Synthesis, structural characterization, antimicrobial and cytotoxic effects of aziridine, 2-aminoethylaziridine and azirine complexes of copper(ii) and palladium(ii)

Article abstract of DOI:10.1039/c2dt12107g

The synthesis, spectroscopic and X-ray structural characterization of copper(ii) and palladium(ii) complexes with aziridine ligands as 2-dimethylaziridine HNCH₂CMe₂ (a), the bidentate N-(2-aminoethyl)aziridines C₂H₄NC₂H ₄NH₂ (b) or CH₂CMe₂NCH ₂CMe₂NH₂ (c) as well as the unsaturated azirine NCH₂CPh (d) are reported. Cleavage of the cyclometallated Pd(ii) dimer [μ-Cl(C₆H₄CHMeNMe₂-C,N)Pd]₂ with ligand a yielded compound [Cl(NHCH₂CMe₂)(C ₆H₄CHMe₂NMe₂-C,N)Pd] (1a). The reaction of the aziridine complex trans-[Cl₂Pd(HNC₂H ₄)₂] with an excess of aziridine in the presence of AgOTf gave the ionic chelate complex trans-[(C₂H₄NC ₂H₄NH₂-N,N′)₂Pd](OTf) ₂ (2b) which contains the new ligand b formed by an unexpected insertion and ring opening reaction of two aziridines ("aziridine dimerization"). CuCl₂ reacted in pure HNC₂H ₄ or HNCH₂CMe₂ (b) again by "dimerization" to give the tris-chelated ionic complex [Cu(C ₂H₄NC₂H₄NH₂-N,N′) ₃]Cl₂ (3b) or the bis-chelated complex [CuCl(C ₂H₂Me₂NC₂H₂Me ₂NH₂-N,N′)₂]Cl (4c). By addition of 2H-3-phenylazirine (d) to PdCl₂, trans-[Cl₂Pd(NCH ₂CPh)₂] (5d) was formed. All new compounds were characterized by NMR, IR and mass spectra and also by X-ray structure analyses (except 3b). Additionally the cytotoxic effects of these complexes were examined on HL-60 and NALM-6 human leukemia cells and melanoma WM-115 cells. The antimicrobial activity was also determined. The growth of Gram-positive bacterial strains (S. aureus, S. epidermidis, E. faecalis) was inhibited by almost all tested complexes at the concentrations of 37.5-300.0 μg mL ^-1. However, MIC values of complexes obtained for Gram-negative E. coli and P. aeruginosa, as well as for C. albicans yeast, mostly exceeded 300 μg mL^-1. The highest antibacterial activity was achieved by complexes 1a and 2b. Complex 2b also inhibited the growth of Gram-negative bacteria.

Full text of DOI:10.1039/c2dt12107g

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2012, 41, 5925
www.rsc.org/dalton
PAPER
Synthesis, structural characterization, antimicrobial and cytotoxic effects of
aziridine, 2-aminoethylaziridine and azirine complexes of copper(II) and
palladium(II)†‡
E. Budzisz,*a R. Bobka,b A. Hauss,b J. N. Roedel,b S. Wirth,b I.-P. Lorenz,*b B. Rozalska,c M. Więckowska-
Szakiel,c U. Krajewskad and M. Rozalskid
Received 4th November 2011, Accepted 8th March 2012
DOI: 10.1039/c2dt12107g
The synthesis, spectroscopic and X-ray structural characterization of copper(II) and palladium(II)
complexes with aziridine ligands as 2-dimethylaziridine HNCH2CMe2 (a), the bidentate N-(2-
aminoethyl)aziridines C2H4NC2H4NH2 (b) or CH2CMe2NCH2CMe2NH2 (c) as well as the unsaturated
azirine NCH2CPh (d) are reported. Cleavage of the cyclometallated Pd(II) dimer [μ-Cl(C6H4CHMeNMe2-
C,N)Pd]2 with ligand a yielded compound [Cl(NHCH2CMe2)(C6H4CHMe2NMe2-C,N)Pd] (1a). The
reaction of the aziridine complex trans-[Cl2Pd(HNC2H4)2] with an excess of aziridine in the presence of
AgOTf gave the ionic chelate complex trans-[(C2H4NC2H4NH2-N,N′)2Pd](OTf)2 (2b) which contains the
new ligand b formed by an unexpected insertion and ring opening reaction of two aziridines (“aziridine
dimerization”). CuCl2 reacted in pure HNC2H4 or HNCH2CMe2 (b) again by “dimerization” to give the
tris-chelated ionic complex [Cu(C2H4NC2H4NH2-N,N′)3]Cl2 (3b) or the bis-chelated complex [CuCl
(C2H2Me2NC2H2Me2NH2-N,N′)2]Cl (4c). By addition of 2H-3-phenylazirine (d) to PdCl2, trans-[Cl2Pd
(NCH2CPh)2] (5d) was formed. All new compounds were characterized by NMR, IR and mass spectra
and also by X-ray structure analyses (except 3b). Additionally the cytotoxic effects of these complexes
were examined on HL-60 and NALM-6 human leukemia cells and melanoma WM-115 cells. The
antimicrobial activity was also determined. The growth of Gram-positive bacterial strains (S. aureus,
S. epidermidis, E. faecalis) was inhibited by almost all tested complexes at the concentrations of
37.5–300.0 μg mL−1. However, MIC values of complexes obtained for Gram-negative E. coli and P.
aeruginosa, as well as for C. albicans yeast, mostly exceeded 300 μg mL−1. The highest antibacterial
activity was achieved by complexes 1a and 2b. Complex 2b also inhibited the growth of Gram-negative
bacteria.
polymerization reactions6 or as natural and synthetic
Introduction
pharmaceuticals.7–9 Though the parent aziridine C2H4NH is
classified as mutagenic,10,11 there are some aziridine-containing
The high interest that the chemistry of aziridines attracts is gener-
ated by the manifold applications of these smallest saturated
azaheterocycles.1–3 Aziridines are not only used as reactive
synthons in organic synthesis, in the synthesis of peptides
and natural products,4,5 but also as monomeric units in
natural compounds known to be useful as chemotherapeutics to
combat cancer targeting biochemical processes. Good examples
are the family of mitomycins and acinomycins.12–14 Their phys-
iological effect relies on their poor stability towards ring opening
followed by alkylation and cross-linking to form DNA inter-
strands. This leads to the inhibition of DNA replication and to
cell death. There are also some man-made aziridine derivatives
with similar antitumor capabilities based on the exact same cyto-
toxic effect, e.g. some aziridinylbenzoquinones,15,16 TEM,17 or
thioTEPA.18 This ring-opening reaction of aziridines by nucleo-
philic attack is very similar to that of isoelectronic oxiranes and
thiiranes. With regard to coordination chemistry, however, the
reactivity of nucleophilic aziridines towards electrophilic tran-
sition metal centers differs strongly from those of oxiranes and
thiiranes with a only few exceptions.19–21 While the latter act
as oxidizing agents towards organometallic complexes resulting
in the formation of oxo- or thiocomplexes via ethene
aDepartment of Cosmetic Raw Materials Chemistry, Faculty of
Pharmacy, Medical University of Lodz, Muszynski Str. 1, 90-151 Lodz,
Poland. E-mail: elzbieta.budzisz@umed.lodz.pl
bDepartment of Chemistry, Ludwig-Maximilians-University,
Butenandtstr. 5-13 (D), D-81377 Munich, Germany.
E-mail: ipl@cup.uni-muenchen.de
cDepartment of Immunology and Infectious Biology, University of Lodz,
Banacha 12/16, 90-237 Lodz, Poland
dDepartment of Pharmaceutical Biochemistry, Medical University of
Lodz, Muszynski Str. 1, 90-151 Lodz, Poland
†Dedicated to Prof. Dr Wolfgang Beck on the occasion of his 80th
birthday.
