trans-Chloromethylbis(dimethyl sulfoxide)platinum(II): X-ray Structure, Mechanism of Isomerization, and Its Use as a Precursor to Organoamine Complexes of Variable Geometrical Configurations

Article abstract of DOI:10.1021/ic960428s

An unusual 2:1 aggregate between the complex trans-[PtCl(CH₃)(DMSO)₂] (1; DMSO = dimethyl sulfoxide) and the organotin compound bis(μ ₃-oxo)bis(μ-chloro)bis(μ-dimethyltin(IV)) bis(chlorodimethyltin(IV)) [Cl(CH₃)₂-SnOSn(CH₃)₂Cl]₂ has been isolated and characterized by X-ray analysis. The crystals belong to the triclinic space group P1? with lattice constants a = 9.373(2) A?, b = 9.576(1) A?, c = 14.087(3) A?, α = 70.29(1)°, β = 72.50(1)°, γ = 72.21(2)°, and Z = 2. Least-squares refinement of the structure led to an R factor of 2.37%. ¹H, ¹³C, and ¹⁹⁵Pt NMR measurements revealed that in chloroform solution complex 1 gives a mixture of four different species, which have been unambiguously identified as the starting complex 1 in equilibrium with cis-[PtCl(CH₃)-(DMSO)₂] and the two corresponding isomeric aqua-species cis and trans-[PtCl(CH₃)(DMSO)(OH₂)]. The ¹⁹⁵Pt NMR magnetization transfer technique allowed determination of the rate of interconversion among the various complexes, showing that the direct trans-cis isomerism between the [PtCl(CH₃)(DMSO)₂] species is negligible and that the geometrical interconversion occurs through a water-catalyzed pathway. The exchange between free and coordinated DMSO in cis- and trans-[PtCl(CH₃)(DMSO)₂] has been measured by ¹H NMR magnetization transfer experiments. The molecule of DMSO in the position trans to a methyl group was found to be 10-fold more labile than that trans to another sulfur bonded dimethyl sulfoxide. The reactivity of complex 1 in chloroform with a series of monodentate nitrogen ligands having widely different electronic and steric properties has been investigated by ¹H NMR spectroscopy. The utility of this system as precursor for the synthesis of cis- and trans-[PtCl(CH₃)(DMSO)(am)] is discussed together with the evidence for the factors promoting the prevalence of a geometrical configuration.

Full text of DOI:10.1021/ic960428s

Inorg. Chem. 1996, 35, 7691-7698
7691
trans-Chloromethylbis(dimethyl sulfoxide)platinum(II): X-ray Structure, Mechanism of
Isomerization, and Its Use as a Precursor to Organoamine Complexes of Variable
Geometrical Configurations
Raffaello Romeo,*,† Luigi Monsu` Scolaro,† Nicola Nastasi,† Brian Ernest Mann,*,‡
Giuseppe Bruno,† and Francesco Nicolo`†
Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Universita` di Messina,
Istituto di Chimica e Tecnologia dei Prodotti Naturali (ICTPN-CNR) Sezione di Messina,
Salita Sperone 31, 98166 Vill. S. Agata, Messina, Italy, and Department of Chemistry,
University of Sheffield, Sheffield, U.K.
ReceiVed April 19, 1996X
An unusual 2:1 aggregate between the complex trans-[PtCl(CH3)(DMSO)2] (1; DMSO ) dimethyl sulfoxide)
and the organotin compound bis(µ3-oxo)bis(µ-chloro)bis(µ-dimethyltin(IV))bis(chlorodimethyltin(IV)) [Cl(CH3)2-
SnOSn(CH3)2Cl]2 has been isolated and characterized by X-ray analysis. The crystals belong to the triclinic
space group P1h with lattice constants a ) 9.373(2) Å, b ) 9.576(1) Å, c ) 14.087(3) Å, R ) 70.29(1)°, â )
72.50(1)°, γ ) 72.21(2)°, and Z ) 2. Least-squares refinement of the structure led to an R factor of 2.37%. 1H,
13C, and 195Pt NMR measurements revealed that in chloroform solution complex 1 gives a mixture of four different
species, which have been unambiguously identified as the starting complex 1 in equilibrium with cis-[PtCl(CH3)-
(DMSO)2] and the two corresponding isomeric aqua-species cis and trans-[PtCl(CH3)(DMSO)(OH2)]. The 195Pt
NMR magnetization transfer technique allowed determination of the rate of interconversion among the various
complexes, showing that the direct trans-cis isomerism between the [PtCl(CH3)(DMSO)2] species is negligible
and that the geometrical interconversion occurs through a water-catalyzed pathway. The exchange between free
1
and coordinated DMSO in cis- and trans-[PtCl(CH3)(DMSO)2] has been measured by H NMR magnetization
transfer experiments. The molecule of DMSO in the position trans to a methyl group was found to be 10-fold
more labile than that trans to another sulfur bonded dimethyl sulfoxide. The reactivity of complex 1 in chloroform
with a series of monodentate nitrogen ligands having widely different electronic and steric properties has been
investigated by 1H NMR spectroscopy. The utility of this system as precursor for the synthesis of cis- and trans-
[PtCl(CH3)(DMSO)(am)] is discussed together with the evidence for the factors promoting the prevalence of a
geometrical configuration.
Introduction
sulfoxide is difficult to remove,6 while the presence of a second
molecule, even when in the cis position, enhances the reactivity,
The chemistry of sulfoxide complexes with transition metal
ions has received considerable attention due to the importance
of their use as labile synthetic precursors1 and potential
antitumor agents2 and to their role as catalytic intermediates. A
great deal of work has been addressed to the study of the
reactivity and the clarification of the mechanism of substitution
in square-planar complexes of platinum(II) containing dimethyl
sulfoxide as the coordinating molecule. As a ligand it exhibits
a quite large trans effect3 and a relatively weak trans influence.4
It can be considered a poor nucleophilic agent,5 resembling
ethene. Acting as a leaving group, sulfoxides display a mutual
labilization effect. It is well-established that a single dimethyl
and this property has been investigated from a kinetic point of
view7 and exploited in inorganic synthesis.8 Analogous orga-
nometallic species of the type cis-[Pt(R)2(DMSO)2] (R ) Me,
aryl group; DMSO ) dimethyl sulfoxide), reported by Eaborn
et al.,9 behave in a similar way, and both sulfoxide ligands can
be easily replaced by bidentate chelating ligands. The mech-
(3) (a) Romeo, R., Tobe, M. L. Inorg. Chem. 1974, 13, 1991. (b) Elding,
L. I.; Groning, O. Inorg. Chem. 1978, 17, 1872. (c) Tobe, M. L.;
Treadgold, A. T.; Cattalini, L. J. Chem. Soc., Dalton Trans. 1988,
2347.
(4) Rochon, F. D.; Kong P. C.; Melanson, R. Inorg. Chem., 1990, 29,
2708. Melanson, R.; Hubert, J.; Rochon, F. D. Acta Crystallogr., Sect.
B: Struct. Crystallogr. Cryst. Chem. 1976, 32, 1914.
(5) (a) Elding, L. I.; Groning, A. B. Inorg. Chim. Acta 1978, 31, 243. (b)
Annibale, G.; Cattalini, L.; Canovese, L.; Michelon, G.; Marangoni,
P.; Tobe, M. L. Inorg. Chem. 1983, 22, 975. (c) Fanizzi, F. P.; Intini,
F. P.; Maresca, L.; Natile, G.; Uccello-Barretta, G. Inorg. Chem. 1990,
29, 929.
(6) (a) Romeo, R.; Cusumano, M. Inorg. Chim. Acta 1981, 49, 167. (b)
Braddock, P. D.; Romeo, R.; Tobe, M. L. Inorg. Chem. 1974, 13,
1170.
(7) (a) Lanza, S.; Minniti, D.; Romeo, R.; Tobe, M. L. Inorg. Chem. 1983,
22, 2006. (b) Cattalini, L.; Marangoni, G.; Michelon, G.; Paolucci,
G.; Tobe, M. L. Inorg. Chem. 1981, 20, 71. (c) Bonivento, M.;
Canovese, L.; Cattalini, L.; Marangoni, G.; Michelon, G.; Tobe, M.
L. Inorg. Chem. 1981, 20, 1493.
† Universita` di Messina.
‡ University of Sheffield.
X Abstract published in AdVance ACS Abstracts, November 15, 1996.
(1) Davies, J. A. AdV. Inorg. Chem. Radiochem. 1981, 24, 115. Davies,
J. A.; Hartley, F. R. Chem. ReV. 1981, 81, 79.
(2) (a) Farrell, N.; Kiley, D. M.;Schmidt, W.; Hacker, M . Inorg. Chem.
1990, 29, 397. (b) Lempers, E. L. M.; Bloemink, M. J.; Reedijk, J.
