Studies of mononuclear and dinuclear complexes of dibromodimethylplatinum(IV): Preparation, characterization and crystal structures

Article abstract of DOI:10.1016/j.ica.2008.06.025

A number of complexes of the types [PtBr₂Me₂(N^{frown}N)] (N^{frown}N = 4,4′-di-Me-2,2′-bpy (1); 4,4′-di-t-Bu-2,2′-bpy (2); 2,2′-bpz (3); bpym (4)) and [PtBr₂Me₂(L)₂] (L = H-pz (5)

Full text of DOI:10.1016/j.ica.2008.06.025

Inorganica Chimica Acta 362 (2009) 1323–1332
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Inorganica Chimica Acta
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Studies of mononuclear and dinuclear complexes of dibromodimethylplatinum(IV):
Preparation, characterization and crystal structures
Mairéad E. Kelly a, Santiago Gómez-Ruiz b, Ralph Kluge a, Kurt Merzweiler a, Dirk Steinborn a,
Christoph Wagner a, Harry Schmidt a,
*
a Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Kurt-Mothes-Str. 2, 06120 Halle, Germany
b Departamento de Química Inorgánica y Analítica, Universidad Rey Juan Carlos, Móstoles 28933, Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
A number of complexes of the types [PtBr2Me2(N_N)] (N_N = 4,40-di-Me-2,20-bpy (1); 4,40-di-t-Bu-2,20-
bpy (2); 2,20-bpz (3); bpym (4)) and [PtBr2Me2(L)2] (L = H-pz (5); 4-Me-H-pz (6); H-idz (7); H-im (8);
H-bim (9); quaz (10)) are reported. Characterization by NMR (1H, 13C and 195Pt), IR and EI-MS is given.
In addition, crystal structures of several of these complexes are described. Furthermore, interactions
Article history:
Received 5 February 2008
Received in revised form 16 June 2008
Accepted 20 June 2008
Available online 27 June 2008
within these structures including intramolecular hydrogen bonding and
reported. The reactivity of selected mononuclear complexes was investigated and yielded two dinuclear
complexes [PPh4][(PtBrMe2)2( -Br)( -pz)2] (11) and [(PtBr2Me2)2( -bpym)] (12), respectively. The latter
p–p stacking interactions are
Keywords:
l
l
l
Dibromodimethylplatinum(IV)
Dinuclear complexes
X-ray crystal structures
N-donor heterocyclic ligands
complex is accompanied by a solid-state structure. Finally, the thermal stability of all complexes is
reported.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
characterization of a second dinuclear complex, a neutral bipyrim-
idine bridged complex with two dibromodimethylplatinum(IV)
A goal of our work was the preparation of multinuclear plati-
num(IV) complexes. As part of our investigations, we prepared a
number of mononuclear complexes incorporating the PtBr2Me2
moiety. Ligand exchange reactions of platinum(IV) complexes,
either organometallic or inorganic, with nitrogen donors generally
result in stable complexes. The ability of such complexes to behave
as antitumor agents has been demonstrated [1]. Organometallic
platinum(IV) complexes obtained from the Pope cluster
([(PtMe3I)4]) and resulting in trimethylplatinum(IV) derivatives
are prevalent in the literature. Complexes of dimethylplatinum(IV)
are relatively sparse owing more than likely to the limited syn-
thetic routes for the preparation of a suitable starting material.
To date the reactivity of the polynuclear complex [(PtBr2Me2)n]
with various donor ligands has been examined [2–4], although
only two solid-state structures containing the PtBr2Me2 moiety in
mononuclear complexes [5,6] and a small number of platinum(IV)
bromo bridged complexes have been reported [7]. The preparation
of dinuclear complexes with bridging pyrazolato ligands, including
numerous group 8–10 organometallic complexes, has been widely
reported [8–13].
centers, is also described. In addition, the preparation and charac-
terization, including several solid-state structures, of several
[PtBr2Me2(N_N)] and [PtBr2Me2(L)2] complexes (N_N is a chelat-
ing bidentate nitrogen donor ligand and L a monodentate nitrogen
donor ligand) is reported here.
2. Results and discussion
2.1. Preparation
Compounds 1–10 were prepared by direct combination of a
stoichiometric amount of the respective ligand with [(PtBr2Me2)n]
as shown in Scheme 1, path A and B. The syntheses are similar to
procedures described for complexes with chelating nitrogen donor
ligands, such as [PtBr2Me2(2,20-bpy)] [2], or other complexes of the
generic type [PtBr2Me2(L)2], where L is monodentate donor ligand
[14].
The attack of bidentate nitrogen donors (path A) breaks up the
coordination polymer [(PtBr2Me2)n] yielding mononuclear com-
plexes of the type [PtBr2Me2(N_N)] (N_N = 4,40-di-Me-2,20-bpy
(1); 4,40-di-t-Bu-2,20-bpy (2); 2,20-bpz (3); bpym (4)). Similarly,
the reaction of monodentate nitrogen donor ligands with
[(PtBr2Me2)n] (path B) led to complexes of the type [PtBr2Me2(L)2]
where L = pyrazole (H-pz) (5); 4-methyl-pyrazole (4-Me-H-pz) (6);
indazole (H-idz) (7); imidazole (H-im) (8); benzimidazole (H-bim)
(9); quinazoline (quaz) (10). Complexes 1–10 are of moderate
Herein a new member of this series, [PPh4][(PtBrMe2)2(l-Br)(l-
pz)2] (11), and its solid-state structure, the first such dibromodim-
ethylplatinum(IV) dinuclear structure of this type, is reported. The
* Corresponding author. Tel.: +34 5 5525726; fax: +34 5 5527028.
E-mail address: h.schmidt@chemie.uni_halle.de (H. Schmidt).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.06.025

1324
M.E. Kelly et al. / Inorganica Chimica Acta 362 (2009) 1323–1332
Scheme 1.
solubility in common organic solvents (methylene chloride, ace-
tone) are air and moisture stable and were generally obtained in
good to excellent yields, as shown in Table 1.
X-ray diffraction. Dinuclear complexes 11 and 12 were character-
ized by a combination of some of these techniques, as discussed
below. Thermogravimetric monitored decomposition of 1–7 and
9, respectively, generally appears to proceed via reductive elimina-
tion of MeBr. Complex 10 undergoes thermal decomposition with
the initial elimination of Br2. Fig. 1 shows the thermal decomposi-
tion of 7. The percentage mass lost at Tdec (176 °C) approximates to
the mass of MeBr, thus indicating the formation of the platinum(II)
complex [PtBrMe(H-idz)2]. The dinuclear complexes 11 and 12 are
significantly more thermally stable by ca. 40 K than their mononu-
clear starting complexes 5 and 4, respectively. Complex 11 appears
to decompose again with the elimination of MeBr but the mass loss
observed for 12 is consistent with reductive elimination of Br2.
In addition, the homodinuclear complex [PPh4][(PtBrMe2)2(
l-
Br)( -pz)2] (11) was obtained, as illustrated by Scheme 2, on reac-
l
tion of [PtBr2Me2(H-pz)2] (5) with stoichiometric amounts of KOH
and [(PtBr2Me2)n] followed by the addition of [PPh4]Br.
The dinuclear complex [(PtBr2Me2)2(l-bpym)] (12) may be pre-
pared by reacting [PtBr2Me2(bpym)] (4) in chloroform with one
equivalent of [(PtBr2Me2)n], as shown in Scheme 3, or by stirring
[(PtBr2Me2)n] with half an equivalent of the bipyrimidine ligand.
Although complex 8, [PtBr2Me2(H-im)2], was not possible to
isolate in sufficient purity for full characterization the mononu-
clear complexes 1–7, 9, and 10 were characterized by NMR (1H;
13C; 195Pt), EI-MS, IR, elemental analysis and, in some cases, by
2.2. Spectroscopic characterization
2.2.1. Mononuclear complexes 1–10
Table 2 shows selected NMR data for both mononuclear (1–10)
and dinuclear complexes (11 and 12).
Table 1
Summary of complexes isolated, the yield and decomposition temperatures
Since only one set of signals assignable to the methyl ligands
bonded to platinum is present in the respective 1H and 13C NMR
spectra of 1–10, it is clear that both methyl ligands are chemically
equivalent. The magnitudes of the 2JPt,H coupling constant (ca. 70–
73 Hz) and the CH3 chemical shift (1.79–2.21 ppm) indicate the
trans configuration of nitrogen donor ligands to the methyl ligands.
