Mixed ligand gold(I) complexes of phosphines and thiourea and X-ray structure of (thiourea-κS)(tricyclohexylphosphine)gold(I)chloride

Article abstract of DOI:10.1016/S0277-5387(03)00129-3

A series of mixed ligand gold(I) complexes with thiourea (Tu) and various phosphines, [R₃PAuTu]Cl, have been prepared and characterized by elemental analysis, IR and NMR (¹³C, ¹⁵N and ³¹P) spectroscopies and X-ray crystallography. The spectral data of all complexes are consistent with the sulfur coordination of thiourea to gold(I). The single crystal X-ray structure of the complex [Cy₃P-Au-Tu]Cl revealed that the geometry is not perfectly linear at the gold(I) with a P-Au-S bond angle of 168.54(9)°. The Au-P and Au-S distances are 2.274(2) and 2.295(2) A?, respectively.

Full text of DOI:10.1016/S0277-5387(03)00129-3

Polyhedron 22 (2003) 1349Á1354
/
www.elsevier.com/locate/poly
Mixed ligand gold(I) complexes of phosphines and thiourea and X-
ray structure of (thiourea-kS)(tricyclohexylphosphine)gold(I)chloride
Anvarhusein A. Isab a,*, Mohammed Fettouhi a,*, Saeed Ahmad a, Lahce`ne Ouahab b
a Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
b Laboratoire de Chimie du Solide et Inorganique Mole´culaire, UMR 6511, CNRS-Universite´ de Rennes1, Campus de Beaulieu, 35042, Rennes Cedex,
France
Received 27 November 2002; accepted 11 February 2003
Abstract
A series of mixed ligand gold(I) complexes with thiourea (Tu) and various phosphines, [R3PAuTu]Cl, have been prepared and
characterized by elemental analysis, IR and NMR (13C, 15N and 31P) spectroscopies and X-ray crystallography. The spectral data of
all complexes are consistent with the sulfur coordination of thiourea to gold(I). The single crystal X-ray structure of the complex
[Cy3PÁ
P and AuÁ
/
AuÁ
/
Tu]Cl revealed that the geometry is not perfectly linear at the gold(I) with a PÁ
/
AuÁ
/
S bond angle of 168.54(9)8. The AuÁ
/
˚
S distances are 2.274(2) and 2.295(2) A, respectively.
/
# 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Gold(I) complexes; X-ray structures; Thiourea
1. Introduction
phosphines, thiones and selenones [14,15]. As a part of
our continuing research program in this area, here we
Recent interest in gold(I) complexes with sulfur and
phosphorus donor ligands was stimulated by the anti-
arthritic properties exhibited by some gold compounds
like myocrisin, solganol and auranofin [1,2].
report the synthesis and characterization of phosphineÁ
gold(I) complexes of thiourea.
/
Thiourea (Tu) and imidazolidine-2-thione and its
derivatives are simple sulfur containing ligands and
thus gold(I) complexes of thiourea are expected to
form useful additional new compounds, which may
serve as models for presently available therapeutic
agents. The ability of thiourea (Tu) to form stable
adducts with a variety of transition metals (Cu, Ag, Au
and Pt) is well established and the structures of several
2. Experimental
2.1. Chemicals
Thiourea, MeOD, NH4NO3, Me2S and all solvents
were obtained from the FlukaÁ
Germany. 13C and 15N labelled (ꢀ
thiourea was obtained from Isotec Co, USA. HAuCl4×
3H2O and all phosphines were obtained from the Strem
Chemical Co.
/
Aldrich Chemical Co.,
/98% each atom)
/
such complexes have been determined [3Á
We have been interested in the spectral and structural
chemistry of goldÁphosphorus and goldÁsulfur interac-
tions involving phosphines, heterocyclic thiones and
thiolates [11Á13]. We have also studied the solution
equilibria of cyanogold(I) complexes for a series of
/
11].
/
/
/
2.2. Synthesis of the complexes
All [R3PAuTu]Cl complexes were prepared by the
addition of thiourea to the corresponding precursor
complexes, R3PAuCl. The R3PAuCl complexes were
* Corresponding authors. Tel.: ꢀ
4277.
E-mail
fettouhi@kfupm.edu.sa (M. Fettouhi).
/
966-3-860-2645; fax: ꢀ
/
966-3-860-
Isab),
prepared by adding phosphines to the slurry of Me2SÁ
/
addresses:
aisab@kfupm.edu.sa (A.A.
