Isolation of 1,4-Li2-C6H4 and its reaction with [(Ph3P)AuCl]

Article abstract of DOI:10.1039/b925355f

The difficulty in generating 1,4-Li₂-C₆H₄ utilising the lithium halogen exchange reaction on 1,4-Br₂-C ₆H₄, 1,4-I₂-C₆H₄ and 1-Br-4-I-C₆H₄ is revisited and only on treatment of 1,4-I₂-C₆H₄ with 2 molar equivalents of n-BuLi can 1,4-Li₂-C₆H₄1 be isolated in excellent yield. Treatment of 1 with two equivalents of [ClAu(PPh₃)] gives [1,4-(Ph₃PAu)₂-C₆H₄] 2a in excellent yield. Subsequent treatment of 2a with 2.5 molar equivalents of PPh ₂Me, PPhMe₂ or PMe₃ affords the PPh₃ substituted compounds [1,4-(LAu)₂-C₆H₄] (L = PPh₂Me 2b, PPhMe₂2c, PMe₃2d) in essentially quantitative yields. On treatment of 1,4-Br₂-C₆H ₄ or 1-Br-4-I-C₆H₄ with 2 molar equivalents of n-BuLi only mono-lithiation takes place to give 1-Br-4-Li-C₆H ₄3 as shown through the isolation of essentially 1:1 molar equivalents of Ph₂PC₆H₄-4-Br and Ph ₂PBu on treatment with 2 molar equivalents of ClPPh₂. Treatment of 3, prepared by lithium/iodine exchange on 1-Br-4-I-C ₆H₄, with [ClAu(PPh₃)] affords [(Ph ₃P)Au(C₆H₄-4-Br)] 4 as expected and in addition [(Ph₃P)Au(n-Bu)(C₆H₄-4-Br)₂] 5, indicating the straightforward chloride/aryl exchange at gold may proceed in competition with oxidative addition of the n-BuI, generated in the initial lithium/iodine exchange reaction, to some 'aurate' complex Li[Au(C ₆H₄-4-Br)₂] 6 formed in situ followed by reductive elimination of Br-C₆H₄-4-n-Bu in a manner that mimics lithium diorganocuprate chemistry. All of the gold-containing compounds have been spectroscopically characterised by ¹H and ³¹P-{¹H} NMR and in addition compounds 2a-d and 5 by single crystal X-ray diffraction studies. The solid state structures observed for 2a-d are dictated by non-conventional hydrogen bonding and the packing requirements of the phosphine ligands. For 2a and 2b there is no close Au...Au approach, however for 2c and 2d the reduction in the number of phenyl rings allows the formation of Au...Au contacts. For 2c and 2d the extended structures appear to be helical chains with Au...Au contact parameters of 3.855(5) A and C-Au-Au-C 104.1(3)° for 2c and 3.139(4) A and C-Au-Au-C -92.0(2)° for 2d. The Au...Au approach in 2c is longer than is normally accepted for an Au...Au contact and is dictated by ligand directed non-conventional hydrogen bonding to the aurated benzene ring and the π-stacking requirements of the phosphine ligand. By comparison of the structures 2a-2d with other structures in the database it is evident that the aurophilic interaction is a poor supramolecular synthon in the presence of non-conventional hydrogen bond donors. Searches of the CCDC database suggest that the observed parameters for the Au...Au contact in 2c sit close to the cut-off point for observing this type of contact. In addition to aurophilic contacts and non-conventional hydrogen bonds there are a number of halogenated solvent C-Cl...Au contacts observed in the structures of 2a and 2d. The nature of these contacts have implications for the accepted van der Waals radius of gold which should be extended to 2 A.

Full text of DOI:10.1039/b925355f

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Isolation of 1,4-Li2-C6H4 and its reaction with [(Ph3P)AuCl]†
Kevin R. Flower,*a A. T. McGown,b Philip J. Miles,a Robin G. Pritcharda and John E. Warrena
Received 2nd December 2009, Accepted 23rd January 2010
First published as an Advance Article on the web 2nd March 2010
DOI: 10.1039/b925355f
The difficulty in generating 1,4-Li2-C6H4 utilising the lithium halogen exchange reaction on
1,4-Br2-C6H4, 1,4-I2-C6H4 and 1-Br-4-I-C6H4 is revisited and only on treatment of 1,4-I2-C6H4 with 2
molar equivalents of n-BuLi can 1,4-Li2-C6H4 1 be isolated in excellent yield. Treatment of 1 with two
equivalents of [ClAu(PPh3)] gives [1,4-(Ph3PAu)2-C6H4] 2a in excellent yield. Subsequent treatment of
2a with 2.5 molar equivalents of PPh2Me, PPhMe2 or PMe3 affords the PPh3 substituted compounds
[1,4-(LAu)2-C6H4] (L = PPh2Me 2b, PPhMe2 2c, PMe3 2d) in essentially quantitative yields. On
treatment of 1,4-Br2-C6H4 or 1-Br-4-I-C6H4 with 2 molar equivalents of n-BuLi only mono-lithiation
takes place to give 1-Br-4–Li-C6H4 3 as shown through the isolation of essentially 1 : 1 molar
equivalents of Ph2PC6H4-4-Br and Ph2PBu on treatment with 2 molar equivalents of ClPPh2. Treatment
of 3, prepared by lithium/iodine exchange on 1-Br-4-I-C6H4, with [ClAu(PPh3)] affords
[(Ph3P)Au(C6H4-4-Br)] 4 as expected and in addition [(Ph3P)Au(n-Bu)(C6H4-4-Br)2] 5, indicating the
straightforward chloride/aryl exchange at gold may proceed in competition with oxidative addition of
the n-BuI, generated in the initial lithium/iodine exchange reaction, to some ‘aurate’ complex
Li[Au(C6H4-4-Br)2] 6 formed in situ followed by reductive elimination of Br-C6H4-4-n-Bu in a manner
that mimics lithium diorganocuprate chemistry. All of the gold-containing compounds have been
1
spectroscopically characterised by 1H and 31P-{ H} NMR and in addition compounds 2a–d and 5 by
single crystal X-ray diffraction studies. The solid state structures observed for 2a–d are dictated by
non-conventional hydrogen bonding and the packing requirements of the phosphine ligands. For 2a
and 2b there is no close Au ◊ ◊ ◊ Au approach, however for 2c and 2d the reduction in the number of
phenyl rings allows the formation of Au ◊ ◊ ◊ Au contacts. For 2c and 2d the extended structures appear
◦
˚
to be helical chains with Au ◊ ◊ ◊ Au contac◦t parameters of 3.855(5) A and C–Au–Au–C 104.1(3) for 2c
˚
and 3.139(4) A and C–Au–Au–C -92.0(2) for 2d. The Au ◊ ◊ ◊ Au approach in 2c is longer than is
normally accepted for an Au ◊ ◊ ◊ Au contact and is dictated by ligand directed non-conventional
hydrogen bonding to the aurated benzene ring and the p-stacking requirements of the phosphine
ligand. By comparison of the structures 2a–2d with other structures in the database it is evident that the
aurophilic interaction is a poor supramolecular synthon in the presence of non-conventional hydrogen
bond donors. Searches of the CCDC database suggest that the observed parameters for the Au ◊ ◊ ◊ Au
contact in 2c sit close to the cut-off point for observing this type of contact. In addition to aurophilic
contacts and non-conventional hydrogen bonds there are a number of halogenated solvent C–Cl ◊ ◊ ◊ Au
contacts observed in the structures of 2a and 2d. The nature of these contacts have implications for the
˚
accepted van der Waals radius of gold which should be extended to 2 A.
