Chiral rodlike platinum complexes, double helical chains, and potential asymmetric hydrogenation ligand based on "linear" building blocks: 1,8,9,16-Tetrahydroxytetraphenylene and 1,8,9,16-tetrakis(diphenylphosphino) tetraphenylene

Article abstract of DOI:10.1021/ja051013l

This paper is concerned with the synthesis of 1,8,9,16- tetrahydroxytetraphenylene (3a) via copper-(II)-mediated oxidative coupling, its resolution to optical antipodes, and its conversion to 1,8,9,16- tetrakis(diphenylphosphino)tetraphenylene (3b). On th

Full text of DOI:10.1021/ja051013l

Published on Web 06/10/2005
Chiral Rodlike Platinum Complexes, Double Helical Chains,
and Potential Asymmetric Hydrogenation Ligand Based on
“Linear” Building Blocks:
1,8,9,16-Tetrahydroxytetraphenylene and
1,8,9,16-Tetrakis(diphenylphosphino)tetraphenylene
Hai-Yan Peng,† Chi-Keung Lam,‡ Thomas C. W. Mak,‡ Zongwei Cai,§
Wai-Tang Ma,§ Yu-Xue Li,| and Henry N. C. Wong*,†,‡
Contribution from the Shanghai-Hong Kong Joint Laboratory in Chemical Synthesis and
The State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, The Chinese Academy of Sciences, 354 Feng Lin Road, Shanghai 200032, China,
Department of Chemistry, The Chinese UniVersity of Hong Kong,
Shatin, New Territories, Hong Kong SAR, China, and Department of Chemistry, Hong Kong
Baptist UniVersity, Kowloon Tong, Kowloon, Hong Kong SAR, China
Received February 17, 2005; E-mail: hncwong@cuhk.edu.hk
Abstract: This paper is concerned with the synthesis of 1,8,9,16-tetrahydroxytetraphenylene (3a) via copper-
(II)-mediated oxidative coupling, its resolution to optical antipodes, and its conversion to 1,8,9,16-tetrakis-
(diphenylphosphino)tetraphenylene (3b). On the basis of these chiral “linear” building blocks, three rodlike
chiral complexes, triblock (R,R,R,R)-17 and (S,S,S,S)-20 and pentablock (R,R,R,R,R,R,R,R)-22, were
constructed. As a hydrogen bond donor, racemic and optically active 3a was allowed to assemble with
linear acceptors to afford highly ordered structures. A 1:1 adduct of 4,4′-bipyridyl and (()-3a exists in a
dimeric form of 3a linked by 4,4′-bipyridyl through hydrogen bonds. Pyrazine serves as a short linker between
achiral parallel chains each formed by (()-3a, while self-assembly of homochiral 3a into alternate parallel
chains occurs in the adduct of 5,5′-dipyrimidine with (()-3a. Self-assembly of (S,S)-3a or (R,R)-3a with
4,4′-dipyridyl yielded a packing of chiral double helical chains formed by chiral tetrol 3a molecules. A novel
chiral ligand, (S,S)-23, derived from 3a was used in the asymmetric catalytic hydrogenation of R-aceta-
midocinnamate, yielding up to 99.0% ee and 100% conversion.
the central cyclooctatetraene ring of 1,5 chiral tetraphenylenes
Introduction
can be realized although very few nonracemic tetraphenylene
Tetraphenylene (1) and its derivatives1-6 form interesting
clathrate inclusion compounds2,3 and exhibit interesting elec-
tronic properties.4,6b Due to the high barrier for inversion of
derivatives6 are known. It is therefore of interest to prepare
optically active tetraphenylenes, which may be employed as
chiral building blocks7-9 for 3-dimensional scaffold construction.
A program has been initiated in our laboratories in the syntheses
of building blocks 2-6. It is noteworthy that 2,10a 3, and 5 are
chiral while 410b and 610c are achiral. Geometrically, 3 is a linear
unit containing reactive sites which point in opposite directions,
while the reactive sites of 4 are orientated at an idealized angle
† Shanghai-Hong Kong Joint Laboratory in Chemical Synthesis, Shanghai
Institute of Organic Chemistry.
‡ The Chinese University of Hong Kong.
§ Hong Kong Baptist University.
| The State Key Laboratory of Organometallic Chemistry, Shanghai
Institute of Organic Chemistry.
(1) Rapson, W. S.; Shuttleworth, R. G.; van Niekerk, J. N. J. Chem. Soc. 1943,
326-327.
