Abstract

Molecular knots1 and entanglements are featured in cyclic
DNA2 and some proteins3 and are thought to play an
important role in the chemical and physical properties of both
natural and synthetic polymers.4 Sauvage and co-workers
prepared the first synthetic molecular trefoil knot by connecting
the end-groups of a linear two-metal-ion double helicate.5
However, the earliest published idea for a template synthesis of a
trefoil knot is Sokolov’s proposal6 for assembling three ligands
around a metal center to generate the three crossings necessary7
in the cyclized product. Several groups have attempted to prepare
trefoil knots using this strategy thus far without achieving the
ultimate goal,8 although Hunter has succeeded in synthesizing a
trefoil knot by folding a single ligand strand around a transition
metal ion,9 and Siegel has made a ‘trefoil knotted cyclophane’
10
using a related triskelion approach featuring a covalently bonded
scaffold.11