Synthesis, characterization, and properties of binuclear gold(I) phosphine alkynyl complexes

Article abstract of DOI:10.1021/om1000919

Reactions of gold salts with various π-conjugated dialkynes have led to two homologous series of binuclear alkynylgold(I) complexes, linear rigid-rod Cy₃PAu-C≡C-(CH=CH)_n-C≡C-AuPCy₃ (n = 1-3, all-trans) (2a-c) and photochromic LAu-C≡C-DTE-C≡C-AuL (DTE = 1,2-di(2-methylthien-3-yl)cyclopentene or 1,2-di(2-methylthien-3-yl)-3,3,4,4,5, 5-hexafluorocyclopentene) (L = PCy₃, tricyclohexylphosphine or PPh₃, triphenylphosphine) (4a-d). The photophysical properties of these complexes have been investigated. The emission spectra exhibited a progressive red-shift with increasing length of the bridge between the two Au(I) in the linear metal complexes 2. Photochromic alkynylgold(I) complexes 4 also exhibited fluorescence properties, and the emission wavelength was found to change upon variation of the dithienylethene (DTE) linkers as well as of the auxiliary phosphine ligands. It is revealed that the binuclear alkynylgold complexes with DTE units show photochromic behavior and that the efficiencies of the photochromic processes and conversions from the open- to the closed-ring isomers in the photostationary state (PSS) are greatly improved upon the introduction of gold. The photochromic process was also found to show complete reversibility, with restoration of the luminescence and NMR signals upon exposure to visible light.

Full text of DOI:10.1021/om1000919

2808 Organometallics 2010, 29, 2808–2814
DOI: 10.1021/om1000919
Synthesis, Characterization, and Properties of Binuclear Gold(I)
Phosphine Alkynyl Complexes
Yan Lin, Jun Yin, Jingjing Yuan, Ming Hu, Ziyong Li, Guang-Ao Yu, and Sheng Hua Liu*
Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry,
Central China Normal University, Wuhan 430079, P.R. China
Received February 4, 2010
Reactions of gold salts with various π-conjugated dialkynes have led to two homologous series of
binuclear alkynylgold(I) complexes, linear rigid-rod Cy3PAu-CꢀC-(CHdCH)n-CꢀC-AuPCy3
(n=1-3, all-trans) (2a-c) and photochromic LAu-CꢀC-DTE-CꢀC-AuL (DTE = 1,2-di(2-
methylthien-3-yl)cyclopentene or 1,2-di(2-methylthien-3-yl)-3,3,4,4,5,5-hexafluorocyclopentene)
(L=PCy3, tricyclohexylphosphine or PPh3, triphenylphosphine) (4a-d). The photophysical proper-
ties of these complexes have been investigated. The emission spectra exhibited a progressive red-shift
with increasing length of the bridge between the two Au(I) in the linear metal complexes 2.
Photochromic alkynylgold(I) complexes 4 also exhibited fluorescence properties, and the emission
wavelength was found to change upon variation of the dithienylethene (DTE) linkers as well as of the
auxiliary phosphine ligands. It is revealed that the binuclear alkynylgold complexes with DTE units
show photochromic behavior and that the efficiencies of the photochromic processes and conversions
from the open- to the closed-ring isomers in the photostationary state (PSS) are greatly improved
upon the introduction of gold. The photochromic process was also found to show complete
reversibility, with restoration of the luminescence and NMR signals upon exposure to visible light.
Introduction
nature make the rigid metal alkynyl moiety an attractive and
promising candidate for the construction of linear-chain
metal-containing materials, which may possess unique prop-
erties such as electrical conductivity,2-4 liquid-crystalline
properties,5 or nonlinear-optical behavior.6 Among these,
alkynylgold(I) complexes, especially those with tertiary
phosphine ligands, have received much attention, not only
due to their stability and ease of preparation but also because
of their rich photophysical properties.7,8
Conjugated bimetallic acetylide complexes are attracting
considerable current interest1 because of their potential
applications in many areas of material science. The linear
geometry of the alkynyl unit together with its π-unsaturated
*To whom correspondence should be addressed. E-mail: chshliu@
mail.ccnu.edu.cn.
