The use of imidazolium-2-dithiocarboxylates in the formation of gold(I) complexes and gold nanoparticles

Article abstract of DOI:10.1021/ic9021504

The imidazolium-2-dithiocarboxylate ligands IPr 3 CS₂, IMes 3 CS₂, and IDip 3 CS₂ react with [AuCl(PPh3)] to yield [(Ph₃P)Au(S₂C 3 IPr)]+, [(Ph₃P)Au(S ₂C 3 IMes)]+, and [(Ph

Full text of DOI:10.1021/ic9021504

1784 Inorg. Chem. 2010, 49, 1784–1793
DOI: 10.1021/ic9021504
The Use of Imidazolium-2-dithiocarboxylates in the Formation of Gold(I)
Complexes and Gold Nanoparticles†
Saira Naeem,‡ Lionel Delaude,§ Andrew J. P. White,‡ and James D. E. T. Wilton-Ely*,‡
‡Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ,
U.K. and §Centre for Education and Research on Macromolecules (CERM), Institut de Chimie (B6a),
ꢀ
ꢁ
ꢁ
Universite de Liege, Sart-Tilman par 4000 Liege, Belgium
Received October 30, 2009
The imidazolium-2-dithiocarboxylate ligands IPr CS2, IMes CS2, and IDip CS2 react with [AuCl(PPh3)] to yield
þ3
3
3
[(Ph3P)Au(S2C IPr)]þ, [(Ph3P)Au(S2C IMes)] , and [(Ph3P)Au(S2C IDip)]þ, respectively. The compounds
3
3
3
[(L)Au(S2C IMes)]þ are prepared from the reaction of IMes CS2 with [AuCl(L)] (L = PMe3, PCy3, CNtBu). The
carbene-containing precursor [(IDip)AuCl] reacts with IPr CS2 and IMes CS2 to afford the complexes
3
3
3
3
[(IDip)Au(S2C IPr)]þ and [(IDip)Au(S2C IMes)]þ with two carbene units, one bound to the metal center and the
other to the dithiocarboxylate unit. Treatment of the diphosphine-gold complex [(dppm)(AuCl)2] with 1 equiv of
3
3
IMes CS2 yields [(dppm)Au2(S2C IMes)]2þ, while the reaction of [L2(AuCl)2] (L2 = dppb, dppf) with 2 equiv of
3
3
3
IMes CS2 results in[(L2){Au(S2C IMes)}2]2þ. The homoleptic complexes [Au(S2C IPr)2]2þ, [Au(S2C IMes)2]2þ
,
3
3
3
and [Au(S2C IDip)2]2þ are obtained from the reaction of [AuCl(tht)] with 2 equiv of the appropriate imidazolium-2-
3
dithiocarboxylate ligand. The compounds [(Ph3P)Au(S2C NHC)]þ (NHC = IMes, IDip) and [(IDip)Au(S2C NHC)]þ
(NHC = IPr, IMes) are characterized crystallographically. The IMes CS2 ligand is also used to prepare functionalized
3
3
3
gold nanoparticles with diameters of 11.5 ((1.2) and 2.6 ((0.3) nm.
Introduction
xanthate species. Extensive reviews of the chemistry of dithio
ligands indicate that the situation has improved little over the
years.2
Along with phosphorus donors, gold(I) chemistry has
traditionally been dominated by sulfur-based ligands, with
many complexes finding applications in fields as diverse as
medicine, electronics, and decoration.1 Yet, compared to
metal compounds of dithiocarbamate2a-c or even xanthate
ligands,2a,b,d examples of dithiocarboxylate complexes
(LnMS2CR, where R is a carbon-based substituent) are still
scarce in theliterature.2a,b This difference may be explainedat
least in part by the more challenging synthesis of dithiocar-
boxylate ligands compared to analogous dithiocarbamate or
The lack of exploration in the field of dithiocarboxylate
ligands may be contrasted with the explosion of interest in N-
heterocyclic carbenes (NHCs)3 since the first representative
of this new class of divalent carbon species was isolated and
characterized in 19913a (although earlier contributions were
also important3b,c). Often seen as an excellent alternative to
phosphines, imidazol-2-ylidene derivatives have been em-
braced by those involved in catalysis. Perhaps the most
prominent examples of NHCs as ancillary ligands are found
in second-generation alkene metathesis catalysts, such as the
Grubbs benzylidene complexes [Ru(dCHPh)(NHC)Cl2-
(PCy3)] (Scheme 1).4 The tunable, electron-rich nature and
steric bulk of these heterocycles, alongside their lack of
lability, offer excellent catalytic attributes that have been
successfully employedwith many more transition metalsthan
just ruthenium.5 In gold(I) chemistry,6 Burini et al.7 and then
Raubenheimer et al.8 pioneered the preparation of
(homoleptic) gold NHC complexes. Later, Nolan and co-
workers provided straightforward syntheses of [(NHC)-
AuCl] derivatives (Scheme 1)9 and exploited the use of such
† Dedicated to Prof. Dr. Hubert Schmidbaur on the occasion of his 75th
birthday.
*To whom correspondence should be addressed. E-mail: j.wilton-ely@
imperial.ac.uk.
(1) Gold;Progress in Chemistry, Biochemistry and Technology; Schmidbaur,
H., Ed.; John Wiley & Sons Inc.: New York, 1999.
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Prog. Inorg. Chem. 2005, 53, 71–561. (d) Tiekink, E. R. T.; Haiduc, I. Prog.
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1991, 113, 361–363. (b) Ofele, K. J. Organomet. Chem. 1968, 12, 42–43.
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141–142. (d) Carbene Chemistry: From Fleeting Intermediates to Powerful
Reagents; Bertrand, G., Ed.; Marcel Dekker: New York, 2002. (e) N-Hetero-
cyclic Carbenes in Synthesis; Nolan, S. P., Ed.; Wiley-VCH: Weinheim,
Germany, 2006. (f) N-Heterocyclic Carbenes in Transition Metal Catalysis;
Glorius, F., Ed.; Topics in Organometallic Chemistry; Springer: Berlin, 2007;
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€
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r
pubs.acs.org/IC
Published on Web 01/20/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 4, 2010 1785
Scheme 1. Notable Examples of Complexes Bearing NHC Ligands
Scheme 3. Imidazolium-2-dithiocarboxylate Ligands Used in This
Work
Scheme 2. Imidazoliumcarboxylate and -dithiocarboxylate Zwitter-
ions Derived from NHCs
ligands for monovalent gold complexes, whether homoleptic
or with a range of phosphorus- or carbon-based coligands.
Furthermore, we show that they are also able to function as
surface units for nanoparticles of gold.
complexes in catalysis,10 building on early work by Teles etal.
on gold(I) compounds for the addition of alcohols to
alkynes.11
The discovery that NHCs react with carbon dioxide to
form carboxylate inner salts allowed the use of zwitterionic
Results and Discussion
Formation of Gold(I) Complexes. Our recent work on
gold(I) complexes has centered on the incorporation of
gold units into multimetallic systems using the zwitter-
ionic dithiocarbamate S2CNC4H8NH2.14 This led us to
investigate similar reactions using betaines obtained from
the reaction of NHCs (generated in situ) with carbon
disulfide (Scheme 3).15 The steric tunability of these
ligands and their stability to loss of the CS2 moiety made
them attractive species with which to explore gold(I)
chemistry. To date, the coordination behavior of
NHC CO2 adducts to generate carbene ligands within the
3
coordination sphere of the metal, while permitting the easy
storage and manipulation of otherwise oxygen- and moist-
ure-sensitive carbene species (Scheme 2).12 This approach has
been extended very recently to the reaction of NHCs with
carbon disulfide to yield zwitterionic imidazolium-2-dithio-
carboxylate betaines.13a Unlike their carboxylate analogues,
these species are not expected to readily eliminate carbon
disulfide upon reaction with metals. Preliminary studies
indicate that this is indeed the case with ruthenium and
osmium compounds.13b In this report, we detail the first
NHC CS2 zwitterions has been investigated with only a
3
few transition-metal salts (including one trivalent gold
example),16 and much of this work enjoyed only limited
characterization, lacking NMR or structural studies, for
example. A very recent example of chelation to ruthen-
ium(II) arene complexes has also been published.13b To
the best of our knowledge, no gold(I) complexes have
been reported so far.
in-depth study of the coordination chemistry of NHC CS2
3
zwitterions with gold and we show that they are excellent
The most habitual starting point for gold(I) chemistry
is the archetypal complex [AuCl(PPh3)]. Treatment of
a dichloromethane solution of this compound with a
slight excess of the least bulky imidazolium-2-dithiocar-
€
(5) (a) Herrmann, W. A.; Kocher, C. Angew. Chem., Int. Ed. Engl. 1997,
36, 2162–2187. (b) Jafarpour, L.; Nolan, S. P. Adv. Organomet. Chem. 2001, 46,
181–222. (c) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290–1309.
