Successive catalytic reactions specific to Pd-based rotaxane complexes as a result of wheel translation along the axle

Article abstract of DOI:10.1039/b917053g

Rotaxane-structure-specific Pd-catalyzed rearrangement of propargyl or allyl urethane groups to oxazolidinone moieties proceeded efficiently. The conversion took place successively by the translation of the wheel along the axle, thus providing a novel macrocyclic catalytic system. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b917053g

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Successive catalytic reactions specific to Pd-based rotaxane complexes
as a result of wheel translation along the axlew
Norihito Miyagawa,a Masahiro Watanabe,a Takanori Matsuyama,a Yasuhito Koyama,a
Toshiyuki Moriuchi,b Toshikazu Hirao,b Yoshio Furushoc and Toshikazu Takata*a
Received (in Cambridge, UK) 18th August 2009, Accepted 22nd December 2009
First published as an Advance Article on the web 18th January 2010
DOI: 10.1039/b917053g
Rotaxane-structure-specific Pd-catalyzed rearrangement of
propargyl or allyl urethane groups to oxazolidinone moieties
proceeded efficiently. The conversion took place successively by
the translation of the wheel along the axle, thus providing a novel
macrocyclic catalytic system.
moiety produced the cyclic derivative 9 only by heating in
MeOH. The process formally involves two hydroamination
reactions of the urethane N–H to the alkyne group.9 The
structure of 9 was examined by IR, NMR, and MS spectra and
finally determined by X-ray single crystal structure analysis
(Fig. 2).10 The X-ray analysis indicated that the newly formed
double bond adopted a syn-conformation, possibly due to
steric constraint from the macrocycle component; this finding
was also supported by a CPK model study. The hydroamination
of 3 was performed under various conditions and the results
are summarized in Table 1. While protic and small-size
solvents such as MeOH and H2O were absolutely indispensable
for the reaction (Entries 1, 2, and 5), a prolonged reaction time
also worked effectively under base-free conditions. After con-
siderable elaborations, Mg(OMe)2 was found to be the most
suitable cocatalyst (Entries 9 and 10) to shorten the reaction
time and give 9 in a high yield.
The mechanical axle-wheel linkage that is characteristic of
rotaxanes1 has the potential to be utilized in catalytic systems.
Rowan et al. have reported polyene epoxidation on the axle
catalyzed by a manganese porphyrin-functionalized wheel.2 In
this system, the translation of the wheel along the axle
component enabled a catalytic reaction. In addition, we have
previously reported asymmetric benzoin condensations
catalyzed by thiazolium-functionalized [2]rotaxanes,3 which
induced through-space enantioselective catalysis. Rotaxane
catalysts are associated with ‘‘macrocyclic catalysts’’ like
l-exonuclease for DNA duplex formation4 and with ‘‘linear
molecular motors,’’5 which are regarded to be one of the major
targets of rotaxane chemistry. The unique rotaxane catalysis
prompted us to design a novel rotaxane-based catalytic
system that exploits the versatility of transition metals using
a Pd-containing macrocycle. We believe that such rotaxane
catalysts will be applicable in a variety of fruitful systems such
as polymer modification, substrate-specific reactions, and
linear molecular motors (Fig. 1).6,7
Allyl-urethane-functionalized [2]rotaxanate 6 was quantitatively
converted to the cyclization product by the same procedure
(Scheme 2). The product consisted of two compounds: syn–
anti diastereomers 10 and 11 (1 : 1) with chiral centers at the
oxazolidinone moieties. The diastereomers were separated by
chromatography and analyzed by 1H NMR (Fig. 3) and
structure simulation by DFT calculations (6-31G**,
B3LYP).10
The much higher conversion of 6 relative to that of 3 is
possibly due to not only the high reactivity of the olefin moiety
to hydoroamination, but also due to the higher stability of
the oxazolidinone moiety of 10 and 11 in basic conditions
compared with that of the oxazolidone moiety of 9.
As shown in 1H NMR spectra (Fig. 3), the key signals of the
olefinic protons and urethane N–H protons of 6 clearly
appeared in toluene-d8 at 100 1C, while these signals in CDCl3
Herein, we describe the highly efficient successive catalysis
on the axle component of our Pd-based rotaxanes and the
application of these complexes to establish an unprecedented
‘‘macrocyclic catalyst’’ system.