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pubs.acs.org/Organometallics
Published on Web 05/28/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 12, 2010 2809
Scheme 1
In recent years, much attention has been paid to the
bimetallic complexes, obtained upon irradiation with UV light,
have extended π-conjugated systems similar to that of {Au}-
(μ-CꢀC-(CdC)4-CꢀC)-{Au} (Scheme 1). To better under-
stand their luminescence behavior, the analogous bimetallic
polyenediyl complexes {Au}-(μ-CꢀC-(CdC)n-CꢀC)-
{Au} (n = 1, 2, 3) have also been synthesized and have been
found to exhibit rich photophysical behavior. The properties of
all of the complexes have been compared in detail in order to
probe the effects of the various linking units and phosphine
auxiliaries.
switching of physical properties by using appropriate stimuli
to obtain functional materials.9 Chromism is regarded as an
effective switching mechanism. Application of simple stimuli
such as light or electricity to chromic compounds brings
about changes of their structures, which eventually affect
their physicochemical properties. Dithienylethene (DTE)
derivatives are recognized as highly efficient organic photo-
chromism compounds with respect to such features as fast
response and fatigue resistance.10 Because metal-coordina-
tion complexes provide their own diverse assortment of
photophysical and electrochemical characteristics, the com-
bination of a DTE system with a metal ion should facilitate
such application of switching devices.11 In our previous
work, we constructed a photoswitchable organometallic
molecular wire by combining a DTE unit with a redox-active
ruthenium metal center. It was found that binuclear ruthe-
nium vinyl complexes with dithienylethene units exhibited
switching behavior triggered by either photochemical or
electrochemical stimuli.12
Despite numerous studies on the luminescence of alkyny-
lgold(I) species, to the best of our knowledge there have not
hitherto been any reports of such systems incorporating a DTE
unit in the main skeleton. Inspired by recent reports on the
successful development of new photochromic materials that
combine metals and dithienylethene moieties, we considered it
an attractive goal to synthesize new gold(I) complexes with
photoswitchable dithienylethene linkers. Herein, we report the
first examples of binuclear alkynylgold(I) complexes
{Au}-( μ-CꢀC-DTE-CꢀC)-{Au} containing dithieny-
lethene. It is revealed that these complexes show photochromic
behavior and that the efficiencies of their photochromic
processes and conversions of the open-ring to the closed-ring
isomers in the photostationary state (PSS) are greatly im-
proved by the introduction of the metal. The luminescent
properties of these complexes have been found to be perturbed
by exposure to UV and visible light. The closed isomers of the
Results and Discussion
Synthesis and Characterization. The ligand precursors poly-
enediynes 1a,4b 1b,4a and 1c,4d and the photochromic terminal
diacetylenes 3a12 and 3b13 were prepared according to the
previously reported procedures. Scheme 2 outlines the general
synthetic route used to obtain the binuclear alkynylgold(I)
complexes. The precursor diacetylene ligands were used to
form binuclear alkynylgold(I) complexes by the classical dehy-
drohalogenation reaction between alkynes and chlorogold(I)
phosphine complexes in the presence of a base.14 Treatment of
diacetylenes HCꢀC-(CdC)n-CꢀCH (n = 1-3, all-trans)
and HCꢀC-DTE-CꢀCH with 2 equiv of [AuCl(L)] in the
presence of excess NaOH in MeOH solution gave the desired
complexes as air-stable solids inhigh purity. The products were
found to be highly soluble in chlorinated solvents such as
CH2Cl2. All of the newly synthesized alkynylgold(I) complexes
1
were characterized by H and 31P{1H} NMR spectroscopies
and gave satisfactory elemental analyses. The structure of 2a
was also verified by X-ray crystallography (Figure 1).
The 31P NMR spectrum of 2a displays a sharp singlet at δ =
56.63 ppm, which is slightly downfield from that of Au(PCy3)Cl
(δ = 54.46 ppm), indicating a symmetrical arrangement of
PAuCꢀC groups in solution. The 1H NMR spectrum in CD2Cl2
shows a singlet at δ=5.84 ppm, characteristic of an alkenic H.
The 13C NMR spectrum in CD2Cl2 features two doublets at δ=
144.90 ppm (2JPC = 131.9 Hz) and δ = 102.75 ppm (3JPC
=
24.4 Hz), attributable to the R- and β-acetylide carbon atoms of
AuCꢀC, respectively. The other complexes (2b, 2c) display
similar chemical shifts in their spectra, in accordance with those
of other previously reported alkynylgold(I) complexes.7c-f
Several related photochromic alkynylgold(I) complexes 4
have similar NMR spectral properties to those of the above
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Organometallics. 2009, 28, 6402.

2810 Organometallics, Vol. 29, No. 12, 2010
Lin et al.
Figure 1. Molecular structure of 2b.
