Synthesis, characterisation and biological activity of cycloaurated organogold(III) complexes with imidate ligands

Article abstract of DOI:10.1016/j.poly.2006.08.009

The reactions of the cycloaurated gold(III) complexes (2-bp)AuCl₂ (2-bp = 2-benzylpyridyl) or (damp)AuCl₂ (damp = Me₂NCH₂C₆H₄) with an excess of sodium saccharinate (Nasacc), potassium phthalimidate (Kphth), or with isatin and trimethylamine in refluxing methanol results in the successful isolation of a series of new gold(III) imidate complexes. These were characterised by NMR and IR spectroscopies, and by X-ray structure determinations on (2-bp)Au(sacc)₂ and (2-bp)Au(phth)₂. In both structures, the planes of the saccharinate and the phthalimidate ligands are orientated almost perpendicular to the gold coordination plane. As expected from trans-influence considerations, the Au-N_(imidate) bond lengths trans to the aryl carbon atoms are longer than the Au-N_(imidate) bond lengths trans to the pyridyl groups. The complexes have also been characterised by electrospray ionisation MS; in the presence of halide ligands, one imidate ligand is readily displaced. Anti-tumour (P388 murine leukemia) and selected anti-microbial data for the new complexes are reported. Surprisingly, all three damp complexes had low anti-tumour activity, which is likely to be a consequence of the poor solubility of these complexes. The synthesis and characterisation of a related gold(III) bis(amidate) complex derived from sulfathiazole is also described.

Full text of DOI:10.1016/j.poly.2006.08.009

Polyhedron 26 (2007) 204–213
www.elsevier.com/locate/poly
Synthesis, characterisation and biological activity of cycloaurated
organogold(III) complexes with imidate ligands
*
Kelly J. Kilpin, William Henderson , Brian K. Nicholson
Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand
Received 13 June 2006; accepted 14 August 2006
Available online 18 August 2006
Abstract
The reactions of the cycloaurated gold(III) complexes (2-bp)AuCl2 (2-bp = 2-benzylpyridyl) or (damp)AuCl2 (damp = Me2NCH2-
C6H4) with an excess of sodium saccharinate (Nasacc), potassium phthalimidate (Kphth), or with isatin and trimethylamine in refluxing
methanol results in the successful isolation of a series of new gold(III) imidate complexes. These were characterised by NMR and IR spec-
troscopies, and by X-ray structure determinations on (2-bp)Au(sacc)2 and (2-bp)Au(phth)2. In both structures, the planes of the saccha-
rinate and the phthalimidate ligands are orientated almost perpendicular to the gold coordination plane. As expected from trans-influence
considerations, the Au–N(imidate) bond lengths trans to the aryl carbon atoms are longer than the Au–N(imidate) bond lengths trans to the
pyridyl groups. The complexes have also been characterised by electrospray ionisation MS; in the presence of halide ligands, one imidate
ligand is readily displaced. Anti-tumour (P388 murine leukemia) and selected anti-microbial data for the new complexes are reported. Sur-
prisingly, all three damp complexes had low anti-tumour activity, which is likely to be a consequence of the poor solubility of these com-
plexes. The synthesis and characterisation of a related gold(III) bis(amidate) complex derived from sulfathiazole is also described.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Gold complexes; Imidate ligands; Crystal structures; Electrospray mass spectrometry; Biological activity
1. Introduction
We have been investigating the synthesis and biological
properties of cycloaurated complexes that contain a range
of ancillary ligands, derived from both the damp system as
well as other cycloaurated complexes that are more readily
prepared in one step from HAuCl4. Complexes containing
chelating thiosalicylate (SC6H4CO2) ligands have been
found, by ourselves [6,7] and others [8], to show promising
biological activity, and we have recently turned our atten-
tion to the investigation of complexes with nitrogen and
oxygen donor ligands. Examples of catecholate [9], amido-
phenolate [9], ureylene [10], lactam [11], and auracyclic
bis(amidate) [12] complexes have all been prepared, with
a number showing promising anti-tumour activity. In this
paper, we report studies on the synthesis, characterisation
and biological activity of cycloaurated gold(III) complexes
containing monodentate imidate ligands derived from sac-
charin, phthalimide and isatin.
The search for potent anti-tumour activity has been one
of the driving forces for recent activity in the chemistry of
cycloaurated gold(III) complexes [1–3], in light of the well-
developed medicinal chemistry of platinum(II), and the
similarities between this metal centre and gold(III),
imparted by their isoelectronic nature. In cycloaurated
complexes, the ligand, typically a bidentate nitrogen–
carbon donor, stabilises the square-planar gold(III) state
towards reduction. Most work has been carried out with
the damp complex 1 [1], because of its typical good solubil-
ity characteristics and tendency to promote good anti-
tumour activity in the corresponding acetate derivative.
Developments in this area have been thoroughly reviewed
[4,5].
*
Although imidate derivatives of cycloaurated com-
plexes are new, gold(III) imidate complexes have a long
Corresponding author. Fax: +64 7 838 4219.
E-mail address: w.henderson@waikato.ac.nz (W. Henderson).
