22 Molecular Recognition by Inclusion …
467
Fig. 22.9 a Rychlewska’s bis(triphenylacetamides) host of chiral 1,2-diamines. b Schematic
drawing of host–guest interactions in inclusion crystals with dimethyl sulfoxide guest
This host also included methanol, ethanol, and 2-propanol accompanied with
one water molecule. But longer-chain alcohol molecules such as n-butanol and
sec-butanol were not included. Furthermore, inclusion of chiral molecules was
unsuccessful. However, further modification of this host molecule might bring
enantioselective inclusion.
As another example, inclusion ability was obtained by introducing a trityl group
to the structure. A silatrane has a unique structure with an intramolecular Si-N coordination bond. Introduction of the trityl group to the amino group of [1-[(N-methylN-tritylamino)methyl]silatrane brings inclusion ability for this tritylated product
(Fig. 22.10) [27]. Inclusion crystals of 1:1 (host/guest) with a benzene molecule
were obtained after the recrystallization from a mixture of benzene and heptane.
The X-ray diffraction study shows that the geometry of the coordination center of
silicon and the existence of an intramolecular Si-N coordination bond are typical for
silatranes. The trityl group made a void to include a benzene molecule.
In the organic chemistry, we often need to separate racemic compounds and a
mixture of structural isomers. For example, there are mixtures of o-, m-, and pdisubstituted benzenes, of linear and branched alkanes, etc. Even if the host molecules
are achiral, they can recognize one structural isomer from a mixture of isomers based
on whether the molecular shapes match the void that occurred in the crystal lattice
or not.
In 2019, Barton and her coworkers developed a new wheel-and-axle host design of
achiral diamines that have two 9-phenyl-9-xanthenyl or (9-phenyl-9-thioxanthenyl)
groups with structures similar to a trityl group. The xanthenyl and thioxanthenyl
Fig. 22.10 Formation of inclusion crystals by tritylated 1-[(N-methyl)methyl]silatrane
467
Fig. 22.9 a Rychlewska’s bis(triphenylacetamides) host of chiral 1,2-diamines. b Schematic
drawing of host–guest interactions in inclusion crystals with dimethyl sulfoxide guest
This host also included methanol, ethanol, and 2-propanol accompanied with
one water molecule. But longer-chain alcohol molecules such as n-butanol and
sec-butanol were not included. Furthermore, inclusion of chiral molecules was
unsuccessful. However, further modification of this host molecule might bring
enantioselective inclusion.
As another example, inclusion ability was obtained by introducing a trityl group
to the structure. A silatrane has a unique structure with an intramolecular Si-N coordination bond. Introduction of the trityl group to the amino group of [1-[(N-methylN-tritylamino)methyl]silatrane brings inclusion ability for this tritylated product
(Fig. 22.10) [27]. Inclusion crystals of 1:1 (host/guest) with a benzene molecule
were obtained after the recrystallization from a mixture of benzene and heptane.
The X-ray diffraction study shows that the geometry of the coordination center of
silicon and the existence of an intramolecular Si-N coordination bond are typical for
silatranes. The trityl group made a void to include a benzene molecule.
In the organic chemistry, we often need to separate racemic compounds and a
mixture of structural isomers. For example, there are mixtures of o-, m-, and pdisubstituted benzenes, of linear and branched alkanes, etc. Even if the host molecules
are achiral, they can recognize one structural isomer from a mixture of isomers based
on whether the molecular shapes match the void that occurred in the crystal lattice
or not.
In 2019, Barton and her coworkers developed a new wheel-and-axle host design of
achiral diamines that have two 9-phenyl-9-xanthenyl or (9-phenyl-9-thioxanthenyl)
groups with structures similar to a trityl group. The xanthenyl and thioxanthenyl
Fig. 22.10 Formation of inclusion crystals by tritylated 1-[(N-methyl)methyl]silatrane