(Triphenylarsine)gold(I) complexes: Synthesis of an oxonium salt and redistribution of the arsine ligands

Article abstract of DOI:10.1515/znb-1998-0208

The reaction of [(Ph₃As)AuCl] with Ag₂O in the presence of NaBF₄ in tetrahydrofuran affords three products, identified as [(Ph₃As)₄Au]BF₄ (40.3%), [(Ph₃As)₂Au]BF₄

Full text of DOI:10.1515/znb-1998-0208

(Triphenylarsine)gold(I) Complexes: Synthesis of an Oxonium Salt
and Redistribution of the Arsine Ligands
Upendra M. Tripathi, Annette Schier, Hubert Schmidbaur*
Anorganisch-chemisches Institut der Technischen Universität München,
Lichtenbergstr. 4, D-85747 Garching, Germany
Z. Naturforsch. 53 b, 171-174 (1998); received December 23, 1997
Gold(I) Complexes, Arsine Complexes, Oxonium Salts, Gold Clusters
The reaction of [(Ph3As)AuCl] with Ag20 in the presence of NaBF4 in tetrahydrofuran
affords three products, identified as [(Ph3As)4.Au]BF4 (40.3%), [(Ph3As)2Au]BF4 (16.4%) and
{[(Ph3As)Au]3 0 }BF4 (17.3%). The properties of the main product agree well with recent
literature data. The other two compounds are new and have been identified by their analytical,
spectroscopic, and crystallographic data. The structures are isomorphous with those of the
analogous Ph^P complexes. Variations in the stabilities are discussed in terms of kinetic and
thermodynamic effects.
oroborate in tetrahydrofuran, mixtures of products
Introduction
were obtained in all experiments. This result indi-
cated that bonding of the arsine ligand to the gold
center was much more labile, and that redistribution
of ligands is a major complication not observed with
the phosphine analogues.
Extraction of the reaction mixtures with
dichloromethane followed by layering of the solu-
tions with diethyl ether gave a crop of crystals com-
posed of three different components, which could
be separated under a microscope. Red needles, pale
yellow plates and colourless prisms were isolated
in 17.3, 16.4 and 40.3% yield, respectively (calcu-
lated relative to the arsenic content). There is also a
large amount of dark insoluble material containing
the excess of the silver oxide and sodium tetrafluo-
roborate, and finely devided gold metal.
Tertiary phosphines are the most common lig-
ands in modem coordination chemistry of univalent
gold [1], Labile gold-element bonds are readily sta-
bilized by phosphines as auxiliary donors at two-,
three- or four-coordinate gold(I) centers. Clustering
of gold(I) at Main Group and Transition Elements
as heteroatoms is also most common for systems
with terminal phosphine ligands [2 ], while several
attempts to obtain similar compounds with other
auxiliary ligands than phosphines have often met
with failure.
In the present work we therefore undertook a
study of some simple arsenic analogues in order
to delineate further the stability borderlines deter-
mined by the ligands L for compounds of the type
[(LAu)„E]+, with L = Ph3As, E = N (n = 4) and
E = O (n = 3). The corresponding phosphorus com-
pounds (L = PPh3) are classics of gold heterocluster
chemistry [2, 3].
The main product (1) was identified as
[tetrakis(triphenylphosphine)gold(I)] tetrafluoro-
borate, m.p. 268-269 °C, through its analytical,
spectroscopic and crystallographic data (Experi-
mental Part). The compound has just recently been
fully characterized [8].
Results and Discussion
(Ph3As)AuCl + Ag20 + NaBF4
When the method established for the synthe-
sis of {tris[(triorganophosphine)gold(I)]oxonium}
salts [2-7] was applied to the preparation of the
triphenylarsine analogue starting from silver oxide,
chloro(triphenylarsine)gold(I) and sodium tetraflu-
-> [(Ph3As)4Au]+BF4-
1
[(Ph3As)2Au]+BF4~
2
{[(Ph3As)Au]30 } +BF4-
* Reprint requests to Prof. Dr. H. Schmidbaur.