0277-5387/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2006.08.009

K.J. Kilpin et al. / Polyhedron 26 (2007) 204–213
205
history. As long ago as 1929, Pope filed a patent claiming
to have synthesised a range of gold(III) succinimidate
complexes [13]. Subsequently, Kharasch and Isbell
reported [14] the formation of gold(III) imidate complexes
[Au(imidate)4]À (imidate = anion of succinimide, phthali-
mide, saccharin or diethyl barbituric acid), which were
reformulated by Tyabji and Gibson [15]. Malik et al.
[16] demonstrated that the product of the reaction
between [AuCl4]À and N-methylhydantoin was actually a
gold(I) complex, and suggested that Kharasch’s original
Au(III) tetrasuccinimidate complex was also a gold(I)
bis(imidate) complex. Only recently, a stable gold(III)
complex 2 was reported [17], containing four deproto-
nated hydantoin ligands, an arrangement thought to be
impossible (on steric grounds) by Tyabji and Gibson.
Few other gold(III) imidate complexes have been
reported, though there are many examples of both gold(I)
[18–23] and platinum(II) [24–29] imidate complexes,
derived from a range of ligands such as saccharin, phthal-
imide, and isatin.
ing methanol afforded products 4–9 in good yields. The
reactions involving isatin required the use of Me3N to
remove the imide proton whereas preformed salts of sac-
charin and phthalimide were used, and additional base
was unnecessary for these ligands. The products 4–9 were
characterised by ESI MS, NMR and IR spectroscopies,
together with elemental microanalysis. The damp com-
plexes 5 and 9 were, surprisingly, only sparingly soluble
in (CH3)2SO and CDCl3, but the other complexes were sol-
uble in common organic solvents such as dichloromethane,
acetone and (CH3)2SO.
1H NMR spectroscopy of the 2-benzylpyridyl deriva-
tives was used to determine sample purity, however full
assignment proved difficult due to the presence of four
non-equivalent aromatic rings and hence the presence of
complex multiplets in the aromatic region. The methylene
protons of the benzylpyridyl ligand are expected to appear
as a doublet of doublets, due to geminal coupling between
protons in equatorial and axial environments of a puckered
six-membered ring, as previously described by Fuchita
et al. [30] In the phthalimide 6 and isatin 8 derivatives,
the CH2 signals were very broad and barely visible above
the baseline, as illustrated in Fig. 1 for (2-bp)Au(phth)2
(6); heating effected convergence of the two broad methy-
lene proton signals, giving a broad singlet (Fig. 1). For
the saccharin derivative 4 the CH2 resonances were
resolved into two broad doublets.
2. Results and discussion
2.1. Synthesis and characterisation of gold(III) imidate
complexes derived from saccharin, phthalimide and isatin
The reactions of (damp)AuCl2 (1) or (2-bp)AuCl2 (3)
with an excess of either sodium saccharinate (Nasacc),
potassium phthalimidate (Kphth) or isatin (Hisa) in reflux-
The 1H NMR spectrum of (damp)Au(phth)2 (7) showed
two singlets at d 3.32 and 4.53 due to the methyl and
a 303 K
*
5.50
4.50
4.00
3.50
ppm
b 328 K
*
5.50
4.50
5.0
4.00
3.50
ppm
8.0
7.0
6.0
4.0
3.0
9.0
ppm
Fig. 1. 1H NMR spectra (300 MHz) of the complex (2-bp)Au(phth)2 (6) at temperatures of (a) 303 K and (b) 328 K, in CDCl3 solution, showing the
fluxionality of the benzylpyridyl group. The peaks marked are due to CHCl3 (7.26 ppm).
*

206
K.J. Kilpin et al. / Polyhedron 26 (2007) 204–213
Table 1
methylene protons of the damp ligand, respectively; this
complex contains a plane of symmetry co-planar to the
gold coordination plane. However, both (damp)Au(sacc)2
(5) and (damp)Au(isa)2 (9) were poorly soluble in all com-
mon NMR solvents with the exception of CDCl3, in which
they were soluble enough to acquire very weak spectra. In
contrast to the bis(phthalimidate) species, these complexes
do not have a plane of symmetry through the Au plane,
due to the unsymmetrical nature of the saccharin and isatin
ligands. As a result, the methylene and methyl group pro-
tons are in different chemical environments giving rise to
two singlets from the methyl protons and two doublets
(due to geminal H–H coupling) from the methylene
protons.
Ions observed in positive-ion ESI mass spectra for the complex (2-
bp)Au(phth)2 (6) (=M) at a cone voltage of 20 V
Ionisation
aid
Observed ions (m/z)
NaCl
680 (100%, [M+Na]+),
565 (78%, [MÀphth+MeO+Na]+),
569 (35%, [MÀphth+Cl+Na]+), 1337 (28%, [2M+Na]+)
590 (100%, [MÀphth+py]+)
Pyridine (py)
NaBPh4
Et4NCl
680 (100%, [M+Na]+), 511 (60%, [MÀphth]+)
676 (100%, [MÀphth+Cl+Et4N]+),
787 (85%, [M+Et4N]+), 511 (63%, [MÀphth]+)
787 (100%, [M+Et4N]+),
Et4NBr
722 (67%, [MÀphth+Br+Et4N]+)
The IR spectrum of isatin shows strong absorptions in
the carbonyl region at 1748, 1728 and 1617 cmÀ1; coordi-
nation to gold results in a decrease in the stretching fre-
quency of these bands to 1736, 1692 and 1605 cmÀ1 for
the benzylpyridyl derivative 8, and to 1730, 1701, 1682
and 1603 cmÀ1 for the damp derivative 9. The NH stretch,
present at 3192 cmÀ1 in the free ligand, is absent in the
spectra of the gold complexes, indicating coordination
through the nitrogen atom. This effect was less pronounced
in the saccharin and phthalimide complexes, as the regions
of interest contained a large number of strong overlapping
bands.
auracyclic bis(amidate) species [7], but in general, auracy-
clic systems are much more robust towards MS-induced
fragmentation, or reaction with halide ligands [6,7,9–11].
