Metallophilic bonding and agostic interactions in gold(I) and silver(I) complexes bearing a thiotetrazole unit

Article abstract of DOI:10.1021/ic102595d

Gold(I) and silver(I) complexes of 1-methyl-5-thio-tetrazole (1) have been prepared and the coordination chemistry of this ligand toward metal-phosphine frameworks has been explored. As indicated by IR and Raman data, ligand 1 is deprotonated and the resu

Full text of DOI:10.1021/ic102595d

ARTICLE
pubs.acs.org/IC
Metallophilic Bonding and Agostic Interactions in Gold(I) and Silver(I)
Complexes Bearing a Thiotetrazole Unit
Adriana Ilie,†,‡ Ciprian I. Ra-t,‡ Susanne Scheutzow,† Christiane Kiske,† Karin Lux,† Thomas M. Klap€otke,†
Cristian Silvestru,‡ and Konstantin Karaghiosoff*,†
†Department of Chemistry, Ludwig-Maximilians-University Butenandtstrasse. 5-13 (Haus D), Munich, D-81377, Grosshadern,
Germany
‡Faculty of Chemistry & Chemical Engineering, Babes-Bolyai University, Arany Janos str. No. 11, 400028, Cluj-Napoca, Romania
S Supporting Information
b
ABSTRACT: Gold(I) and silver(I) complexes of 1-methyl-5-thio-tetrazole (1) have been prepared and the coordination chemistry
of this ligand toward metal-phosphine frameworks has been explored. As indicated by IR and Raman data, ligand 1 is deprotonated
and the resulted anion acts as a bidentate (S,N)-tetrazole-5-thiolato unit in the new gold(I) complexes, [Au(SCN4Me)(PPh3)] (2),
[{Au(SCN4Me)}2(μ-dppm)] (3), and [{Au(SCN4Me)}2(μ-dppe)] (4), while it is coordinated only through the sulfur atom as its
neutral tetrazole-5-thione form in the silver(I) derivative, [Ag(HSCN4Me)(PPh3)]2(OTf)2 (5). Further characterization of the new
compounds was performed using multinuclear (1H, 13C, 31P, 19F) NMR spectroscopy, mass spectrometry, and DSC measurements.
Single-crystal X-ray diffraction studies revealed basically linear P-M-S arrangements in complexes 3-5. The bidentate (S,N)
coordination pattern results in a T-shaped (S,N)PAu core in 3 and 4, whereas, in 5, a similar coordination geometry is achieved in the
dimer association based on S-bridging ligand 1. Herein, weak (C)H Au and (C)H Ag agostic interactions were observed. An
3 3 3
3 3 3
intramolecular Au Au contact occurs in 3, while in 4 intermolecular aurophilic bonds lead to formation of a chain polymer. An
3 3 3
intermolecular Ag Ag contact is also present in the dimer unit of 5. Low-temperature 31P NMR data for 5 evidenced the presence
of monomer and dimer units in solution. Theoretical calculations on model of the complexes 2 and 4 are consistent with the
geometries found by X-ray diffraction studies.
3 3 3
X-ray diffraction (XRD) study revealed the thione nature of 1 in
the solid state.12 The coordination chemistry of thiotetrazoles,
including 1, toward metal atoms is strongly related to their thiol
(1a, 1-methyl-1H-tetrazole-5-thiol) or thione [1b, 1-methyl-1H-
tetrazole-5(4H)-thione] tautomers (see Figure 1). As a conse-
quence, 1 can act as neutral ligand bound to a metal atom
through the sulfur atom of the thione tautomer (A) or as a
monoanionic ligand bound to the metal either through a nitrogen
atom (B, deprotonated 1b) or a sulfur atom (C, deprotonated
1a) (see Figure 1).
1. INTRODUCTION
Complexes bearing the M-S (M = Au, Ag) bond have raised
continuously increasing interest, because of their use in
pharmacology1 and thin films,2 as well as glass and ceramic
technology.3 A variety of heterocyclic ligands have been used to
study their complexation abilities with heavy metals,4 and, among
them, thiotetrazoles have proved to be promising ligands. Their
relative stability to oxidation and high coordination ability5 lead
to applications in photothermographic and photographic
materials,6 or use as capping agents for the stabilization of gold
nanoparticles.7 However, research on coordination chemistry of
thiotetrazoles toward gold and silver has been scarcely reported.
The first Au(I) and Ag(I) complexes with thiotetrazoles, i.e.,
[M(HSCN4R)] [M = Au(I), Ag(I); R = Ph, 1-MeOC6H4,
3-ClC6H4, 2-MeC6H4],8 were synthesized by Agarwala et al.,
while Beck et al. managed to also incorporate phosphine frag-
ments, e.g., [Au(SCN4R)(PPh3)] (R = Me, Ph) and
[Ag(SCN4R)(PPh3)2].9 In such gold(I) complexes,9 aurophili-
city (the affinity between gold atoms)10 was noted. The struc-
tures of the first ionic Au(III) compounds with monodentate
tetrazole-5-thiolato ligands, e.g., [{(2-Me2HNCH2)C6H4}Au-
2. RESULTS AND DISCUSSION
Ligand 1 was prepared following a straightforward strategy.13
The synthetic route for the preparation of [Au(SCN4
Me)(PPh3)] (2) differs from the strategy used by Beck et al.9
Thus, 2 was obtained in high yields from equimolar amounts of 1
and the precursor [AuCl(PPh3)], using THF as a solvent. The
reaction of 1 with [Au2Cl2(μ-dppm)] (dppm = Ph2PCH2PPh2)
or [Au2Cl2(μ-dppe)] (dppe = Ph2PCH2CH2PPh2), respectively,
in 2:1 molar ratio, yielded the target compounds [{Au(SCN4
Me)}2(μ-dppm)] (3) and [{Au(SCN4Me)}2(μ-dppe)] (4)
(Scheme 1). These synthetic procedures required the use of
NEt3 as a base to trap the resulting HCl. Complex [Ag(HSCN4
(SCN4Me)3], [PPh4][Au(SCN4Me)4] 0.5H2O, were also re-
3
ported by Abram et al.11
In this context, we set out to design, prepare, and characterize
gold(I) and silver(I) complexes of 1-methyl-5-thio-tetrazole (1),
using different phosphine-metal moieties and taking into account
the coordination versatility of the thio ligand. A single-crystal
Received: December 31, 2010
Published: February 10, 2011
r
2011 American Chemical Society
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Figure 1. Thiol and thione tautomers for thiotetrazole 1 and coordina-
tion patterns toward a metal atom.
Scheme 1. Synthesis of Complexes 2-5. a
Figure 2. Variable-temperature 31P NMR spectra of a solution of 5 in
CD2Cl2. The marked signals correspond to dimer (*) and monomer
(b).
