Synthesis and structures of palladium(II) and platinum(II) complexes containing heterocyclic thiolate ligands formed by cycloaddition reactions of coordinated azides

Article abstract of DOI:10.1139/V08-115

The phosphine-stabilized azido complexes [M(N₃) ₂(PTA)₂] (M = Pd, Pt; PTA = 1,3,5-triaza-7- phosphaadamantane) were prepared in high yields by a ligand exchange reaction from cis-[Pd(N₃)₂(tmeda)] and

Full text of DOI:10.1139/V08-115

146
Synthesis and structures of palladium(II) and
platinum(II) complexes containing heterocyclic
thiolate ligands formed by cycloaddition reactions
of coordinated azides1
Angela Fleischer, Alexander Roller, Vladimir B. Arion, Bernhard K. Keppler, and
Fabian Mohr
Abstract: The phosphine-stabilized azido complexes [M(N3)2(PTA)2] (M = Pd, Pt; PTA = 1,3,5-triaza–7-
phosphaadamantane) were prepared in high yields by a ligand exchange reaction from cis-[Pd(N3)2(tmeda)] and cis-
[Pt(N3)2(cod)], respectively. The Pd and Pt complexes [M(N3)2(PTA)2] undergo cycloaddition reactions with various
isothiocyanates to give complexes containing anionic, S-coordinated tetrazole-thiolate ligands of the type trans-
[M(SCN4R)2(PTA)2] (M = Pd, Pt; R = Et, allyl, Me, Ph). The molecular structures of several of these derivatives were
determined by X-ray crystallography.
Key words: palladium, platinum, thiolate, heterocycle, azide, cycloaddition.
Résumé : On a préparé les complexes azido stabilisés par une phosphine [M(N3)2(PTA)2] [M= Pd, Pt; PTA = 1,3,5-
triaza-7-phosphaadamantane] avec des rendements élevés en procédant à une réaction d’échange de ligand à partir res-
pectivement du cis-[Pd(N3)2(tmeda)] et cis-[Pt(N3)2(cod)]. Les complexes du Pd et du Pt [M(N3)2(PTA)2] subissent des
réactions de cycloaddition avec divers isothiocyanates pour conduire à la formation de complexes contenant des ligands
anioniques tétrazole-thiolate, S-coordinés, du type trans-[M(SCN4R)2(PTA)2] (M = Pd, Pt; R = Et, allyle, Me, Ph). Les
structures molécules de plusieurs de ces dérivés ont été déterminées par la diffraction des rayons X.
Mots-clés : palladium, platine, thiolate, hétérocycle, azide, cycloaddition.
[Traduit par la Rédaction] Fleischer et al. 150
Introduction
9). These results show that the resulting heterocycle is S-
coordinated to the metal (Chart 1) rather than N-coordinated,
as originally suggested by Beck and co-workers in 1972 (5).
A computational study of the reaction mechanism leading to
the S-coordinated tetrazole-thiolato complex has also been
carried out (10).
We have been exploring the structures and reactivity of
precious metal complexes containing the water-soluble phos-
phine ligand 1,3,5-triaza–7-phosphaadamantane (PTA) (11–
14). In this context, water-soluble Pt(II) complexes contain-
ing heterocyclic thiolate ligands showed promising in vitro
cytotoxicity against various tumour cell lines (15). To gener-
ate a library of new water-soluble Pd and Pt complexes with
a variety of substituted tetrazole-thiolates from one common
precursor, we investigated the cycloaddition of isothio-
cyanates to PTA-stabilized Pd and Pt azido complexes. Some
preliminary results of this study are reported herein.
Azido complexes of palladium stabilized by phosphine
ligands were first reported by Beck et al. in 1965 (1). In a
series of papers, the group showed that the coordinated
azido groups undergo cycloaddition reactions with nitriles,
alkynes, and isothiocyanates to give metal-coordinated
tetrazolates (Chart 1) (2–6). Since then, several groups have
studied reactions of phosphine-stabilized Pd and, to a much
lesser extent, Pt azido complexes with various nitriles and
isocyanides. In contrast, cycloaddition reactions with
isothiocyanates have only recently been studied in detail (7–
Received 9 April 2008. Accepted 14 May 2008. Published on
the NRC Research Press Web site at canjchem.nrc.ca on
27 August 2008.
This article is dedicated to my mentor and friend Dick
Puddephatt in recognition of his outstanding contributions to
the chemistry of the precious metals.
