Anticancer activity of multinuclear arene ruthenium complexes coordinated to dendritic polypyridyl scaffolds

Article abstract of DOI:10.1016/j.jorganchem.2009.06.028

The rational development of multinuclear arene ruthenium complexes (arene = p-cymene, hexamethylbenzene) from generation 1 (G¹) and generation 2 (G²) of 4-iminopyridyl based poly(propyleneimine) dendrimer scaffolds of the type, DAB-(

Full text of DOI:10.1016/j.jorganchem.2009.06.028

Journal of Organometallic Chemistry 694 (2009) 3470–3476
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Anticancer activity of multinuclear arene ruthenium complexes coordinated
to dendritic polypyridyl scaffolds
Preshendren Govender a, Nathan C. Antonels a, Johan Mattsson b, Anna K. Renfrew c, Paul J. Dyson c,
a,
John R. Moss a, Bruno Therrien b, , Gregory S. Smith
*
*
a Department of Chemistry, University of Cape Town, Private Bag, Rondebosch 7701, South Africa
b Institut de Chimie, Université de Neuchâtel, Case postale 158, CH-2009 Neuchâtel, Switzerland
c Institut des Sciences et Ingénierie Chimiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
The rational development of multinuclear arene ruthenium complexes (arene = p-cymene, hexamethyl-
benzene) from generation 1 (G1) and generation 2 (G2) of 4-iminopyridyl based poly(propyleneimine)
dendrimer scaffolds of the type, DAB-(NH2)n (n = 4 or 8, DAB = diaminobutane) has been accomplished
in order to exploit the ‘enhanced permeability and retention’ (EPR) effect that allows large molecules
to selectively enter cancer cells. Four compounds were synthesised, i.e. [{(p-cymene)RuCl2}4G1] (1),
[{(hexamethylbenzene)RuCl2}4G1] (2), [{(p-cymene)RuCl2}8G2] (3), and [{(hexamethylbenzene)RuCl2}8G2]
(4), by first reacting DAB-(NH2)n with 4-pyridinecarboxaldehyde and subsequently metallating the imi-
nopyridyl dendrimers with [(p-cymene)RuCl2]2 or [(hexamethylbenzene)RuCl2]2. The related mononu-
clear complexes [(p-cymene)RuCl2(L)] (5) and [(hexamethylbenzene)RuCl2(L)] (6) were obtained in a
similar manner from N-(pyridin-4-ylmethylene)propan-1-amine (L). The molecular structure of 5 has
been determined by X-ray diffraction analysis and the in vitro anticancer activities of the mono-, tetra-
and octanuclear complexes 1–6 studied on the A2780 human ovarian carcinoma cell line showing a close
correlation between the size of the compound and cytotoxicity.
Received 17 April 2009
Received in revised form 8 June 2009
Accepted 19 June 2009
Available online 26 June 2009
Keywords:
Bioorganometallic chemistry
Poly(propyleneimine)
Medicinal chemistry
Ruthenium
Dendrimers
Anticancer drugs
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
therapies compounds containing titanium [6], gold [7] and ruthe-
nium [8] centres have been established and some have already en-
The use of transition metal complexes as potential therapeutics
and in diagnostic medicine is of considerable importance and a
number of excellent reviews and books are available [1]. The field
stemmed from the discovery of the anticancer activity of the com-
plex cis-diamminedichloroplatinum(II), cisplatin, one of the most
widely used anticancer drugs effective against testicular cancer
and other tumours [2]. Second generation alternatives to cisplatin,
viz. carboplatin and oxaliplatin, are also effective chemotherapeu-
tic agents for certain cancers [3]. Nevertheless, despite the suc-
cesses of cisplatin and related platinum antitumour agents,
research into non-platinum anticancer agents has evolved due to
problems associated with platinum-based chemotherapies. Nota-
bly, the application of cisplatin in the clinic is marred by side-ef-
fects and drug resistance. Perhaps the most distressing side-
effect is that cisplatin-induced frameshift [4] and base substitution
[5] mutations may be responsible for secondary malignancies ob-
served decades after patients have been treated and cured with
this drug. In order to overcome the limitations of platinum based
tered early clinical trials. From these studies ruthenium
compounds have been shown to display less general toxicity than
their platinum counterparts [9], and like platinum compounds are
also able to interact with DNA and proteins [10]. The majority of
ruthenium compounds evaluated for anticancer activity are coor-
dination compounds with the ruthenium in the +3 oxidation state.
