Single-turn helix-coil strands stabilized by metal...metal and π-π Interactions of the alkynylplatinum(II) terpyridyl moieties in meta -phenylene ethynylene foldamers

Article abstract of DOI:10.1021/ja208444c

Dinuclear alkynylplatinum(II) terpyridyl complexes with oligomeric bridge consisting of five repeating meta-phenylene ethynylene (mPE) units have been found to exhibit a strong tendency to fold back onto themselves to form short helical strands through th

Full text of DOI:10.1021/ja208444c

ARTICLE
pubs.acs.org/JACS
Single-Turn HelixꢀCoil Strands Stabilized by Metal Metal and πꢀπ
3 3 3
Interactions of the Alkynylplatinum(II) Terpyridyl Moieties in
meta-Phenylene Ethynylene Foldamers
Sammual Yu-Lut Leung, Anthony Yiu-Yan Tam, Chi-Hang Tao, Hoi Shan Chow, and
Vivian Wing-Wah Yam*
Institute of Molecular Functional Materials (Areas of Excellence Scheme, University Grants Committee (Hong Kong)) and
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
S Supporting Information
b
ABSTRACT: Dinuclear alkynylplatinum(II) terpyridyl com-
plexes with oligomeric bridge consisting of five repeating
meta-phenylene ethynylene (mPE) units have been found to
exhibit a strong tendency to fold back onto themselves to form
short helical strands through the stabilization of Pt Pt and
3 3 3
πꢀπ interactions. The steric bulk of the terpyridine ligands and
the length of the oligomeric bridge have been found to affect the
extent of the intramolecular Pt Pt interaction that governs
3 3 3
the stabilization of the short helical strand in solution. Their folding properties via Pt Pt and πꢀπ stacking interactions have been
3 3 3
studied by 1H NMR, 2D ROESY NMR, electronic absorption, and emission spectroscopies.
’ INTRODUCTION
nucleic acids, can be mimicked by foldamers which have attracted
enormous interest in biology and nanosciences.5 The process of
folding is driven by noncovalent interactions such as hydrogen
bonding,6 metal coordination,7 and πꢀπ stacking interactions.8
meta-Phenylene ethynylene oligomers are one of the well-known
classes of foldamers with six repeating units constituting one turn
and that undergo a conformation transition from random coil to
helical strand with at least nine aromatic rings stacking together
in acetonitrile or at low temperature.5b These molecules can fold back
on themselves to enable the favorable πꢀπ interactions to occur
between the stacking aromatic repeating units to form a secondary
structure.5b Numerous examples demonstrating the utilization of
hydrogen bonding and πꢀπ stacking interactions in the stabilization
of helical conformations in the organic systems are known.5ꢀ8
Although works on the utilization of metalꢀligand coordination to
construct foldamer structures are also known,9 unlike their organic
counterparts, the reversibility of the folding process is limited due to
the presence of the strong metalꢀligand interactions. Conversely, the
For decades, there has been tremendous interest in designing
new classes of luminescent square-planar d8 platinum(II) poly-
pyridyl complexes, not only because of their intriguing spectro-
scopic and luminescence properties,1ꢀ4 but also their propensity
to exhibit metal metal interaction.1aꢀc,2aꢀ2e,3 Particularly, a
3 3 3
class of platinum(II) terpyridyl complexes was shown to exhibit
interesting polymorphism in the solid state by forming extended
linear chains or dimeric structures which governed the spectro-
scopic and luminescence properties.2,3a Recently, our group has
utilized the intermolecular self-assembly of alkynylplatinum(II)
terpyridyl moieties via Pt Pt and πꢀπ stacking interactions to
3 3 3
demonstrate a remarkable color change and luminescence en-
hancement induced by the presence of polyelectrolytes3dꢀf and
gel formation.3gꢀi On the other hand, the alkynylplatinum(II)
terpyridyl complexes have also been found to aggregate in the
presence of single-strand DNA and aptamers with the growth of a
characteristic NIR emission.3jꢀl Apart from the intermolecular
self-association, a series of dinuclear platinum(II) terpyridyl
complexes, in which the two platinum(II) units are linked through
a flexible bridge, have been demonstrated to serve as synthetic
organometallic analogues of hairpin DNA.3m Therefore, the
alkynylplatinum(II) terpyridyl system is believed to be a versatile
moiety in serving as a spectroscopic reporter as well as in
providing a control over aggregation properties for the construc-
tion of self-assembled architectures.
exploitation of metal metal interactions in stabilizing foldamers in
3 3 3
helical conformations has essentially been unexplored. In view of the
propensity of the alkynylplatinum(II) terpyridyl system to exhibit
reversible intramolecular Pt Pt and πꢀπ interactions in dinuclear
3 3 3
complexes upon introduction of external stimuli,3m it is anticipated
that such interaction may provide a driving force for the folding
process, or even stabilizing the folded structure in a helical conforma-
tion in solutions and serving as a spectroscopic reporter for the
probing of folded or unfolded state in the spectroscopic and lum-
inescence study.
Recently, there has been a growing interest in the study of
polymeric or oligomeric molecular strands that are capable of
constructing well-defined secondary conformations in molecular
architectures, especially the helix-type in solution.5ꢀ8 The for-
mation of secondary structures, for instance in proteins and
Received: September 7, 2011
Published: December 20, 2011
r
2011 American Chemical Society
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Herein, we report a series of dinuclear platinum(II)ꢀcontaining
meta-phenylene ethynylene (mPE) oligomers of various lengths, end-
capped with symmetric or unsymmetric platinum(II) terpyridine
is given in the Supporting Information. The complexes were
prepared according to modification of a literature procedure for
other related alkynylplatinum(II) terpyridine complexes.2d Com-
plexes 1ꢀ4 and 6 were synthesized by reacting the correspond-
ing meta-PEs (H-(CtC-1,3-C6H4)n-CtCH, n = 3ꢀ6) with
[(tBu3trpy)PtCl](OTf) (molar ratio 1:2 for 1ꢀ4, 1:1 for 6) in
degassed N,N-dimethylformamide containing triethylamine in
the presence of a catalytic amount of copper(I) iodide. The
unsymmetric dinuclear alkynylplatinum(II) complex 5 was pre-
pared according to the procedure similar to that described for the
symmetric species, except 6 and [(Et3trpy)PtCl](OTf) were
used in 1:1 molar ratio. The reaction mixture was stirred over-
night at room temperature. Chromatography on silica gel using
dichloromethaneꢀacetone mixture (10:1 v/v) as eluent, fol-
lowed by the diffusion of diethyl ether vapor into acetonitrile
solution gave 1ꢀ6 as yellow to orange solids. All the complexes
have been well characterized by 1H and 13C NMR, IR spectros-
copy, FAB mass spectrometry, and elemental analyses.
units (1ꢀ5) (Scheme 1). Their folding properties via Pt Pt and
3 3 3
1
πꢀπ stacking interactions have been studied by H NMR, 2D
ROESY NMR, electronic absorption, and emission spectroscopies. A
mononuclear complex (6) with five repeating mPE units has also
been synthesized for comparison studies.