‡CCDC 849020–849023. For crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c2dt12107g
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 5925–5933 | 5925

View Article Online
elimination,22–26 aziridines usually remain intact and prefer
metal coordination via the nitrogen atom. Therefore, only one
example of two-fold breakage of C–N bonds, elimination of
ethene and formation of an imido complex is known in the litera-
ture.26 However, many aziridine complexes of a variety of tran-
sition metals with up to four aziridine ligands are currently
known, most of which have been published by us.27–41 Ring
opening reactions especially with functionalized metal carbonyls
have also been reported, e.g. with hydrido carbonyl complexes
to form β-aminoacyl complexes via M–C addition42–46 or with
halogenido carbonyl complexes to form five-membered ami-
nooxycarbene complexes.47,48
Transition metal-mediated ring opening reactions of aziridine
ligands yielding aminoethylaziridine-N,N′ complexes by “aziri-
dine dimerization” was first observed by Beck et al.49 and Fritz
et al.50 The first examples of such an aziridine dimer template
have been structurally characterized by X-ray determination in
the case of a cationic Co(III) complex bearing two dimerized 2-
methylaziridine ligands.51 We later reported further examples of
analogous complexes with dimerized aziridine ligands.52,53 Fur-
thermore, most recently a novel route to N-(2-aminoethyl)aziri-
dines was developed based on the one reported by Beck et al.49
utilizing a Cu(II)-mediated template dimerization of aziridine
ligands.53
In this paper we report on the synthesis and characterization
of new palladium(II) and copper(II) complexes with dimerized
aziridine ligands as well as of palladium(II) complexes with one
N-bound aziridine ligand and two azirine ligands, respectively.
Hitherto, only a few azirine complexes of transition metals are
known.54,55 Usually they undergo ring-opening or rearrangement
reactions in the presence of transition metals.56,57 Because of the
successful employment of aziridine-containing mitomycin
derivatives in cancer therapy, some of their transition metal com-
plexes have been synthesized, which did not show significant
differences in biological activity compared to the uncoordinated
compounds.58 The cis-bisaziridine Pt(II) complex59,60 analogous
to cisplatin showed no better activity, but had higher selectivity.
Therefore all the synthesized complexes here have been investi-
gated for their biological activity.
(NHCH2CMe2)Pd (1a) (Scheme 1). Light yellow 1a is obtained
with 50% yield, and is air-stable, soluble in polar solvents
(CH2Cl2), but insoluble in non-polar solvents (n-pentane). The
spectroscopic characterization showed the evidence of S,S and R,
R enantiomers due to N chirality at the aziridine nitrogen.
The starting material for the synthesis of complex 2b is the
bisaziridine complex trans-[Cl2Pd(NHC2H4)2].62 When it is
treated with at least 3 equivalents of aziridine HNC2H4 and 2
equivalents of AgOTf in CH2Cl2 at r.t., the cationic square
planar palladium(II) complex [(C2H4NC2H4NH2-N,N′)2Pd]-
(OTf)2 (2b) with
2
OTf− as counteranions is formed
(Scheme 2). As already published by us in the case of copper(II)
complexes, the bidentate β-aminoethylaziridine ligand b is
formed by a metal-induced dimerization reaction. Hitherto, this
unusual reaction was only observed for HNC2H452 and its mono-
63
and dimethyl derivatives HNCH2CHMe51 and HNCH2CMe2
as is also shown in the following syntheses of complexes 3b and
4c. Thus, it seems that this “aziridine dimerization” is limited by
steric reasons. Yellow 2b is soluble in polar solvents, even
methanol, but insoluble in non-polar solvents such as n-pentane,
and under argon it can be stored indefinitely.
The first aziridine complexes of copper(II) have been pub-
lished by Edwards et al. in 196164,65 and by Beck et al. in
1973,49 but without any structural characterization. Beck et al.
also observed the first “aziridine dimerization” induced by metal
coordination.49 This has been recently proven by our own results
with some aziridine complexes of copper(II). In most cases,
however, several derivatives of aziridines kept intact and coordi-
nated as ligands in 1 : 2, 1 : 3 and 1 : 4 molar ratios to Cu(II)
centers.53,66,67 To increase this stoichiometry and to obtain hex-
aaminecopper(II) analogous complexes, we decided to use a
large excess of aziridine and to avoid using any solvent. There-
fore, anhydrous CuCl2 was added directly to the liquid aziridines
C2H4NH or CH2CMe2NH (a), respectively. As shown in
Scheme 3, two different ionic complexes with different stoichi-
ometry and coordination geometry were obtained depending on
the substituents. In the case of aziridine, C2H4NH, the tris-che-
lated octahedral complex [(C2H4NC2H4NH2-N,N′)3Cu]Cl2 (3b)
resulted and in the case of the 2,2-dimethylderivative the bis-
chelated trigonal bipyramidal complex [(CH2CMe2NCH2C-
Me2NH2-N,N′)ClCu]Cl (4c). Both complexes, however, again
contain the corresponding “dimerized” aziridines as ligands b
and c. Our attempts to obtain single crystals of 3b by recrystalli-
sation were not successful, because it was destroyed by any
longer attack of polar solvents. Using methanol for instance,
caused the formation of the bis-chelated complex trans-
[(C2H4NC2H4NH2-N,N′)2(HOMe)2Cu]Cl2 with two MeOH
ligands in axial positions as proven by X-ray structural
Results and discussion
Synthesis of the complexes 1a, 2b, 3b, 4c and 5d
The cleavage reaction of the chlorido-bridged dimer bis[μ-Cl(S)-
2-{1-(dimethylamino)ethyl}phenyl-C,N-palladium(II)]61 with an
excess of 2,2-dimethylaziridine (a) in CH2Cl2 affords the
square planar palladium(II) complex Cl(C6H4CHCH3NMe2-C,N)-
Scheme 1 Synthesis of the neutral palladium(II) complex 1a with ligand 2,2-dimethylaziridine (a).
5926 | Dalton Trans., 2012, 41, 5925–5933
This journal is © The Royal Society of Chemistry 2012

View Article Online
Scheme 4 Synthesis of the neutral palladium(II) complex 5d with
ligand 2H-3-arylazirin (d).
Scheme 2 Synthesis of the ionic palladium(II) complex 2b with ligand
N-(2-aminoethyl)aziridine (b) formed by metal-induced “aziridine
dimerization” of C2H4NH.
spectroscopy was not possible because of their paramagnetic
properties.
The IR spectrum of 1a shows ν(NH) absorptions slightly
shifted by coordination to lower frequencies at about 3100 cm−1
.
Somewhat lower are found the ν(CH) bands (2971–2833 cm−1).
Two striking absorptions between 1600 and 1500 cm−1 are
assigned to ν(CvC) of the N,N-dimethylbenzylamine moiety. In
the IR spectrum of 2b, analogous absorptions for ν(NH) and
ν(CH) are found in the same region as for 1a. Besides this, a
weak band for δ(NH2) at 1608 cm−1 is observed. Additionally,
the typical strong bands of the triflate anion appear in the region
1280–1030 cm−1 for the ν(CF3) and ν(SO3) vibrations. The IR
spectra of the ionic copper complexes 3b and 4c are very similar
to each other and similar to that of 2b. The ν(NH) and ν(CH)
absorptions are found at 3240–3100 and 3000–2870 cm−1
respectively, as well as the δ(NH2) at 1604 (3b) and 1602 cm−1
(4c). The azirine complex 5d shows only the ν(CN) absorption
at 1771 cm−1 as significant, besides the expected ones for ν(CH)
and ν(CvC).
Scheme 3 Synthesis of the ionic copper(II) complexes 3b and 4c with
ligands N-(2-aminoethyl)aziridine (b) and N-(2-amino-2-methylpropyl)-
2,2-dimethylaziridine (c) both again formed by metal-induced “aziridine
dimerization”.
