Tuning the electronic properties of dppz-ligands and their palladium(ii) complexes

Article abstract of DOI:10.1039/b926233d

New organometallic palladium complexes of the general type [(RR′dppz)Pd(Me)L]ⁿ⁺ (RR′dppz = derivatives of dipyrido[3,2-a:2′,3′-c]phenazine with RR′ = 11-Cl, 11,12-Cl₂, 11-CF₃, 11-NO₂, 11-NH₂; L = Cl, 1-methyluracilate (n = 0), pyridine, cytosine, caffeine, or 1-methylcytosine, (all n = 1) were characterised and studied in detail by electrochemical and spectroscopic (NMR, UV/Vis- absorption and emission) methods. EPR spectroscopy and density functional calculations reveal markedly tuneable lowest unoccupied molecular orbitals (LUMO) located at the dppz ligands. Cytotoxicity experiments on HT-29 colon carcinoma and MCF-7 breast cancer cell lines show promising activities for selected compounds.

Full text of DOI:10.1039/b926233d

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Tuning the electronic properties of dppz-ligands and their palladium(II)
complexes†
a
b
a
c
a
Katharina Butsch, Ronald Gust, Axel Klein,* Ingo Ott and Marco Romanski
Received 11th December 2009, Accepted 1st March 2010
First published as an Advance Article on the web 25th March 2010
DOI: 10.1039/b926233d
n+
New organometallic palladium complexes of the general type [(RR¢dppz)Pd(Me)L] (RR¢dppz =
derivatives of dipyrido[3,2-a:2¢,3¢-c]phenazine with RR¢ = 11-Cl, 11,12-Cl
2
, 11-CF
3
, 11-NO ,
2
1
1-NH
2
; L = Cl, 1-methyluracilate (n = 0), pyridine, cytosine, caffeine, or 1-methylcytosine, (all n = 1)
were characterised and studied in detail by electrochemical and spectroscopic (NMR, UV/Vis-
absorption and emission) methods. EPR spectroscopy and density functional calculations reveal
markedly tuneable lowest unoccupied molecular orbitals (LUMO) located at the dppz ligands.
Cytotoxicity experiments on HT-29 colon carcinoma and MCF-7 breast cancer cell lines show
promising activities for selected compounds.
Introduction
many of these complexes. The vast majority of dppz-complexes
II 4,7,8
II 8,9
I
8,10
0
8
III 11
II 12
studied so far contain Ru ,
Os , Re , Mo , Co , Ni ,
Recently there has been much interest in the analysis and ap-
plication of transition metal complexes bearing the dipyrido[3,2-
a:2,3-c]phenazine (dppz) ligand. The heterocyclic p system of dppz
combines the chelating function of a-diimines (“polypyridines”)
such as 2,2¢-bipyridine (bpy), or 1,10-phenanthroline (phen)
with the electron and proton transfer capacity of 1,4-diazines
II 8,13
I
8,10c
II
or Pt ,
and Cu ,
while only a few Pd compounds such
as [(11-Rdppz)Pd(Me)(MeCN)][BArF], (R = NO
2
, COOH, Cl,
(en = ethylendiamine),
5
14
H, CH
(dppz)
3
, or NH
Pd][BF
2
), [(dppz)Pd(en)]Cl
2
15
[
2
4
]
2
II
and [(dppz)
2
Pd][PF
6
]
2
,
were reported. How-
1
ever, for these Pd complexes neither their “light switch” nor their
cytotoxic properties were investigated. Instead, the latter com-
2
(pyrazines, quinoxalines, phenazines, etc.) (Scheme 1).
15
plexes are used as catalysts for the CO/styrole-polymerisation.
II
Related Pt complexes [(dppz)Pt(tN∧C)]CF
3
SO
](CF
-methylimidazole or 4-aminopyridine) have been reported to
effectively bind to double-stranded DNA and the cytotoxicity of
(dppz)Pt (tN∧C)]CF SO against human carcinoma KB-3-1 and
its multidrug-resistant subclone KB-V1 cell lines, was found to be
3
(tN∧C = 4-
tert-butyl-2-phenylpyridine) and [(dppz)Pt(L)
2
3
3 2
SO )
(L =
1
[
3
3
1
3
1
0 and 40 times higher, respectively, than cisplatin.
Detailed studies have revealed that the dppz ligand has three
Scheme 1 The dppz-ligand, shown as a schematic transition metal
complex, consists of a chelating a-diimine (bpy) part and a strongly
electron-accepting phenazine (phz) part; ML
close lying lowest unoccupied molecular orbitals (LUMO) which
determine largely the electrochemical and photophysical proper-
n
= transition metal and n
co-ligands.
ties. The a-diimine acceptor orbitals b
1
(y) and a
2
(c) lie above
the phenazine-based p* MO, b
1
(phz) and the two parts are
It has been established for a number of complexes that
8
electronically rather separated. These orbitals can be influenced
through various modification strategies. i) Coordination of dppz
usually lowers the a-diimine-centred LUMOs, in the case of
strongly electrophilic metal ions the levels might even cross. This
effect can be finely tuned through variation of the co-ligands
3
such systems can be used as “molecular light switches” (e.g.
2
+
4
5
[
(dppz)Ru(bpy) ] ) and as catalysts. They owe this application
2
to the planar dppz part of such complexes allowing intercalation
8
6
into DNA, which is the reason for the cytotoxic properties of
on the metal and, of course, by changing the redox state of the
a
Universit a¨ t zu K o¨ ln, Institut f u¨ r Anorganische Chemie, Greinstraße 6,
16-18
metal.
ii) Protonation and solvation effects mainly affect the
D-50969, K o¨ ln, Germany. E-mail: axel.klein@uni-koeln.de
b
phenazine part, in both cases the N9 and N14 atoms are the main
Institut f u¨ r Pharmazie, Pharmazeutische Chemie, Freie Universit a¨ t Berlin,
17,19
targets.
iii) Modification of the dppz-ligand by substitution
K o¨ nigin-Luise-Strasse 2+4, D-14195, Berlin, Germany
c
Institute of Pharmaceutical Chemistry, Technische Universit a¨ t Braun-
of H or C atoms as well as prolongation of the p-systems is also
schweig, Beethovenstrasse 55, D-38106, Braunschweig, Germany
20-24
feasible.
A great diversity of substituted dppz-ligands is already
†
Electronic supplementary information (ESI) available: Further figures
known, some of them have markedly different electrochemical and
with absorption-, excitation- and emission spectra of free ligands and
complexes and drawings of the calculated LUMOs of cdppz, dcdppz
and tfmdppz can be viewed. Also, a table summarising short H ◊ ◊ ◊ F
22
optical properties, which opens various possibilities for appli-
cation e.g. the 3,6-dibutyl substituted benzodipyridophenazines
contacts in the crystal structure of [(dppz)Pd(Me)(Py)][SbF
6
], and tables
23
can be used as ion sensing materials while complexes of
listing absorption, emission and electrochemical data of free ligands
and complexes are provided. CCDC reference number 750425. For ESI
and crystallographic data in CIF or other electronic format see DOI:
II
Ru with phenazine-substituted ligands such as 12-NO
2
-dppz
1
0.1039/b926233d
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Dalton Trans., 2010, 39, 4331–4340 | 4331

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and 12-Cl-dppz are known to catalyse the water gas shift
24
reaction.
Furthermore, it can be expected that the substituents influence
the intercalating properties and therefore the compound’s toxicity.
Till now this was mainly investigated using dppz-compounds
25
with an extended aromatic system and water-soluble ionic dppz
26
analogues (with an ethyl-bridge between N4 and N5). Recent
III
investigations on Ir complexes bearing alkynyl-dppz derivatives
27
as ligands can trigger the oxidation and reduction of DNA bases.