’ RESULTS AND DISCUSSION
The syntheses of mPE oligomers are based on Sonogashira
coupling reactions. Detailed synthetic route for the mPE oligomers
Scheme 1. Structures of Dinuclear and Mononuclear
Alkynylplatinum(II) Terpyridyl Complexes 1ꢀ6
1
The H NMR spectra for all the complexes were studied in
both CDCl3 and CD3CN at 298 K. Interestingly, while all the
1H NMR spectra showed well-resolved sharp signals with well-
defined coupling patterns, the dinuclear complexes with five or
six repeating mPE units (3ꢀ5) in CD3CN showed signals that
are unusually upfield-shifted from those in CDCl3, suggesting the
1
presence of molecular association in CD3CN. The H NMR
spectra were found to be independent of concentration within
the concentration range of 10ꢀ3ꢀ10ꢀ5 M, suggestive of molec-
ular association that is intramolecular in nature. Variable-
temperature 1H NMR experiments were then performed, which
showed that the dinuclear complexes with five or six repeating
mPE units (3ꢀ5) displayed upfield-shifted terpyridine proton
signals upon a decrease in temperature in CD3CN (Supporting
Information Figures S1ꢀS3). Solvent titration experiments on 3
(Figure 1) also showed that in general, starting from 30%
CD3CN onward, the proton signals on both phenyl rings and
terpyridines became significantly upfield shifted. The upfield
shifts observed in the NMR spectra upon decreasing the tem-
perature or switching to a more polar solvent are attributed to
πꢀπ stacking interactions between the platinum(II) terpyridyl
moieties themselves. Similar upfield shifts have also been found
in other related systems.3m,n,8j In addition to the 1D NMR
experiment, the protons of the 40- and 4000-tert-butyl groups on
the terpyridines displayed strong NOE signals with the phenyl
Figure 1. 1H NMR spectral traces at different compositions of CD3CN in CDCl3 for 3 (5 ꢁ 10ꢀ5 M, 500 MHz, 298 K). Proton signals correspond to
the terpyridyl moiety (().
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Figure 3. (a) UVꢀvis absorption spectral traces of 3 in CH2Cl2 (6.0 ꢁ
10ꢀ5 M) with increasing CH3CN content at 298 K. The inset shows the
absorbance ratio A500 nm/A422 nm as a function of solvent compositions.
(b) UVꢀvis spectra of 3 (4.6 ꢁ 10ꢀ5 M) in CH3CN with decreasing
temperature from 353 to 293 K. The inset shows the expansion of the
UVꢀvis absorption spectra in the 430ꢀ550 nm region.
However, upon increasing the CH3CN content in CH2Cl2, the
dinuclear complex 3 with mPE pentamer showed a decrease in
the intraligand [π f π*(alkynyl)] absorption band at 338 nm
and the appearance of an absorption tail at 500 nm (Figure 3a),
whereas the mononuclear complex 6 did not show such a change
but instead showed a typical negative solvatochromism4b at
480 nm in CH3CN under similar dilute concentrations (10ꢀ5 M)
(Figure S4). To further investigate the differences in the absorp-
tion behavior of the di- and mononuclear platinum complexes,
variable-temperature UVꢀvis absorption spectroscopy on 3 and
6 was performed. Upon decreasing the temperature from 353 to
293 K in CH3CN, the UVꢀvis spectrum of 3 showed an increase
in the low-energy absorption tail (Figure 3b), similar to the ob-
servation of increasing the polarity of the solvent with increasing
acetonitrile content, while temperature has a negligible effect on
the UVꢀvis spectrum of 6 under such dilute concentration
conditions. Furthermore, the absorbance drop of the high-energy
absorption band at 338 nm is indicative of a configuration transfor-
mation of the mPE units from the transoid to the cisoid form, similar
to that reported by Moore and co-workers.5b,8a,8b,8g,8h The UVꢀvis
absorption traces of 3 (3.0 ꢁ 10ꢀ5 M) in CH2Cl2 with increasing
CH3CN content ranging from 250 to 550 nm are shown in Figure
S5. These, together with the appearance of the low-energy absorp-
tion tail typical of metalꢀmetal-to-ligand charge-transfer (MMLCT)
transition, as well as the good agreement with Beer’s law in the
concentration range of 5.94 ꢁ 10ꢀ6 to 7.43 ꢁ 10ꢀ4 M for 3 in
CH3CN (Figure S6), are suggestive of molecular self-association
that leads to the intramolecular self-assembly of the two terminal
platinum(II) terpyridyl moieties to form a single-turn helical
strand. A plot of A500 nm/A422 nm against % CH3CN in CH2Cl2
showed a sigmoidal curve, supportive of cooperative folding
1
1
Figure 2. (a) Partial Hꢀ H ROESY spectrum of 3 (3 ꢁ 10ꢀ4 M,
500 MHz, 298 K) for the tert-butyl groups on terpyridine and aryl region
in CD3CN. (b) Partial 1Hꢀ H ROESY spectrum of 3 (7 ꢁ 10ꢀ4 M, 500
1
MHz, 298 K) for the tert-butyl groups on terpyridine and aryl region in
CDCl3.
rings on mPE in the 2D ROESY NMR spectrum of 3 in CD3CN
as shown in Figure 2a, with a distance of 3.14ꢀ3.82 Å10 estimated
from the integrals of the cross-peaks. This suggested that the
platinum(II) terpyridyl moieties would have a close proximity
with the phenyl rings to self-assemble in acetonitrile. On the
contrary, these NOE signals were absent in CDCl3, in which the
molecules adopted a random coil conformation with the two
platinum(II) terpyridyl moieties being far away from each other
(Figure 2b). Therefore, it is suggested that there is a conforma-
tional change for the complexes with five or six repeating units
under different solvent and temperature environments.
In the UVꢀvis absorption study, complexes 1ꢀ6 gave pale
yellow solutions in CH2Cl2 with the intense intraligand (IL)
[π f π*] transitions of the terpyridyl and alkynyl ligands at
302ꢀ340 nm and the low-energy absorptions at 412ꢀ470 nm
assigned as metal-to-ligand charge-transfer (MLCT) [dπ(Pt) f
π*(tpy)] transitions mixed with alkynyl-to-terpyridine ligand-to-
ligand charge transfer (LLCT) [π(CtC) f π*(tpy)] character.
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Table 1. A Summary of ΔG(pure CH3CN) for Complexes
3ꢀ5
complexes
ΔG/kcal molꢀ1
3
4
5
ꢀ2.3 ( 0.1
ꢀ1.2 ( 0.2
ꢀ3.3 ( 0.2
Figure 5. Fraction of fold against percentage of CH3CN in CH2Cl2 for
3ꢀ5.
concentration range of 10ꢀ6 to 10ꢀ4 M, disfavoring the possible
involvement of an association that is intermolecular in nature.
The ΔG(CH3CN) values of 3ꢀ5 are summarized in Table 1 and
the plots of the fraction of fold versus solvent composition for
3ꢀ5 are shown in Figure 5.