(d) Herrmann, W. A.; Weskamp, T.; Bohm, V. P. W. Adv. Organomet. Chem.
2002, 48, 1–69. (e) Crudden, C. M.; Allen, D. P. Coord. Chem. Rev. 2004, 248,
2247–2273. (f) Scott, N. M.; Nolan, S. P. Eur. J. Inorg. Chem. 2005, 1815–1828.
(g) Dragutan, I.; Dragutan, V.; Delaude, L.; Demonceau, A. Arkivoc 2005, 10,
206–253. (h) Garrison, J. C.; Youngs, W. J. Chem. Rev. 2005, 105, 3978–4008.
(i) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122–3172.
(j) McGuinness, D. Dalton Trans. 2009, 6915–6923.
(6) Raubenheimer, H. G.; Cronje, S. Chem. Soc. Rev. 2008, 37, 1998–
2011.
(7) Bonati, F.; Burini, A.; Pietroni, B. R.; Bovio, B. J. Organomet. Chem.
1989, 375, 147–160.
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1996, 511, 177–184.
(9) de Fremont, P.; Scott, N. M.; Stevens, E. D.; Nolan, S. P. Organo-
metallics 2005, 24, 2411–2418.
€
boxylate ligand used in this study, IPr CS2, in the
3
presence of NH4PF6 led to a pale-brown solid in 73% yield
(Scheme 4). Apart from the resonance due to the hexa-
fluorophosphate counteranion, only one singlet in the 31P
NMR spectrum was observed at 36.0 ppm, indicating
the formation of a single new product. The presence of
the isopropyl-substituted dithiocarboxylate ligand was
evidenced by a doublet at 1.55 ppm and a septet at
4.87 ppm, showing mutual coupling of 6.8 Hz. To lower
field, in addition to resonances for the PPh3 ligand,
was a singlet at 7.36 ppm attributed to the HCdCH
unit of the imidazole ring. The overall composition as
(10) (a) Fructos, M. R.; Belderrain, T. R.; de Fremont, P.; Scott, N. M.;
Nolan, S. P.; Diaz- Requejo, M. M.; Perez, P. J. Angew. Chem., Int. Ed. 2005,
44, 5284–5288. (b) Marion, N.; Nolan, S. P. Chem. Soc. Rev. 2008, 37, 1776–
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1782. (c) Marion, N.; Ramon, R. S.; Nolan, S. P. J. Am. Chem. Soc. 2009, 131,
448–449.
(11) Teles, J. H.; Brode, S.; Chabanas, M. Angew. Chem., Int. Ed. 1998,
37, 1415–1418.
(12) (a) Tudose, A.; Demonceau, A.; Delaude, L. J. Organomet. Chem.
(14) (a) Wilton-Ely, J. D. E. T.; Solanki, D.; Hogarth, G. Eur. J. Inorg.
Chem. 2005, 4027–4030. (b) Knight, E. R.; Solanki, D.; Hogarth, G.; Holt, K. B.;
Thompson, A. L.; Wilton-Ely, J. D. E. T. Inorg. Chem. 2008, 47, 9642–9653.
(c) Knight, E. R.; Leung, N. H.; Thompson, A. L.; Hogarth, G.; Wilton-Ely,
J. D. E. T. Inorg. Chem. 2009, 48, 3866–3874.
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2006, 691, 5356–5365. (b) Tudose, A.; Delaude, L.; Andre, B.; Demonceau, A.
Tetrahedron Lett. 2006, 47, 8529–8533. (c) Duong, H. A.; Tekavec, T. N.; Arif,
A. M.; Louie, J. Chem. Commun. 2004, 112–113. (d) Voutchkova, A. M.;
Appelhans, L. N.; Chianese, A. R.; Crabtree, R. H. J. Am. Chem. Soc. 2005, 127,
17624–17625. (e) Voutchkova, A. M.; Feliz, M.; Clot, E.; Eisenstein, O.;
Crabtree, R. H. J. Am. Chem. Soc. 2007, 129, 12834–12846.
(13) (a) Delaude, L.; Demonceau, A.; Wouters, J. Eur. J. Inorg. Chem.
2009, 1882–1891. (b) Delaude, L.; Sauvage, X.; Demonceau, A.; Wouters, J.
Organometallics 2009, 28, 4056–4064.
(15) (a) Kuhn, N.; Bohnen, H.; Henkel, G. Z. Naturforsch., B: Chem. Sci.
1994, 49, 1473–1480. (b) Kuhn, N.; Niquet, E.; Steimann, M.; Walker, I. Z.
Naturforsch., B: Chem. Sci. 1999, 54, 1181–1187. (c) Kuhn, N.; Steimann, M.;
Weyers, G. Z. Naturforsch., B: Chem. Sci. 1999, 54, 427–433. (d) Delaude, L.
Eur. J. Inorg. Chem. 2009, 1681–1699.
(16) (a) Borer, L. L.; Kong, J. V. Inorg. Chim. Acta 1986, 122, 145–148.
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129, 223–226.

1786 Inorganic Chemistry, Vol. 49, No. 4, 2010
Naeem et al.
Scheme 4. Preparation of the Gold(I) Imidazolium-2-dithiocarboxylate Complexes
When the bulkier IMes CS2 betaine was allowed to
react with [AuCl(PPh3)] and NH4PF6 under the same
experimental conditions, [(Ph3P)Au(S2C IMes)]PF6 (2)
3
3
was isolated in 84% yield (Scheme 4). The new ligand was
readily identified by singlets at 2.25 and 2.37 ppm for the
o- and p-methyl substituents of the mesityl groups. The
aromatic meta proton appeared as a singlet at 7.08 ppm,
slightly upfield from the imidazole HCdCH proton at
7.41 ppm. Single crystals of the complex were grown, and
a structural study was undertaken (Figure 1). The data
obtained will be discussed in the context of the other
structures bearing NHC CS2 ligands (vide infra).
The most sterically demanding ligand used in this work
was the IDip CS2 zwitterion, which formed [(Ph3P)-
3
3
Au(S2C IDip)]PF6 (3) with [AuCl(PPh3)] and NH4PF6.
3
1H NMR analysis of this compound revealed doublets at
1.24 (JHH = 7.1 Hz) and 1.36 (JHH = 6.7 Hz) ppm for the
methyl groups, while a septet for the CHMe2 protons
was noted at 2.66 (JHH = 6.8 Hz) ppm. The remaining
aromatic resonances of the S2C IDip unit were obscured
3
˚
Figure 1. Molecular structure of 2. Selected bond lengths (A) and angles
by features due to the triphenylphosphine ligand. In order
to investigate the effect on the structure of an increase in
steric bulk from IMes CS2 to IDip CS2, a structural
(deg); Au-P(31) 2.2622(7), Au-S(1) 2.3223(7), S(1)-C(2) 1.708(3),
C(2)-C(4) 1.487(4), C(2)-S(3) 1.640(3), C(4)-N(5) 1.334(3), C(4)-N(8)
1.337(3); P(31)-Au-S(1) 178.94(3), C(2)-S(1)-Au 102.03(9). Hydro-
gen atoms and the hexafluorophosphate counteranion are omitted for
clarity.
3
3
investigation was carried out (Figure 2 and the Structural
Discussion section).
The observation of the fascinating phenomenon of
aurophilic interactions;bonding contacts between for-
mally closed-shell d10 gold(I) centers;depends on the
steric profile of the ligand set in these (typically) linear
compounds.17 Adjustment of the steric attributes of
the molecule was achieved by replacing the complex
[AuCl(PPh3)] with [AuCl(PCy3)], which reacted smoothly
[(Ph3P)Au(S2C IPr)]PF6 (1) was based on an abundant
3
molecular ion in the ES mass spectrum at m/z 687 and
good agreement of elemental analysis. Although crystals
suitable for X-ray diffraction analysis could not be
obtained, linear coordination was assumed with the
possibility of interaction with the other sulfur donor of
the dithiocarboxylate ligand (i.e., anisobidentate coor-
dination).
(17) Schmidbaur, H.; Schier, A. Chem. Soc. Rev. 2008, 37, 1931–1951.

Article
Inorganic Chemistry, Vol. 49, No. 4, 2010 1787
˚
Figure 3. Molecular structure of 7. Selected bond lengths (A) and angles
(deg); Au-C(21) 2.025(3), Au-S(1) 2.3047(8), S(1)-C(2) 1.701(4),
C(2)-C(4) 1.495(5), C(2)-S(3) 1.639(4), C(4)-N(5) 1.336(5), C(4)-N(8)
1.345(5), C(21)-N(25) 1.341(4), C(21)-N(22) 1.347(4); C(21)-Au-S(1)
175.98(9), C(2)-S(1)-Au 106.99(12). Hydrogen atoms and the hexa-
fluorophosphate counteranion are omitted for clarity.
