Coordination of the Hetero(N,S)-bidentate Ligand 1-Methyl-2-(methylthiomethyl)-1H-benzimidazole to [(Ph3P)Au]+ Exclusively through the Imine Nitrogen Donor

Article abstract of DOI:10.1515/znb-1999-1221

1-Methyl-2-(methylthiomethyl)-1H-benzimidazole (mmb, N^∧S) was reacted with Ph₃PAuCl/AgPF₆ in THF to yield [(Ph₃P)Au(mmb)](PF₆) which could be crystallographically characterized. The Au⁺ ion is almost linearly coordinated by the triphenylphosphine P and the imine N atom of a monodentate N^∧S ligand. There is no gold(I)-sulfur bonding as the distance of ca. 3.02 A indicates. Similarly, close intermetallic contacts between the gold centers are absent. Both effects are attributed to the positive charge on the metal.

Full text of DOI:10.1515/znb-1999-1221

1606
Notizen
chelate ligand l-methyl-2 -(methylthiomethyl)-l//-
benzimidazole (mmb) [5].
Coordination of the Hetero(N,S)-
bidentate Ligand l-Methyl-2-
The N S ligands were structurally shown to
bind as chelates to Rhm, Ir111, Cu1, Cu11 and Ag1
centers [6-9], As ligand to quinone-copper units
the NaS molecules permit the observation of an
unusual reversible valence tautomer equilibrium
(1) [5,7],
(methylthiomethyl)-l//-benzimidazole
to [(Ph3P)Au)]+ Exclusively through
the Imine Nitrogen Donor
Markus Albrecht, Klaus Hiibler, and
Wolfgang Kaim
Institut für Anorganische Chemie, Universität
Stuttgart, Pfaffenwaldring 55. D-70550 Stuttgart,
Germany
(NAS)Cu'(Q -)
Q = o-quinone
(NaS)Cu"(Q2‘)
(1)
Reprint requests to Prof. Dr. W. Kaim.
Fax: (+49) 711685-4165.
E-mail: kaim@iac.uni-stuttgart.de
The stability of the P-Au bond in the
[(Ph3P)Au]+fragment raised the question whether
the NaS ligand would bind in bi- or monodentate
fashion and, if the latter were true, which of the
donor centers would be coordinated, the softer
thioether sulfur or one of the more basic nitro-
gen atoms.
Z. Naturforsch. 54b, 1606-1608 (1999);
received September 17, 1999
Gold(I) Complex, Benzimidazole Ligand,
Thioether
l-Methyl-2-(methylthiomethyl)-l//-
benzimidazole (mmb, NAS) was reacted with
Results and Discussion
Ph3PAuCl/AgPF6
in
THF
to
yield
[(Ph3P)Au(mmb)](PF6) which could be crystallo-
graphically characterized. The Au+ion is almost
linearly coordinated by the triphenylphosphine P
and the imine N atom of a monodentate NAS li-
gand. There is no gold(I)-sulfur bonding as the
distance of ca. 3.02 A indicates. Similarly, close
intermetallic contacts between the gold centers
are absent. Both effects are attributed to the posi-
tive charge on the metal.
Addition of l-methyl-2-(methylthiomethyl)-l//-
benzimidazole
to
the
freshly
prepared
[(Ph3P)Au](PF6) system in THF yielded colorless
[(Ph3P)Au(mmb)](PF6) in good yield. Elemental
analysis, NMR characterization ('H, 13C, 3 1 P; see
Exp. Section) and especially the X-ray diffraction
study (Table I) established the identity of the com-
pound.
The result of the structure determination is il-
lustrated in Fig. 1, showing one of the two crystal-
lographically independent cations.
The gold(I) cation in [(Ph3P)Au(mmb)](PF6) is
coordinated almost linearly (ca. 175°) by the tri-
phenylphosphine P atom and by the imine center
of the NaS ligand. At 3.028(3)/3.017(2) A the Au-
S distance is close to the sum of the van der Waals
radii and certainly much longer than the
The affinity between gold in low oxidation states
and sulfur centers of corresponding ligands is well
established and of considerable practical value.
This includes the stability of gold thiolate drugs
for treating rheumatoid arthritis [1 ,2 ], the forma-
tion of self-assembled thiol monolayers on gold
surfaces [3] and the process of gilding by using Au/
S-based preparations [1,4]. Among the possible
sulfur-containing ligands for Au1 are thioethers
which have been studied e.g. in the form of com-
plexes [XAu(SR2)]n+, X = Hal and n = 0 [4] or X =
PPh3 and n = 1 [1].
2.3228(12)
A
found for [(Ph3P)Au(Me2S)]-
(03SCF3) [1]. Compounds of Ag1 or Cu1 with N S
ligands have metal sulfur^ distances of about 2.70
A (Ag1) and 2.43-2.62 A (Cu1) [6,9]. The bond
parameters in Fig. 1 clearly illustrate that the gold
center in [(Ph3P)Au(mmb)](PF6) is two-coordi-
nate and the NAS ligand effectively monodentate.
Interestingly, it is not the soft thioether sulfur
atom but the more basic imine nitrogen site of
NAS which is preferred by the gold(I) center. As
has been noted before [4], the [(PPh3)Au]+ion has
a “hard” electrophilic character, similar to H+,
which would explain its preference for neutral N
over neutral S donors.
Herein we report the result of the reaction be-
tween the Ph3PAuCl/AgPF6 system and the N,S-
mmb
0932-0776/99/1200-1606 $06.00 © 1999 Verlag der Zeitschrift für Naturforschung, Tübingen •www.znaturforsch.com
D
Brought to you by | New York University Bobst Library Technical Services
Authenticated
Download Date | 6/17/15 5:21 PM

