Synthesis and structure of an unexpected platinum π complex formed from substituted 1,4-diamino ligands through an elimination process

Article abstract of DOI:10.1002/chem.200401228

An unusual reactivity of cis-1,2-bis[(N,N-dimethylamino)methyl] cyclohexane with PtCl₂ was observed, resulting in the formation of a platinum(II) π-olefin complex instead of the conventional square-planar cis Pt^II coordination complex with the diamino ligand. This behavior was interpreted on the basis of the steric hindrance of the dimethylamino groups whose electron lone pairs are barely accessible to a platinum atom, which can make it difficult for both dimethylamino groups to bind platinum at the same time. This complex has been physically and spectroscopically characterized and its structure has been confirmed by using X-ray diffraction analyses on single crystals.

Full text of DOI:10.1002/chem.200401228

Synthesis and Structure of an Unexpected Platinum p Complex Formed from
Substituted 1,4-Diamino Ligands through an Elimination Process
Marina Gay,[a, b] ꢀngel M. MontaÇa,*[a] Virtudes Moreno,*[b] Mercꢁ Font-Bardia,[c] and
Xavier Solans[c]
Abstract: An unusual reactivity of cis-
1,2-bis[(N,N-dimethylamino)methyl]
cyclohexane with PtCl2 was observed,
resulting in the formation of a plati-
num(ii) p-olefin complex instead of the
conventional square-planar cis PtII co-
ordination complex with the diamino
ligand. This behavior was interpreted
on the basis of the steric hindrance of
the dimethylamino groups whose elec-
tron lone pairs are barely accessible to
a platinum atom, which can make it
difficult for both dimethylamino groups
to bind platinum at the same time. This
complex has been physically and spec-
troscopically characterized and its
structure has been confirmed by using
X-ray diffraction analyses on single
crystals.
Keywords: antitumor agents · di-
amines · elimination · pi complex ·
platinum
Introduction
the other, have motivated efforts to develop new antitumor
agents with improved therapeutic properties. The goals for
the design of new platinum complexes are the synthesis of
compounds that remain active against cisplatin-resistant
cells, with a wider spectrum of antitumor activity, and with
lower toxicity than cisplatin. In order to explore possibilities
of improving antitumor activity of these kind of compounds,
we have been working on the design of new platinum(ii)
complexes with cytotoxic activity to establish structure–ac-
tivity relationship rules that could contribute to a better un-
derstanding of their mechanisms of action and to obtain
new hits and leads with promising cytoregulatory properties.
In this context, we have been working on the synthesis of
a chemical library of 1,4-diaminoligands with different de-
grees of substitution on the nitrogen atoms in order to pre-
pare the corresponding platinum(ii) complexes to evaluate
their cytotoxic activity. When we reacted 1,2-bis(N,N-dime-
thylaminomethyl)cyclohexane as a ligand with PtCl2, we ob-
tained an unexpected organometallic compound of plati-
num(ii) instead of the usual seven-membered ring chelate
formed by coordination of a platinum atom to both nitrogen
atoms of the diamino groups. Formally, one of the dimethyl-
amino groups was lost during the reaction, resulting in the
formation of a carbon–carbon double bond that coordi-
nated to platinum(ii). These kind of amino–olefin plati-
num(ii) dichloride complexes have been previously reported
in the literature,[3,4] but what is really new in the present
work, to the best of our knowledge, is the unusual formation
process of a p complex from a N,N-disubstituted 1,4-diamine
ligand.