or Grignard reagent.5 Other routes have been utilised, for example,
Schmidbaur et al.6 and Fackler et al.7 independently showed
that NaBPh4 acted as a phenylating agent towards gold(I) and
more recently the use of boronic acids to effect aryl transfer
to gold(I) in the presence of a base has been developed.8 This
latter methodology shows that incorporation of functional groups
not classically tolerated by either Grignard or lithium reagents is
now possible and broadens the potential scope for this class of
compound. In 2003 Schmidbaur et al. reported the preparation
of bis(triphenylphosphine)gold(I) hydrocarbon species including
those based on alkanes and arenes and noted that analogous
complexes of benzene could not be prepared.9 More recently Gray
et al. have made some diaurated naphthalene and pyrene based
compounds.8d
Introduction
Compounds containing a gold-aryl bond have been known1 for
nearly 80 years although full characterisation did not take place
until 1959.2 Regular reviews3 on this branch of chemistry have
appeared since the 1970 s with an extensive review published in
2005.4 Aryl groups are typically introduced to the gold centre on
reaction of an appropriate gold(I) precursor with an organolithium
aSchool of Chemistry, University of Manchester, Manchester, UK M13 9PL.
E-mail: k.r.flower@manchester.ac.uk
bSchool of Environmental and Life Sciences, University of Salford, Salford,
UK M5 4WT
† Electronic supplementary information (ESI) available: Packing diagrams
and additional scattering diagrams generated from CCDC. CCDC refer-
ence numbers 756405 for 2a, 756406 for 2b, 756407 for 2c, 756408 for
2d and 688498 for 5. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b925355f
One much discussed characteristic of gold(I) complexes in the
solid state is the closed shell d10 ◊ ◊ ◊ d10 aurophilic interaction
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(Au ◊ ◊ ◊ Au).10 Calculations have shown this interaction to be due
to correlation and relativistic effects11 and can be comparable
in strength to hydrogen bonds. In some cases compounds with
aurophilic contacts have been found to display packing sim-
ilarities to classically hydrogen-bonded systems.12 Other work
has suggested that the Au ◊ ◊ ◊ Au interaction exhibits no specific
features and it is unreasonable to use the term aurophilic and
metallophilic interactions.13 The nature and scope of the Au ◊ ◊ ◊ Au
interaction has been subject to several CCDC database searches in
attempts to understand the nature of this solid state interaction.14
We have recently shown that phosphorane dihalogen adducts
of the charge transfer spoke type are a good starting point in
attempting to mimic the solid state structures of phosphine gold(I)
halides and are helpful in teasing out issues that influence the
formation of Au ◊ ◊ ◊ Au contacts in the solid state.15 Herein we
describe the problems associated with the double lithiation of 1,4-
dihalobenzenes, a suitable method for the isolation of 1,4-Li2C6H4
1 and its subsequent use for the preparation of the compounds
[1,4-(LAu)-C6H4] (L = PPh3 2a, PPh2Me 2b, PPhMe2 2c, PMe3
2d). In addition we report the lithium/halogen exchange reaction
carried out on Br-C6H4-4-I gives 1-Br-C6H4-4-Li which when
quenched with [(Ph3P)AuCl] leads to the isolation of both [(4-
Br-C6H4)Au(PPh3)] 4 and [(4-Br-C6H4)2Au(n-Bu)PPh3] 5 and a
similarity of this chemistry to that of lithium diorganocuprate
chemistry is drawn. The solid state structures of 2a–d along with
a number of new database searches are used to discuss the relative
merits of the Au ◊ ◊ ◊ Au and Au ◊ ◊ ◊ X (X = halogen) interactions,
the distance to which they can be considered a valid contact and
the implication this has for the van der Waals radius of gold.
achieve direct dilithiation was sought and an adaptation of the
method of Fossatelli et al.23 was developed. They suggest that when
attempting to dilithiate [1,4-Br2-C6H4] where the quench is effected
by reactive electrophiles n-BuLi and the electrophile may co-exist,
thereby giving the desired di-substituted product after a sequence
of lithium/bromine exchange and derivatisation reactions. On
investigation of the dilithiation of [1,4-I2-C6H4] they concluded
that 100% dilithiation could be achieved when the diiodobenzene
was used along with three equivalents of n-BuLi, with the key to
dilithiation being the absolute need to keep the mono-lithio species
in solution. This approach although repeatable is not satisfactory
for the clean preparation of 2a. We have found, however, that by
carrying out the lithium/iodine exchange reaction with n-BuLi
in diethylether only 2 molar equivalents are required to effect
100% conversion of 1,4-I2-C6H4 to 1 and that 1 can be readily
isolated as a pyrophoric off-white crystalline solid, in essentially
quantitative yield, on addition of hexane to the reaction mixture
after 20 min. 1 can be reacted prior to isolation with electrophiles
such as Ph2PCl to give 1,4-(Ph2P)2C6H4 and [(Ph3P)AuCl] to
give the sought after [1,4-(Ph3PAu)2(C6H4)] 2a in excellent yield,
Scheme 1. However, the purity and yields of 1,4-(Ph2P)2C6H4
and [1,4-(Ph3PAu)2(C6H4)] 2a are significantely improved through
reaction with the relevant electrophile and isolated 1. It should be
noted here that the lithium/iodine exchange reaction appears to
be solvent specific and does not proceed cleanly to give 1 in THF
or hexane.
Results and discussion
Many approaches for the dilithiation of 1,4-Br2-C6H4 have been
described in the literature. The earliest being that of Gilman and
Melstrom16 in which 3 eq. of n-BuLi were reacted with 1,4-Br2-
C6H4 in Et2O at low temperature. Many variations based on this
protocol have since been published, with those of Ipaktschi17
and Buchwald18 using 4 eq. of t-BuLi to dilithiate 1,4-Br2-
C6H4, and others in which n-BuLi is refluxed for up to 48 h
with 1,4-Br2-C6H4.19,20 Screttas21 has described the dilithiation
of 1,4-Cl2-C6H4 by reacting 1,4-Cl2-C6H4 with 4 eq. of lithium
naphthalide at low temperature and the reaction of Li metal
with 1,4-Br2-C6H4 described by Bloomfield.22 Attempts to utilise
many of these methods for the preparation of 2a only resulted in
mixtures and none of the desired product. An attempt to prepare
1,4-(Ph2P)2C6H4 by dilithiation of 1,4-Br2-C6H4 using n-BuLi
followed by reaction with 2 molar equivalents of Ph2PCl, to check
whether dilithiation was actually taking place, resulted in two
main components: Ph2P(4-Br-C6H4) and Ph2P(n-Bu) in essentially
1 : 1 molar ratio. Only minute quantities of 1,4-(Ph2P)2C6H4 could
be observed in the crude material indicating that dilithiation was
definitely not taking place prior to the addition of ClPPh2. This is
consistent with the report of Baldwin20 who reported low yields of
1,4-(Ph2P)2C6H4 and suggested that the reaction should be carried
out in a sequential fashion: this approach gives 1,4-(Ph2P)2C6H4
in 80% yield. Unfortunately the sequential lithiation approach
does not work for the preparation of 2a as Li[(n-Bu)Au(C6H4-4-
Br)] is formed through PPh3 displacement rather than the desired
lithium/halogen exchange, see later. A reproducible approach to
Scheme 1 Synthesis 2a–2d:(i) 2 n-BuLi, Et2O, 253 K, 20 min; (ii) 2
[(Ph3P)AuCl], Et2O, 24 h; (iii) 2.5 L, CH2Cl2, 15 min.
