Platinum(II) and palladium(II) complexes derived from the monoanion of isatin (2,3-dihydroindole-2,3-cHone, Hisat); crystal structure of cis-[Pt(isat)2(PPh3)2]

Article abstract of DOI:10.1039/a704803c

A number of platinum(II) and palladium(II) complexes containing the monoanion of isatin (2,3-dihydroindole-2,3-dione, Hisat) have been synthesized by reaction of the metal halide complex with isatin, in the presence of triethylamine. The complexes have been characterised by NMR and IR spectroscopies and elemental analysis. A single-crystal X-ray diffraction study has been carried out on cis-[Pt(isat)₂(PPh₃)₂], which shows two cis-isat ligands with their dicarbonyl functions pointing in opposite directions. Electrospray mass spectrometry was also used for characterisation; the complexes show a strong tendency to form aggregate ions with ammonium ions, and both mono- and di-cationic species are observed.

Full text of DOI:10.1039/a704803c

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Platinum(II) and palladium(II) complexes derived from the monoanion
of isatin (2,3-dihydroindole-2,3-dione, Hisat); crystal structure of cis-
[Pt(isat)2(PPh3)2]
Justin M. Law, William Henderson* and Brian K. Nicholson
Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand
A number of platinum() and palladium() complexes containing the monoanion of isatin (2,3-dihydroindole-
2,3-dione, Hisat) have been synthesized by reaction of the metal halide complex with isatin, in the presence of
triethylamine. The complexes have been characterised by NMR and IR spectroscopies and elemental analysis.
A single-crystal X-ray diffraction study has been carried out on cis-[Pt(isat)2(PPh3)2], which shows two cis-isat
ligands with their dicarbonyl functions pointing in opposite directions. Electrospray mass spectrometry was also
used for characterisation; the complexes show a strong tendency to form aggregate ions with ammonium ions, and
both mono- and di-cationic species are observed.
The amide functionality, RC(O)NHRЈ, is able to form a range
O
of stable metal complexes bonding as its monoanion, and such
ligands are able to stabilise transition-metal centres in high
oxidation states.1 There is current interest in the chemistry of
transition-metal amides, since such complexes may possess bio-
logical activity, for example as second-generation antitumour
drugs2 and may be implicated in the interactions of platinum
(and other transition-metal) complexes with biological mol-
ecules such as proteins and peptides.3 Platinum–amide com-
plexes are also intermediates in catalytic hydration reactions of
nitriles.4
O
O
N
O
N
H
Ph3P
Pt
PPh3
H
1
Hisat
O
Isatin (2,3-dihydroindole-2,3-dione, Hisat) is a highly conju-
gated, intense orange compound, and hence may find potential
application as a chromophoric labelling agent in its metal com-
plexes. To the best of our knowledge, only one platinum-group-
metal complex has been derived from isatin, the platinum
hydride 1, formed by oxidative addition of the N᎐H bond of
isatin to a zerovalent platinum complex.5 Gold() complexes of
isatin, its 5-bromo derivative and some related dye molecules
have also been recently reported.6 Other isatin complexes have
been synthesized with main-group metals, including the
L
L
N
L
L
M
N
O
O
M
Cl
2
O
2a M = Pt; L = PPh3
2b M = Pt; L2 = dppe
3a M = Pt; L = PPh3
3b M = Pt; L2 = dppe
3c M = Pt; L2 = dppp
3d M = Pd; L2 = bipy
attempt to synthesize the monosubstituted compounds of type
2. This was successful for cis-[PtCl(isat)(PPh3)2] 2a, but no other
mono-isat compounds could be isolated pure. However, in the
reaction between cis-[PtCl2(dppe)] and isatin a mixture of
the starting material, the monosubstituted 2b and the di-
substituted 3b compounds was formed. It was decided therefore
to repeat the reaction using 2 molar equivalents of isatin,
and the four bis-isat complexes cis-[Pt(isat)2(PPh3)2] 3a, cis-
[Pt(isat)2(dppe)] 3b, cis-[Pt(isat)2(dppp)] 3c (dppp = Ph2PCH2-
CH2CH2PPh2) and [Pd(isat)2(bipy)] 3d were thus prepared in
moderate to high yields. All of these complexes are dark
red crystalline or microcrystalline solids, and all except the
palladium complex 3d melt with decomposition at temperatures
above 180 ЊC. The palladium complex did not melt below
320 ЊC, the limit of the apparatus used.
organotin compound SnBun (isat),7 and a range of phenyl-
3
antimony complexes.8
Additional interest in the synthesis of transition-metal com-
plexes of isatin results from the presence of the carbonyl func-
tions, which might themselves possess ligand properties towards
other metals, leading to the formation of bi- and multi-metallic
co-ordination assemblies. Recently, there has been interest
in this field, where a range of multimetallic structures based
upon amide complexes has been synthesized.9 The related 2-
pyridonate ligand also forms a diverse range of materials,10 the
chemistry of which is summarised in two recent reviews.11 The
presence of two adjacent carbonyl groups in isatin, both of
which could potentially act as ligands towards other metal
centres, offers a new dimension in this area; we note that metal
complexes of the related α,β-diketo ligands oxalate12 and
oxamidate13 are well known to form interesting co-ordination
networks.
Crystal structure of cis-[Pt(isat)2(PPh3)2] 3a
The crystal structure of complex 3a, Fig. 1, showed the
platinum atom co-ordinated to two triphenylphosphine and
two isat ligands, in a cis-square planar geometry, as expected.
The isat ligands co-ordinate through deprotonated nitrogen
atoms. Selected bond lengths and angles are given in Table 1.
