Naphthalimide-tagged ruthenium-arene anticancer complexes: Combining coordination with intercalation

Article abstract of DOI:10.1021/om3007079

Ruthenium(II) arene compounds have been modified with the naphthalimide group, tethered via the arene ligand, i.e. {dichloro[η⁶-N- (phenylalkyl)(4-dimethylamino)-1,8-naphthalimide](pta)ruthenium(II)} (alkyl = methyl, ethyl, propyl, pta = 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane), or via an imidazole group, i.e. {dichloro(η⁶-arene)(N-[3-(imidazol- 1-yl)propyl]-1,8-naphthalimide)ruthenium(II)} (arene = p-cymene, toluene). All the compounds are reasonably cytotoxic (ca. 2-49 μM) toward cancer cells, and the arene-linked compounds also display selectivity in that they are less cytotoxic toward model healthy cells. Mechanistic studies show that the ruthenium center does not readily react with DNA but preferentially binds to proteins. In contrast, the naphthalimide group is a strong DNA intercalator, and combined, the complexes might be expected to simultaneously cross-link DNA and proteins.

Full text of DOI:10.1021/om3007079

Article
pubs.acs.org/Organometallics
Naphthalimide-Tagged Ruthenium−Arene Anticancer Complexes:
Combining Coordination with Intercalation†
Kelly J. Kilpin, Catherine M. Clavel, Fabio Edafe, and Paul J. Dyson*
́ ́ ́
Institut des Sciences et Ingenierie Chimiques, Ecole Polytechnique Federal de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
S
* Supporting Information
ABSTRACT: Ruthenium(II) arene compounds have been
modified with the naphthalimide group, tethered via the arene
ligand, i.e. {dichloro[η6-N-(phenylalkyl)(4-dimethylamino)-
1,8-naphthalimide](pta)ruthenium(II)} (alkyl = methyl,
ethyl, propyl, pta = 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]-
decane), or via an imidazole group, i.e. {dichloro(η6-arene)-
(N-[3-(imidazol-1-yl)propyl]-1,8-naphthalimide)ruthenium-
(II)} (arene = p-cymene, toluene). All the compounds are
reasonably cytotoxic (ca. 2−49 μM) toward cancer cells, and
the arene-linked compounds also display selectivity in that
they are less cytotoxic toward model healthy cells. Mechanistic
studies show that the ruthenium center does not readily react
with DNA but preferentially binds to proteins. In contrast, the
naphthalimide group is a strong DNA intercalator, and combined, the complexes might be expected to simultaneously cross-link
DNA and proteins.
studied, and mechanistic studies and rational ligand design have
resulted in many different classes of organometallic anticancer
compounds.8−10
INTRODUCTION
■
Organometallic chemistry has had a profound impact on
medicinal chemistry, with the majority of pharmacologically
active compounds employing organometallic reagents, catalysts,
and intermediates in their synthesis.1,2 In addition to this highly
important application, organometallic compounds also display
highly interesting medicinal traits in their own right, with
properties somewhat intermediate between classical inorganic
drugs and organic drug molecules.3−5 A number of metal-
locenes were evaluated for anticancer activity shortly after the
introduction of cisplatin into the clinic, and titanocene
dichloride, Ti(η5-C5H5)2Cl2, was identified as a promising
drug candidate.6 Indeed, Ti(η5-C5H5)2Cl2 underwent extensive
evaluation as an anticancer drug, in many different in vitro and
in vivo models as well as on patients, but was finally not
approved for clinical use.7 Nevertheless, these studies inspired
the search for anticancer drugs containing metal−carbon bonds
and over the years many interesting and unique properties have
emerged. Indeed, the influence of the metal type, oxidation
state, ligands, and charge on anticancer activity has been
†Invited award article: Paul Dyson was the recipient of the
Centennial Memorial Sacconi Medal in 2011 for his
contributions to organometallic chemistry. The award is given
by the Italian Chemical Society on behalf of the Luigi Sacconi
Foundation. Luigi Sacconi was a prolific inorganic/organo-
metallic chemist whose research is an indispensable part of
modern inorganic chemistry textbooks. He founded the highly
reputed school of inorganic chemistry in Florence that today
explores the frontiers of bioinorganic chemistry, material
chemistry, and sustainable chemistry and catalysis.
In our own studies on the anticancer properties of
organometallic compounds that began in the mid-1990s, we
became interested in the application of ruthenium(II) arene
compounds.11 Such compounds are widely used as catalysts,
which in combination with various ligands lead to a wide and
diverse range of organic transformations.12,13 However, at first
it was not apparent that these compounds would also display
remarkable chemotherapeutic properties. After struggling for
some time, we discovered the so-called RAPTA complexes, the
prototype being RAPTA-C, Ru(η6-p-cymene)(pta)Cl2, contain-
ing the phospha-adamantane ligand 1,3,5-triaza-7-
phosphatricyclo[3.3.1.1]decane, abbreviated pta.14 Like cispla-
tin and titanocene dichloride, there are two chloride ligands
that can potentially be hydrolyzed to give an “activated”
complex that subsequently reacts with targets such as DNA
the classic (presumed) target of most metal-based anticancer
drugs. Moreover, the amphiphilic pta ligand provides ideal
properties for physiological environments, being soluble in
water and organic solvents, and hence with the potential for
facile transport in the body combined with the ability to cross
lipophilic cell membranes. Finally, the arene ligand may be
systematically modified to fine-tune the properties of the
compound. It was subsequently shown that RAPTA-C exhibits
antitumor,15 antimetastatic,16 and antiangiogenic17 properties
Received: July 26, 2012
© XXXX American Chemical Society
A
dx.doi.org/10.1021/om3007079 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
in vivo with negligible side effects observed. Nevertheless, in
the same way that organometallic chemists working on catalysis
modify the ligands to improve or modulate the catalytic
properties of a complex (consider for example the kinetic,
mechanistic, and synthetic studies that have seen the utility and
scope of Grubbs’s first-generation metathesis catalyst expand
over the years),18,19 we set out to enhance the efficacy of
RAPTA-C on the basis of a mechanistic approach. Many of
these studies are summarized in a relatively recent review.20
While many themes and variations have been developed, two
main approaches show considerable potential and were, in part,
inspired by the elegant studies of Jaouen, who showed that
organometallic units tethered to biologically active organic
molecules may exhibit new and enhanced anticancer proper-
ties.21 Specifically, a ferrocene derivative of tamoxifen, a
selective estrogen receptor modulator used to treat breast
cancer, extends the activity of the molecule to highly invasive
breast tumors. In our first approach,22 biologically active groups
are tethered to the η6-arene via a suitable linker unit (Figure
1)it should be noted that the role of both the ruthenium(II)
enzyme, such that both the ruthenium ion and imidazole bind
at different locations within the active site.28
In both the approaches described above, the role of the
ruthenium(II) arene unit is quite broad, as it is potentially able
to coordinate to many biomolecules and has been shown to
bind to the histones in the nucleosome core in preference to
the DNA.29 In the compounds described to date, the tethered
organic molecule has a much more selective function: e.g.,
inhibition of specific enzymes leading to synergies between the
inorganic and organic subunits of the structure. On the basis of
the observed histone binding we hypothesize that tethering a
DNA intercalator to the ruthenium(II) arene unit may allow
both histone binding and DNA intercalation, enhancing the
cytotoxic effect of the compound. Such a mechanism differs
from that of platinum-based anticancer compounds that
potentially coordinate and intercalate with DNA alone.30
RESULTS AND DISCUSSION
■
Naphthalimides were first recognized as intercalating cytotoxic
agents in the early 1980s,31 and since then many derivatives
have been evaluated for antitumor activity, with two examples
of this class of compound (mitonafide and amonafide) entering
clinical trials.32,33 In addition to the biological activity of the
group, the naphthalimide unit is an attractive intercalating unit
to tether to the ruthenium structure, as it has rich and well-
studied photophysical properties,34,35 which can be exploited to
probe interactions with DNA.36,37
Two types of napthalimide-tagged ruthenium(II) arene
complexes were prepared using the methodologies depicted
in Schemes 1 and 2. For the synthesis of the RAPTA-type
complexes 5a−c, in which the naphthalimide is tagged to the
arene ligand via an aliphatic chain, the precursor cyclohexadiene
ligands (3a−c) were synthesized by the reaction of N,N-
dimethylnaphthalic anhydride 1a with 2a−c in refluxing
toluene to afford the ligands as yellow solids in good yields.
Subsequent reaction of 3a−c with RuCl3·3H2O in refluxing
acetone/water (5/1) produced the ruthenium(II) arene
complexes 4a−c as dark orange solids. The mononuclear
RAPTA-type complexes were obtained by the reaction of the
dimeric complexes 4a−c with 2 equiv of pta in methanol/
dichloromethane (Scheme 1).
Figure 1. Illustration of the two approaches used to tether biologically
active organic groups to the ruthenium(II) arene unit via either the η6-
arene (top) or an imidazole ligand in place of the pta (bottom).
