Coordination isomerism in salicylhydroxamate complexes of platinum(II) and palladium(II)

Article abstract of DOI:10.1039/b303367h

The syntheses of a range of platinum(II) and palladium(II) complexes containing salicylhydroxamate ligands are described. The ancillary ligands, together with the synthetic route, influence the coordination mode of the salicylhydroxamate ligand. Reaction of cis-[PtCl₂(PPh₃)₂] with salicylhydroxamic acid and trimethylamine in hot methanol gave O,O′-bonded [Pt{OC(=NO)C₆H₄OH} (PPh₃)₂], but [PtCl₂(cod)] (cod = cycloocta-1,5-diene) gave N,O-bonded [Pt{OC₆H₄C(O)NOH} (cod)]. Ligand substitution gives other N,O bonded complexes, including [Pt{OC₆H₄C(O)NOH}(PPh₃)₂]. Reaction of K₂PtCl₄ with 2 equiv. of EPh₃ (E = As or Sb), salicylhydroxamic acid and excess trimethylamine gives products whose structures depend on E; AsPh₃ gives [Pt{OC(=NO)C₆H₄-OH} (AsPh₃)₂], while SbPh₃ gives [Pt{OC₆H₄C(O)NOH} (SbPh₃)₂].

Full text of DOI:10.1039/b303367h

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Coordination isomerism in salicylhydroxamate complexes of
platinum(II) and palladium(II)
William Henderson,*a Cameron Evans,a Brian K. Nicholsona and John Fawcettb
a Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand
b Department of Chemistry, University of Leicester, Leicester, UK LE1 7RH
Received 25th March 2003, Accepted 12th May 2003
First published as an Advance Article on the web 28th May 2003
The syntheses of a range of platinum() and palladium() complexes containing salicylhydroxamate ligands
are described. The ancillary ligands, together with the synthetic route, influence the coordination mode of the
salicylhydroxamate ligand. Reaction of cis-[PtCl2(PPh3)2] with salicylhydroxamic acid and trimethylamine in
hot methanol gave O,OЈ-bonded [Pt{OC(᎐NO)C H OH}(PPh ) ], but [PtCl (cod)] (cod = cycloocta-1,5-diene)
᎐
6
4
3
2
2
gave N,O-bonded [Pt{OC6H4C(O)NOH}(cod)]. Ligand substitution gives other N,O bonded complexes, including
[Pt{OC6H4C(O)NOH}(PPh3)2]. Reaction of K2PtCl4 with 2 equiv. of EPh3 (E = As or Sb), salicylhydroxamic
acid and excess trimethylamine gives products whose structures depend on E; AsPh gives [Pt{OC(᎐NO)C H -
᎐
3
6
4
OH}(AsPh3)2], while SbPh3 gives [Pt{OC6H4C(O)NOH}(SbPh3)2].
[Pt{OC(᎐NO)C H OH}(PPh ) ] 2a,11 and the analogue
1
Introduction
᎐
6
4
3 2
[Pt{OC(᎐NO)C H OH}(SOMe ) ]12 containing salicylhydrox-
᎐
6
4
2 2
Hydroxamic acids, containing the –C(O)NHOH functionality,
are potent metal complexing agents, able to coordinate to
a wide range of metal ions.1–3 Nature has employed the
hydroxamate functional group to great effect in, for example,
microbial iron() complexing agents (siderophores), which,
together with synthetic siderophores often have extremely high
binding affinities for this metal ion.4 Hydroxamate ligands
typically coordinate as a bidentate chelating ligand, by co-
ordination of the carbonyl oxygen and the deprotonated OH
group to the metal centre. However, other binding modes are
possible, such as through nitrogen, or an ancillary donor group
in the ligand, and this is one of the features which has attracted
interest in this class of ligand.2,5 Following on from our recent
studies into platinum group metal and gold complexes of the
(sulfur–oxygen donor) thiosalicylate ligand,6,7 we were inter-
ested in extending our studies to complexes of deprotonated
salicylhydroxamic acid 1. This ligand presents a number of
potential binding modes to metal ions (Scheme 1) either in the
traditional O,OЈ binding mode A, or in alternative modes
involving the nitrogen atom and/or the phenolic oxygen (B–D).
Complexes of this ligand have been synthesised previously, for
example, a range of first row transition metals,8 copper()9 and
nickel().10 Hambley and co-workers have recently reported
some platinum() and palladium() complexes containing
deprotonated salicylhydroxamic acid ligands.11,12 In these
studies, two different binding modes were highlighted.
amate dianion ligands, have the well-established O,OЈ binding
mode (A, Scheme 1). In contrast, the complex [Pd{(OC6-
H C(OH)(᎐NOH)} ] contained the (monoanionic) ligand co-
᎐
4
2
ordinated through the deprotonated phenolic oxygen, and the
nitrogen atom, related to mode B in Scheme 1; this represented
a unique binding mode for this ligand. In this paper, we have
extended these studies, and report the syntheses of a range of
complexes containing salicylhydroxamate dianion ligands. It is
found that the ancillary ligands, and the synthetic route
employed, bear a strong influence on the binding mode of the
salicylhydroxamate ligand.
Scheme 1
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 2 6 9 1 – 2 6 9 7
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Table 1 Selected bond lengths (Å) and bond angles (Њ) for [Pt{O-
C6H4C(O)NOH}(PPh3)2] 3b
2
Results and discussion
Chemistry of the bis(triphenylphosphine)platinum(II) salicyl-
hydroxamate system
Pt(1)–O(1)
N(1)–C(7)
O(1)–C(1)
C(6)–C(7)
P(1)–C(21)
P(1)–C(11)
P(2)–C(41)
P(2)–C(51)
2.0313(14)
Pt(1)–N(1)
N(1)–O(3)
O(2)–C(7)
2.0327(17)
1.421(2)
1.257(2)
1.334(3)
1.340(2)
1.492(3)
1.817(2)
1.833(2)
1.818(2)
1.837(2)
The complex [Pt{OC(᎐NO)C H OH}(PPh ) ] 2a has been
᎐
6
4
3 2
previously synthesised by Hambley and co-workers, by the
reaction of cis-[PtCl2(PPh3)2] with salicylhydroxamic acid in
methanol with aqueous NaOH, and has been characterised by
an X-ray diffraction study.11 However, 31P NMR data were not
reported for the complex. We find that the reaction, when
carried out with trimethylamine as the base in hot methanol,
gives the same product as an authentic sample prepared using
the literature method, but does not require the pH to be
monitored. The 31P–{1H} NMR spectrum of this complex
shows a single species, with resonances at δ 11.1 and 9.5,
showing coupling to 195Pt of 3299 and 3786 Hz respectively. The
difference between the two coupling constants is surprisingly
large, and indicates that the two O donor groups have quite
different trans influences.