At a cone voltage of 20 V, the compound (damp)Au
(sacc)2 (4) showed a strong peak in the ESI mass spectrum
at m/z 465 (100% relative intensity) which was assigned as
the cation [(damp)2Au]+. This ion was not observed at
higher cone voltages (>40 V), and had considerably
reduced intensity when NaCl was added to promote ionisa-
tion of the neutral 4. The cation [(damp)2Au]+ was not
1
detected in the H NMR spectrum but is visible in the
ESI spectrum due to it having a high ionisation efficiency,
exacerbated by the low solubility of 4. The analogous
methoxy-substituted cation [(MeO-damp)2Au]+ has previ-
ously been observed in ESI MS analyses [32].
The imidate complexes have also been characterised by
ESI MS. As the bis(imidate) complexes 4–9 are neutral,
NaCl was typically added as an ionisation aid. However,
along with the anticipated [M+Na]+ ions, a common ion
assigned as [M-imidate+Cl+Na]+ was visible, even at low
cone voltages. This ion could either arise from the
mono(imidate) complex (as an impurity in the sample) or
displacement of an imidate ligand by chloride during ESI
MS analysis. The fragment ion [M-imidate]+ was also often
observed and, in some cases, [M-imidate + OMe + Na]+.
In order to ascertain if the chloride ion was displacing
the imidate ligand a small amount of NaBPh4 was added
as a (chloride-free) sodium source to complex 6. The ion
[M-imidate+Cl+Na]+ was no longer detected, suggesting
that such species are only formed when chloride ions are
present. Addition of small amounts of Et4NX (X = Cl,
Br) to 6 also produced additional ions corresponding to
[M-imidate+X+Et4N]+, providing further evidence that
halide ions can displace the imidate ligand. Table 1 details
the range of ions observed when complex 6 was analysed in
the presence of various ionisation aids. Addition of pyri-
dine (py) exclusively produced the ion [MÀphth+py]+.
Together, these ESI MS investigations appear to suggest
that one of the monodentate imidate ligands is labile
towards displacement by halide and other ligands. This
is likely to be the imidate ligand trans to the high trans-
influence aryl carbon; studies of the dissociation of acetate
from (damp)Au(OAc)2 have previously shown that one
acetate, presumably the one trans to the aryl group, was
also readily labilised [31]. Labilisation of one amidate
donor ligand by halide was previously observed for certain
2.2. Synthesis and characterisation of a gold(III)
sulfathiazole complex
The complex (2-bp)AuCl2 (3) was also reacted with sul-
fathiazole [4-amino-N-(thiazol-2-yl)benzenesulfonamide,
stzH (10)], giving the bis(sulfathiazole) complex 11 in
excellent yield as a yellow solid. This complex was poorly
soluble in all solvents with the exception of (CH3)2SO and
HC(O)NMe2 (DMF), but was successfully characterised
by NMR, ESI MS, IR, and elemental microanalysis.
The mode of co-ordination to the gold is unclear, as sul-
fathiazole has three available nitrogen binding sites.
Attempts at growing X-ray quality single crystals (by slow
evaporation of a saturated DMF solution, or by vapour
diffusion of methanol into a DMF solution) were unsuc-
cessful thus the structure was unable to be assigned unam-
biguously. An X-ray crystal structure of the isoelectronic
platinum(II) sulfathiazole complex cis-[Pt(stz)2(PPh3)2]
has confirmed bonding of the sulfathiazole anions
through the thiazole nitrogen [33]. Structures of other
transition metal [Co(II) [34] and Cu(II) [35]] sulfathiazole
complexes indicate the ligand bonded to the metal centre
via the thiazole nitrogen. However, an X-ray crystal struc-
ture has also been solved showing sulfathiazole bridging
two independent Cu atoms through amide and thiazole
nitrogens [36].

K.J. Kilpin et al. / Polyhedron 26 (2007) 204–213
207
The 1H NMR spectrum of complex 11 was very compli-
2.3. X-ray crystal structures of (2-bp)Au(sacc)2 (4) and
(2-bp)Au(phth)2 (6)
cated, however the signal from the amino (NH2) protons
was visible, only very slightly shifted (d = 5.69) from free
sulfathiazole (d = 5.75), indicating that bonding to the gold
centre is not through the amino group. The IR spectrum of
11 provides evidence for coordination to the gold through
the thiazole nitrogen. Sulfathiazole has a strong absorption
at 3350 cmÀ1 due to NH2 stretching and 11 also has absorp-
tions in this region (3430 cmÀ1) suggesting that the NH2
group remains intact. Likewise, the absorptions due to
SO2 stretching and bending modes are not greatly shifted
upon coordination (1136 and 1323 cmÀ1 in sulfathiazole
compared with 1131 and 1323 cmÀ1 in 11). However, the
S–N stretching frequency of the thiazole ring has decreased
from 1531 to 1459 cmÀ1 upon coordination, indicating that
coordination probably occurs through Nthiazole. The values
obtained are very comparable to the Pt(II) sulfathiazole
complexes, again supporting binding through the thiazole
nitrogen. This observation has been noted before in other
metal-sulfathiazole compounds [37,38].