Since the discovery of cisplatin as an antitumor agent, many
platinum compounds have been synthesized, but only a few
are being currently used in clinical therapy (cisplatin, carbo-
platin, oxaliplatin, and nedaplatin).[1,2] In spite of the great
efficiency of the aforementioned platinum complexes
against ovarian, bladder, and testicular cancers, these drugs
display limited activity against some of the most common
tumors in colon and breast cancer. In addition, other limita-
tions are observed in cisplatin chemotherapy, such as a vari-
ety of adverse effects and acquired resistance. The great suc-
cess of cisplatin on the one hand, and these limitations on
[a] M. Gay, Dr. ꢀ. M. MontaÇa
Departamento de Quꢁmica Orgꢂnica
Universidad de Barcelona, Facultad de Quꢁmica
c/Martꢁ i Franquꢃs 1–11, 08028, Barcelona (Spain)
Fax : (+34)93-339-78-78
E-mail: angel.montana@ub.edu
[b] M. Gay, Dra. V. Moreno
Departamento de Quꢁmica Inorgꢂnica
Universidad de Barcelona, Facultad de Quꢁmica
c/Martꢁ i Franquꢃs 1–11, 08028, Barcelona (Spain)
Fax : (+34)93-490-77-25
E-mail: virtudes.moreno@qi.ub.es
[c] M. Font-Bardia, Dr. X. Solans
Departamento de Cristalografꢁa y Depꢄsitos Minerales
Universidad de Barcelona, Facultad de Geologꢁa
c/Martꢁ i Franquꢃs s/n, 08028, Barcelona (Spain)
Fax : (+34)93-402-13-40
E-mail: xavier@natura.geo.ub.es
2130
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DOI: 10.1002/chem.200401228
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FULL PAPER
The preparation and structural characterization of the
new compound is reported here, and a possible mechanism
to explain its formation from the diamino ligand is also pro-
posed. The organometallic compound is being evaluated as
a potential antitumor compound due to accepted knowledge
that the main pharmacological target of platinum com-
pounds is DNA,[5,2f] so in this case the platinum–carbon
bond could facilitate the formation of a DNA adduct[6] be-
cause of an enhanced trans effect.[3]
conformation, placing the dimethylamino and the methyl-
idene groups in a quasi-diaxial position, thus energetically
unfavorable. Even though the other diastereoisomer could
have formed, but was not detected, the isolated and charac-
terized isomer 6 should be the major isomer according to
the mass balance. The stereoselection in metal–olefin com-
plexation is well known in the literature when applied to
chiral ligands.[8]
NMR studies on complex 6: The assignment of individual
proton signals in the 1H NMR spectrum was based on
J(H,H) coupling constant values and was confirmed by 2D
COSY experiments. The effect of the coordination of the
methylidene group ligand to platinum and the back-dona-
tion effect were observed by using 1H NMR spectroscopy.
Thus, protons H1’’ in 6 appeared at higher fields (d=4.21
and 4.51 ppm) than similar hydrogens belonging to a typical
non-coordinated double bond (d=4.63 and 4.88 ppm, re-
spectively). Moreover, 195Pt satellites were observed in the
1H NMR spectrum for the two protons H1’’ (2J(Pt, H1’’a)=
Results and Discussion
The synthesis of this new compound was carried out starting
from commercially available cis-3,3,6,6-tetrahydrophthalic
anhydride.[7] Hydrolysis of anhydride 1 led to the formation
of cis-3,3,6,6-tetrahydrophthalic acid 2, whose amidation was
easily accomplished by refluxing it with hexamethylphos-
phorus triamide (HMPT) in benzene. Diamine 4 was ob-
tained by reduction of diamide 3 with LiAlH4. Catalytic hy-
drogenation of 4 afforded the desired saturated diamine 5.
The synthetic pathway to prepare ligand 5 and the yields of
each step are shown in Scheme 1.
2
65.7 Hz, J(Pt, H1’’b)=76.8 Hz) (see Figure 1).
The preparation of platinum(ii) complex 6 was carried out
by using PtCl2 as reagent and CH2Cl2 as solvent (see
Scheme 2). Diamine 5 was completely soluble in CH2Cl2,
but PtCl2 was only partially soluble in it at 258C, which ex-
plains the low reaction rate (15 days of reaction time were
necessary in order to get complete conversion of the sub-
strate). Complex 6 was isolated as a yellow solid and was
purified by crystallization in hot acetonitrile, affording
yellow crystals suitable for X-ray analysis.
Complex 6 was studied, in the solid state, by using ele-
mental analysis, mass spectrometry, and FTIR spectroscopy
1
and, in solution, by using high-field H NMR spectroscopy.
Its structure was confirmed by X-ray diffraction analysis.
It is worth noting that only one of the two possible dia-
stereoisomers of p complex 6 has been detected and isolat-
ed. Analysis by using molecular modeling suggests that the
p complexation of platinum by the other face of the methyl-
idene group should result in modification of the cyclohexane
Figure 1. Detail of the 195Pt satellites for the H1’’ signal in the 1H NMR
spectrum of 6 (300 MHz).
