Rotaxane synthesized by end-capping via hydroruthenation of axle terminal acetylene and its derivation to η3-allylrutheniuni complex-containing rotaxane

Article abstract of DOI:10.1246/cl.2006.212

The hydroruthenation of pseudorotaxane 1-DB24C8 having an alkyne moiety at the axle terminal with RuHCl(CO)(PPh₃)₃ gave [2]rotaxane 2 with an alkenylruthenium complex moiety in a good yield. The carbometalation of allenes with 2 resulted in the formation of the corresponding [2]rotaxanes 3 with η³-allylruthenium complex moieties in good yields. Copyright

Full text of DOI:10.1246/cl.2006.212

212
Chemistry Letters Vol.35, No.2 (2006)
Rotaxane Synthesized by End-capping via Hydroruthenation of Axle Terminal Acetylene
and Its Derivation to ꢀ3-Allylruthenium Complex-containing Rotaxane
Hisahiro Sasabe,1 Nobuhiro Kihara,ꢀ1 Kazuhiko Mizuno,1 Akiya Ogawa,1 and Toshikazu Takataꢀ2
1Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka 599-8531
2Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552
(Received November 29, 2005; CL-051480; E-mail: ttakata@polymer.titech.ac.jp)
.
The hydroruthenation of pseudorotaxane 1 DB24C8 having
i) DB24C8
ii) RuHCl(CO)(PPh3)3
an alkyne moiety at the axle terminal with RuHCl(CO)(PPh3)3
gave [2]rotaxane 2 with an alkenylruthenium complex moiety
in a good yield. The carbometalation of allenes with 2 resulted
in the formation of the corresponding [2]rotaxanes 3 with ꢀ3-
allylruthenium complex moieties in good yields.
PF6
O
N
H2
CHCl3, rt
1
PF6
O
O
O
O
N
Recently, rotaxanes with active catalytic sites have been
receiving much attention because the cooperation of their com-
ponents is the basic feature of the biomimetic catalyst.1 Rowan
and Nolte have developed the first [2]rotaxane catalyst that mim-
ics the DNA ꢁ-exonuclease.1a We have reported [2]rotaxane
catalysts for asymmetric benzoin condensation mimicking a
Vitamin B1-catalyzed system.1b These findings clearly suggest
the potential usefulness of a rotaxane catalyst for the develop-
ment of a unique and sophisticated catalyst system. However,
the introduction of a catalytic site into rotaxanes still represents
a challenging task, although various synthetic methods of rotax-
anes have been developed so far.2
O
O
H2
O
O
O
Ru
2: Ru = [Ru].Et2O
[Ru] = RuCl(CO)(PPh3)2
R
R
3a: R = Ph (75%)
3b: R = Cy (61%)
3: Ru =
[Ru]
Scheme 1.
1H NMR spectrum similar to that observed in related systems.10
By the addition of 1.0 equiv. of RuHCl(CO)(PPh3)3 to the solu-
.
Recently, we have reported the synthesis of vinylsilane-
terminated [2]rotaxanes by RuHCl(CO)(PPh3)3-catalyzed hy-
drosilylation of alkyne moieties of the axle components.3 The
reaction proceeds via the alkenylruthenium species, Ru(CH=
CHR)Cl(CO)(PPh3)2,4 which is the important intermediate in
various organic transformations.5 Meanwhile, the ꢀ3-allylruthe-
nium complex, which can be synthesized via the carbometala-
tion of the alkenylruthenium complex with allenes,5e has been
reported to react as an ambiphilic allylation reagent,6 a catalyst
for cyclization reactions,7 and a precursor of various ruthenium
complexes.8 Thus, rotaxanes possessing alkenyl- or ꢀ3-allylru-
thenium complex moieties can be regarded as useful intermedi-
ates for the construction of rotaxane catalysts and functionalized
rotaxanes. In this report, the efficient end-capping synthesis of
ruthenium complex-functionalized [2]rotaxanes and its deriva-
tion to rotaxanes bearing ꢀ3-allylruthenium complex moieties
will be described.
The pair of sec-ammonium salt axle and dibenzo-24-crown-
8 (DB24C8) wheel is one of the most effective combinations for
the construction of rotaxanes.2 The authors chose ammonium
salt 1 with a terminal alkyne group as the axle component. Since
the reactivity of functional groups on the axle is strongly
suppressed due to the steric hindrance of DB24C8 when the axle
is surrounded by the wheel,3,9 an axle component with a long
spacer between the ammonium and alkyne moieties was
designed and synthesized (Scheme 1).
tion of 1 DB24C8, the ruthenium complex was completely dis-
solved within 30 min. The initial clear colorless solution turned
to clear reddish orange as the reaction progressed, indicating the
formation of alkenylruthenium complex 2 through the hydrome-
talation of the axle terminal alkyne moiety. The purity of 2
isolated by the repeated precipitation in Et2O reached 95% by
1H NMR (yield 96%). [2]Rotaxane 2 was characterized by
