The cycloauration of pyridine-2-thiocarboxamide ligands

Article abstract of DOI:10.1016/j.ica.2009.10.003

Reactions of H[AuCl₄] with N-substituted 2-pyridine thiocarboxamide ligands 2-(C₅H₄N)C(S)NHR (R = p-C₆H₄Me, CH₂Ph, Me, p-C₆H₄OMe) gave cycloaurated derivatives {(C₅H₄N)C(S)NR}AuCl₂, with the ligand bonded as the thiol tautomer through the deprotonated SH group and the pyridine N atom to give a five-membered metallacyclic ring. The X-ray structure determination of the R = CH₂Ph derivative shows a square-planar gold(III) complex that dimerises in the solid state by weak Au···S intermolecular interactions. In contrast, in the reaction of H[AuCl₄] with 2-(C₅H₄N)C(S)NHR where R = 2-pyridyl, the ligand was oxidised to give a 1,2,4-thiadiazolo[2,3-a]pyridinium heterocyclic ring that was crystallographically characterised.

Full text of DOI:10.1016/j.ica.2009.10.003

Inorganica Chimica Acta 363 (2010) 41–48
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
The cycloauration of pyridine-2-thiocarboxamide ligands
*
Kelly J. Kilpin, William Henderson , Brian K. Nicholson
Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2009
Received in revised form 1 October 2009
Accepted 2 October 2009
Available online 8 October 2009
Reactions of H[AuCl4] with N-substituted 2-pyridine thiocarboxamide ligands 2-(C5H4N)C(S)NHR (R = p-
C6H4Me, CH2Ph, Me, p-C6H4OMe) gave cycloaurated derivatives {(C5H4N)C(S)NR}AuCl2, with the ligand
bonded as the thiol tautomer through the deprotonated SH group and the pyridine N atom to give a
five-membered metallacyclic ring. The X-ray structure determination of the R = CH2Ph derivative shows
a square–planar gold(III) complex that dimerises in the solid state by weak AuꢀꢀꢀS intermolecular interac-
tions. In contrast, in the reaction of H[AuCl4] with 2-(C5H4N)C(S)NHR where R = 2-pyridyl, the ligand was
oxidised to give a 1,2,4-thiadiazolo[2,3-a]pyridinium heterocyclic ring that was crystallographically
characterised.
Keywords:
Gold complexes
Cyclometallated ligands
Thioamide ligands
Sulfur ligands
Ó 2009 Elsevier B.V. All rights reserved.
Crystal structure
1. Introduction
tre via the pyridyl nitrogen and sulfur atoms, 3. In these cases,
five-membered chelates result. However, coordination via the
As part of studies on cycloaurated gold(III) complexes [1] we are
investigating ligands based on deprotonated amide donors, which
form a comparable range of complexes to the more traditional
cycloaurated complexes with neutral nitrogen and anionic
carbon ligands [2]. In this contribution the synthesis and character-
isation of N-substituted pyridine-2-thiocarboxamide complexes of
gold(III) is reported, through direct reaction of the ligands with
H[AuCl4]. The combination of soft sulfur and harder nitrogen do-
nors, with the potentially oxidising gold(III) centre is of interest,
especially since gold(III) dithiocarbamate complexes (RR’NCS2)
AuCl2 show anticancer activity [3–6].
The most attractive preparative method to N-substituted 2-
pyridine thiocarboxamide ligands 2-(C5H4N)C(S)NHR involves
the reaction of a primary amine with sulfur in refluxing 2-meth-
ylpyridine in the presence of catalytic Na2Sꢀ9H2O (a modified
Willgerodt–Kindler reaction) [7]. Yields are excellent (>70%) and
the steric and electronic properties of the products are readily
tuned by varying the amines used. Such ligands have the poten-
tial to coordinate to metal centres in different ways, Scheme 1.
Deprotonation of the ligand may occur prior to coordination
and because thioamides have two tautomeric forms they may
act as either a monoanionic N,N0 (coordination of thioketo tauto-
mer 1) or S,N (coordination of the thiol form 2) bidentate ligand.
Alternatively, the neutral ligand may coordinate to the metal cen-
amide nitrogen and the sulfur (either as the neutral ligand 4 or
after deprotonation 5) would give four-membered metallacycles.
In the case of the deprotonated ligand both tautomeric forms will
again be possible but only the thioketo isomer 5 is shown in
Scheme 1.