3
0939-5075/98/0200-0171 $ 06.00 (c) 1998 Verlag der Zeitschrift für Naturforschung. All rights reserved.
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172
U. M. Tripathi et al. • (Triphenylarsine)gold(I) Complexes
Table I. Crystal data, data collec-
tion, and structure refinement for
compounds 2 and 3.
2
3
Crystal data
Formula
Mr
Crystal system
Space group
a (A)
C^H^oAstAuBF4
896.22
C54H45ASSAu^BF-^O
1612.37
monoclinic
P2\/c
12.731(2)
24.853(4)
16.018(2)
98.90(1)
5007.1(13)
2.139
[a]
monoclinic
C2/c [No. 15]
21.743(2)
12.493(1)
24.391(3)
92.74(1)
6617.9(11)
1.799
R = X(|IF0I - IFCI| / IlFol;
wR2= {[Xw(F02 - Fc2)2] /
[b]
X[w(F02)2]}1/2;w = l/[a2(F02) +
(ap)2 + bp]; p = (F02 + 2Fc2)/3;
a = 0.0188 (2), 0.0652 (3);
b = 36.30 (2), 51.10(3).
b (A)
c (A)
0 o ,
V(A3)
Pcalc (gem -)
Z
8
4
F(000)
3456
3016
/i(Mo K a ) (cm-1)
64.78
107.89
Data collection
-52
-74
T (°C)
Scan mode
10
U)
hkl range
-2 7 —27,0— 15,0—31 -1 5 — 15, 0—>29, 0—>19
0.64
7325
0.64
8056
sin(#/A)max (A-1)
Measured reflections
Refis. used for refinement
Absorption correction
Fmin/Fmax
7160 [/fin, = 0.0201]
psi-scans
0.654/0.999
7778 [/?in, = 0.0278]
psi-scans
0.920/1.000
Refinement
Refined parameters
H atoms (found/calcd)
Final R values [I > 2<r(I)]
R l [a]
433
0/30
192
0/45
0.0423
0.0484
wR2[b]
0.0732
0.1096
< 0.001
< 0.001
(shift/error)max
/9fin(max/min) (eA-3)
1.044/-1.083
1.730/-0.928
The analytical data of the pale yellow crystals (2), iment (Caption to Fig. 1). The anion is crystallo-
m. p. 211-212 °C, suggested the presence of the graphically disordered, but the positioning of the
corresponding 1:2 complex of Au+BF4~ and tri- fluorine atoms could be resolved in a split model
phenylarsine, which had not been reported in the calculation. The situation is similar for the phos-
literature. The structure of the compound was de- phorus analogue [9]. The main difference between
termined by a single crystal X-ray diffraction study. the two structures (with Ph^P and Ph^As ligands) is
The crystals are monoclinic, space group C2/c, the variation in the Au-E and C-E distances (E = P,
with 8 formula units in the unit cell. The com- As). The data reflect the difference in the covalent
pound is thus isomorphous with the corresponding radii of phosphorus and arsenic in good agreement
triphznylphosphine complex [9]. The lattice con- with previously tabulated values.
tains bis(triphenylarsine)gold(I) cations loosely as-
sociated with the tetrafluoroborate anions (Fig. 1,
Table I).
The ion pair has no crystallographically imposed
symmetry owing to an irregular orientation of the
six phenyl groups. Under the influence of the ap-
proaching anion the Asl-Au-As2 axis is signifi-
cantly bent [166.07(2)°], but the Au-As bonds are
The red needles (3), m. p. 228 - 229°C, were iden-
tified as the tris[(triphenylarsine)gold(I)]oxonium
tetrafluoroborate by the analytical, spectroscopic
and structural data. The compound crystallizes in
the monoclinic space group P2j/c with 4 formula
units in the unit cell. It is isomorphous with the cor-
responding phosphorus compound (Fig. 2) [2,3].
