Acetonimine and 4-imino-2-methylpentan-2-amino platinum(II) complexes: Synthesis and in vitro antitumor activity

Article abstract of DOI:10.1021/ic8012359

The reaction of [Pt(dmba)(PPh₃)Cl] [where dmba = N,C-chelating 2-(dimethylaminomethyl)phenyl] with aqueous ammonia in acetone in the presence of AgClO₄ gives the acetonimine complex [Pt(dmba)(PPh ₃)(NH=CMe₂)]ClO₄ (1). The reaction of [Pt(dmba)(DMSO)Cl] with aqueous ammonia in acetone in the presence of AgClO ₄ gives a mixture of [Pt(dmba)(NH=CMe₂) ₂]ClO₄ (2) and [Pt(dmba)(imam)]ClO₄ (3a) (where imam = 4-imino-2-methylpentan2-amino). [Pt(dmba)(DMSO)Cl] reacts with [Ag(NH=CMe₂)₂]ClO₄ in a 1:1 molar ratio to give [Pt(dmba)(DMSO)-(NH=CMe₂)]ClO₄ (4). The reaction of [Pt(dmba)(DMSO)Cl] with 20% aqueous ammonia in acetone at 70°C in the presence of KOH gives [Pt(dmba)(CH₂COMe)(NH=CMe₂)] (5), whereas the reaction of [Pt(dmba)(DMSO)Cl] with 20% aqueous ammonia in acetone in the absence of KOH gives [Pt(dmba)(imam)]Cl (3b). The reaction of [NBu ₄]₂[Pt₂(C₆F₅) ₄(μ-Cl)₂] with [Ag(NH=CMe₂) ₂]ClO₄ in a 1:2 molar ratio produces cis-[Pt(C ₆F₅)₂(NH=CMe₂)₂] (6). The crystal structures of 1·2Me₂CO, 2, 3a, 5, and 6 have been determined. Values of IC₅₀ were calculated for the new platinum complexes against a panel of human tumor cell lines representative of ovarian (A2780 and A2780cisR) and breast cancers (T47D). At 48 h incubation time complexes 1, 4, and 5 show very low resistance factors against an A2780 cell line which has acquired resistance to cisplatin. 1, 4, and 5 were more active than cisplatin in T47D (up to 30-fold in some cases). The DNA adduct formation of 1, 4, and 5 was followed by circular dichroism and electrophoretic mobility.

Full text of DOI:10.1021/ic8012359

Inorg. Chem. 2008, 47, 10025-10036
Acetonimine and 4-Imino-2-methylpentan-2-amino Platinum(II)
Complexes: Synthesis and in Vitro Antitumor Activity
Jose´ Ruiz,*,† Venancio Rodr´ıguez,*,† Natalia Cutillas,† Gregorio Lo´pez,† and Delia Bautista‡
Departamento de Qu´ımica Inorga´nica and S.U.I.C., Edificio S.A.C.E.,
UniVersidad de Murcia, E-30071-Murcia, Spain
Received July 3, 2008
The reaction of [Pt(dmba)(PPh3)Cl] [where dmba ) N,C-chelating 2-(dimethylaminomethyl)phenyl] with aqueous
ammonia in acetone in the presence of AgClO4 gives the acetonimine complex [Pt(dmba)(PPh3)(NHdCMe2)]ClO4
(1). The reaction of [Pt(dmba)(DMSO)Cl] with aqueous ammonia in acetone in the presence of AgClO4 gives a
mixture of [Pt(dmba)(NHdCMe2)2]ClO4 (2) and [Pt(dmba)(imam)]ClO4 (3a) (where imam ) 4-imino-2-methylpentan-
2-amino). [Pt(dmba)(DMSO)Cl] reacts with [Ag(NHdCMe2)2]ClO4 in a 1:1 molar ratio to give [Pt(dmba)(DMSO)-
(NHdCMe2)]ClO4 (4). The reaction of [Pt(dmba)(DMSO)Cl] with 20% aqueous ammonia in acetone at 70 °C in the
presence of KOH gives [Pt(dmba)(CH2COMe)(NHdCMe2)] (5), whereas the reaction of [Pt(dmba)(DMSO)Cl] with
20% aqueous ammonia in acetone in the absence of KOH gives [Pt(dmba)(imam)]Cl (3b). The reaction of
[NBu4]2[Pt2(C6F5)4(µ-Cl)2] with [Ag(NHdCMe2)2]ClO4 in a 1:2 molar ratio produces cis-[Pt(C6F5)2(NHdCMe2)2] (6).
The crystal structures of 1· 2Me2CO, 2, 3a, 5, and 6 have been determined. Values of IC50 were calculated for the
new platinum complexes against a panel of human tumor cell lines representative of ovarian (A2780 and A2780cisR)
and breast cancers (T47D). At 48 h incubation time complexes 1, 4, and 5 show very low resistance factors
against an A2780 cell line which has acquired resistance to cisplatin. 1, 4, and 5 were more active than cisplatin
in T47D (up to 30-fold in some cases). The DNA adduct formation of 1, 4, and 5 was followed by circular dichroism
and electrophoretic mobility.
Introduction
at room temperature, decomposing readily to give acetonine
(2,2,4,4,6-pentamethyl-2,3,4,5-tetrahydropyrimidine) and
NH3.5 Its difficult synthesis3,4 and handling may account for
the scarcity of acetonimine complexes of transition metals
reported so far (Mo, W, Cr,6-8 Ni,9 Ru,10,11 Os,12 Au,13,14
Pd,15 Pt,16,17 Ag, and Rh18-20), none of which has been
obtained using acetonimine itself.
The synthesis of the cis and trans isomers of the aceton-
imine platinum [PtX2(NHdCMe2)2] and [PtX2(NHdCMe2)-
(NH3)] (X ) Cl, I) has been recently reported by Natile et
al.16 These complexes display a tumor cell growth inhibitory
potency similar to that of the corresponding Pt(II) complexes
with iminoethers (PtsN(H)dC(OR)R′),21-24 in addition the
ability to circumvent (either partially or completely) cisplatin
With metallopharmaceuticals playing a significant role in
therapeutic and diagnostic medicine, the discovery and
development of new metallodrugs remain an ever-growing
area of research in medicinal inorganic chemistry.1 Cisplatin,
carboplatin, and oxaliplatin are at present the only metal-
based anticancer agents in worldwide clinical use. The metal
complexes are used in about 50% of all tumor therapies and
display a remarkable therapeutic activity in a series of solid
tumors. Nevertheless, severe dose-limiting side effects and
intrinsic or acquired resistance are the main drawbacks
associated with this kind of therapy.2
Acetonimine (Me2CdNH) can be prepared from acetone
and ammonia at high temperature and pressure and with the
use of a catalyst.3,4 However, acetonimine is unstable, even
(2) Jakupec, M. A.; Galanski, M.; Arion, V. B.; Hartinger, C. G.; Keppler,
B. K. Dalton Trans. 2008, 183–194.
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Commun. 1988, 18, 1501–1511.
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3178.
* To whom correspondence should be addressed. E-mail: jruiz@
um.es. Fax: +34 968 364148. Tel: +34 968 367455.
†
Departamento de Qu´ımica Inorga´nica.
S.U.I.C., Edificio S.A.C.E.
‡
(1) Ray, S.; Mohan, R.; Singh, J. K.; Samantaray, M. K.; Shaikh, M. M.;
(5) Findeisen, K.; Heitzer, H.; Dehnicke, K. Synthesis 1981, 702–704.
(6) King, R. B.; Douglas, W. M. Inorg. Chem. 1974, 13, 1339–1342.
Panda, D.; Ghosh, P. J. Am. Chem. Soc. 2007, 129, 15042–15053.
10.1021/ic8012359 CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 21, 2008 10025
Published on Web 10/10/2008

