Gold coordination by a tertiary phosphine with three thioether functions

Article abstract of DOI:10.1515/znb-1997-0213

The reaction of tris(phenylthiomethyl)phosphine with equimolecular amounts of [AuPPh₃]⁺[BF₄]^- affords the complex (tris(phenylthiomethyl)phosphine)(triphenylphosphine)-gold(I) tetrafluoroborate 1 in good yield. The X-ray diffraction analysis of this product shows an unusual conformation with the three CH₂SPh arms of the phosphine folded back towards the metal atom shielding the P-Au-P' unit. The reaction of the same substrate with Bis(tetrahydrothiophene)gold(I) perchlorate in a 1:1 molar ratio leads to the displacement of both weakly coordinated tht ligands, and a dimeric product [AuP(CH₂Sph)₃]₂(ClO₄)₂ 2 is obtained.

Full text of DOI:10.1515/znb-1997-0213

Gold Coordination by a Tertiary Phosphine with Three Thioether Functions
Stefan Fuchs, José M. López-de-Luzuriaga, M. Elena Olmos, Alexander Sladek,
Hubert Schmidbaur*
Anorganisch-chemisches Institut der Technischen Universität München
Lichtenbergstrasse 4, D-85748 Garching, Germany
Z. Naturforsch. 52 b, 217-220 (1997); received December 16, 1996
Gold(I) Coordination, Tris(phenylthiomethyl)phosphine, Ambidentate P/S3-Ligand
The reaction of tris(phenylthiomethyl)phosphine with equimolecular amounts of
[AuPPh3]+[BF4]~ affords the complex (tris(phenylthiomethyl)phosphine)(triphenylphosph-
ine)-gold(I) tetrafluoroborate 1 in good yield. The X-ray diffraction analysis of this prod-
uct shows an unusual conformation with the three ChLSPh arms of the phosphine folded back
towards the metal atom shielding the P-Au-P' unit. The reaction of the same substrate with
Bis(tetrahydrothiophene)gold(I) perchlorate in a 1:1 molar ratio leads to the displacement of
both weakly coordinated tht ligands, and a dimeric product [AuP(CH2SPh)3]2(C104)2 2 is
obtained.
Introduction
ligand is readily prepared from phenylthiomethyl-
lithium and triphenylphosphite. Its ligand properties
have not been probed to date, but the corresponding
phosphine sulfide has recently been applied success-
fully in the coordination chemistry of the low-valent
coinage metals [7].
The majority of gold compounds used in mod-
em technology and medicine are based on sys-
tems where the metal is coordinated by phosphorus
and/or sulfur ligands [1]. This is true in particu-
lar for “liquid golds” used for gilding [2 ] and for
the drugs successfully applied for the treatment of
rheumatoid arthritis and even cancer [3]. Tertiary
phosphines are clearly superior to all other ligands
in gold chemistry, but sulfur containing ligands are
more versatile owing the better leaving group prop-
erties of thiol and thioether functions and to their
useful redox properties.
Results and Dicussion
The reaction between a freshly prepared solution
of [AuPPh3]+[BF4]~ and an equimolecular amount
of (PhSCH2)3P in tetrahydrofuran at 0°C for 1 h af-
fords the cationic complex 1 formulated in equation
1 in high yield. The product is a stable, colorless
crystalline solid, soluble in common polar organic
solvents.
A combination of two independent ligands with
P- and S-donor functionality at a common metal
center may often be the configuration of choice
to secure both stability and reactivity for a given
substrate. The same combination can be achieved
if the phosphine and thioether functionalities are
present in the same ligand. We have therefore ini-
tiated preparative and structural studies on com-
pounds based on the P-Au-S moiety [4], includ-
ing those where ambidentate ligands contain mixed
functions and offer polyfunctionality [5].
Ph— s-
P + [AuPPh3][BF4]
Ph— s
Ph— S
S— Ph
^ P —Au—PPh3
[BF4]
(1)
/~S— Ph
Z— S— Ph
The 31 P{1H} NMR spectrum of complex 1 at
room temperature in CDCI3 shows only one broad
signal at 6 = 42.5 ppm. However, this resonance
splits into the expected AB system as the temper-
ature is lowered to -60 °C (see Experimental Sec-
tion). This behaviour suggests a rapid ligand ex-
change in solution, which is slowed down at low
In the present paper we report our results with
the ligand tris(phenylthiomethyl)phosphine [6 ] as
a multi/mixed-functional donor for gold(I). This
* Reprint requests to Prof. Dr. H. Schmidbaur.