(7) (a) Lehn J.-M. Science 1985, 227, 849-856. (b) ComprehensiVe Supramo-
lecular Chemistry; Lehn, J.-M., Chair Ed.; Atwood, J. L., Davies, J. E. D.,
MacNicol, D. D., Vo¨gtle, F., Executive Eds.; Pergamon Press: Oxford,
1996.
(8) (a) Baxter, P. N. W. In ComprehensiVe Supramolecular Chemistry; Sauvage,
J.-P., Hosseini, M. W., Eds.; Pergamon Press: Oxford, 1996; Vol. 9, pp
65-212. (b) Fujita, M. In ComprehensiVe Supramolecular Chemistry;
Sauvage, J.-P., Hosseini, M. W., Eds.; Pergamon Press: Oxford, 1996;
Vol. 9, pp 253-282. (c) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem.
ReV. 2000, 100, 853-908. (d) Olenyuk, B.; Fechtenko¨tter, A.; Stang, P. J.
J. Chem. Soc., Dalton Trans. 1998, 1707-1728. (e) Stang, P. J.; Olenyuk,
B. Acc. Chem. Res. 1997, 30, 502-518. (f) Fujita, M. Chem. Soc. ReV.
1998, 27, 417-425.
(2) For reviews, see: (a) Mak, T. C. W.; Wong, H. N. C. Top. Curr. Chem.
1987, 140, 141-164. (b) Mak, T. C. W.; Wong, H. N. C. In ComprehensiVe
Supramolecular Chemistry; MacNicol, D. D., Toda, F., Bishop, R., Eds.;
Pergamon Press: Oxford, 1996; Vol. 6, pp 351-369.
(3) (a) Man, Y. M.; Mak, T. C. W.; Wong, H. N. C. J. Org. Chem. 1990, 55,
3214-3221. (b) Wong, H. N. C.; Man, Y. M.; Mak, T. C. W. Tetrahedron
Lett. 1987, 28, 6359-6362. (c) Huang, N. Z.; Mak, T. C. W. J. Chem.
Soc., Chem. Commun. 1982, 543-544. (d) Schwager, H.; Spyroudis, S.;
Vollhardt, K. P. C. J. Organomet. Chem. 1990, 382, 191-200.
(4) Scholz, M.; Gescheidt, G. J. Chem. Soc., Perkin Trans. 2 1994, 735-740.
(5) Rashidi-Ranjbar, P.; Man, Y. M.; Sandstro¨m, J.; Wong, H. N. C. J. Org.
Chem. 1989, 54, 4888-4892.
(6) (a) Rajca, A.; Safronov, A.; Rajca, S.; Shoemaker, R. Angew. Chem., Int.
Ed. Engl. 1997, 36, 488-491. (b) Rajca, A.; Safronov, A.; Rajca, S.;
Wongsriratanakul, J. J. Am. Chem. Soc. 2000, 122, 3351-3357. (c) Rajca,
A.; Wang, H.; Bolshov, P.; Rajca, S. Tetrahedron Lett. 2001, 57, 3725-
3735.
(9) Jiang, H.; Lin, W. J. Am. Chem. Soc. 2003, 125, 8084-8085.
(10) (a) Wen, J.-F.; Hong, W.; Yuan, K.; Mak, T. C. W.; Wong, H. N. C. J.
Org. Chem. 2003, 68, 8918-8931. (b) Hui, C. W.; Mak, T. C. W.; Wong,
H. N. C. Tetrahedron 2004, 60, 3523-3531. (c) Lai, C. W.; Chi, K.; Hung,
K.; Mak, T. C. W.; Wong, H. N. C. Org. Lett. 2003, 5, 823-826.
9
10.1021/ja051013l CCC: $30.25 © 2005 American Chemical Society
J. AM. CHEM. SOC. 2005, 127, 9603-9611
9603

A R T I C L E S
Scheme 1
Peng et al.
of 90° (Scheme 1). In this manner, the functional groups of
these building blocks could be interconnected with guest
molecules via noncovalent interaction,7,8 or with central metal
linkages via covalent interaction,7-9 forming ordered linear, 2-
and 3-dimensional scaffolds. Herein we report the synthesis of
optically active 1,8,9,16-tetrahydroxytetraphenylene (3a) and
1,8,9,16-tetrakis(diphenylphosphino)tetraphenylene (3b). On the
basis of the linear property of 3, chiral rodlike platinum
complexes were constructed, while self-assembly of 3a formed
double helical chains through hydrogen bonds. An effective
chiral ligand, (S,S)-23, derived from 3a was also employed in
the asymmetric catalytic hydrogenation of R-acetamidocin-
namate. This linear ligand is the first example of a tetraphe-
nylene backbone introduced into an effective catalytic ligand
as a source of chirality.