It has been proposed that in this oxidation state ruthenium is less
active and is reduced in vivo to more active ruthenium(II) com-
plexes, a process favoured in the hypoxic environment of a tumour
[11]. However, it should be noted that ruthenium(II) compounds
also exhibit a low general toxicity and since cancer cells can also
become oxidized at certain stages of their growth cycle oxidation
of the ruthenium cannot be excluded [12]. Since
p-coordinated
arenes are known to stabilize ruthenium in its +2 oxidation state,
the potential of arene ruthenium(II) complexes as anticancer
agents, and their associated aqueous chemistry, is being increas-
ingly investigated. The first complex evaluated of this kind was
[Ru(benzene)(metronidazole)Cl2] which presented a higher activ-
ity compared to the antitumour drug metronidazole itself [13].
More recently the hydrophilic phosphine-containing [Ru(p-cyme-
ne)(pta)Cl2] (pta = 1,3,5-triaza-7-phosphatricyclo [3.3.1.1] decane),
phosphite-containing [Ru(p-cymene)(P-sugar)Cl2] [14], and
* Corresponding authors. Tel.: +27 0 21 650 5279; fax: +27 0 21 689 7499.
E-mail addresses: bruno.therrien@unine.ch (B. Therrien), gregory.smith@uct.ac.za
(G.S. Smith).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.06.028

P. Govender et al. / Journal of Organometallic Chemistry 694 (2009) 3470–3476
3471
diamine-containing [Ru(arene)(YZ)(Cl)][PF6] (arene = p-cymene or
biphenyl; YZ = chelating diamine) [15] compounds have been
investigated for anticancer activity. A few recent studies describing
polynuclear organometallic Ru complexes with anticancer activity
have been reported. A few dinuclear arene Ru complexes that exhi-
bit a cytotoxic effect against cancer cells are known. Complexes
with sulfoxide [16] and ethylendiamine [17] ligands were found
to be relatively inactive in vitro, whereas pyrone-derived dinuclear
complexes have demonstrated in vitro anticancer activity in the
although tumour targeting of arene ruthenium compounds via
covalent attachment to recombinant human serum albumin via a
pH cleavable linker has been reported [32].
2. Results and discussion
2.1. Synthesis and characterisation of iminopyridyl-functionalised
dendritic ligands G1 and G2
low lM range [18–20]. The in vitro anticancer activity of the latter
A first- (G1) and second-generation (G2) iminopyridyl dendri-
mer based on a poly(propyleneimine) scaffold was synthesised
via a standard Schiff-base reaction. The 4-pyridylimine-functional-
ised dendritic ligands (G1–G2) were synthesised by the reaction of
4-pyridinecarboxaldehyde with DAB-(NH2)n (n = 4, 8 for G1 and G2,
respectively) (Fig. 1). The dendritic ligands are isolated as orange-
yellow oils, in moderate yields. They are soluble in dichlorometh-
ane, chloroform, methanol, diethyl ether and tetrahydrofuran.
The Schiff base condensation reaction is confirmed by appear-
ance of the peak in the range between 8.17 and 8.23 ppm assigned
to the imine protons for G1 and G2. Two distinct doublets
(3J ꢀ 6.00 Hz) are observed for the aromatic protons on the 4-pyr-
idyl rings. 13C{1H} NMR spectra for both ligands (G1–G2) show sim-
ilar spectra. Aliphatic carbons were seen in the region of 25–
60 ppm and aromatic carbons in the region of 120–150 ppm for
both generations. As expected for both ligands the imine-carbon
was the most deshielded signal at 159 ppm. For both G1 and G2,
the IR spectra show two absorption bands of strong intensity at
ꢀ1647, 1599 cmÀ1 and are assigned to the (C@N)imine and
(C@N)aromatic vibrations respectively.
compounds are determined to some extent by their lipophilicity
[20], and their mononuclear analogues are not active in cell cul-
tures [21]. In addition, dinuclear complexes and tri- and tetranu-
clear clusters such as [H3Ru3(benzene)(hexamethylbenzene)2O]+
[22] and [H4Ru4(benzene)4]2+ [23] have been studied in vitro or
in vivo for their activity, and some show promise against cis-
platin-resistant cell lines. These latter compounds are relatively
large and it is not clear how they enter cancer cells. In this respect,
however tumours can be specifically targeted by exploiting the ‘en-
hanced permeability and retention’ (EPR) effect. The EPR effect is a
phenomenon in which macromolecules can accumulate at the tu-
mour site due to an increase in blood vessel permeability within
diseased tissues compared to normal tissues [24]. The normal
endothelial layer surrounding the blood vessels feeding healthy
tissues restricts the size of molecules that can diffuse from the
blood. In contrast, the endothelial layer of blood vessels in diseased
tissues is more porous providing access to the surrounding tissue.
