Metal-assisted assembly of pyridine-containing arylene ethynylene strands to enantiopure double helicates

Article abstract of DOI:10.1021/ja048327d

Pyridine-containing arylene ethynylene strands were connected to the 2- and 2′-positions of (R)- and (S)-1,1′-binaphthyl templates. The arylene ethynylene moieties underwent intramolecular coordination with Ag(I) or Cu(I) ion to afford enantiopure double helicates. The double-helical structure was elucidated on the basis of circular dichroic (CD) spectra. The importance of intramolecular complexation of the double strands for the helicate formation was confirmed by comparison with a ligand bearing a single strand. Connection of the strands through an ether linkage enabled a sorting out of the Cotton effect induced by double-helical arylene ethynylene moieties. The CD exciton chirality method unambiguously proved that the termini of the strands approach each other upon complexation and that the sense of the induced helicity is the same as predicted by molecular modeling.

Full text of DOI:10.1021/ja048327d

Published on Web 07/30/2004
Metal-Assisted Assembly of Pyridine-Containing Arylene
Ethynylene Strands to Enantiopure Double Helicates
Akihiro Orita,† Takehiro Nakano,† De Lie An,† Kazumi Tanikawa,†
Kan Wakamatsu,‡ and Junzo Otera*,†
Contribution from the Departments of Applied Chemistry and Chemistry,
Okayama UniVersity of Science, Ridai-cho, Okayama 700-0005, Japan
Received March 23, 2004; E-mail: otera@high.ous.ac.jp
Abstract: Pyridine-containing arylene ethynylene strands were connected to the 2- and 2′-positions of
(R)- and (S)-1,1′-binaphthyl templates. The arylene ethynylene moieties underwent intramolecular
coordination with Ag(I) or Cu(I) ion to afford enantiopure double helicates. The double-helical structure
was elucidated on the basis of circular dichroic (CD) spectra. The importance of intramolecular complexation
of the double strands for the helicate formation was confirmed by comparison with a ligand bearing a
single strand. Connection of the strands through an ether linkage enabled a sorting out of the Cotton effect
induced by double-helical arylene ethynylene moieties. The CD exciton chirality method unambiguously
proved that the termini of the strands approach each other upon complexation and that the sense of the
induced helicity is the same as predicted by molecular modeling.
Introduction
by the Cozzi/Siegel strategy. On the basis of molecular
modeling, pyridine was found to be a suitable donor unit due
Extensive attention has been paid to the self-assembly of
double helicates, some now available even in enantiomerically
pure form.1 Metal coordination chemistry has played a pivotal
role for this purpose since the pioneering work by Lehn et al.2
The most common way to arrive at homochiral helicates is to
introduce a chiral center into the backbone of the ligand strand.3
Spontaneous resolution is also effective on some occasions.4
Another strategy is to attach ligand strands to a chiral template
as developed by Cozzi and Siegel and co-workers.5 During a
project on arylene ethynylene chemistry, we reported the syn-
thesis of an enantiopure double-helical phenylene ethynylene
cyclophane.6 Consequently, we have become interested in
acyclic analogues because no such motif is known, in contrast
to extensive work on the relevant single helices.7 Inspection of
molecular models suggested to us that the double-helix arrange-
ment would be feasible if the strands with alternating ethynylene/
meta-arylene arrays were connected to the 2- and 2′-positions
of a 1,1′-binaphthalene template. However, preliminary experi-
ments soon revealed that no helical structures could be attained
by use of simple phenylene ethynylene chains due to the lack
of effective interactions between them. We were then intrigued
(3) (a) Libman, J.; Tor, Y.; Shanzer, A. J. Am. Chem. Soc. 1987, 109, 5880-
5881. (b) Shanzer, A.; Libman, J.; Lifson, S. Pure. Appl. Chem. 1992, 64,
1421-1435. (c) Koert, U.; Harding, M. M.; Lehn, J.-M. Nature 1990, 346,
339-342. (d) Zarges, W.; Hall, J.; Lehn, J.-M.; Bolm, C. HelV. Chim. Acta
1991, 74, 1843-1852. (e) Enemark, E. J.; Stack, T. D. P. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 996-998. (f) Constable, E. C.; Kulke, T.;
Neuburger, M.; Zehnder, M. Chem. Commun. 1997, 489-490. (g) Baum,
G.; Constable, E. C.; Fenske, D.; Kulke, T. Chem. Commun. 1997, 2043-
2044. (h) Baum, G.; Constable, E. C.; Fenske, D.; Housecroft, C. E.; Kulke,
T. Chem. Commun. 1998, 2659-2660. (i) Baum, G.; Constable, E. C.;
Fenske, D.; Housecroft, C. E.; Kulke, T. Chem. Eur. J. 1999, 5, 1862-
1873. (j) Baum, G.; Constable, E. C.; Fenske, D.; Housecroft, C. E.; Kulke,
T.; Neuburger, M.; Zehnder, M. J. Chem. Soc., Dalton Trans. 2000, 945-
959. (k) Bowyer, P. K.; Porter, K. A.; Rae, A. D.; Willis, A. C.; Wild, S.
