt(pm)2Cl2V
The crystal structures of two ionic dimers (R ) n-Bu and Me)
were determined.
IR Spectroscopy. The IR spectrum of pyrimidine has been
reported, and our assignments (Experimental Section) are based
on these studies.9,10 The vibrations of coordinated pyrimidine
were observed at higher or energies similar to those of the free
ligand. The ν(S-O) vibrations absorb at higher energy than in

Novel Pyrimidine-Bridged Pt(II) Complexes
Inorganic Chemistry, Vol. 40, No. 20, 2001 5239
Table 2. 195Pt Chemical Shifts (ppm) of the Complexes
{Pt(R2SO)Cl2}2(µ-pm) (in CD2Cl2) and ∆δ (δdimer - δmonomer
monomers (106 and 102 ppm, respectively5). In a series of cis-
and trans-Pt(DPhSO)(R-CN)Cl2 complexes,19 the ∆δtrans-cis
values were between 134 and 138 ppm. As shown in Table 2,
the δ(195Pt) of these dimers are close to those determined for
the cis- and trans-Pt(R2SO)(pm)Cl2 compounds since the ∆δ
(δdimer - δmonomer) values are very small. The cis dimers were
observed at slightly lower fields than the cis monomers (∆δ )
13 and 19 ppm), while surprisingly, the trans dimers were found
at slightly higher fields than the corresponding trans monomers
(∆δ ) -7 to -14 ppm). This difference might be due to the
greater bulkiness around the Pt atom in the cis configuration
compared to the one in the trans isomers. Rotation around the
Pt-N bond might be more limited in the cis configuration than
in the trans isomers.
5
)
R2SO
trans
∆δ
cis
∆δ
∆δtrans-cis
DMSO
TMSO
DPrSO
DBuSO
DBzSO
DPhSO
-3081
-3066
-3067
-3069
-3090
-3155
-11
-10
-8
-9
-2941
-2955
13
19
128
135
-12
-7
the free sulfoxides, since the ligands are bonded to Pt by the S
atom. The ν(S-O) energies are identical in the cis and trans
compounds. The IR spectra of the cis isomers showed two ν-
(Pt-Cl) bands at average values of 353 and 321 cm-1, while
only one vibration mode was observed for the trans complexes
at about 349 cm-1. Similar results have been reported for the
monomers Pt(R2SO)(pm)Cl2.5 One absorption band observed
around 450 cm-1 was assigned to a ν(Pt-S) vibration, as
suggested in the literature,4,11-14 while a band at 520 cm-1 was
assigned to the ν(Pt-N) vibration, based also on the published
results.15,16
195Pt NMR Spectroscopy. The 195Pt NMR spectra of all the
pyrimidine-bridged dinuclear complexes were measured in CD2-
Cl2, and the results were compared with those observed for the
monomeric species Pt(R2SO)(pm)Cl2. The chemical shifts are
summarized in Table 2. All the complexes are pure, as shown
by 195Pt, 1H, and 13C NMR spectroscopy. The 195Pt NMR signals
of the trans dinuclear species were observed at higher fields
(between -3066 and -3155 ppm) than the cis analogues (av
-2948 ppm), as reported for the monomeric species Pt(R2SO)-
(pm)Cl2.5 They are also in agreement with the published values
for Pt(DMSO)(NH3)Cl2 (-3045 for cis and -3067 ppm for
trans11,17) and Pt(DMSO)(L)Cl2 (L ) pyridine derivative, -2856
to -3043 ppm11,18) and those published for Pt(R2SO)(R-CN)-
Cl2 (-3041 to -3186 ppm).19
The ∆δtrans-cis values are 128 and 134 ppm. The correspond-
ing values were between 102 and 192 ppm for the monomers
Pt(R2SO)(pm)Cl2.5 The cis dimers are observed at lower fields,
since the (d-d)π bonds are more effective in the cis configu-
ration. The π bonds decrease the electron density on the Pt atom,
causing a deshielding effect on the Pt atom in the cis compound.
The group of Marzilli18 has observed for Pt(DMSO)(pyridine)-
Cl2 a ∆δtrans-cis value of 162 ppm. This ∆δtrans-cis value was
found to vary with the bulkiness of the sulfoxide in the
monomeric compounds Pt(R2SO)(pm)Cl2.5 For the dinuclear
species, there are not enough data to reach a similar conclusion,
since the cis compounds could be synthesized with only two
ligands. Our values of 128 and 134 ppm on the dimers are
slightly larger than those reported for the corresponding
The 195Pt NMR chemical shifts seem to be dependent on the
substituents on the sulfoxide ligands. The DPhSO complex is
observed at much higher field than the others. The difference
does not seem to depend on the presence of an aromatic group,
since the DBzSO complex is observed in the same region as
the other alkyl sulfoxides. But it contains a methylene group
between the sulfoxide group and the phenyl ring, which reduces
the steric hindrance around the binding atom. The shielded
resonance observed for the DPhSO compound might then be
due to the greater bulkiness around the S atom in this ligand.
