Multimetallic arrays: Bi-, Tri-, Tetra-, and hexametallic complexes based on Gold(l) and Gold(lll) and the surface functionalization of Gold nanoparticles with transition metals

Article abstract of DOI:10.1021/ic802442d

Reaction of [AuCI(PPh₃)] with the zwtteron S ₂CNC₄H₈NH₂ yields [(Ph ₃P)Au(S₂CNC₄H₈NH₂)] BF₄. Treatment of this species with NEt₃ and CS ₂ followed by [AuCI(PPh₃)] leads to [{(Ph ₃P)Au}₂(S₂CNC₄H₈NCS ₂)], which can also be obtained directly from [AuCI(PPh₃)] and KS₂CNC₄H₈NCS₂K. A heterobmetallic variant, [(dppm)₂Ru(S₂CNC ₄H₈- NCS₂)Au(PPh₃)]+, can be prepared by the sequential reaction of [(dppm)₂Ru(S ₂CNC₄H₈NH₂)]²⁺ with NEt₃ and CS₂followed by [AuCI(PPh₃)]. Reaction of the same ruthenium precursor with [(dppm)(AuCI)₂] under similar conditions yields the trimetallic complex [(dppm)₂Ru(S ₂CNC₄H₈NCS₂)Au₂(dppm)] ²⁺. Attempts to prepare the compound [(dppm)Au₂(S ₂CNC₄H₈NH₂)]²⁺ from [(dppm)(AuCI)₂] led to isolation of the known complex [{(dppm)- Au₂}₂(S₂CNC₄H₈NCS ₂)]²⁺ via a symmetrization pathway. [{(dppf)Au ₂}₂(S₂CNC₄H₈NCS ₂)]²⁺ was successfully prepared from [(dppf)(AuCI) ₂] and crystallographically characterized. In addition, a gold(lll) trimetallic compound, [{(dppm)₂Ru(S₂CNC₄H ₈NCS₂)}₂Au]³⁺, and a tetrametallic gold(l) species, [{(dppm)₂Ru(S₂CNC₄H ₈NCS₂)Au}₂]²⁺, were also synthesized. This methodology was further exploited to attach the zwitterionic (dppm)₂Ru(S₂CNC₄H₈NCS₂) unit to the surface of gold nanoparticles, which were generated in situ and found to be 3.4 (±0.3) and 14.4 (±2.5) nm in diameter depending on the method employed. Nanoparticles with a mixed surface topography were also explored.

Full text of DOI:10.1021/ic802442d

Inorg. Chem. 2009, 48, 3866-3874
Multimetallic Arrays: Bi-, Tri-, Tetra-, and Hexametallic Complexes
Based on Gold(I) and Gold(III) and the Surface Functionalization of Gold
Nanoparticles with Transition Metals
Edward R. Knight,† Nina H. Leung,† Amber L. Thompson,† G. Hogarth,‡
and James D. E. T. Wilton-Ely*,†,§,⊥
Chemistry Research Laboratory, UniVersity of Oxford, Mansfield Road, Oxford OX1 3TA, U.K.,
Department of Chemistry, UniVersity College London, 20 Gordon Street,
London WC1H 0AJ, U.K., and Department of Chemistry, Imperial College London, South
Kensington Campus, London SW7 2AZ, U.K.
Received December 24, 2008
Reaction of [AuCl(PPh3)] with the zwitterion S2CNC4H8NH2 yields [(Ph3P)Au(S2CNC4H8NH2)]BF4. Treatment of this
species with NEt3 and CS2 followed by [AuCl(PPh3)] leads to [{(Ph3P)Au}2(S2CNC4H8NCS2)], which can also be
obtained directly from [AuCl(PPh3)] and KS2CNC4H8NCS2K. A heterobimetallic variant, [(dppm)2Ru(S2CNC4H8-
NCS2)Au(PPh3)]+, can be prepared by the sequential reaction of [(dppm)2Ru(S2CNC4H8NH2)]2+ with NEt3 and CS2
followed by [AuCl(PPh3)]. Reaction of the same ruthenium precursor with [(dppm)(AuCl)2] under similar conditions
yields the trimetallic complex [(dppm)2Ru(S2CNC4H8NCS2)Au2(dppm)]2+. Attempts to prepare the compound
[(dppm)Au2(S2CNC4H8NH2)]2+ from [(dppm)(AuCl)2] led to isolation of the known complex [{(dppm)-
Au2}2(S2CNC4H8NCS2)]2+ via a symmetrization pathway. [{(dppf)Au2}2(S2CNC4H8NCS2)]2+ was successfully prepared
from [(dppf)(AuCl)2] and crystallographically characterized. In addition, a gold(III) trimetallic compound,
[{(dppm)2Ru(S2CNC4H8NCS2)}2Au]3+, and a tetrametallic gold(I) species, [{(dppm)2Ru(S2CNC4H8NCS2)Au}2]2+, were
also synthesized. This methodology was further exploited to attach the zwitterionic (dppm)2Ru(S2CNC4H8NCS2)
unit to the surface of gold nanoparticles, which were generated in situ and found to be 3.4 ((0.3) and 14.4 ((2.5)
nm in diameter depending on the method employed. Nanoparticles with a mixed surface topography were also
explored.
Introduction
In the solid state, dithiocarbamate complexes of gold often
display short gold-gold inter- or intramolecular contacts.
The presence of such interactions between formally closed-
shell gold(I) centers has led to a great deal of interest in
polymetallic assemblies of monovalent gold. This phenom-
enon of “aurophilicity”3 is attributed to correlation effects
and electrostatic contributions.4 Of all the donor types
employed in the construction of these compounds, sulfur and
phosphorus species are the most common, and their com-
pounds have found use in fields as diverse as medicine,
electronics, and the decoration of ceramics.5
The vast number of dithiocarbamate complexes reported
for the d-block elements1 confirms the versatility of this
ligand, allowing it to accommodate the varied requirements
of the metals involved. In particular, the extensive metal-
centered electrochemistry of dithiocarbamate complexes2 and
the ability to stabilize a range of oxidation states are
important features in their applications, which encompass
materials science, medicine, and agriculture.1
* To whom correspondence should be addressed. E-mail: j.wilton-
ely@imperial.ac.uk.
†
University of Oxford.
University College London.
Imperial College London.
Current address: Imperial College London.
(3) (a) Schmidbaur, H. Gold Bull. 2000, 33, 3–10. (b) Schmidbaur, H.;
Schier, A. Chem. Soc. ReV. 2008, 37, 1931–1951. (c) Katz, M. J.;
Sakaib, K.; Leznoff, D. B. Chem. Soc. ReV. 2008, 37, 1884–1895.
(4) (a) Pyykko¨, P. Angew. Chem., Int. Ed. 2004, 43, 4412–4456. (b)
Runeberg, N.; Schu¨tz, M.; Werner, H. J. J. Chem. Phys. 1999, 110,
7210–7215.
‡
§
⊥
(1) Hogarth, G. Prog. Inorg. Chem. 2005, 53, 71–561.
(2) Bond, A. M.; Martin, R. L. Coord. Chem. ReV. 1984, 54, 23–98.