Structure determination of complex 6 by X-ray crystallogra-
phy: Details of the structure determination are given in the
Experimental Section. Crystallographic data and selected
bond distances and angles are quoted in Tables 1 and 2. In
Figure 2, an ORTEP view of the X-ray crystal structure of 6
is shown. This molecular representation shows that the
structure of 6 corresponds to the diastereoisomer that has
the lower steric hindrance between the methyl groups and
the cyclohexane ring. Complex 6 adopts a square-planar ge-
ometry, in which the C=CH2 group is located perpendicular
to the plane containing the platinum and chlorine atoms.
Angles of the C=CH2 moiety indicate that the double-bond
Abstract in Spanish: Se ha observado una reactividad inusual
de
cis-1,2-bis[(N,N-dimetilamino)metil]ciclohexano
con
PtCl2, que conduce a la formaciꢀn de un complejo p-olefꢁni-
co de platino (ii) en lugar del complejo de coordinaciꢀn con-
vencional cis cuadrado plano de PtII con el ligando diamina-
do. Este comportamiento se puede interpretar sobre la base
del impedimento estꢂrico de los grupos dimetilamino, cuyos
pares de electrones solitarios son difꢁcilmente accesibles al
ꢃtomo de platino y este hecho dificulta que ambos grupos di-
metilamino puedan coordinarse al platino al mismo tiempo.
Este compuesto se ha caracterizado fꢁsica y espectroscꢀpica-
mente y su estructura se ha confirmado mediante difracciꢀn
de rayos X de monocristal.
À
geometry is not exactly coplanar. Moreover, the C2’ C1’’
bond length is 1.38 ꢆ. These two experimental data are con-
sistent with a back-donation effect. In addition, it is possible
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ꢀ. M. MontaÇa, V. Moreno, et al.
Scheme 1. Synthetic pathway of ligand 5. a) H2O/HCl, RT, 16 h; b) HMPT, N2, anhydrous benzene, reflux, 30 min; c) LiAlH4, N2, anhydrous Et2O, reflux,
1 h; d) H2, Pd/C, EtOH, RT, 7 h.
Table 2. Selected bond lengths [ꢆ] and angles [8] for compound 6.
À
Pt N1
2.077(4)
2.120(4)
2.149(6)
2.2876(18)
2.3409(14)
1.463(8)
1.520(6)
1.526(6)
1.586(8)
1.485(8)
1.529(7)
1.624 (10)
1.484(10)
1.488(8)
1.550(8)
1.383(6)
97.12(18)
91.0(2)
Cl1-Pt-Cl2
C1-N1-Pt
C1’’’-N1-Pt
C1iv-N1-Pt
C1’’-C2’-Pt
C1’-C2’-Pt
95.84(6)
104.2(3)
114.0(3)
115.4(3)
70.0(3)
98.2(4)
124.1
72.3(3)
108.5(4)
108.9(4)
105.6(5)
111.4(4)
118.3(5)
122.0(5)
103.1(5)
115.2(4)
113.0(4)
113.1(5)
113.3(5)
107.4(6)
109.3(5)
114.5(4)
113.3
À
Pt C1’’
À
Pt C2’
À
Pt Cl1
À
Pt Cl2
À
N1 C1
À
N1 C1’’’
C3’-C2’-Pt
Scheme 2. Synthesis of compound 6. a) CH2Cl2, RT, 15 days.
Table 1. Crystal data for compound 6.
