Metallophilicity: The dimerization of bis[(triphenylphosphine)gold(I)]chloronium cations

Full text of DOI:10.1021/ja010398e

5106
J. Am. Chem. Soc. 2001, 123, 5106-5107
Metallophilicity: The Dimerization of
Bis[(triphenylphosphine)gold(I)]chloronium Cations
Armin Hamel, Norbert W. Mitzel, and Hubert Schmidbaur*
Anorganisch-chemisches Institut
Technische UniVersita¨t Mu¨nchen,
D-85747 Garching, Germany
ReceiVed February 14, 2001
The current literature reflects a rapidly growing interest in
closed-shell interactions between the metal centers of complexes
of the heavy late transition elements.1 The effects of 5d10-5d10
interactions on structure and bonding of such complexes are
particularly obvious for coordination compounds of gold(I)
(“aurophilicity”),2 but similar phenomena have been reported for
several of the neighboring elements of gold in the Periodic Table
(“metallophilicity”).3 It appears that weak attractive forces
between metal atoms or cations with seemingly saturated electron
configurations play an important role in determining the config-
uration, conformation, and oligomerization of complexes.4
In this communication we report the unprecedented dimeriza-
tion of the bis[(triphenylphosphine)gold(I)]chloronium cation in
its hexafluoroantimonate(VI) salt. Salts with this chloronium
cation {[(Ph3P)Au]2Cl}+X- were first observed by Uson et al. in
1979.5 The crystal structure of the perchlorate salt (1, containing
1 mol equiv of CH2Cl2) was determined by Jones et al. in 1980,
and the cation was shown to be monomeric and to have the
expected angular structure6 which is similar to that of the neutral,
isoelectronic sulfide and selenide complexes [(Ph3P)Au]2S/Se.7-9
The angles Au-Cl-Au in 1 were found to be extremely small
[80.7 and 82.7° for two independent cations in the unit cell] and
to be associated with short aurophilic contacts of 3.035 and 3.085
Å, respectively.6 The corresponding bromonium tetrafluoroborate
Figure 1. Molecular structure of a dication in [{[(Ph3P)Au]4Cl2}2+]-
(SbF6-)2, 2, with atomic numbering (ORTEP, 50% probability ellipsoids,
H atoms omitted for clarity). The asymmetric unit contains two
independent dications of S4 symmetry with very similar dimensions, of
which only one is shown. Selected bond lengths [Å] and angles [deg]
(with the second decation in brackets): Au1-Au1A 3.0734(4) [3.0788-
(4)], Au1-P1 2.250(2) [2.252(2)], Au1-Cl1 2.355(2) [2.366(2)], P1-
Au1-Cl1 170.99(8) [171.12(7)], Au1-Cl1-Au1C 101.4(1) [102.0(1)],
Au1A-Au1-Au1B 72.73(1) [73.38(1)].
salt was recently reported from this laboratory10 and showed an
analogous structure, but with an Au-Br-Au angle of 96.83(3)°
and a correspondingly longer Au- -Au contact of 3.6477(1) Å.
This work also included chloronium salts with phosphines other
than Ph3P.9,10 The present work is also important, because it
describes some of the most stable halonium ions reported so far.11
Treatment of (Ph3P)AuCl with only half a mole equivalent of
AgSbF6 in tetrahydrofuran/dichloromethane at -78 °C under
protection against incandescent light leads to the precipitate of
AgCl and a clear colorless solution. Filtration and partial
evaporation of the solvents from the filtrate under vacuum give
colorless crystals in 84% yield, which were identified as
[{[(Ph3P)Au]4Cl2}2+](SbF6-)2 (2):
(1) Pyykko¨, P. Chem. ReV. 1997, 97, 597.
(2) (a) Scherbaum, F.; Grohmann, A.; Huber, B.; Kru¨ger, C.; Schmidbaur,
H. Angew. Chem., Int. Ed. Engl. 1988, 27, 1602. (b) Schmidbaur, H., Ed.
Gold: Progress in Chemistry, Biochemistry and Technology; J. Wiley &
Sons: Chichester, 1999. (c) Schmidbaur, H. Interdiscip. Sci. ReV. 1992, 17,
213. (d) Schmidbaur, H. Gold Bull. 1990, 23, 11. (e) Schmidbaur, H. Gold
Bull. 2000, 33, 3. (f) Schmidbaur, H. Chem. Soc. ReV. (London) 1995, 24,
391.
4[(Ph3P)AuCl] + 2AgSbF6 f
2+
-
(3) (a) Pyykko¨, P.; Li, J.; Runeberg, N. Chem. Phys. Lett. 1994, 218, 133.
(b) Bennett, M. A.; Contel, M.; Hockless, D. C. R.; Welling, L. Chem.