2a reacts cleanly with 2.5 molar equivalents of PPh2Me, PPhMe2
or PMe3 in CH2Cl2 to give the PPh3 exchanged products [1,4-
(LAu)2(C6H4)] (L = PPh2Me 2b, PPhMe2 2c, PMe3 2d) in
essentially quantitative yield. All of the compounds 2a–d have
1
been characterised by microanalysis (C, H and P), 1H and 31P{ H}
NMR spectroscopy see experimental and by single crystal X-ray
diffraction studies, see Table 1 for crystallographic data and Fig. 1–
4 for ORTEP representations of the molecular structures showing
˚
the atomic numbering schemes and selected bond lengths (A) and
angles (◦).
Compounds 2a–d were found to crystallise in one of two space
groups either P21/n for 2a and 2b or C2/c for 2c and 2d,
see supplementary material† for packing diagrams. Considering
initially the nearest neighbour Au ◊ ◊ ◊ Au contact distances the
data suggest that there is no meaningful aurophilic interaction in
compounds 2a–c. However, consideration of the torsion angles14a
raises the possibility of an Au ◊ ◊ ◊ Au contact in 2c. The skew
3510 | Dalton Trans., 2010, 39, 3509–3520
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Table 1 Crystallographic data for 2a–d and 5
2a·1.8CH2Cl2
2b
2c
2d. 2CHCl3
5
Empirical Formula
Fw
T/K
C21.9H18.8PCl1.8Au
573.93
150
Monoclinic
P21/n
8.2662(5)
17.3899(11)
14.2615(9)
C32H30P2Au2
870.2
200
Monoclinic
P21/n
8.4871(3)
10.8176(4)
15.1648(7)
C22H26P2Au2
746.3
200
Monoclinic
C2/c
11.5373(3)
13.6031(3)
14.1294(3)
C14H24P2Cl6Au2
860.91
200
Monoclinic
C2/c
24.5474(3)
9.1914(2)
12.2193(2)
C34H32PBr2Au
828.35
150
Crystal System
Space Group
Triclinic
¯
P1 (No 2)
˚
a/A
10.8504(6)
11.4943(6)
14.3012(8)
91.006(3)
110.699(3)
111.903(2)
1524.94(8)
2
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
91.437(1)
90.89(1)
95.933(1)
113.807(1)
3
˚
V/A
2049.4(2)
2
1.860
0.07 ¥ 0.03 ¥ 0.03
1.74–27.77
1392.11(10)
2
2.077
0.08 ¥ 0.15 ¥ 0.15
3.0–26.5
2205.63(9)
4
2.247
0.07 ¥ 0.12 ¥ 0.18
3.3–26.5
2522.39(8)
4
2.267
0.10 ¥ 0.15 ¥ 0.15
3.3–27.5
Z
Dc/Mg m-3
1.804
0.10 ¥ 0.15 ¥ 0.15
3.0–24.88
Crystal size/mm
q Range for data collections
(◦)
˚
l/A
0.67100
21858
5700
0.030
Semi-empirical from
equivalents
2.158 and -0.771
0.71703
6795
2849
0.073
Semi-empirical from
equivalents
-2.64 and 4.73
0.71703
8775
2291
0.050
Semi-empirical from
equivalents
-2.59 and 2.77
0.71703
25385
2881
0.077
Semi-empirical from
equivalents
-1.88 and 2.94
0.71703
8162
5179
0.137
Semi-empirical from
equivalents
-1.907 and 0.251
Reflections collected
Unique reflections
R(int)
Absorption correction
Largest diff. between peak
-3
˚
and hole/e A
R indices observed data
R1
0.0327
0.0840
0.0584
0.1782
0.0453
0.1265
0.0403
0.1034
0.0789
0.2379
wR2
Data/restraints/parameters
Goodness-of-fit
5700/0/233
1.04
2849/0/164
1.08
2291/0/119
1.06
2881/0/113
1.07
5179/0/343
1.02
Fig. 1 ORTEP representation of the molecular st◦ructure of 2a. Ellipsoids
at 30%.a Selected bond lengths (A) and angles ( ) Au(1)–C(1) 2.041(4),
˚
Au(1)–P(1) 2.293(1), Au(1) ◊ ◊ ◊ Au(1)b 8.266(4), C(1)–Au(1) ◊ ◊ ◊ Au(1)b
105.0(3), P(1)–Au(1) ◊ ◊ ◊ Au(1)b 88.9(4), C(1)–Au(1)–P(1) 175.49(12),
C(1)–Au(1) ◊ ◊ ◊ Au(1)b–C(1)b 180.0, P(1)–Au(1) ◊ ◊ ◊ Au(1)b–P(1)b 180.0.
Symmetry related atoms generated by: a(-x, -2y, -z), b(1+x, y, z).
Fig. 2 ORTEP representation of the molecular s◦tructure of 2b. Ellipsoids
a
˚
at 30%. Selected bond lengths (A) and angles ( ) Au(1)–C(1) 2.064(12),
Au(1)–P(1) 2.295(3), Au(1) ◊ ◊ ◊ Au(1)b 5.936(5), C(1)–Au(1) ◊ ◊ ◊ Au(1)b
91.9(3), P(1)–Au(1) ◊ ◊ ◊ Au(1)b 65.4(4), C(1)–Au(1)–P(1) 178.5(4),
C(1)–Au(1) ◊ ◊ ◊ Au(1)b–C(1)b - 180.0, P(1)–Au(1) ◊ ◊ ◊ Au(1)b–P(1)b–180.0.
Symmetry related atoms generated by: a(-x, -2y, -z), b(1+x, y, z).
orientation of the P–Au–C vector14a in 2c is comparable to
that seen in 2d, Fig. 5, however the Au ◊ ◊ ◊ Au contact distance
˚
˚
at 3.855(5) A is significantly longer than for 2d 3.139(3) A
and would normally be considered to be too long for it to be
a meaningful, notwithstanding the crystallographic similarities
between the two compounds. This Au ◊ ◊ ◊ Au contact distance
anomaly in crystallographically similar compounds has been
observed previously in the isomorphous compounds [(Me3P)AuX]
(X = Cl I,24 Br, II25) where I is considered to be an infinite helical
chain linked by Au ◊ ◊ ◊ Au contacts and II a trimer as one Au ◊ ◊ ◊ Au
said this is quite a remarkable change in the nature the aurophilic
contact resulting from a single phenyl-for-methyl group exchange
in the phosphine ligand or is it? Perusal of the literature shows the
closest related matched pair to 2c and 2d is [(LAu)2C2] (L = PMe3
III and PPhMe2 IV) reported by Schmidbaur in 2003.26 In both
˚
III and IV there are strong aurophilic contacts: 3.0747(8) A in III
˚
˚
contact is beyond the normally accepted range at 3.980(2) A. That
and 3.3016(3) A in IV. So why the substantial difference in 2c and
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Fig.
