Preparative routes to the first tri- and tetra(alkynyl)gold(III) compounds: (L)Au(C=CR)3 and [ER4]_ [Au(C≡CR) 4]-

Article abstract of DOI:10.1021/om050038q

The preparation of tri(alkynyl)gold(III) complexes (RC≡C) ₃Au(L) as metastable compounds was discussed. It was found that the complex can be prepared if a small and strong trialkylphosphine donor was introduced as an auxiliary ligand L. The complex with L = PMe₃ was crystallize in a solvent-free form and as a 1:1 solvate with CH ₂Cl₂. The results show that the stability of polyalkynyl complexes of gold(III) centers appears to be generally lower than that of the isoelectronic platinum(II) centers.

Full text of DOI:10.1021/om050038q

Organometallics 2005, 24, 2289-2296
2289
Preparative Routes to the First Tri- and
Tetra(alkynyl)gold(III) Compounds: (L)Au(CtCR)3 and
[ER4]+ [Au(CtCR)4]-
Oliver Schuster and Hubert Schmidbaur*
Department Chemie, Technische Universita¨t Mu¨nchen, 85747 Garching, Germany
Received January 18, 2005
(Me3P)Au(CtCPh)3 (1) was prepared as the first trialkynylgold(III) complex via three
different routes: Treatment of solvated AuCl3 with 3 equiv of PhCtCLi in the presence of
PMe3, or of (Me3P)AuBr2Cl with the same reagent, gives high to medium yields of the product
(1), which is also available from equimolar quantities of (Me3P)AuCtCPh and (PhCtC)2-
TlCl. The same reactions fail with less powerful donors (PPh3) or more bulky ligands
(PiPr3). The products of reductive elimination, PhCtCCtCPh and (R3P)AuCtCPh, are
obtained instead. The molecular structure of compound 1 has been determined from single
crystals of a monoclinic, solvent-free phase and a triclinic 1:1 solvate (1)‚CH2Cl2. In the
square-planar environment of the gold(III) center one of the three phenylethynyl groups
exhibits the trans influence of the PMe3 ligand. The reactions of 1 with PPh3, HCl, and I2
were studied, but no stable functional poly(alkynyl)gold(III) compounds could be isolated.
Serendipitously, single crystals of a byproduct, [(PhCtC)Me2PCH2Au(CtCPh)3], were found
to grow from one of the reaction mixtures. The molecular structure has been determined,
but no efficient synthetic pathway could be found. Salts with the tetra(phenylethynyl)aurate-
(III) anion [Au(CtCPh)4]- were obtained from compound 1 upon treatment with PhCtCLi.
The complex ion undergoes facile reductive elimination of PhCtCCtCPh to produce the
n
[Au(CtCPh)2]- anion. After metathesis with Bu4N+Br-, mixed-anion salts with nonstoi-
chiometric composition were precipitated as colorless, diamagnetic solids. From this product
mixture, single crystals with the anion ratio 1:1 could be grown for structure determina-
tion: [nBu4N]2[Au(CtCPh)4][Au(CtCPh)2]‚(CH2Cl2). The structure of the reference compound
[nBu4N][Au(CtCPh)2] has also been determined. The anions have square-planar and linear
structures, respectively, with very small variations in the bond distances and angles.
Introduction
ligands L and anionic substituents X (Scheme 1). The
relation between gold(III) and gold(I) species is best
illustrated by the redox equilibrium represented by eq
2, which combines a reductive elimination of X2 from a
gold(III) complex (L)AuX3 and an oxidative addition of
X2 to the corresponding gold(I) complex (L)AuX.
Cyanide complexes of gold(I) are key compounds in
gold chemistry and technology.1 Most of the gold recov-
ered from ores, or recycled after usage, is processed by
reactions with aqueous solutions of alkali cyanides, and
most electrochemical gilding techniques rely on cyanide
baths.
By contrast, cyanide complexes of gold(III) are, due
to their low redox stability, a virtually unexplored class
of compounds. This fact can be traced back to the
observation reported in the earliest literature, that the
complex ion, tetracyanoaurate(III), [Au(CN)4]-, is easily
reduced to dicyanoaurate(I), [Au(CN)2]-, and dicyano-
gen, (CN)2, upon warming (eq 1).2
For X representing the halogens X ) Cl, Br, the
equilibrium is known to be shifted to the left-hand side
under standard conditions and with water and most
other solvents as the medium.2 However, for X ) I the
gold(III) complexes are only stable with strong and
small donor ligands L, e.g., PMe3 or PEt3. The donor
capacity of PPh3 is insufficient, and the steric effect
of P(iPr)3 is prohibitive, for the formation of the cor-
responding (R3P)AuI3 complexes. Gold(I) polyiodides
(R3P)AuI‚xI2 are formed instead.3
The stability of square-planar gold(III) complexes
(n-1)
[(L)nAuX4-n
]
(n ) 0, 1, 2) generally depends very
strongly on the specific properties of the neutral donor
(1) Schmidbaur, H.; Grohmann, A.; Olmos, M. E. In Gold: Progress
in Chemistry, Biochemistry and Technology; Schmidbaur, H., Ed.;
Wiley: Chichester, 1999; p 647.
Gold(III) pseudohalide complexes (L)AuY3 with Y
representing not only cyanide but also Y ) cyanate,
(2) Raubenheimer, H. G.; Cronje, S. In Gold: Progress in Chemistry,
Biochemistry and Technology; Schmidbaur, H., Ed.; Wiley: Chichester,
1999; p 557.
(3) Schneider, D.; Schier, A.; Schmidbaur, H. J. Chem. Soc., Dalton
Trans. 2004, 1995.