Commun. 1998, 2401. (c) Catalano, V. J.; Bennet, B. L.; Muratidis, S.; Noll,
B. C. J. Am. Chem. Soc. 2001, 123, 173. (d) Cheng, E.; Leung, K. H.;
Miskowski, V. M.; Yam, V.; Phillips, D. L. Inorg. Chem. 2000, 39, 3690. (e)
Munakata, M.; Wu, L. P.; Kurodo-Sowa, T. AdV. Inorg. Chem. 1999, 46,
173. (f) Singh, K.; Long, J. R.; Stavropoulos, P. J. Am. Chem. Soc. 1997,
119, 2943. (g) Schumann, H.; Janiak, C.; Pickardt, J.; Bo¨rner, U. Angew.
Chem., Int. Ed. Engl. 1987, 26, 789. (h) Janiak, C.; Hofmann, R. J. Am. Chem.
Soc. 1990, 112, 5924. (i) Pyykko¨, P.; Schneider, W.; Bauer, A.; Bayler, A.;
Schmidbaur, H. Chem. Commun. 1997, 1111.
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32, 3748. (b) Davila, R. M.; Staples, R. J.; Elduque, A.; Harlass, M.; Kyle,
L.; Fackler, J. P., Jr. Inorg. Chem. 1994, 33, 5940. (c) Vickery, J. C.; Balch,
A. L. Inorg. Chem. 1997, 36, 5978. (d) Crespo, O.; Fernandez, E. J.; Jones,
P. G.; Laguna, A.; Lopez-de-Luzuriaga, J. M.; Mendia, A.; Olmos, E. Chem.
Commun. 1998, 2233. (e) Wang, S.; Garzon, G.; King, C.; Wang, J. C.;
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Sands, L. M.; Trofimenko, S. Chem. Commun. 1997, 1691.
2AgCl +
[{[(Ph3P)Au]4Cl2} ](SbF6 )2
2
Solutions of compound 2 in trichloromethane-d show only one
31P resonance in the NMR spectrum with a chemical shift (31.62
ppm) similar to that of 1 (31.50 ppm).10 In the 1H and 13C NMR
spectra there is only one set of phenyl resonances indicating
equivalent phenyl groups in solution. In the mass spectrum of
the compound (FD) the cation [(Ph3P)Au]2Cl+ is the parent peak
at m/z 955 (37Cl).12
Crystals of 2 (from dichloromethane/pentane)13 are tetragonal,
space group I4h. Surprisingly, the lattice is composed of tetra-
nuclear dications (Figure 1) and hexafluoroantimonate anions.
There are two different dications each with crystallographically
imposed S4 symmetry and with very similar geometrical details
(caption to Figure 1). Two quarters taken from two different
dications therefore represent the asymmetric unit of the crystal.
The gold atoms are at the corners of a bisphenoid with contacts
Au1-Au1* 3.0734(4) and Au2-Au2* 3.0788(4) Å in the two
(5) Uson, R.; Laguna, A.; Castrillo, M. V. Synth. React. Inorg. Met.-Org.
Chem. 1979, 9, 317.
(6) Jones, P. G.; Sheldrick, G. M.; Uson, R.; Laguna, A. Acta Crystallogr.
1980, B36, 1486.
(7) Schmidbaur, H.; Franke, R.; Eberlein J. Chem.-Ztg. 1975, 99, 91.
(8) (a) Lensch, C.; Jones, P. G.; Sheldrick, G. M. Z. Naturforsch. 1982,
37b, 944. (b) Mu¨ller, A.; Krickemeyer, E.; Sprafke, A.; Schladerbeck, N. H.;
Bo¨gge, H. Chimia 1988, 42, 68. (c) Jones, P. G.; Tho¨ne, C. Chem. Ber. 1991,
124, 2725. (d) Canales, F.; Gimeno, C.; Laguna, A.; Dolores Villacampa, M.
Inorg. Chim. Acta 1996, 244, 95. (e) Chen, B.-L.; Mok, K.-F.; Ng, S.-Ch. J.
Chem. Soc., Dalton Trans. 1998, 4035.
(10) Bayler, A.; Bauer, A.; Schmidbaur, H. Chem. Ber./Recl. 1997, 130,
115.
(11) (a) Olah, G. A. Halonium Ions; Wiley-Interscience: New York, 1975.
(b) Olah, G. A.; Prakash, G. K. S.; Sommer J. Superacids; John Wiley &
Sons: New York, 1985.
(9) Hofreiter, S.; Paul, M.; Schmidbaur, H. Chem. Ber. 1995, 128, 901.
