Study of Pt(II)-cyclic amines complexes of the types cis- and trans-Pt(amine)2I2 and cis- and trans-Pt(amine) 2(NO3)2 and their aqueous products

Article abstract of DOI:10.1016/j.ica.2004.12.030

Complexes of the types cis- and trans-Pt(amine)₂I₂ containing cyclic amines were synthesized and studied mainly by IR and multinuclear NMR spectroscopies. The compounds were converted to cis- and trans-Pt(amine)₂(NO₃)₂, which were also investigated. The hydrolysis and the aquation reactions of the latter compounds were then studied in D₂O in different conditions of pH. In acidic medium, the aqueous product is [Pt(amine)₂(D₂O) ₂]²⁺ and for a few amines, [Pt(amine)₂(D ₂O)(NO₃)]⁺ was detected. In basic pH, the main product is Pt(amine)₂(OD)₂ and Pt(amine) ₂(OD)(NO₃) was detected for several compounds. In neutral pH, the cis isomers form between two and four species in fresh solutions. The most shielded species in ¹⁹⁵Pt NMR is the monoaqua-monohydroxo complex cis-[Pt(amine)₂(D₂O)(OD)]⁺ and the less shielded compound is the dihydroxo-bridged dimer [Pt(amine)₂(μ- OD)₂Pt(amine)₂]²⁺, which were observed for all the compounds. For a few amines, the monohydroxo-bridged dimer [Pt(D ₂O)(amine)₂(μ-OD)Pt(OD)(amine)₂] ²⁺ was detected and for cyclohexylamine, a fourth signal was assigned to a cyclic hydroxo-bridged trimer [(Pt(amine)₂(μ-OD)) ₃]³⁺. ¹⁹⁵Pt NMR spectroscopy has shown that the concentration of the monomer decreases with time, while the concentration of the dimers increases. Only one product was observed for the trans isomers in neutral pH. The signal was assigned to the monoaqua-monohydroxo species trans-[Pt(amine)₂(D₂O)(OD)]⁺. The ¹³C and ¹H NMR spectra of most of the complexes were measured. All the coupling constants ^2,3J(¹⁹⁵Pt- ¹H) and ^2,3J(¹⁹⁵Pt-¹³C) are larger in the cis compounds than in the trans isomers.

Full text of DOI:10.1016/j.ica.2004.12.030

Inorganica Chimica Acta 358 (2005) 2040–2056
www.elsevier.com/locate/ica
Study of Pt(II)-cyclic amines complexes of the types cis- and
trans-Pt(amine)2I2 and cis- and trans-Pt(amine)2(NO3)2 and
their aqueous products
*
Fernande D. Rochon , Viorel Buculei
´ ´ ´ ` ´ ´
Departement de chimie, Universite du Quebec a Montreal, C.P. 8888, Succ. Centre-ville, Montreal, Canada H3C 3P8
Received 4 November 2004; accepted 28 December 2004
Available online 11 February 2005
Abstract
Complexes of the types cis- and trans-Pt(amine)2I2 containing cyclic amines were synthesized and studied mainly by IR and mul-
tinuclear NMR spectroscopies. The compounds were converted to cis- and trans-Pt(amine)2(NO3)2, which were also investigated.
The hydrolysis and the aquation reactions of the latter compounds were then studied in D2O in different conditions of pH. In acidic
medium, the aqueous product is [Pt(amine)2(D2O)2]2+ and for a few amines, [Pt(amine)2(D2O)(NO3)]+ was detected. In basic pH, the
main product is Pt(amine)2(OD)2 and Pt(amine)2(OD)(NO3) was detected for several compounds. In neutral pH, the cis isomers
form between two and four species in fresh solutions. The most shielded species in 195Pt NMR is the monoaqua–monohydroxo com-
plex cis-[Pt(amine)2(D2O)(OD)]+ and the less shielded compound is the dihydroxo-bridged dimer [Pt(amine)2(l-OD)2Pt(amine)2]2+
,
which were observed for all the compounds. For a few amines, the monohydroxo-bridged dimer [Pt(D2O)(amine)2(l-OD)Pt(OD)(a-
mine)2]2+ was detected and for cyclohexylamine, a fourth signal was assigned to a cyclic hydroxo-bridged trimer [(Pt(amine)2(l-
OD))3]3+ 195Pt NMR spectroscopy has shown that the concentration of the monomer decreases with time, while the concentration
.
of the dimers increases. Only one product was observed for the trans isomers in neutral pH. The signal was assigned to the mono-
aqua–monohydroxo species trans-[Pt(amine)2(D2O)(OD)]+. The 13C and 1H NMR spectra of most of the complexes were measured.
All the coupling constants 2,3J(195Pt–1H) and 2,3J(195Pt–13C) are larger in the cis compounds than in the trans isomers.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Platinum; Amine; Iodo; Nitrato; Hydrolysis; NMR; Aquation; IR
1. Introduction
of a large chloride concentration (103 mM) and can
cross the cell membrane because of its neutrality. The
chloride ion concentration is much lower (4 mM) inside
the cells, and in these conditions, cis-Pt(NH3)2Cl2 can
produce different ionic species. Its mechanism of action
involves aquation or hydrolysis reactions, which have
been studied in a few laboratories. One of the ionic spe-
cies is the aqua-chloro complex cis-[Pt(NH3)2(OH2)
Cl]Cl, which can either bind to DNA [3] leading to the
eventual destruction of the cell, or react with water to
produce the diaqua species. The latter compound in
neutral medium will exist mainly in the form of the
The antitumor properties of cis diamine Pt(II) com-
pounds are now well known. The compound cisplatin
(cis-Pt(NH3)2Cl2) is still the most widely used drug in
chemotherapy. Its mechanism of action has been studied
by several authors, but there are still many uncertainties,
since its reactions are extremely complex [1,2]. The drug
remains mostly unchanged in the plasma in the presence
*
Corresponding author. Tel.: +1 514 987 3000/4896; fax: +1 514
987 4054.
E-mail address: rochon.fernande@uqam.ca (F.D. Rochon).
monoaqua–monohydroxo
complex
[3–6]
cis-
0020-1693/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.12.030

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
2041
[Pt(NH3)2(OH)(OH2)]+, which can also bind to DNA
[3]. The monoaqua–monohydroxo compound in neutral
pH has been shown in a few laboratories to produce dif-
ferent oligomeric species, which have been characterized
by 195Pt NMR [7–9] and by crystallographic methods
[10–14]. Some of these oligomers are toxic and could
be partially responsible for the toxicity of cisplatin
[15,16]. It is therefore very important to study the aqua-
tion and hydrolysis reactions of a complex prior to its
development as an antitumor drug.
bought from Aldrich, while silver nitrate was purchased
from Analar. D2O, DMF-d7 and CD3COCD3 were ob-
tained from CDN Isotopes. The NaOD solution
(0.4 M) was prepared by dissolving NaOH in D2O.
The NMR spectra were measured on a Varian Gem-
ini 300BB. The fields were 300.070, 75.460 and
64.395 MHz for 1H, 13C and 195Pt, respectively. For
the 195Pt NMR spectra, K2[PtCl4] (ꢀ1628 ppm in D2O
with KCl) or K[Pt(DMSO)Cl3] (ꢀ2998 ppm in D2O)
were the external standards. The NMR spectra of the
diiodo and dinitrato complexes were measured in
CD3COCD3, while the aquation and hydrolysis reac-
tions were studied in D2O. The pH values were mea-
sured on a Fisher Scientific Accumet-15 pH-meter,
using a combined electrode Ag/AgCl (Fisher Scientific)
at room temperature. For the pD values, the pH values
were increased by 0.4 [35].
A good review of the influence of the structure on the
activity of Pt drugs has been published [17]. When the
ligand NH3 in cisplatin is replaced by primary amines,
the antitumor properties can increase, especially with
cyclic amines [18–21], but the latter compounds have of-
ten a more limited activity spectrum. Furthermore, sev-
eral of the most active compounds are quite insoluble
[22]. In the amine system, the most active compounds
usually have the cis geometry, although a few trans com-
pounds have been shown to possess some antitumor
properties. Our research group has recently undertaken
a systematic study on complexes of the types cis- and
trans-Pt(amine)2I2 with different aliphatic amines [23].
We have transformed these complexes into cis- and
trans-Pt(amine)2(NO3)2, which have also been studied
in the solid state by IR and in solution in acetone by
195Pt, 1H and 13C NMR spectroscopy [24]. Conductivity
measurements in acetone have shown that the dinitrato
complexes are not dissociated. We have subsequently
studied their aquation and hydrolysis reactions in water
at three different conditions of pH, acidic, neutral and
basic [25]. Although a few studies in the literature were
made on cis compounds [7–9,25–33] (especially cis-
Pt(NH3)2Cl2), few studies have been reported on trans
complexes [25,34]. A tentative preliminary study has
also been reported [32] on trans-Pt(Ypy)2(NO3)2 where
Ypy = pyridine derivative.
We have now made a similar study on Pt(II)-cyclic
amine compounds. We have first synthesized the cis
and trans diiodo compounds which were characterized
by IR and by multinuclear magnetic resonance spectros-
copy in order to determine the purity of the compounds.
These were then converted into the dinitrato complexes,
which were also similarly characterized. Finally, the
aquation and hydrolysis reactions of the dinitrato com-
pounds were studied in different conditions of pH. The
dichlorodiamine complexes were also synthesized from
the diaqua species and their 195Pt NMR spectra mea-
sured. The results on these cyclic amines Pt(II) com-
plexes are described below.
The aquation or hydrolysis of the dinitrato complexes
were studied in three different conditions of pH. The
dinitrato complexes (12–15 mg) were dissolved in 1 mL
of D2O with slight heating (40–45°). The concentration
of the solution is about 0.03 M and the pD is acidic
1
(2.5–2.9). The 195Pt, H and 13C NMR were measured
directly on these fresh D2O solutions. The pD of another
fresh solution was adjusted to about 7 with NaOD and
the NMR spectra were measured immediately. The pD
of a third fresh D2O solution of the dinitrato complex
was adjusted between 9.9 and 10.4 just before recording
the NMR spectra. In a typical experiment, the dinitrato
compound was dissolved in D2O with heating in a hot
water bath. For the products in acidic and basic pH,
the 195Pt NMR spectrum was measured immediately
1
during about 1–3 h, the H spectrum was then recorded
for 30–60 min and the 13C spectrum was measured over-
night (ꢁ15 h). At neutral pH, where the number of spe-
cies in solution is usually greater, the accumulation time
was 2–3 times longer. A few NMR tubes were left stand-
ing at about 4° and the 195Pt NMR spectra were later
remeasured in order to see the evolution of the different
species with time.
2.1. Pt(amine)2I2
The compounds cis- and trans-Pt(amine)2I2 were syn-
thesized as described in our recent publication on ali-
phatic amines [23].
cis-Pt(cpra)2I2: Yield = 85%, m.p. 116–180 °C (dec).
IR (cmꢀ1): m(N–H): 3240s, 3195s, 3110w; m(C–H)
2990m, 2935w; d(N–H): 1570s, 1565s; d(C–H): 1450m,
1425m, 1380s; m(C–N): 1255s, 1195s; m(Pt–N): 563m;
Other bands: 1110m, 1095m, 1050w, 1015s, 920m,
1
820m. NMR (d(ppm)): H: NH 4.607s + d; H1 2.792m;
2. Experimental
H2 0.905; H3 0.732m; 13C: C1 hidden by the solvent,
C2 7.322.
K2[PtCl4] was purchased from Johnson–Matthey and
was recrystallized in water before use. The amines were
cis-Pt(cba)2I2:
Yield = 74%,
m.p. = 114–179 °C
(dec.). IR (cmꢀ1): m(N–H): 3220m, 3192s, 3125m;