In the second series of compounds, where the naphthalimide
group is tagged to the ruthenium(II) arene center via an
imidazole ligand, complexes 8a,b and 9a,b were prepared by the
reaction of either [Ru(η6-p-cymene)Cl2]2 or [Ru(η6-toluene)-
Cl2]2 with 2 equiv of the appropriate imidazole−naphthalimide
ligand 7a,b in dichloromethane (Scheme 2).
arene unit and the selected biological groups are distinct from
those of ferrocene and tamoxifen. Selection of the biological
group requires a knowledge of both the mechanism of action of
the ruthenium(II) arene unit and the organic molecule so that
complementary functionalities can work together in a
synergistic manner. Moreover, in cancer chemotherapy drug
combinations are virtually always applied,23,24 and in this sense
the organometallic and organic components can be viewed as a
covalently linked drug combination, with the added possible
advantage that the compounds reach the tumor site
simultaneously. In the second approach the biologically active
organic group is attached to the ruthenium(II) arene unit via an
imidazole ligand in place of pta (Figure 1).25 This approach was
in part motivated from the structure of NAMI-A, one of the
two ruthenium(III) coordination complexes currently under-
going clinical trials, which contains an imidazole ligand among
others.26,27 The imidazole moiety is relatively stable but has
also been shown to dissociate on binding to a zinc-containing
1
All new complexes were characterized by H, 13C{1H}, and
(where appropriate) 31P{1H} NMR spectroscopy, HR-ESI mass
spectrometry, IR spectroscopy, and elemental analysis. A
distinctive spectroscopic feature of complexes 5a−c is the
singlet in the 31P{1H} NMR spectra at ca. −34 ppm, consistent
with related complexes.22 The H NMR spectra of all the
1
complexes contain peaks between 5 and 6 ppm that are
characteristic of the η6-coordinated arene. In 8a,b and 9a,b
there is little change in position of the proton signals of the p-
cymene and toluene rings in comparison to those observed in
the parent dimers [Ru(η6-p-cymene)Cl2]2 and [Ru(η6-
toluene)Cl2]2. The peaks for the imidazole protons are
observed at higher frequencies in the complexes (8a,b and
9a,b) relative to the free ligands (7a,b), confirming
coordination to the ruthenium center via the imidazole N
1
atom. In both sets of compounds the H NMR signals of the
B
dx.doi.org/10.1021/om3007079 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 1. Synthesis of Napthalimide-Tagged RAPTA-Type Complexes, 5a−c
Scheme 2. Synthesis of Naphthalimide-Tagged Complexes 8a,b and 9a,b
naphthalimide moiety remain essentially unchanged, indicating
the naphthalimide does not interact with the ruthenium center
and thus is free to interact with DNA.
solution, with the behavior of the prototype RAPTA complex,
RAPTA-C, being the subject of in-depth studies.38 To
determine the influence of the pendant naphthalimide group
on hydrolysis, and aquatic stability more generally, the aqueous
stability of 5a−c was evaluated using 31P{1H} NMR spectros-
copy, as the chemical shift of the pta ligand can be used to
monitor the extent of hydrolysis. Analogous to the case for
RAPTA-C, the naphthalimide complexes 5a−c undergo
aquation in aqueous solution, characterized by a shift in the
31P{1H} NMR spectra from −32 to −28 ppm. Irrespective of
the length of the linker between the η6-arene and the
naphthalimide, 5a−c undergo complete conversion to the
monoaquated form within 30 min. Exchange of both chloride
ligands was not observed, even after 48 h. However, upon the
The structure of the compounds was corroborated by HR
ESI-MS. The most abundant peak observed in the spectra of
the RAPTA-type complexes (5a−c) were those assigned to [M
+ H]+ ions. Conversely, the spectra of the imidazole complexes
(8a,b, 9a,b) were dominated by species assigned to [M − Cl]+
ions. Presumably, the difference in the spectra is due to the
presence of the pta ligand in 5a−c, which contains basic
nitrogen atoms that are protonated under the experimental
conditions employed.
The chloride ligands coordinated to ruthenium−arene
complexes are known to undergo hydrolysis in aqueous
C
dx.doi.org/10.1021/om3007079 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
addition of AgBF4 to forcibly remove both chloride ligands, a
peak appeared in the 31P{1H} NMR spectra, which we assign to
be the doubly aquated species. This species was not observed in
the absence of silver salts. Notably, over this time period, the
1H NMR spectra indicated that the arene remained coordinated
to the ruthenium centersignals for the free arene ligands
were not observed.
active against the cisplatin-resistant A2780R cell line (notably
5b); therefore, only these complexes were studied further. It is
noteworthy that 5b, containing the ethyl linker, is the most
active of the RAPTA-type series of compounds.
Naphthalimides are known to intercalate DNA, and
consequently the interaction of 5b with DNA was investigated
initially by NMR spectroscopy, using the nucleoside guanosine
as a model for DNA, as the N7 nitrogen is the usual binding
site for ruthenium- and platinum-based compounds.40,41 The
frequency of the H8 proton (adjacent to N7 of guanosine) did
not change following incubation with 5b (1/1) in D2O/d6-
Similar behavior was observed for the imidazole-linked
1
compounds 8a,b and 9a,b. H NMR spectroscopy indicated
that in aqueous solution the imidazole (and hence the
naphthalimide) remains coordinated to the ruthenium over
48 h. However, as with the pta complexes 5a−c, hydrolysis of
the chloride ligands takes place over 30 min, resulting in
multiple peaks assigned to the imidazole (but always to higher
frequency in comparison with the free ligands 7a,b). The
number of peaks present suggest that, in contrast to the pta
complexes 5a−c, both the mono- and diaquated species are
formed with the imidazole complexes 8a,b and 9a,b.
Biological Studies. The cytotoxicities of the ligands and
complexes were determined using the MTT assay in
comparison to RAPTA-C on cisplatin-sensitive and -resistant
human ovarian carcinoma (A2780 and A2780R, respectively)
and human embryonic kidney cells (HEK, a model for healthy
cells) (see Table 1 and Figure S19 (Supporting Information)).
1
DMSO (9/1). The H NMR spectrum did reveal the presence
of the hydrolysis product, and while the hydrolysis product is
considered to be activated, direct reaction (coordination) with
the isolated guanosine base was not observed. However, when
the concentration of guanosine is increased, the frequency of
the naphthalimide protons decreases, indicative of π-stacking
interactions in solution and demonstrating that π-stacking is
preferred over coordination of the ruthenium center (see the
Supporting Information, Figure S15). After 24 h incubation,
two new peaks appear in the 31P{1H} NMR spectrum at −29.5
and −29.7 ppm, assigned to the guanosine-coordinated
diastereoisomers (see the Supporting Information, Figure
S16). The presence of the guanosine adduct was additionally
confirmed using HR-ESI MS (see the Supporting Information,
Figure S17). It is noteworthy that these guanosine adducts were
only observed after a significant incubation time, in the
presence of an excess (5 equiv) of guanosine. These results
differ significantly when compared with those for RAPTA-C,
which is far more reactive toward the base (complete
conversion to the guanosine adduct after 12 h, 1 equiv).40
It has previously been shown that the photophysical
properties of the naphthalimide unit can be exploited to
delineate interactions with DNA.36,37 Thus, UV−vis spectrom-
etry was used to monitor changes to 5b as increasing amounts
of ct-DNA were added to a phosphate-buffered solution of the
complex (Figure 2a). A bathochromic shift of λmax of the
naphthalimide moiety of 10 nm (λmax of free 5b 445 nm, λmax of
bound 5b 455 nm), accompanied by a decrease in intensity of
the absorbance band at 445 nm of approximately 20%, was
observed upon the addition of ct-DNA. These observations are
consistent with those reported in the literature36 and are
indicative of a weak naphthalimide−DNA interaction; however,
the results are not diagnostic for a particular type of binding,
since both intercalated and externally bound drugs display the
same changes to their UV−vis spectra on interacting with
DNA.
In addition to the UV−vis absorption spectra, the steady-
state emission spectra (excitation at 485 nm) of 5b upon
addition of increasing amounts of ct-DNA were recorded
(Figure 2b). As expected, in phosphate-buffered solution the
fluorescence of 5b is essentially quenched,34,35 but on addition
of DNA the emission is enhanced by a factor of 5, along with a
blue shift of λmax of 4 nm (λmax of free 5b 548 nm, λmax of bound
5b 544 nm). These data are consistent with weak interactions
with DNA, as an association with less polar binding sites of
DNA would decrease the stability of the excited state.
Circular dichroism (CD) spectroscopy was also used to
investigate the interaction of 5b with ct-DNA (Figure 3). Upon
addition of 5b ([DNA]/[5b] = 0 → 20) to a solution of ct-
DNA, the CD trace characteristic of B-DNA was significantly
altered, especially at high drug concentrations ([DNA]/[5b] =
2). Specifically, a substantial decrease in the ellipticity of the
Table 1. IC50 Values (μM) Determined by the MTT Assay
after 72 h Exposure of the Compounds to A2780, A2780R,
and HEK Cells
a
b
c
A2780
A2780R
HEK
5a
8.53 1.41
2.31 0.1
6.45 0.46
6.89 1.49
2.25 0.23
9.09 1.72
16.61 1.13
6.60 0.21
17.43 0.33
35.7 0.8
5b
5c
7b
38
28.1 0.8
30
3
49
36
6
3
8b
32
33
3
4
3
9b
3
48.3 0.1
26
7a
18.5 0.3
6.1 1.1
6.5 1.5
230
4
29.3
8a
7.8 0.4
8.6 1.8
270
12.7 0.2
18.4 1.3
9a
RAPTA-C
>1000
a
b
Human ovarian carcinoma, cisplatin-sensititve cells. Human ovarian
c
carcinoma, cisplatin-resistant cells. Human embryonic kidney cells.
