Synthesis and reactivity of water-soluble platinum(II) complexes containing nitrogen ligands

Article abstract of DOI:10.1016/S0022-328X(03)00540-0

A series of water-soluble platinum(II) complexes containing bidentate imino pyridine ligands L of the general formula LPtX₂ (X=Cl or Me) have been prepared. The dichloro complexes are very stable in water or dimethyl sulfoxide (DMSO), even at elevated temperatures, whereas the dimethyl complexes are less stable in these strongly polar solvents. In DMSO, an equilibrium between the complex LPtMe₂ and (DMSO)₂PtMe₂ is observed, whereas in water decomposition is observed within 1 day at room temperature.

Full text of DOI:10.1016/S0022-328X(03)00540-0

Journal of Organometallic Chemistry 679 (2003) 110Á115
/
www.elsevier.com/locate/jorganchem
Synthesis and reactivity of water-soluble platinum(II) complexes
containing nitrogen ligands
George J.P. Britovsek *, Grace Y.Y. Woo, Nitinan Assavathorn
Department of Chemistry, Imperial College London, Exhibition Road, London SW7 2AY, UK
Received 16 April 2003; received in revised form 5 June 2003; accepted 6 June 2003
Abstract
A series of water-soluble platinum(II) complexes containing bidentate imino pyridine ligands L of the general formula LPtX2
(XꢀCl or Me) have been prepared. The dichloro complexes are very stable in water or dimethyl sulfoxide (DMSO), even at elevated
/
temperatures, whereas the dimethyl complexes are less stable in these strongly polar solvents. In DMSO, an equilibrium between the
complex LPtMe2 and (DMSO)2PtMe2 is observed, whereas in water decomposition is observed within 1 day at room temperature.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Nitrogen ligands; Water-soluble; Platinum; Catalysis
1. Introduction
hydroxy groups, have also been employed to increase
the hydrophilicity of ligands and their metal complexes
[5].
Organic transformations catalysed by transition me-
tals in aqueous media have become increasingly attrac-
tive due to the benign nature of water and the cost
benefits [1]. Much work has been done in recent years to
develop water-soluble phosphine ligands for transition
metals, and sulfonated phosphines such as TPPTS are
Whereas a considerable amount of research has been
devoted to the development of water-soluble phos-
phines, nitrogen based ligands have received compara-
tively little attention so far. In the limited number of
examples, the hydrophilicity has been introduced either
through an ionic substituent (cationic or anionic) or a
polyhydroxy substituent (as in carbohydrates). Sulfo-
nated bipyridine ligands of type A were among the first
examples of nitrogen ligands developed for applications
now quite common [2Á
phosphine ligands have even found industrial applica-
tion, for example in the RhoˆneÁPoulenc/Ruhrchemie
hydroformylation process of propylene to butyralde-
hyde [4]. Other transformations of alkenes such as
hydrogenation, alkylation, isomerisation and oxidation
to form ketones or epoxides have also been reported [1]
and, more recently, the hydration of alkynes [6,7].
/
5]. Some of these water-soluble
/
in aqueous solution (see Fig. 1) [8Á
several other monodentate [12] and bidentate ligands,
either with ionic (B and C) [13Á15] or polyhydroxy (D)
[16Á19] substituents have been developed. Examples of
/11]. Subsequently,
/
/
multidentate ligands are the tridentate tris(pyrazo-
lyl)methane (E) [20] and the tris(pyridyl)amine [21]
derivatives as well as tetradentate porphyrin ligands
[22]. An additional class of water-soluble nitrogen
ligands worth mentioning in this context are amino
acids, which have been studied extensively in combina-
tion with platinum [23].
Although sulfonate substituents (Ã
most popular, a number of other substituents such as
carboxylate (Ã
CO2ꢁ), phosphonate (ÃPO23ꢁ) and poly-
/
SO3ꢁ) have been
/
/
* Corresponding author. Address: Department of Chemistry,
Imperial College London, Frankland Road, London SW7 2AY, UK.