Furthermore, diseased tissue does not usually have a lymphatic
drainage system so once macromolecules have entered the tissue
they are retained. Indeed, a tetraruthenium cluster was even found
to be highly active against the polio virus without damaging the
host cells, thereby offering the potential of developing highly selec-
tive drugs [23].
2.2. Synthesis and characterisation of ruthenium complexes 1–6
The dinuclear arene ruthenium complexes [(arene)RuCl2]2 (are-
ne = p-cymene, hexamethylbenzene) react with the dendritic ligands
G1 and G2 by stirring at room temperature in dichloromethane to
yield the neutral tetranuclear (1–2) and octanuclear (3–4) ruthenium
metallodendrimers (Fig. 2). The yellow-orange solids (1–4) are
isolated as air-stable solids in high yields (79–98%). The complexes
aresolubleinmostorganicsolventssuchasdichloromethane, chloro-
form, ethanol, dimethylsulfoxide, acetone, acetonitrile, diethyl ether
and tetrahydrofuran.
In order to exploit size selective uptake of drugs into tumour
cells effectively, large compounds are required, and in recent years,
dendrimers have found potential as molecular tools in biological
applications [25], especially as nano-carriers [26], diagnostic
agents [27] and as chemotherapeutics [28]. Moreover, another
advantage of dendrimers is their multivalency, which leads to in-
creased interaction between a dendrimer-drug conjugate and a
target bearing multiple receptors, further improving the selectivity
to cancer cells. With the aim of reducing the inherent problems re-
lated to cisplatin such as poor water solubility, high toxicity and
side effects, the combination of platinum-based drugs with den-
dritic systems is very appealing. However, transition metal com-
plexes with anticancer activity, based on a dendritic scaffold are
quite rare. Duncan et al. reported the conjugation of cisplatin to
a polyamidoamine (PAMAM) dendrimer, modified on the periph-
ery with sodium carboxylate functionalities [29]. The dendrimer-
platinate is water soluble and displayed antitumour activity when
administered intravenously against a B16F10 melanoma, whereas
cisplatin was inactive. Using the commercially available butanedi-
amine poly(propyleneimine) dendrimer (DAB(PA)4) which pro-
The 1H NMR spectra of 1–4 shows broadened peaks upon com-
plexation of the multinuclear ruthenium moieties. The aliphatic
protons of the dendritic core and side arms occur at similar shifts
to those of the dendritic ligand precursors. Evidence for the coordi-
nation of the ruthenium metal to the aromatic nitrogen atom can
be seen by a shift in the doublet (assigned to aromatic protons
on the carbon adjacent to pyridyl nitrogen atom) from 8.66 to
9.10 ppm. A shift in the signal is due to the electron-withdrawing
effects of the coordinating metal, resulting in the signals being
shifted downfield. There is also no distinct shift in the imine proton
suggesting no coordination at this position. The 1H NMR spectrum
for the second generation complexes (3–4) showed similar shifts to
the first generation. This alludes to coordination at the pyridyl
nitrogen only and not the imine nitrogen. This is further confirmed
by IR spectroscopic studies. Infrared spectroscopic studies show a
shift in the (C@N)aromatic peak from a lower wavenumber to a high-
er wavenumber at around 1615 cmÀ1. The (C@N)imine absorption
band remains unchanged at around 1646 cmÀ1. These shifts were
as a direct result of the synergic effect. The second generation den-
dritic complexes show similar trends. The ruthenium functional-
ised dendrimers (1–4) were precipitated with the inclusion of
solvent, trapped between the dendritic arms. The elemental analy-
sis data correlates with the inclusion of 2 molecules and 4 mole-
cules of dichloromethane for 1 and 3, respectively.
vides four peripheral amine groups
a series of tetranuclear
platinum compounds were synthesised. The cationic compound
[DAB(PA)4-{Pt(NH3)2Cl}4]4+ was designed to overcome cisplatin
resistance [30], while the neutral derivative DAB(PA)4-
{Pt(dmso)(L)}4 (L = meso-1,2-bis(4-fluorophenyl)ethylenediamine)
was prepared to increase selectivity for breast cancer cells [31].
With the established anticancer activity of arene ruthenium com-
plexes and the current interest in dendrimers for biological appli-
cations, we decided to explore the synthesis of multinuclear
ruthenium complexes based on a poly(propyleneimine) scaffold
and investigate their cytotoxicity against A2780 human ovarian
cancer cell line. As far as we are aware these studies are the first
to target arene ruthenium compounds using this approach

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P. Govender et al. / Journal of Organometallic Chemistry 694 (2009) 3470–3476
1
2
Fig. 1. First- and second-generation of iminopyridyl dendritic ligands G1 and G2.