Structure determinations of 4 and 6 were carried out in
order to ascertain the geometry and orientation of the sac-
charinate and phthalimidate ligands around the gold centre.
Views of the structures are shown in Figs. 2–5 along with
the atom numbering schemes. A comparison of important
bond lengths and angles is presented in Table 2, while com-
parisons of the geometric parameters of the coordinated
ligands with free saccharin [39] and phthalimide [40] are
given in Tables 3 and 4, respectively.
In both cases, the geometry around the gold atom is
essentially square-planar. No atom deviates from the
least-squares plane [defined by N(1), N(2), N(3), Au(1)
and C(41) for the saccharin derivative 4; N(1), N(2), N(3),
Au(1) and C(12) for the phthalimide derivative 6] by more
˚
than 0.040 or 0.0675 A, respectively. The Au–Nimidate bond
lengths in the structures are very comparable; as expected,
the Au–Nimidate bond lengths trans to the benzylpyridyl
-
Me
Me
O
O
Cl
Cl
N
N
Au
HN
N
Cl
Cl
N
Au
Au
N
Au
Me
S
O
Me
O
O
4
2
1
2
4
3
O
O
O
O
Me
Me
Me
Me
N
N
N
N
Au
Au
N
Au
N
S
O
O
O
2
2
2
5
7
6
O
O
Me
Me
O
N
N
O
Au
N
Au
N
N
S
O
S
HN
NH2
2
2
O
8
10
9
N
Au
N
S
O
N
S
NH2
O
2
11

208
K.J. Kilpin et al. / Polyhedron 26 (2007) 204–213
C(11)
O(12)
C(16)
C(17)
N(1)
Au(1
N(2)
N(3)
S(1)
C(35)
C(47)
O(13)
N(1)
N(3)
C(41)
O(11)
C(35)
Au(1)
O(23)
C(47)
C(41)
C(46)
C(46)
C(27)
C(26)
N(2)
O(22)
S(2)
Fig. 4. Side view of the X-ray crystal structure of the complex
(2-bp)Au(sacc)2 (4) showing the orientation of the saccharinate ligands
with respect to the gold coordination plane. Thermal ellipsoids are shown
at the 30% probability level. Solvent of crystallisation and the atoms
completing the benzyl and pyridyl rings have been omitted for clarity.
C(21)
O(21)
Fig. 2. Perspective view of the X-ray crystal structure of the complex
(2-bp)Au(sacc)2 (4) showing the atom labelling scheme. Thermal ellipsoids
are shown at the 30% probability level. The solvent of crystallisation has
been omitted for clarity.
N(3)
Au(1)
C(6)
N(2)
C(32)
C(37)
C(12)
C(7)
N(1)
C(5)
C(31)
C(38)
C(12)
O(3)
O(4)
C(7)
N(3)
C(6)
Au(1)
Fig. 5. Side view of the X-ray crystal structure of the complex
(2-bp)Au(phth)2 (6) showing the orientation of the phthalimidate ligands
with respect to the gold coordination plane. Dichloromethane of solvation
and atoms completing the benzyl and pyridyl rings have been omitted for
clarity. Thermal ellipsoids are shown at the 40% probability level.
O(1)
N(2)
O(2)
C(5)
N(1)
C(28)
C(27)
C(21)
C(22)
C@O and S@O bond lengths in the saccharin ligand signif-
icantly increase. This effect is less pronounced in the phtha-
limidate complex.
In both structures, the planes of the saccharin and the
phthalimide ligands are orientated almost perpendicular
to the coordination plane of the gold (Figs. 4 and 5), most
probably to reduce steric interactions between the bulky
imidate ligands. This particular ligand orientation has been
observed previously in the similar square-planar plati-
num(II) isatin complex cis-[Pt(isat)2(PPh3)2] [42]. In the
structure of the saccharin complex 4, the plane of the
ligand coordinated through N(1) has a dihedral angle of
58.70ꢁ relative to the gold co-ordination plane, whereas
the ligand coordinated through N(2) has an angle of
85.21ꢁ. The bis(phthalimide) structure is such that the
plane of the phthalimide ligand co-ordinated through
Fig. 3. Perspective view of the X-ray crystal structure of the complex
(2-bp)Au(phth)2 (6) showing the atom labelling scheme. Thermal
ellipsoids are shown at the 50% probability level. The dichloromethane
of crystallisation has been omitted.
carbon are longer than those trans to the benzylpyridine
nitrogen due to the phenyl ligand having a higher trans
influence than the pyridyl nitrogen ligand [41].