Nr
Complex
Yield (%)
Tdec (°C)
1
2
3
4
5
6
7
8
[PtBr2Me2(4,40-di-Me-2,20-bpy)]
[PtBr2Me2(4,40-di-t-Bu-2,20-bpy)]
[PtBr2Me2(2,20-bpz)]
[PtBr2Me2(bpym)]
[PtBr2Me2(H-pz)2]
[PtBr2Me2(4-Me-H-pz)2]
[PtBr2Me2(H-idz)2]
[PtBr2Me2(H-im)2]
[PtBr2Me2(H-bim)2]
[PtBr2Me2(quaz)2]
[PPh4][(PtBrMe2)2(
73
87
94
61
98
251–254
245–250
198–201
212–216
132–136
127–132
1
74
These findings are paralleled by JPt,C couplings ranging from
100
100a
85
45
56
176–180
501.4–529.9 Hz and Pt–CH3 chemical shifts between ꢀ4.6 and
ꢀ10.8 ppm. The values agree with those reported in the literature
for similar complexes such as [PtBr2Me2(py)2] [3]. Thus, one isomer
is formed in each reaction with the bromo ligands in the ‘‘axial”
positions and the methyl and nitrogen donor ligands mutually
trans configured in the ‘‘equatorial” plane (configuration index:
OC–6–13).
b
9
157–159
160–163
198–200
255–258
10
11
12
l
-Br)(
l-pz)2]
[(PtBr2Me2)2(
l
-bpym)]
100
a
Spectroscopic yield.
Not determined.
b

M.E. Kelly et al. / Inorganica Chimica Acta 362 (2009) 1323–1332
1325
Scheme 2.
Scheme 3.
ven for 1–12 in Table 2. The chemical shift range of the resonances
observed in the 195Pt NMR spectra of 1–10 between ꢀ2668 and
ꢀ2308 ppm is consistent with values found for similarly config-
ured platinum(IV) complexes [3]. The 195Pt NMR spectra of 1–4
([PtBr2Me2(N_N)]) have dPt values between ꢀ2668 and
ꢀ2550 ppm, relative to a H2[PtCl6] standard in D2O (d 0 ppm). On
the other hand, 5–10 ([PtBr2Me2(L)2]) have shifts at lower field
with dPt varying between ꢀ2458 and ꢀ2308 ppm. This may be
attributed to the ‘‘chelate ring effect” in 1–4 which results in an in-
creased shielding of the platinum relative to similar complexes
without chelate ligands [15,16].
EI-MS was possible for 1–7. In general the formation of the
molecular cationic radical is followed by fragmentation proceeding
mainly via successive reductive elimination (neutral loss) of two
MeBr. The distinctive isotopic pattern concurring with the pres-
ence of the PtBr2Me2 core and the corresponding ligand is found
for the molecular cationic radical of each respective complex, as
listed in Section 4.
Fig. 1. Thermal decomposition of
7 as given by the thermogravimetric and
differential thermogravimetric curves.
2.2.2. Dinuclear complexes 11 and 12
Both the 1H and 13C NMR spectra of [PPh4][(PtBrMe2)2(
l
-Br)(
pz)2] (11) are consistent with the formation of one isomer in which
bridging pyrazolato ligands ( -pz) are trans configured to the
l-
The signals arising from the aromatic nitrogen donor ligands of
1–10 have a downfield coordination induced shift of ca. 1 and
5 ppm in the 1H and 13C NMR spectra respectively. A summary of
l
methyl ligands and the bridging bromo ligand is trans configured
the chemical shift data for a-C–H to the coordinating nitrogen is gi-
to the terminal bromo ligands. The upfield shift of the methyl res-
Table 2
Selected 1H, 13C and 195Pt NMR data for mononuclear (1–10) and dinuclear (11 and 12) complexes
a
Complex
Solvent
d(Pt–CH3) (2JPt,H
)
d(Pt–CH3) (1JPt,C
)
Aromatic Pt–N– CH dH; dC
dPt
1
2
3
4
5
6
7
8
CDCl3
CDCl3
CDCl3
(D3C)2NCDO
CDCl3
CDCl3
D3COD
CDCl3
(D3C)2CO
CDCl3
CDCl3
2.11 (70.8)
2.12 (70.6)
2.21 (72.9)
2.20 (72.8)
1.84 (72.4)
1.86 (72.2)
1.79 (70.6)
2.04 (72.6)
2.16 (71.4)
2.21 (71.8)
1.72 (66.6)
2.25 (74.7)
ꢀ6.1 (518.6)
ꢀ6.2 (515.7)
ꢀ4.6a
C6H 8.75; 146.7
C6H 8.74; 146.9
C6H 8.90; 141.2
C6H 9.48; 155.6
C3H 8.18; 139.2
C3H 7.95; 139.2
ꢀ2550
ꢀ2556
ꢀ2668
ꢀ2613
ꢀ2431
ꢀ2417
ꢀ2340
ꢀ2458
ꢀ2308
ꢀ2413
ꢀ2287
ꢀ2618
ꢀ5.9 (529.9)
ꢀ10.4 (504.9)
ꢀ10.8 (501.4)
ꢀ10.8 (506.7)
ꢀ9.6 (502.9)
ꢀ8.1 (517.8)
ꢀ7.8
C3H 8.77; 135.1
b
9
C2H 8.56; 146.0
C4H 9.96b; C2H 9.55b
C3/5H 7.58; 136.8
C4/6H 9.90d
10
11
12c
ꢀ12.6
d
(D3C)2NCDO
Chemical shifts: (ppm); couplings in brackets: (Hz).
a
Not observed.
Assignment of carbon atom not possible.
Data presented are those assigned to 12 in the presence of degradation products (see text).
Solubility insufficient for acquisition.
b
c
d

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M.E. Kelly et al. / Inorganica Chimica Acta 362 (2009) 1323–1332
onance in 1H NMR spectrum by approximately 0.2 ppm relative to
that of 5 and the decrease in magnitude of the 2JPt,H coupling (5/11:
72.4/66.6 Hz) is in accord with values previously reported for
pyrazolato bridged complexes and illustrates the stronger trans
influence of the pyrazolato ligand relative to the neutral pyrazole
ligand [8]. The substantial upfield shift of C4H (5/11: 6.37/
to A2X) verifies the formation of dinuclear 12 with D2h molecular
symmetry in solution. As described above for the mononuclear
1–10, the proton resonances of the ligand are gradually shifted
downfield in going from the free ligand to the chelating mode of
4 to the bridging mode of 12.
Although the low solubility of 12 and the presence of multiple
components in DMF-d7 prevented acquisition of satisfactory 13C
NMR data, it was possible to obtain a spectrum of the mixture in
195Pt NMR. The observation of three signals confirms the presence
of the three platinum species in solution as depicted in Scheme 3,
12: dPt ꢀ2618 ppm; 4: dPt ꢀ2613 ppm; [PtBr2Me2(DMF-d7)2]: dPt
ꢀ1892 ppm. The most highfield shifted resonance assignable to
12 is shifted just 5 ppm relative to the signal of 4, indicating the
similarity of their coordination environment. Negative mode ESI-
MS of 12 in MeOH shows the presence of the anionic methoxy
[M+OCH3]ꢀ adduct. In the positive mode ESI-MS spectrum the so-
dium adduct [M+Na]+ is found. The isotopic patterns emerging in
both modes are satisfactory fits to the expected respective isotopic
patterns (see Section 4). In addition, microanalysis of the powder
isolated from the reaction is consistent with the formation of 12
only.
5.83 ppm) and the equivalence of C3H and C5H (
a-C–H to coordi-
nated nitrogen atoms) in the 1H NMR spectrum of 11 also agree
with the bridging mode of the pyrazolato ligand and Cs molecular
point group symmetry in solution. The same trend in resonance
shift relative to 5 was also observed in 13C NMR spectrum of 11.
In the 195Pt NMR spectrum of 11 the equivalence of the platinum
atoms is verified by the presence of one resonance at dPt
ꢀ2287 ppm, approximately 144 ppm downfield from the signal
observed for 5. The negative mode ESI-MS spectrum of compound
11 shows the presence of the anion [C10H18Br3N4Pt2]ꢀ and the iso-
topic pattern is in good agreement with the calculated pattern for
an anion of this elemental composition, as shown in Fig. 2. The
spectrum in the positive mode shows the tetraphenylphospho-
nium cation.