Analysis of the platinum co-ordination plane revealed that
P(2) and N(1) were raised slightly above the plane (by 0.064 and
0.081 Å, respectively) while P(1) and N(2) were below the plane
Results and Discussion
Initially, isatin (Hisat) was treated with some platinum dichlor-
ide complexes of the type cis-[PtCl2L2] [L = PPh3, L2 = 1,2-
bis(diphenylphosphino)ethane (dppe) or cycloocta-1,5-diene
(cod)] and one palladium complex, [PdCl2(bipy)] (bipy = 2,2Ј-
bipyridine), in a 1:1 ratio, with added triethylamine, in an
J. Chem. Soc., Dalton Trans., 1997, Pages 4587–4594
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Fig. 1 Molecular structure of cis-[Pt(isat)2(PPh3)2] 3a, showing the atom numbering scheme
Table 1 Selected bond lengths (Å) and angles (Њ) for cis-[Pt(isat)2-
H
O
N
O
Ph3P
N
(PPh3)2] 3a, with estimated standard deviations in parentheses
L
O
O
N
Pt
NH2
Pt
Pt᎐N(1)
Pt᎐P(2)
N(1)᎐C(78)
N(2)᎐C(88)
O(1)᎐C(78)
O(3)᎐C(88)
2.050(2)
2.2956(7)
1.358(4)
1.357(4)
1.221(4)
1.218(4)
Pt᎐N(2)
Pt᎐P(1)
N(1)᎐C(71)
N(2)᎐C(81)
O(2)᎐C(77)
O(4)᎐C(87)
2.060(2)
2.2959(7)
1.409(4)
1.410(4)
1.206(4)
1.205(4)
N
Ph3P
L
O
O
5a L = PPh3
5b L–L = dppe
4
N(1)᎐Pt᎐N(2)
N(1)᎐Pt᎐P(1)
C(71)᎐N(1)᎐Pt
C(88)᎐N(2)᎐Pt
C(78)᎐N(1)᎐C(71) 109.1(2)
O(1)᎐C(78)᎐N(1) 127.6(3)
O(2)᎐C(77)᎐C(76) 130.7(3)
O(3)᎐C(88)᎐N(2) 127.9(3)
O(4)᎐C(87)᎐C(86) 130.2(3)
84.71(9)
99.48(7)
127.3(2)
124.0(2)
N(2)᎐Pt᎐P(2)
P(2)᎐Pt᎐P(1)
C(78)᎐N(1)᎐Pt
C(81)᎐N(2)᎐Pt
C(88)᎐N(2)᎐C(81) 109.5(2)
O(1)᎐C(78)᎐C(77) 125.1(3)
O(2)᎐C(77)᎐C(78) 124.5(3)
O(3)᎐C(88)᎐C(87) 125.1(3)
O(4)᎐C(87)᎐C(88) 125.1(3)
90.36(7)
96.71(3)
123.6(2)
126.6(2)
planarity being 0.021 Å for C(77) in the first isat ligand and
0.020 Å for C(88) in the second. Both of the ligand planes are
almost perpendicular to the platinum co-ordination plane, with
dihedral angles of 79.19(6) and 74.95(7)Њ, for the ligands co-
ordinated through N(1) and N(2), respectively. As in complex 4,
these ligand planes are oriented so that the carbonyls of the
two molecules point in opposite directions. This is illustrated
in Fig. 2 which views complex 3a parallel to the platinum co-
ordination plane.
(by 0.067 and 0.081 Å, respectively). This indicates a minor
distortion of the co-ordination toward a tetrahedral geometry,
presumably to relieve the steric crowding of the bulky ligands in
this complex. The bulky phosphine ligands give a P(1)᎐Pt᎐P(2)
angle of 96.71(3)Њ, and there is a correspondingly small
N(1)᎐Pt᎐N(2) angle of 84.71(9)Њ. Similar angular deformations
were observed for the azetidin-2-one complex 4.14
The Pt᎐P bond lengths are equal [2.296(1) Å], but Pt᎐N(2)
appears to be slightly longer than Pt᎐N(1) [2.060(2) and
2.050(2) Å, respectively]. Similar Pt᎐N bond lengths have been
found for 414 [2.03(1) and 2.05(1) Å], and also for the orotic
acid (2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid)
complex 5a [2.056(6) Å].15 However, the Pt᎐P distances for these
two complexes were significantly shorter than those in 3a, being
2.266(3) and 2.291(3) Å for 4 and 2.265(3) and 2.262(3) Å for
5a.
In the crystal structure of the free isatin molecule16 a long
C᎐C bond of 1.555(3) Å [cf. approximately 1.48 Å for a normal
C(sp2)᎐C(sp2) single bond17] was observed between the two
carbonyl groups. This was attributed to repulsion between the
non-bonded lone pairs on the oxygen atoms, and is also seen in
complex 3a, with distances of 1.565(4) Å for C(77)–C(78) and
1.566(4) Å for C(87)–C(88).
NMR spectroscopy
(a) 31P-{1H}. The 31P-{1H} NMR spectra of the isat com-
plexes 2 and 3 are as expected; 3a showed a single resonance
with 195Pt satellites, and a 195Pt᎐31P coupling constant of 3284
Hz. By comparison, the phthalimido complex 6 showed a simi-
lar value of 3340 Hz.18 For the dppe complex 3b a 1JPtP value of
3173 Hz was observed, which is slightly lower than the P trans
to N values of 3322 Hz for the dppe platinum amide complex
The isat ligands are planar, with the greatest deviations from
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original dichloride and the bis-amido complexes, this showed
an increase of 37 Hz for P trans to Cl, and a decrease of 46 Hz
for P trans to N.