P(1)–C(31)
P(1)–Pt(1)
P(2)–C(61)
P(2)–Pt(1)
1.823(2)
2.2648(5)
1.824(2)
2.2596(5)
O(1)–Pt(1)–N(1)
O(1)–Pt(1)–P(1)
C(7)–N(1)–O(3)
O(3)–N(1)–Pt(1)
O(1)–C(1)–C(2)
O(2)–C(7)–N(1)
N(1)–C(7)–C(6)
84.04(6)
86.88(4)
111.42(15)
119.01(12)
116.81(18)
120.22(18)
118.35(17)
N(1)–Pt(1)–P(2)
P(2)–Pt(1)–P(1)
C(7)–N(1)–Pt(1)
C(1)–O(1)–Pt(1)
O(1)–C(1)–C(6)
O(2)–C(7)–C(6)
92.04(5)
97.017(18)
127.91(13)
120.11(12)
124.42(18)
121.42(18)
bonded isomer 2a described by Hambley and coworkers11
provides an excellent reference point for discussion of the
structure, since the ancillary ligands are the same. The N,O
isomer 3b has both a shorter C–O bond distance [C(7)–O(2)
1.257(2) Å] and a longer C–N bond distance [C(7)–N(1)
1.334(3) Å] than the O,OЈ isomer 2a, which has C–O 1.322(6)
and C–N 1.297(6) Å, consistent with the oxamate (as opposed
to oximate) binding in 3a. The palladium salicylhydroxamate
When the complex [PtCl2(cod)] (cod = cycloocta-1,5-diene) is
reacted with salicylhydroxamic acid and trimethylamine base
in hot methanol, a pale yellow microcrystalline solid 3a was
obtained, which analyses for [Pt(salicylhydroxamate)(cod)].
1
The complex shows two cod CH resonances in the H NMR
spectrum at δ 5.66 and 5.42, showing coupling to 195Pt of ca. 69
and 62 Hz respectively. A broad peak at δ 10 is assigned to an
OH proton, which exchanges on shaking with D2O. Two
cod CH and two CH2 resonances were also observed in the
13C–{1H} NMR spectrum, with the CH resonances showing
monoanion complex [Pd{(OC H C(OH)(᎐NOH)} ] likewise
᎐
6
4
2
has a C᎐N double bond, with a bond length of 1.294(4) Å.11
᎐
Unsurprisingly, the phenolic C–O bond has a similar bond
length in 3b [1.340(2) Å] to the uncoordinated version (with an
OH group) in 2a [1.349(7) Å].
1
different J(PtC) couplings of 157 and 171 Hz. Reaction of
complex 3a with 2 equiv. of triphenylphosphine in dichloro-
methane leads to a pale yellow complex 3b which analyses as
[Pt(salicylhydroxamate)(PPh3)2], but which has a different
melting point and spectroscopic properties to complex 2a
prepared directly from cis-[PtCl2(PPh3)2]. Thus, the 31P–{1H}
NMR spectrum of complex 3b shows two resonances at
δ 22.2 and 6.0 with 1J(PtP) 3455 and 3594 Hz respectively.
In order to unequivocally ascertain the mode of binding
of the salicylhydroxamate ligand to the platinum centre in 3b,
an X-ray structure determination was carried out. Crystals of
the complex were obtained from a CDCl3 solution. The molec-
ular structure and atom numbering scheme are shown in Fig. 1,
while Table 1 gives selected bond lengths and angles.
The platinum–phosphorus bond lengths also merit discus-
sion. In the N,O isomer 3b, the Pt–P bond distances are, on
average, slightly longer [2.2648(5) and 2.2596(5) Å] than in the
O,OЈ isomer 2a [2.2062(13) and 2.2335(17) Å], suggesting that
the donor groups in the N,O binding mode have a slightly
greater trans influence. In addition, the difference in the Pt–P
bond distances for the O,OЈ isomer 2a (0.0273 Å) is greater than
for the N,O isomer 3b (0.0052 Å), which is consistent with the
observation that difference in the 1J(PtP) coupling constants (of
the two PPh3 ligands) in the NMR spectrum of the O,OЈ isomer
(3299 and 3786 Hz) are greater than for the N,O isomer (3455
and 3594 Hz).
The platinum–salicylhydroxamate system of 3b is non-
planar, being puckered along the O(1) ؒ ؒ ؒ N(1) axis (Fig. 2a)
with an angle between the platinum coordination plane [defined
The structure determination indicates that the salicylhydrox-
amate ligand coordinates to platinum through the phenolate
oxygen and the nitrogen atom of the hydroxamic acid, forming
a six-membered chelate ring system (B, Scheme 1). The O,OЈ
Fig. 2 The degree of puckering and twisting of the salicylhydroxamate–
platinum system in (a) [Pt{OC6H4C(O)NOH}(PPh3)2] 3b and (b) [Pt-
{OC6H4C(O)NOH}(SbPh3)(p-NC5H4Me)] 5b, with only the donor
atoms of the ancillary ligands shown.
Fig. 1 Molecular structure of [Pt{OC6H4C(O)NOH}(PPh3)2] 3b,
showing the atom numbering scheme.
D a l t o n T r a n s . , 2 0 0 3 , 2 6 9 1 – 2 6 9 7
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Table 2 Selected 13C–{1H} NMR data for platinum() and pal-
by the atoms P(1), P(2), Pt(1), O(1) and N(1)] and the salicyl-
hydroxamate ligand [defined by atoms O(1), C(1)–C(6) and
C(7)] being 41.87(5)Њ. The hydroxamic acid moiety is also
twisted out of the plane of the benzene ring, Fig. 2a, with an
angle of 14.9(2)Њ between the planes defined by the benzene ring
(and associated phenolate oxygen) [C(1)–C(6) and O(2)] and
the plane defined by C(7), O(2) and N(1). This puckering
and twisting is reminiscent of that observed previously in
platinum() thiosalicylate complexes,7 and indicates somewhat
of a mismatch in size between the metal centre and the
preferred bite angle of the ligand, resulting in a ligand
deformation. The salicylhydroxamate ligand binding in the N,O
mode has a greater ‘bite’ angle [as indicated by the bond angle
O(1)–Pt(1)–N(1) 84.04(6)Њ] compared to the O,OЈ binding
mode in 2a [where the O–Pt–O bite angle is 79.21(13)Њ]. The
greater bite angle results in a slight decrease in the P(1)–Pt(1)–
P(2) bond angle in 3b [97.017(18)Њ] compared with the
corresponding angle in 2a [100.59(5)Њ]. By comparison,
ladium() salicylhydroxamate complexes, with the assignment of the
ligand binding modea
Complex
δ
13C
Assignment
2a
2b
2c
3a
3b
3c
3d
4
167.5, 157.0
167.3, 157.0
168.0, 157.0
162.4, 160.0
163.0, 161.1
162.9, 161.0
162.6, 160.9
164.5, 157.1
164.0, 159.0
O,OЈ
O,OЈ
O,OЈ
N,O
N,O
N,O
N,O
O,OЈ
N,O
5a
a Complexes with 13C NMR resonances at ca. δ 157 and 168 are
assigned the O,OЈ binding mode A; those with resonances at ca. δ 159–
160 and 163–164 are assigned the N,O mode B. Refer to Scheme 1.
