Dinuclear organoplatinum(II)-methyldiphenylphosphine complexes of nicotinic acid

Article abstract of DOI:10.1016/S0022-328X(00)00375-2

The preparation and characterisation of a series of novel, dinuclear organoplatinum(II) complexes of methyldiphenylphosphine, trans-[Pt(PMePh₂)₂(C₅H₄N(CO ₂H))-μ-aryl-Pt(PMePh₂)₂(

Full text of DOI:10.1016/S0022-328X(00)00375-2

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 607 (2000) 222–226
Dinuclear organoplatinum(II)-methyldiphenylphosphine complexes
of nicotinic acid
Michael G. Crisp, Simon M. Pyke, Louis M. Rendina *
Department of Chemistry, The Uni6ersity of Adelaide, Adelaide, SA 5005, Australia
Received 6 March 2000; received in revised form 6 June 2000
Dedicated to Professor M.A. Bennett, FRS, on the occasion of his 65th birthday and in recognition of his outstanding contributions to
organometallic chemistry.
Abstract
The preparation and characterisation of a series of novel, dinuclear organoplatinum(II) complexes of methyldiphenylphosphine,
trans-[Pt(PMePh2)2(C5H4N(CO2H))-m-aryl-Pt(PMePh2)2(C5H4N(CO2H))](OTf)2 (aryl=phenyl, 4,4%-biphenyl, 4,4%%-p-terphenyl, or
4,4%-benzophenone; OTf=triflate), in which nicotinic acid acts a nitrogen-donor ligand are described. The key structural feature
of each complex is the presence of a carboxylic acid group at each end of the molecule. This allows for their association via
intermolecular hydrogen-bonds in low polarity solvents. The complexes are potentially useful tectons (building blocks) for the
construction of metal-containing supramolecular assemblies. © 2000 Published by Elsevier Science S.A. All rights reserved.
Keywords: Dinuclear platinum complex; Hydrogen-bonding; Tecton; Nicotinic acid; Methyldiphenylphosphine
Herein we describe the preparation and characterisa-
tion of a series of novel, dinuclear organoplatinum(II)
complexes of methyldiphenylphosphine which contain
nicotinic acid as a nitrogen-donor ligand at each plat-
inum center. Such complexes are potentially useful
tectons that may allow one to construct discrete,
supramolecular aggregates such as nanoscale cyclic en-
tities in solution. The preparation and solution be-
haviour of related triphenylphosphine complexes has
already been reported elsewhere [7], and the synthesis
of the less sterically-demanding methyldiphenylphos-
phine complexes would allow for a study of the self-as-
sociation properties of the tectons in non-aqueous
solution as a function of phosphine steric bulk.
1. Introduction
The hydrogen bond has long been known to play a
pivotal role in controlling self-assembly processes in
numerous biological and/or organic supramolecular
systems [1]. In contrast, only more recently have major
advances been made in the use of the coordinate-cova-
lent bond for the construction of large molecular
polygons and polyhedra by self-assembly [2].
Combining the coordinate-covalent and hydrogen-
bonding motifs may greatly expand the utility of metal
complexes as tectons (building blocks) in the construc-
tion of large molecular polygons and other types of
supramolecular arrays [3]. In crystal engineering stud-
ies, for example, the hydrogen-bonding motif has been
exploited in the synthesis of network solids that incor-
porate transition metal centres [3,4]. In contrast, there
are few studies that provide evidence for the formation
of discrete, metal-containing supramolecular aggregates
in solution [5,6].
2. Results and discussion
The novel, linear bis(iodo) precursor complexes 1–3
were prepared by an oxidative-addition reaction em-
ploying the platinum(0) precursor Pt(PMePh2)4 and the
diiodo derivatives of benzene, 4,4%-biphenyl, or 4,4%%-p-
terphenyl (Scheme 1). Alternatively, 4,4%-diiodoben-
zophenone was used to afford the bis(iodo) precursor 7
* Corresponding author. Tel.: +61-8-83034269. fax: +61-8-
83034358.
E-mail address: lou.rendina@adelaide.edu.au (L.M. Rendina).