All the naphthalimide complexes are far more active than the
prototype complex RAPTA-C, indicating that the naphthali-
mide moiety plays an important role in the cytotoxic
mechanism. Furthermore, the compounds containing the
unsubstituted naphthalimide group (7b−9b) are less active
than the analogous compounds which contain the dimethyla-
mino substituent group (7a−9a), which may indicate that DNA
intercalation is playing a role in the cytotoxic mechanism, as it
has been shown that the presence of an internal charge transfer
in the napthalimide group (present in 7a−9a, absent in 7b−9b)
enhances interaction with DNA.39 The imidazole complexes
(8a,b and 9a,b) are slightly less active than the RAPTA-type
complexes (5a−c), and importantly, the RAPTA-type com-
plexes are consistently selective toward cancer cell lines
(A2780/A2780R) over the HEK cells, supporting the previous
observation that the pta ligand endows compounds with some
degree of selectivity. This selectivity is somewhat lost when the
naphthalimide moiety is tethered via the imidazole and the pta
ligand is absent. Overall, the RAPTA-type complexes, 5a−c,
show the highest selectivity toward cancer cells and are also
D
dx.doi.org/10.1021/om3007079 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Taken together, these data clearly indicate that the
naphthalimide group is interacting with DNA. Although the
results do not explicitly confirm this interaction is via
intercalation, the secondary structure of B-DNA is significantly
altered. However, in comparison with data obtained for known
naphthalimide intercalators, it is not unreasonable to suggest
that the ruthenium conjugates also interact with DNA via
intercalation. These noncovalent naphthalimide/DNA inter-
actions appear to dominate over Ru−DNA binding inter-
actions, which are slow in comparison to those for RAPTA-C,
which may bind to DNA without altering the secondary
structure.
In addition to interactions with DNA, ESI MS was utilized to
investigate the binding of 5b to the protein ubiquitin (Ub).
Compound 5b readily binds to the protein, as after only 1 h
incubation (5b/Ub 1/5) the ruthenium adduct [Ub+5b-Cl2] is
observed (see the Supporting Information, Figure S18). Over
time, the intensity of this peak increases, and the appearance of
a new peak arising from further loss of the pta ligand is
observed. Importantly, in all the ruthenium/Ub adducts, the
arene−naphthalimide units remain coordinated to the
ruthenium center. Thus, it is not unreasonable to propose
that the naphthalimide group may intercalate DNA with the
ruthenium unit simultaneously coordinating to a protein.
CONCLUSIONS
■
Two series of ruthenium(II) arene complexes were prepared
with pendant naphthalimide (DNA intercalating) moieties
one in which the naphthalimide is connected via the arene unit
and in the other an imidazole linker. In both series of
complexes the naphthalimide increases the cytotoxicity of the
ruthenium(II) arene unit. The greatest selectivity toward cancer
cells over model healthy HEK cells is observed for the former
series, which are also active against the cisplatin-resistant cells.
Subsequent studies suggest that intercalation of the naph-
thalimide group is the dominant interaction with DNA, whereas
the ruthenium center prefers to bind to proteins. As such, it is
possible that these compounds have a double-action mecha-
nism, which could be responsible for the increased activity in
comparison with RAPTA-C and also for overcoming cisplatin
acquired drug resistance. Further studies are required to fully
delineate the mechanism of action at a cellular level. It should
also be noted that the approach used here not only extends our
own studies but builds on an impressive body of research on
anticancer organometallic compounds.
Figure 2. (a) UV−vis spectra (300 − 650 nm) of 5b (0.02 mM,
phosphate buffer, 10 mM, pH 7.4) in the presence of increasing
concentrations of ct-DNA (0−0.7 mM). Inset: plot of A/A0 vs
[DNA]/[5b]. (b) Steady-state emission of 5b (0.02 mM, phosphate
buffer, 10 mM, pH 7.4) in the presence of increasing concentrations of
ct-DNA (0−2.5 mM), λex 485 nm. Inset: plot of I/I0 vs [DNA]/[5b].
EXPERIMENTAL SECTION
■
1,3,5-Triaza-7-phosphatricyclo[3.3.1.1]decane (PTA)43 and the ami-
noalkyl-cyclohexadienes 2a,44 2b,45 and 2c46 were synthesized using
literature procedures; all other reagents and solvents were obtained
1
from commercial sources and used without further purification. H
(400.13 MHz), 31P{1H} (161.98 MHz), and 13C{1H} (100.62 MHz)
NMR spectra were recorded at 25 °C on a Bruker Avance II 400
spectrometer and referenced to residual solvent peaks (CDCl3 1H
7.26, 13C{1H} 77.16; CD2Cl2 1H 5.30, 13C{1H} 53.84; d6-DMSO H
1
Figure 3. CD spectra (210−340 nm) of ct-DNA (150 mM, phosphate
buffer, 10 mM, pH 7.4) in the presence of 5b at varying [DNA]/[5b]
ratios.
2.50, 13C{1H} 39.52) or reported relative to 85% H3PO4. IR spectra
were recorded on a Perkin-Elmer Spectrum One FT-IR spectrometer,
and melting points were determined on an SMP3 Stuart melting point
apparatus and are uncorrected. Elemental analysis was carried out by
the microanalytical laboratory at EPFL. HR-ESI MS were obtained on
a ThermFinnigan LCQ Deca XP Plus Quadrupole ion-trap instrument
in the positive ion mode. UV−vis experiments were conducted on a
Jasco V-550 spectrometer, Fluorescence spectra were acquired on a
Varian Cary Eclipse spectrofluorimeter, and circular dichroism
negative band (240 nm) was observed. Again, these results
contrast with those obtained for RAPTA-C, which at the same
concentrations has no effect on the secondary structure of
DNA.42
E
dx.doi.org/10.1021/om3007079 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
experiments were conducted on a Jasco J-810 spectropolarimeter with
10 accumulations per spectra. All photochemistry spectra were
acquired using quartz cells (Helma Analytics) with a path length of
1 cm.
CH2); 13C{1H}, δ 164.6 (CO), 164.0 (CO), 157.0 (Ar-C-NMe2),
132.7 (Ar-C), 132.5 (Ar-C), 131.2 (Ar-C), 131.0 (Ar-C), 130.3 (Ar-C),
125.4 (Ar-C), 125.0 (Ar-C), 124.5 (Ar-C), 124.1 (Ar-C), 123.2 (Ar-C),
120.7 (Ar-C), 115.2 (Ar-C), 113.4 (Ar-C), 44.9 (N-CH3), 38.9 (CH2),
35.9 (CH2), 29.1 (CH2), 26.9 (CH2). HR ESI-MS: m/z 347.175 ([M +
H]+, calcd for C22H23N2O2 347.176).
Synthesis. 4-N,N-Dimethylaminonaphthalene-1,8-dicarboxi-
mide (1a). Dimethylamine (10 mL, 40% aqueous solution, excess)
and CuSO4·5H2O (5 mol %) were added to a suspension of 4-
bromonaphthalene-1,8-dicarboximide (5.00 g) in DMF (30 mL). The
mixture was refluxed for 3 h, after which time the solvent was removed
under vacuum. The product was crystallized from hot methanol to give
a yellow solid. Yield: 3.84 g (88%). Mp: 206 °C. Anal. Calcd for
C14H11NO3: C, 69.70; H, 4.60; N, 5.81. Found: C, 69.46; H, 4.54; N,
5.87. IR ν (cm−1): 1748, 1713, 1581, 1563, 1391, 1340, 1308, 1081,
1016, 989, 779, 753, 721, 467, 494. NMR (CDCl3): 1H, δ 8.57 (dd, J =
7.3, 1.1 Hz, 1H, Ar-H), 8.51 (dd, J = 8.4, 1.1 Hz, 1H, Ar-H), 8.47 (d, J
= 8.0 Hz, 1H, Ar-H), 7.69 (dd, J = 8.4, 7.3 Hz, 1H, Ar-H), 7.13 (d, J =
8.0 Hz, 1H, Ar-H), 3.18 (s, 6H, N-CH3); 13C{1H}, δ 161.8 (CO),
160.8 (CO), 158.0 (Ar-C-NMe2), 135.0 (Ar-C), 133.0 (Ar-C), 132.9
(Ar-C), 132.9 (Ar-C), 124.9 (Ar-C), 124.8 (Ar-C), 119.3 (Ar-C), 113.3
(Ar-C), 109.6 (Ar-C), 44.7 (N-CH3). HR ESI-MS: m/z 242.081 ([M +
H]+, calcd for C14H12NO3 242.082).