much smaller separation of the two resonances, with a singlet
at δ 163.0 and a doublet at δ 161.1 [with J(PC) 6.6 Hz]. The
cod complex 3a shows two resonances in the C–O region of the
13C–{1H} NMR spectrum, at δ 162.4, and at 160.0, the latter
showing coupling to 195Pt of 43.5 Hz, and this complex is thus
assigned the N,O binding mode.
[Pt{OC(᎐NO)C H OH}(SOMe ) ] has an intermediate O–Pt–O
᎐
6
4
2 2
bite angle of 82.16(14)Њ.12
The CDCl3 of crystallisation is weakly hydrogen-bonded
to oxygen O(1), with a D ؒ ؒ ؒ O distance of 2.09 Å. Hydrogen
H(3) is also weakly hydrogen-bonded intramolecularly to O(2)
with a H(3) ؒ ؒ ؒ O(2) distance of 2.03 Å; the O(2)–C(7)–N(1)–
O(3) torsion angle is Ϫ0.59Њ, which facilitates this interaction.
There are no unusual intermolecular interactions. By
comparison, the O,OЈ isomer contains a similar intramolecular
hydrogen bond, between the phenolic OH proton and the
oximate nitrogen.
Synthesis and characterisation of other salicylhydroxamate
derivatives
Complexes of the salicylhydroxamate ligand, with platinum()
or palladium(), and various ancillary ligands, have been
synthesised either directly (from the metal halide complex) or,
in the case of platinum complexes, by ligand substitution of the
cod ligand from 3a. 13C–{1H} NMR spectroscopy has been
used to assign the binding modes of other complexes described
in this paper, with 31P–{1H} NMR spectroscopy also employed
where possible. The appropriate 13C NMR data and the ligand
binding mode assignments are summarised in Table 2 for the
various complexes reported in this paper.
The chemistry of the platinum()–1,1Ј-bis(diphenylphos-
phino)ferrocene (dppf )–salicylhydroxamate system mirrors
that of the triphenylphosphine system. Thus, reaction of
[PtCl2(dppf )] with salicylhydroxamic acid and trimethylamine
base gives the O,OЈ isomer 2b, which has resonances in the
31P–{1H} NMR spectrum at δ 10.7 and 8.5, with 195Pt–31P
coupling constants of 3348 and 3862 Hz respectively. These
values are very similar to the corresponding O,OЈ isomer of the
triphenylphosphine system, i.e. 2a. Two resonances at δ 167.3
and 157.0 in the 13C–{1H} NMR spectrum confirm the O,OЈ
binding mode. In contrast, the reaction of [Pt{OC6H4-
C(O)NOH}(cod)] 3a with dppf gives the N,O isomer 3c, which
has 31P NMR resonances at δ 20.3 and 5.0, with 1J(PtP) values
of 3497 and 3708 Hz respectively. The greater chemical shift
separation of the two phosphine resonances, and the closer
similarity of the corresponding 195Pt–31P coupling constants, by
comparison with the triphenylphosphine analogue, indicates
the N,O isomer in this case. Like the PPh3 system, the N,O
bonded dppf complex 3c undergoes an isomerisation in CDCl3
solution to the O,OЈ isomer 2b over the period of several
days.
The O,OЈ bonded isomer 2a appears to be the more stable
of the two isomers, and several lines of evidence point towards
this conclusion. Firstly, the bite angle of the salicylhydroxamate
ligand in the O,OЈ isomer is smaller than in the N,O isomer 3b
(which requires puckering of the ligand in order to coordinate
more effectively). Secondly, the electrospray mass spectra of the
two isomers at a low cone voltage (20 V) appear very similar,
with [M ϩ H]ϩ the base peak (m/z 871), and [2M ϩ H]ϩ (m/z
1741) also seen as a lower intensity ion. However, at an elevated
cone voltage (80 V), fragmentation is seen, giving the ion
[Pt(C6H4PPh2)(PPh3)]ϩ (m/z 718), formed by cyclometallation
of a triphenylphosphine ligand, and loss of the salicylhydrox-
amate ligand. The intensity of this ion in the spectrum of the
N,O isomer 3b (ca. 85%) was significantly greater than that
from the O,OЈ isomer 2a (ca. 33%), suggesting that the N,O
isomer is more susceptible to fragmentation, as a result of
reduced stability compared to the O,OЈ isomer. Thirdly, the O,O
isomer 2a melts at 280–282 ЊC, while the N,O isomer 3b initially
melts at ca. 210 ЊC, resolidifies, and then remelts at 280–282 ЊC,
suggesting that a thermal isomerisation reaction might be
occuring to give the O,OЈ-isomer 2a. Heating a sample of the
N,O isomer to 250 ЊC for 5 min resulted in (incomplete) conver-
sion to the O,OЈ isomer 2a, while heating a sample of 2a under
the same conditions resulted in no change to the 31P NMR
spectrum. A fourth piece of evidence pointing towards the
greater stability of the O,OЈ isomer is the fact that the reaction
mixture between [Pt{OC6H4C(O)NOH}(cod)] and 2 equiv. of
PPh3 initially gives solely the N,O isomer [δ 31P 22.3 and 6.1] but
on prolonged standing (several days) in the CDCl3 solution, a
small amount of the O,OЈ isomer [δ 31P 11.1, 9.5] was seen to
form. It is worth noting that theoretical calculations on the
salicylhydroxamate monoanion complex [Pd{(OC6H4C(OH)-
When [PdCl2(PPh3)2] is reacted with salicylhydroxamic acid
under the usual conditions, a maroon solid is obtained. Two 31
P
NMR resonances are observed [δ 31.5 and 28.6], the chemical
shift difference ∆δ (2.9 ppm) being much closer to the small
(᎐NOH)} ] indicated that the N,O isomer observed experi-
᎐
2
mentally is the most stable in this case.11 Hambley and co-
workers have suggested that the O,OЈ binding mode is stabilized
by the presence of soft ligands trans to the hydroxamate
ligand.12
shift difference for the O,OЈ bonded [Pt{OC(᎐NO)C H OH}-
᎐
6
4
(PPh3)2] 2a [∆δ 1.6 ppm] than the N,O bonded [Pt{OC6-
H4C(O)NOH}(PPh3)2] 3b [∆δ 16.2 ppm]. Hence the palladium
complex is assigned the O,OЈ bonded structure 4 (consistent
with its preparation from the dichloride). The 13C–{1H} NMR
spectrum of 4 shows a doublet of doublets at δ 164.5 [J(PC)
15.9 and 2.4] and a singlet at δ 157.1, consistent with O,OЈ
bonding (Table 2).