0022-328X/00/$ - see front matter © 2000 Published by Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00375-2

M.G. Crisp et al. / Journal of Organometallic Chemistry 607 (2000) 222–226
223
with a bridging 120° s-aryl ligand (Scheme 2). The
double oxidative-addition methodology that we em-
ployed in the preparation of the bis(iodo) species was
previously reported for the synthesis of the analogous
triphenylphosphine and triethylphosphine complexes
[8]. The resulting bis(iodo) complexes 1–3 and 7 were
then treated with two equivalents of AgOTf in CH2Cl2
solution, leading to the quantitative formation of the
corresponding labile bis(triflato) species [9,10]. Al-
though the triflato complexes could be isolated by
careful evaporation of the solvent, it was more conve-
nient to filter off the AgI precipitate and immediately
proceed with the addition of two equivalents of nico-
tinic acid to afford the target complexes 4–6 and 8 as
off-white solids in high yield and purity (Schemes 1 and
2).
1
The assignment of resonances in the H-NMR spec-
tra of the bis(iodo) complexes 1–3 and 7 was facilitated
by means of 2D-NMR (COSY) experiments. In gen-
eral, one can readily distinguish three sets of aromatic
1
protons in the H-NMR spectra of the bis(iodo) com-
plexes. One set of signals, which appears as a complex
multiplet, is attributed to the phenyl protons of the
Scheme 2.
phosphine ligand. The bridging s-phenyl ligand pro-
tons in 1 appear as a singlet owing to the symmetry of
the complex, whereas for complexes 2, 3 and 7, the
characteristic AA%XX% resonances that appear upfield of
the phenylphosphine multiplet are due to the ortho and
meta protons of the bridging s-aryl ligand. For com-
plexes 1, 2 and 7, the ortho proton signals are flanked
by 195Pt satellites (I=1/2; natural abundance=33.8%)
3
with JPtH=48–55 Hz, which is typical for s-arylplat-
inum(II) complexes [8]. The platinum satellite signals of
3 were obscured by the meta proton resonances, hence
3
the magnitude of JPtH could not be determined for this
1
complex. In the H-NMR spectra of complexes 1-3 and
7, the PꢀMe protons appear as a multiplet centred at l
1.4–2.1, which constitutes the X part of an AMM%X3X3%
spin system (where A=195Pt, M=31P, and X=1H). At
this stage, we are unable to extract reasonable coupling
data from the spectra, but related spin systems have
been reported elsewhere [11], and a theoretical analysis
of spin systems of the type MM%XnXn% (where n=3 and
6) has been described previously by Harris [12].
The 1H-NMR assignments for the nicotinic acid
complexes 4–6 and 8 were confirmed by means of
Scheme 1.

224
M.G. Crisp et al. / Journal of Organometallic Chemistry 607 (2000) 222–226
2D-NMR (COSY) spectroscopy. The assignments of
the bridging aryl ligand and phosphine ligand protons
correspond very closely to those described above for
the bis(iodo) precursors. The pyridyl H2 proton always
appears as a singlet that is shifted downfield owing to
its proximity to the electronegative nitrogen atom. The
H4 and H6 protons appear as doublets (coupled to H5),
with H6 being shifted downfield with respect to H4
owing to its proximity to the nitrogen atom. The H5
resonance was obscured by other aromatic signals. The
CO2H signal appears as a broad singlet and, as ex-
pected, its chemical shift is strongly dependent on tem-
species in their spectra and, instead, the pyridyl ligands
in these complexes were readily lost and peaks corre-
sponding to the resulting species [M−2OTf−2C5H4N-
(CO2H)]2+ were identified. Similar behaviour has also
been observed in the mass spectra of related
triphenylphosphine systems [7].
3. Conclusions
In this work we have demonstrated that a variety of
dinuclear organoplatinum(II) complexes of methyldi-
phenylphosphine with hydrogen-bonding functionality
are readily prepared by a facile oxidative addition
reaction utilising the platinum(0) precursor Pt(PMe-
Ph2)4 and diiodoaryl compounds, followed by exchange
of the coordinated halide with nicotinic acid. The over-
all size of the tecton is governed by the nature of the
bridging s-aryl ligand, whilst the shape of the tecton is
largely dependent on the s-aryl bridging angle, i.e. ca.