10.1021/om050038q CCC: $30.25 © 2005 American Chemical Society
Publication on Web 03/31/2005

2290 Organometallics, Vol. 24, No. 10, 2005
Schuster and Schmidbaur
Scheme 1
subsequent addition of a toluene solution of 1 equiv of
PMe3 at this temperature, afforded a 51% isolated yield
of (PhCtC)3Au(PMe3) (1) as a colorless crystalline solid
[eq 3].
isocyanate, thiocyanate, etc., appear to resemble the
iodide complexes, and very little information is available
on their range of stability.2
By contrast, the same reaction with the PPh3 lig-
and gave only products of reductive elimination, i.e.,
PhCtCAu(PPh3) and PhCtCCtCPh or PhCtCX (X )
Br, Cl), regardless if AuCl3 or AuBr3 was employed as
THF solvate or as the PPh3 complex, respectively [eq 4,
5]. Treatment of the mixed-halide complex (Me3P)-
AuClBr2, obtained from (Me3P)AuCl and an equimolar
quantity of Br2 in dichloromethane at 0 °C, with 3 equiv
of PhCtCLi also led to product 1, but with only 30%
yield [eq 6]. Recrystallization from dichloromethane/
pentane gave, next to familiar crystals of 1, very few
differently shaped crystals suitable for X-ray diffraction
studies. The byproduct was identified as [dimethyl-
(phenylethynyl)phosphoniummethylide]tri(phenyl-
ethynyl)gold(III), (PhCtC)Me2PCH2Au(CtCPh)3, 2. Sev-
eral routes for a rational sythesis of this complex have
been probed, but all attempts were unsuccessful.
This is also true for complexes with alkynyl (acetylide)
substituents, which can be classified as isoelectronic
with cyanides. Solely three references can be quoted in
which organogold complexes with an alkynyl group
attached to a gold(III) center have been identified.4-7
In all cases only one -CtC-R group is associated
with two alkyl groups and a tertiary phosphine ligand:
cis-R2(R′CtC)Au(PR′′3). The compounds were found
to undergo facile reductive elimination of R2 and/or
R-CtC-R′ on heating, depending on the nature of the
substituents.
In the present account we report the first synthesis
of tri- and tetra(alkynyl)gold(III) complexes. This work
is an extension of our earlier studies of alkynylgold(I)
chemistry.8 Alkynylgold compounds are important build-
ing blocks for the construction of extended one- or two-
dimensional frameworks.9-17 The rigid-rod nature of the
acetylide group combined with the linear or rectangular
motif at the gold centers is ideal for the design of square-
grid materials.
Preparation, Reactions, and Stability of Tris-
(alkynyl)gold(III) Complexes: (PhCtC)3Au(PR3).
Several routes were probed for the preparation of tri-
(alkynyl)gold(III) complexes, three of which were finally
found to give access to significant yields of the expected
products.
The seemingly most obvious pathway that uses
anhydrous gold trichloride and 3 equiv of an alkynyl-
lithium reagent requires carefully controlled conditions
and a powerful tertiary phosphine as an auxiliary ligand
in order to be successful. Thus, the reaction of a solution
of AuCl3 in tetrahydrofuran (THF) with a solution of 3
equiv of LiCtCPh in the same solvent at -78 °C, upon
In a third variant, bis(phenylethynyl)thallium(III)
chloride was used as an oxidant for phenylethynylgold-
(I) complexes. This reaction was again successful with
the PMe3 complex (giving a 36% yield of 1). With PPh3
or PiPr3 the desired products could be obtained but
showed very low thermal stability and decomposed
within minutes. Only the products of reductive elimina-
tion could be isolated. By immediate analysis of the
1
reaction mixtures, however, H and 31P NMR data of
(4) Johnson, A.; Puddephatt, R. J.; Quirk, J. L. J. Chem. Soc., Chem.
Commun. 1972, 938.
the intermediates were obtained [eqs 7, 8].
(5) Johnson, A.; Puddephatt, R. J. J. Chem. Soc., Dalton Trans.
1977, 1384.
(6) Komiya, S.; Ozaki, S.; Shibue, A. J. Chem. Soc., Chem. Commun.
1986, 1555.
(7) Schuster, O.; Liau, R.-Y.; Schier, A.; Schmidbaur, H. Inorg. Chim.
Acta 2005, in press.
(8) Liau, R.-Y.; Schier, A.; Schmidbaur, H. Organometallics 2003,
22, 3199, and references therein.
(9) Irwin, M. J.; Vittal, J. J.; Puddephatt, R. J. Organometallics
1997, 16, 3541.
(10) Mohr, F.; Eisler, D. J.; McArdle, C. P.; Atieh, K.; Jennings, M.
C.; Puddephatt, R. J. J. Organomet. Chem. 2003, 670, 27.
(11) Mohr, F.; Puddephatt, R. J. J. Organomet. Chem. 2004, 689,
374.
(12) Vicente, J.; Chicote, M.-T.; Alvarez-Falcon, M. M.; Bautista, D.
Organometallics 2004, 23, 5707.
(13) Vicente, J.; Chicote, M.-T.; Alvarez-Falcon, M. M.; Fox, M. A.;
Bautista, D. Organometallics 2003, 22, 4792.
(14) Vicente, J.; Chicote, M. T.; Abrisqueta, M. D.; Ramirez de
Arellano, M. C.; Jones, P. G.; Humphrey, M. G.; Cifuentes, M. P.;
Samoc, M.; Luther-Davies, B. Organometallics 2000, 19, 2968.
(15) Bardaji, M.; Jones, P. G.; Laguna, A. J. Chem. Soc., Dalton
Trans. 2002, 3624.
The thallium(III) reagent employed in the preparation
of the gold(III) complex has been synthesized for the
first time from anhydrous TlCl3 and PhCtCLi, in the
molar ratio 1:2, in tetrahydrofuran at -78 °C. The
product was isolated in 69% yield as a colorless, micro-
crystalline solid and characterized by analytical and
spectroscopic data. The NMR spectra recorded in THF-
d8 showed no multiplicity due to separate coupling to
(16) Bardaji, M.; Laguna, A.; Jones, P. G. Organometallics 2001,
20, 3906.
(17) Mueller, T. E.; Choi, S. W.-K.; Mingos, D. M. P.; Murphy, D.;
Williams, D. J.; Yam, V. W.-W. J. Organomet. Chem. 1994, 484, 209.

Tri- and Tetra(alkynyl)gold(III) Compounds
Organometallics, Vol. 24, No. 10, 2005 2291
205Tl and 203Tl (I ) 1/2; natural abundance 70.5 and
29.5%, respectively). Only broad signals were recorded.