13C–{1H} NMR spectroscopy can also be used to determine
the binding mode of the salicylhydroxamate ligand. The O,O-
bonded isomer 2a shows a broad resonance at δ 167.5 and
a singlet at δ 157.0. In contrast, the N,O isomer 3b shows a
D a l t o n T r a n s . , 2 0 0 3 , 2 6 9 1 – 2 6 9 7
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Table 3 Selected bond lengths (Å) and bond angles (Њ) for [Pt{-
OC6H4C(O)NOH}(SbPh3)(p-NC5H4Me)] 5b
The reactions of [PtCl2(EPh3)2] (generated in situ from
K2PtCl4 and EPh3; E = As or Sb) with salicylhydroxamic acid
and trimethylamine give yellow solids which analyse for
[Pt(salicylhydroxamate)(EPh3)2]. However, 13C–{1H} NMR
data suggest that these two complexes do not have the same
structure. The AsPh3 complex 2c shows two singlets at δ 168.0
and 157.0, and is assigned the O,OЈ binding mode (analogous
to the lighter PPh3 congener), but in contrast, the SbPh3
complex shows signals at δ 164.0 and 159.7, and is assigned the
N,O binding mode 5a (Table 2). Supporting evidence for the
assignment of the stibine complex comes from X-ray crystallo-
graphic characterisation of a ligand-substituted derivative,
described in the next section.
Pt(1)–N(1)
Pt(1)–N(2)
Sb(1)–C(19)
Sb(1)–C(13)
O(2)–C(1)
N(1)–C(1)
1.972(4)
2.049(4)
2.117(6)
2.129(5)
1.263(6)
1.333(7)
Pt(1)–O(3)
Pt(1)–Sb(1)
Sb(1)–C(25)
O(1)–N(1)
O(3)–C(7)
C(1)–C(2)
1.999(4)
2.5060(7)
2.122(5)
1.421(6)
1.317(6)
1.481(8)
N(1)–Pt(1)–O(3)
N(1)–Pt(1)–Sb(1)
C(19)–Sb(1)–C(25)
C(25)–Sb(1)–C(13)
C(25)–Sb(1)–Pt(1)
C(7)–O(3)–Pt(1)
C(1)–N(1)–Pt(1)
O(2)–C(1)–N(1)
N(1)–C(1)–C(2)
91.78(17)
91.57(13)
102.6(2)
100.5(2)
122.85(15)
125.4(3)
130.9(4)
120.6(5)
119.5(5)
O(3)–Pt(1)–N(2)
N(2)–Pt(1)–Sb(1)
C(19)–Sb(1)–C(13)
C(19)–Sb(1)–Pt(1)
C(13)–Sb(1)–Pt(1)
C(1)–N(1)–O(1)
O(1)–N(1)–Pt(1)
O(2)–C(1)–C(2)
83.05(16)
93.62(12)
98.8(2)
115.59(15)
112.90(15)
113.9(4)
The reaction of the cod complex 3a with excess triphenyl-
phosphite gave white microcrystals of the phosphite complex
3d, which is proposed on the basis of 13C NMR data to have the
N,O bonded structure (refer to Table 2).
115.1(3)
119.9(5)
and 2.0327(17) Å respectively], due to the lower trans influence
of triphenylstibine and 4-methylpyridine compared with tri-
phenylphosphine.13,14 In 5b the O(3)–Pt(1)–N(1) bond angle
[91.78(17)Њ] is even larger than in the N,O-triphenylphosphine
complex [84.04(6)Њ], while the Sb(1)–Pt(1)–N(2) bond angle
between the pyridine and stibine ligands is more acute, at
93.62(12)Њ. Compared with the N,O bonded bis(triphenyl-
phosphine) complex 3b, the stibine complex 5b is much less
puckered; the angle between the planes defined by the Pt co-
ordination sphere [Sb(1), N(1), Pt(1), O(3), N(2)] and the ligand
[O(3) and C(1)–C(7)] is only 3.2Њ, as shown in Fig. 2b. Likewise,
the twist angle of the hydroxamate group [defined by N(1), C(1)
and O(2)] and the plane of the ligand [O(3) and C(1)–C(7)] is
4.7Њ. The sterically less demanding ligands in the case of 5b
allow contraction of the Sb–Pt–N angle, with concomitant
widening of the N–Pt–O salicylhydroxamate angle, so less
puckering and twisting of the ligand is required to match the
metal and ligand requirements.
The Pt–Sb distance of 2.5060(7) Å is similar to the Pt–Sb
distance of 2.507(2) Å in the compound [Bu4N][PtI3(SbPh3)],13
and the average Pt–Sb distance of 2.503(1) Å in two independ-
ent molecules in the structure of cis-[PtCl2(SbPh3)2].15 It is
worth noting that there have only been eight previous structure
determinations on Pt–SbPh3 complexes.16 The Pt–N distance to
the pyridine [2.049(4) Å] appears normal compared to Pt–N
bond lengths of 2.01(1) and 2.04(1) Å in cis-[PtCl2(pyridine)2].17
The complex dimerises by formation of two O–H ؒ ؒ ؒ O
X-Ray structure determination of
[Pt{OC6H4C(O)NOH}(SbPh3)(p-NC5H4Me)] 5b
Reaction of the bis(triphenylstibine) complex 5a with excess
4-methylpyridine in dichloromethane solution resulted in
formation of yellow crystals of the mono(stibine) complex
[Pt{OC6H4C(O)NOH}(SbPh3)(p-NC5H4Me)] 5b, which was
characterised by elemental analysis, and an X-ray diffraction
study.
The molecular structure and atom numbering scheme are
shown in Fig. 3, while Table 3 gives selected bond lengths and
angles. The structure determination confirms the N,O binding
mode of the ligand, and allows comparison with the triphenyl-
phosphine complex described above. The phenolate oxygen is
trans to the SbPh3 ligand, while the coordinated N(OH) group
is trans to the 4-methylpyridine ligand. The stibine ligand trans
to the N(OH) group of 5a might be expected to be substituted
more readily, because in the triphenylphosphine–platinum
N,O structure 3b, the phosphine trans to the N(OH) group
has the longer Pt–P bond distance. This would account for the
formation of the observed isomer of [Pt{OC6H4C(O)NOH}-
(SbPh3)(p-NC5H4Me)] 5b.