Scheme 2
linear rigid-rod alkynylgold(I) species. The 31P NMR spectra
of 4a-d each feature a sharp singlet at δ = 56.11, 40.73,
56.12, and 41.69 ppm, respectively. The presence of the DTE
phosphine analogues, R3PAu-CꢀC-AuPR3 (R = Ph,15
NpPh2,16 Np2Ph,17 Cy7c). The longer Au-P bond distances
compared to those in the chlorogold phosphine complexes are
in line with the higher trans influence of the alkynyl group.18
Compound 2a contains a trans carbon-carbon double bond
(C(21)-C(21a)); the C(21a)-C(21)-C(20) angle is 133.4(16)°,
which is larger than the corresponding angles in the (CH)n-
bridged binuclear metallic complexes [RuCl(CO)(PMe3)3]2-
( μ-(CHdCH)n) (n = 4 (125.8°),3d n = 5 (125.5°)4d).
Electronic Absorption and Emission Spectroscopy of Linear
Rigid-Rod Alkynylgold(I) Complexes. The electronic absorp-
tion and emission data of complexes 2a-c are summarized in
Table 3, while Figure 2 shows their respective absorption
spectra in dichloromethane at 298 K. They all exhibit three
absorption peaks with similarly structured absorption bands
at lower energies, which may be assigned as metal-perturbed
intraligand (IL) [πfπ*(CꢀC)] transitions with some metal-
to-ligand charge-transfer (MLCT) character. These bands are
significantly red-shifted compared to those of the free poly-
enediyl derivatives Me3SiCꢀC-(CHdCH)n-CꢀCSiMe3
(n=1, 2, 3) (1a, <312 nm; 2a, <322nm;3a, < 352 nm), presu-
mably due to perturbation from the Au-C interactions. In the
homologous series of Cy3PAu-CꢀC-(CHdCH)n-CꢀC-
AuPCy3 (n = 1, 2, 3, all-trans), the corresponding absorption
bands are bathochromically shifted with increasing extent of
π-conjugation along the main chain, which will cause a narrow-
ing of the πfπ* energy gap.
1
unit is indicated by the H and 13C NMR spectra, which
feature characteristic singlet signals for the thiophene and
methyl moieties in CDCl3 solution.
X-ray Structure of 2a. The molecular structure of Cy3PAu-
CꢀC-CHdCH-CꢀC-AuPCy3 (2a) is depicted in Figure 1.
The crystallographic details and selected bond distances as
well as angles are given in Tables 1 and 2, respectively. As
shown in Figure 1, the C-Au-P and Au-C-C dihedral
angles are 177.6(3)° and 171.1(9)°, respectively, which in-
dicate linear geometry, typical of the sp hybridization found
in alkynylgold(I) complexes. The CꢀC bond length is
˚
1.181(11) A, and this bond length, along with those of the
˚
˚
Au-C (2.018(8) A) and Au-P (2.2807(18) A) bonds,
are comparable to those observed in other alkynylgold(I)
(15) Bruce, M. I.; Grundy, K. R.; Liddell, M. J.; Snow, M. R.;
Tiekink, R. T. J. Organomet. Chem. 1988, 344, C49–C52.
(16) Muller, T. E.; Choi, S. W. K.; Mingos, D. M. P.; Murphy, D.;
Williams, D. J.; Yam, V. W. W. J. Organomet. Chem. 1994, 484, 209.
(17) Muller, T. E.; Mingos, D. M. P.; Williams, D. J. J. Chem. Soc.,
Chem. Commun. 1994, 1787.
(18) (a) Angermaier, K.; Zeller, E.; Schmidbaur, H. J. Organomet.
Chem. 1994, 472, 371. (b) Assefa, Z.; McBurnett, B. G.; Stables, R. J.;
Fackler, J. P., Jr.; Assmann, B.; Angermaier, K.; Schmidhaur, H. Inorg.
Chem. 1995, 34, 75. (c) M€uller, T. E.; Green, J. C.; Mingos, D. M. P.;
McPartlin, C. M.; Whittingham, C.; Williams, D. J.; Woodroffe, T. M.
J. Organomet. Chem. 1998, 551, 31.

Article
Organometallics, Vol. 29, No. 12, 2010 2811
Table 1. Crystal Data, Data Collection, and Refinement
Parameters for 2a
Table 3. Electronic Absorption and Emission Data for
Compounds 2
2a
absorptiona λmax/nm
excitation
λmax/nm
emissionb
max/nm
compd
(ε /104 L mol-1 cm-1
)
λ
formula
fw
C
42H68Au2 P2
1028.84
293(2) K
triclinic
2a
2b
2c
292(2.74), 308(4.72), 326(6.26)
316(2.73), 336(5.18), 355(6.31)
342(3.77), 360(6.32), 381(6.75)
300
355
379
344, 356
367, 385, 409
404, 424, 450
temp (K)
cryst syst
space group
P2(1)/c
a All absorption spectra were recorded in CH2Cl2 at 298 K. [2] = 2 ꢁ
˚
a (A)
9.4064(9)
9.9279(9)
12.4727(11)
109.6070(10)
103.1490(10)
100.197(2)
1026.90 (16)
1
10-5 mol L-1 b Measured in CH2Cl2 at 298 K.