3866 Inorganic Chemistry, Vol. 48, No. 8, 2009
10.1021/ic802442d CCC: $40.75  2009 American Chemical Society
Published on Web 03/18/2009

Homo- And Heterometallic Complexes Based on Au, Fe, and Ru
Scheme 1. Binding Modes of Gold in Selected Dithiocarbamate Compounds
Dithiocarbamate and other sulfur-donor ligands have been
reviewed in a number of contexts.1,6,7 The bonding modes
adopted by gold(I) with dithiocarbamates can often vary
despite the limitations created by the inherent preference for
a linear coordination geometry.1,6,7As a result monodentate
coordination is common, and an asymmetric anisobidentate
mode (A, Scheme 1) is not unusual.8 This is found to be the
case in monomeric gold(I) phosphine complexes with dithio-
carbamates where the two gold-sulfur distances differ
significantly. Another commonly observed mode is that in
which each sulfur atom bonds to a single gold atom. The
short Au-Au distance in such compounds constitutes a
stabilizing metal-metal interaction.3c Both dppm and dppf
often coordinate in this fashion, and the (dppm)Au2 unit is
known to coordinate to dithiocarbamates in this mode (B,
Scheme 1).
A crystallographic study of the compound [Au2(S2CNEt2)2]
(C, Scheme 1) has shown the intramolecular Au-Au distance
to be 2.78 Å,9 which is considerably shorter than the
metal-metal distance of 2.88 Å in gold metal.10 As with
much chemistry of monovalent gold, phosphine co-ligands
have been used extensively in dithiocarbamate com-
plexes.1,6,7 In particular, bidentate and monodentate modes
have been investigated in complexes based on polyphosphine
backbones.11
modifying the substituents on the nitrogen atom, and have
instead largely concentrated on the commercially available
dimethyl- and diethyldithiocarbamate salts.1,6,7
Recent work employing gold(III) bis(dithiocarbamate)
nodes14 in the construction of supramolecular networks15 by
Beer has provided an excellent illustration of the potential
of this ligand class. Our recent contributions in this area have
focused on the use of a zwitterionic piperazine dithiocar-
bamate, S2CNC4H8NH2.16 This species can be used to
coordinate to a first metal center, while retaining the potential
to bond to a second on deprotonation and functionalization
with CS2. A general strategy for the synthesis of multimetallic
complexes is being developed using this method.16 Here we
wish to report the application of this approach to the
construction of homo- and heteronuclear compounds based
on gold in its most common oxidation states.
Results and Discussion
Gold Complexes. A number of symmetrical bimetallic
transition metal complexes has been prepared using the
bridging ligand, KS2CNC4H8NCS2K,17 We have also shown
that this double salt readily reacts with 2 equiv of cis-
[RuCl2(dppm)2] to yield the homobimetallic compound
[{(dppm)2Ru}2(S2CNC4H8NCS2)]2+ by displacement of both
chloride ligands.16a,b In the sphere of gold chemistry, this
approach has been used independently in the preparation by
Yam, Li, Yu, and co-workers of the gold(I) tetrametallic
Very recently dithiocarbamates have been reported to act
as good ligands for gold surfaces, either in the coating of
nanoparticles12 or to form monolayers on Au(111) surfaces.13
While polyfunctional variants of many ligands have been
used to create multimetallic systems, this approach has rarely
been exploited with dithiocarbamates. With gold in particular,
almost all previous reports have ignored the potential of
(12) (a) Wessels, J. M.; Nothofer, H.-G.; Ford, W. E.; von Wrochem, F.;
Scholz, F.; Vossmeyer, T.; Schroedter, A.; Weller, H.; Yasuda, A.
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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.;
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R., Jr.; D´ıaz, A.; Cao, R.; Otero, A.; Cea, R.; Rodr´ıguez-Argu¨elles,
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6990–7002. (b) Wong, W. W. H.; Cookson, J.; Evans, E. A. L.;
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Chem. Commun. 2005, 2214–2216.
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2008, 47, 9642–9653. (c) Knight, E. R.; Cowley, A. R.; Hogarth, G.;
Wilton-Ely, J. D. E. T. Dalton Trans. 2009, 607–609. (d) Macgregor,
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Inorganic Chemistry, Vol. 48, No. 8, 2009 3867

Knight et al.
Scheme 2. Preparation of Mono-, Bi-, and Hexametallic Complexesa
a
(i) CS2, short stir; (ii) CS2 long stir; (iii) ClAu(PPh3); (iv) NEt3, CS2, [ClAu(PPh3)]; (v) 2 dppf(AuCl)2.
complex [{(dppm)Au2}2(S2CNC4H8NCS2)](PF6)2.18 A par-
ticularly intriguing feature of this species is the chiral, cyclic,
supramolecular structure in which 16 gold units are held
together by aurophilic interactions in the solid state. The same
researchers have recently reported fascinating arrangements
using a different bis(dithiocarbamate) ligand to prepare an
Au12 cluster with D2 symmetry19 and an unprecedented Au36
arrangement directed by aurophilic interactions.20
In the context of our ongoing research focusing on the
zwitterion S2CNC4H8NH2 and, to a lesser extent, KS2-
CNC4H8NCS2K,16a,b we chose to explore the reactivity of
these ligands toward gold. Surprisingly, it appears from our
literature searches that, apart from the aforementioned
[{(dppm)Au2}2(S2CNC4H8NCS2)](PF6)2, no other gold com-
plexes have been reported bearing these dithiocarbamate
ligands. Stirring a solution of [AuCl(PPh3)] with S2-
CNC4H8NH2 in the presence of NaBF4 yielded the bright
yellow mononuclear complex [(Ph3P)Au(S2CNC4H8NH2)]-
BF4 (1). Two distinct piperazine environments were observed
as multiplets at 3.31 and 4.36 ppm, while a larger multiplet
integrating to 15 protons was observed in the aromatic region
for the triphenylphosphine protons. The presence of this
ligand was also confirmed by a singlet in the 31P NMR
spectrum at 38.0 ppm. Good elemental analysis and mass
spectrometry data confirmed the overall composition (Scheme
2). In the light of the fascinating structural complexity found
in the tetragold compound mentioned above,18 two sym-
metrical piperazine-bridged gold complexes were synthe-
sized using the double salt as a linker. Treatment of
KS2CNC4H8NCS2K with 2 equiv of [AuCl(PPh3)] led to
smooth formation of [{(Ph3P)Au}2(S2CNC4H8NCS2)] (2)
through loss of the chloride ligands (Scheme 2). A singlet
piperazine resonance at 4.33 ppm was seen in the 1H NMR
spectrum, and integration of the relevant resonances indicated
the presence of two triphenylphosphine ligands. The equiva-
lence of the two ends of the molecule was confirmed by a
singlet in the 31P NMR spectrum at 35.9 ppm. The composi-
tion of 2 was supported by elemental analysis and a
molecular ion in the Fast Atom Bombardment (FAB) mass
spectrum at m/z ) 1153. Anisobidentate coordination was
assumed based on literature precedent for [(R3P)Au-
(S2CNR’2)] complexes.1
Employing the same method, a tetragold species
[{(dppf)Au2}2(S2CNC4H8NCS2)](PF6)2 (3) was prepared,
which gave rise to a new phosphine resonance at 32.0 ppm
in the 31P NMR spectrum. In addition to broadened reso-
nances for the cyclopentadienyl protons of the dppf ligand,
a singlet resonance was found for the piperazine protons at
1
4.59 ppm in the H NMR spectrum. Elemental analysis, IR
spectroscopy, and mass spectrometry further confirmed the
formulation. Diffraction quality single crystals were grown
by diffusion of diethyl ether vapor onto an acetonitrile/
methanol (1:1) solution of 3 and the structure determined
(Figure 1).