The complex [(PtBr2Me2)2(l-bpym)] (12) was found to be too
insoluble in most common organic solvents such as methanol,
chloroform and nitromethane to obtain NMR spectra. The 1H
NMR spectrum of the dinuclear 12 in DMF-d7 contains three sets
of signals arising from the dinuclear complex itself (60%) and equal
amounts of each [PtBr2Me2(bpym)] 4 (20%) and [PtBr2Me2(DMF-
d7)2] (20%) which results from solvation of [(PtBr2Me2)n] in DMF-
There is a significant amount of literature dealing with the
assignment of IR spectra of dinuclear complexes with bridging
bipyrimidine ligands [17–19]. The IR spectra of mononuclear 4
and dinuclear 12 show marked differences for the imine C@N
stretching vibration. The spectrum of 4 has two absorptions at
1555 and 1573 cmꢀ1 while the spectrum of 12 contains only one
absorption band assignable to the aromatic imine C@N stretching
vibration at 1576 cmꢀ1, as may be expected for the symmetrical
dinuclear complex 12.
d7 [2]. Scheme
4 illustrates the process yielding 4 and
[PtBr2Me2(DMF-d7)2] from 12 in solution, as monitored by 1H NMR.
Fig. 3 shows the aromatic region of the spectrum in DMF-d7 of
the free ligand (spin system A2X), 4 (ABX) and the dinuclear com-
plex 12 (A2X). The increased symmetry in going from 4 to 12 (ABX
2.3. Single crystal studies
2.3.1. Structures of mononuclear complexes 2, 5–7 and 10
Single crystals suitable for X-ray diffraction analysis were ob-
tained for the mononuclear complexes 2, 5–7 and 10. Selected
bond lengths and angles are given in Table 3.
All these complexes crystallize in discrete molecules with an
approximate octahedral arrangement of the ligator atoms around
the platinum. Complex 2 has molecular point group symmetry Cs
and complexes 6, 7 and 10 have crystallographically imposed C2
symmetry. In accord with the NMR spectroscopic results all com-
plexes exhibit two bromo ligands in mutual trans position and
two methyl ligands trans to the N-donor atoms. Due to the bite
of the bpy ligand in 2 (Fig. 4), the N–Pt–N0 angle (75.2(3)°) is signif-
icantly smaller than 90°. All X–Pt–X0 angles (X, X0 = Br, C, N) be-
tween cis standing ligands in the complexes with monodentately
bound N-donor ligands (Figs. 5 and 6, 5–7 and 10) are between
86.8(6)° and 92.6(1)°.
In complexes 2, 5–7 and 10 the Pt–C bonds (2.035(4)–
2.081(7) Å), the Pt–N bonds (2.170(3)–2.206(9) Å) and the Pt–Br
bonds (2.445(7)–2.47(1) Å) are in the expected range [20]. The an-
gle between the least-square plane of the bpy ligand and the
[PtC2N2] plane in 2 (Fig. 4) is 4.8(2)°. The interplanar angles
tween the least-squares planes of the monodentately bound N-het-
erocyclic ligands and the [PtC2N2] coordination plane are 43.2(3)–
c be-
Fig. 2. Isotopic pattern of [C10H18Br3N4Pt2]ꢀ from the negative mode ESI-MS
spectrum of 11. Calculated intensities are indicated by horizontal lines.
Scheme 4.

M.E. Kelly et al. / Inorganica Chimica Acta 362 (2009) 1323–1332
1327
Fig. 3. Comparison of aromatic region from the 1H NMR spectra of dinuclear 12 (A2X spin system), mononuclear 4 (ABX) and the free bipyrimidine ligand (A2X), all measured
in DMF-d7. *Solvent.
Table 3
Selected bond distances (in Å) and angles (in °) of 2, 5, 6, 7 and 10
2
5
6
7
10
Pt–C
2.081(7)
2.06(1)
2.06(1)
2.19(1)
2.206(9)
2.47(1)
2.453(2)
178.4(5)
179.1(5)
90.9(4)
178.5(1)
79.4(7)
65.9(6)
2.035(4)
2.043(9)
2.042(6)
Pt–N
2.172(6)
2.170(3)
2.452(1)
178.7(2)
2.182(7)
2.457(1)
177.6(3)
2.204(5)
2.445(7)
178.1(2)
Pt–Br
C–Pt–N
2.452(1) 2.450(1)
173.8(3)
N–Pt–N
Br–Pt–Br
ca
75.2(3)
178.1(5)
88.4(2)
179.9(1)
56.9(2)
90.2(3)
178.8(1)
43.2(3)
88.6(2)
177.0(1)
49.1(4)
a
Interplanar angle between the least-squares plane of the monodentately bound aromatic ligand and [PtC2N2] plane.
56.9(2)° for 6, 7 and 10 but 79.4(7)° and 65.9(6)° for 5, as shown in
Table 3. Most of these interplanar angles are in the range reported
for Pt(II) and Pt(IV) complexes having non-bridging non-chelating
six-membered heterocyclic nitrogen donor ligands (median 39.9°;
lower/upper quartile 29.3/45.2°; n = 15; n = number of observa-
tions) [21].
24.7°) are in the range typical for such interactions [24]. Further-
more, the C3–H bonds of these rings interact with the pyrazole rings
bound via N3 of the neighboring molecules in an edge-to-face
Intramolecular N–Hꢁ ꢁ ꢁBr hydrogen bonds (Table 4) in 5 and 6
indicated by Nꢁ ꢁ ꢁBr distances less than the sum of the van der
Waals radii (3.40 Å) were identified [22]. Although the values must
not be overestimated due to calculated hydrogen atom positions
the N–Hꢁ ꢁ ꢁBr angles were also found to be in the expected range
[23].
In crystals of the complexes 5, 7 and 10 weak intermolecular
forces govern the molecular packing. In crystals of 5 the pyrazole
rings bound via N1 of two neighboring molecules are p–p interact-
ing (Fig. 7). The geometrical parameters (interplanar distance:
3.22 Å; centroidꢁ ꢁ ꢁcentroid distance 3.60(1) Å; displacement angle1
1
Displacement angle: Angle between the vector connecting the centroids and
normal to the plane of the ring.
Fig. 4. Molecular structure of 2. Displacement ellipsoids at 30% probability.

1328
M.E. Kelly et al. / Inorganica Chimica Acta 362 (2009) 1323–1332
Fig. 5. Molecular structures of 5 and 6. Displacement ellipsoids at 30% probability.
Fig. 6. Molecular structures of 7 and 10. Displacement ellipsoids at 30% probability.
Table 4
Summary of parameters (distances in Å, angles in °) in crystals of 5–7 indicating weak
hydrogen bonding interactions
Complex
5
Nꢁ ꢁ ꢁBr
N–Hꢁ ꢁ ꢁBra
N2ꢁ ꢁ ꢁBr1
N4ꢁ ꢁ ꢁBr2
N2ꢁ ꢁ ꢁBr
N2ꢁ ꢁ ꢁBr
3.23(1)
3.32(1)
3.30(1)
3.38(1)
N2–Hꢁ ꢁ ꢁBr1
N4–Hꢁ ꢁ ꢁBr2
N2–Hꢁ ꢁ ꢁBr
N2–Hꢁ ꢁ ꢁBr
125
117
113
146
6
7
a
Based on calculated positions of hydrogen atoms.
(C–Hꢁ ꢁ ꢁ
p
type) interaction. The geometrical parameters (C3ꢁ ꢁ ꢁcen-
troid distance 3.460(1) Å; estimate C3–H8ꢁ ꢁ ꢁcentroid angle 155.0°)
are in the expected range [24].