iv
À
N1 C1
C2’-C1’’-Pt
C1-N1-C1’’’
C1-N1-C1iv
C1’’’-N1-C1iv
N1-C1-C1’
C1’’-C2’-C1’
C1’’-C2’-C3’
C6’-C1’-C2’
C6’-C1’-C1
C2’-C1’-C1
C1’-C6’-C5’
C4’-C5’-C6’
C5’-C4’-C3’
C4’-C3’-C2’
C1’-C2’-C3’
H1a’’-C1’’-H1b’’
C2’’-C1’’-H1a’’
C2’’-C1’’-H1b’’
À
C1 C1’
À
C1’ C6’
À
C1’ C7’
À
C6’ C5’
molecular formula
C10H19Cl2NPt
419.25
À
C5’ C4’
formula weight [gmolÀ1
]
À
C4’ C3’
T [K]
293(2)
À
C3’ C2’
l (MoKa) [ꢆ]
0.71069
À
C2’ C1’’
crystallographic system
monoclinic
N1-Pt-C1’’
N1-Pt-C2’
C1’’-Pt-C2’
N1-Pt-Cl1
C1’’-Pt-Cl1
C2’-Pt-Cl1
N1-Pt-Cl2
C1’’-Pt-Cl2
C2’-Pt-Cl2
space group
a [ꢆ]
b [ꢆ]
c [ꢆ]
a [8]
P21/m
8.4980(10)
16.5210(10)
9.5350(10)
37.79(16)
179.19(11)
82.63(14)
88.35(17)
84.67(14)
158.98(13)
163.12(12)
90
b [8]
113.106(10)
g [8]
90
116.3
116.3
V [ꢆ3]
Z
1231.3(2)
4
2.262
11.793
792
2.47–33.40
1calcd [MgmÀ3
]
m [mmÀ1
F (000)
V [8]
]
h, k, l range
À11ꢀhꢀ10, 0ꢀkꢀ24,
0ꢀlꢀ13
number of registered reflections
number of independent reflections
[Rint (on F)]
method of refinement
number of data
7247
2960
0.0355
full-matrix least-squares on F2
2960
number of parameters
goodness-of-fit on F2
R final [I>2s(I)]
127
1.117
R1 =0.0317, wR2 =0.0987
R1 =0.0365, wR2 =0.1021
0.787 and À0.886
R index (all data)
largest difference peak and hole
[eꢆ3]
Figure 2. ORTEP view of molecule 6.
to observe that the cyclohexane ring adopts a chair confor-
mation to minimize the steric repulsions. Finally, the C1-N1-
C1iv angle (105.68) is large enough to minimize the steric re-
pulsion between the methyl groups.
ble seven-membered ring chelate 5’. The second step could
be the abstraction of a hydride group by the platinum
atom.[9] A third step, involving a molecular rearrangement,
is imagined to generate the precursory cis-diaminodichloro-
platinum(ii) complex 5’’’. A final step in which the dimethyl-
amine ligand is shifted by the p system of the methylidene
group could afford the final complex 6. This behavior could
Proposed formation mechanism of compound 6: A possible
mechanism to explain the formation of complex 6 is shown
in Scheme 3. The first step could be the labile ligand coordi-
nation on the amino groups by platinum, forming an unsta-
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Platinum Complexes
FULL PAPER
Scheme 3. Proposal of a mechanism for the formation of complex 6.
(2 mL), hexamethylphosphorous triamide (0.32 mL, 1.765 mmol) was
added and the mixture refluxed for 30 min. The resulting cloudy solution
was allowed to cool down to room temperature and a saturated aqueous
solution of NaHCO3 (2 mL) was added under strong stirring. The layers
were separated and the aqueous layer was extracted with methylene
chloride (4ꢇ2 mL). The organic phases were combined, dried over
MgSO4, filtered, and concentrated to dryness to give a colorless oil that
solidified after a few hours to form a white solid. The solid was washed
with hexane and purified by crystallization from ether at À788C (348 mg,
88%). M.p. 65–708C; 1H NMR (200 MHz, CDCl3, 258C): d=2.03–2.12
(m, 2H; H3, H6), 2.31–2.47 (m, 2H; H3, H6), 2.73 (s, 3H; H1’’’, H1iv,
H1v, or H1vi), 2.75 (s, 3H; H1’’’, H1iv, H1v, or H1vi), 2.85 (s, 3H; H1’’’, H1iv,
H1v, or H1vi), 2.87 (s, 3H; H1’’’, H1iv, H1v, or H1vi), 2.85–2.92 (m, 2H; H1,
H2), 5.52–5.55 ppm (m, 2H; H4, H5); 13C NMR (50 MHz, CD3OD): d=
26.5 (C3, C6), 35.5 (C1iv, C1vi), 36.0 (C1, C2), 37.4 (C1’’’, C1v), 124.9 (C4,
C5), 174.0 ppm (C1’, C1’’); IR (KBr): n˜ =3010, 2930, 1645 (C=O),
1090 cmÀ1; MS (70 eV, DIP-CI-NH3): m/z (%): 225 (100) [M+H]+, 180
(12) [MÀNMe2]+, 171 (3) [M+H]+.
be interpreted on the basis of the steric hindrance of the di-
methylamino groups that would create high steric strain on
the seven-membered ring of the diamino complex 5’. On the
other hand, the electron lone pairs of both nitrogen atoms
are barely accessible simultaneously by the platinum atom
which could destabilize the diamino complex.