Both saccharinate and phthalimidate ligands are essen-
tially planar. Tables 3 and 4 compare selected bond lengths
of the free saccharin and phthalimide molecules with those
of the coordinated ligands. Upon coordination to gold, the

K.J. Kilpin et al. / Polyhedron 26 (2007) 204–213
209
Table 2
arrangement of the two SO2 groups trans to each other
appears to be a common trend. Examples of six co-ordinate
octahedral structures where the SO2 groups occupy oppo-
site binding sites in a trans configuration are vast [43]. In
square pyramidal complexes there are examples of both
cis [44] and trans [45] arrangements of the saccharinate
ligands. Interestingly, in the linear Hg(saccharinate)2 mol-
ecule the saccharinate ligands are orientated so the SO2
groups are positioned on the same side [46].
˚
Comparison of selected bond lengths (A) and angles (ꢁ) between
(2-bp)Au(sacc)2 (4) and (2-bp)Au(phth)2 (6)
4
6
Bonds
Au–Nbenzylpyridyl
Au–Cbenzylpyridyl
Au–Ntrans to C
Au–Ncis to C
2.041(4)
2.021(4)
2.118(4)
2.015(4)
2.046(10)
2.041(11)
2.117(9)
2.007(9)
Angles
Nbenzylpyridyl–Au–Cbenzylpyridyl
89.4(2)
90.4(2)
90.5(2)
89.8(2)
88.3(4)
90.5(4)
90.2(4)
91.1(4)
3. Biological activity
N
cis to C–Au–Ntrans to C
Cbenzylpyridyl–Au–Ncis to C
benzylpyridyl–Au–Ntrans to C
N
The anti-tumour and anti-microbial activities of the
bis(imidate) complexes were determined and data are
reported in Table 5. The benzylpyridyl complexes 6 and 8
have IC50 values that are very comparable to the auracyclic
bis(amidate) products reported by us in a previous paper
[12]. The other bis(imidate) complexes show low anti-
tumour activity towards the P388 murine leukaemia cell
line. There are two likely reasons for this. Firstly, the damp
complexes 5, 7 and 9 all have surprisingly low solubilities in
common solvents when compared to other damp complexes
reported in the literature, where there are many examples
often showing excellent anti-tumour activity [1–5].
Secondly, the greater lability of monodentate ligands
relative to the more stable and less labile metallacyclic
products may have an influence on the biological activity.
ESI MS results indicate that one imidate ligand is lost very
easily, and such reactions might prevent the complex from
reaching its biological target. Continuing the analogy with
platinum(II) systems, it is known that replacement of
monodentate ligands (such as chloride in cisplatin) with a
bidentate chelating ligand (such as cyclobutane-1,1-dicarb-
oxylate in carboplatin) slows the rate of hydrolysis and
moderates the toxicity of the platinum-based drug [47].
Table 3
˚
Comparison of selected bond lengths (A) between saccharin and the
coordinated saccharinate ligands of 4
Bond
Saccharin
[28]
Ligand co-ordinated
through N(1)
Ligand co-ordinated
through N(2)
C@O
S@O
1.214
1.409
1.429
1.369
1.633
1.221(5)
1.444(3)
1.444(3)
1.389(6)
1.647(4)
1.216(6)
1.434(3)
1.443(3)
1.383(6)
1.662(4)
N–C
N–S
Table 4
˚
Comparison of selected bond lengths (A) between phthalimide and the
coordinated phthalimidate ligands of 6
Bond
Phthalimide [29]
Ligand co-ordinated
through N(2)
Ligand co-ordinated
through N(3)
C@O
1.216
1.222
1.381
1.395
1.212(15)
1.237(16)
1.367(14)
1.382(16)
1.228(17)
1.235(16)
1.363(16)
1.387(17)
C–N
N(2) is at an angle of 71.60ꢁ, while the N(3)-coordinated
ligand is at an angle of 89.53ꢁ, with respect to the gold
coordination plane.
4. Conclusions
New gold(III) bis(imidate) complexes (imidate = anion
of saccharin, phthalimide, isatin) have successfully been
synthesised and characterised. To the best of our knowl-
edge, these are the first gold compounds of this type to
Interestingly, the saccharin ligands are orientated so that
the SO2 groups are trans to each other, as seen in Fig. 4.
Although no crystal structures of square-planar bis(saccha-
rin) metal complexes could be found in the literature, the
Table 5
Anti-tumour (P388) and anti-microbial activities for gold(III) bis(imidate) derivatives
a
Compound
Anti-tumour IC50
ng mLÀ1
Anti-microbialb activityc
lM
Ec
Bs
Pa
Ca
Tm
Cr
(2-bp)Au(sacc)2 (4)
(damp)Au(sacc)2 (5)
(2-bp)Au(phth)2 (6)
(damp)Au(phth)2 (7)
(2-bp)Au(isa)2 (8)
(damp)Au(isa)2 (9)
>25000
>25000
3258
>25000
6894
>34.3
>36.0
5.0
>40.1
10.5
2
1
N/T
2
4
1
7
4
10
5
8
4
2
–
N/T
–
6
–
5
–
5
4
4
–
2
3
5
3
5
3
–
–
N/T
–
–
–
>25000
>40.1
N/T = not tested.
a
The concentration of the sample required to reduce the cell growth of the P388 leukaemia cell line (ATCC CCL 46) by 50%.
Ec = Escherichia coli, Bs = Bacillus subtilis, Pa = Pseudomonas aeruginosa, Ca = Candida albicans, Tm = Trichophyton mentagrophytes, Cr = Clado-
b
sporium resinae.
c
Inhibition zone as an excess radius (mm) from a 6 mm disc containing 2 lg of sample; – denotes no observed activity.