The [2]rotaxanates containing propargyl urethane and allyl
urethane moieties (3 and 6) were prepared according to our
reported method with slight modifications (Scheme 1).7,8
During the recrystallization process of 3, we unexpectedly
found that the cyclization reaction of the propargyl urethane
a Department of Organic and Polymeric Materials,
Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku,
Tokyo 152-8552, Japan. E-mail: ttakata@polymer.titech.ac.jp
b Department of Applied Chemistry, Graduate School of Engineering,
Osaka University, Yamada-oka, Suita, Osaka 565-0871, Japan.
E-mail: moriuchi@chem.eng.osaka-u.ac.jp
c Department of Molecular Design and Engineering,
Graduate School of Engineering, Nagoya University, B2-3 (611),
Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan.
E-mail: furusho@apchem.nagoya-u.ac.jp
w Electronic supplementary information (ESI) available: Experimental
details and characterization data. CCDC 246459 & 756922. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b917053g
Fig. 1 Design of movable catalyst system.
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Scheme 2 Reagents and Conditions: (a) Mg(OMe)2 (0.4 M in MeOH),
reflux, 10 min (99%, 10:11 = 1 : 1).
Scheme 1 Reagents and Conditions: (a) macrocycle 7 (1.0 equiv.),
CH2Cl2, RT, 1 h; (b) R-NCO 8 (2.1 equiv.), DBTDL (0.1 equiv.),
CH2Cl2, RT, 1 h (84%, 2 steps); (c) macrocycle 7 (1.0 equiv.), CH2Cl2,
RT, 1 h; (d) R-NCO 8 (2.1 equiv.), DBTDL (0.1 equiv.), CH2Cl2, RT,
1 h (83%, 2 steps). DBTDL: dibutyltin dilaurate.
Fig. 3 Partial 1H NMR spectra (400 MHz) of 6 (i) toluene-d8 at
398 K(II) CDCl3 at 298 K, 10 (iii) CDCl3 at 298 K, and 11 (iv) CDCl3
at 298 K.
Based on these selective reactions, rotaxanates with two
pyridine groups, four reactive points in the axle, and a Pd-
containing macrocyclic component were synthesized (12 and
13, Scheme 3). Through investigation with variable temperature
1H NMR (VT-NMR), we found that the wheel component of
12 and 13 could alternate between the pyridine stations on the
axle, namely the macrocycle transports the Pd metal along the
axle.11 The hydroaminations of 12 and 13 were conducted
under similar conditions to those of 3 and 6 (Scheme 3).
A solution of 12 in MeOH–THF was refluxed for 1 min in
the presence of Mg(OMe)2.12 Repeated purification with
preparative HPLC afforded a product in a low yield (16%),
which was eventually determined to be isomerized rotaxanate
14. Similar to the conversion of 3 to 9, the four propargyl
urethane moieties of 12 were all converted to oxazolidone
moieties, as is suggested by the spectroscopic and elemental
analyses of 14. Contrary to the conversion of 12 to 14,
treatment of 13 with Mg(OMe)2 for 90 min afforded iso-
merized rotaxanate 15 in a quantitative yield, which proves
that the translation of the macrocyclic catalyst enabled a clean
successive reaction.
Fig. 2 X-Ray crystal structure of Pd-rotaxanate 9.
at room temperature disappeared owing to the coalescent
rotamers. The olefin and urethane signals of 6 disappeared
as methine (signal d) and methylene protons (signal c) of the
oxazolidinone moieties appeared. The aromatic proton signals
of the wheel component of 10 (signals a and b) were split into
two couplets, contrary to the aromatic proton signals of 11.
This is possibly a result of the structural asymmetry of the axle
component relative to the wheel component in 10, as is
confirmed by the simulated structures.10
Table 1 Effects of solvents and additives for macrocycle-catalyzed hydroamination reaction of Pd-rotaxanate 3
Entry
Solvent
Additive (equiv.)
Temp.
Time/h
Yield (%)
1
2
3
4
5
6
7
8
9
10
MeOH
EtOH
i-PrOH
t-BuOH
MeOH–H2O (20 : 1)
THF
THF
THF–H2O (20 : 1)
MeOH
MeOH–H2O (4 : 1)
—
—
—
—
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
20
20
27
22
20
24
39
1
12
33
NRa
NRa
63
—
Et3N (2.0)
PPh3 (2.0)
NaOHb
Mg(OMe)2c
Mg(OMe)2
Decomp.
