Published on Web 01/29/2003
2+
A [2]Catenane Constructed around a Ru(Diimine)3 Complex Used as a
Template
Pierre Mobian, Jean-Marc Kern,* and Jean-Pierre Sauvage*
Laboratoire de Chimie Organo-Mine´rale, UMR 7513 du CNRS, UniVersite´ Louis Pasteur, Faculte´ de Chimie,
4, rue Blaise Pascal, 67070 Strasbourg Cedex, France
Received July 8, 2002 ; E-mail: mobian@chimie.u-strasbg.fr, jmk@chimie.u-strasbg.fr, sauvage@chimie.u-strasbg.fr
Octahedral transition metal centers have only been scarcely used
as templates for synthesizing topologically nontrivial molecules such
as catenanes and knots. An early example is dealing with the use
of a bis-terpy complex (terpy ) 2,2′,6′,2′′-terpyridine).1 A spec-
tacular synthetic achievement was recently reported that was based
on two terdentate ligands entwined around a first-row transition
metal.2 Knots have been made using two octahedral iron centers,
each metal being coordinated to two terpy derivatives.3 An “open”
knot was also described whose synthesis was made possible by
knotting a long molecular thread incorporating three bidentate
chelates around a zinc(II) atom.4
Until now, tris-bidentate chelate complexes have not been utilized
for making [2]catenanes. This is understandable in view of the
success of the tetrahedral copper(I) center for promoting interlocking
or knotting of various molecular stringlike fragments.5 It may also
be explained by the difficulty of entwining two threads using three
chelates gathered around a transition metal center. We now report
2+
such an example based on a Ru(diimine)3 derivative.
The design of the system and the synthetic strategy are depicted
in Figure 1. The main point of the design is the observation that it
should be possible to incorporate two bidentate chelates of the
octahedron in a ring and subsequently to thread a fragment
containing the third chelate through the ring. This second process
would of course be driven by coordination to the central metal.
Tetradentate ligands consisting of two separate bidentate ligands
connected by an appropriate spacer and leading to C2-symmetric
complexes have already been reported. A particular interesting
example is that of von Zelewsky’s chiragens,6 consisting of two
chiral bipy derivatives (bipy ) 2,2′-bipyridine). Our group has also
proposed a bis-phen molecule leading to a Ru(phen)32+-derivative
with a clearly identified axis bearing chemical functions.7,8 In the
present work, the substitution positions on the phen nuclei attached
to the functions to be used for further derivatization are different
than those corresponding to the previous axis-containing complex,
as shown in Figure 2. They seem to be appropriate to the formation
of cyclic complexes.
The synthetic procedure starts with the preparation of a large
ring incorporating two phen units. The choice of the ring was
dictated by CPK models and by synthesis considerations.
The precursors and the open-chain and cyclic compounds
incorporating two phen fragments are represented in Figure 3.
1 was prepared in four steps from 3-bromo-8-amino-1,10-
phenanthroline (see Supporting Information). It is a 50-membered
ring which, on CPK models, looks adapted to the formation of
octahedral bis-phen complexes, the two phen fragments being
disposed cis to one another in the metal coordination sphere.
Interestingly, the substitution positions of the p-alkoxyphenyl groups
(8 and 8′ in 1) are determining. By contrast, if p-anisyl groups are
introduced para to the N-atoms of the phen nuclei (positions 7 and
7′), wrapping the corresponding ligand around an octahedron leads
Figure 1. (a) Schematic representation of a transition metal-complexed
[2]catenane containing two different rings. One of the macrocycles
incorporates a bidentate chelate, whereas the other contains two bidentate-
coordinating fragments with a cis arrangement. (b) Synthetic strategy.
to a system with a clearly identified axis.7,8 The key step of the
present work is the coordination reaction, supposed to lead to the
cyclic complex (Figure 2b). Several first-row transition metals were
tested (Zn2+ and Fe2+ in particular), leading to limited success.
However, ruthenium(II) afforded the desired complex.
Complex 22+ was formed by reacting 1 and Ru(DMSO)4Cl2 9 in
refluxing 1,2-dichloroethane under high dilution conditions. The
bis-chloro intermediate complex was not isolated. The crude mixture
from the reaction between 1 and Ru(DMSO)4 Cl2 was heated under
-
reflux in CH3CN-H2O (80:20 v/v) to afford [22+]‚2PF6 as an
orange solid in 21% yield after anion exchange. It is noteworthy
that 22+ is a rare example of a bis-phen or, more generally, a bis-
bidentate octahedral complex with a cis-arrangement, inscribed in
a ring.
The next step was carried using 3, a 2,2′-bipyridine derivative
analogous to a previously described example,10 and the macrocyclic
complex 22+. Threading does take place under relatively harsh
conditions (ethylene glycol: 140 °C) and the catenane precursor
4
2+ was obtained with a surprisingly good yield of 56%. This step,
which is identical to passing a long thread (44 atoms) through the
eye of a needle, represents also a key reaction whose success was
9
2016
J. AM. CHEM. SOC. 2003, 125, 2016-2017
10.1021/ja0209215 CCC: $25.00 © 2003 American Chemical Society
Mobian, Pierre