B. Chem. Commun. 1998, 1153-1154. (l) Mu¨rner, H.; von Zelewsky, A.;
Hopfgartner, G. Inorg. Chim. Acta 1998, 271, 36-39. (m) Mamula, O.;
von Zelewsky, A.; Bernardinelli, G. Angew. Chem., Int. Ed. 1998, 37, 290-
293. (n) Mamula, O.; von Zelewsky, A.; Bark, T.; Bernardinelli, G. Angew.
Chem., Int. Ed. 1999, 38, 2945-2948. (o) Mamula, O.; Monlien, F. J.;
Porquet, A.; Hopfgartner, G.; Merbach, A. E.; von Zelewsky, A. Chem.
Eur. J. 2001, 7, 533-539. (p) Muller, G.; Bu¨nzli, J.-C. G.; Riehl, J. P.;
Suhr, D.; von Zelewsky, A.; Mu¨rner, H. Chem. Commun. 2002, 1522-
1523.
(4) (a) Kra¨mer, R.; Lehn, J.-M.; De Cian, A.; Fischer, J. Angew. Chem., Int.
Ed. Engl. 1993, 32, 703-706. (b) Kersting, B.; Meyer, M.; Powers, R. E.;
Raymond, K. N. J. Am. Chem. Soc. 1996, 118, 7221-7222.
(5) (a) Woods, C. R.; Benaglia, M.; Cozzi, F.; Siegel, J. S. Angew. Chem., Int.
Ed. Engl. 1996, 35, 1830-1833. (b) Annunziata, A.; Benaglia, M.; Cinquini,
M.; Cozzi, F.; Woods, C. R.; Siegel, J. S. Eur. J. Org. Chem. 2001, 173-
180.
(6) (a) An, D. L.; Nakano, T.; Orita, A.; Otera, J. Angew. Chem., Int. Ed. 2002,
41, 171-173. (b) Orita, A.; An, D. L.; Nakano, T.; Yaruva, J.; Ma, N.;
Otera, J. Chem. Eur. J. 2002, 8, 2005-2010.
† Department of Applied Chemistry.
‡ Department of Chemistry.
(1) For some representative reviews: (a) Lehn, J.-M. Supramolecular Chem-
istry, VCH: Weinheim, Germany, 1995. (b) Lehn, J.-M. Angew. Chem.,
Int. Ed. Engl. 1988, 27, 89-112. (c) Lehn, J.-M. Angew. Chem., Int. Ed.
Engl. 1990, 29, 1304-1319. (d) Lindsey, J. S. New J. Chem. 1991, 15,
153-180. (e) Constable, E. C. Tetrahedron 1992, 48, 10013-10059. (f)
Piguet, C.; Bernardinelli, G.; Hopfgartner, G. Chem. ReV. 1997, 97, 2005-
2062. (g) Albrecht, M. Chem. Soc. ReV. 1998, 27, 281-287. (h) Albrecht,
M. Chem. Eur. J. 2000, 6, 3485-3489. (i) Holliday, B. J.; Mirkin, C. A.
Angew. Chem., Int. Ed. 2001, 40, 2022-2043. (j) Hill, D. J.; Mio, M. J.;
Prince, R. B.; Hughes, T. S.; Moore, J. S. Chem. ReV. 2001, 101, 3893-
4011.
(7) For the most recent papers: (a) Cary, J. M.; Moore, J. S. Org. Lett. 2002,
4, 4663-4666. (b) Matsuda, K.; Stone, M. T.; Moore, J. S. J. Am. Chem.
Soc. 2002, 124, 11836-11837. (c) Zhao, D.; Moore, J. S. J. Am. Chem.
Soc. 2002, 124, 9996-9997. (d) Ku¨bel, C.; Mio, M. J.; Moore, J. S. J.
Am. Chem. Soc. 2002, 124, 8605-8610. (e) Nishinaga, T.; Tanatani, A.;
Oh, K.; Moore, J. S. J. Am. Chem. Soc. 2002, 124, 5934-5935. (f) Zhao,
D.; Moore, J. S. J. Org. Chem. 2002, 67, 3548-3554. (g) Tanatani, A.;
Hughes, T. S.; Moore, J. S. Angew. Chem., Int. Ed. 2002, 41, 325-328.