1607
Notizen
Table I. Crystallographic data for
[(Ph3P)Au(mmb)](PF6).
A structure related to that of the cation
[(Ph3P)Au(mmb)]+has been described earlier for
neutral (Ph3P)Au(dedtc), where dedtc is mono-
dentate diethyldithiocarbamate with a bonding
(2.338(3) A) and non-bonding Au-S distance
(3.015(3) A) [10]. Even 2,2'-bipyridine with two
equivalent chelate donor centers binds in unsym-
metrical fashion to the [(Ph3P)Au]+fragment with
Au-N distances of 2.166(2) and 2.406(2) Ä and an
obtuse angle P-Au-N of 157.1(1)° [11]. Related
“2 +1 ” coordination has similarly been observed
for Hg11 and Cu1 species [12].
There are no significant intermolecular interac-
tions in the crystal of [(Ph3P)Au(mmb)](PF6),
specifically, the metal-metal distances of >6.5 A
are outside of any bonding range. We attribute this
result to the positive charge at the gold(I) centers,
the Au+-Au+electrostatic repulsion and steric ef-
fects override the relativistic effects deemed re-
sponsible for aurophilic attractions [13].
Empirical formula
Formula weight
Wavelength (A)
Crystal system
Space group
C28H27AuFhN2P2S
796.48
0.71073
monoclinic
P2(l)/n
10.7529(7)
19.4625(10)
28.431(2)
90.549(8)
5949.8(7)
4
«(A)
b
c
(A)
(A)
^ ( 1
V (A3)
Z
Calc, density (Mg/m~3)
Absorption coefficient,
F(000)
Ö-Range (°)
Limiting indices
1.778
5.182
3104
2.02 to 25.95
u
( m m 1)
-12<
h <13, -23< k <23,
-34< / <34
46298
11555
Reflections collected
Independent reflections
0.1192
11555 / 0/721
0.555
Rl = 0.0353, wR2 = 0.0465
Rl = 0.1370, wR2 = 0.0635
0.501 and -1.323
^int
Data / Restraints / Parameters
Goodness-of-fit on F2a
Final R indices [I>2o(I)]
R Indices (all data) bc
Largest diff. peak and hole (e A -3)
Experimental Section
aGOF = {Lw(\F0\2-Fc\2)2l(n-m))ll2\n = number of
data; m - number of variables.
All experiments were carried out under an at-
mosphere of dry argon. Standard equipment was
used throughout.
bR
cRn. = {2 [v v (IF J2- IF cl2)2]/Z[vv(F04)])1/2.
=
(2 IIF 0 I- IF CII )/2 IF 0 l.
(1-Methyl-2-(methylthiomethyl)-lH-
benzimidazole)(triphenylphosphine)gold(I)
hexafluorophosphate
A solution of 50 mg (0.1 mmol) of Ph3PAuCl in
15 ml of THF was treated at 0 °C with a solution of
26 mg (0.1 mmol) of AgPF6 in 3ml of THF. After
1 0 min strirring and filtration, 2 0 mg (0 . 1 mmol) of
l-methyl-2 -(methylthiomethyl)-l//-benzimidazole
[5] was added in 5 ml of THF and the mixture
warmed to room temperature. After 30 min stir-
ring, volume reduction to 5 ml and cooling to 4 °C,
64 mg (0.08 mmol, 80%) of colorless needles
were obtained.
]H NMR (acetonitrile-d?): <3 = 2.11 (s, 3H,
NCH3), 4.17 (s, 2H,
S
CH3), 3.90 (s, 3H,
CH2SCH3), 7.45-7.53 (m, 2 H, imidazole), 7.59-
7.69 (m, 16H, 1H im. + 15H PPh3), 7.87-7.91 (m,
1H, im.). 13C NMR (acetonitrile-fi??, assignment
based on DEPT 135-spectroscopy); d = 16.40
(SCH3), 29.84 (CH2 SCH3), 31.97 (NCH3), 112.37,
118.58 (C-5,6 imidazole), 125.41, 125.71 (C-4,7
Fig. 1. Molecular structure of
the cation
in
[(Ph3P)Au(mmb)](PF6) with atomic numbering. (OR-
TEP, 50% probability ellipsoids; hydrogen atoms are ob-
mitted for clarity; only one of the two crystallographi-
cally independent species is shown). Selected distances
[Ä] and angles [°]: Au(l)-N(ll) 2.080(6), Au(2)-N(21)
2.076(6); Au(l)-P(l) 2.235(2), Au(2)-P(2) 2.234(2);
Au(l)-S(l) 3.028(3), Au(2)-S(2) 3.017(2); N (ll)-
Au(l)-P(l) 175.49(19), N(21)-Au(2)-P(2) 174.1(2);
im.), 129.20 (d,
Jc.p = 58.7 Hz, PPh3), 130.62 (d,
Jc.p = 10.4 Hz, PPh3), 133.50 (s, PPh3), 135.14 (d,
Jc-p= 12.2 Hz, PPh3), 135.65, 139.91 (C-3a,7a im.),
S(l)-Au(l)-P(l)
109.53(08),
S(2)-Au(2)-P(2)
156.53 (C-2 im.). 31P NMR (acetonitrile-rf?):
30.01 (s, PPh3), -143.89 (sept, JP.F= 706 Hz, PF6).
d =
110.24(07); N(ll)-Au(l)-S(l) 74.3(2), N(21)-Au(2)-
S(2) 74.1(2).
Brought to you by | New York University Bobst Library Technical Services
Authenticated
Download Date | 6/17/15 5:21 PM