120° for the 4,4%-benzophenone ligand, and ca. 180° for
the mono-, bi- and ter-phenyl derivatives. These fea-
tures allow for the construction of a variety of
supramolecular aggregates by self-association in low
polarity solvents. We are currently studying the effect
of phosphine steric bulk on the self-association process
in conjunction with other related species [7], and the
results of this work will be reported elsewhere.
perature and concentration as
a consequence of
intermolecular hydrogen-bonding in low polarity sol-
vents such as CDCl3. At this stage, we cannot rule out
hydrogen-bonding interactions of the complexes with
the triflate ions, although comprehensive NMR titra-
tion studies with the related triphenylphosphine com-
plexes do not support this notion [7]. The presence of
small amounts of water also has a considerable influ-
ence on the chemical shift of the carboxyl proton. For
example, a CD2Cl2 solution of 8 (0.05 mol dm−3, 298
K) gives rise to a hydroxyl resonance at l 5.7 when
special precautions in the drying and handling of the
complex (or solvent) are not observed. If the complex is
dried by means of an azeotropic distillation using tolu-
ene, then the CO2H signal moves to l 9.3. When the
same NMR experiment is performed under strictly
anhydrous conditions, a chemical shift of l 11.7–12.0 is
observed for the carboxyl resonance and its linewidth
narrows considerably.
The 31P{1H}-NMR spectra of all complexes prepared
in this work show the expected singlet flanked by 195Pt
satellite signals, consistent with mutually trans phos-
4. Experimental
1
phine ligands. The magnitude of JPtP (ca. 3000 Hz) for
4.1. General
all complexes falls in the range that is typical for
trans-substituted s-arylplatinum(II) complexes [11]. As
expected, there are only minor differences observed in
All reactions were performed under a N2 atmosphere
using standard Schlenk techniques. All solvents were
carefully dried and purified in the following manner:
CH2Cl2 was distilled from CaH2, and toluene was pre-
dried over CaSO4 followed by distillation from sodium.
Nicotinic acid and Pt(PMePh2)4 were stored in a desic-
cator over P2O5.
1
the magnitude of JPtP upon substitution of the iodo
ligand with the pyridyl group, largely because the
195Ptꢀ31P coupling is predominantly influenced by the
nature of the trans ligand which, for the complexes
prepared in this work, is always a tertiary phosphine.
Despite
the
magnetic
inequivalence
of
the
All 1D- and 2D-NMR spectra were recorded by
methyldiphenylphosphine ligands in complexes 4–6 and
8, which results in a complex multiplet for the PꢀMe
group in the corresponding 1H-NMR spectra (vide
supra), there is no fine structure apparent in the 31P
resonance.
Positive-ion ESI-MS with 6 showed the expected
molecular ion peak for the monomeric dinuclear species
[M−2OTf−2H]+ at m/z 1662. We were unable to
identify peaks that corresponded to any type of non-co-
valent aggregate, even at high concentrations in low
polarity solvents such as 1,2-dichloroethane. Complexes
4, 5 and 8 failed to show any evidence of an intact
means of a Varian Gemini 2000 (1H at 300.10 MHz, 31
P
at 121.50 MHz) spectrometer. Chemical shifts are re-
ported in ppm with respect to TMS reference (1H) or a
sealed external standard of 85% H3PO4 (31P). Electro-
spray Ionisation (ESI) Mass Spectra were obtained with
a Finnegan LCQ mass spectrometer. HPLC grade
methanol was used as the solvent. Elemental analyses
were determined by Chemical and Microanalytical Ser-
vices Pty Ltd, Melbourne (Australia).
Tetrakis(methyldiphenylphosphine)platinum(0) [13]
and 4,4%-diiodobenzophenone [14] were prepared ac-
cording to the literature procedures.

M.G. Crisp et al. / Journal of Organometallic Chemistry 607 (2000) 222–226
225
4.2. Trans-1,4-phenyl-
bis[(iodo)bis(methyldiphenylphosphine)]diplatinum(II) (1)
column of Celite filter-aid. A suspension of nicotinic
acid (0.011 g, 0.086 mmol) in CH2Cl2 (5 ml) was added
to the filtrate, and the mixture was stirred at room
temperature for 1.5 h. A small quantity of unreacted
nicotinic acid was removed by filtration through a pad
of Celite. After evaporation of the filtrate to dryness,
the residue was recrystallised from CH2Cl2–acetone to
1,4-Diiodobenzene (0.064 g, 0.194 mmol) and tetrak-
is(methyldiphenylphosphine)platinum(0) (0.388 g, 0.390
mmol) were placed in a Schlenk flask containing a
magnetic stirring bar and fitted with a reflux condenser.
