(Trimethylphosphine)(triphenylsilyl)gold(I) and related compounds

Article abstract of DOI:10.1515/znb-1999-0108

Mononuclear coordination compounds of the type (R₃P)AuSiR'₃ with R = R' = Ph and R = Me, R' = Ph have been obtained from reactions of the corresponding halide complexes (R₃P)AuCl with the silyllithium reagent LiSiPh_3<

Full text of DOI:10.1515/znb-1999-0108

(Tnmethylphosphine)(triphenylsilyl)gold(I) and Related Compounds
M iguel M onge O roza, A nnette Schierb, H ubert Schm idbaur1’ "'
a Dipartamento di Quimica. Universidad de La Rioja,
Obispo Bustamente 3, E-26001 Logrono, Spain
b Anorganisch-chemisches Institut der Technischen Universität München,
Lichtenbergstrasse 4, D-85747 Garching, Germany
Z. Naturforsch. 54 b, 26-29 (1999); received October 27, 1998
Gold-Silicon Compounds, Silyl-Gold Compounds, (Phosphine)gold(I) Complexes
Mononuclear coordination compounds of the type (R3P)AuSiR'3 with R = R’ = Ph and
R = Me, R' = Ph have been obtained from reactions of the corresponding halide complexes
(RiPjAuCl with the silyllithium reagent LiSiPh.v The fully phenylated species undergoes ligand
redistribution in solution to give homoleptic ionic species. (M e.^A uSiPhi is less susceptible
to this process and crystallizes from solutions as the heteroleptic complex. The crystal structure
of this compound has been determined by X-ray diffraction. In the crystal lattice the molecules
are not associated.
Introduction
of his product was incom plete. W ork by W ilkinson
et al. in 1 970 [10] provided further evidence for the
existence of this type of com plexes by identifying
(Ph3P)A uSiM e3, but structural data could only be
obtained by Schubert et al. in 1986 for both mono-
and binuclear species [11 - 14], The latter are best
represented as ion pairs w ith aurophilic bonding,
e.g. [(M ePh2P)2A u]+[Ph3S iA u C ir.
M etal-silyl com pounds are an im portant class of
reagents for the introduction of silyl groups through
nucleophilic substitution reactions. Silyl derivatives
have been obtained for most Alkali, Earth A lkaline
and Earth M etals, as well as for alm ost all groups
of the Transition M etals [1].
Silyl-m ercury com pounds are particularly well
represented in the literature and served as key
reagents in several fundam ental syntheses [1]. By
contrast, the silyl chem istry of the coinage m etals is
poorly developed, and for gold there are only half
a dozen references, m ost of them dating from very
recent years [2], Com plexes with silicon-containing
substituents (but w ithout direct Au-Si interactions)
[3] w ere prepared already in the 1960s, but the exis-
tence of m olecular com pounds with a discrete Au-
Si bond have been confirm ed by structure analyses
only as late as 1986 (below).
In our own experim ents we could confirm the ex-
istence of this ion pair, and also obtained the 1:1
com plex (Ph3P)A uSiPh3 by treatm ent of the salt
with one equivalent of Ph3P in dichlorom ethane.
[(Ph3P)2Au]Cl was form ed as a by-product (eq. (1))
(Experim ental Part). However, like previous inves-
tigators, we w ere unable to crystallize the silylated
neutral com ponent. Both the m ass and N M R spec-
tra gave evidence that the solid and the solutions
contained [(Ph3P)2A u]+ cations, suggesting a lig-
and redistribution equilibrium involving this cation
and the hom oleptic anion [(P h^S i^A u]- (eq. (2)).
Follow ing recent work in the realm of gold-
germ anium com pounds [4 - 8] we have also resum ed
studies of the corresponding silicon species. The
present paper is a first account of this exploratory
preparative and structural work.