Surprisingly, few N-substituted pyridine-2-thiocarboxamide
complexes of the platinum group metals or gold appear to have
been reported. Palladium(II) complexes have been reported for
the three coordination modes that are described in Scheme 1
(complexes 6a, b, 7a, 8, Scheme 2) [8–10]. Platinum(II) complexes
also exist, with the ligand coordinated via either the S,N (6c) or
N,N0 (7b) binding modes. One example (9) of an S,N-coordinated
gold(III) complex is reported, synthesised by the extraction of
gold(III) from HCl solution by the ligand. However, structural
characterisation by X-ray crystallography was not reported for
any of the above complexes, the coordination mode of the ligand
being assigned using IR, UV–Vis and NMR spectroscopy. There is
one structurally characterised example of a gold(I) complex, 10;
the thiol tautomer is deprotonated and the ligand is coordinated
to the gold through the sulfur atom, with a weak interaction be-
tween the gold and the pyridyl nitrogen [11].
To the best of our knowledge, there are no examples of palla-
dium, platinum or gold four-membered ring systems formed from
N-substituted pyridine-2-thiocarboxamide ligands, although the
Polish literature cites several examples of related four-membered
cationic auracycles formed from the coordination of neutral thio-
carboxamide ligands (11a–c, Scheme 2) [12].
* Corresponding author. Fax: +64 7 838 4219.
E-mail address: w.henderson@waikato.ac.nz (W. Henderson).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.10.003

42
K.J. Kilpin et al. / Inorganica Chimica Acta 363 (2010) 41–48
R
N
S
R
N
H
SH
N
N
MLx
MLx
R
N
R
S
HN
R
N
S
S
N
MLx
N
N
MLx
MLx
1
2
3
R
R
N
NH
N
MLX
MLX
S
S
N
4
5
Scheme 1. Possible bidentate coordination modes of N-substituted pyridine-2-thiocarboxamide ligands.
Me
HN
R1
N
Ph
R2
S
N
N
S
N
S
N
S
N
PdCl2
M
M
N
N
S
N
R2
R1
Ph
Me
6a M=Pd, R1=o-tolyl, R2=H
7a M=Pd
7b M=Pt
8
6b M=Pd, R1=Me,
R2=4-Me
6c M=Pt, R1=o-tolyl, R2=H
S
R
AuCl2
NH
Me
MeO
N
S
N
N
S
Au
AuCl2
PPh3
O
N
9
10
11a R=Me
11b R=Ph
11c R=2-furyl
Scheme 2. Examples of palladium, platinum and gold coordination complexes formed with N-substituted pyridine-2-thiocarboxamide ligands.

K.J. Kilpin et al. / Inorganica Chimica Acta 363 (2010) 41–48
43
2. Results and discussion
2.1. Reaction of N-substituted pyridine-2-thiocarboxamide ligands
with H[AuCl4]
Reactions of ligands 12a–d with one molar equivalent of
H[AuCl4] in water gave the cycloaurated compounds 13a–d in
moderate to good yields, Scheme 3. The reactivity of the ligands to-
wards H[AuCl4] was dependent on the N-substituent; for the
methyl derivative (12a), the reaction took place rapidly (15 min)
at room temperature. However, when the N-substituent was more
electron-withdrawing (e.g. 12c and 12d) the reaction needed to be
refluxed before any reaction was observed. The benzyl substituted
ligand 12b required stirring at room temperature for 5 h and any
heating of this solution to reflux gave metallic gold. When two
equivalents of 12a were reacted with H[AuCl4] and NH4PF6 the
bis(ligand) complex 14 was formed in moderate yields. Complexes
13a–c were poorly soluble in MeOH, CH2Cl2, CHCl3 and acetone;
complex 13d, with a methoxy substitutuent, was much more solu-
ble in CH2Cl2, CHCl3 and acetone. The complexes are soluble in
DMSO but decomposition occurred after approximately 6 h in
solution.
Fig. 1. Molecular structure of 13b showing one of the unique molecules present in
the asymmetric unit, and the atom numbering scheme. Thermal ellipsoids are
shown at the 50% probability level.
2.2. X-ray crystal structure of 13b
Table 1
Selected structural parametersa for 13b (both molecules), with esds in parentheses.
The structure determination of 13b confirms that the ligand is
coordinated to gold as its deprotonated thiol tautomer, through
the sulfur and the pyridyl nitrogen atoms. The remaining two coor-
dination sites on the square–planar gold are occupied by cis chlo-
ride ligands. The compound crystallised with two independent
molecules in the asymmetric unit, which differ mainly in the con-
formation of the benzyl substituents. The molecular structure and
atom labelling scheme of one molecule is shown in Fig. 1 and se-
lected bond parameters are in Table 1. Excluding the benzyl moi-
ety, the core of the molecule is essentially planar. In molecule 1
the benzyl ring is tilted from the main plane of the molecule at
an angle of 18.88(8)°, however in molecule 2 the benzyl phenyl
ring is twisted out of the plane of the molecule by 58.80(4)°. The
two molecules in the asymmetric unit form dimeric aggregates
through weak intermolecular AuꢀꢀꢀS interactions [3.498 and
3.556 Å (Fig. 2)]. While there are many complexes with AuꢀꢀꢀS
interactions involving gold(I), interactions with gold(III) are rather
rarer, all having slightly shorter AuꢀꢀꢀS distances than observed in
13b. The closest analogues are complexes derived from the cycloa-
urated 2-phenylpyridine ligand, containing, respectively, thiocya-
nate [13] or chelating dithiolate ligands [14].
