Gold(I) alkynyl complexes containing a flexible, biphenyl-derived bis(alkyne)

Article abstract of DOI:10.1016/j.ica.2011.03.019

2,2′-Diethynylbiphenyl was prepared in a three step sequence from commercially available 2,2′-bis(bromomethyl)biphenyl and subsequently reacted with the phosphinegold(I) complexes [AuCl(P)] (P = PEt₃, PCy₃, P^tBu₃, PPh₃, PTA) in the presence of base to give the bis(alkynyl) gold(I) complexes [(P)Au(deb)Au(P)] in good yields as air-stable solids. The compounds were fully characterized spectroscopically and the solid state structures of 2,2′-diethynylbiphenyl as well as the PEt₃ complex were determined by X-ray diffraction. Both solution and solid-state luminescence spectra of the gold complexes were recorded.

Full text of DOI:10.1016/j.ica.2011.03.019

Inorganica Chimica Acta 374 (2011) 171–174
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Gold(I) alkynyl complexes containing a flexible, biphenyl-derived bis(alkyne)
b
b,
Michael Weishäupl a, Christian Robl a, Wolfgang Weigand a, , Sebastian Kowalski , Fabian Mohr
⇑
⇑
a Institut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universität Jena, 07743 Jena, Germany
b Fachbereich C, Anorganische Chemie, Bergische Universität Wuppertal, 42119 Wuppertal, Germany
a r t i c l e i n f o
a b s t r a c t
2,20-Diethynylbiphenyl was prepared in a three step sequence from commercially available 2,20-bis(bro-
momethyl)biphenyl and subsequently reacted with the phosphinegold(I) complexes [AuCl(P)] (P = PEt3,
PCy3, PtBu3, PPh3, PTA) in the presence of base to give the bis(alkynyl) gold(I) complexes [(P)Au(de-
b)Au(P)] in good yields as air-stable solids. The compounds were fully characterized spectroscopically
and the solid state structures of 2,20-diethynylbiphenyl as well as the PEt3 complex were determined
by X-ray diffraction. Both solution and solid-state luminescence spectra of the gold complexes were
recorded.
Article history:
Available online 11 March 2011
Professor Dr. Wolfgang Kaim zum 60.
Geburtstag gewidmet.
Keywords:
Gold
Alkyne
Ó 2011 Elsevier B.V. All rights reserved.
X-ray structure analysis
Luminescence
Rotationally chiral ligand
1. Introduction
solution of compound 1 crystals suitable for X-ray diffraction
were obtained. There are two crystallographically independent
Alkynyl complexes of gold have long been investigated due to
their interesting photophysics, non-linear optical properties, liquid
crystal behavior, their application in homogenous catalysis as well
as their fascinating supramolecular architectures [1–7]. In particu-
lar, dinuclear gold complexes containing bridging bis(alkynes) are
of interest, since linking two linear Au-alkyne-Au units may lead to
enhancement of luminescence and also give rise to further inter-
esting structural features. An example of this, albeit with another
metal, is the recent report from the group of Wong who reported
the self assembly and luminescence of some platinum(II) com-
plexes containing various bis(alkynes) [8]. Given our past interest
in the structures and properties of gold alkynyl complexes
[9–14], we wished to study some gold(I) phosphine complexes
containing bis(alkynes) with a flexible biphenyl-based backbone,
the results of this study are presented herein.
molecules of 1 (Fig. 1) lying on a twofold axis which were
identified as the P- and M-enantiomers. The bond lengths and
angles in both molecules are virtually identical and are similar
to other aromatic dialkynes such as 1,4-diethynylbenzene [16] or
1,4-diethynylnaphthalene [17]. The planes of the two phenyl rings
are rotated against each other by angles of 115.2° (P-enantiomer)
and 112.7° (M-enantiomer), respectively.
H2deb reacts with two equivalents of the chlorogold(I) phos-
phine complexes [AuCl(P)] (P = PEt3, PCy3, PtBu3, PPh3, PTA) in
the presence of base to give the bis(alkynyl) gold(I) complexes
[(P)Au(deb)Au(P)] (1a P = PEt3, 1b PCy3, 1c PtBu3, 1d PPh3, 1e
PTA) in good yields as air-stable solids (Scheme 1).
Apart from the PTA (PTA = 1,3,5-triaza-7-phosphaadamantane)
derivative 1e which is insoluble in all common solvents, complexes
1a–1d were soluble in chlorinated solvents and acetone. Our expe-
rience with gold(I) complexes containing PTA has shown that in
some cases very soluble (also in water) complexes form, in other
cases they are insoluble in all common solvents [9,18,19]. Com-
pounds 1a–1d were fully characterized by spectroscopic tech-
niques and, in the case of 1a, by single crystal X-ray diffraction.
Complexes 1a–1d show singulet resonances in their 31P{1H} NMR
spectra with chemical shifts typical for alkynylgold(I) phosphine
complexes. Deprotonation of the alkyne is evident from the ab-
sence of the acetylenic proton signal in the 1H NMR spectra of com-
pounds 1a–1d as well as the disappearance of the „C–H band in
the IR spectrum of 1a–1e. In addition, the IR spectra of complexes
2. Results and discussion
2,20-Diethynylbiphenyl 1 (abbreviated here as H2deb or deb
after deprotonation) was prepared in a three step sequence from
commercially available 2,20-bis(bromomethyl)biphenyl following
the procedure by Staab [15]. By slow evaporation of an ether
⇑
Corresponding authors.
E-mail addresses: wolfgang.weigand@uni-jena.de (W. Weigand), fmohr@uni-
wuppertal.de (F. Mohr).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.03.019