Inorg. Chem. 1991, 30, 201. (c) Lippard, S. J. Pure Appl. Chem. 1987,
59, 731. (d) Reedijk, J. Pure Appl. Chem. 1987, 59, 181. (e) Sherman,
S. E.; Lippard, S. J. Chem. ReV. 1987, 87, 1153. (f) Nicolini, M.,
Ed.Platinum and Other Metal Coordination Compounds in Cancer
Chemiotherapy; Martinus Nijhoff Pubishing: Boston, 1988. (g) Pasini,
A.; Zunino, F.; Angew. Chem. 1987, 99, 632. (h) Farrel, N. Transition
Metal Complexes as Drugs and Chemotherapeutic Agents; Kluwer
Academic Publishers : Dordrecht, The Netherlands, 1989. (i) Mestroni,
G.; Alessio, E.; Sava, G.; Pacor, S.; Coluccia, M. In Metal Complexes
in Cancer Chemotherapy; Keppler, B. K., Ed.; VCH Verlag: Wein-
heim, Germany, 1994.
(8) Romeo, R.; Minniti, D.; Lanza, S.; Tobe, M. L. Inorg. Chim. Acta
1977, 22, 87.
(9) Eaborn, C.; Kundu, K.; Pidcock, A. J. J. Chem. Soc., Dalton Trans.
1981, 933.
S0020-1669(96)00428-4 CCC: $12.00 © 1996 American Chemical Society

7692 Inorganic Chemistry, Vol. 35, No. 26, 1996
Romeo et al.
procedure. An 80.2 mg (0.2 mmol) sample of complex 1 was dissolved
in the minimum amount of dichloromethane (∼10 mL) and reacted
under stirring with the stoichiometric amount of the proper nitrogen
ligand. After 30 min, pentane was added and the reaction mixture was
cooled to allow precipitation. The solid precipitate was collected,
washed with several small portions of cold pentane, and dried under
vacuum. The yields were almost quantitative.
anism of these reactions has been investigated in great detail
and provides the first example of a dissociative activation
pathway for the nucleophilic substitution process in square-
planar platinum(II) complexes.10
Despite the large amount of data available for the structural
characterization and the reactivity of complexes containing two
sulfoxide molecules spanning mutual cis positions, there are
scarce reports on complexes containing two sulfoxide ligands
in trans configuration and, to the best of our knowledge, none
involving organometallic species. This stereochemistry is
adopted only in the case of sterically hindered ligands such as
diisoamyl sulfoxide.11 Usually the trans isomer prefers to
interconvert into the more stable cis species, and only in some
instances has been it possible to isolate these intermediates.12
cis(C,N)-Chloromethyl(dimethyl sulfoxide)(n-propylamine)plati-
num(II), cis(C,N)-[PtCl(CH3)(DMSO)(PrnNH2)] (2). 1H NMR: δ
3.49 (br s, 2JPtH ) 58 Hz, 2H, NH2), 3.41 (s, 3JPtH ) 26 Hz, 6H), 2.92
(m, Jav ) 7 Hz, 2H), 1.69 (m, Jav ) 7 Hz, 2H), 0.98 (t, Jav ) 7 Hz,
3H), 0.79 (s, 2JPtH ) 83 Hz, 3H). Anal. Calcd for C6H18ClNOPtS: C,
18.83; H, 4.74; N, 3.66. Found: C, 19.21; H, 4.61; N, 3.80.
cis(C,N)-Chloromethyl(dimethyl sulfoxide)(pyridine)platinum(II),
cis(C,N)-[PtCl(CH3)(DMSO)(py)] (3). 1H NMR: δ 8.73 (m, 3JPtH
42 Hz, Jav ) 5 Hz, 2H, H2), 7.88 (m, Jav ) 7 Hz, 1H, H4), 7.45 (m, Jav
)
For example, enriched solutions of trans-[PtCl2(Prn SO)2] have
2
3
2
) 7 Hz, 2H, H3), 3.52 (s, JPtH ) 26 Hz, 6H), 0.90 (s, JPtH ) 83 Hz,
3H). Anal. Calcd for C8H14ClNOPtS: C, 23.85; H, 3.50; N, 3.48.
Found: C, 24.02; H, 3.55; N, 3.30.
been prepared by photochemical isomerization of the stable cis
isomer.13 The complexes trans-[PtCl2(DMSO)2] and trans-
[PtCl2(Et2SO)2]14 have been obtained by a bridge splitting
reaction or by immediately precipitating the compound prepared
from a proper labile precursor.15
Following these considerations, we thought it of interest to
study the solution behavior of the organometallic complex trans-
[PtCl(CH3)(DMSO)2] as a simple model compound using NMR
spectroscopy in an aprotic solvent. In this paper we report also
the unusual X-ray structure of a cocrystallization product
between the polynuclear tin(IV) compound bis(µ3-oxo)bis(µ-
chloro)bis(µ-dimethyltin(IV))bis(chlorodimethyltin(IV)) and the
complex under investigation. The application of this compound
as a useful synthon for the preparation of asymmetric organo-
metallic species containing four different groups coordinated
to the metal center is discussed.
cis(C,N)-Chloromethyl(dimethyl sulfoxide)(2-methylpyridine)-
platinum(II), cis(C,N)-[PtCl(CH3)(DMSO)(2-Mepy)] (4). 1H NMR:
3
δ 8.64 (dd, JPtH ) 42 Hz, Jav ) 5 Hz, 1H, H6), 7.73 (m, Jav ) 7 Hz,
1H), 7.36 (m, Jav ) 7 Hz, 1H), 7.26 (m, Jav ) 5 Hz, 1H), 3.51 (s, 3JPtH
4
2
) 27 Hz, 6H), 3.00 (s, JPtH ) 8.7 Hz, 6H, Me), 0.74 (s, JPtH ) 84
Hz, 3H). Anal. Calcd for C9H16ClNOPtS: C, 25.93; H, 3.87; N, 3.36.
Found: C, 25.80; H, 3.78; N, 3.48.
trans(C,N)-Chloromethyl(dimethyl sulfoxide)(2,6-dimethylpyridine)-
platinum(II), trans(C,N)-[PtCl(CH3)(DMSO)(2,6-Me2py)] (5). 1H
NMR: δ 7.59 (t, 3JHH ) 7 Hz, 1H, H4), 7.14 (d, 3JHH ) 7 Hz, 2H, H3),
3.24 (s, 3JPtH ) 37 Hz, 6H), 3.08 (s, 4JPtH ) 7.3 Hz, 6H, Me), 0.71 (s,
2JPtH ) 75 Hz, 3H). Anal. Calcd for C10H18ClNOPtS: C, 27.88; H,
4.21; N, 3.25. Found: C, 28.01; H, 4.11; N, 3.09.
trans(C,N)-Chloromethyl(dimethyl sulfoxide)(2-methylquinoline)-
platinum(II), trans(C,N)-[PtCl(CH3)(DMSO)(2-Mequin)] (6). 1H
NMR: δ 9.78 (d, Jav ) 9 Hz, 1H), 8.21 (d, Jav ) 9 Hz, 1H), 7.85 (m,
4
Experimental Section
2H), 7.57 (t, Jav ) 8 Hz, 1H), 7.41 (d, Jav ) 8 Hz, 1H), 3.30 (s, JPtH
3
3
) 6.7 Hz, 3H), 3.22 (s, JPtH ) 35 Hz, 3H), 3.16 (s, JPtH ) 35 Hz,
Materials. K2PtCl4 was obtained from Strem and was purified by
dissolving it in water and filtering. Tetramethyltin was received from
Aldrich, and its purity was checked by 1H NMR. Dimethyl sulfoxide
was purified by liquid chromatography on alumina under argon and
stored over molecular sieves. The solvents used, except those for NMR
measurements, were purified and dried by standard techniques. All of
the other reagents were the best commercially available materials and
were used as received or were purified by distillation or crystallization
when needed. Microanalysis was performed by Analytical Laboratories,
Engelskirchen. Elemental analyses were consistent with theoretical
formulas.
Preparation of Complexes. The title complex, trans-[PtCl(CH3)-
(DMSO)2] (1), was prepared according to Eaborn et al.9 The complex
was purified by several crystallizations from dichloromethane/diethyl
ether mixtures.