Figure 4. (a) UVꢀvis absorption spectral traces of 5 in CH2Cl2 (3.3 ꢁ
10ꢀ5 M) with increasing CH3CN content at 298 K. The inset shows the
absorbance ratio A500 nm/A422 nm as a function of solvent compositions.
(b) UVꢀvis spectra of 5 (6.6 ꢁ 10ꢀ5 M) in CD3CN with decreasing
temperature from 353 to 293 K. The inset shows the expansion of the
UVꢀvis absorption spectra in the 430ꢀ550 nm region.
In CH2Cl2 at 298 K, emission bands of 1ꢀ6 at 577ꢀ582 nm
were observed upon excitation at λ > 400 nm, which are assigned
as an excited state of predominantly 3MLCT/3LLCT character.
Interestingly, upon increasing the CH3CN content, complex 3
showed a growth of a low-energy emission band at 685 nm
(Figure 3a, inset).5b,8a,8b,8g,8h A helix stabilization energy ΔG-
(CH3CN) of ꢀ2.3 kcal molꢀ1 was obtained for 3 in CH3CN.
Detailed calculation of the helix stabilization energy (ΔG) for
3ꢀ5 is given in the Supporting Information.
3
typical of a MMLCT emission with the diminution of the
3MLCT/3LLCT emission typical of the monomeric alkynyl-
platinum(II) terpyridine system (Figure 6a). The emission
spectral changes of 3 without normalization are shown in Figure
S10 to show the quenching effect of the solvent. Similar
observation was also found for 4 and 5 (Figures S11 and 6b)
upon increasing the acetonitrile content. It is interesting to note
that 4 with a mPE hexamer showed incomplete switching-off of
the monomeric 3MLCT/3LLCT emission even in CH3CN
(Figure 7), in accordance with the proposition that the mPE
hexamer would form a less stable helical strand due to the
misalignment of the terminal platinum(II) terpyridyl moieties.
For 1 and 2 with shorter mPE units (n = 3, 4), only negative
solvatochromism was observed for the MLCT transition in
CH3CN (Figure S7), consistent with the shorter length of the
mPE oligomers that would not allow the two terminal platinum-
(II) terpyridyl moieties to construct a turn. However, when
increasing the repeating units to six (n = 6), 4 exhibited similar
trends as 3 upon increasing the CH3CN content or decreasing
the temperature in CH3CN (Figure S8) but with a less negative
ΔG(CH3CN) of ꢀ1.2 kcal molꢀ1. This less favorable ΔG value
is probably associated with the misalignment of the two terminal
platinum(II) terpyridyl units for the flexible mPE hexamer to
construct a turn to form a less stable helical strand due to one
more repeating unit added.
3
Interestingly, the low-energy MMLCT emission band in 3ꢀ5
remained even when the concentration was decreased from
10ꢀ4 M to concentrations as dilute as 10ꢀ7 M, confirming the
involvement of an intramolecular association. On the contrary,
the emission maxima of 1, 2, and 6 showed only a slight blue shift
relative to those observed in CH2Cl2 (Figure S12) due to the
t
More interestingly, 5 with one of the Bu3terpy ligands
replaced by the less sterically bulky triethyl-substituted terpyr-
idine ligand exhibited a more dramatic increase in the MMLCT
absorption tail upon increasing the acetonitrile content (Figure 4a)
or decreasing the temperature (Figure 4b). The drop of the high-
energy absorption band upon increasing acetonitrile content for
5 (3.6 ꢁ 10ꢀ5 M) is shown in Figure S9. A more negative
ΔG(CH3CN) of ꢀ3.3 kcal molꢀ1 was obtained for 5, indicating
that the variation in the steric bulk on the terpyridine ligands
3
negative solvatochromism,4b with no formation of MMLCT
emission bands and hence no formation of helical strands. The
3
lack of MMLCT emission of 1, 2, and 6 in the same concen-
tration range of 10ꢀ6 to 10ꢀ4 M as those of 3ꢀ5 is further
supportive of the lack of involvement of intermolecular interac-
tions, which is typically found for tert-butyl substituted terpyridyl
platinum(II) complexes.3a,d,n,4a The fact that 3MMLCT emission
is observable in 3ꢀ5, especially in 3 and 4 with both ligands being
tBu3trpy, is possibly a result of the tethering together of the two
Pt-tBu3trpy units via mPE linkers of the appropriate chain length
that aided the bringing together of the two end-groups into close
would alter the extent of the intramolecular Pt Pt interaction
3 3 3
that governs the stabilization of the short helical strand in
solution. Similar to complex 3, both complexes 4 and 5 exhibited
absorption bands at 510 nm that obey Beer’s law within the
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Figure 8. (a) Emission spectra of 3 (6.0 ꢁ 10ꢀ5 M) with decreasing
temperature from 353 to 293 K. Excitation wavelength = 428 nm. (b)
Emission spectra of 5 (3.3 ꢁ 10ꢀ5 M) with decreasing temperature from
353 to 293 K. Excitation wavelength = 427 nm.
Figure 6. (a) Normalized emission spectral traces at 596 nm for 3 in
CH3CNꢀCH2Cl2 mixtures, 0ꢀ100% (6.0 ꢁ 10ꢀ5 M) upon increasing
the CH3CN fraction. Excitation wavelength = 447 nm. (b) Normalized
emission spectral traces at 624 nm for 5 in CH3CNꢀCH2Cl2 mixtures,
0ꢀ100% (3.3 ꢁ 10ꢀ5 M) upon increasing the CH3CN fraction.
Excitation wavelength = 454 nm.
Figure 9. Folding and unfolding of the platinum(II) complexes by
temperature and solvent modulation.
Figure 7. Emission spectra of in CH3CN for 3 (black), 4 (blue), and 5
(red) at 298 K.
CH3CN. It is also interesting to note that a direct correlation of the
extent of Pt Pt interactions with the stability of the foldamers can
3 3 3
proximity for Pt Pt and πꢀπ interactions to occur.11 It is
be inferred as 5, with the strongest extent of Pt Pt and πꢀπ
3 3 3
3 3 3
likely that such intramolecular Pt Pt and πꢀπ interactions
interactions as reflected from its lowest 3MMLCT emission energy
and the complete switching-off of its monomeric emission, gives the
most stable foldamer. Thus, it is believed that the two platinum(II)
terpyridyl moieties at the termini have the ability to stabilize the
short helical strands with five or six repeating units of mPE through
3 3 3
would also help to stabilize these short helical strands in a
cooperative and synergistic manner. In the variable-temperature
luminescence study, upon decreasing the temperature, a decrease
3
in monomeric MLCT/3LLCT emission and a growth of the
3MMLCT emission were observed in 3 and 4 (Figure 8a and
Figure S13), whereas 5showed a red shift in the 3MMLCT emission
with no signs of any monomeric 3MLCT/3LLCT emission bands in
CH3CN even at high temperature (Figure 8b). These, together with
the helix stabilization energy obtained from the UVꢀvis absorption
the intramolecular Pt Pt and πꢀπ interactions in CH3CN or at
3 3 3
low temperature as depicted schematically in Figure 9.
