Reactivity of platinum(II) triphenylphosphino complexes with nitrogen donor divergent ligands

Article abstract of DOI:10.1016/j.poly.2016.09.016

Dinuclear platinum(II) complexes [{PtCl₂(PPh₃)}₂(μ-N–N)], where N–N is a divergent bidentate nitrogen ligand, were prepared by reacting cis-[PtCl₂(PPh₃)(NCMe)] with N–N in a Pt/N–N molar ratio 2. The (trans,trans)-isomers were obtained as kinetic products and recovered in good yields and high purity {1, N–N?=?pyrazine (pyrz); 2, N–N?=?4,4′-bipyridyl (bipy); 3, N–N?=?piperazine (pipz); 4, N–N?=?p-xylylendiamine (xylN₂)}. Cis-[PtCl₂(PPh₃)(NCMe)] was also reacted with the tridentate divergent ligand 2,4,6-tris-(pyrid-4′-yl)1,3,5-triazine (py3TRIA) in molar ratio 3 with formation of the trinuclear (trans,trans,trans)-[{PtCl₂(PPh₃)}₃(μ-py3TRIA)], 5. On the other hand, the treatment of cis-[PtCl₂(PPh₃)(NCMe)] with the monodentate pyridine (py) produced a mixture of both trans-[PtCl₂(PPh₃)(py)] (6a) and cis-[PtCl₂(PPh₃)(py)] (6b). The reactions of cis-[PtCl₂(PPh₃)(NCMe)] with N–N?=?pyrz, bipy, pipz, carried out with a Pt/N–N molar ratio 1, were monitored by³¹P NMR spectroscopy. Equilibria were observed in solution, involving dinuclear (trans–trans)-[{PtCl₂(PPh₃)}₂(μ-N–N)], mononuclear [PtCl₂(PPh₃)(N–N)] and free N–N. The addition of an excess of the divergent ligand allowed the complete conversion to the corresponding mononuclear complexes. With the heteroaromatic ligands both geometric isomers were observed (7a, 7b and 8a, 8b, for pyrz and bipy derivatives, respectively) while with pipz the trans-isomer only was detected, 9. In the system involving bipy, the scarcely soluble dinuclear (cis,cis)-[{PtCl₂(PPh₃)}₂(μ-bipy)], 2b, was also obtained. Products 2, 2b, 3·2(CHCl₃) and 6a·0.5(C₂H₄?Cl₂) were structurally characterized by single crystal X-ray diffraction methods.

Full text of DOI:10.1016/j.poly.2016.09.016

Polyhedron 119 (2016) 403–411
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Reactivity of platinum(II) triphenylphosphino complexes with nitrogen
donor divergent ligands
⇑
Daniela Belli Dell’ Amico, Luca Bellucci, Luca Labella, Fabio Marchetti, Simona Samaritani
Dipartimento di Chimica e Chimica Industriale, Università di Pisa, via Giuseppe Moruzzi 13, Pisa I-56124, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 June 2016
Accepted 7 September 2016
Available online 15 September 2016
Dinuclear platinum(II) complexes [{PtCl2(PPh3)}2(l-N–N)], where N–N is a divergent bidentate nitrogen
ligand, were prepared by reacting cis-[PtCl2(PPh3)(NCMe)] with N–N in a Pt/N–N molar ratio 2. The
(trans,trans)-isomers were obtained as kinetic products and recovered in good yields and high
purity {1, N–N = pyrazine (pyrz); 2, N–N = 4,40-bipyridyl (bipy); 3, N–N = piperazine (pipz); 4, N–N =
p-xylylendiamine (xylN2)}. Cis-[PtCl2(PPh3)(NCMe)] was also reacted with the tridentate divergent ligand
2,4,6-tris-(pyrid-40-yl)1,3,5-triazine (py3TRIA) in molar ratio 3 with formation of the trinuclear (trans,
Keywords:
Platinum(II)
Triphenylphosphine
Dinuclear complexes
Divergent ligands
Cis–trans isomerism
trans,trans)-[{PtCl2(PPh3)}3(l-py3TRIA)], 5. On the other hand, the treatment of cis-[PtCl2(PPh3)(NCMe)]
with the monodentate pyridine (py) produced a mixture of both trans-[PtCl2(PPh3)(py)] (6a) and
cis-[PtCl2(PPh3)(py)] (6b). The reactions of cis-[PtCl2(PPh3)(NCMe)] with N–N = pyrz, bipy, pipz, carried
out with a Pt/N–N molar ratio 1, were monitored by 31P NMR spectroscopy. Equilibria were observed
in solution, involving dinuclear (trans–trans)-[{PtCl2(PPh3)}2(l-N–N)], mononuclear [PtCl2(PPh3)(N–N)]
and free N–N. The addition of an excess of the divergent ligand allowed the complete conversion to
the corresponding mononuclear complexes. With the heteroaromatic ligands both geometric isomers
were observed (7a, 7b and 8a, 8b, for pyrz and bipy derivatives, respectively) while with pipz the
trans-isomer only was detected, 9. In the system involving bipy, the scarcely soluble dinuclear
(cis,cis)-[{PtCl2(PPh3)}2(
were structurally characterized by single crystal X-ray diffraction methods.
Ó 2016 Elsevier Ltd. All rights reserved.
l
-bipy)], 2b, was also obtained. Products 2, 2b, 3ꢀ2(CHCl3) and 6aꢀ0.5(C2H4 Cl2)
1. Introduction
tridentate 2,4,6-tris-(pyrid-40-yl)1,3,5-triazine) (py3TRIA) [8] was
studied. The use of a precursor with a single available coordination
site on platinum, due to the facile nitrile substitution, prevents the
formation of derivatives with a nuclearity higher than the denticity
of the divergent ligand. Moreover, the presence of the phosphorous
donor ligand in the platinum coordination sphere influences the
stereochemistry of the processes; in addition it allows the tracking
of the reactions via 31P NMR spectroscopy providing useful pieces
of information also in the presence of equilibria involving several
species. The outcome of the reactions in dependence on the molar
ratio between reagents is here reported and discussed, as well as
the stereochemistry of the products.
Divergent ligands are molecules containing at least two func-
tional groups able to coordinate metal ions in a non-chelating fash-
ion to afford oligo- or polynuclear architectures. In the field of
platinum complexes, N-donor divergent bidentate ligands consti-
tute important building blocks in the synthesis of polynuclear 2D
and 3D supramolecular derivatives [1] with potential applications
in the fields of luminescent materials [2] and medicinal chemistry
[3]. While ionic supramolecular coordination compounds of plat-
inum (mainly tri- and tetranuclear) originate from well-studied
self-assembly procedures [4,5], much less is known about neutral
dinuclear complexes [6]. Thus, with the aim to prepare dinuclear
species and in the context of our studies concerning the synthesis
of platinum(II) complexes containing the PPh3 ligand [7], the reac-
tivity of cis-[PtCl2(PPh3)(NCMe)] [7e] towards N–N divergent
bidentate nitrogen donor ligands (pyrz, bipy, pipz and xylN2) has
been investigated. In addition, the reactivity towards the
2. Experimental
2.1. Materials and general methods
All manipulations were performed under
a
dinitrogen
atmosphere, if not otherwise stated. Solvents and liquid reagents
were dried according to reported procedures [9]. 1H, 13C, 31P and
195Pt NMR spectra were recorded with a Bruker ‘‘Avance DRX400”
⇑
Corresponding author.