The hexametallic compound has S-C-S bond angles of
123.9(5)° and 124.6(5)°, the smallest of which is significantly
smaller than those of 125.0(7)° and 129.0(7)° in
[Au2(S2CNEt2)2].9 The most directly comparable structure
is [{(dppm)Au2}2(S2CNC4H8NCS2)]2+; however, the S-C-S
angles of the eight different molecules that make up the Au16
ring in the solid state structure of this complex range from
112.3(6)° to 145.0(10)°),18 making the comparison less
helpful. The C-S bond distances found in compound 3,
which range between 1.727(9) and 1.743(9) Å are, on
average, marginally longer than those of 1.701(8) and
1.730(8) Å in the previously reported complex [{(dppm)2Ru}2-
(17) Some metal complexes of piperazine bis(dithiocarbamates) have been
reported: (a) Esmadi, F. T.; Irshaidat, T. Z. A. Synth. React. Inorg.
Met.-Org. Chem. 2000, 30, 1347–1362. (b) Glidewell, C.; Johnson,
I. L. Polyhedron 1988, 7, 1371–1375. (c) Siddiqi, K. S.; Zaidi, F. R.;
Zaidi, S. A. A. Synth. React. Inorg. Met.-Org. Chem. 1980, 10, 569–
578. (d) Marcotrigiano, G.; Pellacani, G. C.; Preti, C.; Tosi, G. Bull.
Chem. Soc. Jpn. 1975, 48, 1018–1020. (e) Hulanicki, A.; Shishkova,
L. Chem. Anal. (Warsaw) 1965, 10, 837–845. (f) Yin, H. D.; Ma,
C. L.; Wang, Y.; Fang, H. X.; Shao, J. X. Acta Chim. Sinica 2002,
60, 897–903. (g) Yin, H.; Wang, C. Appl. Organomet. Chem. 2004,
18, 145–146. (h) Tian, L.; Shang, Z.; Yu, Q.; Li, D.; Yang, G. Appl.
Organomet. Chem. 2004, 18, 253–254. (i) Yin, H. D.; Wang, C. H.;
Xing, Q. J. Chin. J. Struct. Chem. 2004, 23, 490–493. (j) Tombeux,
J.; van Poucke, L. C.; Eeckhaut, Z. Spectrochim. Acta 1972, 28A,
1943–1947.
(18) Yu, S.-Y.; Zhang, Z.-X.; Cheng, E. C.-C.; Li, Y.-Z.; Yam, V. W.-W.;
Huang, H.-P.; Zhang, R. J. Am. Chem. Soc. 2005, 127, 17994–17995.
(19) Sun, Q.-F.; Lee, T. K.-M.; Li, P.-Z.; Yao, L.-Y.; Huang, J.-J.; Huang,
J.; Yu, S.-Y.; Li, Y.-Z.; Cheng, E. C.-C.; Yam, V. W.-W. Chem.
Commun. 2008, 5514–5516.
(20) Yu, S.-Y.; Sun, Q.-F.; Lee, T. K.-M.; Cheng, E. C.-C.; Li, Y.-Z.; Yam,
V. W.-W. Angew. Chem., Int. Ed. 2008, 47, 4551–4554.
3868 Inorganic Chemistry, Vol. 48, No. 8, 2009

Homo- And Heterometallic Complexes Based on Au, Fe, and Ru
Figure 1. Molecular structure of the dication in [{(dppf)Au2}2(S2CNC4H8NCS2)](PF6)2 (3). Selected bond lengths (Å) and angles (deg): Au1-P1 ) 2.268(2),
Au1-S1 ) 2.324(2), Au1-Au2 ) 3.0072(4), Au2-P2 ) 2.273(2), Au2-S2 ) 2.323(2), Au3-P3 ) 2.268(2), Au3-S3 ) 2.336(2), Au3-Au4 ) 3.0368(4),
Au4-P4 ) 2.267(2), Au4-S4 ) 2.3220(19), S1-C1 ) 1.733(8), S2-C1 ) 1.743(9), S3-C6 ) 1.727(9), S4-C6 ) 1.739(9), N1-C1 ) 1.307(10),
N2-C6 ) 1.325(11), P1-Au1-S1 ) 168.16(8), P2-Au2-S2 ) 171.72(8), P3-Au3-S3 ) 170.40(8), P4-Au4-S4 ) 167.05(8), S1-C1-S2 ) 123.9(5),
S3-C6-S4 ) 124.6(5).
(S2CNC4H8NCS2)](BF4)2.16a In compound 3, the C-N bond
distances in the dithiocarbamate unit are 1.307(10) and
1.325(11) Å, indicating the multiple bond character present
(average distance for C-N is 1.47 Å and 1.29 Å for C)N).21
The ruthenium example mentioned above displays a regular
chair conformation for the piperazine ring; however, in
compound 3 the ring is twisted between boat and chair
conformations. The intramolecular gold-gold distances
within each digold unit are Au(1)-Au(2): 3.0072(4) Å and
Au(3)-Au(4): 3.0368(4) Å. Although much greater than
those found in [Au2(S2CNEt2)2] (2.78 Å) and [{(dppm)Au2}2-
(S2CNC4H8NCS2)]2+ (2.90 Å), these distances are still
significantly shorter than the sum of the van der Waals radii
(3.32 Å)10 and indicate a significant metal-metal interaction.3
The view along the gold-gold interactions reveals a “crossed
swords” arrangement of the P-Au-S linkages, which is a
common feature in previously reported gold(I) complexes.22
It has been noted that the flexibility afforded by the Cp rings
in the dppf ligand permits subtly different structures to be
formed compared to other diphosphine digold units.23
Complexes Combining Ruthenium and Gold. A pre-
liminary study16a demonstrated how the functionalization of
[Ru(S2CNC4H8NH2)(dppm)2](BF4)2 with NEt3 and CS2 gen-
erates the metala-dithiocarbamate species [Ru(S2CNC4-
H8NCS2)(dppm)2] in situ. Furthermore, addition of metal
fragments to this species permits bimetallic species to be
prepared. If an identical fragment is introduced, symmetrical
species, such as [{(dppm)2Ru}2(S2CNC4H8NCS2)]2+, are
obtained; however, the great advantage of this approach lies
in the access it provides to heterobimetallic species.
spectrum apart from greater activity in the aromatic region.
However, a molecular ion at m/z ) 1566 and elemental
analysis data confirmed the formulation as [(dppm)2Ru(S2-
CNC4H8NCS2)Au(PPh3)]BF4 (4).
In situ generation of [(dppm)2Ru(S2CNC4H8NCS2)] and
subsequent treatment with [(dppm)(AuCl)2] led to the het-
erotrimetallic complex [(dppm)2Ru(S2CNC4H8NCS2)Au2-
(dppm)](BF4)2 (5). The 31P NMR spectrum displayed a new
broadened singlet at 37.8 ppm, corresponding to the dppm
ligand spanning two gold centers, while those bonded in a
bidentate fashion at ruthenium gave rise to triplets at -5.0
and -18.3 ppm (JPP ) 35.5 Hz). In addition to consistent
1H NMR and IR spectroscopic data, a molecular ion at m/z
) 1883 and elemental analysis confirmed the formulation.