We have recently embarked on a research program
towards the synthesis of water-soluble complexes based
Tel.: ꢂ
/
44-20-7594-5863; fax: ꢂ44-20-7594-5810.
/
E-mail address: g.britovsek@imperial.ac.uk (G.J.P. Britovsek).
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00540-0

G.J.P. Britovsek et al. / Journal of Organometallic Chemistry 679 (2003) 110Á
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111
(1)
on nitrogen ligands. These complexes have potential
applications in catalysis, for example CÃH activation in
should be noted that for all preparations strictly
anhydrous solvents and a nitrogen atmosphere are
required; sulfonated iminopyridines are very moisture-
/
water (Shilov chemistry) [24] or as anti-cancer agents
[25,26]. Here we present our initial studies on the
synthesis and characterization of platinum(II) dihalide
and dialkyl complexes containing sulfonated imino
pyridine ligands and their stability in strongly polar
solvents such as H2O and dimethyl sulfoxide (DMSO).
sensitive. 2,6-Dialkyl sulfanilic acids 1cÁ
from the corresponding aniline and H2SO4 [27]. Under
the conditions used for the successful preparation of 1aÁ
/d were prepared
/
c, the reaction of the bulkier 2,6-diisopropylphenyl
derivative 1d with pyridine carboxaldehyde gave repeat-
edly a mixture of product and starting materials, which
could not be separated. In addition to the series of
bidentate ligands, we also prepared a potentially triden-
tate ligand 2e from pyridine dicarboxaldehyde and 1c, as
shown in Eq. (1). The same procedure affords the
bis(imino)pyridine derivative 2e in good yield.
2. Results and discussion
Sulfonated iminopyridine ligands 2aÁc were prepared
/
by condensation of pyridine carboxaldehyde and the
sodium salt of the appropriate sulfanilic acid via a
method recently described by Buffin (Scheme 1) [14]. It
Platinum(II) dihalide complexes 3aÁc (see Scheme 1)
/
are prepared by the addition of the iminopyridine
ligand, dissolved in a minimal amount of DMSO, to
PtCl2(SMe2)2 (mixture of cis and trans). Precipitation of
the product with dichloromethane affords the dichloro
complexes 3aÁc in good yield and purity, which can be
/
freed from residual DMSO by dissolving in methanol
and precipitation with diethyl ether. It should be noted
that these Pt(II) complexes are insoluble in common
organic solvents such as dichloromethane, thf or tolu-
ene, but very soluble in polar solvents such as water,
DMSO or DMF and, unlike the free ligands, are very
stable in water. For example, a solution of 3b in D2O,
heated at 80 8C for 24 h, did not show any change or
signs of decomposition. Reaction of the potentially
tridentate ligand 2e with PtCl2(SMe2)2 in DMSO at
room temperature for 2 days resulted in a dark orange
solution, which upon addition of DCM yielded an
orange product. However, 1H-NMR in d6-DMSO
revealed only the presence of starting materials. The
same reaction in methanol at room temperature also
only yielded the starting materials back after workup.
Similar difficulties have been encountered with the
tridentate ligand terpyridine (terpy) [28].
Fig. 1. Examples of water-soluble nitrogen ligands.

112
G.J.P. Britovsek et al. / Journal of Organometallic Chemistry 679 (2003) 110Á
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Scheme 1.
1
Platinum(II) dimethyl complexes 4aÁ
/
c are prepared
either solvent show a clean H-NMR spectrum of the
complex. However, typically within a day, decomposi-
by a similar procedure, using [PtMe2(m-SMe2)]2 as the Pt
precursor (see Scheme 1). The reactions were carried out
in a small amount of DMSO as the solvent and the
products were precipitated by the addition of toluene,
washed with toluene and dichloromethane to afford the
pure dark-red complexes. When the reaction was carried
out in methanol, a complex mixture of products was
obtained, which was not further investigated.