Similarly,
p–p interactions are found between the respective
Fig. 7. Illustration of face-to-edge and
solid-state structure of 5. Displacement ellipsoids at 30% probability.
p–p interaction between molecules in the
aromatic ligands in crystals of 7 and 10, as shown for 7 in
Fig. 8a. Due to a crystallographic inversion center the indazole
(7) and quinazoline (10) rings of neighbored molecules in crystals
of 7/10 are parallel. In crystals of 7 the fused benzene portions
share the most overlap (planeꢁ ꢁ ꢁplane distance 3.49 Å, cen-
troidꢁ ꢁ ꢁcentroid distance 3.67 Å; 18.2°). Quite similar values were
Two methyl ligands, a terminal and a bridging bromo ligand and
two bridging pyrazolato ligands surround each platinum in an
approximate octahedral arrangement. The interplanar angles of
the least-squares planes of the pyrazolato rings to the equatorial
[PtC2N2] planes are between 52.1(5)° and 56.6(5)°. Although the
octahedral arrangement around the Pt2 atom is more distorted
(Br3–Pt2–Br2 177.6(1)°) than the arrangement around Pt1 (C–
Pt1–N 178.9(4)°), no unusual deviation from the expected angles
is observed. The distance between the platinum(IV) centers is
3.593(1) Å, eliminating the possibility of a direct interaction be-
tween them.
found for the
p–p interactions between the fused benzene rings
in crystals of 10 (planeꢁ ꢁ ꢁplane distance 3.49 Å; centroidꢁ ꢁ ꢁcentroid
distance 3.62 Å; displacement angle 15.1°).
Furthermore weak intermolecular N–Hꢁ ꢁ ꢁBr hydrogen bonds
between neighboring molecules were found in crystals of 7
(Fig. 8b). Compared with the aforementioned intramolecular
hydrogen bonds (Table 4) the Nꢁ ꢁ ꢁBr distance of 3.38(1) Å indicates
that the intermolecular hydrogen bonds are weaker than the intra-
molecular ones.
To date only three crystal structures with platinum(IV) bridged
to a second metal center via pyrazolato ligands have been pub-
lished [1d,8]. The Pt–C bond lengths in 11 are comparable with
those found in similar structures [1d,8]. In addition, the Pt–C bond
lengths of 11 are slightly longer than the same bonds in mononu-
clear 5 with pyrazole ligands. This may be correlated with the
2.3.2. Molecular structure of the dinuclear complex 11
The crystal structure of the dinuclear compound 11,
[PPh4][(PtBrMe2)2(l-Br)(l-pz)2], consists of discrete ions. There is
no evidence of unusual interionic interactions. The arrangement
of the anion is illustrated in Fig. 9 and selected bond lengths and
angles are given in Table 5.
2
smaller JPt,H coupling constant found for Pt–CH3 of 11 (66.6 Hz)
relative to that found for 5 (72.4 Hz), indicating the stronger trans

M.E. Kelly et al. / Inorganica Chimica Acta 362 (2009) 1323–1332
1329
Fig. 8.
p–p interactions between parallel indazole ligands (a) and hydrogen bonding (b) within the solid-state structure of 7. Displacement ellipsoids at 30% probability,
hydrogen atoms omitted for clarity.
pared and characterized. The crystal structures of these complexes
illustrated many weak inter- and intramolecular interactions,
which are favourable with such heteroaromatic systems [24]. The
preparation of dinuclear platinum(IV) complexes using mononu-
clear starting complexes was demonstrated by the syntheses of
two homodinuclear platinum(IV) compounds. The neutral
rimidine complex 12, [(PtBr2Me2)2( -bpym)], was characterized
in solution, although it was found to decompose in solvents with
high donor capability. The -pyrazolato complex 11, [PPh4]
[(PtBrMe2)2( -Br)( -pz)2], was characterized both in solution and
l-bipy-
l
l
l
l
by X-ray diffraction, the first solid-state structure of a dimethyl-
platinum(IV) complex of this type.
4. Experimental
4.1. General comments
All reactions were performed under an argon atmosphere using
the standard Schlenk techniques. Reactions were carried out in
dried solvents (CHCl3 over CaH2, MeOH over Mg/NaBH4/Fepc
(H2pc = phthalocyanine) distilled prior to use. 1H and 13C NMR
spectra were recorded on Varian Gemini 2000 (200 and
400 MHz) and Varian Unity 500 (500 MHz) spectrometers. 1H
and 13C NMR chemical shifts are relative to solvent signals: chloro-
form-d1 dH 7.24, dC 77.0; methanol-d4 dH 3.30, dC 49.0; DMF-d7 dH
2.74, dC 30.1 and acetone-d6 dH 2.04, dC 29.8. Assignment of NMR
signals was partially revealed by COSY, HMBC and NOE experi-
ments. 195Pt NMR data are referenced relative to H2[PtCl6] in D2O
(dPt 0). IR spectra were recorded on a Galaxy Mattson 5000 FT-IR
spectrometer using KBr pellets. Microanalyses were performed at
the microanalytical laboratory of Martin-Luther-Universität
Halle-Wittenberg using CHNS-932 (LECO) and Vario EL (Elemen-
taranalysensysteme) elemental analyzers. TG and DTA were pre-
Fig. 9. Molecular structure of [(PtBrMe2)2(l-Br)(l
-pz)2]ꢀ anion in the solid-state
structure of 11. Displacement ellipsoids at 30% probability.
Table 5
Selected angles and bond lengths for 11
Selected bond lengths (Å)
Selected bond angles (°)
Pt1–C
Pt2–C
Pt1–N
Pt2–N
Pt1–Br1/Br2
Pt2–Br3/Br2
2.12(1)/2.13(1)
2.15(1)/2.13(1)
2.167(8)/2.144(9)
2.162(9)/2.162(9)
2.413(1)/2.502(1)
2.405(1)/2.493(1)
C–Pt1–N
C–Pt2–N
N–Pt1–N
N–Pt2–N
Br–Pt1–Br
Br–Pt2–Br
178.9(4)/179.9(4)
179.4(4)/178.3(4)
89.1(3)
88.8(3)
179.2(1)
177.6(1)
influence of the
l-pyrazolato relative to the neutral pyrazole li-
gand, as is expected. The Pt–N as well as the terminal and bridging
Pt–Br bond lengths in 11 show no significant differences from re-
ported bond lengths of these types [7,8,20].
formed on
a STA 449C (Netzsch). Argon was used as the
protective and purge gas (30 ml/min). Samples were heated to
1000 °C at a heating rate of 10 K/min in an Al2O3 crucible. EI–MS
was determined by slow heating of samples to a maximum of
350 °C and an ionisation energy of 70 eV on an AMD 402 (AMD
Intectra GmbH). ESI-MS for 11 and 12 was recorded on a Finnigan
Mat spectrometer LCQ using the following conditions: carrier gas:
3. Summary
A series of platinum(IV) mononuclear complexes with the
PtBr2Me2 moiety and aromatic nitrogen donor ligands were pre-
N2, flow rate: 8 ll/min, spray voltage: 4.1 kV, temperature of the

1330
M.E. Kelly et al. / Inorganica Chimica Acta 362 (2009) 1323–1332
capillary: 150 °C, voltage of the capillary: 34 V. 2,20-Bipyridine and
its derivatives, bipyrimidine, pyrazole, 4-methyl-pyrazole, imidaz-
ole, indazole, benzimidazole, quinazoline and tetraphenylphospho-
nium bromide were used as purchased (Aldrich/Acros). 2,20-
Bipyrazine and [(PtBr2Me2)n] were prepared as described in the lit-
erature [25,3].
d ꢀ4.6 (s, CH3), 141.2 (s, C6H), 145.0 (s, C3H), 147.4 (s, C2), 148.7
(C5H). 195Pt NMR (107 MHz, CDCl3): d ꢀ2668 (s). EI-MS m/z for
([C10H12Br2N4Pt]+Å) 543; found 543; m/z (Intensity calc./found)
for cationic radical [C10H12Br2N4Pt]+Å, %) 540 (35/35), 541 (39/
40), 542 (97/97), 543 (80/79), 544 (100/100), 545 (47/47), 546
(45/45).
4.1.1. General procedure for the synthesis of 1–10
4.1.5. [PtBr2Me2(bpym)] (4)
[(PtBr2Me2)n] (52 mg, 0.14 mmol) and the appropriate ligand
(0.14 mmol) were added to a Schlenk flask. The reagents were al-
lowed to stir under Ar at ambient temperature in CHCl3 (10 ml)
for 24 h or until the reaction mixture became transparent. The yel-
low colored solution was then evaporated to dryness. The residue
was dissolved in a minimum of CHCl3 (ca. 2 ml) and the product
was precipitated on addition of n-pentane (ca. 8 ml). 2 mol equiv-
alents of the ligand were used for 5–10. Deviations from this pro-
cedure are given in each case.