(h) Ma, L.; Hu, Q.-S.; Vithrana, D.; Wu, C.; Kwan, C. M. S.; Pu, L.
Macromolecules 1997, 30, 204-218. (i) Le´re-Porte, J.-P.; Moreau, J. J.
E.; Serein-Spiran, F.; Nakim, S. Chem. Commun. 2002, 3020-3021. (j)
Prince, R. B.; Okada, T.; Moore, J. S. Angew. Chem., Int. Ed. 1999, 38,
233-236.
(2) Lehn, J.-M.; Rigault, A.; Siegel, J. S.; Harrowfield, J.; Chevrier, B.; Moras,
D. Proc. Natl. Acad. Sci. U.S.A. 1987, 84, 2565-2569.
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J. AM. CHEM. SOC. 2004, 126, 10389-10396
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A R T I C L E S
Orita et al.
Scheme 1
to fitness of the metal-nitrogen coordination bond in the rigid
arylene ethynylene double-helical systems.8 The binaphthyl
group was a stereogenic template of choice because of its facile
availability.9 Herein we report that the pyridine-containing
arylene ethynylene strands can be assembled through metal
coordination to form novel enantiopure double helicates.
required residues containing four aromatic rings was attempted
but failed, probably because of the steric congestion of the
reaction sites in 6. Accordingly, this template was converted to
8 by reaction with more reactive 7. The Sonogashira coupling
of this intermediate with 14 smoothly took place to afford a
reasonable yield of (R)-1. The enantiomer (S)-1 was obtained
analogously. The structures of the compounds were fully
confirmed by elemental analysis, mass spectrometry, and NMR
spectroscopy (Figure 1a).
Metal complexation was straightforward. To a tetrahydrofuran
(THF) solution of either (R)- or (S)-1 (1 equiv) was added a
THF solution of AgPF6 (2.2 equiv) in the dark at room
temperature (Scheme 2). The complex 2a precipitated im-
mediately as a white solid. The 1H NMR spectrum of 2a
revealed that Ha and Hc experienced an appreciable upfield shift
relative to 1, while the Hb resonance was shifted downfield
(Figure 1b). In the complex, Ha and Hc are situated in the
diamagnetic region of the binaphthyl group, and Hb is deshielded
by a phenyl ring of the counterpart strand. These shifts suggest
that the freely moving strands in 1 are immobilized as in 2a.
The corresponding copper(I) complexes 2b were obtained
analogously as yellow precipitates when (R)- or (S)-1 was added
to [(CH3CN)4Cu]PF6 (2.2 equiv) in CH2Cl2. NMR spectra of
Results and Discussion
After screening a variety of arrays of the benzene and pyridine
rings in the strand, we concluded that intervention of two
pyridine rings gave rise to the most effective complexation. One
pyridine ring in each strand is not sufficient to induce effective
metal complexation, while three pyridines result in insoluble
complexes. The synthetic procedure for the requisite substrate
(R)-1 is shown in Scheme 1. The n-hexyl groups attached to
the terminal benzene rings are necessary to impart better
solubility. First, direct Sonogashira coupling between 6 and the
(8) Metal complexes with linear ethynylpyridines: (a) Potts, K. T.; Horwitz,
C. P.; Fessak, A.; Keshavarz-K, M.; Nash, K. E.; Toscano, P. J. J. Am.
Chem. Soc. 1993, 115, 10444-10445. (b) Sun, S.-S.; Lees, A. J. Am. Chem.
Soc. 2000, 122, 8956-8967. (c) Kawano, T.; Kuwana, J.; Shinomaru, T.;
Du, C.-X.; Ueda, I. Chem. Lett. 2001, 1230-1231. (d) Kawano, T.;
Shinomaru, T.; Ueda, I. Org. Lett. 2002, 4, 2545-2547. (e) Kawano, T.;
Kato, T.; Du, C.-X.; Ueda, I. Bull. Chem. Soc. Jpn. 2003, 76, 709-719.
(f) Kawano, T.; Kuwana, J.; Ueda, I. Bull. Chem. Soc. Jpn. 2003, 76, 789-
797. (g) Tomozaki, K.-y.; Yu, L.; Wei, L.; Lindsey, J. S. J. Org. Chem.
2003, 68, 8199-8207. (h) Chi, K.-W.; Addicott, C.; Arif, A. M.; Das, N.;
Stang, P. J. J. Org. Chem. 2003, 68, 9798-9801.
(9) For the use of binaphthyl derivatives as stereogenic core, see Pu, L. Chem.
