Chemical topology: Complex molecular knots, links, and entanglements

Abstract

The role of covalent, coordinative, and supramolecular interactions utilized by chemists and biochemists, when they are assembling molecular knots and links, are presented. The Trefoil Knot comprises a simple overhand knot where the two ends have been connected and can exist in left-handed and right-handed forms. A molecular Trefoil Knot displays inherent topological chirality and any representation of its graph cannot be deformed in 3D space to its mirror image, and exists as two enantiomers. A significant increase in knot yields is achieved by replacing the polymethylene linker with a meta-phenylene bridge, a change of design that resulted in the quantitative assembly of the precursor double helical complex. Alkene metathesis is particularly suited to macrocyclizations involving Cu(I)-templated species as it is a thermodynamically controlled reaction. It also avoids the need for addition of destabilizing bases, such as NaH, which are required when alkylation is the final step in the reaction sequence.