(Trimethylphosphine)tri(phenylethynyl)gold(III), 1,
forms colorless crystals that melt at 114-115°C with
decomposition to give equimolar quantities of (Me3P)-
AuCtCPh and PhCtCCtCPh. The crystals are readily
soluble but show limited stability in polar solvents.
Decomposition is discernible within days. The solutions
in CD2Cl2 show NMR spectra that are fully compatible
with the proposed structure. Owing to the rigid square-
planar configuration at the gold(III) center (5d8), sepa-
rate 13C signals are recorded for cis and trans ethynyl
groups, with small and large J(PC) coupling constants,
respectively (Experimental Section). In the IR spectrum
of the solid (in KBr) there are two ν(CtC) absorption
agents. In all cases only the products of reductive
elimination were obtained.
It was only in the reaction of PhCtCLi with the
complex (Me3P)Au(CtCPh)3 (1)swith its Me3P-induced
stabilitysthat a product containing the symmetrical
[Au(CtCPh)4]- anion could be obtained [eq 10]. Since
this complex ion shows limited thermal stability, the
fairly slow metathesis with nBu4N+Br- at room tem-
perature is accompanied by reductive elimination of
PhCtCCtCPh, generating the anion [Au(CtCPh)2]-.
The isolated polycrystalline solid contained the
gold(III) and gold(I) anions in a ratio of ca. 1:3. Recrys-
tallization from dichloromethane/pentane finally af-
forded colorless single crystals with a clean 1:1 stoichi-
ometry (3, mp 129-130 °C). Unexpectedly, the solutions
of the compounds in CD2Cl2 gave only one set of 1H and
13C resonances for the alkynyl groups of the anions. The
sp-carbon atoms neigbouring the metal centers, which
should be most affected by a change in the oxidation
state of the metal, show either no signal (C1) or only a
signal of very low (C2) intensity. Thus no assignments
could be made. Similar results were obtained by Bayo´n
et al. in an investigation of the 1H NMR spectra of
gold(I) and (III) complexes with isocyanide ligands
(isolobal to ethynyl groups).18 Rapid interionic exchange
of alkynyl groups cannot be ruled out as the origin of
the phenomenon.
bands at 2107 and 2144 cm-1
.
Attempts to substitute the PMe3 ligand by PPh3 in
CH2Cl2 or THF solution were not successful in the
temperature range from 20 to 60 °C, indicating that the
stronger donor is not readily replaced by the weaker one
even if an excess of the latter is employed and/or
reduced pressure applied to evaporate the volatile PMe3.
At higher temperatures decomposition of the substrate
with reductive elimination of PhCtCCtCPh is ob-
served.
The reaction of complex 1 with hydrogen chloride in
dichloromethane affords (Me3P)AuCl, PhCtCH, and
PhCtCCtCPh, which clearly can be classified as the
products of a substitution followed or accompanied by
a reductive elimination. This result shows that the
di(ethynyl)gold(III) complexes cis- or trans-(Me3P)Au-
(CtCPh)2Cl, with one tertiary phosphine and one
chloride ligand, are unstable [eq 9].
The presence of large amounts of the gold(I) salt in
the reaction mixture obtained from a gold(III) precur-
sor indicates extensive reductive elimination of
PhCtCCtCPh. This byproduct was indeed discovered
in all experiments, and the yield was approximately
equivalent to that of the gold(I) compound.
For comparison, the corresponding “pure” di(phenyl-
ethynyl)gold(I) salt nBu4N+[Au(CtCPh)2]- (4) was pre-
pared from Ph3PAuCtCPh and PhCtCLi in diethyl
ether. The slurry of the reactants cleared, and upon
addition of nBu4N+Br-, a precipitate of LiBr was ob-
served. The product was isolated in 69% yield from the
solid that remained after evaporation of the diethyl
ether by extraction with benzene and again evaporating
the solvent (mp 111-113 °C, from dichloromethane/
pentane). Solutions of 4 in CD2Cl2 provided the same
set of NMR parameters as 3. The anion [Au(CtCPh)2]-
has been reported previously with a variety of coun-
terions.19-32
The reaction of complex 1 with iodine in dichlo-
romethane was followed by NMR spectroscopy and
shown to produce Me3PAuI and an unstable compound
that can be assigned the formula trans-(Me3P)Au-
(CtCPh)2I but could also not be isolated. Attempts to
trap it by methylation with MeLi under mild conditions
[to give (Me3P)Au(CtCPh)2Me] or by quaternization
with PMe3 [to give (Me3P)2Au(CtCPh)2 I-] were not
+
successful. NMR evidence for the former was obtained,
however, in the reaction mixture obtained from equimo-
lar quantities of (Me3P)AuMe and (PhCtC)2TlCl in
dichloromethane at -78 °C. The compound could not
be separated from the byproduct (Me3P)AuCtCPh. The
same reaction with (Ph3P)AuMe instead of (Me3P)AuMe
yielded soleley the gold(I) complexes (Ph3P)AuCtCPh
and (Ph3P)AuMe together with elimination products.
This observation confirms the stabilizing role of tri-
methylphosphine in alkynylgold(III) complexes not
matched by triphenylphosphine.
Preparation and Reactions of Tetra(phenyl-
ethynyl)aurates(III): M[Au(CtCPh)4]. Several routes
to the elusive tetra(alkynyl)aurates(III) were probed and
proved unsuitable. These included the reaction of tet-
rahalogenoaurates(III) with an excess of alkynyllithium
or -Grignard reagents and the oxidative addition of
halogen to dialkynylaurates(I) followed by alkynylmetal
(18) Bayon, R.; Coco, S.; Espinet, P.; Fernandez-Mayordomo, C.;
Martin-Alvarez, J. M. Inorg. Chem. 1997, 36, 2329.
(19) Li, D.; Hong, X.; Che, C. M.; Lo, W. C.; Peng, S. M. J. Chem.
Soc., Dalton Trans. 1993, 2929.
(20) Abu-Salah, O. M. Polyhedron 1992, 11, 951.
(21) Abu-Salah, O. M. J. Chem. Res., Synop. 1992, 348.