In conclusion, we have designed a series of short meta-phenylene
ethynylene foldamers as a first example which involves the use of
metal metal interaction to control the helixꢀcoil folding transi-
3 3 3
3
study and the observation that 5 showed the lowest MMLCT
tion. The versatile behavior of the Pt Pt and πꢀπ interactions
3 3 3
emission energy (Figure 7), suggested that 5 would adopt the most
of alkynylplatinum(II) terpyridyl moiety also provides an attrac-
tive spectroscopic probe for the study and understanding on the
folding mechanism of metal-containing foldamers. It is envisaged
stable helical strand stabilized by Pt Pt and πꢀπ interactions
3 3 3
of the platinum(II) terpyridine units even at high temperature in
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that metal metal interactions will play an important role in the
stabilization of helical strands in solution.
Hc), 7.50 (m, 6H, Ha, Hd and He), 7.34 (t, 3J = 7.7 Hz, 1H, Hg),
7.31 (t, 3J = 7.7 Hz, 2H, Hb); 3.12 (s, 2H, ꢀCtCH). 13C NMR
(100.6 MHz, CDCl3, 298 K, relative to Me4Si): 135.2, 134.7,
132.0, 131.9, 131.6, 128.5, 123.4, 122.6 (phenyl C), 89.1, 89.0,
82.7, 77.9 (CtC). Positive FAB-MS: ion clusters at m/z 327.67
[M]+. Elemental analyses calcd (%) for C26H14: C 95.68, H 4.32.
Found: C 95.43, H 4.22.
3 3 3
’ EXPERIMENTAL SECTION
Materials and Reagents. Potassium tetrachloroplatinate(II) (K2[PtCl4]
(Chem. Pur., 98%)), 3-bromoiodobenzene (Apollo Scientific Ltd.), 1,
3-diiodobenzene (Alfa Aesar Chemical Co. Ltd.), tetra-n-butylammonium
fluoride (Sigma-Aldrich Co. Ltd., 1.0 M), trimethylsilylacetylene (GFS
Chemical Co. Ltd.), triisopropylacetylene (GFS Chemical Co. Ltd.),
and triethylamine (Apollo Scientific Ltd.) were purchased from the
corresponding chemical company. Dichloromethane (Sigma-Aldrich
Co. Ltd., ACS spectrophotometric grade) and acetonitrile (Acros Organics
Co. Ltd., spectroscopic grade) were used for spectroscopic studies without
further purification.
L3: To a 250-ml two-necked round-bottomed flask fitted with a
magnetic stirrer were added 1-bromo-3-trimethylsilylethynylben-
zene (6.15 g, 24.3 mmol), bis(triphenylphosphine)palladium(II)
dichloride (0.85 g, 1.2 mmol), tetrakis(triphenylphosphine)palladium-
(0) (1.40 g, 1.2 mmol), and copper(I) iodide (0.23 g, 1.2 mmol). The
mixture was evacuated and flushed with nitrogen three times. Dry
tetrahydrofuran (500 mL) and dry triethylamine (150 mL) were then
transferred to the mixture. 1-Ethynyl-3-triisopropylsilylethynylbenzene
(6.86 g, 24.3 mmol) was then added dropwise by a syringe. The
reaction was heated to reflux for 24 h. The resulting mixture was
evaporated to dryness and the residue was purified by column
chromatography (70ꢀ230 mesh) using hexane as the eluent to give
L3 as a colorless oil. Yield: 7.62 g (69%). 1H NMR (400 MHz, CDCl3,
298 K, relative to Me4Si): δ = 7.63 (m, 2H, Hc and Hf), 7.44 (m, 4H,
Ha, Hd, He and Hh), 7.28 (t, 3J = 7.8 Hz, 2H, Hb and Hf), 1.26 (m,
3H, ꢀSi{CH(CH3)2}3), 1.13 (d, 18H, ꢀSi{CH(CH3)2}3), 0.25 (s,
9H, ꢀSi(CH3)3). 13C NMR (100.6 MHz, CDCl3, 298 K, relative to
Me4Si): 135.1, 131.9, 131.7, 131.3, 128.4, 123.9, 123.5, 123.3, 123.2
(phenylC), 106.1, 104.1, 95.1, 91.5, 89.1, 89.0 (CtC), 18.7 (primary C
on ꢀSiiPr3 group), 11.3 (tertiary C on ꢀSiiPr3 group), 0.0 (primary C
on ꢀSiMe3 group). Positive FAB-MS: ion clusters at m/z 555.0 [M]+.
Elemental analyses calcd (%) for C38H42Si2: C 82.25, H 7.63. Found: C
82.07, H 7.70.
Synthesis. The synthetic schemes for ligands L1ꢀL8 are given in
the Supporting Information. All reactions were carried out under an
inert atmosphere of nitrogen using standard Schlenk techniques.
Syntheses of L1ꢀL8.
L1: To a 250-mL two-necked round-bottomed flask fitted with a
magnetic stirrer were added 1,3-diiodobenzene (0.63 g, 1.9
mmol), bis(triphenylphosphine)palladium(II) dichloride (0.07
g, 0.1 mmol), tetrakis(triphenylphosphine)palladium(0) (0.11 g,
0.1 mmol), and copper(I) iodide (0.02 g, 0.1 mmol). The mix-
ture was evacuated and flushed with nitrogen three times. Dry
tetrahydrofuran (50 mL) and triethylamine (20 mL) were then
transferred to the mixture. After stirring for 30 min, 1-ethynyl-3-
triisopropylsilylethynylbenzene (1.24 g, 4.4 mmol) was then
dropwise added by a syringe. The reaction mixture was heated
to reflux for 48 h. The resulting mixture was evaporated to dryness
and the residue was purified by column chromatography (70ꢀ
230 mesh) using hexane as the eluent to give L1 as a colorless oil.