Ru
Cl
Ru
N
N
N
N
Cl
Cl
Cl
Ru
Cl
Ru
Cl
N
N
Cl
Cl
Cl
Cl
N
N
Cl
Cl
Ru
N
Ru
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Ru
N
Ru
Cl
Cl
N
N
N
N
N
N
Cl
Cl
N
Cl
N
Cl
N
N
N
N
Ru
Cl
Ru
Cl
N
N
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
N
N
Ru
Ru
Ru
Ru
Ru
Ru
Cl
Cl
Cl
Cl
Fig. 2. Tetra- and octanuclear arene ruthenium dendritic systems 1–4.
For comparison, the analogous mononuclear ruthenium com-
plexes (5–6) were synthesised. These were prepared by reacting
the ligand, N-(pyridin-4-ylmethylene)propan-1-amine (L), with
the dinuclear arene ruthenium complexes [(arene)RuCl2]2 (are-
ne = p-cymene, hexamethylbenzene) in dichloromethane at room
temperature, see Scheme 1.
2
2
The mononuclear ruthenium complexes (5–6) are isolated as
yellow-orange solids in high yields. They are air-stable and soluble
in dichloromethane, chloroform, ethanol, dimethylsulfoxide, ace-
tone, acetonitrile, diethyl ether and tetrahydrofuran. The aromatic
protons adjacent to the pyridyl nitrogen atom appear more down-
field than for the uncoordinated ligand (8.66–9.10 ppm), while the
imine protons remain at the same position as for the dendritic li-
gand (ꢀ8.2 ppm). A shift in the (C@N)aromatic absorption band in
Scheme 1. Synthesis of the mononuclear arene ruthenium complexes 5 and 6.
the IR spectrum of 5 and 6 is seen from around 1550–1615 cm-1
.
coordination of the ruthenium metal occurred to the aromatic
nitrogen atom was further confirmed by the X-ray structure anal-
ysis of complex 5.
The (C@N)imine absorption band around 1647 cmÀ1 remains con-
stant and confirms that no coordination occurred at this site. The

P. Govender et al. / Journal of Organometallic Chemistry 694 (2009) 3470–3476
3473
Table 1
2.3. X-ray diffraction study of complex 5
IC50 values of cisplatin and complexes 1 – 6 on A2780 human ovarian cancer cell line.a
X-ray quality crystals for complex 5 were obtained by slow dif-
fusion of hexane into a concentrated dichloromethane solution of
5. The molecular structure of 5 shows that, like other arene ruthe-
nium complexes [33], the metal centre adopts a piano-stool, pseu-
do-tetrahedral geometry, with ruthenium coordinated by the
arene ligand, two chlorides and the iminopyridyl ligand. An ORTEP
drawing of 5 is shown in Fig. 3 together with selected bond lengths
and angles.
The distance between the ruthenium atom and the centre of the
C6H4 aromatic ring of the p-cymene ligand is 1.670(4) Å. The Ru–N
and Ru–Cl bond distances in 5 are comparable to those reported in
the pyridine (py) derivatives [(1,3,5-trimethylbenzene)RuCl2(py)]
[34] and [(hexamethylbenzene)RuCl2(py)] [35]. Similarly, the
Cl–Ru–N and Cl–Ru–Cl bond angles of complex 5 [84.8 (2) and
87.0(2)°] are similar to those in [(1,3,5-trimethylbenzene)-
RuCl2(py)] and [(hexamethylbenzene)RuCl2(py)]. As suggested
previously, only the aromatic nitrogen atom is found to be coordi-
nated to the ruthenium atom, thus validating the coordination
mode proposed in complexes 1–6.
Compounds
1
2
3
4
5
6
cisplatin
1.6
IC50
(lM)
43
40
21
20
98
94
a
Maximum error is <
5 lM.
atively low for ruthenium compounds. These are the first examples
of ruthenium-arene-dichloro complexes with an imino-pyridine li-
gand to be tested for in vitro activity. However, analogous hexa-
methylbenzene and p-cymene cyanopyridine complexes have
previously been reported to show significant unwinding of super-
coiled DNA and also inhibit haem polymerase activity. In contrast,
[(p-cymene)Ru(pyridine)Cl2] was found to show negligible activity
in the TS/A cell line [36].