A further Ru2Au compound, [{(dppm)2Ru(S2CNC4H8-
NCS2)}2Au](BF4)3 (6) was prepared, but of very different
composition to 5. With this complex the investigations were
extended to gold(III), using the well-known propensity of
the d8 metal center to accommodate two dithiocarbamate
moieties in a square planar motif.14 Synthesis was achieved
by in situ functionalization of [(dppm)2Ru(S2CNC4H8-
NH2)](BF4)2 with NEt3, CS2 followed by addition of half an
equivalent of HAuCl4 (Scheme 3). A distinctive color change
was observed from pale yellow to dark brown, and the
formulation of the complex was indicated by a molecular
ion at m/z ) 2410 in the FAB mass spectrum. This was
further supported by elemental analysis.
A tetrametallic Ru2Au2 species was also obtained on treat-
ment of a solution of the zwitterion [(dppm)2Ru(S2CNC4H8-
NCS2)] (generated in situ, as above) with an equimolar
equivalent of [AuCl(tht)] (tht ) tetrahydrothiophene). The
chloride and thiacycle ligands were readily displaced to
give a dication as shown in Scheme 3. Spectroscopic data
were found to be similar to the other complexes bearing the
(dppm)2Ru(S2CNC4H8NCS2) unit, so confirmation of the
composition rested on mass spectrometry (MALDI) and
elemental analysis, both of which were in agreement with
the formulation [{(dppm)2Ru(S2CNC4H8NCS2)}Au]2(BF4)2
(7).
Sequential treatment of a solution of [(dppm)2Ru(S2-
CNC4H8NH2)](BF4)2 with NEt3, CS2, and [ClAu(PPh3)]
resulted in a colorless product, which displayed a new,
somewhat broadened singlet in the 31P NMR spectrum at
1
37.5 ppm. Little change was observed in the H NMR
(21) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.;
Taylor, R. J. Chem. Soc., Perkin Trans. 1987, S1–S19.
(22) (a) Zank, J.; Schier, A.; Schmidbaur, H. J. Chem. Soc., Dalton Trans.
1998, 323–324. (b) Wilton-Ely, J. D. E. T.; Schier, A.; Mitzel, N. W.;
Nogai, S.; Schmidbaur, H. J. Organomet. Chem. 2002, 643, 313–323.
(23) Gimeno, M. C.; Laguna, A. Gold Bull. 1999, 32, 90–95.
Inorganic Chemistry, Vol. 48, No. 8, 2009 3869

Knight et al.
Scheme 3. Preparation of Heterometallic Complexesa
a
(i) NEt3, CS2, [AuCl(PPh3)]; (ii) NEt3, CS2, [dppm(AuCl)2]; (iii) NEt3, CS2, 0.5 HAuCl4; (iv) NEt3, CS2, [AuCl(tht)].
The dithiocarbamate complex [(dppm)Au2(S2CNC4H8-
NH2)]2+ was considered to be a potentially useful starting
point for further reactions; however, reaction of [(dppm)-
(AuCl)2] with the zwitterion S2CNC4H8NH2 led to isolation
of the previously reported bimetallic complex [{(dppm)-
Au2}2(S2CNC4H8NCS2)]2+ (Supporting Information).18 Such
symmetrization behavior has also been observed by us in
some palladium and platinum compounds.24
ammination reaction occurs between piperidine and
[Ni(S2CNH2)2], with the -NH2 acting as a leaving group.
Xanthates, with a more electrophilic carbon due to the
increased electronegativity of oxygen, show similar substitu-
tion reactions. For example, the same paper reports that the
xanthate [Ni(S2COEt)2] also reacts with piperidine to form
the bis(dithiocarbamate). Nucleophilic substitution reactions
of dithiocarbamates have also been demonstrated with
palladium and platinum but in all reported cases a primary
amine is replaced by a secondary amine.
Attempts to form symmetrical bimetallic complexes with
[LAuCl] (where L ) CNtBu and As(C6H4Me-2)Ph2) were
ultimately unsuccessful. In both cases a yellow precipitate
formed immediately upon reaction of the relevant gold(I)
chloride with the double salt. The yellow product turned
brown on drying in air, and this brown solid proved insoluble
in all common laboratory solvents. It is likely that both of
the ligands (L) were displaced, and reaction with the double
salt led to formation of a gold polymer. When L )
As(C6H4Me-2)Ph2, the insoluble product was analyzed to
give a composition that fitted that of a gold (II) polymer
[Au(S2CNC4H8NCS2)]n.
Symmetrization and ligand exchange have some precedent
in dithiocarbamate chemistry. Indeed, Laguna and co-
workers11h have successfully used this approach to prepare
themixeddithiocarbamateylidespecies[Au2{µ-(CH2)2PPh2}(µ-
S2CNR2)] from the reaction of [Au2{µ-(CH2)2PPh2}2] and
[Au2(µ-S2CNR2)2]. However, the process here is not a
straightforward substitution pathway as a new CS2 unit needs
to be generated to convert [(dppm)Au2(S2CNC4H8NH2)]2+
to [{(dppm)Au2}2(S2CNC4H8NCS2)]2+. This may be achieved
by deprotonation of the ammonium unit in [(dppm)Au2-
(S2CNC4H8NH2)]2+ to form [(dppm)Au2(S2CNC4H8NH)]+,
which could then use the amine nitrogen to attack the CS2
carbon of another [(dppm)Au2(S2CNC4H8NH2)]2+ molecule,
displacing a piperazine unit and generating the symmetrical
product [{(dppm)Au2}2(S2CNC4H8NCS2)]2+.
Functionalization of Gold Nanoparticles. The generation
of the metala-dithiocarbamate [LnM(S2CNC4H8NCS2)] un-
derpinned the synthetic routes described above. The applica-
tion of such species to the emerging field of functionalized
gold nanoparticles was then explored.16c These materials
have received much attention26 since their pioneering de-
velopment27 but very few reports exist in which the surface
It has been demonstrated by Fackler and Coucouvanis25
that nucleophilic substitution can occur at the carbon atom
of coordinated dithiocarbamates. They reported that a trans-
(24) 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, in press, DOI: 10.1039/b821947h.
(25) Fackler, J. P., Jr.; Coucouvanis, D.; Seidel, W. C.; Masek, R. C.;
Holloway, W. Chem. Commun. 1967, 924–925.
(26) Daniel, M.-C.; Astruc, D. Chem. ReV. 2004, 104, 293–346.
