An All-in-One Synthetic Strategy for Linear Metalla[4]Catenanes

One fascinating and challenging synthetic target in the field of mechanically interlocked molecules is the family of linear [4]catenanes, which are topologically identical to the logo of automobile maker Audi. Herein, we report an all-in-one synthetic strategy for the synthesis of linear metalla[n]catenanes (n = 2-4) by the coordination-driven self-assembly of Cp*Rh-based (Cp* = eta(5)-pentamethylcyclopentadienyl) organometallic rectangle pi-donors and tetracationic organic cyclophane pi-acceptors. We selected the pyrenyl group as the pi-donor unit, leading to homogeneous metalla[2]catenanes and cyclic metalla[3]catenanes via pi-stacking interactions. By taking advantage of the strong electrostatic interactions between pi-donor units and pi-acceptor units, a heterogeneous metalla[2] catenanes and linear metalla[3]catenanes, respectively, could be obtained by the simple stirring of homogeneous metalla[2]catenanes with a suitable tetracationic cyclophane. On this basis, this all-in-one synthetic strategy was further used to realize a quantitative one-step synthesis of a linear metalla[4]catenanes via the self-assembly of cyclic metalla[3]catenanes and tetracationic cyclophanes. All heterogeneous metalla[n]catenanes (n = 2-4) were fully characterized by single-crystal X-ray analysis, NMR spectroscopy and electrospray ionization mass spectrometry.

Automated summary

This study reports an all-in-one synthetic strategy for the synthesis of linear metalla[n]catenanes by the coordination-driven self-assembly. The strategy was successfully used to synthesize metalla[2]catenanes and metalla[3]catenanes via pi-stacking interactions. Additionally, a quantitative one-step synthesis of a linear metalla[4]catenanes was achieved through the self-assembly of cyclic metalla[3]catenanes and tetracationic cyclophanes.