Results and discussion
F. Mohr.2 Fachbereich C–Anorganische Chemie, Bergische
Universität Wuppertal, 42119 Wuppertal, Germany.
A. Fleischer, A. Roller, V.B. Arion, and B.K. Keppler.
Institut für Anorganische Chemie, Universität Wien, 1090
Wien, Austria.
The PTA stabilized Pd and Pt bis(azido) complexes
[M(N3)2(PTA)2] (M = Pd 1, Pt 2) are readily prepared in
high yields by displacement of the tmeda or cod ligands
from cis-[Pd(N3)2(tmeda)] and cis-[Pt(N3)2(cod)], respec-
tively. Both complexes are poorly soluble in water and insol-
uble in chlorinated solvents, acetone, and alcohols, but
readily soluble in DMSO. The 31P{1H} NMR spectra of
1This article is part of a Special Issue dedicated to Professor
R. Puddephatt.
2Corresponding author: (e-mail: fmohr@uni-wuppertal.de).
Can. J. Chem. 87: 146–150 (2009)
doi:10.1139/V08-115
© 2008 NRC Canada

Fleischer et al.
147
Chart 1.
Scheme 1.
Fig. 1. Molecular structure of complex 3a. Ellipsoids show 50%
probability levels. Hydrogen atoms have been omitted for clarity.
Selected bond distances (Å) and angles (°): Pd1–P1 2.3054(4),
Pd1–S1 2.3434(4), S1–C7 1.7250(15), C7–N5 1.3348(18), C7–
N4 1.3485(18), N4–N7 1.3576(17), N7–N6 1.2934(18); P1–Pd1–
S1 89.390(13), C7–S1–Pd1 100.88(5).
complexes 1 and 2 show singlet resonances at –29.90 and
–59.09 ppm, respectively. The IR spectra of both com-
pounds show strong bands between 2020 and 2050 cm–1 due
to the coordinated azido ligand. The positive ion ES-MS
spectra of both complexes show a single, intense peak with
m/z of 527 (1) and 616 (2), corresponding to the Na adduct
of the molecular ions. The observed isotopic distribution
patterns are in perfect agreement with the proposed formu-
las. Attempts to obtain X-ray diffraction quality crystals of
these complexes failed, as the initially yellow or colorless
DMSO solutions darkened and eventually decomposed to
give a metallic mirror over a period of 2–3 days. However,
the solid samples are stable in air at ambient temperatures
for months.
Complex 1 reacts with the isothiocyanates RNCS (R = Et,
allyl, Me, Ph) in CH2Cl2 at room temperature over a period
of ca. 18 h to give orange solutions, which, upon layering
with Et2O, afford crystals of the Pd tetrazole-thiolato com-
plexes trans-[Pd(SCN4R)2(PTA)2] (R = Et 3a, allyl 3b, Me
3c, Ph 3d) after several days (Scheme 1).
ray diffraction studies of compounds 3a, 3b, and 3d; the mo-
lecular structures are shown in Figs. 1–3.
In all three complexes, the palladium is coordinated by
two tetrazolate-thiolates (via the sulfur atom) and two PTA
ligands in a square planar geometry with a trans configura-
tion. The Pd–P and Pd–S bond distances of (ca. 2.30 and
2.34 Å, respectively) are very similar to those observed in
other PTA complexes of palladium containing thiolate lig-
ands, e.g., trans-[Pd(SPyridine)2(PTA)2] (14). The C–S bond
lengths of ca. 1.72 Å are also similar to those observed in
other tetrazole-thiolate complexes of Pd (7) but shorter than
in Pd complexes containing pyridine thiolate ligands (1.75
Å) (14).
