Self-assembly in gold(I) chemistry: A double-stranded polymer with interstrand aurophilic interactions

Article abstract of DOI:10.1002/anie.200353127

Raising the gold standard: Hybrid organic-inorganic side-by-side double-chain polymers have been prepared in which individual polymer chains are connected through the aurophilic interactions of gold (1) centers (see picture). The use of alternative isomers of the monomeric building blocks leads to the formation of dimeric or trimeric complexes.

Full text of DOI:10.1002/anie.200353127

Angewandte
Chemie
further highlights their potential in the field of hybrid
organic–inorganic molecular materials.
The synthetic strategy was to eliminate HCl from the
ortho (1), meta (2), and para (3)isomers of [AuCl(Ph 2PC6H4-
CO2H)],[13,14] to yield the corresponding oligomers or poly-
mers [{Au(Ph2PC6H4CO2)}n], with the expectation that the
degree of aggregation would be different for the different
isomers. Preliminary experiments with [AuCl(4-Ph2P-
C6H4CO2H)] (3), which forms a hydrogen-bonded dimer in
the solid state (Figure 1), were unsuccessful since the complex
Au–Au Interactions
Figure 1. A view of the hydrogen-bonded dimeric structure of 3.
Self-Assembly in Gold(i) Chemistry: A Double-
Stranded Polymer with Interstrand Aurophilic
Interactions**
was resistant to dehydrochlorination with mild bases and was
decomposed by stronger ones. However, success was achieved
by a two-step reaction involving abstraction of the chloride
ligand from each complex 1–3 using silver(i)trifluoroacetate
to form the corresponding gold(i)trifluoroacetate complex,
which was not isolated but was treated in situ with a base to
eliminate trifluoroacetic acid and give the product, as out-
lined in Scheme 1. Complex 1 gave a mixture of dimer 4 and
trimer 5, while complex 2 gave only a molecular triangle 6,
and complex 3 gave an insoluble polymer 7.
The soluble complexes 4–6 were characterized in solution
by NMR spectroscopy and ESI mass spectrometry. Com-
plex 6 gave a singlet in the 31P NMR spectrum (in CDCl3)at
d = 28.8 ppm and a peak at m/z = 1639 in the ESI-MS (in
CH2Cl2/CH3CN, with CsI present to enhance ionization),
which corresponds to the [{Au(Ph2PC6H4CO2)}3]·Cs+ ion, and
indicates the presence of the molecular triangle structure
only. Complexes 4 and 5 formed an equilibrium mixture in
solution. Thus, the 31P NMR spectrum gave two resonances at
d = 33.0 (trimer)and 27.9 ppm (dimer)while the ESI-MS
contained two major ions at m/z = 1639 and 1137 correspond-
ing to [{Au(Ph2PC6H4CO2)}n]·Cs+, with n = 3 or 2, respec-
tively. Crystallization of the mixture gave the molecular
triangle complex 5, whose structure is shown in Figure 2. The
18-membered macrocycle contains three linear gold(i)units
with gold atoms separated by 3.56–4.31 Š, which is too long to
be indicative of aurophilic bonding. Molecular modeling
indicates that the dimer 4 has more ring strain than 5 but that
this is compensated by the presence of a shorter Au···Au
contact of approximately 2.9 Š. In solution, 4 will also be
favored with respect to 5 through entropic effects.
Fabian Mohr, Michael C. Jennings, and
Richard J. Puddephatt*
There has been remarkable progress and interest in the design
and synthesis of hybrid organic–inorganic molecular materi-
als, and a key strategy is to design simple building blocks that
can be induced to form complex molecular structures by self-
assembly.[1] Gold(i)centers are particularly versatile as
components of such building blocks based on their tendency
for linear coordination,[2,3] their high reactivity towards ligand
substitution,[2] and their ability to form secondary aurophilic
bonds that can be used to direct the self-assembly.[2–9] These
properties have made it possible to design macrocycles,
molecular triangles, catenanes, and polymers with gold(i)
centers coordinated to a phosphane and a nitrogen or carbon
donor ligand.[2–10] The gold–carboxylate linkage is important
in self-assembled monolayers on gold colloids[11] and is well
known in simple complexes,[2,12] but it has not yet been
exploited in molecular materials. Here we show that a simple
condensation procedure can lead to the self-assembly of a
cyclic dimer or trimer, or of a linear polymer for gold(i)
complexes of the three isomers of diphenylphosphanylben-
zoic acid, and that the polymer forms a remarkable double-
stranded structure through aurophilic attractions. The ligands
themselves are already known to give interesting gold
compounds[13,14] and bimetallic compounds,[15] and this work
[*] Dr. F. Mohr, Dr. M. C. Jennings, Prof. R. J. Puddephatt
Department of Chemistry
Complex 7 was insufficiently soluble for characterization
in solution, but the remarkable structure shown in Figure 3
was determined using crystals that were grown by the
diffusion of 2,2’-bipyridyl into a solution of [Au(O2CCF3)(4-
Ph2PC6H4CO2H)] in CHCl3. The structure (Figure 3)contains
infinite polymer chains [{Au(4-Ph2PC6H4CO2)}n]; there is a
degree of helicity in these chains arising from the usual
University of Western Ontario
London, Ontario N6A 5B7 (Canada)
Fax: (+1)519-661-3022
E-mail: pudd@uwo.ca
[**] We thank NSERC (Canada) for financial support. R.J.P. holds a
Canada Research Chair.
Angew. Chem. Int. Ed. 2004, 43, 969 –969
DOI: 10.1002/anie.200353127
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969

