Coordination of pyridinethiols in gold(I) complexes

Article abstract of DOI:10.1021/ic700453t

High-yield synthesis of gold(I) thionato complexes, bis(pyridine-2- thionato)gold(I) chloride (1) and bis(pyridine-4-thionato)gold(I) chloride (2), are described. According to their solid-state structures, a linear coordination of Au(I), equiplanar coordination of the ligands and two weak γ-agostic interactions are found in both of these complexes despite of different relative positions of N and S atoms in the pyridinethionato ligands. Density functional theory calculations on 1 and 2 reproduce the observed X-ray structures. Even though the C-H...Au interactions of Au(I) and two pyridine moieties (2.83 and 2.88 A in 1 and 2.86 A in 2) are relatively weak, according to calculations they seem to provide further stabilization for the coordination and orientation of the ligands. In 1 the shortest Au...Au distances of 3.50 A indicate that aurophilic interactions, even though weak, are present in the solid state, whereas in 2 these interactions are absent.

Full text of DOI:10.1021/ic700453t

Inorg. Chem. 2007, 46, 9954−9960
Coordination of Pyridinethiols in Gold(I) Complexes
Minna T. Ra
Markku Leskela
1is a1 1
nen,† Nino Runeberg,† Martti Klinga,† Martin Nieger,† Michael Bolte,‡ Pekka Pyykko,†
†
,†
1, and Timo Repo*
Department of Chemistry, UniVersity of Helsinki, P.O. Box 55, FI-00014 UniVersity of Helsinki,
Finland, Institut f u¨ r Anorganische Chemie, Johann Wolfgang Goethe-UniVersit a¨ t Frankfurt am
Main, Max-Von-Laue-Strasse 7, D-60438 Frankfurt/Main, Germany
Received March 8, 2007
High-yield synthesis of gold(I) thionato complexes, bis(pyridine-2-thionato)gold(I) chloride (1) and bis(pyridine-4-
thionato)gold(I) chloride (2), are described. According to their solid-state structures, a linear coordination of Au(I),
equiplanar coordination of the ligands and two weak
despite of different relative positions of N and S atoms in the pyridinethionato ligands. Density functional theory
calculations on 1 and 2 reproduce the observed X-ray structures. Even though the C ‚‚‚Au interactions of Au(I)
γ-agostic interactions are found in both of these complexes
−H
and two pyridine moieties (2.83 and 2.88 Å in 1 and 2.86 Å in 2) are relatively weak, according to calculations they
seem to provide further stabilization for the coordination and orientation of the ligands. In 1 the shortest Au‚‚‚Au
distances of 3.50 Å indicate that aurophilic interactions, even though weak, are present in the solid state, whereas
in 2 these interactions are absent.
Introduction
the N atom and thus form supramolecules, such as molecular
dots or molecular wires. Furthermore, different donor atoms
2
Gold complexes bearing a gold-sulfur bond have been
within the same ligand can provide different coordination
modes and thus tune both the stability and reactivity of a
of interest for pharmacological, thin film, glass, and ceramic
1
applications. Coordination chemistry of gold complexes
5
complex.
having both S and N functionalities in the same heterocycle
has recently attracted considerable interest, and several Au-
2
(3) (a) Bardaj ´ı , M.; Connelly, N. G.; Gimeno, M. C.; Jones, P. G.; Laguna,
A.; Laguna, M. J. Chem. Soc., Dalton Trans. 1995, 2245-2250 and
references therein. (b) Abram, U.; Mack, J.; Ortner, K.; M u¨ ller, M. J.
Chem. Soc., Dalton Trans. 1998, 1011-1019. (c) Us o´ n, R.; Laguna,
A.; Laguna, M.; Jim e´ nez, J.; G o´ mez, M. P.; Sainz, A. J. Chem. Soc.,
Dalton Trans. 1990, 3457-3463. (d) Vicente, J.; Chicote, M.-T.;
Rubio, C. Chem. Ber. 1996, 129, 327-330. (e) Vicente, J.; Chicote,
M.-T.; Saura-Llamas, I.; Lagunas, M. C. J. Chem. Soc., Chem.
Commun. 1992, 915-916. (f) Akrivos, P. D.; Hadjikakou, S. K.;
Karagiannidis, P. Polyhedron 1994, 13, 753-758. (g) Love, J. C.;
Wolfe, D. B.; Chabinyc, M. L.; Paul, K. E.; Whitesides, G. M. J. Am.
Chem. Soc. 2002, 124, 1576-1577. (h) Hao, L.; Mansour, M. A.;
Lachicotte, R. J.; Gysling, H. J.; Eisenberg R. Inorg. Chem. 2000, 39,
5520-5529. (i) Cookson, P. D.; Tiekink, E. R. T. J. Chem. Soc.,
Dalton Trans. 1993, 259-263.
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J. M.; Vegas, A.; Mart ´ı nez-Ripoll, M. Inorg. Chem. 1991, 30, 3743-
3749. (b) Tzeng, B.-C.; Huang, Y.-C.; Wu, W.-M.; Lee, S.-Y.; Lee,
G.-H.; Peng, S.-M. Cryst. Growth Des. 2004, 4, 63-70. (c) Friedrichs,
S.; Jones, P. G. Z. Naturforsch. 2004, 59b, 1429-1437. (d) Schulz
Lang, E.; Marceli Fernandes, R., Jr.; Souza Lemos, S.; Schulz Lang,
L.; Burrow, R. A. Acta Crystallogr., Sect. E 2002, 58, m469-m470.
(e) Dodds, C. A.; Garner, M.; Reglinski, J.; Spicer, M. D. Inorg. Chem.
2006, 45, 2733-2741. (f) Ahmad, S.; Isab, A. A.; Perzanowski H. P.