tion is observed to occur for all complexes 4aÁc in both
/
solvents, giving rise to a mixture of products. Besides the
signals for the starting complex, the decomposition
products in d6-DMSO can be readily identified as free
ligand and cis-[PtMe2(d6-Me2SO)2] based on the known
chemicals shifts of the ligand and cis-[PtMe2(Me2SO)2]
which has been prepared previously [29]. These observa-
tions reveal that the bidentate ligand is being displaced
from the metal by the DMSO solvent, according to
The dimethyl complexes 4aÁ
/
c have been characterized
by 1H-NMR and microanalysis. Noteworthy are the
(2)
195Pt satellites on the imine proton (JPtÃH
the two different Pt-methyl signals (JPtÃH
:
/
33 Hz) and
Eq. (2).
Similar reactions to the reverse reaction of Eq. (2),
where the DMSO ligands in cis-[PtR2(Me2SO)2] (Rꢀ
methyl or phenyl) are displaced by bidentate nitrogen
ligands such as bipyridine or phenanthroline, have been
studied previously in benzene and in acetonitrile solu-
:
/
85 Hz),
confirming the complex formation. 1H-NMR spectra
have been recorded in d6-DMSO and D2O. 13C-NMR
spectra could not be obtained due to decomposition in
these solvents (vide infra). Freshly prepared samples in
/

G.J.P. Britovsek et al. / Journal of Organometallic Chemistry 679 (2003) 110Á
/115
113
tion [30Á
/
32]. It appears that, due to the presence of the
ques, or in a conventional nitrogen-filled glove box.
NMR spectra were recorded on a Bruker AC-250
spectrometer at 250 MHz (1H) and 62.9 MHz (13C) at
293 K; chemical shifts for 1H and 13C-NMR are
referenced to the residual protio impurity and to the
13C-NMR signal of the deuterated solvent. Mass spectra
were recorded on either a VG Autospec or a VG
Platform II spectrometer. Elemental analyses were
performed by the Science Technical Support Unit at
the London Metropolitan University.
large excess of DMSO, in the case of complexes 4aÁ
/c the
sulfonated iminopyridine ligands are competing for
coordination with the DMSO solvent, resulting in an
equilibrium. Similar observations have been made for
cis-[PtMe2(Me2SO)2] in D2O and CD3CN as the sol-
vent, which results in an equilibrium between the
starting complex, the solvento species cis-[PtMe2(Me2-
SO)(D2O)] or cis-[PtMe2(Me2SO)(CD3CN)], respec-
tively, and free DMSO [32,33]. The equilibrium (Eq.
(2)) can be reversed by the addition of toluene or DCM,
resulting in the precipitation of the Pt(II) complexes.
This strategy is successfully exploited in the synthesis of
3.2. Solvents and reagents
complexes 4aÁ
in DMSO.
In D2O, decomposition of 4aÁ
/
c from cis-[PtMe2(Me2S)]2 and the ligand
Toluene and pentane were dried by passing through a
column, filled with commercially available Q-5 reagent
(13 wt.% CuO on alumina) and activated alumina
(pellets, 3 mm). Benzene and DMSO were dried by
prolonged reflux over a suitable drying agent (Na and
CaH2, respectively) under an atmosphere of nitrogen,
and distilled prior to use. DMF was dried and distilled
/c is also observed, but
in this case a more complex mixture of products is
obtained which could not be analysed. Considering that
D2O easily displaces a DMSO ligand in the complex cis-
[PtMe2(Me2SO)2] [33], and that DMSO can displace the
nitrogen ligand, we believe that in this case the
sulfonated iminopyridine ligands are displaced by
D2O, followed by deuterolysis of the ligand and further
degradation of the resulting aqua alkyl platinum com-
plexes. Traces of methane are also observed, but no
formation of Pt(0). From these observations it is clear
that these water-soluble nitrogen ligands provide insuf-
ficient stabilization of platinum(II) dialkyl complexes in
strong donor solvents such as DMSO or D2O. The
different behaviour of the dialkyl Pt(II) complexes
compared to the dichloro complexes is ascribed to the
stronger trans effect of the methyl ligands, thereby
˚
over molecular sieves (4 A). Methanol and ethanol were
dried by heating under reflux with sodium metal and
then distilled under nitrogen. Diethyl ether and tetra-
hydrofuran were dried over sodium metal with a
benzophenone ketyl indicator, whereas dichloromethane
was dried over CaH2. PtCl2(SMe2)2 and [PtMe2(m-
SMe2)]2 were prepared according to literature proce-
dures [34,35]. Ligands 2a and 2b were prepared accord-
ing to the procedure described by Buffin [14]. 2,6-
dimethylsulfanilic acid 1c was prepared according to a
literature procedure [27]. All other chemicals and NMR
solvents were obtained commercially and used as
received.