1
The H and 13C NMR spectra of 1a point to the evidence of
the intact N-bound aziridine ligand a. The CH3 and CH2 proton
signals show the typical low field shifts caused by metal coordi-
nation. The CH3 signals are found at 1.53 and 1.52 ppm instead
of 0.96 ppm for free a, the CH2 signals lie at 2.50 and 2.09 ppm
(1.26 ppm free a). Analogously, the signals of the Cq and CH2
carbon atoms appear about +8 and +4 ppm further downfield
than those of free a (Cq 31.0 ppm, CH2 33.3 ppm). Concerning
the CH3 carbon signals, complexation causes only slight shifts
of about 0.3 and 1.0 ppm. It should be mentioned that both
the 1H and 13C NMR spectra of 1a show a pair for each
signal (which overlap in some cases) suggesting the presence
of diastereomers in 1a, which contains an asymmetric carbon
and nitrogen atom. Starting off enantiomerically pure (S,S)-
[C6H4CHCH3NMe2PdCl]2, the coordination of the incoming
bridge-splitting aziridine a is completely regioselective. This is
caused by the known electronic directing effect of Pd–Cl
bonds68–70 to yield pure (SC,SN) and (SC,RN)–1a with the az-N
taking up the position trans to the NMe2 group. As the corre-
sponding proton signals of both diastereomers are finely separ-
ated, especially at the chiral amine ligand, the integration of the
signals of C6H4CHMeNMe2 delivers a ratio of about 40 : 60 (SC,
SN) : (SC,RN) enantiomers. The new dimerized ligand b can be
analysis.53 4c is soluble in slightly polar solvents such as
acetone or dichloromethane, insoluble in non-polar solvents such
as n-pentane. Both complexes are air-stable.
Azirine ligands were mentioned in palladium(II) complexes by
several groups in 1978.54–56 One of them presented with trans-
[(2H-3-tolylazirine)2Cl2Pd] the only example structurally charac-
terized by diffraction studies.55 The syntheses of azirine com-
plexes turned out to be difficult because of subsequent
rearrangement reactions in the presence of metal complexes and
too long reaction times. If the reaction can be stopped, however,
it is possible to isolate some palladium(II) complexes of the type
trans-[(2H-3-arylazirine)2Cl2Pd] (aryl = C6H5 (d), C6H4Cl,
C6H4Br) by the reaction of PdCl2 and 2H-3-arylazirine in aceto-
nitrile.66 Here we only present the synthesis and structural
characterization of the phenyl derivative 5d (Scheme 4), once
formed and isolated, stable enough for the implemented analyti-
cal and biological studies in low concentration. 5d is obtained as
air-stable orange yellow powder in 65% yield and is soluble in
CH2Cl2 and CHCl3, but insoluble in n-hexane.
1
well observed in its H and 13C NMR spectra by the signals of
the ethane bridge. They are shifted downfield to 2.34 and
2.90 ppm or 42.87 and 62.56 ppm, respectively compared to the
C2H4 signals of the aziridine ring (1.40 and 1.87 ppm or 28.30
and 33.98 ppm, respectively). The protons of the NH2 group
could not be detected clearly as they are shifted to low field and
overlayed by the signals of the C2H4 bridge.
Spectroscopic characterization
All the complexes have been characterized by their H and 13C
NMR, IR and mass spectra with the exception of the copper(II)
1
complexes 3b and 4c, where characterization by NMR
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 5925–5933 | 5927

View Article Online
1
The azirine ligand in 5d shows a low field shift in the H and
13C NMR spectra compared to free ligand d only for the methyl-
ene protons. Because both ligands d are chemically equivalent,
only one signal for CH2 at 20.9 ppm (d: 19.2 ppm) is observed.
While the azirine Cq signal of 5d is slightly shifted to lower field
at 166.8 ppm (d: 165.3 ppm), the Cq signal of the phenyl ring is
found at higher field (121.6 ppm, d: 125.1 ppm). In both spectra
of 5d the three types of protons and C atoms appear separately
and can be easily identified (see Experimental part).
The mass spectrum (FAB+) of 1a features the parent peak with
m/z = 362 for [M+] at relatively low intensity (22%) with the
typical isotope pattern. In the further fragmentation, first the loss
of Cl (m/z = 325, 100%) and then of aziridine a with m/z = 254
(13%) occurs. In the mass spectrum of 2b not only the parent
signal for the cation with m/z = 277 (80%) [M+] and one at m/z
= 191 (48%) [M2+ − b] after elimination of one ligand b was
detected, but also a signal at m/z = 427 (93%) [M2+ + OTf] with
one triflate still attached to the complex.
Fig. 1 Molecular structure of complex 1a with selected bond lengths
(Å) and angles (°). Sc,RN isomer, only one of the four independent mol-
ecules in the asymmetric unit is shown. Thermal ellipsoids are drawn at
the 30% probability level, H atoms are omitted for clarity. Pd1–N1
2.047(3), Pd1–N2 2.099(3), Pd1–C5 1.983(3), Pd1–Cl1 2.4326(8), N1–
C1 1.495(4), N1–C2 1.483(4), C1–C2 1.476(5), C1–C3 1.521(5), C1–
C4 1.506(4); C5–Pd1–N1 90.94(12), C5–Pd1–N2 81.41(12), N1–Pd1–
Cl1 91.75(8), N2–Pd1–Cl1 96.06(7), N1–Pd1–N2 171.67(10), C5–Pd1–
Cl1 176.06(10), C2–C1–N1 59.9(2), C1–C2–N1 60.7(2), C2–N1–C1
59.4(2).
The mass spectra of both copper(II) complexes 3b and 4c
show the cation parent peaks at m/z = 321 (4%) and m/z = 383
(67%). For 3b a signal at higher mass at m/z = 356 for [M2+
+
Cl] is observed as well as the corresponding signals after frag-
mentation of n b ligands (n = 1, 2). The mass spectrum of 4c
shows the expected fragmentation pattern with signals at m/z =
348 (30%) [M+ − Cl], 240 (100%) [M+ − c] and 205 (74%) [M+
− Cl − c]. In the case of the azirine complex 5d the parent
signal [M+] was not detected, but there was a signal at m/z = 377
(100%) [M+ − Cl].
In the UV/Vis spectra of both Cu(II) complexes 3b and 4c a
broad, unstructured absorption is observed with a maximum at
721 nm (3b, ε = 279 L mol−1 cm−1) and 796 nm (4c, ε = 380 L
mol−1 cm−1). In spite of the low symmetry caused by the chelat-
ing ligands, no shoulder or splitting is observable. The measured
values, however, correspond to those of similar Cu(II) complexes
with coordination numbers of five and six.71,72
Fig. 2 Molecular structure of complex 2b with selected bond lengths
(Å) and angles (°). H atoms and anions (triflate) are omitted for clarity.
Thermal ellipsoids are drawn at the 30% probability level. Pd1–N1
2.0339(16), Pd1–N2 2.0458(18), N1–C1 1.487(3), N1–C2 1.478(3),
C1–C2 1.477(3), C3–C4 1.499(3); N1–Pd1–N2 82.71(7), N1–Pd1–N2i
97.29(7), N1–Pd1–N1i 180.0, N2–Pd1–N2i 180.0, N1–C1–C2 59.82
(13), N1–C2–C1 60.44(13), C1–N1–C2 59.74(14).
Molecular structures of 1a, 2b, 4c and 5d
Single crystals of the complexes were grown from their solutions
in CH2Cl2 (1a, 4c and 5d) or CH3OH (2b) by isothermic diffu-
sion of n-pentane. Their solid-state structures have been solved
by X-ray diffraction and are shown in Fig. 1–4 together with
selected bond lengths and bond angles. The crystallographic data
are summarized in Table 1.
As expected for the 4d8 configuration, 1a exhibits a slightly
distorted square planar geometry at palladium(II) with a small tilt
from planarity of only 4.43° between the C5–Pd1–N2 and Cl1–
Pd1–N1 planes (Fig. 1). The cis angles at the Pd1 center range
between 81° and 96°. The five-membered dimethyl-1-pheny-
lethaneamine-2-C,N chelate ring adopts the envelope confor-
mation with palladium and the three carbon atoms C5, C10 and
C11 being essentially coplanar (dihedral angle Pd1–C5–C10–
C11 = 1.57°). The nitrogen atom of NMe2 lies 0.726 Å off this
plane. The aziridine ring is almost an equilateral triangle as its
C–C and C–N bond lengths (1.476(5) Å and 1.483(4)/1.495(4)
Å, respectively) and angles (59.4(2)–60.6(2)°) differ only
slightly from those for free aziridine in the solid state.73 It is
noteworthy that the Pd1–N2 bond (2.099(3) Å) is somewhat
longer than that of Pd1–N1 (2.047(3) Å). All other Pd1–X
distances (X = C5: 1.983(3) Å, X = Cl: 2.4326(8) Å) lie in the
expected range.