The neutral complexes of the type [PtCl(CH3)(DMSO)(am)] (am )
n-propylamine (PrnNH2), pyridine (py), 2-methylpyridine (2-Mepy), 2,6-
dimethylpyridine (2,6-Me2py), 2-methylquinoline (2-Mequin), 5-ami-
noquinoline (5-AQ-N1), 3,8-bis(dimethylamino)acridine, or acridine
orange (AO)) were prepared by following essentially the same
2
3H), 0.88 (s, JPtH ) 76 Hz, 3H). Anal. Calcd for C13H18ClNOPtS:
C, 33.44; H, 3.89; N, 3.00. Found: C, 33.8; H, 3.95; N, 2.85.
cis(C,N)-Chloromethyl(dimethyl sulfoxide)(5-aminoquinoline-
N1)platinum (II), cis(C,N)-[PtCl(CH3)(DMSO)(5-AQ-N1)] (7). 1H
3
NMR: δ 9.02 (d, JPtH ) 46 Hz, Jav ) 5 Hz, 1H, H2), 8.60 (d, Jav
)
8 Hz, 1H, H4), 8.34 (d, Jav ) 8 Hz, 1H, H8), 7.66 (m, Jav ) 8 Hz, 1H,
H7), 7.37 (dd, 3JHH ) 8 Hz, 3JHH ) 5 Hz, 1H, H3), 6.87 (d, Jav ) 8 Hz,
3
1H, H6), 4.35 (br s, 2H, NH2), 3.60 (s, JPtH ) 26 Hz, 3H), 3.56 (s,
3JPtH ) 26 Hz, 3H), 0.79 (s, JPtH ) 84 Hz, 3H). Anal. Calcd for
2
C12H17ClN2OPtS: C, 30.81; H, 3.66; N, 5.99. Found : C, 31.03; H,
3.5; N, 6.01.
trans(C,N)-Chloromethyl(dimethyl sulfoxide)(3,6-bis(dimethyl-
amino) acridine)platinum(II), trans(C,N)-[PtCl(CH3)(DMSO)(AO)]
4
(8). 1H NMR: δ 8.65 (d, JHH ) 2 Hz, 2H, H2,9), 8.34 (s, 1H, H10),
3
3
4
7.69 (d, JHH ) 9 Hz, 2H, H5,6), 7.06 (dd, JHH ) 9 Hz, JHH ) 2 Hz,
3
2H, H4,7), 3.23 (s, 12H, NMe2), 2.90 (s, JPtH ) 31 Hz, 6H), 1.13 (s,
2JPtH ) 76 Hz, 3H). Anal. Calcd for C20H28ClN3OPtS: C, 40.78; H,
4.79; N, 7.13. Found: C, 41.10; H, 4.61; N, 7.00.
Some of the complexes (am ) tert-butylamine (ButNH2), diisopro-
pylamine (Pri2NH2), triethylamine (Et3N), 4-(dimethylamino)pyridine
(4-(NMe2)py), 2-chloropyridine (2-Clpy), 2-phenylpyridine (2-Phpy),
and acridine (Acr)) were prepared in situ by following the same general
procedure. An 8 mg (0.02 mmol) sample of complex 1 dissolved in
0.5 mL of chloroform-d was reacted with the stoichiometric amount
of the proper nitrogen ligand in an NMR tube. All of the complexes
(10) (a) Lanza, S.; Minniti, D.; Moore, P.; Sachinidis, J.; Romeo, R.; Tobe,
M. L. Inorg. Chem. 1984, 23, 4428. (b) Lanza, S.; Minniti, D.; Romeo,
R.; Moore, P.; Sachinidis, J.; Tobe, M. L. J. Chem. Soc., Chem.
Commun. 1984, 542. (c) Alibrandi, G.; Bruno, G.; Lanza, S.; Minniti,
D.; Romeo, R.; Tobe, M.L. Inorg. Chem. 1987, 26, 185. (d) Minniti,
D.; Alibrandi, G.; Tobe, M. L.; Romeo, R. Inorg. Chem. 1987, 26,
3956. (e) Frey, U.; Helm, L.; Merbach, A. E.; Romeo, R. J. Am. Chem.
Soc. 1989, 111, 8161. (f) Alibrandi, G.; Minniti, D.; Monsu` Scolaro,
L.; Romeo, R. Inorg. Chem. 1989, 28, 1939. (g) Romeo, R.; Grassi,
A.; Monsu` Scolaro, L. Inorg. Chem. 1992, 31, 4383.
(11) Price, J. H.; Williamson, A. N.; Schramm, R. F.; Wayland, B. B. Inorg.
Chem. 1972, 11, 1280.
(12) Davies, J. A.; Sood, A. Inorg. Chem. 1985, 24, 4213.
(13) Price, J. H.; Birk, J. P.; Wayland, B. B. Inorg. Chem. 1978, 17, 2245.
(14) Annibale, G.; Bonivento, M.; Canovese, L.; Cattalini, L.; Michelon,
G.; Tobe, M. L. Inorg. Chem. 1985, 24, 797.
1
were characterized by H NMR spectroscopy. Some of the signals
were not assignable or resolvable due to the overlap with signals of
the corresponding isomer and/or the free ligand.
cis(C,N)-Chloromethyl(dimethyl sulfoxide)(tert-butylamine)plati-
num(II), cis(C,N)-[PtCl(CH3)(DMSO)(ButNH2)] (9A). 1H NMR: δ
2
3
3.59 (v br s, JPtH ) 60 Hz, 2H, NH2), 3.41 (s, JPtH ) 27 Hz, 6H),
2
1.41 (s, 9H), 0.80 (s, JPtH ) 83 Hz, 3H).
trans(C,N)-Chloromethyl(dimethyl sulfoxide)(tert-butylamine)-
platinum(II), trans(C,N)-[PtCl(CH3)(DMSO)(ButNH2)] (9B). 1H
NMR: δ 3.26 (s, 3JPtH ) 39 Hz, 6H), 1.39 (s, 9H), 0.47 (s, 2JPtH ) 74
Hz, 3H).
(15) Annibale, G.; Bonivento, M.; Cattalini, L.; Tobe, M. L. J. Chem. Soc.,
Dalton Trans. 1992, 3433.

trans-[PtCl(CH3)(DMSO)2]
Inorganic Chemistry, Vol. 35, No. 26, 1996 7693
Table 1. Crystallographic Data
cis(C,N)-Chloromethyl(dimethyl sulfoxide)(diisopropylamine)-
platinum(II), cis(C,N)-[PtCl(CH3)(DMSO)(Pri2NH2)] (10A). 1H
NMR: δ 3.57 (m, 2H), 3.41 (s, 3JPtH ) 26 Hz, 6H), 1.47 (d, 3JHH ) 7
formula
fw
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
C9H27Cl3O3PtS2Sn2
786.25
triclinic
V, Å3
1105.5(4)
2
2.362
23
9.106
0.024
0.058
Z
F
3
2
calcd, g/cm3
Hz, 6H), 1.36 (d, JHH ) 7 Hz, 6H), 0.74 (s, JPtH ) 84 Hz, 3H).
trans(C,N)-Chloromethyl(dimethyl sulfoxide)(diisopropylamine)-
platinum(II), trans(C,N)-[PtCl(CH3)(DMSO)(Pri2NH2)] (10B). 1H
NMR: δ 3.54 (m, 2H), 3.23 (s, 3JPtH ) 39 Hz, 6H), 1.42 (d, 3JHH ) 6
P1h
T, °C
µ, cm-1
R
9.373(2)
9.576(1)
14.087(3)
70.29(1)
72.50(1)
72.21(2)
a
3
2
Rw
Hz, 6H), 1.32 (d, JHH ) 6 Hz, 6H), 0.45 (s, JPtH ) 75 Hz, 3H).
cis(C,N)-Chloromethyl(dimethyl sulfoxide)(triethylamine)plati-
num(II), cis(C,N)-[PtCl(CH3)(DMSO)(Et3N)] (11). 1H NMR: δ 3.48
3
3
3
(s, JPtH ) 28 Hz, 6H), 3.14 (q, JHH ) 7 Hz, 6H), 1.28 (t, JHH ) 7
2
2
2
a w ) [σ2(Fo ) + (0.0372P)2 + 0.45P]-1 with P ) [max(0,Fo ) +
Hz, 9H), 0.76 (s, JPtH ) 85 Hz, 3H).
2Fc2]/3.
cis(C,N)-Chloromethyl(dimethyl sulfoxide)(4-(dimethylamino)-
pyridine) platinum(II), cis(C,N)-[PtCl(CH3)(DMSO)(4-(NMe2)py)]
3
(12). 1H NMR: δ 8.18 (m, JPtH ) 41 Hz, Jav ) 7 Hz, 2H, H2), 6.47
X-ray Data Collection and Structure Refinement. A colorless
crystal was mounted on a glass fiber, and the corresponding X-ray
diffraction measurements were performed at room temperature with a
Siemens R3m/v automatic four-circle diffractometer using graphite-
monochromated Mo KR radiation. Cell parameters were obtained by
least-squares refinement of the setting angles of 25 accurately centered
reflections with 15° e 2θ e 30°. Data collection was performed up
to 2θ ) 55° by the variable-speed w-2q scan method, measuring 5928
reflections of which 4843 were unique (Rint ) 2.37%). The intensities
of three standard reflections, monitored after every 197 measurements,
showed only statistical fluctuations. The reflection intensities were
corrected for Lorentz-polarization and absorption effects.17
The structure was solved by standard Patterson methods and
subsequently completed by a combination of least-squares technique
and Fourier syntheses by using SHELXTL-PLUS.18 Subsequently the
model refinement was carried out with SHELXL-9319 by full-matrix
least-squares technique based on F2. A set of 2505 reflections was
considered and observed by the threshold Fo g 7σ(Fo), with resolution
up to 0.9 Å.