The bond lengths within the salicylhydroxamate ligand are
very similar to those of the N,O-bonded bis(triphenyl-
phosphine) complex 3b; the C(1)–O(2) and C(1)–N(1) bond
distances of 1.263(6) and 1.333(7) Å are consistent with C᎐O
᎐
double and C–N single bonds. The Pt(1)–O(3) [1.999(4) Å]
and Pt(1)–N(1) [1.972(4) Å] distances are shorter than their
counterparts in the triphenylphosphine analogue 3b [2.0313(14)
hydrogen bonds between C᎐O and N–OH groups, as shown in
᎐
Fig. 4. The O(1) ؒ ؒ ؒ O(2) distance is 2.719 Å, and the O(1)–H(1)
bond distance is 0.820 Å, with an O(1)–H(1)–O(2) angle of
158.4Њ. The O(1)–N(1)–C(1)–O(2) torsion angle is Ϫ1.6Њ. This
dimerisation might be facilitated by the coplanarity of the
NOH and C᎐O groups in this particular complex, a feature not
᎐
present in the triphenylphosphine analogue 3b.
Fig. 4 Diagram showing the formation of hydrogen-bonded dimers
between pairs of molecules of [Pt{OC6H4C(O)NOH}(SbPh3)(p-NC5-
H4Me)] 5b.
Fig.
3
Molecular structure of [Pt{OC6H4C(O)NOH}(SbPh3)-
(p-NC5H4Me)] 5b showing the atom numbering scheme.
D a l t o n T r a n s . , 2 0 0 3 , 2 6 9 1 – 2 6 9 7
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Table 4 Biological activity data for selected salicylhydroxamate complexes
Antimicrobial activityb
a
P388 IC50
/
Pseudomonas
aeruginosa
Candida
albicans
Trichophyton
mentagrophytes
Cladosporium
resinae
Complex
ng mLϪ1 (/µM)
Eschericia coli
Bacillus subtilis
2a
2b
3a
3b
3c
4
12898 (14.8)
10788 (12.0)
785 (1.7)
1382 (1.6)
16368 (18.1)
22712 (29.1)
0
0
5
0
0
0
0
0
12
0
0
1
0
0
1
0
0
0
0
0
5
0
0
0
0
0
8
0
0
0
0
0
2
0
0
0
a The concentration of sample in ng mLϪ1 (µM) required to reduce the cell growth of the P388 leukemia cell line (ATCC CCL 46) by 50%. b Inhibition
zone as excess radius (mm) from a 6 mm diameter disc containing 2 mg of sample
Biological activity
ISOTOPE simulation program.18 IR spectra were recorded as
KBr disks on a Perkin Elmer 1500 series instrument. Melting
points were recorded on a Reichert-Jung hotstage apparatus,
and are uncorrected. Elemental analyses were carried out by
the Campbell Microanalytical Laboratory, Department of
Chemistry, University of Otago, New Zealand.
The availability of different coordination isomers in the current
work offered the opportunity to test the effect of this on the
biological activity of the complexes. A selection of complexes
was assayed for activity against P388 murine leukemia cells, and
against 3 fungi and 3 bacteria, and data are summarised in
Table 4. The N,O-bonded complexes 3a and 3b both show good
activity against the P388 leukemia cells, with IC50 values of
1.7 and 1.6 µM respectively. The other complexes, including the
triphenylphosphine-containing O,OЈ isomer 2a, and both dppf
isomers 2b and 3c, are essentially inactive. In the antimicrobial
screen, only the cyclooctadiene complex 3a showed any activity,
with some selectivity against Bacillus subtilis.
Biological assays were carried out by the commercial service
offered by the Marine Chemistry Group, Department of
Chemistry, Canterbury University, New Zealand. Samples were
dissolved in 3 : 1 methanol–dichloromethane prior to testing.
Antitumour assays were carried out by determining, by means
of a two-fold dilution series, the concentration of sample in ng
mLϪ1 required to reduce the cell growth of the P388 leukemia
cell line (ATCC CCL 46) by 50%. The sample of interest was
incubated for 72 h with the P388 Murine Leukemia cells. IC50
values were determined by measurement of the absorbance
values when the yellow dye MTT tetrazolium is reduced by
healthy cells to the purple dye MTT formazan. The antimicro-
bial assays were carried out by measuring the inhibition zone as
an excess radius (mm) from a 6 mm diameter filter paper disk
containing 2 mg of sample, which was placed on a seeded agar
plate containing the organism tested.
Discussion and conclusions
In this paper we have described syntheses of a series of
platinum() and palladium() complexes containing salicyl-
hydroxamate ligands. In some cases, complexes containing
the ligand coordinated through the N and the deprotonated
phenolic oxygen are obtained (the N,O binding mode A,
Scheme 1) while in others, an alternative binding mode employ-
ing the two other oxygen atoms (the O,OЈ binding mode B) is
seen. 13C–{1H} and 31P–{1H} NMR spectroscopy can be used
to determine the ligand binding mode in individual cases.
The nature of the ancillary ligands appears to play a role in
determining the isomer formed. When the ligand is a relatively
bulky ligand, viz. triphenylphosphine, triphenylarsine or dppf,
the O,OЈ isomer is formed, possibly because the resulting
five-membered chelate ring gives a more acute ‘bite’ at the metal
centre, allowing the P–Pt–P or As–Pt–As bond angle to open
out to relieve steric congestion. However, when a smaller ligand
is used – e.g. cyclooctadiene, but also triphenylstibine, where the
long Pt–Sb bond results in less effective steric bulk at the metal
centre than for AsPh3 or PPh3 – the N,O isomer is formed.
Ligand substitution of the cod ligand then allows access to
a range of N,O bonded complexes which are not directly
accessible from the phosphine–halide complexes. The salicyl-
hydroxamate ligand has clearly produced some unanticipated
results, and merits further investigation with other metal
systems.
Materials and methods
Reactions were carried out in air, in reagent grade methanol,
with no further purification. Water was single-distilled prior to
use. The following compounds were used as supplied from
commercial sources: K2PtCl4 (Johnson Matthey), salicyl-
hydroxamic acid (Sigma), triphenylphosphine (BDH), tripheny-
larsine
(Aldrich),
triphenylstibine
(triphenylantimony)
(Aldrich), triphenylphosphite (Aldrich), aqueous trimethyl-
amine (33%, BDH), 4-methylpyridine (BDH), 1,1Ј-bis-
(diphenylphosphino)ferrocene (Aldrich). The compounds
[PtCl2(cod)]19 and [PdCl2(cod)]20 were prepared following the
literature methods. The complexes cis-[PtCl2(PPh3)2] and
[PdCl2(PPh3)2] were prepared by ligand substitution of the
cod ligand in the appropriate [MCl2(cod)] complex with the
stoichiometric quantity of the phosphine in dichloromethane.