˚
Figure 2. Molecular structure of 3. Selected bond lengths (A) and angles
(deg); Au-P(41) 2.2595(5), Au-S(1) 2.3147(5), S(1)-C(2) 1.7027(14),
C(2)-C(4) 1.483(2), C(2)-S(3) 1.6420(16), C(4)-N(8) 1.343(2),
C(4)-N(5) 1.343(2); P(41)-Au-S(1) 173.63(2), C(2)-S(1)-Au
104.76(6). Hydrogen atoms and the hexafluorophosphate counteranion
are omitted for clarity.
product showed doublets for the isopropyl methyl groups
(1.31 and 1.38 ppm) and a septet (2.86 ppm) showing
mutual coupling of 6.9 Hz for the isopropyl groups of the
IDip ligand. The remaining protons of the metal-bonded
with IMes CS2 to afford [(Cy3P)Au(S2C IMes)]PF6 (4)
3
3
in 75% yield. This new compound displayed spectro-
scopic features similar to those of 2 apart from multiplets
attributed to the cyclohexyl protons between 1.24 and
2.08 ppm in the 1H NMR spectrum. In order to provide a
contrast to 4, the precursor [AuCl(PMe3)], bearing the
smallest readily available phosphine, was employed
carbene were observed at 7.24 (s, HCdCH), 7.40(d, JHH
=
7.8 Hz), and 7.62 (t, JHH = 7.8 Hz) ppm. An abundant
molecular ion at m/z 813 in the electrospray (ES) mass
spectrum and good agreement of the elemental analysis
with calculated values supported the formulation as
to prepare [(Me3P)Au(S2C IMes)]PF6 (5). A doublet at
3
[(IDip)Au(S2C IPr)]PF6 (7). The pale-green complex
3
1.58 ppm in the 1H NMR spectrum, showing coupling to
the phosphorus nucleus of 11.2 Hz, was assigned to the
protons of the trimethylphosphine ligand. The precursor
[AuCl(CNtBu)] also offers a low steric encumbrance at
the gold center and has been used to generate thiolate
complexes with unusual solid-state structures.18 Its reac-
[(IDip)Au(S2C IMes)]PF6 (8) was also prepared in a
3
similar fashion (Scheme 4). Single crystals of complexes
7and 8were grown and their molecular structures determined
by X-ray diffraction (Figures 3 and 4). These compounds
provide fascinating examples of molecular architectures
in which the carbene motif is bonded directly to the metal
as well as via an intermediate dithiocarboxylate unit
(see the Structural Discussion section).
tion with IMes CS2 in the presence of NH4PF6 led to the
3
elimination of NH4Cl and formation of [(tBuNC)Au-
(S2C IMes)]PF6 (6) in 93% yield (Scheme 4). The reten-
3
The synthesis of digold compounds bearing the
NHC CS2 ligands was then explored. The length of the
tion of the isonitrile ligand was clearly indicated by the
singlet observed at 1.54 ppm for the tert-butyl group in
the 1H NMR spectrum. Unfortunately, no single crystals
of complexes 4-6 could be obtained with which to
ascertain the effect of the diverse steric profiles of these
3
hydrocarbon bridge in the compounds [{Ph2P(CH2)nPPh2}-
(AuCl)2] has been shown to influence the diverse extended
structures in the solid state.1 Longer bridges such as those in
[(dppb)(AuCl)2] [dppb = 1,4-bis(diphenylphosphino)but-
ane] do not display intramolecular aurophilic interactions,
while shorter ones, especially [(dppm)(AuCl)2] [dppm =
1,1-bis(diphenylphosphino)methane] favor “A-frame” com-
plexes with short contacts between the neighboring gold
centers. Incorporation of this motif in compounds with
dithio ligands (e.g., [(dppm)Au2(S2CNR2)]þ) has been
reported.19 The reaction of [(dppb)(AuCl)2] or [(dppf)-
(AuCl)2] [dppf = 1,10-bis(diphenylphosphino)ferrocene]
ligands on potential Au Au contacts.
3 3 3
Although phosphine complexes of the general formula
[AuCl(PR3)] have long been the traditional starting point
for much gold(I) chemistry, the development of NHCs as
alternative ligands to phosphines has led to the incorpora-
tion of these excellent donors into gold complexes.6,9
Thus, a dichloromethane solution of [AuCl(IDip)] was
treated with the least bulky of the dithiocarboxylate
ligands used in this study, IPr CS2, to afford a purple
3
with 2 equiv of IMes CS2 led to the green, dicatio-
nic complexes [(dppb){Au(S2C IMes)}2](PF6)2 (9) and
3
product in 71% yield (Scheme 4). In addition to reso-
nances for the IPr CS2 ligand, H NMR analysis of the
1
3
3
[(dppf){Au(S2C IMes)}2](PF6)2 (10) in 88% and 90%
yields, respectively (Scheme 4). The dppb ligand gave rise
3
(18) (a) Wilton-Ely, J. D. E. T.; Schier, A.; Schmidbaur, H. Organometallics
2001, 20, 1895–1897. (b) Wilton-Ely, J. D. E. T.; Ehlich, H.; Schier, A.; Schmidbaur,
H. Helv. Chim. Acta 2001, 84, 3216–3232. (c) Wilton-Ely, J. D. E. T.; Schier, A.;
Mitzel, N. W.; Schmidbaur, H. Inorg. Chem. 2001, 40, 6266–6271. (d) Wilton-
Ely, J. D. E. T.; Schier, A.; Mitzel, N. W.; Nogai, S.; Schmidbaur, H.
J. Organomet. Chem. 2002, 643, 313–323.
(19) (a) Tang, S. S.; Chang, C.-P.; Lin, I. J. B.; Liou, L.-S.; Wang, J.-C.
Inorg. Chem. 1997, 36, 2294–2300. (b) Tang, S. S.; Lin, I. J. B.; Liou, L.-S.;
Wang, J.-C. J. Chin. Chem. Soc. 1996, 43, 327–335. (c) Bardaji, M.; Laguna, A.;
Laguna, M. J. Chem. Soc., Dalton Trans. 1995, 1255–1258.

1788 Inorganic Chemistry, Vol. 49, No. 4, 2010
Naeem et al.
Figure 5. TEM images of (left) NP1 and (right) NP2.
singlet at 7.07 ppm observed in the spectrum of the free
ligand. Related dithiocarbamate compounds, such as
[Au2(S2CNEt2)2],22 are notable for the very short gold-gold
contacts seen in the solid state; however, no crystals
suitable for X-ray diffraction of complexes 12-14 could
be obtained.
Nanoparticle Preparation. Since their early develop-
ment,23 monolayer-protected gold nanoparticles have
been the focus of sustained interest.24 In these materials,
thiols are by far the most commonly used surface units,
and only recently have alternative sulfur-based mole-
cules, such as dithiocarbamates,25 been used to protect
the metal surface. We have recently investigated the use of
metalladithiocarbamates to functionalize the surface of
gold nanoparticles with ruthenium and nickel units.14,26
˚
Figure 4. Molecular structure of 8. Selected bond lengths (A) and angles
(deg); Au-C(31) 2.017(4), Au-S(1) 2.2912(10), S(1)-C(2) 1.702(5),
C(2)-C(4) 1.494(5), C(2)-S(3) 1.643(4), C(4)-N(8) 1.333(6), C(4)-N(5)
1.339(6), C(31)-N(32) 1.341(5), C(31)-N(35) 1.348(5); C(31)-Au-S(1)
169.54(11), C(2)-S(1)-Au 105.30(15). Hydrogen atoms and the hexa-
fluorophosphate counteranion are omitted for clarity.
to multiplets at 1.62 and 2.37 ppm in the 1H NMR spectrum
of complex 9, in addition to resonances for the IMes CS2
3
unit, which were similar to those observed in the spectra of
the monometallic complexes 2, 4-6, and 8. In complex 10,
the presence of the ferrocenyl unit was indicated by two
In order to broaden the scope of NHC CS2 ligands in
gold chemistry, the potential of IMes CS2 for the pre-
3
3
1
paration of gold nanoparticle materials was explored.
Citrate-stabilized gold nanoparticles were generated27
from HAuCl4, and a dichloromethane-methanol solu-
broad singlets at 4.23 and 4.38 ppm in the H NMR
spectrum. Integration of the spectra for both 9 and 10
clearly indicated that two dithiocarboxylate ligands
were present, rather than a single ligand forming a metalla-
tion of IMes CS2 was added to the resulting suspension.