Figure 1. ORTEP drawing of 3a (solvent EtOAc).
Results and Discussion
Synthesis of 1,8,9,16-Tetrahydroxytetraphenylene (3a) and
1,8,9,16-Tetrakis(diphenylphosphino)tetraphenylene (3b). One
way to synthesize tetraphenylenes is via copper(II)-mediated
oxidative coupling.13-15 This approach was adopted in our
synthesis and resolution of 3a, the procedures being shown in
Scheme 2. Thus, the iodination of 711 afforded 8,12 whose
oxidative coupling via its corresponding lithium salt13-15 led
to the formation of a mixture of compounds, whose careful
chromatography resulted in the separation of a product in a
disappointing yield of 13%. This compound exhibited strong
signals at m/z 424 in its mass spectrum. Elemental analysis and
the mass spectrum combine to indicate the molecular formula
Figure 2. ORTEP drawing of 10.
424.16888, which is in good agreement with the theoretical
value of 424.16746 for the molecular formula C28H24O4 of 9.
Optimization procedures revealed that the presence of tetram-
ethylethylenediamine (TMEDA) was crucial to the coupling
while the change of n-BuLi to t-BuLi or CuCl2 to CuBr2 showed
very little influence. After repeated trials of employing different
equivalents of TMEDA, it was eventually found that the
presence of 2 equiv of TMEDA resulted in the formation of 9
in the best yield of 29%.
1
of 9. The structure of 9 was also supported by its H NMR
spectrum (300 MHz, CDCl3), which exhibited a singlet at δ
3.65 ppm that can be assigned to the four methoxy groups.
Moreover, three AMX-type doublets of doublets centered at δ
7.19 ppm (J ) 7.6, 8.2 Hz), 6.86 ppm (J ) 1.1, 7.6 Hz), and
6.79 ppm (J ) 1.1, 8.2 Hz) can be attributed to three types of
protons in the benzene rings. The molecular ion peak of
compound 9 in its EI mass spectrum was observed at m/z
The demethylation of 9 with boron tribromide yielded 3a,
whose structure was determined by spectroscopic methods and
was also confirmed by an X-ray study (Figure 1). NMR
spectroscopy and MS, as well as elemental analysis, are in full
agreement with the assigned structure. The highly symmetrical
structure of 3a can be demonstrated by the appearance of only
one singlet at δ 8.74 ppm for the hydroxyl proton and three
AMX-type doublets of doublets centered at δ 6.97 (dd, J )
7.5, 8.0 Hz), 6.62 (d, J ) 8.0 Hz), and 6.55 (d, J ) 7.5 Hz)
(11) Baker, W.; Barton, J. W.; McOmie, J. F. W. J. Chem. Soc. 1958, 2658-
2663.
(12) Cereghetli, M.; Schmid, R.; Schonhner, P.; Rageot, A. Tetrahedron Lett.
1996, 37, 5343-5346.
(13) Rajca, A.; Wang, H.; Bolshov, P.; Rajca, S. Tetrahedron 2001, 57, 3725-
3735.
(14) Kabir, S. M. H.; Iyoda, M. Synthesis 2000, 13, 1839-1842.
(15) Kabir, S. M. H.; Hasegawa, M.; Kuwatani, Y.; Yoshia, M.; Matsuyama,
H.; Iyoda, M. J. Chem. Soc., Perkin Trans. 1 2001, 159-165.