Molecule 1
Molecule 2
Bond lengths (Å)
Au–Cl(1)
Au–Cl(2)
Au–S(1)
Au–N(1)
N(1)–C(5)
C(5)–C(6)
C(6)–S(1)
C(6)–N(2)
N(2)–C(7)
2.2709(6)
2.3289(6)
2.2747(6)
2.051(2)
1.359(3)
1.479(3)
1.772(3)
1.273(3)
1.454(3)
2.2746(7)
2.3353(6)
2.2723(6)
2.050(2)
1.365(3)
1.479(3)
1.767(3)
1.278(3)
1.459(3)
Bond angles (°)
Cl(1)–Au–Cl(2)
Cl(2)–Au–N(1)
Cl(1)–Au–S(1)
S(1)–Au–N(1)
Au–N(1)–C(5)
N(1)–C(5)–C(6)
C(5)–C(6)–S(1)
C(6)–S(1)–Au
C(6)–N(2)–C(7)
90.58(2)
95.29(6)
87.70(2)
86.42(6)
118.95(16)
118.1(2)
117.69(18)
98.77(8)
118.6(2)
91.35(2)
95.45(6)
86.48(2)
86.71(6)
118.58(16)
118.0(2)
117.98(18)
98.59(8)
117.6(2)
a
Independent molecules
1 and 2 contain gold atoms Au(1) and Au(2),
respectively.
The C(6)–S(1) bond lengths of 1.772(3) Å (molecule 1) and
1.767(3) Å (molecule 2) are longer than the C@S bond length (ca.
1.64 Å) in previously characterised N-substituted pyridine-2-thio-
carboxamide ligands [15,16]. In addition, the C(6)–N(2) bond
lengths in 13b (1.273(3) and 1.278(3) Å for molecules 1 and 2)
are shorter than in the free ligands (ca. 1.33 Å). The Au–Cl(1) bonds
(trans to N) are significantly shorter than the Au–Cl(2) ones (trans
to S) as expected from their relative trans influences.
Me
N
R
N
S
S
R
N
H
S
Au
PF6
N
N
N
Au
Cl
Cl
2
12a R=Me
13a R=Me
14
12b R=CH2Ph
12c R=C6H4Me-p
12d R=C6H4OMe-p
13b R=CH2Ph
13c C6H4Me-p
13d C6H4OMe-p
Scheme 3. N-substituted pyridine-2-thiocarboxamide ligands used in this study and the resulting thiocarboxamide complexes formed.

44
K.J. Kilpin et al. / Inorganica Chimica Acta 363 (2010) 41–48
ꢁ160 ppm in the metallacycle, resulting from the reduced C–S
bond order on coordination.
Characterisation of cycloaurated complexes by infrared spec-
troscopy is of little use. Other than the loss of the N–H stretch that
is present in the ligand the main diagnostic band in the cycloaurat-
ed complexes would be in the C–S stretching region. However, the
C–S stretch in the region of 600–700 cmꢂ1 is weak and difficult to
assign due to the multitude of other vibrations that occur in this
region (e.g. aromatic C–H bending) [17].
Because of the lack of easily ionisable groups on the cycloaurat-
ed complexes they gave only weak ESI mass spectra. Minor
[M+Na]+ ions were seen, but the main peaks were from cationic
species [(L)2Au]+, analogous to 14, which were presumably only
present in trace amounts, as the samples were pure by NMR and
microanalysis. We have previously seen this type of ion in
poorly-ionising Au(III) dichloride complexes and found that addi-
tion of pyridine to the sample immediately before analysis resulted
in substitution of a chloride ligand giving a cationic species which
was more visible [18]. However this method was unsuccessful
when applied to the cycloaurated complexes 13a–d; addition of
pyridine apparently caused decomposition of the metallacycle.
Fig. 2. Diagram showing the gold-sulfur interactions between the two molecules in
the asymmetric unit of 13b. The different orientations of the phenyl rings can also
clearly be seen. Hydrogen atoms have been omitted for clarity and thermal
ellipsoids are shown at the 50% probability level.