Yellow powder. Yield: 67 mg (61%). Tdec 212–216 °C; Dm 17.5%
(calc. for MeBr). Found: 19.0%. Anal. Calc. for C10H12Br2N4Pt
(543.12): C, 22.11; H, 2.23; N, 10.32. Found: C, 22.00; H, 2.44; N,
9.63%. IR (cmꢀ1):
m 3418 (m), 3048 (w), 2905 (w), 1573 (s), 1555
(s), 1406 (s), 1228 (w), 1100 (w), 1013 (w), 756 (m), 686 (m),
669 (m). 1H NMR (400 MHz, (D3C)2NCDO):
d 2.20 (s+d,
3
2JPt,H = 72.8 Hz, 6H, CH3), 8.25 (t, JH,H = 5.1 Hz, 2H, C5H), 9.47–
9.49 (m, 2H, C6H), 9.51–9.53 (m, 2H, C4H). 13C NMR (125 MHz,
1
(D3C)2NCDO): d ꢀ6.6 (s+d, JPt,C = 529.9 Hz, CH3), 125.8 (s+d,
2
3JPt,C = 10.4 Hz C5H), 155.6 (s+d, JPt,C = 10.4 Hz C6H), 161.3 (s, C2),
4.1.2. [PtBr2Me2(4,40-di-Me-2,20-bpy)] (1)
161.9 (s, C4H). 195Pt NMR (107 MHz, (D3C)2NCDO): d ꢀ2613 (s).
EI-MS calc. m/z for ([C10H12Br2N4Pt]+Å) 544; found 544; m/z (Inten-
sity calc./found) for cationic radical [C10H12Br2N4Pt]+Å, %) 540 (36/
41), 541 (40/43), 542 (98/92), 543 (80/79), 544 (100/100), 545
(45/46), 546 (44/47), 547 (5/12).
Yellow powder. Yield: 69 mg (73%). Tdec 251–254 °C;
Dm 16.7%
(calc. for MeBr). Found: 15.6%. Anal. Calc. for C14H18Br2N2Pt
(569.19): C, 29.54; H, 3.19; N, 4.92. Found: C, 29.30; H, 3.25; N,
4.84%. IR (cmꢀ1):
m 3448 (s), 2964 (w), 2904 (m), 1616 (s), 1487
(w), 1444 (m), 1410 (m), 1248 (w), 1026 (s), 835 (s), 553 (w),
2
521 (w). 1H NMR (400 MHz, CDCl3): d 2.11 (s+d, JPt,H = 70.8 Hz,
4.1.6. [PtBr2Me2(H-pz)2] (5)
6H, PtCH3), 2.59 (s, 6H, C4CH3), 7.47 (d, JH,H = 5.6 Hz, 2H, C3H),
Yellow microcrystalline solid. Yield: 110 mg (98%). Tdec 132–
3
8.03 (s, 2H, C5H), 8.75 (d+dd, JH,H = 5.6 Hz, JPt,H = 11.7 Hz, 2H,
136 °C;
C8H14Br2N4Pt (521.11): C, 18.44; H, 2.71; N, 10.75. Found: C,
19.10; H, 2.88; N, 10.87%. IR (cmꢀ1):
3345 (s), 2907 (s), 1466
Dm 18.2% (calc. for MeBr). Found: 20.5%. Anal. Calc. for
3
3
C6H). 13C NMR (125 MHz, CDCl3): d ꢀ6.1 (s+d, JPt,C = 518.6 Hz,
1
PtCH3), 21.7 (s, C4CH3), 124.2 (s+d, JPt,C = 7.4 Hz, C3H), 127.6 (s+d,
m
3
3JPt,C = 11.8 Hz, C5H), 146.7 (s+d, JPt,C = 13.3 Hz, C6H), 151.2 (s,
(w), 1390 (m), 1357 (s), 1119 (m), 1043 (s), 758 (s), 679 (m),
2
C4CH3), 154.5 (s, C2). 195Pt NMR (107 MHz, CDCl3): d –2550 (s).
EI-MS: calc. m/z for ([C14H18Br2N2Pt]+Å) 570; found 570; m/z (Inten-
sity calc./found) for cationic radical [C14H18Br2N2Pt]+Å, %) 566 (34/
36), 567 (39/34), 568 (96/99), 569 (81/69), 570 (100/100), 571
(47/43), 572 (44/42), 572 (6/7).
581 (m). 1H NMR (400 MHz, CDCl3): d 1.84 (s+d, JPt,H = 72.4 Hz,
2
6H, CH3), 6.37 (m, 2H, C4H), 7.58 (s, 2H, C5H), 8.18 (m, 2H,
C3H), 11.20 (s(br), 2H, N1H); 13C NMR (100 MHz, CDCl3):
d
1
3
ꢀ10.4 (s+d, JPt,C = 504.9, CH3), 106.9 (s+d, JPt,C = 9.7 Hz, C4H),
3
2
129.2 (s+d, JPt,C = 6.5 Hz, C5H), 139.2 (s+d, JPt,C = 11.8 Hz, C3H);
195Pt NMR (107 MHz, CDCl3): d 2431 (s). EI-MS: calc. m/z for
([C8H14Br2N4Pt]+Å) 521; found 521; m/z (Intensity calc./found) for
cationic radical ([C8H14Br2N4Pt]+Å, %) 518 (36/29), 519 (39/46),
520 (98/91), 521 (79/61), 522 (100/100), 523 (43/36), 524 (43/
42).
4.1.3. [PtBr2Me2(4,40-di-t-Bu-2,20-bpy)] (2)
Yellow microcrystalline solid. Yield: 70 mg (87%). Tdec 245–
250 °C;
C20H30Br2N2Pt (653.35): C, 36.77; H, 4.63; N, 4.29. Found: C,
36.45; H, 4.59; N, 4.13%. IR (cmꢀ1):
3438 (s), 2966 (s), 2906 (s),
Dm 13.6% (calc. for MeBr). Found: 14.5%. Anal. Calc. for
m
2361 (s), 2335 (s), 1617 (s), 1551 (w), 1460 (m), 1410 (s), 1261
4.1.7. [PtBr2Me2(4-Me-H-pz)2] (6)
(m), 1092 (s), 1025 (s), 883 (w), 801 (m), 661 (w). 1H NMR
Bright yellow microcrystalline solid from CHCl3/hexane at
(400 MHz, CDCl3):
d
1.44 (s, 18H, C(CH3)3), 2.12 (s+d,
ꢀ18 °C. Yield: 44 mg (74%). Tdec 127–132 °C;
Dm 17.3% (calc. for
MeBr). Found: 18.8%. Anal. Calc. for C10H18Br2N4Pt (549.16): C,
2JPt,H = 70.6 Hz, 6H, PtCH3), 7.50–7.63 (m, 2H, C5H), 8.15 (s, 2H,
C3H), 8.74 (m, 2H, C6H). 13C NMR (125 MHz, CDCl3): d ꢀ6.2 (s+d,
1JPt,C = 515.7 Hz, PtCH3), 30.5 (s, C(CH3)3), 35.5 (s, C(CH3)3), 120.2
21.87; H, 3.30; N, 10.20. Found: C, 22.06; H, 3.45; N, 10.23%. IR
(cmꢀ1):
m 2912 (w), 1475 (w), 1390 (w), 1227 (s), 1168 (s), 1059
3
3
(s+d, JPt,C = 8.8 Hz, C3H), 124.3 (s+d, JPt,C = 13.3 Hz, C5H), 146.9
(s), 999 (s), 966 (m), 821 (w), 657 (s), 543 (m). 1H NMR
2
2
(s+d, JPt,C = 13.3 Hz, C6H), 154.7 (s, C4C(CH3)3), 163.9 (s, C2). 195Pt
(400 MHz, CDCl3): d 1.86 (s+d, JPt,H = 72.2 Hz, 6H, PtCH3), 2.07 (s,
NMR (107 MHz, CDCl3):
d
ꢀ2556 (s). EI-MS: calc. m/z for
6H, C4CH3), 7.33 (s, 2H, C5H), 7.95 (s, 2H, C3H), 11.12 (s(br), 2H,
([C20H30Br2N2Pt]+Å) 654; found 654; m/z (Intensity calc./found) for
cationic radical [C20H30Br2N2Pt]+Å, %) 650 (32/33), 651 (39/36),
652 (93/95), 653 (83/77), 654 (100/100), 655 (51/51), 656 (45/
41), 657 (9/10), 658 (7/8).