3870 Inorganic Chemistry, Vol. 48, No. 8, 2009

Homo- And Heterometallic Complexes Based on Au, Fe, and Ru
Scheme 4. Functionalization of Gold Nanoparticles with Ruthenium
found that the value of the SPR band can depend on
interparticle interactions, surface charge, and the solvent
system used. For example, in chloroform solution, the SPR
band is often observed to be shifted away from the typical
value.30 From the diameter of the gold nanoparticles
determined by TEM measurements, the approximate number
of gold atoms in NP1 was calculated to be around 1600 with
550 at the surface. This contrasts with the substantially
greater surface area of NP2 (11000 surface atoms with
145000 core gold atoms). The surface area will be an
important variable in the application of nanoparticle materials
in applications such as sensing and catalysis. In preliminary
work aimed at the latter application, it was discovered that
the nanoparticles display well-behaved, reversible electro-
chemistry with a Ru(II)/Ru(III) couple at 0.73 V (vs Fc/
Fc+). This potential is slightly shifted from that found in
the complex [Ru(S2CNC4H8NH2)(dppm)2](BF4)2.16b Astruc
and co-workers31,32 have recently demonstrated the potential
for sensing anions using dendronized nanoparticle surfaces
of ferrocenyl-amide units. The preorganization of the transi-
tion metals units because of their immobilization on the gold
surface gives rise to a positive dendritic effect leading to
much greater shifts in the CV trace from interactions with
anions than found using unbound species in solution. The
anions can be washed from the electrode modified with the
nanoparticles and the system reused.
Units
is modified to incorporate transition metal functionality.28
Despite the widespread use of thiols to stabilize gold colloids,
dithiocarbamates were only first used very recently in this
manner.12 The first report of complexed metals being tethered
to the surface through dithiocarbamates appeared shortly
afterward.12c
In a modification of the procedure reported by Brust and
Schiffrin,27b the zwitterionic complex [Ru(S2CNC4H8NCS2)-
(dppm)2] was generated in situ and added to a solution of
HAuCl4 reduced by sodium borohydride in the presence of
the phase transfer agent, n-tetraoctylammonium bromide
(Scheme 4).
To further explore the potential for surface modification
of these materials, a mixed surface topology was introduced.
This was achieved by treatment of the TOAB-stabilized
nanoparticles with equimolar quantities of 1-dodecanethiol
and the metala-dithiocarbamate [Ru(S2CNC4H8NCS2)-
(dppm)2] using a method pioneered by Astruc and co-workers
for mixtures of thiols.32 Unlike materials NP1 and NP2, the
nanoparticles (NP3) obtained from the thiol/metala-dithio-
carbamate mixture proved to be insoluble in all common
laboratory solvents. As a result, analysis was limited to EDX,
solid state IR spectroscopy, and TEM. After repeated
washing with dichloromethane, water, and methanol to
remove species not attached to the surface, NP3 showed the
presence of Au, Ru, S, and P (EDX), while a ν(CS) stretch
characteristic of a coordinated dithiocarbamate ligand (999
cm-1) was evident in the solid state infrared spectrum (KBr
disk) along with similar bands to those observed in a
spectrum of the free thiol (measured as a thin film). However,
the TEM images showed agglomerated nanoparticles rather
than discrete units (Figure 2), and the insolubility of the
material is probably connected to the interparticle interac-
tions. The origin of this aggregation is difficult to determine
unambiguously but could be due to an absence of electrostatic
The black material obtained (NP1) was characterized by
multinuclear NMR spectroscopy (31P, 1H) in CDCl3 (in which
it is sparingly soluble), revealing broadened resonances at
chemical shifts slightly displaced from those observed in the
molecular precursor. Transmission Electron Microscopy
(TEM) was used to analyze the average diameter of the
nanoparticles, which was revealed to be 3.4 ((0.3) nm
(Figure 2). While the method employed above is widespread,
an alternative method has been reported in which nanopar-
ticles are prepared by reduction of HAuCl4 with NaBH4 in
the presence of trisodium citrate.29 The citrate surface species
can then be displaced by thiols or, in our modification, the
zwitterion [Ru(S2CNC4H8NCS2)(dppm)2]. This yielded blue
nanoparticles (NP2), which were shown by TEM to be of
larger diameter (14.4 ( 2.5 nm) than NP1 (Figure 2). Both
NP1 and NP2 were analyzed by UV-vis spectroscopy and
found to display absorptions with λmax ) 265, 333 nm. These
bands are also observed in [Ru(S2CNC4H8NH2)(dppm)2]
16b
(BF4)2 and were assigned to LMCT behavior. Surface
plasmon resonance bands (SPR) at around 520 nm are often
observed for nanoparticles with sizes in the range 2-20 nm;
however, the bands attributed to SPR were observed at 574
and 683 nm for NP1 and NP2, respectively. Reports have
(27) (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.
(30) (a) Huang, S.; Minami, K.; Sakaue, H.; Shingubara, S.; Takahagi, T.
J. Appl. Phys. 2002, 92, 7486–7490. (b) 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.
(31) (a) Astruc, D.; Daniel, M.-C.; Ruiz, J. Chem.Commun. 2004, 2637–
2649. (b) Labande, A.; Ruiz, J.; Astruc, D. J. Am. Chem. Soc. 2002,
124, 1782–1789. (c) Labande, A.; Astruc, D. Chem. Commun. 2000,
1007–1008.
(28) Wilton-Ely, J. D. E. T. Dalton Trans. 2008, 25–29.
(29) Grabar, K. C.; Freeman, R. G.; Hommer, M. B.; Natan, M. J. Anal.
Chem. 1995, 67, 735–743.
(32) Daniel, M.-C.; Ruiz, J.; Nlate, S.; Blais, J.-C.; Astruc, D. J. Am. Chem.
Soc. 2003, 125, 2617–2628.
Inorganic Chemistry, Vol. 48, No. 8, 2009 3871

Knight et al.
Figure 2. TEM images of nanoparticles NP1 (left), NP2 (center) and NP3 (right).
repulsion in the areas covered by thiols rather than cationic
metal units. The average diameter of these nanoparticles NP3
was found to be approximately 3 nm. Such agglomeration
is similar to that observed in TEM images of nanopar-
ticles linked by 1,4-cyclohexane-bis(dithiocarbamate) and
1,4-phenylene-bis(dithiocarbamate).12a
of the approach described here is illustrated by its application
to the introduction of transition metals onto the surface of
gold nanoparticles, paving the way for facile functionalization
of these materials for applications in catalysis and sensing.
Experimental Section
Direct synthesis of nanoparticles from molecular precur-
sors in a “one pot” procedure was also explored using the
precedent of Nakamoto and co-workers,33 who found that
thermolysis of a gold(I) thiolate complex, [C14H29Me3N]-
[Au(SC12H25)2], at 180 °C for 5 h under nitrogen produces
gold nanoparticles passivated by a thiolate shell. However,
under modified conditions (ethanol reflux, addition of
NaBH4), complexes 6 (AuIII) and 7 (AuI) failed to yield gold
nanoparticles with Ru(S2CNC4H8NCS2)(dppm)2 surface groups
(TEM). Despite this “one pot” method not being successful,
the fact that the ligand S2CNC4H8NH2 can be prepared in
multigram quantities in 30 min16b and that it readily forms
dithiocarbamate complexes with many transition metal
complexes (all under aerobic conditions) means that this
methodology can be used to introduce a wide variety of metal
units onto the surface of gold nanoparticles in just a few
hours. This is in contrast to the much more demanding
synthesis of (mainly polydentate) chelates with long thiol
tethers, which has been the previous method of choice for
attaching transition metal units to gold nanoparticles.28
General Comments. All experiments were carried out under
aerobic conditions, and the majority of the complexes appear
indefinitely stable toward the atmosphere in solution or in the solid
state. Solvents were used as received from commercial sources.
