6338 Inorg. Chem. 2009, 48, 6338–6340
DOI: 10.1021/ic9008366
Combining Dynamic Heteroleptic Complex Formation with Constitutional Dynamic
Synthesis: A Facile Way to M3LL0 Cage Assemblies
Jian Fan,† Jan W. Bats,‡ and Michael Schmittel*,†
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†Center for Micro- and Nanochemistry and Engineering, Organische Chemie I, Universitat Siegen,
::
‡
Adolf-Reichwein-Strasse, 57068 Siegen, Germany, and Institut fur Organische Chemie und Chemische
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Biologie, Johann Wolfgang Goethe-Universitat, Max-von-Laue-Strasse 7, D-60438 Frankfurt am Main,
Germany
Received April 29, 2009
The quantitative preparation of heteroleptic copper(I) complexes
arising from a combination of 2,9-diarylphenanthrolines and imi-
nopyridines (Schiff bases) is described. This strategy was applied
to construct mono- and binuclear complexes but equally a discrete
three-dimensional M3LL0 cage. By means of a constitutional
dynamic synthesis, the heteroleptic aggregates were equally
prepared from four-component mixtures using the copper(I) center
as a catalyst for the in situ generation of the iminopyridine ligands.
ligands to minimize strain and stress within such a cage make
it a rather difficult topology. Herein, we demonstrate a facile
approach to the M3LL0 cage structure based on two develop-
ments that will be detailed below: (i) a protocol to prepare
dynamic heteroleptic mono- and polynuclear [Cu(phen1)(imi-
nopyridine)]þ complexes and (ii) a four-component self-as-
sembly procedure combining heteroleptic complex formation
with constitutional dynamic imine bond formation.
The quantitative formation of a dynamic heteroleptic com-
plex necessitates the preferential selection of two or more types
of ligands from a mixture while avoiding the formation of
alternative homoleptic complexes.4 Over the years, our group
has developed a powerful strategy to construct dynamic
heteroleptic metal complexes, such as tetracoordinated [M
(phen1)(phen2)]nþ and [M(phen1)(bipy)]nþ as well as penta-
coordinated [M(phen1)(terpy)]nþ motifs (phen = phenanthro-
line, bipy = 2,20-bipyridine, and terpy = terpyridine).5-7 All
of these heteroleptic motifs are based on the use of a bulky 2,9-
diarylphenanthroline, such as L1 (Chart 1). The principal
structural and bonding features are as follows: (i) the combi-
nation of the ligand L1 and the metal ion will generate a [M-
(L1)]nþ unit but not a homoleptic complex [M(L1)2]nþ because
of the steric hindrance between the bulky aryl substituents of
L1. As a result, the metal ion is “frustrated” and readily
Interest in hollow structures (cages, polyhedra, and cap-
sules) arises because of not only the complexity and beauty of
these structures but also their potential applications in the
areas of separation, encapsulation, and catalysis.1 In the past
decade, a large number of polynuclear complexes MxLyL0z
have been synthesized by combining organic ligands and
transition-metal salts.2 Notably, the heteroleptic cage struc-
ture M3LL0 has rarely been reported up to now.3 Because the
M3LL0 cage is comprised of only two ligands, this structure
represents, from a complexity point of view, the simplest type
of a heteroleptic cage; however, the strict geometric require-
ments such as the size-match and shape similarity of the
*To whom correspondence should be addressed. E-mail: schmittel@
chemie.uni-siegen.de.
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(5) [M(phen1)(phen2)]nþ: (a) Schmittel, M.; Ganz, A. Chem. Commun.
::
1997, 999. (b) Schmittel, M.; Luning, U.; Meder, M.; Ganz, A.; Michel, C.;
Herderich, M. Heterocycl. Commun. 1997, 3, 493.
(6) [M(phen1)(bipy)]nþ: Schmittel, M.; Ganz, A.; Schenk, W. A.; Hagel,
M. Z. Naturforsch. B 1999, 559.
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Published on Web 06/15/2009
2009 American Chemical Society