ReV. 1998, 98, 2405-2494.
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Pyridine-Containing Arylene Ethynylene Strands
A R T I C L E S
Figure 1. 1H NMR spectra of 1 and 2a: (a) 1 in CDCl3; (b) 2a in acetone-d6.
Scheme 2
these complexes exhibited slightly broad signals, possibly due
to dynamic dissociation. Such slight instability may be ascribed
to the two-coordinate metal complex.10 Some two-coordinate
Cu(I) and Ag(I) complexes are known,3f,11 and a dynamic change
of bonding mode was suggested for Cu(I)11b and Ag(I)11e
complexes. Confirmation of the 2:1 metal/1 stoichiometry of
complexes 2a and 2b was attempted by electrospray and matrix-
assisted laser desorption ionization time-of-flight (MALDI-TOF)
mass spectrometries. However, both methods gave rise to no
(11) (a) Sorrel, T. N.; Borovik, A. S. J. Am. Chem. Soc. 1986, 108, 5636-
5637. (b) Piguet, C.; Bernardinelli, G.; Williams, A. F. Inorg. Chem. 1989,
28, 2920-2925. (c) Ru¨ttimann, S.; Piguet, C.; Bernardinelli, G.; Bocquet,
B.; Williams, A. F. J. Am. Chem. Soc. 1992, 114, 4230-4237. (d) Cardina,
R.; Williams, A. F.; Piguet, C. HelV. Chim. Acta 1998, 81, 548-557.
(10) Metal coordination with the acetylene moiety is not plausible because no
complexes were formed with phenylene/ethynylene analogues without
pyridine spacers. 13C NMR spectra also did not indicate such interactions.
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A R T I C L E S
Orita et al.
Figure 2. UV/Vis and CD spectra of 1 and 2: (a, left panel) UV/vis spectra of (R)-1 in CH2Cl2, (R)-2a in 95:5 CHCl3/DMF, and (R)-2b in CH2Cl2; (b, right
panel) CD spectra of (R)- and (S)-1 in CH2Cl2, (R,P)- and (S,M)-2a in 95:5 CHCl3/DMF, and (R)- and (S)-2b in CH2Cl2.
parent peak, but a peak appeared assignable to the 1:1 species
corresponding to 1/Ag+ or 1/Cu+ in which one of the metal
ions and all PF6 anions had been removed from 2a and 2b,
probably because of weak coordination bonding and possibly
metal-metal repulsion in the multimetal coordination. This
nevertheless does not mean that 2a and 2b possess a 1:1 compo-
sition. The 2:1 stoichiometry is supported by titration experi-
ments in circular dichroic (CD) spectra (vide infra). Furthermore,
1H NMR spectrum of a 1:1 mixture of 1 and AgPF6 exhibited
only broad signals, in contrast to the sharp signals of 2a.
While complexes 2a,b exhibited no significant difference
from free 1 in UV-vis spectra, [R]D values were greatly altered
(Scheme 2). The negative value of (R)-1 was converted to large
Figure 3. CD spectral changes upon titration of (R)-1 with AgPF6 in 95:5
CHCl3/DMF.
positive values upon complexation, and the reverse transition
occurred on complexation of (S)-1. Since such enormous
band reached an upper limit at the 2:1 metal/1 ratio and
variation cannot be induced solely by deformation of the
experienced no more enhancement beyond this ratio.
binaphthyl core, it is reasonable to conclude that the chirality
Control experiments suggest that these features do not arise
has emerged from the strands as well. Similar behavior found
from a dimer or higher oligomers. A ligand with a single strand,
in the Cozzi-Siegel protocol with oligo(bipyridine ether) strands
(R)-3, that necessarily leads to intermolecular association upon
was attributed to double-helix formation.5
interaction with metals was synthesized (Scheme 3). Treatment
of 3 with 1 equiv of AgPF6 or [(CH3CN)4Cu]PF6 afforded white
Analysis of CD spectra also supported the emergence of
chirality in the strands (Figure 2). The strong Cotton effect with
or yellow precipitates. However, these precipitates exhibited
a zero point at 320 nm observed for (R)- and (S)-1 disappeared
[R]D values and CD spectra similar to those of free 3.14 This
in the complexes. Alternatively, the silver complexes exhibited
suggest either that no effective intermolecular complexation
a strong peak at 345 nm and a medium peak at 310 nm, whereas
occurred or that the P- and M-sense helicates were formed in
equal amounts even if the complex had been formed in solution
providing an unequivocal evidence for no intermolecular
complexation in 2. Apparently, the twin strands in 1 are crucial
for enantiomerically pure double-helix formation through in-
tramolecular coordination.