The structures of complexes 3a, 3b, and 3d were deter-
mined by X-ray crystallography, and in addition, 1H and
31P{1H} NMR spectra were recorded. Since we were at this
stage not interested in isolating bulk samples of the materi-
als, only NMR scale experiments were performed, and thus
no other analytical techniques were used to characterize the
compounds. In the case of the Me derivative (3c), the crys-
tals were of poor quality so only 1H and 31P{1H} NMR
spectra are available for this compound. The 31P{1H} NMR
spectra of complexes 3a–3d consist of a singlet resonance at
ca. –56 ppm, which is shifted by ca. 27 ppm from that of the
azido precursor. These chemical shifts are very similar to
those observed in other Pd PTA complexes containing
thiolate ligands (14). The 1H NMR spectra of complexes 3a–
3d show, in addition to the signals from the tetrazole sub-
stituents, a singlet and an AB-quartet because of the PCH2N
and NCH2N protons of the PTA ligands, respectively. The
proposed structures of the complexes were confirmed by X-
It was also attempted to prepare analogous complexes us-
ing the Pt precursor [Pt(N3)2(PTA)2] 2. In this case, however,
the cycloaddition reaction was considerable slower (ca. 2–
3 days were required for all of complex 2 to be consumed),
compared with the Pd series. This difference in reaction rate
between Pd and Pt complexes has also been observed by
Kim et al. (7). Furthermore, it was only possible to obtain
crystalline material for the product derived from phenyl
isothiocyanate (4d) upon layering the sample with Et2O. The
spectroscopic data of complex 4d is essentially identical to
1
that of its Pd congener 3d. The JPt-P coupling constant of
© 2008 NRC Canada

148
Can. J. Chem. Vol. 87, 2009
Fig. 2. Molecular structure of complex 3b. Ellipsoids show 50%
probability levels. Hydrogen atoms have been omitted for clarity.
Selected bond distances (Å) and angles (°): Pd1–P1 2.2949(4),
Pd1–S1 2.3328(4), S1–C7 1.7213(14), C7–N5 1.3472(18), C7–
N4 1.3345(18), N4–N7 1.3672(18), N7–N6 1.2944(1); P1–Pd1–
S1 93.400(13), C7–S1–Pd1 104.14(5).
Fig. 4. Molecular structure of complex 4d·CH2Cl2. Ellipsoids
show 50% probability levels. Hydrogen atoms and the disordered
CH2Cl2 molecule have been omitted for clarity. Selected bond
distances (Å) and angles (°): Pt1–P1 2.2897(10), Pt1–
S1 2.3393(9), S1-C7 1.717(4), C7–N4 1.331(5), C7–N1 1.355(5),
N4–N3 1.364(5), N3–N2 1.282(5); P1–Pt1–S1 87.21(3), C7–S1–
Pt1 102.44(13).
Fig. 3. Molecular structure of complex 3d. Ellipsoids show 50%
probability levels. Hydrogen atoms have been omitted for clarity.
Selected bond distances (Å) and angles (°): Pd1–P1 2.3018(7),
Pd1–S1 2.3406(6), S1–C7 1.717(3), C7–N4 1.349(3), C7–
N7 1.324(3), N4–N5 1.365(3), N5–N6 1.292(3); P1–Pd1–
S1 90.98(2), C7–S1–Pd1 101.29(9).
The molecular structure of 4d is very similar to that of the
Pd derivative 3d: Pt shows square planar coordination geom-
etry with a trans arrangement of pairs of identical ligands.
Bond lengths and angles in 4d are also typical for complexes
of this kind.
In conclusion, we have shown that the reaction of various
isothiocyanates with a PTA-stabilized Pd azido complex
gives trans Pd complexes containing anionic, S-coordinated
tetrazole-thiolate ligands. This coordination mode of the
cycloaddition product was confirmed by crystallographic
studies. In the case of platinum, the same reaction occurs,
but the rate of the reaction is considerably slower. Further
work is currently in progress to develop a suitable prepara-
tion method for larger quantities of these complexes and to
study their biological activity.