For the silver complex 5, the 31P NMR spectrum, recorded at
room temperature, exhibits a broad resonance in the δ range of
11-12 ppm, probably because of dissociative processes involv-
ing cleavage of S-AgPPh3 and/or Ag-PPh3 bonds, observation
well-documented in case of phosphine complexes in the case
of phosphine complexes of coinage metals.14 Given these results,
variable-temperature NMR studies in solution were performed
(Figure 2). At low temperature (-85 °C), the 31P NMR
spectrum recorded in CD2Cl2 shows the presence of two
resonances, each of them with a pattern of doublet of doublets
due to the couplings with 107Ag and 109Ag isotopes, thus
indicating the presence of two species containing silver-
phosphine moieties which were assumed to be a monomer
and a dimer species.
The coordination number (CN) around a silver atom in a
silver-phosphine species can be estimated on the basis of the
magnitude of the silver-phosphorus coupling constant. Thus, it
was reported that the 1J(P,107Ag) coupling constants are inver-
sely proportional to the coordination number of the silver atom15
and increase with decreasing Ag-P distances.16 Hence, the
observed coupling constants for 5 may be assigned to the
monomer (1J(P,107Ag) of 417.5 Hz, CN = 2) and dimer
(1J(P,107Ag) of 318.5 Hz, CN = 3) species, respectively. The
intensity of the signals suggests that the monomer is the
predominant species in solution at lower temperatures. On the
basis of the 31P NMR investigations, it can be concluded that, in a
a Reagents and conditions: (i) [AuCl(PPh3)], THF, Et3N, r.t., 80%; (ii)
[Au2Cl2(μ-dppm)], THF, Et3N, r.t., 91%; (iii) [Au2Cl2(μ-dppe)],
THF, Et3N, r.t., 81%; and (iv) [Ag(OTf)(PPh3)], CH2Cl2, r.t. 85%.
Me)(PPh3)]2(OTf)2 (5) was prepared from 1 and [Ag(OTf)
(PPh3)], in 1:1 molar ratio, using CH2Cl2 as a solvent.
The 1H NMR studies revealed several diagnostic characteristics.
Compared to the free ligand 1, new resonances (i.e., a triplet at δ =
3.7 ppm and a broad singlet at δ = 3.1 ppm) appear for complexes
3 and 4, respectively, and were assigned to methylene and ethylene
protons in the diphosphine moieties. At a first glance, the 13C
NMR spectra of 2, 3, and 5 exhibit the expected resonances. For
the carbon of the tetrazole ring, an upfield shift was noted, with
respect to thefreeligand(Δδ = 5.92 ppm in 2, Δδ= 5.75ppmin3,
Δδ = 2.61 ppm in 5), which is indicative for the formation of the
complexes. For3, the aromatic carbons gave triplet resonances due
to geminal and long-range phosphorus-carbon coupling systems.
In the aromatic region of 2 and 5, the 31P-13C couplings resulted
in doublet resonances. The 31P NMR spectra of complexes 2-4,
measured at room temperature in CDCl3, showed one resonance
at δ = 37.8 (2), 30.9 (3), and 38.3 ppm (4), respectively, the
chemical shifts being in the usual region for the corresponding
phosphorus ligands coordinated to Au(I).
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solution of 5, there is an equilibrium between monomer and
dimer units.
During the ES-MS analyses of gold(I) complexes 2, 3, and 4,
the formation of several gold species was observed. The ES-MS
of 2 shows the molecular peak at m/z = 575.3 [MþH]þ and a
peak at m/z = 721.4, because of the monocharged species
[Au(PPh3)2]þ. A different fragmentation pattern was noticed
in the case of 3 and 4, which lose the thiotetrazole fragment under
the ionization conditions of ES-MS. The mass spectrum of 3
exhibits the main peak at m/z = 893.1 assigned to the fragment
[Au2(SCN4Me)(μ-dppm)]þ, whereas, in 4, along with
[Au2(SCN4Me)(μ-dppe)]þ fragment at m/z = 907.1, a lower
mass fragment at m/z = 824.1 is due to the loss of the second
thiotetrazole unit. The ES-MS of 5 exhibits the base peak at
631.2, corresponding to a [Ag(PPh3)2]þ fragment.
Comparative analysis of IR and Raman spectra of ligand 1 with
those of complexes 2-5 confirmed the formation of the metal-
sulfur species. The characteristic bands of the ligand 1,8a,17 i.e.,
ν(N-CdS) at 1506 cm-1 and ν(CdS) at 1349, 1043, and 781
cm-1, disappear in 2-4. However, the appearance of a new split
band at 711/692 cm-1 for 2, 704/688 cm-1 for 3, and 702/698
cm-1 for 4, because of the contributions from the ν(C-S)
stretching vibration, suggests the presence of the deprotonated 1
as a thiolato moiety attached to the gold center (pattern C,
Figure 1). The CdS stretching frequencies are observed for 5
and shift downward to ∼1337, 1014, and 750 cm-1, because of
coordination. This observation underlines that 1 is coordinated
as its thione tautomer in 5. The bidentate (S,N) coordination
pattern of the thiolato moiety to gold is clearly indicated in the
Raman spectra of 2-4, where the ν(Au-N) vibrations18 were
located at 432 cm-1 in 2 and 438 cm-1 in 3 and 4. For 5, no band
could be assigned to the ν(Ag-N) vibration. In the region of
340-450 cm-1, which is characteristic for vibrations of the
metal-sulfur bonds, a band, which is not present in the spectrum
of the free ligand, appears in the spectra of the complexes and it
was assigned to ν(M-S) vibration: 346 cm-1 in 2, 343 cm-1 in 3,
339 cm-1 in 4 (M = Au), and 350 cm-1 in 5 (M = Ag).
The thermal stability of 2-5 was determined using DSC
measurements. The DSC revealed high thermal stabilities with
high exothermic decompositions. Compound 2 melts at 154 °C
and decomposes at 218 °C. For compounds 3 and 4, only the
decomposition points were observed at 247 and 255 °C, respec-
tively. By contrast, the silver complex 5 with a melting point at
159 °C has two decomposition points, which were observed at
209 and 280 °C, respectively.