There is a clear trend between the size of the dendritic com-
pound and cytotoxicity, i.e. the monoruthenium compounds have
modest cytotoxicity whereas [{(p-cymene)RuCl2}8G2]
3 and
[{(hexamethylbenzene)RuCl2}8G2] 4 are cytotoxic. Based on this
observation, the biological properties of 3 and 4 are worth studying
further as they may be able to target cancerous tissues more effec-
tively than smaller compounds by exploiting the enhanced perme-
ability and retention effect, a property that needs to be evaluated
in vivo. Moreover, the activity shown here for 3 and 4 is not too dis-
similar to that of the multinuclear arene ruthenium adduct of re-
combinant human serum albumin [26], but the facile synthesis
and considerably lower cost of the dendrimer system, cannot be
overlooked.
2.4. Anticancer activity of complexes 1–6
The ability of 1–6 to inhibit cancer cell growth was evaluated
in vitro using the biological MTT assay which measures mitochon-
drial dehydrogenase activity as an indication of cell viability using
the A2780 ovarian cancer cell line. The compounds were incubated
at various concentrations (in triplicate) in the A2780 cells and cell
viability was measured after an incubation period of 72 hours. Each
experiment was conducted in duplicate and the IC50 values (inhibi-
tion of cancer cell growth at the 50% level) listed in Table 1 are cal-
culated as an average over the two experiments.
3. Experimental
3.1. General remarks
All compounds display moderate anti-proliferative activity in
the A2780 cell line. While the IC50 values determined are higher
than that of cisplatin, the most active compounds, 3 and 4, are rel-
All reagents were purchased either from Aldrich or Fluka and
used as received. [(p-cymene)RuCl2]2, [(hexamethylben-
zene)RuCl2]2 [37] were prepared according to the literature meth-
ods. The NMR spectra were recorded on a Varian Unity 400
spectrometer (1H: 400 MHz, 13C: 100 MHz) or Varian Mercury
300 (1H: 300 MHz, 13C: 75 MHz) at ambient temperature unless
stated otherwise. Infrared (IR) absorptions were measured on a
Perkin-Elmer Spectrum One FT-IR spectrometer in dichlorometh-
ane using NaCl solution cells. Microanalyses were carried out using
a Fisons EA 110 CHNS elemental analyser. For certain dendrimers,
the analyses are outside acceptable limits, and are ascribed to the
encapsulation of solvent molecules and other inorganic salts by
dendritic compounds. Melting points were determined using a Ko-
fler hot stage microscope (Riechart Thermover) and are corrected.
Mass spectrometry was carried out at the University of Stel-
lenbosch on a Waters API Quattro Micro triple quadrupole mass
spectrometer. Data were recorded using Electrospray Ionisation
(ESI) mass spectrometry in the positive-ion mode.
3.2. Synthesis of dendrimers G1 and G2
A solution of 4-pyridinecarboxaldehyde (1.23 mL, 0.129 mmol)
in dry toluene (5.00 mL) was added dropwise to an ice-cooled solu-
tion of DAB-(NH2)4 (1.006 g, 3.18 mmol) in dry toluene (50.0 mL).
The reaction mixture was stirred at room temperature in the pres-
ence of anhydrous MgSO4 (ꢀ10 g) for 24 h. The slurry was filtered
and the solvent removed by rotary evaporation yielding an orange
residue. The residue was dissolved in dichloromethane (20 mL),
and washed copiously with H2O (6 Â 20 mL). The organic layer
was collected and dried over anhydrous MgSO4. After filtration
by gravity, the solvent removed by rotary evaporation to yield
the product as an oil, which was dried in vacuo.
Fig. 3. Molecular structure of the mononuclear complex 5 showing ellipsoids at the
50% probability level. Selected bond lengths (Å) and angles (°): Ru(1)–N(1) 2.128(9),
Ru(1)–Cl(1) 2.406(3), Ru(1)–Cl(2) 2.405(3), N(2)–C(16) 1.34(3), N(2)–C(17) 1.49(3);
N(1)–Ru(1)–Cl(1) 84.8(2), N(1)–Ru(1)–Cl(2) 87.0(2), Cl(1)–Ru(1)–Cl(2) 87.65(12),
C(13)–C(16)–N(2) 115(2), C(16)–N(2)–C(17) 125(2).