1H NMR and IR spectra. In Figure 1a, benzylic protons of the
ammonium group (He and Hd) appeared at 4.48–4.37 ppm with
complex coupling, which is characteristic of crown ether–
ammonium salt type rotaxanes.2,10 Vinyl protons (Ha and Hb)
were observed at 8.49 and 5.61 ppm with coupling constant
J ¼ 13:2 Hz, which coincides with that of corresponding vinyl-
ruthenium complexes.11
The reactivity of the alkenylruthenium complex moiety of 2
was examined to characterize it as the ‘‘reactive’’ rotaxane and to
finally confirm the structure of 2 by deriving it to a stable prod-
uct. Two allenes were chosen as reactants. The reaction was
conducted by mixing phenylallene with freshly prepared 2 at
ambient temperature. The reaction proceeded smoothly within
2 h to give the corresponding ꢀ3-allylruthenium complex-con-
taining [2]rotaxane 3a12 in 75% yield by purification with prep-
arative HPLC (eluent: CHCl3). When less reactive cyclohexylal-
lene5e was used, similar ruthenium complex-containing [2]rotax-
ane 3b was obtained in 61% yield. These results clearly indicate
that 2 is a useful reactive [2]rotaxane for further functionaliza-
tion. It should be noted that no degradation of rotaxane structure,
like dethreading of the axle component during the insertion of
allene into the Ru-complex moiety of 2, occurred, confirming
that the Ru complex moiety is sufficiently bulky as end-cap.
The addition of 1.2 equiv. of DB24C8 to a suspension of 1 in
CHCl3 at ambient temperature resulted in the dissolution of 1 to
give a clear colorless solution. The formation of pseudorotaxane
.
(1 DB24C8) was confirmed by the characteristic change of
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.2 (2006)
213
References and Notes
(a)
PF6
γ
1
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f
f
e
d
Hb
c
N
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O
[Ru] Et2O
Ha
2
β
α
2
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(b)
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i
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g
Hc
He
Hd
i
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4
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Hb
Ha
[Ru]
Hd
Ph
4
*
d
e
b
c
a
6
7
7
6
5
4
3
2ppm
1
Figure 1. Partial H NMR spectra of (a) rotaxane 2, (b) rotax-
ane 3a, and (c) ruthenium complex 4 in CDCl3. Asterisk (ꢀ)
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The structure of [2]rotaxane 3 was characterized by
1H NMR and IR spectra and elemental analyses. Benzylic
protons of the ammonium group (Hg and Hh) were observed at
4.51–4.38 ppm with complex coupling similarly to the case of
2. Vinylic and allylic protons (Ha{e) were observed as reported
for a similar (2-alkeyl-ꢀ3-allyl)ruthenium complex.8 The crystal
of 3 was stable under air at ambient temperature, indicating that
3 can be easily handled for further reaction. Meanwhile, 3 was
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at that temperature.13
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In conclusion, alkenylruthenium complex-terminated [2]-
rotaxane was prepared in a high yield and derived to correspond-
ing [2]rotaxanes carrying ꢀ3-allylruthenium complex moieties
by reaction with allenes. The potential reactivity of 2 as demon-
strated in the present paper points to the likelihood of various
functionalizations of rotaxane. Further study of these [2]rotax-
ane ruthenium complexes is under progress.
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1
12 3a: Yellow solid. H NMR (400 MHz, CDCl3) ꢂ 7.40–6.78
(m, 57H), 6.59 (d, 1H, J ¼ 15:6 Hz), 5.01 (s, 2H), 4.51–
4.48 (m, 2H), 4.41–4.38 (m, 2H), 4.18 (d, 1H, J ¼ 6:4 Hz),
4.07 (brs, 8H), 3.71 (brs, 8H), 3.40 (brs, 9H), 2.95 (d, 1H,
J ¼ 4:9 Hz), 2.13 (s, 6H) IR (NaCl) 1931, 1541, 1506,
1456, 1435, 1252, 1123, 841, 746, 696, 557, 519 cmꢂ1. Anal.
This paper is dedicated to Dr. Saburo Nakanishi on his 65th
birthday. We thank Dr. Yoshio Furusho of Yashima Super-struc-
tured Helix Project (ERATO, JST) for his helpful comments.
This work was performed with the financial support of the
Ministry of Education, Culture, Sports, Science and Technology
through a Grant-in-Aid for Scientific Research.
.
Calcd for C96H97ClF6NO10P3Ru (CHCl3)0:75: C, 62.55; H,
5.30; N, 0.75%. Found: C, 62.58; H, 5.44; N, 0.83%.
13 J. Lopez, A. Romero, A. Santos, A. Vegas, A. M.
Echavarren, P. Noheda, J. Organomet. Chem. 1989, 373,
249.
Published on the web (Advance View) January 21, 2006; DOI 10.1246/cl.2006.212