1
(b) H. All of the complexes 2 and 3 showed the absence of
1
the broad isatin amide proton resonance, at δ 7.93 in the H
NMR spectrum. The 1H NMR spectrum of 2a showed a com-
plex multiplet between δ 7.9 and 7.1, due to the phenyl protons.
A doublet and a triplet of doublets are seen at higher field due
3
to the isat group, both showing JHH of ca. 7 Hz. The latter
proton also showed 4JHH coupling of 0.7 Hz. Unfortunately, the
other doublet and triplet of doublets expected were obscured by
the phenyl resonances. The spectrum of complex 3a was simpler
than that of 2a, as the phosphine ligands are now equivalent.
(c) 13C-{1H}. In the spectrum of complex 2a the two isat car-
bonyls appeared at δ 192 and 168, respectively, with the high-
field signal due to the carbonyl adjacent to the amido nitrogen.
The two triphenylphosphine ligands are inequivalent, resulting
in the observation of twice as many phenyl carbon signals as for
a symmetrical complex. Additionally, carbons located close to
one of the phosphorus atoms show coupling to that atom. All
of the other phenyl carbons, with the exception of the para
carbons, showed phosphorus–carbon coupling. One of these
Fig. 2 Structure of cis-[Pt(isat)2(PPh3)2] 3a viewed parallel to the plat-
inum co-ordination plane, showing how the carbonyl groups of the two
isatin ligands point in opposite directions. Only P-bonded atoms of the
phenyl rings are shown, and the atoms of the front isatin ligand are
shown as black circles
O
1
resonances appeared as a doublet, with a JPC value of 62 Hz.
Ph3P
Another singlet, observed at slightly higher field, was assigned
as half of the second doublet expected. The other half was
assumed to be obscured under a larger, adjacent resonance.
Both of these resonances were absent from the distortionless
enhancement of polarisation transfer (DEPT) 135 spectrum,
confirming their assignment as quaternary carbons. The ortho
carbons appeared as two doublets, with 2JPC couplings of about
10 Hz for each.
For complexes 3a–3c two carbonyl resonances for the isat
ligand were seen, e.g. for 3a at δ 188 and 166 with the latter
being the amide carbonyl. The highest-field resonances in the
spectra of 3b and 3c were for the methylene carbons of the dppe
or dppp ligands. In the spectrum of 3b the methylene carbons
were observed as a doublet of doublets, due to coupling to two
phosphorus atoms. A multiplet was seen for the dppp PCH2
carbons of 3c, as a result of coupling to both phosphorus
atoms, while the central methylene carbon appeared as a
higher-field singlet.
Pt
N
Ph3P
2
O
6
[PtMe{NHC(O)Me}(dppe)]19 and 3294 Hz for the 5-amino-
orotic acid platinum complex 5b.15 In the spectrum of 3c
the JPtP value of 2963 Hz was small compared to that of the
triphenylphosphine 3a and dppe 3b complexes, reflecting the
pattern for the starting platinum dichloride complexes, and is
the usual effect of increasing the chelate ring size from five
atoms to six.
The mixed-ligand complex 2a showed an AB spin system,
indicative of two phosphorus atoms in different environments,
coupling to each other (JPP 18 Hz), with associated platinum
satellites. The chloride ion has the lowest trans influence, and
the phosphorus trans to this ligand showed the highest coupling
to platinum (3832 Hz). Conversely, the amido ligand had a
higher trans influence, resulting in a lower coupling constant,
3101 Hz, for the trans phosphorus atom. Also evident from this
spectrum was the exaggerated difference in Pt᎐P coupling in
asymmetric species. This effect has been observed previously20
and is seen in cis-phosphine platinum complexes where two dif-
ferent groups occupy the sites trans to the phosphorus atoms. In
1
The bipy palladium complex 3d showed the simplest of all
the carbon NMR spectra, as it lacked phosphorus coupling.
Hence, each of the thirteen carbon environments in the com-
plex appeared as a singlet, with carbonyl resonances at δ 189
and 169, the latter being assigned to the amide carbonyl.
Infrared spectroscopy
1
such complexes, the lowest JPtP value is lowered relative to a
symmetrical analogue, while the highest is raised, leading to an
increase in the difference between the two coupling constants.