Ruiz et al.
resistance.16 Ketimines and iminoethers are very similar (sp2-
hybridization of the nitrogen atom like in pyridine, a proton
still bound to nitrogen like in secondary aliphatic amines,
the ligand extending in a plane with the steric bulk localized
only on one side of the donor atom), the main advantage of
symmetrical ketimines (like acetonimine), with respect to
iminoethers, being the lack of geometric isomerism about
the CdN double bond.
Scheme 1
nyl] has been prepared in high yield from the corresponding
chloroplatinum complex [Pt(dmba)(PPh3)Cl]26 by reaction
with 20% aqueous ammonia in acetone at room temperature
(Scheme 1).
In view of the general interest in acetonimine as li-
gand,6-20 in the present study, our initial aim was to syn-
thesize platinum organometallic complexes derived from the
N,C-chelating 2-(dimethylaminomethyl)phenyl (dmba) and
pentafluorophenyl C6F5 groups with the acetonimine ligand.
To the best of our knowledge,25 the complexes herein
reported represent the first examples of 4-imino-2-methyl-
pentan-2-amino (imam) platinum complexes and the first
platinum complexes containing acetonimine and a σ-metal
carbon bond.
Values of IC50 were calculated for the new platinum
complexes against a panel of human tumor cell lines
representative of ovarian (A2780 and A2780cisR) and breast
cancers (T47D, cisplatin resistant). At 48 h incubation time
complex 1 was about 30-fold more active than cisplatin in
T47D. Complexes 1, 4, and 5 show very low resistance
factors against an A2780 cell line which has acquired
resistance to cisplatin.
Complex 1 is a white air-stable solid that decomposes on
heating above 200 °C in a dynamic N2 atmosphere. Its
acetone solution shows a conductance value corresponding
to 1:1 electrolytes (ΛM ) 130 S cm2 mol-1).27 An IR band
is observed at approximately 1096 which is assigned to the
ν3 mode of free perchlorate (Td symmetry). The observation
of an additional band at approximately 622 cm-1 for the ν4
mode confirms the presence of free perchlorate.28 The NH
stretching mode for the complex is found in the 3200 cm-1
region, and the CdN vibration is at approximately 1650
cm-1. The 1H NMR spectrum of complex 1 at room
temperature shows that both the N-methyl and the CH2
groups of the dmba are diastereotopic, two separate signals
being observed for the former and an AB quartet for the
latter (some broadening being observed); 195Pt satellites are
observed as shoulders for the N-methyl protons. The rather
bulky PPh3 ligand hinders the rotation of the acetonimine
ligand about the PtsN bond, breaking the symmetry of the
platinum coordination plane. In complex 1 the PPh3-trans-
to-NMe2 ligand arrangement in the starting product26 is
preserved, after chlorine abstraction and acetonimine coor-
dination, as can be inferred from the small, but significant,
coupling constants 4JP-H (ranging from 2.4 to 3.4 Hz) of the
NMe2 and the CH2N protons with the phosphorus atom.29
Results and Discussion
Dmba Complexes. The acetonimine dmba complex 1
[where dmba ) N,C-chelating 2-(dimethylaminomethyl)phe-
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1
The H NMR spectrum of 1 exhibits also a NH proton
resonance as a broad singlet in the region of 10 ppm and
reveals the inequivalence of the Me groups of the imine
ligands, arising from restricted rotation around the CdN bond
at room temperature: a singlet at δ 2.18 for the methyl group
trans to NH and a doublet (4JHH ) 1.2 Hz) at δ 1.70 ppm
for the methyl group cis to NH with respect to the azomethine
double bond (195Pt satellites are observed as shoulders for
the resonance at δ 2.18). A NOESY experiment performed
on complex 1 has confirmed this assignment. A much
stronger crosspeak was observed between the more shielded
methyl and the iminic proton, clearly indicating that the more
shielded methyl is cis to the iminic proton with respect to
the azomethine double bond. Therefore the criterion of bigger
coupling between methyl group and iminic proton trans to
(16) Boccarelli, A.; Intini, F. P.; Sasanelli, R.; Sivo, M. F.; Coluccia, M.;
Natile, G. J. Med. Chem. 2006, 49, 829–837.
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P. G.; Bautista, D. Inorg. Chem. 2006, 45, 5201–5209.
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Chem. 2003, 42, 7644–7651.
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Alvarez-Falco´n, M. M. Inorg. Chem. 2006, 45, 181–188.
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2002, 21, 4560–4563.
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N.; Cocker, D.; Leng, M.; Sivo, M. F.; Intini, F. P.; Natile, G. J. Inorg.
Biochem. 1999, 77, 31–35.
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M. Anti-Cancer Drug Des. 1999, 14, 253–264.
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A. L.; van Klink, G. P. M.; van Koten, G. Organometallics 2002, 21,
264–271.
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Giordano, D.; Intini, F. P.; Caputo, P.; Natile, G. J. Med. Chem. 1993,
36, 510.
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Nucleic Acids Res. 2003, 31, 6450.
(25) CCDC CSD, version 5.29, November 2007.
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(28) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coor-
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10026 Inorganic Chemistry, Vol. 47, No. 21, 2008

Pt(II) Acetonimine and Imam Complexes
Scheme 2
one another can be misleading in the case of acetonimine
complexes of platinum(II), as suggested previously by Natile
et al.16,30 A unique resonance (doublet JPt-P ) 4100 Hz) is
observed in the 195Pt NMR spectrum of complex 1 at δ
-4063.
PtCCCN chelate ring is faster than the NMR time scale at
room temperature.31,32 The assignments given in the Ex-
perimental Section for complex 3b were supported by the
pertinent heteronuclear (1H-13C) COSY spectra.
The acetonimine complex 4 has been prepared in high
yield from the corresponding chloroplatinum complex [Pt-
(dmba)(DMSO)Cl] by reaction with the transmetalating
agent18 [Ag(NHdCMe2)2]+ in a 1:1 molar ratio in dichlo-
romethane (Scheme 2). The precipitation of AgCl produces
two free acetonimine ligands, one of which occupies a vacant
position at the Pt center. Again, as observed in complex 1,
the rather bulky DMSO ligand hinders the rotation of the
acetonimine ligand about the PtsN bond, breaking the
symmetry of the platinum coordination plane as observed
When we reacted [Pt(dmba)(DMSO)Cl]26 with 20% aque-
ous ammonia in acetone at room temperature for 4 h in the
presence of AgClO4, a mixture of [Pt(dmba)(NHdCMe2)2]-
ClO4 (2) and [Pt(dmba)(imam)]ClO4 (3a) in a 5:2 ratio
(Scheme 2), which contains the imam ligand (N,N-NHd
C(Me)CH2C(Me)2NH2 ) 4-imino-2-methylpentan-2-amino)
was obtained. To the best our knowledge no imam platinum
complexes have been previously reported in the literature.25
Upon heating a solution of 2 + 3a (5:2) at 70 °C in a Carius
tube for 24 h, no changes have been observed.
1
in the H NMR.
When [Pt(dmba)(DMSO)Cl] was treated with 20% aque-
ous ammonia in acetone at room temperature for 24 h,
[Pt(dmba)(imam)]Cl (3b) is obtained (Scheme 2). The for-
mation of complexes [Rh(Cp*)Cl(imam)]Cl and [Rh(Cp*)-
Cl(imam)]ClO4 by an intramolecular aldol-type self-
condensation of two acetonimine ligands, promoted by
gentle heating or by the addition of various ligands, has
been recently reported.19
The NH stretching modes for 3b are found in the
3250-3150 cm-1 range. The 1H NMR spectrum of complex
3b shows the presence of the dmba ligand, and the observa-
tion of the NCH2 and NMe2 proton signals as singlets
suggests that the inversion of the configuration at the
When [Pt(dmba)(Cl)(DMSO)] is heated with 20% aqueous
ammonia in acetone at 70 °C for 1 h in the presence of KOH,
complex 5 is obtained (Scheme 2). Complex 5 is a white
air-stable solid that decomposes on heating above 150 °C in
a dynamic N2 atmosphere. It is also stable at room temper-
ature in organic solvent solutions. The analytical data are
consistent with the proposed formula. The FAB mass
spectrum shows a peak at m/z ) 443 ([Pt(dmba)(CH2COMe)-
(NHdCMe2)]+, 18%). The NH stretching mode for complex
5 is found in the 3220 cm-1 region and the CdN vibration
at approximately 1660 cm-1. The IR spectrum shows also
(31) Ruiz, J.; Rodr´ıguez, V.; Cutillas, N.; Pardo, M.; Pe´rez, J.; Lo´pez, G.;
Chaloner, P.; Hitchcock, P. B. Organometallics 2001, 20, 1973–1982.
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Chaloner, P. A.; Hitchcock, P. B. J. Chem. Soc., Dalton Trans. 1999,
2939–2946.
(30) Natile, G.; Maresca, L.; Cattalini, L. J. C. S. Chem. Commun. 1976,
24–25.
Inorganic Chemistry, Vol. 47, No. 21, 2008 10027