In this work we present a series of new organopalladium com-
n+
plexes [(dppz)Pd(Me)L] with various dppz ligands (RR¢dppz)
and co-ligands of biological relevance as Cl, 1-methyluracilato
Scheme 3 Two different synthetic routes (A) and (B) for the synthesis of
n+
[
(RR¢dppz)Pd(Me)L] with partial numbering; COD = 1,5-Cyclooctadi-
(
(
n = 0), pyridine, cytosine, caffeine, or 1-methylcytosine (n = 1)
ene, L = various N-donor ligands.
Scheme 2). The objectives of this study were manifold. First,
we wanted to explore the resulting electronic properties upon
substitution at the 11 and 12 position of the dppz ligand. Secondly,
fine-tuning of the electronic properties was sought by varying the
synthesis can either be performed [route (A)] by exchanging the
COD ligand by RR¢dppz prior to abstraction of the chlorido
ligand and introduction of the N-donor ligand. Route B starts with
the chlorido-to-N-ligand exchange, followed by the replacement
of the COD ligand. The first part of route B to the COD-complexes
[(COD)Pd(Me)L] has been recently described. Both routes
have their advantages and drawbacks. The main characteristic
of route A is the virtual insolubility of the chlorido complexes
obtained in the first step. As a consequence the products could
hardly be characterised in solution by NMR, optical spectroscopy
or electrochemical methods and purification by recrystallisation
is foreclosed. On the other hand high yields were obtained.
The main drawback however is that due to the insolubility of
II
complex fragments [Pd (Me)L] (L = anionic ligands as chlorido
II
+
or uracilato) or [Pd (Me)L] (L = various neutral N-donor
ligands) and co-ligands. Finally the antiproliferative properties of
representative compounds were investigated to establish if these
compounds exhibit cell toxicity potentially useful for anticancer
treatment.
n+
31
[
(dppz)Pd(Me)Cl] the second reaction proceeds extremely slowly
n+
Scheme 2 Target complexes [(RR¢dppz)Pd(Me)L] with partial number-
and filtration of precipitated AgCl leads to a huge loss of product
decreasing the overall yields to 5–10%. Route B suffers mainly
from the instability of the COD-complexes [(COD)Pd(Me)L] .
Both their formation and their reaction with RR¢dppz ligands
is accompanied by marked decomposition leading to black
material (presumably elemental Pd). However, since the precursor
ing; L = pyridine, 1-methylcytosine (1MeCyt), cytosine (Cyt), caffeine =
1
,3,7-trimethylxanthine (Caf), (all n = 1) or 1MeUra = 1-methyluracilato
n+
(
n = 0). R, R¢ = H, Cl, CF
3 2 2
, NO , NH .
n+
Results and discussion
complexes [(COD)Pd(Me)L] are readily available, all reactions
occur rapidly and precursors and products are highly soluble,
route B turned out to be more favourable. For the final pro-
ducts containing various N-donor ligands as cytosine (Cyt), 1-
methylcytosine (1MeCyt), 1-methyluracilato (1MeUra), pyridine
Preparation of the RR¢dppz ligands
The a-diimine ligand dppz and its derivatives were prepared by a
Schiff-base condensation of pdo (1,10-phenanthroline-5,6-dione)
and substituted o-phenylene diamines in ethanol and were isolated
in excellent yields. An exception is the amino-substituted dppz,
which had to be synthesised from the nitro-derivative by reduction
(
Py) and caffeine (Caf, 1,3,7-trimethylxanthine) both routes were
investigated, however only the variants with the best yield and
purity were reported in the Experimental Section in detail.
While the neutral chlorido complexes were virtually insolu-
28
using Pd/C in H -atmosphere. The resulting dppz-derivatives are
2
+
-
ble, the cationic complexes [(RR¢dppz)Pd(Me)L] with [SbF
6
]
sparingly soluble and can therefore be separated by precipitation
in good yield and purity. Some of the herein presented dppz
derivatives have already been synthesised in the same way, such
counter ions exhibit fair to good solubility with a remarkably
good solubility for the caffeine complexes. The neutral complex
containing the 1-methyluracilato ligand [(dppz)Pd(Me)(1MeUra)]
is almost insoluble. Due to these marked differences in solubility
we have concentrated our efforts to generate a series using different
RR¢dppz ligands in complexes containing the caffeine co-ligand
and another series using the parent dppz ligand and various co-
ligands.
28
as ndppz (R = H, R¢ = NO
2
) and adppz (R = H, R¢ = NH
2
),
while cdppz (R = H, R¢ = Cl) and dcdppz (R = Cl, R¢ = Cl)
have been reported in the form of rhenium complexes which have
been synthesised from the corresponding pdo complexes and 1-Cl-
29
or 1,2-Cl
R¢ = CF
2
-phenylene-4,5-diamine. The ligand tfmdppz (R = H,
3
) is reported herein for the first time.
The obtained Pd-compounds were analysed by NMR spec-
troscopy. As expected, the two different co-ligands coordinating
to the square planar configured Pd lower the symmetry of the
Preparation of the palladium complexes
II
Two different preparative routes (see Scheme 3) to prepare the
S
symmetrical dppz ligands (C2V to C ) dppz and dcdppz. As a
consequence all heteroaromatic protons exhibit individual signals.
The unsymmetrical RR¢dppz ligands show separate resonances
II
n+
target Pd complexes [(RR¢dppz)Pd(Me)L] were compared. In
30
both cases starting from readily available [(COD)Pd(Me)Cl]. The
4
332 | Dalton Trans., 2010, 39, 4331–4340
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1
13
(
H, C) for the phenazine part, while for the bpy-part the signals
are detectable across the connecting rings. This is also important
for the further spectroscopic and electrochemical measurements
where we also do not expect any discrimination of the E and Z
isomers. The complete assignment of proton signals in Table 1 is
for positions 1,8, 2,7 and 3,6 completely overlap.
For their complexes all heteroaromatic protons exhibit individ-
ual signals, however, no spectroscopic evidence was found for E
1
1
1
or Z isomers in H spectra. In the case of the caffeine complexes
based on H COSY, H NOESY for the complexes and additionally
1
3
1
13
also the C spectra (even at 600 MHz) did not show splitting
of the signals, which would be expected for E and Z isomers.
Since the discriminating effect should be most pronounced for
complexes containing very different co-ligands we investigated the
gradient selected H, C HSQC and HMBC experiments for the
free ligands. The signal for the methyl co-ligand in the complexes
II
is observed for all the Pd complexes around 1.0 ppm.
+
in situ generated solvent complex [(tfmdppz)Pd(Me)(Acetone)] .