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P. Govender et al. / Journal of Organometallic Chemistry 694 (2009) 3470–3476
3.2.1. Data for dendritic ligand G1
3.3.3. [{(p-cymene)RuCl2}8G2] (3)
Pale yellow oil, yield 1.48 g (67.9%). 1H NMR (400 MHz, CDCl3):
dppm = 1.42 (m, 4H, CH2), 1.83 (qn, 8H, CH2), 2.38 (br t, 4H, CH2),
2.52 (m, 8H, CH2), 3.63 (t, 8H, 3J = 7.53 Hz, CH2), 7.52 (d, 8H, 3J =
6.04 Hz, Arpyr), 8.23 (s, 4H, imine), 8.63 (d, 8H, 3J = 6.02 Hz,
Arpyr). 13C {1H} NMR (100 MHz, CDCl3): dppm = 25.3, 28.3, 51.7,
54.1, 59.8 (CH2); 121.8, 150.4 (CH, Arpyr); 143.0 (C, Arpyr); 159.0
Yellow-orange solid, yield 0.30 g (98.1%). M.p.: 214 °C (decom-
pose, without melting). 1H NMR (300 MHz, CDCl3): dppm = 1.32 (d,
48H, 3J = 6.92 Hz, CHMe2), 1.35–1.48 (overlapping m, 12H, CH2),
1.78 (m, 16H, CH2), 2.09 (s, 24H, CH3), 2.30–2.53 (overlapping m,
36H, CH2), 2.97 (m, 8H, CHMe2), 3.67 (m, 16H, CH2), 5.28 (d, 16H,
3J = 6.02 Hz, Arp-cy), 5.49 (d, 16H, 3J = 6.01 Hz, Arp-cy), 7.49 (d, 16H,
3J = 6.61 Hz, Arpyr), 8.19 (s, 8H, imine), 9.05 (d, 16H, J3 = 6.53 Hz,
Arpyr). 13C {1H} NMR (75 MHz, CDCl3): dppm = 18.2, 22.2 (CH3,
p-cy), 27.1, 38.8, 51.4, 55.2, 58.8 (CH2), 122.5, 155.3 (CH, pyr),
144.2 (C, pyr), 30.6, 82.0, 83.0 (CH, p-cy), 97.4, 103.2 (C, p-cy),
158.3 (CH, imine). IR (NaCl cells, CH2Cl2, cmÀ1): m(imine, C@N) 1646
(s), m(pyr, C@N) 1614 (s). Anal. Calc. for C168H232Ru8Cl16N22.4CH2Cl2:
C, 48.32; H, 5.66; N, 7.21. Found: C, 48.37; H, 6.03; N, 6.61%. MS
(CH, imine). IR (NaCl cells, CH2Cl2, cmÀ1): m(imine
1648 (s),
C@N)
m(aromatic
1599 (s). Anal Calc. for C40H52N10.
1/2CH2Cl2: C,
C@N)
68.00; H, 7.47; N, 19.58. Found: C, 68.42; H, 7.50; N, 20.02%.
3.2.2. Data for dendritic ligand G2
Pale yellow oil, yield 1.47 g (75.4%). 1H NMR (300 MHz, CDCl3):
dppm = 1.39 (br m, 4H, CH2), 1.47 (br m, 8H, CH2), 1.72 (m, 16H,
CH2), 1.94-2.44 (overlapping m, 36H, CH2), 3.56 (br t, 16H,
3J = 6,49 Hz, CH2), 7.48 (d, 16H, 3J = 6.03 Hz, Arpyr), 8.17 (s, 8H,
imine), 8.57 (d, 16H, 3J = 5.99 Hz, Arpyr). 13C {1H} NMR (75 MHz,
CDCl3): dppm = 24.8, 25.2, 28.3, 51.7, 52.2, 52.3, 54.3, 59.8 (CH2);
121.8, 150.4 (CH, Arpyr); 142.9 (C, Arpyr); 159.0 (CH, imine). IR (NaCl
(ESI, m/z): 569.0 [M-7Cl + 3CH2Cl2 + CH3CN]7+
.
3.3.4. [{(hexamethylbenzene)RuCl2}8G2] (4)
Yellow-orange solid, yield 0.23 g (91.7%). M.p.: 194 °C (decom-
pose, without melting). 1H NMR (400 MHz, CDCl3, d ppm): 1.31
(br m, 4H, CH2), 1.63 (br m, 8H, CH2), 1.87 (m, 8H, CH2), 1.99 (s,
144H, CH3), 2.15–2.38 (overlapping m, 24H, CH2), 2.50 (m, 4H,
CH2,), 2.60 (m, 16H, CH2), 3.69 (m, 16H, CH2), 7.54 (d, 16H,
3J = 6.0 Hz, Arpyr), 8.23 (s, 8H, imine), 8.78 (d, 16H, 3J = 5.6 Hz, Arpyr).
13C {1H} NMR (100 MHz, CDCl3, d ppm): 15.4 (CH3, HMB); 25.3–
58.9 (CH2), 91.4 (C, HMB), 122.5, 155.0 (CH, pyr); 144.1 (C, pyr);
cells, CH2Cl2, cmÀ1): m(imine
1648 (s), m(aromatic
1599 (s).