0939-5075/97/200-0217 $ 06.00 (c) 1997 Verlag der Zeitschrift für Naturforschung. All rights reserved.
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218
St. Fuchs et al. • Gold Coordination by a Tertiary Phosphine with Three Thioether Functions
Table I. Crystallographic data for compound 1.
1
Empirical formula
Formula weight
Crystal system
Space group (No.)
a [A]
b[A\
C39HiöAuBF4PtS3
936.49
orthorhombic
Pbca (No.61)
19.978(2)
15.610(2)
24.526(3)
7649(1)
1.627
c [A l
V [A ]
Pcalc [gem -]
Z
8
41.41
-74
ju(Mo-Kq) [cm-1]
T[°C]
Radiation
Scan
hkl Range
Mo-Kq
tjj
-25,-19, +30
7064
7064
5373
Measured reflections
Unique reflections
Observed reflections
(with F0 > 4<r(F0))
Refined parameters
wR2 *
Rbasedon F (OMIT4) **
pfin(max/min) [eA-1J ***
Absorption corr.:
Fig. 1. Molecular structure of the cation complex
1 with atomic numbering (ORTEP, hydrogen atoms
omitted). Selected bond lengths (A) and angles (°):
Au-P(l) 2.2923(13), Au-P(2) 2.3036(13), S(l)-C(2)
1.797(6), S(2)-C(l) 1.805(6), S(3)-C(3) 1.790(6), P(l)-
Au-P(2) 174.37(5), S(2)-C(l)-P(l) 115.7(3), S(l)-C(2)-
P(l) 115.6(3), S(3)-C(3)-P(l) 113.6(3).
487
0.0792
0.0371
+ 1.22 /-1.78
empirical
0.7440 / 0.9984
/ = 0.0385, k= 1.4403
Tmin/Tmax
Weighting scheme ****
* wR2 = [I w(F02- Fc2)2/X w(F02)2]1/2;
**/? = i ( ||F 0|- |F C||)/X|Fo|;
*** Residual electron densities located at the gold atom;
**** w = l/(cj2(Fo2)+(l-p)2+k-p), p = Max(F2,0)+2-F2/3.
temperature. The 'H NMR spectrum is less sensi-
tive to changes in temperature. It exhibits a multiplet
for the phenyl groups and a singlet (6 = 3.8 ppm)
for the methylene groups. The coupling constant
2J(PH) appears to be accidentally zero.
Single crystals of compound 1 suitable for X-
ray diffraction studies were obtained by layering
a dichloromethane solution of this complex with
diethyl ether at room temperature for 48 h. The
crystals are orthorhombic, space group Pbca, with
Z = 8 formula units in the unit cell (Table I). The
lattice is built of independent monomeric complex
cations and anions, and no unusual sub-van der
Waals contacts are observed between these com-
ponents. The structure of the cation is shown in
Fig. 2. A view of the cation complex 1 along the axis
P( 1)-Au-P(2) (ORTEP, hydrogen atoms omitted).
Fig. 1. It has no crystallographically imposed sym- ideal value for a linear geometry. Very surprisingly
metry, but approaches closely the symmetry require- the three CF^SPh arms are folded back towards
ments of point group C3.The PPI13 and P(CH2SPh)3 the metal atom, thus shielding the Pl-Au-P2 unit
units are in a staggered conformation (Fig. 2) and very effectively. The S - Au contacts are found to
be rather long, however, and are not indicative of
the angle Pl-Au-P2 of 174.37(5)° is close to the
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St. Fuchs et al. • Gold Coordination by a Tertiary Phosphine with Three Thioether Functions
219
any significant Au - S bonding [Au-Sl = 3.908(1),
Au-S2 = 4.255(1), Au-S3 = 3.862(1) A],
diethyl ether (20 ml) afforded complex 1 as a white solid
(yield 0.06 g, 65%).
C39H36AuBF4P2S3
The reaction of the free phosphine with
Calcd C 49.5 H 3.83 S 10.16%,
Found C 48.9 H 3.61 S 10.08%.
NMR:31P{1H} (CDCI3,25°C): 642.4 (br); -60°C: 6A42.2
(IP), 6b 38.9 (IP) [2J(A-B) = 331.3 Hz]; 'H (CDC13,
25°C): 6 3.8 (CH2, s, 6H), Ö.8-7.5 (Ph, m, 30H). FAB
mass spectrum: m/z = 858.8 (M+, 100%).