.
˚
b (A)
3
˚
c (A)
R (deg)
β (deg)
γ (deg)
-3
˚
V (A
Z
)
Dcalcd (g cm-3
)
1.664
0.40 ꢁ 0.20 ꢁ 0.10
cryst size (mm)
F(000)
508
KappaCCD
diffractometer
radiation
Mo KR
7.240
1.82-27.00
-10 to 12, -12 to 10, -15 to 14
4022
abs coeff (mm-1
θ range (deg)
hkl range
)
total no. of rflns
no. of unique rflns
no. of obsd rflns (I > 2σ(I)
no. of restraints/params
a, b, for Wa
final R
Rw
3503
3104
3/360
0.0221, 0.0000
0.0350
0.0856
Figure 2. Absorption spectrum of (Cy3P)AuCꢀC-(CHdCH)n-
CꢀCAu(PCy3) (2) in CH2Cl2 solution at 298 K. ([2] = 2.0 ꢁ 10-5
mol dm-3; red, 2a; green, 2b; black, 2c).
R (all data)
Rw (all data)
0.0391
0.0872
0.965
1.302, -1.304
Figure 3 shows the absorption spectral changes of com-
pounds 3b and 4c. Upon illumination at a wavelength of 302
nm, the solutions of 3b and 4c in dichloromethane reached a
photostationary state, whereby the colorless solutions of the
open-ring isomers turned purple and dark blue, respectively,
showing new bands at 379 and 577 nm (for 3b) and at 385 and
601 nm (for 4c). These colored solutions were bleached by
subsequent irradiation with visible light (λ > 420 nm), owing
to the compounds reverting to their original open-ring states.
As is evident from Table 4, the absorption maxima of the
open-ring and closed-ring forms were dependent on the
central switching units at the reaction centers. The closed
isomers of the hexahydro switches (4a, 4b) turned dark red,
while the hexafluoro switches (4c, 4d) became dark blue upon
UV irradiation. This was because the absorption maxima of the
hexafluoro compounds were bathochromically shifted to the
region 601-605 nm, while those of the hexahydro compounds
were only shifted to 530-536 nm. Different ancillary phosphine
ligands did not cause notable shifts of the absorption maxima
of the open-ring and closed-ring forms. The photochromic
process was reversible, and no apparent deterioration of 4c was
observed after repeating the process several times (Figure 4).
The photochromic alkynylgold(I) complexes also exhibited
fluorescence in CH2Cl2 solutions. In each case, the emission
energy was found to change upon variation of both the linking
moieties and the auxiliary phosphine ligands. Table 4 shows the
emission data for complexes 4a-d at 298 K. The emission
wavelengths of the hexafluoro compounds (4c, 4d) are longer
than those of their hexahydro analogues (4a, 4b). The emissions
of 4a and 4c are also red-shifted relative to those of 4b and 4d,
which can be rationalized by the fact that the PCy3 ligand is
electron-donating in nature and renders the Au(I) center more
electron-rich. The fluorescence intensity decreased along with
the photochromism on going from the ring-opened to the ring-
closed form upon irradiation at 302 nm, as shown in Figure 5.
The obvious emission quench at the photostationary state
(PSS) may be attributed to the formation of the closed isomers.
goodness of fit/F2
largest diff peak, hole (e A
-3
˚
)
a W = 1/[σ2(Fo)2 þ (aP)2 þ bP], where P = (Fo þ Fc2)/3.
2
Table 2. Selected Bond Lengths and Bond Angles of Complex 2a
˚
bond length (A)
˚
bond length (A)
Au(1)-C(19)
Au(1)-P(1)
C(19)-C(20)
P(1)-C(13)
2.018(8)
P(1)-C(1)
P(1)-C(7)
C(20)-C(21)
C(21)-C(21a)
1.861(8)
1.864(8)
1.386(13)
1.25(2)
2.2807(18)
1.181(11)
1.835(9)
bond angle
(deg)
bond angle
(deg)
C(19)-Au(1)-P(1)
C(19)-C(20)-C(21) 178.1(13) C(21a)-C(21)-C(20) 133.4(16)
177.6(3)
C(20)-C(19)-Au(1) 171.1(9)
At 298 K, all of the polyenediyl-linked metal complexes
display a fluorescence peak near 400 nm in CH2Cl2 solution,
characterized by the small Stokes shift between the bands in the
absorption and the emission spectra. The emission wavelengths
of the compounds are bathochromically shifted with increasing
value of n because of the higher degree of π-conjugation.