Syntheses of the following compounds have been described
elsewhere: KS2CNC4H8NCS2K,17j [AuCl(PPh3)],34 [dppm-
(AuCl)2],34 [dppf(AuCl)2],35 and [(dppm)2Ru(S2CNC4H8NH2)]-
(BF4)2.16b Fast Atom Bombardment (FAB) mass spectral data were
obtained using an Autospec Q instrument. The mass spectra for
compounds 2 and 5 were obtained from the EPSRC National Mass
Spectrometry Service Centre, University of Wales Swansea. Infrared
data were obtained using a Perkin-Elmer Paragon 1000 FT-IR
spectrophotometer, KBr plates were used for solid state IR
spectroscopy, and characteristic phosphine-associated infrared data
are not reported. NMR spectroscopy was performed at 25 °C using
a Varian Mercury 300 spectrometer in CDCl3 unless otherwise
indicated. All couplings are in hertz. Elemental analysis data were
obtained from London Metropolitan University. Samples were
recrystallized from a mixture of dichloromethane and ethanol for
elemental analysis. Solvates were confirmed by integration of the
1H NMR spectrum. Transmission Electron Microscopy (TEM) was
performed at University College London using a JEOL 100
instrument operating at 100 kV. A JEOL JEM-2000F instrument
fitted with a Link Pentafet EDX detector operating at 200 kV was
used for Energy Dispersive X-ray (EDX) analysis at the University
of Oxford (Begbroke Science Park). The procedures given provide
materials of sufficient purity for synthetic and spectroscopic
purposes.
Conclusion
This report demonstrates a versatile approach to the linking
of mono- and digold units through a piperazine-based
dithiocarbamate spacer. The application to heterometallic
assemblies is particularly significant, as demonstrated by the
gold-ruthenium species prepared. Such mixed-metal species
are not usually accessible using conventional bifunctional
spacers. Unexpectedly, the attempted preparation of
[(dppm)Au2(S2CNC4H8NH2)]2+ as an entry point to this
chemistry was subverted by a symmetrization process.
However, this drawback was successfully avoided by prepar-
ing heterometallics commencing from the opposite end of
the molecule, by generation of the metala-dithiocarbamate
[(dppm)2Ru(S2CNC4H8NCS2)] unit. The versatility and utility
Synthesis of [(Ph3P)Au(S2CNC4H8NH2)]BF4 (1). S2CNC4H8-
NH2 (98 mg, 0.604 mmol) and NaBF4 (88 mg, 0.802 mmol) were
dissolved in methanol (20 mL) and added to a dichloromethane
solution (20 mL) of [AuCl(PPh3)] (200 mg, 0.404 mmol). The
reaction was stirred for 2 h in the dark, and then all solvent removed.
Acetone (50 mL) was added to dissolve the crude product, and the
solution filtered through diatomaceous earth to remove NaCl and
(34) Schmidbaur, H.; Wohlleben, A.; Wagner, F.; Orama, O.; Huttner, G.
Chem. Ber. 1977, 110, 1748–1754.
(35) Hill, D. T.; Girald, 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.
(33) Nakamoto, M.; Yamamoto, M.; Fukusumi, M. Chem. Commun. 2002,
1622–1623.
3872 Inorganic Chemistry, Vol. 48, No. 8, 2009

Homo- And Heterometallic Complexes Based on Au, Fe, and Ru
excess NaBF4. All solvent was again removed, and the residue
triturated in diethyl ether (30 mL) to give a bright yellow product,
which was washed with diethyl ether (10 mL) and dried. Yield:
168 mg (59%). IR (KBr/nujol): 1708, 1607, 1587, 1311, 1260, 1240,
1082 (VB-F), 998 (VCS) cm-1. NMR 1H: 3.31, 4.36 (s x 2, NC4H8N,
8H), 7.34-7.48 (m, C6H5, 15H) ppm. 31P: 38.0 (s, PPh3) ppm. MS
(ES) m/z (abundance %): 621 (68) [M]+. Analysis: Calculated for
C23H25AuBF4N2PS2: C, 39.0; H, 3.6; N, 4.0%. Found: C, 39.1; H,
3.7; N, 4.0%.
Synthesis of [{(Ph3P)Au}2(S2CNC4H8NCS2)] (2). (a) KS2-
CNC4H8NCS2K (25 mg, 0.079 mmol) was dissolved in methanol
(10 mL) to which a dichloromethane solution (10 mL) of [Au-
Cl(PPh3)] (80 mg, 0.162 mmol) was added. The reaction was stirred
for 3.5 h in the dark and then all solvent removed. Diethyl ether
(15 mL) was added, and the solid triturated in a sonic bath. The
cream product was filtered and washed with water (10 mL), ethanol
(10 mL), and hexane (10 mL). Yield: 83 mg (89%). (b) Compound
1 (20 mg, 0.028 mmol) was dissolved in acetone (5 mL), and one
drop (excess) each of NEt3 and CS2 were added and the reaction
stirred for 10 min. To this was added a dichloromethane solution
(10 mL) of [AuCl(PPh3)] (14 mg, 0.028 mmol). The reaction was
stirred for 1 h, and all solvent removed. The same workup was
employed as in (a) to give 29 mg (90%) of product. IR (KBr/nujol):
1272, 1247, 1201, 996 (VCS), 907 cm-1. NMR 1H: 4.33 (s, NC4H8N,
8H), 7.41-7.64 (m, C6H5, 30H) ppm. 31P: 35.9 (s, PPh3) ppm. MS
(FAB) m/z (abundance %): 1155 (2) [M]+. Analysis: Calculated
for C42H38Au2N2P2S4: C, 43.7; H, 3.3; N, 2.4%. Found: C, 43.7;
H, 3.2; N, 2.3%.
(3) [M]+. Analysis: Calc. for C74H67AuBF4N2P5RuS4: C, 53.8; H,
4.1; N, 1.7%. Found: C, 54.0; H, 4.0; N, 1.6%.
Synthesis of [(dppm)2Ru(S2CNC4H8NCS2)Au2(dppm)]-
(BF4)2 (5). [Ru(S2CNC4H8NH2)(dppm)2][BF4]2 (75 mg, 0.062
mmol) was dissolved in dichloromethane (10 mL), treated with NEt3
(3 drops, excess), and stirred for 5 min. Carbon disulfide (2 drops,
excess) was added, and the reaction stirred for 5 min. [(dppm)-
(AuCl)2] (53 mg, 0.062 mmol) was added as a solid and the reaction
stirred for 1 h. Ethanol (10 mL) was added and the pale yellow
product precipitated under reduced pressure. This was washed with
ethanol (10 mL), hexane (10 mL) and dried. Yield: 120 mg (94%).
IR (KBr/nujol): 1308, 1277, 1216, 1157, 1098, 1056 (VBF), 998
V(CS), 912 cm-1. NMR 1H: 3.74, 3.92, 4.13, 4.28 (m × 4, NC4H8N,
8H), 4.56, 4.94 (m × 2, PCH2P, 6H), 6.50, 6.63, 7.04, 7.31, 7.61,
7.73 (m × 6, C6H5, 60H) ppm. 31P NMR: -18.3, -5.0 (t × 2,
dppmRu, JPP ) 35.5 Hz), 37.8 (s(br), dppmAu) ppm. MS (FAB)
m/z (abundance %): 1883 (15) [M]+. Analysis: Calculated for
C81H74Au2B2F8N2P6RuS4: C, 47.2; H, 3.6; N, 1.4%. Found: C, 47.2;
H, 3.5; N, 1.3%.