[(Ph3P)2A u]+[(Ph3S i)A u C ir + Ph3P -►
[(Ph3P)2A u]+ C I“ + (Ph3P)A uSiPh3
(1)
(2)
2 (Ph3P)AuSiPh3 -+
[(Ph3P)2A u]+[(Ph3Si)2A u ]-
Results and Discussion
Our studies were more successful when w ork-
ing with the sm aller tertiary phosphines, and the
trim ethylphosphine hom ologue could finally be
crystallized:
The first com pound with an Au-Si bond, (tri-
phenylphosphine)(triphenylsilyl)gold(I), was pre-
pared by Baird in 1966 [9], but the characterization
(M e3P)AuCl + LiSiPh3 —>
Reprint requests to Prof. Dr. H. Schmidbaur.
LiCl + (M e3P)A uSiPh3
(3)
0932-0776/99/0100-0026 $ 06.00 © 1999 Verlag der Zeitschrift für Naturforschung, Tübingen • www.znaturforsch.com
K
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M. M. Qroz et al. ■(Trimethylphosphine)(triphenylsilyl)gold(I) and Related Compounds
Fig. 2. Projection of the molecular structure of Me^P-Au-
SiPh3 along the P-Au-Si axis showing the quasi random
orientation of the three phenyl groups.
Fig. 1. Molecular structure of Me^P-Au-SiPhvCORTEP
drawing with 50% probability ellipsoids, H-atoms omit-
ted for clarity). Selected bond lengths [A] and ansles [°]:
Au-P 2.3520 (14), Au-Si 2.3617(14); P-Au-Si 178.68(5).
The configuration of the gold atom in the title
com pound is close to linear [P-Au-Si 178.68(5)°].
The A u-P and A u-Si distances are not very different
[2.3520(14) vs. 2.3617(14) A] and sim ilar to refer-
ence data in the literature [11]. Likewise, all C-P-C
and C-Si-C angles are sm aller than the tetrahedral
standard, a com m on feature of gold(I) com plexes of
tertiary phosphines.
It appears that the ligand characteristics of
[R3P]0 and [R3Si]- groups at an Au(I) center
are structurally very similar. There are therefore
many structural parallels betw een com pounds of the
type [(R 3P)A uSiR 3] and the isoelectronic cations
[(R^P)2A u]+ [ 12] and probably the as yet unknown
The product was obtained in low yield (37 %)
as a colourless crystalline solid, sensitive to air and
m oisture, soluble in di- and trichlorom ethane, ben-
zene and tetrahydrofuran, but sparingly soluble in
diethyl ether or pentane. The m ass spectrum (FAB)
shows the parent ion at m/z = 532. The NM R spectra
o f solutions in benzene-dö have 1H resonances at b
7 .0 -8 .1 (m, 15H, Ph) and 0.38 (d, J(P,H) = 8.8 Hz,
9H, M e), and a 31P resonance at 6 29.6 (s, { 1H}).
C rystals o f (M e3P)A uSiPh3 (from dichloro-
m ethane/pentane) are m onoclinic, space group
P2]/c, w ith 4 m olecules in the unit cell. The lat-
tice is com posed of molecules w ith no crystallo-
graphically im posed symmetry (Fig. 1). M ost sur-
prisingly, there are no short m term olecular contacts
(A u-A u) betw een the monomers, //zterm olecular
gold-gold bonding has been observed in many cases
w ith ligands of sim ilar bulk, and therefore it is not
very likely that steric effects are preventing the
expected [15] close metal-metal contact in the ti-
tle com pound. This suggests that the high electron
density at the gold atoms caused by the low elec-
tronegativity of the silicon atom may reduce the
donor/acceptor properties in the present case.
[(R3Si)2A u]~ anions.
The conform ation of the two ligands in
(M e3P)A uSiPh3 is staggered indicating that there
is com m unication betw een the R substituents at
P
and Si. The m utual orientation of the three
phenyl groups does not follow the com m on pro-
peller m odel, but is quasi random as shown in the
projection along the P-A u-Si axis (Fig. 2).