The cation of compound 2b has an inversion center at the
Pd(II) center surrounded by four nitrogen atoms in a square
planar geometry (Fig. 2). The trans N–Pd1–N angles are exactly
180°, while the cis N–Pd1–N angles vary between 82.7° and
97.3° because of the five-membered chelating ligand in a twist
configuration. Both of the intact aziridine rings are orientated
almost vertical (81.54°) to the molecular square plane. The Pd1–
N2 bond length (2.0458(18) Å) is only slightly longer than that
of Pd1–N1 (2.0339(16) Å). The same is observed for the C–C
bonds of the ethane bridge (C3–C4 1.499(3) Å) and of the aziri-
dine ring (1.477(3) Å). The C–N bonds (1.476(3)/1.485(3) Å)
and all angles of the aziridine ring (59.74(14)–60.44(13)°) show
similar values to those in 1a.
5928 | Dalton Trans., 2012, 41, 5925–5933
This journal is © The Royal Society of Chemistry 2012

View Article Online
126.67(15)° and N6–Cu1–N8 96.5(2)°). The trans-axial angle
N5–Cu1–N7 (172.8(2)°) is also affected. The angles between
equatorial and axial ligands show values larger than 90°
(90.6–94.7°) with the only exception of those two (N5–Cu1–N6
83.0(2)°, N7–Cu1–N8 82.8(2)°) caused by both five-membered
chelate systems in twist conformation. All structural parameters
of both aziridine rings range within normal values and corre-
spond to those in 1a and 2b.
Analogous trigonal bipyramidal Cu(II) complexes are rarely
found in the literature. Normally, analogous geometries can be
74
formed by multidentate ligands, e.g. [(Cu(tren)NH3)ClO4]2 or
by special polyhedral structures, e.g. in the tetrameric adaman-
tane-analogous μ4-oxo-complex [(μ4-O)(μ4-Cl)(C2H4NHCu)4].75
The square planar azirine complex of palladium(II) 5d (Fig. 4)
is slightly distorted because of the two different ligands, two
chlorido ligands and two azirine-N atoms each in trans positions
(N1–Pd1–N2 179.3(3)°, Cl1–Pd–Cl2 179.38(5)°). The planes of
the azirine rings form different small angles to the equatorial
PdN2Cl2 plane (Δ1 = 2.56 and 3.78°) as well as to the phenyl
plane (Δ2 = 4.48 and 5.63°). Therefore, one can say that the
whole molecule is nearly planar. Both Pd–Cl1/Cl2 and Pd–N1/
N2 bond lengths are nearly equal, the latter ones of course are
shorter because of their sp2-hybridized N-atoms than those in the
aziridine complexes mentioned above. This is also observed in
the structural parameters of the unsaturated azirine ring (N1–C1
1.504(7), N1–C2 1.245(6) and C1–C2 1.463(7) Å; C1–N1–C2
63.5(3), N1–C1–C2 49.6(3) and N1–C2–C1 66.9(3)°) which
differ significantly from those of the saturated aziridine rings.
Fig. 3 Molecular structure of complex 4c with selected bond lengths
(Å) and angles (°). Thermal ellipsoids are drawn at the 30% probability
level, H atoms, anions (chlorine) and a second molecular unit are
omitted for clarity. Cu1–Cl2 2.309(2), Cu1–N5 2.066(7), Cu1–N6 2.105
(5), Cu1–N7 2.074(6), Cu1–N8 2.145(6), N5–C17 1.517(8), N5–C18
1.495(8), C17–C18 1.513(10), N5–C21 1.484(8), N6–C22 1.467(9),
C21–C22 1.540(8); N5–Cu1–N7 172.8(2), N6–Cu1–N8 96.5(2), N6–
Cu1–Cl2 136.80(19), N8–Cu1–Cl2 126.67(15), N5–Cu1–N6 83.0(2),
N5–Cu1–N8 94.5(2), N5–Cu1–Cl2 94.7(2), N7–Cu1–N6 90.6(2), N7–
Cu1–N8 82.8(2), N7–Cu1–Cl2 92.30(15), N5–C17–C18 59.1(4), N5–
C18–C17 60.5(4), C17–N5–C18 60.3(4).
Biological studies
The cytotoxicity of the complexes 1a, 2b, 3b, 4c and 5d was
assayed against human HL-60 and NALM-6 leukemia cells and
melanoma WM-115 cells. During these tests no signs of
decomposition were noticed. Cisplatin and carboplatin were used
as reference compounds. Cells were exposed to a broad range of
drug concentrations (10−7 to 10−3 M) for 48 h and cell viability
was analyzed by MTT assay. IC50 values are presented in
Table 2. The complexes 2b, 3b and 5d exhibited the highest
cytotoxic activity for HL-60 and NALM-6 cell lines, with IC50
values in the range of 1.5–8.2 μM. Interestingly, compound 3b
was even more effective then reference drug cisplatin in the case
of human skin melanoma WM-115 cells.
Fig. 4 Molecular structure of complex 5d with selected bond lengths
(Å) and angles (°). Thermal ellipsoids are drawn at the 30% probability
level, H atoms are omitted for clarity. Pd1–N1 1.994(4), Pd1–N2 1.973
(4), Pd1–Cl1 2.3009(15), Pd1–Cl2 2.2957(15), N1–C1 1.504(7), N1–C2
1.245(6), C1–C2 1.463(7); N1–Pd1–N2 179.3(3), N1–Pd1–Cl1 92.09
(14), N1–Pd1–Cl2 87.89(15), Cl1–Pd1–Cl2 179.38(5), C1–N1–Pd1
137.5(3), C1–N1–C2 63.5(3), N1–C1–C2 49.6(3), N1–C2–C1 66.9(3).
It was found that the growth of Gram-positive bacterial strains
(S. aureus, S. epidermidis and E. faecalis) was inhibited by
almost all tested complexes at the concentrations of
37.5–300.0 μg mL−1 (Table 3). On the other hand, MIC values
of complexes obtained for Gram-negative E. coli and P. aerugi-
nosa, as well as for C. albicans yeast, exceeded 300 μg mL−1
.
In the unit cell of complex 4c are two independent molecular
units with only a few slight differences in their structural par-
ameters. Therefore, only one is discussed and shown in Fig. 3.
The Cu(II) center shows a distorted trigonal bipyramidal geome-
try surrounded by four nitrogen atoms and one chlorido ligand.
This and both NH2 groups lie within the equatorial plane, while
both aziridine N atoms occupy the trans-axial positions. The
equatorial angles differ greatly because of the steric demand of
the chlorido ligand (N6–Cu1–Cl2 136.80(19)°, N8–Cu1–Cl2
The exception was activity of 2b against E. coli and P. aerugi-
nosa (at 75.0 μg mL−1) and 1a with the MIC for E. coli equal to
150.0 μg mL−1. In general, the highest activity was achieved by
2b. MICs of this complex were relatively low: 37.5 μg mL−1 for
S. aureus and 18.75 μg mL−1 for S. epidermidis. The second
complex with noticeable antimicrobial activity was 1a. It inhib-
ited growth of Gram-positive cocci (S. aureus, S. epidermidis
and E. faecalis) at a concentration range of 75.0–150.0 μg mL−1
.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 5925–5933 | 5929

View Article Online
Table 1 Crystallographic data for complexes 1a, 2b, 4c and 5d
Compound
1a
2b
4c
5d
Formula
FW
T/K
C14H23ClN2Pd
361.22
200(2)
C8H20N4Pd, 2 (CF3O3S)
576.83
200(2)
C16H36ClCuN4, Cl
418.94
200(2)
C16H14Cl2N2Pd
411.62
200(2)
Wavelength/Å
Crystal system
Space group
a/Å
b/Å
c/Å
0.71073
Monoclinic
P21
10.7546(5)
26.4634(11)
11.0319(4)
90
0.71073
Monoclinic
P21/c
11.6261(3)
9.8324(2)
9.8676(2)
90
0.71073
Orthorhombic
Pna21
24.9994(5)
9.0537(1)
18.8146(3)
90
0.71073
Orthorhombic
Pca21
21.4333(5)
5.6449(1)
12.6506(3)
90
α/°
β/°
92.912(3)
90
3135.6(2)
8
1.53036
1.340
111.658(2)
90
1048.36(4)
2
1.82736
1.170
90
90
90
90
γ/°
V/Å3
4258.44(12)
8
1.3069
1.281
1784
0.16 × 0.04 × 0.03
3.2 to 26.00
−30 ≤ h ≤ 30
−11 ≤ k ≤ 11
−23 ≤ l ≤ 23
7966
1530.58(6)
4
1.78631
1.554
816
0.18 × 0.05 × 0.02
3.61 to 27.48
−27 ≤ h ≤ 27
−7 ≤ k ≤ 7
−16 ≤ l ≤ 16
3291
Z
ρc/g cm−3
μ/mm−1
F(000)
Crystal size/mm
θ range/°
Index range
1472
576
0.34 × 0.24 × 0.15
3.78 to 27.62
−13 ≤ h ≤ 14
−34 ≤ k ≤ 23
−14 ≤ l ≤ 14
18 229
0.14 × 0.10 × 0.04
3.99 to 27.52
−15 ≤ h ≤ 15
−12 ≤ k ≤ 12
−12 ≤ l ≤ 12
4640
Refls. collected
Independent refls.