3
ORTEP representation of the molecular structure of
˚
2c. Ellipsoids at 30%.a Selected bond lengths (A) and angles
(◦) Au(1)–C(1) 2.067(8), Au(1)–P(1) 2.291(2), Au(1) ◊ ◊ ◊ Au(1)b
3.855(3), C(1)–Au(1) ◊ ◊ ◊ Au(1)b 93.6(2), P(1)–Au(1) ◊ ◊ ◊ Au(1)b 91.2(4),
C(1)–Au(1)–P(1)
175.2(2),
C(1)–Au(1) ◊ ◊ ◊ Au(1)b–C(1)b
104.1(2),
P(1)–Au(1) ◊ ◊ ◊ Au(1)b–P(1)b–103.4(2). Symmetry related atoms generated
by: a(1-x, -y, 1-z), b(1-x, y, 1.5-z).
Fig. 4 ORTEP representation of the molecular s◦tructure of 2d. Ellipsoids
a
˚
at 30%. Selected bond lengths (A) and angles ( ) Au(1)–C(1) 2.054(10),
Au(1)–P(1) 2.295(3), Au(1) ◊ ◊ ◊ Au(1)b 3.139(4), C(1)–Au(1) ◊ ◊ ◊ Au(1)b
92.4(2), P(1)–Au(1) ◊ ◊ ◊ Au(1)b 93.4(4), C(1)–Au(1)–P(1) 174.2(4),
C(1)–Au(1) ◊ ◊ ◊ Au(1)b–C(1)b - 92.0(2), P(1)–Au(1) ◊ ◊ ◊ Au(1)b–P(1)b 87.8(2).
Symmetry related atoms generated by: a(-x, -2y, -z), b(-x, y, 1/2-z).
2d? It appears to be the result of differences in hydrogen bonding.
In the extended structures of III and IV it is evident that there are
hydrogen bond contacts between the H3CP groups and the p–cloud
˚
˚
of the ethyne bridge circa 2.8 A for III and H3CP circa 2.7 A and
˚
Ph-H 2.8 A contacts for IV in addition to the Au ◊ ◊ ◊ Au contacts,
see Fig. 6. For 2d two CHCl3 molecules of crystallisation hydrogen
bond to the p–cloud of the benzene ring CH-p circa 2.4 A, and
Fig. 5 ORTEP representation of the Au ◊ ◊ ◊ Au linked helical chains in 2c
and 2d, ellipsoids at 30% and Ph group of the PPhMe2 ligand in 2c omitted
for clarity.
˚
happily co-exist with the formation of an aurophilic contact. The
H3CP groups no longer engage in hydrogen bonding. So, on
exchanging an ethynyl bridge for a benzene bridge noticeably
changes the hydrogen bonding pattern. Considering 2c it is
immediately evident that there is a considerable difference in the
hydrogen bonding motif than seen for 2d. The PhMe2P ligand
hydrogen bonds to the p–cloud of the benzene ring with three
non-conventional hydrogen bonds27 on each side of the benzene
the similarities and dissimilarities of solid state structures of
matched [LAuX] (L = phosphine and X = halide) and R3EX2
(R = alkyl, aryl; E = P, As: X = Br, I).15 From an empirical
perspective, therefore, hydrogen bonding and phenyl embraces as
well as the Au–X bond behaving as a hydrogen bond acceptor
appear to be more important supramolecular synthons than
aurophilic contacts in determining the overall crystal packing in
these systems. This interpretation accounts nicely for the drastic
change in the nature of the aurophilic contact on going from 2c
to 2d.
˚
ring circa 3.2 A which prevents the formation of an analogous
aurophilic contact as seen in 2d. This observation can not be solely
dependent upon the steric bulk of the phosphine ligand leading
to an interpretation that non-conventional hydrogen bonding
exerts far more influence as a supramolecular synthon than the
aurophilic contact, notwithstanding the calculated strength of
aurophilic contacts.11 It appears that the ligand phenyl and methyl
group hydrogen bonding to the aurated benzene ring must exert a
greater stabilising affect than the formation of a strong aurophilic
contact. In addition to this hydrogen bonding there are also phenyl
embraces28 that add additional stability to the molecular crystal
and augment the stabilisation effect of the hydrogen bonds. These
observations fit well with our recent suggestion that the hydrogen
bond acceptor strength of the Au–X bond exerts more influence
in the crystal packing than the aurophilic interaction based upon
As previously mentioned, in 2d the only phenyl ring present
is the central benzene core and it engages in strong non-
conventional hydrogen bonding27 to two chloroform◦ solvate
˚
molecules [C(7)–H(7) 1.00 A, C(7)–H(7)–C(1) 174.29(3) , C(7)–
˚
H(7) ◊ ◊ ◊ C(1) 2.389(4) A], Fig. 7. The CHCl3 is also involved
˚
in a close C–Cl ◊ ◊ ◊ Au approach [C(7)–Cl(3) 1.716(3) A, C(7)–
◦
˚
H(7)–C(1) 140.76(3) , C(7)–Cl(3) ◊ ◊ ◊ Au(1) 3.625(4) A]. A search
of the CCDC database (HCl2C–Cl ◊ ◊ ◊ Au) shows this example
to be the closest yet observed approach of this type. The
29
˚
typical distances previously observed being 3.9–4 A. Shorter
Cl ◊ ◊ ◊ Au approaches have been observed in gold(I) complexes
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Fig. 7 ORTEP representation of Cl3CH ◊ ◊ ◊ Ph interactions in 2d.
the database.32 The chloroform solvates also prevent the formation
of any aryl stacking motifs. The PMe3 methyl groups are also
prevented from engaging in any hydrogen bonding interactions.
This is also seen in the solid state structure of [(Me3P)AuI] V,33 but
in this case is due to the poor hydrogen bond acceptor capability
of the Au–I bond.15
The complete absence of an Au ◊ ◊ ◊ Au contact in 2a and 2b is
therefore a direct result of the increasing number of phenyl rings
and their solid state interactions, rather than simply the increasing
bulk of the ligand as many compounds containing either PPh334 or
PPh2Me35 ligands are known that contain close Au ◊ ◊ ◊ Au contacts.
In 2a the CH2Cl2 solvates engage in a series of close contacts to the
gold centres. Like the CHCl3 solvate in 2d one CH bond points
˚
at the aurated◦C(1) atom [C(1 s)–H(1 s) 0.991(5) A, C(1 s)–H–
˚
C(1) 172.22(6) , C(1 s)–H(1 s) ◊ ◊ ◊ C(1) 2.913(5) A]. This contact
distance is longer than that observed in 2a and is presumably due to
the differing acidities of the respective C–H bonds. It also appears
˚
˚
to bridge two Au centres [C(1 s)–Cl(1 s) 1.757(3) A, C(1 s)–Cl(1 s)–
◦
C(1) 163.70(3) , C(1 s)–Cl(1 s) ◊ ◊ ◊ Au(1) 3.663(4) A], [C(1 s)–Cl(2 s)
◦
˚
1.768(3) A, C(1 s)–Cl(2 s)–C(1) 80.54(3) , C(1 s)–Cl(2 s) ◊ ◊ ◊ Au(1)
3.840(5) A], giving rise to an extended Au ◊ ◊ ◊ Cl–(CH2)–Cl ◊ ◊ ◊ Au
˚
chain, Fig. 8.