Toluene (20 ml) was added to the flask, and the mixture
was stirred at 85°C for 24 h. The solvent was removed
in vacuo, and the residue was washed repeatedly with
n-hexane to give 1 as an off-white solid (0.070 g, 24%).
1H-NMR (CDCl3): l 7.61–7.26 (m, 40H, PPh2), 6.53 (s,
1
give 4 as a pale yellow solid (0.064 g, 99%). H-NMR
(CDCl3): l 9.88 (s, 2H, OH), 8.44 (s, 2H, H2), 8.39 (d,
3
3
2H, JHH=5.4 Hz, H6), 7.87 (d, 2H, JHH=7.8 Hz,
H4), 7.60–7.20 (m, 40H, PPh2), 6.97 (m, 6H, H5 and
Ho), 1.70 (m, 12H, PꢀMe). 31P{1H}-NMR (CDCl3): l
8.6 (s, 1JPtP=2855 Hz). Anal. Calc. for
C72H66F6N2O10P4Pt2S2·4CH2Cl2: C, 42.43; H, 3.47; N,
1.30. Found: C, 42.13; H, 3.10; N, 1.62%.
3
4H, JPtH=55 Hz, PtꢀPhꢀPt), 1.37 (m, 12H, PꢀCH3).
31P{1H}-NMR (CDCl3): l 3.9 (s, 1JPPt=2880 Hz).
Anal. Calc. for C58H56I2P4Pt2: C, 45.80; H, 3.71.
Found: C, 45.67; H, 3.70%.
4.6. Trans-4,4%-biphenyl-bis[(nicotinic
acid)bis(methyldiphenylphosphine)]diplatinum(II)
bis(triflate) (5)
4.3. Trans-4,4%-biphenyl-bis[(iodo)-
bis(methyldiphenylphosphine)]diplatinum(II) (2)
The complex was prepared from 2 by a similar
Following a similar procedure to that described in
Section 4.2, 4,4%-diiodobiphenyl and tetrakis(methyl-
diphenylphosphine)platinum(0) were reacted to give 2
procedure to that described in Section 4.5, and it was
1
isolated as a pale yellow solid (yield 64%). H-NMR
1
(CDCl3): l 9.29 (s, 2H, OH), 8.43 (s, 2H, H2), 8.26 (d,
as an off-white solid (yield 63%). H-NMR (CDCl3): l
3
3
3
2H, JHH=6.0 Hz, H6), 7.89 (d, 2H, JHH=6.6 Hz,
7.62–7.24 (m, 40H, PPh2), 6.72 (d, 4H, JHH=8.4 Hz,
3
3
H4), 7.60–7.20 (m, 40H, PPh2), 6.82 (d, 4H, JHH=8.3
3JHPt=48 Hz, Ho), 6.49 (d, 4H, JHH=8.4 Hz, Hm),
Hz, Ho), 6.59 (d, 4H, 3JHH=8.3 Hz, Hm), 1.91 (m, 12H,
1.91 (m, 12H, PꢀCH3). 31P{1H}-NMR (CDCl3): l 4.3
1
1
PꢀCH3). 31P{1H}-NMR (CDCl3): l 9.2 (s, JPtP=2933
(s, JPPt=2929 Hz). Anal. Calc. for C64H60I2P4Pt2: C,
Hz). Anal. Calc. for C78H70F6N2O10P4Pt2S2: C, 49.63;
H, 3.74; N, 1.48. Found: C, 49.83; H, 4.01; N, 1.38%.
48.13; H, 3.79. Found: C, 48.22; H, 3.81%.