Crystal structure of [(dppz)Pd(Me)(Py)][SbF ]
6
1
3
For this complex we were able to observe double sets of C signals
for the carbon atoms on the bpy part of the ligand with a splitting
of the signals for the E and Z isomers of around 0.2 ppm (1 : 1
ratio), while no splitting for the corresponding H signals could
be observed (See ESI†). This is in line with previous findings
Single crystals of [(dppz)Pd(Me)(Py)][SbF ] were obtained from a
6
saturated toluene–acetone solution and the crystal and molecular
structure were determined from XRD. The compound crystallised
in the triclinic space group P 1¯ (for details see Table 2) and exhibits
1
+
5
on related complexes as [(CH
3
dppz)Pd(Me)(MeCN)] . Thus, an
a number of intermolecular contacts, mainly due to p-stacking
isomeric discrimination in the bpy-part of the dppz ligand is only
possible for very different co-ligands (which is not the case for our
complexes), while the phenazine is kind of “magnetically isolated”
and does not show any sign of discrimination. This “isolation” is
of the dppz ligand, while the pyridine co-ligand is not involved
in such p-stacking (closest distance > 10 A˚ ). The completely
planar dppz ligands of complex molecules form two different
types of layers (A and B), both with a tail-to-tail orientation
(Fig. 1 and 2). The shortest distance between two molecules of
1
13
13
13
also evident from the fact that no H C or
C C correlations
1
a
Table 1 Selected H NMR data of the dppz ligands and palladium complexes
Compounds
adppz
H1
H8
H3
H6
H10
H13
H2
H11
H12
H7
Solvent
9.59
9.75
9.67
9.88
9.69
9.70
9.87
9.94
9.55
9.73
9.80
9.50
9.72
9.83
9.63
9.86
9.94
9.39
9.77
9.88
9.59
9.90
9.67
9.92
9.80
9.77
9.99
10.06
9.55
9.83
9.94
9.50
9.82
9.98
9.63
9.95
10.09
9.39
9.88
10.02
9.23
8.55
9.29
9.12
8.69
8.77
8.84
9.27
9.27
9.08
8.45
9.28
9.54
8.69
9.33
9.25
8.72
9.22
9.11
8.68
9.23
9.21
9.29
9.78
9.13
9.18
9.25
9.33
9.27
9.51
9.33
9.28
9.10
9.33
9.33
9.50
9.38
9.22
9.54
9.34
7.37
8.16
8.37
8.43
8.40
8.35
8.49
8.52
8.29
8.00
8.67
8.48
8.60
8.70
9.27
9.33
9.31
8.52
8.19
8.71
8.14
8.32
8.37
8.43
8.40
8.35
8.49
8.52
8.28
8.45
8.45
8.48
8.60
8.70
8.50
8.77
8.76
8.32
8.78
8.19
7.76
7.34
7.81
7.99
7.90
8.19
8.25
8.18
7.76
8.05
8.15
7.78
8.06
8.17
7.84
8.40
8.22
7.70
8.07
8.43
—
—
7.37
8.07
7.94
8.04
8.02
8.19
8.20
8.21
7.84
8.40
8.45
—
7.76
7.73
7.81
8.17
8.17
8.35
8.38
8.43
7.76
8.05
8.15
7.78
8.06
8.42
7.84
8.40
8.47
7.70
8.07
8.82
CDCl
(CD
CDCl
CDCl
CDCl
3
+
[
(adppz)Pd(Me)(Caf)]
3
)
2
3
3
3
CO
dppz
7.94
8.04
8.02
8.19
8.20
8.21
—
—
—
—
—
—
—
—
—
—
—
—
[
[
[
[
[
(dppz)Pd(Me)Cl]
(dppz)Pd(Me)(1MeUra)]+
(dppz)Pd(Me)(1MeCyt)]
(CD
(CD
(CD
3
3
3
)
)
)
2
2
2
3
CO
CO
CO
+
(dppz)Pd(Me)(Cyt)]
(dppz)Pd(Me)(Caf)]
+
cdppz
CDCl
CD
(CD
CDCl
CD
(CD
CDCl
[
[
(cdppz)Pd(Me)Cl]
(cdppz)Pd(Me)(Caf)]
2
Cl
)
2
+
3
2
CO
dcdppz
3
[
[
(dcdppz)Pd(Me)Cl]
(dcdppz)Pd(Me)(Caf)]
—
—
2
Cl
)
2
+
3
2
CO
ndppz
8.67
8.89
8.87
8.00
8.60
8.37
3
[
[
(ndppz)Pd(Me)Cl]
(ndppz)Pd(Me)(Caf)]
DMF-D7
+
(CD
CDCl
CD
(CD
3
)
3
2
CO
tfmdppz
[
[
(tfmdppz)Pd(Me)Cl]
(tfmdppz)Pd(Me)(Caf)]
2
Cl
)
2
+
3
2
CO
a
-
6
Chemical shifts/ppm; numbering of the protons according to Scheme 3; counter ion [SbF ] .
a
6
Table 2 Crystal data of [(dppz)Pd(Me)(Py)][SbF ]
¯
Crystal system/space group
Triclinic/P1
Indices
-11 < h < 11
-12 < k < 12
-21 < l < 21
695.9/21569
6186/0/334
1.096
0.0640/0.1658
0.1641/0.1660
0.1293
Cell a/A˚
9.1170(50)
10.1420(50)
16.5120(50)
82.022(5)
80.729(5)
68.043(5)
1392.46(33); 2
1.71
b/A˚
c/A˚
F(000)/refl. coll.
Data/restr./param.
GOOF on F
◦
a ( )
◦
2
b ( )
◦
g ( )
Final Rs [I > 2s(I)]
Final Rs (all data)
R(int)
V/ A˚ ; Z
3
-1
Density/g cm
m/mm
-1
1.677
Largest peak diff.
3.111/-2.101
a
˚
-1
Obtained by X-ray diffraction from single crystals at T = 173(2) K, l = 0.71073 A, empirical formula: C24
H
18
N
5
PdSbF
6
(718.6 g mol ). Further
details in the Experimental Section and the ESI.† The crystal structure contains disordered solvent molecules which could not be refined successfully, the
corresponding electron density was squeezed. As a result the overall quality of the structure is poor.
This journal is © The Royal Society of Chemistry 2010
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Additionally to the p-stacking there are a number of H-bridging
contacts in the crystal structure of [(dppz)Pd(Me)(Py)][SbF ],
6
mainly between dppz protons and the fluorine atoms of the counter
ions (the shortest contacts are listed in the ESI†). However, all of
˚
these contacts are quite long (shortest: 2.420(5) A) and we do
not suppose that they have a marked influence on the complex
molecule geometry.
While the dppz ligand is completely coplanar to the co-
ordination plane (N,N,Pd,C,N) the molecular structure of
+
[
(dppz)Pd(Me)(Py)] reveals that the pyridine co-ligand is
◦
markedly tilted with a torsion angle of 63.448(4) , which cir-
cumvents intermolecular stacking in this part of the molecule
Fig. 1 Representation of the molecule layers with two different types of
p-stacking in the crystal structure of [(dppz)Pd(Me)(Py)][SbF ], protons
6
and counter ions omitted for clarity.
(
see above). The ligand bite angles around the Pd atom sum
◦
◦
up to 360 [with Ndppz–Pd–Ndppz = 79.731(17) ; Ndppz–Pd–Npy =
◦
◦
◦
9
7.491(18) ; Ndppz–Pd–C = 94.571(19) ; Npy–Pd–C = 88.318(17) ].
˚
The distance Pd–Npy = 2.0390(5) A is comparable to the trans
˚
located Ndppz–Pd = 2.0243(5) A bond length, while the cis located
˚
N
dppz–Pd = 2.1404(9) A is markedly longer. This is in line with the
expected trans influence of the strong methyl co-ligand (C–Pd =
˚
.0382(8) A).
2
Absorption and emission spectra
All free ligands and the corresponding Pd complexes
II
[
(RR¢dppz)Pd(Me)(Caf)][SbF
6
] (Caf = caffeine) were submitted to
a comparative study of their absorption and luminescence proper-
ties. Generally, dppz complexes have been intensely investigated for
Fig. 2 Stacking in [(dppz)Pd(Me)(Py)][SbF
(
6
] (left) and [(dppz)Ni-
Mes)Br] (right), each exhibiting two types of stacking in layer A (top)
and layer B (bottom); The interlayer distances for [(dppz)Ni(Mes)Br] are
.885(4) A˚ (layer A) and 3.796(5) A˚ (layer B); protons and counter ions
are omitted for clarity.
their interesting photophysical properties to which they owe their
12b
17,32
special orbital occupation (see Introduction).