In an early search of the CCDC database Parthasarathy et al.36
showed that the C–X bonds (X = F, Cl, Br, I), although considered
to be poor ligands, behave as electron donors to metal centres
by making close approaches, within the sum of the van der
Waals radii,37 to metal centres. The◦favoured M–Cl ◊ ◊ ◊ C angle
was found to be clustered around 100 . In the same study36 it was
found that when the C–X bond behaves as an electron acceptor,
engaging in halogen bonding,38 the favoured angle of approach
is clustered around 165◦. A repeat search of the CCDC database
looking for C–Cl ◊ ◊ ◊ M (M = any transition metal) contacts still
shows the preference to clustered around 100◦ for the M ◊ ◊ ◊ Cl–C
angle with the presence of a second cluster centred around 155◦
is beginning to emerge, see supplementary material. Clearly the
bridging CH2Cl2 in 2a fulfils the generic criteria for these contacts
to be real. It presumably also accounts for the virtual insolubility
of this compound after recrystallisation from CH2Cl2. Narrowing
the search to consider just CH2Cl2 approaches to a gold(I) centre
by a C–Cl bond in compounds of the type [LAuC] the average
Fig. 6 Hydrogen bond and aurophilic contacts in III, IV, 2c and 2d.
30
˚
of the type [ClAuL] with the shortest being 3.472 A. In
addition to there being a close (HCl2C–Cl ◊ ◊ ◊ Au) contact
the chloroform molecules also form infinite chains linked by
{Cl ◊ ◊ ◊ ClC(HCl)Cl ◊ ◊ ◊ Cl ◊ ◊ ◊ ClC(HCl)Cl ◊ ◊ ◊ } contacts, see sup-
˚
plementary material. The Cl ◊ ◊ ◊ Cl distance at 3.316 A is noticeably
shorter than that observed in the solid state structure of CHCl3,
3.596 A.31 Infinite chains of this type are not without precedent in
˚
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Fig. 10 Scatter plot of Cl ◊ ◊ ◊ Au–Cl versus Au ◊ ◊ ◊ Cl.
Fig. 8 ORTEP representation of the secondary Cl2CH2 interactions
in 2a.
39
˚
approach is found to be about 4 A. Similar results were found
for searches carried out on the analogous gold chlorides [LAuCl].
If these are van der Waals rather than strong M ◊ ◊ ◊ Cl–CH2Cl
contacts this would suggest a more realistic van der Waals radius
˚
for gold of approximately 2 A. Due to the limited number of data
points available for C–Cl ◊ ◊ ◊ Au contacts an additional search was
carried out to look at all close non-bonded Au ◊ ◊ ◊ Cl–Au contacts
in two coordinate [LAuCl] systems to see if the nature of the two
contacts show any similarities. The search parameters used are
illustrated in Fig. 9.
◦
˚
Fig. 11 Scatter plot of Au ◊ ◊ ◊ Cl–Au ( ) versus Au ◊ ◊ ◊ Au (A).
˚
to be◦approximately 2 A. Considering the scatter plots of Au ◊ ◊ ◊ Cl–
˚
Au ( ) versus Au ◊ ◊ ◊ Au (A) and Cl–Au ◊ ◊ ◊ Au–Cl torsion angle
versus Au ◊ ◊ ◊ Au represented as Fig. 11 and 12 significant clustering
is again observed in both. If the compact nature of the clusters can
be taken to indicate the range and scope of a meaningful Au ◊ ◊ ◊ Au
contact, the data represented in both plots suggest that Au ◊ ◊ ◊ Au
˚
contacts are possible out to at least 3.8 A and compare favourably
Fig. 9 Parameters used in the search of the CCDC.
with the data observed for Au–Cl ◊ ◊ ◊ Au and C–Cl ◊ ◊ ◊ Au contacts.
A close inspection of the structures represented by the data points
˚
˚
The search examined contacts up to 5 A much longer than
in the region 3.9–4.2 A show that the two ClAuL fragments tend
the normally accepted range, to see if any clear cut off could be
determined. The data obtained are illustrated in a series of scatter
plots, Fig. 10–12. Fig. 10 indicates that the closest non-bonded Au–
Cl ◊ ◊ ◊ Au approaches occur, as might be expected, when the Au–
Cl ◊ ◊ ◊ Au angle approaches 90 ( ) 10◦ and cluster in the range 3.4–
4 A and as the angle opens up beyond 120 the Cl ◊ ◊ ◊ Au distance
increases rapidly. Since the nature of the C–Cl ◊ ◊ ◊ Au contacts
observed in 2a and 2d appear comparable in nature to the non-
bonded contacts Au–Cl ◊ ◊ ◊ Au observed in compounds of the type
[ClAuL] and they further support a van der Waals radius for gold
to line up with each other in a head to tail fashion, torsion angles
180◦. This orientation is dictated by the packing requirements of
the ligands, which are not necessarily sterically bulky. The illusion
that is created however is that as the ligand volume increases so the
molecular Au–X vectors slide past each other as if moving along an
upward inclined arc (to q ª 90◦) until the Au–X bonds are parallel.
This initially decreases the Au ◊ ◊ ◊ Cl distance while the Au ◊ ◊ ◊ Au
distance increases until both simultaneously increase. The search
criteria used to investigate the nature of Au–Cl ◊ ◊ ◊ Au interactions
were then used to look at analogous bromo- and iodo-containing
◦
˚
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not the requirements of the Au ◊ ◊ ◊ Au contact and the presence
of an Au ◊ ◊ ◊ Au contact is not simply related to the perceived
bulk of the ligand. So, what do these observations mean for
the range of Au ◊ ◊ ◊ Au contacts and its utility as supramolecular
synthon? It is has been suggested elsewhere for the Au ◊ ◊ ◊ Au
contact to be a good supramolecular synthon,14a ie. one that
directs the crystal packing, the two L–Au–X vectors have to be at
essentially 90◦ to each other and with the Au ◊ ◊ ◊ Au distance less
˚
than 3.32 A. The data presented for 2d support this suggestion in
principle. The structure found for 2d displays an Au ◊ ◊ ◊ Au contact
˚
distance of 3.139(4) A with a C–Au ◊ ◊ ◊ Au–C torsion angle of
- 92.0(2)◦, but can the Au ◊ ◊ ◊ Au contact really be considered a
good supramolecular synthon in general? In this case possibly,
but only because there is no strong alternative director of the
packing present. As soon as a phenyl ring is incorporated into
the ligand system, 2c, the parameters of the Au ◊ ◊ ◊ Au contact fall
to the very fringes of what can be interpreted as a meaningful
attractive aurophilic contact. The ligand cannot be considered
sterically demanding and so negates the steric argument for weak
or absent aurophilic contacts. Hydrogen bonding is clearly more
important. The hydrogen bonds that are observed may be weaker
than calculated aurophilic contacts but there are more of them
and it appears the sum of the whole is more important. Once
again these observations seem to fit nicely with a view expressed
by Dance in a review:28b “It is important to consider the complete
structure of the molecular crystal and all of the intermolecular
space.” As for the maximum length of a meaningful Au ◊ ◊ ◊ Au
contact, the data from the CCDC database searches, presented
here, suggest that aurophilic contacts are observable up to about
Fig. 12 Scatter plot of Cl–Au ◊ ◊ ◊ Au–Cl torsion angle versus Au ◊ ◊ ◊ Au.