210
K.J. Kilpin et al. / Polyhedron 26 (2007) 204–213
be reported. The X-ray crystal structures of (2-bp)Au
(sacc)2 (4) and (2-bp)Au(phth)2 (6) have been solved and
indicate that the imidate anions are co-ordinated to the
gold centre through Au–N bonds. In both cases, the planar
imidate ligands are orientated perpendicular to the gold
co-ordination plane.
crystals were deposited. These were filtered, washed with
water (2 · 10 mL) and diethyl ether (10 mL) then dried
under vacuum to give 142 mg (84%) of product. M.p.
196–198 ꢁC (decomp.). Anal. Calc. for C23H20N3O6S2Au:
C, 39.7; H, 2.9; N, 6.0. Found: C, 39.7; H, 3.1; N, 5.9%.
IR: t(C@O) 1695 cmÀ1; t(SO2, sym) 1317, 1291 cmÀ1
;
t(SO2, asym) 1159, 1167 cmÀ1. ESMS: Cone voltage
20 V: NaCl added, m/z 571 (100%, [M-sac+Cl+Na]+),
465 (30%, [(damp)2Au]+), 718 (10%, [M+Na]+); pyridine
5. Experimental
1
5.1. General
added, m/z 592 (100%, [M-sac+py]+). H NMR, d 3.43
(s, 3H), 3.49 (s, 3H), 4.20 (br d, 1H), 5.06 (br d, 1H),
7.09 (t, 1H), 7.13–7.24 (m, 4H), 7.68–7.71 (m, 6H), 8.0
(d, 1H). The compound was too insoluble for a satisfactory
13C–{1H} NMR spectrum.
General experimental techniques were as previously
described [9]; routine ESI mass spectra were recorded on
a VG Platform II instrument, using methanol as the mobile
phase. Assignment of mass spectrometric isotope patterns
was aided by the ISOTOPE program [48]. All NMR spectra
were acquired in CDCl3, with the exception of 11
[(CD3)2SO]. Integration of the H NMR spectra indicated
that 7 and 8 crystallised with approximately 1.0 and
0.12 mol of dichloromethane, respectively.
All reactions were carried out with no attempts to
exclude light or air. The solvents used were LR grade. Tri-
methylamine (Eastman, 25% aqueous solution), sodium
saccharinate (Aldrich), potassium phthalimidate (Merck),
isatin (BDH) and sulfathiazole (BDH) were used as sup-
plied. The cycloaurated gold(III) complexes (2-bp)AuCl2
(3) [49] and (damp)AuCl2 (1) [50,51] were prepared by
modified literature methods.
5.4. Synthesis of (2-bp)Au(phth)2 (6)
1
The complex (2-bp)AuCl2 (3) (200 mg, 0.46 mmol) and
potassium phthalimidate (340 mg, 1.8 mmol) were added
to methanol (50 mL) and refluxed with stirring for 1 h, dur-
ing which time a pale yellow solution formed. Water
(30 mL) was added, resulting in the immediate deposition
of white microcrystals. After cooling to room temperature,
the suspension was filtered, washed with water (2 · 10 mL)
and diethyl ether (10 mL) then dried under vacuum to give
254 mg (84%) of product. Anal. Calc. for C28H18N3O4Au:
C, 51.2; H, 2.8; N, 6.4. Found: C, 50.4; H, 2.8; N, 6.4%.
IR: t(C@O) 1690 cmÀ1 (s) and 1664 cmÀ1 (s). ESI MS:
Cone voltage 20 V, NaCl added: m/z 680 (100%,
[M+Na]+), 565 (78%, [MÀphth+MeO+Na]+), 569 (35%,
5.2. Synthesis of (2-bp)Au(sacc)2 (4)
1
[MÀphth+Cl+Na]+), 1337 (27%, [2M+Na]+). H NMR,
The complex (2-bp)AuCl2 (3) (100 mg, 0.23 mmol) and
sodium saccharinate (190 mg, 93 mmol) were added to
methanol (25 mL) and refluxed with stirring for 2 h. After
cooling to room temperature, water (50 mL) was added,
resulting in the rapid deposition of white microcrystals.
These were filtered, washed with water (2 · 10 mL) and
diethyl ether (10 mL) and dried under vacuum to give
158 mg (93%) of product. For microanalysis the crude
product was recrystallised by vapour diffusion of diethyl
ether into a dichloromethane solution of the product at
room temperature to give white crystals. M.p. 131–
134 ꢁC. Anal. Calc. for C26H18N3O6S2Au: C, 42.8; H, 2.5;
N, 5.8. Found: C, 42.2; H, 2.8; N, 5.5%. IR: t(C@O)
1686 cmÀ1 (s); t(SO2, sym) 1291 cmÀ1 (s), t(SO2, asym)
1155 cmÀ1 (br s). ESI MS: Cone voltage 20 V: NaCl added,
d 4.15 (br d, 1H), 5.15 (br d, 1H), 6.95 (t, 1H), 7.10 (t,
1H), 7.17 (d, 1H), 7.38 (m, 3H), 7.51 (m, 5H), 7.62 (m,
2H), 7.69 (d, 1H), 7.97 (t, 1H), 9.15 (d, 1H). 13C–{1H}
NMR, d 47.6 (CH2), 122.1–157.8 (aryl C), 177.3, 172.8
(C@O).