The ligands all
show strong (and partly structured) absorption bands in the range
3
of 200–300 nm (lAbs1 in Table 3) which can be assigned to p–p*
10c
transition in the bipyridine part of the dppz ligand and bands in
the range of 350–400 nm (lAbs2 and lAbs3 in Table 3), which are due
10b,32
˚
such an A-layer is 3.362(7) A, while the shortest distance for two
to p–p* transition centred in the phenazine part of the ligand.
In comparison to many other dppz complexes of low-valent
˚
molecules sharing a B-layer is 3.375(7) A. Both values lie in the
range of the stacking distance in graphite (3.8 A). The previously
reported complex [(dppz)Ni(Mes)Br] which has a quite similar
molecular structure also exhibits two types of dppz-stacked layers
Fig. 2) and it is interesting to note that altogether four different
II
II 8,13
˚
metals as Ru or Pt
no metal-to-ligand charge transfer
12b
(MLCT) absorption bands were observed in the visible range. We
suppose that they occur at wavelengths < 380 nm and were thus
obscured by the strong intra-ligand transitions. Our assumption
(
II
II
variations of dppz p-stacking are observed in these two structures,
all with approximately the same stacking distance of 3.8 A.
is based on comparison to related Ni and Pt complexes
˚
e.g. the complex [(dppz)Ni(Mes)Br] exhibits a long-wavelength
a
Table 3 Main absorption and emission maxima of selected RR¢dppz ligands and complexes
b
c
-3d
Compound
Tfmdppz
l
Abs1
l
Abs2
l
Abs3
l
Exc
l
Em
f 10
293 (27)
272 (87)
293 (34)
292 (30)
292 (21)
275 (51)
298 (42)
286 (55)
295 (24)
278 (81)e
293 (69)
304 (205)
360 (14)
360 (15)
359 (20)
360 (18)
366 (14)
369 (11)
373 (16)
371 (14)
371 (18)
372 (17)
308 (70)
391(49)
379 (14)
378 (15)
379 (21)
379 (20)
386 (17)
389 (12)
391 (14)
391 (11)
392 (26)
393 (22)
447 (26)
472 (53)
410
470
400
450
420
450
410
450
500
460
470
450
521
585
535
565
515
625
513
575
543
578
558
586
4.99
2.13
12.3
6.20
0.66
24.7
46.7
60.9
1.63
9.42
1.07
+
[
(tfmdppz)Pd(Me)(Caf)]
dppz
(dppz)Pd(Me)(Caf)]
cdppz
(cdppz)Pd(Me)(Caf)]
ndppz
(ndppz)Pd(Me)(Caf)]
dcdppz
(dcdppz)Pd(Me)(Caf)]
adppz
(adppz)Pd(Me)(Caf)]
+
[
+
[
+
[
+
[
e
e
+
[
17.99
a
Measured in DMF, absorption, excitation and emission maxima l/nm, for absorption maxima with molar extinction coefficients e/10 dm mol cm-1
3
3
-1
b
c
in parentheses. Excitation maxima obtained from excitation spectra recorded on the maximum value for the long-wavelength emission. Emission
maxima recorded upon irradiation at lExc
d
e
. Quantum yield. From ref. 28.
4
334 | Dalton Trans., 2010, 39, 4331–4340
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1
2b
absorption band at 467 nm, [(dppz)Pt(Mes)Cl] at 428 nm,
Table 4 Ealectrochemical data of RR¢dppz ligands and selected
complexes
while for [(dppz)Pd(Mes)Cl] the band is shifted to l < 380 nm
all in DMF). The thus observed sequence Pd > Pt > Ni
for the long-wavelength MLCT energy is in agreement with
II
II
II
(
Compound
E1/2 Red 1 E1/2 Red 2 or Epc DERed1 - ERed2
decreasing 2nd ionisation energies (IE): 19.43 eV for Pd > 18.56
ndppz
tfmdppz
dcdppz
cdppz
dppz
-1.19
-1.38
-1.42
-1.53
-1.64
-1.85
-1.03
-1.74
0.55
0.80
0.78
0.80
0.78
0.72
0.57
0.72
0.79
0.73
0.78
0.86
0.51
0.74
0.74
0.69
0.71
33
-2.14
eV for Pt > 18.17 eV for Ni and also with increasing valence
p-electron binding energies: 50.9 eV (Pd-4p) < 51.7 eV (Pt-
-2.14
-2.31
34
5
p) < 66.2 eV (Ni-3p). Instead of being directly visible through
-2.26
II
detectable MLCT transitions the coordination of Pd to the
RR¢dppz ligand has a marked effect on the intensities of the
intra-ligand absorption bands. While the extinction coefficients
e decrease for the phenazine-centred transitions, absorptions in
the bipyridine part gain in intensity. The energy of the long-
wavelength absorption bands of the substituted dppz ligands
adppz
-2.57
+
[
[
[
(ndppz)Pd(Me)(Caf)]
(tfmdppz)Pd(Me)(Caf)] -1.20
(dcdppz)Pd(Me)(Caf)]
-1.56
+
-2.02
+
-1.23
-1.27
-1.38
-1.44
-1.04
-1.25
-1.33
-1.34
-1.35
-2.06
+
[(cdppz)Pd(Me)(Caf)]
-2.01
+
[(adppz)Pd(Me)(Caf)]
-2.14
+
[
[
[
(dppz)Pd(Me)(Caf)]
(ndppz)Pd(Me)Cl]
(tfmdppz)Pd(Me)Cl]
-2.21
-1.55
~
~
follow the series dppz = tfm > cdppz > dcdppz = ndppz >
adppz. The adppz ligand exhibits the lowest energy absorption
which is due to the stabilisation of the lowest two singlet excited
b
b
b
b
-1.96 (irr)
-2.03 (irr)
-1.93 (irr)
-2.06 (irr)
[(dcdppz)Pd(Me)Cl]
[
[
(cdppz)Pd(Me)Cl]
(dppz)Pd(Me)Cl]
35
states. In this context it is difficult to rationalise why electron-
withdrawing groups NO and Cl also exhibit a bathochromic
shift compared to dppz as observed for the electron-releasing
NH group. Furthermore, substitution with CF has almost no
a
2
Potentials in V vs. ferrocene/ferrocenium from cyclic voltammetry or
square wave voltammetry in 0.1 M DMF/nBu NPF solutions at 298 K;
4
6
Half wave potentials E1/2 given for reversible processes, Epc for irreversible
processes. B for the calculation of DERed1 - ERed2
rendering these values less accurate.
2
3
Epc(Red2) was used for
+
effect. The corresponding complexes [(RR¢dppz)Pd(Me)(Caf)]
interestingly do not follow the above series of bathochromic shift,
although the transitions should still be the same after coordination
(
phz-based).
All free ligands and their Pd complexes exhibit luminescence at
II
ambient temperature in DMF solution. When irradiating into the
long-wavelength absorption band, emission maxima ranging from
4
50 (dppz) to 625 nm (dcdppz) were detected with quantum yields
varying from 0.06 to 0.0007. In most cases the complexes exhibit
lower emission energies and at the same time higher quantum
yields in comparison to the free ligands (the latter is not true
36
for tfmdppz and dppz). This is contrary to the energy-gap-law
Fig. 3 Cyclic voltammograms of [(dppz)Pd(Me)Cl] in nBu
4
NPF
6
/DMF
and points to a complex emission behaviour. Also, the emission
energies do not correlate to the maximum absorption energy
solution (left) and [(ndppz)Pd(Me)Cl] nBu
4
NPF
6
/DMF solution (right)
-1
at ambient temperature and 100 mV s scan rate.