Rint
10 459
0.0295
2400
0.0142
4295
0.0275
3291
0.041
Completeness to θ
Data/restraints/parameters
S on F2
99.4%
10 459/1/649
1.001
R1 = 0.0221, wR2 =
0.0494
99.5%
2400/0/169
1.104
R1 = 0.0228, wR2 =
0.0523
99.4%
4295/1/416
1.021
R1 = 0.0465, wR2 =
0.1204
99.7%
3291/1/191
1.049
R1 = 0.0322, wR2 =
0.0730
Final R indices [I > 2σ(I)]
R indices (all data)
R1 = 0.0247, wR2 =
0.0504
0.021(14)
0.483/−0.550
R1 = 0.0278, wR2 =
0.0546
R1 = 0.0692, wR2 =
0.1352
R1 = 0.0473, wR2 =
0.0808
Absolute structure parameter
Largest difference peak/hole
−
0.29(6)a
0.47(7)a
0.605/−0.552
1.208/−0.366
2.186/−0.618
[e Å−3
]
CCDC
849020
849021
849022
849023
a Structures 4c and 5d refined as twins (twinned by inversion) yielding BASF 0.2926 (4c) and 0.4697 (5d). The determination of the absolute
structures is not possible.
Table 2 IC50 values (in μM) for complexes 1a, 2b, 3b, 4c and 5d
Table 3 Antimicrobial activity of complexes. MIC values (μg mL−1
)
were determined by broth microdilution assay, according to CLSI
recommendations
a
Compounds
HL-60
NALM-6 IC50
WM 115
1a
2b
3b
4c
56.4 2.3
8.2 0.3
1.53 0.30
50.3 2.8
4.6 0.7
0.8 0.1
4.3 1.3
48.7 1.0
7.2 0.5
0.58 0.10
48.1 3.0
5.8 1.1
0.7 0.3
0.7 0.2
62.4 3.4
47.6 1.0
5.9 0.9
51.4 3.9
84.6 2.8
18.2 4.3
422.2 50.2
MIC (μg mL−1
)
Microorganism
1a
2b
3b
4c
5d
5d
S. aureus (ATCC
29213)
S. epidermidis (ATCC
12228)
E. faecalis (ATCC
29212)
E. coli (NCTC 8196)
P. aeruginosa (NCTC
6749)
150.0
75.0
150.0
150.0
37.5
300.0
300.0
300.0
>300.0 300.0
>300.0 300.0
>300.0 300.0
Cisplatin
Carboplatin
18.75
150.0
75.0
a IC50 – concentration of a tested compound required to reduce the
fraction of surviving cells to 50% of that observed in the control, non-
treated cells. Data represents the mean value of at least three
experiments, each performed at five repeats S.D.
>300.0 >300.0 >300.0
>300.0 >300.0 >300.0
>300.0 75.0
C. albicans (ATTC
10231)
>300.0 >300.0 >300.0 300.0
>300.0
Conclusion
In the present paper the synthesis, characterization and crystal
structures of three square planar palladium(II) complexes (1a, 2b
and 5d) containing the ligands 2-dimethylaziridine-N (a), N-(2-
aminoethyl)aziridine-N,N′ (b) and 2H-3-phenylazirine (d) as
well as of two copper(II) complexes (octahedral 3b and trigonal
bipyramidal 4c), where ligands b and c are dimers of the parent
aziridine C2H4NH and its 2-dimethyl derivative a, are reported.
This unexpected dimerization occurs via insertion and ring
opening reaction of two aziridines by metal-induced activation.
Though aziridines are considered to be highly mutagenic, all the
complexes have been examined for cytotoxic and antimicrobial
properties. To the best of our knowledge this is the first time
such directed investigations have been carried out. All the novel
5930 | Dalton Trans., 2012, 41, 5925–5933
This journal is © The Royal Society of Chemistry 2012

View Article Online
aziridine-containing complexes are promising compounds with
high antitumor activity and two of them, 1a and 2b, also show
remarkable antibacterial activity. Many natural or synthetic com-
pounds show activity against Gram-positive bacteria but not
against Gram-negative species or fungi, which have evolved sig-
nificant permeability barriers. Thus, it is worth emphasizing that
in our experiments the Gram-negative bacteria were susceptible
to damage by one of complexes used (2b). It suggests that this
compound may easily penetrate biological membranes probably
without any help of active transport mechanisms and may be
promising as a future therapeutic agent and alternative to anti-
biotics. However, on the basis of this study it is difficult to
predict its mechanisms of action.
palladium(II)]61 (71 mg, 0.122 mmol) in 5 mL CH2Cl2. After
12 h of stirring at r.t., the solvent was removed in vacuo and the
residue was purified by stirring in dry n-heptane (10 mL) for
12 h at r.t. Yield 44 mg (0.122 mmol, 50%), light grey powder,
m.p. 157 °C. Elemental analysis: Found: N, 7.72; C, 46.58; H,
6.45. Calc. for C14H23ClN2Pd (361.22 g mol−1): N, 7.76; C,
46.55; H, 6.42%. IR: νmax/cm−1 (KBr) 3139vs (NH), 3105s,
2971s (CH), 2912m (CH), 2856m (CH), 2833w (CH), 2788w,
1579w, 1458s, 1446s, 1384s, 1370m, 1340s, 1290w, 1251w,
1175w, 1175w, 1146m, 1114s, 1062w, 1030w, 1011m, 981w,
939s, 921s, 812s, 786w, 756vs, 729s, 661w, 557w. 1H NMR
(270.17 MHz, CD2Cl2): δ = 7.00–6.82 (m, 4H, Ar-CH), 3.62
3
and 3.53 (two signals for S,S and S,R enantiomer, quartet, JH–H
= 6.5 Hz, 0.4H and 0.6H, CHMe), 2.75 and 2.59 (s, 1.5H each,
NCH3), 2.63 and 2.56 (s, 1.5H each, NCH3), 2.50 (d, br, 3JH–NH
Experimental
3
2
= 5.9 Hz, 1H, az-CH2), 2.09 (d, br, JH–NH = 7.4 Hz, JH–H
=
2.1 Hz, 1H, az-CH2), 1.53 (s, 3H, az-CH3), 1.52 (s, 3H, az-
CH3), 1.46 and 1.42 (s, JH–H = 6.5 Hz, 1.5H each, CHCH3).
Materials and methods
3
13C NMR, DEPT: (67.93 MHz, CD2Cl2): δ = 154.0 and 153.6
(Ar-Cq), 147.5 and 147.2 (Ar-Cq-Pd), 131.6 (Ar-CH), 124.5 and
124.8 (Ar-CH), 124.2 and 124.1 (Ar-CH), 122.1 and 122.0 (Ar-
CH), 76.2 and 75.6 (>CHCH3), 52.2 and 51.9 (>NCH3), 48.0
and 47.2 (>NCH3), 38.9 and 38.7 (az-Cq), 37.5 and 37.4 (az-
CH2), 25.8 and 25.5 (az-CH3), 25.4 and 25.0 (az-CH3), 20.9 and
19.2 (>CHCH3). MS (FAB+): m/z (%) = 362 (22) [M+], 325
(100) [M+ − Cl], 254 (13) [M+ − Cl − a], 211 (11) [Pd + Cl + a].