Experimental Section
Materials and methods: All reactants were purchased from commercial
suppliers and used without further purification. Reactions that required
an inert atmosphere were conducted under dry nitrogen and the glass-
ware was oven dried (1208C). THF, Et2O, and benzene were distilled
from sodium/benzofenone prior to use. CH2Cl2 was dried by refluxing it
over CaH2 under nitrogen. Elemental analyses (C, H, N, S) were carried
out on a Carlo Erba EA1108 apparatus. Infrared spectra were recorded
on a FTIR NICOLET 510 spectrophotometer in a 4000–400 cmÀ1 range.
NMR spectra were obtained on a Varian Gemini-200, a Varian Unity-300
plus, or a Varian VXR-500 apparatus using CDCl3 or [D6]DMSO as sol-
vent. 1H NMR spectra were obtained at 200, 300, or 500 MHz frequencies
and chemical shifts are given in ppm relative to tetramethylesilane
(TMS). 13C NMR and distortionless enhancement by polarization transfer
(DEPT) experiments were recorded at 50 or 75 MHz and were refer-
enced to the 77.0 ppm resonance of CDCl3. Mass spectra were run on a
Fisons VG Quattro triple quadrupole analyzer in the m/z 1800–200
range, using MeCN–H2O as solvent under electrospray (ES-MS), or on a
Hewlett-Packard 5890 mass spectrometer using a chemical ionization
(CI) technique (conditions are specified for each case, DIP=direct inser-
tion probe, FAB-MS=fast atom bombardment mass spectrometry,
NBA=3-nitrobenzyl alcohol). Melting points were measured on a Galen-
kamp and a Stuart Scientific SMP3 apparatus. Conductivity was mea-
sured on CRISON Micro CM 2200 equipment.
Synthesis of dimethyl-({(1R*,6S*)-6-[(dimethylamino)methyl]cyclohex-3-
en-1-yl}methyl)amine (4): To a suspension of lithium aluminum hydride
(70 mg, 1.837 mmol) in anhydrous diethyl ether (2 mL), a solution of dia-
mide 3 (300 mg, 1.531 mmol) in dry THF (1 mL) was added. The mixture
was refluxed for 1 h and was then quenched by slow and cautious addi-
tion of water (0.12 mL) in an ice bath. Afterwards, NaOH aqueous so-
lution (15% w/w, 0.12 mL) and water (0.38 mL) were successively added.
The resulting white precipitate was filtered off, washed twice with ether,
and discarded. The organic solutions were combined together, dried over
anhydrous magnesium sulfate, filtered, and concentrated to dryness
1
under vacuum to give a colorless oil (300 mg, 82%). H NMR (200 MHz,
CDCl3, 258C): d=2.20 (s, 12H; H1’’’, H1iv, H1v, H1vi), 1.87–2.30 (m, 10H;
H1’, H2’, H5’, H6’, H1, H1’’), 5.64 ppm (s, 2H; H3’, H4’); 13C NMR
(50 MHz, CD3OD): d=28.3 (C2’, C5’), 33.0 (C1’, C6’), 46.0 (C1’’’, C1iv,
C1v, C1vi), 60.6 (C1, C1’’), 125.9 ppm (C3’, C4’); IR (film): n˜ =3020, 2970,
2940, 2900, 2860, 2820, 2770, 1650, 1095 cmÀ1; MS (70 eV, DIP-CI-NH3):
m/z (%): 214 (3) [M+NH4]+, 197 (33) [M+H]+, 184 (100) [MÀMe]+.
Synthesis of cis-cyclohex-4-ene-1,2-dicarboxylic acid (2): 3,3,6,6-Tetrahy-
drophthalic anhydride (1.178 g, 7.09 mmol) was dissolved in acetic acid
(2 mL) and water (10 mL). To this, four drops of 36% w/w hydrochloric
acid were added. The mixture was stirred overnight at room temperature.
