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キーワード:
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要旨:
The pairing of ions of opposite charge is a fundamental
principle in chemistry, and is widely applied in synthesis
and catalysis. In contrast, cation–cation association remains an
elusive concept, lacking in supporting experimental evidence.
While studying the structure and properties of 4-oxopiperidinium
salts [OC5H8NH2]X for a series of anions X- of
decreasing basicity, we observed a gradual self-association of
the cations, concluding in the formation of an isolated
dicationic pair. In 4-oxopiperidinium bis(trifluoromethylsulfonyl)
amide, the cations are linked by N-H···O=C hydrogen
bonds to form chains, flanked by hydrogen bonds to the anions.
In the tetra(perfluoro-tert-butoxy)aluminate salt, the anions
are fully separated from the cations, and the cations associate
pairwise by N-C-H···O=C hydrogen bonds. The compounds
represent the first genuine examples of self-association of
simple organic cations based merely on hydrogen bonding as
evidenced by X-ray structure analysis, and provide a paradigm
for an extension of this class of compounds.