Can. J. Chem. 2002, 80, 1279-1284. (g) Isab, A. A.; Ahmad, S. J.
Inorg. Biochem. 2002, 88, 53-60. (h) Dickson, P. N.; Wehrli, A.;
Geier, G. Inorg. Chem. 1988, 27, 2921-2925. (i) Tzeng, B.-C.; Chan,
C.-K.; Cheung, K.-K.; Che, C.-M.; Peng, S.-M. J. Chem. Soc., Chem.
Commun. 1997, 135-136.
(
2
I) complexes containing pyridine-4-thione (4-PS), pyridine-
2
c,d,3
2b,c,3b-d,f,g,4
-thione (2-PS),
or similar ligands
have been
reported. While coordinated to the Au atom through S, these
ligands may coordinate to other transition metals through
*
To whom correspondence should be addressed. E-mail: timo.repo@
helsinki.fi. Tel.: +358-9191-50194. Fax: +358-9191-50198.
†
University of Helsinki.
Johann Wolfgang Goethe-Universit a¨ t Frankfurt am Main.
‡
(
1) See for example (a) Dash, K. C.; Schmidbaur, H. Met. Ions Biol. Syst.
1
982, 14, 179-205. (b) Lorber, A.; Simon, T. M. Gold Bull. 1979,
12, 149-158. (c) Sutton, B. M.; McGusty, E.; Walz, D. T.; DiMartino,
M. J. J. Med. Chem. 1972, 15, 1095-1098. (d) Shaw, C. F.; III; Beery,
A.; Stocco, G. C. Inorg. Chim. Acta 1986, 123, 213-216. (e) Bain,
C. D.; Whitesides, G. M. Angew. Chem., Int. Ed. 1989, 28, 506-512.
(f) Gold. Progress in Chemistry, Biochemistry and Technology;
Schmidbaur, H., Ed.; John Wiley and Sons Ltd.: London, 1999.
2) (a) Nunokawa, K.; Onaka, S.; Mizuno, Y.; Okazaki, K.; Sunahara,
T.; Ito, M.; Yaguchi, M.; Imai, H.; Inoue, K.; Ozeki, T.; Chiba, H.;
Yosida, T. J. Organomet. Chem. 2005, 690, 48-56 and references
therein. (b) Nunokawa, K.; Onaka, S.; Tatematsu, T.; Ito, M.; Sakai,
J. Inorg. Chim. Acta 2001, 322, 56-64 and references therein. (c)
Onaka, S.; Yaguchi, M.; Yamauchi, R.; Ozeki, T.; Ito, M.; Sunahara,
T.; Sugiura, Y.; Shiotsuka, M.; Nunokawa, K.; Horibe, M.; Okazaki,
K.; Iida, A.; Chiba, H.; Inoue, K.; Imai, H.; Sako, K. J. Organomet.
Chem. 2005, 690, 57-68 and references therein. (d) Jia, G.; Pud-
dephatt, R. J.; Vittal, J. J. Polyhedron 1992, 11, 2009-2014.
(
9954 Inorganic Chemistry, Vol. 46, No. 23, 2007
10.1021/ic700453t CCC: $37.00
© 2007 American Chemical Society
Published on Web 10/11/2007

Gold(I) Pyridinethione Complexes
Scheme 1. Synthesis of Complexes 1-4a
Characteristic of gold(I) complexes in the solid state are
the short-range Au‚‚‚Au contacts which arise from correlation
6
and relativistic effects. Such ‘aurophilic’ interactions have
4
b,6a,7
comparable strength with hydrogen bonding.
Agostic
8
interactions in gold complexes have not received as much
attention as the other secondary interactions. In general, these
are weak, short-range interactions that can be present in an
electron-deficient metal complex with a free coordination
site, assuming that the ligand framework is not sterically too
hindered and the electronic effects do not prevent the
9
interaction. In an agostic interaction an intramolecular
σ-bond, such as C-H, of the ligand orients toward a metal
center. These kinds of interactions have an essential role for
example in catalytic olefin polymerization.10 Experimental
evidence for the presence of the agostic interactions has been
obtained by means of X-ray and neutron diffraction and
NMR spectroscopy. Density functional theory (DFT) is the
method most often applied in calculations.9
,11
The presence of C-H‚‚‚Au agostic interactions have been
reported for only a few gold thione12 and phosphine
complexes. In general, studies of C-H‚‚‚metal agostic
interactions including both crystallographic measurements
and theoretical considerations are rare, and for Au complexes,
such studies do not exist.14 Herein, the syntheses and the
solid-state structures of two Au(I) bis(pyridinethionato)
complexes (1-2, Scheme 1) are described. These complexes
are of particular interest, as they are considered to play a
13
a
All reactions were performed at room temperature in MeOH using
HAuCl4‚4H2O as a starting material. For the successful synthesis of 1, 2,
and 4, 4 equiv of the ligand were needed, while 3 formed with 2 equiv.
The unambiguous structure of 3 remained unclear.
key role in the oxidation of elemental gold by O
2
in alcohol
solutions.15 Both complexes were modeled using the DFT
method together with one additional gold species which was
observed during the ionization of 1 and 2. According to the
calculations, agostic interactions are present in all of these
complexes even though the interactions are inherently
(
(
(
5) Crespo, O.; Fern a´ ndez, E. J.; Jones, P. G.; Laguna, A.; L o´ pez-de-
Luzuriaga, J. M.; Monge, M.; Olmos, M. E.; P e´ rez, J. Dalton Trans.
2003, 1076-1082.
6) (a) Schmidbaur, H. Gold. Bull. 2000, 33, 3-10. (b) Pyykk o¨ , P.; Zhao,
Y. Angew. Chem., Int. Ed. Engl. 1991, 30, 604-605. (c) Pyykk o¨ , P.
Angew. Chem., Int. Ed. 2004, 43, 4412-4456.