The lattice is composed of dimeric cations and
equivalent within the accuracy limits of the exper- tetrafluoroborate anions. The two components of
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173
U. M. Tripathi et al. • (Triphenylarsine)gold(I) Complexes
0
Fig. 2. Molecular structure of compound 3 (ORTEP draw-
ing with 50% probability ellipsoids, H-atoms omitted for
clarity). Selected bond lengths [A] and angles [°]: Aul-O
2.050(8), A u2-0 2.035(8), Au3-0 2.026(8), A u l-A u 2
3.0208(7), Aul•••Au3 3.0295(8), Au2---Au3 3.1553(8),
Aul-- Au3' 3.0506(8), Aul-Asl 2.2204(14), Au2-As2
2.3176(14), Au3-As3 2.3227(14); A ul-0-A u2 95.4(3),
A ul-0-A u3 96.0(3), Au2-0-Au3 102.0(3), A sl-A ul-0
176.2(2), As2-Au2-0 178.3(2) As3-Au3-0 176.6(2).
Fig. 1. Molecular structure of compound 2 (ORTEP draw-
ing with 50% probability ellipsoids. Only one position
of the disordered BF4- is shown, H-atoms are omitted
for clarity). Selected bond lengths [A] and angles [°]:
Au-Asl 2.3988(6), Au-As2 2.3957(6), A u -F l 3.382(1);
Asl-Au-As2 166.07(2).
kinetic lability of the (arsine)gold compounds which
release their ligands readily in substitution reac-
tions with other nucleophiles in the reaction mix-
ture. The results also suggest, however, that the salt
[(Ph3As)4Au]BF4 is an energy sink and draws ar-
sine ligands away from all other components of the
system. (After long reaction times at ambient tem-
perature only this product can be isolated and no
oxonium salt is left in the reaction mixture.) This
is surprising since there is no such tendency for
the related triphenylphosphine systems. It therefore
appears that geometrical factors (the ratio of the
element radii Au/As versus Au/P) play a signifi-
cant role in determining the thermodynamics of the
reactions, which together with the kinetic effects
make the preparation of (arsine)gold(I) clusters a
much more delicate task. Thus all attempts to pre-
pare the tetrakis[(triphenylarsine)gold(I)] ammo-
nium tetrafluoroborate failed [10], while the anal-
ogous triphenylphosphine complex is well estab-
lished [2, 11 -13].
the cation dimers are related by a crystallographi-
cally imposed center of inversion in the center of the
square of gold atoms Aul Au3-Aul'-Au3'. The core
of the dication is an aggregate of two OAU3 pyra-
mids facing edges (Aul-Au3 versus Aul'-Au3').
The gold atoms thus form a six-membered ring in
a chair conformation with Au--Au contacts in the
narrow range from 3.0208(7) to 3.1553(8) A. These
short contacts are responsible for the dimerization
and contribute considerably to the overall stability
of the hexanuclear dication [2 ].
The angles at the gold atoms are all close to 180°
showing that the gold-gold contacts do not perturb
significantly the geometry of the O-Au-As bonding.
However, the angles at the oxygen atoms are all
smaller than the tetrahedral standard and reflect very
nicely the influence of Au--Au bonding at the basis
of the OAU3 pyramids.
These observations are all very similar to those
reported for the corresponding triphenylphosphine
complex [3], Again, major differences are only
found for the Au-P/Au-As and P-C/As-C distances
which are mainly determined by the covalent radii
of phosphorus and arsenic. The results therefore
suggest that structure and bonding in the trigoldox-
onium compounds with phosphine/arsine ligands is
not very different and dominated by the core ele-
ments [2].
Experimental Part
General: All experiments were carried out in an at-
mosphere of dry nitrogen. Solvents were distilled and
saturated with nitrogen. (Ph3As)AuCl was prepared fol-
lowing the literature procedure [14], NMR spectra: Jeol
GX 400. Mass spectra: Finnigan MAT 90 (FAB, 4-nitro-
benzyl alcohol matrix). Microanalysis was by in-house
equipment for combustion and atomic absorption spec-
The difficulties encountered in the synthesis of
the arsenic compound can be ascribed to a greater troscopy techniques.
