A new series of dinuclear Au(I) complexes linked by diethynylpyridine groups

Article abstract of DOI:10.1039/b716664h

A series of novel digold complexes incorporating ethynyl pyridine derivatives as a spacer unit, [(R₃P)Au(C≡C)X(C≡C) Au(PR₃)] (R = Ph, X = 2,5-pyridine (1); R = Cy (cyclohexane), X = 2,5-pyridine (2); R = Ph, X = 2,6-pyridine (3); R = Ph, X = 2,5′- bipyridine (4); R = Ph, X = 2,6′-bipyridine (5)), has been synthesised. All the complexes have been characterised spectroscopically and the structures determined by single-crystal X-ray crystallography. The central (C≡C)(X)(C≡C) unit is essentially linear for complexes 1, 2 and 4 and kinked for complexes 3 and 5, but only in 1, with the shortest spacer group and the less bulky phosphine ligand, is there evidence of d¹⁰... d¹⁰ Au...Au interactions (Au-Au 3.351(2) Ae. The solution UV/visible absorption and emission spectra for all the complexes are similar to those of the free ligands suggesting that the spectra are dominated by π-π* ligand-centred transitions and this is confirmed by DFT calculations. The Royal Society of Chemistry.

Full text of DOI:10.1039/b716664h

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
A new series of dinuclear Au(I) complexes linked by diethynylpyridine
groups†‡
Peiyi Li,a Birte Ahrens,b Andrew D. Bond,a John E. Davies,a Olivia F. Koentjoro,b Paul R. Raithby*b and
Simon J. Teatc
Received 30th October 2007, Accepted 18th December 2007
First published as an Advance Article on the web 24th January 2008
DOI: 10.1039/b716664h
A series of novel digold complexes incorporating ethynyl pyridine derivatives as a spacer unit,
[(R3P)Au(C≡C)X(C≡C)Au(PR3)] (R = Ph, X = 2,5-pyridine (1); R = Cy (cyclohexane), X =
2,5-pyridine (2); R = Ph, X = 2,6-pyridine (3); R = Ph, X = 2,5ꢀ-bipyridine (4); R = Ph, X =
2,6ꢀ-bipyridine (5)), has been synthesised. All the complexes have been characterised spectroscopically
and the structures determined by single-crystal X-ray crystallography. The central
(C≡C)(X)(C≡C) unit is essentially linear for complexes 1, 2 and 4 and kinked for complexes 3 and 5,
but only in 1, with the shortest spacer group and the less bulky phosphine ligand, is there evidence of
d10 · · · d10 Au · · · Au interactions (Au–Au 3.351(2) A). The solution UV/visible absorption and emission
˚
spectra for all the complexes are similar to those of the free ligands suggesting that the spectra are
dominated by p–p* ligand-centred transitions and this is confirmed by DFT calculations.
Extensive studies have been carried out on linear gold(I)
acetylides and isocyanide systems13 and on related polynuclear,
Introduction
phosphine-bridged complexes.15 The emission originating from
these compounds is linked to the presence or absence of gold–gold
interactions in the solid state structures of these materials, and is
highly dependent on the acetylide chain length between adjacent
gold centres, the bonding properties of the linking groups, and the
nature of the phosphine ligands.19–21
The large role the spacer group plays on the luminescence
properties of gold(I) acetylide complexes is highlighted in several
studies involving a variety of aromatic rings such as 1,3-diethynyl-
benzene, 1,3-diethynylmesitylene, 1,4-diethynylbenzene, 1,4-di-
ethynylmesitylene, 1,4-diethynyldurene, 9,10-dithynylanthracene,
diethynylthieno[3,2-b]thiophene, diethynylthieno[3,2-b:2ꢀ,3ꢀ-d]-
thiophene and pyridine,19–26 and a number of metal-containing
species.27 The emission in these complexes is attributed to a p–
p*(acetylide):[r(Au–P)→p*(acetylide)] state. In view of the short
intermolecular Au · · · Au separation observed, a metal-centred
3[(dd*)1(pr)1] excited state has been suggested to account for the
red shift in emission energy observed in the solid state.23
Compared to benzene or thiophene, pyridine is electron defi-
cient; and consequently the metal acetylide complexes should have
increased electron affinity and improved electron-transporting
properties.28 This is borne out in a series of comparative
studies of platinum(II) poly-yne complexes and polymers that
have arene groups and heterocyclic spacer groups linking the
metal acetylide units.29 In the platinum poly-yne complexes with
bis(ethynyl)oligopyridine as the spacer group in the backbone, the
metal complexes exhibit a decrease in thermal stability with an
increased number of pyridine units in the spacer group.30
The area of transition metal acetylide chemistry has seen increased
interest because of the potential application of metal acetylide
complexes, oligomers and polymers in the area of opto-electronics
where these species1 could act as “molecular wires” in devices
such as light emitting diodes, lasers, photocells, and field effect
transistors.2–8 Metal containing poly-ynes are also potential can-
didates as low-dimensional conductors and non-linear optical
materials.9–11
Gold(I) acetylide complexes are of particular interest because
of their luminescent properties,12 which are a consequence of
aurophilic d10 · · · d10 Au · · · Au interactions. Aurophilic d10 · · · d10
Au · · · Au interactions may contribute bonding interactions to the
structure of ca. 30 kJ mol−1, a value comparable to hydrogen
bonds, when the Au · · · Au distance is in the range of 2.5–
3.9 A.13,14 In addition, the linear arrangement of the acetylide unit
˚
and its proven ability to participate in extended, delocalised
p-bonding interactions has stimulated interest in the use of
gold acetylide in electronic applications.15 In this context, Wade
et al. have examined diethynyl-para-carboranes16 and carborane
gold derivatives17 with a view to exploiting their physical and
electronic properties. More generally, gold acetylides have been
shown to exhibit a range of interesting properties including optical
nonlinearity, liquid crystallinity and electrical conductivity.18
aDepartment of Chemistry, University of Cambridge, Lensfield Road,
Cambridge, UK CB2 1EW
bDepartment of Chemistry, University of Bath, Claverton Down, Bath, UK
BA2 7AY. E-mail: p.r.raithby@bath.ac.uk
cSTFC Daresbury Laboratory, Daresbury, Warrington, UK WA4 4AD
Here we describe a detailed study on a series of digold diyne
complexes with pyridine or bipyridine spacer groups where not
only the chain length but also the geometry of the chain and the
bulk of the substituent ligands has been altered systematically to
† Dedicated to Professor Ken Wade on the occasion of his 75th birthday
in recognition of his outstanding contribution to chemistry.
‡ CCDC reference numbers 665741–665745. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b716664h
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 1635–1646 | 1635
©

View Article Online
Scheme 1
the asymmetric acetylide complex 1 the 31P{ H} NMR spectrum
displays two signals at d 42.69 and 42.80. The position of these
signals is similar to that in a range of related gold phosphine
acetylenic complexes.20,21 In the mass spectra of the complexes
a molecular ion peak [M]+ or [M + H]+ is present in all cases,
however, the most intense peak in all the spectra is at m/z 459 (477),
that can be attributed to the [AuPPh3]+ ([AuPCy3]+) fragment.
Peaks related to [Au(PPh3)2]+ ([Au(PCy3)2]+) and [M + Au]+ are
also seen. It appears that the fragmentation favours the generation
of mono-positive ions.
1
probe the effect on the formation of the intermolecular aurophilic
Au · · · Au interactions.
Results and discussion
Synthesis of dinuclear gold(I) r-acetylides
The series of five gold(I) diyne complexes complexes
[(R3P)Au(C≡C)X(C≡C)Au(PR3)] (R = Ph, X = 2,5-pyridine (1);
R = Cy, X = 2,5-pyridine (2); R = Ph, X = 2,6-pyridine (3);
R = Ph, X = 2,5ꢀ-bipyridine (4); R = Ph, X = 2,6ꢀ-bipyridine
(5)) were prepared by the reaction of gold(I) phosphine chloride
with the appropriate terminal alkyne in the presence of methanolic
NaOMe,31 which acts as both a base and as a chloride abstractor, to
yield yellow to orange-yellow crystalline solids (Scheme 1). Since
the terminal alkynes were not particularly stable in the presence
of light they were prepared immediately prior to the reaction
via treatment of the bis-trimethylsilyl derivatives with KOH in
dichloromethane.
The 1H and 13C NMR spectra of gold(I) r-acetylides were very
similar to that obtained for the trimethylsilyl-protected ligands
and the related platinum-containing complexes23 which indicates
that there was little change to the ligand upon the coordination
to the gold moiety. This indicates that the interaction between the
Au(I) centre and the acetylide ligand is not significant enough to be
dissimilar from the trimethylsilyl group. It seems the large gold unit
separates the phosphine ligand and the acetylide ligand into two
almost independent units. This is confirmed by the electronic
structure calculations performed on these molecules (vide infra).
The IR spectrum of all the dinuclear gold(I) r-acetylides com-
pounds 1–5 show a fairly strong characteristic m(C≡C) absorption
band in the region of 2110–2120 cm−1 (see the Experimental
section). The 1H NMR spectra for the five complexes show
resonances in the aromatic region representative of the presence
of the appropriate pyridine or bipyridine spacer unit. The 13C
NMR spectra of compounds 1–5 clearly show acetylene carbon
resonances in the region of 100–104 ppm, as well as resonances
in the aromatic region. All the symmetric dinuclear gold(I) r-
Solid state molecular structure of dinuclear gold(I) r-acetylides
The structures of compounds 1–5 have been determined by single
crystal X-ray crystallography. Selected bond lengths and bond
angles of five complexes are listed in Table 1 and their molecular
structures are presented in Fig. 1–5. In agreement with the
spectroscopy all the structures confirm that the complexes are
dinuclear with the gold phosphine units linked by the diethynyl
spacer groups. To a first approximation the coordination geometry
at the gold centres in all five complexes is linear and two-coordinate
1
acetylides compounds, 2–5, display a singlet in their 31P{ H} NMR
spectra, at d 57.22 for the cyclohexyl phosphine in 2 and in the
range d 42.72–42.78 for the triphenylphosphine groups in 3–5. For
1636 | Dalton Trans., 2008, 1635–1646
This journal is
The Royal Society of Chemistry 2008
©