NRa
10
48
68
c
10 min
10 min
a
b
No reaction. 0.01 M. 0.4 M.
c
ꢀc
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Successive catalytic reactions on the rotaxane axle using this
unique system might provide new insights into selective
conversion reactions, efficient polymer transformations, and
linear molecular motor systems. The scope and limitations of
catalytic reactions with Pd-based rotaxanes would be an
important focus for future investigations.
This work was supported by Grant-in-Aid for Scientific
Research on Priority Areas (No. 18064008, Synergy of Elements)
from the Ministry of Education, Culture, Sports, Science and
Technology, Japan.
Notes and references
1 (a) Molecular Catenanes, Rotaxanes, and Knots, ed. J.-P. Sauvage and
C. Dietrich-Buchecker, Wiley-VHC, Weinheim, 1999; (b) J.-P. Sauvage,
Acc. Chem. Res., 1990, 23, 319; (c) H. W. Gibson, M. C. Bheda and
P. T. Engen, Prog. Polym. Sci., 1994, 19, 843; (d) D. B. Amabilino and
Scheme
MeOH–THF), reflux,
MeOH–THF), reflux, 90 min (99%).
3
Reagents and Conditions: (a) Mg(OMe)2 (0.4
M
M
in
in
1
min (16%); (b) Mg(OMe)2 (0.4
J. F. Stoddart, Chem. Rev., 1995, 95, 2725; (e) G. Vogtle, T. Dunnwald
¨
¨
and T. Schmidt, Acc. Chem. Res., 1996, 29, 451; (f) A. Harada, Adv.
Polym. Sci., 1997, 133, 141; (g) T. J. Hubin and D. H. Busch, Coord.
Chem. Rev., 2000, 200–202, 5; (h) T. Takata and N. Kihara, Rev.
Heteroat. Chem., 2000, 22, 197; (i) N. Kihara and T. Takata, J. Synth.
Org. Chem. Jpn., 2001, 59, 206; (j) T. Takata, N. Kihara and
Y. Furusho, Adv. Polym. Sci., 2004, 171, 1; (k) T. Takata, Polym.
J., 2006, 38, 1.
2 P. Thordarson, E. J. A. Bijsterveld, A. E. Rowan and R. J.
M. Nolte, Nature, 2003, 424, 915.
3 Y. Tachibana, N. Kihara and T. Takata, J. Am. Chem. Soc., 2004,
126, 3438.
Thus, products 14 and 15 were formed by successive catalytic
isomerization caused by the translation of the Pd-carrying wheel
along the axle component. VT-NMR analyses revealed that the
wheel component of [2]rotaxane 15, together with the Pd atom,
could alternate between pyridine moieties on the axle. On the
other hand, the central axle p-phenylene bisoxazolidone moiety
of 14 was too bulky to allow for translation of the wheel. This is
consistent with the low conversion yield of 12.
From the efficient successive transformation described
above, we postulated that native wheel component 7 alone
enables the intermolecular catalytic reaction where size-
selection of the substrate can occur if the rotaxane-like inter-
mediate is formed. To investigate this theory, model reactions
were carried out using two substrates that possessed two allyl
urethane moieties: simple substrate 16 and end-bulky substrate
18 (Scheme 4). The intermolecular hydroamination of 16 with
a stoichiometric amount of 7 in the presence of Mg(OMe)2
smoothly proceeded to give the cyclization compound 17 in a
quantitative yield. This reaction required a much greater time
than the rotaxane system. The use of a catalytic amount of 7
(20 mol%) also achieved a quantitative yield at 50 1C in the
presence of Mg(OMe)2 (0.8 M in MeOH). On the other hand,
no reaction occurred when 18 was similarly treated with 7.