Figure 3. Structure of molecule 3b, showing the atom numbering
scheme. Displacement ellipsoids are depicted at the 50% probability
level. Hydrogen atoms (except those involved in agostic interactions)
are omitted for the sake of clarity. Selected bonds lengths (Å): Au-
(3) Au(4), 3.1046(3); Au(3)-S(3), 2.3277(14); Au(4)-S(4),
3 3 3
2.3207(13); Au(3)-P(3), 2.2531(14); Au(4)-P(4), 2.2608(13); Au-
(3)-N(12), 3.146(5); Au(4)-N(16), 3.113(5); C(41) Au(3),
3 3 3
3.429(6); H(41) Au(3), 2.82; C(57) Au(4), 3.410(5); H-
3 3 3
3 3 3
(57) Au(4), 2.82; Au(3)-S(3), 2.3277(14); Au(4)-S(4),
3 3 3
2.3207(13); S(3)-C(30), 1.749(5); and S(4)-C(32), 1.737(5); angles
(degrees): P(3)-Au(3)-S(3), 169.13(5); P(4)-Au(4)-S(4),
173.03(5); Au(3)-N(12)-C(30), 75.45(3); Au(4)-N(16)-C(32),
75.73(3); C(41)-H(41) Au(3), 123.3(4); and C(57)-H-
3 3 3
(57) Au(4), 121.5(3).
3 3 3
P
sum of the covalent and van der Waals radii, rcov(Au,Au) =
P
2.68 Å, rvdW(Au,Au) = 3.4 Å].19 Also note that the nitrogen
atoms are weakly coordinated to the gold atoms in 3b [Au(3)-
N(12), 3.146(5) Å; Au(4)-N(16), 3.113(5) Å], while in 3a, no
intramolecular N f Au interaction is present [the shortest
nonbonding gold-nitrogen distances are Au(1) N(4),
3 3 3
P
The structure of complexes 3 and 4 was established by X-ray
diffraction (XRD) studies. Single crystals were obtained from
methylene chloride/diethyl ether (1:4 by volume) by slow
diffusion at room temperature (for 3 and 4) or by slow evapora-
tion of a methylene chloride solution (for 5). The crystal
structure of 3 contains two independent molecules and, there-
fore, subsequent discussion at the molecular level will refer to
molecules 3a and 3b (see Figure 3).
3.342(5) Å; Au(2) N(8), 3.281(4) Å; cf. rvdW(Au,N) =
3 3 3
3.25 Å].19 If intramolecular N f Au interactions are taken into
account the coordination number of the gold atoms is increased
to three in molecule 3b and the coordination geometry can be
described as T-shaped, whereas in 3a, the gold atoms remain
dicoordinated.
The presence of (C)H Au20 and (C)H Ag21 agostic
3 3 3
3 3 3
interactions have not received much attention so far. For all
complexes discussed in this work, such interactions were ob-
served. Thus, in 3a and 3b, there are agostic intramolecular
In both molecules, the gold atoms are dicoordinated with an
almost-linear S-Au-P fragment [P(1)-Au(1)-S(1),
173.05(5)°; P(2)-Au(2)-S(2), 176.74(5)° in 3a; P(3)-Au-
(3)-S(3), 169.13(5)°; P(4)-Au(4)-S(4), 173.03(5)° in 3b].
(C)H Au interactions that involve aromatic hydrogen atoms
3 3 3
in their calculated position20h [H(12) Au(1) 2.94 Å and
3 3 3
Intramolecular Au Au (aurophilic) interactions were ob-
H(29) Au(2) 2.99 Å in 3a; H(41) Au(3), 2.82 Å and
3 3 3
3 3 3
3 3 3
3 3 3
P
served in both cases and they are likely to induce the deviation
H(57) Au(4), 2.82 Å in 3b; cf. rvdW(Au,H) = 3.15 Å].19
from linearity of the S-Au-P systems. The Au-Au distance in
The crystal of the related complex 4 contains three indepen-
dent molecules: 4a, 4b, and 4c. The tetrazole-5-thiolato ligand is
coordinated through sulfur to the gold center, resulting in an
the molecules of 3 are significantly different: Au(1) Au(2),
3 3 3
3.2142(3) Å in 3a, and Au(3) Au(4), 3.1046(3) Å in 3b [cf.
3 3 3
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1.737(5) Å in 3b, 1.746(7) in 4a, 1.720(6) in 4b, and 1.705(8)
in 4c]. This indicates that the ligand is coordinated in the thiolato
form. The magnitude of the Au-P distances [2.2529(14) Å,
2.2603(14) Å in 3a, 2.2531(14) Å, 2.2608(13) Å in 3b,
2.2618(17) Å in 4a, 2.2577(15) Å in 4b, and 2.2487(16) Å in
4c] compares well with those found in the starting materials
[Au2Cl2(μ-dppm)] [2.2384(15) Å] and [Au2Cl2(μ-dppe)]
[2.2305(30) Å, 2.2289(36) Å], respectively. In contrast to 3,
the molecules of 4 do not exhibit intramolecular Au-Au inter-
actions [the nonbonding Au Au distances are in the range of
3 3 3
6.7038(6)-6.8977(6) Å]. This behavior is due to the trans
arrangement of the AuSR fragments, with respect to the P-
C-C-P skeleton. However, intermolecular Au-Au short con-
tacts are observed [Au(10) Au(2), 3.1038(4)Å] between
3 3 3
molecules 4a and 4b, because of the low coordination number
and linear geometry of gold(I), which were found to be an
excellent basis for the construction of one-dimensional polymers
with gold atoms at regular intervals (see Figure 5). The Au-
(10) Au(2) distance resemble the values found in the litera-
3 3 3
ture for gold(I) complexes.23 Moreover, the polymeric chain is
stabilized through weak intermolecular (C)H Au agostic
3 3 3
interactions [H(80) Au(2), 2.84 Å]. In addition, weak inter-
3 3 3
molecular S Au interactions are also established between
3 3 3
Figure 4. Structure of molecule 4c, showing the atom numbering
scheme. Displacement ellipsoids are depicted at the 50% probability
level. Hydrogen atoms (except those involved in agostic interactions)
are omitted for the sake of clarity. Selected bonds lengths (Å): Au(3)-
S(3), 2.3214(16); Au(3)-P(3), 2.2487(16); Au(3)-N(12), 3.111(9);
C(32) Au(3), 3.460(6); H(32) Au(3), 2.91; C(38) Au(3),
molecules 4a and 4b, i.e., S(10) Au(2), 3.3821(19) Å,; S-
3 3 3
P
(2) Au(10), 3.4370(16) Å [c.f. rvdW(S,Au) = 3.55 Å]19
3 3 3
(Figure 5). Molecule 4c, because of the intramolecular N f Au
coordination, is not involved in any Au-Au intermolecular
interaction. Moreover, the sulfur atoms in 4c remain free of
any intermolecular contacts with gold atoms.
