DOI: 10.1002/chem.201405090
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Rotaxanes
Synthesis of [3]Rotaxanes that Utilize the Catalytic Activity of
a Macrocyclic Phenanthroline–Cu Complex: Remarkable Effect of
the Length of the Axle Precursor
Yoshiaki Yamashita,[a] Yuichiro Mutoh,[a] Ryu Yamasaki,[a] Takeshi Kasama,[b] and
Shinichi Saito*[a]
Abstract: [3]Rotaxanes, which consist of one macrocyclic
phenanthroline compound and two axle components, were
prepared by the oxidative dimerization of an alkyne com-
pound with bulky tris[4’-cyclohexyl-(1,1’-biphenyl)-4-yl]meth-
yl blocking group. The catalytic activity of a macrocyclic phe-
nanthroline–Cu complex was utilized to thread the two axle
components inside the ring. The alkyne compound with
chain of 15 or 20 methylene groups gave [3]rotaxanes in
high yields, whereas the axle with a chain of six methylene
groups afforded a [3]rotaxane in very poor yield. We also ex-
amined the effect of the ring size on the synthesis of [3]ro-
taxanes. [3]Rotaxanes were not isolated when a macrocyclic
phenanthroline compound with a smaller ring size was used.
Introduction
and [3]rotaxanes composed of two axle and one ring compo-
nents (type 2.1).[3] A [3]rotaxane of type 1.2 was synthesized by
using the template method,[4] clipping method,[5] or threading
reaction mediated by a macrocyclic metal complex.[6] On the
other hand, a [3]rotaxane of type 2.1 is less accessible and the
first synthesis was reported in 2006 by Anderson and co-work-
ers,[7] which utilize the ability of a cyclodextrin compound to
accept two guest molecules in its cavity. The synthesis of
a [3]rotaxane of type 2.1 was also achieved by using the tem-
plate method[8] and a catalytic threading reaction.[9]
Rotaxane is an interlocked compound, which consist of ring
and axle components.[1] These units are expected to be the
key elements of a molecular machine or other molecular devi-
ces.[2] A prefix in the bracket of the name of a rotaxane de-
scribes the number of the components of
a rotaxane
(Figure 1). Thus, a [2]rotaxane consists of one axle and one
ring component. Similarly, a [3]rotaxane consists of three com-
ponents, and there are two types of [3]rotaxane: [3]rotaxanes
composed of one axle and two ring components (type 1.2)
The [3]rotaxane of type 2.1 would be more difficult to syn-
thesize than type 1.2 because the installation of the second
axle component to the [2]rotaxane is frequently inhibited due
to the presence of the axle component inside the ring. Al-
though it is obvious that a sufficiently large ring would be re-
quired to incorporate two axle components, the structural re-
quirements of the components for the synthesis of a [3]rotax-
ane remains unclear.
We developed a new method in 2006 for the synthesis of
a [2]rotaxane that utilized the oxidative dimerization of an
alkyne and was mediated by a macrocyclic phenanthroline–Cu
complex.[10] We also reported the synthesis of a [2]rotaxane
with a bulky tris[4’-cyclohexyl-(1,1’-biphenyl)-4-yl]methyl block-
ing group with a large 37-membered macrocyclic phenanthro-
line moiety.[11] In principle, it is possible to synthesize a [3]rotax-
ane by using a catalytically active macrocyclic metal complex.
Thus, a [3]rotaxane of type 2.1 could be synthesized when the
metal-catalyzed bond-forming reaction proceeded twice inside
the ring (Scheme 1). The only example of this approach has
been recently reported by Leigh and co-workers.[9] In their
study, a [3]rotaxane was isolated in 51% yield by carrying out
the reductive homocoupling reaction of an excess (20 equiv)
of an alkyl bromide and a macrocyclic terpyridine–Ni complex.
Figure 1. The structure of [2] and [3]rotaxanes.
[a] Y. Yamashita, Dr. Y. Mutoh, Dr. R. Yamasaki, Prof. S. Saito
Department of Chemistry, Faculty of Science
Tokyo University of Science
1-3 Kagurazaka, Shinjuku, Tokyo 162-8601 (Japan)
[b] Prof. T. Kasama
Research Center for Medical and Dental Science
Tokyo Medical and Dental University
1-5-45 Yushima, Bunkyo, Tokyo 113-8510 (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201405090.
Chem. Eur. J. 2014, 20, 1 – 8
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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