In the infrared spectra of the isat complexes 2 and 3 the region
1750–1500 cmϪ1 is the most diagnostic. Free isatin shows three
bands at 1748, 1728 and 1616 cmϪ1, attributed to C᎐O and C᎐C
1
᎐
᎐
The complex cis-[PtCl2(PPh3)2] has a JPtP value of 3673 Hz,
stretches. For complexes of this ligand four strong bands are
resolved in this region, e.g. 1732, 1685, 1605 and 1586 cmϪ1 for
2a and these vary little for all of the complexes 2 and 3. The
overall lowering of frequency suggests that co-ordination of the
with P trans to Cl, while cis-[Pt(isat)2(PPh3)2] 3a has a coupling
constant of 3284 Hz, with P trans to N. For the asymmetric
species, cis-[PtCl(isat)(PPh3)2] 2a, however, the value for P trans
to Cl increases to 3832 Hz, and that for P trans to N decreases
to 3101 Hz. Typical coupling constants for triphenylphosphine
trans to chloride occur around 3700 Hz.21
nitrogen to the metal withdraws electron density from the C᎐C
᎐
and C᎐O groups. Roundhill23 noted corresponding weakening
᎐
of carbonyl bonds for similar cyclic amide complexes of plat-
inum and palladium, and frequencies in the range 1612–1578
cmϪ1 have been observed for platinum complexes with ligands
of the type NHC(O)R (R = Me or Ph).24
The dppe platinum complex 2b also showed the expected AB
2
spin pattern, but with a lower JPP than that of the triphenyl-
phosphine analogue 2a, as expected.15,22 A lower exaggeration
1
in the JPtP difference was seen, on comparison with the tri-
phenylphosphine analogue 2a. The 31P-{1H} NMR spectrum of
the crude product showed three complexes, namely the starting
material, the intermediate monoamido complex 2b and the bis-
amido product 3b. The complex 2b showed coupling constants
of 3656 Hz for the phosphorus trans to chloride, and 3126
Hz for phosphorus trans to nitrogen. On comparison with the
Electrospray mass spectrometry (ESMS)
Electrospray mass spectrometry is finding increasing utility in
the characterisation of inorganic complexes,25 and several types
of platinum() amide complexes have been investigated by
ESMS.14,26–28 The compounds described here were studied using
J. Chem. Soc., Dalton Trans., 1997, Pages 4587–4594
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Fig. 3 Positive-ion electrospray mass spectrum (MeCN–water solution, cone voltage 20 V) of the bis(isat) complex 3b: (a) full mass-range
spectrum, with ion assignments, illustrating the strong propensity to aggregate with ammonium ions; (b) high-resolution expansion of the region m/z
865–915, showing contributions from various mono- and di-cationic species; the inset shows the calculated isotope patterns for the [M ϩ H]ϩ ion
(upper) and the [2M ϩ H ϩ NH4]2ϩ ion (lower)
the positive-ion mode, and there are two ways that a molecule
may obtain such a charge. First, a positively charged species,
such as a proton or a metal ion, may attach itself to the com-
plex. Hence, at low cone voltages, this method often shows a
high abundance of molecular ions, [M ϩ H]ϩ, where M is the
original complex molecule. Secondly, a complex may lose a
negatively charged group. This fragmentation mechanism is
seen especially at higher cone voltages. Both of these methods
can help in the characterisation of a complex. Additionally,
comparison of the experimental and calculated isotope patterns
can provide support for ion assignments.
Positive-ion ESMS data for complexes 2 and 3 are summar-
ised in Table 2, and the general behaviour of the isat complexes
is illustrated by discussion of the properties of the chloro–isat
complex 2a and the bis(isat) complexes 3a and 3b. The com-
plexes show a very strong propensity to form aggregates with
adventitious ammonium ions (from the acetonitrile mobile
phase used), including multiply charged species. Presumably
this behaviour results from the presence of the α,β-diketo
moiety of the isatin ligand(s), which is expected to be an excel-
lent hydrogen-bond acceptor from the ammonium ion donors.
The azetidinone complex 4 also showed a tendency to aggregate
with ammonium ions, though to a far lesser extent.14
Overall, the ESMS behaviour of the bis(isat) complexes 3a
and 3b were similar. For 3b at a cone voltage of 5 V the main
species present was an ammonium adduct, [M ϩ NH4]ϩ, and
the dimeric form, [2M ϩ 2NH4]2ϩ, was observed as smaller
peaks between those of the monomer. The protonated species
[M ϩ H]ϩ was present at just under a quarter of the intensity of
the major ion. Fig. 3(a) shows the 20 V spectrum of complex
3b, while Fig. 3(b) shows a high-resolution expansion of the m/z
865–915 region. At 20 V, the main peak was the aggregate
[3M ϩ 2NH4]2ϩ
[2M ϩ NH4]ϩ and [3M ϩ NH4]ϩ ions. Several additional
dicationic species were also observed, namely [2M ϩ 2NH4]2ϩ
,
together with [M ϩ H]ϩ, [M ϩ NH4]ϩ,
,
[2M ϩ H ϩ NH4]2ϩ and [5M ϩ 2NH4]2ϩ. It is noteworthy that
no [2M ϩ 2H]2ϩ ion was observed as small peaks of 0.5 mass
unit separation superimposed on the [M ϩ H]ϩ pattern at m/z
886, presumably due to the poorer hydrogen-bond donor cap-