E-mail address: simona.samaritani@unipi.it (S. Samaritani).
http://dx.doi.org/10.1016/j.poly.2016.09.016
0277-5387/Ó 2016 Elsevier Ltd. All rights reserved.

404
D. Belli Dell’ Amico et al. / Polyhedron 119 (2016) 403–411
spectrometer, in CDCl3 solution if not otherwise stated. Chemical
shifts were measured in ppm (d) from TMS by residual solvent
peaks for 1H and 13C, from aqueous (D2O) H3PO4 (85%) for 31P
and from aqueous (D2O) hexachloroplatinic acid for 195Pt. A sealed
capillary containing C6D6 was introduced in the NMR tube to lock
the spectrometer to the deuterium signal when non-deuterated
solvents were used. FTIR spectra in solid phase were recorded with
a Perkin–Elmer ‘‘Spectrum One” spectrometer, equipped with an
ATR accessory. Elemental analyses (C, H, N) were performed at
Dipartimento di Scienze e Tecnologie Chimiche, Università di
diffusion of pentane vapors. A single crystal was selected for
X-ray diffraction analysis, which confirmed trans,trans geometry.
2.2.4. (Trans,trans)-[{PtCl2(PPh3)}2(l-xylN2)], 4
37% yield. Anal. Calc. for C44H42Cl4N2P2Pt2: C, 44.3; H, 3.6; N,
2.4%. Found: C, 44.1; H, 3.4; N, 2.4%. IR (ATR, cmꢂ1): 3207; 3056;
1568; 1098; 990; 743; 691; 1H NMR: 7.73 (m, 10H, Harom), 7.45
(m, 24H, Harom), 4.25 (m, 4H), 3.60 (m, 4H); 13C NMR: 138.2,
134.8 (JC–P = 10.0 Hz), 131.0 (JC–P = 2.0 Hz), 129.2, 128.5
(1JC–P = 63.0 Hz), 128.0 (JC–P = 11.0 Hz), 48.1; 31P NMR: 3.87
(1JP–Pt = 3646 Hz); 195Pt NMR: ꢂ3606 (1JPt–P = 3646 Hz);
Udine. Cis-[PtCl2(PPh3)(NCMe)], [7e] trans-[Pt2(l-Cl)2Cl2(PPh3)2]
[7e] and 2,4,6-tris-(pyrid-40-yl)-1,3,5-triazine [8] were prepared
according to a reported procedure. In the text the following
abbreviations were used: 4,40-bipyridyl (bipy); pyrazine (pyrz);
piperazine (pipz); p-xylylendiamine (xylN2); pyridine (py);
2.3. Preparation of mononuclear derivatives
2.3.1. Synthesis of trans- + cis-[PtCl2(PPh3)(Py)] (6a + 6b)
2,4,6-tris-(pyrid-40-yl)-1,3,5-triazine
oethane (1,2-DCE).
(py3TRIA);
1,2-dichlor-
A suspension of cis-[PtCl2(PPh3)(NCMe)] (0.254 g, 0.445 mmol)
in 15.0 mL of 1,2-DCE was treated, under stirring, with pyridine
(Py/Pt molar ratio = 1.1). The reaction was monitored by 31P NMR
spectroscopy. The mixture was refluxed until the precursor signal
disappeared, substituted by two new signals (2 h), then it was
cooled. A fine yellow precipitate was filtered, washed with cold
heptane and dried under vacuum (10ꢂ2 mmHg). 64% yield. Anal.
Calc. for C23H20Cl2NPPtꢀ1/2 C2H4Cl2: C, 43.9; H, 3.4; N, 2.1%. Found:
C, 43.7; H, 3.8; N, 2.0%. IR (ATR, cmꢂ1): 3064; 1481; 1096; 996;
752; 690; 1H NMR (solvent, the two trans and cis isomers, 6a and
6b, in approximately 1:1 molar ratio, were observed): 9.03 (m,
2.2. General procedure for the synthesis of dinuclear species (trans,
trans)-[{PtCl2(PPh3)}2( -N–N)]
l
A
suspension of cis-[PtCl2(PPh3)(NCMe)] (ꢁ1.0 mmol) in
1,2-DCE (5.0–10.0 mL) was treated with a solution of the divergent
ligand N–N in the minimal amount of the same solvent
(Pt/N–N molar ratio = 2.0). The resulting yellow solution was
refluxed under stirring until the complete conversion was obtained
3
3
31P NMR). A yellow, fine solid separated out of the solution on
2H, JH–Pt = 32 Hz, NCH, trans isomer), 8.45 (m, 2H, JH–Pt = 40 Hz,
NCH cis isomer), 7.83 (m, 8H), 7.69 (m, 6H), 7.45 (m, 14H), 7.33
(m, 6H), 6.93 (m, 2H); 13C NMR (trans and cis isomers): 153.4,
151.4, 138.5, 137.4, 134.7 (JC–P = 10.0 Hz), 134.6 (JC–P = 10.0 Hz),
131.2, 130.9, 128.5 (1JC–P = 55.0 Hz, 2C), 128.3 (JC–P = 11.0 Hz),
128.1 (JC–P = 11.0 Hz), 125.9, 125.1; 31P NMR (trans and cis iso-
mers): 7.24 (1JP–Pt = 3904 Hz, cis isomer); 2.59 (1JP–Pt = 3581 Hz,
trans isomer); 195Pt NMR (trans and cis isomers): ꢂ3379
(1JPt–P = 3904 Hz, cis isomer); ꢂ3540 (1JPt–P = 3581 Hz, trans iso-
mer); A sample of solid was dissolved in CHCl3 and crystallized
by slow diffusion of pentane vapors. Some single crystals were
selected for X-ray diffraction analysis, which revealed the trans
stereochemistry of the complex. 31P NMR (crystals in CDCl3, freshly
prepared solution): 2.59 (1JP–Pt = 3581 Hz).
(
cooling to room temperature (25 °C) or after heptane addition
(10.0–15.0 mL). The solid was filtered, washed with two portions
of heptane and dried under vacuum (10ꢂ2 mmHg). For each dinu-
clear complex the isolated product% yield, the elemental analysis
and the spectroscopic (IR and NMR) characterization are reported
below.
2.2.1. (Trans,trans)-[{PtCl2(PPh3)}2(l-pyrz)], 1
73% yield. Anal. Calc. for C40H34Cl4N2P2Pt2: C 42.3, H 3.0, N 2.5%.