AuCl in acetone under N2 and stirring for half an hour
0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0277-5387(03)00129-3

1350
A.A. Isab et al. / Polyhedron 22 (2003) 1349Á1354
/
[11]. The labelled thiourea was mixed with unlabelled
thiourea to give ꢀ
10% 13C and 15N labelled thiourea.
The phosphines used in the study were; Me3P, Et3P,
Table 2
Crystallographic data for [Cy3PÁ
/
AuÁTu]Cl
/
/
Formula
Fw
[C19H37N2PSAu]Cl
Ph3P, Cy3P, CyPh2P, (o-Tol)3P, (m-Tol)3P, (p-Tol)3P
588.95
orthorhombic
Pna21
(where Cyꢁ
/
cyclohexyl, Tolꢁtolyl).
/
Crystal system
Space group
T (K)
293(2)
2.2.1. Preparation of [Ph3PAuTu]Cl
[Ph3PAuCl] (0.494 g, 1 mmol) was dissolved in 20 cm3
of MeOH. Thiourea (0.076 g, 1 mmol) was added as a
˚
l (A)
0.71073
1.676
6.582
rcalc (g cmꢂ3
)
m (mmꢂ1
F(000)
Unit cell dimensions
)
1168
solid to the solution. The solution was stirred for 15Á20
/
min. The resulting colorless solution was filtered and
kept in a refrigerator at 4 8C for crystallization. A total
of 0.394 g of the product was obtained corresponding to
69% after crystallization.
A similar procedure was followed for the rest of the
syntheses where [R3PAuTu]Cl complexes were first
dissolved in MeOH or acetone followed by addition of
1 equivalent of solid thiourea into the solution. As a
˚
a (A)
16.8506(2)
16.9731(5)
8.1590(5)
2333.5(2)
4
˚
b (A)
˚
c (A)
3
˚
V (A )
Z
u range (8)
Index ranges
No. collected
No. observed
2.40Á
215
5137
/
27.47
ꢂ/
/h 5
/
21, ꢂ
/
215
/
k 5
/
22, ꢂ
/
105
/
l 510
/
3504 (Iobs
0.0412
0.0937
1.42
ꢁ
/2s(I))
result, white crystalline products were obtained in 60Á
/
R (Iobs
wR2
ꢁ
/
2s(I))
70% yield. The complex [(m-Tol)3PAuTu]Cl was pre-
pared in acetonitrile and [(CyPh2)PAuTu]Cl was iso-
lated from a mixture of acetone and hexane. The
complex [(p-Tol)3PAuTu]Cl could not be isolated in
the solid state and therefore it was studied by preparing
it in the solution form. The elemental analysis, % yield,
m.p., etc. of these complexes are given in Table 1.
ꢂ3
˚
rmax (e A
)
ꢂ3
˚
rmin (e A
)
ꢂ/1.06
connected atoms. For the NH2 groups, a planar
geometry was assumed for the SꢀC(NH)2 moiety.
/
Selected bond lengths and angles are given in Table 3.
Complete bond lengths and bond angles, anisotropic
thermal parameters and calculated hydrogen coordi-
2.3. X-ray data collection and structure determination
A colorless needle-shaped crystal of the complex
[Cy3PAuTu]Cl was mounted on a glass fiber. Data
collection was performed on a kappa CCD four circle
Table 3
Selected bond lengths (A) and bond angles (8) for [Cy3PÁ
˚
/
AuÁTu]Cl
/
EnrafÁ
/
Nonius diffractometer, equipped with graphite
˚
0.71073 A).
Bond lengths
AuÁ/P
2.274(2)
2.295(2)
1.828(10)
1.847(9)
PÁ
SÁ
N1Á
N2Á
/
C1
1.846(9)
1.704(9)
1.320(11)
1.310(11)
monochromatized Mo Ka radiation (lꢁ
/
AuÁ/S
/C19
Intensity data were corrected for Lorentz and polariza-
tion effects. Effective absorption correction was per-
formed (SCALEPACK) [16] and the structure was solved
and refined by full-matrix least-squares method, on F2,
using SHELXS-97 and SHELXL-97, respectively [17,18].