N1H). 13C NMR (125 MHz, CDCl3): d ꢀ10.8 (s+d, JPt,C = 501.4 Hz,
1
PtCH3), 8.8 (s, C4CH3), 117.3 (s, C4CH3), 128.2 (s, C5H), 139.2 (s,
C3H). 195Pt NMR (107 MHz, CDCl3): d ꢀ2417 (s). EI-MS: calc. m/z
for ([C8H18Br2N4Pt]+Å) 549; found 549; m/z (Intensity calc./found)
for cationic radical [C10H18Br2N4Pt]–H2)+Å, %) 544 (35/41), 545
(39/47), 546 (97/91), 547 (80/79), 548 (100/100), 549 (45/52),
550 (44/43), 551 (5/10).
4.1.4. [PtBr2Me2(2,20-bpz)] (3)
As in Section 4.1.1. except CHCl3 (50 ml). Filtered the reaction
mixture before precipitating an orange powder from CHCl3/pen-
tane. Yield: 47 mg (94%). Tdec 198–201 °C;
D
m 17.5% (calc. for
4.1.8. [PtBr2Me2(H-idz)2] (7)
MeBr). Found: 15.5%. Anal. Calc. for C10H12Br2N4Pt (543.12): C,
Product isolated directly after removal of solvent, yellow micro-
22.11; H, 2.23; N, 10.32. Found: C, 21.66; H, 2.30; N, 9.83%. IR
crystalline solid. Yield: 112 mg (100%). Tdec 176–180 °C; Dm 15.3%
(calc. for MeBr). Found: 17.2%. Anal. Calc. for C16H18Br2N4Pt
(cmꢀ1):
m
3418 (m), 3050 (w), 2908 (w), 1404 (s), 1308 (w),
1157 (s), 1047 (s), 843 (m), 472 (s). 1H NMR (500 MHz, CDCl3):
(621.23): C, 30.93; H, 2.92; N, 9.02. Found: C, 31.45; H, 3.12; N,
2
d 2.21 (s+d, JPt,H = 72.9 Hz, 6H, CH3), 8.89–8.90 (dd+ddd(br),
9.06%. IR (cmꢀ1):
m
3346 (s), 2910 (s), 1627 (m), 1511 (m), 1355
(s), 1243 (m), 1088 (s), 960 (m), 857 (w), 750 (s), 650 (s), 428
(m), 310 (m). 1H NMR (400 MHz, CDCl3):
2.04 (s+d,
3JH,H = 2.8 Hz, JH,H = 1.4 Hz, 2H, C6H), 9.06 (d, JH,H = 2.8 Hz, 2H,
5
3
3
C5H), 9.70 (d, JH,H = 1.3 Hz, 2H, C3H). 13C NMR (100 MHz, CDCl3):
d

M.E. Kelly et al. / Inorganica Chimica Acta 362 (2009) 1323–1332
1331
2JPt,H = 72.6 Hz, 6H, CH3), 7.18 (m, 2H, C6H), 7.46 (m, 2H, C7/8H),
(125 MHz, CDCl3): d ꢀ12.6 (s, CH3), 103.6 (s, C4H), 116.9 (d,
JP,C = 89.7 Hz, Ph–C), 130.5 (d, JP,C = 12.9 Hz, Ph–C), 134.2 (d,
JP,C = 10.2 Hz, Ph–C), 135.8 (d, JP,C = 2.7 Hz, Ph–C), 136.8 (s(br), C3/
5H). 195Pt NMR (107 MHz, CDCl3): d ꢀ2287 (s). Negative mode
ESI-MS: (CH2Cl2) calc. m/z for [C10H18Br3N4Pt2]ꢀ 824. Found:
[C10H18Br3N4Pt2]ꢀ 824; m/z (Intensity calc./found) for
([C10H18Br3N4Pt2]ꢀ, %) 821 (45/47), 822 (64/66), 823 (97/88), 824
(94/83), 825 (100/100), 826 (70/59), 827 (56/44), 828 (27/17). Po-
sitive mode ESI-MS: (CH2Cl2) calc. m/z for [C24H20P]+ 339. Found:
[C24H20P]+ 339.
3
7.74 (d, JH,H = 8.3 Hz, 2H, C5H), 8.77 (s(br), 2H, C3H), 11.34 (s(br),
2H, N1H). 13C NMR (125 MHz, CDCl3): d ꢀ9.6 (s+d, 1JPt,C = 502.9 Hz,
CH3), 110.2 (s, C6H), 121.5 (s, C4H), 122.3 (s, C5H), 123.1 (s, C3a),
3
135.1 (s+d, JPt,C = 10.7 Hz, C3H), 139.9 (s,
C
7a). 195Pt NMR
(107 MHz, CDCl3):
d
ꢀ2458 (s). EI-MS: calc. m/z for
([C16H18Br2N4Pt]+Å) 622; found 622; m/z (Intensity calc./found) for
cationic radical ([C16H18Br2N4Pt]–H2)+Å, %) 616 (33/36), 617 (39/
40), 618 (95/92), 619 (82/78), 620 (100/100), 621 (49/49), 622
(44/41), 623 (7/10), 624 (8/7).
4.1.9. [PtBr2Me2(H-im)2] (8)
4.1.13. Synthesis of [(PtBr2Me2)2(l-bpym)] (12)
Yellow solid residue. Yield (crude): 18 mg (100%). 1H NMR
[(PtBr2Me2)n] (39 mg, 0.10 mmol) and bipyrimidine (8 mg,
0.05 mmol) were stirred in CHCl3 (3 ml) for 30 h. Alternatively,
[(PtBr2Me2)n] (19 mg, 0.05 mmol) and 4 (28 mg, 0.05 mmol) were
stirred in CHCl3 (3 ml) for 24 h. In either case, the resulting powder
was then filtered and washed with portions of CHCl3 (2 ꢂ 5 ml) and
MeOH (1 ꢂ 10 ml). The dark yellow powder was dried under vac-
2
(400 MHz, CD3OD) 1.79 (s+d, JPt,H = 70.6 Hz, 6H, CH3), 7.04 (s,
2H, CH), 7.41 (s(br), 2H, CH), 8.06 (s(br), CH, CH). 13C NMR
1
(125 MHz, CD3OD) ꢀ10.8 (s+d, JPt,C = 506.7 Hz, CH3), 117.3 (s+d,
JPt,C = 11.7 Hz), 128.5 (s+d, JPt,C = 7.9 Hz), 138.2 (s+d, JPt,C = 17.6 Hz).
195Pt NMR (107 MHz, CD3OD) ꢀ2340 (s).
uum. Yield: 47 mg (100%). Tdec 255–258 °C;
Dm 17.2% (calc. for
4.1.10. [PtBr2Me2(H-bim)2] (9)
Br2). Found: 18.0%. Anal. Calc. for C34H38Br3N4PPt2 (928.07): C,
Bright yellow microcrystalline solid from acetone/pentane at
15.53; H, 1.95; N, 6.04. Found: C, 15.29; H, 2.03; N, 5.50%. IR
ꢀ18 °C. Yield: 94 mg (85%). Tdec 157–159 °C;
D
m 15.3% (calc. for
(cmꢀ1):
m 3443 (m), 3072 (w), 2904 (m), 1576 (s), 1416 (s), 1259
MeBr). Found: 12.8%. Anal. Calc. for C16H18Br2N4Pt (621.23): C,
(w), 1140 (w), 1034 (m), 813 (m), 742 (m), 684 (w). 1H NMR
2
30.93; H, 2.92; N, 9.02. Found: C, 30.85; H, 3.26; N, 8.68%. IR
(400 MHz, (D3C)2NCDO): d 2.25 (s+d, JPt,H = 74.7 Hz, 12H, CH3),
(cmꢀ1):
m
3224 (s), 2979 (w), 2904 (m), 1622 (w), 1504 (s), 1417
8.73 (t, JH,H = 5.4 Hz, 2H, C5H), 9.90 (d, JH,H = 5.4 Hz, 4H, C4/6H);
3
3
(s), 1306 (m), 1254 (s), 968 (w), 740 (s), 442 (m). 1H NMR
signals from 4: d 2.11 (s+d, JPt,H = 72.6 Hz, 6H, CH3), 8.73 (t,
2
2
(400 MHz, (D3C)2CO): d 2.16 (s+d, JPt,H = 71.4 Hz, 6H, CH3), 7.00–
3JH,H = 5.2 Hz, 2H, C5H), 9.47–9.50 (m, 4H, C4/5H); [PtBr2Me2(DMF-
7.04 (m, 2H, C5H), 7.20–7.24 (m, 2H, C6H), 7.60–7.63 (m, 2H,
d7)2] 2.03 (s+d, JPt,H = 79.5 Hz, CH3). 195Pt NMR (107 MHz,
2
C7H), 7.80–7.82 (m, 2H, C4H), 8.56 (s+d, JPt,H = 7.9 Hz, 2H, C2H)
(D3C)2NCDO): d ꢀ1896 (s, [PtBr2Me2(DMF-d7)2]) ꢀ2613 (s, 4),
ꢀ2618 (s, 12). Negative mode ESI-MS: (MeOH) calc. m/z for
[C12H18Br4N4Pt2] 928.08. Found: [C12H18Br4N4Pt2+OCH3]ꢀ 954.8
(954.76); m/z (Intensity calc./found) for [C12H18Br4N4Pt2+OCH3]ꢀ,
%) 957 (72/56), 958 (81/56), 959 (100/100), 960 (85/74), 961 (80/
74), 962 (50/45). Positive mode ESI-MS: (MeOH) Calc. m/z for
[C12H18Br4N4Pt2] 928.07. Found: [C12H18Br4N4Pt2+Na]+ 950.5
(951.06); m/z (Intensity calc./found) for [C12H18Br4N4Pt2+Na]+, %)
947 (28/27), 948 (42/47), 949 (72/73), 950 (81/85), 951 (100/
100), 952 (84/71), 953 (79/39).