Photochromic Behavior of the DTE Complexes. The photo-
physical data of the photochromic compounds 3a, 3b, and
4a-d measured in CH2Cl2 are shown in Table 4. All of the
synthesized dithienylethene compounds 3 and 4 were found
to undergo reversible photochromic reactions upon alter-
nating irradiation with UV light (302 nm) and visible light
(λ > 420 nm) by using cutoff filters. All of the metal complexes
display similarly structured absorption bands, both in the open
and closed forms. We find that the position of the absorption
band shows a bathochromic shift after coordination of the
metal entities to form the alkynylgold(I) complexes. These
observations are consistent with increased π-delocalization
through the metal groups due to metal-to-ligand back-donation
to the π* orbital.

2812 Organometallics, Vol. 29, No. 12, 2010
Lin et al.
Table 4. Electronic Absorption, Quantum Yields, Conversions (PSS) for Photochromic Compounds 3, 4
absorptiona λmax/nm (ε/104 L mol-1 cm-1 Φb
)
conversionc
(open f closed) (%)
compd
open
closed
Φo-c
Φc-o
3a
262(3.08)
260(3.50)
340(0.84)
518(0.89)
379(0.38)
577(0.40)
349(1.39)
530(1.63)
355(1.74)
536(2.25)
385(1.40)
601(2.10)
387(1.29)
605(1.99)
0.49
0.045
50
3b
4a
4b
4c
4d
0.39
0.61
0.78
0.41
0.72
0.012
0.0063
0.040
0.0096
0.011
78
92
284(3.22) 305(3.02) 320(2.95)
275(4.00) 288(4.07) 312(3.88)
283(4.47) 297(5.27) 312(4.85)
301(4.93) 316(4.72)
85
95
>95
a All absorption spectra were recorded in CH2Cl2 at 298 K. C = 2 ꢁ 10-5 mol L-1
.
b Quantum yields of cyclization (Φo-c) and cycloreversion
3
(Φc-o). c Determined by 1H NMR in CDCl3.
Figure 3. UV-vis spectral changes upon 302 nm light irradiation (observed in CH2Cl2, 2.0 ꢁ 10-5 mol dm-3). (a) 3b; (b) 4c.
Figure 4. Reversible photochromism of 4c monitored by
UV-vis spectroscopy ([4c] = 2.0 ꢁ 10-5 mol/L; alternating
UV (20 S) and visible light (3 min) irradiations) in air atmo-
sphere at room temperature.
The blue fluorescence of the solution could be recovered by
using visible light to induce the formation of the open-ring
isomers.
Figure 5. Emission spectral changes of compound 4b upon UV
and Vis light irradiation.
The photochromic behavior of the binuclear alkynylgold-
(I) complexes (4a-d) and their corresponding diacetyl pre-
cursors (3a, 3b) was examined by means of NMR
spectrometry. The ratios between the closed and open iso-
mers at the photostationary state were measured from the 1H
NMR spectra. The characteristic shifts of their Me and
groups attached to the thiophene rings appeared at δ = 1.73
ppm for 4cO and δ = 2.06 ppm for 4cC, and the 1H NMR
signal of the protons attached to the thiophene rings ap-
peared at δ = 7.17 ppm for 4cO and δ = 6.29 ppm for 4cC.
Thus the chemical shift of the protons on the thiophene rings
appeared at higher field compared to that in the case of 4cO,
while the chemical shift of the methyl protons appeared at
lower field, in accordance with our previous report.12 Similar
shift changes have also been observed in the 1H NMR
spectra of other dithienylethene compounds (Table 5). The
1
thiophene groups were observed in the H NMR spectra
(CDCl3, 1.0 ꢁ 10-2 mol dm-3). Irradiation with UV light
caused the appearance of a new set of singlets with the
concomitant disappearance of the singlets of the original
state. As shown in Figure 6, the 1H NMR signal of the methyl

Article
Organometallics, Vol. 29, No. 12, 2010 2813
Table 6. 1H NMR Chemical Shifts of Opened and Closed-Ring
Isomers for 3, 4
open
δthiophene-H
closed
δthiophene-H
compd
δMe
δMe
3a
3b
4a
4b
4c
4d
1.89
1.90
1.71
1.76
1.73
1.79
6.97
7.24
6.92
6.95
7.17
7.18
1.95
2.13
1.97
1.94
2.06
2.10
6.18
6.45
6.01
6.05
6.29
6.32
Figure 7. Visible absorption changes of 3b, 4c, and 4d upon UV
light irradiation. The absorptions were monitored at the max-
ima of the visible absorptions (3bO, 577 nm; 4cO, 601 nm; 4dO,
605 nm).