Experimental
PTA (1,3,5-triaza–7-phosphaadamantane), cis-[Pt(N3)2(cod)]
(cod = 1,5-cyclooctadiene), and cis-[Pd(N3)2(tmeda)] (tmeda =
N,N,N′,N′-tetramethylethylenediamine) were prepared fol-
lowing published procedures (16, 17). All solvents and
chemicals were sourced commercially and used as received.
1H, 13C, and 31P{1H} NMR spectra were recorded on a
Bruker Avance III 500 MHz instrument using residual sol-
vent signals as reference. Mass spectra (ES-MS positive ion
mode) were measured on a Bruker Esquire 3000 spectrome-
ter and IR spectra on a Bruker FT-IR instrument as KBr
disks. Elemental analyses were carried out by staff of the
microanalytical laboratory of the Institute of Inorganic
Chemistry at the University of Vienna.
2458 Hz observed in the 31P{1H} NMR spectrum of 4d is
consistent with a trans configuration, similar to what has
been reported for other trans Pt complexes containing PTA
and thiolate ligands (15). This trans geometry was confirmed
by X-ray crystallography; the molecular structure of
4d·CH2Cl2 is shown in Fig. 4.
© 2008 NRC Canada

Fleischer et al.
149
[Pd(N3)2(PTA)2] (1)
trans-[Pd{SCN4(Me)}2(PTA)2] (3c)
1
To a CH2Cl2 solution of cis-[Pd(N3)(tmeda)] (0.300 g,
1.142 mmol) was added a solution of PTA (0.359 g, 2.284
mmol) in CH2Cl2 (15 mL). After stirring the mixture for 2 h,
the yellow solid was isolated by filtration, washed with
Et2O, and dried. Yield: 0.496 g, 86%. IR (KBr disk, cm–1) ν
Yellow crystals. H NMR (500 MHz, CDCl3, 25 °C, ppm)
δ: 4.33–4.49 (m, 12 H, NCH2N), 4.16 (s, 12 H, PCH2P),
4.00 (s, 6 H, Me). 31P{1H} NMR (202 MHz, CDCl3, 25 °C,
ppm) δ: –56.25.
1
trans-[Pd{SCN4(Ph)}2(PTA)2] (3d)
(N3): 2040, 2019. H NMR (500 MHz, DMSO-d6, 25 °C,
ppm) δ: 4.47 (AB quart, J = 12.6 Hz, 12 H, NCH2N), 4.35
(s, 12 H, PCH2P). 13C{1H} NMR (126 MHz, DMSO-d6,
25 °C, ppm) δ: 51.30 (br s, PCH2N), 71.64 (s, NCH2N).
31P{1H} NMR (202 MHz, DMSO-d6, 25 °C, ppm) δ: –29.90.
ES-MS m/z: 527 [M + Na]+. Calcd. for C12H24N12P2Pd (504.77):
C 28.55, H 4.79, N 33.30; found C 28.72, H 4.81, N 33.06.
Orange crystals. 1H NMR (500 MHz, CDCl3, 25 °C, ppm)
δ: 7.87 (d, J = 7.6 Hz, 4 H, o-Ph), 7.60 (t, J = 7.6 Hz, 4 H,
m-Ph), 7.54 (t, J = 7.3 Hz, 2 H, p-Ph), 4.36 (AB quart, J =
13.2 Hz, 12 H, NCH2N), 4.16 (s, 12 H, PCH2P). 31P{1H}
NMR (202 MHz, CDCl3, 25 °C, ppm) δ: –55.61.
trans-[Pt{SCN4(Ph)}2(PTA)2] (4d)
1
Colourless crystals. H NMR (500 MHz, CDCl3, 25 °C,
[Pt(N3)2(PTA)2] (2)
ppm) δ: 7.84 (d, J = 7.6 Hz, 4 H, o-Ph), 7.62 (t, J = 6.9 Hz,
4 H, m-Ph), 7.56 (t, J = 7.3 Hz, 2 H, p-Ph), 4.37 (AB quart,
J = 13.2 Hz, 12 H, NCH2N), 4.17 (s, 12 H, PCH2P). 31P{1H}
To a suspension of cis-[Pt(N3)2(cod)] (0.100 g, 0.258
mmol) in CH2Cl2 was added PTA (0.081 g, 0.516 mmol).