Note: the hits with a torsion angle of 0◦ at circa 4.4 A are the result of
˚
non-next nearest neighbour interactions.
compounds. Essentially the same scatter patterns are observed,
but indicate that the maximal distance for an Au ◊ ◊ ◊ Au contact
25
˚
could be extended to 3.98 A, II. The final search carried out
looked at the related two coordinate [LAuC] system. Once again
identical clustering patterns are observed. What is remarkable
about these searches is that they all show the same clustering
patterns, see supplementary material for a series of scatter plots
(similar to Fig. 11–12) that combine data points from all of the
searches. They appear to indicate a similar broad region in which
aurophilic contacts may be observed and they all indicate that
˚
4 A. This in turn impacts on the value quoted for the van der
Waals radius used in such searches.37 Based on the available data
from the CCDC database it ought to be considered to be in the
˚
this is out to about 4 A. What also becomes apparent is that
˚
region 1.9–2.1 A. Is there any other data to support this assertion?
˚
above 4 A the nearest neighbour contact is generally expected
It has been reported that Au ◊ ◊ ◊ Au interactions may occur in the
to give a torsion angle of 180◦. A significant anomaly to this
observation is seen for the compounds [1,9-(Ph2PAuX)2-C14H8]
(X = Cl VI, Br VII)40 which have Au ◊ ◊ ◊ Au contact distances
range 2.47 = Redi < Re(Au ◊ ◊ ◊ Au) < Revdw (Au ◊ ◊ ◊ Au) = 3.22–
di
4.0 A, where R e is the distance in the 197Au2 (gas) molecule in the
˚
X1 R+g state,41 so there is other experimental evidence to support
using this value. Further there is ample evidence to suggest the
van der Waals radius of neighbouring mercury be considered to
◦
˚
of 4.449(5) and 4.451(5) A with torsion angles of 90 . What is
immediately evident though, Fig. 13, is that the orientation of
the “Au ◊ ◊ ◊ Au contact” is a result of the packing being driven by
the packing requirements of the diphenylanthracenylphosphine
ligand, further supporting the argument15 that: the nature of the
Au ◊ ◊ ◊ Au contact is determined by the requirements of the ligands,
42
37
˚
˚
be 2.1 A rather than the often quoted 1.55 A. The nature of
any observed interaction at this extreme is going to be weak. For
VI and VII, even though the skew torsion angle is 90◦, and this
feature is normally considered a good criteria for an aurophilic
contact,14a there can be no attractive aurophilic contact there.
In an attempt to prepare 2a by a stepwise lithiation process
using n-BuLi and 1-Br-4-I-C6H4, Scheme 2, the initial step
proceeds to give 4-Li-C6H4Br 3 which reacts with [(Ph3P)AuCl] to
give [(Ph3P)Au(C6H4-4-Br)] 4 (82%) and [(Ph3P)Au(n-Bu)(C6H4-
4-Br)2] 5 (10%). The isolation of 5 was somewhat surprising and
its presence was initially observed as a low intensity signal at
24.2 ppm in the 31P{ H} NMR spectrum of crude 4. Compound 5
1
could be extracted from the crude by washing with hexane. Slow
evaporation of the hexane gave suitable crystals of 5 for a single
crystal X-ray diffraction analysis, see Table 1 for crystallographic
data and Fig. 14 for an ORTEP representation of the molecular
structure showing the ato◦mic numbering scheme and selected bond
˚
lengths (A) and angles ( ). From these observations it is evident
that the reaction between 1-Br-4-Li-C6H4 and [ClAu(PPh3)] is
not just a simple metathesis reaction but must be made up of a
Fig. 13 Illustration of the Au ◊ ◊ ◊ Au approach in VI.
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evident that 5 slowly decomposes to 4 by reductive elimination
of 1-Br-4-n-Bu-C6H4 and with a half life of approximately 24 h.
Notwithstanding the slow decomposition of 5 an interpretable
1
13C{ H}-NMR spectrum was recorded. The data obtained are
interesting when considered in conjunction with the data of Ogle
et al.43 who have recently reported the preparation and spectral
characterisation of some neutral triorganocopper(III) complexes at
low temperature using rapid injection nuclear magnetic resonance
spectroscopy (RI–NMR); a technique they have applied to look
at other reactive copper systems.44 For 4 the aurated aromatic
2
carbon resonates at 170.4 ppm JPC = 118.1 Hz which is as
expected for a linear gold(I) phosphine species.45 On oxidative
addition of n-BuI the aurated phenyl carbon resonance shifts to
2
162.7 ppm and displays a much reduced JPC = 10.0 Hz which
is consistent with a cis P–C orientation. The aurated n-butyl
2
carbon atom resonates at 38.1 ppm with a JPC = 104.7 Hz
consistent with a trans P–C geometry, Fig. 15, and is consistent
with the crystallographically determined structure. These data
therefore correlate nicely with the RI-NMR data observed for
related thermally unstable triorganocopper complexes of the type
[R2R’CuL],43 where for [Me2(Et)Cu(PPh3)] the observed trans
2JPC = 118.0 Hz and is similar to that seen for 3, 104.7 Hz.
Unfortunately the cis coupling was not resolved, but it is likely
to be similar in magnitude to that observed for 5.
Scheme 2 Reagents: (i) n-BuLi, Et2O, 253 K, 30 min; (ii) [ClAu(PPh3)]
18 h
The similarity in behaviour between Li[Me2Au] and Li[Me2Cu]
was originally remarked upon by Teutsch when studying the ring
opening of epoxides where he postulated the presence of a transient
Cu(III) intermediate.46 As long ago as 1973 Tamaki and Kochi
reported47 that the oxidative addition of alkyl halides to Li[Me2Au]
gave rise to the trans products [(Me)2AuR(PPh3)] which on heating
led to three decomposition processes:48 (i) alkyl rearrangement,
(ii) cis trans isomerisation and (iii) reductive elimination. The
nature of these process was studied theoretically and compared
to related copper systems.49 Considering, the renaissance of gold
in homogeneous catalysis50 we wondered whether any other
oxidative addition/reductive elimination process was feasible for
the formation of C–C bonds in this system. An attempted oxidative
addition of acetyl chloride to Li[(F5C6)2Au] was reported by
Uson et al. in 1977 in the expectation of generating a gold(III)
complex.51 Unfortunately they were unable to isolate a Au(III)
species andonly isolated the gold(I) compound [(F5C6)AuCl]- from
the reaction mixture. We suspected, based on the observations
above, that their reaction would also have led to the formation of
the pentafluorophenylmethyl ketone C6F5C(O)Me via an oxidative
addition reductive elimination pathway. So in a related reaction, 6
was reacted with 2-Br-benzoylchloride in ether and found to give
the expected asymmetric diphenyl ketone via an oxidative addition
reductive elimination pathway, Scheme 3.