Found: C, 42.0; H, 2.8; N, 2.4%. IR (ATR, cmꢂ1): 3107, 1484, 1435,
1422, 1167, 1098, 879, 744, 690; 1H NMR: 9.33 (m, 4H, NCH),
7.79 (m, 12H, Harom phosphine), 7.48 (m, 18H, Harom phosphine);
13C NMR: 147.1, 134.9 (JC–P = 10.0 Hz), 131.2, 128.2, 128.3
(1JC–P = 63.0 Hz), 128.2 (JC–P = 11.0 Hz); 31P NMR: 2.80
(1JP–Pt = 3725 Hz); 195Pt NMR: ꢂ3561 (1JPt–P = 3725 Hz).
2.3.2. Synthesis of trans- + cis-[PtCl2(PPh3)(pyrz)] (7a + 7b)
Method a.
A
suspension of 0.139 g (0.244 mmol) of
cis-[PtCl2(PPh3)(NCMe)] in 15.0 mL of 1,2-DCE was treated with a
large excess of pyrazine (pyrz/Pt molar ratio = 10) and refluxed
(3 h). A yellow solution was initially obtained and, upon cooling,
a colorless powder formed, which was filtered, washed with hep-
tane, dried and characterized (7b, isomer cis, 0.0129 g, 14% yield).
The filtrate was treated under vacuum (10ꢂ2 mmHg) up to dryness.
The solid residue was washed with several portions of diethyl
ether to remove the pyrazine excess. The light yellow powder
was dried under vacuum (trans + cis isomers, 7a + 7b; 0.0178 g,
21% yield). Anal. Calc. for C22H19Cl2N2PPt: C, 43.4; H, 3.2; N, 4.6%.
Found: C, 43.6; H, 3.0, N, 4.6%. IR (ATR, cmꢂ1): 3053; 1482; 1417;
1098; 996; 804; 746; 692; 1H NMR (isomer cis): 8.40 (dd, 2H,
2.2.2. (Trans,trans)-[{PtCl2(PPh3)}2(l-bipy)], 2
60% yield. Anal. Calc. for C46H38Cl4N2P2Pt2: C, 45.6; H, 3.2; N,
2.3%. Found: C, 45.3; H, 3.0; N, 2.3%. IR (ATR, cmꢂ1): 3052; 1610;
1481; 1220; 1095; 812; 743; 690; 1H NMR: 9.22 (m, 4H, NCH),
7.83 (m, 12H, Harom phosphine), 7.68 (m, 4H, NCHCH), 7.47 (m,
18H, Harom phosphine); 13C NMR: 152.2, 146.3, 134.9
(JC–P = 10.3 Hz), 131.0, 128.5 (1JC–P = 65.3 Hz), 128.0 (JC–P
=
11.3 Hz), 122.8; 31P NMR: 2.64 (1JP–Pt = 3611 Hz); 195Pt NMR:
ꢂ3538 (1JPt–P = 3611 Hz). A sample of solid was dissolved in CHCl3
and crystallized by slow diffusion of pentane vapors. A single crys-
tal was selected for X-ray diffraction analysis, which confirmed the
(trans,trans) stereochemistry.
5
3
3JH–H = 4.4 Hz, JH–H = 1.3 Hz, JH–Pt = 41 Hz, PtNCH), 8.18 (dd, 2H,
5
3JH–H = 4.4 Hz, JH–H = 1.3 Hz, PtNCHCH), 7.69 (m, 6H, Harom
2.2.3. (Trans,trans)-[{PtCl2(PPh3)}2(
l
-pipz)], 3
phosphine), 7.48 (m, 3H, Harom phosphine), 7.37 (m, 6H, Harom
91% yield. Anal. Calc. for C40H40Cl4N2P2Pt2: C, 42.0; H, 3.5; N,
2.5%. Found: C, 41.8; H, 3.3; N, 2.6%. IR (ATR, cmꢂ1): 3227; 3190;
3055; 1482; 1098; 880; 745; 690; 1H NMR: 7.69 (m, 12H, Harom),
phosphine); 1H NMR (isomer trans, selected signals from 1H NMR
3
of the mixture): 9.09 (m, 2H, JH–Pt = 21 Hz, PtNCH), 8.79 (m, 2H,
PtNCHCH), 7.81 (m, 6H, Harom phosphine), 7.50 (m, 9H, Harom
phosphine). 31P NMR (isomer cis): 7.13 (1JP–Pt = 3808 Hz); 31P
NMR (isomer trans, selected signal from 31P NMR of the mixture):
2.68 (1JP–Pt = 3661 Hz).
A solution of 7b in CDCl3 was monitored through 1H NMR spec-
troscopy. Formation of 7a, 1 and free pyrazine was observed. The
2
7.43 (m, 18H, Harom), 3.96 (bs, JH–Pt = 68.5 Hz, 2H, NH), 3.58 (m,
4H, CHH), 3.36 (m, 4H, CHH). 13C NMR: 134.8 (JC–P = 10.0 Hz),
131.0, 128.3 (1JC–P = 63.0 Hz), 128.0 (JC–P = 11.0 Hz), 48.7; 31P
NMR: 3.56 (1JP–Pt = 3603 Hz); 195Pt NMR: ꢂ3606 (1JPt–P = 3603 Hz).
A sample of solid was dissolved in CHCl3 and crystallized by slow

D. Belli Dell’ Amico et al. / Polyhedron 119 (2016) 403–411
405
Table 1
Crystal data and structure refinements for compounds 2–3.a
Compound
2
2b
3ꢀ2(CHCl3)
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
46H38Cl4N2P2Pt2
C46H38Cl4N2P2Pt2
C42H42Cl10N2P2Pt2
1381.39
monoclinic
C2/c (No. 15)
25.1921(5)
16.3487(3)
14.0157(3)
–
1212.70
monoclinic
P21/c (No. 14)
10.0774(19)
9.5758(18)
28.126(5)
–
1212.70
orthorhombic
Pbca (No. 61)
10.8826(4)
15.5332(5)
24.8585(9)
–
b (Å)
c (Å)
a
(°)
b (°)
99.639(8)
–
2675.8(9)
2
1.505
5.510
–
–
103.0420(10)
–
5623.6(2)
4
1.632
5.539
c
(°)
U (Å3)
4202.1(3)
4
1.917
Z
Dcalc (mg mꢂ3
)
l
(mmꢂ1
)
7.018
hmax (°)
23.81
25.79
30.45
No. measured
No. unique [Rint
No. parameters
17,030
4081 [0.0404]
255
0.0294, 0.0650
0.0440, 0.0688
0.879
13,715
3928 [0.0597]
253
0.0408, 0.0808
0.0870, 0.0941
0.976
28,828
8269 [0.0354]
281
0.0478, 0.1362
0.0863, 0.1593
0.794
]
R1, wR2 [I > 2
r
(I)]a
R1, wR2 [all data]a
Goodness of fit on F2
b
a
Crystal data and structure refinements for complex 6a are reported in Table 5SI.
