Specific Noncovalent Association of Truncated exo-Functionalized Triangular Homochiral Isotrianglimines through Head-to-Head, Tail-to-Tail, and Honeycomb Supramolecular Motifs

Abstract

Chiral isotrianglimines were synthesized by the [3 + 3] cyclocondensation of ( R , R )-1,2-diaminocyclohexane with C5-substituted isophthalaldehyde derivatives. The substituent’s steric and electronic demands and the guest molecules’ nature have affected the conformation of individual macrocycles and their propensity to form supramolecular architectures. In the crystal, the formation of a honeycomb-like packing arrangement of the simplest isotrianglimine was promoted by the presence of toluene or para -xylene molecules. A less symmetrical solvent molecule might force this arrangement to change. Polar substituents present in the macrocycle skeleton have enforced the self-association of isotrianglimines in the form of tail-to-tail dimers. These dimers could be further arranged in higher-order structures of the head-to-head type, which were held together by the solvent molecules. Non-associating isotrianglimine formed a container that accommodated acetonitrile molecules in its cavity. The calculated dimerization energies have indicated a strong preference for the formation of tail-to-tail dimers over those of the capsule type.

Dynamic and solid-state behaviour of bromoisotrianglimine

“…Therefore, the synthesis of the brominated isotrianglimine was first explored. The C-5 brominated isotrianglimine has been previously synthesised and reported to form the [3+3] macrocycle in yields of 69% & 97%; 50,51 the presence or absence of [2+2] macrocycle in reaction mixtures is rarely discussed. In our hands, reacting 5-bromoisopthaladehyde with RR-CHDA or SS-CHDA in chloroform at an overall concentration of 0.1 M overnight produced a mixture of the [2+2] and [3+3] macrocycles (Figure 1a).…”

“…In our hands, reacting 5-bromoisopthaladehyde with RR-CHDA or SS-CHDA in chloroform at an overall concentration of 0.1 M overnight produced a mixture of the [2+2] and [3+3] macrocycles (Figure 1a). As only 1 H NMR spectra for the isolated [3+3] macrocycle was reported, 50,51 both 2D and diffusion NMR was carried out to complete the assignment for the mixture of macrocycles and to enable reaction monitoring over time. Diffusion-ordered spectroscopy provides information about the rate of diffusion of different species in a solution.…”

“…Macrocycles of [3+3] isotrianglimines with functionalisation at the C-5 position have the ability to self-assemble in several different possible arrangements: (i) tail-to-tail dimer; (ii) head to-head-dimer; and (iii) head-to-tail dimer (Figure 5). 73,74…”

“…However, this study exclusively focused on the [3+3] derivatives. 50 Here, we focus on isotrianglimines formed using 5-bromoisotrianglimine, first characterising the mixture using diffusion NMR (Figure 1) to enable assignments for the different macrocyclic species present in solution. With this in hand, VT-NMR experiments were carried out to probe both conversion between different macrocyclic species and the conformational behaviour of the macrocycles in solution.…”

Imine- and Amine-Type Macrocycles Derived from Chiral Diamines and Aromatic Dialdehydes

“…They can act as hosts for small organic guest molecules, form dimers and capsules or self-associate into larger structures. The formation of various noncovalent aggregates of these macrocycles was demonstrated by Kwit, Janiak and others for solid, liquid, and gas phases [88][89][90][91][92][93][94][95].…”