Crystallographic data are given in Table 2. Hydrogen
atoms were included at calculated positions with iso-
tropic thermal parameters proportional to those of the
PÁ/C13
/C19
PÁ/C7
/C19
Bond angles
PÁAuÁ
C13ÁPÁ
C13ÁPÁ
C7ÁPÁ
/
/
S
168.54(9)
111.2(4)
107.3(4)
106.9(4)
C13Á
C7ÁPÁ
C1ÁPÁ
C19Á
/PÁ
/
Au
113.0(3)
106.6(3)
111.8(3)
110.0(3)
/
/C7
/
/
Au
/
/C1
/
/
Au
/
/C1
/SÁ
/Au
Table 1
Elemental analysis, m.p., IR frequencies (cmꢂ1) and % yield of [R3PAuTu]Cl complexes
Complex
Found (Calc.) %
C
m.p. (8C)
n(Cꢀ/S)
% Yield
H
N
S
[Me3PAuTu]Cl
[Et3PAuTu]Cl a
[Cy3PAuTu]Cl
12.7 (12.5)
19.8 (19.7)
38.7 (39.9)
40.7 (40.0)
40.4 (39.6)
43.3 (43.1)
41.9 (43.1)
3.5 (3.4)
4.6 (4.5)
6.4 (6.3)
3.3 (3.4)
4.8 (4.4)
4.5 (4.1)
4.1 (4.1)
7.4 (7.3)
6.6 (6.6)
5.4 (4.8)
5.4 (4.9)
5.4 (4.9)
4.7 (4.6)
4.5 (4.6)
8.0 (8.3)
7.2 (7.5)
4.8 (5.4)
5.7 (5.6)
6.0 (5.6)
4.6 (5.2)
4.4 (5.2)
199Á
135Á
204Á
146Á
112Á
199Á
124Á
/
200
136
206
148
114
201
125
716
718
690
710
694
712
692
63
71
61
69
60
66
58
/
/
[Ph3PAuTu]Cl
/
[CyPh2PAuTu]Cl
[(o-Tol)3PAuTu]Cl
[(m-Tol)3PAuTu]Cl
/
/
/
a
Also reported earlier in Ref. [24].

A.A. Isab et al. / Polyhedron 22 (2003) 1349Á
/1354
1351
in the non-centrosymmetric space group Pna21. The
crystal structure, depicted in Fig. 1, shows that the
geometry is not perfectly linear, with a PÁ
/
AuÁS bond
/
angle of 168.54(9)8. The deviation from linearity is
ascribed to the intramolecular AuÁ Á ÁN2 contact with a
˚
distance of 3.418(3) A. The AuÁ
/
S and AuÁP bond
/
˚
distances are 2.295(2) and 2.274(2) A, respectively.
These values are in agreement with those found in other
thiourea-containing gold(I) complexes [9,10]. One nitro-
gen atom of thiourea (N1) is in close contact with the
˚
chloride ion with a N1Á Á ÁCl distance of 3.219(3) A,
indicating N1Á
phorus atom in the complex has a usual tetrahedral
environment, as in the other phosphine gold(I) com-
/
HÁ Á ÁClꢂ hydrogen bonding. The phos-
plexes [22,23]. The average C(Cy)Á
/
PÁC(Cy) and
/
Fig. 1. ORTEP diagram of [Cy3PAuTu]Cl, showing the atomic
numbering scheme. Displacement ellipsoids are drawn at the 50%
probability level.
C(Cy)ÁPÁAu angles are 108.5 and 110.58, respectively.
/
/
The three cyclohexyl groups adopt chair conformations,
similar to those found in Cy3PAuCN and Cy3PAuCl. A
layer based molecular packing is observed, in which the
nates are deposited as supplementary materials. The
drawing was prepared with ORTEP3 for windows [19,20].
The ORTEP atomic labeling scheme is given in Fig. 1.
rings of the neighboring molecules stack on top of each
˚
other. The shortest goldÁgold distance is 8.159 A, ruling
/
out any metalÁ
3.2. IR studies
In the IR spectra of the complexes, the n(Cꢀ
/metal interaction.
2.4. IR and NMR measurements
The solid-state IR spectra of the complexes were
recorded on a Perkin Elmer FTIR 180 spectrophot-
/S) mode
of Tu was observed at a lower frequency compared to
that for free Tu at 730 cmꢂ1. There are also strong
absorptions around 1500 and 3200 cmꢂ1 corresponding
to n(CN) and n(NH2) modes, respectively, for Tu in all
complexes. The IR frequencies of the complexes are
given in Table 1.
The ambidentate ligand, thiourea {SC(NH2)2} is
potentially capable of bonding via the sulfur or nitrogen
atom [24]. A low frequency shift of the n(Cꢀ
ometer using KBr pellets in the 4000Á
400 cmꢂ1 range.