were summarized in Table 4. These values were evaluated by
the standard procedure using 1,2-bis(2-methyl-5-phenyl-3-
thienyl)perfluorocyclopentene as a standard.19 The photocy-
clization quantum yield of 3a in CH2Cl2 solution was 0.49(302 nm)
at room temperatue. When the metal groups attached to the
reaction centers, the photocyclization quantum yields in-
creased to 0.61 for 4a and 0.78 for 4b. The same promotion
in the cyclization quantum yields was also observed for
hexafluoro systems. However, the values of the photocyclor-
eversion quantum yields were irregular. It is worth noting that
the efficiencies of the cyclization and cycloreversion were also
dependent on the metalation. As can be seen from Figure 7,
the ring-closing rates for 3b, 4c, and 4d were comparable, but
the metal complexes 4 reached photostationary states more
efficiently than the free DTE molecules 3 (i.e., ca. 60 s for 3b;
ca. 20 s for 4c and 4d). However, more significant differences
were observed for the reverse ring-opening process, whereby
the metal complexes 4 reverted to their open isomers more
slowly than the metal-free species (i.e., ca. 2 min for 3b and
within3 min for4cand4d). Itis notable thatdifferent ancillary
phosphine ligands (Ph or Py) had little effect on the efficiency
of this conversion. A similar tendency was also observed upon
comparison of the photochemical efficiencies of 4a and 4b
with that of 3a. This suggests that metalation has a significant
impact on the stability of the ring-closed isomers, in accor-
dance with the findings of Akita’s11i and our group12 on how
different metal species influence the efficiencies of cyclization
and cycloreversion.
Figure 6. 1H NMR spectral changes upon 302 nm light irradia-
tion (observed in CDCl3). (a) 3b; (b) 4c (* methyl signal).
Table 5. Excitation and Emission Data for Photochromic
Compounds 3, 4
excitation
max/nm
emissiona
max/nm
excitation
λ
emissiona
nm
/
max
compd
λ
λ
compd
max/nm
3a
364
409, 432
3b
343
378, 397,
419, 444
395, 422
398, 442
4a
4c
368
385
416, 433
436, 460
4b
4d
350
352
a All absorption spectra were recorded in CH2Cl2 at 298 K, C = 2 ꢁ
10-5 mol L-1
.
3
31P NMR signal appears as the same sharp singlet in both the
open-ring and closed-ring isomers, indicating that the spacer
has little effect on the environment of the phosphine.
As shown in Table 4 and Figure 6, the photocyclization
1
yield of 3bC from 3bO was 78% according to H NMR
analysis, while the yields of 4cC and 4dC from their corre-
sponding open-ring isomers were improved to 95% (Table
6). Similar promotion was also observed for their hexahydro
counterparts (from 50% (3a) up to 92% (4a) and 85% (4b)).
The higher photocyclization yields of the metal alkynyl
complexes can be ascribed to the metalation.
Metalation led to notable differences both in the photo-
cyclization yields and quantum yields compared with those of
the free DTE alkynes. The quantum yields of the photocycli-
zation and photocycloreversion reaction of these compounds
(19) Irie, M.; Lifka, T.; Kobatake, S.; Kato, N. J. Am. Chem. Soc.
2000, 122, 4871.

2814 Organometallics, Vol. 29, No. 12, 2010
Lin et al.
Conclusions
2c: Yield, 0.050 g, 46%. Anal. Calcd for C46H72P2Au2: C,
51.11; H, 6.71. Found: C, 51.09; H, 6.20. 1H NMR (400 MHz,
CD2Cl2): δ 1.21-1.97 (m, 66 H, Cy), 5.64 (d, 2H, J (HH) =
15.2 Hz, ꢀCCHdCH), 6.13 (m, 2H, ꢀCCHdCHCHd), 6.36
(m, 2H, ꢀCCHdCHCHd). 31P NMR (160 MHz, CDCl3): δ
56.62 (s). 13C NMR (100 MHz, CD2Cl2): δ 26.22, 27.37, 31.02,
103.49, 114.68, 133.34, 139.56, 146.29.