3 3 3
3 3 3
3 3 3
3.58(1); H(38) Au(3), 3.01; S(3)-C(44), 1.705(8); P(3)-C(43),
3 3 3
Single-crystal XRD analysis revealed that the crystal of 5
contains dinuclear dications (Figure 6). The carbon-sulfur
bonds [S(2)-C(39), 1.689(5) Å; and S(1)-C(37), 1.687(6)
Å] in 5 are rather small when compared to the corresponding
bonds found in 3 and 4, thus suggesting that ligand 1 coordinates
to silver center in the thione form. The asymmetric bridging
sulfur atoms from thione tautomers of ligand 1 generate a strictly
planar, rhombic Ag2S2 core [Ag(1)-S(2), 2.4802(17) Å; Ag-
1.838(6); P(3)-C(31), 1.809(6); P(3)-C(37), 1.809(6); angles (°):
P(3)-Au(3)-S(3), 174.76(6); Au(3)-S(3)-C(44), 95.2(2);
C(32)-H(32) Au(3),
118.4(4);
C(38)-H(38) Au(3),
3 3 3
3 3 3
120.4(5); Au(3)-P(3)-C(31), 110.7(2); Au(3)-P(3)-C(37),
116.3(2); and Au(3)-P(3)-C(43), 112.27(18).
almost-linear P-Au-S arrangement, ranging from 173.41(7)°
in 4b and 174.76(6)° in 4c (see Figure 4) to 175.19(6)° in 4a.
The coordination sphere of Au is accomplished in 4c via an N f
Au interaction [N(12)-Au(3), 3.111(9) Å], therefore the
coordination geometry around Au(I) can be described as
(1) S(1), 2.9434(15) Å; Ag(2)-S(1), 2.4632(16) Å; Ag-
3 3 3
P
(2) S(2), 2.9305(15) Å] [c.f.
rcov(Ag,S) = 2.38 Å,
3 3 3
P
rvdW(Ag,S) = 3.55 Å].19 The endocyclic bond angles (i.e.,
S(1)-Ag(1)-S(2)/S(1)-Ag(2)-S(2), 112.03(5)/112.98(5)°;
Ag(1)-S(1)-Ag(2)/Ag(1)-S(2)-Ag(2), 67.46(4)/67.49(4)°)
differ considerably from those found in other sulfur-bridged
species containing Ag(I).24 The formation of the dimer in the
T-shaped. Two agostic interactions [H(32) Au(3), 2.91 Å;
3 3 3
H(38) Au(3), 3.01 Å] per gold atom are also present. By
3 3 3
contrast, in molecules 4a and 4b, no intramolecular N f Au
interaction was observed [nonbonding N Au, 3.293(6) Å in
3 3 3
4a and 3.390(7) Å in 4b]; however, 4a is stabilized by
solid state is achieved because of the strength of the Ag
S
3 3 3
(C)H Au contacts [H(2) Au(1), 2.94 Å; H(130A) Au-
interactions between the two mononuclear units. This is sup-
3 3 3
3 3 3
3 3 3
(1), 2.95 Å]. (See the Supporting Information.) The agostic
interaction with a distance of ca. 2.8 Å can be considered to be
fairly weak,20f but they provide additional stabilization for 3a, 3b,
4a, and 4c and strengthen their overall geometry. The
ported by literature data on Ag-S bonds and contacts24,25 and
also suggests that the weaker Ag S distances are probably the
3 3 3
major reason for the pattern of the dynamic 31P NMR spectra (i.
e., cleavage of the dinuclear dications and appearance of signals
corresponding to the mononuclear anions). Interestingly, the
formation of the Ag2S2 core resulted in a short transannular
Ag(1) Ag(2) distance [3.0287(6) Å] which might suggest an
(C)H Au distances observed for complexes 3 and 4 are in
3 3 3
the middle of the range of agostic interactions previously
reported for gold(I) complexes.20c-20g
3 3 3
P
The Au-S bond lengths in 3a [Au(1)-S(1), 2.3322(14) Å;
Au(2)-S(2), 2.3210(14) Å], 3b [Au(3)-S(3), 2.3277(14) Å;
Au(4)-S(4), 2.3207(13) Å], 4a [Au(1)-S(1), 2.3444(17) Å],
4b [Au(2)-S(2), 2.3256(15) Å], and 4c [Au(3)-S(3),
2.3214(16) Å], respectively, are in the range reported for gold
thiolato and thionato complexes.22 It is worth mentioning that, in
3 and 4, the carbon-sulfur bond distances do not resemble the
value measured for the free ligand 1 [1.677(1) Å], being
considerably longer [1.741(5)/1.739(6) Å in 3a, 1.749(5)/
intermetallic interaction [c.f. rvdW(Ag,Ag) = 3.4 Å].19 In the
mononuclear unit, the P-Ag-S fragment is close to the line-
arity [P(2)-Ag(1)-S(2), 151.77(6)°; P(1)-Ag(2)-S(1),
149.09(6)°]. If the additional Ag-S interactions leading to the
dimer unit is considered, the coordination geometry around
Ag(I) atoms is best described as distorted T-shaped (or, alter-
natively, as distorted trigonal planar). Consequently, this ar-
rangement in the Ag2S2 core can be considered as a consequence
of steric repulsions between the two monomers. The dinuclear
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Figure 5. Chain polymer association of alternating 4a and 4b molecules in the crystal of 4, based on Au Au and S Au interactions. Hydrogen
3 3 3
3 3 3
atoms are removed for clarity; symmetry equivalent atoms are (1 - x, -y, 1 - z) and (1 - x, 1 - y, -z), denoted by the “prime” (0) and “double prime”
(00) symbols, respectively. Selected bond distances (Å): Au(10) Au(2), 3.1038(4); S(10) Au(2), 3.3821(19); S(2) Au(10), 3.4370(16).
3 3 3
3 3 3
3 3 3
dication of 5 also exhibits weak intramolecular (C)H Ag
agostic interactions, similar to those we found in gold(I) com-
In the theoretical model 3A, the largest differences were found
3 3 3
for the Au Au interactions, which are overestimated by 7.6%
3 3 3
plexes 3 and 4 (i.e., H(26) Ag(1), 2.95 Å; H(12) Ag(2),
and 11.4%, with respect to molecules 3a and 3b, respectively.
The calculated Au-P and Au-S bond lengths are slightly longer
(0.01-0.03 Å) than those found in the molecular structure
determined by XRD on single crystals. The calculated P-C-P
angle was determined to be 0.25° smaller and 1.75° larger than
those measured for molecules 3a and 3b, respectively. The
calculated P-Au-S angles display relative deviations ranging
from -1.0% to 5.5% and the Au-S-C angles show relative
deviations ranging from 1.7% to 4.9%. Important differences
between model 3A and [{Au(SCN4Me)}2(μ-dppm)] (3) are
found in the orientation of the tetrazole rings. Thus, in 3A, the
3 3 3
3 3 3
P
3.05 Å [c.f. rvdW(Ag,H) = 3.15 Å].19 In the crystal of 5, the
triflate counterions are involved in weak Ag O cation-anion
interactions [2.998(5) and 3.067(5) Å, c.f.