3
12.15 (s(br), 2H, N1H). 13C NMR (100 MHz, (D3C)2CO): d ꢀ8.1
1
(s+d, JPt,C = 517.8 Hz, CH3), 113.8 (s, C7H), 121.3 (s, C4H), 123.0 (s,
C5H), 124.4 (s, C6H), 133.9 (s, C7a), 140.7 (s, C3a), 146.0 (s+d,
2JPt,C = 14.9 Hz, C2H). 195Pt NMR (107 MHz, (D3C)2CO): d ꢀ2308 (s).
4.1.11. [PtBr2Me2(quaz)2] (10)
Yellow powder. Yield: 19 mg (45%). Tdec 160–163 °C;
Dm 24.7%
(calc. for Br2). Found: 22.4%. Anal. Calc. for C18H18Br2N4Pt (645.25):
C, 33.51; H, 2.81; N, 8.68. Found: C, 32.74; H, 3.01; N, 8.63%. IR
(cmꢀ1):
m 2975 (w), 2908 (s), 2809 (w), 1621 (s), 1585 (s), 1488
(m), 1378 (s), 1309 (w), 1211 (m), 1155 (s), 1062 (w), 962 (m),
4.2. X-ray crystallography
929 (m), 873 (w), 788 (s), 752 (s), 634 (s), 543 (w), 487 (w). 1H
2
NMR (400 MHz, CDCl3): d 2.21 (s+d, JPt,H = 71.8 Hz, 6H, CH3),
Pink crystals of 2 and yellow crystals of 5 and 7 suitable for X-
ray crystallographic measurements were obtained by slow evapo-
ration of a chloroform solution of the respective complex. Dark
yellow crystals of 6 were obtained by slow evaporation of a
dichloromethane solution of 6. Complex 10 crystallized as small
cube-like yellow crystals by slow evaporation of a chloroform/pen-
tane solution. Yellow cube-like crystals of 11 were obtained by
slow evaporation of a methanol/chloroform solution from the
mother-liquor. Tables 6 and 7 show crystallographic data and
collection parameters.
Intensity data were collected on a STOE-STADI IV at 293(2) K
(2), STOE-IPDS (5, 9, 7, 11) at 220(2) K or on a CCD Oxford Xcal-
ibur S diffractometer (6) at 130(2) K all with Mo K
(k = 0.7103 Å, graphite monochromator). Absorption corrections
for 5, 9, 7 and 11 were made using the IPDS software package
and absorption correction of 2 was made with X-RED32 [26a,b].
7.77 (m, 2H, C7H), 8.02–8.08 (m, 6H, C5/6/8H), 9.55 (s(br), 2H,
3
C2H), 9.96 (s+d, JPt,H = 14.5 Hz, 2H, C4H). 13C NMR (125 MHz,
CDCl3): d ꢀ7.8 (s, CH3), 124.7 (s, C8a), 128.4# (s, CH), 128.4# (s,
CH), 129.3 (s, C7H), 136.7 (s, C5H), 149.8 (s, C4a), 154.5# (s(br),
CH), 161.4# (s(br), CH). 195Pt NMR (107 MHz, CDCl3): d ꢀ2413 (s).
# – not distinguishable by NOE, HMBC or COSY experiments.
4.1.12. Synthesis of [PPh4][(PtBrMe2)2(l-Br)(l-pz)2] (11)
To a transparent solution of 5 (14 mg, 0.02 mmol) in MeOH
(5 ml) 2 equiv. of a solution of KOH in MeOH (1.05 M) were added.
The mixture was stirred for at least 72 h. To this mixture
[(PtBr2Me2)n] (9 mg, 0.02 mmol) was added and the reaction mix-
ture was allowed to stir a further 48 h. To the transparent reaction
mixture at 0 °C, a solution of [PPh4]Br (9 mg, 0.02 mmol) in CHCl3
(1 ml) was added. A yellow precipitate formed, was filtered,
washed with a small portion of ice cold MeOH (3 ml) and dried un-
der vacuum to yield a yellow microcrystalline solid. Yield: 15 mg
a radiation
A semi-empirical correction was made for 6 with SCALE
[26c]. All structures were solved by direct methods with SHELX
3 ABSPACK
-
(56%). Tdec 198–200 °C;
D
m 8.2% (calc. for MeBr). Found: 8.4%. Anal.
97 [27a] and refined using full-matrix least-square routines
against F2 with SHELXL-97 [27b]. Non-hydrogen atoms were re-
fined with anisotropic displacement parameters. Hydrogen atoms
were included in the models by calculating the positions (riding
model) and refined with calculated isotropic displacement
parameters. Illustrations were generated using DIAMOND 3.0 soft-
ware [28].
Calc. for C34H38Br3N4PPt2 (1163.53): C, 35.10; H, 3.29; N, 4.82.
Found: C, 34.16; H, 3.45; N, 4.54%. IR (cmꢀ1):
m 2901 (m), 1437
(m), 1110 (s), 1051 (s), 724 (m), 689 (m), 526 (s). 1H NMR
2
(400 MHz, CDCl3): d 1.72 (s+d, JPt,H = 66.6 Hz, 12H, CH3), 5.83
(s(br), 2H, C4H), 7.42–7.54 (m, 16H, Ph–H), 7.58 (d(br),
3JH,H = 1.9 Hz, 4H, C3/5H), 7.75–7.78 (m, 4H, Ph–H). 13C NMR

1332
M.E. Kelly et al. / Inorganica Chimica Acta 362 (2009) 1323–1332
Table 6
Appendix A. Supplementary material
Crystallographic and data collection parameters for complexes 2, 5 and 6
Complex
2
5
6
CCDC 676492, 676493, 676494, 676495, 676496 and 676497
contain the supplementary crystallographic data for 2, 5, 6, 7, 10
and 11. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/da-
ta_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.ica.2008.06.025.
Empirical formula
Formula weight
Crystal system
Space group
Z
a (Å)
b (Å)
c (Å)
C20H30Br2N2Pt C8H14Br2N4Pt C10H18Br2N4Pt
653.37
orthorhombic triclinic
Cmca
8
13.755(2)
20.249(3)
16.693(1)
90
90
90
521.14
549.19
orthorhombic
Pcca
ꢀ
P1
2
4
7.127(2)
8.138(2)
12.007(3)
85.07(3)
84.01(3)
73.34(3)
662.4(3)
2.613
12.757(1)
8.376(1)
14.085(1)
90
90
90
1505.0(1)
2.424
14.62
a
(°)
b (°)
(°)
V (Å3)
References
c
[1] [a] M.D. Hall, H.R. Mellor, R. Callaghan, T.W. Hambley, J. Med. Chem. 50 (15)
(2007) 3403;
4649.3(9)
1.867
9.48
q
l
(g cmꢀ3
(Mo K
)
[b] L.R. Kelland, G. Abel, M.J. McKeage, M. Jones, P.M. Goddard, M. Valenti, B.A.