R(Fo) =
R
jjFoj ꢂ jFcjj/
R
jFoj; Rw(F2o) = [
R
[w(F2o ꢂ F2c)2]/
R
[w(F2o)2] ; w = 1/[
r
2(Fo2) + (AQ)2 + BQ] where Q = [MAX(Fo2,0) + 2F2c]/3; GOF = [
R
[w(F2o–F2c)2]/(N–P)] , where N, P are the
b
½
½
numbers of observations and parameters, respectively.
equilibrium composition was reached after about 48 h. The relative
concentrations of the species involved in the equilibrium were
obtained by the integrals of the signals at 9.09 and 8.79 ppm for
7a, 8.40 and 8.18 ppm for 7b, 9.33 ppm for 1, 8.62 ppm for free
pyrz.
pipz/3 molar ratios 0.5 and 2, respectively. After each addition
the system was monitored by 1H and 31P NMR (Table 4SI).
2.4. X-ray structure determinations
Method b. A suspension of 0.201 g (0.177 mmol) of 1 in 1,2-DCE
(9.0 mL) was treated with 0.0400 g of pyrazine (0.500 mmol, pyrz/
Pt molar ratio = 1.42) under stirring at room temperature and
turned quickly to a yellow-green solution. A sample of the solution
was analyzed after 30 min (31P NMR) and showed two signals:
2.78 ppm (65%, JP–Pt = 3685 Hz), 6.36 ppm (35%, JP–Pt = 3790 Hz).
After 30 min the mixture was concentrated under vacuum until a
pale yellow solid formed. After two days the solid was filtered,
washed with heptane (2 ꢃ 2.0 mL) and dried under vacuum (63%
yield). 1H and 31P NMR, carried out in CDCl3 solution showed the
presence of isomer cis (66%) and isomer trans (34%, cfr. characteri-
zation described for method a).
The X-ray diffraction experiments were carried out at room
temperature by means of a Bruker Smart Breeze CCD diffractome-
ter operating with graphite-monochromated Mo Ka radiation. The
samples were sealed in glass capillaries and their lattice parame-
ters were evaluated as a preliminary step to the crystallographic
study (Table 1). On the basis of these results the intensity data col-
lections were done up to the limits mentioned in the table. The low
limit adopted in the collection of intensities of 2ꢀis mainly due to
the disorder which sharply cuts down the diffraction intensities
at high h values. The intensities were corrected for Lorentz and
polarization effects and for absorption by means of a multi-scan
method [10]. The structure solutions were obtained by the auto-
matic direct methods contained in SHELX97 program [11]. After
the completion of the main molecule model, the difference Fourier
maps of 2, 3 and 6a showed clusters of broad maxima placed
within cavities still present in the crystal structure. These were
regarded as the crystallization solvent molecules affected by differ-
ent degrees of disorder. In the crystal structure of 3 a cluster of
maxima was attributed to a disordered chloroform molecule, while
in the structure of 6a the cluster was recognized as a 1,2-dichlor-
oethane placed on an inversion centre. The residual maxima in
the difference Fourier maps of the structures of 2 and 3, are prob-
ably due to a heavily disordered solvent molecule, most likely n–
heptane, but cannot be fitted with any reasonable conformer of
this species. So the intensity data for those two structures were
treated with the SQUEEZE [12] procedure in order to remove the con-
tribution of the disordered solvent still missing from the model.
After the introduction of hydrogen atoms in calculated positions
all the heavy atoms of the main molecules were refined with ani-
sotropic displacement parameters up to the reliability factors
listed in Table 1. The presence of disorder limits the accuracy of
some of these refinements but still lets discuss with a sufficient
degree of reliability the connectivity and conformation of the main
molecules.
1
1
2.3.3. Treatment of 2 with bipy with formation of trans- + cis-
[PtCl2(PPh3)(bipy)] (8a + 8b)
To a solution of (trans,trans)-[{PtCl2(PPh3)}2(l-bipy)], 2, in
CD2Cl2 bipy was added in two portions corresponding to bipy/2
molar ratios 1 and 2, respectively. After each addition the system
was monitored by 1H-and 31P NMR spectroscopies (Table 3SI).
2.3.4. Isomerization of 2 to (cis,cis)-[{PtCl2(PPh3)}2(
l-bipy)], 2b
A sample of (trans,trans)-[{PtCl2(PPh3)}2( -bipy)] was dissolved
l
in chloroform in the presence of a slight amount of bipyridyl. After
two weeks, colorless crystals separated out of the solution. 1H NMR
(CDCl3): 8.55 (m, 4H, NCH); 7.72 (m, 12H, Harom phosphine); 7.49
(m, 6H, Harom phosphine); 7.38 (m, 12H, Harom phosphine); 7.00
(m, 4H, NCHCH). A single crystal was selected for X-ray diffraction
analysis, which confirmed the (cis,cis) stereochemistry.
2.3.5. Treatment of 3 with pipz with formation of trans-[PtCl2(PPh3)
(pipz)], 9
To a solution of (trans,trans)-[{PtCl2(PPh3)}2(l-pipz)], 3, in
CD2Cl2 piperazine was added in two portions corresponding to

406
D. Belli Dell’ Amico et al. / Polyhedron 119 (2016) 403–411
Cl
Cl
PPh
3
1,2-DCE
reflux
PPh
Ph P
Pt
Pt
N
N
2
Cl
Pt NCMe
Cl
+
3
N
N
3
Cl
Cl
1-4
4,4'-bipyridyl (bipy,trans,trans-2)
N
N
N
N
pyrazine (pyrz,1)
(X-ray diffraction)
H2
N
N
N
=
H
N
piperazine (pipz,trans,trans- 3)
p-xylylendiamine (pxylN2,4)
N H
(X-ray diffraction)
N H 2
Scheme 1. Synthesis of the dinuclear complexes 1–4.
Table 2
Cl
Cl
Pt
Cl
Cl
Cl
Observed 31P NMR signals in dinuclear complexes 1–4.
Ph P
Pt
N
N
PPh
3
Cl
Pt
N
N
Pt Cl
3
Product
N–N
d/ppm (1JP–Pt/Hz)
Cl
PPh
PPh
3
3
1
2
3
4
pyrz
bipy
pipz
pxylN2
2.79 (3728)
2.64 (3611)
3.56 (3603)
3.87 (3646)
trans,trans
cis,cis
Cl
Pt
Cl
Cl
Pt Cl
PPh
Ph P
3
N
N
3
In addition to the aforementioned software, other control calcu-
lations and preparation of publication material were performed
with the programs contained in the suite WINGX [13].
trans,cis
Fig. 1. Possible geometric isomers for [{PtCl2(PPh3)}2(
l-N–N)] complexes.
while the formation of other geometric isomers was not
observed. As for our cases, the prompt isomerisation of the
precursor, cis-[PtCl2(NCMe)(PPh3)] [7d,e], to the trans-complex
(T = 80 °C) is consistent with the formation of the trans,trans
dinuclear isomer as kinetic product, in view of the well-known
trans effect exerted by triphenylphosphine. Nevertheless,
geometrical isomerization of the product in solution (Fig. 1)
could not be excluded a priori. As a matter of fact, the presence
of a single signal with satellites in 31P NMR spectra of complexes
1–4 allowed to rule out the trans,cis geometry, but both trans,
trans and cis,cis isomers were compatible with the observed
pattern.