Yield: 0.56 g (46%). 1H NMR (400 MHz, CDCl3, 298 K, relative
to Me4Si): δ = 7.71 (t, 4J = 1.4 Hz, 1H, Hf), 7.67 (t, 4J = 1.4 Hz,
2H, Hc), 7.48 (m, 6H, Ha, Hd and He), 7.33 (t, 3J = 7.7 Hz, 1H,
3
Hg), 7.31 (t, J = 7.7 Hz, 2H, Hb); 1.26 (m, 6H, ꢀSi{CH-
(CH3)2}3), 1.14 (d, 36H, ꢀSi{CH(CH3)2}3). 13C NMR (100.6
MHz, CDCl3, 298 K, relative to Me4Si): 135.2, 134.6, 132.4,
131.4, 130.1, 128.4, 123.6, 123.5 (phenyl C), 89.7, 89.0, 82.4, 78.3
(CtC), 18.7 (primary C on ꢀSiiPr3 group), 11.3 (tertiary C
on ꢀSiiPr3 group). Positive FAB-MS: ion clusters at m/z 640.4
[M]+. Elemental analyses calcd (%) for C44H54Si2: C 82.69, H
8.52. Found: C 82.45, H 8.50.
L4: To a solution of L3 (8.74 g, 19.3 mmol) in tetrahydro-
furan (200 mL) and methanol (50 mL) was added potassium
carbonate (7.97 g, 57.8 mmol). The solution was stirred over-
night. The reaction mixture was diluted with dichloromethane
(500 mL) and brine (250 mL). The organic phase was washed
with brine three times, and dried over anhydrous MgSO4. The
solvent was removed, and the resulting oil was purified by
column chromatography (70ꢀ230 mesh) using hexane as the
eluent to give L4 as a colorless oil. Yield: 6.62 g (90%). 1H NMR
(400 MHz, CDCl3, 298 K, relative to Me4Si): δ = 7.66 (t, 3J =
1.1 Hz, 1H, Hf), 7.64 (t, 3J = 1.1 Hz, 1H, Hc), 7.49 (dt, 3J = 7.7 Hz,
4J = 1.3 Hz, 1 H, He), 7.44 (m, 3H, Ha, Hd and Hh), 7.31 (t, 3J =
3
L2: To a solution of L1 (0.60 g, 0.9 mmol) and tetrahydrofuran
(200 mL) was added a solution of tetra-n-butylammonium
fluoride (0.1 M) in tetrahydrofuran (3 mL). The solution was
stirred for 15 min and the solvent was removed. The brown solid
was washed with plenty of methanol to give a white solid. Yield:
7.8 Hz, 1H, Hg), 7.29 (t, J = 7.8 Hz, 1H, Hb), 3.16 (s, 1H,
ꢀCtCH), 1.26 (m, 3H, ꢀSi{CH(CH3)2}3), 1.13 (d, 18H,
ꢀSi{CH(CH3)2}3). 13C NMR (100.6 MHz, CDCl3, 298 K, rela-
tive to Me4Si): 135.2, 135.1, 132.1, 132.0, 131.9, 131.3, 128.5,
128.4, 124.0, 123.4, 123.1, 122.5 (phenyl C), 91.5, 89.2, 88.8, 82.7
(CtC), 18.7 (primary C on ꢀSiiPr3 group), 11.3 (tertiary C on
ꢀSiiPr3 group). Positive FAB-MS: ion clusters at m/z 383.61
1
0.29 g (98%). H NMR (400 MHz, CDCl3, 298 K, relative to
Me4Si): δ = 7.72 (t, 4J = 1.4 Hz, 1H, Hf), 7.69 (t, 4J = 1.4 Hz, 2H,
1052
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ARTICLE
[M]+. Elemental analyses calcd (%) for C27H30Si: C 87.08, H
7.10. Found: C 87.29, H 7.21.
solid. Yield: 4.12 g (80%). 1H NMR (400 MHz, CDCl3, 298 K,
relative to Me4Si): δ = 7.70 (t, 4J = 1.4 Hz, 2H, Hf), 7.69 (t, 4J =
1.4 Hz, 2H, Hc), 7.48 (m, 8H, Ha, Hd, He and Hh), 7.36 (t, 3J = 7.7
Hz, 2H, Hg), 7.32 (t, 3J = 7.7 Hz, 2H, Hb), 3.09 (s, 2H, ꢀCtCH).
13C NMR (100.6 MHz, CDCl3, 298 K, relative to Me4Si): 138.6,
137.5, 132.0, 130.4, 125.7, 124.4 (phenyl C), 89.5, 89.3, 84.2,
80.0, 77.4 (CtC). Positive FAB-MS: ion clusters at m/z 427.5
[M]+. Elemental analyses calcd (%) for C34H18: C 95.75, H 4.25.
Found: C 95.64, H 4.20.
L5: The titled compound was prepared according to the pro-
cedure similar to that described for the preparation of L1, except
L4 (1.68 g, 4.4 mmol) was used in place of 1-ethynyl-3-triiso-
propylsilylethynylbenzene to give L5 as a colorless oil. Yield: 0.72
g (45%). 1H NMR (400 MHz, CDCl3, 298 K, relative to Me4Si):
δ = 7.72 (t, 4J = 1.5 Hz, 2H, Hf), 7.66 (t, 4J = 1.5 Hz, 1H, Hk), 7.50
(m, 6H, He, Hh and Hi), 7.47 (dt, 3J = 7.7 Hz, 4J = 1.3 Hz, 2H, Hd),
7.45 (dt, 3J = 7.9 Hz, 4J = 1.3 Hz, 2H, Ha), 7.36 (t, 3J = 7.7 Hz, 1H,
Hj), 7.35 (t, 3J = 7.7 Hz, 2H, Hg), 7.30 (t, 3J = 7.8 Hz, 2H, Hb),
1.26 (m, 6H, ꢀSi{CH(CH3)2}3), 1.14 (d, 36H, ꢀSi{CH-
(CH3)2}3). 13C NMR (100.6 MHz, CDCl3, 298 K, relative to
Me4Si): 135.3, 134.6, 133.7, 131.8, 131.5, 123.7, 123.6, 122.3
(phenyl C), 89.8, 89.5, 88.5, 83.4, 79.3 (CtC), 18.7 (primary C
on ꢀSiiPr3 group), 11.3 (tertiary C on ꢀSiiPr3 group). Positive
FAB-MS: ion clusters at m/z 840.3 [M]+. Elemental analyses
calcd (%) for C60H62Si2: C 87.08, H 7.10. Found: C 87.00,
H 7.31.
L8: The titled compound was prepared according to the pro-
cedure similar to that described for the preparation of L3, except
L7 (5.15 g, 12.1 mmol) was used in place of 1-ethynyl-3-
triisopropylsilylethynylbenzene and then followed by the depro-
tecton of TMS with TBAF to give L8 as a white solid. Yield: 5.45
g (72%). 1H NMR (400 MHz, CDCl3, 298 K, relative to Me4Si):
δ =7.73(t, 4J=1.4Hz, 2H, Hk), 7.71(t, 4J= 1.4 Hz, 2H, Hf), 7.66(t,
4J = 1.4 Hz, 2H, Hc), 7.49 (m, 10H, Hd, He, Hh, Hi and Hl), 7.43 (dt,
3J=7.7Hz, 4J=1.3Hz, 2H, Ha), 7.36(t, 3J= 7.7 Hz, 2H, Hj), 7.35(t,
3J = 7.7 Hz, 2H, Hg), 7.29 (t, 3J = 7.6 Hz, 2 H, Hb), 3.10 (s, 2H,
ꢀCtCH). 13C NMR (100.6 MHz, CDCl3, 298 K, relative to
Me4Si): 135.2, 134.7, 132.0, 131.6, 131.5, 128.6, 128.5, 123.5, 123.4,
122.6 (phenyl C), 89.2, 89.1, 89.0, 82.7, 79.2, 79.0, 77.9 (CtC).
Positive FAB-MS: ion clusters at m/z 627.7 [M]+. Elemental
analyses calcd (%) for C50H26: C 95.82, H 4.18. Found: C 95.98,
H 4.24.
Syntheses of 1ꢀ6.