172
M. Weishäupl et al. / Inorganica Chimica Acta 374 (2011) 171–174
Fig. 1. Molecular structure of compound 1. Ellipsoids show 50% probability levels and hydrogen atoms are shown as spheres with arbitrary radii.
P
2 [AuCl(P)]
NaOMe
Au
Au
P
P = PEt3 (1a), PCy3 (1b), PtBu3 (1c), PPh3 (1d), PTA (1e)
(1)
Scheme 1.
1a–1e show a shift of the C„C stretching frequency to ca.
2100 cmꢀ1, as is typically observed in gold(I) alkynyl complexes.
Given the good solubility of compounds 1a–1d in halogenated sol-
vents, we were able to also record 13C{1H} NMR spectra and could
unambiguously identify the signals from the acetylenic carbon
atoms. The signal due to the carbon atom attached to the gold atom
appears as a doublet (2JP–C of 140 (1a), 133 (1b), 129 (1c), 144 (1d)
Hz) at in the range of 138–143 ppm, whilst the other acetylenic
carbon resonance is seen at around 100 ppm as a doublet with a
linear (ca. 178°), as expected for a gold(I) compound. The two aryl
rings of the biphenyl unit are twisted by about 110° with respect to
each other, thus preventing any aurophilic AuꢁꢁꢁAu interactions
[20,21]. Furthermore, there are also no intermolecular AuꢁꢁꢁAu
interactions between adjacent molecules. Bond lengths and angles
of 1a (given in the figure caption) are typical for phosphine gold(I)
alkynyl complexes.
Room temperature luminescence spectra of gold complexes
1a–1e were recorded in solution (where possible) as well as in
the solid-state (Table 1).
3
much smaller JP–C coupling constant of 27 (1a), 25 (1b), 24 (1c),
27 (1d) Hz. The molecular structure of the PEt3 derivative 1a was
determined by single crystal X-ray diffraction (Fig. 2). 1a is situated
on a twofold axis running through the C–C single bond of the
biphenyl group. The molecule consists of the deprotonated deb
ligand bridging two Et3PAu units. The C1–Au–P angle is almost
In the case of the complexes 1a–1d, the solution emission
spectra show a broad peak around 390 nm as well as a shoulder
at ca. 430–450 nm, the position and intensity of the latter varies
with solvent. In CH2Cl2 the shoulder is more intense than in
benzene, which could be due to a stronger interaction (p–p type
Fig. 2. Molecular structure of complex 1a. Ellipsoids show 50% probability levels and hydrogen atoms are shown as spheres with arbitrary radii. Selected bond lengths (Å):
Au–P 2.272(1), Au–C1 1.998(5), C1–C2 1.197(7). Selected bond angles (°): P–Au–C1 178.3(2), Au–C1–C2 176.7(5).