2.3. Spectroscopic characterisation of cycloaurated complexes 13a–d
Cycloauration of ligands 12a–d results in three main NMR spec-
tral changes. Firstly, coordination of the electron-withdrawing gold
atom to the pyridyl nitrogen causes a significant downfield shift
(CDCl3 1.4 ppm; d6-DMSO 1 ppm) for the proton adjacent to the
nitrogen (H-1, Fig. 3). The amide proton is lost upon coordination
and is not observed in the spectra of the cyclometallated com-
plexes; the H-7 protons change from a doublet in the free ligands
12a and 12b to a singlet in the metallacycles 13a and 13b as they
are no longer coupled to the NH proton. The most obvious change
in the 13C{1H} spectra is the signal assigned to the thioketone car-
bon (C-6), which moves upfield from ꢁ190 ppm in the ligand to
2.4. Reaction of N-(2-pyridyl)pyridine-2-thiocarboxamide 15 with
H[AuCl4]
Cycloauration of 15 was investigated as there was the possibil-
ity of forming either a five- or six-membered cyclometallated ring
Fig. 3. 1H NMR spectra (CDCl3) of (a) 12a and (b) 13a, showing the changes in the spectra upon coordination of the ligand to gold. The insets show the enlarged aromatic
regions (ligand assignment from Ref. [7]).
Cl
Cl
S
N
Au
N
H[AuCl4]
S
N
H[AuCl4]
N
N
N
H
S
N
15
N
N
Au
Cl
Cl
H[AuCl4]
H[AuCl4]
S
N
N
N
S
N
N
N
Au
Cl
AuCl4
Cl
16
Scheme 4. Possible reaction products of the ligand 15 with H[AuCl4], including the salt 16 obtained by oxidation and ring closure of the ligand.

K.J. Kilpin et al. / Inorganica Chimica Acta 363 (2010) 41–48
45
with the thioamide acting as an S,N donor or an N,N0-coordinated
S
N
COPh
N
five-membered auracycle, Scheme 4. However, when 15 was re-
acted with one equivalent of H[AuCl4], instead of cycloauration,
the ligand was oxidised by the gold followed by internal cyclisation
to form a 1,2,4-thiadiazolo[2,3-a]pyridinium heterocyclic ring sys-
tem, with an [AuCl4]ꢂ counter ion, 16. An X-ray crystallographic
study gave the molecular structure shown in Fig. 4, with selected
bond lengths and angles in Table 2.
N
S
N
COPh
N
N
Cu Cl
Cl
Cu
Cl
17
18
Crystals of 16 were grown by diffusion of methanol into a DMSO
solution of the crude sample. However, microanalysis of the crys-
tals was inconsistent with the X-ray result so the crystal chosen
for the diffraction study may not have been representative of the
entire sample. Indeed, the crude yield is also inconsistent with
the formulation 16 and it is probable that the cation has crystal-
lised with [AuCl2]ꢂ and Clꢂ anions as well as [AuCl4]ꢂ, though this
was not confirmed.
Few X-ray structural studies have been carried out on 1,2,4-thi-
adiazolo[2,3-a]pyridine ring systems. Compound 17 [19] and the
copper complex 18 [20,21] represent the closest examples of struc-
turally characterised compounds. As with the neutral species 17
and 18, the cationic moiety of 16 is essentially planar. The C(6)–
N(2) bond is 1.293(13) Å, very close to that expected for a C@N
bond. The bonds C(5)–C(6), C(7)-N(2) and C(6)–S(1) all have dis-
tances which fall between the values expected for either a double
or a single bond, suggesting conjugation. The [AuCl4]ꢂ anion has a
regular square–planar geometry, as expected.
NMR spectroscopy and ESI mass spectrometry are consistent
with the X-ray structural analysis. The proton adjacent to the
pyridinium nitrogen (H-11) is further downfield (ꢁ0.7 ppm) than
in the free ligand, however a greater shift (ꢁ1 ppm) would be ex-
pected if a cycloaurated complex had formed. In addition, the car-
bon arising from the thioketone group (C-6) has shifted upfield
from 188.2 ppm in the ligand to 181.9 ppm in the cation. In the
cycloaurated complexes, the corresponding shift is greater
-2e-/-H+ (80%)
S
N
S
N
Ph
+2e-/+H+ (90%)
ascorbic acid (75%)
N
H
Ph
N
19
20
Scheme 5. Electrochemical synthesis 1,2,4-thiadiazolo[2,3-a]pyridinium species.
(ꢁ30 ppm). The ESI mass spectrum shows a single peak at m/z
214.043 which corresponds to the parent cation of 16.