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174
Preparation of the Compounds: Silver oxide was pre-
U. M. Tripathi et al. • (Triphenylarsine)gold(I) Complexes
Structure determinations
pared from KOH (5.63 g, 100 mmol) and AgN0 3 (8.54
g, 50 mmol) in water, washed till alkali-free, and dried in
a vacuum. This material was suspended in tetrahydrofu-
ran (500 ml) and treated with (Ph3As)AuCl (3.01 g, 5.59
mmol) and NaBF4 (3.68 g, 33.53 mmol) with stirring at
room temperature. After 3 h all volatiles were removed
in a vacuum at room temperature to leave a dark brown
residue, which was washed three times with benzene (20
ml) to remove unreacted (Ph3As)AuCl and then extracted
three times with dichloromethane (20 ml). The volume of
the extract was reduced to 10 ml in a vacuum and layered
with diethyl ether (30 ml). After 2 d a crop of crystals
was obtained, the components of which were carefully
separated under a microscope.
a) Colourless prisms (1), 0.85 g (40.3 % based on
As), m.p. 268-269 °C; analytical, spectroscopic, and
X-ray data are in agreement with those reported for
[(Ph3As)4Au]BF4 [8 ],
b) Pale yellow plates (2), 0.41 g (16.4 %), m. p. 211 -
212 °C.
Suitable crystals of 2 and 3 were mounted in glass cap-
illaries and used for measurements of precise cell con-
stants and intensity data collection. During data collec-
tion, three standard reflections were measured periodi-
cally as a general check of crystal and instrument stabil-
ity. No significant changes were observed for both com-
pounds. Diffraction intensities were corrected for Lp and
for absorption effects (psi-scans). The thermal motion
of all non-hydrogen atoms of compound 2 was treated
anisotropically, whereas the phenyl rings and the BF4~
anion of compound 3 were refined with isotropic con-
tributions. All hydrogen atoms were placed in idealized
calculated positions and allowed to ride on their corre-
sponding carbon atom with UjS0(fix) = 1.5 Ueq (C). The
anion of 2 was disordered and refined in split positions
with site occupation factors of 50/50. Further information
on crystal data, data collection, structure solution and re-
finement is summarized in Table I. Important interatomic
distances and angles are summarized in the correspond-
ing figure captions. Anisotropic thermal parameters, ta-
bles of distances and angles, and atomic coordinates have
been deposited with Fachinformationszentrum Karlsruhe,
Gesellschaft für wissenschaftlich-technische Information
mbH, D-76344 Eggenstein-Leopoldshafen. The data are
available on request on quoting CSD No. 408769 (2) and
408870 (3).
Elemental analysis for C36H30AS2AUBF4 (896.22).
Calcd C 48.25 H 3.34 Au 21.98%,
Found C 48.10 H 3.33 Au 22.16%.
'H NMR (CDC13): 6 7.60 - 7.53, m, Ph. I3C{'H} NMR
(CDCI3): 6 133.27, 132.16, 130.34, 129.92 (s, Ph for o,
p, m, and ipso, respectively). MS (FAB): m/z = 809.3
(100%, [M+]).
c) Red needles (3), 0.52 g (17.3 %), m.p. 228-229°C
(decomposition).
Elemental anlysis for C54H 45AS3AU 3BF4O (1612.37)
Acknowledgement
Calcd C 40.23 H 3.33 Au 36.66 F4.71%,
This work was supported by Deutsche Forschungs-
gemeinschaft, by Fonds der Chemischen Industrie, by
Alexander von Humboldt Stiftung, and - through the do-
nation of chemicals - by Degussa AG and Heraeus GmbH.
The authors are grateful to Mr. J. Riede for establishing
the X-ray data sets.
Found C 40.10 H 3.10 Au 36.90 F4.62%.
‘H NMR (CDCI3): 6 7.56 (t, 9H, J = 6.95 Hz, Ph-p),
7.32 (t, 18H, J = 7.32 Hz, Ph-m), 7.47 (d, 18H, J = 7.32
Hz, Ph-o). 13C{'H} NMR (CDCI3): 6 133.24, 131.74,
130.97, 130.06 (s, Ph for o, p, ipso, and m, respectively).
MS (FAB): m/z = 1525.5 (15% [{[(Ph3As)Au]30}]+).
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