Ruiz et al.
Scheme 3
one band, assignable to ν(CdO), in the region of 1630 cm-1,
which is similar to that reported for terminal acetonyl
platinum(II)33,34 and palladium(II)31,35 complexes. The sin-
1
glet signals observed in the H NMR spectrum of 5 at δ
2.59 and 1.92 are assignable to the methylene and methyl
protons of the acetonyl ligand, respectively (coupling to 195Pt
is observed for these two signals). Further, in contrast with
what happened for complexes 1 and 4, a unique singlet
resonance for the NsMe groups and a singlet resonance for
the CH2 protons of bonded C6H4CH2NMe2 are observed
(coupling to 195Pt is also observed) as a result of the free
rotation of the acetonimine ligand about the PtsN bond in
the presence of the sterically less demanding acetonyl ligand.
In accord with the structure of the related palladium complex
[Pd(dmba)(t-BuNC){CH2C(O)CH3}],31 a MeCOCH2-trans-
to-NMe2 ligand geometry for monomer 5 is proposed. Proton
NOE difference spectra confirmed this suggestion. This
structure was also confirmed by X-ray diffraction (vide infra).
Figure 1. ORTEP representation (50% probability) of 1·2Me2CO. Selected
bond lengths (Å) and angles (deg): Pt(1)-C(1) ) 2.022(2), Pt(1)-N(2) )
2.091(2), Pt(1)-N(1) ) 2.1370(19), Pt(1)-P(1) ) 2.2301(6), C(1)-Pt(1)-
N(2) ) 173.12(8), C(1)-Pt(1)-N(1) ) 82.04(8), N(2)-Pt(1)-N(1) )
91.18(7), C(1)-Pt(1)-P(1) ) 95.37(7), N(2)-Pt(1)-P(1) ) 91.49(5),
N(1)-Pt(1)-P(1) ) 174.92(5). Hydrogen bonds (Å) and angles (deg):
H(02)· · ·O(3) ) 2.21(3), N(2) · · ·O(3) ) 3.050(3), N(2)-H(02)· · ·O(3) )
177(3), H(9B) · · ·O(2) ) 2.54, C(9) · · ·O(2) ) 3.498(3), C(9)-H(9B)· · ·O(2)
164.4, C(10) · · ·O(2)#1 ) 2.53, C(10) · · · O(2)#1 ) 3.384(3), C(10)-H(10B) · · ·
O(2)#1 ) 145.4 (symmetry transformations used to generate equivalent
atoms: #1, -x + 1, -y + 1, -z + 1).
1
The H NMR spectrum of 5 exhibits also a NH proton
resonance as a broad singlet in the region of 10 ppm.
Complex cis-[Pt(C6F5)2(NHdCMe2)2]. The reaction of
cis-[NBu4]2[Pt2(C6F5)4(µ-Cl)2]36 and [Ag(NHdCMe2)2]+ in
a 1:2 molar ratio produces the neutral bis(acetonimine) com-
plex cis-[Pt(C6F5)2(NHdCMe2)2] (6) in high yield (Scheme
3). The reaction takes place without isomerization.
The IR spectrum of complex 6 shows the characteristic
absorptions of the C6F5 group (1630 m, 1490 vs, 1050 s,
and 950 vs cm-1)37 and a split band at approximately 800
cm-1 assigned to the cis-Pt(C6F5)2 moiety.38,39 The 19F NMR
spectrum of 6 shows the expected three signals for two
equivalent C6F5 rings with relative intensities of 2Fo:1Fp:
2Fm. The 1H NMR spectrum of 6 exhibits a singlet at δ 2.37
and a doublet (4JHH ) 1.4 Hz) at δ 2.12 ppm for the methyl
groups of the acetonimine ligands. Again, the signal at higher
field has greater coupling with the iminic proton (Pt satellites
are observed as shoulders for the signal at lower field).
Crystal Structures of 1 · 2Me2CO, 2, 3a, 5, and 6. All
the structures display some common features. Thus, in all
cases, the Pt atom is in a distorted square planar environment;
the mean deviations from planarity for the Pt atom and its
four immediate neighbors is e0.05 Å except for 6 (0.06 Å).
The cation of 1 · 2Me2CO is depicted in Figure 1. Coor-
dination at platinum is approximately square planar, although
the angles around platinum deviate from 90° due to the bite
of the cyclometallated ligand. The C(1)-Pt-N(1) angle of
82.04(8) is within the normal range for such dmba metal
complexes.39-45 The PPh3 ligand is trans to the nitrogen
donor, displaying no tendency to occupy the position trans
to the σ-bound orthoplatinated aryl group.46 The cyclomet-
allated ring is puckered with the nitrogen atom significantly
out of the plane defined by the platinum and carbon atoms,
a feature which is quite commonly observed in cyclomet-
allated dmba complexes.39,42-44 In the crystal, the perchlorate
anion is bridging four complex cations through N-H · · ·O
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10028 Inorganic Chemistry, Vol. 47, No. 21, 2008

Pt(II) Acetonimine and Imam Complexes
Figure 4. View of the C-H/π interactions in complex 2.
Figure 2. View of the C-H/π interactions in complex 1·2Me2CO.
Figure 5. ORTEP representation (50% probability) of 3a. Selected bond
lengths (Å) and angles (deg): Pt(1)-N(3) ) 2.002(2), Pt(1)-C(1) )
2.002(3), Pt(1)-N(1) ) 2.085(2), Pt(1)-N(2) ) 2.157(2), N(3)-Pt(1)-C(1)
) 92.83(11), N(3)-Pt(1)-N(1) ) 175.12(10), C(1)-Pt(1)-N(1) ) 82.30(11),
N(3)-Pt(1)-N(2) ) 89.86(10), C(1)-Pt(1)-N(2) ) 177.30(11), N(1)-
Pt(1)-N(2) ) 95.01(10). Hydrogen bonds (Å) and angles (deg): H(02B) · · ·
O(3) ) 2.32(3), N(2) · · ·O(3) ) 3.159(4), N(2)-H(02B)· · ·O(3) ) 153(3),
H(02A)· · ·O(1)#1 ) 2.13(3), N(2)· · ·O(1)#1 ) 3.030(4), N(2)-H(02A)· · ·
O(1)#1 ) 172(4), H(03) · · ·O(2)#2 ) 2.40(3), N(3) · · ·O(2)#2 ) 3.105(3),
N(3)-H(03)· · ·O(2)#2 ) 133(3), H(7B) · · ·O(2)#3 ) 2.56, C(7) · · ·O(2)#3
) 3.515(4), C(7)-H(7B)· · ·O(2)#3 ) 161.1, H(9A) · · ·O(3) ) 2.42,
C(9)· · ·O(3) ) 3.395(4), C(9)-H(9A)· · ·O(3) ) 171.8, H(11B) · · ·O(2)#1
) 2.47, C(11) · · ·O(2)#1 ) 3.438(4), C(11)-H(11B)· · ·O(2)#1 ) 166.2,
H(13C)· · ·O(1) ) 2.56, C(13) · · ·O(1) ) 3.480(4), C(13)-H(13C)· · ·O(1)
) 155.6 (symmetry transformations used to generate equivalent atoms: #1,
-x + 1, y - 1/2, -z + 1; #2, x, y, z + 1; #3, -x + 2, y - 1/2, -z + 1).
Figure 3. ORTEP representation (50% probability) of 2. Selected bond
lengths (Å) and angles (deg): Pt(1)-C(1) ) 1.990(3), Pt(1)-N(2) )
2.006(3), Pt(1)-N(1) ) 2.072(3), Pt(1)-N(3) ) 2.116(3), C(1)-Pt(1)-N(2)
) 92.18(12), C(1)-Pt(1)-N(1) ) 82.65(12), N(2)-Pt(1)-N(1) ) 174.73(10),
C(1)-Pt(1)-N(3) ) 174.43(11), N(2)-Pt(1)-N(3) ) 91.02(11), N(1)-
Pt(1)-N(3) ) 94.06(11). Hydrogen bonds (Å) and angles (deg): H(02) · · ·
O(3)#1 ) 2.18(4), N(2) · · ·O(3)#1 ) 3.006(4), N(2)-H(02)· · ·O(3)#1 )
171(4), H(03) · · ·O(2) ) 2.42(4), N(3) · · ·O(2) ) 3.219(4), N(3)-H(03) · · ·O(2)
) 155(4), H(11B) · · · O(4)#2 ) 2.51, C(11) · · · O(4)#2 ) 3.397(5),
C(11)-H(11B)· · ·O(4)#2 ) 150.9, H(15A)· · ·O(1) ) 2.47, C(15)· · ·O(1)
) 3.442(5), C(15)-H(15A) · · · O(1) ) 170.6 (symmetry transformations
used to generate equivalent atoms: #1, x + 1, y - 1, z; #2, -x + 1, -y +
1, -z).
through N-H · · · O and C-H · · · O bonds in which the NH,
CH3, and CH groups are involved and also π interactions
(O1· · ·C10 contact of 3.197 Å). Additionally, CH/π interac-
tions47 are observed (Figure 4).
and C-H· · ·O bonds in which the NH, CH3, and CH groups
are involved. Figure 2 shows intermolecular CH/π interac-
tions,47 the distance H35 · · ·centroid (C1C2C3C4C5C6) being
2.749 Å.
Figure 3 shows the X-ray structure of the cationic complex
of 2. The Pt-N(3) (acetonimine) distance (2.116 Å) trans
to the carbon atom is longer than the Pt-N(2) (acetonimine)
distance (2.006 Å), due to higher trans-influence of the C
atom than that of the N atom (dmba, sp3). The imino ligands
are planar, and the relative orientation of the acetonimine
ligands is head to tail (HL). Both acetonimine ligands show
CdN bond lengths (1.281(5) and 1.277(5) Å). In the crystal,
the perchlorate anion is bridging five complex cations
A drawing of the cationic complex of 3a is shown in
Figure 5. The platinum atom is located in a slightly distorted
square-planar environment, surrounded by the C and N atoms
of the cyclometallated dmba ligand and the N atoms of the
imam ligand. The six-membered PtsN(3)sC(10)sC(11)s
C(12)sN(2) chelate ring adopts a screw-boat conformation
with the C(12) and the C(11) atoms lying 0.37 Å below and
0.36 Å above the plane, respectively, of the other four atoms.
The PtsN(2) (amine) distance (2.157(2) Å) trans to the
carbon atom is longer than the PtsN(3) (imine) (2.002(2)
Å) due to higher trans influence of the C. In the crystal, the
perchlorate anion is bridging four complex cations through
N-H· · ·O and C-H· · ·O bonds in which the NH, NH2, CH3,
(47) Nishio, M. CrystEngComm 2004, 6, 130–158.
Inorganic Chemistry, Vol. 47, No. 21, 2008 10029