3 3 3
P
rvdW(Ag,O) =
3.1 Å].19
Selected data and parameters from the X-ray data collection
and structure refinement are given in Table 1.
Theoretical Calculations. For a better understanding of the
bonding between the phosphine ligands and the gold-containing
fragments, theoretical calculations at the density functional
theory (DFT) level were carried out on models of compounds
1-5. To reduce the computation time, the phenyl groups were
replaced by methyl groups in the phosphine ligands. Details
regarding computational procedures can be found in the Experi-
mental Section. Comparisons of salient experimental bond
lengths and bonding angles of the measured molecular structures
to the theoretically calculated structures are listed in Tables S7-
S12 in the Supporting Information.
Au Au-S-C angles are -72.21° and 67.63°, whereas they
3 3 3
are 80.13° and -135.17° in molecule 3a, and -72.36° and
161.61° in the molecule 3b, respectively. These values suggest
that intermolecular interactions between the tetrazole groups
and the hydrogen atoms play an important role for the geometry
that the molecules adopt in the solid state. In contrast to the
solid-state structure of 3, in the calculated model system 3A,
For model system 2A, the largest differences between the
calculated arrangement and the measured structure was found
for the S-Au-P angle (5.2%). This small difference for the
bonding angle is not surprising, taking into account that
[Au(SCN4Me)(PPh3)] (2) forms dimers in the solid state
there are short intramolecular N H contacts between the
3 3 3
hydrogen atoms of the methyl group of a SCN4Me unit and the
nitrogen atoms of the tetrazole-5-thiolate unit bonded to the
other gold atom of the molecule (see Table S8 in the Supporting
Information).
through Au S interactions.9b The S-Au and P-Au bond
To investigate if model 3A has geometry similar to that found
in the measured structure 3 when the correlation effects are
included, a geometry optimization at the MP2 level was carried
3 3 3
lengths are 0.02 Å larger in the theoretical model than the
experimentally determined values found for 2. The N Au
3 3 3
distance is 0.08 Å larger in 2A than in 2.9b To estimate the
out.26 The Au Au distance is 3.15342 Å, which is 0.304 Å
3 3 3
stabilization energy of the Au N interaction, an investigation
shorter than the value calculated at the BP86/TZ2P level. The
P-Au bond lengths have relative deviations ranging from 0.7%
to 1.0%, whereas the Au-S and S-C bond lengths have relative
deviations between 5.9% and 6.0%, compared to the values found
for 3. The P-Au-S and Au-S-C bonding angles are smaller
than those found in the crystal structure. Also, in the optimized
arrangement of model 3A at the MP2 level, a short intramole-
3 3 3
of the energy barrier for the rotation of the tetrazole fragment
around the S-C bond was carried out. The energy minimum
corresponds to a N(Me)-C-S-Au torsion angle of 178.56°, a
value which is 6.42% larger than that observed (167.79°) in the
solid state. The calculated energy required for the rotation of the
tetrazole fragment around the S-C bond is 5.77 kcal/mol. This
value indicates that the rotation is possible at room temperature.
cular N H contact of 2.59 Å is present.
3 3 3
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Inorganic Chemistry
ARTICLE
The energy decomposition analysis (EDA) method was
employed before to describe the coordinative bonds of phos-
phine ligands to transition-metal centers.27,28 A detailed descrip-
tion of the terms used in the analysis of the bonding energy can
be found elsewhere.28 A summary of the EDA of P-M bonds for
models 2A and the mononuclear cation [Ag(HSCN4Me)-
(PMe3)]þ (5A) is listed in Table 2.
The bond dissociation energy, ΔE (where ΔE = -De), of the
phosphine ligands is 6 kcal/mol smaller for 5A, compared to 2A.
The ionic (2A, 72.32%; 5A, 71.22%) and covalent (2A, 27.68%;
5A, 28.78%) contributions to the bonding energy have compar-
able values. These results are similar to those reported for the
complexes of [(Me3P)M(CO)5] (M = Cr, Mo, W), where the
percentage of the electrostatic interaction also is greater than that
of the covalent contributions.
In summary, the theoretical calculations at the BP86/TZ2P
level on models of the complexes 2 and 4 are consistent with the
geometries found via XRD on single crystals. The bonding
between the gold-tetrazole-5-thiolato fragments and methylpho-
sphine ligands is mainly electrostatic. The bonding in the
monomeric cation 5A is slightly weaker than that found in the
gold neutral analogue, 2A. The Au Au interactions found in 3
3 3 3
are better described by calculations at the MP2 level of theory.
’ CONCLUSIONS
In conclusion, we have developed an efficient method to
prepare metal-thiotetrazole complexes. The molecular struc-
tures established by single-crystal XRD confirm their initial
formulation suggested by IR and NMR analyses. However, a
different structural framework was observed for 5, which crystal
contains a dinuclear dication built through bridges established by
sulfur atoms of the thione tautomers of 1. Intramolecular
Figure 6. Structure of the dinuclear dication in 5, showing the atom
numbering scheme. Displacement ellipsoids are depicted at the 50%
probability level. Hydrogen atoms (except those involved in agostic
interactions and those bonded to tetrazole) are omitted for the sake of
clarity. Selected bonds lengths (Å): Ag(1) Ag(2), 3.0287(6); Ag-
3 3 3
(1)-S(1), 2.9434(15); Ag(1)-S(2), 2.4802(17); Ag(1)-P(2),
2.4047(17); Ag(2)-S(1), 2.4632(16); Ag(2)-S(2), 2.9305(15); Ag-
(2)-P(1), 2.3980(16); C(12) Ag(2), 3.647(6); H(12) Ag(2),
Au Au interactions were detected in 3, whereas in 4, inter-
3 3 3
3 3 3
3 3 3
3.05; C(26) Ag(1), 3.568(6); H(26) Ag(1), 2.95; angles (°):
3 3 3
3 3 3
molecular aurophilic bonding leads to the formation of a chain
polymer. As indicated by IR and confirmed by single-crystal XRD
in gold(I) tetrazole-5-thiolates 2, 3, and 4, the coordination also
occurs through the nitrogen atom. The weak agostic interactions
S(1)-Ag(1)-S(2), 112.03(5); S(1)-Ag(2)-S(2), 112.98(5); Ag-
(1)-S(1)-Ag(2), 67.46(4); Ag(1)-S(2)-Ag(2), 67.49(4); P(1)-
Ag(2)-S(1), 149.09(6); P(2)-Ag(1)-S(2), 151.77(6); P(2)-Ag-
(1)-S(1), 95.59(5); P(1)-Ag(2)-S(2), 97.10(5); C(12)-H-
(12) Ag(2), 122.1(3); C(26)-H(26) Ag(1), 123.5(3).