2042
F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
m(C–H): 2980m, 2955m, 2865w; d(N–H): 1565w; d(C–
H): 1460w, 1430m, 1382m; m(C–N): 1235s, 1205m,
1160m, 1075s; m(Pt–N): 580w, 530w. Other bands:
935w, 885w, 760w. NMR (d (ppm)): 1H: NH
4.658s + d; H1 3.894m; H2 2.305; H3 2.165; H4 1.658.
13C:1 52.885; C2 31.667; C3 14.243.
cis-Pt(cba)2(NO3)2: Yield = 67%, m.p. = 118–149 °C
(dec.). IR (cmꢀ1): m(N–H): 3260s, 3225s, 3130m; m(C–
H): 2980s, 2960m, 2865w; d(N–H): 1580m; m4(NO3):
1504s; d(C–H): 1465m, 1430m, 1380s; m2(NO3): 1275s;
m(C–N): 1180m, 1095s; m1(NO3) : 976s; m6(NO3): 776m;
m5(NO3): 703w; m(Pt–N): 572w, 512m; m(Pt–O): 332m;
Other bands : 944m, 930w, 740w, 636w. NMR (d
(ppm)): H: NH 5.327s + d; H1 3.483m; H2 2.338m; H3
2.111m; H4 1.669m; 13C: C1 53.447; C2 hidden by the
solvent; C3 14.167.
cis-Pt(cpa)2(NO3)2: Yield = 72%, m.p. = 101–133 °C
(dec.). IR (cmꢀ1): m(N–H): 3255s, 3235s, 3140m; m(C–
H): 2960s, 2910m, 2860m; d(N–H): 1575m; m4(NO3):
1503s; d(C–H): 1460s, 1385m, 1360m; m2(NO3): 1272s;
m(C–N): 1145w, 1055w; m1(NO3): 980s; m6(NO3): 785m;
m5(NO3): 703w; m(Pt–N): 565w, 520m; m(Pt–O): 334m;
Other bands: 940s, 830w, 410w. NMR (d (ppm)):1H:
NH 5.195s + d; H1 3.276m; H2 2.153m; H3 1.726m; H4
1.585m; 13C: C1 59.564; C2 33.852; C3 24.442.
cis-Pt(cha)2(NO3)2: Yield = 79%, m.p. = 98–122 °C
(dec.). IR (cmꢀ1): m(N–H): 3260s, 3220s, 3130m; m(C–
H): 2935s, 2855s; d(N–H): 1585m; m4(NO3): 1502s;
d(C–H): 1465s, 1445s, 1380s; m2(NO3): 1280s; m(C–N):
1160m, 1080w, 1055m; m1(NO3): 978s; m6(NO3): 795m;
m5(NO3): 705w, m(Pt–N): 565w, 530m, m(Pt–O): 335m;
Other bands: 1020w, 950m, 895m, 755m, 640w. NMR
(d (ppm)):1H: NH 5.130s + d; H1 2.514m; 13C: C1
56.953; C2 34.362; C3 25.990; C4 25.611.
cis-Pt(cpa)2I2: Yield = 69%, m.p. = 117–176 °C (dec.).
IR (cmꢀ1): m(N–H): 3220m, 3170s, 3055m; m(C–H) 2930s,
2835m; d(N–H): 1563s; d(C–H): 1465w, 1445m, 1380m;
m(C–N): 1205m, 1110m, 1070m; m(Pt–N): 575w, 543w.
1
1
Other bands: 1040w, 975m, 730w. NMR (d (ppm)): H:
NH 4.471s + d; H1 3.747m; H2 2.085m; H31.734m; H4
1.580m. 13C: C159.290; C2 34.490; C3 24.169.
cis-Pt(cha)2I2:
Yield = 78%,
m.p. = 116–162 °C
(dec.). IR (cmꢀ1): m(N–H): 3240s, 3220s, 3195s, 3110m;
m(C–H): 2925s, 2910s, 2860s; d(N–H): 1570s; d(C–H):
1450s, 1385s, 1365m; m(C–N): 1240s, 1225s, 1195s,
1095s; m(Pt–N): 585w, 505w; Other bands: 1335m,
1305m, 1080m, 1060m, 1040s, 960m, 885m, 830m,
610w. NMR (d (ppm)): 1H: NH 4.385s + d; H1
3.542m; 13C: C1 56.665; C2 35.158; C3 26.021; C4 25.672.
trans-Pt(cpra)2I2: Yield = 56%, m.p. = 157–177 °C
(dec.). IR (cmꢀ1): m(N–H): 3225s, 3205s; m(C–H):
2945w, 2925m; d(N–H): 1565s; d(C–H): 1460w, 1380s;
m(C–N): 1245w, 1200m, 1110m; m(Pt–N): 468w; Other
1
bands: 1025m, 960w, 820m. NMR (d (ppm)): H : NH
4.098s + d; H1 2.768; H2 0.745; H3 0.646; 13C: C1
31.378; C2 7.762.
trans-Pt(cba)2I2: Yield = 61%, m.p. = 158–174 °C
(dec.). IR (cmꢀ1): m(N–H): 3225s, 3205s, 3110s; m(C–
H): 2980s, 2955m, 2875m; d(N–H): 1570s; d(C–H):
1465m, 1440m, 1385s; m(C–N): 1235s, 1215s, 1150s,
1095s; m(Pt–N): 478w; Other bands: 955m, 905m,
790m, 745w, 620m. NMR (d (ppm)): 1H: NH
4.164s + d; H1 3.695m; H2 2.162m; H3 2.067m; H4
1.598m; 13C: C1 53.887; C2 31.940; C3 14.273.
trans-Pt(cpa)2I2: Yield = 59%, m.p. = 144–174 °C
(dec.). IR (cmꢀ1): m(N–H): 3225s, 3205s, 3110m; m(C–
H): 2930s, 2840m; d(N–H): 1570s; d(C–H): 1455m,
1382m; m(C–N): 1245s, 1205m, 1120m; m(Pt–N): 485w;
Other bands: 1060m, 1025m, 885w. NMR (d (ppm)):
1H : NH 3.959s + d; H1 3.562m; H2 1.921m; H3 1.707;
H4 1.537; 13C: C1 60.808; C2 34.533; C3 23.987.
trans-Pt(cha)2I2: Yield = 63%, m.p. = 138–164 °C
(dec.). IR (cmꢀ1): m(N–H): 3220w, 3195s, 3110m; m(C–
H): 2960m, 2915m; d(N–H): 1563s; d(C–H): 1435m,
1380s; m(C–N): 1260w, 1235m, 1205m, 1160m; m(Pt–
N): 455w; Other bands: 1060m; 945m, 890w, 760w,
620w. NMR (d (ppm)): 1H: NH 3.888s + d; H1
3.044m; 13C: C1 58.122; C2 35.431; C3 26.066; C4 25.474.
trans-Pt(cpra)2(NO3)2: Yield = 86%, m.p. = 129–
161 °C (dec.). IR (cmꢀ1): m(N–H): 3240s, 3150m; m(C–
H): 2940s, 2835m; d(N–H): 1583s; m4(NO3): 1508s;
d(C–H): 1460w, 1435w, 1382m; m2(NO3): 1265s; m(C–
N): 1160m, 1070m; m1(NO3): 965s; m6(NO3): 785s;
m5(NO3): 705s; m(Pt–N): 512m; m(Pt–O): 340m; Other
bands: 930m, 895w. NMR (d (ppm)):1H: NH
4.909s + d; H1 2.357m; H2 0.711m; H3 0.637m; 13C: C1
hidden by the solvent, C2 6.001.
trans-Pt(cba)2(NO3)2: Yield = 79%, m.p. = 127–
159 °C (dec.). IR (cmꢀ1): m(N–H): 3280m, 3240s,
3150m; m(C–H): 2960s, 2930m, 2885w; d(N–H): 1570s;
m4(NO3): 1509s; d(C–H): 1475m, 1420m, 1385m;
m2(NO3): 1270s; m(C–N): 1155m, 1075m, 1055w;
m1(NO3): 960s; m6(NO3): 775w; m5(NO3): 702w; m(Pt–N):
507w; m(Pt–O): 345m; Other bands: 1010s, 865w,
750m. NMR (d (ppm)): 1H: NH 4.988s + d; H1
3.365m; H2 2.264m; H3 2.103m; H4 1.653m; 13C: C1
52.157; C2 30.574; C3 14.470.
trans-Pt(cpa)2(NO3)2: Yield = 76%, m.p. = 112–
147 °C (dec.). IR (cmꢀ1): m(N–H): 3260s, 3230m,
3185w; m(C–H): 2985s, 2935m, 2880w; d(N–H): 1580m;
m4(NO3): 1505s; d(C–H): 1455w, 1385s; m2(NO3): 1266s;
m(C–N): 1160m, 1080m, 1055w; m1(NO3): 964s;
m6(NO3): 775m; m5(NO3): 705w; m(Pt–N): 495w; m(Pt–
O): 342m; Other bands: 1015m, 855w, 815w. NMR (d
2.2. Pt(amine)2(NO3)2
The compounds cis- and trans-Pt(amine)2(NO3)2
were synthesized by methods similar to those described
on aliphatic amines [24].
1
(ppm)): H: NH 4.797s + d; H1 3.190m; H2 2.092m; H3
1.759; H4 1.577; 13C: C1 58.076; C2 33.731; C3 24.564.