C@N)
C@N)
Anal. Calc. for C88H120N22.1/2CH2Cl2: C, 69.54; H, 7.98; N, 20.16.
Found: C, 69.24; H, 8.18; N, 20.49%.
3.3. Synthesis of complexes 1–4
158.9 (C, imine). IR (NaCl cells, CH2Cl2, cmÀ1): m(imine,
1646
C@N)
The dimer [(arene)RuCl2]2 (0.35 mmol, 0.213 g for 1;
0.081 mmol, 0.056 g for 2; 0.307 mmol, 0.199 g for 3; 0.248 mmol,
0.168 g for 4) was dissolved in dry dichloromethane (30 mL). To
this was added a solution of the dendritic ligand in dichlorometh-
ane (5 mL): G1 (0.17 mmol, 0.117 g for 1; 0.041 mmol, 0.027 g for
2), and G2 (0.077 mmol, 0.114 g for 3; 0.041 mmol, 0.062 g for 4).
The reaction mixture was allowed to stir at room temperature
for 5 h. The solvent was reduced to 3 mL, and the product was pre-
cipitated with petroleum ether. The resulting yellow–orange pre-
cipitate was filtered, washed with petroleum ether and dried in
vacuo.
(s), m(pyr, C@N) 1613 (s). Anal. Calc. for C184H264Ru8Cl16N22.2CH2Cl2:
C, 51.60; H, 6.24; N, 7.12. Found: C, 51.69; H, 6.43; N, 6.82%. MS
(ESI, m/z): 631.0 [M-7Cl + 5CH2Cl2 + 2CH3CN]7+
.
3.4. Synthesis of the mononuclear complexes 5 and 6
The N-(pyridin-4-ylmethylene)propan-1-amine (L), was pre-
pared by the reaction of 4-pyridinecarboxaldehyde (0.107 g,
0.723 mmol for 5; 0.030 g, 0.200 mmol for 6) with n-propylamine
in diethyl ether. [(p-cymene)RuCl2]2 (0.223 g, 0.362 mmol) or
[(hexamethylbenzene)RuCl2]2 (0.068 g, 0.100 mmol) was dissolved
in dry dichloromethane (30 mL). A solution of the N-(pyridin-4-
ylmethylene)propan-1-amine (0.107 g, 0.723 mmol) in dry dichlo-
romethane (5 mL) was added dropwise and the reaction mixture
was allowed to stir for 5 hours. The solvent was reduced to approx-
imately 3 mL, and the product was precipitated with petroleum
ether. The orange-yellow precipitate was washed with petroleum
ether and dried in vacuo.
3.3.1. [{(p-cymene)RuCl2}4G1)] (1)
Yellow-orange solid, yield 0.26 g (79.1%). M.p.: 165 °C (decom-
pose, without melting). 1H NMR (300 MHz, CDCl3): dppm = 1.30 (d,
24H, 3J = 6.87 Hz, CHMe2), 1.47 (br m, 4H, CH2), 1.83 (br m, 8H,
CH2), 2.09 (s, 12H, CH3), 2.44–2.97 (overlapping m, 12H, H2, H3),
2.97 (m, 4H, CHMe2), 3.67 (m, 8H, H5), 5.28 (d, 8H, 3J = 6.09 Hz,
Arp-cy), 5.70 (d, 8H, 3J = 5.70 Hz, Arp-cy), 7.49 (d, 8H, 3J = 6.15 Hz,
Arpyr), 8.20 (s, 4H, imine), 9.06 (d, 8H, 3J = 5.42 Hz, Arpyr). 13C {1H}
NMR (100 MHz, CDCl3): dppm = 18.3, 22.3 (CH3, p-cy), 27.1, 31.5,
51.2, 53.7, 58.8 (CH2), 122.5, 155.3 (CH, pyr); 139.8 (C, pyr), 30.7,
82.1, 83.3 (CH, p-cy); 97.5, 103.3 (C, p-cy); 158.4 (CH, imine). IR
3.4.1. [(p-cymene)RuCl2(L)] (5)
Yellow–orange solid, yield 0.15 g (91.1%). M.p.: 163-166 oC. 1H
NMR (400 MHz, CDCl3): dppm = 0.97 (t, 3H, 3J = 7.39 Hz, CH3), 1.32
(d, 6H, 3J = 6.93 Hz, CHMe2), 1.75 (m, 2H, CH2), 2.11 (s, 3H, CH3),
3.00 (m, 1H, CHMe2), 3.66 (t, 2H, 3J = 6.47 Hz, CH2), 5.23 (d, 2H,
3J = 5.93 Hz, Arp-cy), 5.45 (d, 2H, 3J = 5.92 Hz, Arp-cy), 7.60 (d, 2H, 3J
= 6.53 Hz, Arpyr), 8.27 (s, 1H, imine), 9.10 (d, 2H, 3J = 6.43 Hz, Arpyr).