3
cycle.14b,20,21 This is in contrast to the product of IMes CS2
An instant darkening of the reaction mixture indicated
the displacement of the citrate shell and the formation of
IMes CS2-stabilized nanoparticles (NP1). The excess
3
with [(dppm)(AuCl)2], which was formulated as [(dppm)-
{Au2(S2C IMes)}](PF6)2 (11) on the basis of the ratio bet-
ween the methylene protons at 3.72 (t, JHP = 12.3 Hz) ppm
and the resonances of the IMes CS2 ligand. This composi-
3
3
ligand present was removed by washing with dichloro-
methane, and the displaced citrate was eliminated by
washing with water (Scheme 5). The material proved
soluble in deuterated acetone, and a 1H NMR spectrum
revealed broadened resonances at chemical shifts similar
3
tion was further supported by elemental analysis and mass
spectrometry data.
Many dithio ligands, such as dithiocarbamates,2c form
homoleptic digold complexes of the form [Au2(S2CNR2)2].
To investigate whether the dithiocarboxylate ligands
examined in this study followed the same reacti-
vity, [AuCl(tht)] (tht = tetrahydrothiophene) was treated
(23) (a) Giersig, M.; Mulvaney, P. Langmuir 1993, 9, 3408–3413. (b) Brust,
M.; Walker, M.; Bethell, D.; Schiffrin, D. J.; Whyman, R. J. Chem. Soc., Chem.
Commun. 1994, 801–802. (c) Brust, M.; Fink, J.; Bethell, D.; Schiffrin, D. J.;
Kiely, C. J. J. Chem. Soc., Chem. Commun. 1995, 1655–1656. (d) Hostetler,
M. J.; Wingate, J. E.; Zhong, C.-J.; Harris, J. E.; Vachet, R. W.; Clark, M. R.;
Londono, J. D.; Green, S. J.; Stokes, J. J.; Wignall, G. D.; Glish, G. L.; Porter,
M. D.; Evans, N. D.; Murray, R. W. Langmuir 1998, 14, 17–30.
(24) (a) Daniel, M.-C.; Astruc, D. Chem. Rev. 2004, 104, 293–346.
(b) Sperling, R. A.; Gil, P. R.; Zhang, F.; Zanella, M.; Parak, W. J. Chem. Soc.
Rev. 2008, 37, 1896–1908. (c) Wilson, R. Chem. Soc. Rev. 2008, 37, 2028–2045.
(d) Ofir, Y.; Samanta, B.; Rotello, V. M. Chem. Soc. Rev. 2008, 37, 1814–1825.
(e) Laaksonen, T.; Ruiz, V.; Liljeroth, P.; Quinn, B. M. Chem. Soc. Rev. 2008, 37,
1836–1846.
with 1 equiv of each NHC CS2 betaine in the presence
of NH4PF6 to give the brown digold complexes
3
[Au2(S2C NHC)2](PF6)2 [NHC = IPr (12), IMes (13),
IDip (14); Scheme 4]. This formulation followed from
3
spectroscopic and analytical data. The 1H NMR spectra
(in CD2Cl2) of compound 14 and the free IDip CS2
3
ligand displayed similar resonances, with a few notable
differences. One such divergence was the broad singlet
observed in complex 14 for the isopropyl CHMe2 protons
at 2.52 ppm rather than the sharp septet seen in the
spectrum of the ligand at 2.97 (JHH = 6.8 Hz) ppm. A
similar broadening was also observed for the HCdCH
imidazole proton at 7.46 ppm in contrast to the sharp
(25) (a) Wessels, J. M.; Nothofer, H.-G.; Ford, W. E.; von Wrochem, F.;
Scholz, F.; Vossmeyer, T.; Schroedter, A.; Weller, H.; Yasuda, A. J. Am.
ꢀ
Chem. Soc. 2004, 126, 3349–3356. (b) Zhao, Y.; Perez-Segarra, W.; Shi, Q.; Wei,
A. J. Am. Chem. Soc. 2005, 127, 7328–7329. (c) Vickers, M. S.; Cookson, J.;
Beer, P. D.; Bishop, P. T.; Thiebaut, B. J. Mater. Chem. 2006, 16, 209–215.
(d) Cormode, D. P.; Davis, J. J.; Beer, P. D. J. Inorg. Organomet. Polym. 2008,
18, 32–40. (e) Sharma, J.; Chhabra, R.; Yan, H.; Liu, Y. Chem. Commun. 2008,
2140–2142.
(26) (a) Knight, E. R.; Cowley, A. R.; Hogarth, G.; Wilton-Ely, J. D. E. T.
Dalton Trans. 2009, 607–609. (b) Knight, E. R.; Leung, N. H.; Lin, Y. H.;
Cowley, A. R.; Watkin, D. J.; Thompson, A. L.; Hogarth, G.; Wilton-Ely, J. D. E. T.
Dalton Trans. 2009, 3688–3697.
(27) Grabar, K. C.; Freeman, R. G.; Hommer, M. B.; Natan, M. J. Anal.
Chem. 1995, 67, 735–743.
(20) Canales, F.; Gimeno, M. C.; Jones, P. G.; Laguna, A.; Sarroca, C.
Inorg. Chem. 1997, 36, 5206–5211.
(21) Gimeno, M. C.; Laguna, A. Gold Bull. 1999, 32, 90–95.
(22) Heinrich, D. D.; Wang, J. C.; Fackler, J. P., Jr. Acta Crystallogr.,
Sect. C 1990, C46, 1444–1447.

Article
Inorganic Chemistry, Vol. 49, No. 4, 2010 1789
Scheme 5. Preparation of Gold Nanoparticles (NP1 and NP2) with IMes CS2 Surface Units
3
to those found in free IMes CS2. IR spectroscopy showed
examples of NHC CS2 coordinated to gold(I), but the
Au-S(1) distances of 2.3047(8) and 2.2912(10) A in 7 and
8 are longer than those found in comparable isonitrilethiolate
3
3
˚
peaks almost identical with those displayed by the ligand
itself, including νNCN and νSCS absorptions at 1486 and
1049 cm-1, respectively. The lack of change in the IR data
upon coordination of these ligands has been commented
on recently in a study on ruthenium arene complexes.13b
Analysis of NP1 using transmission electron microscopy
(TEM) revealed nanoparticles of diameter 11.5 ((1.2)
nm, as shown in Figure 5.
species, such as the 1,3,4-thiadiazole-2,5-disulfide com-
t
18a
˚
pound, [(C2N2S3)(AuCN Bu)2] [2.279(2) and 2.272(2) A]
t
29
˚
or [( BuNC)Au(SC6H4CO2H-2)] [2.278(5) A]. The Au-S
distances of 2.3223(7) and 2.3147(5) A found for 2 and 3,
˚
˚
respectively, are shorter than that of 2.3334(11) A found for
[(Ph3P)Au(S2CNC4H8)].28 The C(2)-S(3) bond lengths of
˚
In a similar fashion, the more direct method pioneered
by Brust et al.23b was used to form nanoparticles of
smaller size (NP2) starting from HAuCl4, tetraoctylam-
1.640(3), 1.6420(16), 1.639(4), and 1.643(4) A are all sub-
stantially shorter than the C(2)-S(1) bond lengths [1.708(3),
˚
1.7027(14), 1.701(4), and 1.702(5) A] of the sulfur atom [S(1)]
monium bromide (TOAB), IMes CS2, and sodium bor-
3
coordinated directly to the metal, indicating some multiple-
bond character. The corresponding distances for the free
ohydride (Scheme 5). This material was washed with
water; however, removal of free IMes CS2 proved more
ligand are between these values at 1.667(3) A.13a Given that
˚
3
˚
problematic because of its similar solubility to the nano-
particle material itself. Eventually, it was found that
warming in acetonitrile dissolved all of the solid and
cooling at -20 °C led to crystallization of the free
the sum of the van der Waals radii for gold and sulfur is 3.46 A,
˚
the Au-S3 distance of 3.3549(8) A in 2 indicates a weak
˚
˚
interaction, although those of 3.4825(5) A in 3, 3.5612(9) A in
˚
7, and 3.4817(11) A in 8 are too long to be considered as
IMes CS2 zwitterions. Repeating this procedure and
significant bonding interactions. It is perhaps surprising that
there is no more interaction between this arm of the chelate
and the metal center (particularly for 3), given the precedent
for such anisobidentate coordination in gold dithiocarba-
mate compounds, such as [(Ph3P)Au(S2CNC4H8)], which
3
removing the crystals formed allowed the unbound sur-
face units to be separated. TEM imaging (Figure 5)
indicated that the nanoparticles were of average diameter
2.6 ((0.3) nm and showed extensive interparticle agglo-
meration (Figure 5).