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
2043
trans-Pt(cha)2(NO3)2: Yield = 87%, m.p. = 106–
137 °C (dec.). IR (cmꢀ1): m(N–H): 3260s, 3235s,
3165m; m(C–H): 2935s, 2860; d(N–H): 1595s; m4(NO3):
1505s; d(C–H): 1450s, 1380s; m2(NO3): 1265s; m(C–N):
1160m, 1130w, 1095s; m1(NO3): 962s; m6(NO3): 782w;
m5(NO3): 705w; m(Pt–N): 505w; m(Pt–O): 344w; Other
bands: 1000s, 885m, 935s, 840w. NMR (d (ppm)):1H:
NH 4.717s + d; H1 2.478m; 13C: C1 55.587; C2 34.126;
C3 26.081; C4 25.641.
trans-Pt(cpa)2(OD)2: NMR (d (ppm)): 1H: H1
3.224m; H2 2.099m; H3 1.696; H4 1.572. 13C: C1
56.995; C2 33.439; C3 23.437.
trans-Pt(cha)2(OD)2: NMR (d (ppm)): 1H: H1
2.395m. 13C: C1 54.078; C2 34.077; C3 24.982; C4 24.602.
2.5. trans-[Pt(amine)2(D2O)(OD)](NO3)
trans-[Pt(cpra)2(D2O)(OD)](NO3): NMR (d (ppm)):
1H: H1 2.330m; H2 0.692m; H3 0.669m.
2.3. Pt(amine)2(D2O)2](NO3)2
trans-[Pt(cba)2(D2O)(OD)](NO3): NMR (d (ppm)):
1H: H1 3.395m; H2 2.318m; H3 1.947m; H4 1.712m.
trans-[Pt(cpa)2(D2O)(OD)](NO3): NMR (d (ppm)):
1H: H1 3.207m; H2 2.153m; H3 1.721; H4 1.614.
trans-[Pt(cha)2(D2O)(OD)](NO3): NMR (d (ppm)):
1H: H1 2.364m.
cis-[Pt(cpra)2(D2O)2](NO3)2: NMR (d (ppm)): 1H:
NH 5.489s + d; H1 2.337m; H2 0.758; H3 0.642m; 13C:
C1 29.751; C2 5.634.
cis-[Pt(cba)2(D2O)2](NO3)2: NMR (d (ppm)): 1H: NH
5.46s + d; H1 3.330m; H2 2.312; H3 1.956; H4 1.683. 13C:
C1 51.895; C2 30.793; C3 13.498.
2.6. Pt(amine)2Cl2
cis-[Pt(cpa)2(D2O)2](NO3)2: NMR (d (ppm)): 1H: NH
5.341s + d; H1 3.137m; H2 2.163m; H3 1.707m; H4
1.579m. 13C: C1 55.568; C2 33.498; C3 22.948.
cis-[Pt(cha)2(D2O)2](NO3)2: NMR (d (ppm)): 1H: NH
5.229s + d; H1 2.342m. 13C: C1 55.902; C2 33.348; C3
24.788; C4 24.545.
The cis- and trans-Pt(amine)2Cl2 were synthesized by
an adapted version of DharaÕs method [36]. The diaqua
species obtained from the cis and trans diiodo com-
pounds were reacted with KCl. The precipitate was
washed with water and dried.
1
trans-[Pt(cpra)2(D2O)2](NO3)2: NMR (d (ppm)): H:
NH 4.917s + d; H1 2.321m; H2 0.725m; H3 0.621m;
13C: C1 28.248; C2 5.360.
trans-[Pt(cba)2(D2O)2](NO3)2: NMR (d (ppm)): H:
NH 4.939s + d; H1 3.345m; H2 2.338m; H3 1.968m; H4
1.690m; 13C: C1 50.657; C2 30.251; C3 13.057.
3. Results and discussion
1
3.1. Pt(amine)2I2
1
trans-[Pt(cpa)2(D2O)2](NO3)2: NMR (d (ppm)): H:
The cis diiodo compounds were synthesized by a
modified DharaÕs method [23,36] from the aqueous reac-
tion of K2[PtI4] with the amine. Compounds with cyclo-
NH 4.879s + d; H1 3.159m; H2 2.165m; H3 1.726; H4
1.595; 13C: C1 54.977; C2 33.257; C3 23.515.
trans-[Pt(cha)2(D2O)2](NO3)2: NMR (d (ppm)):1H:
NH 4.788s + d; H1 2.350m; 13C: C1 54.794; C2 33.773;
C3 24.864; C4 24.575.
propylamine
(cpra),
cyclobutylamine
(cba),
cyclopentylamine (cpa) and cyclohexylamine (cha) were
studied. A slight excess of amine (Pt:amine = 1:2.3) was
used to maximize the yields which varied between 69%
and 85%. The pale yellow precipitate was purified and
characterized by IR and multinuclear NMR
spectroscopies.
2.4. Pt(amine)2(OD)2
cis-Pt(cpra)2(OD)2: NMR (d (ppm)): 1H: H1
2.287m; H2 0.648; H3 0.625m. 13C: C1 29.372; C2
5.846.
The trans compounds were prepared by heating the
tetrasubstituted compound in ethanol.
1
cis-Pt(cba)2(OD)2: NMR (d (ppm)): H: H1 3.307m;
½PtðamineÞ ꢂI2 ! trans ꢀ PtðamineÞ I2 # þ2amine
H2 2.272; H3 1.845; H4 1.611. 13C: C1 51.622; C2
30.297; C3 13.131.
4
2
The intermediate [Pt(amine)4]I2 was synthesized from
the aqueous reaction of K2[PtI4] with a large excess of
amine similarly to KauffmanÕs method [37]. The yields
for trans-Pt(amine)2I2 from K2[PtCl4] (between 56%
and 63%) are lower, since it is difficult to obtain the tet-
rasubstituted compound quantitatively. All the com-
pounds were pure as shown by NMR spectroscopy.
The decomposing points are shown in Section 2. The
cis isomers start to decompose before the trans com-
pounds. The cis compounds were found by DSC to
isomerize to the trans compounds. The isomerization
temperature (temperature at minimum peak height)
1
cis-Pt(cpa)2(OD)2: NMR (d (ppm)): H: H1 3.157m;
H2 2.093m; H3 1.678m; H4 1.550m. 13C: C1 57.769; C2
33.394; C3 23.467.
1
cis-Pt(cha)2(OD)2: NMR (d (ppm)): H: H1 2.332m.
13C: C1 55.128; C2 33.925; C3 25.031; C4 24.621.
trans-Pt(cpra)2(OD)2: NMR (d (ppm)): 1H: H1
2.329m; H2 0.689m; H3 0.664m. 13C: C1 28.172; C2
5.512.
trans-Pt(cba)2(OD)2: NMR (d (ppm)): 1H: H1
3.377m; H2 2.337m; H3 1.919m; H4 1.660m. 13C: C1
50.848; C2 30.313; C3 13.405.