9
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1,8,9,16-Tetrasubstituted Tetraphenylene Synthesis
A R T I C L E S
Scheme 2
Scheme 3
ppm for benzene protons. Carbon-13 signals appear at δ 154.2,
143.8, 127.1, 124.2, 118.5, and 113.4 ppm in d6-DMSO. The
molecular ion peak of compound 3a in its EI mass spectrum
was observed at m/z 368.10044, which is in good agreement
with the theoretical value of 368.10049 for the molecular
formula C24H16O4 of 3a. The resolution of 3a was performed
through (S)-camphorsulfonylation.16 It was also found that the
diastereomeric tetrakis-(S)-camphorsulfonates of (()-3a, namely,
10 and 11, were chromatographically separable using a 3:1
mixture of benzene and ethyl acetate as an eluent mixture. Due
to the fact that the absolute configuration of the (S)-camphor-
sulfonyl group is defined, an X-ray crystallographic analysis
of the less polar biscamphorsulfonate 10 therefore led us to
confirm the absolute structure of its appended 3a to be of (S,S)-
configuration (Figure 2). In this manner, the absolute stereo-
chemistry of 11 with an appended (R,R)-3a was also indirectly
confirmed. A subsequent desulfonylation generated the enan-
tiomerically pure (S,S)-3a and (R,R)-3a. The former showed a
negative first Cotton effect at 286 nm and a positive second
Cotton effect at 236 nm, while the latter exhibited a positive
first Cotton effect at 286 nm and a negative second Cotton effect
at 236 nm as can be seen in the Supporting Information.
Compound (S,S)-3a exhibited a specific rotation of [R]20D -55.8
(MeOH, c ) 1.05), which is opposite to that of (R,R)-3a, [R]20
D
+55.3 (MeOH, c ) 1.07).
The quest for substituted tetraphenylenes that contain other
functional groups as metal coordination sites promoted us to
undertake the transformation of hydroxyl groups of 3a to 3b
(Scheme 3). Thus, compound (S,S)-3a was readily converted
into the triflate (S,S)-12 with triflic anhydride in the presence
of pyridine. The palladium-catalyzed phosphinylation of (S,S)-
12 with diphenylphospine oxide proceeded smoothly.18 Although
in theory three diphosphinylated products may be formed, only
(S,S)-13 was detected, whose structure was determined by X-ray
studies (Figure 3). Reduction of (S,S)-13 by trichlorosilane gave
the corresponding phosphine (S,S)-14.19 A second phosphiny-
lation of (S,S)-14 led to the desired tetraphosphinyltetraphe-
nylene (S,S)-15,18 as depicted in Figure 4. Reduction of (S,S)-
15 with trichlorosilane19 eventually furnished (S,S)-3b in a total
(17) See the Supporting Information.
(18) Xie, J.-H.; Wang, L.-X.; Fu, Y.; Zhu, S.-F.; Fang, B.-M.; Duan, H.-F.;
Zhou, Q.-L. J. Am. Chem. Soc. 2003, 125, 4404-4405.
(19) Takaya, H.; Akutagawa, S.; Noyori, R. Org. Synth. 1989, 67, 20-30.
(16) Chow, H.-F.; Wan, C.-W.; Ng, M.-K. J. Org. Chem. 1996, 61, 8712-
8714.
9
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A R T I C L E S
Scheme 4
Peng et al.
yield of 32%. Only one peak at δ -13.2 ppm in its 31P NMR
spectrum (121.5 MHz, C6D6) proved that this is a signal for a
trivalent phosphine. A protonated molecular ion peak of
compound 3b in its ESI mass spectrum was observed at m/z
1041.3092, which is in good agreement with the theoretical
value of 1041.3073 for its molecular formula C72H53P4. Com-
Scheme 5
pound (S,S)-3b showed a specific rotation of [R]20D +62.1 (CH2-
Cl2, c ) 0.33). In a similar manner, (R,R)-3b was also
realized,which gave[R]20 -64.0 (CH2Cl2, c ) 1.10).
D
Formation of Chiral Rodlike Platinum Complexes. With
(S,S)-3a, (R,R)-3a, (S,S)-3b, and (R,R)-3b in hand, we then
explored the possibilities for the formation of chiral platinum
complexes. The reaction of (R,R)-3a with 2 equiv of (R)-
(BINAP)PtCO3 (16)10a,20 afforded a symmetrical complex
showing a single peak at δ 4.90 ppm (JPt-P ) 3655 Hz) in its
31P NMR spectrum. The structure of this complex can be
assigned as (R,R,R,R)-17, as depicted in Scheme 4. The
protonated molecular ion peak of compound 17 in its ESI-TOF
mass spectrum17 was observed at m/z 1999.4169, which is in
good agreement with the theoretical value of 1999.4072 for the
molecular formula C112H77O4P4195Pt2. The enantiomer, namely,
Figure 3. ORTEP drawing of 13.
(S,S,S,S)-17, was also accordingly realized, and provided [R]20
D
-796 (THF, c ) 0.28), which is opposite to that of (R,R,R,R)-
17, [R]20 +788 (CH2Cl2, c ) 1.23).