weakening the PtÃ/N bonds.
In conclusion, we have prepared a series of water-
soluble Pt(II) dichloro and dimethyl complexes contain-
ing sulfonated iminopyridine ligands. The dichloro
complexes are stable in strongly polar solvents such as
H2O and DMSO, whereas the dimethyl complexes
slowly decompose in these solvents at room tempera-
ture. These studies have shown that for the application
of platinum complexes in strongly polar media such as
H2O, in particular where metal carbon bonds are
involved (e.g. Shilov chemistry), strong metal ligand
interactions will be required to prevent catalyst degra-
dation. We are currently investigating other, more
strongly coordinating, water-soluble nitrogen and oxy-
gen ligands, with the aim to generate Pt(II) complexes
that show greater stability in such strongly polar
environments.
3.3. 2,6-Diisopropyl sulfanilic acid
In a 250 ml round-bottomed flask, concentrated
H2SO4 (12.25 g, 0.125 mol) was added to water (23
ml). To this mixture, 2,6-diisopropylaniline (22.15, 0.125
mol) was added dropwise over 20 min via a dropping
funnel. Water was then removed by distillation under
vacuum (water pump) and the reaction mixture was
heated to 260 8C for 3 h. NaOH solution (7.5 g, 120 ml
H2O) was added to the cooled reaction mixture. This
mixture was heated again and filtered hot. The filtrate
was acidified with concentrated HCl to pH 2.5 and then
cooled to initiate precipitation. To this suspension,
water (175 ml) was added and then heated to 90 8C,
during which 20% Na2CO3 was added to obtain pH 8.
Charcoal (2.5 g) was added to the mixture, after which it
was filtered hot. NaCl (20 g) was added to the filtrate
and HCl was added dropwise to initiate product
precipitation. The resulting precipitate was isolated by
filtration to afford 2,6-diisopropyl sulfanilic acid as a
white solid.
3. Experimental
3.1. General
All moisture-sensitive compounds were manipulated
using standard vacuum line, Schlenk or cannula techni-

114
G.J.P. Britovsek et al. / Journal of Organometallic Chemistry 679 (2003) 110Á115
/
Yield: 10.3 g (32%). 1H-NMR (250 MHz, d6-DMSO):
1c (0.99 g, 4.44 mmol) was added to dry ethanol (70 ml).
Pyridine dicarboxaldehyde (0.30 g, 2.22 mmol) was
dissolved in dry benzene (10 ml) in a separate schlenk
flask and then added. A further 10 ml of dry benzene
was added to the mixture and then heated under reflux
for 2 h. All solvent was distilled off and the yellow
residue was washed with dry pentane and dried under
vacuum overnight, affording the product as a yellow
d 7.41 (s, 2H, Ar-H), 3.15 (sept, 2H, CH(CH3)2), 1.16
(d, 12H, CH(CH3)2). 13C-NMR (62.9 MHz, D2O): d
146.6, 140.08, 127.70, 121.20, 27.04 (CH), 23.35 (CH3).
EI mass spectrum (m/z): 257 (40, [M]ꢂ), 242 (100, [Mꢁ
/
Me]ꢂ).