In hindsight it is not surprising that oxidation and cyclisation of
15 has occurred. Chemical and electrochemical oxidation of N-(2-
pyridyl)thiocarboxamides has previously been used in the synthe-
sis of 1,2,4-thiadiazolo[2,3-a]pyridinium species. For example,
ˇ
Tabakovic et al. have shown that oxidation of 19 at a graphite an-
ode gives the cation 20, with the process being reversible either by
reduction at a platinum cathode or by reaction with ascorbic acid
(Scheme 5) [22]. Other oxidants such as nitrosobenzene [23], sulfu-
ryl chloride [24] and Cu(III) ions [25] have also been shown to oxi-
dise 2-pyridylthioamides to heterocyclic species.
3. Conclusions
A series of new gold(III) complexes containing deprotonated
pyridine-2-thiocarboxamide ligands have been synthesised and
fully characterised, including the X-ray crystal structure of one
example, which confirms N,S chelation of the ligand, and the pres-
ence of a dimeric motif in the crystal through AuꢀꢀꢀS interactions
Unlike the more common cycloaurated complexes that contain
monoanionic C,N donor ligands these compounds show limited
stability, decomposing over a short period of time (approximately
6 h in solution), and may be of limited utility as precursors for fur-
ther investigation of their coordination chemistry. The 2-pyridyl
substituted ligand does not undergo analogous cyclometallation
but instead the ligand is oxidised and a heterocyclic ring system
is formed.
4. Experimental
General experimental procedures were as described previously
[2]. The N-substituted pyridine-2-thiocarboxamides 12a–d were
prepared by the literature method [7], with their purity assessed
by 1H NMR spectroscopy. H[AuCl4]ꢀ4H2O was prepared from gold
metal by the literature procedure [26]. High resolution ESI mass
spectra were recorded on a Bruker MicrOTOF instrument calibrated
using a sodium formate standard; a drop of aqueous NaCl solution
was added to the methanolic analyte solution, to promote ionisa-
tion through formation of [M+Na]+ ions. H atoms in NMR spectral
assignments are numbered according to the C atom they are
bonded to.
Fig. 4. Structure of the ionic components of 16 showing the atom labelling scheme.
Thermal ellipsoids are shown at the 50% probability level.
Table 2
Selected structural parameters for the cation of 16 (esds in parentheses).
Atoms
Lengths (Å)
Atoms
Angles (°)
N(3)–C(7)
C(7)–N(2)
N(2)–C(6)
C(6)–S(1)
S(1)–N(3)
C(5)–C(6)
1.378(12)
1.376(12)
1.293(13)
1.727(10)
1.704(8)
C(4)–C(5)–C(6)
N(1)–C(5)–C(6)
C(5)–C(6)–S(1)
C(5)–C(6)–N(2)
N(2)–C(6)–S(1)
C(6)–S(1)–N(3)
S(1)–N(3)–C(7)
N(3)–C(7)–N(2)
C(7)–N(2)–C(6)
123.0(9)
113.0(9)
115.5(7)
127.4(9)
117.1(8)
87.2(4)
112.3(6)
113.3(8)
110.1(8)
1.462(14)
4.1. Synthesis of 13a
Ligand 12a (0.200 g, 1.30 mol) and H[AuCl4]ꢀ4H2O (0.536 g,
1.30 mol) were stirred in water (20 mL) for 20 min during which

46
K.J. Kilpin et al. / Inorganica Chimica Acta 363 (2010) 41–48
3
3
time a brown solid formed. The mixture was filtered and the brown
solid washed with water (2 ꢃ 10 mL) and isopropanol (1 ꢃ 10 mL)
and air dried to give 0.413 g (76%) of 13a. Anal. Calc. for
C7H7N2SCl2Au: C, 20.1; H, 1.7; N, 6.7. Found: C, 20.4; H, 1.9; N,
7.00 (d, J8,9 = 8.4 Hz, 2H, H-8), 7.29 (d, J9,8 = 8.4 Hz, 2H, H-9),
3
3
4
8.08 (ddd, J2,1 = 6.0 Hz, J2,3 = 7.6 Hz, J2,4 = 1.4 Hz, 1H, H-2), 8.34
(dd, J4,3 = 7.9 Hz, J4,2 = 1.4 Hz, 1H, H-4), 8.48 (ddd, J3,2 = 7.6 Hz,
3
4
3
3J3,4 = 7.9 Hz, J3,1 = 1.1 Hz, 1H, H-3), 9.69 (dd, J1,2 = 6.0 Hz,
4J1,3 = 1.1 Hz, 1H, H-1); 13C{1H} d 20.6 (C-11), 120.3 (C-8), 126.7
(C-4), 129.8 (C-9), 130.0 (C-2), 135.6 (C-10), 143.6 (C-3), 144.6
(C-7), 148.5 (C-1), 157.2 (C-5), 161.9 (C-6) ppm. ESI-MS: m/z
516.957 (100%, [M+Na]+, calc 516.958), 651.095 (49%, [(L)2Au]+,
calc 651.095), 494.971 (14%, [M+H]+, calc 494.976).