[Au(tht)2l+C10 4_ in
a
1:1
molar ratio in
dichloromethane at room temperature leads to the
displacement of both weakly coordinated tetrahy-
drothiophene ligands, and the dinuclear product for-
mulated in eq. (2 ) is obtained.
Ph—S— ^
Bis[tris(phenylthiomethyl)phosphine]gold(I) perchlorate
(2)
2 Ph— s ------ P + 2 [Au(tht)2]C104 ~ ; 4tht
Ph— S
-
—
'
To a solution of tris(phenylthiomethyl)phosphine (0.12
g, 0.30 mmol) in 20 ml of dichloromethane was added
bis(tetrahydrothiophene)gold(I) perchlorate (0.14 g, 0.30
mmol) and the mixture was stirred for 1h. Evaporation of
the solvent to ca. 5 ml and addition of diethyl ether gave
complex 2 as a white solid (yield 0.15 g, 72%).
C42H42Au2C12OgP2S6
(C104)2 (2)
2
Calcd C 36.2 H 3.03 S 13.1%,
Found C 36.8 H 3.44 S 13.45%.
Its 31 P{1H} NMR spectrum shows only one sin-
glet at 6 = 29.1 ppm, and the resonances due to the
methylene protons in the !H NMR spectrum appear
also as a singlet. Both spectra are not temperature-
dependent, which suggests a rapid site exchange of
the gold atom between the sulfur atoms, which is
rapid on the NMR time scale even at -60°C.
N M R^'Pj'H } (CDCI3, 25°C): 6 29.1, (s); 'H (CDCI3,
25°C): 6 3.7 (CH2, s, 12H), 7.2-7.4 (Ph, m, 30H). FD mass
spectrum: m/z = 597 [M2+, 3.5%], 1293 [(M+C104)+,
100%].
Crystal Structure Determination
A suitable crystal of compound 1 was sealed under
argon at dry ice temperature into a glass capillary and
examined directly on the diffractometer. Data were cor-
rected for Lorentz polarization and absorption effects.
Experimental Part
All experiments were carried out routinely under an
atmosphere of dry, pure nitrogen. Standard equipment The structure was solved by direct methods and refined
was used throughout. [AuPPh3][BF4] was prepared in by full-matrix least-squares calculations. The thermal
motion was treated anisotropically for all non-hydrogen
atoms. All hydrogen atoms were treated isotropically.
situ by reaction of AgBF4 and AuClPPh} in THF accord-
ing to a standard procedure, and [Au(tht)2]C104 [8] and
(PhSCH2)3P [6] according to the literature. The NMR Further information on the structure determinations may
be obtained from Fachinformationszentrum Karlsruhe,
Gesellschaft für wissenschaftlich-technische Information
spectra were recorded in CDCI3 with SiMe4 as internal
standard for1H, and H3P0 4 (85%) as external standard for
31P{1H} on a JEOL GX 400 spectrometer. Mass spectra mbH, D-76344 Eggenstein-Leopoldshafen, Germany, on
were obtained on a Varian MAT 311A spectrometer.
quoting the CSD number 406499.
Caution: Perchlorate salts are potentially dangerous.
Acknowledgements
This work was supported by Deutsche Forschungsge-
meinschaft, by Fonds der Chemischen Industrie, by the
Alexander von Humboldt Foundation (through a fellow-
ship to J. M. L.-de-L.) and by DAAD (through a fellow-
ship to M. E. O.). The authors are grateful to Mr. J. Riede
for establishing the X-ray data set, to F. R. Kreissl for the
mass spectrometric measurements, and to Degussa AG
and Heraeus GmbH for the donation of chemicals.
[Tris(phenylthiomethyljphosphine](triphenylphosph-
ine)gold(I) tetrafluoroborate (1)
To a freshly prepared solution of [AuPPh3]+[BF4]~
(0.10 mmol) in 15 mL of thf was added
tris(phenylthiomethyl)phosphine (0.04 g, 0.10 mmol) and
the mixture was stirred for 30 min. Evaporation of the sol-
vent to a residual volume of ca. 5 ml and addition of
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220
St. Fuchs et al. • Gold Coordination by a Tertiary Phosphine with Three Thioether Functions
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