The solvent was removed under vacuum to give a white solid (1.171 g,
100%). M.p. 169–1708C; 1H NMR (200 MHz, CDCl3, 258C): d=2.36–
2.69 (m, 4H; H3, H6), 3.10 (dd, J1(H,H)=5.1, J2(H,H)=5.1 Hz, 2H; H1,
H2), 5.69 ppm (s, 2H; H4, H5); 13C NMR (50 MHz, CD3OD): d=23.2
Synthesis of dimethyl-({(1R*,2S*)-2-[(dimethylamino)methyl]cyclohex-
yl}methyl)amine (5): A solution of diamine 4 (150 mg, 0.765 mmol) in ab-
solute ethanol (5 mL) was added under a nitrogen atmosphere to a 10%
Pd/C catalyst (30 mg). The reaction mixture was pumped out and back-
filled with hydrogen four times in order to remove traces of oxygen
which could passivate the catalyst. A hydrogen atmosphere was establish-
ed and the reaction mixture was stirred strongly for 7 h. The catalyst was
removed by filtration through Celiteꢈ and the organic solution concen-
trated to dryness to give a colorless oil (133 mg, 88%). The conversion
and the chemical selectivity were observed to be complete by using TLC
and GC analyses but the yield was not quantitative due to the adsorption
of a certain amount of product onto the fine particles of catalyst, even
though we tried to release it by suspending the catalyst fine powder in
(C3, C6), 36.8 (C1, C2), 122.3 (C4, C5), 173.3 ppm (C1’, C1’’); IR (KBr):
À1
À
n˜ =3300–2300 (COO H), 1680 cm (C=O); MS (70 eV, DIP-CI-NH3):
m/z (%): 205 (10) [M+N2H7]+, 188 (100) [M+NH4]+, 171 (3) [M+H]+.
Synthesis of cis-N,N,N’,N’-tetramethylcyclohex-4-ene-1,2-dicarboxamide
(3): To a suspension of 2 (300 mg, 1.765 mmol) in anhydrous benzene
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ꢀ. M. MontaÇa, V. Moreno, et al.
ethanol in a sonication ultrasound bath. 1H NMR (200 MHz, CDCl3,
258C): d=1.34–1.56 (m, 8H; H3’, H4’, H5’, H6’), 1.94–2.03 (m, 2H; H1’,
H2’), 2.19 (s, 12H; H1’’’, H1iv, H1v, H1vi), 2.25–2.32 ppm (m, H1; H1’’);
13C NMR (50 MHz, CD3OD): d=23.6 (C4’, C5’), 27.6 (C3’, C6’), 35.4
(C1’, C2’), 45.7 (C1’’’, C1iv, C1v, C1vi), 60.0 ppm (C1, C1’’); IR (film): n˜ =
2927, 2855, 2815, 2763, 1458, 1261, 1169, 1040 cmÀ1; MS (70 eV, DIP-CI-
NH3): m/z (%): 200 (15) [M+H]+, 199 (100) [M+H]+, 184 (37)
[MÀMe]+.
final R(on F) factor was 0.031, wR(on [F]2) was 0.098, and goodness of fit
was 1.117 for all observed reflections. The number of refined parameters
was 127. The maximum shift/esd=0.00 and the mean shift/esd=0.00. The
maximum and minimum peaks in the final difference synthesis were
0.787 and À0.886 eꢆÀ3, respectively.
CCDC-257127 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Synthesis of dichloro{h2-dimethyl[(2-methylidenecyclohex-1-yl)methyl]-
amino}platinum(ii) (6): A solution of 5 (170 mg, 0.859 mmol) in dry
CH2Cl2 (20 mL) was added to a brown suspension of PtCl2 (228 mg,
0.859 mmol) in CH2Cl2 (50 mL), in the dark. The reaction mixture was
stirred at room temperature (258C) for fifteen days. After this time, the
formation of metallic platinum (Pt0) was observed. The suspension was
filtered to remove metallic platinum particles and stirred for two addi-
tional days. A yellow solid then formed, which was filtered out and dried.
The mother liquor from the filtration was concentrated to dryness to
obtain an orange oil that was lixiviated with acetonitrile at room temper-
ature. The remaining residue on the flask was a homogeneous yellow
solid of the same composition as the solid obtained by filtration. Both
solids were combined together, dissolved in hot acetonitrile, and left to
stand at room temperature for two days to obtain yellow crystals
Acknowledgement
We thank the Spanish Ministry of Education and Science for financial
support (Projects PB-98-1236 and BQU2002-00601). A fellowship to
M.G. from the University of Barcelona is also gratefully acknowledged.