3
(m, Jav ) 7 Hz, 2H, H3), 3.49 (s, JPtH ) 25 Hz, 6H), 3.07 (s, 6H,
2
NMe2), 0.88 (s, JPtH ) 84 Hz, 3H).
cis(C,N)-Chloromethyl(dimethyl sulfoxide)(2-chloropyridine)-
platinum(II), cis(C,N)-[PtCl(CH3)(DMSO)(2-Clpy)] (13A). 1H
3
NMR: δ 8.68 (m, JPtH ) 43 Hz, 1H), 7.84 (m, 1H), 7.59 (m, 1H),
7.40 (m, 1H), 3.54 (s, 3JPtH ) 28 Hz, 3H), 3.53 (s, 3JPtH ) 29 Hz, 3H),
2
0.78 (s, JPtH ) 83 Hz, 3H).
trans(C,N)-Chloromethyl(dimethyl sulfoxide)(2-chloropyridine)
platinum(II), trans(C,N)-[PtCl(CH3)(DMSO)(2-Clpy)] (13B). 1H
3
NMR: δ 8.75 (m, JPtH ∼ 15 Hz, 1H), 7.79 (m, 1H), 7.53 (m, 1H),
7.38 (m, 1H), 3.33 (s, 3JPtH ) 34 Hz, 3H), 3.24 (s, 3JPtH ) 39 Hz, 3H),
2
0.77 (s, JPtH ) 78 Hz, 3H).
cis(C,N)-Chloromethyl(dimethyl sulfoxide)(2-phenylpyridine)-
platinum(II), cis(C,N)-[PtCl(CH3)(DMSO)(2-Phpy)] (14A). 1H NMR:
δ 8.94 (dd, Jav ) 6 Hz, 3JPtH ) 42 Hz, 1H, H6), 8.06 (m, 2H), 7.92 (m,
1H), 7.60 (m, 1H), 7.53 (m, 3H), 7.44 (m, 1H), 3.47 (s, 3JPtH ) 27 Hz,
3
2
3H), 3.23 (s, JPtH ) 27 Hz, 3H), 0.29 (s, JPtH ) 84 Hz, 3H).
trans(C,N)-Chloromethyl(dimethyl sulfoxide)(2-phenylpyridine)
platinum(II), trans(C,N)-[PtCl(CH3)(DMSO)(2-Phpy)] (14B). 1H
NMR: δ 9.01 (m, 3JPtH < 20 Hz, 1H, H6), 8.16 (m, 2H), 3.00 (s, 3JPtH
) 40 Hz, 3H), 2.19 (s, 3JPtH ) 36 Hz, 3H), 0.54 (s, 2JPtH ) 75 Hz, 3H).
cis(C,N)-Chloromethyl(dimethyl sulfoxide)(acridine)platinum(II),
cis(C,N)-[PtCl(CH3)(DMSO)(Acr)] (15A). 1H NMR: δ 9.69 (d, Jav
) 9 Hz, 2H), 9.04 (s, 1H), 8.05 (m, 4H), 7.63 (d, Jav ) 8 Hz, 2H),
The hydrogen atoms, even though most of them appeared on the
difference syntheses, were generated in calculated positions by con-
siderations based on stereochemistry with an unique fixed isotropic
thermal parameter (Uiso ) 0.080 Å2), and during the refinement they
were allowed to ride on their respective parent carbons, which type
determines the fixed length of the corresponding C-H bonds. The
structure model, with all non-hydrogen atoms anisotropic, was refined
3
2
3.68 (s, JPtH ) 27 Hz, 6H), 0.70 (s, JPtH ) 83 Hz, 3H).
2
by minimizing the function ∑w(Fo - Fc2)2 with convergence to R )
trans(C,N)-Chloromethyl(dimethyl sulfoxide)(acridine)platinum-
(II), trans(C,N)-[PtCl(CH3)(DMSO)(Acr)] (15B). 1H NMR: δ 9.94
(d, Jav ) 9 Hz, 2H), 9.01 (s, 1H), 8.08 (d, Jav ) 8 Hz, 2H), 8.01 (t, Jav
2
2
∑|Fo - Fc|/∑|Fo| ) 0.024 and R′ ) [∑w(Fo - Fc2)2/∑w(Fo )2]1/2
)
2
0.046 with the final weighting scheme w-1 ) [σ2 (Fo ) + (0.0372P)2
+ 0.45P] with P ) (max(0,Fo ) + 2Fc2)/3 and by considering an
2
3
) 9 Hz, 2H), 7.60 (d, Jav ) 8 Hz, 2H), 3.10 (s, JPtH ) 34 Hz, 6H),
extinction parameter refined to 0.0021(2).
2
1.07 (s, JPtH ) 72 Hz, 3H).
The last difference map showed some significant electron density
residuals (maximum ) 1.25 e Å-3) at about 1 Å from the platinum
and tin atoms. Neutral-atom scattering factors and anomalous disper-
sion corrections, automatically used by the program, come from ref
20.
Data reduction and drawings were performed with the Siemens
SHELXTL-PLUS package, while the final geometrical calculations were
carried out with the PARST program21 on a DEC MicroVax/3400
computer.
Instrumentation. The NMR spectra were recorded on Bruker ARX
300, AMX 400, and WH 400 NMR spectrometers. The 1H magnetiza-
tion transfer measurements were performed on a Bruker ARX-300 NMR
spectrometer. The probe tuning was optimized before beginning the
measurements. The 180° pulse was determined by nulling the signal.
The T1 values were estimated from 5T1-π-t-π/2 measurements. The
magnetization transfer measurements were performed using the pulse
sequence 5T1-π(selective)-t-π/2(general), with t values of 0.0001,
0.001, 0.002, 0.004, 0.008, 0.016, 0.032, 0.064, 0.100, 0.200, 0.500,
1.000, 2.000, and 10.000 s. A Gaussian shaped pulse (256 points, 47
Table 1 reports the details of the crystallographic measurements.
Results are given in Table 2.
1
dB, 20 ms) was used for the selective H π-pulse.
The 195Pt magnetization transfer measurements were performed on
a Bruker ARX-300 NMR spectrometer operating at 64.2 MHz, and
referenced to ¥ 21.4, with high frequency taken as being positive. The
probe tuning was optimized before beginning the measurements. The
180° pulse was determined by nulling the signal. The T1 values were
estimated from 5T1-π-t-π/2 measurements. The magnetization
transfer measurements were performed using the pulse sequence 5T1-
π(selective)-t-π/2(general) pulse sequence, with t values of 0.000003,
0.001, 0.002, 0.004, 0.008, 0.016, 0.032, 0.064, 0.100, 0.200, and 1.0
s. A Gaussian shaped pulse (256 points, 29 dB, 1 ms) was used for
the selective 195Pt π-pulse.
Results and Discussion
The synthesis of the complex trans-[PtCl(CH3)(DMSO)2] was
reported by Eaborn et al.9 by reacting cis-[PtCl2(DMSO)2] with
a 2-fold quantity of tetramethyltin as methylating agent. The
reaction is conducted in dimethyl sulfoxide as solvent at 80 °C
for an average time of 24 h, and the yields (ranging from 20 to
(17) Kopfmann, G.; Huber, R. Acta Crystallogr., Sect. B: Struct. Crys-
tallogr. Cryst. Chem. 1968, 24, 348.
(18) SHELXTL-PLUS, Version 4.2; Siemens Analytical X-ray Instruments
Inc.: Madison, WI, 1991.
(19) Sheldrick, G. M. SHELXL-93, Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1994.
(20) International Tables for X-ray Crystallography; Wilson, A. J. C., Ed.;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; Vol.
C.
Variable temperature measurements were obtained by using a Bruker
standard accessory. The temperature within the probe was checked
by the methanol or ethylene glycol method.16
(16) Van Geet, A. L. Anal. Chem. 1968, 40, 2227. Van Geet, A. L. Anal.
Chem. 1970, 42, 679.
(21) Nardelli, M. Comput. Chem. 1983, 7, 95 (version locally modified).

7694 Inorganic Chemistry, Vol. 35, No. 26, 1996
Romeo et al.