2044
F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
slightly increases with the size of the ring (130° for cpra,
157° for cba and 164° for cpa). The H associated with
the isomerization are ꢀ23, ꢀ33 and ꢀ15 kJ/kg for the
cis the cpra, cba and cpa complexes, respectively.
The IR spectra of the complexes were measured in the
solid state and the main bands are shown in Section 2.
Most cis compounds (C2v symmetry for the squeleton
PtN2I2) have shown two m(Pt–N) vibrations between
505 and 585 cmꢀ1, while the trans analogues (C2h sym-
metry) have shown only one band between 455 and
485 cmꢀ1 as expected from group theory [38]. The
assignments are based on similar data found in the liter-
ature [39–45]. The vibrations in cyclic amines complexes
seem slightly more energetic than those in the aliphatic
amine compounds [23]. Our values on the cis cba and
cpa agree with those reported earlier [39].
The NMR spectra of all the diiodo complexes were
measured in CD3COCD3. Several of these compounds
are soluble in normal chloroform but they decompose
quite rapidly in CDCl3. Similar problems were observed
with CD2Cl2. DMSO reacts rapidly with the compounds
and was rapidly eliminated. DMF reacts more slowly
and isomerization of some of the cis compounds is pos-
sible. Acetone was chosen, since no reaction was ob-
served over a longer period of time, even if it is not a
completely inert solvent. No solvolysis was observed in
acetone for the aliphatic amines system [23]. The cis di-
chloro compounds can isomerize to the trans com-
pounds in acetone, but no isomerization was observed
for the diiodo complexes after one week of standing in
CD3COCD3.
like sulfoxides, which contain empty p* orbitals can ac-
cept electron density from platinum, which reduces the
electron density on the metallic center. For these com-
pounds, the cis isomers are more stable than the trans
compounds, since the p-bonding is much more efficient
in the cis geometry. Pyridines also contains empty p*
orbitals which can form p-bonds with platinum, but to
a much smaller extent. Amines cannot accept p back-
donation and the trans compounds are more stable than
the cis analogues.
Since the chemical shifts of the cis and trans com-
plexes were very similar, we have remeasured the 195Pt
NMR spectra in DMF, where the difference is usually
larger. The results are also presented in Table 1. The
Dd values are slightly larger, ranging between 16 and
38 ppm. The signals were found at lower fields in
DMF than in acetone (ave. 34 ppm for the cis com-
pounds and 18 ppm for the trans isomers). The cis iso-
mers seem to be more influenced by the solvent than
the trans analogues, probably because of greater steric
hindrance around the Pt atom.
In order to verify if the cis complexes could isomerize
in the two solvents, we have remeasured the 195Pt NMR
spectra after two weeks in the refrigerator. In acetone,
cis-Pt(cha)2I2 showed only one signal corresponding to
the cis isomer, while in DMF, two signals were ob-
served. The trans compound was observed in a 13% pro-
portion. Therefore isomerization of the cis diiodo
compounds to the trans isomers occurs in DMF.
The strength of the r(Pt–N) bond should be related
to the basicity of the ligand. The formation of the r
bond (amine ! Pt) should transfer some electron den-
sity from the amine to the platinum atom, resulting in
a shielding on the Pt atom and a deshielding effect on
the ligands (1H and 13C signals). But we have found
no relation between the pKa values [47,48] of the proton-
ated amines and the d(Pt) of the cis or trans complexes.
The pKa values are measured in a solvent (water or alco-
hol) and are influenced by the presence of the substitu-
ents on the protonated N atom. The proton affinity
value, which is measured in the gas phase is probably
a better indicator of basicity, but these values are still
not common in the literature. We have found no corre-
lation between the d(Pt) of the complexes and the pub-
lished proton affinity of the amine.
The 195Pt NMR signals of the cis diiodo compounds
were observed between ꢀ3338 and ꢀ3378 ppm and be-
tween ꢀ3342 and ꢀ3400 for the trans analogues (Table
1). The Dd between the two isomers is very small for the
cpra, cpa and cha complexes (ave. 5 ppm), but slightly
larger for the cba compounds (22 ppm). For the ali-
phatic primary amines complexes, the Dd values were
also quite small [23] contrary to the results reported
for the secondary amine complexes (Me2NH,
Dd ꢃ 180 ppm) and for pyridine [46] derivatives
(Dd ꢃ ꢀ70 ppm), where the cis compounds were ob-
served at higher fields than the trans analogues. Ligands
Table 1
d(195Pt) and Dd = dcis ꢀ dtrans (ppm) of the complexes Pt(amine)2I2
1
The H NMR spectra are shown in Section 2. The
2
amine chemical shifts and the coupling J(195Pt–NH2)
Amine
pKa [47,48]
Solvent
cis
trans
Dd
are shown in Table 2. The chemical shifts of the cis com-
pounds are found at lower fields (between 4.38 and
4.66 ppm) than those of the trans analogues (between
Cpra
8.67
acetone
DMF
ꢀ3353
ꢀ3319
ꢀ3362
ꢀ3344
9
25
Cba
Cpa
Cha
9.34
9.98
9.85
acetone
DMF
ꢀ3378
ꢀ3400
22
38
2
3.89 and 4.16 ppm). The coupling constants J(195Pt–
ꢀ3346
ꢀ3384
NH2) are larger for the cis compounds (ave. 69 Hz) than
for the trans complexes (ave. 60 Hz) as observed for the
aliphatic amines system [23]. The positions of the signals
of the amine protons were plotted versus the pKa of the
protonated amine in order to study the influence of the
acetone
DMF
ꢀ3340
ꢀ3303
ꢀ3343
ꢀ3326
3
23
acetone
DMF
ꢀ3338
ꢀ3342
4
16
ꢀ3307
ꢀ3323

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
2045
Table 2
d(1H) (ppm), 2J(195Pt–1HN) and J(195Pt–C) (Hz) of Pt(amine)2I2 in CD3COCD3
Amine
Cpra
NH
2J(195Pt–NH)
2J(195Pt–C1)
3J(195Pt–C2)
a
cis
4.607
4.098
68
59
n.o.
24
trans
14
19
Cba
Cpa
Cha
cis
4.658
4.480 [39]b
4.164
70
39
trans
cis
61
68
16
17
31
35
4.471
4.340 [39]b
3.959
trans
cis
59
14
18
25
38
4.385
69
64
61
56
4.521 [52]
3.888
4.023 [52]
trans
12
24
a
Hidden by solvent.
In DMF.
b
basicity of the ligands on the chemical shifts. Fig. 1 shows
that there seems to be a shielding effect on the NH2 signals
as the basicity of the protonated amine increases, but the
effect is small, probably close to the experimental errors.
In cyclic amine complexes, the two protons on each
carbon atom are not equivalent. The one on the same
side as the N atom will be more deshielded than the
other. The separation between the two signals will be
larger for the protons closer to the amine group. In gen-
eral, the chemical shifts of the protons on the carbon
atoms are more shielded in the trans complexes than
than for the trans isomers and they are shown in the sup-
plementary material (Table S1). Acetone is not an inert
solvent for amines and these values might not be
significant.
The 13C NMR spectra of the diiodo complexes were
also measured in acetone and the results are shown in
Section 2. In general, the cis compounds are observed
at higher fields than the trans compounds (especially
for C1, the closest to the amine group), which is in agree-
ment with the 195Pt NMR results. A decrease of electron
density on the ligand should be accompanied by an in-
crease of electron density on the Pt atom. Therefore
the cis compounds are less shielded in 195Pt NMR and
more shielded in 13C NMR than the trans analogues.
A study of the correlation between the chemical shifts
(of C1 and C2) and the pKa of the protonated amines
was made and a linear relationship was observed (Figs.
2 and 3). As the basicity of the amine increases, the
3
in the cis geometry. The coupling constants J(195Pt–
H1) could not be calculated, since H1 is a low intensity
multiplet. In the cha compounds, the signals could not
be assigned except for the amine protons and H1.
1
The H NMR spectra of the free amines were mea-
sured in acetone and the Dd (dcomplex ꢀ damine) were cal-
culated. These values are greater for the cis compounds
cis
trans
4.8
cpra
4.6
cba
cpa
4.4
4.2
cha
cba
cpa
cpra
4
cha
9.8
3.8
8.6
8.8
9
9.2
9.4
9.6
10
pKa
Fig. 1. d(NH2) vs. pKa of the protonated amine for the complexes Pt(amine)2I2.

2046
F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
C1
C2
60
cba
cpa
cpa
cha
cha
50
40
30
20
10
0
cba
cpra
cis
8.6
8.8
9
9.2
9.4
9.6
9.8
10
10.2
pKa
Fig. 2. d(C1) and d(C2) vs. pKa of the protonated amine for the complexes cis-Pt(amine)2I2.
P
chemical shifts are observed towards lower field as
expected.
Dd are more negative for the cis isomers than for
the trans compounds, but since acetone is not an inert
solvent for amines, they are probably not significant.
3
The coupling constants J(195Pt–13C2) vary between
35 and 39 Hz for the cis compounds and between 24
and 31 Hz for the trans analogues (Table 2). The
2J(195Pt–13C1) coupling constants are smaller as usually
observed, probably because of inadequate orientation of
the orbitals. The average values are 18 Hz for the cis
complexes and 14 Hz for the trans isomers. These results
show that these coupling constants can be reasonably
used to determine the geometry of such compounds. A
4J(195Pt–13C3) coupling constant of 14 Hz was detected
for cis-Pt(cpa)2I2.
3.2. Pt(amine)2(NO3)2
The dinitrato complexes were prepared by the reac-
tion (in the dark around 5 °C) of the diiodo complexes
with a slight excess (10%) of silver nitrate in acetone,
as reported for aliphatic amines [24].
PtðamineÞ I2 þ 2AgðNO3Þ ! PtðamineÞ ðNO3Þ þ 2AgI #
2
2
2
The 13C NMR spectra of the free amines were also
measured in acetone and the Dd (dcomplex ꢀ damine) were
calculated. These values are all negative and they are
shown in the supplementary material (Table S2). The
The time of reaction varied between 4 and 8 h. cis and
trans compounds with the four cyclic amines were syn-
thesized but the cis cyclopropylamine complex decom-
posed during its isolation. It was also synthesized by
C1
C2
70
cha
cpa
60
50
cba
cpra
cpra
40
30
20
10
0
cha
cpa
cba
trans
8.6
8.8
9
9.2
9.4
pKa
9.6
9.8
10
10.2
Fig. 3. d(C1) and d(C2) vs. pKa of the protonated amine for the complexes trans-Pt(amine)2I2.