28
˚
displays a corresponding Au-S distance of 3.0440(13) A.
Nevertheless, the preparation of NP1 and NP2 illus-
trates that imidazolium-2-dithiocarboxylates are suitable
protecting groups for gold nanoparticles and thereby
extends the scope of dithio surface units in this arena
beyond dithiocarbamates.
Despite the conducive planarity of the heterocyclic unit, the
formation of intermolecular Au Au contacts is prevented
3 3 3
by the steric demands of the substituents. The cationic nature
of the IMes CS2 unit is not reflected in any difference of the
3
C(4)-N(8) or C(4)-N(5) bond lengths in the heterocycle
compared to the Dip carbene unit; however, these distances
˚
Structural Discussion
are shorter than 1.374(6) and 1.387(6) A found for the free
ligand.13a
The geometryat gold isalmost linearin allfourstructurally
characterized complexes with L-Au-S angles lying between
178.94(3)° for 2 and 169.54(11)° for 8. The Au-P distances of
Conclusions
˚
2.2622(7) (2) and 2.2595(5) (3) A are comparable to that of
The first examples of gold(I) complexes of dithiocarboxy-
late ligands derived from NHCs have been prepared and
˚
2.2447(10) A reported for the dithiocarbamate compound
[(Ph3P)Au(S2CNC4H8)],28 while the Au-C(Dip) bond dista-
characterized (structurally in four cases). The NHC CS2
3
˚
˚
nces of 2.025(3) A for 7 and 2.017(4) A for 8 are considerably
zwitterions act as excellent donors for a range of mono-
and bimetallic gold complexes with phosphine, carbene, and
isonitrile coligands. These complexes expand significantly the
underexplored dithiocarboxylate class of sulfur donors,
˚
greater than that of 1.942(3) A found in the precursor,
[(IDip)AuCl].9 This suggests that IMes CS2 exerts a superior
3
trans influence over chloride. There are no previously reported
(28) Ho, S. Y.; Tiekink, E. R. T. Z. Kristallogr.;New Cryst. Struct. 2004,
219, 73–74.
(29) Schneider, W.; Bauer, A.; Schmidbaur, H. Organometallics 1996, 15,
5445–5446.

1790 Inorganic Chemistry, Vol. 49, No. 4, 2010
Naeem et al.
which has long remained a poor relation of the ubiquitous
dithiocarbamate and numerous xanthate ligands. Further-
more, imidazolium-2-dithiocarboxylate betaines can be used
to form monolayers on the surface of gold nanoparticles in a
manner similar to that of dithiocarbamates.
Preparation of [(Ph3P)Au(S2C IMes)]PF6 (2). A dichloro-
methane solution (10 mL) of [AuCl(PPh3)] (45 mg, 0.091 mmol)
was treated with a solution of IMes CS2 (38 mg, 0.100 mmol) in
3
3
dichloromethane (5 mL). Upon addition of NH4PF6 (30 mg,
0.184 mmol) in methanol (5 mL), a green coloration appeared.
The reaction was stirred for 1 h and then all solvent removed.
The crude product was dissolved in dichloromethane (10 mL)
and filtered through Celite to remove NH4Cl and excess
NH4PF6. Pentane (15 mL) was added and the solid triturated
ultrasonically to give a pale-green solid. This was filtered,
washed with pentane (10 mL), and dried. Yield: 75 mg (84%).
Experimental Section
General Comments. All experiments were carried out under
aerobic conditions, and the complexes obtained appear rela-
tively stable toward the atmosphere, whether in solution or in
the solid state. Some decomposition to the gold colloid was
occasionally observed, indicated by a purple coloration. Re-
agents and solvents were used as received from commercial
sources. The following complexes and ligands were prepared as
described elsewhere: [AuCl(PR3)] (R = Me,30 Cy,31 Ph32),
[dppf(AuCl)2],33 [dppm(AuCl)2],34 [dppb(AuCl)2],35 [AuCl(tht)],36
[AuCl(IDip)],9 [AuCl(CNtBu)],37 IPr CS2,13 IMes CS2,13 and
IR (Nujol/KBr): ν(PF) 1722, 1566, 1311, 1209, 1055, 839 cm-1
.
31P NMR: 35.1 (s, PPh3) ppm. 1H NMR: 2.25 (s, o-CH3, 12H),
2.37 (s, p-CH3, 6H), 7.08 (s, m-C6H2, 4H), 7.41 (s, HCdCH,
2H), 7.45-7.60 (m, C6H5, 15H) ppm. MS (ES þve; abundance):
m/z 839 (100) [M]þ. Elem anal. Calcd for C40H39AuF6N2P2S2:
C, 48.8; H, 4.0; N, 2.9. Found: C, 48.9; H, 4.1; N, 2.9.
Preparation of [(Ph3P)Au(S2C IDip)]PF6 (3). A dichloro-
3
3
3
IDip CS2.13 ES and fast atom bombardment (FAB) mass
methane solution (10 mL) of [AuCl(PPh3)] (50 mg, 0.101 mmol)
was treated with a solution of IDip CS2 (47 mg, 0.101 mmol) in
3
spectrometry data were obtained using Micromass LCT
Premier and Autospec Q instruments, respectively. IR data
were obtained using a Perkin-Elmer Paragon 1000 FT-IR
spectrometer, KBr plates were used for solid-state IR spec-
troscopy, and characteristic triphenylphosphine-associated
IR data are not reported. NMR spectroscopy was performed
at 25 °C using Varian Mercury 300 and Bruker AV400
spectrometers in CDCl3 unless otherwise indicated. All
couplings are in hertz. Resonances in the 31P NMR spectrum
due to the hexafluorophosphate counteranion were ob-
served in all cases but are not included below. Elemental
analysis data were obtained from London Metropolitan
University. The procedures given provide materials of suffi-
cient purity for synthetic and spectroscopic purposes. TEM
was performed at UCL using a JEOL 100 instrument oper-
ating at 100 kV.
3
dichloromethane (5 mL). Upon addition of NH4PF6 (33 mg,
0.203 mmol) in methanol (5 mL), a green coloration appeared.
The reaction was stirred for 1 h and then all solvent removed.
The crude product was dissolved in dichloromethane (10 mL)
and filtered through Celite to remove NH4Cl and excess
NH4PF6. Pentane (15 mL) was added and the crude product
triturated ultrasonically to give a green solid. This was filtered,
washed with pentane (10 mL), and dried. Yield: 62 mg (58%). A
purple coloration was observed in the solid state, indicating the
formation of a gold colloid. IR (Nujol/KBr): ν(PF) 1711, 1587,
1554, 1327, 1275, 1212, 1101, 1070, 839 cm-1
PPh3) ppm. 1H NMR: 1.24 (d, CH3, 12H, JHH = 7.1 Hz), 1.36
(d, CH3, 12H, JHH = 6.7 Hz), 2.66 (sept, CHMe2, 4H, JHH
.
31P NMR: 35.4 (s,
=
6.8 Hz), 7.38-7.63 (m, C6H5 þ C6H3 þ HCdCH, 15H þ 6H þ
2H) ppm. MS (ES þve; abundance): m/z 923 (100) [M]þ. Elem
anal. Calcd for C46H51AuF6N2P2S2: C, 51.7; H, 4.8; N, 2.6.
Found: C, 51.7; H, 4.8; N, 2.6.
Preparation of [(Ph3P)Au(S2C IPr)]PF6 (1). A dichloro-
methane solution (10 mL) of [AuCl(PPh3)] (40 mg, 0.081 mmol)
was treated with a solution of IPr CS2 (19 mg, 0.083 mmol) in
3
Preparation of [(Cy3P)Au(S2C IMes)]PF6 (4). A dichloro-
3
3
methane solution (10 mL) of [AuCl(PCy3)] (40 mg, 0.078 mmol)
was treated with a solution of IMes CS2 (31 mg, 0.082 mmol) in
dichloromethane (5 mL). Upon addition of NH4PF6 (26 mg,
0.160 mmol) in methanol (5 mL), a purple coloration appeared.
The reaction was stirred for 1 h and then all solvent removed.
The crude product was dissolved in dichloromethane (10 mL)
and filtered through Celite to remove NH4Cl and excess
NH4PF6. Hexane (15 mL) was added and the crude product
triturated ultrasonically to give a brown solid. This was filtered,
washed with hexane (10 mL), and dried. Yield: 49 mg (73%). IR
3
dichloromethane (5 mL). Upon addition of NH4PF6 (25 mg,
0.153 mmol) in methanol (5 mL), a green coloration appeared.