4
3
6.4%. NMR (CDCl3): 1H
d 3.50 (s, 3H, H-7), 7.75 (ddd,
3
4
3J2,1 = 6.1 Hz, J2,3 = 7.0 Hz, J2,4 = 2.1 Hz, 1H, H-2), 8.19 (ddd,
3
4
3J3,2 = 7.0 Hz, J3,4 = 8.1 Hz, J3,1 = 1.4 Hz, 1H, H-3), 8.23 (dd,
4
3
3J4,3 = 8.1 Hz, J4,2 = 2.1 Hz, 1H, H-4), 9.93 (dd, J1,2 = 6.1 Hz,
4J1,3 = 1.4 Hz, 1H, H-1); 13C{1H} d 40.8 (C-7), 127.0 (C-3), 128.5
(C-2), 142.3 (C-4), 148.3 (C-1), 158.6 (C-5), 162.3 (C-6) ppm. ESI-
MS: m/z 499.034 (100%, [(L)2Au]+, calc 499.032), 440.930 (78%,
[M+Na]+, calc 440.927), 418.947 (65%, [M+H]+, calc 418.945).
CH3
11
10
9
7
7
N
CH3
8
4
N
6
5
4
3
6
5
3
2
S
N
S
2
Au
N
1
Cl
Au
Cl
1
Cl
Cl
NMR numbering scheme for 13c.
4.4. Synthesis of 13d
NMR numbering scheme for 13a.
4.2. Synthesis of 13b
Ligand 12d (0.100 g, 0.41 mmol) and H[AuCl4]ꢀ4H2O (0.169 g,
0.41 mmol) were refluxed in water (15 mL) for 1 h during which
time a dark coloured solid formed. The solution was cooled and fil-
tered and the solid washed with water (2 ꢃ 10 mL) and isopropa-
nol (1 ꢃ 10 mL). Air drying gave 0.107 g (51%) of 13d as a dark
brown solid. Anal. Calc. for C13H11N2OSCl2Au: C, 30.6; H, 2.2; N,
5.5. Found: C, 29.8; H, 2.2; N, 5.1%. NMR (CDCl3): d 3.85 (s, 3H,
Ligand 12b (0.100 g, 0.44 mmol) and H[AuCl4]ꢀ4H2O (0.180 g,
0.44 mmol) were stirred in water (10 mL) for 5.5 h during which
time a pale yellow solid formed. The solution was filtered and
the solid washed with water (2 ꢃ 10 mL) and isopropanol
(1 ꢃ 10 mL) and air dried to give 0.107 g (49%) of 13b. Anal. Calc.
for C13H11N2SCl2Au: C, 31.5; H, 2.2; N, 5.7. Found: C, 31.8; H, 2.3;
3
3
N, 5.5%. NMR (d6-DMSO): 1H
d 4.79 (s, 2H, H-7), 7.31 (d,
H-11), 6.97 (d, J9,8 = 9.0 Hz, 2H, H-9), 7.22 (d, J8,9 = 9.0 Hz, 2H,
3
3
4
3
3J11,10 = 7.4 Hz, 1H, H-11), 7.38 (t, J10,9/11 = 7.4 Hz, 2H, H-10), 7.47
H-8), 7.77 (ddd, J2,1 = 6.0 Hz, J2,3 = 7.6 Hz, J2,4 = 1.6 Hz, 1H, H-2),
3
3
4
3
3
3
8.23 (ddd, J3,2 = 7.6 Hz, J3,4 = 8.1 Hz, J3,1 = 1.3 Hz, 1H, H-3), 8.43
(d, J9,10 = 7.4 Hz, 2H, H-9), 8.02 (ddd, J2,1 = 6.0 Hz, J2,3 = 7.7 Hz,
3
4
3
4J2,4 = 1.7 Hz, 1H, H-2), 8.23 (dd, J4,3 = 8.0 Hz, J4,2 = 1.7 Hz, 1H,
3
4
(dd, J4,3 = 8.1 Hz, J4,2 = 1.6 Hz, 1H, H-4), 9.96 (dd, J1,2 = 6.0 Hz,
4J1,3 = 1.3 Hz, 1H, H-1); 13C{1H} d 55.7 (C-11), 114.6 (C-9), 124.1
(C-8), 127.4 (C-4), 128.5 (C-2), 140.4 (C-7), 142.1 (C-3), 148.6 (C-
1), 158.4 (C-6), 158.9 (C-10), 159.8 (C-5) ppm. ESI-MS: m/z
683.088 (100%, [(L)2Au]+, calc 683.084), 532.957 (10%, [M+Na]+,
calc 532.953).