View Article Online
Fig. 1 The solid state structure of [(Ph3P)Au(C≡C)(2,5-pyridine)(C≡C)Au(PPh3)] 1 showing the Au · · · Au interactions between adjacent molecules.
The pyridine nitrogen atom is disordered over two symmetry related sites. The atoms denoted “A” are related to those in the asymmetric unit by the
symmetry operation −1 − x, 2 − y, −z.
gold(I) r-acetylide complexes,19,21,24–39 spanning the narrow range
◦
˚
Table 1 Selected bond lengths (A) and bond angles ( ) of 1–5
˚
of 1.984(15)–2.013(5) A. Similarly, the Au–P bond distances are
Au–C(≡C) Au–P
C≡C
(C≡)C–Au–P C≡C–Au
comparable to those found in known phosphine gold(I) r-acetylide
complexes (2.2736–2.290 A)23,25,31–56 but they are longer than those
˚
1
2
3
4
5
2.11(5)
2.289(11)
2.2823(19) 1.212(11) 175.7(2)
1.10(5)
168.0(14)
162(5)
of chlorogold(I) phosphines,57,58 consistent with the stronger trans-
influence of the alkynyl group than the chloride. The C≡C bond
1.998(7)
1.984(15)
2.011(4)
2.013(5)
173.2(8)
167.4(14)
169.2(4)
178.6(4)
2.279(4)
1.21(2)
168.6(5)
2.2769(11) 1.197(6)
2.2738(12) 1.157(6)
174.84(12)
177.68(12)
lengths are typical of di-substituted carbon–carbon triple bonds
20,21,23,25,31–56
˚
and fall in the reported range of 1.157–1.206 A.
It is
thus evident that significant changes in the spacer group have little
effect on the intramolecular bond lengths of Au–C(≡C), Au–P and
C≡C units but, on the other hand, these changes do govern the
crystal packing and the intermolecular interactions as discussed
in the following paragraphs.
Aurophilicity is the result of relativistic effects on Au(I) caused
by non-covalent attractions between these d10 metal ions.59–61
˚
˚
An Au · · · Au distance below 3.3 A (smaller than 3.6 A, the
sum of Au(I) van der Waals radii62) is thought to provide an
Au · · · Au interaction of similar strength to hydrogen bonds.
Aurophilicity is responsible for various interesting molecular
and supramolecular architectures. In the solid state structure
of 1 short intermolecular Au · · · Au interactions are observed
˚
with a separation of 3.351(2) A, and each [(Ph3P)Au(C≡C)(2,5-
pyridine)(C≡C)Au(PPh3)] molecular unit sits on a crystallo-
graphic centre of symmetry located at the centre of the pyridine
ring; the pyridine nitrogen atom was treated in the refinement
as being disordered over two symmetry related positions as was
the related carbon atom. The Au(I) centre is linked to another
Au(I) centre from a neighbouring molecule via an Au · · · Au
interaction (Fig. 1) so that loose chain-like polymers are formed.
The two Au · · · Au interactive {PPh3Au–C≡C–} vectors are anti-
parallel with torsion angles (C≡C–Au · · · Au–C≡C) of 178.7◦.
The formation of these chain-like polymers generated by the
Au(I) · · · Au(I) interactions is a common feature of the chemistry of
metal acetylides21 and isocyanides13 and is particularly prevalent
when the spacer groups are relatively short and the auxiliary
phosphine ligands are not bulky.
Fig.
2
The molecular structure of [(Cy3P)Au(C≡C)(2,5-pyri-
dine)(C≡C)Au(PCy3)] 2 showing the atom numbering scheme. The
atom denoted “A” is related to those in the asymmetric unit by the
symmetry operation 1 − x, 1 − y, 1 − z. The disordered dichloromethane
molecule has been omitted for clarity and the pyridine nitrogen is
disordered over the four equivalent positions on the pyridine ring and
refined with partial occupancy as are the related carbon atoms.
as would be expected for Au(I) systems. In the structures of 2, 4
and 5 the C–Au–P and C≡C–Au angles do not show substantial
deviations from linearity. However, in the structures of 1 and 3
there are larger deviations from linearity that can be attributed
to intermolecular interactions. All Au–C(≡C) bond lengths are
unexceptional when compared to those of published phosphine
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 1635–1646 | 1637
©

View Article Online
Fig. 3 The molecular structure of [(Ph3P)Au(C≡C)(2,6-pyridine)(C≡C)Au(PPh3)] 3 showing the atom numbering scheme. The atoms denoted “A” are
related to those in the asymmetric unit by the symmetry operation −1 − x, 2 − y, −z.
Fig. 4 The molecular structure of [(Ph3P)Au(C≡C)(2,5ꢀ-bipyridine)(C≡C)Au(PPhR3)] 4 showing the atom numbering scheme. The atoms denoted “A”
are related to those in the asymmetric unit by the symmetry operation 1 − x, 2 − y, 2 − z.
Fig. 5 The molecular structure of [(Ph3P)Au(C≡C)(2,6ꢀ-bipyridine)(C≡C)Au(PPh3)] 5 showing the atom numbering scheme. The atoms denoted “A”
are related to those in the asymmetric unit by the symmetry operation −x, −y, 1 − z. Only one orientation of the disordered phenyl group is shown for
clarity and the disordered dichloromethane molecule is also omitted.
1638 | Dalton Trans., 2008, 1635–1646
This journal is
The Royal Society of Chemistry 2008
©