General Synthesis of Compounds LAu-CꢀC-DTE-CꢀC-
AuL (4). The terminal diacetylene 3 (0.11 mmol) was dissolved in
an anhydrous methanol (10 mL) under nitrogen. This solution
was added to the dry THF solution (10 mL) of AuClL (0.20 mmol),
and the mixture was stirred at room temperature. The methanol
solution (5 mL) of NaOH (200 mg, 0.5 mmol) was added
dropwise to the mixture. After 2 h, a precipitate (4a, 4b, light
red; 4c, 4d, light blue) appeared in the solution. The precipitate
was collected by filtration with a suction filter and washed with
MeOH, H2O, and ether successively. The powder was dried
under vacuum for 2 h.
Two new series of binuclear alkynylgold(I) complexes,
linear rigid-rod and photochromic complexes, have been
successfully synthesized and structurally characterized. The
complexes have been shown to exhibit photoluminescence
properties, and the emission wavelength was found to
change upon variation of the linkers as well as of the
auxiliary phosphine ligands. Photochromic alkynylgold(I)
complexes show reversible photochromic behavior; the
efficiencies of their photochromic processes and conversions
from the open- to the closed-ring isomers in the photosta-
tionary state (PSS) are greatly improved by the introduction
of gold.
Experimental Section
4a: Yield, 0.080 g, 63%. Anal. Calcd for C55H80Au2P2S2: C,
52.38; H, 6.39. Found: C, 52.65; H, 6.63. 1H NMR (400 MHz,
CDCl3): δ 1.26-1.99 (m, 74 H, Cy, CH3, CH2), 2.69 (t, J = 7.4
Hz, 4 H, CH2), 6.92 (s, 2 H, thiophene-H). 31P NMR (160 MHz,
CDCl3): δ 56.11 (s). 13C NMR (100 MHz, CDCl3): δ 13.70
(CH3), 22.55, 26.75, 27.19, 30.56, 32.73, 38.71, 96.50, 121.07,
131.86, 132.34, 133.80, 134.44, 135.04, 139.97, 141.27.
4b: Yield, 0.088 g, 72%. Anal. Calcd for C55H44Au2P2S2: C,
53.93; H, 3.62. Found: C, 53.76; H, 3.53. 1H NMR (400 MHz,
CDCl3): δ 1.76 (s, 6 H, CH3), 1.97-2.01 (m, 2 H, CH2), 2.71 (t,
J = 7.4 Hz, 4 H, CH2), 6.95 (s, 2 H, thiophene-H), 7.45-7.57 (m,
30 H, Ph). 31P NMR (160 MHz, CDCl3): δ 40.73 (s). 13C NMR
(100 MHz, CDCl3): δ 14.26 (CH3), 22.60, 38.71, 96.56, 120.62,
129.03, 129.31, 131.52, 132.37, 133.89, 134.33, 135.12.
General Materials. All manipulations were carried out under
a nitrogen atmosphere by using standard Schlenk techniques unless
otherwise stated. Solvents were distilled under nitrogen from
sodium-benzophenone (diethyl ether, THF) or calcium hydride
(dichloromethane). Triethylamine were freshly distilled over KOH
pellets. The starting materials TMS-CꢀC-(CHdCH)n-CꢀC-
TMS (n= 1,2,3),4b,a,d [(R3P)AuCl],20,21 1,2-bis(5-ethynyl-2-methyl-
thiophen-3-yl)cyclopentene (3a),12 and 1,2-bis(5-ethynyl-2-methyl-
thiophen-3-yl)perfluorocyclopentene (3b)13 were prepared according
to literature methods. Elemental analyses (C, H, N) were
performed by the Microanalytical Services, College of Chem-
istry, CCNU. 1H, 13C, and 31P NMR spectra were collected on
American Varian Mercury Plus 400 spectrometer (400 MHz).
1H and 13C NMR chemical shifts are relative to TMS, and 31
P
4c: Yield, 0.12 g, 88%. Anal. Calcd for C55H74Au2F6P2S2: C,
48.25; H, 5.45. Found: C, 48.06; H, 5.65. 1H NMR (400 MHz,
CDCl3): δ 1.26-1.99 (m, 72 H, Cy, CH3), 7.17(s, 2 H, thiophene-
H). 31P NMR (160 MHz, CDCl3): δ 56.12 (s). 13C NMR (100
MHz, CDCl3): δ 14.30 (CH3), 25.85, 27.09, 30.71, 33.20, 94.48,
123.83, 124.30, 130.48, 140.92, 142.46, 143.75.