Synthesis of [{(dppm)2Ru(S2CNC4H8NCS2)}2Au](BF4)3 (6).
[Ru(S2CNC4H8NH2)(dppm)2](BF4)2 (100 mg, 0.083 mmol) was
dissolved in a mixture of chloroform (10 mL) and methanol (10
mL), treated with NEt3 (5 drops, excess) and stirred for 5 min.
Carbon disulfide (4 drops, excess) was added, and the reaction
stirred for 5 min. Tetrachloroauric acid (14 mg, 0.041 mmol) was
added as a solution in methanol (7 mL) causing a color change
from yellow to brown. The reaction was stirred for 3 h. All solvent
was removed, and the residue was taken up in a minimum amount
of chloroform and filtered through diatomaceous earth (Celite).
Ethanol (30 mL) was added, and the brown product precipitated
under reduced pressure. This was washed with ethanol (10 mL),
hexane (10 mL), and dried. Yield: 69 mg (63%). The complex can
be recrystallized from dichloromethane and ethanol. IR (KBr/nujol):
1277, 1216, 1095, 1057 (VB-F), 998 (VC-S) cm-1. NMR 1H (CD2Cl2):
3.66, 3.76, 4.16, 4.25 (m × 4, NC4H8N, 16H), 4.52, 4.95 (m × 2,
PCH2P, 2 × 4H), 6.49, 6.95, 7.08, 7.34, 7.65 (m × 5, C6H5, 80H)
ppm. 31P NMR (CD2Cl2): -18.3, -4.9 [t × 2, dppm, JPP ) 34.6
Hz] ppm. MS (FAB) m/z (abundance %): 2694 (2) [M + 3BF4 +
Na]+, 2606 (1) [M + 2BF4 + Na]+, 2410 (1) [M]+. Analysis:
Calculated for C112H104AuB3F12N4P8Ru2S8 ·4CH2Cl2: C, 46.3; H,
3.8; N, 1.9%. Found: C, 46.2; H, 3.5; N, 2.1%.
Synthesis of [{(dppm)2Ru(S2CNC4H8NCS2)}Au]2(BF4)2 (7). A
solution of [Ru(S2CNC4H8NH2)(dppm)2][BF4]2 (100 mg, 0.083
mmol) in dichloromethane (30 mL) and methanol (15 mL) was
treated with NEt3 (4 drops, excess) followed by a 5 min stir and
carbon disulfide (3 drops, excess) followed by a 10 min stir. A
colorless dichloromethane solution (20 mL) of [AuCl(tht)] (27 mg,
0.083 mmol) was added, and the yellow solution became progres-
sively darker during a 20 min stir. All volatiles were removed under
vacuum leaving a yellow-brown crude solid which was taken up
in a minimal amount of dichloromethane and filtered through
diatomaceous earth (Celite). Ethanol (10 mL) was added, and the
product was precipitated under reduced pressure. The brown solid
was isolated by filtration and washed with cold ethanol (5 mL)
and dried. Yield: 98 mg (85%). IR (KBr/nujol): 1604, 1386, 1235,
1152, 1060 (VB-F), 999 (VC-S) cm-1. NMR 1H (CD2Cl2): 3.37-4.28
(m, NC4H8N, 16H), 4.52, 4.93 (m × 2, PCH2P, 2 × 4H), 6.48,
6.78-7.77 (m × 2, C6H5, 80H) ppm. 31P NMR (CD2Cl2): -17.9,
-5.0 (m × 2, dppm) ppm. MALDI-MS m/z (abundance %): 2691
(3) [M + BF4]+, 2609 (1) [M]+. Analysis: Calculated for
C112H104Au2B2F8N4P8Ru2S8: C, 48.4; H, 3.8; N, 2.0%. Found: C,
48.4; H, 3.8; N, 2.0%.
Synthesis of [{(dppf)Au2}2(S2CNC4H8NCS2)](PF6)2 (3).
KS2CNC4H8NCS2K (11 mg, 0.035 mmol) was dissolved in
methanol (10 mL). A dichloromethane solution (10 mL) of
[(dppf)(AuCl)2] (75 mg, 0.074 mmol) was added dropwise followed
by a solution of NH4PF6 (15 mg, 0.092 mmol) in methanol (10
mL). The reaction was stirred for 3 h at 5 °C and then all solvent
removed. The residue was taken up in a minimum volume of
dichloromethane and filtered through diatomaceous earth (Celite).
Diethylether (15 mL) was added to precipitate the yellow product.
This was washed with diethylether (5 mL) and dried. Yield: 66
mg (74%). IR (KBr/nujol): 1311, 1279, 1173, 1101, 1032, 997
(VC-S), 837 (VP-F) cm-1. NMR 1H (CD2Cl2): 4.34, 4.52 (s(br) × 2,
C5H4, 2 × 8H), 4.59 (s, NC4H8N, 8H), 7.53-7.70 (m, C6H5, 40H)
ppm. 31P (CD2Cl2): 32.0 (s, dppf) ppm. MS (FAB) m/z (abundance
%): 2277 (10) [M
+
PF6]+. Analysis: Calculated for
C74H64Au4F12Fe2N2P6S4: C, 36.7; H, 2.7; N, 1.2%. Found: C, 36.6;
H, 2.8; N, 1.3%.
Synthesis of [(dppm)2Ru(S2CNC4H8NCS2)Au(PPh3)]BF4 (4).
[Ru(S2CNC4H8NH2)(dppm)2][BF4]2 (100 mg, 0.083 mmol) was
dissolved in dichloromethane (10 mL), treated with NEt3 (5 drops,
excess), and stirred for 5 min. Carbon disulfide (3 drops, excess)
was added, and the reaction stirred for 5 min. [AuCl(PPh3)] (41
mg, 0.083 mmol) was added as a solid, and the reaction was stirred
for 1 h. All solvent was removed, and the residue was taken up in
a minimum amount of dichloromethane and filtered through
diatomaceous earth (Celite). The crude product was redissolved in
dichloromethane (5 mL) and diethylether (30 mL) added to
precipitate the colorless product. This was washed with diethylether
(10 mL) and dried. Yield: 87 mg (63%). IR (KBr/nujol): 1310,
1
1277, 1207, 1055 (νBF), 997 (νCS) cm-1. NMR H (d6-acetone):
3.73, 3.92, 4.14, 4.23 (m × 4, NC4H8N, 8H), 4.75, 5.36 (m × 2,
PCH2P, 2 × 2H), 6.69, 7.00, 7.24, 7.40, 7.60, 7.63 (m × 6, C6H5,
55H) ppm. 31P (d6-acetone): -18.0, -3.0 (t × 2, dppm, JPP ) 34.5
Hz), 37.5 (s(br), PPh3) ppm. MS (FAB) m/z (abundance %) ) 1566
Inorganic Chemistry, Vol. 48, No. 8, 2009 3873

Knight et al.