After stirring for ca. 2 h, the colourless solid was isolated by
filtration, washed with Et2O, and dried to give 0.129 g
(84%) of the complex. IR (KBr disk, cm–1) ν(N3): 2052,
NMR (202 MHz, CDCl3, 25 °C, ppm) δ: –63.80 (JP-Pt
=
2458 Hz).
1
2036. H NMR (400 MHz, DMSO-d6, 25 °C, ppm) δ: 4.46
X-ray crystal structure determinations3
(AB quart, J = 12.6 Hz, 12 H, NCH2N), 4.25 (s, 12 H,
PCH2P). 31P {1H} NMR (162 MHz, DMSO-d6, 25 °C, ppm)
δ: –59.09 (JPt-P = 3140 Hz). ES MS m/z: 616 [M + Na]+.
Calcd. for C12H24N2P2Pt (593.42): C 24.29, H 4.08, N
28.32; found C 24.50, H 4.03, N 28.39.
X-ray diffraction quality crystals of compounds 3a, 3b,
3d, and 4d·CH2Cl2 were mounted in a cryoloop with a drop
of oil and placed into the cold stream (100 K) of a Bruker
X8 APEX II CCD diffractometer with graphite-
monochromated Mo Kα radiation (λ = 0.710 73 Å), con-
trolled by a Pentium-based PC running the SAINT software
package (18). Single crystals were positioned at 40 mm from
the detector and 1843, 2075, 1599, and 4656 frames were
measured, each for 70, 20, 70, and 5 s over 1° scan width for
3a, 3b, 3d, and 4d·CH2Cl2, correspondingly. Crystal data,
data collection parameters, and structure refinement details
for 3a, 3b, 3d, and 4d·CH2Cl2 are given in Table 1. The
structures were solved by direct methods and refined on F2
by full-matrix least-squares techniques using the SHELXTL
software package (19, 20); scattering factors were taken
from the literature (21). The co-crystallized CH2Cl2 mole-
cule in 4d·CH2Cl2 was found disordered over two positions
with site occupation factors 0.61:0.39. The disorder was
solved by using SADI and EADP restraints. All non-
hydrogen atoms were refined with anisotropic displacement
parameters. Hydrogen atoms were placed at calculated posi-
tions or localized on difference Fourier maps and
isotropically refined. Calculated hydrogen atoms have as-
signed thermal parameters equal to either 1.5 (methyl hydro-
gen atoms) or 1.2 (non-methyl hydrogen atoms) times the
thermal parameters of the atom to which they were attached.
The graphics were prepared by using ORTEP (22).
Preparation of the cycloaddition products
To a suspension of [M(N3)2(PTA)2] (M = Pd, Pt) (25 mg)
in CH2Cl2 (5 mL) was added an excess (ca. 0.2 mL) of
RNCS (R = Et, allyl, Me, Ph). The mixture was left to stir
for ca. 18 h at room temperature during which all solid had
dissolved. Et2O was carefully layered onto the solution and
after standing for 2–4 days, crystals could be harvested.
NMR data was obtained by re-dissolving the crystals in a
suitable deuterated solvent. In case of the Pt derivative, the
reaction required much longer time (assessed by the time
taken for 2 to completely dissolve), and crystals were only
obtained when using phenyl isothiocyanate. Using this pro-
cedure the following compounds were prepared.
trans-[Pd{SCN4(Et)}2(PTA)2] (3a)
Orange crystals. 1H NMR (500 MHz, CDCl3, 25 °C, ppm)
δ: 4.34–4.43 (m, 18 H, NCH2N, CH3CH2N), 4.15 (s, 12 H,
PCH2P), 1.58 (t, J = 7.3 Hz, 6 H, CH3CH2N). 31P{1H} NMR
(202 MHz, CDCl3, 25 °C, ppm) δ: –56.12.