But for Pt-amine complexes, the δ(Pt) were found at lower fields
for amines containing bulky substituents on the binding
atom.20,21 Another explanation was examined, namely, inverse
polarization of the π electrons of the SdO bond. This
phenomenon has been suggested in the literature to explain some
13C NMR results on Pt-CtO22 and Pt-carboxylato complexes.23
This effect would be present in all Pt-R2SO complexes, but it
is more important for a ligand containing electroattracting
aromatic groups directly on the binding atom. This effect, which
will be discussed further in the 13C NMR spectroscopic section,
would increase the electron density on the Pt atom and therefore
shift its NMR signal to higher field.
1H and 13C NMR Spectroscopies. The pyrimidine signals
of the complexes will first be discussed. The chemical shifts
are shown in the Experimental Section, and the values ∆δ
(δcomplex - δligand) and the coupling constants with 195Pt are listed
in Tables 3 and 4. Three signals are observed in the 1H and 13
C
spectra of free pyrimidine (C2V symmetry).
In the pyrimidine-bridged Pt(II) dimers, the symmetry of the
aromatic ligand is the same (Scheme 1). The signal of H2 which
is close to two nitrogen atoms is a singlet, since the 14N isotope
has a large quadrupolar moment, which leads to a broadening
of the signal. The resonance of H4 and H6 consists of a doublet
of doublets, whereas the one of H5 is a doublet of triplets. All
the J(1H-1H) coupling constants are identical in the cis and
trans configurations of the dimers and are normal.24,25 However,
as observed in the Pt(R2SO)(pm)Cl2 series,5 the coupling
constants 4J(1H4,6-1H2) (0.7 Hz) are quite small. Kaufmann et
al. have also observed similar coupling constants in trans-{Pt-
(PEt3)Cl2}2(µ-pm) and trans-Pt(PEt3)(pm)Cl2.3
(11) Kukushkin, V. Yu.; Belsky, V. K.; Konovalov, V. E.; Kirakosyan, G.
A.; Konovalov, L. V.; Moiseev, A. I.; Tkachuk, V. M. Inorg. Chim.
Acta 1991, 185, 143-154.
(12) Kukushkin, Yu. N.; Spevak, V. N. Russ. J. Inorg. Chem. 1973, 18,
240-243.
(13) Kukushkin, Yu. N.; Pakhomova, I. V. Russ. J. Inorg. Chem. 1971,
16, 226-228.
The pyrimidine proton signals are shifted toward lower field
upon coordination. The average chemical shift variations of the
(14) Johnson, B. F. G.; Walton, R. A. Spectrochim. Acta 1966, 22, 1853-
1858.
(15) Kukushkin, Yu. N.; Ivannikova, N. V.; Khokhryakov, K. A. Russ. J.
Inorg. Chem. 1970, 15, 1595-1598.
(20) Pregosin, P. S. Coord. Chem. ReV. 1982, 44, 247-291.
(21) Rochon, F. D.; Doyon, M.; Butler, I. S. Inorg. Chem. 1993, 32, 2717-
2723.
(22) Cooper, D. G.; Powell, J. Inorg. Chem. 1977, 16, 142-148.
(23) Rochon, F. D.; Gruia, L. Inorg. Chim. Acta 2000, 306, 193-204.
(24) Brown, D. J.; Evans, R. F.; Batterham, T. J. The Chemistry of
Heterocyclic Compounds. The Pyrimidines; John Wiley and Sons:
New York, 1970; Vol. 16, Chapter 13, Suppl. 1.
(16) Nakamoto, K.; McCarthy, P. J.; Fujita, J.; Condrate, R. A.; Behnke,
G. T. Inorg. Chem. 1965, 4, 36-42.
(17) Kerrison, S. J. S.; Sadler, P. J. J. Chem. Soc., Chem. Comm. 1977,
861-863.
(18) Marzilli, L. G.; Hayden, Y.; Reily, M. D. Inorg. Chem. 1986, 2, 5,
974-978.
(19) Rochon, F. D.; Boutin, S.; Kong, P.-C.; Melanson, R. Inorg. Chim.
Acta 1997, 264, 89-100.
(25) Reddy, G. S.; Hobgood, R. T., Jr.; Goldstein, J. H. J. Am. Chem. Soc.
1962, 84, 336-340.