As described above, double-helix formation induces a dra-
matic variation of CD spectra at around 350 nm. However, this
region is covered by a strong band derived from a chromophore
associated with the binaphthyl-arylacetylene moiety, as is
evident from the spectrum of 2,2′-bis(phenylethynyl)-1,1′-
binaphthalene.6 To sort out the contribution of the double-helical
arylene ethynylene motif, substrates 4 without binaphthyl-
acetylene connection were synthesized (Scheme 4). As expected,
only a broad peak was observed at 310 nm in the copper
complexes.12 Such spectral changes were characteristic of
double-helix formation in our previous study on chiral acetylenic
cyclophanes.6 It is highly probable, therefore, that double
helicates are formed in both silver and copper complexes. The
completely reversed spectral profiles of the complexes derived
from antipodal (R)- and (S)-1 imply that the helical modes of
strands in these complexes are heterochiral.13 The 2:1 metal/1
stoichiometry of the complexes was confirmed on the basis of
CD spectra through titration with the metal (Figure 3). Upon
increasing the amount of the silver salt added to (R)-1, the
negative-sign band at 340 nm diminished gradually while a new
positive-sign band at 345 nm appeared. The intensity of this
these compounds were almost transparent above 300 nm in CD
spectra (Figure 4). On the other hand, both silver and copper
complexes gave rise to characteristic bands in this region, though
(12) A strong band at 323 nm was observed in CD spectra of single-helical
phenylene ethynylenes: Gin, M. S.; Yokozawa, T.; Prince, R. B.; Moore,
J. S. J. Am. Chem. Soc. 1999, 121, 2643-2644. CD spectra for alternating
binaphthylene/diyne units were also reported: Chow, H.-F.; Ng, M.-K.
Tetrahedron: Asymmetry 1996, 7, 2251-2262.
(13) Helical polysilanes exhibited similar bias in CD spectra resulting in positive
and negative sign bands from P- and M-screw-sense backbones, respec-
tively: Fujiki, M. J. Am. Chem. Soc. 1994, 116, 11976-11981.
(14) [R]31 values: -74.4 (c 0.50, CH2Cl2) for (R)-3; -93.4 (c 0.50, THF) for
D
(R)-3/AgPF6; -56.5 (c 0.53, CH2Cl2) for (R)-3/[(CH3CN)4Cu]PF6. CD
spectra are shown in Supporting Information.
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Pyridine-Containing Arylene Ethynylene Strands
A R T I C L E S
Scheme 3
the ∆ꢀ values are not so large as those observed for the
complexes with 1.
for the Ag(I) complex based on AM1 calculations18 is shown
in Figure 7. Notably, the angle between the transition dipole
moments for the La absorption band was found to be 86.5°.
1
As depicted in Scheme 2, molecular modeling leads to (R,P)-
and (S,M)-conformers for both enantiomers. To confirm the
sense of the helicity, we invoked the CD exciton chirality
method.15 A chromophore to be attached should exhibit a Cotton
effect at a long wavelength because the compound has conju-
gated aromatic acetylene moieties. Since an anthryl chromophore
has a 1La absorption band in the long-wavelength region,
although its intensity is rather weak,16 we synthesized ligands
(R)- and (S)-5 according to the procedure shown in Scheme 5.
The metal complex of (R)-5 should give rise to the negative
exciton chirality, as depicted in Figure 5, and vice versa. The
CD spectra of 5 are transparent in the region above 400 nm
(Figure 6). On the other hand, the negative exciton chirality
was explicitly observed upon interaction of (R)-5 with AgPF6:
a first negative Cotton effect at 485 nm (∆ꢀ ) -70) and a
second Cotton effect at 438 nm (∆ꢀ ) 41).17 The antipodal (S)-5
exhibited a completely reversed feature. The optimized structure
This is important because no CD exciton coupling arises when
the two dipole moments are aligned in parallel or antiparallel.
Apparently, the metal complexation causes both ends of the
strands to approach each other, and the sense of helicity thus
induced is consistent with the prediction on the basis of
molecular modeling. The copper complex also exhibited virtu-
ally the same chirality although the Cotton effects were detected
faintly.
In summary, incorporation of pyridine moieties into the
arylene ethynylene strands induced assembly to double helicates.
The helicate formation could be unambiguously elucidated by
characteristic variations of [R]D values and CD spectra. The CD
exciton chirality method enabled us to assign the sense of
helicity, which is consistent with prediction by molecular
modeling. Further investigations of this novel class of com-
pounds are in progress in our laboratories.