3
3
4
H-4), 8.41 (ddd, J3,2 = 7.7 Hz, J3,4 = 8.0 Hz, J3,1 = 1.4 Hz, 1H, H-3),
9.66 (dd, J1,2 = 6.0 Hz, J1,3 = 1.4 Hz, 1H, H-1); 13C{1H} d 55.8 (C-
7), 126.6 (C-4), 127.0 (C-11), 127.8 (C-9), 128.4(C-10), 129.6 (C-
2), 138.6 (C-8), 143.5 (C-3), 148.2 (C-1), 157.1 (C-5), 161.5 (C-6)
ppm. ESI-MS: m/z 651.099 (100%, [(L)2Au]+, calc 651.095),
516.962 (5%, [M+Na]+, calc 516.958).
3
4
OCH3
11
10
9
10
7
8
9
N
7
N
11
8
4
4
6
6
5
3
2
5
3
2
S
S
N
N
Au
Au
1
Cl
1
Cl
Cl
Cl
NMR numbering scheme for 13b.
4.3. Synthesis of 13c
NMR numbering scheme for 13d.
4.5. Synthesis of 14
Ligand 12c (0.200 g, 0.88 mmol) and H[AuCl4].4H2O (0.362 g,
0.88 mmol) were refluxed in water (20 mL) for 1 h during which
time a dark brown solid formed. The solution was filtered and
the dark brown solid was washed with water (2 ꢃ 10 mL) and iso-
propanol (1 ꢃ 10 mL) and air dried to give 0.385 g (88%) of 13c.
Anal. Calc. for C13H11N2SCl2Au: C, 31.5; H, 2.2; N, 5.7. Found: C,
31.9; H, 2.2; N, 5.6%. NMR (d6-DMSO): 1H d 2.34 (s, 3H, H-11),
Ligand 12a (0.050 g, 0.33 mmol), H[AuCl4].4H2O (0.066 g,
0.16 mmol) and NH4PF6 (0.054 g, 0.33 mmol) were stirred in water
(10 mL) for 20 min. The pale brown solid that formed during this
time was filtered, washed with water (2 ꢃ 10 mL) and isopropanol
(10 mL), and air dried to give 0.081 g (79%) of 14. Anal. Calc. for
C14H14N4F6PS2Au: C, 26.1; H, 2.2; N, 8.7. Found: C, 25.5; H, 2.2;
N, 8.3%. NMR (d6-DMSO): 1H d 3.56 (s, 3H, H-7), 8.07 (ddd,

K.J. Kilpin et al. / Inorganica Chimica Acta 363 (2010) 41–48
47
3
4
3J2,1 = 5.6 Hz, J2,3 = 7.6 Hz, J2,4 = 1.4 Hz, 1H, H-2), 8.28 (dd,
Table 3
4
3
3J4,3 = 7.9 Hz, J4,2 = 1.4 Hz, 1H, H-4), 8.49 (ddd, J3,2 = 7.6 Hz,
Unit cell and crystallographic refinement data for 13b and 16.
3J3,4 = 7.9 Hz, J3,1 = 1.0 Hz, 1H, H-3), 8.89 (d, J1,2 = 5.6 Hz, 1H, H-
1); 13C{1H} d 41.2 (C-7), 125.5 (C-4), 129.9 (C-2), 143.5 (C-3),
148.1 (C-1), 154.4 (C-5), 160.7 (C-6) ppm. ESI-MS: m/z 499.033
(100%, [(L)2Au]+, calc 499.032).
4
3
Complex
13b
16
Formula
Mr
T (K)
Crystal system
Space group
a (Å)
C13H11AuCl2N2S C11H8AuCl4N3S
495.16
90
553.03
90
monoclinic
P21/c
7.8738(4)
28.0459(14)
7.2397(4)
90
108.677(3)
90
1514.54(14)
4
2.425
0.1239, 0.0460
2679
2594
triclinic
ꢀ
P1
7
7.6029(1)
13.6803(2)
13.7727(2)
90.542(1)
103.635(1)
91.901(1)
1391.14(3)
4
CH3
b (Å)
c (Å)
N
a
(°)
6
S
b (°)
c
(°)
5
V (Å3)
Au
PF6
4
3
Z
N
Dcalc (g cmꢂ3
)
2.364
0.5557, 0.1356
6673
Tmax,
min
1
Number of unique reflections
Number of observed reflections
2
2
5957
[I > 2r(I)]
R1[I > 2
wR2 (all data)
Goodness-of-fit (GOF)
r
(I)]
0.0156
0.0361
1.039
0.0369
0.0910
1.082
NMR numbering scheme for 14.