Experimental Part
All experiments were routinely carried out under pure
dry nitrogen. Standard equipment was used throughout.
(Triphenylphosphine)(triphenylsilyl)gold(I)
(Ph2M eP)A uSiPh3 is also
a m onom er [ 11],
and it is only the partially halogenated anion
[C lA uSiPh^]- which features aurophilic bonding
when associated with the [(Ph3P)2A u]+ cation [ 12].
//zrram olecular A u-A u contacts are observed in
(dppm )(A uSiPh3)2 [13].
[(Ph3P)2Au]+[(Ph3Si)A uC ir (247 mg, 0.20 mmol)
[13] was dissolved in dichloromethane (20 ml) and treated
with triphenylphosphine (90 mg, 0.20 mmol) at 20°C with
protection against light. After 1 h of stirring the reaction
mixture was filtered and the filtrate evaporated to dryness
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M. M. Oroz et al. ■(Trimethylphosphine)(triphenylsilyl)gold(I) and Related Compounds
in a vacuum. The brown residue was recrystallized from
pentane/diethyl ether. The light brown powder (106 mg,
72% yield) decomposes upon heating, is sensitive to air
and moisture, soluble in dichloromethane and tetrahydro-
furan, slightly soluble in diethyl ether and chloroform,
and insoluble in pentane.
3,P{'H} NMR (CDCI3, 20°C): 6 41.5 ppm (s, broad);
-60°C: 6 42.5 and 56.7 (for [(Ph3P)2Au]+). MS (FAB):
m/z = 721 [(Ph3P)2Au]+; 719 [M+H]+; 641 [M-Ph]+; 459
[(Ph3P)Au]+; 379 [Ph2SiAu]+.
collection. During data collection three standard reflec-
tions were measured periodically as a general check of
crystal and instrument stability. No significant changes
were observed. Graphite-monochromated MoKQ radia-
tion was used. The structure was solved by direct meth-
ods and refined by full matrix least-squares calculations
y?2
on F .
Crystal data for C2\Fh_AAuPSi
Mx = 532.43, light brown crystals (0.6 x 0.33 x 0.2
mm), monoclinic, a = 10.745(1), b = 10.072(1), c =
18.517(2) Ä, 0 = 92.75(1)°, space group P2,/c, Z = 4,
V= 2001.7(3) A3, peak = 1-767 g cm-3, F(000) = 1032;
T = -78 °C. Data were corrected for Lorentz, polariza-
tion, and absorption effects [/i(MoKQ) = 74.89 cm-1 ].
5842 measured [(sin 9/A)max = 0.64Ä- 1], 4356 unique re-
flections (/?jnt = 0.0740); 217 refined parameters, w/?2 =
0.0841, R = 0.0356 for 3940 reflections with F0 > 4a(F0)
used for refinement. Residual electron densities: +2.327/
-2.324. The function minimized was: w/?2 = {[Zw(F02 -
Fc2)2]/I[w(F02)2]},/2 ; w = \/[a2(FQ2) + (ap)2 + bp]\ p =
(F02 + 2Fc2)/3; a = 0.3182, b = 32.46. All non-hydrogen
atoms were refined with anisotropic displacement param-
eters. All hydrogen atoms were calculated and allowed to
ride on their corresponding C atoms with fixed isotropic
contributions [C/iS0(fix) = 1.5 x Ueq of the attached C].
Important interatomic distances and angles are shown in
the figure caption. Anisotropic thermal parameters and
tables of interatomic distances and angles have been
deposited with the Fachinformationszentrum Karlsruhe,
Gesellschaft für wissenschaftlich-technische Information
mbH, D-76344 Eggenstein-Leopoldshafen. The data are
available on request on quoting CSD No. 410351.
C36H30AuPSi (718.66)
Calcd C 60.17 H4.21 %,
Found C 59.66 H 4.53 %.