Fig. 14 ORTEP representation of the molecular structure of 5 showing
the atomic numbering scheme. Selected bond lengths (A) and angles
˚
(◦):Au(1)–C(19) 2.101(17); Au(1)–C(25) 2.082(17); Au(1)–C(31) 2.113(16);
Au(1)–P(1) 2.381(4); C(19)–Au(1)–C(25) 171.5(6); C(19)–Au(1)–C(31)
87,6(7); C(25)–Au(1)–C(31) 87.8(7); C(31)–Au(1)–P(1) 176.0(6);
C(19)–Au(1)–P(1) 93.9(5); C(25)–Au(1)–P(1) 91.3(4).
series of interlinked reactions which ultimately lead to the expected
product 4.
Compound 4 formed by the expected metathesis reaction must
readily react with excess 3 in the reaction mixture to give the aurate
complex Li[(4-Br-C6H4)2Au] 6 and with time 6 equilibrates with
the remaining [ClAu(PPh3)] to give 4. During this equilibration
process the n-BuI that was generated in the lithium/iodine
exchange reaction, Scheme 2, is not an innocent by-stander. It
slowly, and competitively oxidatively adds to 6 affording 5. In an
attempt to maximise the yield of 5, 6 was generated directly from
the reaction of [ClAu(PPh3)] and 2 equivalents of 3 and left to
react with n-BuI for 24 h. The crude reaction mixture was found
to contain 4, 5 and 1-Br-4-n-Bu-C6H4. 5 was extracted from the
crude mixture with hexane and spectroscopically characterised,
see experimental. While recording the NMR spectra it became
1
The 13C{ H}-NMR spectrum of the crude material displayed
a ketone carbonyl resonance at 194.8 ppm. The aurated phenyl
resonance observed for 4 at 170.4 ppm was also observed. This
is indicative of oxidative addition of the acid chloride followed
by reductive elimination of the ketone. Treatment of 4 with n-
BuLi gives Li[(4-Br-C6H4)Au(n-Bu)] 7 which appears (by NMR)
to react selectively with 2-Br-benzoylchloride to give exclusively
=
the mixed n-butyl-2-bromo-phenyl ketone (C O, 203.2 ppm)
with no evidence for the diphenyl ketone and a resonance at
170.4 ppm indicating the presence of 4. This observation is
1
further supported by the 31P{ H}-NMR data where only one
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1
Fig. 15 Selected 13C-{ H} spectral portions for 1 and 3 illustrating the magnitude of the coupling constants 2JPC. (a) Au(I)-C(Ph); (b) Au(III)-C(Ph); (c)
Au(III)-C(Bu).
conjunction with searches using the CCDC database strongly
indicate that meaningful Au ◊ ◊ ◊ Au contacts can be observed to
˚
a limit of 4 A and that the van der Waals radius for gold
˚
ought to be increased to 2.0 A. In the preparation of [(4-Br-
C6H4)Au(PPh3)] 4 via halide/aryl-group metathesis (using in situ
generated 1-Br-4-Li-C6H4 3 via lithium iodine/exchange) also
generates Li[(4-Br-C6H4)2Au] 6 in situ which slowly equilibrates
with unreacted [(Ph3P)AuCl] to give 4. Compound 6 behaves in
an analogous manner to diorganocuprates utilising the n-BuI,
generated in the lithium/iodine exchange reaction, to undergo
oxidative addition to give 5 followed by reductive elimination
to give 4 and 1-Br-4-n-Bu-C6H4. The related gold and copper
complexes display comparable spectroscopic features including JPC
coupling constants. As expected the gold complexes are kinetically
less labile. Compound 6 also reacts with acid chlorides to give
ketones by an oxidative addition/reductive elimination process.
Scheme 3 Ketone formation through reaction of benzoylchloride with
Li[(4-Br-C6H4)2Au] 6.
resonance (d = 44.8 ppm) is observed and is again with consistent
with the formation of 4. No resonance corresponding to [(n-
Bu)Au(PPh3)] 8 (d = 47.6 ppm) was seen. This pattern of reactivity
is also consistent with the inability to form 2a by a stepwise
lithium/halogen exchange procedure.
Experimental
Conclusion
General considerations: Hexane and diethyl-ether were dried
by refluxing over sodium-potassium alloy and distilled prior
to use. [ClAu(PPh3)] was prepared on adding a stoichiometric
amount of PPh3 to [ClAu(THT)]52 in CH2Cl2. All other chemicals
were obtained from commercial sources and used as received.
1,4-Li2-C6H4 1 has been isolated for the first time as a pyrophoric
off-white solid using a reproducible stoichiometric lithium/iodine
exchange reaction. It has been used to prepare [1,4-(Ph3PAu)2-
C6H4] 2a which readily undergoes ligand substitution reactions
with more basic phosphines to give [1,4-(LAu)2-C6H4] (L =
PPh2Me 2b, PPhMe2 2c, PMe3 2d). The presence of aurophilic
contacts in these structures is determined by the non-conventional
hydrogen bonding requirements of the ligands. The nature of
the solid state interactions in 2c and 2d when considered in
1
1H-NMR (200.2 MHz) and 31P { H}-NMR (81.3 MHz) were
recorded on a Bruker DPX200 spectrometer. Proton spectra were
referenced either to CHCl3 (d = 7.26) or CH2Cl2 (d = 5.29) and
1
31P { H}-NMR were referenced externally to 85% H3PO4 (d =
0.0). Elemental analyses were performed by the Microanalytical
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Service, School of Chemistry, The University of Manchester,
Manchester, UK. The syntheses of all compounds were carried out
under an argon atmosphere using standard Schlenk techniques.
Final purification of the gold-containing compounds was carried
out in the open.
[(4-Br-C6H4)Au(PPh3)] 4. To 4-I-Br-C6H4 (0.227 g, 0.8 mmol)
dissolved in Et2O (10 mL) was added n-BuLi (0.5 mL, 1.6 M
hexane) at -78 ◦C. After 15 min [ClAu(PPh3)] (0.396 g, 0.8 mmol)
was added and the solution allowed to warm to room temperature
and stirred for 18 h. H2O (0.2 mL) was added and after 10 min
the solvent removed in vacuo. Redissolution in CH2Cl2, drying
over MgSO4, filtration through celite followed by slow addition
of hexane effected the precipitation of 4 (0.4 g, 82%); Elemental
analysis (Calc %):C 47.1 (46.9), H 3.2 (3.1), P 5.2 (5.0); NMR
(CDCl3 d ppm, J = Hz): Bruker DPX 400; 1H 7.48–7.0 (m, Ph-H);
Syntheses
[1,4-Li2-C6H4]·nEt2O 1. n-BuLi (20 mL, 1.6 M) was added
to a Schlenk flask (100 mL) under an atmosphere of dry argon
and the hexane removed under reduced pressure. To the viscous
residue was added Et2O (25 mL) and the solution cooled to 253 K
and 1,4-I2-C6H4 (5.28 g, 16 mmol) added in one solid portion with
vigorous stirring and the reaction stirred for an additional 20 min.