1608
Notizen
C28H27AuF6N^P2S (796.48)
were added to the structure model in calculated
positions with isotropic temperature factors 2 0 %
(CH) or 50% (CH3) higher than those of the cor-
responding carbon atoms. Crystallographic data
for the structural analysis have been deposited
with the Cambridge Crystallographic Data Centre,
CCDC No. 134342. Copies of the information may
be obtained free of charge from: The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ,
UK, Fax. (int. code) +44 (1223)336-033, or Email:
deposit@ccdc.cam.ac.uk or
Calcd C 42.22 H 3.42 N3.52%,
Found C 43.40 H 3.34 N3.53%.
X-ray crystallography
Single crystals of [(Ph3P)Au(mmb)](PF6) were
grown by cooling a saturated solution in dichloro-
methane/n-pentane (4/1) at 4 °C. The dimensions
of the crystal chosen were 0.08 x 0.08 x 0 .2 mm.
Reflections were collected on an IPDS (Stoe)
system at 295 K with graphite-monochromated
Mo-Ka radiation. The structure was solved by di-
rect methods and refined by full-matrix least-
square calculations using the Shelxtl Version 5.1
[14]. There are two crystallographically indepen-
dent ion pairs in the unit cell, differentiated by
indices 1 and 2 .
www: http://www. ccdc.cam.ac.uk.
Acknowledgements
This work has been supported by the Deutsche
Forschungsgemeinschaft (DFG). We also thank
Dr. F. Lissner for the crystallographic measure-
Anisotropic thermal parameters were refined
for all non-hydrogen atoms. The hydrogen atoms ments.
[1] A. Sladek, H. Schmidbaur, Z. Naturforsch. 51b,
1207 (1996) and literature cited.
[2] R. Bau, J. Am. Chem. Soc. 120, 9380 (1998) and
literature cited.
[7] J. Rail, M. Wanner, M. Albrecht, F. M. Hornung, W.
Kaim, Chem. Eur. J. 5, 2802 (1999).
[8]M. Albrecht, T. Scheiring, T. Sixt, W. Kaim, J. Orga-
nomet. Chem., in press.
[9] M. Albrecht, K. Hübler, W. Kaim. Z. Anorg. Allg.
Chem., in press.
[10] J. G. Wijnhoven, W. P. J. H. Bosman, P. T. Beurskens,
J. Cryst. Mol. Struct. 2. 7 (1972).
[3] A. Kumar, N. L. Abbott, E. Kim, H. A. Biebuyck,
G. A. Whitesides, Acc. Chem. 28, 219 (1995).
[4] a) R. J. Puddephatt, “The Chemistry of Gold”,
Elsevier, Amsterdam (1978);
b) H. Schmidbaur (Ed.), “Gold: Progress in Chemis-
try, Biochemistry and Technology”, Wiley-VCH,
Weinheim (1999).
[11] W. Clegg, Acta Crystallogr. B32, 2712 (1976).
[12] A. F. Stange, T. Sixt, W. Kaim, J. Chem. Soc., Chem.
Commun., 469 (1998).
[5] J. Rail, E. Waldhör, B. Schwederski, M. Schwach, S.
Kohlmann, W. Kaim, “Bioinorganic Chemistry:
Transition Metals in Biology and their Coordination
Chemistry”, Hrsg. A. X. Trautwein, p. 476. VCH,
Weinheim (1997).
[13] a) H. Schmidbaur, Interdisciplinary Science Rev. 17,
213 (1992);
b) P. Pyykkö, Chem. Rev. 97 (1997) 597.
[14] Shelxtl Version 5.1, Bruker Analytical X-ray Sys-
tems, 1998.
[6] M. Albrecht, K. Hübler, T. Scheiring, W. Kaim. In-
org. Chim. Acta 287, 204 (1999).
Brought to you by | New York University Bobst Library Technical Services
Authenticated
Download Date | 6/17/15 5:21 PM