Murrer, K.R. Harrap, Cancer Res. 53 (1993) 2581;
a
) (mmꢀ1
)
16.60
476
F(000)
Scan range (°)
Reciprocal lattice segments h, k, l ꢀ8 ? 16
2496
1016
´
[c] R. Lindner, G.N. Kaluderovic, R. Paschke, Ch. Wagner, D. Steinborn,
2.01 < h < 25.97 2.62 < h < 25.89 2.89 < h < 28.27
Polyhedron 27 (2007) 914;
ꢀ8 ? 8
ꢀ9 ? 9
ꢀ14 ? 14
3947
2355
1891
ꢀ16 ? 17
ꢀ10 ? 11
ꢀ18 ? 18
14343
1874
1207
´
´
´
´
[d] G.N. Kaluderovic, D. Miljkovic, M. Momcilovic, V.M. Djinovic, M.M.
Stojkovic´, T.J. Sabor, V. Trajkovic´, Int. J. Cancer 116 (2005) 479.
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Chem. 74 (1996) 2008.
0 ? 24
0 ? 20
4247
2386
1791
Reflections collected
Reflections independent
Observed reflections
[4] J.R. Hall, G.A. Swile, Aust. J. Chem. 24 (1971) 423.
[5] R. Contreas, M. Valderrama, C. Beroggi, D. Boys, Polyhedron 20 (2001) 3127.
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E 63 (8) (2007) m1985.
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325 (1987) 261;
Data/restraints/parameters
2386/0/120
1.108
2355/0/139
1.037
1874/0/80
0.957
Goodness-of-fit on F2
R1, wR2 [I > 2
R1, wR2 (all data)
r(I)]
0.0436, 0.0867 0.0584, 0.1539 0.0215, 0.0404
0.0728, 0.1006 0.0694, 0.1653 0.0415, 0.0464
1.16 and ꢀ1.25 3.09 and ꢀ3.01 2.46 and ꢀ0.95
Largest difference in peak and
[b] A.T. Hutton, B. Shabanzadeh, B.L. Shaw, J. Chem. Soc., Chem. Commun.
(1982) 1345;
[c] C.R. Baar, G.S. Hill, J.J. Vittal, R.J. Puddephatt, Organometallics 17 (1998) 32;
[d] E.W. Abel, A.R. Khan, K. Kite, K.G. Orrell, V. Šik, T.S. Cameron, R. Cordes, J.
Chem. Soc., Chem. Commun. (1979) 713;
hole (e Åꢀ3
)
Tmin/Tmax
0.10/0.20
0.06/0.17
0.45/1.0
[e] W. Massa, G. Baum, B.-S. Seo, J. Lorberth, J. Organomet. Chem. 352 (1988)
415;
[f] P.V. Bernhardt, C. Gallego, M. Martinez, Organometallics 19 (2000) 4862.
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Lamata, J. Ferrer, J. Organomet. Chem. 606 (2000) 197.
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Esteban, S. Troimenko, Inorg. Chem. 35 (1996) 2549.
[10] D. Carmona, J. Ferrer, F.J. Lahoz, L.A. Oro, J. Reyes, M. Esteban, J. Chem. Soc.,
Dalton Trans. (1991) 2811.
[11] G.W. Bushnell, D.O.K. Fjeldsted, S.R. Stobart, M.J. Zaworotko, S.A.R. Knox, K.A.
Macpherson, Organometallics 4 (1985) 1107.
[12] K.A. Beveridge, G.W. Bushnell, S.R. Stobart, J.L. Atwood, M.J. Zaworotko,
Organometallics 2 (1983) 1447.
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(1992) 87.
[14] P. Beagley, E.J. Starr, J. Basca, J.R. Moss, A.T. Hutton, J. Organomet. Chem. 645
(2002) 206.
[15] E.C. Alyea, A. Somogyvari, Magn. Reson. Chem. 24 (1986) 357.
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[17] S. Lanza, Inorg. Chim. Acta 75 (1983) 131.
Table 7
Crystallographic and data collection parameters for complexes 7, 10 and 11
Complex
7
10
11
Empirical formula
Formula weight
Crystal system
Space group
Z
C16H18Br2N4Pt C18H18Br2N4Pt C34H38Br3N4PPt2
621.25
orthorhombic tetragonal
Pbcn
645.27
1163.56
orthorhombic
Pbca
ꢀ
I42d
4
8
8
a (Å)
b (Å)
c (Å)
10.546(2)
9.220(2)
18.391(3)
90
90
90
1788.1(6)
2.308
12.32
1160
16.327(2)
16.327(2)
13.839(2)
90
90
90
3689.4(9)
2.323
11.95
2432
16.656(3)
17.956(4)
24.306(4)
90
90
90
7270(2)
2.126
11.06
a
(°)
b (°)
(°)
V (Å3)
c
q
l
(g cmꢀ3
(Mo K
)
[18] J.D. Scott, R.J. Puddephatt, Organometallics 5 (1986) 1538.
[19] M. Bochmann, G. Wilkinson, G.B. Young, J. Chem. Soc., Dalton Trans. (1980)
1879.
[20] [a] H.C. Clark, G. Ferguson, V.K. Jain, M. Parvez, Organometallics 2 (1983) 806;
[b] R.J. Klingler, J.C. Huffman, J.K. Kochi, J. Am. Chem. Soc. 104 (1982) 2147;
[c] J.T. Burton, R.J. Puddephatt, N.L. Jones, J.A. Ibers, Organometallics 2 (11)
(1983) 1487;
a
) (mmꢀ1
)
F(000)
4368
Scan range (°)
2.93 < h < 25.89 1.93 < h < 26.02 2.07 < h < 26.05
Reciprocal lattice segments h, k, l ꢀ12 ? 12
ꢀ19 ? 19
ꢀ19 ? 17
ꢀ17 ? 17
10073
1794
1594
ꢀ20 ? 20
ꢀ22 ? 22
ꢀ29 ? 28
49385
7119
4860
ꢀ11 ? 11
ꢀ20 ? 22
Reflections collected
Reflections independent
Observed reflections
10414
1704
[d] R.P. Hughes, J.T. Sweetser, M.D. Tawa, A. Williamson, C.D. Incarvito, B.
Rhatigan, A.L. Rheingold, G. Rossi, Organometallics 20 (2001) 3800;
[e] A. Canty, R.T. Honeyman, B.W. Skelton, A.H. White, J. Organomet. Chem.
396 (1990) 105;
1299
Data/restraints/parameters
1704/0/106
1.044
1794/0/116
0.960
7119/0/402
0.947
Goodness-of-fit on F2
[f] K. Hindmarsch, D.A. House, M.M. Turnbull, Inorg. Chim. Acta 257 (1997) 11.
[21] Cambridge Structural Database (CSD), University Chemical Laboratory,
Cambridge, 2006.
R1, wR2 [I > 2
R1, wR2 (all data)
r
(I)]
0.0468, 0.1169 0.0254, 0.0450 0.0496, 0.1104
0.0611, 0.1253 0.0329, 0.0466 0.780, 0.1204
1.80 and ꢀ3.68 0.46 and ꢀ0.55 1.72 and ꢀ2.12
[22] J.E. Huheey, E.A. Keiter, R.L. Keiter, Inorganic Chemistry
– Principles of
Largest difference in peak and
Structure and Reactivity, 4th ed., HarperCollins College Publishers, 1993.
[23] L. Brammer, E.A. Burton, P. Sherwood, Cryst. Growth Des. 1 (2001) 277.
[24] C. Janiak, J. Chem. Soc., Dalton Trans. (2000) 3885.
hole (e Åꢀ3
)
Tmin/Tmax
0.05/0.11
0.15/0.28
0.14/0.26
[25] R.J. Crutchley, A.B.P. Lever, Inorg. Chem. 21 (1982) 2276.
[26] [a] IPDS – Software Package, Stoe & Cie, 1999;
[b] X-RED32, Empirical Absorption Correction, Stoe & Cie, 1996;
[c] SCALE3 ABSPACK: Empirical Absorption Correction, CRYSALIS – Software Package,
Oxford Diffraction Ltd., 2006.
[27] [a] G.M. Sheldrick, SHELXS-97, Program for Crystal Structure Solution Göttingen,
1997;
Acknowledgements
The authors acknowledge Dr. T. Müller for thermogravimetric
analysis, Merck for gifts of chemicals and Deutsche Forschungs-
gemeinschaft for financial support.
[b] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structures,
Göttingen, 1997.
[28] K. Branderburg, Diamond, Release 2, Crystal Impact GbR, Bonn, 1997.