3. Results and discussion
3.1. Syntheses
The syntheses of the dinuclear complexes 1–4, [{PtCl2(PPh3)}2-
(l-N–N)], were carried out by reacting cis-[PtCl2(PPh3)(NCMe)]
[7e] with the nitrogen bidentate divergent N–N ligands in molar
ratio 2:1 (Scheme 1).
The reactions were carried out in refluxing 1,2-DCE for two rea-
sons: (a) under these conditions fast isomerisation of the precursor
to the trans form is observed; (b) at lower temperature attack to
the nitrile is possible in the case of the secondary and primary
amine [7b,d]. The processes were monitored by 31P NMR
spectroscopy and in all cases the signal attributable to the
platinum precursor (4.83 ppm, JP–Pt = 3570 Hz) disappeared in
about 3 h, while a new signal with satellites was observed
(Table 2).
A yellow, crystalline solid product separated out of each reac-
tion mixture or precipitated upon addition of heptane. Spectro-
scopic analyses were carried out on the isolated complexes. The
31P, 13C and 195Pt NMR (CDCl3) spectra were in agreement with
the presence of a single product. In the 1H NMR spectra the N–N
hydrogen atoms closest to the coordination centers showed down-
field shifted signals with respect to the free ligand (Table 1SI).
Moreover, in each case, the integration of the observed 1H NMR
signals matched with a 1:2 molar ratio between the coordinated
N–N and PPh3, in accordance with the dinuclear nature of the com-
plexes. Elemental analyses too were in good agreement with the
proposed formulas.
Single crystal X-ray diffraction studies established the square
planar coordination around platinum centers and the trans,trans
geometry for complexes 2 and 3 (See Section 3.2).
1
1
Since the observed 31P NMR chemical shifts and JP–Pt coupling
constants (Table 2) are similar for all dinuclear compounds 1–4, we
can assign them a common trans,trans geometry. The pure com-
plexes do not isomerize in CHCl3 solution, as checked by 31P NMR.
The synthetic procedure can be extended to higher nuclearity
complexes following the denticity of the divergent ligand. As an
example, the tridentate ligand py3TRIA [8] was reacted with
trans-[Pt(l-Cl)2Cl2(PPh3)2] in 1,2-DCE affording a product identi-
fied as (trans,trans,trans)-[{PtCl2(PPh3)}3(l-py3TRIA)], 5 (see exper-
imental details and discussion in SI).
Within this study the reaction of cis-[PtCl2(PPh3)(NCMe)] [7e]
with N–N in 1/1 molar ratio (Scheme 2) was tested. It is
expected the formation of mononuclear complexes, retaining one
dangling donor atom on the bidentate divergent ligand (Scheme 2).
Similar dinuclear complexes containing pyrazine-derived
ligands had been described in a previous study [6a] concerning
the reactivity of chloro-bridged dinuclear derivatives [Pt2(l-
Cl)2Cl2L2], (L = PEt3, PMe2Ph, PMePh2, ethylene). In the article, the
authors underline the importance of the molar ratio between the
reagents in directing the synthesis to dinuclear or mononuclear
derivatives. The dinuclear products showed trans,trans geometry,
Cl
PPh
3
N
N
Ph P
Pt
N
N
Cl
Pt NCMe
Cl
+
3
Cl
Scheme 2. Synthesis of mononuclear complexes.

D. Belli Dell’ Amico et al. / Polyhedron 119 (2016) 403–411
407
Cl
Cl
PPh
3
Pt Cl
Cl
N
N
2 Ph P
Pt
Cl
N
N
Ph P
Pt
Cl
N
N
+
3
3
Scheme 3. Equilibrium between mononuclear and dinuclear species.
Table 3
However, the literature reports that mononuclear species of the
type trans-[PtCl2L(N–N)] (L = phosphine or CH2 = CH2 and N–N a
bidentate divergent hetero-aromatic base) are in equilibrium with
Selected 1H (Pt-NCH) and 31P NMR signals of free pyrz, 1, 6 and 7 in CDCl3.
Species
1H/ppm (3JH–Pt/Hz)
31P/ppm (1JP–Pt/Hz)
the corresponding trans,trans dimers [{PtCl2(PPh3)}2(l-N–N)]
(Scheme 3) [6a].
pyrazine
1
6a
6b
7a
7b
8.59
/
9.33 (nd)
9.03 (32)
8.45 (40)
9,09 (21)
8,40 (41)
2.79 (3728)
2.59 (3583)
7.24 (3902)
2.69 (3662)
7.13 (3810)
When the reaction between cis-[PtCl2(PPh3)(NCMe)] and pyra-
zine was carried out with molar ratio 1:1, preliminary results
showed the presence of a complex system containing the dinuclear
trans,trans derivative 1, free pyrazine and two mononuclear prod-
ucts, as revealed by the 1H NMR spectrum of the reaction mixture.
The most reasonable hypothesis was that both geometrical isomers
of the mononuclear product were formed. Nevertheless, in previ-
ous experiences concerning the preparation of [PtCl2(PPh3)
nd = not detectable.
pyrazine in molar ratio 1:1. The reaction, carried out with an excess
of pyrazine, yielded a suspension of a colourless solid that was
recovered by filtration and characterized by NMR spectroscopy.
Its 31P NMR (CDCl3) spectrum showed a single signal at 7.13 ppm
(1JP–Pt = 3810 Hz), while the integration of 1H NMR signals con-
firmed the mononuclear nature of the product, that was supported
also by elemental analysis data. On the basis of 31P NMR analogy
with 6b, the complex was identified as cis-[PtCl2(PPh3)(pyrz)]
(7b). From the filtrate of the reaction mixture a second crop of solid
was obtained, containing 7b and a second product showing the
same composition, corresponding to the geometric isomer
trans-[PtCl2(PPh3)(pyrz)] (7a) according to its NMR spectral
features. Selected 1H and 31P NMR signals of 7a, 7b are reported
in Table 3, together with those of 1, 6a, 6b and free pyrazine.
