Covalent Template Approach Toward Functionalized Oligo-Alkyl-Substituted Shape-Persistent Macrocycles:  Synthesis and Properties of Rings with a Loop

Abstract

The synthesis, properties, and conformation of shape-persistent macrocycles with extraannular oligoalkyl groups and an intraannular bis(hydroxymethyl)biphenylene diester are investigated. The key step in the preparation is the template-supported Glaser coupling of rigid bisacetylenes which allows obtaining the cyclic product in 81% yield. Contrary to the initial expectations, the compounds do not exhibit liquid crystalline phases. This could be explained by a nonplanar conformation of the molecules because the biphenylene bridge is longer than the diameter of the rings. On the other hand, scanning tunneling microscopy investigations indicate that the intraannular biphenylene bridge can be located in the same plane as the aromatic backbone of the macrocycles on graphite. Modeling involving molecular mechanics and molecular dynamics simulations unraveled this apparent inconsistency by showing that the molecules adopt a nonplanar conformation in the absence of the solid support whereas planarization takes place when they are adsorbed on the graphite surface.

Shape‐Switchable Azo‐Macrocycles

“…Shape persistent macrocycles comprising similar polyalkyl substituents have already been reported by Höger et al. [104][106][184] [196]- [198] Increased adsorption properties of these macrocycles with an increasing number of alkyl chains were observed. The driving force for the adsorption of the macrocycles at the surface is the nonspecific attractive van der Waals (vdW) interaction of the rigid and the flexible ring parts, including the alkyl chains, with the graphite surface.…”

“…[100]- [102] Shape persistent two dimensional oligomers such as spoked wheels [103] as well as shape persistent macrocycles based on a phenyl ethynyl backbone have been immobilized on graphite. [104]- [106] In Figure 5 the deposition from solution to the surface of highly oriented pyrolytic graphite (HOPG) is shown. The shape persistent macrocycle (A in Figure 5) forms a highly ordered and stable monolayer at the solution HOPG surface interface.…”

Highly Strained Phenylene Bicyclophanes

“…The central unit is neither able to rotate, nor able to move into the plane of the structure (Figure 1 b) and will therefore point into the volume phase. [2] We assumed that small cyclic oligo(meta-/ para-phenylene)s with an intraannular central aromatic unit would fulfill these criteria. However, the synthesis of such cyclophanes is challenging owing to their high strain energy.…”

Shape‐Persistent Macrocycles Based on Acetylenic Scaffolding

“…The ring-closing step to 148-151 relied on acetylenic homocoupling of the two halves of the macrocycle, which typically provided only moderate yields. In an effort to increase the quantity of these macrocycles available for study, the covalent template approach has been applied, converting 152 to 153 and 154 in excellent yields over the three steps [118]. Unlike 148-151, however, attempts to melt the template-bound SPMs 153 and 154 into a LC phase were unsuccessful.…”