acity, and smaller size, of a proton when compared to an
ammonium ion. The [2M ϩ H ϩ NH4]2ϩ ion exists only as a
2ϩ ion, with no monocation of the same m/z possible, and this
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Table 2 Positive-ion ESMS data for complexes 2a, 3a and 3b, recorded in MeCN–water solution
Complex
Cone voltage/V
20
ta/min
Observed ions (m/z, %)b
2a
0
[M ϩ H]ϩ (902, 77), [M Ϫ Cl ϩ MeCN]ϩ (906, 35%), [M ϩ NH4]ϩ/[2M ϩ 2NH4]2ϩ (919, 26),
unidentified (1003, 9), [3M ϩ 2NH4]2ϩ (1370, 100)
27.5
21
[M Ϫ Cl]ϩ (865, 14), [M Ϫ Cl ϩ NH3]ϩ (882, 38), [M ϩ H]ϩ (902, 44), [M Ϫ Cl ϩ MeCN]ϩ (906,
100), [3M ϩ 2H]2ϩ (1352, 16), [3M ϩ 2NH4]2ϩ (1370, 29)
5
[M Ϫ Cl ϩ NH3]ϩ (882, 25), [M ϩ H]ϩ (902, 54), [M Ϫ Cl ϩ MeCN]ϩ (906, 100), [M ϩ NH4]ϩ/
[2M ϩ 2NH4]2ϩ (919, 22), [3M ϩ 2H]2ϩ (1352, 12), [3M ϩ 2NH4]2ϩ (1370, 47)
[Pt(o-C6H4PPh2)(PPh3)]ϩ (718, 32), [M Ϫ isat]ϩ (755, 47), [Pt(o-C6H4PPh2)(MeCN)]ϩ (759, 29),
[M Ϫ isat ϩ MeCN]ϩ (796, 22), [M Ϫ Cl]ϩ (865, 100), [M ϩ H]ϩ (902, 29)
60
16.8
3a
5
20
40
[M ϩ H]ϩ (1012, 69), [M ϩ NH4]ϩ/[2M ϩ 2NH4]2ϩ (1029, 100)
[M ϩ H]ϩ (1012, 100), [M ϩ NH4]ϩ/[2M ϩ 2NH4]2ϩ (1029, 79)
[M Ϫ isat]ϩ (865, 100), [M ϩ H]ϩ (1012, 32), unidentified (1393, 6), [3M ϩ 2NH4]2ϩ (1536, 6),
[2M ϩ NH4]ϩ (2041, 6)
ϩ KCl
ϩ KCl ϩ NaCl
20
20
60
[M ϩ H]ϩ (1012, 18), [M ϩ K]ϩ (1051, 100)
[M ϩ H]ϩ (1012, 21), [M ϩ Na]ϩ (1034, 89), [2M ϩ Na ϩ K]2ϩ (1043, 27), [M ϩ K]ϩ (1051, 100)
[M ϩ Na]ϩ (1034, 100), [M ϩ K]ϩ (1051, 69)
3b
5
20
[M ϩ H]ϩ (886, 23), [M ϩ NH4]ϩ (903, 100), [2M ϩ 2NH4]2ϩ (903.5, 27)
[M ϩ H]ϩ (886, 93), [2M ϩ H ϩ NH4]2ϩ (895, 23), [M ϩ NH4]ϩ (903, 85), [2M ϩ 2NH4]2ϩ (903.5,
27), [3M ϩ 2NH4]2ϩ (1347, 100), [2M ϩ NH4]ϩ (1790, 48), [5M ϩ 2NH4]2ϩ (2232, 3), [3M ϩ
NH4]ϩ (2674, 4)
a Solvolysis was observed to occur with the chloro complex 2a; times refer to time of spectrum acquisition after dissolution of the sample in the
ESMS mobile phase. b The m/z values refer to the most abundant ion in the isotope distribution pattern. In isotope patterns of some of the higher-
and lower-mass intensity, species contributions from aggregate species having higher m and z cannot be ruled out.
Fig. 4 Positive-ion electrospray mass spectrum (cone voltage 20 V) of a freshly prepared MeCN–water solution of complex 2a, with ion assign-
ments. The inset shows the high-resolution isotope pattern of the m/z 900–910 region, showing contributions from the ions [M ϩ H]ϩ (m/z 902) and
[M Ϫ Cl ϩ MeCN]ϩ (m/z 906). On allowing the solution to stand the latter ion increases in intensity with a concomitant decrease in the former
is clearly observed in Fig. 3(b). No [M ϩ 2NH4]2ϩ ion was
observed, presumably because such an ion would have a rela-
tively high charge density, and would tend to aggregate or
fragment to form other ions.
For complex 2a spectra were run at cone voltages between 5
and 60 V, producing varying amounts of fragmentation. Over
the time of the experiment, the low-cone-voltage spectra
showed changes due to solvolysis reactions. The spectrum of a
freshly prepared solution, at a cone voltage of 20 V, illustrated
in Fig. 4, showed a strong aggregate-ion peak corresponding to
[3M ϩ 2NH4]2ϩ (the same major species as observed for 3b at
20 V) together with an [M ϩ H]ϩ ion. Over the course of several
minutes the solvolysis product [M Ϫ Cl ϩ MeCN]ϩ increased
in intensity, eventually becoming the dominant species in the
spectrum. The intensity of the [3M ϩ 2NH4]2ϩ aggregate also
decreased, while another aggregate, [3M ϩ 2H]2ϩ, appeared,
together with another solvolysis product, [M Ϫ Cl ϩ NH3]ϩ. A
small peak, due to [M Ϫ Cl]ϩ, had also formed. After almost 30
min had elapsed after sample preparation the intensity of the
ammonium aggregate and the [M ϩ H]ϩ ion had both fallen
markedly, while the [M Ϫ Cl ϩ NH3]ϩ ion had increased. The
acetonitrile solvolysis product had increased to more than twice
the intensity of any other peak. At the low cone voltage of 5 V
fragmentation of ions is unlikely. The complex 2a was dissolved
in acetonitrile–water 21 min before the 5 V spectrum was
obtained, hence the solvolysis reactions previously observed
were already underway before the spectrum was run. This was
seen in the spectrum, where the acetonitrile solvolysis product
J. Chem. Soc., Dalton Trans., 1997, Pages 4587–4594
4591

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was almost twice as intense as that of the [M ϩ H]ϩ ion.
Along with these ions, the two aggregates [3M ϩ 2NH4]2ϩ
and [3M ϩ 2H]2ϩ were again observed. We have previously
described analogous solvolysis reactions of related platinum()
complexes containing chloride and anionic amide ligands
derived from diethylbarbituric acid (1H,3H,5H-5,5-diethyl-
pyrimidine-2,4,6-trione).26
by substitution with the stoichiometric amount of ligand in
CH2Cl2 solution.32
AR grade solvents were used. Methanol was used as sup-
plied, while others were distilled from the following drying
agents: dichloromethane (calcium hydride), light petroleum,
b.p. 40–60 ЊC (calcium hydride) and diethyl ether (sodium–
benzophenone).
