N-Methylated Diphenylguanidines: Conformations, Propeller-Type
Molecular Chirality, and Construction of Water-Soluble Oligomers
with Multilayered Aromatic Structures
The crystal structures of
N,N‘-diphenylguanidine (1) and its
N-methylated derivatives were
investigated, and the conformational properties of these molecules were
utilized to construct water-soluble
oligomers with multilayered aromatic structures.
N,N‘-Diphenylguanidine (1) afforded two
types of crystals,
chiral (P212121) and
racemic (P21/c), upon
recrystallization from EtOH. In both crystals, 1 exists
in the (E,Z)
conformation, in which one C−N bond (length: 1.28−1.30 Å)
attached to a phenyl ring shows double-bond
character. In contrast,
N,N‘-dimethyl-N,N‘-diphenylguanidine
(4a) exists in the (Z,Z) conformation
with the
two aromatic rings facing each other. As judged from the crystal
structures of several N-methylated compounds,
the conformational preferences of diphenylguanidines appear to be
related to those of aromatic anilides.
N,N,N‘,N‘‘-Tetramethyl-N‘,N‘‘-diphenylguanidinium
iodide (6) afforded chiral crystals, like 1 and
N-methyl-N,N‘-diphenylguanidine (2). The absolute
structure of each enantiomeric propeller conformation of 6
was
determined by X-ray analysis using the Bijvoet difference method.
The Z-conformational preference of
4
allowed us to synthesize oligomeric di- or tetraguanidines
(9−12) which have multilayered aromatic
structures
both as a crystal and in organic and aqueous solvents.