(C)H M observed in the measured structures are consistent
3 3 3
3 3 3
3 3 3
with those mentioned in the literature. Nevertheless, they
provide additional stability for the structures.
The bond lengths and the bonding angles in model system 4A
calculated at DFT are slightly overestimated. The largest devia-
tion, compared to the structure of 4 (5.0%), was found for the
Au-S-C bonding angle.
’ EXPERIMENTAL SECTION
General. All manipulations were carried out under vacuum or
argon, using standard Schlenk line techniques in anhydrous solvents.
Dry tetrahydrofuran (THF) was obtained by distillation under argon
over sodium and benzophenone. All other solvents and reagents were
purchased from commercial suppliers and used without further purifica-
tion. Other starting materials were prepared according to the literature:
Calculations on the dication dimer [Ag(HSCN4Me)
2þ
(PMe3)]2 (5B) did not reproduce the geometry found for
2þ
the [Ag(HSCN4Me)(PPh3)]2 cation in the solid state. The
Ag Ag distance is 5.1754 Å, 70.9% larger than the distance
3 3 3
determined for 5. Also, in the model system [Ag(HSCN4Me)
(PMe3)]2(OTf)2 (5C), optimized at the BP86/TZ2P theory
level, the equilibrium geometry is not consistent with the
arrangement found in 5. Although the covalent and coordinative
bonds compare well to the experimental values, the secondary
[AuCl(PPh3)],29
[Au2Cl2(μ-dppm)],30
[Au2Cl2(μ-dppe)],31
[Ag(OTf)(PPh3)].32 1H, 13C, 19F, and 31P NMR were recorded using
various spectrometers (Jeol Eclipse 270, Jeol Eclipse 400, Bruker DPX-
500, and Bruker-360). The spectra were measured in CDCl3 or CD2Cl2.
The chemical shifts (δ) are quoted in units of ppm, relative to external
standards Me4Si (1H, 13C), 85% H3PO4 (31P), and CCl3F (19F).
Multiplicities are abbreviated as follows: br, broad; s, singlet; d, doublet;
t, triplet; and m, multiplet. Coupling constants (J) are given in Hertz
(Hz). The mass spectra were obtained via an electrospray ionization
(ES) technique, using a Finnigan LCQ instrument. Melting points were
determined using differential scanning calorimetry (Linseis DSC PT-10
instrument). Measurements were performed at a heating rate of 5 °C/
min in closed aluminum containers with a hole (1 μm) on the top for gas
bonding Ag Ag and Ag S distances are 30.0%-36.6%
3 3 3
3 3 3
larger in 5C than the corresponding values of 5. The calculated
Ag O distances are shorter or larger than the experimental
3 3 3
ones (see Table S12 in the Supporting Information). Never-
theless, the arrangement found in 5C is closer to the geometry
found in 5, compared to that found in the dication 5B, thus
suggesting that the secondary interactions between the anions
and the dication play an important role for the stability of the
Ag2S2 core.
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Inorganic Chemistry
ARTICLE
Table 1. Crystallographic Data for 3-5
3
4
5
formula
FW [g/mol]
crystal system
space group
color/habit
size [mm3]
a [Å]
C
29H28Au2N8P2S2
C30H30Au2N8P2S2
1022.64
C42H38Ag2N8P2S4F6O6
1270.76
1008.61
triclinic
triclinic
monoclinic
P21/c (14)
colorless plate
0.3 ꢀ 0.1 ꢀ 0.02
20.7270(12)
9.0502(4)
28.0743(15)
90
P1(2)
P1(2)
colorless plate
0.15 ꢀ 0.13 ꢀ 0.03
12.6579(3)
15.1948(3)
17.7332(4)
89.517(2)
74.754(2)
78.006(2)
3214.97(13)
4
colorless block
0.2 ꢀ 0.2 ꢀ 0.1
13.2564(7)
13.5584(7)
15.7146(9)
68.583(5)
72.896(5)
69.334(5)
2415.6(2)
3
b [Å]
c [Å]
R [deg]
β [deg]
γ [deg]
V [Å3]
109.715(6)
90
4957.6(5)
4
Z
F
calcd[g/cm3]
2.084
2.109
1.703
μ[mm-1
]
9.380
9.365
1.100
F(000)
1912
1458
2544
λMo KR[Å]
0.71073
0.71073
0.71073
T [K]
100
173
200
θ min/max [°]
Refl. collected
Refl. Independ.
Refl. observed
No. parameters
Rint
4.11/26.00
49623
4.09/26.00
17509
4.18/25.09
18778
12595
9462
8705
8836
6542
3054
775
597
639
0.0578
0.0455
0.0810
R1 (obs)
0.0436
0.0556
0.1511
wR2 (all data)
0.0428
0.0537
0.0445
S
0.785
0.850
0.568
resd. dens. [e/Å3]
device type
solution
-0.80, 1.46
Oxford Xcalibur3 CCD
SIR-92
-1.80, 1.60
Oxford Xcalibur3 CCD
SIR-92
-0.62, 0.56
Oxford Xcalibur3 CCD
SIR-92
refinement
absorption correction
CCDC
SHELXL-97
multiscan
797943
SHELXL-97
multiscan
797942
SHELXL-97
multiscan
797941
MULTIRAM 1064 2000R NIR FT-Raman instrument equipped with
a Nd:YAG laser (1064 nm). The intensities are reported in percentages
relative to the most intense peak and are given in parentheses. Thin-layer
chromatography (TLC) was performed on aluminum oxide 60 F254
neutral plates or silica-gel-coated aluminum F254 plates from Merck. All
plates were visualized by UV irradiation at 254 nm and/or staining with
potassium permanganate.