General Procedure for Preparation of Naphthalimide Ligands
3a−c and 7a,b. Under an atmosphere of nitrogen, the 1,8-
dicarboximide 1a,b (1 equiv), the appropriate amine 2a−c or 6 (1.4
equiv), and dry NEt3 (2 equiv) were refluxed over molecular sieves in
toluene (150 mL) for 2−3 days. While hot, the solution was filtered
through Celite and the filter cake washed with hot toluene (2 × 25
mL). The solvent was removed under reduced pressure, and the
residue was taken up in CH2Cl2 (50 mL) and washed with saturated
NaHCO3 (2 × 50 mL), H2O (2 × 50 mL), and brine (50 mL) and
dried over NaSO4. After evaporation, the residue was crystallized from
hot MeOH and dried in vacuo.
N-[1-(Cyclohexa-1,4-dienyl)methyl](4-dimethylamino)-1,8-naph-
thalimide (3a). (4-Dimethylamino)naphthalene-1,8-dicarboximide
(1a; 1.50 g, 6.2 mmol, 1 equiv), (cyclohexa-1,4-dienyl)methylamine
(2a; 0.93 g, 8.7 mmol), and NEt3 (1.73 mL, 12.4 mmol, 2 equiv) were
reacted in toluene (110 mL) for 2 days. Workup as described above,
followed by crystallization from hot MeOH, gave 1.22 g (60%) of 3a
as a yellow solid. Mp: 145 °C. Anal. Calcd for C21H20N2O2·H2O: C,
71.97; H, 6.33; N, 8.00. Found: C, 71.87; H, 6.05; N, 7.38. IR ν
(cm−1): 1686, 1650, 1587, 1575, 1377, 1341, 1240, 779, 761, 652, 504,
495, 466, 458. NMR (CDCl3): 1H, δ 8.59 (dd, J = 7.3, 0.9 Hz, 1H, Ar-
H), 8.46 (d, J = 8.2 Hz, 1H, Ar-H), 8.44 (dd, J = 8.5, 0.9 Hz, 1H, Ar-
H), 7.67 (dd, J = 7.3, 8.5 Hz, 1H, Ar-H), 7.13 (d, J = 8.2 Hz, 1H, Ar-
H), 5.61 (m, 3H, diene C-H), 4.71 (s, 2H, CH2), 3.11 (s, 6H, N-CH3),
2.71 (m, 4H, diene C-H2); 13C{1H}, δ 164.7 (CO), 164.1 (CO),
156.9 (Ar-C-NMe2), 132.9 (Ar-C), 131.3 (Ar-C), 131.3 (Ar-C), 130.4
(Ar-C), 130.3 (Ar-C), 125.5 (Ar-C), 125.1 (Ar-C), 124.1 (Ar-C), 123.1
(Ar-C), 123.2 (Ar-C), 120.3 (Ar-C), 115.2 (Ar-C), 113.5 (Ar-C), 45.0
(N-CH3), 44.9 (N-CH2), 27.9 (CH2), 26.6 (CH2). HR ESI-MS: m/z
333.160 ([M + H]+, calcd for C21H19N2O2 333.160).
N-[3-(Cyclohexa-1,4-dienyl)propyl](4-dimethylamino)-1,8-naph-
thalimide (3c). (4-Dimethylamino)naphthalene-1,8-dicarboximide
(1a; 1.50 g, 6.2 mmol, 1 equiv), (cyclohexa-1,4-dienyl)propylamine
(2c; 1.18 g, 8.7 mmol), and NEt3 (1.73 mL, 12.4 mmol, 2 equiv) were
reacted in toluene (110 mL) for 3 days. Workup as for 3b gave 1.50 g
(66%) of 3c as a yellow solid. Mp: 104 °C. Anal. Calcd for
C23H24N2O2: C, 76.64; H, 6.71; N, 7.77. Found: C, 76.49; H, 6.69; N,
7.84. IR ν (cm−1): 1690, 1645, 1574, 1348, 778, 758, 658, 469. NMR
1
(CDCl3): H, δ 8.58 (d, J = 7.5 Hz, 1H, Ar-H), 8.48 (m, 2H, Ar-H),
7.67 (m, 1H, Ar-H), 7.14 (d, J = 8.1 Hz, Ar-H), 5.68 (m, 2H, diene C-
H), 5.50 (br s, 1H, diene C-H), 4.16 (t, J = 7.6 Hz, 2H, N-CH2), 3.11
(s, 6H, N-CH3), 2.64 (br s, 4H, diene CH2), 2.12 (t, J = 7.8 Hz, 2H,
CH2), 1.88 (m, 2H, CH2); 13C{1H}, 164.7 (CO), 164.2 (CO),
156.8 (Ar-C-NMe2), 134.3 (Ar-C), 132.6 (Ar-C), 131.2 (Ar-C), 131.1
(Ar-C), 130.3 (Ar-C), 125.4 (Ar-C), 125.1 (Ar-C), 124.5 (Ar-C), 124.3
(Ar-C), 123.3 (Ar-C), 118.7 (Ar-C), 115.4 (Ar-C), 113.6 (Ar-C), 45.0
(N-CH3), 40.3 (CH2), 35.1 (CH2), 29.0 (CH2), 26.9 (CH2), 25.7
(CH2). HR ESI-MS: m/z 361.191 ([M + H]+, calcd for C23H25N2O2
361.192).
N-[3-(Imidazol-1-yl)propyl](4-dimethylamino)-1,8-naphthalimide
(7a). (4-Dimethylamino)naphthalene-1,8-dicarboximide (1a; 1.00 g,
4.14 mmol, 1 equiv), 1-(3-aminopropyl)imidazole (6; 0.73 g, 5.80
mmol, 1.4 equiv), and NEt3 (0.83 g, 8.24 mmol, 2 equiv) were refluxed
in dry toluene (100 mL) over molecular sieves for 48 h to give 1.18 g
(82%) of 7a as an orange-yellow solid. Mp: 118−119 °C. Anal. Calcd
for C20H20N4O2·0.5MeOH: C, 67.55; H, 6.09; N, 15.38. Found: C
67.96; H, 5.57; N, 15.07. IR ν (cm−1): 1692, 1644, 1587, 1360, 1349,
1225, 1073, 1052, 777, 758, 736, 661. NMR (CDCl3): 1H, δ 8.54 (d, J
= 7.3 Hz, 1H, Ar-H), 8.43 (m, 2H, Ar-H), 7.64 (m, 1H, Ar-H), 7.54 (s,
1H, Im-H), 7.09 (d, J = 8.1 Hz, 1H, Ar-H), 7.03 (s, 1H, Im-H), 7.00 (s,
1H, Im-H), 4.21 (t, J = 6.9 Hz, 2H, N-CH2-CH2), 4.05 (t, J = 7.4 Hz,
2H, CH2-CH2-Im), 3.10 (s, 6H, N-CH3), 2.24 (m, 2H, CH2-CH2-
CH2); 13C{1H}, δ 164.8 (CO), 164.2 (CO), 157.3 (Ar-C-NMe2),
137.3 (Im-C), 133.0 (Ar-C), 131.6 (Ar-C), 131.3 (Ar-C), 130.4 (Im-
C), 129.6 (Ar-C), 125.3 (Ar-C), 125.0 (Ar-C), 122.8 (Ar-C), 118.8
(Im-C), 114.5 (Ar-C), 113.4 (Ar-C), 45.1 (CH2), 44.9 (N-CH3), 37.6
(CH2), 29.9 (CH2). HR ESI-MS: m/z 349.167 ([M + H]+, calcd for
C20H21N4O2 349.166).
N-[3-(Imidazol-1-yl)propyl]-1,8-naphthalimide (7b). 1,8-Naph-
thalic anhydride (1b; 1.69 g, 8.6 mmol, 1 equiv), 1-(3-aminopropyl)-
imidazole (1.50 g, 12.0 mmol, 1.4 equiv), and NEt3 (1.74 g, 17.2
mmol, 2 equiv) were refluxed in dry toluene (150 mL) over molecular
sieves for 3 days. The hot solution was filtered through Celite and the
filter cake washed with hot toluene (2 × 25 mL). The solvent was
removed under reduced pressure and the residue taken up in CH2Cl2
(50 mL) and washed with saturated NaHCO3 (2 × 50 mL), H2O (2 ×
50 mL), and brine (50 mL) and dried over NaSO4. After evaporation,
the residue was crystallized from hot MeOH and dried in vacuo to give
1.04 g (40%) of 7b as white crystals. Mp: 166−168 °C. Anal. Calcd for
C18H15N3O2: C, 70.81; H, 4.95; N, 13.76. Found: C, 70.62; H, 5.06;
N, 13.69. IR ν (cm−1): 1688, 1647, 1623, 1583, 1440, 1384, 1340,
1235, 1081, 1049, 1037, 907, 844, 778, 765, 726, 670. NMR (CDCl3):
1H, 8.61 δ (d, J = 7.3 Hz, 2H, Ar-H), 8.23 (d, J = 7.8 Hz, 2H, Ar-H),
N-[2-(Cyclohexa-1,4-dienyl)ethyl](4-dimethylamino)-1,8-naph-
thalimide (3b). (4-Dimethylamino)naphthalene-1,8-dicarboximide
(1a; 1.52 g, 6.3 mmol, 1 equiv), (cyclohexa-1,4-dienyl)ethylamine
(2b; 1.09 g, 8.8 mmol), and NEt3 (1.75 mL, 12.6 mmol, 2 equiv) were
reacted in toluene (120 mL) for 2 days. The hot solution was filtered
through Celite and the filter cake washed with hot toluene (2 × 25
mL). The solvent was removed under reduced pressure, and the
residue was taken up in CH2Cl2 (50 mL) and washed with saturated
NaHCO3 (2 × 50 mL), H2O (2 × 50 mL), and brine (50 mL) and
dried over NaSO4. After evaporation, the residue was crystallized from
hot MeOH and dried in vacuo to give 1.29 g (59%) of 3b as an orange
solid. Mp: 132 °C. Anal. Calcd for C22H22N2O2: C, 76.28; H, 6.40; N,
8.09. Found: C, 76.06; H, 6.42; N, 8.01. IR ν (cm−1): 1685, 1640,
7.77 (m, 2H, Ar-H), 7.56 (s, 1H, Im-H), 7.04 (s, 1H, Im-H), 7.01 (s,
1H, Im-H), 4.25 (t, J = 6.7 Hz, 2H, N-CH2-CH2), 4.08 (t, J = 7.1 Hz,
2H, CH2-CH2-Im), 2.27 (m, 2H, CH2-CH2-CH2); 13C{1H}, δ 164.3
(CO), 137.3 (Im-C), 134.5 (Ar-C), 131.7 (Ar-C), 131.5 (Ar-C),
129.7 (Im-C), 128.2 (Ar-C), 127.1 (Ar-C), 122.5 (Ar-C), 118.8 (Im-
C), 45.1 (CH2), 37.8 (CH2), 29.8 (CH2). HR ESI-MS: m/z 306.125
([M + H]+, calcd for C18H16N3O2 306.124).