4.6. Reaction of 15 with H[AuCl4]
Ligand 15 (0.100 g, 0.46 mmol) was stirred in aqueous (15 mL)
H[AuCl4]ꢀ4H2O (0.190 g, 0.46 mmol) for 1 h. The solution was fil-
tered leaving a brown/orange solid that was washed with water
(2 ꢃ 10 mL) and isopropanol (1 ꢃ 10 mL) and dried to give
0.144 g of 16. Anal. Calc. for C11H8N3SCl4Au: C, 23.9; H, 1.5; N,
7.6. Found: C, 26.8; H, 1.8; N, 6.9%. NMR (d6-DMSO): 1H: d 7.90
present in the free pyridyl ring of 16 an inspection of temperature
factors was used to assign N(1) and C(4). The pyridyl ring is orien-
tated so that N(1) and S(1) are cis to each other. Inversion of C(4)
and N(1) (with N(1) and N(2) cis to each other) resulted in in-
creases in both R1 and wR2. After a final refinement cycle of 16
there was still a significant amount of residual electron density
present. Refinement excluding the high angle data (above 50°) re-
3
3
3
(dd, J2,1 = 4.6 Hz, J2,3 = 7.6 Hz, 1H, H-2), 8.04 (dd, J10,11 = 6.6 Hz,
3
3
3J10,9 = 7.4 Hz, 1H, H-10), 8.28 (dd, J3,2 = 7.6 Hz, J3,4 = 7.7 Hz, 1H,
duced, but did not totally eliminate, this problem.
A peak
3
3
H-3), 8.42 (d, J4,3 = 7.7 Hz, 1H, H-4), 8.60 (dd, J9,10 = 7.4 Hz,
(2.05 e Åꢂ3) remained approximately 1.6 Å from S(1) and this
was assigned as an artefact as it could not be modelled in any
chemically sensible way.
3J9,8 = 8.5 Hz, 1H, H-9), 8.73 (d, J8,9 = 8.5 Hz, 1H, H-8), 8.88 (d,
3
3J1,2 = 4.6 Hz, 1H, H-1), 9.75 (d, J11,10 = 6.6 Hz, 1H, H-11); 13C{1H}
3
d 121.6 (C-4), 122.8 (C-10), 123.2 (C-8), 130.2 (C-2), 138.6 (C-11),
139.6 (C-3), 142.9 (C-9), 146.2 (C-5), 151.0 (C-1), 161.2 (C-7),
181.9 (C-6) ppm. ESI-MS: m/z 214.043 (100%, [16-AuCl4]+, calc
214.043).
Acknowledgements
We thank the University of Waikato for financial support, Pat
Gread with technical maintenance of the electrospray mass spec-
trometer, and Scott Carter for preparation of the thioamide ligands.
KJK thanks The Tertiary Education Commission (Top Achievers
Doctoral Scholarship) and the New Zealand Federation of Graduate
Women (Merit Award for Doctoral Study). Dr. Tania Groutso (Uni-
versity of Auckland) and Dr. Jan Wikaira (University of Canterbury)
are thanked for collection of the X-ray data sets.
8
3
4
N
S
7
9
5
6
2
N
10
N
1
11
AuCl4
Appendix A. Supplementary material
NMR numbering scheme for 16.
CCDC 742305 and 742304 contain the supplementary crystallo-
graphic data for 13b and 16. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2009.10.003.
4.7. X-ray crystal structure determinations of 13b and 16
Crystals of 13b were grown by slow diffusion of diethyl ether
into a dichloromethane solution of the compound and 16 was crys-
tallised by slow diffusion of methanol into a solution of the com-
pound in DMSO, both at room temperature. Unit cell dimensions
and reflection data for 13b were collected at the University of
Auckland on a Bruker Smart CCD Diffractometer and for 16 at the
University of Canterbury on a Bruker Apex II Diffractometer.
Semi-empirical absorption corrections were applied by SADABS
[27]. Crystal and refinement data for the two complexes are pre-
sented in Table 3.
Both structures were solved by Patterson methods of SHELXS-97
[28]. The gold atoms were initially located, and all other non-
hydrogen atoms were found by a series of difference maps (SHEL-
XL-97 [29]) and refined anisotropically. Hydrogen atoms were
placed in calculated positions. Because of the pseudo symmetry
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