Bigger, better, faster: molecular shuttles with sterically non-hindering biisoquinoline chelates

In the past, a variety of mechanically interlocked systems such as catenanes and rotaxaneswere constructed on the basis of Cu(I) coordination chemistry and endocyclic 1,10-phenanthroline ligands. This review reports on the coordination chemistry of a new family of endocyclic bidentate chelators that are sterically non-hindering, namely 8,80-diaryl-substituted 3,30-biisoquinolines. These ligands allow the construction of new multi-component assemblies that are inaccessible with the previously investigated 1,10-phenanthrolines. On the one hand, the sterically non-hindering nature of the new endocyclic chelators makes three component entanglements around octahedral metal centres such as iron(II), cobalt(II) and ruthenium(II) readily possible. On the other hand, it permits the construction of copper-based molecular shuttles that exhibit shuttling kinetics that excels over those of previously investigated analogous systems with 1,10-phenanthrolines. Thus, within this class of molecular machines, a bigger chelator leads to faster molecular movement, i.e. to a better performance of the molecular machine