Clickable Norbornene-Based Zirconium Carboxylate Polyhedra

A common way to modify the properties of metal-organic polyhedra (MOPs) is to install pendant functionalities on the organic bridging ligands. These groups can then participate in coupling reactions to further decorate a given architecture. Via exploitation of click chemistry, it is possible to access a diverse library of MOPs that share a common core, which can reduce both synthetic complexity and cost. Herein, we report the formation of a reactive norbornene-based MOP through a one-pot tandem coordination-driven self-assembly/Diels-Alder reaction between fumaric acid and zirconocene dichloride (Cp₂ZrCl₂). The generality of this tandem process was illustrated by the subsequent synthesis of a norbornene-based Zr cluster formed from maleic acid and Cp₂ZrCl₂. We demonstrate post-assembly modification of this cage using versatile thiol-ene click chemistry, resulting in the formation of either individual functionalized MOPs or cross-linked polymer/MOP hybrid composites. The physical properties of these composites can be controlled by the addition of poly(ethylene glycol) diacrylate as a co-monomer, allowing for the synthesis of free-standing, flexible films at MOP loadings of 30-60% (w/w). These results demonstrate the effectiveness of thiol-ene click chemistry as a method of MOP functionalization, expanding the toolbox for the synthesis of new advanced materials.