(22) Abu-Salah, O. M.; Razzak, A.; Al-Ohaly, A.; Mutter, Z. F. J.
Organomet. Chem. 1990, 391, 267.
(23) Abu-Salah, O. M. J. Organomet. Chem. 1990, 387, 123.

2292 Organometallics, Vol. 24, No. 10, 2005
Schuster and Schmidbaur
Structural Studies. Compound 1 crystallizes in a
solvent-free triclinic form, space group P1h, with Z ) 2
molecules in the unit cell. The molecule has no crystal-
lographically enforced symmetry. A dichloromethane
solvate of 1:1 stoichiometry can be obtained as mono-
clinic crystals (space group P21/c, Z ) 4). There are no
unusual sub-van der Waals contacts between the com-
plex and solvent molecules.
Both types of crystals feature similar, equivalent
molecules (1) with the gold atom in a square-planar
coordination distinguishing the singular trans from the
two equivalent cis phenylethynyl ligands (Figure 1).
Owing to the trans influence of the powerful PMe3
donor, the Au-C bond lengths for the trans substituents
[2.018(3) and 2.026(5) Å] are slightly, but significantly
longer than for the cis substituents [2 × 2.003(5) and
2.001(3)/2.006(3) Å, respectively]. The CtC distances
are not affected by the trans influence and show only
marginal variations [trans: 1.197(5); cis: 1.201(5),
1.203(5); trans: 1.195(7); cis: 1.200(7), 1.207(7) Å]. The
two Au-P distances [2.3191(9) and 2.3218(14) Å] show
no significant difference in the solvent-free and solvated
form. All P-Au-C and C-Au-C angles are almost
linear or rectangular, and the linearity is extended in
the ethynyl carbon chains with only a slight curvature.
Crystals of (PhCtC)Me2PCH2Au(CtCPh)3‚CH2Cl2, 2,
are triclinic (space group P1h, Z ) 2) with one ylide
complex and one solvent molecule in the asymmetric
unit (Figure 2). The gold atom is in a square-planar
environment with the ylide ligand as a monodentate
σ-donor. The overall geometry of the (PhCtC)3Au unit
resembles very closely that of the PMe3 complex 1. The
bond Au1-C1 connecting the ylide function with the
metal atom is a true σ single bond [2.125(10) Å]
complemented by a P1-C1 single bond of 1.790(10) Å
at a quasi-tetrahedral carbon atom with an angle
Au1-C1-P1 of 113.7(5)°. The phosphorus atom is a
tetrahedral onium center with one phenylalkynyl and
two methyl substituents. There is ample precedent for
this type of ylide coordination to gold(I) and gold(III),1
but complex 2 is the first case in which a tri(alkynyl)-
gold unit is stabilized by a phosphorus ylide. The
packing of the zwitterionic complex molecules and the
solvent in the unit cell shows no anomalies or peculiari-
ties. The intermolecular Au‚‚‚Au contact [3.744 Å] is
beyond the limit commonly considered to be the thresh-
old between aurophilic and van der Waals bonding.
Crystals of the reference compound 4 are orthorhom-
bic (space group Pbca, Z ) 8) with one cation and one
anion in the asymmetric unit, which contains no solvent.
The cation has the standard conformation of extended
n-butyl groups at a tetrahedrally coordinated nitrogen
Figure 1. Molecular structure of compound (Me3P)Au-
(CtCPh)3, 1 (ORTEP drawing with 50% probability el-
lipsoids; H atoms omitted for clarity). (a) Solvent-free;
selected bond lengths [Å] and angles [deg]: Au1-P1
2.3191(9), Au1-C11 2.018(3), Au1-C21 2.006(3), Au1-C31
2.001(3), C11-C12 1.197(5), C21-C22 1.201(5), C31-C32
1.203(5); P1-Au1-C11 176.70(10), P1-Au1-C21 88.74-
(11), P1-Au1-C31 91.73(11), Au1-C11-C12 177.4(3),
Au1-C21-C22 174.6(3), Au1-C31-C32 172.8(3), C11-
Au1-C21 90.79(14), C11-Au1-C31 88.53(12), C21-Au1-
C31 176.31(12). (b) 1:1 CH2Cl2 solvate; selected bond
lengths [Å] and angles [deg]: Au1-P1 2.3218(14), Au1-
C11 2.026(5), Au1-C21 2.003(5), Au1-C31 2.003(6), C11-
C12 1.195(7), C21-C22 1.207(7), C31-C32 1.200(7); P1-
Au1-C11 173.27(15), P1-Au1-C21 84.92(14), P1-Au1-
C31 91.52(14), Au1-C11-C12 174.5(5), Au1-C21-C22
172.5(4), Au1-C31-C32 173.2(5), C11-Au1-C21 91.1(2),
C11-Au1-C31 92.2(2), C21-Au1-C31 175.58(19).
atom, while the anion resembles a weightlifting gear
unit with the planes of the terminal phenyl groups
approximately at a right angle. The two Au-C bonds
are of equal length at 1.989(5) and 1.995(6) Å, as are
the two CtC distances at 1.209(6) and 1.200(6) Å
(Figure 3). The anions are separated from each other
by the cations such that no aurophilic interactions are
discernible. There is no evidence for π-π stacking of the
phenyl groups or phenyl embrace of aryl hydrogen
atoms.
The mixed-anion salt 3 crystallizes as a dichlo-
romethane solvate (triclinic, space group P1h, Z ) 1). In
both types of anions the gold atom resides in a center
of inversion, such that the asymmetric unit of the
crystals contains one cation and one-half of each anion
(Figure 4). The cation has a conformation similar to that
of salt 4, and the solvent molecule has no sub-van der
Waals contacts with the ions.
(24) Abu-Salah, O. M.; Al-Ohaly, A. R. A. J. Chem. Soc., Dalton
Trans. 1988, 2297.
(25) Abu-Salah, O. M.; Al-Ohaly, A. R.; Al-Qahtani, H. A. Inorg.
Chim. Acta 1986, 117, L29.
(26) Abu-Salah, O. M.; Al-Ohaly, A. R. A.; Knobler, C. B. J. Chem.
Soc., Chem. Commun. 1985, 1502.