Experimental Section
(15) (a) Harada, N.; Nakanishi, K. Circular Dichroic Spectroscopy-Exciton
Coupling in Organic Stereochemistry; University Science Books: Mill
Valley, CA, 1983. (b) Nakanishi, K.; Berova, N. In Circular Dichroism
Principles and Applications; Nakanishi, K., Berova, N., Woody, R. W.,
Eds; VCH Publishers Inc.: New York, 1994.
(16) (a) Harada, N.; Takuma, Y.; Uda, H. J. Am. Chem. Soc. 1976, 98, 5408-
5409. (b) Harada, N.; Takuma, Y.; Uda, H. Bull. Chem. Soc. Jpn. 1977,
50, 2033-2038. (c) Harada, N.; Takuma, Y.; Uda, H. J. Am. Chem. Soc.
1977, 100, 4029-4036.
Preparation of (R,P)-2a. A 10 mL flask was charged with (R)-1
(24.6 mg, 0.020 mmol) and THF (2 mL), and then AgPF6 (11.1 mg,
(17) A very broad trough of the 1La absorption band was observed for 2,2′-
substituted 9,9′-bianthryls: Toyota, S.; Shimasaki, T.; Tanifuji, N.; Waka-
matsu, K. Tetrahedron: Asymmetry 2003, 14, 1623-1629.
(18) Stewart, J. J. P. MOPAC 2002; Fujitsu Limited: Tokyo, Japan, 2001.
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A R T I C L E S
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Scheme 4
(5% DMF in CHCl3, 8.15 × 10-5 M): λmax (ꢀmax) ) 228 nm (13.9 ×
104), 281 nm (11.9 × 104), 325 nm (10.3 × 104). CD (c 8.15 × 10-5
M in 5% DMF in CHCl3, 0.1 cm cell): θ ) -1.1, ∆ꢀ ) -40.6 (at
244 nm); θ ) 3.1, ∆ꢀ ) 113.6 (at 278 nm); θ ) -1.7, ∆ꢀ ) -61.9
(at 307 nm); θ ) -0.5, ∆ꢀ ) -16.9 (at 319 nm); θ ) -7.6, ∆ꢀ )
-284.3 (at 344 nm).
Preparation of (R,P)-2b. A 10 mL flask was charged with (R)-1
(24.6 mg, 0.020 mmol) and dichloromethane (2 mL), and then
[Cu(MeCN)4]PF6 (16.4 mg, 0.044 mmol) in dichloromethane (2 mL)
was added. After the mixture had been stirred at room temperature for
3 h, the solvent was evaporated in vacuo. The yellow solid obtained
30.1
was used for the spectroscopic measurements. (R,P)-2b: [R]D
)
)
+623.74 (c 0.4, CH2Cl2). UV/Vis (CH2Cl3, 8.15 × 10-5 M): λmax (ꢀmax
) 218 nm (10.8 × 104), 280 nm (9.0 × 104), 309 nm (9.1 × 104). CD
(c 8.15 × 10-5 M in CH2Cl2, 0.1 cm cell): θ ) 0.3, ∆ꢀ ) -9.2 (at
230 nm); θ ) -0.3, ∆ꢀ ) -9.5 (at 237 nm); θ ) 2.2, ∆ꢀ ) -80.2 (at
269 nm); θ ) -2.6, ∆ꢀ ) -95.7 (at 308 nm); θ ) -1.1, ∆ꢀ ) -39.3
(at 344 nm).
Figure 4. CD spectra of 4 and their metal complexes in THF.