5240 Inorganic Chemistry, Vol. 40, No. 20, 2001
Ne´de´lec and Rochon
3
Table 3. 1H NMR ∆δ (δcomplex - δligand) (ppm) and J(195Pt-1H) (Hz) of Pyrimidine in (NBu4)2[(PtCl3)2(µ-pm)] and the Complexes
{Pt(R2SO)Cl2}2(µ-pm)
ligand
Cl
DMSO
TMSO
DPrSO
DBuSO
H2
H4,6
H5
∆δav
3J(195Pt-1H2)
3J(195Pt-1H6)
1.062
0.809
0.826
0.834
0.674
0.850
-0.904
0.692
0.955
0.666
0.611
0.630
0.614
0.371
0.619
-1.337
0.463
0.665
-0.160
0.381
0.387
0.351
0.237
0.356
-0.594
0.291
0.366
0.559
0.603
0.618
0.603
0.413
0.611
-1.043
0.477
0.663
trans
trans
trans
cis
trans
cis
24
23
20
25
20
26
20
20
28
32
31
42
29
40
30
31
DBzSO
DPhSO
trans
trans
3
Table 4. 13C NMR ∆δ (δcomplex - δligand) (ppm) and J(195Pt-13C)
(Hz) of Pyrimidine in (NBu4)2[(PtCl3)2(µ-pm)] and the Complexes
{Pt(R2SO)Cl2}2(µ-pm)
efforts to crystallize this compound in order to study its crystal
structure, but we were not successful.
In 13C NMR spectroscopy, the variation on the chemical shift
(∆δ) of C2 for the trans complexes follows the order of the
δ(195Pt). In contrast to the proton signals, the 13C NMR
resonances showed greater ∆δ values for the cis dimers
compared to the trans compounds, especially for C2. This study
seems to indicate that the platinum-pyrimidine bond is more
complicated than expected, especially with mixed-ligands
capable of forming π bonds.
ligand
C2
C4,6
C5
∆δav 3J(195Pt-13C5)
Cl
5.45 2.94 -0.28
2.76
3.27
DMSO
TMSO
DPrSO
trans 3.24 4.21
1.41
1.33
1.02
1.26
1.01
0.61
0.60
1.14
trans 3.10 4.11
trans 3.11 4.06
3.16
3.06
4.21
3.06
3.12
2.63
3.31
28
25
35
25
35
DBuSO cis
trans 3.13 4.05
cis 4.24 3.82
5.72 4.92
DBzSO
DPhSO
trans 2.52 3.70
trans 3.42 4.33
The chemical shifts of the sulfoxide ligands are presented in
the Experimental Section, and the values ∆δ (δcomplex - δligand
)
are listed in Tables 5 and 6. The multiplicity of the signals and
the coupling constants J(1H-1H) are identical to those deter-
mined in the complexes cis- and trans-Pt(R2SO)(pm)Cl2.5 The
1H spectrum of the DMSO dimer showed only one peak for
the methyl groups, but two large multiplets were observed for
the hydrogen atoms located in ortho, meta, and para position
of the DPhSO ligand. For TMSO, all the geminal methylene
protons possess different chemical environments. Each R proton
consists of a doublet of doublets of doublets with coupling
constants 2J ) 14.2, 3J ) 7.0, and 3J ) 7.0 Hz. For the DPrSO
and DBuSO complexes, the geminal methylene protons also
have different chemical environments due to limited rotation.
Scheme 1
pyrimidine protons ∆δav (Table 3) are higher for the trans
isomers, in agreement with the 195Pt chemical shifts, which were
observed at higher fields for the trans compounds. These results
seem to suggest a potential π-back-bonding with pyrimidine,
but to a much smaller extent than with sulfoxides, as discussed
for the complexes Pt(R2SO)(pm)Cl2.5 Again, π-bonding seems
much more important in the cis complexes than in the trans
isomers. The ∆δav value is larger for the DPhSO complex
compared to the other trans analogues, in agreement with the
195Pt NMR results. The proton H2 is the most affected by
coordination and seems to be the most dependent on the nature
of the sulfoxide ligand.
2
The signals of the R protons are again a ddd, with J ) 13.0,
3J ) 11.2, and 4J ) 5.1 Hz. The separation between the signals
of the geminal protons decreases as the distance from the
coordination site increases (Table 5). For DBuSO, this difference
is smaller in the trans complexes (0.415, 0.128, and 0.00 ppm)
than in the cis isomers (0.568, 0.349, and 0.007 ppm). The
signals of the Hγ protons in the cis DBuSO complex consist of
a doublet of triplets of quadruplets (dtq), while a sextuplet was
observed in trans-{Pt(DBuSO)Cl2}2(µ-pm) (the two Hâ are felt
as equivalent).
Kaufmann and co-workers have characterized trans-{Pt(PR3)-
Cl2}(µ-pm) (R ) Et and n-Bu) by 1H NMR in the same solvent
(CD2Cl2).3 For these phosphine ligands the average ∆δ (δcomplex
The 13C NMR chemical shift variations (∆δ) are in agreement
with those reported for K[Pt(R2SO)Cl3]26 and Pt(R2SO)(pm)-
- δligand) values were 0.948, 0.651, and 0.243 ppm for H2, H4,6
,
5
Cl2 complexes. The signal of the R DPhSO carbon atoms is
and H5, respectively, compared with our values 0.827, 0.600,
and 0.355 ppm for the trans R2SO dinuclear complexes, and
1.062, 0.666, and -0.160 ppm for the ion [(PtCl3)2(µ-pm)]-.
