Synthesis and Structure of N‐Hetero‐ortho‐phenylene Hexamers Containing 2,3‐Substituted Pyridine Moieties

Abstract

N‐Hetero‐ortho‐phenylene hexamers with two 2,3‐substituted pyridine moieties (i.e., 1a–c) were prepared by palladium‐catalyzed homocoupling with pyridine‐directed C–H cleavage as the key step. The conformations of the resulting hexamers in solution and in the solid state were investigated by computational methods, X‐ray analysis, and 1H NMR spectroscopy. Calculations at the SCS‐MP2/def2‐TZVPP//B97‐D3(bj)/def2‐SVP level suggested that helical folding of 1a as the pyridine moieties are stacked is thermally more stable than the equivalent folding in the unsubstituted ortho‐phenylene hexamer. The conformations of single crystals of 1 were consistent with the optimized structures obtained by DFT calculations. Except for rotation of the terminal phenyl groups, only one set of signals corresponding to a helical conformation was observed by analysis of 1 by 1H NMR spectroscopy in CDCl3 solution.

Helical Folding of Hydroxy‐Substituted N‐Hetero‐ortho‐phenylenes Directed by Intramolecular Hydrogen Bonds

“…Elemental analyses were performed with a Perkin–Elmer 2400 series II CHN analyzer. (2‐Dicyclohexylphosphino‐2′,4′,6′‐triisopropyl‐1,1′‐biphenyl)[2‐(2′‐amino‐1,1′‐biphenyl)]palladium(II) methanesulfonate (XPhos Pd G4), 2,2′‐bis(3‐chloropyridin‐2‐yl)biphenyl, 1‐bromo‐2‐(methoxymethoxy)benzene and 1‐(methoxymethoxy)‐3‐methoxybenzene were prepared by reported methods.…”

“…Elemental analyses were performed with a Perkin-Elmer 2400 series II CHN analyzer. (2-Dicyclohexylphosphino-2′,4′,6′-triisopropyl-1,1′-biphenyl)[2-(2′-amino-1,1′-biphenyl)]palladium(II) methanesulfonate (XPhos Pd G4), [10] 2,2′-bis(3-chloropyridin-2-yl)biphenyl, [9] 1-bromo-2-(methoxymethoxy)benzene [14] and 1-(methoxymethoxy)-3-methoxybenzene [15] were prepared by reported methods. Crystallography: A suitable crystal was mounted by using mineral oil on to a glass fiber and transferred to the goniometer of a Rigaku VariMax Saturn CCD diffractometer with graphite-monochromated Mo-Kα radiation (λ = 0.71070 Å).…”

“…X‐ray analysis revealed 3/1 helical folding stabilized by stacked pyridine moieties. Moreover, only the helical conformation was detected by 1 H NMR spectroscopy in CDCl 3 solution . DFT calculations on the N‐ o Ps suggested that the pyridine moieties selectively stabilized the 3/1 helices.…”

“…Moreover, only the helical conformation was detected by 1 H NMR spectroscopy in CDCl 3 solution. [9] DFT calculations on the N-oPs suggested that the pyridine moieties selectively stabi- [a] 2353 which indicates the high stability of the helical folding in CDCl 3 solution. DFT calculations on the rotation of a single bond in the obtained compound indicated that the intramolecular hydrogen bonds led to exceptional stabilization of the closed helical folding.…”

Two‐Step Mechanochromic Luminescence of N,N′‐Bis‐Boc‐3,3′‐di(pyren‐1‐yl)‐2,2′‐biindole

“…It is well known that ortho-phenylenesa nd their heteroaromatic analogues form flexible helical structures, in which intramolecular stacking occurs betweenaromatic rings 1and 4 (Figure 1a). [11] Inspired by our recently developed mechanochromic fluorophores, N-tert-butoxycarbonyl (Boc)-2,3-disubstituted indole derivatives, [12] we designed N,N'-bis-Boc-3,3'-diaryl-2,2'biindole derivatives 1a-c,a st hese should exhibit relatively flexible intramolecular stacking between the two aryl moieties at the 3-and 3'-position ( Figure 1b). Herein,w er eport the synthesis and emissionp roperties of the diarylbiindoled erivatives 1a-c.A mong these, 3,3'-dipyrenyl-substituted derivative 1c exhibited partially overlapping intramolecular stacking of pyrene rings in the crystalline state, which result in at wo-step mechanochromic luminescencet hat may adopt three different colors.…”