13a
weak.
7) (a) Schmidbaur, H. Gold Bull. 1990, 23, 11-21. (b) Schmidbaur, H.;
Scherbaum, F.; Huber, B.; M u¨ ller, G. Angew. Chem., Int. Ed. Engl.
Experimental Section
1
988, 27, 419-421. (c) Tzeng, B.-C.; Schier, A.; Schmidbaur, H.
1
13
Inorg. Chem. 1999, 38, 3978-3984.
General. H and C NMR spectra were measured with a Varian
Gemini 200 apparatus and ESI -TOF MS with a Bruker micrOTOF
(
8) Brookhart, M.; Green, M. L. H. J. Organomet. Chem. 1983, 250, 395-
+
408.
mass spectrometer. IR spectra were recorded with a Perkin-Elmer
Spectrum One, and elemental analyses were performed with an EA
1110 CHNS-O CE instrument. All chemicals were purchased from
Aldrich and used as received. Crystals suitable for X-ray measure-
ments were selected and mounted on a glass fiber using the oil
drop method,16 and the data were collected at 173 or 123 K using
a Nonius KappaCCD diffractometer. The intensity data were
corrected for Lorentz and polarization effects and for absorption
by the multiscan method. The crystal structures were solved using
either SIR200218a or SHELX9718b and refined with SHELX97.
Graphics were obtained using the SHELXTL program package.
All nonhydrogen atoms were refined anisotropically except in
2-pyridinium disulfide dichloride, where a disordered methanol
solvent was refined isotropically. The hydrogen atoms were
(
9) (a) Clot, E.; Eisenstein, O. Principles and Applications of Density
Functional Theory in Inorganic Chemistry I; Kaltsoyannis, N.,
McGrady, J. E., Eds.; Springer-Verlag: Berlin, Heidelberg, 2004; Vol.
1
12, pp 2-4. (b) Calhorda, M. J. Chem. Commun. 2000, 801-809.
(
10) see for example (a) Meier, R. J.; Aagaard, O. M.; Buda, F. J. Mol.
Catal. A 2000, 160, 189-197. (b) Zeller, A.; Strassner, T. J.
Organomet. Chem. 2006, 691, 4379-4385. (c) Mashima, K.; Naka-
mura, A. J. Organomet. Chem. 1992, 428, 49-58. (d) Grubbs, R. H.;
Coates, G. W. Acc. Chem. Res. 1996, 29, 85-93.
11) (a) Kr u¨ ger, S.; Stener, M.; Mayer, M.; N o¨ rtemann, F.; R o¨ sch, N. J.
Mol. Struct. (Theochem) 2000, 527, 63-74. (b) Popelier, P. L. A.;
Logothetis, G. J. Organomet. Chem. 1998, 555, 101-111 and
references therein.
(
17
18b
19
(
12) (a) Friedrichs, S.; Jones, P. G. Z. Naturforsch. 2004, 59b, 49-57. (b)
Friedrichs, S.; Jones, P. G. Z. Naturforsch. 2004, 59b, 793-801. (c)
Friedrichs, S.; Jones, P. G. Z. Naturforsch. 2004, 59b, 1429-1437.
13) (a) Baukova, T. V.; Kuz’mina, L. G.; Oleinikova, N. A.; Lemenovskii,
D. A.; Blumenfel’d, A. L. J. Organomet. Chem. 1997, 530, 27-38.
(
(b) Baukova, T. V.; Kuz’mina, L. G.; Oleinikova, N. A.; Lemenoskii,
D. A. IzV. Akad. Nauk, Ser. Khim. 1995, 2023-2034.
(16) Kottke, T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615.
(17) Nonius COLLECT; Nonius BV: Delft, The Netherlands, 2002.
(18) (a) Burla, M. C.; Camalli, M.; Carrozzini, G. L.; Cascarano, G.;
Giacovazzo, C.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 2003,
36, 1103. (b) Sheldrick, G. M. SHELX97 Program for the Solution
and Refinement of Crystal Structures; University of G o¨ ttingen:
G o¨ ttingen, Germany, 1997.
(
14) (a) Brady, E. D.; Clark, D. L.; Gordon, J. C.; Hay, P. J.; Keogh, D.
W.; Poli, R.; Scott, B. L.; Watkin, J. G. Inorg. Chem. 2003, 42, 6682-
6
690. (b) Cooper, A. C.; Clot, E.; Huffman, J. C.; Streib, W. E.;
Maseras, F.; Eisenstein, O.; Caulton K. G. J. Am. Chem. Soc. 1999,
1
21, 97-106. (c) Ujaque, G.; Cooper, A. C.; Maseras, F.; Eisenstein,
O.; Caulton K. G. J. Am. Chem. Soc. 1998, 120, 361-365.
(
15) R a¨ is a¨ nen, M. T.; Kemell, M.; Leskel a¨ , M.; Repo, T. Inorg. Chem.
(19) Sheldrick, G. M. SHELXTL Version 5.10; Bruker AXS Inc.: Madison,
WI, 1997.
2007, 46, 3251-3256.
Inorganic Chemistry, Vol. 46, No. 23, 2007 9955

R a1 is a1 nen et al.
Figure 1. Tautomeric and mesomeric forms of pyridine-4-thiol. Pyridine-
-thiol has corresponding forms.
2
Figure 2. Solid-state structure of bis(2-pyridinium)disulfide dichloride
which forms during the synthesis of 1. Crystals suitable for X-ray
measurement were obtained from a saturated MeOH solution. A disordered
solvent molecule with a site occupation factor of 0.5 has been omitted for
clarity. Displacement ellipsoids are depicted at the 30% probability level,
and hydrogen bonds are represented by dashed lines. Selected bond lengths
and angles are given in the Supporting Information.
introduced into their calculated positions or were picked from
residual electron density map and refined with fixed geometry with
respect to their carrier atoms.