4.4. Trans-4,4%%-p-terphenyl-bis[(iodo)-
bis(methyldiphenylphosphine)]diplatinum(II) (3)
4.7. Trans-4,4%%-p-terphenyl-bis[(nicotinic
acid)bis(methyldiphenylphosphine)]diplatinum(II)
bis(triflate) (6)
Following a similar procedure to that described in
Section 4.2, 4,4%%-diiodo-p-terphenyl and tetrakis-
(methyldiphenylphosphine)platinum(0) were reacted to
give 3 as an off-white solid (yield 96%). 1H-NMR
(CDCl3): l 7.51–7.27 (m, 40H, PPh2), 6.84 (d, 4H,
The complex was prepared from 3 by a similar
procedure to that described in Section 4.5, and it was
1
isolated as a pale yellow solid (yield 86%). H-NMR
(CDCl3): l 8.83 (s, 2H, OH), 8.46 (s, 2H, H2), 8.29 (d,
3
3JHH=8.1 Hz, Ho), 6.72 (d, 4H, JHH=8.4, Hm), 2.00
3
3
2H, JHH=4.8, H6), 7.91 (d, 2H, JHH=7.5 Hz, H4),
7.57–7.24 (m, 40H, PPh2), 1.64 (m, 12H, PꢀCH3).
31P{1H}-NMR (CDCl3): l 9.2 (s, 1JPPt=2882 Hz).
ESI-MS: m/z 1662 [M−2OTf−2H]+. Anal. Calc. for
C84H74F6N2O10P4Pt2S2: C, 51.38; H, 3.80; N, 1.43.
Found: C, 51.22; H, 3.75; N, 1.50%.
(m, 12H, PꢀCH3). 31P{1H}-NMR (CDCl3): l 4.3 (s,
1JPPt=2918 Hz). Anal. Calc. for C70H64I2P4Pt2·
0.5CH2Cl2: C, 49.36; H, 3.82. Found: C, 49.19; H,
3.71%.
4.5. Trans-1,4-phenyl-bis[(nicotinic
acid)bis(methyldiphenylphosphine)]diplatinum(II)
bis(triflate) (4)
4.8. Trans-4,4%-benzophenone-bis[(iodo)-
bis(methyldiphenylphosphine)]diplatinum(II) (7)
Trans-1,4-phenyl-bis[(iodo)bis(methyldiphenylphos-
phine)]diplatinum(II) (0.065 g, 0.043 mmol) was sus-
pended in CH2Cl2 (25 ml), and a suspension of AgOTf
(0.021 g, 0.084 mmol) in CH2Cl2 (5 ml) was added to
the flask. The mixture was stirred in the dark for 4 h,
and AgI was removed by filtration through a short
Following a similar procedure to that described in
Section 4.2, 4,4%-diiodobenzophenone and tetrakis-
(methyldiphenylphosphine)platinum(0) were reacted to
give 7 as an off-white solid (yield 96%). 1H-NMR
(CDCl3): l 7.78–7.44 (m, 40H, PPh2), 6.93 (d, 4H,
3
3
3JHH=8.0 Hz, JPtH=54 Hz, Ho), 6.78 (d, 4H, JHH
=

226
M.G. Crisp et al. / Journal of Organometallic Chemistry 607 (2000) 222–226
6.8 Hz, Hm), 2.10 (m, 12H, PꢀCH3). 31P{1H}-NMR
(CDCl3): l 3.9 (1J PtP=2886 Hz). Anal. Calc. for
C65H60I2OP4Pt2: C, 48.04; H, 3.72. Found: C, 47.97; H,
3.61%.
Cao, K. Chen, J. Fan, J. Manna, B. Olenyuk, J.A. Whiteford,
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4.9. Trans-4,4%-benzophenone-bis[(nicotinic
acid)bis(methyldiphenylphosphine)] diplatinum(II)
bis(triflate) (8)
The complex was prepared from 7 by a similar
procedure to that described in Section 4.5, and it was
1
isolated as a pale yellow solid (yield 97%). H-NMR
3
(CDCl3): l 9.29 (s, 2H, OH), 8.86 (d, 2H, JHH=4.2
3
Hz, H6), 8.54 (s, 2H, H2), 7.88 (d, 2H, JHH=8.1 Hz,
H4). 31P{1H}-NMR (CDCl3): l 8.5 (1JPtP=2857 Hz).
Anal. Calc. for C79H70F6N2O11P4Pt2S2·0.5CH2Cl2: C,
48.77; H, 3.65; N, 1.43. Found: C, 48.72; H, 3.51; N,
1.43%.
Acknowledgements
We thank Ms W. Holstein (The University of Ade-
laide) and Professor B.K. Nicholson (University of
Waikato, NZ) for recording the ESI mass spectra. We
also thank the Australian Research Council for finan-
cial support.
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