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
2047
the reaction of the diiodo compound with silver nitrate
in water, but it also decomposed while being isolated.
The other compounds are stable in air at room temper-
ature, contrary to the aliphatic amine complexes. The
yields varied between 67% and 87%. Their decomposi-
tion points are lower than those of the diiodo analogues
and the cis dinitrato compounds are thermodynamically
less stable than the trans analogues.
and 86 cmꢀ1 for trans). For the compounds cis and
trans-Pt(Ypy)2(NO3)2, the m1 band was also found less
energetic in the trans complexes (ave. Dm1 = 120 versus
90 cmꢀ1 for the cis isomers), suggesting a more covalent
character of the Pt–O bonds in the trans geometry [49].
Our results on the aliphatic amines system seemed to
indicate that the covalency of the Pt–O bonds in the
cis and trans compounds is not very different in the
two isomers [24].
The stretching energy of a more covalent bond
should increase and these results can be compared to
the energies of the m(Pt–O) vibrations. For the cis com-
plexes, two m(Pt–N) and two m(Pt–O) bands are expected
from group theory for the squeleton PtN2O2 (C2v sym-
metry), while one m(Pt–N) and one m(Pt–O) are predicted
The compounds were characterized in the solid state
by IR spectroscopy. The assignments of the main bands
are shown in Section 2 and are based on published work
on similar compounds [38–40,46,49]. The notation of
Nakamoto [38] was used for the bands involving the nit-
rato ligands. The symmetry of the free nitrate ion is D3h,
with a bond order of 113, while in the monodentate coor-
dinated nitrato ligand, the N–O(Pt) bond order is close
to 1. The p electronic density is then delocalized on only
two N–O bonds resulting in a bond order of 112 for the
latter two bonds. The approximate symmetry of coordi-
for the trans analogues [38].
A study on cis-
Pt(NH3)2(NO3)2 has shown that these vibrations are
often coupled with other vibrations [51]. The bands as-
signed to these vibrations are shown in Table 4. For
the m(Pt–O) vibrations, only one band was observed
for the cis and the trans compounds, between 332 and
345 cmꢀ1. The position of the band is not very different
for the different isomers, although it appears slightly lar-
ger for the trans compounds (ave. 343 versus 334 cmꢀ1).
The energy of these vibrations are quite low and close to
the energy of m(Pt–Cl) vibrations, but they are difficult to
assign with certainty, since the intensity of the bands are
weak. They are probably not pure and might couple
with other vibrations. Similar results were reported for
aliphatic amines complexes [24].
The m(Pt–N) bands were assigned based on some pub-
lished works [24,38,40,51,52]. We have observed two
bands for the cis isomers around 520 cmꢀ1 (ms) and
570 cmꢀ1 (mas) and only one for the trans compounds
around 500 cmꢀ1 as expected (Table 4). For the trans
complexes, the energies are slightly higher than those
of the corresponding iodo complexes, suggesting that
the covalency of the Pt–N bonds are greater in the dinit-
rato compounds than in the diiodo analogues. The re-
duced polarizability of the nitrato ligand compared to
the iodo ligand could increase the energy of the m(Pt–
N) vibrations. The trans influence of the iodo ligand is
larger than the one of the nitrato ligand, which could
ꢀ
nated NO3 is C2v. It has been suggested that the posi-
ꢀ
tion of the m1 band (at 1049 cmꢀ1 [38] in free NO3
)
gives important information on the covalent character
of the Pt–O bond [50]. Because of the reduction in sym-
metry of the coordinated nitrato ligand, some of the
vibration modes, which were degenerate in the free
ion, will be split. This is the case for the m3 stretching
mode in D3h(E), which will separate into the m2(A1)
and m4(B2) stretching modes in C2v symmetry [38]. The
energy difference between the two latter modes
(D = m4 ꢀ m2) should also give additional information
on the covalent character of the Pt–O bond [31,50].
For ionic nitrate D = 0 cmꢀ1, while it is 385 cmꢀ1 in
CH3ONO2 a totally covalent compound [31].
The values of D as well as the energy difference (Dm1)
between the m1 band for free nitrate and the coordinated
nitrato ligands are shown in Table 3. The average value
D(m4 ꢀ m2) is 227 cmꢀ1 in the cis complexes and 240 cmꢀ1
in the trans isomers. For the aliphatic amines system
[24], the values were slightly different, 252 cmꢀ1 (cis)
and 238 cmꢀ1 (trans) and for cis and trans-Pt(Ypy)2-
(NO3)2, (Ypy = pyridine derivative) the average values
were closer, 233 cmꢀ1 (cis) and 264 cmꢀ1 (trans) [49].
The position of m1 for our compounds is slightly dif-
ferent in the two geometries (ave. Dm1 71 cmꢀ1 for cis
Table 4
m(Pt–O) and m(Pt–N) for the complexes Pt(amine)2(NO3)2
Table 3
D(m4 ꢀ m2) and Dm1 (cmꢀ1
Amine
m(Pt–O)
m(Pt–N)
)
in the complexes cis and trans-
cis
trans
cis
trans
Pt(amine)2(NO3)2
Cpra
Cba
340
345
342
344
345
346
562
512
507
495
505
Amine
cis-PtL2(NO3)2 trans-PtL2(NO3)2
332
334
335
334
332
330
350
570
565
565
512
520
530
D(m4 ꢀ m2)
Dm1
D(m4 ꢀ m2)
Dm1
Cpa
Cha
Cpra
Cba
Cpa
243
239
239
237
234
84
89
85
87
94
229
231
222
215
73
69
71
64
Cha [52]
Amines (ave) [24]
NH3 [51]
PhCH2NH2 [52]
340
360
514
558
458
461
Cha
Cha [52]

2048
F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
also increase the energy of the m(Pt–N) vibrations in the
cis-dinitrato complexes.
The complexes Pt(amine)2(NO3)2 were characterized
probably due to a reduction in the solvation of the metal
center as the size of the ligand increases.
The d(Pt) values were plotted versus the pKa of the
protonated amines or the proton affinity, but no corre-
lation could be observed. The d(Pt) do not seem to be
very influenced by the basicity of the ligands. Acetone
is not an inert solvent for platinum and solvation
around the Pt atom is probably a more important factor
in determining the 195Pt NMR chemical shifts.
1
by multinuclear (195Pt, H and 13C) magnetic resonance
in acetone. The complexes were pure and are not disso-
ciated in acetone as shown by conductivity
measurements.
The 195Pt chemical shifts of the dinitrato complexes
are listed in Table 5. The nitrato ion is a weak ligand
and its polarizability is smaller than the one of the iodo
ligand. Therefore the Pt d orbital coefficient in Ramsey
equation is larger for the dinitrato complex and the Pt
signals will be observed at much lower field than for
the diiodo compounds. The cis isomers were observed
at higher fields (ave. ꢀ1693 ppm) than their trans ana-
logues (ave. ꢀ1561 ppm). The difference (Dd) between
the cis and trans isomers (ave. ꢀ132 ppm) is much larger
than for the corresponding diiodo compounds.
1
The H NMR chemical shifts are listed in Section 2.
The spectrum of the cha complexes has been published,
but only the –NH2 was reported at 5.521 (cis) and 4.859
(trans) ppm [52]. The NH2 and H1 chemical shifts of all
the cis compounds are more deshielded than the corre-
sponding values for the trans isomers. These results
are in agreement with the d(Pt) values, where the cis
compounds were observed at higher fields than the cor-
responding trans isomers. A larger reduction of electron
density on the ligand in the cis compounds should be
associated with a greater electron density on the plati-
num atom (d(Pt) at higher fields). Therefore the r bonds
seem stronger in the cis compounds than in the trans iso-
mers. A linear relationship was found between the
d(NH2) and d(Pt) as expected for the cis complexes,
but not for the trans isomers. The solvent effect is prob-
ably more important in the trans geometry, where steric
hindrance is reduced and the molecules of solvent can
approach closer to the Pt atom.
The solvent effect is an important factor in these stud-
ies, especially for solvents like water which can coordi-
nate to platinum. The dinitrato complexes were
measured in deuterated acetone, a solvent which could
coordinate to Pt, but not as easily as water. Therefore
the solvent effect should be considerably reduced com-
pared to water, but should not be neglected. For square
planar complexes, the molecules of solvent can normally
approach and weakly bind to the Pt atom on both sides
of the coordination plane. For complexes containing
more bulky ligands close to the binding site, the mole-
cules of solvent cannot approach the Pt atom easily,
resulting in a decrease of the electronic density around
the Pt nucleus. Nitrato ligands are more bulky than iodo
or chloro ligands. Therefore the presence of the nitrato
ligands should have an influence of the solvation of
the Pt atom. There are three studies published in the lit-
erature on dinitrato complexes. For the NH3 dinitrato
[34] complexes, the Dd value is ꢀ179 ppm (in DMF),
for primary aliphatic amines [24], the ave. reported value
is ꢀ125 ppm (in acetone), for secondary amines [24],
Ddave = ꢀ44 ppm (in acetone) and for pyridine deriva-
tives [49], Ddave = ꢀ59 ppm (in CDCl3 or CD2Cl2).
There seems to be a slight shielding effect on the Pt
atom as the size of the ring decreases, at least for the
cis compounds. The cyclohexylamine complexes are ob-
served at slightly lower fields than the others. This is
2
The J(195Pt–1HN) coupling constants are shown in
Table 6. They are larger in the cis configuration, where
the ave. value is 67 Hz compared to 60 Hz (ave.) for
the trans isomers. The average values were found to be
69 Hz (cis) and 60 Hz (trans) for the corresponding dii-
odo complexes. In the dinitrato primary aliphatic
amines, these values were 67 (cis) and 58 (trans) Hz
3
[24]. The J(195Pt–1H) coupling constants usually also
depend on the geometry of the complex. They are diffi-
cult to observe in the cyclic amines system because of the
multiplicity of the signals. But they were observed for
cis-Pt(cpa)2(NO3)2 (42 Hz) and for trans-Pt(cpra)2-
(NO3)2 (27 Hz). For the aliphatic amine compounds,
they ranged between 35 and 47 Hz for the cis complexes
and between 32 and 33 Hz for the trans isomers [24].
1
The H NMR spectra of the free amines were also
measured in acetone and the Dd (dcomplex ꢀ damine) val-
ues calculated (supplementary material, S3) in order to
evaluate the effect of platinum coordination on the li-
gands. All the Dd values for H1 are negative (about
Table 5
d(195Pt), Dd (dcis ꢀ dtrans) (ppm) of the complexes Pt(amine)2(NO3)2
ꢀ0.5 ppm), while for most of the other protons, the val-
P
ues are positive. The total values ( Dd) are smaller for
the trans compounds than the corresponding cis ana-
logues. Again, acetone is probably not an inert solvent
for the amines and these values might not be very
significant.
Amine
cis
trans
Dd
Cpra
Cba
ꢀ1560
ꢀ1572
ꢀ1569
ꢀ1542
ꢀ1570
ꢀ1413
ꢀ1706
ꢀ1690
ꢀ1682
ꢀ1698
ꢀ1592
ꢀ134
ꢀ121
ꢀ140
ꢀ125
ꢀ179
Cpa
Cha
The 13C NMR chemical shifts of the complexes are
also shown in Section 2. A few signals could not be
R-NH2 ave. [24]
NH3 in DMF [34]