Table 1
(22 mg, 0.109 mmol). An aqueous solution (10 mL) of NaBH4 (91
mg, 2.408 mmol) was slowly added dropwise to the stirred reaction
mixture over 10 min. The burgundy solution became a dark black
mixture which was left to stir for 3 h. Chloroform (100 mL) was added,
and the organic (lower) layer was collected and the mixture stored at
-18 °C for 12 h. The supernatant was decanted off and chloroform
(20 mL) was added to remove excess thiol, and the mixture was stored
for a further 12 h at -18 °C. The supernatant was decanted off, and
the black solid collected by filtration, washed with dichloromethane
(50 mL), water (50 mL), and methanol (50 mL) and dried.
Crystallography. Crystals of 3 were grown by slow diffusion of
diethyl ether vapor onto an acetonitrile/methanol (1:1) solution of the
complex. Single crystal X-ray data were collected using graphite
monochromated Mo KR radiation (λ ) 0.71073 Å) on an Enraf-Nonius
KappaCCD diffractometer. The diffractometer was equipped with a
Cryostream N2 open-flow cooling device,36 and the data were collected
at 150(2) K. Series of ω-scans and φ-scans were performed in such a
way as to cover a sphere of data to a maximum resolution between
0.70 and 0.77 Å. Cell parameters and intensity data for 3 were
processed using the DENZO-SMN package,37 and the structure was
solved by direct methods and refined by full-matrix least-squares on
F2 using SHELXTL software.38 Intensities were corrected for absorp-
tion effects by the multiscan method based on multiple scans of
identical and Laue equivalent reflections (using the SORTAV
software).39
Where possible non-hydrogen atoms were refined with aniso-
tropic displacement parameters, and the hydrogen atoms were
positioned geometrically and refined using a riding model. In the
case of the disordered hexafluorophosphate anion, and the partially
occupied ether solvent molecule, anisotropic refinement was not
possible, so they were modeled with isotropic displacement
parameters. Refinement of the Flack x parameter40 gave a value of
-0.002(4) (given 8531 Friedel equivalent reflections). Crystal data
and structure refinement parameters are included in Table 1.
Crystallographic data (excluding structure factors) for the structure
of 3 has been deposited with the Cambridge Crystallographic Data
Centre (CCDC 699269). Copies of the data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
http://www. ccdc.cam.ac.uk/data_request/cif.
3·1.75(Et2O)
chemical formula
Fw
C81H81.5Au4F12Fe2N2O1.75P6S4
2552.66
orthorhombic
orange block
0.30 × 0.12 × 0.09
Pca21
35.0136(3)
11.0802(1)
22.1520(2)
8594.04(13)
4
crystal system
crystal color
crystal size (mm)
space group
a (Å)
b (Å)
c (Å)
V (Å3)
Z
Dcalcd (g/cm3)
T (K)
1.970
150(2)
7.413
µ(Mo KR) (mm-1
)
Flack x (8531 Friedel pairs)
F(000)
-0.002(4)
4902
60097
reflections collected
unique reflections (Rint)
R1 (I > 2σ(I))
18911 (8.20%)
4.15%
wR2 (all data)
8.86%
Synthesis of NP1. An aqueous solution (7 mL) of HAuCl4 (18.6
mg, 0.055 mmol) was rapidly stirred with a chloroform solution (7
mL) of the phase transfer reagent TOAB (89.9 mg, 0.164 mmol)
-
until complete transfer of the AuCl4 anion had occurred. The
organic layer was collected, to which was added a chloroform
solution (7 mL) of [Ru(S2CNC4H8NCS2)(dppm)2] (152 mg, 0.137
mmol), freshly prepared in situ from [Ru(S2CNC4H8NH2)(dppm)2]-
(BF4)2 (165 mg, 0.137 mmol), NEt3 (5 drops, excess), and carbon
disulfide (4 drops, excess). The orange solution was stirred at 4 °C
for 10 min. An aqueous solution (15 mL) of NaBH4 (116 mg, 3.07
mmol) was added dropwise over 10 min to the stirred solution at
4 °C, causing a color change from orange to dark brown. The
solution was stirred for a further 2 h with the temperature below
10 °C. The organic layer was isolated and washed with water (3 ×
5 mL) and then concentrated (∼ 5 mL) under reduced pressure.
Water was added to precipitate the dark brown product, and the
mixture stored at -18 °C for 18 h. The supernatant liquid was
decanted, and the product washed with water (5 × 10 mL), warm
ethanol (3 × 10 mL), and dried.
Synthesis of NP2. HAuCl4 (11.2 mg, 0.033 mmol) in water (35
mL) was brought to the boil with vigorous stirring. To this solution
was added trisodium citrate (37.8 mg, 0.129 mmol) in water (4 mL),
and boiling continued for 10 min. The heating source was removed,
and the reaction stirred for a further 15 min. In a separate reaction
flask, [Ru(S2CNC4H8NH2)(dppm)2](BF4)2 (100 mg, 0.083 mmol) was
dissolved in methanol (10 mL), treated with NEt3 (5 drops, excess),
and the reaction stirred for 5 min. Carbon disulfide (4 drops, excess)
was added, and the reaction stirred for 5 min. This solution was added
dropwise to the previously prepared citrate stabilized nanoparticles
resulting in precipitation of a fine blue solid. The reaction was stirred
for a further 3 h, stored at -18 °C for 18 h, and the blue precipitate
collected by filtration and washed with water (5 × 10 mL), warm
ethanol (3 × 10 mL), and air-dried.
Acknowledgment. Merton College is gratefully acknowl-
edged for the provision of a Fellowship by J.D.E.T.W.-E.
We thank the OUP John Fell Fund for consumables and
Johnson Matthey Ltd for a generous loan of ruthenium
trichloride and tetrachloroauric acid. We thank Dr. S. Firth
(UCL) and Dr. Yi Du (Oxford) for measurement of TEM
images and Dr. K. B. Holt (UCL) for electrochemical
measurements.
Supporting Information Available: Crystallographic data for
the structure of 3. This material is available free of charge via the
Internet at http://pubs.acs.org.
Synthesis of NP3. A colorless solution of the phase transfer agent,
TOAB (419 mg, 0.766 mmol) in toluene (10 mL), was rapidly stirred
with a yellow aqueous solution (10 mL) of HAuCl4 (86 mg, 0.219
mmol) until complete transfer of [AuCl4]- had occurred. The organic
layer was isolated. [Ru(S2CNC4H8NH2)(dppm)2](BF4)2 (132 mg, 0.109
mmol) was dissolved in dichloromethane (10 mL) and treated with
NEt3 (3 drops, excess), followed by a 5 min stir, and carbon disulfide
(2 drops, excess), added followed by another 5 min stir. This yellow
solution was added to the organic layer together with dodecanethiol
IC802442D
(36) Cosier, J.; Glazer, A. M. J. Appl. Crystallogr. 1986, 19, 105–107.
(37) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode, Methods Enzymol.; Carter, C. W.,
Sweet, R. M., Eds.; Academic Press: New York, 1997; p 276.
(38) SHELXTL, version 5.1; Bruker Analytical X-ray Instruments Inc.:
Madison, WI, 1999.
(39) Blessing, R. H. Acta Crystallogr. 1995, A51, 33–38.
(40) Flack, H. D. Acta Crystallogr. 1983, A39, 876–881.
3874 Inorganic Chemistry, Vol. 48, No. 8, 2009