D
Another triblock platinum complex utilizing (S,S)-3b as the
central building framework was also synthesized (Scheme 5).
First, the conversion of (S,S)-3b to its platinum complex resulted
in (S,S)-18, which was converted to platinum carbonate (S,S)-
19.10a,20 In a similar manner, (R,R)-19 was also obtained from
(R,R)-3b. The reaction of (S,S)-19 with 2 equiv of (S)-BINOL
afforded a symmetric triblock complex, (S,S,S,S)-20,10a,20
whose structure was substantiated by MS17 and microanalysis,
1
as well as by H and 31P NMR spectroscopy, which exhibited
only one singlet at δ 2.33 ppm (JPt-P ) 3655 Hz). The
protonated molecular ion peak of compound 20 in its ESI-TOF
mass spectrum was observed at m/z 1999.4211, matching the
theoretical value of 1999.4072 for the molecular formula
C
112H77O4P4195Pt2.
(20) Tudor, M. D.; Becker, J. J.; White, P. S.; Gagne´, M. R. Organometallics
2000, 19, 4376-4380.
Figure 4. ORTEP drawing of 15.
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1,8,9,16-Tetrasubstituted Tetraphenylene Synthesis
A R T I C L E S
Figure 5. Optimized structures of 17, 20, and 22.
Scheme 6
Table 1. Symmetry and the Dimensions (nm) of 17, 20, and 22
Eventually, a pentablock chiral platinum complex was real-
ized on the basis of the aforementioned results. The reaction of
(R,R)-3a at room temperature with 1 equiv of (R)-(BINAP)-
PtCO3 (16) gave (R,R,R)-21 in a yield of 75%.10a,20 Then 1 equiv
of (R,R)-19 was allowed to react at room temperature with 2
equiv of (R,R,R)-21, leading to a symmetrical complex with
only two singlets seen at δ 10.41 (JPt-P ) 3661 Hz) and 5.07
(JPt-P ) 3702 Hz) ppm in its 31P NMR spectrum. The IR
spectrum of this complex demonstrates the disappearance of
the characteristic strong absorptions of the CdO double bond
at 1672 and 1622 cm-1 as detected for (S,S)-19. Element analysis
and mass spectrometric analysis led us to assign the molecular
formula of (R,R,R,R,R,R,R,R)-22 to this complex, as shown in
Scheme 6. Complex 22 was analyzed by using matrix-assisted
laser desorption/ionization time-of-flight mass spectrometry
(MALDI-TOFMS) with dithranol as matrix. The protonated
molecular ion peak of compound 22 was observed at m/z 3795.4
with a small peak intensity. Fragment ions at m/z 850.172 and
1182.250 were also detected with their accurate masses and
isotope patterns matching the theoretical values for the molecular
formulas of C44H34P2O2195Pt and C68H46P2O4195Pt, respectively.
dimensions (nm)
structure
symmetry
length
width
height
(R,R,R,R)-17
(S,S,S,S)-20
(R,R,R,R,R,R,R,R)-22
D2
D2
D2
2.5776
2.5684
4.7502
1.2684
1.3446
1.1640
0.9606
1.1906
1.3448
were fully optimized with the B3LYP21c-e method. In this
manner, the symmetry and the dimensions (nm) of 17, 20, and
22 are shown in Table 1. The optimized structures of 17, 20,
and 22 were all rodlike in nanoscale (Figure 5).21d
Supramolecular Assembly of (()-3a and (S,S)-3a with
Hydrogen Bond Acceptors. With reference to the “saddle”-
like structure of tetrol 3a, it can be seen that the hydroxyl groups
on the C-1 and C-16 positions are close to each other, and so
are those on the C-8 and C-9 positions. The two pairs of
hydroxyl groups of tetrol 3a extend in opposite directions, which
may be expected to assemble with hydrogen bond acceptors
into highly ordered molecular scaffolds. Some nitrogen acceptors
were then added into an ethanol solution of 3a, yielding
crystalline adducts after a few days.10a In the molecular structure
of the 1:1 adduct of 4,4′-bipyridyl and (()-3a, 3a exists in a
dimeric form through two O-H‚‚‚O hydrogen bonds, and such
Unfortunately, attempts to obtain single crystals of complexes
17, 20, and 22 have so far been unfruitful. To have a better
understanding of these rodlike structures, density functional
studies have been performed with the Gaussian 98 program.21a
For C and H, the 3-21G basis set was used, for O and P, the
6-31G(d) basis set was used, and for Pt, the Lanl2DZ basis set
with an effective core potential (ECP)21b was used. These models
(21) (a) Frisch, M. J.; et al. Gaussian 98, Revision A.11; Gaussian, Inc.:
Pittsburgh, PA, 2001. (b) Wadt, W. R.; Hay, P. J. J. Chem. Phys. 1985,
82, 284-298. (c) Becke, A. D. Phys. ReV. 1988, A38, 3098-3100. (d)
Becke, A. D. J. Chem. Phys. 1993, 98, 1372-1377, 5648-5652. (e) Lee,
C.; Yang, W.; Parr, R. G. Phys. ReV.1988, B37, 785-789. (d) See the
Supporting Information.