At 60 V fragmentation of the various solvated ions began to
occur. The predominant ions are [M Ϫ Cl]ϩ (m/z 865) and
[M Ϫ isat]ϩ (m/z 755), followed in intensity by [M ϩ H]ϩ and
[M Ϫ isat ϩ MeCN]ϩ. Orthometallation of one of the phenyl
rings of the triphenylphosphine ligands was observed by ions
at m/z 718 [Pt(o-C6H4PPh2)(PPh3)]ϩ and 754 [Pt(o-C6H4PPh2)-
(PPh3) ϩ MeCN]ϩ, typical of other (triphenylphosphine)plat-
inum complexes studied at high cone voltages.26,27
The NMR spectra were obtained on a Bruker AC300P spec-
trometer in CDCl3 unless otherwise stated, 1H spectra at 300.13
MHz, 13C-{1H} at 75.47 MHz, and 31P-{1H} at 121.5 MHz, the
latter referenced to external 85% H3PO4 (δ 0.0). Electrospray
mass spectra were obtained on a VG Platform II mass spec-
trometer, in positive-ion mode with acetonitrile–water (1:1 v/v)
as the mobile phase. Theoretical isotope patterns were calcu-
lated using the ISOTOPE program, version 1.6.6 d1.33 Melting
points were determined on a Reichert Thermopan instrument,
and are uncorrected. Infrared spectra were obtained as KBr
discs, using a Perkin-Elmer 1600 Series FTIR instrument.
Elemental analyses were carried out by the University of Otago
Campbell Microanalytical Laboratory.
Owing to the apparent effectiveness of the isatin complexes
to aggregate with ammonium cations, an investigation was car-
ried out into the ability of the complexes 2a and 3a to co-
ordinate alkali-metal cations. The spectrum of 2a with added
KCl contained most of the peaks seen in the previous 20 V
spectrum, together with the Kϩ adducts [M ϩ K]ϩ and [3M ϩ
K ϩ NH4]2ϩ
.
Syntheses
Addition of KCl to complex 3a gave, at 20 V, [M ϩ K]ϩ as the
main ion at m/z 1051; the isotope pattern of this ion appeared
‘filled-in’ suggesting that there was a small contribution from
[2M ϩ 2K]2ϩ, though individual peaks were not resolved.
Addition of both KCl and NaCl to 3a yielded three different
alkali-metal adducts in the 20 V spectrum, with [M ϩ K]ϩ the
most intense, followed by [M ϩ Na]ϩ at m/z 1034. The dicat-
ion [2M ϩ K ϩ Na]2ϩ was observed at m/z 1043, showing
isotope peaks separated by m/z 0.5, with no contribution from
a monocation possible. The isotope pattern for the [M ϩ Na]ϩ
ion appeared more filled-in than that for [M ϩ K]ϩ suggesting
a greater tendency of the higher charge-density Naϩ to con-
tribute to dicationic species. (It is worth noting that this trend
is the opposite to that observed for proton versus ammonium
aggregation for 3b, though presumably in this case the
extremely small size of the proton places constraints on
cis-[PtCl(isat)(PPh3)2] 2a. Isatin (0.019 g, 0.128 mmol) was
added to a stirred suspension of cis-[PtCl2(PPh3)2] (0.101 g,
0.128 mmol) in methanol (20 cm3). Triethylamine (0.5 cm3,
excess) was added and the solution stirred and heated at 45–
50 ЊC for 3.5 h. The solvent was removed under reduced pres-
sure, and the red solid redissolved in dichloromethane (40
cm3). Water (2 × 70 cm3) was used to extract the NEt3HϩClϪ
produced in the reaction. The organic phase was separated,
dried with anhydrous MgSO4, filtered and the filtrate evapor-
ated to dryness. The red solid was recrystallised from dichloro-
methane and light petroleum, washed with light petroleum
and dried under vacuum, yielding 0.096 g (83%) of dark red
crystals of complex 2a, m.p. 262 ЊC (Found: C, 58.8; H,
3.9; N, 1.6. C44H34ClNO2P2Pt requires C, 58.6; H, 3.8; N,
1.6%). NMR: 31P-{1H}, AB spin system, δ 17.0 (d, P trans Cl,
2
1
2
1JPtP 3832, JPP 18) and 7.8 (d, P trans N, JPtP 3101, JPP
aggregation.) On increasing the cone voltage to 60
V
18); 13C-{1H} [in CDCl –(CD ) SO], δ 192 (s, C᎐O, isat),
[M ϩ Na]ϩ became the major alkali-metal adduct, and the
fragmentation of the dications was indicated by the observ-
ation of fully resolved isotope patterns for both [M ϩ Na]ϩ
and [M ϩ K]ϩ, and disappearance of the [2M ϩ Na ϩ K]2ϩ
ion.
᎐
3
3 2
167.6 (s, amide C᎐O, isat), 164.0 (s, isat), 141.0 (s, isat),
᎐
2
2
138.5 (d, Ph ortho-C, JPC 9.9), 137.5 (d, Ph ortho-C, JPC
10.3), 135.0 (s, Ph para-C), 134.5 (s, Ph para-C), 132.9 (d, Ph
ipso-C, JPC 61.5), 131.7 (pseudo-t, Ph meta-C), 131.0 [s, half
1
of doublet (other half obscured by previous resonance), Ph
ipso-C], 126.7 (s, isat), 124.4 (s, isat, quaternary carbon),
124.1 (s, isat) and 117.9 (s, isat); 1H, δ 7.9–7.1 (m, Ph and
In another experiment pyridine was added to a fresh solution
of complex 2a, to examine the effect of a strongly co-ordinating
ligand. At 5 V the pyridine had replaced the chloride ion almost
completely, yielding the [M Ϫ Cl ϩ pyridine]ϩ ion at m/z 944.