3.4. General synthesis of sodium 2,6-dialkylsulfanilate 1c
and 1d
1
solid in 78% yield. H-NMR (250 MHz, d6-DMSO): d
8.40 (d, 2H, py-H), 8.38 (s, 2H, HCÄ
H), 7.34 (s, 4H, Ar-H), 2.09 (s, 12H, CH3). 13C-NMR
(62.9 MHz, d6-DMSO): d 163.1 (CHÄN), 153.8, 150.0,
143.6, 138.4, 125.4 (ArCm), 122.9, 120.7, 17.88 (CH3).
/
N), 8.19 (t, 1H, py-
In a 100 ml round-bottom-flask, NaOMe was dis-
solved in dry methanol (30 ml), after which one
equivalent of the dialkylsulfanilic acid was added. The
solution was stirred for 30 min during which the sodium
salt precipitates. Methanol was evaporated, affording
the sodium salt as a white solid, which was pure by
NMR.
1c: Yield 93%. H-NMR (250 MHz, D2O): d 7.33 (s,
2H, Ar-H), 2.16 (s, 6H, CH3). 13C-NMR (62.9 MHz,
D2O): d 147.21, 135.10, 127.84, 126.37, 19.45 (CH3).
1
1d: Yield 81%. H-NMR (250 MHz, D2O): d 7.43 (s,
/
FAB(ꢂ
/
) mass spectrum (m/z): 569 ([Mꢂ
Na]ꢂ, 7), 546
/
([M]ꢂ, 10). Anal. Calc. for C23H21N3S2O6Na2: C, 50.64;
H, 3.88; N, 7.70. Found: C, 50.49; H, 3.68; N, 7.50%.
1
3.7. 2-((3-Sulfonyl-phenylimino)methyl)pyridine
platinum(II) dichloride 3a
The sulfonated imino pyridine ligand 2a (191 mg, 0.67
mmol) was dissolved in a small amount of DMSO (1
ml). This solution was transferred to a separate Schlenk
flask containing PtCl2(SMe2)2 (262 mg, 0.67 mmol). The
yellow colour changed to orange-red within 15 min.
After stirring overnight, dichloromethane was added to
precipitate the product, which was filtered and washed
with DCM. In order to remove small residues of
DMSO, the complex was dissolved in methanol, pre-
cipitated with diethyl ether and dried under vacuum.
Complexes 3b and 3c were prepared by the same
procedure.
2H, Ar-H), 2.90 (sept, 2H, CH(CH3)2), 1.13 (d, 12H,
CH(CH3)2). 13C-NMR (62.9 MHz, D2O): d 145.51,
136.79, 135.38, 123.06, 29.94 (CH), 24.35 (CH3).
3.5. 2-((2,6-Dimethyl-4-sulfonyl-
phenylimino)methyl)pyridine 2c
In a 3-necked 250 ml round-bottom flask equipped
with a reflux condenser and a nitrogen inlet, sodium 2,6-
dimethylsulfanilate (2 g, 8.97 mmol) was added to a
solution of dry ethanol (100 ml) and dry benzene (20 ml)
under an atmosphere of nitrogen. The resulting mixture
was heated to reflux and anhydrous methanol was
added until all of the salt had dissolved. 2-pyridinecar-
boxaldehyde (0.85 ml, 8.97 mmol) was then added
dropwise. The solution was heated until approximately
half of its original volume remained and then cooled to
ambient temperature to initiate product precipitation.
After the addition of diethylether (30 ml), the product 2c
was isolated by filtration and washed with diethyl ether.
Yellow solid. Yield: 2.24 g (80%). 1H-NMR (250
MHz, d6-DMSO): d 8.69 (d, 1H, py-H), 8.25 (s, 1H,
1
3a: Brown solid. Yield: 218 mg (59%). H-NMR (250
MHz, d6-DMSO): d 9.47 (d, 1H, py-H), 9.33 (s, 1H,
HCÄ/N), 8.44 (t, 1H, py-H), 8.25 (d, 1H, py-H), 7.99 (t,
1H, py-H), 7.65 (m, 2H, Ar-H), 7.40 (m, 2H, Ar-H).