(27) Abu-Salah, O. M.; Al-Ohaly, A. R. A.; Al-Showiman, S. S.; Al-
Najjar, I. M. Trans. Met. Chem. 1985, 10, 207.
(28) Abu-Salah, O. M. J. Organomet. Chem. 1984, 270, C26.
(29) Abu-Salah, O. M. J. Chem. Res., Synop. 1984, 187.
(30) Abu-Salah, O. M.; Al-Ohaly, A. R. J. Organomet. Chem. 1983,
255, C39.
(31) Abu-Salah, O. M.; Al-Ohaly, A. R. Inorg. Chim. Acta 1983, 77,
L159.
(32) Nast, R.; Schneller, P.; Hengefeld, A. J. Organomet. Chem.
1981, 214, 273.

Tri- and Tetra(alkynyl)gold(III) Compounds
Organometallics, Vol. 24, No. 10, 2005 2293
Conclusions
The results of the present study have shown that tri-
(alkynyl)gold(III) complexes (RCtC)3Au(L) can be
prepared as metastable compounds if a small and
strong trialkylphosphine donor is introduced as an
auxiliary ligand L. Already a switch to triarylphos-
phines or to a bulky trialkylphosphine lowers the
stability threshold toward reductive elimination of the
dialkyne RCtCCtCR, and only alkynylgold(I) com-
plexes (RCtC)Au(L) are obtained. The complex with L
) PMe3 has been crystallized in a solvent-free form and
as a 1:1 solvate with CH2Cl2. In the two forms the
complex has the same square-planar structure. Deter-
mination of the molecular structure of (PhCtC)Me2-
PCH2Au(CtCPh)3 (2), a byproduct of the synthesis of
1, provided the proof that ylides also have the capability
to stabilize tri(alkynyl)gold(III) complexes.
Tetra(alkynyl)aurates(III) [Au(CtCR)4]- can be pre-
pared with large, nonpolarizing counterions such as
nBu4N+, but all preparative routes probed in the study
led to significant side reactions producing also the
dialkyne and leaving the [Au(CtCR)2]- anion. Both
types of anions cocrystallize with the cation in different
stoichiometries.
Single crystals were obtained for the 1:1 ratio of
anions as a dichloromethane solvate, [nBu4N]2[Au-
(CtCPh)2][Au(CtCPh)4]‚(CH2Cl2) (3). The reference
compound [nBu4N] [Au(CtCPh)2] (4) has also been
structurally characterized. The geometry of the anions
and of the [(PhCtC)3Au(PMe3)] complex (1) and its
dichloromethane solvate shows only minor variations,
which in the latter cases can be ascribed to the trans
influence of the trialkylphosphine ligand. Two alkynyl
groups in trans position at a gold(III) center appear to
lower the stability of the complexes greatly such that
reductive elimination of dialkynyl is easily induced
either in the reaction mixture of any preparative at-
tempts or upon heating of the products.
Figure 2. Molecular structure of [(PhCtC)Me2PCH2]Au-
(CtCPh)3‚CH2Cl2, 2 (ORTEP drawing with 50% probability
ellipsoids; H atoms omitted for clarity). Selected bond
lengths [Å] and angles [deg]: Au1-C1 2.125(10), Au1-C11
2.056(12), Au1-C21 2.114(11), Au1-C31 2.143(11), C11-
C12 1.196(15), C21-C22 1.281(14), C31-C32 1.269(14),
P1-C1 1.790(10), P1-C2 1.844(11), P1-C3 1.887(10), P1-
C41 1.727(12), C41-C42 1.240(16); C1-Au1-C11 178.9-
(4), C1-Au1-C21 85.2(4), C1-Au1-C31 92.3(4), Au1-
C11-C12 175.5(9), Au1-C21-C22 174.5(9), Au1-C31-
C32 173.4(9), C11-Au1-C21 94.3(4), C11-Au1-C31
88.3(4), C21-Au1-C31 174.6(4), C1-P1-C41 109.3(5),
P1-C41-C42 174.6(10).
The stability of polyalkynyl complexes of gold(III)
centers appears to be generally lower than that of
the isoelectronic platinum(II) centers, for which a
greater variety of coordination compounds is readily
available.33 It remains to be demonstrated that there
are donors, other than phoshines and ylides, that can
be successfully employed as auxiliary ligands L for
(RCtC)3Au(L) complexes.
Figure 3. Molecular structure of [(n-Bu)4N][Au(CtCPh)2],
4 (ORTEP drawing with 50% probability ellipsoids; H
atoms omitted for clarity). Selected bond lengths [Å] and
angles [deg]: Au1-C11 1.989(5), Au1-C21 1.995(5),
C11-C12 1.209(6), C21-C22 1.200(6); C11-Au1-C21
176.69(17), Au1-C11-C12 171.3(4), Au1-C21-C22
178.2(4).
Experimental Section
The Au-C distances of the [Au(CtCPh)2]- anion
[1.995(7) Å] are similar to those in the reference salt 4,
but significantly shorter than those in the [Au(CtCPh)4]-
anion [2.017(6) and 2.018(6) Å]. The difference of the
CtC bond lengths is smaller, but follows the same
trend: 1.189(9) Å for Au(I) vs 1.197(8) and 1.199(9) Å
for Au(III). This result suggests weaker bonding of the
phenylethynyl groups in the Au(III) case as also shown
by the low stability of this square-planar anion toward
reductive elimination of PhCtCCtCPh.
General Procedures. All organometallic syntheses were
performed in a dry deoxygenated dinitrogen atmosphere using
standard Schlenk techniques. All solvents were distilled from
an appropriate drying agent and stored over molecular sieves
(4 Å) and under nitrogen. Unless otherwise stated solutions
were protected against light. Most standard chemicals were
purchased from Aldrich or Fluka and used without further
purification, or prepared by literature procedures: AuCl3,34
TlCl3,35 (Me3P)AuCl,36 (Ph3P)Au(C2Ph),37 (Me3P)Au(C2Ph),7
[(i-Pr)3P]Au(C2Ph),7 and (Me3P)AuMe.37
The planes of the phenyl groups of trans ethynyl
groups are parallel for the [Au(CtCPh)2]- and the
[Au(CtCPh)4]- anions, and for the latter the orientation
is roughly perpendicular to the AuC4 reference plane.