Synthesis of Gold Complexes 1-4. Bis(pyridine-2-thionato)-
gold(I) chloride (1) was synthesized under Ar atmosphere using
the standard Schlenk techniques. 2-PS (0.718 g, 6.46 mmol) and
Figure 3. (a) Solid-state structure of Au(I) complex 1 bearing 2-PS ligands.
Chloride as a counterion, disordered atoms, and hydrate are not shown for
clarity. Displacement ellipsoids appear at the 30% probability level and
hydrogen atoms are in their calculated positions. (b) The modeled structure
of 1 with two C-H‚‚‚Au (2.884 Å) agostic interactions. (c) The modeled
structure of the unsymmetric conformer with one C-H‚‚‚Au (2.890 Å) and
one N-H‚‚‚Au (2.593 Å) agostic interaction. (d) The modeled structure of
the conformer with two N-H‚‚‚Au (2.659 Å) agostic interactions. The
γ-agostic interactions are represented by dashed lines.
HAuCl
4 2
‚4H O (0.665 g, 1.61 mmol) were dissolved in dry MeOH
(30 mL), and the immediately formed suspension was stirred for 3
h. The suspension was filtered in air and solvents were removed
from the filtrate in a vacuum, yielding a crude product of 1 as a
yellow powder that was purified by recrystallization from MeOH
(
0.51 g, 70%). Needles suitable for X-ray crystallographic measure-
ment were obtained from CHCl (Figure 3a). Anal. Calcd for
Cl Au : C 26.41, H 2.22, N 6.16, S 14.10; Found: C
7.13, H 2.21, N 5.50, S 13.87%. H NMR (200 MHz, CDCl
.21 (s, 2H, CH), 7.68 (s, 4H, CH), 8.30 (s, 2H, CH), 15.53 (s,
3
C
10
H N S
10 2 2
1
1
1
acetonitrile, and THF were added. Anal. Calcd for C10
Au : C 26.41, H 2.22, N 6.16, S 14.10; Found: C 26.79, H 2.27,
N 6.08, S 13.52%. H NMR (200 MHz, DMSO-d
H, CH), 8.22 (s, 4H, CH) ppm. 13C NMR (50 MHz, DMSO-d
δ 127.39, 137.12, 174.17 ppm. IR: ν ) 787 (CH), 1461 (pyridine
10 2 2 1
H N S Cl -
2
7
2
1
3
): δ
1
1
H, NH) ppm. 1 C NMR (50 MHz, CDCl
3
6
): δ 7.86 (s,
):
3
): δ 118.21, 130.23,
4
6
39.42, 141.04, 166.23 ppm. IR: ν ) 750 (CH), 1446 (pyridine
-
1
3d,20
ring), 1583 (pyridine ring), 1606 cm (pyridine ring).
(
HRMS
]+ 419 (100, calcd 418.995,
10 2 2 1
ESI -TOF) m/z (%):[C10H N S Au
-
1
3d,20
+
ring), 1589 (pyridine ring), 1613 cm (pyridine ring).
HRMS
+
+
found 418.993, error 4.49 ppm), 496 (34), 725 (15). A considerable
amount (0.36 g) of a side-product was obtained as a yellow powder
when the MeOH suspension was filtered. According to X-ray
crystallographic measurement from the needles formed in MeOH,
the side-product is a bis(2-pyridinium)disulfide dichloride (5, Figure
(ESI -TOF) m/z (%): [C10H N S Au ] 419 (100, calcd 418.9945,
10 2 2 1
found 418.9969, error 1.30 ppm), 496 (1), 726 (3).
Di(4-pyridyl)disulfide gold(III) trichloride (3) was prepared by
3
adding MeOH (7 mL) and CHCl (5 mL) to the Schlenk containing
HAuCl ‚4H O (0.23 g, 0.57 mmol) and di(4-pyridyl)disulfide (0.25
4
2
2
).
Bis(pyridine-4-thionato)gold(I) chloride (2) was synthesized by
a similar method as that for complex 1, starting from HAuCl
O (0.100 g, 0.24 mmol) and 4-PS (0.110 g, 0.99 mmol) in 10
g, 1.13 mmol). The bright yellow suspension which was formed
immediately was stirred at room temperature for 2 h. The suspension
was filtered and the obtained yellow powder was washed with
MeOH and dried in a vacuum (0.23 g, 77%). Complex 3 is slightly
4
‚
4H
2
mL of MeOH. The yellow precipitate obtained was washed with
MeOH and dried in a vacuum (0.068 g, 62%). Crystals suitable
for X-ray analysis were obtained by a slow evaporation of solvents
from the MeOH filtrate to which small amounts of EtOH,
soluble in DMSO. Anal. Calcd for C10
H
8
N
2
S
2
Cl
3 1
Au : C 22.94, H
1
.54, N 5.35, S 12.25; Found: C 23.08, H 1.71, N 5.08, S 12.16%.
1
): δ 8.01 (d, 3JHH ) 6.4 Hz, 4H,
): δ
22.14, 144.23, 153.68 ppm. IR: ν ) 793 (CH), 1479 (pyridine
H NMR (200 MHz, DMSO-d
CH), 8.72 (s, 4H, CH) ppm. 13C NMR (50 MHz, DMSO-d
1
6
6
(
20) Colthup, N. B.; Daly, L. H.; Wiberley, S. E. Introduction to Infrared
-
1
ring), 1566 (pyridine ring), 1600 (pyridine ring), 1618 cm
and Raman Spectroscopy, 2nd ed.; Academic Press, Inc.: New York,
(pyridine ring).20 HRMS (ESI -TOF) MS m/z (%): 325 (34), 380
+
1975; p 322.