Ruiz et al.
Figure 6. Hydrogen bonds and C-H/π interactions for 3a.
Figure 7. ORTEP representation (50% probability) of one of the three
independent molecules of complex 5. Selected bond lengths (Å) and angles
(deg): Pt(1)-C(11) ) 1.997(5), Pt(1)-C(1) ) 2.078(5), Pt(1)-N(2) )
2.097(4),Pt(1)-N(1))2.134(4),C(11)-Pt(1)-C(1))96.5(2),C(11)-Pt(1)-
N(2) ) 174.72(17), C(1)-Pt(1)-N(2) ) 86.75(18), C(11)-Pt(1)-N(1) )
82.06(18), C(1)-Pt(1)-N(1) ) 178.02(18), N(2)-Pt(1)-N(1) ) 94.59(15).
Figure 8. Schematic showing the chain formed by hydrogen bonding in
complex 5.
Table 1. Hydrogen Bonds for Complex 5 [Å and deg]a
D-H· · ·A
d(D-H) d(H· · ·A) d(D · · ·A) <(DHA)
N(4)-H(04)· · ·O(3)
N(2)-H(02)· · ·O(2)#1
N(6)-H(06)· · ·O(1)#2
C(6)-H(6C)· · ·O(2)#1
0.90(4)
0.90(4)
0.90(4)
0.98
2.00(4)
2.08(4)
1.98(4)
2.51
2.877(5)
2.973(5)
2.873(5)
3.346(7)
165(5)
170(5)
169(5)
143.3
and CH2 groups are involved. Intermolecular CH/π interac-
tions47 are also observed (Figure 6).
The crystal structure of compound 5 shows three inde-
pendent molecules in the asymmetric unit. The structure of
the first molecule of the unit cell is shown in Figure 7.
Coordination at platinum is approximately square planar,
although the angles around platinum deviate from 90° due
to the bite of the cyclometallated ligand. The C(1)-Pt-N(1)
angle of 82.06(18) is within the normal range for such dmba
metal complexes.39-44 A MeCOCH2-trans-to-NMe2 ligand
geometry for monomer 5 is observed, displaying the acetonyl
group (which has a strong trans influence) no tendency to
occupy the position trans to the σ-bound orthoplatinated aryl
group.46 The imino ligand is planar and rotated with respect
to the coordination plane by approximately 84.7°. The CdN
bond distance [1.277(6) Å] is in the range found for the other
a Symmetry transformations used to generate equivalent atoms: #1, x -
1/2, -y + 1/2, z + 1/2; #2, -x + 1, -y + 1, -z + 1.
structurally characterized acetonimine complexes (1.25-1.30
Å).25 The length of the carbon-oxygen double bond
[1.242(6) Å] is longer than that found in other palladium-
or platinum-enolate complexes.31,33,35 The enolate ligand
is nearly perpendicular to the mean coordination plane
(dihedral angle 78.91°). As can be seen in Figure 8 and Table
1 in the crystal the NH hydrogen atoms of the acetonimine
and the O atom of the acetonyl group are involved in
intermolecular N-H· · ·O hydrogen bonds leading to hydro-
gen-bonded zigzag chains.
10030 Inorganic Chemistry, Vol. 47, No. 21, 2008

Pt(II) Acetonimine and Imam Complexes
Figure 9. View of the C-H/π interactions in complex 5.
Figure 11. ORTEP representation (50% probability) of one of the two
independent molecules of 6. Selected bond lengths (Å) and angles (deg):
Pt(1)-C(21) ) 2.006(2), Pt(1)-C(11) ) 2.008(2), Pt(1)-N(1) ) 2.0673(19),
Pt(1)-N(2))2.0747(19),C(21)-Pt(1)-C(11))89.37(9),C(21)-Pt(1)-N(1)
) 178.07(8), C(11)-Pt(1)-N(1) ) 89.72(8), C(21)-Pt(1)-N(2) ) 92.23(8),
C(11)-Pt(1)-N(2) ) 173.49(8), N(1)-Pt(1)-N(2) ) 88.87(7).
Table 2. Hydrogen Bonds for Complex 6 (Å and deg)a
D-H· · ·A
d(D-H) d(H· · ·A) d(D· · ·A) <(DHA)
C(36)-H(36A)· · ·F(46)#1 0.98
2.48
3.279(3)
3.055(2)
3.241(2)
3.331(3)
2.871(2)
138.7
N(4)-H(04)· · ·F(56)#1
N(3)-H(03)· · ·F(16)#2
C(5)-H(5A)· · ·F(12)#3
N(1)-H(01)· · ·F(22)#3
0.89(3)
2.40(3)
2.47(3)
2.40
131(2)
162(3)
159.3
0.80(3)
0.98
0.81(3)
2.29(3)
129(3)
a Symmetry transformations used to generate equivalent atoms: #1, -x
+ 1, -y + 1, -z + 1; #2, -x + 1/2, y + 1/2, -z + 1/2; #3, -x, -y, -z
+ 1.
In the crystal, a rather complex three-dimensional mac-
romolecular network structure is observed built up by
extensive hydrogen bonding, which involves the NH groups
or the C-H51-56 of the acetimino ligands and the ortho- or
para-fluorine atoms of the pentafluorophenyl rings neighbor-
ing molecules (Table 2). There is also a intermolecular
contact F15 · · · F55 (Figure 12). The influence of these
fluorine-based interactions seems to be a relevant, non-
casual phenomenon to be taken into account in crystal
engineering.44,52,56 F15 is also involved in intermolecular
C-F · · · πF interactions (F15 · · · C55, 2.982 Å; F15 · · · C56,
3.156 Å, Figure 12).44,52,56 Other intermolecular interac-
tion contact observed is of the type C-F · · · πacetonimine
(F23 · · · C4, 3.157 Å).
Figure 10. View of the C-H· · ·Pt interaction in complex 5.
On the other hand, H46C of the acetonimine ligand of
molecule 3 is close to the platinum atom of molecule 2, with
a Pt(2)· · ·H(46C) distance of 2.839 Å and a Pt(2) · · ·H(46C)-
C(46) angle of 162.3°, which indicates the presence of
an anagostic C-H · · · Pt interaction is observed (Figure
9).48,49 Intermolecular CH/π interactions47 are also ob-
served (Figure 10).
The crystal structure of compound 6 shows two indepen-
dent molecules in the asymmetric unit with the platinum
atoms in slightly distorted square planar geometries. In the
first molecule (Figure 11) the angle between the two C6F5
rings is 89.37(9)°, and the imino ligands are planar and
mutually perpendicular (86.34(1)°). The relative orientation
of the acetonimine ligands is head to head (HH), contrary
to that observed for complex 2. The CdN bond distances
[1.274(3) and 1.277(3) Å] are in the range found for the other
structurally characterized acetonimine complexes (1.25-1.30
Å).25 The PtsN distances (2.0647-2.074 Å) lie within the
range reported in complexes containing the {Pt(C6F5)2N2}
moiety such as [Pt(C6F5)2(pz· · ·H· · ·pz] (pz ) pyrazolate)50
and cis-[Pt(C6F5)2(HmtpO)2] (HmtpO ) 4,7-dihydro-5-me-
thyl-7-oxo[1,2,4]triazolo[1,5-a]pyrimidine).44
Biological Assays. Circular Dichroism Spectroscopy.
The circular dichroism (CD) spectra of calf thymus DNA
alone and incubated with the acetonimine platinum(II)
compounds 1, 4, and 5 at 37 °C for 24 h at several molar
ratios were recorded.
(50) Lo´pez, G.; Ruiz, J.; Vicente, C.; Mart´ı, J. M.; Garc´ıa, G.; Chaloner,
P. A.; Hitchcock, P. B.; Harrison, R. M. Organometallics 1992, 11,
4090–4096.
(51) Althoff, G.; Ruiz, J.; Rodr´ıguez, V.; Lo´pez, G.; Pe´rez, J.; Janiak, C.
CrystEngComm 2006, 8, 662–665.
(52) Vangala, V. R.; Nangia, A.; Lynch, V. M. Chem. Commun. 2002,
1304–1305.
(53) Babudri, F.; Farinola, G. M.; Naso, F.; Ragni, R. Chem. Commun.
2007, 1003–1022.
(54) Kasai, K.; Fujita, M. Chem. Eur. J. 2007, 13, 3089–3105.
(55) Ruiz, J.; Villa, M. D.; Rodr´ıguez, V.; Cutillas, N.; Vicente, C.; Lo´pez,
G.; Bautista, D. Inorg. Chem. 2007, 46, 5448–5449.
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104, 6908–6914.
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Organometallics 1997, 16, 1846–1856.
Inorganic Chemistry, Vol. 47, No. 21, 2008 10031