Thus, H2 and H5 of pyrimidine are the most affected by the
presence of the second ligand. The deshielding order for H2 is
Cl- > PR3 > R2SO, whereas the opposite order was found for
H5. However, the ∆δav study shows similar values for all the
three types of compounds (0.559 ppm for Cl-, 0.596 ppm for
R2SO, and 0.623 ppm for PR3). It is difficult to discuss the
results observed for the cis dimers, since only two compounds
could be synthesized. The ∆δav value for the cis DBuSO
complex is slightly lower than the corresponding value for the
trans isomer. The cis DBzSO complex is totally different, since
all the signals are shifted to higher fields. The study on this
complex was repeated a few times in order to confirm the results.
The same spectra were always obtained. We have made some
very shielded (∆δ ) -4.22 ppm) upon coordination. All the
sulfoxide signals are less deshielded upon coordination than
other types of ligands. We have suggested that the presence of
inverse polarization of the π electrons in the SdO bond might
be responsible for this phenomenon observed in complexes of
the type K[Pt(R2SO)Cl3].26 Bonding of the sulfoxide ligand to
the metal atom would reduce the π-electronic density on the O
atom and increase it on the S atom and its neighboring atoms,
including the Pt atom. This explanation has been suggested in
the literature to explain the 13C NMR spectra of Pt-CO22 and
Pt-carboxylate complexes.23 The chemical shifts in 13C NMR
spectroscopy are particularly dependent on such mesomeric
effects. The inverse polarization of the π electrons in the SdO
(26) Bensimon, C. M.Sc. Thesis, Universite´ du Que´bec a` Montre´al,
Montre´al, Canada, 1986.

Novel Pyrimidine-Bridged Pt(II) Complexes
Inorganic Chemistry, Vol. 40, No. 20, 2001 5241
3
Table 5. 1H NMR ∆δ (δcomplex - δligand) (ppm) and J(195Pt-1H) (Hz) of the Sulfoxides in the Complexes {Pt(R2SO)Cl2}2(µ-pm)
R2SO
HR
0.946
Hâ
Hγ
Hδ
3J(195Pt-1HR)
DMSO
TMSO
DPrSO
DBuSO
trans
trans
trans
cis
trans
cis
23
1.234, 0.845
1.083, 0.672
1.148, 0.580
1.090, 0.675
1.160, 0.568
1.222, 0.681
0.303
0.252, 0.022
0.476, 0.353
0.599, 0.250
0.495, 0.367
0.229 (ortho)
0.296 (ortho)
0.086
0.147
0.141, 0.134
0.161
0.137 (meta+para)
0.135 (meta+para)
0.086
0.073
0.082
DBzSO
DPhSO
26
trans
trans
Table 6. 13C NMR ∆δ (δcomplex - δligand) (ppm) and J(195Pt-13C) (Hz) of the Sulfoxides in the Complexes {Pt(R2SO)Cl2}2(µ-pm)
R2SO
CR
Câ
Cγ
Cδ
Cꢀ
2J(195Pt-13CR)
3J(195Pt-13Câ)
DMSO
TMSO
DPrSO
DBuSO
trans
trans
trans
cis
trans
cis
3.66
2.66
2.44
2.19
2.76
1.64
2.95
-4.22
64
62
52
53
49
49
55
-0.93
0.32
0.02
23
-0.58
-0.63
-0.58
1.321
1.06
-0.07
-0.03
0.176
0.27
0.00
25
DBzSO
DPhSO
-0.79
-0.52
2.75
-0.27
-0.64
trans
trans
-0.47
2.10
bond would be more important in the DPhSO complex, since
the two electroattracting phenyl groups are attached directly on
the S atom.
Coupling Constants with 195Pt. In 1H and 13C NMR,
satellites arising from the coupling with the 195Pt nucleus are
observed for H2, H6, and C5 (3J) of the pyrimidine ligand (Tables
3
3 and 4). The J(195Pt-1H6) values are geometry-dependent.
They vary between 28 and 32 Hz for the trans dimers, while a
higher value (40-42 Hz) was observed for the cis compounds,
27-29
as reported for Pt(py)2X2
(py ) pyridine derivative), for
cis-[Pt(NH3)2(pm)2](ClO4)2,1 and for cis- and trans-Pt(R2SO)-
(pm)Cl2.5 However, lower values were reported for trans-{Pt-
Figure 1. Labeled diagram of the complexed anion in the crystal
(NBu4)2[(PtCl3)2(µ-pm)] (II). The ellipsoids correspond to 40% prob-
ability.