All experiments were performed under a dry argon atmosphere
using Schlenk line techniques. The separation of phases in het-
erogeneous reaction mixtures was carried out by centrifugation
with subsequent pipetting or by filtration. Reagents were com-
mercially available and used without further purification. The
61
starting complexes [μ-Cl(C6H4CHMeNMe2-C,N)Pd]2
and
62
trans-[C2H4NHPdCl]2 were prepared according to literature
methods. The solvents were purified by standard procedures;
CH2Cl2 was distilled from calcium hydride, n-pentane from
lithium aluminium hydride and methanol from MgH2. All dried
solvents were stored under a dry Ar atmosphere with 3 Å mol-
ecular sieves. NMR spectra were recorded using a Jeol Eclipse
270 or a Jeol Eclipse 400 spectrometer operating at 270 MHz
(1H) and 68 MHz (13C) or 400 MHz (1H) and 100 MHz (13C),
[Bis(N-(2-aminoethyl)aziridine-N,N′)palladium(II)]bis(trifluor-
methansulfonate) (2b). To
a
suspension of 100 mg
(0.380 mmol) trans-[bis(aziridine)dichloridopalladium(II)]
((C2H4N)2Cl2Pd)62 in 20 mL CH2Cl2, 205 mg (0.797 mmol)
AgOTf was added. After stirring at r.t. for 24 h the precipitate of
AgCl was separated by centrifugation. The resulting solution
was combined with 61.4 μL (1.14 mmol) aziridine C2H4NH,
whereby it become clouded. After stirring again at r.t. for 24 h
the solvent was removed in vacuo. The crude residue was
purified by stirring in n-hexane and separation by pipetting two
times; afterwards it was dried in vacuo. Yield 108 mg
(0.187 mmol, 50%), light yellow solid, m.p. 176 °C (dec.).
Elemental analysis: Found: C, 21.09; H, 3.88; N, 9.15. Calc. for
C10H20F6N4O6PdS2 (576.83 g mol−1): C, 20.82; H, 3.49; N,
9.71%. IR: νmax/cm−1 (KBr) 3252m, 3154w, 2926w, 1608w,
1448w, 1280s, 1246s, 1166s, 1032s, 990w, 957w, 906w, 829w,
1
respectively. The H and 13C chemical shifts were determined
relative to TMS as an internal standard. IR spectra were recorded
using a Perkin Elmer Spectrum One FT-IR-Spectrometer in the
range of 4000–400 cm−1. UV/visible (UV/Vis) data were
recorded with a Varian Cary 50 UV/Vis spectrophotometer at
room temperature. Mass spectra were obtained with a JEOL
MStation MS-700, NBA matrix (FAB). Multi-isotope containing
fragments refer to the isotope with the highest abundance.
Elemental analyses were performed by the Microanalytical Lab-
oratory of the Department of Chemistry, LMU Munich, using a
Heraeus Elementar Vario El. Single crystal X-ray data were col-
lected with a Nonius Kappa CCD diffractometer (2b, 4c, 5d)
equipped with a rotating anode generator or an Oxford Diffrac-
tion XCalibur diffractometer (1a), both using graphite-mono-
chromated Mo-Kα radiation (λ = 0.71073 Å). Structures were
solved by direct methods using the SHELXS software and
refined on F2 by full-matrix least-squares with SHELXL-97.76
CCDC numbers in Table 1 contain the supplementary crystallo-
graphic data for this paper.‡
1
805w, 750w, 639s, 574w, 517m, 408w. H NMR (399.78 MHz,
CD3OD): δ = 2.90 (t, 3J = 5.6 Hz, 4H, en-CH2), 2.34 (t, 3J = 5.6
Hz, 4H, en-CH2), 1.87 (t, 3J = 2.2 Hz, 4H, az-CH2), 1.40 (t, 3J =
2.2 Hz, 4H, az-CH2). 13C NMR (100.53 MHz, CD3OD): δ =
1
121.83 (q, JC-F = 319 Hz, CF3), 62.56 (en-CH2), 42.87 (en-
CH2), 33.98 (az-CH2), 28.30 (az-CH2). MS (FAB+): m/z (%) =
427 (93) [M2+ + OTf], 277 (80) [M2+], 191 (48) [M2+ − b].
[Tris(N-(2-aminoethyl)aziridine-N,N′)copper(II)]dichloride (3b).
The aziridine C2H5NH (8 mL, 149 mmol) was cooled down to
−10 °C. Then anhydrous CuCl2 (1.55 g, 11.5 mmol) was added
in small portions while stirring for 4 h. After warming up to r.t.
the blue mixture was stirred for 3 d and then the excess of
C2H5NH was removed in vacuo. The residue was purified by
stirring in n-hexane overnight and dried in vacuo after separation
from n-hexane by pipette. Yield 4.35 g (11.0 mmol, 96%), blue
Synthesis of the palladium(II) and copper(II) complexes 1a, 2b,
3b, 4c and 5d
Chlorido-(2,2-dimethylaziridine)-[2-{1-(dimethylamino)ethyl}-
phenyl-C,N]-palladium(II) (1a). 6 equivalents of 2,2-dimethyla-
ziridine (a) (66.1 μL, 0.732 mmol) were added to a solution
of bis[μ-chlorido-[(S)-2-{1-(dimethylamino)ethyl}phenyl-C,N-
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 5925–5933 | 5931

View Article Online
powder, m.p. 111 °C (dec.). Elemental analysis: Found: C,
36.65; H, 7.67; N, 21.12. Calc. for C12H30Cl2CuN6 (392.86 g
mol−1): C, 36.69; H, 7.70; N, 21.39%. UV/Vis: λmax(CH2Cl2)/
nm 721 (ε/L mol−1 cm−1 279). IR: νmax/cm−1 (KBr) 3192s,
3101s, 2995w, 2966w, 2882m, 1660w, 1602m, 1448m, 1359w,
1323w, 1293w, 1259m, 1222w, 1152m, 1097w, 1063m, 1008s,
936s, 902w, 861s, 834w, 816w, 787w, 755m, 708w, 553w, 450w.
MS (FAB+): m/z (%) = 356 (5) [M2+ × Cl], 321 (4) [M2+],
and antibiotics (100 μg mL−1 streptomycin and 100 U mL−1
penicillin). For melanoma WM-115 cells Dulbecco’s minimal
essential medium (DMEM) instead of RPMI 1640 was used.
Cells were grown in 37 °C in a humidified atmosphere of 5%
CO2 in air.
Cytotoxicity assay by MTT. Cytotoxicity of complexes 1a,
2b, 3b, 4c, 5d, cisplatin and carboplatin was determined by
the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
bromide, Sigma, St. Louis, USA) assay as described.77 Briefly,
after 46 h of incubation with drugs, the cells were treated with
the MTT reagent, and incubation was continued for 2 h. MTT–
formazan crystals were dissolved in 20% SDS and 50% DMF at
pH 4.7 and absorbance was read at 562 nm on an ELISA-plate
reader (ELX 800, Bio-Tek, USA). The values of IC50 (the con-
centration of the tested compound required to reduce the cells
survival fraction to 50% of the control) were calculated from
concentration–survival curves and used as a measure of cellular
sensitivity to a given treatment. Complexes, cisplatin and carbo-
platin were tested for their cytotoxicity in final concentrations
from 10−7 to 10−3 M. As a control, cultured cells were grown in
the absence of drugs. Data points represent means of 3–4 exper-
iments, each performed at five repeats S.D.
270 (100) [M2+ + Cl − b], 240 (31) [M2+ − b], 184 (36) [M2+
Cl − 2b].