Table 2. Selected Bond Distances (Å), Bond Angles (deg) and
Torsion Angles (deg)
Bond Distances
Pt-C(1)
2.049(7)
2.261(2)
1.470(5)
1.774(8)
1.776(8)
2.047(5)
2.102(5)
2.890(3)
3.295(1)
2.094(8)
2.521(2)
3.442(2)
Pt-Cl(1)
2.416(2)
2.257(2)
1.767(7)
1.473(5)
1.787(8)
2.088(8)
2.104(8)
3.293(3)
2.029(5)
2.096(7)
2.736(2)
Pt-S(1)
Pt-S(2)
S(1)-O(1)
S(1)-C(3)
S(2)-C(4)
Sn(1)-O(3)
Sn(1)-O(3)′
Sn(1)-Cl(2)
Sn(1)‚‚‚Sn(1)′
Sn(2)-C(7)
Sn(2)-Cl(3)
Sn(2)...Cl(1)
S(1)-C(2)
S(2)-O(2)
S(2)-C(5)
Sn(1)-C(8)
Sn(1)-C(9)
Sn(1)...Cl(3)′
Sn(2)-O(3)
Sn(2)-C(6)
Sn(2)-Cl(2)
Figure 1. ORTEP drawing of the 2:1 aggregate between trans-[PtCl-
(CH3)(DMSO)2] and [Cl(CH3)2SnOSn(CH3)2Cl]2, showing the labeling
of the non-H atoms. Thermal ellipsoids are drawn at the 40% probability
level.
Angles
C(1)-Pt-S(2)
89.7(2)
C(1)-Pt-S(1)
89.6(2)
178.2(3)
90.76(6)
107.9(3)
101.5(4)
107.4(3)
107.4(4)
102.3(5)
109.8(3)
111.2(3)
135.1(4)
74.5(2)
geometry is close to the mirror symmetry with the sulfoxide
O(1) and O(2) atoms almost lying on the coordination mean
plane. As can be seen from the O(1)-S(1)-Pt-C(1) and
O(2)-S(2)-Pt-C(1) torsion angles, 3.0(4) and 2.9(4)°, respec-
tively, both the oxygen atoms are oriented toward the methyl
group C(1)H3. Such an orientation avoids the hindering effects
of the DMSO methyl groups on C(1)H3 and, at the same time,
favors short (O(1)‚‚‚C(1) ) 3.09(1) Å and O(2)‚‚‚C(1) ) 3.07-
(1) Å) interactions. Both DMSO ligands are coordinated
through the S atom to the metal center, as expected.
S(2)-Pt-S(1)
176.80(7) C(1)-Pt-Cl(1)
90.04(7) S(1)-Pt-Cl(1)
124.41(7) O(1)-S(1)-C(2)
S(2)-Pt-Cl(1)
Pt-Cl(1)-Sn(2)
O(1)-S(1)-C(3)
O(1)-S(1)-Pt
108.1(4)
120.2(2)
110.0(3)
107.8(4)
119.4(2)
108.8(3)
110.0(3)
102.6(3)
106.5(3)
147.8(3)
93.7(3)
C(2)-S(1)-C(3)
C(2)-S(1)-Pt
O(2)-S(2)-C(4)
C(4)-S(2)-C(5)
C(4)-S(2)-Pt
C(3)-S(1)-Pt
O(2)-S(2)-C(5)
O(2)-S(2)-Pt
C(5)-S(2)-Pt
O(3)-Sn(1)-C(8)
C(8)-Sn(1)-C(9)
O(3)-Sn(1)-Cl(2)
O(3)-Sn(2)-C(6)
O(3)-Sn(2)-Cl(3)
C(6)-Sn(2)-Cl(3)
C(7)-Sn(2)-Cl(2)
O(3)-Sn(1)-C(9)
O(3)′-Sn(1)-C(9)
O(3)-Sn(2)-C(7)
C(7)-Sn(2)-C(6)
C(7)-Sn(2)-Cl(3)
O(3)-Sn(2)-Cl(2)
C(6)-Sn(2)-Cl(2)
Cl(1)...Sn(2)-C(7)
Cl(1)...Sn(2)-O(3)
Cl(1)...Sn(2)-Cl(2)
104.1(3)
86.5(2)
97.7(2)
The Pt-S(1) and Pt-S(2) bond distances, 2.261(2) and 2.257-
(2) Å, respectively (mean 2.259(2) Å), are shorter than the
corresponding mean value 2.292(3) Å reported for the complex
trans-dichlorobis(di-n-propyl sulfoxide)platinum(II)23 that is the
unique example of a trans-bis(sulfoxide)platinum(II) compound
reported so far. Since in both complexes relevant steric
repulsions of the sulfoxide groups are not seen with the other
two adjacent ligands, this difference in the trans Pt-S distances
seems to be due entirely to the different electron-donor ability
of the alkyl substituents on the sulfur atom. Unfortunately, the
lack of other structural data does not allow one to ascertain
whether this trend is confirmed and to search for a correlation
between the electron-donating characteristics of the substituents
and the ground-state trans influence of various sulfoxides.
A number of investigations on the trans influence of
sulfoxides did not show significant lengthening of the trans Pt-
Cl bonds, which varied in the limits of the statistical signifi-
cance.4 Further investigations24 suggested that in [PtCl3L]-
complexes the Pt-Cl bond trans to L becomes weaker in the
order PEt3 > DMSO >ethylene > amines, Cl-. However, when
a statistically more consistent set of data is considered,25 it is
confirmed that the trans influence of DMSO relative to chloride
is very weak (the mean Pt-Cl bond length increases from 2.299-
(2) Å, when trans to Cl, O, or N ligands, to 2.312(1) Å, when
trans to S). It is interesting therefore to look at the trans
influence relative to the Pt-DMSO bond. Inspection of the
Pt-S bond distances of almost 50 compounds25 having only
one S bonded sulfoxide per metal atom gives an average of
2.207(3) Å, spanning in a rather wide range (from 2.168(2) to
2.257(8) Å). The Pt-S distances observed for the two trans
sulfur bonded DMSO groups (2.261-2.257 Å) are considerably
longer than those observed for Pt-DMSO distances trans to
oxygen-bonded DMSO in the tetrakis(dimethyl sulfoxide)-
platinum(II) cation (2.205-2.208 Å)26 and still longer than those
trans to chloride (2.185-2.233 Å) and trans to nitrogen (2.209-
2.224 Å) . Only the Pt-S distances trans to a strong σ-donor
78.4(2)
88.4(2)
77.0(3)
176.3(2)
88.4(3)
Cl(3)-Sn(2)-Cl(2) 164.70(8)
Cl(1)...Sn(2)-C(6)
72.2(2)
94.23(8)
80.56(6)
Cl(1)...Sn(2)-Cl(3)
101.00(7) Sn(2)-Cl(2)-Sn(1)
Sn(2)-O(3)-Sn(1) 126.5(3)
Sn(1)-O(3)-Sn(1)′ 105.2(2)
Sn(2)-O(3)-Sn(1)′ 128.3(3)
Torsion Angles
74(1) Cl(1)-Pt-S(2)-O(2) 178.8(3)
S(1)-Pt-S(2)-O(2)
S(1)-Pt-S(2)-C(4) -161(1)
45%) depend on both the time and the control of the temper-
ature. The original assignment9 of the trans geometry was based
on the presence of a single band for the νPtCl stretching frequency
in the IR spectrum (275 cm-1) and of a simple pattern for the
1
coordinated dimethyl sulfoxide in the H NMR spectrum.
Crystal Structure. Several attempts at growing crystals of
pure samples of complex 1 from different solvents, were
unsuccessful. Crystals suitable for X-ray analysis were obtained
on cooling a solution of the crude reaction product in dichlo-
romethane.
The solid state analysis reveals that the platinum(II) complex
1 cocrystallizes with the polynuclear tin(IV) compound bis(µ-
3-oxo)bis(µ-chloro)-bis(µ-dimethyltin(IV))bis(chlorodimethyltin-
(IV)) [Cl(CH3)2SnOSn(CH3)2Cl]2. The crystal structure of the
title compound is constituted by two platinum complexes that
are interacting with a central distannoxane moiety through a
Pt-Cl-Sn interaction (Figure 1). While the molecular structure
of trans-[PdCl2(DMSO)2] has been known for many years,22
this determination is, to the best of our knowledge, the first
study on the crystal structure of a trans-(dimethyl sulfoxide)-
platinum(II) compound. The platinum atom displays, at first
glance, a square-planar coordination. The weighted least-
squares plane through the Pt and the four atoms of the
coordination sphere indicates that this portion of the molecule
slightly deviates from planarity toward a tetrahedral arrangement
of the metal (deviations (Å): Pt, 0.0060(5); C(1), 0.072(1); S(1),
-0.052(2); S(2), -0.058(2); Cl(1), 0.003(2)). The Pt complex
(23) Melanson, R.; Rochon, F. D. Acta Crystallogr., Sect. C: Struct.
Crystallogr. Cryst. Chem. 1988, 44, 1893.
(24) Sotman, S. S.; Fundamenskii, V. S.; Kukushkin, V. Yu.; Pankova, E.
Yu. Zh. Obshch. Khim. 1988, 58, 2297.
(22) Bennett, M. J.; Cotton, F. A.; Weaver, D. L.; Williams, R. J.; Watson,
(25) Caligaris, M.; Carugo, O. Coord. Chem. ReV. 1996, 153, 1-23.
(26) Elding, L. I.; Oskarsson, A. Inorg. Chim. Acta 1987, 130, 209.