(PR3)Cl2}2(µ-pm) (21 Hz).3 Similarly, the J(Pt-C5) coupling
3
constants for the pyrimidine-bridged dimers seem also geometry-
dependent. The average values are 35 and 26 Hz for the cis
and trans complexes, respectively (Table 4). These values are
identical to those reported for cis- and trans-Pt(R2SO)(pm)Cl2.5
structures) Pt-Cl bond in trans position to a Cl- ligand (2.299-
(3) Å) is slightly longer than the one in trans position to
pyrimidine (2.288(3) Å). The average Pt-N bonds located in
trans position to a Cl- ligand are 2.032(7) for I and 2.025(8) Å
for II, slightly longer than the values reported for trans-Pt-
(pm)2X2 (av 2.011(6) Å),2 where the Pt-N bonds are in trans
position to pyrimidine. These results suggest that the trans
influence of the Cl- ligand is slightly larger than that of
pyrimidine. The angles around the Pt atoms are close to the
values expected for square-planar coordination. The best planes
were calculated through the two Pt planes and through the
pyrimidine ligand. The dihedral angles between the Pt and the
pyrimidine planes are 47.9(2)° and 42.3(2)° for I and 46.8(2)°
and 40.5(2)° for II. The dihedral angle between the two platinum
planes is 74.9(1)° (I) and 75.3(1)° (II).
The pyrimidine bonds and angles agree well with the values
reported for the free ligand,30 for the complexes trans-Pt-
(pm)2X2,2 and for cis- and trans-Pt(R2SO)(pm)Cl2.5 The angle
N-C-N is larger (av 124.9(9)°) than the other internal angles.
No H-bonding is expected in this type of structure. The ions
are held together by electrostatic and van der Waals forces.
The crystal structures of the two complexes trans-(R2SO)-
Cl2Pt(µ-pm)Pt(R2SO)Cl2 (R2SO ) DMSO (III), DPrSO (IV))
and of cis-(DBuSO)Cl2Pt(µ-pm)Pt(DBuSO)Cl2 (V) were studied
by X-ray diffraction methods. Crystal III contained 0.5 molecule
of CH2Cl2 per dinuclear species (the C atom is located on a
2-fold axis). The butyl chains in crystal V are very disordered,
and the different components intermingle. Crystal V did not
3
The J(195Pt-H2) coupling constants seem also to depend on
the geometry of the complexes, although the differences are
smaller. Values of ∼25 Hz were found in the cis compounds,
while these values are ∼20 Hz for the corresponding trans
isomers (Table 3). We have already reported similar results for
Pt(R2SO)(pm)Cl2 (∼23 Hz for cis and ∼20 Hz for trans).5 A
value of 16 Hz was published for trans-{Pt(PR3)Cl2}2(µ-pm).3
These results indicate that NMR is an excellent and easy method
to determine unambiguously the geometry of these complexes.
The sulfoxide proton signals are often broad, and conse-
quently, the 195Pt satellites overlap with the other signals, except
for DMSO and DBzSO. 3J(195Pt-1HR) values of 23-26 Hz were
2
measured. In 13C NMR, the coupling constants J(195Pt-13CR)
are between 49 and 64 Hz (Table 6). These constants seem to
vary with the nature of the sulfoxide. A few coupling constants
3J(195Pt-13Câ) were observed between 23 and 25 Hz, in
agreement with the values reported for the K[Pt(R2SO)Cl3]
complexes.26
Crystal Structures. The crystal structures of (NMe4)2-
[(PtCl3)2(µ-pyrimidine)] (I) and (NBu4)2[(PtCl3)2(µ-pyrimidine)]
(II) were determined. Figure 1 shows the dinuclear anion in
crystal II. Selected bond distances and angles for the two
structures are shown in Table 7. The average (of the two
(27) Ha, T. B. T.; Souchard, J.-P.; Wimmer, F. L.; Johnson, N. P.
Polyhedron 1990, 9, 2647-2649.
(28) Tessier, C.; Rochon, F. D. Inorg. Chim. Acta 1999, 295, 25-38.
(29) Tessier, C.; Rochon, F. D. Inorg. Chim. Acta 2001, in press.
(30) Wheatley, P. J. Acta Crystallogr. 1960, 13, 80-85.