/
The 31P NMR spectra were recorded at a frequency of
202.35 MHz, using 0.269 s acquisition time, 5.00 s pulse
delay and 6.20 ms pulse width (458). The 31P NMR
chemical shifts were measured relative to the internal
reference 85% H3PO4.
The 13C NMR spectra were obtained at the frequency
of 125.65 MHz with 1H broadband decoupling at 298 K.
The spectral conditions were: 32 k data points, 0.967 s
acquisition time, 1.00 s pulse delay and 458 pulse angle.
The 13C chemical shifts were measured relative the
internal reference TMS.
/
S) absorp-
tion and a high frequency shift of the band around 3200
cmꢂ1 in the gold(I) complexes indicates the existence of
the thione form of Tu in the solid state.
The 15N NMR spectra were recorded at 50.55 MHz
using NH415NO3 in D2O as an external reference, which
lies at 375.11 ppm relative to pure MeNO2, 380.2 ppm
[21]. The spectral conditions for 15N were: 32 k data
points, 0.721 s acquisition time 2.50 s delay time, 608
pulse angle and approximately 15 000 scans.
3.3. 31P NMR studies
The 31P NMR spectra of the complexes were recorded
in MeOD. In the 31P NMR spectra of all [R3PAuTu]Cl
complexes, a sharp singlet was observed for R3P. No
coupling with 13C of labelled thiourea was observed in
any complex. The 31P NMR chemical shifts of several
gold(I) complexes are given in Table 4. The 31P
resonance in the thiourea complexes appears downfield
compared to the R3PAuCl complexes. A downfield shift
in the 31P resonance of the phosphines in [R3PAuTu]Cl
complexes is related to the p accepting ability of the
phosphines from gold(I). The donation of electron
density by Tu to gold(I) increases the back donation
from gold(I) to phosphines, which would increase the
3. Results and discussion
3.1. X-ray structure description
The single crystal X-ray structure of the complex
[Cy3PAuTu]Cl, as a representative for the entire series,
has been determined. The crystallographic data and the
selected bond lengths and bond angles are given in
Tables 2 and 3, respectively. The compound crystallizes
double bond character of the AuÁ
deshielding effect at the phosphorus atom. In R3PAuCN
/P bond resulting in a

1352
A.A. Isab et al. / Polyhedron 22 (2003) 1349Á1354
/
Table 4
31P NMR chemical shifts (ppm) of various R3PAuX complexes in
MeOD
density producing a partial double bond character in the
CÁN bond, as observed in the other metal complexes of
/
thiourea [6,25]. A typical 13C NMR spectrum for the
[Cy3PAuTu]Cl complex is given in Fig. 2.
R3P
d [R3PAuCl]
d [R3PAuTu]ꢀ
d [R3PAuCN] a
A correlation between the basicity of phosphines and
the 13C chemical shift (Table 5) is observed for
[R3PAuTu]Cl complexes. The basicities or electronega-
tivites of phosphines are measured in terms of the
wavenumbers, n(CO) for the complex, [R3PNi(CO)3]
[26]. The n(CO) values of the phosphines are compared
in Table 5. A decrease in n(CO) is associated with a
decrease in electronegativity or an increase in basicity of
the phosphine.
Cy3P
Et3P
54.37
32.81
58.01
37.90
53.53
35.35
Me3P
ꢂ
/
9.56
ꢂ
/
1.86
ꢂ3.09
/
(CyPh2)P
(o-Tol)3P
(p-Tol)3P
(m-Tol)3P
Ph3P
43.67
6.29
46.89
13.75
34.96b
37.05
37.01
44.04
37.38
34.45
35.79
39.37
30.13
32.28
32.22
a
Values taken from Ref. [11].
The complex was prepared in solution.
b
With an increase in the electronegativity of the
S shift difference also
phosphine, the 13C NMR ꢁCꢀ
/
complexes, where CN is a p acceptor ligand (with less
donation of electron density to gold(I)), the 31P reso-
nance appears upfield compared to that for Tu com-
plexes [11] (Table 4). As a result of the stronger AuÁ
bond in [R3PAuTu]Cl complexes, their AuÁP bond
lengths should be smaller compared to that in
R3PAuCN. The AuÁP bond length in [Cy3PAuTu]Cl
is found to be 2.274 A, while in Cy3PAuCN, it is 2.287 A
[23]. This difference clearly shows that [R3PAuTu]Cl
type complexes have greater p character in the AuÁ
bond than their R3PAuCN analogues.