For both isomers it was possible to measure 3JH–Pt for hydrogen
atoms closest to coordinated nitrogen, with cis isomer showing a
higher coupling constant. It has to be underlined that trans
mononuclear 7a and dinuclear 1 complexes show very similar
(NHRR0)] with
a series of monodentate aliphatic amines
[7a–d,14], the exclusive formation of trans-[PtCl2(PPh3)(NHRR0)]
complexes was observed and no isomerisation of the product
was detected, probably because of the higher stability of these
geometric isomers [7a–d,14]. It could be expected that also the
reaction sketched in Scheme 2 afforded the trans isomer of the
mononuclear product. Anyway, since heteroaromatic bases in
place of amines could in principle affect the relative stability of
the two geometrical isomers [15], we first studied the reaction
between cis-[PtCl2(PPh3)(NCMe)] [7e] and pyridine, as the
monodentate base allowed to reduce the number of species
present at equilibrium. The reaction, monitored by 31P NMR
spectroscopy, proceeded to completion in a couple of hours with
formation of two products. Two signals of about the same
intensity [2.59 ppm (1JP–Pt = 3583 Hz) and 7.24 ppm (1JP–Pt
=
3902 Hz)] were observed. Moreover, the solid product obtained
after the work up of the reaction mixture showed an elemental
analysis in agreement with the formula [PtCl2(PPh3)(py)].
Solutions of the product revealed in the 31P NMR spectrum the
two signals previously observed in the spectrum of the reaction
mixture. These data showed that we were dealing with the two
geometrical isomers cis- and trans-[PtCl2(PPh3)(py)] (Scheme 4).
A sample was dissolved in CHCl3 and pentane was added by
slow diffusion with formation of single crystals suitable for X-ray
diffraction studies which showed that the isomer trans-
[PtCl2(PPh3)(py)] had been separated by crystallization (Fig. 1SI).
The NMR spectra of a freshly prepared solution of the crystals
allowed the assignment of the resonances due to the trans isomer
and as a consequence also to the cis isomer. At variance with the
previously reported cases involving the aforementioned amines
[7a–d]. both the geometric isomers formed with pyridine
(Scheme 4).
31P NMR chemical shifts and JH–Pt coupling constants, so that it
1
is necessary to carry out an accurate integration of 1H NMR signal
to clearly distinguish between the two species. A mixture of the
two isomers 7a and 7b was also obtained by reacting
trans-[Pt2(l-Cl)2Cl2(PPh3)2] with a slight excess of pyrazine (pyrz/
Pt molar ratio = 1.3).
In a further experiment, the formation of the mononuclear
derivatives was studied starting from the dinuclear complex 1 that
was dissolved in CDCl3 into an NMR test tube and treated with por-
tions of pyrazine (Table 2SI). After the first addition corresponding
to a pyrz/1 molar ratio = 1), both 1 and 7a were observed (1H and
31P NMR). After the further addition (pyrz/1 molar ratio = 2), sig-
nals due to 1 disappeared and the mononuclear trans-complex 7a
was initially detected as the main component. However, partial
isomerisation to the cis-complex 7b was soon observed in solution
(Scheme 5). Although both isomers were present in solution, the
lower solubility of 7b allowed its separation in pure form.
A sample of pure 7b was dissolved in CDCl3 and 1H and 31P NMR
spectra were recorded. They clearly show both partial isomerization
This outcome supported our hypothesis concerning the forma-
tion of both geometrical isomers of the mononuclear product
[PtCl2(PPh3)(pyrz)] by reacting cis-[PtCl2(PPh3)(NCMe)] with
Cl
Cl
Pt
PPh
3
Cl
Pt NCMe
Cl
x
Ph P
Py
Pt
Py
(1-x) Ph P
Cl
+
+
3
3
Cl
Py
6b
6a
7.24 ppm (1JP-Pt = 3902 Hz)
2.59 ppm (1JP-Pt = 3583 Hz)
(X-ray diffraction)
Scheme 4. Synthesis of [PtCl2(py)(PPh3)].

408
D. Belli Dell’ Amico et al. / Polyhedron 119 (2016) 403–411
PPh3
Pt
PPh3
Cl
Cl
Cl
N
Cl
Pt
N
Cl
Ph3P
Pt
N
Cl
N
N
+
N
Cl
Pt
Cl
N
N
PPh3
7b
7a
1
Scheme 5. Equilibria for the system 1/pyrz.
to 7a and partial dimerization to 1. The equilibrium composition at
room temperature was reached in about 48 h. The 1H NMR spec-
trum integrals allowed the assessment of the equilibrium constant
concerning the reaction sketched in Scheme 3 (N–N = pyrz). The
constant, calculated as K = {[1] ꢃ [pyrz]}/{[7a] + [7b]}2, corre-
sponded to about 5.4 ꢃ 10ꢂ3. This value is similar to that reported
in the literature for an analogous system where only the trans iso-
mer of the mononuclear species was detected [6a].
(trans,trans)-[PtCl2(PPh3)2(µ-bipy)] + bipy
trans-[PtCl2(bipy)(PPh3)]
2
8a
(cis,cis)-[PtCl2(PPh3)2(µ-bipy)] + bipy
cis-[PtCl2(bipy)(PPh3)]
2b
8b
X-ray diffraction
The reaction of the trans,trans dinuclear 2 complex with bipy to
obtain the mononuclear derivative [PtCl2(PPh3)(bipy)], was simi-
larly monitored by 1H and 31P NMR in CD2Cl2 as solvent. Selected
spectroscopic data are reported in Table 3SI, together with the
characteristic resonances for dinuclear 2 in the same solvent. Since
1H NMR signals of different species were partially superposed, it
was not possible to integrate them correctly, nevertheless the main
features of the system could be described.
Scheme 6. Equilibria involving the system ‘‘2/bipy”.
H H
β
α
γ
H
[Pt]
NH
H
ε
δ
N H
For a bipy/2 molar ratio of 1, 31P NMR spectrum did not vary
appreciably, while two new signals with the same intensity
appeared in the 1H NMR spectrum (9.14 and 8.79 ppm), besides a
multiplet due to free bipy (8.75 ppm) and the signal of dinuclear
2 (9.20 ppm). Signals at 9.14 and 8.79 ppm were ascribed, in anal-
ogy with the system 1/pyrz, to trans-[PtCl2(PPh3)(bipy)] (8a). It has
to be noted that 31P NMR signals of 2 and 8a were not distinguish-
able in CD2Cl2. For a bipy/2 molar ratio of 2, the signals due to 2
disappeared in 1H NMR spectrum, where, besides the multiplets
due to free bipy and 8a, a new one at 8.59 ppm was attributed to
the mononuclear species cis-[PtCl2(PPh3)(bipy)] (8b). The molar
ratio between 8a and 8b was estimated about 1. In a few days a
colorless solid separated out and single crystals were chosen for
structural X-ray determination (Fig. 5). Quite unexpectedly, the
solid turned out to be the dinuclear complex with cis,cis geometry
α
H
H
β
H H
γ
δ
Fig. 3. Magnetically non-equivalent piperazine hydrogen nuclei in 9.
effect of free ligands in the isomerization processes concerning
platinum(II) complexes.
For the system ‘‘3 + piperazine”, where a secondary aliphatic
diamine was involved, the formation of a single product was
revealed by 31P and 1H NMR spectroscopy in the presence of an
excess of the ligand, reasonably the mononuclear complex trans-
[PtCl2(PPh3)(pipz)] (9), by comparison with the NMR parameters
of the products discussed before (Table 4SI).
(cis,cis)-[{PtCl2(PPh3)}2(
l
-bipy)], 2b.