5242 Inorganic Chemistry, Vol. 40, No. 20, 2001
Ne´de´lec and Rochon
Table 7. Selected Bond Distances (Å) and Angles (deg) in Crystals
I and II
I
II
Pt-Cl (trans to Cl-)
2.309(3)
2.310(3)
2.294(3)
2.298(3)
2.300(3)
2.296(3)
2.021(7)
2.042(7)
1.343(11)
1.373(13)
2.306(3)
2.290(3)
2.301(3)
2.282(3)
2.283(3)
2.274(3)
2.028(8)
2.022(8)
1.332(12)
1.372(14)
177.4(1)
90.7(1)
90.4(1)
178.6(1)
90.5(1)
90.7(1)
176.8(3)
89.8(3)
89.2(3)
179.4(2)
89.6(3)
89.1(3)
121.3(8)
125.3(10)
117.4(9)
121.0(11)
118.0(11)
Pt-Cl (trans to pm)
Pt-N
N-C (pm) av
C-C (pm) av
Cl-Pt-Cl
179.3(1)
90.5(1)
90.2(1)
177.9(1)
91.7(1)
90.1(1)
179.4(2)
89.0(2)
90.4(2)
178.3(2)
89.5(2)
88.7(2)
121.0(6)
124.5(8)
117.9(7)
120.6(8)
118.4(9)
Figure 3. Labeled diagram of trans-(DPrSO)Cl2Pt(µ-pm)Pt(DPrSO)-
Cl2 (IV). The ellipsoids correspond to 30% probability.
N-Pt-Cl
Pt-N-C (av)
N-C-N
C-N-C (pm) (av)
N-C-C (pm) (av)
C-C-C (pm)
Figure 4. Labeled diagram of cis-(DBuSO)Cl2Pt(µ-pm)Pt(DBuSO)-
Cl2 (V). The ellipsoids correspond to 30% probability. Only one
component is shown for each butyl chain.
90.8(4)° (cis-DBuSO, V). In the trans complexes, this angle
seems to depend on the bulkiness of the sulfoxide. When R2-
SO is replaced by Cl, the steric hindrance is reduced and the
angle is larger (74.9(1)° for I and 75.3(1)° (II)). For the cis-
DBuSO complex, the conformation of the molecule is quite
different. The two coordination Pt planes are perpendicular to
each other in order to reduce the steric hindrance caused by the
presence of the bulky sulfoxides located in cis position to the
pyrimidine ligand.
Packing forces are important factors in the orientation of the
pyrimidine ring, when there is no steric hindrance. No π-stacking
is possible in the cis compound, since the bulky sulfoxide ligands
prevent the close contact of the pyrimidine ligands. In the trans
crystals, the packing of the molecules is more efficient. In the
DPrSO complex (IV), π-π stacking can be observed. The
distance between the pyrimidine rings is 3.88 Å, but the aromatic
rings are not perfectly stacked. An angle of 15.5° is observed
between the planes.
In the DMSO complex, the oxygen atom of the sulfoxide
ligands are far from the coordination plane (deviations ) -1.19-
(2) and 1.29(2) Å), while they are much closer in the DPrSO
crystal (deviations ) 0.259(16) and 0.208(11) Å). In the cis
dinuclear complex, the deviation of the O atom is 0.31(2) Å
from the coordination plane. The O atom of the sulfoxide ligand
is often in the Pt plane, especially for bulky ligands in order to
reduce the steric hindrance.
Figure 2. Labeled diagram of trans-(DMSO)Cl2Pt(µ-pm)Pt(DMSO)-
Cl2 in crystal III. The ellipsoids correspond to 30% probability.
diffract very well, and the thermal factors of the atoms are high.
Attempts to prepare crystals of better quality failed. Furthermore,
the crystals were not very stable. Although the bond distances
and angles involving the sulfoxide ligand are not very good
(high standard deviations because of the disorder), the data on
this compound are reported in this paper in order to confirm
that the compound has indeed the cis geometry. Bond distances
and angles related to the DBuSO ligand in crystal V will not
be further discussed. Labeled diagrams of crystals III, IV, and
V are shown in Figures 2, 3, and 4. Selected bond distances
and angles are listed in Table 8.
The cis dimeric compound (V) contains a 2-fold axis. The
atoms C2 and C5 of the bridged pyrimidine are located on the
axis. The two trans compounds (III and IV) do not contain
any element of symmetry. The coordination around the Pt atoms
is square planar as expected. The best planes were calculated,
and the dihedral angles between the Pt coordination planes and
the pyrimidine ligand are 47.7(7)° and 62.0(6)° for III, 44.4-
(4)° and 46.0(4)° for IV, and 55.6(5)° for V. These angles are
smaller than those reported in the monomers Pt(R2SO)(pm)-
Cl2,5 where these values vary between 62.6(2)° and 79.5(3)°.
The dihedral angles between the two Pt coordination planes are
60.8(3)° (trans-DMSO, III), 48.7(2)° (trans-DPrSO, IV), and
The angles around the Pt atoms are close to the expected
square planar values. The average Pt-Cl bonds (trans to Cl-)

Novel Pyrimidine-Bridged Pt(II) Complexes
Inorganic Chemistry, Vol. 40, No. 20, 2001 5243
Table 8. Selected Bond Distances (Å) and Angles (deg) in Crystals
III-V
sulfoxide ligands are normal and similar in all the compounds.