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A R T I C L E S
Peng et al.
Figure 6. (a) A perspective view of the molecular aggregate of the 1:1 adduct of 4,4′-bipyridyl and (()-3a. (b) A perspective view of crystal packing
(viewed down the c axis).
Figure 7. 1:1 adduct of pyrazine and (()-3a. (a) A perspective view of crystal packing (viewed down the c axis). (b) Hydrogen-bonded layer in the crystal
structure of (()-3a‚C4H4N2. The tetrol molecules are linked by pairs of O-H‚‚‚O hydrogen bonds into a chain running parallel to the c axis, and such chains
are cross-bridged by O-H‚‚‚N hydrogen bonds (pyrazine molecules as acceptors) to form a corrugated layer. For clarity all hydrogen atoms have been
omitted except those of the hydroxyl groups.
Scheme 7
pyrazine) suitable to act as linker? (2) What will happen if
optically pure 3a is used? Are there any dimers formed from
the same enantiomeric tetrol and linked into double helical
chains?
The answer to the first question is yes. A 1:1 adduct was
obtained from the mixture of pyrazine and (()-3a in ethanol
solution, whose structure was determined by NMR and X-ray
studies. Dimers composed by two heterochiral molecules form
hydrogen bonds with each other, which result in parallel chains,
while pyrazine acts as a linker between adjacent dimers (Scheme
8 and Figure 7).
Notably, the hydroxyl groups hydrogen bonding with nitro-
gens of pyrazine are on the C-1 and C-8 positions, being
different from those on the C-1 and C-9 positions with 4,4′-
bipyridyl.
In the 1:1 adduct of 5,5′-dipyrimidine and (()-3a, only two
nitrogens of the four of 5,5′-dipyrimidine formed hydrogen
bonds with the hydroxyl groups of 3a. The hydroxyl groups
hydrogen bonding with nitrogens of 5,5′-dipyrimidine are on
the C-1 and C-8 positions. Self-assembly of homochiral tetrol
dimers are linked by 4,4′-bipyridyl through O-H‚‚‚N hydrogen
bonds, as shown in Scheme 7 and Figure 6. The same adduct
was also obtained from THF and MeOH-toluene.
From Figure 6, it can be concluded that (1) the two tetrol
molecules of one dimer are enantiomers and (2) these dimers
are not hydrogen bond saturated. They are separate from each
other and do not hydrogen bond to those close to them. If each
dimer links with two neighboring ones, chains will be composed.
So two questions arise: (1) Is the molecule of dipyridyl too
long to link the dimers, which makes the dimers (close in space)
far from hydrogen bonding? Are shorter molecules (such as
9
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1,8,9,16-Tetrasubstituted Tetraphenylene Synthesis
A R T I C L E S
Scheme 8
Scheme 9
The homochiral tetrol molecules are linked by pairs of
O-H‚‚‚O hydrogen bonds into a chiral double helical chain
running parallel to the a axis, and adjacent chains of opposite
chirality are cross-bridged by O-H‚‚‚N hydrogen bonds to form
a corrugated layer, as shown in Figure 8.
molecules gives parallel chains, while 5,5′-dipyrimidine mol-
ecules array as linear linkers between these parallel chains, as
depicted in Scheme 9.
Figure 8. A perspective view of crystal packing of the 1:1 adduct of 5,5′-
dipyrimidine and (()-3a (viewed down the b axis).
