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.