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1
(201 mg, 58%). M.p. 223–2258C; H NMR (300 MHz, [D6]DMSO, 258C):
d=1.11 (dddd, J1(H,H)=3.8, J2(H,H)=J3(H,H)=J4(H,H)=12.1 Hz, 1H;
H6’a), 1.35 (ddddd, J1(H,H)=J2(H,H)=3.9, J3(H,H)=J4(H,H)=
J5(H,H)=12.7 Hz, 1H; H4’a), 1.59 (ddddd, J1(H,H)=J2(H,H)=3.9,
J3(H,H)=J4(H,H)=J5(H,H)=12.9 Hz, 1H; H4’b), 1.75–1.80 (m, 1H;
H5’a), 1.93–2.02 (m, 2H; H5’b, H6’b), 2.22 (dd, J1(H,H)=4.3, J2(H,H)=
12.2 Hz, 1H; H1a), 2.27–2.29 (m, 1H; H3’b), 2.40 (ddd, J1(H,H)=4.1,
J2(H,H)=J3(H,H)=12.3 Hz, 1H; H3’b), 2.67 (dddd, J1(H,H)=J2(H,H)=
3.9, J3(H,H)=J4(H,H)=12.3 Hz, 1H; H1’), 2.79–2.96 (m, 1H; H1b), 2.83
(s, 3H; H1’’’), 2.92 (s, 3H; H1iv), 4.21 (s, 1H; H1’’a), 4.21 (d, J(Pt,H)=
65.7 Hz, 1H; H1’’a), 4.59 (s, 1H; H1’’b), 4.59 ppm (d, J(Pt,H)=76.8 Hz,
À
1H; H1’’b); IR (KBr): n˜ =3070 (Csp2 H, st), 2927, 2855, 1650 (C=C, st),
1508, 1462, 1451, 1119, 1009, 926, 831 cmÀ1; FAB-MS (NBA) m/z: 498,
460, 383; elemental analysis calcd (%) for C10H19Cl2NPt (419.25 gmolÀ1):
C 28.65, H 4.57, N 3.34; found: C 28.96, H 4.79, N 3.45.
X-ray diffraction analysis:
A [PtCl2L’] prismatic crystal (0.1ꢇ0.1ꢇ
0.2 mm) was selected and mounted on a MAR345 image plate detector
system. Unit-cell parameters were determined from automatic centering
of 6697 reflections (3<V<318) and refined by using the least-squares
method. Intensities were collected with graphite monochromatized MoKa
radiation. 7247 reflections were measured in the range 2.47<V<33.40,
2960 of which were non-equivalent by symmetry (Rint (on I)=0.035).
2543 reflections were assumed as observed by applying the condition I>
2s(I). Lorentz polarization and absorption corrections were made.
[9] R. G. Nuzzo, T. J. McCarthy, G. M. Whitesides, J. Am. Chem. Soc.
1981, 103, 3404–3410.
The structure was solved by direct methods using the SHELXS computer
program[10] and refined by using the full-matrix least-squares method
with the SHELXS-96 computer program,[11] using 2960 reflections (very
negative intensities were not assumed to be present). The function mini-
mized was: ꢀw[F2oÀFc2]2, where w=[s2(I)+(0.0745P)2 +(0.4463P)]À1, and
P=[F2o +2F2c]/3; f, f’, and f’’ were taken from the International Tables of
X-ray Crystallography.[12] All the H atoms were computed and refined
using a riding model with isotropic temperature factor equal to 1.2 times
the equivalent temperature factor of the atoms which are linked. The
[10] G. M. Sheldrick, SHELX, a computer program for determination of
crystal structure, University Gçttingen, Germany, 1996.
[11] G. M. Sheldrick, SHELXS-96, a computer program for determina-
tion of crystal structure, University Gçttingen, Germany, 1996.
[12] International Tables of X-ray Crystallography, Vol. IV, Kynoch, 1974,
pp. 99–100 and 149.
Received: November 30, 2004
Published online: February 15, 2005
2134
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Chem. Eur. J. 2005, 11, 2130 – 2134