Polymers and rings in gold(I) diphosphine complexes: Linking gold rings through aurophilic interactions

Article abstract of DOI:10.1039/b103020p

Gold(I) complex cations of empirical formula Au[Ph₂P(CH₂)_nPPh₂]⁺ crystallize as rings [Au₂{Ph₂P(CH₂)_n PPh₂}₂]²⁺ when n = 3

Full text of DOI:10.1039/b103020p

Polymers and rings in gold( ) diphosphine complexes: linking gold
I
rings through aurophilic interactions
Marie-Claude Brandys and Richard J. Puddephatt*
Department of Chemistry, University of Western Ontario, London, Canada, N6A 5B7.
E-mail: pudd@uwo.ca
Received (in Columbia, MO, USA) 3rd April 2001, Accepted 24th April 2001
First published as an Advance Article on the web 21st June 2001
Gold(
I
)
complex cations of empirical formula
crystallize as rings
the preference for the anti conformation prevail and lead to the
novel polymeric structure of 2 (Fig. 1). The NMR data suggest,
but do not prove, that the solid state structures are maintained in
solution.
Au[Ph2P(CH2)nPPh2]+
[Au2{Ph2P(CH2)nPPh2}2]2+ when n = 3 or 5 but as a polymer
[{Au[Ph2P(CH2)nPPh2]}x]x+ when n = 4. In favorable cases,
the ring complexes can be connected through aurophilic
bonding by addition of [Au(CN)2]2, and crystals contain
pentagold units when n = 3 or polymeric pleated chains
when n = 5.
Can the rings 1 (Scheme 1) be linked to form polymers? The
complexes 1 were reacted with potassium dicyanoaurate in the
expectation that both ionic and aurophilic attractions between
the cationic and anionic gold(
) centres in 1 and [Au(CN)2]2
I
would promote association. In solution, these reactions lead to
mixtures containing the original ions and the neutral diphos-
In the context of the rapidly developing field of coordination
polymers,1 and of gold(
I
) diphosphine complexes that may have
interesting photophysical and biological properties,2 this article
reports two new one-dimensional polymers containing gold(
diphosphine units, one being the first polymer containing linear
gold( ) centres with only diphosphine ligands and the other the
phine gold( ) cyanide complexes 3 (Scheme 2) as established by
I
NMR [1H, 13C on 13CN enriched samples, 31P; complexes 3 are
2
I)
readily identified by the large coupling J(PC)].† Crystalliza-
tion from these solutions gave 3 when n = 1 or 2, but the linked
ring complex 4 when n = 3 and the novel polymer 5 when n =
5 (Scheme 2). Both 4 and 5 crystallized as the dicyanoaurate
salts and so also contain free [Au(CN)2]2 anions.‡
I
first to contain gold rings stitched together by using aurophilic
attractions.1,3 The factors that are important in giving self-
assembly of polymeric structures are elucidated.
The structures of 4 and 5 are shown in Fig. 2. In complex 4
two rings are connected by an [Au(CN)2]2 ion through
aurophilic interactions to give the unit [{Au2(m-
Ph2PCH2CH2CH2PPh2)2}2{Au(CN)2}]3+, with only one of the
The complexes of empirical formula AuX[Ph2P(CH2)nPPh2]
have been suggested to exist as ring complexes [Au2{m-
Ph2P(CH2)nPPh2}2]2+(X2)2,4 though more complex structures
may be formed in cases when the anion X2 is also a ligand to
+
two AuP2 centres of each ring involved in Au…Au bonding.
give a higher coordination number than two at gold(
I
).1,4
However, in complex 5 all the AuP2 centres are involved in
+
However, it is now shown that the derivatives with X =
CF3CO2, prepared as in Scheme 1, exist as rings 1 when n = 1,
2, 3 or 5 but as a unique polymeric chain complex 2 when n =
4.
The ring complexes 1 give sharp singlet resonances in the 31
P
NMR spectra while 2 gives several overlapping and broader
resonances.† The complexes were isolated as the trifluoro-
acetate salts, and complexes 1c and 2 were characterized by X-
ray structure determination (Fig. 1).‡
Why does complex 2 have a structure that is different from
the others? The answer is not obvious but can be analyzed in
terms of two effects. First, when n = 1 or 2, the ring structure
is favored because transannular Au…Au attractions are possi-
ble1–4 and this effect is dominant in these cases. Second, there
is a relative preference for the anti, rather than syn, orientation
of the two PPh2 groups, and hence formation of chains rather
than rings, when n is an even integer.1 Only when n = 4 does
Fig. 1 Structures of the cationic units in (a) the ring complex 1c and (b) the
polymeric complex 2. For clarity, thermal ellipsoids are not shown for
phenyl carbon atoms.
Scheme 1 P = PPh2.
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Chem. Commun., 2001, 1280–1281
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b103020p