Ruiz et al.
pattern has been found previously in some others dmba
phosphine platinum complexes.39,44 On the other hand,
complexes 4 and 5 (lanes 3 and 4, respectively) delayed the
mobility of the ccc form.
The behavior observed for the electrophoretic mobility for
the platinum complexes indicates that some conformational
changes occurred. This means that the degree of superhelicity
of the DNA molecules has been altered.
Cytotoxicity Studies. Values of IC50 were evaluated for
complexes 1, 4, and 5 and cisplatin against a panel of human
tumor cell lines representative of ovarian (A2780 and
A2780cisR) and breast cancers (T47D, cisplatin resistant).
A2780cisR encompasses all of the known major mechanisms
of resistance to cisplatin: reduced drug transport,62 enhanced
DNA repair/tolerance,63 and elevated GSH levels.64 Table
3 shows the IC50 values and the resistance factors (RF) of
the new platinum complexes. The ability of complexes 1, 4,
and 5 to circumvent cisplatin acquired resistance was
determined from the resistance factor (RF), defined as the
ratio of IC50 resistant line to IC50 parent line. An RF of <2
was considered to denote noncross-resistance.65 Especially
noteworthy are the very low resistance factors (RF) of these
new complexes at 48 h (RF ) 1.2-1.4) indicating efficient
circumvention of cisplatin resistance (Table 3).
On the other hand, at 48 h incubation time complexes 1,
4, and 5 were more active than cisplatin in T47D (up to 30-
fold in the case of complex 1).
Complexes 3b and 6 show no good response against these
lines, probably because the formation of a PtsN7 covalent
bond with a guanine base is more difficult for these com-
plexes, as the bidentate ligand (for 3b) or the two acet-
onimine ligands (for 6) occupy two sites of binding in the
coordination sphere of platinum(II).
Figure 12. Intermolecular F· · ·F and C-F· · ·πF interactions in 6.
The changes in ellipticity and wavelength caused by the
new platinum(II) compounds 1 and 4 are significant (Figure
13). Complex 1 reduces the ellipticity of the positive and
negative band with increasing values of ri. An upshift in the
λmax (batochromic effect) is also observed. These results
suggest modifications in the secondary structure of DNA
caused by complexes 1 and 4, clearly indicating the trans-
formation from the DNA B form to the DNA C form, with
increasing winding of the DNA helix by rotation of the
bases.57-60
Experimental Section
Gel Electrophoresis of Compound-pBR322 Complexes.
The influence of the compounds on the tertiary structure of
DNA was determined by their ability to modify the elec-
trophoretic mobility of the covalently closed circular (ccc)
and open (oc) forms of pBR322 plasmid DNA. The com-
plexes 1, 4, and 5 were incubated at the molar ratio ri )
0.50 with pBR322 plasmid DNA at 37 °C for 24 h.
Representative gel obtained for the Pt complexes 1, 4, and
5 are shown in Figure 14. The behavior of the gel electro-
phoretic mobility of both forms, ccc and oc, of pBR322
plasmid and DNA:cisplatin adducts is consistent with previ-
ous reports.61 When the pBR322 was incubated with the
platinum compound 1 (lane 2) a single footprinting for both
forms, ccc and oc, coalescent form, was observed. A similar
Instrumental Measurements. The C, H, and N analyses were
performed with a Carlo Erba model EA 1108 microanalyzer.
Decomposition temperatures were determined with a SDT 2960
simultaneous DSC-TGA of TA instrument at a heating rate of 5
°C min-1 and the solid samples under nitrogen flow (100 mL
min-1). The 1H, 13C, 31P, 19F, and 195Pt NMR spectra were recorded
on a Bruker AC 200E, Bruker AC 300E, or Bruker AV 400
spectrometer, using SiMe4, H3PO4, CFCl3, and Na2[PtCl6] as
standards. Infrared spectra were recorded on a Perkin-Elmer 1430
spectrophotometer using Nujol mulls between polyethylene sheets.
Mass spectra (positive-ion FAB) were recorded on a V.G. Au-
toSpecE spectrometer and measured using 3-nitrobenzyl alcohol
as the dispersing matrix.
Materials. The starting complexes [Bu4N]2[Pt2(C6F5)4(µ-Cl)2],36
[Pt(dmba)Cl(L)] (L ) PPh3 and DMSO),26 and [Ag(NHdCMe2)]-
(56) Reichenbacher, K.; Suss, H. I.; Hulliger, J. Chem. Soc. ReV. 2005,
34, 22–30.
(57) Macquet, J. P.; Butour, J. L. Biochimie 1978, 60, 901–914.
(58) Brabec, V.; Kleinwa¨chter, V.; Butour, J.; Johnson, M. P. Biophys.
Chem. 1990, 35, 129–141.
(62) Loh, S. Y.; Mistry, P.; Kelland, L. R.; Abel, G.; Harrap, K. R. Br. J.
Cancer 1992, 66, 1109–1115.
(63) Goddard, P. M.; Orr, R. M.; Valenti, M. R.; Barnard, C. F.; Murrer,
B. A.; Kelland, L. R.; Harrap, K. R. Anticancer Res. 1996, 16, 33–
38.
(59) Cervantes, G.; Prieto, M. J.; Moreno, V. Metal Based Drugs 1997, 4,
9.
(60) Cervantes, G.; Marchal, S.; Prieto, M. J.; Pe´rez, J. M.; Gonza´lez, V. M.;
Alonso, C.; Moreno, V. J. Inorg. Biochem. 1999, 77, 197–203.
(61) Ushay, H. M.; Tullius, T. D.; Lippard, S. J. Biochemistry 1981, 20,
3744–3748.
(64) Behrens, B. C.; Hamilton, T. C.; Masuda, H.; Grotzinger, K. R.;
Whang-Peng, J.; Louie, K. G.; Knutsen, T.; McKoy, W. M.; Young,
R. C.; Ozols, R. F. Cancer Res. 1987, 47, 414–418.
(65) Kelland, L. R.; Barnard, C. F. J.; Mellish, K. J.; Jones, M.; Goddard,
P. M.; Valenti, M.; Bryant, A.; Murrer, B. A.; Harrap, K. R. Cancer
Res. 1994, 54, 5618–5622.
10032 Inorganic Chemistry, Vol. 47, No. 21, 2008

