The Rise and Promise of Molecular Nanotopology

Abstract

Molecular nanotopology-a term we coined recently-is a rapidly developing field of research that is emerging out of the confluence of chemical topology with the mechanical bond. By focusing on the increased research activities in this field, it is clear that a new discipline is ready to receive recognition in its own right. In this Mini-Review, we address the historical development of chemical topology and describe how the rational design and practical synthesis of molecular links and knots with mechanical bonds, together with interwoven extended frameworks, have led to the rapid establishment of molecular nanotopology as a discipline. Representative examples are highlighted in order to offer the reader an extensive overview of ongoing research. We spotlight the major challenges facing chemists and materials scientists and provide some pointers as to how molecular nanotopology is going to develop in the years ahead.

Mechanically interlocked molecular handcuffs

“…4.2.1 Handcuff rotaxanes with four mechanical bonds -(4) handcuff [2]rotaxanes. Quadruply interlocked [2]rotaxanes were rst reported by Böhmer and co-workers 82,83 who made use of the well-dened hydrogen-bonded arrangement between two urea functionalised calix [4]arenes (see Section 3.2.2) to organise the components for mechanical bonding. In the rst instance, 82 a tetraloop calixarene was prepared by olen metathesis of an tetra-bis(alkenyl) functionalised calix [4]arene, 84 where adjacent alkenyl arms were coupled to produce the four new macrocycles.…”

“…Quadruply interlocked [2]rotaxanes were rst reported by Böhmer and co-workers 82,83 who made use of the well-dened hydrogen-bonded arrangement between two urea functionalised calix [4]arenes (see Section 3.2.2) to organise the components for mechanical bonding. In the rst instance, 82 a tetraloop calixarene was prepared by olen metathesis of an tetra-bis(alkenyl) functionalised calix [4]arene, 84 where adjacent alkenyl arms were coupled to produce the four new macrocycles. When mixed with a second calix [4]arene derivative carrying four pendent alkylmaleimide arms in apolar solvents, heterodimeric capsules of the two calixarenes formed, with the alkylmaleimide arms threaded through each of the four loops of the host component (Fig.…”

“…In the rst instance, 82 a tetraloop calixarene was prepared by olen metathesis of an tetra-bis(alkenyl) functionalised calix [4]arene, 84 where adjacent alkenyl arms were coupled to produce the four new macrocycles. When mixed with a second calix [4]arene derivative carrying four pendent alkylmaleimide arms in apolar solvents, heterodimeric capsules of the two calixarenes formed, with the alkylmaleimide arms threaded through each of the four loops of the host component (Fig. 14a).…”

“…Catenane structures based upon the tetraloop calixarene described above have also been synthesised by the Böhmer group. [95][96][97] The assembly of heterodimeric capsules between the tetraloop calix [4]arene and calix [4]arenes substituted with four terminal olen groups allowed for a ring closing metathesis reaction to occur between the adjacent alkenyl residues, forming a multiply catenated architecture.…”

“…Fig.14Structures of (4)handcuff[2]rotaxanes. (a) Diels-Alder reactions between maleimide and anthracene units to stopper a dimeric calix[4]arene capsule; (b) Addition of acid or base to a copper phthalocyanine-porphyrin handcuff rotaxane moves the handcuff position along the axle and controls the spin-spin communication between the metal centres; (c) a phthalocyanine-porphyrin handcuff rotaxane acting as a receptor for a third tetraanionic porphyrin. Hydrogen atoms have been omitted on the two views of the single crystal X-ray structure; (d) proposed mechanism for oxygen reduction in an oxo-bridged handcuff rotaxane.…”