M. Weishäupl et al. / Inorganica Chimica Acta 374 (2011) 171–174
173
temperature 0.10 mmol solid 2,20-diethynylbiphenyl (H2deb) was
added and the mixture stirred for 15–20 h. After this time the sol-
vent was removed and the residue extracted with CH2Cl2 and
passed through Celite. Addition of hexane precipitated the com-
plexes as pale brown to colorless solids. Using this procedure the
following complexes were prepared:
Table 1
Luminescence data for complexes 1a–1e.
a,b
kem (nm)a,b solution
kem (nm)
solid-state
c
1a
1b
1c
1d
1e
CH2Cl2 390, 442 (s)
C6H6 390, 433 (s)
CH2Cl2 387, 431 (s)
C6H6 388, 433 (s)
CH2Cl2 388, 427 (s)
C6H6 389, 429 (s)
CH2Cl2 388, 447 (s)
C6H6 390, 430 (s)
–
459
527
482
484
577
3.2. [(Et3P)Au(deb)Au(PEt3)] 1a
Pale brown solid 91% yield. 1H NMR (CD2Cl2): d 7.50 (part of
ABCD spin system, 3JHD
¼ 7:8, 4JHD
¼ 1:3 Hz, 2HD, dep), 7.41
—HC
—HB
¼ 7:7, JHA
¼ 1:4 Hz, 2HA,
3
4
a
b
c
(part of ABCD spin system, JHA
Excitation at 350 nm.
At 25 °C.
s denotes shoulder.
—HB
—HC
deb), 7.21 (part of ABCD spin system, 3JHB
¼ 7:7, 3JHB
¼ 7:4,
—HA
—HC
4JHA
¼ 1:4, 3JHC
¼ 7:8, 4JHB
¼ 1:3 Hz, 4HB,C, deb), 1.78 (m,
—HC
—HD
—HD
12H, PCH2), 1.15 (m, 18H, PCH2CH3); 13C{1H} NMR (CD2Cl2): d
4
interactions) between benzene and the complexes, thus affecting
the rotation about the biphenyl axis. This is further supported by
the fact that the intensity of the shoulder in CH2Cl2 decreases with
increasing steric bulk of the phosphine. In the solid-state, the
major broad band in the room temperature emission spectra of
all five complexes is shifted to higher wavenumbers (450–480 nm);
in complex 1e the band appears at 577 nm. The observed emission
bands may be assigned (based on comparison to similar phosphine
gold(I)alkynyl species [22,23]) to arise from a mixture of metal-
143.68, 134.16, 131.06, 127.23, 126.09, 125.12 (d, JP–C = 2.5 Hz)
2
3
deb, 141.77 (d, JP–C = 140 Hz, C„CAu), 102.31 (d, JP–C = 27 Hz,
1
C„CAu), 18.21 (d, JP-C = 33 Hz, P–C), 9.17 (P–C–C); 31P{1H} NMR
(CD2Cl2): d 37.22; IR (KBr disk): 2107 cmꢀ1
m(C„C); Anal. Calc.
for C28H38Au2P2 (830.49)%: C, 40.50; H, 4.61. Found: C, 40.50; H,
4.81%.
3.3. [(Cy3P)Au(deb)Au(PCy3)] 1b
perturbed
p–
p⁄ IL and
r
–
p⁄ MLCT states. The variation of the emis-
Colorless solid 82% yield. 1H NMR (CD2Cl2): d 7.51 (m, 2H, dep),
7.44 (m, 2H, deb), 7.21 (m, 4H, deb), 1.20–2.00 (m, 66H, PCy3);
13C{1H} NMR (CD2Cl2): d 143.56, 134.19, 131.16, 127.21, 125.95,
sion maxima depending on the nature of the phosphines can be
explained by the fact that stronger donor ligands make the gold(I)
center more electron rich, thus increasing the energy level of the
4
2
125.24 (d, JP–C = 2.7 Hz) deb, 143.24 (d, JP–C = 133 Hz, C„CAu),
3
r
(Au–P) orbital which results in a slightly lower
r
–
p⁄ emission
101.01 (d, JP–C = 25 Hz, C„CAu), 33.71, 31.26, 27.72, 26.53
energy.
(PCy3); 31P{1H} NMR (CD2Cl2): d 56.53; IR (KBr disk): 2107 cmꢀ1
In conclusion, we present here the preparation, structures and
luminescence studies of some phosphine gold(I)alkynyl complexes
containing a rotationally chiral bis(alkyne) in the backbone.
m(C„C); Anal. Calc. for C52H74Au2P2 (1155.05)%: C, 54.06; H, 6.46.
Found: C, 54.06; H, 6.62%.
3.4. [(tBu3P)Au(deb)Au(PtBu3)] 1c
3. Experimental
Colorless solid 89% yield. 1H NMR (CD2Cl2): d 7.52 (m, 4H, dep),
7.19 (m, 4H, deb), 1.48 (s, 54H, PtBu3); 13C{1H} NMR (CD2Cl2): d
All reactions were carried out under dry, oxygen free dinitrogen
using standard schlenk techniques. Solvents were dried over LiAlH4
and distilled under dinitrogen before use. 2,20-Diethynylbiphenyl
(1) was prepared following the method of Staab [15]. The gold
complexes [AuCl(P)] (P = PEt3, PtBu3, PCy3, PPh3, PTA) were pre-
pared by treating [AuCl(tht)] (tht = tetrahydrothiophene) [24] with
equimolar amounts of the phosphine. All other chemicals were
sourced commercially and used as received. 1H, 13C{1H} and
31P{1H} NMR spectra were recorded on Jeol EX 400 or Bruker
Avance 600 instruments using residual solvent signals as reference.
Mass spectra (FAB positive ion mode) were measured on a Finigan
MAT 90 spectrometer and IR spectra on a Nicolet 520 FT-IR instru-
ment as KBr disks. Luminescence spectra were measured on a
Perkin Elmer LS50B instrument. Elemental analyses were carried
out by staff of the microanalytical laboratory in house. Labels used
in the assignment of proton NMR data are shown below:
4
142.81, 133.57, 130.95, 126.65, 125.28, 124.64 (d, JP–C = 3.0 Hz)
2
3
deb, 141.73 (d, JP–C = 129 Hz, C„CAu), 101.45 (d, JP–C = 24 Hz,
C„CAu), 38.94 (d, JP–C = 17 Hz, PtBu3), 32.21 (PtBu3); 31P{1H}
1
NMR (CD2Cl2): d 92.32; IR (KBr disk): 2108 cmꢀ1
m(C„C); Anal.
Calc. for C40H62Au2P2 (998.82)%: C, 48.10; H, 6.26. Found: C,
47.71; H, 6.08%.
3.5. [(Ph3P)Au(deb)Au(PPh3)] 1d
Cream colored solid 86% yield. 1H NMR (CD2Cl2): d 7.4–7.6 (m,
34H, dep, Ph3P), 7.24 (m, 4H, deb); 13C{1H} NMR (CD2Cl2): d
4
143.73, 134.29, 131.17, 127.34, 126.37, 124.90 (d, JP–C = 2.8 Hz)
2
deb, 134.87, 132.01, 130.55, 129.65 (PPh3), 137.99 (d, JP–
3
C = 144 Hz, C„CAu), 102.69 (d, JP–C = 27 Hz, C„CAu); 31P{1H}
NMR (CD2Cl2): d 41.74; IR (KBr disk): 2114 cmꢀ1
m(C„C); Anal.
Calc. for C52H38Au2P2 (1118.76)%: C, 55.83; H, 3.42. Found: C,
55.71; H, 3.56%.
3.1. Preparation of the deb gold complexes
HC
3.6. [(PTA)Au(deb)Au(PTA)] 1e
HB
HA
HD
Cream colored solid 96% yield. IR (KBr disk): 2098 cmꢀ1
m
(C„C); Anal. Calc. for C28H32N6Au2P2 (908.47)%: C, 37.02; H,
P
Au
3.55; N, 9.25. Found: C, 36.93; H, 3.76; N, 9.41%.
Au
P
3.7. X-ray structure determination
X-ray diffraction intensities were recorded at 213 K with a Sie-
A suspension of [AuCl(P)] (0.20 mmol) in MeOH (20 mL) was
treated with sodium metal (ca. 30 mg). After ca. 30 min at room
mens P4 diffractometer using graphite monochromatized Mo K
a
radiation. An empirical absorption correction was applied for 1a

