N-Methylated Diphenylguanidines:  Conformations, Propeller-Type Molecular Chirality, and Construction of Water-Soluble Oligomers with Multilayered Aromatic Structures

Abstract

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.

Pyridin-2-yl Guanidine Derivatives: Conformational Control Induced by Intramolecular Hydrogen-Bonding Interactions

“…However, in the crystal structure of N,N'-dimethyl-N,N'-diphenylguanidine the C-N double bond is localized over the unsubstituted N atom, 24 similar to what is observed in our neutral guanidines. Regarding the hydrochloride salts 3d and 3e and the hydrobromide salt of 24 very similar C-N distances are obtained for the three C-N bonds involved in the guanidinium group (between 1.31 and 1.38 Å)…”

Helicogenicity of solvents in the conformational equilibrium of oligo(m-phenylene ethynylene)s: Implications for foldamer research

“…As with biological macromolecules (9), solvent-induced equilibrium shifting from the folded to the unfolded state involves disruption of these noncovalent interactions through either competitive solvation or changes in the bulk properties of the medium. In the foldamer field, the impact of solvent on foldable chains has been addressed only recently, and of these studies, only a limited scope of solvents has been explored (7,(10)(11)(12)(13)(14)(15)(16)(17). This fact is surprising considering the ease with which this experimental variable can be modulated and the information that can be obtained about the nature of the driving forces involved in the folding reaction.…”

Absolute Helical Arrangement of Stacked Benzene Rings: Heterogeneous Double‐Helical Interaction Comprising a Hydrogen‐Bonding Belt and an Offset Parallel Aromatic–Aromatic‐Interaction Array

“…[2] There are several types of helical structure: a single strand that folds helically owing to solvophobic effect [3] or guest ligation, [4] a double or multiple helix of strands derived from cation or anion ligation, [5] or hydrogen bonding, [6] and a helical super-structure formed by conformationally helical or discotic small molecules through columnar stacking supported by hydrogen bonds, [7] for other examples see ref. [8]. In helical structures, a parallel aromatic-aromatic interaction [9] is often a very important driving force to stabilize the structure, and sometimes hydrogen bonding or other weak intermolecular interactions assist the formation of the highly ordered helical arrangement.…”