trans-[Pd{SCN4(CH2CHCH2)}2(PTA)2] (3b)
Orange crystals. 1H NMR (500 MHz, CDCl3, 25 °C, ppm)
δ: 5.98–6.09 (m, 2 H, NCH2CH=CH2) 5.39 (d, J = 10.1 Hz,
2 H, NCH2CH=CH2), 5.32 (d, J = 17.0 Hz, 2 H,
NCH2CH=CH2), 4.96 (d, J = 5.9 Hz, 4 H, NCH2CH=CH2),
4.38 (AB quart, J = 12.6 Hz, 12 H, NCH2N), 4.14 (s, 12 H,
PCH2P). 31P{1H} NMR (202 MHz, CDCl3, 25 °C, ppm) δ:
–55.84.
Acknowledgements
FM thanks the University of Vienna and Bernhard
Keppler for a visiting professorship. To Bernhard and all the
members of his research group many thanks for access to all
3 Supplementary data for this article are available on the journal Web site (canjchem.nrc.ca) or may be purchased from the Depository of Un-
published Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 3806. For more in-
formation on obtaining material refer to cisti-icist.nrc-cnrc.gc.ca/cms/unpub_e.shtml. CCDC 688299–688302 contain the crystallographic
data for this manuscript. These data can be obtained, free of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (Or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2008 NRC Canada

150
Can. J. Chem. Vol. 87, 2009
Table 1. Crystallographic and refinement details of complexes 3a, 3b, 3d, and 4d·CH2Cl2.
Compound
Formula
3a
3b
3d
4d·CH2Cl2
C18H34N14P2PdS2
C20H34N14P2PdS2
C26H34N14P2PdS2
C28H38Cl4N14P2PtS2
FW
679.05
Triclinic
P-1
703.07
Triclinic
P-1
775.13
Monoclinic
P21/n
1033.67
Monoclinic
P21/c
Crystal system
Space group
a (Å)
b (Å)
c (Å)
6.354 10(10)
10.549 5(3)
10.937 8(3)
106.484(2)
92.9180(10)
106.8810(10)
665.62(3)
1
6.253 40(10)
9.779 7(2)
12.424 9(3)
99.106(2)
101.1290(10)
103.4310(10)
708.57(3)
1
9.316 2(3)
11.729 2(6)
21.741 0(10)
90
92.048(3)
90
1609.63(13)
2
1.599
10.899 8(9)
18.024 0(13)
9.837 1(8)
90
100.500(5)
90
1900.2(3)
2
1.807
α (°)
β (°)
γ (°)
V (Å3)
Z
Dcalcd (g cm–3)
1.694
1.648
µ (mm–1)
F(000)
1.014
348
0.955
360
0.850
792
4.212
1024
Reflections
Unique Reflections (Rint)
22 043
3887 (0.0363)
26 570
4154 (0.0385)
48 582
4716 (0.0980)
134 597
4369 (0.0539)
Parameters
169
178
205
239
θ range (°)
2.40–30.08
0.0211
0.0587
2.48–30.05
0.0218
0.0515
2.56–30.09
0.0394
0.0920
2.21–27.50
0.0309
0.0782
R1 (I > 2σ(I))a
wR2 (all data)b
GOFc
1.009
0.509, –0.388
1.055
0.699, –0.406
0.984
0.821, –1.166
1.080
1.612, –1.667
Largest diff. peak, hole (e Å–3)
aR1 = Σ||Fo| – |Fc|| / Σ|Fo|.
bwR2 = {Σ[w (Fo2 – Fc2)2] / Σ[w(Fo2)2 ]}1/2.
cGOF = {Σ[w(Fo2 – Fc2)2] / (n – p)}1/2, where n is the number of reflections and p is the total number of parameters refined.
11. F. Mohr, E. Cerrada, and M. Laguna. Organometallics, 25, 644
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12. F. Mohr, S. Sanz, E. Vergara, E. Cerrada, and M. Laguna. Gold
the facilities and for making my stay in Vienna so enjoyable
and productive.
Bull. 36, 212 (2006).
13. F. Mohr, S. Sanz, E.R.T. Tiekink, and M. Laguna.
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