The reaction was stirred for 1 h and then all solvent removed.
The crude product was dissolved in dichloromethane (10 mL)
and filtered through Celite to remove NH4Cl and excess
NH4PF6. Ethanol (15 mL) was added and the solvent volume
reduced until precipitation of the green solid was complete. This
was filtered, washed with ethanol (10 mL) and pentane (10 mL),
and dried. Yield: 59 mg (75%). IR (Nujol/KBr): ν(PF) 1712,
(Nujol/KBr): ν(PF) 1566, 1311, 1209, 1055, 839 cm-1
.
31P
NMR: 36.0 (s, PPh3) ppm. 1H NMR: 1.55 (d, CH3, 12H, JHH
=
6.8 Hz), 4.87 (sept, CHMe2, 2H, JHH = 6.8 Hz), 7.36 (s,
HCdCH, 2H), 7.54-7.66 (m, C6H5, 15H) ppm. MS (ES þve;
abundance): m/z 687 (100) [M]þ. Elem anal. Calcd for
C28H31AuF6N2P2S2: C, 40.4; H, 3.8; N, 3.4. Found: C, 40.3;
H, 3.8; N, 3.4.
1607, 1557, 1300, 1230, 1170, 1114, 1069, 1041, 1005, 839 cm-1
.
31P NMR: 56.7 (s, PCy3) ppm. 1H NMR: 1.24-1.45, 1.71-1.91,
1.96-2.08 (m ꢀ 3, Cy, 33H), 2.24 (s, o-CH3, 12H), 2.39 (s, p-
CH3, 6H), 7.08 (s, m-C6H2, 4H), 7.36 (s, HCdCH, 2H) ppm. MS
(ES þve; abundance): m/z 858 (100) [M]þ. Elem anal. Calcd for
C40H57AuF6N2P2S2: C, 47.9; H, 5.7; N, 2.8. Found: C, 48.0; H,
5.6; N, 2.8.
(30) Bruce, M. I.; Horn, E.; Matisons, J. G.; Snow, M. R. Aust. J. Chem.
1984, 37, 1163–1170.
(31) Bailey, J. J. Inorg. Nucl. Chem. 1973, 35, 1921–1924.
(32) Schmidbaur, H.; Wohlleben, A.; Wagner, F.; Orama, O.; Huttner, G.
Chem. Ber. 1977, 110, 1748–1754.
(33) Hill, D. T.; Girard, G. R.; McCabe, F. L.; Johnson, R. K.; Stupik,
P. D.; Zhang, J. H.; Reiff, W. M.; Eggleston, D. S. Inorg. Chem. 1989, 28,
3529–3533.
(34) (a) Berners-Price, S. J.; Sadler, P. J. Inorg. Chem. 1986, 25, 3822–
3827. (b) Brandys, M.-C.; Jennings, M. C.; Puddephatt, R. J. J. Chem. Soc.,
Dalton Trans. 2000, 4601–4606.
(35) Schmidbaur, H.; Bissinger, P.; Lachmann, J.; Steigelmann, O. Z.
Naturforsch., B: Chem. Sci. 1992, 47, 1711–1716.
Preparation of [(Me3P)Au(S2C IMes)]PF6 (5). A dichloro-
3
methane solution (10 mL) of [AuCl(PMe3)] (30 mg, 0.097 mmol)
was treated with a solution of IMes CS2 (41 mg, 0.108 mmol) in
3
dichloromethane (5 mL). Upon addition of NH4PF6 (32 mg,
0.196 mmol) in methanol (5 mL), a green coloration appeared.
The reaction was stirred for 30 min and then all solvent removed.
The crude solid was dissolved in dichloromethane (10 mL) and
filtered through diatomaceous earth (Celite) to remove NH4Cl
and excess NH4PF6. All solvent was again removed and the
green product triturated ultrasonically in diethyl ether (20 mL).
This was filtered, washed with diethyl ether (15 mL), and
dried. Yield: 65 mg (84%). IR (solid): ν(PF) 1608, 1558, 1486,
(36) Uson, R.; Laguna, A.; Vicente, J. J. Organomet. Chem. 1977, 131,
471–475.
(37) Eggleston, D. S.; Chodosh, D. F.; Webb, R. L.; Davis, L. L. Acta
Crystallogr., Sect. C. 1986, 42, 36–38.
1465, 1420, 1381, 1293, 1115, 1065, 1006, 958, 828 cm-1 31P
.

Article
Inorganic Chemistry, Vol. 49, No. 4, 2010 1791
NMR: -4.1 (s, PMe3) ppm. 1H NMR: 1.58 (d, CH3, 9H, JHP
=
0.028 mmol) was treated with a solution of IMes CS2 (21 mg,
3
11.2 Hz), 2.27 (s, o-CH3, 12H), 2.42 (s, p-CH3, 6H), 7.11 (s,
m-C6H2, 4H), 7.38 (s, HCdCH, 2H) ppm. MS (FAB þve;
abundance): m/z 653 (95) [M]þ. Elem anal. Calcd for
C25H33AuF6N2P2S2: C, 37.6; H, 4.2; N, 3.5. Found: C, 37.5;
H, 4.3; N, 3.4.
0.055 mmol) in dichloromethane (5 mL). Upon addition of
NH4PF6 (14 mg, 0.086 mmol) in methanol (5 mL), a green
coloration appeared. The reaction was stirred for 40 min and
then all solvent removed. The crude product was dissolved in
dichloromethane (10 mL) and filtered through Celite to remove
NH4Cl and excess NH4PF6. Diethyl ether (20 mL) was added
and the solid triturated ultrasonically to give a green solid. This
was filtered, washed with diethyl ether (10 mL), and dried. Yield:
46 mg (88%). IR (Nujol/KBr): ν(PF) 1607, 1556, 1308, 1231,
Preparation of [(tBuNC)Au(S2C IMes)]PF6 (6). A dichloro-
3
methane solution (10 mL) of [AuCl(CNtBu)] (30 mg, 0.095 mmol)
was treated with a solution of IMes CS2 (38 mg, 0.100 mmol) in
3
dichloromethane (5 mL). Upon addition of NH4PF6 (31 mg,
0.190 mmol) in methanol (5 mL), a green coloration appeared.
The reaction was stirred for 1 h and then all solvent removed.
The crude product was dissolved in dichloromethane (10 mL)
and filtered through Celite to remove NH4Cl and excess
NH4PF6. All solvent was again removed and the crude solid
triturated ultrasonically in diethyl ether (20 mL). The green
product was filtered, washed with diethyl ether (10 mL), and
dried. Yield: 71 mg (93%). IR (Nujol/KBr): ν(CN) 2258, 2234,
ν(PF) 1607, 1557, 1309, 1232, 1193, 1116, 1070, 1037, 1005, 931,
839 cm-1. 1H NMR: 1.54 (s, 9H, tBu), 2.21 (s, o-CH3, 12H), 2.38
(s, p-CH3, 6H), 7.07 (s, m-C6H2, 4H), 7.40 (s, HCdCH, 2H)
ppm. MS (ES þve; abundance): m/z 660 (62) [M]þ. Elem anal.
Calcd for C27H33AuF6N3PS2: C, 40.4; H, 4.1; N, 5.2. Found: C,
40.3; H, 4.1; N, 5.2.
1157, 1104, 1068, 1005, 931, 839 cm-1
.
31P NMR: 31.9 (s, dppb)
1
ppm. H NMR: 1.62, 2.37 (m ꢀ 2, CH2, 8H), 2.24 (s, o-CH3,
24H), 2.31 (s, p-CH3, 12H), 7.02 (s, m-C6H2, 8H), 7.39 (s,
HCdCH, 4H), 7.41-7.56 (m, C6H5, 20H) ppm. MS (FAB þve;
abundance): m/z 1727 (5) [M þ PF6]þ. Elem anal. Calcd for
C72H76Au2F12N4P4S4: C, 46.2; H, 4.1; N, 3.0. Found: C, 46.2;
H, 4.1; N, 3.1.