5.5. Synthesis of (damp)Au(phth)2 (7)
The complex (damp)AuCl2 (1) (100 mg, 0.25 mmol) and
potassium phthalimidate (186 mg, 1 mmol) were added to
methanol (30 mL) and refluxed with stirring for 2 h, during
which time white microcrystals were deposited. The mix-
ture was cooled, filtered then washed with methanol
(2 · 10 mL) and diethyl ether (10 mL). The crude product
was recrystallised by vapour diffusion of pentane into a
dichloromethane solution of the crude product. The col-
ourless crystals were filtered, washed (petroleum spirits)
then dried under vacuum to give 133 mg (86%) of product.
M.p. 192 ꢁC (decomp.). Anal. Calc. for C25H20N3O4Au Æ
1.06CH2Cl2: C, 43.9; H, 3.1; N, 5.9. Found: C, 44.3; H,
3.1; N, 6.1%. IR: t(C@O) 1686 cmÀ1 (s) and 1655 cmÀ1
(s). ESI MS: Cone voltage 20 V: m/z 646 (100%,
[M+Na]+), 477 (82%, [MÀphth]+), 1269 (27%,
1
m/z 605 (100%, [M-sac+Cl+Na]+). H NMR, d 4.17 (d,
1H), 5.11 (d, 1H), 7.01–8.04 (m, 15H), 9.26 (d, 1H). 13C–
{1H} NMR, d 47.5 (CH2), 120.5–157.3 (aryl C), 182.7,
184.5 (C@O).
5.3. Synthesis of (damp)Au(sacc)2 (5)
The complex (damp)AuCl2 (1) (100 mg, 0.25 mmol) and
sodium saccharinate (206 mg, 1 mmol) were dissolved in
refluxing methanol (30 mL) to give a colourless solution.
During two hours of refluxing with stirring, white micro-
1
[2M+Na]+). H NMR, d 3.32 (s, 6H), 4.53 (s, 2H), 5.30
(s, 2.11H, from CH2Cl2), 6.69 (d, 1H), 7.01 (t, 1H), 7.19,
(d, 1H), 7.25 (t, 1H), 7.56 (m, 4H), 7.68 (m, 4H).

K.J. Kilpin et al. / Polyhedron 26 (2007) 204–213
211
13C–{1H} NMR, d 53.5 (CH2Cl2), 53.0 (CH3), 75.5 (CH2),
122.4–144.5 (aryl C), 172.7, 177.5 (C@O).
product was then washed with ice-cold methanol
(2 · 10 mL) and diethyl ether (10 mL) before being dried
under vacuum giving 324 mg (81%) of 11. M.p. 194–
196 ꢁC (decomp.). Anal. Calc. for C30H26N7O4S4Au: C,
41.2; H, 3.0; N, 11.2. Found: C, 40.8; H, 3.0; N, 10.9%.
IR: t(NH) 3430 cmÀ1 (w), t(SN) 1459 cmÀ1 (vs), t(SO2,
sym) 1323 cmÀ1 (s), t(SO2, asym) 1131 cmÀ1 (s). ESI MS:
Cone voltage 20 V: NaCl added, m/z 677 (100%, [M-
stz+Cl+Na]+), 896 (72%, [M+Na]+). 1H NMR, d 4.64
(br s, 2H), 5.69 (s, 4H, NH2), 5.75 (br s, 2H), 6.51 (d,
2H), 6.56 (d, 1H), 6.66 (d, 1H), 6.77 (d, 1H), 6.90 (t, 1H),
7.13 (d, 1H), 7.21 (t, 1H), 7.31 (d, 1H), 7.36 (d, 1H), 7.52
(t, 1H), 8.02 (d, 1H), 8.22 (t, 1H), 8.55 (d, 1H). The com-
pound was too insoluble for a satisfactory 13C–{1H}
NMR spectrum.
5.6. Synthesis of (2-bp)Au(isa)2 (8)
The complex (2-bp)AuCl2 (3) (200 mg, 0.46 mmol) and
isatin (270 mg, 1.84 mmol) were added to refluxing metha-
nol (40 mL). While stirring, trimethylamine (2 mL, excess)
was added, resulting in the solution changing from deep
red to bright orange. The solution was further refluxed with
stirring for 20 min. Water (50 mL) was added, resulting in
the deposition of orange microcrystals which were collected
by filtration. The crude product was recrystallised from
dichloromethane and pentane, filtered, washed with water
(2 · 10 mL) and diethyl ether (10 mL) and dried under vac-
uum to give 266 mg (88%) of 8. M.p. 225 ꢁC (decomp.).
Anal. Calc. for C28H18N3O4Au Æ 0.12CH2Cl2: C, 50.6; H,
2.8; N, 6.3. Found: C, 49.7; H, 3.0; N, 6.3%. IR: t(C@O)
1736 cmÀ1 (s), 1692 cmÀ1 (s) and 1605 cmÀ1 (s). ESI MS:
Cone voltage 20 V: m/z 680 (100%, [M+Na]+), 569 (67%,
[M-isa + Cl + Na]), 565 (56%, [M-isa+MeO+Na]+). 1H
NMR, d 4.35 (br. s, 2H), 5.33 (s, 0.24H, from CH2Cl2),
6.87 (t, 1H), 6.95 (t, 1H), 7.01 (d, 1H), 7.18–7.51 (m,
11H), 7.81 (d, 1H), 8.06 (t, 1H). 13C–{1H} NMR, d 47.7
(CH2), 53.5 (CH2Cl2), 112.4–157.3 (aryl C), 162.9, 166.8,
185.1, 189.0 (C@O).