1
1572, 1383, 1352, 786, 757. NMR (CDCl3): H, δ 8.57 (dd, J = 7.2,
1.1 Hz, 1H, Ar-H), 8.44 (d, J = 8.2 Hz, 1H, Ar-H), 8.42 (dd, J = 8.5,
1.1 Hz, 1H, Ar-H), 7.65 (dd, J = 8.5, 7.2 Hz, 1H, Ar-H), 7.11 (d, J =
8.2 Hz, 1H, Ar-H), 5.72 (m, 2H, diene C-H), 5.52 (br s, 1H, diene C-
H), 4.26 (t, J = 7.7 Hz, 2H, N-CH2), 3.10 (s, 6H, N-CH3), 2.80 (m,
2H, diene CH2), 2.65 (m, 2H, diene CH2), 2.37 (t, J = 7.7 Hz, 2H,
Bis{dichloro[η6-N-(phenylmethyl)(4-dimethylamino)-1,8-
naphthalimide]ruthenium(II)} (4a). 3a (253 mg, 0.77 mmol, 4 equiv)
and RuCl3·3H2O (50 mg, 0.19 mmol, 1 equiv) were refluxed in
acetone/water (5/1, 30 mL) for 18 h, during which time an orange-
F
dx.doi.org/10.1021/om3007079 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
brown precipitate formed. While hot, the solid was isolated by
filtration, washed with diethyl ether (3 × 10 mL), and dried in vacuo.
The solid was used in the next step without further purification. Yield:
an orange-brown solid (37 mg, 57%). Mp: 178 °C dec. Anal. Calcd for
C28H32N5O2PCl2Ru·0.5H2O: C, 49.26; H, 4.88; N, 10.27. Found: C,
49.24; H, 4.91; N, 10.33. IR ν (cm−1): 1685, 1644, 1582, 1385, 1355,
1013, 970, 947, 780, 758, 576. NMR (CD2Cl2): 1H, δ 8.49 (dd, J = 7.2,
1.1 Hz, 1H, Ar-H), 8.45 (dd, J = 8.5, 1.1 Hz, 1H, Ar-H), 8.41 (d, J =
8.2 Hz, 1H, Ar-H), 7.66 (dd, J = 8.5, 7.2 Hz, 1H, Ar-H), 7.11 (d, J =
8.4 Hz, 1H, Ar-H), 5.56 (m, 4H, Ru−Ar-H), 5.17 (t, J = 5 Hz, 1H, Ru-
Ar-H), 4.51 (s, 6H, PTA), 4.47 (t, J = 7.3 Hz, 2H, Ar-CH2), 4.28 (s,
6H, PTA), 3.11 (s, 6H, N-CH3), 2.80 (t, 2H, J = 7.3 Hz); 31P{1H}, δ
−34.15; 13C{1H}, δ 164.9 (CO), 164.2 (CO), 157.9 (Ar-C-
NMe2), 133.2 (Ar-C), 132.1 (Ar-C), 131.5 (Ar-C), 130.9 (Ar-C), 125.8
(Ar-C), 125.3 (Ar-C), 123.4 (Ar-C), 114.8 (Ar-C), 113.7 (Ar-C), 105.8
(d, J = 4 Hz, Ru-C), 88.8 (d, J = 6 Hz, Ru-C), 86.7 (d, J = 3 Hz, Ru-C),
80.1 (Ru-C), 73.93 (d, J = 7 Hz, N-CH2-N, PTA), 45.2 (N-CH3), 40.3
(CH2), 32.9 (CH2 (second PTA signal under solvent, ca. 54 ppm)).
HR ESI-MS: m/z 674.079 ([M + H]+, calcd for C28H33N5O2PCl2Ru
674.082).
1
69 mg (71%). NMR (d6-DMSO): H, δ 8.53 (d, J = 8.6 Hz, 1H, Ar-
H), 8.48 (d, J = 7.0 Hz, 1H, Ar-H), 8.36 (d, J = 8.3 Hz, 1H, Ar-H),
7.76 (m, 1H, Ar-H), 7.22 (d, J = 8.3 Hz, 1H, Ar-H), 6.04 (m, 4H, Ru-
Ar-H), 5.83 (t, J = 5.4 Hz, 1H, Ru-Ar-H), 5.03 (s, 2H, CH2), 3.11 (s,
6H, N-CH3).
Bis{dichloro[η6-N-(phenylethyl)(4-dimethylamino)-1,8-
naphthalimide]ruthenium(II)} (4b). 3b (265 mg, 0.77 mmol, 4 equiv)
and RuCl3·3H2O (50 mg, 0.19 mmol, 1 equiv) were refluxed in
acetone/water (5/1, 30 mL) for 4 h. While hot, the solution was
filtered to remove a black solid and the filtrate was evaporated to
dryness. The residue was suspended in hot EtOH (50 mL), and the
undissolved solid was isolated by filtration, washed with diethyl ether
(3 × 10 mL), and dried in vacuo. The solid was used in the next step
without further purification. Yield: 36 mg (37%). NMR (d6-DMSO):
1H, δ 8.52 (d, J = 8.6 Hz, 1H, Ar-H), 8.43 (d, J = 6.9 Hz, 1H, Ar-H),
{Dichloro[η6-N-(phenylpropyl)(4-dimethylamino)-1,8-
naphthalimide](pta)ruthenium(II)} (5c). A solution of 4a (50 mg,
0.05 mmol, 1 equiv) and PTA (15 mg, 0.09 mmol, 2 equiv) in
CH2Cl2/MeOH (60 mL, 2/1) were reacted for 3 h. Workup gave 5a
as an orange-brown solid (54 mg, 83%): Mp: 159 °C dec. Anal. Calcd
for C29H34N5O2PCl2Ru·1.5H2O: C, 48.73; H, 5.22; N, 9.80. Found: C,
48.67; H, 5.04; N, 9.79. IR ν (cm−1): 1684, 1643, 1581, 1386, 1360,
1241, 1013, 971, 947, 779, 757, 578. NMR (CD2Cl2): 1H, δ 8.53 (d, J
= 7.1 Hz, 1H Ar-H), 8.45 (m, 2H, Ar-H), 7.67 (m, 1H, Ar-H), 7.13 (d,
J = 8.1 Hz, 1H, Ar-H), 5.54 (m, 4H, Ru-Ar-H), 5.10 (br t, 1H, Ru-Ar-
H), 4.52 (s, 6H, PTA), 4.28 (s, 6H, PTA), 4.22 (t, J = 7.0 Hz, 2H, Ar-
CH2), 3.11 (s, 6H, N-CH3), 2.57 (t, J = 7.2 Hz, 2H, CH2), 2.06 (m,
2H, CH2); 31P{1H}, δ −34.34; 13C{1H}, δ 165.1 (CO), 164.5 (C
O), 157.7 (Ar-C-NMe2), 133.1 (Ar-C), 132.0 (Ar-C), 131.4 (Ar-C),
130.9 (Ar-C), 128.9 (d, J = 9 Hz, Ru-C), 125.8 (Ar-C), 125.4 (Ar-C),
123.6 (Ar-C), 115.2 (Ar-C), 113.8 (Ar-C), 88.1 (Ru-C), 88.0 (Ru-C),
87.4 (Ru-C), 79.7 (Ru-C), 73.7 (br, N-CH2-N, PTA), 52.6 (d, J = 17
Hz, P-CH2, PTA), 45.2 (N-CH3), 39.8 (CH2), 30.9 (CH2), 28.1
(CH2). HR ESI-MS: m/z 688.095 ([M + H]+, calcd for
C29H35N5O2PCl2Ru 688.095).
