FULL PAPER
DOI: 10.1002/chem.201101839
Construction of Hydrogen-Bonded Ternary Organic Crystals Derived from
l-Tartaric Acid and Their Application to Enantioseparation of
Secondary Alcohols
Koichi Kodama,* Eriko Sekine, and Takuji Hirose[a]
Abstract: Ternary organic crystals con-
sisting of an l-tartaric acid-derived di-
carboxylic acid, a commercially avail-
able achiral diamine, and a chiral sec-
ondary alcohol have been developed
and characterized by X-ray crystallog-
raphy. 1D, 2D, and 3D hydrogen-
bonded supramolecular networks were
constructed, depending on the struc-
ture of the diamine used. Benzylic and
aliphatic secondary alcohols were
enantioselectively incorporated into
the crystal and were successfully enan-
tioseparated with up to 86 and 79%
enantiomeric excess (ee), respectively.
Selective incorporation of one enantio-
mer of 2-butanol, which is a small
chiral aliphatic alcohol, was achieved
by the cooperative effects of hydrogen
bonds, CH···p interactions, and van der
Waals interactions between the guest
and host molecules, with the aid of two
water molecules. The high host poten-
tial of the binary supramolecular
system is mainly attributed to the
skewed conformation of two rigid aro-
matic groups of tartaric acid deriva-
tives, which prevents dense packing of
the molecules and enhances the forma-
tion of multicomponent inclusion crys-
tals.
Keywords: crystal engineering
·
enantioselectivity · supramolecular
chemistry · tartaric acid
Introduction
compounds must be tested in a trial-and-error manner to
find the best host–guest combination. When a mixture of
two compounds is used to construct a supramolecular chiral
host system, on the other hand, tuning of the host systems
can be easily achieved by simple variation of the combina-
tion rather than the multistep synthesis of elaborate chiral
molecules in an enantiopure form.[7] In this case, enantiose-
paration of the guest compounds is achieved by the forma-
tion of ternary cocrystals.
In the field of crystal engineering, a variety of promising
supramolecular synthons have been reported to exert con-
trol over the molecular arrangement in the solid state.[1]
One of the enthusiastically studied topics in this field is the
design and synthesis of multicomponent, metal-free organic
crystals, including cocrystals and organic salts. Multicompo-
nent organic crystals not only serve to deepen the under-
standing of supramolecular chemistry, but have also been
successfully applied to the control of the solubility of phar-
maceuticals, in catalysis, in gas storage, and so forth.[2–4] In
particular, the design of multicomponent organic crystals
(consisting of more than three components) is an advanta-
geous method for facile tuning of physical and chemical
properties by judicious variation of the constituents. Even
though several studies have successfully obtained ternary or-
ganic crystals with an appropriate arrangement of supra-
molecular synthons, the rational design of these assemblies
remains an unresolved challenge.[5]
The hydrogen-bonded carboxylate–ammonium pair is one
of the most reliable supramolecular synthons and has been
applied to the construction of various supramolecular mate-
rials, such as liquid crystals and gels.[8] Previously, we report-
ed that various combinations of achiral carboxylic acids and
enantiopure erythro-2-amino-1,2-diphenylethanol could
serve as binary supramolecular chiral host systems for enan-
tioselective inclusion of various aromatic alcohols and sulf-
oxides.[9] In these systems, a 1D columnar hydrogen-bonded
network was constructed by the carboxylate–ammonium
pair and the guest molecules were included in the asymmet-
ric channel created between the columnar structures to form
ternary cocrystals. Various racemates could be efficiently
separated by simply varying the achiral carboxylic acid com-
ponent of the host systems. However, this system failed to
separate small chiral aliphatic alcohols, such as 2-butanol,
because of the flexible structure and small difference in the
sizes of the two alkyl groups around the stereogenic center.
In addition, enantiopure 2-amino-1,2-diphenylethanol is an
artificially developed chiral compound and is not very cost
effective for large-scale preparation. Therefore, our objec-
tive is to design new supramolecular chiral host systems that
meet this demand.
Another important application of multicomponent crys-
tals is enantioseparation by inclusion crystal formation.[6] In
conventional unimolecular host systems, several chiral host
[a] Dr. K. Kodama, E. Sekine, Prof. T. Hirose
Department of Applied Chemistry
Graduate School of Science and Engineering
Saitama University, 255, Shimo-Okubo
Sakura-ku, Saitama, 338-8570 (Japan)
Fax : (+81)48-858-9548
Supporting information for this article is available on the WWW
Chem. Eur. J. 2011, 17, 11527 – 11534
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