Communications
(Au(1)···Au(2) = 3.1643(9)Š) to give a racemic P,M
double-helical structure. Complex 7 appears to be the
first example of a hybrid organic–inorganic double-chain
polymer of this type. However, there is a related
nÀ
inorganic double-chain polymer containing [AuSe5]n
ions, in which chains are connected through aurophilic
[16]
interactions (Au···Au = 2.950(3)Š).
In addition, the
antiarthritic drug gold thiomalate contains a classic
chiral double-helical structure with chains connected
through interchain aurophilic bonds (Au···Au =
[17]
3.227(5)Š).
Together, these structures demonstrate
the remarkable ability of gold(i)centers to form several
classes of double-stranded polymeric structures through
aurophilic bonding.
Experimental Section
4, 5:
A solution of [AuCl(2-Ph2PC6H4CO2H)] (0.050 g,
0.093 mmol)in CH 2Cl2 (10 mL)was treated with AgO 2CCF3
(0.021 g, 0.095 mmol)for 0.5 h. The solution was filtered
through celite. Et3N (0.010 g, 0.099 mmol)was then added to
the filtrate, the volume was reduced to 5 mL, and pentane
(20 mL)was added to precipitate the product as a pale-yellow
solid. Yield: 54%. 31P NMR (CDCl3): d = 33.0 (5); 27.9 ppm (4).
À1
=
À
IR (KBr disk): n˜ = 1635 (s, C O), 1336 cm (s, C O); ESI-MS
(m/z): 1639 [5+Cs]+, 1137 [4+Cs]+; elemental analysis (%)
calcd for C19H14AuO2P: C 45.4, H 2.8, found: C 45.2, H 2.9.
6: This complex was prepared similarly from [AuCl-
Scheme 1. Self-assembly processes from monomers 1–3.
(3-Ph2PC6H4CO2H)]. Yield: 40%. 31P NMR (CDCl3): d =
À1
=
28.8 ppm; IR (KBr disk): n˜ = 1627 (s, C O), 1334 cm (s,
+
À
C O); ES-MS (m/z): 1639 [6+Cs] ; elemental analysis (%)
calcd for C19H14AuO2P: C 45.4, H 2.8, found: C 45.1, H 2.5.
7: This was prepared similarly from [AuCl(4-Ph2PC6H4CO2H)],
but precipitated on addition of Et3N, and was isolated at that stage by
filtration. Yield: 65%. IR (KBr disk): n˜ = 1625 (s, C O), 1334 cmÀ1 (s,
=
À
C O); elemental analysis (%) calcd for [C 19H14AuO2P·0.25CH2Cl2]:
C 44.8, H 2.8, found: C 44.6, H 2.8.
X-ray structure analysis:[18] Nonius Kappa-CCD diffractometer
(MoKa radiation), data collection and refinement SHELXTL-NT
V6.1, empirical absorption correction. CCDC-221124–6 contain the
supplementary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html
(or from the Cambridge Crystallographic Data Centre, 12, Union
Road, Cambridge CB21EZ, UK; fax: (+ 44)1223-336-033; or
deposit@ccdc.cam.ac.uk).
Figure 2. A view of the molecular triangle structure of 5.
Received: October 21, 2003 [Z53127]
Keywords: gold · macrocycles · polymers · self-assembly ·
.
supramolecular chemistry
Figure 3. Two views of the double-stranded polymeric structure of 7.
Only the gold atoms are labeled with the labels 1–4 representing
Au(1)–Au(4), respectively, and only the ipso carbon atoms of the
phenyl groups are shown for clarity.
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¯
[18] 3: C19H15AuClO2P, Mr = 538.70, triclinic, space group P1, Z = 4,
a = 12.0996(3), b = 12.4632(3), c = 13.7806(3)Š, a = 112.200(1),
b = 91.268(1), g = 108.774(1)8, V= 1797.04(7)Š 3, T= 148(2)K,
m(MoKa) = 8.432 mmÀ1
,
18665 reflections, 8195 independent
reflections, R1 [I > 2s(I)] = 0.069, wR2 = 0.160. 5·3.25acetone:
66.75H61.5Au3O9.25P3, Mr = 1695.47, monoclinic, space group P21/
c, Z = 4, a = 13.6996(2), b = 19.7912(3), c = 23.1202(3)Š, b =
97.756(1), T= 150(2)K, m(MoKa) =
V= 6211.3(1)Š 3,
C
7.202 mmÀ1, 62032 reflections, 10958 independent reflections,
R1 [I > 2s(I)] = 0.044, wR2 = 0.110. 7·6.5CHCl3: C82.5H62.5Au4-
Cl19.5O8P4, Mr = 2784.85, monoclinic, space group P21/c, Z = 4,
a = 34.8469(3), b = 12.6874(1),c = 23.3187(2)Š, b = 108.645(1)8,
V= 9768.5(1)Š 3, T= 150(2)K, m(MoKa) = 6.638 mmÀ1, 86413
reflections, 16218 independent reflections, R1 [I > 2s(I)] = 0.074,
wR2 = 0.151.
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