View Article Online
Fig. 6 The crystal structure of [(Ph3P)Au(C≡C)(2,6-pyridine)(C≡C)Au(PPh3)] 3 showing the nature of the intermolecular interactions.
In [(Ph3P)Au(C≡C)(2,5-pyridine)(C≡C)Au(PPh3)] 2 the spacer
group is the same as in 1 but the triphenylphosphine groups,
coordinated to the two gold centres, have been replaced by
tricyclohexylphosphine groups. This change has a marked effect
on the intermolecular interactions exhibited in the structure of
2, although the situation is complicated in the solid state be-
cause the molecule co-cystallises with a disordered molecule of
dichloromethane. While the molecule crystallises in the same
to 1 which has the same auxiliary phosphine group as 3 the
intermolecular interactions are significantly different. The shortest
˚
intermolecular Au · · · Au contact in 3 is at 3.677(1) A which is
˚
ca. 0.32 A longer than in 1 and slightly longer than the sum
of the van der Waals radii. In addition, there is a short contact
between Au(1) and the a-carbon of the acetylene group C(1B),
˚
also related by the symmetry operation −x, −y, −z, at 3.55(2) A,
which may be indicative of a favourable intermolecular interaction
(Fig. 6). As with 1 the Ph3PAu–C≡C units are anti-parallel with
a P–Au · · · Au–P torsion angle of −180◦. The intermolecular
interactions in the crystal are completed by a p–p stacking
interaction between the central pyridine ring on one molecule and
one of the phenyl rings [C(21)–C(26)] on an adjacent molecule
(again related by the symmetry operation −x, −y, −z) where the
angle between the rings is 15.2◦ and the centroid–centroid distance
¯
space group as 1, P1 (No. 2), and the centre of the pyridine
ring is again located on a crystallographic centre of symmetry
(in this instance the pyridine nitrogen atom was refined as being
disordered over the four possible sites on the ring with occupancies
for nitrogen and carbon on each site summing to unity; on
each site the carbon and nitrogen were constrained to have the
same atomic coordinates), the packing arrangement is different
and there are no Au · · · Au interactions; the shortest intermolec-
˚
is 3.89 A.
˚
ular Au · · · Au contact being 5.545(1) A. A similar change in
The structure of 3 may also be contrasted with that
Au · · · Au distances has been observed previously in the related
pair of molecules [(MeO)3PAu(C≡C)(C6H4)(C≡C)AuP(OMe)3]54
where the intermolecular Au · · · Au separations are 3.1733(2)
of [(Tol3P)Au(C≡C)(3,5-pyridine)(C≡C)Au(PTol3)]26 (Tol
=
C6H4CH3) in which there are intermolecular aurophilic Au · · · Au
˚
contacts of 3.2265(5) A and the molecular chains are arranged
˚
and 3.5995(3) A, indicative of Au · · · Au interactions, and
so that the Tol3PAu–C≡C units of two vicinal molecules are
effectively perpendicular (P–Au · · · Au–P 89◦). The C(acetylenic
a-carbon)–(pyridine centroid)–C(acetylenic a-carbon) angle is
121.55◦. Thus, in digold complexes with relatively short di-
ethynylpyridine spacer groups there is a propensity to form au-
rophilic Au · · · Au contacts to produce molecular chains, although
the shape of the spacer group and the packing arrangement may
differ, provided that the auxiliary phosphine groups are not too
bulky to prevent a close approach between the gold centres.
In the structure of [(Ph3P)Au(C≡C)(2,5ꢀ-bipyridine)(C≡C)-
Au(PPh3)] 4 the spacer group has been extended to include two
aromatic rings while the linear nature of the molecular backbone
has been retained. The molecular structure of 4 is displayed in
Fig. 4. The molecule sits on a crystallographic centre of symmetry
located at the mid-point of the C(6)–C(6A) bond [where C(6A) is
related to C(6) by the symmetry operation 1 − x, 2 − y, 2 − z]
and, as a consequence, the two rings of the bipyridyl unit are
precisely co-planar. The bipyridine group adopts the expected
trans configuration to minimise the steric congestion between
aromatic protons. There are no short aurophilic Au · · · Au contacts
[Cy3PAu(C≡C)(C6H4)(C≡C)AuPCy3],56 where the Au · · · Au sep-
˚
aration of 5.648(1) A is significantly too long to be considered
an interaction. While this difference may be attributed to the
difference in steric bulk between the phosphorus donor ligands
in the two examples electronic factors cannot be excluded. The
Tolman cone angles for the phosphines and phosphate are 170◦
(Cy), 145◦ (Ph) and 107◦ (OMe), respectively.63 In the case of
2 compared to 1 the situation is further complicated as 2 co-
crystallises with a molecule of dichloromethane solvent which
exhibits short contacts with the central pyridine ring (the carbon of
˚
the dichloromethane molecule has contacts of 3.108 and 3.446 A
with the N(4) and C(5) or their symmetry equivalents).
In complex 3 the 2,5-pyridine ligand present in 1 and 2 is
replaced by a 2,6-pyridine ligand which, of necessity, intro-
duces non-linearity into the molecular backbone. The structure
of [(Ph3P)Au(C≡C)(2,6-pyridine)(C≡C)Au(PPh3)] 3 is shown in
Fig. 3. In the crystal the molecule sits on a crystallographic 2-fold
rotation axis that passes through N(1) and C(5) and the C(3)–
(pyridine ring centroid)–C(3A) angle is 116.02◦. By comparison
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 1635–1646 | 1639
©

View Article Online
◦
˚
in the crystal structure with the shortest intermolecular Au · · · Au
Table 2 Selected bond lengths (A) and bond angles ( ) of 6–8
˚
distance being 7.069(1) A. The absence of aurophilic interactions
Au–C(≡C) Au–P
C≡C
(C≡)C–Au–P
C≡C–Au
in digold ethynyl complexes with longer spacer groups is acommon
feature of the structural chemistry of these systems even when
moderately sized auxiliary phosphines are present.21 In 4 the
shortest intermolecular contact to the gold centre is from a phenyl
6
7
8
1.988
1.989
1.988
2.351
2.351
2.351
1.224
1.225
1.224
179.6
179.9
179.8
178.5
179.9
178.9
˚
hydrogen atom on an adjacent molecule (Au1 · · · H11B 3.30 A,
H11B being related by the symmetry operation 3 − x, 0.5 + y,
1.5 − z).
The geometry optimised structures of 6–8 presented the same
gross structural features as the experimentally determined struc-
tures, having rod-like molecular backbones with each Au(I) centre
assuming a linear two-coordinated geometry. The Au–C bond
In the structure of [(Ph3P)Au(C≡C)(2,6ꢀ-bipyridine)(C≡C)-
Au(PPh3)] 5 a kink has been introduced into the longer spacer
group in order to assess whether this makes a difference to the
nature of the intermolecular interactions and mirrors the compar-
ison between the structures of 1 and 3 discussed above. The discrete
molecules of 5, illustrated in Fig. 5, sit on crystallographic centres
of symmetry located at the mid-point of the C(2)–C(2A) bonds
[where C(2A) is related to C(2) by the symmetry operation −x,
−y, 1 − z] and, as in the case of 4, the bipyridine group is precisely
planar by crystal symmetry. In 5 the shortest intermolecular
˚
˚
is 1.988–1.989 A in length (c.a. 1.984(15)–2.11(5) A for the
crystallographically determined structures). The Au–P bond is
˚
˚
2.351 A, while the C≡C is 1.224–1.225 A, both bonds being
slightly longer that those found in experimentally determined
structures of phosphine gold(I) r-acetylides. In the geometry
optimised structure of each of 6–8 there is less than 1◦ deviation
from linearity in the two C–Au–P and C≡C–Au bond angles,
which is one of the primary differences in structure compared to
the solid state structures of 1–5. This difference is not surprising
since the larger deviation from linearity in 1–5 is attributed to
crystal packing forces and intermolecular interactions, especially
the presence of Au · · · Au interactions which is not taken in account
in the calculations on 6–8.
˚
Au · · · Au contact is 4.785(1) A, which is considerably shorter than
the distance found in 4, but still much too long to be considered
as an aurophilic interaction. Thus, again, despite the difference
in the geometry the presence of the longer spacer group does not
favour formation of aurophilic interactions between molecules in
the solid state. The situation in the crystal structure of 5 is slightly
complicated by the presence of a disordered dichloromethane
molecule in the lattice but this does not form any short contacts
with the central backbone of the molecule.
An analysis of the orbital structure of 6–8 reveals the HOMO
(highest occupied molecular orbital) is calculated to be essentially
delocalised over the central portion of the molecular framework
comprising the acetylene units and spacer group with negligible
interaction with the Au(I) centres. For each system the HOMO is
bonding in character between the carbon atoms of the acetylenic
carbon atoms and anti-bonding with respect to the C(sp)–
C(sp2) ethynyl–aromatic bonds, while the converse is true of the
LUMO. These interactions are illustrated for 6 in Fig. 7.
From the structural data obtained from the structures of 1–
5 it is apparent that the formation of intermolecular aurophilic
interactions in the solid state is not favoured by the presence
of longer spacer groups in complexes with the general formula
[(R3P)Au(C≡C)X(C≡C)Au(PR3)] regardless of whether the back-
bone geometry of the molecules is linear or kinked. However,
other factors such as the bulk of the auxiliary phosphine ligands
and the electronic properties of the central spacer group and the
phosphines must also play a part in the final packing arrangement
of the molecules.
Electronic structure of dinuclear gold(I) r-acetylides
Then, in order to obtain more information regarding the elec-
tronic properties of these [(R3P)Au(C≡C)X(C≡C)Au(PR3)] (X =
pyridine or bipyridine) complexes, at least within the individual
molecular units, density functional theory (DFT) calculations
were undertaken. Geometry optimisation was performed on [H3P–
Au–C≡C–X–C≡C–Au–PH3] (X = 2,5-pyridine (6); X = 2,5ꢀ-
bipyridine (7); X = 2,6ꢀ-bipyridine (8)) using the solid state
molecular structure of 1, 4, and 5 as a starting point. The process
follows that described in the Experimental section and selected
bond lengths and angles for 6–8 are summarised in Table 2, which
can be compared to the data relating to the crystallographically
determined structures (Table 1). While quantitative agreement
between the observed and calculated data is not expected due the
nature of the calculations and structural approximations involved,
the optimised geometry of 6–8 is in good general agreement with
the experimentally observed structural trends which allows for a
high degree of confidence in the accuracy of the computations,
and the conclusions drawn from them.
Fig. 7 (a) HOMO and (b) LUMO orbitals of 6.
Electronic and emission spectroscopy of dinuclear gold(I)
r-acetylides
The absorption and emission spectra of the dinuclear gold(I) r-
acetylides 1–5 were measured at room temperature, from 10−5
M
samples in CH2Cl2, and the results are summarised in Table 3
together with equivalent data for the desilylated terminal di-ynes.
In general, the profiles of the absorption spectra of the dinuclear
gold(I) r-acetylides are similar to that of the equivalent acetylide
ligands with the kmax position shifting to longer wavelengths. The
strong dependence of the absorption spectra profile of the gold
1640 | Dalton Trans., 2008, 1635–1646
This journal is
The Royal Society of Chemistry 2008
©