8.31 (d, J = 8.3 Hz, 1H, Ar-H), 7.75 (m, 1H, Ar-H), 7.21 (d, J = 8.3
Hz, 1H, Ar-H), 5.93 (m, 2H, Ru-Ar-H), 5.80 (d, J = 6.0 Hz, 2H, Ru-
Ar-H), 5.72 (t, J = 5.5 Hz, 1H, Ru-Ar-H), 4.35 (t, J = 6.5 Hz, 2H,
CH2), 3.10 (s, 6H, N-CH3), 2.78 (t, J = 6.5 Hz, 2H, CH2).
Bis{dichloro[η6-N-(phenylpropyl)(4-dimethylamino)-1,8-
naphthalimide]ruthenium(II)} (4c). 3c (548 mg, 1.53 mmol, 4 equiv)
and RuCl3·3H2O (100 mg, 0.38 mmol, 1 equiv) were refluxed in
acetone/water (5/1, 60 mL) for 2 h. While hot, the solution was
filtered to remove a black solid and the filtrate was evaporated to
dryness. The residue was suspended in hot EtOH (50 mL) and the
undissolved solid isolated by filtration, washed with diethyl ether (3 ×
10 mL), and dried in vacuo. The solid was used in the next step
without further purification. Yield: 88 mg (44%). NMR (d6-DMSO):
1H, δ 8.52 (d, J = 8.8 Hz, 1H, Ar-H), 8.47 (d, J = 6.9 Hz, 1H, Ar-H),
8.35 (d, J = 8.3 Hz, 1H, Ar-H), 7.76 (m, 1H, Ar-H), 7.23 (d, J = 8.3
Hz, 1H, Ar-H), 5.96 (m, 2H, Ru-Ar-H), 5.81 (d, J = 5.9 Hz, 2H, Ru-
Ar-H), 5.71 (t, J = 5.5 Hz, 1H, Ru-Ar-H), 4.11 (t, J = 6.9 Hz, 2H,
CH2), 3.10 (s, 6H, N-CH3), 3.05, (m, 2H, CH2), 1.99 (m, 2H, CH2).
General Procedure for the Preparation of {Dichloro[η6-N-
(phenylalkyl)(4-dimethylamino)-1,8-naphthalimide](pta)-
ruthenium(II)} (5a−c). PTA (2 equiv) was added to a solution of the
appropriate ruthenium dimer 4a−c (1 equiv) in CH2Cl2/MeOH (2/
1) and the solution was stirred at room temperature under N2, with
the extent of the reaction being monitored by 31P{1H} NMR
spectroscopy. When deemed complete (by disappearance of free PTA
at ca. −90 ppm), the solution was filtered and evaporated to dryness.
The solid was redissolved in a minimum amount of CH2Cl2 and
precipitated with Et2O at −18 °C.
General Procedure for the Preparation of {Dichloro(η6-arene)(N-
[3-(imidazol-1-yl)propyl]-1,8-naphthalimide)ruthenium(II)} (8a,b
and 9a,b). To a solution of either [Ru(η6-p-cymene)Cl2]2 or
[Ru(η6-toluene)Cl2]2 (1 equiv) in CH2Cl2 (100 mL) the appropriate
imidazole-linked naphthalimide 7a,b (2 equiv) was added and the
solution stirred at room temperature for 18 h. The solution was
reduced in volume (ca. 10 mL) and filtered through a plug of Celite.
Addition of diethyl ether to the filtrate resulted in the precipitation of a
yellow or orange solid which was isolated by filtration, washed with
diethyl ether (3 × 10 mL), and dried in vacuo.
{Dichloro[η6-N-(phenylmethyl)(4-dimethylamino)-1,8-
naphthalimide](pta)ruthenium(II)} (5a). A solution of 4a (50 mg,
0.05 mmol, 1 equiv) and PTA (16 mg, 0.10 mmol, 2 equiv) in
CH2Cl2/MeOH (60 mL, 2/1) was reacted for 3 h. Workup gave 5a as
an orange-brown solid (50 mg, 73%). Mp: 225 °C dec. Anal. Calcd for
C27H30N5O2PCl2Ru·2.5H2O: C, 46.02; H, 5.01; N, 9.94. Found: C,
46.03; H, 4.56; N, 9.85. IR ν (cm−1): 1684, 1642, 1578, 1376, 1336,
1013, 970, 945, 777, 755, 742, 574. NMR (CD2Cl2): 1H, δ 8.54 (d, J =
7.3 Hz, 1H Ar-H), 8.46 (m, 2H, Ar-H), 7.67 (m, 1H, Ar-H), 7.12 (d, J
= 8.3 Hz, 1H, Ar-H), 6.10 (d, J = 6.2 Hz, 2H, Ru-Ar-H), 5.61 (m, 2H,
Ru-Ar-H), 5.21 (t, J = 5.3 Hz, 1H, Ru-Ar-H), 4.94 (s, 2H, CH2), 4.56
(s, 6H, PTA), 4.38 (s, 6H, PTA), 3.12 (s, 6H, N-CH3); 31P{1H}, δ
−34.12; 13C{1H}, δ 165.3 (CO), 164.5 (CO), 158.1 (Ar-C-
NMe2), 133.5 (Ar-C), 132.5 (Ar-C), 131.8 (Ar-C), 131.0 (Ar-C), 128.8
(Ar-C), 125.7 (Ar-C), 125.3 (Ar-C), 123.2 (Ar-C), 114.2 (Ar-C), 113.7
(Ar-C), 97.3 (d, J = 2 Hz, Ru-C), 91.6 (d, J = 5 Hz, Ru-C), 86.6 (d, J =
5 Hz, Ru-C), 83.5 (Ru-C), 74.0 (J = 7 Hz, N-CH2−N, PTA), 45.1 (N-
CH3), 42.8 (CH2) (second PTA signal under solvent, ca. 54 ppm). HR
ESI-MS: m/z 660.063 ([M + H]+, calcd for C27H31N5O2PCl2Ru
660.067).
{Dichloro(η6-p-cymene)(N-[3-(imidazol-1-yl)propyl](4-dimethyla-
mino)-1,8-naphthalimide)ruthenium(II)} (8a). [Ru(η6-p-cymene)-
Cl2]2 (88 mg, 0.14 mmol, 1 equiv) and 7a (100 mg, 0.29 mmol, 2
equiv) gave 8a as an orange solid. Yield: 158 mg (84%). Mp: 174−175
°C. Anal. Calcd for C30H34N4O2Cl2Ru·1.5H2O: C, 52.85; H, 5.47; N,
8.22. Found: C, 52.86; H, 5.28; N, 7.70. IR ν (cm−1): 1691, 1647,
1576, 1391, 1370, 1358, 1245, 778, 158, 743, 662. NMR (CDCl3): 1H,
δ 8.57 (d, J = 7.6 Hz, 1H, Ar-H), 8.47 (m, 2H, Ar-H), 7.70 (s, 1H, Im-
H) 7.67 (m, 1H, Ar-H), 7.33 (s, 1H, Im-H), 7.13 (d, J = 8.2 Hz, 1H,
Ar-H), 7.02 (s, 1H, Im-H), 5.45 (d, J = 6.0 Hz, 2H, Ar-H), 5.27 (d, J =
6.0 Hz, 2H, Ar-H), 4.21 (t, 2H, J = 6.7 Hz, N-CH2-CH2), 4.01 (t, J =
7.3 Hz, 2H, CH2-CH2-Im), 3.13 (s, 6H, N-CH3), 2.99 (spt, J = 7.1 Hz,
1H, Ar-CH), 2.25 (m, 2H, CH2-CH2-CH2), 2.18 (s, 3H, Ar-CH3), 1.28
(d, J = 7.1 Hz, 6H, CH3); 13C{1H}, δ 164.8 (CO), 164.2 (CO),
157.5 (Ar-C-NMe2), 140.1 (Im-C), 133.1 (Ar-C), 132.2 (Im-C), 131.8
(Ar-C), 131.4 (Ar-C), 130.5 (Ar-C), 125.4 (Ar-C), 125.0 (Ar-C). 122.8
(Ar-C), 119.5 (Im-C), 114.5 (Ar-C), 113.5 (Ar-C), 102.8 (Ru-C), 97.4
(Ru-C), 82.7 (Ru-C), 81.7 (Ru-C), 46.1 (CH2), 44.9 (N-CH3), 37.1
(CH2), 30.8 (Ar-CH-Me2), 29.4 (CH2), 22.5 (C-CH3), 18.6 (Ar-CH3).
HR ESI-MS: m/z 619.139 ([M − Cl]+, calcd for C30H34N4O2ClRu
619.142).
{Dichloro[η6 -N-(phenylethyl)(4-dimethylamino)-1,8-
naphthalimide](pta)ruthenium(II)} (5b). A solution of 4b (50 mg,
0.05 mmol, 1 equiv) and PTA (15 mg, 0.10 mmol, 2 equiv) in
CH2Cl2/MeOH (60 mL, 2/1) was reacted for 3 h. Workup gave 5b as
{Dichloro(η6-p-cymene)(N-[3-(imidazol-1-yl)propyl]-1,8-
naphthalimide)ruthenium(II)} (8b). [Ru(η6-p-cymene)Cl2]2 (100 mg,
G
dx.doi.org/10.1021/om3007079 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
0.23 mmol, 1 equiv) and 7b (100 mg, 0.7 mmol, 2 equiv) gave 8b as
an orange-yellow solid. Yield: 170 mg (85%). Mp: 163−164 °C. Anal.