The average S-O bond lengths are 1.46(2) (III) and 1.462(13)
Å (IV). The S-C bond might depend on the lengths of the
alkyl chains. The average values are 1.77(3) Å for the DMSO
compound and 1.80(2) Å for the DPrSO complexes.
III
IV
V
Pt-Cl (trans to Cl-)
2.298(7)
2.296(7)
2.292(7)
2.295(6)
2.295(4)
2.296(4)
2.278(4)
2.309(4)
In the pyrimidine ligands, the average N-C distances are
1.35(3), 1.34(2), and 1.32(2) Å, while the average C-C bond
lengths are 1.36(3), 1.36(2), and 1.41(2) Å for crystals III to
V, respectively. These distances are in agreement with those
determined in free pyrimidine (1.33(1) and 1.37(1) Å, respec-
tively).30 The average Pt-N-C angles are 123(2)° (III), 120.3-
(9)° (IV), and 123(2)° (V). The internal N-C-C (av 123(2)°)
and N-C-N (av 125(2)°) angles are larger than the C-N-C
(av 116(2)°) and C-C-C angles (av 116(2)°). All these angles
are in agreement with those of the free ligand30 and the values
Pt-Cl (trans to pm)
Pt-Cl (trans to R2SO)
Pt-S
2.272(5)
2.311(6)
2.171(7)
2.224(7)
2.241(9)
2.04(2)
2.02(2)
1.46(2)
1.77(3)
1.35(3)
1.36(3)
176.7(3)
91.3(3)
88.8(6)
176.8(6)
113.2(9)
111.4(11) 108.2(5)
123(2)
99.6(15)
110.4(16) 109.4(8)
128(2)
115(2)
123(2)
119(3)
2.218(3)
2.221(4)
Pt-N
2.099(10) 2.01(2)
2.103(11)
1.459(12) 1.457(14)
S-O (av)
S-C (av)
1.80(2)
1.34(2)
1.36(2)
177.0(1)
91.3(2)
88.7(3)
178.2(3)
118.0(5)
1.83(2)
1.32(2)
1.41(2)
90.4(5)
91.3(2) 176.3(2)
87.5(5) 177.8(5)
90.9(5)
115.2(6)
107.9(9)
123(2)
N-C (pm) (av)
C-C (pm) (av)
Cl-Pt-Cl (av)
S-Pt-Cl (av)
N-Pt-Cl
5
reported in Pt(R2SO)(pm)Cl2 and in trans-Pt(pm)2X2.2 The
binding of pyrimidine to the Pt atom does not change the internal
angle at the N atom, as it does in the hydrochlorides of
pyrimidine and pyrimidin-2-one.42,43 The protonation at N1 in
both these compounds increased 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, coordination
to the platinum atom does not affect the structure of the
pyrimidine ligand.
N-Pt-S
Pt-S-O (av)
Pt-S-C (av)
Pt-N-C (av)
C-S-C (av)
C-S-O (av)
N-C-N
120.3(9)
102.7(9)
120.7(12) 127(3)
119.3(11) 115(2)
121.1(13) 126(2)
118.2(12) 111(2)
C-N-C (pm) (av)
N-C-C (pm) (av)
C-C-C (pm)
Conclusion
The reaction of K2[PtCl4] with pyrimidine produced a novel
pyrimidine-bridged ionic dimeric anion [Cl3Pt(µ-pm)PtCl3]-.
The crystal structures of the NMe4 and N(n-Bu)4 complexed
salts were determined by X-ray diffraction. Crystal structures
of pyrimidine-bridged Pt complexes have not been reported yet
in the literature.
Two methods were developed for the synthesis of new mixed-
ligand dinuclear platinum(II) complexes of the types cis- and
trans-(R2SO)Cl2Pt(µ-pm)Pt(R2SO)Cl2. The compounds were
characterized by infrared and multi-NMR spectroscopies and a
few by crystallographic methods. The trans compounds were
prepared using K[Pt(R2SO)Cl3] and pm in water, whereas
methanol was used for the preparation of the cis isomers. In an
organic solvent like methanol, the trans compounds are first
formed, and with R2SO ) DBuSO and DBzSO, they isomerize
to the cis isomers. No isomerization was observed for the other
sulfoxides. The cis complexes were observed at lower field in
195Pt NMR spectroscopy than their trans analogues. These
results can be explained by more effective (d-d)π bonds in
the cis isomers.
Inversed polarization of the SdO bond was suggested to
explain the 13C NMR results. This effect would be more
important in the DPhSO complex, which contains two elec-
troattracting groups located directly on the binding atom, which
would increase the electron density on the S atom and its
neighbors. This phenomenon would also explain partially the
high-field 195Pt NMR chemical shift observed for this compound.