10.1021/ja010398e CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/03/2001

Communications to the Editor
J. Am. Chem. Soc., Vol. 123, No. 21, 2001 5107
Scheme 1. Dimerization of Two Digoldchloronium Cations {[(R3P)Au]2Cl}+
independent dications. The arrangement of the four gold atoms
may also be described as two edge-sharing triangles with an angle
between two planes of 94.8° and 96.3°, respectively (dashed line
in Scheme 1). Each of the chlorine atoms is spanning two opposite
gold atoms with angles Au1-Cl1-Au1* 101.4(1)° and Au2-
Cl2-Au2* 102.0(1)° and transannular metal-metal distances of
Au1-Au1** 3.645 Å and Au2-Au2** 3.679 Å.
An inspection of the structure shows that two dinuclear
chloronium cations (as found in 1)6 have undergone an intimate
aggregation (Scheme 1). This association is drastically affecting
the structure of the monomeric units as shown most clearly by a
widening of the Au-Cl-Au angle by no less than 20°, from 81.7°
in 1 to 101.7° in 2 (average). The newly formed inter-cationic
Au- -Au contacts in the dimer (3.075 Å, average) are virtually
the same, however, as the intramolecular contacts in the monomer
(1: 3.065 Å). It should be noted that the dimerization occurs
against electrostatic repulsion, which appears to be offset by the
gain in the number of aurophilic interactions (2 vs 4).
oligomerization in the two compounds may therefore be ascribed
to differences in the general (nondirectional) lattice energy. Recent
quantum-chemical calculations (relativistic DFT)14 on the dimer-
ization of the related oxonium cations of the type {[(R3P)Au]3O}+
have shown that the distribution of charge in the lattice has a
great influence on the mode of association and the stability of
-
the resulting polynuclear units. With small monoanions [ClO4
in 1], ionic lattices with an equal number of monocations are
preferred over the combination with only half the number of
-
dications, while for larger anions [SbF6 in 2] the dimerization
of the anions is supported by the lattice.
The spectroscopic data of the solutions of 2 indicate that the
tetranuclear dications are dissociated into the conventional di-
nuclear monocations by solvation in dichloromethane, which again
confirms the importance of the lattice electrostatics for the
aggregation of the components. As a more general conclusion
our results show that the unexpected absence of metallophilic
interactions in an ionic solid6 (as in 1) or in solution may only
be a consequence of the relative lattice energies (solvation
energies). A change of counterion (solvent) may be sufficient to
induce fundamental changes.
There are no conspicuous contacts between dications and anions
in the lattices of compounds 1 and 2. The different degree of
(12) Preparation: A solution of (Ph3P)AuCl (240 mg, 0.485 mmol) in
dichloromethane (20 mL) is slowly added under stirring at -78 °C and
protection against incandescent light to a slurry of AgSbF6 (83.3 mg, 0.243
mmol) in tetrahydrofuran (20 mL). A precipitate of AgCl is formed, which,
after having been stirred for another 2 h and warmed up to ambient
temperature, is removed by filtration. The volume of the filtrate is reduced to
3 mL under vacuum and pentane is added to precipitate the product (242 mg,
84% yield, after drying in a vacuum, mp 142 °C dec). Elemental analysis:
found C 36.36, H 2.54; calcd. for C36H30Au2ClF6P2Sb (1189.84) C 36.80, H
2.58.
Acknowledgment. This work was supported by Deutsche For-
schungsgemeinschaft, Fonds der Chemischen Industrie, and Degussa AG.
Supporting Information Available: Displacement ellipsoid plot,
tables of crystal data, structure refinement details, atomic coordinates,
bond lengths and angles, and anisotropic parameters for 2 (PDF). This
material is available free of charge via the Internet at http://pubs.acs.org.
(13) Crystallographic data for 2: C36H30Au2ClF6P2Sb crystal system
tetragonal, space group I4h, a ) 25.7515(2) Å, c ) 13.9439(2) Å, T ) 163(2)
K, Z ) 8, R1 ) 0.0384 [I > 2σ(I)], wR2 ) 0.0934 (all data), GoF ) 1.033.
The crystal was an inversion twin with a contribution of the minor component
at 0.232(6). The twinning was modeled by the respective routines in the
SHELX97 program.15 The scattering contributions of a highly disordered
dichloromethane molecule in 2 were taken into account by using the
SQUEEZE method followed by an absorption correction with DELABS. Both
procedures are part of the PLATON suite of programs.16
JA010398E
(14) (a) Chung, S.-C.; Kru¨ger, S.; Schmidbaur, H.; Ro¨sch, N. Inorg. Chem.
1996, 35, 5385. (b) Nesmeyanov, A. N.; Perevalova, E. G.; Struchkov, Yu.
T.; Antipin, M. Yu.; Grandberg, K. I.; Dyadchenko, V. P. J. Organomet. Chem.
1980, 201, 343.
(15) SHELXL-97, Sheldrick, G. M., Universita¨t Go¨ttingen 1997.
(16) Sluis, P. v. d.; Spek, A. I. Acta Crystallogr. A 1990, 46, 194.