+
[Bis{N-(2-amino-2-methylpropyl)-2,2-dimethylaziridine-N,N′}
chlorido-copper(II)]chloride (4c). The synthesis of 4c takes place
analogously to that of 3b: Cooling of aziridine CH2CMe2NH
(1 mL, 11.1 mmol), slowly adding 130 mg (0.967 mmol) anhy-
drous CuCl2, reaction time 2 days and the same procedure of
purification. Yield 388 mg (0.930 mmol, 96%), turquoise
powder, m.p. 174 °C (dec.). Elemental analysis: Found: C,
45.93; H, 8.71; N, 13.42. Calc. for C16H36Cl2CuN4 (418.94 g
mol−1): C, 45.87; H, 8.66; N, 13.37%. UV/Vis: λmax(CH2Cl2)/
nm 796 (ε/L mol−1 cm−1 380). IR: νmax/cm−1 (KBr) 3239s,
3136s, 2992m, 2968s, 2878m, 2734w, 1604m, 1476m, 1461m,
1393m, 1382s, 1373m, 1348m, 1338m, 1282w, 1236m, 1199m,
1151m, 1111m, 1067w, 1024w, 999m, 948m, 932m, 924m,
867m, 812s, 773m. MS (FAB+): m/z (%) = 383 (67) [M+], 348
(30) [M+ − Cl], 240 (100) [M+ − c], 205 (74) [M2+ − Cl − c].
Following the suggestion of a reviewer that the dinuclear
Cu(II) complex [(μ-Cl)(CH2CMe2NH)2ClCu]2 (synthesized from
CuCl2 in CH2Cl2 solution)67 could be a possible intermediate in
the formation of 4c, we repeated the synthesis of 4c as described
above with this complex instead of CuCl2. Indeed we were able
to detect 4c in the products of this reaction with MS (FAB+) but
further purification was not possible.
Antibacterial activity
Microorganisms. Gram-positive bacteria: Staphylococcus
aureus ATCC 29213; S. epidermidis ATCC 12228; Enterococcus
faecalis ATCC 29212; two Gram-negative bacteria: Escherichia
coli NCTC 8196; Pseudomonas aeruginosa NCTC 6749, and
yeast Candida albicans ATCC 10231, were used. The organisms
were stored in TSB with 15% glycerol at −70 °C, and in each
experiment cultures were established from the original stock.
trans-Bis[(2H-phenylazirine)dichlorido]palladium(II)
(5d).
Antibacterial activity testing. The susceptibility of microor-
ganisms to complexes was determined by the standard CLSI
(Clinical and Laboratory Standards Institute) broth microdilution
method. Sterile stock solutions of each compound at the concen-
tration of 60.0 mg mL−1 were prepared in DMSO. The agent
concentration range used in the antimicrobial tests was
0.29–300.0 μg mL−1 prepared for bacteria in Mueller–Hinton
broth (Difco, USA), and for yeast in RPMI-1640 medium sup-
plemented with L-glutamine and NaHCO3 (Biomed, Poland).
Since stock solutions of chemicals were prepared in DMSO, this
solubilizer alone was used as a control. To specify the minimal
inhibitory concentrations (MIC), turbidometric (OD600) studies
were carried out using the multifunction counter Victor2
(Wallac, Finland). MIC was estimated as the lowest concen-
tration of antimicrobial agent which gave drop in OD600 equal to
the medium negative control (below 0.05), after 24 h at 37 °C of
co-incubation.
193 mg (0.744 mmol) of PdCl2 in 20 mL of CH3CN was heated
to reflux until it dissolved. Small amounts of insoluble com-
ponents were filtered off and the solvent distilled off in vacuo.
The orange yellow residue was dissolved in a mixture of 30 mL
CH2Cl2 and 10 mL CH3CN. The resulting solution was com-
bined with 174 mg (1.488 mmol) 2H-3-phenylazirine d and
stirred at r.t. for 0.5 h. The solvent was removed in vacuo. Yield
200 mg (0.419 mmol, 65%), yellow-orange powder, m.p. 154 °C
(dec.). Elemental analysis: Found: C, 46.22; H, 3.26; N, 6.70.
Calc. for C16H14Cl2N2Pd (411.62 g mol−1): C, 46.69; H, 3.43;
N, 6.81%. IR: νmax/cm−1 (KBr) 3049w, 1777vs, 1597w, 1491w,
1450m, 1326w, 1308w, 1265w, 1185w, 1132w, 1020s, 874m,
1
767s, 699m, 682s, 543m. H NMR (399.78 MHz, CDCl3): δ =
8.37–8.34 (m, 4H, CH), 7.75–7.71 (m, 2H, CH), 7.65–7.61 (m,
4H, CH), 2.23 (s, 4H, CH2). 13C NMR (100.53 MHz, CDCl3): δ
= 166.8 (Cq), 133.6 (CH), 132.4 (CH), 129.3 (CH), 121.6 (Cq),
20.9 (CH2). MS (FAB+): m/z (%) = 377 (100) [M+ − Cl].
Cell and cytotoxicity assay
Acknowledgements
Cell cultures. Human skin melanoma WM-115 cells as well
as human leukemia promyelocytic HL-60 and lymphoblastic
NALM-6 cell lines were used. Leukemia cells were cultured in
RPMI 1640 medium supplemented with 10% fetal bovine serum
This work was supported by grants from the Medical University
of Lodz No. 503/3-066-02/503-01 (to E. Budzisz) and No. 503/
3-015-02/503-01 (to M. Rozalski and U. Krajewska). We thank
Dr Karin Lux for the assistance in crystal structure solution.
5932 | Dalton Trans., 2012, 41, 5925–5933
This journal is © The Royal Society of Chemistry 2012

View Article Online
37 S. v. Beckerath, I.-P. Lorenz, R. Fawzi and M. Steimann, Z. Naturforsch.,
B: Chem. Sci., 1996, 51b, 959–962.
Notes and references
38 R. B. Cheikh, R. Chaabouni, M. C. Bonnet and F. Dahan, Polyhedron,
1998, 17, 185–192.
39 R. Wilberger, H. Piotrowski, M. Warchhold and I.-P. Lorenz, Z. Anorg.
Allg. Chem., 2003, 629, 2485–2492.
40 R. Wilberger, C. Krinninger, H. Piotrowski, P. Mayer, M. Ossberger and
I.-P. Lorenz, Z. Anorg. Allg. Chem., 2004, 630, 1495–1500.
41 I.-P. Lorenz, C. Krinninger, R. Wilberger, R. Bobka, H. Piotrowski,
M. Warchhold and H. Nöth, J. Organomet. Chem., 2005, 690, 1986–
1993.
42 W. Beck, W. Danzer and R. Höfer, Angew. Chem., 1973, 85, 87–88.
43 W. Beck, W. Danzer, A. T. Liu and G. Huttner, Angew. Chem., 1976, 88,
511–512.
44 A. T. Liu, W. Beck, G. Huttner and H. Lorenz, J. Organomet. Chem.,
1977, 129, 91–96.
45 W. Danzer, R. Hoefer, H. Menzel, B. Olgemoeller and W. Beck, Z. Natur-
forsch., B: Chem. Sci., 1984, 39b, 167–179.
46 M. M. Singh and R. J. Angelici, Inorg. Chem., 1984, 23, 2691–2698.
47 M. M. Singh and R. J. Angelici, Inorg. Chem., 1984, 23, 2699–2705.
48 R. Wilberger, Ph.D. Thesis, LMU, Munich, 2002.
49 R. Höfer, W. Beck and A. Engelmann, Chem. Ber., 1973, 106, 2590–
2600.
1 J. B. Sweeney, Chem. Soc. Rev., 2002, 31, 247–258.
2 I. D. Watson, L. Yu and A. K. Yudin, Acc. Chem. Res., 2006, 39, 194–
206.
3 D. M. Noll, T. M. Mason and P. S. Miller, Chem. Rev., 2006, 106, 277–
301.
4 B. M. Trost and D. R. Fandrick, Org. Lett., 2005, 7, 823–826.
5 V. K. Yadav and V. Sriramurthy, J. Am. Chem. Soc., 2005, 127, 16366–
16367.
6 O. Ihata, Y. Kayaki and T. Ikariya, Macromolecules, 2005, 38, 6429–
6434.
7 J. A. Katzenellenbogen, K. E. Carlson, D. F. Heiman, D. W. Robertson,
L. L. Wei and B. S. Katzenellenbogen, J. Biol. Chem., 1983, 258, 3487–
3495.
8 B. S. Iyengar, S. M. Sami, S. E. Tarnow, W. A. Remers, W. T. Bradner
and J. E. Schurig, J. Med. Chem., 1983, 26, 1453–1457.