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
2049
Table 6
d(1H) (ppm), 2J(195Pt–NH) and J(195Pt–C) (Hz) of Pt(amine)2(NO3)2 in CD3COCD3
Amine
Cpra
Cba
NH
H1
2J(195Pt–NH)
2J(195Pt–C1)
3J(195Pt–C2)
trans
4.909
2.357
62
n.o.
28
cis
trans
5.327
4.988
3.483
3.365
68
60
22
17
29
Cpa
Cha
cis
trans
5.195
4.797
3.276
3.190
68
61
21
16
36
28
cis
5.130
2.514
2.478
66
64
58
56
19
15
35
25
5.521 [52]
4.717
4.859 [52]
trans
detected because they are hidden under the solvent peak.
The C1 and C2 signals are more deshielded in the cis iso-
mers than those of the trans analogues. This is consistent
with the more upfield 195Pt chemical shifts observed for
average values are 21 Hz (cis) and 16 Hz (trans). No
4J(195Pt–13C3) coupling could be detected.
The 13C NMR spectra of the free amines were also
measured in acetone and the Dd (dcomplex ꢀ damine) val-
ues were calculated (supplementary material, Table
1
the cis complexes and with the results obtained in H
NMR. No correlation was found between d(C1) or
d(C2) with d(Pt), but we have found a linear relationship
between d(C1) and the pKa of the protonated amines
(Fig. 4). The deshielding of the C1 signals increases with
an increase in the pKa values. The stronger bases will
cause a greater reduction of electron density on C1 as
expected.
S4). Most of the Dd values for C1 are negative. The total
P
values ( Dd) are smaller for the trans compounds than
for the cis analogues. Again, acetone might not an inert
solvent for the amines and these values are probably not
very important.
3.3. Aquation in acidic medium
Several 2J(195Pt–13C1) and 3J(195Pt–13C2) coupling
constants have been calculated. These are shown in Ta-
ble 6. They are also dependent on the geometry of the
The aquation and hydrolysis reactions of the cis and
trans dinitrato compounds were studied in three differ-
ent conditions of pH, acidic, neutral and basic. When
the cis and trans dinitrato compounds are dissolved in
water or D2O (ꢁ0.03 M, heating in a water bath is re-
quired especially for the trans isomers), the pH of the
solution is acidic (pD = 2.5 to 2.9). In these conditions,
the diaqua species are formed
3
compounds. For J, the average value is 36 Hz for the
cis complexes and 28 Hz for the trans isomers, similar
to the results obtained for the equivalent diiodo com-
plexes. The 2J(195Pt–13C) coupling constants are smaller,
probably because of inadequate orientation of the orbi-
tals [53] as reported for other similar compounds. The
cis
trans
60
cpa
59
58
57
56
55
cpa
cha
cha
cba
54
53
cba
52
9.3
9.4
9.5
9.6
9.7
9.8
9.9
10
pKa
Fig. 4. d(C1) vs. pKa of the protonated amine of the complexes Pt(amine)2(NO3)2.

2050
F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
and the diaqua/monoaqua-mononitrato ratio was
similar.
The 1H NMR chemical shifts of the diaqua com-
PtðamineÞ ðNO3Þ þ 2D2O
2
! ½PtðamineÞ 2ðD2OÞ ꢂðNO3Þ
2
2
2
These D2O solutions were characterized by multinuclear
1
plexes are listed in Section 2 and the d(NH) in Table
8. Although the NH2 protons in the free amines are
not detected in D2O because of fast exchange, they are
usually observed in the complexes. Their NH2 chemical
shifts are at much lower fields for the cis isomers, which
is in agreement with the 195Pt NMR results, where the
cis compounds were observed at higher fields than
the trans isomers. An increase of electron density on the
Pt atom (shielding effect), will correspond to a decrease
of electron density on the ligands (deshielding effect).
Furthermore, the 2J(195Pt–1HN) coupling constants
could be calculated and they are also shown in Table
8. They are larger for the cis isomers, with an average
value of 63 Hz, while it is 57 Hz for the trans complexes.
(
195Pt, H and 13C) magnetic resonance spectroscopy.
The complex cis-Pt(cpra)2(NO3)2 could not be isolated
as mentioned earlier, but its aquation could be studied.
The reaction of the cyclopropylamine diiodo compound
was performed with silver nitrate in D2O and the NMR
spectrum of the resulting solution (after the filtration of
AgI) was measured immediately.
The 195Pt NMR results on the cis and trans diaqua
species are shown in Table 7. The trans diaqua isomers
were observed at much lower fields that the cis ana-
logues. The Dd (dcis ꢀ dtrans) values range between
ꢀ169 and ꢀ206 ppm. For primary aliphatic amines,
these values were very similar (between ꢀ161 and
ꢀ188 ppm) [25]. No correlation was found between the
d(Pt) of the diaqua complexes with the pKa of the pro-
tonated amines or with the size of the amine ring.
For most compounds, only one signal assigned to
the diaqua compound was observed. For two com-
pounds, a second species observed in smaller concen-
tration was detected. This second signal was assigned
to the monoaqua–mononitrato compound, which was
observed for trans-[Pt(cpra)2(D2O)(NO3)]NO3 (in a
15% proportion) and for cis-[Pt(cha)2(D2O)(NO3)]NO3
(14%). These species were observed at slightly higher
fields than the diaqua compounds (ꢃ13 ppm). Mono-
aqua–mononitrato species have been reported for the
cis-diamine system [26] and a few other amines [25]
3
For two compounds, the J(195Pt–1H) coupling con-
stants were calculated. The value is 33 Hz for the cis
cba complex and 26 Hz for the trans isomer. These cou-
pling constants depend on the geometry of the com-
pounds as observed for other similar Pt(II) compounds
[23–25,32,46,49].
1
The H NMR spectra of the free amines were mea-
sured in D2O and the Dd (dcomplex ꢀ damine) calculated.
These values are shown in the supplementary material
(Table S5). These values are not very dependent on the
geometry of the complexes.
For the cis cha monoaqua–mononitrato species, the
signal of the NH2 protons was not observed, but H1
was found at slightly lower field (2.468 ppm) than the
Table 7
d(195Pt) and Dd = dcis ꢀ dtrans (ppm) of the complexes [Pt(amine)2(D2O)2](NO3)2
Amine
cis
trans
Dd
Cpra
Cba
ꢀ1706
ꢀ1537 (ꢀ1549a)
ꢀ1541
ꢀ169
ꢀ1747
ꢀ206
Cpa
Cha
ꢀ1721
ꢀ1536
ꢀ185
ꢀ1711 (ꢀ1724a)
ꢀ1699 ! ꢀ1749
ꢀ1584 ! ꢀ1593
ꢀ1513
ꢀ198
R-NH2 [25,27,28]
NH3 [26,34,53]
ꢀ1515 ! ꢀ1588
ꢀ1374
ꢀ161 ! ꢀ188
ꢀ210
a
[Pt(amine)2(D2O)(NO3)](NO3).
Table 8
d(1H) (ppm), J(195Pt–1H) and J(195Pt–13C) (Hz) of [Pt(amine)2(D2O)2](NO3)2
Amine
Cpra
NH
2J(195Pt–NH)
3J(195Pt–H1)
2J(195Pt–C1)
3J(195Pt–C2)
cis
5.489
4.917
64
17
15
27
22
trans
Cba
Cpa
Cha
cis
5.460
4.939
65
58
33
26
16
13
28
24
trans
cis
5.341
4.879
61
56
16
13
26
21
trans
cis
trans
5.229
4.788
15
11
29
20

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
2051
one of the diaqua compound (2.342 ppm) as expected
from the 195Pt NMR results. No J(195Pt–1H) coupling
could be detected for this species, because of its low
concentration.
Table 9 shows also the Dda (ddiaqua ꢀ ddihydroxo) val-
ues for the cis and trans compounds. For the cis ana-
logues, all the dihydroxo compounds were observed at
lower fields than the cis diaqua compounds with an
average Dda = ꢀ20 ppm, in agreement with the results
on the Pt(NH3)2 system (ꢀ12 ppm, [34]), and the pri-
mary aliphatic amines (ꢀ17 ppm [25,27,28]) as shown
in Table 9. Nevertheless, all the trans dihydroxo com-
pounds were observed at slightly higher fields than the
trans diaqua species (ave. Da = 27 ppm) as observed
for the NH3 (11 ppm) [34] and the aliphatic amine series
(ave. 23 ppm) [25].
The signals of the cis dihydroxo complexes were ob-
served at slightly lower fields than the corresponding
diaqua compounds (Dda is negative). The shielding of
a heavy atom like the 195Pt nucleus has been expressed
in the Ramsey equation, which contains some C terms
representing the metallic coefficients of the platinum d
orbitals. A more covalent bond will result in a decrease
in the C terms and hence a shielding of the 195Pt signals.
D2O is a more polarizable molecule than ODꢀ, leading
to a more covalent Pt–OD2 bond (in the diaqua system)
compared to the Pt–OD bond in the dihydroxo com-
plex. Therefore the diaqua compounds should be ob-
served at higher fields than the dihydroxo complexes,
as observed in the literature cited above and in our cis
diamine complexes.
The 13C NMR chemical shifts are shown in Section 2
and the J(195Pt–13C) coupling constants are listed in
Table 8. The signals of the cis compounds were observed
at lower fields than those of the trans isomers as ex-
pected from the 195Pt NMR results, where the cis com-
pounds were observed at higher fields. Again an
increase of electron density on Pt (shielding effect) will
correspond to a deshielding effect on the ligand as ob-
1
served also in H NMR for the NH2 protons. The 13C
NMR spectra of the free amines were also measured
in D2O and the Dd (dcomplex ꢀ damine) calculated (Table
S6). These values emphasize the fact that the Dd values
are much larger for the cis isomers than for the trans
compounds. No correlation were found between d(Pt)
or the pKa values with the 13C chemical shifts.
2
The coupling constant J(195Pt–13C1) are slightly lar-
ger in the cis configuration (ave. 16 Hz versus 13 Hz).
These values are quite small probably due to inadequate
3
orientation of the orbitals. The J(195Pt–13C) values are
larger in the cis configuration (ave. 28 Hz) than in the
trans geometry (ave. 22 Hz) as observed for other re-
lated compounds.
In the trans series, the reverse was observed. The
trans dihydroxo complexes were observed at higher
fields than the diaqua compounds (Dda is positive).
The solvent effect probably plays a more important role
in the trans geometry, where the bulkiness of the amine
is less important and the molecules of solvent can more
easily approach the Pt atom. It might also be quite dif-
ferent for an ionic complex like [Pt(amine)2(D2O)2]2+
and for a neutral compound like Pt(amine)2(OD)2.
The different conformations of the molecules in solution
might also play an important factor. In the cis geometry,
the different conformations are probably more limited
than in the trans geometry.
3.4. Hydrolysis in basic medium
When the pD of the diaqua complex is raised with
NaOD to 9.6–10.2, the dihydroxo species are formed
ODꢀ
2þ
½PtðamineÞ ðD2OÞ ꢂ ! PtðamineÞ ðODÞ
2
2
2
2
Similarly to the diaqua species, the cis dihydroxo com-
pounds were observed at higher fields (ave.
ꢀ1702 ppm) than the trans analogues (ave.
ꢀ1559 ppm). The average difference between the two
isomers Ddcis–trans is ꢀ143 ppm, slightly lower than the
value found for the diaqua compounds (ꢀ190 ppm).
The pertinent data on dihydroxo complexes found in
the literature are also included in Table 9. Our Dd values
on the cyclic amine compounds are close to the ones re-
ported for the primary aliphatic amines (ave. Ddcis–trans
is ꢀ140 ppm) [25].
No correlations of the d(Pt) of the dihydroxo com-
pounds with the basicity of the amines were detected.
In water, the solvent effect should be the most important
factor, especially since the basicities of the different
amines are not very different.
Table 9
d(Pt), Dd and Dda (ppm) of the complexes Pt(amine)2(OD)2
Amine
cis
trans
Dd
Ddacis
Ddatrans
Cpra
Cba
ꢀ1692
ꢀ1559 (ꢀ1573a)
ꢀ1564
ꢀ133
ꢀ158
ꢀ138
ꢀ144
ꢀ140
ꢀ187
ꢀ14
ꢀ25
ꢀ22
ꢀ17
ꢀ17
ꢀ12
22
23
25
37
23
11
ꢀ1722
Cpa
Cha
ꢀ1699 (ꢀ1712a)
ꢀ1694 (ꢀ1709a)
ꢀ1708
ꢀ1561
ꢀ1550
R-NH2 (ave) [25]
NH3 [34]
ꢀ1570
ꢀ1572
ꢀ1385
a
Pt(amine)2(OD)(NO3).