L6: The titled compound was prepared according to the pro-
cedure similar to that described for the preparation of L2, except
L5 (0.76 g, 0.9 mmol) was used in place of L1 to give a white
solid. Yield: 0.43 g (90%). 1H NMR (400 MHz, CDCl3, 298 K,
relative to Me4Si): δ = 7.71 (t, 4J = 1.4 Hz, 1H, Hk), 7.69 (t, 4J =
1.4 Hz, 2H, Hf), 7.67 (t, 4J = 1.4 Hz, 2H, Hc), 7.51 (m, 6H, He,
Hh and Hi), 7.47 (dt, 3J = 7.7 Hz, 4J = 1.3 Hz, 2H, Hd), 7.45 (dt,
3J = 7.7 Hz, 4J = 1.3 Hz, 2H, Ha), 7.37 (t, 3J = 7.7 Hz, 1H, Hj), 7.35
3
(t, 3J = 7.7 Hz, 2H, Hg), 7.33 (t, J = 7.6 Hz, 2H, Hb), 3.09 (s,
2H, ꢀCtCH). 13C NMR (100.6 MHz, CDCl3, 298 K, relative
to Me4Si): 135.2, 134.7, 132.0, 131.6, 131.5, 128.6, 128.5, 123.5,
123.4, 122.6 (phenyl C), 89.2, 89.1, 89.0, 82.7, 79.2, 79.0, 77.9
(CtC). Positive FAB-MS: ion clusters at m/z 527.8 [M]+.
Elemental analyses calcd (%) for C42H22: C 95.79, H 4.21.
Found: C 95.85, H 4.17.
1: To a solution of L2 (30 mg, 0.09 mmol) and [(tBu3tpy)PtCl]
(OTf)2 (143 mg, 0.18 mmol) in degassed N,N-dimethylformamide
(30 mL) containing triethylamine (5 mL) was added a catalytic
amount of CuI. The solution was stirred overnight at room temperature.
After removing the solvent, the reaction mixture was purified by
chromatography on silica gel using dichloromethaneꢀacetone mixture
(10:1 v/v) as eluent, followed by the diffusion of diethyl ether vapor into
acetonitrile solution to give 1as a yellow solid. Yield: 100 mg (60%). 1H
NMR (500 MHz, CD3CN, 298 K, relative to Me4Si): δ = 8.89 (d with
Pt satellites, 3J = 6.0 Hz, 4H, Hd), 8.21 (s, 4H, Hb), 8.15 (d, 4J = 1.9 Hz,
4H, Ha),7.66(t, 4J= 1.3 Hz, 1H, Hj), 7.62(t, 4J=1.3Hz, 2H, Hg), 7.60
(dd, 3J=6.0 Hz, 4J= 2.1 Hz, 4H, Hc), 7.47(dd, 3J=8.2 Hz, 4J=1.3Hz,
2H, Hi), 7.42 (dt, 3J=7.7Hz,4J= 1.3 Hz, 2H, He),7.36(dt,3J=7.7Hz,
4J = 1.3 Hz, 2H, Hh), 7.31 (t, 3J = 7.7 Hz, 3H, Hf and Hj), 1.59 (s, 18H,
L7: The titled compound was prepared according to the pro-
cedure similar to that described for the preparation of L3, except
3,30-bis(ethynyl)tolane (2.7 g, 12.1 mmol) was used in place of
1-ethynyl-3-triisopropylsilylethynylbenzene and then followed
by the deprotecton of TMS with TBAF to give L7 as a white
t
t
ꢀ Bu), 1.51 (s, 36H, ꢀ Bu). 13C NMR (125.8 MHz, CD3CN, 298 K,
relative to Me4Si): δ = 168.5, 167.8, 159.6, 155.0 (quaternary C on
terpyridyl), 154.8 (tertiary C on terpyridyl), 135.7, 135.2, 133.2, 132.5,
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ARTICLE
t
130.4, 130.3, 129.8, 128.5, 124.4, 124.1 (phenyl C), 126.8, 123.7, 122.2
(tertiary C on terpyridyl), 103.6 (PtꢀCtC), 101.2 (PtꢀCtC), 90.8,
(primary C on ꢀ Bu). IR (nujol): 2122 cmꢀ1 (CtC). Positive
FAB-MS: ion clusters at m/z 858.3 [M ꢀ 2OTf]2+. Elemental
t
89.5, (CtC),38.1,37.1(quaternaryCon ꢀ Bu), 30.7, 30.3 (primary C
analyses calcd (%) for C98H90F6N6O6Pt2S2 CHCl3: C 55.68, H
3
t
on ꢀ Bu). IR (nujol): v = 2119 cmꢀ1 (CtC). Positive FAB-MS: ion
4.30, N 3.94. Found: C 55.73, H 4.47, N 3.86.
clusters at m/z 760.7 [M ꢀ 2OTf]2+. Elemental analyses calcd
(%) for C82H82F6N6O6Pt2S2: C 54.24, H 4.55, N 4.63. Found: C
54.41, H 4.56, N 4.67.
4: The titled complex was prepared according to the procedure
similar to that described for the preparation of 1, except L8 (57 mg,
0.09 mmol) was used in place of L2. Yield: 106 mg (56%).1H NMR
(500 MHz, CD3CN, 330 K, relative to Me4Si): δ = 8.84 (d with Pt
satellites, 3J = 6.0 Hz, 4H, Hd), 8.18 (s, 4H, Ha), 8.13 (d, 4J = 2.0 Hz,
4H, Hb), 7.72 (t, 4J = 1.3 Hz, 2H, Hf), 7.71 (t, 4J = 1.3 Hz, 2H, Hk),
7.64 (dd, 3J = 6.0 Hz, 4J = 2.1 Hz, 4H, Hc), 7.61 (dt, 3J = 7.1 Hz, 4J =
1.7 Hz, 2H, He), 7.59 (dt, 3J=7.1Hz,4J=1.7Hz,2H,Hh), 7.55 (dt, 3J=
7.1 Hz, 4J = 1.7 Hz, 2H, Hi), 7.48 (m, 8H, Hg, Hl and Hn), 7.44 (t, 3J =
7.8 Hz, 2H, Hj), 7.26 (dt, 3J = 7.1 Hz, 4J = 1.7 Hz, 2H, Hm), 7.22 (dt,
3J = 7.1 Hz, 4J = 1.7 Hz, 2H, Hp), 7.19 (dt, 3J = 7.1 Hz, 4J = 1.7 Hz, 2H,
2: The titled complex was prepared according to the procedure
similar to that described for the preparation of 1, except L7 (39 mg,
0.09 mmol) was used in place of L2. Yield: 116 mg (67%).1H NMR
(500 MHz, CD3CN, 330 K, relative to Me4Si): δ = 8.78 (d with Pt
satellites, 3J = 6.0 Hz, 4H, Hd), 8.17 (s, 4H, Ha), 8.12 (d, 4J = 2.0 Hz,
4H, Hb), 7.82 (t, 4J = 1.3 Hz, 2H, Hf), 7.62 (t, 4J = 1.3 Hz, 2H, Hk),
7.64 (dd, 3J = 6.0 Hz, 4J = 2.1 Hz, 4H, Hc), 7.60 (m, 4H, He and Hh),
7.57 (dt, 3J = 7.1 Hz, 4J = 1.7 Hz, 2H, Hi), 7.48 (m, 4H, Hg and Hl),
t
t
Ho), 1.51 (s, 18H, ꢀ Bu), 1.46 (s, 36H, ꢀ Bu). 13C NMR (125.8
MHz, CD3CN, 298 K, relative to Me4Si): δ = 168.5, 168.0, 159.8,
155.1 (quaternary C on terpyridyl), 154.4 (tertiary C on terpyridyl),
137.5, 137.4, 134.8, 136.4, 136.2, 132.4, 130.4, 130.1, 130.9, 125.4,