13C {1H} NMR (100 MHz, CDCl3): dppm = 11.8 (CH3), 18.2, 22.3 (CH3,
p-cy), 23.8, 63.6 (CH2), 30.7, 82.2, 83.1 (CH, p-cy), 97.3, 103.6 (C, p-
cy), 122.5, 155.3 (CH, pyr), 144.6 (C, pyr), 157.3 (CH, imine). IR
(NaCl cells, CH2Cl2, cmÀ1): m(imine,
1646 (s), m(pyr,
1615
C@N)
C@N)
(s). Anal. Calc. for C80H108Ru4Cl8N10.11/2CH2Cl2: C, 48.34; H, 5.52;
N, 6.92. Found: C, 48.22; H, 5.15; N, 6.74%. MS (ESI, m/z): 565.0
[M + 4H + 4CH2Cl2 + H2O]4+
.
3.3.2. [{(hexamethylbenzene)RuCl2}4G1] (2)
(NaCl cells, CH2Cl2, cmÀ1): m(imine,
1647 (s), m(pyr,
1615
Yellow-orange solid, yield 0.050 g (86.5%). M.p.: 188 °C (decom-
pose, without melting). 1H NMR (300 MHz, CDCl3, d ppm): 1.44 (br
m, 4H, CH2), 1.85 (br m, 8H, CH2), 1.97 (s, 72H, CH3), 2.49–2.58
(overlapping m, 12H, CH2), 3.67 (m, 8H, CH2), 7.51 (d, 8H,
3J = 6.4 Hz, Arpyr), 8.23 (s, 4H, imine), 8.78 (d, 8H, 3J = 6.3 Hz, Arpyr).
13C {1H} NMR (75 MHz, CDCl3, d ppm): 15.4 (CH3, HMB); 24.2, 26.2,
51.0, 53.4, 58.2 (CH2); 91.4 (C, HMB); 122.5, 155.0 (CH, pyr); 143.9
(C, pyr); 158.9 (CH, imine). IR (NaCl cells, CH2Cl2, cmÀ1): m(imine, C@N)
C@N)
C@N)
(s). Anal. Calc. for C19H26RuCl2N2: C, 50.22; H, 5.77; N, 6.16. Found:
C, 49.96; H, 5.38; N, 5.99%. MS (ESI, m/z): 419.1 [MÀCl]+.
3.4.2. [(hexamethylbenzene)RuCl2(L)] (6)
Orange solid, yield 0.15 g (91.1%). M.p.: 139 oC (decompose,
without melting). 1H NMR (400 MHz, CDCl3, d ppm): 0.96 (t, 3H,
3J = 7.4 Hz, CH3), 1.74 (m, 2H, CH2), 2.03 (s, 18H, CH3), 3.66 (t, 2H,
3J = 6.9 Hz, CH2), 7.57 (d, 2H, 3J = 6.4 Hz, Arpyr), 8.26 (s, 1H, imine),
8.86 (d, 2H, 3J = 6.2 Hz, Arpyr). 13C {1H} NMR (100 MHz, CDCl3, d
ppm): 11.8 (CH3), 15.4 (CH3, HMB), 23.8, 63.6 (CH2), 91.4 (C,
1646 (s), m(pyr,
1614 (s). Anal. Calc. for C88H124Ru4Cl8N10.
C@N)
CH2Cl2: C, 51.03; H, 6.06; N, 6.69. Found: C, 51.01; H, 5.85; N,
6.39%. MS (ESI, m/z): 635.0 [MÀ3Cl]3+
.

P. Govender et al. / Journal of Organometallic Chemistry 694 (2009) 3470–3476
3475
HMB), 122.5, 155.1 (CH, pyr), 144.2 (C, pyr), 157.5 (CH, imine). IR
(NaCl cells, CH2Cl2, cmÀ1): m(imine,
1646 (s), m(pyr, 1614
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.jorganchem.2009.06.028.
C@N)
C@N)
(s). Anal. Calc. for C21H30RuCl2N2: C, 52.28; H, 6.27; N, 5.81. Found:
C, 51.84; H, 5.94; N, 5.47%. MS (ESI, m/z): 447.1 [MÀCl]+.
3.5. X-ray crystallography
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