9956 Inorganic Chemistry, Vol. 46, No. 23, 2007

Gold(I) Pyridinethione Complexes
Table 1. Cell Parameters and Specific Data Collection Parameters for 1, 2, and 5
1
2
5
a
formula
fw (g mol-1)
T (K)
C10H12N2OS2ClAu
472.75
173(2)
C10H12N2OS2ClAu
454.74
123(2)
C10H10N2S2Cl2‚×baCH3OH
307.23
173(2)
cryst syst
space group
unit cell dimens
a (Å)
b (Å)
c (Å)
monoclinic
C2/c
monoclinic
C2/c
monoclinic
P21/n
14.837(1)
13.797(1)
6.995(1)
100.15(1)
1409.4(2)
4
10.030(2)
10.860(2)
11.787(2)
98.04(1)
1271.3(4)
4
5.389(1)
11.128(1)
23.774(2)
90.73(2)
1425.6(3)
4
â(°)
3
V (Å )
Z
Dcalc (Mg m-3)
2.228
10.908
2.376
1.436
0.730
abs coeff (mm-1)
12.083
0.25 × 0.12 × 0.06
9164
1448
78
0.0176
0.0382
1.558
3
cryst dimens (mm )
no. of data collected
no. of data refined
no. of params
0.50 ×0.09 × 0.07
0.50 × 0.04 ×0.03
9576
8229
1516
135
0.0354
0.0964
2127
154
0.0489
0.1409
0.550
b
R1 [I > 2σ(I)]
c
wR2 (all data)
residual density (e Å-3)
1.331
a
Disordered methanol was refined isotropically using a site occupation factor 0.5. b R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑[w(Fo - Fc ) ]/∑[w(Fo ) ]]1/2.
c
2
2 2
2 2
(
5
48), 419 (72), 453 (100), [C10
22.8933, found 522.8942, error -1.70 ppm).
Phenylthiolate)gold(I) (4) was synthesized by adding thiophenol
0.25 mL, 2.43 mmol) into a yellow MeOH (7 mL) solution of
HAuCl ‚4H O (0.25 g, 0.61 mmol). The yellow suspension im-
H
9
N
2
S
2
Cl
3
Au
1
]+ 523 (46, calcd
augmented with double polarization functions, TZVPP, together
with the corresponding auxiliary density-fitting (RI) basis set, as
implemented in TURBOMOLE. On gold we employed a 19-valence
electron scalar relativistic pseudopotential together with a
(9s7p5d2f)/[7s5p3d2f] basis set.26 All geometries were fully
optimized and they represent minimum structures, as confirmed
by vibrational frequency calculations (Supporting Information).
(
2
5
(
4
2
mediately formed was stirred at room temperature for 2 min. After
filtration, washing with MeOH, and drying in a vacuum, the
complex was obtained as a yellow powder (0.09 g, 70%). The
complex was insoluble in common solvents; therefore, NMR spectra
Results and Discussion
could not be obtained.21 Anal. Calcd for C
.65, S 10.47; Found: C 23.34, H 1.40, S 10.27%. IR: ν ) 733
CH), 1022 (benzene ring), 1437 (benzene ring), 1473 (benzene
6
5 1 1
H S Au : C 23.54, H
The chemical reactivity of pyridinethiols and their coor-
dination chemistry with Au is related to their tautomeric and
mesomeric forms: thiol, thione, and zwitterionic form
(Figure 1). Depending on the reaction, they can act as a
typical anionic thiolato ligand or when in the thione form as
a neutral ligand. The zwitterionic structure is an important
intermediate having certain flexibility in the coordination
mode. For example, in the recently reported oxidation of
elemental gold the zwitterionic form of the 4-PS specifically
1
(
-
1
20
ring), 1576 (benzene ring), 3051 cm (CH). EI-MS m/z (%):
+
+
+
[
[
C
C
6
H
5
S] 109 (100), [C12
]+ 218 (99). It is noteworthy that, if the reaction is
10 2
S
H
10
]
9
154 (27), [C12H S] 185 (28),
12
H
continued for more than ca. 1 h, the color of the suspension begins
to change: first to white, then to light gray, and finally to pale
violet. After 22 h of stirring, the suspension was filtered and the
pale violet powder was washed with MeOH and dried in a vacuum.
This product was also completely insoluble in common solvents.
According to elemental analysis, the product is a 1:1 mixture of
15
has a crucial role. In solution, pyridinethiols have a
27
13
preference for the thione form and according to C NMR
data, 2- and 4-PS favor the thione form in MeOH solution.
While crystallizing from MeOH, this isomer remains.28
Au(I) thionato complexes 1 and 2 bearing 4-PS and 2-PS,
respectively, were synthesized in MeOH at room temperature
(phenylthiolate)gold(I) and gold(I) chloride (C
6 5 2 1 2
H S Cl Au , Calcd
C 13.38, H 0.94, S 5.95; Found: C 13.42, H 0.93, S 5.85%). EI-
+
+
6 5 10 2
MS m/z (%):[C H S] 109 (92), [C12H S ] 218 (100). When the
solvent was evaporated from the MeOH filtrate, colorless needles,
which were identified by X-ray crystallography as diphenyl
disulfide, were crystallized as a side-product (Supporting Informa-
tion).
with high yields from corresponding thiols and HAuCl ‚
4
4H O. From these complexes 1 was previously reported as
2
Computational Methods. All quantum chemical calculations
were performed with the TURBOMOLE program package22 version
(24) (a) Eichkorn, K.; Treutler, H.; O¨ hm, O.; H a¨ ser, M.; Ahlrichs, R. Chem.