Calcd for C28H29N3O2Cl2Ru·H2O: C, 53.41; H, 4.97; N, 6.68. Found:
C, 53.16; H, 4.96; N, 6.34. IR ν (cm−1): 1697, 1656, 1588, 1439, 1387,
1346, 1234, 1093, 1056, 833, 779, 739. NMR (CDCl3): 1H, δ 8.61 (d,
J = 7.4 Hz, 2H, Ar-H), 8.26 (d, J = 8.0 Hz, 2H, Ar-H), 8.01 (s, 1H, Im-
H), 7.79 (m, 2H, Ar-H), 7.35 (s, 1H, Im-H), 7.02 (s, 1H, Im-H), 5.45
(d, J = 5.9 Hz, 2H, Ar-H), 5.27 (d, J = 5.9 Hz, 2H, Ar-H), 4.23 (t, J =
6.9 Hz, 2H, N-CH2-CH2), 4.03 (t, J = 7.1 Hz, 2H, CH2-CH2-Im), 2.99
(spt, J = 7.3 Hz, 1H, Ar-CH), 2.26 (m, 2H, CH2-CH2-CH2), 2.19 (s,
3H, Ar-CH3), 1.29 (d, J = 7.3 Hz, 6H, CH3); 13C{1H}, δ 164.4 (C
O), 140.1 (Im-C), 134.6 (Ar-C), 132.3 (Im-C), 131.8 (Ar-C), 131.7
(Ar-C), 128.3 (Ar-C), 127.2 (Ar-C), 122.4 (Ar-C), 119.5 (Im-C), 102.8
(Ru-C), 97.4 (Ru-C), 82.7 (Ru-C), 81.7 (Ru-C), 46.1 (CH2), 37.4
(CH2), 30.8 (Ar-CH-Me2), 29.3 (CH2), 22.4 (C-CH3), 18.7 (Ar-CH3).
HR ESI-MS: m/z 576.097 ([M − Cl]+, calcd for C28H29N3O2ClRu
576.099).
lium bromide). Cells were seeded in 96-well plates as monolayers with
100 μL of cell solution (approximately 20 000 cells) per well and
preincubated for 24 h in medium supplemented with 10% FCS.
Compounds were prepared as DMSO solutions and then dissolved in
the culture medium and serially diluted to the appropriate
concentration, to give a final DMSO concentration of 0.5%. A 100
μL portion of the drug solution was added to each well, and the plates
were incubated for another 72 h. Subsequently, MTT (5 mg/mL
solution) was added to the cells and the plates were incubated for a
further 2 h. The culture medium was aspirated, and the purple
formazan crystals formed by the mitochondrial dehydrogenase activity
of vital cells were dissolved in DMSO. The optical density, directly
proportional to the number of surviving cells, was quantified at 590 nm
using a multiwell plate reader, and the fraction of surviving cells was
calculated from the absorbance of untreated control cells. Evaluation is
based on means from two independent experiments, each comprising
three microcultures per concentration level.
{Dichloro(η6-toluene)(N-[3-(imidazol-1-yl)propyl](4-dimethylami-
no)-1,8-naphthalimide)ruthenium(II)} (9a). [Ru(η6-toluene)Cl2]2
(76 mg, 0.14 mol, 1 equiv) and 7a (100 mg, 0.29 mmol, 2 equiv)
gave 9a as a yellow solid. Yield: 148 mg (84%). Mp: 140−141 °C.
Anal. Calcd for C27H28N4O2Cl2Ru·1.5H2O: C, 50.70; H, 4.89; N, 8.76.
Found: C, 50.62; H, 4.67; N, 8.16. IR ν (cm−1): 1683, 1638, 1581,
ASSOCIATED CONTENT
■
S
* Supporting Information
Figures giving NMR and HR-ESI MS spectra of selected
compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
1
1389, 1357, 844, 779, 757, 736, 659, 619. NMR (CDCl3): H, δ 8.57
(d, J = 7.2 Hz, 1H, Ar-H), 8.46 (m, 2H, Ar-H), 8.01 (s, 1H, Im-H),
7.68 (m, 1H, Ar-H), 7.35 (s, 1H, Im-H), 7.12 (d, J = 8.1 Hz, 1H, Ar-
H), 7.03 (s, 1H, Im-H), 5.66 (m, 2H, Ar-H), 5.55 (t, J = 5.3 Hz, 1H,
Ar-H), 5.33 (d, J = 5.7 Hz 2H, Ar-H), 4.21 (t, J = 6.8 Hz, 2H, N-CH2-
CH2), 4.01 (t, J = 7.2 Hz, 2H, CH2-CH2-Im), 3.13 (s, 6H, N-CH3),
2.27 (m, 2H, CH2-CH2-CH2), 2.22 (s, 3H, Ar-CH3); 13C{1H}, δ 165.2
(CO), 164.5 (CO), 157.8 (Ar-C-NMe2), 140.7 (Im-C), 133.4
(Ar-C), 132.6 (Im-C), 132.1 (Ar-C), 131.7 (Ar-C), 130.8 (Ar-C), 125.6
(Ar-C), 125.4 (Ar-C), 123.1 (Ar-C), 119.9 (Im-C), 114.7 (Ar-C), 113.7
(Ar-C), 99.9 (Ru-C), 86.6 (Ru-C), 80.1 (Ru-C), 79.8 (Ar-C), 46.4
(CH2), 44.9 (N-CH3), 37.4 (CH2), 29.7 (CH2), 19.5 (Ar-CH3). HR-
ESI MS: m/z 577.094 ([M − Cl]+, calcd for C27H28N4O2ClRu
577.095).
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: paul.dyson@epfl.ch. Tel: +41-21-6939854. Fax: +41-
21-6939780.
Notes
The authors declare no competing financial interest.
Biography
{Dichloro(η6-toluene)(N-[3-(imidazol-1-yl)propyl]-1,8-
naphthalimide)ruthenium(II)} (9b). [Ru(η6-toluene)Cl2]2 (86 mg,
0.16 mmol, 1 equiv) and 7b (100 mg, 0.33 mol, 2 equiv) gave 9b as an
orange-yellow solid. Yield: 157 mg (84%). Mp: 216 °C. Anal. Calcd for
C25H23N3O2Cl2Ru·H2O: C, 51.10; H, 4.29; N, 7.16. Found: C, 51.46;
H, 4.02; N, 7.03. IR ν (cm−1): 1698, 1654, 1586, 1519, 1439, 1341,
1245, 1232, 1169, 1090, 1052, 897, 848, 779, 739, 653, 629, 540. NMR
(CDCl3): 1H, δ 8.62 (d, J = 7.5 Hz, 2H, Ar-H), 8.26 (d, J = 8.6 Hz, 2H,
Ar-H), 8.01 (s, 1H, Im-H), 7.79 (m, 2H, Ar-H), 7.36 (s, 1H, Im-H),
7.04 (s, 1H, Im-H), 5.67 (m, 2H, Ar-H), 5.56 (t, J = 5.4 Hz, 1H, Ar-
H), 5.34 (d, J = 5.8 Hz, 2H, Ar-H), 4.24 (t, J = 6.8 Hz, 2H, N−CH2-
CH2), 4.03 (t, J = 7.2 Hz, 2H, CH2-CH2-Im), 2.28 (m, 2H, CH2-CH2-
CH2), 2.24 (s, 3H, Ar-CH3); 13C{1H}, δ 164.4 (CO), 140.4 (Im-C),
134.5 (Ar-C), 132.4 (Im-C), 131.8 (Ar-C), 131.7 (Ar-C), 128.3 (Ar-C),
127.2 (Ar-C), 122.4 (Ar-C), 119.6 (Im-C), 99.6 (Ru-C), 86.3 (Ru-C),
81.5 (Ru-C), 79.8 (Ru-C), 46.1 (CH2), 37.4 (CH2), 29.3 (CH2), 19.2
(Ar-CH3). HR ESI-MS: m/z 534.050 ([M − Cl]+, calcd for
C25H23N3O2ClRu 534.052).
Since 2008 Paul Dyson has been the chairman of the Institute of
Chemical Sciences and Engineering at the Swiss Federal Institute of
Technology in Lausanne (Ecole Polytechnique Federale de Lausanne,
́ ́
EPFL), having moved to the EPFL in 2002 to head the Laboratory of
Organometallic and Medicinal Chemistry. He grew up in the U.K.,
completing his doctoral thesis in transition-metal carbonyl cluster
chemistry at the University of Edinburgh. Prior to his appointment at
the EPFL he held positions at the Imperial College of Science,
Technology and Medicine (1994−1998) and the University of York
(1998−2002) as a Royal Society University Research Fellow.
Photophysical Experiments with DNA. Freshly prepared solutions
of ct-DNA (Sigma Aldrich) were used for all experiments. The DNA
concentration (based on the nucleotide bases) was determined
spectrophotometrically using an ε260 value of 6600 M−1 cm−1. A
solution of DNA in phosphate buffer (pH 7.4, 10 mM) gave a ratio of
UV absorbance at 260 and 280 nm of ≥1.8, indicating the DNA was
sufficiently free of protein contamination.