NMR chemical shifts are relative to 85% H3PO4. UV-vis
spectra were obtained on U-3310 UV spectrophotometer. Fluo-
rescence spectra were recorded on a Hitachi-F-4500 fluores-
cence spectrophotometer. UV light was irradiated using ZF5
UV lamp (302 nm), and visible light irradiation (λ > 420 nm)
was carried out by using a LZG 220 V 500W tungsten lamp with
cutoff filters. The quantum yields were determined by compar-
ing the reaction yields of the diarylethenes against 1,2-bis(2-
methyl-5-phenyl-3-thienyl)perfluorocyclopentene.
General Synthesis of Compounds Cy3PAu-CꢀC-(CHdCH)n-
CꢀC-AuPCy3 (n = 1, 2, 3) (2). To a methanolic solution (30 mL)
of TMS-CꢀC-(CHdCH)n-CꢀC-TMS (n = 1, 2, 3; 0.1 mmol)
and Cy3PAuCl (0.2 mmol) was added an excess of NaOH (0.2 g,
5 mmol), and the mixture was stirred for 1 h. The brown solid was
collected by filtration. Then the brown solid washed with water,
methanol, and diethyl ether, in turn. The crude product was purified
by column chromatography (Al2O3, CH2Cl2) to give a pale-yellow
solid and dried under vacuum.
4d: Yield, 0.95 g, 71%. Anal. Calcd for C55H38Au2F6P2S2: C,
49.56; H, 2.87. Found: C, 49.38; H, 2.96. 1H NMR (400 MHz,
CDCl3): δ 1.79 (s, 6 H, CH3), 7.18 (s, 2 H, thiophene-H),
7.46-7.57 (m, 30 H, Ph). 31P NMR (160 MHz, CDCl3): δ 41.69
(s). 13C NMR (100 MHz, CDCl3): δ 14.39 (CH3), 95.14, 123.29,
124.27, 129.19, 130.66, 131.60, 134.14, 134.28, 135.43, 141.35.
Crystallographic Details for 2a. Crystals suitable for X-ray
diffraction were grown from a dichloromethane of solution 2a
layered with hexane. A crystal with approximate dimensions of
0.40 ꢁ 0.20 ꢁ 0.10 mm3 was mounted on a glass fiber for diffraction
experiment. Intensity data were collected on a Nonius Kappa CCD
˚
diffractometer with Mo KR radiation (0.71073 A) at 293 K. The
structure was solved by a combination of direct methods
(SHELXS-97) and Fourier difference techniques and refined by
full-matrix least-squares (SHELXL-97). All non-H atoms were
refined anisotropically. The hydrogen atoms were placed in the
ideal positions and refined as riding atoms. Further crystal data and
details of the data collection are summarized in Table 1.
2a: Yield, 0.051 g, 50%. Anal. Calcd for C42H68P2Au2: C,
49.03; H, 6.66. Found: C, 49.63; H, 6.19. 1H NMR (400 MHz,
CD2Cl2): δ 1.20-1.96 (m, 66 H, Cy), 5.84 (s, 2H, CHd). 31P
NMR (160 MHz, CDCl3): δ 56.63 (s). 13C NMR (100 MHz,
CD2Cl2): δ 26.23, 27.38, 31.02, 33.38, 102.75, 120.54, 144.90.
2b: Yield, 0.065 g, 61%. Anal. Calcd for C44H70P2Au2: C,
50.10; H, 6.69. Found: C, 50.04; H, 6.15. 1H NMR (400 MHz,
CD2Cl2): δ 1.12-1.99 (m, 66 H, Cy), 5.60 (m, 2H, ꢀCCHdCH),
6.34 (m, 2H, ꢀCCHdCH). 31P NMR (160 MHz, CDCl3): δ
56.59 (s). 13C NMR (100 MHz, CD2Cl2): δ 26.23, 27.39, 31.03,
33.40, 103.19, 114.01, 139.66, 145.43.
Acknowledgment. We acknowledge financial support
from National Natural Science Foundation of China
(nos. 20772039, 20931006)
Supporting Information Available: Spectral changes upon UV
irradiation of 4a, 4b, and 4d, and X-ray crystallographic file
(CIF) for compound 2a. This material is available free of charge
via the Internet at http://pubs.acs.org.
(20) McAuliffe, C. A.; Parish, R. V.; Randall, P. D. J. Chem. Soc.,
Dalton Trans. 1979, 1730.
(21) Cross, R. J.; Davidson, M. F. J. Chem. Soc., Dalton Trans. 1986,
411.