A small peak due to [M Ϫ Cl ϩ NH3]ϩ was also seen at m/z
882. Very little change was seen on increasing the cone voltage
to 20 V. However, at 60 V, the principal ion was [M Ϫ Cl]ϩ,
together with a small amount of the two orthometallated
species observed earlier.
These experiments show that there is a strong tendency for
the isatin complexes to aggregate about cations, at least under
mass spectrometric conditions. The ESMS technique thus may
provide an excellent small-scale, rapid screening mechanism for
directing future studies aimed at isolating higher aggregates on
a synthetic scale.
3
3
isat), 6.97 (d, isat, JHH 6.9) and 6.61 (td, 1 H, isat, JHH 7.2,
4JHH 0.7 Hz). IR: ν max = 1732vs, 1685vs, 1605vs and 1586vs
cmϪ1
.
cis-[Pt(isat)2(PPh3)2] 3a. The complex cis-[PtCl2(PPh3)2]
(0.100 g, 0.127 mmol), isatin (ca. 0.1 g, 0.7 mmol) and NEt3 (0.5
cm3, excess) were allowed to react as above for 89 h. The
product was worked up as above, although the dichloro-
methane solution was filtered before washing with water, to
remove undissolved excess of isatin. Recrystallisation of the
product from hot methanol, followed by addition of diethyl
ether to complete precipitation, yielded 0.057 g (44%) of red
crystals of 3a, after washing with diethyl ether and drying
under vacuum. A suitable crystal was characterised by X-ray
crystallography. M.p. 268 ЊC (decomp.) (Found: C, 61.6; H, 4.0;
N, 3.1. C52H38N2O4P2Pt requires C, 61.7; H, 3.8; N, 2.8%).
Experimental
Cycloocta-1,5-diene and 1,3-bis(diphenylphosphino)propane
(Aldrich), isatin (BDH), and triphenylphosphine (Pressure
Chemical Co.) were used as supplied. 1,2-Bis(diphenyl-
phosphino)ethane29 and [PdCl2(bipy)]30 were prepared by lit-
erature methods. Triethylamine was distilled before use. The
complex [PtCl2(cod)] was synthesized by the literature pro-
cedure,31 and the phosphineplatinum complexes cis-[PtCl2-
(PPh3)2], [PtCl2(dppe)] and [PtCl2(dppp)] were prepared from it
1
NMR: 31P-{1H}, δ 3.76 (s, JPtP 3284); 13C-{1H}, δ 187.8 (s,
C᎐O, isat), 165.7 (s, amide C᎐O, isat), 159.8 (s, isat), 137.9 (s,
᎐
᎐
isat), 134.7 (pseudo-t, Ph, JPC 5.0), 130.9 (s, Ph), 128.0 (pseudo-
1
3
t, Ph, JPC 5.4), 127.8 (dd, Ph, JPC 66.7, JPC 8.9), 123.4 (s,
isat), 121.4 (s, isat), 120.6 (s, isat) and 115.6 (s, isat); 1H, δ 7.62–
3
4
7.55 (m, Ph), 7.32–7.24 (m, Ph), 7,20 (dd, isat, JHH 7.2, JHH
1.3), 7.17–7.09 (m, Ph), 6.93 (d, 2 H, isat, 3JHH 7.2) and 6.56 (td,
4592
J. Chem. Soc., Dalton Trans., 1997, Pages 4587–4594

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3
4
1
3
2 H, isat, JHH 7.4, JHH 0.9 Hz). IR: ν max = 1735vs, 1678vs,
1606vs and 1586vs cmϪ1
(s), 122.6 (s) and 117.1 (s, isat); H, δ 8.74 (d, 2 H, bipy, JHH
7.8), 8.56 (dd, 2 H, bipy, 3JHH 5.6, 4JHH 1.4), 8.46 (td, 2 H, bipy,
3JHH 7.8, 4JHH 1.3), 7.78 (m, 2 H, bipy), 7.42 (td, 2 H, isat, 3JHH
.
4
3
7.7, JHH 1.3), 7.31 (d, 2 H, isat, JHH 7.9), 7.20 (dd, 2 H, isat,
cis-[Pt(isat)2(dppe)] 3b. The complex cis-[PtCl2(dppe)] (0.050
g, 0.076 mmol), isatin (ca. 0.1 g, 0.7 mmol) and NEt3 (0.5 cm3)
were allowed to react as above, for ca. 2.5 d. The solvent was
removed by rotary evaporation and the product redissolved in
dichloromethane (70 cm3). The solution was washed with ten
portions (20–30 cm3) of distilled water in a separating funnel, to
remove triethylammonium chloride and some of the excess of
isatin. The red solution was separated and dried as above, the
solvent removed under reduced pressure, and the resulting red
solid recrystallised by dissolving in hot methanol and allowing
to cool. Crystallisation was aided by the addition of diethyl
ether. The solid was filtered off, washed with diethyl ether and
dried under vacuum to give 0.019 g (28%) of 3b as dark red
crystals, m.p. 315 ЊC (decomp.) (Found: C, 56.7; H, 3.8; N, 3.2.