View Article Online
Table 3 Absorption and emission spectra of dinuclear gold(I) r-acetylides 1–5
Absorption
Emissiona
k/nm (e/104 dm3 mol−1 cm−1
)
k/nm (relative intensityb)
2,5-Diethynyl pyridine
261(∼2.4), 281(∼1.1), 289(∼1.2), 298(∼1.0)
268(1.6), 276(1.9), 299(3.2), 313(4.5), 332(8.2)
236(2.4), 299(3.0), 313(3.6), 331(6.4)
—
1
2
344(1), 382(sh, 0.35), 493(0.09), 528(0.06)
349(1), 383(sh, 0.38), 494(0.17), 528(0.11)
—
339(1), 355(sh, 0.82), 436(0.07), 464(0.05)
—
2,6-Diethynyl pyridine
283(sh, ∼1.4), 291(∼1.6), 300(∼1.5)
3
261(4.8), 285(sh, 2.1), 307(sh, 2.1), 317(2.6), 324(2.5)
268(∼2.3), 301(sh, ∼3.2), 313(∼4.2), 327(∼3.3)
2,5ꢀ-Diethynyl
bipyridine
4
341(7.9), 359(7.4)
247(∼2.2), 297(∼1.8), 309(∼1.6)
368(0.75), 388(1)
—
2,6ꢀ-Diethynyl
bipyridine
5
280(4.9), 312(3.0), 324(sh, 2.5)
342(1), 448(0.05)
a Excited at kmax b Intensity of the strongest peak is assigned as 1.
.
Table 4 Absorption and emission data of 2
k/nm (CH2Cl2)
acetylenic unit, which emphasises the importance of the linear
geometry of a spacer for effective conjugation. This is supported
by the electronic structure calculation for the HOMO of 8 as
depicted in Fig. 8.
k/nm (toluene)
Abs.
Em.a
299, 312, 331
349, 383(sh), 494(w), 528(w)
300, 313, 333
348, 385(sh), 494(vw)
a Excited at kmax
.
compounds on their respective ligands hints at the ligand-centred
(LC) nature of these transitions. Although the insensitivity of low
energy absorption bands towards the auxiliary ligand of Au(I) (1
vs. 2) precludes the Au(I)-centred origin of the transitions, the red-
shift on binding to an Au centre is consistent with the extension
of p-conjugation onto the Au(I) centres through the acetylenic
bridges. Therefore, transitions in these absorption spectra are
ligand-dominated p–p*, but may mix with a little r(Au–C) in
the HOMO and possibly some Au 6pp character in the LUMO.23
Although the possibility of a MLCT origin for these absorption
bands cannot be totally ruled out, it is probably of minor
importance, since the representative examples show no significant
change in their absorption and emission behaviour in the less polar
toluene with respect to the more polar dichloromethane (Table 4).
This is confirmed by the electronic structure of 6, which gives rise to
a HOMO that originates solely from ligand orbital contributions
(Fig. 7).
There is little electronic interaction between the two Au moieties
in dinuclear gold(I) compounds through a two-ring bridge (4 and
5). However, such electronic interaction is detectable between the
two platinum centres in the related two-ring di-yne complexes,
[(tBu3P)2Pt(C≡C)(bipyridine)(C≡C)Pt(PtBu3)2], because of the
better orbital matching between the platinum centres and the
acetylide ligand than in gold(I) r-acetylides.23 It is likely that
the electronic communication between the two gold centres in
three-ring di-yne complexes is even more remote, since this kind
of electronic communication decreases drastically as the distance
between two metal centres increases.64
Fig. 8 (a) HOMO and (b) LUMO orbitals of 8.
The emission behaviour of the dinuclear gold(I) complexes are
similar to their absorptions in terms of their emission maxima
as a function of the bridging heterocyclic rings. Each individual
excitation spectrum has a similar profile to its absorption,
suggesting the emission arises from the lowest-energy absorption
band. The variation in the excitation wavelength has little influence
on the emission spectrum, indicating a single emissive state or
multiple states that are in equilibrium. There is always some
overlap between the low-energy onset of an absorption spectrum
and the high-energy end of the corresponding emission spectrum.
The Stokes shifts of these dinuclear complexes are small to modest.
Such a closeness of the emission spectrum to the absorption spec-
trum suggests the origin of the lowest emission state is a singlet.
Several dinuclear gold(I) complexes are found to have emissive
states with a lifetime of the order of nanoseconds,12,14 which
somewhat strengthens the singlet origin argument. The emission
of gold(I) acetylides is strongly dependent on the acetylide ligands,
yet nearly independent of the ancillary ligands around Au(I) (1 vs.
2). Based on these observations, the lowest emission state in these
gold complexes can be tentatively assigned as ligand-dominated
1(p–p*).
There is a sequential increase in the absorption maxima as the
number of bridging aromatic rings increases (1, 2 and 4). However,
for cases where the spacer unit is a 2,6ꢀ-pryridine group (3 and 5)
there was no obvious red shift observed on proceeding from 2,6-
pyridine to 6,6ꢀ-disubstituted 2,2ꢀ-bipyridine (Table 3). Here, the
6,6ꢀ-linkage obviously disrupts the direct p-delocalisation to the
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 1635–1646 | 1641
©

View Article Online
Table 5 Absorption and emission data of 4 and 5 in CH3OH–CH2Cl2 (1 : 1) and in the presence of Zn(BF4)2 and CF3COOH at room temperature
4 k/nm
5 k/nm
ccomplex (∼10−5 M) in CH3OH–CH2Cl2 (1 : 1)a
Zn(BF4)2 (∼10−3 M)
CF3COOH (∼10−3 M)
Abs.
Em.
Abs.
Em.a
Abs.
Em.a
341(7.4), 357(6.7)
370(0.69), 390(1)
303(3.9), 311(4.0), 361(8.3), 378(8.7)
398(1), 413(0.96)
317(2.9), 362(4.2), 378(4.4)
439(br)
276(5.2), 313(br, 3.2)
350(1)
269(5.6), 358(2.4), 373(2.7)
387(1), 403(sh, 0.88)
268(4.3), 360(2.1), 375(sh, 1.9)
422(br)
a Excited at kmax
.
Reactivity studies on [(R3P)Au(C≡C)X(C≡C)Au(PR3)] (R = Ph,
X = 2,5ꢀ-bipyridine (4); R = Ph, X = 2,6ꢀ-bipyridine (5))
the analogous species of 4, despite the shorter kmax of 5 in its
Zn2+/H+ unbound form. In the studies reported here there was
no discernable decomposition of the starting gold complexes as
has been observed in protonation studies on other alkynylgold
complexes that contain pyridine units.65 The 31P NMR spectra do
not indicate the presence of additional phosphorus environments
upon reaction with Zn2+ or H+.
Complexes 4 and 5 each have a bipyridine spacer group that is
not coordinated to a metal and is thus available for binding to
metal ions or alternatively protons through the nitrogen donor
atoms. Upon exposure of 4 and 5 to Zn(BF4)2 the maxima of the
absorption spectra red-shifts towards longer wavelengths (Table 5)
and exposure to CF3COOH induces very similar changes (Fig. 9).
Given that excess CF3COOH is used, it is likely that both nitrogen
atoms of the bipyridine group are protonated. The bipyridine can
adopt a cisoid conformation when it chelates to Zn2+ via the two
imine nitrogen atoms. However, this is unlikely to be the adopted
conformation for a doubly protonated bipyridine because of steric
factors. The doubly protonated bipyridine is more likely to adopt a
transoid conformation. The apparent resemblance in the absorp-
tion profiles in the presence of Zn(BF4)2 and CF3COOH strongly
suggests the predominant role of electrostatic perturbation, rather
than the forced coplanarity by zinc(II) chelation, since protonated
bipyridine does not necessarily enforce coplanarity between the
two pyridine rings. Even though there is overall similarity between
the Zn2+-coordinated species and the protonated one, the spectrum
associated with the protonated species is broader and the vibronic
structure in the bands is less distinct, indicating the presence of a
small amount of charge transfer.
The interaction of bipyridine with metal ions or protons will
modify the electronic and optical properties of a conjugated system
with built-in bipyridine units in its backbone. This has been
exploited to tune the performances of a number of bipyridine-
containing conjugated polymers.66–69 The ions Zn2+ and H+ both
exert a similar influence on the absorption of 4 and 5, yet each
has a very different effect on the emission in a CH2Cl2–MeOH
mixed solvent (Fig. 10). The causes may be traced to the higher
polarisability of H+ and possible hydrogen bonding between
protonated 4 or 5 and methanol. It is clear that much more
significant geometric relaxations from the H+ polarisation and
hydrogen bonding occur in the excited state before it deactivates
to the lowest emission state, as manifested by the longer kem of 4
and 5 on binding to H+ than on binding to Zn2+. The broadness
and lack of structure in the emission profile for both protonated
species also indicates increased charge transfer character of its
excited state, when compared to the comparatively sharper and
vibronically structured emission of the Zn2+-coordinated species.
Although the coordination of Zn2+ or protonation only results in
differences in lower energy absorption bands between 4 and 5, the
differences in their emission are evident. The Zn2+/H+-bound 4
emits at lower energies than the analogous species of 5, suggesting
that the expanded p-electron cloud of 4 in its excited state is
more susceptible to the polarised Zn2+/H+ than more confined
p-electron cloud of 5 in its excited state. The emission of Zn2+/H+-
bound 4 is also significantly enhanced, whereas no appreciable
Fig. 9 Absorption spectrum of complex 4 in CH2Cl2–CH3OH (I) and in
the presence of CF3COOH (II).
The ortho-linkage of gold(I) ethynyl groups with respect to the
nitrogen atoms in 5, where a larger induction effect on binding
to Zn2+/H+ is expected, gives rise to a larger bathochromic shift
than its 5,5ꢀ-analogue 4. The presence of gold(I) ethynyl groups
attached in a meta position experience less of an induction
effect on binding to Zn2+/H+, such that the Zn2+-coordinated
or protonated complex 5 exhibits similar absorption energies to
Fig. 10 Emission spectra of complex 4 in CH2Cl2–CH3OH (I) and in the
presence of CF3COOH (II).
1642 | Dalton Trans., 2008, 1635–1646
This journal is
The Royal Society of Chemistry 2008
©