13C-NMR (62.9 MHz, d6-DMSO): d 172.8, 167.0, 158.3,
149.0, 147.6, 140.5, 134.3, 129.4, 127.4, 125.9, 126.7,
120.5. FAB(ꢂ
) mass spectrum (m/z): 551 ([M]ꢂ, 15).
Anal. Calc. for C12H9N2SO3NaPtCl2: C, 26.19; H, 1.65;
/
N, 5.09. Found: C, 26.27; H, 1.69; N, 4.91%.
3b: Orange solid. Yield: 360 mg (69%). 1H-NMR (250
MHz, D2O): d 9.04 (s, 1H, HCÄ
/
N), 9.01 (d, 1H, py-H),
HCÄ
(dd, 1H, py-H), 7.32 (s, 2H, Ar-H), 2.09 (s, 6H, Ã
13C-NMR (62.9 MHz, d6-DMSO): d 163.78 (s, HC Ä
153.63, 149.66, 143.89, 137.24, 125.96, 125.36, 120.92,
CH3). FAB mass spectrum (m/z): 313 ([M]ꢂ,
/
N), 8.20 (d, 1H, py-H), 7.99 (t, 1H, py-H), 7.61
CH3).
N),
8.16 (t, 1H, py-H), 8.06 (d, 1H, py-H), 7.72 (d, 2H, Ar-
H), 7.65 (t, 1H, py-H), 7.50 (d, 2H, Ar-H). 13C-NMR
/
/
(62.9 MHz, D2O): d 175.7 (s, HC Ä
150.8, 146.1, 143.7, 133.0, 132.8, 128.6, 127.6. FAB(ꢁ
mass spectrum (m/z): 550 ([M]ꢁ, 25), 527 ([MꢁNa]ꢁ,
/N), 159.1, 152.3,
/)
17.90 (s, Ã
/
/
46). Anal. Calc. for C14H13N2SO3Na: C, 53.84; H, 4.20;
N, 8.97. Found: C, 53.94; H, 4.00; N, 8.84%.
100). Anal. Calc. for C12H9N2SO3NaPtCl2: C, 26.19; H,
1.65; N, 5.09. Found: C, 26.17; H, 1.62; N, 4.92%.
1
3c: Orange solid. Yield: 0.56 g (76%). H-NMR (250
3.6. 2,6-bis((2,6-Dimethyl-4-sulfonyl-
phenylimino)methyl)pyridine 2e
MHz, D2O): d 9.31 (d, 1H, py-H), 9.04 (s, 1H, HCÄ
/
N),
8.33 (t, 1H, py-H), 8.14 (d, 1H, py-H), 7.88 (t, 1H, py-
H), 7.54 (s, 2H, Ar-H), 2.27 (s, 6H, CH3). 13C-NMR
In a 3-necked 250 ml round-bottom flask equipped
with a suba seal, reflux condenser and a nitrogen inlet,
(62.9 MHz, D2O): d 176.73 (s, HC Ä
/
N), 158.89, 152.80,
149.58, 144.89, 144.00, 135.22, 132.88, 132.69, 127.56,

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115
[2] M.Y. Darensbourg, Inorg. Syn. 32 (1998) 1.
[3] W.A. Herrmann, C.W. Kohlpainter, Angew. Chem. Int. Ed. Engl.
32 (1993) 1524.
19.87 (s, CH3). FAB(ꢂ) mass spectrum (m/z): 579
/
([M]ꢂ, 14). Anal. Calc. for C14H13N2PtCl2NaSO3: C,
29.08; H, 2.27; N, 4.84. Found: C, 28.83; H, 2.24; N,
4.75%.
[4] B. Cornils, E.G. Kuntz, J. Organomet. Chem. 502 (1995)
177.
[5] C.-J. Li, T.-H. Chan, Organic Reactions in Aqueous Media,
Wiley, New York, 1997.