The configuration of the complexes can be determined by
the study of the Pt-Cl stretching vibrations. Two ν(Pt-Cl)
vibrations were observed for the cis compounds and only one
for the trans isomers. The geometry of the compounds can also
are 2.295(7) Å for III and 2.295(4) Å for IV. In crystal V, the
Pt-Cl bond located in trans position to the sulfoxide is longer
(2.311(6) Å) than the one trans to Cl- (2.272(5) Å). The average
Pt-S distance is 2.226(6) Å for III and IV. These values agree
well with those reported in the literature for similar com-
pounds.7,31-40 The average Pt-N bond is 2.066(15) Å for III
and IV and 2.01(2) Å for V. The Pt-N bonds located in trans
position to the sulfoxide ligand are much longer than those
located in trans position to Cl- as observed in trans-Pt(TMSO)-
(pm)Cl2 (2.063(5) Å).5 In trans-Pt(pm)2Cl2, the Pt-N bond was
2.008(5) Å (trans to pm).2 The Pt-N bond in trans position to
PEt3 is even much longer (av 2.14(1) Å in trans-{Pt(PEt3)Cl2}3-
(µ-triazine)3). The Pt-N bond seems to be more sensitive to
the trans ligand than the Pt-Cl bond. All these results indicate
that the trans influence vary in the order PR3 . R2SO . Cl-
> pm.
The S atom in the sulfoxide ligands is in an approximate
tetrahedral environment. The C-S-C angles (av 99.6(15)° for
DMSO and 102.7(9)° for DPrSO) are smaller than the angles
observed in other Pt-R2SO structures.7,31-41 This angle often
varies with the bulkiness of the sulfoxide ligand, as observed
in this study. The bond distances and angles of the different
(31) Melanson, R.; Rochon, F. D. Acta Crystallogr. 1978, B34, 1125-
1127.
(32) Caruso, F.; Spagna, R.; Zambonelli, L. Acta Crystallogr. 1980, B36,
713-715.
(33) Viossat, B.; Khodadad, P.; Rodier, N. Acta Crystallogr. 1991, C47,
1316-1317.
(34) Belsky, V. K.; Konovalov, V. E.; Kukushkin, V. Yu. Acta Crystallogr.
1991, C47, 292-294.
(35) Cornia, A.; Fabretti, A. C.; Bonivento, M.; Cattalini, L. Inorg. Chim.
Acta 1997, 255, 405-409.
(36) Melanson, R.; Rochon, F. D. Acta Crystallogr. 1977, B33, 3571-
(41) Melanson, R.; de la Chevrotie`re, C.; Rochon, F. D. Acta Crystallogr.
1985, C41, 1428-1431. Melanson, R.; Rochon, F. D. Acta Crystallogr.
1987, C43, 1869-1872. Antolini, L.; Folli, U.; Iarossi, D.; Schenetti,
L.; Taddei, F. J. Chem. Soc., Perkin Trans. 2 1991, 955-961.
Ebbighausen, J.; Farrell, N.; Lo¨vqvist, K.; Oskarsson, Å. Acta
Crystallogr. 1996, C52, 1091-1093.
3573.
(37) Lo¨vqvist, K.; Oskarsson, Å. Acta Crystallogr. 1992, C48, 2073-2075.
(38) Belsky, V. K.; Konovalov, V. E.; Kukushkin, V. Yu.; Moiseev, A. I.
Inorg. Chim. Acta 1990, 169, 101-107.
(39) Rochon, F. D.; Kong, P.-C.; Melanson, R. Inorg. Chim. Acta 1994,
216, 163-167.
(42) Furberg, S.; Aas, J. B. Acta Chem. Scand. 1975, A29, 713-716.
(43) Singh, C. Acta Crystallogr. 1965, 19, 861-864.
(40) Melanson, R.; Rochon, F. D. Acta Crystallogr. 1984, C40, 793-795.

5244 Inorganic Chemistry, Vol. 40, No. 20, 2001
Ne´de´lec and Rochon
be determined unambiguously from the coupling constants
between the pyrimidine atoms and 195Pt. The coupling constants
The CIF tables of the five crystal structure determinations
have been deposited at the Cambridge Data File Centre. The
deposit numbers are CCDC 166032-166036.
3
3
3J(195Pt-1H2), J(195Pt-1H6), and J(195Pt-13C5) are larger in
the cis isomers than in the trans complexes.
The crystal structure determinations of one cis complex and
two trans compounds confirmed the IR and NMR results. The
comparison of the Pt-ligand bond distances gave interesting
information on the trans influence of the different ligands.
Sulfoxides have clearly a larger trans influence than chlorides
or pyrimidine. Our results on the Pt-N bonds seem to indicate
that the trans influence of chlorides is slightly larger than that
of pyrimidine.
Acknowledgment. The authors are grateful to the Natural
Sciences and Engineering Reseach Council of Canada for
financial support of the project.
Supporting Information Available: Crystal data for 1-5. This
material is available free of charge via the Internet at http://pubs.acs.org.
IC001392D