W. H. Acta Crystallogr. 1967, 23, 788.

trans-[PtCl(CH3)(DMSO)2]
Inorganic Chemistry, Vol. 35, No. 26, 1996 7695
Pt-C(phenyl) bond are considerably longer (2.315-2.324 Å).27
Thus, a trans influence order for platinum of O < N = Cl < S
< C can be derived, if cis effects and packing forces are
considered of minor importance as compared to the trans
influence.
The Pt-C(1) bond (2.049(7) Å) is comparable with the
corresponding distance (2.056(5) Å) found in the cation [Pt-
(CH3)(1,10-phenanthroline)(DMSO)]+ 28 where a pyridine ni-
trogen is in the trans position with respect to the methyl group,
while it is somewhat shorter than the distances usually reported
in other trans-chloromethylplatinum complexes.29 The C(1)-
Pt-S(1) and C(1)-Pt-S(2) bond angles, like other bond angles
at the metal center, are nearly the ideal values denoting the
absence of steric strains in the Pt fragment. The tetrahedral-
distorted arrangement and the geometric features of the sulfurs
(mean values: S-O ) 1.471(5) Å and S-C ) 1.776(8) Å)
agree with the values reported for other Pt-DMSO complexes.25
The Pt-Cl bond length (2.416(2) Å) is significantly longer than
the distances usually reported, because of both the strong trans
influence of the opposite methyl group and the interaction with
one tin atom of the distannoxane system (Cl(1)-Sn(2) ) 3.442-
(2) Å). This interaction and the ensuing presence of the
stannoxane seem to play a crucial role in the formation and in
the stabilization of the crystal lattice.
A molecular structure of the distannoxane fragment has been
already reported in the literature.30 It reflects the well-known
property of the association of organotin units by oxygen bridges
and consists of [ClMe2SnOSnMe2Cl]2 dimeric units with
crystallographic inversion point at the center. The central part
of the unit consists of a four-membered Sn(1)O(3)Sn(1′)O(3′)
ring. On this plane the other two exocyclic tins Sn(2) and Sn-
(2′) are aligned. All tin atoms display a distorted arrangement
between the octahedral and trigonal-bipyramidal limiting ge-
ometries. The presence of a square-planar platinum(II) moiety
in the lattice does not seem to produce significant effect on
bond distances and bond angles of the distannoxane fragment
(the highest angle difference regards C(6)-Sn(2)-C(7): 147.8-
(3)° Vs 140.6(9)°, respectively).
Figure 2. (a) 300.13 MHz 1H NMR spectrum of [PtCl(CH3)(DMSO)2]
in CDCl3 at 273 K. (b-e) Difference spectra between spectrum a and
spectra recorded with 195Pt decoupling (b) at δ 645, (c) at δ 629, (d) at
δ 422, and (e) at δ 151.
The molecular packing (Figure SI 1, Supporting Information))
is mainly determined by van der Waals interactions and by weak
intermolecular hydrogen bonds.
1
NMR Measurements. The H NMR spectrum of [PtCl-
(CH3)(DMSO)2] in CDCl3 at 273 K is shown in Figure 2a. The
spectrum showed signals due to DMSO at δ 3.49 (3JPtH ) 36
Hz), 3.42 (3JPtH ) ) 24 Hz), 3.34 (3JPtH ) 36 Hz), 3.32 (3JPtH
) 36 Hz), 3.21 (3JPtH ) 8 Hz), and 2.58, and Pt-Me signals at
δ 1.17, (2JPtH ) 73 Hz), 0.98 (2JPtH ) 80 Hz), and 0.93 (2JPtH
) 86 Hz). The 195Pt NMR spectrum of the same solution
showed signals at δ 645, 629, 422, and 151, see Figure 3. The
13C NMR spectrum is closely similar to the proton spectrum.
In fact it exhibits different series of slightly broad signals: (i)
a singlet at δ -1.8 (1JPtC ) 660 Hz) for a methyl group and a
singlet with satellite peaks at δ 44.4 (2JPtC ) 59 Hz) consistent
with a S bonded dimethyl sulfoxide; (ii) a singlet at δ 0.5 (no
coupling constant was detected even at low temperature) and
two different singlets at δ 46.4 (2JPtC ) 70 Hz) and 44.1 (2JPtC
) 19 Hz) for two different S bonded dimethyl sulfoxides; (iii)
only a minor species is detected at δ 45.9 (no coupling constants
were observable); (iv) a singlet at δ 40.9 due to free dimethyl
sulfoxide.
Figure 3. 64.2 MHz 195Pt NMR spectrum of [PtCl(CH3)(DMSO)2] in
CDCl3 at 296 K.
(27) Bardi, R.; Del Pra, A.; Piazzesi, A. M.; Trozzi, M. Cryst. Struct.
Commun. 1981, 10, 301.
(28) Bruno, G.; Nicolo`, F.; Scopelliti, R.; Arena, G. Acta Crystallogr., Sect.
C: Struct. Crystallogr. Cryst. Chem. 1996, C52, 827.
(29) (a) Goel, A. B.; Goel, S.; van Derveer, D. Polyhedron 1984, 3, 373.
(b) Bardi, R.; Piazzesi, A. M. Inorg. Chim. Acta 1981, 17, 249.
(30) Harrison, P. H.; Begley, M. J.; Molloy, K. C. J. Organomet. Chem.
1980, 186, 213, and references cited therein.
The 195Pt NMR signals were tied to the 1H NMR signals by
selective 195Pt decoupling (see Figure 2), and the results are
summarized in Table 3. Clearly there are four species present.
The major species has been unambiguously identified. The
X-ray structure clearly demonstrates that trans-[PtCl(CH3)-
(DMSO-S)2] is present in the crystal. When some of these

7696 Inorganic Chemistry, Vol. 35, No. 26, 1996
Romeo et al.
Table 3. 1H and 195Pt NMR Data for the Four Species Present in a Solution of [PtCl(CH3)(DMSO)2] in CDCl3 at 273 K
δ (DMSO), ppm
(3JPtH, Hz)
δ (Pt-CH3), ppm
(2JPtH, Hz)
compound
δ (195Pt),a ppm
trans-[PtClMe(DMSO)2]
cis-[PtClMe(DMSO)2]
cis-[PtClMe(DMSO)(OH2)]
trans-[PtClMe(DMSO)(OH2)]
3.42 (24)
3.49 (36); 3.21 (8)
3.34 (36)
0.98 (80)
1.17 (73)
0.98 (87)
0.93 (83)
151
422
629
645
3.32 (36)
a The corresponding shifts relative to [PtCl6]2- are, in parentheses, δ 151 (-4352), 422 (-4082), 629 (-3876), and 645 (-3860).
crystals are dissolved in CD2Cl2/CDCl3 at 190 K, only one
species is detected in the 1H NMR spectrum at low temperature
at δ 3.42 (3JPtH ) 24 Hz) and 0.98 (2JPtH ) 80 Hz). On warming
1
to room temperature, the other three species appear in the H
NMR spectrum. Decoupling the 195Pt at δ 151 removes 195Pt
coupling from these signals (see Figure 2e, where the effect of
195Pt decoupling is shown as a difference spectrum).
Magnetization transfer measurements were performed on
trans- and cis-[PtCl(CH3)(DMSO)2] in CDCl3 at 298 K, using
When the 195Pt NMR signal at δ 422 is decoupled, coupling
1H NMR spectroscopy. The signal at δ 2.58 due to free DMSO
was inverted and the transfer to the sites at δ 3.42 and 3.21
monitored. No transfer to the DMSO signal at δ 3.49 was
detected, showing that the DMSO trans to chloride in cis-[PtCl-
(CH3)(DMSO)2] does not exchange at a significant rate. The
signals at δ 3.32 and 3.34 were too weak to observe if transfer
occurred and partially obscured at 298 K by the broadened
signals due to the major cis- and trans-[PtCl(CH3)(DMSO)2]
isomers. No direct exchange was detected between cis- and
trans-[PtCl(CH3)(DMSO)2]. The results of the analysis are
shown in Scheme 1.
1
is removed from the DMSO H NMR signals at δ 3.49 and
3.21, and the methyl signal at δ 1.17 (see Figure 2d). Both of
these DMSO signals show substantial 3JPtH coupling constants,
showing that they are both S bonded. Therefore, this species
is cis-[PtCl(CH3)(DMSO-S)2]. The trans-influence of methyl
and chloride permits the assignment of the DMSO signals.31
3
The DMSO signal at δ 3.49, JPtH ) 36 Hz, must arise from
3
DMSO trans to chloride, and that at δ 3.21, JPtH ) 8 Hz, is
due to DMSO trans to methyl.