C42H32N2O4P2Pt requires C, 57.0; H, 3.6; N, 3.2%). NMR:
3JHH 7.6, JHH 1.2) and 6.83 (t, 2 H, isat, JHH 7.5 Hz). IR:
4
3
ν max = 1727vs, 1676vs, 1605vs and 1587vs cmϪ1
.
Crystallography
Dark red crystals of complex 3a were obtained from methanol–
diethyl ether at 4 ЊC. Preliminary precession photography indi-
cated a monoclinic lattice. Unit-cell dimensions and intensity
data were collected using a Siemens SMART CCD diffract-
ometer, with Mo-Kα X-radiation (λ = 0.710 73 Å). The data col-
lection nominally covered over a hemisphere of reciprocal
space, by a combination of three sets of exposures with dif-
ferent φ angles. The crystal to detector distance was 5.0 cm.
The data set was corrected empirically for absorption using
SADABS34 (Tmax,min 0.704, 0.479).
31P-{1H}, δ 35.8 (s, JPtP 3173); 13C-{1H}, δ 189.5 (pseudo-t,
1
C᎐O, isat), 165.7 (s, amide C᎐O, isat), 161.1 (s, isat), 137.9 (s,
᎐
᎐
Crystal data. C52H38N2O4P2Pt, Mr = 1011.87, monoclinic,
space group P21/c, a = 11.2066(1), b = 18.0691(1), c =
21.1167(2) Å, β = 97.808(1)Њ, U = 4236.34(6) Å3, Z = 4, Dc =
1.587 g cmϪ3, µ(Mo-Kα) = 3.438 mmϪ1, F(000) 2016, T = 293(2)
K, crystal size = 0.14 × 0.28 × 0.32 mm.
isat), 133.4 (s, Ph), 132.3 (s, Ph), 129.2 (pseudo-t, Ph, JPC 5.7),
127.0 (d, Ph, JPC 61.8), 123.4 (s, isat), 121.2 (s, isat), 120.2 (s,
isat), 115.6 (s, isat) and 27.4 (dd, dppe CH2, 1JPC 42.9, 2JPC 6.8);
1H, δ 7.9–7.3 (m, 21 H, Ph), 7.1–6.9 (m, 6 H, isat), 6.51 (td, 2 H,
3
4
isat, JHH 7.3, JHH 0.8) and 2.5–2.3 (m, 4 H, dppe CH2). IR:
ν max = 1729vs, 1677vs, 1607vs and 1587vs cmϪ1
A total of 26 163 reflections were collected, over a range of
.
1.49 < θ < 28.27Њ, of which 9527 were independent (Rint
=
0.023). The structure was solved by direct methods (SHELXS
86)35 and developed routinely. Refinement (SHELXL 93)36 was
by full-matrix least squares on F2 and converged to R1 = 0.0242,
wR2 = 0.0542 [for 8359 data with I > 2σ(I)], and R1 = 0.0316,
wR2 = 0.0584 (all data), with goodness of fit = 1.089. In the
final difference map the largest features were at ϩ0.838 and
cis-[Pt(isat)2(dppp)] 3c. The complex cis-[PtCl2(dppp)] (0.101
g, 0.149 mmol), isatin (0.044 g, 0.299 mmol) and NEt3 (0.5 cm3)
were allowed to react as above, for 1 h. The product was worked
up as above, although it was only washed with a single portion
of distilled water. Recrystallisation, first by slow diffusion of
pentane into dichloromethane and then from methanol and
diethyl ether, yielded 0.074 g (55%) of dark red crystals of 3c,
after washing with diethyl ether and drying under vacuum, m.p.
180 ЊC (decomp.) (Found: C, 56.1; H, 4.3; N, 2.9. C43H34N2-
O4P2Pt requires C, 57.4; H, 3.8; N, 3.1%). Free isatin was
Ϫ1.098 e ÅϪ3
.
CCDC reference number 186/724.
Acknowledgements
observed in the NMR spectra of this complex. NMR: 31P-{1H},
The University of Waikato and the New Zealand Lottery
Grants Board are acknowledged for financial support of this
work. We thank Associate Professor C. E. F. Rickard and
Dr. L. J. Baker (University of Auckland) for collection of the
X-ray data set, and Johnson Matthey plc for a generous loan of
platinum. Dr. R. A. Thomson is thanked for literature searches.
1
δ Ϫ11.0 (s, JPtP 2963); 13C-{1H}, δ 188.4 (pseudo-t, C᎐O, isat,
᎐
JPC 2.8), 165.4 (s, amide C᎐O, isat), 160.5 (s, isat), 137.9 (s, isat),
᎐
133.4 (pseudo-t, Ph, JPC 5.2), 132.2 (pseudo-t, Ph, JPC 5.0),
131.3 (d, Ph, JPC 31.3), 128.5 (pseudo-t, Ph, JPC 5.4), 128.1 (s,
unchanged isatin), 127.7 (s, unchanged isatin), 126.2 (s,
unchanged isatin), 125.4 (s, unchanged isatin), 123.4 (s, isat),
121.1 (s, isat), 120.6 (s, isat), 115.8 (s, isat), 22.4 (m, dppp PCH2)
and 18.0 (s, dppp CCH2C); 1H, δ 7.8–7.2 (m, Ph), 7.20–7.00 (m,
isat), 6.93 (d, isat, 3JHH 6.9), 6.59 (td, 2 H, isat, 3JHH 7.2, 4JHH 1.3
Hz), 2.97 (m, 4 H, dppp CH2P) and 2.2 (m, 2 H, dppp CCH2C).
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