Modular Synthesis of Linear Bis- and Tris-monodentate Fused [6]Polynorbornane-Based Ligands and their Assembly into Coordination Cages

A modular approach has been developed for the synthesis of rigid linear di- and tritopic ligands based on a fused [6]polynorbornane scaffold. The design provides up to three sites for installing functionality, including both ends and a central position with the advantage that each region can be independently addressed during synthesis. To illustrate the utility of the approach, both pyridyl and picolyl units were incorporated to provide six new ligands, with centers and ends either matched or mismatched. Indeed, both [M2L4] cages with endohedral functionality and [M3L4] complexes were cleanly produced from these ligands with assembled structures confirmed by using H-1 NMR spectroscopy, HRMS, and molecular modelling.