increases (see Table 5), e.g. the chemical shift difference
between free Tu and [Cy3PAuTu]Cl is 2.78 ppm where
as for [Et3PAuTu]Cl, [Me3PAuTu]Cl and [Ph3PAuTu]Cl
it is 5.14, 6.2 and 8.33 ppm, respectively. A similar
observation is made for the coupling constants,
/
P
/
1J(13CÁ31
stronger as the electronegativity of the phosphine
increases. Thus, the AuÁS bond would be strongest
/
P). This shows that the AuÁ/S bond becomes
/
˚
˚
/
when R3P is PPh3 while it would be weakest for the
Cy3P complex.
/P
3.5. 15N NMR studies
3.4. 13C NMR studies
The 15N chemical shift in all complexes were observed
at a downfield position compared to that for the free
ligand. The 15N chemical shifts for [R3PAuTu]Cl com-
plexes are given in Table 5. The coupling constant,
The 13C NMR chemical shifts for the ꢁCꢀ
of Tu in [R3PAuTu]Cl complexes are given in Table 5
along with the values of electronic parameter, n(CO) for
/
S carbon
1J(13CÁ15N) could not be resolved by 15N NMR. A
/
the phosphines. The ꢁCꢀ
as a triplet in 13C NMR due to coupling with 15N with a
1J(13CÁ15
N) value of 15.7 Hz. Only small changes were
observed in the coupling constant on complexation with
gold(I). An upfield shift is observed in the ꢁCꢀ
resonance of Tu on its complexation with gold(I). The
upfield shift is attributed to a lowering of ꢁCꢀS bond
order upon coordination and a shift of N0C electron
/
S resonance of Tu appeared
downfield shift in the 15N resonance in all complexes
demonstrates that the nitrogen of Tu is not involved in
bonding to gold(I) since metal binding through nitrogen
should cause an upfield shift in the 15N resonance of Tu
/
/S
[27,28]. As discussed earlier the AuÁS bond would be
/
strongest when R3P is PPh3 while it would be weakest
for the Cy3P complex. This observation can also be
verified by 15N NMR where there is a greater shift for
the more electronegative PPh3 ligand compared to the
less electronegative Cy3P.
/
/
Table 5
13C and 15N NMR chemical shifts for [R3PAuTu]Cl complexes and IR
a
wavenumbers for R3PNi(CO)3 complexes
3.6. Conductance studies
R3P/Tu
n (CO) in cmꢂ1 of R3P a
d
13C (ꢁCꢀ
/S)
d
15N
Tu
Cy3P
185.54
182.76
180.40
179.34
177.26
178.58
181.24 b
177.33
177.21
103.65
104.74
106.77
106.47
Whether these complexes remain as two coordinates
or possess a trigonal structure in solution can be
established by conductivity measurements. The molar
conductance for a representative complex [Me3PAu-
Tu]Cl was measured in MeOH. The molar conductances
of some compounds are given in Table 6. By comparison
with the conductances of the compounds with a known
number of ions, it was proved that the solution consists
of two ionic species. Thus the complexes remain as two
coordinates in solution.
2056.4
2061.7
2064.1
2064.8
2066.6
2066.7
Et3P
Me3P
(CyPh2)P
(o-Tol)3P
(p-Tol)3P
107.64
107.32
(m-Tol)3P 2067.9
Ph3P
2068.9
a
The values are taken from Ref. [26].
The complex was prepared in solution.
b

A.A. Isab et al. / Polyhedron 22 (2003) 1349Á
/1354
1353
Fig. 2. The 13C{1H} NMR spectrum of [Cy3PAuTu]Cl in MeOD.
Table 6
Molar conductances and the number of ions in solution for some
compounds in MeOH
Data Centre, CCDC No. 187414. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (fax: ꢀ44-1223-336033; e-mail: deposit@
/
Compound
Molar conductance
No. of ions in solution
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
[Me3PAuTu]Cl
[Me3PAuCl]
NH4NO3
95.7
1.8
2
0
2
86.5
Acknowledgements
4. Conclusions
This research was supported by the KFUPM Re-
search Committee under project no. CY/NMR-STU-
DIES/214.
The study provides useful information about the
nature of bonding in gold(I) complexes. The chemical
shifts for different complexes presented here would
provide a basis for understanding and predicting the
interaction of gold(I) with other phosphine and thione
ligands. The X-ray results support the structures in-
ferred from IR and NMR data.
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