6. X-ray crystallography
X-ray intensity data were collected on a Bruker CCD
diffractometer using standard procedures and software.
Empirical absorption corrections were applied (SADABS)
[52]. Structures were solved by direct methods and devel-
oped and refined on F 2o using the SHELX programmes [53]
operating under WINGX [54,55]. Hydrogen atoms were
included in calculated positions. For both structures there
was potential pseudo symmetry which could have led to
disorder between the phenyl and pyridyl rings of the
cyclometallated ligand. However, as found for other
examples [12], the assignment of the metallated C and
N atoms could be done unambiguously, showing there
was no disorder. As discussed earlier [12]: (i) the N posi-
tion was revealed with higher electron density than the C
in the difference map; (ii) the Uiso values for the atoms
were similar when refined as allocated, but were quite dif-
ferent if the assignment was reversed, and R1 values
increased in each case on changing the assignment; (iii)
the differences in the Au–N distances to the sacc or phth
ligands were consistent with the expected trans influences
of C and N as assigned.
5.7. Synthesis of (damp)Au(isa)2 (9)
The complex (damp)AuCl2 (1) (100 mg, 0.25 mmol) and
isatin (148 mg, 1 mmol) were stirred in refluxing methanol
(30 mL). Trimethylamine (2 mL, excess) was added, result-
ing in the solution turning from orange to deep red, and the
mixture was refluxed for a further 10 min during which
time orange microcrystals were deposited. After cooling
to room temperature, the product was filtered, washed with
water (2 · 10 mL) and diethyl ether (10 mL) and dried
under vacuum to give 117 mg (75%) of product. M.p.
210–212 ꢁC (decomp.). Anal. Calc. for C25H20N3O4Au: C,
48.2; H, 3.2; N, 6.7. Found: C, 47.7; H, 3.4; N, 6.7%. IR:
t(C@O) 1730 cmÀ1 (s), 1701 cmÀ1 (m), 1682 cmÀ1 (s),
1603 cmÀ1 (s). ESI MS: Cone voltage 20 V: m/z 646
(100%, [M+Na]+), 465 (55%, [(damp)2Au]+), 678 (35%,
6.1. Structure of (2-bp)Au(sacc)2 (4)
White prism crystals of 4 (M.p. 131–134 ꢁC) were
obtained from CH2Cl2/Et2O.
1
[M+Na+MeOH]+), 1269 (27%, [2M+Na]+). H NMR, d
3.24 (s, 3H), 3.48 (s, 3H), 4.17 (d, 1H), 4.89 (d, 1H), 6.85
(t, 1H), 6.92 (t, 1H), 7.06–7.39 (m, 13H), 7.43 (t, 1H).
The compound was too insoluble for a satisfactory 13C–
{1H} NMR spectrum.
Crystal
data:
C26H18AuN3O6S2 Æ 0.5CH2Cl2 Æ 0.5-
C4H10O, M = 809.04, orthorhombic, space group Pccn,
˚
a = 15.7051(2), b = 18.7045(3), c = 19.5764(1) A, V =
5750.7(1) A , T = 84(2) K, Z = 8, Dcalc = 1.869 g cmÀ3
,
3
˚
l(Mo Ka) = 5.405 mmÀ1, F(000) = 3168; 32131 reflections
collected with 2ꢁ < h < 26ꢁ, 5862 unique (Rint = 0.0309) used
after correction for absorption (Tmax,min = 0.521, 0.385).
Crystal dimensions = 0.22 · 0.20 · 0.14 mm3.
5.8. Synthesis of (2-bp)Au(stz)2 (11)
The complex (2-bp)AuCl2 (3) (200 mg, 46 mmol) and
sulfathiazole (10) (257 mg, 1 mmol) were stirred in reflux-
ing methanol (25 mL). Trimethylamine (2 mL, excess)
was added, resulting in the rapid deposition of pale yellow
microcrystals. The mixture was refluxed with stirring for a
further 2 h before being cooled in ice and filtered. The
When the main molecule had been refined, there was sig-
nificant residual electron density around special positions
with 2-fold symmetry at 41; 14; z. These appeared to be a mix-
ture of CH2Cl2 and Et2O, but were very disordered and
could not be sensibly modelled. This electron density was

212
K.J. Kilpin et al. / Polyhedron 26 (2007) 204–213
excluded using the SQUEEZE procedure of PLATON [56]
and refinement was continued against the modified hkl data
with just the main molecule.
Refinement on F 2o converged at R1 = 0.0327 [I > 2r(I)]
and wR2 = 0.0569 (all data), GoF = 1.140. The structure
of 4 is illustrated in Fig. 2, with selected bond parameters
summarised in Tables 2 and 3.
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Crystal data: C28H18AuN3O4 Æ CH2Cl2, M = 742.35,
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3
˚
˚
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