Cell Culture and Evaluation of the Anticancer Activity. The
human A2780 and A2780cisR ovarian carcinoma and HEK (human
embryonic kidney) cells were obtained from the European Collection
of Cell Cultures (Salisbury, U.K.). A2780 and A2780R cells were
grown routinely in RPMI-1640 medium, while HEK cells were grown
with DMEM medium, with 10% fetal calf serum (FCS) and antibiotics
at 37 °C and 5% CO2. Cytotoxicity was determined using the MTT
assay (MTT = 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazo-
ACKNOWLEDGMENTS
■
We thank the New Zealand Foundation of Research Science
and Technology for a Postdoctoral Fellowship (EPFL1001) to
K.J.K. and the Swiss National Science Foundation (C.M.C.) for
financial support. Ms. Step
in the synthesis of selected compounds.
́
hanie Crot is thanked for assistance
H
dx.doi.org/10.1021/om3007079 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(38) Scolaro, C.; Hartinger, C. G.; Allardyce, C. S.; Keppler, B. K.;
Dyson, P. J. J. Inorg. Biochem. 2008, 102, 1743−1748.
(39) Stevenson, K. A.; Yen, S. F.; Yang, N. C.; Boykin, D. W.; Wilson,
W. D. J. Med. Chem. 1984, 27, 1677−1682.
(40) Dorcier, A.; Hartinger, C. G.; Scopelliti, R.; Fish, R. H.; Keppler,
B. K.; Dyson, P. J. J. Inorg. Biochem. 2008, 102, 1066−1076.
(41) Kurzwernhart, A.; Kandioller, W.; Bartel, C.; Bachler, S.; Trondl,
R.; Muhlgassner, G.; Jakupec, M. A.; Arion, V. B.; Marko, D.; Keppler,
B. K.; Hartinger, C. G. Chem. Commun. 2012, 48, 4839−4841.
(42) Snelders, D. J. M.; Casini, A.; Edafe, F.; van Koten, G.; Klein
Gebbink, R. J. M.; Dyson, P. J. J. Organomet. Chem. 2011, 696, 1108−
1116.
REFERENCES
■
(1) Doucet, H.; Hierso, J.-C. Curr. Opin. Drug Discovery Dev. 2007,
10, 672−690.
(2) Zapf, A.; Beller, M. Top. Catal. 2002, 19, 101−109.
(3) Hartinger, C. G.; Dyson, P. J. Chem. Soc. Rev. 2009, 38, 391−401.
(4) Beletskaya, I. P.; Ananikov, V. P. Organometallics 2011, 30, 5−6.
(5) Fossey, J. S. Annu. Rep. Prog. Chem., Sect. B: Org. Chem. 2011,
107, 91−101.
(6) Kopf, H.; Kopf-Maier, P. Angew. Chem. 1979, 91, 509−509.
̈
̈
(7) Strohfeldt, K.; Tacke, M. Chem. Soc. Rev. 2008, 37, 1174−1187.
(8) Gasser, G.; Ott, I.; Metzler-Nolte, N. J. Med. Chem. 2010, 54, 3−
25.
(43) Daigle, D. J.; Decuir, T. J.; Robertson, J. B.; Darensbourg, D. J.
In Inorganic Syntheses; Darensbourg, M. Y., Ed.; Wiley: New York,
1998; Vol. 32, pp 40−45.
(9) Hillard, E. A.; Jaouen, G. Organometallics 2011, 30, 20−27.
(10) Therrien, B. Top. Curr. Chem. 2012, 319, 35−56.
(11) Dyson, P. J. Chimia 2011, 65, 730−733.
(44) Ang, W. H.; Daldini, E.; Juillerat-Jeanneret, L.; Dyson, P. J.
Inorg. Chem. 2007, 46, 9048−9050.
(12) Bozec, H. L.; Touchard, D.; Dixneuf, P. H. In Advances in
Organometallic Chemistry; Stone, F. G. A., Robert, W., Eds.; Academic
Press: New York, 1989; Vol. 29, pp 163−247.
(45) Crabb, T. A.; Wilkinson, J. R. J. Chem. Soc., Perkin Trans. 1 1975,
1465−1470.
(13) Therrien, B. Coord. Chem. Rev. 2009, 253, 493−519.
(14) Allardyce, C. S.; Dyson, P. J.; Ellis, D. J.; Heath, S. L. Chem.
Commun. 2001, 1396−1397.
(46) Fujimoto, R. A.; Boxer, J.; Jackson, R. H.; Simke, J. P.; Neale, R.
F.; Snowhill, E. W.; Barbaz, B. J.; Williams, M.; Sills, M. A. J. Med.
Chem. 1989, 32, 1259−1265.
(15) Chatterjee, S.; Kundu, S.; Bhattacharyya, A.; Hartinger, C.;
Dyson, P. J. Biol. Inorg. Chem. 2008, 13, 1149−1155.
(16) Scolaro, C.; Bergamo, A.; Brescacin, L.; Delfino, R.; Cocchietto,
M.; Laurenczy, G.; Geldbach, T. J.; Sava, G.; Dyson, P. J. J. Med. Chem.
2005, 48, 4161−4171.
(17) Nowak-Sliwinska, P.; van Beijnum, J. R.; Casini, A.; Nazarov, A.
̀
A.; Wagnieres, G.; van den Bergh, H.; Dyson, P. J.; Griffioen, A. W. J.
Med. Chem. 2011, 54, 3895−3902.
(18) Astruc, D. New J. Chem. 2005, 29, 42−56.
(19) Schrodi, Y.; Pederson, R. L. Aldrichim. Acta 2007, 40, 45−52.
(20) Ang, W. H.; Casini, A.; Sava, G.; Dyson, P. J. J. Organomet.
Chem. 2011, 696, 989−998.
(21) Hillard, E. A.; Vessier
2010, 32, 81−117.
̀
es, A.; Jaouen, G. Top. Organomet. Chem.
(22) Ang, W. H.; Parker, L. J.; De Luca, A.; Juillerat-Jeanneret, L.;
Morton, C. J.; Lo Bello, M.; Parker, M. W.; Dyson, P. J. Angew. Chem.,
Int. Ed. 2009, 48, 3854−3857.
(23) Pegram, M. D.; Konecny, G. E.; O’Callaghan, C.; Beryt, M.;
Pietras, R.; Slamon, D. J. J. Natl. Cancer Inst. 2004, 96, 739−749.
(24) Chou, T.-C. Pharmacol. Rev. 2006, 58, 621−681.
(25) Vock, C. A.; Ang, W. H.; Scolaro, C.; Phillips, A. D.;
Lagopoulos, L.; Juillerat-Jeanneret, L.; Sava, G.; Scopelliti, R.; Dyson,
P. J. J. Med. Chem. 2007, 50, 2166−2175.
(26) Rademaker-Lakhai, J. M.; van den Bongard, D.; Pluim, D.;
Beijnen, J. H.; Schellens, J. H. M. Clin. Cancer Res. 2004, 10, 3717−
3727.
(27) Hartinger, C. G.; Zorbas-Seifried, S.; Jakupec, M. A.; Kynast, B.;
Zorbas, H.; Keppler, B. K. J. Inorg. Biochem. 2006, 100, 891−904.
(28) Casini, A.; Temperini, C.; Gabbiani, C.; Supuran, C. T.; Messori,
L. ChemMedChem 2010, 5, 1989−1994.
(29) Wu, B.; Ong, M. S.; Groessl, M.; Adhireksan, Z.; Hartinger, C.
G.; Dyson, P. J.; Davey, C. A. Chem. Eur. J. 2011, 17, 3562−3566.
(30) Dhar, S.; Lippard, S. J. In Bioinorganic Medicinal Chemistry;
Alessio, E., Ed.; Wiley-VCH: Weinheim, Germany, 2011; pp 79−95.
(31) Brana, M. F.; Castellano, J. M.; Roldan
́
, C. M.; Santos, A.;
̃
Vaz
́
quez, D.; Jimen
́
ez, A. Cancer Chemother. Pharm. 1980, 4, 61−66.
(32) Ingrassia, L.; Lefranc, F.; Kiss, R.; Mijatovic, T. Curr. Med. Chem.
2009, 16, 1192−1213.
(33) Bailly, C. Chem. Rev. 2012, 112, 3611−3640.
(34) Kucheryavy, P.; Li, G.; Vyas, S.; Hadad, C.; Glusac, K. D. J. Phys.
Chem. A 2009, 113, 6453−6461.
(35) Alexiou, M. S.; Tychopoulos, V.; Ghorbanian, S.; Tyman, J. H.
P.; Brown, R. G.; Brittain, P. I. J. Chem. Soc., Perkin Trans. 2 1990,
837−842.
(36) Banerjee, S.; Kitchen, J. A.; Gunnlaugsson, T.; Kelly, J. M. Org.
Biomol. Chem. 2012, 10, 3033−3043.
(37) Veale, E. B.; Gunnlaugsson, T. J. Org. Chem. 2010, 75, 5513−
5525.
I
dx.doi.org/10.1021/om3007079 | Organometallics XXXX, XXX, XXX−XXX