Phys. Lett. 1995, 242, 652-660. (b) Eichkorn, K.; Weigend, F.;
Treutler, O.; Ahlrichs, A. Theor. Chem. Acc. 1997, 97, 119-124.
5
.8. The geometric structures were optimized using the gradient-
2
3
corrected functional BP86. The resolution of the identity (RI)
approximation of the Coulomb interaction24 was used in the
calculations. We employed the standard triple-ú valence basis set
(
25) Andrae, D.; H a¨ ussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor.
Chim. Acta 1990, 77, 123-141.
(
26) (a) Gilb, S.; Weis, P.; Furche, F.; Ahlrichs, R.; Kappes, M. M. J. Chem.
Phys. 2002, 116, 4094-4101. (b) Pyykk o¨ , P.; Runeberg, N.; Men-
dizabal, F. Chem. Eur. J. 1997, 3, 1451-1457.
(
(
(
21) Bachman, R. E.; Bodolosky-Bettis, S. A.; Glennon, S. C.; Sirchio, S.
(27) Stoyanov, S.; Petkov, I.; Antonov, L.; Stoyanova, T.; Karagiannidis,
P.; Aslanidis, P. Can. J. Chem. 1990, 68, 1482-1489.
A. J. Am. Chem. Soc. 2000, 122, 7146-7147.
22) Ahlrichs, R.; B a¨ r, M.; H a¨ ser, M.; Horn, H.; K o¨ lmel, C. Chem. Phys.
Lett. 1989, 162, 165-169.
(28) (a) Etter, M. C.; MacDonald, J. C.; Wanke, R. A. J. Phys. Org. Chem.
1992, 5, 191-200. (b) Flakus, H. T.; Tyl, A.; Jones, P. G. Spectrochim.
Acta Part A. 2002, 58, 299-310. (c) Muthu, S.; Vittal, J. J. Cryst.
Growth Des. 2004, 4, 1181-1184.
23) (a) Becke, A. D. Phys. ReV. A 1988, 38, 3098-3100. (b) Perdew, J.
P. Phys. ReV. B 1986, 33, 8822-8824.
Inorganic Chemistry, Vol. 46, No. 23, 2007 9957

R a1 is a1 nen et al.
porting Information) was observed also in the synthesis of
4
starting from HAu(III)Cl
As reported previously, gold complexes bearing 2-PS
ligands are more soluble than their analogues bearing 4-PS
4
and thiophenol.
2
d
ligands. In accordance with this, complex 1 is soluble in
common solvents whereas 2 is only slightly soluble in DMSO
and MeOH. Single crystals suitable for X-ray analysis were
3
easily obtained for 1 in CHCl , while freshly prepared 2 was
successfully recrystallized from MeOH. The crystal structure
of 1 revealed two independent complex molecules with a
site occupation factor of 0.5 (Figure 3a and Table 1). The
structure is fully disordered, which implies that the -S1-
Au-S1A- molecule occupies every second crystallographic
site while the -S2-Au-S2A- molecule occupies the other
sites. The latter is spatially approximately at a right angle to
the former with the gold atom lying always at the center of
3
0
the symmetry. In general, Au(I) complexes prefer a linear
3
c,f
Figure 4. (a) Solid-state structure of complex 2 bearing 4-PS ligands.
Displacement ellipsoids appear at the 50% probability level, and hydrogen
atoms are in their calculated positions except the ones bonded to N atoms
which were situated from the difference map. (b) Computationally optimized
structure of cationic gold(I) complex 2. The agostic interactions and the
N-H‚‚‚Cl hydrogen bond (Å) are represented by dashed lines.
geometry and due to symmetric reasons the S-Au-S
angle in 1 is exactly 180.0°.
In the solid-state structure of 2, the Au atom lies at the
center of symmetry with equiplanar ligand coordination
Figure 4a and Table 1). The S-Au-S angle is 180° and
(
the coordination sphere of the Au(I) is accomplished by
two γ-agostic interactions (C-H‚‚‚Au distances are 2.86 Å).
In the structure Cl counterion forms a moderately strong
a side-product during the synthesis of chloro-(2-(N,N-
dimethylammoniummethyl)phenyl)-bis(2-mercaptopyridium)-
3
b
gold(III) chloride when an excess of 2-PS was used. In
complex synthesis a rapid reduction of Au(III) to Au(I) was
observed when excess of thiol was present. Some thiol was
oxidized simultaneously with the Au(III) reduction to dis-
ulfide. For example, bis(2-pyridinium)disulfide dichloride
was formed as a side-product during the synthesis of 1
31
N-H‚‚‚Cl hydrogen bonding (2.09(4) Å) that results in the
ion lying practically in the same plane as the rest of the
complex. In all, a variety of secondary interactions are present
in the solid-state structure of 2 and it is clear that they are
competing with each other and the resulting continuous
supramolecular network is a compromise between them. In
this structure aurophilic interactions are overruled by the
(
Figure 2, Table 1). Although HAu(III)Cl
4
is commonly used
2
9
as a starting material for the synthesis Au(I) complexes,
3
2
other weak interactions.