Computational Details. Theoretical calculations at the DFT
level were carried out using the ADF software package33 on models of
compounds 2-5, using methylphosphine ligands. The geometries
optimizations were performed using the BP86 functional and the
TZ2P basis set, as implemented in the ADF software package. The
inner electrons were treated by frozen-core approximation, using the
large core option. The relativistic effects were considered using the zero-
order regular approximation (ZORA). To reduce the calculation time,
the model arrangements 4A, 5B, and 5C were optimized in the Ci point
group. The energy minima of the equilibrium geometries were verified
by frequency calculations. For the arrangements 2A-5A, 5B and 5C
negative frequencies (1 for 2A and 5A, 2 for 3A and 4A, 4 for 5B and 5C)
were obtained in the range of 0-50 cm-1. Calculations of the gradients
along the corresponding normal modes for the imaginary frequencies
Table 2. Energy Decomposition Analysis of the P-M Bonds
in the Model Complexes [Au(SCN4Me)(PMe3)] (2A) and
[Ag(HSCN4Me)(PMe3)]þ (5A) at the BP86/TZ2P Level
Energy (kcal/mol)
2A
-61.71
5A
-56.22
ΔEint
ΔEPauli
ΔEelstat
ΔEsteric
ΔEorb
182.89
-176.90 (72.32%)a
93.48
-106.62 (71.22%)a
5.99
-13.14
-43.08 (28.78%)a
3.71
-67.71 (27.68%)a
3.23
ΔEprep
ΔE (= -De)
-58.48
-52.51
a Values given in parentheses represent the proportion of the sum
EelstatþEorb
.
release with a nitrogen flow of 5 mL/min. IR spectra were measured in
the attenuated total reflection mode (ATR) on a Perkin-Elmer
Spectrum BX II. Raman spectra were recorded using a Bruker
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Inorganic Chemistry
ARTICLE
confirmed that the optimized arrangements are energy minima. The
bonding between the phosphine ligands and metal centers were
investigated using the energy decomposition scheme implemented in
ADF,34 based on the method of Morokuma and Ziegler.35,36 Model 3A
was studied at the MP2 theory level with a LANL2DZ basis set,37 using
the GAMESS software package.38 The basis set used for the P atoms was
augmented with one polarization and one diffuse function.39 The data
were taken from the EMSL Basis Sets Library.40 The coordinates of
the optimized structures and other relevant data are provided as
Supporting Information.
Crystal Structure Analysis. The crystallographic data were
collected using an Oxford Xcalibur3 diffractometer with a Spellman
generator (voltage of 50 kV, current of 40 mA) and a Kappa CCD area
detector with graphite-monochromated Mo KR radiation (λ = 0.71073 Å).
The data collection was undertaken using the CrysAlis CCD software,41
and the data reduction was performed with the CrysAlis Red software.42
The structures were solved with SIR-9243 and refined with SHELXL-
9744 implemented in the program package WinGX45 and finally checked
using PLATON.46 CCDC file numbers CCDC-797943 (for 3), CCDC-
797942 (for 4) and CCDC-797941 (for 5) contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre (www.ccdc.
cam.ac.uk/data request/cif).
Synthesis of [HSCN4Me] (1). To a solution of MeNCS (50 g,
0.68 mol) in H2O (500 mL) was added NaN3 (67.36 g, 1.04 mol). The
reaction mixture was stirred under reflux conditions for 6 h. The solution
was then cooled and filtered from any insoluble material present. It was
extracted twice with Et2O, to remove any unreacted isothiocyanate. The
aqueous layer was cooled and acidified with concentrated HCl (60 mL)
topH 3. Furthermore, itwas extractedthreetimeswith Et2O. Theorganic
layer was dried over MgSO4. Afterward, the solvent was evaporated in
vacuum. Recrystallization from chloroform and petroleum ether afforded
white crystals of 1. Yield (21.8 g, 28%); m.p. = 124.6-125.9 °C; 1H NMR
(400 MHz, CDCl3, 25 °C, TMS) δ = 3.92 (s, 3H, Me), 14.48 ppm (s, H,
NH); 13C NMR (100 MHz, CDCl3, 25 °C, TMS) δ = 33.98 (s, Me),
164.02 ppm (s, CN4-ring); MS (ESþ): m/z = 117 [MþH]þ.
pentane 3:1); 1H NMR (500 MHz, CDCl3, 25 °C, TMS): δ = 3.72 (t,
2J(H,P) = 11.5 Hz, 2H, -CH2-), 3.9 (s, 6H, Me), 7.30 (t, 3J(H,H) = 7.5
Hz, 8H, H-meta), 7.37 (t, 3J(H,H) = 7.5 Hz, 4H, H-para), 7.7 ppm (dd,
3J(H,H) = 7 Hz, 3J(H,P) = 21 Hz 8H, H-ortho); 13C NMR (100 MHz,
CDCl3, 25 °C, TMS): δ = 29.6 (s, -CH2-), 34.1 (s, Me), 128.1 (t, 1J(C,
3
P) = 31 Hz, C-ipso), 129.4 (t, J(C,P) = 6.5 Hz, C-meta), 132.2 (s,
C-para), 133.5 (t, 2J(C,P) = 8 Hz, C-ortho), 158.3 ppm(s, CN4-ring); 31
P
NMR (162 MHz, CDCl3, 25 °C, H3PO4 85%): δ = 30.9 ppm (s, 2P,
PPh2); IR (ATR, cm-1): ν = 970 (w), 998 (w), 1027 (w), 1100 (s) (CN4
ring), 1269 (m), 1316 (vw) (N-NdN), 704 (vw), 688 (vs) (C-S);
Raman (100 mW, 25 °C, cm-1): ν = 999 (vs), 1028 (m), 1082 (w), 1103
(w) (CN4 ring), 1271 (m) (-N-NdN), 683 (w), 706 (w) (C-S), 343
(vw) (Au-S); MS (ESþ): m/z = 893.1 [Au2(SCN4Me)(μ-dppm)]þ.
Synthesis of [{Au(SCN4Me)}2(μ-dppe)] (4). To a solution of
HSCN4Me (0.010 g, 0.086 mmol) in 15 mL of anhydrous THF was
added [Au2Cl2(μ-dppe)] (0.037 g, 0.043 mmol), and the reaction
mixture was stirred for 3 h at room temperature under argon. The
resulting yellow solution was treated dropwise with anhydrous NEt3
(0.087 g, 0.086 mmol). After stirring for an additional 1 h, the solution
was concentrated under reduced pressure and precipitated with hexane
to give 4 as a yellow solid. Yield: 0.035 g (81%); Rf = 0.77 (AcOEt/
pentane 3:1); 1H NMR (500 MHz, CDCl3, 25 °C, TMS): δ = 3.07 (s, br,
4H, -CH2-CH2-), 3.9 (s, 6H, Me), 7.5-7.47 (m, 12H, H-meta þ
H-para), 7.98-7.95 ppm (m, 8H, H-ortho); 31P NMR (109 MHz,
CDCl3, 25 °C, H3PO4 85%): δ = 38.2 ppm (s, 2P, PPh2); IR (ATR, cm-1):
ν = 967 (w), 997 (w), 1026 (w), 1037 (w), 1077 (w), 1106 (w) (CN4
ring), 1264 (w), 1276 (m), 1318(w) (-N-NdN), 690 (s), 702 (s),
698 (s) (C-S); Raman (100 mW, 25 °C, cm-1): ν = 1000 (vs), 1028
(m), 1078 (vw), 1107 (w) (CN4 ring), 1277 (m) (-N-NdN),
699(w), 706 (m) (C-S), 339 (s) (Au-S), MS (ESþ): m/z = 907.1
[Au2(SCN4Me)(μ-dppe)]þ, 824.1 [Au2S(μ-dppe)]þ.