2052
F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
The 195Pt NMR spectra of these solutions have
3.5. Study of the cis complexes in neutral pH
shown the presence of a single signal, except for the
cis cpa (12%) and cha (9%) and the trans cpra (11%)
complexes, which showed a second weaker signal at
slightly higher fields (13–14 ppm) than the dihydroxo
species (Table 9). It was assigned to the presence of
the complex Pt(amine)2(OD)(NO3). This species was re-
ported in the literature only for trans-Pt(EtNH2)2(OD)-
(NO3) [25].
The pD of the fresh diaqua species were adjusted to
about 7 with NaOD (0.4 M). The study on the cis com-
pounds at neutral pD was made only by Pt NMR spec-
troscopy since several species were detected. The 195Pt
NMR spectra of these fresh solutions were recorded
immediately. The results are shown in Table 11 with
the proportion of each species. The percentage values
are very approximate. Our assignments for the different
signals are based on the results published in the litera-
ture, especially for the cis-Pt(NH3)2 system [26,34] and
the aliphatic amine complexes [25,27,28].
For all the cis complexes, the NMR spectra have
shown the presence of between two and four species in
solution. For all the amines, the signal observed at high-
est field (between ꢀ1693 and ꢀ1733 ppm) was assigned
to the monoaqua–monohydroxo complex, cis-[Pt(ami-
ne)2(D2O)(OD)]+, which was found close to the chemi-
cal shifts of the diaqua and the dihydroxo species. In
fresh solutions, the proportion of this species varies be-
tween 30% and 65%. No correlation could be found be-
tween the 195Pt chemical shifts of these species with
either the pKa of the protonated amines or the proton
affinity.
The proton NMR signals of the dihydroxo species are
shown in Section 2. The NH2 signals are not observed in
basic pH. The proton chemical shifts of the trans iso-
mers were observed at lower fields than those of the
cis compounds. The Dd (dcomplex ꢀ damine) values are lar-
ger for the trans compounds (Table S7). A few coupling
3
constants J(195Pt–H) and are shown in Table 10. They
seem larger in the cis compound (33 Hz) than in the
trans isomers (26 Hz).
The 13C NMR chemical shifts are listed in Section 2
and the coupling constants J(195Pt–13C) are shown in
Table 10. For C1, the signals in the cis compounds were
observed at lower fields than in the trans compounds
are expected from the Pt NMR results. The Dd
(dcomplex ꢀ damine) values are larger for the trans com-
pounds than in the cis isomers. These values are shown
in the supplementary material (Table S8). Again the
J(195Pt–13C) are larger in the cis configuration (Table 10).
The signal observed at lowest field (ave. ꢀ1346 ppm)
was assigned to the dihydroxo-bridged dimers
Table 10
d(1H1) (ppm), J(195Pt–1H1) and J(195Pt–13C1) (Hz) of Pt(amine)2(OD)2
Amine
Cpra
H1
3J(195Pt–H1)
2J(195Pt–C1)
3J(195Pt–C2)
cis
trans
2.287
2.329
16
13
28
20
25
Cba
Cpa
Cha
cis
trans
3.307
3.377
33
27
18
14
25
20
cis
3.157
3.224
15
12
26
21
trans
cis
2.332
2.395
16
12
26
22
trans
Table 11
d(Pt) (ppm) of the species observed in neutral pH for cis-Pt(amine)2(NO3)2
Amine
Cpra
[PtL2(D2O)(OD)]+
Monohydroxo-bridged dimer
Dihydroxo-bridged dimer
Trimer
Dd1
Dd2
ꢀ1694 (60%)
ꢀ1308 (40%)
398
ꢀ1695 (30%)a
ꢀ1307 (70%)a
Cba
Cpa
ꢀ1733 (35%)
ꢀ1732 (15%)b
ꢀ1672 (15%)
ꢀ1672 (25%)b
ꢀ1349 (50%)
ꢀ1350 (60%)b
75
399
371
ꢀ1704 (65%)
ꢀ1350 (35%)
ꢀ1705 (30%)a
ꢀ1350 (70%)a
Cha
NH3 [34]
R-NH2 (ave) [25,27,28]
ꢀ1693 (30%)
ꢀ1590
ꢀ1619 (15%)
ꢀ1547
ꢀ1375 (25%)
ꢀ1161
ꢀ1566 (35%)
ꢀ1510
92
42
41
336
428
375
ꢀ1723
ꢀ1682
ꢀ1348
ꢀ1623
a
After 1 week.
After 2 weeks.
b

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
2053
cis-[Pt(amine)2(l-OD)2Pt(amine)2]2+ (Scheme 1), which
was observed at 376 ppm (ave.) from the diaqua
compounds. The value Dd2 in Table 11 corresponds to
ddihydroxo-bridged dimer ꢀ ddiaqua. These results are in agree-
ment with those reported for a few similar studies [25–
28]. In the cis-Pt(aliphatic amine)2 system, this dimer
was observed at 375 ppm (ave.) from the diaqua com-
plex [25]. The crystal structures of several compounds
of this type have been published [10–14,30]. The signals
for these species are found at much lower fields than the
other compounds, because of the important strain inside
the four-membered ring. In fresh solutions, the propor-
tion of this species varies between 25% and 50%.
A fourth signal was observed for the cha complex at
ꢀ1566 ppm (35%). It was assigned to the presence of tri-
mers [(Pt(amine)2(l-OD))3]3+, which have been reported
for the ligands NH3 [26,54], ethylenediamine and its
methyl derivatives [30], diaminocyclohexane [33] and a
few aliphatic amines [27,28]. No hydroxo-bridged tetra-
mers could be detected in this study. The structure of a
cyclic hydroxo-bridged tetramer was reported with eth-
ylenediamine [55]. These oligomeric species are usually
formed after a longer time in solution.
The 195Pt NMR spectrum of the cpra and cpa com-
plexes was remeasured after one week. The same two
signals were observed, but the intensity of the mono-
mer decreased to 30% and the one of the dihydroxo-
bridged dimer increased to 70% (Table 11). The cba
solution was also remeasured after standing in the
refrigerator for two weeks. Three species were again
detected. The concentration of the monomers had de-
creased from 35% to 15%, the monohydroxo-bridged
dimer increased from 15% to 25%, while the concentra-
tion of the dihydroxo-bridged dimer also increased
from 50% to 60%.
A third signal observed in fresh solutions of the cis
cba and cha compounds at ꢀ1646 ppm (ave.) was as-
signed to the monohydroxo-bridged dimer cis-[Pt(ami-
ne)2(D2O)(l-OD)Pt(amine)2(OD)]2+ (Scheme 1), which
is probably in equilibrium with its diaqua cis-[Pt(ami-
ne)2(D2O)(l-OD)Pt(amine)2(D2O)]3+ and its dihydroxo
analogues. The monohydroxo-bridged dimer was found
at lower field (ave. 84 ppm) than the cis-[Pt(amine)2-
(D2O)2]2+ species. The difference Dd1 in Table 11 corre-
sponds to dmonohydroxo-bridged dimer ꢀ ddiaqua. This dimer
These preliminary results on the changes of these
solutions with time show that the monomer is rapidly
formed and its concentration decreases with time, while
the formation on the monohydroxo-bridged dimer is
much slower. The dihydroxo-bridged dimer is formed
also quite rapidly and its concentration increases with
time. The proportions of the different species depend
has
been
reported
for
cis-[Pt(NH3)2(D2O)(l-
OD)Pt(NH3)2(D2O)]3+, at 47 ppm [26] from the diaqua
monomer cis-[Pt(NH3)2(D2O)2]2+ and for some primary
aliphatic amine complexes at ꢀ1682 ppm (ave.), 32 ppm
from the diaqua species [25,27,28]. In fresh solutions, the
proportion of this dimer is about 15%.
n+
D
+
O
amine
amine
amine
amine
D
amine
O
Pt
Pt
D
Pt
Y
Y
O
amine
D
monohydroxo-bridged dimer
Y = H2O or OH
monoaquamonohydroxo
3+
2+
D
O
D
amine
amine
O
amine
amine
amine
amine
Pt
Pt
Pt
D
Pt
D
O
D
amine
amine
O
O
dihydroxo-bridged dimer
Pt
amine
amine
hydroxo-bridged trimer
Scheme 1. Hydrolyzed species for the cis isomers.