Silver and copper complexes of (R)-3 were prepared by the analogous
31.1
procedure for 2a and 2b. (R)-3/AgPF6 complex: a white foam, [R]D
0.044 mmol) in THF (2 mL) was added. After the mixture had been
stirred at room temperature for 1 h in the dark, the solvent was
evaporated in vacuo. The obtained crude solid was washed repeatedly
with THF (2 mL × 5). After drying in vacuo, the white solid obtained
) -93.39 (c 0.500, THF). UV/Vis (THF, 1.1 × 10-4 M): λmax (ꢀmax
)
) 223 nm (6.0 × 104), 279 nm (8.8 × 104), 327 nm (5.9 × 104). CD
(c 1.1 × 10-4 M in THF, 0.1 cm cell): θ ) -1.1, ∆ꢀ ) -36.7 (at 230
nm); θ ) 0.3, ∆ꢀ ) 9.4 (at 241 nm); θ ) -1.3, ∆ꢀ ) -31.1 (at 276
1
was used for the spectroscopic measurements. H NMR (acetone-d6)
nm); θ ) 3.9, ∆ꢀ ) 107.7 (at 307 nm); θ ) -3.4, ∆ꢀ ) -93.1 (at
500 MHz: δ 0.83-0.88 (m, 6H), 1.23-1.30 (m, 12H), 1.54 (t, J )
7.3 Hz, 4H), 2.55 (t, J ) 7.0 Hz, 4H), 5.94 (d, J ) 7.9 Hz, 2H), 6.87
(t, J ) 8.3 Hz, 2H), 7.06 (t, J ) 8.2 Hz, 4H), 7.08 (t, J ) 8.2 Hz, 4H),
7.20-7.27 (m, 6H), 7.31 (t, J ) 7.6 Hz, 4H), 7.35 (s, 2H), 7.50-7.65
(m, 8H), 7.68 (t, J ) 7.6 Hz, 2H), 7.77 (t, J ) 8.2 Hz, 2H), 7.89 (d,
J ) 8.2 Hz, 2H), 8.14 (d, J ) 7.9 Hz, 2H). [R]D30.2 ) +1765.10 (c 0.4,
acetone). UV/Vis (5% DMF in CHCl3, 8.15 × 10-5 M): λmax (ꢀmax) )
228 nm (14.4 × 104), 280 nm (12.5 × 104), 327 nm (10.7 × 104). CD
(c 8.15 × 10-5 M in 5% DMF in CHCl3, 0.1 cm cell): θ ) 1.3, ∆ꢀ )
47.6 (at 243 nm); θ ) -3.0, ∆ꢀ ) -111.5 (at 279 nm); θ ) 1.7, ∆ꢀ
) 64.3 (at 307 nm); θ ) 0.6, ∆ꢀ ) 22.5 (at 319 nm); θ ) 7.7, ∆ꢀ )
285.7 (at 344 nm). Enantiomer (S,M)-2a was prepared from (S)-1
analogously. (S,M)-2a: [R]D30.2 ) -1742.82 (c 0.5, acetone). UV/Vis
31.1
335 nm). (R)-3/[Cu(MeCN)4]PF6 complex: a yellow solid, [R]D
)
(c -56.51, CH2Cl2). UV/Vis (CH2Cl2, 8.82 × 10-5 M): λmax (ꢀmax) )
220 nm (8.1 × 104), 279 nm (8.7 × 104), 310 nm (8.1 × 104). CD (c
8.82 × 10-5 M in CH2Cl2, 0.1 cm cell): θ ) -0.9, ∆ꢀ ) -30.7 (at
230 nm); θ ) 0.3, ∆ꢀ ) 9.5 (at 242 nm); θ ) -0.7, ∆ꢀ ) -26.5 (at
276 nm); θ ) 3.0, ∆ꢀ ) 101.7 (at 307 nm); θ ) -2.0, ∆ꢀ ) -70.1
(at 335 nm).
Silver and copper complexes of 4 were prepared by the analogous
30.7
procedure for 2a and 2b. (R)-4/AgPF6 complex: a white foam, [R]D
) -186.37 (c 1.000, THF). UV/Vis (THF, 6.4 × 10-5 M): λmax (ꢀmax
)
) 237 nm (15.7 × 104), 298 nm (6.4 × 104), 327 nm (6.6 × 104). CD
(c 6.4 × 10-5 M in THF, 0.1 cm cell): θ ) -0.2, ∆ꢀ ) -7.2 (at 217
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Pyridine-Containing Arylene Ethynylene Strands
A R T I C L E S
Figure 5. Correlation between the structure of metal complex of (R)-5 and the negative CD exciton chirality.
Figure 6. UV/Vis and CD spectra of 5 and their Ag+ complexes: (a) UV/vis spectra of (R)-5 and its AgPF6 complex in THF; (b) CD spectra of (R)- and
(S)-5 and their AgPF6 complexes in THF.
Scheme 5
nm); θ )1.8, ∆ꢀ ) 88.0 (at 234 nm); θ ) -2.3, ∆ꢀ ) -110.9 (at 250
8.1 × 10-5 M in THF, 0.1 cm cell): θ ) -3.3, ∆ꢀ ) -124.0 (at 227
nm); θ ) 4.1, ∆ꢀ ) 151.9 (at 239 nm); θ ) -0.1, ∆ꢀ ) -2.2 (at 294
nm); θ ) 0.4, ∆ꢀ ) 19.0 (at 287 nm); θ ) 0.1, ∆ꢀ ) 4.7 (at 306 nm);
28.6
θ ) 0.9, ∆ꢀ ) 42.2 (at 329 nm). (S)-4/AgPF6 complex: [R]D
)
nm); θ ) 0.2, ∆ꢀ ) 6.3 (at 308 nm); θ ) -1.2, ∆ꢀ ) -44.9 (at
37.5
-176.20 (c 0.500, THF). UV/Vis (THF, 8.1 × 10-5 M): λmax (ꢀmax) )
231 nm (18.8 × 104), 297 nm (5.7 × 104), 325 nm (6.2 × 104). CD (c
337 nm). (R)-4/[Cu(MeCN)4]PF6 complex: a yellow solid, [R]D
:
+202.95 (c 0.400, THF). UV/Vis (THF, 6.6 × 10-5 M): λmax (ꢀmax) )
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A R T I C L E S
Orita et al.