Synthesis of [Pt{OC(᎐NO)C H OH}(PPh ) ] 2a
᎐
6
4
3 2
A suspension of cis-[PtCl2(PPh3)2] (300 mg, 0.380 mmol) and
salicylhydroxamic acid (300 mg, 1.960 mmol) in methanol (30
mL) with trimethylamine solution (2 mL, excess) was refluxed
for 1 h giving a yellow suspension. After cooling to room
temperature, the yellow solid was filtered off, washed with water
(10 mL) and diethyl ether (10 mL) and dried under vacuum to
give 2a (295 mg, 89%). Mp decomp. >240 ЊC, melting 280–282
ЊC. Found: C, 59.4; H, 3.8; N, 1.6. C43H35NO3P2Pt requires C,
59.3; H, 4.05; N, 1.6%. 31P–{1H} NMR, δ 11.1 [d, 1J(PtP) 3299,
3
Experimental
3.1 Instrumentation
All NMR spectra were recorded in CDCl3 solution on a Bruker
AC300P instrument, as follows: H (300.13 MHz), 13C–{1H}
1
(75.47 MHz), 31P–{1H} (121.51 MHz). 1H and 13C NMR spec-
tra were referenced relative to residual CHCl3, while 31P NMR
spectra were referenced relative to external 85% H3PO4 (δ 0.0).
Electrospray mass spectra were recorded on a VG Platform II
instrument, using acetonitrile–water (1 : 1 v/v) as the mobile
phase and solvent; further details have been described pre-
viously.6,7 Assignment of major ions was aided by use of the
1
2
2J(PP) 23] and 9.5 [d, J(PtP) 3786, J(PP) 23 Hz]. 13C–{1H}
NMR, δ 167.5 (s, br), 157.0 (s), 134.8–114.9 (m, Ph). ESMS:
cone voltage 20 V, [M ϩ H]ϩ (m/z 871, 100%), [2M ϩ H]ϩ (m/z
1741, 38%). Cone voltage 80 V, [Pt(C6H4PPh2)(PPh3)]ϩ (m/z 718,
33%), [M ϩ H]ϩ (m/z 871, 100%), [2M ϩ H]ϩ (m/z 1741, 5%).
D a l t o n T r a n s . , 2 0 0 3 , 2 6 9 1 – 2 6 9 7
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Synthesis of [Pt{OC(᎐NO)C H OH}(dppf)] 2b
[M ϩ H]ϩ (m/z 871, 100%), plus several other low intensity
ions.
᎐
6
4
To a suspension of [PtCl2(cod)] (300 mg, 0.802 mmol) in
methanol (30 mL) was added dppf (444 mg, 0.802 mmol) and
the mixture stirred and warmed gently, to generate [PtCl2-
(dppf )] in situ. To the resulting orange suspension was added
salicylhydroxamic acid (400 mg, 2.613 mmol) and trimethyl-
amine solution (2 mL, excess) and the mixture refluxed for 2.5
h. After cooling to room temperature, the resulting orange solid
product was filtered off, washed with water (10 mL) and diethyl
ether (10 mL) and dried under vacuum to give 2b (475 mg,
66%). Mp > 260 ЊC (decomp.). Found: C, 53.9; H, 3.5; N, 1.5.
C41H33NFeO3P2Pt requires C, 54.7; H, 3.7; N, 1.6%. 31P–{1H}
NMR, δ 10.7 [d, J(PtP) 3348, J(PP) 24] and 8.5 [d, J(PtP)
3862, 2J(PP) 24]. 13C–{1H} NMR, δ 167.25 [dd, br, J(PC) ca. 10,
3 Hz], 157.0 (s), 135.1–114.9 (m, Ph), 76.4–73.2 (m, Cp). ESMS:
cone voltage 20 V, [M ϩ H]ϩ (m/z 901, 100%), [2M ϩ H]ϩ (m/z
1800, 8%).
Synthesis of [Pt{OC6H4C(O)NOH}(dppf)] 3c
The complex [Pt{OC6H4C(O)NOH}(cod)] (100 mg, 0.220
mmol) and dppf (122 mg, 0.220 mmol) were dissolved in
dichloromethane (3 mL) to give an orange solution. Diethyl
ether (ca. 10 mL) was added, giving orange microcrystals which
were filtered off, washed with ether and dried under vacuum to
give 3c (179 mg, 90%). Mp > 260 ЊC. Found: C, 51.1 H, 4.0; N,
1.45. C41H33NFeO3P2PtؒCH2Cl2 requires C, 51.2; H, 3.6; N,
1.4%; the presence of CH2Cl2 of crystallisation was confirmed
by NMR spectroscopy. 31P–{1H} NMR, δ 21.6 [d, 1J(PtP) 3497,
1
2
1
1
2
2J(PP) 27] and 5.1 [d, J(PtP) 3708, J(PP) 27 Hz]. 13C–{1H}
NMR, δ 162.9 (s), 161.0 (s), 135.0–113.4 (m, Ph), 73.1–70.1 (m,
C5H4). ESMS: cone voltage 20 V, [M ϩ H]ϩ (m/z 901, 100%),
[2M ϩ H]ϩ (m/z 1800, 3%).
Synthesis of [Pt{OC6H4C(O)NOH}{P(OPh)3}2] 3d
Synthesis of [Pt{OC(᎐NO)C H OH}(AsPh ) ] 2c
᎐
6
4
3 2
The complex [Pt{OC6H4C(O)NOH}(cod)] (100 mg, 0.220
mmol) was dissolved in dichloromethane (2 mL) and triphenyl-
phosphite (3 drops) added. Addition of ether (2 mL) followed
by partial evaporation of the solvent gave white microcrystals
which were filtered off, washed with diethyl ether (5 mL) and
dried under vacuum to give 3d (90 mg, 42%). Mp 160–164 ЊC.
Found: C, 53.4; H, 3.6; N, 1.5. C43H35NO9P2Pt requires C, 53.4;
To a solution of K2PtCl4 (300 mg, 0.723 mmol) in water (5 mL)
and methanol (35 mL) was added triphenylarsine (442 mg,
1.444 mmol) and the mixture warmed with stirring to give a
pale yellow suspension. Salicylhydroxamic acid (300 mg, 1.960
mmol) and aqueous trimethylamine (2 mL, excess) were added
in succession, and the mixture refluxed for 1 h to give a yellow
suspension. After cooling to room temperature, the product
was filtered off, washed with water (10 mL), diethyl ether
(10 mL) and dried under vacuum to give a yellow powder of 2c
(545 mg, 79%). Mp 248–250 ЊC. Found: C, 53.9; H, 3.6; N, 1.5.