(lAbs3), or in other words the Stokes-shifts vary largely from 1600
-
1
to 6200 cm (see ESI†). Obviously the origin of the emission is
not the same for all ligands and complexes. This is not unexpected
in view of the complex luminescence behaviour of the free ligand
releasing (NH ) effects of the substituents. For the corresponding
2
complexes these series can also be observed, while the absolute
values were increased by only about 0.1 to 0.2 V and the differences
between corresponding positively charged and neutral complexes
is even smaller (0.05 to 0.1 V). The latter difference is virtually zero
for ndppz complexes. Calculating the differences between the first
and second reduction potential (DERed1 - ERed2 ) (Table 4) reveals
that the differences for all ligands and complexes are about 0.8 V
with the exception of ndppz and its complexes (DERed1 - ERed2 ~ 0.5
V). In similarity to a number of investigated dppz complexes of
various transition metals we can assign the first reduction potential
17
dppz. Since the substitution and coordination gives rise to a
marked altering of the luminescence it would be worth studying
the luminescence properties of our complexes in detail, including
the investigation of life-times. Such a study is under way.
Electrochemical properties and EPR spectroscopy
II
The redox properties of the dppz derivatives and of selected Pd
complexes were studied in DMF solutions. All systems exhibit a
number of reduction waves (at least three), while only the Pd
of all ligands and complexes to the phenazine-based b p* orbital
1
II
as the lowest unoccupied MO. The large values of about 0.8 for
DERed1 - ERed2 indicate that the second reduction is also phenazine-
based. Related values have been observed for dppz complexes of
complexes can be oxidised in the accessible potential range. While
many of the one-electron reduction processes occur reversibly,
the one-electron oxidations (all around 0.3 V) are irreversible.
Fig. 3 shows two representative examples, Table 4 lists data of the
free ligands and selected complexes (Cl or caffeine co-ligands),
complete data is supplied in the ESI.†
The first reduction potential for the free ligands decreases along
the series ndppz > tfmdppz > dcdppz > cdppz > dppz > adppz.
In contrast to the long-wavelength absorptions this series reflects
II
0
I
I 2,8
Pt , Mo , Cu and Re .
An interesting aspect is that the chlorido complexes
[(RR¢dppz)Pd(Me)Cl] exhibit an irreversible second reduction,
while these waves are reversible for the cationic counterparts. We
assume that the irreversibility is caused by the splitting of the
chlorido ligand after the second reduction. This behaviour has
been investigated in detail for corresponding nickel complexes
II
the expected electron-withdrawing (NO
2
, CF
3
, Cl) or electron-
[(N∧N)Ni (Mes)X] (N∧N = various a-diimine chelate ligands
This journal is © The Royal Society of Chemistry 2010
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3
7
such as bpy or phen; Mes = mesitylene; X = halogenido).
contributions from H10 (0.084 mT, H13 (0.067 mT) and H12
(0.055 mT). The electron density of the SOMO was calculated by
Although, for the nickel complexes reduction occurs essen-
tially diimine-ligand based, the X-co-ligand is rapidly cleaved
after one-electron uptake. Since dppz, compared to the a-
diimine ligands used in this study, is superior concerning the
stabilisation of extra electrons, the first reduction of the com-
plexes [(RR¢dppz)Pd(Me)Cl] occurs reversibly, and only the
second leads to the cleavage of Cl . The cationic complexes
(RR¢dppz)Pd(Me)(Caf)] do obviously not cleave their caffeine
co-ligand, which is either due to the charge or the p-acceptor
character of all of this ligand. For the corresponding ndppz com-
plex [(ndppz)Pd(Me)Cl] the second reduction is also completely
reversible (Fig. 3). Furthermore, as mentioned already above for
the ndppz ligand and its complexes DERed1 - ERed2 values of about
DFT for adppz and ndppz confirming that for the NO
2
-derivative
marked spin-density is located in the substituent, while the NH
2
-
group does not participate (Fig. 4; for details of the calculations
see ESI†).
The Pd complexes [(ndppz)Pd(Me)(Caf)][SbF
6
] and [(adppz)-
-
Pd(Me)(Caf)][SbF ] were electrolysed in a THF–DMF mixture
6
+
[
and spectra were recorded at 298 K. In both cases unresolved
broad isotropic lines were observed with g = 2.0055 for the ndppz
complex (total spectral width DH = 28 mT) and 2.0037 for the
adppz derivative (DH = 48 mT). Their g-values match closely with
those of the corresponding uncoordinated dppz-ligands.
0
.5 V were observed. Very obviously, in these cases the reduction
Cytotoxicity
behaviour is markedly altered through the substituent -NO
2
.
Finally, selected complexes were evaluated for their effects on
cell growth inhibition of HT-29 colon carcinoma and MCF-
To verify this hypothesis EPR experiments and DFT cal-
culations were carried out on the mono-reduced states of
the ligands ndppz and adppz (the latter representing the
7
breast adenocarcinoma cells (see Table 5). Since dppz was
38
II
recently tested for its antiproliferative effects, two corresponding
organometallic Pd complexes were chosen, one containing a
biorelevant co-ligand (1MeUra). Furthermore, Pd complexes of
two substituted dppz-derivatives (dcdppz and tfmdppz) were
tested in comparison to the free ligands. This choice was motivated
from the question if the substitution inhibits DNA intercalation
and thus markedly decreases the antiproliferative effect. Inter-
estingly, for some of the complexes promising antiproliferative
effects in the range of the well known anticancer drug cis-
platin could be noted. The complexes [(dppz)Pd(Me)(1MeUra)],
majority of the RR¢dppz ligands) and their Pd complexes
[
(RR¢dppz)Pd(Me)(Caf)][SbF ] at ambient temperature. Upon in
6
situ reduction of the adppz ligand a five-line signal is observed at
g = 2.0038 (Fig. 4). Such hyperfine splitting has been observed
for dppz and also many dppz complexes and is due to the
dominant coupling of the unpaired electron to the two nitrogen
1
4
atoms ( N, I = 1, 99.636% nat. abundance) in the phenazine
ring. The spectral simulation was carried out assuming two
coupling constants a of 0.596 and 0.437 mT respectively for
N
the two (magnetically non-equivalent) phenazine N atoms, the
8
[(dcdppz)Pd(Me)Cl] and [(tfmdppz)Pd(Me)(Caf)][SbF ] were the
6
corresponding value for dppz is 0.505 mT. While Kaim et al.
most active compounds in this series, whereas [(dppz)Pd(Me)Cl]
and [(tfmdppz)Pd(Me)Cl] were either inactive or of lower activity.
The free ligands dcdppz and tfmdppz were used as references
and afforded cell growth inhibitory activity for tfmdppz but
not for dcdppz. For the dcdppz derivative this indicates that
complexation led to a substantial increase in biological activity.