9 G. Sosnovsky and M. Konieczny, Synthesis, 1978, 583–585.
10 R. Kho, J. A. Hodges, M. R. Hansen and H. O. Villar, J. Med. Chem.,
2005, 48, 6671–6678.
11 S. R. Rajski and R. M. Williams, Chem. Rev., 1998, 98, 2723–2796.
12 M. M. Paz, G. Suresh Kumar, M. Glover, M. J. Waring and M. Tomasz,
J. Med. Chem., 2004, 47, 3308–3319.
50 H. P. Fritz and G. Hierl, Z. Naturforsch., B: Chem. Sci., 1971, 26b, 476.
51 M. Kojima, A. Sakurai, M. Murata, K. Nakajima, S. Kashino and
Y. Yoshikawa, J. Coord. Chem., 1997, 42, 95–106.
52 C. Krinninger, Ph.D. Thesis, LMU, Munich, 2005.
53 R. Bobka, Ph.D. Thesis, LMU, Munich, 2007.
13 K. Yokoi, K. Nagaoka and T. Nakashima, Chem. Pharm. Bull., 1986, 34,
4554–4561.
14 S. C. Schold Jr., J. E. Herndon, P. C. Burger, E. C. Halperin, N. A. Vick,
J. G. Cairncross, D. R. Macdonald, E. J. Dropcho, R. Morawetz and D.
D. Bigner, et al., J. Clin. Oncol., 1993, 11, 77–83.
15 Y.-C. Peng, H.-S. Kuo, H.-D. Tsai, Y.-P. Yang and Y.-L. Lin, Bioorg.
Med. Chem., 2006, 14, 263–272.
54 K. Dietliker, U. Schmid, G. Mukherjee-Mueller and H. Heimgartner,
Chimia, 1978, 32, 164–166.
55 A. Hassner, C. A. Bunnell and K. Haltiwanger, J. Org. Chem., 1978, 43,
57–61.
16 M. J. v. Maanen, C. J. M. Smeets and J. H. Beijnen, Cancer Treat. Rev.,
2000, 26, 257–268.
56 P. F. Dos Santos Filho and U. Schuchardt, J. Organomet. Chem., 1984,
263, 385–393.
57 H. Alper and J. E. Prickett, Inorg. Chem., 1977, 16, 67–71.
58 T. Izumi and H. Alper, Organometallics, 1982, 1, 322–325.
59 B. S. Iyengar, T. Takahashi, W. A. Remers and W. T. Bradner, J. Med.
Chem., 1986, 29, 144–147.
17 Y. Palom, M. F. Belcourt, S. M. Musser, A. C. Sartorelli, S. Rockwell and
M. Tomasz, Chem. Res. Toxicol., 2000, 13, 479–488.
18 I.-P. Lorenz and J. Kull, Angew. Chem., 1986, 98, 276–278.
19 J. Amarasekera, T. B. Rauchfuss and S. R. Wilson, J. Am. Chem. Soc.,
1988, 110, 2332–2334.
20 R. F. Heck, J. Am. Chem. Soc., 1963, 85, 1460–1463.
21 D. Milstein and J. C. Calabrese, J. Am. Chem. Soc., 1982, 104, 3773–
3774.
60 M. Galanski and B. K. Keppler, Pharm. Unserer Zeit, 2006, 35, 118–
123.
61 S. B. Wild, Coord. Chem. Rev., 1997, 166, 291–311.
62 J. N. Roedel, R. Bobka, M. P. Pfister, M. Rieger, B. Neumann and I.-
P. Lorenz, Z. Naturforsch., B: Chem. Sci., 2007, 62b, 1095–1101.
63 R. Bobka, J. N. Roedel, B. Neumann, T. Nigst and I.-P. Lorenz, Polyhe-
dron, 2008, 27, 955–961.
64 T. B. Jackson and J. O. Edwards, J. Am. Chem. Soc., 1961, 83, 355–360.
65 T. B. Jackson and J. O. Edwards, Inorg. Chem., 1962, 1, 398–401.
66 J. N. Roedel, Ph.D. Thesis, LMU, Munich, 2008.
67 J. N. Roedel, R. Bobka, B. Neumann, B. Weber, P. Mayer and I.-
P. Lorenz, Z. Anorg. Allg. Chem., 2007, 633, 1171–1177.
68 P. H. Leung, A. C. Willis and S. B. Wild, Inorg. Chem., 1992, 31, 1406–
1410.
69 B.-H. Aw, T. S. A. Hor, S. Selvaratnam, K. F. Mok, A. J. P. White, D.
J. Williams, N. H. Rees, W. McFarlane and P.-H. Leung, Inorg. Chem.,
1997, 36, 2138–2146.
70 P.-H. Leung, K.-H. Ng, Y. Li, A. J. P. White and D. J. Williams, Chem.
Commun., 1999, 2435–2436.
71 A. B. P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Amsterdam,
2nd edn., 1984.
72 G. A. McLachlan, G. D. Fallon, R. L. Martin and L. Spiccia, Inorg.
Chem., 1995, 34, 254–261.
73 N. W. Mitzel, J. Riede and C. Kiener, Angew. Chem., 1997, 109, 2299–
2300, (Angew. Chem., Int. Ed. Engl., 1997, 36, 2215–2216).
74 M. Duggan, N. Ray, B. Hathaway, G. Tomlinson, P. Brint and K. Pelin, J.
Chem. Soc., Dalton Trans., 1980, 1342–1348.
75 S. Putzien, S. Wirth, J. Nicolas Roedel and I.-P. Lorenz, Polyhedron,
2011, 30, 1747–1751.
22 I.-P. Lorenz, J. Messelhäuser, W. Hiller and K. Haug, Angew. Chem.,
1985, 97, 234–235.
23 I.-P. Lorenz, J. Messelhäuser, W. Hiller and M. Conrad, J. Organomet.
Chem., 1986, 316, 121–138.
24 M. Herberhold and B. Schmidkonz, J. Organomet. Chem., 1988, 358,
301–320.
25 G. Beuter, S. Drobnik, I.-P. Lorenz and A. Lubik, Chem. Ber., 1992, 125,
2363–2366.
26 L. M. Atagi, D. E. Over, D. R. McAlister and J. M. Mayer, J. Am. Chem.
Soc., 1991, 113, 870–874.
27 C. A. Root and J. W. Allison, Inorg. Chem., 1970, 9, 2791–2792.
28 D. V. Lefemine, M. Dann, F. Barbatschi, W. K. Hausmann, V. Zbinovsky,
P. Monnikendam, J. Adam and N. Bohonos, J. Am. Chem. Soc., 1962,
84, 3184–3185.
29 J. C. Barnes, J. Iball and T. J. R. Weakley, Acta Crystallogr., Sect. B:
Struct. Crystallogr. Cryst. Chem., 1975, 31, 1435–1437.
30 F. Porta, M. Pizzotti, G. La Monica, L. A. Finessi, S. Cenini, P. L. Bellon
and F. Demartin, J. Chem. Soc., Dalton Trans., 1984, 2409–2414.
31 V. B. Ukraintsev, S. V. Yakovlev and Y. N. Kukushkin, Zh. Obshch.
Khim., 1987, 57, 1906–1907.
32 V. B. Ukraintsev, S. V. Yakovlev and Y. N. Kukushkin, Russ. J. Gen.
Chem., 1987, 57, 1704–1705.
33 D. C. Ware, B. G. Siim, K. G. Robinson, W. A. Denny, P. J. Brothers and
G. R. Clark, Inorg. Chem., 1991, 30, 3750–3757.
34 D. C. Ware, D. S. Mackie, P. J. Brothers and W. A. Denny, Polyhedron,
1993, 12, 1371–1376.
35 W. R. Cantrell Jr, G. B. Richter-Addo and J. A. Gladysz, J. Organomet.
Chem., 1994, 472, 195–204.
36 D. C. Ware, D. S. Mackie, P. J. Brothers and W. A. Denny, Polyhedron,
1995, 14, 1641–1646.
76 G. M. Sheldrick, Acta Crystallogr., Sect. A, 2008, 64, 112–122.
77 E. Budzisz, U. Krajewska, M. Rozalski, A. Szulawska, M. Czyz and
B. Nawrot, Eur. J. Pharmacol., 2004, 502, 59–65.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 5925–5933 | 5933