View Article Online
change in emission intensity is observed for 5 on binding to
16.7 mmol) was added. The reaction mixture was left with stirring
for 20 h at 75 ◦C. The completion of the reaction was determined
by silica TLC and IR spectroscopy. The solution was allowed to
cool down to room temperature, filtered and the solvent mixture
removed under reduced pressure. The residue was subjected to
silica column chromatography using dichloromethane–hexane (1 :
1) to afford the product as a white solid in 68% yield (0.9 g). IR
(CH2Cl2): m(C≡C) 2159 cm−1. 1H NMR (d, 400 MHz, CDCl3): 0.27
Zn2+/H+.
Conclusion
A study of a series of digold ethynyl complexes with pyridine
or bipyridine spacer groups that have the general formula
[(R3P)Au(C≡C)X(C≡C)Au(PR3)] (R = Ph, X = 2,5-pyridine (1);
R = Cy (cyclohexane), X = 2,5-pyridine (2); R = Ph, X = 2,6-
pyridine (3); R = Ph, X = 2,5ꢀ-bipyridine (4); R = Ph, X =
2,6ꢀ-bipyridine (5)), shows that the formation of an aurophilic
Au · · · Au interaction only occurs in complex 1, in the solid
state, when the spacer group, X, is relatively short and when the
auxiliary phosphine ligand is not excessively bulky. This obser-
vation supports conclusions drawn previously from the analysis
of the structures of a series of digold ethynyl complexes with
various length spacer groups.21 However, the length and geometric
configuration of the spacer group and the bulk of the phosphine
ligand represent only the steric factors that contribute to the solid
state packing of these complexes and electronic factors have not
been taken into consideration. Solution absorption and emission
spectroscopy, supported by DFT calculations, show that there
is little contribution from the gold centres to the delocalisation
within the complexes and the p-orbitals extend only over the
central spacer group and the two acetylene bonds. In solution,
the bipyridine complexes 4 and 5 are capable of coordinating Zn2+
ions or protons and this coordination is characterised from both
absorption and emission studies.
ꢀ
(s, 18H, H of TMS), 7.84 (dd, 3JHH = 8.2, 4JHH = 2.1, 2H, H4 and 4 ),
ꢀ
8.34 (dd, 3JHH = 8.2, 4JHH = 0.7, 2H, H3 and 3 ), 8.71 (dd, 4JHH = 2.1,
ꢀ
4JHH = 0.7, 2H, H6 and 6 ). 13C NMR (d, 400 MHz, CDCl3): −0.20
(C of TMS); 99.44, 101.74 (–C≡C–); 120.33 (ipso-C), 120.46,
139.75, 152.05, 154.19 (ipso-C) (aromatic C of pyridines). ESI
(m/z): 349.12 (Calc. Mr = 348.598). Anal. Calc. for C20H24N2Si2:
C, 68.91; H, 6.94; N, 8.04. Found: C, 68.83; H, 6.94; N, 7.98%.
6,6ꢀ-Bis(trimethylsilylethynyl)-2,2ꢀ-bipyridine. This compound
was synthesised by the same method as for 5,5ꢀ-bis(trimethyl-
silylethynyl)-2,2ꢀ-bipyridine but using 0.7 g (2.2 mmol) of 6,6ꢀ-
dibromo-2,2ꢀ-bipyridine. The product was purified by silica col-
umn chromatography with dichloromethane–hexane (2 : 3) as
eluent. The product was obtained as a white solid in a 74% yield
(0.57 g). IR (CH2Cl2): m(C≡C) 2160 cm−1. 1H NMR (d, 400 MHz,
CDCl3): 0.28 (s, 18H, H of TMS), 7.47 (dd, 3JHH = 7.8 Hz, 4JHH
=
ꢀ
ꢀ
3
1.0 Hz, 2H, H5 and 5 ), 7.75 (t, JHH = 7.8 Hz, 2H, H4 and 4 ), 8.41
ꢀ
3
4
(dd, JHH = 7.8 Hz, JHH = 1.0 Hz, 2H, H3 and 3 ). 13C NMR (d,
400 MHz, CDCl3): −0.25 (C of TMS); 94.52, 103.94 (–C≡C–);
121.10, 127.77, 136.94, 142.35 (ipso-C), 155.71 (ipso-C) (aromatic
C of pyridines). ESI (m/z): 349.12 (Calc. Mr = 348.598). Anal.
Calc. for C20H24N2Si2: C, 68.91; H, 6.94; N, 8.04. Found: C, 67.78;
H, 6.98; N, 7.90%.
Experimental
General
Complex synthesis
All reactions were carried out under an atmosphere of dry
nitrogen using standard Schlenk techniques. Solvents were freshly
distilled, dried and degassed by standard procedures before use.70
Infrared spectra were recorded using a NaCl cell on a PERKIN
ELMER PARAGON 1000 FT-IR spectrometer. UV/vis spectra
were recorded on Perkin-Elmer Lamda-12 spectrometer and
Cary 100 Bio UV-visible spectrometer. 1H, 13C and 31P NMR
spectra were recorded on Bruker28 DRX-400/500 spectrome-
ters. Chemical shifts in ppm are relative to the residue solvent
resonance (1H and 13C) and external 85% H3PO4 (31P). Mass
spectra were recorded on KRATOS CONCEPT/MSI CONCEPT
IH/MICROMASS PLATFORM-LC mass spectrometers. Ele-
mentary analyses were performed at Department of Chemistry,
University of Cambridge. Solution emission spectra were recorded
at 293 K on AMINCO Bowman Series 2 Luminescence Spec-
trometer as 10−5 mol dm−3 solutions in CH2Cl2. [AuPPh3Cl],71
[Au(PCy3)Cl],72 2,5-bis(trimethylsilylethynyl)pyridine73 and 2,6-
bis(trimethylsilylethynyl)pyridine73 were prepared by literature
methods.
General synthetic procedure for preparing the Au(I) complexes.
To a freshly prepared terminal alkyne (ca. 0.2 mmol, from the
reaction of trimethylsilyl-protected alkyne with KOH–MeOH) in
CH2Cl2 (30 mL) was added gold(I) phosphine chloride (stoichio-
metric amount), followed by MeOH–NaOMe (20 mL, containing
ca. 2–30 mg Na). The mixture was stirred under N2 at room
temperature overnight and then filtered through cellulose. The
filtrate was evaporated to dryness under reduced pressure. CH2Cl2
was added to the residue and the resulting suspension was stirred
for 15 min and filtered. The filtrate was reduced in volume, loaded
on to a short alumina column, and then eluted with mixed solvents
of THF (or ethyl acetate)–hexane. The solvents were removed
in vacuo to yield pale yellow powders. Pure products were obtained
either by layering concentrated CH2Cl2 solution with hexane, or by
diethyl ether vapour diffusion into concentrated CH2Cl2 solutions.
[(Ph3PAu)(C≡C)(2-(C5H3N)-5)(C≡C)(AuPPh3)] (1). Synthe-
sis was by the general procedure using a freshly prepared alkyne
from 35 mg (0.13 mmol) 2,5-bis(trimethylsilylethynyl)pyridine and
130 mg (0.26 mmol) [Au(PPh3)Cl]. Yield: 92 mg (67%) yellow
Ligand syntheses
1
crystalline solid. IR (CH2Cl2): m(C≡C) 2121 cm−1. H NMR (d,
5,5ꢀ-Bis(trimethylsilylethynyl)-2,2ꢀ-bipyridine. To a solution of
500 MHz, CDCl3): 7.29 (dd, 3JHH = 8.1 Hz, 4JHH = 0.8 Hz, 1H, H3),
i
3
4
5,5ꢀ-dibromo-2,2ꢀ-bipyridine (1.2 g, 3.8 mmol) in Pr2NH–THF
7.30–7.56 (m, 30H, H of PPh3), 7.61 (dd, JHH = 8.1 Hz, JHH =
(70 cm3, 1 : 1 v/v) under nitrogen was added a catalytic mixture of
CuI (20 mg), Pd(OAc)2 (20 mg) and PPh3 (60 mg). The solution was
stirred for 20 min at 50 ◦C and then trimethylsilylethyne (1.64 g,
2.1 Hz, 1H, H4), 8.64 (dd, 4JHH = 2.1 Hz, 4JHH = 0.8 Hz, 1H, H6).
13C NMR (d, 500 MHz, CDCl3): 100.96, 101.17 (–C≡C–); 119.42
(ipso-C), 125.94, 138.48, 141.57 (ipso-C), 153.09 (aromatic C of
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 1635–1646 | 1643
©