Preparation of [(dppf){Au(S2C IMes)}2](PF6)2 (10). A di-
3
chloromethane solution (10 mL) of [(dppf)(AuCl)2] (50 mg,
0.049 mmol) was treated with a solution of IMes CS2 (37.4 mg,
3
0.098 mmol) in dichloromethane (10 mL). The addition of
NH4PF6 (24 mg, 0.147 mmol) in methanol (5 mL) resulted in
a green coloration. The reaction was stirred for 1 h and then all
solvent removed. The crude product was dissolved in dichloro-
methane (10 mL) and filtered through Celite to remove NH4Cl
and excess NH4PF6. The solvent was again removed and the
crude solid triturated ultrasonically in diethyl ether (20 mL) to
yield a green solid. This was filtered, washed with diethyl ether
(10 mL), and dried. Yield: 88 mg (90%). IR (Nujol/KBr): ν(PF)
1612, 1563, 1484, 1438, 1380, 1313, 1231, 1173, 1103, 1066, 1032,
Preparation of [(IDip)Au(S2C IPr)]PF6 (7). A dichloro-
methane solution (10 mL) of [AuCl(IDip)] (50 mg, 0.081 mmol)
was treated with a solution of IPr CS2 (20 mg, 0.088 mmol) in
3
3
dichloromethane (5 mL). Upon addition of NH4PF6 (27 mg,
0.166 mmol) in methanol (5 mL), a purple coloration appeared.
The reaction was stirred for 30 min and then all solvent removed.
The crude product was dissolved in dichloromethane (10 mL)
and filtered through diatomaceous earth (Celite) to remove
NH4Cl and excess NH4PF6. All solvent was again removed
and the pale-purple product triturated ultrasonically in diethyl
ether (20 mL). This was filtered, washed with diethyl ether
(15 mL), and dried. Yield: 55 mg (71%). IR (solid): ν(PF)
1597, 1563, 1475, 1422, 185, 1365, 1354, 1330, 1256, 1207,
1007, 828 cm-1 31P NMR: 29.9 (s, dppf) ppm. 1H NMR: 2.26 (s,
.
o-CH3, 24H), 2.28 (s, p-CH3, 12H), 4.23, 4.38 (s ꢀ 2, C5H4, 2 ꢀ
4H), 6.99 (s, m-C6H2, 8H), 7.39-7.60 (m, C6H5 þ HCdCH,
20H þ 4H) ppm. MS (FAB þve; abundance): m/z 1854 (3) [M þ
PF6]þ, 1328 (42) [M - IMesCS2]þ. Elem anal. Calcd for
C78H76Au2F12FeN4P4S4: C, 46.9; H, 3.8; N, 2.8. Found: C,
47.0; H, 3.9; N, 2.8.
1
1181, 1137, 1092, 1062, 876, 832 cm-1. H NMR: 1.31, 1.38
Preparation of [(dppm){Au2(S2C IMes)}](PF6)2 (11). A di-
3
chloromethane solution (10 mL) of [(dppm)(AuCl)2] (34 mg,
0.040 mmol) was treated with a solution of IMes CS2 (16 mg,
(d ꢀ 2, MeIDip, 2 ꢀ 12H, JHH = 6.9 Hz), 1.46 (d, MeIPr, 12H,
JHH = 6.7 Hz), 2.68 (sept, CHMeIDip, 4H, JHH = 6.9 Hz), 4.62
3
0.042 mmol) in dichloromethane (5 mL). The addition of
NH4PF6 (15 mg, 0.092 mmol) in methanol (5 mL) resulted in
a green coloration. The reaction was stirred for 40 min and then
all solvent removed. The crude product was dissolved in di-
chloromethane (10 mL) and filtered through Celite to remove
NH4Cl and excess NH4PF6. Ethanol (15 mL) was added and the
solvent volume reduced to precipitate an olive-green solid. This
wasfiltered, washedwithcoldethanol(10mL) andhexane(10mL),
and dried. A further crop could be obtained by removing all
solvent and triturating the solid in diethyl ether (20 mL). Yield:
49 mg (85%). IR (Nujol/KBr): ν(PF) 1606, 1555, 1308, 1230,
(s(br), 2H, CHMeIPr), 7.24 (s, 2H, HCdCHIDip), 7.38 (s, 2H,
HCdCHIPr), 7.40 (d, 4H, m-C6H3, JHH = 7.8 Hz), 7.62 (t, 2H, p-
C6H3, JHH = 7.8 Hz) ppm. MS (FAB þve; abundance): m/z 813
(100) [M]þ, 585 (12) [M - S2C IPr]þ. Elem anal. Calcd for
3
C37H52AuF6N4PS2: C, 46.3; H, 5.5; N, 5.8. Found: C, 46.2; H,
5.4; N, 5.8.
Preparation of [(IDip)Au(S2C IMes)]PF6 (8). A dichloro-
3
methane solution (10 mL) of [AuCl(IDip)] (50 mg, 0.081 mmol)
was treated with a solution of IMes CS2 (34 mg, 0.089 mmol) in
3
dichloromethane (5 mL). Upon addition of NH4PF6 (26 mg,
0.160 mmol) in methanol (5 mL), a green coloration appeared.
The reaction was stirred for 30 min and then all solvent removed.
The crude product was dissolved in dichloromethane (10 mL)
and filtered through diatomaceous earth (Celite) to remove
NH4Cl and excess NH4PF6. All solvent was again removed
and the pale-green product triturated ultrasonically in diethyl
ether (20 mL). This was filtered, washed with diethyl ether (15 mL),
and dried. Yield: 69 mg (77%). IR (solid): ν(PF) 1608, 1558,
1486, 1462, 1421, 1384, 1365, 1330, 1230, 1183, 1117, 1071,
1156, 1101, 1068, 1000, 931, 838 cm-1 31P NMR: 28.4 (s, dppm)
.
ppm. 1H NMR: 2.28 (s(br), o-CH3, 12H), 2.34 (s, p-CH3, 6H),
3.72 (t, CH2, 2H, JHP = 12.3 Hz), 7.08 (s, m-C6H2, 4H),
7.29-7.63 (m, C6H5 þ HCdCH, 20H þ 2H) ppm. MS (ES þve;
abundance): m/z 1158 (28) [M]þ. Elem anal. Calcd for
C47H46Au2F12N2P4S2: C, 39.0; H, 3.2; N, 1.9. Found: C, 38.9;
H, 3.0; N, 1.8.
Preparation of [Au2(S2C IPr)2](PF6)2 (12). [AuCl(tht)] (17.5 mg,
0.055 mmol) and IPr CS2 (13 mg, 0.057 mmol) were dissolved in
3
1007, 932, 835, 760 cm-1. 1H NMR: 1.15, 1.23 (d ꢀ 2, MeIDip
,
3
2 ꢀ 12H, JHH = 6.9 Hz), 2.12 (s, o-CH3, 12H), 2.12 (s, p-CH3,
6H), 2.47 (sept, CHMeIDip, 4H, JHH = 6.9 Hz), 7.02 (s(br),
HCdCHIDip/IMes, 4H), 7.28 (d, m-C6H3, 4H, JHH = 7.8 Hz),
7.29 (s, m-C6H2, 4H), 7.54 (t, p-C6H3, 2H, JHH = 7.8 Hz) ppm.
MS (FAB þve; abundance): m/z 965 (100) [M]þ, 585 (9) [M -
dichloromethane (15 mL), and a methanolic solution (10 mL) of
NH4PF6 (18 mg, 0.110 mmol) was added. The reaction was stirred
for 1 h and then all solvent removed. The crude product was
dissolved in dichloromethane (10 mL) and filtered through Celite
to remove NH4Cl and excess NH4PF6. Ethanol (20 mL) was added
and the solvent volume reduced until precipitation of the red-brown
product was complete. This was filtered, washed with ethanol
(10 mL) and hexane (10 mL), and dried. Yield: 37 mg (59%). IR
(Nujol/KBr): ν(PF) 1566, 1317, 1260, 1210, 1180, 1138, 1060,
S2C IMes]þ. Elem anal. Calcd for C49H60AuF6N4PS2: C, 53.0;
3
H, 5.4; N, 5.0. Found: C, 52.9; H, 5.5; N, 4.9.
Preparation of [(dppb){Au(S2C IMes)}2](PF6)2 (9). A di-
chloromethane solution (10 mL) of [(dppb)(AuCl)2] (25 mg,
3

1792 Inorganic Chemistry, Vol. 49, No. 4, 2010
Naeem et al.
Table 1. Crystallographic Data for Compounds 2, 3, 7, and 8
data
2
3
7
8
formula
solvent
fw
[C40H39AuN2PS2](PF6)
0.55CH2Cl2 0.45Et2O
1064.82
[C46H51AuN2PS2](PF6)
Et2O
1143.03
[C37H52AuN4S2](PF6)
[C49H60AuN4S2](PF6)
CH2Cl2
1195.99
3
958.88
T (°C)
space group
-100
-100
-100
-100
P212121 (No. 19)
13.11504(16)
13.99608(18)
24.7953(3)
P21 (No. 4)
10.65689(11)
13.57473(13)
18.59207(17)
P21/n (No. 14)
13.39748(6)
13.32238(6)
23.37032(12)
Iba2 (No. 45)
16.89890(8)
31.95473(15)
19.98864(11)
˚
a (A)
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
V (A )
Z
101.3289(9)
100.4298(5)
3
˚
4551.41(10)
4
1.554
0.710 73
3.516
0.027
2637.21(5)
2
4102.36(3)
4
10 793.86(9)
8
1.472
1.541 84
7.517
0.028
F
calcd (g cm-3
λ (A)
)
1.439
0.710 73
2.986
0.021
0.033
1.553
1.541 84
8.557
0.030
0.080
˚
μ (mm-1
)
R1 (obs)a
wR2 (all)b
0.055
0.074
P
P
P
P
a R1 =
Fo| - |Fc
/
|Fo|. b wR2 = { [w(Fo2 - Fc2)2]/ [w(Fo2)2]}1/2; w - 1 = σ2(Fo2) þ (aP)2 þ bP.