3.8. 2-((3-Sulfonyl-phenylimino)methyl)pyridine
platinum(II) dimethyl 4a
[6] L.W. Francisco, D.A. Moreno, J.D. Atwood, Organometallics 20
(2001) 4237.
[7] D.W. Lucey, J.D. Atwood, Organometallics 21 (2002) 2481.
[8] G. Sprintschnik, H.W. Sprintschnik, P.P. Kirsch, D.G. Whitten,
J. Am. Chem. Soc. 99 (1977) 4947.
A mixture of [PtMe2(m-SMe2)]2 (130 mg; 0.23 mmol)
and the sulfonated iminopyridine ligand 2a (125 mg;
[9] S. Anderson, E.C. Constable, K.R. Seddon, J.E. Turp, J.E.
Baggott, M.J. Pilling, J. Chem. Soc. Dalton Trans. (1985) 2247.
[10] W.A. Herrmann, W.R. Thiel, J.G. Kuchler, Chem. Ber. 123
(1990) 1953.
0.44 mmol) is dissolved in a small amount of DMSO (B
/
0.5 ml) and stirred at room temperature overnight. After
the addition of an excess toluene (ca. 10 ml), the
suspension is stirred overnight, filtered, washed with
toluene and finally with dichloromethane. Complexes 4b
and 4c were prepared by the same procedure.
[11] W.A. Herrmann, W.R. Thiel, J.G. Kuchler, J. Behm, E.
Herdtweck, Chem. Ber. 123 (1990) 1963.
[12] P.K. Baker, A.E. Jenkins, A.J. Lavery, D.J. Muldoon, A.
Shawcross, J. Chem. Soc. Dalton Trans. (1995) 1525.
[13] G.-J. ten Brink, I.W.C.E. Arends, R.A. Sheldon, Science 287
(2000) 1636.
1
4a: Red/purple solid. Yield: 191 mg (85%). H-NMR
(250 MHz, D2O): d 9.19 (s, 1H, CH Ä
8.86 (m, 1H, 6-pyrH), 7.8Á7.0 (m, ArH and pyrH), 0.94
(s, 3H, PtÃCH3, JHÃPt 80 Hz), 0.50 (s, 3H, PtÃCH3,
JHÃPt 84 Hz).
4b: Dark-red solid. Yield: 173 mg (84%). H-NMR
(250 MHz, D2O): d 9.27 (s, 1H, CH ÄN, JHÃPt 31 Hz),
8.88 (d, 1H, 6-pyrH, Jꢀ5.3 Hz, JHÃPt 20 Hz), 8.09 (t,
1H, 4-pyrH, Jꢀ7.7 Hz), 7.90 (d, 1H, 3-pyrH, Jꢀ7.4
Hz), 7.77 (d, 2H, ArH, Jꢀ8.4 Hz), 7.61 (t, 1H, 5-pyrH,
Jꢀ6.6 Hz), 7.18 (d, 2H, ArH, Jꢀ8.4 Hz), 0.98 (s, 3H,
PtÃCH3, JHÃPt 85 Hz), 0.52 (s, 3H, PtÃCH3, JHÃPt
/
N, JHÃPt
ꢀ/30 Hz),
/
[14] A. Kundu, B.P. Buffin, Organometallics 20 (2001) 3635.
[15] C. Bubert, J. Blacker, S.M. Brown, J. Crosby, S. Fitzjohn, J.P.
Muxworthy, T. Thorpe, J.M.J. Williams, Tetrahedron Lett. 42
(2001) 4037.
/
ꢀ
/
/
ꢀ
/
1
[16] M.L. Ferrara, I. Orabona, F. Ruffo, M. Funicello, A. Panunzi,
Organometallics 17 (1998) 3832.
/
ꢀ
/
/
ꢀ
/
[17] M.L. Ferrara, F. Giordano, I. Orabona, A. Panunzi, F. Ruffo,
Eur. J. Inorg. Chem. (1999) 1939.