View Article Online
pyridine); 129.07, 129.16, 129.40 (d, ipso-C), 129.84 (d, ipso-C),
NMR (d, 500 MHz, CDCl3): 7.43–7.75 (m, 30H, H of PPh3), 7.85
ꢀ
1
131.52, 134.22, 134.33 (C of PPh3). 31P{ H} NMR (d, 400 MHz,
(dd, 3JHH = 8.3 Hz, 4JHH = 2.1 Hz, 2H, H4 and 4 ), 8.26 (dd, 3JHH
=
ꢀ
CDCl3): 42.69, 42.80. LSIMS (m/z): 1044.2 (Calc. Mr = 1043.648).
Anal. Calc. for Au2C44H32NP2: C, 51.78; H, 3.19; N, 1.34. Found:
C, 51.69; H, 3.19; N. 1.37%.
8.3 Hz, 4JHH = 0.8 Hz, 2H, H3 and 3 ), 8.76 (dd, 4JHH = 2.1 Hz, 4JHH
=
ꢀ
0.8 Hz, 2H, H6 and 6 ). 13C NMR (d, 500 MHz, CDCl3): 100.89,
101.10 (–C≡C–); 120.19, 121.71 (ipso-C), 139.86, 152.50, 153.08
(ipso-C) (aromatic C of pyridines); 129.11, 129.20, 129.34 (ipso-
[(Cy3PAu)(C≡C)(2-(C5H3N)-5)(C≡C)(AuPCy3)] (2). Synthe-
sised by the general procedure using a freshly prepared alkyne
from 40 mg (0.15 mmol) 2,5-bis(trimethylsilylethynyl)pyridine and
150 mg (0.30 mmol) [Au(PCy3)Cl]. Yield: 92 mg (58%) yellow
C), 129.79 (ipso-C), 131.58, 134.21, 134.32 (C of PPh3). 31P{ H}
1
NMR (d, 400 MHz, CDCl3): 42.78. LSIMS (m/z): 1121 (Calc.
Mr = 1120.734). Anal. Calc. for Au2C50H36N2P2: C, 53.59; H,
3.24; N, 2.50. Found: C, 53.34; H, 3.37; N. 2.31%.
1
crystalline solid. IR (CH2Cl2): m(C≡C) 2117cm−1. 31P{ H} NMR
[(PPh3Au)(C≡C)(6-(C5H3N)(C5H3N)-6ꢀ)(C≡C)(AuPPh3)] (5).
Synthesised by the general procedure using a freshly prepared
alkyne from 40 mg (0.115 mmol) 6,6ꢀ-bis(trimethylsilylethynyl)-
2,2ꢀ-bipyridine and 115 mg (0.23 mmol) [Au(PPh3)Cl]. Yield: 47mg
(37%) light yellow solid. IR (CH2Cl2): m(C≡C) 2116cm−1. 1H NMR
(d, 400 MHz, CDCl3): 57.22. LSIMS (m/z): 1080 (Calc. Mr =
1079.688). Anal. Calc. for Au2C45H69NP2·1.25CH2Cl2: C, 46.83;
H, 6.08; N, 1.18. Found: C, 46.80; H, 6.04; N. 1.10%.
[(PPh3Au)(C≡C)(2-(C5H3N)-6)(C≡C)AuPPh3)] (3). Synthe-
sised by the general procedure using a freshly prepared alkyne
from 35 mg (0.13 mmol) 2,6-bis(trimethylsilylethynyl)pyridine and
130 mg (0.26 mmol) [Au(PPh3)Cl]. Yield: 100 mg (75%) yellow
ꢀ
(d, 500 MHz, CDCl3): 7.41–7.57ꢀ(m, 32H, H5 and 5 and H of PPh3),
7.63 (t, 3JHH = 7.8 Hz, 2H, H4 and 4 ), 8.42 (dd, 3JHH = 7.8 Hz, 4JHH
=
ꢀ
1.1 Hz, 2H, H3 and 3 ). 13C NMR (d, 500 MHz, CDCl3): 103.42,
103.63 (–C≡C–); 119.61, 127.16, 136.22, 143.40 (ipso-C), 155.75
(ipso-C) (aromatic C of pyridines); 129.06, 129.15, 129.47 (ipso-
1
crystalline solid. IR (CH2Cl2): m(C≡C) 2115 cm−1. H NMR (d,
500 MHz, CDCl3): 7.24 (s, 1H, H4), 7.39–7.56 (m, 32H, H3 and 5
and H of PPh3). 13C NMR (d, 500 MHz, CDCl3): 103.02 (br, –
C≡C–); 125.08, 135.26, 144.24 (ipso-C) (aromatic C of pyridine);
129.02, 129.11, 129.66 (d, ipso-C), 130.10 (ipso-C), 131.41, 134.24,
1
C), 129.91 (ipso-C), 131.53, 134.24, 134.35 (C of PPh3). 31P{ H}
NMR (d, 400 MHz, CDCl3): 42.73. LSIMS (m/z): 1121 (Calc.
Mr = 1120.734). Anal. Calc. for Au2C50H36N2P2: C, 53.59; H,
3.24; N, 2.50. Found: C, 53.14; H, 3.45; N. 2.46%.
1
134.35 (C of PPh3). 31P{ H} NMR (d, 400 MHz, CDCl3): 42.72.
LSIMS (m/z): 1044.2 (Calc. Mr = 1043.648). Anal. Calc. for
Au2C45H33NP2: C, 51.78; H, 3.19; N, 1.34. Found: C, 51.66; H,
3.28; N. 1.24%.
X-Ray crystallography
For crystal data, see Table 6.
[(PPh3Au)(C≡C)(5-(C5H3N)(C5H3N)-5ꢀ)(C≡C)(AuPPh3)] (4).
Synthesised by the general procedure using a freshly prepared
alkyne from 40 mg (0.115 mmol) 5,5ꢀ-bis(trimethylsilylethynyl)-
2,2ꢀ-bipyridine and 115 mg (0.23 mmol) [Au(PPh3)Cl]. Yield:52mg
Data collection and reduction. The crystals of 1–5 were
mounted in inert oil on glass fibres. Data were measured using
˚
Mo-Ka radiation (k = 0.71069 A) with a Bruker Kappa CCD
1
(40%) pale yellow powder. IR (CH2Cl2): m(C≡C) 2117 cm−1. H
diffractometer (2–5) and on a Bruker AXS SMART CCD
Table 6 Details of the crystal data, data collection parameters and structure refinement for complexes 1–5
1
2
3
4
5
Empirical formula
Formula weight
Temperature/K
Wavelength (k)/A
Crystal system
C44H32Au2N2P2
1044.59
180(2)
C46H71Au2Cl2NP2
1164.81
180(2)
C45H33Au2NP2
1043.60
180(2)
0.71069
Monoclinic
C2/c (No. 15)
26.524(4)
8.705(2)
18.646(3)
90
120.30(3)
90
3717.1(16)
4
1.865
8.004
C50H36Au2N2P2
1120.68
180(2)
0.71069
Monoclinic
P21/c (No. 14)
7.0693(1)
13.7695(4)
21.3934(6)
90
96.947(2)
90
2067.16(9)
2
1.800
7.204
C52H40Au2Cl4N2P2
1290.53
180(2)
˚
0.6887
0.71073
0.71069
Triclinic
Triclinic
Triclinic
¯
¯
¯
Space group
P1 (No. 2)
P1 (No. 2)
P1 (No. 2)
˚
a/A
8.881(2)
13.638(3)
16.551(3)
74.65(3)
83.64(3)
71.06(3)
1827.8(6)
2
9.1956(3)
10.3609(3)
12.8658(4)
103.998(2)
100.256(2)
96.941(2)
1153.00(6)
1
9.4980(12)
10.9270(8)
12.4680(16)
72.057(6)
81.173(5)
79.945(6)
1205.3(2)
1
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
Volume/A
Z
Dc/Mg m−3
1.898
8.139
1.678
6.571
1.778
6.405
l/mm−1
Crystal size/mm
0.12 × 0.08 × 0.08
1.75–20.00
9084
3749
0.0949
2053
12/195
1.045
0.0817
0.2231
0.30 × 0.18 × 0.05 0.03 × 0.03 × 0.01
0.30 × 0.07 × 0.05
3.53–27.49
18945
4705
0.0699
3943
0/253
1.040
0.0309
0.12 × 0.08 × 0.05
2.93–25.02
10292
4218
0.0348
3668
419/363
1.041
0.0314
0.0655
h range/◦
3.62–27.48
12208
5234
1.78–25.08
5889
Reflections collected
Independent reflections
Rint
3264
0.0904
1856
0.1206
4596
Observed reflections [I>2r(I)]
Restraints/parameters
Goodness of fit
R1 [I>2r(I)]
38/246
1.048
0.0579
0.1603
0/227
1.032
0.0529
0.2116
wR2 (all data)
0.0764
1644 | Dalton Trans., 2008, 1635–1646
This journal is
The Royal Society of Chemistry 2008
©