The solvent volume was then reduced by approximately half and
hexane (100 mL) added to effect full precipitation of [1,4-Li2-
C6H4]·nEt2O The precipitated [1,4-Li2-C6H4]·nEt2O was collected
on glass sinter (No 4) under argon, washed with hexane (3 ¥
10 mL) and dried in vacuo. It was then transferred to a glovebox
for storage. The number of Et2O molecules of crystallisation were
calculated by quenching a known mass of 1 with ClSiMe3 in Et2O
and assuming 100% conversion to [1,4-(Me3Si)2-C6H4] and from
the yield back calculating the formula weight. The typical yield is
2–2.4 g, 70–75%; formula weight range 160–190 g mol-1. Caution:
this compound is extremely pyrophoric.
1
13C-{ H} 170.4 (d, JPC 118.1); 140.71, 134.3 (d, JPC 13.5); 131.2,
130.7 (d JPC 49.8), 130.2, 129.0 (d, JPC 10.5), 119.9; Bruker DPX
1
200: 31P-{ H} 44.8 s.
[(4-Br-C6H4)2Au(Bu)(PPh3)] 5. The methodology was the
same as for the preparation of 4 save [ClAu(PPh3)] (0.198 g,
0.4 mmol) was added and after 18 h the solvent was removed
and the crude extracted with hexane (10 mL). Reduction of the
solvent volume afforded 5 (80 mg, 24%). Elemental analysis (Calc
%): C 48.9 (49.3), H 3.6 (3.9), P 3.5 (3.7); NMR (CDCl3, d ppm, J
= Hz) Bruker DPX 400: 1H 7.8–7.0 (m, 23H, Ph-H), 2.1 (bm, 2H,
1
CH2), 1.4 (bm, 4H CH2), 0.9 (bm 3H, CH3); 13C-{ H} 162.7 (d, JPC
10.1); 136,7, 134.1 (d, JPC 13.6); 130.6 130.4, 128.2 (d JPC 10.8);
117.5; 38.1 (d, JPC 10.1); 32.4 (d, JPC 10.1); 26. 7 (d, JPC 10.1) 13.9;
1
Bruker DPX 200: 31P-{ H} 24.2 s.
[1,4-(Ph3PAu)2-C6H4]·2CH2Cl2 2a. To [1,4-Li2-C6H4]·nEt2O
(0.09 g, 0.5 mmol) suspended in Et2O (30 mL) was added
[ClAuPPh3] (0.495 g, 1 mmol) and the reaction mixture stirred
under an argon atmosphere. After 72 h water (0.1 mL) was added
and the mixture stirred for an additional 10 min. The precipitate
was collected by filtration and washed with water (2 ¥ 5 mL) and
EtOH (2 ¥ 5 mL) and dried under suction. The crude product was
dissolved in boiling CH2Cl2 (100 mL) and filtered, quickly, through
warm celite. Addition of EtOH (10 mL) and concentration of
the solution under reduced pressure effected crystallisation of
2a·2CH2Cl2 (white, 0.49 g, 85%).
X-ray crystallography
Crystals suitable for X-ray crystallography for 2a were grown by
slow cooling of a saturated CH2Cl2 solution for compounds 2b,
2c and 2d, slow evaporation of NMR samples and 5 by slow
evaporation of a hexane solution.
Data collection for 2a: A suitable single crystal was coated
in inert perfluoropolyether oil and mounted on a single glass
wool strand of ca. 3 mm in length glued to a glass fibre. All
measurements were carried out on Station 9.8. CCLRC Daresbury
Laboratory, Daresbury, UK using a standard Bruker SMART
charge-coupled device (CCD) 1 K area-detector diffractometer
controlled using the SMART software package version 5.054.53
This software was also used for indexing, cell refinement and data
reduction. For 2b, 2c, 2d and 5 data collections were carried out
using j and w scans on a Nonius Kappa CCD diffractometer
employing graphite monochromated Mo-Ka radiation (l =
Elemental Analysis: C44H38P2Cl4Au2 requires: C, 45.4, H, 3.3, P
5.3; Found C, 45.6, H, 3.4, P, 5.2; 1H CD2Cl2:7.5 (m, 15H, Ph-H);
1
7.32 (s, 4H, Ph-H); 31P-{ H} CD2Cl2:44.5 (s).
[1,4-(Ph2MePAu)2-C6H4] 2b. To 2a (0.233 g, 0.2 mmol) slurried
in CH2Cl2 (5 mL) with continuous stirring under a stream of argon
was added PPh2Me (0.07 mL, 0.5 mmol). After 1 h the solution was
filtered through celite and EtOH (10 mL) added. Concentration of
the solution under reduced pressure effected crystallisation of 2b
(white, 0.155 g, 89%). Elemental Analysis: C32H30P2Au2 requires:
C, 44.2, H, 3.5, P 7.1; found C, 44.4, H,3.8, P, 6.9; 1H CDCl3:7.6
(m, 20H, Ph-H); 7.38 (s, 4H, Ph-H), 2.12 (d, 6H, CH3, JPH 8.5 Hz;
˚
0.71073 A). Experimental details are presented in Table 1. The
crystal structures were solved by direct methods using SHELXS-
97 and refined by full-matrix least-squares with SHELXL-97.54
Crystallographic data for the structural analysis (CIF)† has been
deposited with the Cambridge Crystallographic Data Centre,
CCDC No. 756405 for 2a and CCDC No. 756406 for 2b
CCDC No. 756407 for 2c and CCDC No. 756408 for 2d and
CCDC No. 688498 for 5. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
1
31P-{ H} CDCl3:30.5 (s).
In a similar fashion compounds [1,4-(PhMe2PAu)2-C6H4] 2c,
(white, 94%) elemental analysis: C22H26P2Au2 requires: C, 35.4,
1
H, 3.5, P 8.3; found C, 35.6, H,3.5, P, 8.6; H CDCl3:7.6 (m,
10H, Ph-H); 7.38 (s, 4H, Ph-H), 1.76 (d, 12H, CH3, JPH 8.6 Hz;
1
31P-{ H} CDCl3:18.8 (s), and [1,4-(Me3PAu)2-C6H4]·2CHCl3 2d
(white, 92%) elemental analysis: C14H24P2Cl6Au2 requires: C, 19.5,
H, 2.8, P 7.2; found: C, 19.2, H, 3.1, P 7.4; 1H CDCl3:7.41 (s, 4H,
Acknowledgements
1
Ph-H), 1.43 (d, 18H, CH3, JPH 8.6 Hz; 31P-{ H} CDCl3:8.4 (s),
We thank UMIP and Modern Biosciences for the financial support
of this work and PJM thanks the EPSRC for a DTA award.
were prepared.
3518 | Dalton Trans., 2010, 39, 3509–3520
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The Royal Society of Chemistry 2010
©

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(b) I. Dance, Mol. Cryst. Liq. Cryst., 2005, 440, 265–293 and refs
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3520 | Dalton Trans., 2010, 39, 3509–3520
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The Royal Society of Chemistry 2010
©