Pt(II) Acetonimine and Imam Complexes
Figure 13. Circular dichroism spectra of DNA and DNA incubated with complex 1, complex 4, and complex 5 at different ri.
(dd, 1H, aromatic of dmba, JHH ) 7.5 Hz, JHH ) 0.6 Hz), 6.83
(vtd, 1H, aromatic of dmba, JHH ) 7.5 Hz, JHH ) 1.2 Hz), 6.47
(dd, 1H, aromatic of dmba, JHH ) 7.5 Hz, JHP ) 2.7 Hz, JHPt ) 43
Hz), 6.32 (vtd, 1H, aromatic of dmba, JHH ) 7.5 Hz, JHH ) 1.2
Hz), 4.29 (dd, 1H, CH2N, JHH ) 13.5 Hz, JHP ) 2.4 Hz), 4.21 (dd,
1H, CH2N, JHH ) 13.5 Hz, JHP ) 3.43 Hz), 2.92 (d, 3H, NMe2,
JHP ) 2.7 Hz, JHPt ) 12 Hz), 2.89 (d, 3H, NMe2, JHP ) 3.0 Hz, Pt
satellites are observed as shoulders), 2.18 (s, 3H, CMe2, trans-CH3
to NH, Pt satellites are observed as shoulders), 1.70 (d, 3H, CMe2,
cis-CH3 to NH, JHH ) 1.2 Hz). 13C{1H} (acetone-d6): δ(SiMe4)
187.2 (CdN), 149.6 (s, aromatic C of dmba), 139.2 (d, aromatic
Figure 14. Modification of the gel electrophoretic mobility of pBR322
plasmid incubated with the new platinum compounds: lane 1, pBR; lane 2,
1; lane 3, 4; lane 4, 5; lane 5, pBR-cisplatin.
CH of dmba, JCP ) 6.5 Hz), 137.0 (d, aromatic C of dmba, JCP
)
Table 3. IC50 (µM) and resistance factors for Cisplatin and Complexes
1, 4, and 5
7.2 Hz), 135.9 (d, ortho-C PPh3, JCP ) 11.2 Hz), 132.4 (d, para-C
PPh3, JCP ) 2.6 Hz), 130.1 (d, ipso-C PPh3, JCP ) 61.3 Hz), 129.5
(d, meta-C PPh3, JCP ) 11.1 Hz), 125.7 (d, aromatic CH dmba,
JCP ) 2.5 Hz), 125.0 (aromatic CH dmba), 122.7 (aromatic CH
dmba), 73.9 (CH2NMe2), 51.5 (NMe2), 28.4 (HNdCMe2), 27.9
(HNdCMe2). 31P NMR (acetone-d6): δ(H3PO4) 21.3 (s, JPtP ) 4100
Hz). 195Pt NMR (acetone-d6): δ(Na2[PtCl6]) -4063 (d, JPt-P ) 4100
Hz). Positive-ion FAB mass spectrum: m/z 648 ([Pt(dmba)(PPh3)-
(HNdCMe2)]+, 24%).
T47D
48 h
A2780
48 h
A2780cisR
complex
48 h (RF)a
1
4
5
1.2
3.1
14
0.85
0.77
1.7
1.2 (1.4)
1.0 (1.3)
2.0 (1.2)
1.1 (12.9)
cisplatin
37
0.85
a The numbers in parentheses are the resistance factors RF (IC50 resistant/
IC50 sensitive).
ClO418 were prepared by procedures described elsewhere. Solvents
were dried by the usual methods. The sodium salt of calf thymus
DNA, EDTA (ethylenediaminotetracetic acid), and Tris-HCl (tr-
is(hydroxymethyl)-aminomethane-hydrochloride) used in the cir-
cular dichroism (CD) study were obtained from Sigma-Aldrich
(Madrid, Spain); HEPES (N-(2-hydroxyethyl)piperazine-N′-ethane-
sulfonic acid) was obtained from ICN (Madrid, Spain), and pBR322
plasmid DNA was obtained from Boehringer-Mannheim (Man-
nheim, Germany).
Warning! Perchlorate salts of metal complexes with organic
ligands are potentially explosiVe. Only small amounts of material
should be prepared, and these should be handled with great caution.
Preparation of Complex [Pt(dmba)(NHdCMe2)(PPh3)](ClO4)
(1). AgClO4 (49.8 mg, 0.24 mmol) was added to an acetone (20
mL) solution of [Pt(dmba)(Cl)(PPh3)] (150 mg, 0.24 mmol). After
the resulting suspension was stirred at room temperature in the
darkness for 30 min, it was filtered through Celite, and NH3 (443
µL of 20% aqueous NH3, 4.8 mmol) was added. The solution was
stirred at room temperature for 4 h, and the solvent was evaporated
to dryness. The residue was treated with acetone and ether to give
a white precipitate that was filtered off and air-dried.
Reaction of [Pt(dmba)(Cl)(DMSO)] with AgClO4 and NH3
in Acetone. AgClO4 (70.5 mg, 0.34 mmol) was added to an acetone
(20 mL) solution of [Pt(dmba)(Cl)(DMSO)] (150 mg, 0.34 mmol).
After the resulting suspension was stirred at room temperature in
the darkness for 30 min, it was filtered through Celite, and NH3
(628 µL of 20% aqueous NH3, 6.8 mmol) was added. The solution
was stirred at room temperature for 4 h, and the solvent was
evaporated to dryness. The residue was treated with acetone and
ether to give a white precipitate that was filtered off and air-dried.
A mixture of complexes [Pt(dmba)(NHdCMe2)2]ClO4 (2) and
[Pt(dmba){NHC-(Me)CH2C(Me2)NH2}]ClO4 (3a) was obtained in
a 5:2 ratio.
1
Data for Complex 2. H NMR (acetone-d6): δ(SiMe4) 10.34
(br, 1H, NH), 10.12 (br, 1H, NH), 7.10-6.72 (m, 4H, aromatics of
dmba), 4.03 (s, 2H, CH2, JPtH ) 41.7 Hz), 2.84 (s, 6H, NMe2, JPtH
) 35.7 Hz), 2.48 (d, 3H, CMe, trans-CH3 to NH, JHH ) 0.6 Hz, Pt
satellites are observed as shoulders), 2.38 (d, 3H, CMe, trans-CH3
to NH, JHH ) 0.9 Hz, Pt satellites are observed as shoulders), 2.34
(d, 3H, CMe, cis-CH3 to NH, JHH ) 1.5 Hz), 2.25 (d, 3H, CMe,
cis-CH3 to NH, JHH ) 1.5 Hz).
1
Data for Complex 3a. H NMR (acetone-d6): δ(SiMe4) 10.17
(br, 1H, NH), 7.13-6.95 (m, 4H, aromatics of dmba), 4.52 (br s,
2H, NH2, Pt satellites are observed as shoulders), 4.05 (s, 2H, CH2N,
JPtH ) 42 Hz), 2.90 (s, 6H, NMe2, JPtH ) 34.8 Hz), 2.71 (s, 2H,
CCH2 of imam ligand, Pt satellites are observed as shoulders), 2.42
(d, 3H, CMe, JHH ) 1.5 Hz), 1.47 (s, 6H, CMe2).
Data for Complex 1. Yield: 99 mg, 83%. Anal. Calcd for
C30H34ClN2O4PPt: C, 48.17; H, 4.58; N, 3.74. Found: C, 47.92; H,
4.71; N, 3.75. Mp: 254 °C (dec). ΛM: 130 S cm2 mol-1. IR (Nujol,
cm-1): ν(NH) 3236, ν(CdN) 1660. 1H NMR (acetone-d6): δ(SiMe4)
9.92 (br, 1H, NH), 7.76 (m, 6H, PPh3), 7.51 (m, 9H, PPh3), 7.10
Inorganic Chemistry, Vol. 47, No. 21, 2008 10033