View Article Online
diffractometer on Station 9.8 of the STFC Daresbury Laboratory
References
(1) using silicon monochromated radiation of wavelength k =
1 P. Nguyen, P. Go´mez-Elipe and I. Manners, Chem. Rev., 1999, 99,
1515; N. J. Long and C. K. Williams, Angew. Chem., Int. Ed., 2003, 42,
2586.
˚
0.6887 A; both instruments were fitted with an Oxford Cryostream
low-temperature attachment.
2 D. Beljonne, H. F. Wittmann, A. Ko¨hler, S. Graham, M. Younus, J.
Lewis, P. R. Raithby, M. S. Khan, R. H. Friend and J. L. Bredas,
J. Chem. Phys., 1996, 105, 3868.
3 J. H. Burroughs, D. D. C. Bradley, A. R. Brown, R. N. Marks, K.
Mackay, R. H. Friend, P. L. Burn and A. B. Holmes, Nature, 1990,
347, 539.
4 N. Tissler, G. J. Denton and R. H. Friend, Nature, 1996, 82, 695.
5 J. M. Halls, C. A. Walsh, N. C. Greenham, E. A. Marseglia, R. H.
Friend, S. C. Moratti and A. B. Holmes, Nature, 1995, 376, 498.
6 G. Yu, J. Gao, J. C. Hummelen, F. Wudl and A. J. Heeger, Science,
1995, 270, 1789.
Structure solution and refinement. Structures were solved by
direct methods (SHELXS-8674) and subjected to full-matrix least-
squares refinement on F2 (program SHELXL-9775 for 1, 2, 4 and 5
and SHELXL-93 for 376). Despite the use of synchrotron radiation
crystals of 1 gave very weak diffraction patterns and in the
refinement to compensate for this only the gold and phosphorus
atoms were assigned anisotropic displacement parameters and
hydrogen atoms were not included in the model. One of the phenyl
rings was clearly disordered over two sites and the two rings were
refined as rigid groups with partial occupancies that summed to
unity. The pyridine nitrogen atom was treated in the refinement
as being disordered over two symmetry related positions. In the
crystal structure of 2, in the central arene ring the nitrogen atom
was treated as being disordered over four positions in the ring and
was refined with 25% occupancy on each site. The four C–H groups
in the ring were then refined with 75% occupancy. The crystal
structure also included a molecule of dichloromethane solvent that
was disordered over two sites and the two orientations were refined
so that the occupancy summed to unity. In the crystal structure of
5 one of the phenyl rings was disordered over two positions and
the two orientations were refined with partial occupancies that
summed to unity. There was also a disordered dichloromethane
molecule in the lattice, disordered over two orientations. This
was again modelled and refined in two orientations with the
atomic occupancies summed to unity. Excluding the exceptions
mentioned above non-hydrogen atoms were generally refined with
anisotropic displacement parameters and hydrogen atoms were
included using a riding model.
7 F. Garnier, R. Hajlaoui, A. Yasser and P. Svwastra, Science, 1994, 265,
1684.
8 H. Sirringhaus, N. Tissler and R. H. Friend, Science, 1998, 280, 1741.
9 J. B. Torrance, Low Dimensional Conductors and Superconductors,
NATO ASI Ser., Ser. B, 1987, 155, 113.
10 T. B. Marder, G. Lesley, Z. Yuan, H. B. Fyfe, P. Chow, G. Stringer,
I. R. Jobe, N. J. Taylor, I. D. Williams and S. K. Kurtz, Materials for
Nonnlinear Optics: Chemical Perspectives, ACS Symp. Ser., 1991, 455,
605.
11 H. B. Fyfe, M. Mlekuz, G. Stringer, N. J. Taylor and T. B. Marder,
Inorganic and Organometallic Polymers with Special Properties, NATO
ASI Ser., Ser. E, 1992, 206, 331.
12 V. W.-W. Yam and K. M.-C. Wong, Top. Curr. Chem., 2005, 257, 1.
13 R. J. Puddephatt, Chem. Commun., 1998, 1055.
14 V. W. W. Yam and K. K.-W. Lie, Chem. Soc. Rev., 1999, 28.
15 V. W. W. Yam, K. K.-W. Lie and K. M.-C. Wang, J. Organomet. Chem.,
1999, 578, 3.
16 A. S. Batsanov, M. A. Fox, J. A. K. Howard, J. A. H. MacBridge and
K. Wade, J. Organomet. Chem., 2000, 610, 20.
17 A. S. Batsanov, M. A. Fox, T. G. Hibbert, J. A. K. Howard, R. Kivekas,
A. Laromaine, R. Sillanpaa, C. Vinas and K. Wade, Dalton Trans.,
2004, 3822.
18 I. R. Whittall, A. M. McDonagh, M. G. Humphrey and M. Samoc,
Adv. Organomet. Chem., 1999, 43, 349.
19 M.-C. Brandys, M. C. Jennings and R. J. Puddephatt, J. Chem. Soc.,
Dalton Trans., 2000, 4601.
20 P. Li, B. Ahrens, K.-H. Choi, M. S. Khan, P. R. Raithby, P. J. Wilson
and W.-Y. Wong, CrystEngComm, 2002, 4, 405.
21 P. Li, B. Ahrens, N. Feeder, P. R. Raithby, S. J. Teat and M. S. Khan,
Dalton Trans., 2005, 874.
DFT calculations
22 J. Vicente, M. T. Chicote, M. M. Alvarez-Falco´n, M.-D. Abrisqueta,
F. J. Herna´ndez and P. G. Jones, Inorg. Chim. Acta, 2003, 347, 67.
23 M. J. Irwin, J. J. Vittal and R. J. Puddephatt, Organometallics, 1997, 16,
3541.
The crystal structures of 1, 4, and 5 were used as starting
geometries for the geometry optimisations of [H3P–Au–C≡C–
X–C≡C–Au–PH3] (X = 2,5-pyridine (6); X = 2,5ꢀ-bipyridine
(7); X = 2,6ꢀ-bipyridine (8)) using Gaussian03.77 The geometry
optimisation was performed at a B3LYP level78 using as a basis set
3-21G** for Au and 6-31G** for all other atoms.
24 V. W. W. Yam and S. W. K. Choi, J. Chem. Soc., Dalton Trans., 1996,
4227.
25 V. W. W. Yam, S. W. K. Choi and K. K. Cheung, Organometallics, 1996,
15, 1734.
26 J. Vicente, M.-T. Chicote, M. M. Alvarez-Falco´n and D. Bautista,
Organometallics, 2004, 23, 5707.
27 J. Vicente, M. T. Chicote, M. M. Alvarez-Falco´n and P. G. Jones,
Organometallics, 2005, 24, 2764.
28 T. Yamamoto, K. Sugiyama, T. Kushida, T. Inoue and T. Kanbara,
J. Am. Chem. Soc., 1996, 118, 3930.
Acknowledgements
We are grateful to the EPSRC for funding for a post doctoral
fellowship (to O. F. K.), an EPSRC Senior Fellowship (to
P. R. R.) and for a grant to purchase the Bruker Nonius Kappa
CCD diffractometer. We acknowledge a grant from the EPSRC
National Service for Computational Software to undertake DFT
calculations and the STFC for a beamtime allocation. We are
also grateful for financial support from the European Commis-
sion project SANEME (under the framework of the 5th IST
programme, contract number IST-1999-10323). P. L. thanks the
Cambridge Overseas Trust and the Overseas Research Scheme
for financial support. The award of a DAAD grant (Gemeinsames
Hochschulsonderprogramm III von Bund und La¨ndern) (to B. A.)
is gratefully acknowledged.
29 M. S. Khan, M. K. Al-Suti, M. R. A. Al-Mandhary, B. Ahrens, J. K.
Bjernemose, M. F. Mahon, L. Male, P. R. Raithby, R. H. Friend, A.
Ko¨hler and J. S. Wilson, Dalton Trans., 2003, 65; M. S. Khan, M. R. A.
Al-Mandhary, M. K. Al-Suti, B. Ahrens, M. F. Mahon, L. Male, P. R.
Raithby, C. E. Boothby and A. Ko¨hler, Dalton Trans., 2003, 74; M. S.
Khan, M. R. A. Al-Mandhary, M. K. Al-Suti, F. R. Al-Battashi, S.
Al-Saadi, B. Ahrens, J. K. Bjernemose, M. F. Mahon, P. R. Raithby,
M. Younus, N. Chawdhury, A. Ko¨hler, E. A. Marseglia, E. Tedesco, N.
Feeder and S. J. Teat, Dalton Trans., 2004, 2377.
30 M. S. Khan, M. R. A. Al-Mandhary, M. K. Al-Suti, A. K. Hisham,
P. R. Raithby, B. Ahrens, M. F. Mahon, L. Male, E. A. Marseglia, E.
Tedesco, R. H. Friend, A. Ko¨hler, N. Feeder and S. J. Teat, J. Chem.
Soc., Dalton Trans., 2002, 1358.
31 I. R. Whittall, M. G. Humphrey and D. C. R. Hockless, Aust. J. Chem.,
1997, 50, 991.
This journal is
The Royal Society of Chemistry 2008
Dalton Trans., 2008, 1635–1646 | 1645
©