9
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A R T I C L E S
Scheme 10
Peng et al.
were reported by Pringle25 and Feringa26 which showed high
enantioselectivities in the rhodium-catalyzed hydrogenation of
acetamidocinnamate. Encouraged by these results, a novel linear
ligand (23) based on 3a was designed, and was easily prepared
in one step from 3a and hexamethylphosphorus triamide as
shown in Scheme 11. The NMR and mass spectroscopies of 23
as well as its element analysis are in full accord with the
assigned structure. There is only one signal at δ 145.7 ppm for
aminophosphite in its 31P NMR spectrum. The molecular ion
peak of compound 23 in its EI mass spectrum was observed at
m/z 514.
The asymmetric hydrogenation of olefin substrate 24 was
readily catalyzed by Rh(COD)2BF4 utilizing (S,S)-23 as a ligand
(Scheme 12). The hydrogenation reaction of phenyl 2-aceta-
midocinnamate (24a) was performed in CH2Cl2 at 15 °C under
a H2 pressure of 20 atm in the presence of 1 mol % Rh catalyst
formed in situ from [Rh(COD)2BF4] and (S,S)-23, resulting in
(R)-25 in 95.6% ee. Toluene was found to be not a good solvent
for this reaction (Scheme 12, entries 1 and 2), maybe due to
the poor solubility of the catalytic species in toluene. A higher
pressure of H2 (30 atm) gave a slightly lower ee value (Scheme
12, entries 1 and 3). A lower pressure of H2 (10 atm) also
resulted in a slightly lower ee value (Scheme 12, entries 5 and
6). Low temperature (0 °C) decreased the conversion to 10%,
and only 5% ee was realized (Scheme 12, entry 4). A slightly
higher enantioselectivity was obtained when the hydrogenation
reaction was carried out at 25 °C (Scheme 12, entry 5).
The asymmetric hydrogenation of various acetamidocin-
namate derivatives (24b-e) was investigated in CH2Cl2 at 25
°C under a pressure of 20 atm (Scheme 12, entries 7-10).
Higher enantioselectivities were achieved when more sterically
hindered or electron-deficient substrates were employed. For
all methyl esters, the conversions are quantitative and the
enantioselectivities (94.9-99.0% ee) are comparable to those
achieved with other monodentate phosphorus ligands and
bidentate phosphorus ligands (e.g., CAMP, 90%,23 BINAP, 67-
100%,24 MonoPHOS, 93.2-99.8%,26 and SIPHOS, 95.6-
99.3%27). It is expected that oligomeric or polymeric complexes
may form when 23 is allowed to react with 1 equiv of [Rh-
(COD)2BF4], although the possibility of forming a square
complex cannot be ruled out.8 We were unable to dissolve the
solids that formed in these reactions. This result might be
indicative of formation of oligomeric or polymeric mixtures.28
Scheme 11
The answer to the second question is also yes. In the 1:1
adduct of (S,S)-3a with 4,4′-dipyridyl, the latter serves as a linker
between parallel chiral double helical chains formed by self-
assembly of (S,S)-3a, as shown in Scheme 10 and Figure 9.
The same result from (R,R)-3a and 4,4′-dipyridyl also confirmed
such an arrangement.
From Figure 9b, it can be seen that the tetrol molecules are
linked by pairs of O-H‚‚‚O hydrogen bonds into a chiral double
helical chain running parallel to the [101] axis, and such chains
are cross-bridged by O-H‚‚‚N hydrogen bonds (4,4′-dipyridyl
molecules as acceptors) to form a corrugated layer (see Figure
9a).
Conclusion
In conclusion, we have synthesized chiral 1,8,9,16-tetrahy-
droxytetraphenylene (3a) and 1,8,9,16-tetrakis(diphenylphos-
phino)tetraphenylene (3b). These chiral building blocks were
employed to construct two chiral rodlike triblock platinum
complexes, (R,R,R,R)-17 and (S,S,S,S)-20, and one chiral rodlike
pentablock complex, (R,R,R,R,R,R,R,R)-22.
The shorter acceptor, pyrazine, reacted with (S,S)-3a or (R,R)-
3a, resulting in 1:1 adducts. Unfortunately, no crystals were
obtained from the mixture of pyrazine and optically pure 3a
under the same conditions. Self-assembly of 5,5′-dipyrimidine
and optically pure 3a is under way.