the mechanism for the Au(III) reduction with thiols is not
unambiguously understood. According to the results above,
it seems to be analogous with the classical organometallic
The Au-S bond lengths in 1 and 2 (2.305(3) and 2.312-
(4) Å for 1 and 2.2942(9) Å for 2) are in the range reported
2a-d,3a-c,4a
chemistry. When HAu(III)Cl
- or 4-PS, bis(pyridinium-2-thiolato)gold(III) chloride or bis-
pyridinium-4-thiolato)gold(III) chloride and two HCl mol-
4
is treated with an excess of
for gold thiolato and thione complexes,
but the C-S
2
(
bonds (1.700(5) and 1.734(6) Å for 1 and 1.736(3) Å for 2)
possess significant double bond character, as they are
noticeably shorter than the sum of covalent radii of C and S
ecules are presumably formed. The former can then undergo
reductive elimination, and as a result disulfide and Au(I) are
observed. Due to the reaction, disulfide was isolated as the
HCl salt. On the basis of the results above, it is clear why,
for example, complex 2 is not achievable when starting from
di(4-pyridyl)disulfide. Instead, a gold(III) complex (3) with
an intact S-S bond was obtained (Scheme 1). The reductive
elimination of Au(III) and the formation of disulfide (Sup-
3
3
(1.81 Å), and resemble the value measured for the free
thione ligand (1.717(2) Å, see Supporting Information). This,
together with two different trends in C-C bond distances
(1.365-1.378 and 1.409-1.436 Å) in the pyridyl rings of
the complexes, indicates that the ligands are coordinated in
1
3
the thione form. Furthermore, C NMR spectra support the
thione form. In the spectrum of 4-PS, a shift of the C-S
Table 2. Selected Bond Lengths and Angles in the Measured and Modeled Structures of Complexes 1 and 2
measured 1
modeled 1
modeled 1a
measured 2
modeled 2
Au-S (Å)
C-S (Å)
C-N (Å)
2.305(3) 2.312(4)
1.734(6) 1.700(5)
1.37
2.315 2.315
1.724 1.724
1.361
2.264 2.264
1.710 1.710
1.350
2.2942(9)
1.736(3)
1.355(4)
1.356(4)
2.316 2.316
1.717 1.717
1.363
1
1
1
.40
.37
.41
1.377
1.360
1.365
S-Au-S (deg)
C-H‚‚‚Au (Å)
180
2.83
180.0
2.884
180.0
2.768
180.00(4)
2.86
179.9
2.863
2.88
a
Results obtained at the MP2 level.
958 Inorganic Chemistry, Vol. 46, No. 23, 2007
9

Gold(I) Pyridinethione Complexes
Table 3. Distances of C-H‚‚‚Au Agostic Interactions in Gold(I) Complexes.
complex
C-H‚‚‚Au (Å)
2.95, 3.07
2.83, 2.85, 2.91, 3.19
3.07, 3.09
3.16, 3.20
2.93
ref
12c
12c
12b
12b
12a
bis(imidazolidine-2-thione)gold(I) di(methanesulfonyl)amide
bis(1-methyl-imidazolidine-2-thione)gold(I) di(methanesulfonyl)amide
bis(imidazolidine-2-thione)gold(I) camphor-10-sulfonate
bis(1-methyl-imidazolidine-2-thione)gold(I) camphor-10-sulfonate
bis(imidazolidine-2-thione)gold(I) chloride
bis(1-methyl-imidazolidine-2-thione)gold(I) chloride
µ-diphenylphosphinoethane-bis-aurio(2,2′-diphenylmethane)
2.80, 3.09
2.62
2.75, 3.00
2.92, 3.01, 3.06
2.6, 3.0
12a
13a
13a
13a
13a
13b
(
(
(
µ2-1,2-bis(o-phenylene)ethane)-bis(triphenylphosphine-gold(I))
µ2-2,2′-bis(phenylene)methane)-(µ2-1,2-bis(diphenylphosphino)ethane-di-gold(I)
µ4-1,2-bis(phenylene)ethane)-tetrakis(triphenylphosphine-gold(I)) bis(tetrafluoroborate)
µ-diphenylphosphinoethane-bis-aurio(2,2′-diphenylmethane)
2.63
1
2
2.83, 2.88
2.86
this work
this work
carbon appears at 190.34 ppm relative to DMSO-d
at 176.23 ppm, relative to CDCl ) and in the spectrum of 2
at 175.38 ppm in DMSO-d (in 1 at 164.93 ppm in CDCl ).
When the measured crystal structures of 1 and 2 are
compared with their modeled structures, they appear to be
very similar (Figures 3a,b and 4, Table 2). For both
complexes, the energetic minimum (their energies are
virtually the same) is achieved with an overall planar
geometry and linear coordination of the gold(I) ion. In the
modeled structures, the C-H‚‚‚Au γ-agostic distances are
6
(in 2-PS
interactions are competing with each other, even small
modifications in complex structure can change the relative
strength of the interactions. For example, the crystal structure
of bis(pyridine-2-thionato)gold(I) perchlorate, differing from
1 only by the counterion, has been previously determined,3c
but the structure of this complex appears to be different. In
bis(pyridine-2-thionato)gold(I) perchlorate structure, auro-
philicity is clearly present as pentameric clusters of the Au
complex are formed having Au‚‚‚Au distances of ca. 3.3 Å.1
Aurophilic interactions are weaker in 1, as the shortest
measured Au‚‚‚Au distance is 3.50 Å. Instead, γ-agostic
interactions, absent from the structure with the perchlorate
counterion, provide additional stabilization for 1 and strengthen
its overall planar geometry.
3
6
3
4b
2.884 and 2.863 Å for 1 and 2, respectively, whereas in the
measured structures, which have hydrogen atoms in their
calculated positions, these distances are 2.83 and 2.88 Å for
1
and 2.86 Å for 2.34 The agostic interaction with ca. 2.8 Å
13a
+
distance can be considered to be fairly weak. Nevertheless,
they provide additional stabilization for the Au(I) complexes
studied. For comparison, we calculated the optimized
structures of two other possible conformers for 1 (Figure
During the ESI -MS analysis of gold(I) thione complexes
1 and 2, the formation of several gold species (m/z ) 496,
615, 692, 726, 803, and 922) was observed. Previously,
similar behavior has been reported in FAB-MS measure-
2
d
3c,d). These conformers correspond to structures with one
ments. On the basis of high-resolution MS identification,
these species have either one of the following ligands or
different combinations of them: pyridine-4-thione, pyridine-
4-thiolato, and di(4-pyridyl)sulfide. It should be emphasized
C-H‚‚‚Au and one N-H‚‚‚Au or two N-H‚‚‚Au γ-agostic
interactions, respectively. The calculated energies of these
three conformers are virtually identical.