174
M. Weishäupl et al. / Inorganica Chimica Acta 374 (2011) 171–174
Table 2
Appendix A. Supplementary material
Crystallographic data data for 1 and 1a.
1
1a
CCDC 777705 and 777706 contain the supplementary crystallo-
graphic data for 1 and 1a, respectively. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
doi:10.1016/j.ica.2011.03.019.
Formula
C
16H10
C28H38Au2P2
830.46
0.2 ꢂ 0.3 ꢂ 0.4
monoclinic
C2/c
22.705(3)
10.4254(14)
15.968(2)
131.00(1)
2852.5(7)
4
Mr
202.24
Crystal size (mm3)
0.6 ꢂ 0.7 ꢂ 0.9
monoclinic
C2
10.379(2)
9.643(2)
11.895(2)
96.68(1)
1182.4(4)
4
Crystal system
Space group
a (Å)
b (Å)
c (Å)
References
b (°)
V (Å3)
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Z
Dcalcd (g cmꢀ3
)
1.136
0.064
1.934
10.400
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l
(Mo K
a
) (mmꢀ1
)
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F(0 0 0) (e)
T (K)
hkl range
424
213
ꢀ14 6 h 6 +14
ꢀ13 6 k 6 + 13
ꢀ16 6 l 6 +16
3451
3130
0.0272
148
0.0420/0.0680
2.704
1576
213
ꢀ26 6 h 6 +26
ꢀ12 6 k 6 0
ꢀ18 6 l 6 +18
5007
2517
0.0432
149
0.0400/0.0478
1.023
Reflections measured
Reflections unique
Rint
Parameters refined
R(F)/wR(|F|2) (all reflexions)
Goodness-of-fit (GOF) on |F|2
D
qfin (maximum/minimun), (e Åꢀ3
)
+0.164/ꢀ0.156
+0.721/ꢀ0.631
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and an empirical extinction correction for both compounds. The
phase problem was solved by direct methods and the structural
model was completed by subsequent difference Fourier syntheses.
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anisotropic displacement parameters [25]. Further crystallographic
details are compiled in Table 2.
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Acknowledgments
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M.W. thanks the Hanns-Seidel-Stiftung e.V. for a scholarship.
We also thank the Fonds der Chemischen Industrie for support of
this work.