For the tfmdppz derivatives activity could be increased upon
also reported coupling constants aN4,5 of 0.021 mT and aH10,13 of
8
0
.183 mT we were not able to include further nuclei into our
simulation due to the poor spectral resolution. Nevertheless, we
can state that the amino group does not contribute markedly to the
singly occupied molecular orbital (SOMO), while the asymmetric
substitution leads to slight asymmetry between the contributions
of N9 and N14. For ndppz a far more complicated signal was
obtained (Fig. 4, g = 2.0053), for which the simulation yielded
complexation for [(tfmdppz)Pd(Me)(Caf)][SbF ] but not for its
6
neutral methyl chlorido analogue [(tfmdppz)Pd(Me)Cl]. As we
coupling constants a
N
(phz) = 0.350 and 0.317 mT and a
N
(NO
2
) =
noted for the dppz ligand IC50 values below 2 mM in a previous
0
.234 mT respectively. Further splitting was simulated assuming
39
study it can be concluded that in the case of [(dppz)Pd(Me)Cl]
and [(dppz)Pd(Me)(1MeUra)] complexation had a negative ef-
fect on the triggering of antiproliferative effects. The related
II
Pt complex [Pt(dppz)(tN∧C)]CF
3
SO
3
(tN∧C = 4-tert-butyl-2-
phenylpyridine) has been reported to exhibit high antiproliferative
effects when tested against KB-3-1 and KB-V1 cell lines with
Table 5 Cytotoxicity of selected compounds in HT-29 and MCF-7 cells
expressed as IC50 values obtained in two independent experiments
a
b
Compound
IC50 HT-29/mM
IC50 MCF-7/mM
c
cisplatin
7.0 ±2.0
> 100
3.7 ± 1.3
2.2 ± 0.4
> 100
> 100
5.1 ± 0.1
10.2± 4.8
2.0 ±0.3
> 100
1.9 ± 0.2
2.8 ± 1.6
> 100
9.8 ± 10.5
1.6 ± 0.1
7.2± 2.7
[
[
[
(dppz)Pd(Me)Cl]
(dppz)Pd(Me)(1MeUra)]
(dcdppz)Pd(Me)Cl]
dcdppz
(tfmdppz)Pd(Me)Cl]
[(tfmdppz)Pd(Me)(Caf)][SbF
tfmdppz
[
Fig. 4 Top: a) EPR spectra and simulation of electrochemically re-
duced ndppz (left) and adppz (right), both generated and measured in
6
]
CH
2
Cl
2
/nBuNPF
6
at 298 K. Bottom: Calculated (B3-LYP, TZVP) electron
a
b
c
Incubation time 72 h. Incubation time 96 h. From ref. 38
density for the LUMOs of ndppz (left) and adppz (right).
4
336 | Dalton Trans., 2010, 39, 4331–4340
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1
13
19
LD50 values of 1.7 ± 0.5 and 1.0 ± 0.5 mMol compared to
cisplatin (22.1 ± 3.6 and 39.1 ± 1.7 respectively). Unfortunately,
from this small number of examples we cannot draw unequivocal
structure–activity correlations and further testing is necessary. In
general, the cytotoxic effects of polypyridyl complexes seem to
be the consequence of multiple factors including the size of the
Avance II 300 MHz ( H: 300.13 MHz, C: 75.47 MHz, F:
1
282.35 MHz), Bruker Avance 400 MHz ( H: 400.13 MHz,
C: 100.61 MHz, F: 376.50 MHz), using a triple resonance
H, F,BB inverse probe head or a Bruker Avance II 600 MHz ( H:
600.23 MHz, C: 150.93 MHz). The unambiguous assignment
of the H and C resonances was obtained from H COSY, H
NOESY, gradient selected H, C HSQC and HMBC experiments.
All D-NMR experiments were performed using standard pulse
1
3
19
1
19
1
1
3
1
13
1
1
38-42
1
13
polypyridyl ligands and cellular uptake.
Distinctive effects on
39,42
42,43
2
cellular metabolism
and cell membrane integrity
have been
reported recently highlighting the complicated biological profile of
these species and suggesting a more detailed biological evaluation
of these type of metal complexes.
However, one important thing can be concluded from our
experiment, that is that the complexes remain stable under the
experimental conditions and do not produce free dppz ligand.
sequences from the Bruker pulse program library. Chemical
1
13
shifts were relative to TMS for H and C, and CCl
3
F for
1
9
F. Due to the fact that the signals of the aromatic ligands in
1
the H spectra are of higher order, the assignments (d or dd
etc.) of the multiplicity of the signals denote only the observed
shape of the signals. Thus coupling constants were not given.
UV/Vis absorption spectra were measured using a Varian Cary50
Scan photospectrometer. UV/Vis emission spectra were obtained
using a Spex FlouroMax-3 spectrometer. Electrochemical studies
were carried out on an Autolab PGSTAT30 potentiostat and
function generator in 0.1 M nBu NPF /DMF solutions using a
Conclusions
For the synthesis of the new organometallic palladium complexes
n+
of the type [(RR¢dppz)Pd(Me)L] (RR¢dppz = derivatives of
4
6
three-electrode configuration (glassy carbon working electrode, Pt
counter electrode, Ag/AgCl reference). Half-wave (E1/2), anionic
(Epa) or cationic peak potentials (Epc) are given with respect to
the ferrocene/ferrocenium couple, which also serves as internal
reference. EPR spectra were recorded in the X band using a Bruker
ELEXSYS 500E equipped with a Bruker Variable Temperature
Unit ER 4131VT.
dipyrido[3,2-a:2¢,3¢-c]phenazine with RR¢ = 11-Cl, 11,12-Cl
2
,
11-CF
3
, 11-NO
2
, 11-NH
2
; L = Cl, 1-methyluracilate (n = 0),
pyridine, cytosine, caffeine, or 1-methylcytosine, (all n = 1) two
alternative routes were described. However due to the extremely
bad solubility of the neutral complexes [(RR¢dppz)Pd(Me)Cl] the
n+
route via the COD derivatives [(COD)Pd(Me)L] gave higher
yields in shorter time and is more promising for further related
synthesis. UV/Vis absorption and emission data gives no clear
correlation for influence of the electron-withdrawing or -releasing
substituents which is due to the very complex excited state
Crystal structure determination
Performed at 173(2) K, using graphite-monochromatised Mo-Ka
II
properties of dppz and its derivatives. Complexation with Pd
˚
radiation (l = 0.71073 A) on an IPDS I (STOE and Cie). The
does not alter this complicated behaviour. In contrast to this,
crystal was fixed in a loop with frozen fluorinated oil. The struc-
electrochemical investigations reveal that CF
general electron-withdrawing effect, while NH
3
and Cl exert a
releases electron-
44
ture was solved by direct methods (SHELXS-97) and refined
2
2
by full-matrix least-squares techniques against F (SHELXL-
density, as expected. The electrochemical and EPR results point
to mainly phenazine-centred first and second reductions. A
closer inspection of adppz and ndppz and their complexes by
EPR spectroelectrochemistry combined with quantum chemical
calculations (DFT) reveals the expected asymmetric distribution
of the electron density of the phenazine-based LUMO. The
4
5
9
7). Absorption correction was carried out using X-RED and
46
X-SHAPE (STOE). The non-hydrogen atoms were refined with
anisotropic displacement parameters without any constraints. The
hydrogen atoms were included by using appropriate riding models.
Quantum chemical calculations
most interesting substituent is 11-NO
2
, which markedly alters the
LUMO/SOMO exhibiting high spin-density of the SOMO on the
47
48,49a
DFT calculations with B3-LYP function and basis set TZVP
NO
2
nitrogen atom and a reductive electrochemistry at rather high
49
were performed with the program Turbomol using a z-matrix
produced with GaussView using standard bond-lengths and -
n+
potentials. Generally, the Pd complex fragments [Pd(Me)L] (n =
50
0
or 1) form stable bonds to the dppz ligands but their electronic
angles, and idealising the dppz scaffold to be completely planar.