There are a number of possibilities for the remaining two
minor species. Each one has only one type of DMSO bonded
to the platinum, and the 3JPtH coupling constants show that the
DMSO ligands are S bonded. The two possible dimers [Pt2-
(CH3)2(DMSO-S)2(µ-X)2] (X ) Cl, OH) can be rejected as the
1H and 13C NMR spectra of the compounds would show [A3X]2
(for the Me-Pt) and [A6X]2 (for the DMSO) signals due to the
1
Scheme 1. Results of the H Magnetization Transfer
Measurements on [PtCl(CH3)(DMSO)2] at 298 K (Rates
(s-1) for Exchange of DMSO)
[
195Pt2(CH3)2(DMSO-S)2(µ-X)2] isotopomer, and no such signals
were detected.32 The most reasonable interpretation is that the
two compounds are isomers of [PtCl(CH3)(OH2)(DMSO)].33
Addition of DMSO to the solution leads to the disappearance
of the signals of the aqua species. This hypothesis is further
supported by the observation that the 195Pt NMR spectrum of a
sample of complex in D2O exhibits a completely reversed pattern
for the intensities of the peaks; see Figure SI 2 (Supporting
Information). The signals have moved to low frequency,
presumably as a result of a solvent shift. The major signals
are at δ 611 and 602 and are probably the two isomers of [PtCl-
(CH3)(OH2)(DMSO)] observed in CDCl3. The signal at δ 112
is probably due to trans-[PtCl(CH3)(DMSO)2]. New unassigned
signals are observed at δ 824 and 540. Easy hydrolysis of the
dialkyl [Pt(CH3)2(DMSO)2] complex has already been re-
ported.35
The most interesting feature that emerges from the rate data
in Scheme 1 is the great dependence of the lability of the various
S-bonded DMSO upon the nature of the trans group. The
sequence is as follows: CH3 > DMSO . Cl. The somewhat
high trans labilizing effect of a molecule of DMSO toward
another trans DMSO is not unexpected, in view of the known
experimental difficulty in synthesizing bis(dimethyl sulfoxide)
complexes of trans geometry.
Magnetization transfer measurements were performed on
[PtCl(CH3)(DMSO)2] in CDCl3 at 298 K, using 195Pt NMR
spectroscopy. The aim was to check for the involvement of
the minor aqua-species in the exchange. The signals at δ 151,
422, and 629 were selectively inverted in three separate
magnetization transfer experiments. The three sets of data were
combined and were analyzed using the previously published
program.36 As the exchange is fast compared with T1 of the
195Pt, the relaxation is averaged over the sites. However, the
195Pt T1 values were determined at 273 K, and the ratio of the
values was imposed on the fitting program. The derived rate
constants were found to be insensitive to the relative values
chosen for the T1 (195Pt). No significant rate of exchange was
detected between the sites at δ 151 and 422. The results are
summarized in Scheme 2.
There are three isomers possible, A-C. Isomer C can be
eliminated as 3JPtH for the DMSO protons is comparable to that
found in both cis- and trans-[PtCl(CH3)(DMSO)2] for the
DMSO trans to Cl or DMSO. In cis-[PtCl(CH3)(DMSO)2], the
large trans-influence of the methyl group on the trans DMSO
3
causes the JPtH coupling constant to be 8 Hz.
(31) Pregosin, P. S. Annu. Rep. NMR Spectrosc. 1986, 17, 285.
(32) J(195Pt195Pt) is expected to be larger than 100 Hz; see: (a) Boag, N.
M.; Browning, J.; Crocker, C.; Goggin, P. L.; Goodfellow, R. J.;
Murray, M.; Spencer, J. L. J. Chem. Res., Synop. 1978, 228. (b) Kiffen,
A. A.; Masters, C.; Visser, J. P. J. Chem. Soc., Dalton Trans. 1975,
1311. (c) Huis, R.; Masters, C. J. Chem. Soc., Dalton Trans. 1976,
1796.
(33) Although the solvents for the synthesis were dried, the NMR solvents
were not, and the 1H NMR spectrum has a signal attributable to water
at δ ) 1.60.
(34) The corresponding shifts relative to [PtCl6]2- are δ 824 (-3682), 611
(-3894), 602 (-3903), 540 (3964), and 112 (-4391).
(35) Minniti, D.; Parisi, M. F. Inorg. Chim. Acta 1991, 188, 127.
(36) Grassi, M.; Mann, B. E.; Pickup, B. T.; Spencer, C. M. J. Magn. Reson.
1986, 69, 92

trans-[PtCl(CH3)(DMSO)2]
Inorganic Chemistry, Vol. 35, No. 26, 1996 7697
1
Table 4. Selected H NMR Data for Platinum(II) Complexes of the Type [Pt(Me)Cl(DMSO)(am)] in Chloroform-da
δ(Pt-CH3), ppm
(2JPtH, Hz)
δ(Me2SO), ppm
(3JPtH, Hz)
δ(aromatics),b ppm
(3JPtH, Hz)
complex
am
others
2 (cis-C,N)
3 (cis-C,N)
4 (cis-C,N)
5 (trans-C,N)
6 (trans-C,N)
PrnNH2
py
2-Mepy
2,6-Me2py
2-Mequin
0.79 (83)
0.90 (83)
0.74 (84)
0.71 (75)
0.88 (76)
3.41 (26)
3.52 (26)
3.51 (27)
3.24 (37)
3.16 (35)
3.22 (35)
3.60 (26)
3.56 (26)
2.90 (31)
3.41 (27)
3.26 (39)
3.41 (26)
3.23 (39)
3.48 (28)
3.49 (25)
3.54 (28)
3.53 (29)
3.33 (34)
3.24 (39)
3.47 (27)
3.23 (27)
3.00 (40)
2.19 (36)
3.68 (27)
3.10 (34)
3.49 (58)c (NH2)
8.73 (42)
8.64 (42)
3.00 (8.7)d (Me)
3.08 (7.3)d (Me)
3.30 (6.7)d (Me)
7 (cis-C,N)
5-AQ-N1
0.79 (84)
9.02 (46)
4.35 (NH2)
8 (trans-C,N)
9A (cis-C,N)
9B (trans-C,N)
10A (cis-C,N)
10B (trans-C,N)
11 (cis-C,N)
AO
1.13 (76)
0.80 (83)
0.47 (74)
0.74 (84)
0.45 (75)
0.76 (85)
0.88 (84)
0.78 (83)
3.23 (NMe2)
ButNH2
ButNH2
Pri2NH
Pri2NH
Et3N
3.59 (60)c (NH2)
12 (cis-C,N)
13A (cis-C,N)
4-(NMe2)py
2-Clpy
8.18 (41)
8.68 (43)
3.07 (NMe2)
13B (trans-C,N)
14A (cis-C,N)
2-Clpy
2-Phpy
2-Phpy
0.77 (78)
0.29 (84)
0.54 (75)
8.75 (∼15)
8.94 (42)
14B (trans-C,N)
9.01 (<20)
15A cis-C,N)
15B (trans-C,N)
Acr
Acr
0.70 (83)
1.07 (72)
c
2
d 4
195
a Chemical shifts are reported in parts per million units downfield from Me4Si. b H6 on the pyridine ring.
J
.
J
195
1
1
.
Pt H
Pt H
Scheme 2. Results of the 195Pt Magnetization Transfer
Measurements on [PtCl(CH3)(DMSO)2] at 298 K (rates
in s-1)
Scheme 3. Alternative Exchange Mechanism Compatible
with 195Pt Magnetization Transfer Measurements on
[PtCl(CH3)(DMSO)2] at 298 K (rates in s-1)
The kinetic data in Schemes 1 and 2 permit the assignment
of the compounds with 195Pt chemical shifts at δ 645 and 629.
The 1H NMR magnetization transfer data shows that the DMSO
significance of the result is not the absolute rate constants but
that DMSO exchange and isomerization of [PtCl(CH3)(DMSO)2]
is strongly catalyzed by adventitious water in the solvent. The
absolute rates will depend on the quantity of water present.
Reactivity toward Nitrogen Ligands. The addition of the
equimolar amount of a nitrogen ligand am to a dichloromethane
or chloroform solution of complex 1 led to the rapid substitution
of one sulfoxide ligand yielding the species [PtCl(CH3)(DMSO)-
(am)] containing four different groups coordinated to the
platinum(II) center. This neutral reaction product is the only
species obtained, even in the presence of a large excess of added
ligand. Depending on the electronic and steric properties of
the ligand, different patterns of behavior can be recognized: (i)
fast build-up of a stable isomer; (ii) fast formation of an isomer
that interconverts very slowly; (iii) the formation of an equi-
librium mixture containing both isomers and the starting
material. Some of these complexes (2-8) have been isolated
as solids and fully characterized by elemental analyses and 1H
NMR spectroscopy. All of the other compounds (9-15) were
prepared directly in situ and characterized by 1H NMR
spectroscopy. Table 4 reports the most relevant NMR data.