841 cm-1. 1H NMR: 1.59 (d, CH3, 24H, JHH = 6.8 Hz), 4.96 (sept,
CHMe2, 4H, JHH = 6.8 Hz), 7.45 (s, HCdCH, 4H) ppm. MS
(FAB þve; abundance): m/z 850 (52) [M]þ, 653 (78) [M - Au]þ.
Elem anal. Calcd for C20H32Au2F12N4P2S4: C, 21.1; H, 2.8; N, 4.9.
Found: C, 21.2; H, 2.9; N, 4.7.
with water (30 mL) to remove excess sodium citrate and cold
dichloromethane (20 mL) to remove excess ligand. The dichloro-
methane washings yielded 16 mg of IMes CS2, indicating that
3
only 14 mg (0.037 mmol) had been required in the surface
functionalization of the nanoparticles (1:1 Au-ligand ratio).
The black solid was dried under vacuum. IR: 1607, 1563, 1486,
Preparation of [Au2(S2C IMes)2](PF6)2 (13). A dichloro-
3
ν
NCN1459, 1378, 1222, 1165, 1104, 1049, νSCS 931, 865 cm-1. 1H
methane solution (10 mL) of [AuCl(tht)] (32 mg, 0.100 mmol)
was treated with a solution of IMes CS2 (38 mg, 0.100 mmol) in
NMR (acetone-d6): 2.30 (s, p-CH3, 6H), 2.38 (s, o-CH3, 12H),
7.04 (s, m-C6H2, 4H), 7.60 (s, HCdCH, 2H) ppm.
3
dichloromethane (5 mL) and NH4PF6 (35 mg, 0.215 mmol) in
methanol (5 mL). The reaction was stirred for 1 h and then all
solvent removed. The crude product was dissolved in dichloro-
methane (10 mL) and filtered through Celite to remove NH4Cl
and excess NH4PF6. Diethyl ether (15 mL) was added and the
solid triturated ultrasonically to give a dark-brown solid. This
was filtered, washed with diethyl ether (10 mL), and dried. Yield:
68 mg (47%). IR (Nujol/KBr): ν(PF) 1606, 1554, 1307, 1231,
1170, 1117, 1070, 931, 837 cm-1. 1H NMR: 2.16 (s, o-CH3, 24H),
2.36 (s, p-CH3, 12H), 7.05 (s, m-C6H2, 8H), 7.53 (s, HCdCH,
4H) ppm. MS (FAB þve; abundance): m/z 1155 (21) [M]þ. Elem
anal. Calcd for C44H48Au2F12N4P2S4: C, 36.6; H, 3.4; N, 3.9.
Found: C, 36.7; H, 3.5; N, 4.0.
Preparation of NP2. An aqueous solution (10 mL) of HAuCl4
(17 mg, 0.050 mmol) and TOAB (109.4 mg, 0.200 mmol) in
chloroform (15 mL) were stirred rapidly together for 15 min
until phase transfer was complete. The lower organic layer was
cooled to 4 °C and treated with IMes CS2 (28.5 mg, 0.075 mmol)
3
as a dichloromethane solution (5 mL). The reaction was stirred
for 10 min, and then sodium borohydride (38 mg, 1.005 mmol)
was added rapidly, leading to a darkening of the solution. After
2 h of stirring below 10 °C, the organic layer was separated and
washed with water (3 ꢀ 10 mL). The volume was concentrated to
ca. 5 mL and ethanol (20 mL) added to precipitate the crude
black solid. Centrifugation allowed the solvent to be decanted,
leaving a black product, which was dried under vacuum. Excess
ligand was removed by dissolving the material in warm acetoni-
trile, cooling the solution overnight at -20 °C, and then
Preparation of [Au2(S2C IDip)2](PF6)2 (14).[AuCl(tht)] (9.6mg,
3
0.030 mmol) and IDip CS2 (14 mg, 0.030 mmol) were dissolved in
3
dichloromethane (15 mL), and a methanolic solution (10 mL) of
NH4PF6 (21 mg, 0.129 mmol) was added. The reaction was stirred
for 1 h and then all solvent removed. The crude product was
dissolved in dichloromethane (10 mL) and filtered through Celite to
remove NH4Cl and excess NH4PF6. Ethanol (20 mL) was added
and the solvent volume reduced until precipitation of the orange-
red product was complete. This was filtered, washed with ethanol
(10 mL) and hexane (10 mL), and dried. Yield: 26 mg (54%). IR
(Nujol/KBr): ν(PF) 1555, 1212, 1154, 1072, 844 cm-1. 1H NMR:
1.19, 1.29 (d ꢀ 2, CH3, 48H, JHH = 6.7 Hz), 2.52 (s(br), CHMe2,
8H), 7.35 (d, m-C6H3, 8H, JHH = 8.0 Hz), 7.46 (s(br), HCdCH,
4H), 7.59 (t, p-C6H3, 4H, JHH = 8.0 Hz) ppm. MS (FAB þve;
abundance): m/z 1322 (27) [M]þ, 1125 (100) [M - Au]þ. Elem anal.
Calcd for C56H72Au2F12N4P2S4: C, 41.7; H, 4.5; N, 3.5. Found: C,
42.0; H, 4.6; N, 3.7.
removing the crystalline material. IR: 1604, 1562, 1486 νNCN
,
1459, 1447, 1378, 1223, 1166, 1105, 1051 νSCS, 930, 868 cm-1. 1H
NMR (acetone-d6): 2.31 (s, p-CH3, 6H), 2.38 (s, o-CH3, 12H),
7.03 (s, m-C6H2, 4H), 7.59 (s, HCdCH, 2H) ppm.
Crystallography
Table 1 provides a summary of the crystallographic data
for compounds 2, 3, 7, and 8. The data were collected using
Oxford Diffraction Xcalibur 3 (2 and 3) and PX Ultra (7 and
8) diffractometers, and the structures were refined based
on F2 using the SHELXTL and SHELX-97 program sys-
tems.38 The absolute structures of 2 and 3 were determined
by a combination of R-factor tests [for 2, R1þ = 0.027,
R1- = 0.070; for 3, R1þ=0.021, R1-=0.066] and by use of
Preparation of NP1. An aqueous solution (30 mL) of HAuCl4
(10.8 mg, 0.032 mmol) was heated to reflux, and sodium citrate
(38 mg, 0.129 mmol) in water (5 mL) was added, causing a
darkening of the color. The reaction was stirred at reflux for 10
min and then for a further 15 min at room temperature. A
the Flack parameter [for 2, xþ = 0.000(3); for 3, xþ
=
0.0000(18)]. The absolute structure of 8 was shown to
be a partial polar twin by a combination of R-factor tests
[R1þ = 0.032, R1- = 0.041] and by use of the Flack
dichloromethane-methanol (5:10 mL) solution of IMes CS2
3
(30 mg, 0.079 mmol) was added dropwise and the reaction
stirred for a further 2 h. The resulting suspension was left to
stand and the supernatant decanted, and the solid was washed
(38) SHELXTL PC, version 5.1; Bruker AXS: Madison, WI, 1997.
Sheldrick, G. SHELX-97; Institut Anorg. Chemie: Gottingen, Germany, 1998.
€

Article
Inorganic Chemistry, Vol. 49, No. 4, 2010 1793
parameter [xþ = 0.319(6), x- = 0.681(6)]. CCDC 745830-
745833.
Fell Fund for consumables and Johnson Matthey
Ltd. for a generous loan of hydrogen tetrachloroau-
rate.
Acknowledgment. Merton College, Oxford, U.K., is
gratefully acknowledged for the provision of a Fel-
lowship (J.D.E.T.W.-E.) in the early part of this
work. Dr. S. Firth (UCL) is thanked for TEM
measurements. We are grateful to the OUP John
Supporting Information Available: Crystallographic data in
CIF format and anisotropic displacement ellipsoid plots for the
structures of 2, 3, 7, and 8. This material is available free of
charge via the Internet at http://pubs.acs.org.