View Article Online
32 G. Jia, R. J. Puddephatt, J. D. Scott and J. J. Vittal, Organometallics,
1993, 12, 3565.
33 M. A. MacDonald, R. J. Puddephatt and G. P. A. Yap, Organometallics,
2000, 19, 2194.
34 W. J. Hunks, M. A. MacDonald, M. C. Jennings and R. J. Puddephatt,
Organometallics, 2000, 19, 5063.
35 N. C. Payne, R. Ramachandran and R. J. Puddephatt, Can. J. Chem.,
1995, 73, 6.
58 R. C. Bott, G. A. Bowmaker, R. W. Bucklery, P. C. Healy and M. C. S.
Perera, Aust. J. Chem., 1999, 52, 271.
59 P. Pyykko¨, J. Li and N. Runeberg, Chem. Phys. Lett., 1994, 218, 133.
60 H. Schmidbaur, Gold: Progress in Chemistry, Biochemistry and Tech-
nology, J. Wiley & Sons, Chichester, 1999.
61 H. Schmidbaur, W. Graf and G. Mu¨ller, Angew. Chem., Int. Ed. Engl.,
1988, 27, 417.
62 A. Bondi, J. Phys. Chem., 1964, 68, 441.
63 C. A. Tolman, Chem. Rev., 1977, 77, 313.
64 O. F. Koentjoro, R. Rousseau and P. J. Low, Organometallics, 2001, 20,
4502.
65 N. C. Habermehl, F. Mohr, D. J. Eisler and R. J. Puddephatt,
Can. J. Chem., 2006, 84, 111.
66 Y. Eichen, G. Nakhmanovich, V. Gorelik, O. Epshtein, J. M. Poplawski
and E. Ehrenfreund, J. Am. Chem. Soc., 1998, 120, 10463.
67 G. Zotti, S. Zecchin, G. Schiavon, A. Berlin and M. Penso, Chem.
Mater., 1999, 11, 3342.
68 L. Trouillet, A. De Nicola and S. Guillerez, Chem. Mater., 2000, 12,
1611.
36 D. Li, X. Hong, C. M. Che, W. C. Lo and S. M. Peng, J. Chem. Soc.,
Dalton Trans., 1993, 2929.
37 S. J. Shieh, X. Hong, S. M. Peng and C. M. Che, J. Chem. Soc., Dalton
Trans., 1994, 3067.
38 B. C. Tzeng, W. C. Lo, C. M. Che and S. M. Peng, Chem. Commun.,
1996, 181.
39 T. E. Mu¨ller, S. W. K. Choi, D. M. P. Mingos, D. Murphy, D. J. Williams
and V. W. W. Yam, J. Organomet. Chem., 1994, 484, 209.
40 C. M. Che, H. K. Yip, W. C. Lo and S. M. Peng, Polyhedron, 1994, 13,
887.
41 M. I. Bruce and D. N. Duffy, Aust. J. Chem., 1986, 39, 1697.
42 M. I. Bruce, K. R. Grundy, M. J. Liddell, M. R. Snow and E. R. T.
Tiekink, J. Organomet. Chem., 1988, 344, C49.
69 M. Bouachrine, J.-P. Le`re-Porte, J. J. E. Moreau, F. Serein-Spirau and
C. Torreilles, J. Mater. Chem., 2000, 10, 263.
43 G. A. Carriedo, V. Riera, X. Solans and J. Solans, Acta Crystallogr.,
Sect. C, 1988, 44, 978.
70 W. F. L. Armarengo and D. D. Perrin, Purification of Laboratory
Chemicals, 4th edn, Butterworth Heinemann, Bath, UK, 1996.
71 M. I. Bruce, B. K. Nicholson and O. Bin Shawkataly, Inorg. Synth.,
1989, 26, 325.
44 R. H. Naulty, M. P. Cifuentes, M. G. Humphrey, S. Houbrechts, C.
Boutton, A. Persoons, G. A. Heath, D. C. R. Hockless, B. Luther-
Davies and M. Samoc, J. Chem. Soc., Dalton Trans., 1997, 4167.
45 I. R. Whittall, M. G. Humphrey, M. Samoc, B. Luther-Davies and
D. C. R. Hockless, J. Organomet. Chem., 1997, 544, 189.
46 I. R. Whittall, M. G. Humphrey, S. Houbrechts, J. Maes, A. Persoons,
S. Schmid and D. C. R. Hockless, J. Organomet. Chem., 1997, 544, 277.
47 L. Lu, S.-Y. Poon and W.-Y. Wong, J. Organomet. Chem., 2005, 690,
5036.
72 R. Uson, A. Laguna and M. Laguna, Inorg. Synth., 1989, 26, 86.
73 S. Takahashi, Y. Kuroyama, K. Sonogashira and N. Hagihara, Synthe-
sis, 1980, 627.
74 G. M. Sheldrick, SHELXS-86, Program for Crystal Structure Solution,
University of Go¨ttingen, Germany, 1986.
75 G. M. Sheldrick, SHELXL-97, Program for refinement of crystal
structures, University of Go¨ttingen, Germany, 1997.
76 G. M. Sheldrick, SHELXL-93, Program for Crystal Structure Refine-
ment, University of Go¨ttingen, Germany, 1993.
48 O. Schuster, R.-Y. Liau, A. Schier and H. Schmidbaur, Inorg. Chim.
Acta, 2005, 358, 1429.
49 G. Hogarth and M. M. Alvarez-Falco´n, Inorg. Chim. Acta, 2005, 358,
1386.
50 W. M. Khairul, L. Porres, D. Albesa-Jove, M. S. Senn, M. Jones, D. P.
Lydon, J. A. K. Howard, A. Beeby, T. B. Marder and P. J. Low, J. Cluster
Sci., 2006, 17, 65.
51 G. Ferguson, J. F. Gallagher, J. D. Kennedy, A.-M. Kelleher and T. R.
Spalding, Dalton Trans., 2006, 2133.
52 J. Vicente, M.-T. Chicote, M. M. Alvarez-Falco´n and P. G. Jones,
Organometallics, 2005, 24, 5956.
53 M. I. Bruce, M. Jevric, B. W. Skelton, M. E. Smith, A. H. White and
N. N. Zaitseva, J. Organomet. Chem., 2006, 691, 361.
54 D. Millar, L. N. Zakharov, A. L. Rheingold and L. H. Doerrer, Acta.
Crystallogr., Sect. C, 2005, 61, m90.
55 O. Schuster, U. Monkowius, H. Schmidbaur, R. S. Ray, S. Kruger and
N. Rosch, Organometallics, 2006, 25, 1004.
56 H.-Y. Chao, W. Lu, Y. Li, M. C. W. Han, C.-M. Che, K.-K. Chung and
N. Zhu, J. Am. Chem. Soc., 2002, 124, 14696.
57 N. C. Baenziger, W. E. Bennett and D. M. Soboroff, Acta Crystallogr.,
Sect. B, 1976, 32, 962.
77 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven, K. N.
Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone,
B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,
M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X.
Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. Ochterski, P. Y. Ayala, K. Morokuma, G. A.
Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul,
S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P.
Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-
Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill,
B. G. Johnson, W. Chen, M. W. Wong, C. Gonzalez and J. A. Pople,
GAUSSIAN 03 (Revision C.01), Gaussian, Inc., Wallingford, CT,
2004.
78 A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
1646 | Dalton Trans., 2008, 1635–1646
This journal is
The Royal Society of Chemistry 2008
©