/
/
/
[18] C. Borriello, M.L. Ferrara, I. Orabona, A. Panunzi, F. Ruffo, J.
Chem. Soc. Dalton Trans. (2000) 2545.
[19] S. Kolaric, V. Sunjic, J. Mol. Catal. 110 (1996) 181.
/
/
/
ꢀ
/
/
ꢀ
/
[20] W. Klaui, M. Berghahn, G. Rheinwald, H. Lang, Angew. Chem.
¨
85 Hz). Anal. Calc. for C14H15N2SO3NaPt: C, 33.01; H,
Int. Ed. Engl. 39 (2000) 2464.
[21] T. Funabiki, D. Sugio, N. Inui, M. Maeda, Y. Hitomi, Chem.
Commun. (2002) 412.
2.97; N, 5.50. Found: C, 33.13; H, 3.08; N, 5.38%.
1
4c: Dark-red solid. Yield: 182 mg (74%). H-NMR
(250 MHz, D2O): d 9.30 (s, 1H, CH Ä
9.04 (d, 1H, 6-pyrH), 8.21 (t, 1H, 4-pyrH, Jꢀ
7.99 (d, 1H, 3-pyrH, Jꢀ7.5 Hz), 7.76 (t, 1H, 5-pyrH,
Jꢀ6.3 Hz), 7.56 (s, 2H, ArH), 2.13 (s, 6H, ArCH3),
0.99 (s, 3H, PtÃCH3, JHÃPt 84 Hz), 0.27 (s, 3H, PtÃ
CH3, JHÃPt 86 Hz). Anal. Calc. for C16H19N2SO3-
/
N, JHÃPt
ꢀ
/
36 Hz),
[22] C.A. Koval, S.M. Drew, R.D. Noble, J. Yu, Inorg. Chem. 29
(1990) 4708.
/7.8 Hz),
[23] K. Severin, R. Bergs, W. Beck, Angew. Chem. Int. Ed. Engl. 37
(1998) 1634.
/
/
[24] J.A. Labinger, J.E. Bercaw, Nature 417 (2002) 507.
[25] Z. Guo, P.J. Sadler, Adv. Inorg. Chem. 49 (2000) 183.
[26] J. Reedijk, PNAS 100 (2003) 3611.
/
ꢀ
/
/
ꢀ
/
NaPt: C, 35.76; H, 3.56; N, 5.21. Found: C, 35.86; H,
3.53; N, 5.12%.
[27] A. Courtin, H. von Tobel, P. Doswald, Helv. Chim. Acta 61
(1978) 3079.
[28] G. Annibale, M. Brandolisio, B. Pitteri, Polyhedron 14 (1995)
451.
[29] C. Eaborn, K. Kundu, A. Pidcock, J. Chem. Soc. Dalton Trans.
(1981) 933.
Acknowledgements
[30] S. Lanza, D. Minniti, P. Moore, J. Sachinidis, R. Romeo, M.L.
Tobe, Inorg. Chem. 23 (1984) 4428.
We thank Johnson Matthey for a generous loan of
K2[PtCl4] and the Department of Chemistry, Imperial
College London, for funding.
[31] D. Minniti, G. Alibrandi, M.L. Tobe, R. Romeo, Inorg. Chem. 26
(1987) 3956.
[32] S. Lanza, G. Alibrandi, L. Monsu` Scolaro, S. Sergi, Inorg. Chim.
Acta 201 (1992) 137.
[33] D. Minniti, M.F. Parisi, Inorg. Chim. Acta 188 (1991) 127.
[34] R. van Asselt, E. Rijnberg, C.J. Elsevier, Organometallics 13
(1994) 706.
References
[35] G.S. Hill, M.J. Irwin, C.J. Levy, L.M. Rendina, R.J. Puddephatt,
Inorg. Syn. 32 (1998) 149.
[1] B. Cornils, W.A. Herrmann (Eds.), Aqueous-Phase Organome-
tallic Catalysis, Weinheim, Wiley-VCH, 1998.