C43H35NAs2O3Pt requires C, 53.9; H, 3.7; N, 1.5%. 13C–{1H}
NMR, δ 168.0 (s), 157.0 (s), 133.6–115.0 (m, Ph). ESMS: cone
voltage 20 V, [M ϩ H]ϩ (m/z 959, 100%), [2M ϩ H]ϩ (m/z 1916,
10%).
1
H, 3.65; N, 1.45%. 31P–{1H} NMR, δ 67.44 [d, J(PtP) 5277,
2J(PP) 66.4], 62.04 [d, 1J(PtP) 5649, 2J(PP) 66.4]. 13C–{1H}
NMR, δ 162.6 (s, br), 160.9 [d, J(PC) ca. 7.5 Hz], 150.9 (m),
129.9–116.4 (m). ESMS: cone voltage 20 V, [M ϩ H]ϩ (m/z 967,
100%).
Synthesis of [Pd{OC(᎐NO)C H OH}(PPh ) ] 4
᎐
6
4
3 2
To a suspension of [PdCl2(PPh3)2] (400 mg, 0.570 mmol) and
salicylhydroxamic acid (400 mg, 2.613 mmol) in methanol
(30 mL) was added trimethylamine solution (2 mL, excess). The
mixture was refluxed for 25 min giving deep maroon micro-
crystals in a red solution. After cooling to room temperature
and standing overnight, the product was filtered off, washed
with water (10 mL) and diethyl ether (10 mL) and dried under
vacuum to give 4 (365 mg, 82%). Mp 224–226 ЊC. Found: C,
66.3; H, 4.5; N, 1.8. C43H35NO3P2Pd requires C, 66.0; H, 4.5; N,
Synthesis of [Pt{OC6H4C(O)NOH}(cod)] 3a
To a suspension of [PtCl2(cod)] (1.50 g, 4.01 mmol) and salicyl-
hydroxamic acid (1.10 g, 7.2 mmol) in methanol (50 mL) was
added trimethylamine solution (3 mL, excess), and the mixture
refluxed for 1 h to give a yellow suspension. Water (50 mL) was
added to the hot suspension which was cooled and allowed to
stand overnight. The resulting pale yellow microcrystalline
solid was filtered off, washed with water (2 × 10 mL) and diethyl
ether (2 × 10 mL) and dried under vacuum to give 3a (1.74 g,
96%). Mp 202–204 ЊC. Found: C, 39.8; H, 3.6; N, 3.1. C15H17-
NO3Pt requires C, 39.7; H, 3.8; N, 3.1%. 1H NMR, δ 10.0 (s, br,
2
2
1.8%. 31P–{1H} NMR, δ 31.5 [d, J(PP) 40.5], 28.6 [d, J(PP)
40.5]. 13C–{1H} NMR, δ 164.5 [dd, J(PC) 15.9, 2.4 Hz], 157.1
(s), 134.7–114.9 (m, Ph). ESMS: cone voltage 20 V, [M ϩ H]ϩ
(m/z 782, 100%), [Pd {OC(᎐NO)C H O}(PPh ) ]ϩ (m/z 1412,
᎐
2
6
4
3 4
2
OH), 8.20–6.79 (m, Ph), 5.66 [m, CH of cod, J(PtH) 69], 5.42
18%).
2
[m, CH of cod, J(PtH) 62], and 2.78–2.35 (m, CH2 of cod).
13C–{1H} NMR, δ 162.4 (s), 160.0 [s, J(PtC) 43.5], 131.3, 130.5,
119.2, 117.8, 116.4 (s, Ph), 98.5 [s, CH of cod, 1J(PtC) 157], 94.2
[s, CH of cod, 1J(PtC) 171 Hz], 31.3 (s, CH2 of cod), and 28.7 (s,
CH2 of cod). ESMS: cone voltage 20 V, [M ϩ H]ϩ (m/z 455,
100%), [2M ϩ H]ϩ (m/z 909, 65%), [3M ϩ H]ϩ (m/z 1363, 10%).
Synthesis of [Pt{OC6H4C(O)NOH}(SbPh3)2] 5a
To a solution of K2PtCl4 (300 mg, 0.723 mmol) in water (5 mL)
was added triphenylstibine (511 mg, 1.448 mmol) and methanol
(35 mL), and the mixture warmed with stirring to give a yellow
precipitate. Salicylhydroxamic acid (300 mg, 1.960 mmol) and
aqueous trimethylamine (2 mL) were added and the mixture
refluxed for 1 h to give a yellow suspension. After cooling to
room temperature the product was filtered, washed with water
(10 mL), diethyl ether (10 mL) and dried under vacuum to give
a bright yellow powder, yield 549 mg (72%). Mp decomp. > 220
ЊC. Found: C, 49.3; H, 3.2; N, 1.3. C43H35NO3PtSb2 requires C,
49.1; H, 3.4; N, 1.3%. Mp decomp. > 220 ЊC. ESMS: cone
voltage 20 V, [M ϩ H]ϩ (m/z 1054, 100%), [2M ϩ H]ϩ (m/z 2104,
5%).
Synthesis of [Pt{OC6H4C(O)NOH}(PPh3)2] 3b
The complex [Pt{OC6H4C(O)NOH}(cod)] (100 mg, 0.220
mmol) and triphenylphosphine (116 mg, 0.443 mmol) were
dissolved in dichloromethane (2 mL), and after several minutes,
diethyl ether (ca. 20 mL) was added until the solution turned
cloudy. On standing, a pale yellow microcrystalline solid
formed, which was filtered off, washed with ether (10 mL) and
dried under vacuum to give 3b (185 mg, 96%). Mp > 210 ЊC,
then resolidified to melt at 280–282 ЊC. Found: C, 58.6; H,
3.9; N, 1.6. C43H35NO3P2Pt requires C, 59.3; H, 4.05; N, 1.6%.