Doing so, one ignores a ring-torsion vibration, occurring for the
ring connecting the bipyridine part and the phenazine part. This
simplification is justified as dppz is known to be completely planar
in crystal structures. Results were visualised with the program
II
II
I
influence is far smaller than observed e.g. for Ru , Pt or Cu
complex fragments. This is obvious from very high energy MLCT
transitions and very small stabilisation of the LUMOs (by 0.1
to 0.2 V) upon coordination. Nevertheless, the complexes seem
to remain stable during cytotoxicity experiments on HT-29 colon
carcinoma and MCF-7 breast cancer cell lines. And the results of
this preliminary study revealed promising activities for some of
the compounds.
51
Molden.
Cytotoxicity
The antiproliferative effects of the compounds were determined
following an established procedure. In short, cells were sus-
pended in cell culture medium (HT-29: 2850 cells mL , MCF-
: 10000 cells mL ), and 100 mL aliquots thereof were plated
38
Experimental
-1
-
1
7
Instrumentation
◦
in 96 well plates and incubated at 37 C: 5% CO
2
for 48 h
Elemental analyses were carried out on HEKAtech CHNS
EuroEA 3000 Analyzer. NMR spectra were recorded on Bruker
(HT-29) or 72 h (MCF-7). The compounds were freshly di-
luted/suspended in dimethylformamide (DMF) and the resulting
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solutions/suspensions were diluted with cell culture medium to the
desired concentrations (final DMF concentration: 0.1% v/v). The
medium in the plates was replaced with medium containing the
compounds in graded concentrations (six replicates). After further
incubation for 72 h (HT-29) or 96 h (MCF-7) the cell biomass was
determined by crystal violet staining and the IC50 values were
determined as those concentrations causing 50% inhibition of
cell proliferation. Results were calculated from two independent
experiments.
(1 H, dd, Hdppz6), 9.78 (1 H, dd, Hdppz1), 9.64 (1 H, dd, Hdppz3), 8.43
(2 H, m, Hdppz10,13), 8.17 (1 H, dd, Hdppz7), 8.04 (2 H, dd, Hdppz11,12),
7.99 (1 H, dd, Hdppz2), 1.17 (3 H, s, HPd-CH3).
[
(tfmdppz)Pd(Me)Cl]. Yield: 66% of a colourless solid.
Found: C, 47.32; H, 2.41; N, 11.01. Calc. for C20 Pd:
C, 47.36; H, 2.38; N, 11.05%); d (300 MHz; CD Cl ): 9.88 (1 H,
(
H
12Cl
1
F
3
N
4
H
2
2
m, Hdppz8), 9.77 (1 H, m, Hdppz1), 9.54 (1 H, dt, Hdppz6), 9.11 (1 H,
dt, Hdppz3), 8.78 (1 H, s, Hdppz10), 8.60 (1 H, dd, Hdppz13), 8.19 (1 H,
dd, Hdppz12), 8.07 (2 H, m, Hdppz2,7), 1.14 (3 H, s, HPd-CH3).
Materials and procedures
[(cdppz)Pd(Me)Cl]. Yield: 82% of a grey solid. (Found: C,
4
2
9
8
8
8.22; H, 2.53; N, 11.87. Calc. For C19
H
12Cl
2
N
4
Pd: C, 48.18; H,
Solvents (CH
2
Cl , THF, toluene, diethyl ether and MeCN)
2
.55; N, 11.83%); d (300 MHz; CD Cl
H
2
2
): 9.83 (1 H, dd, Hdppz8),
were dried using a MBRAUN MB SPS-800 solvent purifi-
cation system. All preparations and physical measurements
in this work were carried out in dry solvents under argon,
using Schlenk techniques. 1,10-phenanthroline was supplied
.73 (1 H, dd, Hdppz1), 9.51 (1 H, dd, Hdppz6), 9.08 (1 H, dd, Hdppz3),
.45 (1 H, d, Hdppz10), 8.40 (1 H, d, Hdppz13), 8.05 (2 H, m, Hdppz2,7),
.00 (1 H, m, Hdppz12), 1.13 (3 H, s, HPd-CH3).
from Chempur, AgSbF
10%) were obtained from Fluka, caffeine was obtained from
Acros Organics and o-phenylenediamines were obtained from
6
from ABCR. Cytosine and Pd/C
[(ndppz)Pd(Me)Cl]. Yield: 99% of an orange solid. (Found: C,
(
47.12; H, 2.52; N, 14.49. Calc. for C19
H
12Cl
1
N
5
O
2
Pd: C, 47.13; H,
2.50; N, 14.46%); d (300 MHz; (CD
H
)
3 2
NCO): 9.95 (1 H, m, Hdppz8),
52
7n
Alfa Aesar. 1,10-Phenanthrolinedione (pdo) and dppz and
9.86 (1 H, m, Hdppz1), 9.50 (1 H, m, Hdppz6), 9.33 (1 H, s, Hdppz10),
9.25 (1 H, m, Hdppz12), 8.89 (1 H, m, Hdppz13), 8.77 (1 H, m, Hdppz3),
8.40 (1 H, m, Hdppz7), 1.19 (3 H, s, HPd–CH3).
24,28
28
5,24
the derivatives ndppz,
adppz and cdppz
were synthe-
sised according to literature procedures. 1-Methylcytosine was
prepared following a procedure published by Kistenmacher
[
(dcdppz)Pd(Me)Cl]. Yield: 84% of a greenish solid. Found:
C, 48.30; H, 2.36; N, 11.82. Calc. for C19 Pd: C, 48.29; H,
): 9.82 (1 H, dd, Hdppz8),
53
30
et al. The palladium precursor complexes [(COD)Pd(Me)Cl]
and [(COD)Pd(Me)L][SbF
] (L = cytosine, 1-methylcytosine,
-methyluracil and caffeine) were synthesised as previously
described.
H
11Cl
2
N
4
6
2
9
8
.35; N, 11.85%); d
H
(300 MHz; CD
2
Cl
2
31
1
.72 (1 H, dd, Hdppz1), 9.54 (1 H, dd, Hdppz6), 9.10 (1 H, dd, Hdppz3),
.60 (2 H, d, Hdppz10,13), 8.06 (2 H, m, Hdppz2,7), 1.14 (3 H, s, HPd-CH3).
General procedure for the Schiff base condensation of
dppz-derivatives
General procedure for the preparation of complexes
n+
[
(RR¢dppz)Pd(Me)(L)][SbF
6
] from [(COD)Pd(Me)(L)] (Route B)
In a typical reaction 1 eq (14 mmol, 3.0 g) of pdo was mixed with
n+
An appropriate amount of [(COD)Pd(Me)(L)] (0.95 eq) dis-
solved in 50 mL of THF was admixed to a solution of the RR¢dppz
ligand in 50 mL of toluene and 1–2 mL of methanol and the
mixture was stirred at ambient temperature overnight. Solvents
were removed under vacuum at ambient temperature to yield
the crude products as coloured solids. The solids were washed
with acetone to remove free COD and RR¢dppz and yield pure
products.
3
00 mL ethanol to give an incomplete solution. The corresponding
o-phenylenediamine (14 mmol, 1 eq) was dissolved in ethanol and
◦
both mixtures were combined and stirred at 80 C overnight. The
solvent was removed under vacuum to yield the products as solids.
The crude products were recrystallised from methanol.
tfmdppz. Yield: 78% of a colourless solid. (Found: C, 65.25; H,
2.34; N, 15.25. Calc. for C19
H
9
F
3
N
4
: C, 65.15; H, 2.59; N, 15.39%);
d
H
(300 MHz; CDCl ): 9.39 (2 H, m, H1,8), 9.22 (2 H, m, H3,6), 8.52
3
[
(dppz)Pd(Me)(1MeCyt)][SbF
Found: C, 37.73; H, 2.70; N, 12.84. Calc. for C24
C, 37.70; H, 2.64; N, 12.82%); d (300 MHz; (CD
6
]. Yield: 75% of a yellow solid.