1H NMR spectrum of mononuclear complex 9 is characterized
by five signals for non-equivalent hydrogen atoms (Fig. 3), while
a signal with satellites is present in the 31P NMR spectrum, with
values of chemical shift and coupling constants very close to those
observed for the trans dinuclear precursor. Moreover, at variance
with systems containing heteroaromatic ligands (py, pyrz and
bipy), no isomerization of the piperazine complexes was observed.
When the preparation of 9 was attempted by using a stoichio-
metric amount of piperazine, an equilibrium involving 3, 9 and
the free ligand was again observed (Scheme 3). The integration of
1H NMR signals allowed an assessment of the constant of the equi-
librium K = {[3] ꢃ [piper]}/[9]2, corresponding to about 0.15.
Despite the very scarce solubility of the complex 2b in CD2Cl2 it
was possible to carry out a 1H NMR experiment, showing the fol-
lowing, not previously observed signals (Fig. 2): d 8.55 (m, 4H,
Ha); 7.72 (m, 12H, PPh3); 7.49 (m, 6H, PPh3); 7.38 (m, 12H,
PPh3); 7.00 (m, 4H, Hb).
All these data can be rationalized by the simultaneous presence
of equilibria concerning the nuclearity of the species, their geomet-
rical isomerism and, finally, their solubility (Scheme 6). It is to be
underlined that trans to cis isomerization of both mononuclear
and dinuclear species appears detectable only in the presence of
free ligand. This behavior is in agreement with the known catalytic
3.2. Structural determinations
α
β
Selected bond lengths and angles for complexes 2, 2b and 3
(Figs. 4–6) are summarized in Table 4. The Pt coordination is
square planar with very little distorsions presumably due to the
encumbrance of the different ligands. The Cambridge Crystallo-
graphic Database [12] contains the structural data of several
N
N
[Pt]
[Pt]
α
β
Fig. 2. Magnetically non-equivalent bipy hydrogen nuclei in 2b.

D. Belli Dell’ Amico et al. / Polyhedron 119 (2016) 403–411
409
Fig. 4. View of the molecular structure of 2 as found in the crystals of 2. Thermal ellipsoids are at 20% probability. ’ = 3 ꢂ x, ꢂy, 2 ꢂ z.
Fig. 5. View of the molecular structure of 2b. Thermal ellipsoids are at 20% probability. ’ = 2 ꢂ x, ꢂy, 1 ꢂ z.
Fig. 6. View of the molecular structure of 3 as found in the crystals of 3ꢀ2(CHCl3). Thermal ellipsoids are at 20% probability. ’ = 1 ꢂ x, 1 ꢂ y, 2 ꢂ z.
compounds including the unit {PtCl2aminophosphine}, more com-
monly with the chloride ligands in trans configuration (43 exam-
ples) and less commonly in the cis one (8 examples). The bond
lengths we found in our compounds (Table 4) are all within the
range of expected values: 2.30(2) Å for PtꢂCl trans to Cl, 2.36
(1) Å for PtꢂCl trans to the phosphine, 2.03(2) Å for PtꢂN trans to
Cl, 2.13(4)Å for PtꢂN trans to the phosphine and 2.23(1) Å for PtꢂP.
The molecular structures of 2 and 2b are reported in Figs. 4 and 5.

410
D. Belli Dell’ Amico et al. / Polyhedron 119 (2016) 403–411
Table 4
agreement with previous data,[7a–d,14] where platinum(II)
Bond lenghts [Å] and angles [°] around Pt atom.
complexes containing amines of the type (trans)-[PtCl2(PPh3)
(RR0NH)] did not show any isomerization to the cis isomers in
solution, probably for the significantly higher stability of the
2
2b
3
Pt–N
Pt–P
Pt–Cl(1)
Pt–Cl(2)
2.102(5)
2.035(6)
2.249(2)
2.299(2)
2.348(2)
93.25(18)
175.22(18)
86.55(18)
91.44(8)
178.58(8)
88.74(8)
2.138(5)
2.2388(15)
2.289(2)
2.2872(18)
179.79(15)
89.07(17)
83.61(17)
90.78(7)
isomer having the
amine.
p-acid phosphine trans to the rather basic
2.2272(14)
2.2731(16)
2.2791(16)
178.47(13)
87.85(13)
88.82(13)
93.67(6)
N–Pt–P
Acknowledgements
N–Pt–Cl(1)
N–Pt–Cl(2)
P–Pt–Cl(1)
P–Pt–Cl(2)
Cl(1)–Pt–Cl(2)
The authors thank the Università di Pisa for financial support
(Fondi di Ateneo 2015). S. Samaritani is grateful to the financial
support provided by Università di Pisa—Progetti di Ricerca di Ate-
neo 2015—‘Sintesi e studio delle proprietà di composti di metalli di
transizione come agenti Antitumorali’ (PRA_2015_0055). Thanks
are due to Dr. Simone Barondi for preliminary experiments.
89.66(6)
176.67(6)
96.55(7)
172.19(7)
The metal coordination planes in 2 are parallel and almost
coplanar (deviation 0.23 Å). The plane of the bipyridyl ligand
makes with them a dihedral angle of 53.4°.
Appendix A. Supplementary data
In 2b (Fig. 5) platinum coordination planes are parallel and
almost coplanar (deviation 0.20 Å) and make a dihedral angle of
70.7° with the plane of the bipyridyl ligand. It is worth to note that
each phosphine ligand have a phenyl group slanted towards the
nearest pyridyl ring. The two rings are almost parallel (dihedral
angle 13.9°) with a relatively short distance between the centroids
Experimental details concerning the preparation of 5 as well as
some spectroscopic data are reported as Supplementary Informa-
tion. CCDC 1484284–1484287 contain the supplementary crystal-
lographic data for the derivatives 2, 2b, 3 2(CHCl3) and 6a 0.5
(C2H4Cl2). These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif. Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.poly.
2016.09.016.
(3.56 Å), suggesting an intramolecular p-stacking interaction.
The platinum coordination planes in 3 (Fig. 6) are again parallel
and almost coplanar. The hydrogen atom connected with the nitro-
gen N(1) also lies on the metal coordination plane with a N(1)ꢂPt
(1)ꢂCl(2) angle of 83.3°, suggesting at some extent a HꢀꢀꢀCl(2)
interaction.
References
[1] B.H. Northrop, Y.-R. Zheng, K.-W. Chi, P. Stang, J. Acc. Chem. Res. 42 (2009)
1554 (and ref. therein).
[2] (a) S. Culham, P.-H. Lanoë, V.L. Whittle, M.C. Durrant, J.A.G. Williams, V.N.