compounds, how the distance between phosphorus donors is
critical in determining if the rings can be linked to give extended
structures.
We thank the NSERC (Canada) for financial support and for
a scholarship to M.-C. B. and R. J. P. thanks the Government of
Canada for a Canada Research Chair. We thank Dr M. C.
Jennings for X-ray data collection.
Notes and references
† Selected data: for 1 and 2: d(31P) in CD3OD: 1a, 38.3; 1b, 41.1; 1c, 44.3;
1d, 45.6; 2, 44.7. For 3a: d(13CN) 155.7; d(31P) 34.9. For 3b: d(13CN) 155.9
[J(PC) 132 Hz]; d(31P) 33.5. For 3c: d(13CN) 157.2 [J(PC) 123 Hz]; d(31P)
31.9. For 3d: d(13CN) 157.7 [J(PC) 124 Hz]; d(31P) 35.8.
Complexes were prepared in methanol solution, NMR data were obtained
in CD2Cl2/CD3OD solution, and crystals were grown by slow diffusion of
pentane into these solutions.
‡ Crystal data: for 1c·2CH2Cl2: C60H56Au2Cl4F6O4P4, M
= 1586.61,
orthorhombic, space group Pna21, a = 22.7641(8), b = 13.3249(3), c =
19.5994(8) Å, V = 5945.1(3) Å3, Z = 4, R1 = 0.0739 and wR2 = 0.1787
for 12645 reflections with I > 2s(I) at 150 K.
For 2: C30H28AuF3O2P2, M = 736.43, monoclinic, space group Pc, a =
6.7570(1), b = 11.7756(3), c = 20.3694(5) Å, b = 93.629(1)°, V =
1617.50(6) Å3, Z = 2, R1 = 0.0752 and wR2 = 0.2057 for 8807 reflections
with I > 2s(I) at 300 K.
Scheme 2 P = PPh2.
For 3a: C27H22Au2N2P2, M = 830.34, monoclinic, space group C2/c, a
= 22.039(1), b = 7.4488(3), c = 18.3838(6) Å, b = 122.193(2)°, V =
2554.0(2) Å3, Z = 4, R1 = 0.0364 and wR2 = 0.0883 for 3723 reflections
with I > 2s(I) at 200 K.
For 3b: C28H24Au2N2P2, M = 844.36, monoclinic, space group P21/n, a
= 12.597(1), b = 11.4020(9), c = 19.258(1) Å, b = 108.34(6)°, V =
2625.5(4) Å3, Z = 4, R1 = 0.0641 and wR2 = 0.1676 for 4262 reflections
with I > 2s(I) at 298 K.
For 4: C58H52Au4N4P4, M = 1716.78, monoclinic, space group P21/n, a
= 26.860(1), b = 17.425(1), c = 28.026(1) Å, b = 96.439(4)°, V =
13034(1) Å3, Z = 10, R1 = 0.1357 and wR2 = 0.3699 for 15165 reflections
with I > 2s(I) at 200 K.
For 5: C62H60Au4N4P4, M = 1772.89, monoclinic, space group P21/c, a
= 13.7149(3), b = 25.056(1), c = 19.4449(8) Å, b = 97.46(2)°, V =
6625.5(4) Å3, Z = 5, R1 = 0.0561 and wR2 = 0.1633 for 13231 reflections
with I > 2s(I) at 296 K.
CCDC 164205–164210. See http://www.rsc.org/suppdata/cc/b1/
b103020p/ for crystallographic data in CIF or other electronic format.
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Fig. 2 Structures of the linked ring complex cations in (a) complex 4 and (b)
complex 5. The parameters corresponding to aurophilic attractions are: for
complex 4, Au(1)–Au(5) 3.059(3) Å, Au(2)–Au(5) 3.034(3) Å; Au(1)–
Au(5)–Au(2) 172.1(1)°. For complex 5, Au(1)–Au(4) 2.9906(8), Au(2)–
Au(4) 3.0665(8) Å, Au(1)–Au(4)–Au(2) 165.26(3)°.
Au…Au bonding and so the pleated-chain polymeric structure
[{Au2[m-Ph2P(CH2)5PPh2]2}2{Au(CN)2}2]x2x+ results. By in-
spection of Fig. 2, it is immediately clear that the structure
observed for 5 would not be possible for 4 because the
transannular Au…Au distance is too short to allow both gold
atoms to be linked to approximately collinear [Au(CN)2]2
units. Phenyl–phenyl repulsions prevent bridging in other ways
to link units of 1a, 1b or 1c.
The complexes 4, 2 and 5, as the dicyanoaurate salts, give
rather similar solid state emission spectra, with maxima at 419,
414 and 411 nm, respectively. This indicates that the extended
structures present in 2 (n = 4) and 5 (n = 5) do not greatly
affect the photophysical properties of the complexes, when
compared to the more limited association in 4.
The ability to control the self-assembly of extended structures
is becoming increasingly important. This article shows how
conformational differences in simple, commonly used diphos-
phine ligands can be used to control whether ring or polymeric
structures will be formed in gold( ) complexes and, for the ring
I
Chem. Commun., 2001, 1280–1281
1281