Asymmetric Hydrogenation of Olefins. Early examples
concerning asymmetric transition-metal-catalyzed hydrogenation
reactions of prochiral olefins were reported independently by
Horner22a and Knowles22b in 1968. The ligands used are chiral
monophosphanes, but low ee values were obtained. A larger
number of bidentate ligands with excellent selectivities, such
as CAMP23 and BINAP,24 were subsequently designed and
tested. Recently monodentate phosphite and phosphoramidites
(23) (a) Vineyard, B. D.; Knowles, W. S.; Sabadky, M. J.; Bachman, G. L.;
Weinkauff, D. J. Am. Chem. Soc. 1977, 99, 5946-5952. (b) Knowles, W.
S.; Sabacky, M. J.; Vineyard, B. D.; Weinkauff, D. J. J. Am. Chem. Soc.
1975, 97, 2567-2568.
(24) Miyashita, A.; Yasuda, A.; Takaya, H.; Toriumi, K.; Ito, T.; Souchi, T.;
Noyori, R. J. Am. Chem. Soc. 1980, 102, 7932-7934.
(25) Claver, C.; Fernandez, E.; Gillon, A.; Heslop, K.; Hyett, D. J.; Martorell,
A.; Orpen, A. G.; Pringle, P. G. Chem. Commun. 2000, 961-962.
(26) van Berg, M.; Minnaard, A. J.; Schudde, E. P.; van Esch, J.; Vries, A. H.
M.; Vries, J. G.; Feringa, B. L. J. Am. Chem. Soc. 2000, 122, 11539-
11540.
(27) Fu, Y.; Xie, J.-H.; Hu, A.-G.; Zhou, H.; Wang, L.-X.; Zhou, Q.-L. Chem.
Commun. 2002, 480-481.
(28) Wang, X.; Ding, K. J. Am. Chem. Soc. 2004, 126, 10524-10525.
(22) (a) Horner, L.; Siegel, H.; Buthe, H. Angew. Chem. 1968, 80, 1034-1035.
(b) Knowles, W. S.; Sabacky, M. J. Chem. Commun. 1968, 1445-1446.
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9610 J. AM. CHEM. SOC. VOL. 127, NO. 26, 2005

1,8,9,16-Tetrasubstituted Tetraphenylene Synthesis
A R T I C L E S
Figure 9. (a) A perspective view of crystal packing of the 1:1 adduct of 4,4′-dipyridyl and (S,S)-3a (viewed down the b axis). For simplicity the 4,4′-
dipyridyl molecule is represented by a rigid rod. (b) Hydrogen-bonded layer in the crystal structure of (S,S)-3a‚C10H8N2. For clarity all hydrogen atoms have
been omitted.
Scheme 12
There are no intermolecular hydrogen bonds involving the
hydroxyl groups of 3a, except that they form hydrogen bonds
with the solvent molecules. Highly ordered structures were
obtained when linear acceptors formed hydrogen bonds with
3a. In the 1:1 adduct of 4,4′-bipyridyl and (()-3a, tetrol 3a
existing in a dimeric form is linked by 4,4′-bipyridyl through
hydrogen bonds. Pyrazine serves as a short linker between
achiral parallel chains each formed by (()-3a, while self-
assembly of homochiral tetrol molecules into alternate parallel
chains occurs in the adduct of 5,5′-dipyrimidine with (()-3a.
Self-assembly of (S,S)-3a or (R,R)-3a with 4,4′-dipyridyl yielded
a packing of chiral double helical chains formed by chiral tetrol
molecules.
may indicate the potential of tetraphenylene derivatives in
asymmetric catalysis.
Acknowledgment. This work was supported by grants from
the Research Grants Council of the Hong Kong Special Admin-
istrative Region, China (Project CUHK 4264/00P), and the
Croucher Foundation (Hong Kong). H.-Y.P. acknowledges with
thanks the Croucher Foundation (Hong Kong) for a Shanghai
Studentship. The Science and Technology Commission of the
Shanghai Municipality also partially supported this program.
We thank Professor Li-Xin Dai and Xue-Long Hou for helpful
discussions and Dr. Xi-Cheng Dong for molecular models.
Supporting Information Available: Experimental details,
computation results, X-ray crystallographic data of 3a, 10, 13,
15, and adducts of 3a with acceptors, CD spectrum of (S,S)-3a
and (R,R)-3a, and complete ref 21a. This material is available
free of charge via the Internet at http://pubs.acs.org.
An effective linear chiral ligand, (S,S)-23, has been developed
for the catalytic hydrogenation of acetamidocinnamate deriva-
tives. This is the first example of a chiral tetraphenylene
derivative being used as an effective catalytic hydrogenation
ligand. The high enantioselectivity (up to 99% ee) and stability
JA051013L
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