These results indicate that Pd-templated macrocyclic catalyst 7
leads to the enzyme-like substrate-specific reaction of 16 to
form 17, in which the penetration of the substrate into the
cavity of 7 possibly accelerates the reaction.13
4 R. Kovall and B. W. Matthews, Science, 1997, 277, 1824.
5 (a) C. A. Schalley, K. Beizai and F. Voegtle, Acc. Chem. Res., 2001,
34, 465; (b) E. R. Kay and D. A. Leigh, Top. Curr. Chem., 2005,
262, 133; (c) V. Balzani, M. Clemente-Leon, A. Credi,
M. Semeraro, M. Venturi, H.-R. Tseng, S. Wenger, S. Saha and
J. F. Stoddart, Aust. J. Chem., 2006, 59, 193.
6 For selected reviews of palladium chemistry as the representative
class of transition metal, see: (a) Transition Metal Reagent and
Catalysts, Innovation in Organic Synthesis, ed. J. Tsuji, John Wiley
& Sons, 2000; (b) A. F. Littke and G. C. Fu, Angew. Chem., Int.
Ed., 2002, 41, 4176; (c) L. Ackermann, Synthesis, 2006, 1557;
(d) K. C. Nicolaou, D. J. Edmonds and P. G. Bulger, Angew.
Chem., Int. Ed., 2006, 45, 7134.
7 Y. Furusho, T. Matsuyama, T. Takata, T. Moriuchi and T. Hirao,
Tetrahedron Lett., 2004, 45, 9593.
8 For related reports, see: (a) D. A. Leigh, P. J. Lusby, A. M. Z. Slawin
and D. B. Walker, Angew. Chem., Int. Ed., 2005, 44, 4557; (b) A.-M.
L. Fuller, D. A. Leigh, P. J. Lusby, A. M. Z. Slawin and
D. B. Walker, J. Am. Chem. Soc., 2005, 127, 12612;
(c) J. D. Crowley, K. D. Hanni, A.-L. Lee and D. A. Leigh,
¨
J. Am. Chem. Soc., 2007, 129, 12092; (d) J. D. Crowley,
D. A. Leigh, L. P. J. Lusby, R. T. McBurney, L.-E. Perret-Aebi,
C. Petzold, A. M. Z. Slawin and M. D. Symes, J. Am. Chem. Soc.,
2007, 129, 15085; (e) W.-C. Hung, L.-Y. Wang, C.-C. Lai, Y.-H. Liu,
S.-M. Peng and S.-H. Chiu, Tetrahedron Lett., 2009, 50, 267.
9 For related reports concerning hydroamination reaction, see:
(a) M. Kimura, Y. Wakamiya, Y. Horino and Y. Tamaru, Tetrahedron
Lett., 1997, 38, 3963; (b) Y. Horino, M. Kimura, S. Tanaka,
T. Okajima and Y. Tamaru, Chem.–Eur. J., 2003, 9, 2419;
(c) K. Suzuki, R. Ushijima, T. Miyano and S. Nakagawa, Heterocycles,
1989, 29, 497; (d) N. Morita and N. Krause, Org. Lett., 2004, 6, 4121.
10 See, electronic supplementary informationw (ESI).
Thus, we found that a Pd-based rotaxane skeleton is
critical to accelerating the above hydroamination reactions.
11 For reports about metal transfer system between ligands in inter-
locked structure, see: (a) J.-P. Sauvage, Acc. Chem. Res., 1998, 31,
611; (b) U. Letinois-Halbes, D. Hanss, J. M. Beierle, J.-P. Collin
´
and J.-P. Sauvage, Org. Lett., 2005, 7, 5753.
12 The prolonged reaction time resulted in the decrease of yield, due
to solvolysis of the oxazolidone moieties of 14.
13 Treatment of 16 and 18 with an acyclic Pd catalyst with a similar
structure to that of 7 but without the tetra(ethyleneoxy) moiety,
gave cyclization products (50 1C, 19 h), respectively. This result
undoubtedly confirms the essential significance of the macrocyclic
catalyst in the size-selective reaction.
Scheme
4 Reagents and Conditions: (a) 7 (100 mol% to 16),
Mg(OMe)2 (0.4 M in MeOH), 30 1C, 30 h (99%); (b) 7 (20 mol% to
16), Mg(OMe)2 (0.8 M in MeOH), 50 1C, 19 h (99%); (c) 7 (100 mol%
to 18), Mg(OMe)2 (0.4 M in MeOH), 30 1C, 30 h (N.R.).
ꢀc
This journal is The Royal Society of Chemistry 2010
1922 | Chem. Commun., 2010, 46, 1920–1922