Note that in compound 4 the planes of the two phenyl
rings are perpendicular to each other.
(33) Belluco, U.; Bertani, R.; Michelin, R. A.; Mozzon, M. J. Orga-
nomet. Chem. 2000, 600, 37.
(34) Schmidbaur, H. Organogold Compounds; Slawisch, A., Ed.;
Springer-Verlag: Berlin, 1980.
(35) Brauer, G. Handbuch der pra¨parativen anorganischen Chemie;
Enke Verlag: Stuttgart, 1981.
(36) Angermaier, K.; Zeller, E.; Schmidbaur, H. J. Organomet. Chem.
1994, 472, 371.

2294 Organometallics, Vol. 24, No. 10, 2005
Schuster and Schmidbaur
Figure 4. Crystal structure of [(n-Bu)4N]2[Au(CtCPh)4][Au(CtCPh)2]‚2CH2Cl2, 3 (ORTEP drawing with 50% probability
ellipsoids; H atoms omitted for clarity). Selected bond lengths [Å] and angles [deg]:Au1-C11 2.017(6), Au1-C21 2.018(6),
Au1-C31 1.995(7), C11-C12 1.197(8), C21-C22 1.199(9), C31-C32 1.189(9); C11-Au1-C21 91.7(2), Au1-C11-C12 179.4-
(6), Au1-C21-C22 177.1(5).
NMR spectra were obtained on JEOL-400 or JEOL-270
spectrometers. Chemical shifts are reported in δ values relative
to the residual solvent resonances converted to TMS (1H, 13C).
31P{1H} NMR spectra are referenced to external aqueous
H3PO4 (85%). IR spectra were measured on a Perkin-Elmer
FT-IR 577 spectrometer.
Warnings. Thallium compounds are toxic and must be
handled with care. Although thallium is classified as a
cumulative poison, as are lead and mercury, it must be
emphasized that it is gradually excreted from the body as a
result of soft-tissue turnover.38
(0.33 mmol) of AuCl3 in THF (40 mL) at -78 °C. After 1 h of
stirring 0.33 mL of PMe3 (0.33 mmol, 1 M in toluene) was
added and the mixture allowed to warm to room temperature.
After removal of the solvent at room temperature, a brown
slurry remained, which was redissolved in dichloromethane,
and LiCl was removed by extraction with 3 × 50 mL of water.
After filtration of the organic phase through anhydrous
MgSO4, n-pentane was added to precipitate 102 mg (51% yield)
of colorless crystals; mp (dec) 114-115 °C.
Route b. The reaction of freshly prepared (Me3P)AuX3 [from
1.24 g (4.0 mmol) of (Me3P)AuCl by adding 0.21 mL (4.0 mmol)
of bromine in dichloromethane at 0 °C] with 3 equiv (12.0 mL,
12.0 mmol, 1.0 M) of LiCCPh at -78 °C in THF yielded, after
workup as described for route a, 717 mg (30% yield) of colorless
crystals; mp (dec) 112-114 °C.
Chloro[bis(phenylethynyl)thallium(III). TlCl3 (1.24 g,
4.0 mmol), dissolved in 15 mL of THF, was treated with 2 equiv
(8 mL, 8 mmol, 1.0 M in THF) of LiCCPh at -78 °C. With
continued stirring, the resultant solution was allowed to warm
to room temperature and stirred for 30 min. After filtration a
few drops of diluted aqueous HCl were added before the
solvents were removed in vacuo. Recrystallization of the
residue from dichloromethane/n-pentane at -30 °C gave 1.24
g (69% yield) of a white microcrystalline product; mp (dec)
135 °C. 1H NMR (THF-d8, RT): δ 7.28-7.55 [m, C6H5].
Route c. The synthesis was carried out with 77 mg (0.2
mmol) of (Me3P)Au(C2Ph) and 91 mg (0.2 mmol) of (PhC2)2-
TlCl using the same procedure as described for trans-
(Me3P)Au(CCPh)2Me. Colorless crystals (44 mg, 36% yield)
were collected after recrystallization from dichloromethane/
n-pentane at -30 °C; mp (dec) 114-117 °C. 1H NMR (CD2Cl2,
2
1
13C{1H} NMR (THF-d8, RT): δ 106.6 [d, JTlC ) 2161.2 Hz,
RT): δ 1.97 [d, JHP ) 12.8 Hz, 9 H, P(CH3)], 7.21-7.58
[m, 15 H, C6H5]. 13C{1H} NMR (CD2Cl2, RT): δ 13.8 [d,
Tl-CtC-Ph]. 122.9 [d, 2JTlC ) 189.0 Hz, Tl-CtC-Ph], 128.2 [s,
i-(C6H5)], 128.4 [s, o-(C6H5)], 131.5 [s, p-(C6H5)], 132.2 [s,
m-(C6H5)]. IR (KBr) [cm-1]: 2160 (s), ν (CtC). Anal. Calc for
C16H10ClTl (442.09 g‚mol-1): C, 43.47; H, 2.28. Found: C,
43.39; H, 2.18.
2
1JCP ) 41.5 Hz, P(CH3)], 93.3 [d, JCP ) 12.3 Hz, cis-Au-
2
CtC-Ph], 94.1 [d, JCP ) 212.5 Hz, trans-Au-CtC-Ph], 104.1
[d, 3JCP ) 40.7 Hz, trans-Au-CtC-Ph], 105.7 [d, 3JCP ) 3.0 Hz,
4
cis-Au-CtC-Ph], 125.8 [s, cis-i-(C6H5)], 126.0 [d, JCP ) 23.0
Hz, trans-i-(C6H5)], 127.3 [s, trans-o-(C6H5)], 127.7 [s, cis-o-
(C6H5)], 128.4 [s, trans-p-(C6H5)], 128.5 [s, cis-p-(C6H5)], 131.8
[s, cis-m-(C6H5)], 132.0 [s, trans-m-(C6H5)]. 31P{1H} NMR (CD2-
Cl2, RT): δ -9.0 [s, P(CH3)]. IR (KBr) [cm-1]: 2107 (vw), ν
(trans-CtC); 2144 (m), ν (cis-CtC). Anal. Calc for C27H24AuP‚
0.33CH2Cl2 (604.73 g‚mol-1): C, 54.29; H, 4.11. Found: C,
54.33; H, 4.11.
trans-Bis(phenylethynyl)methyl(trimethylphosphine)-
gold(III). A sample of (Me3P)AuMe (29 mg, 0.1 mmol) was
dissolved in 2 mL of dichloromethane and cooled to -78 °C.