Synthesis of [Ag(HSCN4Me)(PPh3)]2(OTf)2 (5). To a solution
of HSCN4Me (0.021 g, 0.188 mmol) in 20 mL of anhydrous CH2Cl2 was
added [Ag(OTf)(PPh3)] (0.097 g, 0.187 mmol), and the reaction
mixture was stirred for 2 h without light, at room temperature under
argon. The resulting colorless solution was concentrated under reduced
pressure and precipitated with hexane to give 5 as a white solid. Yield:
0.041 g (85%); Rf = 0.91 (AcOEt/pentane 3:1); m.p. = 159 °C; 1H NMR
(500 MHz, CDCl3, 25 °C, TMS): δ = 3.8(s, 6H, Me), 7.4-7.39 ppm(m,
15H, H-ortho þ H-meta þ H-para); 13C NMR (90 MHz, CDCl3, 25 °C,
TMS): δ = 34.5 (s, Me), 120.06 (d, 1J(C,P) = 319.4 Hz, C-ipso); 129.09
Synthesis of [Au(SCN4Me)(PPh3)] (2). To a solution of
HSCN4Me (0.0096 g, 0.082 mmol) in 15 mL of anhydrous THF was
added [AuCl(PPh3)] (0.041 g, 0.082 mmol), and the reaction mixture
was stirred for 3 h at room temperature under argon. The resulting
colorless solution was treated dropwise with anhydrous NEt3 (0.083 g,
0.082 mmol). After stirring for an additional 1 h, the solution was
concentrated under reduced pressure and precipitated with hexane to
give 2 as a white solid. Yield: 0.038 g (80%); Rf = 0.82 (AcOEt/pentane
3:1); m.p. = 154 °C; 1H NMR (270 MHz, CDCl3, 25 °C, TMS): δ =
3.94 (s, 3H, Me), 7.64-7.53 (m, 9H, H-ortho, H-para), 7.51-7.44 ppm
(m, 6H, H-meta); 13C NMR (62 MHz, CDCl3, 25 °C, TMS): δ = 33.9
(s, Me), 128.8 (d, 1J(C,P) = 40.6 Hz, C-ipso), 129.2 (d, 3J(C,P) = 8.1 Hz,
C-meta), 131.8 (s, C-para), 134.2 (d, 2J(C,P) = 9.3 Hz, C-ortho), 158.1
ppm (s, CN4-ring); 31P NMR (109 MHz, CDCl3, 25 °C, H3PO4 85%)
δ = 37.9 ppm (s, P, PPh3); IR (ATR, cm-1): ν = 967 (vw), 998 (w),
1026 (w), 1037 (w), 1076 (w), 1102 (m) (CN4 ring), 1269 (w), 1308
(vw) (N-NdN), 692 (vs), 711 (m) (C-S); Raman (100 mW, 25 °C,
cm-1): ν = 999 (w), 1027 (m), 1077 (w), 1102 (m) (CN4 ring), 1270
(m) (-N-NdN), 694 (w), 713 (vw) (C-S), 346 (vw) (Au-S); MS
(ESþ): m/z = 575.3 [MþH]þ, 721.4 [Au(PPh3)2]þ.
2
(s, C-meta), 130.8 (s, C-para), 133.7 (d, J(C,P) = 15.3 Hz, C-ortho),
161.4 ppm (s, CN4-ring); 31P NMR (162 MHz, CD2Cl2, 25 °C, H3PO4
85%): δ = 11.4 ppm (s, 2P, PPh3); 31P NMR (162 MHz, CD2Cl2, -
85 °C, H3PO4 85%): δ = 10.3 (dd, 1J(P,107Ag) = 417.5, 1J(P,109Ag) =
481.0 Hz), 11.3 (dd, 1J(P,107Ag) = 318.5, 1J(P,109Ag) = 367.6 Hz); IR
(ATR, cm-1): ν = 960 (w), 1014 (vs), 1072 (w), 1097 (m) (CN4 ring),
1524 (m) (N-CdS), 1337 (m), 1014 (ws), 750 (s) (CdS), 1233 (s)
(νasSO3), 1203 (vs) (νs CF3), 1164 (s) (νasCF3), 1042 (w) (νsSO3);
Raman (100 mW, 25 °C, cm-1): ν = 999 (vs), 1026 (m) (CN4 ring),
1285 (vw) (N-NdN), 1586 (m) (N-CdS), 2966 (w), 3060 (m),
3142 (vw), 3169 (vw) (N-H and C-H), 758 (w), 1343 (m) (CdS),
1234 (vw) (νasSO3), 1183 (vw) (νsCF3), 1157 (vw) (νasCF3), 1097 (w)
(νsSO3), 350 (vw) (Ag-S); MS (ESþ): m/z = 631.2 [Ag(PPh3)2]þ.
’ ASSOCIATED CONTENT
Synthesis of [{Au(SCN4Me)}2(μ-dppm)] (3). To a solution of
HSCN4Me (0.010 g, 0.086 mmol) in 15 mL of anhydrous THF was
added [Au2Cl2(μ-dppm)] (0.036 g, 0.043 mmol), and the reaction
mixture was stirred for 3 h at room temperature under argon. The
resulting yellow solution was treated dropwise with anhydrous NEt3
(0.087 g, 0.086 mmol). After stirring for an additional 1 h, the solution
was concentratedunder reduced pressure andprecipitatedwithhexane to
give 3 as a light orange solid. Yield: 0.040 g (91%); Rf = 0.48 (AcOEt/
S
Supporting Information. NMR spectra, XRD studies,
b
and theoretical calculations. The crystal structures of compounds
3, 4, and 5 have been deposited at the Cambridge Crystal-
lographic Data Centre and allocated the deposition numbers
CCDC-797943, CCDC-797942, and CCDC-797941. This
material is available free of charge via the Internet at http://
pubs.acs.org.
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Inorganic Chemistry
ARTICLE
’ AUTHOR INFORMATION
(14) (a) Muetterties, E. L.; Alegranti, C. W. J. Am. Chem. Soc. 1972,
94, 6386–6391. (b) Barron, P. F.; Dyason, J. C.; Healy, P. C.; Engelhardt,
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’ ACKNOWLEDGMENT
Financial support from Deutscher Akademischer Austausch
Dienst (DAAD), CNCSIS-UEFISCSU TD66/2007 (Romania)
is gratefully acknowledged.
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