2054
F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
Table 13
d(195Pt) and Dd = dcis ꢀ dtrans (ppm) of the complexes Pt(amine)2Cl2 in
also on the pH, which might vary slightly for the differ-
ent compounds.
DMF-d7
Amine
cis
trans
Dd
3.6. Study of the trans isomers in neutral pH
Cpra
Cba
Cbaa
Cpa
Cpab
Cha
Chab
a
ꢀ2190
ꢀ2211
21
12
ꢀ2225
ꢀ2237
A similar study on the trans complexes was per-
1
ꢀ2226 (60%)
ꢀ2204
ꢀ2237 (40%)
ꢀ2222
formed by 195Pt and H NMR spectroscopy. For all
18
9
compounds, only one 195Pt NMR signal assigned to
the monoaqua–monohydroxo monomers trans-[Pt(ami-
ne)2(D2O)(OD)]+ was observed (Table 12). The ave. va-
lue is ꢀ1549 ppm, an intermediate value between the
diaqua compounds (ave. ꢀ1532 ppm) and the dihydroxo
species (ave. ꢀ1559 ppm). In the literature, the monohy-
droxo-bridged dimer has been suggested for the trans-
Pt(NH3)2 system [34], the trans pyridine compounds
[32] and for the trans aliphatic amine system [25]. This
signal was observed at slightly lower field than the one
of the monomer and it has been suggested that the con-
centration of this species increases with time. We have
remeasured the 195Pt NMR spectrum of the trans cba
compound after six months, but no new species were de-
tected. No oligomeric forms were identified in this work
on the trans complexes with cyclic amines.
ꢀ2203 (25%)
ꢀ2208
ꢀ2222 (75%)
ꢀ2217
ꢀ2208 (35%)
ꢀ2217 (65%)
After 10 days.
b
After 1 week.
NMR spectra of fresh and older DMF solutions. The
cis compounds can isomerize to the trans complexes in
DMF, but the reverse is not true, since the trans isomers
are thermodynamically more stable. Therefore, we be-
lieve that our assignments are now correct.
The 195Pt chemical shifts are shown in Table 13. For
the four cyclic amines, the cis compounds are observed
at slightly lower fields than the trans analogues as ob-
served for the diiodo complexes, but the differences be-
tween the two isomers are smaller. The Dd values vary
between 9 and 21 ppm, while it is between 16 and
38 ppm for the diiodo compounds (in DMF). Fresh
DMF solutions of the dichloro complexes showed the
presence of only one species. The 195Pt NMR spectra
of the cis cpa and cha compounds were remeasured after
one week at about 4 °C. Two signals were then ob-
served. The second peak was assigned to the presence
of the trans isomers, which was detected in about 70%
proportion. The spectrum of the cis cba complex was
remeasured after 10 days at about 4 °C and two signals
were also noted. The sample contained about 60% of the
cis isomer and 40% of the trans compound. Therefore
isomerization of the cis–Pt(amine)2Cl2 complexes to
the trans isomers occurs in DMF. If the solutions are
kept in the cold, the isomerization is quite slow, but it
could be faster with more bulky ligands. In our work,
the isomerization of the complexes with the larger rings
(cpa and cha) seems faster than the one of cis-
Pt(cba)2Cl2.
1
The H NMR spectra were measured and are shown
in Section 2. The amine protons were not detected. No
correlation was found between d(H1) (or others) with
the d(Pt) or the basicity of the amine. The
3J(195Pt–1H1) coupling constant for only the trans cyclo-
propylamine complex was observed. The value of 24 Hz
is similar to those of the trans-diaqua or dihydroxo com-
plexes (ave. 26 Hz).
3.7. Pt NMR study of cis-Pt(amine)2Cl2
During our study on the dicyclic amine complexes,
the dichloro compounds were synthesized and they were
characterized by Pt NMR spectroscopy. Although the
chemical shifts of cis- and trans-Pt(cba)2Cl2 (in DMF)
have been reported in 1993 by our group [39], the assign-
ment for the two different isomers was not certain. The
chemical shifts of the cis and trans cba isomers are very
close (about 10 ppm) and in the past our experimental
error was about 5 ppm. We have more experience
now with the tuning of the probe and the use of the
external references and we have reduced the experimen-
tal errors. Furthermore, we have measured the 195Pt
4. Conclusion
The complexes with cyclic amines cis- and trans-Pt
(amine)2I2 were synthesized and characterized in the so-
lid state and in solution (acetone) by multinuclear (195Pt,
1H and 13C) magnetic resonance spectroscopy. The 195Pt
NMR spectra have shown that the cis isomers are
slightly less shielded than the trans compounds (ave.
Dd = 10 ppm). The difference is larger when the solvent
was DMF (ave. Dd = 26 ppm). The coupling constants
2J(Pt–1HN) and 2,3J(Pt–13C) are larger for the cis com-
pounds than in the trans isomers.
Table 12
d(195Pt)
(ppm)
of
the
hydrolyzed
product
trans-
[Pt(amine)2(OD)(OD2)]+
Amine
d(195Pt)
Dd1
Dd2
H1
Cpra
Cba
ꢀ1548
ꢀ1551
ꢀ1556
ꢀ1539
ꢀ1377
ꢀ1556
11
13
6
ꢀ11
ꢀ10
ꢀ19
ꢀ16
2.330
3.395
3.207
2.364
Cpa
Cha
11
NH3 [34]
R-NH2 (ave. [25])

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 358 (2005) 2040–2056
2055
The diiodo complexes were reacted with AgNO3 to
produce cis- and trans-Pt(amine)2(NO3)2, which were
similarly characterized. The dinitrato compounds are
stable in air except cis-Pt(cyclopropylamine)2(NO3)2
which could not be isolated. The cis dinitrato complexes
were observed at much higher fields in 195Pt NMR than
the trans isomers with an average Dd of 132 ppm. The
coupling constants 2J(Pt–1HN) and 2,3J(Pt–13C) are lar-
ger for the cis compounds than for the trans isomers.
When the complexes cis- and trans-Pt(amine)2(NO3)2
are dissolved in D2O, the pD is acidic and the main
product is the diaqua complexes. For a few cyclic
amines, the monoaqua–mononitrato species were de-
tected in a proportion of about 14%, at slightly higher
fields than the diaqua species. In 195Pt NMR, the cis-
[Pt(amine)2(D2O)2]2+ were observed at higher fields than
the corresponding trans isomers with an average Dd of
190 ppm. Again, the coupling constants 2,3J(Pt–1H)
and 2,3J(Pt–13C) are larger for the cis compounds than
for the trans isomers. The cis diaqua compounds were
observed at slightly higher fields than the corresponding
dinitrato complexes, while the trans diaqua compounds
were found at slightly lower fields than the correspond-
ing dinitrato complexes. In fact, it is difficult to compare
these values, since the dinitrato compounds were mea-
sured in acetone, while the diaqua species were mea-
sured in water. The solvent effect is very important in
195Pt NMR, where the solvent molecules can approach
the Pt atom on both sides of the planar molecules and
cause a shift towards higher fields. The solvation is
probably more important in the trans compounds than
in the cis complexes, where steric hindrance is more
important in the cis geometry, especially with ligands
like cyclic amines, which take lots of space on both sides
of the Pt plane. The effect is much greater in a solvent
like water and usually the chemical shifts are more
shielded in water than in an organic solvent (around
50 ppm).
ture [34]. For complexes of the type Pt(amine)2X2, the
DE difference will be larger when the two ligands
(amines and X) are far from each other in the trans
influence series [57]. The trans influence difference be-
tween amine and aqua ligands is quite large [58], result-
ing in a much lower shielding for the trans complexes
than for the cis isomers (Dd(Pt) ꢁ 190 ppm). The same
is true for the diamine dihydroxo complexes, although
the difference is slightly smaller (Dd(Pt) ꢁ 143 ppm).
This might suggest that the trans influence of the hy-
droxo ligand is closer to the one of amines than the
aqua ligand.
At neutral pH, the behavior of the cis compounds is
very different from the one of the trans complexes. The
trans isomers produced a single species, trans-[Pt(ami-
ne)2(OD)(D2O)]+ which was observed between the dia-
qua and the dihydroxo complexes. No oligomers were
detected even after six months. For the cis isomers, be-
tween two and four different signals were observed.
The highest field signal was assigned to the monomer
cis-[Pt(amine)2(OD)(D2O)]+, while the lowest field signal
was assigned to the dihydroxo-bridged dimer, cis-[Pt(a-
mine)2(l-OD)2Pt(amine)2]2+. These two species were
observed for all the four cyclic amines. The dihydroxo-
bridged dimers are observed at much lower fields, be-
cause of the strain around the Pt atom, caused by the
presence of the 4-membered ring. For cyclobutylamine
and cyclohexylamine, the monohydroxo-bridged com-
pound cis-[Pt(amine)2(D2O)(l-OD)Pt(amine)2(OD)]2+
was observed. For cyclohexylamine, a fourth signal as-
signed to the trimer [(Pt(amine)2(l-OD))3]3+ was de-
tected. The concentration of each species varied with
time. The presence of the monoaqua-monohydroxo
compound is important in fresh solutions and its con-
centration decreases with time, while the proportion of
the dimers increased. No cyclic tetramers could be de-
tected as observed in the ethylenediamine system [55].
A more systematic study of the different species present
in solution as a function of time might show the presence
of these species in small concentration after a longer per-
iod of time.
In basic pH, hydrolysis occurs and the dihydroxo
compounds are formed. The monohydroxo–mononit-
rato compound was detected (ꢃ11%) for a few cis and
trans complexes at slightly higher fields. In 195Pt
NMR, the compounds cis-Pt(amine)2(OD)2 were found
at lower fields than the diaqua analogues (ave.
Dd = 20 ppm), while the reverse was observed for the
trans compounds. The complexes trans-Pt(amine)2(OD)2
were found at higher field than their diaqua analogues
(ave. Dd = 24 ppm). Here the different charges on the
complexes might play an important role in the solvation
of the different species.
Acknowledgements
The authors are grateful to the Natural Sciences and
Engineering Research Council of Canada for financial
support of the project.
In 195Pt NMR spectroscopy, the cis diaqua and
dihydroxo complexes were observed at higher fields
than the trans analogues. The difference in d(Pt) be-
tween the cis and the trans compounds might also be
due to differences in the DE values for the two isomers
in the Ramsey equation [56] as suggested in the litera-
Appendix A. Supplementary material
The supplementary tables S1 to S8 are available from
the authors. Supplementary data associated with this
article can be found, in the online version, at
doi:10.1016/j.ica.2004.12.030.

2056
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