Structures and Oxidation Properties of Phenylene-Bridged Diazacycloalkanes: Ring Size Effects on Structures and Properties

Abstract

Phenylenediamine derivatives have been investigated as functional molecules because of their characteristic oxidation properties. In this study, phenylene-bridged diazacycloalkanes, that is, C10, C12, and C14, in which numbers indicate the lengths of a side chain, were synthesized, and the effects of the macroring size on their structures and oxidation properties were investigated. X-ray crystallography revealed that the structures around the nitrogen atoms were remarkably dependent on the chain lengths. The benzene plane of C10 is arranged almost perpendicular to the macroring to avoid steric contact. However, the benzene plane of C14 and alkyl frame were co-planar. Stabilization resulting from conjugation was comparable to destabilization caused by macroring strain according to DFT calculations. Structural differences between C10 and C14 caused changes in the NMR chemical shifts of the inner methylene protons and first oxidation potentials in solution. Notably, the properties of C12 can be analyzed as those of distributed structures, which is of interest with respect to exploiting the metastable structure of the molecules. The observed relationships between the steric structures and properties can facilitate the design of functional molecules containing phenylenediamine moieties.

Synthesis and rotational dynamics of diazamacrocycles having bridged 1,4-naphthylene as framed molecular rotors

“…Two inequivalent signals of the α-CH 2 protons were observed at low temperatures, and they showed typical coalescence at 270 K. The most stable structure of C18Np that is dominant at low temperature is possibly a co-planar structure between the naphthalene ring and the macrocycles, where the conjugation between the lone pair on the nitrogen atoms and the π-orbitals on the naphthalene stabilize the structure. 9 The 13 C NMR spectrum of C18Np recorded at 240 K (Fig. 6) showed nine methylene signals, the number of which was identical to those at 300 K, indicating that the naphthalene ring of the most stable structure was oriented perpendicular to the macrocycle to avoid steric contact, as in the other framed rotors.…”

“…The observed relationship between rotation and molecular component size can facilitate the design of novel molecular rotors based on bridged macrocycles, since functional molecules containing p-phenylenediamine moieties have been widely investigated because of their unique redox properties. 9,14 Experiment General All reactions were performed under anhydrous conditions using argon, unless otherwise stated. All NMR spectra were recorded on a Bruker AVANCEIII 500 spectrometers.…”

“…The observed relationship between rotation and molecular component size can facilitate the design of novel molecular rotors based on bridged macrocycles, since functional molecules containing p -phenylenediamine moieties have been widely investigated because of their unique redox properties. 9,14…”

“…1). [6][7][8][9] The first diazamacrocycle with a bridged phenylene C10 was reported as a molecular vase by Luttringhaus 6 in 1947. Schill 7,8 reported C10 and C12 as model precursors for catenanes, while synthetic protocols such as the direct cyclization of p-phenylenediamine with α,ω-dihaloalkanes in the presence of K 2 CO 3 were established in 1983.…”

“…Our group recently reported the synthesis, crystal structure, and redox properties of C10 , C12 , and C14 . 9 However, the rotational dynamics in phenylene-bridged diazamacrocycles could not be investigated owing to the highly symmetric structures of the compounds. In other words, as a result of the high symmetry of the molecules, the rotational state of the molecules in solution could not be distinguished from the suppressed state based on the change in signals in the temperature-dependent NMR spectra.…”