Ruiz et al.
Table 4. Crystal Structure Determination Details
parameter
1·2Me2CO
2
3a
5
6
empirical formula
fw
cryst system
a (Å)
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
C36H46ClN2O6PPt
864.26
triclinic
C15H26ClN3O4Pt
542.93
triclinic
C15H26ClN3O4Pt
542.93
monoclinic
9.3719(4)
10.3163(4)
9.6044(4)
90
93.592(2)
90
926.76(7)
100(2)
P21
C15H24N2OPt
443.45
monoclinic
14.0193(6)
26.1617(11)
14.2020(6)
90
112.707(2)
90
4805.1(4)
100(2)
P21/n
12
8.755
52064
9824
0.0301
0.0298
0.0702
2
C18H14F10N2Pt
643.40
monoclinic
9.2445(4)
20.1630(11)
20.8673(10)
90
91.291(2)
90
3888.6(3)
100(2)
P21/n
9.5629(4)
12.3783(5)
16.8813(7)
70.351(2)
77.702(2)
85.013(2)
1838.48(13)
100(2)
9.0918(3)
9.5904(4)
12.4696(5)
80.297(2)
72.744(2)
65.489(2)
943.47(6)
100(2)
temp (K)
space group
Z
j
P1
2
j
P1
2
2
8
µ (mm-1
)
3.978
21245
8230
0.0178
0.0199
0.0480
7.601
10276
3820
0.0156
0.0195
0.0487
2
7.738
9674
3703
0.0156
0.0120
0.0291
7.318
44273
8995
0.0188
0.0161
0.0386
reflns collected
independent reflns
R(int)
R1 [I > 2σ(I)]a
wR2 (all data)b
a R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) [∑[w(Fo2 - Fc )2]/∑w(Fo )2]0.5
.
w ) 1/[σ2(Fo ) + (aP)2 + bP], where P ) (2Fc2 + Fo )/3 and a and b are constants
b
2
2
set by the program.
Preparation of Complex [Pt(dmba){NHC(Me)CH2C(Me2)NH2}]-
Cl (3b). To a solution of [Pt(dmba)(Cl)(DMSO)] (150 mg, 0.34
mmol) in acetone (20 mL) was added 20% aqueous NH3 (157 µL,
1.69 mmol). The resulting suspension was stirred at room temper-
ature for 24 h. Then, a white solid was collected by filtration and
air-dried.
Data for Complex 3b. Yield: 85 mg, 52%. Anal. Calcd for
C15H26ClN3Pt: C, 37.62; H, 5.47; N, 8.77. Found: C, 37.41; H, 5.35;
N, 8.79. Mp: 254 °C (dec). IR (Nujol, cm-1): ν(NH) 3277, 3159,
ν(CdN) 1650. 1H NMR (D2O): δ(SiMe4) 7.10-6.81 (m, 4H,
aromatics of dmba), 3.91 (s, 2H, CH2N, JPtH ) 40.2 Hz), 2.78 (s,
6H, NMe2, JPtH ) 34.5 Hz), 2.45 (s, 2H, CCH2 of imam ligand),
2.11 (s, 3H, CMe), 1.24 (s, 6H, CMe2). 13C{1H} (D2O): δ(SiMe4)
184.4 (CdN), 149.2, 136.4 (aromatic C of dmba), 130.8, 125.0,
124.6, 121.8 (aromatics CH of dmba), 75.0 (CH2N), 51.8 (NMe2),
49.9 (NCMe2), 47.3 (CH2C), 29.6 (CMe), 26.3 (CMe2). 195Pt NMR
(D2O): δ(Na2[PtCl6]) -3282 (s). Positive-ion FAB mass spectrum:
m/z 443 ([Pt(dmba)(imam)]+, 67%).
NMR (DMSO-d6): δ(Na2[PtCl6]) -3705 (s). Positive-ion FAB mass
spectrum: m/z 464 ([Pt(dmba)(DMSO)(HNdCMe2)]+, 100%).
Preparation of Complex [Pt(dmba)(NHdCMe2){CH2C(O)CH3}]
(5). To a solution of [Pt(dmba)(Cl)(DMSO)] (150 mg, 0.34 mmol)
in acetone (20 mL) was added 20% aqueous NH3 (157 µL, 1.69
mmol). The resulting suspension was stirred at room temperature
for 1 h, and a solution of KOH (99 mg, 1.77 mmol) in MeOH (10
mL) was then added. The resulting mixture was stirred at 70 °C
for 1 h, and the yellow solution obtained was concentrated to
dryness. The residue was then treated with 1:4 Et2O-hexane and
the suspension was filtered off to separate the pale yellow solid 5,
which was washed with hexane and air-dried.
Data for Complex 5. Yield: 80 mg, 53%. Anal. Calcd for
C15H24N2OPt: C, 40.63; H, 5.45; N, 6.32. Found: C, 40.55; H, 5.31;
N, 6.29. Mp: 156 °C (dec). IR (Nujol, cm-1): ν(NH) 3224, ν(CdN)
1662, ν(CdO) 1634. 1H NMR (acetone-d6): δ(SiMe4) 9.80 (br, 1H,
NH), 7.46 (dd, 1H, aromatic of dmba, JHH ) 7.4 Hz, JHH ) 1.2
Hz, JPtH ) 46.4 Hz), 6.93-6.80 (m, 3H, aromatics of dmba), 3.76
(s, 2H, CH2N, JPtH ) 25.8 Hz), 2.69 (s, 6H, NMe2, JPtH ) 22.8
Hz), 2.59 (s, 2H, CH2CO, JPtH ) 120 Hz), 2.37 (s, 3H, CMe2, trans-
Me to NH, Pt satellites are observed as shoulders), 2.18 (d, 3H,
Preparation of Complex [Pt(dmba)(NHdCMe2)(DMSO)](ClO4)
(4). To a solution of [Pt(dmba)(Cl)(DMSO)] (150 mg, 0.34 mmol)
in CH2Cl2 (20 mL) was added [Ag(NHdCMe2)2]ClO4 (108.8 mg,
0.34 mmol). AgCl immediately formed. The resulting suspension
was stirred for 1 h and then filtered through Celite. The filtrate
was then evaporated to dryness. The residue was treated with Et2O
to yield a white solid, which was filtered, washed with Et2O, and
air-dried.
CMe2, cis-Me to NH, JHH ) 1.5 Hz), 1.92 (s, 3H, COCH3, JPtH
)
18 Hz). 13C{1H} (acetone-d6): δ(SiMe4) 181.7 (C)N), 150.4, 142.4
(aromatic C of dmba), 134.5, 125.3, 122.4, 121.8 (aromatics CH
of dmba), 73.7 (CH2N), 51.3 (NMe2), 30.6-29.0 (CH3CO and
HNdCMe2, overlapped with acetone-d6 signals), 26.6 (HNdCMe2),
19.6 (CH2CO). 195Pt NMR (acetone-d6): δ(Na2[PtCl6]) -3455 (s).
Positive-ion FAB mass spectrum: m/z 443 [Pt(dmba)(NHdCMe2)-
{CH2C(O)CH3}]+, 18%).
Data for Complex 4. Yield: 162 mg, 85%. Anal. Calcd for
C14H25ClN2O5PtS: C, 29.82; H, 4.47; N, 4.97; S, 5.68. Found: C,
30.10; H, 4.73; N, 4.94; S, 5.44. Mp: 200 °C (dec). ΛM: 135 S cm2
Preparation of Complex cis-[(C6F5)2Pt(NHdCMe2)2] (6). [Ag-
(NHdCMe2)2]ClO4 (80 mg, 0.248 mmol) was added to a solution
of [Bu4N]2[(C6F5)4Pt2(µ-Cl)2] (200 mg, 0.124 mmol) in CH2Cl2 (20
mL). The resulting suspension was stirred for 30 min and filtered
though Celite. The resulting solution was evaporated to dryness,
and then Et2O (30 mL) was added and filtered through florisil
to remove the insoluble [Bu4N]ClO4. The clear solution was
concentrated (1 mL) and the addition of hexane caused the
precipitation of a white solid which was collected by filtration
and air-dried.
1
mol-1. IR (Nujol, cm-1): ν(NH) 3258, ν(CdN) 1664. H NMR
(CDCl3): δ(SiMe4) 10.35 (br, 1H, NH), 7.70 (d, 1H, aromatics of
dmba, JHH ) 6.3 Hz), 7.11 (m, 3H, aromatics of dmba), 4.56 (d,
1H, CH2N, JHH ) 13.2 Hz), 3.62 (d, 1H, CH2N JHH ) 13.2 Hz),
3.46 (s, 3H, Me of DMSO, JHPt ) 35.7 Hz), 3.13 (s, 3H, Me of
DMSO, Pt satellites are observed as shoulders), 2.86 (s, 3H, NMe2,
JHPt ) 31.5 Hz), 2.64 (s, 3H, NMe2, JHPt ) 39.0 Hz), 2.60 (s, 3H,
CMe2, trans-CH3 to NH), 2.38 (d, 3H, CMe2, JHH ) 1.5 Hz, cis-
CH3 to NH). 13C{1H} (DMSO-d6): δ(SiMe4) 188.9 (CdN), 148.0,
137.6 (aromatics C of dmba), 134.4, 125.6, 125.1, 122.0 (aromatics
CH of dmba), 73.6 (CH2NMe2), 51.7 (NMe2), 51.2 (NMe2), 44.6
(DMSO), 45.5 (DMSO), 28.6 (HNdCMe2), 27.7 (HNdCMe2). 195Pt
Data for Complex 6. Yield: 130 mg, 81%. Anal. Calcd for
C18H14 F10N2Pt: C, 33.60; H, 2.19; N, 4.35. Found: C, 33.61; H,
2.19; N, 4.30. Mp: 252 °C (dec). IR (Nujol, cm-1): ν(NH) 3306,
10034 Inorganic Chemistry, Vol. 47, No. 21, 2008