124.4, 124.3, 124.2, 123.6 (phenyl C), 126.9, 123.8, 122.2 (tertiary Con
terpyridyl), 103.3 (PtꢀCtC), 101.1 (PtꢀCtC), 91.8, 90.1, 89.6,
3
t
7.44 (t, J = 7.8 Hz, 2H, Hj), 1.51 (s, 18H, ꢀ Bu), 1.46 (s,
t
36H, ꢀ Bu). 13C NMR (125.8 MHz, CD3CN, 298 K, relative to
Me4Si): δ = 168.5, 168.0, 159.8, 155.1 (quaternary C on terpyridyl),
154.4 (tertiary C on terpyridyl), 137.6, 137.4, 134.5, 130.4, 130.1,
130.9, 125.4, 124.4, 124.3, 124.2, 123.6 (phenyl C), 127.0,
123.4, 122.6 (tertiary C on terpyridyl), 103.1 (PtꢀCtC), 101.0
(PtꢀCtC), 91.8, 90.1, 89.6, 89.5 (CtC), 38.2, 37.1 (quaternary C
t
89.5 (CtC), 38.2, 37.1 (quaternary Con ꢀ Bu), 30.8, 30.4 (primary C
t
on ꢀ Bu). IR (nujol): 2120 cmꢀ1 (CtC). Positive FAB-MS: ion
clusters at m/z 910.1 [M ꢀ 2OTf]2+. Elemental analyses calcd (%) for
t
t
on ꢀ Bu), 30.8, 30.4 (primary C on ꢀ Bu). IR (nujol): 2120 cmꢀ1
(CtC). Positive FAB-MS: ion clusters at m/z809.3 [M ꢀ 2OTf]2+.
Elemental analyses calcd (%) for C90H86F6N6O6Pt2S2: C 56.42,
H 4.52, N 4.39. Found: C 56.14, H 4.44, N 4.45.
C106H94F6N6O6Pt2S2 2CHCl3: C 55.08, H 4.11, N 3.57. Found: C
3
55.18, H 4.40, N 3.45.
5: To a solution of 6 (24 mg, 0.02 mmol) and [(Et3trpy)PtCl]-
(OTf) (13 mg, 0.02 mmol) in degassed N,N-dimethylformamide
(30 mL) containing triethylamine (5 mL) was added a catalytic
amount of CuI. The solution was stirred overnight at room
temperature. After removing the solvent, the reaction mixture
was purified by chromatography on silica gel using dichloromethaneꢀ
acetone mixture (10:1 v/v) as eluent, followed by the diffusion of
diethyl ether vapor into acetonitrile solution to give 5 as a orange
solid. Yield: 20 mg (56%).1H NMR (500 MHz, CD3CN, 350 K,
relative to Me4Si): δ = 8.72 (d with Pt satellites, 3J = 6.0 Hz, 2H,
Ha), 8.67 (d with Pt satellites, 3J = 6.0 Hz, 2H, Hj), 8.19 (s, 2H,
Hd), 8.03 (d, 4J = 2.0 Hz, 2H, Hc), 7.95 (s, 2H, Hm), 7.90 (t, 4J =
1.3 Hz, 1H, He), 7.86 (t, 4J = 1.3 Hz, 1H, Hi), 7.85 (t, 4J = 1.3 Hz,
1H, Hf), 7.81 (d, 4J = 2.0 Hz, 2H, Hl), 7.75 (dd, 3J = 6.0 Hz, 4J =
2.1 Hz, 2H, Hb), 7.65 (m, 5H, phenyl Hs), 7.60 (dt, 3J = 7.1 Hz,
4J = 1.7 Hz, 1H, phenyl H), 7.56 (dd, 3J = 6.0 Hz, 4J = 2.1 Hz, 2H,
Hk), 7.50 (m, 6H, phenyl Hs), 7.44 (m, 5H, phenyl Hs), 7.36
(dt, 3J = 7.1 Hz, 4J = 1.7 Hz, 1H, Hg), 7.33 (dt, 3J = 7.1 Hz, 4J =
1.7 Hz, 1H, Hh), 2.97 (q, 2H, ꢀCH2ꢀ), 2.93 (q, 4H, ꢀCH2ꢀ),
3: The titled complex was prepared according to the procedure
similar to that described for the preparation of 1, except L6
(47 mg, 0.09 mmol) was used in place of L2. Yield: 96 mg
(53%).1H NMR (500 MHz, CD3CN, 298 K, relative to Me4Si):
δ = 8.71 (d with Pt satellites, 3J = 6.0 Hz, 4H, Hd), 8.18 (s, 4H,
Hb), 8.03 (d, 4J = 2.0 Hz, 4H, Ha), 7.83 (t, 4J = 1.3 Hz, 2H, Hg),
7.78 (t, 4J = 1.3 Hz, 1H, Ho), 7.71 (dd, 3J = 6.0 Hz, 4J = 2.1 Hz, 4H,
Hc), 7.64 (m, 4H, He and Hm), 7.57 (m, 4H, Hh and Hj), 7.51 (t,
3J = 7.8 Hz, 1H, Hn), 7.50 (t, 3J = 7.8 Hz, 2H, Hf), 7.43 (dt, 3J = 7.1
Hz, 4J = 1.7 Hz, 2H, Hi), 7.39 (t, 3J = 7.4 Hz, 2H, Hk), 7.37 (dt,
t
3J = 7.1 Hz, 4J = 1.7 Hz, 2H, Hl), 1.58 (s, 18H, ꢀ Bu), 1.48 (s,
t
36H, ꢀ Bu). 13C NMR (125.8 MHz, CD3CN, 298 K, relative to
Me4Si): δ = 168.5, 167.9, 159.8, 155.1 (quaternary C on terpyridyl),
154.4 (tertiary C on terpyridyl), 136.5, 135.5, 135.1, 134.7, 132.8,
132.7, 132.6, 132.4, 130.4, 130.1, 129.9, 128.4, 124.4, 124.3,
124.2, 123.8 (phenyl C), 126.9, 123.8, 122.2 (tertiary C on
terpyridyl), 103.2 (PtꢀCtC), 101.0 (PtꢀCtC), 90.8, 90.0,
t
89.8, 89.4 (CtC), 38.2, 37.1 (quaternary C on ꢀ Bu), 30.8, 30.4
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Journal of the American Chemical Society
ARTICLE
t
t
1.57 (s, 9H, ꢀ Bu), 1.44 (t, 3H, ꢀCH3), 1.40 (s, 18H, ꢀ Bu), 1.32
(t, 6H, ꢀCH3). 13C NMR (125.8 MHz, CD3CN, 298 K, relative to
Me4Si): δ = 168.5, 168.0, 161.3, 160.9, 160.0, 159.7, 155.2, 155.0
(quaternaryCon terpyridyl), 154.1, 153.9 (tertiary C on terpyridyl),
137.0, 136.6, 135.7, 135.3, 134.9, 133.0, 132.7, 132.6, 132.5, 132.4,
132.2, 130.5, 130.4, 130.2, 130.1, 130.0, 129.9, 129.0, 127.0, 126.0,
124.5, 124.3, 124.2, 124.1, 123.6 (phenyl C), 128.4, 128.3, 124.0,
123.9, 122.2, 120.3 (tertiary C on terpyridyl), 102.9, 102.6
(PtꢀCtC), 101.0, 100.3 (PtꢀCtC), 96.3, 91.3, 90.9, 90.8,
Chinese Academy of Sciences. The UVꢀvisible spectra were obtained
using a Hewlett-Packard 8452A diode array spectrophotometer. Emis-
sion spectra at room temperature were recorded on a Spex Fluorolog-3
model FL3-211 fluorescence spectrofluorometer equipped with an
R2658P PMT detector. Variable-temperature UVꢀvis absorption and
emission spectra were obtained using a Varian Cary 50 UVꢀvis spectro-
photometer and a Spex Fluorolog-3 model FL3-211 fluorescence spec-
trofluorometer equipped with an R2658P PMT detector, respectively.