After addition of (PhC2)2TlCl (44 mg, 0.1 mmol) the mixture
was stirred for 30 min and subsequently drawn into a syringe.
Therein it was allowed to warm with shaking. Thirty seconds
after the precipitation of TlCl was observed, the suspension
was immediately filtered through a syringe filter into n-
pentane kept at -78 °C. A colorless precipitate consisting of
(Me3P)Au(C2Ph)2Me and (Me3P)Au(C2Ph) was obtained, which
could not be separated. Residual (Me3P)AuMe was detected
in the mother liquor by NMR spectroscopy. 1H NMR (CD2Cl2,
RT): δ 1.36 [d, 3JHP ) 10.4 Hz, 3 H, trans-P-Au-CH3], 1.80 [d,
2JHP ) 11.6 Hz, 9 H, P(CH3)], 7.18-7.48 [m, C6H5]. 31P{1H}
NMR (CD2Cl2, RT): δ -5.3 [s, P(CH3)].
(Triphenylphosphine)tris(phenylethynyl)gold(III) and
[Tri(isopropyl)phosphine]tris(phenylethynyl)gold-
(III). Samples of the corresponding (R3P)Au(C2Ph) complexes
were dissolved in CD2Cl2 and reacted with an excess of (PhC2)2-
TlCl. NMR spectra were recorded immediately. (Ph3P)Au-
(C2Ph)3: 1H NMR (CD2Cl2, RT): δ 6.95-7.77 [m, C6H5].
31P{1H} NMR (CD2Cl2, RT): δ 20.0 [s, P(C6H5)]. [(i-Pr)3P]Au-
3
(C2Ph)3: 1H NMR (CD2Cl2, RT): δ 1.49 [dd, JHP ) 16.1 Hz,
3JHH ) 7.2 Hz, 18 H, P(CH(CH3)2)], 3.20 [m, 3 H, P(CH(CH3)2)],
7.15-7.40 [m, 15 H, C6H5]. 31P{1H} NMR (CD2Cl2, RT): δ 68.7
[s, P(CH(CH3)2)].
(Trimethylphosphine)tris(phenylethynyl)gold(III), 1.
Route a. A 1.0 mL portion of a solution of LiCCPh (1.0 mmol,
1 M in THF) was added dropwise to a suspension of 100 mg
[(Phenylethynyl)dimethylphosphoniummethylide]tri-
(phenylethynyl)gold(III), 2. Crystals of this compound were
obtained as a byproduct of the synthesis of complex 1 via route
b; mp 129-130 °C.
(37) Schmidbaur, H.; Schier, A. In Science of Synthesis Vol. 3;
Thieme: New York, 2003.
(38) Marko´, I.; Southern, J. M. J. Organomet. Chem. 1990, 3368.

Tri- and Tetra(alkynyl)gold(III) Compounds
Organometallics, Vol. 24, No. 10, 2005 2295
Table 1. Crystal Data, Data Collection and Structure Refinement Details
(Me3P)Au(C2Ph)3
(Me3P)Au(C2Ph)3‚CH2Cl2
[(PhCC)Me2PCH2Au(CCPh)3‚CH2Cl2
empirical formula
Mr
C
27H24AuP
C28H26AuCl2P
661.32
C36H28AuCl2P
759.42
576.40
cryst syst
space group
a/Å
triclinic
Ph1
monoclinic
P21/c
13.1163(2)
16.2269(3)
14.1022(3)
90
triclinic
Ph1
9.2632(1)
11.1278(2)
12.1561(2)
82.9382(6)
73.8315(6)
78.4370(9)
1176.05(3)
1.628
8.9539(5)
12.9892(4)
15.4944(11)
83.782(5)
79.916(5)
78.659(2)
1734.47(19)
1.454
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
117.6935(7)
90
2657.64(9)
1.653
F
calc/g cm-3
Z
2
4
2
F(000)
560
1288
744
µ (Mo KR) (cm-1
T/K
)
63.32
58.10
44.62
143
143
143
refls measd
refls unique
25 643
67 806
69 364
4054 [Rint ) 0.042]
265/0
4834 [Rint ) 0.084]
292/0
5443 [Rint ) 0.076]
373/0
refined params/restraints
R1 [I g 2σ(I)]
0.0231
0.0615
a ) 0.0366
b ) 0.6137
1.200/-1.421
0.0372
0.0961
a ) 0.0532
b ) 4.6363
2.295/-2.518
0.0597
0.1425
a ) 0.0697
b ) 1.9959
1.982/-1.712
wR2a
weighting scheme
σfin(max/min)/e Å-3
2
2
2
a wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo2)2]}1/2; w ) 1/[σ2(Fo2) + (ap)2 + bp]; p ) (Fo2+ 2Fc )/3.
Table 2. Crystal Data, Data Collection, and Structure Refinement Details
[(n-Bu)4N][Au(C2Ph)2] [(n-Bu)4N]2[Au(C2Ph)2][Au(C2Ph)4]‚2CH2Cl2
empirical formula
C
32H46AuN
C82H106Au2Cl4N2
1655.42
Mr
641.66
cryst syst
space group
a/Å
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
orthorhombic
Pbca
17.2772(1)
18.3213(2)
18.6586(2)
90
triclinic
Ph1
8.9747(2)
12.4383(3)
17.9334(5)
78.1633(12)
84.1125(13)
78.1765(19)
1913.93(8)
1.436
90
90
5906.21 (10)
1.443
F
calc/g cm-3
Z
8
1
F(000)
2592
838
µ (Mo KR) (cm-1
T/K
)
50.00
40.11
143
143
refls measd
refls unique
124 873
5427 [Rint ) 0.072]
311/0
53 832
6583 [Rint ) 0.061]
413/0
refined params/restraints
R1 [Ig 2σ(I)]
0.0400
0.1260
a ) 0.0895
b ) 6.5974
1.728/-1.508
0.0400
0.0848
a ) 0.0136
b ) 4.6269
0.943/-0.878
wR2a
weighting scheme
σfin(max/min)/e Å-3
a wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo2)2]}1/2; w ) 1/[σ2(Fo2) + (ap)2 + bp]; p ) (Fo + 2Fc )/3.
