Molecular Complexes of Diethyl N,N′-1,3-Phenyldioxalamate and Resorcinols: Conformational Switching through Intramolecular Three-Centered Hydrogen-Bonding

Abstract

The mechanochemically induced complexation between diethyl N,N′-1,3-phenyldioxalamate tweezers and resorcinol, orcinol, 4,6-di-tert-butyl-1,3-benzenediol, and 4-hexyl-1,3-benzenediol is described. IR-spectroscopy, X-ray powder diffraction, 13C CPMAS, and single X-ray diffraction allowed establishing the structures of the complexes as hydrogen-bonded heterodimers and heterotetramers. Complexation occurs through O–H···OC hydrogen-bonding interactions with the participation of phenolic OH and amide carbonyl groups. The initial conformation and steric factors coming from the 1,3-benzenediols exert a strong influence on the final structure of the complex formed. Complexation twists both oxalyl arms by 180°, strengthens the intramolecular (amide)CO···H(Csp 2)···OC(amide) three-centered hydrogen bond, and moves apart the oxalyl arms to allow the accommodation of the 1,3-benzenediol inside the cavity. The supramolecular architectures of the complexes in 1-D are directed by R 1 2(6), R 2 2(10), and R 1 2(6) adjacent hydrogen-bonding ring motifs; meanwhile, the 2-D and 3-D arrays are driven by multipolar interactions. Theoretical DFT calculations at the B3LYP/6-31G(d,p) level of theory were performed to support the experimental findings. The complexes herein reported constitute the first examples of molecular complexes with phenyldioxalamate.

Mechanochemical Complexation of Diethyl N,N´-[1,3-(2-methyl)phenyl]dioxalamate and Resorcinol: Conformational Twist and X-Ray Helical Supramolecular Architecture

“…These changes suggest the formation of an O-HÁÁÁO=C hydrogen bond synthon. The O-H and C=O frequency shifts are in agreement with those observed in other resorcinol complexes with theophylline [30] or diethyl N,Ń -[1,3-phenyl]dioxalamate [20]. It is worthy to note that the N-H stretching band appears shifted to higher frequency (Dm(N-H) = 133 cm -1 ) and overlapped with the O-H stretching band in 1Á2 powd and 1Á2 cryst in regard to 1 (Fig.…”

“…This conformation avoids the formation of a cavity and prevents further association into the characteristic R 2 2 (10) homodimer when the endo(sp)-endo(sp) conformation prevails [20].…”

“…The second dimension array is depicted by the interlink of adjacent meso-helices through parallel displaced (pd)-p-stacking interaction [40] between the aromatic rings of compound 1, Cg(1), Symmetry codes (i) = -x, 1-y, -z; (ii) = x, -y, 1/2?z In the N,N 0 -1,3-phenyldioxalamate (4) and resorcinol complex (Fig. 1) [20], the absence of substitution in the C-2 position of the aromatic ring in the phenyldioxalamate allows the formation of the three centered hydrogen bond scheme C=OÁÁÁH(C-2)ÁÁÁO=C interactions after the complexation, depicted by the S(6)S(6) graph set motif. A cavity is formed by the endo(sp)-endo(sp) conformation of both oxalyl arms (Fig.…”

“…In this context, we recently reported the first phenyldioxalamate molecular complex mechanochemically formed by diethyl N,N 0 -1,3-phenyldioxalamate and resorcinol ( Fig. 1), stabilized by O-HÁÁÁO=C hydrogen bonding interactions [20].…”

“…Classical hydrogen bond parameters which define this interaction are: (a) the OÁÁÁX distance must be less than the sum of their van der Waals radii (geometric parameter), and (b) the directionality of the interaction, where the O-HÁÁÁX angle must be closely to 180° [18]. The hydrogen bond motifs found for this heterosynthon are reviewed elsewhere [19,20].…”