105), 277 nm (2.6 × 105), 313 nm (1.5 × 105), 458 nm (1.0 × 105),
483 nm (1.1 × 105). CD (THF, 5.58 × 10-5 M, 0.1 cm cell): θ ) 5.4,
∆ꢀ ) 29.6 (at 239 nm); θ ) -21.3, ∆ꢀ ) -115.6 (at 276.5 nm);
θ ) 13.5, ∆ꢀ ) 73.4 (at 307 nm); θ ) 4.1, ∆ꢀ ) 22.3 (at 322 nm);
θ ) 27.9, ∆ꢀ ) 151.5 (at 344.5 nm); θ ) 1.2, ∆ꢀ ) 6.6 (at 381 nm);
θ ) 7.6, ∆ꢀ ) 41.2 (at 438 nm); θ ) -12.9, ∆ꢀ ) -70.1 (at 485.5
nm). Enantiomer (S)-5/AgPF6 was prepared from (S)-5 analogously.
(S)-5/AgPF6: CD (THF, 5.99 × 10-5 M, 0.1 cm cell): θ ) 21.9, ∆ꢀ
) 110.8 (at 276.5 nm); θ ) -15.4, ∆ꢀ ) -78.2 (at 307.5 nm); θ )
-4.8, ∆ꢀ ) -24.2 (at 321.5 nm); θ ) -30.0, ∆ꢀ ) -151.8 (at 344
nm); θ ) -2.0, ∆ꢀ ) -10.1 (at 382.5 nm); θ ) -9.0, ∆ꢀ ) -45.8
(at 439.5 nm); θ ) 13.4, ∆ꢀ ) -67.9 (at 486 nm).
Figure 7. Structure of (R)-5/2Ag+ optimized by AM1 calculations.
The experimental details for arylene ethynylene ligands are given
in Supporting Information.
232 nm (14.1 × 104), 296 nm (5.4 × 104), 339 nm (4.2 × 104). CD (c
6.6 × 10-5 M in THF, 0.1 cm cell): θ ) 2.0, ∆ꢀ ) 94.2 (at 227 nm);
θ ) -2.3, ∆ꢀ ) -105.6 (at 240 nm); θ ) 0.4, ∆ꢀ ) 19.1 (at 336 nm).
(S)-4/[Cu(MeCN)4]PF6 complex: [R]D29.2 ) -200.68 (c 0.500, THF).
UV/Vis (THF, 8.1 × 10-5 M): λmax (ꢀmax) ) 232 nm (16.1 × 104),
284 nm (5.8 × 104), 322 nm (5.1 × 104). CD (c 8.1 × 10-5 M in THF,
0.1 cm cell): θ ) -2.8, ∆ꢀ ) -103.1 (at 227 nm); θ ) 4.1, ∆ꢀ )
149.2 (at 239 nm); θ ) -0.1, ∆ꢀ ) -15.5 (at 335 nm).
Acknowledgment. We thank M. Yasui and H. Mitsuta for
their technical assistance. Financial support from New Energy
and Industrial Technology Development Organization (NEDO)
of Japan for Industrial Technology Research Grant Program
(01B68006d) and the Sumitomo Foundation to A.O. is gratefully
acknowledged.
Preparation of (R)-5/AgPF6 Complex. A 10 mL flask was charged
with (R)-1 (12.0 mg, 0.0066 mmol) and THF (2 mL), and then AgPF6
(3.8 mg, 0.015 mmol) in THF (0.4 mL) was added. After the mixture
had been stirred at room temperature for 1.5 h in the dark, the solvent
was evaporated in vacuo. The orange solid obtained was used for the
Supporting Information Available: Syntheses and spectro-
scopic characterizations of 1, 3-5, 9, 11-19, 21-23, and 25
(PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
22.6
CD measurements. (R)-5/AgPF6: [R]D ) +445.51 (c 0.068, CH2-
Cl2). UV/Vis (CH2Cl2, 5.58 × 10-5 M): λmax (ꢀmax) ) 218 nm (2.3 ×
JA048327D
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10396 J. AM. CHEM. SOC. VOL. 126, NO. 33, 2004