2
2
2
2
Tetra(n-butyl)ammonium [bis(phenylethynyl)]aurate-
(I), 4. A suspension of 112 mg of (Ph3P)Au(C2Ph) (0.2 mmol)
in diethyl ether (50 mL) was treated with 1 equiv of LiCCPh
(0.2 mL, 0.2 mmol, 1 M in THF) to give a clear solution. A
white precipitate (LiBr) formed overnight upon addition of 64
mg of [(n-Bu)4N]Br (0.2 mmol). The solvents were removed and
the residue was extracted with benzene (2 × 30 mL). Removal
of the solvent from the combined benzene extracts and
recrystallization of the residue from dichloromethane/n-pen-
tane yielded 83 g (69% yield) of colorless crystals; mp 111-
113 °C. 1H NMR (CD2Cl2, RT): δ 0.98, t, 2JHH ) 7.4 Hz, 12 H,
p-(C6H5)], 131.7 [s, m-(C6H5)], Au-CtC-Ph was not observed.
IR (KBr) [cm-1]: 2098 (s), ν (CtC). Anal. Calc for C32H46AuN
(641.68 g‚mol-1): C, 59.90; H, 7.23. Found: C, 59.80; H, 7.04.
Bis[tetra(n-butyl)ammonium] bis(phenylethynyl)au-
rate(I) tetrakis(phenylethynyl)aurate(III), 3. The com-
pound was synthesized in the same manner as described for
3 from 115 mg of (Me3P)Au(C2Ph)3 (0.2 mmol), 0.2 mL of
LiCCPh (0.2 mmol, 1 M in THF), and 64 mg of [(n-Bu)4N]Br
(0.2 mmol) in diethyl ether. Extraction and recrystallization
from dichloromethane/pentane afforded two kinds of crystals:
3 and [(n-Bu)4N]2Au(C2Ph)4Au(C2Ph)2; mp 129-130 °C. 1H
2
N-CH2-CH2-CH2-CH3], 1.39-1.48 [m,
8
H, N-CH2-CH2-
NMR (CD2Cl2, RT): δ 0.98, t, JHH ) 7.4 Hz, 12 H, N-CH2-
CH2-CH3], 1.55-1.72 [m, 8 H, N-CH2-CH2-CH2-CH3], 3.20-
3.28 [m, 8 H, N-CH2-CH2-CH2-CH3], 7.05-7.43 [m, 10 H,
Au-CtC-C6H5]. 13C{1H} NMR (CD2Cl2, RT): δ 13.7 [s, N-CH2-
CH2-CH2-CH3], 20.1 [s, N-CH2-CH2-CH2-CH3], 24.4 [s, N-CH2-
CH2-CH2-CH3], 59.4 [s, N-CH2-CH2-CH2-CH3], 102.6 [s, Au-
CtC-Ph], 125.3 [s, i-(C6H5)], 127.5 [s, o-(C6H5)], 127.9 [s,
CH2-CH2-CH3], 1.35-1.48 [m, 8 H, N-CH2-CH2-CH2-CH3],
1.56-1.71 [m, 8 H, N-CH2-CH2-CH2-CH3], 3.18-3.27 [m, 8 H,
N-CH2-CH2-CH2-CH3], 7.08-7.49 [m, Au-CtC-(C6H5)]. 13C{1H}
NMR (CD2Cl2, RT): δ 13.8 [s, N-CH2-CH2-CH2-CH3], 20.2 [s,
N-CH2-CH2-CH2-CH3], 24.5 [s, N-CH2-CH2-CH2-CH3], 59.6 [s,
N-CH2-CH2-CH2-CH3], 102.8 [s, Au-CtC-Ph], 125.7 [s, i-(C6H5)],

2296 Organometallics, Vol. 24, No. 10, 2005
Schuster and Schmidbaur
126.8 [s, o-(C6H5)], 128.3 [s, p-(C6H5)], 132.0 [s, m-(C6H5)],
Au-CtC-Ph was not observed. Anal. Calc for product mixture
[Au(III)/Au(I) ) 1/3]: C, 62.46; H, 7.06; N, 2.02. Found: C,
61.75; H, 6.29; N, 1.82.
lection, and structure refinement are summarized in Tables 1
and 2. Important interatomic distances and angles are shown
in the figure captions. Complete lists of displacement param-
eters and tables of interatomic distances and angles have been
deposited with the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, UK. The data are
available on request on quoting CCDS-266848-266852.
Crystal Structure Determinations. The single crystals
were placed in inert oil on the top of a glass pin and transferred
to the cold gas stream of the diffractometer. Crystal data were
collected using a Nonius DIP2020 system with monochromated
Mo KR (λ ) 0.71073 Å) radiation at -130 °C. The structures
were solved by direct methods (SHELXS-97) and refined by
full matrix least-squares calculations on F2 (SHELXL-97).39
Non-hydrogen atoms were refined with anisotropic displace-
ment parameters. Hydrogen atoms were placed in idealized
positions and refined using a riding model with fixed isotropic
contributions. Further information on crystal data, data col-
Acknowledgment. This work was supported by
Deutsche Forschungsgemeinschaft, Fonds der Chemis-
chen Industrie, Volkswagenstiftung, and Heraeus GmbH.
Supporting Information Available: Details of crystal
data, data collection, and structure refinement and tables of
atomic coordinates, isotropic and anisotropic thermal param-
eters, and all bond lengths and angles. This material is
available free of charge via the Internet at http://pubs.acs.org.
(39) Sheldrick, G. M. SHELXL-97: Programs for Crystal Structure
Analysis; University of Go¨ttingen, 1997.
OM050038Q