Kozhevnikov, Inorg. Chem. 52 (2013) 10992;
4. Conclusions
(b) H. Jude, J.A. Krause Bauer, W. Connick, B, Inorg. Chem. 44 (2005) 1211;
(c) W. Lu, M.C.W. Chan, K.-K. Cheung, C.-M. Che, Organometallics 20 (2001)
2477;
The preparation of dinuclear complexes [{PtCl2(PPh3)}2-
(l-N–N)], where N–N = nitrogen bidentate divergent ligand, can
be carried out with good yields starting from cis-[PtCl2(PPh3)
(NCMe)], with an accurate control of the molar ratio between
reagents (Pt/N–N molar ratio = 2). Products, characterized by
trans,trans geometry, appear stable in solution for many days. If a
different molar ratio between reagents is used (Pt/N–N molar
ratio = 1) equilibria are established involving the already described
dinuclear derivatives, the corresponding mononuclear complexes
[PtCl2(PPh3)(N–N)] and the free ligand. Equilibrium constants were
estimated as instability constants of the mononuclear species con-
taining pyrazine (K = 5.4ꢀ10ꢂ3) and piperazine (K = 0.15). The com-
parison between the obtained values shows the higher stability of
the mononuclear species containing the heteroaromatic base. The
existence of such equilibria suggests some prudence in planning
syntheses involving the mononuclear complexes of the type here
described. For instance, they could in principle be considered suit-
able precursors of heterobimetallic dinuclear compounds, as they
retain one dangling donor atom on the bidentate divergent ligand,
able to penetrate the coordination sphere of another metal, Never-
theless, in view of their facile dimerization, a mixture of products
could be obtained. Under the conditions useful to obtain mononu-
clear derivatives, the geometrical isomerization of the species in
solution was observed with the heteroaromatic bases pyrazine
and 4,40-bipyridyl. Moreover, besides isomerization and dimeriza-
tion equilibria, solubility can play a role. For instance, in the case of
the bipy based system, the very low solubility of the dinuclear (cis,
(d) B.W. Pfennig, C.J. Mordas, A. McCloskey, J.V. Lockard, P.M. Salmon, J.L.
Cohen, D.F. Watson, A.B. Bocarsly, Inorg. Chem. 41 (2002) 4389;
(e) K.P. Balashev, O.R. Khanukaeva, Russ. J. Gen. Chem. 71 (2001) 1149.
[3] (a) L. Senerovic, M.D. Zivkovic, A. Veselinovic, A. Pavic, M.I. Djuran, S. Rajkovic,
J. Nikodinovic-Runic, J. Med. Chem. 58 (2015) 1442;
ˇ
ˇ ´
(b) S. Jovanovic´, J. Bogojeski, M. Petkovic´, Z.D. Bugarcic, J. Coord. Chem. 68
(2015) 3148;
(c) M. Mounir, J. Lorenzo, M. Ferrer, M.J. Prieto, O. Rossell, F.X. Avilès, V.
Moreno, J. Inorg. Biochem. 101 (2007) 660;
(d) V. Brabec, J. Kasparkova, Drug Resist. Updates 8 (2005) 131;
(e) S. Komeda, G.V. Kalayda, M. Lutz, A.L. Spek, Y. Yamanaka, T. Sato, M.
Chikuma, J. Reedijk, J. Med. Chem. 46 (2003) 1210;
(f) J.W. Cox, S.J. Berners-Price, M.S. Davies, Y. Qu, N. Farrell, J. Am. Chem. Soc.
123 (2001) 1316.
[4] T.R. Cook, P.J. Stang, Chem. Rev. 115 (2015) 7001.
[5] (a) For some recent articles see: V.S. Pavan, K. Neti, M.L. Saha, X. Yan, Z. Zhou,
P.J. Stang Organometallics 34 (2015) 4813;
(b) X. Yan, T.R. Cook, P. Wang, F.P. Huang, J. Stang Nat. Chem. (2015), http://dx.
doi.org/10.1038/NCHEM.2201;
(c) Y. Ye, T.R. Cook, S.-P. Wang, J. Wu, S. Li, P.J. Stang, J. Am. Chem. Soc. 137
(2015) 11896.
[6] (a) A. Albinati, F. Isaia, W. Kaufmann, C. Sorato, L.M. Venanzi, Inorg. Chem. 28
(1989) 1112;
(b) W. Kaufmann, L.M. Venanzi, A. Albinati, Inorg. Chem. 27 (1988) 1178.
[7] (a) L. Dalla Via, A.N. García-Argáez, E. Agostinelli, D. Belli Dell’Amico, L. Labella,
S. Samaritani, Bioorg. Med. Chem. 24 (2016) 2929;
(b) D. Belli Dell’Amico, L. Dalla Via, A.N. Garcia-Argaez, L. Labella, F. Marchetti,
S. Samaritani, Polyhedron 82 (2015) 685;
(c) L. Dalla Via, A.N. Garcia-Argaez, A. Adami, S. Grancara, P. Martinis, A.
Toninello, D. Belli Dell’Amico, L. Labella, S. Samaritani, Bioorg. Med. Chem. 21
(2013) 6965;
(d) D. Belli Dell’Amico, C. Broglia, L. Labella, F. Marchetti, D. Mendola, S.
Samaritani, Inorg. Chim. Acta 395 (2013) 181;
cis)-[{PtCl2(PPh3)}2(l-bipy)], 2b, allowed its isolation and struc-
tural characterization.
With the secondary diamine piperazine, only products (both
dinuclear and mononuclear) with trans geometry were observed,
even when an excess of the ligand was added. This result is in
(e) D. Belli Dell’Amico, L. Labella, F. Marchetti, S. Samaritani, Dalton Trans. 41
(2012) 1389.
[8] H.L. Anderson, S. Anderson, J.K.M. Sanders, J. Chem. Soc. Perkin Trans. 1 (1995)
2231.
[9] W.L.F. Armarego, D.D. Perrin, Purification of Laboratory Chemicals,
Butterworth-Heinemann, 1996.

D. Belli Dell’ Amico et al. / Polyhedron 119 (2016) 403–411
411
[10] G.M. Sheldrick, SADABS, Program for empirical absorption correction,
University of Göttingen, Germany, 1996.
[14] (a) F.J. Ramos-Lima, A.G. Quiroga, B. García-Serrelde, F. Blanco, A. Carnero, C.
Navarro-Ranninger, J. Med. Chem. 50 (2007) 2194;
[11] G.M. Sheldrick, SHELX97 – Programs for Crystal Structure Analysis (Release
97-2), Institüt für Anorganische Chemie der Universität, Tammanstrasse 4,
D-3400 Göttingen, Germany, 1998.
(b) F.J. Ramos-Lima, A.G. Quiroga, J.M. Pérez, M. Font-Bardía, X. Solans, C.
Navarro-Ranninger, Eur. J. Inorg. Chem. (2003) 1591.
[15] D. Mendola, N. Saleh, N. Vanthuyne, C. Roussel, L. Toupet, F. Castiglione, T.
Caronna, A. Mele, J. Crassous, Angew. Chem., Int. Ed. 53 (2014) 5786.
[12] A.L. Spek, Acta Crystallogr., C 71 (2014) 9.
[13] L.J. Farrugia, J. Appl. Crystallogr. 32 (1999) 837.