(Trimethylphosphine)(triphenylsilyl)gold(I)
A solution of (Me3P)AuCl (186 mg, 0.60 mmol) in
tetrahydrofuran (20 ml) was treated with a solution of
Ph3SiLi (0.60 mmol) in 6 ml of tetrahydrofuran at 0°C
with stirring and protection against light. After 30 min the
reaction was stopped by addition of a small piece of dry
ice (C 02, to trap the excess of silyllithium reagent), and
the solvent was removed in a vacuum. Addition of diethyl
ether (30 ml) and filtration gave a clear brown solution.
Reduction of the volume of the solution to 2 ml and
addition of pentane led to the precipitation of the product
(120 mg, 37% yield). The light brown solid decomposes
upon heating, is sensitive to air and moisture, dissolves in
benzene, tetrahydrofuran and dichloromethane, is slightly
soluble in diethyl ether and insoluble in pentane.
'H NMR (C6D6, 25°C): 6 7.0-8.1 (m, 15H, Ph); 0.38
[d, 7(P,H) = 8.8 Hz, 9H, Me], 31P {'H}: 6 29.6, s. MS
(FAB): m/z = 532 [M]+.
C2]H24AuPSi (532.43)
Calcd C 47.4 H 4.54 %,
Found C 47.1 H 4.64 %.
Acknowledgements
Crystal structure determination
This work was supported by Deutsche Forschungs-
gemeinschaft and Fonds der Chemischen Industrie. The
authors thank Mr. J. Riede for establishing the X-ray data
set.
The sample was mounted in a glass capillary on an
Enraf Nonius CAD4 diffractometer and used for mea-
surements of precise cell constants and intensity data
[3] A. Shiotani, H. Schmidbaur, J. Am. Chem. Soc. 92,
7003 (1970); H. Schmidbaur, M. Bergfeld, Inorg.
Chem. 5, 2069(1966).
[4] A. Bauer, A. Schier, H. Schmidbaur, J. Chem. Soc.,
Dalton Trans. 1995, 2919.
[1] D. A. Armitage in Comprehensive Organometallic
Chemistry, (G. Wilkinson, F. G. A. Stone, E. W.
Able, editors), Vol. 2, pp. 99 and 102, Pergamon,
Oxford (1982).
[2] Gold: Progress in the Chemistry, Biochemistry and
Technology; H. Schmidbaur (ed.), J. Wiley & Sons,
Chichester (1999).
[5] A. Bauer, H. Schmidbaur, J. Am. Chem. Soc. 118,
5324(1996).
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29
M. M. Oroz et al. • (Trimethylphosphine)(triphenyIsilyl)gold(I) and Related Compounds
[6] R Pyykkö, W. Schneider, A. Bauer, A. Bayler, H.
Schmidbaur, J. Chem. Soc., Chem. Commun. 1997,
1111.
[11] U. Schubert, J. Meyer, J. Organomet. Chem. 303,
C5 (1986).
[12] J. Meyer, J. Willnecker, U. Schubert, Chem. Ber.
[7] A. Bauer, W. Schneider, H. Schmidbaur, Inorg.
Chem. 36, 2225 (1997).
[8] A. Bauer, H. Schmidbaur, J. Chem. Soc., Dalton
Trans. 1997, 1115.
122, 223 (1989).
[13] J. Meyer, H. Piana, H. Wagner, U. Schubert, Chem.
Ber. 123, 791 (1990).
[14] H. Piana, H. Wagner, U. Schubert, Chem. Ber. 124,
[9] M. C. Baird, J. Inorg. Nucl. Chem. 29, 367 (1966).
[10] G. Yagupsky, W. Howat, K. Shortland, G. Wilkin-
son, Chem. Commun. 1970, 1369.
63 (1991).
[15] H. Schmidbaur, Gold. Bull. 23, 11 (1990); Chem.
Soc. Rev. 24, 391 (1995); Interdisc. Sei. Rev. 17,
213 (1992).
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