Again, three different isomers are possible, and for the sake of
comparison we refer to the same geometrical arrangement used
for the aqua species (A-C, see structure diagram). Isomer C
trans to methyl in cis-[PtCl(CH3)(DMSO)2] is lost at 16 s-1
,
while the 195Pt NMR data shows that cis-[PtCl(CH3)(DMSO)2]
is converted to the compound with δ(195Pt) 629 at 15 s-1. It is
therefore probable that this compound is B. This leaves the
compound with δ(195Pt) of 645 to be A. The rate of exchange
between trans-[PtCl(CH3)(DMSO)2] and A and B of (1.3 + 1.2)
s-1 is close to double that of the rate of DMSO leaving trans-
[PtCl(CH3)(DMSO)2]. This arises as either DMSO can leave
trans-[PtCl(CH3)(DMSO)2] and convert it to A or B, but only
one DMSO exchanges with free DMSO.
The magnetization transfer data are not very sensitive to the
presence of exchange between trans-[PtCl(CH3)(DMSO)2] and
B and between cis-[PtCl(CH3)(DMSO)2] and A. The data can
also be fitted with the rates in Scheme 3 with only a small
increase in the error between the experimental and calculated
data. Attempts to fit the data with A and B reversed gave a far
worse fit.
A comparison of Schemes 2 and 3 shows that the calculated
rates are sensitive to the exchange mechanisms assumed in the
analysis and should not be taken as being accurate. The problem
arises as a result of the rapid exchange between A and B. The

7698 Inorganic Chemistry, Vol. 35, No. 26, 1996
Romeo et al.
3
can be ruled out as the JPtH coupling constants for the
process which takes place with complete retention of the
configuration. We have no detailed kinetic data for the
isomerization of these organoamine compounds, except the
observation through the NMR spectra that, as time goes on,
the trans(C,N) configuration tends to convert slowly to the
cis(C,N) analogue. Considering the complexity of the starting
system, made up by cis and trans sulfoxide and aqua complexes
in mutual fast exchange, it is difficult to recognize which of
the four is the most reactive species. However, the kinetic data
from Schemes 1-3 suggest that the lability of the sulfoxide
trans to the methyl group in the compound cis-[PtCl(CH3)-
(DMSO)2] is very high and would lead to the fast formation of
the trans(C,N) isomer in the reaction with a nitrogen ligand.
This kinetically favored product isomerizes in a subsequent step
to the more stable cis(C,N) compound. The isomerization
process could be catalyzed by DMSO or water, and its rate is
essentially related to the steric properties of the entering nitrogen
ligand.
coordinated dimethyl sulfoxide are in the range 25-40 Hz,
which is well above the usual values observed for a DMSO
ligand trans to a methyl group. The assignment to the A isomer
(amine cis to the methyl group, cis(C,N)) or to the B isomer
(amine trans to the methyl group, trans(C,N)) can be made, in
the case of pyridine or substituted pyridines, on the basis of
3
the magnitude of the values observed for the JPtH coupling
constants on the H6 hydrogen of the aromatic ring. This
criterion has been applied recently to the complex [Pt(CH3)-
(phen)(DMSO)]+ (phen ) 1,10-phenanthroline) to distinguish
the H2 proton (trans to the methyl group, 3JPtH ) 16.5 Hz) from
the H9 proton (trans to DMSO) which shows satellite peaks
due to 195Pt coupling at a much higher frequency (3JPtH ) 44
Hz).37 For example, in the case of the ligand 2-Clpy, the isomer
B (trans(C,N)) can be recognized from the H6 peak at δ 8.75
3
with a JPtH coupling constant of about 15 Hz. A further
distinction between isomers A and B can be made on the basis
of the values of the coupling constants of the coordinated
dimethyl sulfoxide, whether in trans position to an amine
(cis(C,N)) or to a chloride (trans(C,N)). These 3JPtH values for
the A isomers (cis(C,N)) are all characterized by values ranging
from 25 to 29 Hz. In this latter configuration, the bond axis
CH3-Pt-Cl of the starting trans-[PtCl(CH3)(DMSO)2] complex
is maintained and therefore the 2JPtH coupling constants for the
methyl groups, all in the range 83-85 Hz, give a further
indication of the geometry of the compounds.
The 1H NMR spectra of the complexes containing the ligands
2-Clpy, 2-Phpy, 2-Mequin, and 5-AQ-N1 exhibit a double peak
for the coordinated DMSO. These findings suggest that, as
expected, the torsion angle between the coordination plane and
the plane of the ligand must be significantly high (the values
of torsion angles for platinum-pyridine complexes are all within
the range 45-60°)38 and that the rotation of the ligand around
the Pt-N bond is slow in the NMR time scale. Under these
circumstances the two methyl groups become diastereotopic and
give two distinct resonances.
In the case of the most sterically hindered ligands, such as
2-Mequin, AO, 2,6-Me2py, and Acr, the B isomer is the only
detectable species in solution. The presence of a methyl group
and/or of a condensed aromatic ring in both of the ortho
positions with respect to the donor nitrogen atom seems to be
a prerequisite for the isolation of complexes in a trans(C,N)
configuration. With less sterically demanding ligands such as
2-Clpy an equilibrium mixture containing unreacted complex
1 and both of the two isomers of [PtCl(CH3)(DMSO)(am)] is
obtained, even in the presence of a slight excess of the ligand.
With less bulky ligands, such as pyridine, the only product
obtained in solution soon after mixing the reagents is the stable
cis(C,N) complex. Thus, the configuration of the reaction
product between complex 1 and aliphatic or heterocyclic
nitrogen bases depends strongly upon the steric requirements
of the entering ligand. A similar pattern of behavior has already
been observed by several groups for the reaction of cis-[PtCl2-
(DMSO)2] with nitrogen-donor ligands.39 A kinetic study of
these reactions by Annibale et al.40 has revealed that the
conversion to the most stable isomer is a multistep displacement
Conclusions
The molecular structure of the title compound has shown that
the trans-influence of a sulfur bonded DMSO, taking as index
the Pt-S lengthening of another trans bonded DMSO, is
significantly higher than that of chloride or of ligands with
oxygen or nitrogen donor ligands but still less than that of a σ
Pt-C bond. This order of ground state destabilization is
reflected in the lability of the trans dimethyl sulfoxide, as shown
by magnetization transfer experiments. The facile removal of
the molecule of dimethyl sulfoxide trans to a methyl group or
to another DMSO from the coordination sphere of the metal
leads to the formation of aqua-species that were found to be
key intermediates in the trans to cis conversion of 1. The
mechanism of isomerization of square-planar platinum(II)
complexes has received extensive investigation and usually
occurs through associative catalytic or dissociative pathways.41
The discovery of a water-catalyzed pathway for [PtCl(CH3)-
(DMSO)2] introduces a new possibility and calls for a careful
analysis of the role of water in ligand exchange and isomer-
ization processes involving square-planar complexes.
The complex trans-[PtCl(CH3)(DMSO)2] offers a convenient
key for accessing a series of new organometallic species of the
type [PtCl(CH3)(DMSO)(am)] containing four different groups.
The relative stability of the two obtained isomers depends mainly
on the steric requirements imposed by the entering ligand.
Again, the role of the water and/or of the leaving sulfoxide in
catalyzing the isomerization process is of central interest in the
understanding of the reactivity of such organometallic com-
plexes, and it is currently under investigation.
Acknowledgment. We are grateful to the MURST and the
CNR for funding this work.
Supporting Information Available: Figures SI 1 and SI 2 showing
the unit cell of the 2:1 aggregate and the 195Pt spectrum of compound
1 in D2O, respectively, text detailing complete crystallographic work,
and tables giving structure determination parameters, bond distances,
bond angles, anisotropic thermal parameters, and hydrogen atom
coordinates (11 pages). Ordering information is given on any current
masthead page.
IC960428S
(37) Romeo, R.; Arena, G.; Monsu` Scolaro, L.; Plutino, M. R. Inorg. Chim.
Acta 1995, 240, 81.
(38) Romeo, R. Arena, G.; Monsu` Scolaro, L.; Plutino, M. R.; Bruno, G.;
Nicolo`, F. Inorg. Chem. 1994, 33, 4029, and references cited therein.
(39) (a) Kong, P. C.; Iyamuremye, D.; Rochon, F. D. Can. J. Chem. 1976,
54, 3224. (b) Reily, M. D.; Wilkowsky, K.; Shinozuka, K.; Marzilli,
L. G. Inorg. Chem. 1985, 24, 27. (c) Marzilli, L. G.; Hayden, Y.;
Reily, M. D. Inorg. Chem. 1986, 25, 974.
(40) Annibale, G.; Bonivento, M.; Cattalini, L.; Tobe, M. L. J. Chem. Soc.,
Dalton Trans. 1992, 3433.
(41) See for example: (a) Anderson, G. K.; Cross, R. J. Chem. Soc. ReV.
1980, 9, 185. (b) Wilkins, R. G. Kinetics and Mechanism of Reactions
of Transition Metal Complexes; VCH Verlag: Weinhein, Germany,
1991. (c) Romeo, R. Comments Inorg. Chem. 1990, 11, 21.