So far, the agostic interactions are known only for six other
(
29) (a) Li, C.-K.; Cheng, E. C.-C.; Zhu, N.; Yam, V. W.-W. Inorg. Chim.
Acta 2005, 358, 4191-4200. (b) Steigelmann, O.; Bissinger, P.;
Schmidbaur, H. Angew. Chem. 1990, 102, 1473-1475. (c) Schmid-
baur, H.; Wohlleben, A.; Wagner, F.; Orama, O.; Huttner, G. Chem.
Ber. 1977, 110, 1748-1754.
1
2
gold complexes bearing heterocyclic ligands.
The
C-H‚‚‚Au distances in 1 (2.83 and 2.88 Å) and 2 (2.86 Å)
are in the middle of the range of agostic interactions
previously reported for gold(I) complexes (Table 3). As weak
(30) It is probable that in the crystal of 1 several hydrogen bonds stabilize
the internal structure (see Supporting Information). However, the
intermolecular hydrogen bonding has to be studied very carefully
because chloride ions, as well as water molecules with a site occupation
factor of 0.5, occupy only every second site from the symmetry allowed
sites deduced from the coordinates.
(
31) Steiner, T., Angew. Chem., Int. Ed. 2002, 41, 48-76.
(
32) Another polymorph of 2 was also obtained where the molecules are
stacked one upon the other with Au‚‚‚Au distances of ∼3.44 Å, which
is an indication of aurophilic interactions. The polymorph was obtained
in space group P21/n by crystallization from MeOH or EtOH/2-
propanol (3:1 v/v). Unit cell: a ) 17.011(3) Å, b ) 11.425(2) Å, c
3
)
6.793(1) Å, â ) 99.79(3)°, V ) 1301.0(4) Å , Z ) 4. The crystals
were twins with at least three different domains. Due to the quality of
the data, C and N atoms could be only refined isotropically (even
after treatment as a twin).
(
33) Robinson, W. R.; Odom, J. D.; Holtzclaw, H. F., Jr. General Chemistry,
10th ed.; Houghton Mifflin Company: Boston, 1997; p 172.
(
34) It should be noted that in the measured structures of 1 and 2 C-H
bond length used for aromatic hydrogens is 0.95 Å, whereas in the
corresponding calculated structures the C-H bond length is 1.087 or
1
.088 Å. Therefore, the similarity of the measured and modeled
Figure 5. Computationally optimized structure of gold(I) cation (m/z )
structure is better seen by comparing the Cagostic‚‚‚Au distances. For
1 the measured distance is 3.432(6) and 3.374(6) Å vs 3.494 Å in the
modeled structure and for 2 the 3.410(3) Å (measured) and 3.471 Å
(modeled).
+
4
96, C15H13N3S2Au) observed in the gas phase during ESI -MS measure-
ments of 1 and 2. The agostic interactions (Å) are represented by dashed
lines.
Inorganic Chemistry, Vol. 46, No. 23, 2007 9959

R a1 is a1 nen et al.
that these species are present only in the gas phase. The
cation m/z ) 496 was modeled, and its optimized structure
is given in Figure 5. The ligands of the Au(I) cation are 4-PS
and di(4-pyridyl)sulfide, both having a coordination bond
to Au. Also in this structure the presence of two γ-agostic
interactions with distances of 2.891 and 2.900 Å provide an
energetic minimum. Calculated IR spectra of this species,
together with the spectra of the cations of 1 and 2, are given
in the Supporting Information.
in Au(I) complexes. As Au(I) cannot be considered to be
very electron deficient, it is reasonable that the γ-agostic
interactions observed are relatively weak. In spite of this,
they provide additional stabilization for the structures. Weak
interactions are competing with each other in the packing
of the complexes, which indicates their similar strength. For
example, weak aurophilic interactions are present in 1,
whereas in 2 they are overruled by hydrogen bonding and
agostic interactions.
Conclusions
Acknowledgment. The financial support of the Magnus
Ehrnrooth Foundation, the University of Helsinki, and
Academy of Finland (209739, 204408, 200903, 206102) is
gratefully acknowledged. P.P. and N.R. belong to the Finnish
Centre of Excellence in Computational Molecular Science.
The computational resources were partially provided by the
Center for Scientific Computing (CSC), Espoo, Finland.
1
and 2 were synthesized from HAuCl
4 2
‚4H O and pyri-
dine-2-thiol or pyridine-4-thiol, respectively. Simultaneous
reduction of Au(III) and formation of disulfide indicate that
the reaction proceeds via a reductive elimination mechanism.
Due to the presence of the thione form of the ligand, N in
the heterocycle carries a proton and loses its ability to
coordinate with Au.
The solid-state and calculated structures of 1 and 2
revealed distinctive planar geometry and linear coordination
for Au(I) complexes, regardless of the relative position of
the nitrogen atom in the pyridine moiety. The distances of
the C-H‚‚‚Au agostic interactions observed are in ac-
cordance with the previously reported agostic interactions
Supporting Information Available: Crystallographic data for
complexes 1 and 2, bis(2-pyridinium)disulfide dichloride methanol
solvate, diphenyl disulfide, and pyridine-4-thione; calculated
vibrational spectra for all the computationally studied species.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC700453T
9960 Inorganic Chemistry, Vol. 46, No. 23, 2007