Synthesis of [Pt{OC6H4C(O)NOH}(SbPh3)(p-NC5H4Me)] 5b
1
2
31P–{1H} NMR, δ 22.2 [d, J(PtP) 3455, J(PP) 26] and 6.0
To a solution of complex 5a (200 mg, 0.190 mmol) in distilled
dichloromethane (5 mL) was added 4-methylpyridine (5 drops)
and the solution allowed to stand for 3 days. The resulting
yellow crystals were filtered, washed with diethyl ether (5 mL)
and dried, yield 85 mg (56%). Mp decomp. > 190 ЊC. Found: C,
[d, J(PtP) 3594, J(PP) 26]. 13C–{1H} NMR, δ 163.0 (s, br),
161.1 [d, J(PC) 6.6 Hz], 134.8–115.8 (m, Ph). ESMS: cone
voltage 20 V, [M ϩ H]ϩ (m/z 871, 100%), [2M ϩ H]ϩ (m/z 1741,
20%); cone voltage 80 V, [Pt(C6H4PPh2)(PPh3)]ϩ (m/z 718, 85%),
1
2
D a l t o n T r a n s . , 2 0 0 3 , 2 6 9 1 – 2 6 9 7
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Table 5 Crystal, collection and refinement data for [Pt{OC6H4C(O)NOH}(PPh3)2] 3b and [Pt{OC6H4C(O)NOH}(SbPh3)(p-NC5H4Me)] 5ba
3b
5b
Empirical formula
Formula weight
C44H36Cl3NO3P2Pt
990.12
C31H27N2O3PtSb
792.39
Crystal system
Space group
Triclinic
P1
Triclinic
P1
¯
¯
a/Å
b/Å
c/Å
α/Њ
10.5685(1)
11.9897(1)
17.6626(2)
91.247(1)
100.125(1)
116.025(1)
1967.42(3)
2
10.0243(11)
10.6353(9)
14.590(3)
106.725(19)
100.613(15)
102.365(19)
1404.0(3)
2
β/Њ
γ/Њ
V/Å3
Z
Temperature/K
Reflections collected
Independent reflections [Rint
150(2)
17595
7447 [0.0161]
3.893
0.0148, 0.0372
0.0156, 0.0375
200(2)
8032
7628 [0.0254]
5.973
0.0381, 0.0915
0.0461, 0.0958
]
Absorption coefficient/mmϪ1
Final R1, wR2 indices [I > 2σ(I )]
R1, wR2 indices (all data)
a Programs used: SHELX9721 and SADABS.22
3 R. C. Mehrotra, in Comprehensive Coordination Chemistry,
Pergamon, Oxford, 1982, section 15.9.
4 A. E. Crumbliss, in Handbook of Microbial Iron Chelates, ed.
G. Winkelman, CRC Press, Boca Raton, FL, 1991, pp. 177–233;
M. J. Miller, Chem. Rev., 1989, 89, 1563.
5 A. Dobosz, N. M. Dudarenko, I. O. Fritsky, T. Glowiak,
A. Karaczyn, H. Kozlowski, T. Y. Sliva and J. Swiatek-Kozlowska,
J. Chem. Soc., Dalton Trans., 1999, 743.
46.8; H, 3.4; N, 3.5. C31H27N2O3PtSb requires C, 47.0; H, 3.4;
N, 3.5%. ESMS: cone voltage 20 V, [M ϩ H]ϩ (m/z 793, 100%),
[2M ϩ H]ϩ (m/z 1585, 20%).
X-ray structure determinations of
[Pt{OC6H4C(O)NOH}(PPh3)2] 3b and [Pt{OC6H4C(O)NOH}-
(SbPh3)(p-NC5H4Me)] 5b
6 W. Henderson, B. K. Nicholson, A. G. Oliver and C. E. F. Rickard,
J. Organomet. Chem., 2001, 625, 40; W. Henderson, B. K. Nicholson,
S. J. Faville, D. Fan and J. D. Ranford, J. Organomet. Chem., 2001,
631, 41.
7 W. Henderson, L. J. McCaffrey and B. K. Nicholson, J. Chem. Soc.,
Dalton Trans., 2000, 2753; L. J. McCaffrey, W. Henderson,
B. K. Nicholson, J. E. Mackay and M. B. Dinger, J. Chem. Soc.,
Dalton Trans., 1997, 2577.
8 E. M. Khairy, M. M. Shoukry, M. M. Khalil and M. M. A.
Mohamed, Transition Met. Chem., 1996, 21, 176; E. C. OЈBrien,
S. Le Roy, J. Levaillain, D. J. Fitzgerald and K. B. Nolan, Inorg.
Chim. Acta, 1997, 266, 117.
9 B. R. Gibney, D. P. Kessissoglou, J. W. Kampf and V. L. Pecoraro,
Inorg. Chem., 1994, 33, 4840.
Crystals of 3b were obtained by slow evaporation of a CDCl3
solution. The complex crystallises with one molecule of CDCl3
of crystallisation per molecule of complex. Found: C, 53.2; H,
3.35; N, 1.3. C43H35NO3P2PtؒCDCl3 requires C, 52.6; H, 3.7; N,
1.4%. Crystals of 5b were obtained directly from the reaction
mixture.
Crystal data, together with acquisition and refinement details
for both structures are summarised in Table 5.
CCDC reference numbers 206449 (3b) and 206448 (5b).
See http://www.rsc.org/suppdata/dt/b3/b303367h/ for crystal-
lographic data in CIF or other electronic format.
10 A. J. Stremmler, J. W. Kampf, M. L. Kirk and V. L. Pecoraro, J. Am.
Chem. Soc., 1995, 117, 6368.
11 M. D. Hall, T. W. Failes, D. E. Hibbs and T. W. Hambley, Inorg.
Chem., 2002, 41, 1223.
12 T. W. Failes and T. W. Hambley, Aust. J. Chem., 2003, 56, 45.
13 O. F. Wendt and L. I. Elding, J. Chem. Soc., Dalton Trans., 1997,
4725.
14 T. G. Appleton and M. A. Bennett, Inorg. Chem., 1978, 17, 738.
15 O. F. Wendt, A. Scodinu and L. I. Elding, Inorg. Chim. Acta, 1998,
277, 237.
16 Cambridge Structural Database, CCDC, Cambridge, release 5.24,
December 2002.
17 P. Colamarino and P. L. Orioli, J. Chem. Soc., Dalton Trans., 1975,
1656.
Acknowledgements
We thank the Universities of Waikato and Leicester for
financial support of this work. The New Zealand Lottery
Grants Board is thanked for a grant in aid towards the
mass spectrometer, and the generous loan of platinum from
Johnson Matthey plc is acknowledged. We also thank Gill Ellis
(University of Canterbury) for the biological assays, Dr. Ralph
Thomson (University of Waikato) for some of the NMR spec-
tra, Sarah Devoy for experimental assistance, and Associate
Professor Cliff Rickard (University of Auckland) for collection
of the data set of 3b.
18 L. J. Arnold, J. Chem. Educ., 1992, 69, 811.
19 J. X. McDermott, J. F. White and G. M. Whitesides, J. Am. Chem.
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20 D. Drew and J. R. Doyle, Inorg. Synth., 1972, 13, 52.
21 G. M. Sheldrick, SHELX97 Programs for the Solution and
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