The temperature was maintained by a Varian Cary Single cell Peltier
thermostat.
t
90.0, 89.9, 89.8, 89.7 (CtC), 38.2, 37.1 (quaternary C on ꢀ Bu),
38.0, 37.5 (secondary C on ꢀEt), 30.9, 30.3 (primary C on ꢀEt),
30.8, 30.4 (primary C on ꢀ Bu). IR (nujol): 2120 cmꢀ1 (CtC).
t
’ ASSOCIATED CONTENT
Positive FAB-MS: ion clusters at m/z 818.8 [M ꢀ 2OTf]2+.
Elemental analyses calcd (%) for C92H78F6N6O6Pt2S2: C 57.66,
H 4.20, N 4.80. Found: C 57.80, H 4.10, N 4.59.
S
Supporting Information. The synthetic routes for
b
meta-phenylene ethynylene oligomers (n = 3, 4, 5, 6). Variable-
1
temperature H NMR experiments for 3ꢀ5 in CDCl3 and
CD3CN. Calculation of the distances between protons on mPE
and 40- and 4000-tBu groups for 3 in CH3CN. UVꢀvis absorption
spectra of 1, 2, and 6 in CH2Cl2 and CH3CN at 298 K. UVꢀvis
absorption spectral traces of 4 in CH2Cl2 with increasing
CH3CN content at 298 K and decreasing the temperature from
353 to 293 K. Calculation of helix stabilization energy of 3ꢀ5.
Emission spectral traces for 4 in CH3CNꢀCH2Cl2 upon in-
creasing the CH3CN fraction and decreasing the temperature
from 353 to 293 K. Emission spectra of 1, 2, and 6 in CH2Cl2 and
CH3CN at 298 K. This material is available free of charge via the
Internet at http://pubs.acs.org.
6: To a solution of L6 (168 mg, 0.32 mmol) and [(tBu3trpy)PtCl]-
(OTf)2 (250 mg, 0.32 mmol) in degassed N,N-dimethylformamide
(30 mL) containing triethylamine (5 mL) was added a catalytic
amount of CuI. The solution was stirred overnight at room tem-
perature. After removing the solvent, the reaction mixture was
purified by chromatography on silica gel using dichloromethaneꢀ
acetone mixture (10:1 v/v) as eluent, followed by the diffusion of
diethyl ether vapor into acetonitrile solution to give 6 as a yellow
solid. Yield: 110 mg (27%). 1H NMR (500 MHz, CD3CN, 298 K,
relative to Me4Si): δ = 8.91 (d with Pt satellites, 3J = 6.0 Hz, 2H,
Hd), 8.21 (s, 2H, Hb), 8.13 (d, 4J = 1.9 Hz, 2H, Ha), 7.66 (m, 2H, Hg
and Hj), 7.65 (t, 4J = 1.2 Hz, 1 H, Ho), 7.63 (t, 4J = 1.2 Hz, 1H, Hr),
7.59 (dd, 3J = 6.0 Hz, 4J = 2.1 Hz, 2H, Hc), 7.57 (t, 4J = 1.4 Hz,
1H, Hw), 7.47 (m, 8H, He, Hf, Hh, Hi, HK, Hl, Hm, and Hp), 7.41 (dt,
3J = 7.8 Hz, 4J = 1.4 Hz, 1H, Hu), 7.36 (m, 4H, Hn, Hq, Ht and Hx),
7.32 (t, 3J = 7.5 Hz, 1H, Hs), 7.31 (t, 3J = 7.5 Hz, 1H, Hv), 3.41 (s,
’ AUTHOR INFORMATION
Corresponding Author
wwyam@hku.hk
’ ACKNOWLEDGMENT
V.W.-W.Y. acknowledges the support from The University of
Hong Kong under the Distinguished Research Achievement
Award Scheme and the URC Strategic Research Theme on
Molecular Materials. This work has been supported by the
University Grants Committee Areas of Excellence (AoE)
Scheme (AoE/P-03/08) and a General Research Fund (GRF)
grant from the Research Grants Council of Hong Kong Special
Administrative Region, P. R. China (HKU 7060/09P). S.Y.-L.L.
acknowledges the receipt of a postgraduate studentship and
A.Y.-Y.T. acknowledges the receipt of a University Postdoctoral
Fellowship, both administered by The University of Hong Kong.
1H, ꢀCtCH), 1.58 (s, 9H, ꢀ Bu), 1.48 (s, 18H, ꢀ Bu). 13C NMR
(125.8 MHz, CD3CN, 298 K, relative to Me4Si): δ = 168.4, 167.7,
159.6, 154.9 (quaternary C on terpyridyl), 154.8 (tertiary C on
terpyridyl), 135.8, 135.6, 135.4, 135.3, 135.2, 133.1, 132.9, 132.7,
132.6, 132.5, 132.4, 132.3, 130.3, 130.2, 130.1, 130.0, 129.8, 128.6,
124.4, 124.2, 124.1, 124.0, 123.7 (phenyl C), 126.7, 123.5, 122.2
(tertiary C on terpyridyl), 103.5 (PtꢀCtC), 101.1 (PtꢀCtC),
90.9, 90.0, 89.9, 89.8, 89.5, 83.2, 79.9 (CtC), 38.1, 37.1 (quaternary
t
t
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reported relative to tetramethylsilane, (CH3)4Si. Negative-ion FAB
mass spectra were recorded on a Thermo Scientific DFS high resolution
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