OPdSb:
CO): 9.77 (1 H,
(
1 H, s, H10), 8.32 (1 H, dd, H13), 8.00 (1 H, dd, H12), 7.70 (2 H, m,
(
H
3 2
)
20
F
6
N
7
H
2,7); d
F
(376.50 MHz; CDCl ):–62.62 (3 F, s, CF ).
3
3
H
dcdppz. Yield: 77% of a grey powder. (Found: C, 61.44; H,
.24; N, 15.82. Calc. for C18 Cl : C, 61.56; H, 2.30; N, 15.95%);
(300 MHz; CDCl ): 9.50 (2 H, m, H1,8), 9.28 (2 H, m, H3,6), 8.43
dd, Hdppz8), 9.70 (1 H, dd, Hdppz1), 9.18 (1 H, dd, Hdppz6), 8.77 (1 H,
dd, Hdppz3), 8.35 (3 H, m, Hdppz7,10,13), 8.19 (3 H, m, Hdppz2,11,12), 7.99
(1 H, d, H1MeCy6), 6.22 (1 H, d, H1MeCy5), 3.60 (3 H, s, H1MeCy-CH3),
0.98 (3 H, s, HPd–CH3).
2
d
(
H
8
2
N
4
H
3
2 H, d, H10,13), 7.78 (2 H, d, H2,7).
[
(dppz)Pd(Me)(1MeUra)]. Yield: 16% of a pale red solid.
Found: C, 54.51; H, 3.40; N, 15.89. Calc. for C24 Pd: C,
54.51; H, 3.43; N, 15.89%); d (300 MHz; CDCl ): 9.80 (1 H, m,
General procedure for the synthesis of [(RR¢dppz)Pd(Me)Cl]
(
H
18
N
6
O
2
The precursor complex [(COD)Pd(Me)Cl] (1 eq) was dissolved in
H
3
CH
2
Cl
2
. Then a solution of the desired RR¢dppz ligand (1 eq)
H
H
H
H
dppz8), 9.83 (1 H, m, Hdppz1), 9.13 (1 H, m, Hdppz6), 8.69 (1 H, m,
in toluene was added to the reaction mixture. The reaction was
performed at ambient temperature overnight. The formed solid
was filtered off and washed with acetone : pentane, 1 : 1 to yield
the pure products.
dppz3), 8.40 (2 H, m, Hdppz12,13), 8.17 (1 H, m, Hdppz7), 8.02 (2 H, m,
dppz11,12), 7.90 (1 H, m, Hdppz2), 7.15 (1 H, d, H1MeU6), 5.80 (1 H, d,
1MeU5), 3.45 (3 H, s, H1MeU-CH319), 1.08 (3 H, s, HPd–CH3).
[
(dppz)Pd(Me)(Cyt)][SbF
(Found: C, 36.87; H, 2.46; N, 13.05. Calc. for C23
C, 36.80; H, 2.42; N, 13.06%); d (300 MHz; (CD
6
]. Yield: 68% of a yellow solid.
OPdSb:
CO): 9.99 (1 H,
[
(dppz)Pd(Me)Cl]. Yield: 88% of a yellow solid. (Found: C,
1.99; H, 2.91; N, 12.76. Calc. For C19 Pd: C, 51.96; H,
.98; N, 12.76%); d (300 MHz; CDCl ): 9.92 (1 H, dd, Hdppz8), 9.88
H
3 2
)
18
F
6
N
7
5
2
H
13Cl
1
N
4
H
H
3
dd, Hdppz8), 9.87 (1 H, dd, Hdppz1), 9.25 (1 H, dd, Hdppz6), 8.84 (1 H,
4
338 | Dalton Trans., 2010, 39, 4331–4340
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View Article Online
dd, Hdppz3), 8.49 (2 H, m, Hdppz10,13), 8.38 (1 H, m, Hdppz7), 8.25 (1 H,
m, Hdppz2), 8.20 (2 H, m, Hdppz11,12), 7.90 (1 H, d, HCyt6), 6.22 (1 H,
d, HCyt5), 1.00 (3 H, s, HPd–CH3).
washed with pentane and crystallised from acetone : pentane, 1 : 1.
Products were isolated in very low yields (0.5–5.0%).
For analytical data of [(dppz)Pd(Me)(Cy)][SbF
Pd(Me)(1MeCy)][SbF ], [(dppz)Pd(Me)(1MeUra)] and [(dppz)-
Pd(Me)(Caf)][SbF ] see above. In the case of [(dppz)Pd(Me)(Py)]-
SbF ] only a few yellow crystals were obtained (yield 2%). (Found:
C, 40.23; H, 2.50; N, 9.74. Calc. for C24 PdSb: C, 40.12; H,
.52; N, 9.75).
6
], [(dppz)-
6
[
(dppz)Pd(Me)(Caf)][SbF
Found: C, 38.97; H, 2.77; N, 13.41. Calc. for C27
C, 38.90; H, 2.78; N, 13.44%); d (300 MHz; (CD
6
]. Yield: 42% of a colourless solid.
PdSb:
CO): 10.06
6
(
H
23
F
3 2
)
6
N
8
O
2
[
6
H
H
18
F
6
N
5
(
(
(
(
1 H, m, Hdppz8), 9.94 (1 H, m, Hdppz1), 9.33 (1 H, m, Hdppz6), 9.27
1 H, s, Hdppz3), 8.85 (1 H, s, HCafC–H), 8.52 (2 H, m, Hdppz10,13), 8.43
1 H, m, Hdppz7), 8.21 (2 H, m, Hdppz11,12), 8.18 (1 H, m, Hdppz2), 4.29
3 H, s, HCaf7-CH3), 4.24 (3 H, s, HCaf3-CH3), 3.37 (3 H, s, HCaf1-CH3),
2
Acknowledgements
1
.16 (3 H, s, HPd–CH3).
We thank Dr Axel Jacobi von Wangelin, University of Cologne,
for the use of the Parr-Apparatus, Dr Ingo Pantenburg and
Ms. Ingrid M u¨ ller, for the collection of crystal data, Andreas
O. Sch u¨ ren for EPR measurements (all University of Cologne),
[
(tfmdppz)Pd(Me)(Caf)][SbF ]. Yield: 49% of a colourless
6
solid. The product was found to be co-crystallised to 0.5
eq of toluene which could not be removed under reduced
pressure. (Found: C, 39.94; H, 2.75; N, 11.82. Calc for
Johnson Matthey (JM) for a generous loan of K
the “Studienstiftung des Deutschen Volkes” for financial support
KB).
2
PdCl
4
and
C
d
28
H
22
F
9
N
8
O
2
PdSb·0.5 C
7
8
H : C, 39.92; H, 2.77; N 11.82%);
H
(300 MHz; (CD CO): 10.02 (1 H, m, Hdppz8), 9.88 (1 H, m,
)
3 2
(
H
H
H
H
H
dppz1), 9.34 (1 H, m, Hdppz6), 8.85 (1 H, s, HCafC–H), 8.82 (1 H, s,
dppz13), 8.71 (1 H, m, Hdppz10), 8.68 (1 H, m, Hdppz3), 8.43 (1 H, m,
dppz7), 8.37 (1 H, m, Hdppz12), 8.19 (1 H, m, Hdppz2), 4.28 (3 H, s,
Caf7-CH3), 4.24 (3 H, s, HCaf3-CH3), 3.36 (3 H, s, HCaf1-CH3), 1.17 (3 H, s,
Pd–CH3).
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2
2
◦
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◦
8
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This journal is © The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 4331–4340 | 4339

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