Pt(II) Acetonimine and Imam Complexes
ν(CdN) 1662, ν(Pt-C6F5) 806, 796. 1H NMR (CDCl3): δ(SiMe4)
8.77 (br, 2H, NH), 2.37 (s, 6H, CMe2, trans-CH3 to NH, Pt satellites
are observed as shoulders), 2.12 (d, 6H, CMe2, cis-CH3 to NH,
a density of 5 × 103 cells/well with 100 µL of medium and
were then incubated for 48 h. After attachment to the culture
surface the cells were incubated with various concentrations of
the compounds tested freshly dissolved in DMSO and diluted
in the culture medium (DMSO final concentration 1%) for 48 h
at 37 °C. The cells were fixed by adding 10 µL of 11%
glutaraldehyde. The plates were stirred for 15 min at room
temperature and then washed three to four times with distilled
water. The cells were stained with 100 µL of 1% crystal violet.
The plate was stirred for 15 min and then washed three to four
times with distilled water and dried. One hundred microliters
of 10% acetic acid were added, and it was stirred for 15 min at
room temperature. Absorbance was measured at 595 nm in a
Tecan Ultra Evolution spectrophotometer.
JHH ) 1.4 Hz). 19F (CDCl3): δ(CFCl3) -120.6 (m, 4Fo, JPtFo
)
470.7 Hz), -162.9 (t, 2Fp, Jmp ) 20.7 Hz), -164.9 (m, 4Fm).
13C{1H} (CDCl3): δ(SiMe4) 184.5 (C)N), 29.8 (Me, JCPt ) 24.7
Hz), 26.6 (Me, JCPt ) 48.4 Hz). 195Pt NMR (CDCl3): δ(Na2[PtCl6])
-3540 (vt, JPtF ) 465.4 Hz). Positive-ion FAB mass spectrum:
m/z 643 (M)+ 5%.
X-ray Crystal Structure Analysis. Suitable crystals from
1·2Me2CO and 5 were grown from acetone. Crystals of 2 and 3a
were grown from dichloromethane/hexane. Crystals of 6 were
grown from dichloromethane/toluene/hexane. The crystal and
molecular structures of the compounds 1·2Me2CO, 2, 3a, 5, and 6
have been determined by X-ray diffraction studies (Table 4).
Compounds 1·2Me2CO, 2, 3a, 5, and 6 were measured on a
Bruker Smart Apex diffractometer. Data were collected using
monochromated Mo KR radiation in ω scan mode. Absorption
corrections were applied on the basis of multiscans (Program
SADABS66). All structures were solved by direct methods using
SHELX-9767 and refined anisotropically on F2. The NH2 hydrogens
were refined freely with SADI, the NH hydrogens were refined
freely, the ordered methyl groups were refined using rigid groups
(AFIX 137), and the other hydrogens were refined using a riding
model.
The effects of complexes were expressed as corrected pertentage
inhibition values according to the following equation,
% inhibition ) [1 - (T/C)] × 100
(1)
where T is the mean absorbance of the treated cells and C the mean
absorbance in the controls.
The inhibitory potential of compounds was measured by cal-
culating concentration-percentage inhibition curves, and these curves
were adjusted to the following equation:
E ) Emax/[1 + (IC50)/C)n]
(2)
Special Features. For the compound 1·2Me2CO: One of acetone
molecules is well resolved, but the other is disordered over two
sites with occupation 53:47.
were E is the percentage inhibition observed, Emax is the maximal
effects, IC50 is the concentration that inhibits 50% of maximal
growth, C is the concentration of compounds tested, and n is the
slope of the semilogarithmic dose-response sigmoid curves. This
nonlinear fitting was performed using GraphPad Prism 2.01, 1996
software (GraphPad Software Inc.).
For comparison purposes, the cytotoxicity of cisplatin was
evaluated under the same experimental conditions. All compounds
were tested in two independent studies with triplicate points. The
in vitro studies were performed in the USEF platform of the
University of Santiago de Compostela (Spain).
For the compound 3a: The Flack parameter refined to 0.038(5).
Biological Assays. Circular Dichroism Study. Spectra were
recorded at room temperature on an Applied Photophysics Π*-
180 spectrometer with a 75 W xenon lamp using a computer
for spectral substraction and smooth reduction. The platinum
samples (ri ) 0.1, 0.3, 0.5) were prepared by addition of aliquots
of each compound, from stock solutions (1 mg/mL, 2% in
DMSO), to a solution of calf thymus DNA (Sigma) in TE buffer
(20 µg/mL), and incubated for 24 h at 37 °C. As a blank, a
solution of each compound in TE buffer (50 mM NaCl, 10 mM
Tris-HCl, 0.1 mM EDTA, pH 7.4) was used. Each sample was
scanned twice in a range of wavelengths between 220 and 330
nm. The drawn CD spectra are the means of two independent
scans. The ellipticity values are given in millidegrees (mdeg).
Electrophoretic Mobility Study. pBR322 plasmid DNA of 0.25
µg/µL concentration was used for the experiments. Four microliters
of charge maker were added to aliquot parts of 20 µL of the
complex: DNA compound containing 0.7 µg of DNA previously
incubated at 37 °C for 24 h. The mixtures underwent electrophoresis
in agarose gel 1% in 1 × TBE buffer (45 mM Tris-borate, 1 mM
EDTA, pH 8.0) for 5 h at 30 V. Gel was subsequently stained in
the same buffer containing ethidium bromide (1 µg/mL) for 20 min.
The DNA bands were visualized with a Typhoon 9410 Variable
Mode Imager (Amersham Biosciences).
Conclusions
This is the first report of the synthesis of imam com-
plexes of platinum. The first organometallic acetonimine
platinum complexes have also been prepared. Strong
supramolecular interactions are present in all the struc-
tures. Complex cis-[Pt(C6F5)2(NHdCMe)2] (6) exhibits a
head to head orientation of the acetonimine moieties,
whereas the relative orientation of the acetonimine ligands
in [Pt(dmba)(NHdCMe2)2]ClO4 (2) is head to tail (HL).
Values of IC50 were calculated for the complexes 1, 4,
and 5 against the human tumor cell lines A2780,
A2780cisR and T47D. At 48 h incubation time complex
1 was about 30-fold more active than cisplatin in T47D.
Complexes 1, 4, and 5 show very low resistance factors
against a A2780 cell line which has acquired resistance
to cisplatin. Circular dichroism and electrophoretic mobil-
ity indicate interaction of the new platinum complexes
with DNA.
Cell Line and Culture. The T-47D human mammary adeno-
carcinoma cell line used in this study was grown in RPMI-1640
medium supplemented with 10% (v/v) fetal bovine serum (FBS)
and 0.2 unit/mL bovine insulin in an atmosphere of 5% CO2 at 37
°C. The human ovarian carcinoma cell lines (A2780 and
A2780cisR) used in this study were grown in RPMI 1640 medium
supplemented with 10% (v/v) fetal bovine serum (FBS) and 2 mM
L-glutamine in an atmosphere of 5% CO2 at 37 °C.
Acknowledgment. This work was supported by the
Direccio´n General de Investigacio´n del Ministerio de Ciencia
y Tecnolog´ıa (Project No. CTQ2005-09231-C02-01/BQU),
Cytotoxicity Assay. Cell proliferation was evaluated by assay
of crystal violet. T-47D cells plated in 96-well sterile plates at
Inorganic Chemistry, Vol. 47, No. 21, 2008 10035

Ruiz et al.
Supporting Information Available: X-ray crystallography data
in CIF format for complexes 1·2acetone, 2, 3a, 5, and 6. This material
is available free of charge via the Internet at http://pubs.acs.org.
Spain, and the Fundacio´n Se´neca de la Comunidad Au-
to´noma de la Regio´n de Murcia (Project No. 00448/PI/04),
Spain. We thank the Screening Unit of the Institute for
Industrial Pharmacy of the Universidad de Santiago de
Compostela (Spain) for the in vitro studies.
IC8012359
(66) Sheldrick, G. M. SADABS,. Program for Empirical Absoption Cor-
rection of Area Detector Data; University of Go¨ttingen: Go¨ttingen,
Germany, 1996.
(67) Sheldrick, G. M. SHELX-97; An integrated system for solVing and
refining crystal structures from diffraction data; University of Go¨t-
tingen: Go¨ttingen, Germany, 1997.
10036 Inorganic Chemistry, Vol. 47, No. 21, 2008